FPGAs Used in Power Electronics

Realizing many projects in which FPGAs were used for controllig power electronic components gave us a lot of experience in this sector. When using the latest components, an algorithm in an FPGA might indeed run with a sampling frequency of 20MS/s. This provides the opportunity of utilizing the switching times of modern power transistors. Whereas processors can only count and switch on instruction or interrupt level (interrupt latency), FPGAs are able to do that on cycle level. As a consequence, the jitter is reduced, and the interruptions caused by that are moved to higher-frequency ranges. Here, they will be easier suppressed by the mostly given controlled systems featuring low pass characters. Because of the simultaneous processing in the FPGA, the signal processing, the sequence control system, the supervision or the triggering of signals can be provided at the same time. That is why FPGAs act as a tremendous platform for implementing algorithms, e.g. for circuit amplifiers, circuit controllers or piezo controllers.

Controllers for piezo actuators

Piezo actuators are increasingly being used for the active vibration damping in adaptive systems. The actuators' non-linear behavior makes it impossible to use the standard controllers and systems. The DSPs frequently used for controlling piezos, however, only support linear algorithms like FIR filters to a decent degree, as they map the multiply-accumulate operations required for that directly on hardware. Even low-cost FPGAs, having more than ten multipliers, offer a considerably higher computing power than DSPs. The better algorithm mapping together with the higher computing power allow algorithms that are more extensive, and show improved controlling results. As a result, new controller concepts for piezo actuators can be realized according to the boost converter principle. The latter not only allows to generate a high voltage from a low voltage. The electrical charge stored in the actuator will be buffered in a capacitor when discharging, in order to bring it back to the actuator during the next cycle. This causes the efficiency factor of the system to increase significantly. A boost converter makes it possible to charge piezo actuators with a capacity of up to 10 �F within one millisecond. The controller for such a driver had been implemented in an FPGA by employers of abaxor engineering as early as 1999. The calculations were made with a sampling rate of 2.5 MS/s and a resolution of 16 Bit.

Circuit controllers

The demands on circuit controllers are constantly increasing: lower output voltages with higher currents and lower ripple. With the help of digital controllers, these and other demands can be realized by simpler means. Microcontrollers often do not provide sufficient computing power, in particular problems will arise when it comes to controlling several voltages. In addition, errors within a function might cause the whole controller to collapse. As a result, supervising functions are often realized externally. As for non-simultaneously operating functional units in the FPGA, this risk does not exist. Supervising functions can be integrated into FPGA, utilizing its high computing power. By means of this, the integration level will be increased, and the PCB design will be simplified. Fusion FPGAs by Actel offer an excellent alternative in this respect. Due to the integrated analog components like:

• 30-channel AD converter with up to 600kS/s and a resolution of 12 Bit
• Gate driver for FETs
• Hardware support for current and voltage monitoring

the external circuit complexity is also reduced. There is only one external supply voltage needed, the second one will be generated by internal charge pumps. This requires only one external transistor. Actel's antifuse technology ensures that no external configuration memory will be needed. This is a crucial condition for the "Live At Power-Up" ability, in other words the immediate availability of FPGAs after applying the supply voltage. Fusion FPGAs, in this respect, allow solutions that are much more flexible than it would be possible in analog or microcontroller-based configurations.