The paper proposes a shaft-position/speed-estimating technique for a micropermanent-magnet synchronous motor. Based on the characteristics of the micromotor, the back EMF of the motor can be detected. In addition, the shaft position/speed can be estimated according to the back EMF. Finally, a closed-loop sensorless adjustable speed-control system is implemented. The controlled speed range is from 600 to 36000 rev/min. A DSP is used to estimate the shaft position/speed and to execute the speed-loop control algorithm. In addition, some hardware circuits, including current-controlled circuits, PWM circuits, and an inverter are implemented to control the current of the micromotor. Satisfactory performance, including a wide adjustable speed range, good transient responses, and good load-disturbance responses can be achieved. Experimental results validate the theoretical analysis and show the correctness and feasibility of the proposed estimation technique.
The paper presents five structured design methodologies for third-order LCC voltage-output resonant converters. The underlying principle of each technique is based on an adaptation of a FMA equivalent circuit that accommodates the nonlinear behaviour of the converter. In contrast to previously published methods, the proposed methodologies explicitly incorporate the effects of the transformer magnetising inductance. Furthermore, a number of the methodologies allow the resonant-tank components to be specified at the design phase, thereby facilitating the use of standard off-the-shelf components. A procedure for sizing the filter capacitor is derived, and the use of error mapping, to identify parameter boundaries and provide the designer with a qualitative feel for the accuracy of a proposed converter design, is explored.
The paper presents the system analysis and circuit design of a half-bridge zero-voltage-switching (ZVS) flyback converter with synchronous rectifier. The leakage inductance and output capacitance of active switches are used to realise ZVS operation during the transition state between two switches. The switching power loss of active switches can be reduced to a minimum due to the ZVS operation such that the high-efficiency circuit can be achieved. The circuit-operation principle, mathematical analysis and design example of a half-bridge ZVS flyback converter with synchronous rectifier are explained and analysed. The synchronous rectifier is used at the transformer-secondary side to reduce further the conduction loss and to increase the circuit efficiency. Finally the experimental results from a 24 V/7 A output load with 100 kHz switching-frequency prototype circuit are provided to verify the theoretical analysis.
A high-performance bidirectional DC/AC power converter is required in low emission and high-efficiency propulsion systems such as electric vehicles and hybrid electric vehicles. A general six-switch full-bridge inverter topology with a high efficient interior permanent magnet alternator is adopted to explore the constant-voltage, constant-current and pulsating-current charging processes. In addition, useful information such as maximum conversion ratio, average armature current, armature current ripple and output voltage ripple are derived based on the equivalent circuit model where the armature resistance of the alternator and the conduction resistance of the power switch are considered. A 32 bit digital signal processor, TI 2812, is used to implement the switching strategies and the control algorithms. Experimental results indicate that the performance of the proposed control strategy is satisfactory for all of the popular charging strategies employed. Compared with the traditional claw pole alternator, the proposed strategy exhibits a significant improvement in output efficiency.
To reduce the voltage distortion in a distribution network, parallel (shunt) harmonic impedances (SHIs) can be strategically positioned in the network. However, to avoid the additional cost of adding SHIs to the distribution network, the SHI function can be implemented as a secondary function of convertors connecting loads or generators to the mains. A control strategy for a single-phase bidirectional full-bridge AC–DC convertor is proposed. This control strategy allows a fixed resistive impedance to be programmed for harmonics, independent of the direction of the fundamental power flow. Hence, the bidirectional rectifier obtained behaves, as a secondary function, like a resistive SHI, providing damping for resonances and resulting in an overall improvement of the voltage distortion in the distribution network. The theoretical results obtained are verified by using an experimental test setup. The superior damping potential of the experimental bidirectional rectifier with the proposed control scheme is demonstrated by a comparison with experimental results previously obtained for ‘classical’ control schemes.
Robust position control for a linear permanent-magnet synchronous motor servo drive is presented, considering the constituted component match under unknown mass and large command change. First, a field-weakening forcing current control scheme is developed to yield close current transient tracking response. In the proposed position control scheme, a cascaded two-degrees-of-freedom controller is quantitatively designed, and an internal robust model following controller (RMFC) is arranged to let the prescribed response be preserved under varying plant parameters and operating conditions. Then an identification scheme is devised to obtain a mass estimate from the compensating control signal generated by the RMFC. Finally, in making the large command positioning control, a match between the motor drive constituted components is considered. The amplitudes and/or ramping rate of step and ramp commands are determined according to the identified mass and the ratings of the inverter and motor. In this case, the response time is also predicable. Through applying the proposed simple command shaping control approach, quantitative positioning control performance under unknown mass and efficient capability utilisation of inverter and motor can be achieved, and the instability caused by nonlinearities under excessive saturation can be avoided.
Sensor count reduction for high-performance induction motor (IM) drives is considered. A novel strategy to compute the three phase currents, based on a single current sensor and an adaptive observer, is proposed. The observer estimates the motor state variables, allowing then implementing an IM field-oriented controlled (FOC) drive with closed speed loop based only on DC-link measurements. To demonstrate the practical feasibility of this proposal, representative experimental results, obtained with a FOC experimental prototype, are presented. The FOC prototype showed results similar to those from a conventional FOC drive with individual phase current sensors. The sensor count reduction achieved represents a significant cost diminution in the implementation of low-power high-performance drives
A new digital voltage controller is proposed, derived in agreement with the internal model principle for three-phase inverters with Delta Y transformer at the Output. A dynamic model of the inverter, transformer, filter and load in stationary alpha-beta co-ordinates is derived and a decoupling method is proposed. The proposed digital controller is not prone to amplify DC components, which can lead to output transformer saturation. Additionally, this digital controller results in a simple form and is well Suited for fixed-point implementation. Experimental results. implemented in a 16-bit DSP controller, validate the theoretical developments and demonstrate the good steady-state performance of the proposed controller under both nonlinear balanced and unbalanced loads.
A very simple method for determining squirrel-cage induction motor parameters is presented, and some problems in the determination of parameters with two methods proposed in IEEE Standard 112 are discussed and clarified. The double-cage model is used to describe the motor response for the entire operating range. Equivalent circuit parameters are calculated from data of three tests: no-load test, locked-rotor test and overload test. The method has the advantage of not requiring torque measurements. It is formulated as an iterative algorithm, and has been tested with 16 motors of different power ratings, showing very good convergence. The influence of measurement errors on the stability of the proposed method has been studied and its behaviour is very good.
An integral variable-structure grey control for a magnetic levitation system for position tracking is presented. The sliding-mode control is insensitive to system uncertainties and disturbances when it is within expected limits. It produces chattering when uncertainty values are overestimated, or steady-state error when underestimated. The method uses a mathematically simple and computationally efficient grey compensator for the integral variable structure controller to reduce chattering and steady-state error. The stability of this magnetic levitation system is proven by using the Lyapunov function. The experimental results verify that the proposed controller is valid for a magnetic levitation system.
A novel soft-switching PWM utility frequency AC to high-frequency AC power conversion circuit, incorporating boost-half-bridge inverter topology, which is more suitable and acceptable for cost effective consumer induction heating applications, is presented. The operating principle and the operation modes are described using equivalent circuits with the operating voltage and current waveforms. The operating performances are illustrated and evaluated, including the power regulation and power conversion efficiency against duty cycle characteristics based on the power dissipation as compared with those of the previously developed high-frequency inverter. The practical effectiveness of the power converter is substantially proved, based on experimental results from a practical design example.
The computer-simulation model of the dual-stator-winding induction machine in which the space harmonics of the stator windings and those of the rotor circuits are accounted for has been presented. The winding-function method is used to calculate the inductances in the machine. The phase-voltage and torque equations thus obtained are further transformed to the rotor reference frame to facilitate simplicity of modelling and using an n x n complex-variable reference frame transformation. Simulation results of the no-load starting transient are presented with the response of the machine to a change in the load torque. The balance of the paper presents an approach, using the stator-winding and rotor-bar currents determined from the coupled-circuit model and the winding functions of the stator windings and the rotor loops, to generate the airgap flux density. A simplified correction scheme, using the B/H curve of the magnetic steel material to account for magnetic saturation in the airgap is introduced, improving the prediction accuracy. Some measurements of no-load and full-load flux densities confirm the computer simulation and FEA results.
A very-low-cost active power filter with power-factor-correction capability for solving power quality problem is proposed. Model-based cascade controller design is presented for the control of the shunt active filter. Harmonic reductions and power-factor correction will both be carried out by the proposed filter. Discussions on the design of the current and voltage control loops are given. Circuit implementation of the proposed control scheme is presented and experimental results are included to demonstrate the effectiveness of the proposed design scheme.
Nowadays fractional-slot windings are proposed for synchronous motors for different purposes: reduction of end-winding losses, reduction of torque ripple, reduction of mutual coupling among the phases, fault-tolerant applications, and so on. The design of the single-layer fractional-slot synchronous motors is dealt with, in which each slot contains only one side coil. The star of slots, introduced some time ago, proves itself to be again appropriate. After a brief review of the classical theory of the star of slots, its application is extended to the design of these unconventional windings. Thanks to its graphical representation, a simple analytical formulation is carried out describing the harmonic contents of the winding distribution. Finally, the star of slots allows simple rules for the design of fractional-slot single-layer windings to be determined. As a special case, it is used to determine the synchronous motor winding solutions suitable for critical fault-tolerant applications.
The paper presents a systematised and generalised methodology of second-order output filter for inverters that synthetise sinusoidal voltage waveforms through space-vector pulse-width modulation (PWM). The objective of this methodology is to determine the largest natural frequency of the filter that ensures specification of the maximum total harmonic distortion (THD) admissible in the output voltages of the PWM inverter. The proposed methodology is discussed in detail, including the description of the steps needed to derive the design procedure for different topologies of voltage inverters, and the procedure for obtaining the design curves. To illustrate the use of the proposed methodology, detailed design procedures are given for single-phase, three-phase three-wire and three-phase four-wire filter topologies. Finally, examples are presented which include experimental results demonstrating the validity of the proposed design methodology.
Control of the brushless doubly fed machine (BDFM) based on traditional multiple reference frames is complex. To simplify the control scheme, a new and simpler derivation of the dq model of the BDFM is proposed, leading to a unified-reference-frame model. This way, a simple dq model can be established, which could be an interesting tool for control-synthesis tasks. In order to determine the unified reference dq model, restrictions related to BDFM operation, as well as the exact rotor-cage configuration, have been considered. The proposed model has been validated by several experimental results. The work could facilitate future research on improved BDFM field-oriented control strategies.
The split ratio, i.e. the ratio of the stator bore diameter to the stator outer diameter, is one of the most important design parameters for cylindrical permanent magnet brushless machines. The optimal split ratio is investigated analytically for both brushless AC and DC motors having either overlapping or non-overlapping windings, and accounting for the influence of the airgap flux distribution, the stator tooth-tips and the end-windings. It is shown that the split ratio can significantly influence the torque capability and efficiency of a permanent magnet brushless motor.
The increase of nonlinear loads in networks involves rises in harmonic currents, resulting in voltage distortion that can affect other sensitive loads. The series voltage compensators are the devices used to reduce voltage deformation in networks of nonnegligible impedance. The control technique of the series compensator is one factor which can improve the operation of the series compensator, in order to reduce voltage disturbances existing in the network. The control of devices controlled by PWM permits the use of classical linear strategies and nonlinear control. Initially, in the paper, the linear and discrete model of the voltage compensator is obtained by using an original linearisation method for systems controlled by PWM, which shows better behaviour than conventional methods. Then a control algorithm is developed in minimum time based on the linear model obtained. The control algorithm has been simulated and has subsequently been implemented in a laboratory prototype of the series compensator, giving very satisfactory results.
