【 Weak current College 】 inverter issues on

With the universal converter market's growing prosperity, not including OEM import converter, converter, exceed 25 million Yuan, the converter and its ancillary equipment installation, commissioning, maintenance and repair of the workload that give users a significant direct and indirect losses. This article will address the reasons for the above problems, according to the practical application of a large number of users, from the application environment, electromagnetic interference and anti-interference, power quality, electrical insulation, and other aspects of the analysis, made some suggestions for improvement.

2 working environment issues

In the converter in the practical application, since domestic customers in addition to a few private rooms, most of them in order to reduce costs, the inverter installed directly in the industrial field. The work site in General is dust, temperature, the humidity in the South there is a big problem. For the cable industry and metal dust, ceramics, textile and other industries have corrosive gas and dust, in mine, etc, explosion-proof requirements, etc. It must, in accordance with the situation to make the appropriate countermeasures.

2.1 inverter installation design basic requirements

(1) the converter should be installed in a control cabinet.
(2) it is best to install the converter in the control cabinet within the Central; frequency changer to vertically installed, just above and below to avoid the installation may stop the exhaust, intake of large components.
(3) on the bottom edge of converter, distance control cabinet top, bottom, or divisions, or large components must be installed, and so the minimum spacing should be greater than 300mm.
Cabinet installation inverter basic requirements
(4) if the special users in use need to remove the keyboard, the keyboard, pore converter Panel, be sure to use the tape seal or use fake strictly Panel replacement to prevent large amountsof dust into the inverter.
(5) the inverter to be undergoing scheduled maintenance, timely cleaning dust inside.
(6) other basic installation and usage requirements must comply with the user manual for instructions; if you have questions please contact the appropriate manufacturer's technical support staff.

2.2 dust control cabinet design requirements

In many places, especially the dust than metal dust, flocks of establishments using inverter, take proper and reasonable protection measures are necessary, appropriate dust control measures to ensure the inverter function is very important. General requirements for the control cabinet as a whole should be sealed, through specially designed inlet, outlet for ventilation; control cabinet top should have the safety net and protective roof outlet; control cabinet bottom should have a floor and air inlet, entry hole and install dustproof mesh.

(1) control cabinet of duct to design reasonable, exhaust patency, avoid cabinet form vortex in a fixed location, in the form of dust buildup.
(2) control cabinet above the top outlet to install protective cover to prevent debris directly into the hands of the top cover height; protective to reasonable, does not affect the exhaust. Protective cover side outlet to install protective NET, prevent debris directly into the hands of flocks.
(3) if the use control cabinet top side exhaust, outlet must have a safety net.
(4) it is important to ensure that control cabinet top of axial-flow fan rotate in the right direction, to exhaust. If the fan installed in the control cabinet top external, you must ensure that protective cover and fan are sufficient height; if the fan installed on the top of the internal control cabinet, install the screws must use only top-shells, prevent loss caused in the Cabinet fan components and equipment damage. Recommended for fans and retrofitting plastic between the Cabinet or rubber damper washer, can significantly reduce fannoise and vibration.
(5) the control cabinet's front and back doors and other joints, you want to use gasket or sealant to seal the deal, will prevent dust to enter.
(6) control cabinet bottom, side panel of all the air inlet, entry hole, dust-proof network installed. Blocking of flocks sundries. Dust networks should be designed to be removable for easy cleaning and maintenance. Dustproof mesh grid to small, can effectively block the small flocks of (and general household anti mosquito screens similar to the grid); or a case-by-case basis to determine the appropriate size of the grid. Dust networks around and control cabinet in combination with the Department to work with closely.
(7) on the control cabinet must carry out regular maintenance, timely clean internal, external, flocculation of dust, hair and other debris. Maintenance cycle may, under specific circumstances, but should be less than 2 to 3 months; a place for serious dust, recommended maintenance cycle in about 1 month.

Dust control cabinet installation requirements

2.3 7、it mildew control cabinet design requirements

Most of the inverter manufacturers internal PCB, metal structures are not anti-wet moldy special processing, if the inverter long in this State, the metal structure is prone to corrosion, conductive copper in high-temperature operation, compounded by the corrosion process. For computer control board and driving power plate of fine copper wire, as a result of corrosion will be damaged, therefore, apply to damp and and contain corrosive gases, must use the inverter's internal design with basic requirements, such as printed circuit board must adopt three prevention paint spraying, for structural components must be in the process of Nickel-chromium-plating, etc. In addition, you also need to adopt other positive, effective and reasonable protection against moisture, corrosion gas measures.

(1) control cabinet can be installed on a separate, sealed rooms withair conditioning, this method if the control device, the cost of establishing the engine room below the showcase separate confined disposal occasions, at which point the control cabinet can be used as a dust or general environmental design.
(2) separate inlet. Separate inlet can be located at the bottom of the control cabinet, through independent confined trench and external clean environment connection, this method will need to install an air intake Department, dust-proof network if ditch less than 5 m and above, you can consider adding blower.
(3) Within the closed control cabinet can be equipped with desiccant moisture absorption or adsorption of toxic gases of active materials and recently replaced.

3 interference problems

3.1 inverter on the interference of microprocessor-based control panel

In the injection moulding machines, elevators, etc., control systems, the use of computer or PLC control, system design or renovation process, be sure to note the converter to computer control board interference problems. Because the user's own design of microprocessor-based control panels generally poor level of technology, does not comply with the EMC international standards, inverter, produced by conduction and radiation interference, often resulting in control systems are not working properly, and therefore need to take the necessary measures.

(1) good grounding. Motor control system such as strong electric should grounded through reliable earthing grounding bus, microcomputer control plate shield, it is best to separate earthing. For some jamming serious occasions, it is recommended to place sensors, I/O interface screen and control panel is connected to the control of land. [3]

(2) to the computer control panel input power retro EMI-filter, common mode inductors, high frequency magnetic ring, low cost. Can inhibit conducted interference. In addition to radiation interference serious occasions, such as GSM, around exists or PHS stations, you can add to the microcomputer control sheet metal mesh shielding enclosures for shielding.
Microprocessor-based control panel power anti-jamming measure

(3) to enter the frequency converter with EMI filter, can inhibit the inverter to the power grid, conduction interference with input AC and DC reactor L1, L2, improves the power factor, reduce pollution, the combined effect of harmonics. In some distance between the motor and frequency inverter over 100m occasions, you will need to add the inverter side AC output reactors L3, resolved because the output wire-to-ground distribution parameters caused by leakage current protection and reduce external radiation interference. A proven method is to use pipe threading or shielded cable, and the steel shell or cable shield and reliable connection to the Earth. Please note that without adding AC output reactors L3, with pipe thread or shielded cables of methods to increase the output to ground of distributed capacitance, prone to over-current. Of course, in practice generally only take one or several methods.

Reduce the frequency of external control device of interference

(4) on analog sensors detect input and analog control signal electrical shielding and isolation. The inverter control system consisting of the design process, we recommend that you try not to use analog control, in particular control distance greater than 1M, cross-control cabinet installation. Because converters generally have more •8, switching frequency input output, you can meet the requirements. If you want to use the analog control, it is recommended that must use shielded cables and sensor side or inverter side to achieve remote grounding. If the interference is still seriously, you need to implement the DC/DC isolation measures. You can use standard DC/DC module or use V/F conversion, use frequency isolated Lotus set input method.

3.2 inverter itself anti-jamming problems

When the inverter power supply system in the vicinity, there are high-frequency impulse load such as welder, electroplating, electrolysis power source power supply or use of slip ring power supply, inverter itself easily because of interference protection. It is recommended that the user uses the following measures:

(1) in the frequency converter input side added inductance and capacitance, constitute an LC filter network.
(2) inverter power cable directly from a transformer side power supply.
(3) the conditions permitting, you can use a separate transformer.
(4) the use of external switch quantity control Terminal control, the connection line is long, it is recommended to use shielded cables. When the control line and main circuit power are laid in the trench, in addition to the control line must use shielded cables, the main circuit line must be steel shield for threading, decrease mutual interference to prevent incorrect operation of the inverter.
(5) the use of external analog control Terminal control, if the connection line 1 m or less, the use of shielded cables connected, and implements inverter side grounding it; if the line is long, spot jamming serious occasions, it is recommended that you install the inverter DC/side DC isolation module or use a V/F conversion, using frequency directives control the given mode.
(6) the use of external communication control Terminal control, recommended STP and inverter side of shield earthing (PE), if the interference is very serious, it is recommended that the shielding to receipt control power (GND). For RS232 communication method, note the control line try not to exceed 15m, if you want to lengthen, must reduce the communication baud rate, to around 100m normal communication baud rate is less than 600bps. For RS485 communication, you must also consider the terminal match resistance, etc. For field bus speed control systems, communication cable must be used for the cable and adopt more grounded way in order to improve reliability.

4 power quality issues

In the high-frequency impulse load such as welder, electroplating, electrolysis power, power supply, voltage often flicker; in a workshop, there are hundreds of inverter normovolemic rectifying load as you work, power system harmonics is very large, for power quality has a serious pollution, on the device itself also has considerable damage, the light is not capable of continuous uptime, the resulting device input circuit damage. You can take the following measures:

Centralized rectification DC total bus power supply

(1) in the high-frequency impulse load such as welder, electroplating, electrolysis power source power supply, etc it is recommended that the user adds the static var compensator, increase the power and quality.
(2) in the frequency converter comparison set workshop, it is recommended that the centralized rectification, the DC bus power supply in total. We recommend that users use 12 pulse rectifier mode. The advantage is that the harmonic minor, sectionCan, especially suitable for frequent play brake, electric power to run and run simultaneously.
(3) converter input side with passive LC filter, decrease the input harmonic, improve power factor, low cost, high reliability and good effect.
(4) and is equipped with a frequency converter input side PFC devices work best, but the costs are relatively high.

5 motor shaft voltage of leakage, and bearing currents issues

Inverter-driven motor, motor models and Csf for stator casing between equivalent capacitance, stator and rotor Csr as the equivalent capacitance between the Crf for rotor and equivalent capacitance between the enclosure, Rb-bearing on the shaft of the electric resistance; Cb and Zb-bearing oil film capacitor and non-linear impedance.

High-frequency PWM pulse input, motor voltage within distributed capacitance coupling effect constitute a system of common-mode loop, thus giving rise to the leakage current, voltage and current of the bearing axis.

Inverter-driven motor models of induction motor

Leakage current is PWM voltage three-phase power supply is very transient voltage unbalance between the Csf and the Earth. Its size and PWM DV/dt size relative to the size of the switching frequency, its direct result will lead to a leakage protection device action. In addition, for legacy machines, because of its poor insulation materials, and after a long run of aging, some after frequency conversion of the insulation damage. Therefore, we recommend that before upgrading, you must test for insulation. For the new variable-frequency motor insulation, requirements than a standard motor with high a level.

Bearing current major presence in three ways: dv/dt current, EDM (ElectricDischargeMachining)-current and current loop. The size of the axis voltage not only with the motor parts within the parameters of the coupling capacitor and pulse voltage rise time and amplitude. Dv/dt current major and PWM rise time tr, tr, dv/dt current amplitude increases; the higher the carrier frequency inverters, bearing currents of dv/dt-current components. EDM current certain contingency occurs only when the bearing with grease layer breakdown or bearing internal exposure, stored in the electronic rotor Earth capacitor charge of Crf (1/2Crf×Urf) through the bearing equivalent circuit of Rb, Cb and Zb on and spark discharges causing decrease, reduce the bearing finish life, serious damage caused directly. The extent of the damage depends primarily on the axis voltage and stored in the e-Crf rotor Earth capacitor size.

Loop current in power transformer grounding wire, wire, electrical ground the inverter and motor load and earth ground between loop (such as water pump load). Loop current main cause conducted interference and ground jamming, inverter and motor. Avoid or reduce the circulation is to minimize the impedance of the ground loop. Because of the frequency converter grounding wire (PE inverter) General and electrical grounding wire (PE motor 1) connected to a point, therefore, must as far as possible, bold motor grounding cable diameter, decrease the resistance between the two, inverter and the power of the Earth with ground wire copper bus or dedicated grounding cable, to ensure good grounding. For diving deep-well pump this load, ZE motor 2 grounding impedance may be less than ZE transformer and ZE converter, easy formation and circulation, it is recommended to disconnect the ZE inverter, anti-jamming performance better.

The inverter output strings consisting of inductance, RC sine wave filter is suppressing shaft voltage and an effective way of bearing currents. There are a number of manufacturers to provide a standard filter.

6 closing

This article from the converter to the practical application of system problems, from application environment, electromagnetic compatibility and power quality, electrical insulation, etc, to put forward some solutions to problems and suggestions for improvement, for inverter in the practical application of a reference value.