Implement variable switching times for inverter.

I have a motor control scheme, where I have to switch certain switches for half of sampling time. For e.g. if the switching sequence is [1 0 1] : Here Inverter legs 1,2,3 will have : Leg 1 upper sw on, lower off ; Leg 2: upper sw off, lower on ; Leg 3: upper sw on, lower off . However, this sequence will take the switching time as sampling time.

Now, I want to implement the switching sequence such that say the sequence is [1 1 0], then

Here Inverter legs 1,2,3 will have : Leg 1 upper sw on, lower off ; Leg 2: upper sw on, lower off ; Leg 3: upper sw off, lower on. But, each of these states will take the switching time as half the sampling time or 1/3rd the sampling time .

Below shown is the normal switching implementation:

How can I add the timing information to achieve the required swtiching and timing?

Answer 1

[Shreshth]

Hello Siddhi,

The information provided by you it is clear that you adjust the switching sequence so that, for example, with a sequence of [1 1 0], the inverter legs 1, 2, and 3 would be configured as: Leg 1 with the upper switch on and the lower switch off; Leg 2 with the upper switch on and the lower switch off; and Leg 3 with the upper switch off and the lower switch on. Yet, in this scenario, each state should persist for only half or one-third of the sampling time.

For this purpose you need to divide the sampling period into two intervals of T/2. For one-third the sampling time, you would divide the sampling period into three intervals of T/3.

Here's how you can implement it for each case:

1. Half the Sampling Time (T/2):

For a switching sequence [1 1 0], you would set:

0 to T/2,

• Leg 1: upper switch ON, lower switch OFF
• Leg 2: upper switch ON, lower switch OFF
• Leg 3: upper switch OFF, lower switch ON

T/2 to T,

• Leg 1: upper switch ON, lower switch OFF
• Leg 2: upper switch ON, lower switch OFF
• Leg 3: upper switch OFF, lower switch ON

2. One-Third the Sampling Time (T/3):

For a switching sequence [1 1 0], you would set:

0 to T/3,

• Leg 1: upper switch ON, lower switch OFF
• Leg 2: upper switch ON, lower switch OFF
• Leg 3: upper switch OFF, lower switch ON

T/3 to 2T/3,

• Leg 1: upper switch ON, lower switch OFF
• Leg 2: upper switch ON, lower switch OFF
• Leg 3: upper switch OFF, lower switch ON

2T/3 to T,

• Leg 1: upper switch ON, lower switch OFF
• Leg 2: upper switch ON, lower switch OFF
• Leg 3: upper switch OFF, lower switch ON

For both cases, the switching sequence [1 1 0] does not change throughout the sampling period, so the state of each leg remains the same for each interval. However, if you had a different sequence for each interval, you would implement the corresponding states for each interval.

You can setup a model in Simulink using the motor control blockset where you would typically use a combination of PWM generation blocks and logic to control the timing of the switching states.

You can refer to the below documentation by MathWorks on motor control blockset.

https://in.mathworks.com/help/mcb/getting-started-with-mcb.html?s_tid=CRUX_lftnav

Hope this helps.

Regards,

Shubham Shreshth.