Basic knowledge of the principle of the inverter

After the three-phase 380V grid voltage is input from the L1, L2, L3 input terminals of the inverter, it must first be rectified by the rectifier bridge of the inverter, and then filtered by the capacitor to output a DC voltage of about 530V (this is what we often use) The most common test point to judge whether the rectification part of the inverter is good or bad.

Of course, the rectifier bridge is initially subjected to power-off test) and then through the inverter circuit, by controlling the on-off of the inverter circuit to output the voltage of the appropriate frequency we want (the most important thing for the inverter to convert the inverter is to control the inverter circuit. Turn off to control the output frequency), there are countless kinds of inverter faults. Fortunately, the inverters tend to be intelligent. The general faults can detect them themselves and display their codes on the control panel. Users only need to check The user manual can be used to determine the cause of the failure.

However, sometimes, when the inverter is running or starting up or when loading, the indicator light does not light up, the fan does not turn, and there is no output. At this time, we beginners do not know what to do. In fact, it is very simple, we just need to break the power supply of the inverter. Power off test its rectifier part and inverter part, in most cases, you can know the fault.

Here are a few things to note:

Can not be measured immediately after power off, because there are large capacitors in the inverter with hundreds of volts of high voltage, must wait for ten minutes and then test!

â–¶ Test of rectifier bridge and inverter circuit before power-on of inverter

The specific measurement methods are as follows:

Find the "+" and "-" of the DC output of the inverter, adjust the multimeter to the measuring diode, and connect the black pen to the "+" meter to the input terminals L1, L2, L3 of the inverter. If the upper half of the rectifier bridge is In good condition, the multimeter should show a pressure drop of 0.3... If the meter is damaged, the multimeter will display a "1" overrange.

Instead, connect the red test lead to the "-" black test lead to L1, L2, L3 end to get the same result above. If "1" appears, the rectifier bridge is damaged. Then test its inverter circuit, the method is as follows: adjust the multimeter to the resistance × 10 files and connect the black meter to the "+" red meter to the output end of the inverter U, V, W should have a resistance of several tens of ohms, the reverse should gigantic. Conversely, the red test lead is connected to "-" to repeat the above process, and the same result should be obtained.

In this way, when the measurement determines that the rectification part and the inverter part of the inverter are intact, the DC output of the inverter is measured to see if there is about 530V high voltage. Note that sometimes the multimeter displays tens of volts. Everyone thinks that the rectifier circuit works. In fact, it does not work. It will output a high voltage of about 530V in normal operation, and the voltage of several tens of volts is induced inside the inverter. If there is no high voltage around 530V, there is always a problem with the power supply.

Some inverters are caused by a small chip resistor of the power supply board being burned, resulting in the power board not working, so that the inverter has no display and no output, the fan does not turn, and the indicator light does not light. In this way, it is possible to initially determine which part of the inverter has failed, and then focus on testing the suspected fault part when disassembling the machine.

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technical foundation

1. Electro nic Line Shafting---ELS, many industrial production lines are composed of multiple machines with a moving relationship between the axes. In the past, mechanical mechanisms were used to connect the shafts. If the shafts were connected electronically, each state had its own drive motor, which was called "Electro nic Line Shafting" (ELS).

2, Auto Tuning , a technology commonly used in magnetic beam vector inverters, can automatically monitor (find) motor parameters such as slip frequency / field current / torque current / stator impedance / rotor impedance / Stator inductive reactance / rotor inductive reactance, etc. With these parameters, you can make [special data estimation] and [slip (slip) compensation]. Also because of this technology, you can still get good without encoder operation. Operation accuracy.

3, no encoder operation, in the speed control, compared with the open loop of the old variable frenquency inverter, the magnetic beam vector inverter internally achieves a closed loop by the speed observation calculation function. The motor side can achieve good speed without the encoder. Accuracy. No encoder operation has the following benefits:

1), the wiring is fine;

2), do not have to worry about the impact of RF noise on the encoder low voltage signal;

3), in the case of multiple vibrations, there is no need to worry about the high failure rate of the encoder.

4. Vector control of the inverter . In the AC motor, the rotor generates a magnetic field by the stator winding induced current. The stator current contains two parts to affect the magnetic field, and the other part affects the motor output torque. To use the AC motor, speed and torque control are required. In this case, it is necessary to be able to control the current that affects the torque, and the magnetic flux vector control can separate the two parts for independent control. (The physical quantity having the magnitude and direction is called a vector).

5, Field WeakeningField Weakening line can be used to weaken the field current of the motor, change the balance with the magnetic field, so that the motor runs above the basic speed.

6. For fixed torque applications , where the required torque does not change due to speed, it is often used in [fixed torque applications]. For loads such as conveyor belts. [Constant torque application] usually requires a large starting torque. Constant torque application] It is easy to have motor heating problem at low speed operation. The solution is as follows:

(1) increase the motor power;

(2) Use a dedicated motor for the inverter with constant speed cooling (ie, the cooling method of the motor is forced air cooling).

7, variable torque applications are more common in centrifugal loads, such as pumps / fans / fans, etc., the purpose of using the inverter is generally energy-saving

For example, when the fan is running at 50% speed, the required torque is less than that required for full speed operation. The variable torque inverter can only give the torque required by the motor to achieve energy saving. A brief peak load in a secondary application usually does not require additional energy to the motor. Therefore, the overload capability of the variable torque converter can be applied to most applications.

The overload (current) capability of a fixed-torque frequency converter must be 150%/1 minute of the rated value, while the overload (current) capability required for a variable-torque frequency converter is only required to be rated at 120%/1 minute. Because centrifugal mechanical applications rarely exceed the rated current. In addition, the starting torque required for variable torque applications is also smaller than the fixed torque.

8. Inverter-specific motor, so-called [Inverter-duty Motor]

The main features are as follows:

1) Separate type of it is ventilated (it is air-cooled);

2) 10Hz-60Hz is the constant torque output

3) High starting torque

4) Low noise

5) The motor is equipped with an encoder.* However, not all motors known as inverter-specific motors have the above features.

9. About speed control

1) Speed ​​regulation: adjust the running speed of the equipment according to the working conditions to achieve energy saving, reducing wear and on-demand production.

2) DC Controler/motor: The DC controller is used to adjust the DC motor to achieve the adjustment speed.

3) AC inverter/motor: The three-phase alternating current of the inverter output frequency changes to control the speed of the AC motor.

4) Vector vector inverter: Through complex calculation and transformation, the AC inverter controls the AC motor according to the control mode of the DC motor, thus achieving precise speed control, torque control, and improved output torque.

5) Servo control system (Servo co ntrol system): Introduce speed feedback or position feedback components in the motion system to achieve extremely precise speed control, positioning control and high dynamic response through negative feedback.

10. Several common industrial components

1) Tacho-generator: A speed measuring component with alternating current and direct current.

2) Resolver: An economical and accurate speed and angular displacement measuring component.

3) Optical encoder (Encoder): A precise angular displacement, rotational speed measuring component suitable for use as a feedback component in position control systems.

4) PLC: Industrial calculation and control device, realize logic, timing, calculation and other control functions, generally as the upper host of the entire automation control system.

5) HMI (Human-Machine Interface): Human-machine interface.

6) Field-Bus System: A serial communication bus system applied to the industrial control field, which greatly reduces the wiring cost and improves the anti-interference ability of the control.

7) Distributed control: Different from the traditional centralized control, it emphasizes the intelligence of each node device. Generally, the sub-devices are connected by the field bus system. Greatly improve the flexibility and reliability of the system application, and reduce the computing burden of the host computer.

11. Terms about the motor

1) Protection Code: (IP**) One of the IEC standards to examine the ability of a device to prevent foreign matter from entering and waterproofing. The two numbers represent the ability to prevent foreign objects and water resistance, respectively. The higher the value, the more small objects can be prevented from entering and subject to more intense water flow impact. Generally, IP54 (dustproof, anti-splashing water) equipment with the above protection level can be directly applied to the open air.

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