Dynamic Analysis of Modular Multilevel Converters

Harnefors, Lennart; Antonopoulos, Antonios; Norrga, Staffan; Ängquist, Lennart; Nee, H-P

doi:10.1109/tie.2012.2194974

Cited by 564 publications

(395 citation statements)

References 23 publications

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“…It is assumed that the equivalent switching frequency is high enough and the capacitor voltages are balanced at all times [6][7][8]. Hence, the averaged equivalent circuit of MMC can be obtained, as presented in Fig.…”

Section: Hss Modelling Of MMCmentioning

confidence: 99%

“…However, compared with conventional VSCs, MMCs have much more complex internal dynamics [6][7][8], such as harmonic circulating currents and capacitor voltage fluctuations, which might have detrimental effects on the operation stability of the interconnected system, especially for renewable energy integration applications [9][10][11]. For instance, a subsynchronous oscillation (SSO) phenomenon was observed in a real MMC-HVDC project for wind farm integration in China [10], where the oscillation frequency is approximately 21 Hz in the ac phase currents (as shown in Fig.…”

Section: Introductionmentioning

confidence: 99%

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Sub‐synchronous oscillation mechanism and its suppression in MMC‐based HVDC connected wind farms

Lyu

Cai

Ամին

et al. 2018

IET Generation, Transmission & Distribution

107

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A subsynchronous oscillation (SSO) phenomenon in a wind farm integrated with a modular multilevel converter (MMC)-based high-voltage direct current (HVDC) transmission system has been recently observed in the real world. An attempt is made in this paper to contribute to the understanding of the root cause of the SSO in the MMC-HVDC connected wind farms by the impedance-based analysis. For that, the small-signal impedance model of the MMC is first developed based on the harmonic state-space (HSS) modelling method, which is able to include all the internal harmonic dynamics of MMC. An inherent low-frequency resonance peak in the MMC system excluding any control influence is identified by its terminal impedance characteristics. Arguably, this could be the reason why the SSO phenomenon occurs in the MMC-HVDC connected wind farms. In addition to that, the influence factors, such as main circuit parameters, controller parameters, and power level, on the stability of the interconnected system are examined by the impedance-based Nyquist plots, which can provide guidelines for the system design in order to guarantee the stability of the interconnected system. Based on the mechanism analysis, a stabilization control method for suppressing the SSO in the MMC-HVDC based wind farms is also proposed. Finally, the theoretical analysis and stabilization control method are validated by both time-domain simulations and on-site recorded waveforms in a real MMC-HVDC system for wind farm integration in China.

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Section: Hss Modelling Of MMCmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Sub‐synchronous oscillation mechanism and its suppression in MMC‐based HVDC connected wind farms

Lyu

Cai

Ամին

et al. 2018

IET Generation, Transmission & Distribution

107

View full text Add to dashboard Cite

show abstract

“…The differential voltage v diff is described in (7). The differential current is controlled by the sum of v p and v n .…”

Section: B Mathematical Modelmentioning

confidence: 99%

“…The HVDC systems have to be designed and controlled to provide high efficiency, availability and reliability during steady state operation as well as during fault conditions being very challenging at DC side [3], [4], [5], [6]. In general, the MMC particularly profits from its scalability to different power and voltage levels by using standard components (IGBTs) [1], [7]. Since a very high number of IGBTs is required to block high voltages, even low switching frequency methods can achieve a suitable output waveforms [8], [9].…”

Section: Introductionmentioning

confidence: 99%

Thermal Analysis and Balancing for Modular Multilevel Converters in HVDC Applications

Hahn

Andresen

Buticchi

et al. 2018

IEEE Trans. Power Electron.

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Abstract-The modular multilevel converter (MMC) has become a very attractive solution for interfacing high voltages in 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. However, the nearest level modulation requires a capacitor voltage balancing algorithm, which can result in unbalanced loading for the power semiconductors in the different submodules. Particularly at low power factor operation, which could occur in case of low-voltage ride through and of reactive power injection, the conventional algorithm is not effective anymore. This article provides thermal stress analysis of the MMC in operation and proposes a thermal balancing approach, which is embedded in the capacitor voltage balancing algorithm. The purpose of the thermal balancing is to achieve similar stress distribution among the different submodules to enhance the lifetime. The junction temperatures in the different submodules are studied for HVDC applications and the article proves experimentally, that the thermal balance within the submodules is significantly improved.

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“…MMC-HVDC has a lot more advantages than two-level or three-level VSC-HVDCs, such as lower harmonic components at the Alternating Current (AC) side of the converter [4], greater reduction of the switching frequency, fewer losses [5] and operation consistency for the switching devices in series in an arm is not necessary [6]. There has been extensive research on MMC systems, and most of this research has been concentrated on mathematical modeling [7]- [9], modulation mode [10]- [12], and control strategies [13]- [16]. Physical verification plays an important role in testing control devices, planning the primary system and engineering operation, since it is closer to the practical project.…”

Section: Introductionmentioning

confidence: 99%

A Hardware-in-the-loop Platform for Modular Multilevel Converter Simulations

Liu¹,

Tian²,

Wang³

et al. 2016

Journal of Power Electronics

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In this paper, a hardware-in-the-loop simulation platform for MMCs is established, which connects a real time digital simulator (RTDS) and a designed MMC controller with optical fiber. In this platform, the converter valves are simulated with a small time step of 2.5 microsecond in the RTDS, and multicore technology is implemented for the controller so that the parallel valve control is distributed between different cores. Therefore, the designed controller can satisfy the requirements of real-time control. The functions of the designed platform and the rationality for the designed controller are verified through experimental tests. The results show that different modulation modes and various control strategies can be implemented in the simulation platform and that each control objective can been tracked accurately and with a fast dynamic response.

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Dynamic Analysis of Modular Multilevel Converters

Cited by 564 publications

References 23 publications

Sub‐synchronous oscillation mechanism and its suppression in MMC‐based HVDC connected wind farms

Sub‐synchronous oscillation mechanism and its suppression in MMC‐based HVDC connected wind farms

Thermal Analysis and Balancing for Modular Multilevel Converters in HVDC Applications

A Hardware-in-the-loop Platform for Modular Multilevel Converter Simulations

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