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Modular Multilevel Converter (MMC) has great application prospects for the flexible HVDC transmission, high-power motor drive and so on. In this paper, a discrete-time model of the MMC based on the virtual ergodic method is proposed for the typical MMC topology. First, the MMC topology is analyzed and its continuous-time model is established. Then, the state equation in the continuous-time model is...
Injection of both positive and negative sequence currents is desirable for three-phase voltage source converters under unbalanced grid fault condition. However, the 2nd order oscillation exists in the positive and negative sequence synchronous reference frame. Several approaches have been reported to cope with this 2nd order oscillation. In this paper, a simple yet efficient control method in double...
This paper proposes a transformer-less modular multilevel DC/DC converter. The proposed converter can be used to interconnect two HVDC systems with different dc voltage levels and realize bidirectional power flow. Based on the arm energy balance condition, the optimal design arming at minimum inner circulating current is presented. A power close-loop control method is adopted to regulate the converter...
Vector control is the most commonly used control strategy for modular multilevel converter (MMC) based HVDC system. However, due to the complicated structure of MMC, there is no precise mathematical model for the outer DC voltage loop. The conventional model ignores the capacitor voltage dynamics, and the AC voltage boosted operation scenario is not considered. This paper proposes a small signal model...
Modular multilevel converter (MMC) is a promising topology of Voltage Source Converter based High voltage Direct Current (VSC-HVDC) system with many outstanding advantages such as low switching frequency, low voltage distortion and harmonics. Pre-charge process is one of the core issues of MMC based system, especially for the MMC with DC fault blocking capability. In this paper, considering a novel...
Active Thermal Control (ATC) consists in driving power switches in a less efficient way when low load conditions are present. The resulting wasted power is used to self-heat the device, reducing amplitude and occurrence of thermal cycles and hence improving the reliability. This paper presents a novel way to control losses, and hence temperature, of both positive- and negative-current devices in half-bridge...
The multilevel converter is a prospective topology for both Medium Voltage and High Voltage Direct Current (HVDC) applications. In high power application, the forward topology is applied to increase the power region. In this paper, a novel forward-mode five-level inverter is presented which combines the features of the conventional multilevel converters and forward topology. The converters can transfer...
This paper studies the balance problems of neutral-point potential in three level neutral-point clamped inverter. Based on double modulation wave pulse control strategy, a new offset voltage algorithm is proposed. This control strategy can completely eliminate the low-frequency fluctuations in neutral-point potential. The size of neutral-point current is changed by changing the zero-state duty cycle...
A 4.6–5.6 GHz constant KVCO LC-VCO applied in PLL frequency synthesizer is presented in this paper. With constant KVCO LC-VCO and programmable charge pump, the frequency synthesizer is able to obtain constant bandwidth. Furthermore, the VCO has a low KVCO which will result low phase noise. An Optimized automatic frequency calibrator (AFC) is proposed, the AFC can select the sub-band which is nearest...
The paper firstly establishes a passivity-based control (PBC) of a double-fed inductor generator (DFIG). A new control method of the DFIG is proposed with the outer speed loop controlled by a full-order terminal sliding mode (TSM) controller to undertake maximum wind power point tracking (MPPT), while the inner current control loop is a PBC designed to manage the three-phase PWM rectifier. Simulation...
With the continuous development of high frequency inverter technology and multilevel inverter technology, all kinds of novel high frequency multilevel inverter are put forward and studied. And among them, the interleaved flyback three-level inverter (IFTLI) has a better work performance. In this paper, the control methods of single-phase IFTLI will be studied in-depth. Firstly, the instantaneous voltage...
This paper proposes a full-order terminal sliding-mode based energy saving control for the grid-connected converter of induction motor systems. DC-link voltage and currents controllers of the converter are designed respectively using the full-order terminal sliding manifold and the related control strategies. The chattering in the sliding-mode control is attenuated, and continuous control signals...
This paper presents an improved model predictive control strategy with fixed switching frequency. The proposed method adds four virtual voltage vectors to the four real voltage vectors of the conventional finite control set model predictive control to reduce the harmonic content of the grid current and uses a modulator to realize fixed switching frequency. Furthermore, a novel cost function, which...
Wireless power transfer has been introduced as a proper replacement for conventional cable power transfer systems recently. With the developments of the electric transportation, transferring power wirelessly has been found to introduce several advantages in charging Lithium-Ion batteries. Among different configurations of wireless power transfer, Series Parallel structure is found to be more interesting...
This paper presents a two-stage optimization approach to mitigate the rapid voltage fluctuations and minimize the power losses of distribution systems due to the high penetration of photovoltaic (PV) generation. The first stage is a day-ahead optimal strategy which aims to minimize the total voltage deviations and power losses within the constraints of the daily maximum allowable number of operations...
With the rapid development of hardware and the improvement of control performance requirements, digital control is widely used in power electronics. And due to the mature analysis methods and convenient implantation, the traditional linear control strategies, such as PID control, are directly applied to the design of digital controllers in industrial application. However, as the control delay and...
Cascaded multilevel inverter (MLI) topologies have received an attractive solution for grid connected PV system. In this paper, two-cascaded MLI topologies are presented for grid connected PV system. These are seven level cascaded H-bridge multilevel inverter and three phase cascaded voltage source multilevel inverter. In both presented MLI configurations, each PV module is connected to one DC-DC...
This paper discusses the active and reactive power control method for a modular multilevel converter (MMC) based grid-connected PV system. The voltage vector space analysis is performed by using average value models for the feasibility analysis of reactive power compensation (RPC). The proposed double-loop control strategy enables the PV system to handle unidirectional active power flow and bidirectional...
The fast and accurate control of renewable energy grid side converter (GSC) under normal and abnormal grid conditions is necessary to ensure the injection of high quality power and to enhance the power system stability. Accurate control of GSC is achieved by the stable and fast response of current and PQ controllers. In the event that the grid voltage becomes unbalanced due to the presence of grid...
A multi-time scale coordinated voltage control strategy in an islanded microgrid (MG) is proposed in this paper. The strategy is comprised of local voltage control of distributed generators (DGs), secondary voltage control (SVC) based on PI regulators and a proposed tertiary voltage control (TVC) strategy. A multi-objective function of the TVC is designed to achieve a compromise among three objectives:...
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