| The designed PWM rectifier control strategy based on the balanced grid voltage will appear abnormal operation state, mainly for its presence of the negative sequence current component in the network side resulting in alternating current asymmetry. In addition, the DC voltage will be present in the second harmonic fluctuations, making the DC voltage waveform distortion. Therefore, for the study of the three-phase voltage-type PWM rectifier control strategy under unbalanced conditions is particularly important,and the paper is organized as following:Firstly, this paper analyzes the main circuit topology and operating principle of the three-phase voltage-type PWM rectifier. Secondly, the paper also explains the unbalanced three-phase grid concept, as well as its damage and research methods. Thirdly, the mathematical model of the three phase voltage-type PWM rectifier under stationary coordinate system and the two-phase synchronous rotating coordinate system is derived. Comparing of these two models, the paper decides to design the control strategy in the two-phase synchronous rotating coordinate system.Secondly, on the basis of the theoretical research, the paper presents symmetry line current control strategy and the DC voltage harmonic suppression control strategy for the problems appearing in three-phase voltage-type PWM rectifier under unbalanced conditions. At the same time, it also proposes an AC-DC PWM rectifier side coordinate control strategy innovatively using the weighted thought.Thirdly, by analyzing the notch, T/ 4 delay law and the second-order generalized integral(SOGI), this paper decides to adopt the SOGI method to extract the positive and negative power component for its simple algorithm structure, easy implementation, low frequency suppression characteristics and well dynamic response.In addition, the paper describes the parameters of the design principles of the voltage and current PI controllers, as well as the whole system stability. Finally, the simulation model is built in PSIM 9.0 to validate the correctness of the proposed control strategy.Finally, a rated power of 20 k W voltage-type PWM rectifier is developed, giving its detailed design scheme of the hardware and control system and the corresponding software control subroutine flow chart. Due to the experimental conditions, the unbalance control strategy under balanced conditions is verified by the experimental, the results show that the control strategy proposed in this paper can achieve the control effect of high power factor, low harmonic distortion.This paper focuses on the control technology of the three-phase voltage-type PWM rectifier under unbalance conditions and proposes the corresponding control strategy. The simulation and experimental results verify the proposed control strategy in this paper, and the content in this paper can provide reference and improvements for the conventional PWM rectifier control technology. |
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