Voltage Vector Selection Research Articles

Vector Strategy of Formation of the Compensating Current of Shunt Active Filter In Sliding Mode

A space-vector strategy for controlling of a three-phase shunt active power filter (SAPF), which is connected to a utility grid in which there is a nonlinear load, is proposed. The filter consists of a semiconductor voltage inverter with fully controlled switches, a capacitive storage and a single-link output RL filter. The DC voltage of the storage capacitor is stabilized by a second-order sliding mode, which is based on the implementation of a finite double-twisting algorithm. To form the compensation current, an indirect control strategy and a space-vector algorithm for tracking the instantaneous value of the current of the "parallelogram" type are used. Space-vector method avoids ambiguity in the choice of vectors of the output voltage of the inverter under the solution of the problem of current tracking. The proposed algorithm uses the methods of projective geometry to determine the relative position of the spatial vectors of voltages and currents of the power supply system, so it does not contain the difficult mathematical operations for calculating inverse trigonometric functions. The selection of the appropriate output voltage vector of the SAPF inverter on the location of the end of the current error vector relative to some switching lines is based. Switching lines from the projections of the two-dimensional sliding surface on the plane α-β are formed. These projections are subject to further linear transformation, the matrix of which is non-degenerate. Linear transformation of projections of these sliding surfaces includes sequential operations of rotation at a fixed angle, parallel movement and application of the rotation matrix. This rotation matrix has constant coefficients, which change abruply at some points in time. The classical method of equivalent control is applied. The transition from one group of coefficients to another occurs based on the spatial location of the equivalent control vector, the coordinates of which are calculated in real time. The choice of the rotation matrix provides unambiguous determination of the spatial position and the choice of the corresponding output voltage vector of the SAPF inverter. A simulation model of the power supply system with a two-dimensional sliding mode and taking into account the features that are inherent in the real-time sliding mode is built, and the simulation results are analyzed. The "switching freeze" method to eliminate chattering was used. The proposed strategy with the traditional three-channels hysteresis algorithm of the compensation current tracking according to the criteria of the number of switches is compared.

Proportional Usage of Low-Level Actions in Model Predictive Control for Six-Phase Electric Drives

Finite Control-Set Model Predictive Control (FCS-MPC) appears as an interesting alternative to regulate multiphase electric drives, thanks to inherent advantages such as its capability to include new restrictions and fast-transient response. Nevertheless, in industrial applications, FCS-MPC is typically discarded to control multiphase motors because the absence of a modulation stage produces a high harmonic content. In this regard, multi-vectorial approaches are an innovative solution to improve the electric drive performance taking advantage of the implicit modulator flexibility of Model Predictive Control (MPC) strategies. This work proposes the definition of a new multi-vectorial set of control actions formed by a couple of adjacent large voltage vectors and a null voltage vector with an adaptative application ratio. The combination of two large voltage vectors provides minimum x-y current injection whereas the application of a null voltage vector reduces the active voltage production. Moreover, the optimum selection of the null voltage vector for each couple of large voltage vectors permits reducing the switching frequency. On the other hand, the active application time for this couple is estimated through an analytic function based on the operating point. This procedure avoids the use of an iterative process to define the duty cycles, hence significatively decreasing the computational burden.

A Modified Model Predictive Torque Control with Parameters Robustness Improvement for PMSM of Electric Vehicles

Model predictive torque control with duty cycle control (MPTC-DCC) is widely used in motor drive systems because of its low torque ripple and good steady-state performance. However, the selection of the optimal voltage vector and the calculation of the duration are extremely dependent on the accuracy of the motor parameters. In view of this situation, A modified MPTC-DCC is proposed in this paper. According to the variation of error between the measured value and the predicted value, the motor parameters are calculated in real-time. Meanwhile, Model reference adaptive control (MRAC) is adopted in the speed loop to eliminate the disturbance caused by the ripple of real-time update parameters, through which the disturbance caused by parameter mismatch is suppressed effectively. The simulation and experiment are carried out on MATLAB / Simulink software and dSPACE experimental platform, which corroborate the principle analysis and the correctness of the method.

Hybrid intelligent controller based torque ripple minimization in switched reluctance motor drive

An inherent torque ripple characterizes switched reluctance technology from conventional technology. The ultimate aim of this paper is to reduce the torque ripple of the switched reluctance motor drive using genetic neural network controller based direct torque scheme. In the proposed controller network appropriate bits of data are chosen for training and testing. The proper selection of the learning rate and momentum will help in weight adjustment. Here the error is reduced which proves that the selection of voltage vectors from the vector table is precise and its results in better torque response over a wide range of speed. The simulation results reveal that the torque ripples vary between 3.25% to 1.7% for the variation in load torque and the drive speed. The experimental results for the proposed controller reveal that the torque ripple varies between 3.7% to 2.1%. Both the simulation and hardware results illustrate the efficiency of the controller.

A finite set-model predictive control based on FPGA flatform for eleven-level cascaded H-Bridge inverter fed induction motor drive

Model predictive control has been considered as a powerful alternative control method in power converters and electrical drives recently. This paper proposes a novel method for finite control set predictive control algorithm foran induction motor fed by 11-level cascaded H-Bridge converter. To deal with the high computation volume of MPC algorithm applied for CHBconverter, 7-adjacent vectors method is applied for calculating the desired voltage vector which minimizes the cost function. Moreover, by utilizingfield programmable gate array (FPGA) platform with its flexible structure,the total execution time reduces considerably so that the selected voltage vector can be applied immediately without delay compensation. This method improves the dynamic responses and steady-state performance of the system. Finally, experimental results verify the effectiveness of control design

Performance analysis and enhancement of direct power control of DFIG based wind system

<span lang="EN-US">The paper proposes a complete modeling and control technique of variable speed wind turbine system (WTS) based on the doubly fed induction generator (DFIG). Two levels back-to-back converter is used to ensure the energy transfer between the DFIG rotor and the grid. The wind turbine to operate efficiently, a maximum power point tracking (MPPT) algorithm is implemented. Then, direct power control (DPC) strategy has been combined with the MPPT technique in order to guarantee the selection of the appropriate rotor voltage vectors and to minimize the active and reactive power errors. Finally, the simulation is performed by using MATLAB/simulink platform basing on 7.5KW DFIG wind generation system, and the results prove the effectiveness of our proposed control technique.</span>

Improved Model Predictive Current Control for Three-Phase Three-Level Converters With Neutral-Point Voltage Ripple and Common Mode Voltage Reduction

An improved two-stage model predictive current control (MPCC) for three-phase three-level converters in the paper, which can simultaneously achieve common-mode voltage (CMV) reduction, effective dc-link capacitor voltage control, and decreased computational burden, is proposed. Compared to the other current control strategies, it has the capability of handling multiple control objectives and possesses a simple structure. Furthermore, it greatly reduces the CMV since the peak CMVs of all the candidate voltage vectors are constrained to be less than one sixth of the dc-link voltage. In addition, an optimal two-stage voltage vector selection mechanism is employed in the proposed method. It helps to significantly reduce the computational complexity. Simulation and experimental results are provided to verify the effectiveness of the proposed method.

Improved Model Predictive Control With New Cost Function for Hybrid-Inverter Open-Winding PMSM System Based on Energy Storage Model

Conventional model predictive control (C-MPC) usually leads to considerable torque and current ripples since only one voltage vector is applied. In addition, the C-MPC applied in the hybrid-inverter) driven open-winding permanent magnet synchronous motor (OW-PMSM) suffers from complex tuning work of weighting factors and iterated evaluation work of all potential vectors because the capacitor voltage constraint in cost function is related to the switching states. In this article, an improved three-vector MPC based on energy storage model is proposed for the HI-OW-PMSM system. Firstly, a new prediction model of dc-link capacitor voltage based on energy storage model is proposed thus the capacitor voltage constraint is decoupled to the three-phase switching states. Furthermore, a novel restructured cost function without weighting factors can be obtained. Accordingly, by using the new prediction model and the novel cost function, the voltage reference can be easily obtained and a three-vector based prediction strategy without sector division can be carried out to achieve optimal voltage vectors selection and duty cycle calculation. Therefore, the system performance is improved and the calculation burden is also reduced. Finally, comparative experimental studies are carried out to validate the effectiveness of the proposed improved three-vector MPC method.

Parameter-Free Predictive Control of IPM Motor Drives With Direct Selection of Optimum Inverter Voltage Vectors

Parameter dependence is a drawback of the model predictive control of electric motor drives. In this article, a predictive current control (PCC) for an interior permanent magnet (IPM) motor independent of the motor parameters is presented. The motor current time-derivatives (slopes) are expressed as functions of the phase angles of the inverter basic voltage vectors. The slopes are then predicted independent of the motor parameters and are used in selecting the optimum inverter voltage vectors. In addition, a method is used for avoiding the time-consuming evaluations of a cost function to select an optimum inverter voltage vector. By this method, the reference current slopes are used for a direct optimum voltage vector selection. As a result, the control performance is improved under the parametric uncertainties and the execution time of the control code is shortened in comparison to the conventional predictive method. The effectiveness of the proposed method and its superiority over the conventional and a recently presented PCC method are confirmed through the simulation and experimental results.

Harmonics Reduction using a Modified Controller for Doubly Fed Induction Generator

This paper discusses a control system for the converter of doubly fed induction generator (DFIG) driven by wind energy. The converter of DFIG consists of two main parts; rotor side converter (RSC) and grid side converter (GSC). Two advanced control methods for GSC are presented here in this paper; vector control strategy based on pulse width modulation (PWM) and direct power control (DPC). DPC is based on switching table for voltage vector selection. In addition to grid voltage position, direct and quadrature current components are used here as inputs to the switching table instead of active and reactive powers respectively. This paper proposes a modified switching table for DPC to reduce ripples and total harmonic distortion (THD) of current produced by GSC. A Simulink model for 9 MW wind system based on DFIG is given in this paper. Simulation results are given for PWM, DPC and Proposed system for GSC. In view of THD calculations and simulation results a comparative study and conclusion are given in the end of this paper.

Model Predictive Torque Control for Multilevel Inverter fed Induction Machines Using Sorting Networks

Model Predictive Control is a promising technique for electric drive control, as it enables optimization for multiple parameters and offers reliable operation with non-linear systems. For induction machine drives it can be realized using separate cost functions for the torque and the stator flux. Although this eliminates the problem of calculating any weighting factor, the selection of the final voltage vector requires an additional sorting algorithm. By increasing the number of voltage levels or the prediction horizon, the sorting algorithm becomes more and more time-intensive, which can severely impair the performance of the control algorithm. This paper introduces a novel hybrid sorting algorithm consisting of two sorting networks and a merging step. As a case study, the described control method is applied for an induction machine with high rated frequency fed by a three-level inverter, while also discussing the implementation issues. Experimental results verify the operation of the devised sorting algorithm.

Robust Model Predictive Flux Control of PMSM Drive Using a Compensated Stator Flux Predictor

In the model predictive control of permanent magnet synchronous motor (PMSM), predictive flux control (PFC) has been widely studied because it does not need the complicated setting of weight factor. In predictive flux control, the prediction of stator flux vector is usually based on the voltage model. However, the mismatched resistance parameter and current sampling errors will lead to stator flux prediction errors, resulting in the degradation of control performance and even the system instability. To solve this problem, this paper proposes a compensated stator flux predictor based-predictive flux control (CSFP-PFC) of permanent magnet synchronous motor. In the proposed method, stator flux vector is firstly expressed at the rotor reference frame. Then, a compensated stator flux predictor is firstly constructed based on stator current prediction error. The accurate prediction of stator flux vector will ensure the selection of optimal voltage vector. Experimental results verify the effectiveness of the proposed algorithm.

Model-Free Predictive Current Control for SynRM Drives Based on Optimized Modulation of Triple-Voltage-Vector

A model-free predictive current control for synchronous reluctance motor drives based on triple-voltage-vector with optimized duty ratio modulation is presented in this paper. The proposed scheme introduces an effective and low complexity strategy of selecting candidate voltage vectors to largely reduce computational loadings. First, the basic voltage vectors are organized to apportion six regions, representing six composite switching modes. Each region comprises two active voltage vectors and a zero voltage vector modulated by distinct duty ratios. The scheme starts from the selection of an initial basic voltage vector corresponding to a predefined cost function. The second candidate voltage vector then follows, which is chosen from the region adjacent to the initial one. The third vector is a default zero voltage vector. As a result, voltage vectors outside the selected regions are excluded from the process. Moreover, the adjustable feature makes the optimization of duty ratios adaptive. Finally, the proposed method is experimentally put to tests under various operating conditions utilizing the synchronous reluctance motor drives. Experimental results are presented to demonstrate the effectiveness of the proposal.

Combinative Voltage Vector-Based Model Predictive Control for Performance Improvement of Quasi Z-Source Inverter

Model predictive control (MPC) has been commonly recognized as a promising control strategy for the quasi Z-source inverter (qZSI). However, large control error is regarded as an innate drawback of MPC due to only one voltage vector applied per control cycle. In this paper, an improved MPC, namely combinative voltage vectors based MPC, is proposed for the qZSI to reduce the control error and improve steady-state performance. Two different voltage vectors are applied in one control cycle, so that the cost function value can be reduced. The errors of the inductor current, the capacitor voltage, and the output current of the qZSI included in the cost function can be decreased greatly. Furthermore, the performance investigation of the proposed method indicates that the two selected voltage vectors consisting of a non-shoot-through vector and a shoot-through vector is of help in shorting the charge-discharge period of inductor. Thus, the inductor current ripple as well as the total harmonics distortion (THD) of the output current is greatly reduced. The experimental results show the validity and the advantages of the proposed method.

Fault-tolerant control of an open-winding brushless doubly-fed wind power generator system with dual three-level converter

To improve the fault redundancy capability for the high reliability requirement of a brushless doubly-fed generation system applied to large offshore wind farms, the control winding of a brushless doubly-fed reluctance generator is designed as an open-winding structure. Consequently, the two ends of the control winding are connected via dual three-phase converters for the emerging open-winding structure. Therefore, a novel fault-tolerant control strategy based on the direct power control scheme is brought to focus in this paper. Based on the direct power control (DPC) strategy, the post-fault voltage vector selection method is explained in detail according to the fault types of the dual converters. The fault-tolerant control strategy proposed enables the open-winding brushless doubly-fed reluctance generator (BDFRG) system to operate normally in one, two, or three switches fault of the converter, simultaneously achieving power tracking control. The presented results verify the feasibility and validity of the scheme proposed.

Comparative Analysis Methods of Direct Torque Control for Induction Motor (Dept.E)

In this article we propose two approaches to improve the direct torque control (DTC) of an aduction motor (IM) such as fuzzy logic (FL) and artificial neural network (ANN), applied in witching select voltage vector. Slaulation results of two approaches compared with those of muveantional direct torque control (DTC). The comparison results of the (FL_DTC) and (ANN DTC) illustrate the reduction in the torque and stator flux ripples. The validity of the proposed methods is confirmed by the simulative results. The two approaches are explained in clear details which are designed using SIMULINK vader Matlab Ver.7.7 software package. Also, MATLAB2008/FUZZY toolbox is used to implement the fuzzy logic coptroller. Both systems are lawlated under the same conditions

Model Predictive Control for Virtual Synchronous Generator with Improved Vector Selection and Reconstructed Current

Due to the large-scale renewable energy connected to the power grid by power electronic converters, the inertia and stability of the power grid is declining. In order to improve the inertia and support the grid recovery, the three-phase converter works as a virtual synchronous generator (VSG) to respond to the frequency and voltage changes of the power grid. This paper proposes a model predictive control for the virtual synchronous generator (MPC-VSG) strategy, which can automatically control the converter output power with the grid frequency and voltage changes. Further consideration of fault-tolerant ability and reliability, the method based on improved voltage vector selection, and reconstructed current is used for MPC-VSG to ensure continuous operation for three-phase converters that have current-sensor faults, and improve the reconstruction precision. The proposed method can respond to the frequency and voltage changes of the power grid and has fault-tolerant ability, which is easy to realize without pulse width modulation (PWM) and a proportional-integral (PI) controller. The effectiveness of the proposed control strategy is verified by experiment.

Novel model predictive direct power control strategy for grid‐connected three‐level inverters

Conventional switching table-based direct power control (DPC) usually suffers from higher power ripples due to the heuristic nature of the switching table. This study presents a novel model predictive DPC (MPDPC) strategy for grid-connected three-level inverters. In the proposed MPDPC strategy, a new synchronous frame-based predictive model is first developed and the conjugate of the complex power is then chosen as the control variable to simplify the analysis. Based on the newly developed predictive model, new principles of the voltage vector selection are further derived with the strict analytical proof to match all the control requirements, including the active and reactive power control, neutral point potential balance control, as well as the avoidance of the high voltage jumps. Finally, experimental results are provided to support the theoretical study and confirm the effectiveness of the proposed MPDPC strategy, as well as to demonstrate better performance in both steady-state and dynamic responses over the conventional DPC.

Improved Direct Torque Control Method for Dual-Three-Phase Permanent-Magnet Synchronous Machines With Back EMF Harmonics

In this article, we propose a novel switching-table-based direct torque control (ST-DTC) method to eliminate the current harmonics in dual-three-phase permanent-magnet synchronous machines due to the back electromotive force (back EMF) harmonics and voltage vector selection. By employing a novel space voltage vector selection strategy and the optimal action time for different groups of vectors, a novel ST-DTC method is developed. Furthermore, in order to implement standard pulsewidth modulation (PWM) switching sequence, a centralization PWM method for 36 voltage vectors is introduced. The proposed method can effectively reduce the phase current harmonics caused by both back EMF distortion and voltage vector selection, and still reserve the advantages of the conventional ST-DTC, such as fast torque response and simple structure. Its effectiveness is verified by simulations and experiments.

Field oriented control based on a 24-sector vector space decomposition for dual three-phase PMSM applied on electric ship propulsion

<p><span lang="EN-US">A Field Oriented Control (FOC) strategy based on a 24-Sector Vector Space Decomposition (24SVSD) technique used to control a Dual Three-Phase Permanent Magnet Synchronous Motor (DTP-PMSM) applied on electric ship propulsion prototype is presented in this paper. This machine is supplied by Dual Three-Phase Voltage Source Inverter (DTP-VSI). This study carried out on these multiphase machines has revealed that the large zero sequence harmonic current components on (z<sub>1</sub>, z<sub>2</sub>) subspace, constitutes major drawbacks; despite their advantages. The machine’s dynamic model is accomplished in three two-dimensional and orthogonal subspaces. In order to reduce more extra stator harmonic currents that produces losses, the current work is also concering of to consider the three different approaches for the sake of boosting the machine’s efficiency. Thus, the principle selection of the reference voltage vector and the time calculation method are presented in details. The proposed strategy effectiveness is validated by simulation results.</span></p>