Article

Digital current-control schemes

IEEE Industrial Electronics Magazine (Impact Factor: 4.03). 04/2009; 3(1):20 - 31. DOI: 10.1109/MIE.2009.931894
Source: IEEE Xplore

ABSTRACT

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 [1]. In addition, passive solutions are not effective for applications in which the nonlinear load exhibits fast transients.

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    • "A number of control methods have been reported in the literature such as proportional-integral (PI) control [7], hysteresis control [7], dead-beat control [8], repetitive-based control [9], adaptive control [10], and nonlinear control [11]. Also, there has been tremendous progress during the last decade in current control techniques for active power filters [12] [13] [14] [15] [16] including of a proportional controller plus multiple sinusoidal signal integrators [12], a PI controller plus a series of resonant controllers [13] [14], or vector PI (VPI) controllers [15]. 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.
    Full-text · Article · Mar 2014 · Electric Power Systems Research
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    • "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 [11]–[13]. 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.
    Preview · Article · Aug 2013 · IEEE Transactions on Power Systems
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    • "As most DG units are connected to the electrical network via a voltage-source inverter (VSI), microgrid control involves the control of these inverters[15]. In the grid-connected mode, currently, the DG units are equipped with a grid-following control that is generally current-controlled[16]–[18]. The primary function of these controllers is to inject a specified amount of power into the network. "
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    ABSTRACT: To achieve the environmental goals set by many governments, an increasing amount of renewable energy, often delivered by distributed-generation (DG) units, is injected into the electrical power system. Despite the many advantages of DG, this can lead to voltage problems, especially in times of a high local generation and a low local load. The traditional solution is to invest in more and stronger lines, which could lead to massive investments to cope with the huge rise of DG connection. Another common solution is to include hard curtailment; thus, on-off control of DG units. However, hard curtailment potentially leads to on-off oscillations of DG and a high loss of the available renewable energy as storage is often not economically viable. To cope with these issues, applying a grid-forming control in grid-connected DG units is studied in this paper. The voltage-based droop control that was originally developed for power sharing in islanded microgrids, enables an effective way for soft curtailment without communication. The power changes of the renewable energy sources are delayed to more extreme voltages compared to those of the dispatchable units. This restricts the renewable energy loss and avoids on-off oscillations.
    Preview · Article · Apr 2013 · IEEE Transactions on Power Delivery
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