Research On Modular NPC-TL-HB Inverters

The topology of NPC-TL-HB inverter is modeled and analyzed in this paper.It is found that the output voltage of the inverter module is affected by many factors under the open-loop control strategy.In order to improve the steady and dynamic performance of the output voltage of the inverter module,two control strategies,Proportional Integral double close loop control and Proportional Resonance single close loop control,are compared and studied respectively.The results show that under the condition of resistive load,both control schemes have good control effect.However,under the condition of nonlinear load,the control effect of Proportional Resonance is better than that of Proportional Integral double loop control.At the same time,When the load is non-linear,the output current of the inverter module will have a big impact,which will bring a certain risk to the reliable and stable operation of the module.Aiming at the problem that the output current of sudden impact load is too large to damage the inverter module,a mixed software and hardware current limiting protection strategy is studied,in which the software current limiting adopts the step-down circuit to reduce the output voltage reference to a smaller value to reduce the output current,and the hardware current limiting adopts the Cycle By Cycle protection current limiting strategy.Compared with the traditional CBC protection strategy and the novel CBC protection strategy,it is found that the novel one has a long protection period and is more reliable.In order to improve the load capacity of the inverter module,a master-slave parallel control strategy suitable for the industrial field is studied.The complex parallel control is decoupled into synchronous control and current sharing control.Synchronous control uses Synchronous Bus and CAN communication master-slave control logic,current sharing control uses Current Sharing Bus to calculate the average output current of each module in the parallel system,and then superimposes the difference between output current and average current of each module into the output voltage reference,in order to realize stable and reliable operation of multiple modules.The parallel experiment results of several modules prove the validity and reliability of the parallel control strategy.