The stator temperature of the three phase induction motor with Z-source inverter drive is experimentally studied in this paper along with the comparison of the stator temperature of three phase induction motor with PWM drive. Z-source inverter employs an unique impedance network coupled with inverter circuit and rectifier. The inverter system using IGBT's, provide ride-through capability during voltage sags, reduces the line harmonics, improves power factor, increases reliability, reduces electromagnetic interference noise and low common mode noise. The line harmonic simply dissipate as heat in the stator windings, this has been minimized using Z-source filter. Â© 2013 IEEE

Manjesh, M.

Rajesh, B.

ePrints@Bangalore University

  Heat measurement at various parts of Three Phase Induction Motor at Low Speed using Z-source Filter.  Rajesh B.1     Manjesh.2 1 Department of Electronic Science, Bangalore University, Bangalore  E-mail: rajeshb0201@gmail.com  2 Department of Electronic Science, Bangalore University, Bangalore  Abstract- The stator temperature of the three phase induction motor with Z-source inverter drive is experimentally studied in this paper along with the comparison of the stator temperature of three phase induction motor with PWM drive. Z-source inverter employs an unique impedance network coupled with inverter circuit and rectifier.  The inverter system using IGBT’s, provide ride-through capability during voltage sags, reduces the line harmonics, improves power factor, increases reliability, reduces electromagnetic interference noise and low common mode noise. The line harmonic simply dissipate as heat in the stator windings, this has been minimized using Z- source filter. Keywords - Induction motor drive, harmonics, Z-source inverter, Voltage sag.  I. INTRODUCTION  The voltage source inverter present negligible switching losses and EMI generation at the line frequency. The voltage source inverter requires an output LC filter to provide sinusoidal voltage compared with current source inverter.  The LC filter causes additional power loss and control complexity.  The voltage source converter is widely used. However it has the following limitations:  1. The upper and lower devices of each phase leg cannot be switched on simultaneously either by purpose or by EMI noise [6].  A shoot through would occur and destroy the devices. Minimum dead time is provided to both upper and lower switches to avoid short circuit and distortion in the output voltage wave form. 2. The AC output voltage is limited below and cannot exceed the DC bus voltage or the DC bus voltage has to be greater than the AC input voltage.  Therefore the voltage source inverter is a buck inverter for DC to AC power conversion and the voltage source converter is a boost rectifier for AC to DC power conversion.  For applications where over drive is desirable and available DC voltage is limited, an additional DC-DC boost converter is needed to obtain a desired AC output [3]. The additional power converter stage increases system cost and lower the efficiency. 3. An Output filter is needed for providing a sinusoidal voltage compared with the current source inverter, which causes additional power loss and control complexity.   However the current source converter has the following conceptual and theoretical barriers and limitations. 1. Any one of the switch from the upper and one from the lower switch have to be maintained on at any time.  Otherwise, an open circuit of the DC inductor would occur and destroy the devices. Overlap time for safe current commutation is needed in the current source converter, which also causes waveform distortion. 2. The AC output voltage has to be greater than the original DC voltage that feeds the DC inductor or the DC voltage produced is always smaller than the ac input voltage.  Therefore, the current source inverter is a boost inverter for DC to AC power conversion and the current source converter is a buck rectifier for AC to DC power conversion [4].  For applications where a wide voltage range is desirable, an additional DC-DC buck converter is needed.  Both the voltage source converter and current source converter have the following common problem.  1. They are either a boost or a buck converter and cannot be a buck-boost converter.  That is the output voltage range is limited to either greater of smaller than the input voltage. 2. The main circuit is not being interchangeable.  In other words, neither the voltage source converter main circuit can be used for the current source converter and nor vice versa.  II. Z- SOURCE INVERTER  Z-source Inverter is used to overcome the traditional source inverters.  It employs a unique impedance network coupled with the inverter main circuit to the power source.  It consists of voltage source from the AC to DC converter, impedance network, three phase inverter and three phase induction motor.  The AC voltage is rectified by the Converter, the rectifier output DC voltage fed to the impedance network, which consists of two equal inductors and two equal capacitors.  The network inductors are connected in series arm and capacitors are connected in diagonal arms.  The impedance network is used to buck or boost the input voltage depends on boosting factor.  This network also act as a second order filter and it should required less capacitance. The PWM inverter consists of six switches.  These inverters use a unique impedance network, coupled between the power source and converter circuit, to provide both voltage buck and boost properties, which cannot be achieved with conventional voltage source and current source inverters.  The unique feature of the Z-source inverter is that the output AC voltage can be any value between zero and   infinity regardless of DC voltage.  That is, the Z-source inverter is a buck-boost inverter that has a wide range of voltage. To describe the operating principle and control of the Z source inverter in Fig.1.  The traditional three-phase voltage source inverter has six active vectors when the DC voltage is impressed across the load and two zero vectors when the load terminals are shorted through either the lower or upper three devices respectively.  However, three phases Z-source Inverter Bridge has one extra zero state when the load terminals are shorted through both the upper and lower devices of any one phase leg, any two phase legs, or all three phase legs.  This shoot-through zero state is forbidden in the traditional voltage source inverter, because it would cause a shoot-through.  The Z-source network makes the shoot-through zero state possible. This shoot-through zero state provides the unique buck-boost feature to the inverter.   III.  Z-SOURCE INVERTER FED INDUCTION MOTOR WITH V/F CONTROL.  A V/F control method is used in this study to operate the three phase induction motor at low speed to maintain the torque constant, with torque load 0.21Nm.  For small drives with no significant inductance, the line current becomes discontinuous and the DC voltage is closer to 1.141 times the line to line input voltage, the low output voltage significantly limits output power that is proportional to the square of the voltage.  It is a very undesirable situation for many applications because the motor and drive system has to be oversized for a required power.  The voltage sags can interrupt an induction motor drive system and shut down critical loads and processes. The DC capacitor in induction motor drives is a relatively small energy storage element, which cannot hold DC voltage above the operating level under such voltage sags.  Lack or ride through capacity is a serious problem for sensitive loads driven by [1,2], [7].     Solutions have been sought to boost ride-through [9, 2].  The industrial drives provide options using fly back converter or boost converter with energy storage to achieve ride-through however, these options come with penalties of cost, size and complexity. Inrush and harmonic current from the diode rectifier can disturb the line.  Low power factor in another issue of the traditional induction motor drives [5].  Performance and reliability are compromised by the voltage source inverter structure, because miss switching from EMI can cause shoot-through that leads to destruction of the inverter, the dead time that is needed to avoid shoot-through creates distortion and unstable operation at low speeds, and common mode voltage causes shaft current and premature failures of the motor. A recently developed new inverter, the Z-source inverter [1], has a niche for drives systems to overcome the aforementioned problems [8].  The Z-source inverter system can produce an output voltage greater than the AC input voltage by controlling the boost factor, which impossible for the traditional induction motor drive systems.  A Z-source inverter based induction motor drive can:  1. Produce any desired output voltage, even greater than the line voltage, regardless of the input voltage, thus reducing motor ratings. 2. Provide ride-through during voltage sags without any additional circuits. 3. Improve power factor, reduce harmonic current and common-mode voltage. 4. Reduction of line harmonic causes reduction in stator winding temperature of the induction motor. In this paper and Atmel 89S52 microcontroller used to drive the Z-source inverter with software dead time between upper and lower IGBT’s. To measure the stator temperature of phase induction motor a temperature sensor J-type thermocouple is fixed at stator windings of the induction motor, these J-type thermocouples are connected to temperature module kit, connected between induction motor and computer is shown in the Fig.2, the temperature samples are recorded on the computer.  The experiment is studied at low speed with V/F control is used to drive the three phase induction motor. The measurement of stator winding temperature of three phase induction motor is studied with PWM drive without Z-source filter. The temperature measurements compared with PWM drive Z-source filter.  The experiment is studied with V/F control method for a frequency 5Hz, the temperature difference obtained practically is shown in the table1. The values of L1=L2=20mH, and C1=C2=1000uF/450V is used for the experiment.    IV. RESULTS  The Induction motor has been run for 180 minutes with torque load of 0.21Nm. The comparison of the temperature of stator windings of three phase induction motor with and without Z-source filter is carried out for low frequency is as shown in the Fig.3 and Fig.4. The table below shows the Fig 1: Z-Source PWM Inverter Drive   temperature variations at 180th minute, at different parts of the motor.  Table1: Measurement of Temperature at various parts of the three phase induction motor. Measurements at various parts Temperature values with normal PWM drive Predicted Temperature Temperature values with Z-source Inverter drive Top of Stator Winding-1 49 48.24 44.3 Bottom of Stator Winding-2 48.6 48.69 44.1 Frame (Yolk) 48 47.1 40.5 Outer body 46 42.94 38.1 Ambient 26 26 26            V. CONCLUSION   The study of temperature with Z-source filter and without Z-source filter of the stator winding in an induction motor has been studied. From the experimental results it is concluded that the rate of rise of stator winding temperature of three phase induction motor with Z-source filter is found to be less compared to regular PWM drive.   REFERENCES  [1] Fang Zheng Peng, Z-Source Inverter. IEEE Trans. Industry Applications. 39: 2003, 2. Wuhan,China. [2] Fukuda, S., Y.Kubo and M. Kitano, 2002. “Introduction to a hybrid multi converter systems and its control strategy,” in Proc. PCC’02 Conf., Osaka, Japan, pp: 372-377. [3] Pillai, S.K. and IIT Bombay, “Analysis of Thyristor Power conditioned motors” University Press.  [4] Bimal Bose, “Modern Power Electronics and AC Drives”, Prentice Hall. [5] Maria Imecs, M. Andrzej Traxzynadlowski, I. Ioan Incae and Csaba Szabo, 2005. “Vector Control Schemes for Tandem converter fed induction motor drvives” IEEE transactions on Power Electronics, 20(2). [6] Kim, Y. and S.Sul, 2001. A novel ride-through system for adjustable-speed drives using common mode voltage. IEEE Trans. Ind. Applicat., 37: 1373-1382. [7] Duran-Gomez, J.L., P.N. Enjeti and A. Von Jouanne, 2002. An approach to achieve ride through of an adjustable-speed drive with fly back converter modules power by super capacitors.  IEEE Trans. Ind. Applicat., 38: 514-522. [8] Comptun, K.T., 1947. Electric Circuit Hand Book. 6th Ed., London. [9] Vonjouanne, A., P.N.Enjeti and B.Banerjee, 1999. Assessment of ride through alternatives for adjustable speed drives.  IEEE.Trans.Ind. Applicat., 35:908-916.   BIOGRAPHIES  Manjesh obtained his Ph.D in march 2012, presently working as Associate  Professor, Electronic Science Department, Bangalore University, Karnataka, India. He is working on Power Electronics and Motor drives, Temperature analysis of motor drives etc.     Fig.3.Measurement of stator temperature of Induction motor with PWM drive. With V=41V, f=5Hz, torque load=0.18Nm Fig.4.Measurement of stator temperature of Induction motor drive with Z-source filter, V=41V, f=5Hz, torque load=0.18Nm Rajesh B obtained his B.Sc and M.Sc in Bangalore University in the year 2009 and 2011 respectively. Presently he is a Research Scholar under the guidance of Dr. Manjesh, Associate Professor, Bangalore University, Bangalore.   

Heat measurement at various parts of three phase induction motor at low speed using Z-source filter

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Heat measurement at various parts of three phase induction motor at low speed using Z-source filter

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