# Three-Phase Unbalance Analysis Method Based on Three-Phase Motor Current Instantaneous Information
###### Abstract  
Motor current signal analysis is a common method that can be applied to the monitoring and diagnosis of electromechanical equipment. Three-phase unbalance will increase the line power loss and affect the safe operation of power-using equipment. To quickly analyze motor current three-phase unbalance, we propose a method to analyze three-phase unbalance by calculating the coefficient of variation of the three-phase current's instantaneous frequency and instantaneous amplitude. Simulations were conducted to analyze the effects of amplitude deviation and phase deviation on the coefficient of variation of instantaneous frequency and instantaneous amplitude. The three-phase unbalance with continuous amplitude change was simulated and its instantaneous performance was analyzed. Experiments were conducted to compare and analyze the instantaneous information characteristics of the motor with the continuous changing of three-phase unbalance under different speed conditions. Simulations and experiments show that the proposed method in this paper can analyze three-phase unbalance. three-phase unbalance; motor current; park vector demodulation; instantaneous frequency; instantaneous amplitude; coefficient of variation +
Footnote †: journal: Applied Sciences  
detection methods is of great significance to improve the operational reliability of industrial equipment [11]. Many researchers have studied the voltage/current three-phase unbalance. [PERSON], [PERSON] et al. [12] developed a model based on multiple symmetrical components to detect the lower and upper sidebands of the current fundamental frequency to characterize the broken bars and then analyze the forward and reverse rotational differential frequency of multiple symmetrical components that lead to rotor current imbalance. [PERSON], [PERSON] et al. [13] used the standard deviation of rotor slot harmonic amplitudes in three-phase currents as an indicator of voltage unbalances and applied it to resistive minor short-circuit faults in the early stages of the fault. [PERSON], [PERSON] et al. [14] developed a model based on a modified winding function and a finite element-based model to simulate motors with different eccentricity conditions, and experiments were conducted on a three-phase commercial reluctance synchronous motor with medium-to-high eccentricity to reduce the effects of supply imbalance and internal asymmetry and to detect eccentricity using residual cancellation techniques. [PERSON], K et al. [15] proposed the Hilbert modulus current space vector and Hilbert phase current space vector as fault features, analyzed the magnitude of the fault-related spectral components via fast Fourier transform (FFT) analysis, and used support vector machine (SVM) for the classification of induction motors for applications, such as voltage unbalance fault detection. [PERSON], [PERSON] et al. [16] proposed a method to apply time-synchronous averaging (TSA) to the Park vector of the stator current to diagnose defects in three-phase wound-rotor induction motors. [PERSON], [PERSON] et al. [17] proposed calculating the symmetrical components of the stator currents, estimating the power supply fundamental frequency and the three-phase quantities based on the maximum likelihood estimator, and then applying the generalized likelihood ratio test for unbalance fault detection. [PERSON], [PERSON] et al. [18] proposed a monitoring method based on Hilbert transform (HT), TSA, and MCSA, which can detect a small fraction of short-circuit turns in the rotor winding of a wound rotor motor under low or no-load conditions. [PERSON] et al. [19] detected unbalanced supply voltage conditions online by monitoring the relevant indicators calculated by the symmetrical component of the voltage and experimentally verified it under several different operating conditions. [PERSON], [PERSON] et al.