Design and study of electromagnetic compatibility of automotive electrical appliances Liu Xinliang (Electricity Division of Product Engineering Department of Shanghai Volkswagen Automotive Co., Ltd., electromagnetic compatibility of Shanghai system has been systematically discussed from three aspects: electromagnetic environment analysis, electromagnetic compatibility design, electromagnetic compatibility test/evaluation; In particular, it systematically analyzes the radio interference conditions in the electromagnetic environment, the high-frequency disturbance emission and the high-frequency electromagnetic interference immunity, and the electrostatic discharge interference rarely involved in the domestic automotive electrical test.
Often attaches importance to electromagnetic disturbance control. Some national and international organizations such as the German Electrical Engineers Association (VDE), the International Electrotechnical Commission (IEC), and the International Special Committee on Radio Interference (CISPR) have established a worldwide and organized electromagnetic disturbance problem. Research cars have long been the focus of electromagnetic compatibility research. Especially after the 1960s, a large number of automotive electrical installations have been introduced. Many countries and international organizations have introduced product electricity for automobiles. The increase of automotive microelectronic equipment is also very fast. The semiconductor logic devices are quite sensitive to electromagnetic interference. In addition, the wavelength of the automotive wiring harness and the high-field-strength frequency band (SW) can be compared. Therefore, there are hidden dangers of strong electromagnetic interference to the in-vehicle electronic system in these frequency bands. The low voltage and high current load characteristics of the vehicle electrical appliance cause its on/off process to generate a lot of pulsed interference on the power supply line, which further aggravates the harsh electromagnetic environment of the vehicle electrical appliance. To this end, the standardization organization collaborates with manufacturers to develop/reference some electromagnetic immunity (EMS). The US automobile OEMs attach great importance to the research and development of EMI and EMS. For example, the Volkswagen (VW) Group established electromagnetic compatibility in the early 1990s. The center is directly translated into electromagnetic compatibility for interference emission, line conduction pulse interference, and 1 bowing electrical equipment or system. According to GB/T4365-1995, it is defined as: “The ability of a device or system to work properly in its electromagnetic environment and not constitute an unacceptable electromagnetic disturbance to anything in the environment†111. That is, equipment (sub-system, system) is common The ability to perform their respective functions in an electromagnetic environment does not result in or is not allowed to be degraded by electromagnetic interference emissions from other devices in the same electromagnetic environment, nor does it cause other devices (subsystems, systems) in the same electromagnetic environment. Degraded by or caused by electromagnetic harassment. 21. EMC is a "study in a limited space, time, and spectrum resources, various electrical equipment (generalized also including organisms) can coexist, and A cutting-edge comprehensive science that does not cause degradation. 3. The theoretical foundations involved include mathematics, electromagnetic field theory, antenna and wave propagation, circuit theory, signal analysis, communication theory, materials science, biomedicine, and mechanical structures. Electromagnetic compatibility issues involve a very wide range of areas such as power, communications, transportation, aerospace, military, computer, and medical.
Since the use of electrical energy for ignition in 1860, the car began a history of electromagnetic disturbances to the surrounding electromagnetic environment. Developed countries are not as low as automotive C radio wave immunity, signal line coupling immunity and electrostatic discharge immunity, and use the relevant TL-EMC standard for EMC testing and certification of parts and vehicle. Described in this article.
2 Electromagnetic environment of automobile The load on the vehicle electrical system is diverse. There are resistive/inductive loads with small impedance and large current, as well as small current and high voltage generating devices and high frequency oscillating signal sources. They are not only externally potential. The harassment emission source is also a source of disturbance to the vehicle-mounted electrical appliances itself; in addition, because the highly mobile car may also be in various imaginable complex electromagnetic fields from low frequency to high frequency, the resulting electromagnetic interference coupling will also affect the automotive electronics. The normal operation of the electrical system. The voltages in automotive electrical systems can be grouped into the following five categories: normal operating voltage, abnormal steady-state voltage, radio interference voltage, transient overvoltage, and electrostatic discharge.
21 normal working voltage In the automotive electrical system with a nominal voltage of 12V, the normal voltage is the normal working voltage provided by the alternator to the powered equipment, generally 12 5~145V. When the car is running normally, the power supply voltage is generally around 142V. However, the supply voltage of the car will change with different working conditions. Under the idling condition, when the electric system has a large load and the battery is partially discharged, the battery voltage may drop to about 10V.
22 Abnormal steady-state voltage In addition to the abnormal voltage caused by short-time short-circuit or power-down, when the battery such as partial discharge starts at low temperature, the voltage of nominal value 12V may drop to about 8V; when the voltage regulator of the alternator In the event of a fault, the excitation current does not pass through the regulator, but directly forms a loop. The output voltage of the alternator will rise to 18V. This voltage may cause the electrolyte to boil and cause the voltage to be as high as 75 ~ 130V. The battery jumper is loose and may be generated. 24V voltage output; during vehicle repair, a 12V back pressure may occur in the error of positive and negative polarity adjustment.
23 Radio Interference Voltage The radio interference voltage on a car comes from two aspects: the source of external interference and the source of interference inside the vehicle. Due to its high maneuverability, the car may be in various imaginable electromagnetic fields, from the low frequency of the 162/3 Hz rail transit line to the GHz high frequency of the radar device. The electromagnetic field strength allowed in the German highway space from 0.15 to 1000 MHz. On the one hand, the lines of the automotive electronic system constitute many undesired sensitive antennas, but on the other hand, the shielding effect obtained by the length and the connection with the vehicle body reduces the range of sensitive frequencies, so that the sensitivity range of the automobile is reduced to 6 MHz to 1 GHz. The short-wave transmitting station of the fixed short-wave transmitting station has a high electromagnetic field near the short-wave transmitting station with high power. The field strength of the German short-wave transmitting antenna near Nauen is as high as 120V/m. FM FM radio and TV transmission due to the antenna The way of setting the field strength generated in the highway space - generally only 10V / 32 mobile phone electromagnetic field strong mobile phone is a potential direct interference source. A network car phone can directly generate a field strength of 40V / m near the car, this field strength As the distance increases, the important mobile communication bands are attenuated according to the E-law. There are amateur bands (power <750W), 2m, 4m, and mobile phone bands (C, D, and ENet frequencies are 470MHz, 960MHz, and 1880MHz, respectively). Electromagnetic field emission power of mobile phones in the frequency range below 1000 MHz, except for these intentional electromagnetic waves
33 Self-generated harassment The internal disturbance of self-generated harassment in the car is mainly caused by various transient electric pulses in the electric vehicle system, sparks between the contacts of the distributor and the gap between the spark plugs, and high-speed friction between the wheels and the ground, body and air. Electrostatic discharge. These self-generated disturbances may cause interference to other electrical appliances in the environment through their own electronic devices. These spontaneous disturbances can be further divided into three groups: broadband interference generated by the device; b spectrum range from 10 kHz to 500 MHz Wideband interference from DC motors and discrete output stages; narrowband interference from on-board digital computers (various ECUs and in-vehicle office digital devices) with a base frequency of ~4000MHz in the c-spectrum range.
When these sources of interference are not descrambled, the voltage induced on the receiving antenna of the car can reach 50 (1 speak V. 24 transient overvoltage. The switching process of the inductive load such as relay or motor on the power supply line can cause interference to the vehicle electrical system. Normal transient overvoltages These transient overvoltages can be divided into energy signals (ms range) and high frequency pulse groups (Ps range). When there is no descrambling, the open circuit voltage of these sources can reach 1kV. 241 The over-voltage of the load abrupt over-voltage can be generated when the alternator suddenly throws a load, such as when the alternator is under rated load and suddenly disconnects from the discharging battery, it will generate severe transient over-voltage when the car is running. The alternator and the battery are suddenly disconnected, and the transient overvoltage amplitude can reach 75 ~ 125V, and the rise time can last 100 decay time can last 100~200ms. This transient overvoltage will generate considerable for electronic products. Power shock.
242 Inductive Load Disconnected Overvoltage The inductive load on the car includes an ignition coil, an electromagnetic relay, an air conditioner clutch, various motors, and an electric horn. This change in transient overvoltage is related to the nature, size, and line impedance of the load. It occurs with a high amplitude negative pulse and a subsequent low amplitude positive pulse. The maximum peak value is up to 300V and the duration is 300ms2. Excitation attenuation overvoltage When the ignition switch is off, the alternator field winding is disconnected from the battery, but there is still electrical connection with other loads. At this time, there is still a self-induced electromotive force on the field winding. The negative pulse pulse amplitude depends on the break. Turn on the instantaneous load and regulator status. If the ignition switch is turned off when the primary ignition circuit is turned off, the strongest transient overvoltage transient overvoltage is generated up to a magnitude of 120V for 200ms. The 244 mutual coupling transient voltage vehicle wires are spread throughout the vehicle. And these long wires are often tied tightly into a wire harness. Unshielded wiring and grounding impedance naturally produce quasi-static inductive/capacitive coupling and resistive coupling in automotive electrical systems. When the potential in adjacent wires changes stepwise, coupling occurs between the inductance and capacitance between the wires. For example, in a three-core cable with a length of 10 m, the signal source Ui between the line terminals 1 and 2 is a thyristor chopper circuit, and the load impedance R2 between the end line terminals 2 and 3 is 100 kO. When the chopping pulse width is When the 5ms chopping voltage is 300V, the voltage induced on the resistor R2 is the term 85, electromagnetic interference and electromagnetic compatibility.
Zhang Linchang. Electromagnetic compatibility and its standards. '97 Beijing International Conference on Electromagnetic Compatibility Standardization.
Liao Chuanshu, Dai Wei. The electromagnetic environment of automotive electronics. Car power (responsibility editor Cheng Cheng)
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