This presentation gives an insight into Pulsed Power Technology and to introduce the concept of resonance in Marx Generator. Conventional Marx Generator First described by Ervin Otto in 1942. At start a number of capacitors are charged in parallel and then discharged in series via spark gap switches. It ideally produces a voltage of n x V, n being the number of stages. Performance of the largely Marx generator depends upon selection of capacitor and the discharge timing. Doping of electrodes in spark gap with radioactive isotopes improves switching performance.
Resonant Switch Converters
Resonant Switch Converters are mainly divided into two. They are
- Zero Current Switching - Topology in which the switch turns on and off at zero current
- Zero Voltage Switching - Topology in which the switch turns on and off at zero voltage
Resonance phenomenon in power electronics reduces the switching losses. The switches are turned on or off at zero current or voltage.
General configuration of Marx Generator
- Consists of an AC - DC converter, voltage regulator, DC - AC converter and the Marx Topology
- The large capacitor provides the rest of the topology with a smooth and continuous voltage level
- Single leg inverter is used so as to utilize fewer active power switches
- Three levels of voltage applied to the inductor
- Each two stage of the topology consists of two capacitors, two diodes and two power switches
- Has three switching states
Switches S1 and S3 are turned on. As S1 is on positive voltage appears at the output of inverter. Diodes D1, D3 and DS3 are forward biases and C1 and C3 are being charged. Reverse energy transmission prevented by the diodes. Therefore the capacitors keep the charge till the load supplying mode. S2 and S3 are turned ON. As S2 is ON negative voltage appears at the output of inverter. Diodes D2 and D4 are forward biased. Hence capacitors C2 and C4 are charged with reverse polarity. The capacitors keep the charge till the load supplying mode. All the switches except S4 are turned OFF. S4 connects the capacitors in series. All the diodes are bypassed. The output high voltage pulse will be eight times the input voltage. Breakdown phenomenon at he load side due to high voltage.
Analysis of the circuit done in two modes
- Single shunt operation
- Done initially
- To test the capability of the Generator in producing the pulses
- Repetitive mode operation
- The single shut operation is extended to get this mode
The component behaviour during resonance is expressed as follows during the positive charging mode. Switching frequency cannot be more than the resonant frequency unless inverter switches have anti parallel diodes.Capacitor charge and inductor charge different in two half cycles. Generated voltage levels are impossible to control. Causes malfunction to the normal operation of the converter. Bidirectional switching state installed to give feasibility.