Abstract : This paper introduces the debugging method of using a Siemens 6RA70 DC speed controller to drive an old model Mitsubishi compound-wound DC motor in heavy-load applications. Keywords : Siemens 6RA70 DC speed controller, compound-wound motor winding modification, manual system optimization, heavy-load application. The 1549 production line of Taiyuan Iron & Steel's hot strip mill underwent a complete electrical and automation system upgrade in 2002. The electrical control system was designed by Siemens AG of Germany. The rolling process technical indicators, including transmission, pressing, roll bending, roll shifting, lubrication, roll changing, cooling, looper, side guide, shape control, and measurement systems, are jointly realized by more than 30 sets of TDC control systems. The mill motor drive is controlled by the SIMADYN-D system. The technical upgrade adopted the most advanced fieldbus control technology, with communication systems including GDM network, industrial Ethernet, and PROFIBUS-DP network. The GDM network transmits high-speed global process control data, and the industrial Ethernet exchanges data with each PC terminal through an HMI server, providing an operating interface for program debugging, fault diagnosis, and screen display. The C2 and C4 roller conveyor motors on the rolling mill are second-hand Mitsubishi compound-wound DC motors imported from Japan when the factory was established in 1992. Their armature, excitation, commutation, and compensation windings are somewhat unique, resulting in poor speed regulation performance and high energy consumption. This article will describe the debugging method for using a Siemens 6RA70 DC speed controller to drive the older model Mitsubishi compound-wound DC motors in heavy-load applications, as well as the dynamic optimization and debugging of the current regulator and speed regulator after the winding structure of the compound-wound motor has been changed. 1. Compound Excited Motor Winding Structure and Transmission Control Method 1.1 Basic Technical Data of Motor Motor Power: 55KW Rated Speed: 512RPM Stator Winding Voltage: 220V Rotor Winding Voltage: -220V——+220V Manufacturer: Mitsubishi Electric, Japan 1.2 Starting and Commutating Principles of the Original Transmission System As shown in Figure 1 [align=center] Figure 1: Schematic Diagram of the Original Transmission System[/align] As shown in the figure, the rotor winding consists of three coils: L1, L2, and L3, where L1 is the armature winding, L2 is the commutation winding, and L3 is the torque compensation winding; the stator winding consists of one coil: L4 R1, 2—accelerating resistors R3—energy consumption resistors R4, 5—voltage divider resistors XC1—line contactor AC1, 2—accelerating resistors FC—forward contactor BC—reverse contactor 1.3 Analysis of the Shortcomings of the Original Transmission System 1.3.1 The system operating speed is constant and cannot be adjusted, making it impossible to match the speed with other equipment on the rolling line 1.3.2 Low power factor 1.3.3 High energy consumption, unable to meet the requirements of current refined equipment management 1.3.4 System aging, high failure rate, affecting production progress, high maintenance costs, etc. 2. Four-quadrant operation of the all-digital DC speed control system 2.1 Basic principle of the control system The new speed control system adopts SIEMENS 6RA70 SIMOREG DC MASTER series rectifier, the main technical features are as follows: 6RA70 is an all-digital compact rectifier, the input is a three-phase power supply, which can supply power to the armature and excitation of the variable speed DC drive, select the four-quadrant operation device, the transmission control, regulation, monitoring and additional functions are all implemented by the microprocessor. The device software is stored in flash EPROM. Power section: armature and excitation circuit The armature circuit is a three-phase bridge circuit: the power section is two three-phase fully controlled bridges (B6)A, (B6)C. The excitation circuit adopts a single-phase half-controlled bridge B2HZ. The power components of the armature and excitation circuits are electrically insulated thyristor modules, and their heat sinks are not energized. Cooling: Forced air cooling (fan). The control principle is shown in Figure 2: [align=center] Figure 2.1[/align][align=center] Figure 2.2[/align] 2.2 Functional Description of the Modified Transmission System 2.2.1 Control Commands and Speed ​​Setpoints According to the process requirements, this system should have two working modes: continuous production and equipment maintenance (automatic and manual). That is, during continuous production, it is in automatic mode, and the C roller conveyor receives start and stop commands and speed setpoints (continuously variable) from the TDC process control system. The TDC communicates with the 6RA70 via fieldbus. During equipment maintenance, it is in manual mode, and the C roller conveyor receives start and stop commands and speed setpoints (multiple fixed setpoints) from the field control panel. For this purpose, the 6RA70 needs to be equipped with a CBP2 communication board and a CUD2 terminal expansion board, as shown in Figure 3. [align=center] Figure 3.1 CBP2 Communication Board Figure 3.2 CUD1+CUD2[/align] 2.2.2 BICO Data Group Switching The switching between the two sets of BICO data groups is achieved by a selector switch, input via DI. The control principle is shown in Figure 4. [align=center] Figure 4.1[/align][align=center] Figure 4.2[/align] 2.3 Motor Winding Change As shown in Figure 1, when the original transmission system is running, the motor can rotate in both directions, the current flowing through L1 and L2 is reversible, while the current flowing through L3 is unidirectional, and the excitation is voltage-controlled. The control principle of the new system is shown in Figure 2.1. The current flowing through L4 can be dynamically adjusted, therefore, the excitation is current-controlled; the control of the armature will be very difficult: if the armature windings L1, L2 and L3 are connected in series, a reversible current will flow through L3. Practice has shown that when the current of L3 is reversed, the transmission control system oscillates, and the motor temperature rises rapidly. If the armature windings L1 and L2 are connected in series, and L3 is short-circuited, the motor cannot complete the heavy load start. Therefore, motor winding modification is necessary. Detailed solutions are not covered in this article. 2.4 Manual Optimization of System Current Regulator and Speed ​​Regulator After motor modification, optimized operation is performed during commissioning, following this order: pre-control and current regulator, speed regulator, excitation reduction control, friction torque and moment of inertia compensation. During motor operation, especially under heavy load, commutation sparks are large. Therefore, only manual system optimization is possible. 2.5 Load Commissioning The Drivemonitor commissioning software allows for convenient setting of transmission system parameters, online monitoring, and recording of dynamic and static characteristic curves. The debugging parameters and waveforms are shown in Figure 5: [align=center] Figure 5.1 Parameter setting interface[/align][align=center] Figure 5.2 Jogging and starting characteristic curves[/align][align=center] Figure 5.3 Stable operation characteristic curve[/align] [align=center] Figure 5.4 Acceleration operation characteristic curve[/align][align=center] Figure 5.5 Deceleration and stopping characteristic curves[/align] 3. Conclusion After the equipment debugging was completed, the first test run was successful, energy consumption was reduced, and control accuracy was greatly improved. Currently, the system is running stably.