Abstract
Ensuring the stability of DC-link voltage in grid-connected photovoltaic (PV) systems plays a critical role in their reliable and continuous operation. DC voltage fluctuation and, in the worst case, DC voltage collapse will dramatically hamper real and reactive power delivery to the grid. This is more the case in single-stage inverters with no DC-DC boost stage, and the DC voltage has a varying nature. This paper proposes a new control approach for ensuring DC-link voltage stability in single-stage PV systems. The proposed control strategy is based on an adaptive hysteresis band controller (HBC), supplementing the conventional control blocks. This strategy offers the capability to prevent fast discharge of DC-link capacitor and keeps it within acceptable limits by quickly modifying phase shift applied to inverter PWM through quick calculations. Results show that the approach greatly improves PV system performance, in various operating modes. The proposed control scheme is implemented in the real-time simulator, OPAL-RT, OP5600 to verify its applicability and effectiveness in real time.
Highlights
Prospective utilization of photovoltaic (PV) systems is gaining ever-increasing ground both as standalone and grid-connected distributed generation [1]
The higher the rate of voltage drop in the DC-link capacitor and PV active power output, the larger the correction term applied to the PI controller phase shift output and the sharper the overall drop of pulse width modulation (PWM) phase shift will be, yielding greater energy saving for the capacitor to charge back to normal level
The first is maximum power point tracking (MPPT) mode when the PV system is connected to the grid
Summary
Prospective utilization of photovoltaic (PV) systems is gaining ever-increasing ground both as standalone and grid-connected distributed generation [1]. In single-stage grid-connected PV systems, both loops should be realized simultaneously in one power conversion stage, simplifying the system topology at the cost of complicating the control circuit. This topology may make the DC-link voltage more vulnerable to radiation and network disturbances [21]. As the PV array enters into the current source region, and the value of voltage derivate of PV power exceeds a threshold, a correction term proportional to this derivative is added cumulatively to the phase shift of the inverter PWM in each time step This method may not be fast enough to compensate DC-link voltage as it accomplishes the correction function in several time steps.
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