| As an important equipment in low-voltage electrical appliances,circuit breakers are often used in low-voltage power distribution systems,transmission systems,and other electrical equipment,which is responsible for breaking,bearing the normal or abnormal(such as short circuit)current.In the overload protection test of the circuit breaker,the quality of the test current is the key to the success of the test.Therefore,in the circuit breaker overload protection test,the constant current source equipment is essential.Along with the development of intelligent high power and high stability constant current source products,the frequency adjustment constant current source is increasingly required,which can meet the requirements of different countries.In order to obtain a stable power supply for the circuit breaker overload protection test,and to meet the demand of different frequencies of the three-phase AC constant current source,a AC-DC-AC variable frequency constant current source based on the rectifier circuit and the three-level inverter circuit was designed.The operating principle and control algorithm of the rectifier circuit and the three level inverter circuit based on IGBT switching device were mainly studied.The main circuit and the control ability of the AC-DC-AC converter are verified with the PSIM simulation software.IGBT driver circuit,bidirectional thyristor trigger circuit,current signal acquisition circuit,zero crossing acquisition circuit and communication circuit were designed.The 16-bit dsPIC digital signal controller was chosen as the control chip.The constant current source driver signals were controlled and the real-time current signals were captured by using the SPWM control system.Then,the PID closed-loop regulation of the system was achieved through the current data feedback.At last,the real-time detection and human-computer interaction of the upper computer were obtained by using Modbus field bus communication technology. |
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