CN112421671A

CN112421671A - Photovoltaic power station power control method and system

Info

Publication number: CN112421671A
Application number: CN201910766914.1A
Authority: CN
Inventors: 钱敏慧; 赵大伟; 姚良忠; 朱凌志; 姜达军; 刘艳章; 陈宁; 吴福保; 丁杰; 彭佩佩; 胡东平; 唐亮; 孙辰军; 王卓然
Original assignee: State Grid Corp of China SGCC; China Electric Power Research Institute Co Ltd CEPRI; State Grid Hebei Electric Power Co Ltd
Current assignee: State Grid Corp of China SGCC; China Electric Power Research Institute Co Ltd CEPRI; State Grid Hebei Electric Power Co Ltd
Priority date: 2019-08-20
Filing date: 2019-08-20
Publication date: 2021-02-26

Abstract

The invention provides a power control method of a photovoltaic power station, which comprises the following steps: bringing the grid-connected point signals and the control parameters into a pre-constructed photovoltaic power station power control model, and adjusting the active/reactive current output value of the photovoltaic power station; and controlling the active/reactive frequency of the grid-connected point of the photovoltaic power station to a power grid dispatching set value based on the active/reactive current output value of the photovoltaic power station. The technical scheme provided by the invention adopts a modularized thought, and reflects active/reactive operation dynamics of different types and scales of photovoltaic power stations connected into a power grid through a photovoltaic power station active/reactive control structure which is obtained by dividing and comprises a field station level active/reactive control module, a photovoltaic inverter control module and a photovoltaic inverter power grid interface module.

Description

Photovoltaic power station power control method and system

Technical Field

The invention relates to the technical field of modeling simulation of photovoltaic power stations in new energy power generation technology, in particular to a power control method of a photovoltaic power station.

Background

The photovoltaic power generation has randomness, volatility and intermittence, and large-scale access of the photovoltaic power generation has great influence on safe and stable operation of a power system. With the increasing proportion of photovoltaic power generation in an electric power system, the influence of the photovoltaic power generation on a power grid is evolved from an individual or local operation control problem to a system-level safety and stability control problem, and a short-term electromagnetic and electromechanical transient process is gradually transited to a medium-and-long-term dynamic process. Under abnormal meteorological conditions such as large-scale cloud system motion, sand storm, solar eclipse and the like, the photovoltaic power generation output may change greatly in a short time, so that a high-risk 'climbing event' is formed, and the frequency stability of the power system is influenced. In some areas, sand storm and large-scale cloud system movement phenomena occur repeatedly, and solar eclipse phenomena are observed, the processes usually last for several minutes to several hours, and in areas with large and concentrated photovoltaic power generation loading capacity, abnormal weather causes great influence on new energy power generation output, and seriously threatens the safe and stable operation of a local power system.

In recent years, both academic circles and electric power enterprises carry out deep research on photovoltaic power generation grid-connected problems, research focuses mainly on the aspects of wind power/photovoltaic power generation fault ride-through technology, active and reactive control technology, static and transient stability analysis and the like, adopted models generally consider various links such as a power electronic converter/inverter, a generator, a wind turbine, active and reactive control, fault ride-through control and the like, and mainly pay attention to microsecond-level new energy power generation dynamic characteristics, the research time range generally does not exceed one minute, the method belongs to the field of electromagnetic transient or electromechanical transient research, and the method mainly solves the problem of coordination control of short time scales of elements or local areas. The existing standard of photovoltaic grid-connected operation clearly stipulates that a photovoltaic power station has an active/reactive control function, the power output of a grid-connected point of the photovoltaic power station is adjusted according to a control instruction issued in real time or preset by power grid scheduling, the time scale of the whole dynamic adjustment process is about the second-minute level, and the dynamic adjustment process belongs to a slow adjustment process.

The existing photovoltaic power generation model comprises an electromechanical transient state model and an electromagnetic transient state model, the body control model of the photovoltaic power generation unit is concerned more, and the active/reactive control of the photovoltaic power generation station level is less involved. Meanwhile, a traditional model is modeled according to the actual electrical connection and control structure of the photovoltaic power station, specifically, a field station level power control system model is required to be modeled, and a photovoltaic power generation unit model is required to be modeled, wherein when the field station level control system model is modeled, if the power station adopts the constant active power control physical model, the constant active power control model is established according to the actual system, the model does not have the frequency modulation control function, and if the photovoltaic power station with the frequency modulation function is modeled, the field station level power control system model is required to be established according to the actual frequency modulation control system of the power station. Namely, the modeling needs to be repeated according to different application scenes, and the process is complicated.

Disclosure of Invention

Aiming at the grid-connected standard requirements of the photovoltaic power station, a model capable of accurately reflecting the active/reactive power control slow regulation process of the photovoltaic power station needs to be established, the medium-long-term operation characteristics of the photovoltaic power station are analyzed, the power grid planning design and the production operation of scheduling operators are guided, and meanwhile, different application scenes can be reflected by adjusting different control parameters.

The invention provides a method for realizing power control of a photovoltaic power station, which is suitable for the slow regulation of the whole dynamic regulation process with the time scale of about second-minute level, and provides a model basis for grid-connected analysis of large-scale new energy accessed to a power system by abstracting a photovoltaic power station model with an active/reactive control function into a field station level active/reactive control module, a photovoltaic inverter control module and a photovoltaic inverter power grid interface control module by adopting a modular design idea and accurately reflecting the dynamic response characteristic of active/reactive power control of the photovoltaic power station by setting different control parameters.

The technical scheme provided by the invention is as follows:

a power control method of a photovoltaic power station is suitable for slow regulation of the time scale of the whole dynamic regulation process about the second-minute level, and comprises the following steps:

bringing the grid-connected point signals and the control parameters into a pre-constructed photovoltaic power station power control model, and adjusting the active/reactive current output value of the photovoltaic power station;

controlling the active/reactive frequency of a grid-connected point of the photovoltaic power station to a power grid dispatching set value based on the active/reactive current output value of the photovoltaic power station;

the photovoltaic power station power control model comprises: the system comprises a station level active/reactive control module, a photovoltaic inverter control module and a photovoltaic inverter power grid interface module;

the control parameters include: an active/reactive control instruction, an auxiliary frequency control signal, a power grid actual operation condition signal, a PI regulator parameter of a station level active/reactive control module, a system frequency set value and an active/reactive priority signal which are dispatched by a power grid;

the point-of-connection point signal includes: the grid-connected point voltage value, the grid-connected point reactive power measured value, the system frequency measured value, the node voltage amplitude and the current value amplitude of the grid-connected point sending line of the node and the photovoltaic power station.

Preferably, the photovoltaic power station power control model includes:

the system comprises a station level active/reactive control module, a photovoltaic inverter control module and a photovoltaic inverter power grid interface module;

the station level active/reactive control module comprises: the station level active control module and the station level reactive control module;

the station level active control module comprises: the system comprises a first-order filtering device, a time delay control device, an auxiliary frequency control device and an active control PI regulator with set regulation parameters;

the station level reactive power control module comprises: the power supply comprises a first-order filtering device, a line compensation device, a reactive power amplitude limiting device, a lead-lag control device and a reactive control PI regulator with set adjusting parameters;

the photovoltaic inverter control module includes: delay control and current amplitude limiting control;

the photovoltaic inverter grid interface module includes: time delay control and controlled alternating current source.

Further, the bringing of the grid-connected point signal and the control parameter into a photovoltaic power station power control model constructed in advance to adjust the active/reactive current output value of the photovoltaic power station includes:

the station level active/reactive power control module calculates active/reactive power reference values required to be output by each photovoltaic power generation unit of the photovoltaic power station according to the grid-connected point signals and the control parameters; the photovoltaic inverter control module calculates and obtains an active/reactive current reference value of each photovoltaic power generation unit corresponding to each photovoltaic inverter according to the active/reactive power priority signal based on the active/reactive power reference value;

and the photovoltaic inverter power grid interface module adjusts the active/reactive current output value of a controllable alternating current source which is connected with each photovoltaic power generation unit and the power grid according to the active/reactive current reference value.

Further, the station level active/reactive power control module calculates an active/reactive power reference value to be output by each photovoltaic power generation unit of the photovoltaic power station according to the grid-connected point signal and the control parameter, and includes:

the station level active control module calculates active power reference values required to be output by each photovoltaic power generation unit of the photovoltaic power station according to the system frequency measured value, active control instructions issued by power grid dispatching, auxiliary frequency control signals and a system frequency set value;

and the field station level reactive power control module calculates to obtain a reactive power reference value to be output by each photovoltaic power generation unit of the photovoltaic power station according to the voltage value of the grid-connected point, the reactive power measured value of the grid-connected point, the voltage amplitude of the node, the current value amplitude of a circuit sent by the grid-connected point of the node and the photovoltaic power station, a reactive power control instruction issued by power grid dispatching and a power grid actual operation condition signal.

Further, the station level active control module calculates active power reference values to be output by each photovoltaic power generation unit of the photovoltaic power station according to the system frequency measurement value, the active control instruction issued by the power grid dispatching, the auxiliary frequency control signal and the system frequency set value, and the method comprises the following steps:

judging whether the station level active control module works in a constant active power mode or a frequency modulation control mode according to the auxiliary frequency control signal value;

when the station level active control module works in a constant active power mode, the reference value of the active power of the whole station of the photovoltaic power station is equal to an active power instruction value issued by power grid dispatching;

when the station level active control module works in a frequency modulation control mode, calculating to obtain a whole station active power reference value of the photovoltaic power station according to a system frequency measurement value, a system frequency set value and an active power instruction value issued by power grid scheduling;

and calculating the active power reference value of each photovoltaic power generation unit based on the active power reference value of the whole photovoltaic power generation station according to the operation working condition of each photovoltaic power generation unit in the power station.

Further, the calculating to obtain the active power reference value of the whole photovoltaic power station according to the system frequency measurement value, the system frequency set value and the active power instruction value issued by the power grid dispatching includes:

obtaining a frequency adjustment reference value based on the system frequency measurement value and a set system frequency value;

and taking the frequency regulation reference value as an additional control signal, and obtaining the active power reference value of the whole photovoltaic power station through a PI regulator and a delay control link together with an active power instruction value issued by power grid dispatching.

Further, the obtaining a frequency adjustment reference value based on the system frequency measurement value and the set system frequency value includes:

calculating a difference value between a system frequency measurement value and a set system frequency value, and comparing the difference value with a set over-frequency action threshold value and an under-frequency action threshold value;

when the difference is larger than the set overfrequency action threshold, multiplying the frequency difference by a set overfrequency modulation coefficient to obtain a frequency adjustment reference value;

and when the difference is larger than the set under-frequency action threshold value, multiplying the frequency difference by the set under-frequency modulation coefficient to obtain a frequency adjustment reference value.

Further, the station level reactive power control module calculates to obtain a reactive power reference value to be output by each photovoltaic power generation unit of the photovoltaic power station according to a grid-connected point voltage value, a grid-connected point reactive power measured value, a node voltage amplitude, a current value amplitude of a line sent by a grid-connected point of the node and the photovoltaic power station, a reactive power control instruction issued by power grid dispatching and a power grid actual operation condition signal, and the method comprises the following steps:

judging whether the station-level reactive power control module works in a constant reactive power control mode or a constant voltage control mode according to the actual running condition signal value of the power grid;

when the station level reactive power control module works in a constant reactive power control mode, obtaining a whole station reactive power reference value of the photovoltaic power station according to a reactive power instruction value issued by power grid dispatching and a grid-connected point reactive power measured value;

when the station level reactive power control module works in a constant voltage control mode, calculating according to the node voltage amplitude, the current value amplitude of a line sent by a node and a photovoltaic power station grid-connected point and the voltage value of the grid-connected point to obtain a reactive power reference value of the whole photovoltaic power station;

and calculating the reactive power reference value of each photovoltaic power generation unit based on the whole station reactive power reference value of the photovoltaic power station according to the operation working condition of each photovoltaic power generation unit in the power station.

Further, the obtaining of the reference value of the reactive power of the whole photovoltaic power station according to the reactive power instruction value issued by the power grid dispatching and the measured value of the reactive power of the grid-connected point includes:

calculating a difference value between the reactive power instruction value and a first-order filtered photovoltaic power station grid-connected point reactive power measured value, and judging whether the difference value exceeds a set reactive power regulation control dead zone;

when the difference exceeds a set reactive power regulation control dead zone, the difference is subjected to a PI regulator and a lead-lag link to obtain a reference value of the reactive power of the whole photovoltaic power station;

and when the difference value does not exceed the set reactive power regulation control dead zone, the reference value of the reactive power of the whole photovoltaic power station is equal to the current reactive power output of the photovoltaic power station.

Further, the step of calculating a reactive power reference value of the whole photovoltaic power station according to the node voltage amplitude, the current value amplitude of the line sent by the node and the photovoltaic power station grid-connected point and the grid-connected point voltage value comprises the following steps:

calculating to obtain a photovoltaic power station grid-connected point voltage reference value in consideration of voltage drop of a grid-connected point according to the node voltage amplitude and the current value amplitude of a grid-connected point sending line of the photovoltaic power station and the node;

calculating the difference value between the grid-connected point voltage reference value after first-order filtering and the node voltage amplitude value, and judging whether the difference value exceeds a set reactive power regulation control dead zone or not;

when the difference exceeds a set reactive power regulation control dead zone, the difference is subjected to a PI regulator and a lead-lag control link to obtain a reactive power reference value of the whole photovoltaic power station;

Further, the calculation formula of the grid-connected point voltage reference value of the photovoltaic power station is as follows:

V_comp＝|V_reg-(R_c+jX_c)×I_branch|

wherein, V_compFor grid-connected point voltage reference value, V, of photovoltaic power station_regIs the node voltage amplitude, R_cTo send out line resistance, X_cTo send out line reactance, I_branchThe current value amplitude of a line sent out by a node and a grid-connected point of the photovoltaic power station is shown, and j is an imaginary part unit of line impedance.

Further, the calculating, by the photovoltaic inverter control module, an active/reactive current reference value of each photovoltaic power generation unit corresponding to each photovoltaic inverter according to the active/reactive priority signal based on the active/reactive power reference value includes:

determining the active/reactive power control priority of the photovoltaic power station based on the active/reactive priority semaphore, and calculating the maximum value and the minimum value of the active/reactive current to obtain the active/reactive current limit range;

dividing the active/reactive power reference value by the voltage value of the photovoltaic inverter terminal after filtering treatment after a time delay control link to obtain active/reactive current semaphore;

judging whether the active/reactive current semaphore is within the active/reactive current limit range or not, and when the active/reactive current semaphore is within the active/reactive current limit range, the active/reactive current reference value is equal to the active/reactive current semaphore;

otherwise, the active/reactive current semaphore outputs the maximum/minimum value of the active/reactive current after current amplitude limiting control as the active/reactive current reference value.

Further, the maximum value and the minimum value of the active/reactive current are calculated according to the following formula:

wherein, I_pmaxIs the maximum value of the active current, I_pminIs the minimum value of the active current, I_qmaxIs the maximum value of the reactive current, I_qminIs the minimum value of the reactive current, I_maxAt maximum apparent current, I_pcmd0Is an active current semaphore, I_qcmd0And Pqflag is active/reactive priority semaphore.

Further, the photovoltaic inverter grid interface module adjusts an active/reactive output value of a controllable alternating current source connecting each photovoltaic power generation unit and the grid according to the active/reactive current reference value, and includes:

inputting the active/reactive current reference value into a photovoltaic inverter power grid interface module after a time delay control link;

and a controllable alternating current source in the photovoltaic inverter power grid interface module outputs an active/reactive current value to the power grid according to the delayed active/reactive current reference value.

A photovoltaic power plant power control system, the system comprising:

the photovoltaic power station power control module is used for bringing the grid-connected point signals and the control parameters into a pre-constructed photovoltaic power station power control model and adjusting the active/reactive current output value of the photovoltaic power station;

and the adjusting module is used for controlling the active/reactive frequency of the grid-connected point of the photovoltaic power station to a power grid dispatching set value based on the active/reactive current output value of the photovoltaic power station.

The photovoltaic power station power control module comprises a station level active control unit, a station level reactive control unit, a photovoltaic inverter control unit and a photovoltaic inverter power grid interface unit:

the station level active control unit is used for calculating an active/reactive power reference value to be output by the photovoltaic power generation unit of the photovoltaic power station according to a system frequency measurement value, an active control instruction issued by power grid dispatching, an auxiliary frequency control signal and a system frequency set value;

the field station level reactive power control unit is used for calculating to obtain a reactive power reference value required to be output by each photovoltaic power generation unit of the photovoltaic power station according to a grid-connected point voltage value, a grid-connected point reactive power measured value, a node voltage amplitude, a current value amplitude of a line sent by a grid-connected point of the node and the photovoltaic power station, a reactive power control instruction issued by power grid dispatching and a power grid actual operation condition signal;

the photovoltaic inverter control unit is used for calculating and obtaining an active/reactive current reference value of each photovoltaic power generation unit corresponding to each photovoltaic inverter based on the active/reactive power reference value;

and the photovoltaic inverter power grid interface unit is used for adjusting the active/reactive output value of a controllable alternating current source which is connected with each photovoltaic power generation unit and the power grid according to the active/reactive current reference value.

Compared with the prior art, the invention has the beneficial effects that:

the invention provides a power control method of a photovoltaic power station, which is suitable for slow regulation of the whole dynamic regulation process with time scale of about second-minute level, and is used for bringing a grid-connected point signal and control parameters into a photovoltaic power station power control model which is constructed in advance and regulating the active/reactive current output value of the photovoltaic power station; and controlling the active/reactive frequency of the grid-connected point of the photovoltaic power station to a power grid dispatching set value based on the active/reactive current output value of the photovoltaic power station. The technical scheme provided by the invention designs a photovoltaic power station active/reactive power control structure comprising a station level active/reactive power control module, a photovoltaic inverter control module and a photovoltaic inverter network interface module, responds to a dispatching instruction of a power grid, and realizes the change of the active/reactive power of a photovoltaic power generation unit to a set value.

According to the technical scheme provided by the invention, the working mode of active/reactive power control is determined by setting different control parameters, namely the auxiliary frequency control signal, the power grid actual operation condition signal and the active/reactive power priority signal are 1 or 0, so that the active/reactive power control method can accurately reflect the active/reactive power operation dynamics of different types and scales of photovoltaic power stations connected into the power grid, and the model has good adaptability.

The technical scheme provided by the invention has universality, the model structure of the system is easily expanded to renewable energy grid-connected active/reactive power control systems such as wind power plants, and the like, and the application prospect is wide.

Drawings

FIG. 1 is a flow chart of a photovoltaic power plant power control method of the present invention;

FIG. 2 is a block diagram of a photovoltaic power plant power control method and system in an embodiment of the invention;

fig. 3 is a schematic diagram of a station level active/reactive control module according to an embodiment of the present invention;

FIG. 4 is a schematic diagram of a photovoltaic inverter control module in an embodiment of the present invention;

FIG. 5 is a schematic diagram of a grid interface control module of the photovoltaic inverter in an embodiment of the invention;

FIG. 6 is a schematic diagram of a model of a photovoltaic power plant connected to a power grid in an embodiment of the invention;

fig. 7 is a graph showing an active power scheduling issuing instruction value curve and an active power measurement value curve of a grid-connected point of a photovoltaic power station in the embodiment of the present invention;

FIG. 8 is a graph of reactive power scheduling issued instruction value curves and photovoltaic power station grid-connected point no-power measurement values in the embodiment of the present invention;

fig. 9 is a schematic structural diagram of a power control system for a photovoltaic power station according to the present invention.

Detailed Description

For a better understanding of the present invention, reference is made to the following detailed description taken in conjunction with the accompanying drawings and examples. It is to be understood that the embodiments described are only a few embodiments of the present invention, and not all embodiments.

Example 1:

the photovoltaic power station power control method provided by the embodiment of the invention is suitable for slow adjustment with the time scale of about second-minute level in the whole dynamic adjustment process, and the specific implementation process is shown in fig. 1 and comprises the following steps:

s101: bringing the grid-connected point signals and the control parameters into a pre-constructed photovoltaic power station power control model, and adjusting the active/reactive current output value of the photovoltaic power station;

s102: and controlling the active/reactive frequency of the grid-connected point of the photovoltaic power station to a power grid dispatching set value based on the active/reactive current output value of the photovoltaic power station.

Specifically, step S101, the grid-connected point signal and the control parameter are brought into a photovoltaic power station power control model that is constructed in advance, and an active/reactive current output value of the photovoltaic power station is adjusted, including:

step S101-1, establishing a photovoltaic power station power control model, specifically comprising:

step S101-1-1, dividing a photovoltaic power station model into a station level active/reactive power control module, a photovoltaic inverter control module and a photovoltaic inverter power grid interface module based on the electric quantity interaction of power and current between a photovoltaic power station and a power grid;

the established model is suitable for the steady-state operation condition of the power system. When the voltage of the grid-connected point of the photovoltaic power station is at a low voltage set value V_dipAnd a high voltage set value V_upWhen the interval is within, the photovoltaic power station is called to operate under a steady-state operation condition; when the voltage of the grid-connected point end of the photovoltaic power station is lower than a low voltage set value V_dipWhen the grid-connected point voltage of the photovoltaic power station is higher than the high voltage set V, the photovoltaic power station is called to operate in a low voltage ride through mode_upIn the meantime, the photovoltaic power station is called to operate in a high voltage ride through mode, and the high/low voltage ride through modes of the photovoltaic power station are transient operation working conditions. The photovoltaic power station model does not cover the transient operation condition;

step S101-1-2, the station level active/reactive power control module comprises: station level active control module and station level reactive control module:

the station level active control module comprises first-order filtering, delay control, auxiliary frequency control and an active control PI regulator with set regulation parameters;

the station level reactive power control module comprises first-order filtering, line compensation, reactive power amplitude limiting, lead-lag control and a reactive power control PI regulator with set adjusting parameters;

s101-1-3, the photovoltaic inverter control module comprises time delay control and current amplitude limiting control;

s101-1-4, a photovoltaic inverter power grid interface module comprises a time delay control and controlled alternating current source;

s101-2, calculating to obtain an active power reference value required to be output by each photovoltaic power generation unit of the photovoltaic power station by the station level active control module according to a system frequency measurement value, an active control instruction issued by power grid dispatching, an auxiliary frequency control signal and a system frequency set value; the method specifically comprises the following steps:

s101-2-1, judging whether the station level active control module works in a constant active power mode or a frequency modulation control mode according to the auxiliary frequency control signal value;

wherein, the auxiliary frequency control signal is Boolean quantity, and the value is 1 or 0;

when the value of the auxiliary frequency control signal is 1, the station level active control works in a constant active power mode; when the value of the auxiliary frequency control signal is 0, the station level active control works in a frequency modulation control mode;

step S101-2-2, when the field station level active control module works in a constant active power mode, the active power reference value of the whole station of the photovoltaic power station is equal to an active power instruction value issued by power grid dispatching;

step S101-2-3, when the station level active control module works in a frequency modulation control mode, obtaining a frequency adjustment reference value based on a system frequency measurement value and a set system frequency value, and specifically comprising:

step S101-2-3-1, calculating a difference value between a system frequency measurement value and a set system frequency value, and comparing the difference value with a set over-frequency action threshold value and an under-frequency action threshold value;

step S101-2-3-2, when the difference value is larger than the set overfrequency action threshold value, multiplying the frequency difference value by the set overfrequency frequency modulation coefficient to obtain a frequency adjustment reference value; when the difference value is larger than the set under-frequency action threshold value, multiplying the frequency difference value by the set under-frequency modulation coefficient to obtain a frequency adjustment reference value;

s101-2-3-3, taking the frequency regulation reference value as an additional control signal, and obtaining the active power reference value of the whole photovoltaic power station through a PI regulator and a delay control link together with an active power instruction value issued by power grid dispatching;

s101-2-4, calculating an active power reference value of each photovoltaic power generation unit based on an active power reference value of the whole photovoltaic power generation station according to the operation working condition of each photovoltaic power generation unit in the power station;

step S101-3, calculating by the field station level reactive power control module according to a grid-connected point voltage value, a grid-connected point reactive power measured value, a node voltage amplitude, a current value amplitude of a line sent by a grid-connected point of a node and a photovoltaic power station, a reactive power control instruction issued by power grid dispatching and a power grid actual operation condition signal to obtain a reactive power reference value to be output by each photovoltaic power generation unit of the photovoltaic power station, and specifically comprising the following steps:

step S101-3-1, judging whether the station level reactive power control module works in a constant reactive power control mode or a constant voltage control mode according to the actual running condition signal value of the power grid;

wherein, the actual running condition signal of the power grid is Boolean quantity, and the value is 1 or 0;

when the signal value of the actual operation condition of the power grid is 1, the station level reactive power control works in a constant reactive power control mode; when the signal value of the actual operation condition of the power grid is 0, the station level reactive power control works in a constant voltage control mode;

step S101-3-2, when the field station level reactive power control module works in a constant reactive power control mode, obtaining a whole station reactive power reference value of the photovoltaic power station according to a reactive power instruction value issued by power grid dispatching and a grid-connected point reactive power measured value; the method specifically comprises the following steps:

step S101-3-2-1, calculating a difference value between a reactive power instruction value and a first-order filtered reactive power measured value of a grid-connected point of the photovoltaic power station, and judging whether the difference value exceeds a set reactive power regulation control dead zone;

s101-3-2-2, when the difference value exceeds a set reactive power regulation control dead zone, the difference value is subjected to a PI regulator and a lead-lag link to obtain a reactive power reference value of the whole photovoltaic power station;

s101-3-2-3, when the difference value does not exceed the set reactive power regulation control dead zone, the reference value of the reactive power of the whole photovoltaic power station is equal to the current reactive power output of the photovoltaic power station;

step S101-3-3, when the station level reactive power control module works in a constant voltage control mode, calculating according to the node voltage amplitude, the current value amplitude of a line sent by a node and a photovoltaic power station grid-connected point and the voltage value of the grid-connected point to obtain a reactive power reference value of the whole photovoltaic power station, and the method specifically comprises the following steps:

step S101-3-3-1, calculating to obtain a photovoltaic power station grid-connected point voltage reference value obtained by calculating voltage drop of a grid-connected point according to a node voltage amplitude and a current value amplitude of a grid-connected point sending line of a node and a photovoltaic power station;

the calculation formula of the grid-connected point voltage reference value of the photovoltaic power station is as follows:

V_comp＝|V_reg-(R_c+jx_c)XI_branch|

wherein, V_compFor grid-connected point voltage reference value, V, of photovoltaic power station_regIs the node voltage amplitude, R_cTo send out line resistance, X_cTo send out line reactance, I_branchSending out the current value amplitude of the line for the grid-connected point of the node and the photovoltaic power station, wherein j is the imaginary part unit of the line impedance;

step S101-3-3-2, calculating a difference value between a grid-connected point voltage reference value after first-order filtering and a node voltage amplitude value, and judging whether the difference value exceeds a set reactive power regulation control dead zone or not;

s101-3-3-3, when the difference value exceeds a set reactive power regulation control dead zone, the difference value is subjected to a PI regulator and a lead-lag control link to obtain a reactive power reference value of the whole photovoltaic power station;

s101-3-3-4, when the difference value does not exceed a set reactive power regulation control dead zone, the reference value of the reactive power of the whole photovoltaic power station is equal to the current reactive power output of the photovoltaic power station;

step S101-4, calculating the active/reactive current reference value of each photovoltaic power generation unit corresponding to each photovoltaic inverter by the photovoltaic inverter control module according to the active/reactive priority signal based on the active/reactive power reference value, and specifically comprising the following steps:

s101-4-1, dividing an active/reactive power reference value by a photovoltaic inverter terminal voltage value after filtering treatment after a delay control link to obtain an active/reactive current semaphore;

step S101-4-2, calculating the maximum value and the minimum value of the active/reactive current based on the active/reactive priority semaphore to obtain the limit range of the active/reactive current;

the maximum and minimum active/reactive current values are calculated as follows:

Step S101-4-3, judging whether the active/reactive current semaphore is within the active/reactive current limit range, and when the active/reactive current semaphore is within the active/reactive current limit range, the active/reactive current reference value is equal to the active/reactive current semaphore; otherwise, the active/reactive current semaphore outputs the maximum/minimum value of the active/reactive current as the active/reactive current reference value after current amplitude limiting control;

step S101-5, the photovoltaic inverter power grid interface module adjusts the active/reactive output value of the controllable alternating current source connecting each photovoltaic power generation unit and the power grid according to the active/reactive current reference value, and the method specifically comprises the following steps:

step S101-5-1, inputting the active/reactive current reference value into a photovoltaic inverter power grid interface module after a time delay control link;

and S101-5-2, outputting an active/reactive current value to the power grid by a controllable alternating current source in the photovoltaic inverter power grid interface module according to the delayed active/reactive current reference value.

Example 2:

the existing photovoltaic grid-connected operation standard, for example, in the industry standard national standard 19964 and 2012 'technical specification of photovoltaic power station access power system' that needs to be satisfied in China, clearly specifies that a photovoltaic power station needs to have an active/reactive control function, adjusts the power output of a grid-connected point of the photovoltaic power station according to a control instruction issued in real time or set in advance by power grid scheduling, and the time scale of the whole dynamic adjustment process is about the second-minute level, which belongs to the slow adjustment process.

According to the embodiment of the invention, a model is abstracted into three submodules of a station level active/reactive power control system, a photovoltaic inverter control module and a photovoltaic inverter network interface according to a modular design idea, as shown in fig. 2, the method comprises the following steps:

(1) the station level active/reactive control module can calculate the active/reactive power which needs to be injected into the power grid by the photovoltaic power station in the current operation state according to the active/reactive control instruction issued by the power grid dispatching.

(2) The photovoltaic inverter control module receives the photovoltaic inverter active/reactive power instruction value signals output by the station level active/reactive control module, obtains the photovoltaic inverter active/reactive current reference value through calculation, and sends the photovoltaic inverter active/reactive current reference value to the photovoltaic inverter power grid interface control module.

(3) The photovoltaic inverter power grid interface module takes the controlled current source as an interface between the photovoltaic power generation unit and a power grid, and realizes the change of the active/reactive power of the photovoltaic power generation unit to a set value by controlling the active/reactive output value of the alternating current source.

Specifically, the structure and specific implementation of each sub-module are as follows:

the station level active/reactive control module not only has the function of responding to an active power control instruction issued by power grid dispatching, but also has the function of responding to power grid frequency regulation, and the semaphore F is set_{req_flag}It is determined whether to add an auxiliary frequency control element. The additional frequency control unit compares the system frequency measured value F_reqAnd a set value F_{req_ref}The difference of (a): if the frequency difference exceeds the over-frequency action threshold fdbd1, the frequency modulation controller is actuated to multiply the frequency deviation signal by a frequency modulation coefficient (over-frequency) D_upObtaining a frequency adjustment reference signal; (2) if the frequency difference exceeds the under-frequency action threshold fdbd2, the frequency controller is actuated to multiply the frequency deviation signal by a frequency modulation factor (under-frequency) D_dnAnd obtaining a frequency adjustment reference signal. And then, the frequency regulation reference signal is used as an additional control signal to act on an active control link together with an active power set value plant _ ref issued by scheduling, and a final active power reference value signal P of the photovoltaic power station is obtained through calculation of a PI (proportion integration) regulator_refIf the active control of the photovoltaic power station does not include the frequency control function, the active power set value plant _ ref sent by scheduling is the active power reference value P of the photovoltaic power station_ref(see fig. 3).

Over-frequency/under-frequency action thresholds fdbd1 and fdbd2 of station level active control system module and PI regulator parameter K_pg(coefficient of proportionality), K_igParameters (integral coefficient) and the like can be set according to the actual operation condition of the photovoltaic power station.

The station level reactive power control object can be a reactive power instruction (reactive power control mode) issued by scheduling, or a preset voltage (constant voltage control mode) of a certain node in the system, and the control mode is represented by a semaphore R according to the actual running condition of the power grid_{ref_flag}And (4) determining.

If the station level reactive power control adopts constant voltageIn the control mode, the input signal is the set node voltage amplitude V_regAnd the current value I of the line sent by the node and the grid-connected point of the photovoltaic power station_branchAnd calculating and acquiring a grid-connected point voltage reference value of the photovoltaic power station after the voltage drop of the line is calculated and calculated according to the following formula:

V_comp＝|V_reg-(R_c+jX_c)XI_branch|

wherein, V_compFor grid-connected point voltage reference value, V, of photovoltaic power station_regIs the node voltage amplitude, R_cTo send out line resistance, X_cTo send out line reactance, I_branchAnd sending out the current value amplitude of the line for the grid-connected point of the node and the photovoltaic power station.

Grid-connected point voltage reference value signal V_compAfter the first-order filtering step, the voltage value V of the grid-connected point is compared with the voltage value V of the grid-connected point_regComparing the difference, and if the voltage difference exceeds a reactive power regulation control dead zone dbd, obtaining a reactive power reference value Q of the photovoltaic inverter through a PI control link and a lead-lag link according to the difference signal_ext。

If the station level reactive power control adopts a reactive power control mode, if the reactive power command value Q issued by power grid dispatching is adopted_refAnd the filtered photovoltaic power station grid-connected point reactive power measured value Q_branchIf the difference exceeds the reactive power regulation action dead zone, the difference signal is subjected to a PI control link and an advance-lag link to obtain a reactive power reference value Q of the photovoltaic inverter_ext。

The photovoltaic inverter control module calculates the active/reactive power reference value signals received from the station level active/reactive power control module through the corresponding control links and obtains the active/reactive current reference value signals through the relevant control links.

The method for acquiring the active current reference value signal of the photovoltaic inverter in the photovoltaic inverter control module comprises the following steps: inputting a station level active power reference value signal P_refAfter a time delay link, dividing the voltage value V by the voltage value V of the photovoltaic inverter terminal after filtering treatment_t-filtCalculating and judging whether the obtained semaphore is within the limit range of reactive current [ I ]_pmin,I_pmax]In the method, a current reference value signal I is obtained after an amplitude limiting link_pcmd(as shown in fig. 4). The active power output of the photovoltaic inverter is limited by the rated capacity of the inverter, and the active power output is ensured to be in a normal power operation interval [ P_min,P_max]In order to avoid the "climbing event", the active power up/down regulation change rate limit dP needs to be set_max/dP_minThe specific parameter setting can be set according to the operation condition of the photovoltaic power station under the condition of meeting the requirement of the industry standard, for example, the industry standard to be met in China can be national standard 19964 and 2012 'technical provisions for accessing the photovoltaic power station to the power system'.

The method for acquiring the photovoltaic inverter reactive current reference value signal in the photovoltaic inverter control module comprises the following steps: the input station level reactive power reference value signal Q_extAfter a time delay link, dividing the voltage value V by the voltage value V of the photovoltaic inverter terminal after filtering treatment_t-filtCalculating and judging whether the obtained semaphore is within the limit range of reactive current [ I ]_qmin,I_qmax]In the method, a current reference value signal I is obtained after an amplitude limiting link_qcmdAs shown in fig. 4.

The method comprises the steps that a photovoltaic power station needs to determine the current active/reactive power control priority according to scheduling requirements, when a specific model is implemented, the active/reactive priority is determined by setting an active/reactive priority semaphore Pqflag, and the maximum value I of active/reactive current is determined_pmax、I_qmaxAnd a minimum value I_pmin、I_qmin。

If the reactive power is prioritized (Pqflag is equal to 0), the maximum value of the active/reactive current is calculated as follows:

wherein, I_maxIs the maximum apparent current.

If active power is preferred (Pqflag is 1), the method for calculating the maximum value of the active/reactive current is as follows:

the grid interface layer of the photovoltaic inverter takes a controlled current source as an interface between a photovoltaic power generation unit and a grid, and the active/reactive current reference value I output by the control layer of the photovoltaic inverter_pcmd/I_qcmdAnd inputting the active/reactive current value into a power grid interface layer through a time delay link, adjusting the active/reactive current value of the alternating current source according to the active/reactive current reference value, and finally changing the active/reactive power output value of the photovoltaic power generation unit (as shown in figure 5). Time constant T of delay link_gThe method can be set according to the actual operation performance of the inverter, and a controlled current source model of a simulation platform can be adopted by a power grid interface layer.

The circuit parameters appearing in fig. 2, 3, 4, 5 are as follows:

V_regcalculating the voltage value of the grid-connected point for the load flow; q_refIs a reactive power instruction value; v_refIs the voltage value of the grid connection point; p_refIs an active power reference value; p_branchThe active power measured value of the grid-connected point is obtained; f_{req_ref}Setting a system frequency value; f_reqIs a system frequency measurement; q_extIs a reactive power reference value; p_refIs an active power reference value; i is_qcmdIs a reactive current reference value; i is_pcmdIs an active current reference value; i is_qwIs a reactive current value; i is_pIs the value of the active current;

the plant _ ref is an active power set value dispatched in a scheduling manner; f_{req_flag}For auxiliary frequency control signals (0-exit, 1-input); p_minIs the minimum value of active power; p_maxThe maximum value of active power; t is_pDelaying for active measurement; t is_lagDelaying for active control; k_pg、K_igAdjusting parameters for active control PI; d_dnAdjusting the frequency modulation control gain for the upper part; d_upAdjusting the frequency modulation control gain for the down regulation; fdbd is a frequency modulation control action dead zone;

I_branchsending out a line current value for the photovoltaic power station; q_branchIs a grid-connected point reactive power measurement; r_{ref_flag}The actual operation condition semaphore of the power grid is obtained; q_minIs the minimum value of reactive power; q_maxIs the maximum value of reactive power; k_p、K_iAdjusting parameters for reactive power control PI; dbd is a reactive control dead zone; r_c、X_cIs the line impedance; t is_fltrFiltering time delay for a reactive control link; t is_ft、T_fvThe time constant of the leading and lagging links is reactive control;

T_pordactive control delay parameters; t is_iqA reactive power control delay parameter is obtained; dP_maxThe maximum value of the active power change rate; dP_minIs the minimum value of the active power change rate; i is_pmaxThe maximum value of the active current; i is_pminIs the minimum value of active current; i is_maxIs the maximum value of the current; pqflag is active/reactive priority semaphore; t is_iqDelaying for reactive power control; i is_qmaxIs the maximum value of the reactive current; i is_qminIs the minimum value of the reactive current; i is_pcmdIs an active current reference value; i is_qcmdIs a reactive current reference value; v_t-filtIs a photovoltaic inverter terminal voltage value; t is_gAnd controlling delay parameters for the power grid interface.

By taking a PowerFactory platform as an example, the method provided by the invention is adopted to establish a photovoltaic power station model, and whether the active power and reactive power output of a grid-connected point of the photovoltaic power station can accurately respond to a power grid dispatching instruction is observed by changing an active power and reactive power instruction value signal issued by power grid dispatching so as to verify the accuracy of the established model.

In the simulation process, the capacity of a photovoltaic power station is set to be 50MWp, the photovoltaic power station is composed of 100 photovoltaic inverters with the single machine capacity of 500kW, the electrical connection of the photovoltaic power station access system is shown in figure 6, a specific simulation model is equivalent by adopting a single machine multiplication method, and one photovoltaic inverter model is equivalent to a photovoltaic power station model. The simulation comparison of the active/reactive power instruction value issued by scheduling and the active/reactive power of the grid-connected point of the photovoltaic power station is respectively shown in fig. 7 and fig. 8, and it can be known from the figure that when the power grid scheduling active/reactive control instruction changes, the active/reactive power measured value of the grid-connected point of the photovoltaic power station can accurately track the scheduling instruction, and the accuracy of the established model is also verified.

Example 3:

based on the same inventive concept, the present invention further provides a power control system of a photovoltaic power station, as shown in fig. 9, the system includes:

the station level active control unit is used for calculating an active/reactive power reference value required to be output by the photovoltaic power generation unit of the photovoltaic power station according to the system frequency measurement value, an active control instruction issued by power grid dispatching, an auxiliary frequency control signal and a system frequency set value;

the station level reactive power control unit is used for calculating to obtain a reactive power reference value to be output by each photovoltaic power generation unit of the photovoltaic power station according to the voltage value of the grid-connected point, the reactive power measured value of the grid-connected point, the voltage amplitude of the node, the current value amplitude of a line sent by the grid-connected point of the node and the photovoltaic power station, a reactive power control instruction issued by power grid dispatching and a power grid actual operation condition signal;

and the photovoltaic inverter power grid interface unit is used for adjusting the active/reactive output value of the controllable alternating current source which is connected with each photovoltaic power generation unit and the power grid according to the active/reactive current reference value.

As will be appreciated by one skilled in the art, embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.

The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.

These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.

These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.

The present invention is not limited to the above embodiments, and any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention are included in the scope of the claims of the present invention which are filed as the application.

Claims

1. A power control method for a photovoltaic power station is characterized by comprising the following steps:

2. The photovoltaic power plant power control method of claim 1, wherein the photovoltaic power plant power control model comprises:

3. The method of power control for photovoltaic plants of claim 2, wherein said bringing grid-connected point signals and control parameters into a pre-constructed photovoltaic plant power control model to adjust active/reactive current output values of a photovoltaic plant comprises:

4. The method of claim 3, wherein the calculating, by the station-level active/reactive control module, the active/reactive power reference value to be output by each photovoltaic power generation unit of the photovoltaic power station according to the grid-connected point signal and the control parameter comprises:

5. The power control method for the photovoltaic power station of claim 4, wherein the calculating of the active power reference value to be output by each photovoltaic power generation unit of the photovoltaic power station by the station-level active control module according to the system frequency measurement value, the active control command issued by the power grid dispatching, the auxiliary frequency control signal and the system frequency set value comprises:

6. The power control method for the photovoltaic power station of claim 5, wherein the step of calculating the active power reference value of the whole photovoltaic power station according to the system frequency measurement value, the system frequency set value and the active power instruction value issued by the power grid dispatching comprises the following steps:

7. The photovoltaic power plant power control method of claim 6 wherein deriving the frequency adjustment reference based on the system frequency measurement and the set system frequency value comprises:

8. The method for controlling power of a photovoltaic power plant according to claim 4, wherein the station-level reactive power control module calculates a reactive power reference value to be output by each photovoltaic power generation unit of the photovoltaic power plant according to a grid-connected point voltage value, a grid-connected point reactive power measurement value, a node voltage amplitude, a current value amplitude of a grid-connected point output line of the photovoltaic power plant, a reactive power control command issued by power grid dispatching and a power grid actual operation condition signal, and the method comprises the following steps:

9. The method for controlling power of a photovoltaic power plant according to claim 8, wherein the obtaining of the reference value of reactive power of the whole photovoltaic power plant according to the reactive power instruction value issued by the power grid dispatching and the reactive power measured value of the grid-connected point comprises:

10. The method for controlling power of a photovoltaic power plant of claim 8, wherein the step of calculating the reactive power reference value of the whole photovoltaic power plant according to the node voltage amplitude, the current value amplitude of the sending line of the node and the grid-connected point of the photovoltaic power plant and the voltage value of the grid-connected point comprises the steps of:

11. The photovoltaic power plant power control method of claim 10, wherein the photovoltaic power plant grid-connected point voltage reference is calculated as follows:

V_comp＝|V_reg-(R_c+jX_c)×I_branch|

12. The method of claim 3, wherein the photovoltaic inverter control module calculates an active/reactive current reference value of each photovoltaic power generation unit corresponding to each photovoltaic inverter according to the active/reactive priority signal based on the active/reactive power reference value, and comprises:

13. The photovoltaic power plant power control method of claim 12 wherein the active/reactive current maximum and minimum values are calculated as follows:

14. The photovoltaic power plant power control method of claim 3 wherein the photovoltaic inverter grid interface module adjusts the active/reactive output of the controllable ac current source connecting the photovoltaic power generation units to the grid based on the active/reactive current reference, comprising:

15. A photovoltaic power plant power control system, comprising:

16. The photovoltaic power plant power control system of claim 15, wherein the photovoltaic power plant power control module comprises a site level active control unit, a site level reactive control unit, a photovoltaic inverter control unit, and a photovoltaic inverter grid interface unit: