Voltage Vector Selection Research Articles

Double Vectors Model Predictive Torque Control Without Weighting Factor Based on Voltage Tracking Error

In order to reduce the computation burden and eliminate the weighting factor in conventional model predictive torque control (MPTC), this paper proposes an improved MPTC algorithm without the use of weighting factor. Based on the deadbeat direct torque and flux control, the reference voltage vector, which would be applied in the next period, is predicted to avoid testing all feasible voltage vectors, hence reducing the computation burden of conventional MPTC. Moreover, the torque and flux error-based cost function of conventional MPTC is replaced by the voltage vector tracking error-based cost function; thus, the weighting factor of stator flux in conventional MPTC, which is always necessary because of the different units between torque and flux, is eliminated. Furthermore, two voltage vectors, which include an active vector and a null vector, are applied during one control period to improve steady-state performance. The durations of the selected voltage vectors are determined based on the principle of voltage vector tracking error minimization. Moreover, to further improve the steady-state performance, a different vector selection way, in which the second voltage vector is not fixed as a null vector but selected in a border range, is introduced. The selection process of candidate voltage vectors is analyzed, and the duration is calculated. Simulation and experimental results both show the validity of the proposed control approach.

Torque‐ripple reduction of SRM using optimised voltage vector in DTC

High torque ripple is inherent in switched reluctance motors (SRMs) because of the motor's doubly salient structure and highly non-uniform torque and magnetisation characteristics. Direct torque control (DTC) for SRM is one of the torque ripple reduction strategies which gets wide attention for its simpleness and effectiveness. In this study, aiming at the torque ripple phenomenon of DTC for SRM, a novel method for torque-ripple reduction is proposed. With the new methods, sector zones were redivided into 9 and 12 sector zones based on six sector zones and new control rules were adopted. Consequently, the proposed methods make the selection of voltage vector more precise. A 12/8-pole three-phase SRM drive system was designed to verify the effectiveness of the proposed new methods. The results verified that the improved DTC algorithms with 9 and 12 sector zones could indeed minimise the torque ripple to a great extent.

High Performance Direct Torque Control of Induction Motor Drives: Problems and Improvements

This paper presents some of the main problems, as well as their root causes, of Direct Torque Control (DTC) 3-phase induction motor drive. The high torque ripple in DTC drive due to the hysteresis controller inevitably becomes worst with the discrete implementation of the drive system. The hysteresis controller also causes variable switching frequency that depends on operating conditions, especially the speed. The simplification used in stator flux expression for voltage vectors selection in flux control results in a poor flux regulation at low speed. To overcome these problems, techniques that have been implemented at UTM-PROTON Future Drive Laboratory (UPFDL) are presented and described. Some experimental results obtained from the previous works are also presented and discussed.

Constant Switching Frequency and Torque Ripple Minimization of DTC of Induction Motor Drives with Three-level NPC Inverter

<p>Direct Torque Control (DTC) is widely applied for ac motor drives as it offers high performance torque control with a simple control strategy. However, conventional DTC poses some disadvantages especially in term of variable switching frequency and large torque ripple due to the utilization of torque hysteresis controller. Other than that, performance of conventional DTC fed by two-level inverter is also restricted by the limited numbers of voltage vectors which lead to inappropriate selection of voltage vectors for different speed operations. This research aims to propose a Constant Switching Frequency (CSF) torque controller for DTC of induction motor (IM) fed by three-level Neutral-Point Clamped (NPC) inverter. The proposed torque controller utilizes PI controller which apply different gain for different speed operation. Besides, the utilization of NPC inverter provides greater number of voltage vectors which allow appropriate selection of voltage vectors for different operating condition. Using the proposed method, the improvement of DTC drives in term of producing a constant switching operation and minimizing torque ripple are achieved and validated via experimental results.</p>

Optimal Voltage Vector Selection Method for Torque Ripple Reduction in the Direct Torque Control of Five-phase Induction Motors

Optimal Voltage Vector Selection Method for Torque Ripple Reduction in the Direct Torque Control of Five-phase Induction Motors

Reconfiguration of T-Type Inverter for Direct Torque Controlled Induction Motor Drives Under Open-Switch Faults

This paper identifies possible topological reconfigurability of a T-type inverter for direct torque controlled (DTC) induction motor drives when an open-switch fault occurs. In open-switch fault, inverter current path is different than normal path. This causes undesirable inverter switching states. Since DTC is based on a voltage vector selection criterion, open-switch fault causes ambiguous torque control. Analysis of DTC drive under two different inverter open-switch fault conditions viz. half-bridge and neutral-point switch fault are presented. The operation of the inverter in DTC mode against faults is achieved by simple topological reconfiguration.

Deadbeat Model-Predictive Torque Control With Discrete Space-Vector Modulation for PMSM Drives

This paper proposes an alternative strategy of finite-control-set model-predictive torque control (MPTC) to reduce the computational burden and the torque ripple and decouple the switching frequency from the controller sampling time. An improved discrete space-vector modulation (DSVM) technique is utilized to synthesize a large number of virtual voltage vectors. The deadbeat (DB) technique is used to optimize the voltage vector selection process, avoiding enumerating all the feasible voltage vectors. With this proposed method, only three voltage vectors are tested in each predictive step. Based on the improved DSVM method, the three candidate voltage vectors are calculated by using a novel algebraic way. This new strategy has the benefits of both the MPTC method and the DB method. The effectiveness of the proposed strategy is validated based on a test bench.

Improved Direct Power Control of Shunt Active Power Filter with Minimum Reactive Power Variation and Minimum Apparent Power Variation Approaches

Direct Power Control technique has become popular in the grid connected Voltage Source Converter (VSC) applications due to its simplicity, direct voltage vector selection and improved dynamic performance. In this paper, a direct method to determine the effect of voltage vector on the instantaneous active and reactive power variations is developed. An alternative Look Up Table is proposed which minimizes the commutations in the converter and results in minimum reactive power variation. The application of suggested table is established for Shunt Active Power Filter (SAPF) application. The Predictive Direct Power Control method, which minimizes apparent power variation, is further investigated to reduce commutations in converters. Both the methods are validated using 2 kVA laboratory prototype of Shunt Active Power Filters (SAPF).

Torque Ripple Reduction in Direct Torque Control of Five-Phase Induction Motor Using Fuzzy Controller with Optimized Voltage Vector Selection Strategy

This paper presents a torque ripple reduction method of direct torque control (DTC) using fuzzy controller with optimal selection strategy of voltage vectors in a five-phase induction motor. The conventional DTC method has some drawbacks. First, switching frequency changes according to the hysteresis bands and motor's speed. Second, the torque ripple is rapidly increased in long control period. In order to solve these problems, some/most papers have proposed torque ripple reduction methods by using the optimal duty ratio of the non-zero voltage vector. However, these methods are complicated in accordance with the parameter. If this drawback is eliminated, the torque ripple can be reduced compared with conventional method. In addition, the DTC can be simply controlled without the use of the parameter. Therefore, the proposed algorithm is changing the voltage vector insertion time by using the designed fuzzy controller. Also, the optimized voltage vector selection method is used in accordance with the torque error. Simulation and experimental results show effectiveness of the proposed control algorithm.

Reduction of Common-Mode Voltages for Five-Level Active NPC Inverters by the Space-Vector Modulation Technique

In this paper, a novel space-vector pulse-width modulation (PWM) scheme for reducing the common-mode voltage (CMV) in the three-phase five-level active neutral-point clamped (5L-ANPC) inverter is proposed, where only the 55 selected voltage vectors among the entire 125 that produce low values of the CMV are utilized. This PWM scheme can significantly reduce the CMV without the increase of switching losses and total harmonic distortion of the output voltages. With the 55 selected voltage vectors, the inverter can still operate up to the maximum modulation index. In addition, the capacitor voltages are controlled by redundant switches of the 5L-ANPC inverters. It has been shown that the peak value of the CMV is decreased to one-twelfth of the dc-link voltage from the simulation and experimental results.

Improvements in direct torque control of induction motor for wide range of speed operation using fuzzy logic

The main objective of this paper is to ameliorate the performance of direct torque control of induction motor for a wide range of speed control using fuzzy logic. The major drawbacks of conventional direct torque control are high torque, flux ripples and poor dynamic response at low speed. In this paper the CDTC is improved by fuzzy logic switching controller and fuzzy logic duty cycle controller. In FDTC with FDCC the selected voltage vector is applied only for the duty cycle time period (δ) determined. Simulation results validate that the proposed scheme shows improved dynamic performance of the drive for a wide range of speed (0–100rad/s) and the torque and flux ripples are reduced by 90% compared to CDTC.

Finite-State Model Predictive Current Control for Surface-Mounted Permanent Magnet Synchronous Motors Based on Current Locus

Finite-state model predictive control (FS-MPC) is computationally expensive, as it uses all voltage vectors available for prediction and estimation. This paper proposes a novel finite-state model-based predictive current control (MPCC) scheme to overcome the drawbacks of FS-MPC. A reference frame based on the prediction of the current locus when a zero-voltage vector is employed is established to reduce the computational requirements; specifically, only one zero-voltage vector must be predicted compared with the seven required in conventional FS-MPC. The selection of the optimal voltage vector is based on the direction of the current locus in the established reference frame instead of a cost function, which is necessary and time consuming in conventional FS-MPC. Zero-voltage vectors are also selected by contrasting the distance between the reference and predictive currents to reduce the torque ripple of the proposed method. Simulation and experimental results are presented and confirm the efficient performance of the proposed MPCC.

Direct Torque Control of Induction Motor with Common-Mode Voltage Elimination

If the common-mode voltage in the induction motor drive is not eliminated, it may cause failure of motor bearings and malfunctioning of the electrical equipment associated with the drive. This article proposes the modified direct torque control technique to control the induction motor fed by three-level inverter, commonly called a neutral-point-clamped inverter. The selective voltage vectors in three-level inverter determine elimination of the common-mode voltage. The classic three-level direct torque control based on selection of 6-full, 6-half, and 2-zero voltage vectors out of available 27 is modified so that the 6-intermediate voltage vectors and a zero voltage vector are employed. A comparative investigation with another three-level direct torque control method which reduces both common-mode voltage and torque ripple is also carried out. These methods are compared with classic two-level direct torque control method in context of common-mode voltage, torque ripple, current total harmonic distortion (THD) and DC-link utilization. The simulation and experimental results validate the proposed common-mode voltage elimination and common-mode voltage reduction direct torque control techniques.

Selection of Voltage Vectors in Three-Level Five-Phase Direct Torque Control for Performance Improvement

This paper presents a Direct Torque Control (DTC) strategy for the five-phase induction motor driven by a three-level five-phase inverter in order to improve the performance of the five-phase induction motor. In the proposed DTC technique, only 22 voltage vectors out of 243 available voltage vectors in a three-level five-phase inverter are selected and are divided in 10 sectors each with a width of <TEX>$36^{\circ}$</TEX>. The four different DTC combinations (DTC-I, II, III and IV) for a three-level five-phase induction motor drive are investigated for improving the performance of five-phase induction motor. All four of the DTC strategies utilize a combination of the same large and zero voltage vectors, but with different medium voltage vectors. Out of these four techniques, DTC-II gives the best performance when compared to the others. This DTC-II technique is analyzed in detail for improvements in the performance of five-phase induction motor in terms of torque ripple, x-y stator flux and Total Harmonics Distortion (THD) of the stator phase current when compared to its two-level counterparts. To verify the effectiveness of the proposed three-level five-phase DTC control strategy, a DSP based experimental system is build. Simulation and experimental results are provided in order to validate the proposed DTC technique.

Switching losses minimization by using direct torque control of induction motor

Direct torque control is becoming the industrial standards for induction motor torque control. This paper presents switching loss minimization technique of improved direct torque control (DTC) of induction motor. Direct torque control (DTC) of an induction motor supplied by a voltage source inverter is a simple scheme that does not need long computation time, can be implanted without speed sensors and is insensitive to parameter variations. In principle, the motor terminal voltages and currents are used to estimate the motor flux and torque. Based on the instantaneous errors in torque and stator flux magnitude and estimates of the flux position, a voltage vector is selected to limit the flux and torque errors within their flux and torque hysteresis bands. In the conventional DTC, the selected voltage vector applies for the whole switching period, irrespective of the magnitude of the torque error. DTC drive gives variable switching frequency and high torque ripple. DTC gives torque and flux ripples because no any VSI states are capable to generate the exact voltage vector from switching table required to make zero both the torque electromagnetic error and the stator flux error. To minimize this problem, a torque hysteresis band with variable amplitude fuzzy logic controller is proposed. The fuzzy logic controller is used to reduce the flux and torque ripples and it improves performance DTC especially at low speed. A duty ratio control scheme for an inverter-fed induction machine using DTC method is presented in this article. The use of the duty ratio control gives improved steady state torque response, with less torque ripple than the conventional DTC. Fuzzy logic control (FLC) used to implement the duty ratio controller. Total harmonic distortion (THD) calculation of electromagnetic torque, rotor speed and stator current of DTC and DTC with fuzzy has done successfully in this article. With the help of FLC with duty ratio, 8% THD in torque, speed and stator current have minimized compared with DTC (Uddin and Hafeez, 2012). In this paper, switching loses minimization technique through THD minimization. Switching losses are minimized because the transistors are only switched when it is needed to keep torque and flux within their hysteresis bounds, improve efficiency & reduced losses. Direct torque control with the fuzzy logic controller has verified by MATLAB SIMULINK and experimentally.

Predictive current control in multifunctional grid connected inverter interfaced by PV system

This study deals with a three-phase double-stage multifunctional grid-connected inverter interfaced with a photovoltaic system. The studied system consists of a photovoltaic array, a dc-dc boost converter and a three-phase voltage source inverter connected to the utility at the point of common coupling. To ensure the multifunctional feature, we propose a predictive current control which uses a discrete-time model of the system to predict the future value of the filter current for different voltage vectors. Selection of the optimal voltage vector aims to minimize the error between reference and predicted current by using a cost function. Then, perturb and observe Maximum Power Point Tracking is applied to the dc-dc boost converter to extract maximum power from the photovoltaic array. The main benefits of the proposed system are: harmonic and reactive current elimination, reactive power compensation and feeding photovoltaic power into the utility. The proposed control algorithm is performed on a Matlab⧹Simulink™ environment, simulation and experimental results confirm the effectiveness of the proposed control method in term of total harmonic distortion and power factor correction. The performance of the proposed control has been compared with hysteresis and direct power control strategies. Dynamic state results show that the proposed method provides a better performance and more stability under fast environmental conditions changing than hysteresis current control.

Dynamic Performance Evaluation of a Nine-Phase Flux-Switching Permanent-Magnet Motor Drive With Model Predictive Control

Multiphase flux-switching permanent-magnet (FSPM) motor drives are nowadays considered for various applications due to numerous advantages when compared with their three-phase counterparts. In principle, stator-flux-oriented control of a nine-phase flux-switching permanent-magnet (FSPM) (9P-FSPM) motor can be realized theoretically by using four pairs of synchronous current controllers in conjunction with eight conventional proportional-integrals (PIs), for alleviation of the coupling effects and unwanted low-order stator current harmonics. In practice, however, drive performance will deteriorate if the PI-based current controller is not well tuned for optimum response to every dynamic scenario due to nonlinearity. In order to enhance dynamic performance of the drive system, a fully-decoupled model predictive control algorithm with fixed switching frequency is developed for the 9P-FSPM motor. The main contribution is comprehensive and detailed description of precise modeling of the 9P-FSPM motor and the controller design process. Also, some practical hints are given for implementation, such as the elimination of low-order harmonic currents and the selection of active voltage vector in the nine-phase drive system. Both simulation and experimental results are presented to validate the effectiveness of the developed current controller and the high dynamic performance of the 9P-FSPM motor drive.

A Direct Thrust Control Scheme for Linear Permanent Magnet Synchronous Motor Based on Online Duty Ratio Control

Linear permanent magnet synchronous motors, especially those with low inductance and short pole pitch, exhibit significant ripple in flux and thrust force under conventional direct thrust force control. Aimed at reducing ripple in the flux and the force, a duty ratio control scheme for direct thrust force control of linear permanent magnet synchronous motors is proposed. The effect of inverter voltage vectors on the flux and the thrust force is analyzed. Subsequently, a precise expression for the online computation of the required duty ratio is derived. Compared to the state-of-the-art duty ratio control, the proposed approach eliminates the need to tune gains. The proposed online duty ratio calculation is based on the selected voltage vector from the switching table and takes into account the mover's speed. The proposed approach retains the characteristics of the conventional direct thrust control in terms of fast transient and steady-state responses for both flux and thrust force. Experimental results demonstrate a faster transient response and negligible steady-state error for flux, force, and speed responses under the proposed approach when compared to the state of the art.

Vector selection approach‐based hexagonal hysteresis space vector current controller for a three phase diode clamped MLI with capacitor voltage balancing

The purpose of this study is to provide a broad idea about current control scheme and equilibrating voltages in DC-link capacitors of the neutral-point clamped multilevel inverter (NPC-MLI), using an innovative hexagonal space vector hysteresis current control (SVHCC) scheme. The main ideology is to force the literal current vector to reach the reference current vector through an appropriate voltage vector selection sequence. This proposed scheme defines two hexagonal hysteresis bands encompassing the error vector, as a first step. With respect to the error vector location, the selection of the adjacent vector is acted to minimise the error vector. In addition to the error vector selection, the capacitor voltage is also equilibrated by controlling the degree of freedom available in selecting the switching vectors. The SVHCC scheme is intelligent in performing modulation depth dependent selection of switching vectors between the groups namely closest three vector and preferred three vector (PTV). This scheme balances the DC-link capacitors’ voltages within a tolerance limit for any value of modulation index. The proposed scheme is asserted through MATLAB/Simulink software. The superiority of the proposed technique is validated through the 2 kW NPC-MLI supported with SPARTAN III 3AN –XC3S400 field programmable gate array.

Minimizing Torque and Flux Ripples and Improving Dynamic Response of PMSM Using a Voltage Vector With Optimal Parameters

In this paper, a new predictive direct torque control (DTC) method is proposed, which improves the dynamic response of the conventional DTC in the transient state and yields the minimum torque and flux ripples in the steady state through an optimal voltage vector. At the steady state, the magnitude, phase, and time duration of the voltage vector are adjusted in a manner where the minimum torque and flux ripples are obtained; whereas in the transient state, the voltage vector parameters are adjusted in a manner where the fastest dynamic response is achieved. The space-vector modulation is used in synthesizing the selected voltage vector where a fixed switching frequency is achieved. In order to improve the control system efficiency, the principle of maximum torque per ampere is adopted in obtaining the commanding stator flux magnitude. To investigate the effectiveness of the proposed method, the steady-state and transient-state performances are tested in MATLAB software and in practice. The simulation and experimental results confirm that the proposed method yields the minimum torque and flux ripples while improving the dynamic response of the conventional DTC. The comparative investigation with an existing predictive DTC method indicates that the proposed method has a better performance in both the steady state and transient state.