DG-IRMCK203 Datasheet, PDF (61/67 Pages) International Rectifier – Application Developer’s Guide

IRMCK203 Application Developer’s Guide
PWM Carrier Period
Input variable PwmCval controls the duration of a PWM cycle. It should be populated by the system clock frequency
(Clk) and Pwm frequency (PwmFreq) selection. The variable should be calculated as:
PwmCval = Clk /(2 * PwmFreq) −1
The input resolution of the Space Vector PWM modulator signals U_Alpha and U_Beta is 16-bit signed integer.
However, the actual PWM resolution (PwmCval) is limited by the system clock frequency.
Deadtime Insertion Logic
Deadtime is inserted at the output of the PWM Generation Module. The resolution is 1 clock cycle, or 30 nsec at a
33.3 MHz clock and is the same as those of the voltage command registers and the PWM carrier frequency register.
The deadtime insertion logic chops off the high side commanded volt*seconds by the amount of deadtime and adds the
same amount of volt*seconds to the low side signal. Thus, it eliminates the complete high side turn on pulse if the
commanded volt*seconds is less than the programmed deadtime.
PhaseU
PWMUH
PWMUL
Deadtime
Deadtime
Figure 26. Deadtime Insertion
The deadtime insertion logic inserts the programmed deadtime between two high and low side of the gate signals
within a phase. The deadtime register is also double buffered to allow “on the fly” deadtime change and control while
PWM logic is inactive.
Symmetrical and Asymmetrical Mode Operation
There are two modes of operation available for PWM waveform generation, namely the Center Aligned Symmetrical
PWM (Figure 24) and the Center Aligned Asymmetrical PWM (Figure 27). The volt-sec can be changed every half
a PWM cycle (Tpwm) since PwmLoad occurs every half a PWM cycle (compare Figure 24 and Figure 27). With
Symmetrical PWM mode, the inverter voltage Config = 0), the inverter voltage can be changed at two times the rate of
the switching frequency. This will provide an increase in voltage control bandwidth, however, at the expense of
increased current harmonics.
The mode of operation is selected using the PwmConfig field of the PwmConfig write register group (described in
Section 4.2.1). To select Center Aligned Asymmetrical PWM, set the PwmConfig field to ‘0’. To select Center
Aligned Symmetrical PWM, set the field to ‘1’.
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