Exploration of new vehicle power supply system

introduction

With the rapid development of automobile industry, people are increasingly pursuing the safety, environmental protection, economy, comfort and other performance of automobiles. Thus, the number of on-board electrical and electronic devices increases rapidly. For example, it has become a trend to use electromagnetic or electric actuators to replace hydraulic and pneumatic actuators. This makes the electric power provided by on-board power supply more and more large. It is the trend to update the on-board power supply system. The on-board power supply system is mainly composed of battery, generator and voltage regulator. The battery and generator are connected in parallel in the vehicle circuit. The generator is the main power supply and the battery is the auxiliary power supply. To improve the electrical power of the on-board power supply, it is natural to start from the battery and generator. Therefore, this paper makes the following exploration on the vehicle power supply system.

1 Existing problems of traditional on-board power supply system

At present, the power consumption of luxury cars is generally 1~3KW, but by 2010, the power consumption of luxury cars will reach more than 10KW. If the 12V low-voltage power supply system is still used, the power supply will bear great pressure. In order to ensure the normal operation of the on-board electrical equipment, it is necessary to increase the cross-sectional area of the harness, which will increase the cost of the vehicle and is not conducive to the optimization of the equipment. For this reason, countries around the world are studying 42V or 48V power supply systems. Theoretically, if the voltage is increased by three times, the current will be reduced by 65%, and the cross-sectional area of the harness will also be greatly reduced. However, the voltage upgrade has brought new problems, that is, the development of new batteries and generators, and the corresponding electrical equipment and electronic devices on the vehicle should also be upgraded, which obviously has a great impact on the current on-board power supply system and electrical equipment, especially in China's national conditions, which is difficult to promote and implement in the short term.

The updating and upgrading of storage battery involves many problems, such as volume, reliability, cost and so on. On-board generators include excitation generators and permanent magnet generators, while traditional excitation generators generally use silicon rectifier alternators, and it is impossible to increase power by increasing the size of the generator. At present, the silicon rectifier alternator generates electricity from the excitation current provided by the battery or self-excitation to the excitation coil, but its efficiency is not high (2W engine power is required for each 1W of electric energy generated), and the output characteristics at idle speed are only 1/4 of the output at full load, low speed power generation is poor, poor reliability, complex technology, short service life, and high failure rate.

2. Development overview of on-board generator

2.1 Overview of improvement of traditional on-board excitation generator

1) The excitation circuit with brush is changed to brushless circuit, which reduces brush and brush ring and avoids friction and poor contact between carbon brush and brush ring. At present, the alternator is widely used, which improves the working efficiency, but increases the magnetic field air gap, large magnetic leakage, low material utilization and high cost;

2) Change the traditional six-tube rectifier circuit to nine-tube, eight-tube and 11-tube rectifier circuit to improve the output power;

3) The output power can be increased by series-parallel conversion of two rectifier bridges with double "Y" windings;

4) Change the traditional mechanical contact regulator to transistor or integrated circuit regulator;

However, these measures have not solved the problems of low efficiency, poor power generation at low speed, poor reliability, complex process, short service life and high failure rate.

2.2 Current development of on-board permanent magnet generator

In recent years, with the development of permanent magnet materials, permanent magnet generators for vehicles have attracted more and more attention in the industry because of their simple structure, high specific power, and good low-speed characteristics. Therefore, the permanent magnet generator with high efficiency, high cost performance and high stability will have high theoretical research value and broad application prospects.

Therefore, the vehicle permanent magnet generator, with its advanced structure and excellent performance, determines the vitality and market competitiveness of the product, will replace the silicon rectifier generator, improve the overall level of the automotive electrical system, and promote the technological progress of China's automotive industry. But at present, the key problems to be solved are:

1) Control of output voltage of vehicle permanent magnet generator: Because the speed and load variation range of vehicle generator in use are large, and it also works in parallel with the battery, it has high requirements for the stability of its output voltage. The rectification constant voltage of permanent magnet generator is the control of the main circuit, which is bound to face the problem of direct control of large current, which puts forward higher requirements for electronic components. Therefore, the voltage control of permanent magnet generator is the key issue, and it is also the key issue to develop permanent magnet generator at present. Although the permanent magnet generator can maintain its magnetic field without external energy, it also makes it extremely difficult to adjust and control its magnetic field from the outside, which limits the application scope of the permanent magnet generator. There are many voltage regulation methods for permanent magnet generators. At present, the typical voltage regulation methods are: (1) parallel and serial electronic regulators; (2) Silicon controlled bridge semi-controlled rectification and voltage stabilization scheme; (3) Adjust the armature winding; (4) Adjust the effective magnetic field; (5) Hybrid excitation.

At present, the regulation circuit of permanent magnet generator in China generally adopts single-phase or three-phase half-controlled bridge rectifier and voltage stabilizing circuit, PWM controlled rectifier and voltage stabilizing circuit, and mechanical regulated rectifier and voltage stabilizing circuit. Compared with the three-phase full-controlled bridge rectifier and voltage stabilizing circuit controlled by the single-chip microcomputer, the cost is lower, and two or more voltages can be controlled at the same time with better effect, which has better practical value.

At present, one of the widely favored schemes is to use three-phase half-controlled bridge rectifier circuit. Among the existing rectifier and voltage stabilizing circuits, the three-phase half-controlled rectifier bridge is controlled by voltage comparison control. Although this mode can realize voltage stabilization, its voltage stabilization performance depends heavily on the operating conditions such as load and speed and relevant parameters. The changes of operating conditions and relevant parameters will affect its voltage stabilization accuracy, and will lead to the oscillation of output voltage, even out of control.

2) Structural design of permanent magnet generator for vehicles and selection of permanent magnet materials: if the permanent magnet generator is improperly designed or used, it may produce irreversible demagnetization (or demagnetization) under the action of armature reaction generated by impact current or severe mechanical vibration when the temperature is too high (neodymium iron boron permanent magnet) or too low (ferrite permanent magnet), which will reduce the performance of the motor, Even if it cannot be used, it is necessary to research and develop the methods and devices for checking the thermal stability of permanent magnet materials suitable for motor manufacturers, and analyze the anti-demagnetization ability of various structural forms to ensure that the permanent magnet generator will not lose its excitation during design and manufacturing.

3 Research ideas of new power supply system

3.1 Voltage upgrade of new power supply system

Because there are many types of automotive electrical appliances, different electrical equipment have different requirements for power supply, some can use 14V, some can use 42V or other kinds of voltage. In this case, the dual-circuit or multi-voltage power supply system can be considered. The existing problems are: the need to configure 12V and high-voltage battery pack, which increases the load of the vehicle, occupies more space and increases the cost; There is also electromagnetic interference generated by DC/DC converter; High voltage transient phenomenon and suppression control method; The power flow direction and distribution of dual-voltage electrical system during vehicle operation; In particular, the safety problem during high-voltage operation, the safety insurance setting is the number one problem, and the standards for insulation and insurance setting should be formulated again.

In view of the above problems, I think another dual-power or multi-power supply scheme can be adopted: that is, the battery still uses the traditional 12V power supply, while the armature winding of the generator uses two or more independent armature windings of 14V and 42V, so that two or more output voltages can be obtained at the same time. The 12V battery is mainly used for the starter, ignition system and some traditional electrical equipment during startup. The 14V of the generator is used for traditional electrical appliances and timely recharge the 12V battery, while the 42V is used for some high-power or some new electrical appliances. The adoption of this power supply system scheme is more conducive to the stable development of the automobile industry.

3.2 Voltage control of new power supply system

The voltage regulating circuit of the generator is regulated by two sets of voltage regulating devices, 14V and 42V. In order to simplify the control circuit and achieve good control effect, these two sets of voltage regulating devices are three-phase full-controlled bridge rectifier circuits controlled by thyristor uniformly distributed by single chip computer. The thyristor bridge semi-controlled rectification and voltage stabilization scheme controlled by a single chip computer with multiple voltages simultaneously: each voltage adopts a group of independent three-phase full-controlled bridge rectification and voltage stabilization circuits, and the trigger circuit of the thyristor is controlled by different I/O ports of the single chip computer according to the reference circuit, sampling detection circuit, comparison circuit and protection circuit. Since the single-chip microcomputer needs 5V DC power supply or is directly supplied by the battery after voltage transformation, another group of 5V windings should be extracted from the armature winding and output after rectification and voltage stabilization.

4 Conclusion

Through research and development, a permanent magnet generator for vehicles that can output 14V and 42V constant DC voltage in the range of 500r/m~10000r/m and under load change conditions is developed to meet the use needs of different electrical equipment for vehicles.