Cyril Spiteri Staines

Sensorless control of induction Machines at zero and low frequency using zero sequence currents

This paper considers both flux and rotor position estimations for sensorless control of delta-connected cage induction machines (IMs) at low and zero frequency operation. The variation of leakage inductance due to either saturation or rotor slotting is tracked by measuring the derivative of the zero sequence current in response to the application of appropriate voltage test vectors. The method requires only a single extra sensor. It requires access to machine phase windings and is appropriate for integrated-type induction motor drives. Both a closed-slot and an open-slot machine is used to demonstrate rotor flux and rotor position tracking, respectively. Experimental results are presented showing sensorless torque control and sensorless speed and position control at low and zero frequencies.

Analysis and Compensation of Inverter Nonlinearity Effect on a Sensorless PMSM Drive at Very Low and Zero Speed Operation

It has been well established in the literature that inverter nonlinearity effects afflict saliency-based sensorless drives. The inverter nonlinearity leads to the generation of signals that corrupt the useful position information. The resulting effect differs depending on the injection approach utilized in the drive. Various compensation techniques to overcome this effect have been published in the literature. This paper is concerned with the zero-vector current-derivative technique. The effect of the varying ON-state resistance of the inverter power devices on the position signal is investigated in detail. Knowledge of the source of the corrupting signals facilitates compensation and determines its applicability. Two approaches for inverter nonlinearity compensation are compared. The first approach utilizes a lookup table from offline-processed data, while the second one is a simpler approach based on the current-dependent resistance characteristic of the inverter switching devices. Experimental performance under sensorless condition is shown for both approaches.

A zero speed operation sensorless PMSM drive without additional test signal injection

The inherent back EMF and the saliency of AC machines can be utilized to identify the rotor/flux position. A novel technique, which takes both of these effects into account is proposed in this paper. No additional test signals are injected into the machine and the difficulties in sensing the machine terminal voltage at low speed is eased. Only three standard current transducers are used in the drive system. For the position/speed estimator only the machine current derivative during the relatively long (at low speed) zero voltage vectors is used as feedback. Practical results show the operation of the drive at several torque and speed conditions including stand still.

Sensorless Control of Induction Machines at Low and Zero Speed by Using PWM Harmonics for Rotor-Bar Slotting Detection

This paper presents the use of the inherent high-frequency pulsewidth modulation (PWM) harmonics for sensorless control of ac machines. The amplitude and position of the PWM voltage harmonics cannot be controlled independently and are determined by the fundamental machine operation. However, they do form a high-frequency excitation and can provide information on saliencies within ac machines. This paper examines the feasibility of sensorless control based on extracting the rotor-bar slot position information for a cage induction machine using PWM harmonics. The position-signal demodulation and compensation schemes used are derived. Experimental results are provided for an off-the-shelf induction motor operating under sensorless current, speed, and position control, including zero excitation and zero speed.

A periodic burst injection method for deriving rotor position in saturated cage-salient induction motors without a shaft encoder

This paper describes a new method for estimating the incremental rotor position for an induction machine without using a shaft sensor. The method assumes a saturated induction motor having an engineered cage saliency spanning one pole pitch. The voltage source inverter driving the machine is also used to inject a high frequency signal which is needed to detect position. The paper discusses two ways in which this can be achieved. This method has been proven successful with a loaded machine at low speeds and overcomes problems associated with saturation.

Sensorless Direct Torque Control of a Surface Mounted PMSM using High Frequency Injection

This paper proposes the high frequency (hf) voltage injection technique to DTC drives with the objective of extending their performance to the low and zero speed region. The simplicity of the original DTC algorithm is not compromised. The hf carrier is introduced by the direct modification of the fundamental voltage vectors. The position signal is then obtained from the direct demodulation of the resulting hf currents. Both simulation and experimental results are shown

'Low cost' three phase to single phase matrix converter

his paper presents the design and implementation of a single leg matrix converter. It shows the basic operation of this type of converter, the modulation used and its implementation on a low cost microcontroller. Four-step current commutation is used for switching between two bi-directional switches. The final system is implemented to control the speed of a single-phase induction motor.

Sensorless speed, position and torque control using AC machine saliencies

This paper describes various methods aimed at tracking the flux and rotor position for cage induction machines without a shaft sensor using specially designed saliencies or natural saliencies. The estimation methods employ a high frequency (HF) signal or test vectors to detect the machine saliency. As is common knowledge, multiple saliences can cause problems to track only one particular saliency. Ways to overcome this problem for rotor position and rotor flux tracking are discussed. The performance of these methods is investigated at all loads at low and zero speed and also at zero fundamental frequency.

Sensorless Control of Induction Machines by Using PWM Harmonics for Rotor Bar Slotting Detection

The paper presents the use of the inherent high frequency PWM harmonics for sensorless control of AC machines. The amplitude and position of the PWM voltage harmonics cannot be controlled and depends on the fundamental machine operation. The paper examines the feasibility of sensorless control based on the extracted rotor bar slot position information in the case of a cage induction machine. The position signal demodulation and compensation schemes used are discussed. Experimental results of sensorless torque, speed and position control at loaded conditions including zero excitation and zero speed are given for an off-the-shelf induction machine.

Sensorless position control of a PMSM for steer-by-wire applications

This paper shall present the design and implementation of a MATLAB/Simulink Model for the sensorless control of a PMSM in a steer-by-wire application. Simulation results for position, speed and current loops in both open-loop and closed-loop sensorless modes are shown. The sensorless method is based on the tracking of saliencies by high frequency injection.