ABSTRACT : Implementation and application of high voltage large capacity synchronous machine with digital vector control. KEY WORD : Large capacity drive, vector control, digital, control method. Abstract : This paper describes the implementation and application of a high voltage large capacity synchronous machine using fully digital vector control. Keywords : High-power frequency converter, vector control, fully digital, control method . 1. Introduction With the rapid development of power electronics technology, computer technology, and automatic control technology, AC speed regulation has become a trend, replacing DC speed regulation. Variable frequency speed regulation offers excellent speed regulation and braking performance, as well as high energy efficiency. Recently, the National Development and Reform Commission listed high-voltage frequency converters as one of the first 50 key energy-saving products to be promoted. Rongxin Power Electronics Co., Ltd. is a national key high-tech enterprise specializing in the research and development and production of high-voltage, high-power power electronic flexible transmission and distribution and automation equipment. One of Rongxin Company's leading products—the High Voltage Motor Variable Frequency Speed ​​Control Device (RHVC)—is a series of energy-saving speed control products for high voltage motors developed using internationally advanced IGBT power unit series multilevel technology, digital control technology, SPWM pulse width modulation technology, and superconducting heat pipe heat dissipation technology. Rongxin Power Electronics Co., Ltd. adopted high-voltage frequency conversion retrofitting for the main ventilation fan of the Tieling Coal Group's Daxing Mine, selecting a power unit series multilevel high-voltage frequency converter to achieve energy savings and stepless speed regulation of the main ventilation fan. 2. The Necessity of Frequency Conversion Retrofitting for the Daxing Mine Fan The main ventilation fan of the Tieling Coal Group's Daxing Mine uses a synchronous motor, and speed regulation of AC synchronous motors is a major challenge in the field of electrical drives. The difficulty lies in the fact that, compared to the operation of ordinary asynchronous motors, the angle between the armature voltage vector and the rotor magnetic pole position must be within a certain range during synchronous motor operation; otherwise, the system will lose synchronization. Therefore, the requirements for high-voltage frequency converters when performing frequency conversion speed regulation on synchronous motors are also different. The specific requirements are as follows: (1) It can solve the problem of synchronous motor starting and synchronizing; (2) It can solve the coordinated control of output voltage and excitation current during the speed regulation of synchronous motors; (3) The output voltage and current harmonics of the frequency converter should be as small as possible. The main ventilation fan of Daxing Mine of Tiemei Group is responsible for the main ventilation task in the mine. The current problems of the system are: (1) Low adjustment accuracy, poor linearity and poor real-time performance; (2) The use of damper adjustment causes the pipeline pressure to increase, resulting in a large amount of energy waste; (3) When starting directly, it causes serious power grid fluctuations and large mechanical shocks, affecting the system's operational reliability and lifespan. In view of the above problems, the existing fan is transformed by frequency conversion technology, and a perfect harmonic-free high-power frequency converter is used to realize the stepless speed regulation technology of the synchronous motor of the main ventilation fan. 3. Design of high-voltage frequency conversion speed regulation device 3.1. System composition The high-voltage frequency converter adopts the high-performance, mature, safe and reliable perfect harmonic-free power unit series multi-level technology. The entire frequency conversion system mainly consists of a fully digital controller and a frequency conversion power unit. The heat dissipation technology utilizes a high-efficiency heat pipe radiator independently developed by the company. The system structure diagram is shown in Figure 1: [align=center] Figure 1 System Structure Diagram[/align] 3.2. Fully Digital Vector Control Technology Scheme Principle 3.2.1 Fully Digital Vector Control Principle The RHVC series high-voltage frequency converter adopts rotor speed feedback vector control technology. The control system uses a dual closed-loop structure of speed loop and current loop. The speed loop uses a PID regulator, which can effectively limit the overshoot of the dynamic response and accelerate the response speed. Under the rotor magnetic field positioning coordinates, the motor stator current is decomposed into excitation current and torque current. Maintaining the excitation current constant, controlling the torque current also controls the motor torque. In actual operation, the difference between the given speed and the actual speed is used to generate the torque current IT through PID regulation. After vector transformation, IT and IM are transformed into the three-phase given currents Ia*, Ib*, and Ic* of the motor. These are compared with the motor operating current to generate three-phase drive signals. The key to the fully digital system is the digitization of the current loop, which involves implementing the analog current loop in a hybrid analog-digital frequency converter system digitally. The core objective is to improve the processing speed of the current loop, achieving or approaching the response speed of the analog current loop. Current microprocessors (DSPs) and A/D converters can meet the hardware requirements. The other aspect lies in the optimization of the control strategy and software. Good system hardware and software design is essential for the practical application of the developed system. While meeting performance requirements, it is crucial to fully utilize hardware resources, increase integration, reduce hardware costs, and achieve the goal of productization. The control principle block diagram of the entire system is shown in Figure 2. [align=center]Figure 2 Control Principle[/align] 3.2.2 Hardware Main Control Implementation The system uses a DSP digital signal processor as the main control CPU. Programmable logic devices (PLDs) perform some algorithm calculations, waveform generation, and various signal processing. The unit status information is serially encoded by the PLDs and then transmitted to the main controller's receiving board via optical fiber. The main controller's receiving board performs serial-to-parallel decoding and transmits the data to the main control CPU. The main control CPU adjusts the system's control state based on the unit status information. The speed measurement method uses variable M/T speed measurement, which can achieve high-precision speed measurement requirements. The current detection element in this system is a Hall effect current transformer made based on the magnetic field compensation principle to meet the requirements of real-time current monitoring. The overall hardware principle block diagram is shown in Figure 3. [align=center]Figure 3 Main Controller Structure Diagram[/align] 3.3. The frequency conversion power module receives three-phase 6000V AC power from the grid, which is converted into 15 groups of 690V by an isolation phase-shifting transformer, supplying 15 power units respectively. The single-phase SPWM waves output by the 5 power units on each phase are superimposed and connected in a Y-shape to form a high-quality sine wave output with a line voltage of 6000V, which is then supplied to the high-voltage synchronous motor to drive the fan. Fiber optic isolation technology is used between the main control cabinet and the power cabinet, achieving complete isolation between high and low voltage, providing extremely high safety. The power units adopt AC-DC-AC frequency conversion technology, with single-phase output. The IGBT components use advanced and efficient heat pipe cooling technology, greatly improving operational reliability. High-voltage frequency converter parameters : Rated capacity: 2000kVA Input voltage: 6000V+15%-30% High-voltage grid frequency: 45～55HZ Output voltage: 0～6000V Output frequency: 0～50HZ Output voltage harmonic content: < 4% Power factor: 96% Overload capacity: 120% (5 minutes) Efficiency: 96% Cooling method: Heat pipe cooling Operating ambient temperature: -20°C — +45°C Motor parameters : Rated voltage: 6KV Rated power: 1600KW Rated current: 150A Rated speed: 500r/m Power factor: 95% Excitation current: 180A Excitation voltage: 80V 3.4 High-voltage frequency converter application design Based on the current situation of the main ventilation fan in Daxing Mine of Tiemei Group, a one-to-one working mode of one high-voltage frequency converter is adopted to realize stepless speed regulation control of the synchronous motor of the main ventilation fan. The fan motor is controlled by a high-voltage frequency converter. The original damper adjustment is opened to the maximum. The air volume adjustment is achieved by controlling the motor speed, so as to achieve real-time and precise air volume adjustment. In steady state, the input and output waveforms of the frequency converter are shown in Figure 4 and Figure 5 respectively: [align=center] Figure 5 Frequency converter output (motor) voltage and current waveforms[/align] (1) After adopting the high-voltage frequency conversion stepless speed regulation technology, the speed of the fan motor can be easily adjusted down from the current rated speed to obtain the air volume required for production; (2) The motor does not have to work at the rated speed all the time, which greatly reduces the wear of the system machinery and extends the service life of the equipment; (3) Automatic adjustment of the fan can be realized by communicating with the control center; (4) Under the condition that the air volume is met, considerable energy-saving effect can also be achieved by frequency conversion control. The motor achieves true soft start, and the starting current is controlled below the rated current. 4. Economic benefits of variable frequency speed control system for ventilation fan The fan is a square torque load. The air volume Q of the fan is proportional to the speed n, while the power P of the fan is proportional to the cube of the speed n. Fan air volume Q = K1n (1) Fan air pressure P = K2n2 (2) Fan power P = K2n3 (3) Annual power consumption (current is the actual operating value): P = UI (4) The damper opening is taken as 60%. The actual operating current before the modification is 146A, and after the modification it is 92A. According to existing experience and on-site measurement, from formula (4), the annual power consumption before the modification is 13.2 million kWh, and after the modification it is 8.32 million kWh. The annual power saving of variable frequency is 2.2 million yuan. The equipment investment can be fully recovered in about two years. 5. Innovation Points (1) Principle Innovation: The control method adopts fully digital vector control, and RHVC can also realize forward rotation, reverse rotation, traction, electric braking and other functions to meet the load speed regulation needs of lifting, traction and other four-quadrant operation. (2) Technological Innovation: The frequency converter adopts fully digital synchronous start and can realize fly-start. (3) Structural Innovation: The high-efficiency heat pipe heat dissipation technology independently developed is adopted, which greatly improves efficiency compared with the traditional air-cooled heat dissipation design and completely eliminates the heat island effect of high-power device IGBT. (4) Process Innovation: The thermal grease is applied between IGBT and heat sink using a semi-automatic coating machine. Its characteristics are accurate thickness, uniform distribution, increased thermal conductivity of high-power device and energy saving. 6. Conclusion The speed regulation of synchronous motor is a major problem in the electrical drive industry. In recent years, the application of high-voltage frequency conversion speed regulation has been a research topic for frequency converter manufacturers in China. The successful application of Rongxin Power Electronics Co., Ltd.'s high-voltage frequency converter on the synchronous motor of the main fan of Daxing Mine has obvious demonstration significance. Practical applications have shown that the application of high-voltage frequency converters in the retrofitting of synchronous motor systems will inevitably achieve good operational results and economic benefits.