Gytis Petrauskas

This research addresses the challenge of a voltage increase on 0.4 kV power distribution lines with high photovoltaic solar plants penetration. Connecting a large number of photovoltaic solar plants to power distribution lines causes a significant voltage rise, which leads to the automatic shutdown of these plants in emergency mode. This seriously hinders the use of solar energy. PV solar plant inverters use reactive power generation or consumption technology to regulate the voltage level, but it is effective only when the line X/R ratio is sufficient. This publication proposes an innovative and easily implemented method for voltage rise mitigation, based on the connection of additional inductive chokes to the power distribution line. The method will expand and fully implement existing voltage regulation measures in already installed PV solar plant inverters, which other methods do not. A methodology for selecting the additional inductance value is presented. Reactive power control methods are compared, and recommendations for the use of methods are presented. An equation is proposed for calculating the coupling point voltage of a PV solar plant inverter using the Q = f(U) diagram. The effectiveness of this method is based on mathematical calculations, simulation, and experimental verification, using typical Lithuanian power distribution lines configurations.

More and more light-emitting diode lighting devices (LED) are being connected to modern power distribution lines. In addition to its many positive features, this poses problems in terms of reactive power compensation. The large number of LEDs interacting with traditional reactive power compensators leads to a harmful phenomenon—overcompensation. This was experimentally determined in the investigated power distribution lines. Along with LEDs, a large number of devices with variable frequency drives (VFD) are connected to the same power distribution lines. This study presents an innovative approach to conventional diode rectifier supply side AC-DC-AC VFDs. It is proposed to use these VFDs as a reactive power compensation device while maintaining their main functions—motor powering and motor speed control. Minor improvements have been proposed to enable these VFDs to provide and draw out reactive power, thereby keeping power factors close to the unit in LED-loaded power distribution lines. The proposed improvements are based on the interaction between the power distribution lines inductivity and the DC circuit capacitance of the VFD. It has been shown that the power factor can be controlled by varying the capacity of the DC circuit. The ability of the AC-DC-AC VFD to compensate for the reactive power provided by the light-emitting diode lighting devices was confirmed by mathematical calculations and experimentally with a laboratory prototype.

In this study, an innovative approach to matrix-converter-based AC-–AC variable frequency drives (VFDs) is introduced. The possibility of using AC–AC matrix VFDs for reactive power compensation in conventional AC–DC–AC VFD-loaded power distribution lines is investigated. It is found that the interaction of a large number of conventional AC–DC–AC VFDs with a conventional capacitor-based local compensation device leads to overcompensation in 0.4 kV power distribution lines. This is due to the fact that the conventional compensation device is designed to compensate the lagging reactive power produced by inductive loads, such as AC motors. This highlights the demand for the compensation of leading reactive power that is not predicted by the designer. To solve this problem, the modification of a certain number of previously installed VFDs by replacing their conventional AC–DC–AC converters with AC–AC matrix converters is proposed. This can lead to improvements in the power factor in 0.4 kV power distribution lines. In this study, the range of reactive power produced by conventional AC–DC–AC VFDs was determined mathematically, by simulation, and experimentally. The range of reactive power produced by the novel AC–AC matrix VFD was also determined. On that basis, the number of VFDs to be modified is defined to keep the power factor close to unity.

The analysis presented in this paper is focused on the harmonics distortion damping in the case of bidirectional power-flow of the electronics device—matrix converter as an interface between two power sources. Bidirectional energy flow takes place in the matrix converter that is used in renewables, hybrid transformers, microgrids, etc. It is observed that the matrix converter generates sinusoidal voltage with some amount of harmonic distortion and worsens in the quality of power in the utility grid. Taking into account the bi-directional energy flow and the matrix converter operation principle, four key requirements for the filters are formulated. Six theoretically possible filter topologies are investigated for compliance with these requirements. Two of the filter topologies are recognized as complying with these requirements and applicable for the switching ripple harmonics damping in the utility grid connected matrix converter in the case of bidirectional power flow. The suitability of these topologies was verified by MATLAB/Simulink simulation. Using the proper filter topology will significantly reduce the size, weight and cost of the components of the filter, as well as the utility grid’s pollution by switching ripple harmonics. It is appropriate to apply such filters to matrix converters that operate in wind turbines installed in doubly fed induction generators. These filters should also be used in hybrid transformers and other high-power devices with matrix converters.

In this paper, a novel approach to matrix-converter-based variable frequency drives is presented. It is proposed that these drives are used to provide or draw out reactive power from the power distribution line, keeping the power factor close to unit and, simultaneously, performing their primary function of motor powering and speed control. This application of matrix-converter-based variable frequency drives is required due to the need to compensate for capacitive reactive power generated by light emitting diode lighting devices. In this study, the reactive power compensation range of the matrix-converter-based variable frequency drive is determined, and a method is proposed to extend the compensation range.