TIDA-010210: PWM Switching strategy for ANPC inverter

Namita Pawar

Part Number: TIDA-010210
Other Parts Discussed in Thread: TMS320F28377D, , AMC3302

Tool/software:

Hi,

I am referring the design guide for 11kW 3 phase ANPC. The application note states that "Optimized control scheme needs only 6 PWMs
versus 9 PWMs for standard implementation".

Question 1: Is this 6PWMs switching strategy done for some reason or the microcontroller is not having sufficient PWM signals? Any advantage of using 4PWM to 6PWM generation using AND and OR logic as shown below.

I am using TMS320F28377D for the ANPC Inverter. The PWM strategy used is as bellow.

PWM Signal	Switch	Frequency
EPWM1A	Q2A	Low Frequency
EPWM1B	Q3A	Low Frequency
EPWM2A	Q1A	300kHz
EPWM2B	Q5A	300kHz
EPWM3A	Q6A	300kHz
EPWM3B	Q4A	300kHz
EPWM4A	Q2B	Low Frequency
EPWM4B	Q3B	Low Frequency
EPWM5A	Q1B	300kHz
EPWM5B	Q5B	300kHz
EPWM6A	Q6B	300kHz
EPWM6B	Q4B	300kHz
EPWM7A	Q2C	Low Frequency
EPWM7B	Q3C	Low Frequency
EPWM8A	Q1C	300kHz
EPWM8B	Q5C	300kHz
EPWM11A	Q6C	300kHz
EPWM11B	Q4C	300kHz

Question 2: Is this 18 PWM strategy is okay? Can we program 300KHZ switching frequency for the ePWM?

I have seen most of the app note for ANPC which uses outer 4 switches as high frequency switching and inner 2 switch as low frequency.

Question 3: Any advantage we get when we use outer high frequency switching(Q1, Q5, Q6, Q4 switches at 300kHz)? If we change this to inner high frequency switching(Q2,Q3 = 300kHz) what will be impact in terms of power loss, efficiency.

Please help with your answer on the questions asked. It will help in understanding ANPC inverter design strategy.

Thanks,

Namita

8 months ago

0 Vedatroyee Ghosh 7 months ago

TI__Intellectual 865 points

Hi Namita,

1. Yes the PWM configuration is done in the above way to optimize implementation on a standard MCU.

2. More information on the implementation of the switching scheme can be found in the design guide (TIDA-010210 reference design | TI.com under design files) and the software user guide (available with the code in C2000WARE-DIGITALPOWER-SDK Software development kit (SDK) | TI.com).

3. Use of 300kHz needs to be studied in terms of losses, efficiency etc. Increasing the switching frequency will reduce the magnetics, however the design of EMI filter stage will need to be able to be compliant with industry standards. The hardware of TIDA-010210 is designed and tested for a switching frequency of 100kHz.

Thanks & best regards,

Veda

0 Namita Pawar 7 months ago in reply to Vedatroyee Ghosh

Intellectual 770 points

Thank you Vedatroyee for the answer.

I have one more question related to sampling frequency used in the same 11kW application. What is ADC sampling frequency used for current monitoring.

Do we need high bandwidth isolation amplifier if we go for switching frequency around 300kHz. I could see AMC3302 isolation amplifier used is having bandwidth of 340kHz.

Please help with your inputs.

Thanks,

Namita

0 Vedatroyee Ghosh 7 months ago in reply to Namita Pawar

TI__Intellectual 865 points

Hi Namita,

The ADC sampling rate (and interrupt service routine) currently is 50kHz.

Please follow the thread for more information regarding the switching frequency and sampling frequency : (+) TIDA-010210: Switching Frequency - Simulation, hardware & system design tools forum - Simulation, hardware & system design tools - TI E2E support forums.

Thanks & best regards,

Veda