Abstract — The identification of faults in voltage source inverter is highly required to ensure the reliability of the inverter. Early detection of the faults can greatly assist in maintenance of the system by avoiding possibly harmful damage borne out. This paper presents the analysis of short-circuit switches fault of voltage source inverter (VSI) using time frequency distribution (TFD). The TFD which is spectrogram represents current signal of the VSI in time-frequency representation (TFR) that provides temporal and spectral information of the signal. From the TFR, parameters of the signal are estimated such as average current, root mean square (RMS), total harmonic distortion (THD), total waveform distortion (TWD) and total non-harmonic distortion (TnHD). The results shows that the analysis using spectrogram gives information of the current signal of the VSI to identify short- circuit switches and can be implemented for faults detection system. I. INTRODUCTION As the backbone of modern industry, voltage source inverter (VSI) plays role in motor drives, power supplies, power quality conditioners, etc. The design and control technique of VSI have matured in commercial products as a result of efforts to enhance their performance. It estimated 82.5 percent of increasing fault in the power drives because of design and control techniques [1]. The VSI faults can cost maintenance increase, power electronics damage and reduces efficiency. Previously, the majority about 70% of these faults was related to power switches, such as open circuit faults, short- circuit faults and gate-misfiring faults [2]. The faults caused include of transistor failure, pulse width modulation (PWM) and inverter leg open [3]. Typically, short-circuit switches fault occurs in power drives frequently than open-circuit switch. In most previous study, VSI faults are normally analyzed in frequency domains, and the fast Fourier transform (FFT) is used for transformation technique. However, VSI faults signal are usually in non-stationary pattern depend on caused of faults. Thus, this technique is suitable for stationary signals and does not provide temporal information [4]. To overcome these limitations, time frequency distribution (TFD) such spectrogram is used to analyze the condition of VSI faults. This paper presents the analysis of short-circuit VSI switches faults using spectrogram. Spectrogram is performed to represent VSI fault current in time-frequency representation (TFR) for fault pattern identification of short-circuit fault. From the TFR, parameters of VSI current signal are estimated and then, the characteristic of the signal are calculated to indentify the short-circuit switches faults. II. SHORT-CIRCUIT FAULTS OF VSI SWITCHES Short-circuit switch faults of VSI with DC supply of 50V is modeled as presented in Fig. 1. The model consists of a three- phase inverter, equipped with an induction motor, pulse width modulation (PWM) and fault generation. In theoretical, the three phase inverter switches are controlled in pairs (S11, S12), (S21, S22) and (S31, S33). In the operation, only one switch in a pair closed and the other is open. The output voltage can be +Vdc, -Vdc or zero, depending on which switches are closed. The switching of inverter is controlled by comparison of a sinusoidal control and a pulse width modulation (PWM). The sinusoidal control waveform establishes the desired fundamental frequency of the inverter output, while the triangular waveform establishes the switching frequency of the inverter. The most advantages of PWM is reduction in filter requirements to decrease harmonics and easier to control the output voltage amplitude [5]. Fig. 1 Short-circuit faults model of VSI switches. A switching function of the VSI is defined as Fig. 2, where j represents the phase, and variable p and n, respectively, represent the upper and lower component of the phase leg. Where the three-phase VSI is considered, j= {a, b, c}. The switching status represent in term of “1” when the switch is closed and “0’ when open [6]. Short-Circuit Switches Fault Analysis of Voltage Source Inverter using Spectrogram A. R. Abdullah 1 , N. S. Ahmad 2 , N. Bahari 3 , M. Manap 4 , A. Jidin 5 , M. H. Jopri 6 1,2,3,5 Faculty of Electrical Engineering, Universiti Teknikal Malaysia Melaka (UTeM), Malacca Malaysia 4,6 Faculty of Engineering Technology, Universiti Teknikal Malaysia Melaka (UTeM), Malacca Malaysia E-mail: 1 abdulr@utem.edu.my, 2 nursumayyahahmad@gmail.com, 3 hazlina@utem.edu.my, 4 mustafa@utem.edu.my, 5 auzani@utem.edu.my, 6 hatta@utem.edu.my IM Gate Signal Pulse Width Modulation Fault Generation 1808 2013 International Conference on Electrical Machines and Systems, Oct. 26-29, 2013, Busan, Korea 978-1-4799-1447-0/13/$31.00 ©2013 IEEE