EPE Association: EPE 2020 - DS3c: Solid State Transformers

EPE 2020 - DS3c: Solid State Transformers
You are here: EPE Documents > 01 - EPE & EPE ECCE Conference Proceedings > EPE 2020 ECCE Europe - Conference > EPE 2020 - Topic 02: Power Converter Topologies and Design > EPE 2020 - DS3c: Solid State Transformers

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   Hybrid Multiple Chopper Cells of PWM and Square-wave Operation for Solid-state Transformer
By Naoto KIKUCHI [View]
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Abstract: This paper proposes a modulation method combining PWM and square-wave drive for solid-state transformers (SSTs). Modular multilevel configurations based on input series and output parallel (ISOP) have been widely used. The advantage of ISOP configuration is that low on-resister and low-switching-loss devices are available because the applied voltage on each cell is divided by the number of cells. For this reason, SST based on the ISOP configuration is widely used in a medium-voltage system. However, this configuration has a problem that a high number of medium frequency devices, such as SiC-MOSFET, increases the cost of SST. In order to solve above problem, a reduction method of medium frequency devices are proposed. In the proposed method, one cell is driven with the PWM operation in order to compensate for the harmonic component. The other cells are driven by square-wave operation. Thus, the power factor correction (PFC) is held by different switching frequencies in each cell converter operated.Owing to the proposed operation, the medium frequency driving devices can be replaced with low-frequency devices, such as Si-IGBT, for cost-saving. As the drawback of the proposed control, the conduction time is unbalanced in the square wave cells. Thus, this paper also proposes the sorting operation to balance the output power of cells operated with square-wave drive. From the experimental results, THD of the input current is 2.91\%, the input power factor is 0.99, the maximum efficiency is 94.2\% at 0.3p.u.(1.p.u.=1.0 k W).

   Optimization of medium-frequency transformers with large capacity and high insulation requirement
By Xuan GUO [View]
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Abstract: The application of traction power electronic transformers (PETs) requires high efficiency and power density, where insulation becomes a key factor in the transformer design process. This paper presents a model-based optimization design and engineering realization that considers the electromagnetic, geometric and insulating properties of the transformer. To accurately model the transformer considering the geometric asymmetry caused by high insulation requirement, a hybrid distributed inductance model is put forward. Based on the optimized pareto domain obtained by the optimization method, one can get the most suitable optimal design point of the volume and the efficiency of the transformer. A 140kW, 85kV insulation prototype has been designed and the static parameters measurement experiments and simulation results verified the theoretical design. The electricity and insulation experiments will be done in the future due to COVID-19.

   Power Losses Calculation for Medium Voltage DC/DC Current-Fed Solid State Transformer for Battery Grid-Connected
By Essam HUSSAIN [View]
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Abstract: Current fed solid-state transformers (CF-SSTs) offer substantial weight and size reduction advantages over 50/60Hz traditional transformers. CF-SSTs have low source current ripple which makes it suitable for the connection of large batteries in the medium voltage grid. However, power losses are high compare to the traditional one due to the high operating frequency range. Therefore, power losses calculations are the main key to select the main design parameters. Unlike most of the published work dealing one aspect of power losses or a specific element and only consider voltage fed Solid State Transformers topology (VF-SSTs), this paper presents a power losses calculation method for CF-SSTs considering all the power losses, the shape of the voltage waveforms, cores dimensions and manufacturer datasheets are main paper pros. ANSYS and Matlab Simulink are employed to validate the analytical equations. Due to simplicity, this method can be used for optimization.

EPE 2020 - DS3c: Solid State Transformers
You are here: EPE Documents > 01 - EPE & EPE ECCE Conference Proceedings > EPE 2020 ECCE Europe - Conference > EPE 2020 - Topic 02: Power Converter Topologies and Design > EPE 2020 - DS3c: Solid State Transformers
	[return to parent folder]

	Hybrid Multiple Chopper Cells of PWM and Square-wave Operation for Solid-state Transformer By Naoto KIKUCHI	[View] [Download]
Abstract: This paper proposes a modulation method combining PWM and square-wave drive for solid-state transformers (SSTs). Modular multilevel configurations based on input series and output parallel (ISOP) have been widely used. The advantage of ISOP configuration is that low on-resister and low-switching-loss devices are available because the applied voltage on each cell is divided by the number of cells. For this reason, SST based on the ISOP configuration is widely used in a medium-voltage system. However, this configuration has a problem that a high number of medium frequency devices, such as SiC-MOSFET, increases the cost of SST. In order to solve above problem, a reduction method of medium frequency devices are proposed. In the proposed method, one cell is driven with the PWM operation in order to compensate for the harmonic component. The other cells are driven by square-wave operation. Thus, the power factor correction (PFC) is held by different switching frequencies in each cell converter operated.Owing to the proposed operation, the medium frequency driving devices can be replaced with low-frequency devices, such as Si-IGBT, for cost-saving. As the drawback of the proposed control, the conduction time is unbalanced in the square wave cells. Thus, this paper also proposes the sorting operation to balance the output power of cells operated with square-wave drive. From the experimental results, THD of the input current is 2.91\%, the input power factor is 0.99, the maximum efficiency is 94.2\% at 0.3p.u.(1.p.u.=1.0 k W).

	Optimization of medium-frequency transformers with large capacity and high insulation requirement By Xuan GUO	[View] [Download]
Abstract: The application of traction power electronic transformers (PETs) requires high efficiency and power density, where insulation becomes a key factor in the transformer design process. This paper presents a model-based optimization design and engineering realization that considers the electromagnetic, geometric and insulating properties of the transformer. To accurately model the transformer considering the geometric asymmetry caused by high insulation requirement, a hybrid distributed inductance model is put forward. Based on the optimized pareto domain obtained by the optimization method, one can get the most suitable optimal design point of the volume and the efficiency of the transformer. A 140kW, 85kV insulation prototype has been designed and the static parameters measurement experiments and simulation results verified the theoretical design. The electricity and insulation experiments will be done in the future due to COVID-19.

	Power Losses Calculation for Medium Voltage DC/DC Current-Fed Solid State Transformer for Battery Grid-Connected By Essam HUSSAIN	[View] [Download]
Abstract: Current fed solid-state transformers (CF-SSTs) offer substantial weight and size reduction advantages over 50/60Hz traditional transformers. CF-SSTs have low source current ripple which makes it suitable for the connection of large batteries in the medium voltage grid. However, power losses are high compare to the traditional one due to the high operating frequency range. Therefore, power losses calculations are the main key to select the main design parameters. Unlike most of the published work dealing one aspect of power losses or a specific element and only consider voltage fed Solid State Transformers topology (VF-SSTs), this paper presents a power losses calculation method for CF-SSTs considering all the power losses, the shape of the voltage waveforms, cores dimensions and manufacturer datasheets are main paper pros. ANSYS and Matlab Simulink are employed to validate the analytical equations. Due to simplicity, this method can be used for optimization.