An effective MPPT control techniques for active and reactive power control in grid connected PV system

Abstract

In the current power demand situation, the participation of renewable energy sources (RESs) such as wind, solar, geothermal and hydro are increasing continuously. Amongst RESs, solar- based power generation is more adopted due to the source availability and numerous technolog- ical advancement. Especially, the grid connected or grid-interfaced photovoltaic (GIPV) system is being accepted widely due to the cost effectiveness and ease of maintenance, as they elim- inate the need of installing batteries to store energy. Nevertheless, there are still many issues

in the way to accept the GIPV system generally. In this respect, customers are facing some important issues such as the system size, surplus power and bounded use of the PV system. Moreover, it is also facing less effective maximum power point tracking (MPPT) techniques and control strategies to extract and exchange the power, respectively. Hence, to resolve these problems, such novel schemes are required which can reduce the size of the system, improves the MPPT and inverter control performances, utilized for the active power generation and re- active power compensation. Additionally, to expand the application of the PV system in other areas like electric vehicle (EV) based transportation system, a control scheme is also required. Hence, four different control schemes are proposed to resolve the aforementioned problems.

Firstly, a novel control approach for a GIPV system has been developed. This novel ap- proach introduces a sensorless DC-link voltage control for a two-stage three-phase GIPV sys- tem, which reduces the system size and cost. The proposed two-stage system includes an intermediate boost converter (IBC) and pulse width modulation (PWM) strategy based voltage source inverter (VSI). In the first-stage control, the intermediate converter is incorporated with the MPPT technique. Amongst the various available MPPT techniques, due to ease of mainte- nance, the incremental conductance algorithm is implemented to enhance the voltage level of the PV array under variable irradiance condition. Further, the second-stage control of VSI deals with DC-link voltage regulation (outer-loop) and current control (inner-loop) matching with the conventional scheme. Distinctively, the proposed scheme avoids the outer-loop and controls the inner-loop. Hence, the reduction of DC-link high voltage sensor minimizes the cost as well as the size of the system. However, the DC-link voltage remains maintained through power balancing. Therefore, the removal of the outer-loop controller enhances the system stability and the dynamic response of the system under variable irradiance conditions.

In the second work, a GIPV system resolves the issue of surplus active power and inade- quate performance of the existing MPPT techniques. Whereas, the surplus active power causes the overvoltage problem during peak hours of power generation at the point of common cou- pling in low or medium voltage level grid. Additionally, inadequate performance of the MPPT technique results in the power loss due to high settling time during the sudden change in ir- radiance. Therefore, to solve the surplus power problem and improve the MPPT algorithm performance in variable irradiance conditions a novel control strategy has been proposed. In this control strategy, a derated power generation mode (DPGM) control get activated to cur- tail the active power. Additionally, a drift-free (named as modified) perturb & observe (P&O) technique used to improve the performance of the MPPT algorithm. Consequently, the DPGM control scheme with the IBC shaves the surplus active power during the peak hours of power generation. Furthermore, the modified P&O (MP&O) algorithm deals with the fluctuation of irradiance during non-peak hours. Thus, the proposed control scheme appears more efficient for the system during the peak hours of power generation. Besides, it reduces power loss and settling time during the change in irradiance for non-peak hours. In third work, the generated power is utilized from the connected local linear/non-linear loads and the rest of the power is transferred to the grid. Therefore, when the local load is present with the GIPV system, it demands reactive power compensation. The compensation is fulfilled either by the PV inverter or grid. However, the inverter transferring power with full capacity would have no margin to generate reactive power. Therefore, the reactive power demand is supplied from the grid, which causes an extra burden on the grid. Thus, to reduce the burden on the grid, a GIPV system with MP&O, MPPT technique has proposed in the third scheme. In third scheme, the proposed technique uses an IBC which extracts maximum power more efficiently as compared to the traditional MPPT technique. On the other hand, it curtails the generated active power and provides a margin for the PV inverters to generate reactive power. Further, the PV inverter generates active and reactive power to the local load and transfer power to the grid using inverter control. The inverter control comprises of instantaneous active and reactive power control. In this control scheme, it maintains voltage profile and provides more dynamically stable system under fluctuating weather conditions.