A Three-Level Converter with Dynamic and Adaptive Common-Mode Voltage Suppression

本项目旨在通过在三电平T型变流器(3L-TTC)中采用自适应方法来降低可调三相速度驱动器(ASD)的共模电压(CMV)。众所周知，从3L-TTC的可用开关状态的角度来看，只选择那些具有零共模电压的开关状态就可以获得零共模电压(ZCMV)。在这种情况下，两个半桥必须同时切换，才能从3L-TTC的空间矢量图中的无CMV电压矢量移动到下一个电压矢量。然而，在两个半桥同时切换的过程中，由于栅极控制信号的潜伏期、半导体输出电压的上升和下降时间、半桥内的死区时间以及开关和整流过程的延迟，仍然会出现较短的CMV。虽然持续时间很短，但这些CMV脉冲可以在电机中产生很大的轴承电流。在该方法中，变流器交流侧的CMV将与开关事件期间的瞬时相电流一起被测量。在切换过程中，采用自适应补偿方法抵消剩余的短脉冲CMV。这将通过对半桥的切换事件实施额外的轻微延迟来实现。这些延迟预计离线并存储在查找表(LUT)中，并且在切换期间基于在线观察到的CMV定期更新和改进，从而考虑到根据温度或老化的漂移影响。基于所提出的方法，无源滤波器的尺寸以共模(CM)扼流圈的形式表示，电磁干扰(EMI)伴随着CMV，并且在电机运行的情况下，轴承电流的影响可以减小。

This project proposal aims to reduce the common-mode voltage (CMV) for an adjustable 3-phase speed drive (ASD) by using an adaptive method in a 3-level T-type converter (3L-TTC). As it is well known, from the perspective of the available switching states of a 3L-TTC, a zero common-mode voltage (ZCMV) can be obtained by selecting only those switching states with zero CMV. In this case, two half-bridges have to switch simultaneously to move from a CMV-free voltage vector to the next in the space vector diagram of the 3L-TTC. Nevertheless, during the simultaneous switching of two half-bridges, a short CMV will still appear due to the latency of gate control signals, rise and fall times of the semiconductors output voltage, the dead-time and the delays of the switching and commutation process within the half-bridges. Although of short duration, these CMV impulses can create significant bearing currents in an electrical machine. In the proposed method, the CMV at the converter's AC side will be measured together with the instantaneous phase currents during the switching event. An adaptive compensation method will be implemented to cancel out the remaining short pulse CMV during the switching events. This will be achieved by implementing an additional slight delay for the switching events of the half-bridges. Those delays are anticipated offline and stored in a look-up-table (LUT) and are regularly updated and improved based on the observed CMV online during switching, thus taking into account drift effects according to temperature or aging. Based on the proposed method, the size of passive filters in terms of common-mode (CM) chokes, the electromagnetic interference (EMI) concomitant with the CMV, and in the case of motor operation, the effect of bearing currents can be reduced.