Bosch Internship presentation

Engineering Electronics Power Drives and Generator (AE / EEG1)

Internship PresentationGeeth Prajwal Reddy Putchakayala

M.Sc. Electrical Power Engineering

Rheinisch- Westfälische Technische Hochschule Aachen

Matrikel No. 340998

Supervisors

Mr. Zoltan Ersek Dr. Paul Mehringer


Company Profile

Development, production and sale of microelectronic products for

automotive and non-automotive applications. Core competencies are system

integration and application engineering for automobiles

Robert Bosch GmbH – Automotive Electronics Division

Areas of operation

• Electronic Control Units (ECUs)

• Contract manufacture of ECUs

• Body electronics and ECU components

• Power electronics and modules

• Mechatronic modules for electric power steering

• Semiconductors

• Sensors

• eBike systems

Headquarters : Reutlingen, Stuttgart


Objective of Internship

The objective of the internship is to develop a control

strategy for the torque control of an electrically excited five

phase synchronous machine without using PWM. The

control strategy should also be able to operate the machine

from 0 RPM to high speeds and must also be able to limit

the high starting currents in the phase windings of the

machine.

The object for the investigation into the use of block

commutation is to reduce the size of the DC link capacitance

required by avoiding the use of Field Oriented Control (FOC)

at low speed.

Internship Presentation


Machine Modeling and Model IntegrationThe machine model and the power converter was integrated with the

Drive control system. Based on the actual machine in use, the parameters were

calculated and incorporated into the machine model. Parameter matching

between the inverse model and the machine model was also performed.

5ϕ Voltage Source Inverter 5ϕ EESM



Variable Width Block CommutationThe algorithm for the variable width block commutation was developed

and coded in Matlab embedded function and incorporated into the Simulink

model of the Drive.Variable Width Block commutation involves three states :

1. Phase connected to positive rail of the battery

2. Phase connected to negative rail of the battery

3. Floating phase



Starting Torque and Starting CurrentExternal rotational speed variation, from 0 to 3000 RPM, was incorporated in

the Simulink model and the conditions were evaluated, particularly the case of starting.

High starting torque was an objective, thus the machine was also subjected to a high

starting current. Thus, an optimal starting procedure was devised to generate the high

starting torque, while restricting the stator phase currents to 250 A



Starting Current Limiter RoutineThe starting current was limited to 250 A using a current regulator to

complement the control of the phase switched in the inverter. When the current limit is

crossed, the regulator immediately floats that phase in order to restrict the current rise

further. The results of the current limiter is as follows :



Drive operation & Torque tracking:The result of the variable width block commutation torque control

algorithm of the synchronous machine prove that the control algorithm is well

capable of operating the motor from 0 RPM & beyond while simultaneously

controlling the torque produced by the motor based on the torque request

provided.



Response of the Internal Combustion EnginePrimary application of the drive system is to start an internal

combustion engine quickly and also provide the necessary torque as requested

by the ECU to boost the IC operation. Startup of the IC is determined by the

time taken to attain 350 RPM and it is observed that with the use of the control

algorithm, IC startup was performed in 0.65 seconds, with the use of a 12 volt

battery supply.

Rotational speed of IC

engine

Motor Torque – Yellow

IC engine load torque

- Pink

Rotational angle

of IC engine



Hardware Implementation of the Drive system

Hardware implementation and testing involved five major steps :

1. Porting of Matlab Simulink model control algorithm to dSPACE Rapid

prototyping.

2. Design of dSPACE ControlDesk GUI for drive control.

3. Design of a driver circuit to trigger the switches of the five phase VSI

4. Assembly and interfacing of the driver, inverter and machine with the

dSPACE system.

5. Preparation of the test bench and interfacing the connections of the

measurement and the supply systems with the drive system and their

calibration.



Porting to dSPACEThe control algorithm is ported into the dSPACE system using the Matlab

Simulink blocks, Xilinx Toolbox and the RTI programming blocks. The control algorithm

is split up to operate between the DS1005 FPGA and microcontroller in the dSPACE

system.

The FPGA, operating at 10 ns, includes the following functionalities :

• Input interface: Reads data from the measurement sensors and translates them to

appropriate current ad voltage values using the ADCs onboard the FPGA.

• Monitoring system: Monitors the voltage and current parameters of the drive and

shuts down the system incase of error.

• Current Limiter: Implements the phase current regulation function

• IdleState: Idle state is one of the states of the machine during which the all low side

switches of the VSI are turned ON to charge the Bootstrap capacitances of the drive

• Dead Time: Software code to implement variable deadtime among the switches in

each phase leg of the VSI.

• Output Interface: Generates the gating pattern signals to the driver circuit, through

the Digital_I/O ports of the FPGA, from the timing data calculated by the control

algorithm in the microcontroller.



FPGA Model

Monitoring System

Current Limiter

Gating Pulse Generator

Output Interface



Microcontroller ModelThe Data between the FPGA and the microcontroller is communicated

through the PHS Bus of the dSPACE system. The microcontroller uses the

dSPACE ADC module to read the data from mechanical sensors



dSPACE ControlDesk 5.2 GUIGraphic user interface was developed in ControlDesk 5.2 software to

facilitate the testing, monitoring and operation of the drive system.



Driver Circuit for the Voltage source Inverter

In order to translate the gating signals generated by the FPGA of

dSPACE to trigger the switches of the VSI, a Bootstrap driver is used. Three

driver circuits were designed, but due to certain problems with the first two, the

final driver circuit was used for the driver implementation.


Driver Circuit 1

Driver was unable to generate the gating signal

for the high side switch with the phase line as

reference

Driver Circuit 2 - Infineon-TLE7185E

Used for testing the power stages, due to

space and size constraints, it wasn’t possible

to mount on the machine


Driver Circuit for the Voltage source Inverter

The third driver circuit was operational and was made to size and

dimension to be suitable to mount on the drive. The image shows the driver

circuit mounted on the Voltage source inverter



Integration to Test Bench

All the individual components of the drive were assembled together and mounted

on the Test bench and the measurement sensors and power supply were connected

Several problems had come up during

the setup of the drive at the test bench that were

subsequently resolved :

•Lack of rotor position sensor, was resolved by

performing software integration of the rotor

speed using initial angle.

•Calibration of LEM modules and

implementation of conversion ratio, in FPGA

code, to scale the LEM outputs (in mV) to their

equivalent current measurement (in A).

•Grounding connections among the different

power supplies and sensors

•Interfacing the sensors to the dSPACE system

to read data for the control algorithm


Drive Operation

With all the problems resolved, all the monitoring and safety systems

were verified and measures were taken to prevent overvoltage spikes due to the

connecting cables, with the use of Zener Diode.

Finally the Drive was turned ON and it was observed that despite small

glitches in the starting operation and mild toggling of the rotor, the synchronous

motor was in fact operational with the use of variable width block commutation

algorithm even for low speed operations .

The toggling of the rotor was caused due to the improper connection of

the phase windings to the appropriate phase legs of the VSI due to improper

marking of the phase windings on the machine. This problem was resolved by

operating the machine as an alternator and from the observation of the current

waveforms induced in the stator phase winding, the correct phases were identified

and the reconnected correctly.


Documents

Bosch Internship presentation