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Scientists in the Emirates have conceived a new space vector pulse width modulation method that reportedly reduces switching losses and increase efficiency in three-phase photovoltaic inverters. The proposed technique was found to have a higher efficiency, while providng lower common-mode voltage, leakage current and total harmonic distortion compared to traditional pulse width modulation approaches.
Researchers at Khalifa University in the United Arab Emirates have developed a novel space vector pulse width modulation (SVPWM) technique for controlling the switches and reducing switching losses in three-phase photovoltaic inverters.
The proposed approach is intended to reduce the common-mode voltage (CMV), which is generated by the switching operation of pulse width modulation (PWM) inverters and commonly leads to bearing failure and electromagnetic interference (EMI) noises and, in some cases, to ground leakage current, insulation failure, and motor bearing failure.
In the study “An energy efficient control method of a photovoltaic system using a new three-phase inverter with a reduced common mode voltage,” published in Heliyon, the group stated that the new SVPWM method effectively reduces inverter losses, minimizes the derivative of the voltage with respect to time (dv/dt) of the CMV, lowers the maximum peak value of the CMV, and simplifies the computation of the duty cycle.
The proposed technique is conceived to be used in inverters featuring one 3-level leg, two 2-level legs, and 12 possible switching states – 10 active vectors and 2 zero vectors. “These extra voltage vectors help to reduce the maximum peak value of the CMV as well as the dv/dt,” the scientists explained. “The new SVPWM generates the reference output voltage using just eight vectors.”
The performance of the new method was tested through a series of simulations and compared to that of other conventional pulse width modulation (PWM) techniques. The scientists assumed a switching frequency of 2 kHz, a DC link voltage of 100 V, a load resistance of 11 Ω, a load inductance of 0.06 H, a PV parasitic capacity of 500 nF, and a DC link capacitor of 4,700 μF.
The analysis showed that the peak value of the CMV achieved by the new technique was up to 33.33% lower than the value reached by the conventional PWM methods. The new approach was also found to achieve 12.92 % lower total losses, 0.65% higher efficiency, and to require less complex and numerous mathematical calculations to calculate the duty cycles and identify the sectors compared to existing PWM approaches.
The researchers also said the new technique is able to obtain a balanced DC-link voltage and a higher efficiency at a higher modulation index compared to traditional PWM methodologies.
“To conclude, the proposed PWM provides higher efficiency, lower CMV, leakage current and total harmonic distortion (THD) of phase current compared to the other PWMs,” they added. “The new SVPWM offers the best THD of phase currents which is 32.8 % lower than the THD of phase current in other PWMs.”
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