Scientists in the Middle East have developed a series active filter to improve power quality in grid-tied PV systems, consisting of an inductor, two capacitors and four transistor-diode pairs. The filter reduces the total harmonic distortion of voltage and current waves at the output of the inverter.
An Iraqi-Lebanese research team has proposed using a series active filter on the DC side of grid-connected PV systems to improve power quality.
Active power filters are increasingly used in PV systems to simultaneously compensate for current harmonics and voltage unbalance.
“The use of filters in systems has increased due to the significant improvement in power quality at the inverter output and the power supplied to the loads or grid due to the reduction of the ripple factor on the DC side” , the researchers explain.
The ripple factor is the peak-to-peak value of the AC component of the current at the inverter input divided by the rated DC input.
“Reducing the ripple factor on the DC side has a significant impact on improving the power quality at the inverter output, the power supplied to the loads or the overhead network, so the use of filters in these systems is increased,” the researchers said.
In their article “Improve the power quality and stability of a grid-connected PV system by using a series filter,” recently published in Heliyon, The researchers describe an active filter designed to reduce voltage and current fluctuations on the DC side of a PV system. The proposed filter, consisting of an inductor, two capacitors and four transistor-diode pairs, is connected to the DC busbar and operates via a conventional controller.
The filter is controlled by a sinusoidal pulse width modulation (SPWM), which is common switching technology for power switching converters. It determines the frequency and nature of the inverter’s AC output voltage.
“The principle of the proposed filter on the DC side of PV systems is to reduce the amount of high-frequency electromagnetic interference (EMI) that can damage sensitive electronics,” the academics explained. “Series filters work by creating an impedance match between the source and the load to ensure that the voltage across both remains the same. This equalization reduces any voltage spikes and prevents them from damaging downstream equipment.”
The proposed filter reduces the noise generated by switching inverters and other system components, reportedly increasing the overall efficiency and reliability of PV systems. The researchers claim that the active filter significantly reduces harmonic distortion, reducing total harmonic distortion by 2.8% for voltage and 9.58% for current.
“The addition of the filter improves the transient response and stability of the system. This is demonstrated by a 50% reduction in the maximum exceedance when exposed to test input signals,” the researchers said. “By prioritizing the transient response and using SPWM, the method goes beyond fundamental harmonic reduction and addresses the dynamic performance of the system.”
The researchers also noted that the active filter improved the transient response of the PV system by reducing the maximum overshoot value relative to the test input signals.
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