A brief discussion on the control function of frequency converter

Inverter control function

1. Setting the inverter output frequency The inverter output frequency can be set in the following ways.

① Use the function keys on the operation panel to set the frequency.

②Preset the function parameter code.

③Set the frequency using the potentiometer on the operation panel.

④ External terminal control frequency, including three methods of setting frequency, namely external analog setting, multi-stage speed regulation setting (also called switch setting) and network communication setting.

2. Limit frequency and avoidance frequency

(1) Maximum frequency fmax The maximum frequency that the inverter is allowed to output is generally the rated frequency of the motor. In Siemens MM440, it is set in P1082, such as P1082 = 50Hz. The industrial frequency in my country is 50Hz, so the maximum frequency is set to 50Hz in many cases. However, some motors have an exception if their own speed exceeds 50Hz (such as variable frequency motors).

(2) The basic frequency fb is also called the reference frequency or base frequency. It is set only in the U/f mode. It refers to the value fN reached by f when the output voltage U=UN (rated voltage), which is generally the rated frequency. The relationship between the output frequency and voltage of the inverter is shown in Figure 2-1.

Frequency and voltage relationship diagram

Limit the output frequency range of the inverter, thereby limiting the speed range of the motor and preventing accidents caused by incorrect operation. (3) Upper limit frequency fH The maximum frequency allowed by the inverter output. The upper and lower limit frequencies are shown in Figure 3-2.

Online and offline frequency

(4) The lower limit frequency fL is the lowest frequency allowed by the inverter output. In Siemens MM440, it is set in P1080, such as P1080 = 0Hz. For ordinary three-phase asynchronous AC motors, if there are no special requirements, the lower limit frequency can be set to 0Hz and the upper limit frequency can be set to 0Hz.

(5) Avoidance frequency is also called skip frequency. To avoid transmission system resonance, avoidance frequency should be set. It is the frequency that the inverter skips and does not run. Generally, more than three avoidance frequencies can be set. The avoidance frequencies are shown in Figure 3-2.

Avoidance frequency

Three ways to set avoidance frequency:

① Set the upper and lower frequencies of the avoidance frequency. For example, if you set 43Hz and 39Hz, the avoidance frequency range is 39~43Hz.

② Set the avoidance frequency value and avoidance frequency range. In Siemens MM440, set the jump frequency in P1091 (also in P1092, P1093 and P1094), and set the jump frequency width in P1101. For example, if P1091=40Hz and P1101=2Hz, the avoidance frequency range is 38~42Hz.

③Only set the avoidance frequency, and the avoidance frequency range is set by the inverter.