Mainly based on the performance of the circuit, for digital signal 3.3V circuits, 2. There may also be a need to separate the ground of 5V circuits and 5V circuits. Even for digital circuits with the same power supply, there are sometimes wiring requirements, such as the grounding of high current IO parts, which may need to be handled separately.

    The earth generally refers to the casing, which requires ESD and shielding. Sometimes the circuit is connected to the casing through a 1M resistor, and sometimes directly. It should be handled according to the requirements of the application and ESD.

    In short, the logical connection characteristics of the ground and the physical characteristics on the PCB need to be distinguished. In theory, the ground is at zero voltage, but in practical PCBA, there is a lot of noise and rebound in the ground.

    Regarding grounding: digital grounding, analog grounding, signal grounding, AC grounding, DC grounding, shielding grounding, floating grounding

    In addition to proper grounding design and installation, it is also necessary to properly ground various signals. In the control system, there are generally the following types of ground wires:

    (1) Digitally: also known as logically, it is the zero potential of various switching signals (digital signals).

    (2) Simulated ground: refers to the zero potential of various analog signals.

    (3) Signal ground: usually the ground of the sensor.

    (4) AC ground: The ground wire of an AC power supply, which is usually a place that produces noise.

    (5) DC ground: The ground of a DC power supply.

    (6) Shielding ground: also known as casing ground, is designed to prevent electrostatic induction and magnetic field induction.

    The above ground wire handling is an important issue in system design, installation, and debugging. Below are some opinions on grounding issues:

    (1) The control system should be grounded at one point. In general, high-frequency circuits should be grounded at multiple points nearby, while low-frequency circuits should be grounded at one point. In low-frequency circuits, the wiring and inductance between components are not a big problem, but the interference caused by the loop formed by grounding is significant. Therefore, a point is often used as the grounding point; But one point grounding is not suitable for high frequencies, because at high frequencies, there is inductance on the ground wire, which increases the impedance of the ground wire, and at the same time, inductive coupling occurs between the ground wires. Generally speaking, when the frequency is below 1MHz, one point of grounding can be used; When above 10MHz, use multi-point grounding; Between 1-10MHz, one or multiple grounding points can be used.

    (2) The communication and signal points cannot be shared. Due to the presence of several mV or even several V voltage between two points of a power supply ground wire, this is a very important interference for low-level signal circuits and must be isolated and prevented.

    (3) Comparison between floating ground and grounding. The whole aircraft floats in the air, which means that all parts of the system are floating on the ground. This method is simple, but the insulation resistance between the entire system and the ground cannot be less than 50M Ω. This method has a certain anti-interference ability, but once the insulation drops, it will cause interference. Another method is to ground the casing and float the rest. This method has strong anti-interference ability, is safe and reliable, but it is relatively complex to implement.

    (4) Simulated. The connection method of simulated ground is very important. In order to improve the ability to resist common mode interference, shielded floating technology can be used for analog signals. The grounding treatment of specific analog signals should be strictly designed according to the requirements in the operation manual.

    (5) Shielded ground. In order to reduce capacitance coupling noise in the signal, accurately detect and control it, it is necessary to adopt shielding measures for the signal in the control system. The grounding method for shielding varies depending on the purpose of the shielding. Electric field shielding solves the problem of distributed capacitance, generally grounded; Electromagnetic field shielding mainly avoids high-frequency electromagnetic field radiation interference such as radar and radio. Made of low resistance metal materials with high conductivity, it can be grounded to the ground. Magnetic field shielding is used to prevent magnetic induction in magnets, motors, transformers, coils, etc. The shielding method is to use high conductivity magnetic materials to close the magnetic circuit, and it is generally better to ground it. When the signal circuit is grounded at one point, the shielding layer of the low-frequency cable should also be grounded at one point. If there is more than one shielding layer on the cable, noise current will be generated, forming a source of noise interference. When a circuit has an ungrounded signal source connected to a grounded amplifier in the system, the shielding at the input end should be connected to the common end of the amplifier; On the contrary, when a grounded signal source is connected to an ungrounded amplifier in the system, the input terminal of the amplifier should also be connected to the common terminal of the signal source.

    For the grounding of electrical systems, it should be classified according to the requirements and purposes of grounding. Different types of grounding should not be simply or arbitrarily connected together, but should be divided into several independent grounding subsystems, each with its own common grounding point or grounding main line, and finally connected together to implement overall grounding.

    Q&A

    Q1: Why is grounding necessary?

    Answer: The introduction of grounding technology was originally a protective measure taken to prevent power or electronic equipment from being struck by lightning. The purpose was to introduce the lightning current generated by lightning through lightning rods to the ground, thereby playing a role in protecting buildings. At the same time, grounding is also an effective means of protecting personal safety. When the phase lines (such as poor insulation of wires, aging of circuits, etc.) come into contact with the equipment casing due to certain reasons, the equipment casing will be dangerous

    Voltage is generated, and the resulting fault current will flow through the PE line to the ground, thereby providing protection. With the development of electronic communication and other digital fields, considering only lightning protection and safety in grounding systems is far from sufficient

    I have requested it. For example, in communication systems, the interconnection of signals between a large number of devices requires each device to have a reference ground as the signal reference ground. Moreover, with the complexity of electronic devices, signal frequencies are increasing. Therefore, in grounding design, electromagnetic compatibility issues such as signal interference must be given special attention. Otherwise, improper grounding will seriously affect the reliability and stability of system operation. Recently, signal backflow technology for high-speed signals

    The concept of "land" was also introduced in the article.

    Q2: Definition of Grounding

    Answer:

    In modern grounding concepts, for line engineers, the meaning of this term is usually ‘the reference point of line voltage‘; For system designers, it is often a cabinet or rack; For electrical engineers, it means green safety ground wire or connecting to the ground. A common definition is "grounding is the low impedance channel through which current returns to its source.". Please note that the requirements are "low impedance" and "path".
    Q3: Common grounding symbols

    Answer:

    PE, PGND, FG - protective ground or casing; BGND or DC-RETURN-DC-48V (+24V) power supply (battery) return current; GND - workplace; DGND - Digital Ground; AGND - Simulated ground; LGND - Lightning protection ground GND is often used as a voltage reference point in circuits. Electrically speaking, GND is divided into power ground and signal ground. PG stands for Power Ground. The other is Signal Ground. Actually, they may be connected together (not necessarily mixed together!). Two names, mainly for the purpose of analyzing circuits. Furthermore, there are two types of "ground" that must be distinguished due to different circuit forms: digital ground, analog ground. Both digital ground and analog ground have signal ground and power ground. Some circuits can be directly connected between digital ground and analog ground, some circuits need to be connected with reactors, and some circuits cannot be connected.

    Q4: Suitable grounding method

    Answer:

    There are various grounding methods, including single point grounding, multi-point grounding, and mixed types of grounding. Single point grounding can be divided into series single point grounding and parallel single point grounding. Generally speaking, single point grounding is used for simple circuits, distinguishing grounding between different functional modules, and low-frequency (f<1MHz) electronic circuits. When designing high-frequency (f>10MHz) circuits, it is necessary to use multi-point grounding or multi-layer boards (complete ground plane layers).

    Q5: Introduction to Signal Backflow and Cross Segmentation

    Answer: For an electronic signal, it needs to find a path for the lowest impedance current to return to ground, so how to handle this signal return becomes very crucial.

    Firstly, according to the formula, it can be known that the radiation intensity is directly proportional to the circuit area. That is to say, the longer the path that reflow needs to take, the larger the formed loop, and the greater the interference from external radiation. Therefore, when laying out PCB boards, it is necessary to

    Minimize the area of power and signal circuits as much as possible.

    Secondly, for a high-speed signal, providing a good signal return can ensure its signal quality. This is because the characteristic impedance of the PCB transmission line is generally calculated based on the ground layer (or power layer) as a reference. If

    There is a continuous ground plane near the high-speed line, so that the impedance of this line can remain continuous. If there is no ground reference near a section of the line, the impedance will change, and the discontinuous impedance will affect the integrity of the signal. So, when wiring, it is necessary to allocate the high-speed line to a layer close to the ground plane, or to walk one or two ground wires next to the high-speed line, to serve as a shield and provide nearby backflow.

    Thirdly, why do we try not to divide the wiring across power sources when it comes to wiring? This is also because after the signal crosses different power layers, its return path will be very long, making it susceptible to interference. Of course, it is not a strict requirement to not cross power division. It is acceptable for low-speed signals because the interference generated can be ignored compared to the signal. For high-speed signals, it is necessary to carefully check and try not to cross them. You can adjust the wiring of the power supply section. (This is for the situation of multiple power supplies on multi-layer boards)

    Q6: Why do we need to separate analog and digital ground, and how do we separate them?

    Answer: Both analog and digital signals need to return to the ground because digital signals change rapidly, causing significant noise on the digital ground. Analog signals require a clean ground reference for operation. If analog and digital are mixed together, noise will affect the analog signal.

    Generally speaking, analog ground and digital ground need to be processed separately, and then connected together through thin wiring or single point connection. The overall idea is to try to block the noise from the digital ground from flowing to the analog ground as much as possible. Of course, this is not a very strict requirement that analog and digital ground must be separated. If the digital ground near the analog part is still very clean, it can be combined together.

    Q7: How to ground the signal on the board?

    Answer: For general devices, nearby grounding is the best option. After adopting a multi-layer board design with a complete ground plane, grounding for general signals is very easy. The basic principle is to ensure continuity of wiring and reduce the number of through holes; Near ground level or power supply level, etc.

    Q8: How to ground the interface components of a single board?

    Answer: Some boards may have external input and output interfaces, such as serial connectors, network RJ45 connectors, etc. If their grounding design is not good, it can also affect normal operation, such as network port interconnection errors, packet loss, etc., and become an external electromagnetic interference source, sending out the noise inside the board. Generally speaking, a separate interface ground will be separated, and the connection with the signal ground will be connected through thin wiring, which can be connected in series with a resistance of 0 ohms or a small resistance value. Thin wiring can be used to block signal ground noise from passing to the interface ground. Similarly, careful consideration should be given to filtering the interface ground and interface power supply.
    Q9: How is the shielding layer of a shielded cable grounded?

    Answer: The shielding layer of the shielded cable should be connected to the interface ground of the single board instead of the signal ground. This is because there are various noises on the signal ground. If the shielding layer is connected to the signal ground, the noise voltage will drive the common mode current to interfere outward along the shielding layer. Therefore, poorly designed cables are generally the largest noise output source of electromagnetic interference. Of course, the prerequisite is that the interface ground should also be very clean and used for labeling in the mixed circuit. VCC represents analog signal power supply, GND represents analog signal ground, VDD represents digital signal power supply, and VSS represents digital power supply ground.

    VCC mainly represents the power supply of Bipolar circuits, C represents the collector, and the power supply is generally connected to the collector of NPN (or the emitter of PNP). When integrated circuits first appeared, only NPN transistors were used, and later PNP transistors were integrated. VDD/VSS generally represents the power and ground of MOS circuits, while D/S respectively represents the Drain/Source of MOS transistors.

    1、 Explain that VCC: C=circuit represents the meaning of a circuit, that is, the voltage connected to the circuit;

    VDD: D=device represents the working voltage inside the device;

    VS: S=series means common connection, usually referring to the voltage at the common ground terminal of the circuit.

    2、 Explanation

    1. For digital circuits, VCC is the power supply voltage of the circuit, VDD is the operating voltage of the chip (usually Vcc>Vdd), and VSS is the grounding point.

    2. Some ICs have both VDD and VCC pins, indicating that these devices have their own voltage conversion function.

    3. In field-effect transistors (or COMS devices), VDD is the drain, VSS is the source, and VDD and VSS refer to the component pins, not the supply voltage.

    VDD: Power supply voltage (unipolar device); Power supply voltage (4000 series digital circuit); Drain voltage (field-effect transistor)

    VCC: Power supply voltage (bipolar device); Power supply voltage (74 series digital circuit); Voice controlled carrier

    ControlledCarrier

    VS: Ground or power negative pole

    VEE: Negative voltage supply; Source of field-effect transistor (S)

    VPP: Programming/erasing voltage.

    Detailed explanation:

    In electronic circuits, VCC is the power supply voltage of the circuit, and VDD is the operating voltage of the chip:

    VCC: C=circuit represents the meaning of a circuit, which is the voltage connected to the circuit,

    D=device represents the meaning of the device, which is the working voltage inside the device. In ordinary electronic circuits, Vcc is generally greater than Vdd!

    VS: S=series means public connection, which is the negative pole.

    Some ICs have both VCC and VDD,

    This device has a voltage conversion function.

    In the "field effect" of COMS components, VDD is the drain pin of CMOS, and VSS is the source pin of CMOS,

    This is a component pin symbol, which does not have the name "VCC". Your question contains three symbols: VCC/VDD/VSS,

    This is obviously a circuit symbol

    Grounding technology in electromagnetic compatibility

    Abstract: This article discusses the grounding technology in electromagnetic compatibility, including the types and purposes of grounding, grounding methods, calculation of grounding resistance, and grounding of equipment and systems. Its main purpose is to improve the electromagnetic compatibility capability of power electronic equipment.

    Keywords: Grounding technology; Electromagnetic compatibility; interfere
    1.Introduction

    Grounding technology was first applied in strong electrical systems (power systems, transmission and transformation equipment, electrical equipment). For the safety of equipment and personnel, the grounding wire is directly connected to the ground. Due to the very large capacitance of the earth, the potential of the earth can generally be considered as zero potential. Later, grounding technology was extended and applied to weak current systems. For power electronic equipment, when the grounding wire is directly connected to the ground or a conductor used as a reference potential, there should be no voltage drop when the current passes through the reference potential. However, due to unreasonable grounding, electromagnetic interference such as common ground interference and ground loop interference can be introduced, leading to abnormal operation of power electronic equipment. It can be seen that grounding technology is one of the important contents of electromagnetic compatibility technology for power electronic equipment, and it is necessary to conduct detailed discussions on grounding technology.

    2.Types and purposes of grounding

    Power electronic equipment is generally grounded for the following purposes:

    2.1 Safe grounding

    Safe grounding is about grounding the casing. One is to prevent the accumulation of charges on the casing, which may cause electrostatic discharge and endanger equipment and personal safety; Secondly, when the insulation of the equipment is damaged and the casing is charged, the protection action of the power supply is triggered to cut off the power supply, in order to protect the safety of workers.

    2.2 Lightning protection grounding

    When power electronic devices are struck by lightning, whether it is direct or induced, they will suffer great damage. To prevent lightning strikes, lightning rods are installed to prevent endangering equipment and personal safety during lightning strikes.

    The above two types of grounding are mainly for safety considerations, and both should be directly connected to the ground.

    2.3 Work grounding

    Working grounding is a reference potential provided for the normal operation of a circuit. The reference potential can be set as a point, segment, or block in the circuit system. When the reference potential is not connected to the earth, it is considered as the relative zero potential. This relative zero potential will change with changes in the external electromagnetic field, leading to instability in the operation of the circuit system. When the reference potential is connected to the earth, it is considered as the zero potential of the earth and does not change with changes in the external electromagnetic field. But incorrect grounding can actually increase interference. For example, common ground interference, ground loop interference, etc.

    To prevent mutual interference between various circuits during operation and ensure their compatibility. According to the nature of the circuit, the working grounding is divided into different types, such as DC grounding, AC grounding, digital grounding, analog grounding, signal grounding, power grounding, power grounding, etc. The different grounding methods mentioned above should be set separately.

    2.3.1 Signal ground

    The signal ground is a common reference ground wire for sensors and signal sources with various physical quantities and zero potential. Due to the generally weak signal and susceptibility to interference, higher requirements are placed on the signal ground.

    2.3.2 Simulated ground

    Simulated ground is the common reference ground wire for zero potential in analog circuits. Due to the fact that analog circuits undertake both the amplification of small signals and the power amplification of large signals; There are both low-frequency amplification and high-frequency amplification; Therefore, analog circuits are both susceptible to interference and may generate interference. Therefore, the selection of grounding points for simulation grounding and the laying of grounding wires should be fully considered.

    2.3.3 Digital ground

    Digital ground is the common reference ground wire for zero potential in digital circuits. Due to the operation of digital circuits in a pulse state, especially when the front and back edges of the pulse are steep or the frequency is high, it is easy to cause interference to analog circuits. Therefore, the selection of grounding points for digital grounding and the laying of grounding wires should also be fully considered.

    2.3.4 Power supply ground

    The power source ground is the common reference ground wire for the zero potential of the power source. Due to the fact that the power supply often supplies power to various units in the system simultaneously, and the power supply properties and parameters required by each unit may vary greatly, it is necessary to ensure both the stable and reliable operation of the power supply and the stable and reliable operation of other units.

    2.4 Shield grounding

    Shielding and grounding should be used in conjunction to achieve the desired shielding effect.
    For example, electrostatic shielding. When a complete metal shield is used to surround a positively charged conductor, an equal amount of negative charge will be induced on the inner side of the shield, and an equal amount of positive charge will appear on the outer side of the shield. Therefore, there is still an electric field on the outer side. If the metal shielding body is grounded, the positive charge on the outer side will flow into the ground, and there will be no electric field on the outer side, that is, the electric field with a positively charged conductor will be shielded inside the metal shielding body.

    For example, alternating electric field shielding. To reduce the coupling interference voltage of alternating electric fields on sensitive circuits, a metal shield with good conductivity can be installed between the interference source and the sensitive circuit, and the metal shield can be grounded. As long as the metal shielding body is well grounded, the coupling interference voltage of the alternating electric field on sensitive circuits can be reduced.

    The above two types of grounding are mainly considered for electromagnetic compatibility.

    3 Grounding methods

    The following grounding methods are adopted for work grounding according to the working frequency:

    3.1 Single point grounding

    For low operating frequencies (<1MHz), a single point grounding method is adopted (that is, a structural point in the entire circuit system is regarded as a grounding reference point, all ground connections are connected to this point, and a safety grounding bolt is set) to prevent circuit coupling caused by common ground impedance between two grounding points. The single point grounding method for multiple circuits can be divided into series and parallel. Due to the circuit coupling of common ground impedance caused by series grounding, it is best to use parallel single point grounding for low-frequency circuits.

    To prevent interference from power frequency and other stray currents on the signal ground wire, the signal ground wire should be insulated from the power ground wire and the casing ground wire. And only connect to the safety grounding bolts of the power ground, casing ground, and grounding wire connected to the ground (except for floating ground).

    The relationship between the length of a ground wire and its cross-section is:

    S> 0.83L (1)

    In the formula: L - length of the ground wire, m;

    S - Cross section of ground wire, mm2.

    3.2 Multi point grounding

    For high operating frequencies (>30MHz), a multi-point grounding method is adopted (i.e., in this circuit system, a grounding plate is used to replace the respective ground circuit of each part of the circuit). Because the inductance of the grounding lead is proportional to frequency and length, when the operating frequency is high, it will increase the common ground impedance, thereby increasing the electromagnetic interference generated by the common ground impedance. Therefore, the length of the ground wire is required to be as short as possible. When using multi-point grounding, try to find the closest low resistance grounding ground for grounding.

    3.3 Mixed grounding

    Circuits with operating frequencies ranging from 1 to 30MHz adopt a hybrid grounding type. When the length of the grounding wire is less than 1/20 of the working signal wavelength, single point grounding is used; otherwise, multi-point grounding is used.

    3.4 Floating Ground

    Floating type refers to the circuit where there is no conductor connecting the ground to the ground. Its advantage is that the circuit is not affected by the earth‘s electrical performance; Its disadvantage is that the circuit is easily affected by parasitic capacitance, which causes changes in the ground potential of the circuit and increases the induced interference to the analog circuit; Due to the lack of conductor connection between the ground and the ground of the circuit, it is easy to accumulate static electricity and cause electrostatic discharge, which may cause electrostatic breakdown or strong interference. Therefore, the effect of floating ground is not only limited to

    It depends on the insulation resistance of the floating ground, as well as the parasitic capacitance of the floating ground and the frequency of the signal.

    4 Grounding resistance

    4.1 Requirements for grounding resistance

    The smaller the grounding resistance, the better, because when there is current flowing through the grounding resistance, it will generate voltage. This voltage not only generates electromagnetic interference from common ground impedance, but also causes equipment to be affected by reactive overvoltage and poses a threat to personnel from electric shock injuries. Therefore, it is generally required that the grounding resistance be less than 4 Ω; For mobile devices, the grounding resistance can be less than 10 Ω.

    4.2 Methods for reducing grounding resistance

    The grounding resistance consists of grounding wire resistance, contact resistance, and ground resistance. There are three methods to reduce the grounding resistance for this purpose:

    ——To reduce the resistance of the grounding wire, it is necessary to choose multi stranded thin wires with a large total cross-section and short length.

    ——To reduce contact resistance, it is necessary to tightly and firmly connect the grounding wire to the grounding bolt and grounding electrode, and increase the contact area and tightness between the grounding electrode and the soil.

    ——To reduce ground resistance, it is necessary to increase the surface area of the grounding electrode and increase the conductivity of the soil (such as injecting salt water into the soil).

    4.3 Calculation of grounding resistance

    The grounding resistance R of the vertical grounding electrode is:

    R=0.366（ ρ/ L) Lg (4L/d) Ω (2)

    In the formula: ρ—— Soil resistivity, Ω · m;

    L - depth of the grounding electrode in the ground, m;

    D - diameter of the grounding electrode, m.

    For example, loess ρ Taking 200 Ω· m, L is 2cm, and d is 0.05m, the vertical grounding electrode grounding resistance R is 80.67 Ω. If saline water is injected into the soil ρ When it drops to 20 Ω· m, the grounding resistance R of the grounding electrode is 8.067 Ω.

    5 shielded ground
    5.1 Grounding of the shielding cover of the circuit

    Various signal sources, amplifiers, and other circuits that are susceptible to electromagnetic radiation interference should be equipped with shielding covers. Due to the presence of parasitic capacitance between the signal circuit and the shielding case, it is necessary to connect the end of the signal circuit ground wire to the shielding case to eliminate the influence of parasitic capacitance, and ground the shielding case to eliminate common mode interference.

    5.2 Grounding of cable shielding layer

    5.2.1 Grounding of the shielding layer of low-frequency circuit cables

    The shielding layer of low-frequency circuit cables should be grounded at one point, and the grounding point of the shielding layer should be consistent with the grounding point of the circuit. For multi-layer shielded cables, each shielding layer should be grounded at one point, and each shielding layer should be insulated from each other.

    5.2.2 Grounding of shielding layer for high-frequency circuit cables

    The shielding layer of high-frequency circuit cables should be grounded using a multi-point grounding method. When the length of the cable is greater than 0.15 times the wavelength of the working signal, a multi-point grounding method with an interval of 0.15 times the wavelength of the working signal is adopted. If it cannot be achieved, at least ground both ends of the shielding layer.

    5.3 Grounding of the shielding body of the system

    When the entire system needs to resist external electromagnetic interference or prevent the system from generating electromagnetic interference, the entire system should be shielded and the shielding body should be connected to the system ground.

    6 Equipment location

    A device often contains multiple circuits to meet design requirements, such as low-level signal circuits (such as high-frequency circuits, digital circuits, analog circuits, etc.) and high-level power circuits (such as power supply circuits, relay circuits, etc.). In order to install circuit boards and other components, and to resist external electromagnetic interference, a casing with certain mechanical strength and shielding effectiveness is required for the equipment. The grounding of typical equipment is shown in Figure 1.

    The grounding of equipment should pay attention to the following points:

    ——The 50Hz power supply neutral wire should be connected to a safety grounding bolt. For independent equipment, the safety grounding bolt should be installed on the metal casing of the equipment and have a good electrical connection;

    ——To prevent the casing from being charged and endangering personal safety, it is not allowed to use the power supply neutral wire as a ground wire to replace the casing ground wire;

    ——To prevent interference from high voltage, high current, and high power circuits (such as power supply circuits, relay circuits) on low-level circuits (such as high-frequency circuits, digital circuits, analog circuits, etc.), separate their grounding. The former is the power ground (strong current ground), while the latter is the signal ground (weak current ground), and the signal ground is divided into digital ground and analog ground. The signal ground should be insulated from the power ground and the chassis ground;

    ——For the signal ground wire, an additional signal ground bolt (insulated from the equipment casing) can be installed. There are three ways to connect the signal ground bolt to the safety ground bolt (depending on the grounding effect): first, it is not connected and becomes a floating ground type; The second is to connect directly and become a single point grounded type; The third is through one three μ F capacitors are connected and become DC floating ground and AC grounded. The other grounding points finally converge on the safety grounding bolt (which should be located at the incoming line of the AC power supply), and then the grounding electrode is buried in the soil through the grounding wire.

    7 Systematically

    When multiple devices form a system, the grounding of the system is shown in Figure 2.

    The grounding of the system should pay attention to the following points:

    ——Refer to the grounding precautions of the equipment;

    ——The equipment casing is connected to the cabinet casing using the equipment casing ground wire;

    ——The cabinet casing is connected to the system casing using the cabinet casing ground wire;

    ——For the system, safety grounding bolts are installed on the metal casing of the system and have good electrical connections;

    ——When there are too many cabinets and equipment in the system, it will lead to too many digital ground wires, analog ground wires, power ground wires, and cabinet shell ground wires. For this, it can be considered to lay two semi circular grounding busbars that are parallel to each other and insulated from the system casing. One is the signal grounding busbar, and the other is the shielding grounding and cabinet casing grounding busbar; Each signal ground in the system is connected to the signal ground bus nearby, and the shielding ground and cabinet shell ground in the system are connected to the shielding ground and cabinet shell ground bus nearby; The middle of the two semi circular grounding busbars is close to the safety grounding bolt, and the shielding ground and cabinet shell grounding busbars are connected to the safety grounding bolt; Connect the signal ground bus to the signal ground bolt;

    ——When the system is powered by a three-phase power supply, due to the different electricity consumption and timing of each load, it will inevitably lead to three-phase imbalance, causing the center point potential of the three-phase power supply to shift. Therefore, the power supply neutral wire is connected to a safety grounding bolt to force the center point potential of the three-phase power supply to remain at zero, thereby preventing interference caused by the center point potential shift of the three-phase power supply;

    ——The grounding electrode shall be made of galvanized steel pipe, with an outer diameter of not less than 50mm and a length of not less than 2.0m; When burying, the grounding electrode is inserted into the surface layer to a certain depth and saltwater is poured in. Generally, the grounding resistance is required to be less than 4 Ω. For mobile equipment, the grounding resistance can be less than 10 Ω.

    8 Conclusion

    For the safety of equipment and personnel, as well as the normal and reliable operation of power electronic equipment, it is necessary to study grounding technology. Grounding can be directly connected to the ground or to a conductor as a reference potential. Unreasonable grounding can actually introduce electromagnetic interference, leading to abnormal operation of power electronic equipment. Therefore, grounding technology is one of the important technologies in electromagnetic compatibility, and research on grounding technology should be fully valued.