Device for detecting voltage of three-phase neutral point clamped PWM (pulse-width modulation) inverter

Abstract

The invention discloses a device for detecting the voltage of a three-phase neutral point clamped PWM (pulse-width modulation) inverter. The device comprises a resistance partial voltage measuring device and a phase output voltage end pulse width measuring device, wherein the resistance partial voltage measuring device comprises eight partial voltage resistors; the phase output voltage end pulse width measuring device comprises four comparison amplifiers connected with the eight partial voltage resistors of the resistance partial voltage measuring device; four calculation value obtaining devices are respectively used for obtaining pulse widths of high electrical level and low electrical level output by the four comparison amplifiers within one PWM period; an output phase voltage average value is calculated according to the calculation result of the four calculation value obtaining device within one PWM period; in this way, an output average phase voltage can be measured precisely and reliably under any situation or operation condition.

Description

technical field [0001] The invention relates to a device for detecting the output voltage of a three-phase neutral point clamping type PWM inverter, which belongs to the technical field of power electronics. Background technique [0002] At present, the method of adjusting the running speed of the motor by changing the frequency usually requires variables such as the inverter output voltage reference torque, magnetic flux and frequency to make the motor control reach the optimal state. These parameters can be averaged within 1 PWM carrier cycle output by the inverter. Therefore, a device and method for accurately measuring the average phase voltage of the frequency converter is required to achieve the best performance of motor control. [0003] Usually, the midpoint of the on-time and off-time of the switching device is used as the calculation point of the average voltage. If the actual phase voltage changes linearly during the rising phase and the falling phase, this method...

AI Technical Summary

Problems solved by technology

[0003] Usually, the midpoint of the on-time and off-time of the switching device is used as the calculation point of the average voltage. If the actual phase voltage changes linearly during the rising phase and the falling phase, this method can correctly calculate the average voltage, such as figure 1 As shown, however, in actual situations the actual voltage at the switch position does not always change linearly due to the influence of the dead time, such as figure 2 As shown, if half of the DC voltage is directly compared with the instantaneous voltage, a large error will be generated, especially when the phase current is close to zero, the actual voltage changes very sharply. If the above method is used, a larger error will be generated. When The situation is exacerbated when the switching frequency increases, so the method of comparing the instantaneous phase voltage and DC link voltage is not reliable

[0004] This problem can be solved by using an analog integrator and AD converter, but this method requires higher cost, and the analog components may introduce new errors

Images