Joseph Cilia

A speed identifier for induction motor drives using real-time adaptive digital filtering

A novel sensorless speed identifier for real-time application in induction motor drives under steady-state and transient conditions is proposed. It is based on the calculation of rotor slot harmonic (RSH) frequencies using an adaptive digital filter. It outperforms other analog or spectrum-based RSH speed identifiers in terms of accuracy and speed of response. The new identifier measures the speed with less than 0.1% error by processing the stator current on a sample-by-sample basis. It is also capable of tracking speed transients of high slew rates with high accuracy. The authors believe this to be the first effective tracking of RSHs during transients ever reported. The proposed algorithm is computationally very efficient and requires only a single processor for its real-time implementation. Simulated and experimental data were used to validate the algorithm.

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.

Sensorless position detection for vector controlled induction motor drives using an asymmetric outer-section cage

This paper describes a new method of obtaining a rotor position signal from a cage induction machine operating without a mechanical sensor. The method is based on introducing a circumferential variation in the resistance of the outer section of either a double cage or deep bar cage rotor. Simulation results for a linear double cage machine show that the method is feasible and provides incremental rotor position tracking with good dynamics. The paper describes an implementation of the method for a 30 kW double cage machine having variable gauge copper wire in the outer slots. It is shown that whilst the rotor position-dependent signals are robust to changes in load, interference harmonics arising from slot saturation and rotor slot harmonics cause problems for rotor position tracking. These problems are discussed in relation to the present method and that of designed asymmetries in general.

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.

The Use of Small Voltage Vectors of Matrix Converters in Direct Torque Control of Induction Machines

The effects on torque performance when using small voltage vectors of Matrix Converters is investigated in this paper. These vectors are used in order to reduce the electromagnetic torque ripple which appears when Direct Torque Control technique is used in Induction Motors. Direct Torque Control for Induction Motors using Matrix Converters is reviewed and it is pointed out the problem of the electromagnetic torque ripple which is one of the most important drawbacks of the Direct Torque Control. A new look-up table for Direct Torque Control using small vectors of Matrix Converters is developed. With the new look-up table, the system will differentiate between small and large torque errors and consequently reduce the electromagnetic torque ripple. A comparison between the classical Direct Torque Control using Matrix Converters and the proposed method is carried out. Results which demonstrate the improvement of the novel Direct Torque Control are shown.

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.