High Voltage SSTC Inverter System

High Voltage SSTC Multiplying Inverter Controller

Conceptual Block Diagram

Introduction

Every year, I come up with a particular project which I build in the beginning portion of the year and then showcase

at a variety of tesla and educational events later in the year. In 2002, I built a 1kW Solid State Tesla Coil. In 2003,

I designed and built the most impressive Stereo Audio Modulated PlasmaSonic SSTC system. This year, I plan on

building an advanced microprocessor controlled SSTC system utilizing a switching inverter topology that is most

commonly utilized in DC-AC 50/60Hz Power Inverters. Steve Ward is one of the first persons to actually use

this topology, which was pointed out by Dan Strother in 2002, and has already gotten fantastic results.

I plan to baseline my design from this particular topology and make the necessary modifications to be able to run at

150kHz, 3000V p-p output reliably with output power reaching about 5kW maximum. Each stage of the inverter

will be identical and built as an individual module.

Conceptual System Block Diagram

Conceptual Controller Block Diagram

Conceptual Controller Front Panel Design

Click here to see conceptual front panel layout.

Theory of Operation

Graphical Operational Diagram

First Cycle of Operation ("A" MOSFETs conducting)

The above diagram illustrates the first cycle of operation of the Multiplying Inverter circuit. In this cycle, the "A"

MOSFETs are conducting and the major current paths are highlighted in purple and blue. In the top portion

of the circuit, the two storage capacitors are discharged into the load (primary) with the input AC source voltage

superimposed on top of this voltage to give:

Output Voltage = Vinput + (2*Vinput)

where Vinput = magnitude of input AC source at the time of discharge

This discharge path is highlighted in purple. The resulting output waveform across the load is positive in nature

and shown in purple. In the bottom portion of the circuit, the two storage capacitors are being charged up to

the magnitude of the AC source. This charge current path is highlighted in blue.

It is important to note that the second and third diodes in the top portion of the circuit have little effect on the

output path of the circuit in this particular cycle.

Second Cycle of Operation ("B" MOSFETs conducting)

The above diagram illustrates the second cycle of operation of the Multiplying Inverter circuit. In this cycle, the "B"

MOSFETs are conducting and the major current paths are highlighted in purple and blue. In the bottom portion

of the circuit, the two storage capacitors which were previously charged in the last cycle, are being series discharged

into the load (primary) with the input AC source voltage superimposed on top of this voltage to give:

Output Voltage = Vinput + (2*Vinput)

where Vinput = magnitude of input AC source at the time of discharge

This discharge path is highlighted in purple. Because this energy is being discharged through the bottom of the load (primary),

the output waveform is relatively negative in nature and shown in purple on the right.

Again, it is important to note that the second and third diodes in the bottom portion of the circuit have little

effect on the output path of the circuit in this particular cycle.

Microprocessor Controlled System

One of the exciting things I've always wanted to do with the SSTC is to actually custom design a switching controller

using a PIC microcontroller. Typically, you would never use a microcontroller in a switching power supply due to the

fact that the closed-loop response of a microcontroller type feedback circuit would be very slow. However, since

we are running open-loop (at least in this particular design), its not really an issue. With a microcontroller, I will be

able to have a friendly user interface which will utilizing several pushbuttons and an optical rotary encoder switch or

two. Also, a professional amber-backlit 4-Line LCD display will be used to provide feedback to the user.

Design Goals

Input Voltage

240VAC, 60Hz maximum

Output Voltage

3000V p-p

Output Power

5kW Maximum

Output Frequency

150kHz maximum

User Interface

PIC Microprocessor Controlled

Backlit 4x20 Line LCD Display

Adjustable Output Frequency (50kHz to 150kHz) Digitally Controlled

Coarse Adjust (+/- 1kHz)

Fine Adjust (+/- 0.1kHz)

Adjustable Duty Cycle (0 to 50%)

Burst Mode (User sets #bursts, pulsewidth, deadtime)

Output Voltage / Current Feedback (LCD displayed)

Input Voltage / Current Feedback (LCD displayed)

Enclosure

Shielded Rack-Mount Enclosure

(Necessary for shielding microprocessor and LCD)

Preliminary Design Verifications

1. Develop detailed PSPICE Simulation with complete parasitics and real-world models

2. Gate Drive / Transformer Design

3. Test operation of microcontroller and LCD within close vicinity of existing SSTC to verify operation in shielded and

non-shielded enclosure

4. Simulate and test operation of SSTC using long lead length output cables connecting SSTC output driver and primary coil

of SSTC resonator.

Last modified August 16, 2005 08:05:20 PM