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: The realization and application of high-frequency high-power synchronous machine adopts all-digital vector control method.
Keywords: high-power inverter, vector control, all-digital, control method
1 Introduction
With the rapid development of power electronics, computer technology and automatic control technology, AC speed control has become a development trend to replace DC speed control technology. The frequency conversion speed regulation has excellent speed control and braking performance, high efficiency and energy saving effect. The National Development and Reform Commission recently listed high-voltage frequency conversion as the first batch of 50 key energy-saving products.
Rongxin Power Electronics Co., Ltd. is a national key high-tech enterprise specializing in R&D and production of high-voltage, high-power power electronic flexible transmission and distribution and automation equipment. One of Rongxin's leading products, the high-voltage motor variable frequency speed control device (RHVC), is based on the internationally advanced IGBT power unit series multilevel technology, digital control technology, SPWM pulse width modulation technology and super heat pipe heat dissipation technology. Made of series of high-voltage motor energy-saving speed adjustment products
Rongxin Power Electronics Co., Ltd. adopted the high-voltage frequency conversion transformation for the main fan of Daxing Mine of Tiemei Group, and used a multi-level high-voltage inverter connected in series with the power unit to achieve energy saving and stepless speed regulation of the main fan.
2. The necessity of frequency conversion of Daxing Mine Fan
The main ventilators of the Daxing Mine of Tiemei Group adopt synchronous motors, and the speed regulation of AC synchronous motors is a major problem in the field of electric drives. The difficulty lies in that compared with the operation of the ordinary asynchronous motor, when the synchronous motor is running, the angle between the armature voltage vector and the rotor pole position must be within a certain range, otherwise the system will lose its synchronization. Therefore, there are some differences in the requirements for high-voltage frequency conversion devices when synchronous motors are used in frequency conversion speed control transformation. The specific requirements are as follows:
(1) It can solve the problem of synchronous motor start-up;
(2) It can solve the coordinated control of output voltage and excitation current in the synchronous motor speed regulation process;
(3) The output device's output voltage and current harmonics should be as small as possible.
The main ventilator of the Daxing Mine of Tiemei Group is responsible for the main ventilation task under the mine, and there are currently problems in the system:
(1) Low adjustment accuracy, poor linearity, and poor real-time performance;
(2) Adopt damper adjustment, resulting in increased pipeline pressure, resulting in a large amount of wasted electricity;
(3) When starting directly, it causes severe grid fluctuations and large mechanical shocks that affect the operational reliability and life of the system.
In view of the existence of the above problems, the frequency conversion technology of the existing fan was reformed, and the perfect fanless harmonic power inverter was used to realize the stepless speed regulation technology of the main fan synchronous motor.
3, high voltage variable frequency speed control device design
3.1. System Components
The high-voltage frequency converter adopts the perfect non-harmonic power unit series multi-level technology with excellent performance, mature technology, and safety and reliability. The entire frequency conversion system is mainly composed of all-digital controllers, variable-frequency power units, etc. The heat-dissipation technology adopts an efficient heat pipe radiator independently developed by the company. The system structure is shown in Figure 1:
Figure 1 System Structure
3.2. The principle of the fully digital vector control method
3.2.1 Principle of Full Digital Vector Control
RHVC series high-voltage frequency converters use vector control technology with rotor speed feedback. The control system adopts a double closed loop structure with a speed loop and a current loop. The speed loop adopts a PID regulator, which can effectively limit the overshoot of the dynamic response and speed up the response speed. The stator current of the motor is decomposed into excitation current and torque current in the rotor magnetic field positioning coordinates. Keeping the excitation current constant and controlling the torque current also control the motor torque. The difference between the given speed and the actual speed in actual operation generates a torque current IT through PID adjustment. After vector transformation, IT and IM are converted into motor three-phase given currents Ia*, Ib*, Ic*, which are compared with the motor running current to generate three-phase driving signals. The key to the system's all-digital is the digitalization of the current loop, which is to realize the analog current loop in the digital-analog hybrid frequency conversion system by digital means. Its core enhances the processing speed of the current loop and reaches or approaches the response speed of the analog current loop. According to the current microprocessor DSP, A / D device level, can meet the needs of the hardware; the other is the control strategy and control software optimization. Good system hardware and software design are the assurance that the developed system is practical. On the basis of satisfying the performance requirements, we must make full use of hardware resources, increase the degree of integration to reduce hardware costs, and achieve product goals. The control block diagram of the entire system is shown in Figure 2.
Figure 2 Control principle
3.2.2 Hardware Master Control Implementation Section
The system consists of a DSP digital signal processor as the main control CPU. The programmable logic device realizes the calculation of some algorithms and the waveform generation and processing of various signals. The status information of the unit is sent through the optical fiber to the main controller after being serially encoded by the programmable logic device. The receiving board of the controller, the main controller receiving board performs serial to parallel decoding and transfers to the main control CPU; the main control CPU adjusts the control status of the system according to the unit status information; the speed measurement mode adopts variable M/T speed measurement and can achieve high Accuracy speed requirements. The current detection element in this system selects the Hall effect current transformer made according to the principle of magnetic field compensation to meet the requirements of monitoring the current in real time. The overall hardware block diagram is shown in Figure 3.
Figure 3 main controller structure
3.3. Variable frequency power module
The three-phase 6000V alternating current sent from the power grid is converted into 15 groups of 690V to supply 15 power units through the isolated phase-shifting transformers. The single-phase SPWM waves output from the 5 power units on each phase are superimposed and then Y-connected. A high-quality sine wave output with a line voltage of 6000 V is supplied to the high-voltage synchronous motor drive fan.
The fiber-optic isolation technology is used between the main control cabinet and the power cabinet to achieve complete isolation of high pressure and low pressure, and it has extremely high safety. The power unit adopts AC-DC-AC frequency conversion technology, single-phase output, and IGBT components adopt advanced and efficient heat pipe heat dissipation technology, which greatly improves the work reliability.
High-voltage inverter 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: Heat pipe cooling
Working environment 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
In view of the current situation of the main ventilators of the Daxing Mine of Tiemei Coal Group, a step-by-step speed control scheme for the main fan synchronous motor was implemented using a high-voltage inverter and a one-to-one work method. The fan motor is controlled by a high-voltage inverter, and the original damper adjustment opening degree is opened to the maximum. The adjustment of the air volume is achieved by controlling the motor rotation speed to achieve real-time and accurate adjustment of the air volume. In steady state, the input and output waveforms of the inverter are shown in Figure 4 and Figure 5 respectively:
(a) Measured input line voltage waveform (X-5ms grid, Y-5kV/division)
(b) Measured input current waveform (X-5ms grid, Y-10A/div)
Figure 4 Inverter input current and voltage waveforms
(a) Measured output line voltage waveform (X-5ms grid, Y-5kV/division)
(b) Measured output current waveform (X-5ms grid, Y-10A/div)
Figure 5 Inverter output (motor) voltage and current waveforms
(1) After adopting the high-voltage frequency conversion stepless speed regulation technical scheme, the speed of the fan motor can be conveniently adjusted downward 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 system mechanical wear and prolongs the service life of the equipment;
(3) The automatic adjustment of the fan can be realized through the communication connection with the control center;
(4) Under the condition of satisfying the air volume through frequency conversion control, considerable energy-saving effects can also be achieved. The motor achieves a true soft start and the starting current is controlled below the rated value.
4. The economic benefits of fan frequency conversion speed regulation system
The fan is a squared torque load. The air flow Q of the fan is proportional to the speed n, and the power P of the fan is proportional to the cube of the speed n.
Fan air flow Q = K1n (1)
Fan wind pressure P = K2 n2 (2)
Fan power P = K2 n3 (3)
The annual power consumption is (current is the actual value of the operation):
P = UI (4)
The throttle opening is taken as 60%, the actual operating current before the transformation is 146A, after the transformation is 92A, according to the existing experience and field measurement, from the type (4) can be obtained before the transformation of 13.2 million degrees of electricity, after the transformation of 8.32 million degrees The annual energy saving of the frequency conversion is 2.2 million yuan, and the equipment investment can be fully recovered in about two years.
5, innovation
(1) Principle innovation: The control method adopts all-digital vector control. At the same time, RHVC can also realize functions such as forward rotation, reverse rotation, traction, and electric braking to meet the requirements of load-speed regulation for four-quadrant operation such as lifting and traction.
(2) Technological innovation: The frequency converter adopts all-digital synchronous start-up, and at the same time, it can realize the start of the coaster.
(3) Structural innovation: Using self-developed high-efficiency heat pipe heat dissipation technology, the efficiency of traditional air-cooled heat dissipation design has been greatly improved, and the heat island effect of high-power device IGBT has been completely eliminated.
(4) Process innovation: A semi-automatic coating machine is used to realize thermal grease coating between IGBT and heat sink. Its characteristic is accurate thickness, uniform distribution, increase of high-power device thermal conductivity and energy saving.
6 Conclusion
The speed regulation of synchronous motors is a major problem in the electric drive industry. In recent years, the application of high-voltage variable frequency speed control has been the subject of research by China's inverter manufacturers. The successful use of high-voltage frequency converters from Rongxin Power Electronics Co., Ltd. in the Daxing Mine fan-fan synchronous motor has demonstrated its significance. The practical application shows that the application of high-voltage frequency converters to the synchronous motor system will surely achieve good operating results and economic benefits.
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About the Author:
Li Xing (1958-), male, Shaanxi Fufeng, bachelor degree, professor-level senior engineer, engaged in the research of frequency converter and other technical work.