EPE Association: EPE 2016 - DS2h: HVDC & FACTS

EPE 2016 - DS2h: HVDC & FACTS
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 - DS2h: HVDC & FACTS

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   A Comparative Assessment of Different Balancing Control Algorithms for Modular Multilevel Converter (MMC)
By Ahmed ZAMA [View]
[Download]

Abstract: Thanks to scalability, performance and efficiency, the Modular Multilevel Converter (MMC), since itsinvention, becomes an attractive topology in industrial applications such as high voltage direct current(HVDC) transmission system. To control such device, the Balancing Control Algorithm (BCA) forsubmodule capacitors is a key issue. Lots of papers have been written in this field, but most of thempresent methods without showing their associated advantages and drawbacks neither comparing withprevious works. Therefore, this paper presents a comparative analysis of different BCAs based onstaircase modulation technique. The obtained results show the advantages and drawbacks for eachmethod regarding the switching frequency and the voltage ripple. Finally, some discussions andrecommendations are given for MMC sizing (submodule capacitors, converter losses) and control (BCAsampling time) users.

   A Modular Bi-Directional Hybrid Circuit Breaker for Medium and High Voltage DC Networks
By Jaganath KRISHNAN [View]
[Download]

Abstract: The development of dc transmission and distribution technologies are gaining traction. With renewableenergy being fed to the grid constantly increasing, there is growing interest in development of dc grids.A major hindrance for their development is attributed to the lack of protection during short-circuit fault.Hybrid circuit breakers, a combination of mechanical and semi-conductor devices are understood to bethe most effective method to protect dc grids against such faults. Several of such hybrid breakers arepublished and patented but still a practical high voltage dc breaker has not been developed. In this papera novel modular hybrid circuit breaker is presented. This paper tries to address limitations present inexisting breakers and a scalable model which can be used for both medium and high voltage dc networksis proposed.

   A New Protection Scheme for HVDC Circuit Based on MMC Topology with Controllable Fault Current
By Xu JIANG [View]
[Download]

Abstract: This paper proposes a new protection scheme for the HVDC circuit, which is based on the MMC topology with the double thyristor switches sub-modules. Although the MMC with double Thyristor switches in each sub-module has the ability to clear the short circuit fault, the duration of AC and DC short circuit currents is not controllable. Former work solved the problem of the long duration of the AC short circuit current, the duration of the DC short circuit current still depends on the location of the fault, which could affect the restart of the MMC system. The new protection scheme can solve both problems and during normal operation the loss energy is less than that of the HVDC breaker topology in the former work. The advantages of HVDC breaker topology in the former work are still persisted in the new HVDC breaker topology. In order to verify the validity of the new protection scheme, a simulation has been used.

   Active Ripple Energy Storage for a Cascaded H-Bridge Multilevel Converter
By Daniele PETRILI [View]
[Download]

Abstract: This paper presents a modular multilevel Chain-link converter with reduced energy storage requirement by utilizing an active filter storage method at the converter cell level. The active filter circuit and control are analyzed in detail. A comparison with the conventional cell proves the effectiveness of the reactive energy storage reduction.

   Active Thermal Balancing for Modular Multilevel Converters in HVDC Applications
By Frederik HAHN [View]
[Download]

Abstract: The modular multilevel converter (MMC) has become a very attractive solution for interfacing high voltages hybrid networks. The MMC enables scalability to different power levels, full controllability provided by IGBTs and can achieve very high efficiencies by using a low switching frequency method as the nearest level modulation (NLM). However, in order to limit failures of the power modules, the thermal stress of the submodules (SMs) should be properly studied. For NLM a capacitor voltage balancing algorithm is required and this algorithm, as demonstrated in this paper, offers already good thermal balance among the cells of the MMC. However, at low power factor, operation which could occur in case of low-voltage ride through and of reactive power injection, the mentioned algorithm is not effective anymore. This paper proposes an active thermal balancing algorithm which is embedded in the previously mentioned capacitor voltage balancing algorithm. The purpose of the active balancing is to achieve an equal heat distribution among the submodules to enhance the lifetime. The junction temperatures with and without active thermal balancing are studied in simulation for an HVDC application. The paper proves that thermal balance of MMC can be significantly improved.

   CAPACITOR CURRENT MINIMIZATION AND LOSSES ANALYSIS IN MODULAR MULTILEVEL CONVERTER FOR HVDC APPLICATIONS
By Luis VACCARO [View]
[Download]

Abstract: In this paper the effects of the circulating currents on the modular multilevel converter, for HVDC applications, are presented. The first part is a review of an analytical study of the converter, aimed to minimize the capacitors rms current. In the second part the effects on the converter efficiency and on the safe operating area (SOA) margins are studied.

   Comparison of Modular Multilevel Converter based HV DC-DC-Converters
By Andre SCHOEN [View]
[Download]

Abstract: Efficient HVDC-DC converters are one key component of a future HVDC backbone grid. In this paper threepromising MMC based HVDC-DC converter topologies, namely the front-to-front converter, the HVDC autotransformer and the modular multilevel DC converter are compared in terms of functionality, conversion efficiencyand topology effort.

   Comparison of shunt connected tapping concepts in HVDC transmission systems
By Andre BIRKEL [View]
[Download]

Abstract: In this paper two tapping topologies will be compared in terms of efficiency and utilization of the installedsemiconductors. Both topologies consist of a shunt connected two stage concept with a resonant DC/DCconverter, followed by a medium power inverter on the low voltage side to supply an AC grid.

   Computationally Efficient Method for Simulating Current Source Modular Multilevel Converter
By Mukeshkumar BHESANIYA [View]
[Download]

Abstract: The simulation of current source modular multilevel converter (CSMMC) based systems with large numberof submodules require significant computational efforts. In this paper, a simplified model of CSMMCis developed to reduce the computational complexity while maintaining the accuracy of the traditionaldetailed model. The model is constituted using controlled current sources in each arm of the converter.The controlled output of the current source is determined, considering the variation in the total submoduleinductor currents and the switching due to modulation. Since the dynamics of the submoduleinductors are reproduced in the arm level model of the converter, the arm currents of the proposed modelprovide the accurate representations of the actual converter waveforms. The accuracy of the proposedmodel is validated for the different simulation studies on CSMMC based STATCOM test system with thetraditional and the proposed method in PSCAD/EMTDC. The computing performance of the proposedmodel is also compared with the traditional detailed model and the results show that the simulation speedwith the proposed model increases drastically.

   Dynamic impact of MMC controllers on DC voltage droop controlled MTDC grids
By Julian FREYTES [View]
[Download]

Abstract: The Modular Multilevel Converter (MMC) has enhanced the feasibility of Multi-Terminal DC grids (MTDC). For controlling the DC bus voltage in the MTDC grids, the droop control is the most promised technique. This paper evaluates the dynamic impact of the way of controlling the MMC on the MTDC grids. Results are compared with a simplified model that highlights the key elements for the dynamic behavior of the DC bus voltage, the droop parameter and the equivalent DC bus capacitor.

   Impact and Opportunities of Medium-Voltage DC Grids in Urban Railway Systems
By Arne HINZ [View]
[Download]

Abstract: Due to the increasing number of power-electronic components connected to the grid, medium-voltage dc (MVDC) grids are a promising alternative to established ac distribution grids. Within this work, the advantages and additional flexibility of substations for (urban) railways connected to future MVDC distribution grids are investigated. Possible topologies are presented and the efficiencies are compared.

   Injection Capability of Delta Connected STATCOM in Imbalanced Situations
By Duro BASIC [View]
[Download]

Abstract: In this paper we investigate limitations of delta connected multilevel STATCOMs based on chain links of H bridge cells/modules in compensation of positive sequence reactive and/or negative sequence currents. Particular attention is paid on the effect of grid voltage imbalance on balance of arm capacitor voltages and required supplementary zero and/or negative sequence current injections.

   Model-Predictive Modulation Strategy for a Hybrid Si-SiC Cascaded H-Bridge Multi-Level Converter
By Ilka JAHN [View]
[Download]

Abstract: This paper analyses new model-predictive modulation strategies applied to hybrid Silicon Silicon-Carbidecascaded H-bridge (CHB) converters. The analysis identifies a suitable ratio of Silicon to Silicon-Carbidecells and the appropriate modulation strategy applied to this topology concept. The evaluation is based onsemiconductor losses and harmonic performance.

   One-Pulse Control for Modular Multilevel Converter based STATCOM
By Yushi KOYAMA [View]
[Download]

Abstract: This paper reports an investigation results for one-pulse control methods for modular multilevel converter (MMC) based static synchronous compensator (STATCOM). MMC-STATCOM has cascaded full-bridge inverter cells in each phase arm, and the phase arms are configured with delta connection. In proposed MMC-STATCOM, an one-pulse control is applied. With one-pulse control, every cell outputs one positive and one negative pulse during a system voltage cycle. Since switching frequency is very low, extremely low switching losses can be provided.Cells have a capacitor, and the capacitor voltages should be balanced. Average voltages of the capacitors in each phase arm can be balanced by injecting zero sequence current which flows through delta connection loop. Individual capacitor voltages among arm cells are balanced by sorting algorithm. Cells are sorted by the capacitor voltage and pulse-order (PO) is determined. According to PO, the output of the cells turns ON and OFF, and one-pulse voltage is output. Lower voltage cell is charged more and higher voltage cell is discharged more, therefore the capacitor voltages are balanced. However, the capacitor voltage cannot be controlled in the cells which are not involved with the output. The uncontrolled cells have the last order or previous ones in PO. The capacitor voltage of the uncontrolled cell decreases because of self-discharge. Conventional sorting algorithm is insufficient. In proposed control method, to solve this problem, put the last order cell in a controllable order. This control allows all the capacitor voltages to be balanced including the uncontrolled cells. The proposed control methods were confirmed by experimental model MMC-STATCOM. The STATCOM with one-pulse control operated under steady state and the unbalanced system voltages. The STATCOM kept stable operation under the both conditions. And all the capacitor voltages were balanced even it has the uncontrolled cells.

   Optimum Semiconductor Voltage Level for MMC Sub-modules in HVDC Applications
By Rodrigo ALVAREZ [View]
[Download]

Abstract: This paper presents a comparison of the achievable submodule utilization, losses and other basic figures of merit for the design of the modular multilevel converter half bridge submodules for transmission applications. Based on those figures of merit, a method to find out the optimum semiconductor voltage level for MMC submodules in HVDC Applications for a given power and boundary condition is elucidated. Based on the boundary conditions used for the examples of this paper, 4.5 kV blocking voltage is the optimum voltage level for semiconductors at transmission power of less than 900 MW. For higher transmission power the better performance was achieved by the submodule based on the 6.5 kV IGBT.

   Rugged MMC converter cell for high power applications
By Bjoern OEDEGARD [View]
[Download]

Abstract: A converter cell for a Modular Multilevel Converter (MMC) suitable for the Chain-Link Converter topology is presented. IGCT semiconductors are being used as the main switch technology thanks to features like inherent stable Short Circuit Failure Mode (SCFM) capability very low overall losses superior load cycling capabilitiesThe cell makes use of a single thyristor switch to protect the cell against catastrophic damages in all relevant failure modes. The same thyristor enables continued operation of the chain-link converter after a single cell level failure. A comparison of losses in a STACOM application between IGBT plastic modules and hermetically sealed RC-IGCT press pack devices is presented.

EPE 2016 - DS2h: HVDC & FACTS
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 - DS2h: HVDC & FACTS
	[return to parent folder]

	A Comparative Assessment of Different Balancing Control Algorithms for Modular Multilevel Converter (MMC) By Ahmed ZAMA	[View] [Download]
Abstract: Thanks to scalability, performance and efficiency, the Modular Multilevel Converter (MMC), since itsinvention, becomes an attractive topology in industrial applications such as high voltage direct current(HVDC) transmission system. To control such device, the Balancing Control Algorithm (BCA) forsubmodule capacitors is a key issue. Lots of papers have been written in this field, but most of thempresent methods without showing their associated advantages and drawbacks neither comparing withprevious works. Therefore, this paper presents a comparative analysis of different BCAs based onstaircase modulation technique. The obtained results show the advantages and drawbacks for eachmethod regarding the switching frequency and the voltage ripple. Finally, some discussions andrecommendations are given for MMC sizing (submodule capacitors, converter losses) and control (BCAsampling time) users.

	A Modular Bi-Directional Hybrid Circuit Breaker for Medium and High Voltage DC Networks By Jaganath KRISHNAN	[View] [Download]
Abstract: The development of dc transmission and distribution technologies are gaining traction. With renewableenergy being fed to the grid constantly increasing, there is growing interest in development of dc grids.A major hindrance for their development is attributed to the lack of protection during short-circuit fault.Hybrid circuit breakers, a combination of mechanical and semi-conductor devices are understood to bethe most effective method to protect dc grids against such faults. Several of such hybrid breakers arepublished and patented but still a practical high voltage dc breaker has not been developed. In this papera novel modular hybrid circuit breaker is presented. This paper tries to address limitations present inexisting breakers and a scalable model which can be used for both medium and high voltage dc networksis proposed.

	A New Protection Scheme for HVDC Circuit Based on MMC Topology with Controllable Fault Current By Xu JIANG	[View] [Download]
Abstract: This paper proposes a new protection scheme for the HVDC circuit, which is based on the MMC topology with the double thyristor switches sub-modules. Although the MMC with double Thyristor switches in each sub-module has the ability to clear the short circuit fault, the duration of AC and DC short circuit currents is not controllable. Former work solved the problem of the long duration of the AC short circuit current, the duration of the DC short circuit current still depends on the location of the fault, which could affect the restart of the MMC system. The new protection scheme can solve both problems and during normal operation the loss energy is less than that of the HVDC breaker topology in the former work. The advantages of HVDC breaker topology in the former work are still persisted in the new HVDC breaker topology. In order to verify the validity of the new protection scheme, a simulation has been used.

	Active Ripple Energy Storage for a Cascaded H-Bridge Multilevel Converter By Daniele PETRILI	[View] [Download]
Abstract: This paper presents a modular multilevel Chain-link converter with reduced energy storage requirement by utilizing an active filter storage method at the converter cell level. The active filter circuit and control are analyzed in detail. A comparison with the conventional cell proves the effectiveness of the reactive energy storage reduction.

	Active Thermal Balancing for Modular Multilevel Converters in HVDC Applications By Frederik HAHN	[View] [Download]
Abstract: The modular multilevel converter (MMC) has become a very attractive solution for interfacing high voltages hybrid networks. The MMC enables scalability to different power levels, full controllability provided by IGBTs and can achieve very high efficiencies by using a low switching frequency method as the nearest level modulation (NLM). However, in order to limit failures of the power modules, the thermal stress of the submodules (SMs) should be properly studied. For NLM a capacitor voltage balancing algorithm is required and this algorithm, as demonstrated in this paper, offers already good thermal balance among the cells of the MMC. However, at low power factor, operation which could occur in case of low-voltage ride through and of reactive power injection, the mentioned algorithm is not effective anymore. This paper proposes an active thermal balancing algorithm which is embedded in the previously mentioned capacitor voltage balancing algorithm. The purpose of the active balancing is to achieve an equal heat distribution among the submodules to enhance the lifetime. The junction temperatures with and without active thermal balancing are studied in simulation for an HVDC application. The paper proves that thermal balance of MMC can be significantly improved.

	CAPACITOR CURRENT MINIMIZATION AND LOSSES ANALYSIS IN MODULAR MULTILEVEL CONVERTER FOR HVDC APPLICATIONS By Luis VACCARO	[View] [Download]
Abstract: In this paper the effects of the circulating currents on the modular multilevel converter, for HVDC applications, are presented. The first part is a review of an analytical study of the converter, aimed to minimize the capacitors rms current. In the second part the effects on the converter efficiency and on the safe operating area (SOA) margins are studied.

	Comparison of Modular Multilevel Converter based HV DC-DC-Converters By Andre SCHOEN	[View] [Download]
Abstract: Efficient HVDC-DC converters are one key component of a future HVDC backbone grid. In this paper threepromising MMC based HVDC-DC converter topologies, namely the front-to-front converter, the HVDC autotransformer and the modular multilevel DC converter are compared in terms of functionality, conversion efficiencyand topology effort.

	Comparison of shunt connected tapping concepts in HVDC transmission systems By Andre BIRKEL	[View] [Download]
Abstract: In this paper two tapping topologies will be compared in terms of efficiency and utilization of the installedsemiconductors. Both topologies consist of a shunt connected two stage concept with a resonant DC/DCconverter, followed by a medium power inverter on the low voltage side to supply an AC grid.

	Computationally Efficient Method for Simulating Current Source Modular Multilevel Converter By Mukeshkumar BHESANIYA	[View] [Download]
Abstract: The simulation of current source modular multilevel converter (CSMMC) based systems with large numberof submodules require significant computational efforts. In this paper, a simplified model of CSMMCis developed to reduce the computational complexity while maintaining the accuracy of the traditionaldetailed model. The model is constituted using controlled current sources in each arm of the converter.The controlled output of the current source is determined, considering the variation in the total submoduleinductor currents and the switching due to modulation. Since the dynamics of the submoduleinductors are reproduced in the arm level model of the converter, the arm currents of the proposed modelprovide the accurate representations of the actual converter waveforms. The accuracy of the proposedmodel is validated for the different simulation studies on CSMMC based STATCOM test system with thetraditional and the proposed method in PSCAD/EMTDC. The computing performance of the proposedmodel is also compared with the traditional detailed model and the results show that the simulation speedwith the proposed model increases drastically.

	Dynamic impact of MMC controllers on DC voltage droop controlled MTDC grids By Julian FREYTES	[View] [Download]
Abstract: The Modular Multilevel Converter (MMC) has enhanced the feasibility of Multi-Terminal DC grids (MTDC). For controlling the DC bus voltage in the MTDC grids, the droop control is the most promised technique. This paper evaluates the dynamic impact of the way of controlling the MMC on the MTDC grids. Results are compared with a simplified model that highlights the key elements for the dynamic behavior of the DC bus voltage, the droop parameter and the equivalent DC bus capacitor.

	Impact and Opportunities of Medium-Voltage DC Grids in Urban Railway Systems By Arne HINZ	[View] [Download]
Abstract: Due to the increasing number of power-electronic components connected to the grid, medium-voltage dc (MVDC) grids are a promising alternative to established ac distribution grids. Within this work, the advantages and additional flexibility of substations for (urban) railways connected to future MVDC distribution grids are investigated. Possible topologies are presented and the efficiencies are compared.

	Injection Capability of Delta Connected STATCOM in Imbalanced Situations By Duro BASIC	[View] [Download]
Abstract: In this paper we investigate limitations of delta connected multilevel STATCOMs based on chain links of H bridge cells/modules in compensation of positive sequence reactive and/or negative sequence currents. Particular attention is paid on the effect of grid voltage imbalance on balance of arm capacitor voltages and required supplementary zero and/or negative sequence current injections.

	Model-Predictive Modulation Strategy for a Hybrid Si-SiC Cascaded H-Bridge Multi-Level Converter By Ilka JAHN	[View] [Download]
Abstract: This paper analyses new model-predictive modulation strategies applied to hybrid Silicon Silicon-Carbidecascaded H-bridge (CHB) converters. The analysis identifies a suitable ratio of Silicon to Silicon-Carbidecells and the appropriate modulation strategy applied to this topology concept. The evaluation is based onsemiconductor losses and harmonic performance.

	One-Pulse Control for Modular Multilevel Converter based STATCOM By Yushi KOYAMA	[View] [Download]
Abstract: This paper reports an investigation results for one-pulse control methods for modular multilevel converter (MMC) based static synchronous compensator (STATCOM). MMC-STATCOM has cascaded full-bridge inverter cells in each phase arm, and the phase arms are configured with delta connection. In proposed MMC-STATCOM, an one-pulse control is applied. With one-pulse control, every cell outputs one positive and one negative pulse during a system voltage cycle. Since switching frequency is very low, extremely low switching losses can be provided.Cells have a capacitor, and the capacitor voltages should be balanced. Average voltages of the capacitors in each phase arm can be balanced by injecting zero sequence current which flows through delta connection loop. Individual capacitor voltages among arm cells are balanced by sorting algorithm. Cells are sorted by the capacitor voltage and pulse-order (PO) is determined. According to PO, the output of the cells turns ON and OFF, and one-pulse voltage is output. Lower voltage cell is charged more and higher voltage cell is discharged more, therefore the capacitor voltages are balanced. However, the capacitor voltage cannot be controlled in the cells which are not involved with the output. The uncontrolled cells have the last order or previous ones in PO. The capacitor voltage of the uncontrolled cell decreases because of self-discharge. Conventional sorting algorithm is insufficient. In proposed control method, to solve this problem, put the last order cell in a controllable order. This control allows all the capacitor voltages to be balanced including the uncontrolled cells. The proposed control methods were confirmed by experimental model MMC-STATCOM. The STATCOM with one-pulse control operated under steady state and the unbalanced system voltages. The STATCOM kept stable operation under the both conditions. And all the capacitor voltages were balanced even it has the uncontrolled cells.

	Optimum Semiconductor Voltage Level for MMC Sub-modules in HVDC Applications By Rodrigo ALVAREZ	[View] [Download]
Abstract: This paper presents a comparison of the achievable submodule utilization, losses and other basic figures of merit for the design of the modular multilevel converter half bridge submodules for transmission applications. Based on those figures of merit, a method to find out the optimum semiconductor voltage level for MMC submodules in HVDC Applications for a given power and boundary condition is elucidated. Based on the boundary conditions used for the examples of this paper, 4.5 kV blocking voltage is the optimum voltage level for semiconductors at transmission power of less than 900 MW. For higher transmission power the better performance was achieved by the submodule based on the 6.5 kV IGBT.

	Rugged MMC converter cell for high power applications By Bjoern OEDEGARD	[View] [Download]
Abstract: A converter cell for a Modular Multilevel Converter (MMC) suitable for the Chain-Link Converter topology is presented. IGCT semiconductors are being used as the main switch technology thanks to features like inherent stable Short Circuit Failure Mode (SCFM) capability very low overall losses superior load cycling capabilitiesThe cell makes use of a single thyristor switch to protect the cell against catastrophic damages in all relevant failure modes. The same thyristor enables continued operation of the chain-link converter after a single cell level failure. A comparison of losses in a STACOM application between IGBT plastic modules and hermetically sealed RC-IGCT press pack devices is presented.