Voltage Vector Selection Research Articles

An Improved Direct Torque Control of Three-Level Dual Inverter Fed Open-Ended Winding Induction Motor Drive Based on Modified Look-Up Table

The induction motor (IM) drive with direct torque control scheme (DTC) turns prominent for industrial applications. However, it retains disadvantage of high torque ripples. The conventional look-up table for DTC scheme is structured with selection of reverse voltage vectors (VVs) when flux and torque errors crosses lower hysteresis boundary condition. This results in higher torque ripples and increase in switching frequency. In this article, modified look-up table for DTC of three-level dual voltage source inverter fed open-ended winding IM drive is proposed, where the VVs selection for lower hysteresis boundary conditions of torque and flux are restructured with null voltage states. The selection of suitable null voltage switching states from the various possible combinations of dual inverter switchings is based on minimization of switching state transitions. To nullify flux instability at zero speed, proper active VVs are placed at hysteresis flux +1 and torque 0 condition in the modified look-up table. These overall effective modifications in the proposed DTC scheme enjoys the benefits of reduction in torque ripple, switching frequency, and stable flux maintenance. The MATLAB simulations and practical investigations are conducted for existing and proposed DTC schemes. From these results, the benefits of the proposed DTC over existing DTC schemes are verified.

Predictive direct torque control for permanent-magnet synchronous machines based on duty ratio modulation

In this paper, Two-step model predictive control based on duty ratio modulation of permanent magnet synchronous machine (PMSM) is proposed. There is a large amount of computation in the two-step predictive control. In this paper, a fast vector selection method is proposed to solve the problem of computational complexity. The proposed voltage vector selection method avoids the complete enumeration for testing all feasible voltage vector, and the calculation method of duty are discussed. This control method achieves a constant switching frequency, and the torque fluctuation is smaller, inheriting the advantages of predictive control response speed. To investigate the effectiveness of the proposed method, two-step predictive direct torque control based on duty ratio modulation (TSPTC-DM), comparison of one-step predictive direct torque control based on duty ratio modulation (OSPTC-DM) and finite control set model predictive torque control (FCS-MPTC) is shown.

Predictive Torque Control for PMSM Based on Weighting Factor Elimination and Fast Voltage Vector Selection

In this article, an improved predictive torque control (PTC) for permanent magnet synchronous motor (PMSM) based on weighting factor elimination and fast voltage vector selection is proposed to improve the problems of tedious tuning of weighting factor and heavy computation burden in the conventional PTC. First, a universal scheme, which can be applicable to both surface-mounted PMSM (SPMSM) and interior PMSM (IPMSM), is proposed to convert the control of electromagnetic torque and stator flux amplitude to the control of stator flux vectors. Since the units of stator flux vectors are the same, the weighting factor in the cost function can be eliminated. Second, the control of stator flux vectors is further converted to the control of stator voltage vectors. On this basis, a fast voltage vector selection scheme based on a graphical analysis method is proposed to pick out the one nearest to the reference stator voltage vector among all the candidate voltage vectors in the finite control set (FCS) directly. Therefore, the computation burden of the proposed PTC strategy can be reduced greatly owing to the elimination of the online rolling optimization. The feasibility and effectiveness of the proposed strategy are verified by simulations and experiments.

Improved Deadbeat FC-MPC Based on the Discrete Space Vector Modulation Method with Efficient Computation for a Grid-Connected Three-Level Inverter System

The utilization of three-level T-type (3L T-type) inverters in finite set-model predictive control (FS-MPC) of grid-connected systems yielded good performance in terms of current ripples and total harmonic distortions. To further improve the system’s performance, discrete space vector modulation (DSVM) was utilized to synthesize a higher number of virtual voltage vectors. A deadbeat control (DBC) method was used to alleviate the computational burden and provide the optimum voltage vector selection. However, 3L inverters are known to suffer from voltage deviation, owing to the imbalance of the neutral-point voltage. We have proposed a simplified control strategy for balancing the neutral point in the FS-MPC with DSVM and DBC of grid-connected systems, not requiring a weighting factor or additional cost function calculation. The effectiveness of the proposed method was validated using simulation and experiment results. Our experimental results show that the execution time of the proposed algorithm was significantly reduced, while its current quality performance was not affected.

An improved model predictive control of low voltage ride through in a permanent magnet synchronous generator in wind turbine systems

AbstractThis research investigates a wind energy conversion system based on a permanent magnet synchronous generator (PMSG). In addition, a model predictive control (MPC) is proposed for the PMSG in normal and fault conditions. The most efficient mode of the control algorithm is found for maximum power point tracking in normal conditions and fast dynamic response in fault conditions following the selection of the optimum voltage vector. This method prevents a sudden increase in the DC‐link voltage by storing the active power in the generator rotor inertia. Moreover, during the low voltage, the grid code adoption of the reactive current is injected into the grid side. The performance of the proposed control scheme is evaluated for a wind power generator using MATLAB software. The simulation results demonstrate that the proposed method can safeguard the DC‐link during the fault.

A Novel Space-Vector Modulation Method for Nine-Switch Converter

Nine-switch converter (NSC) has been presented as a dual-output converter with common frequency (CF) or different frequency (DF) operation modes. This paper proposes a novel space-vector modulation (SVM) method for the NSC that supports both the CF and DF modes. This method is based on the simplification of the space-vector diagram of NSC into that of six-switch converter, and the SVM method for NSC can be done like conventional SSC. The proposed voltage vector selection method without using common logical xor operation and the calculation method for dwelling times of voltage vectors are described in detail. In addition, the modulation indices for two ac terminals of NSC have been analyzed deeply, and the derived fitting equations can guide engineering application. The performance of the proposed SVM is verified by the simulation and experimental results, and the low total harmonic distortions and harmonic components for phase currents prove the effectiveness of the proposed method.

Performance enhancement in a multilevel inverter fed PTC induction motor drive by optimal voltage vector selection

<p>This paper proposes a novel predictive control strategy for a multilevel inverter fed Induction Motor Drive (IMD) with optimal voltage vector selection at every sampling interval. The proposed predictive control strategy, apart from enhancing the dynamic speed and torque responses of the drive, strives to reduce the number of switching transitions by choosing optimal voltage vector, thereby reducing the switching losses significantly. The algorithm put forth here chooses the most suitable switching state among the redundant switching combinations, such that minimum number of switches change their states from the previous switching combination to the present one. This results in perceptible reduction in the switching losses thereby increasing the efficiency of the converter. The proposed Predictive Torque Control (PTC) strategy is modeled and simulated in Matlab/ Simulink environment and the results are reported for a 2-level and 3-level inverter fed IMD configurations. The results demonstrate the effectiveness of the proposed PTC for both 2-level and 3-level inverter fed IMDs.</p>

Model Predictive Thrust Force Control of a Linear Flux-Switching Permanent Magnet Machine With Voltage Vectors Selection and Synthesis

To reduce the thrust force ripple of a complementary and modular linear flux-switching permanent magnet machine, a model predictive thrust force control (MPTFC) is developed and implemented in this paper based on the active voltage vectors selection (AVVS) and two-voltage-vector synthesis (TVVS). First, the active voltage vectors are screened and assigned to the specific sector, instead of traversing all the possible vectors, and consequently, significantly decrease prediction workload. Second, for the elimination of the weighting factor in the conventional MPTFC, the control object is transformed from the thrust force and stator flux to the stator flux only by using the load angle. Third, to achieve the steady-state performance improvement, the TVVS approach is applied in each control period, where the optimal TVVS and its dwell time are simultaneously obtained by only one cost function. Both simulated and experimental results verify that the steady-state performance improvement can be realized by the developed MPTFC through comparing with normal hysteresis current control and conventional MPTFC strategies.

A Simplified Predictive Torque Control Scheme for Open-End Winding Induction Motor Drive

Variable speed induction motor (IM) drives with predictive torque control (PTC) technique is an advancing technology nowadays. The PTC technique is introduced for dual-inverter fed open-end winding IM (OEWIM) configuration owing to its benefits. The conventional PTC requires flux weighting factor assignment because of two different control objectives (torque and flux) in single cost function. This weighting factor selection plays a key role in selecting optimal voltage vector for better torque and flux response. Several analytical and empirical methods are introduced for optimal selection of weighting factor, which demands more computation time. This paper aims to develop modified PTC, eliminating flux weighting factor. The flux control objective is replaced by an equivalent reactive torque control. Thus making two control objectives of the same units and eliminating the requirement of flux weighting factor in cost function. Furthermore, nearest voltage vector selection strategy is introduced to limit the number of prediction voltage vectors in each sampling period. Thus, overall computational burden is reduced achieving minimum torque and flux ripples. The performance of the proposed PTC for multilevel inversion fed OEWIM is evaluated through MATLAB/Simulink simulations and experimental analysis. To highlight its benefits, these results are compared with those of the conventional and recent PTC techniques.

Study on the fuzzy proportional–integral–derivative direct torque control strategy without flux linkage observation for brushless direct current motors

Considering the difficulty in setting and observing the flux linkage in the existing direct torque control for the brushless direct current motor, which is the cumbersome torque calculation method in direct torque control systems without flux linkage observation, the torque observation, voltage vector selection, and speed loop were studied further in such systems. The fuzzy proportional–integral–derivative direct torque control strategy is presented without flux linkage observation. In terms of torque observation, the cumbersome counter electromotive force calculation method was abandoned, and observation was made combining the three-phase current and Hall signal. In terms of optimal choice of voltage vector, the voltage vector selection table was built using the voltage hysteresis output and Hall signal. In terms of rotation speed control, the adaptive fuzzy proportional–integral–derivative was used to replace the traditional proportional–integral–derivative for the proportional–integral–derivative parameter self-adjustment. A control system simulation model was set up in MATLAB/Simulink for simulation verification. A hardware experimental platform was set up using DSP2812 as the main control board for experimental verification. The research results show that the fuzzy proportional–integral–derivative direct torque control without flux linkage observation further increased the dynamic response rate of the motor speed and reduced the electromagnetic torque ripple amplitude; thus, it is more suitable for application in high-precision and high-stability systems.

A Novel Vector Control Strategy for a Six-Phase Induction Motor with Low Torque Ripples and Harmonic Currents

In this paper, a new vector control strategy is proposed to reduce torque ripples and harmonic currents represented in switching table-based direct torque control (ST-DTC) of a six-phase induction motor (6PIM). For this purpose, a new set of inputs is provided for the switching table (ST). These inputs are based on the decoupled current components in the synchronous reference frame. Indeed, using both field-oriented control (FOC) and direct torque control (DTC) concepts, precise inputs are applied to the ST in order to achieve better steady-state torque response. By applying the duty cycle control strategy, the loss subspace components are eliminated through a suitable selection of virtual voltage vectors. Each virtual voltage vector is based on a combination of a large and a medium vector to make the average volt-seconds in loss subspace near to zero. Therefore, the proposed strategy not only notably reduces the torque ripples, but also suppresses the low frequency current harmonics, simultaneously. Simulation and experimental results clarify the high performance of the proposed scheme.

Study on a Novel Predictive Torque Control Strategy Based on the Finite Control Set for PMSM

In this paper, a novel predictive torque control (PTC) strategy based on the finite control set for the permanent magnet synchronous motor (PMSM) was proposed to overcome the large flux and torque ripples of the traditional direct torque control (TDTC). First, in the PTC, the complete decoupling of the stator flux and torque in the stator flux coordinate system enables a simpler PTC. Second, compared with the traditional predictive torque control (TPTC), using the magnitude comparison of the flux and torque errors, the selected voltage vector for each control cycle was reduced from eight to one, which greatly reduces the computation and complexity. What is more, the duty cycle modulation was used to fix the switching frequency to solve the problem that the switching frequencies of TDTC and TPTC are not fixed. Finally, the simulation results verified the superiority of PTC in reducing the torque and flux ripples.

Improved DTC strategy of doubly fed induction motor using fuzzy logic controller

Abstract This paper presents an improved Direct Torque Control (DTC) strategy for a Doubly Fed Induction Machine (DFIM) powered by two voltage source inverters (VSI) at two levels. This strategy is based on the fuzzy logic controller. The main objective is to improve the performance of the system by reducing electromagnetic torque ripples and improving the currents shape by optimization of the total harmonic distortion (THD). The hysteresis regulators and voltage vectors selection table of the conventional DTC are replaced by fuzzy logic blocks to realize fuzzy DTC control. The two control strategies are simulated in the MATLAB/SIMULINK environment followed by a comparative analysis to validate the effectiveness of the proposed strategy. Many improvements in term of rise time, torque ripples, flux ripples and current harmonics have been done, namely stator and rotor flux ripple and torque ripple have been reduced more than 50%, 69.2% and 47.7% respectively. The stator and rotor currents THD have been reduced around 84.5% and 84.3% respectively.

A Modified Sensorless Control Scheme for Interior Permanent Magnet Synchronous Motor Over Zero to Rated Speed Range Using Current Derivative Measurements

This paper proposes a modified sensorless control technique for an interior permanent magnet synchronous motor over its full-speed range based on current derivative measurements and fundamental pulsewidth modulation excitation (FPE). The proposed method employs measurement of the current derivative at only one active-voltage vector at low speeds, and at one active-voltage vector and one zero-voltage vector at medium and high speeds during each pulsewidth modulation (PWM) cycle, in contrast to two active- and two zero-voltage vectors in the conventional FPE method. The theoretical analysis is developed based on the three-phase model of the machine. The rotor position and speed are estimated at PWM frequency. In addition, the selection voltage vectors for current derivative measurement as well as the pulse stretching scheme for extending and compensating the selected voltage vectors is proposed in order to improve the accuracy of the current derivative measurement and to minimize the current distortion. The experimental results show that the proposed method results in a considerable improvement of the estimation accuracy at low speeds, a significant reduction of current distortion compared to the conventional FPE method and a full-speed range operation from no load to full load.

Modeling, Analysis and Evaluation of Modified Model Predictive Control Method for Parallel Three-Level Simplified Neutral Point Clamped Inverters

Parallel three-level simplified neutral point clamped inverters (3L-SNPCIs) are applied in this paper because of fewer switching devices, low harmonic, larger power capacity and more flexibility. However, the challenge of zero-sequence circulating current (ZSCC) is inevitable, which causes the output current distortion and system instability. The conventional control and modulation methods introduced by far cannot solve them properly due to the limitations of fewer voltage vectors selection. To overcome these limitations, a modified model predictive control (MMPC) strategy is proposed based on the discrete mathematical model of parallel 3L-SNPCIs. The MMPC strategy realizes circulating current suppression and neutral-point voltage balancing by selecting P-type or N-type small voltage vector. In addition, the control objectives are optimized and the implementation is simplified, which can reduce the burden of calculation and reserve the advantages of the conventional model predictive control (MPC) algorithm. The proposed control strategy can be flexibly extended to parallel multilevel inverters. The efficiency of the proposed method is proved by simulation and experimental results under various conditions.

Torque and Flux Ripples Minimization of Permanent Magnet Synchronous Motor by a Predictive-Based Hybrid Direct Torque Control

This paper proposes a hybrid control strategy for a permanent magnet synchronous motor (PMSM) drive based on a finite-set predictive control (FS-PC). The most efficient mode of the control algorithm is found for the minimum torque and flux ripple in a steady state, with fast dynamic responses, as well as the conventional direct torque control (DTC), following the selection of an optimum voltage vector. The rationale of the proposed control method is that it is composed of DTC and a FS-PC. On the other hand, the optimization process is carried out using a combination of DTC and FS-PC. Compared with the conventional model predictive control methods, the proposed method adopts a measure like that of DTC to reach the optimal switching state of the inverter by minimizing the cost function. However, the method has a simple computational function for such a purpose. Taking into account the simulation and experimental results, it can be stated that the proposed method, which uses hybrid strategy, has high dynamic responses to the lower torque and the flux ripples with a simple structure and implementation, indicating the validity of this method for PMSM drive.

A Computationally Efficient FCS-MPC Method Without Weighting Factors for NNPCs With Optimal Duty Cycle Control

In this paper, a computationally efficient finite control-set model predictive control (FCS-MPC) method without weighting factors is proposed for nested neutral point-clamped converters (NNPCs) with optimal duty cycle control. The aim of this paper is to design a modification of the FCS-MPC scheme that improves the steady-state performance, as well as to avoid the weighting factors selection while remaining computationally feasible. First, in order to improve the calculation efficiency, a simplified computational method is proposed by introducing the Lyapunov principle into the design of sector distribution method based on space vector modulation technique, and eliminates unwanted switching states. Second, aiming at improving the steady-state control performance, an optimal duty cycle control technique is incorporated into the proposed FCS-MPC strategy to determine the time duration of the selected voltage vector. In that sense, a new FCS of candidate voltage vectors with different duty cycles are synthesized without sacrificing the simplicity of the control structure. Besides, in order to avoid the selection of weighting factors, the proposed method replaces the single cost function with simplified multiobjective optimization strategy based on a fuzzy-decision-making method. Finally, the performance of the proposed strategy for NNPCs is evaluated by simulation studies in various operating conditions.

Modified MPC with extended VVs for grid‐connected rectifier

This article presents an alternative finite control set model predictive control (FCS-MPC) implementation to reduce the input current ripple of a two-level three-phase grid-connected rectifier. With the proposed approach, an improvement in the input current ripple is obtained by integrating the virtual vectors in the conventional FCS-MPC structure. The synthesis of the virtual vector is conceptualised from the discrete space vector modulation approach which combines several switching states during the sampling period to create new virtual voltage vectors. However, with this approach, the number of voltage vectors becomes higher, making it challenging to implement this algorithm in a standard control platform. To overcome this problem, a two-stage optimisation method is proposed to optimise the voltage vector selection process, avoiding evaluating all the feasible voltage vectors without any performance sacrifice. Experimental results are presented; showing that the proposed technique provides lower input current ripple compared to the conventional FCS-MPC with an acceptable computational effort.

An improved finite control-set model predictive control for nested neutral point-clamped converters under both balanced and unbalanced grid conditions

Finite control-set model predictive control (FCS-MPC) is an alternative strategy, in particular, for multi-level converters. However, the computational burden is rapidly increased with the number of voltage vectors to be predicted and objectives to be controlled. This will hinder the development of the FCS-MPC strategy. In this paper, an improved FCS-MPC is proposed for nested neutral point-clamped converters (NNPCs) under both balanced and unbalanced grid conditions. Specifically, to reduce the computational burden, an optimized voltage vector selection process based on deadbeat technique is embedded into the proposed design. Meanwhile, a simplified cascade-free control strategy is presented to directly govern the DC-link voltage and reactive power in NNPCs while the flying capacitor voltages are maintained balanced. Moreover, the inclusion of a power compensation approach is presented for the FCS-MPC method in an attempt to obtain desired grid-side currents under nonideal grid-side voltage conditions. The novelty of this work lies not only in a compatible reference design that directly allows to formulate the optimal control problem using a simplified cascade-free control strategy, but also in the utilization of combining the proposed FCS-MPC and the power compensation technique for suppressing the distorted grid-side currents under unbalanced grid conditions. The performance of the proposed strategy for NNPCs is evaluated by simulation studies in various operating conditions.

A Novel Model Predictive Control of Cascade Multilevel Inverter for Solar PV System

In this paper, an improved finite control set model predictive control(FCS-MPC) applying to solar PV system is proposed. Calculation grows exponentially when voltage level increased in traditional FCS-MPC for multilevel cascaded inverters. With applications of current delay compensation, feedback compensation and reference current correction, tracking feature is improved and current harmonic distortion is reduced. Simplification of the voltage vector selection, by taking the calculations of complex partition voltage vector tracking to be done in a single partition, is also adopted, in which calculation has been drastically reduced. Proposed algorithm is validated with Simulation of comparison traditional FCS-MPC in MATLAB.