Why FPGAs and SoCs are the best for Digital Control of Power Electronics

June 15, 2021, 12 Noon PDT

Digital Control of Power Electronics is more and more the norm. Microprocessors and DSP provide good platforms for control. They are somewhat constrained by their processing speed and their peripherals. Field programmable gate arrays (FPGAs) and Systems on Chips (SoCs) provide the best control platform for digital power electronics. 

This webinar covers why you should consider an FPGA or SoC based platform for your next digital power electronics development. 

The regular ELMG Digital Power Webinars provide great information on the science, art and joy of digital control of power electronics.

All of these are very useful for power converter control. However, there are some differences with a digital controlled converter compared with an analog controller. These differences can be problematic if you are not ready for them.

Using FPGA and Systems on Chip (where there is a processor and FPGA fabric) in digital control systems for power converters is a great choice. The flexibility and power of the FPGA is suitable for 

  • high performance power converters
  • high switching frequency systems with GaN and SiC
  • low latency high bandwidth control

MCU and DSP replacement with FPGA

MCU/DSP devices are a common tool to implement control algorithms, protection, logic and sequencing for control power hardware, using code such as ASM, C or C++.  However, they do not have the power and flexibility of FPGAs or SoC where the solution can be implemented in a classic register transfer language such as VHDL, Verilog or System Verilog, or C type coding using High Level Synthesis and Software Defined Systems on Chip. 

The fabric in the FPGA provides the ability to create custom switching control peripherals. It is also possible to have multiple instances of the same switching control managing multiple converters simultaneously.

Implement the digital power control in the fabric

The entire power converter controller can also be implemented completely in the fabric to provide a very low delay in the feedback compensator. This maximises the control bandwidth by limiting the phase delay from processing and allows the minimization of the output filter component size.  

The configurability of the FPGA fabric allows the use of the right number of bits for the control. (Eighteen bits has proved itself to be the best choice.)

FPGAs and SoCs provide a powerful upgrade path from DSP and MCU controllers.  

Another way is to use an FPGA with a processor, or processors, inside it. These processors can be soft-cores like Xilinx’s Microblaze, or ARM M1 or M3 or hard-cores like the twin ARM A9s in Xilinx’s Zynq series. Reports on FPGA development projects show that almost 50% have some sort of processor.  This processor allows you to directly port your code from your MCU/DSP to the Zynq/Microblaze and be ready to go. This may seem counterproductive as going from one processor to another without really gaining FPGA power is work for no reward.  The advantages come when you move parts of your code (the high intensity tasks such as the control algorithms) from C to the FPGA hardware. This provides a power boost for the important parts of your code whilst still having the simplicity of C for the easy flow of your code. A good analogy would be that the FPGA parts are the equivalent of the ASM parts on the MCU/DSP but with the superman type speed advantage of doing things in parallel in the FPGA fabric.

Tools for development

Xilinx has also combined the HLS and the C coding options with their SDSoC product. It is designed for the Zynq and Ultrascale SoCs. The coding is done in C. However, it is also possible to use HLS to accelerate certain parts of the code for you to gain the most benefit. Getting the most out of the FPGA or SoC solution does require either the HLS toolchain and training in that or writing your own RTL in an HDL. Another option is to purchase IP that other companies have written. This allows you to create a fast and efficient system without needing to know any coding of an FPGA in HDL or C. ELMG Digital Power has a large suite of power electronics IP to get your application off the ground fast.

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