Power converters

Website:	Moodle ZČU
Kurs:	KEV/EMB Elektromobilita - podklady k výuce
Buch:	Power converters

Gedruckt von:	Nepřihlášený host
Datum:	Montag, 9. November 2026, 00:02

Beschreibung

Power semiconductor converters for vehicles with electric or hybrid drive. Traction inverters for supplying the electric motor from the traction battery.

Inhaltsverzeichnis

1. Introduction
2. Power converters for electric vehicles
3. Other components
4. Traction inverter operation within the drive
5. Output voltage of three-phase inverters

1. Introduction

Variable-speed drive

Variable-speed electric drives always consist of an electric motor, a power semiconductor converter and a control unit with control algorithms.
The power converter provides a controlled 3-phase voltage (voltage and frequency control).
Together with the control algorithms, the power inverter provides torque control or higher speed control.
For electric and hybrid cars, the power converter provides the interface and power transfer between the DC source (traction battery) and the electric motor.

Constant-speed electric drive

The electric motor is directly connected to a constant voltage and frequency AC source (ie 3f of the mains).
Constant speed of the stator magnetic flux, unregulated speed, unregulated torque.

2. Power converters for electric vehicles

Main traction converters of electric vehicles - three-phase voltage inverters. Comparison of converters of electric cars and public transport vehicles.

2.1. Main traction converter

Three-phase voltage-source inverter

The three-phase voltage-source inverter is the dominant type of the main traction converter of electric cars and public transport vehicles.

Three-phase voltage-source inverter

Three-phase voltage-source inverter (CREE SiC), 900 V, 250 kW (RICE FEL/ZČU)

Three-phase inverter for automotive (Bosch)

Traction converter (SiC) Porsche Taycan, 800 V

_{https://www.bosch-mobility-solutions.com

https://www.porsche.com}

2.2. Three-phase voltage-source inverter

2.3. Application comparison

Public transport vehicles

Traction trolley power supply - stable (with a certain tolerance) DC voltage
Large installation space (roof containers)
Air-cooled inverters
Modularity
Noise level requirements: yes, but limited

Trolleybus Škoda 31Tr (250 kW)

Containers for traction equipment of public transport vehicles

Electric and hybrid cars

Traction battery supply → significant difference between charged and discharged battery voltage.
Limited space for drive installation
Liquid cooling
Modularity? There is not much space.
Noise level requirements: high

Nissan Leaf (BEV)

Limited space for drive installation in VW ID.3

Voltage drop of traction battery during driving

_{https://www.skoda.cz

https://www.nissan.cz

https://www.volkswagen.de}

2.4. Design comparison of inverters for EV

Inverter for public transport vehicles

IGBT technology
Air-cooled inverter
Bulky C filter on the DC side
Bulky cooler
The power of the inverter shown in the figure is approx. 10 - 20 kW

Three-phase inverter for electric vehicles supplied by trolley wire

Traction inverter for electric and hybrid cars

SiC technology (however, IGBT or MOSFET is still the most widespread technology in electric cars)
Liquid-cooled inverter
Small C filter or none
Small dimensions of the heatsink and the entire inverter (high power density)
Power up to 200 kW

Three-phase inverter for traction battery powered vehicles

2.5. Three-phase inverters for electric drives powered by a traction trolley

2.6. Three-phase inverter for traction battery powered electric vehicles

2.7. Main parts of electric drive

2.8. Switching frequency

Low switching frequency

High current ripple
Low current quality (harmonic distortion)
Additional losses
Noise

Load voltage and current - low switching frequency

High switching frequency

Small current ripple
High current quality - low harmonic distortion
High efficiency
Noise reduction

High switching frequency

2.9. Noise

Magnetostriction

Magnetic field tied with the switched current causes mechanical oscillations in all magnetically conductive materials.
Mechanical oscillations generate noise corresponding to the switching frequency.

Switching frequency above 20 kHz is not audible. The upper limit depends on age.
Standard IGBT technology:

For power of 100 kW is the switching frequency above 20 kHz practically not achievable (switching losses to high).
High switching frequencies achievable with SiC technology.

2.10. Modern power switches

Blocking voltage

IGBT: < 6500V
Si MOSFET: < 950V
SiC MOSFET: < 3300 V
GaN: < 650V

Trends and future

Increase in blocking voltage and rated current
Increase in switching frequency
Decrease in losses
Size reduction

_{https://www.infineon.com}

2.11. Power losses

Example of a 100 kW converter

The inverter consists of six switches, ie three modules - half-bridges.
Each module produces 700 W losses.
A 100 kW inverter with 98% efficiency produces 2 kW of power output.
Losses must be diverted from a very small area of the chip.
Thermal resistance and heatsink temperature are key factors.
Water cooling offers the optimal solution.

_{https://www.infineon.com

https://www.brusa.biz}

3. Other components

Sensors, control HW, control SW.

3.1. Sensors

Voltage sensors
Current sensors
Rotor speed / position sensors

_{www.lem.com

www.sensimatech.com

https://www.brusa.biz}

3.2. Control HW

Control microcontrollers designed to control electric drives and power converters (eg Texas Instruments TMS320F28xxx)
Peripherals adapted for these applications

ADC
PWM, dead time units
QEP
...

Texas Instruments TMS320F28xxx microcontroller for controlling drives and power converters and its peripherals (detail ADC)

Texas Instruments TMS320F28xxx microcontroller for controlling drives and power converters and its peripherals (PWM peripherals detail)

_www.ti.com

3.3. Principle of control algorithms

Proper operation of the whole system is strongly dependent on the position/speed sensor.
Special attention is paid to sensorless methods, but they still suffer by poor performance at very low speeds.
Sensorless techniques are used for fault diagnostic (sensor data validation).
The control algorithm has crucial impact on drive performance and effectivity – it makes the drive unique.

3.4. Cascade structure of drive control

4. Traction inverter operation within the drive

Acceleration, motor and generator mode, torque characteristics of induction machines, traction characteristics of a drive.

4.1. Start-up

Voltage and current (single phase) of a motor supplied by a three-phase inverter during start-up of the drive

4.2. Drive in motor and generator mode

4.3. Voltage and frequency change for induction machine

Torque characteristics of induction machine

4.4. Drive characteristics

Torque-speed characteristic of regulated electric drive

Torque and power of PMSM

_{https://www.brusa.biz}

4.5. Influence of battery voltage drop

Voltage drop during traction battery discharge

Influence of battery discharge on torque and power

5. Output voltage of three-phase inverters

What voltage do we have available on the AC side of the traction converter at a given traction battery voltage? How can the drive control maximize the output voltage?

5.1. Basic variables

Output voltage

$U_{A0}$ phase voltage of the inverter
$U_{zA}$ phase voltage of the load
$U_{AB}$ phase-phase voltage

For the 1^st harmonic component:

$U_{A0}(1) = U_{zA}(1)$ … viz KEV/PVE2
$U_{AB}(1) = √3U_{A0}(1) = √3U_{zA}(1)$

Example

Battery voltage \ (U_ {dc} = 400 V \), what is the available voltage on the motor?

5.2. Sinusoidal PWM

Maximum of the 1^st harmonic

$U_{A0}(1)$ : U_dc/2=400/2=200 V (rms value 141 V)
$U_{zA}(1)$ : U_dc/2=400/2=200 V (rms value 141 V)
$U_{AB}(1)$ : U_dc/2 √3=400/2 √3=346 V (rms value 245 V)

5.3. Square-wave control

Maximum of the 1^st harmonic

$U_{A0}(1): \frac{2U_{dc}}{\pi} = \frac{2∙400}{3,1416} = 255 V$ ,

i.e. rms value of the 1^st harmonic: 180 V,
rms value of the square-wave voltage $U_{A0}$ : 200 V

$U_{zA}(1): \frac{2U_{dc}}{\pi} = \frac{2∙400}{3,1416} = 255 V$ ,

i.e. rms value of the 1^st harmonic: 180 V,
rms value of the square-wave voltage $U_{zA}$ : 189 V

$U_{AB}(1): \frac{2U_{dc}}{\pi}\sqrt{3} = \frac{2∙400}{3,1416}\sqrt{3} = 441 V$

i.e. rms value of the 1^st harmonic: 312 V,
rms value of the square-wave voltage $U_{AB}$ : 326 V

5.4. Voltage increase by zero-sequence component - principle

Non-rotating components can be used to increase the output voltage of the inverter.
Vector PWM (SVPWM) and PWM injecting the 3rd harmonic or sawtooth signal (TIPWM) work with the non-rotating component.
Both SVPWM and TIPWM lead to an equivalent output voltage - both modulations actively inject a non-rotating component in the form of a sawtooth signal.

Basic inverter voltage vectors for SVPWM

TIPWM (triangular signal injection PWM)

5.5. Voltage increase by zero-sequence component - example

Maximum output voltage – SVPWM a TIPWM

Hexagon inscribed circle:

$\frac{2}{3}U_{dc}cos⁡(\frac{\pi}{6}) = \frac{2}{3}400\frac{\sqrt{3}}{2} = 231 V$

$U_{A0}(1)$ : 231 V, 163 V_rms
$U_{zA}(1)$ : 231 V, 163 V_rms
$U_{AB}(1)$ : 400 V, 283 V_rms

5.6. Summary

Example

Battery voltage \ (U_ {dc} = 400 V \), what is the available voltage on the motor?

Control	$U_{A0}(1)$ [V]		$U_{zA}(1)$ [V]		$U_{AB}(1)$ [V]
	max	rms	max	rms	max	rms
Sinusoidal PWM	200	141	200	141	346	245
TIPWM	231	163	231	163	400	283
SVPWM	231	163	231	163	400	283
Square-wave control	255	180	255	180	441	312