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The MMC is an emerging and highly attractive multilevel converter topology for medium and high voltage applications. Various modulation strategies are being used to control the MMC system. Balancing the cascaded submodule voltages and eliminating the second order circulating current in the leg of the MMC system are the main concerns of many researchers in the area of MMC system. Mostly, for circulating...
The four-level Hybrid Clamped Converter (4L-HCC) is emerging as a promising DC/AC converter topology for high-efficiency medium-voltage drives. However, without proper control, the voltage fluctuation of the DC-link capacitors will be excessive, resulting in distorted AC current and stability issue in low frequency operation. In reality, the distorted current makes it impractical for motor drive during...
This paper presents a new control strategy for Modular Multilevel Matrix converters where the output frequency is higher then the input frequency. In operating points when ωout ≥ ωin the energy pulsation in the converter cells are dominated by the second harmonic of the input frequency. These energy pulsations can be identified and compensated by inducing additional currents. The results are verified...
Modular multilevel converters (MMCs), with the filter-less and transformer-less features, are considered as a promising topology for high-efficiency medium voltage (MV) high voltage (HV) drive systems. However, at low frequencies (< 30 Hz), a large current ripple flowing through the capacitors of each submodule will cause significant capacitor voltage fluctuation. This paper proposes an optimal...
This paper deals with the AC and DC dynamic voltage control in a hybrid DC/AC Microgrid (MG) with central and distributed Battery Energy Storage Systems (BESSs), applying a power sharing mechanism between the different devices in the MG. The MG is composed by a multiport transformation center and two fixed frequency 3 phase AC Nanogrids (NGs) coupled to a DC bus through 3-phase Power Electronic Converters...
This paper proposes a fixed frequency based sliding mode (SM) controller for transformer-less single phase inverter for photovoltaic (PV) application with active power decoupling minimizing the capacitance requirement. Unlike conventional power decoupling techniques in full bridge converters, the proposed technique incorporates a large sinusoidal swing of the half-bridge capacitor voltages and a limited...
This paper proposes a control structure of SST (Solid-state-transformer), which consists of MMC (Modular Multi-level Converter) based AC/DC converters and isolated DC/DC converters, to reduce the size of capacitors. The phase separated configuration requires a high capacitance needed for smoothing capacitors due to instantaneous power oscillation at the double line frequency. This paper proposes an...
A control scheme using space vector modulation for the modular multilevel matrix converter (MMMxC) without circulating current control is investigated. The circulating current flows spontaneously among all the nine arms to balance capacitor voltage of cells. A small arm inductor is inserted into each arm to suppress the di/dt and peak value of transient arm current at the moment of switching the cells...
We propose a plug-and-play realization of the virtual infinite capacitor (VIC), which is an electronic circuit recently proposed in the literature for DC voltage filtering. The VIC is meant to replace large, expensive and unreliable electrolytic capacitors, and is mainly intended for applications where random fluctuations of the DC bus voltage may occur (i.e., the VIC is not tuned to one particular...
Available fractional-order PIλDμ controllers introduced in the literature use discrete component realizations, where the approximations of fractional-order integration and differentiation operations is performed using appropriately configured RC networks. A novel re-configurable fractional-order PIλ controller, suitable for brake and throttle control in an autonomous vehicle, is presented in this...
This paper addresses the proposal and simulation of a direct voltage and frequency control (DVFC) of an offshore wind farm (OWF) with LCC-HVDC connection. The proposed control system allows the connection of the OWF to the LCC rectifier by generating a controlled voltage and frequency in a capacitor bank. The decoupled control of the d-q component of the voltage at the capacitor bank, connected to...
Single-phase two-stage inverters generally use an intermediate capacitor to buffer the power imbalance between DC input and AC output. However, the resultant low-frequency voltage ripple on this intermediate capacitor may produce low-frequency ripple at the source side, especially when the front-end dc/dc converter operates in continuous conduction mode (CCM). Some common solutions to reducing this...
Inverters in back to back (B2B) connection are utilized to convert the voltage and frequency of the power source to another format. Typical application of inverters is the wind power system. This study presents a B2B inverter for equal voltage and frequency format conversion in which one inverter works to get power from the grid to charge the DC capacitor and another inverter returns most of the active...
The modular multi-level converter (MMC) is considered as the state of the art converter among multilevel topologies. The harmonic suppression of circulating current is the inherent problem needed to be solved. In this paper, a new control strategy is proposed. The strategy includes the double fundamental frequency, negative sequence rotating coordinate transformation and the four fundamental frequency,...
The objective of this experimental research is to examine the effects of variable operating speeds and capacitance on the terminal voltage and frequency of a stand-alone self-excited induction generator (SEIG)-based flywheel energy storage system (FESS). The experiments were carried out under the no-load and on-load conditions using the SEIG-based FESS prototype, given the variable operating speeds...
Many efforts have been made to improve the performance of power electronic systems with active capacitive DC-link module in terms of power density as well as reliability. One of the attractive solution is an active capacitive DC-link with the series-connected circuit because of handling small-rated power. However, in the existing control method of this circuit, the DC-link current of the backward-stage...
A novel variable frequency variable duty cycle (VFVD) control scheme using off-line digital control by only sensing the output voltage is proposed. Designed for a 6 kV 40 kHz series resonant DC-DC converter in solid state transformer application, it realizes cycle-by-cycle resonant current limiting and zero voltage switching (ZVS) at any load condition. According to the state plane analysis, with...
Due to the low inductance of an LCL-filter, the grid current generated by an LCL-filtered Voltage Source Inverter (VSI) is sensitive to low-order grid-voltage harmonics. This issue is especially tough for the control system with Inverter Current Feedback (ICF), because the grid-current harmonics can freely flow into the filter capacitor without control. To cope with this issue, this paper develops...
A new ripple current reduction method utilizing a LLC type ripple current steering circuit is proposed in this paper to significantly reduce 100Hz ripple current in an isolated DC-AC dual active bridge (DAB) converter. Unlike some of the proposed ripple reduction methods for which auxiliary circuit consists of additional switches is applied, this new method benefits from less switching components...
The feature of power current sources for pulse-arc welding is superimposing of current pulses with a defined shape, size and frequency on the main welding current. The purpose of this paper is to explore the possibilities to control the parameters of superimposed pulses by a particular (additional) welding inverter current source with improved parameters. The current pulse superimposed to the basic...
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