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The English translation of the inverter is VFD (Variable-frequency Drive), which may be one of the few examples of modern technology by the Chinese reverse translated into English. ( But VFD also be interpreted as Vacuum fluorescent display, vacuum fluorescent tube , so this translation is not commonly used ) . Inverter and inverter technology is the application of microelectronics technology , by changing the frequency and amplitude of the electrical operating power way to control AC motors power transmission components . Drive In , South Korea and other Asian areas affected by the impact of the Japanese manufacturers have been called VVVF (Variable Voltage Variable Frequency Inverter).

First, the basics inverter
1, what is the frequency ? [ 1 ]

Drive is the use of power semiconductor devices role will be off frequency to another frequency power conversion power control device. It mainly consists of two

 Inverter circuit points , one of the main circuit ( rectifier , electrolytic capacitors and inverter module ) , and second, the control circuit ( switching power supply board , control board ) . CPU is installed in the control circuit board, the operating software of the inverter burn the CPU, the same type of drive software is fixed, the only exception is the three crystal frequency , the software can be changed according to needs.

2 , What is the difference PWM and PAM is ?

English PWM Pulse Width Modulation ( Pulse Width Modulation ) acronym , according to certain rules changing the pulse width of the pulse train , the way to adjust the value of a tune output and waveform.

PAM is the English Pulse Amplitude Modulation ( pulse amplitude modulation ) acronym is changed according to certain rules pulse amplitude pulse train , a modulation to regulate the output magnitude and waveform.

3 , voltage- and current- What is the difference ?

The main circuit of the inverter can be divided into two categories : voltage is converted to DC voltage source inverter AC and DC circuit filter is capacitive ; current -mode DC into AC current source inverter , dc loop filter inductor .

4 , Why voltage and frequency changes in proportion to the drive ?

Torque of the asynchronous motor within the motor rotor flux interaction between the current flowing generated at rated frequency, but only if a certain voltage to reduce the frequency , then the flux is too large, the saturation magnetic circuit , serious the burning motor . Therefore, the frequency and voltage to be proportional to change , that change while the frequency inverter output voltage control , the motor flux constant, avoiding weak magnetic and magnetic saturation phenomena arise. This control method used for fan and pump energy-saving inverter.

5 , using the motor drive frequency power supply voltage drops the current increases ; For inverter-driven , if the frequency decreases voltage drop, then the current is increased ?

Frequency down ( low ) , if the same power output , the current increases, but the torque under certain conditions , the current is almost constant .

6, an inverter is used , the motor starting current , starting torque how ?

An inverter is used , with the acceleration of the motor corresponding increase in the frequency and voltage , the starting current is limited to 150% of rated current ( according to different models , 125% to 200% ) . Starting frequency power direct labor , the starting current of 6 to 7 times the rated current , therefore, will have an impact on the mechanical and electrical . With inverter drive can smoothly start ( start time becomes longer ) . Starting current 1.2 to 1.5 times the rated current , starting torque of 70% to 120% of rated torque ; For enhanced with torque converter automatic function , the starting torque of 100% or more , you can start with a full load .

7, V / f mode What does this mean ?

When the frequency is proportional to the voltage drop V also declined , this question has been answered 4 instructions. And V f is the ratio between the motor characteristics is considered a pre-determined , there are several features usually stored in the controller means (ROM) , and can be used to switch or select the dial

8, according to the proportion of the land reform V and f, the torque of the motor change?

Completely reduce the frequency in proportion to the decrease in voltage, the impedance becomes small since the DC resistance constant, would result in a tendency to produce with a reduced torque at low speeds. Therefore, when a given frequency V / f, to make the output voltage is increased some in order to obtain a high starting torque , such compensation called enhanced start. You can use various methods to achieve , there are ways to automatically, select V / f mode or adjust the potentiometer methods

9 , written in the manual speed range 60 ~ 6Hz, namely 10:1 , then no output below 6Hz power it?

In 6Hz still output power, but according to the temperature rise and motor starting torque of the size and other conditions, the lowest frequency of use to take about 6Hz, this time the motor rated torque output without causing severe heat problems. The actual inverter output frequency ( starting frequency ) based on models for the 0.5 ~ 3Hz.

10 , for a combination of general motors is also required in certain torque above 60Hz , can ?

Normally when not. 50 or 60Hz ( 50Hz or more modes have ) voltage constant, a substantially constant power characteristics , require the same torque at high speed , you must pay attention to the choice of the motor and the inverter capacity .

11 , the so-called open-loop What does this mean ?

Used to set the motor speed detector means (PG), the actual speed back to the control means controls , called "closed-loop " operation without PG is called " open loop ." Universal Converter mostly open-loop mode , and some models use options available for PG feedback speed sensorless closed-loop control method is based on the mathematical model based on the projected actual speed of the motor flux , the equivalent of using a virtual speed sensor a closed loop control .

12 , the actual speed for a given speed deviation how to do ?

Open-loop , the inverter output if a given frequency , the motor is running with load , the motor speed in the range of the rated slip ( 1% to 5% ) change. For high speed accuracy requirements , even if the load changes also require nearly the speed of operation of a given situation , the drive can be used with PG feedback function ( optional part ) .

13 , if the motor with PG , and feedback to improve the accuracy of the speed of it?

Inverter with PG feedback function , accuracy is improved. However, the accuracy depends on the value of the speed itself PG output frequency accuracy and resolution.

14 , the stall prevention function is what does this mean ?

If given the acceleration time is too short , the inverter output frequency far exceeds the speed ( electric angular frequency ) changes, the drive will overcurrent flows due to tripping , running stop , which is called a stall . In order to prevent stalling the motor continues to run , it is necessary size of the current detection frequency control . When the current is too large to accelerate the appropriate acceleration rate slowed . The same is true when you slow down. Combination of the two is the stall function.

15 , there is acceleration time and deceleration time can be given models, and ramp time together models were given , what is the significance ?

Acceleration and deceleration of the aircraft can be given for a short time to accelerate, decelerate slowly were occasions , or for a small machine requires strict tact time given occasion is appropriate, but for the fan drive and other occasions, acceleration and deceleration time is longer, acceleration time and deceleration time can be given together .

16 , what is the regenerative braking ?

If the motor is in operation reduced the command frequency , the motor becomes a generator state asynchronous operation , while working as a brake , which is called regenerative ( electric ) braking.

17 , whether to get a greater braking force ?

Renewable energy from the motor out of the filter capacitor converter piling in , due to the relationship between the capacity and voltage of the capacitor , the regenerative braking force general inverter rated torque of about 10% to 20 %. If using optional parts brake unit , can reach 50 % to 100 %.

18 , please indicate protective function of the inverter ?

Protection functions can be divided into the following two categories :

( 1 ) detection to automatically perform corrective action after an abnormal state , such as over-current stall prevention, regenerative overvoltage stall prevention .

( 2 ) detection of power semiconductor devices PWM control signal abnormalities blockade , the motor automatically stop. Such as over-current cut off , regenerative overvoltage cut semiconductor cooling fan overheating and momentary power failure protection.

19 Why clutch continuous load , protection of the inverter on the action ?

When the load is connected with the clutch , dramatic changes in an instant , the motor no-load state to slip from a large area connections, resulting in a large current flows through the inverter over-current trip , not running.

20 , in the same factory moving large motors together , the inverter will stop running , which is why ?

Will flow through the motor when starting and capacity corresponding starting current, motor stator side of the transformer voltage drop , high motor capacity when this drop impact is large, connected to the same transformer inverter will make undervoltage or instantaneous stop judgment, and thus sometimes protection (IPE) action , resulting stop.

21 , what is the frequency resolution ? What is the significance ?

For digital control inverter , even when the frequency command is an analog signal level output frequency is also given . The smallest unit level difference is called frequency resolution.

Frequency resolution is usually a value of 0.015 ~ 0.5Hz. Example, the resolution of 0.5Hz, then the above 23Hz can be changed 23.5,24.0 Hz, therefore the motor is also a class action to follow . Such as continuous coiling for control purposes has caused problems. In this case , if the resolution is about 0.015Hz, the four steps of the motor 1 is 1r/min hereinafter also can be fully adapted . In addition, some models given resolution and output resolution is not the same .

22 Are there restrictions on the installation direction installing the inverter .

The internal structure of the inverter and back considering the cooling effect , the relationship of the upper and lower ventilation is also important, and therefore , the type of the disc in the unit , are hung on the wall in longitudinal position, as vertically.

10:23 Can not soft start the motor directly into a fixed frequency inverter ?

At very low frequencies is possible, but if given the same frequency is high frequency power directly start conditions are similar. The starting current flowing through the large (6 to 7 times the rated current ) , due to the inverter over-current cut off , the motor will not start .

24 , when the motor running over 60Hz attention to what the problem ?

Over 60Hz operation should note the following

( 1 ) Machinery and equipment operating at the speed necessary to fully possible ( mechanical strength , noise, vibration , etc. ) .

( 2 ) the motor enters the constant power output range , the output torque can be maintained for a work ( fans, pumps and other shaft power increases in proportion to the cube of the speed , it also increases a little attention to the speed ) .

( 3 ) produce bearing life issues , to be fully taken into account.

( 4 ) For the above motor capacity especially 2 -pole motor , running at 60Hz over to carefully discuss with manufacturers.

25 , drive gear motor drive can do ?

Depending on the structure and lubrication gear , you need to pay attention to several issues . The structure of the gear 70 ~ 80Hz usually considered the maximum limit , the lubricating oil used in the continuous operation at low speed and the like related to gear damage .

26 , the drive can be used to drive a single- phase motor it? You can use single-phase power supply?

Substantially not used. For the governor switch starter -type single-phase motors , the operating point in the speed range below the burning auxiliary winding ; For capacitor start or capacitor run way will induce capacitor explosion. Inverter power is usually 3 -phase, but for small capacity models are also useful for single-phase power operation .

27 , the power consumption of the drive itself, how much ?

It models the inverter running status , frequency of use and other relevant, but it is very difficult to answer . However, in less than about 60Hz inverter efficiency of 94 % to 96% , according to which the projected loss, but built-in regenerative braking formula (FR-K) inverter, if the loss is taken into account when braking , power consumption becomes large , the operator must pay attention to the disc design .

28 , why not at 6 ~ 60Hz continuous operation throughout the region to use ?

Usually the use of the motor fan is mounted on the outer end of the ring shaft or the rotor blade cooling , the cooling effect is reduced if the rate of decrease , and therefore can not withstand the same high-speed heating operation , the load torque must be reduced at low speeds , or using large capacity inverter and motor combination , or using special motors.

29 , what is the use of a motor with brake should pay attention to ?

Excitation circuit brake power should be taken from the input side of the inverter . If the inverter output power when the brake is actuated to cause over-current cut off. Therefore, the brake action to stop the inverter output before .

30 , want to use the drive with a drive to improve the power factor capacitor motor , the motor does not move, please explain why.

Inverter current flows in the power factor correction capacitors , due to its charging current caused by the inverter overcurrent (OCT), so we can not start, as a countermeasure , connect the capacitor after the removal operation , and even improve the power factor , the input side of the inverter access AC reactor is valid.

31 , the inverter has a long life ?

Although the drive is stationary devices, but it does have a filter capacitor , the device consumes as cooling fans , if they carry out regular maintenance , is expected to have more than 10 years of life.

32 , the drive built-in cooling fan , how the wind direction ? What happens if the fan is broken ?

Also whether the small-capacity cooling fan models. Fan models, the wind direction is from the bottom up , so the installation of the drive where the upper and lower do not put impede suction and discharge of machinery and equipment . Also, do not place the top of the drive span of parts. When a fan fails, the fan stops detecting a cooling fan on the overheat detection or protection

33 , the filter capacitor is a consumable item , then how to judge its life ?

The filter capacitor is used as a capacitor , the capacitance over time and gradually reduced , the electrostatic capacitance measured periodically to reach 85% of the rated capacity of the product as a benchmark to judge the life time .

34 Are there restrictions on the installation direction installing the inverter .

Should be a basic collection in the tray , the problem is the use of a large fully enclosed structure plate dimensions , occupying a large space , the cost is relatively high . Its measures are:

( 1 ) the actual disk device designed to heat needed for ;

( 2 ) using an aluminum heat sink, the cooling fins or the like to increase the cooling area ;

( 3 ) the use of heat pipes .

Furthermore, the back drive has been developed of the type can be exposed .

35 , want to improve the existing conveyor speed to 80Hz operation, the capacity of the drive how to choose ?

Power consumption and speed is proportional to the conveyor belt , so if you want to run 80HZ , power inverter and motor must be in proportion to the increase of 80HZ/50HZ, ie 60% ​​increase in capacity.

Precautions Maintenance and inspection are:

( 1) Turn off the input power , the wait at least five minutes before you can start checking ( also formally charging light emitting diode is off ) may cause an electric shock .

( 2 ) Maintenance , inspection and parts replacement must be performed by qualified personnel . ( Before starting work , remove all metal objects ( watches , bracelets, etc. ) , use of tools with insulated protection )

( 3 ) Do not attempt to change frequently , otherwise easily cause electrical shock and damage the product.

Prior ( 4 ) drive repair, required to confirm the input voltage is wrong, will appear 380V 220V class inverter power access among bombing ( fried capacitors , varistors , modules, etc. ) .

Drive mainly composed of a semiconductor element , therefore, must be checked daily to prevent, such as temperature , humidity, dust and adverse operating environment vibration and to prevent other failures caused by parts life .

Check items :

( 1 ) Daily inspection : Please check whether the required work . When the inverter with a voltmeter work , check the input and output voltages.

( 2 ) Regular inspection : Inspect all only when the drive is stopped to inspect the place .

( 3 ) parts replacement : Life is largely about parts and installation conditions .

 Second, the drive works
The main circuit is to transform part of the induction motor to provide power supply regulator FM , the main circuit of the inverter can be divided into two categories [ 1 ] : voltage is converted to DC voltage source inverter AC and DC circuit filtering is a capacitor. Current -mode DC into AC current source inverter , the DC loop filter inductor . It consists of three parts , the frequency power into DC power , " rectifier " , absorbed in the converter and the inverter voltage ripple generated "flat -wave loop" , as well as the DC power into AC power "reverse transformer . "

( 1 ) Rectifier: lot recently used the diode converter , which the frequency is converted into a DC power supply . Also used two transistors constituting inverter inverter inverter , due to its power direction reversible , can be regenerated running.

( 2 ) Smoothing circuit: DC voltage rectified in the rectifier , comprising six times the frequency of the pulse power supply voltage , in addition to the ripple current generated by the inverter DC voltage also changes . In order to suppress voltage fluctuations , inductors and capacitors used to absorb the pulsating voltage (current ) . Installed capacity hours, if the power supply and the main circuit devices have margin , can save a simple smoothing inductive loop .

( 3 ) Inverter: In contrast with the rectifier , the inverter converting the DC power to AC power frequency required to determine the time for the switching device 6 is turned on, turn-off can be obtained three -phase AC output . Pwm to voltage -type inverter as an example shows the switching time and voltage waveforms.

Asynchronous motor control circuit to supply ( voltage , frequency adjustable ) circuit provides a control signal to the main circuit , which has a frequency and voltage "operation circuit", the main circuit "voltage , a current detection circuit," motor "speed detection circuit ", the control signal calculating circuit for amplifying the" drive circuit ", and the inverter and the motor ," Protection Circuit "component.

( 1 ) operation circuit : current , voltage signal from an external speed or torque command is compared with the operation detecting circuit determines the output voltage of the inverter frequency .

( 2 ) voltage and current sensing circuit : the main circuit to detect potential isolation voltage and current .

( 3 ) Drive circuit : the drive circuit of the main circuit device . It is isolated from the main circuit and control circuit of the device turned off.

( 4) The speed detection circuit : the asynchronous motor is mounted on the drive shaft speed detector (tg, plg , etc. ) signals for the speed signal into the arithmetic circuit , according to the instructions and make the operation of the motor at the command speed.

( 5 ) protection circuits: a main circuit detecting voltage , current, etc. , when an overload occurs or the abnormal over- voltage , in order to prevent damage to the inverter and the induction motor , the inverter is stopped or inhibit voltage and current values ​​. [ 2 ]

 Third, the role of the inverter
Inverter with integrated high voltage power transistor technology and electronic control technology, has been widely used . Effect is to change the frequency of the AC power frequency and amplitude of the motor , thereby changing the magnetic field of its movement cycle , the motor speed to achieve smooth control purposes . The inverter makes simplify complex speed control with inverter + AC squirrel-cage induction motor combination can replace most of the original work done by a DC motor , reducing the volume and reduce the maintenance rate, so that the transmission technological development to a new stage . [ 3 ]

 Fourth, the composition of the inverter
Inverter is usually divided into four parts: the rectifier unit , high-capacity capacitors , inverters and controllers.

□ rectifier unit will operate fixed frequency alternating current is converted to direct current.

□ high-capacity energy storage capacitor after conversion .

□ inverter from the power switching transistor array of the electronic switch, the DC power into a different frequency , width and amplitude of the square wave.

□ controller work according to set procedures to control the amplitude and pulse width of the output square wave , sine wave so that superposition approximation AC drive AC motors.

 Fifth, the inverter history
Inverter technology background is extensive demand birth AC motor variable speed . Traditional DC converter technology and high failure rate due to the large volume of applications is limited.

□ 20 after the 1960s, the universal application of power electronic devices and upgrades thyristor . But its speed performance far unable to meet their needs.

□ 20 centuries since the 1970s , research variable voltage variable frequency pulse width modulation (PWM-VVVF) speed to get a breakthrough, since the 1980s to improve microprocessor technology makes various optimization algorithms can be easily implemented . □ 20 1980 VVVF inverter technology in the late United States, Japan , Germany, Britain and other developed countries of practical goods into the market, has been widely used . The first drive is probably the Japanese bought the British patent developed . However, the U.S. and Germany, with the advantages of electronic components and electronic production technology, high-end products to market faster . In China 's first production of the drive may be assembled motor factory in Dalian Fuji products. Currently at low (380V) and medium power range , Chinese production is believed to drive quality has stabilized.

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