(23期已送排）一种基于最近电平调制方式的MMC电压均衡改进方法

最近电平逼近是模块化多电平换流器的主要调制策略之一,在电平数较多的换流器中具有明显的优势。为保证均压效果,通常都需要实时采集各个子模块的电容电压进行排序,在实际工程中则需要大量的电压采集模块来实现。针对上述问题,提出了一种替换方法,即通过桥臂电流对各个子模块投入时间的积分量来进行排序,间接实现了电容电压排序的效果,这种方法可以有效的减少传感器的数量。同时,在提出的替换方法的基础上,引入子模块间允许的电压最大偏差,在系统输出特性允许范围的前提下,大大的降低了因排序而导致的IGBT开关频率。最后通过RT-LAB仿真平台搭建了21电平的的MMC仿真模型,对两种电压均衡方法下IGBT开关频率和子模块电容电压进行比较,仿真结果验证了所提方法的可行性及有效性。

An Improved Voltage Balancing Method Based on MMC Nearest Level modulation

Nearest level modulation is one of the main modulation strategies of the modular multilevel converter,which has obvious advantages in the converter with large number of voltage levels.To ensure the effect of voltage balancing,the capacitor voltages of sub-modules are usually required to be collected and sorted all the time,and a large number of voltage acquisition modules are needed to achieve this goal in practical engineering.In view of the above,this paper proposes a replacement method,and the integral amounts of bridge arm current is.used for modules conduction time to sort,that indirectly realizes the effect of voltages sorting,and the method can effectively reduce the voltage sensors.Meanwhile,on the basis of the replacement method,this paper introduces the maximum voltage deviation among sub-modules,on the premise that the system output characteristics in allowable range,which can greatly reduce the frequency of IGBT switching caused by sorting.Finally,the model of MMC with 21 levels is realized by RT-LAB,and the IGBT switching frequencies and sub-module capacitance voltages under two voltage balancing methods are compared,and the simulation results show that the proposed method is feasible and effective.