Petar Matic

Discrete Rotor Flux and Speed Estimators for High-Speed Shaft-Sensorless IM Drives

In numerous motor drive applications, high rotor speed is the key factor for system cost, performance, and overall energy efficiency. As a result of energy crises and global market competition, the specified rotor speed and fundamental frequency of the induction motor (IM) in many drive applications noticeably go up. For the same cost and efficiency reasons, that increase of inverter fundamental output frequency cannot be followed with the increase of pulsewidth modulation (PWM) frequency. Therefore, a very low ratio between the PWM and motor fundamental frequencies is to be expected in the near future. In this paper, the shaft-sensorless drive performance is investigated at high speeds, with a very low sampling to fundamental frequency ratio. As a result, two main problems with rotor flux estimators were discovered: the integration problem in the current-based rotor flux model and the phase error in the voltage-based rotor flux model. Both problems were addressed, and a proper joint solution is suggested. The effectiveness of the proposed solution is tested in a model-reference-adaptive-system-based high-speed shaft-sensorless IM drive. The experimental results collected from the digitally controlled IM drive with a low frequency ratio validate the proposed solution.

Thermal Protection of Vector-Controlled IM Drive Based on DC Current Injection

A technique for stator-resistance-based thermal protection suitable for a low-cost vector-controlled induction machine (IM) drive is suggested in this paper. In order to provide accurate stator resistance monitoring at medium and high speeds, the dc signal injection-based method is selected. The main property of the scheme is that small regulated dc current is periodically injected in the stator windings without interrupting the flux and torque control loops. In the proposed scheme, inverter nonlinearities are properly compensated and accurate resistance estimation is achieved with minimal level of injected dc current. This results in consistent and controllable torque ripple, which is minimal and constant for any actual stator resistance value. Estimated stator resistance can be also used for control algorithm tuning. The method is implemented in a fixed-point microprocessor and tested on a low-cost shaft-sensorless IM drive under various operation modes.

A novel direct torque and flux control algorithm for the induction motor drive

In this paper a new sensorless Direct Torque Control (DTC) algorithm for induction motor drive is proposed and tested. This algorithm provides decoupled control of the torque and flux with constant inverter switching frequency and a minimum torque and flux ripple. Compared to the other DTC methods, this algorithm is much simpler and has less mathematical operations, and can be implemented on most existing digital drive controllers. Algorithm is based on imposing the flux vector spatial orientation and rotation speed, which defines the unique solution for reference stator voltage. The implementation of the control scheme using DSP-based hardware is described, with complete experimental evidence and the straightforward implementation instructions.

Speed Regulated Continuous DTC Induction Motor Drive in Field Weakening

The paper describes sensorless speed controlled continuous Direct Torque Control (DTC) Induction Motor (IM) drive in the field weakening regime. Drive comprises an inner torque loop an ...

Induction motor torque control in field weakening regime by voltage angle control

This paper presents a novel algorithm for the induction motor torque control in field weakening region. Proposed method insures maximum DC bus utilization and offers DTC performance through the stator voltage angle control. The algorithm is simple, without the outer flux loop nor the inner current loop. Dynamic response is preserved over wide speed range by means of gain-scheduling. The paper comprises the implementation details and experimental results.

Stator Voltage Vector Direct Torque Control of induction machine

This paper presents improved high speed Induction Motor (IM) torque control algorithm that achieves full inverter voltage utilization in field weakening and smooth speed transition from the base speed to high speed region. The Stator Voltage Vector Direct Torque Control (SVV DTC) algorithm simultaneously controls IM torque and rotor flux by regulating stator voltage angle and amplitude in the base speed region, and by regulating only the voltage angle in the field weakening region. Fast torque dynamics is obtained in wide speed range by using torque regulator with variable gain. The main benefit from the proposed algorithm is in field weakening range, in which the machine is supplied by maximal available voltage without outer flux trajectory reference. This approach enables full utilisation of both magnetic material of the machine and power capabilities of the inverter, which is not possible with traditional vector drives with current regulators. Transition from base speed region to field weakening is obtained by simply limiting the output voltage. Experimental results gathered on the high speed low cost IM drive confirm the effectiveness of the proposed SVV DTC approach.

Non – Regenerative IPMSM Drive Braking Scheme Based on q – Axis Current Component Limiting

In the paper a non-regenerative braking scheme for high speed Interior Permanent Magnet Synchronous Motor (IPMSM) drive is presented. Due to price constraints, general purpose electric drives with IPMSMs are not equipped with a drive converter which allows energy recovery to the primary source. These drives are usually used for driving strictly reactive loads, in which braking mode is used only during deceleration. Therefore, in these drives it is necessary to use methods for dissipating braking energy in the motor itself and in the inverter. The paper provides theoretical analysis of various methods for non-regenerative IPMSM braking schemes, mathematical models, and the proposal of one solution suitable for use in high-speed applications based on limiting q – axis current component. Proposed solution controls recovery energy by keeping DC link voltage within given voltage margin, thus preventing unacceptable voltage rise during braking. Braking strategy is added into common IPMSM Field Oriented Control (FOC) control structure with Maximum Torque Per Ampere (MTPA) and Field Weakening (FW) algorithms. During the braking, MTPA strategy is suspended and non – regenerative braking is performed instead. In the proposed braking scheme voltage margin is also taken into account, by selecting proper d-axis reference current adjusted to the available voltage, so the scheme is also applicable in FW mode.

Convergence and stability analysis of IM rotor time constant estimators based on MRAS scheme

In this paper, the convergence and the stability analysis of two Induction Motor (IM) rotor time constant (Tr) estimators are performed. Both estimators are Model Reference Adaptive System (MRAS) based, first considering the rotor flux vector, second the reactive power as the state variable. The stability analysis is based on Lyapunov and Popov criteria, passivity formalism and positive real function concept. Performances and asymptotic stability of both estimators for selected adaptive mechanisms are demonstrated through computer simulations using dynamic model of vector controlled IM drive.

Performance analysis of control schemes for direct torque control of dual three-phase induction machine

In this paper performance analysis of Direct Torque Control (DTC) schemes for control of dual three-phase induction machine is presented. Several hysteresis comparator based DTC schemes with variable switching frequency and a space vector modulation based DTC scheme with constant switching frequency are under the scope. The schemes are modeled and systematically analyzed by intensive computer simulations. The results of these two DTC approaches are compared. Criteria for performance analysis are quality of torque control, x1-y1 subspace copper losses and simplicity of implementation.

Space Vector Representation of Induction Motor Model in Field Weakening Regime

In this paper a space vector model of an induction motor in a field weakening regime is detailed. Stator and rotor flux space vector trajectories are shown in a complex plane for the case when the machine is supplied by limited voltage.