Paolo Giangrande

End Effects in Linear Tubular Motors and Compensated Position Sensorless Control Based on Pulsating Voltage Injection

The sensorless position control of permanent-magnet (PM) synchronous motors can be successfully implemented by superimposing a high-frequency voltage signal on the control voltage. In this paper, the position estimation is obtained by means of a high-frequency sinusoidal voltage signal injected along the estimated -axis. Several methods proposed in the literature obtain the position estimation by tracking the zero condition of the high-frequency current component. We propose a new approach that also exploits the -axis high-frequency current component and allows working with injected voltage signal of reduced amplitude, thus reducing noise and additional losses. The main contribution of this paper relies in the compensation of the motor end effects due to the finite length of the tubular motor armature. These effects must be taken into account in the motor modeling because they cause an error in the position estimation that varies with the motor position. The modeling of the phenomenon and a proper compensation technique are proposed in this paper. Last, a simplified integral-type controller is used to estimate motor position instead of the commonly adopted proportional-integral controller plus integrator, and this requires a low-effort design. Experiments on a linear tubular PM synchronous-motor prototype are presented to validate the theoretical analysis and evidence the feasibility of the proposed sensorless technique.

Sensorless Position Control of Permanent-Magnet Motors With Pulsating Current Injection and Compensation of Motor End Effects

The sensorless position control of permanent-magnet motors is successfully implemented by superimposing a high-frequency voltage signal on the voltage reference or adding a high-frequency current signal to the current reference. The former approach is usually preferred because of its simplicity, although the latter one may allow better performance. This paper presents a new algorithm for the sensorless control of low-saliency permanent-magnet synchronous motors based on high-frequency sinusoidal current signal injection into the d-axis. Different from the related literature, the position information is derived by analyzing the measured high-frequency currents. The amplitude of the d-axis voltage reference is also exploited to improve performance. A proportional-integral (PI) controller plus a resonant term (PI-RES) is adopted to ensure the accurate tracking of both the dc and high-frequency components of the d -axis current reference. The main advantages of the proposed approach are the increased accuracy and sensitivity with respect to the approach based on voltage injection, the insensitiveness to inverter nonlinearities that are compensated by the current regulation loop, the actual control on the injected current value, and the practical absence of acoustic noise. Experiments on a linear tubular permanent-magnet synchronous motor prototype have been carried out to verify the aforementioned advantages. This paper also presents a discussion of the parameters of the PI-RES.

Sensorless control of PM motor drives — A technology status review

The control of Brushless Permanent Magnet Motors require rotor position information that can be measured by means of a position sensor. The motion sensorless control aims at eliminating the motor position sensor and its corresponding electronic conditioning circuits, cabling and connectors. Besides a clear cost reduction, the motion sensorless drives have better reliability when compared with their position sensor-based counterparts. The research conducted in the last two decades has provided many different solutions that are used in many applications. Nevertheless, the literature reports just a few survey papers dealing with this important topic. This paper intends providing a comprehensive review of the sensorless control solutions, including the machine influence on the sensorless drive performance.

Self-commissioning of Interior Permanent Magnet Synchronous Motor Drives With High-Frequency Current Injection

In this paper, a simple and robust method for parameter estimation at rotor standstill is presented for interior permanent magnet (IPM) synchronous machines. The estimated parameters are the stator resistance through dc test, the dq inductances using high-frequency injection, and the permanent magnet flux by means of a closed-loop speed control maintaining rotor stationary. The proposed method does not require either locking the rotor or additional/special power supplies. The validity of the suggested method has been verified by implementation on two IPM motor prototypes. Finally, the estimated parameters have been compared against results obtained through finite-element simulations and with machine magnetic characterization, separately performed, to validate the methods effectiveness. Saturation and cross-saturation effects are taken care of through amplitude modulation and cross-axis current application, respectively.

Model based design of a sensorless control scheme for permanent magnet motors using signal injection

The sensorless control schemes based on machine saliency detection by signal injection commonly adopt a position observer to estimate the motor position. The position observer usually employs proportional-integral-derivative- (PID-) type controllers and low-pass-filters (LPFs) whose parameters need to be properly tuned to achieve satisfactory, or at least stable, performances. Generally, the position observers are tuned with trial and error procedures that require commissioning time and control design experience. This paper deals with the observer modelling and tuning. In particular, the observer model is used for a model-based position control tuning and the effectiveness of the proposed procedure is confirmed by the good agreement of theoretical and experimental results. The experimental test have been realized using both a linear tubular permanent magnet motor (LTPM) and a rotating internal permanent magnet motor (IPM) to demonstrate that the motor control performances can be predicted only if the observer behaviour is considered.

Sensorless Control of Linear Tubular Permanent Magnet Synchronous Motors Using Pulsating Signal Injection

Direct drives with linear permanent magnet synchronous motors (LPMSMs) are recently attracting the attention of both industry and academia. On the one hand such electric drives permit to reduce size and increase reliability thanks to the lack of mechanical reduction and transmission devices. On the other hand precision positioning requires linear position sensing with a measuring range (and size) equal to the motor allowed travel. It is clear the advantage of sensorless control in such applications in terms of reduced hardware complexity, cost and maintenance requirements. This paper presents a position sensorless control scheme based on high frequency signal injection. A pulsating voltage is superimposed to the control voltage along the estimated d-axis direction. Then a novel demodulation procedure implemented in stationary coordinates is proposed to extract position information. The procedure has a reduced computational cost if compared to the alternatives already proposed in the related literature and requires no tuning effort. A demonstration of the algorithm convergence valid in transient conditions, and a novel method to measure the high frequency motor impedance are also presented. The proposed approach is well suited for motors with reduced magnetic saliency such as tubular LPMSM. The above considerations are validated by extensive experiments.

Analysis of two-part rotor, axial flux permanent magnet machines

This paper presents a study of the effects obtained when a portion of permanent magnet material is replaced by a soft magnetic composite piece over the rotor poles of an axial flux machine. This technical solution can be adopted to increase the machine inductance in order to limit short circuit currents or to increase the motor saliency and implement sensorless control schemes based on high frequency signal injection. Some design rules for the design of the soft magnetic poles have been derived in order to obtain the desired inductance and/or saliency. The analysis has been validated with finite element analisys and numerical simulations using Matlab/Simulink environment. Some preliminary experimental results have also been reported.

Modelling of linear motor end-effects for saliency based sensorless control

In linear motors, the open structure of the armature produces the so called end-effect. The end-effect introduces non-idealities in the motor magnetic model in dq-synchronous coordinates that require a specific modelling with respect to the well known models of rotating (cylindrical) machines. In particular, for saliency based sensorless control, the end-effect introduces an error in the estimated position that must be taken into account and properly compensated. This paper introduces a general mathematical modeling of the end-effect that can be applied to all linear machines. Based on such model, modified position observers are proposed for sensorless control using pulsating or rotating voltage vectors. Experimental results are presented to verify the feasibility of the proposed method, with reference to the case of a linear tubular permanent magnet motor.

Sensorless position control of linear tubular motors with pulsating voltage injection and improved position observer

The sensorless position control of permanent magnet motors can be successfully implemented by superimposing a high-frequency voltage on the control voltage. The accuracy of the method relies on a fast and accurate signal processing of the measured quantities and on the compensation of the inverter and motor non idealities. In this paper the position estimation is obtained by adding a high-frequency sinusoidal voltage at the output of the d-axis current controller. According to several methods proposed in the literature the position estimation is obtained by minimizing the high-frequency q-axis current. We propose a new approach that also exploits the analysis of the d-axis high-frequency current. Since this current has reasonable amplitude regardless the position estimation error, the proposed approach allows working with injected voltage of reduced amplitude thus reducing noise and additional losses. Moreover a simple I-type controller is used to estimate rotor position and it requires a low-effort design. Experiments on a linear tubular permanent-magnet motor prototype are presented to compare the performances of the considered estimation techniques.

Analytical Thermal Model for Fast Stator Winding Temperature Prediction

This paper introduces an innovative thermal modeling technique which accurately predicts the winding temperature of electrical machines, both at transient and steady state conditions, for applications where the stator Joule losses are the dominant heat source. The model is an advanced variation of the classical lumped-parameter thermal network approach, with the expected degree of accuracy but at a much lower computational cost. A seven-node thermal network is first implemented and an empirical procedure to fine-tuning the critical parameters is proposed. The derivation of the low computational cost model from the thermal network is thoroughly explained. A simplification of the seven-node thermal network with an equivalent three-node thermal network is then implemented, and the same procedure is applied to the new network for deriving an even faster low computational cost model. The proposed model is then validated against experimental results carried on a permanent magnet synchronous machine which is part of an electro-mechanical actuator designed for an aerospace application. A comparison between the performance of the classical lumped-parameter thermal network and the proposed model is carried out, both in terms of accuracy of the stator temperature prediction and of the computational time required.