Three-phase PWM converter in voltage unbalance condition and optimal control method of three-phase PWM converter

Abstract

The invention relates to the field of stable operation of three-phase PWM converters, in particular to a three-phase PWM converter in a voltage unbalance condition and an optimal control method of the three-phase PWM converter, and aims at effectively solving the problem of secondary fluctuations of a negative sequence component of AC side current and active power of the three-phase PWM converter in the voltage unbalance condition. The three-phase PWM converter comprises a three-phase full-bridge rectifier circuit and a power compensation circuit. The converter is based on harmonic detection and proportional-integral and harmonic control principles and is applied to a mathematical model of the three-phase PWM converter in an alpha-beta coordinate system free of phase detection for control; the controller comprises an AC controller and a DC controller; and elimination of the secondary fluctuations of negative sequence current and the active power is achieved through control on positive and negative sequence current of an AC side, the AC side current and DC voltage.

Description

technical field [0001] The invention belongs to the field of stable operation of three-phase PWM converters, in particular to a three-phase PWM converter under unbalanced voltage conditions and an optimization control method thereof. Background technique [0002] The three-phase PWM converter realizes the grid-side current symmetry, unit power factor operation, and fast dynamic response. At the same time, it can also realize two-way flow of power. It truly realizes "green power conversion", so it is widely used in active power filters. (APF), new uninterruptible power supply (UPS), distributed power generation and energy storage technology fields, etc. The high performance of the three-phase PWM converter is under the condition of balanced input voltage on the AC side, but the actual voltage imbalance occurs from time to time, such as weak power grids in remote areas, uneven distribution of three-phase loads in micro-grids, and high-power loads. , and the limitations of dis...

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Problems solved by technology

The high performance of the three-phase PWM converter is under the condition of balanced input voltage on the AC side, but the actual voltage imbalance occurs from time to time, such as weak power grids in remote areas, uneven distribution of three-phase loads in micro-grids, and high-power loads. , and the limitations of distributed generation, these will make the voltage unbalanced, the unbalanced voltage will cause the DC bus voltage to fluctuate, and the AC side current contains odd harmonics, which will affect the normal operation of the three-phase PWM converter

[0004] At present, there are many methods for improving the performance of three-phase PWM converters under unbalanced voltage conditions. The main three methods are: 1. Constant power control method: constant power control allows the DC voltage to fluctuate to a certain extent, so the output filter The capacitance will decrease accordingly. When the input voltage is unbalanced, the negative sequence current output from the unbalanced phase will increase, further deteriorating the power quality of the system. , the sinusoidal symmetry of the input current can be achieved, but the DC side voltage will produce secondary fluctuations. In order to eliminate the secondary fluctuations of the DC voltage, the electrolytic capacitors on the DC side will be increased or even super capacitors will be used, which will reduce the dynamic response of the system. At the same time, the capacity Large electrolytic capacitors and super capacitors increase the volume and cost of the three-phase PWM conversion device; 3. Coordinated control method of constant power and direct current: the control goal is to choose which one is important according to actual needs, so that the secondary fluctuation of active power is eliminated, There will be a negative sequence component in the AC side current, suppressing the negative sequence current on the AC side, and there will be secondary fluctuations in active power. If the two are coordinated and controlled, the system will still have negative sequence current and power secondary fluctuations

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