Design of DC‐side fault current limiter for MMC‐HVDC systems: Safety of the MMC along with frequency stability

Abstract

A high voltage direct current system based on the modular multi‐level converter (MMC‐HVDC) is introduced as a suitable device for transmission of bulk powers over long distances. A pole‐to‐pole DC‐side fault is a significant challenge for the MMC‐HVDC system. Three main problems are the appearance of voltage spikes following a fast DC fault current break up, frequency instability due to insufficient inertia (networks such as renewable energy‐based systems) and destruction of anti‐parallel diodes within the MMC due to the high fault current. This study proposes a novel method for limiting DC fault current, improving isolation of the three‐phase AC system from the DC‐side. The suggested design employs high power resistors as virtual load such that continuity in active power flow will be kept on. Further, this prevents frequency deviation from exceeding the allowable limits. Also, transient over‐voltages will be limited which are coming from stray inductances linked with electromagnetic effects of fault current level. Simulations and design practical issues have verified the validity of the proposal by using MATLAB/Simulink.

Joint Limiting Control Strategy Based on Virtual Impedance Shaping for Suppressing DC Fault Current and Arm Current in MMC-HVDC Systems

“…Some studies have proposed superconducting fault current limiters to prevent instability [17], but their applications in practical projects require further verification. Similarly, some resistive and capacitive fault-current limiters have been reported in [18] and [19].…”

Review, Classification and Loss Comparison of Modular Multilevel Converter Submodules for HVDC Applications

“…In terms of the pole-to-ground fault in bipolar MMC systems, the faulty converter should be blocked to ensure the other converters can still operate normally while the dc component of the current is reduced [20]. Aiming to protect the MMC from damage due to dc-side faults, a virtual load configuration connected in parallel with a hybrid dc circuit breaker (DCCB) was proposed in [21], which can limit the dc-fault currents and improve the dc-fault tolerance of the converter. As the dc-fault current flows through the converter, the SMs need to have the ability to withstand this rising current for the period before any dc protection is activated [22].…”

Unbalanced power control of a modular multilevel converter with photovoltaic resources and the capacitor voltage ripple analysis

“…It mainly embodies [1][2][3][4] in: Modular design, high number of output levels, easy to achieve capacity expansion and increase voltage level and so on. It was originally applied in the medium and highvoltage direct current (HVDC) transmission and distribution fields [1,2,5,6], its modular structure enables the integration of distributed energy resources (DERs), whether they are PV systems [7,8] or energy storage [9][10][11][12][13]. These integrated DERs generally recommend using a dc/dc converter [8][9][10][11] to control the power of each sub-module from one DER into each submodule of the MMC.…”