For information on the principles of chopper-fed internal speed control and high-voltage frequency converters, readers can refer to relevant materials. This article attempts to discuss the performance comparison of the two from multiple aspects, offering only one perspective for reference. Motor Requirements Chopper-fed internal speed control requires a special motor, while high-voltage frequency converters can use any asynchronous motor. Internally fed motors have complex manufacturing processes, are non-standard products, and may be more troublesome to maintain, with higher maintenance costs than ordinary motors. Furthermore, the rotor has slip rings, increasing maintenance workload. Internally fed speed control systems have low reliability at high power levels, which is related to the motor itself. High-voltage frequency converters can drive multiple systems simultaneously. For pump-type loads, switching between running and standby motors is often necessary, a requirement that internally fed speed control motors cannot meet. Additionally, due to the complex manufacturing process of slip rings at high speeds, chopper-fed internal speed control cannot be used with two-pole motors. Power Factor High-voltage frequency converters maintain a power factor above 0.96 on the grid side across the entire load range, so no additional power factor compensation measures are required. The power factor of the chopper-controlled internal feed-in speed regulation section can reach around 0.9, but this is only a small part of the system power. The power factor on the grid side decreases with decreasing speed, falling below the power factor of the asynchronous motor itself. The power factor of the speed regulation system is between 0.5 and 0.7. Users can purchase compensation cabinets to improve the power factor, but the power factor changes with the load, making compensation very complicated. There is no good technical solution to this problem. Harmonics High-voltage frequency converters use multi-pulse rectification on the grid side and multi-stage PWM modulation on the motor side, resulting in grid-side current harmonics of less than 4% and motor-side harmonics of less than 2%. Internal feed-in speed regulation converters use 6-pulse rectification and inversion, so harmonics exist in the rotor winding, converter, and internal feed-in winding. The stator winding will definitely be affected, and its harmonic situation is worse than that of high-voltage converters. Efficiency Variable frequency speed regulation and cascade speed regulation (internal feed-in speed regulation is another type of cascade speed regulation) are both recognized as highly efficient speed regulation methods in the technical field. The efficiency of high-voltage variable frequency speed control is generally around 96%-97%. The efficiency of internal feed rate speed control is not significantly better than that of variable frequency speed control because: (1) due to the internal feed rate winding, the efficiency of the motor is definitely lower than that of the standard asynchronous motor; (2) during speed control operation, some energy circulates between the stator winding, rotor winding, speed control device, and internal feed rate winding; (3) the power factor of the system is low and the copper loss is large; (4) there are harmonics in the rotor winding, converter, and internal feed rate winding, which affect the efficiency of the motor; (5) the coupling efficiency between the stator winding and the internal feed rate winding is low. At present, efficiency test data of the internal feed rate speed control system cannot be provided, and it is unfounded to claim that its efficiency is high. Speed ​​range The speed range of high-voltage frequency converters is 0-200%, which is stepless speed control in the full range. The speed range of internal feed rate speed control is generally 70%-95%, and above 95%, it must be switched to power frequency operation. If the speed range is to be increased, the price advantage will no longer exist, and the technical difficulty will also increase. Speed ​​Control Accuracy Variable frequency speed control can precisely adjust the motor speed with an error within a few revolutions per second. Feedforward speed control relies on the power derived from the rotor to adjust the speed; the functional relationship between the two is very complex, allowing only approximate adjustment. Starting Method Variable frequency speed control can achieve a completely soft start. With feedforward speed control, even with a frequency-sensitive resistor in series with the rotor, the starting current can still reach about three times the rated current. During startup, it is necessary to first run at the mains frequency, disconnect the starting resistor, then connect the converter, and then adjust the speed, causing significant inconvenience. In some operating conditions, this operation is not permitted. Power-Off Method High-voltage frequency converters have no special requirements for the operating sequence. In case of a fault, users are allowed to directly disconnect the high-voltage switch on the grid side, just as before the frequency converter was installed. With feedforward speed control, when stopping, it is necessary to first run at the mains frequency, disconnect the converter, and then disconnect the motor. Directly disconnecting the motor is an abnormal operation that is not allowed; users must design the process to meet this requirement. Adaptability to Power Grid High-voltage frequency converters have extremely strong adaptability to the power grid, allowing voltage fluctuations of ±15%, uninterrupted operation even with a 35% voltage drop, continued full-load operation even with a 5-cycle voltage loss, and uninterrupted operation even with a 3-second voltage loss. Internal feeder speed control, due to its active inverter component, is less capable of achieving these functions if the power grid fails, causing inverter failure. Price Internal feeder speed control has a price advantage when dealing with smaller speed ranges and lower power requirements. Footage Internal feeder speed control has no transformer, resulting in a smaller footprint. Development Trends Internationally, variable frequency speed control is the trend in technological development. Japanese and German companies that previously produced and sold cascade speed control systems have now shifted to variable frequency speed control because its advantages are obvious.