Principles for inverter selection
1. Fully understand the performance requirements of the controlled object. Generally speaking, if the requirements for starting torque, speed regulation accuracy, and speed regulation range are high, you need to consider using a vector frequency converter. Otherwise, a general-purpose frequency converter will suffice.Understand the load characteristics, if it is a general purpose In this case, you need to determine whether the inverter is G type or P type.
2Understand the main nameplate parameters of the motor used: rated voltage and rated current.
3. Determine the maximum current that may occur in the load, and use this current as the rated current of the selected inverter. If thecurrent is smaller than the rated current of the adapted motor, select the corresponding inverter according to the adapted motor and consider the cost factor. If you choose a general-purpose inverter, you can chooseP type machine.
4. In the following situations, it is necessary to consider increasing the capacity by one level:
1) Long-term high temperature and large load;
2) Sites where abnormal or faulty shutdowns may have catastrophic consequences;
3) The target load fluctuates greatly;
4) The on-site power grid is low for a long time and the load is close to the rated value;
5) Wound motor, synchronous motor or multi-pole motor ( span>6extremely above).
Fully understanding the options supported by each inverter is the basis for correct selection.
How to choose an inverter
The correct selection of the frequency converter is very critical for the normal operation of the control system. When selecting an inverter, you must fully understand the characteristics of the load driven by the inverter. In practice, people often divide production machinery into three types: constant torque load, constant power load and fans and water pumps.load.
1. Constant torque load
Load torque TL has nothing to do with speed n, TL always remains constant or basically constant at any speed. For example, friction loads such as conveyor belts, mixers, and extruders, as well as potential energy loads such as cranes and hoists, are all constant torque loads.
When the frequency converter drives a load with constant torque, the torque at low speed must be large enough and it must have sufficient overload capacity. If stable operation at low speed is required, the heat dissipation capacity of the standard asynchronous motor should be considered to avoid excessive temperature rise of the motor.
2. Constant power load
Machine tool spindle and rolling mill, paper machine , the torque required by the coiler, uncoiler, etc. in the plastic film production line is generally inversely proportional to the rotation speed. This is the so-called constant power load. The constant power property of the load should be within a certain range of speed changes. When the speed is very low, due to the limitation of mechanical strength, TL cannot increase infinitely and transform into constant torque properties at low speed. The constant power zone and constant torque zone of the load have a great influence on the selection of the transmission scheme. When the motor is in constant flux speed regulation, the maximum allowable output torque remains unchanged, which is a constant torque speed regulation; while in field weakening speed regulation, the maximum allowable output torque is inversely proportional to the speed, which is a constant power speed regulation. If the constant torque and constant power speed regulation range of the motor is consistent with the constant torque and constant power range of the load, that is, the so-called “matching” situation, the capacity of the motor and the capacity of the frequency converter are both minimum. .
3. Fan and pump loads
In various fans, water pumps, and oil pumps , as the impeller rotates, the resistance generated by the air or liquid within a certain speed range is roughly proportional to the square of the speed n. As the rotational speed decreases, the rotational speed decreases by the square of the rotational speed. The power required for this load is proportional to the third power of the speed. When the required air volume and flow rate decrease, the frequency converter can be used to adjust the air volume and flow rate through the speed adjustment method, which can greatly save electric energy. Since the power required at high speed increases too quickly with the speed and is proportional to the cube of the speed, fans and pumps should generally not be operated beyond the industrial frequency.
Types of frequency converters
Frequency converters are generally divided into four types: mini type, general type, vector type, and special type.
1. Mini inverter
More suitable for customers with small equipment. Mini inverters are exquisite in appearance, easy to operate, and lightweight. Compact designFeatures excellent design and performance. Obviously, it is suitable for some customers who make small equipment.
2. Universal inverter
Full-featured, powerful and stable, suitable for driving conventional loads: such as mechanical processing equipment, Roche fans also need to be universal sex converter.
3. Vector inverter
The performance is better than that of general-purpose inverter, and it is suitable for some loads with large inertia and requiring low frequency and high torque starting (that is, It is said to ensure that it can operate under load even at low frequency) load conditions.
4. Special-purpose inverters
Special-purpose inverters are targeted at designated industries.
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