A grid-connected ac-dc microgrid energy storage capacity decoupling configuration method

Abstract

This invention relates to a decoupled configuration method for energy storage capacity in grid-connected AC / DC microgrids within the field of power system grid configuration technology. It includes the following steps: Step 1, control of the AC-side energy storage charging and discharging process; Step 2, determination of the AC-side energy storage capacity; Step 3, control of the DC-side energy storage charging and discharging process; and Step 4, determination of the DC-side energy storage capacity. It utilizes a tie-line power control method to achieve charging and discharging control of the AC / DC microgrid, a power exchange error probabilistic statistical method to achieve energy storage power and capacity configuration, a DC bus control method to achieve voltage and power control, and a voltage regulation error probabilistic statistical method to achieve energy storage power and capacity configuration. This invention offers advantages such as high determinism in energy storage configuration, good reliability of decoupled configuration, simplicity, effective control, high reliability, and good economy.

Description

Technical Field

[0001] This invention relates to a method for decoupling the energy storage capacity configuration of grid-connected AC / DC microgrids in the field of power system grid configuration technology. Background Technology

[0002] In power systems, the energy storage configuration of the power grid is an integral part of microgrids and plays a crucial role in ensuring the economy and reliability of the power system. Compared to the energy storage capacity configuration of a simple AC microgrid, the energy storage capacity configuration of an AC / DC microgrid is more complex. Current technologies for energy storage capacity configuration in AC / DC microgrids suffer from several shortcomings: insufficient integrated strategies, inadequate decoupling configurations, poor control determinism, and low economic efficiency. Summary of the Invention

[0003] The purpose of this invention is to provide a decoupled configuration method for energy storage capacity in grid-connected AC / DC microgrids. It scientifically utilizes a comprehensive energy storage configuration strategy to achieve better decoupled configuration of AC / DC side energy storage capacity, effectively improves the determinism of energy storage capacity configuration, and greatly improves the reliability of control effect.

[0004] A method for decoupling the energy storage capacity configuration of a grid-connected AC / DC microgrid is designed, comprising the following steps: Step 1, control of the AC side energy storage charging and discharging process; Step 2, determination of the AC side energy storage capacity; Step 3, control of the DC side energy storage charging and discharging process; Step 4, determination of the DC side energy storage capacity.

[0005] Step one, control of the AC-side energy storage charging and discharging process, based on the AC / DC microgrid with tie-line power control, controls the charging and discharging process of the AC-side energy storage. The method for step one is as follows:

[0006] (1) Based on the requirements of grid-connected microgrids and their tie-line power control, energy storage is used as a current source and PQ control mode is adopted to carry out charging and discharging control in accordance with the power control requirements of the tie-line between the microgrid and the main grid.

[0007] (2) Energy storage control is based on the principle of extending the service life of energy storage. Integral control is adopted. Microgrid control adopts the control mode of fixed switching power of tie line, that is, only when the microgrid output power is equal to the target value, the control ends and the error is 0. During the control process, if other conditions remain unchanged, it takes 4T-5T to reach the control target, where T is the inertial time constant of the control link.

[0008] Step two, determining the AC-side energy storage capacity: Based on power exchange error probability statistics, the AC-side energy storage capacity is determined. The method for step two is as follows:

[0009] (1) For the error between the direct exchange power and the target exchange power under no energy storage regulation, if the daily regional prediction error follows a normal distribution, then the energy storage power controlled for it also follows a normal distribution. Based on statistical data, the energy storage capacity can be determined at a confidence level of 0.99; the operating power of the energy storage corresponding to the regional prediction error. It also conforms to a normal distribution. ,in Indicates expectation as The sum and variance are The energy storage power P follows a normal distribution; therefore, based on statistical analysis, at a confidence level of 0.99, the energy storage power P is determined to be... E Configuration meets requirements:

[0010] (1)

[0011] (2) Microgrid AC-side energy storage capacity configuration, for each control cycle governing equations It can be written as:

[0012] (2)

[0013] assumed During the control cycle If the internal parameters remain essentially unchanged, then the change in stored energy during the control period is as follows:

[0014] Let i represent the i-th control process; the energy change of the stored energy with a total of 1440 min / t of control operations per day is as follows:

[0015] (3)

[0016] As can be seen from equation (3), the energy storage capacity is determined by... The probability distribution of energy storage capacity obtained by integrating over a day is as follows: ,in, The expected value calculated by equation (3); For the reason Considering the variance calculated after equation (3); similarly, using a confidence level of 0.99, the energy storage capacity configuration equation is: ,in Confidence level; Configure capacity for AC-side energy storage.

[0017] Step three, control of the DC-side energy storage charging and discharging process, based on DC bus control, controls the charging and discharging process of the DC-side energy storage in the AC / DC microgrid. The method for step three is as follows:

[0018] (1) For DC-side microgrid energy storage, a control method is adopted to stabilize the DC bus voltage using energy storage. P / V droop control is used on the DC side, and the relationship diagram can be represented as follows:

[0019] (4)

[0020] (2) The control of energy storage is based on the principle of extending the service life of energy storage, and integral control is adopted. The DC side of the microgrid adopts a stable DC bus voltage control mode. In this control process, if other conditions remain unchanged, it takes 4T-5T to reach the control target, where T is the inertial time constant of the control link. The power control of energy storage can be expressed as: .

[0021] Step four, determining the DC-side energy storage capacity: Based on voltage regulation error probability statistics, the DC-side energy storage capacity is determined, thereby achieving decoupling of the AC / DC energy storage capacity configurations on different sides of the AC / DC microgrid. The method for step four is as follows:

[0022] (1) For the voltage error between the target voltage value and the voltage value without energy storage regulation, the daily voltage error follows a normal distribution. Based on statistical data, the energy storage capacity can be determined at a confidence level of 0.99; the operating power of the energy storage corresponding to the regional prediction error can also be determined. It also conforms to a normal distribution. ,in Indicates expectation as The variance is Following a normal distribution, based on statistical analysis, it is determined that the energy storage power configuration meets the requirements at a 0.99 confidence level: .

[0023] (2) The energy storage capacity is determined by The probability distribution of energy storage capacity obtained by integrating over a day is as follows: ,in, for The expected value calculated by integrating over a day; For the formula The variance is calculated after considering the time integration; similarly, using a confidence level of 0.99, the energy storage capacity configuration equation is: ,in Confidence level; Configure capacity for DC-side energy storage.

[0024] The beneficial technical effects of this invention are as follows: By employing tie-line power control technology to control the charging and discharging process of AC-side energy storage, a comprehensive energy storage configuration strategy is scientifically utilized. Simultaneously, by using a power exchange error probabilistic statistical method to determine the AC-side energy storage capacity, the determinism of energy storage capacity configuration is improved. Furthermore, the introduction of a decoupling configuration method enables the configuration of energy storage capacity on both AC and DC sides. This invention also boasts advantages such as simple method, effective control, high reliability, and good economy. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the AC / DC microgrid energy storage configuration according to an embodiment of the present invention;

[0026] Figure 2 This is a schematic diagram of the microgrid AC side energy storage control block diagram according to an embodiment of the present invention;

[0027] Figure 3 This is a schematic diagram of the energy storage active voltage droop control according to an embodiment of the present invention;

[0028] Figure 4 This is a schematic diagram of the microgrid DC-side energy storage control block diagram according to an embodiment of the present invention;

[0029] Figure 5 This is a control flowchart of the method described in this invention. Detailed Implementation

[0030] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments.

[0031] Step 1: Construct a charging and discharging control method for AC-side energy storage in an AC / DC microgrid based on tie-line power control;

[0032] Step 2: Method for determining AC-side energy storage capacity based on power exchange error probability statistics;

[0033] Step 3: A method for charging and discharging energy storage on the DC side of an AC / DC microgrid based on DC bus control;

[0034] Step four: Based on the method for determining the DC-side energy storage capacity determined by the probability statistics of voltage regulation error, the configuration of energy storage capacity on the AC and DC sides of the AC / DC microgrid is decoupled.

[0035] Specifically, the AC-side energy storage charging and discharging control method based on tie-line power control in step one is as follows:

[0036] a. Based on the requirements of the tie-line power control of the grid-connected microgrid, energy storage is used as a current source, and the PQ control mode is adopted to carry out charging and discharging control according to the tie-line power control requirements between the microgrid and the main grid.

[0037] Specifically, in this embodiment, the schematic diagram of the AC / DC microgrid energy storage configuration is as follows: Figure 1 As shown, distributed power sources and energy storage devices are connected to both the AC and DC buses, and the AC and DC buses are connected by interconnection conversion devices, providing a bidirectional power channel. This topology can effectively reduce power conversion stages, but its operation and control strategy is relatively complex. In addition to stabilizing the AC bus voltage frequency and DC bus voltage, power control between the AC and DC microgrids must also be considered.

[0038] against Figure 1 In grid-connected operation, the AC / DC microgrid operates in power-sharing mode, with the external grid providing the voltage and frequency reference for the AC system. Distributed power sources (such as photovoltaics) in the AC main microgrid operate in MPPT mode, and energy storage in the AC microgrid acts as a current source, employing PQ control and charging / discharging control according to the power control requirements of the tie-line between the microgrid and the main grid. At this time, the controllable resource of the AC microgrid is the AC bus energy storage device. The control target value for the tie-line exchange power is defined as P, and the actual value of the tie-line exchange power is... The energy storage output power is Due to the fluctuating characteristics of distributed energy resources and loads, the actual value of tie-line switching power will inevitably fluctuate over time. By controlling energy storage, the actual value of tie-line switching power can be changed to meet the control objectives.

[0039] b. Considering the principle of extending the service life of energy storage, integral control is adopted for energy storage control, and its control equation is as follows:

[0040] (1)

[0041] The microgrid control adopts a tie-line constant switching power control mode, which means that the microgrid output power is kept equal to the target value, and the control ends when the error is about 0.

[0042] Specifically, in this embodiment, the microgrid AC-side energy storage control block is as follows: Figure 2 As shown in the figure. Where T is the integral time constant, in seconds. During the control process, if other conditions remain unchanged, 4T-5T is required to achieve the control objective.

[0043] Specifically, the method for determining the AC-side energy storage capacity based on the probability statistics of power exchange error in step two is as follows:

[0044] a. For the error between the direct exchange power and the target exchange power under no energy storage regulation, if the daily regional prediction error follows a normal distribution, then the energy storage power controlled for it also follows a normal distribution. Based on statistical data, the energy storage power can be determined at a confidence level of 0.99. The operating power of the energy storage corresponding to the regional prediction error is then calculated. It also conforms to a normal distribution.

[0045]

[0046] in Indicates expectation as The variance is The energy storage capacity follows a normal distribution. Based on statistical analysis, at a 0.99 confidence level, the energy storage capacity configuration meets the requirements:

[0047]

[0048] b. Microgrid AC-side energy storage capacity configuration

[0049] For each control cycle governing equations It can be written as:

[0050] (2)

[0051] Assume P Err If the energy remains essentially constant within the control period Δt, then the change in stored energy within the control period is as follows:

[0052]

[0053] i represents the i-th control process. The energy change of the stored energy with a total of 1440 min / t control operations per day is as follows:

[0054] ;

[0055] The above formula can be simplified to:

[0056] (3)

[0057] As can be seen from equation (3), the energy storage capacity is determined by... The probability distribution of energy storage capacity obtained by integrating over a day is as follows:

[0058]

[0059] in, The expected value calculated by equation (3); For the formula Considering the variance calculated after equation (3), similarly, using a confidence level of 0.99, the energy storage capacity configuration equation is:

[0060]

[0061] in Confidence level; Configure capacity for AC-side energy storage.

[0062] The calculation method is illustrated below:

[0063] Assumption The error distribution is statistically approximated to satisfy:

[0064]

[0065] The expected value is expressed in kW. Using a simplified method, the confidence interval for a 0.99 confidence level is determined using the following formula:

[0066]

[0067] Therefore, the energy storage capacity configuration is 0.876kW.

[0068] Assume that the probability distribution of energy storage capacity is obtained statistically:

[0069]

[0070] The mathematical expectation unit is kWh. Based on a simplified method, the confidence interval is determined at a confidence level of 0.99 using the following formula:

[0071]

[0072] Therefore, the energy storage capacity configuration is 2.3 kWh.

[0073] Specifically, step three is a DC-side energy storage charging and discharging control method for AC / DC microgrids based on DC bus control:

[0074] a. For DC-side microgrid energy storage, a control method is adopted to stabilize the DC bus voltage using energy storage. P / V droop control is used on the DC side. Figure 3 The relationship between voltage change and active power change is shown in the graph:

[0075] It can be represented as:

[0076] (4)

[0077] b. Considering the principle of extending the service life of energy storage, integral control is adopted for energy storage control, and the DC side of the microgrid adopts a stable DC bus voltage control mode.

[0078] It can be represented as:

[0079] (5)

[0080] Specifically, in this embodiment, the microgrid DC-side energy storage control block diagram is as follows: Figure 4 As shown.

[0081] In this control process, if other conditions remain unchanged, it takes 4T~5T to achieve the control target. T is the inertial time constant of the control element.

[0082] make For each control cycle You can take =4T~5T. The control equation (5) can be written for the control period as:

[0083] (6)

[0084] Specifically, the method for determining the DC-side energy storage capacity based on the probability statistics of voltage regulation error in step four is as follows:

[0085] a. For the voltage error between the target voltage value and the voltage value without energy storage regulation, the daily voltage error follows a normal distribution. Based on statistical data, the energy storage capacity can be determined at a confidence level of 0.99. The operating power of the energy storage corresponding to the regional prediction error is then calculated. It also conforms to a normal distribution.

[0086]

[0087] in, Indicates expectation as The variance is The energy storage capacity follows a normal distribution. Based on statistical analysis, at a 0.99 confidence level, the energy storage capacity configuration meets the requirements:

[0088]

[0089] b. Energy storage capacity is determined by The probability distribution of energy storage capacity obtained by integrating over a day is as follows:

[0090]

[0091] in, for The expected value calculated by integrating over a day; For the formula The variance is calculated after considering the time integration. Similarly, using a confidence level of 0.99, the energy storage capacity configuration equation is:

[0092]

[0093] in Confidence level; Configure capacity for DC-side energy storage.

[0094] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for decoupling the energy storage capacity configuration of a grid-connected AC / DC microgrid, characterized in that... Includes the following steps: Step 1: Control of AC side energy storage charging and discharging process; Step 2: Determination of AC side energy storage capacity; Step 3: Control of DC side energy storage charging and discharging process; Step 4: Determination of DC side energy storage capacity. In the AC-side energy storage charging and discharging process control stage of step one, the AC / DC microgrid based on tie-line power control controls the charging and discharging process of AC-side energy storage. In the AC-side energy storage capacity determination stage of step two, the AC-side energy storage capacity is determined based on the power exchange error probability statistics. In the DC-side energy storage charging and discharging process control stage of step three, the charging and discharging process of the DC-side energy storage of the AC / DC microgrid is controlled based on DC bus control. In the fourth step, the DC-side energy storage capacity determination stage, the DC-side energy storage capacity is determined based on the voltage regulation error probability statistics, thereby achieving the decoupling of the AC and DC side energy storage capacity configurations of the AC / DC microgrid. The control of the DC-side energy storage charging and discharging process in step three includes voltage power control and energy storage power control, and the specific control process is as follows: Voltage and power control: For DC-side microgrid energy storage, a control method is adopted to stabilize the DC bus voltage through energy storage; P / V droop control is used on the DC side, and the empirical formulas for voltage and active power changes are as follows: ； Energy storage power control: Energy storage control is based on the principle of extending the service life of energy storage, and adopts integral control. The DC side of the microgrid uses a control mode that stabilizes the DC bus voltage. In this control process, if other conditions remain unchanged, it takes 4T-5T to reach the control target, where T is the inertial time constant of the control loop. The empirical formula for energy storage power control is: ; in, The operating power of energy storage; The determination of DC-side energy storage capacity in step four includes energy storage power configuration and energy storage capacity configuration. The specific configuration process is as follows: Energy storage power configuration: For the voltage error between the target voltage value and the voltage value without energy storage regulation, the daily voltage error follows a normal distribution. Based on statistical data, the energy storage capacity can be determined at a confidence level of 0.99; the operating power of the energy storage corresponding to the regional prediction error. It also conforms to a normal distribution. ,in Indicates expectation as The variance is Given a normal distribution, based on statistical analysis and with a confidence level of 0.99, the empirical formula for energy storage power configuration is as follows: ; Energy storage capacity configuration: Energy storage capacity is composed of The probability distribution of energy storage capacity obtained by integrating over a day is as follows: ,in, for The expected value calculated by integrating over a day; For the formula The variance is calculated after considering time integration; similarly, using a confidence level of 0.99, the empirical formula for energy storage capacity configuration is: ,in Confidence level; Configure capacity for DC-side energy storage.

2. The method for decoupling the energy storage capacity configuration of a grid-connected AC / DC microgrid according to claim 1, characterized in that, The control of the AC side energy storage charging and discharging process in step one includes the following control process and control mode: Charge and discharge control: Based on the requirements of grid-connected microgrids and their tie-line power control, energy storage is used as the current source, and PQ control mode is adopted to carry out charge and discharge control according to the power control requirements of the tie-line between the microgrid and the main grid. Control mode: Energy storage control is based on the principle of extending the service life of energy storage and adopts integral control. Microgrid control adopts the control mode of constant switching power of tie line, that is, only when the microgrid output power is equal to the target value, the control ends and the error is 0. During the control process, if other conditions remain unchanged, it takes 4T-5T to reach the control target, where T is the inertial time constant of the control link.

3. The method for decoupling the energy storage capacity configuration of a grid-connected AC / DC microgrid according to claim 1, characterized in that, Step two, determining the AC-side energy storage capacity, includes energy storage power configuration and energy storage capacity configuration. The specific configuration process is as follows: Energy storage power configuration: For the error between the direct exchange power and the target exchange power under no energy storage regulation, if the daily regional prediction error follows a normal distribution, then the energy storage power controlled for it also follows a normal distribution; when targeting Based on statistical data, the energy storage power can be determined at a confidence level of 0.99; the operating power of the energy storage corresponding to the regional prediction error can also be determined. It also conforms to a normal distribution. ,in Indicates expectation as The sum and variance are The energy storage configuration follows a normal distribution. Based on statistical analysis, and with a confidence level of 0.99, the empirical formula for a satisfactory energy storage configuration is as follows: ; Energy storage capacity configuration: Regarding the energy storage capacity configuration on the AC side of the microgrid, for each control cycle... governing equations It can be written as: ; Assume During the control cycle If the internal parameters remain essentially unchanged, then the change in stored energy during the control period is as follows: Let i represent the i-th control process; the empirical formula for the change in energy storage when the total number of control operations per day is 1440 min / t is: ; Based on the aforementioned empirical formula for energy storage change, the energy storage capacity is determined by... The probability distribution of energy storage capacity obtained by integrating over a day is as follows: ,in, This is the expected value calculated based on the empirical formula for changes in energy storage. For the reason The variance value is calculated based on the empirical formula for energy storage capacity variation; similarly, using a confidence level of 0.99, the empirical formula for energy storage capacity configuration is: ,in Confidence level; Configure capacity for AC-side energy storage.

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