PFC Cuk Converter Fed BLDC Motor Drive IEEE PAPERS/eee based/eee b… · MATLAB/Simulink environment and a hardware prototype of proposed drive is developed to validate its performance

0885-8993 (c) 2013 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. Seehttp://www.ieee.org/publications_standards/publications/rights/index.html for more information.

This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI10.1109/TPEL.2014.2309706, IEEE Transactions on Power Electronics

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Abstract— This paper deals with a power factor correction

(PFC) based Cuk converter fed brushless DC motor (BLDC) drive as a cost effective solution for low power applications. The speed of the BLDC motor is controlled by varying the DC bus voltage of voltage source inverter (VSI) which uses a low frequency switching of VSI (electronic commutation of BLDC motor) for low switching losses. A diode bridge rectifier (DBR) followed by a Cuk converter working in discontinuous conduction mode (DCM) is used for control of DC link voltage with unity power factor at AC mains. Performance of the PFC Cuk converter is evaluated in four different operating conditions of discontinuous and continuous conduction mode (CCM) and a comparison is made to select a best suited mode of operation. The performance of the proposed system is simulated in MATLAB/Simulink environment and a hardware prototype of proposed drive is developed to validate its performance over a wide range of speed with unity power factor at AC mains.

Index Terms— CCM, Cuk converter, DCM, PFC, BLDC Motor, Power Quality

I. INTRODUCTION RUSHLESS DC (BLDC) motors are recommended for many low and medium power drives applications because of their high efficiency, high flux density per unit volume,

low maintenance requirement, low EMI problems, high ruggedness and a wide range of speed control [1, 2]. Due to these advantages, they find applications in numerous areas such as household application [3], transportation (hybrid vehicle) [4], aerospace [5], heating, ventilation and air conditioning (HVAC) [6], motion control and robotics [7], renewable energy applications [8, 9] etc. The BLDC motor is a three phase synchronous motor consisting of a stator having a three phase concentrated windings and a rotor having permanent magnets [10, 11]. It doesn’t have mechanical brushes and commutator assembly, hence wear and tear of the brushes and sparking issues as in case of conventional DC machines are eliminated in BLDC motor and thus has low EMI problems. This motor is also referred as electronically commutated motor (ECM) since an electronic commutation based on the Hall-Effect rotor position signals is used rather than a mechanical commutation [12, 13].

Manuscript received September 1, 2013, revised January 3, 2013 and

accepted for publication February 22, 2014. Copyright (c) 2009 IEEE. Personal use of this material is permitted.

However, permission to use this material for any other purposes must be obtained from the IEEE by sending a request to [email protected].

Vashist Bist and Bhim Singh are with the Department of Electrical

Engineering, Indian Institute of Technology Delhi, New Delhi-110016, INDIA (e-mail: [email protected], [email protected]).

There is a requirement of an improved power quality as per

the international power quality (PQ) standard IEC 61000-3-2 which recommends a high power factor (PF) and low total harmonic distortion (THD) of AC mains current for Class-A applications (<600W, <16A) which includes many household equipments [14]. The conventional scheme of a BLDC motor fed by a diode bridge rectifier (DBR) and a high value of DC link capacitor draws a non-sinusoidal current, from AC mains which is rich in harmonics such that the THD of supply current is as high as 65%, which results in power factor as low as 0.8 [15]. These types of power quality indices can’t comply with the international PQ standards such as IEC 61000-3-2 [14]. Hence, single-phase power factor correction (PFC) converters are used to attain a unity power factor at AC mains [16, 17]. These converters have gained attention due to single stage requirement for DC link voltage control with unity power factor at AC mains. It also has low component count as compared to multi stage converter and therefore offers reduced losses [17].

Conventional schemes of PFC converters fed BLDC motor drive utilize an approach of constant DC link voltage of the VSI and controlling the speed by controlling the duty ratio of high frequency pulse width modulation (PWM) signals [18-21]. The losses of VSI in such type of configuration are considerable since switching losses depend on the square of switching frequency (Psw_loss α fS

2). Ozturk et. al. [18] have proposed a boost PFC converter based direct torque controlled (DTC) BLDC motor drive. They have the disadvantages of using a complex control which requires large amount of sensors and higher end digital signal processor (DSP) for attaining a DTC operation with PFC at AC mains. Hence, this scheme is not suited for low cost applications. Ho et. al. [19] have proposed an active power factor correction (APFC) scheme which uses a PWM switching of VSI and hence has high switching losses. Wu et al. [20] have proposed a cascaded buck-boost converter fed BLDC motor drive, which utilizes two switches for PFC operation. This offers high switching losses in the front end converter due to double switch and reduces the efficiency of overall system. Gopalarathnam et. al. [21] have proposed a single ended primary inductance converter (SEPIC) as a front end converter for PFC with DC link voltage control approach, but utilizes a PWM switching of VSI which has high switching losses. Bridgeless configurations of PFC buck-boost, Cuk, SEPIC and Zeta converters have been proposed in [22-25] respectively. These configurations offer reduced losses in the front end converter but at the cost of high number of passive and active components [22-25].

PFC Cuk Converter Fed BLDC Motor Drive

Vashist Bist, Student Member, IEEE and Bhim Singh, Fellow, IEEE

B



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Selection of operating mode of front end converter is a

trade-off between the allowed stresses on PFC switch and cost of the overall system. Continuous conduction mode (CCM) and discontinuous conduction mode (DCM) are the two different modes of operation in which a front end converter is designed to operate [16, 17]. A voltage follower approach is one of the control techniques which is used for a PFC converter operating in DCM. This voltage follower technique requires a single voltage sensor for controlling the DC link voltage with a unity power factor. Therefore, voltage follower control has an advantage over a current multiplier control of requiring a single voltage sensor. This makes the control of voltage follower a simple way to achieve PFC and DC link voltage control, but at the cost of high stress on PFC converter switch [16, 17]. On the other hand, the current multiplier approach offers low stresses on the PFC switch, but requires three sensors for PFC and DC link voltage control [16, 17]. Depending on design parameters, either approach may force the converter to operate in DCM or CCM. In this work, a BLDC motor drive fed by a PFC Cuk converter operating in four modes/control combinations is investigated for operation over a wide speed range with unity power factor at AC mains. These include a CCM with current multiplier control, and three DCM techniques with voltage follower control.

II. SYSTEM CONFIGURATION Figs. 1-2 show the PFC Cuk converter based VSI fed

BLDC motor drive using a current multiplier and a voltage follower approach respectively. A high frequency metal oxide semiconductor field effect transistor (MOSFET) is used in Cuk converter for PFC and voltage control [26-30], whereas insulated gate bipolar transistor’s (IGBT) are used in the VSI for its low frequency operation. BLDC motor is commutated electronically to operate the IGBT’s of VSI in fundamental

frequency switching mode to reduce its switching losses. The PFC Cuk converter operating in CCM using a current multiplier approach is shown in Fig. 1; i.e. the current flowing in the input and output inductors (Li and Lo), and the voltage across the intermediate capacitor (C1) remain continuous in a switching period. Whereas, Fig. 2 shows a Cuk converter fed BLDC motor drive operating in DCM using a voltage follower approach. The current flowing in either of the input or output inductor (Li and Lo) or the voltage across the intermediate capacitor (C1) become discontinuous in a switching period [31, 32] for a PFC Cuk converter operating in DCM. A Cuk converter is designed to operate in all three discontinuous conduction modes and a continuous conduction mode of operation and its performance is evaluated for a wide voltage control with unity power factor at AC mains.

III. OPERATION OF CUK CONVERTER IN DIFFERENT MODES The operation of Cuk converter is studied in four different

modes of CCM and DCM. In CCM, the current in inductors (Li and Lo) and voltage across intermediate capacitor C1 remain continuous in a switching period [33]. Moreover, the DCM operation is further classified into two broad categories of discontinuous inductor current mode (DICM) and discontinuous capacitor voltage mode (DCVM). In DICM, the current flowing in inductor Li or Lo becomes discontinuous in their respective modes of operation [31, 32]. While in DCVM operation, the voltage appearing across the intermediate capacitor C1 becomes discontinuous in a switching period [34, 35]. Different modes for operation of CCM and DCM are discussed as follows.

A. CCM Operation The operation of Cuk converter in CCM is described as

follows. Figs. 3(a) and (b) show the operation of Cuk

Fig. 1. A BLDC motor drive fed by a PFC Cuk converter using a current multiplier approach.



3

converter in two different intervals of a switching period and Fig. 3(c) shows the associated waveforms in a complete switching period. Interval I: When switch Sw in turned on, inductor Li stores energy while capacitor C1 discharges and transfers its energy to DC link capacitor Cd as shown in Fig. 3(a). Input inductor current iLi increases while the voltage across the intermediate capacitor VC1 decreases as shown in Fig. 3(c). Interval II: When switch Sw is turned off, then the energy stored in inductor Lo is transferred to DC link capacitor Cd, and inductor Li transfers its stored energy to the intermediate capacitor C1 as shown in Fig. 3(b). The designed values of Li, Lo and C1 are large enough such that a finite amount of energy is always stored in these components in a switching period.

B. DICM (Li) Operation The operation of Cuk converter in DICM (Li) is described

as follows. Figs. 4(a)-(c) show the operation of Cuk converter in three different intervals of a switching period and Fig. 4(d) shows the associated waveforms in a switching period. Interval I: When switch Sw in turned on, inductor Li stores energy while capacitor C1 discharges through Switch Sw to transfer its energy to the DC link capacitor Cd as shown in Fig. 4(a). Input inductor current iLi increases while the voltage across the capacitor C1 decreases as shown in Fig. 4(d). Interval II: When switch Sw is turned off, then the energy stored in inductor Li is transferred to intermediate capacitor C1 via diode D, till it is completely discharged to enter DCM operation. Interval III: During this interval, no energy is left in input inductor Li, hence current iLi becomes zero. Moreover, inductor Lo operates in continuous conduction to transfer its energy to DC link capacitor Cd.

C. DICM (Lo) Operation The operation of Cuk converter in DICM (Lo) is described

as follows. Figs. 5(a)-(c) show the operation of Cuk converter in three different intervals of a switching period and Fig. 5(d) shows the associated waveforms in a switching period. Interval I: As shown in Fig. 5(a), when switch Sw in turned on, inductor Li stores energy while capacitor C1 discharges through switch Sw to transfer its energy to the DC link capacitor Cd. Interval II: When switch Sw is turned off, then the energy stored in inductor Li and Lo is transferred to intermediate capacitor C1 and DC link capacitor Cd respectively. Interval III: In this mode of operation, the output inductor Lo is completely discharged hence its current iLo becomes zero. An inductor Li operates in continuous conduction to transfer its energy to the intermediate capacitor C1 via diode D.

D. DCVM (C1) Operation The operation of Cuk converter in DCVM (C1) is described

as follows. Figs. 6(a)-(c) show the operation of Cuk converter in three different intervals of a switching period and Fig. 6(d) shows the associated waveforms in a switching period. Interval I: When switch Sw in turned on as shown in Fig. 6(a), inductor Li stores energy while capacitor C1 discharges through switch Sw to transfer its energy to the DC link capacitor Cd as shown in Fig. 6(d). Interval II: The switch is in conduction state but intermediate capacitor C1 is completely discharged, hence the voltage across it becomes zero. Output inductor Lo continues to supply energy to the DC link capacitor. Interval III: As the switch Sw is turned off, input inductor Li starts charging the intermediate capacitor, while the output inductor Lo continues to operate in continuous conduction and supplies energy to the DC link capacitor.

N*

Electronic Commutation

Voltage Controller

Ref. Voltage Generator

Vdc*

Saw ToothPWM

Generator

3

VdcVe

Vcd

+-

md

6

Single Phase AC

Supply

DBRPFC Based Cuk Converter

Sw

Ls

D

Cd

Li C1 Lo

Vdc +

-Cf

DC FilterLf

VSI

BLDC Motor

HallSignals

S5

S6

S1

S2

a bcib

ia

ic

iLi+ -

vC1 iLo

+vSW

-iSW

+

Vin

+

-Vs

is

S4

S3

H1-H3

-

Fig. 2. A BLDC motor drive fed by a PFC Cuk converter using a voltage follower approach.



4

(a) Interval I (b) Interval II

iLi

VC1

iLo

Vdc

Vg Sw On Sw Off

I II t

(c) Waveforms

Fig. 3. Operation of Cuk converter in CCM during (a-b) different intervals of switching period and (c) the associated waveforms.

IV. DESIGN OF A PFC CUK CONVERTER A PFC based Cuk converter fed BLDC motor drive is

designed for DC link voltage control of VSI with power factor correction at the AC mains. The Cuk converter is designed for a CCM and three different DCMs. In DCM, any one of the energy storing elements Li, Lo or C1 are allowed to operate in discontinuous mode whereas in CCM, all these three parameters operate in continuous conduction. The design and selection criterion of these three parameters is discussed in the following section. The input voltage Vs applied to the DBR is given as,

s m Lv (t) V Sin(2 f t) 220 2Sin(314t)V= π = (1)

where Vm is the peak input voltage (i.e. √2Vs, Vs is the rms value of supply voltage), fL is the line frequency i.e. 50 Hz.

The instantaneous voltage appearing after the DBR is as,

( ) ( )minV (t) V Sin t 220 2 Sin 314t V= ω =

(2)

where | | represents the modulus function. The output voltage, Vdc of Cuk converter is given as [15],

( )

( )dc inD

V V t1 D

=−

(3)

where D represents the duty ratio. The instantaneous value of duty ratio, D(t) depends on the

input voltage appearing after DBR, Vin(t) and the required DC link voltage, Vdc.

Hence the instantaneous duty ratio, D(t) is obtained by substituting (2) in (3) and rearranging it as,

( )

dc dc

min dc dc

V VD(t)

V (t) V V Sin t V= =

+ ω + (4)

The Cuk converter is designed to operate from a minimum DC voltage of 40V (Vdcmin) to a maximum DC link voltage of 200V (Vdcmax). The PFC converter of maximum power rating of 350W (Pmax) is designed for a BLDC motor of 251W (Pm) (full specifications given in Table I) and the switching frequency (fS) is taken as 20kHz. Since the speed of the BLDC motor is controlled by varying the DC link voltage of the VSI, hence the instantaneous power, Pi at any DC link voltage (Vdc) can be taken as linear function of Vdc. Hence for a minimum value of DC link voltage as 40V, the minimum power is calculated as 70W.

A. Design of Li for Continuous or Discontinuous Current Conduction

The critical value of input inductor Lic is expressed as [17],

( )

2sin in

icS S Sin i

2s dc

S i in dc

V (t)D(t) R D(t) V D(t)L

2I (t)f 2f P 2f

VV1

2f P V t V

= = =

=+

⎛ ⎞⎜ ⎟⎝ ⎠

⎛ ⎞⎛ ⎞⎜ ⎟⎜ ⎟

⎝ ⎠⎝ ⎠

(5)

where Rin(t) is the input side resistance, and Iin(t) is the input side current after DBR.


(c) Interval III (d) Waveforms

Fig. 4. Operation of Cuk converter in DICM (Li) during (a-c) different

intervals of switching period and (d) the associated waveforms.



5

Hence the critical value of input side inductor is directly

proportional to the rms value of supply voltage; therefore the worst case design occurs for the minimum value of supply voltage (i.e. Vs=Vsmin=85V). Now the critical value of input inductor at the maximum DC link voltages of 200V at the peak value of supply voltage (i.e. √2Vsmin) is calculated as,

2smin dcmax

ic200maxS smin dcmax

2

V V1L

2f P 2V V

1 85 200322.3 H

2x20000 350 85 2 200

=+

= = μ+

⎛ ⎞⎛ ⎞⎜ ⎟⎜ ⎟

⎝ ⎠ ⎝ ⎠⎛ ⎞ ⎛ ⎞

⎜ ⎟⎜ ⎟ ⎝ ⎠⎝ ⎠

(6)

And the critical value of input inductor at the minimum value of DC link voltages of 40V at the peak value of supply voltage is calculated as,

2smin dcmin

ic40S min smin dcmin

2

V V1L

2f P 2V V

1 85 40644.25 H

2x20000 70 85 2 40

=+

= = μ+

⎛ ⎞⎛ ⎞⎜ ⎟⎜ ⎟

⎝ ⎠ ⎝ ⎠⎛ ⎞ ⎛ ⎞

⎜ ⎟⎜ ⎟ ⎝ ⎠⎝ ⎠

(7)

Hence the value of critical input inductance is obtained lower at maximum DC link voltage. Therefore, the critical value of input inductor is selected lower than Lic200. The performance of the Cuk converter feeding BLDC motor drive is analyzed for different values of input side inductor i.e.

300µH, 200µH and 100µH respectively. Fig. 7(a) shows the variation of THD of supply current at AC mains for the proposed BLDC motor drive with DC link voltage for different values of input side inductor. A high THD of AC mains current is obtained at higher values of input side inductor which doesn’t comply with the IEC 61000-3-2 [14]. Hence the input inductor (Li) of the order of 100µH is selected for its operation in discontinuous conduction to achieve a low value of THD of supply current at AC mains.

The value of input inductor to operate in CCM is decided by the amount of permitted ripple current (η) and is as [17],



Fig. 6. Operation of Cuk converter in DCVM (C1) during (a-c) different intervals of switching period and (d) the associated waveforms.

TABLE I SPECIFICATIONS OF BLDC MOTOR

S.

No. Parameters Values

1. No. of Poles (P) 4 Poles 2. Rated Power (Prated) 251.32W 3. Rated DC link Voltage (Vrated) 200V 4. Rated Torque (Trated) 1.2Nm 5. Rated Speed (ωrated) 2000rpm 6. Back EMF Constant (Kb) 78V/krpm 7. Torque Constant (Kt) 0.74Nm/A 8. Phase Resistance (Rph) 14.56Ω, 9. Phase Inductance (Lph) 25.71mH

10. Moment of Inertia (J) 1.3x10-4Nm/s2

Sw D Cd

C1 Lo

Vdc

+-

Li

R

Inductor Charging

Capacitor Charging



Fig. 5. Operation of Cuk converter in DICM (Lo) during (a-c) different intervals of switching period and (d) the associated waveforms.



6

( )

2sin in

iccmS S Sin i2s dc

S i in dc

V (t)D(t) R D(t) V D(t)L

I (t)f f P f

VV1

f P V t V

= = =η η η

=η +

⎛ ⎞⎜ ⎟⎝ ⎠

⎛ ⎞⎛ ⎞⎜ ⎟⎜ ⎟

⎝ ⎠⎝ ⎠

(8)

The maximum inductor ripple current is obtained at the rated condition i.e. Vdc=200V for a minimum supply voltage (Vsmin=85V). Hence the input side inductor is designed at the peak value of minimum supply voltage (i.e. Vs=√2Vsmin) as,

2smin dcmax

iccmmaxS smin dc

2

V V1L

f P 2V V

1 85 2002.57mH

0.25x20000 350 85 2 200

=η +

= =+

⎛ ⎞⎛ ⎞⎜ ⎟⎜ ⎟

⎝ ⎠ ⎝ ⎠⎛ ⎞ ⎛ ⎞

⎜ ⎟⎜ ⎟ ⎝ ⎠⎝ ⎠

(9)

where the permitted amount of ripple current is selected as 25% of the input current.

Hence the input side inductor of 2.5mH is selected for its operation in continuous conduction.

B. Design of Lo for Continuous or Discontinuous Current Conduction

The critical output side inductor is designed as [17],

( )

( ) ( )

dc dc in dcoc

Lo S S Sin in2S dc dc

Si in in dc

V 1 D(t) V D(t) R V D(t)L

2I (t)f 2I (t)f 2V (t)f

V VV

P 2V t f V t V

−= = =

=+

⎛ ⎞⎛ ⎞⎜ ⎟⎜ ⎟

⎝ ⎠ ⎝ ⎠

(10)

The maximum current ripple in an inductor occurs at the maximum power and for minimum value of supply voltage (i.e. Vsmin=85V). Hence the output inductor is calculated at the peak of supply voltage (Vin=√2Vsmin). The critical value of inductor corresponding to maximum DC link voltage of 200V (i.e. Vdcmax) is given as,

2smin dcmax dcmax

oc200max Ssmin smin dcmax

2

V V VL

P 2 2V f 2V V

85 200 200536 H

350 2 2x85x20000 85 2 200

=+

= = μ+

⎛ ⎞⎛ ⎞⎜ ⎟⎜ ⎟

⎝ ⎠ ⎝ ⎠⎛ ⎞ ⎛ ⎞

⎜ ⎟⎜ ⎟ ⎝ ⎠⎝ ⎠

(11)

Moreover, the critical value of output side inductor at peak of Vsmin and minimum DC link voltage of 40V is given as,

2smin dcmin dcmin

oc40min Ssmin smin dcmin

2

V V VL

P 2 2V f 2V V

85 40 40214.4 H

70 2 2x85x20000 85 2 40

=+

= = μ+

⎛ ⎞⎛ ⎞⎜ ⎟⎜ ⎟

⎝ ⎠ ⎝ ⎠⎛ ⎞ ⎛ ⎞

⎜ ⎟⎜ ⎟ ⎝ ⎠⎝ ⎠

(12)

Hence, the critical value of output inductor is to be selected lower than Loc40. The performance of the proposed BLDC motor drive is analyzed for different values of output side inductor i.e. 200µH, 130µH and 70µH respectively.

(a)

(b)

Fig. 7. Variation of THD of supply current at AC mains with change in DC link voltage for (a) different values of input side inductors (Li) and (b) different values of output side inductors (Lo).

Fig. 7(b) shows the variation of THD of supply current at AC mains for the proposed BLDC motor drive with DC link voltage for different values of output side inductor. A high THD of AC mains current is obtained at higher values of output side inductor which doesn’t comply with the IEC 61000-3-2 [14]. Hence the output inductor (Lo) of the order of 70µH is selected for its operation in discontinuous conduction to achieve a low value of THD of supply current at AC mains.

The value of output inductor to operate in CCM is decided by the amount of permitted ripple current (λ) and is as [17],

( )

( ) ( )

dc dc in dcoccm

Lo S S Sin in2s dc dc

Si in in dc

V 1 D(t) V D(t) R V D(t)L

I (t)f I (t)f V (t)f

V VV

P V t f V t V

−= = =

λ λ λ

=λ +

⎛ ⎞⎛ ⎞⎜ ⎟⎜ ⎟

⎝ ⎠ ⎝ ⎠

(13)

Hence the maximum current occurs at maximum DC link

0

10

20

30

40

50

40 60 80 100 120 140 160 180 200

THD

of S

uppl

y C

urre

nt (%

)

DC Link Voltage (V)

Li=100uHLi=200uHLi=300uH

Li=100µHLi=200µHLi=300µH

0

10

20

30

40

50

40 60 80 100 120 140 160 180 200

THD

of S

uppl

y C

urre

nt (%

)

DC Link Voltage (V)

Lo=70uHLo=130uHLo=200uH

Lo=70µHLo=130µHLo=200µH

Very high harmonic

distortion in supply current

Lo = 4.3mH (For All Cases)

Very high harmonic

distortion in supply current

Li = 2.5mH (For All Cases)



7

voltage (i.e. Pmax) and the minimum supply voltage of 85V (i.e. Vsmin). Hence the value of output inductor (Lo) for a permitted maximum ripple current of 25% is calculated as,

2smin dcmax dcmax

occmmax Ssmin smin dcmax

2

V V VL

P 2V f 2V V

85 200 2004.29mH

350 0.25x 2x85x20000 85 2 200

=λ +

= =+

⎛ ⎞⎛ ⎞⎜ ⎟⎜ ⎟

⎝ ⎠ ⎝ ⎠⎛ ⎞ ⎛ ⎞

⎜ ⎟⎜ ⎟ ⎝ ⎠⎝ ⎠

(14) Hence Lo of 4.3mH is selected for operation of output

inductor (Lo) in continuous conduction.

C. Design of C1 for Continuous or Discontinuous Voltage The critical value of intermediate capacitance C1c is as [17],

( )( )

dc1c

LC1 S

V D tC

2V t f R= (15)

Hence by substituting the expressions of intermediate capacitor voltage, VC1(t)=Vdc+Vin(t), emulated load resistance, RL=Vdc

2/Pi and D(t) from equation (4) in equation (15) and rearranging it one obtains,

( ) ( ) ( )

( )( )

dc dc1c 2

Sdc in dc i in dc

i2

S in dc

V VC

2 V V t f V P V t V

P

2f V t V

=+ +

=+

⎛ ⎞⎜ ⎟⎝ ⎠ (16)

Now the maximum ripple in intermediate capacitor occurs at the maximum value of supply voltage (i.e. Vsmax=270V). Hence the critical value of intermediate capacitance is calculate at maximum DC link voltage (Vdcmax=200V) as,

( )

( )

max1c200 2

smaxS dcmax

2

PC

2f 2V V

35025.84nF

2x20000 270 2 200

=+

= =+

(17) And the critical value of intermediate capacitance at

minimum DC link voltage (Vdcmin=40V) is calculated as,

( )

( )

min1c40 2

smaxS dcmin

2

PC

2f 2V V

709.83nF

2x20000 270 2 40

=+

= =+

(18)

Hence an intermediate capacitor is selected less than C1c40. Therefore, the value of intermediate capacitor is taken as 9.1nF for its operation in discontinuous conduction.

The value of intermediate capacitance to operate in CCM with a permitted tipple voltage of κ% is given as [17],

( )( )

( ) ( ) ( )

( )( )

dc1ccm

LC1 S

dc dc2

Sdc in dc i in dc

i2

S in dc

V D tC

V t f R

V V

V V t f V P V t V

P

f V t V

=κ

=κ + +

=κ +

⎛ ⎞⎜ ⎟⎝ ⎠

(19)

Hence the value of intermediate capacitor is calculated at maximum ripple voltage in C1 which occurs at maximum value of supply voltage (i.e. Vsmax=270V) and maximum DC link voltage and is given as,

( )

( )

max1ccm 2

smaxS dcmax

2

PC

f 2V V

3500.516 F

0.1x20000 270 2 200

=κ +

= = μ+

(20)

where κ is selected as 10% of the maximum voltage appearing across the intermediate capacitor.

Hence the intermediate capacitor of 0.66µF is selected for this application for intermediate capacitor operating in continuous conduction.

D. Design of DC link Capacitor (Cd)

The value of DC link capacitor is calculated by [17],

( )dc i dc id 2

dc dc dc

I P V PC

2 V 2 V 2 V= = =

ωΔ ωδ ωδ (21)

Now the value of DC link capacitor is calculated at maximum value of DC link voltage given as,

maxd200 2 2

dcmax

P 350C 348.33 F

2 V 2x314x0.04x200= = = μ

ωδ

(22)

where δ represents the permitted ripple in DC link voltage which is taken as 4% of Vdc.

And the DC link capacitance at minimum value of DC link voltage (Vdcmin) is expressed as,

mind40 2 2

dcmin

P 70C 1741.6 F

2 V 2x314x0.04x40= = = μ

ωδ (23)

Hence the value of DC link capacitor is taken higher than the Cd40 to ensure a ripple of DC link voltage less than 4% even at lower values of DC link voltages. Hence the DC link capacitor of 2200µF is selected for the application.

Table II shows the specification of the PFC Cuk Converter and the selected values of input and output inductors, intermediate capacitor and the DC link capacitor for a PFC Cuk converter operating in different modes of conduction.

E. Design of Filter Parameters (Lf and Cf) A low pass LC filter is used to avoid the reflection of

higher order harmonics in supply system. The maximum value of filter capacitance is given as [36],



8

TABLE II DESIGN PARAMETERS IN DIFFERENT MODES OF OPERATION

Specifications ↓ Values

Supply Voltage (Vs)

Rated: 220V, (Universal Mains: 85-270V)

DC Link Voltage (Vdc)

Rated: 200V, (40V-200V)

Power (P) Rated: 350W, (70W-350W)

Switching Frequency (fs)

20kHz

Operation ↓ Li Lo C1 Cd

CCM 2.5mH 4.3mH 0.66µF

2200μF DICM (Li) 100µH 4.3mH 0.66µF

DICM (Lo) 2.5mH 70μH 0.66µF

DCVM (C1) 2.5mH 4.3mH 9.1nF

( )

( )

max smmax

m mL L

P 2 VIC tan( ) tan( )

V V

350 2 / 220tan(1 ) 401.98nF

314x220 2

= θ = θω ω

= =

(24)

where Im and Vm are the peak value of supply current and supply voltage respectively and θ is the displacement angle between supply voltage and supply current respectively. Hence a value of filter capacitor, Cf is taken as 330nF.

Now, the value of filter inductor is designed by considering the source impedance (Ls) of 4-5% of the base impedance. Hence the additional value of inductance required is given as,

( ) ( )

2s

req s reqf 2 2c oLf

2

req 22 -9

V1 1L = L +L =L +0.04

4π f C ω P

1 1 220L = - 0.04

314 3504π x 2000 x330x10

= 1.573mH

⇒

∴

⎛ ⎞⎛ ⎞⎜ ⎟⎜ ⎟⎝ ⎠⎝ ⎠

⎛ ⎞⎜ ⎟⎝ ⎠

(25)

where fc is the cut-off frequency which is selected such that fL<fc<fS; hence it is taken as fS/10.

Hence a LC filter is selected with inductance Lf and capacitance Cf as 1.57mH and 330nF respectively. Therefore, an input side LC filter with Lf =1.57mH and Cf =330nF is taken for harmonics suppression at the AC mains.

V. CONTROL OF PFC CUK CONVERTER FED BLDC MOTOR DRIVE

Two different control schemes of PFC Cuk converter are the current multiplier and the voltage follower approach for its operation in CCM and DCM respectively. A brief description of both control schemes is presented in this section.

A. Current Multiplier Approach for Cuk Converter Operating in CCM

An equivalent reference voltage (Vdc*) corresponding to the

particular reference speed (N*) is generated by a ‘Reference Voltage Generator’ as the speed of BLDC motor which is proportional to the DC link voltage of the VSI. Fig. 1 shows the Cuk converter feeding BLDC motor drive using a current multiplier approach. A reference voltage is generated by the product of speed and the voltage constant (Kb) of the BLDC motor and is given as,

* *dc bV k N= (26)

This reference voltage is compared with the sensed DC link voltage (Vdc) to generate a voltage error (Ve). The voltage error Ve at any instant ‘k’ is given as,

*

e dc dcV (k) V (k) V (k)= − (27)

This voltage error is given to voltage proportional-integral (PI) controller for generation of a controlled output (Vc) as,

c c pv e e eivV (k) V (k 1) k V (k) V (k 1) k V (k)= − + − − + (28)

where kpv is the proportional gain and kiv is the integral gain of the voltage PI controller.

The reference current (iin*) is generated by multiplying the controller output with the unit template of supply voltage as,

* scin

m

v (k)i (k) V (k)

V= (29)

where vs(k)/Vm is the unit template of supply voltage, vs and Vm represents the amplitude of supply voltage.

This reference current is compared with the sensed input current to generate a current error given as,

*

e in ini (k) i (k) i (k)= − (30)

This current error is given to the current controller to generate a controlled output (Vcc) given as,

cc cc e e epi iiV (k) V (k 1) k i (k) i (k 1) k i (k)= − + − − + (31)

where kpi and kii are the proportional and integral gain of the current PI controller.

Finally the controller output (Vcc) is compared with the high frequency saw tooth waveform to generate the PWM signal to be given to PFC converter switch as,

cc w wd 0m (t) V (t) then S 1, else S =< = (32)

where Sw denotes the switching signals as 1 and 0 for MOSFET to switch on and off respectively.

B. Voltage Follower Approach for Cuk Converter Operating in DCM

In this approach, a reference voltage (Vdc*) corresponding to the particular reference speed (N*) is generated similar to the current multiplier approach as,

* *dc bV k N= (33)

where kb represents the BLDC motor’s voltage constant and N* is the reference speed.

Now this reference voltage is compared with sensed DC link voltage (Vdc) to generate a voltage error (Ve). The voltage error Ve at any instant ‘k’ is given as,



9

*

e dc dcV (k) V (k) V (k)= − (34)

This voltage error is given to the voltage PI controller to generate a controlled output (Vcd) given as,

pv e e ecd cd ivV (k) V (k 1) k V (k) V (k 1) k V (k)= − + − − + (35) where kpv and kiv are the proportional and integral gain of the voltage PI controller. Finally the controller output (Vcd) is compared with the high frequency saw-tooth waveform to generate the PWM signal to be given to PFC converter switch as,

w wd cd 0m (t) V (t) then S 1, else S =< = (36)

where Sw denotes the switching signals as 1 and 0 for MOSFET to switch on and off respectively.

VI. SIMULATED PERFORMANCE OF PROPOSED BLDC MOTOR DRIVE

The performance of Cuk converter fed BLDC motor drive is simulated for four different modes in MATLAB/Simulink environment. The performance of each mode of operation is evaluated on the basis of various performance parameters. Supply voltage (vs) and supply current (is) are used for estimating the power quality of the system. The speed (N), electromagnetic torque (Te) and the stator current (ia) of the BLDC motor is used for determining the satisfactory operation of the BLDC motor. Whereas, the DC link voltage (Vdc), inductor’s currents (iLi and iLo), intermediate capacitor’s voltage (VC1), switch voltage (Vsw) and switch current (isw) are used for the performance evaluation of the PFC Cuk converter. Power quality indices such as power factor (PF), displacement power factor (DPF), crest factor (CF) and total harmonic distortion (THD) of supply current are analyzed for determining power quality at AC mains.

A. Performance of BLDC Motor fed by a Cuk Converter operating in CCM

The circuit configuration and control of PFC Cuk converter operating in CCM are shown in Fig. 1. The parameters selected for this converter to operate in CCM are as follows:

Input inductor (Li) = 2.5mH, output inductor (Lo) = 4.3mH, intermediate capacitor (C1) = 0.66μF and DC link capacitor (Cd) = 2200μF.

Fig. 8 shows the performance of proposed BLDC motor drive fed by a PFC Cuk converter operating in CCM. Fig. 8 shows the steady state performance demonstrating the associated waveforms for 3 cycles of line frequency. The input inductor current iLi, output inductor current iLo and intermediate capacitor’s voltage VC1 are continuous in operation while the supply current iS, is sinusoidal and in phase with the supply voltage vS which shows a unity power factor at AC mains. Table III shows the performance of proposed BLDC motor fed by a PFC Cuk converter operating in CCM over a wide range of DC link voltage control (i.e. speed control) with unity power factor operation at AC mains [14]. Table VII shows the peak voltage and current stress of PFC converter switch for different modes of operation. The

peak voltage and current stresses of 560V and 8.1A are obtained at rated condition in this mode of CCM.

B. Performance of BLDC Motor fed by a Cuk Converter operating in DICM (Li)

The circuit configuration and control of PFC Cuk converter operating in DICM mode of operation with input inductor (Li) operating in discontinuous conduction are shown in Fig. 2.

Fig. 8. Simulated performance of BLDC motor drive with Cuk converter operating in CCM

TABLE III PERFORMANCE OF BLDC MOTOR DRIVE WITH CUK

CONVERTER OPERATING IN CCM

Vdc (V)

Speed (rpm)

THD of Is (%) DPF PF Is (A)

40 320 7.42 0.998 0.9953 0.445

60 530 6.81 0.9984 0.9961 0.578

80 740 5.54 0.9987 0.9972 0.713

100 940 4.85 0.9995 0.9983 0.847

120 1150 4.68 0.9998 0.9987 0.982

140 1360 4.32 0.9998 0.9989 1.115 160 1560 4.02 0.9999 0.9991 1.248

180 1770 3.91 0.9999 0.9991 1.384

200 1980 3.85 0.9999 0.9992 1.517



10

The parameters selected for this converter to operate in DICM (Li) are as follows:

Input inductor (Li) = 100μH, output inductor (Lo) = 4.3mH, intermediate capacitor (C1) = 0.66μF and DC link capacitor (Cd) = 2200μF.

The steady state performance of Cuk converter fed BLDC motor drive operating in DICM with input inductor operating in discontinuous conduction is shown in Fig. 9. The input inductor current iLi is discontinuous as shown in Fig. 9; while the output inductor current iLo and intermediate capacitor’s voltage VC1 remain continuous. Table IV shows the improved power quality operation of BLDC motor fed by a Cuk Converter operating in DICM (Li) over a wide range of speed control. As shown in Table VII, peak voltage stress of 570V and peak current stress of 33.1A are obtained at rated condition in this mode of DICM (Li).

C. Performance of BLDC Motor fed by a Cuk Converter operating in DICM (Lo)

The circuit configuration and control of PFC Cuk converter operating in DICM mode of operation with output inductor (Lo) operating in discontinuous conduction are shown in Fig. 2. The parameters selected for this converter to operate in DICM (Lo) are as follows:

Input inductor (Li) = 2.5mH, output inductor (Lo) = 70μH, intermediate capacitor (C1) = 0.66μF and DC link capacitor (Cd) = 2200μF.

Fig. 10 shows the performance of proposed BLDC motor drive fed by a PFC Cuk converter operating in DICM (Lo). A discontinuous output inductor current iLo is obtained while the input inductor current iLi and intermediate capacitor’s voltage VC1 remain in continuous conduction operation. Table V shows the performance of BLDC motor drive fed by a Cuk converter operating in DICM (Lo) over a wide range of DC link voltage control (i.e. speed control). An improved power quality operation is achieved for the complete range of speed control. The peak voltage and current stress of 560V and 20.5A is obtained at rated condition in this mode of DICM (Lo) as shown in Table VII, which is quite acceptable for a power rating of 350W.

D. Performance of BLDC Motor fed by a Cuk Converter operating in DCVM (C1)

The circuit configuration and control of PFC Cuk converter operating in DCVM mode of operation with intermediate capacitor (C1) operating in discontinuous conduction are shown in Fig. 2. The parameters selected for this converter to operate in DCVM (C1) are as follows:

Input inductor (Li) = 2.5mH, output inductor (Lo) = 4.3mH, intermediate capacitor (C1) = 9.1nF and DC link capacitor (Cd) = 2200μF.

The steady state performance of the BLDC motor drive fed by a Cuk converter operating in DCVM is shown for 3 cycles of line frequency in Fig. 11. In this mode, the voltage across the intermediate capacitor (VC1) remains discontinuous while the currents in input and output inductors (iLi and iLo) remain in continuous conduction. A near unity power factor operation

is achieved at the AC mains for a wide range of DC link voltage control (i.e. speed control) as shown in Table VI. As shown in Table VII, the peak current stress of 10.5A is obtained which is low and of the order of peak current stress as obtained in CCM; but a very high voltage stress of 1950V is obtained at rated condition which makes this configuration difficult to realize in practice.

Fig. 9. Simulated performance of BLDC motor drive with Cuk converter

operating in DICM (Li).

TABLE IV

PERFORMANCE OF BLDC MOTOR DRIVE WITH CUK CONVERTER OPERATING IN DICM (Li)

Vdc (V)

Speed (rpm)


40 320 8.82 0.9942 0.9903 0.448

60 530 7.96 0.9959 0.9927 0.597 80 740 6.82 0.9965 0.9942 0.746

100 940 5.96 0.9969 0.9951 0.895

120 1150 5.21 0.9977 0.9963 1.046

140 1360 5.01 0.9982 0.9969 1.194

160 1560 4.83 0.9989 0.9977 1.344

180 1770 4.69 0.9993 0.9982 1.492 200 1980 4.25 0.9997 0.9988 1.641



11

E. Comparative Analysis of Proposed BLDC Drive with PFC Cuk Converter in Different Modes of Operation The performance of Cuk converter feeding a BLDC motor has been analyzed for different continuous and discontinuous modes of operation. The stress on PFC converter switch in case of PFC Cuk converter operating in CCM is very low, but it utilizes a current multiplier approach for PFC operation which requires three sensors (i.e. two voltages and one current sensor), which is not recommended for low cost and low

power applications. The performance in terms of power quality is obtained satisfactory in all configurations. Figs. 12(a) and 12(b) show the variation of THD of supply current and power factor at AC mains with DC link voltage. The THD of supply current obtained is below 9% in all modes which is well acceptable in IEC 61000-3-2 which recommends a THD of supply current of the order of 19% for class-A applications (household equipments) [14]. The power factor obtained is above 0.99 for all conditions which shows a unity power factor operation at the AC mains.

Fig. 11. Simulated performance of BLDC motor drive with Cuk

converter operating in DCVM.

TABLE VI PERFORMANCE OF BLDC MOTOR DRIVE WITH CUK

CONVERTER OPERATING IN DCVM (C1)

Vdc (V)

Speed (rpm)


40 320 6.14 0.9947 0.9928 0.493

60 530 5.52 0.9965 0.995 0.629

80 740 4.89 0.9974 0.9962 0.763 100 940 4.01 0.9977 0.9969 0.899

120 1150 3.45 0.998 0.9974 1.033

140 1360 3.08 0.9988 0.9983 1.168

160 1560 2.79 0.999 0.9986 1.302

180 1770 2.53 0.9993 0.999 1.438

200 1980 2.25 0.9995 0.9992 1.572

Fig. 10. Simulated performance of BLDC motor drive with Cuk

converter operating in DICM (Lo).

TABLE V PERFORMANCE OF BLDC MOTOR DRIVE WITH CUK

CONVERTER OPERATING IN DICM (Lo)

Vdc (V)

Speed (rpm)


40 320 5.89 0.9959 0.9942 0.446

60 530 5.69 0.9965 0.9949 0.581

80 740 4.98 0.9971 0.9959 0.719 100 940 4.52 0.9978 0.9968 0.855

120 1150 4.11 0.9985 0.9977 0.993

140 1360 3.62 0.9992 0.9985 1.128

160 1560 2.85 0.9998 0.9994 1.265

180 1770 2.25 0.9999 0.9996 1.403

200 1980 1.81 0.9999 0.9997 1.537



12

(a)

(b)

Fig. 12. Variation of (a) THD of supply current and (b) power factor with DC link voltage for different configuration of PFC Cuk converter Fed BLDC

motor drive.

An analysis based on the peak voltage across the switch and current stress through the switch is also carried out to determine the feasibility and the stress constraints of the proposed scheme. Figs. 13(a) and 13(b) show the peak voltage and current stress variation with the load on the BLDC motor. As shown in Fig. 13(a), the voltage stress of DCVM (C1) is very high (1950V) and can’t be recommended because of higher switch rating requirement; whereas, the voltage stress for the remaining three modes are of the order of 560V which is acceptable. Now the choice among the two configurations of DICM is decided on the basis of peak current stress as shown in Fig. 13(b). A lower current stress in DICM (Lo) is obtained which makes it suitable for the particular application. Moreover, EMI problems in DICM (Li) configuration are high because of the input side inductor which in series with the supply operating in discontinuous mode. A comparative analysis of four different modes of operation is summarized in Table VIII. Based on this analysis, a hardware prototype of the BLDC motor drive with Cuk converter operating in DICM (Lo) is developed as discussed in next section.

F. Comparative Evaluation of Proposed Configuration with Conventional Schemes

This section deals with a comparative study of three configurations of BLDC motor drive. The proposed configuration is compared with a conventional DBR fed BLDC motor drive and a conventional single-switch PFC converter feeding BLDC motor drive via a PWM based switching of VSI [18-20]. The evaluation is based on the control requirement, sensor requirement, system complexity, losses in a drive system and the overall cost of system.

Table IX shows a comparative performance of the proposed configuration with the conventional scheme of BLDC motor drives. The proposed configuration requires a single voltage sensor for DC link voltage control as compared to other two configurations, which reduces the cost of overall system. The

0

2

4

6

8

10

40 60 80 100 120 140 160 180 200

THD

of S

uppl

y C

urre

nt (%

)

DC Link Voltage (V)

CCMDCM (Li)DCM (Lo)DCM (C1)

0.988

0.992

0.996

1

1.004

40 60 80 100 120 140 160 180 200

Pow

er F

acto

r

DC Link Voltage (V)


TABLE VII STRESS ON PFC CONVERTER SWITCH FOR DIFFERENT CONFIGURATION OF CUK CONVERTER FED BLDC MOTOR DRIVE

Load (%)

CCM DICM (Li) DICM (Lo) DCVM (C1)

Vswp (V)

Iswp (A)

Iswr (A)

Vswp (V)

Iswp (A)

Iswr (A)

Vswp (V)

Iswp (A)

Iswr (A)

Vswp (V)

Iswp (A)

Iswr (A)

10 550 4.2 0.412 560 18.4 0.414 550 8.2 0.411 620 4.9 0.413

20 550 4.6 0.513 560 19.1 0.516 550 9.1 0.517 770 5.3 0.514

30 550 5.1 0.613 560 19.9 0.617 550 10.3 0.617 910 5.7 0.613

40 550 5.7 0.714 560 21.5 0.714 550 11.2 0.715 1050 6.2 0.716

50 560 6.3 0.815 570 24.2 0.817 560 12.3 0.818 1210 6.9 0.817

60 560 6.9 0.917 570 26.5 0.921 560 13.5 0.923 1370 7.3 0.919

70 560 7.1 1.025 570 28.5 1.029 560 14.8 1.031 1510 7.9 1.027

80 560 7.6 1.123 570 29.8 1.125 560 15.9 1.127 1670 8.5 1.126

90 560 7.9 1.217 570 31.2 1.219 560 17.5 1.221 1820 9.2 1.219

100 560 8.1 1.318 570 33.1 1.331 560 20.5 1.312 1950 10.5 1.325



13

sensor requirement in a conventional PFC based BLDC motor drive is highest due to the use of PWM based switching of BLDC motor which requires two current sensors and one voltage sensor for DC link voltage control. Moreover, a simple control loop for DC link voltage control and to achieve electronic commutation is used which requires a low cost processor for the development purpose.

Hence, the simplicity, low losses in VSI due to fundamental switching, requirement of minimum amount of sensing and a much simple approach of speed control with a power factor correction at AC mains make the proposed drive a good solution for low power application.

VII. HARDWARE VALIDATION OF PROPOSED DRIVE A DSP (Digital Signal Processor TI-TMS320F2812) is

used for the development of proposed BLDC motor drive. Isolation between the DSP based controller and gate drivers of solid state switches of VSI and PFC converter is provided using an opto-coupler. The pre-filtering and isolation circuits for Hall Effect position sensor are also developed for sensing the rotor position signals. Moreover, software based moving average filter (MAF) is also developed for sensing the Hall signals [37]. The performance of the proposed drive is

evaluated for a wide range of speed control with unity power factor operation at AC mains.

A. Steady State Performance of the Proposed Drive Figs. 14(a) and 14(b) show the operation of proposed

BLDC motor drive for a DC link voltage (Vdc) of 200V and 50V respectively. The supply current (is) achieved is sinusoidal in nature and is in phase with the supply voltage (vs) demonstrating the unity power factor at AC mains. The DC link voltage (Vdc) is maintained at the desired value and the frequency of stator current (ia) of the BLDC motor is used for the determination of speed of BLDC motor. The frequency of the stator current as shown in Figs. 14(a) and (b) are of the order of 80Hz and 18Hz respectively (electronic commutation of BLDC Motor). This frequency is very low as compared to PWM based control of VSI for controlling the speed of BLDC motor drive. Hence, the switching losses in VSI corresponding to such low frequency are very low as compared to PWM based switching of VSI. The variation of speed and the DC link voltage with reference voltage at analog to digital converter (ADC) of DSP are shown in Table X.

TABLE VIII COMPARATIVE ANALYSIS OF VARIOUS MODES OF OPERATION

Attributes CCM DCM (Li) DCM (Lo) DCM (C1)

Sensor’s Requirement 3 (2V, 1C) 1 (V) 1 (V) 1 (V)

Control Complex Easy Easy Easy

Filter Requirement No Yes No No

Voltage Stress Low Low Low Very High

Current Stress Low High Medium Low

Cost of PFC system High Low Low Low

Inductor Rating Low High (Li) High (Lo) Low

Capacitor Rating Low Low Low Very High

TABLE IX COMPARATIVE ANALYSIS OF PROPOSED CONFIGURATION

WITH CONVENTIONAL SCHEMES

Schemes Conventional (No PFC)

Conventional (PFC) Proposed

Attributes ↓

Variable DC Bus - No Yes

Control (BLDC Motor)

Current Controlled (Complex)

Current Controlled (Complex)

Electronic Commutation

(Simple)

Control (PFC) - Voltage Follower

Voltage Follower

Sensor (BLDC Motor)

2-Current + 1-Hall

2-Current + 1-Hall 1-Hall

Sensor (PFC) - 1-Voltage 1-Voltage

Losses (VSI) High High Low

PFC - Yes Yes

Cost Medium High Low

(a)

(b)

Fig. 13. Variation of (a) switch peak voltage and (b) peak current with load for different configuration of Cuk converter Fed BLDC motor drive.

0

400

800

1200

1600

2000

10 20 30 40 50 60 70 80 90 100

Peak

Vol

tage

Str

ess (

V)

Load (%)


0

5

10

15

20

25

30

35

40

10 20 30 40 50 60 70 80 90 100

Peak

Cur

rent

Str

ess (

A)

Load (%)




14

B. Operation of Cuk Converter operating in DICM (Lo)

Figs. 15(a) and 15(b) show the waveforms of current in input and output inductors (iLi and iLo) and intermediate capacitor’s voltage (VC1) to demonstrate the DICM operation of output inductor Lo. As shown in these figures, the current in input inductor (iLi) and voltage across intermediate capacitor (VC1) remain continuous but the current in output inductor becomes discontinuous for a switching period. Fig. 15(c) shows the voltage and current of the PFC converter’s switch with peak voltage and current stress of 580V and 19A respectively.

C. Dynamic Performance of the Proposed Drive

Fig. 16(a) shows the dynamic performance of the proposed BLDC motor drive during starting at DC link voltage of 50V. This stator current (ia) of BLDC motor and supply current waveforms are recorded to show the limited overshoot during

SCh. 1(V ): 500V/div.

LiCh. 2(i ): 2A/div.

C1Ch. 3(V ): 500V/div.

aCh. 4(i ): 20A/div.

SV

Lii

C1V

Loi

Continuous Input Inductor Current

Continuous Intermediate Capacitor Voltage

Discontinuous Output Inductor Current

Fig. 15(a)

SCh. 1(V ): 500V/div.

LiCh. 2(i ): 2A/div.

C1Ch. 3(V ): 500V/div.

aCh. 4(i ): 20A/div.

SV

Lii

C1V

LoiPeak Inductor Current 22A≈

Peak Capacitor Voltage 540V≈

Peak Inductor Current 2.4A≈

Fig. 15(b)

SWCh. 3(V ): 200V/div.

SWCh. 4(i ): 20A/div.

SWV

SWi

Peak Voltage Stress on Switch 580V≈

Peak Current Stress on Switch 19A≈

Fig. 15(c)

Fig. 15. Test results of proposed BLDC Motor drive showing (a) Supply voltage with inductors currents and intermediate capacitor’s voltage and (b) its enlarged waveforms. (c) Waveform of voltage and current stress on PFC converter switch.

TABLE X VARIATION OF DC LINK VOLTAGE AND SPEED WITH REFERNCE

VOLTAGE

Vref (V) 0.7 0.95 1.1 1.25 1.35 1.45 1.52 1.61 1.67

Vdc (V) 40 60 80 100 120 140 160 180 200

Speed (rpm) 320 520 730 930 1150 1350 1540 1750 1960

SCh. 1(V ): 200V/div.

SCh. 2(i ): 5A/div.

dcCh. 3(V ): 200V/div.

aCh. 4(i ): 5A/div.

SV

Si

dcV

ai

PFC Operation

Fig. 14(a)

SCh. 1(V ): 500V/div.

SCh. 2(i ): 1A/div.


aCh. 4(i ): 1A/div.

SV

Si

dcV

ai

PFC Operation

Fig. 14(b)

Fig. 14. Steady state performance of Cuk converter fed BLDC motor drive at rated condition with DC link voltage as (a) 200V and (b) 50V.



15

the dynamic conditions. Fig. 16(b) shows the dynamic performance of the proposed BLDC motor drive during speed control which is obtained by step change in DC link voltage from 100V to 150V. Moreover, the dynamic performance of proposed BLDC motor drive during step change in supply voltage from 250V to 180V is shown in Fig. 16(c). The

change in DC link voltage is obtained with smooth transition and limited overshoot in supply current and stator current of BLDC motor; which demonstrates a satisfactory closed loop performance of the proposed drive.

D. Unity Power Factor Operation of the Proposed Drive Supply voltage (vs), supply current (is), active (Pac),

reactive (Pr) and apparent (Pa) powers are measured on a ‘Fluke’ make power quality analyzer to demonstrate the power quality indices such as PF, DPF and THD of supply current. Figs. 17(a)-(c) and Figs. 17(d)-(f) show the results obtained at DC link voltage of 200V and 50V respectively. Moreover, Figs. 17(g)-(i) and Figs. 17(j)-(l) show the performance at supply voltages of 90V and 270V respectively. An improved power quality is obtained in all these conditions and the obtained power quality indices are within the recommended limits of IEC 61000-3-2 [14]. A satisfactory performance of the proposed BLDC motor drive fed by a PFC Cuk converter is achieved and is demonstrated through simulated and experimental results. Thus, the proposed drive is suitable for achieving a unity power factor at AC mains over a wide range of speed control at universal AC mains.

(a) (b) (c)

(d) (e) (f)

(g) (h) (i)

(j) (k) (l) Fig. 17. Power quality indices of proposed BLDC motor drive at rated load on BLDC motor with (a-c) DC link voltage as 200V at rated conditions (d-f) DC link voltage as 50V at rated conditions (g-i) DC link voltage as 200V and supply voltage as 90V at rated load (j-l) DC link voltage as 200V and supply voltage as 270V at rated load.

SCh. 1(V ): 500V/div.

SCh. 2(i ): 1A/div.


aCh. 4(i ): 5A/div.

SV

Si

dcV

ai

Step Change in DC Link Voltage

Limited Overshoot in Stator Current

Fig. 16(a)

SCh. 1(V ): 500V/div.

SCh. 2(i ): 5A/div.


aCh. 4(i ): 5A/div.

SV

Si

dcV

ai

Step Change in DC Link Voltage

Fig. 16(b)

SCh. 1(V ): 500V/div.

SCh. 2(i ): 5A/div.


aCh. 4(i ): 5A/div.

SV

Si

dcV

ai

Step Change in Supply Voltage

DC Link Voltage Remaining Constant

Fig. 16(c)

Fig. 16. Test results of proposed BLDC motor drive at rated load on BLDC motor during (a) Starting at DC link voltage of 50V (b) Step change in DC link voltage from 100V to 150V and (c) Change in supply voltage from 250V to 170V.



16

VIII. CONCLUSION A Cuk converter for VSI fed BLDC motor drive has been

designed for achieving a unity power factor at AC mains for the development of low cost PFC motor for numerous low power equipments such fans, blowers, water pumps etc. The speed of the BLDC motor drive has been controlled by varying the DC link voltage of VSI; which allows the VSI to operate in fundamental frequency switching mode for reduced switching losses. Four different modes of Cuk converter operating in CCM and DCM have been explored for the development of BLDC motor drive with unity power factor at AC mains. A detailed comparison of all modes of operation has been presented on the basis of feasibility in design and the cost constraint in the development of such drive for low power applications. Finally, a best suited mode of Cuk converter with output inductor current operating in DICM has been selected for experimental verifications. The proposed drive system has shown satisfactory results in all aspects and is a recommended solution for low power BLDC motor drives.

APPENDIX

Detuning Phenomenon in a Cuk Converter: “Detuning phenomenon” represents the inability of a PFC converter to maintain a sinusoidal supply current at near zero-crossings of the supply voltage [38]. This distortion of the supply current at its zero crossing results in high THD of supply current and directly affects the power factor at AC mains. Now considering a case of a PFC Cuk converter fed BLDC motor drive with Cuk converter operating in DCM with output inductor (Lo) is designed to operate in DCM. During the PFC operation, the supply current is in phase with the supply voltage and it is sinusoidal in nature. The input power at zero crossings of supply voltage is very low and the duty ratio is unity. Hence, a distortion in input inductor current occurs due to inability of the input inductor to maintain a continuous current through it. Fig. 18 shows the distortion of supply current near zero crossing for a PFC Cuk converter fed BLDC motor drive with Cuk converter operating in DICM (Lo).

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Fig. 18. Waveform of the supply current showing the ‘control detuning

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17

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Vashist Bist (S’13) received his Diploma and B.E. in Instrumentation and Control Engineering from Sant Longowal Institute of Engineering and Technology (SLIET Longowal), Punjab, India in 2007 and 2010 respectively. He is currently pursuing his PhD in the Department of Electrical Engineering, Indian Institute of Technology Delhi.

His areas of interests include power electronics, electrical machines and drives. He is a student member of IEEE.

Bhim Singh (SM’99–F’10) received the Bachelor

of Engineering (Electrical) degree from the University of Roorkee, Roorkee, India, in 1977, and M.Tech. (Power Apparatus and Systems) and Ph.D. degrees from the Indian Institute of Technology Delhi (IITD), New Delhi, India, in 1979 and 1983, respectively. In 1983, he joined the Department of Electrical Engineering, University of Roorkee, as a Lecturer. He became a Reader there in 1988. In December 1990, he joined the Department of Electrical Engineering, IIT

Delhi, India, as an Assistant Professor. Where he has became an Associate Professor in 1994 and a Professor in 1997. He has been ABB Chair Professor from September 2007 to September 2012. Since October 2012, he is a CEA Chair Professor.

He has received Khosla Research Prize of University of Roorkee in the year 1991. He is recipient of JC Bose and Bimal K Bose awards of The Institution of Electronics and Telecommunication Engineers (IETE) for his contribution in the field of Power Electronics. He is also a recipient of Maharashtra State National Award of Indian Society for Technical Education (ISTE) in recognition of his outstanding research work in the area of Power Quality. He has received PES Delhi Chapter Outstanding Engineer Award for the year 2006. Professor Singh has also received Khosla National Research Award of IIT Roorkee in the year 2013.

He has been the General Chair of the IEEE International Conference on Power Electronics, Drives and Energy Systems (PEDES’2006), Co-General Chair of (PEDES’2010) held in New Delhi. He has guided 45 Ph.D. dissertations 139 ME/M.Tech. theses and 60 BE/B.Tech. projects. He has been granted one US patent and filed twelve Indian patents. He has executed more than sixty sponsored and consultancy projects.

His fields of interest include power electronics, electrical machines, electric drives, power quality, renewable energy, flexible ac transmission systems (FACTS), and high voltage direct current (HVDC) transmission systems.

Prof. Singh is a Fellow of The Indian National Science Academy (FNA), the Indian National Academy of Engineering (FNAE), The National Academy of Science, India (FNASc), The Indian Academy of Sciences, India (FASc), The World Academy of Sciences (FTWAS), Institute of Electrical and Electronics Engineers (FIEEE), the Institute of Engineering and Technology (FIET), Institution of Engineers (India) (FIE), and Institution of Electronics and Telecommunication Engineers (FIETE) and a Life Member of the Indian Society for Technical Education (ISTE), System Society of India (SSI), and National Institution of Quality and Reliability (NIQR).

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PFC Cuk Converter Fed BLDC Motor Drive IEEE PAPERS/eee based/eee b… · MATLAB/Simulink environment and a hardware prototype of proposed drive is developed to validate its performance