Abstract: This paper establishes a fully digital, high-performance general-purpose variable frequency speed control system based on direct torque control (DVT) technology and using a TMS320C240DSP as the control core. The relevant software and hardware design schemes are presented. Test results show that the system has excellent dynamic and static performance. Keywords: Direct Torque Control (DVT), DSP, Inverter Research of DSR Inverters Yu Bin Jia Yaqiong (Hunan Institute of Technology, Hengyang 421008, China) Abstract: This paper establishes a fully digital, high-performance general-purpose variable frequency speed control system based on direct torque control (DVT) technology and using a TMS320C240DSP as the control core. The software and hardware design schemes are presented. Test results show that the system has excellent dynamic and static performance. Keywords: DSR; DSP; Inverters 0 Introduction With the development of VLSI and control theory, high-speed, highly integrated, and low-cost microcontrollers and dedicated chips have emerged, making fully digital AC speed control systems possible. Replacing analog devices with software allows for convenient modification of control strategies and correction of control parameters. Furthermore, it provides functions such as fault detection, self-diagnosis, and upper-computer management and communication. Following this development trend, many chip manufacturers have dedicated themselves to the research and production of digital motor microcontrollers, such as the popular Motorola MC68HC16 series, Intel MCS96 series, and TI's TMS320X24X series. Texas Instruments (TI) invented the first digital signal processor (DSP) in 1982 and launched the TMS320C240 digital motor microcontroller in 1997. This chip, designed for next-generation AC motor control, combines the high-speed computing power of a DSP with efficient motor control capabilities, making it arguably the most competitive digital motor controller in the industry. This paper, also based on this development trend, uses the latest inverter chips and inverter control theory to focus on the research of new intelligent inverters. 1. Main characteristics of direct torque control Direct torque control variable frequency speed regulation technology, known as DSR (Direkte Selbstregelung) in German and DSC (Direct Self-control) in English, is a new type of high-performance AC variable frequency speed regulation technology that has been developed in the last 10 years after vector control variable frequency speed regulation technology. Direct torque control has the following main characteristics: (1) Direct torque control analyzes the mathematical model of AC motor and controls the flux linkage and torque of the motor in the direct stator coordinate system. It does not require comparison, equivalence, or transformation between AC motor and DC motor: it does not require imitating the control of DC motor, nor does it require simplifying the mathematical model of AC motor for decoupling. It eliminates complex transformations and calculations such as vector rotation transformation. Therefore, the signal processing work required is particularly simple, and the control signal used allows the observer to make a direct and clear judgment on the physical process of AC motor. (2) Direct torque control uses stator flux linkage for field orientation, which can be observed as long as the stator resistance is known. In contrast, vector control uses rotor flux linkage for field orientation, and observing rotor flux linkage requires knowing the rotor resistance and inductance of the motor. Therefore, direct torque control greatly reduces the problem that the control performance of vector control technology is easily affected by parameter changes. (3) Direct torque control uses the concept of space vector to analyze the mathematical model of a three-phase AC motor and control its various physical quantities, making the problem particularly simple and clear. (4) Direct torque control emphasizes the direct control and effect of torque. It includes two meanings: ① direct control of torque; ② direct control of torque. 1) Direct torque control is different from the famous vector control method. It does not indirectly control torque by controlling current, flux linkage, etc., but directly controls torque as the controlled variable. Therefore, it does not strive to obtain an ideal sine wave waveform, nor does it specifically emphasize the circular trajectory of flux linkage. On the contrary, from the perspective of controlling torque, it emphasizes the direct control effect of torque, so it adopts the concept of discrete voltage state and hexagonal flux linkage trajectory or approximately circular flux linkage trajectory. 2) Direct control of torque is implemented by direct torque control technology. Its control method involves comparing the detected torque value with the set torque value using a two-point torque regulator with a hysteresis loop, limiting torque fluctuations within a certain tolerance range. The size of the tolerance is controlled by a frequency regulator. Therefore, its control effect does not depend on whether the mathematical model of the motor can be simplified, but rather on the actual torque condition. Its control is both direct and simple. This direct torque control method is also called "direct self-control." This "direct self-control" concept is used not only for torque control but also for flux linkage control and flux linkage self-control. However, it uses torque as the central focus for comprehensive control. 2. Implementation Scheme High integration and a streamlined circuit structure are guarantees of system reliability. Based on comprehensive evaluation of performance, cost, and reliability, the system adopts a fully digital design and uses the latest chips. The main circuit uses the PS11032 from Mitsubishi's ASIPM PS1103X series intelligent power module, and the control circuit uses the TMS320C240 from Texas Instruments' C23x series DSP controller. This greatly simplifies the system hardware and reduces the system design workload. The system functional block diagram is shown in Figure 1. 2.1 Main Circuit Design The frequency converter mainly consists of two parts: the main circuit and the control circuit. The main circuit mainly comprises a rectifier circuit, a DC intermediate circuit, an inverter circuit, and related auxiliary circuits. In this system, the main circuit uses Mitsubishi Electric's latest intelligent power module, the PS11032. Because the drive circuit within the PS11032 is configured with optimal IGBT drive conditions, the distance between the drive circuit and the IGBT is very short, and the output impedance is very low; therefore, no reverse bias is required. Most conveniently, the PS11032 can be directly connected to the CPU without an isolation circuit. The input pin of the PS11032's drive circuit is directly connected to the CPU's output pin through a 10k current-limiting resistor and a 5.1k pull-up resistor. 2.2 Control Circuit Design The control circuit is the most important part of the frequency converter circuit; its quality determines the performance of the frequency converter. The main function of the control circuit is to detect various signals obtained from the detection circuit, provide the necessary gate-level drive signals for the main circuit of the frequency converter, and provide necessary protection for the frequency converter and the asynchronous motor. The control circuit is based on the TMS320C240 DSP, configured with 32k words of program memory and 8k words of data memory. In the system design, the C240 ​​uses a 20MHz external crystal oscillator, and its single-cycle instruction capability enables it to achieve a processing power of 20 MIPS. The C240 ​​has a 4K-word Flash EEPROM, and we further expanded it with 32k words of SRAM program space and 8k words of SRAM data space. The system program was written using a modular approach based on function blocks, which facilitates free combination according to function and makes programming and debugging convenient. At power-on, the main program performs a self-test, then transfers the system program from the EPROM to RAM to utilize the DSP's speed, initializes system parameters, and is mainly responsible for background tasks such as display refresh. The flowchart is shown in Figure 2. 2.2.1 Connection of Dual A/D Converters and Detection Circuit The TMS320C240 is equipped with two 8-channel, 10-bit A/D converters with sampling/holding capabilities, capable of parallel processing of analog signals, including feedback signals for speed, position, temperature, voltage, and current sensing. To ensure the accuracy and speed of stator current detection, we used a KT series Hall sensor from Kehai, whose output is a 0-5V signal. After adjustment by the AD623 instrumentation amplifier, it is directly connected to the A/D converter configured in the TMS320C240. The inverter DC voltage, sampled by a voltage sensor and adjusted by the AD623 instrumentation amplifier, is also directly connected to the A/D converter configured in the TMS320C240. The speed detection circuit uses a photoelectric encoder, which directly converts the analog signals of motor angle and displacement into digital signals. Its output signal is directly connected to the quadrature encoder pulse unit configured in the TMS320C240. Each of the two A/D converters handles two analog signals and reserves interfaces for system expansion or upgrades. The A/D interrupt response subroutine samples repeatedly and reads the results into memory, as shown in Figure 3. 2.2.2 SPI and SCI Serial Ports and Communication Circuits The TMS32OC240 chip peripherals also include an asynchronous serial communication port (SCI) and a synchronous serial communication port (SPI). The SCI port, or General Asynchronous Receiver/Transmitter (DART), is used to communicate with standard devices such as PC serial ports, and can use protocols such as RS-232/485, with a maximum baud rate of 625kbps. The SPI port can be used for synchronous data communication, with a maximum baud rate of 2.5Mbps. Typical applications include external I/O or peripheral expansion, such as shift registers, display drivers, and A/D converters. SPI 1-1 has three communication lines: the serial input data line SPISOMI, the serial output data line SPISIMO, and the synchronous clock line SPICLK. The other control line, SPISTE, is the slave select line. In the system, a serial EEPROM chip X25045 is extended using the SPI serial interface of the TMS320C240. The X25045 can provide 512 bytes of EEPROM for saving system settings. Simultaneously, an ADM233 is used to extend an RS232 interface, enabling communication with a computer and data exchange. 2.2.3 Human-Machine Interface Circuit The human-machine interface circuit uses an LCD display (20 characters x 2 lines). Before the inverter runs, it displays the inverter's set values; during inverter operation, it acts as a monitor, displaying the motor's operating status and real-time basic operating data, such as motor current, voltage, inverter output frequency, and speed; when an inverter malfunctions, it displays the type of fault and the operating status at the time of the fault, facilitating fault analysis. There are 11 buttons in total, including function keys and setting keys. The function keys are forward, reset, reverse, and stop keys, used to issue operating commands to the inverter. The setting keys include mode keys, programming keys, increase keys, decrease keys, left shift keys, right shift keys, and Enter key. The mode keys are used to change the monitoring mode; the programming keys are used to change the function mode and enter or exit the programming state; the increase and decrease keys change the setting value; the left and right shift keys move the cursor; and the Enter key is used to enter the setting screen of the cursor-indicated item and confirm the selection. The keyboard is connected to the PI0~PI10 extended signal lines, with the strobe address being OOOOH. All keyboard signal lines are also connected to a GAL16V8. The GAL16V8 performs a bitwise AND operation on all signals and outputs the result to the INT3 interrupt pin. Thus, pressing any key generates an INT3 interrupt. 3. Simulation Results This paper performs fuzzy control simulation on the system. The speed setpoint jump response curves are shown in Figures 4 and 5. 4. Conclusion The simulation results show that the system can respond quickly when the given speed jumps. Torque and current fluctuations are small, and it can quickly reach stability when the speed jumps; the static error is small, exhibiting excellent static and dynamic performance. References: [1] Wang Xiaoming, Wang Ling. DSP Control of Electric Motors - TI Company DSP Application [M]. Beijing: Beijing University of Aeronautics and Astronautics Press. 2004 [2] Qin Jirong, Shen Anjun. Modern DC Servo Control Technology and System Design [M]. Beijing: Machinery Industry Press. 1999 [3] Liu Heping, Yan Liping, Zhang Xuefeng et al. TMS320LF240xDSP Structure, Principle and Application [M]. Beijing: Beijing University of Aeronautics and Astronautics Press. 2002 [4] Sun Jianbo, Gong Shiying, Dong Yahui. Simulation Study on Speed ​​Regulation System of Permanent Magnet Brushless DC Motor [J]. Micro Motor, 2001.2, 25-28 [5] Zhang Shen. Principle and Application of DC Brushless Motor [M]. Beijing: Machinery Industry Press, 1996 [6] Zhang Yu, Chen Jingwei, Liang Zhenhong. Fully Digital Vector Control of Permanent Magnet Synchronous Motor Based on DSP [J]. Servo Technology, 2001.3, 48-50. Author Biography: Yu Bin (1979-), male, from Yangzhou, Jiangsu Province, lecturer, major research direction: information processing and DSP.