Statistical characterisation of harmonic current emission for large photovoltaic plants

Abstract

SUMMARY Harmonic current emission of photovoltaic (PV) systems is a well‐known problem. However, its quantitative characterisation, which requires the compilation and use of abundant statistical data, had never been satisfactorily dealt with. This paper discusses the multifaceted statistical characterisation of these emissions in a large PV plant. The topics addressed are harmonic current magnitude and its phase angle in relation to PV power output level and background harmonic voltages. Harmonic current emission in PV systems should be recorded during any single 1‐week period throughout a full year. Because power quality metres are expensive, it is more economical to measure this type of emission with simple, cost‐effective equipment. This paper thus presents a new assessment method for harmonic emission based on PV power output level, which is the main parameter affecting the emission, and which is easily monitored by most PV inverters. This new method uses statistical data to define a dependence model for the PV power output of PV harmonic current emissions. Such a model is rarely provided by PV inverter manufacturers. However, the simpler dependence model required for this method can be obtained by inexpensive power quality metres. This new method also produces accurate results at low process costs. Copyright © 2013 John Wiley & Sons, Ltd.

A Modular AC-DC Power Converter with Zero Voltage Transition for Electric Vehicles

“…In Figure 2a the transition occurs from SQ 1 to SQ 2 during the first semi cycle; whereas in the second semi cycle, the transition occurs from SQ 5 to SQ 4 . The transition between adjacent active vectors implies a switching state change in one matrix converter leg.…”

“…The overlap period finishes when i LS reaches the same magnitude with an opposite sign, such that the first semi cycle becomes to an end. The second semi cycle is a mirror of the first since the complementary switching states of SQ 1 and SQ 2 , SQ 4 and SQ 5 respectively, are used to operate the matrix converter and because the H bridge has clamped v xy to −V o .…”

“…sv 0 is located at the origin of the α-β plane. (1, 1, 0) SQ 3 (0, 1, 0) SQ 4 (0, 1, 1) SQ 5 (0, 0, 1) SQ 6 (1, 0, 1) The H-bridge switching states Sx and Sy are presented in Figure 2d,e, with a duty cycle of 50% and a short-circuit period, TSV0H, that generates the voltages vxG (Figure 2f), and vyG (Figure 2g) referred to the G node of the DC rail. The H-bridge voltage (Figure 2h), vxy = vxG − vyG, clamps the secondary side of the transformer to zero Volts when the H bridge is in the short-circuit state.…”

“…Electric Vehicle (EV) systems need to consider power quality regulations that typically include the harmonic emission during the charging and transient states, which have been analyzed with different standards and methods as the works described in [4,5]. Moreover, high-frequency switching techniques can increase the power quality, density and energy transfer reliability of AC-DC power converters without altering the basic topology configuration, keeping output controllability and reliability [6]; however, high AC line currents, drawn by the converter to rapidly charge the storage devices distributed along the traction DC link of the EV, may endanger the EV charger operator or impair the charger connector and, therefore, the supply drawn currents are limited to gain reliability causing slow energy transfer [7].…”

A Piecewise Bound Constrained Optimization for Harmonic Responsibilities Assessment under Utility Harmonic Impedance Changes

“…In a real power grid, the utility harmonic voltage fluctuates due to the load fluctuation. The utility harmonic voltage has a certain influence on the amplitude as well as angle of the harmonic current which affects the harmonic voltage [17,18]. Under certain condition, the harmonic voltage and current all fluctuate simultaneously.…”