Research And Implementation On Low-frequency Sine Wave Current Source For Testing

A low-frequency sine wave current source is widely used in fields of grounding grid fault diagnosis, communication, radar, etc. The source has many characteristics of higher output precision, stable frequency and low total harmonic distortion (THD). In this paper a low-frequency sine wave current source is designed for grounding grid fault diagnosis. The basic principles, structures and characteristics of linear current source and switching current source have been studied deeply; meanwhile, the implementation scheme of all kinds of sine wave current source has been compared as well. According to the low-frequency sine wave current source's characteristics of low frequency, high frequency stability, and large output current in grounding grid fault diagnosis, the circuit design which consists of a pre-regulation switching voltage source, switching DC voltage source, linear DC sine wave current source, H-bridge and the intelligent controller is proposed. H-bridge can convert polarity. Linear DC sine wave current source is the output stage. By its small output ripple and fast response, the output accuracy of sine wave can be improved. The switching DC voltage source is the middle stage, which can provide the full-wave rectified sine wave voltage for output circuit to reduce the voltage difference of the output stage regulator transistor and improve the efficiency of the whole system. The pre-regulation switching voltage source is the input stage, which can pre-regulation input voltage to ensure adjustment sensitivity of the middle stage output waveform. LPC2138 is used as the intelligent controller of the power supply, which mainly completes voltage measurement of load resistance, generates low-frequency sine wave reference signals and PWM complementary pulses, provides reference signals for the pre-regulation switching voltage source, switching DC voltage source, linear DC sine wave current source, and controls the work stage of H bridge.According to the design scheme, the software programme and the hardware circuit are completed, and the entire system has been tested and analyzed. The test results show that the technical parameters of current source satisfy the requirements for grounding grid fault diagnosis completely, and verify the scheme's feasibility.