Triggering Circuit of Induction Furnace With Power Quality Analysis

Transcription

1 International Conference on Electrical, Electronics, and Optimization Techniques (ICEEOT) Triggering Circuit of Induction Furnace With Power Quality Analysis Ronal S. Parmar 1 Department of Electrical Engineering Birla Vishwakarma Mahavidyalaya V. V. Nagar, Gujarat, India parmar.ronal@gmail.com Swapnil V. Arya 2 Department of Electrical Engineering Birla Vishwakarma Mahavidyalaya V. V. Nagar, Gujarat, India arya.bvm@gmail.com Abstract This paper contains simulations of a six-pulse Induction Furnace with 500 Hz output frequency and 500V output voltage. Comparison of thyristor based inverter and IGBT based inverter shown in the paper, and simulation of IGBT based inverter is shown because it has higher efficiency, faster switching. Rectifier section is diode based for the simplicity constrain. The model of the induction furnace was implemented in MATLAB software and output wave form analyzed. A. Basic Block Diagram II. INDUCTION FURNACE Keywords Current Source ; Voltage Source inverter; Zero Current Switching; Zero Voltage Switching; I. INTRODUCTION The induction furnaces are used to heat metals through electromagnetic induction principle. Induction heating is widely used in the metal industry for melting or heating thin slab in continuous casting plants because of better heating efficiency, high production rate and clean working environment. Induction furnaces have very high power consumption and non-linear characteristics [2]. Usually a typical induction furnace is designed with a topology formed by an AC DC converter (rectifier), DC link filter, DC AC converter (inverter) and an induction coil. For Induction coil, Power sources of several ranges have been developed from 1 KW to 10 MW, with operating frequencies from 10 Hz to 60 MHz, which depends on dimension and quality of the material to heat, load operating temperature, treatment of the piece and physical load distribution inside of furnace coil [6]. If the inverter operates in frequency it will allow to transfer maximum power to the induction coil [3]. To transfer maximum power to the load it becomes necessary adjusting the inverter frequency to natural resonant frequency. In this paper, the simulation and results of induction furnace are presented. The rated output voltage and frequency of mentioned induction furnace is 500Vand 500 Hz, respectively. The input voltage and rated frequency are 415V and 50Hz. Fig. 1. A scheme of 3-phase power circuit simulation model of induction furnace [1] Figure 1 shows scheme of 3-phase, power circuit simulation of the Induction Furnace. The basic portions of this circuit are as follows: i. Three Phase full bride Rectifier DC link Filter Single phase full bride iv. Resonant circuit for Induction Coil v. gate driver circuit B. Rectifier This circuit converts AC voltage into DC voltage. Till now most research has been carried out in a field of differential topology in terms of selection of semiconductor switches for the rectifier. If the load is variable and source voltage is also variable at that time a topology with rectifier as thyristor or any other controllable switch can be used. Whereas, the diode is a better option if constant load is used [5]. Normally for low power application uncontrolled rectifiers are used. When we convert AC power into DC, the output value of voltage is 130% of input voltage. C. DC Link Filter Filter design for full bridge is important because the output of rectifier contains undesirable ripples. In many /16/$ IEEE

2 application ripples should be in specified limit. Normally in industry 3% ripple is permissible [4]. To reduce ripple from the output of rectifier we add a filter. The filter is classified into three types as below: a. Capacitive filter RF. / For finding the proper value of the capacitor to limit the ripple in waveform equation (1) is used. Capacitive filter is used for low power application because when capacitor charging at that time it acts like a short circuit so simple capacitor filter is not suitable for high power application [4]. b. Inductive filter RF. / For finding the proper value of the inductor to limit the ripple in waveform equation n (2) is used. Inductor filter permits large current without a serious change in output voltage. This is the reason it is suitable for large power application [4]. c. Capacitive inductive filter The followings are some salient features of this filter: i. Is used to improve the filtering action of rectified voltage and current. (1) (2) The function of a capacitor is smooth out the variation in voltage while inductor is used to smooth out the variations in current. Because uniform flow of current, the capacitive-inductive filter is widely used in high power application. iv. A large value of the capacitor and inductor is needed when they used alone, to achieve the same result from capacitiveinductive filter very small value of the capacitor and inductor is needed when they use together [4]. D. The inverter converts DC voltage into AC voltage. Here, the is used to change the frequency using IGBT or MOSFET [3,6,7]. Normally, two types of inverter are used in induction furnaces. IGBT based or Thyristor based. A comparison of both topologies shown in below Table I [2,3]. Rectifier Table I. Comparison of IGBT and thyristor based inverter IGBT based The rectifier is diode based, 3-phase full bride or uncontrolled rectifier in IGBT based Thyristor based The rectifier is thyristor based or controlled rectifier The inverter is thyristor based Starting circuit Not required Required Output voltage gain Possible Not possible Power factor Good Poor Control Easy Complex Efficiency Good Poor Cost Size Low (compare to thyristor based) Small (gate driver requires in only ) Expensive Large (gate driver requires at both sides) From Table I, it can be seen that IGBT based inverter is better than thyristor based inverter. Therefore, in our simulation, we have used IGBT based inverter. E. Resonance Circuit for Induction Coil Induction furnace has a purely inductive load. Load power factor is very poor because of inductive and overall performance of the furnace also low. Therefore, to improve power factor and efficiency, we add capacitor in series or parallel with inductor coil. It helps to create a condition between inductor and capacitor. [7, 11] Resonant circuits are classified into three types as follows: i. Series Parallel Hybrid Fig. 2. Series Resonance Fig. 3. Parallel Resonance Fig. 4. Hybrid Resonance (LCL / CCL) Table II. Comparison of all circuits Series Resonance Parallel Hybrid Switching losses Moderate High Low Simplicity for protection and Very easy Easy Complex maintenance ZVS & ZCS Both ZCS Both Flow of current Part of load Full through inverter current - Higher operating Possible Less possible Can be obtained

3 frequency from a configuration Weight Light Medium Heavy Output power More voltage More current - Efficiency Medium Poor 80-90% Device cost Higher Lower Moderate Power rating of semiconductor Higher Lowest Moderate switch P.F at al load Good Poor Better Construction Simple Moderate Complex Impedance Minimum at Minimum at Freq. - On load switching losses Higher Lower Moderate Quality factor X L / R R / X L - Resonance frequency Current at π 1 R LC L - V/ R V / (L / CR) - In Table II, it can be seen all three types comparison. In that hybrid is far better as compared to series and parallel. But for low power application parallel is much better than hybrid [7, 11]. F. Gate driver circuit Gate driver circuitry is designed for driving (i.e. To turn on and off) any semiconductor switch. Here IGBT switch is to be derived by the gate driver, so for that control pulses are obtained from Arduino UNO, in that ATmega328P IC has been used for this purpose and then the controlled pulses from the Arduino are given to gate driver circuitry (basically an Optocoupler IC) then the gate driver gives optically isolated control pulses to IGBT gate. Basic block diagram of the gate driver circuitry has been shown below in Fig.6. Induction Coil 285µH Operating Frequency 500Hz IGBT Rectifier Diode B. Suggested Control method Output power obtained from the coil of induction furnace is not constant. For application that require constant current, we go for CSI, whereas if the load metal is variable (because of which the inductance of a coil change which varies the current), there VSI is more suitable [5,7]. For gating proper output voltage we recommended two solutions as below: i. Single phase switch converts into IGBT switches For Triggering of these switches SPWM technique is used. C. Single line diagram for simulation Fig. 6. SLD for simulation D. MATLAB Simulation Results i. DC Link voltage Fig. 5. Gate driver circuit for IGBT In Fig. 5, 1KΩ resistor is used for limiting current to gate pulse, and 0.5KΩ resistor is used to discharge insulated gate capacitor. If the capacitor is not discharged then after disconnection of the gate pulses IGBT continuous triggering until the insulated gate of the IGBT is fully discharged. Fig. 7. DC link output voltage In Fig. 7, it can be seen that the output of the rectifier is almost 586V, it is 130% of input voltage. The constant voltage is obtained using LC filter Output voltage III. SIMULATION A. Design values for the proposed MATLAB model Table III. Input design values for the proposed MATLAB Model Power Voltage Furnace Current 10KW 415V 10A Fig. 8. output voltage (MI 0.9)

4 Fig.13. Shows the Total Harmonic Distortion (THD) measurement at supply voltage waveform. Harmonic distortion is reduced by adding passive filter at source side. E. PROTEUS Simulation of GATE driver circuit Fig. 9. output voltage (MI 0.3) Output Current Fig. 10. Current through induction coil (MI -0.9) Fig. 11. Current through induction coil (MI -0.3) In Fig. 8, 9, 10 & 11, it can be seen that if there is the reduction in modulation index than the average value of voltage and current reduces. iv. Supply Voltage Fig. 14. Proteus Simulation circuit of GATE driver circuit In Fig. 14, control circuit of induction furnace is shown. This circuit generates a gate pulse for inverter IGBTs. F. Proteus Simulation Output Fig. 12. Input voltage of induction furnace In Fig. 12, it can be seen that the input voltage waveform is distorted because of switching in the converter. It is also caused by non-linear nature of the load. v. THD Measure at source voltage Fig. 13. THD measurement of supply voltage Fig. 15. Control circuit output from Arduino Figure 15 shows the output of the control circuit, i.e. gate pulse for full bridge IGBTs inverter. IV. CONCLUSION This paper shows Simulation of induction furnace with parallel load. It has been observed that by adding Capacitor-inductor filter at rectifier output, ripple is controlled and provide constant voltage and smooth current to an inverter. Moreover, in inverter using IGBT with SPWM technique, control of output voltage of

5 induction furnace is possible by changing modulation index. It is suggested that passive filter can be added to reduce TDH in source voltage. V. ACKNOWLEDGMENT We are highly indebted to Mr. B. G. Shah (Pioneer Furnace Ltd.) for their guidance and constant supervision as well as for providing necessary information regarding the project. VI. REFERENCES [1] Alexander C. Moreira: Electrical Modelling And Power Quality Analysis Of Three-Phase Induction Furnace, IEEE ICHQP 2014, pp [2] B. R. Pulley: Latest Development In Static High Frequency Power Sources For Inductionheatin, industrial Industrial Electronics and Control Instrumentation, IEEE Transaction, Vol.17, No , pp [3] Ricardo Fuentes, Patricia Lagos, Joege Estrada: Self-Resonant Induction Furnance With IGBT Technology, IEEE ICIEA 2009, pp [4] Sudeep Pyakuryal, Mohammad Martin: Filter Design For AC To DC Converter, IRJES, Vol.2, No , pp [5] Arash Kiyoumarsi: Closed Loop Power Control Of An Induction Furnace, IEEE ICEM 2008, pp [6] Sanjay R Joshi, Viralkumar Solanki: Simulation of Induction Furnace And Comparison With Actual Induction Furnace, IJRTE, Vol.2, No , pp [7] Sibylle Dieckerhoff: Design Of An IGBT-Based LCL-Resonant For High-Frequency Induction Heating, Industrial Application Conference IEEE 1999, Vol.3, pp [8] M. M. Makrani, R. D. Patel: Simulation Of H-Bridge Used For Induction Melting Furnace, IJERT, Vol.2, No , pp: