EPE Association: EPE 2019 - DS1h: Power Electronics in Transmission and Distribution Systems

EPE 2019 - DS1h: Power Electronics in Transmission and Distribution Systems
You are here: EPE Documents > 01 - EPE & EPE ECCE Conference Proceedings > EPE 2019 ECCE Europe - Conference > EPE 2019 - Topic 06: Grids, Smart Grids, AC & DC > EPE 2019 - DS1h: Power Electronics in Transmission and Distribution Systems

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   Compensation of the high-frequency ground fault current components in medium voltage grids
By Pavel SMIRNOV [View]
[Download]

Abstract: A single-phase ground fault is one of the most frequent faults in distribution grids. Despite the abilityof the continuous operation with a sustained fault, the ground fault current has to be compensated untilit would be cleared or self-cleared. In addition the ground fault introduces a high frequency distortionto a grid. This work proposes a control algorithm for an active ground fault current compensator. Thealgorithm allows not only eliminating the main component of the ground fault current, but high-frequency components. The concepts of compensation values determination, control structures andsimulation results are presented.

   Fast Voltage Stabilization Control of Split DC Bus Midpoint in 3P4W Shunt APFs
By Xinwei XU [View]
[Download]

Abstract: A midpoint voltage balancer (MVB) based on dual-switching-leg is proposed in this paper. The MVB provides fast voltage stabilization of the midpoint in three-phase four-wire (3P4W) shunt active power filters (APFs). Interleaved control is adopted in the MVB to prevent high-frequency current circulation in split capacitors, and to facilitate an accurate neutral current tracking. All switches of the MVB operate in zero-voltage switching (ZVS) mode when the neutral current is smaller than the nominal phase current of the APF. MATLAB simulation is carried out to verify the effectiveness of the MVB. A 20 kVA prototype has been built, and experimental results show that the voltage ripple of the midpoint is maintained within 1.5\% of the total dc bus voltage even under severe neutral current transient.

   Grid-tied Inverters in Renewable Energy Systems: Harmonic Emission in 2 to 9 kHz Frequency Range
By Hansika RATHNAYAKE [View]
[Download]

Abstract: Grid distortion due to the high switching frequency of energy conversion systems has become a major concern that reduces power quality in renewable energy systems. However, the existing international standards (IEC 61000-3-2&12&16 and IEEE Std. 519) list grid harmonic limitations only up to the 40th or 50th harmonic. Due to limited knowledge of supraharmonic (Harmonics above 2 kHz) currents and voltages, an appropriate standard for this high frequency range is yet to be published. This paper presents an analysis of grid current distortion in the frequency range of 2 to 9 kHz when an active front end inverter is connected to the grid under different filter designs. New filter design approach is used to reduce or eliminate harmonics at frequencies beyond the ranges considered in conventional standards. The results show significant mitigation of high frequency harmonics in stiff grids. High frequency harmonic behavior with conventional and newly designed filters connected to a weak grid, are compared to find small amplitude current and voltage harmonics using the new filters. Furthermore, this study highlights the need for a new standard to address supraharmonics caused by grid-tied inverters.

   Influence of the operating frequency on DC-DC converters for HVDC grids
By Juan PAEZ [View]
[Download]

Abstract: While several DC-DC converters for HVDC have been proposed in literature, comparison studies are needed to identify the best circuit for a particular case of application. This paper proposes an analytical methodology that allows to assess rapidly the comparison of DC-DC converters. It was applied to evaluate two modular DC-DC structures, one isolated circuit and one non isolated circuit, focusing in the variation of the operating frequency for different DC voltage transformation ratios. The results show that the non-isolated structure presents better indicators compared to the isolated circuit for all the considered cases.

   Initial report on effect evaluation of the first regenerative inverter installed in DC railway power supply system of East Japan Railway Company
By Hidenori SATO [View]
[Download]

Abstract: East Japan Railway Company (hereinafter referred to as JR-EAST) have introduced energy storage systems (hereinafter referred to as ESS) and regenerative inverters to reduce electric energy by effectively utilizing regenerative energy generated at the time of braking by the rolling stocks. The regenerative inverter at Fukiage Substation (hereinafter referred to as SS) on Takasaki Line started to use in 2018. It is important to verify the energy saving effect of the regenerative inverter in order to make plans to introduce the equipment in the future. However, little study has been done to evaluate energy saving effect of regenerative inverter in detail. Therefore, the energy saving effect of the regenerative inverter at Fukiage SS on Takasaki Line was analyzed, and the authors report the result.

   Large Signal Stability Assessment of the Grid-Connected Converters based on its Inertia
By Bahram SHAKERIGHADI [View]
[Download]

Abstract: The nonlinear characteristic of the grid-connected voltage source converters (VSCs) affects the stability assessment of power-electronic-based (PE-based) power system. Therefore, an appropriate model of the VSC that shows its nonlinear behavior is needed in order to evaluate the system stability, especially when the system is subjected to a large disturbance. In this paper, a nonlinear model of the grid-connected VSC based on its dynamic inertia is presented. In order to assess the large-signal stability of the system, the dynamic model of the equivalent synchronous machine (ESM) is monitored, then based on the inertia of the ESM, the stability margin of the system is determined. Results show that the stability boundaries can be determined based on the nonlinear model of the ESM inertia of the grid-connected VSC subjected to a large disturbance.

   Modeling and Frequency Analysis of a Dual H-bridge Current Flow Controller in Meshed HVDC systems
By Wei LIU [View]
[Download]

Abstract: This paper investigates the modeling and operation of dual H-bridge current flow controllers (CFCs) in meshed high-voltage direct-current (HVDC) systems. Two operating modes of the CFC device, namely the `buck mode' and the `boost mode', are defined and analyzed. Small-signal models of the dual H-bridge CFC are derived in the s-domain for each operating mode. A frequency sweep procedure is carried out using PSIM to obtain frequency domain representations of the CFC to verify the validity and accuracy of the small-signal models. The dynamic performance of the dual H-bridge CFC is verified through time-domain simulations conducted in PSCAD/EMTDC.

   Modern Control Method of MMC-STATCOM for Future Power Grids
By José Manuel CAJIGAL-NÚÑEZ [View]
[Download]

Abstract: Nowadays, renewable energies are fed into the grid via converter systems. Compared to conventional feed-in via synchronous generators, which exhibit the behavior of a controlled voltage source, converter-based systems behave like a controlled current source. This is primarily accounted to the control algorithms that are implemented in the converter systems and require a significant change in the energy transition. Essential grid functionalities are currently covered by conventional power plants, which are reliable and constantly connected to the grid but must be substituted by renewable energy sources in the long term to comply with the requirements of the energy transition. In order to evaluate a modern control method, a DFT-based control method is used as a basis and afterwards implemented on a conventional MMC STATCOM. Based on this model, the performance is investigated and discussed by means of simulation in the course of the paper.

   New Topology and Functionalities of a Hybrid Transformer for Flexible Operation of Distribution and Transmission Systems
By Pascal WINTER [View]
[Download]

Abstract: Due to the progress of the energy transition, an increasing percentage of converter-based grid components leads to a change of the grid characteristics. Increased controllability is able to improve the operation of future power grids and contribute to a stable grid operation. This contribution presents the magnetically integrated concept of a hybrid transformer. This concept enables increased voltage and current scalability in terms of converter components, increased controllability of the distribution grid as well as additional system services. In order to implement these extended properties of the transformer, a modification of the magnetic core as well as the winding configuration is necessary.

   Operating range extension of cascaded H-bridge star using hybrid converter topology for STATCOM under unbalanced conditions
By Ehsan BEHROUZIAN [View]
[Download]

Abstract: A controller for a hybrid converter for STATCOMapplications, based on a cascaded H-bridge star in series with a generic converter connected at the star point, is proposed. The controller utilizes the generic converter in an optimized way to maximize the operating range of the converter, with focus on unbalanced operating conditions. So for each operating condition, the generic converter reference voltage minimizes the voltage rating of the star part. Theoretical investigations of the hybrid converter using the proposed control approach show that the hybrid converter allows to effectively extend the operating range of the converter under unbalanced conditions of the system, given that the generic converter is large enough to circulate the needed active power between the converter phase legs. This indicates that, depending on the requirements from the operator in terms of negative-sequence injection capability, the hybrid converter can be a valuable solution to overcome the limitations of the CHB star.

   Performance Analysis of Two-Level as-well-as Three-Level T-NPC Inverter based Distributed Generation with Voltage Compensation Capability
By P. N. TEKWANI [View]
[Download]

Abstract: Due to increasing power demand in the recent scenario, intensely integrated penetration of distributed generation (DG) has become need of the day. Grid-tied inverter based DG is becoming popular due to its effective controllability. However, voltage unbalance is observed sometime at the Point of Common Coupling (PCC) due to fluctuating demands of injection of active-reactive power by the DG into the Grid. This paper presents realization of two different topologies of grid tied inverter - conventional two-level three-phase four-wire, and three-level T-type Neutral Point Clamped (T-NPC) based DG, both controlled by three-phase damping control strategy. Simulation studies presented indicate effective operational control for DG based on both these topologies of inverter under various operating conditions. The primary function of DG, which is to inject power into the grid and decrease the burden on the conventional generation system is analyzed. Effective behavior of the proposed two-level as-well-as three-level DG without giving rise to voltage unbalance issue is presented in this paper. Detailed analysis of unbalance index and total harmonic distortion (THD) for PCC voltages and currents is presented. Also, performance of both the proposed DGs for fulfilling load requirement during operation in islanding mode are presented. Satisfactory voltage compensation capability of DGs is depicted from the presented results for single-phase asymmetric fault and three-phase symmetric faults. Low voltage ride through capability, reduction in unbalance index, and THD within the standard limits are the main features of the presented DG systems.

   Power Converters Classification and Characterization in Power Transmission Systems
By Taoufik QORIA [View]
[Download]

Abstract: Because of the throng of control strategies based voltage source converters recently proposed in the literature; their classification is becoming a trending topic. The high similarities of the proposed control strategies mostly lead to confusions and a misunderstanding of vocabulary. Hence, this paper looks first to ease the classification of power converters operation only based on their physical nature. Subsequently, power converters will be characterized in the power system only based on their transient behavior in response to grid disturbances.

   Swiss competence center on energy research FURIES - Overview and contributions in the area of Power Electronics and Smartgrids
By Patrick FAVRE-PERROD [View]
[Download]

Abstract: This paper introduces a special session on results of the Swiss competence center on energy research FURIES that has been established in coordination with the Swiss Energy strategy 2050 with the specific aim to develop, promote and deploy power grid-related innovative solutions toward the im-plementation of the Swiss Energy Strategy 2050. This contribution will report on activities within WP 3, 'AC/DC multi-terminal grids and power electronics'. This WP includes three subtasks with contributions from the major Swiss technical universities: Multi-terminal HVDC system design, fault detection and clearing in multi-terminal HVDC, enabling component and converter technolo-gies and applications. The spectrum of the center's activities is briefly introduced and as an illustra-tive example, the contributions of the SCCER FURIES in relation with HVDC grids are summa-rized. These contributions include: new high power DC testing methods and laboratories, new DC breaker principles and fault location techniques, AC/DC grid resonance analysis and novel converter technologies.

EPE 2019 - DS1h: Power Electronics in Transmission and Distribution Systems
You are here: EPE Documents > 01 - EPE & EPE ECCE Conference Proceedings > EPE 2019 ECCE Europe - Conference > EPE 2019 - Topic 06: Grids, Smart Grids, AC & DC > EPE 2019 - DS1h: Power Electronics in Transmission and Distribution Systems
	[return to parent folder]

	Compensation of the high-frequency ground fault current components in medium voltage grids By Pavel SMIRNOV	[View] [Download]
Abstract: A single-phase ground fault is one of the most frequent faults in distribution grids. Despite the abilityof the continuous operation with a sustained fault, the ground fault current has to be compensated untilit would be cleared or self-cleared. In addition the ground fault introduces a high frequency distortionto a grid. This work proposes a control algorithm for an active ground fault current compensator. Thealgorithm allows not only eliminating the main component of the ground fault current, but high-frequency components. The concepts of compensation values determination, control structures andsimulation results are presented.

	Fast Voltage Stabilization Control of Split DC Bus Midpoint in 3P4W Shunt APFs By Xinwei XU	[View] [Download]
Abstract: A midpoint voltage balancer (MVB) based on dual-switching-leg is proposed in this paper. The MVB provides fast voltage stabilization of the midpoint in three-phase four-wire (3P4W) shunt active power filters (APFs). Interleaved control is adopted in the MVB to prevent high-frequency current circulation in split capacitors, and to facilitate an accurate neutral current tracking. All switches of the MVB operate in zero-voltage switching (ZVS) mode when the neutral current is smaller than the nominal phase current of the APF. MATLAB simulation is carried out to verify the effectiveness of the MVB. A 20 kVA prototype has been built, and experimental results show that the voltage ripple of the midpoint is maintained within 1.5\% of the total dc bus voltage even under severe neutral current transient.

	Grid-tied Inverters in Renewable Energy Systems: Harmonic Emission in 2 to 9 kHz Frequency Range By Hansika RATHNAYAKE	[View] [Download]
Abstract: Grid distortion due to the high switching frequency of energy conversion systems has become a major concern that reduces power quality in renewable energy systems. However, the existing international standards (IEC 61000-3-2&12&16 and IEEE Std. 519) list grid harmonic limitations only up to the 40th or 50th harmonic. Due to limited knowledge of supraharmonic (Harmonics above 2 kHz) currents and voltages, an appropriate standard for this high frequency range is yet to be published. This paper presents an analysis of grid current distortion in the frequency range of 2 to 9 kHz when an active front end inverter is connected to the grid under different filter designs. New filter design approach is used to reduce or eliminate harmonics at frequencies beyond the ranges considered in conventional standards. The results show significant mitigation of high frequency harmonics in stiff grids. High frequency harmonic behavior with conventional and newly designed filters connected to a weak grid, are compared to find small amplitude current and voltage harmonics using the new filters. Furthermore, this study highlights the need for a new standard to address supraharmonics caused by grid-tied inverters.

	Influence of the operating frequency on DC-DC converters for HVDC grids By Juan PAEZ	[View] [Download]
Abstract: While several DC-DC converters for HVDC have been proposed in literature, comparison studies are needed to identify the best circuit for a particular case of application. This paper proposes an analytical methodology that allows to assess rapidly the comparison of DC-DC converters. It was applied to evaluate two modular DC-DC structures, one isolated circuit and one non isolated circuit, focusing in the variation of the operating frequency for different DC voltage transformation ratios. The results show that the non-isolated structure presents better indicators compared to the isolated circuit for all the considered cases.

	Initial report on effect evaluation of the first regenerative inverter installed in DC railway power supply system of East Japan Railway Company By Hidenori SATO	[View] [Download]
Abstract: East Japan Railway Company (hereinafter referred to as JR-EAST) have introduced energy storage systems (hereinafter referred to as ESS) and regenerative inverters to reduce electric energy by effectively utilizing regenerative energy generated at the time of braking by the rolling stocks. The regenerative inverter at Fukiage Substation (hereinafter referred to as SS) on Takasaki Line started to use in 2018. It is important to verify the energy saving effect of the regenerative inverter in order to make plans to introduce the equipment in the future. However, little study has been done to evaluate energy saving effect of regenerative inverter in detail. Therefore, the energy saving effect of the regenerative inverter at Fukiage SS on Takasaki Line was analyzed, and the authors report the result.

	Large Signal Stability Assessment of the Grid-Connected Converters based on its Inertia By Bahram SHAKERIGHADI	[View] [Download]
Abstract: The nonlinear characteristic of the grid-connected voltage source converters (VSCs) affects the stability assessment of power-electronic-based (PE-based) power system. Therefore, an appropriate model of the VSC that shows its nonlinear behavior is needed in order to evaluate the system stability, especially when the system is subjected to a large disturbance. In this paper, a nonlinear model of the grid-connected VSC based on its dynamic inertia is presented. In order to assess the large-signal stability of the system, the dynamic model of the equivalent synchronous machine (ESM) is monitored, then based on the inertia of the ESM, the stability margin of the system is determined. Results show that the stability boundaries can be determined based on the nonlinear model of the ESM inertia of the grid-connected VSC subjected to a large disturbance.

	Modeling and Frequency Analysis of a Dual H-bridge Current Flow Controller in Meshed HVDC systems By Wei LIU	[View] [Download]
Abstract: This paper investigates the modeling and operation of dual H-bridge current flow controllers (CFCs) in meshed high-voltage direct-current (HVDC) systems. Two operating modes of the CFC device, namely the `buck mode' and the `boost mode', are defined and analyzed. Small-signal models of the dual H-bridge CFC are derived in the s-domain for each operating mode. A frequency sweep procedure is carried out using PSIM to obtain frequency domain representations of the CFC to verify the validity and accuracy of the small-signal models. The dynamic performance of the dual H-bridge CFC is verified through time-domain simulations conducted in PSCAD/EMTDC.

	Modern Control Method of MMC-STATCOM for Future Power Grids By José Manuel CAJIGAL-NÚÑEZ	[View] [Download]
Abstract: Nowadays, renewable energies are fed into the grid via converter systems. Compared to conventional feed-in via synchronous generators, which exhibit the behavior of a controlled voltage source, converter-based systems behave like a controlled current source. This is primarily accounted to the control algorithms that are implemented in the converter systems and require a significant change in the energy transition. Essential grid functionalities are currently covered by conventional power plants, which are reliable and constantly connected to the grid but must be substituted by renewable energy sources in the long term to comply with the requirements of the energy transition. In order to evaluate a modern control method, a DFT-based control method is used as a basis and afterwards implemented on a conventional MMC STATCOM. Based on this model, the performance is investigated and discussed by means of simulation in the course of the paper.

	New Topology and Functionalities of a Hybrid Transformer for Flexible Operation of Distribution and Transmission Systems By Pascal WINTER	[View] [Download]
Abstract: Due to the progress of the energy transition, an increasing percentage of converter-based grid components leads to a change of the grid characteristics. Increased controllability is able to improve the operation of future power grids and contribute to a stable grid operation. This contribution presents the magnetically integrated concept of a hybrid transformer. This concept enables increased voltage and current scalability in terms of converter components, increased controllability of the distribution grid as well as additional system services. In order to implement these extended properties of the transformer, a modification of the magnetic core as well as the winding configuration is necessary.

	Operating range extension of cascaded H-bridge star using hybrid converter topology for STATCOM under unbalanced conditions By Ehsan BEHROUZIAN	[View] [Download]
Abstract: A controller for a hybrid converter for STATCOMapplications, based on a cascaded H-bridge star in series with a generic converter connected at the star point, is proposed. The controller utilizes the generic converter in an optimized way to maximize the operating range of the converter, with focus on unbalanced operating conditions. So for each operating condition, the generic converter reference voltage minimizes the voltage rating of the star part. Theoretical investigations of the hybrid converter using the proposed control approach show that the hybrid converter allows to effectively extend the operating range of the converter under unbalanced conditions of the system, given that the generic converter is large enough to circulate the needed active power between the converter phase legs. This indicates that, depending on the requirements from the operator in terms of negative-sequence injection capability, the hybrid converter can be a valuable solution to overcome the limitations of the CHB star.

	Performance Analysis of Two-Level as-well-as Three-Level T-NPC Inverter based Distributed Generation with Voltage Compensation Capability By P. N. TEKWANI	[View] [Download]
Abstract: Due to increasing power demand in the recent scenario, intensely integrated penetration of distributed generation (DG) has become need of the day. Grid-tied inverter based DG is becoming popular due to its effective controllability. However, voltage unbalance is observed sometime at the Point of Common Coupling (PCC) due to fluctuating demands of injection of active-reactive power by the DG into the Grid. This paper presents realization of two different topologies of grid tied inverter - conventional two-level three-phase four-wire, and three-level T-type Neutral Point Clamped (T-NPC) based DG, both controlled by three-phase damping control strategy. Simulation studies presented indicate effective operational control for DG based on both these topologies of inverter under various operating conditions. The primary function of DG, which is to inject power into the grid and decrease the burden on the conventional generation system is analyzed. Effective behavior of the proposed two-level as-well-as three-level DG without giving rise to voltage unbalance issue is presented in this paper. Detailed analysis of unbalance index and total harmonic distortion (THD) for PCC voltages and currents is presented. Also, performance of both the proposed DGs for fulfilling load requirement during operation in islanding mode are presented. Satisfactory voltage compensation capability of DGs is depicted from the presented results for single-phase asymmetric fault and three-phase symmetric faults. Low voltage ride through capability, reduction in unbalance index, and THD within the standard limits are the main features of the presented DG systems.

	Power Converters Classification and Characterization in Power Transmission Systems By Taoufik QORIA	[View] [Download]
Abstract: Because of the throng of control strategies based voltage source converters recently proposed in the literature; their classification is becoming a trending topic. The high similarities of the proposed control strategies mostly lead to confusions and a misunderstanding of vocabulary. Hence, this paper looks first to ease the classification of power converters operation only based on their physical nature. Subsequently, power converters will be characterized in the power system only based on their transient behavior in response to grid disturbances.

	Swiss competence center on energy research FURIES - Overview and contributions in the area of Power Electronics and Smartgrids By Patrick FAVRE-PERROD	[View] [Download]
Abstract: This paper introduces a special session on results of the Swiss competence center on energy research FURIES that has been established in coordination with the Swiss Energy strategy 2050 with the specific aim to develop, promote and deploy power grid-related innovative solutions toward the im-plementation of the Swiss Energy Strategy 2050. This contribution will report on activities within WP 3, 'AC/DC multi-terminal grids and power electronics'. This WP includes three subtasks with contributions from the major Swiss technical universities: Multi-terminal HVDC system design, fault detection and clearing in multi-terminal HVDC, enabling component and converter technolo-gies and applications. The spectrum of the center's activities is briefly introduced and as an illustra-tive example, the contributions of the SCCER FURIES in relation with HVDC grids are summa-rized. These contributions include: new high power DC testing methods and laboratories, new DC breaker principles and fault location techniques, AC/DC grid resonance analysis and novel converter technologies.