Sensorless Control Method Research Articles

A Position Sensorless Control Strategy for the BLDCM Based on a Flux-Linkage Function

A novel sensorless control strategy for the brushless dc motor (BLDCM) is proposed in this paper. The proposed strategy is realized by employing new flux-linkage functions and can be applied to drive the sensorless BLDCM in the high-speed and low-speed ranges with highly accurate and reliable commutation. Another attractive feature is that the jumping edges of the flux-linkage functions are utilized to determine the commutation points, so there is no threshold needed as compared with other sensorless control methods. In addition, the three-phase current control method is adopted, and terminal voltages in flux-linkage function expressions can be easily obtained by calculation. By this way, the sample delay and the influence of the floating phase voltage can be eliminated, which can improve the accuracy and reliability of the sensorless control strategy. The effectiveness of the proposed strategy is verified by experimental results.

Sliding mode observer for sensorless control of surface permanent magnet synchronous motor equipped with LC filter

This study proposes a sliding mode observer (SMO) based method for sensorless speed control of surface permanent magnet synchronous motor equipped with LC filter. To deal with side effects of pulse width modulation technique, LC filters are equipped between inverters and motors in some industrial applications. Therefore, filter input currents rather than stator currents will be measured by current sensors on the inverter board. Sensorless operation becomes complicated due to the differences between filter input and stator currents. When only inverter-side current sensors are installed, the mathematical model of the LC filter should be considered. Hereby, the proposed SMO takes the LC filter into consideration, so additional measurement of stator currents is not necessary. Back electromotive forces of the PMSM are estimated by the SMO, and the rotor speed and position are calculated by the phase locked loop. The proposed approach features simplicity, and it is suitable for medium- and high-speed ranges. Simulation and experimental results confirm the effectiveness of the proposed method.

자속 포화에 의한 PMSM 센서리스 위치 추정 오차 분석 및 보상 기법

For a pump or a compressor motor, a high periodic load torque variation is induced by the mechanical works, and it causes system vibration and noise. To minimize these problems, load torque compensation method, injecting periodic torque current, could be utilized. However, with the sensorless control method, which is usually utilized in the pump and compressor for low cost, the periodic torque current degrades the accuracy of the rotor position estimation owing to the inductance variation. This paper analyzes the rotor position and speed estimation error of sensorless control method with constant motor parameters under period loading. Assuming the constant speed by the accurate load torque compensation, the speed error equation is derived in frequency domain with inductance depending on the stator current. Further, it is also shown that the rotor position error could be minimized by compensating the inductance variation. The simulation and experimental results verify that the derived speed error model and the validity of the inductance compensation method.

Flux Observer Model for Sensorless Control of PM BLDC Motor With a Damper Cage

Sensorless control methods are commonly employed to derive the rotor position and speed information indirectly in permanent magnet (PM) brushless motor drives. Thereinto, the simple yet effective flux observer method is extensively applied in a wide range of applications. However, damper cage is sometimes employed in the rotor of certain PM brushless motor. Normally, high-order current harmonic components occur in such damper cage during operations. The introduction of these extra current contents can significantly hinder the performance of the conventional flux observer. By applying Park transformation, the fundamental harmonic components of stator phase currents, flux linkages, and voltages during steady-state operation, become constants under rotor synchronous reference frame, while the currents in the rotor damper cage are still alternating. In this paper, an improved flux observer method is proposed to filter the harmonic contents under the rotor synchronous reference frame for PM brushless motor with rotor damper cage. The validity and performance of the proposed flux observer are verified by both numerical analysis and experimental results.

Sensorless Control Scheme of IPMSMs Using HF Orthogonal Square-Wave Voltage Injection Into a Stationary Reference Frame

This paper proposes a new sensorless control scheme of interior permanent magnet synchronous motors (IPMSMs) using high-frequency (HF) orthogonal square-wave voltage injection into a stationary reference frame (SRF). This method is an improvement on the conventional HF rotating sinusoidal voltage injection into the SRF. First, discrete sequences of the HF currents are applied to establish the whole signal process. Then, a position estimation method without low-pass filters is proposed, and the phase shifts caused by high-pass filters are also reduced. Therefore, the proposed sensorless control method would not be adversely affected by digital filters, which can solve the common drawbacks of the current SRF-based injection methods. Furthermore, the digital delay in drive systems is considered, and its negative influence can be eliminated as well. The sensorless control method is verified by experiments on a 2.2-kW IPMSM drive platform.

Prediction-Error-Driven Position Estimation Method for Finite-Control-Set Model Predictive Control of Interior Permanent-Magnet Synchronous Motors

This paper proposes a prediction-error-driven position estimation method based on the current prediction errors of the finite-control-set model predictive control (FCS-MPC) for the position-sensorless control of interior permanent-magnet synchronous motors, which operate in the whole speed range, including zero speed. The method is customized for FCS-MPC with which switching devices are directly controlled without modulators, whereas the conventional sensorless control methods usually presume the use of modulators. In the low-speed region, the proposed method fully exploits the inherent excitation of the discrete switching of the FCS-MPC to extract the position information. Under the low-current condition, an active vector injection technique is designed to automatically maintain sufficiently rich excitation for the position estimation while exerting a minimum impact on the fundamental control. The resultant current ripples and acoustic noises are lower compared with conventional injection methods. A novel initial polarity detection method based on magnetic saturation effect and inductance identification is also proposed to prevent pole ambiguity. The high-speed region position estimation uses the excitation from the back electromotive force, which is also reflected in the current prediction errors, permitting the use of one simple linear estimator in the whole speed range. Finally, the effectiveness and benefits of the proposed method are validated by experimental results.

Online sensorless position estimation for switched reluctance motors using characteristics of overlap position based on inductance profile

This study proposes an online sensorless position estimation method using switched reluctance motor (SRM) characteristics of overlapped position. The SRM drive system operation requires rotor position information of the motor to apply or commutate the current flowing in each phase winding. Conventional position sensorless control methods have some limitations due to complicated calculations, large memory space requirements dependency on lookup tables, and drive limitations for specific motors. To overcome these limitations, the proposed method uses the characteristics of the overlapping position of the SRM to estimate the rotor position information and hybrid sensorless control by varying the control method according to the operating section. The proposed sensorless position estimation method is verified experimentally using a 400 W 4/2 SRM.

Low-Cost Position Sensorless Speed Control of PMSM Drive Using Four-Switch Inverter

A low-cost position sensorless speed control method for permanent magnet synchronous motors (PMSMs) is proposed using a space vector PWM based four-switch three-phase (FSTP) inverter. The stator feedforward d q -axes voltages are obtained for the position sensorless PMSM drive. The q-axis current controller output with a first order low-pass filter formulates the rotor speed estimation algorithm in a closed-loop fashion similar to PLL (Phase Lock Loop) and the output of the d-axis current controller acts as the derivative representation in the stator feedforward voltage equation. The proposed method is quite insensitive to multiple simultaneous parameter variations such as rotor flux linkage and stator resistance due to the dynamic effects of the PI current regulator outputs that are used in the stator feedforward voltages with a proper value of K gain in the q-axis stator voltage equation. The feasibility and effectiveness of the proposed position sensorless speed control scheme for the PMSM drive using an FSTP inverter are verified by simulation and experimental studies.

Sensorless Control Strategy for IPMSM to Reduce Audible Noise by Variable Frequency Current Injection

High-frequency (HF) signal injection is widely used in sensorless control schemes to drive interior permanent-magnet synchronous motors at low speeds, acquiring a good dynamic and a steady performance. However, the audible noise created by the injected HF signal is an obvious defect and restricts its application. In this paper, a variable frequency current injection method is proposed to reduce the noise. First, the theoretical basis of the variable frequency signal injection is analyzed and the demand from the injected signal is proposed. Second, a modified resonant controller is applied to realize the variable current injection and provide a zero steady-state control error. A linear active disturbance rejection controller that contains a resonant observer is applied to realize the q -axis current control and acquire rotor position information. Third, a sweep-frequency switching strategy is proposed to disperse harmonic energy. The energy of injected HF current is further extended by the proposed method when compared to the random switching method. Finally, the related experimental results are presented to verify the sensorless control method proposed.

Speed Sensorless Vector Control Based on Full-order Adaptive Observer for Induction Motor Drives at Low Speed

This paper presented a speed sensorless vector control method based on adaptive full-order state observer for induction motor. The rotor speed estimated by an adaptive full-order observer is fed back to the vector control system as a feedback signal to form a closed-loop control of speed. In addition, the stator resistance is also recognized and updated in real time, so the effect of change of stator resistance on accuracy of speed estimation can be eliminated. The parameter identification system is achieved according to the Popov’s hyperstability theory, therefore the system is stable enough even at very low speed. The simulation and experimental results illustrated the correctness and effectiveness of the presented control algorithm.

Simulation of Sensorless Control for the Start-up of Large-Scale Synchronous Condenser Using Static Frequency Converter

In this paper, the structural characteristics of large synchronous condensers and the working principle of static frequency converter are studied firstly. Intermittent commutation and natural commutation are adopted by the inverter on the machine side in low-speed and high-speed stage respectively. Second, methods of sensorless control in different conditions are proposed. The initial rotor position is estimated through two methods, the terminal voltage method and the rotor-flux-oriented method. And similar methods are used in low-speed stage. Besides, phase-locked loop is used in high-speed. Finally, simulation models are established in PSCAD/EMDTC. The rotor-flux-oriented method used in standstill condition and low-speed stage shows better accuracy. And the phase-locked loop is also effective in high-speed stage. Therefore, the sensorless control methods are feasible.

Extended Sliding Mode Disturbance Observer-Based Sensorless Control of IPMSM for Medium and High-Speed Range Considering Railway Application

The sliding mode observer (SMO)-based approach known for its robustness towards parameter variation (external disturbance) has been used for the sensorless motor drive system. Delay compensation is commonly added to overcome the phased delay resulted from the introduction of the low-pass filter for chattering suppression. In this paper, a new extended sliding mode disturbance observer (ESMDO)-based sensorless control of interior permanent magnet synchronous motor for the medium and high-speed range is presented. The effect of parameter variation and coordinate transformation is considered as a lumped disturbance, and ESMDO is designed to compensate for the imminent impact of such scenarios. A Lyapunov stability theory is adopted to guarantee the stability of the proposed ESMDO-based sensorless control method. The ESMDO has an inbuilt low-pass filter and does not introduce a phased delay. A very large load change/reference speed variation may result in system instability or require higher controller gains that lead to system chattering. Hence, a PI-based compensation is incorporated to achieve a smooth and robust sensorless control algorithm considering the d-axis disturbance. Finally, extensive simulation and hardware-in-the-loop (HIL) test using the TMS320F28335 control unit in a real-time environment are conducted to verify the effectiveness of the proposed sensorless control method.

A Simple and Robust Sensorless Control Based on Stator Current Vector for PMSG Wind Power Systems

This paper proposes a novel sensorless control based on the stator current vector for permanent-magnet synchronous generators in variable-speed wind energy conversion systems. In the proposed method, the rotor angle and speed are estimated indirectly from the stator currents, where only the stator inductance is required regardless of the stator resistance. In addition, the proposed method uses one current control loop to regulate the stator current magnitude, rather than two current control loops. To eliminate the current measurement noise, the second-order generalized integrator (SOGI) with a frequency-locked loop (FLL) is utilized, which can improve the estimation performance. The proposed sensorless control method with the SOGI-FLL is simple and easy to implement while achieving a fast and accurate estimation performance of the rotor angle and speed. The feasibility of the proposed method has been verified by simulation and experimental results.

Robust load angle direct torque control with SVM for sensorless induction motor using sliding mode controller and observer

The AC drives direct torque control (DTC) technique has been designed to obtain a high performance for flux and torque control. Because of some downsides, the space vector modulation (SVM) has been proposed for the improvement of classical DTC strategy. Besides, the sliding mode control proofs that it can solve robustness and disturbances problems. Furthermore, it has taken a grand part in sensorless applications. In this paper, a robust modified DTC scheme will be presented for induction motor drive basing on various control strategies. Firstly, ripples reduction strategy based on load torque angle variation and SVM will be presented. This technique is known as load angle SVM-DTC. Secondly, a sliding mode speed controller will be used instead of the conventional PI for speed control loop. Moreover, this paper aims to design a dual sliding mode observer for speed/flux and load torque estimation. They can improve the control performances by decreasing the cost and increasing the reliability of the global control system. The proposed sensorless control method will be investigated by simulation and experimentally using MATLAB/Simulink in real time environment using dSpace 1104.

Sensorless Control of Brushless Doubly Fed Induction Machine Using a Control Winding Current MRAS Observer

In order to realize sensorless control for brushless doubly fed induction machine (BDFIM), this paper presents a model reference adaptive system (MRAS) observer, designed based on the error of the control winding current. Furthermore, a phase-locked loop is employed to estimate the current winding position and rotor speed. Consequently, a detailed theoretical derivation proves that the MRAS observer is stable and the dynamic performance is good. Thus, it does not cause any estimated speed error in steady state. Moreover, the estimated position error is bounded and trivial, thus its effects on the sensorless control of the BDFIM are neglected. The correctness, feasibility, and robustness of the proposed sensorless control method are verified by means of experimental validation on a 30 kW test rig.

Robust load angle direct torque control with SVM for sensorless induction motor using sliding mode controller and observer

The AC drives direct torque control (DTC) technique has been designed to obtain a high performance for flux and torque control. Because of some downsides, the space vector modulation (SVM) has been proposed for the improvement of classical DTC strategy. Besides, the sliding mode control proofs that it can solve robustness and disturbances problems. Furthermore, it has taken a grand part in sensorless applications. In this paper, a robust modified DTC scheme will be presented for induction motor drive basing on various control strategies. Firstly, ripples reduction strategy based on load torque angle variation and SVM will be presented. This technique is known as load angle SVM-DTC. Secondly, a sliding mode speed controller will be used instead of the conventional PI for speed control loop. Moreover, this paper aims to design a dual sliding mode observer for speed/flux and load torque estimation. They can improve the control performances by decreasing the cost and increasing the reliability of the global control system. The proposed sensorless control method will be investigated by simulation and experimentally using MATLAB/Simulink in real time environment using dSpace 1104.

Design and Implementation of Three-Phase Current Sensorless Control for PFC Bridge Converter With Considering Voltage Drops of Power Semiconductors

Three-phase bridge converter is popular in ac-dc power conversion. The conventional sensor control with inner current loop and outer voltage loop is often used to control the three-phase bridge converter. Many three-phase sensorless control methods had been proposed to control the bridge converter with considering the inductance and inductor resistance. In this paper, the voltage drop of the power semiconductor is first considered in the proposed three-phase current sensorless control method. At first, the dynamic behaviors of three-phase bridge converter for power factor correction (PFC) applications are studied, and its equivalent three-switch model is developed. Based on this developed model, three-phase current sensorless control with only voltage controller is proposed. Additionally, the voltage-loop transfer function of PFC bridge converter controlled by the proposed method is modeled, and the result is helpful to obtain the controller parameter. The proposed control method is implemented on the DSP-based platform for evaluation. Finally, the provided simulation and experimental results demonstrate the performance of the proposed method.

Dynamic Performance of Estimator-based Speed Sensorless Control of Induction Machines Using Extended and Unscented Kalman Filters

Abstract This paper presents an estimator-based speed sensorless field-oriented control (FOC) method for induction machines, where the state estimator is based on a self-contained, non-linear model. This model characterises both the electrical and the mechanical behaviours of the machine and describes them with seven state variables. The state variables are estimated from the measured stator currents and from the known stator voltages by using an estimator algorithm. An important aspect is that one of the state variables is the load torque and, hence, it is also estimated by the estimator. Using this feature, the applied estimator-based speed sensorless control algorithm may be operated adequately besides varying load torque. In this work, two different variants of the control algorithm are developed based on the extended and the unscented Kalman filters (EKF, UKF) as state estimators. The dynamic performance of these variants is tested and compared using experiments and simulations. Results show that the variants have comparable performance in general, but the UKF-based control provides better performance if a stochastically varying load disturbance is present.

Research on speed sensorless control of Maglev train with double-end power supply

Background: The core technology of the stable operation of the maglev train is how to accurately obtain the train speed, position and motor angle information.
 Aim: Using speed sensorless control method to estimate the speed and position of the maglev train.
 Methods of the studies: In the double-end power supply mode of the maglev train, the principle of the extended back electromotive force (EEMF) of the AC motor is extended to the control of the long stator permanent magnet synchronous linear motor.
 Results: The mathematical model for the power supply system of long-stator permanent magnet linear synchronous motor is established; based on the principle of EEMF of rotating motor, the EEMF observer is designed. The speed of the maglev train and the rotor angle are obtained by the method of phase locked loop (PLL).
 Conclusion: Through the semi-physical simulation experiment, the speed sensorless control method is verified to be effective.

Sensorless Control for Joint Drive Unit of Lower Extremity Exoskeleton with Cascade Feedback Observer

In this paper, a sensorless control method for joint drive unit driven by BLDC motor of low extremity exoskeleton, cascade feedback observer identification method, is proposed. The cascade feedback observer identification method is based on improved Integral-Switching-Function Sliding-Mode-Observer (ISF-SMO) and adaptive FIR filter. The improved Integral-Switching-Function Sliding-Mode-Observer is used to identify the back-EMF of motor. The sliding mode surface redesigned according to Integral-Switching-Function (ISF) eliminates the inevitable chattering problem in conventional Sliding-Mode-Observer (SMO). The stability condition of Integral-Switching-Function Sliding-Mode-Observer is obtained with Lyapunov function. Meanwhile, considering the estimation error and system instability caused by the mismatch between the actual resistance value (Rs) and the set resistance value, the LMS algorithm is used to estimate the resistance value online according to the structure of adaptive FIR filter. When system is running, the modified Integral-Switching-Function Sliding-Mode-Observer and adaptive FIR filter are used to modify the back-EMF and the resistance value by cascading feedback relation, and the modified back-EMF value is taken as the final output of the system. Because of considering the uncertainty of resistance caused by temperature variation, the robustness and stability of the cascade feedback observer can be improved. Meanwhile, higher estimation accuracy is obtained, and operation range of sensorless control is extended, which is suitable for motor in low speed region. Finally, the correctness and validity of the proposed method are verified by simulations and experiments.