EV Charging Infrastructures

Cheatsheet Content

### Significance of EV in Transportation - **Electrified Modes:** Railways, trams, trolleybuses haul locomotives using electricity. - **Catenary Systems:** Conductive wires overhead for on-the-go electricity tapping (safe, reliable, redundant). - **Public Transportation:** Well-suited for fixed routes, HV electrical systems, power processing, protection, and control. - **Private Transportation:** Fossil fuels offer freedom but have limited availability and high cost. Current infrastructure for refueling IC engines is mature and cost-effective. - **Alternative Modes Expectations:** - Robustness like IC engines. - Greater freedom of movement. - Accessible refueling points, similar to conventional. - Comparable range to conventional vehicles. ### Charging Architecture & Grid Connection - **Key Functional Blocks (AC Charging):** - **AC Input Filter:** Smooths incoming AC power, reduces EMI, protects from high-frequency noise. - **AC/DC PFC Boost Converter:** Converts AC to DC, improves power factor, reduces distortion, enhances grid compatibility. - **DC Link Capacitor:** Stores energy, smooths voltage ripple, acts as buffer, stabilizes DC voltage. - **DC/DC Converter:** Steps down DC voltage for EV battery charging, adjusts voltage/current for optimal performance. - **DC Output Filter:** Reduces high-frequency noise and ripple for clean, stable DC power delivery. - **Control & Monitoring (DSP/Microcontroller):** Continuously monitors, provides feedback, adjusts converters, optimizes performance, ensures safety (overcurrent, overvoltage, thermal conditions). #### 1. On-Board Charging - **Definition:** Integrated within EVs to convert external AC power to DC for battery. Essential for home/public charging. - **Key Elements:** - **AC Inlet:** Connects to external power (Level 1 or 2). - **AC/DC Converter:** Converts AC to regulated DC, typically with PFC. - **Battery Management System (BMS):** Monitors/regulates charging, ensures performance/safety. - **Control Unit:** Oversees operations, manages power flow, coordinates communication. - **Cooling System:** Prevents overheating. - **Connector & Cables:** Safe, insulated connections. - **Benefit:** Allows flexible and efficient charging from various sources. #### 2. Off-Board Charging - **Definition:** External devices supplying DC power directly to EV battery. Used in public/fast-charging stations for rapid charging. - **Key Elements:** - **AC Input:** Receives three-phase AC from grid via transformer. - **Rectifier (AC/DC Converter):** Converts AC to DC, incorporates PFC. - **Power Conditioning Unit (PCU):** Regulates DC power to EV battery. - **Solid-State Transformer (SST):** Replaces LF transformers, improves efficiency, power density, enables bi-directional power flow (V2G). - **Cooling System:** Manages heat from high-power components. - **Control & Communication Systems:** Coordinate between station and EV, ensure charging parameters are safe. - **Benefits:** Fast/ultra-fast charging, significantly higher power levels, reduced charging times. ### EV Integration with the Grid #### 1. AC Bus Architecture - **Setup:** EV charging stations connect to a common AC bus, which interfaces with the grid. - **Power Source:** AC bus receives power via a step-down transformer from the utility grid (250V to 480V). - **AC/DC Converter:** Each charging station has its own AC/DC converter for rectification. - **Functional Description:** - **Modular Approach:** Each charging unit has its own AC/DC rectifier. - **Power Factor Correction (PFC):** Rectifiers include PFC circuits for grid power quality. - **Advantages:** Scalable modular design, mature AC protection equipment, accommodates multiple stations. - **Challenges:** Grid synchronization complexity, reactive power control, potential islanding, potential inefficiencies (multiple rectification stages), increased filters/controllers. #### 2. DC Bus Architecture - **Setup:** Grid supplies power to a centralized AC/DC converter feeding a common DC bus. EV chargers connect directly to this DC bus, eliminating individual rectifiers. - **SST:** May use Solid-State Transformer (SST) for enhanced power density and efficiency. - **Functional Description:** - **Centralized Conversion:** Single, high-capacity AC/DC converter for the DC bus. - **Efficient Power Distribution:** Common DC bus reduces conversion losses. - **Bidirectional Power Flow:** SST enables Vehicle-to-Grid (V2G) functionality. - **Advantages:** - **Higher Efficiency:** Fewer conversion stages. - **Scalability:** Multiple chargers easily added without individual rectifiers. - **Improved Power Quality:** SST provides fault current limitation and isolation. #### 3. Comparison of AC vs. DC Topology | Parameter | AC Bus Topology | DC Bus Topology | |--------------------------|---------------------------------------------------|-------------------------------------------------------| | Conversion Stages | AC/DC rectifier at each charging unit | Centralized AC/DC conversion for the DC bus | | Power Factor Control | PFC required for each charger | Centralized PFC | | System Efficiency | Lower due to multiple AC/DC conversion | Higher due to fewer conversions | | Grid Synchronization Complexity | High | Low | | Grid Integration Flexibility | Moderate | High (with bidirectional power flow) | | Scalability | Easy but with added complexity per unit | High scalability with reduced complexity | | Capital Cost | Lower initial cost | Higher due to centralized infrastructure | | Power Quality | Less optimal (PFC per charger) | Superior (with SST and DC power flow) | ### EV-Charger Classifications #### 1. Slow/Moderate Chargers - **Definition:** Low-capacity chargers (up to 15 kW DC, 22 kW AC) as per Ministry of Power guidelines. - **Types:** - **Bharat AC001 (IS-60309):** Basic AC charger, recharges three vehicles concurrently, 415V 3-phase input, 230V AC output (15A, 3.3 kW per connector). Used for light EVs (e-2W, e-3W, e-4W). - **LEV AC Charger (IS-60309 & IS 17017 Part22/Sec1:2021):** Single-connector AC charger for light EVs, 240V AC (16A). Communicates via Bluetooth Low Energy (BLE). - **Combo LEV AC/DC Charge Point (IS-17017-Part2/Sec7):** Supplies both AC and DC power from a single connector. Input: 230V (single-phase) or 415V (three-phase). Output: AC up to 240V/32A, DC up to 120V/100A. Max charging rate: 7.0 kW (AC), 12.0 kW (DC). - **Bharat DC001:** Delivers Direct Current (DC) power. Input: 3-phase 415V (5-wire). Output: 48V or 72V DC, max 200A. Single GB/T vehicle connector. - **Type-II AC Charger (IS-17017-Part2/Sec2):** Available in 7.4 kW (single-phase), 11 kW (three-phase), and 22 kW (three-phase) models. ### Fast Chargers - **Purpose:** Swiftly recharge EV batteries (up to 80% in 15 minutes). - **Power Rating:** Typically 25 to 500 kW. Crucial for long-distance travel. - **Operation:** Directly supplies DC power to EV's on-board controller. - **Applications:** Four-wheelers, ebuses, trucks. - **Protocols:** CCS-II, CHAdeMO, Pantograph charging. #### 1. CCS-II (IS 17017-Part2/Sec3) - **Description:** European protocol for high-power DC fast charging of e-4W and heavy-duty EVs. - **Specifications:** Input: 415V AC nominal. Output: Up to 1500V DC, 250A. - **Communication:** Uses power line communication (PLC) over the control pilot. #### 2. CHAdeMO Charger (IS 17017-Part2/Sec3) - **Description:** Global quick charging method, standard since March 2013 (TEPCO, Nissan, Mitsubishi, Fuji Heavy Industries, Toyota). "Charge de Move" or "charge for moving." Popular in Japan and Europe for e-4W and heavy-duty EVs. - **Specifications:** Input: 415V AC nominal. Output: Up to 1500V DC, 250A. - **Communication:** Controller receives EV commands via CAN bus; charger sets current based on command. ### Methods of Charging EV - **Challenge:** Charging time and limited battery life. Need for infrastructure to match gasoline refueling speed. - **Categories:** - **Conductive Charging:** Level 1, Level 2, Level 3. - **Inductive Charging:** Static Inductive, Dynamic Inductive. - **Battery Swapping:** Side Swapping, Rear Swapping, Bottom Swapping, Top Swapping. #### Technical Details of EV Charger - **EVSE (Electric Vehicle Supply Equipment):** More than just a connector. Includes mechanical/electrical protection, environmental considerations, user interface, control, communication interface. - **On-Board Charger (part of EV):** Converter is part of EV. - **Off-Board Charger (part of EVSE):** Includes converter, converter control, filter, charging options. Converter is crucial. - **Charging Mode:** Constant Current Constant Voltage (CCCV) or Constant Power Constant Voltage (CPCV). - **PWM Pulses:** Generated to control current/voltage based on operation mode. - **Control Algorithm:** Synchronized with BMS to manage charging/discharging, current/voltage limits. - **AC Filter & DC Filter:** Reduce high-frequency current harmonics and ripples. ### System Based Approach to Understand AC Charging Station - **Level 2 Commercial EV Station:** Feeds AC power from grid directly into EV. - **Components:** - **Current & Voltage Monitoring:** Subsystem monitors power transfer. - **AC Power Relay:** Connects/disconnects EV based on host controller. - **Vehicle Interface Analog Front End:** Controls pilot signal, enables handshake between EV and EVSE, negotiates power status. - **AC/DC Converter:** Provides auxiliary supply for system components. - **Host Microcontroller (MCU):** System controller, manages housekeeping services. - **Vehicle Communication Module:** Interfaces like CAN, RS-485, Ethernet for communication. - **Human-Machine Interface (HMI):** Visual status updates for user experience. ### Power Architectures in EVSE and Onboard Chargers #### 1. Power Factor Correction (PFC) - **Function:** First step in power stage. Transforms input current to sinusoidal waveform in phase with grid voltage. Reduces harmonics, improves power factor. - **Output:** Generates regulated output voltage for downstream DC/DC converter. #### 2. Single-Phase Architecture - **Input:** Single-phase PFC, takes single phase and neutral. - **PFC Options:** Single-stage boost PFC (simplicity, low cost) or interleaved dual-stage PFC (EMI filter design, smaller storage, better thermal dissipation). - **DC/DC:** Follows PFC, provides galvanic isolation, generates output based on high-voltage battery charging profile. - **Topologies:** Resonant inductor-inductor-capacitor (LLC) half bridge, hard-switched half bridge, phase-shifted full bridge, dual half bridge. #### 3. Three-Phase Architecture - **Purpose:** Higher power delivery using three-phase input source. - **Configuration:** Combines three single-phase modules. Input can be phase-to-neutral or phase-to-phase. - **Benefits:** Simpler/more efficient power conversion circuits. Reduced current stress and filtering efforts. Smaller components, lower cost, reduced control complexity for MCU. - **PFC Topology:** Three-phase active bridge is common. - **Control:** Can use one MCU to control PFC and DC/DC. - **Gate Drivers:** Isolated or half-bridge gate drivers with high floating voltage capability are required for PFC stage. Non-isolated gate driver for conventional boost architecture (PFC transistors on low side). ### System Based Approach to Understand DC Charging Station - **Key Difference from AC Stations:** Presence of Power Factor Correction (PFC) and DC-to-DC power stage. - **PFC Stage:** Ensures input current is in phase with grid voltage, improving power factor. - **Multilevel AC/DC Stage:** Converts poly-phase AC from grid to high-voltage DC. - **Second DC/DC Stage:** Generates stable DC for transfer to EV, bypassing onboard charger. - **Power Stage Architectures:** Single-phase and three-phase are most popular for active PFC. #### Level 3 DC Fast Chargers - **Power Range:** 50kW to 300kW. - **Voltage Output:** 300V to 800V DC. - **Charging Time:** Charges existing EV batteries within 30 minutes. - **Placement:** Chargers are off-board due to high power flow, reducing vehicle weight/volume. - **Power Delivery:** Off-board DC fast chargers directly connect to EV battery, bypassing on-board charger. - **Control:** Power control unit (Fig. 1.21.c) uses PI/PID, fuzzy logic, adaptive, sliding mode, neural network controllers. - **Safety:** Managed by charger and BMS. - **DC Output:** Directly fed to battery (2V-450V DC, up to 200A charging current). - **Communication:** Direct communication required (power line communication or CAN network). - **Standards:** J1772 CCS, CHAdeMO, Tesla Supercharger. - **System Requirements:** Microcontrollers and digital power controllers for AC/DC and DC/DC converters' power loops. - **Gate Drivers & Sensors:** Gate drivers/relays for power flow control. Current sensors for feedback. - **HMI (Human-Machine Interface):** Overall system supervisor.