A bidirectional DC/DC converter charge/discharge ...download.xuebalib.com/15lqAylMZvaU.pdf · Conventional solar energy illumination systems consist of two-stage power converter architectures

INTERNATIONAL JOURNAL OF CIRCUIT THEORY AND APPLICATIONSInt. J. Circ. Theor. Appl. 2015Published online in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/cta.2079

A bidirectional DC/DC converter charge/discharge controller forsolar energy illumination system integrating synchronous

rectification SEPIC converter and active clamp flyback converter

Yu-En Wu*,†, Kuo-Chan Huang and Ming-Xuan Li

Department of Electronic Engineering, National Kaohsiung First University of Science and Technology, Kaohsiung,Taiwan

SUMMARY

This paper presents a novel bidirectional DC-to-DC converter charge/discharge controller for solar energy illu-mination system. The bidirectional converter architecture integrates the synchronous rectification Single EndedPrimary Inductor Converter (SEPIC) converter and an active clamp flyback converter. In addition to fully usethe properties of the shared components and compensate for the shortcomings of conventional two-stage illumi-nation systems, the proposed system has the advantages of soft-switching, simple structure, and high efficiency.During daytime, a SEPIC converter with synchronous rectification function was used to charge the lead acidbattery through three-stage charging and maximum power point tracking. At night, the battery discharges, driv-ing and dimming high-brightness LEDs using the active clamp flyback converter. Finally, a solar energy illumi-nation system with both a 160W charge/discharge controller and an 80W LED driver was implemented toverify the feasibility and practicality of the proposed system. Copyright © 2015 John Wiley & Sons, Ltd.

Received 23 September 2014; Revised 15 February 2015; Accepted 17 February 2015

KEY WORDS: bidirectional DC/DC converter; maximum power point tracking (MPPT); solar energyillumination system; charge/discharge controller

1. INTRODUCTION

Conventional streetlight systems mostly operate on grid through long-distance power lines, whichtransmit electricity to every streetlight. This not only causes substantial loss of power but can alsoresult in the collective shutdown of streetlights during regional system failures. Presently,maintenance personnel must inspect streetlights lamp-by-lamp to determine the point of malfunction.This involves an enormous cost in manpower. In recent years, solar energy illumination systemshave received increased attention in various national markets. Additionally, the development and useof LED-related products have promoted the wide application of energy-saving illumination systems,which include streetlight systems found in everyday life.

Conventional solar energy illumination systems consist of two-stage power converter architectures[1–6]. The first stage DC/DC converter is responsible for charging controls and maximum power pointtracking (MPPT) [7]; the second stage DC/DC converter is responsible for driving and dimming theoutput of the high-brightness LEDs (HBLEDs). In these systems, HBLEDs do not operate duringdaytime; thus, the second stage DC/DC converter does not need to operate at the same time as theMPPT converter. By contrast, at night, the first stage DC/DC converter does not need to engage incharging functions—rather, the second stage DC/DC converter drives the HBLEDs for lighting

*Correspondence to: Yu-En Wu, Department of Electronic Engineering, National Kaohsiung First University of Scienceand Technology, Kaohsiung, Taiwan.†E-mail: [email protected]

Copyright © 2015 John Wiley & Sons, Ltd.

Y.-E. WU, K.-C. HUANG AND M.-X. LI

functions. These systems waste components, so a bidirectional DC/DC converter system has beenproposed [8–21].

An architecture proposed by Reference [8] integrated a buck–boost converter with a boostconverter. This achieves the purpose of sharing components and saved costs. This architectureuses two switches to replace the output diodes but belongs to a nonisolated structure, and the twoswitches lack synchronous rectification functions. The bidirectional converter proposed by [9]integrated a SEPIC converter with a flyback converter. The architecture uses a common core forthe transformer in the converter. However, an additional inductor is required in this architecture,which also involved a large number of switches. In addition, increasing emphasis has been placedon soft-switching type bidirectional DC/DC converters. In References [14–17], the soft-switchingfunction is available regardless of whether the converter is charging or discharging. However, thisarchitecture is complex and involves a large number of power switches and energy-storageinductors, increasing component costs. A SEPIC-boost converter architecture proposed by [10]was used in emergency illumination systems. In general mode, a SEPIC converter with powerfactor correction was used to drive HBLEDs, and the SEPIC’s second inductor L2 was used tocharge battery for emergency power. During emergency power failures and disaster, batterypower drives the HBLEDs in emergency mode through a boost converter, which is integrated byan external diode and a switch. The power switch of this architecture is in a normally closedstate in emergency mode without frequent applications. Moreover, an additional power switch isrequired to be integrated into the boost converter, and it cannot provide appropriate chargingmethods for different storage batteries. Reference [18] proposed a bidirectional converter, whichintegrated a SEPIC converter with a Zeta converter for lighting system. The architecturepossesses high flexibility for stepping-up or stepping-down input voltage but still belongs to anonisolated structure, and the two switches lack synchronous rectification and soft-switchingfunctions.

Therefore, this study proposed a novel bidirectional DC/DC converter in which two switches canmutually coordinate swapping based on the provided mode. This enables the synchronousrectification function during daytime charging, and soft-switching (zero-voltage switching, ZVS)functions for lighting at night by forming an active clamp circuit that enhances efficiency.Furthermore, this system only used one transformer to integrate the dual inductor in the SEPICconverter and the transformer in the flyback converter.

2. THE SMART SOLAR ENERGY ILLUMINATION SYSTEM ARCHITECTURE

Figure 1 shows the block diagram of solar energy illumination system architecture proposed in this study.The system replaced the conventional solar energy illumination system, which requires two-stage design.This architecture comprised a Photovoltaic (PV) module, bidirectional DC/DC converter, battery,HBLED module, and microprocessor (MCU), which are separately described as follows:

Figure 1. Block diagram of solar energy illumination system with a novel bidirectional DC/DC converter.MCU, microprocessor; PWM, pulse-width modulation.

Copyright © 2015 John Wiley & Sons, Ltd. Int. J. Circ. Theor. Appl. (2015)DOI: 10.1002/cta

A NOVEL BIDIRECTIONAL DC/DC CONVERTER CHARGE/DISCHARGE CONTROLLER

Co

(1) PV module: The single AJP-M660 PV module has a maximum output power of 215W and amaximum open circuit voltage of 36V, a short-circuit current of 7.83A, a peak-power voltageof 29.94V, and a peak power current of 7.18A.

(2) Bidirectional DC/DC converter: The novel bidirectional DC/DC converter proposed in thisstudy is a charge/discharge controller integrated with synchronous rectification SEPIC converterand active clamp flyback converters. The bidirectional converter primarily uses the properties ofstep up/down voltage and positive output of SEPIC converter, and the dual inductor architecturecan be realized through a common core to simplify the integration of other architectures andshare components. The flyback converter can obtain high step up/down gain ratios by adjustingthe transformer turns ratios. The windings of the built-in transformer can be used as the energystorage component without additional inductors, thus greatly reducing component costs.

(3) Battery: Two 12V, 20Ah lead-acid batteries were in series, meeting the 24V system design re-quirement. PV module during daytime is charged to battery and used to lighting the HBLEDmodule at night.

(4) HBLEDmodule: XP-G series HBLEDs fromCree Inc. (North Carolina, USA) were used. The 80Wmodule was composed of 16 sets of 5W HBLEDs in series.

(5) Microprocessor: A 16-bit dsPIC30F4011 MCU by Microchip Technology Inc. (West ChandlerBlvd. USA) was used as the control core of the system. The primary functions of the MCU wereanalog-to-digital conversion, pulse-width modulation (PWM) control, three-stage charging,MPPT, dimming cycle generation, and transmission, reception, and processing of packet data.

2.1. Analysis of the proposed bidirectional DC/DC converter

Figure 2 shows the circuit of the bidirectional DC/DC converter proposed in this paper. Thisarchitecture features a SEPIC converter with complementary dual-switch common core synchronousrectification functions. During battery discharge, using the SEPIC clamp capacitor Cclamp and mainswitch S1 to integrate the active clamp function of flyback converter, and the secondary output fromthe third-winding flyback converter was used to drive HBLED module. Relay 1 and Relay 2 in thearchitecture function as a double-pole double-throw (DPDT) relay for connecting the HBLEDmodule and disconnecting the PV module at night.

2.1.1. Daytime charging mode analysis of the bidirectional DC/DC converter. Figure 3 shows anequivalent circuit of the bidirectional DC/DC converter in daytime charging mode. The DPDT relayis open in daytime mode, during which internal Relay 1 is normally closed (on) and Relay 2 isnormally open (NO, off) and the third winding of the bidirectional DC/DC converter is also open. Inthis mode, the circuit architecture belongs to a synchronous rectification common core SEPICconverter. To maintain normal operation, the synchronous rectification function (PWM signal of S2)must be activated in continuous conduction mode (CCM); if the synchronous rectification function

Figure 2. Circuit of the proposed bidirectional DC/DC converter. DPDT, double-pole double-throw.

pyright © 2015 John Wiley & Sons, Ltd. Int. J. Circ. Theor. Appl. (2015)DOI: 10.1002/cta

Figure 3. Equivalent circuit of daytime charging mode (synchronous rectification SEPIC converter). DPDT,double-pole double-throw.

Figure 4. Main component waveforms of the synchronous rectification SEPIC converter.


is activated in discontinuous conduction mode, the problem of reverse charging in Cb may arise.Figure 4 shows the main component waveforms of the synchronous rectification SEPIC converter.This circuit is analyzed as follows:



(1) Mode 1 [t0–t1], as shown in Figure 5(a). The component waveforms during the t0–t1 period areshown in Figure 4. When S1 is turned on and S2 is turned off, PV power charges L1, Cclamp dis-charges to storage inductor L2, and output capacitor Cb supplies energy to the battery. Thus, theinductor currents iL1 and iL2 linearly increase as they simultaneously pass through S1, andVcclamp and Vcb slightly decrease. When S1 is turned on, the following conditions areestablished:

VL1 ¼ Vpv (1)

VL2 ¼ Vcclamp (2)

Equation 1 can be rearranged to obtain the current variation through L1:

ΔiL1ton

¼ Vpv

L1(3)

Similarly, the current variation through L2 can be obtained as Equation 4:

ΔiL2ton

¼ VCclamp

L2(4)

Mode 2 [t1–t2], as shown in Figure 5(b). The component waveforms during the t1–t2 period are shownin Figure 4. When S1 and S2 are turned off, and the S2 body diode is turned on, this period is the deadtime of the PWM signal of the two switches. The energy generated by PV module and stored in L1

charges Cclamp and Cb; energy stored in L2 also charges Cb. At this time, the inductor currents iL1and iL2 linearly decrease and Vcclamp and Vcb slightly increase. When S1 is turned off, the followingconditions are established:

VL1 ¼ Vpv � Vcclamp þ Vbattery

� �(5)

VL2 ¼ �Vbattery (6)

Figure 5. Operation principles of the synchronous rectification SEPIC converter: (a) operation mode 1, (b)operation mode 2, and (c) operation mode 3. DPDT, double-pole double-throw.



Equation 5 can be rearranged to obtain the current variation through L1:

ΔiL1toff

¼ Vpv� Vcclamp þ Vbattery

� �L1

(7)

Similarly, the current variation through L2 can be obtained as Equation 8:

ΔiL2toff

¼ �Vbattery

L2(8)

Mode 3 [t2–t3], as shown in Figure 5(c). The component waveforms during the t2–t3 period are shownin Figure 4. When S1 is turned off and S2 is turned on, voltage and current conditions in each compo-nent are identical to Mode 2. S2 is closed in this mode to allow current through the S2 body diode topass through S2. Because of forward voltages in the body diodes on power switches are normallyhigher than general Schottky diodes, which compromise efficiency. However, power switches havea smaller on-resistance Rds(on) where the majority of the current is directed, thus resulting in smallpower switch losses and high efficiency.Mode 4 [t3–t4]: The component waveforms during the t3–t4 period are shown in Figure 4. When S1 andS2 are turned off, and the S2 body diode is turned on, this period is the dead time of the PWM signal ofthe two switches. The voltage and current conditions for each component are identical to Mode 2and Mode 3.

In combination with the earlier equations, current variations through L1 are identical whether S1 isopened or closed. The following is obtained based on the voltage-second balance:

Vpv

L1ton ¼ VCclampþ Vbattery� Vpv

L1toff (9)

Then, the following can be obtained by rearranging Equation 9:

VCclamp ¼ 11� D

� �Vpv� Vbattery (10)

Similarity, whether S1 is turned on or off, current variations through L2 are also identical. Thefollowing is obtained based on voltage-second balance:

VCclamp

L2ton ¼ Vbattery

L2toff (11)

The following can be obtained by rearranging Equation 11:

VCclamp ¼ 1� D

D

� �Vbattery (12)

Then, the following can be obtained by rearranging Equations 11 and 12:

Vbattery

Vpv¼ D

1� D

� �(13)

Equation 13 describes the step-up mode when D> 0.5 and the step-down mode when D< 0.5. Therange of Vpv in the currently proposed system is 20–36V, and the battery output is 24V.



2.1.2. Nighttime lighting mode analysis of the bidirectional DC/DC converter. Figure 6 is anequivalent circuit of the bidirectional DC/DC converter in nighttime lighting mode. The DPDT relaysupplies power from the 24V battery. During this period, the internal connection of the DPDT relayconsists of a disconnected relay contact 1 and connected relay contact 2, and open first-winding L1

of the bidirectional DC/DC converter. The battery supplies power to the HBLED module in thismode. The S1 and Cclamp of the SEPIC converter from daytime mode are used to integrate the activeclamp circuit of the flyback converter, achieving the function of dual soft-switching. This modeoperates in CCM. Figure 7 shows the main component waveforms of the active clamp flybackconverter. The circuit analysis is described as follows:

(1) Mode 1 [t0–t1], as shown in Figure 8(a). Where Lm and Lr are magnetized inductor and leakageinductor of the transformer, respectively, and the leakage inductor acts as resonant inductor. Thecomponent waveforms during the t0–t1 period are shown in Figure 7. At t0, S2 is turned on andS1 is turned off, the primary magnetized Lm and resonant Lr inductors are in a linear chargingstate. The primary voltage Vpri (t) approximately equals the battery voltage Vb, the magnetizedinductor current iLm equals to the resonant inductor current iLr (t), and the S2 output parasitic ca-pacitor voltage is equal to zero (Vcs2 (t) = 0). In this mode, S1 and the secondary output diode Do

are turned off, input energy is stored in Lm, clamp capacitor voltage is equal to nVo, and clampcapacitor current is equal to zero (iclamp (t) = 0).

In this mode (t= t1), iLr (t) is expressed as follows:

iLr t1ð Þ ¼ iLm t0ð Þ ¼ Vb

Lr ¼ Lmt1� t0ð Þ (14)

(2) Mode 2 [t1–t2], as shown in Figure 8(b). The component waveforms during the t1–t2 period areshown in Figure 7. When S2 and S1 are turned off, and Do is still in off state, CS2 is equal to CS1,CS2 is charged by iLm through series-resonance, and Vcs2 is changed from a zero to Vb

+Vclamp≈Vb+ nVo. CS1 discharges Lr and Lm. The energy of Lr and Lm considerably exceedthe energy of CS1, thus Vcs1 can be fully discharged from Vb+ nVo to zero. CS1 and Cclamp isin series, thus the capacitance after series connection is approximately equal to CS1 becauseCclamp>>CS1. In addition, the CS1 and CS2 are also in parallel connection. Thus the capacitanceon the equivalent circuit is Cr =CS1 +CS2. When charging in this resonant method, the chargingtime between t1 and t2 is short and almost shows a linear characteristic.

Figure 6. Equivalent circuit of nighttime lighting mode (active clamp flyback converter). DPDT, double-pole double-throw.


Figure 7. Main component waveforms of the active clamp flyback converter.


In this mode, the primary voltage of the transformer is shown as follows:

Vpri tð Þ ¼ Vb� Vcr tð Þ≈Vb� iLr t1ð ÞCr

t � t1ð Þ (15)

VCs2 is boosted to Vb+nVo in this mode until termination when VCs1 decreases to zero.

(3) Mode 3 [t2–t3], as shown in 8(c). The component waveforms during the t2–t3 period are shown inFigure 7. At t2, when CS2 is charged to Vb+ nVo, the S1 body diode is turned on andCclamp>>CS2, thus the energy stored in Lm and Lr charges Cclamp through the S1 body diode.During this period, the current path is Lr⇒Lm⇒Cclamp. The primary voltage equation of thetransformer is shown as the following equation:

Vpri tð Þ ¼ �Vclamp tð Þ Lm

Lmþ Lr(16)

(4) Mode 4 [t3–t4], as shown in 8(d). The component waveforms during the t3–t4 period are shown inFigure 7. During this period, S2 is turned off, and the S1 body diode from Mode 3 is turned on toclamps VCs1 at zero. Thus, switch S1 ZVS can be achieved.

VCs2 is shown in the following equation:

VCs2 tð Þ ¼ Vb þ Vclamp tð Þ (17)


Figure 8. Operation principles of the active clamp flyback converter: (a) operation mode 1, (b) operationmode 2, (c) operation mode 3, (d) operation mode 4, (e) operation mode 5, (f) operation mode 6, (g) oper-

ation mode 7, and (h) operation mode 8. DPDT, double-pole double-throw.


The iLm and iDo equations are shown as follows:

iLm tð Þ ¼ iLm t3ð Þ � nVo

Lmt � t3ð Þ (18)

iDo ¼ n iLm tð Þ � iLr tð Þð Þ (19)

(5) Mode 5 [t4 –t5], as shown in Figure 8(e). The component waveforms during the t4–t5 period areshown in Figure 7. At t4, S1 is turned on and iclamp=0, thus Cclamp can transmit energy back to Lr.iclamp(t) is reversed. When VCs2≈Vb+ nVo, S1 is turned off and this mode is terminated.



During this period, VCs2 is expressed as follows:

VCs2 tð Þ ¼ Vb þ Vclamp tð Þ (20)

The iLm and Do current equations are shown as follows:


Lmt � t4ð Þ (21)

iDo tð Þ ¼ n iLm tð Þ � iLr tð Þð Þ (22)

(6) Mode 6 [t5–t6], as shown in Figure 8(f). The component waveforms during the t5–t6 period areshown in Figure 7. When S2 and S1 are turned off, due to the continuity of inductor currentsmust be maintained, CS2 discharges to Lr and the inductor currents charge CS1. VCs2 isdischarged from Vb+ nVo to zero and VCs1 is charged until Vb+Vclamp≈Vb+ nVo. This is sim-ilar to Mode 2 in which the CS1 and CS2 are treated as in parallel, thus the capacitance on theequivalent circuit is expressed as Cr =CS1 +CS1. In this mode, the Do remains turned on inwhich Vpri=�nVo. The iLm equation is as follows:


Lmt � t5ð Þ (23)

The iDo equation is as follows:

iDo tð Þ ¼ n iLm tð Þ � iLr tð Þð Þ (24)

(7) Mode 7 [t6–t7], as shown in Figure 8(g). The component waveforms during the t6–t7 period areshown in Figure 7. At t6, the VCs2 at S2 is equal to zero and the S2 body diode is turned on. VLr isequal to Vb+ nVo, iLr increases linearly, and Vpri is equal to �nVo. This mode is terminated whenS2 is turned on. In this mode, iLr (t) is expressed as follows:

iLr tð Þ ¼ iLr t6ð Þ þ Vbþ nVo

Lrt � t6ð Þ (25)

The S2 body diode, Lr, and the primary of transformer formed a current loop, in which Vpri= nVo andVLr is equal to Vb+ nVo. iDo is attenuated through the following relationship:

diDo

dt¼ n

nVo

Lm� Vbþ nVo

Lr

� �(26)

Assuming Lm>>Lr, the previous equation can be simplified:

diDo

dt¼ n

Vbþ nVo

Lr

� �(27)

(8) Mode 8 [t7–t8], as shown in Figure 8(h). The component waveforms during the t7–t8 period areshown in Figure 7. At t7, before iLr changes to a positive value, S2 is turned on. The S2 bodydiode on Mode 7 clamps VCs2 at zero, thus ZVS can be achieved. At the same time, the second-ary iDo linearly decreases and the primary iLr linearly increases. At t8, Mode 8 terminates whenthe secondary iDo=0 and Do turned off.



The iLr(t) and iLm(t) equations are shown as follows:

iLr tð Þ ¼ iLr t7ð Þ ¼ Vbþ nVo

Lrt � t7ð Þ (28)


Lmt � t7ð Þ (29)

Subsequently, the system is repeated with the initial conditions at t0.

2.1.3. Design of the integrated inductors and turn-ratio of three-winding transformer. The proposedsynchronous rectification SEPIC converter is operated in CCM mode, its duty cycle is shown asEquation 30.

Dsepic ¼ Vbattery

Vpv þ Vbattery(30)

Thus, the maximum duty cycle is

Dsepic maxð Þ ¼ Vbattery

Vpv minð Þ þ Vbattery(31)

The variation of inductor current iL1 is shown as Equation 32.

ΔiL1toff

¼ VCclampþ Vbattery� Vpv

L1(32)

The variation of inductor current iL2 is shown as Equation 33.

ΔiL2toff

¼ Vbattery

L2(33)

According to Equations 31–33, the inductor value can be determined.

L1 ¼ L2 ¼Vpv minð Þ�Dsepic maxð Þ

ΔIL�f(34)

If L1 and L2 have a common core, the inductor can be replaced with 2L and Equation 34 can beexpressed as the follows:

Lcoupled ¼Vpv minð Þ�Dsepic maxð Þ

2�ΔIL�f(35)

Because the primary side of Flyback converter is the common core inductor L2 of SEPIC converter,the winding of transformer only considers the turns ratio.

Due to inductance in common core SEPIC architecture must be the same turns ratio, so the turnsratio N1:N2 is designed to 1:1 in this paper. In addition, the Flyback architecture is used to drive theLED at nighttime mode, so N2: N3 can follow Equation (36) and the input and output specificationsto design, where Dflyback is the duty ratio of Flyback architecture.



Vo

Vbattery¼

N3N2

� �Df lyback

1� Dflyback

� � (36)

2.1.4. Property comparison of bidirectional DC/DC converter. Table I shows the propertiescomparison of the novel bidirectional DC/DC converter with relevant literature [8–10, 18].References [8] and [18] were constituted by buck–boost and SEPIC–Zeta, respectively, although thenumber of switches used only two, but the efficiency is limited by the hard-switching. Thearchitecture of References [9] and [10] were constituted by SEPIC-flyback and SEPIC-boost,respectively; it used three switches and required an additional inductor to storage energy, so thecircuit structure and control were more complicated, and the efficiency was poor. Therefore, it canbe seen from Table I that the proposed bidirectional converter possesses the advantages of soft-switching, simple structure, high efficiency, and practicability.

2.2. System software planning

Figure 9 shows a system program flow chart. When operating in daytime mode, the systemexecutes the three-stage charging and MPPT procedures. By contrast, when operating innighttime mode, the system executes the HBLEDs driving and dimming procedures. Thisdaytime–nighttime operating mode can also be directly switched through the MCU. The three-stage charging and MPPT procedures, and HBLED driving and dimming procedure are describedin detail as follows:

2.2.1. Three-stage charging and maximum power point tracking procedure [22–26]. In thisprocedure, PV module is used to charge the battery. However, the output power of the PV moduleis dependent on the variation in illumination, temperature, and other factors. When the powergenerated becomes insufficient for the charging mode, MPPT must be executed to charge the batteryusing the optimal output of the PV module. To satisfy this condition, the initial voltage of thebattery is detected prior to executing this procedure to determine the battery capacity and subsequentexecuting constant current, voltage, and floating charging mode. Figure 10 shows the three-stagecharging and MPPT process flow chart. As the system is executing each charging mode during thecharging process, if the output voltage of the PV module is less than 20V, the charging procedure isterminated. The overall flow process is described as follows:

(1) Execute constant current charging when the battery voltage is less than 25.6V.

Table I. Properties comparison of various bidirectional DC/DC converters.

BidirectionalDC-to-DCconverter

Reference[8]

Reference[9]

Reference[10]

Reference[18]

The proposed bidirectionalDC-to-DC converter in

this paper

Synchronousrectification

No No No No Daytime charging

Soft-switching No No No No Nighttime LED lightingNumber ofswitches

2 3 3 2 2

Energy storagecomponentsharing

Yes Yes, but requiresan additionalinductor

Yes, but requiresan additionalinductor

No Yes, a three-windingcommon core typesingle transformer

Isolation No Yes No No YesEfficiency insamespecification

Low Low High Medium High

Cost Low Medium High Medium Low


Figure 9. Flowchart of system program. PWM, pulse-width modulation; MPPT, maximum power pointtracking; UART, Universal Asynchronous Receiver/Transmitter; A/D, Analog-to-Digital Converter.


(2) Execute constant voltage charging when the battery voltage is greater than 25.6V and less than26.2V.

(3) Execute floating charging when the battery voltage is greater than 26.2V, using the constantvoltage (27.3V) and low currents.

(4) When charging using the constant current or constant voltage, if the output power of the PVmodule is less than that demanded by the battery, the slope-climbing MPPT charging methodis used until charging current (voltage) returns to 5.5A (28.8V), the system resumes to constantcurrent (voltage) charging mode.

2.2.2. High-brightness light-emitting diodes driving and dimming procedures [27]. During thesystem operates in nighttime mode, the system executes the HBLED driving and dimmingprocedures, as shown in Figure 11. In this procedure, the MCU transmits packets containing datasuch as switch commands and dimmer cycles as the system implements dimming control. As thesystem executes the constant current driving, the HBLED module current is constantly detected. Ifthe detected current differs from the necessary current, the duty of the PWM signal is first changed.The procedure is terminated if the driving current remains at an abnormal stage.

3. EXPERIMENTAL RESULTS

The smart solar energy illumination system proposed in this study uses a novel bidirectional DC/DCconverter, and a dsPIC30F4011 MCU as the control core. A system was implemented in this studyconsisting of a 160W solar energy charge/discharge controller, and an 80W LED driverbidirectional converter, to verify its feasibility and practicality. The respective electricalspecifications are shown in Table II.

The specifications of the electronic components are shown in Table III. The system consists of twoswitches that are complementary operation. During the dead time of the PWM driving signals, switchcurrents bypass their respective parasitic diodes. Thus, a low cut-in voltage and a fast reverse recoverytime must be emphasized when selecting power switches. The implementation results of various


Figure 10. Flowchart of three-stage charging and MPPT procedures. MPPT, maximum power pointtracking.


system functions are verified through Human Machine Interface (HMI) monitoring and separatelypresented in the following sections.

3.1. Measurements of the novel bidirectional DC/DC converter

Figure 12 shows the photograph of the proposed bidirectional DC/DC converter in this paper. Thefollowing sections separately describe the daytime charging mode-synchronous rectification SEPICconverter and nighttime lighting mode-active clamp flyback converter.

3.1.1. Daytime charging mode—synchronous rectification SEPIC converter. Figure 13 is the controlwaveforms of the Vgs1/Vds1 and Vds2/Vgs2 of S1 and S2. The measured efficiency of the synchronousrectification SEPIC converter are 90.5% under a full load (160W), 92.5% under a half load (80W),and 88.7% under a light load (20W), respectively. The overall efficiency diagram is shown inFigure 14.


Table II. Electrical specifications of the proposed smart solar energy illumination system.

Daytime solar energy charger(synchronous rectificationSEPIC converter)

Nighttime high-brightness LED driver(active clamp flyback converter)

Photovoltaic input voltage, VPV 20–36V Storage battery voltage, Vbattery 23–25.4VCharging voltage, Vbattery 24V LED driving voltage 48VCharging current, Ibattery 0.5–5.5A LED driving current 0.15–1.5ASwitch frequency, fs 70 kHz Switch frequency, fs 50 kHz

Figure 11. Flowchart of HBLED driving and dimming procedure. PWM, pulse-width modulation.

Table III. Component specifications of the novel bidirectional DC/DC converter.

L1 100μHThree-winding transformer

turns ratio 1:1:1.5

L2 100μH Do BYV42Cclamp 9.4μF S1 FDP150N10ACb 470μF S2 FDP150N10ACo 100μF




3.1.2. Nighttime lighting mode—active clamp flyback converter. Figure 15 shows the Vgs1/Vds1 andVds2/Vgs2 waveforms of S1 and S2 of the active clamp flyback converter. Figure 16 shows the ZVSwaveforms of S1 and S2 of the active clamp flyback converter. Both switches were turned on whenswitching voltage values returned to zero. Figures 17 and 18 show the inductor current waveform ofsynchronous rectification SEPIC converter and transformer input current waveform of active clampflyback converter, respectively. The overall efficiency diagram of the active clamp flyback converteris shown in Figure 19. It is above 93.6% under constant load.

3.1.3. Power budget of the proposed system.3.1.3.1. Daytime charging mode—synchronous rectification SEPIC converter. (1) Power switchesloss: includes conduction loss and switching loss

Figure 12. Photograph of the novel bidirectional DC/DC converter.

Figure 13. Vgs1/Vds1 and Vds2/Vgs2 waveforms of S1 and S2 of the synchronous rectification SEPIC converter.



a. Conduction loss:

PS1 ¼ VDS1*IDS1*D ¼ 3 Wð Þ

PS2 ¼ VDS2*IDS2*D ¼ 2:3 Wð Þ

PS;total ¼ PS1 þ PS2 ¼ 5:3 Wð Þ

Figure 14. Overall efficiency curve of the synchronous rectification SEPIC converter.

Figure 15. Vgs1/Vds1 and Vds2/Vgs2 waveforms of S1 and S2 of the active clamp flyback converter.


Figure 16. Zero-voltage switching waveforms of S1 and S2 of the active clamp flyback converter.

Figure 17. Inductor current measured waveform of synchronous rectification SEPIC converter.


b. Switching loss:

It is calculated by the VDS * IDS crossover area during both switches turned on and turned off, thecalculation results are 2.6W.

(2) Inductance lossa. Copper loss:

Copper loss is generated by the loss of the transformer winding resistance. In day mode, L3 windingis under open circuit state, counting only the copper loss of L1 and L2, which is 6.89W.

b. Iron loss:


Figure 18. Transformer input current measured waveform of active clamp flyback converter.

Figure 19. The efficiency curve of the active clamp flyback coverter.

Table IV. Power loss of synchronous rectification SEPIC converter.

Component Loss calculation

Power switch conduction ‘loss 5.3WPower switch switching loss 2.6WInductor copper loss 6.89WInductor iron loss 0.87WTotal 15.66WCalculated efficiency 91.3%Measured efficiency 90.5%

Table V. Power loss of active clamp flyback converter.

Component Loss calculation

Power switch conduction loss 2.02WPower switch switching loss 0.455WInductor copper loss 2.642WInductor iron loss 0.36WTotal 5.47WCalculated efficiency 94.3%Measured efficiency 93.6%



Figure 20. Waveforms of battery voltage and current during constant current charging and PV module out-put voltage and current in daytime mode.

Figure 21. Measured results of maximum power point tracking.

igure 22. Current and voltage waveforms of the high-brightness LED module in (a) 20% and (b) 100%dimming cycle.


F



In this paper, transformer employs the ER-35 core, and according to the data provided by themanufacturer and the daytime mode specifications, the calculated iron loss is 0.87W.

According to the earlier calculation, the total power loss of synchronous rectification SEPICconverter under daytime charge mode is listed in Table IV. The total loss is 15.66W, and thecalculated efficiency and the measured efficiency are 91.3% and 90.5%, respectively.3.1.3.2. Nighttime lighting mode—active clamp flyback converter. (1) Power switches loss: includesconduction loss and switching loss

a. conduction loss:

PS1 ¼ VDS1*IDS1*D ¼ 0:52 Wð ÞPS2 ¼ VDS2*IDS2*D ¼ 1:5 Wð ÞPS;total ¼ PS1 þ PS2 ¼ 2:02 Wð Þ

b. Switching loss:

Because both switches possess turned-on ZVS feature, so only calculate the loss of both switches inturned-off state is 0.455W.

(2) Inductance lossa. Copper loss:

L1 is under open-circuit state in nighttime mode, so only calculate the copper loss of L2 and L3 is2.642W.

b. Iron loss:

According to the data provided by the manufacturer and the nighttime mode specifications, thecalculated iron loss is 0.36W.

Therefore, the total power loss of active clamp Flyback converter under nighttime lighting mode islisted in Table V. The total loss is 5.47W, and the calculated efficiency and the measured efficiency are94.3% and 93.6%, respectively.

3.2. Measurement results of three-stage charging and maximum power point tracking

For simplicity, only the constant current and voltage measurement waveforms are presented in thissection. Figure 20 shows the waveforms of the battery voltage and current during constant currentcharging (5.5A) and PV module output voltage and current. In charging mode, the voltagegradually increased. Next, the battery voltage and current during constant voltage charging (28.8V),the current gradually decreased in this state. Figure 21 shows the MPPT curve during MPPTprocessing; it can be obvious that the effect of MPPT is excellent.

3.3. High-brightness light-emitting diodes driving and dimming procedure

A 200Hz frequency of feedback dimming signals was used to determine various dimming cycles andmeasure the voltage and current of the HBLED module to conduct verification. Figure 22 shows thevoltage and current waveforms of the HBLED module in a 20% and 100% dimming cycle. It can beseen that the proposed illustration system can accurately dim and drive the HBLED.

4. CONCLUSION

This study proposed a solar energy illumination system with a novel DC/DC converter charge/dischargecontroller. This architecture is integrated with a synchronous rectification SEPIC converter and an activeclamp flyback converter, which was efficiently shared components to reduce greatly the system



components, cost and power loss, and achieve a high efficient charger and HBLED driver. Additionally,operational principle, steady-state analysis, and design of the proposed system have been described indetail. An experimental prototype has been implemented in this study consisting of a 160W solar energycharge/discharge controller and an 80W LED driver bidirectional converter. The experimental results canclearly verify the feasibility and practicality of the proposed system.

REFERENCES

1. Tseng SY, Kuo JS, Wang SW, Hsieh CT. Buck-boost combined with active clamp flyback converter for PV powersystem. IEEE Power Electronics Specialists Conference, 2007; 138–144.

2. Jianping Z, Yingping Z, Ning Yang. Research on driving circuits of PV hybrid LED street lighting system. Interna-tional Conference on Computer Distributed Control and Intelligent Environmental Monitoring (CDCIEM), 2011;257–260.

3. Ali M, Orabi M, Abdelkarim E, Qahouq JAA, Aroudi AE. Design and development of energy-free solar street LEDlight system. IEEE PES Conference on Innovative Smart Grid Technologies - Middle East (ISGT Middle East), 2011;1–7.

4. Zhang H, Liu X, Kedia M, Balog RS. Photovoltaic hybrid power harvesting system for emergency applications.IEEE 39th Photovoltaic Specialists Conference (PVSC), 2013; 2902–2907.

5. Huang BJ, Wu MS, Hsu PC, Chen JW, Chen KY. Development of high-performance solar LED lighting system.Energy Conversion and Management 2010; 51(8):1669–1675.

6. Tseng SY, Wang HY, Chen CC. PV power system using hybrid converter for LED indictor applications. EnergyConversion and Management 2013; 75:761–772.

7. Esram SRT, Chapman PL. Comparison of photovoltaic array maximum power point tracking techniques. IEEETransactions on Energy Conversion 2007; 22(2):439–449.

8. Hua CC, Chuang CW, Wu CW, Chuang DJ. Design and implementation of a digital high-performance photovoltaiclighting system. Proceedings of the IEEE Industrial Electronics and Applications Conference, 2007; 2583–2588.

9. Kim SS, Choi DK, Jang SJ, Lee TW, Won CY. The active clamp SEPIC-flyback converter. Proceedings of the IEEEPower Electronics Specialists Conference, 2005; 1209–1212.

10. Chen Zl, Yang SX, Wang GH, Wang Jj. Application of emergency power and power factor correction SEPIC-boostpower converter. The 11th Taiwan Power Electronics Conference and Exposition, 2012.

11. Duan RY, Lee JD. High-efficiency bidirectional DC-DC converter with coupled inductor. IET Power Electronics2012; 5(1):115–123.

12. Lin CC, Yang LS, Wu GW. Study of a non-isolated bidirectional DC-DC converter. IET Power Electronics 2013;6(1):30–37.

13. Chen LR, Chu NY, Wang CS, Liang RH. Design of a reflex-based bidirectional converter with the energy recoveryfunction. IEEE Transactions on Industrial Electronics 2008; 55(8):3022–3029.

14. Lee YS, Member, Cheng GT. Quasi-resonant zero-current-switching bidirectional converter for battery equalizationapplications. IEEE Transactions on Industrial Electronics 2006; 21(5):1213–1224.

15. Jin K, Member MY, Ruan X, Min X. Three-level bidirectional converter for fuel-cell/battery hybrid power system.IEEE Transactions on Industrial Electronics 2010; 57(6):1976–1986.

16. a) Li H, Fang ZP, Lawler JS. A natural ZVS medium-power bidirectional DC-DC converter with minimum numberof devices. IEEE Transactions on Industry Applications 2003; 39:525–535; b) Jain M, Daniele M, Jain PK. A bidi-rectional DC-DC converter topology for low power application. IEEE Transactions on Power Electronics 2000;15:595–606.

17. Jung DY, Hwang SH, Ji YH, Lee JH, Jung YC, Won CY. Soft-switching bidirectional DC/DC converter with a LCseries resonant circuit. IEEE Transactions on Power Electronics 2013; 28:1680–1690.

18. Zhong YH, Hong C. Integrated solar controller for solar powered off-grid lighting system. Energy Procedia 2011;12:570–577.

19. Chiu HJ, Lo YK, Kuo SW, Cheng SJ, Lin FT. Design and implementation of a high-efficiency bidirectional DC-DCConverter for DC micro-grid system applications. International Journal of Circuit Theory and Applications 2014;42(11):1139–1153.

20. Chang YH. Design and analysis of power-CMOS-gate-based switched-capacitor DC–DC converter with step-downand step-up modes. International Journal of Circuit Theory and Applications 2003; 31(5):483–511.

21. Ismail EH, Fardoun AA, Zerai AA. Step-up/step-down DC-DC converter with near zero input/output current ripples.International Journal of Circuit Theory and Applications 2014; 42(4):358–375.

22. Chen LR. A design of an optimal battery pulse charge system by frequency-varied technique. IEEE Transactions onIndustrial Electronics 2007; 54(1):398–405.

23. Darla RB. Development of maximum power point tracker for PV panels using SEPIC converter. Telecommunica-tions Energy Conference, INTELEC, 2007; 650–655.

24. Chung HSH, Tse KK, Hui SYR, Mok CM, Ho MTL. A novel maximum power point tracking technique for solarpanels using a SEPIC or Cuk converter. IEEE Transactions on Power Electronics 2003; 18(3):717–724.

25. Li CH, Zhu XJ, Cao GY, Sui S, Hu MR. Dynamic modeling and size optimization of stand-alone photovoltaic powersystems using hybrid energy storage technology. Renewable Energy 2009; 34:815–826.



26. Chen M, Rincon-Mora GA. Accurate electrical battery model capable of predicting runtime and I-V performance.IEEE Transactions on Energy Conversion 2006; 21(2):504–511.

27. Oh IH. An analysis of current accuracies in peak and hysteretic current controlled power LED drivers. Proceedings ofthe IEEE Applied Power Electronics Conference, 2008; 572–577.


本文献由“学霸图书馆-文献云下载”收集自网络，仅供学习交流使用。

学霸图书馆（www.xuebalib.com）是一个“整合众多图书馆数据库资源，

提供一站式文献检索和下载服务”的24 小时在线不限IP

图书馆。

图书馆致力于便利、促进学习与科研，提供最强文献下载服务。

图书馆导航：

图书馆首页文献云下载图书馆入口外文数据库大全疑难文献辅助工具

http://www.xuebalib.com/cloud/

http://www.xuebalib.com/

http://www.xuebalib.com/cloud/


http://www.xuebalib.com/vip.html

http://www.xuebalib.com/db.php

http://www.xuebalib.com/zixun/2014-08-15/44.html


Documents

A bidirectional DC/DC converter charge/discharge ...download.xuebalib.com/15lqAylMZvaU.pdf · Conventional solar energy illumination systems consist of two-stage power converter architectures