Abstract
Model predictive control (MPC) method has been recognized as one of the most promising technologies for the modular multilevel converter (MMC) due to the fast dynamic response and its simple realization. However, conventional finite control set (FCS) MPC methods for MMC are facing some challenges, such as high computation burden, poor steady-state performance, dependence on weighting factors, and variable switching frequency. In order to solve these problems, a novel sliding-discrete-control-set (SDCS) modulated MPC (MMPC) is proposed for MMC in this paper. Based on the adaptive search step in the output current control, only three control sets are evaluated in each period. In addition, the independent circulating current controller is applied in the proposed MMPC method. With the circulating current controller, the circulating currents are well regulated, and the arm capacitor voltage balancing is realized by circulating current injection. As a result, there is no weighting factor involved in the proposed MMPC method. Compared with the conventional MPC methods, the proposed method obtains a fixed switching frequency in each submodule (SM) and a low comparable computation burden. Simulation and experimental results verify the effectiveness of the proposed method.
Highlights
Nowadays, the modular multilevel converter (MMC) has emerged as one the most popular topologies in various high voltage applications, such as high power direct current (HVDC) power transmission [1], motor drives [2], energy storage system [3], power electronic transformers [4], and so on
In [6], a finite control set (FCS) model predictive control (MPC) method is proposed for MMC with multiple control targets, including the output current, the circulating current, and the capacitor voltages
A modulated model predictive control (MMPC) method is proposed for MMC in voltage source converter (VSC) high voltage direct current (HVDC) application in [20]
Summary
The modular multilevel converter (MMC) has emerged as one the most popular topologies in various high voltage applications, such as high power direct current (HVDC) power transmission [1], motor drives [2], energy storage system [3], power electronic transformers [4], and so on. In [6], a finite control set (FCS) MPC method is proposed for MMC with multiple control targets, including the output current, the circulating current, and the capacitor voltages. In [13], a fast MPC is proposed with three evaluated control sets to limit the voltage and the current ripple, and the capacitor voltage balancing is realized by sorting method This method avoids the prediction of the capacitor voltages, and the calculation amount decreases. A modulated model predictive control (MMPC) method is proposed for MMC in voltage source converter (VSC) HVDC application in [20] This method is designed by controlling the duty cycle instead of controlling the switching signals or output voltage levels presented in the above FCS-MPC methods. Where icirj is the circulating current; udc is the DC side voltage of MMC; iuj and ilj are the arm current of the upper and the lower arm
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