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In this article, a phase-locked loop (PLL) rotor position and speed observer, including an integrated decoupled stator current observer, is proposed for wide-speed-range sensorless control of permanent magnet synchronous motor (PMSM) drives. This new PLL scheme consists of two interconnected observers: 1) a second-order PLL position observer using the direct current error as correction term and 2) a third-order extended Luenberger speed observer, based on the mechanical model of the drive, using the quadrature current error as the correction term. The estimated speed is just an unrefined reference for the position integrator, and it is further corrected by the PLL. The current observer is a subsystem integrated as a PLL phase detector. Key relations between the current errors and the position and speed errors are proven, and a practical two-step observer design method is presented. A method for real-time identification of the stator resistance at low speeds and of the permanent magnet flux at high speeds is proposed, using the current errors in the current reference frame. Experimental results for a 0.5-kW surface-mounted PMSM drive confirm the effectiveness, excellent dynamic performance, and robustness of the new PLL observer. Stable motor and generator operation at 15 r/min (0.01 p.u.) with ramp and step speed reversals, high-speed operation, and stator resistance adaptation is shown. [ABSTRACT FROM AUTHOR]

A new supertwisting sliding-mode direct torque and flux controller (STSM-DTC) is proposed and investigated for induction motor drives. The supertwisting algorithm is a second-order sliding-mode control (SMC) that operates without high-frequency chattering and preserves the robustness properties of the classical SMC. The new STSM-DTC scheme uses torque and stator flux controllers implemented in the stator flux reference frame and it does not employ current controllers as in the conventional vector control. Both controllers contain a design parameter that allows adjusting their behavior between a linear proportional–integral (PI) like operation and a constant-gain classical sliding-mode behavior. Experimental tests show that STSM-DTC displays a very robust behavior, similar to a conventional SMC, and it works without notable steady-state chattering, as a PI controller. This article presents theoretical aspects for the new STSM-DTC scheme, stability analysis, design and implementation details, and relevant experimental results for a sensorless induction motor drive. The scheme is compared to a second-order sliding-mode controller and a linear PI controller. A robustness assessment against DTC with PI controllers, based on experimental tests, is also included. [ABSTRACT FROM AUTHOR]

This paper describes a direct-torque-controlled (DTC) induction motor (IM) drive that employs feedback linearization and sliding-mode control (SMC). A new feedback linearization approach is proposed, which yields a decoupled linear IM model with two state variables: torque and stator flux magnitude. This intuitive linear model is used to implement a DTC-type controller that preserves all DTC advantages and eliminates its main drawback, the flux and torque ripple. Robust, fast, and ripple-free control is achieved by using SMC with proportional control in the vicinity of the sliding surface. SMC assures robustness as in DTC, while the proportional component eliminates the torque and flux ripple. The torque time response is similar to conventional DTC and the proposed solution is flexible and highly tunable due to the P component. The controller design is presented, and its robust stability is analyzed in simulations. The sliding controller is compared with a linear DTC scheme with and without feedback linearization. Extensive experimental results for a sensorless IM drive validate the proposed solution. [ABSTRACT FROM AUTHOR]

This paper investigates the application, design, and implementation of the square root unscented Kalman filter (UKF) (SRUKF) for induction motor (IM) sensorless drives. The UKF uses nonlinear unscented transforms (UTs) in the prediction step in order to preserve the stochastic characteristics of a nonlinear system. The advantage of using the UT is its ability to capture the nonlinear behavior of the system, unlike the extended Kalman filter (EKF) that uses linearized models. The SRUKF implements the UKF using square root filtering to reduce computational errors. We discuss the theoretical aspects and implementation details of the SRUKF for IM drives. Experimental results for a direct-torque-controlled drive are presented for a wide speed range of operation, with focus on low-speed performance. A comparison with the conventional EKF and the UKF is included. Our results show that the SRUKF is a viable and powerful tool for IM state estimation. [ABSTRACT FROM AUTHOR]

This paper investigates the application, design, and implementation of unscented Kalman filters (KFs) (UKFs) for induction motor (IM) sensorless drives. UKFs use nonlinear unscented transforms (UTs) in the prediction step in order to preserve the stochastic characteristics of a nonlinear system. The advantage of using UTs is their ability to capture the nonlinear behavior of the system, unlike extended KFs (EKFs) that use linearized models. Four original variants of the UKF for IM state estimation, based on different UTs, are described, analyzed, and compared. The four transforms are basic, general, simplex, and spherical UTs. This paper discusses the theoretical aspects and implementation details of the four UKFs. Experimental results for a direct-torque-controlled IM drive are presented and compared with the EKF. The focus of this study is on low-speed performance. It is concluded that the UKF is a viable and powerful tool for IM state estimation and that basic and general UTs give more accurate results than simplex and spherical UTs. [ABSTRACT FROM PUBLISHER]

The operation of switch-mode converters results in electromagnetic noise propagating throughout the power electronic system. Pulsewidth modulation (PWM) strategies with fixed switching frequency generate harmonics in the spectra of converter voltages and currents. Random PWM techniques allow the elimination of the harmonics, resulting in a continuous spectrum of noise, i.e., a spectrum retaining all frequency components. As a next step in advanced spectral shaping, a method presented in this paper produces spectral nulls at selected frequencies. This allows the carving of communication channels in the noise and the removal of spectral power at frequencies potentially harmful for the system. The theoretical analysis, computer simulations, implementation details, and experimental results are presented. [ABSTRACT FROM AUTHOR]

A new family of speed-sensorless sliding-mode observers for induction motor drives has been developed. Three topologies are investigated in order to determine their feasibility, parameter sensitivity, and practical applicability. The most significant feature of all schemes is that they do not require the rotor speed adaptation, i.e., they are inherently sensorless observers. The most versatile and robust is a dual-reference-frame full-order flux observer. The other two schemes are flux observers implemented in stator frame and rotor frame, respectively. These are simpler than the first one and make use of the sliding-mode invariance over a specified range of modeling uncertainties and disturbances. Main theoretical aspects, results of parameter sensitivity analysis, and implementation details are given for each observer in order to allow the comparison. Experimental results with the dual-reference-frame observer, considered the most adequate for practical applications, are presented and discussed. Sensorless operation with a sliding-mode direct-torque-controlled drive at very low speeds is demonstrated. It is concluded that the new proposed observers represent a feasible alternative to the classical speed-adaptive flux observers. [ABSTRACT FROM AUTHOR]

This paper compares four current control structures for selective harmonic compensation in active power filters. All controllers under scrutiny perform the harmonic compensation by using arrays of resonant controllers, one for the fundamental and one for each harmonic of interest, in order to achieve zero phase shift and unity gain in the closed-loop transfer function for selected harmonics. The complete current controller is the superposition of all individual harmonic controllers and may be implemented in various reference frames. The analysis is focused on the comparison of harmonic and total closed-loop transfer functions for each controller. Analytical similarities and differences between schemes in terms of frequency response characteristics are emphasized. It is concluded that three of them have identical harmonic behavior despite the fact that their implementation is significantly different. It emerges that the fourth one has superior behavior and robustness and can stably work at higher frequencies than the others. Theoretical findings and analysis are supported by comparative experimental results on a 7.kVA laboratory setup. The highest harmonic frequency that can be stably compensated with each control method has been determined, indicating significant differences in the control performance. [ABSTRACT FROM AUTHOR]

A new current control scheme for selective harmonic compensation is proposed for shunt active power filters. The method employs an array of resonant current controllers, one for the fundamental, and one for each harmonic, implemented in fundamental reference frame in order to reduce the overall computational effort. The proposed controller design is based on the pole-zero cancellation technique, taking into account the load transfer function at each harmonic frequency. Two design methods are provided, which give controller transfer functions with superior frequency response. The complete current controller is realized as the superposition of all individual harmonic controllers. The frequency response of the entire closed loop control is optimal with respect to filtering objectives, i.e., the system provides good overall stability and excellent selectivity for interesting harmonics. This conclusion is supported by experimental results on a 7.6-kVA laboratory filter, indicating a reduction in current THD factor from 34% to 2%, while the highest harmonic compensated is the 37th harmonic current. [ABSTRACT FROM AUTHOR]

This paper describes the control and parallel operation of two active power filters (APFs). Possible parallel operation situations of two APFs are investigated, and then the proposed topology is analyzed. The filters are coupled in a combined topology in which one filter is connected in a feedback loop and the other is in a feedforward loop for harmonic compensation. Thus, both active power filters bring their own characteristic advantages, i.e., the feedback filter improves the steady-state performance of the harmonic mitigation and the feedforward filter improves the dynamic response. Another characteristic of the proposed topology is the possibility of joint operation of both filters either as frequency-sharing or load-sharing, with or without redundancy. The frequency-sharing operation is possible due to the control algorithm, which is based on selective harmonic compensation using equivalent harmonic integrators. Implementation details and a discussion on the efficiency improvement for various switching frequencies are provided. The evaluation of the proposed topology concludes that this approach is very practical for achieving both low and high order harmonic compensation and stable grid operation. This is supported by extensive measurement results on a 15-kVA laboratory setup, indicating a reduction in total harmonic current distortion from the existing 30% to less than 2% for a typical adjustable speed drive application. [ABSTRACT FROM AUTHOR]

Two flux observers for wide speed range direct torque control (DTC) of sensorless induction-motor drives are presented and compared. The first one is a full-order sliding-mode observer with proportional plus integral (PI) compensation, without rotor speed adaptation. The second one is based on a zero phase-delay-improved integrator of the voltage model, which uses only a PI flux amplitude control with stator-flux reference magnitude in the correction loop. In both cases, an estimated dc offset is built tip and memorized by the PI integral component and this totally compensates for all dc offsets and drifts originated in the acquisition channels. Two feasible solutions for on-line stator-resistance identification are proposed. Simulation and experimental results prove the accuracy, robustness, and high-dynamic performance of both observers when employed in sensorless DTC drives. The effectiveness of state estimation is confirmed by a steady state and transient sensorless operation at very low speed with rated load torque and step-speed reversal. [ABSTRACT FROM AUTHOR]

Permanent magnet-assisted reluctance synchronous machine (PM-RSM) starter alternator systems are credited with good performance for wide speed range in hybrid electric vehicles. This paper proposes a motion-sensorless motor/generator control of PM-RSM from zero speed up to maximum speed, using direct torque and flux control with space vector modulation. A quasioptimal stator flux reference with a flux versus torque functional is proposed. A stator flux observer in wide speed range uses combined voltage-current models for low speeds, and only the voltage model for medium to high speeds, both in proportional-integral closed loop. A novel rotor speed and position observer with a fusion strategy employs signal injection and only one D-module vector filter in stator reference-for low speed, combined with a speed observer from the stator flux vector estimation-for medium-high speed. The proposed system is introduced piece by piece and then implemented on a dSpace 1103 control board with a 350-A metal-oxide-semiconductor field-effect transistor-pulse-width modulation converter connected to a 42-Vdc, 55-Ah battery, and a 140-Nm peak torque PM-RSM. Extensive experimental results from very low speed to high speed, regarding observers and drive responses, including artificial loading (motoring and generating), seem very encouraging for future starter-alternator systems. [ABSTRACT FROM AUTHOR]

State observers are key components of modern ac drives. The paper presents a comparative analysis of two state observers for induction-motor (IM) drives: the speed-adaptive observer and the inherently sensorless observer. The adaptive observer employs the time-variable full-order motor model with the rotor speed as the adaptive quantity. Thus, the speed estimation accuracy significantly impacts on the flux observer. It is shown that the popular model reference adaptive system (MRAS) speed estimator displays reduced bandwidth, and does not deliver adequate performance for the flux estimation. The inherently sensorless observer employs a full-order dual reference-frame model in order to eliminate the speed adaptation. In this way, it becomes decoupled from the speed estimator and its performance is superior to that of its adaptive counterpart. Theoretical aspects and comparative simulation results are discussed for both observers. Comparative experimental results for both observers are presented. Very low-speed-operation (3 r/min) capability of the drive with the sensorless observer is demonstrated. [ABSTRACT FROM AUTHOR]

A sensorless induction machine drive is presented, in which the principles of variable-structure control and direct torque control (DTC) are combined to ensure high-performance operation in the steady state and under transient conditions. The drive employs a new torque and flux controller, the "linear and variable-structure control," which realizes accurate and robust control in a wide speed range. Conventional DTC transient merits are preserved, while the steady-state behavior is significantly improved. The full-order state observer is a sliding-mode one, which does not require the rotor speed adaptation and provides accurate state estimation in the entire speed range. The proposed scheme is a complete variable-structure solution that allows persistent sensorless operation of the drive at very low speeds, including zero and 3 r/min, with full load. Simulations and extensive experimental results confirm the robustness, accuracy, quickness, and low-chattering operation of the drive. [ABSTRACT FROM AUTHOR]

A sensorless hybrid direct torque control (DTC) drive for high-volume low-cost industrial, domestic, and automotive applications has been developed using the inexpensive TMS329F243 digital signal processor controller. Under transient operating conditions, the drive is controlled using the classic bang-bang DTC. In the steady state, using linear torque and flux controllers, the control system generates a reference voltage vector for the inverter feeding the induction motor. The vector is then realized using the well-known space-vector pulsewidth modulation (SVPWM) technique. As a result, the irregular switching pattern typical for the classic DTC strategy is replaced with a quasi-optimal one, typical for the SVPWM. Description of the drive, including, a novel motor state observer, is followed by selected experimental results confirming its excellent operating characteristics. [ABSTRACT FROM AUTHOR]

A family of variable-structure controllers for induction machine drives is presented, in which the principles of direct torque control (DTC), variable-structure control (VSC), and space-vector pulse width modulation are combined to ensure high-performance operation, both in the steady state and under transient conditions. Three new VSC schemes are designed following the DTC voltage-control-based philosophy. These provide robust, fast, and accurate torque and flux control, without the penalty of high chattering. Comparative results demonstrate that proposed techniques preserve the DTC transient merits, while the steady-state behavior is significantly improved. Experimental results prove the strong robustness, accuracy, quickness, and low-ripple sensorless operation of the drive that uses the new schemes. [ABSTRACT FROM AUTHOR]

A sensorless induction motor drive is presented, in which the principles of sliding-mode control, direct torque control (DTC), and space-vector modulation are combined to ensure high-performance operation, both in the steady state and under transient conditions. Merits of the classic DTC transient behavior are preserved, while the steady-state operation is significantly improved. The torque and flux controllers, and motor state observer are of the sliding-mode type. The inverter is directly controlled on the basis of torque and flux errors, using space-vector pulsewidth modulation. Computer simulations and experimental results presented demonstrate the robustness, accuracy, quickness, and low-chattering, wide-speed-range operation of the drive. [ABSTRACT FROM AUTHOR]

Focuses on a study which proposed a direct torque and flux control strategy for induction motor (IM) sensorless drive. Background information on IM sensorless drives; Details on the proposed IM sensorless drive; Description of flux and speed estimator; Simulation results; Experimental results; Conclusions.