If you want to do inverter maintenance, of course, it is very important to understand some of the basic knowledge of electronics, and can not wait to be. Here we share the basic knowledge of inverter maintenance. After everyone's reading, if there are inappropriate places, I hope you correct me. If you feel supportive, give me some encouragement! Welcome everyone to reprint.

How the inverter works

The frequency converter is a device that converts the power frequency power supply (50Hz or 60Hz) into various frequency AC power sources to realize the variable speed operation of the motor, wherein the control circuit completes the control of the main circuit, and the rectifier circuit converts the alternating current into direct current, and the middle of the direct current. The circuit smoothes the output of the rectifier circuit, and the inverter circuit converts the DC power back into AC power. For inverters such as vector control inverters that require large amounts of computation, sometimes a CPU for torque calculations and some corresponding circuits are needed. This is the definition of the most frequency converter in the inverter repair.

There are many classification methods of frequency converters. According to the classification of main circuit work methods, they can be divided into voltage-type inverters and current-type inverters; according to the classification of switching methods, they can be divided into PAM-controlled inverters, PWM-controlled inverters and high carrier frequencies. PWM control inverter; classified according to the working principle, can be divided into V/f control inverter, slip frequency control inverter and vector control inverter, etc.; in the inverter repair, according to the purpose of classification, can be divided into general inverter, High-performance special inverters, high-frequency inverters, single-phase inverters and three-phase inverters.

The non-intelligent control methods used in the AC frequency converter include V/f coordinated control, slip frequency control, vector control and direct torque control. The V/f control is intended to obtain the ideal torque-speed characteristic, which is based on the idea of ​​changing the power supply frequency while performing the speed control while ensuring that the magnetic flux of the motor is not changed. The general-purpose inverter basically adopts this. A control method. V/f control converter structure is very simple, but this kind of frequency changer adopts the open-loop control method, can't achieve higher control performance, moreover, in the low frequency, must carry on the torque compensation, in order to change the low frequency torque characteristic. In inverter repair, slip frequency control is a direct control torque control method. It is based on V/f control, according to know the actual speed of asynchronous motor corresponding to the power frequency, and according to the desired transfer Moments to adjust the output frequency of the inverter can make the motor have a corresponding output torque. The vector control is to control the magnitude and phase of the stator current of the motor through the vector coordinate circuit so as to achieve the control of the excitation current and the torque current of the motor in the d, q, and 0 coordinate axes respectively, thereby achieving the purpose of controlling the motor torque. By controlling the sequence and time of the actions of each vector and the action time of the zero vector, various PWM waves can be formed to achieve various control purposes. Direct torque control uses the concept of space vector coordinates, analyzes the mathematical model of the AC motor in the stator coordinate system, controls the flux linkage and torque of the motor, and measures the stator resistance to achieve the purpose of observing the stator flux linkage, thus eliminating the need for Complicated transformation calculations such as vector control, the system is intuitive and concise, and the calculation speed and accuracy are improved compared to vector control methods.

First, the difference between analog and digital power

Many people who have just entered the electronics industry and the automation industry have doubts about analog electronic circuits and digital electronic circuits. It is even more unknown to those who have just entered this line. Of course, they must be familiar with the maintenance and maintenance of inverters.

So-called analog electronic circuits are actually relative to digital electronic circuits.

Modular power: generally refers to analog signals with frequencies below 100 megahertz, voltages within tens of volts, and the analysis/processing of this signal and the use of related devices. The signals above 100 MHz HZ belong to the category of high-frequency electronic circuits. The signals above 100 volts belong to the category of strong or high voltage electricity.

The number of electricity: generally refers to the analysis and processing of signals through digital logic and calculations, the composition and use of digital logic circuits.

The input and output ends of the digital power are generally composed of the modular power, and the basic logic element constituting the power of the digital power is the saturation characteristic and the cut-off characteristic of the tertiary tube in the mode power.

Since the digital power can be integrated on a large scale, complex mathematical operations can be performed, and it is insensitive to parameters such as temperature, interference, and aging. Therefore, it is the future direction of development. However, in the real world, information is analogous to information (light, radio, heat, cold, etc.). Modular power cannot be eliminated, but for a system, the power module may be reduced. The ideal composition is: analog input - AD sampling (digital) - digital processing - DA conversion - analog output.

Second, the difference between op amp and comparator

The operational amplifier and dedicated comparator are more common in the control circuit of the inverter main control board, and its role does not have to be described by me. It is clearer than I to do this.

1. The op amp can be connected as a comparative output and the comparator is a comparison. So why are there two products sold separately in the market? What are their similarities and differences?

2. The comparator output is generally OC for level conversion; the comparator does not have frequency compensation; the SLEW RATE is larger than the same level, but the amplifier is easy to self-excite.

The open-loop gain of the comparator is much higher than that of a normal amplifier, so a small difference between the positive and negative terminals of the comparator causes the output to change.

3, the frequency response is on the one hand, the other when the op amp output is unstable when the comparator does not necessarily meet the requirements of the latter logic circuit.

4. The comparator is open-collector output, easy to output TTL level, and the operational amplifier has a saturation voltage drop, inconvenient to use.

The difference between operational amplifiers and dedicated comparators can be divided into the following points:

1, the flipper speed of the comparator is fast, about NS order of magnitude, and the operational amplifier turnover speed is generally US order of magnitude (except special high-speed op amp)

2, op amp can input negative feedback circuit, and the comparator can not use negative feedback, although the comparator also has two inputs in phase and inversion, because there is no phase compensation circuit inside, if you enter negative feedback, the circuit can not work stably, There is no internal phase compensation circuit, which is why the comparator is faster than the amplifier.

3, op amp input primary generally push-pull circuit, bipolar output, and most of the comparator output is a collector-level open circuit structure, it requires a pull-up resistor, unipolar output, easy to connect with the digital circuit.

What is the difference between Schottky diodes and fast recovery diodes?

Fast recovery diodes refer to diodes with a short reverse recovery time (below 5 μs). Gold-doping methods are used in many processes. There are PN junction structures on structures, and some use improved PIN structures. The forward voltage drop is higher than the normal diode (1-2V), and the reverse withstand voltage is mostly below 1200V. From the performance can be divided into two levels of fast recovery and ultra-fast recovery. The former has a reverse recovery time of several hundred nanoseconds or more, and the latter is less than 100 nanoseconds.

Both types of tubes are commonly used to switch power supplies.

Schottky diode and fast recovery diode difference: the former's recovery time is about 100 times smaller than the latter, the former's reverse recovery time is about a few nanoseconds~!

The former has the advantages of low power consumption, high current, high speed ~! Electrical characteristics are of course diodes A ~!

The fast recovery diode uses a gold-doped, simple diffusion process in the manufacturing process to obtain a higher switching speed and a higher withstand voltage. At present, fast recovery diodes are mainly used as rectifier elements in inverter power supplies.

Schottky diodes: The reverse withstand voltage is 40V-50V lower, the on-state voltage drop is 0.3-0.6V, and the reverse recovery time is less than 10nS. It is a "metal semiconductor junction" diode with Schottky characteristics. Its forward voltage is lower. In addition to the material of the metal layer, gold, molybdenum, nickel, titanium and other materials can also be used. Its semiconductor material uses silicon or gallium arsenide, mostly N-type semiconductors. This device is conductive by majority carriers, so its reverse saturation current is much larger than a PN junction that conducts with minority carriers. Since the storage effect of minority carriers in a Schottky diode is very small, its frequency response is limited only by the RC time constant, and therefore, it is an ideal device for high frequency and fast switching. Its operating frequency can reach 100GHz. Also, MIS (metal-insulator-semiconductor) Schottky diodes can be used to make solar cells or light emitting diodes.

Fast-recovery diode: With a forward voltage drop of 0.8-1.1V, 35-85nS reverse recovery time, switching quickly between on and off, increasing the frequency of use of the device and improving the waveform. The fast recovery diode uses a gold-doped, simple diffusion process in the manufacturing process to obtain a higher switching speed and a higher withstand voltage. At present, fast recovery diodes are mainly used as rectifier elements in inverter power supplies.

Fourth, the inverter - the role of electrolytic capacitors in the circuit

1, the role of filtering, in the power circuit, the rectifier circuit will AC into a pulse of DC, and after the rectifier circuit access to a larger capacity electrolytic capacitor, using its charge and discharge characteristics, so that the rectified pulsating DC voltage becomes Relatively stable DC voltage. In practice, in order to prevent changes in the supply voltage of various parts of the circuit due to changes in the load, electrolytic capacitors of several tens to hundreds of microfarads are generally connected at the output end of the power supply and the power supply input end of the load. Since a large-capacity electrolytic capacitor generally has a certain inductance, and high frequency and impulse interference signals cannot be effectively filtered out, a capacitor having a capacity of 0.001 to 0.1 pF is connected in parallel at both ends to filter out high frequencies. And pulse interference.

2, Coupling: In the process of transmission and amplification of low-frequency signals, in order to prevent the quiescent operating points of the two-stage circuits from affecting each other, capacitive coupling is often used. In order to prevent excessive low-frequency component loss in the signal, an electrolytic capacitor with a larger capacity is generally used.

Second, the electrolytic capacitor judgment method

The common faults of electrolytic capacitors are capacity reduction, capacity disappearance, breakdown short circuit, and leakage current. The change in capacity is caused by the gradual drying of the electrolytic solution during the use or placement of the electrolytic capacitor, and the breakdown and leakage are generally added. The voltage is too high or the quality is poor. Judging the power supply capacitance is generally measured using the multimeter's resistance file. The specific method is: short-circuit the two pins of the capacitor to discharge, and use the black meter of the multimeter to connect the positive electrode of the electrolytic capacitor. The red meter pen is connected to the negative electrode (for the analog multimeter, the meter is intermodulated when measured with a digital multimeter).

The needle should swing in the direction of the smallest resistance and then gradually return to infinity. The larger the swing of the hand or the slower the speed of return, the greater the capacity of the capacitor, and vice versa, the smaller the capacity of the capacitor. If the hands and needles no longer change somewhere in the middle, it indicates that the capacitor is leaking. If the resistance indicator is very small or zero, it indicates that the capacitor has broken through the short circuit. The voltage of the battery used by the multimeter is generally very low, so it is more accurate to measure the low-voltage capacitor. When the voltage of the capacitor is high, although the measurement is normal at the time of striking, it may cause leakage or shock when the voltage is high. Wear phenomenon.

Third, the use of electrolytic capacitors precautions

1. Since the electrolytic capacitor has positive and negative polarity, it cannot be reversed when it is used in a circuit. In the power supply circuit, when the positive voltage is output, the positive electrode of the electrolytic capacitor is connected to the output terminal of the power supply, and the negative electrode is grounded. When the negative voltage is output, the negative electrode is connected to the output terminal, and the positive electrode is grounded. When the filter capacitor in the power supply circuit is reversed in polarity, the filtering effect of the capacitor is greatly reduced. On the one hand, the power supply output voltage fluctuates. On the other hand, due to the reverse power supply, the electrolytic capacitor equivalent to a resistor heats up at this time. When the reverse voltage exceeds a certain value, the reverse leakage resistance of the capacitor will become very small, so that the power-on operation for a short time can cause the capacitor to burst due to overheating and damage.

2. The voltage applied across the electrolytic capacitor must not exceed its allowable operating voltage. When designing the actual circuit, a certain margin should be provided according to the specific conditions. When designing the filter capacitor of the regulated power supply, if the AC supply voltage is 220~ Transformer secondary rectification voltage up to 22V, at this time select the electrolytic capacitor voltage is 25V can generally meet the requirements. However, if the AC power supply voltage fluctuates greatly and it may rise above 250V, it is better to choose an electrolytic capacitor with a withstand voltage of 30V or more.

3, electrolytic capacitors should not be close to high-power heating elements in the circuit to prevent the electrolyte from accelerating drying due to heat.

4. For the filtering of positive and negative polarity signals, two electrolytic capacitors can be connected in series with the same polarity as a non-polarized capacitor.

Fifth, the color ring resistance estimation

In order to enable the majority of beginners to rapidly calculate the resistance value of the excellent ring resistance, the author summarizes the fast-acting color ring resistance "sense" according to practical experience for beginners.

The commonly used color ring resistors are mostly four-ring resistors, and a few are five-ring resistors, and five-ring resistors are precision resistors with small errors. The representation of the two color ring resistors is shown in Fig. 1, and the illustration is shown in Fig. 2. The meaning of the envelope is shown in the attached table.

The following is a quick calculation of “quadrilateral” with a four-ring resistor as an example, but it is also applicable to the calculation of the resistance value of a five-loop resistor.

The color ring resistance is four rings, orange is ten thousand yellow hundred thousand,

A ring is connected to a second ring, and the green ring is a megohm level.

Brown 1 red 2 orange is 3, blue and purple gray row.

Yellow 4 Green 5 Blue is 6 and the resistance error percentage is

Violet 7 gray 8 white is 9, much worse than the four rings.

Black is O to be counted, Purple 1 to Blue Point 2,

The range of resistance is set in three rings, and the green point is 5 to remember the heart.

What time is several Euro gold and silver ring, brown l red 2 gold is 5,

Black, brown, and red are thousands, and colorless 20 silver is halved.

In “Jingle”, “a ring and a ring is connected” means that two numbers are consecutively written, such as a ring is brown, and a second ring is red, that is, it is written as 12. “Black is O without counting” means that the color circle is

A black ring can be written directly as O. For example, the green and black rings are directly written as 50. “The three-ring set of the resistance range, and several points of several gold and silver rings” means that the resistance of the resistor is determined by the third ring, and the third ring It is gold and silver ring, indicating that the resistance of the resistor is within a few euros, such as 5.1Q for green, brown, and gold rings, and 0.51 for green, brown, and silver. “Black Ten Brown, Red, and Hundred” means that when the third ring of the resistor is a black ring, the resistance of the resistor is within a few tens of euros, and when the brown ring is a ring, the resistance is within a few hundred Euros, and when the red ring is a resistance, Thousands or less. For example, orange, orange, and black are 33Ω; orange, orange, and brown are 330Ω, while orange, orange, and red are 3300Ω, and so on. “The percentage of resistance error is less than the fourth ring”. It means that the error of the color ring resistance is calculated with the percentage. The error depends on the color of the fourth ring. If the color is gold, then the error of the resistance is ± 5%, the colorless ring is ± 20%, and the silver ring is ± 10%. The above three errors apply to the four-ring resistance, and the error of the five-ring resistance is to see In the fifth ring, the error of the purple ring is ±o.1%, the error of the blue ring is ±0.2%, the error of the green ring is ±O.5%, the error of the brown ring is ±1%, and the error of the red ring is ±2%. .

Sixth, inverter - basic knowledge of varistors

1. What is "varistor"

"The varistor is a Chinese noun, meaning "the resistance value changes with voltage in a certain range of current and voltage" or "resistance value is sensitive to voltage". The corresponding English name is "Voltage Dependent Resistor". "Abbreviated as" VDR ".

The resistive body material of the varistor is a semiconductor, so it is a variety of semiconductor resistors. The zinc oxide (ZnO) varistors, which are now widely used, are composed of a divalent element (Zn) and a hexavalent element oxygen (O). So from a material point of view, a zinc oxide varistor is a "II-VI oxide semiconductor."

In Taiwan, China, varistors are named for their use as “sudge absorbers.” Varistors are sometimes referred to as “electric shock (surge) suppressors (absorbers)” according to their use. .

2, inverter maintenance entry - varistor circuit "safety valve" role

What is the use of varistors? The most important feature of a varistor is that when the voltage applied to it is lower than its threshold "UN", the current flowing through it is extremely small, which is equivalent to a dead valve. When the voltage exceeds UN, the current flows through. Its current surge is equivalent to the valve opening. With this feature, it is possible to suppress abnormal overvoltages that often occur in the circuit and protect the circuit from overvoltage damage.

3, inverter maintenance entry - application type

For different applications, the purpose of applying a varistor is that the voltage/current stress acting on the varistor is not the same.

Therefore, the requirements for varistors are also different. It is important to note that this difference is used correctly.

4, inverter maintenance entry - circuit function varistors

The varistor is mainly used for transient over-voltage protection, but its similarity to the voltage-voltage characteristics of a semiconductor regulator tube also enables it to have a variety of circuit element functions. For example, it can be used as:

(1) DC high-voltage low-current regulators, whose stable voltage can be as high as several thousand volts or more, which cannot be achieved by silicon regulators.

(2) Voltage fluctuation detection element.

(3) DC battery displacement unit.

(4) Pressure equalizing element.

(5) Fluorescence activation element

5, inverter maintenance entry - the basic characteristics of protective varistors

(1) Protection characteristics: When the impact strength of the impact source (or the inrush current Isp = Usp/Zs) does not exceed the specified value, the limit voltage of the varistor must not exceed the impact withstand voltage (Urp) that the protected object can withstand. .

(2) Impact resistance, that is, the varistor itself should be able to withstand the specified inrush current, impact energy, and average power when multiple shocks occur in succession.

(3) There are two life characteristics, one is the continuous operating voltage life, that is, the varistor should be able to work reliably for a specified time (hours) at the specified ambient temperature and system voltage conditions. The second is the impact life, that is, the number of shocks that can reliably withstand the specified impact.

(4) After the varistor is interposed in the system, in addition to the protection function of the "safety valve", it will also bring in some additional effects. This is the so-called "secondary effect" and it should not reduce the normal working performance of the system. There are mainly three factors to be considered at this time. One is the varistor's own capacitance (tens to tens of thousands of PF), the second is the leakage current under the system voltage, and the third is the varistor's non-linear current through the source impedance. The effect of coupling on other circuits.

Seventh, inverter maintenance entry - LED test

The quality of the test LED can be tested by testing the forward and reverse resistance of an ordinary silicon diode. Refer to the clock type multimeter dial in the R*100 or R*1K file, use a black meter to connect the anode of the LED, and the red meter to the cathode. The measured forward resistance should be 20=40K; use a black meter to connect the LED cathode, and the red meter should be connected. Positive pole, measured reverse resistance should be greater than 500K. With a digital multimeter dial in the diode file, the black meter pen is connected to the anode of the LED, the red meter is connected to the cathode, and the resistance value is infinite. The black meter pen is connected to the anode of the light emitting diode, the red meter is connected to the anode, and the light emitting diode is slightly bright, indicating normal. Measurement method as shown

Inverter maintenance entry - circuit analysis diagram

For the inverter repair, only understanding the above basic circuit is far from enough, and the following major circuits must be deeply understood. The main circuit is mainly composed of a rectifier circuit, a current limiting circuit, a filter circuit, a braking circuit, an inverter circuit, and a detection sampling circuit. Figure 2.1 shows its structure.

1) Drive circuit

The driving circuit is the six PWM signals generated by the CPU in the main control circuit. After being photoelectrically isolated and amplified, the driving circuit provides the driving signal as a commutation device (inverter module) of the inverter circuit.

The various requirements for the driver circuit vary depending on the converter device. At the same time, some developers have developed many dedicated driver modules that are suitable for various converter components. Some brands and models of inverters directly use special drive modules. However, most of the inverters use a drive circuit. From the point of view of repair, more typical drive circuits are introduced here. Figure 2.2 is the more common drive circuit (drive circuit power shown in Figure 2.3

The driver circuit consists of an isolation amplifier circuit, a driver amplifier circuit, and a driver circuit power supply. The three upper arm drive circuits are three independent drive power circuits, and the three lower arm drive circuits are a common drive power circuit.

2) Protection circuit

When the frequency converter is abnormal, in order to minimize the loss caused by the frequency converter, it can even reduce to zero. Each brand of frequency converter pays great attention to the protection function and tries to increase the protection function and improve the effectiveness of the protection function.

In the field of inverter protection functions, manufacturers can make every effort to solve problems and make good articles. In this way, the diversity and complexity of the inverter protection circuit are formed. There is a conventional detection protection circuit and software integrated protection function. Some inverter drive circuit modules, intelligent power modules, rectifier combination module, etc., have a protection function inside.

The circuit shown in Figure 2.4 is a more typical over-current detection protection circuit. The current sampling, signal isolation amplification, signal amplification output consists of three parts.

3) Switching power supply circuit

The switching power supply circuit provides low voltage power to circuits such as operation panels, main control boards, drive circuits, and fans. Figure 2.5 shows the structure of the Fuji G11 switching power supply circuit.

The DC high-voltage P terminal is added to the primary end of the high-frequency pulse transformer. After the switching regulator is connected in series with the other primary terminal of the pulse transformer, it is connected to the DC high-voltage N terminal. The switch tube is periodically turned on and off, so that the primary DC voltage is replaced by a rectangular wave. Coupled to the secondary by the pulse transformer, and then after rectification and filtering, to obtain the corresponding DC output voltage. It also compares and samples the output voltage to control the pulse width modulation circuit to change the pulse width to stabilize the output voltage.

4) Communication circuit on the main control board

When the inverter is controlled by programmable (PLC) or host computer, human-machine interface, etc., signals must be transmitted to each other through the communication interface. Figure 2.6 shows the communication interface circuit of the LG inverter.

When communicating with the frequency converter, a two-wire RS485 interface is usually used. The same is true for Siemens drives. The two lines are used to transmit and receive signals, respectively. Before the frequency converter transmits the signal after receiving the signal, these two signals all pass the integrated circuit such as the buffer A1701, 75176B, in order to guarantee the good communication result.

Therefore, the communication interface circuit on the main control board of the inverter mainly refers to this part of the circuit, as well as the signal anti-interference circuit.

5) External control circuit

Inverter external control circuit mainly refers to frequency setting voltage input, frequency setting current input, forward rotation, reverse rotation, jog and stop operation control, multi-speed control. The frequency setting voltage (current) input signal enters the CPU through the A/D conversion circuit in the inverter. Some other controls are transmitted to the CPU through optocoupler isolation of the input circuit in the inverter.

In the following article, upload the maintenance knowledge of the inverter for everyone to share!

According to everyone's proposal to me and support to me, I will now give you the basic and basic knowledge of some inverters.

Inverter switching power supply circuit

Inverter switching power supply mainly includes input grid filter, input rectifier filter, inverter, output rectifier filter, control circuit, and protection circuit. Switching power supply circuit as shown below, is a switching circuit composed of UC3844:

Switching power supplies mainly have the following features:

1, small size, light weight: Because there is no frequency converter, so the volume and weight of suction linear power supply 20 ~ 30%

2, low power consumption, high efficiency: power transistor work in the switch state, so the transistor's upper power consumption, high conversion efficiency, generally 60 ~ 70%, while the linear power supply is only 30 ~ 40%

Ball Valves

There are five general body styles of ball Valves: single body, three-piece body, split body, top entry, and welded. The difference is based on how the pieces of the valve-especially the casing that contains the ball itself-are manufactured and assembled. The valve operation is the same in each case.

In addition, there are different styles related to the bore of the ball mechanism itself.

Ball valves in sizes up to 2 inch generally come in single piece, two or three piece designs. One piece ball valves are almost always reduced bore, are relatively inexpensive and generally are throw-away. Two piece ball valves are generally slightly reduced (or standard) bore, they can be either throw-away or repairable. The 3 piece design allows for the center part of the valve containing the ball, stem & seats to be easily removed from the pipeline. This facilitates efficient cleaning of deposited sediments, replacement of seats and gland packings, polishing out of small scratches on the ball, all this without removing the pipes from the valve body. The design concept of a three piece valve is for it to be repairable.

Stainless Steel Ball Valves, Brass Ball Valves, Sanitary Ball Valves, Water Ball Valves

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