Frequency inverters have numerous setting parameters, each with a specific range of selection. It's common to encounter issues where incorrect parameter settings prevent the inverter from functioning properly.
Therefore, debugging a frequency inverter begins with correctly setting its parameters. Here are 16 basic methods for setting inverter parameters for reference:
01 Control Mode
This refers to speed control, torque control, PID control, or other methods. Once a control mode is selected, static or dynamic identification is usually necessary based on control precision.
02 Minimum Operating Frequency
This is the lowest speed at which the motor can operate. When running at low speeds, the motor's cooling performance is poor, and prolonged operation can lead to motor burnout. Additionally, the current in the cable increases at low speeds, potentially causing the cable to overheat.
03 Maximum Operating Frequency
The typical maximum frequency for inverters is up to 60Hz, with some reaching 400Hz. High frequencies allow motors to operate at high speeds, which can strain the bearings and rotors of standard motors beyond their rated speed, challenging their ability to withstand the centrifugal forces.
04 Carrier Frequency
The higher the carrier frequency is set, the greater the high-order harmonic components will be. This is closely related to cable length, motor heating, cable heating, and inverter heating.
05 Motor Parameters
Inverter parameters include motor power, current, voltage, speed, and maximum frequency, all of which can be directly obtained from the motor nameplate.
06 Skip Frequency
Resonance might occur at certain frequency points, particularly with taller structures. When controlling compressors, it's crucial to avoid frequencies that could cause surge.
07 Acceleration/Deceleration Time
Acceleration time is the duration from 0 to maximum frequency, while deceleration time is from maximum frequency back to 0. These times are generally set based on the rise or fall of the frequency setting signal. During acceleration, the rate of increase must be limited to prevent overcurrent; during deceleration, the rate must be controlled to avoid overvoltage.
- Acceleration Time Settings: Limit acceleration current below the inverter's overcurrent capacity to avoid tripping due to overcurrent stall.
- Deceleration Time Settings: Prevent excessive voltage in the smoothing circuit to avoid tripping due to overvoltage stall. These times can be calculated based on load but are often initially set longer based on load and experience, then adjusted by observing for overcurrent or overvoltage alarms during motor start-stop tests.
08 Torque Boost
Also known as torque compensation, this compensates for the torque drop at low speeds due to the stator winding resistance by increasing the V/f ratio in the low-frequency range. Automatic setting adjusts voltage during acceleration to boost starting torque. Manual compensation requires selecting an optimal curve based on load characteristics, particularly startup characteristics. Incorrect settings for variable torque loads can lead to excessive low-speed voltage, wasting energy, or insufficient torque causing poor motor acceleration.
09 Electronic Thermal Overload Protection
This function protects the motor from overheating by calculating temperature rise based on running current and frequency. It's suitable for "one motor per inverter" setups; for "multiple motors per inverter," thermal overload relays should be installed on each motor. The setting value (%) is calculated as [(Motor Rated Current / Inverter Rated Output Current) × 100%].
10 Frequency Limit
This sets the upper and lower limits for inverter output frequency to protect equipment from damage due to setting errors or external signal failures. These settings should be based on practical needs and can serve as speed limits for applications like conveyor belts, where setting a lower maximum frequency reduces mechanical wear.
11 Bias Frequency
Also known as deviation or frequency bias setting, this adjusts the output frequency when the frequency setting signal from an external analog source is at its minimum. Some inverters allow setting the bias polarity when the signal is at 0%. If the inverter outputs xHz when the frequency setting is 0%, setting a negative bias of xHz can adjust the output back to 0Hz.
12 Frequency Setting Signal Gain
This function is only effective when using an external analog signal for frequency setting. It compensates for discrepancies between the external voltage and the inverter's internal reference (+10V) and facilitates the selection of analog voltages. When the input signal is at its maximum, the frequency output percentage is calculated and set accordingly. For instance, if an external 0-5V signal corresponds to 0-50Hz output, set the gain to 200%.。
13 Torque Limitation
This includes both driving and braking torque limits. It calculates torque based on output voltage and current, improving response to load impacts during acceleration, deceleration, and constant speed. Torque limitation enables automatic speed control, ensuring the motor follows the set torque values even if acceleration or deceleration times are shorter than load inertia time.
- Driving Torque: Provides high starting torque, controlling motor slip during steady-state to keep torque within set limits, preventing tripping from sudden load increases or short acceleration times.
- Braking Torque: A lower setting increases braking force, suitable for rapid acceleration/deceleration. Setting it too high might lead to overvoltage alarms. Setting to 0% minimizes regenerative energy, allowing deceleration without braking resistors, but might cause brief motor freewheeling in some loads, causing inverter restarts and current fluctuations.
14 Acceleration/Deceleration Curve Selection
Inverters typically offer linear, non-linear, and S-curve options, with linear being the most common. Non-linear is suited for variable torque loads like fans, while S-curves are for constant torque loads, offering smoother acceleration/deceleration. Selection should consider load torque characteristics, though exceptions exist; an example is a boiler draft fan where switching from non-linear to S-curve resolved tripping issues due to reverse load from smoke flow.
15 Vector Control
Based on the principle that asynchronous motors share torque generation mechanisms with DC motors, vector control decomposes stator current into field and torque components for individual control, achieving DC motor-like performance. Most modern inverters use sensorless vector control, compensating for load variations without external feedback, suitable for most applications. Slip compensation control adjusts speed deviations due to load changes, mainly for positioning.
16 Energy-saving Control
For fans and pumps (variable torque loads), where torque decreases with the square of speed, inverters with energy-saving features use specific V/f patterns to enhance efficiency by automatically lowering output voltage based on load current. This can be enabled or disabled depending on the situation.
It's worth noting that electronic thermal overload protection and frequency limits are advanced features, but some users find them unusable due to:
- Discrepancy between motor parameters and inverter requirements.
- Lack of understanding of parameter functionalities, like energy-saving control only being applicable in V/f mode, not vector control.
- Vector control enabled without proper motor parameter setup or incorrect data reading.
