Enhanced Efficient EMT-Type Model of the MMCs Based on Arm Equivalence

Abstract

The large number of switching elements in modular multilevel converters (MMCs) contribute a tremendous computational burden for electromagnetic transient (EMT) simulation programs. Detailed equivalent models (DEMs) and average value model (AVMs) are currently two major types of accurate and efficient model. However, the DEMs are still computationally inefficient for the simulation scenarios in large-scale MMC based high-voltage direct current (MMC-HVDC) grids, as the models represent all submodule (SMs) switching events, and memorize all individual capacitor voltages. Though the AVMs provide a faster simulation speed by using a single equivalent capacitor on the DC side, they have a relatively low simulation accuracy compared to DEMs, especially under blocked mode. This paper proposes an enhanced computationally efficient model based on arm equivalence (AEM), which can accurately represent the dynamic behaviors in both de-blocked and blocked modes. Compared to the DEMs, the proposed AEM is more efficient, with no loss of accuracy, and the simulation speed is irrespective of the SM number. The accuracy and computational efficiency of the proposed model were validated against the DEM and AVM through several simulation scenarios in a two-terminal MMC-HVDC system on the power systems computer aided design/ electromagnetic transient in DC system (PSCAD/EMTDC) program.

A Detailed Review of MMC Circuit Topologies and Modelling Issues

“…AVM has compromised accuracy compared to detailed ECM, especially under blocked mode. erefore, a fast, efficient model referred to as the arm equivalence model (AEM) is proposed [120]. AEM gives identical results compared to detailed ECM in both deblocked and blocked mode for dynamic studies.…”

“…Similar to AVM, simulation speed does not depend on the number of SMs in AEM. However, AEM is 45% slower than AVM [120]. Hybrid cascaded multilevel converters (HCMCs) are emerging converter technologies for HVDC/MTDC systems.…”

Seven Level Voltage Source Converter Based Static Synchronous Compensator with a Constant DC-Link Voltage

“…The voltage source converter (VSC) with PI controller limiters, decoupled link, hysteresis current, individual phase voltage, and current techniques is currently being implemented [17][18][19]. The bulk power rating of the high voltage direct current power transmission system's performance is estimated via modular level converters with mean value and equivalent versions of submodule circuits [20]. The irregular power losses, switching losses, and dynamic efficiency are improved with a dual-loop control scheme of half-bridge multi level inverters based on STATCOM [21].…”