Full-bridge MMC DC fault ride-through and STATCOM operation in multi-terminal HVDC grids

Abstract

This paper investigates a control structure to enhance the DC fault ride-through capability of a full-bridge modular multilevel converter (MMC) station, while ensuring a stable controlled operation as a STATCOM during DC faults without the need for fault isolation. Taking advantage of the switching states of a full-bridge submodule, a DC current controller is proposed, which provides the DC voltage reference for the modulation when a DC fault is detected. By changing the outer controllers strategy from DC voltage or active power control to converter energy control during a fault, the decoupling of the converter operation from the DC side dynamics is realized. In this paper, the focus is on the control methodology at all times of operation and the evaluation of the STATCOM control during a fault. To this end, extensive simulations were performed on a three-terminal high voltage direct current (HVDC) grid in radial configuration and a pole-to-pole DC fault case was investigated. The results showed that the AC voltage and current were controlled within limits at all times, while the full-bridge MMC was able to provide reactive power support to the AC grid. Moreover, using the proposed control methodology, the transients at the operation transition points between STATCOM and inverter/rectifier operation were minimized and the stations were able to safely ride through the fault.

Common-Mode Voltage Elimination in Multilevel Power Inverter-Based Motor Drive Applications

“…where i represents each phase of the converter, and v Li and v U i the lower-arm and upper-arm voltage of each phase (see Fig. 6c) [117]- [119].…”

Fast DC Fault Current Suppression and Fault Ride-Through in Full-Bridge MMCs via Reverse SM Capacitor Discharge

“…The DC side voltage needs to be synthesized as zero [37] by the MMC arms after DC side fault detection to clear the fault and allow the MMC to operate as a STATCOM. This can be achieved by simply removing the DC component from the arm voltage references [37,38]. Figure 4c This is because the SMs will be inserted in reverse polarity and therefore the arm voltage range will need to be changed from ([0,1]) to ([0,−1]).…”

“…The DC side voltage needs to be synthesized as zero [37] by the MMC arms after DC side fault detection to clear the fault and allow the MMC to operate as a STATCOM. This can be achieved by simply removing the DC component from the arm voltage references [37,38]. Figure 4c Another essential change in the MMC control to maintain energy balance when operating as a STATCOM during the fault is in the outer controllers as suggested by the authors in [38], more specifically in the / loop that provides the reference for the daxis current.…”

Review on topology‐based dc short‐circuit fault ride‐through strategies for MMC‐based HVDC system

“…By decoupling the dc grid voltage from the SM capacitor voltage, each arm acts as a virtual dc link. With capacitor energy control, the FBSM MMC can work as a STATCOM while riding through dc fault [56, 62]. However, the device count and power losses are high, especially with the increase of SM numbers [63].…”