summary
In 2007, Orui Transmission developed the EPS2000 dedicated frequency converter based on the industry characteristics of emergency power supply, wind power generation, and photovoltaic power generation. It is mainly used as an inverter for DC power supply in industries such as emergency power supply, wind power generation, and photovoltaic power generation, offering rich functionality and good adaptability.
This article briefly introduces the application of the Orui EPS2000 series frequency inverter in off-grid wind power generation, describes the system connection, and provides wiring diagrams and actual test results.
Keywords: green energy, Orui transmission, dedicated inverter
I. Introduction
my country's 11th Five-Year Plan outlined a goal of reducing energy consumption per unit of GDP by approximately 20% and total emissions of major pollutants by 10% during the 11th Five-Year Plan period. Under this backdrop, my country's wind power technology and equipment manufacturing capabilities have progressed rapidly, leading to significant development in wind power generation. Currently, the electricity generated by wind farms consisting of medium to large-scale (hundreds of kilowatts to megawatts) wind turbines can only be connected to the grid. This is due to two reasons: firstly, the short cycle life of lead-acid batteries, while other rapidly developing large-scale energy storage technologies are still relatively unknown; and secondly, following the development path of Western Europe.
When discussing wind power, a type of green energy, people tend to focus excessively on grid-connected wind power. However, off-grid wind power is another option for the development of wind power in China. Currently, small wind turbines (below tens of kilowatts) paired with lead-acid batteries to form an independently operating power supply system is the most typical example of distributed power supply.
The so-called "off-grid wind power generation" means that the terminal load of large-scale wind power generation is no longer the power grid, and it is also different from the small independent power supply system matched with lead-acid batteries. Instead, the wind power is directly transmitted to certain special enterprises. Its advantages are: (1) It can simplify the large number of auxiliary equipment required for grid-connected wind power generation, and significantly reduce the facility scale and cost of wind power plants; (2) Wind power generation can be directly applied to certain specific industries after simple processing, and enterprises can enjoy lower wind power prices and save costs; (3) It reduces the impact on the power grid system when wind power generation is connected to the grid.
In my country's vast western regions and numerous islands, where access to large power grids is difficult, the number of small, independently operated wind turbines is steadily increasing. With rising living standards and decreasing wind turbine prices, it is possible to gradually develop small local power grids centered around medium and large wind turbines, providing electricity for residential and industrial use to scattered villages and towns. These distributed wind power stations, not connected to the main grid, must be equipped with appropriately sized energy storage devices to effectively utilize wind power and ensure the continuity and stability of power supply.
Therefore, combining it with large-scale energy storage is a development and expansion of the simple "off-grid wind power generation". It is suitable for both large and small wind farms, and can improve the quality and economy of distributed power supply, and explore a new way of wind energy utilization with Chinese characteristics and independent intellectual property rights.
II. Industry Introduction and Original System Analysis
Off-grid wind power generation systems consist of: a wind turbine generator, a charger, and a digital inverter. The wind turbine generator comprises a nose cone, rotor, tail fin, and blades. Each part is crucial, and their functions are as follows: the blades receive wind power and convert it into electrical energy through the nose cone; the tail fin ensures the blades always face the wind direction to maximize wind energy; the rotor allows the nose cone to rotate flexibly, enabling the tail fin to adjust its direction; the rotor in the nose cone is a permanent magnet, and the stator windings cut magnetic lines of force to generate electricity.
Wind turbines output alternating current ranging from 13 to 25V. This current must be rectified by a charger before being used to charge the batteries, converting the electrical energy generated by the wind turbine into chemical energy. Once the batteries are connected in parallel and reach a certain voltage, the chemical energy in the batteries is converted into 220V AC mains power through a dedicated EPS2000 inverter with various protection circuits, ensuring the operation of equipment in homes, small farms, mobile base stations, etc. Off-grid wind power generation typically ranges from 0.2kW to 160kW.
Previously, inverters for off-grid wind power systems were all independently developed, resulting in high R&D costs, poor stability, and limitations in power output. Therefore, small wind power equipment manufacturers considered using dedicated variable frequency inverters as the core inverter. The Orui EPS2000 dedicated variable frequency inverter was developed specifically for this market.
III. Application Cases of Orui Transmission EPS2000 Dedicated Inverter in Off-Grid Wind Power Generation Industry
Frequency converters are widely used in drive systems in the wind power industry, primarily for two applications: connecting to generators and in doubly-fed induction generators (DFIGs) to ensure they operate in the same direction, at the same frequency, and under the same voltage. Currently, the most prevalent frequency converter brands in this market are foreign. Due to the high technological barriers in this field, these foreign brands hold a monopolistic position in this crucial component market.
In 2007, Orui Transmission developed the EPS2000 dedicated frequency converter inverter, tailored to the specific needs of industries such as emergency power supply, wind power generation, and photovoltaic power generation. This product utilizes a professional motor frequency conversion control chip, employs a modular and electromagnetic compatibility design approach, and is manufactured using advanced production processes and rigorous quality management. It features waveform optimization, automatic voltage adjustment, instantaneous current limiting, and a rich array of input/output interfaces. Primarily used as an inverter for DC power supply in industries such as emergency power supply, wind power generation, and photovoltaic power generation, it boasts rich functionality and excellent adaptability.
EPS2000 Series Dedicated Frequency Inverter Functions:
1. DC power supply available, wide input voltage range: No external power supply is required when using DC power supply, DC voltage range is 260～580V;
2. Flexible output voltage setting: The inverter output voltage can be flexibly set to adapt to sinusoidal inverters with different turns ratios;
3. Automatic Voltage Regulation (AVR) function: can adjust and stabilize the output voltage according to changes in DC voltage or load;
4. Instantaneous power failure protection: By setting the voltage at the main circuit switch engagement point, the DC main switch of the inverter is controlled to close or open, preventing instantaneous power failure and tripping (DC side input air switch).
5. Multi-channel and multi-functional characterization: Multiple inverter states are characterized by 2 relay outputs and 2 OUT outputs, including fan fault output, undervoltage output, and overcurrent output;
6. Forced start function: When the forced start signal is valid, the inverter will not report an undervoltage fault when the battery voltage drops to the inverter's undervoltage point. Instead, it will continue to output voltage and current according to its maximum capacity to ensure that special equipment does not need to be powered off.
7. Running time can be automatically recorded: convenient for users to view;
8. Cooling fan control: Automatically detects temperature and controls fan operation according to set values, which saves battery power;
9. Instantaneous current limiting function: When starting a cold resistive load, it can achieve the function of preventing overcurrent during startup;
10. Standard Modbus serial communication protocol: It can easily connect the host computer and PLC to achieve remote monitoring;
11. Zero-second switching function: By selecting an EPS mains synchronization card, it is possible to easily achieve "zero-second switching" between mains frequency power and emergency power.
The following is a system block diagram of the Orui EPS2000 frequency converter inverter in an off-grid wind power generation system, including terminal wiring, parameter adjustment, and measured waveforms.
The EPS2000-0300T3C is used as the main inverter after the battery pack, while the EPS2000-0022T3B is used on the yaw motor. The controller receives the wind turbine's angle of attack from the anemometer and transmits the commands to the yaw motor, which then fine-tunes the blade angle. Figure 3 shows the system block diagram of the inverter in an off-grid wind power generation system.
Figure 3: Block diagram and waveforms of each stage of the application of the Orui frequency inverter in wind grid-connected wind power generation.
EPS2000 Series Wiring and Related Parameter Settings (Taking the Use of EPS2000-0300T3C in a Wind Power Generation Company in Qingdao as an Example):
Parameter setting reference (the field uses 30 batteries, and the inverter output is required to be 230V, taking 30KW as an example): By adjusting the parameters, the output frequency, output voltage, undervoltage protection point, undervoltage self-recovery point, overvoltage protection point, etc. can be flexibly set, and can be output to the entire wind turbine generator system through passive contacts.
Below is the waveform after the field inverter has been processed by a sine wave filter (Figure 5).
IV. Conclusion
The system provides smooth start-up and shutdown of the wind turbine during power generation, with minimal current surge during load startup, ensuring reliable operation and enhancing the overall stability of the power generation system. It also simplifies operation, reduces equipment maintenance, effectively lowers wind turbine noise, minimizes the mechanical impact on the power grid and wind turbine during motor start-up and shutdown, extends equipment lifespan, and improves efficiency. This frequency conversion control scheme has excellent prospects for widespread application in wind power generation control.
