Summary
In grid‐connected (GC) photovoltaic (PV) system with a three‐phase voltage source inverter (VSI), one major requirement is that the DC‐side voltage should be greater than the inverter AC‐side voltage. In many PV installations, this is difficult to attain without an additional DC‐DC converter. For such scenarios, a three‐phase differential boost inverter, where input DC voltage can be less than AC‐side voltage, is a promising configuration. For GC PV systems integrated with such power electronic switching converters, the power quality control also plays a significant importance. In this paper, a novel power quality control technique for such a GC PV system based on three‐phase differential boost inverter has been proposed and evaluated. The proposed control system consists of three subsystem level control loops: (1) a novel control unit for reference voltage generation required for power quality improvement, (2) a double‐loop control strategy with plug‐in–type repetitive Proportional‐Integral (PI) control for outer loop and feedback linearizing control for inner loop meant for tracking of boost inverter output reference voltages, and (3) another bidirectional DC‐DC converter controller for battery operation. The performance of the proposed control algorithms has been tested under various scenarios, ie, power management, transition between GC to stand‐alone (SA) modes and vice versa, and grid current compensation under unbalanced load, nonlinear load, and unbalanced and distorted grid voltage conditions. Extensive simulation and experimental results are reported for validating the proposed control technique.
This paper proposes an observer-based control scheme for a three-phase differential boost inverter in a hybrid PV-battery system. In a conventional control scheme for three-phase differential boost inverter (DBI)-based PV system, the measurements of input inductor current and voltage across output capacitors are required for obtaining the desired voltage at the load end. In a typical three-phase differential boost inverter operation, four voltage sensors and seven current sensors are required to achieve the desired AC voltage. In this paper, an observer-based strategy for elimination of these sensors without compromising power quality is reported. For estimation of boost inverter inductor current and output capacitor voltage, only DC-link capacitor voltage and the load currents are measured. A super-twisting sliding mode observer is used for estimation of the states of the boost inverter. A comparative study between the first-order sliding mode observer and super-twisting sliding mode observer is also presented. The simulation and experimental results show that the proposed observer-based control scheme works satisfactorily under various operating conditions such as sudden change of load, changes in solar insolation, and also under unbalanced load conditions.
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