The inverter control cabinet is problematic because central air conditioning systems are designed for maximum load with a certain margin. However, in reality, they only operate at full load for a maximum of ten days or even ten hours a year, with the load below 70% for the vast majority of the time. While the chiller unit in a central air conditioning system can automatically adjust its load according to seasonal temperature changes, the chilled water pumps and cooling pumps that are matched to the chiller unit cannot do so automatically and operate at almost 100% load for extended periods. This results in significant energy waste and deteriorates the operating environment and quality of the central air conditioning system.
With the increasing maturity of frequency conversion technology, the organic combination of frequency converters , PLCs, digital-to-analog converters, temperature sensors, temperature modules and other devices forms a closed-loop automatic control system for temperature difference, which automatically adjusts the output flow of the water pump. The use of frequency conversion speed regulation technology can not only maintain the shopping mall temperature at the desired state, making people feel comfortable and satisfied, but also make the entire system work smoothly and stably. More importantly, its energy saving effect is as high as 30% or more, which can bring good economic benefits.
The frequency converter control cabinet (frequency converter electrical control cabinet/electrical control box/electrical control unit) is an electrical control cabinet developed using frequency converters from manufacturers such as Siemens, ABB, Schneider Electric, Fuji Electric, Mitsubishi Electric, Panasonic, Delta Electronics, Shihlin Electric, and Inovance Technology. Depending on the operating conditions, AC input reactors, output reactors, DC reactors, EMI filters, braking units, braking resistors, contactors, intermediate relays, thermal relays, programmable logic controllers (PLCs), programmable operator terminals (GOTs), electricity meters, and cooling fans can be installed inside the cabinet. Fans, etc., are equipped with various control buttons and indicator lights on the frequency converter cabinet panel according to the system operating conditions, such as forward rotation, reverse rotation, motor speed increase, motor speed decrease, jog forward rotation, jog reverse rotation, manual/automatic, emergency stop, frequency conversion/power frequency, PLC control, touch screen, etc. Currently, the more standardized ones include: constant pressure water supply frequency converter control cabinet (1 control 1, 1 control 2, 1 control 3, etc.), escalator frequency converter control cabinet, central air conditioning circulating water pump frequency converter cabinet, fan frequency converter energy saving cabinet, air compressor constant pressure air supply system (frequency converter energy saving soft start control system), etc.
Detailed Explanation of Variable Frequency Drive Control Cabinet Schematic Diagram
Inverter working principle
The main circuit is the power conversion section that provides voltage and frequency adjustable power to the asynchronous motor. The main circuit of a frequency converter can be broadly divided into two categories: voltage-source converters, which convert DC voltage to AC, and current-source converters, which convert DC current to AC, and current-source converters, which use inductors for DC circuit filtering. It consists of three parts: a rectifier that converts the mains frequency power to DC power; a smoothing circuit that absorbs voltage ripples generated in the converter and inverter; and an inverter that converts DC power to AC power.
Inverter wiring diagram
Inverter wiring method
I. Wiring of the main circuit
1. The power supply should be connected to the R, S, T terminals of the inverter input, and must not be connected to the inverter output terminals (U, V, W), otherwise the inverter will be damaged. After wiring, all loose wire ends must be cleaned up. Loose wire ends may cause abnormalities, malfunctions, and faults; the inverter must always be kept clean. When drilling holes on the control panel, be careful not to let debris or dust enter the inverter.
2. Do not connect anything other than the recommended braking resistor option between terminals + and PR, or short-circuit it under any circumstances.
3. Electromagnetic interference: The inverter's input/output (main circuit) contains harmonic components, which may interfere with nearby communication equipment. Therefore, installing optional radio noise filters FR-BIF, FRBSF01, or FR-BLF line noise filters can minimize interference.
4. During long-distance cabling, the parasitic capacitance charging current of the cabling can reduce the fast response current limiting function, causing malfunctions in instruments connected to the secondary side. Therefore, the maximum cabling length should be less than the specified value. If the cabling length must be exceeded, Pr. 156 should be set to 1.
5. Do not install power capacitors, surge suppressors, or radio noise filters on the output side of the frequency converter. Otherwise, it will cause frequency converter failure or damage to the capacitors and surge suppressors.
6. To keep the voltage drop within 2%, use appropriate wires for wiring. When the wiring distance between the frequency converter and the motor is long, especially under low-frequency output conditions, the motor torque will decrease due to the voltage drop in the main circuit cable.
7. After operation, any changes to the wiring must be made only after the power has been disconnected for at least 10 minutes and the voltage has been checked with a multimeter. For a period of time after power is off, dangerously high voltage may still be present on the capacitors.
II. Wiring of the control circuit
The control circuits of frequency converters can be broadly divided into two types: analog and digital.
1. Shielded or twisted-pair cables should be used for wiring the control circuit terminals, and they must be wired separately from the main circuit and high-voltage circuit (including 200V relay program circuit).
2. Since the frequency input signal of the control circuit is a small current, in the case of contact input, in order to prevent poor contact, two parallel nodes or double contacts should be used for the small signal contacts.
3. For the wiring of the control circuit, cables with a diameter of 0.3 to 0.75 square meters are generally selected.
III. Ground wire connection
1. Due to leakage current in the frequency converter, the frequency converter and motor must be grounded to prevent electric shock.
2. Use a dedicated grounding terminal for the frequency converter. For grounding wire connections, use tin-plated crimp terminals. When tightening the screws, be careful not to damage the screw threads.
3. Tin plating does not contain lead.
4. Use a thicker wire diameter for the grounding cable, which must be equal to or greater than the specified standard. The grounding point should be as close as possible to the frequency converter, and the grounding wire should be as short as possible.
Inverter wiring precautions
1. The frequency converter itself has strong electromagnetic interference, which can interfere with the operation of some equipment. Therefore, we can add a cable sleeve to the output cable of the frequency converter.
2. The control lines inside the frequency converter or control cabinet should be at least 100mm away from the power cables, etc.
3. A user manual should be included with your purchase of the frequency inverter. If not, you can download it from the official website of the brand you purchased from. The user manual is quite detailed, including product introduction, working principle, installation and commissioning, etc.
