Silvio Stasi

A new EKF-based algorithm for flux estimation in induction machines

A reduced-order algorithm for estimating the rotor flux components of induction motors with schemes such as field-oriented control is described. The algorithm is based on the extended Kalman filter (EKF) theory and estimates the desired quantities online using only measurements of the stator voltages and currents and the rotor speed. The online adaptation of the inverse rotor time constant makes it possible to obtain very accurate estimates of rotor flux components, in spite of temperature and magnetic saturation effects. The algorithm order reduction decreases the computational complexity and makes the proposed estimator superior to others based on EKF theory. >

Improved rotor speed estimation using two Kalman filter-based algorithms

This paper proposes the application of two new Kalman filter-based algorithms to realise a speed-sensorless vector control of induction motor drives. The first one is a linear Kalman filter (LKF)-based algorithm that estimates the equivalent disturbance torque, which is compensated by the injection of a feedforward signal. The latter is an extended Kalman filter (EKF)-based algorithm used to obtain a correct implementation of sensorless vector control, since it estimates both the rotor flux components and speed. The mathematical EKF-model is accurate because of the equivalent-disturbance compensation obtained from the LKF-based observer. The rotor speed estimate is very good in the whole velocity range including zero value. The results show the effectiveness of the proposed control scheme.

Comparison of spectral estimation techniques applied to induction motor broken bars detection

This paper presents a performance comparison among some of the most effective spectral estimation techniques applied to the fault diagnosis of induction machines. The diagnostic test is based on the analysis of the current space vector during motor starting via short-time analysis, using a sliding window and different spectral estimation algorithms. Differently from most of the diagnostic techniques already proposed in the technical literature, the approach, presented in this work, is effective regardless of the load condition of the machine. Algorithms based on the FFT or optimal band-pass filters (nonparametric methods), on the estimation of a linear time-invariant model of the signal (parametric methods), and on the eigenanalysis of the autocorrelation matrix (high-resolution methods) have been used to process the motor current space-vector. Experiments prove that both parametric and high-resolution methods overcome the FFT-based approaches, keep only the principal frequency components of the signal and decrease the noise influence, thus permitting a better interpretation of the current vector spectrum and an automatic fault detection procedure.

Kalman filter estimators applied to robust control of induction motor drives

This paper proposes the contemporaneous application of two Kalman filter-based algorithms to realise a robust control of induction motor drives. The first one (EKF, extended Kalman filter) is used to obtain a correct implementation of direct vector control, since it estimates the rotor flux components, rotor time constant, rotor resistance, and leakage reactance. The on-line adaptation of electrical parameters makes it possible to obtain very accurate estimates of rotor flux components, in spite of temperature and saturation effects. The second one (LKF, linear time invariant Kalman filter) estimates the equivalent disturbance to realise the rejection of external disturbances and robustness to mechanical-parameter variations.

Reactive Power Flow Control for PV Inverters Voltage Support in LV Distribution Networks

This paper proposes a reactive power flow control pursuing the active integration of photovoltaic systems in LV distribution networks. An alternative power flow analysis is performed according to the specific characteristics of LV networks, such as high resistance/reactance ratio and radial topologies. The proposed solution gives high performances, in terms of rms-voltage regulation, by estimating the reactive power reference on each node considering the influence of the rest of the nodes in terms of active and reactive power demanded/generated by them. The local control of each photovoltaic system is based on the power converter control, interfacing these units with the grid and the loads respectively. The local control is designed on the basis of locally measured feedback variables. Photovoltaic units thus guarantee universal operation, being able to change between islanding-mode and grid-connected mode without disrupting critical loads connected to them, and allowing smooth transitions. Exhaustive results are also included and discussed in this paper.

Analysis techniques for detection of IM broken rotor bars after supply disconnection

This paper presents some analysis techniques of the space-vector of voltages induced in the stator windings after supply disconnection, to detect broken rotor bars in squirrel cage induction machines. When the motor is disconnected from the supply no currents flow in the stator windings and the voltages measurable at its terminals are due to flux produced by rotor currents. When the rotor is healthy, the voltages measured at motor terminals are almost sinusoidal because of the symmetry of rotor windings. When there are broken rotor bars, the magneto-motive force (m.m.f.) generated by rotor windings results distorted, and some particular harmonics, contained in the voltages induced in the stator windings, increase their amplitudes. The diagnostic technique is based on monitoring these voltage harmonics and analyzing the space vector of the voltages induced in the stator windings via MUSIC pseudospectrum and Short-Time MUSIC (STMUSIC) time-frequency pseudo-representation. The MUSIC algorithm is based on the eigen-analysis of the autocorrelation matrix, and permits to evidence the principal harmonic frequencies of the signal and decrease the noise influence, thus allowing a better detection of the broken rotor bars. The results obtained using MUSIC and STMUSIC algorithm have been compared experimentally with those obtained by FFT and STFFT respectively, and two different sized induction motors have been tested, to demonstrate the superiority of the former approach. Differently from most of the diagnostic techniques already proposed in the technical literature, the proposed approach is effective regardless the load condition of the machine, source characteristics and iron saturation.

Sensorless control of PM synchronous motors based on LKF estimation of rotor position

This paper presents a novel PMSM sensorless control scheme based on a linear Kalman filter (LKF) observer. The LKF algorithm is able to estimate rotor position and current components in the stator reference frame by measuring stator currents, and using a mathematical model based on the voltage equations of motor. The proposed observer is linear but time-varying because the rotor speed is treated as a model parameter to be updated on-line. Estimation of rotor speed is performed in two steps: firstly a rough speed estimation is obtained by processing the estimates of rotor position; then a simple speed observer is used to improve the accuracy of speed estimates. The observer output, i.e. the final speed estimate, is fed back to both the speed control loop and LKF algorithm. Sensitivity to strong stator resistance variations makes this sensorless algorithm unsuitable for operation at very low speed; good performances are obtained in the speed range from 10% of rated speed to full speed.

SiC MOSFET Dual Active Bridge converter for harsh environment applications in a more-electric-aircraft

Due to size and weight limitations, possible integrations of power electronics devices with electrical machines and propulsion engines are welcome in More-Electric-Aircrafts (MEA). Consequently, power converters are required to operate in harsh environments with high temperatures. SiC power devices are preferable in this context since they can tolerate high junction temperature and contribute reducing size and weight of the cooling system. In this paper, a 270/28 V SiC MOSFET Dual Active Bridge (DAB) converter is presented. In particular, its thermal behavior in harsh environments is investigated. Using two different tools, the performances of the system are analyzed at two levels: the single SiC MOSFET power module and the complete DAB converter. Results confirm the feasibility of the proposed power stage also when the ambient temperature rises above 300 C.

A ground power unit based on paralleled interleaved inverters for a More-Electric-Aircraft

In the More-Electric-Aircrafts the role of the power converters is fundamental and in the last years the amount of electric power has increased rapidly. In this paper a power conversion stage is proposed and controlled for the Ground Power Unit of a More-Electric-Aircraft. The power conversion topology is based on paralleled converters with interleaved modulation which allows to overcome constraints due to low ratio between the switching frequency and the fundamental frequency (400 Hz) and to minimize the size of the filtering elements. Simulation results prove the effectiveness of the proposed solution.

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.