If the high reliability of the inverter body is alone, and the inverter selection and capacity matching are not appropriate, the variable frequency speed control system can not achieve high reliability or even operation. To do this, we must:
First, according to the nature of the load, the inverter type is selected correctly. The general principle is what kind of inverter with the nature of the load characteristics.
(1) Constant torque production equipment - The load torque is basically constant within the speed regulation range. A frequency converter with constant torque performance should be selected. Its overload capacity is maintained at 150% of rated current for 1 minute.
(2) Square torque production equipment--In the speed regulation range, the load torque is proportional to the square of the speed, ie Mâˆn2, centrifugal fan, water pump is its typical representative. A frequency converter with Mâˆn2 characteristics has a small overload capability, and 110%-120% of rated current is overloaded for 1 minute.
(3) Constant power load production equipment - In the speed regulation range, the speed is low and the torque is large; the high speed torque is small, that is, M?NC (constant). Typical equipment such as machine tools and winding mechanisms.
Of course, some inverter manufacturers' products are universal and do not share constant torque and square torque load. Both loads are available. The constant power load characteristic is realized by the V/F ratio, and there is no constant power performance of the inverter.
In summary, the choice of inverter model should be compatible with the load torque. Inverters with constant torque characteristics can be used for fan pump loads. Conversely, inverters with square torque characteristics must never be used for loads with constant torque characteristics. Secondly, according to the motor brand rating parameters to match the inverter capacity, usually matching principle: PEINV ≥ PEmotor (kW) IEINV ≥ 1.1-1.2 IEmotor (A)
Pay attention to the current parameter, because the power consumption of the power electronic module is IX â–³ U (the product of current and tube voltage drop), and is not directly related to the output voltage of the inverter. The output power of the inverter is proportional to the product of the output voltage and output current. In practice, the output current has often exceeded, but the output power has not exceeded, resulting in a failure of the power electronic power module to burn out. Therefore, the current indicator should be mainly considered. The main circuit structure of the variable frequency speed control has various application forms and can be matched in the following manner:
(1) One-to-one single motor frequency conversion speed regulation mode Because the frequency converter has a soft start (low-voltage low-frequency start--step-up boosted up-conversion speed), there is no inrush current phenomenon.
Therefore, use IEINV ≥ (1.1-1.2) IE motor
According to the determined IEINV current value, check the product catalog to find a suitable inverter (2) Multi-motor variable frequency speed control mode (multi-motor sharing one large inverter)
For example, there are N motors with the same parameters, and the synchronous starter motor is K sets. The maximum current condition is when the (NK) motor has started, it is under high frequency and high voltage operation, and finally the K motor is directly started (the direct starting current is very high. Large, asynchronous motor 5-7 times, permanent magnet synchronous motor 10-14 times, set to IQ motor).
The sufficient and necessary conditions for selecting a frequency converter are: a.IEINV a≥(1.1-1.2)[N x IE motor] b.IEINV b≥(1.1-1.2)[(NK) x IE motor +K x IQ motor] In IEINV and IE INV select the value of the current, and then check the product catalog to determine the specifications of the inverter. (3) Multi-inverter multi-motor variable frequency speed control mode with shared DC power supply (inverter and motor still belong to 1-to-1 mode)
With the advancement of frequency conversion technology, a small inverter multi-motor scheme (substantially similar to 1 to 1 variable frequency speed regulation) and a shared DC power supply scheme have appeared (multiple inverters share one DC power supply, one inverter drives one) Motor.)
Common DC power supply current calculation formula: IE con≥(1.1-1.2)[IE motor1+ ......+IE motorn] or (1.1-1.2) x N x IE motor
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