A Two-Time-Scale Voltage Control Method for Active Distribution Networks

Abstract

This invention discloses a two-time-scale voltage control method for an active distribution network, comprising the following steps: Step S1, for the centralized level, over a long time scale, optimizing the reactive power output of the photovoltaic inverter with minimizing network active power loss as the objective function, and determining the reactive power output benchmark value of the photovoltaic inverter within the optimization interval; Step S2, for the local level, over a short time scale, relying on the local controller, using a hybrid logic dynamic method to model the photovoltaic inverter and its complex control logic, and controlling the distribution network voltage by combining the reactive power output benchmark value and the hybrid logic. The scheme considers the communication status between the master station and the local controller, and the control framework for cooperation between the centralized and local levels. Different local control logics are adopted for the inverter according to different communication conditions, which can overcome the problem of untimely voltage regulation caused by communication conditions.

Description

Technical Field

[0001] This invention relates to the field of power regulation technology, specifically to a two-time-scale voltage control method for an active distribution network. Background Technology

[0002] A high proportion of renewable energy grid integration will become a fundamental characteristic of future power systems. Active distribution networks are an effective solution for handling large-scale intermittent renewable energy grid integration. The integration of renewable energy into active distribution networks brings a large number of inverter devices requiring management. Simultaneously, the integration of advanced communication and control technologies into distribution networks deepens the coupling between information and physical systems, bringing complex impacts to the operation and control of distribution networks. Therefore, how to manage the inverter devices brought about by renewable energy grid integration based on communication conditions is an urgent problem to be solved.

[0003] Existing research manages the output of renewable energy inverters through centralized, distributed, and local hierarchical approaches. With centralized and distributed management methods, when a communication failure occurs between the master station and the local controller controlling the inverter's output, the output of the affected inverter cannot be adjusted, potentially leading to severe overvoltage in the system. Local management methods cannot achieve coordinated operation between inverters.

[0004] The information disclosed in the background section is only intended to enhance the understanding of the background of this application, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0005] The purpose of this invention is to solve the problem of untimely voltage regulation caused by the susceptibility of renewable energy inverters to communication conditions. It proposes a two-time-scale voltage control method for active distribution networks. The scheme considers the communication status between the master station and the local controller, and a control framework for cooperation between centralized and local levels. At the hourly time scale, a reference value for the reactive power output of the renewable energy inverter is generated. At the second-level time scale, when communication between the master station and the local controller is normal, the local controller controls the reactive power output of the inverter based on the reference value. When communication between the master station and the local controller is abnormal, the local controller adjusts the reactive power output of the inverter based on real-time voltage measurements and the inverter's reactive power output reference value before the communication interruption. This overcomes the problem of untimely voltage regulation caused by communication conditions.

[0006] In a first aspect, one technical solution provided in the embodiments of the present invention is a method for active distribution network voltage control with two time scales, comprising the following steps:

[0007] Step S1: For the centralized hierarchy, optimize the reactive power output of the photovoltaic inverter over a long time scale with the objective function of minimizing network active power loss, and determine the baseline value of reactive power output of the photovoltaic inverter within the optimization interval.

[0008] Step S2: For the local level, within a short time scale, relying on the local controller, a hybrid logic dynamic method is used to model the photovoltaic inverter and its complex control logic, and the distribution network voltage is controlled by combining the reactive power output reference value and the hybrid logic.

[0009] Preferably, step S1 includes the following steps:

[0010] S11. Obtain basic information about the active distribution network;

[0011] S12. Determine the objective function for the hourly-level optimization problem at the centralized level. The objective function is a single optimization objective that minimizes the distribution network loss, and its expression is as follows:

[0012]

[0013] Where i and j are the busbar numbers, ij is the branch from busbar i to busbar j, and P ij,t and Q ij,t Let r be the active and reactive power on branch ij. ij V is the resistance of branch ij. subs This refers to the voltage amplitude of the substation.

[0014] S13. Determine the constraints for the centralized hierarchical hourly-level voltage reactive power optimization problem;

[0015] S14. Solve the objective function to obtain the reactive power baseline value of the photovoltaic inverter within the optimized interval;

[0016] S15. The local controller uses the reactive power output reference value obtained by the master station optimization to control the photovoltaic inverter.

[0017] Preferably, the basic information of the active distribution network includes: a1. Network topology; a2. Feeder length, model, current limit, and capacity limit; a3. Bus number where the photovoltaic system is located, and the capacity of the photovoltaic system; a4. Bus number where the master station, local controller, and sensor are located; a5. Communication status between the master station, local controller, and sensor; a6. Predicted curves of photovoltaic output and load power on an hourly time scale.

[0018] Preferably, the constraints include: active power balance constraints of linear nodes in the AC distribution network, reactive power balance constraints of linear nodes in the AC distribution network, linear Ohm's law constraints of the AC distribution network, upper and lower limits of bus voltage constraints of the AC distribution network, feeder capacity constraints of the AC distribution network, upper and lower limits of feeder current constraints of the AC distribution network, and power constraints of the photovoltaic grid-connected inverter.

[0019] Preferably, step S2 includes the following steps:

[0020] When the communication between the master station and the local controller is normal, the local controller uses the photovoltaic inverter reactive power output reference value obtained by the master station to control the photovoltaic inverter.

[0021] When communication between the master station and the local controller is abnormal, the local controller uses the reactive power output benchmark value of the photovoltaic inverter obtained by the master station before the communication interruption as a benchmark, and adjusts the output of the photovoltaic inverter according to the local voltage measurement value of the bus node and the local control method to perform real-time reactive power adjustment. This achieves optimization of power loss of the distribution network under normal communication conditions and control of distribution network voltage under abnormal communication conditions.

[0022] Preferably, the output of the photovoltaic inverter is adjusted based on the local voltage measurement value of the bus node and the local control method, including the following specific steps:

[0023] Obtain the reactive power reference value of the photovoltaic inverter obtained by solving the optimization problem, and obtain the measured value of the bus voltage amplitude and the active power output value of the photovoltaic inverter at the current time;

[0024] Obtain the current communication status between the local controller and the master station;

[0025] Based on the local controller, when the communication between the master station and the local controller is normal, the local controller uses the reactive power output reference value of the photovoltaic inverter to control the reactive power output of the photovoltaic inverter. When the communication between the local controller and the master station is abnormal, the local controller adjusts the reactive power output of the photovoltaic inverter according to the local control logic.

[0026] Preferably, based on the local control logic of the local controller, the photovoltaic inverter includes three operating states:

[0027] State 1: Reactive power output is constant at the baseline value;

[0028] State 2: Reactive power output increases and exceeds the baseline value;

[0029] State 3: Reactive power output is reduced and falls below the baseline value.

[0030] The beneficial effects of this invention are as follows: This invention considers the communication status between the master station and the local controller, and targets a control framework that coordinates centralized and local levels. On an hourly timescale, it generates a reactive power output reference value for the renewable energy inverter. On a second-scale, when communication between the master station and the local controller is normal, the local controller controls the inverter's reactive power output based on the reference value. When communication between the master station and the local controller is abnormal, the local controller adjusts the inverter's reactive power output based on real-time voltage measurements and the inverter's reactive power output reference value before the communication interruption. This overcomes the problem of untimely voltage regulation caused by communication conditions.

[0031] The above description of the invention is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described below. Attached Figure Description

[0032] Other features, objects, and advantages of the invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings. The drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings.

[0033] Figure 1 This is a flowchart of an active distribution network voltage control method with two time scales according to the present invention. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only one preferred embodiment of this invention and are only used to explain this invention. They do not limit the scope of protection 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.

[0035] Before discussing the exemplary embodiments in more detail, it should be mentioned that some exemplary embodiments are described as processes or methods depicted as flowcharts. Although the flowcharts describe the operations (or steps) as sequential processes, many of the operations (or steps) can be performed in parallel, concurrently, or simultaneously. Furthermore, the order of the operations can be rearranged. The process can be terminated when its operation is completed, but it may also have additional steps not included in the figures; the process may correspond to a method, function, procedure, subroutine, subroutine, etc.

[0036] Example: Figure 1 As shown, an active distribution network voltage control method with two time scales includes the following steps: Step S1: For the centralized level, over a long time scale, optimize the reactive power output of the photovoltaic inverter with the objective function of minimizing network active power loss, and determine the reactive power output benchmark value of the photovoltaic inverter within the optimization interval.

[0037] Specifically, step S1 includes the following steps:

[0038] S11. Obtain basic information about the active distribution network.

[0039] Specifically, the basic information of an active distribution network includes: a1. Network topology; a2. Feeder length, type, current limit, and capacity limit; a3. Bus number where the photovoltaic system is located, and the capacity of the photovoltaic system; a4. Bus numbers where the master station, local controllers, and sensors are located; a5. Communication status between the master station, local controllers, and sensors; a6. Predicted curves of photovoltaic output and load power on an hourly time scale.

[0040] S12. Determine the objective function for the hourly-level optimization problem at the centralized level. The objective function is a single optimization objective that minimizes the distribution network loss, and its expression is as follows:

[0041]

[0042] Where i and j are the busbar numbers, ij is the branch from busbar i to busbar j, and P ij,t and Q ij,t Let r be the active and reactive power on branch ij. ij V is the resistance of branch ij. subs This refers to the voltage amplitude of the substation.

[0043] S13. Determine the constraints for the centralized hierarchical hourly-level voltage reactive power optimization problem.

[0044] Specifically, the constraints include: active power balance constraints of linear nodes in the AC distribution network, reactive power balance constraints of linear nodes in the AC distribution network, linear Ohm's law constraints of the AC distribution network, upper and lower limits of bus voltage constraints of the AC distribution network, feeder capacity constraints of the AC distribution network, upper and lower limits of feeder current constraints of the AC distribution network, and power constraints of the photovoltaic grid-connected inverter.

[0045] S14. Solve the objective function to obtain the reactive power baseline value of the photovoltaic inverter within the optimized interval.

[0046] S15. The local controller uses the reactive power output reference value obtained by the master station optimization to control the photovoltaic inverter.

[0047] Step S2: For the local level, within a short time scale, relying on the local controller, a hybrid logic dynamic method is used to model the photovoltaic inverter and its complex control logic, and the distribution network voltage is controlled by combining the reactive power output reference value and the hybrid logic.

[0048] Specifically, step S2 includes the following steps:

[0049] When the communication between the master station and the local controller is normal, the local controller uses the photovoltaic inverter reactive power output reference value obtained by the master station to control the photovoltaic inverter.

[0050] When communication between the master station and the local controller is abnormal, the local controller uses the reactive power output benchmark value of the photovoltaic inverter obtained by the master station before the communication interruption as a benchmark, and adjusts the output of the photovoltaic inverter according to the local voltage measurement value of the bus node and the local control method to perform real-time reactive power adjustment. This achieves optimization of power loss of the distribution network under normal communication conditions and control of distribution network voltage under abnormal communication conditions.

[0051] Specifically, adjusting the output of the photovoltaic inverter based on the local voltage measurement value of the bus node and the local control method includes the following specific steps:

[0052] Obtain the reactive power reference value of the photovoltaic inverter obtained by solving the optimization problem, and obtain the measured value of the bus voltage amplitude and the active power output value of the photovoltaic inverter at the current time;

[0053] Obtain the current communication status between the local controller and the master station;

[0054] Based on the local controller, when the communication between the master station and the local controller is normal, the local controller uses the reactive power output reference value of the photovoltaic inverter to control the reactive power output of the photovoltaic inverter. When the communication between the local controller and the master station is abnormal, the local controller adjusts the reactive power output of the photovoltaic inverter according to the local control logic.

[0055] Specifically, based on the local control logic of the local controller, the photovoltaic inverter includes three operating states:

[0056] State 1: Reactive power output is constant at the baseline value;

[0057] State 2: Reactive power output increases and exceeds the baseline value;

[0058] State 3: Reactive power output is reduced and falls below the baseline value.

[0059] To further elaborate on the local control logic of the photovoltaic inverter described in this embodiment, it can be described by the following proposition, where δ i,t,1 δ i,t,2 and δ i,t,3The introduced binary logic variable, V, is used to represent the state of the PV inverter. i,t Let i be the voltage amplitude of bus i. and V These are the upper and lower limits of the bus voltage amplitude.

[0060] Proposition 1: When the voltage amplitude V of bus i i,t Within the constraints, the reactive power output of the inverter remains constant at a baseline value, and its propositional logic can be mathematically expressed as follows:

[0061] Proposition 2: When the voltage amplitude V of bus i i,t When the upper limit is exceeded, the reactive power output of the inverter is lower than the reference value. The mathematical expression of its propositional logic is as follows:

[0062] Proposition 3: When the voltage amplitude V of bus i i,t When the lower limit is exceeded, the inverter's reactive power output is higher than the reference value; its propositional logic mathematical expression is: [V i,t ≤ V ]→[δ i,t,3 =1).

[0063] Furthermore, the logical relation of Proposition 1 can be transformed into a set of linear inequalities:

[0064]

[0065] Furthermore, the logical relation of Proposition 2 can be transformed into a linear inequality:

[0066]

[0067] Furthermore, the logical relation of Proposition 3 can be transformed into a linear inequality:

[0068]

[0069] Furthermore, since an inverter can only be in one output state, it can be represented by the following equation:

[0070] δ i,t,1 +δ i,t,2 +δ i,t,3 =1

[0071] In the formula, s is a negative number, which is much smaller than VV i,t , and V i,t -V; α is a small positive number.

[0072] The voltage state and reactive power output equations of the photovoltaic inverter are shown below:

[0073]

[0074] The changes in voltage amplitude and reactive power output are shown below:

[0075]

[0076] In the formula, V represents the voltage amplitude of bus i after local regulation, Δt represents the control interval of the local controller, and V i,t To adjust the voltage amplitude of bus i locally, The decrease in the voltage amplitude of bus i. This represents the increase in the voltage amplitude at bus i. To adjust the reactive power output of the inverter locally, The inverter reactive power output baseline value for the k-th scheduling cycle is sent from the master station to the local controller. This represents the increase in reactive power output of the inverter. ω represents the decrease in reactive power output of the inverter; ω represents the gain of the inverter. The sensitivity coefficient of the voltage amplitude of bus i to the reactive power injection of bus i.

[0077] The specific embodiments described above are preferred embodiments of the active distribution network two-time-scale voltage control method of the present invention, and are not intended to limit the specific scope of the present invention. The scope of the present invention includes but is not limited to the specific embodiments described above. All equivalent changes made in accordance with the shape and structure of the present invention are within the protection scope of the present invention.

Claims

1. A two-time-scale voltage control method for an active distribution network, characterized in that: Includes the following steps: Step S1: For the centralized hierarchy, optimize the reactive power output of the photovoltaic inverter over a long time scale with the objective function of minimizing network active power loss, and determine the baseline value of reactive power output of the photovoltaic inverter within the optimization interval. Step S2: For the local level, within a short timescale, relying on the local controller, a hybrid logic dynamic method is used to model the photovoltaic inverter and its complex control logic. This involves combining the reactive power output reference value and the hybrid logic to control the distribution network voltage. Specifically, this includes: When the communication between the master station and the local controller is normal, the local controller uses the photovoltaic inverter reactive power output reference value obtained by the master station to control the photovoltaic inverter. When communication between the master station and the local controller is abnormal, the local controller uses the reactive power output benchmark value of the photovoltaic inverter obtained by the master station before the communication interruption as the benchmark, and adjusts the output of the photovoltaic inverter according to the local voltage measurement value of the bus node and the local control method to perform real-time reactive power adjustment, so as to optimize the power loss of the distribution network under normal communication conditions and control the distribution network voltage under abnormal communication conditions. The adjustment of the photovoltaic inverter output based on the local voltage measurement value of the bus node and the local control method includes the following specific steps: Obtain the reactive power reference value of the photovoltaic inverter obtained by solving the optimization problem, and obtain the measured value of the bus voltage amplitude and the active power output value of the photovoltaic inverter at the current time; Obtain the current communication status between the local controller and the master station; Based on the local controller, when the communication between the master station and the local controller is normal, the local controller uses the reactive power output reference value of the photovoltaic inverter to control the reactive power output of the photovoltaic inverter. When the communication between the local controller and the master station is abnormal, the local controller adjusts the reactive power output of the photovoltaic inverter according to the local control logic.

2. The active distribution network two-time-scale voltage control method according to claim 1, characterized in that: Step S1 includes the following steps: S11. Obtain basic information about the active distribution network; S12. Determine the objective function for the hourly-level optimization problem at the centralized level. The objective function is a single optimization objective that minimizes the distribution network loss, and its expression is as follows: ； in, and For the busbar number, For from the busbar to bus The side road, and branch road Active power and reactive power on branch road The resistance, This refers to the voltage amplitude of the substation. S13. Determine the constraints for the centralized hierarchical hourly-level voltage reactive power optimization problem; S14. Solve the objective function to obtain the reactive power baseline value of the photovoltaic inverter within the optimized interval; S15. The local controller uses the reactive power output reference value obtained by the master station optimization to control the photovoltaic inverter.

3. The active distribution network two-time-scale voltage control method according to claim 2, characterized in that: The basic information of the active distribution network includes: a1. Network topology; a2. Feeder length, model, current limit, and capacity limit; a3. Bus number where the photovoltaic system is located, and the capacity of the photovoltaic system; a4. Bus numbers where the master station, local controller, and sensors are located; a5. Communication status between the master station, local controller, and sensors; a6. Predicted curves of photovoltaic output and load power on an hourly time scale.

4. The active distribution network two-time-scale voltage control method according to claim 2, characterized in that: The constraints include: active power balance constraints of linear nodes in the AC distribution network, reactive power balance constraints of linear nodes in the AC distribution network, linear Ohm's law constraints of the AC distribution network, upper and lower limits of bus voltage constraints of the AC distribution network, feeder capacity constraints of the AC distribution network, upper and lower limits of feeder current constraints of the AC distribution network, and power constraints of the photovoltaic grid-connected inverter.

5. The active distribution network two-time-scale voltage control method according to claim 1, characterized in that: Based on the local control logic of the local controller, the photovoltaic inverter includes three operating states: State 1: Reactive power output is constant at the baseline value; State 2: Reactive power output increases and exceeds the baseline value; State 3: Reactive power output is reduced and falls below the baseline value.

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