RRCAT- Raja Ramanna Centre for Advanced Technology, Indore

The Power Supplies Division has also developed the power supplies for various applications other than magnets. Some of these miscellaneous developments are listed as follows:

Laser Diode Drivers [ Go to Top ]
Current-sourcing power supplies for driving various laser diodes in CW, pulsed or combined mode have been developed. Different techniques have been used for the development.

A 5 V- 50 A , 0.1 % current stability CW laser diode driver has been developed using 3 phase LCC resonant converter working above resonance. Use of three-phase eliminates need of filter capacitor at the output which gives inherent protection to the series connected laser diodes.

Another power supply has been developed to energize a string of four laser diodes (type TH-Q1201-A1) rated to deliver a rectangular current pulse of 0-80 A, with pulse width of 50-200 mS and pulse repetition rate 1 Hz to 1 kHz. It’s a two-stage power supply of which the first stage is a two switch DC-DC forward converter switching at 100 kHz. In the second stage, a high-current MOSFET is used in linear mode. A 125 A/ 10 V CW/pulsed laser diode driver also follows this scheme.

A versatile laser diode driver power supply has been developed with varied operational requirements. The peculiarities of specifications are: wide range variation in pulse width (500 ns to CW), frequency (single-shot to 1 kHz) and output current (10 mA to 5 A). Moreover, it should also be possible to bias the pulse current to the diode by a DC current. High frequency switch-mode circuits are not used to develop the current sources since requirements of fast transient response and wide setting range of output current conflict. Instead, MOSFET operating in linear mode is used. However, a two-switch forward converter operating at 100 kHz is used at the front-end for AC-DC step-down conversion with output voltage regulation and input power-factor-correction. A microprocessor – controlled front panel and RS232 interface provides individual control of each parameter while the backlit LCD display provides visual confirmation of operating parameters.

A ± 50V/±20A programmable power supply required by chemical lab is developed based on high frequency switching of MOSFETS in bridge configuration at the output stage. Microcontroller is used for generation of different waveforms of output current which forms the reference of current loop.Current-sourcing power supplies for driving various laser diodes in CW, pulsed or combined

A project for DSP based control of power supply was taken up. Texas instruments TMS320F2812 DSP was selected for this purpose. DSP TMS3202812 starter kit was used for programming. All the issues for developing the control software and debugging it were identified. Control of transport line 3 quadrupole magnet power supply (145 A /19 V) was done through DSP. The first part of this project has been successfully completed. This part involves generating six pulses to fire six SCRs of the rectifier using a single sync signal, implementing slow start feature, PID control of filter capacitor voltage, capacitor current feedback to damp filter capacitor voltage, over current and over voltage protection etc. The developed code provides flexibility to user for selection of open loop or closed loop control operation. The system has been thoroughly tested and working well. The second part of this project (controlling the inverter using the same DSP kit) is now being taken up.

A high voltage pulsed power supply for carrying out experiments on diode electron gun is developed to meet the following specifications: Pulse Amplitude – 500mA @ 40 kV maximum, Pulse width – 2 msec, Pulse repetition rate – 1 Hz , Rise / Fall time £ 325 nsec, Pulse top flatness within ±2.5% of the peak voltage.

The scheme uses a doubly tuned circuit and two thyratrons. In the implemented scheme, the maximum working voltage is equal to the load voltage reducing the safety requirements (as compared to PFN). Less number of components, simpler tuning, lower working voltage and hence the associated benefits in device and component ratings make this scheme attractive at the expense of loss of efficiency. There are three stages of the power supply. An AC to DC converter and then a doubly tuned circuit follow a switching circuit. The diode electron gun is coupled to the high voltage power supply through an oil immersed pulse transformer having ratio 1:5. The balanced arrangement of high voltage application to the gun offers minimum stray capacitive coupling to the earth via the filament transformer improving rise and fall times of the pulse.

DCCTs are used as the precision DC current sensors. Two prototypes of 300 A DCCTs have been developed based on zero-flux principle. Difference in the peak magnetising currents during positive and negative half cycles is sensed for the zero-flux operation. Zeranin strip is used to convert current into voltage signal.

Principal advantages of planar structure over conventional components include higher ratio of surface area to volume, better heat removal, smaller size, low-profile shape, better predictability as well as repeatability of parameters and lower leakage inductance. A planar transformer has been developed for a 1 kW power supply. The design parameters of the prototype transformer are as follows: turns ratio 6:1, core 2* ELP 43/10/28 with I 43/4/28, N_p = 18, N_s = 3, peak flux density = 0.2, secondary RMS current 35 A. Total loss in the transformer is 25 W giving 97.5 % efficiency with 35 ^oC temperature rise at full load. A new technique of core-extension has evolved to help reducing temperature rise, AC losses and HF shielding. Photograph shows the prototype development.

Programmable DC electronic load (50V/100V, 500W) was developed as an prototype development to test the idea of an inductive electronic load. MOSFETs operating in parallel and in saturation region are used to control the power dissipated. A simple and effective technique for adding inductive characteristics in a dissipative electronic load is experimentally validated. Load resistance and inductance can be adjusted to desired value over a wide range. The additional feature offers flexible operation and eliminates the bulky and costly inductance for testing of power supplies as a dummy load. The proposed technique simulates the exponential current response to applied voltage step and attenuation of ripple in the load current.

A 25 kW/ 25 kHz power supply for MOVPE system in SSLD, RRCAT has been developed based on a novel high-frequency LCL-T resonant inverter. It is required to heat graphite susceptor to 1200 0C. The scheme offers many advantages over conventional series resonant and parallel resonant scheme. The converter offers high current gain, which in turn reduces the current rating of the secondary winding of matching transformer and the feeder to coil. Coil current is constant irrespective of changes in effective load resistance due to temperature or work-piece change. Transformer design is further simplified since its turns ratio is no longer dependent of the Q of the resonant network.

Two-stage conversion strategy is adopted for the development of the induction heating power supply. The first stage is a dc-dc buck converter with lossless turn-on and turn-off snubbers and the second stage is the free-running LCL-T resonant inverter. Phase-locked-loop is implemented to track the resonant frequency. The power supply is housed in standard 24 U rack. The following figures show photographs of the power supply, which has been tested in the lab to heat graphite susceptor in air to 1200 0C.

A compact, scalable, standard 4U card sized constant-current Ultra Capacitor Charger (UCC) using high frequency, soft-switching resonant converter has been developed. Ultracapacitors, also known as Supercapacitors, offer many advantages over batteries such as large number of charge-discharge cycles, low ESR, high efficiency, high power density and low heating. Therefore, ultracapacitors are being increasingly used in portable electrical and electronic devices and transportation in conjunction with batteries. It is hoped that in near future, automotive industry will deploy ultracapacitors as a replacement for batteries. Another advantage of ultracapacitor is its ability of being charged quickly.
The power converter is an inherent current source with passive output voltage clamping capable of direct parallel operation (to increase output current) without any current sharing control. Required control and interface is simple and therefore rugged for industrial application. The developed charger has been designed for ± 48 V DC input, 10 A output current, 15 V maximum charging voltage and tested with 58 F ultracapacitor. The same card can easily be re-configured for other specific application requirements.


*Photograph of ultracapacitor charger*

Power Supply for Electroplating: [ Go to Top ]

A bipolar pulsed power supply for electroplating applications in Chemical lab rated for ±1000A is made. Number of forward and backward cycles, pulse widths, and current amplitude in both directions are programmable. The power supply after testing was handed over to Chemical lab for their use.


*Photographs of power supplies for electroplating*

Capacitor Charging Power Supply Using Resonant Converter [ Go to Top ]

The capacitor charging power supply (CCPS) has been developed which will charge a 100uF energy storage capacitor from 0V to 600V in 35ms exhibiting a charging power of 514.28 J/s at a repetition rate of 25 Hz. Topology selection is based on the fact that the series resonant converter with switching frequency below 50% of the resonant frequency (f_s ≤ 0.5 f_r) will act as a current source. The complete process is divided into three modes: (1) High Power charging mode (2) Low Power Refresh mode (3) Output Pulse delivery mode.


*Photographs of CCPS using resonant converter*

Improved Capacitor Charging Power Supply using Flyback Converter [ Go to Top ]

An improved capacitor charging scheme using a flyback converter has been designed and implemented. The scheme makes the best use of available charging time keeping average and peak current through the switches low. Secondly this scheme ensures the turn on of primary switches when secondary current has already gone to zero, thus ensuring zero current turn on for primary switches. Moreover these objectives have been accomplished without sensing high frequency pulse currents thereby improving upon the noise performance and circuit complexity. Scheme uses commonly available ICs like op amps, timers, monoshots etc. So this scheme is quite simple, inexpensive, reliable and rugged for applicable power range of flyback converters.

In the scheme, charging capacitor voltage has been sensed and the same has been used to assess the decay of secondary charging current to zero. Switches in the primary of the flyback transformer are turned on to store energy in flyback transformer, once this assessed time is elapsed. For this to work, a non linear characteristic curve which generates the triggers to primary switches on the basis of sensed capacitor voltage, has been implemented in the scheme. One capacitor charging power supply has been developed in lab using this scheme. Power supply was tested to charge a capacitor of 3 mF to 300 volts at 1 Hz repetition.

Photographs of CCPS using flyback converter

25 kVA ,430 Hz Inverter for HPIA [ Go to Top ]

A prototype 25 kVA ,430 Hz inverter was developed and was used to energies the primary winding to generate output DC voltage upto 190 kV. It is based on dual half-bridge inverter scheme. The prototype inverter is rated for 175 V/ 175 A rms output at 430 Hz. The IGBTs are switched at 20 kHz in sinusoidal PWM with unipolar voltage switching. Loss-less turn-off snubber is used to minimize the turn-off switching losses and stresses in the IGBTs.

Photographs of prototype 25 kVA inverter

Special Transformers and Inductors [ Go to Top ]

0.16 mA, 700 A, 430 Hz inductor using METGLAS core

This inductor is being used in 150 kVA, 430 Hx power converter for HPIA. It is designed and constructed using Iron based Metglas [2605 SA1 AMCC 1000] cores and epoxy-cast coil. The cooling method adopted here is water cooling technique. In this shell type inductor, OFHC copper conductor has been used for winding.

Photograph of 0.16 mA, 700 A, 430 Hz inductor using METGLAS core

7.5 kVA 25 kHz 400V/10 kV ferrite cored oil-cooled single-phase transformer

The 25 kHz transformer bank is designed and developed for -20 kV/1A power supply and is made of three 1-Ф 7.7 kVA 200V/10 kV transformers. In this oil-cooled ferrite-cored transformer bank, method adopted for high voltage winding is different from that used in the conventional transformer. Here, with a view to minimizing distributed winding capacitance, crossover technique has been used. Besides, litz wires have been used for high current coils required in these.

(a)

(b)

Photographs of (a) three star-connected single-phase transformers with voltage-doubler rectifier plus filter and (b) its assembly in oil tank.