Seeking High Voltage Power Supply
Status: Search Completed
A client is seeking a power supply designer/developer that can, in the short term (6-8 weeks), provide 5-10 units of the specified power supply configuration intended for a proprietary high power based application.
Nice to Haves
This power source must be able to produce a high voltage output in "open circuit" condition, (in the order of 15 KV – 30 KV). The power source must then also show a “current source” behavior in the “closed circuit” condition, and regulate the output voltage in the 2 – 4 KV range.
To achieve this, we designed a 50 KHz inverter configuration with a resonant stage connected to an elevator transformer, as shown in figure 1.
Figure 1 (click on image to enlarge).
The voltage from the grid is rectified and then inverted into a 50 KHz square signal, and then connected into an L-C resonator. The output of the resonator (voltage in the capacitor) is then connected to the primary winding of the elevator transformer. The transformer has a winding relation of 1:9, and it can withstand a voltage in the primary winding of 1.5 – 1.8 KV. The resonator allows the voltage to increase in the primary “open circuit” operation, (the system is unloaded), with a resultant voltage in open circuit of more than 15 KV in the secondary winding. When the secondary is loaded it starts drawing power from the power source, and then the resonating characteristic is reduced, allowing the voltage to decrease and the current to increase. The series inductor in the resonator is then used as a current limiting impedance in the circuit (ballast). Nevertheless, the control board has its own current limiting sensor to avoid dangerous over-current operation.
The resonator circuit uses only a capacitor and an inductor tuned to work at a frequency of 50 KHz. Inductor: The resonator inductor ordering parameters are:
In our case, to be able to meet those parameters we designed an inductor with:
The resonator capacitor ordering parameters are:
For the capacitor we connected a 3 x series array of capacitors, each one with:
HV Transformer specifications.
The HV transformer ordering parameters are:
In our case, to be able to meet those parameters we designed a transformer with:
Control board and inverter specifications
To be able to create the 50 KHz square AC signal, we used a full bridge IGBT inverter. The PWM controller used, is an UC3895 from Texas Instruments, and uses a technique called "Phase shift modulation" PWM, which increases the efficiency and suppress the noise significantly compared to conventional PWM technologies. The inverter is configured as a current source controller/limiter, and it uses a Hall Effect current sensor (LEM15) which is able to sense DC and AC currents at high frequencies. The IGBTs used must be suitable to work at high speed, at least at 100 KHz in hard switching mode (WARP devices). And the inverter should be able to source at least 3 KW of power. There is a proposed circuit shown in figure 2, which we already tested and uses the UC3895 controller.
Figure 2 (click on image to enlarge).
General parameters for the inverter: