This article mainly introduces some common fault diagnosis and maintenance methods of the inverter, and briefly describes the causes of the fault and the prevention and control countermeasures. Need to understand the inverter maintenance knowledge, you can start from the following five aspects.

First, understand the difference between analog and digital power

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.

Because 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

Operational amplifiers and dedicated comparators are common in the control circuit of the inverter main control board

1. The op amp can be connected as a comparative output and the comparator is a comparison.

2. The comparator output is generally OC for level conversion; the comparator has no frequency compensation, and the SLEW RATE is larger than the same level amplifier, 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, 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 an open-collector output, which is easy to output TTL level, while the op amp has a saturation voltage drop and is inconvenient to use.

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

6, the op amp can input negative feedback circuit, and the comparator can not use negative feedback, although the comparator also has two input terminals in phase and inversion, because there is no phase compensation circuit inside, if the input 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.

7, 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.

Schottky diodes are diodes based on barriers formed by metal and semiconductor contacts. Schottky diodes for short, with a forward voltage drop (0.4–0.5V) and short reverse recovery time (10 -40 nanosecond), and the reverse leakage current is large, the withstand voltage is low, generally less than 150V, and is mostly used in low voltage applications.

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 ~!

Fast recovery diode in the manufacturing process using gold-doped, simple diffusion and other processes, can obtain a higher switching speed, but also can get a higher voltage. The current fast recovery diode is mainly used in inverter power supply rectifier components.

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 Schottky diodes is minimal, their 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 diodes: 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. Fast recovery diode in the manufacturing process using gold-doped, simple diffusion and other processes, can obtain a higher switching speed, but also can get a higher voltage. The current fast recovery diode is mainly used in inverter power supply rectifier components.

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 load changes, electrolytic capacitors of several tens to hundreds of microfarads are generally connected to the output end of the power supply and the power 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 0.001–0.lpF is connected in parallel at both ends thereof to filter out high frequencies. And pulse interference.

2. Coupling function: In the transmission and amplification process of low-frequency signals, in order to prevent the static working points of the two-stage circuit from affecting each other, capacitor 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 capacitor is generally measured using the resistance of the multimeter. 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 hands or the slower the return speed, the greater the capacity of the capacitors, and the smaller the capacity of the capacitors. If the hands and needles no longer change somewhere in the middle, indicating that this capacitor leakage, such as the resistance indication value is very small or zero, it shows that the capacitor has penetrated the short circuit. The voltage of the battery used by the multimeter is generally very low, so it is more accurate when measuring the capacitor with low voltage resistance. When the voltage resistance of the capacitor is high, although the measurement is normal at the time of striking, it may be leaked or struck when the voltage is high. Wearing 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 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 output voltage is negative, 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, 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 will work soon, you can make the capacitor due to overheat and burst damage.

2. The voltage applied across the electrolytic capacitor must not exceed its allowable operating voltage. In the design of 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~ The rectification voltage of the class can reach 22V, at this time choose the electrolytic capacitor with the withstand voltage of 25V generally can meet the requirement. 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 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.

V. Frequency Converter – Basics of Varistors

1. What is “varistor”

“The varistor is a Chinese noun, meaning “the resistance value varies with voltage within 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 resistor 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 after their use and are called “sudge absorbers.” Varistors are sometimes referred to as “electric shock (surge) suppressors (absorbers)” depending on their use.

2, the 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, it 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, application type

For different application occasions, the purpose of applying varistors, the voltage/current stress acting on the varistors is not the same, so the requirements for varistors are also not the same. It is very important for correct use to distinguish this difference. of.

4. Varistors for circuit functions

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, the basic performance 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 inserted into 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”. 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.

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