DC pre-excitation for three level variable-frequency speed-governing system start process

Abstract

The invention relates to a dc pre-excite magnet method which adds the motivating torque of the variable-frequency control system and reduces the motivating current to improve the motivating function of the variable-frequency device-motor system in the field of power electron technology. It first ascertains the pre-excite magnet scheme to choose the excite magnet voltage vector direction and the motivating voltage vector direction by park equation; it chooses the excite magnet voltage vector direction PPP and PNP vector for the three levels middle level principle and space vector PWM pulse generating rule; it ascertains the object current and decides the time, size of the vector by the motor inner parameter; it generates the voltage vector pulse sequence by the object current and computes the best excite magnet angle and excite magnet current combined to the three levels variable-frequency device self character.

Description

technical field [0001] The invention mainly relates to increasing the starting torque of the frequency conversion speed regulation system, reducing the starting current so as to improve the starting performance of the frequency converter-motor system, and belongs to the technical field of power electronics application. Background technique [0002] The two major development trends of today's variable frequency speed regulation systems are: 1) high voltage and large capacity; 2) high performance small and medium capacity systems. For the former, users are more concerned about the reliability in the application; for the latter, they mainly expect to obtain satisfactory performance indicators, such as low-speed high-torque, waveform distortion rate, etc. Among them, the starting performance index is almost one of the most important indexes to measure all frequency conversion speed regulation systems. Different application occasions have different starting requirements for vari...

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Problems solved by technology

[0004] 1) Although the starting current is large, the output mechanical torque at this time is not large. Therefore, when the load is loaded with large torque, the system often cannot start normally;

[0005] 2) Excessive starting current can easily cause the midpoint voltage to shift and make the inverter unable to start normally;

[0006] 3) In order to avoid excessive inrush current damage to switching devices, it is often necessary to increase the device margin in the design, which greatly increases the cost

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