Analytical circuit oriented modelling and performance assessment of modular multilevel converter

Abstract

This study presents a detailed time domain model of a modular multilevel converter (MMC) to provide an alternative form of evaluation of the converter dynamic performance, for example, during AC or DC fault conditions. The purpose of the model is to accurately reflect the converter behaviour to be used in control systems design. It can also be beneficial to predict the steady state or transient state of the converter with fixed or variable inputs. In an MMC, the capacitor voltages are modulated using pulse-width modulation (PWM) to fabricate a sinusoidal output voltage. With time, and because of the PWM action, the capacitors get charged or discharged. Therefore the circuit behaves as a time-variant circuit. The analysis is based on the equivalent circuit derived from the converter differential expressions at any time instant in a piecewise fashion. The usefulness and accuracy of the theoretical study is validated for the three-phase MMC topology by simulation results with respect to normal operation, start-up process, cell short-circuit fault, line-to-ground and DC-side fault conditions. Experimental tests are carried out through a scaleddown laboratory prototype.

Review of dc–dc converters for multi‐terminal HVDC transmission networks

“…For many decades researchers have recognised the possibilities multi-terminal high-voltage dc (HVDC) transmission networks can offer when compared with well-established high-voltage ac systems [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. For the majority of this period, the difficulty of power reversal in complex multi-terminal networks based on line commutating converter high-voltage dc (LCC-HVDC) technology has prevented development of generic dc grids with seamless control over the power flow in any of its branches [16].…”

Input‐series and output‐series connected modular single‐switch flyback converter operating in the discontinuous conduction mode

“…The constants k n in (14) define the initial fraction of voltage disturbance that appears on each input-voltage module from the total positive disturbance (V i ). To meet Kirchhoff's voltage law, the sum of disturbance voltages on the input of each module is equal to zero.…”

“…The time evolution of the input voltage on each module is obtained by applying inverse Laplace transform in (23) and replacing the result in (14). The results obtained are written as…”

“…Even though there is continuous progress in the high-voltage high-power fully controlled semiconductors [7,8], new strategies are necessary to meet the voltage requirements of the systems, such as (a) series connection of power devices [9, 10], (b) multilevel topologies [11][12][13][14], and (c) modular converter [15][16][17][18][19][20][21][22][23][24][25][26][27]. Connecting devices in series is the direct way to reach higher nominal voltages; however, it makes fail to achieve high efficiency and high-power density.…”

Carrier‐less fault‐tolerant stochastic synthesis in multi‐cell multi‐level converters: a central limit approach to highly‐dimensional power electronic systems

“…A well-known example of such class of converters is the MMC structure proposed in [1][2][3][4]. In such deterministic synthesis concepts [5][6][7], the higher the number of cells, the greater the complexity of the command chain, which is realised in practice with optical fibres and optoelectronic transmitter/receivers for the feedback, acknowledgement, and switching signals. By either generating the switching signals inside the cells upon reception of the voltage command, or by letting the central controller to generate directly each single switch command, the number of communication channels easily reach the order of hundreds, even when multiplexing techniques together with addressing schemes of the cells are employed [8].…”