Electronics Module

What are the main components in an electric drive system.

High voltage battery, PMSM motor, charger, inverter

How does a battery work?

Energy is stored within the chemical bonds of the compounds inside a battery

Energy is converted into electrical energy through electrochemical reactions

Reactions take place at two distinct electrodes which allows an electric current to flow through an external circuit

Which two cell properties lay the base for the cell’s energy capacity?

Oxidation: Loss of electrons
Reduction: Gain of electrons

How is a Li-ion cell constructed, and what are the different parts called?

What is the main purpose of the electrolyte, and of the separator in the Li-ion cell?

Transport mechanism for Li-ions

What signifies cells optimized for high energy density compared to high power density?

High energy density: Electrodes are thicker and have larger particles, current conductors are thinner
High power density: Electrodes are thinner and have smaller particles, current conductors are thicker

What is included in a battery pack?

Battery modules made up of electrically connected cells

Why is it important to declare if energy density refers to cell or pack level?

The energy density of a pack is much less as the mass from packaging is included.

Which two performance measures are affected by battery aging?

Capacity and Internal resistance

Which two categories of aging do batteries experience?

Cycle aging: aging from charging and discharging

Calendar aging: gradual loss of battery capacity from time

Describe cell balancing and the two methods.

Cell balancing is a method of addressing cells in a battery pack that vary with SOC, capacity, and temperature, caused by the manufacturing process.

Active: All batteries except the weakest are drained of some energy to balance, then recharged to same voltage

Passive: High SOC cells transfer energy to low SOC cells

Rule for CCCV (Constant current, constant voltage) charging

The charging voltage must always be higher than the battery voltage

List the main parts of an electric machine

Stator - stationary part

Rotor - moving part

Airgap between stator and rotor - where energy is transfered via magnetic fields

Shaft - where load is attached to rotor

Explain the reason for the name synchronous machine

The stator magnetic field and the rotor will be rotating with the same speed, the synchronous speed

Which type of synchronous machine is most used in electric vehicles?

Permanent Magnet Synchronous Motor (PMSM)

Describe the torque producing mechanism in AC permanent magnet synchronous machine (PMSM)

The stator windings create a rotating flux in the radial direction

The permanent magnets strive to align with the rotating flux of the stator

Is there is a misalignment between the stator and rotor flux there will be a torque on the rotor

Describe the torque producing mechanism in a asynchronous machine (IM)

The stator windings create a rotating flux in the radial direction

As this magnetic field rotates, it induces a voltage in the rotor bars

The rotor bars are short circuited, so the induced voltage drives a current into the rotor bars

The current carrying bars are in a external magnetic field so they will experience a force

This force creates a torque that spins the rotor in the same direction as the stator's rotating magnetic field, trying to catch up to it.

Which magnet material is mostly used in electric vehicles PMSM’s? Name the advantages and disadvantages with this material.

NdFeB magnets

They are the strongest but most expensive magnets

Which part/parts of electric machines are most sensitive to high temperatures, and why?

Windings: Resistance increased with temperature and winding insulation degrades reducing lifetime

Permanent magnets: Magnetic strength decreases and risk of demagnatization

Describe the main purpose/function of the power electronic converter in a battery electric drive system?

Convert voltage from battery DC to three phase AC needed by the electric motor

The vary the AC voltage frequency amplitude and phase shift, to control the machine’s torque and speed

Why is energy density often considered the key bottleneck for all-electric aircraft?

Current batteries store a fraction of the energy per kilogram that traditional jet fuel provides leading to a unmanageable weight penalty

Adding more batteries to increase range requires larger wings and more power, which paradoxically demands even more battery weight just to lift the plane