Optimal control study of AC constant power loads based on LCL filter

Abstract

The main circuit of a traditional AC constant power load model takes no account of filter optimization， and the PI （proportional integral） regulator is used in the inner loop of current control. In case of high regulation speed， severe overshoot may occur， resulting in poor model universality and inaccurate transient process. Characterized by its quick dynamic response， small overshoot and achievability， MPC （model predictive control） introduced into current inner loop of AC constant power load model can improve its transient performance. By combining the advantages of traditional PI control and MPC， the paper proposes a new AC constant power laod optimization control strategy—the PI regulator is used for voltage outerloop control， and MPC is used for current innerloop control； the main circuit consists of PWM-based （pulse width modulation） rectifying circuits with LCL filters at AC side and resistors. LCL filters were designed according to the overall inductance， capacitance and resonance frequency. The proposed control strategy and voltage/current PI control strategy were applied to AC constant power load model. The results show that the model using the proposed control strategy improves system robustness and can recover in shorter time after interference； the LCL filters can diminish current harmonic distortion at AC side and enhance the power quality.

Keywords

• ac constant power load
• model predictive control
• pi control
• lcl filter