Common frequency parameters of the inverter - Solutions - Huaqiang Electronic Network

1. Given Frequency

The given frequency is the output frequency of the inverter set by the user according to the production process requirements. For example, when replacing a fan motor from a fixed-frequency power supply to a variable-frequency drive, the set frequency can be 50Hz. There are two common methods: using the inverter's operation panel to input the digital frequency value (e.g., 50Hz), or regulating it via an external reference signal (like a potentiometer for voltage or current control).

2. Output Frequency

The output frequency refers to the actual frequency the inverter produces. When the motor load changes, the inverter adjusts its output frequency to maintain system stability. Therefore, the output frequency usually fluctuates around the given frequency.

3. Reference Frequency

The reference frequency, also known as the base frequency, is typically the rated frequency of the motor. The reference voltage is the inverter’s output voltage at this frequency, often matching the motor’s rated voltage. This relationship is illustrated in Figure 3-3.

4. Upper and Lower Frequency Limits

The upper and lower frequency limits define the maximum and minimum output frequencies of the inverter, denoted as f_H and f_L. These limits help protect the system from excessive speeds that could cause damage. For instance, setting f_H = 60Hz and f_L = 10Hz ensures that if the given frequency is 70Hz or 5Hz, the output will be capped at 60Hz or 10Hz respectively. This feature prevents accidental over-speeding or under-speeding due to errors.

5. Jog Frequency

Jog frequency is the frequency used during manual jogging of the motor before full operation. It allows operators to test the system safely without risking high-speed failures. Many inverters allow users to preset the jog frequency, so they can simply switch to "jog mode" instead of adjusting the frequency each time.

6. Carrier Frequency (PWM Frequency)

The carrier frequency refers to the frequency of the PWM pulses used in the inverter's output. A higher carrier frequency results in smoother current waveforms but increases electromagnetic interference. Inverters typically allow users to adjust this frequency within a range to balance performance and noise. Table 3-5 illustrates the trade-offs between carrier frequency and system performance.

7. Start Frequency

The start frequency is the frequency at which the motor begins running. It can be set to zero, but for heavy loads with high inertia, a higher starting frequency may be needed to provide sufficient torque. Most inverters allow users to predefine this frequency, ensuring the inverter ignores any frequency below it during startup.

8. Multi-Speed Operation

Multi-speed operation allows machines to run at different speeds depending on the production stage. This is achieved through combinations of digital inputs (DINs). For example, four DINs can produce 16 different speed settings. Each combination corresponds to a specific frequency, as shown in Table 3-6.

9. Jump Frequency

Jump frequency, or avoidance frequency, is the frequency range that the inverter avoids to prevent mechanical resonance. If the given frequency falls within this range, the inverter will adjust the output to the nearest safe frequency. This helps avoid damaging vibrations caused by resonance. Most inverters offer multiple jump intervals for flexibility.