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Switching sequences of multilevel inverters have to be properly chosen based on the desired control criteria such as dc-link voltage regulation, common mode voltage reduction, and other application dependent criteria. Control of a converter to satisfy a desired criterion is challenging, especially in high voltage level converters. This paper proposes a simple control method for multilevel inverters with high modularity such as flying capacitor multilevel inverters, H-bridge multilevel inverters, and modular multilevel inverters. It is shown that the method considerably simplifies generation of the switching sequences and fulfills the desired criteria with a reasonable computational cost. The proposed method is computationally efficient in the sense that its implementation for high voltage level inverters requires the same effort as required for a multilevel inverter with a low number of cells. Other prominent advantages of the proposed control method, compared to earlier methods, include its applicability for multiphase multilevel converters and converters with asymmetrical structure and/or unevenly distributed dc voltages, independence from the level number and structure of the converter, and not requiring a lookup table. These advantages make the proposed scheme well suited for high cell-number converters, mainly utilized in FACTS, HVDC, and power quality applications. Simulation and experimental results are presented which verify the performance of the proposed method. [ABSTRACT FROM AUTHOR]

The flying capacitor multilevel inverter (FCMLI) is one of the well-known structures of multilevel inverters having attracted considerable attention because of its merits. In spite of its many advantages, it has some limitations such as high volume and complicated control method because of its bulky capacitors and their voltage balancing requirement. Moreover, the high number of power semiconductors required makes this structure susceptible to failure. To increase the ratio of the number of levels to the number of components, an uneven distribution of capacitor voltages has been suggested in previous reports; however, this approach complicates the control method. Up to now, almost all presented methods suffer from high computational load and/or structure-dependent algorithm. In this paper, a simple state-based and structure-independent method is proposed for capacitor voltage regulation. The proposed method is straightforward and can perform online computation of switching sequences in a computationally efficient manner without any need for stored information or look-up tables. The method is conveniently extendible to any number of cells and levels in an FCMLI structure with arbitrary dc link voltage distribution schemes. Simulation and experimental results show the effectiveness and simplicity of this method. [ABSTRACT FROM PUBLISHER]

Abstract: Three leg inverters for photovoltaic systems have a lot of disadvantages, especially when the load is unbalanced. These disadvantages are for example, small utilization of the DC link voltage, the dependency of the modulation factor of the load current and the superposition of a DC component with the output AC voltage. A solution for these problems is the four-leg inverter. Consequently, generation of balanced voltage with sinusoidal waveform is necessary for these inverters. The power stage model of the 4-leg inverter in rotating coordinates dqo is highly coupled. Consequently, controller design procedure is very difficult and complex. On the other hand, adaptive control for 4-leg inverters has not yet been discussed in the literature. This paper proposes the state feedback approach to decouple the system and convert it to a second-order system which has two poles equal to zero. Then, it suggests a compensator to cancel poles of the closed-loop system and to convert the final system to a desired second-order system. Thanks to use of this strategy the transient performance of the system, such as overshoot and speed of response, becomes greatly adjustable. In addition, an STR (Self-Tuner Regulator) is introduced to tune the state feedback matrix and to guarantee the adaptive performance of the system. Simulation results validate that, by using proposed control strategy, the 4-leg inverter generates balanced voltage, with perfect sinusoidal waveform, in spite of the presence RL time-variant loads. [Copyright &y& Elsevier]

Abstract: Three-leg inverters for photovoltaic systems have many disadvantages, especially when the load is unbalanced. These disadvantages are, for example, small utilization of the DC link voltage, the dependency of the modulation factor of the load current and the superposition of a DC component with the output AC voltage. A solution for these problems is the 4-leg inverter. Most papers dealing with 4-leg inverters suggest classic controllers, such as PI controller, for the system. However, the transient performance of the closed-loop system does not become acceptable. On the other hand, adaptive control of 4-leg inverters has not yet been discussed in the literature. This paper proposes pole-placement control strategy, via state feedback, for 4-leg voltage-source inverters to adjust the transient performance of the closed-loop system. In addition, a STR (self-tuner regulator) is introduced to guarantee the adaptive performance of the controller in the presence of time-variant RL loads. Simulation results validate the theoretical results and proposed control strategy. [Copyright &y& Elsevier]

Abstract: Three leg inverters for photovoltaic systems have a lot of disadvantages, especially when the load is unbalanced. These disadvantages are for example, small utilization of the DC link voltage, the dependency of the modulation factor of the load current and the superposition of a DC component with the output AC voltage. A solution for these problems is the 4-leg inverter. Most papers dealing with 4-leg inverters ignore the effect of digital delays in control loop and suggest classic controllers, such as PI controller. However, the transient performance of the system does not become adjustable by applying classic control techniques. Additionally, adaptive control techniques have not yet been discussed for 4-leg inverters. This paper proposes the pole-placement control strategy via state feedback with integral state, which is a modern control technique, to control the system. Consequently, resulted system becomes highly robust. In addition, it suggests a Self-Tuner Regulator to guarantee the adaptive performance of the final system. Moreover, it proposes a novel model, considering digital delays, for 4-leg inverters. Simulation results show that transient performance of the system becomes accurately adjustable and the 4-leg inverter generates balanced voltage, with sinusoidal waveform, in spite of the presence of RL time variant loads. [ABSTRACT FROM AUTHOR]

Abstract: Three leg inverters for photovoltaic systems have a lot of disadvantages, especially when the load is unbalanced. These disadvantages are for example, small utilization of the DC link voltage, the dependency of the modulation factor of the load current and the superposition of a DC component with the output AC voltage. A solution for these problems is the four-leg inverter. Most papers dealing with 4-leg inverters ignore the effect of digital delays in control loop and suggest classic controllers, such as PI controller. However, the transient performance of the closed-loop system does not become, accurately, adjustable and acceptable, in most cases. This paper proposes a novel model, considering digital delays, for 4-leg inverters. Then, it applies pole-placement control strategy, via state feedback, to adjust the transient performance of the closed-loop system to a desired second-order system. Simulation results validate theoretical results and proposed control strategy. [ABSTRACT FROM AUTHOR]