Abstract : The drive system is an important actuator in the factory, bearing the heavy responsibility of energy conversion and control. This article takes a cold rolling mill as an example and briefly introduces the composition, characteristics, protection function, and main control function of its main drive system. Keywords : IEGT; system; protection; characteristic; control I. Production Line Overview This cold rolling production line is a pickling and rolling continuous production line with an annual production capacity of 1.4 million tons. The product thickness is 0.3-2.0 mm and the width is 800-1680 mm. The rolling line is a five-stand continuous rolling mill with a maximum rolling speed of 1200 m/min. The main drive of the rolling mill adopts a high-voltage asynchronous motor with a rated capacity of 4250kW. The main drive frequency converter is a high-power IEGT frequency converter manufactured by TMEIC of Japan. II. Composition of the Drive System 1. IEGT Component IEGT (Injection Enhanced Gate Transistor) is an injection enhancement gate transistor, a high-power voltage-triggered power transistor manufactured by Toshiba of Japan. Its rated voltage is 4500V and rated current is 4000A. Unlike ordinary thyristors, which can only control turn-on, the IEGT component can control both turn-on and turn-off, with a switching frequency of 500Hz. IEGT is a three-terminal device with three external terminals: collector C, emitter E, and gate G. Its basic structure and graphic symbol are shown in Figure 1. [align=center] Figure 1 Structure and Symbol[/align] IEGT is a new type of power electronic device with voltage-driven MOS gate capable of controlling large currents. The IEGT developed by Toshiba Corporation of Japan utilizes the electron injection enhancement effect, achieving low on-state voltage through an enhanced injection structure. This allows it to combine the advantages of both IGBTs and GTOs: low saturation voltage drop, wide safe operating area, low gate drive power (two orders of magnitude lower than GTOs), and higher operating frequency. IEGTs have potential as a MOS-based power electronic device (if the capacity of a single IEGT inverter can be increased to over 12MVA, it will have excellent application and development prospects), featuring low loss, high-speed operation, high withstand voltage, and intelligent in-situ gate drive. 2. Controlled Objects of the Main Drive System: The controlled objects of the main drive system are the main motors of frames 1# to 5#, and the main motors of the two winding machines. The rated power of the main motors for frames 1# to 5# is 4250KW-2650/2850V-1045A/999A-24.2/50.7HZ-715/1500rpm. The rated power of the two winding machine motors is 2000KW-1890/2435V-703/550A-16.0/50.8HZ-470/1500rpm. The transmission equipment utilizes a high-performance speed measurement tool – a speed resolver – achieving a speed control accuracy of ±0.01%. Its torque control accuracy is ±10%, current control accuracy is ±2%, speed control range is 1:100, and the digital resolution of the speed is 1/25000. The overall efficiency of the frequency converter reaches 98.5%. [align=center]Figure 2 Controlled objects of the main production drive[/align] st1 to st5 are the main motors driven by the main drive; TRA and TRB are the main motors of the winding machines. Figure 2 clearly shows the position of the main motor in the production line (as indicated by the dotted box). The five main motors on each frame are controlled by speed, while the two winding machines are controlled by torque. [align=center] Figure 3: Water Cooling System Diagram of the Main Drive[/align] 3. Pure Water Cooling Unit The simplified diagram of the main drive system shows the cooling circuit and equipment: six drive cabinets are cooled by a cooling water pipe with one inlet and one outlet, which ultimately connects to the pure water cooling unit. The pure water cooling unit (see the dotted box in the lower right corner of Figure 3) is a single unit, its function being to remove heat from the IEGT components and water resistors of each phase. When the motor stops rotating, the heat generated by the IEGT components is not significant, and the pure water temperature rises slowly; when the motor is running, the heat generated by the IEGT components increases, and the pure water temperature rises rapidly, requiring external industrial water to be connected via a heat exchanger to cool the pure water. The maximum allowable temperature of the pure water entering the frequency converter cabinet is 32℃, with a rated flow rate of 1850L/min, driven by two pumps, one on and one on standby. When one pump stops due to a malfunction, another automatically starts. A fault is reported when the pure water flow rate drops below 1530 L/min. The rated flow rate of industrial water is 2000 L/min, with a minimum permissible flow rate of 1700 L/min. The pure water is cooled by an 844 kW heat exchanger. The maximum permissible temperature of the industrial water entering the heat exchanger is 33°C, measured by a thermometer. The maximum permissible temperature of the pure water entering the inverter cabinet is 41°C, measured by a resistance temperature sensor (RTD). Above the pure water cooling unit is a 150 L water tank for replenishing the pure water pipeline. It includes a level detection system with 40 L and 80 L levels serving as the alarm and fault points, respectively. Any malfunction in the pure water cooling unit will cause the inverter to report a fault, thus stopping the main motor. [align=center] Figure 4 MPS System Diagram[/align] 4. Motor Protection System (MPS) The main function of the motor protection system MPS is to protect the motor. The PLC of its control system is Toshiba V series PLC. The control system consists of the following modules: 6 RTD digital input modules RT318, 1 analog input module AD338, 4 digital input modules DI334, 2 relay output modules RO363S, 1 Toshiba V series PLC module S3PU55, 1 Profibus DP slave module PF312, 1 I/O bus module IF721, PF_X, 1 I/O bus module EN751. (1) The main motor is equipped with a resistance temperature sensor RTD (its measurement range is -50℃～270℃). Its feedback signal is connected to the RT318 module (its count value is 800～4000, that is, 0.1℃/count) to complete the conversion of analog to digital, which is used to display the temperature of the main motor stator and bearings. The alarm and fault values ​​for the stator temperature of the main motor are 140℃ and 150℃, respectively, and the alarm and fault values ​​for the bearing temperature are 90℃ and 95℃, respectively. When the temperature of the stator or bearing exceeds this alarm value or fault value, the MPS disconnects the interlock with the transmission cabinet and reports an interlock fault through the transmission cabinet to stop the main motor. (2) Enable the start and run interlock with the main drive. When these interlocks are not met, the main motor cannot start and run. Start interlock: the three-phase temperature value of the stator and the temperature value of the bearing. When the above temperature values ​​are lower than the alarm values ​​of the stator and the bearing, the main drive can start. Run interlock: the pressure of the high and low pressure sliding pumps of the main motor, the low pressure lubrication flow of the main motor, and whether the main motor fan and the high and low pressure lubrication pumps are started. If any of the following conditions are not met, the main motor run interlock is broken, and the main motor stops due to the interlock fault reported by the MPS. The interlocking conditions are: high pressure of main motor lubrication < 5.6 MPaG, low pressure of lubrication < 0.11 MPaG, or low pressure lubrication oil flow < 137 L/min, and the main motor fan and high/low pressure lubrication pumps are not started. III. Self-protection functions ● Current-related protection AC overcurrent: When the inverter's output current exceeds the set value, an overcurrent is detected and the circuit breaker trips instantaneously. IEGT overcurrent: In voltage-type inverters, if two IEGTs on the same phase are simultaneously turned on, a large current will flow through the IEGT, and the charged capacitor will be short-circuited by the IEGT element, causing an instantaneous trip. Overload: The drive execution output calculates the root mean square (RMS) values ​​for 5 minutes and 20 minutes. If this value exceeds the set value, an overload is reported. The 5-minute and 20-minute overload fault values ​​are officially provided: OL: Overload rate T: Overload time (s) For example, when the overload is 150%-60s, 5minRMS=111.8%, 20minRMS=103.1%. Current limiting timer: Current reaches the limit value within any predetermined time period. Stalled rotor: Low-frequency overload. ● Voltage protection: DC overvoltage: DC voltage exceeds the set value. DC undervoltage: DC voltage is lower than the set value. ● Motor speed protection: Overspeed: Motor speed exceeds the predetermined speed. Overfrequency: Output frequency exceeds the set frequency value. Speed ​​detection fault: Speed ​​sensor failure and the difference between the feedback speed and the given speed exceeds the set value and its delay time. ● Control circuit and power supply: Control power supply voltage is lower than the set control power supply detection level. Gate power supply fault: This gate power supply is provided by the control power supply through the pulse transformer on the gate plate; this fault is reported when the gate plate fails. Fuse blown: The fuse blows to prevent further escalation of the fault in the event of a short circuit; fuse blown is detected by a microswitch. Output contactor open: This fault is reported when the output contactor should be closed but is open. CPU fault: A microprocessor fault is detected during control operation; CPU faults on the main board are detected by hardware to protect the CPU. Communication fault: Communication between L1 and the drive, and communication between drives, fails. Pre-charge fault (F_PRE): The pre-charge circuit provides a fuse to prevent a short-circuit fault from escalating further. Ground fault: The ground fault circuit provides a fuse to prevent a ground fault from escalating further; fuse burnout is detected by a microswitch. ● Protection related to motor and brake: Motor overheat: The motor temperature sensor protects the motor by detecting the motor temperature when it exceeds a set value (motor stator: 155℃, motor bearings: 95℃). Motor temperature detector failure: When the motor temperature exceeds 200℃. Motor fan stop: When the motor fan fails to start or stops due to a fault. Electromagnetic brake circuit failure: When a fault occurs in the excitation circuit of the electromagnetic brake. ● Operation-related protection: External equipment electrical readiness condition: Interlock signal for inverter operation. When this signal is disconnected, the inverter stops operating. External interlock: Operation interlock signal from external equipment; this signal is a hardware or serial communication signal. Cabinet door safety switch: Interlock switch on the cabinet door; this switch allows the inverter to be stopped from the cabinet door. ● Pre-charge related protection: Pre-charge fault detection: Pre-charge fault is detected (pre-charge circuit contactor or fuse blown). ● Grounding detection related protection: Rectifier grounding detection: When the grounding circuit and main circuit are grounded with high-voltage impedance and abnormal current is detected. Rectifier grounding detection timer: When abnormal current is detected in the grounding circuit. IV. Features 1. High performance and multi-functionality ▲ Adopts a dedicated high-performance microprocessor (PP7) for power electronic control, realizing fast response function. ● 1ms speed control sampling time. ● Adopts a high-resolution R/D rectifier. ▲ Equipped with a high-speed fiber optic data communication device (TOSLINE-20). ● Fastest 1ms scan transmission, can be loaded with MELPLAC, ISBU transmission. Can be connected to PLCs of other companies via Profibus-DP, Device-Net. ● High-precision vector control can be achieved for synchronous motors and squirrel-cage induction motors. ● Suitable for control of power factor 1. 2. High voltage and large capacity ● The adoption of high voltage and large capacity IEGT power modules and three-level PWM control realizes a maximum output voltage of up to 3.4KV. ● Higher efficiency and smaller size than the original product. ● Parallel connection of 2-bank, 3-bank, and 4-bank combinations achieves large capacity. 3. Easy maintenance ● Comprehensive maintenance and monitoring functions with a compact, multi-functional operation panel. The system can be monitored and debugged through maintenance software tools. ● The use of large-capacity power modules reduces the number of components used. ● Complete equipment protection functions. ● Dual protection of software and hardware. V. Drive Control [align=center] Figure 5 Inverter Control Block Diagram[/align] ▲ Speed ​​control In drive control, speed control loop is mainly used for adjustment. The speed setpoint signal sent from the main PLC to the main drive is processed by the drive to form its own speed setpoint SP_R. The difference between this speed setpoint signal and the encoder speed feedback signal SP_F is calculated, and the difference is output after proportional/integral operation. This output is then processed by speed filtering and torque limiting to form the torque setpoint SFC_T_R. Another approach to speed control involves proportionally calculating the speed setpoint SP_R generated by the transmission itself, and then subtracting this value from the proportionally calculated speed feedback signal SP_F from the encoder, resulting in a difference value A. The difference between the transmission's own speed setpoint SP_R and the speed feedback signal SP_F is then processed through dead-zone and integration to obtain a difference value B. The sum of differences A and B, multiplied by the product of inertia and the inertia itself, plus torque compensation, yields the torque signal T_R for tension control. This function is only effective when tension control is selected. Furthermore, the control response decreases when the rotational inertia of the mechanical equipment is significantly greater than that of the motor, or when the motor shaft resonates. ▲Tension Control If tension control is used, the torque setpoint signal TRQ_REF (obtained by summing SFC_T_R and the torque setpoint input EXT_TRQ) calculated from the speed control result is compared with the external torque setpoint TRNS_R (the sum of the torque setpoint TENS_R1 sent to the drive by L1 and the additional torque setpoint TENS_R_A). Then, after selection control (i.e., calculation of the maximum or minimum value), the drive's own torque setpoint signal T_R is obtained. In this selectable control, during normal operation and when using the speed control loop function for speed limiting, the calculation is based on TENS_R as the torque setpoint (in winding machinery, the calculation is based on the external torque setpoint. However, in the event of a strip breakage, the calculation becomes a speed control calculation). ▲Torque Control We know that in winding machinery, the strip is controlled with a certain tension, which is achieved by the motor torque. Therefore, the main PLC calculates the torque setpoint output by the motor, and the drive equipment controls the motor's output torque based on this torque setpoint. Additionally, speed control is used to control the winding of one coil at the end and the winding of another coil at the beginning. If the torque command from the main PLC malfunctions, such as a belt breakage, it will cause an overspeed fault. In this case, the control mode automatically switches to speed control. ▲IQ Control: The torque command is the result of the speed control input, divided by the magnetic flux to obtain the IQ command. This IQ command and the detected IQ feedback are input to the D/Q current control. After proportional-integral calculation, a result A is obtained. Induced voltage compensation and reactance compensation are added to this result A to obtain the EQ command. ▲ID Control: The magnetic flux command can be obtained from the speed command, and the ID command can be obtained from this magnetic flux command. This ID command and the detected ID feedback are input to the D/Q current control. After proportional-integral calculation, a result B is obtained. Induced voltage compensation and reactance compensation are added to this result B to obtain the ED command. ▲PWM Control: PWM control is familiar to us; it is used to output the gate pulse signal corresponding to the voltage command for each phase. VI. Conclusion There are many well-known manufacturers of high-voltage, high-power frequency converters in the world, and their frequency converters each have their own characteristics. This article takes a continuous rolling mill production line as an example to introduce the components and functions of its main drive control system, the protection functions and characteristics of the transmission system, and briefly describes the implementation process of its main control functions for reference. References: [1] IEGT Inverter, Converter Instruction Manual TOSHIBA MITSUBISHI-ELECTRIC INDUSTRIAL SYSTEMS CORPORATION June, 2004 [2] Zhang Hao, Xu Mingjin, Yang Mei, eds. High Voltage High Power AC Variable Frequency Speed ​​Regulation Technology Beijing, Machinery Industry Press, 2006.7 Author Introduction: Qiao Li, born in 1978, graduated from Hebei Polytechnic University in 2002, and is currently an assistant engineer at Tangshan Iron and Steel Group. Mailing address: Tangshan Iron and Steel Group Cold Rolled Thin Plate Plant Postcode: 063016 Tel: 0315-2703442 Mobile: 13111452922