New energy photovoltaic power station low-voltage grid-connected 380V-110KV group control group frequency modulation solution

The large-scale access of distributed photovoltaic has put forward higher requirements for the carrying capacity and absorption capacity of the distribution network. The photovoltaic power generation output has the characteristics of random fluctuation, intermittent daily cycle and seasonal change, which is significantly different from the conventional power supply, so that the original power balance, matching capacity selection, network security constraints and other boundary conditions of power grid planning have changed greatly. Therefore, it is necessary to make an overall plan for the future construction goals of distributed PV and the current carrying and absorbing capacity of the power grid, laying the foundation for the orderly development of distributed PV on the roof of the whole county, the safe and reliable economic operation of the distribution network and the full absorption of distributed PV.

Power prediction and group control to cope with grid connection difficulties

The output of distributed photovoltaic power generation has strong volatility and randomness, which has three impacts on the operation of the power grid: First, because the output of distributed photovoltaic is zero after the sun goes down, this output characteristic will increase the peak-valley difference of the power grid load, and bring great difficulties to the power grid dispatch. Second, the grid net load is formed after the fusion of the distributed photovoltaic output and the actual power load of the user. Distributed photovoltaic introduces the random fluctuation of solar radiation into the grid net load, which greatly increases its randomness, thus making the accurate prediction of the grid load more difficult. Third, the output characteristics of distributed PV do not match the demand characteristics of the power grid load, and its full absorption faces serious challenges. The above three points lead to the dilemma of power grid dispatching facing "insufficient power supply during peak hours and difficulties in photovoltaic consumption during trough periods".

With the acceleration of the development of rooftop photovoltaic in the whole county, the pressure and challenge brought by the distributed photovoltaic with massive distributed access to the power grid operation will become increasingly prominent, and the distributed power supply must also be organically integrated into the dispatching operation of the whole network. Distributed photovoltaic power prediction and its group control are effective technical means to deal with the above difficulties.

The new energy group control group modulation response system collects and integrates the CT and PT signals of the dot, measures the frequency, calculates the target output of the telekinetic fixed power station issued by dispatching 104 according to the line function of the active power-frequency sag characteristic, calculates and decomposes to the output of the inverter, and sends the target adjustment instructions to each power generation unit quickly through the communication network. The control system of the power generation unit adjusts the load according to the target value, so as to achieve the purpose of frequency response and active support.

2, new energy photovoltaic power station fast frequency modulation scheme design

The new energy photovoltaic power plant station completes the active power frequency control by installing an independent control device, so that the connecting point has the ability to participate in the rapid adjustment of the grid frequency.

Use of fast frequency control and sampling devices;

According to the actual situation of the new energy power station, the AGC and inverter of the power station should be upgraded/reformed to ensure the overall performance of fast frequency response.

When the new energy station is connected to the grid, when the frequency of the grid changes under the influence of external load changes, the current active power output can be automatically calculated and adjusted to balance it with the external load and reduce the frequency change of the grid as much as possible. This process is called the new energy station group control group active and reactive frequency regulation response.

(1) The frequency reflects the balance between active power supply and demand in the power grid

(2) The supply exceeds the demand, the frequency increases, and the work is reduced

(3) In short supply, the frequency is reduced, then the rise is active

(4) Quickly adjust the power generation output and pull back the frequency

(5) Too high or too low frequency is harmful

3, photovoltaic power station frequency modulation implementation plan

(A) Photovoltaic power station group control group response system equipment composition list:

(1) Power control equipment, power control equipment directly and network voltage and current.

(2) Pbox6220, a fast power group control and group adjustment terminal, builds a photovoltaic ring network and forwards the data of the photovoltaic ring network to the power control equipment. The number of connected devices is determined by the number of collector lines and the number of photovoltaic ring networks.

(3) Switch, all the data of Pbox6220 group control terminal is collected and sent to the power control equipment.

(4) Monitor the background.

(5) Four optical fiber jumpers are arranged between each Pbox6220 teamwork control terminal and GPS communication screen optical port (optical fiber ring network interface in photovoltaic area), respectively connected to two optical ports of Pbox6220 fast power teamwork control terminal, and interconnect with Pbox6220 field fast power teamwork control terminal in photovoltaic area.

(2) Photovoltaic power station group control group response system photovoltaic area deployment:

(1) Pbox6220A group control terminal device for fast power acquisition and protocol conversion is deployed on the low-voltage side of the box transformer, which is used for the protocol conversion function and the formation of optical fiber ring network function.

(2) The teamwork control group modulation terminal device is installed on the low-voltage side of the box. Take 220V AC power from the low-voltage side of the box, connect jumper fibers from the original optical fiber distribution frame to build an optical fiber ring network, and connect the inverter.

(3) The ETH4 port of the group control terminal device PBOX6220A is connected to the ring network switch by network cable.

(4) Group control group commissioning terminal device configuration, refer to the online configuration help document.

(5) Check the performance indicators of the inverter, whether it has millisecond power control capability, and decide whether to upgrade according to the situation.

(3) The functions of the group control and group adjustment system of photovoltaic power station:

(1) The functions of AGC, AVC, primary frequency modulation and primary voltage regulation are realized, and the functions of AGC, AVC and primary frequency modulation meet the scheduling requirements.

(2) Active power control time is less than 200ms, dynamic reactive power response time is less than 30ms.

4, the difference between new energy photovoltaic fast frequency and traditional primary frequency modulation

(1) The debugging object is different: traditional primary frequency modulation is completed by the governor of the generator set; New energy fast frequency is done by photovoltaic inverter or wind turbine.

(2) Different response time: traditional frequency modulation response time is long, affected by mechanical equipment and performance, loss; The new energy fast frequency is calculated by electronic equipment, and the response speed and accuracy are high.

(3) Communication methods are different: traditional one-time frequency modulation is communicated through hard wiring, which is greatly affected by site construction; New energy fast frequency can be communicated through the network, and the construction is more flexible.

(4) The action range is different: the traditional frequency modulation action range is small; The new energy fast frequency has a larger adjustable range in suitable weather.

(5) The adjustment accuracy is different: the traditional frequency modulation is differential adjustment; New energy fast frequency is intelligent strategy distribution, more intelligent regulation, better effect.

5, photovoltaic power station primary frequency modulation application value

(1) New energy photovoltaic power station primary frequency modulation safety is higher: fast power regulation New energy fast power regulation for secondary operation, the use of new power electronics technology, high safety. Traditional power regulation Traditional power regulation uses primary equipment, such as rotating machinery, boilers and other equipment, while there is a short circuit current when the power system fails.

(2) The new energy photovoltaic power station has higher reliability of primary frequency modulation: fast power regulation New energy fast power regulation is distributed, even if some inverters/converters fail, the server redistributes the amount of reactive power regulation according to the number of online, to ensure uninterrupted reactive power regulation and high reliability. Traditional power regulation Traditional power regulation is centralized, and the whole station loses the reactive power regulation ability when a fault occurs.

(3) New energy photovoltaic power plant primary frequency regulation speed is fast: fast power regulation new energy power plant rapid power regulation is the use of power electronic equipment and power system for power exchange, relying on high-speed communication network, power control is flexible, the adjustment speed can reach millisecond level. Traditional power regulation Traditional power regulation uses large regulation equipment, power control is not flexible.