The capacity of the frequency converter is directly related to the operation reliability of the frequency conversion speed regulation system. Therefore, a reasonable capacity will ensure the optimal investment.
There are many misunderstandings in the actual operation of the inverter capacity selection. Here are three basic capacity selection methods, which complement each other.
1. From the perspective of current, most Inverter capacity can be expressed from three angles: rated current, available motor power and rated capacity.
The latter two, the inverter manufacturer is given by the Standard Motor produced by the country or the company, or decreases with the output voltage of the inverter, it is difficult to accurately express the capability of the inverter.
When selecting a frequency converter, only the rated current of the frequency converter is a key quantity reflecting the load capacity of the semiconductor frequency conversion device.
The load current does not exceed the rated current of the inverter is the basic principle for selecting the Inverter capacity.
It should be emphasized that the process of the equipment and the motor parameters should be carefully understood before determining the capacity of the inverter, for example, the rated current of submersible pump and winding rotor motor is greater than that of ordinary cage asynchronous motor, and the rated current of roller motors commonly used in metallurgical industry is not only much larger, at the same time, it allows short-term blocking and rotating, and roller drive is mostly multi-motor drive.
It should be ensured that the total load current is not allowed to exceed the rated current of the inverter in the fault-free state.
2. From the perspective of efficiency, the system efficiency is equal to the product of the inverter efficiency and the motor efficiency. Only when both work at higher efficiency, the system efficiency is higher.
From the perspective of efficiency, the following points should be paid attention to when selecting inverter power :(1)
The power value of the inverter is the most suitable when the power value of the motor is the same, so that the inverter can operate at a high efficiency value. (2)
When the power classification of the inverter is different from the motor power classification, the power of the inverter should be as close as possible to the power of the motor, but it should be slightly larger than the power of the motor. (3)
When the motor is frequently started, braked or started under heavy load and works frequently, a higher-level frequency converter can be selected to facilitate long-term and safe operation of the frequency converter. (4)
After testing, the actual power of the motor does have a surplus. You can consider selecting a inverter with a power smaller than the motor power, but pay attention to whether the instantaneous peak current will cause overcurrent protection action. (5)
When the power of the inverter and the motor are different, the setting of the energy-saving program must be adjusted accordingly to achieve higher energy-saving effect.
3. From the perspective of calculating power, the following three calculation formulas must be met for the continuous operation of the inverter :(1)Meet load output: pcn≥pm/η (2)
Meet the motor capacity: pcn≥√ 3KUeIe cos φ × 10-3 (3)
Meet the motor current: in icn≥kie, Pcn is the Inverter capacity (Unit kW)
, PM -- motor shaft output power required by load (Unit kW), Ue is the rated voltage of the motor (Unit V), Ie is the rated current of the motor (Unit A), η for motor efficiency (Usually about 0. 85)Cos φ is the motor power factor (Usually about 0. 75), K is the current waveform compensation coefficient (
Since the output waveform of the frequency converter is not a complete sine wave, but contains components of higher harmonics, its current should be increased, usually K is about 1. 05 ~ 1. 1).
The parameters of this system are brought into the system to obtain the lowest capacity of 88KW, so 100KW and rated current 139 are taken. 26A, so take 150A.
According to the calculated of required parameters can select Siemens MicroMaster430 (Fan pump professional)
Inverter, the specific can choose MM430-
For the 110K inverter, the capacity of the motor is 110kw and the rated current is 205A to meet the use requirements, which can be selected.