LCLR network high frequency heating response The LCLR network is a 3rd order resonant system consisting of two inductors, one capacitor and one resistor. The bode plot below shows the way in which some of the voltages and currents within the network change as the drive frequency is altered. The GREEN traces represent the current passing through the matching inductor, and therefore the load current seen by the inverter. The RED traces represent the voltage across the tank capacitor, which is the same as the voltage across the induction heating work coil. The top graph shows the AC magnitudes of these two quantities, whilst the bottom graph shows the relative phase of the signals relative to the AC output voltage from the inverter. From the amplitude part of the bode plot it can be seen that maximum voltage is developed across the work coil (top red trace) at one frequency only. At this frequency current through the work coil is also maximum and the largest heating effect is developed at this frequency. It can be seen that this frequency corresponds to the maximum load current drawn from the inverter (top green trace.) It is worth noting that the magnitude of the inverter load current has a null at a frequency only slightly lower than that which gives maximum heating. This plot shows the importance of accurate tuning in an induction heating application. For a high Q system these two frequencies are very close together. The difference between maximum power and minimum power can be only a few kilohertz. From the bottom graph we can see that for frequencies below the maximum power point, the work coil voltage (green) is in-phase with the output voltage from the inverter. As the operating frequency increases the phase angle of the work coil voltage changes abruptly through 180 degrees (phase inversion) right at the point where maximum power is being processed. The phase angle of the work coil voltage then remains shifted by 180 degrees from the inverter output voltage for all frequencies above the maximum power point. dw-inductionheating/Technology/LCLR-network-high-frequency-heating-response-305.html
Posted on: Wed, 08 Oct 2014 05:24:57 +0000
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