Attention should be paid to the design of the inverter control cabinet - News - Global IC Trade Starts Here Free Join

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Before designing the inverter control system, it is necessary to understand the system configuration, working mode, environment, control mode, customer specific requirements, specific system, new design system or old equipment transformation system.
For the transformation of old equipment, electrical engineers should know the following technical parameters and requirements.
1. Motor specific parameters: a. Factory date b. Manufacturer (domestic, import) c. Motor rated voltage d. Rated current e. Phase number.
2. The type of load characteristics of the motor.
3. Work system.
4. Motor starting method.
5. Work environment. Such as the site temperature, protection level, electromagnetic radiation level, explosion-proof level, power distribution specific parameters.
6. The actual distance from the installation position of the inverter cabinet to the motor position. (Inverter cabinet to motor distance is a very important parameter)
7. The number and method of the drive motor in the inverter cabinet.
8. Switching relationship between frequency conversion cabinet and old electrical system. Generally, the Δ-Y start and the frequency conversion work are mutually alternate switching protection.
9. Selection parameters and sampling location of the peripheral sensor transmitter of the frequency conversion cabinet.
10. Control mode of the inverter control cabinet, such as manual/automatic, local/remote, range of control signals, whether communication network.
11. Isolation of high-voltage circuits from weak current circuits. Isolation of acquisition and control signals.
12. Power quality of the workplace, such as lightning protection, surge, electromagnetic radiation.
For the new frequency conversion system, the electrical engineer should have a deep understanding of the mechanical load characteristics of the transmission with the mechanical engineer to determine the motor type and capacity. According to the mechanical load characteristics of the motor and the capacity, the type and capacity of the inverter are selected.
At present, there are many types of mechanical load and motor torque characteristics, and three types are commonly used.
1. Constant torque load. For example, conveyor belt, elevator, etc. formula is P=T*N/975 P-motor power T-motor torque N-motor speed versus constant torque, system design should pay attention to:
(1) The motor should be selected for the inverter-specific motor (2) The inverter cabinet should be equipped with a dedicated cooling fan (3) to increase the motor capacity and reduce the load characteristics (4) increase the capacity of the inverter (5) the capacity of the inverter and the motor The capacity relationship should be based on the brand, which is generally 1.1 to 1.5 motor capacity.
2. Square torque load. For example, the formula of the fan and the pump is T=K1*N2, P=K2*N3 P-motor power T-motor torque N-motor speed is general, fan, water pump, adopt frequency conversion energy saving, theoretical and practical proof energy saving It is about 40~50%, and such applications account for about 30~40% of inverter applications.
For square torque loads, system design should pay attention to:
(1) The motor is usually an asynchronous AC motor.
(2) Select the motor protection level and mode according to the environmental requirements.
(3) More than 7.5KW frequency conversion cabinet, ventilation and heat dissipation facilities should be installed (4) The relationship between motor and inverter capacity.
Relationship coefficient Foreign inverter capacity Domestic inverter capacity Foreign inverter capacity quite foreign motor capacity 1.3-1.5 Motor capacity Domestic motor capacity 1.5-2 Motor capacity
3. Constant power load. Such as winch, machine tool spindle.
Formula: P = T * N / 975 = CONT.
Generally, when a certain speed segment is reached, the constant torque is applied, and when the speed exceeds a certain speed, the power is operated at a constant power.
Constant power mechanical characteristics are more complicated.
For each inverter control cabinet, the design is the focus of the entire system, which best reflects the key aspects of product quality. For inverter control cabinets, electrical design engineers should start with the following design aspects.
1. Schematic design of frequency conversion control system
2. Circuit main circuit design.
3. Circuit control circuit design. Including conventional control circuit, 4. plc control interface circuit, 5. inverter networking.
6. Process design of the inverter control cabinet. Including electrical process design, 7. Cabinet sheet metal process design.
Schematic design According to the principle rules described above, refer to the schematic diagram of the inverter control cabinet, and draw the schematic diagram according to actual needs.
Circuit main circuit design. The main loop electrical components are selected in the following order.
(1) Determine the mechanical load characteristics: a. Power b. Torque c. Speed ​​(2) Determine the motor characteristics: a. Rated voltage b. Rated power c. Rated current (3) According to the above conditions and actual customer needs, the following Electrical components trade-offs:
a.TR-transformer is optional and optional according to voltage level standards.
b.FU-fuse wire, generally, choose 2.5-4 times rated inverter current. Note that the fuse is selected for quick melt.
c.QA-open, generally choose 1.2 times rated inverter current
d.KM-contactor, must be selected as rated inverter current
e.LY-Lightning Surge Protector, preferably, special thunderstorm-prone areas, and AC power spikes often occur to protect the inverter system from accidental damage. Generally equipped with a 40KVA surge.
The function of the f.DK-reactor reactor is to suppress the adverse effects caused by the high-order harmonic components of the inverter input and output current, and the role of the filter is to suppress the radio wave interference caused by the inverter, that is, the radio wave noise.
Some inverters have built-in reactors, and in some cases, there are no reactors. In general, how many power inverters are equipped with large reactors, and inverter manufacturers provide parameters. Select the parameters of the reactor, which can be calculated by the following formula
L=(2%~5%)V/6.18*F*I
V-rated voltage V
I-rated current A
F-maximum frequency HZ
LBI/ LBO input and output filters, generally should be configured according to frequency
R-brake resistor calculation is more complicated and should be configured under the guidance of the inverter cabinet manufacturer.
Circuit control loop design, designed according to electrical engineer knowledge and inverter requirements. But should pay attention to:
(1) The input/output weak signal must be isolated from the PLC, instrument, and sensor transmitter. Otherwise, the control system signal is confusing and the system is abnormal.
(2) Interface with the PLC's conventional control system must be installed with a surge absorber. The control power supply should be insulated by an isolation transformer.
Process design of the inverter control cabinet.
(1) Electrical process design Electrical engineer frequency conversion circuit design, the next step is electrical process design, including:
a. How much power inverter
b. What type of cable is equipped?
c. How big the wire diameter
d. How far is it. Generally you can check the form or calculation.
e. Ground wiring.
f. Anti-interference wiring. It is very important. Generally, the shielded cable is used for the strong electric cable. The cable and the shield are fixed on the bottom plate with a metal card. Some shielded metal rings are added to prevent interference.
g. Cable connection configuration for the incoming and outgoing lines.
The design of the cabinet sheet metal process should be designed according to the following principles
1. The ambient temperature of the inverter: The ambient temperature of the inverter is -10 degrees - 50 degrees, and ventilation must be considered.
humidity:
shock:
Gas: whether there is any explosion, corrosive gas
2. The cabinet carries the weight.
3. Convenient transportation. Add a lifting hook, 4. Handling safety.
5. The nameplate of the cabinet, 6. Manufacturer's CI logo.
Conclusion: A high-quality inverter control cabinet, from design, process, manufacturing, transportation, packaging, is a product with higher actual requirements, requires quality assurance of all links, in order to make a higher quality and level of control cabinet.