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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 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]

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]

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 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]

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]