1. Introduction With the continuous advancement of technology, frequency converters are constantly being updated, replaced, upgraded, and evolved, and their applications are becoming increasingly widespread. In particular, the excellent speed regulation, energy saving, and soft-start performance of frequency converters are highly favored by users. As users of frequency converters, mastering and being familiar with the correct on-site commissioning methods and techniques is crucial for the normal operation of the frequency converter, reducing malfunctions, and extending its service life. Based on years of practical experience in frequency converter theoretical research and practical application, the author offers the following points of commissioning experience for exchange with colleagues, hoping to stimulate further discussion. 2. Main Commissioning Steps Commissioning a frequency converter mainly involves the following five steps. 2.1 Inverter System Function Assessment Before commissioning the frequency converter, it is essential to carefully read the instruction manual and related information of the frequency converter to be commissioned, and familiarize yourself with its operating environment and precautions. Especially before powering on the frequency converter, carefully observe and check whether there are obvious signs of fault, such as whether its input and output terminals meet the requirements of the instruction manual. Pay special attention to any new additions. 2.2 Inorganic No-Load Operation Debugging of Frequency Converter The following three steps are the most basic and important debugging operations for the inorganic (i.e., no motor connected) no-load (i.e., motor without load) operation debugging of frequency converter: (1) Ground the grounding terminal of the frequency converter and connect its power input terminal to the power supply through the leakage protection switch; (2) Check whether the factory display of the frequency converter display window is normal. If it is incorrect, it should be reset; otherwise, the supplier should be asked to replace it; (3) Familiarize yourself with the operation keys of the frequency converter. Most frequency converters have six keys: run, stop, prog, data/enter, up▲, down▼. The definitions of the operation keys are basically the same for different frequency converters. In addition, some frequency converters also have function keys such as monitor/display, reset, jog, and shift. These keys need to be debugged. 2.3 Debugging of Variable Frequency Drive with Motor on No-Load Operation The following four steps are crucial for debugging the variable frequency drive with the motor on (i.e., connected to the motor) and without load (i.e., the motor is not under load). (1) Set the motor power, number of pole pairs, and determine the operating current of the variable frequency drive. (2) Set the maximum output frequency and base frequency of the variable frequency drive and set the torque characteristics of the motor. The selection of voltage/frequency (V/F) operating mode includes the maximum operating frequency, the base operating frequency (i.e., the base frequency), and the torque type. • The maximum frequency refers to the highest frequency at which the variable frequency drive motor system can operate. Since the maximum operating frequency of the variable frequency drive itself may be relatively high, when the maximum allowable operating frequency of the motor is lower than the maximum operating frequency of the variable frequency drive, the operating frequency should be set according to the requirements of the motor and its load. • The base operating frequency is the dividing line between constant power control and constant torque control of the motor by the variable frequency drive, and should be set according to the rated voltage of the motor. • The torque type refers to whether the load is a constant torque load or a variable torque load. Users should select one of the operating modes according to the V/F operating mode diagram and load characteristics in the variable frequency drive instruction manual. General-purpose frequency converters are equipped with multiple v/f curves for users to choose from. When using them, the appropriate v/f curve should be selected according to the nature of the load. If it is a fan or pump load, the torque operation code of the frequency converter should be set to variable torque and reduced torque operation characteristics. In order to improve the low-speed performance of the frequency converter during startup and make the output torque of the motor meet the startup requirements of the production load, the starting torque should be adjusted. In the frequency conversion speed regulation system of three-phase asynchronous motor, the torque control is relatively complex. In the low frequency range, since the influence of resistance and leakage reactance cannot be ignored, if v/f is kept constant, the magnetic flux will decrease, thereby reducing the output torque of the motor. Therefore, the voltage should be appropriately compensated in the low frequency range to increase the torque. Generally, the frequency converter is manually set by the user. (3) Set the frequency converter to the built-in keyboard operation mode, press the run key and stop key respectively, and observe whether the motor can start and stop normally. (4) Set the electronic thermal relay function according to the instruction manual of the frequency converter. The threshold value of the electronic thermal relay is defined as the ratio of the rated current of the motor and the frequency converter, which is usually expressed as a percentage. When the inverter output current exceeds its allowable current, the overcurrent protection device will cut off the inverter output. Therefore, the maximum threshold value of the inverter electronic thermal relay shall not exceed the maximum allowable output current of the inverter. The inverter overload protection setting value can be modified. 2.4 Inverter load operation debugging Inverter load (i.e., the inverter is connected to the motor and the motor is loaded) operation debugging, the following five steps must be performed. (1) Manually operate the run stop button on the inverter panel, observe the motor running and stopping process and the inverter display window, and see if there are any abnormal phenomena. (2) If the inverter takes overcurrent protection action during the start/stop of the motor, the acceleration/deceleration time should be reset. The acceleration of the motor during acceleration and deceleration depends on the acceleration torque, while the frequency change rate of the inverter during the start/brake process is set by the user. If the motor rotational inertia or load change accelerates or decelerates according to the preset frequency change rate, the acceleration torque may be insufficient, which may cause the motor to stall, that is, the motor speed and the inverter output frequency are not coordinated, which may cause overcurrent or overvoltage. Therefore, it is necessary to set the acceleration and deceleration times reasonably according to the motor's rotational inertia and load so that the frequency change rate of the inverter can be coordinated with the motor's speed change rate. The method to test whether this setting is reasonable is to first select the acceleration and deceleration times according to experience. If overcurrent occurs during the start-up process, the acceleration time can be appropriately extended; if overcurrent occurs during the braking process, the deceleration time can be appropriately extended. (3) If the inverter still experiences overcurrent protection within the specified time, the start/stop operation curve should be changed, such as from a straight line to an S-shaped, U-shaped, or inverse S-shaped, inverse U-shaped curve. When the motor load inertia is large, a longer start/stop time should be used, and the operation curve type should be set according to its load characteristics. (4) If the inverter still experiences overcurrent protection, the maximum current protection value should be increased, but the protection should not be canceled. At least 10% to 20% protection margin should be left. If this action still occurs, the inverter with a larger power level should be replaced. (5) If the inverter drives the motor to fail to reach the preset speed during startup, there may be two reasons: • Electromechanical resonance occurs in the system, which can be judged by the sound of the motor running. The resonance point can be avoided by setting a frequency jump value (generally, inverters can set three jump points). When an inverter with V/F control mode drives a three-phase asynchronous motor, the motor current and speed will oscillate in certain frequency ranges. In severe cases, the system cannot run, and even overcurrent protection will occur during acceleration, making it impossible for the motor to start normally. This is more serious when the motor is lightly loaded or has a small moment of inertia. Ordinary inverters are equipped with frequency jump function. Users can set the jump point and jump width on the V/F curve according to the frequency points where the system oscillates. When the motor accelerates, it can automatically jump over these frequency ranges to ensure that the system can run normally. • The torque output capacity of the motor is insufficient. The factory parameter settings of inverters of different brands are different. Under the same conditions, the load capacity is different. It may also be due to different inverter control methods, resulting in different motor load capacities; or due to different system output efficiencies; resulting in differences in load capacity. In this situation, the torque boost value can be increased. If it is still insufficient, the manual torque boost function can be used, but it should not be set too high, as this will increase the temperature rise of the motor. If it still does not work, a new control method should be used. 2.5 System Debugging of Inverter Connecting to Host Computer After completing the basic manual settings debugging, if there is a host computer in the system, connect the inverter's control line directly to the host computer's control line, and change the inverter's operating mode to terminal control. According to the needs of the host computer system, adjust the range of the inverter's receiving frequency signal terminal to 0-5V or 0-10V, and the inverter's response speed to analog frequency signal sampling. 2.6 Selection and Trial Use of Inverter Control Method This section only discusses two typical control methods commonly used by inverters: flux vector control and voltage/frequency (V/F) control. (1) Variable Frequency Drive (VFD) Flux Vector Control: Three-phase asynchronous motors and DC motors theoretically share the same torque generation mechanism. Based on the principle that the product of the magnetic field and the current perpendicular to it equals the torque, the stator current supplied to the motor is divided into two parts: the magnetic field current that generates the magnetic field and the torque current that generates the torque. The vector control method decomposes the stator current into the magnetic field current and the torque current, controls them separately, and supplies the combined current to the motor, thus obtaining the same control characteristics as a DC motor. This control method can provide sufficient starting torque and sufficient low-speed torque, and is particularly suitable for situations with large load variations. However, its operating conditions have the following four limitations: The VFD capacity margin is generally required to be one level larger than the motor capacity; The motor has a high number of stages required; It can only be used for single-machine operation; The length of the motor power line cannot be too long. When the above conditions cannot be met, a series of problems such as insufficient torque or motor speed fluctuations will occur. Therefore, unless the load varies greatly, the V/F control method is recommended. (2) Voltage/F (V/F) Control Mode of Inverter The so-called voltage/frequency (V/F) means that the ratio of output voltage and output frequency of the inverter within the controllable range should be kept coordinated. The base frequency is the dividing point between the constant torque characteristic operation and the constant power characteristic operation of the motor. Therefore, the voltage/frequency control mode and characteristics can be set according to the load's requirements for torque and power to achieve the desired control purpose. 3. Precautions during commissioning When commissioning the inverter on site, the following precautions should be taken: (1) Pay attention to the setting of the output frequency range The setting of the inverter's output frequency range is the upper and lower limit values ​​of the inverter's output frequency. The purpose of setting it is to prevent the output frequency from being too high or too low due to misoperation or failure of the external frequency setting signal source, so as to prevent damage to the mechanical equipment. This setting is generally based on the maximum speed of the controlled motor or an empirical value. (2) Pay attention to the setting of the acceleration time The acceleration time is the time required for the output frequency to rise from zero to the maximum frequency, and the deceleration time is the time required for the maximum frequency to drop to zero. The acceleration and deceleration time is determined by the rise and fall of the frequency setting signal. When the motor accelerates, the rise rate of the frequency setting is limited to prevent overcurrent, and the fall rate is set to prevent overvoltage when decelerating. When setting the acceleration time, attention should also be paid to limiting the acceleration current below the inverter's overcurrent capacity to prevent the inverter from tripping due to overcurrent. When setting the deceleration time, attention should also be paid to preventing the voltage of the smoothing circuit from being too high, so as not to cause the inverter to trip due to regenerative overvoltage stall. The acceleration and deceleration time can be calculated according to the load, but it is relatively complicated. The simple method is: according to the load size, first set a longer acceleration and deceleration time based on experience, and then observe whether there are overcurrent or overvoltage alarms during operation. Gradually shorten the set time, and repeat the operation to determine the optimal value, based on the principle that no alarm is issued during operation. (3) Note the setting of motor protection function. In actual engineering, the rated current of the motor should be used as the setting value. This value is the reference value for motor overload. However, it should be noted that this function setting is invalid when one inverter controls multiple motors. (4) Pay attention to the selection of IGBT-related fast-acting fuses. IGBTs are the most important components in frequency converters. They are high-power field-effect transistors, and manufacturers use semiconductor fast-acting fuses to protect them. The fusing time is less than the breakdown time of the IGBT. If its performance changes, it will burn out the IGBT. Therefore, the selection of the fast-acting fuse model is crucial. (5) Pay attention to the setting of the number of automatic fault resets and the reset time. This setting is very important. In actual operation, some faults will inevitably occur occasionally, but they can be automatically overcome instantly, ensuring the smooth operation of the frequency converter without having to search for the fault point. 4. Conclusion This article briefly discusses the specific steps, methods, techniques, key points, and precautions for on-site commissioning of frequency converters. Although there are many types of frequency converters and countless commissioning problems may be encountered, the commissioning principles and related technical points of frequency converters are largely the same. This is the purpose of this article.