Abstract: The successful application of high-performance AC motor control methods such as field-oriented and direct torque control to AC drive electric locomotives will significantly improve locomotive performance. This paper introduces a dual-DSP fully digital motor control system primarily composed of two high-speed digital signal processors. The entire motor drive system is described, and the hardware design of the control system is elaborated in detail. Keywords: Digital control; Motor control 1 Introduction The control system is the core of the AC drive system, determining its main performance and indicators. With the development and maturity of various microprocessors, how to apply digital control technology to AC drive systems is a topic of great interest to researchers. In particular, the application of high-speed digital signal processors (DSPs) in AC drive systems will greatly improve the performance of AC drive control systems, thus attracting widespread attention. This paper proposes a dual-DSP digital control circuit system scheme for high-performance AC drive systems, mainly composed of a 16-bit high-speed fixed-point DSP chip TMS320F243 with programmable I/O ports, a pulse width modulation (PWM) generator, a pulse capture unit, and other integrated peripherals, and a general-purpose 32-bit high-speed floating-point DSP chip TMS320C32. The TMS320F243 is used for voltage and current signal acquisition and analog-to-digital conversion, overcurrent and overvoltage protection, and output PWM signal to drive the power inverter of the AC drive system. The TMS320C32 is responsible for speed signal acquisition and calculation, as well as control algorithm calculation. With appropriate hardware and software coordination, the DSP chips complete common data exchange through dual-port RAM, enabling the two DSPs to operate in parallel. 2. Overall Structure of the Digitally Controlled AC Drive System The AC drive system using dual DSP control consists of a power conversion device, a dual DSP control system, and an induction motor. The DSP fully digital control circuit consists of two DSPs as the core, forming a dual DSP control system used to complete data acquisition (including DC input voltage, AC output voltage and current, motor speed, etc.), data processing (motor current fundamental wave analysis and calculation, electromagnetic torque and flux estimation, etc.), system protection (DC bus overvoltage and overcurrent protection, phase loss protection, overheat protection, etc.), and control functions. The power conversion device consists of a two-point three-phase inverter and an IGBT drive circuit, generating the correct output voltage to supply the three-phase induction motor load based on the PWM signal from the control system. 3. Hardware Structure of the Dual-DSP Control System The digitally controlled transmission system requires both analysis and calculation of the motor's electromagnetic torque and flux, and a complete control function and logic processing interface to fulfill the control requirements. The structural diagram of the entire dual-DSP control system is shown in Figure 1. [align=center]Figure 1 Schematic diagram of the dual-DSP control system[/align] The control system uses a floating-point chip TMS320C32 and a fixed-point chip TMS320F243, respectively. The TMS320C32 has strong computing power, but limited on-chip resources and I/O ports, resulting in weaker logic processing capabilities. It is mainly used for floating-point calculations and data processing (floating-point operations can greatly improve accuracy and dynamic range). Conversely, the F243 has abundant on-chip and off-chip peripheral resources and convenient I/O ports, but its computing accuracy and speed are somewhat limited, so it is used for data acquisition and process control. The two DSP chips exchange data through a dual-port RAM. The complementarity of these two DSP chips fully leverages their respective advantages, achieving an optimal combination for the control system. 3.1 TMS320F243 Subsystem The main functions of the TMS320F243 subsystem include: PWM control signal output, voltage and current acquisition, DA output of intermediate variables, and keyboard display. The TMS320F243 has a processing speed of 20 million instructions per second and features abundant I/O ports, integrated on-chip peripherals, and a dedicated PWM generator. The F243 controller has three full comparator units specifically designed for bridge PWM circuits. A pair of output pins corresponds to a set of bridge arms; when the upper bridge arm is on, the lower bridge arm is off, and vice versa. Embedded within the full comparator units are asymmetric/symmetric waveform generators, dead-time generation circuits, and space vector state machines. Combined with the F243's internal 16-bit timer, various PWM output functions can be easily implemented. The F243's integrated synchronous serial interface SPI, combined with MAXIM's dedicated SPI interface LED digital tube driver chip MAX7219, allows for the construction of a simple and reliable display circuit using only three signal lines. The MAX7219 BCD decoding method is selected, and the CPU communicates synchronously and serially with the MAX7219 on a byte-by-byte basis, minimizing CPU intervention and reducing CPU utilization. The system uses the asynchronous parallel-in/serial-out chip CD4021 to expand eight function keys, and the interface with the F243 uses only three signal lines. When a key is pressed, an external interrupt is requested from the F243. The F243 responds to the interrupt, sequentially reading the status of each key, determining the key code, and executing the corresponding service routine. The high-performance motor control system calculates the motor's flux and electromagnetic torque by real-time acquisition of three-phase output voltage and current and motor speed. To improve control accuracy, high detection precision is required, and synchronous detection of phase voltage and current is preferred. This system uses an AD7864 to simultaneously sample two-phase voltage and current. The AD7864 is a high-speed, low-power, single-supply, four-channel synchronous sampling, 12-bit analog-to-digital converter chip. Featuring a 1.65μs successive approximation A/D converter, four track/hold amplifiers, a 2.5V reference level, an on-chip clock, signal conditioning circuitry, and a high-speed parallel bus interface, the AD7864 can synchronously sample analog input signals from four channels and store the relative phase and magnitude information between the four channels. This makes it particularly suitable for AC motor control, three-phase power grid voltage detection, and other applications. Since digital control algorithms are implemented in control software, and high-performance motor control schemes have complex intermediate variables that cannot be directly observed with an oscilloscope, the AD7836 DA chip is selected to convert intermediate variables into analog signal outputs for easier system debugging, monitoring, and verification. The AD7836 is a 14-bit parallel input, 4-channel analog output D/A converter manufactured by Analog Devices. Its settling time is 16μs, it operates from a dual ±15V power supply, has a reference voltage range of -5V to +5V, and an output voltage range of -10V to +10V. 3.2 TMS320C32 Subsystem The main functions of the TMS320C32 subsystem include: motor speed detection, motor flux and torque state estimation, and inverter output command voltage calculation. This subsystem mainly consists of the DSP chip TMS320C32, two 16-bit FLASH chips AT49F1025, two 16-bit high-speed SRAM chips ISSI61C6416, and a motor speed measurement circuit. The TMS320C32 is a high-performance 32-bit floating-point DSP with a single-cycle instruction execution time of 50ns; a 32-bit floating-point multiplication can be completed in 50ns. Compared with fixed-point arithmetic, floating-point arithmetic has higher precision and does not need to consider overflow issues, resulting in better computational performance. FLASH is used to store the program and initialization data, while SRAM is used to store the real-time running program and data. After the TMS320C32 is reset, the internally stored boot program moves the program and data stored in FLASH to the high-speed SRAM, and then runs in the SRAM. The accuracy of motor speed detection in the transmission system is crucial to the overall system control accuracy. Due to the wide speed range of electric locomotives and the variable number of holes per revolution of the photoelectric encoder, the selection of speed measurement hardware and software schemes and the real-time switching schemes are generally different. In this system, the edge-triggered mode of the TMS320C32 external interrupt and the advantages of its internal 32-bit timer are utilized to measure the speed with high accuracy within the possible motor operating range using a single measurement cycle method. 3.3 Dual DSP Data Exchange Subsystem The dual DSP data exchange subsystem is implemented using dual-port RAM, specifically the IDT7025, an 8K×16-bit high-speed CMOS static dual-port RAM from IDT. In addition to the general functions of dual-port RAM, the IDT7025 also has built-in interrupt logic, enabling more efficient completion of dual DSP communication functions. For example, after F243 transmits the acquired data to the dual-port RAM, it then randomly writes data to a specific address within the dual-port RAM. The interrupt output pin connected to IDT7025 and C32 generates a switching signal, triggering an interrupt in C32. After reading the data, C32 can reset this interrupt signal by reading the specific address within the dual-port RAM. The reverse is also true. The dual-port RAM and its interrupt function enable rapid and convenient data exchange between the two DSPs, enhancing the parallel processing capability of the dual-microcomputer system. 4. Conclusion Compared to other circuit structures, the drive system using dual-DSP digital control has advantages such as high control accuracy, small size, powerful functions, and good stability. Furthermore, it is easy to debug, and the system control scheme is flexible, allowing for rapid modification of control methods and algorithms, greatly reducing the workload of system debugging. References [1] Zhuo Fang, Wang Yue, He Yihong, Li Hongyu, Wang Zhaoan. Three-phase four-wire active power filter implemented with dual DSP control technology. Proceedings of the 7th China Power Electronics and Drive Control Conference CPED'2001. [2] Li Wei. Research on vector control system of induction motor. Doctoral dissertation of Northern Jiaotong University. 2000