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Space Vector Modulation (SVM). Open loop voltage control VSI AC motor PWM v ref Closed loop current-control VSI AC motor PWMi ref i f/back PWM – Voltage.

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Presentation on theme: "Space Vector Modulation (SVM). Open loop voltage control VSI AC motor PWM v ref Closed loop current-control VSI AC motor PWMi ref i f/back PWM – Voltage."— Presentation transcript:

1 Space Vector Modulation (SVM)

2 Open loop voltage control VSI AC motor PWM v ref Closed loop current-control VSI AC motor PWMi ref i f/back PWM – Voltage Source Inverter

3 + v c - + v b - + v a - n N V dc a b c S1 S2 S3 S4 S5 S6 S1, S2, ….S6 va*va* vb*vb* vc*vc* Pulse Width Modulation PWM – Voltage Source Inverter

4 v tri V dc q vcvc q Pulse width modulator vcvc PWM – single phase PWM – Voltage Source Inverter

5 PWM – extended to 3-phase  Sinusoidal PWM Pulse width modulator Va*Va* Pulse width modulator Vb*Vb* Pulse width modulator Vc*Vc* PWM – Voltage Source Inverter

6 SPWM – covered in undergraduate course or PE system (MEP 1532) In MEP 1422 we’ll look at Space Vector Modulation (SVM) – mostly applied in AC drives PWM – Voltage Source Inverter

7 Definition: Space vector representation of a three-phase quantities x a (t), x b (t) and x c (t) with space distribution of 120 o apart is given by: x – can be a voltage, current or flux and does not necessarily has to be sinusoidal a = e j2  /3 = cos(2  /3) + jsin(2  /3) a 2 = e j4  /3 = cos(4  /3) + jsin(4  /3) Space Vector Modulation

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9 Let’s consider 3-phase sinusoidal voltage: v a (t) = V m sin(  t) v b (t) = V m sin(  t o ) v c (t) = V m sin(  t o ) Space Vector Modulation

10 Let’s consider 3-phase sinusoidal voltage: t=t 1 At t=t 1,  t = (3/5)  (= 108 o ) v a = (V m ) v b = (V m ) v c = (V m ) Space Vector Modulation

11 Let’s consider 3-phase sinusoidal voltage: At t=t 1,  t = (3/5)  (= 108 o ) v a = (V m ) v b = (V m ) v c = (V m ) b c a Space Vector Modulation

12 Three phase quantities vary sinusoidally with time (frequency f)  space vector rotates at 2  f, magnitude V m

13 How could we synthesize sinusoidal voltage using VSI ? Space Vector Modulation

14 + v c - + v b - + v a - n N V dc a b c S1 S2 S3 S4 S5 S6 S1, S2, ….S6 va*va* vb*vb* vc*vc* We want v a, v b and v c to follow v* a, v* b and v* c Space Vector Modulation

15 + v c - + v b - + v a - n N V dc a b c From the definition of space vector: S1 S2 S3 S4 S5 S6 Space Vector Modulation v an = v aN + v Nn v bn = v bN + v Nn v cn = v cN + v Nn

16 Space Vector Modulation = 0 S a, S b, S c = 1 or 0v aN = V dc S a, v aN = V dc S b, v aN = V dc S a,

17 Sector 1 Sector 3Sector 4Sector 5 Sector 2 Sector 6 [100] V1 [110] V2 [010] V3 [011] V4 [001] V5 [101] V6 (2/3)V dc (1/  3)V dc Space Vector Modulation

18 Reference voltage is sampled at regular interval, T Within sampling period, v ref is synthesized using adjacent vectors and zero vectors 100 V1 110 V2 If T is sampling period, V1 is applied for T 1, V2 is applied for T 2 Zero voltage is applied for the rest of the sampling period, T 0 = T  T 1  T 2 Sector 1

19 Space Vector Modulation Reference voltage is sampled at regular interval, T If T is sampling period, V1 is applied for T 1, V2 is applied for T 2 Zero voltage is applied for the rest of the sampling period, T 0 = T  T 1  T 2 T T V ref is sampled V1 T1T1 V2 T2T2 T 0 /2 V0 T 0 /2 V7 vava vbvb vcvc Within sampling period, v ref is synthesized using adjacent vectors and zero vectors

20 Space Vector Modulation They are calculated based on volt-second integral of v ref How do we calculate T 1, T 2, T 0 and T 7 ?

21 Space Vector Modulation 100 V1 110 V2 Sector 1  q d

22 Space Vector Modulation Solving for T 1, T 2 and T 0,7 gives: where

23 Space Vector Modulation Comparison between SVM and SPWM SPWM o a b c V dc /2 -V dc /2 v ao For m = 1, amplitude of fundamental for v ao is V dc /2  amplitude of line-line =

24 Space Vector Modulation Comparison between SVM and SPWM SVM We know max possible phase voltage without overmodulation is  amplitude of line-line = V dc Line-line voltage increased by:  15%


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