1. Introduction With the improvement of living standards, people have increasingly higher requirements for their living environment, which has greatly promoted the development of housing design and decoration and related industries. Various new high-quality decorative materials are emerging in an endless stream, and market demand is increasing daily. Patterned glass, with its superior performance and wide range of applications, is increasingly favored by the market. As one of the important processes in the production of patterned glass, the annealing furnace drive control system controls the operation of the press and the drive roller motor of the annealing furnace, ensuring that the required patterns are pressed onto the glass surface, while ensuring that the glass belt runs smoothly through the annealing furnace. Since the quality of control directly affects the quality of patterned glass, the design of the annealing furnace speed control system is highly valued. The development of power electronics technology and the penetration of modern control theory into the field of AC electrical drives have led to the rapid development of AC asynchronous motor drive speed control systems. In recent years, due to the rapid development of power electronic converters and digital signal processors (DSPs), high-performance frequency converters have been continuously introduced, and variable frequency asynchronous motor speed control devices have been increasingly widely used, significantly improving the system's performance in terms of speed accuracy, stability, and dynamic response. This article introduces a speed control system for AC asynchronous motors in an annealing furnace for patterned glass, based on a high-performance frequency converter and employing a sensorless vector control method. 2. Annealing Furnace AC Speed ​​Control System 2.1 System Introduction The structure of the annealing furnace drive system is shown in Figure 1. The patterned glass forming process is briefly described as follows: Glass strips from the melting furnace are pressed by the pattern rollers of the press, forming the desired patterns on the surface of the glass strips. They then continue into the annealing furnace for annealing and cooling to eliminate intermolecular stress and improve glass strength. The system consists of one press pattern roller drive motor (1M) and two annealing furnace drive motors (2M). One annealing furnace drive motor is in operation and the other is on standby, allowing operators to choose either the working or standby motor. The system requires speed control of the three frequency-converted asynchronous motors to ensure the desired patterns are pressed onto the glass surface while ensuring the glass strip passes smoothly through the annealing furnace. Speed ​​fluctuations directly affect the pressed pattern effect and the flatness of the glass surface, placing high demands on the dynamic and static performance of the drive system. The control performance of the annealing furnace drive system plays a crucial role in product quality. To ensure product quality, the transmission system must guarantee the precision of the motor's stable speed operation. The motor's operating speed should be adjusted according to the production of glass of different thicknesses. The production process requires a speed ratio of 1:10, corresponding to a motor operating frequency range of 5–50Hz. Depending on the actual production needs, the speed ratio of the press and annealing furnace motors is not a fixed value and should be adjusted as needed. Furthermore, when the thickness of the glass plate changes, the two motors must meet the requirement of unified adjustment; that is, after adjusting the speed ratio of the annealing furnace and press motors, both speeds must be increased or decreased simultaneously. Therefore, high requirements are placed on dynamic performance, and the transition process should be smooth and short. [align=center] Figure 1 Schematic diagram of the annealing furnace transmission system[/align] 2.2 Annealing Furnace Transmission Control System The annealing furnace transmission speed control system mainly consists of a frequency converter, a speed signal controller, and other corresponding relay logic control circuits. The frequency converter uses the high-performance Yaskawa VS616-G5 from Japan, and the control mode adopts a sensorless vector control method. As is well known, AC motors are multivariable, strongly coupled, nonlinear, and time-varying controlled objects. Using only constant voltage/frequency (U/f) scalar control is often insufficient to meet the requirements of speed control systems for speed accuracy, dynamic performance, and stable torque at low frequencies. Furthermore, the addition of speed sensors in practical engineering leads to increased costs and inconvenient installation and maintenance. Sensorless vector control effectively addresses these contradictions. The Yaskawa VS616-G5 employs high-performance IGBTs and SPWM inverter control technology. The control system utilizes flux observer control based on modern control theory and neural network speed prediction to achieve true current vector control and high-precision torque control. The VS616-G5 features auto-tuning, automatically identifying motor parameters within the range listed on the motor nameplate when using vector control. Therefore, vector control can be applied to both dedicated inverter motors and general-purpose motors, maximizing motor performance. The inverter control principle is shown in Figure 2, applicable to all three motors. [align=center]Figure 2 Variable Frequency Drive (VFD) Control Principle Diagram[/align] The VFD's operating command comes from the control terminal signal, and the motor's start and stop are controlled by opening and closing control terminal 1. The VFD's frequency command comes from control terminals 16 and 17. During normal production, the VFD's speed signal is provided by the Speed ​​Signal Controller (SFC). The main function of the Speed ​​Signal Controller is to provide the VFD with a 0-10V main speed signal. By adjusting different resistors in the SFC control circuit, the 0-10V signal in the output circuit changes according to different requirements to meet the needs of single-mode and unified speed adjustment of the press and annealing kiln motors. Terminals 21 and 22 are connected to the speed display table on the on-site operation control console for operator observation. Fault contact terminals 19 and 20 are connected in series in the motor start control circuit. When the VFD detects an overload or other fault in the motor, it disconnects the motor start circuit for safety reasons. During the production of patterned glass, abnormal situations such as extrusion deformation often occur when the glass strip is placed on the embossing roller and enters the annealing kiln. By utilizing the characteristic of Yaskawa inverters where multi-step speed references have higher priority than master speed reference commands, manual/automatic function switching is achieved through multi-function terminal 5 to solve the aforementioned problems. Specifically, when an abnormal situation occurs during production, rotating the manual/automatic switching knob closes terminal 5, causing the motor to quickly switch to the preset value of the inverter's internal multi-step speed 1 (D1-02), allowing the motor to run at a lower speed for timely intervention by the operator. The basic setting parameters of the inverter operating system are shown in Table 1. Actual operating results show that the application of vector control significantly improves the low-frequency characteristics of the motor, resulting in stable speed and no obvious torque pulsation. 2.3 Speed ​​Signal Controller (SFC) Due to the needs of patterned glass production, the speed adjustment of the working motors is frequent and requires specific conditions, namely, meeting the needs of both single-step and unified adjustment of the annealing kiln drive motor and the press motor. Therefore, a reliable signal source is needed to provide the inverter with the master speed command. This task is accomplished by a specially designed speed signal controller. The main components of the speed signal controller (SFC) are shown in Figure 3. [align=center]Figure 3. Block Diagram of Speed ​​Signal Controller (SFC)[/align] Output channels 1 and 2 of the controller provide 0-10V voltage signals as the reference frequency for the inverter's operation. When the value of resistor Rf is adjusted, the values ​​of output channels 1 and 2 change simultaneously; when the values ​​of resistors Rf1 or Rf2 are adjusted separately, the values ​​of the corresponding output channels change. This satisfies the requirements of both monotonic and unified speed control. The two motors driving the annealing kiln operate in a one-in-one standby mode, and the system strictly prohibits the simultaneous parallel operation of the two motors. Therefore, the system control circuit is equipped with a working motor selection and motor operation interlock relay control circuit. At the same time, the circuit of output channel 2 of the speed signal controller should also be included in this part of the control. That is, the voltage signal from the SFC to the standby motor of the annealing kiln will be shielded, and only the working motor will receive the voltage signal from output channel 2 of the SFC. 3 Conclusion Operating practice shows that the sensorless vector AC speed control system based on a high-performance inverter has many advantages such as high speed regulation accuracy, large speed regulation range, simple structure, reliable operation, and convenient operation. Especially at low frequencies, the speed is stable and there is no torque pulsation. It is very popular in practical applications. At present, this control system has been put into use on many patterned glass production lines in China and has been well received by users. References [1] Yaskawa Electric Corporation, VS616-G5 Instruction Manual, 2002. [2] Chen Boshi. Development and application prospects of frequency converters [J]. Frequency Converter World, 2002 (9). About the author: Li Kangnan is currently an electrical engineer at Hangzhou Design Institute of China New Building Materials Industry, engaged in the design and research of factory automation systems, and his main fields include computer control, electrical drive control and process automation control.