Silverio Bolognani

Sensorless full-digital PMSM drive with EKF estimation of speed and rotor position

This paper concerns the realization of a sensorless permanent magnet (PM) synchronous motor drive. Position and angular speed of the rotor are obtained through an extended Kalman filter. The estimation algorithm does not require either the knowledge of the mechanical parameters or the initial rotor position, overcoming two of the main drawbacks of other estimation techniques. The drive also incorporates a digital d-q current control, which can be easily tuned with locked rotor. The experimental setup includes a PM synchronous motor, a pulsewidth modulation voltage-source inverter, and floating-point digital-signal-processor-based control system.

Design techniques for reducing the cogging torque in surface-mounted PM motors

Several techniques may be adopted in motor design of surface-mounted permanent magnet motors in order to reduce the cogging torque. This paper describes the various techniques, (both classical and innovative techniques), giving for each of them a theoretical justification. To this aim, a simple original model of the cogging torque mechanism and a Fourier analysis are introduced. As a result, it is highlighted that some techniques are not always utilizable, and some of the well known ones may be even depreciatory when not used correctly. In addition, effects on back EMF are discussed.

Extended Kalman filter tuning in sensorless PMSM drives

The use of an extended Kalman filter (EKF) as a nonlinear speed and position observer for permanent-magnet synchronous motor drives is a mature research topic. Notwithstanding, the shift from research prototype to a market-ready product still calls for a solution to some implementation pitfalls. The major and still unsolved topic is the choice of the EKF covariance matrices. This paper replaces the usual trial-and-error method with a straightforward matrices choice. These matrices, possibly combined with a novel self-tuning procedure, should put the EKF drive much closer to an off-the-shelf product. The proposed method is based on the complete normalization of the EKF algorithm representation. Successful experimental results are included in the paper.

Experimental fault-tolerant control of a PMSM drive

The paper describes a study and an experimental verification of remedial strategies against failures occurring in the inverter power devices of a permanent-magnet synchronous motor drive. The basic idea of this design consists of incorporating a fourth inverter pole, with the same topology and capabilities of the other conventional three poles. This minimal redundant hardware, appropriately connected and controlled, allows the drive to face a variety of power device fault conditions while maintaining a smooth torque production. The achieved results also show the industrial feasibility of the proposed fault-tolerant control, that could fit many practical applications.

Design considerations for fractional-slot winding configurations of synchronous machines

This paper presents some design considerations for synchronous machines characterized by a fractional number of slots per pole per phase. The main advantage of this configuration is a smooth torque, which is due to the elimination of periodicity between slots and poles. A second advantage is a higher fault-tolerant capability, making the machine able to work even in faulty conditions. However, the fractional-slot configuration presents a high content of MMF harmonics that may cause an unbalanced saturation and thus an unbearable torque ripple. A method to design fractional-slot machines is illustrated in this paper, including double-layer and single-layer windings. The analytical computation is extended to determine the harmonics of MMF distribution. Their effect is highlighted in isotropic as well as anisotropic machines. Finally, some considerations are reported to avoid unsuitable configurations

Model Predictive Direct Speed Control with Finite Control Set of PMSM Drive Systems

Servo drives and drives for position control require a high dynamic on speed control. In this paper, model predictive direct speed control (MP-DSC) is proposed, which overcomes limitations of cascaded linear controllers. The novel concept predicts the future current and speed states in discrete steps and it selects plant inputs which depends mainly on the predicted speed error. Secondary control objectives, such as maximum torque per ampere tracking are included. MP-DSC uses the finite control set approach which makes it suitable for online predictions with a prediction horizon of a few sample periods. The concept has been developed by simulation and evaluated on an experimental test bench. The overall control behavior is evaluated applying reference and disturbance steps to the system, where MP-DSC shows promising results. A solution for disturbance (e.g., load toque) rejection is proposed, and the effectiveness to avoid control offsets is shown. Furthermore, the dynamic performance and the steady-state behavior of MP-DSC is evaluated and discussed.

Potentials and limits of high-speed PM motors

This paper illustrates the potentials and limits of high-speed permanent-magnet (PM) motors. The effect of the material choice, including PM, stator core and retaining sleeve is highlighted. Slotted and slotless configurations are taken into account and compared, computing magnetic, electrical, mechanical and thermal quantities by means of both an analytical and a finite element approach. In particular, the thermal and the PM demagnetization limits and the rotor losses are evaluated. A criteria of optimisation of the motor structure is described, with the diameter ratio and the iron flux density as main design variables.

Strategies for the Fault-Tolerant Current Control of a Five-Phase Permanent-Magnet Motor

This paper deals with the postfault current control strategies of a five-phase permanent-magnet (PM) motor. The analysis covers both the open circuit of one and two phases and the short circuit at the machine terminal of one phase. The proposed control guarantees safe drive operation after any fault occurrence. For the sake of generality, an analytical model has been used to investigate the properties of each postfault strategy. The results are general, and they apply to PM motor of any power rating. Simulations and experimental results validate the theoretical predictions.

Comparison of PM Motor Structures and Sensorless Control Techniques for Zero-Speed Rotor Position Detection

The rotor position of a synchronous permanent magnet (PM) motor can be detected by means of the injection of a high-frequency stator voltage superimposed to the fundamental component. Thanks to the rotor anisotropy, the corresponding high-frequency current is modulated and used to determine the rotor position. Two techniques are considered: the first one adopts a pulsating voltage vector in the estimated synchronous reference frame, while the second one adopts a rotating voltage vector. These techniques are effective at zero and at low motor speed. The accuracy of the rotor position detection depends strictly on the rotor saliency, that is, on the geometry of the PM rotor. In fact both saturation and d-and q-axis cross-coupling have a heavy influence on the correct rotor position detection. The aim of this paper is to compare the two sensorless control techniques, together with two rotor geometries, that is, IPM and inset rotor. In order to highlight the effectiveness of the sensorless technique, the tests are carried out at various operating conditions. It is found that the effectiveness of the sensorless rotor position detection strongly depends on the PM rotor geometry. Conversely, the choice of the sensorless control technique affects slightly the rotor position detection.

Extended-range PMSM sensorless speed drive based on stochastic filtering

The paper describes the design of a high-performance sensorless permanent magnet synchronous motor (PMSM) drive, capable of starting at full torque even from standstill and able to deliver full torque in 1:12 speed range. Experimental setup, hardware circuitry and software implementation are described into details. Particular emphasis is given to the software control algorithms, that were specifically studied to enhance the overall system performance.