Furthermore, we can see that hybrid vehicles refer to vehicles that use two or more power sources for propulsion, typically including an internal combustion engine and another new energy source. During actual driving, energy can be recovered, stored, and reused, resulting in a high energy efficiency ratio for hybrid vehicles, saving fuel and making them popular among many drivers.
Can plug-in hybrid electric vehicles be charged?
Yes. The biggest feature of plug-in hybrid electric vehicles (PHEVs) is that they can be charged; the car has a battery that can be charged. This means that during daily driving, you can choose to drive in battery-powered mode, and when the battery is low, you can charge it through an external charging port to ensure normal driving next time. The advantage of this is that PHEVs can achieve zero fuel consumption, directly driven by the battery's power. Of course, for long-distance driving, they can also be driven by gasoline, thus achieving the effect of new energy driving for short and medium distances.
Can hybrid vehicles be registered with new energy vehicle license plates?
Pure hybrid vehicles cannot use new energy vehicle license plates, while plug-in hybrid vehicles can. Therefore, we will see a wider range of applications for plug-in hybrids. Compared to pure electric vehicles, they offer a gasoline-powered driving mode, making them a good option while pure electric vehicles have not yet fully resolved their range issues. Pure hybrid vehicles, on the other hand, cannot be connected to an external power source and still require gasoline for propulsion, so they will gradually be replaced by plug-in hybrids and pure electric vehicles.
Why can plug-in hybrid electric vehicles enjoy the same license plate as new energy vehicles?
This is mainly due to the mechanical principles of plug-in hybrid electric vehicles (PHEVs), which include an external charging port. We can determine the pure electric range based on the PHEV's battery capacity, allowing us to utilize that range for commuting. Therefore, PHEVs can achieve the same level of performance as pure electric vehicles for a period of time, which is the primary reason they are eligible for new energy vehicle license plates.
The primary energy source for pure electric vehicles is the power battery system, whose performance directly impacts the vehicle's economy, power, and reliability. The biggest difference between electric vehicles and traditional gasoline-powered vehicles is the use of a power battery for propulsion. As a crucial link connecting the battery pack, the vehicle system, and the motor, the importance of the Battery Management System (BMS) is self-evident. A well-designed BMS can effectively improve battery utilization, prevent overcharging and over-discharging, extend battery life, monitor the operating status of the battery pack and individual cells, effectively prevent battery pack spontaneous combustion, and provide early warning of emergencies, thus buying time for safety.
This article outlines the key technologies in the development of battery management systems (BMS) to provide a theoretical foundation for the design, testing, and production of power battery management systems. The plan is to divide this into five chapters to organize the key technologies in BMS development; today, we will begin with the fourth chapter, a discussion of power battery thermal management design.
As discussed in previous chapters, battery temperature significantly impacts the estimation of battery state parameters and battery balancing strategies. A well-designed battery temperature control system within the battery management system is crucial for battery operation. Therefore, we need to analyze the battery's heat generation and transfer mechanisms, then use a single-cell model to construct a battery pack for simulation design, select a suitable phase change material as the heat storage material during battery operation, and accurately design the battery pack's heat dissipation structure.
The heat generation mechanism of power batteries
The heat generated by lithium-ion batteries is generally divided into four parts: reaction heat, Joule heat, polarization heat, and side reaction heat. Related studies show that when the battery temperature is below 70°C, the battery heat mainly consists of Joule heat and polarization heat. When the battery temperature rises above 70°C, the reaction heat increases significantly and accounts for the majority of the battery heat.
Heat transfer mechanism of power battery
According to the second law of thermodynamics, heat transfer occurs wherever there is a temperature difference, and it always occurs from a higher-temperature object to a lower-temperature object. The three basic modes of heat transfer are conduction, convection, and radiation. For lithium-ion batteries, all three modes of heat transfer may occur.
The porous structure of the positive and negative electrode materials and separator in lithium batteries, coupled with the near-static state of the electrolyte, results in negligible heat convection. The battery casing is opaque and contains encapsulating materials, minimizing internal heat radiation; heat conduction is the primary mode of heat transfer. While the internal heat conduction characteristics of a battery are inherent to its own factors, we cannot alter them. However, we can modify the heat exchange medium and conditions between the battery surface and the external environment. Therefore, we need to consider the heat exchange between the battery and its surroundings to design a more efficient battery thermal management system.
Establishment and Validation of Thermal Model for Single Cell
Establishing a thermal model for a single lithium-ion battery is crucial for simulating real-time heat generation during charging and discharging. Industry standards typically calculate battery thermal properties based on equivalent specific heat capacity, thermal conductivity, density, and heat generation rate. A lithium-ion battery thermal model was established using simulation software (Anasys Fluent) to simulate the heat generation temperature field. Experiments show that the battery temperature rise curve is directly proportional to the battery discharge rate, and the battery thermal model can accurately simulate changes in the battery surface temperature field.
Battery pack heat dissipation methods
Depending on the heat transfer medium, battery cooling methods are mainly divided into three types: air cooling, liquid cooling, and phase change material (PCT) cooling. Air cooling is simple in structure, has no risk of leakage, and is relatively inexpensive. However, its disadvantages include a low heat transfer coefficient with the battery wall and slow heating speed. Liquid cooling has advantages such as a high heat transfer coefficient, fast cooling speed, and small size, but it is heavy, has a risk of leakage, and its structure is relatively complex. Battery thermal management systems using PCTs as the heat dissipation medium can control the maximum temperature difference of the battery pack within a small range due to the constant temperature characteristic of PCTs during phase change. Furthermore, the latent heat of phase change is relatively high, allowing a small amount of material to store a large amount of heat, significantly reducing weight and contributing to vehicle lightweighting. Another significant advantage is that it does not consume battery energy. Phase change materials have become an ideal medium for cooling power batteries.
Currently, the main components of novel lightweight, shape-stable composite phase change materials include paraffin wax, expanded graphite, high-density ethylene, and carbon fiber. There are two current trends in the development of phase change materials:
◎The efficiency of thermally conductive materials is improved by adjusting the component ratio.
◎Optimize the arrangement and strength of phase change materials, for example, by increasing strength through 3D printing of honeycomb structures, while ensuring that the thermal conductivity of the phase change materials is not changed after structural optimization.
Summarize:
1. Battery thermal management systems based on phase change materials (PCMs) offer many advantages; however, PCMs have limited latent heat storage. In extreme cases, the battery cannot absorb all the heat generated, leading to thermal runaway. Therefore, major battery manufacturers often combine PCMs with liquid cooling.
2. Further improve the safety performance and fault diagnosis technology of BMS. Safety performance includes thermal management safety and battery high voltage safety. How to more stably control the internal thermal balance of the battery to prevent damage to the vehicle and driver, especially under the impact of external forces on the vehicle, requires a lot of experimental research on battery management safety performance. When the above measures fail, the battery management system should be able to make timely and effective judgments and warnings to ensure the safety of personnel and vehicles. These will be the key research directions.
The differences between hybrid and plug-in electric vehicles are as follows:
1. Different charging methods. Plug-in hybrid electric vehicles (PHEVs) require charging due to their larger batteries, while regular hybrid electric vehicles (HEVs) do not. PHEVs also have larger batteries and more powerful motors, resulting in a longer driving range in pure electric mode.
2. Different license plate types. Ordinary hybrid vehicles can only use blue license plates, while plug-in hybrid vehicles and pure electric vehicles require green new energy vehicle license plates.
3. Performance, driving range, and fuel consumption differ. Plug-in hybrid electric vehicles (PHEVs) offer stronger performance, longer driving range in pure electric mode, and lower fuel consumption.
4. The functions of the electric motors differ. In ordinary hybrid vehicles, the electric motor mostly serves to assist the engine, only using it to provide power during low-speed driving or starting.
5. Different price ranges. Plug-in hybrid electric vehicles are generally more expensive, and some high-end brands also offer plug-in hybrid versions of their premium models.
