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This article investigates the operation of cascaded H-bridge (CHB) based static synchronous compensator (STATCOM) after failure in its submodules (SMs). Once a switch fails, the corresponding faulty SM is bypassed. In the post-fault operation, a zero-sequence voltage (ZSV) is injected to the converter phases to generate the maximum possible line-to-line voltage. Using a clamping technique, the fundamental component of injected ZSV (FZSV) is minimized according to the operating point of CHB STATCOM. But, FZSV leads to unequal flow of active power into the converter phases. In the proposed method, negative-sequence current is controlled to manage the active power flow within CHB phases. By doing this, the effect of FZSV on active power of CHB phases is compensated and the voltages of capacitors are kept balanced. This method ensures the continuous operation of CHB STATCOM with the minimum over-design and guarantees the voltage balance of capacitors after a failure. The presented simulation and experimental results validate the feasibility and effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Summary: This paper develops model predictive control with a finite control set (FCS‐MPC) for a static synchronous compensator (STATCOM) based on hybrid cascaded H‐bridge and neutral point clamped (HC‐HNPC) multilevel inverter. By applying FCS‐MPC to basic multilevel structures such as the cascaded H‐bridge (CHB), the dynamic performance is improved; but, as the number of output voltage levels increases, the method suffers from a high computation burden as a result of a significant number of switching states. In HC‐HNPC based STATCOM, the number of power switches and switching states is reduced compared to CHB STATCOM for an equal number of output voltage levels. As a result, while keeping the number of output voltage levels the same as CHB, the FCS‐MPC computational burden decreases, and the control objectives are achieved easier. Furthermore, HC‐HNPC STATCOM as a hybrid multilevel STATCOM contains different types of cells with different capacitors voltage. Utilizing the introduced FCS‐MPC, each capacitor voltage is kept balanced without using a complex balancing system. For a detailed investigation, a single‐phase 9‐level HC‐HNPC is employed in this research. The FCS‐MPC control is developed for 9‐level HC‐HNPC STATCOM and the mathematical equations are extracted. Finally, the control performance is verified by simulation and validated with experimental results. [ABSTRACT FROM AUTHOR]

This study presents a STATic synchronous COMpensator (STATCOM) based on hybrid cascaded H‐bridge and full‐bridge neutral point clamped (HC‐FNPC) inverter. The advantages of HC‐FNPC over symmetric and asymmetric cascaded H‐bridge (HB) in STATCOM application are verified in terms of number of power components and voltage balancing capability. A control strategy is proposed to achieve control aims, i.e. reactive current compensation and balancing the voltages of capacitors. HC‐FNPC‐based STATCOM consists of two types of cells, i.e. full‐bridge neutral point clamped (FNPC) and HB cells with one and two capacitors in their DC side, respectively. A hierarchical balancing scheme is proposed to regulate the voltage of capacitors in mixed cells. In the first control layer, the voltage vector of cells is adjusted so that the active power is uniformly distributed among the cells. In the second control layer, the switching redundancies of FNPC are used to provide voltage balancing. The introduced balancing scheme not only provides voltage balance among capacitors, but also distributes the reactive power equally among the cells and increases the reliability in this way. The performance of the proposed control is validated through simulation in MATLAB/SIMULINK environment and experimental results based on a single‐phase nine‐level HC‐FNPC‐based STATCOM laboratory prototype. [ABSTRACT FROM AUTHOR]