Research On Control Of Three-Phase Current Source PWM Rectifier Under Unbalanced Voltage

With the application and development of high-power variable current technology,pulse-width modulated rectifiers are receiving more and more attention from industry and academia.The current source rectifier(CSR)has been applied in data center power supply,airborne power supply and other fields due to its advantages of high reliability in dc short circuit,no pre-charging circuit and wide range of step-down output.At present,the research of three-phase CSR is mainly focused on the condition of grid voltage balance,but the voltage imbalance condition is common in the actual working condition,which will lead to low frequency pulsation on the dc side of CSR and a large number of harmonics in the grid side current,making the performance of the rectifier worse.In this paper,three-phase CSR is taken as the main research object,and the control strategy under unbalanced grid is studied.The main contents are divided into the following aspects:Summarize the current development trend of power electronic equipment,and introduce the research background and significance of CSR;Aiming at the problem that the zero and negative sequence components in the voltage cause a series of hazards to the power system and have an impact on the operational performance of CSR when the power grid voltage is unbalanced,the necessity of studying control strategies for unbalanced conditions is proved.The research status of CSR control strategy and topology at home and abroad is analyzed and summarized,and its application prospect in industrial occasions such as superconducting energy storage is introduced.The working principle of CSR is introduced in terms of topology and operating modes,the mathematical models of CSR in different coordinate systems are established,and the equivalent circuits and control block diagrams are built respectively,and the characteristics of the models and the considerations in the development of control strategies are analyzed.By establishing the mathematical model of CSR under unbalanced grid voltage,the expression of the relationship between dc side output current and grid side current is derived,and the influence of unbalanced conditions on CSR operation performance is clarified.The principle of traditional six-sector space vector pulse width modulation is analyzed,and the implementation method is given.In order to effectively reduce the switching loss,the six sectors are further divided and the switching sequence is optimized to obtain a twelve-sector modulation strategy.Under the condition of three-phase unbalanced grid voltage,the traditional direct power control cannot meet the requirements of CSR operation performance,and more current sensors are required.Therefore,this paper proposes a direct power feedback control strategy without collecting grid-side current,which controls the low-frequency ripple components of active power,and then optimizes the waveform quality of CSR dc side output voltage and current.In the modulation strategy,the notch filter is used to suppress the harmonic component in the modulation signal,which further reduces the low-order harmonic content of the grid-side current.According to the dc side output current,switching function and grid voltage,the grid side current component is calculated indirectly,so that the current sensor is not needed and the hardware circuit cost is reduced.Under the condition of three-phase unbalanced grid voltage,the traditional control strategy commonly used in CSR needs to extract the positive and negative sequence components of voltage and current,but the extraction process is complicated and the calculation amount is large.Therefore,this paper proposes a dc side double closed-loop resonance control strategy without positive and negative sequence components.By directly suppressing the low-frequency pulsation of the dc side voltage,the system power quality is significantly improved under unbalanced conditions.In addition,the filter capacitor current compensation term is introduced into the modulation current reference command to realize the unit power factor operation of the system.The feasibility of the proposed control strategy is verified by Matlab/Simulink simulation model.At the same time,a 3k W three-phase CSR hardware experimental platform is built,and the device selection and circuit design of the experimental prototype are introduced in detail.Finally,based on the model-based design method,the effectiveness of the control strategy in this paper is verified by the automatic code generation technology.