In this comprehensive study, we explore the AC charging system of BYD electric vehicles, with a focus on the 2020 BYD Qin EV model. The AC charging process, often referred to as slow charging, is a critical aspect of electric vehicle operation, enabling users to recharge their vehicles from standard household or commercial AC power sources. We delve into the underlying principles, system components, control mechanisms, and common fault scenarios, providing an in-depth analysis supported by mathematical models, tables, and empirical data. The aim is to offer a robust reference for technicians, engineers, and researchers working on BYD EV systems, emphasizing the importance of reliable charging infrastructure for the widespread adoption of electric mobility.
The charging system in electric vehicles encompasses all devices involved in transferring and converting electrical energy from the AC grid to the vehicle’s traction battery pack. For BYD EV models, this includes AC charging, DC charging, and energy recovery during driving. AC charging, being a static method, is particularly relevant for overnight or long-duration charging scenarios. It typically involves lower power levels compared to DC fast charging, making it suitable for home and workplace installations. The BYD car series, including the BYD Qin EV, incorporates advanced power electronics and battery management systems to ensure efficient and safe charging operations.
Types of charging systems for electric vehicles include AC charging, DC charging, wireless charging, and battery swapping technologies. This paper concentrates on AC charging, which utilizes 220 V or 380 V AC power sources to supply energy to the vehicle’s onboard charger. The charging power varies, with common ratings such as 2 kW (8 A), 3 kW (16 A), 7 kW (32 A), and 40 kW (63 A). The BYD EV models are designed to兼容 with these standards, ensuring broad compatibility with public and private charging infrastructure. The efficiency and reliability of AC charging are influenced by factors like grid stability, ambient temperature, and the vehicle’s battery state of health (SOH).
The slow charging system in the BYD Qin EV comprises several key components: the charging pile, charging gun, charging interface, onboard charger, traction battery pack, power distribution unit, charging indicators, body control module (BCM), high-voltage cables, and the battery management system (BMS). Each component plays a vital role in the charging ecosystem. For instance, the traction battery pack in the 2020 BYD Qin EV consists of 10 modules connected in series, with a total of 112 lithium nickel-cobalt-manganese oxide cells. The overall battery voltage is calculated as $$ V_{total} = 3.65 \, \text{V} \times 112 = 408.8 \, \text{V} $$, with a rated capacity of 130 A·h and an energy content of 53.14 kW·h. This high-voltage system requires precise management to prevent overcharging or thermal events.
The onboard charger and integrated power distribution unit in BYD EV models are responsible for converting AC power to DC power for battery charging. This unit also includes a DC/DC converter for auxiliary systems and manages power distribution during vehicle operation. The charging interface, located on the vehicle’s rear right side for AC charging, adheres to GB/T 20234.2—2015 standards, ensuring safety and interoperability. The battery management system (BMS) monitors critical parameters such as voltage, temperature, state of charge (SOC), and state of health (SOH). It controls contactors, regulates power flow, and triggers alarms for abnormal conditions, thereby safeguarding the BYD car during charging and discharging cycles.
To better illustrate the components and their functions, we present Table 1, which summarizes the key elements of the BYD EV slow charging system.
| Component | Function | Key Parameters |
|---|---|---|
| Charging Pile | Supplies AC power from the grid | Voltage: 220 V/380 V, Current: up to 63 A |
| Charging Gun | Connects the pile to the vehicle interface | Resistance values for connection detection |
| Onboard Charger | Converts AC to DC for battery charging | Efficiency: >90%, Power: 2-40 kW |
| Traction Battery Pack | Stores electrical energy | Voltage: 408.8 V, Capacity: 130 A·h |
| Battery Management System | Monitors and controls battery parameters | SOC, SOH, temperature, voltage limits |
| Body Control Module | Manages vehicle communication and requests | CAN bus integration, signal processing |
The control principles of slow charging in BYD EV models are governed by international standards such as GB/T 27930—2023, which defines the digital communication protocol between non-vehicle conductive chargers and electric vehicles. The charging process involves multiple stages: physical connection completion, low-voltage auxiliary power-up, handshake phase, parameter configuration, charging phase, and charging termination. During the physical connection, the charging gun is inserted into the vehicle’s charging port, triggering a series of electrical signals. The vehicle’s control system detects the connection state through resistance measurements at the CC (connection confirm) port. For example, in the BYD Qin EV, the resistance between the CC port and PE (protective earth) port is measured to determine the connection status and cable capacity. In the unconnected state, no resistance is present; in the semi-connected state, the resistance is approximately 3.5 kΩ (RC + R4); and in the fully connected state, it is about 1.5 kΩ (RC alone). This resistance network allows the onboard charger to ascertain the current equipment capacity, such as identifying a 10 A cable when RC is 1.5 kΩ.
The CP (control pilot) signal is crucial for communication between the charging equipment and the BYD EV. It is generated by the AC supply equipment and can be a 12 V level or a 12 V PWM signal, depending on the switch S1 position. Upon initial connection, the CP signal starts as a 12 V level. When the charging gun is connected, the vehicle’s internal resistor R3 forms a voltage divider with the supply equipment’s resistor R1, reducing the voltage at detection point 1 to 9 V. This indicates a successful connection, and the supply equipment enters a ready state. The PWM duty cycle of the CP signal represents the maximum supply current capability, with valid ranges between 8% and 90% as per standards. The voltage at detection points can be modeled using the voltage divider formula: $$ V_{detection} = V_{source} \times \frac{R_{load}}{R_{source} + R_{load}} $$ where, for instance, $$ V_{detection1} = 12 \, \text{V} \times \frac{R3}{R1 + R3} $$ resulting in 9 V under normal conditions.
After the handshake phase, the vehicle control device closes switch S2, further reducing the voltage at detection points 1 and 2 to 6 V. This action signals the supply equipment to close contactors K1 and K2, initiating the charging process. The high-voltage power distribution unit in the BYD car confirms the connection via CC and CP signals and communicates with the BMS through CAN buses. The BMS then engages contactors—pre-charge, main negative, and main positive—to enable power flow to the battery. Throughout this process, the onboard charger and BMS continuously monitor parameters to ensure safety. For example, the charging current I_charge can be derived from the power equation: $$ P = V \times I $$ where P is the charging power, V is the battery voltage, and I is the current. In the BYD EV, with a typical AC charging power of 7 kW and battery voltage of 408.8 V, the current is approximately $$ I = \frac{P}{V} = \frac{7000}{408.8} \approx 17.12 \, \text{A} $$.
Common faults in the BYD EV slow charging system can be categorized into five primary types, each with distinct symptoms and root causes. We analyze these faults based on circuit principles, signal waveforms, and diagnostic data. For instance, Table 2 outlines the fault types, symptoms, and potential causes, providing a quick reference for troubleshooting.
| Fault Type | Symptoms | Potential Causes |
|---|---|---|
| Type 1 | No仪表 display, charging port light off, gun light green flashing | Low battery voltage, BCM failure, wiring issues |
| Type 2 | 仪表 shows “charging connecting” but no power | Power distribution unit fault, gun malfunction, BMS error |
| Type 3 | False charging indication without gun connection | Charging port abnormality, circuit faults |
| Type 4 | Charging with warning lights and limited EV function | Contactor circuit issues, pre-charge failure |
| Type 5 | Charging initiates but stops after minutes | Temperature sensor faults, wiring shorts, charger internal issues |
As a case study, we examine a Type 5 fault where charging starts normally but disconnects after approximately 5 minutes, with the power distribution unit logging error code P158900 (charging port temperature sampling anomaly). The BYD EV仪表 indicates normal charging initially, but the gun disengages without power display, and an alarm sounds. Data streams reveal “charging port temperature过高,” though the vehicle operates normally in drive mode. Potential causes include a faulty temperature sensor, wiring defects, internal charger issues, or a short circuit between the CP signal and temperature sensor ground, leading to abnormal waveforms and charging termination.
The diagnostic process for this BYD car fault involves systematic checks. First, the low-voltage battery is tested, showing 12.15 V—within normal range. Next, the temperature sensor signal line at the onboard charger connector (BK46/7) is measured; under normal conditions, the voltage should be around 2.5 V at room temperature, but it reads 0 V, indicating a short to ground. Similarly, at the charging port connector (KB53B/7), the voltage is 0 V instead of the expected 2.5 V. The ground line (KB53B/8) shows 2.3 V against a normal value below 0.1 V, confirming a short between the signal and ground lines. Resistance measurement between KB53B/7 and KB53B/8 yields 1.3 Ω, whereas the NTC thermistor should have a resistance of approximately 3.7 kΩ at 16°C, calculated using the Steinhart-Hart equation for thermistors: $$ \frac{1}{T} = A + B \ln(R) + C (\ln(R))^3 $$ where T is temperature in Kelvin, R is resistance, and A, B, C are constants. This discrepancy identifies the fault source.
The root cause analysis reveals that the short circuit in the temperature sensor lines of the BYD EV causes the onboard charger to receive incorrect temperature readings, triggering protective measures that limit or halt charging to prevent thermal runaway. This fault underscores the importance of proper wiring insulation and sensor integrity in electric vehicles. The resistance anomaly can be modeled as $$ R_{actual} = R_{normal} + \Delta R_{fault} $$ where ΔR_fault represents the deviation due to the short, leading to erroneous voltage divisions and signal distortions.
In conclusion, this study provides a detailed examination of the AC charging system in BYD electric vehicles, emphasizing the control logic, component interactions, and fault mechanisms. Through mathematical modeling and practical case analyses, we highlight how issues like sensor shorts can disrupt charging in BYD EV models. The insights gained aid in developing more reliable diagnostic protocols and enhance the overall safety and efficiency of BYD car charging systems. Future work could focus on real-time monitoring algorithms and predictive maintenance strategies to further optimize the charging experience for BYD EV users.