Variable Frequency Drives

M. Nageswar Rao, Sr.Mgr.(EMD)

Date: 01.10.2015

2

Presentation LayoutIntroductionInduction Motor & designsLoad profilesVFDVFDs in marketSavings & Payback

3

Load profilesVariable Torque Loads

centrifugal pumps, fans and blowersTα N2 Pα N3

Constant Torque LoadsPositive displacement

pumpsTraction drives, Conveyors & Hoists.T = Const. Pα N

4

Motor & Load torques

5

Control of drivesFlow control

Condensate waterFeed waterAir flow etc.

Pressure controlDraftPA header pressureSeal air pressureDM water header pressure etc.

6

Control of drives - methodsMechanical

Throttling of pumpsInlet guide vanes/ Outlet damper throttlingHydraulic coupling

ElectricalEddy current clutch couplingVFD

7

Control of drives - methods

100 % Efficiency

80

60

40

20

0 20 40 60 80 100% Speed / Flow

Hydraulic Coupling

Inlet Guide Vane

Outlet Damper Throttling

LCI or VFD Drive

8

Throttling of pumps

9

Energy saving in pump application

10

Payback period with VFD With Throttle With VFD Drive Motor Rating 75 kWThrottle of Valve 30% 0% Speed 100% 70% Rated current of motor 123 123AActual current drawn by motor 100 123APower consumed by motor 60.98 27.08 kW

Power saving 33.90 kWRunning hours 330 days/year, 24hrs/dayTotal running hours 7920 hrs.Tariff 2.2 Rs./kWhSaving/year 5.91 Rs. In lakhs Money saved/month 0.5 Rs. In lakhsCost of VFD with panel 7.3 Rs. In lakhsPayback period 14.83 months

11

VFDVFD means Variable Frequency

Drive, i.e., adjustable speed AC motor drive system to control and/or optimize processes.

AcronymsVariable Frequency Drives (VFD)Variable Speed Drives (VSD)Variable Voltage Variable

Frequency Drives (VVVFD)Inverter Drives

12

VFD converter

13

VFDInput AC power is converted to DC

(Rectification) & this DC power is inverted to AC power of required Voltage & frequency to get Torque & Speed as per process requirement.

Rectification & Inversion are achieved through power electronics devices (Diodes, IGBT, Thyristors).

14

VFD- working principleNs = 120*f/PV = 4.44 f.Φmax.NFlux is made constant (by keeping V/f

=constant)To avoid over-fluxing thereby saturation.To impart rated torque to load even at lower

speeds.

15

VFD- advantageEffective starting & braking of MotorsEffective speed control over wide range.Match to load profilesEnhance overload capability of motors.Provide additional protections to motors.Improve source p.f.

16

Induction Motor- constant Torque & flux weakening zones

17

VFD-TopologiesBased on front end rectifier

NFE (Non-regenerative front-end)AFE (Active front-end)

Based on Inverter VSI (Voltage Source Inverter)CSI (Current Source Inverter)

Based on Inverter PWM controlScalar control (V/f)Vector control

DTC (Direct Torque Control) FOC (Field Oriented Control) SVM (Space Vector Modulation)

18

VFD-LCI

19

VFD-Load Commutated InverterCommutation is the process whereby changing voltage

cause one cell to stop conducting and another to begin.• In case of rectifier bridge, the power system provides the

voltage & energy for commutation, so it is called a line commuted bridge

• In case of Inverter bridge, the requirement is same, but a synchronous motor with leading power factor (current leading voltage) shall be able to provide the voltage (back e.m.f of the motor) & energy for commutation. Hence, the Load (Synchronous machine) helps commutation required for inverting DC to AC. That is why it is called Load commuted inverter.

20

VFD-Load Commutated Inverter6 pulse 12 pulse

21

VFDs in marketABBL&TSchneider ElectricDanfossVaconSEW Euro drivesSiemensMitshubishi

22

Feasibility StudyM/s Schneider Electric conducted feasibility

study at SMPP in June’2013.Total Annual Energy savings = 2,35,10,080

kWhTotal Annual Cost savings = 517 Rs. LakhsTotal investments = 1,758.6 Rs. LakhsPayback Period = 41 Months

23

Feasibility StudySl. No Equipment Annual Savings Investment

Simple Payback Period

    kWh Rs Lakhs Rs. Lakhs Months1 CEP - 1A 19,79,077 43.54 164.00 462 CEP - 1C 16,40,621 36.09 164.00 553 CEP - 2A 16,90,423 37.19 164.00 534 CEP - 2B 12,73,689 28.02 164.00 715 Sea water pump 33,76,800 74.29 200.00 336 Circulating water pumps 1,16,67,600 256.69 692.00 337 Effluent disposal pump 8,67,034 19.07 94.00 608 Potable water pump 42,840 0.94 3.60 469 DM transfer water pump 68,880 1.52 1.75 14

10Sweet water high cap. Pump 1,88,842 4.15 8.80 26

11 fire hydrant pump 5,73,114 12.61 94.00 9012 LDO pressurizing pump 43,720 0.96 2.05 2613 HFO pressurizing pump 97,440 2.14 6.40 36  Total 23,510,080 517 1,758.6 41

24

Thank you all