PV-Inverter This paper presents an enhanced power quality solar photovoltaic (PV) inverter enabling common-mode leakage current elimination. A three-phase transformer-less solar energy conversion system (SECS) is considered here, which, along with peak active-power production from PV-array, ensures different power quality improvement capabilities such as grid current harmonics mitigation, grid-currents balancing, while also offering the grid reactive power support. Unlike conventional power quality inverters, this strategy is a robust with respect to abnormalities in grid-voltages at far radial ends, and does not compromise with the leakage currents caused by parasitic-capacitance of PV-array with ground.
Common practice in the PV inverter power quality control is to neglect the PV leakage-currents, however, they considerably affect the system performance by deteriorating the power quality and causing the safety issues of operating personnel. The standards VDE-00126 and NB/T-32004, therefore, compel the transformer-less PV-systems to operate with leakage current under 300mA range. Various simulation and test results show the satisfactory performance of the presented strategy, even under various grid-side abnormalities. The comparative analysis with state-of-art techniques shows the effectiveness of the strategy. Under all test conditions, the harmonics in grid-currents are observed within limits as per the IEEE-519 and IEC-61727 standards, while the PV leakage-currents are maintained well within the range recommended by VDE-00126 standard.
- Common mode voltage (CMV)
- Kalman filter (KF)
- Leakage Currents
- Power quality and Voltage source Converter (VSC)
Fig. 1. Schematic block diagram of solar energy conversion system
EXPECTED SIMULATION RESULTS:
Fig. 2. System response at unbalanced nonlinear loads (a) vs, is, iL, VAN, VBN, VCN and VCM , (b) ileak, vDVR, iDVR, VDC, VPV, PPV, Pgrid
Fig. 3. System response at abnormal grid voltages (a) vs, is, iL, vDVR, iDVR, VCM , ileak at harmonically polluted grid voltages and (b) vs, is, iL, Qg, VDC, VCM, ileak at unbalanced faults in grid side network
Fig. 4. System response at nonlinear loads (a) Conventional control (b) Control strategy for H9 converter, (c) Presented control, (d) Harmonic spectra of grid current with multi-PR control, (e) Harmonic spectra of grid current with presented control, (f) Comparative chart with state-of-art strategies
Fig. 5. Comparative response of the SECS using (a) Multi-PR controller (b) Presented controller
Fig. 6. System performance under nonlinear loads with load unbalancing event (a) vsab, isa, iLa and ivsca, (b) vsbc, isb, iLb and ivscb, (c) vsab and FFT of vsab, (d) VDC, Ipv, ivsca and isa , (e) vsca, isc, iLc and Ileak, and (f) isa and FFT of isa
An effective Kalman state-estimator based controller for two-stage grid connected solar photovoltaic system has been presented, to address the power quality issues in the grid under normal/abnormal conditions, while also ensuring low leakage currents as per the VDE-00126 and NB/T-32004 standards. The common practice in power quality PV-inverters, is to neglect the solar PV parasitic capacitance, however, they considerably affect the system performance by alleviating leakage currents, increasing grid harmonic currents, while increasing the safety concerns of the operating personnel. The high leakage currents in the system are avoided here, while also maintaining a smooth ripple-free common mode voltage. This controller inherits multifunctional abilities such as harmonics suppression, balancing currents in the grid side network at event of abnormalities in the grid voltages, leakage current elimination, and the reactive power support under grid side voltage sag faults.
It thereby complies with the power quality standards IEEE-519 and IEC-61727, as well as the leakage current standards VDE-00126. Extensive simulation and test results are performed to demonstrate the efficacy of the control approach for SECS at various scenarios such as load unbalances abnormalities in the grid voltages, and solar insolation variation in the presence of PV stray capacitance. These results illustrate the superior response of the proposed strategy in comparison conventional controllers. Even under the huge diversions in grid voltage caused at far distant radial ends, the grid currents are observed balanced and sinusoidal, and the leakage currents are significantly suppressed below 300mA. Practically, the solar PV system is connected to the grid and this system is subjected to incessant disturbances, and the presented controller is fine practical solution accounting to its manifold abilities and self-adapting features to the fluctuations in solar panel side as well as the grid side network.
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