Sayan Acharya

The transient performance of power semiconductor devices relates directly to their available power rating, reliability, and operating lifetime. This paper examines the transient thermal performance of liquid-cooled, silicon carbide power devices subjected to different unsteady electrical loads. The first part uses infrared thermography to examine an observed asymmetrical device thermal time constant when subjected to step-change increases and decreases in current. A theoretical analysis… Show more

The transient performance of power semiconductor devices relates directly to their available power rating, reliability, and operating lifetime. This paper examines the transient thermal performance of liquid-cooled, silicon carbide power devices subjected to different unsteady electrical loads. The first part uses infrared thermography to examine an observed asymmetrical device thermal time constant when subjected to step-change increases and decreases in current. A theoretical analysis connects this behavior to the dependence of mosfet on-resistance on junction temperature. It also identifies three time constants that characterize junction transient response, one each for the die, the module, and the cold plate. The second part extends the transient thermal evaluation to half-sine wave periodic excitations that emulate real-application operating conditions. These experiments show that thermal ripple increases with increasing excitation amplitude but decreases with increasing excitation frequency. They also connect the observed thermal response to the time constants inferred from the step-change experiments. Both parts of the study show the importance of considering transient loads when designing power electronics cooling systems and the role that electrical properties play in determining unsteady thermal response. Show less

For high power medium voltage (MV) grid connected applications $LCL$ filter proves to be an attractive solution to filter out the current harmonics when compared to $L$ or $LC$ filters. The inductance requirement reduces drastically to meet the same Total Harmonic Distortion (THD) standards for grid connections for $LCL$ filters compared to $L$ filter which makes the system dynamics much faster. The increasing use of Silicon Carbide (SiC) based power devices for MV applications has made the… Show more

For high power medium voltage (MV) grid connected applications $LCL$ filter proves to be an attractive solution to filter out the current harmonics when compared to $L$ or $LC$ filters. The inductance requirement reduces drastically to meet the same Total Harmonic Distortion (THD) standards for grid connections for $LCL$ filters compared to $L$ filter which makes the system dynamics much faster. The increasing use of Silicon Carbide (SiC) based power devices for MV applications has made the effects of the parasitic elements in the filter more prominent, due to the high $dv/dt$ experienced by the passive filter elements during device switching transients. This paper addresses the issues associated with the high $dv/dt$ experienced by the $LCL$ filters for SiC-based MV applications. In order to study these effects, the parasitic elements of the inductor are modeled and analyzed. A suitable solution is proposed to improve the overall system performance. The effect of high $dv/dt$ on the filter and the effectiveness of the proposed solution are validated using simulation. Experimental data is also provided to validate the proposed concept. Show less

Recent advancement in the packaging technology for the SiC MOSFETs with blocking voltage of 10 kV or higher have opened up opportunities to consider these devices for medium voltage and high power applications. This paper focuses on the design of a modular medium voltage, high power DC--DC converter enabled by 10 kV SiC MOSFETs which aims at increasing the efficiency, power density and inter-operability. The proposed DC--DC converter is suitable for applications like DC distribution for the… Show more

Recent advancement in the packaging technology for the SiC MOSFETs with blocking voltage of 10 kV or higher have opened up opportunities to consider these devices for medium voltage and high power applications. This paper focuses on the design of a modular medium voltage, high power DC--DC converter enabled by 10 kV SiC MOSFETs which aims at increasing the efficiency, power density and inter-operability. The proposed DC--DC converter is suitable for applications like DC distribution for the data centres, sub-sea power transmission, offshore wind farms and photovolatic energy transmission - distribution - coordination, electric ship DC power transmission and distribution solid state transformer. Show less

For photo-voltaic (PV) inverter applications, the grid code mandates reactive power support to the grid, and the amount of reactive power injection may be limited by the voltage overshoot during the switching transients. For SiC-MOSFET based PV inverters this problem is more pronounced since the voltage and current gradient during switching transitions are much higher than a Si-based power devices. During a gloomy day when the inverter has to operate at PV panel's open circuit voltage, it… Show more

For photo-voltaic (PV) inverter applications, the grid code mandates reactive power support to the grid, and the amount of reactive power injection may be limited by the voltage overshoot during the switching transients. For SiC-MOSFET based PV inverters this problem is more pronounced since the voltage and current gradient during switching transitions are much higher than a Si-based power devices. During a gloomy day when the inverter has to operate at PV panel's open circuit voltage, it becomes harder to push higher currents through the device but also keeping the device within its SOA and low the switching loss at all operating conditions. Slowing down the switching transient could be a remedy but this also increases the converter switching loss. This paper demonstrates an application of dynamic gate resistance modulation technique to keep the SiC-device inside its safe operating area (SOA) while maintaining a low switching loss with minimum voltage and current overshoots. The proposed implementation is verified with hardware test results at high junction temperatures (up to 150°C). Show less

This paper presents a medium voltage power conversion architecture for grid integration of multi-MW permanent magnet synchronous generator (PMSG) based wind energyc-conversion system (WECS). Converting the low voltage power output of the generator to medium voltage, can reduce the diameter of the power cable significantly. As a result, power loss and the overall cost of the system can be minimized. With high frequency transformer based design, the weight of the power conversion system can be… Show more

This paper presents a medium voltage power conversion architecture for grid integration of multi-MW permanent magnet synchronous generator (PMSG) based wind energyc-conversion system (WECS). Converting the low voltage power output of the generator to medium voltage, can reduce the diameter of the power cable significantly. As a result, power loss and the overall cost of the system can be minimized. With high frequency transformer based design, the weight of the power conversion system can be kept low, making it feasible to install the system on the tower of the wind turbine itself. The architecture is built upon modular concept which facilitates to operate the system under partial fault condition. Also, it has the advantage of reaching to a better efficiency by operating part of the conversion system at partial generation condition. Recent advances in wide bandgap (WBG) based switching devices can further enhance the efficiency of the system. The overall control system is designed and the operation of the proposed architecture is validated through simulation and the feasibility of system design is addressed based on the available power devices. Show less

A three phase power block based on novel 1.7
kV/450 A SiC-MOSFET is designed and tested. To benchmark
the performance of the power block, a through comparison is
done with currently standardized 1.7 kV/450 A Si-IGBT based
three phase power block. Key performance indices, including
power rating curves at different switching frequencies and power
factors; temperature ripple at different fundamental frequencies,
are examined. It is shown that the SiC based power block has… Show more

A three phase power block based on novel 1.7
kV/450 A SiC-MOSFET is designed and tested. To benchmark
the performance of the power block, a through comparison is
done with currently standardized 1.7 kV/450 A Si-IGBT based
three phase power block. Key performance indices, including
power rating curves at different switching frequencies and power
factors; temperature ripple at different fundamental frequencies,
are examined. It is shown that the SiC based power block has very
promising potentials in various applications. Simulation and
experiment results are provided to support the claims for SiCMOSFET
based power block. Show less

With the development of Modular structured Voltage Source Converters (VSC), Multi-Terminal DC (MTDC) transmission systems have now become a feasible solution to transmit power at high voltage which greatly improves the electric power transmission system. The MTDC grid has lower capital costs and lower losses than an equivalent AC transmission system. Thus for long distance power transmission MTDC grid becomes a very attractive solution. Since the MTDC network is now built based on VSCs, it… Show more

With the development of Modular structured Voltage Source Converters (VSC), Multi-Terminal DC (MTDC) transmission systems have now become a feasible solution to transmit power at high voltage which greatly improves the electric power transmission system. The MTDC grid has lower capital costs and lower losses than an equivalent AC transmission system. Thus for long distance power transmission MTDC grid becomes a very attractive solution. Since the MTDC network is now built based on VSCs, it automatically offers better quality of transmitted power along with more flexibility in power transmission over the conventional current source converters. However, VSC based MTDC transmission systems are vulnerable to DC side fault and expensive DC circuit breakers are required to protect them against DC fault. This paper compares the DC short circuit fault response of different modular multi-level converters (MMC) inside a MTDC system. For the comparison purpose two different kind of MMC topologies have been considered namely, Modular Multi-level Converter (MMC) with High Frequency DC/DC Isolation Stage and MMC with full bridge sub modules. The paper analyzes the fault current limiting capabilities of each of the converters. PSCAD simulation is also done to prove the relevance of the analysis. Show less

The DC transmission system provides a cost effective solution for long distance power transmission compared to the AC transmission system. Hence, this has increased the emphasis on the development of the DC transmission system. Development of power converter with modular structure has now made it possible to achieve higher voltage and power level. This opens the possibility for further development of a multi-terminal DC grid. Now once the DC grid system has been formed, it is also important to… Show more

The DC transmission system provides a cost effective solution for long distance power transmission compared to the AC transmission system. Hence, this has increased the emphasis on the development of the DC transmission system. Development of power converter with modular structure has now made it possible to achieve higher voltage and power level. This opens the possibility for further development of a multi-terminal DC grid. Now once the DC grid system has been formed, it is also important to include more renewable energy sources directly to the DC grid. Therefore, a power conversion stage is required to condition the available power from a source to the grid. This paper shows the operation and control of such a kind of converter system which integrates the solar cell to the DC grid directly. The paper mainly focuses on control of the series connected DAB that have been integrated to HVDC power network. In order to deliver power in HVDC system, the total number of DABs must be high enough to achieve the DC link voltage. The control in that case must be a combination of current and voltage control. In order to validate the proposed control, complete system has been implemented on Opal-RT™ and hardware in the loop (HIL) using external controller has also been implemented to show the system operation. Show less

The multi-terminal DC grid can be integrated to the existing meshed AC grid system to provide back-up in case of transmission line failure and enhance power transmission capacity and flexibility in existing ac grids. In addition to that, Power oscillations can also be damped effectively through modulation of both active and reactive power of a voltage source converter (VSC) based multi-terminal DC grid. In this paper, the ability of the multi-terminal DC grid to effectively damp the power… Show more

The multi-terminal DC grid can be integrated to the existing meshed AC grid system to provide back-up in case of transmission line failure and enhance power transmission capacity and flexibility in existing ac grids. In addition to that, Power oscillations can also be damped effectively through modulation of both active and reactive power of a voltage source converter (VSC) based multi-terminal DC grid. In this paper, the ability of the multi-terminal DC grid to effectively damp the power oscillation in an interconnected AC grid has been investigated. Also, VSC based MTDC transmission systems are vulnerable to DC side fault. This paper demonstrates a control method of a dc fault resilient voltage source converter that has ultra-fast electronic isolation capability following dc fault which can be protected against dc fault. To verify the control structure, the dynamic performance of the integrated multi-terminal DC grid in a reduced order three-bus AC equivalent power system is investigated through hardware-in-the-loop testing. Controller hardware-in-the-loop simulation of the embedded multi-terminal DC grid in a meshed AC power system is performed by Real Time Digital Simulator (RTDS), and RTDS results are presented to verify the control structure. Show less

Recently, multi-terminal DC (MTDC) system has received more attention in the power transmission areas. Development of modular structured power converter topologies has now enabled the power converter technology to attain high voltage high power ratings. Compared to current source converter technology, voltage source converters have several benefits including higher power quality, independent control of active and reactive power etc. This paper focuses on a unique MTDC system consisting of… Show more

Recently, multi-terminal DC (MTDC) system has received more attention in the power transmission areas. Development of modular structured power converter topologies has now enabled the power converter technology to attain high voltage high power ratings. Compared to current source converter technology, voltage source converters have several benefits including higher power quality, independent control of active and reactive power etc. This paper focuses on a unique MTDC system consisting of terminals with different converter topologies especially considering the fact that each of the terminals may be manufactured by different vendors. In this particular configuration, the MTDC system consists of four terminals namely two advanced modular multi-level converter with high frequency isolation, one standard modular multi-level converter (MMC) with half bridge sub modules and the fourth terminal is modular DC-DC converter which integrates PV along with a Battery energy storage system with the DC grid directly. This paper presents a system level study of hybrid MTDC System. Also the DC fault contingency case has been explored thoroughly. An algorithm has been proposed to prevent the system damage. All the cases have been demonstrated with the PSCAD simulation results. To show the system practically works in real time, the system is also evaluated in a unique real time platform, consisting of interconnected RTDS and OPAL RT systems. Show less