P3-3-Ch18-電網(wǎng)與電力電子系統(tǒng)的接口優(yōu)化

1、1Chapter 18：Optimizing the Utility Interface with Power Electronic Systems18-1 Introduction18-6 Improved Single-Phase Utility Interface18-7 Improved Three-Phase Utility Interface218-1 IntroductionPower quality has become an important issueDiode-Rectifier Bridge1 Generation of Current Harmonics3Diode

2、-Rectifier Bridge waveform4Diode-Rectifier Bridge waveform5Typical Harmonics in the Input Current Single-phase diode-rectifier bridge6Due to harmonic currents injected into the utility grid, the voltage waveform at the point of common coupling will become distortion. PCC is the point of common coupl

3、ing2 Deleterious effects of harmonic current7Deleterious effects of harmonic distortion and a poor Power Factor Increasing power loss in transmission lines, transformers, generators. Overloading the shunt capacitors used by utilities for voltage support. may causing resonance conditions between the

4、capacitive reactance of the shunt capacitors and the inductive reactance of the transmission lines. The utility voltage waveform will also become distorted, adversely affecting other linear loads. Resulting in errors in metering, malfunction of utility relays, interference with communication and con

5、trol signals, and so on.83 Harmonic Guidelines: IEEE 519Commonly used for specifying limits on the input current distortion9Limits on distortion in the input voltage supplied by the utility3 Harmonic Guidelines: IEEE 5191018-6 Improved single-Phase Utility Interface18-6-1 passive filtersThe added in

6、ductor results in a higher effective value of the ac-side inductance Ls, which improve the power factor and reduces harmonics.1112 The effect of Ls on diode rectifier with a capacitor: The power factor is improved from very poor to somewhat acceptable. Harmonics are decreased. The output voltage Vd

7、is lower compared with the no-inductance case. The overall energy efficiency remains essentially the same; there are additional losses in the inductor, but the conduction losses in the diodes are lower.1318-6-2 Power-Factor-Correction (PFC) Circuit Between the utility supply and dc-bus capacitor, a

8、Boost dc-dc converter is introduced. Use a boost dc-dc converter to shape the rectified current.141 Operation principle of PFC By pulse-width-modulating the transistor at a constant switching frequency, the current iL through the Ld is shaped to have the full-wave-rectified waveform. tsinSimilar to

9、)(tvs The input current is is sinusoidal, and in phase with the supply voltage vs. 15)718(2cossinsin)(tIVIVtItVtpssssssinBecause of a fairly large Cd, vd(t)=Vd. Therefore,)918()()()818()()(tiItitiVtpcloaddddd16If Ld is very small, then pin(t)=pd (t). Therefore,)1018(2cos2cos)()(tIItVIVVIVtiItidddssd

10、sscloaddOutput current consists of dc component Id and second harmonic component. 17)1318(2sin21)(,tCIdtiCtvddCdrippledto minimize the ripple of vd an appropriate value of Cd must be chosen.A series-tuned LC filter tuned for twice the ac frequency may be put in parallel with Cd.18Note: Vd must be gr

11、eater than the peak of the supply voltage. sdVV192 Control of PFC(1) the main control objectives to draw a sinusoidal current, in phase with the utility voltage; to maintain Vd at the reference value. RFI1CiLLDTC+-ACAiLiLoadVdPFC control loopV*dARVdsisvsvsvPWM controlMultipileri*LKL20The control obj

12、ectives lead to two control loops: The inner current loop ensures the form of i*L(t) based on the utility voltage is(t). The outer voltage loop determines the amplitude of i*L(t) based on the voltage feedback and regulates the voltage of the PFC to the pre-selected dc voltage. RFI1CiLLDTC+-ACAiLiLoa

13、dVdPFC control loopV*dARVdsisvsvsvPWM controlMultipileri*LKL21Note: The inner current loop is required to have a very high bandwidth compared the outer voltage loop. hence, each loop can be designed separately. 22(2) Voltage loop control principle: If ILoad Vd (V*d) KLi*LiL input power Vd, hence ens

14、ures Vd =const.RFI1CiLLDTC+-ACAiLiLoadVdPFC control loopV*dARVdsisvsvsvPWM controlMultipileri*LKL23(3) Current loop controlThere are various ways to implement the current loop control: Direct current control Constant-frequency control Constant-tolerance-band control Variable-tolerance-band control D

15、iscontinuous-current controlIndirect current control24 Constant-frequency controlThe switch in the step-up converter is turned on by a clock at fixed frequency fs, when iL reaches i*L, the switch is turned off.25 Constant-tolerance-band control2618-6-3 Interface for a Bidirectional power flow1 Thyri

16、stor Converters for 4-Quadrant OperationThe input current is has a distorted and the power factor is low.272 Switch-Mode Converter InterfacesdVV28In the circuit: )2118()2018(dtdiLvvvvssLLconvsSingle-phase voltage source PWM converterD D1 1D D3 3D D4 4D D2 2T T1 1T T3 3T T4 4T T2 2isLsvsvconvABL2C2Cd

17、+-Vd+ vL -29Assuming vs to be sinusoidal, at the line frequency =2f, )2318(1111ssconvLconvsILjVVVV(1) Phasor equation: (2) Phasor diagram: 30(3) The important equations:)2618()cos1 ()sin(111212sconvsssconvsssconvssLjVVIVVLVQVVLVPFor a given vs and the chosen Ls, P and Q can be obtained by controllin

18、g the magnitude and the phase of vconv1.31(4) Switch-Mode Converter ControlThere are various ways to implement the current loop control: Indirect current controlDirect current control32 Indirect Current Control-Base on phasor equation: Rectifier mode11111111)sin(costansinconvconvconvconvsconvsssssLs

19、svtVvVVVLVIILvtVv33Inversion mode11111111)sin(costansinconvconvconvconvsconvsssssLssvtVvVVVLVIILvtVv34Waveforms in the rectifier mode35Waveforms in the rectifier modevconvvconv1vsis36Waveforms in the inversion modevconvvconv1is37Waveforms in the zero load modevconvvconv1is38 Direct Current Control S

20、ingle-phase voltage source PWM converterD D1 1D D3 3D D4 4D D2 2T T1 1T T3 3T T4 4T T2 2isLsvsvconvABL2C2Cd+-Vd+ vL -Note: Vd must be greater than the peak of the supply voltage. sdVV3918-7 Improved Three-Phase Utility Interface Rectifier and Inverter modes based on the direction of power flow)3118(

21、634. 1LLdVV40)3218(cos31dssdVIVIFor rectification at a unity power factor, 1=0, and)3318(3dssdVIVI41Applications 1T2TApplied in electric locomotivesvsLsA1D2D2C+-3T4TB3D4DdC2LVddIvconv42BPNACC1CdLsLsLsLSalor Array43Supplemental material-Active Power FilterS18-1: The following figure shows the single-phase voltage source PWM converters circuit diagr