How to eliminate inverter interference? Inverter interference solution?

The inverter includes a rectifier circuit and an inverter circuit. The input AC power is converted into a DC voltage through the rectifier circuit and the flat circuit, and then the DC voltage is converted into pulses of different widths through the inverter. Voltage (called pulse width modulation voltage, PWM). By using this PWM voltage to drive the motor, the motor torque and speed can be adjusted.
This working principle leads to the following three kinds of electromagnetic interference:

1, harmonic interference:
Rectifier circuits generate harmonic currents that produce a voltage drop across the impedance of the power supply system, causing distortion of the voltage waveform. This distorted voltage interferes with many electronic devices (because most electronic devices only work. In the case of a sinusoidal voltage, the common voltage distortion is that the top of the sine wave flattens. When the harmonic current is constant, the voltage distortion is more serious in the case of a weak power supply. The characteristic of this type of interference is that it will interfere with the equipment that uses the same power grid, and has nothing to do with the distance between the equipment and the frequency converter;

2, RF conducted emission interference:
Since the load voltage is pulsed, the frequency converter draws current from the power grid also in the form of a pulse. This type of pulsed current contains a large number of high-frequency components that form radio frequency interference. This type of interference is characteristic of devices that use the same power grid. Interference, independent of the distance between the equipment and the frequency converter;

3, radio frequency radiation interference:
RF emissions interfere with the input and output cables from the frequency converter. In the above-mentioned case of radio frequency conducted emission interference, when there is radio frequency interference current on the input and output cables of the frequency converter, since the cable is equivalent to the antenna, electromagnetic wave radiation will inevitably occur and radiation interference will occur. The PWM voltage transmitted on the output cable of the inverter also contains rich high-frequency components, which will generate electromagnetic wave radiation and form radiated interference. The characteristic of radiated interference is that the interference phenomenon becomes serious when other electronic devices are close to the inverter.

Solutions to Overcurrent /Overvoltage/Undervoltage of VFD

Overcurrent is the most frequent phenomenon of inverter alarm.
1.1 phenomenon
(1) When restarting, it will trip at a raise speed. This is a very serious phenomenon of overcurrent. The main reasons are: load short circuit, mechanical parts stuck; inverter module damage; motor torque is too small and so on.
(2) Power-on jump, this phenomenon can not be reset generally, mainly due to: bad module, bad drive circuit, bad current detection circuit.
(3) When restarting, it does not immediately trip, but when accelerating, the main reasons are: too short acceleration time setting, too low current limit setting, and high torque compensation (V/F) setting.
1.2 Examples
(1) An LG-IS3-4 3.7kW inverter jumps “OC” as soon as it starts
Analysis and maintenance: Open the cover did not find any signs of burnt, online measurement IGBT (7MBR25NF-120) basic judgment is no problem, to determine the problem, after the removal of the IGBT measured 7 units of high-power transistors turn on and off both well. When measuring the drive circuit of the upper half bridge, it was found that there was a clear difference between the other two circuits. After careful inspection, it was found that the output pin of the optocoupler A3120 was short-circuited to the negative terminal of the power source. After the replacement, the three paths were basically the same. The module is powered on and everything is running fine.
(2) A BELTRO-VERT 2.2kW inverter energizes to jump “OC” and cannot be reset.
Analysis and maintenance: First check the inverter module found no problems. Secondly, there is no abnormality in checking the drive circuit. It is estimated that the problem is not in this block. It may be in the part of the over-current signal processing. After removing the circuit sensor and powering it on, it shows that everything is normal. Therefore, it is considered that the sensor is broken and a new one is found. After loading the experiment, everything is normal. The
2 Overvoltage
Overvoltage alarms usually occur at the time of shutdown. The main reason is that the deceleration time is too short or there is a problem with the braking resistor and the brake unit.
(1) Examples
A Taian N2 series 3.7kW inverter jumps “OU” when it stops.
Analysis and maintenance: Before repairing this machine, we must first understand what causes the “OU” alarm. This is because when the frequency converter is decelerating, the rotor rotor winding cuts the rotating magnetic field faster, and the rotor’s electromotive force and current increase. Make the motor in the power generation state, the energy returned by the diode in the inverter circuit in parallel with the high-power switch tube flows to the DC link, so that the DC bus voltage is increased, so we should focus on checking the brake circuit, measuring the discharge resistance is no problem, When the brake pipe (ET191) was measured, it was found to have broken down. After the replacement, it was powered on, and there was no problem with the quick stop.
3 Undervoltage
Underpressure is also a problem we often encounter in use. Mainly because the main circuit voltage is too low (220V series is lower than 200V, 380V series is lower than 400V), the main reason: a damaged rectifier bridge or SCR three-way work may lead to undervoltage fault Appeared, followed by the main circuit contactor damage, resulting in DC bus voltage loss above the charging resistor may cause undervoltage. There is a voltage detection circuit failure and undervoltage problems.
3.1 Examples
(1) Jump on “Uu” on a CT 18.5kW inverter.
● Analysis and maintenance: After checking that the charging resistance of the rectifier bridge of this inverter is good, but no contactor action is heard after power-on, because the charging circuit of this inverter is not using SCR but by the contactor. The pull-in process completes the charging process, so it is considered that the fault may be in the contactor or the control circuit and the power supply section, and the removal of the contactor alone plus the 24V DC contactor is working properly. Then check the 24V DC power supply. After careful inspection, the voltage is output after being stabilized by the LM7824 regulator. Measure the voltage regulator tube is damaged. After finding a new one, the power is normal after the replacement.
(2) For a DANFOSS VLT5004 inverter, the power-on display is normal, but jump “DC LINK UNDERVOLT” after load.
● Analysis and maintenance: This inverter is special in terms of phenomena, but if you carefully analyze the problem is not so complicated, the inverter also through the charging circuit, contactor to complete the charging process, there is no power Any abnormal phenomenon is estimated to be caused by the voltage drop of the DC circuit when the load is applied, and the voltage of the DC circuit is rectified by the full bridge of the rectifier bridge and then provided by the capacitor after the flat wave. Therefore, the rectifier bridge should be checked and measured. The rectifier bridge was found to have an open bridge and the problem was solved after replacing the new one.

ECOGOO 9000 series VFD Inveter product features

9000 series frequency converter is to use the senseless vector technology, control the output voltage and frequency to change the AC asynchronous motor speed of a power converter. Rely on the current sensor, accurately detect the three-phase output AC signal and the phase angle change, with no vector calculation, automatically correct the frequency in order to achieve the load changes in the motor speed fixed effect.

Built-in automatic tuning of parameters can automatically detect the motor characteristics and automatically set the relevant parameters to ensure that the inverter can continue to optimize the motor operating characteristics and obtain the maximum torque output when the motor operating parameters change over time.

All fields of protection: low voltage, over voltage, over current, to prevent motor stall, overload, overheating and other protection.

Standard V / F mode, no sense of vector mode. Output power (torque) control mode.

Control features designed for industrial machinery: Six multi-function editable digital inputs (99 selectable), three multi-function editable digital outputs (94 selectable), timer / counter, Torque tracking function, flip-flop function, automatic operation function, built-in standard RS485 communication interface, allowing single or multiple inverters at the same time by the host computer to do dynamic control, and can control up to 99 inverters (more than 31 Taiwan must be installed following the amplifier), built-in rich PID function. The output frequency is 0.00 ~ 650.00HZ.

Advanced technology, compact structure, elegant appearance products

Frequency converter circuit board common fault analysis

For the inverter circuit board failures are often frequent in the following situations:

First, the inverter circuit board bad contact: the line plug and the terminal contact is not good, poor contact with the slot card, cable break, when the pass, the components such as Weld, which will lead to bad circuit board caused the inverter Malfunction

Second, the inverter signal interference: For digital circuits, under certain conditions, some failures will be presented. Some circuit board parameters of individual components or the overall performance parameters will be some changes, anti-interference ability tends to the critical point, it may be too much interference affect the control system to make it wrong, resulting in failure of the inverter;

Third, the inverter circuit board moisture, dust and other conductive, short circuit, there resistance effect, but also in the process of thermal expansion and contraction of the resistance value will change, the resistance value with other electrical components have a parallel effect, This effect is relatively strong when it will change the circuit parameters, is the inverter failure;

Fourth, the frequency changer software aspect: Many parameters in the circuit uses the software to adjust intelligently, the margin of some parameters adjusts is too low, is in the provisional construction scope, when the machine running condition conforms to the software reason to judge the breakdown when, then the breakdown reports to the police Will appear.

Most of the VFD circuit board failures are the above four reasons, unless there are some major failures, such as doing the above four, the basic circuit board problems can be solved.

How to deal with the aging of the inverter

Inverter components performance deterioration, not a qualitative change phenomenon, but a quantitative phenomenon, into the machine for many years to use, like the capacitor electrolyte dried up, the transistor to reduce the ability to enlarge, the pin oxide components, etc., with the With the passage of time and gradually changing, so overhaul “old machine”, it is necessary to pay attention to this issue.

The definition of damage to such components, with aging, inefficient, failure, worse performance, with breakdown, open circuit, etc. is not appropriate. Components of the performance deterioration, the extent of its deterioration often vary greatly The phenomenon of failure and detection are also ever-changing, difficult to grasp, and often manifested as a difficult fault, or as a “soft fault”, people scratching his head – check No bad parts, but the circuit is clearly not the normal state! Overhaul of such failures, need to repair the basic skills of electronic circuits solid, years of accumulated experience, and even the psychic quality of maintenance, but also a test.

Fortunately, after all, this type of fault is a minority, generally or components “hard damage” as much. If the maintenance person is willing to accept such a challenge, the overhaul of such a soft fault will also translate into a fun, overhauling process can even become a enjoyable process (ordinary fault on the change, what fun at all It?), People are very sense of accomplishment. In our long-term overhaul work, we always encounter such a failure. We can accept this kind of machine without any modification and enjoy it. What’s wrong with it?

Some components, manufacturers have been given the useful life, such as the inverter cooling fan and electrolytic capacitors, manufacturers given the replacement period of 8-10 years. Fan is a rotating part, such as bearings, rotating parts, there is always wear and tear; In order to enhance the capacitance, the electrolytic capacitor with electrolyte inside, so there is the reverse leakage current production, installation and use should pay attention to its polarity. At the same time, as the service life increases, the electrolyte will inevitably dry up, so that the capacity decreased. After reaching the service life, in principle, the fan and electrolytic capacitor should be replaced, even if the inverter is not damaged.

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