Chapter 3 Basic Control of Power Converters and Motors

Transcription

1 Chapter Basic Control of Power Converters and Motors Control of Converters Basic control principle: duty cycle control Current regulated PWM Control Optimal PWM control Space vector PWM Freq., Phase shifting, and Power Control Control of Motors Constant /f Control ector (Field Oriented) Control of IM ector Control of PM Motor Control of SR Motor Speed Sensorless Control Active & Reactive Power Control F. Z. Peng: Slide 1

2 Control Features of Power Electronics Multi-Control Loop Current Control Loop oltage Control Loop Torque Control Loop Speed Control Loop Position Control Loop Basic Control Schemes Duty Cycle Control Triangular-Wave PWM Control Hysteresis PWM Control / Phase & Synchronous-Frame Xformation Space ector PWM Control ector Control Optimal PWM State Feedback Control (DeadBeat Control) Sliding Mode Control, Fuzzy & Neural Network Control P, PI, PID Control Active & Reactive Power Control Sensorless Control etc. F. Z. Peng: Slide

3 Basic Control Principle of Power Electronics All power electronics can do is to produce digital power by using switches, all power electronics control methods are based on duty cycle control. We will show you later on all control methods can be reduced into the duty cycle control. Principle of the Duty Cycle (or Duty Ratio) Control (Using a dc-dc buck converter as an example to explain): F. Z. Peng: Slide

4 Sp i L * i L i L Sn PWM Inverter -Hysteresis PWM Controlv L Output Sp on Sp off Sn off Sn on Input F. Z. Peng: Slide 4

5 PWM Inverter -Triangular-Wave PWM Control- Sp Carrier i 1 Sn v 1 v 0 Load Reference Sp on Sn off Output Sp off Sn on Input F. Z. Peng: Slide 5

6 abc to α-β Transformation and ectors For three-phase converter systems, often it is more convenient and insightful to transform three-phase (abc) quantities into two phase (α-β) ones for voltage and current according to the following Power Invariant transformation = + α β α j β = a b c In some textbooks, the oltage Invariant transformation is used, in which the factor of is not needed. Also voltage and current vectors cab be expressed in complex form as: I = I + α ji β F. Z. Peng: Slide 6

7 PWM Inverter -Space ector PWM Control- + E/ Gap Gbp Gcp a E b c 4 (011) (010) Im (110) 5 (011) 6 (101) 1 (100) Re E/ Gan Gbn Gcn - Ga Gb Gc Ga, Gb,Gc = 1 or 0 "1" = upper device on; "0" = lower device on 0 (000) 7 (111) Im t 1t * 0, 7 T 1 = 1t / 1 T = t / T 0 +T 7 =T-T 1 -T 1 Re = a +a b +a c where a=e j(π/) T 0 T 1 T T T F. Z. Peng: Slide 7

8 PWM Inverter -Space ector PWM Control- + E E/ Gap E/ Gan Gbp Gbn Gcp Gcn a b c Im T 1 = 1t / 1 - Ga Gb Gc Ga, Gb,Gc = 1 or 0 "1" = upper device on; "0" = lower device on Im t * T = t / T 0 +T 7 =T-T 1 -T 4 (011) (010) (110) 5 (011) 6 (101) = a +a b +a c where a=e j(π/) 1 (100) Re 0 (000) 7 (111) 1t 0, 7 1 T 0 T 1 T T T Re F. Z. Peng: Slide 8

9 Maximum Output AC oltage dc + dc / Gap dc / Gan Gbp Gbn Gcp Gcn a b c - Ga Gb Gc Ga, Gb,Gc = 1 or 0 "1" = upper device on; "0" = lower device on Im Re dc 4 dc 1 dc Six-Step Operation: 4 π dc l l( rms) = = Space-ector PWM: l l( rms) = dc = SPWM: dc l l( rms) = = dc dc dc F. Z. Peng: Slide 9

10 Harmonic Elimination PWM Control v Sp +d 1 M-1 M d i L L L Sn d Using symmetry and Fourie analysis: L v L 0 - d ( ω t) = L ( ωt + π ) no even harmonics ( ωt) = L ( π ωt) no odd cos-terms 4 M j ( ωt) a sin( kωt), where a = 1+ ( 1) cos ka and k = 1,,5,... = k k k = 1,,5,... kπ j= 1 α α α α 1 α 4 M α M j ω t π F. Z. Peng: Slide 10

11 Optimum PWM Control v Sp +d 1 M-1 M i L Sn v L 0 π ω t - d Minimize current THD or Current Klirr Factor Minimize voltage THD or Filter Klirr Factor α α α α 1 α 4 M α M CKF = FKF = k =,5,7,... k =,5,7,... ak ka 1 Gka G1a 1 k F. Z. Peng: Slide 11

12 Deadbeat PWM Control For a n th -order system, the deadbeat control guarantees that the output variable follows the reference only with n-step delay and no steady state error. Draw Circuit here For an inverter feeding a R-L load, the load current will track the reference with only one sampling step delay and no steady-state error, if the inverter voltage is controlled as: * v ( nt + ) = T e where K = 1 e * * ( i ( nt ) + K( i ( nt ) i( nt) ) + / τ T / τ + L, andτ =. R R Draw Waveforms F. Z. Peng: Slide 1

13 Basic Control Theory of PE Circuits -Summary 1 1 S 0 Filtering element L 0 Load L 0 = S S) ( = 0 = d 1 + ( 1 d), where d is the duty cycle or the average of S over one switching cycle. F. Z. Peng: Slide 1

14 Multiple Control Loops Use IM drive systems as an example. F. Z. Peng: Slide 14

15 Nonlinear Phenomena of Power Electronic Circuits and Control Link to../../../presents/nonlinear Phenomena in Power Electronics Circuits and Control.ppt F. Z. Peng: Slide 15