Proposed Direct Power Control Scheme Research Articles

Direct power control of three-phase PWM AC/DC converter based on intelligent approach with dc-bus voltage regulation using sliding mode controller

This research aims to present a novel direct power control (DPC) strategy of three-phase PWM AC/DC converters. In this strategy, the regulation of the dc-bus voltage is based on nonlinear sliding mode controller (SMC), the control of the instantaneous active and reactive power is performed by fuzzy logic controllers (FLC) and also the artificial neural networks (ANN) approach is used to select the switching states of PWM AC/DC converter. The sliding mode control is an effective tool to minimise disturbances. Nevertheless, the chattering phenomenon depicts a major problem for variable structure systems (VSS). To overcome this drawback, a saturation function is employed to decrease chattering effects. The proposed method allows, on the one hand, to steer the dc-bus voltage, the instantaneous active and reactive power to their reference values. On the other hand, it enables to reduce the harmonic disturbances, the power ripples and to realise a unity power factor (UPF) operation. Simulation results are provided to confirm the efficiency, the robustness and the performances of the proposed DPC scheme in different conditions of simulation.

A new switching table based neural network for direct power control of three-phase PWM-rectifier

Direct power control (DPC) is one of the newest techniques to control the PWM converter without network voltage sensors. This control technique is built on the idea of direct torque control (DTC) for an induction motor, which is applied to eliminate the harmonic of the line current and to compensate the reactive power. The principle of this control is based on instant active and reactive power loops. This article proposes an intelligent control approach to improve this control technique, such as artificial neural network (ANN), applied to the switching table. The comparison with conventional DPC shows that the use of DPC-ANN ensures smooth control of active and reactive power in all sectors and reduces current ripple. Finally, the developed DPC was tested by simulation. The results proved the excellent performance of the proposed DPC scheme in comparison with the conventional DPC.

Dynamic performance improvement of single‐phase PWM converters with power hysteresis control scheme

This study presents a direct power control (DPC) scheme with pulse width modulation module and two hysteresis comparators, for the application in single-phase PWM converters to overcome the drawbacks of conventional proportion-integration-based DPC (PI-based DPC), including poor dynamic performance and complexity of tuning PI parameters. According to the outputs of inner-loop power hysteresis controllers, the proposed DPC scheme divides d-q reference frame into four sectors. In each sector, the dynamic power components are estimated to be equivalent as the outputs of PI controllers in PI-based DPC. The proposed DPC scheme provides a new solution of non-linear hysteresis control to achieve fast dynamic performance with constant switching frequency. Additionally, due to inductance parameter mismatch, the effect on powers is analysed in detail, and an inductance parameter on-line estimation method is present and discussed. A comprehensive comparison of conventional table-based DPC, PI-based DPC and the proposed DPC methods has been conducted in this study, including steady-state performance with respect to different factors, and dynamic response under different extreme conditions. The experimental results have verified the effectiveness of the proposed DPC scheme.

Direct Power Control of Doubly Fed Induction Generator Without Phase-Locked Loop Under Harmonically Distorted Voltage Conditions

This paper proposes an improved direct power control (DPC) strategy of the doubly fed induction generator without phase-locked loop (PLL) under harmonically distorted voltage conditions. The proposed DPC scheme is implemented in a virtual synchronous reference frame, so that the potential instability problems caused by PLL can be eliminated. A second-order vector integrator is integrated with DPC to suppress the harmonic components directly, so that three different control targets of smooth stator active and reactive powers, sinusoidal stator current and constant electromagnetic torque, can be achieved. The sequential separations and the complex calculations of the power compensating items can also be eliminated. Meanwhile, a simple grid frequency estimation scheme is proposed, which can make the control strategy self-adaptive to the frequency variation in the practical situation. Finally, the experimental results validate the availability of the proposed DPC strategy.

Advanced Direct Power Control for Grid-connected Distribution Generation System Based on Fuzzy Logic and Artificial Neural Networks Techniques

This paper proposes an improvement of the direct power control (DPC) scheme of a grid connected three phase voltage source inverter based on artificial neural networks (ANN) and fuzzy logic (FL) techniques for the renewable energy applications. This advanced control strategy is based on two intelligent operations, the first one is the replacement of the conventional switching table of a three phase voltage source inverter (VSI) by a selector based on artificial neural networks approach, and the second one is the replacement of the hysteresis comparators by fuzzy logic controllers for the instantaneous active and reactive power errors. These operations enable to reduce the power ripples, the harmonic disturbances and increase the response time period of the system. Finally, the simulation results were obtained by Matlab/Simulink environment, under a unity power factor (UPF). These results verify the transient performances, the validity and the efficiency of the proposed DPC scheme.

Coordinated Direct Power Control of DFIG System Without Phase-Locked Loop Under Unbalanced Grid Voltage Conditions

This paper proposes a coordinated direct power control (DPC) scheme for the rotor-side converter (RSC) and the grid-side converter (GSC) of the doubly fed induction generator (DFIG) under unbalanced grid voltage conditions. In order to eliminate the coupling interactions between the phase-locked loop (PLL) and the local unbalanced network, a virtual phase angle is used to replace the actual one acquired by the PLL. Thus, the PLL is removed out of RSC and GSC in the proposed DPC scheme. During network unbalance, the RSC is controlled to reduce torque ripples, while three selectable control targets are identified for the GSC, i.e., constant total active power, constant total reactive power, and balanced currents. A single-side resonant controller with the frequency discrimination between the positive- and negative-sequence signals of the same frequency is employed in the coordinated DPC scheme to avoid the complex calculations of the power compensating components. Meanwhile, the sequential separations of the voltages and currents are also eliminated. Then, the control performance, including the limits of the dc-link voltage, the dc-capacitor power oscillations, the impacts of the frequency deviations, and the grid synchronization of the proposed DPC strategy, is discussed. Finally, the experimental results of DFIG system verify the effectiveness of the proposed DPC strategy under unbalanced grid voltage conditions.

Direct power control of voltage source inverter in a virtual synchronous reference frame during frequency variation and network unbalance

This study proposes a direct power control (DPC) scheme for grid-connected voltage source inverter (VSI) in a virtual synchronous reference frame during frequency variations and network unbalances. The proposed DPC scheme applies a virtual phase angle instead of the voltage phase angle acquired by the phase-locked loop (PLL) for coordinated transformations. This approach can eliminate the PLL and its low-frequency-oscillatory behaviours during the frequency variations. Meanwhile, two available control targets, that is, smooth active power and smooth reactive power, are defined for the VSI operation during network unbalance. In the proposed DPC scheme, the reduced-order vector integrator is employed to directly regulate the power pulsations caused by the voltage unbalances. Consequently, it can eliminate both the sequential separations of the voltages/currents and the complex calculations of the power compensating components. Then, based on the mathematical model of the VSI control system, the control performance, including the steady-state power errors and the system stability, is fully analysed. Finally, both the simulation and experimental results are provided to confirm the effectiveness of the proposed DPC scheme.

Sliding mode direct power control of RSC for DFIGs driven by variable speed wind turbines

In spite of its several advantages, a classic direct power control (DPC) of doubly fed induction generators (DFIGs) driven by variable speed wind turbines has some drawbacks. In this paper, a simple and robust total sliding mode controller (TSMC) is designed to improve the classical DPC performance without complicating the overall scheme. The TSMC is designed to regulate the DFIG stator active and reactive powers. Two integral switching functions are selected for describing the switching surfaces of the active and reactive powers. Reaching phase stability problem of the classical sliding mode controller is avoided in the proposed TSMC. Neither current control loops nor accurate values of machine parameters are required in the proposed scheme. In addition, axes transformation of the stator voltage and current are eliminated. The grid side converter is controlled based on DPC principle to regulate both DC-link voltage and total reactive power. The feasibility of the proposed DPC scheme is validated through simulation studies on a 1.5MW wind power generation system. The performance of the proposed and conventional DPC schemes is compared under different operating conditions.

Direct power control of shunt active filter using high selectivity filter (HSF) under distorted or unbalanced conditions

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.

Direct power control of DFIGs based wind energy generation systems under distorted grid voltage conditions

This paper presents an improved direct power control (DPC) strategy of a wind turbine driven doubly fed induction generators (DFIGs) connected to distorted grid voltage conditions. A coordinate control strategy of the grid side converter (GSC) and rotor side converter (RSC) of the DFIG is designed to improve the overall scheme performance. The RSC is controlled based on a DPC principle to eliminate the electromagnetic torque and stator reactive power oscillations. The total active and reactive power oscillations are compensated by the GSC control to achieve constant active and reactive powers from the overall DFIG system. A current control scheme consisting of a proportional integral controller and a resonant compensator tuned at six the grid frequency is proposed to provide accurate control of the GSC current. The proposed control scheme removes rotor current regulators and the decomposition process of the rotor and GSC currents. In addition, the proposed scheme preserves the advantages of the classical DPC. The feasibility of the proposed DPC scheme is validated by simulation studies on a 1.5MW wind power generation system under harmonically distorted grid voltage conditions. The performance of the proposed and conventional DPC schemes is compared under the same operating conditions. The proposed scheme results show significant improvements in the scheme performance.

Predictive Direct Power Control of Three-Phase Pulsewidth Modulation (PWM) Rectifier Using Space-Vector Modulation (SVM)

In this paper, we present a direct power control (DPC) of three-phase pulsewidth modulation rectifier with constant switching frequency using space-vector modulation (SVM). The developed DPC scheme is based on the predictive control strategy to achieve direct control of instantaneous active and reactive power of the converter. For this purpose, at the beginning of each switching period, the required rectifier average voltage vector allowing the cancellation of active and reactive power tracking errors, at the end of the switching period, is calculated by means of predictive control algorithm in the sense of deadbeat control. The main advantages of the proposed control, compared to the works published in this subject, are that no need to use predefined switching table and voltage vector or virtual flux position, PI-based active and reactive power control loops are not necessary and constant-switching frequency. The proposed predictive direct power control was tested both in simulations and experimentally and compared with DPC using switching table. Results have proved excellent performance, and verify the validity of the proposed DPC scheme, which is much better than conventional DPC using switching table.

Fuzzy-Logic-Based Switching State Selection for Direct Power Control of Three-Phase PWM Rectifier

This paper proposes a novel and simple direct power control (DPC) scheme of a three-phase pulsewidth-modulated rectifier without the use of a predefined switching table. The converter switching state selection is based on fuzzy logic rules, using the instantaneous active and reactive power tracking errors as fuzzy logic variables. The basic idea of fuzzy rules synthesis is based on the knowledge of the instantaneous variation of active and reactive power. According to the input fuzzy variables and in a specific moment, the best switching state of the converter is chosen to restrict the instantaneous active and reactive power tracking errors simultaneously, for maintaining the DC-bus voltage close to the reference value and guarantying the unity-power-factor operation. The main advantages of the proposed DPC scheme, compared to the classical one, are that it is not necessary to use hysteresis comparators, and smooth control of active and reactive power is obtained during all sectors. Finally, the developed DPC was tested both in simulations and experimentally, and illustrative results are presented here. Results have proven excellent performance, and verify the validity of the proposed DPC scheme which is much better than the classical DPC.