Research On The Control Technology And Fault Diagnosis Of Parallel Inverter

This paper mainly studies the control technology and fault diagnosis of the parallel inverter. With the control strategy based on Average Power Modulating, the control effect is good. The paper also presents the parallel system power switches fault diagnosis method, the hardware circuit is simple and the software calculation is not complex, so the method and procedure is suit for practical use. The paper first analyzes the infection of MOSFET parasitic diode's reverse recovery in half-bridge inverter, then presents how to change the property of the equivalent output impedance of the inverter without influencing its dynamic and static characteristic. Modeling the double loops control inverter which lies in the parallel system, analyzing its circulating current peculiarity. The parallel strategy is presented which is based on Average Power Modulating, it is testified to be feasibile by the means of theory, simulation and experiment, the infection caused by the different values of the inverter's component to the effect of parallel control is also discussed. Finally it is explained how the inverter circuit and the digital control circuit are designed. To realize redundant control, the parallel system must have the capability of fault self-diagnosis. Compared with the faults of single module inverter, the faults of parallel system are much more complicated and harder to be diagnosed. Many faults of parallel system are failures of power switches among which open circuit fault and short circuit fault are the most common cases. Through simulations and experiments, how the faults of the parallel system look like when the power switches are in open circuit or short circuit are analyzed separately, and the damages caused by the faults are analyzed too. The result is that open circuit fault does not affect output voltage of the system, but it apparently affects inductance current and output current of single module inverter. When the open circuit fault happens, the inductance current of the fault module changes regularly, so the phenomenon is fit for fault diagnosis. The short circuit fault is mostly protected by hardware, how this fault influencing systemic output voltage depends on the time the fault taking place. Based on these conclusions, it is proposed that the fault diagnosis can be done through measuring the inductance current of each module. The method of how to modulate and analyze the inductance current is given and the detail procedure of how to make the fault module to withdraw from the parallel system after the fault is found is also showed in this paper. Experiments done on parallel sample inverters showed that the method and procedure could realize not only the fault diagnosis and self-protection, but also the redundant control and hot swap, and thus verified the method and procedure.