Digital current-control schemes
The wide use of nonlinear loads, such as front-end rectifiers connected to the power distribution systems for dc supply or inverter-based applications, causes significant power quality degradation in power distribution networks in terms of current/voltage harmonics, power factor, and resonance problems. Passive LC filters (together with capacitor banks for reactive power compensation) are simple, low-cost, and high-efficiency solutions. However, their performance strongly depends on the source impedance and can lead to unwanted resonance phenomena with the network . In addition, passive solutions are not effective for applications in which the nonlinear load exhibits fast transients.
Available from: Amar Omeiri
- "A number of control methods have been reported in the literature such as proportional-integral (PI) control , hysteresis control , dead-beat control , repetitive-based control , adaptive control , and nonlinear control . Also, there has been tremendous progress during the last decade in current control techniques for active power filters      including of a proportional controller plus multiple sinusoidal signal integrators , a PI controller plus a series of resonant controllers  , or vector PI (VPI) controllers . This is due to the development of powerful and fast microprocessors. "
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ABSTRACT: This paper describes the design of a new configuration of direct power control (DPC) based on high selectivity filters (HSF) to achieve near-sinusoidal source current waveforms under different source voltage conditions. The proposed method uses the high selectivity filters instead of the classical extraction filters (low pass filters). The basic idea of the proposed DPC is to choose the best inverter voltage vector in order to minimize instantaneous active and reactive power errors using two hysteresis comparators. Their outputs associated with a switching table, control the active and reactive powers by selecting the optimal switching states of the inverter. Simulation results have proved excellent performance, and verify the validity of the proposed DPC scheme, which is much better than conventional DPC using low pass filters.
Electric Power Systems Research 03/2014; 108:113–123. DOI:10.1016/j.epsr.2013.11.006 · 1.75 Impact Factor
- "The inverter control of the DG units in grid-connected microgrids is related to the delivery of a certain amount of power to the network's point of view. Generally, grid-following units, with current controllers that track the measured terminal voltage, are used –. The grid stability and power quality remain a task of the transmission system. "
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ABSTRACT: Microgrids are able to provide a coordinated integration of the increasing share of distributed generation (DG) units in the network. The primary control of the DG units is generally performed by droop-based control algorithms that avoid communication. The voltage-based droop (VBD) control is developed for islanded low-voltage microgrids with a high share of renewable energy sources. With VBD control, both dispatchable and less-dispatchable units will contribute in the power sharing and balancing. The priority for power changes is automatically set dependent on the terminal voltages. In this way, the renewables change their output power in more extreme voltage conditions compared to the dispatchable units, hence, only when necessary for the reliability of the network. This facilitates the integration of renewable units and improves the reliability of the network. This paper focusses on modifying the VBD control strategy to enable a smooth transition between the islanded and the grid-connected mode of the microgrid. The VBD control can operate in both modes. Therefore, for islanding, no specific measures are required. To reconnect the microgrid to the utility network, the modified VBD control synchronizes the voltage of a specified DG unit with the utility voltage. It is shown that this synchronization procedure significantly limits the switching transient and enables a smooth mode transfer.
IEEE Transactions on Power Systems 08/2013; 28(3):2545-2553. DOI:10.1109/TPWRS.2012.2226481 · 2.81 Impact Factor
- "The whole control scheme is developed around an inner current control loop implemented in a two-axis synchronous reference frame (dq), which provides the output voltage reference that controls the VSC bridge by means of a PWM generator. Among numerous current control schemes reported in the literature , and starting from the comprehensive comparison from , this paper adopts a PI controller in synchronous reference frame (PI-SRF) for the fundamental current component, whereas for the selective harmonics compensation (HC) multiple sinusoidal signal integrators (SSI) applied in SRF are used. Therefore the proposed controller will have a PI-SSI-SRF structure, as illustrated in Fig. 2 and the transfer function provided in (1), being characterized by a low complexity and adequate regulation performances. "
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ABSTRACT: This paper presents a three-phase battery energy storage system (BESS) operating in both microgrid (MG) connected and islanded modes. When connected to the MG, an enhanced frequency controller, covering the main two frequency control levels, i.e. primary and secondary, governs the BESS active power. If the MG power quality worsens below a certain level, the system is able to switch in island mode and to supply the local loads. The reconnection is accomplished only after the BESS voltage is smoothly resynchronized with the MG voltage. The proposed control solution for a three-phase BESS is assessed by means of computer simulations.
Optimization of Electrical and Electronic Equipment (OPTIM), Brasov, Romania; 05/2012
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