Control strategy for suppression of circulating current using high‐frequency voltage compensation in asynchronous carriers for modular and scalable inverter systems

Abstract

In this study, a circulating current suppression strategy is proposed using high-frequency voltage compensation when asynchronous carriers exist between modules in modular and scalable inverter systems (MSISs). In MSIS, an inverter and a control unit constitute one module. Because each module is connected in parallel, the power capacity and efficiency can be increased. However, according to the switching state in the parallel module, a circulating current can be generated. This current causes stress on the switches. Furthermore, the circulating current not only deteriorates the current control performance but also increases the difficulty of load sharing. In this study, a novel method is proposed to suppress high-frequency circulating current caused by asynchronous carriers. This current can be reduced by generating the same switching pattern in two modules using high-frequency voltage compensation. Simulation and experimental results are presented to verify the proposed method.

The Circulating Current Reduction Control Method for Asynchronous Carrier Phases of Parallel Connected Inverters

“…In case that the generation of ZSCCs is due to the carrier phase error, the carrier phase is directly controlled by applying the control method mentioned in this paper. When the generation of ZSCCs is not due to the carrier phase error, the control method introduced in [13] is applied to suppress the ZSCCs.…”

“…Each term in Equation ( 3) can be expressed with as circulating current generated between two inverters among N parallel-connected inverters using Equation (11). Therefore, the circulating current generated from the k-th inverter to the j-th inverter can be defined with Equation (13).…”

“…Representative causes of circulating currents include the deviations of parameters between individual unit inverter modules, the deviation of voltage and current outputs, and carrier phase errors [7][8][9][10][11][12][13]. Among them, the carrier phase errors can occur when the PWM interleaving method is applied during parallel operation or when individual control units are used by inverter modules.…”

“…Therefore, in order to reduce the circulating currents due to the carrier phase errors, a new appropriate control method is necessary. Although there have been previous studies that proposed control methods for carrier phase error, they have a limitation in that they targeted two parallel inverters [7,12,13].…”

Parallel connected GaN E‐HEMT VSI‐based servo drives for PMSMs

“…In [14] the authors use a closed‐loop PI controller to align the carrier phase difference between two inverters to suppress HFCC. In [30], a high frequency voltage compensation is proposed to reduce HFCC which is caused by asynchronous carrier signals. The variable switching frequency PWM method is used to control HFCC through the synchronisation signal to avoid misalignment of carriers in [31].…”