This paper improves the surface permanent magnet (PM) machine position sensorless drive at low speed. Considering the surface PM machine (SPM) drive, EMF voltage or flux linkage should be estimated for the sensorless drive. Different from EMF voltage, the flux linkage based on the voltage integration is theoretically independent to speed which is suited for the low speed position estimation. In this paper, several improvements on the flux-based sensorless drive are proposed to enhance the low speed dynamic performance. First, a modified voltage integration is develop to remove the flux estimation drift caused by voltage or current offset. This integration contains a high-pass filter (HPF) for the DC drift elimination. In addtion, the filter delay is compensated to maintain the flux phase. Second, inverter deadtime harmonics are decoupled with the knowledge of actual machine phase voltages. It is shown that the position estimation error is decreased for the better low speed performance. According to experimental results, SPM machine sensorless drive is enhanced at 4%∼ 6% speed region from many aspects. They include position signal SNR, position error and drive dynamic response. More importantly, the overall current regulation bandwidth can increase to 1kHz at low speed. It is compatible to standard encoder-based field oriented control (FOC) drives. INDEX TERMS Permanent magnet machine, flux observer and position sensorless drive.
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.
This paper proposes a torque ripple reduction for brushless DC (BLDC) permanent magnetic (PM) motor drive based on the DC-link voltage pulse amplitude modulation (PAM). The proposed method improves torque ripple drawback for BLDC drives at low speed. BLDC drives have the better inverter efficiency and requires low position sensing resolution. However, both freewheeling current during diode conduction and discontinuous motor phase current cause high torque ripples. In this paper, a frontend DC converter is added to improve BLDC torque ripples. Although the integration of DC converter and BLDC drive has been reported, the DC voltage regulation for the BLDC torque ripple compensation is this paper novelty. On the basis, the DC bus is modulated during diode conduction to manipulate the DC current dynamically every BLDC commutation period. In addition considering the discontinuous sixstep commutation, the DC current is also regulated with the 6th-order spatial harmonic to minimize the commutation reflected torque ripple. The proposed torque ripple compensation of BLDC drive is verified by simulation for different PM motor types. According to experimental results, around 40% torque ripple reduction on a PM motor is demonstrated using the proposed BLDC drive with DC voltage modulation.
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.
This paper investigates digital implementation issues on high-speed permanent magnet (PM) machine drives. The machine operating speed is designed beyond 30krpm where the ratio of controller sample frequency over rotor f sample operating frequency f e is less than 5. Because microcontrollers are used in variable frequency drives to realize the field oriented control (FOC), the discretized effects must be considered to maintain the controller stability under low ratios of f sample /f e. In this paper, the FOC based on different digital controllers is compared specifically at low f sample /f e. It is shown that digital controllers using forward difference and bilinear approximation are able to maintain the drive stability if the voltage delay and inductance cross-coupling are compensated. However, the drive performance strongly depends on the accuracy of the inductance parameter. By contrast, the controller using direct digital design achieves the better FOC performance independent to machine parameters. Different types of controllers have experimentally compared to find a suited high-speed FOC drive. This paper includes the design guidance of high-speed FOC drive for PM machines with different time constants. INDEX TERMS Machine drives, digital controller, discrete-time approximation, field oriented control.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.