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4 Digital Signal Controllers
Digital Signal Controllers
By now it should be clear that an inverter is a critical component in the solar power system, and its design
needs to be both flexible for use in different applications, and adaptable to changing conditions within an
application. A control processor for an inverter has to meet a number of real-time processing challenges in
order to effectively execute the precise algorithms required for efficient DC/AC conversion and circuit
protection. MPPT and battery charge control, while only needing near-real time response, do involve
algorithms with a high level of processing.
Digital signal controllers, combining high-performance DSPs and integrated control peripherals, offer an
excellent solution for real-time control of the DC/AC converter bridge, MPPT and protection circuitry in
solar power inverters. DSP controllers inherently support high-speed mathematical calculations for use in
real-time control algorithms. Integrated peripherals such as analog to digital converters (ADCs) and
pulse-width-modulated outputs (PWMs) make it possible to directly sense inputs and control power
MOSFETs, saving system space and expense. On-chip flash memories aid in programming and data
collection, and communication ports simplify design for networking with units such as meters and other
inverters. The higher efficiency of DSP controllers in solar power inverters has already been demonstrated
by designs reporting that conversion efficiency losses were cut by more than 50 percent, as well as
achieving significant cost reductions.(1)
Example: TMS320F28x Digital Signal Processors
An example of such a processor is the Texas Instruments (TI) TMS320F28x ™digital signal controller, a
32-bit device that operates at frequencies up to 150 MHz and provides up to 150 MIPS in performance.
Figure 6 shows the architecture of the F2808, a representative device in this DSP controller family. With
its high level of performance, a single DSP controller can control multiple conversion stages in the same
inverter and have overhead remaining for performing additional functions such as the MPPT algorithm,
battery charge monitoring, surge protection, data logging and communications.
Figure 6. TMS320F2808 Architecture
Integrated functions keep costs efficient along with system operation. F28x controllers feature ultra-fast
12-bit ADCs that provide up to 16 input channels for performing the current and voltage sensing required
to achieve a regular sinusoidal waveform. For safety, the ADCs also provide current sensing in the RCD.
6 TMS320C2000™ DSP Controllers: A Perfect Fit for Solar Power Inverters SPRAAE3 – May 2006
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