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TI Hercules RM46 Three-Phase Generator With Transformers Part 1

martinvalencia
INTRODUCTION

My goal is to design a device that generates a three-phase signal starting from a voltage in DC.

I have a 12VDC power supply and through H bridges, power supply of the transformers in the SCOTT configuration, both transformers with their special connection send me the signals R, S, T plus a Neutral.

Between my airplanes is to vary the voltage of the power supply with a reducing reducer converter.

The system will be controlled by a microcontroller Hercules RM46, this internal has an ETPWM module, which allows me to generate PWM signals with special characteristics, such as bandwidth, phase angle, synchronization in PWM, among others.

Attached

Part 2:

TI Hercules RM46 Three-Phase Generator With IGCM15F60GA Part 2

Microcontroller:

LAUNCHXL2-RM46 Hercules RM46x LaunchPad Development Kit | TI.com

User Guide  

Technical Reference Manual

Facebook:

Electronaplica

BLOCKS DIAGRAM

image

*The image of the transformer is referential

 

CIRCUIT ELECTRICAL BACKGROUND - SCOTT CONNECTION

This is a contribution of Frank Rodrigo Coaquira Molleapaza (Electrical Engineer).

It is a connection of two single-phase transformer to convert a system of three-phase voltages in biphasic and vice versa.

 

 

This arrangement is due to the American engineer Charles F. Scott, who invented it in 1984 while working at the company Westinghouse and is based on the well-known fact that the three-phase star system composed voltage between two phases is in square with the voltage Simple third phase.

 

image

Equation for output V2a:

image

Equation for output V2b:

image

Fragment of text, extracted from the book:

 

Pag 243. “Maquinas Electricas – Jesus Fraile Mora”

 

Conclusion: from the previous fragment, it tells us that you must have two alternating signals of the same frequency with a phase shift of 90 degrees between them.

 

About the Microcontroller

The HerculesTm RM46x LaunchPadTm Development Kit is an inexpensive evaluation platform designed to help you get started quickly in evaluating and developing with the Hercules microcontroller platform. The LaunchPad Development Kit is based on the IEC 61508 SIL 3 certified RM46L852, which is a lockstep ARMRegistered CortexRegistered-R4F based MCU with integrated safety features and peripherals such as two 12-bit ADCs, programmable High-End timers, motor control peripherals (eQEP, eCAP, ePWM), USB, Ethernet, MibSPI and serial communication interfaces. Hercules RM MCUs can help reduce the development effort of IEC 61508 functional safety applications.

 

image

 

ETPWM Enhanced Pulse Width

The enhanced pulse width modulator (ePWM) peripheral is a key element in Modulator controlling many of the power electronic systems found in both commercial and industrial equipments. These systems include digital motor control, switch mode power supply control, uninterruptible power supplies (UPS), and other forms of power conversion. The ePWM peripheral performs a digital to analog (DAC) function, where the duty cycle is equivalent to a DAC analog value; it is sometimes referred to as a Power DAC.

 

As we can see in the image, you can see that ETPWM module uses two output pins of the microcontroller, side A and B, both outputs can be with the same polarity or one in reverse of the other.

 

 

The resolution of the module is of nanoseconds, generating a high resolution in the dutty cycle and in the dead band.

 

image

 

 

Code Example CCSV7

 

int main(void)

{

/* USER CODE BEGIN (3) */

  etpwmDeadBandConfig_t pwm_deadband_config; // declaracion de variable

  etpwmInit();

 

  /*Configuracion del angulo de desfase entre los PWM generados*/

  etpwmSetSyncOut(etpwmREG1, SyncOut_CtrEqZero);

  etpwmSetSyncOut(etpwmREG2, SyncOut_EPWMxSYNCI); //SyncOut_CtrEqZero);

 

  etpwmDisableCounterLoadOnSync(etpwmREG1);

  etpwmEnableCounterLoadOnSync(etpwmREG2, 8300, COUNT_DOWN); // seting del angulo de

 

  /*Configuracion de la banda muerta*/

  pwm_deadband_config.halfCycleEnable = false;

  pwm_deadband_config.inputmode = PWMA_RED_PWMB_FED;

  pwm_deadband_config.outputmode = PWMB_FED_PWMA_RED;

  pwm_deadband_config.polarity = Invert_PWMB;

  /*Iniciando la carga de los valor de la banda muerta 1000---> 510 microsegundos*/

  etpwmSetDeadBandDelay(etpwmREG1, 1000, 1000);

  etpwmEnableDeadBand(etpwmREG1, pwm_deadband_config);

  etpwmSetDeadBandDelay(etpwmREG2, 1000, 1000);

  etpwmEnableDeadBand(etpwmREG2, pwm_deadband_config);

 

 

  while (1)

  ;

  /* USER CODE END */

 

 

    return 0;

}

 

 

Pin Conection

File:LAUNCHXL2 TMS57012 RM46 REVA.pdf - Texas Instruments Wiki

image

 

 

 

Schematic

image

In the schematic there is a simple inverter bridge excited by transistors and using MOSFET to perform the energy switching

Two of these bridges are used for the project.

 

IMPLEMENTATION PHOTOS

In the following images you can see the implementation using only one transformer.

image

image

image

image

  Output voltage waveform

image

  Voltage spectrum

image

 

 

Operation Videos - Spanish

First part of the operation

Second part of the operation

  • in reply to Jan Cumps

    It is true that etpwm, is very powerful Hercules has enough modules to control a three-phase bridge, the example code I put above could help to control the triphasic.

    Once I get some GaN samples for high power, I will try to produce the three-phase signal in this way.

    Saludos amigo!

  • in reply to jc2048

    No, I'm sure of why the graphics come out that way, maybe they'll work out fine if you consider adding a 10k resistor at the half bridge output.

    In reality this works that way with a resistor, I am not working with high currents at the maximum one ampere, so I consider a current in milliamps to exite the internal capacitor of the mosfets, in the datasheet there is a graph of Charge vs excitation voltage, from there my calculations for the exit current of the damper.

     

    image

     

    In this graph selecting a 12 volt work and gives me a load of 55nC.

  • in reply to balearicdynamics

    Hi Enrico, I'm glad you like my work, as presented here is just the initial part in which using a single inverter bridge and a single transformer.

    I'm still working on the implementation of the SCOOT configuration of the transformers, this progress will be presented in the next blog.

    I hope we can work together on some project, with Jan I have done several jobs and it is always nice to have someone else.

     

     

    regards

    Martin

  • in reply to jc2048

    Jon Clift wrote:

     

    Does this Hercules board have enough PWMs for deadband control?

     

     

    It can be independently (or dependently) set for each of the 6 or 7 complementary PWM modules,

     

    image

    Here's a signal that I created with one of these PWM pairs

    image

  • in reply to Jan Cumps

    Does this Hercules board have enough PWMs for deadband control?

     

    Another solution would be to rework the 'driver' (at the moment it's just a level converter from 3.3V to 12V), so that both MOSFETs turn off quicker than they turn on and the switching times of both are similar.

    Personally, I'd look to do both.

     

    An advantage of improving the MOSFET drive would be if Martin wanted to move on from square wave drive to consider sinewave operation [where the PWM would have to have a much shorter period and where you wouldn't want a 20uS deadband].