Sensorless Position Estimation Research Articles

Super Twisting Sliding Mode Control with Compensated Current Controller Dynamics on Active Magnetic Bearings with Large Air Gap

Due to their unique properties, like no mechanical contact and therefore no wear and no lubrication needed, Active Magnetic Bearings (AMBs) have been a dynamic field of research in the past decades. The high non-linearities of AMBs generate many challenges for the control of the otherwise unstable system, thus they need to be addressed to deliver the performance that modern applications require. Integrating the current controller dynamics into the model of a position controller in a cascading control loop helps to improve the performance of the control loop compared to a plain current controlled schema. Further, this nested control loop guarantees the predefined current dynamics of the current controller, tuned according to an industrial criterion. The systems dynamics are modelled and the proposed controller is validated experimentally on a physical test bench. The experimental results show a performant position control with a nested and explicit current controller on an AMB, even with a large air gap and star-connected coils. The trajectory range of the rotor was reduced by 87% to ±20 μm, compared to a plain current-controlled model. The proposed control strategy lays the foundation for further research, especially concerning sensorless position estimation techniques since these usually have limited bandwidth and benefit from a predefined current dynamic.

Design and Implementation of a Driving Strategy for Star-Connected Active Magnetic Bearings with Application to Sensorless Driving

For decades, sensorless position estimation methods gained lots of interest from the research community, especially in the field of electric drives and active magnetic bearings (AMBs). In particular, the direct flux control (DFC) technique promises unique advantages over other sensorless techniques, such as a higher bandwidth, but on the other hand, it requires the coils to be connected in a star topology. Until now, star-point connections are rarely found on active magnetic bearings. In consequence, there is no known publication about the application of the DFC to an AMB to this date. In order to apply the DFC to an AMB, a star-point driving approach for AMBs must be developed beforehand. A star-connected driving approach, capable of driving a four-phase AMB, is proposed and validated against traditional H-bridges in a simulation. Further, the strategy is tested in a physical application and generalised for 4∗n phases. In terms of current dynamics, the simulation results can be compared to the well-known full H-bridge driving. The experiments on the physical application show that the actual current in the coils follows a reference with satisfactory accuracy. Moreover, the inductance measurements of the coils show a strong dependency on the rotor’s position, which is crucial for sensorless operation. A star-point connection delivers a satisfying response behaviour in an AMB application, which makes sensorless techniques that require a star point, such as the DFC, applicable to active magnetic bearings.

Integration of Measurement Vector Insertion With Discontinuous PWM to Improve Saliency-Based Sensorless Drive Position Estimation

Saliency-based position sensorless machine drive with the pulsewidth modulation (PWM) voltage switching frequency injection has advantages of high estimation bandwidth and low acoustic noise. However, multiple currents must be sampled every PWM cycle for spatial saliency calculation. Besides, the switching frequency voltage injection distorts the symmetric PWM voltage pattern. For these saliency-based drives, the PWM injection is the tradeoff between the transient estimation bandwidth and steady state estimation error. This article proposes a modified PWM voltage injection through the measurement vector insertion (MVI) for sensorless position estimation. By integrating the MVI with discontinuous PWM, the proposed injection maintains the symmetric PWM voltage for machine control. This MVI-based PWM (MVIPWM) improves the saliency-based drive among voltage harmonics, current harmonics, and position estimation error. The proposed MVIPWM injection is compared to other PWM injection methods on an interior permanent magnet machine. All advantages of MVIPWM on the saliency-based drive are verified by experimental results.

Flexible Sensorless Position Control of Switched Reluctance Motors considering Both Embrace Design and Magnetic Saturation

Precise estimation of position is essential in the control of switched reluctance motors (SRMs). Traditionally, the intersection of the adjacent inductance can be utilized to estimate the rotor position, however, magnetic saturation brings about variations in the intersection position when the motor is operated at heavy load. To solve this problem, this paper develops a sensorless position estimation strategy considering magnetic saturation and the embrace design. Sensorless control approaches can be chosen interchangeably according to the characteristics of the intersection. Rotor position estimation is achieved by employing six typical inductance positions. No additional position sensor and other detection devices are required. Through simulation and experiment, the feasibility and validity of the proposed position estimation method are verified. The proposed sensorless method is verified for acceleration, constant operated state, and load mutation.

Sensorless Position Control of Linear Electromagnetic Actuator for Gear Shift Unit

Conventional manual transmissions suffer from deterioration due to wear and reduced responsiveness. Therefore, a linear electromagnetic actuator (LEA) for gear shifting has been developed. Since the LEA is a direct drive, it prevents deterioration due to wear and has high responsiveness. In addition, this LEA has a high holding force by detent force at three points. In this paper, sensorless position estimation is performed to simplify the system. Since one coil is not energized during driving in this LEA, so the back-EMF of the unenergized phase can be measured. We propose a sensorless position estimation method that focuses on the variation of the magnetic flux linkage characteristics in the position change. The simulation results show that the sensorless position control is possible.

Sensorless Control of Separately Excited Synchronous Electrostatic Machines

This article presents the analysis and demonstration of sensorless position estimation methodologies for separately excited synchronous electrostatic machines (SEMs). The torque density of the SEM comes at the cost of a high pole count (p >50) along with other enhancements. The high pole count makes the use of high-resolution position sensors necessary, driving up the cost of the system. The sensorless estimation of rotor position is seen as a solution for alleviating the need for high-resolution and high-cost position sensors. Key features of electrostatic machines that make them suitable for sensorless operation are identified. Back MMF (current) based rotor position sensing for medium to high speeds is investigated. High-frequency injection-based position estimation is investigated for zero and low-speed operating regions. The proposed methods are experimentally demonstrated using a current-source inverter-based drive platform.

A Reliable Sensorless Starting Scheme for SRM With Lowered Pulse Injection Current Influences

In this article, a synthetic sensorless starting scheme, which is based on pulse injection technology, is proposed for switched reluctance motor (SRM) drives to enhance the starting reliability. This scheme consists of a set of sensorless position estimation algorithms for different stages of SRM starting. In order to start the SRM from standstill stage smoothly, the initial driving phase is selected by pairwise comparing of the three-phase inductance. Then, to ensure reliable starting acceleration, a double inductance dynamic thresholds algorithm is developed for estimating the direct phase-driving signals. Meanwhile, to estimate the real-time rotor position, a position index pulse estimation algorithm, which is with phase lacking fault-tolerant capability, is developed based on an idle phase inductance threshold. By seamless switching between the above mentioned two algorithms, higher reliability of the sensorless starting control can be achieved. Furthermore, the performance of three pulse injection methods are compared, and the best one is then selected to reduce the influences of the high-frequency pulse signals in the idle phases. The theoretical analysis and experimental results are provided to verify the feasibility of the proposed control scheme.

A fault tolerant sensorless position estimation scheme for switched reluctance motor at low speed

Purpose This paper aims to present a novel position sensorless control scheme with fault-tolerance ability for switched reluctance motor at low speed. Design/methodology/approach First, the detection pulses are injected in the freewheeling and idle intervals of each phase. Second, the aligned position of each phase can be detected by comparing the consecutive rise time of detection current. Third, the whole-region rotor position and real-time rotational speed can be updated four times for the improvement of detection accuracy. Finally, the fault-tolerant control strategy is performed to enhance the robustness and reliability of proposed sensorless scheme under faulty conditions. Findings Based on proposed sensorless control strategy, the estimated rotor position is in good agreement with the actual rotor position and the maximum rotor position error is 1.5°. Meanwhile, the proposed sensorless scheme is still effective when the motor with multiphase loss and the maximum rotor position error is 1.9°. Moreover, the accuracy of the rotor position estimation can be ensured even if the motor is in an accelerated state or decelerated state. Originality/value The proposed sensorless method does not require extensive memory, complicated computation and prior knowledge of the electromagnetic properties of the motor, which is easy to implement. Furthermore, it is suitable for different control strategies at low speed without negative torque generation.

Online Calibration of Sensorless Position Estimation for Switched Reluctance Motors With Parametric Uncertainties

This article proposes an online calibration strategy of sensorless position estimation for switched reluctance motors (SRMs) with parametric uncertainties. For conventional sensorless SRM drives, the voltage drops on power devices and the winding resistance changing with the current and temperature are neglected, which affects the accuracy of the estimated position. In this article, an inductance calculation scheme is proposed to improve the real-time position estimation with these parametric uncertainties. First, the calculation errors of the flux linkage and inductance are both investigated and the error correction of the estimated rotor position is analyzed in detail. Then, the inductance values of the current overlapped phases are calculated. The dc component of the phase inductance is online adjusted, where all three phase inductances can be easily obtained accordingly. Finally, the real-time rotor position is acquired by the coordinate transformation of the calculated three-phase inductance during the current overlapped region. Compared to conventional SRM sensorless drives, the error of the estimated position due to parametric uncertainties can be significantly reduced without pulse injection, extra hardware, and prestored flux linkage and inductance profiles. The simulation and experiments are carried out on three-phase and four-phase SRMs to validate the effectiveness of the proposed scheme.

High frequency injection-based sensorless position estimation in permanent magnet synchronous machines

This paper is concerned with the application of both a high frequency injection voltage together with a Search-based Online Commissionable (SONIC) sensorless position observer for Surface Mounted Permanent Magnet Synchronous Machines. The proposed algorithm is based on an iterative search of position dependent saliency maps commissioned online with the aim to make the technique also applicable to machines with non-ideal sinusoidal saliencies. Experimental results for estimation at low and zero speed are discussed. The paper even presents sensorless current and speed operation of the machine at varying loads.

Sensorless Position Estimation of a Planar Motor Having Multi Movers

A planar motor with multiple movers has been developed to save the temporary storage space and automate packages loading and unloading in small warehouses. We propose a sensorless position estimation method for the multiple movers with permanent magnets and iron cores using each coil’s inductance under the movers. The inductances are measured in real-time using the current response, and each distance between the coil and the iron core is determined. The position measurement accuracy is evaluated using an experimental planar motor.

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.

A Novel Sensorless Rotor Position Estimation Method for PMSM Based on High-Frequency Square-Wave Voltage Injection with Less Iron Loss

A novel sensorless rotor position estimation method for permanent magnet synchronous machine (PMSM) based on high-frequency square-wave (HFSW) voltage injection has been proposed in the article. Comparing with the existing HFSW voltage injection schemes, the proposed method features a unipolar injection into the estimated synchronous reference frame which can decrease the energy loss resulting from HFSW injection and hence improve the system efficiency. A practical calculation method based on the co-simulation platform integrating Matlab and finite-element analysis (FEA) tools are also proposed in the article to study and compare the energy loss resulting from different HF injection schemes. Both simulation and experimental verification are conducted in the article to verify the feasibility of the proposed strategy.

Circuit‐based flux linkage measurement method with the automated resistance correction for SRM sensorless position control

The accuracy of flux linkage measurement is significantly important for a number of sensorless control methods for switched reluctance motor (SRM). This study proposes a novel flux linkage measurement circuit with the automated resistance correction, which comprises only circuit components. During the SRM sensorless operation, the dependence of resistance on temperature leads to the errors in flux linkage measurement and position estimation. The developed scheme is based on the zero-crossing property which asserts that the flux linkage and current pass through zero simultaneously. Hence, the flux linkage error captured at the time when the current falls to zero represents the resistance error and is used for resistance correction. The proposed circuit has been successfully implemented and tested on a sensorless SRM system. Experiment results indicate that the proposed system in sensorless control can be operated stably at different load torques and at the condition of given speed mutation and load mutation, and the speed range in steady state with rated load torque is 0-160 r/min. The overall estimated position error remains within an acceptable margin of 2%. Hence, it significantly improves the sensorless position estimation and thus SRM performance.

Novel laser processed shape memory alloy actuator design with an embedded strain gauge sensor using dual resistance measurements. Part I: Fabrication and model-based position estimation

Shape memory alloys have sparked great amount of interest in the field of actuation over the past decades. Until now, sensorless position estimation of SMA actuators under dynamic unknown applied stresses has not been feasible due to the complexity of the system and the number of unknown parameters which the proposed extra information obtained from the embedded sensor solves. In this paper, a novel laser processed NiTi shape memory alloy (SMA) actuator is proposed containing two different material compositions in one monolithic piece of actuator wire. Each of these compositions behaves differently at room temperature, one exhibits a shape memory effect (SME) for actuation, and the other is pseudo-elastic (PE) which is used to enable an embedded sensor. Fabrication of the wire included laser processing, heat-treatment, and cold-working procedures. The actuator wire was subsequently trained to stabilize its properties using iso-stress thermal cycling. Additionally, a novel model-based sensorless position estimation algorithm is presented. Proposed model can estimate the position of the actuator under varying applied stresses with an approximate accuracy of 95% only using dual resistance measurements across the two different material compositions. The proposed actuator has significant application in robotics, wearables, haptics, automotive, and any other application which the mechanical load is not known in advance.

A Joint Feature Position Detection-Based Sensorless Position Estimation Scheme for Switched Reluctance Motors

For a switched reluctance motor, it is important to simplify the sensorless control method in medium and high speed operation. A key solution is to detect a single feature position in a single electric cycle. Normally, the aligned position is a typical feature position, which needs to be detected. However, it is difficult to locate the aligned position with the traditional phase inductance slope zero-crossing scheme, especially when the turn-on angle is advanced. In this paper, a transformer electromotive force and motional electromotive force crossing point estimation method is presented, which is combined with the phase inductance slope zero-crossing point estimation method to estimate the aligned position. This method is capable of avoiding the error position index pulses generated at the turn-on position and the regions nearby the unaligned position. Only one position index pulse that represents the aligned position in each electric cycle can be estimated. The experimental results verify the validity of the proposed method.

Sensorless position control with a hydraulic stepper drive — Concept, compression modeling and experimental investigation

This paper presents a new type of a linear hydraulic stepper drive for sensorless positioning tasks in hydraulics. The drive transforms pulses sent to switching valves into quite precise motion steps. The drive is realized by a hydraulic cylinder piston unit which displaces defined fluid quantums by limited forward strokes of that piston.A test rig (hydraulic cylinder with a hydraulic stepper unit) was built and experiments were performed to study the positioning accuracy, repeatability, linearity and scattering range of the proposed stepper drive concept. Two different step sizes (5 µm and 15 µm) were tested and investigated. Also a computation model was developed for sensorless position estimation and verified by measurements. The results show the quite good accuracy of the model for all tested operating conditions.An application example is studied, the sensorless control of the deflection of an elastic beam. Its experimental testing was done by hardware in the loop simulation, where the computed beam force is imposed to the physical stepper drive via a controlled hydraulic force. The results proof the practical suitability of the drive concept.

Environmental Robust Position Control for Compact Solenoid actuators by Sensorless Simultaneous Estimation of Position and Force

This paper aims to realize compact actuation systems by sensorless approach. This study adopts solenoid actuators which have advantageous characteristics from the view point in inexpensive cost, simple structure, and high-output force in spite of difficulty in low cost position and force sensing. Some sensorless position estimation techniques for solenoid actuators were reported. However, position and force simultaneous estimation has not sufficiently been achieved. In addition, any real-time feedback control has not been reported. This paper proposes sensorless feedback position control for compact solenoid actuators. The force generation and position/force estimation are conducted by using a dc supply power superposed by an ac component. This control technique has three main features: 1) separation of the power supply into ac and dc components for the position estimation, 2) simultaneous real-time estimation of position and force, and 3) robust feedback position control. Simulations and experiments were conducted for verification of the proposed control with the above three features, and the results indicated that error between the estimation and actual positions was within 0.2 mm. This proposed system offers a new avenue for compact and inexpensive application field.

Pulse Counting Sensorless Detection of the Shaft Speed and Position of DC Motor Based Electromechanical Actuators

Some of DC actuators used in home automation, office automation, medical equipment and automotive systems require a position sensor. In low power applications, the introduction of such a transducer remarkably increases the whole system cost, which justifies the development of sensorless position estimation techniques. The well-known AC motor drive sensorless techniques exploiting the fundamental component of the back electromotive force cannot be used on DC motor drives. In addition, the sophisticated approaches based on current or voltage signal injection cannot be used. Therefore, an effective and inexpensive sensorless position estimation technique suitable for DC motors is presented in this paper. This technique exploits the periodic pulses of the armature current caused by commutation. It is based on a simple pulse counting algorithm, suitable for coping with the rather large variability of the pulse frequency and it leads to the realization of a sensorless position control system for low cost, medium performance systems, like those in the field of automotive applications.

A Position Sensorless Control of Switched Reluctance Motors Based on Phase Inductance Slope

A new sensorless position estimation method for switched reluctance motor (SRM) drives is presented in this paper. This method uses the change of the slope of the phase inductance to detect the aligned position. Since the aligned positions for successive electrical cycle of each phase are apart by a fixed mechanical angle 45° in the case of 12/8 SRM, the speed of the machine can be calculated to estimate the rotor position. Since no prior knowledge of motor parameters is required, the method is easy for implementation without adding any additional hardware or memory. In order to verify the validity of this technique, effects such as changes in the advanced angle and phase lacking faults are examined. In addition, an inductance threshold based sensorless starting scheme is also proposed. Experimental results demonstrate the validity of the proposed method.