基于双PWM变换器的交流电子负载研究

Research on AC Electronic Load for Testing AC Power Based on Dual Single-phase PWM Converter

为节省能源和简化电源设备测试的投入,研究了一种结构简单、可测试交流电能装置各种电特性并将试验电能回馈至电网的交流电子负载。根据其主电路的两级AC/DC/AC变换结构,分析了起传递能量桥梁作用的直流母线电容工作和谐波产生机理,提出了将两级PWM变换器分开控制的方案即前级变换器采用固定开关频率的单P环直接电流控制,后级变换器采用三角波调制的经典电压外环和电流内环的双闭环结构。基于32位定点TMS320F2812DSP控制器设计控制系统,实现了上述设计方案并应用于小功率交流电子负载实验样机。实验论证表明,该方案控制简单易行,可以实现对单相测试电源的阻抗特性精确模拟,同时完成功率因数接近于1的有源逆变,将测试电源电能回馈电网。

A simple kind of AC electronic load with power recovery based on dual single-phase PWM converter of the voltage-source type is studied and especially the principle of dc link capacitor and its harmonic phenomenon are presented in detail. Based on the topology of AC/DC/AC converters, a control strategy-an independent control for the two stages including the triangle wave modulation is put forward, The fixed switching frequency of single P direct current control for the AC/DC stage and the classical dual-loop control （voltage loop and current loop） for the DC/ AC stage, which is suitable for soft start, are applied. The control system based on 32-bit TMS320F2812 DSP controller is designed and used successfully in a low power prototype of AC electronic load. The experimental results show that the characteristics both in simulating the specified impedance approximately and realizing near unity power factor operation verify the described method to be simple and effective. The dc bus voltage regulation starting from cold state with good dynamic response is also achieved. The research can perform power recycle, save the energy, reduce the test cost and is proved to be practical in power recovery.