CN1967961A - Method for merging low-frequency wind generating set into electric network - Google Patents

Abstract

The invention discloses a method for merging a low-frequency wind power generator group into a power grid. In the method, a distributed power supply system is composed of a wind power generator group, a low-frequency step-up transformer, a high-voltage and low-frequency transmission line, an AC frequency converter, and a power frequency step-up transformer. Wind power generation The low-frequency power generated by the machine cluster is raised to low-frequency and high-voltage through the low-frequency step-up transformer, and then input to the AC inverter through the high-voltage and low-frequency transmission line, and then the low-frequency power is converted into power frequency power by the AC frequency converter, and then sent into the inverter through the power frequency step-up transformer. The power frequency power system is output by the power frequency power system. Since the wind turbine is connected to the power frequency grid through the low-frequency transmission system through the AC frequency converter, the wind turbine can be operated at low speed and frequency conversion, thereby simplifying the structure of the wind turbine and reducing the cost; more electric energy can be obtained from the wind field; it is easy to directly Connect wind power to the central area of the power system; reduce voltage fluctuations caused by wind power.

Description

Method for integrating low-frequency wind power generators into the power grid

Technical field

The invention belongs to the technical field of electric engineering, and relates to a method for connecting distributed power sources to a grid, in particular to a method for connecting a group of low-frequency wind power generators to a grid.

Background technique

In the wind power generation system, when the wind power generator runs in parallel with the power grid, the output frequency of the wind power is required to be consistent with the frequency of the power grid, that is, the frequency remains constant. There are mainly two ways to realize generator constant frequency: constant speed and constant frequency and variable speed and constant frequency. Varies with the wind speed, but keeps the frequency constant in a specific way.

In the constant speed and constant frequency system, the synchronous motor or the induction motor is directly connected to the grid. The constant speed and constant frequency wind power generation system has the advantages of simple structure, low cost, strong overload capacity and high operation reliability. It is currently the main wind power generation equipment. . However, in the constant speed and constant frequency wind power generation system, in order to meet the requirements of large and small wind speeds, two asynchronous generators with different capacities and different numbers of poles are generally used. Large-capacity generators generate electricity, and at the same time generally change the angle of attack of the blades through pitch control to adjust the output power, but this can only make the asynchronous generator have a better wind energy utilization coefficient at two different wind speeds, and cannot effectively Utilize wind energy at different wind speeds. On the other hand, wind turbines are directly coupled with the grid, and the characteristics of wind power will directly affect the grid; in addition, most of its power generation equipment is asynchronous generators, which need to consume reactive power while generating active power.

In the variable-speed constant-frequency wind power generation system, there are many schemes in the world, such as the commonly used variable-speed constant-frequency double-fed motor wind power generation system, each wind generator is connected to a double-fed motor and connected to the grid, but all of these methods use a The unit structure controlled by one tower and one motor increases the cost of wind power generation. At present, the new wind power generation system that overcomes the unit structure controlled by one tower and one motor is windformer. Windformer is a new type of wind power generation system developed by ABB. It is directly transmitted to the local high-voltage power grid, and the electrical main system of the wind farm is equivalent to a large-scale high-voltage DC generator. The advantage of this system is that the loss, noise and maintenance work due to the rotation of the gearbox is reduced due to the direct drive without the gearbox. Since the alternator is connected to the power grid through a rectifier-inverter device, the frequency of the generator and the frequency of the power grid are independent of each other, so the inrush current or impact torque generated by the frequency difference when the synchronous generator is connected to the grid usually does not occur The problem is a better and smooth grid connection method.

The disadvantage of this system is that the high-voltage DC generator is expensive and difficult to manufacture; the electric energy is transformed twice, and the loss is large; Using thyristors with high power and high reverse voltage, the price of power electronic devices is relatively high, and the control is complicated. In addition, non-sinusoidal inverters generate high-frequency harmonic currents that flow into the grid during operation, which affects the power quality of the grid.

Contents of the invention

Aiming at the defects or deficiencies in the above-mentioned prior art, the object of the present invention is to provide a method for integrating wind power generators into the power grid with low frequency. This method can connect the wind power generation group to the power grid through the low-frequency power transmission system, and can well solve the bottleneck problem existing in the wind power generation system.

In order to achieve the above tasks, the present invention takes the following technical solutions:

A method for merging a group of wind power generators into a power grid, characterized in that the method comprises a group of wind power generators, a low-frequency step-up transformer, a high-voltage and low-frequency transmission line, an AC/AC converter, and a power frequency step-up transformer to form a distributed power supply system, and the group of wind power generators The low-frequency power is sent out and connected to the primary winding of the low-frequency step-up transformer through the confluence busbar. After being boosted by the low-frequency step-up transformer, it is input to the AC inverter through the high-voltage and low-frequency transmission line, and then the AC inverter converts the low-frequency power into industrial frequency. Electricity is sent to the grid through a power frequency step-up transformer.

In the method of the present invention, since the wind power generating set is connected to the power frequency grid through the AC/AC converter through the low-frequency power transmission system, the wind power generating set can be operated at low speed and frequency conversion, thereby bringing the following advantages: 1. Simplify the structure of the wind power generating set and reduce the cost; 2. .It can obtain more electric energy from the wind farm; 3. It is easy to directly connect the wind power to the central area of the power system; 4. Reduce the voltage fluctuation caused by the wind power.

Description of drawings

Fig. 1 is a schematic structural diagram of a distributed power supply system of the present invention;

The present invention will be further described in detail below in conjunction with the accompanying drawings and principles.

Detailed ways

Referring to Fig. 1, the distributed power system of the present invention is composed of a low-frequency wind power generator group 1, a low-frequency step-up transformer 2, a high-voltage low-frequency transmission line 3, an AC frequency converter 4, a power frequency step-up transformer 5, and a power frequency power system 6.

The three-phase outlet terminal of the low-frequency wind turbine group 1 is connected to the primary winding of the low-frequency step-up transformer 2 through the busbar A, and the secondary winding of the low-frequency step-up transformer 2 is connected to the input terminal C of the AC inverter 4 through the high-voltage low-frequency transmission line 3 , the output terminal D of the AC-AC converter 4 is connected to the input terminal of the power frequency step-up transformer 5 , the output terminal E of the power frequency step-up transformer 5 is connected to the power frequency power system 6 , and is output by the power frequency power system 6 .

The low-frequency wind power generator group 1 includes a plurality of wind power generating devices, and each wind power generating device is composed of a wind turbine, a gear box and a generator.

The AC-AC converter 4 reversely transmits power from the output side to the input side. The AC-AC converter 4 works in the power generation mode, and its positive and negative converter circuits are mainly in the inverter state.

The low-frequency wind generator group 1 generates low-frequency power according to the magnitude of the wind force, and after the low-frequency step-up transformer 2 upgrades it to a low-frequency high voltage, it is input to the AC-AC converter 4 by the high-voltage and low-frequency transmission line 3, and the AC converter 4 converts the low-frequency power into industrial frequency The electric power is sent into the power frequency power system 6 through the power frequency step-up transformer 5, and is output by the power frequency power system 6.

The method of the present invention has the following technical characteristics:

1. Simplify the structure of wind turbines

Due to the use of low-frequency power transmission, the generator generates low-frequency power, the number of pole pairs is reduced, and the manufacturing technology and cost will be greatly reduced; in addition, the speed-up ratio of the speed-up gearbox used is higher than that of several wind power generation systems currently used. Can be much smaller, greatly reducing the volume of the speed-up gearbox. Greatly reduced maintenance costs and manufacturing costs.

2. Get more electricity from the wind farm

Since wind turbines operate at variable speeds, more power can be obtained from the wind farm. Below the rated wind speed, the operation of the wind turbine can not be limited by the wind speed range of power. In this operating area, the wind turbine is controlled with constant pitch, and the main task of the wind turbine control system is to track C _pmax through the control of the speed to obtain the maximum energy.

When the wind speed exceeds the rated wind speed, the energy acquisition will be limited by the physical performance of the unit, and the rotor speed and energy of the wind turbine must be lower than a certain limit value, otherwise the mechanical and fatigue strength of each component will be challenged. Therefore, when the wind speed is above the rated wind speed, the variable pitch constant low frequency control is implemented, and the power generated by the wind turbine is always kept near the rated power by controlling the pitch angle of the wind turbine.

The simulation test shows that if 50/3Hz is used for power generation, when the frequency changes ±10% at this low frequency, the utilization rate of wind energy can be increased by 8%.

3. It is easy to directly connect wind power to the central area of the power system

The wind turbines in the wind farm generate low-frequency electric energy. After being boosted by the low-frequency step-up transformer, the electric energy can be directly sent to the load center through low-frequency long-distance transmission, and then converted into 50Hz electric energy by the AC inverter and sent to the load center grid. This overcomes the limitation that small wind farms should be close to 10kV ~ 35kV power grids and large wind farms should be close to 110kV ~ 220kV power grids in the site selection of traditional wind farms. This can significantly reduce the impact of wind fluctuations on the power system.

4. Reduce voltage fluctuations caused by wind power

The voltage level of the power system depends on the balance of reactive power, and the fluctuation of voltage is determined by the following formula,

$\mathrm{<span\; class="notranslate">\; \&Delta;V</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; Q</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; x</span>}}{\mathrm{<span\; class="notranslate">\; V</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; Q</span>}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;fL</span>}}{\mathrm{<span\; class="notranslate">\; V</span>}}$

Obviously, reducing the transmission frequency can reduce the voltage fluctuation of the power grid.

Claims (4)

1. the method for a merging low-frequency wind generating set into electric network, it is characterized in that, this method is formed distributed power supply system with a wind power generation group of planes, low frequency step-up transformer, high pressure low frequency power transmission circuit, AC-AC frequency converter, duplex frequency boostering transformer, wind-driven generator is mass-sended out low frequency power, after boosting by the low frequency step-up transformer, input in the AC-AC frequency converter by high pressure low frequency power transmission circuit, by AC-AC frequency converter low frequency power is converted to power frequency electric power again, sends into electrical network through duplex frequency boostering transformer.

2. the method for merging low-frequency wind generating set into electric network as claimed in claim 1, it is characterized in that, the three-phase leading-out terminal of a described low frequency wind power generation group of planes is connected with a winding of low frequency step-up transformer through bus rod, the secondary winding of low frequency step-up transformer links to each other with the input of AC-AC frequency converter by high pressure low frequency power transmission circuit, the output of AC-AC frequency converter is connected with the duplex frequency boostering transformer input, the output of duplex frequency boostering transformer is connected with the power frequency electric power system, is exported by the power frequency electric power system.

3. the method for merging low-frequency wind generating set into electric network as claimed in claim 1, it is characterized in that, a described low frequency wind power generation group of planes comprises a plurality of wind power generation plants, each typhoon power generation device is by wind energy conversion system, gear box, generator is formed, and is connected with a winding of low frequency step-up transformer through bus rod.

4. the method for merging low-frequency wind generating set into electric network as claimed in claim 1, it is characterized in that, to the reverse through-put power of input side, AC-AC frequency converter is operated in the generator operation mode to described AC-AC frequency converter from outlet side, and its positive and negative group of convertor circuit mainly is in inverter mode.

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