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Traditionally, photovoltaic power plants use Maximum Power Point Tracking (MPPT) algorithms to produce maximum electrical energy. However, with the increase of grid-installed photovoltaic power plants, power system operators have faced new challenges such as overload, overvoltage, and proper performance during grid voltage disturbances. As a result, network standards and codes have been updated in the direction of photovoltaic systems that are more controllable and compatible with the network. To provide various grid support functions, such as frequency response and voltage support, the Constant Power Generation (CPG) control algorithm is established by grid codes. For this purpose, MPPT algorithms have been replaced by flexible power point tracking (FPPT) algorithms. This paper proposes an algorithm to control photovoltaic systems based on a multi-level cascaded full-bridge (CHB) inverter to achieve constant power generation control by the FPPT method. The required power reference is distributed among the sub-modules of the CHB converter according to the available power of each sub-module in such a way that, as much as possible, each sub-module is loaded equally. Then, the FPPT algorithm with an adaptive voltage step is used to set the power of each submodule in its reference value. The voltage step is calculated adaptively based on the observed condition (transient or steady state) so that the tracking performance has fast dynamics. The effectiveness of the proposed algorithm is evaluated by simulating a 500-kW photovoltaic system directly connected to a 4.7 kV grid. [ABSTRACT FROM AUTHOR]

This research proposes a cost‐efficient microinverter. The proposed microinverter can eliminate the leakage current using common‐ground configuration. It uses three switches and only one of them operates at high frequency. In addition, a passive lossless snubber is applied to limit voltage stress and provide soft‐switching performance for the high‐frequency switch. A pair of coupled inductors is used to provide higher voltage gain which makes it possible to keep the operating duty cycle in the normal range and makes the proposed inverter suitable for AC module application. The input current of the proposed microinverter is continuous which reduces the loss of the input capacitor by high‐frequency current component reduction. The operating principle of the proposed inverter is described in both positive and negative current modes. In positive current mode, the proposed microinverter works similar to SEPIC converter and in negative current mode its performance is similar to CUK converter. The dynamic behavior of the proposed microinverter is analyzed through simulation and a simple PI controller is designed to accommodate the worst case. Theoretical loss analysis is applied and finally the results of this research are compared with other researches. The performance of the proposed inverter is justified by simulation and practical results of a 300‐watts prototype. [ABSTRACT FROM AUTHOR]

In this paper, a high-performance control structure is designed, implemented, and applied to a three-phase series–parallel uninterruptible power supply (UPS). This kind of UPS system provides input power factor correction, output voltage conditioning, and high efficiency. The control strategy proposed in this paper is based on voltage control of the parallel converter and current control of the series converter. It is shown that this strategy improves the system operation, specifically resulting in a smoother and more seamless transition between UPS operating modes. The controller in the proposed strategy is based on combination of two control methods with different characteristics and is therefore called a hybrid structure. To enhance the steady-state performance of the UPS and reach fast error convergence, a repetitive controller is used. In addition, to reach a fast transient response required for control of output voltage, a fast deadbeat is used. The stability of this hybrid controller is discussed, and the design procedure for a typical converter is given. For validation and verification of the theoretical analysis, both experimental and simulation results are shown. [ABSTRACT FROM AUTHOR]