EPE Association: EPE 2019 - DS1i: HVDC & FACTS

EPE 2019 - DS1i: HVDC & FACTS
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 - DS1i: HVDC & FACTS

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   A Comprehensive Analysis of Voltage to Ground of Floating Submodule for MMC
By Jianan CHEN [View]
[Download]

Abstract: Modular multilevel converter (MMC), which are widely used in VSC-HVDC transmission systems, is usually composed of numerous submodules (SMs) whose voltage are floating in respect to ground. During the commutation transient, high dv/dt for SMs will cause common-mode current to flow into the ground through parasitic capacitors, resulting in conducted EMI. Due to the large number of SMs for MMC, the SMs at different positions have different voltage to the ground, and the voltage jump to the ground of the SMs are also affected by the operating conditions. Therefore, this paper comprehensively analysis the change rules of voltage to ground for SMs under different operating conditions and identify the sensitive SMs with respect to dv/dt. The relevant simulation results can verify the analysis results for the position of the sensitive SMs and the voltage jump rules for SMs under different operating conditions. Furthermore, a double-pulse test of SM is implemented to verify that the common-mode current is conducted when the SM is switching.

   A Stored Energy Control Based Active DC Filter for the Alternate Arm Converter with an Extended Overlap Period
By Pierre VERMEERSCH [View]
[Download]

Abstract: The Alternate Arm Converter (AAC) is a multilevel Voltage Source Converter (VSC) suitable for HVDC systems with DC-fault blocking capability. In its 'Short-Overlap' configuration (SO-AAC) it requires a bulky passive DC filter to suppress the DC current ripple caused by the rectification of the grid currents in the DC link. With an Extended-Overlap period (EO-AAC), an active DC filtering control strategy can be implemented thanks the fact that there is always one phase in overlap mode, providing a continuous control of the DC current. Previous works have been realized considering DC inductors at each pole of the DC link. In this paper, a stored energy control assessment is proposed leading to the deduction of a stored energy model allowing a formal DC current control without DC inductors. The proposed control is supported through a static analysis and dynamic simulation in order to demonstrate its effectiveness.

   Applying a 3300V SiC Half-bridge to an MMC Based HVDC System
By Fabian HOHMANN [View]
[Download]

Abstract: A 3.3 kV silicon carbide (SiC) MOSFET is analyzed for the use in a modular multilevel converter (MMC). A laboratory-setup of a submodule is built to characterize the switching behavior. The total losses are calculated for the MMC operation. A comparison to a silicon (Si) based IGBT model is made based on losses and the necessary semiconductor area.

   Back-to-Back HVDC Modular Multilevel Converter for Transient Voltage Dip Mitigation in Passive Networks
By Thomas HOEHN [View]
[Download]

Abstract: For nuclear research laboratories like CERN, where the exceptionally high power quality conditions are required, the immunity against transient voltage dips is of vital importance. By using the traditional HVDC modular multilevel converter in a back-to-back configuration with properly dimensioned submodule capacitors, voltage dips can be mitigated instantaneously, improving power quality of the network. The dimensioning of the capacitors is shown as one of the key elements of this paper. Firstly, the actual voltage dips statistics recorded at CERN are presented and described. Then, the traditional capacitor submodules dimensioning method is presented and compared to the proposed energy design rule. To validate the energy dimensioning and the mitigation performance, a detailed Simulink model of a 220MVA HVDC modular multilevel converter is described and the main results are presented. The paper concludes with the main conclusions of this study and the future works.

   Development and Verification Test of a 6.6-kV 200-kVA Transformerless STATCOM Based on MMCC-SDBC Using SiC MOSFETs
By Laxman MAHARJAN [View]
[Download]

Abstract: This paper discusses development and verification test results of a 6.6-kV 200-kVA transformerlessSTATCOM (static synchronous compensator). The STATCOM is characterized by the use of MMCC-SDBC (modular multilevel cascade converter - single-delta bridge-cells) topology and SiC (silicon carbide) MOSFETs (metal-oxide-semiconductor field-effect transistors). The paper also briefly discusses a control method for the 6.6-kV system with emphasis on a dc-capacitor voltage control. The dc-capacitor voltage control, which consists of an inter-phase balancing control and an intra-phase balancing control,is different from the ones presented earlier. Successful test results confirm the efficacy of the system forthe control of positive- as well as negative-sequence reactive powers.

   Modeling and Analysis of Modular Multilevel Converters connected to Weak AC Grids
By Mohamed Moez BELHAOUANE [View]
[Download]

Abstract: The Modular Multilevel Converter (MMC) represents the recent development among the diverseavailable topologies of VSC and is allegedly the most suitable solution for converters in HVDCtransmission systems. This paper investigates the stability of modular multi-level converters basedHVDC system connected to a weak ac grid. Small signal stability based on eigenvalues analysis is usedto study the interaction between the weak ac grid and the converter. The impact of control parameters,mainly the synchronization system (i.e., Phase Locked Loop) on the stability of the MMC is alsoconsidered in frequency domain. Finally, time-domain simulations and frequency domain analysis arecarried out using MATLAB/Simulink and symbolic toolbox to validate the effectiveness of the proposedstudy.

   Optimal Energy-based Valve Current Reference Generator for MMC VSC-HVDC
By Pablo BRIFF [View]
[Download]

Abstract: In this work, a new energy-based valve current reference generator algorithm is introduced. The proposed method obtains the converter valve current references in the abc coordinate system with the aim to meet the ac and dc power demands while controlling the energy stored in the converter around a desired target value. The advantage of this approach relies on the configurable optimality of the solution. Moreover, the proposed approach does not require the phase angle information for a given ac current demand. In addition to this, the proposed approach outperforms other conventional current and energy control methods in terms of a weighted combination of conduction losses and valves energy deviation from a prescribed target. The method has been validated by simulation results under both steady-state and fault conditions.

   Power Losses of Advanced MMC Submodule Topologies Using Si- and SiC-Semiconductors
By Christopher DAHMEN [View]
[Download]

Abstract: High power Modular Multilevel Converters (MMC) have become key components for many future application fields, particularly, the efficient use of solar and wind power resources and improvement of grid infrastructure (i.e.: multi-terminal HVDC- and MVDC-networks). Further reduction of power losses, capacitor size and footprint of the converters are important issues. Fully electronic failure management and protection are additional important requirements. Main drivers of progress are improved semiconductors (Si and SiC) combined with advanced submodule topologies. The most promising combinations of submodule and semiconductors are investigated and compared by analytical methods - providing general insight. The results clearly show, that essential reduction of power losses and capacitor size are achievable - in addition to fully electronic protection and failure management.

   Resistive balance compensation of a self-powered high voltage switch using series connected IGBTs for HVDC applications
By Chivite JAVIER [View]
[Download]

Abstract: This work presents three methods of resistive balancing for a high voltage switch, that is formed by the series connection of press-pack IGBTs, namely the Director Switch (DS). The switch is a key component that enables two novel HVDC Voltage Sourced Converter (VSC) topologies: the Alternate-Arm Converter (AAC) and the Series Bridge Converter (SBC), which offer fault-blocking capability, a better efficiency, cost and size than the established Modular Multilevel Converter (MMC) solution. An important DS requirement is that the gate electronics for each IGBT shall be self-powered, as breaching the high voltage insulation barrier to ground to provide auxiliary power is unfeasible. This is achieved by storing energy in a capacitive clamp snubber on each IGBT level, which then powers a DC-DC converter. However, due to the constant power load, or negative impedance of the electronics, the capacitor and collector-to-emitter voltage of the IGBTs soon becomes highly imbalanced during operation, causing some of the levels to turn-off, others to take a very high voltage share. A way of maintaining voltage balance is to introduce or emulate a resistive load that can overcome the negative impedance of the electronic load. This is achieved in three different ways. At start up, when a higher current than normal is required, a resistive current is emulated by enabling that higher demand only when the switch voltage is above a given threshold. During operation, a protective crow-bar resistor of a low-ohmic value is modulated with a fixed duty ratio, to emulate a higher resistive value than that present. Finally, a resistive load can be directly connected across the clamp snubber capacitor. All these techniques are complementary and can be used simultaneously. The successful operation of these three techniques is demonstrated by showing experimental results on a 7-level switch, using 2.5 kV press-pack IGBTs.

EPE 2019 - DS1i: HVDC & FACTS
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 - DS1i: HVDC & FACTS
	[return to parent folder]

	A Comprehensive Analysis of Voltage to Ground of Floating Submodule for MMC By Jianan CHEN	[View] [Download]
Abstract: Modular multilevel converter (MMC), which are widely used in VSC-HVDC transmission systems, is usually composed of numerous submodules (SMs) whose voltage are floating in respect to ground. During the commutation transient, high dv/dt for SMs will cause common-mode current to flow into the ground through parasitic capacitors, resulting in conducted EMI. Due to the large number of SMs for MMC, the SMs at different positions have different voltage to the ground, and the voltage jump to the ground of the SMs are also affected by the operating conditions. Therefore, this paper comprehensively analysis the change rules of voltage to ground for SMs under different operating conditions and identify the sensitive SMs with respect to dv/dt. The relevant simulation results can verify the analysis results for the position of the sensitive SMs and the voltage jump rules for SMs under different operating conditions. Furthermore, a double-pulse test of SM is implemented to verify that the common-mode current is conducted when the SM is switching.

	A Stored Energy Control Based Active DC Filter for the Alternate Arm Converter with an Extended Overlap Period By Pierre VERMEERSCH	[View] [Download]
Abstract: The Alternate Arm Converter (AAC) is a multilevel Voltage Source Converter (VSC) suitable for HVDC systems with DC-fault blocking capability. In its 'Short-Overlap' configuration (SO-AAC) it requires a bulky passive DC filter to suppress the DC current ripple caused by the rectification of the grid currents in the DC link. With an Extended-Overlap period (EO-AAC), an active DC filtering control strategy can be implemented thanks the fact that there is always one phase in overlap mode, providing a continuous control of the DC current. Previous works have been realized considering DC inductors at each pole of the DC link. In this paper, a stored energy control assessment is proposed leading to the deduction of a stored energy model allowing a formal DC current control without DC inductors. The proposed control is supported through a static analysis and dynamic simulation in order to demonstrate its effectiveness.

	Applying a 3300V SiC Half-bridge to an MMC Based HVDC System By Fabian HOHMANN	[View] [Download]
Abstract: A 3.3 kV silicon carbide (SiC) MOSFET is analyzed for the use in a modular multilevel converter (MMC). A laboratory-setup of a submodule is built to characterize the switching behavior. The total losses are calculated for the MMC operation. A comparison to a silicon (Si) based IGBT model is made based on losses and the necessary semiconductor area.

	Back-to-Back HVDC Modular Multilevel Converter for Transient Voltage Dip Mitigation in Passive Networks By Thomas HOEHN	[View] [Download]
Abstract: For nuclear research laboratories like CERN, where the exceptionally high power quality conditions are required, the immunity against transient voltage dips is of vital importance. By using the traditional HVDC modular multilevel converter in a back-to-back configuration with properly dimensioned submodule capacitors, voltage dips can be mitigated instantaneously, improving power quality of the network. The dimensioning of the capacitors is shown as one of the key elements of this paper. Firstly, the actual voltage dips statistics recorded at CERN are presented and described. Then, the traditional capacitor submodules dimensioning method is presented and compared to the proposed energy design rule. To validate the energy dimensioning and the mitigation performance, a detailed Simulink model of a 220MVA HVDC modular multilevel converter is described and the main results are presented. The paper concludes with the main conclusions of this study and the future works.

	Development and Verification Test of a 6.6-kV 200-kVA Transformerless STATCOM Based on MMCC-SDBC Using SiC MOSFETs By Laxman MAHARJAN	[View] [Download]
Abstract: This paper discusses development and verification test results of a 6.6-kV 200-kVA transformerlessSTATCOM (static synchronous compensator). The STATCOM is characterized by the use of MMCC-SDBC (modular multilevel cascade converter - single-delta bridge-cells) topology and SiC (silicon carbide) MOSFETs (metal-oxide-semiconductor field-effect transistors). The paper also briefly discusses a control method for the 6.6-kV system with emphasis on a dc-capacitor voltage control. The dc-capacitor voltage control, which consists of an inter-phase balancing control and an intra-phase balancing control,is different from the ones presented earlier. Successful test results confirm the efficacy of the system forthe control of positive- as well as negative-sequence reactive powers.

	Modeling and Analysis of Modular Multilevel Converters connected to Weak AC Grids By Mohamed Moez BELHAOUANE	[View] [Download]
Abstract: The Modular Multilevel Converter (MMC) represents the recent development among the diverseavailable topologies of VSC and is allegedly the most suitable solution for converters in HVDCtransmission systems. This paper investigates the stability of modular multi-level converters basedHVDC system connected to a weak ac grid. Small signal stability based on eigenvalues analysis is usedto study the interaction between the weak ac grid and the converter. The impact of control parameters,mainly the synchronization system (i.e., Phase Locked Loop) on the stability of the MMC is alsoconsidered in frequency domain. Finally, time-domain simulations and frequency domain analysis arecarried out using MATLAB/Simulink and symbolic toolbox to validate the effectiveness of the proposedstudy.

	Optimal Energy-based Valve Current Reference Generator for MMC VSC-HVDC By Pablo BRIFF	[View] [Download]
Abstract: In this work, a new energy-based valve current reference generator algorithm is introduced. The proposed method obtains the converter valve current references in the abc coordinate system with the aim to meet the ac and dc power demands while controlling the energy stored in the converter around a desired target value. The advantage of this approach relies on the configurable optimality of the solution. Moreover, the proposed approach does not require the phase angle information for a given ac current demand. In addition to this, the proposed approach outperforms other conventional current and energy control methods in terms of a weighted combination of conduction losses and valves energy deviation from a prescribed target. The method has been validated by simulation results under both steady-state and fault conditions.

	Power Losses of Advanced MMC Submodule Topologies Using Si- and SiC-Semiconductors By Christopher DAHMEN	[View] [Download]
Abstract: High power Modular Multilevel Converters (MMC) have become key components for many future application fields, particularly, the efficient use of solar and wind power resources and improvement of grid infrastructure (i.e.: multi-terminal HVDC- and MVDC-networks). Further reduction of power losses, capacitor size and footprint of the converters are important issues. Fully electronic failure management and protection are additional important requirements. Main drivers of progress are improved semiconductors (Si and SiC) combined with advanced submodule topologies. The most promising combinations of submodule and semiconductors are investigated and compared by analytical methods - providing general insight. The results clearly show, that essential reduction of power losses and capacitor size are achievable - in addition to fully electronic protection and failure management.

	Resistive balance compensation of a self-powered high voltage switch using series connected IGBTs for HVDC applications By Chivite JAVIER	[View] [Download]
Abstract: This work presents three methods of resistive balancing for a high voltage switch, that is formed by the series connection of press-pack IGBTs, namely the Director Switch (DS). The switch is a key component that enables two novel HVDC Voltage Sourced Converter (VSC) topologies: the Alternate-Arm Converter (AAC) and the Series Bridge Converter (SBC), which offer fault-blocking capability, a better efficiency, cost and size than the established Modular Multilevel Converter (MMC) solution. An important DS requirement is that the gate electronics for each IGBT shall be self-powered, as breaching the high voltage insulation barrier to ground to provide auxiliary power is unfeasible. This is achieved by storing energy in a capacitive clamp snubber on each IGBT level, which then powers a DC-DC converter. However, due to the constant power load, or negative impedance of the electronics, the capacitor and collector-to-emitter voltage of the IGBTs soon becomes highly imbalanced during operation, causing some of the levels to turn-off, others to take a very high voltage share. A way of maintaining voltage balance is to introduce or emulate a resistive load that can overcome the negative impedance of the electronic load. This is achieved in three different ways. At start up, when a higher current than normal is required, a resistive current is emulated by enabling that higher demand only when the switch voltage is above a given threshold. During operation, a protective crow-bar resistor of a low-ohmic value is modulated with a fixed duty ratio, to emulate a higher resistive value than that present. Finally, a resistive load can be directly connected across the clamp snubber capacitor. All these techniques are complementary and can be used simultaneously. The successful operation of these three techniques is demonstrated by showing experimental results on a 7-level switch, using 2.5 kV press-pack IGBTs.