Study On AC Electronic Load With Power Energy Feedback

With the development of power electronics technology, various types of power electronic devices are applied in more and more areas. These devices need to be tested using different loads before they are put into the market. Tests using conventional real load has many problems of large energy loss, poor variability, etc, which makes it hard to meet the requirements of the various testing occasions. To solve the problem, this paper proposes a theory of alternating current electronic load based on power electronic converter.The alternating current electronic load is a kind of device which uses power electronic converters to simulate conventional real load exactly including common linear and non-linear load. Moreover, the energy absorbed from the tested power supply can be fed back to utility grid at unit power factor so that it can decrease the testing cost and enrich the testing load types greatly. At present, the research on AC electronic load mainly aims at controlling the average active power and reactive power supplied by AC source devices. But in these cases, the AC source output current is often distorted and different from that in real load testing circumstance. There have been some AC electronic load products in the market, which can make the output current same as that in real load circumstance, but their power is not so large and the tested energy is used up during tests, which causes much waste. In this paper a new type of AC electronic load is studied, which converges the advantages of the two types of electronic load mentioned above.This paper analyzed the principle of high power energy feedback AC electronic load and DC link AC-DC-AC converter was adopted as the main topology structure. The input rectifier and output inverter were both consisted of voltage source PWM rectifier which can run in four quadrants. The amplitude and phase of input current at the AC power supply being tested side must be strictly controlled by PWM rectifier so that it is just like the special type of load that we have setted. At the side of AC power grid, the output current should have the same frequency and phase with the voltage in order to feed the energy back to power grid at unit power factor. Meanwhile, the amplitude of output current should also be controlled to keep the DC bus voltage stable. Conventional double closed-loop control was adopted in the control of the PWM inverter. The inside current loop assures actual current follows the change of its instruction, and the outside voltage loop keeps DC voltage to be a special constant. The control of the PWM converters combines analog method with digital method to make the current track its instruction quickly and accurately.The specific type and properties of the load can be set by the man-machine interface, and the current value can be calculated by digital signal processor in real time. This paper obtained the frequency domain block diagram using AC small-signal analysis model and the parameters of main circuit components were designed properly. Against the frequency restriction of the high power electronic switches, the paper proposed several improved methods to increase tracking accuracy of the current. The system simulated several different load types on PSIM platform. The results proved the methods to be practical and effective. In the end, the power circuit and control system were designed and the schematic diagram was drew using PROTEL softwear.