Method for realizing selective harmonic elimination modulation by adopting fixed control cycle

Abstract

The invention relates to a method for realizing selective harmonic elimination modulation by adopting a fixed control cycle. The method is technically characterized by comprising the following steps of adopting the fixed control cycle to control the vector decoupling of a PWM (pulse width modulation) rectifier, so as to obtain the amplitude and the angle of the given voltage, and deriving the angle of the given voltage to obtain the frequency of the given voltage; using the angle of the given voltage as an initial value, and carrying out number integration on the frequency, to obtain a relatively continuous angle; carrying out monotone processing on the relatively continuous angle; according to the monotone-processed continuous angle and the received amplitude, searching a table to output the SHEPWM (selective harmonic elimination pulse width modulation) pulse. The method has the advantages that the vector closed loop control method of the fixed cycle is combined with the selective harmonic elimination modulation, so the complicated variable cycle control is avoided, a power converter system has the quick and accurate dynamic response capability and good current harmonic property in the steady state, the low-order harmonics in the output voltage of a converter can be obviously inhibited, and the method is especially suitable for high-power application occasions.

Description

technical field [0001] The invention belongs to the technical field of alternating current power conversion, in particular to a method for realizing specific harmonic elimination modulation by using a fixed control period. Background technique [0002] During the operation of the converter device using PWM modulation, its switching loss increases with the increase of the modulation frequency. The larger the design capacity of the converter device, the lower the modulation frequency correspondingly. Currently, the switching frequency of MW-level converters is Generally around 1kHz. Since reducing the switching frequency will increase the harmonics of the output voltage, it is necessary to increase the capacity of the filter, resulting in an increase in the size and cost of the device. [0003] The specific harmonic elimination modulation method (Specific Harmonic Elimination Pulse Width Modulation, SHEPWM) is an optimized PWM method, which aims to eliminate certain specific ...

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Problems solved by technology

At present, most of the reports on SHEPWM focus on the optimal calculation of the switching angle. There is no relevant literature on how to combine this optimal modulation method with the closed-loop control method to make the system have both fast dynamic response and good steady-state current performance. According to records, this is because SHEPWM is a synchronous modulation. To combine it with a closed-loop control algorithm, the intuitive way is to use variable cycle control, but it is quite difficult to implement

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