 Open Access
 Total Downloads : 2955
 Authors : Kamlesh Kumar Bhartiya, Mr. K.P. Singh, Dr. A. N. Tiwari
 Paper ID : IJERTV1IS4225
 Volume & Issue : Volume 01, Issue 04 (June 2012)
 Published (First Online): 01072012
 ISSN (Online) : 22780181
 Publisher Name : IJERT
 License: This work is licensed under a Creative Commons Attribution 4.0 International License
Analysis of PushPull ClassE Inverter for Induction Heating
1Kamlesh Kumar Bhartiya, 2 Mr. K.P. Singh, 3Dr. A. N. Tiwari

M.Tech(Power Electronics & Drives), Electrical Engineering Department, Madan Mohan Malaviya Engineering College Gorakhpur U.P. India 273010

Associate Professor, Electrical Engineering Department, Madan Mohan Malaviya Engineering College Gorakhpur U.P. India273010

Associate Professor, Electrical Engineering Department, Madan Mohan Malaviya Engineering College Gorakhpur U.P. India273010
Abstract:
Pushpull ClassE seriesparallel resonant inverter based induction heaters proposed in this paper, having high efficiency switching mode tuned circuit consist of two parallel inductor and two capacitor. DC is converted into high frequency AC using ClassE inverter. This proposed topology utilizes a pushpull scheme to realize sinusoidal output voltage. Close loop system is modelled and simulated using Matlab simulink. However, the simplified circuit is only appropriate for applications in which the harmonic content of output is not an important criterion. The complementarily activated configuration will provide continuous highripple frequency input current waveform.
Keywords:
Induction Heating, High Efficiency Power Ampli fier, Simulink, Zero Voltage Switching(ZVS).
INTRODUCTION:
In high efficiency ClassE power amplifier (PA) [2][9], the transistor has been used as switch. The resonator , are used to block high frequencies and DC content, forcing the output current to approximate a sine wave at the fundamental frequency.This paper present a new switchedmode inverter which utilizes a speciallytuned resonant network to achieve zero voltage switching(ZVS) and low voltage stress. This new design also realizes small passive components, fast dynamic response and a high degree of design flexibility.
These characteristic also make the proposed topology advantageous in application requiring very high frequency and duty ratio. The shrinking size of electronics equipment demands ever increasing power densities at high switching frequencies and a nominal part for the circuit technology. In attempt to minimize the part count with ClassE operation, the one inductor one capacitor ClassE high efficiency switchingmode tuned PA [1] provides a more simplified circuit. Nevertheless only for applications in which the harmonic content and the phase modulation noise of output are not important criteria. It is therefore desirable to retain the function of the conventional ClassE features; i.e that the amplifier can be operated with high efficiency at very high frequencies and provides a sinusoidal output waveform and powerhandling capability without increasing the complexity of power circuits.
The proposed pushpull ClassE amplifier and the conventional singleended circuit configuration include one inductor and one capacitor. As expected, the harmonic content of outputvoltage is significantly reduced in the proposed pushpull amplifier. However, the amplitudes of the positive and negative halfcycle in the output voltage waveform are not symmetrical, which may cause a small secondharmonic component characteristics differ appreciably, the appearance of even harmonic must be expected. The approaches presented here can be applied to the analysis and design of other ClassE amplifier configurations or with more complicated circuit in exact designs. Further, it should be noted that for this topology, the circuit described in this paper has to operational
points that are performed by the ZVZS and ZVZC switching. Unlike the single ended ClassE amplifier [1], the push pull architecture is able to achieve a sinusoidal output waveform and high power handling capability. For instance a symmetrical driven pushpull ClassE amplifier has been proposed for high power applications as shown in Fig.1.
With the symmetrical gatedriving signals, theoretically, the even harmonics are entirely cancelled at the load, and thus there are few harmonic distortions (HDs). However the doubled part count configuration incurs penalties on overall efficiency and the design cost. Fortunately, there is more elegant way to further reduce the switching loss, if the switch current increases gradually from zero after switch are closed.
This paper is proposes a pushpull ClassE resonant PA with a simple LC load network and a load resistor in each halfamplifier, as shown in fig.1. An overlap capacitorvoltage waveform is utilized to achieve the nominal ClassE conditions without increasing the complexity of the power circuits.

PRINCIPLE OF OPERATION PUSHPULL CLASSE INVERTER
The basic schematic of the proposed pushpull ClassE seriesparallel LCR resonant PA is shown in fig.1. It contains two transistors [these can be bipolar junction transistors (BJTs) or MOSFETs], two inductors, two capacitors, and a load resistance. Switches and are complementarily activated to drive periodically at the operating frequency as in pushpull switching PA [27], i.e. the switch waveforms are identical, except that the phaseshift between and are with an on duty ratio D of less than 50%. The simplest t ype of halfamplifier as shown in fig1. Is seriespa rallel resonant circuit, which consists of an inductor L in series with a parallel capacitor C and resistor
R. The resistor is the load to wich the AC power
to be delivered, with neither end connected to a ground. It is suitable for a load that is balanced to ground, but most RFpower loads have one end connected to a ground.
The switching sequence and theoretical waveforms for the steadystate operation of proposed amplifier are illustrated in fig.2.
Fig.1. Proposed pushpull ClassE inverter
To reduce the transistor turnon power losses, the switch current increase gradually from zero after the switch is closed. The proposed pushpull Class E PA uses a pair of LC resonant networks with an overlapped capacitorvoltage wave form; this offers additional degrees of freedom, and thus there are two operational points that can validly achieve this situation:
Case 1: [ZeroVoltage ZeroSlope switching (ZVZSS)]:
In this case, the nominal operating conditions of ZVS and zerovoltageslope switching (ZVSS) are simultaneously satified.
Namely
(2D) = 0 (1)
= 0 (2)
Case2: [ZeroVoltage ZeroCurrent switching (ZVZCS)]:
The operation principle in the communication of this case is solved by the following simultaneous equation:
( – 2D) = 0
( 2D)= (3)
Fig.2 Theoretical waveforms
In order to satisfy both cases 1&2, it is necessary to find the current = – by which the switch current increases gradually from zero a time t =
, asshown in fig. 1&2. The duty ratio D must be kept at less than 50% so that the capacitorvoltage waveforms and can be overlapped.

OPERATING PRINCIPLE OF INDUCTION HEATING
The induction heating is mainly based on two well known physical phenomena:

Electromagnetic Induction

The Joule Effect

Electromagnetic Induction
Fig.3 a&b : Induction Law of Faraday
Fig.4: Induction of eddy current
The energy transfer to the object to be heated occurs by means of electromagnetic induction. It is known that in a loop of conductive material an alternating current is induced, when this loop is placed in an alternating magnetic field as shown in fig. 3. The e,m.f. equation is given as:
E = Where E: Voltage [V], : Magnetic flux [Wb], t : ime [s], (4)
When the loop is short circuited, the induced voltage E will cause a current to flow that opposes its cause the alternating magnetic field. This is Faraday Lenzs law see in fig.3b.
If a massive conductor (e.g. a cylinder) is place in the alternating magnetic field instead of shortcircuited loop, then eddy current (Foucault Currents) will be induced here as shown in fig.4. The eddy current heatup the conductor according to the joule effect.

JouleEffect:
When a current I[A] flows through the conductor with resistance R[], power is dissipated in the conductor,
P = Ã—R Watt, (5)
In most applications of induction heating the resistance cannot be just like that. The reason is the nonuniform distribution of current in the conductor.



SIMULATION AND RESULTS:
ClassE power amplifier is shown in fig.5a. High frequency AC input voltage is given to the circuit is
shown in fig.5b. Driving pulses and switch voltages are shown fig.5d. The pulse given to the second switch is shift by with respect to the pulse of switch 1.
Fig.5a. Open loop ClassE Inverter in Induction heating.
In this model the input given to rectifier is high frequency AC, which is converted from DC to AC with the help of single phase inverter. The output of rectifier is DC which is input for ClassE inverter. The output of ClassE inverter is high frequency AC which requires for Induction heating. The output voltage of rectifier has been shown in fig.5c and the output current and voltage across the load of pushpull inverter has been shown in fig.5e, the wave form of current and voltage similar to sine wave.
Fig.5b: Input Voltage to the circuit
Fig.5c. DC Output of Rectifier
Fig.5d Switching Pulses and Voltages of S1 & S2
Fig.5e: High Frequency Current and voltage across Load.
Close loop circuit model is shown in fig.6a. Dc voltage is sensed and it is compared with the reference value. The output of PI controller adjusts the pulse width such that the output is brought back to the constant value. Close loop system uses a semi converter to maintain constant amplitude at the output. The output of the rectifier in the close loop system is shown in fig.6b. The switching pulses and switching voltages are shown in fig.6.c. AC output voltage and current across the load are shown in the fig.6d which is similar in sine wave of high frequency.

CONCLUSION:
A ClassE inverter fed induction heater is studied and simulated using Matlab Simulink. This system has advantages like low switching losses, reduced stress and high power density. In Closed loop model developed, the steady state error in the output is reduced. The simulation results are in line with the predictions.
Fig6.a: Close loop ClassE inverter
Fig.6b: DC output of Rectifier
Fig.6c: Switching Pulses & Voltages across S1&S2
Fig.6d; Voltage and Current across the load
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