The voltage of the car's power supply has changed from 6V in the 1950s to 12V, and it has a history of more than 50 years. Since 1990, the electricity consumption of automobiles has increased by 5% to 8% every year. The history and trend of the average power load are shown in Figure 1. As automotive technology continues to advance, more and more electrical and electronic systems will be applied to automobiles. This article refers to the address: http:// In the 1990s, the idea of ​​improving the vehicle's power supply voltage proposed by car designers quickly won the unanimous approval of car researchers, car manufacturers, and component manufacturers, and set the relevant standards for the 42V voltage of automotive power. The transformation of the automotive power supply system from the existing l4V standard to the 42V standard has become an inevitable development trend and will be rapidly developed in the next few years, leading to a revolution in automotive electrical and electronic products. The implementation of the new power supply system standards for automobiles will have a huge impact on the traditional products of the automotive electronics industry. This is both a challenge and a rare opportunity for China. We should actively participate in research and development in the process of automotive power supply reform, and be in line with international automotive electrical and electronic products. 1 42V automotive electrical system advantages 1.1 Voltage is safe and easy to get According to the European safety law, the safety voltage of the human body is within 50V. Any system exceeding 60V should have special insulation measures at the wires and connections, which will increase the weight and cost of the system. Therefore, the choice of 42V voltage is to meet the needs of electrical energy, as well as the traditional 12V system, even if it touches the electrode or metal body, it will not pose a threat to human safety. The 42V voltage value is three times that of the current automotive generator output voltage of 14V, and its 36V battery is beneficial to use three conventional 12V lead-acid batteries in series. 1.2 Significantly reduce the cost of automotive wiring harnesses Hyundai has a wire length of 2km, more than 2,000 wire ends and more than 350 hubs. The 42V power system can significantly reduce the weight and cost of these wire harnesses. In theory, the same power is transmitted. The current of the 42V system is only one-third of that of the 14V system, which reduces the current load on the motor and power components, and reduces the transmission loss of the wires and power components to nearly nine. One of the parts, and can reduce the cross-sectional area of ​​the wire to reduce the weight. 1.3 A large number of high-tech applications are widely used With the 42V power system, many previously seemingly impractical or impossible technologies have become feasible. In the 42V electrical system, wire control technology, ride comfort control, electronically heated catalytic converter and solenoid valve system, active suspension and electric four-wheel auxiliary drive can be used more effectively, providing more structural improvements for the vehicle. Big possibility (Table 1). With the 42V power system, some long-running accessories such as power steering pumps, water pumps, cooling fans, air conditioning compressors and air pumps are directly driven by the new power system to reduce idle consumption and improve energy efficiency. For electric brake systems, driven directly by the power supply, hydraulic or pneumatic systems are eliminated, resulting in better driving comfort and better fuel economy. 1.4 can greatly improve the efficiency of the generator At present, the efficiency of silicon rectifier generators used in automobiles is below 60c/~. The silicon rectifier generator has a large output current, and the current density of the armature winding is 10 A/ram. A lot of energy is consumed by the field winding, the armature winding and the rectifying element. The 42V power system provides high current output over the entire engine speed range, with motor efficiency of over 80%. The power output reaches 8kw and above. The output of VDO products is 10~15kW, and the efficiency can reach 85%. 1.5 Conducive to the development of hybrid power vehicles After using the 42V power supply, if the power generation integrated device (ISA) is not activated, the following functions can be realized: 1 When the car starts, the starting acceleration performance is enhanced, and the internal combustion engine is accelerated to a speed exceeding the idle speed in a short time (usually 0.1 to 0.2 s), and then the internal combustion engine starts to ignite, and the engine is not idle; 2 The car is in the parking state for a long time. In case of red light, the control system will automatically cut off the internal combustion engine fuel supply and the internal combustion engine will stop running; 3 When the car is driving normally, the ISA is the generator working condition and charging the battery; 4 When the car accelerates or climbs the hill, the ISA works in the motor working condition, providing auxiliary propulsion power for the engine, making the engine work in the high efficiency zone, improving the efficiency and reducing the fuel consumption. 6) It has a certain research basis: As early as the 1990s, Germany established a car power forum with members such as Volkswagen, Audi, BMW, Opel and Porsche. The agency proposed a draft specification for a 14V/42V dual voltage power supply system. In addition, Ford and the Massachusetts Institute of Technology initiated the MIT/7. Industry Alliance, including GM, Daimler-Benz, BMW, Renault, Siemens, Bosch, Motorola, Delphi and other well-known automakers, parts manufacturers and Electronic telecommunications company. The organization mainly studies the impact and implementation of 14V/42V dual voltage power supply systems on automotive electrical and electronic equipment. The American Society of Automotive Engineers (SAE) also established the Dual/High Voltage Vehicle Electronic Systems Committee. At present, the 42V electrical system structure has been recognized by the international automotive industry and has been adopted in some vehicles, such as Volvo's $80 and Ford's hybrid vehicle Explorer. 2 operating mode In the new electrical system, there are two implementations: one is a full-voltage 42V single voltage solution; the other is a 42V/14V dual voltage scheme 5. The single voltage scheme for the 42V electrical system is shown in Figure 2: The 42V single voltage will have a big impact on the current auto parts manufacturers, so promotion has certain difficulties. 2.2 42V/14V dual voltage operation mode Due to the wide range of product technical transformations involved in the 42V power system, there are many voices against voltage upgrades, especially component suppliers, because product retrofits will increase their cost. Therefore, as a transitional phase of 42V/14V The solution of the dual voltage system is being paid more and more attention. Dual-voltage systems have less impact on existing auto parts manufacturers, so the auto industry tends to do so. The dual voltage system shown in Figure 3 requires a DC/DC converter to convert the 42V voltage to a 14V voltage, thus requiring two batteries (12V and 36V). Only when a large number of components are adapted to the 42V vehicle power supply, can mass production of pure 42V vehicle power. The dual voltage system divides the automobile electrical appliance and the electronic control device into two groups according to the power consumption. The traditional medium and small power electrical appliances are a group, such as lamps, instruments, electric wipers, etc., which are powered by 14V power supply; The engine control unit, heating, electric suspension and other electrical appliances are directly powered by a 42V power supply. After the alternator is rectified and regulated, 42V voltage is supplied to the high-power load and the 36V battery is charged, and the 42V voltage is supplied to the l4V electrical system after the DC/DC converter. 3 Design of rare earth permanent magnet generator The shift from 12V to 42V power supply system has also brought about major changes in automotive electrical components, such as new neon batteries, starters, and generators. The 42V automotive power system mainly consists of a 42V generator, a 36V battery and a DC/DC DC converter. The 36V battery can be connected in series by three 12V batteries, and many DC/DC converters have been developed. There are currently three main generators to choose from: 1) Permanent magnet generator. Permanent magnet motors have high energy conversion efficiency and reliability. 2) Brushed silicon rectifier generator. At present, most of the cars used are brushed silicon rectifier generators, but the machine has a carbon brush slip ring device, the carbon brush is easy to wear, the life is short, and the failure rate is high. 3) Brushless silicon rectifier generator. It is easy to maintain and has high reliability, but the machine increases the magnetic field air gap, large magnetic leakage, low material utilization and high cost. At present, rare earth permanent magnet materials have already achieved high cost performance, and modern power electronics technology has laid a foundation for the development of chopper-type electronic voltage regulators. Therefore, the use of rare earth permanent magnet materials and modern power electronic components to develop a simple structure, high power generation efficiency, long life of 42V rare earth permanent magnet generators has a high research value and broad prospects for promotion. The schematic diagram of the designed NdFeB permanent magnet power generator is shown in Figure 4. A three-phase half-controlled bridge rectifier voltage regulator circuit (Figure 5) has also been developed. The circuit consists of a three-phase half-controlled bridge rectifier circuit, a voltage signal sampling circuit and a trigger circuit. When the generator output voltage is lower than the target regulation value, the electronic regulator is a three-phase rectified output. When the output voltage of the generator is higher than the target voltage regulation value, the voltage signal sampling circuit automatically disconnects the three-phase half-bridge rectifier circuit instantaneously, reducing the output of the electric medicine when the generator output voltage is lower than the target voltage regulation value, the three-phase The semi-controlled bridge rectifier circuit resumes its work and resumes. Through rectification and chopping, the DC power of the generator output voltage is guaranteed. 4 performance test 42v permanent magnet generator adopts 12 pole pole shoe star rotor type three-phase permanent magnet synchronous generator, generator rated voltage, 42V; rated power, 3000W; rated speed, 4000r/mln. The magnetic material is selected from NdFeB NTP30H, the residual magnetic induction intensity is Br=1.12T, the magnetic field strength is Hc=790kA/m, and the maximum magnetic energy product is 224-256kJ/m. Under the condition of load power of 2800, 3000 and 3200W, the performance of the newly developed three-phase half-controlled bridge rectifier-regulated NdFeB permanent magnet generator from low speed to high speed is tested. The test results are shown in Table 2. It can be seen from Table 2 that when the generator speed changes from 2000r/min to 4800r/min, the load power is changed from 2800W to 3200W, and the output voltage is stable between 37.17 and 42.63V. This performance index meets the design requirements. 5 Conclusion 1) The current development of automotive power systems from 14V to 42V is an inevitable trend, just as the upgrade of 6V power to the current 12V power supply in the 1950s is unstoppable. 2) As a transitional phase, the study of the 42V/14V dual voltage system will be a research and development hot spot in the automotive industry in the recent period. 3) The implementation of the 42V automotive power supply system standard will have a huge impact on automotive electrical and electronic equipment, and will also bring a new round of technological revolution to the entire automotive industry.
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