Development Of Industrial Frequency Inverter AC Constant Current Source

With the development of power electronic technology, inverter power supplies grow at a high speed and are widely used although their advent is not long. Because of advantages such as high reliability, efficiency and energy-saving, the market prospect for inverter power supplies is favorable.AC constant current sources are in use throughout industry, for example, they are required in parameter measurement of semiconductor devices, property test of low voltage electric apparatus and power supply for instruments. However, at present, AC constant current sources in domestic market mostly adopt traditional linear voltage regulator, characteristic of low accuracy and long response duration. At the same time the supplies foreign imported are expensive.In view of this situation, this subject develops an industrial frequency AC source with high precision constant current output based on inverting, voltage-dropping and current-boosting as well as current feedback technologies. Its output current rang is 1~100A (true RMS), frequency range is 50~60Hz., current precision is 1%, wave distortion doesn't exceed 3% and current setup time is less than 100ms.The supply possesses the virtues of steady performance, high resolution and low distortion with the application of micro-controller PIC18F4620, SPWM generator SA4828, new generation power electronic device IGBT and high-speed A/D converter. Further, it has the option of GPIB and RS-485 communication interfaces to meet a demand of establishing automatic measuring and controlling system expediently and freely.The paper analyses the basic principle of inverter power supply and introduces the supply circuit design, components selection, design attentions and so on. The paper also describes software design in corresponding with the supply hardware, including SA4828 control, output current sampling and communication through RS-485 and GPIB interfaces.In order to test the supply's performance, this subject also develops an AC constant current source analyzer based on virtual instrument technology, which adopts Holl current transducer and data acquisition card as hardware, LabWindows/CVI as software development tool. This analyzer is able to measure the true RMS, frequency and distortion factor of an alternating current precisely. The paper presents the analyzer's hardware and software design, as well as the test result to a standard constant current supply.The industrial frequency inverter AC constant current source is tested by AC constant current source analyzer referred above, and experiments in different loads indicate that the inverter supply successes to come up to the required standard. Test data and waveforms are presented in the end.