Abstract
In this paper, a new One-Cycle-Control (OCC) method is designed for a modular multilevel converter (MMC) based on the principle of the equivalent resistance constant. The proposed controller has a simple structure and a small amount of calculation by cancelling the current inner loop proportional integral (PI) controller and the inverse transform in the traditional direct-quadrature (DQ) control. Compared to the traditional OCC controller, the new one separates the control method from the modulation strategy, making it possible to use not only carrier-based pulse-width modulation (PWM), but also nearest level modulation PWM to generate drive signals. Besides, the independent control of the active and the reactive power is implemented by injecting a reference current with the same phase of the supply voltage or a reference current which lags the supply voltage by π/2 into the controller, so the converter can operate in four quadrants and it can work in either a grid-connect or off-grid environment. The feasibility and the performance of the proposed OCC method have been validated by both the simulation under the MATLAB/SIMULINK (R2012a) environment and experimental results.
Highlights
Modular multilevel converters (MMCs) have attracted wide attention from both industry and academia due to their advantages of full modularity, better scalability, high redundancy, and low switch voltage stress [1,2]
The OCC-based MMC controller has been discussed in Reference [18], but it can only work in the unity power factor rectification mode and the control method must be used in conjunction with the carrier disposition pulse-width modulation (PWM), which reduces the flexibility of the system
This paper proposes a modified OCC for MMCs
Summary
Modular multilevel converters (MMCs) have attracted wide attention from both industry and academia due to their advantages of full modularity, better scalability, high redundancy, and low switch voltage stress [1,2]. The traditional OCC cannot control the reactive component so that the converter can only implement the unit power factor with no ability to output leading or lagging reactive power This problem was discussed in References [14,15]; they let the APF compensate for only the harmonic components of load currents by injecting the reactive currents. The OCC-based MMC controller has been discussed in Reference [18], but it can only work in the unity power factor rectification mode and the control method must be used in conjunction with the carrier disposition PWM, which reduces the flexibility of the system. Compared with the existing OCC-based MMC controller, the modified OCC proposed in this paper can enable the bi-directional power flow, and the power factor can be controlled, which expands the application scope of the control method.
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