Todd D. Batzel

Slotless permanent magnet synchronous motor operation without a high resolution rotor angle sensor

An implementation for sinusoidal current control of a slotless permanent magnet synchronous motor (PMSM) with discrete Hall sensor position feedback is presented. To estimate the rotor position of the slotless PMSM, a flux estimation technique is used that takes advantage of the slotless machines characteristically low inductance to limit flux estimation error. The rotor position is estimated using a reference model and the measured phase currents and voltages. At startup and very low speeds, discrete Hall sensors are used to limit the position estimation error to approximately /spl plusmn/30 electrical degrees and to prevent the flux estimators from drifting due to measurement noise and offset. The proposed sinusoidal control method reduces the torque pulsations present when Hall sensor position feedback alone is used and eliminates the need for high-resolution rotor angle sensors. The proposed control strategy is applied to a slotless PMSM drive system and implemented using a digital signal processor (DSP). Experiments are carried out for the system and the results demonstrate the effectiveness of the control.

Electric propulsion with the sensorless permanent magnet synchronous motor: model and approach

In this paper, a rotor position estimator for the sensorless permanent magnet synchronous motor (PMSM) is developed. The proposed approach exploits the time-scale separation between the electrical and mechanical time constant of the PMSM to formulate a linear observer. The observer produces accurate rotor angle estimates in steady-state and transient, and is attractive for electric propulsion applications due to its independence from mechanical parameters such as load torque, inertia, and friction. The sensorless strategy is well-suited to the nonsaturating slotless PMSM, but the demonstrated robustness of the observer to modeling uncertainties allows for application to slotted construction as well. Experiments are conducted to confirm the effectiveness of the proposed approach.

Decoupled Current Control of Sensorless Induction-Motor Drives by Integral Sliding Mode

This paper discusses the problems of current decoupling control and controller tuning associated with sensorless vector-controlled induction-motor (IM) drives. In field-oriented control, the d-q synchronous-frame currents should be regulated to have independent dynamics such that the torque production of the IM resembles that of a separately excited dc motor. However, these currents are not naturally decoupled, and decoupling compensators should be used. Current loop tuning is an additional problem, since controller gains obtained by theoretical methods or simulation, quite often, do not work well on the real system. This paper proposes a new approach for current control that uses integral-sliding-mode (ISM) controllers to achieve decoupling. The synchronous-frame control voltages are synthesized as the sum of two controller outputs: a traditional one (PI) that acts on an ideal plant model and an ISM controller. The ISM controller decouples the d-q currents and compensates the parameter variations in the current loops of the machine. Simulations and experimental tests on a 0.25-hp three-phase induction machine show satisfactory results.

Electric propulsion with sensorless permanent magnet synchronous motor: implementation and performance

There has recently been considerable interest in using the sensorless permanent magnet synchronous motor (PMSM) for vehicle propulsion systems. While many sensorless PMSM techniques have been presented in the literature, few have discussed in detail the underlying hardware and implementation issues. This work focuses on the implementation and application of a sensorless PMSM strategy that is particularly well suited for vehicle propulsion systems. The selected sensorless PMSM technique is implemented in a real-time motor control system to form a sensorless electric drive prototype. The hardware, strategy and implementation issues associated with the development of the sensorless drive are discussed. Experimental results are included in order to demonstrate the robustness of the implementation and the effectiveness of the sensorless drive under transient operating conditions such as startup and speed reversal.

An approach to sensorless operation of the permanent-magnet synchronous motor using diagonally recurrent neural networks

Due to the drawbacks associated with the use of rotor position sensors in permanent-magnet synchronous motor (PMSM) drives, there has been significant interest in the so-called rotor position sensorless drive. Rotor position sensorless control of the PMSM typically requires knowledge of the PMSM structure and parameters, which in some situations are not readily available or may be difficult to obtain. Due to this limitation, an alternative approach to rotor position sensorless control of the PMSM using a diagonally recurrent neural network (DRNN) is considered. The DRNN, which captures the dynamic behavior of a system, requires fewer neurons and converges quickly compared to feedforward and fully recurrent neural networks. This makes the DRNN an ideal choice for implementation in a real-time PMSM drive system. A DRNN-based neural observer, whose architecture is based on a successful model-based approach, is designed to perform the rotor position estimation on the PMSM. The advantages of this approach are discussed and experimental results of the proposed system are presented.

Commutation torque ripple minimization for permanent magnet synchronous machines with Hall effect position feedback

A permanent magnet synchronous motor (PMSM) with sinusoidal flux distribution is commonly commutated using discrete rotor position feedback from Hall sensors. A commonly used stator current excitation strategy used in such a system is a six-step current waveform. Application of sinusoidal current waveforms is shown to produce smooth torque in the PMSM. This paper shows how a pseudo-sensorless rotor position estimator may be used with Hall sensors to provide sinusoidal current excitation in place of six-step currents to reduce the torque ripple associated with the six-step strategy. Performance evaluation of the rotor position estimator in a PMSM drive is provided through simulation.

Instantaneous voltage measurement in PWM voltage source inverters

The use of pulse width modulated (PWM) inverters is nearly universal in industrial drives, making accurate voltage measurements problematic due to the switching nature of the applied phase voltage. Often, the applied phase voltage is reconstructed by using a combination of the DC link voltage and the commanded PWM duty cycle. Another approach is to apply a low-pass filter to the phase voltage to remove the high frequency PWM switching component, but leaving the fundamental component of interest. In this paper, a strategy for detecting the instantaneous phase voltage is presented. The approach consists of integrating the switched phase voltage over either a full, or half PWM cycle. The integrated signal is then converted to voltage by dividing by the integrating period. Implementation details of the proposed approach are outlined in the paper, and experimental results are used to compare the proposed technique with other methods of voltage measurement in terms of measurement accuracy and transient performance. The results will demonstrate the opportunity for improvements to any inverter-driven motor control system that relies on accurate terminal voltage measurement to estimate internal machine states.

Variable timing control for ARCP voltage source inverters operating at low DC voltage

The Auxiliary Resonant Commutated Pole (ARCP) inverter has been of interest in motor drive applications that can benefit from any combination of increased conversion efficiency, reduced EMI radiation, or higher PWM switching frequency. The ARCP inverter achieves high efficiency by turning the main switches on or off only under zero-voltage conditions. This reduces switching losses in the main circuit, and potentially increases overall conversion efficiency. Furthermore, the reduced loss in the main switch offers opportunity for higher switching frequencies, which is of benefit for ironless low-inductance motors that are widely being used in small to medium power vehicle propulsion applications. The soft-switching ARCP generates an output with significantly reduced dv/dt and di/dt as compared to hard-switched inverters, which tends to reduce EMI emissions. All of these attributes of the soft-switching ARCP are potentially beneficial in electric propulsion or electric vehicle auxiliary applications. In the ARCP inverter, the control signal timing for main and auxiliary switches is critical to maintain the most favorable operating conditions. Many ARCP implementations utilize a variable timing control, where load current polarity and magnitude are used to determine the control signal timing - usually without additional sensors. In this paper, the timing of main and auxiliary switching is examined for low dc bus voltage operation. A variable timing methodology for ARCP switching will be developed specifically to address issues associated with low-voltage ARCP operation. The operation principles are described, and simulation and experimental results are included to demonstrate the approach.

Starting method for sensorless operation of slotless permanent magnet synchronous machines

Slotless permanent magnet synchronous motors (PMSM) are receiving much attention for drive applications because of their high efficiency, high power-to-volume ratio, and their elimination of cogging torque. Furthermore, motor control without a rotational transducer is a subject that is receiving significant attention. In order to eliminate the need for high-resolution rotor position sensors, many sensorless techniques have been developed. It is well known, however, that sensorless operation is problematic at standstill-especially for a round rotor machine such as the slotless PMSM. Unless the initial rotor position is known, it is not possible to start the machine at full torque or to guarantee dither free startup. This paper presents a sensorless drive for a slotless PMSM with emphasis placed on stable startup by estimating the initial rotor position before starting. To estimate initial position, voltage pulses are applied to the stator windings. The resultant current measurements are then used to estimate the initial rotor position before starting. The proposed starting method for standstill rotor position identification is verified by experiment on a slotless PMSM.

Sliding Mode MRAS Speed Estimators for Sensorless Control of Induction Machine under Improper Rotor Time Constant

The paper discusses the speed estimation accuracy of two Sliding Mode Model Reference Adaptive System observers under improper rotor time constant. The SM MRAS observers are used for speed estimation in a sensorless direct field oriented (DFO) induction machine (IM) drive. In a sensorless DFO drive, the rotor fluxes are estimated based on the measured voltages/currents and are used for field orientation. Speed estimation by the rotor flux MRAS method is attractive since the reference quantities (rotor fluxes) are already available. Classic MRAS or SM MRAS speed estimators are viable alternatives and they work well under ideal conditions. The paper analyzes the speed estimation error of the SM MRAS observers under real conditions (improper rotor time constant and nonideal integration) and compares it with the Classic MRAS method.