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Basic knowledge of the principle of the inverter
Inverter operation begins with the three-phase 380V grid voltage being input through the L1, L2, and L3 terminals. This voltage is first rectified by the inverter’s rectifier bridge, then filtered by a capacitor to produce a DC voltage of approximately 530V. This 530V DC output is one of the most commonly used test points to assess the condition of the rectification section. Before any testing, it’s important to perform a power-off check on the rectifier bridge, as this helps identify potential issues.
Once the DC voltage is generated, the inverter circuit controls the switching of its components to regulate the frequency and voltage output, allowing for precise control of motor speed or other applications. The key function of an inverter is to convert the DC voltage into AC at the desired frequency. Inverters are often equipped with built-in diagnostics that can detect and display fault codes on the control panel, making troubleshooting easier for users who refer to the manual.
However, there are times when the inverter fails to operate properly—such as when the indicator light doesn’t turn on, the fan doesn’t run, or no output is present. For beginners, these situations can be confusing. The solution is simple: disconnect the power supply, wait for about ten minutes (to allow capacitors to discharge), and then test both the rectifier and inverter sections. Most common faults can be identified this way.
Before performing any tests, ensure that the inverter has been fully powered down and that all capacitors have discharged. To test the rectifier bridge, use a multimeter set to the diode mode. Connect the black probe to the positive terminal (+) and the red probe to each of the L1, L2, and L3 inputs. A good rectifier should show a voltage drop of around 0.3 volts. If the meter displays “1,†the rectifier is likely damaged.
Next, test the inverter circuit by setting the multimeter to resistance mode (×10). Connect the black probe to the positive terminal and the red probe to the U, V, and W outputs. A healthy inverter should show resistance in the tens of ohms, with a much higher reading in reverse. Repeat the process with the red probe connected to the negative terminal (-) and the black probe to the outputs.
If both the rectifier and inverter circuits are functioning correctly, check the DC output voltage. It should read around 530V. Be cautious—if the multimeter shows only a few volts, it might be due to internal induced voltage rather than actual output. A real 530V output is essential for proper inverter operation.
Some inverters may fail due to a burned resistor on the power board, leading to no display, no fan rotation, and no output. Identifying such issues requires careful inspection and targeted testing once the main components are confirmed functional.
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**Technical Foundations**
1. **Electronic Line Shafting (ELS)** – This technique connects multiple machines electronically instead of mechanically, allowing independent control of each axis using individual motors.
2. **Auto Tuning** – Common in vector-controlled inverters, this feature automatically detects motor parameters like slip frequency, field current, torque current, and reactance. These data enable accurate control without the need for encoders.
3. **Sensorless Operation** – Vector inverters can achieve closed-loop control through internal speed estimation, eliminating the need for an encoder. Benefits include simpler wiring, reduced interference from RF noise, and fewer failures due to vibration.
4. **Vector Control** – This method separates the magnetic flux and torque-producing components of the stator current, enabling precise control of motor speed and torque.
5. **Field Weakening** – Used to reduce the motor’s field current, allowing it to operate above base speed by adjusting the magnetic balance.
6. **Constant Torque Applications** – Often used in conveyor belts, these systems require consistent torque regardless of speed. They may suffer from overheating at low speeds, which can be mitigated by using a motor with forced cooling.
7. **Variable Torque Applications** – Common in centrifugal loads like fans and pumps, these systems benefit from energy savings because torque requirements decrease with speed.
8. **Inverter-Duty Motors** – Designed specifically for inverter use, these motors typically have features like separate ventilation, high starting torque, and low noise. Some models also include encoders.
9. **Speed Control Methods** – Includes DC controllers, AC inverters, vector inverters, and servo systems. Each offers different levels of precision and control depending on the application.
10. **Common Industrial Components** – Such as tachogenerators, resolvers, optical encoders, PLCs, HMIs, field-bus systems, and distributed control systems. These components enhance automation and control in industrial settings.
11. **Motor Terminology** – Includes IP protection ratings and insulation classes. IP ratings define dust and water resistance, while insulation classes indicate maximum temperature limits for safe operation.
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