Difference between CP Vs PP in EV Vehicles

CP vs PP in electric Vehicles

Control Pilot (CP)

The CP manages the actual charging process by establishing communication between the EV and the EVSE. It ensures that charging starts and stops safely, and it controls the amount of current delivered to the vehicle.

How it works:

Voltage Levels: The EVSE generates a square wave signal on the CP line. Different voltage levels of this signal represent different charging states:

• State A (Disconnected): +12V - No connection
• State B (Connected, EV Ready): +9V - Cable connected, EV ready to charge
• State C (Charging): +6V - Charging in progress
• State D (Charging with Ventilation): +3V - Charging with ventilation required (* NA in India*)
• State E (Fault): 0V or other abnormal voltage - Fault detected

Pulse Width Modulation (PWM): When in State C (Charging), the CP signal uses PWM to communicate the maximum available charging current from the EVSE to the EV. The duty cycle of the PWM signal (the proportion of time the signal is high) corresponds to the available current.

 

Key Functions:

• Connection confirmation
• EVSE current capacity advertisement
• Charging start and stop control
• Fault detection
• Ventilation request (if needed)

Proximity Pilot (PP)

The PP is primarily about connection detection and safety interlocks. It ensures that the charging cable is physically connected to the vehicle before charging can begin and prevents hazardous situations like driving off while still plugged in.

How it works:

Resistance: The EV applies a specific resistance across the PP pin and the Protective Earth (PE) pin. This resistance value is determined by a resistor in the charging cable.

Current Rating: The resistance value corresponds to the maximum current the cable can safely handle. This helps prevent overloading the cable.

Detection: The EVSE (charging station) detects this resistance. If the resistance is within the expected range, it confirms a valid connection.

Connector Locking (Type 1): In Type 1 connectors (common in North America), the PP also controls a mechanical locking mechanism that secures the connector to the vehicle during charging. This prevents accidental unplugging.

Connector Locking (Type 2): In Type 2 connectors (common in Europe and increasingly in India), the locking mechanism is separate, but the PP still provides the connection confirmation.

Key Functions:

• Cable connection detection
• Cable current rating identification
• Preventing drive-away during charging (connector locking)

Relationship between CP and PP

The PP and CP work together in a sequence:

Connection: The charging cable is plugged into the EV. The PP detects the connection and the cable's current rating.

Readiness: If the PP signal is valid, the EV signals its readiness to charge via the CP (State B).

Current Information: The EVSE uses the CP signal (PWM in State C) to inform the available charging current.

Charging: The EV's OBC (On-Board Charger) starts drawing current based on the advertised value.

Monitoring: Both CP and PP are continuously monitored during charging. If the PP signal is interrupted (e.g., the cable is unplugged), charging stops immediately. If the CP detects a fault, charging is also interrupted.

                                  

CP vs PP

Under Progress

What is a BMS & What are the Components in Lithium-ion battery BMS?

AI generated Image of BMS

A Battery Management System (BMS) is an electronic system that manages a rechargeable battery (cell or battery pack), by monitoring its state, controlling its environment, and protecting it from operating outside its safe operating area.

1. Battery Monitoring Unit (BMU)

The BMU is the "sensory" part of the BMS. It's typically distributed throughout the battery pack, with individual monitoring circuits for groups of cells or even individual cells in high-precision systems.

These circuits are connected to a central communication bus that relays data to the Battery Control Unit (BCU).

 

Components:

Voltage Sensors: High-precision analog-to-digital converters (ADCs) that measure the voltage of each cell or cell group. Accuracy is crucial here, as even small voltage differences can indicate significant state-of-charge variations.

Current Sensors: Devices that measure the current flowing into and out of the battery pack. Common types include:

Shunt Resistors: Measure voltage drop across a small resistor in the current path. Simple and cost-effective but can generate heat.

Hall Effect Sensors: Measure the magnetic field generated by the current. More accurate and efficient than shunt resistors.

Current Transformers: Measure the current by inducing a current in a secondary winding. Used for high-current applications.

Temperature Sensors: Thermistors or thermocouples placed at strategic locations within the battery pack to monitor temperature.

 

Working:

1. Voltage sensors continuously measure the voltage of each cell or cell group.
2. The current sensor measures the total current flowing in and out of the battery pack.
3. Temperature sensors monitor the temperature at various points in the pack.
4. The BMU converts these analog measurements into digital signals using ADCs.
5. This digital data is then transmitted to the BCU via a communication bus (e.g., CAN, SPI).

2. Battery Control Unit (BCU)

The BCU is the "brain" of the BMS. It's a central processing unit that receives data from the BMU, makes decisions, and controls the battery's operation.

 

Components:

Microcontroller (MCU): A powerful processor that executes the BMS software, performs calculations, and controls the other components.

Memory: Stores the BMS software, battery parameters, and historical data.

Communication Interfaces: Allow the BCU to communicate with the BMU, other vehicle systems (e.g., VCU), and external devices (e.g., chargers).

Gate Drivers: Control the switching of power electronic devices (e.g., MOSFETs) in the charging and discharging circuits.

 

Working:

1. The BCU receives data from the BMU (voltage, current, temperature).
2. The MCU processes this data to:
3. Calculate State of Charge (SOC) and State of Health (SOH).
4. Determine if any protection thresholds have been exceeded.
5. Implement cell balancing algorithms.
6. Control the charging and discharging process.
7. The BCU sends control signals to:
8. Cell balancing circuits: To equalize cell voltages.
9. Charging/discharging circuits: To regulate current and voltage.
10. Cooling/heating systems: To maintain optimal temperature.
11. External systems: To communicate battery status and receive commands.

3. Cell Balancing Circuit

Cell balancing circuits are integrated into the BMU or as separate modules. They are connected to each cell or cell group.

 

Components:

Passive Balancing:

• Resistors: Used to dissipate excess energy from higher-voltage cells.

• Switches (e.g., MOSFETs): Control the connection of the resistors to the cells.

Active Balancing:

• DC-DC Converters (e.g., buck-boost converters): Transfer energy between cells.

• Capacitors or Inductors: Used as energy storage elements in the transfer process.

• Switches (e.g., MOSFETs): Control the flow of energy between cells.

Working:

Passive Balancing: When a cell's voltage exceeds a certain threshold, the corresponding switch is closed, connecting the resistor. The resistor dissipates the excess energy as heat, lowering the cell's voltage.

Active Balancing: Energy is transferred from higher-voltage cells to lower-voltage cells using the DC-DC converter and energy storage elements. This is a more efficient method as it doesn't waste energy as heat.

4. Protection Circuit

The protection circuit is typically implemented within the BCU and uses dedicated hardware and software to ensure fast and reliable response to fault conditions.

Components:

Comparators: Compare measured values (voltage, current, temperature) to predefined thresholds.

Logic Gates: Combine the outputs of the comparators to generate protection signals.

Switches (e.g., MOSFETs, relays): Disconnect the battery from the load or charger in case of a fault.

Working:

1. Comparators continuously monitor voltage, current, and temperature.
2. If any of these parameters exceed their safe limits, the comparators trigger a protection signal.
3. Logic gates combine these signals to generate a final protection command.
4. This command activates the switches, disconnecting the battery to prevent damage.

5. Communication Interface

The communication interface is implemented within the BCU and provides connectivity to external systems.

 

Components:

Communication Controllers: Implement communication protocols such as CAN, LIN, SPI, or UART.

Transceivers: Convert digital signals into signals suitable for transmission over the communication bus.

 

Working:

1. The BCU formats data into messages according to the communication protocol.
2. The transceiver converts these messages into electrical signals.
3. These signals are transmitted over the communication bus to other systems.
4. The receiving system decodes the messages and extracts the data.

Benefits of using a BMS

Using a BMS has many benefits, including:

• Increased battery life: By protecting the battery from operating outside its safe operating area, the BMS can help to extend the battery's life.
• Improved battery performance: By ensuring that all cells in the battery pack are balanced, the BMS can help to improve the battery's performance.
• Enhanced safety: The BMS can help to prevent battery fires and other safety hazards.
• Reduced warranty costs: By protecting the battery from damage, the BMS can help to reduce warranty costs.

Pyrofuse or Pyroswitch and how does it works?

 

Pyrofuse or Pyroswitch 

The "pyro" part refers to the small explosive charge within the device.

When triggered, this charge detonates, breaking a connection within the fuse and interrupting the electrical circuit.

This process happens very rapidly, within milliseconds after the collision and triggered by the VECU of an electric vehicle.

Pyro switch or Pyro fuse is an electrical fuse that uses a small explosive charge to quickly and permanently cut off the flow of current in a circuit.

This is typically used in high-voltage battery systems, such as those found in electric vehicles, to prevent fires or other hazards in the event of a crash or short circuit.

Pyro switch function:

• Initiator: This is the small explosive charge. When an electrical signal is sent, it ignites.
• Gas Generation: The explosion creates a rapid expansion of gas.
• Piston: The force of the expanding gas pushes the piston. This piston is the key to how the switch works.

How this translates to a pyro switch:

1. Enclosure: All of this would be contained within a robust, insulated enclosure (likely plastic or ceramic). This enclosure would be the visible "pyro switch" itself.
2. Terminals: The enclosure would have electrical terminals connected to the circuit that needs to be interrupted.
3. Piston Action: The piston's movement is used to break the electrical connection. There are a couple of ways this could happen:
• Direct Break: The piston could directly separate two electrical contacts, physically opening the circuit.
• Cutting Element: The piston could drive a small cutting element (like a blade) that severs a conductive link within the switch.

Structure of the Pyro switch:

Internal Structure of Autoliv Pyro Saftey switchs

                                                                                      

Imagine a small, rectangular or cylindrical box.

• Casing: The outer casing is made of a dark-coloured, robust plastic or ceramic.
• Terminals: Two or more metal terminals protrude from the casing.
• Internal Mechanism (Invisible): Inside, the initiator, gas generation chamber, and piston are arranged as shown in your image.
• External Indication (Possible): There might be a slight bulge or a line on the casing indicating where the piston moves internally. After activation, this area might be visibly deformed or cracked.

Know about lithium cell models?

 

lithium cell model

Lithium cells come in a wide variety of models, each with its own specific designation. Here are some common examples:

Common Shapes and Sizes

• Cylindrical Cells (like AA or AAA batteries, but bigger):

  • 18650: 18mm in diameter, 65mm long. Common in laptops and flashlights.
  • 21700: 21mm in diameter, 70mm long. Used in electric cars and power tools.
  • 26650 & 32650: Even bigger cylinders, for things that need a lot of power.

• Pouch Cells (flat and flexible):

  • Fit well in slim devices like smartphones and tablets.

• Prismatic Cells (boxy):

  • Rectangular blocks are often used in electric cars and large battery packs.

What those extra numbers and letters mean

• They give you more details about the cell's performance, like how much energy it can store and how quickly it can release. For example, in "18650-30Q", the "30Q" tells you about its discharge rate.

Finding the right battery

• Always check the manufacturer's information for the most accurate details about a specific lithium cell model.