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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 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]