EPE Association: EPE 2017 - DS2k: HVDC & FACTS

EPE 2017 - DS2k: HVDC & FACTS
You are here: EPE Documents > 01 - EPE & EPE ECCE Conference Proceedings > EPE 2017 ECCE Europe - Conference > EPE 2017 - Topic 06: Grids and Smart Grids > EPE 2017 - DS2k: HVDC & FACTS

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   A lifting wavelet-based protection strategy against DC line faults for Zhangbei HVDC grid in China
By Ming KONG [View]
[Download]

Abstract: A four-terminal overhead line demonstration high voltage direct current (HVDC) grid for renewable energy power integration and transmission will be constructed around 2019 in Zhangbei district, northwest of Hebei province of China. As the high failure probability of the overhead and the low damping coefficient of DC grid, the suitable ultra-high speed protection against DC line fault needs to be developed. In this paper, the characteristics of travelling wave of HVDC gird caused by the short circuit fault and lightning are studied. On this basis, a lifting wavelet-based non-unit protection scheme is proposed to detect and identify the fault within several million seconds. Considering the impact of short-circuit resistance, fault location and fault type, the proposed protection strategy is studied and verified by various simulations based on the PSCAD/EMTDC software platform.

   Cell-Level Power Supply for High-Voltage Modular Multilevel Converters
By Andrei BLINOV [View]
[Download]

Abstract: Focus is on the design and development of an auxiliary power supply converter for HVDC and FACTS applications, utilising integrated gate-commutated thyristors. Due to relatively high requirements for gate drive power and operating voltage of 2.8~kV, special measures have to be considered when designing such systems. The tapped-inductor buck converter topology was chosen as the first non-isolated conversion stage to perform step-down and regulation functions. The main focus of this study is on the design and operation of autonomous high-voltage switch with increased operating frequency that consists of eight MOSFETs connected in series. Various converter design constrains associated with inductor design and start-up sequences are analysed as well. The results are verified with a 150~W prototype converter.

   Control of a Transformerless STATCOM Based on the MMCC-SDBC (Modular Multilevel Cascade Converter - Single-Delta Bridge-Cells)
By Laxman MAHARJAN [View]
[Download]

Abstract: This paper describes a transformerless STATCOM (Static synchronous compensator) based on theMMCC-SDBC (modular multilevel cascade converter - single-delta bridge-cells) for independentcontrol of positive- and negative-sequence reactive powers. A three-phase 200-V 6-kVA experimentalsystem is designed, constructed and tested to verify the effectiveness of the topology and the controlmethod including dc voltage regulation.

   DC Voltage Control of MMC-based HVDC grid with Virtual Capacitor Control
By Kosei SHINODA [View]
[Download]

Abstract: Ensuring that the DC voltage remains within an acceptable range is a major concern for HVDC systems. In DC systems, the capacitance is the dominant factor that determines the volatility of the DC voltage against sudden disturbances in analogy to inertia of the AC system characterizing the rate of change of the frequency. As a solution to this problem, the authors of this paper previously proposed a novel control method for Modular Multilevel Converter (MMC), named Virtual Capacitor Control. This enables to make the MMC behave as if there were a physical capacitor whose size is adjustable. Thus, it is possible to attenuate the fluctuations of the DC voltage by virtually enhancing the equivalent capacitance of the system. This paper presents a method to determine the required size of this virtual capacitor to limit the peak of the DC voltage to a desired value in the case of the HVDC grid collecting the power generated by wind farms where a master/slave control may be applied. Its advantages are explicated with analysis on the DC voltage dynamics, and its feasibility is verified by EMT simulations of a three-terminal DC grid.

   Fault Current Behavior of Full Bridge Modular Multilevel Converters after First Blocking
By Xu JIANG [View]
[Download]

Abstract: This paper introduces the fault behavior of full bridge modular multilevel converters (MMCs)considering a non-simultaneous blocking of the two half bridges in each sub-module. In order toprotect IGBTs in the full bridge sub-module, both sides of a full bridge sub-module are not blocked atsame time point. It is assumed that the first blocking of both sides is random in each sub-module, sothere are many possible voltages in each arm after the first blocking. Because of this, there are alsomany possible fault current slopes after the first blocking. The influence of this sequential blocking onthe maximum fault current is analyzed. The threshold current, which has to be decreased due to thisphenomenon, is determined.

   Impact of capacitor balancing strategies on converter ratings for star-connected cascaded H-bridge STATCOM
By Ehsan BEHROUZIAN [View]
[Download]

Abstract: This paper presents a comparison between two DC-voltage balancing strategies for cascaded star-connectedmultilevel STATCOM: zero-sequence voltage, and negative-sequence current control. Different levelsof unbalance and grid strengths are considered. The impact of the control strategies on the convertratings in terms of voltage and current requirements are compared and the operating range of the converterusing each control strategy is theoretically derived. The results show that for a given systemratings, the operating range of the converter using negative-sequence current control is wider than thezero-sequence voltage control when the STATCOM is connected to weak grids. On the contrary, incase of connection to strong grids the zero-sequence voltage control can provide wider operating range.PSCAD simulation results are provided to prove the theoretical results.

   Investigation of dc-network resonance-related instabilities in VSC-based multi-terminal HVDC systems with tests in a Real-Time Digital Simulator
By Gustavo PINARES [View]
[Download]

Abstract: A simplified method is proposed to investigate potential instabilities originated from dc-side resonances in multi-terminal HVDC systems. The method consists of identifying the resonances from the points to where the converters are connected. The method is applied to a four-terminal HVDC system, and the analysis indicates there are two resonance phenomena and a group of converters have the most significant impact on the first resonance, while the others on the second resonance. The four-terminal HVDC system is implemented in a Real-Time Digital Simulator and three dc-network configurations are investigated through the proposed method. The test results show the validity of the theoretical findings.

   MMC Converter Cells Employing Ultrahigh-Voltage SiC Bipolar Power Semiconductors
By Keijo JACOBS [View]
[Download]

Abstract: This paper investigates the benefits of using high-voltage converter cells for transmission applications. These cells employ ultrahigh-voltage SiC bipolar power semiconductors, which are optimized for low conduction losses. The Modular Multilevel Converter with half-bridge cells is used as a test case. The results indicate a reduction of converter volume and complexity, while maintaining low losses and harmonic performance.

   The Application of DC Grids to Enhance the Operation of 25 kV, 50 Hz Railway Systems
By Arne HINZ [View]
[Download]

Abstract: Supplying 25 kV, 50 Hz railway systems is a challenging task due to the load characteristics of those systems. Hence, several approaches are developed to improve their grid integration with the static frequency converter based substations. However, this supply system can be further refined by the application of a dc grid. Hence, this paper presents and discusses one possible approach to enhance the supply of 25 kV, 50 Hz railway systems by applying a dc grid.

   Transient Behaviour of VSC-HVDC Links with DC Breakers Under Faults
By Tim AUGUSTIN [View]
[Download]

Abstract: In future high-voltage direct current (HVDC) systems, a large number of HVDC breakers will be re-quired. In this paper, the influence of HVDC breakers on the transient performance of point-to-pointHVDC links in both asymmetrical and symmetrical monopolar configuration with half-bridge modularmultilevel converters is studied with simulations in PSCAD. As HVDC breakers, the active resonantbreaker and ABB's hybrid breaker are considered. The analyzed scenarios include DC line faults, DCbus faults, and AC faults between the converter and the transformer. The highest DC breaking capabilityis required during DC line faults in the asymmetric and symmetric monopole. The converter stress ishighest for DC bus faults and unbalanced converter AC faults in the asymmetric monopole and for DCbus pole-to-pole faults in the symmetric monopole. During DC pole-to-ground faults in the symmetricmonopole, the HVDC breaker combined with DC side arrestors yields the lowest overvoltage stress onthe cable of the healthy pole. The fault current shapes depend strongly on the interaction of the converterand the travelling waves on the lines, and differ from the fault current shapes in typical HVDC breakertest circuits. Furthermore, the active resonant breaker and the ABB hybrid breaker perform similarly inthe used benchmarks due to the very fast DC line fault detection.

EPE 2017 - DS2k: HVDC & FACTS
You are here: EPE Documents > 01 - EPE & EPE ECCE Conference Proceedings > EPE 2017 ECCE Europe - Conference > EPE 2017 - Topic 06: Grids and Smart Grids > EPE 2017 - DS2k: HVDC & FACTS
	[return to parent folder]

	A lifting wavelet-based protection strategy against DC line faults for Zhangbei HVDC grid in China By Ming KONG	[View] [Download]
Abstract: A four-terminal overhead line demonstration high voltage direct current (HVDC) grid for renewable energy power integration and transmission will be constructed around 2019 in Zhangbei district, northwest of Hebei province of China. As the high failure probability of the overhead and the low damping coefficient of DC grid, the suitable ultra-high speed protection against DC line fault needs to be developed. In this paper, the characteristics of travelling wave of HVDC gird caused by the short circuit fault and lightning are studied. On this basis, a lifting wavelet-based non-unit protection scheme is proposed to detect and identify the fault within several million seconds. Considering the impact of short-circuit resistance, fault location and fault type, the proposed protection strategy is studied and verified by various simulations based on the PSCAD/EMTDC software platform.

	Cell-Level Power Supply for High-Voltage Modular Multilevel Converters By Andrei BLINOV	[View] [Download]
Abstract: Focus is on the design and development of an auxiliary power supply converter for HVDC and FACTS applications, utilising integrated gate-commutated thyristors. Due to relatively high requirements for gate drive power and operating voltage of 2.8~kV, special measures have to be considered when designing such systems. The tapped-inductor buck converter topology was chosen as the first non-isolated conversion stage to perform step-down and regulation functions. The main focus of this study is on the design and operation of autonomous high-voltage switch with increased operating frequency that consists of eight MOSFETs connected in series. Various converter design constrains associated with inductor design and start-up sequences are analysed as well. The results are verified with a 150~W prototype converter.

	Control of a Transformerless STATCOM Based on the MMCC-SDBC (Modular Multilevel Cascade Converter - Single-Delta Bridge-Cells) By Laxman MAHARJAN	[View] [Download]
Abstract: This paper describes a transformerless STATCOM (Static synchronous compensator) based on theMMCC-SDBC (modular multilevel cascade converter - single-delta bridge-cells) for independentcontrol of positive- and negative-sequence reactive powers. A three-phase 200-V 6-kVA experimentalsystem is designed, constructed and tested to verify the effectiveness of the topology and the controlmethod including dc voltage regulation.

	DC Voltage Control of MMC-based HVDC grid with Virtual Capacitor Control By Kosei SHINODA	[View] [Download]
Abstract: Ensuring that the DC voltage remains within an acceptable range is a major concern for HVDC systems. In DC systems, the capacitance is the dominant factor that determines the volatility of the DC voltage against sudden disturbances in analogy to inertia of the AC system characterizing the rate of change of the frequency. As a solution to this problem, the authors of this paper previously proposed a novel control method for Modular Multilevel Converter (MMC), named Virtual Capacitor Control. This enables to make the MMC behave as if there were a physical capacitor whose size is adjustable. Thus, it is possible to attenuate the fluctuations of the DC voltage by virtually enhancing the equivalent capacitance of the system. This paper presents a method to determine the required size of this virtual capacitor to limit the peak of the DC voltage to a desired value in the case of the HVDC grid collecting the power generated by wind farms where a master/slave control may be applied. Its advantages are explicated with analysis on the DC voltage dynamics, and its feasibility is verified by EMT simulations of a three-terminal DC grid.

	Fault Current Behavior of Full Bridge Modular Multilevel Converters after First Blocking By Xu JIANG	[View] [Download]
Abstract: This paper introduces the fault behavior of full bridge modular multilevel converters (MMCs)considering a non-simultaneous blocking of the two half bridges in each sub-module. In order toprotect IGBTs in the full bridge sub-module, both sides of a full bridge sub-module are not blocked atsame time point. It is assumed that the first blocking of both sides is random in each sub-module, sothere are many possible voltages in each arm after the first blocking. Because of this, there are alsomany possible fault current slopes after the first blocking. The influence of this sequential blocking onthe maximum fault current is analyzed. The threshold current, which has to be decreased due to thisphenomenon, is determined.

	Impact of capacitor balancing strategies on converter ratings for star-connected cascaded H-bridge STATCOM By Ehsan BEHROUZIAN	[View] [Download]
Abstract: This paper presents a comparison between two DC-voltage balancing strategies for cascaded star-connectedmultilevel STATCOM: zero-sequence voltage, and negative-sequence current control. Different levelsof unbalance and grid strengths are considered. The impact of the control strategies on the convertratings in terms of voltage and current requirements are compared and the operating range of the converterusing each control strategy is theoretically derived. The results show that for a given systemratings, the operating range of the converter using negative-sequence current control is wider than thezero-sequence voltage control when the STATCOM is connected to weak grids. On the contrary, incase of connection to strong grids the zero-sequence voltage control can provide wider operating range.PSCAD simulation results are provided to prove the theoretical results.

	Investigation of dc-network resonance-related instabilities in VSC-based multi-terminal HVDC systems with tests in a Real-Time Digital Simulator By Gustavo PINARES	[View] [Download]
Abstract: A simplified method is proposed to investigate potential instabilities originated from dc-side resonances in multi-terminal HVDC systems. The method consists of identifying the resonances from the points to where the converters are connected. The method is applied to a four-terminal HVDC system, and the analysis indicates there are two resonance phenomena and a group of converters have the most significant impact on the first resonance, while the others on the second resonance. The four-terminal HVDC system is implemented in a Real-Time Digital Simulator and three dc-network configurations are investigated through the proposed method. The test results show the validity of the theoretical findings.

	MMC Converter Cells Employing Ultrahigh-Voltage SiC Bipolar Power Semiconductors By Keijo JACOBS	[View] [Download]
Abstract: This paper investigates the benefits of using high-voltage converter cells for transmission applications. These cells employ ultrahigh-voltage SiC bipolar power semiconductors, which are optimized for low conduction losses. The Modular Multilevel Converter with half-bridge cells is used as a test case. The results indicate a reduction of converter volume and complexity, while maintaining low losses and harmonic performance.

	The Application of DC Grids to Enhance the Operation of 25 kV, 50 Hz Railway Systems By Arne HINZ	[View] [Download]
Abstract: Supplying 25 kV, 50 Hz railway systems is a challenging task due to the load characteristics of those systems. Hence, several approaches are developed to improve their grid integration with the static frequency converter based substations. However, this supply system can be further refined by the application of a dc grid. Hence, this paper presents and discusses one possible approach to enhance the supply of 25 kV, 50 Hz railway systems by applying a dc grid.

	Transient Behaviour of VSC-HVDC Links with DC Breakers Under Faults By Tim AUGUSTIN	[View] [Download]
Abstract: In future high-voltage direct current (HVDC) systems, a large number of HVDC breakers will be re-quired. In this paper, the influence of HVDC breakers on the transient performance of point-to-pointHVDC links in both asymmetrical and symmetrical monopolar configuration with half-bridge modularmultilevel converters is studied with simulations in PSCAD. As HVDC breakers, the active resonantbreaker and ABB's hybrid breaker are considered. The analyzed scenarios include DC line faults, DCbus faults, and AC faults between the converter and the transformer. The highest DC breaking capabilityis required during DC line faults in the asymmetric and symmetric monopole. The converter stress ishighest for DC bus faults and unbalanced converter AC faults in the asymmetric monopole and for DCbus pole-to-pole faults in the symmetric monopole. During DC pole-to-ground faults in the symmetricmonopole, the HVDC breaker combined with DC side arrestors yields the lowest overvoltage stress onthe cable of the healthy pole. The fault current shapes depend strongly on the interaction of the converterand the travelling waves on the lines, and differ from the fault current shapes in typical HVDC breakertest circuits. Furthermore, the active resonant breaker and the ABB hybrid breaker perform similarly inthe used benchmarks due to the very fast DC line fault detection.