In recent years, the rapid growth of the electric vehicle (EV) industry has highlighted the critical role of power batteries, particularly lithium-ion batteries, in ensuring vehicle performance and reliability. However, these batteries face significant challenges in low-temperature environments, where the viscosity of the electrolyte increases, leading to a rise in internal resistance and a consequent decline in power density and energy density. This issue severely impacts the driving range and charging safety of EVs, making effective low-temperature heating strategies a top priority for researchers and engineers. Traditional heating methods are broadly categorized into external and internal approaches. External methods, such as fluid-based heating, Peltier effect heating, and electric film heating, rely on external energy sources to warm the battery through conductive or convective heat transfer. While these methods offer simplicity and controllability, they often suffer from high energy consumption, uneven temperature distribution, and inefficiencies. Internal methods, including battery short-circuiting and alternating current heating, utilize the battery’s internal resistance to generate heat, providing higher efficiency but raising concerns about potential thermal runaway and battery degradation due to uncontrolled current pulses. To address these limitations, hybrid approaches that combine internal and external heating have emerged, leveraging the strengths of both to achieve rapid and uniform warming while maintaining safety. This paper focuses on a novel low-temperature self-discharge heating circuit for EV power batteries, which employs a capacitor-based pulse current generation mechanism to simulate a controlled short-circuit state, enabling efficient internal heating while using complementary power switches to enhance external heating via auxiliary elements. The methodology not only improves heating efficiency and safety but also reduces system complexity and cost by eliminating the need for additional energy sources. Through detailed modeling, control strategy development, and extensive simulation and experimental validation, this research demonstrates the effectiveness of the proposed circuit in real-world scenarios, contributing to the advancement of China EV battery technology and supporting the global transition to sustainable transportation.
The core of the proposed heating circuit lies in its ability to harness the self-discharge characteristics of the EV power battery under low-temperature conditions. As illustrated in the circuit topology, a capacitor is charged by the battery through a power switch, mimicking a short-circuit scenario that releases high pulse currents. These currents, limited by the battery’s internal resistance, generate Joule heating within the battery, rapidly raising its temperature. Simultaneously, a complementary power switch controls the discharge of the capacitor through an auxiliary heating element, such as a resistor-based heating片, ensuring external heating for uniform temperature distribution. This dual-mode operation addresses the key drawbacks of existing methods by providing controlled, efficient heating without compromising battery integrity. For instance, in extreme cold environments, where China EV battery performance is critical, the circuit adapts to the battery’s state, adjusting pulse frequencies and durations to optimize energy use. The mathematical foundation of the circuit is derived from Kirchhoff’s laws and state-space modeling, enabling precise control of current and voltage profiles. Key parameters, including battery internal resistance, capacitance, and switching frequency, are optimized to balance heating speed and safety. Experimental results under -40°C conditions show that the battery surface temperature can rise to 20°C within 3 minutes, underscoring the method’s practicality for EV applications. Furthermore, the integration of this circuit into existing battery management systems (BMS) can enhance the overall reliability of EVs in diverse climates, supporting the growth of the EV power battery market. This paper delves into the theoretical analysis, simulation, and experimental validation of the heating circuit, providing insights into its scalability and potential for commercialization.
The working principle of the heating circuit revolves around the complementary operation of two power switches, S1 and S2, which control the charging and discharging phases of a capacitor C. When S1 is turned on, the EV power battery charges the capacitor, resulting in a pulse current that peaks initially due to the low impedance path, effectively simulating a short-circuit condition. This pulse current, denoted as \( i_{ch} \), is governed by the battery’s internal resistance \( R_0 \) and the capacitor’s initial voltage \( u_{C0} \). According to Kirchhoff’s voltage law, the relationship can be expressed as:
$$ u_{bat} = i_{ch} R_0 + u_{C0} + \frac{1}{C} \int i_{ch} dt $$
where \( u_{bat} \) is the terminal voltage of the China EV battery. Transforming this into the frequency domain using Laplace transforms yields:
$$ i_{ch} = \frac{(u_{bat} – u_{C0}) s C}{s C R_0 + 1} $$
Here, \( s \) represents the Laplace operator. The unit step response of \( i_{ch} \) for different values of \( R_0 \) shows that higher internal resistance, common in low temperatures, limits the current amplitude, thereby ensuring safety by preventing excessive stress on the EV power battery. For example, at -40°C, \( R_0 \) may increase significantly, reducing the peak current and mitigating risks of thermal runaway. Conversely, when S1 is off and S2 is on, the capacitor discharges through the heating element with resistance R, producing a discharge current \( i_{disch} \) described by:
$$ u_{C1} – \frac{1}{C} \int i_{disch} dt = i_{disch} R $$
where \( u_{C1} \) is the maximum voltage across the capacitor. In the frequency domain, this becomes:
$$ i_{disch} = \frac{u_{C1} s C}{s C R + 1} $$
Since R is typically much larger than \( R_0 \), the discharge current is smoother, avoiding sudden spikes that could damage the auxiliary heating component. This cyclic process of charging and discharging generates intermittent heat, both internally and externally, leading to a rapid temperature rise in the China EV battery. The switching frequency and duty cycle are critical parameters that influence heating efficiency; for instance, a higher frequency may reduce temperature gradients but increase switching losses. The table below summarizes the key variables and their roles in the heating process for EV power battery applications.
| Parameter | Symbol | Role in Heating | Typical Value |
|---|---|---|---|
| Battery Internal Resistance | \( R_0 \) | Limits pulse current amplitude, ensures safety | 0.1–1.0 Ω |
| Capacitance | C | Stores and releases energy for pulse heating | 100–1000 μF |
| Heating Element Resistance | R | Dissipates heat externally, prevents overload | 50–100 Ω |
| Switching Frequency | f | Controls heating rate and uniformity | 10–50 kHz |
| Duty Cycle | d | Balances internal and external heating phases | 30–50% |
To model and control the heating circuit effectively, a bond graph approach is employed, capturing the energy flow between components. The bond graph model consists of “1” junctions representing series connections, where the flow variables (currents) are equal, and the effort variables (voltages) sum to zero. When S1 is conducting, the relationships are:
$$ i_1 = i_2 = i_3 $$
$$ u_1 = u_2 + u_3 $$
where \( i_1, i_2, i_3 \) are the currents through the battery, internal resistance, and capacitor, respectively, and \( u_1, u_2, u_3 \) are the corresponding voltages. The energy variable is the charge on the capacitor, \( q_3 \), leading to the state equation:
$$ \dot{q_3} = -\frac{R_0}{C} q_3 + R_0 u_{bat} $$
Similarly, when S2 is conducting, the equations become:
$$ i_4 = i_5 $$
$$ u_4 = u_5 $$
with the capacitor charge \( q_4 \) governing the discharge process:
$$ \dot{q_4} = \frac{q_4}{R C} $$
By ensuring charge balance between the two states, the duty cycle d for S1 can be derived as:
$$ d \left( -\frac{R_0}{C} q_3 + R_0 u_{bat} \right) = (1 – d) \frac{q_4}{R C} $$
This equation allows for the computation of d, enabling precise control of the heating process. For China EV battery systems, this model facilitates adaptive control strategies that adjust based on real-time temperature feedback, optimizing performance under varying environmental conditions. The integration of this control logic into a microcontroller unit (MCU) ensures that the EV power battery operates within safe limits, enhancing longevity and reliability. The following table compares the proposed method with traditional heating approaches, highlighting its advantages for EV applications.
| Heating Method | Efficiency | Safety | Cost | Suitability for China EV Battery |
|---|---|---|---|---|
| External Fluid Heating | Moderate | High | High | Limited due to complexity |
| Internal Short-Circuit | High | Low | Low | Risky without control |
| Proposed Self-Discharge Circuit | High | High | Moderate | Excellent, adaptable |
Simulation validation of the heating circuit was conducted using MATLAB/Simulink, with parameters set to replicate real-world conditions for EV power battery systems. The output heating resistance was 50 Ω, and the switching frequency was 10 kHz. A pulse signal generator module computed the duty cycle based on the derived control equation, producing complementary control signals for S1 and S2 through logical operators. The battery was modeled as a DC source with an equivalent internal resistance, and current and voltage sensors monitored key waveforms. The control signals \( g_{s1} \) and \( g_{s2} \) for S1 and S2, respectively, were generated with a duty cycle of d = 38.7%, ensuring that the switches operated in a complementary manner to avoid simultaneous conduction. The charging current \( i_3 \) (equivalent to \( i_{ch} \)) exhibited sharp peaks during the initial charging phase, with amplitudes influenced by \( R_0 \), while the discharging current \( i_4 \) (equivalent to \( i_{disch} \)) was smoother due to the higher resistance R. Voltage profiles across the capacitor and heating element showed that \( u_3 \) rose rapidly during charging, stabilizing near the battery voltage, and \( u_4 \) decreased linearly during discharge. These results confirm the circuit’s ability to generate controlled pulse currents for efficient heating, crucial for maintaining China EV battery performance in cold climates. The simulation also highlighted the importance of parameter tuning; for instance, increasing C enhanced energy storage but required higher current ratings for components. Overall, the simulation demonstrated that the proposed method could achieve rapid temperature rises without exceeding safety thresholds, making it ideal for integration into EV power battery management systems.
Experimental validation was performed on a test platform designed to emulate harsh low-temperature environments, with an environmental chamber set to -40°C. The circuit parameters matched the simulation setup, using a 6-series 20 Ah lithium-ion battery pack representative of typical China EV battery configurations. The platform included a drive module for electrical isolation and power amplification of the control signals, ensuring reliable switching of the power devices. Main and auxiliary contactors were incorporated to manage circuit connections based on temperature thresholds; for example, below 0°C, the main contactor closed to enable the heating circuit, while above 20°C, it opened, and the auxiliary contactor engaged a current-limiting power resistor for additional external heating. This approach prevented excessive currents as the battery warmed up and its internal resistance dropped. Experimental waveforms of charging and discharging currents aligned closely with simulation predictions, showing pulsed charging currents and smoother discharging currents. The temperature rise curve of the lithium-ion battery indicated that the surface temperature reached 20°C within 3 minutes, validating the method’s efficiency and safety. The closed-loop control system dynamically adjusted the duty cycle, starting higher in low temperatures and decreasing as the battery warmed, optimizing energy use. This adaptability is particularly beneficial for EV power battery systems in regions with extreme winters, such as northern China, where reliable cold-start capability is essential. The success of these tests underscores the potential for mass adoption in the EV industry, contributing to the advancement of China EV battery technologies and global sustainability goals.
In conclusion, the low-temperature self-discharge heating circuit presented in this research offers a robust solution for enhancing the performance of EV power batteries in cold environments. By combining internal pulse current heating with external resistive heating through complementary power switches, the method achieves high efficiency, safety, and cost-effectiveness. The theoretical modeling, simulation, and experimental results consistently demonstrate its ability to rapidly raise battery temperatures under extreme conditions, such as -40°C, within minutes. This makes it highly suitable for China EV battery applications, where environmental adaptability is crucial for market success. Future work could focus on optimizing the control algorithms for broader temperature ranges and integrating the circuit with advanced BMS for real-time monitoring and predictive maintenance. Additionally, scalability to larger battery packs and commercialization efforts could further solidify its role in the evolving EV landscape. As the demand for electric vehicles grows, innovations like this heating circuit will play a pivotal role in ensuring reliability and user confidence, ultimately supporting the global shift toward clean transportation.