What is Insulator, Insulation Resistance and How to measure IR in Batteries ?

   Figure 1: Insulator in the High Voltage Transformer

Insulator: A material which blocks movement of electric current due to high resistance. The high resistance is due to the higher band gap from Valance to Conduction band.

Insulation Resistance: The insulation resistance is a method used to detect any power leakage inside  HV components (Battery,Inverter,Motor etc).

In this process we will be applying High DC Voltage (500V or 1000V) with miniscule amount of current and resistance is measured.(Typically 550MOhms).

If the component has insulation fault then the resistance value showing in the IR Tester or Megger will  be low and Vice Versa,

                                   

       Figure 2: Showing no insulation Fault (OK)         Figure 3: Shows insulation Fault(Faulty)

Process to Check Insulation Resistance (IR):

1. The above Figure 2 & 3 shows Insulation Tester or Megger to check the Insulation resistance.

2. It has 2 probes one is RED to check the insulation by giving appropriate voltage either 500V or 1000V and the other BLACK probe is a common ground.

3. The IR meter has a (Test ) button, also the test probe too has a push button (Test) to pass the voltage.

4.The common ground probe need to touch the HV component ground or the body ( Typically the HV systems body metal structure is the ground ).

5. The red probe need to touch the LIVE part of the system, in case of batteries it will be battery terminals ( Negative or Positive Terminals).

6.Then the TEST button shoud be pressed, we will get the result (as shown in the above image).

To read more about Batteries -- Click Here

What are Lithium ion Batteries & How LFP batteries work?

                               

                                       Figure 1: 48V LFP battery fixed inside a cabinet.

What are Lithium ion Batteries ?

Lithium ion batteries are the rechargable batteries which has Lithium as cathode active material.

There are different types of Lithium ion batteries like LFP,NMC,NCA etc, All these comes under Lithium family batteries and each one has its advantages and disadvantages.

These batteries having better features compared to other lead acid or VRLA batteries because of the Power electronics components avaialbilty to control each and every parameters of the battery.

For example the monitoring section reads and monitor all real time data's from individual cells and sensors connectd in it, means Voltage of individual cells,battery pack,total voltage,cell temperature,Over current or Under current etc...., each and every parameters of the battery including SOH and SOC also tracked using in-build BMS(Battery Monitoring System).

The Lithium ion batteries have high energy density, means the amount of energy stored per unit volume is higher than the traditional Lead acid batteries hence the size of the battery is smaller.

The Li-ion battery can store as much as twice of the power Lead Acid batterycan hold and also environmentally friendly but these batteries are susceptible to 100% discharge so max 90% discharge is recommended.

Working of LFP battery?

                                                   

                                              Figure 2: Shows movement of Ions & Electrons

Like anyother LMO (Lithium Metal Oxide ) batteries, the working of LFP is similar and the only change is the usage of cathode metal oxides.

Incase of LFP the cathode is Lithium (Ferrous Phosphate) Li-(FePO4), for NMC battery the cathode is a mixed of Lithium (Nickel Manganese Cobalt Oxide) Li(NiMnCoO2).

The Negative electrode of Lithium ion battery is graphite/graphene and the positive electrode is lithium iron phosphate, The electrolytes such as LiPF6(lithium hexafluorophosphate) is used.,The Seperator used in the LFP batteries can be Polyethylene (PE) , Polypropylene (PP).

Charging:

While Charging,the lithium atoms leave the metal oxide structure and ionize into Li+ ions under the release of an electron. In this process Li+ ions diffuse to the negative electrode(anode). 

At the surface of the graphite particles the Li+ ions and electrons recombine with each other forming neutral lithium atoms and are reintercalated into the molecular structure of the graphite.

When no more ions will flow, the battery is fully charged and ready to use.

Discharging

During discharge, lithium atoms oxidize by forming Li+ ions and electrons, whereas Li+ ions move to the positive electrode diffusing through the electrolyte and the separator. The electrons flow from the negative electrode to the positive on the external circuitry, where the resulting current flow can be used to run any type of load.

 At the positive electrode the electrons recombine with the Li+ ions and are stored in the molecular structure of the cathode active material,

When all the ions have moved back, the battery is fully discharged hence it needs charge again.

How Batteries Works ?

What is a Battery?

Figure:1

A Battery is a device which can converts stored chemical energy to electrical energy, the battery consists of single or multiple electrochemical cells connected in series which can be charged or discharged.

As per figure 1, Generally a battery works from the movement of ions through electrolyte & electrons movements in the external load from cathode to anode and Viceversa for Charging & Discharging.

Cathode is a Positive electrode

Anode is a Negative electrode

Electrolyte is a medium in which ions travel from one electrode to other.

Seperator is a material which placed inbetween anode and cathode which physically seperates them still facilitates ion movements while charging and discharging.

Unlike Anode and cathode in power electonics components where Diodes anode is Positive and cathode is Negative, the Battery Anode is Negative and Cathode is Positive.

Types of Batteries:

1.Flooded Batteries ( Wet Batteries)

2.Non Flooded Batteries (Dry Batteries)

1.Flooded Batteries ( Wet Batteries)

  

Figure 2: Panasonic Lead Acid Battery               Figure 2: Lead Acid Battery internal Cell connections

Lead Acid batteries like the ones we are using in our Bikes,Cars,Autos,Heavy Vehicles,Generators  for starting an engine are Flooded batteries.

These batteries are easy to construct and are cheap to manufacture, The electrolytes are 35 to 40% sulfuric acid & 60 to 65%% distilled water.

Since we need to refill the electrolytes and also the chances of leakage of electroyte was observed in these batteries hence it is called as Flooded or Wet batteries.

2.Non Flooded Batteries (Dry Batteries)

These dry batteries are the advanced Lead Acid Batteries which donot need refilling of electrolytes,

Examples like Gel and AGM batteries.

AGM - Absorbent Glass Mat Batteries 

• These Gel or AGM batteries have different electrolyte compared to Wet batteries, 

• In Gel battery the electrolyte is a sulfuric acid in gel state.

• In AGM batteries the electrolyte stuffed in between fibre glass mesh which absorbs and holds the (water & Sulfuric acid) and acts like a sponge or cushion and will allow only required amounts of electrolytes to pass for the ion movements.

Since these batteries doesnt need topping of electrolytes it is called as Dry batteries.

Lithium Ion batteries are also a Dry battery. 

Click To know more about Lithium-ion battery.

Architecture of Electric Vehicles

                          

 EV Architecture is complex and are comprises of Battery,Motor,PDU,MCU,Sensors,Harness,Controls and Aux Systems.

There are 2 types of major architecture in EV Vehicles.

1. 400V EV Architecture which are already available and got matured already.

2. 800V EV Architecture. which are taking control in Luxury space and automotive OEM's now switching focus on this architecture, why? will cover below.

There are advantages and disadvantage in both architecture, will see in details below.

1. 400V EV System Architecture

The 400V architecture is the standard EV architecture which uses Voltage range from 300V to 500V and it is also cheaper to implement, the main reason is that most OEMs have already established suppliers of components and the supply chain is very strong unlike 800V Systems.

The Production cost of 400V Systems are cheaper to manufacture than 800V systems and finally the end users can reap benifit from this cost reduction in the over all purchase price of the EV vehicle.

Thats the reason the 400V Architecture ev vehicles tends to sell more and placed in the mid and cheaper catogory.

TATA  Nexon Max

Lithium ion battery Voltage - 332.8V

Capacity - 120AH

Power - 39.9KW

The TATA Nexon EV Car uses 400V architecture.

2. 800V EV System Architecture

The 800V architecture are usually found in the Luxuary segments of EV vehicles where the arrangements of the components and systems are neater and less clumsey.

There are lot more advantages in 800V system than the 400V systems, simply put the voltages of a system increases then the current needed decreases to get the same amount of power.

Eg: 

Case 1: 400V,200A = 80000W or 80KW

Case 2: 800V,100A = 80000W or 80KW

Take Case 1, Since it uses 400V architecture the max current it can withdraw is around 1C that is 200A to achieve 80KW of power to the load(Motor).

Click to know about C -Rate?

Take Case 2, The 800V architecture uses only 100A to draw maximum power output of 80KW.

Advantages of 400V Architecture:

1. Widespread Infrastructure availability of charging stations upto 150KW Fast chargers and increasing.

2. Lower costs of Subsystems & Components.

3. Overall vehicle purchase cost is low.

4. Matured industry from production to supply chain availablity.

5. Reliable and proven technology.

Disadvantages of 400V Architecture:

1. Limited power output levels due to lower system voltages cap at 400V.

2. Doesnt support Ultra Fast Charging, Limited fast charging capability capped to its system voltage.

3. Increased resistive losses at higher power output.

Advantages of 800V Architecture:

1. Supports Ultra Fast Charging upto 350KW due to its high voltage and lower current requirements.

2. Resistive power losses are low compared to 400V systems since the current needed is less and losses will be low.

3. The sizes of HVcomponents and the cables will be lighter since it uses high voltage and lower current than 400V systems.

4. Higher efficiency and Performance.

5. Overall reduction in Weight of the vehicle.

6. Future proof since the coming years OEM's increasing their focus on 800V architecture.

Disadvantages of 800V Architecture:

1. Few Ultra Fast Charging stations, Infrastucture is not widespread compared to 400V architecture ev vehicles.

2. Higher costs of Components.

3. The overall vehicle costs are higher.

What is Powertrain in EV Vehicles?

Figure : EV drivetrain architecture (reference : MDPI energies).

The Powertrain in EV Vehicles are responsible for delivering and managing electrical power to move a Vehicle.

The EV Power train consists of  below components and systems,

1. Batter Packs (Lithium Ion Battery);
2. Inverters or MCU(Motor Control Unit);
3. E-drive (PMSM Motor);
4. VCU(Vehicle Control Unit;
5. i-PDU(Integrated Power Distribution Unit or All in one combo PDU);
6. Mechanical Transmission (drive shafts, differential gears & EV axles );
7. Thermal management systems ( Liquid Coolant Unit,Refrigerent Unit,Cabin air HVAC Unit).
   

References:

• Fault Diagnosis Methods and Fault Tolerant Control Strategies for the Electric Vehicle Powertrains