I've used a PIC33 in large (20HP to 50HP) 3 phase AC motor controllers to manage power factor, somewhat similar to what goes on in an inverter. In general terms a PIC33 compares to the low end of the STM32F4 or in your case the STM32L4 low power family. Look at the STM32L431 series to start. It has an excellent PWM motor control timer with multiple phases, plus a two output DAC to generate sine waves. The DAC can be driven with DMA transfers which offloads a lot of work from the CPU.
In software terms switching from PIC to ARM is like moving ahead 20 years in technology. The memory model is far simpler and it's all 32-bit wide. DSP isn't confined to a tiny X and Y space and has much better support compared to what Microchip offered in the past. The STM32L4 series is designed for low power operation, ideal for solar use. If needed you can run at up to 80MHz instruction clock, or dynamically scale it down to 4MHz or less for low power.
I recently priced an STM32L431 (256KB flash, 128KB RAM, LQFP64) at under USD$3/1000 at Digi-key. For a commercial purchase you can do even better.
Why drop the PIC33? Start with coding the Cortex M4 DSP and then write some code for the PIC33 DSP. The answer quickly becomes obvious.
Jack Peacock
