Introduction: Dynamic reactive power compensation has developed a variety of specific technology types, in large grid-connected wind farms and photovoltaic power stations, if you want to use compensation technology, according to the operation method, operation principle and operation requirements of the power grid system, to build a special technology selection system, so as to ensure that the final quality of technology use is maintained. In the process of using the technology, it is necessary to configure it correctly according to the specific use method of the technology to ensure that the operation stability of the system is improved.
1. Type and principle of dynamic reactive power compensation technology in large-scale grid-connected wind farms and photovoltaic power stations
1.1 Principles of SVG technology
The principle of SVG technology is a new technology that has been developed at present. The core of this technology is to construct a three-phase fully controlled bridge rectifier inverter circuit based on IGBT, a fast on-off device, combined with pulse modulation technology, in which the AC side is connected to the power grid through reactance elements. SVG technology can be subdivided into current type bridge circuit and voltage type bridge circuit, in which voltage type circuit is more efficient, so it can be mainly considered in engineering.
The power compensation principle of SVG technology is to change the AC side voltage and the node voltage of the SVG technology system, and through analyzing the relative size of the two data, the reactive current of the leading or later and the node voltage is obtained, so as to achieve reactive power compensation. The construction principle of the system is that SVG, inductor and resistor are in series, where the resistance can be ignored, then calculated according to the formula, as follows:
Where UI is the AC side voltage, US is the junction voltage, and XL is the resistance value of the whole system. From the formula, the obtained results are > respectively. 0, < 0 and =0, which correspond to capacitive, inductive and no-load conditions respectively.
1.2 SVC Technology Principles
SVC technology system as a whole can be divided into two types, one is MCR type, the other is TCR type. The technical principle of the former is that the MCR device and two capacitors are configured in the system, and the capacitors include conventional capacitors and inductors, so that the system has the filtering function, and the system can not be automatically mediated. As for the MCR device, the reactor is constructed in series with the thyristor module to compensate the inductive reactive power. The principle is to adjust the conduction Angle of the thyristor system and change the excitation current through the reactance to smoothly adjust the output power of the reactor.
The technical principle of the latter is that a set of TCR device and two filter capacitors are configured in the system, in which TCR contains control, detection and triggering circuits, and detects the variables of the system, after obtaining the detection parameters, accounting and processing the demand variables of the system, and then adjusting the thyristor trigger Angle, so as to change.
To encode the equivalent reactance parameters of the reactor, so as to realize the inductive reactive power output of the reactor of the system. The system is basically the same as the MCR system, so the compensation power output of the TCR system is also the sum of inductive power and capacitive power.
2. Application of dynamic reactive power compensation technology in large-scale grid-connected wind farms and photovoltaic power stations
2.1 Comply with specifications
The construction process of dynamic reactive power compensation system must be able to follow professional norms and systems to ensure that the power supply and distribution system can run stably. From the current system management mode, the first specification to be complied with is the “Technical Specification for grid-connected Design of large wind farms”, which requires that the voltage in the grid should be able to control the range of rated voltage of -3% to +7%, the reactive power regulation speed should meet the voltage regulation needs of the grid, and the dynamic reactive power compensation device should be set up if necessary.
The second is the “Technical Regulations for Wind farm access to the grid”, which requires that the reactive voltage control system should be configured in the wind farm to control the grid-connected voltage, and for the adjustment speed and adjustment accuracy, the voltage adjustment needs should be met.
Finally, the “Technical regulations for photovoltaic power station access to the power system” requires that the power factor of the photovoltaic inverter should be adjustable within the range of lead and lag 0.95, if it can not meet the demand for voltage regulation, it is necessary to configure a dynamic reactive power compensation device in it.
2.2 Compensation mode selection
2.2.1. Typical configuration Scheme
In the selection process of compensation device, it is necessary to analyze the typical configuration technology of the entire power supply and distribution system, to select the application of typical engineering system operation mode of large wind farms and photovoltaic power stations that have been connected to the grid. In this process, three forms of reactive power compensation devices such as SVG, TCR and MCR should be analyzed at the same time. The use method of dynamic compensation device is analyzed, and then the current technical progress is analyzed. Considering that there are differences in the use frequency and usage specifications of dynamic reactive power compensation technology in different construction practices of the system, other types of reactive power compensation technology should be reasonably inserted in the subsequent upgrade process according to the original technical model.
2.2.2. Performance parameter analysis
In the analysis stage of performance parameters, the reactive power regulation range, harmonic content and dynamic response time of SVG, TCR and MCR reactive power compensation devices should be measured. The final results obtained are as follows: In the case of MCR, the response time is 6659 ms, the active power loss is 0.04% to 3.29%, and the total harmonic distortion rate is 3.8%, while the response time of TCR technology is 29.16 ms, the active power loss rate is 0.05% to 9.37%, and the total harmonic distortion rate is 0.37%. The response time of SVG technology is 16.8 ms, the active power loss is 0.67% to 1.86%, and the total harmonic distortion rate is 0.28%.
Through the analysis of the final results, it can be found that the response time of the system in TCR and SVG adjustment mode is millisecond level, and the overall response time is not higher than 30 milliseconds, while the response time of MCR reactive power compensation technology is too slow. The second is that TCR technology has the largest active power loss, and SVG system has the smallest active power loss. The third is harmonic content parameter, TCR technology content is the highest, SVG technology is the lowest.
2.3 System Configuration Methods
After obtaining the characteristics of the three technologies, it is necessary to analyze the voltage value of the circuit system itself, and it can be divided into 35kV and 10kV on the whole. For 35kV direct hanging mode, the advantage is that direct reactive power compensation can be carried out on the side of the fan or photovoltaic collector wire, and the compensation effect is good, and the filtering function can be taken into account. The operation process of the system does not occupy the main variable capacity, and does not need to connect the transformer, each set of equipment can achieve the maximum working capacity, the disadvantage is that the system is a new product, there are certain defects in the cost of construction and the maturity of technology.
For the 10kV buck working mode, its advantage is that the technology is relatively mature, and the system has high operational reliability, but the disadvantage is that a special transformer needs to be set in the area, and the operating capacity of each system is small. At the same time, when compensating the third winding side, it needs to cross the main transformer line, resulting in the compensation effect is weakened.
3. Key points of the use of dynamic reactive power compensation technology in large-scale grid-connected wind farms and photovoltaic power stations
3.1 Overall System Configuration
In the overall configuration process of the system, according to the relevant industry norms, the principles of various technologies and the operation requirements of the entire system, to achieve scientific participation in the relevant technical system, after the integration of the system, it is necessary to study the specific construction plan of the current relevant technical system, so as to allocate professional resources and let professional personnel put into work. All kinds of equipment will be built in a precise and perfect mode. In addition, it is also necessary to check the original reactive power compensation system configuration scheme of the system, and comprehensively study the reactive power compensation system types that occupy the main position in the original system. In the subsequent analysis stage, it is necessary to comprehensively study the working mode, working standard and other input forms of reactive power compensation technology of related systems.
3.2 Analysis of accident types
In the operation process of the dynamic reactive power compensation system, the specific type of equipment will be added to it, which requires that in the actual work stage, a professional emergency plan should be established through a comprehensive analysis of the relevant accident causes, accident impact scope and accident consequences, so that the system can prevent all kinds of faults from being too serious in the subsequent operation. With a certain degree of concealment, it cannot be searched and processed by the staff in advance, and eventually the entire power supply and distribution system fails.
3.3 Construction of emergency plan
In the construction stage of the emergency plan, the entire emergency system can be appropriately graded according to the frequency, scope of impact and cost of handling problems of various types of safety accidents, so that in the subsequent operation stage of the system, professionals can be dispatched to deal with the existing work problems in the first time according to the emergency plan that has been formulated. After the establishment of the emergency plan, all personnel need to strengthen the depth of understanding of it, based on this, to ensure that the emergency plan can be used continuously and effectively.
Conclusion: To sum up, dynamic reactive power compensation technology is needed in the operation phase of wind power grid-connected and photovoltaic power generation systems to ensure the safety of the entire power supply and distribution system. In the operation process of the system, it is necessary to first analyze the various industry norms that need to be complied with during the construction of the system, and then analyze the current uncompensated system, so as to analyze the types of technologies that can be adopted in the entire power supply and distribution line. Finally, it is necessary to invest in relevant technologies and sciences, and analyze the types of safety failures, and formulate emergency plans.
