Condition monitoring of permanent magnet AC machines for all‐electric transportation systems: State of the art

Abstract

The current state of the art on emerging and efficient techniques for condition monitoring of permanent magnet (PM) alternating‐current (AC) machines deployed in electric vehicle (EV) applications is presented. The discussion includes the most common and specific types of faults in PM motors, such as rotor demagnetisation and stator inter‐turn faults, respectively. Fault indicators, such as voltage (vs) and current (is) signals and machine signatures based on motor back electromotive force (EMF) (EB) and magnetic flux (ϕ), are taken into account as a measuring quantity in diagnosing motor faults. Other signatures, including thermal analysis, acoustic noise, and vibrations, are also illustrated as some of the emerging techniques in estimating the performance of EV motors while under operations. In addition, various fault modelling methods, condition monitoring techniques, and comprehensive approaches applied in diagnosing the effect of machine faults during its incipient stages are illustrated. Since most of the fault diagnostic techniques discussed here include only machine‐based quantities as fault indices/indicators, the provided solutions are therefore found to be more reliable and accurate for diagnosing the motor faults. This comprehensive review study is inclusive of the existing fault diagnostic techniques, which are currently employed in industrial and commercial practices, in addition to the new methodologies proposed by the authors. All the given condition monitoring schemes therefore seem significantly vital in estimating the state of health of PM AC machines while under operation in all‐electric transportation systems.

Condition Monitoring of a Three-phase AC Asynchronous Motor based on the Analysis of the Instantaneous Active Electrical Power in No-Load Tests

“…The signals taken into account when monitoring the condition of motors are among the most diverse. The valuable motor output signals provided by the motor and suitable for condition monitoring are acquired by means of appropriate sensors placed on the motor or on its rotor (most frequently vibration sensors [1][2][3][4][5][6][7][8][9][10][11][12], temperature sensors [2][3][4][5][6]10,[13][14][15][16][17][18], instantaneous rotation speed sensors [6,9,14,16,[18][19][20][21] acoustic sensors [5,8,11,12,14], and rarely magnetic field and flux sensors [20,22,23] or stray-flux sensors [6,24]).…”

“…The valuable motor input signals are often acquired from the electrical supply system using appropriate instantaneous voltage and current sensors. The most commonly used input signal in motor condition monitoring is the description of the absorbed current (e. g. by Motor Current Signature Analysis, MCSA [13]) which has been widely used in scientific research [2,4,[6][7][8][9]11,12,14,15,17,18,20,[24][25][26][27][28][29][30][31][32][33][34][35]. The use of voltage sensors is indirect and rarely used on its own, e. g. in unbalancing detection of an AC power supply and overvoltage detection [26], detection of broken bars in stator [13], to prevent the phase-loss [36] or to describe voltage waveform anomalies [2]).…”

“…The most commonly used input signal in motor condition monitoring is the description of the absorbed current (e. g. by Motor Current Signature Analysis, MCSA [13]) which has been widely used in scientific research [2,4,[6][7][8][9]11,12,14,15,17,18,20,[24][25][26][27][28][29][30][31][32][33][34][35]. The use of voltage sensors is indirect and rarely used on its own, e. g. in unbalancing detection of an AC power supply and overvoltage detection [26], detection of broken bars in stator [13], to prevent the phase-loss [36] or to describe voltage waveform anomalies [2]). Otherwise, voltage sensors are almost always combined with the use of current sensors to provide other useful information and signals for monitoring, such as the description of the absorbed instantaneous electrical power or active electrical power [13,19,25,34], as the subject of our previous research [21], the detection of the phase or phase shift of the instantaneous current [30,33,37], or the description of the evolution of the power factor [6,13,17].…”

“…The motor acts as an energy (power) transformer, from electrical to mechanical form. Many normal and abnormal variable mechanical phenomena (e. g. related by bearings condition [1,2,10,11], rotor mechanical imbalance/eccentricity [10,28]) during motor operation (especially at no load) should be reflected (with an amplitude, and the phase at origin of time depending on the frequency) in the evolution of the current, the power factor and especially the instantaneous (and/or active) electrical power. The motor acts as a mechanical load sensor.…”

“…For continuous periodic signals (vibrations, variable part of instantaneous angular speed, currents and, rarely, instantaneous electrical power [34]), the conversion from the time domain to the frequency domain using the Fast Fourier Transform spectrum is widely used [2,6,8,9,17,21,34] to describe the sinusoidal components within (average amplitudes and frequencies). More commonly, the Wavelet Transform is used to detect and describe short (transient) sequences (based on local spectral information) of components within these signals [2, 8, 9, 13, 14, 17, 18, 20, 26, 27, 28, 37, 38 and 39].…”