Abstract
In this paper a hybrid modulated model predictive control (HM2PC) strategy for modular-multilevel-converter (MMC) multi-terminal direct current (MTDC) systems is proposed for supplying power to passive networks or weak AC systems, with the control objectives of maintaining the DC voltage, voltage stability and power balance of the proposed system. The proposed strategy preserves the desired characteristics of conventional model predictive control method based on finite control set (FCS-MPC) methods, but deals with high switching frequency, circulating current and steady-state error in a superior way by introducing the calculation of the optimal output voltage level in each bridge arm and the specific duty cycle in each Sub-Module (SM), both of which are well-suited for the control of the MMC system. In addition, an improved multi-point DC voltage control strategy based on active power balanced control is proposed for an MMC-MTDC system supplying power to passive networks or weak AC systems, with the control objective of coordinating the power balance between different stations. An MMC-HVDC simulation model including four stations has been established on MATLAB/Simulink (r2014b MathWorks, Natick, MA, USA). Simulations were performed to validate the feasibility of the proposed control strategy under both steady and transient states. The simulation results prove that the strategy can suppress oscillations in the MMC-MTDC system caused by AC side faults, and that the system can continue functioning if any one of the converters are tripped from the MMC-MTDC network.
Highlights
In recent years, MMCs are gaining a lot of attention in high power/high voltage applications that involve interfacing high-voltage direct current (HVDC) systems to high voltage three-phaseAC grids due to their high modularity and scalability [1,2]
This paper aims to propose a new Hybrid Model Predictive Control (M2 PC) method for control of the MMC-multi-terminal direct current (MTDC) system that addresses the key limitations faced by the FCS-Model predictive control (MPC) methods
In order to verify the effectiveness of the above predictive control algorithm, a simulation model of the VSC-MTDC system (Figure 1) in MATLAB/Simulink has been developed
Summary
MMCs are gaining a lot of attention in high power/high voltage applications that involve interfacing high-voltage direct current (HVDC) systems to high voltage three-phaseAC grids due to their high modularity and scalability [1,2]. Investment and research in high-voltage direct-current (HVDC) systems has been actively pursued and expanded with the aim of improving the efficiency and reliability of electric power generation, large-capacity power transmission, and linkage among different networks [1,2,3,4,5,6]. When an MMC-HVDC transmission system supplying passive networks is operating normally, its rectifier station generally uses constant current control and constant reactive control, which contains an outer power loop and an inner current loop. In this paper we focus on the control strategy used in the inverter station
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