DLS Digital Controller Tony Dobbing Head of Power Supplies Group

Content of talk J A Dobbing Features and overview Problem of resolution FPGA program structure Performance Development program Conclusions

J A Dobbing DLS Digital Controller Features Implemented on Xilink Spartan FPGA (low cost). Backward compatible with original PSI digital controller. Direct Ethernet connection to computer control network via Colibri PXA270 processor board running EPICS, 312 MHz clock, 64 MB RAM, 32 MB Flash. Remote parameter loading. Direct Ethernet port for Fast Orbit Feedback, with low latency (150  s less than original PSI controller). FPGA program loaded from PXA270 – remote software changes. USB port for local control via Labview application. 64 MB Flash memory (non-volatile), 64 MB DDR SRAM. 50MHz Clock Oscillator.

J A Dobbing ADC/DAC Components 4 Channel 16 bit ADC AD974, for DC link voltage and output voltage monitoring. 4 off 18 bit ADC AD7691, for current measurement, with oversampling 22 bit precision is achieved. 4 Channel DAC LTC2604, to monitor internal signals from front panel.

J A Dobbing DLS Digital Controller Block Diagram 24 V Xilinx Spartan 3S 1600E FPGA FLASH Memory Power Converter PWM signal PWM synchronisation Service PC (serial port) Backplane Computer Network DC Other Controller Cards Analog Sig. Programming Timing System Front Panel Optical Input Control Interlocks, Digital I/O Dual USB UART RAM Colibri Module PXA270 Ethernet Link Reset 4 x DAC 16 bit 4x ADC 16 bit 4X ADC 18 bit Analog Sig. Ethernet Link Fast Orbit Feedback System

J A Dobbing DLS Controller - Module Ethernet Ports USB Port Optical Trig DAC O/P 18 bit ADC Cover PXA270 FPGA

J A Dobbing LabView Interface – Summary and Scope

J A Dobbing LabView Interface – Parameters and Waveforms

J A Dobbing The Problem of Resolution with a Digital Controller Resolution = Clock Period/PWM Period For a power supply operating with a PWM of 100 kHz and a 50 MHz processor clock. Resolution = 20ns/10  s = 0.2% (which is not enough by far)

J A Dobbing Xilink Quadrant Phase Shift Solutions:- Increase clock frequency. Xilink output quadrant phase shift, effectively increases resolution to 4 times clock frequency. E.g. 200 MHz clock with phase shifting gives 125 ppm resolution for 100 kHz PWM. Better but still not enough!

J A Dobbing DLS Controller PWM Resolution 5 ns PWM resolution with 20 ns clock

J A Dobbing Clock Pulse Averaging K + + Round to nearest integer + - Sum Sum errors and add running total to next cycle Integer number of clock pulses/quadrants to PWM generator Modulation Index Convert to clock pulses Average PWM output resolution is now limited only by computation word length.

J A Dobbing Spartan 3E FPGA Structure 3688 Configurable Logic Blocks (CLBs) contain flexible Look-Up Tables that implement logic plus storage elements. CLBs perform a wide variety of logical functions as well as store data. 376 Input/Output Channels with Blocks (IOBs) controlling the flow of data between the I/O pins and the internal logic of the device. Each IOB supports bidirectional data flow plus 3-state operation. 648 Kbits Block RAM provides data storage in the form of 18-Kbit dual-port blocks. 36 Dedicated Multiplier Blocks. Digital Clock Manager (DCM) Blocks provide self-calibrating, fully digital solutions for distributing, delaying, multiplying, dividing, and phase-shifting clock signals.

J A Dobbing FPGA Program Structure ADC interface Register Scaling and filtering Register Feedback Register Modulation index to clock pulses Register PWM Generation Protection Register Load 64 clock pulses or 1.28  s

J A Dobbing Controller Performance - ADC Noise Filter Level (Hz)Noise Level RMS ppm , The noise level of the output current, when Power Supply is running at 1 A

J A Dobbing Waveform Filtered Output Current Unfiltered Output Current Controller Performance - Resolution 100  A/5Hz Waveform and Resulting Unfiltered Output Current and Measured Output Current Filtered at 100 Hz.

J A Dobbing Controller Performance - Stability Stability over 20h with 100 mH Load

J A Dobbing Controller Performance - Linearity

J A Dobbing Development Programme for Booster Fast Orbit Feedback System One controller presently operating on Booster corrector. Upgrade 11 Booster corrector controllers in June Upgrade remaining 33 Booster corrector controllers in August Develop feedback algorithm to exploit reduced latency. Upgrade Storage Ring FOFB system.

J A Dobbing Conclusions All diamond’s power supplies use the original very successful PSI digital controller. The Cirrus ADC used in this controller is no longer available. Diamond now has its own replacement, that is pin compatible and has significantly reduced latency, which makes it better for fast orbit feedback applications. The PXA270 processor eliminated the need for additional hardware between the power supply and computer control network.