Cedric Caruana

Improved Waveform Quality in the Direct Torque Control of Matrix-Converter-Fed PMSM Drives

Despite the ability of matrix converters (MCs) to generate a higher number of voltage vectors compared with standard voltage-source inverters, most of the applications reported in the literature utilize only those having larger amplitudes. This paper investigates the use of MC input voltages with different amplitudes in order to reduce the inherent torque ripple that appears when direct torque control (DTC) is used to drive ac machines, particularly permanent-magnet synchronous motors, as its stator inductance is typically half of that of an induction machine of similar ratings. Utilizing a wider range of input voltage vectors for the MC, but not using the rotating vectors, a new lookup table that distinguishes between small and large torque errors is developed, leading to an enhanced MC-fed DTC. The enhancement enables a reduction in the electromagnetic torque ripple and output-current total harmonic distortion. Furthermore, the proposed control strategy improves the MC voltage transfer ratio up to 86.6% compared with 50% achieved by the conventional DTC using MCs at the expense, however, of slightly decreasing the input power factor control capability. The proposed enhanced MC DTC was tested experimentally, and results comparing its performance with MC DTC using an adapted lookup table are shown.

Performance of HF signal injection techniques for zero-low-frequency vector control of induction Machines under sensorless conditions

A number of HF signal injection techniques have been proposed for the sensorless zero-low-frequency control of induction machines (IMs). This paper reviews these methods and experimentally investigates their performance under true sensorless conditions for a standard cage IM with closed rotor slots. Implementation techniques covering hybrid methods, saliency decoupling, and saliency orientation are discussed. The paper concludes that, while HF techniques can outperform observer-based methods at low frequencies, the robust performance required for industrial application still presents a research challenge.

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.

Sensorless flux position estimation at low and zero frequency by measuring zero-sequence current in delta connected cage induction machines

This paper considers the estimation of both flux and rotor position in delta-connected cage induction machines operating at low and zero frequencies. It is shown that the variation of leakage inductance due to either saturation or rotor slotting can be tracked by measuring the derivative of the zero-sequence current in response to the application of appropriate voltage test vectors. The method requires access to the machine phase windings but needs only a single extra sensor, in the form of a nonintegrating Rogowski coil, which measures directly the zero-sequence current derivative. In this paper, experimental results are presented for the tracking of flux position.This paper considers the estimation of both flux and rotor position in delta-connected cage induction machines operating at low and zero frequencies. It is shown that the variation of leakage inductance due to either saturation or rotor slotting can be tracked by measuring the derivative of the zero-sequence current in response to the application of appropriate voltage test vectors. The method requires access to the machine phase windings but needs only a single extra sensor, in the form of a nonintegrating Rogowski Coil, which measures directly the zero-sequence current derivative. In this paper, experimental results are presented for the tracking of flux position.

Flux position estimation in cage induction machines using synchronous HF injection and Kalman filtering

This paper proposes a new approach to the tracking of the flux position saliency of an induction machine by means of high-frequency signal injection in the synchronous rotating frame. The paper shows that existing synchronous pulsating injection methods perform poorly in the presence of secondary saliencies. A modified scheme is proposed in which a rotating HF field is established in the dq rotating reference frame. The scheme enhances the performance of harmonic elimination methods to reduce the effects of secondary saliencies. A new harmonic elimination method based on the Kalman filter is proposed in the paper. Experimental results are given showing the effectiveness of the harmonic elimination and the resulting tracking of the saturation saliency.

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 flux position estimation at low and zero frequency by measuring zero-sequence current in delta-connected cage induction machines

This paper considers the estimation of both flux and rotor position in delta-connected cage induction machines operating at low and zero frequencies. It is shown that the variation of leakage inductance due to either saturation or rotor slotting can be tracked by measuring the derivative of the zero-sequence current in response to the application of appropriate voltage test vectors. The method requires access to the machine phase windings but needs only a single extra sensor, in the form of a nonintegrating Rogowski Coil, which measures directly the zero-sequence current derivative. In this paper, experimental results are presented for the tracking of flux position.