Implementation using ST7FMC

AN2267

8/19

Figure 8.

PWM on time midpoint identification and control

on time. Based on the previous discussions, this is the right instant to read the

instantaneous DC link current in order to get the average phase current value. Hence the

interrupt associated with U event should be set to the highest priority and the very first

instruction in this Interrupt Service Routine (ISR) should read the DC link current value. In

any case, there is an interrupt latency time of approximately 3-4µs, which is also the typical

conversion time of on-chip Analog to Digital Converter (ADC). If the current feedback analog

input channel was previously selected and set for sampling continuously, then, when the first

instruction in U event interrupt subroutine reads the ADC data register, it will aptly hold the

DC link current value fairly close to that during the middle of PWM on time.

MCP0

PWM

Current

U ISR

U event

Carrier

Ref

U event

t

t

t

t

T

Fig 8a

Fig 8b

Fig 8c

Fig 8d