EPE Association: EPE 2016 - LS5f: Power Quality Issues

EPE 2016 - LS5f: Power Quality Issues
You are here: EPE Documents > 01 - EPE & EPE ECCE Conference Proceedings > EPE 2016 ECCE Europe - Conference > EPE 2016 - Topic 06: Grids and Smart Grids > EPE 2016 - LS5f: Power Quality Issues

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   A Frequency Domain Model for Beat Frequency Oscillation Analysis in Microgrid
By Xiaolong YUE [View]
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Abstract: Power electronic converters are typical nonlinear systems in frequency domain. With a perturbation frequency excitation, the current and voltage of power converters in steady state contain not only perturbation but also many sidebands. In a Microgrid containing a large amount of power converters, one converter's switching frequency ripples are other converters' perturbations and beat frequency components will be generated if switching frequencies of those power converters are different. As the control loops always take high gains in low frequency regions and the low pass filters almost have no effect on low-frequency disturbances, if the beat frequency component has certain values, they may be magnified and presented as oscillations. This paper develops a frequency domain model to describe the characteristics of power converter around switching frequency range and to analyze the high frequency interactions of power converters in Micorgrid. The voltage mode controlled boost converters are illustrated as demonstration. The proposed model indicates that switching frequency affects the output characteristics of power converters significantly. In a system consists of two boost converters in parallel, the beat frequency oscillation that traditional output impedance models fail to explain could be accurately predicted by the proposed model. In addition, based on this model, design guideline is proposed to avoid the potential beat frequency oscillation in parallel system. Simulation results validate the accuracy and effectiveness of the proposed method.

   Control Design of VSIs to Enhance Transient Performance in Microgrids
By Federico DE BOSIO [View]
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Abstract: This paper discusses the control design for an islanded microgrid in order to ensure acceptable performance in terms of voltage quality and load sharing by focusing on transient conditions. To this aim, state feedback decoupling approach has been applied. Experimental tests have been performed to demonstrate the effectiveness of the proposed approach.

   Grid-Connected PV Power Plant Induced Power Quality Problems - Experimental Evidence
By Pertti PAKONEN [View]
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Abstract: This paper presents new findings on phenomena contributing to flicker and voltage variations caused by grid-connected photovoltaic (PV) inverters. The voltage variations caused by two different 6 kW single-phase grid-connected PV inverters were studied during climatic variations by varying their grid-coupling impedance. Two different methods for characterizing the PV-plant induced voltage variations were studied: the short-term flicker index (Pst) and the 10 minute very-short voltage variation value (VSV). The results clearly indicate that PV inverter power fluctuations induced by cloud shading and enhancement have a significant effect on the VSV value, but not on Pst. PV inverters have a clear effect on the Pst as well, but the main contributors are related to the inverter design rather than the power fluctuations caused by clouds. The main contributor in the elevated Pst values could be traced back to the poor design of the maximum power point tracking (MPPT) of the inverters. The MPPT caused subharmonic current variations at a frequency of approximately 8 Hz which is close to the most sensitive frequency of human eye. Another factor causing rapid voltage variations in low irradiance conditions was the current transients related to the inverter start-up and shut-down. Harmonic current distortion is also a potential PV inverter related power quality (PQ) issue. This study indicates that although the current total harmonic distortion (THD) may be very large at low power levels the total demand distortion (TDD) of the PV inverters is almost constant regardless of the output power and the harmonic current had only a very limited effect on the voltage quality even at the weakest network having a short-circuit current of Isc=250 A. Thus, voltage variations caused by the PV inverters were the main PQ issue in the studied networks. The investigations also clearly show that a part of the power quality problems found in the PV plants are caused by the poor design of the PV inverters.

   Study on the Power Quality of More Electric Aircraft Power Grid
By Jiawei CHEN [View]
[Download]

Abstract: A novel active power filter (APF), which utilizes the dual-buck inversion topology that has ex-tremely high reliability and efficiency, is designed for MEA power grid to eliminate harmonics, correct power factor of supplies, and minimize the effect of un-balanced loads in this paper. Opera-tional principle analysis of the proposed APF as well as the detailed design on the system parame-ters are done first. Then, the proposed APF is integrated into a 125kVA frequency-wild hybrid HVAC/HVDC MEA power grid. Simulation studies are finally carried out within the whole flight phases, with and without the proposed APF. The results verified the effectiveness of the proposed APF in improving system power quality.

EPE 2016 - LS5f: Power Quality Issues
You are here: EPE Documents > 01 - EPE & EPE ECCE Conference Proceedings > EPE 2016 ECCE Europe - Conference > EPE 2016 - Topic 06: Grids and Smart Grids > EPE 2016 - LS5f: Power Quality Issues
	[return to parent folder]

	A Frequency Domain Model for Beat Frequency Oscillation Analysis in Microgrid By Xiaolong YUE	[View] [Download]
Abstract: Power electronic converters are typical nonlinear systems in frequency domain. With a perturbation frequency excitation, the current and voltage of power converters in steady state contain not only perturbation but also many sidebands. In a Microgrid containing a large amount of power converters, one converter's switching frequency ripples are other converters' perturbations and beat frequency components will be generated if switching frequencies of those power converters are different. As the control loops always take high gains in low frequency regions and the low pass filters almost have no effect on low-frequency disturbances, if the beat frequency component has certain values, they may be magnified and presented as oscillations. This paper develops a frequency domain model to describe the characteristics of power converter around switching frequency range and to analyze the high frequency interactions of power converters in Micorgrid. The voltage mode controlled boost converters are illustrated as demonstration. The proposed model indicates that switching frequency affects the output characteristics of power converters significantly. In a system consists of two boost converters in parallel, the beat frequency oscillation that traditional output impedance models fail to explain could be accurately predicted by the proposed model. In addition, based on this model, design guideline is proposed to avoid the potential beat frequency oscillation in parallel system. Simulation results validate the accuracy and effectiveness of the proposed method.

	Control Design of VSIs to Enhance Transient Performance in Microgrids By Federico DE BOSIO	[View] [Download]
Abstract: This paper discusses the control design for an islanded microgrid in order to ensure acceptable performance in terms of voltage quality and load sharing by focusing on transient conditions. To this aim, state feedback decoupling approach has been applied. Experimental tests have been performed to demonstrate the effectiveness of the proposed approach.

	Grid-Connected PV Power Plant Induced Power Quality Problems - Experimental Evidence By Pertti PAKONEN	[View] [Download]
Abstract: This paper presents new findings on phenomena contributing to flicker and voltage variations caused by grid-connected photovoltaic (PV) inverters. The voltage variations caused by two different 6 kW single-phase grid-connected PV inverters were studied during climatic variations by varying their grid-coupling impedance. Two different methods for characterizing the PV-plant induced voltage variations were studied: the short-term flicker index (Pst) and the 10 minute very-short voltage variation value (VSV). The results clearly indicate that PV inverter power fluctuations induced by cloud shading and enhancement have a significant effect on the VSV value, but not on Pst. PV inverters have a clear effect on the Pst as well, but the main contributors are related to the inverter design rather than the power fluctuations caused by clouds. The main contributor in the elevated Pst values could be traced back to the poor design of the maximum power point tracking (MPPT) of the inverters. The MPPT caused subharmonic current variations at a frequency of approximately 8 Hz which is close to the most sensitive frequency of human eye. Another factor causing rapid voltage variations in low irradiance conditions was the current transients related to the inverter start-up and shut-down. Harmonic current distortion is also a potential PV inverter related power quality (PQ) issue. This study indicates that although the current total harmonic distortion (THD) may be very large at low power levels the total demand distortion (TDD) of the PV inverters is almost constant regardless of the output power and the harmonic current had only a very limited effect on the voltage quality even at the weakest network having a short-circuit current of Isc=250 A. Thus, voltage variations caused by the PV inverters were the main PQ issue in the studied networks. The investigations also clearly show that a part of the power quality problems found in the PV plants are caused by the poor design of the PV inverters.

	Study on the Power Quality of More Electric Aircraft Power Grid By Jiawei CHEN	[View] [Download]
Abstract: A novel active power filter (APF), which utilizes the dual-buck inversion topology that has ex-tremely high reliability and efficiency, is designed for MEA power grid to eliminate harmonics, correct power factor of supplies, and minimize the effect of un-balanced loads in this paper. Opera-tional principle analysis of the proposed APF as well as the detailed design on the system parame-ters are done first. Then, the proposed APF is integrated into a 125kVA frequency-wild hybrid HVAC/HVDC MEA power grid. Simulation studies are finally carried out within the whole flight phases, with and without the proposed APF. The results verified the effectiveness of the proposed APF in improving system power quality.