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Nur Fairuz Mohamed Yusof
Modified PQ and hysteresis current control in grid-connected single-phase inverter for PV system
Improved control in single phase inverter grid-tied PV system using modified PQ theory
2023
,
Nur Fairuz Mohamed Yusof
,
Dahaman Ishak
,
Muhammad Ammirrul Atiqi Mohd Zainuri
This paper proposes a modified PQ method integrated with hysteresis current control (HCC) used in a grid-connected single-phase inverter for photovoltaic (PV) renewable energy system. The main aim is to achieve a smooth control of unidirectional power flow from the solar PV to the inverter and then from the inverter to the load, and yet bidirectional power flows from/into the utility grid. The system configuration consists of PV array, H-bridge single-phase inverter, ac load and ac grid. Incremental Conductance (InCond) algorithm is used to track the maximum power point of active power (P mpp) available from PV array even under varying environmental and load conditions. The inverter switching modulations are achieved by pre-defined double-band HCC which is calculated to minimize total harmonic distortions (THDs) in the ac output waveforms. The modified PQ method ensures that full synchronization is achieved with the utility grid, unity power factor (PF) is always maintained and bidirectional power flow is properly regulated. The proposed controller of the grid-connected single-phase inverter is tested for various operating conditions under varying loads and solar irradiance levels. The results show that the proposed controller can effectively regulate the delivery of active power and reactive power from the inverter to the connected load. The results also prove that the proposed controller successfully allows bidirectional power flow at the grid side. Total harmonics distortions of the voltage and currents are shown to be less than 5% maximum limit, as recommended in IEEE 519 standard. Another merit of the proposed controller is that it guarantees a unity power factor by forcing the grid voltage and current to be in phase without the use of phase locked loop (PLL) technique. Stable DC-link voltage at the inverter side is achieved without the DC boost converter stage. The efficacy of the proposed controller used in the grid-connected single-phase inverter is proven using MATLAB/Simulink.
2023
,
Nur Fairuz Mohamed Yusof
,
Dahaman Ishak
,
Muhammad Ammirrul Atiqi Mohd Zainuri
,
Muhammad Najwan Hamidi
,
Zuhair Muhammed Alaas
,
Mohamed Mostafa Ramadan Ahmed
Grid-connected reactive-load compensation and harmonic control are becoming a central topic as photovoltaic (PV) grid-connected systems diversified. This research aims to produce a high-performance inverter with a fast dynamic response for accurate reference tracking and a low total harmonic distortion (THD) even under nonlinear load applications by improving its control scheme. The proposed system is expected to operate in both stand-alone mode and grid-connected mode. In stand-alone mode, the proposed controller supplies power to critical loads, alternatively during grid-connected mode provide excess energy to the utility. A modified variable step incremental conductance (VS-InCond) algorithm is designed to extract maximum power from PV. Whereas the proposed inverter controller is achieved by using a modified PQ theory with double-band hysteresis current controller (PQ-DBHCC) to produce a reference current based on a decomposition of a single-phase load current. The nonlinear rectifier loads often create significant distortion in the output voltage of single-phase inverters, due to excessive current harmonics in the grid. Therefore, the proposed method generates a close-loop reference current for the switching scheme, hence, minimizing the inverter voltage distortion caused by the excessive grid current harmonics. The simulation findings suggest the proposed control technique can effectively yield more than 97% of power conversion efficiency while suppressing the grid current THD by less than 2% and maintaining the unity power factor at the grid side. The efficacy of the proposed controller is simulated using MATLAB/Simulink.