Analysis of H-bridge Current Source Parallel Resonant Inverter for Induction Heating Abstract: This paper gives the theory and experimental results for a current-source parallel-resonant inverter employed for induction heating. The analysis is performed in the frequency domain using Fourier series techniques to predict output power, efficiency, dc-to-ac voltage transfer function, and component voltage and current stresses. The inverter consists of four switches, a large choke inductor, and a parallel-resonant circuit. Each switch consists of a MOSFET in series with a fast diode. An inverter was designed and constructed. The dc input voltage was 70 V and the output voltage was a sine wave with a peak value of 100 V at an operating frequency of 83 kHz. The output power at full load was 400 W. Index Terms: induction heating, parallel resonant, current source inverter. 1. Introduction Voltage source inverters suffer from a pulsating input current [1,3]. An alternate topology that draws a constant current from the dc supply is the current source parallel-resonant inverter. The constant current drawing property of the current-source inverter is an advantage over the voltage-driven inverters because of the lack of harmonics introduced to the line[7]. Another advantage of the current-source parallel- resonant inverter topology is that the switches only carry the active power of the resonant circuit [2]. The objectives of this paper are to present an analysis of a full bridge current source parallel-resonant inverter for induction heating, give a design example, and present the experimental results. 2. Principle of Operation Fig. l(a) shows the circuit diagram of the full bridge current source parallel-resonant inverter. It consists of a large choke inductor DC L , four switches S1-S4, and an L LCR , parallel-resonant circuit. The dc input source I V and the filtering choke DC L , form a dc input current source I I . L R is the calculated work-piece resistance reflected to the heating coil terminals[5]. Each switch is made up of a MOSFET in series with a fast recovery diode. This series diode disables the internal body-drain diode of the MOSFET that would normally allow the negative current to flow when the switch is off [4]. The MOSFET’s are driven by rectangular gate-to-source voltages GS V at the operating frequency f = 1/T and an on-duty cycle of approximately 70%. The overlap period ( s μ 1 ) when all switches are on is necessary to prevent the filtering choke from being open circuited. Fig. l(b) shows an equivalent circuit of the inverter with parasitic resistances and offset voltage sources, where DC L R is the equivalent series resistance (ESR) of the input inductor DC L , DS r is the MOSFET on-resistance, F R is the diode forward resistance, F V is the diode offset voltage, Lp R is the equivalent parallel resistance (EPR) of the resonant inductor (work coil without work-piece) L, and Cp R is the EPR of the resonant capacitor C. When switch S4 and S3 are OFF and switch S1 and S2 are ON, the current through the resonant circuit is I I i = . When S1 and S2 are OFF and S3 and S4 are ON, the current through the resonant circuit is I I i - = . Assuming that the input inductor L DC is large enough, the circuit composed of I V , DC L , and S1-S4 can be modeled by a square-wave current source I I i ± = . Shown in Fig. l(c). The resonant frequency of the parallel resonant H.javadi*,A.Shoulaie** *Iran University of Science and Technology, [email protected]** Department of Electrical Engineering, Iran University of Science and Technology, [email protected]435
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Analysis of H-bridge Current Source Parallel Resonant Inverter
for Induction Heating
Abstract: This paper gives the theory and experimental
results for a current-source parallel-resonant inverter
employed for induction heating. The analysis is performed
in the frequency domain using Fourier series techniques to
predict output power, efficiency, dc-to-ac voltage transfer
function, and component voltage and current stresses. The
inverter consists of four switches, a large choke inductor,
and a parallel-resonant circuit. Each switch consists of a
MOSFET in series with a fast diode. An inverter was
designed and constructed. The dc input voltage was 70 V
and the output voltage was a sine wave with a peak value of
100 V at an operating frequency of 83 kHz. The output
power at full load was 400 W.
Index Terms: induction heating, parallel resonant,
current source inverter.
1. Introduction
Voltage source inverters suffer from a pulsating
input current [1,3]. An alternate topology that draws a
constant current from the dc supply is the current
source parallel-resonant inverter. The constant current
drawing property of the current-source inverter is an
advantage over the voltage-driven inverters because of
the lack of harmonics introduced to the line[7].
Another advantage of the current-source parallel-
resonant inverter topology is that the switches only
carry the active power of the resonant circuit [2]. The
objectives of this paper are to present an analysis of a
full bridge current source parallel-resonant inverter for
induction heating, give a design example, and present
the experimental results.
2. Principle of Operation
Fig. l(a) shows the circuit diagram of the full
bridge current source parallel-resonant inverter. It
consists of a large choke inductor DCL , four switches
S1-S4, and an LLCR , parallel-resonant circuit. The dc
input source IV and the filtering choke DCL , form a
dc input current source II . LR is the calculated
work-piece resistance reflected to the heating coil
terminals[5]. Each switch is made up of a MOSFET
in series with a fast recovery diode. This series diode
disables the internal body-drain diode of the
MOSFET that would normally allow the negative
current to flow when the switch is off [4]. The
MOSFET’s are driven by rectangular gate-to-source
voltages GSV at the operating frequency f = 1/T and
an on-duty cycle of approximately 70%. The overlap
period ( sµ1 ) when all switches are on is necessary to
prevent the filtering choke from being open circuited.
Fig. l(b) shows an equivalent circuit of the inverter
with parasitic resistances and offset voltage sources,
where DCLR is the equivalent series resistance
(ESR) of the input inductor DCL , DSr is the
MOSFET on-resistance, FR is the diode forward
resistance, FV is the diode offset voltage, LpR is the
equivalent parallel resistance (EPR) of the resonant
inductor (work coil without work-piece) L, and CpR
is the EPR of the resonant capacitor C.
When switch S4 and S3 are OFF and switch S1
and S2 are ON, the current through the resonant
circuit is IIi = . When S1 and S2 are OFF and S3
and S4 are ON, the current through the resonant
circuit is IIi −= . Assuming that the input inductor