Space Vector Modulation Technique

SVM(space vector modulation) or SVPWM is also called Space Vector Pulse Width Modulation. The main idea of SVPWM is taking the three phase motor stator flux circle as the reference standard, and implement suitable switch based on the different switch modes of three-phase inverter to form a PWM wave, and to track their exact flux circle based on the formation of the actual flux vector. Compared with the traditional SPWM method, SVPWM regards the converting system and the asynchronous motor as a whole so that the model is relatively simple, but the real-time microprocessor control becomes much easier.

 pwm

SVPWM Comparing with PWM and SPWM

PWM: Pulse Width Modulation, when transistor (common MOS, IGBT and other full-controlled devices) is triggered the power supply voltage is applied to the motor; when the transistor is turned off, the DC power supply and the motor disconnect; Changing the on/off time of the transistor (adjusting the duty cycle ton) can adjust the motor voltage, and then the speed would changed accordingly by the motor voltage.

SPWM: sinusoidal pulse width modulation divides the sine half wave into N parts, in each part, after the comparison of Ut triangular wave carrier and three-phase sinusoidal reference voltage signal Ura, Urb and Urc, the generated SPWM pulse sequence waves Uda, Udb, Udc would be regarded as the driving control signals of inverter power switching devices. The fundamental wave of inverter output voltage is the fundamental sine wave required during modulation, so basically the amplitude and frequency of SPWM frequency inverters output voltage can be adjusted by the adjustment of the amplitude and frequency of the sine wave reference signals.

There are huge principle and source difference between SVPWM (space vector pulse width modulation technique) and SPWM, but they are also some common things for them. SPWM is modulated by sine wave and triangular wave, while SVPWM is modulated by triangular wave and sine basic wave that contains certain third harmonic content, which can be proved mathematically.

space vector modulation

Main Features of SVPWM/SVM(space vector modulation)

1. For space vector modulation technique, there is repeat switching between each cell only relates to one device switching, so the switch consumption is small.

2. Using the voltage space vector to generate the three-phase PWM (what is PWM?) wave directly to simplify calculation.

3. The inverter output line voltage fundamental maximum value is the DC side voltage, which is 15% higher than the output voltage of common SPWM inverter.

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