EPE Association: EPE 2017 - LS1b: Control Techniques for Power Converters I (Multi-Level Converters)

EPE 2017 - LS1b: Control Techniques for Power Converters I (Multi-Level Converters)
You are here: EPE Documents > 01 - EPE & EPE ECCE Conference Proceedings > EPE 2017 ECCE Europe - Conference > EPE 2017 - Topic 03: Measurement and Control > EPE 2017 - LS1b: Control Techniques for Power Converters I (Multi-Level Converters)

   [return to parent folder]

   Energy Balancing in the Modular Multilevel Converter under Unbalanced Grid Conditions
By Markus SCHROEDER [View]
[Download]

Abstract: A comprehensive energy balancing concept for the Modular Multilevel Converter (MMC) under unbal-anced grid conditions was proposed. Grid supporting converters need to be able to fed unbalanced gridcurrents; grid failures lead to unbalanced grid voltages. Both unbalanced grid conditions generate energyunbalance inside the MMC. In order to handle these critical operating points, an analytical descriptionof the energy distribution inside the MMC - depending on the grid currents and voltages and basedon a double synchronous reference frame (DSRF) approach - was derived. The obtained mathematicalrelations were presented in a compact representation using matrix notations and an energy balancingconcept was deduced. An implementation to a hardware setup in power electronics laboratory has beenperformed. The proposed concept has been proven and verified with measurement results.

   Higher switching speed of power devices in series connection achieved by modifying the gate driver architecture
By Van-Sang NGUYEN [View]
[Download]

Abstract: This paper presents the study on gate driver circuitries implemented to drive power devices in series connection with the objective to minimize the conducted EMI perturbations and as well to improve the switching speed of the power devices. More specifically, the propagation paths of parasitic currents generated under very high switching speed are studied in different configurations trying to reduce the parasitic capacitance of each gate driver circuit with respect to ground/control reference potential and to minimize the common mode currents. In complex power converters, multi-cell, multi-level or even series connection of power devices, many driver circuits are required and implemented. Similarly, in such converters, there are several dv/dt sources generated at different floating points that are exiting the isolated barriers of the gate drivers (supplies and control signal isolation units) which mean that conducted EMI perturbations can be amplified and the switching speed of the power devices could be affected by multi-parasitic capacitances. Based on previous works, the paper analyses the best possible configurations to minimize the common mode currents in series connected transistor topologies and to reduce the parasitic capacitance of the gate driver circuitries leading as well to a significant improvement of the switching speed of the power devices. In this article, experimental validations are used to approve the analysis.

   Improved Energy Balancing for Modular Multilevel Converters by Optimized Feed-Forward Circulating Currents and Common Mode Voltage
By Hendrik FEHR [View]
[Download]

Abstract: The energy balancing task for modular multilevel converters is solved as an optimization problem, resulting in optimized feed-forward circulating currents and common-mode voltage. In contrast to the classic approach of specifying circulating current components and common-mode voltage, a maximized subset of (transformed) arm energies are specified during optimization in order to identify optimized feed-forward circulating currents and common-mode voltage. By this, the search for a solution is inherently limited to the domain of realistic energy variations. In the proposed approach, a reference trajectory is selected from a family of trajectories such that the balancing goal is met. As a benefit of the optimization, no balancing error remains, even during transfers between operation regimes, i.e. the task of the balancing controller is reduced to the compensation of parameter uncertainties and disturbances. The resulting feed-forward signals considerably improve the balancing as demonstrated by measurements.

   Reducing the Modulation Voltage Error in MMCs by Considering the Capacitor Voltage Change Within One PWM Cycle for Improved Current Control
By Marvin MIDDEKE [View]
[Download]

Abstract: The impact of capacitor voltage changes during the modulation period is examined in order to improve the arm voltage of a modular multilevel converter. Different methods are used to predict and compensate for the capacitor voltage change and the resulting arm voltage error, whereby two of the improvements provide a possibility to easily upgrade existing modulation algorithms. Simulation and measurement results demonstrate a reduced arm voltage error and thus a reduced circulating current in comparison to the case when the voltage change is neglected in the modulator.

EPE 2017 - LS1b: Control Techniques for Power Converters I (Multi-Level Converters)
You are here: EPE Documents > 01 - EPE & EPE ECCE Conference Proceedings > EPE 2017 ECCE Europe - Conference > EPE 2017 - Topic 03: Measurement and Control > EPE 2017 - LS1b: Control Techniques for Power Converters I (Multi-Level Converters)
	[return to parent folder]

	Energy Balancing in the Modular Multilevel Converter under Unbalanced Grid Conditions By Markus SCHROEDER	[View] [Download]
Abstract: A comprehensive energy balancing concept for the Modular Multilevel Converter (MMC) under unbal-anced grid conditions was proposed. Grid supporting converters need to be able to fed unbalanced gridcurrents; grid failures lead to unbalanced grid voltages. Both unbalanced grid conditions generate energyunbalance inside the MMC. In order to handle these critical operating points, an analytical descriptionof the energy distribution inside the MMC - depending on the grid currents and voltages and basedon a double synchronous reference frame (DSRF) approach - was derived. The obtained mathematicalrelations were presented in a compact representation using matrix notations and an energy balancingconcept was deduced. An implementation to a hardware setup in power electronics laboratory has beenperformed. The proposed concept has been proven and verified with measurement results.

	Higher switching speed of power devices in series connection achieved by modifying the gate driver architecture By Van-Sang NGUYEN	[View] [Download]
Abstract: This paper presents the study on gate driver circuitries implemented to drive power devices in series connection with the objective to minimize the conducted EMI perturbations and as well to improve the switching speed of the power devices. More specifically, the propagation paths of parasitic currents generated under very high switching speed are studied in different configurations trying to reduce the parasitic capacitance of each gate driver circuit with respect to ground/control reference potential and to minimize the common mode currents. In complex power converters, multi-cell, multi-level or even series connection of power devices, many driver circuits are required and implemented. Similarly, in such converters, there are several dv/dt sources generated at different floating points that are exiting the isolated barriers of the gate drivers (supplies and control signal isolation units) which mean that conducted EMI perturbations can be amplified and the switching speed of the power devices could be affected by multi-parasitic capacitances. Based on previous works, the paper analyses the best possible configurations to minimize the common mode currents in series connected transistor topologies and to reduce the parasitic capacitance of the gate driver circuitries leading as well to a significant improvement of the switching speed of the power devices. In this article, experimental validations are used to approve the analysis.

	Improved Energy Balancing for Modular Multilevel Converters by Optimized Feed-Forward Circulating Currents and Common Mode Voltage By Hendrik FEHR	[View] [Download]
Abstract: The energy balancing task for modular multilevel converters is solved as an optimization problem, resulting in optimized feed-forward circulating currents and common-mode voltage. In contrast to the classic approach of specifying circulating current components and common-mode voltage, a maximized subset of (transformed) arm energies are specified during optimization in order to identify optimized feed-forward circulating currents and common-mode voltage. By this, the search for a solution is inherently limited to the domain of realistic energy variations. In the proposed approach, a reference trajectory is selected from a family of trajectories such that the balancing goal is met. As a benefit of the optimization, no balancing error remains, even during transfers between operation regimes, i.e. the task of the balancing controller is reduced to the compensation of parameter uncertainties and disturbances. The resulting feed-forward signals considerably improve the balancing as demonstrated by measurements.

	Reducing the Modulation Voltage Error in MMCs by Considering the Capacitor Voltage Change Within One PWM Cycle for Improved Current Control By Marvin MIDDEKE	[View] [Download]
Abstract: The impact of capacitor voltage changes during the modulation period is examined in order to improve the arm voltage of a modular multilevel converter. Different methods are used to predict and compensate for the capacitor voltage change and the resulting arm voltage error, whereby two of the improvements provide a possibility to easily upgrade existing modulation algorithms. Simulation and measurement results demonstrate a reduced arm voltage error and thus a reduced circulating current in comparison to the case when the voltage change is neglected in the modulator.