Keywords: wind power generation, low voltage ride through LVRT, Profibus_DP protocol, Can open protocol
0 Preface
Wind power generation is the most mature, most large-scale development and commercialization development method for new energy development technologies in the world today, but the random changes in wind have led to the wind power generator output usually changing rapidly with the wind speed. Connecting to the grid will have an impact on the power quality and stability of the grid3.
This article introduces an AGP measurement and protection module designed for wind power generation systems. This module can measure traditional electrical parameters such as voltage, current, frequency, and electrical energy. In the event of grid failure, grid frequency, voltage deviation, generator output power is too large, active power When a fault such as reverse flow occurs with the reactive power flow, an alarm signal is issued, and two under-voltage protections according to time are integrated to improve the anti-interference ability of the control system against voltage flicker.
1 Circuit design principle
AGP hardware circuit includes main control chip, power supply, voltage, current signal acquisition circuit, digital input module, relay output module, human-computer interaction unit, RS485 communication interface, Profibus_DP communication protocol interface, Can open communication interface (Figure 1).
Figure 1 Block diagram of hardware circuit
1.1 Main control chip
The MCU chip adopts Freescale's Coldfire-V0 architecture core 32-bit processor MCF51EM256, the clock frequency can be up to 50.33MHz, built-in 256K Flash, 16K RAM, 4 independent 16-bit AD channels, 3 timers, 3 channels SCI communication interface, built-in RTC clock, I2C, SPI, KBI interface and other resources have a very high cost performance.
1.2 Power
AGP uses DC 24V working power supply, using Guangzhou Jinshengyang's wide voltage input DCDC module WRF2405P, operating temperature range -40 ~ 85 ℃, isolation voltage 3000VDC, measured output ripple <1%, at the same time, the design of the power input part adds discharge tube, PTC varistors, TVS tubes, anti-reverse diodes and other devices (Figure 2) have overvoltage and overcurrent protection.
Figure 2 Power circuit
1.3 Signal acquisition circuit (Figure 3)
Signal acquisition includes voltage signal, current signal and frequency signal: voltage signal adopts voltage divider resistance input, current signal adopts transformer isolation input, after the AC signal is raised, the signal is amplified by the amplifier circuit, and finally the signal is sent to the CPU for Software differential operation.
Figure 3 Current signal circuit
1.4 Interface design
AGP interfaces include human-computer interaction unit, RS485 communication interface, and switch input and output interfaces. While designing various interfaces, it is necessary to add components such as electromagnetic compatibility performance, voltage resistance, and contact protection to improve the reliability of the device.
2 Software design method
The software program mainly includes the main program, A / D signal acquisition program, TPM frequency measurement program, electrical parameter calculation program, protection processing program, various communication protocol processing programs, etc. Due to the large content, part of the program flow is now given.
Figure 7 Main program flowchart
Each channel of the MCF51EM256 AD module has A and B channel inputs. After the acquisition of any channel is completed, the built-in PDB module is used to adjust the automatic switching time to achieve the voltage and current phase angle adjustment to achieve the power compensation function. At the same time, it is necessary to deal with AD exceptions, and now give the AD interrupt processing program flow.
Figure 8 Interrupt program flow chart
3 Technical regulations and applications of wind power generation systems
With the continuous expansion of the installed capacity of wind power generation, the State Grid Corporation has put forward a series of requirements for wind turbines, "GB / T 19069-2003 Technical Requirements for Wind Turbine Generator Controllers" and "Implementation Rules for Technical Regulations for Wind Farm Access to the Grid -2009 "clarified the functions that the controller needs to have. Mainly include: grid frequency control, reactive power and grid voltage control, low voltage ride-through (LVRT) control and power quality control.
3.1 Operating frequency of wind farms
Table 2 Wind farm operation at various frequencies
Grid frequency range | Claim |
Below 48Hz | It depends on the lowest frequency that the wind turbine in the wind farm is allowed to run. |
48Hzï¼49.5Hz | Every time the frequency is lower than 49.5Hz, it is required to be able to run for at least 10min. |
49.5Hz-50.5Hz | continue to operate. |
50.5Hzï¼51Hz | Each time the frequency is higher than 50.5Hz, it is required to be able to run for at least 2min; and when the frequency is higher than 50.5Hz, the wind turbine in the stopped state is not allowed to be connected to the grid. |
Higher than 51Hz | Operate according to the power limit of the power grid dispatch department. |
3.2 Wind farm voltage range
Wind power is required when the voltage deviation of the grid connection point of the wind farm is between -10% and + 10%, and the flicker value of the grid connection point meets the national standard power quality regulations on voltage fluctuation and flicker, harmonics of the public power grid, and three-phase voltage imbalance. The wind turbine in the field should be able to operate normally.
3.3 Wind farm low voltage ride through
When the voltage of the grid connection point of the wind farm is in the area of ​​the voltage contour line and above in the figure, the wind turbine in the field must ensure uninterrupted grid operation; when the voltage of the grid connection point is below the voltage contour line in the figure, the wind turbine in the field is allowed to cut off from the grid Out 2.
Figure 9 Regulations for wind farm low voltage ride through requirements
For different European and American national grid companies, there are also differences in the low voltage drop amplitude and ride-through time. The UK is 15% and 140ms, Germany is 15% and 625ms, Denmark is 25% and 100ms, and Spain is 0% and 500ms etc.
3.4 The current grid-connected system of doubly-fed wind turbines
Figure 10 AC excitation variable speed constant frequency wind power inverter circuit diagram
Variable-speed constant-frequency power generation introduces advanced power electronics technology into generator control. The unit uses variable-speed operation to make the speed of the impeller of the wind turbine change with the change of wind speed, and maintain a substantially constant optimal tip speed ratio to obtain the maximum Wind energy utilization efficiency.
During the operation of the variable-speed constant-frequency double-fed generator set, the stator winding is directly connected to the power grid, and the rotor winding is connected to the slip frequency power supply to achieve AC excitation. When the generator rotor frequency changes, the excitation current frequency is controlled to ensure that the stator output frequency is constant4.
3.5 Application CaseAGP can be applied to various types of generator windings. Figure 10 below is a typical application case of the winding structure of a three-phase four-wire generator. The voltage signal is directly connected, and the current signal is connected to the module after being transformed by the transformer. Set relay 1 to overload, overvoltage and overfrequency, relay 2 to undervoltage and underfrequency, relay 3 to reverse power, relay 4 to undervoltage protection A and B according to time, supply the module with DC24V, and the device starts self-check When the device fails the self-test, an alarm signal is issued and the generator set is prohibited from starting. When a fault occurs during the operation of the generator set, the controller executes the deceleration operation after receiving the relay 1 alarm. When the controller receives the relay 2 alarm, adjust the internal parameters of the control to make it normal. After receiving the alarm from relay 3, the generator stops and the grid-connecting switch is opened. When the grid voltage drops significantly, the module automatically calculates the depth and time of the drop, determines whether it can cross the low voltage, and gives the relay 4 diagnostic signal.
Figure 11 AGP300 typical application diagram
4 ConclusionAGP wind power measurement and protection module adopts advanced design scheme, can provide measurement and protection functions for different types of wind turbines (double-fed, permanent magnet direct drive), supports Modbus_RTU, Profibus_DP, Can open communication protocols, compatible with various PLC controls system. The product is stable and reliable, and is an ideal product for the nationalization of wind power equipment.
The article comes from: "Automation Application" 2012, Issue 10.
references:
[1] GB / T 19069-2003 wind turbine generator controller technical conditions "
[2] "Implementation Rules of Technical Regulations for Wind Farm Access to Power Grid-2009"
[3] Wind power generation test technology Yao Xingjia waits Electronic Industry Press
[4] Flexible feed-in operation and control of doubly-fed wind turbine generator Ren Yongfeng An Zhongquan et al. Machinery Press
[5] Design, operation and maintenance of wind power generation system. Ye Hangye is waiting for Electronic Industry Press
[6] Guideline for the Certification of Wind Turbines Edition 2010_R0
[7] Ren Zhicheng, Zhou Zhong, Principles and Application Guide of Electric Power Measurement Digital Instruments, China Electric Power Press, 2007
About the Author:
Yu Jing, female, undergraduate, engineer of Wuhan Ankerui Electric Co., Ltd., the main research direction is intelligent power monitoring and power management system
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