EPE Association: EPE 2016 - LS1d: Standard and Advanced Control Techniques for Power Converters

EPE 2016 - LS1d: Standard and Advanced Control Techniques for Power Converters
You are here: EPE Documents > 01 - EPE & EPE ECCE Conference Proceedings > EPE 2016 ECCE Europe - Conference > EPE 2016 - Topic 03: Measurement and Control > EPE 2016 - LS1d: Standard and Advanced Control Techniques for Power Converters

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   Circulating Current Control for Modular Multilevel Converter based on Selective Harmonic Elimination with Ultra-low Switching Frequency
By ANGEL PEREZ-BASANTE [View]
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Abstract: Multilevel converters (MCs) are utilized in medium voltage (MV) high power applications due to its higher efficiency than two level converters. On the other hand, modular multilevel converters (MMCs) provide several advantages with regard to other MCs, such as higher scalability, reliability and no requirement of a common DC capacitor. Particularly, low switching frequency modulations, such as (2N+1) selective harmonic elimination (SHE) - pulse width modulation (PWM), may improve the efficiency of MMCs when they are utilized in MV and high power applications, where the number of sub-modules is not high. This work presents a new circulating current control for MMC when (2N+1) SHE-PWM is utilized. Therefore, it is possible to operate the converter simultaneously with low switching frequency and low capacitor voltage ripple at every sub-module besides a correct energy balance between arms. In addition, a new method to implement (2N+1) SHE-PWM for MMCs, which is also valid to implement standard SHE-PWM for any MC, is provided. Using this method, different equation systems are not required for every switching pattern. In this way, this technique provides simultaneously both the switching patterns and the firing angles which solve the SHE problem, simplifying the searching task. Simulation results which have been obtained from a MMC with 5 sub-modules at every arm, have validated the novel proposed circulating current control. Furthermore, the spectrum of the simulated line to line voltage waveform has proved the correct performance of the proposed (2N+1) SHE-PWM implementation method. Several sets of angles have been provided throughout the ma range, where 17 harmonics have been controlled.

   Control of Direct AC/AC Modular Multilevel Converters Using Capacitor Voltage Estimation
By Luca BESSEGATO [View]
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Abstract: This paper applies a control method based on current control and sum-capacitor-voltage estimation to the direct ac/ac modular multilevel converter. As capacitor voltages are estimated, their measurements are not needed in the high-level control, which simplifies the communication between the main controller and the submodules of the converter. The stability of the internal dynamics of the converter, using the aforementioned control method, is studied using Lyapunov stability theory, proving that the system is globally asymptotically stable.The behavior of the converter is simulated focusing on three-phase 50 Hz to single-phase 16 2/3 Hz conversion, which is typical for railway power supply systems of some European countries. Simulation results are in agreement with the expected behavior of the converter, both in steady-state and dynamic situations.

   Experimental Evaluation of PWM-Methods for Modular Multilevel Converters
By Hendrik FEHR [View]
[Download]

Abstract: Five sorting-based methods for the modulation of modular multilevel converters are implemented on a test benchand evaluated regarding their switching frequency, voltage balancing capability, harmonics, voltage error, and computation time.In contrast to already published methods, the cells considered here can omit additional switch transitionswhen entering PWM mode. This reduces the switching frequency but complicates harmonic cancellation.One method is able to reduce the rms ripple of the dc current by increasing the likelihoodof suitable duty cycles, eliminating the need for fixed carrier signal assignment.

   Power Balancing in Multi-Converter Systems Composed of Modular Multilevel Converters (MMCs)
By Pawel BLASZCZYK [View]
[Download]

Abstract: Multi-converter systems composed of series or parallel connected modular multilevel converters(MMCs) require a means to manage power sharing between the MMCs by balancing the load duringoperation. Series connected MMCs require proper voltage balancing while parallel connected MMCsrequire proper current balancing. The paper describes this imbalance phenomenon, illustrates thesolution via simulation results, and presents field measurements obtained with a megawatt class mediumvoltage DC test facility.

EPE 2016 - LS1d: Standard and Advanced Control Techniques for Power Converters
You are here: EPE Documents > 01 - EPE & EPE ECCE Conference Proceedings > EPE 2016 ECCE Europe - Conference > EPE 2016 - Topic 03: Measurement and Control > EPE 2016 - LS1d: Standard and Advanced Control Techniques for Power Converters
	[return to parent folder]

	Circulating Current Control for Modular Multilevel Converter based on Selective Harmonic Elimination with Ultra-low Switching Frequency By ANGEL PEREZ-BASANTE	[View] [Download]
Abstract: Multilevel converters (MCs) are utilized in medium voltage (MV) high power applications due to its higher efficiency than two level converters. On the other hand, modular multilevel converters (MMCs) provide several advantages with regard to other MCs, such as higher scalability, reliability and no requirement of a common DC capacitor. Particularly, low switching frequency modulations, such as (2N+1) selective harmonic elimination (SHE) - pulse width modulation (PWM), may improve the efficiency of MMCs when they are utilized in MV and high power applications, where the number of sub-modules is not high. This work presents a new circulating current control for MMC when (2N+1) SHE-PWM is utilized. Therefore, it is possible to operate the converter simultaneously with low switching frequency and low capacitor voltage ripple at every sub-module besides a correct energy balance between arms. In addition, a new method to implement (2N+1) SHE-PWM for MMCs, which is also valid to implement standard SHE-PWM for any MC, is provided. Using this method, different equation systems are not required for every switching pattern. In this way, this technique provides simultaneously both the switching patterns and the firing angles which solve the SHE problem, simplifying the searching task. Simulation results which have been obtained from a MMC with 5 sub-modules at every arm, have validated the novel proposed circulating current control. Furthermore, the spectrum of the simulated line to line voltage waveform has proved the correct performance of the proposed (2N+1) SHE-PWM implementation method. Several sets of angles have been provided throughout the ma range, where 17 harmonics have been controlled.

	Control of Direct AC/AC Modular Multilevel Converters Using Capacitor Voltage Estimation By Luca BESSEGATO	[View] [Download]
Abstract: This paper applies a control method based on current control and sum-capacitor-voltage estimation to the direct ac/ac modular multilevel converter. As capacitor voltages are estimated, their measurements are not needed in the high-level control, which simplifies the communication between the main controller and the submodules of the converter. The stability of the internal dynamics of the converter, using the aforementioned control method, is studied using Lyapunov stability theory, proving that the system is globally asymptotically stable.The behavior of the converter is simulated focusing on three-phase 50 Hz to single-phase 16 2/3 Hz conversion, which is typical for railway power supply systems of some European countries. Simulation results are in agreement with the expected behavior of the converter, both in steady-state and dynamic situations.

	Experimental Evaluation of PWM-Methods for Modular Multilevel Converters By Hendrik FEHR	[View] [Download]
Abstract: Five sorting-based methods for the modulation of modular multilevel converters are implemented on a test benchand evaluated regarding their switching frequency, voltage balancing capability, harmonics, voltage error, and computation time.In contrast to already published methods, the cells considered here can omit additional switch transitionswhen entering PWM mode. This reduces the switching frequency but complicates harmonic cancellation.One method is able to reduce the rms ripple of the dc current by increasing the likelihoodof suitable duty cycles, eliminating the need for fixed carrier signal assignment.

	Power Balancing in Multi-Converter Systems Composed of Modular Multilevel Converters (MMCs) By Pawel BLASZCZYK	[View] [Download]
Abstract: Multi-converter systems composed of series or parallel connected modular multilevel converters(MMCs) require a means to manage power sharing between the MMCs by balancing the load duringoperation. Series connected MMCs require proper voltage balancing while parallel connected MMCsrequire proper current balancing. The paper describes this imbalance phenomenon, illustrates thesolution via simulation results, and presents field measurements obtained with a megawatt class mediumvoltage DC test facility.