Sinusoidal PWM and Space Vector Modulation For Two Level Voltage Source Converter
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1) The document describes a two level voltage source converter (VSC) that can operate as either a rectifier or inverter using carrier-based sinusoidal pulse width modulation (PWM) or space vector modulation (SVM) control techniques. 2) The two level VSC consists of six switches that can be IGBTs or MOSFETs with anti-parallel diodes, allowing bidirectional power flow between the DC and AC sides. 3) Sinusoidal PWM compares a triangular carrier signal to three-phase modulating waves to generate switching pulses for the converter switches, while SVM represents the converter states as space vectors to calculate switching times.
![Space Vector
Space Vectors
Among the eight switching
states, [PPP] and [OOO] are
zero states and the others are
called active states.
The active and zero
switching states can be
represented by active and zero
vectors, respectively.
Space vector diagram for
two-level inverter is shown
Six vectors V1 to V6 form
hexagon with six equal sectors
and zero vector V0 lies in
center of hexagon](https://image.slidesharecdn.com/spvm-140605022805-phpapp01/85/Sinusoidal-PWM-and-Space-Vector-Modulation-For-Two-Level-Voltage-Source-Converter-13-320.jpg)
![Space Vector
+
VDC
-
Vb
Va
Vc
S1 S3 S5
S4 S6 S2
N
R
R R
N
Vdc
3
2
Vdc
3
1
Vdc
3
1
For [POO] the Equivalent Circuit](https://image.slidesharecdn.com/spvm-140605022805-phpapp01/85/Sinusoidal-PWM-and-Space-Vector-Modulation-For-Two-Level-Voltage-Source-Converter-17-320.jpg)
Sinusoidal PWM and Space Vector Modulation For Two Level Voltage Source Converter
- 1. TWO LEVEL VOLTAGE SOURCE CONVERTER Presented By FA13-R09-005 Muqadsa Iftikhar FA13-R09-013 Zunaib Ali FA13-R09-024 Madiha Naeem
- 2. Converters Converters Rectifier Inverter LOAD AC Supply VL IL ~ AC DC _ LOAD DC Supply VL IL ~ DC AC _ Inverter: Fixed DC to three phase variable magnitude and frequency AC for AC Load Rectifier: Fixed magnitude and frequency AC Voltage to adjustable DC voltage for DC Load
- 3. Converters Whether converter serves as an inverter or a rectifier; the power flow in the converter circuit is bidirectional: the power can flow from its DC side to AC side and vice versa. This presentation focuses on the carrier based sinusoidal PWM (SPWM) and space vector modulation (SVM) control techniques for two level inverter. Rectifier & Inverter
- 4. Two Level VSC Circuit diagram for two level voltage source converter is shown. Converter is composed of six switches S1, S2,…, S6 with an anti- parallel free wheeling diode for each switch. Switches can be IGBT, MOSFET depending on power ratings of converter Two Level VSC
- 5. Sinusoidal PWM Vma, Vmb and Vmc are the three-phase sinusoidal modulating waveforms. Vcr is triangular carrier signal. The fundamental-frequency component in the inverter output voltage can be controlled by amplitude modulation index. The frequency modulation index is
- 6. Two Level VSC Two Level VSC Sinusoidal PWM
- 7. Sinusoidal PWM Vma > Vcr The upper switch S1 in the inverter leg is turned on. The resulting voltage VaN , is equal to Vdc. The waveform of has two levels therefore the inverter is referred as two level inverter. The inverter line to line voltage can be obtained by Vab= VaN - VbN
- 8. Sinusoidal PWM Dead Time To avoid possible short circuiting of upper and lower devices in an inverter leg a dead time or blanking time should be implemented during which both the switches must be turned off. The switching frequency of the active switches in the two level inverter can be found from fsw = fcr = fm * mf The magnitude and frequency of fundamental component Vab1 can be independently controlled by ma and fm
- 9. Sinusoidal PWM Synchronous PWM Carrier frequency is varied in accordance with the modulating wave frequency (mf is an integer) Can obtain desired number of pulses and also the optimum pulse width by varying carrier frequency with modulating frequency, hence harmonics can easily be removed Need digital circuits for implementation. Asynchronous PWM Carrier frequency is fixed and independent of modulating wave frequency. No control on number of pulses and also the pulse width as carrier frequency is fixed hence harmonics are more. Easily implemented using analogue circuits.
- 10. Space Vector Modulation Space vector modulation is one of real time modulation techniques Widely used in digital control of Voltage source converter Switching States The switching state P denotes that the upper switch in an inverter leg is ON and the inverter terminal voltage is (VaN ,VbN ,VcN) is positive V. as shown in Table 4-1 Where O denotes that the inverter terminal is zero due to conduction of the lower switch.
- 11. Two Level VSC Two Level VSC Space Vector Modulation
- 12. Space Vector Relation with switching states Table 4-2: Space Vectors, switching states, and on-states switches The possible eight switching states are shown below in Table 4-2
- 13. Space Vector Space Vectors Among the eight switching states, [PPP] and [OOO] are zero states and the others are called active states. The active and zero switching states can be represented by active and zero vectors, respectively. Space vector diagram for two-level inverter is shown Six vectors V1 to V6 form hexagon with six equal sectors and zero vector V0 lies in center of hexagon
- 14. Space Vector Space Vectors In order to derive relationship between the space vectors and switching states assume system is balance Transform 3-phase variables to 2-phase variables through abc/αβ transformation A space vector can be generally expressed in terms of 2-phase voltages in α-β frame
- 15. Space Vector For active switching state POO Following the same procedure all the remaining 6 vectors can be derived Vref Will rotates in the space with the angular velocity R R R N Vdc 3 2 Vdc 3 1 Vdc 3 1
- 16. Space Vector The inverter output frequency corresponds to the rotating speed of Vref where as its output voltage can be adjusted by the magnitude of Vref The angular displacement between Vref and the α-axis of the α-β frame can be obtained by
- 17. Space Vector + VDC - Vb Va Vc S1 S3 S5 S4 S6 S2 N R R R N Vdc 3 2 Vdc 3 1 Vdc 3 1 For [POO] the Equivalent Circuit
- 18. Dwell Time Calculation The dwell time for the stationary vectors essentially represents the duty-cycle time of the chosen switches during a sampling period Ts. Volt-second balancing principle: product of Vref and sampling time Ts equals the sum of the voltage multiplied by the time interval of chosen space vectors
- 21. Modulation Index As length of reference vector Vref represents the peak value of fundamental frequency component in inverter output phase voltage Va1 is the rms value of the fundamental component
- 22. Modulation Index Maximum length of Vref corresponds to radius of the largest circle i.e. inscribed in the hexagon. Hexagon is formed by 6 active vectors of length 2Vdc/3 Maximum modulation index is
- 23. Switching Sequence The switching sequence for given Vref is not unique, but it should satisfy the following two requirements for minimizing the device switching frequency. the transition from one switching state to the next involves only two switches in the same inverter leg, one being switched on and other switched off the transition from Vref moving from one sector in the space vector diagram to the next requires no or a minimum number of switching.
- 25. Switching Sequence It can be observed that