Mitsubishi inverter

Mitsubishiinverter is a power control device that converts power frequency power toanother frequency by using the on/off function of a power semiconductor device.Mitsubishi inverter mainly adopts AC-DC-AC (VVVF frequency conversion or vectorcontrol frequency conversion), first converts the power frequency AC powersupply into DC power through the rectifier, and then converts the DC power intoAC power with frequency and voltage control. Supply the motor. The circuit ofMitsubishi inverter is generally composed of four parts: rectification,intermediate DC link, inverter and control. The rectification part is athree-phase bridge type uncontrollable rectifier, the inverter part is an IGBTthree-phase bridge inverter, and the output is a PWM waveform, and theintermediate DC link is filtering, DC energy storage and buffer reactive power.

Introduction

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Mitsubishiinverter is one of the world-renowned inverters.

 Mitsubishiinverter (Figure 1)

Producedby Mitsubishi Electric Corporation, it has a high market share worldwide.Mitsubishi inverters have been in China for more than 20 years. In the domesticmarket, Mitsubishi has a fairly broad market due to its stable quality andstrong brand influence, and has been widely used in various fields.

Themost widely used Mitsubishi inverters in the market are the A700 series and theE700 series. The A700 series is a general-purpose inverter suitable for highstarting torque and high dynamic response applications. The E700 series issuitable for applications where the functional requirements are simple and thedynamic performance requirements are low, and the price is superior.

Theimpact of electromagnetic interference

Inthe modern industrial control system, the microcomputer or PLC control technologyis often used. In the process of system design or modification, theinterference problem of the Mitsubishi inverter to the microcomputer controlboard must be paid attention to. The external interference source of Mitsubishiinverter is shown in Figure 1. Since the user's own designed microcomputercontrol board generally has poor process level and does not comply with EMCinternational standards, the conduction and radiation interference generatedafter using Mitsubishi inverter often leads to the control system. The work isabnormal, so the necessary measures described below are required.

1.Good grounding. The grounding wire of the strong electric control system suchas motor must be grounded reliably through the grounding busbar, and theshielding ground of the microcomputer control board should be groundedseparately. For some severe interference situations, it is recommended toconnect the sensor and I/0 interface shielding layer to the control ground ofthe control board.

2.Add EMI filter, common mode inductor, high frequency magnetic ring, etc. to theinput power of the microcomputer control board to effectively suppress theconducted interference. In addition, in the case of severe radiationinterference, such as the presence of GSM or PHS base stations, a metal meshshield can be added to the microcomputer control board for shielding.

3.Adding EMI filter to the input end of Mitsubishi inverter can effectivelyrestrain the conduction interference of Mitsubishi inverter to the power grid.Adding input AC and DC reactor can improve the power factor and reduce harmonicpollution. The comprehensive effect is good. When the distance between somemotors and Mitsubishi inverter exceeds 100 m, it is necessary to add an ACoutput reactor to the side of Mitsubishi inverter to solve the leakage currentprotection caused by the distribution parameters of the output wires to theground and reduce the external radiation interference. An effective method isto use a steel pipe to thread or shield the cable and reliably connect thesteel casing or cable shield to the ground. It is worth noting that when the ACoutput reactor is not added, if the steel pipe is threaded or shielded, thedistributed capacitance of the output to the ground is increased, and overcurrentis prone to occur. Of course, one or several methods are generally adopted inpractical applications.

4.Electrically shield and isolate the analog sensor sense input and analogcontrol signals. In the design process of the control system composed ofMitsubishi inverter, it is recommended not to use analog control as much aspossible, especially when the control distance is greater than 1m and installedacross the control cabinet. Because Mitsubishi inverters generally havemulti-speed setting and switching frequency input and output, it can meet therequirements. If it is necessary to use analog control, it is recommended touse shielded cable and ground the remote point on the sensor side or Mitsubishiinverter side. If the interference is still severe, DC/DC isolation measuresare required. A standard DC/DC module can be used, or a method of opticallyisolating the v/f conversion and then using the frequency setting input. [1]

Troubleshooting

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Commonfault analysis

1,UVT failure

UVTis an undervoltage fault. I believe many customers will still encounter suchproblems during use.

 Mitsubishiinverter (Figure 2)

Thecommon undervoltage detection point is the voltage on the DC bus side. After alarge resistance value is divided, a low voltage value is sampled, and aftercomparing with the standard voltage value, the output voltage normal signal,overvoltage signal or undervoltage signal is output. The sampling value of thevoltage signal of Mitsubishi A500 series inverter is obtained from the switchingpower supply side and is isolated by the optocoupler. During the maintenanceprocess, it is found that the damage of the optocoupler occupies a large causeof the undervoltage fault. proportion.

2,E6, E7 failure

E6,E7 failure is no stranger to the majority of users, this is a typicalMitsubishi inverter typical failure, of course, the cause of damage is alsomultifaceted.

(1)The integrated circuit 1302H02 is damaged. This is an IC integrated circuitthat integrates drive waveform conversion and multi-channel detection signals.It has multiple signals associated with the CPU board. In many cases, anysignal of this integrated circuit may cause E6. , E7 alarm;

(2)The signal isolation optocoupler is damaged. There are multiple strong and weaksignals between the IC integrated circuit 1302H02 and the CPU board to beisolated. The damage of the isolated optocoupler is relatively high in thedamage ratio of the components, so in the case of E6 and E7 alarms, it shouldalso be considered. Whether it is caused by such factors;

(3)The connector is damaged or the connector is not in good contact. Since theconnecting cable between the CPU board and the power board is easily bent afterseveral bending, the phenomenon of soldering, etc., if the plug side is improperlyused, the pin bending and breaking may occur. Some of the above reasons mayalso cause E6 and E7 failures.

3,common series of product failure

TheA700 series, E700 series, F700 series and D700 series are being promoted in themarket.

(1)For the A700 series, sometimes a UV (undervoltage) fault is encountered, andthe rectifier circuit can be checked. The rectifier bridge of the A700 series7.5kW or less inverter has a thyristor built in. The inverter is used to cutoff the charging resistor during normal operation. The damage of the built-inthyristor will cause undervoltage faults. The damage of the switching powersupply is also a common fault of the A700 series inverter. The common damagedevice is a M51996 waveform generator chip. The damage of this chip is usuallycaused by the sudden change of the working voltage. The most prone to problemsare the power supply of the chip 14 pin, the 7-pin of the voltage referencevalue adjustment, the 5 pin of the feedback detection, and the 2 pin of thewaveform output. In addition, in the usual maintenance, the CPU board is oftendamaged. Common fault alarms are E6 and E7, and the damaged devices are mainlyconcentrated on the program memory chips of the CPU board and some interfacechips.

(2)For the E700 series inverters, the common faults encountered are Fn faults,which are mainly caused by the damage of the fan. However, the inverter doesnot block the output when there is an alarm.

Thedamage of the power module is also mainly found in the E700 series inverters.For the low-power inverter, because it is an intelligent module that integratesthe power device and the detection circuit, it can only be replaced when themodule is damaged, but the maintenance cost is high and there is no maintenancevalue. For the 5.5KW, 7.5KW E500 series inverter, the PIM power module of 7MBRseries is selected, the replacement cost is relatively low, and some damage canbe done for the damage of such inverter.

Earlyproduct failure

SinceMitsubishi inverters entered the Chinese market earlier, some old products arestill in use. The products that can be encountered in the early stage mainlyinclude the inverters of Z series and A200 series.

Commonfault phenomena of low-power Z024 series inverters are OC, ERR, no display,etc.

Thereare two main reasons for the cause of OC.

1,the drive circuit aging

Dueto the use of a long period of time, it will inevitably lead to the aging ofcomponents.

 Mitsubishiinverter (Figure 3)

Asa result, the driving waveform is distorted and the output voltage is unstable,so an OC alarm occurs frequently when it is operated.

2,the damage of the IPM module will also cause OC alarm

Thepower module used in the Z024 series of machines not only contains overcurrent,undervoltage and other detection circuits, but also includes an amplifier drivecircuit, so no matter the damage of the detection circuit, the damage of thedrive circuit,

Anddamage to high-power transistors can cause OC alarms.

3.The cause of no display failure is mostly caused by damage to the thick film ofthe switching power supply.

4.ERR fault is an undervoltage fault, usually caused by a fault in the voltagedetection loop resistance or wiring, rather than the actual input voltage isreally undervoltage. Most of the OC faults of the A200 series are caused by thedamage of the drive circuit. Its drive circuit uses a thick film circuit in aceramic package, which brings certain difficulties to the maintenance. Thethick film circuit is mainly based on a driving light. A circuit designed to becoupled.

5.In addition, some LV faults will be encountered. The occurrence of undervoltagefaults is mostly due to the fault of the busbar detection circuit. Mitsubishiinverter also designed a thick film circuit for detecting voltage and current.The damage of the switching power supply pulse transformer is also a commonfault of the A200 series inverter. Due to the short circuit of the switchingpower supply output load or the sudden change of the bus voltage, the secondarywinding and the secondary winding are damaged.

Selectionuse

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Selectionmethod

Dueto the continuous development and progress of power electronics technology, thenew control theory is proposed and improved. It is the AC speed controltransmission, especially the Mitsubishi variable frequency speed control withexcellent performance. It has developed rapidly, so the Mitsubishi inverter +is used in the actual work. There are more and more cases of variable frequencymotors, so how to correctly select Mitsubishi inverter is essential for thenormal commissioning operation of mechanical equipment. The selection method isas follows:

1.Select Mitsubishi inverter according to the load torque characteristics ofmechanical equipment

Inpractice, mechanical equipment is often divided into the following threecategories according to different load torque characteristics:

(1)Constant torque load

(2)Constant power load

(3)Fluid load

2.Select the appropriate control mode of Mitsubishi inverter according to theload characteristics.

Thecontrol methods of Mitsubishi inverter are mainly divided into: V/f control,including open loop and closed loop; vector control, including speed sensor andspeed sensor control; direct torque control; the advantages and disadvantagesof the three methods are as follows:

(1)V/f open loop control

Advantages:simple structure, easy adjustment, can be used for universal squirrel cageasynchronous motor;

Disadvantages:Low speed torque is difficult to guarantee, torque control cannot be adopted,and the speed regulation range is small;

Mainlyused occasions: general fan, pump energy-saving speed regulation or oneinverter with multiple motor drive occasions.

(2)V/f closed-loop control

Advantages:simple structure, high speed regulation accuracy, can be used forgeneral-purpose asynchronous motors;

Disadvantages:Low speed torque is difficult to guarantee, torque control cannot be adopted,speed adjustment range is small, and speed sensor should be added;

Mainlyused occasions: used to maintain pressure, temperature, flow, PH and otherprocess occasions.

(3)Vector control without speed sensor

Advantages:no speed sensor is required, the torque response is good, the structure issimple, and the speed control range is wide;

Disadvantages:need to set the motor parameters, must have automatic test function;

Useoccasions: general industrial equipment, most speed control occasions.

(4)Vector control with speed sensor

Advantages:good torque control performance, good torque response, high speed regulationand large speed control range;

Disadvantages:need to correctly set the motor parameters, need automatic test function, highprecision speed sensor;

Usecase: High dynamic performance applications requiring precise control of torqueand speed.

(5)Direct torque control

Advantages:no speed sensor is needed, the torque response is good, the structure issimple, and the speed control range is large;

Disadvantages:need to set the motor parameters, must have automatic test function;

Useoccasions: High dynamic performance applications requiring precise control oftorque, such as cranes, elevators, rolling mills, etc.

3.Use the protective structure of Mitsubishi inverter according to theinstallation environment.

Theprotective structure of Mitsubishi inverter should be adapted to theinstallation environment. It is necessary to consider factors such as ambienttemperature, humidity, dust, pH, corrosive gas, etc., which is related to thelong-term, stable, safe and reliable operation of Mitsubishi inverter. . Theprotective structure of Mitsubishi inverter mainly includes:

(1)Open IP00

(2)Closed IP20, IP21

(3)Sealed IP40, IP41

(4)Closed IP54, IP55

Precautions

1.Select the inverter according to the load characteristics.

 Mitsubishiinverter (Figure 4)

Ifthe load is a constant torque load, select the siemens MMV/MDV inverter. If theload is a fan or a pump type, the siemens ECO inverter should be selected.

2.When selecting the inverter, the actual motor current value should be used asthe basis for the inverter selection. The rated power of the motor can only beused as a reference. In addition, it should be fully considered that the outputof the inverter contains higher harmonics, which will cause the power factorand efficiency of the motor to deteriorate. Therefore, compared with the powerfrequency grid power supply, the motor current is increased by 10% and thetemperature rise is increased by about 20%. Therefore, when selecting the motorand the inverter, the situation should be taken into account, and a marginshould be left to prevent the temperature rise from being too high and affectthe service life of the motor.

3.If the inverter is to run with a long cable, measures should be taken tosuppress the influence of the long cable to the ground coupling capacitor toavoid insufficient output of the inverter. Therefore, the inverter should beamplified by one gear or installed with an output reactor at the output of theinverter.

4.When the inverter is used to control several motors in parallel, it isnecessary to consider the total length of the cable from the inverter to themotor within the allowable range of the inverter. If the specified value isexceeded, enlarge the first or second gear to select the inverter. In addition,in this case, the control mode of the inverter can only be V/F control mode,and the inverter cannot protect the overcurrent and overload protection of themotor. In this case, a fuse is added to each motor to achieve protection.

5.For some special applications, such as high ambient temperature, high switchingfrequency, high altitude, etc., this will cause the inverter to derate, and theinverter needs to be amplified by one gear.

6.When using a frequency converter to control a high speed motor, since thereactance of the high speed motor is small,

 Mitsubishiinverter (Figure 5)

Higherharmonics also increase the output current value. Therefore, when selecting afrequency converter for a high speed motor, it should be slightly larger thanthe inverter of a normal motor.

7.When the inverter is used for a pole-changing motor, pay full attention to thecapacity of the inverter so that its maximum rated current is below the ratedoutput current of the inverter. In addition, when performing the pole numberconversion during operation, the motor should be stopped first, otherwise themotor will be idling, which will cause damage to the inverter.

8.When driving the explosion-proof motor, the inverter has no explosion-proofstructure, and the inverter should be set outside the dangerous place.

9.When the inverter is used to drive the gear reduction motor, the scope of useis restricted by the lubrication method of the rotating part of the gear. Whenthe lubricating oil is lubricated, there is no limit in the low speed range; inthe high speed range exceeding the rated speed, there is a danger that thelubricating oil will be used. Therefore, do not exceed the maximum speedtolerance.