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This paper proposes a novel torque measurement and control technique for cycling-assisted electric bikes (E-bikes) considering various external load conditions. For assisted E-bikes, the electromagnetic torque from the permanent magnet (PM) motor can be controlled to reduce the pedaling torque generated by the human rider. However, the overall cycling torque is affected by external loads, including the cyclist's weight, wind resistance, rolling resistance, and the road slope. With knowledge of these external loads, the motor torque can be adaptively controlled for these riding conditions. In this paper, key E-bike riding parameters are analyzed to find a suitable assisted motor torque. Four different motor torque control methods are proposed to improve the E-bike's dynamic response with minimal variation in acceleration. It is concluded that the wheel acceleration is important to determine the E-bike's synergetic torque performance. A comprehensive E-bike simulation environment is developed with MATLAB/Simulink to evaluate these adaptive torque control methods. In this paper, an integrated E-bike sensor hardware system is built to verify the proposed adaptive torque control. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This article improves the sensorless brushless dc (BLdc) motor drives using the pulse amplitude modulation (PAM) with dc current sensing. Comparing to conventional BLdc drives using pulsewidth modulation (PWM), PAM BLdc drives result in better drive efficiency especially at low speed. However due to six-step commutation, additional position detection issues are resultant for the sensorless operation. They consist of voltage spike at low speed and commutation delay at high speed. In this article, these BLdc position detection issues are improved based on the proposed continuous position estimation. At low speed, the commutation compensation with dc current sensing is developed to minimize the influence of voltage spike. At high speed, several voltage compensation schemes are applied to improve the commutation delay and maximizing high-speed operation region. A 320-W permanent magnet motor prototype is used for the experimental verification of proposed PAM BLdc drive. Comparing to the conventional BLdc drives, the PAM drive with proposed position estimation demonstrates the improvement on both low-speed dynamic response and high-speed steady state stability. [ABSTRACT FROM AUTHOR]

For saliency-based position sensorless drives, the switching frequency pulsewidth modulation (PWM) voltage injection can achieve noise-free position estimation which is suited for high-performance motion systems. However, considering the switching frequency injection, multiple phase currents should be sampled per PWM cycle instead of single average current. It leads to the implementation issue on the space-vector PWM (SVPWM) inverter using shunt resistor current sensing for machine control. In this article, a modified PWM injection instead of SVPWM injection is proposed for the saliency-based drive using shunt current sensing. It is concluded that at least two transient currents can be sampled per PWM cycle based on the proposed PWM control. More importantly, the field-oriented control is maintained when the saliency-based drive is applied. A 2 kW permanent magnet (PM) machine is used for the experimental verification. This article includes the position estimation comparison using either the proposed PWM injection with shunt resistors or standard SVPWM with Hall-effect sensors. [ABSTRACT FROM AUTHOR]

This paper proposes a sensorless vibration harmonic frequency estimation for a servo system driven by a permanent magnet (PM) synchronous machine. Traditional vibration harmonic estimation relies on the measurement using external sensors. An accelerometer is typically installed in the servo system to measure the vibration harmonic signal. Because the accelerometer must be attached on the visibly vibrational location inside the system, this vibration detection results in both issues about installation and reliability. To overcome this drawback, this paper proposes a disturbance observer to estimate the vibration harmonic by using current and position signal. A real-time signal process is developed to identify the vibration frequency from estimated harmonic. A servo system with a 400-W PM machine is built to verify the proposed vibration harmonic and frequency estimation. This paper includes the comparative evaluation between the accelerometer-based vibration harmonic measurement and the sensorless estimation. [ABSTRACT FROM AUTHOR]

This paper improves the position sensorless drive by sensing actual machine phase voltages. A high-bandwidth phase voltage measurement is developed for pulsewidth modulation (PWM) voltage inverters. On the basis, the actual phase voltage is obtained based on the digital integration of PWM voltage using the capture modulator in existing drive microcontrollers (MCU's). Comparing to existing phase voltage measurement, no separated A/D converter and communication hardware are required because PWM pulses are directly measured using MCUs. However, for standard machines without neutral points, only line-to-line ac PWM voltages can be measured for the phase voltage reconstruction. Since the capture based on transistor-transistor logic (TTL) logics receives only digital signals, a preprocess circuit to convert ac PWM line voltages to equivalent digital signals is proposed. This paper clearly explains the voltage sensing hardware using MCU capture modulator. According to experimental results, a 150-MHz sampling rate for phase voltage measurement is achieved based on the proposed capture-based voltage measurement. Although the physical limitation of back electromotive force estimation still appears, the proposed phase voltage measurement substantially enhances the sensorless drive performance at low speed. [ABSTRACT FROM AUTHOR]

This paper analyzes different stator windings configurations for permanent-magnet synchronous machines during the presence of a stator turn fault. Due to the inverter pulsewidth modulation, the fault commonly occurs in variable-frequency permanent-magnet machine drives. In this paper, two types of windings are compared to identify key machine topologies that can achieve the reduced influence of the turn fault. When the machine is operated in real time, the windings with separated neutral points reduce the torque ripple caused by fault-reflected flux harmonics. Analytical models based on equivalent circuits are developed to predict the machine flux and torque waveform during the presence of the turn fault. All developed analytical models are verified by the finite-element analysis and experimental results on a 750-W surface permanent-magnet machine prototype. [ABSTRACT FROM AUTHOR]

This paper analyzes the influence of stator windings turn-to-turn fault on inverter-fed permanent magnet (PM) machines. By adding a secondary neutral point (NP) in stator windings, the turn fault detection and tolerant capability can all improve considering a small turn-to-turn short at an early stage. From the perspective on fault detection, the proposed windings with two NPs increase the equipment impedance per NP. Once a turn fault occurs, the fault-induced voltage harmonic magnitude increases. It results in a better signal-to-noise ratio for the fault detection. From the perspective on tolerant drive, the fault-induced circulating currents can flow across different phase coils in the windings with two NPs. Reduced effect on circulating currents in a faulty machine is achieved due to the current diversion. Turn fault induced additional losses are then decreased compared to conventional windings with only one NP. A 1-kW PM machine with two different windings is tested to verify the fault detection and tolerant performance. [ABSTRACT FROM AUTHOR]

Conventional permanent magnet (PM) machine open-phase fault detection relies on the estimation of current harmonics using available phase current sensors. Because the magnitudes of current harmonic are proportional to the machine load condition, it is still a challenge to detect a phase fault at light load when fault-induced current harmonics are too small to estimate. This paper investigates the phase fault detection specifically for the conditions under low fault harmonic magnitudes. Both fault-induced harmonics in dq currents and neutral point (NP) voltage are analyzed to find a suited signal for the fault detection. By adding a voltage sensor to measure the NP voltage in a PM machine, a better fault detection performance is achieved because the fault harmonic in NP voltage results in the reduced effect on torque loads and sensor measurement errors. A 50-W PM machine is tested to verify the phase fault detection performance under low fault harmonic magnitudes. This paper includes the experimental evaluation on the detection limitation in terms of load capability using current and voltage fault signals. [ABSTRACT FROM PUBLISHER]

Because single-phase dc-excited flux switching machines (DCFSMs) consist of only copper windings and iron cores, they have great potential in low-cost and high-speed applications, such as home appliances. However, similar to other types of single-phase ac machines, single-phase DCFSMs have insufficient initial torque at some rotor positions. A novel single-phase, eight-slot, four-pole DCFSM design is presented in this paper. The key feature of this design is the enhancement of reluctance torque at positions where the machine cannot deliver sufficient initial torque output. This is accomplished by modifying the outline of a section of the rotor. Consequently, the machine has a two-layer rotor structure along the axial direction. The proposed design is validated experimentally using a prototype. The results show that the machine can start from any rotor positions with initial torque higher than 50% of the rated output torque. [ABSTRACT FROM AUTHOR]

This paper aims to improve the full speed sensorless drive for permanent-magnet (PM) synchronous machines on the region of initial zero speed and the region of medium speed. At zero and low speed, the saliency-based drive using the square-wave voltage injection has demonstrated the comparable performance to the sensor-based drive using the encoder with hundreds of pulses per revolution. For PM machines at initial state, the magnet polarity is typically identified based on the injection of voltage pulses before the saliency-based drive. Instead of pulses injection, this paper directly adds the polarity detection capability in the saliency-based drive by superimposing the same square-wave voltage. A fast detection period and negligible current spikes are benefits for the drive using the same square-wave injection voltage for both the polarity detection and position estimation. At medium speed, electromotive force voltage can be estimated to replace the saliency for the sensorless drive. To achieve a smooth operation between two estimation methods, a transition algorithm is also proposed based on a single-phase-lock loop by blending two feedback position signals. According to the experimental evaluation, the reduced power consumption as well as the smooth switch between two different drives is achieved. All the sensorless methods are verified by an interior PM machine with a saliency ratio of 1.37 (Lq/ Ld\,= \,1.37 ). [ABSTRACT FROM AUTHOR]

Although it is widely known that the saliency-based position-sensorless drive is able to achieve the closed-loop control at zero and low speed, there is little literature addressing the consideration on the selection of injection voltage frequency. This paper evaluates the square-wave injection voltage at different frequencies for the design of an interior permanent-magnet (PM) machine sensorless drive. It is shown that more flux saturation on high-frequency (HF) d-axis inductance occurs than the saturation on q-axis inductance due to the magnetic relaxation. The HF saliency ratio \rm(L\rm{qhf}\rm{/ }L\rm{dhf}\rm{)} is increased by increasing the injection frequency. The performance of a saliency-based sensorless drive can be enhanced by properly designing the frequency of injection voltage. This paper also includes the experimental comparison between closed-loop encoder-based and closed-loop saliency-based sensorless operation of an interior PM machine drive. [ABSTRACT FROM AUTHOR]

This paper proposes a stator turn-to-turn fault detection for inverter-fed electric machines using the voltage difference between two neutral points (NP's). By designing machine Y-connected windings with a secondary NP, a voltage difference between two NP's appears once a turn fault occurs. Because this fault signal is induced by the voltage difference between two independent windings, only the turn fault reflected signal is resultant. It leads to an important improvement on the fault detection of electric machines since NP voltages difference is immune to the influence of saliency and flux saturation. In addition, the load and speed affect the signal level and frequency, but not the detection accuracy. It is possible to monitor a small turn fault during the machine real-time operation. A 1-kw permanent magnet machine and a 200-W induction machine with proposed two independent Y-connected windings are tested for the experimental evaluation. [ABSTRACT FROM PUBLISHER]

This paper presents a saliency-based position sensorless drive of permanent-magnet (PM) machines using a single current sensor for cost-effective applications. For the single current sensor system, the dc-link current is measured for the reconstruction of three-phase currents. The phase current reconstruction can only be realized when active voltages are applied. This limitation results in six immeasurable areas for the current reconstruction using the pulsewidth modulation. In order to implement the saliency-based sensorless drive, a square-wave voltage is injected to minimize the harmonics of reconstructed saliency current for the rotor position estimation. By injecting a square-wave voltage on the direction of the rotor $d$-axis, the injection voltage vector is nearly perpendicular to the fundamental voltage vector at low speed. The saliency reflected current or the fundamental current can be separately reconstructed by the dc-link current, leading to the reduced reconstruction errors and improved sensorless performance. By using the proposed signal injection technique on a single sensor system, the saliency-based sensorless drive can work on an interior PM machine with a salient ratio of L_{q}/L_{d} = 1.35 at 1% rated speed (60/6000 r/min) under full torque load based on the experimental evaluation. [ABSTRACT FROM PUBLISHER]

This paper presents a systematic analysis of iron and magnet losses in surface-permanent-magnet (SPM) machines for the position estimation using high-frequency (HF) signal injection. Standard SPM machines with cylindrical rotors are analyzed. It is shown that the magnet eddy current loss due to the superimposed HF signal should be considered for SPM-machine injection-based position estimation. With a proper machine design, the resulting HF armature flux linkage in the magnet can convert to the HF leakage flux in the stator. The decreased magnet eddy current loss can be achieved, leading to better performance on both power conversion and injection-based position estimation. This paper includes the experimental evaluation of two SPM machines with different winding configurations. [ABSTRACT FROM AUTHOR]

This paper presents injection-based self-sensing (position sensorless) control methods for surface permanent magnet (SPM) machines with concentrated windings (CWs) and distributed windings (DWs). Two position-dependent spatial saliency signals are compared. The two signals relate to resistance variation due to high-frequency eddy current losses and to inductance variation due to stator tooth saturation. Finite-element analysis is performed to investigate the properties of two saliency signals in different SPM machines. Implementation methods, as well as advantages for closed-loop control, are discussed. This paper includes experimental evaluation of resistance-based versus inductance-based self-sensing control performance in SPM machines with CWs and DWs. [ABSTRACT FROM PUBLISHER]

This paper proposes an improved method for the estimation of position, velocity, and disturbance torque in a surface permanent-magnet (SPM) machine self-sensing (position sensorless) drive that uses high-frequency (HF) voltage injection. SPM machines traditionally do not have enough position-dependent signals because their symmetric rotors result in near-zero spatial saliency. A separate disturbance observer and a saliency-tracking observer with speed-varying bandwidth (BW) tuning are used together to improve the disturbance rejection performance while maintaining the accuracy of self-sensing position and velocity estimation. According to the experimental evaluation, the proposed estimation method can achieve higher BW for the disturbance estimation and decoupling which can increase the stiffness of SPM machine closed-loop self-sensing control. This paper includes experimental comparative evaluation of closed-loop encoder-based versus closed-loop self-sensing-based operation of a SPM machine drive. [ABSTRACT FROM AUTHOR]

Elimination of externally mounted position sensors and their associated cables is a goal for drive manufacturers. This paper addresses design methods of surface-permanent-magnet (SPM) synchronous machines for saliency-tracking self-sensing (position sensorless) position estimation. Machine spatial saliency is created by stator magnetic saturation due to the rotor zigzag leakage flux from SPMs. Using the machine saliency created by zigzag leakage flux can allow an SPM machine to be suitable for saliency-tracking position estimation without the need of any special rotor design modification. In addition, another major benefit is achieved, i.e., a saliency role reversal whereby Ld > Lq. This has the advantage of reducing machine cross-saturation and increasing the feasible region for closed-loop self-sensing control. All the design procedures are verified by the finite-element analysis, and a 50-W SPM machine is used for experimental evaluation. [ABSTRACT FROM AUTHOR]

This paper proposes a high-resolution permanent magnet (PM) motor drive based on acceleration estimation and control. The PM motor is widely implemented in the printed circuit board (PCB) manufacturing process. To achieve the demanded 1 μm drilling resolution, a sine/cosine incremental encoder is usually installed for motion control. In this paper, several improvements are developed to increase the motion control steady-state accuracy balancing transient response. First, the interpolation of every two encoder counts is proposed to increase the position sensing resolution. In this case, the transient response is improved through the high-resolution position feedback. Second, a closed-loop observer with two independent bandwidths is proposed for acceleration estimation. By using the interpolated position for acceleration estimation, the vibration-reflected high-frequency torque harmonics can be compensated through the acceleration closed-loop control. It reduces the steady-state error under the same sensing hardware. According to experimental results, both transient response and steady-state error can be improved on a PM motor using the proposed position interpolation and acceleration control. [ABSTRACT FROM AUTHOR]

For pulse width modulation (PWM) inverter drives, an LC filter can cascade to a permanent magnet (PM) machine at inverter output to reduce PWM-reflected current harmonics. Because the LC filter causes resonance, the filter output current and voltage are required for the sensorless field-oriented control (FOC) drive. However, existing sensors and inverters are typically integrated inside commercial closed-form drives; it is not possible for these drives to obtain additional filter output signals. To resolve this integration issue, this paper proposes a sensorless LC filter state estimation using only the drive inside current sensors. The design principle of the LC filter is first introduced to remove PWM current harmonics. A dual-observer is then proposed to estimate the filter output current and voltage for the sensorless FOC drive. Compared to conventional model-based estimation, the proposed dual-observer demonstrates robust estimation performance under parameter error. The capacitor parameter error shows a negligible influence on the proposed observer estimation. The filter inductance error only affects the capacitor current estimation at high speed. The performance of the sensorless FOC drive using the proposed dual-observer is comparable to the same drive using external sensors for filter voltage and current measurement. All experiments are verified by a PM machine with only 130 μH phase inductance. [ABSTRACT FROM AUTHOR]

Different from the design of conventional permanent magnet (PM) motors, high-speed motors are primarily limited by rotor unbalanced radial forces, rotor power losses, and rotor mechanical strength. This paper aimed to propose a suitable PM motor with consideration of these design issues. First, the rotor radial force is minimized based on the selection of stator tooth numbers and windings. By designing a stator with even slots, the rotor radial force can be canceled, leading to better rotor strength at high speed. Second, rotor power losses proportional to rotor frequency are increased as motor speed increases. A two-dimensional sensitivity analysis is used to improve these losses. In addition, the rotor sleeve loss can be minimized to less than 8.3% of the total losses using slotless windings. Third, the trapezoidal drive can cause more than a 33% magnet loss due to additional armature flux harmonics. This drive reflected loss is also mitigated with slotless windings. In this paper, six PM motors with different tooth numbers, stator cores, and winding layouts are compared. All the design methods are verified based on nonlinear finite element analysis (FEA). [ABSTRACT FROM AUTHOR]

This paper improves a permanent magnet (PM) machine saliency-based drive performance based on the selection of a suitable injection signal. For the saliency-based position estimation, a persistently high-frequency (HF) voltage signal is injected to obtain a measurable spatial saliency feedback signal. The injection signal can be sine-wave or square-wave alternating current (AC) voltage manipulated by the inverter's pulse width modulation (PWM). Due to the PWM dead-time effect, these HF voltage injection signals might be distorted, leading to secondary harmonics on the saliency signal. In addition, the flux saturation in machine rotors also results in other saliency harmonics. These nonlinear attributes cause position estimation errors on saliency-based drives. In this paper, two different voltage signals are analyzed to find a suited voltage which is less sensitive to these nonlinear attributes. Considering the inverter dead-time, a sine-wave voltage signal reduces its influence on the saliency signal. By contrast, the flux saturation causes the same amount of error on two injection signals. Analytical equations are developed to investigate position errors caused by the dead-time and flux saturation. An interior PM machine with the saliency ratio of 1.41 is tested for the experimental verification. [ABSTRACT FROM AUTHOR]