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Hot!Strange problem with Simulink-Matlab HS-PWM block

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grcatu
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2019/10/23 06:51:10 (permalink)
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Strange problem with Simulink-Matlab HS-PWM block

Hi, I am controlling a three-phase inverter with a DSPIC33 from matlab simulink and I have noticed problems in the generation of PWM when I use dead-times.
I use complementary outputs and with an external dutycycle.
 
When I do not use dead time the 6 PWM outputs are correct and complementary but without dead time.
 
When I use positive dead time in PWM1 and PWM3 one of the signals becomes zero and the shelf is good, usually PWM1H and PWM3L
 
When I use negative dead time in PWM1 and PWM3 one of the signals stays on all the time, causing short circuits, usually the PWM1L and PWM3L,
 
Has someone happened something similar?
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    grcatu
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    Re: Strange problem with Simulink-Matlab HS-PWM block 2019/10/23 14:32:04 (permalink)
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    I have this warning on the wrkspace.. for different values od dead-time
     
    Warning : Dead Time DTR reach the maximum limit allowed : 0.00011734s for channel: 1 3. It is set to this limit.
    Warning : Dead Time DTR reach the maximum limit allowed : 0.00011734s for channel: 1 3. It is set to this limit.
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    Lubin
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    Re: Strange problem with Simulink-Matlab HS-PWM block 2019/10/24 01:47:19 (permalink)
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    Hi,
     
    The warning is ok. The Dead time width is limited by the peripheral hardware. the max dead time allowed should be noticed in the block GUI. The value depends on the clock. If value is set above, the blockset will saturate to the max value and provide such warning.
     
    Regarding issue with deadtime, you might have a look at chip erratas. With some chip, when dead time is used, the PWM duty cycle must remains in a certain limit otherwise issue might happends. The PWM block let the user performs any required limitation on its input value. Thus make sure the PWM duty cycle update value is within a correct range (Check also that initial PWM duty cycle set in the GUI is ok).
     
    You might test DeadTime using a fixed a 50% duty cycle PWM.
     
    Lubin
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