Research On Three Phase Voltage Source PWM Rectifier For Energy Storage System

The Power Conversion System (PCS), using PWM technology, is an important partof Battery Energy Storage System (BESS). The two-stage PCS, which consists of AC/DCconverter and DC/DC converter, have flexible configuration of the battery and can beaccurate and reliable in the management of the battery charge and discharge. Thus it hasbeen widely used in small and medium-sized power battery energy storage system. Basedon the three-phase PWM rectifier with LCL filter used in two-stage PCS, this paperinvestigated the controller strategy of the system both under balance and unbalancecondition, the design method of the inner current loop.After analyzing the principle of the PWM rectifier, this paper presents themathematical model of the system under three-phase coordinate, dq coordinate and the αβcoordinate. The role of PWM rectifier is stabilizing the dc bus voltage, thus themulti-closed-loop control strategy was used. The inner current loop was under the αβcoordinate and PR controller was chosen to eliminate the steady-state error. This paperanalyzes the active damping method, based on feedback of capacitive current, to suppressthe resonant of the LCL filter.The system is of high order and complicated and it is difficult to determine theparameters of the regulator. After discussing the function of parameters, this paper proposedan easy method to design the PR regulator parameters separately, which can guarantee thestability of the system and the performance of the inner current loop.The methods to improving the control performance under unbalance condition arestudied. First of all, this paper used the decoupled double synchronous reference framephase lock loop method to get the phase of the voltage. Two control methods have beenused in this paper. One of them is to balance the grid-side current, the other is to eliminatethe harmonic composition in the dc voltage. The simulation results have verified the theory.The experimental prototype is designed, including the design of a general three-phasevoltage-source rectifier circuit and the programming of digital control based on the DSPplatform. In order to verify the effectiveness of the control strategy and the rationality ofthe design of controller, the experiment has been carried out on the system with a resistor as load. In additional to this, cascade experiment which used a bidirectional DC/DC converteras the load, has also been carried out. The results show that the PWM rectifier is suitablefor using in energy storage system.