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Characteristics of Brushless DC Servo Motors
Small rotational inertia, low starting voltage, and low no-load current; Abandon contact commutation system, greatly increasing motor speed, with the maximum speed reaching up to 100,000 rpm; In performing servo control, brushless servo motors do not require encoders to achieve control of speed, position, and torque; There is no brush wear, in addition to high speed, it also has the characteristics of long lifespan, low noise, and no electromagnetic interference.
Characteristics of Brushed DC Servo Motors
1. Small size, fast action, fast response, high overload capacity, wide speed regulation range
2. Large low-speed torque, small fluctuations, stable operation
3. Low noise, high efficiency
4. Feedback from rear encoder (optional) forms the advantages of DC servo
5. Wide voltage range, adjustable frequency

I. Protection of Servo Motor Oil and Water
A: Servo motors can be used in places that may be exposed to water or water droplets. However, they are not fully waterproof or oil-proof. Therefore, servo motors should not be placed or used in environments where water or oil is present.
B: If a servo motor is connected to a reduction gear, oil sealing should be used when operating the servo motor to prevent the oil from the reduction gear from entering the servo motor.
C: The cable of the servo motor should not be immersed in oil or water.
II. Servo Motor Cable → Reducing Stress
A: Ensure that the cable is not subjected to torque or vertical load due to external bending force or its own weight, especially at the cable outlet or connection point.
B: When the servo motor is in motion, the cable (the one included with the motor) should be firmly fixed to a stationary part (relative to the motor) and an additional cable should be extended using a cable support to minimize bending stress.
C: The radius of the cable’s bend should be as large as possible.
III. Allowable Axial End Load of Servo Motor
A: Ensure that the radial and axial loads applied to the servo motor shaft during installation and operation are within the specified values for each model.
B: Be extra careful when installing a rigid coupling, especially excessive bending loads may cause damage or wear to the axial end and bearings.
C: It is best to use a flexible coupling to reduce the radial load below the allowable value. This is a special design for servo motors with high mechanical strength.
D: For information on allowable axial load, please refer to the “Allowable Axial Load Table” (User Manual).
IV. Servo Motor Installation注意事项
A： When installing or removing coupling components to the axial end of the servo motor， do not directly hit the axial end with a hammer. (Hitting the axial end with a hammer will damage the encoder at the other end of the servo motor shaft.)
B： Strive to align the axial end to the best position (improper alignment may cause vibration or bearing damage).

Users often confuse the functions of electromagnetic braking, regenerative braking, and dynamic braking, and choose the wrong components.
The dynamic brake consists of dynamic braking resistors. When there is a fault, an emergency stop, or a power failure, it uses energy consumption braking to shorten the mechanical feed distance of the servo motor.
Regenerative braking means that when the servo motor is decelerating or stopping, the braking energy is fed back to the DC bus through the inverter and absorbed by the resistive-capacitive circuit.
Electromagnetic braking is achieved by locking the motor shaft through a mechanical device.
The differences among the three are as follows:
(1) Regenerative braking only works when the servo is operating normally. It cannot brake the motor in cases such as faults, emergency stops, or power failures. The dynamic brake and electromagnetic braking do not require power during operation.
(2) The operation of regenerative braking is carried out automatically by the system, while the operation of the dynamic brake and electromagnetic braking requires external relays for control.
(3) Electromagnetic braking is usually activated after SV and OFF, otherwise it may cause overload of the amplifier. The dynamic brake usually starts after SV and OFF or when the main circuit is powered off, otherwise it may cause the dynamic brake resistor to overheat.

I. Confirmation of rotational speed and encoder resolution.
II. Conversion of the load torque on the motor shaft and calculation of acceleration and deceleration torques.
III. Calculation of the load inertia, inertia matching, as an example for Yaskawa servo motors, some products have inertia matching of up to 50 times, but it is better to be smaller in reality, as this is beneficial for accuracy and response speed.
IV. Calculation and selection of regenerative resistors, for servo motors, generally above 2kw, an external configuration is required.
V. Cable selection, encoder cables are twisted shielded, for Yaskawa servo and other Japanese products, absolute value encoders are 6-core, incremental ones are 4-core.

Performance Comparison of Servo Motors and Stepper Motors
Stepper motors, as an open-loop control system, have a fundamental connection with modern digital control technology. In domestic digital control systems, stepper motors are widely used. With the emergence of full-digital AC servo systems, AC servo motors are increasingly applied in digital control systems. To adapt to the development trend of digital control, most motion control systems adopt stepper motors or full-digital AC servo motors as the driving motors. Although they have similar control methods (pulse strings and direction signals), there are significant differences in their performance and application scenarios. Now, let’s compare their performance.
1. Control Accuracy is Different
The step angle of two-phase hybrid stepper motors is generally 1.8° or 0.9°, while that of five-phase hybrid stepper motors is generally 0.72° or 0.36°. Some high-performance stepper motors have smaller step angles after subdivision. For example, the two-phase hybrid stepper motor produced by SANYO DENKI can have its step angle set to 1.8°, 0.9°, 0.72°, 0.36°, 0.18°, 0.09°, 0.072°, or 0.036° through a code switch, which is compatible with the step angles of both two-phase and five-phase hybrid stepper motors.
The control accuracy of AC servo motors is guaranteed by the rotary encoder at the rear end of the motor shaft. Taking the SANYO full-digital AC servo motor as an example, for motors with a standard 2000-line encoder, due to the internal four-fold frequency technology of the driver, the pulse equivalent is 360°/8000 = 0.045°. For motors with a 17-bit encoder, the driver receives 131072 pulses for one revolution of the motor, which means its pulse equivalent is 360°/131072 = 0.0027466°, which is 1/655 of the pulse equivalent of a stepper motor with a step angle of 1.8°.
2. Low-Frequency Characteristics are Different
Stepper motors are prone to low-frequency vibration at low speeds. The vibration frequency is related to the load condition and the performance of the driver. Generally, the vibration frequency is half of the motor’s no-load startup frequency. This low-frequency vibration phenomenon determined by the working principle of stepper motors is very unfavorable for the normal operation of the machine. When stepper motors operate at low speeds, damping technology should be adopted to overcome the low-frequency vibration phenomenon, such as adding a damper to the motor or using subdivision technology in the driver.
AC servo motors operate very smoothly and do not exhibit vibration phenomena even at low speeds. The AC servo system has a resonance suppression function, which can cover the insufficient rigidity of the machinery and has a frequency analysis function (FFT) within the system, which can detect the resonance points of the machinery, facilitating system adjustment.
3. Torque-Frequency Characteristics are Different
The output torque of stepper motors decreases as the speed increases and drops sharply at higher speeds, so their maximum operating speed is generally between 300 and 600 RPM. AC servo motors provide constant torque output, that is, within their rated speed (generally 2000 RPM or 3000 RPM), they can output the rated torque, and above the rated speed, it is constant power output.
4. Overload Capacity is Different
Stepper motors generally do not have overload capacity. AC servo motors have strong overload capacity. Taking the SANYO AC servo system as an example, it has speed overload and torque overload capabilities. Its maximum torque is two to three times the rated torque, which can be used to overcome the inertia torque of the inertia load during the start-up moment. Stepper motors do not have this overload capacity, so when selecting the motor, to overcome this inertia torque, a motor with a larger torque is often required, while the machine does not need such a large torque during normal operation, resulting in a phenomenon of torque waste.
5. Operating Performance is Different The control of stepper motors is of open-loop type. If the starting frequency is too high or the load is too heavy, stepping loss or stall may occur. When stopping, if the speed is too high, overshoot may happen. Therefore, to ensure the control accuracy, the problems of speed increase and decrease should be handled properly. The AC servo drive system is of closed-loop control. The driver can directly sample the feedback signal from the motor encoder, and form a position loop and a speed loop internally. Generally, stepping motor stepping loss or overshoot phenomenon will not occur. The control performance is more reliable.
Six. Different speed response performance
It takes 200 to 400 milliseconds for a stepper motor to accelerate from rest to the working speed (generally several hundred revolutions per minute). The acceleration performance of the AC servo system is better. Taking the Shanyang 400W AC servo motor as an example, it only takes a few milliseconds to accelerate from rest to its rated speed of 3000 RPM, which can be used in control scenarios requiring rapid start and stop.
In conclusion, the AC servo system outperforms the stepper motor in many aspects. However, in some less demanding scenarios, stepper motors are often used as the executive motor. Therefore, in the design process of the control system, various factors such as control requirements and cost should be comprehensively considered, and an appropriate control motor should be selected.

AC Servo Motor
The construction of the stator of an AC servo motor is basically similar to that of a capacitor-split-phase single-phase asynchronous motor. Two windings with an angle of 90° apart are installed on the stator, one is the excitation winding Rf, which is always connected to the AC voltage Uf; the other is the control winding L, which is connected to the control signal voltage Uc. Therefore, an AC servo motor is also called a two-servo motor.
The rotor of an AC servo motor is usually made in a squirrel-cage type, but in order to have a wider speed regulation range, linear mechanical characteristics, no “self-rotation” phenomenon, and fast response performance, compared with ordinary motors, it should have the two characteristics of a larger rotor resistance and a smaller rotational inertia. The most commonly used rotor structures have two forms: one is a squirrel-cage rotor made of high-resistance conductive materials, with high-resistance conductive strips, to reduce the rotational inertia of the rotor, it is made slender; the other is a hollow cup-shaped rotor made of aluminum alloy, with a very thin cup wall, only 0.2-0.3mm, in order to reduce the magnetic resistance of the magnetic circuit, a fixed inner stator is placed inside the hollow cup-shaped rotor. The rotational inertia of the hollow cup-shaped rotor is very small, the response is fast, and it operates smoothly, so it is widely used.
When there is no control voltage for an AC servo motor, only the pulsating magnetic field generated by the excitation winding in the stator exists, and the rotor remains stationary. When there is control voltage, a rotating magnetic field is generated in the stator, and the rotor rotates along the direction of the rotating magnetic field. Under a constant load condition, the speed of the motor changes with the magnitude of the control voltage. When the phase of the control voltage is opposite, the servo motor will reverse.
Permanent Magnet AC Servo Motor
Since the 1980s, with the development of integrated circuits, power electronics technology, and AC variable-speed drive technology, permanent magnet AC servo drive technology has made remarkable progress. Famous electrical manufacturers in various countries have successively launched their own series of AC servo motors and servo drives and continuously improved and updated them. The AC servo system has become the main development direction of contemporary high-performance servo systems, and the original DC servo is facing the crisis of being eliminated. After the 1990s, the commercialized AC servo systems in various countries are those using full-digital control sine-wave motor servo drives. The development of AC servo drive devices in the transmission field is changing rapidly.
Compared with DC servo motors, the main advantages of permanent magnet AC servo motors are:
⑴ No brushes and commutators, so the operation is reliable, and the requirements for maintenance and maintenance are low.
⑵ The stator winding has more convenient heat dissipation.
⑶ The inertia is small, making it easier to improve the system’s speed.
⑷ It is suitable for high-speed and large-moment working conditions.
⑸ It has a smaller volume and weight under the same power.
Comparison of Servo Motors and Single-Phase Asynchronous Motors
The working principle of an AC servo motor is similar to that of a split-phase single-phase asynchronous motor, but the rotor resistance of the former is much larger than that of the latter. Therefore, compared with a single-phase asynchronous motor, servo motors have three significant characteristics:
1. Large starting torque
Due to the large rotor resistance, compared with the torque characteristic curve of an ordinary asynchronous motor, there is a significant difference. It can make the critical slip rate S0 > 1, which not only makes the torque characteristic (mechanical characteristic) closer to linear, but also has a larger starting torque. Therefore, when there is control voltage in the stator, the rotor immediately rotates, that is, it has the characteristics of fast starting and high sensitivity.
2. Wide operating range
3. No self-rotation phenomenon
When a servo motor is operating normally, as long as the control voltage is lost, the motor immediately stops running. When the servo motor loses control voltage, it is in a single-phase operation state. Due to the large rotor resistance, the two opposite rotating magnetic fields in the stator and the rotor interact to produce two torque characteristics (T1-S1, T2-S2 curves) and the combined torque characteristic (T-S curve) The output power of an AC servo motor typically ranges from 0.1 to 100W. When the power supply frequency is 50Hz, the voltage options include 36V, 110V, 220V, and 380V; when the power supply frequency is 400Hz, the voltage options include 20V, 26V, 36V, and 115V, among others.
The AC servo motor operates smoothly with low noise. However, its control characteristics are non-linear, and due to the large rotor resistance and high losses, the efficiency is low. Therefore, compared to a DC servo motor of the same capacity, it has a larger volume and heavier weight, and is thus only suitable for small power control systems ranging from 0.5 to 100W.
Debugging method Announcement
Editor
1. Initialization parameters
Before connecting the wires, initialize the parameters first. [2]
On the control card: Select the control mode; Reset the PID parameters; Set the default enable signal to be off when the control card is powered on; Save this state to ensure that the control card is in this state when powered on again.
On the servo motor: Set the control mode; Set the enable signal to be controlled externally; Set the gear ratio of the encoder signal output; Set the proportional relationship between the control signal and the motor speed. Generally, it is recommended that the maximum design speed during the servo operation corresponds to a control voltage of 9V. For example, Sanoya sets the speed corresponding to a 1V voltage, with the factory value being 500. If you only plan to have the motor operate below 1000 rpm, then set this parameter to 111.
2. Wiring
Power off the control card, connect the signal lines between the control card and the servo. The following lines must be connected: the analog output line of the control card, the enable signal line, and the encoder signal line of the servo output. After checking the wiring for no errors, power on the motor and the control card (and the PC). At this point, the motor should not move, and it can be easily rotated with external force. If not, check the settings of the enable signal and the wiring. Rotate the motor with external force, and check if the control card can correctly detect the change in the motor position. Otherwise, check the wiring and settings of the encoder signal.
3. Test Direction
For a closed-loop control system, if the feedback signal direction is incorrect, the consequences will definitely be disastrous. Open the enable signal of the servo through the control card. At this time, the servo should rotate at a lower speed, which is the so-called “zero drift”. Generally, the control card will have instructions or parameters for suppressing zero drift. Use this instruction or parameter to see if the motor speed and direction can be controlled by this instruction (parameter). If not controlled, check the analog connection and the parameter settings of the control mode. Confirm that a positive number is given, the motor rotates forward, and the encoder count increases; a negative number is given, the motor rotates backward, and the encoder count decreases. If the motor has a load and a limited travel, do not use this method. The test should not apply a voltage too high; it is recommended to be below 1V. If the direction is not consistent, you can modify the parameters on the control card or the motor to make them consistent.
4. Suppress Zero Drift
During closed-loop control, the existence of zero drift has a certain impact on the control effect. It is best to suppress it. Use the parameters on the control card or the servo to suppress zero drift, carefully adjust, and make the motor speed approach zero. Since zero drift also has certain randomness, it is not necessary to require the motor speed to be absolutely zero.
5. Establish Closed-Loop Control
Again, open the servo enable signal through the control card, input a smaller proportional gain on the control card. As to how much is considered small, this can only be judged by experience. If you are not sure, input the minimum value allowed by the control card. Turn on the enable signal of the control card and the servo. At this time, the motor should be able to roughly perform the movement according to the control card’s instructions.
6. Adjust Closed-Loop Parameters
Fine-tune the control parameters to ensure that the motor moves according to the instructions of the control card. This is a necessary task, and this part of the work is more about experience. Here, we can only give a brief overview.

Since the Indramat division of MANNESMANN’s Rexroth company officially launched the MAC permanent magnet AC servo motor and drive system at the Hanover Trade Fair in 1978, this marked the entry of this new generation of AC servo technology into the practical stage. By the mid-1980s, all companies had complete product lines. The entire servo system market shifted to AC systems. The early analog systems had deficiencies in aspects such as zero drift, anti-interference, reliability, accuracy, and flexibility, and could not fully meet the requirements of motion control. In recent years, with the application of microprocessors and new digital signal processors (DSPs), digital control systems have emerged, with the control part being fully carried out by software, known as DC servo systems or three-phase permanent magnet AC servo systems.
Most high-performance electric servo systems adopt permanent magnet synchronous AC servo motors, and the control drivers mostly use fast and precisely positioned full digital position servo systems. Typical manufacturers include German Siemens, American Coromagnon, Japanese Panasonic and ABB, etc.
The small AC servo motor and driver produced by Yaskawa Electric Corporation of Japan, among others, include the D series suitable for CNC machines (with a maximum rotational speed of 1000 r/min and a torque of 0.25 to 2.8 N.m), and the R series suitable for robots (with a maximum rotational speed of 3000 r/min and a torque of 0.016 to 0.16 N.m). Later, six series including M, F, S, H, C, and G were also introduced. In the 1990s, new D series and R series were launched. The old series’ rectangular wave drive and 8051 single-chip microcontroller control were changed to sine wave drive, controlled by 80C, 154 CPUs and gate array chips, with torque fluctuation reduced from 24% to 7% and reliability improved. Thus, within a few years, an eight-series system (power range from 0.05 to 6 kW) was formed, meeting the different needs of various machinery, handling mechanisms, welding robots, assembly robots, electronic components, processing machinery, printing machines, high-speed winding machines, and winding machines.
The Japanese Fanuc (Fanuc) company, renowned for producing CNC machine tools, also launched the S series (13 specifications) and L series (5 specifications) of permanent magnet AC servo motors in the mid-1980s. The L series has a smaller rotational inertia and mechanical time constant, suitable for position servo systems requiring particularly rapid response.
Other Japanese manufacturers, such as Mitsubishi Motors (HC-KFS, HC-MFS, HC-SFS, HC-RFS, and HC-UFS series), Toshiba Machinery (SM series), Tama Iron Works (BL series), Sanyo Electric (BL series), and Rikkyo Motors (S series), among many others, have also entered the competition for permanent magnet AC servo systems.
The MAC series AC servo motors of the Indramat division of Rexroth in Germany have 7 base sizes and 92 specifications.
The IFT5 series of three-phase permanent magnet AC servo motors of Siemens are divided into standard and short types, with a total of 8 base sizes and 98 specifications. It is claimed that this series of AC servo motors is only half the weight of the DC servo motors IHU series with the same output torque, and the accompanying transistor pulse width modulation driver 6SC61 series can control up to 6 axes of motor.
The German Bosch (BOSCH) company produces SD series (17 specifications) and SE series (8 specifications) AC servo motors with ferrite permanent magnets and Servodyn SM series drive controllers. The renowned American servo equipment manufacturing company Gettys, which was once a division of Gould Electronics (Motion Control Division), produced the M600 series AC servo motors and the A600 series servo drives. Later, it merged into AEG and restored the Gettys name, launching the A700 fully digital AC servo system.
The drive division of A-B (ALLEN-BRADLEY) Company produced the 1326 type ferrite permanent magnet AC servo motors and the 1391 type AC PWM servo controllers. The motors included 30 specifications with 3 different base sizes.
I.D. (Industrial Drives) is the industrial drive division of the famous Kollmorgen in the United States. It once produced three series of 41 specifications of brushless servo motors and the BDS3 type servo driver. Since 1989, it has launched a new series of permanent magnet AC servo motors [3], including three types: B (low inertia), M (medium inertia), and EB (explosion-proof), with 5 base sizes (10, 20, 40, 60, 80) and 42 specifications each. All use neodymium iron boron permanent magnetic materials, with a torque range of 0.84 to 111.2 N.m and a power range of 0.54 to 15.7 kW. The accompanying drivers include the BDS4 (analog type), BDS5 (digital type, including position control) and Smart Drive (digital type), with a maximum continuous current of 55 A. The Goldline series represents the latest level of permanent magnet AC servo technology.
Inland, originally a division of Kollmorgen abroad, has now merged into AEG and is known for producing DC servo motors, DC torque motors and servo amplifiers. It produces 17 specifications of SmCo permanent magnet AC servo motors with three base sizes (BHT1100, 2200, 3300) and eight controllers.
The French Alsthom Group produces the LC series (long type) and GC series (short type) AC servo motors with 14 specifications at its Parvex factory in Paris, and also produces the AXODYN series of drivers.
The former Soviet Union developed two series of AC servo motors for CNC machine tools and robot servo control. The 2ДBy series uses ferrite permanent magnet and has two base sizes, each with three core lengths and two winding data, totaling 12 specifications, with a continuous torque range of 7 to 35 N.m. The 2ДBy series uses rare earth permanent magnet and has 6 base sizes and 17 specifications, with a torque range of 0.1 to 170 N.m, and is paired with the 3ДБ type controller.
In recent years, the Japanese Panasonic Company has launched the fully digital MINAS series of AC servo systems. The permanent magnet AC servo motors in this series include the small inertia MSMA series with power ranging from 0.03 to 5 kW, totaling 18 specifications; the medium inertia series includes three series: MDMA, MGMA, and MFMA, with power ranging from 0.75 to 4.5 kW, totaling 23 specifications; and the large inertia MHMA series has a power range of 0.5 to 5 kW, with 7 specifications.
In recent years, Samsung of South Korea has developed fully digital permanent magnet AC servo motors and drive systems. The FAGA series of AC servo motors includes multiple models such as CSM, CSMG, CSMZ, CSMD, CSMF, CSMS, CSMH, CSMN, and CSMX, with power ranging from 15 W to 5 kW. Nowadays, the (Powerrate) comprehensive index is commonly used as the quality factor of servo motors to evaluate the dynamic response performance of various AC and DC servo motors and stepper motors. The power change rate represents the ratio of the continuous (rated) torque of the motor to the rotor’s rotational inertia.
Through calculation and analysis based on the power change rate, it can be known that the technical indicators of permanent magnet AC servo motors are the best among those from the Goldline series of I.D. in the United States, followed by the IFT5 series from Siemens in Germany.

1. The servo system (servo mechanism) is an automatic control system that enables the output controlled quantities such as position, orientation, and state of an object to follow any changes in the input target (or given value). Servo mainly relies on pulses for positioning, and it can be understood in this way: when a servo motor receives one pulse, it will rotate by an angle corresponding to that pulse, thereby achieving displacement. Because the servo motor itself has the function of generating pulses, when the motor rotates by one angle, it will emit a corresponding number of pulses, thus forming a correspondence or called a closed loop. In this way, the system will know how many pulses were sent to the servo motor and how many pulses were returned, allowing for very precise control of the motor’s rotation, enabling precise positioning, reaching 0.001mm. DC servo motors are divided into brushed and brushless motors. Brushed motors have low cost, simple structure, large starting torque, wide speed regulation range, easy control, and require maintenance, but the maintenance is inconvenient (changing carbon brushes), generating electromagnetic interference, and having environmental requirements. Therefore, they can be used in ordinary industrial and civilian scenarios with sensitive costs.
Brushless motors are small in size, light in weight, have high output, fast response, high speed, small inertia, smooth rotation, and stable torque. The control is complex, and it is easy to achieve intelligence. Its electronic commutation method is flexible, allowing for square wave commutation or sine wave commutation. The motor is maintenance-free, has high efficiency, low operating temperature, very little electromagnetic radiation, long lifespan, and can be used in various environments.
2. AC servo motors are also brushless motors, divided into synchronous and asynchronous motors. In motion control, synchronous motors are generally used. They have a wide power range and can achieve large power. High inertia, the highest rotational speed is low, and it decreases rapidly with power increase. Therefore, they are suitable for applications with low-speed and smooth operation.
3. The rotor inside the servo motor is a permanent magnet. The driver controls the U/V/W three-phase electricity to form an electromagnetic field. The rotor rotates under the action of this magnetic field. At the same time, the motor’s built-in encoder provides feedback signals to the driver. The driver compares the feedback value with the target value and adjusts the rotation angle of the rotor. The accuracy of the servo motor depends on the accuracy of the encoder (the number of lines).
The differences in function between AC servo motors and brushless DC servo motors: AC servo motors are better because they are sinusoidal wave controlled, with smaller torque pulsation. DC servo is trapezoidal wave. However, DC servo is simpler and cheaper.

In the 1950s, the main power electronic devices were mercury arc rectifier tubes and high-power vacuum tubes. In the 1960s, the thyristor was developed and became widely used in power electronic circuits due to its reliable operation, long lifespan, small size, and fast switching speed. By the early 1970s, it had gradually replaced the mercury arc rectifier tubes. In the 1980s, the switching current of common thyristors reached several thousand amperes, and the positive and reverse working voltages they could withstand reached several thousand volts. Based on this, a series of derivative devices such as gate-turn-off thyristors, bidirectional thyristors, light-controlled thyristors, reverse-conducting thyristors, and a variety of other new power electronic devices were developed, including unipolar MOS power field-effect transistors, bipolar power transistors, electrostatic induction thyristors, functional combination modules, and power integrated circuits.
All power electronic devices have two working characteristics: conduction and blocking. Power diodes are two-terminal (anode and cathode) devices, and their current is determined by the voltage-voltage characteristics. Apart from changing the voltage between the two terminals, their anode current cannot be controlled, so they are called non-controlled devices. Ordinary thyristors are three-terminal devices, and their gate signal can control the conduction of the device but not its turn-off, so they are called semi-controlled devices. Gate-turn-off thyristors, power transistors, and other devices can control both the conduction and turn-off of the device with their gate signals, so they are called fully-controlled devices. The latter two types of devices are more flexible in control, have simpler circuits, and have fast switching speeds, and are widely used in rectification, inversion, and chopper circuits, being the core components of power electronic devices such as motor speed regulation, generator excitation, induction heating, electroplating, electrolytic power supply, and direct power transmission. These devices constitute the devices not only with small size and reliable operation, but also with very obvious energy-saving effects (generally 10% to 40%).
The positive and reverse voltages that a single power electronic device can withstand are fixed, and the current it can pass is also fixed. Therefore, the capacity of power electronic devices composed of a single power electronic device is limited. Therefore, in practice, multiple power electronic devices are connected in series or parallel to form components, whose voltage and current carrying capacity can be increased by several times, thereby greatly increasing the capacity of power electronic devices. When devices are connected in series, it is hoped that each component can withstand the same positive and reverse voltages; when connected in parallel, it is hoped that each component can share the same current. However, due to the individuality of the devices, when connected in series or parallel, each device cannot evenly share the voltage and current. Therefore, when power electronic devices are connected in series, measures to equalize the voltage should be taken; when connected in parallel, measures to equalize the current should be taken.
When power electronic devices are working, they will generate heat due to power loss. Excessive device temperature will shorten the lifespan and even burn the device. This is the main reason limiting the current and voltage capacity of power electronic devices. Therefore, the cooling problem of the devices must be considered. Common cooling methods include self-cooling, air cooling, liquid cooling (including oil cooling and water cooling), and evaporative cooling.

Power devices are used in almost all areas of the electronics manufacturing industry, including laptops, PCs, servers, monitors, and various peripherals in the computer field; mobile phones, telephones, and other various terminals and central equipment in the network communication field; traditional black-and-white household appliances and various digital products in the consumer electronics field; industrial PCs, various instruments and meters, and various control devices in the industrial control field, etc.
In addition to ensuring the normal operation of these devices, power devices can also play an effective role in energy conservation. Due to the increasing demand for electronic products and the rising energy efficiency requirements, the power device market in China has maintained a relatively fast growth rate.
According to data from the National Bureau of Statistics, in 2010, there were 498 large-scale enterprises in the power device industry in China. The industry achieved a total sales revenue of 101.511 billion yuan, an increase of 6.86% year-on-year; and a total profit of 8.527 billion yuan, an increase of 47.54% year-on-year. From the perspective of enterprise economic types, foreign-funded enterprises had the largest number, accounting for 47.19% of the industry’s total. In terms of the number of enterprises, sales revenue, and asset scale, provinces such as Jiangsu, Guangdong, and Zhejiang had the largest shares [1].