Registration Number MT2291

 

Eligible Parts: 
dsPIC30F6010A 
 
INTRODUCTION 
 
 
The EV Drive team has constructed an inverter using a control board and software based upon 
Microchip’s MC-1 development board, using a dsPIC30F6010A and 3 dual IGBT modules with 
gate driver boards from Powerex. This project is a 100kW 3-phase inverter developed as an open-
source process, which can be continually improved upon.  
 
All components of the inverter design are “off the shelf” units readily available at many 
electronics distributors (Digikey, Mouser, etc).  These parts can also be subject to change with the 
open-source design being modified to suit a user’s needs or improved by advancing technology.  
This facet of the inverter’s design is meant to mesh with an easy application of the system. A user 
should be able to easily obtain all components of the inverter (if not purchasing an assembled 
system), and once constructed it will be able to power a wide range of AC induction motors.  This 
means that the user can select a motor that was not originally designed for a vehicle.  For our 
project we used a motor that was from an elevator. 
 
 
POWER INVERTER 
 
The Powerex CM400DU-12F Insulated Gate Bi-polar Transistors (IGBT) [1] modules and their 
companion BG2B gate driver circuits [2] provide a relatively low cost method for generating 3-
phase AC power from DC power.  The DC power from the EV battery pack is converted to 3-
phase AC for driving an AC induction motor. We configured each phase of the IGBT module 
design with RCD snubber protection (Figure 1) [3].  The gate driver circuit can be seen in the 
BG2B application note from Powerex, using 2 VLA106-15242 DC/DC converters and 2 
VLA503-01 gate drivers.  These gate driver boards are recommended by Powerex for use with 
the dual IGBT modules and provide 2500VAC of control signal isolation via high-speed 
optocouplers and de-saturation detection to prevent short-circuit conditions on the IGBTs.  The 
CM400DU-12F modules are rated with a collector-emitter voltage of 600V and continuous 
emitter current of 400A with a peak rating of 800A.  These modules are also able to provide 
switching speeds up to 30kHz; we used 20kHz.  The frequency range promotes efficient 
operation of the spatial vector modulation (SVM) algorithms used to drive the IGBTs as well as 
bringing the switching noise out of audible range. 
 
 
CONTROL BOARD 
 
The control board of the inverter is primarily a stripped down variant of the Microchip MC-1 
development board [4]. This was done for code compatibility and to reduce actual development 
time.  Several simple changes were made to the PCB design.  The bias resistors on the gate 
drivers were moved to the output of the logic buffer and given the capacity to function as either 
pull-up, pull-down, or float depending on the placement of a jumper.  Regulators were added to 
the board, providing stable +5 and +15 volt sources. Additional decoupling capacitors were 
placed in the circuit to reduce the inevitable noise (motor noise, switching noise) that are inherent 
to the system.  
 

Registration Number MT2291

 

There was a daughter board created to assist in debugging as well as providing an interface to the 
LabVIEW application used for motor tuning.  The daughter board acts as a bridge between CAN 
bus and USB with robust error checking between the two protocols. The daughter board MCU 
and the CAN bus controller were left with separate clocks due to the timing sensitivity of the 
CAN bus.  With some minor modifications, the module could also control an optional LCD 
display.  The module connects to the main board with a 4-pin connector which also provides 
power to the module.  Four of these sockets are provided on the main board. 
 
 
SPACE VECTOR MODULATION 
 
To generate the 3-phase AC power from DC power, the inverter is supplied logic drive signals in 
form of a sine-wave PWM called Space Vector Modulation (SVM).  The SVM software is based 
upon Microchip’s motor control Application Note 908 [5] and is implemented by a 
dsPIC30F6010A based control board.  This 16-bit dsPIC features 8 PWM outputs, a quadrature 
encoder interface (QEI) module and 2 CAN bus modules, making it an optimal MCU for motor 
control.  A QEI rotary shaft encoder is used to measure motor RPM in our system. 
 
PID TUNING 
 
For our electric vehicle project, we decided to use a squirrel-cage AC induction motor.  To uses 
this motor for such an application, it is obvious that some tuning of the motor controller is 
required.  To tune the motor, we developed a LabVIEW application that allows the user to tune 
the PID variables then after starting the motor the user can watch the motor response in real-time. 
 
The response of a motor is critical to the overall operation of the EV system.  When a new motor 
is connected to the motor controller circuit board, the PID parameters must be properly aligned.  
If the motor does not seem to respond very well to an input like stepping on the accelerator, there 
needs to be alterations to the PID control loops. 
 
CAN BUS / LABVIEW INTERFACE 

The Human Machine Interface (HMI) for this project is a LabVIEW 7.1 application built to 
communicate to the CAN bus module with “serial over USB” protocol by FTDI.  We used the 
DLP-USB232M-G integrated module featuring FTDI's FT232BL 2nd generation USB UART [6]. 
This module was an appropriate choice for development because it can be plugged into a standard 
24-pin 0.6in wide DIP socket that is mounted on our daughter board and it could be moved easily 
to another board if required.  FTDI also developed its USB functions as LabVIEW Virtual 
Instruments (VIs) that are called from our HMI, which also made them a good choice for our 
application [7]. For message processing on the daughter board, we used a PIC18F4620 [8] with 
an external CAN bus controller MCP2515 [9] and transceiver MCP2551 [10].  These CAN bus 
control ICs and the MCU are manufactured by Microchip.  

CONCLUSION 

As the Electric Vehicle becomes a more viable alternative for transportation, this project 
will be referenced as one way to accomplish part of the conversion of a gasoline engine 
to an electric motor. Currently the main factors in conversion are safety and battery 
technology. As these concerns are addressed, an open source project will be a welcome 
alternative for those who wish to take on an electric motor modification themselves. 

Registration Number MT2291

 

 
 
System Block Diagram 
 
As seen below in Figure 2-1, the operation of the electric drive system relies on four 
component blocks. “Block 1” is the dsPIC30F6010a microcontroller, which operates the 
SVM software to control the optically isolated gate-drive circuit seen in “Block 2.” The 
gate-drive circuit forwards the control signals to the 3-phase inverter. The inverter is seen 
in “Block 3,” and provides the 3-phase AC voltage and current by converting its’ input 
DC voltage to AC and driving the motor. “Block 4” is the diagnostics and 
communications block. This block uses CANBUS communications to provide 
information to the user about the operation of the inverter and motor. Also, this block is 
used for initial setup and tuning of the drive system. 
 
 
 

Figure 2-1 

 

Block 3 

 

 
 

 

 

 

 

Block 1 

Block 2 

Block 4 

Registration Number MT2291