Average value model of modular multilevel converters for switching overvoltage simulation in VSC‐HVDC grids

Abstract

The first ±500 kV voltage source converter based high voltage direct current (VSC‐HVDC) grid in the world is being built in China. The half‐bridge submodule‐based modular multilevel converter (MMC), the direct current (DC) circuit breaker (DCCB), and the overhead line are used in the project. Switching overvoltage will occur after the DCCB turns off the short circuit current (SCC) in the VSC‐HVDC grid. The existing average value models (AVMs) of MMC still have some limitations in simulating such a kind of overvoltage. The main reason is that these AVMs cannot accurately simulate the working states of MMC in the VSC‐HVDC grid with DCCB. This article summarizes the possible cases of the action strategies between the DCCB and MMC in the VSC‐HVDC grid. Then, the working states of MMC in the different cases are analyzed. Corresponding to different working states, the limitations of existing AVMs are analyzed. The existing AVMs cannot simulate the alternating current or DC components in the arm current before being blocked and the charging process of the submodule capacitor after being blocked. An enhanced AVM is proposed in this article, which can fully simulate the MMC's working states. Simulation results show that the accuracy of the proposed AVM is highly improved over the existing AVMs. Meanwhile, the simulation efficiency of the proposed model is improved over the detailed equivalent model that is highly accurate but relatively low efficient for VSC‐HVDC grid simulations. © 2019 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

On-Site Experimental Analysis for Impact of Wideband Terminal Model to Transient Overvoltage Based on a Full-Scale 200kV MMC-HVDC Converter Station

“…The three main devices in the converter station should be modeled involving parasitic elements. These devices are the smooth reactor, the hybrid DC breaker, and the MMC converter whose wideband models are proposed in [10,11,13]. The DC smoothing reactor is represented by a 𝜋 circuit which contains the inductance Lr, the stray capacitance Cls between windings and the stray capacitance Clg between coils and the ground, as shown in Fig.…”

“…An MMC model was proposed in [13], which is divided into two circuits, the circuit seen from the AC side and the circuit from the DC side. Under normal conditions, switch S5, S6, S9, S10 are open while S3, S4, S7, S8 are close.…”

“…Considering MMC-HVDC converter station is a non-linear system, several circuit models are proposed according to different application object and frequency range. Concerning the research of dynamic response, average value model (AVM) has been proposed by the principle of power balance [12,13]. The converter station model is approximated into a resistanceinductance-capacitance series circuit, which is applied as the CIGRE HVDC benchmark model [14,15].…”

Analysis and suppression of voltage oscillation at DC circuit breaker terminal in DC fault transient process

“…Consequently, the capacitance of the MMC is equivalent to a voltage source. At the same time, L arm and MMC bridge arm equivalent resistance R arm are equivalent to the DC side inductance L dc = 2 L arm /3 and resistance R dc = 2 R arm /3 [15].…”

“…In recent years, the research on the transient voltage characteristics of MMC-HVDC short-circuit faults has focussed on the calculation of overvoltage. References [14,15] studied the models of DCCB and MMC in overvoltage simulation, respectively, analysed the reason for overvoltage caused by DCCB operation, and the limitations of MMC average model. References [16,17] studied the voltage and current characteristics of MMC-HVDC grid DC faults with symmetrical bipolar and symmetrical monopole structures by combining mechanism analysis and electromagnetic transient simulation.…”