Introduction to SVPWM control algorithm with 100% utilization

1. Overview:

In Part 4, we get that the modulation ratio of SPWM is 1 under ideal conditions, and the DC voltage utilization is 0.866, or 86.6%. The voltage utilization is not high, and 13.4% of the bus voltage is not utilized. This article introduces the SVPWM control algorithm with a utilization rate of 100%.

2.SVPWM principle:

SVPWM stands for Space Voltage Vector PWM, which controls the voltage vector to make the motor obtain a circular rotating magnetic field. Ideally, the modulation ratio can reach 1.15. The output line voltage is the bus voltage. Therefore, the DC utilization rate is 1, that is, 100%. It is easier to control digitally, and the DC utilization rate is 15% higher than SPWM. It is widely used in the new energy industry.

The three-phase full-bridge topology consists of 6 switching devices. For each bridge arm, the upper and lower tubes are complementary, so there are eight basic switch combinations. They constitute the 8 basic voltage vectors of SVPWM. Among them, the output line voltage is 0 when the upper tube is fully turned on and the lower tube is fully turned on, so there are two 0 vectors. The other 6 vectors constitute the voltage hexagon of SVPWM and divide the hexagon into 6 sectors. The vector allocation and action time of SVPWM, vector decomposition and coordinate transformation. The calculation process is not derived here.

The basic voltage vector amplitude of linear modulation is 2/3Vbus. The amplitude of the inscribed circle is the output phase voltage amplitude, i.e. Vref:

The output phase voltage is SQRT(3)/3*Vbus, then the output line voltage is Vbus. Therefore, the DC voltage utilization is 1.

There are papers proving that SVPWM space vector control is equivalent to carrier-based SPWM in principle. It can be controlled by injecting zero-sequence voltage into the modulation wave, that is, superimposing the third harmonic control method.

It can be seen that the modulation wave is a saddle wave and the output phase voltage is also a saddle wave.

When the line voltage is synthesized, the third harmonics cancel each other out and the output line voltage becomes a sine wave.