Showing papers on "Stationary Reference Frame published in 2018"

A Two Degrees of Freedom Resonant Control Scheme for Voltage-Sag Compensation in Dynamic Voltage Restorers

Abstract: This paper presents a two degrees of freedom (2DOF) control scheme for voltage compensation in a dynamic voltage restorer (DVR). It commences with the model of the DVR power circuit, which is the starting point for the control design procedure. The control scheme is based on a 2DOF structure implemented in a stationary reference frame ( $\alpha \text{--}\beta$ ), with two nested controllers used to obtain a passband behavior of the closed-loop transfer function, and is capable of achieving both a balanced and an unbalanced voltage-sag compensation. The 2DOF control has certain advantages with regard to traditional control methods, such as the possibility of ensuring that all the poles of the closed-loop transfer function are chosen without the need for observers and reducing the number of variables to be measured. The use of the well-known double control-loop schemes that employ feedback current controllers to reduce the resonance of the plant is, therefore, unnecessary. A simple control methodology permits the dynamic behavior of the system to be controlled and completely defines the location of the poles. Furthermore, extensive simulations and experimental results obtained using a 5-kW DVR laboratory prototype show the good performance of the proposed control strategy.

Stability Analysis of Digital-Controlled Single-Phase Inverter With Synchronous Reference Frame Voltage Control

Abstract: Stability analysis of single-phase power converters controlled in stationary reference frame is now mature and well developed, by using either linear or nonlinear methods. However, for the single-phase converters with synchronous reference frame (SRF) control loops, little work has been done on the evaluation of the nonlinear approaches for stability analysis. In this paper, the stability of a digital-controlled single-phase voltage-source inverter (VSI) with SRF voltage control loop is investigated from the perspective of nonlinear system. The analysis is based on the discrete-time model defined by the stroboscopic map, which is derived using the state-space averaging (SSA) technique. Furthermore, two different nonlinear analysis methods, the Jacobian matrix method and the Lyapunov exponent method, are adopted to analyze the fast-scale stability and the slow-scale stability of the pulsewidth-modulated (PWM) inverter under variations of control parameters; hence, the stability regions can be obtained. The theoretical results indicate that, for the established stroboscopic models, the Jacobian matrix method and the Lyapunov exponent method are mathematically equivalent, which means that the fast-scale stability and the slow-scale stability of the studied single-phase VSI are consistent, especially under linear load conditions. Experimental results under resistive load, inductive–resistive load, and diode rectifier load conditions are presented to support the theoretical results, which also proves that the discrete-time model plus the Jacobian matrix method or the Lyapunov exponent method is capable to investigate the stability of a converter with SRF control loops accurately.

High-Frequency Voltage-Injection Methods and Observer Design for Initial Position Detection of Permanent Magnet Synchronous Machines

Abstract: The information of the initial rotor position is essential for smooth startup and robust control of permanent magnet synchronous machines (PMSMs). RoTating Voltage Injection (RTVI) methods in the stationary reference frame have been commonly adopted to detect the initial rotor position at standstill without any position sensors. However, although the Pulsating sqUare-wave Voltage-Injection (PUVI) method performs better in estimation time and accuracy, it is rarely used because the estimation result may converge to the q -axis. In this paper, this fault convergence is avoided by modifying the initial states of the position observer, and the PUVI method can finally be used for the robust initial rotor position detection. Modified signal processing techniques are proposed for both RTVI and PUVI methods for better implementations in fixed-point processors and easier observer gain designs. Detailed comparisons between these two methods are provided. Furthermore, two position estimation observers, i.e., the proportional–integral observer and the extended state observer are compared, and their parameter tuning methods are studied as well. Both simulation and experimental results are provided for verifications.

A Three-Phase Active Rectifier Topology for Bipolar DC Distribution

Abstract: A new three-phase active rectifier topology is proposed for bipolar dc distribution, which can achieve the independent dc-pole control, with only one two-level voltage source converter and an ac-side grounding inductor. The averaged large-signal model and linearized small-signal model of the rectifier are derived in the stationary reference frame. Moreover, a control system is proposed with proper controller parameters. Besides, the rectifier is tested on an experiment platform. Comprehensive experiment results are given and analyzed to validate the function of the proposed rectifier under different operation conditions, including the rectifier start-up performance, rectifier dynamics with unbalanced dc loads for two poles, and rectifier dynamics with asymmetrical dc voltages for two poles. Finally, the proposed rectifier is compared with other two existing ac–dc conversion approaches, in terms of required number and rating of components as well as power losses with different load imbalance levels, which further highlight some potential benefits of the proposed topology.

Space Vectors and Pseudoinverse Matrix Methods for the Radial Force Control in Bearingless Multisector Permanent Magnet Machines

Abstract: Two different approaches to characterize the torque and radial force production in a bearingless multisector permanent magnet machine are presented in this paper. The first method consists of modeling the motor in terms of torque and force production as a function of the stationary reference frame $ \alpha \hbox{--}\beta$ currents. The current control reference signals are then evaluated adopting the Joule losses minimization as constrain by means of the pseudoinverse matrix. The second method is based on the control of the magnetic field harmonics in the airgap through the current space vector (SV) technique. Once the magnetic field harmonics involved in the torque and force production are determined, the SV transformation can be defined to obtain the reference current SVs. The methods are validated by numerical simulations, finite-element analysis, and experimental tests. The differences in terms of two degrees of freedom levitation performance and efficiency are highlighted in order to give the reader an in-depth comparison of the two methods.

Solar powered sensorless induction motor drive with improved efficiency for water pumping

Abstract: This study deals with a speed sensorless induction motor drive (IMD) with efficiency optimisation. This drive is driven by a solar photovoltaic array for water pumping. The elimination of speed sensor increases the robustness and decreases cost of the IMD. The speed estimation is achieved by rotor flux-oriented control in stationary reference frame. Moreover, the parameters, namely stator resistance adaptation, make the system parameters insensitive. The efficiency of the drive system is enhanced by optimising the excitation current by using a particle swarm optimisation technique. The smooth operation of overall system during starting and steady-state condition is simulated in MATLAB/Simulink environment and validated on a prototype developed in the laboratory. The efficiency of the system with loss minimisation technique is compared with the conventional IMD. Simulated results comply with the test results and a comprehensive comparison is made to validate the suitability of proposed system.

Elastic wave propagation in moving phononic crystals and correlations with stationary spatiotemporally modulated systems

Abstract: This work presents a generalized physical interpretation of unconventional dispersion asymmetries associated with moving phononic crystals (PCs). By shifting the notion from systems with time-variant material fields to physically traveling materials, the newly adopted paradigm provides a novel approach to the elastic dispersion problem and, in the process, highlights discrepancies between moving PCs and stationary ones with dynamic material fields. Equations governing the motion of an elastic rod with a prescribed moving velocity observed from a stationary reference frame are used to predict propagation patterns and asymmetries in wave velocities obtained as a result of the induced linear momentum bias. Three distinct scenarios are presented corresponding to a moving rod with a constant modulus, a spatially varying one, and one that varies in space and time. These cases are utilized to extract and interpret correlations pertaining to directional velocities, dispersion patterns, as well as nature of band gaps between moving periodic media and their stationary counterparts with time-traveling material properties. A linear vertical shear transformation is then derived and utilized to neutralize the effect of the moving velocity on the resultant band diagrams. Finally, dispersion contours associated with the transient response of a finite moving medium are used to validate the entirety of the presented framework.

A novel robust PLL algorithm applied to the control of a shunt active power filter using a self tuning filter concept

Abstract: This paper presents a novel robust phase locking control scheme for active power filters namely multiple self-tuning filters phase locked loop (M-STFs-PLL). This method uses a multiple self-tuning filters in stationary reference frame to cleanly extract and separate the positive and negative sequences voltage to improve the traditional PLL under highly unbalanced and/or distorted source voltage. The resultant M-STFs-PLL conducts then to a fast, precise and robust positive sequence. To demonstrate the effectiveness of the proposed approach, the direct shunt active power filter control method with the proposed PLL scheme is adopted and its performance is verified by means of simulation with different supply systems.

Methodology for Analysis and Design of DiscreteTime Current Controllers for Three-Phase PWM Converters

Abstract: In this work, a methodology for the analysis and design of robust, high bandwidth current controllers for three phase converters is presented. The overall goal is to demonstrate how the proposed model based control structure and the design methodology lead to an optimized digital current controller that exhibits fast and smooth dynamics as well as an excellent disturbance rejection ability. First, accurate discrete time models are derived and used to review classical current control from the perspective of the synchronous and stationary reference frame. Then, implementation options for the synchronous frame proportional integral (SFPI) regulator and the proportional resonant (PR) regulator are discussed and systematically compared in the stationary frame leading to the formulation of a general controller framework based on space vector resonators. It embodies multiple complex resonators and can represent the SFPI regulator, the PR regulator and beyond that any higher order regulator structure. For this framework, a step by step design procedure based on the complex root locus is proposed that allows an insightful optimization of its feedback gains. Finally, the performance of the presented control design techniques is evaluated experimentally.

Frequency-Adaptive Current Controller Design Based on LQR State Feedback Control for a Grid-Connected Inverter under Distorted Grid

Abstract: This paper proposes a frequency-adaptive current control design for a grid-connected inverter with an inductive–capacitive–inductive (LCL) filter to overcome the issues relating to both the harmonic distortion and frequency variation in the grid voltage. The current control scheme consists of full-state feedback control to stabilize the system and integral control terms to track the reference in the presence of disturbance and uncertainty. In addition, the current controller is augmented with resonant control terms to mitigate the harmonic component. The control scheme is implemented in the synchronous reference frame (SRF) to effectively compensate two harmonic orders at the same time by using only one resonant term. Moreover, to tackle the frequency variation issue in grid voltage, the frequency information which is extracted from the phase-locked loop (PLL) block is processed by a moving average filter (MAF) for the purpose of eliminating the frequency fluctuation caused by the harmonically distorted grid voltage. The filtered frequency information is employed to synthesize the resonant controller, even in the environment of frequency variation. To implement full-state feedback control for a grid-connected inverter with an LCL filter, all the state variables should be available. However, the increase in number of sensing devices leads to the rise of cost and complexity for hardware implementation. To overcome this challenge, a discrete-time full-state current observer is introduced to estimate all the system states. When the grid frequency is subject to variation, the discrete-time implementation of the observer in the SRF requires an online discretization process because the system matrix in the SRF includes frequency information. This results in a heavy computational burden for the controller. To resolve such a difficulty, a discrete-time observer in the stationary reference frame is employed in the proposed scheme. In the stationary frame, the discretization of the system model can be accomplished with a simple offline method even in the presence of frequency variation since the system matrix does not include the frequency. To select desirable gains for the full-state feedback controller and full-state observer, an optimal linear quadratic control approach is applied. To validate the practical effectiveness of the proposed frequency-adaptive control, simulation and experimental results are presented.

Analysis of parasitic effects in carrier signal injection methods for sensorless control of PM synchronous machines

Abstract: This study presents the parasitic effects on different carrier signal injection methods with alternative sensing signals for the sensorless control of permanent magnet synchronous machines (PMSMs). The different carrier injection methods are the rotating injection in the stationary reference frame with carrier current sensing and with zero-sequence carrier voltage sensing, the pulsating injection in the estimated synchronous reference frame with carrier current sensing, and pulsating injection in the anti-rotating reference frame with zero-sequence carrier voltage sensing, respectively. The parasitic effects, e.g. the magnetic saturation, inverter non-linearity, iron and PM losses, torque ripple etc. will be fully analysed and compared for these different injection methods. All the theoretical analyses are validated by either finite-element analyses or experiments on a laboratory PM machine.

Design and Implementation of a Feedback Linearization Controlled IM Drive via Simplified Neuro-Fuzzy Approach

Abstract: This research paper introduces an outline of a simplified version of single-input neuro-fuzzy controller (NFC) method via a decoupling-controlled intuitive feedback linearization (FBL) appr...

Power and Voltage Control for Single-Phase Cascaded H-Bridge Multilevel Converters under Unbalanced Loads

Abstract: The conventional control method for a single-phase cascaded H-bridge (CHB) multilevel converter is vector (dq) control; however, dq control requires complicated calculations and additional time delays. This paper presents a novel power control strategy for the CHB multilevel converter. A power-based dc-link voltage balance control is also proposed for unbalanced load conditions. The new control method is designed in a virtual αβ stationary reference frame without coordinate transformation or phase-locked loop (PLL) to avoid the potential issues related to computational complexity. Because only imaginary voltage construction is needed in the proposed control method, the time delay from conventional imaginary current construction can be eliminated. The proposed method can obtain a sinusoidal grid current waveform with unity power factor. Compared with the conventional dq control method, the power control strategy possesses the advantage of a fast dynamic response. The stability of the closed-loop system with the dc-link voltage balance controller is evaluated. Simulation and experimental results are presented to verify the accuracy of the proposed power and voltage control method.

Three-phase three-level T-type grid-connected inverter with reduced number of switches

Abstract: In this study, a three-phase three-level T-type neutral point clamped grid connected inverter with reduced number of switch is proposed for distributed generation systems. The proposed inverter topology has only two legs and totally eight semiconductor switches. Thus, advantageous multi-level inverter technology has been achieved with less number of semiconductor switches resulting in reduced circuit complexity. The proportional-resonant controller in stationary reference frame is designed to control the proposed inverter, thus fast dynamic response and good reference tracking ability is obtained with zero steady-state error. The feasibility and correct operation of the proposed system is validated through MATLAB/Simulink simulation studies. The obtained results show that proposed three-phase three-level T-type inverter exhibits comparable performance with the conventional T-type inverters. Furthermore, total harmonic distortion level of the output current is computed as 2.07%, which is in accordance with the limits specified by the international standards such as IEC61727 and IEEE1547.

Finite Control-Set Predictive Power Control of BLDC Drive for Torque Ripple Reduction

Abstract: Due to advantages as high efficiency and high power density, brushless direct current (BLDC) motor has been used in a wide variety of applications. However, in conventional 120o conducting drive operation it develops significant torque ripple as a result of phase commutation. To reduce torque undulations, in this paper is proposed a power control based on Finite Control-Set Model based Predictive Control (FCS-MPC). The relationship between the control of the power delivered to rotor and torque ripple reduction is presented. The effectiveness of commutation torque ripple reduction of proposed method is presented in comparison with conventional torque control strategy. The results of proposed predictive control approach demonstrate fast torque response with no adjustable gains needed and operates with model variables on stationary reference frame.

Optimal Performance Design Guideline of Hybrid Reference Frame Based Dual-Loop Control Strategy for Stand-Alone Single-Phase Inverters

Abstract: The dual-loop control strategy in a hybrid reference frame (HRF) for single-phase voltage-source inverters in islanded operation mode is studied, which applies a capacitor voltage shaping loop in the synchronous reference frame (SRF) and a capacitor current shaping loop in the stationary reference frame (HRF-based $v+ i_{c}$ control strategy). This strategy is able to achieve the purpose of active damping, fast dynamic response, and zero reference tracking error. However, due to the inherent characteristics of SRF-based voltage loop and the digital control delay, the performance of the system is degraded and the control parameter design of the HRF-based $v+ i_{c}$ control strategy shows great difficulties. To overcome these shortcomings, in this paper, a systematic parameter design guideline for the HRF-based $v+ i_{c}$ control strategy is proposed to ensure the system stability and optimize the performance of the system under control delay condition. The mathematic model of the HRF-based $v+ i_{c}$ control strategy is established with the consideration of control delay in this paper. Based on this model, a satisfactory region of the system stability indexes can be obtained by stability specifications of the system, and the optimal control parameters can be calculated according to the stability indexes selected from the satisfactory region. By using this method, the system stability and robustness can be guaranteed. Finally, the experimental results are presented to validate the effectiveness of the presented optimal control parameter design methodologies.

Chapter 5: Modeling and Control of Three-Phase AC/DC Converter Including Phase-Locked Loop

Abstract: In this chapter, a mathematical model of the power circuit of a three-phase AC/DC converter is developed in the stationary and synchronous reference frames Then, the operation principle of the phasor locked loop is addressed to exact the angle information of the power grid to realize the accurate control synchronized with the power grid Afterward, based on the modeling of the three-phase grid-tied converter, the controller design of the PI (Proportion + Integral) and PR (Proportion + Resonant) is implemented under the synchronous reference frame and stationary reference frame, respectively It is realized by the desired bandwidth and its corresponding phase margin with the aid of Bode plot It is simulation proven that the step response of the inner grid current and outer DC voltage matches their desired bandwidth

A New Sliding-Mode Approach to Control the Active and Reactive Powers with Variable Switching Frequency for Grid-Connected Converter

Abstract: This paper presents the development and implementation of a novel approach of Direct Power Control based on Sliding Mode control approach with Variable Switching Frequency (SM–DPC–VSF) to control the instantaneous active and reactive powers for three-phase grid-connected converters. The improved strategy combines the DPC principle, SM approach, and switching look-up table. The synthesis of the switching table (ST) is based on active and reactive power time derivative behaviours and the redundancy of the applied vector during two successive sectors. The ST is aimed to select the appropriate voltage vector and ensures the VSF operation mode, which simplifies the system design and improves the transient performance system. The SM–DPC–VSF uses an SM based on pre-defined sliding surfaces in powers error that improves the instantaneous power behaviour. The converter model developed in the stationary reference frame eliminates the need of the rotating coordinate transformation and angular information of ...

Steady state error elimination and harmonic compensation using proportional resonant current controller in grid-tied DC microgrids

Abstract: Optimized operation of grid-tied DC microgrids requires the application of an efficient current control strategy. Proportional resonant (PR) control is found to be one of the suitable control schemes to regulate grid currents in grid connected Voltage Source Converters. The paper focuses on achieving minimal steady state error between the desired and actual values of the series injected grid currents in the system. An additional advantage of selective harmonic compensation enhances the employability of this new breed of controllers. Tracking converter reference currents in the stationary reference frame is investigated to cancel out the shortcomings encountered while using conventional method comprising proportional integral controllers. Simulation research is carried out on the specified control area and a detailed discussion of both analytical and simulation results are presented. Simulation results furnished validate the test system connected to a linear inductive load when synchronized with the AC main power grid.

Online Identification of Mutual Inductance of Induction Motor without Magnetizing Curve

Abstract: This paper presents two easy-to-implement methods for online identification of the mutual inductance of induction motors without magnetizing curves. The first one uses the algorithm of a model reference adaptive system. The voltage model in a stationary reference frame is employed as a reference model as it is little affected by the variation of mutual inductances. The current model is used as an adaptive model as it is sensitive to the variation of mutual inductances. The second method is an open-loop method by calculating reactive power of the motor based on the steady-state voltage model in a rotating reference frame. As the reactive power and stator inductance are approximately linear, this method is easy to implement. Simulation results demonstrate that the steady-state errors caused by the mismatch of mutual inductance used in the controller and that of the motor are reduced by the proposed identification methods.

Modelling a Vector Controlled Induction Motor in Simulink

Abstract: A workflow to model an electric motor drive system with a control system in Simulink is presented. The induction motor (IM) is modelled using an equivalent circuit based on the space-vector theory in the stationary reference frame. The motor is controlled using the classical indirect vector control implemented in the rotor flux reference frame that utilizes an ideal converter and modulator. The presented system model can be used as a basis for teaching electrical drives, particularly in the context of learning by doing where the goal is to learn new things using a practical approach. The following approach links the space vector theory to practice and helps students to understand the importance and the value of the theory.

Control of three-phase PWM boost rectifiers using proportional-resonant controllers

Abstract: Voltage-oriented vector control (VOC) using proportional-integral controllers is an attractive control method for three-phase PWM rectifiers, due to relative ease of implementation, being one of the most used methods. However, these controllers present oscillatory DC voltage for unbalanced input voltage and harmonics in the current due to the AC-DC converter switching. Thus, this work presents a control strategy for three-phase driven by sinusoidal PWM in the stationary reference frame using proportional-resonant controllers in the internal current loop. This control strategy presents high dynamic performance, simplicity of implementation, attenuation of harmonics generated by converter switching, reduction of ripple at link-DC voltage and less dependence on physical parameters, since the decoupling term is eliminated. Simulation results show an excellent performance of the proposed method with a ripple reduction of DC-link voltage, THD reduction of the grid current, fast transient response for power variations.

Comparative Study; Different Types of PWM Control Scheme in Three-Phase Four-Wire Shunt Active Power Filter (APF) Topology.

Abstract: This paper focus on the comparative study for five commonly harmonics extraction methods through different types of pulse-width modulation (PWM) designed for three-phase four-wire shunt active power filter (APF). Three harmonics extraction methods consist of instantaneous reactive power theories (IRPT) which are p-q method, modified p-q, and p-q-r method, whilst two other methods are stationary reference frame and vectorial method. Two types of PWM namely; carrier and hysteresis current control were implemented for generating the injected current which are then feedback to the system for correction. The MATLAB/Simulink (MLS) is used to examine the comparison. The results revealed that continuous total harmonics distortion (THD) was establish when applying the hysteresis current control while the p-q-r method produce the preeminent performances in THD reduction with elimination of the neutral current harmonics.

Efficiency Evaluation of Three-phase SiC Power Factor Correction Rectifier with Different Controllers

Abstract: This paper presents a comprehensive design of a 5 kW silicon-carbide (SiC) based three-phase power factor correction (PFC) to achieve high conversion efficiency. It evaluates the efficiency of the converter by comparing two controllers: a controller without harmonic compensation (HC) in the rotational reference frame and a controller with HC in the stationary reference frame. SiC switches, by exhibiting a low capacitive switching loss compared to Si switches, help increasing the switching frequency and reducing the size of the line filter. To achieve a very high efficiency converter, the controller has an impact on the efficiency, especially at low load. Normally, the current quality of grid-connected converter at low load reduces due to the non-linearity of the converter. This reduction influences the efficiency. In this paper, two methods are presented to improve the current quality at low loads: either increasing the converter-side inductance to yield lower current ripple or improving the controller to mitigate the low frequency current harmonics. Both methods are investigated in this work and it is proved that using a proper controller can help reducing the converter-side inductor to 2/3 which has a great impact on the efficiency. An optimized 5 kW SiC based PFC is designed. Maximum measured efficiency of 99% at full load is achieved.

Voltage unbalance compensation by a grid connected inverter using virtual impedance and admittance control loops

Abstract: In this paper, voltage unbalance compensation using DG interfacing inverter is proposed. By using this control method, the DG not only can inject generated power to the grid, but also can compensate the unbalance voltage of the Point of Common Coupling (PCC). A compensation scheme based on negative sequence virtual impedance or admittance is proposed. The control method is designed in stationary reference frame and is based on Proportional-Resonance (PR) controller. The compensation is achieved by using only local measurement. The simulation results in Matlab/Simulink verify the effectiveness of the proposed control method.

A sliding mode flux observer for predictive torque controlled induction motor drive

Abstract: Predictive torque control for induction motor is a control strategy uses the model of the motor drive and an appropriate cost function to directly control torque and flux. This strategy is easy to implement but depends upon parameters of motor drive. This paper presents the design and analysis of a sliding mode flux observer to improve the parameter robustness. The observer estimates the stationary reference frame flux of the induction motor by using sliding mode terms based on the current mismatches and flux mismatches. The novelty is the method use the current mismatches to estimate the flux mismatches in the situation when the real fluxes is not available. Simulations presented in this paper prove the sliding mode observer improve the parameter robustness of predictive torque controlled induction motor drive.

Analysis and Modeling of Three Winding Stator Interturn Fault on Induction Machine for Electric Vehicle Application

Abstract: In this paper, a transient model of an induction machine with a stator interturn fault in three windings of the machine with different percentages of shorted turns is analyzed for electric vehicle application. Stator fault is the most common and severe faults occurs in the motors. Analyzing the effects of a stator turn fault on the motor is a crucial feature in fault diagnosis of electric vehicles. This compels us to develop a model, which helps to analyze the behavior of the machine under stator fault conditions in any of the winding or on multiple windings. The percentage of turns shorted in the machine is varied and complete machine modeling with such a fault is performed in a stationary reference frame. The motivation of this paper is to predict the performance of an electric vehicle drivetrain under abnormal running conditions with a sudden stator fault. Moreover, the stator fault resistances in the three winding fault is also varied. This model helps to design a fault prediction and diagnosis system in electric vehicles to avoid sudden stalling during drive mode. The abnormal behavior in line currents, speed and torque of the induction machine under sudden fault conditions is simulated in MATLAB and the results are presented in this paper.

Fault-tolerant operation with 1-phase open in parallel-connected motor

Abstract: This paper proposes a fault-tolerant operation for 3-phase surface mounted permanent magnet machines in which a parallel-connected motor drives a same mechanical shaft. A healthy 3-phase motor and a faulted 3-phase motor with 1-phase open are operated in parallel. In the stationary reference frame, the d-axis component affects only to the healthy 3-phase motor, whereas both of motors share the q-axis component. It is possible to operate the motor continuously even in a fault circumstance. In this paper, separated d-and q-axis current controllers utilize torque under both normal and the fault conditions of 1-phase open. The output torque is generated up to a sum of the rated torque of healthy and faulted motors. The proposed control method has robust characteristics, which is proved by stability analysis using system transfer function. This paper also presents a method of reducing the torque ripple caused by the correlated voltage circuit. Accordingly, a cost-effective and enhanced reliability system is implemented without any configuration adjustment. The simulation results are presented to verify the performance of proposed fault-tolerant operation.