SVPWM, ePWM waveform pattern getting different as expected?

Dear Community,

I am working BLDC Sensorless Motor Control and referring below example.

Ref.: https://in.mathworks.com/help/mcb/gs/sensorless-foc-pmsm-smo-fo.html

I have used Flux observer as per details mentioned in example.

I have generated code and deployed on Launchpad-F280049C (DRV8320H with custom board) and observed PWM outputs at launchpad ePWM pins. Attached snapshot of the same.

Launchpad not yet connected to Driver board and motor.

Below are my queries.

1. As per PWM waveform and driver truth table, I am getting All 3 High Side MOSFET in ON state. How do I get switching pattern as per SVPWM. How to observe switching pattern of MOSFET and Gate pulses of ePWM?

2.If top 3 mosfet in in ON state, it it chance short-circuit the driver board?

3. How to check switching time between sector U1 to U2 till U6? https://in.mathworks.com/discovery/space-vector-modulation.html

Appreciate your valuable support.

Thanks.

Answer 1

[Bhagyesh]

@KrishnaKumarThanks for your reply.

I have few question. It will be great if you can provide some information on below queries.

1. Run 3-Phase AC Motors in Open-Loop Control and Calibrate ADC Offset: Can this example be used to run BLDC Sensorless motor. As of now I have BLDC motor to begin with.
2. If the switches in each inverter leg are configured to be complementary: I have done this configuration as per above shipping exapmle. Then how should be a configuration can be done to avoid short circuit.?
3. How to check which one is modulation wave and carrier wave.? As very less information is provided on page.

Thanks.

[KrishnaKumar]

1. Yes the example can be used to run a BLDC motor without a sensor.
2. The shipping example uses complementary configuration for switches. The short circuit on the motor terminals occurs naturally as part of applying PWM and should not be a problem. In fact in each PWM cycle, for a small period of time all three switches are on. The main thing to ensure is that the power supply or the DC bus is not shorted to ground through the inverter switches (both top and bottom switch of the same leg should not be on at the same time).
3. With reference to the example, the carrier wave will be a triangular wave that will be configured in the epwm block (counting mode = up-down) with period of 50 microseconds - please refer to block documentation or the controller documentation for more details on this. The modulation wave will be shaped as a sine wave (for https://www.mathworks.com/help/mcb/gs/run-three-phase-AC-motors-open-loop-control-calibrate-adc-offset.html) or the double hump wave (for sensorless example which uses space vector modulation) and is an input to the epwm block. Refer to https://www.mathworks.com/discovery/space-vector-modulation.html for waveshapes of carrier and modulation wave.

Answer 2

[KrishnaKumar]

The referred example uses PWM reference generator block (PWM Reference Generator) to generate the necessary duty cycles to control the inverter switches. The example demonstrates closed loop control and generates necessary duty cycles in simulation to run the same. When the same is deployed on hardware and if the hardware is not connected to the motor, closed loop control cannot be achieved and hence the duty cycle measurements from an unconnected launchpad may just be constant values and not vary with time as seen in your attached picture (the duty cycle seems to be 50% and does not vary).

1. To get the switching pattern as per SVPWM (see PWM Reference Generator) the board would need to be connected to driver + motor. Or alternatively, create a new model to be deployed on your hardware using a sinusoidal input to the PWM reference generator block and measure the duty cycle output in hardware to check the PWM driver and outputs in open loop. This example - Run 3-Phase AC Motors in Open-Loop Control and Calibrate ADC Offset can be a good starting point.
2. If the switches in each inverter leg are configured to be complementary, then turning on all top switches of the inverter should lead to a short circuit on the motor (the three terminals of motor will be shorted).
3. The switching time (or duty cycle) varies as a double hump wave in SVPWM as seen in the picture titled "Gate pulse generation as a result of comparing the modulation wave and the carrier wave." in Space Vector Modulation - MATLAB & Simulink