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Conclusions and experimental results

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4

Conclusions and experimental results

Starting from the ST7MC three-phase asynchronous motor control library, an algorithm for

symmetrical SVPWM has been developed. This section illustrates the measurement carried

out for CPU load evaluation and shows the oscilloscope capture of obtained output

waveforms.

4.1

The CPU load evaluation

The contribution of the implemented algorithm to the CPU load has been estimated

measuring the U interrupt routine execution time at 8 MHz clock frequency with the usage of

ST7MC emulator (ST7MDT50-EMU3). The average execution time of the above mentioned

routine turned out to be equal to:

Equation 23

The contribution of SVPWM implementation to the CPU load has been, therefore, computed

in the exposed situation using relationship:

Equation 24

Table 3.

Variables utilized in SVPWM algorithm

Variable name

Variable size

Physical meaning

Resolution

Phase

16 bit (0x00000xBFFF)

Angle

α

0.234 degrees

SineFreq

16 bit

d

α/dt

0.212 Hz

8 bit

12 bit timer resolution (125 ns)

8 bit

12 bit timer resolution (125 ns)

SineMag

8 bit

≈ 0.0039

t

ex

23.1

µsec

=

CPU

LOAD

t

ex

0.5

t

PWM

REP

COUNTER

1

+

()

⋅⋅

------------------------------------------------------------------------------------------

24.1

=

=

%