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The correct selection of the principle of the variable frequency power supply

The correct selection of the variable frequency power supply is essential to the normal operation of the electronic control system for the mechanical equipment. Select the variable frequency power supply, first in accordance with the type of machinery and equipment, the load torque characteristics, speed range, static speed accuracy requirements of starting torque and use the environment, then decided to use what control mode and variable frequency power supply of the protective structure is the most appropriate. The so-called combined to meet the mechanical equipment, the actual process of production requirements and use occasions premise, to achieve the best value for money of the variable frequency power supply applications.

Select the appropriate control point. According to the load characteristic frequency power supply

Variable frequency power supply is now for sale on the market a wide range of increasingly powerful, functional performance of variable frequency power is increasingly becoming the merits of the determinants of the speed control performance, in addition to the variable frequency power supply manufacturing process "congenital" condition, the variable frequency power supply using what kind of control method is also very important. The following table summarizes the recent years, a variety of performance characteristics of the variable frequency power control mode.

In summary, the asynchronous motor inverter control selection of different control methods, you can get the speed control characteristics of the different performance characteristics.

Second point is selected depending on the installation environment variable frequency power supply of the protective structure

Variable frequency power supply protective structure is fitted, adapt to the environment, it is necessary to consider the factors of the ambient temperature, humidity, dust, pH, corrosive gases, and variable frequency power supply whether the long-term, safe, reliable operation of the stake. Most variable frequency power supply manufacturers can provide the following protective structure for users to choose:

(1) open type IP00, from the front to protect the body can not touch the internal live parts of the variable frequency power supply, suitable for installation in the control cabinet or electrical indoor screen plates, shelves, especially multi-frequency power concentrated than good, but its installation environment requirements.

(2) closed IP20, IP21, this protective structure around the variable frequency power supply has a cover, can be wall-mounted in the building of the wall installation, which applies to most indoor installation environment.

(3) sealed type IP40, IP42, it applies in the industrial field the occasion of poor environmental conditions.

(4) sealed IP54, IP55, it has a dustproof, waterproof protective structure, applicable to industrial site environmental conditions, Shuilin, dust and some corrosive gases occasions.

Load torque characteristics of the third point. Machinery and equipment

Production machinery according to the load torque characteristics of the different people in practice often be divided into three types: constant torque load, constant power load and fluid class load.

A constant torque load

In the type of load, the load torque TL and the speed n contents of any speed TL is always kept constant or substantially constant, the load power is a linear increase with increasing load speed. Conveyors, mixers, extruders, and machinery and equipment feeding mechanism of friction class load as well as cranes, hoists, elevators, gravity load, is a constant torque load.

Frequency conversion the power dragging constant torque nature of the load, the output torque at low speed to be large enough and have sufficient overload capacity. If you need steady speed at low speeds long run, should consider the heat capacity of the standard cage induction motor, to avoid excessive motor temperature rise.

2 constant power load

Such load characteristics substantially inversely proportional to the demand torque TL and the speed n, but its product, i.e., power was kept approximately constant. Metal cutting machine tool spindle mill, paper machine, film production line coiler, uncoiler belong constant power load.

Constant power load nature should certain speed range. Very low speed, the mechanical strength limit, TL impossible to grow indefinitely into the nature of the constant torque at low speeds. The load constant power and constant torque District have a great impact on the choice of transmission scheme. When the motor is in constant flux governor, the maximum allowable output torque constant, belonging to the constant torque speed; weak magnetic speed, the maximum allowed is inversely proportional to the output torque and speed is a constant power speed. If the constant torque and constant power range of the motor at a constant torque and constant power speed range and the load coincident, i.e. the case of the so-called "matching", the capacity of the motor and the inverter power supply capacity Min.

3 fluid class load

Kind of load torque proportional to the square of the speed, power and speed proportional to the cube. All kinds of fans, pumps and oil pumps, all belong to the a typical fluid class load.

The fluid class load by the governor of the variable frequency power to regulate air flow, flow, can significantly save energy. Fluid class load is proportional to the cube of the excessive growth of demand for power in the high-speed, load speed, so it should not make such load ultra-frequency operation.