A method for active power coordinated dispatch of photovoltaic access thermal power plant

Abstract

The application provides an active power coordinated scheduling method of photovoltaic access to a thermal power plant, and belongs to the technical field of power system control. The method comprises the following steps: connecting a photovoltaic component to a plant bus or a low-voltage side of a standby transformer; installing a mutual inductor and an active power transmitter at a photovoltaic switch of a photovoltaic access point, collecting photovoltaic actual generated power when the switch is closed and transmitting the photovoltaic actual generated power to a host DCS, and stopping transmission when the switch is opened; receiving an AGC scheduling instruction by the DCS, obtaining total power by summing up the photovoltaic actual generated power corresponding to the closed switch, and subtracting the total power from the scheduling instruction as a generator set regulation target, so that the generator set tracks the target power generation; calculating the sum of the actual generated power of the generator set and the total photovoltaic actual generated power by the DCS computer, and uploading the sum to a power dispatching center as real-time total generated power of the power plant; and adopting manual switching, and switching in after the generator set is connected to the grid and switching out before the generator set is disconnected. The application reuses existing equipment of the thermal power plant, does not need to add special facilities, simultaneously offsets the influence of photovoltaic power fluctuation, and guarantees controllability and stability of power grid dispatching.

Description

Technical Field

[0001] This invention belongs to the field of power system control technology, specifically relating to a method for coordinated active power dispatching of photovoltaic power plants connected to thermal power plants. Background Technology

[0002] High-power photovoltaic power plants require a complete set of equipment, including dedicated grid-connected transmission lines, main transformers, energy storage devices, reactive power compensation devices, grounding transformers, and AGC and AVC control devices, in order to achieve grid-connected power generation.

[0003] For photovoltaic (PV) power plants located near thermal power plants, the existing transmission and distribution systems and AGC / AVC control devices of the thermal power units can be reused to achieve safe grid connection without the need for additional specialized equipment. This reduces investment costs, shortens the grid connection period, and lowers the operation and maintenance load. The connection methods mainly include connecting to the plant's auxiliary bus and connecting to the low-voltage side of the standby transformer. Regarding voltage regulation, the existing AGC / AVR devices of the thermal power plant can meet the voltage requirements after PV integration, eliminating the need for additional reactive power compensation and automatic reactive power control devices. However, the above connection methods present a significant active power dispatching problem: after the PV power supply to the bus or the low-voltage side of the standby transformer, the active power uploaded by the generator to the grid dispatch is taken from the generator's 20kV outlet (the generator side of the high-voltage transformer), and this value does not include the PV power generation. If the grid continues to regulate the generator's active power output in the original manner, the active power fed into the main transformer will increase compared to when PV was not connected (the increase is approximately equal to the actual PV power generation); moreover, PV power generation is characterized by large power fluctuations and strong intermittency, which can cause abnormal fluctuations in the active power fed into the main transformer. When the photovoltaic grid connection capacity is high and the number of thermal power plants using this connection mode increases, it will affect the controllability of the grid's active power dispatch and is not conducive to the stable operation of the grid. Summary of the Invention

[0004] The purpose of this invention is to solve the problem in the prior art that the dispatch power of photovoltaic access to thermal power plants does not include photovoltaic power, which leads to overshoot and abnormal fluctuations in the grid-connected power of the main transformer, affecting the controllability and stability of the active power dispatch of the power grid. The embodiments of this invention provide a method for coordinated dispatch of active power of photovoltaic access to thermal power plants.

[0005] The method includes the following steps: S1. Connect the photovoltaic modules to the existing electrical system of the thermal power plant, wherein the electrical system is the plant busbar or the low-voltage side of the standby transformer; S2. Install voltage transformers and current transformers at the photovoltaic switch at the photovoltaic access point. The secondary electrical quantities of the voltage transformers and current transformers are connected to the active power transmitter. When the photovoltaic switch is closed, the active power transmitter collects the actual photovoltaic power and transmits it to the distributed control system (DCS) of the thermal power plant in real time. When the photovoltaic switch is opened, the transmission stops. S3. The main distributed control system (DCS) receives the automatic generation control (AGC) scheduling command and obtains the active power automatic regulation target value of the generator set based on the actual photovoltaic power generation. The generator set automatically generates electricity by tracking the regulation target value.

[0006] S4. The main distributed control system (DCS) calculates the sum of the actual active power generated by the generator set and the total actual photovoltaic power generated, and the sum is uploaded to the power dispatch center as the real-time total power generation of the power plant. S5. The grid connection and deactivation are controlled manually. After the generator set completes the grid connection operation and enters a stable operating state, the operation and maintenance personnel manually activate the grid connection. Before the generator set is about to be disconnected from the grid, the operation and maintenance personnel manually deactivate the grid connection.

[0007] Furthermore, in step S1, the photovoltaic module is connected to the photovoltaic access point through a photovoltaic transformer box. The photovoltaic access point is set at a preset position on the low-voltage side of the plant bus or the standby transformer. The photovoltaic access directly reuses the existing power transmission and distribution facilities of the thermal power plant.

[0008] Further, in step S1, the plant busbar is a 6kV high-voltage plant busbar of a thermal power plant, and the 6kV high-voltage plant busbar includes at least one section of dedicated photovoltaic access busbar, which is a pre-planned section of the plant busbar for accessing photovoltaic modules in the thermal power plant. The photovoltaic modules are connected to the 6kV high-voltage plant bus after being stepped down by the photovoltaic transformer. The connection point is set at a preset branch of the 6kV high-voltage plant bus, and the connection location avoids the direct power supply branch of the critical load of the thermal power plant. The low-voltage side of the standby transformer is the low-voltage output terminal of the standby transformer of the thermal power plant. Its voltage level is the same as that of the plant service bus, which is 6kV. When the photovoltaic modules are connected to the low-voltage side of the standby transformer, they are connected to the low-voltage side bus of the standby transformer through a dedicated branch switch and connected to the power transmission and distribution system of the thermal power plant.

[0009] Furthermore, in step S2, the accuracy class of both the voltage transformer and the current transformer is 0.2, and the output electrical quantities of both the voltage transformer and the current transformer are connected to the active power transmitter, the accuracy class of which is 0.2.

[0010] Furthermore, in step S2, the photovoltaic switch corresponds one-to-one with the photovoltaic transformer box, and each photovoltaic switch is used to control the connection and disconnection between the corresponding photovoltaic transformer box and the existing electrical system of the thermal power plant. When any photovoltaic switch is in the closed state, the corresponding active power transmitter collects the actual photovoltaic power generated by the photovoltaic transformer connected to the photovoltaic switch in real time, and transmits the collected actual photovoltaic power to the distributed control system (DCS) of the thermal power plant in real time. When any photovoltaic switch is in the open state, the corresponding active power transmitter stops collecting the actual photovoltaic power generated by the photovoltaic transformer connected to that photovoltaic switch, and does not transmit power data to the host distributed control system (DCS).

[0011] Further, in step S2, the photovoltaic switch is a high-voltage circuit breaker, and the model of the high-voltage circuit breaker is adapted to the electrical system with a voltage level of 6kV. The number of photovoltaic switches is at least two, each corresponding to a different photovoltaic transformer group. The first photovoltaic transformer group corresponds to the first photovoltaic switch, and the second photovoltaic transformer group corresponds to the second photovoltaic switch. When there are multiple photovoltaic transformer groups, the corresponding number of photovoltaic switches are added. The control status of all photovoltaic switches is fed back to the host distributed control system DCS in real time. The host distributed control system DCS determines whether to collect the power data of the corresponding photovoltaic transformer based on the closing / opening status of the photovoltaic switch. The voltage transformer and current transformer adopt a through-hole or fixed installation structure and are installed on the output side of the photovoltaic switch to ensure accurate acquisition of the voltage and current signals output by the photovoltaic transformer box. When the electrical quantities are connected to the active power transmitter, they are connected through shielded cables. The active power transmitter converts the collected voltage and current signals into standard analog or digital signals and transmits them to the host distributed control system (DCS). The delay of the actual photovoltaic power generation data does not exceed 100ms.

[0012] Furthermore, the specific steps of step S3 are as follows: S31. The main distributed control system (DCS) sums up the real-time power data uploaded by the active power transmitters corresponding to all photovoltaic switches in the closed state to obtain the total photovoltaic power generated. If a photovoltaic switch is in the open state, the corresponding power data is counted as 0 in the summation calculation. The formula for calculating the total actual power generated by photovoltaic power is:

[0013] in, for t The total actual photovoltaic power generated at any given time, where n is the total number of photovoltaic switches. for t Time of the first i The state variables of a photovoltaic switch =1 indicates the first i When a photovoltaic switch is in the closed state, the corresponding power data is used in the total power calculation. =0 indicates the first i The photovoltaic switch is in the open state. for t Time of the first i Real-time power of the photovoltaic transformer connected to each photovoltaic switch; S32. The Automatic Generation Control (AGC) dispatch instruction is an active power adjustment instruction issued by the power dispatch center to the thermal power plant. The active power adjustment instruction is updated in real time, and the main distributed control system (DCS) receives the instruction through a dedicated dispatch data network. S33. The calculation process of the active power automatic regulation target value of the generator set is automatically completed by the automatic generation control AGC module of the host distributed control system DCS, and the calculation frequency is the same as the update frequency of the automatic generation control AGC scheduling command. The formula for calculating the target value of active power automatic regulation is:

[0014] in for t The target value for automatic active power control of the generator set at all times. for t AGC dispatch instructions issued by the power dispatch center at all times; S34. After receiving the control target value, the generator set control system automatically adjusts the active power by adjusting the steam inlet of the steam turbine and the combustion intensity parameters of the boiler. During the adjustment process, the operating constraints of the generator set are strictly followed, including minimum stable output, maximum output limit, and ramp rate limit. The active power regulation constraint equation for the generator set is:

[0015] in, This is the minimum stable output of the generator set. for t The actual active power generated by the generator set at any given time. This is the maximum output limit of the generator set. This represents the maximum permissible climbing rate of the generator set.

[0016] Furthermore, the specific steps of step S4 are as follows: S41. The main distributed control system (DCS) collects the actual active power generated by the generator set in real time and continuously updates the total actual photovoltaic power. S42. The main distributed control system (DCS) sums the actual active power generated by the generator set with the updated total photovoltaic power to obtain the real-time total power generation of the power plant. The formula for calculating the real-time total power generation of a power plant is:

[0017] in, for t The power plant's real-time total generating capacity at any given moment. for tThe actual active power generated by the generator set at any given time. for t The actual total power generated by photovoltaic power at any given time; S43. The main distributed control system (DCS) uploads the real-time total power generation of the power plant as feedback data to the power dispatch center, which can obtain the overall power generation of the power plant, including photovoltaic power, in real time.

[0018] Furthermore, in the process of photovoltaic power being connected to a thermal power plant, there is no need to add any dedicated grid-connected transmission lines, main transformers, energy storage devices, or reactive power compensation devices for the photovoltaic modules, and the existing power transmission and distribution system and control facilities of the thermal power plant are reused.

[0019] Furthermore, in the method, after the photovoltaic system is connected to the thermal power plant, voltage regulation is achieved through the thermal power plant's existing automatic voltage control (AVC) device and automatic voltage regulator (AVR) device. The AVC device automatically adjusts the excitation current of the generator set by collecting the bus voltage signal of the power plant's substation, thereby adjusting the reactive power output of the generator. The AVR device, as the core control unit of the generator set excitation system, works in conjunction with the AVC device to respond to voltage changes and compensate for reactive power impacts caused by photovoltaic grid connection.

[0020] As can be seen from the above technical solutions, the present invention has the following advantages: The active power coordinated dispatching method for photovoltaic (PV) power plants in this invention utilizes PV modules connected to the existing plant service bus or the low-voltage side of the standby transformer in the power plant, reusing the original power transmission and distribution system. This eliminates the need for additional dedicated grid-connected transmission lines, main transformers, energy storage devices, and other equipment, reducing PV grid-connection investment costs. By installing instrument transformers and power transmitters at the PV switches, the actual PV power generation is collected in real time and uploaded to the DCS. Combined with the feedback logic of subtracting the total actual PV power generation from the AGC dispatch command and adding the PV power to the generator power, this method overcomes the metering deficiency of existing connection methods where dispatched power does not include PV power. It also solves the problems of overshooting of the main transformer's grid-connected power and abnormal fluctuations caused by PV fluctuations, ensuring that the power plant's total output matches the dispatch command. The method employs a control approach of manual activation after grid connection and manual deactivation before disconnection, adapting to the operating scenarios of thermal power units, avoiding dispatch logic conflicts, and ensuring system stability. Furthermore, it eliminates the need for additional complex control equipment, achieving this through optimization of the existing DCS system logic, reducing maintenance difficulty, and facilitating the controllable dispatching of high-proportion PV-connected thermal power plants by the power grid, ensuring the safe and stable operation of the power grid. Attached Figure Description

[0021] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the description will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a flowchart illustrating the active power coordinated scheduling method for photovoltaic power plants according to the present invention.

[0023] Figure 2 This is a schematic diagram illustrating the logic of the generator tracking automatic power generation control (AGC) power dispatch command and the difference between the actual photovoltaic power generated by the present invention.

[0024] Figure 3 This is a logical diagram illustrating that the power generation for feedback scheduling in this invention is the sum of the actual power generated by the generator and the actual power generated by the photovoltaic system.

[0025] Figure 4 This is a schematic diagram of the main electrical wiring of a thermal power plant according to the present invention.

[0026] Figure 5 This is a schematic diagram of the main photovoltaic electrical wiring of the present invention. Detailed Implementation

[0027] The various embodiments of the present invention will be described more fully in the detailed steps of the active power coordinated dispatch method for photovoltaic power plants connected to thermal power plants, which will be described in detail below. The present invention may have various embodiments, and adjustments and changes may be made therein. However, it should be understood that there is no intention to limit the various embodiments of the present invention to the specific embodiments disclosed herein, but rather the present invention should be understood to cover all adjustments, equivalents, and / or alternatives falling within the spirit and scope of the various embodiments of the present invention.

[0028] It should be understood that, when used in this specification, the term "comprising" indicates the presence of the described features, integrals, steps, operations, elements, and / or components, but does not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components, and / or collections thereof. The terms "comprising," "including," "having," and variations thereof all mean "including but not limited to," unless otherwise specifically emphasized.

[0029] The terms "one embodiment" or "some embodiments" used in this invention mean that one or more embodiments of the invention include the specific features, structures, or characteristics described in that embodiment. Therefore, the terms "in one embodiment," "in some embodiments," "in other embodiments," "in still other embodiments," etc., appearing in different parts of the invention do not necessarily refer to the same embodiment, but rather mean "one or more, but not all, embodiments," unless otherwise specifically emphasized.

[0030] To facilitate a clear description of the technical solution of this invention, the terms "first" and "second" are used to distinguish identical or similar items with essentially the same function and effect. Those skilled in the art will understand that the terms "first" and "second" do not limit the quantity or execution order, and that "first" and "second" are not necessarily different.

[0031] To make the objectives, features, and advantages of this invention more apparent and understandable, specific embodiments and accompanying drawings will be used to clearly and completely describe the technical solutions protected by this invention. Obviously, the embodiments described below are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0032] Please see Figure 4 The diagram shown is a schematic of the main electrical wiring of an existing thermal power plant. Figure 5 The diagram shown is a schematic of the existing photovoltaic electrical main wiring.

[0033] The two 600MW generating units are designed as a unit system and are equipped with a 220kV step-up substation. The generator outlet is connected to two high-voltage transformers and three high-voltage busbars (6kVA, B, and C) are provided for plant use. The two generating units share two start-up and standby transformers, which are connected to the 220kV busbar of the step-up substation. The plant has installed 25.5MWp of photovoltaic modules. After directly connecting the photovoltaic system to two 6kV C busbars, it achieved grid-connected power generation. However, to meet the requirement of independent grid connection for photovoltaic power generation, an independent 35kV main transformer and transmission lines would need to be installed to connect to a substation 21km away from the power plant. Simultaneously, energy storage devices, reactive power compensation devices, and intelligent control systems would need to be installed to meet grid dispatch requirements. Adding land costs and labor costs, the grid connection would be delayed by at least three months. Therefore, directly connecting the photovoltaic system to the 6kV C busbars for grid connection has significant advantages. However, this also brings new power dispatching issues. After the photovoltaic system supplies power to the 6kV busbars, the active power transmitted to the grid by the generator is taken from the generator's 20kV output (the generator side of the high-voltage substation), therefore this power does not include the photovoltaic power generation. Assuming that the dispatching method continues to regulate the active power of generating units as before, although it does not affect the normal power generation of photovoltaic (PV) power, the active power of the main transformer connected to the grid will increase significantly compared to the situation where PV power is not connected, with the same dispatched generator power. The increase is equal to the real-time power generation of PV power (since the PV power is relatively low, its active power losses in the main transformer and power plant transformer are ignored). PV power generation also has the disadvantage of large fluctuations. When the real-time PV power is low, the above problems are not obvious. However, when the actual PV power generation is high, and there are many thermal power plants with such PV connections, the above factors will have a long-term adverse impact on the controllable dispatching of the grid's active power and power flow distribution.

[0034] To eliminate the aforementioned adverse effects, the active power of photovoltaic (PV) power can be included in the generator AGC (Automatic Generation Control) system, treating PV power as part of the thermal power output. This means the generator automatically generates power based on the difference between the AGC's dispatched power command and the actual PV power output. The power output fed back to the dispatch system is the sum of the actual generator output and the actual PV power output, achieving consistency with the AGC's dispatched power command. In other words, while ensuring normal PV power generation, there is no need to install additional PV energy storage or intelligent control devices. This simple innovation of automatic control of thermal power generators eliminates the drawbacks of large fluctuations and intermittent power generation in PV power, achieving balanced power generation from the power plant and meeting dispatch requirements.

[0035] Please see Figure 1 The diagram shows a flowchart of a method for coordinated active power dispatching of photovoltaic power plants connected to thermal power plants. The method includes the following steps: S1. Connect the photovoltaic modules to the existing electrical system of the thermal power plant, wherein the electrical system is the plant busbar or the low-voltage side of the standby transformer; S2. Install voltage transformers and current transformers at the photovoltaic switch at the photovoltaic access point. The secondary electrical quantities of the voltage transformers and current transformers are connected to the active power transmitter. When the photovoltaic switch is closed, the active power transmitter collects the actual photovoltaic power and transmits it to the distributed control system (DCS) of the thermal power plant in real time. When the photovoltaic switch is opened, the transmission stops. like Figure 2As shown, S3. The main distributed control system (DCS) receives the automatic generation control (AGC) scheduling command and obtains the active power automatic regulation target value of the generator set based on the actual photovoltaic power generation. The generator set automatically generates electricity by tracking the regulation target value.

[0036] like Figure 3 As shown, S4. The main distributed control system (DCS) calculates the sum of the actual active power generated by the generator set and the total actual photovoltaic power generated. The sum is uploaded to the power dispatch center as the real-time total power generation of the power plant. S5. The grid connection and deactivation are controlled manually. After the generator set completes the grid connection operation and enters a stable operating state, the operation and maintenance personnel manually activate the grid connection. Before the generator set is about to be disconnected from the grid, the operation and maintenance personnel manually deactivate the grid connection.

[0037] It should be noted that while ensuring normal photovoltaic power generation, there is no need to install photovoltaic energy storage, intelligent control or other devices. The simple innovation of automatic control of thermal power generating units has eliminated the shortcomings of large fluctuations and strong intermittency of photovoltaic power, realizing balanced power generation of power plants and meeting dispatch requirements.

[0038] As a refinement and extension of the specific implementation of the above embodiments, in order to fully illustrate the specific implementation process of this embodiment, another method for testing aircraft wire insulation layer damage faults is provided, which includes the following steps: S1. Connect the photovoltaic modules to the existing electrical system of the thermal power plant, wherein the electrical system is the plant busbar or the low-voltage side of the standby transformer; In step S1, the photovoltaic module is connected to the photovoltaic access point through a photovoltaic transformer box. The photovoltaic access point is set at a preset position on the low-voltage side of the plant bus or the standby transformer. The photovoltaic access directly reuses the existing power transmission and distribution facilities of the thermal power plant.

[0039] In step S1, the plant busbar is a 6kV high-voltage plant busbar of a thermal power plant. The 6kV high-voltage plant busbar includes at least one section of dedicated photovoltaic access busbar. The dedicated photovoltaic access busbar is a pre-planned section of the plant busbar for accessing photovoltaic modules in the thermal power plant. The photovoltaic modules are connected to the 6kV high-voltage plant bus after being stepped down by the photovoltaic transformer. The connection point is set at a preset branch of the 6kV high-voltage plant bus, and the connection location avoids the direct power supply branch of the critical load of the thermal power plant. The low-voltage side of the standby transformer is the low-voltage output terminal of the standby transformer of the thermal power plant. Its voltage level is the same as that of the plant service bus, which is 6kV. When the photovoltaic modules are connected to the low-voltage side of the standby transformer, they are connected to the low-voltage side bus of the standby transformer through a dedicated branch switch and connected to the power transmission and distribution system of the thermal power plant.

[0040] S2. Install voltage transformers and current transformers at the photovoltaic switch at the photovoltaic access point. The secondary electrical quantities of the voltage transformers and current transformers are connected to the active power transmitter. When the photovoltaic switch is closed, the active power transmitter collects the actual photovoltaic power and transmits it to the distributed control system (DCS) of the thermal power plant in real time. When the photovoltaic switch is opened, the transmission stops. In step S2, the accuracy class of both the voltage transformer and the current transformer is 0.2, and the output electrical quantities of both the voltage transformer and the current transformer are connected to the active power transmitter, which has an accuracy class of 0.2.

[0041] In step S2, the photovoltaic switch corresponds one-to-one with the photovoltaic transformer box, and each photovoltaic switch is used to control the connection and disconnection between the corresponding photovoltaic transformer box and the existing electrical system of the thermal power plant. When any photovoltaic switch is in the closed state, the corresponding active power transmitter collects the actual photovoltaic power generated by the photovoltaic transformer connected to the photovoltaic switch in real time, and transmits the collected actual photovoltaic power to the distributed control system (DCS) of the thermal power plant in real time. When any photovoltaic switch is in the open state, the corresponding active power transmitter stops collecting the actual photovoltaic power generated by the photovoltaic transformer connected to that photovoltaic switch, and does not transmit power data to the host distributed control system (DCS).

[0042] In step S2, the photovoltaic switch is a high-voltage circuit breaker, and the model of the high-voltage circuit breaker is adapted to the electrical system with a voltage level of 6kV. The number of photovoltaic switches is at least two, each corresponding to a different photovoltaic transformer group. The first photovoltaic transformer group corresponds to the first photovoltaic switch, and the second photovoltaic transformer group corresponds to the second photovoltaic switch. When there are multiple photovoltaic transformer groups, the corresponding number of photovoltaic switches are added. The control status of all photovoltaic switches is fed back to the host distributed control system DCS in real time. The host distributed control system DCS determines whether to collect the power data of the corresponding photovoltaic transformer based on the closing / opening status of the photovoltaic switch. The voltage transformer and current transformer adopt a through-hole or fixed installation structure and are installed on the output side of the photovoltaic switch to ensure accurate acquisition of the voltage and current signals output by the photovoltaic transformer box. When the electrical quantities are connected to the active power transmitter, they are connected through shielded cables. The active power transmitter converts the collected voltage and current signals into standard analog or digital signals and transmits them to the host distributed control system (DCS). The delay of the actual photovoltaic power generation data does not exceed 100ms.

[0043] S3. The main distributed control system (DCS) receives the automatic generation control (AGC) scheduling command and obtains the active power automatic regulation target value of the generator set based on the actual photovoltaic power generation. The generator set automatically generates electricity by tracking the regulation target value.

[0044] The specific steps of step S3 are as follows: S31. The main distributed control system (DCS) sums up the real-time power data uploaded by the active power transmitters corresponding to all photovoltaic switches in the closed state to obtain the total photovoltaic power generated. If a photovoltaic switch is in the open state, the corresponding power data is counted as 0 in the summation calculation. The formula for calculating the total actual power generated by photovoltaic power is:

[0045] in, for t The total actual photovoltaic power generated at any given time, where n is the total number of photovoltaic switches. for t Time of the first i The state variables of a photovoltaic switch =1 indicates the first i When a photovoltaic switch is in the closed state, the corresponding power data is used in the total power calculation. =0 indicates the first i The photovoltaic switch is in the open state. for t Time of the first i Real-time power of the photovoltaic transformer connected to each photovoltaic switch; S32. The Automatic Generation Control (AGC) dispatch instruction is an active power adjustment instruction issued by the power dispatch center to the thermal power plant. The active power adjustment instruction is updated in real time, and the main distributed control system (DCS) receives the instruction through a dedicated dispatch data network. S33. The calculation process of the active power automatic regulation target value of the generator set is automatically completed by the automatic generation control AGC module of the host distributed control system DCS, and the calculation frequency is the same as the update frequency of the automatic generation control AGC scheduling command. The formula for calculating the target value of active power automatic regulation is:

[0046] in for t The target value for automatic active power control of the generator set at all times. for t AGC dispatch instructions issued by the power dispatch center at all times; S34. After receiving the control target value, the generator set control system automatically adjusts the active power by adjusting the steam inlet of the steam turbine and the combustion intensity parameters of the boiler. During the adjustment process, the operating constraints of the generator set are strictly followed, including minimum stable output, maximum output limit, and ramp rate limit. The active power regulation constraint equation for the generator set is:

[0047] in, This is the minimum stable output of the generator set. for t The actual active power generated by the generator set at any given time. This is the maximum output limit of the generator set. This represents the maximum permissible climbing rate of the generator set.

[0048] S4. The main distributed control system (DCS) calculates the sum of the actual active power generated by the generator set and the total actual photovoltaic power generated, and the sum is uploaded to the power dispatch center as the real-time total power generation of the power plant. The specific steps of step S4 are as follows: S41. The main distributed control system (DCS) collects the actual active power generated by the generator set in real time and continuously updates the total actual photovoltaic power. S42. The main distributed control system (DCS) sums the actual active power generated by the generator set with the updated total photovoltaic power to obtain the real-time total power generation of the power plant. The formula for calculating the real-time total power generation of a power plant is:

[0049] in, for t The power plant's real-time total generating capacity at any given moment. for t The actual active power generated by the generator set at any given time. for t The actual total power generated by photovoltaic power at any given time; S43. The main distributed control system (DCS) uploads the real-time total power generation of the power plant as feedback data to the power dispatch center, which can obtain the overall power generation of the power plant, including photovoltaic power, in real time.

[0050] S5. The grid connection and deactivation are controlled manually. After the generator set completes the grid connection operation and enters a stable operating state, the operation and maintenance personnel manually activate the grid connection. Before the generator set is about to be disconnected from the grid, the operation and maintenance personnel manually deactivate the grid connection.

[0051] In the aforementioned method, during the process of photovoltaic power plant integration, there is no need to add any dedicated grid-connected transmission lines, main transformers, energy storage devices, or reactive power compensation devices for the photovoltaic modules, thus reusing the existing power transmission and distribution system and control facilities of the power plant.

[0052] In the method described above, after the photovoltaic system is connected to the thermal power plant, voltage regulation is achieved through the existing automatic voltage control (AVC) device and automatic voltage regulator (AVR) device of the thermal power plant. The AVC device automatically adjusts the excitation current of the generator set by collecting the bus voltage signal of the power plant's substation, thereby adjusting the reactive power output of the generator. The AVR device, as the core control unit of the generator set excitation system, works in conjunction with the AVC device to respond to voltage changes and compensate for reactive power impacts caused by photovoltaic grid connection.

[0053] It should be noted that during the entire process of connecting photovoltaic (PV) power to a thermal power plant, there is no need to add any dedicated grid-connected transmission lines, main transformers, energy storage devices, or reactive power compensation devices for the PV modules. The existing power transmission and distribution system and control facilities of the thermal power plant are fully reused, thereby significantly reducing the investment cost and construction period of PV grid connection. Among them, dedicated grid-connected transmission lines refer to transmission lines built specifically for PV module grid connection, such as overhead lines or cable lines of 35kV and above; main transformers refer to power transformers specifically configured for PV module voltage boosting and grid connection; energy storage devices refer to battery energy storage systems, flywheel energy storage systems, etc., used to smooth PV power fluctuations; reactive power compensation devices refer to static var generators (SVG), static var compensators (SVC), etc., used to regulate PV grid-connected voltage.

[0054] The total installed capacity of the photovoltaic modules is not less than 25.5 MWp. The photovoltaic modules are connected to the existing electrical system of the thermal power plant through at least two sets of photovoltaic transformer substations. The capacity of each set of photovoltaic transformer substations is reasonably configured according to the installed capacity of the photovoltaic modules to ensure stable output of photovoltaic power. The method is applicable to thermal power plants with unit-based design. The thermal power plant is equipped with core equipment such as a 220kV step-up substation, generators, high-voltage substation transformers, and standby transformers. The rated power of the generators is not less than 600MW. The high-voltage substation transformer is used to step down the generator output voltage (20kV) to the plant service bus voltage (6kV). The standby transformer is connected to the 220kV step-up substation bus to supply power to the plant service when the generator units are out of service. After the photovoltaic and thermal power units are coordinated and dispatched through this method, the active power of the thermal power plant's main transformer to the grid can strictly follow the provincial dispatch AGC dispatch instructions, avoiding active power overshoot and fluctuation problems caused by photovoltaic access, ensuring the controllability and stability of the grid's active power dispatch, and at the same time fully leveraging the environmental benefits of photovoltaic power generation and the utilization efficiency of the existing facilities of the thermal power plant.

[0055] The power fluctuation period of the photovoltaic module is greater than 1 second. This fluctuation period refers to the time it takes for the actual photovoltaic power to change from one stable value to another. Since photovoltaic power fluctuations are affected by natural factors such as cloud movement and changes in sunlight intensity, their fluctuation period is usually between several seconds and tens of seconds, which is much greater than the adjustment response time of the generator unit's steam turbine load (less than 1 second). Therefore, the generator unit can track photovoltaic power fluctuations in a timely manner and offset the impact of fluctuations by adjusting its own output, thus avoiding large fluctuations in the total power generation of the power plant. At the same time, the main DCS system collects the actual photovoltaic power at a frequency of at least 10 times per second to ensure that it can accurately capture the trend of photovoltaic power changes.

[0056] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0057] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for coordinated active power dispatching of photovoltaic power integrated into a thermal power plant, characterized in that, The method includes the following steps: S1. Connect the photovoltaic modules to the existing electrical system of the thermal power plant, wherein the electrical system is the plant busbar or the low-voltage side of the standby transformer; S2. Install voltage transformers and current transformers at the photovoltaic switch at the photovoltaic access point. The secondary electrical quantities of the voltage transformers and current transformers are connected to the active power transmitter. When the photovoltaic switch is closed, the active power transmitter collects the actual photovoltaic power and transmits it to the distributed control system (DCS) of the thermal power plant in real time. When the photovoltaic switch is opened, the transmission stops. S3. The main distributed control system (DCS) receives the automatic generation control (AGC) scheduling command and obtains the active power automatic regulation target value of the generator set based on the actual photovoltaic power generation. The generator set automatically generates electricity by tracking the regulation target value.

2. The active power coordinated dispatch method for photovoltaic power plants according to claim 1, characterized in that, In step S1, the photovoltaic module is connected to the photovoltaic access point through a photovoltaic transformer box. The photovoltaic access point is set at a preset position on the low-voltage side of the plant bus or the standby transformer. The photovoltaic access directly reuses the existing power transmission and distribution facilities of the thermal power plant.

3. The active power coordinated dispatch method for photovoltaic power plants according to claim 1, characterized in that, In step S1, the plant busbar is a 6kV high-voltage plant busbar of a thermal power plant. The 6kV high-voltage plant busbar includes at least one section of dedicated photovoltaic access busbar. The dedicated photovoltaic access busbar is a pre-planned section of the plant busbar for accessing photovoltaic modules in the thermal power plant. The photovoltaic modules are connected to the 6kV high-voltage plant bus after being stepped down by the photovoltaic transformer. The connection point is set at a preset branch of the 6kV high-voltage plant bus, and the connection location avoids the direct power supply branch of the critical load of the thermal power plant. The low-voltage side of the standby transformer is the low-voltage output terminal of the standby transformer of the thermal power plant. Its voltage level is the same as that of the plant service bus, which is 6kV. When the photovoltaic modules are connected to the low-voltage side of the standby transformer, they are connected to the low-voltage side bus of the standby transformer through a dedicated branch switch and connected to the power transmission and distribution system of the thermal power plant.

4. The active power coordinated dispatch method for photovoltaic power integrated into a thermal power plant according to claim 1, characterized in that, In step S2, the accuracy class of both the voltage transformer and the current transformer is 0.2, and the output electrical quantities of both the voltage transformer and the current transformer are connected to the active power transmitter, which has an accuracy class of 0.

2.

5. The active power coordinated dispatch method for photovoltaic power plants according to claim 1, characterized in that, In step S2, the photovoltaic switch corresponds one-to-one with the photovoltaic transformer box, and each photovoltaic switch is used to control the connection and disconnection between the corresponding photovoltaic transformer box and the existing electrical system of the thermal power plant. When any photovoltaic switch is in the closed state, the corresponding active power transmitter collects the actual photovoltaic power generated by the photovoltaic transformer connected to the photovoltaic switch in real time, and transmits the collected actual photovoltaic power to the distributed control system (DCS) of the thermal power plant in real time. When any photovoltaic switch is in the open state, the corresponding active power transmitter stops collecting the actual photovoltaic power generated by the photovoltaic transformer connected to that photovoltaic switch, and does not transmit power data to the host distributed control system (DCS).

6. The active power coordinated dispatch method for photovoltaic power plants according to claim 1, characterized in that, In step S2, the photovoltaic switch is a high-voltage circuit breaker, and the model of the high-voltage circuit breaker is adapted to the electrical system with a voltage level of 6kV. The number of photovoltaic switches is at least two, each corresponding to a different photovoltaic transformer group. The first photovoltaic transformer group corresponds to the first photovoltaic switch, and the second photovoltaic transformer group corresponds to the second photovoltaic switch. When there are multiple photovoltaic transformer groups, the corresponding number of photovoltaic switches are added. The control status of all photovoltaic switches is fed back to the host distributed control system DCS in real time. The host distributed control system DCS determines whether to collect the power data of the corresponding photovoltaic transformer based on the closing / opening status of the photovoltaic switch. The voltage transformer and current transformer adopt a through-hole or fixed installation structure and are installed on the output side of the photovoltaic switch to ensure accurate acquisition of the voltage and current signals output by the photovoltaic transformer box. When the electrical quantities are connected to the active power transmitter, they are connected through shielded cables. The active power transmitter converts the collected voltage and current signals into standard analog or digital signals and transmits them to the host distributed control system (DCS). The delay of the actual photovoltaic power generation data does not exceed 100ms.

7. The active power coordinated dispatch method for photovoltaic power plants according to claim 1, characterized in that, The specific steps of step S3 are as follows: S31. The main distributed control system (DCS) sums up the real-time power data uploaded by the active power transmitters corresponding to all photovoltaic switches in the closed state to obtain the total photovoltaic power generated. If a photovoltaic switch is in the open state, the corresponding power data is counted as 0 in the summation calculation. The formula for calculating the total actual power generated by photovoltaic power is: in, for t The total actual photovoltaic power generated at any given time, where n is the total number of photovoltaic switches. for t Time of the first i The state variables of a photovoltaic switch =1 indicates the first i When a photovoltaic switch is in the closed state, the corresponding power data is used in the total power calculation. =0 indicates the first i The photovoltaic switch is in the open state. for t Time of the first i Real-time power of the photovoltaic transformer connected to each photovoltaic switch; S32. The Automatic Generation Control (AGC) dispatch instruction is an active power adjustment instruction issued by the power dispatch center to the thermal power plant. The active power adjustment instruction is updated in real time, and the main distributed control system (DCS) receives the instruction through a dedicated dispatch data network. S33. The calculation process of the active power automatic regulation target value of the generator set is automatically completed by the automatic generation control AGC module of the host distributed control system DCS, and the calculation frequency is the same as the update frequency of the automatic generation control AGC scheduling command. The formula for calculating the target value of active power automatic regulation is: in for t The target value for automatic active power control of the generator set at all times. for t AGC dispatch instructions issued by the power dispatch center at all times; S34. After receiving the control target value, the generator set control system automatically adjusts the active power by adjusting the steam inlet of the steam turbine and the combustion intensity parameters of the boiler. During the adjustment process, the operating constraints of the generator set are strictly followed, including minimum stable output, maximum output limit, and ramp rate limit. The active power regulation constraint equation for the generator set is: in, This is the minimum stable output of the generator set. for t The actual active power generated by the generator set at any given time. This is the maximum output limit of the generator set. This represents the maximum permissible climbing rate of the generator set.

8. The active power coordinated dispatch method for photovoltaic power plants according to claim 1, characterized in that, The method further includes the following steps: S4. The main distributed control system (DCS) calculates the sum of the actual active power generated by the generator set and the total actual photovoltaic power generated, and the sum is uploaded to the power dispatch center as the real-time total power generation of the power plant. S5. The grid connection and deactivation are controlled manually. After the generator set completes the grid connection operation and enters a stable operating state, the operation and maintenance personnel manually activate the grid connection. Before the generator set is about to be disconnected from the grid, the operation and maintenance personnel manually deactivate the grid connection.

9. The active power coordinated dispatch method for photovoltaic power plants according to claim 8, characterized in that, The specific steps of step S4 are as follows: S41. The main distributed control system (DCS) collects the actual active power generated by the generator set in real time and continuously updates the total actual photovoltaic power. S42. The main distributed control system (DCS) sums the actual active power generated by the generator set with the updated total photovoltaic power to obtain the real-time total power generation of the power plant. The formula for calculating the real-time total power generation of a power plant is: in, for t The power plant's real-time total generating capacity at any given moment. for t The actual active power generated by the generator set at any given time. for t The actual total power generated by photovoltaic power at any given time; S43. The main distributed control system (DCS) uploads the real-time total power generation of the power plant as feedback data to the power dispatch center, and the power dispatch center obtains the overall power generation of the power plant, including photovoltaic power, in real time.

10. The active power coordinated dispatch method for photovoltaic power plants according to claim 1, characterized in that, In the aforementioned method, during the process of photovoltaic power plant integration, there is no need to add any dedicated grid-connected transmission lines, main transformers, energy storage devices and reactive power compensation devices for photovoltaic modules, and the existing power transmission and distribution system and control facilities of the power plant are reused. After photovoltaic power is connected to a thermal power plant, voltage regulation is achieved through the existing automatic voltage control (AVC) device and automatic voltage regulator (AVR) device in the thermal power plant. The AVC device automatically adjusts the excitation current of the generator set by collecting the bus voltage signal of the power plant's substation, thereby adjusting the reactive power output of the generator. The AVR device, as the core control unit of the generator set excitation system, works in conjunction with the AVC device to respond to voltage changes and compensate for reactive power impacts caused by photovoltaic grid connection.

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