A method for switching the operation mode of a multi-substation parallel operation system

Abstract

The present invention provides a method for switching the operation mode of a multi-substation parallel operation system, in which multiple substations are connected and operated in parallel through a DC interconnection system. The DC interconnection system includes a flexible inverter converter (FIC), an energy management system, and energy storage. The energy management system controls and switches the operation mode of the multi-substation parallel operation system. By applying this technical solution, multiple substations can be operated in parallel, and problems such as reverse power transmission of photovoltaic power generation in substations, overloading, and emergency power supply can be solved.

Description

Technical Field

[0001] The present invention relates to the technical field of intelligent power distribution, and particularly to a method for switching the operation system mode of multiple substations operating in parallel. Background Art

[0002] With the increasing penetration rate of distributed intermittent power sources in the distribution network, the construction of substations adapted to the access of new energy has become a key development direction of the new power system. Based on advanced technical means such as network communication, intelligent measurement, data processing, and intelligent decision-making, constructing a micro-power grid with a single distributed power source accessing a substation will result in the problem of difficult consumption when multiple substation micro-power grids coexist in the regional distribution network, which is not conducive to the comprehensive utilization of resources such as distributed power sources, adjustable loads, and energy storage in the system, increases the difficulty of coordinated control of the distribution micro-grid, and the distribution network dispatching automation system is difficult to support. At the same time, traditional substations have problems such as spatio-temporal mismatch between power sources and loads, coexistence of heavy and light loads, and emergency power supply protection. Summary of the Invention

[0003] In view of this, the purpose of the present invention is to provide a method for switching the operation system mode of multiple substations operating in parallel. By orderly controlling the power output of the FIC and energy storage units of the DC interconnected system, the capacity of each substation is dynamically increased, problems such as spatio-temporal mismatch between power sources and loads, coexistence of heavy and light loads, and emergency power supply protection in the substations operating in parallel are solved, the power supply capacity and equipment utilization rate of the substations are improved, and obvious social and economic benefits are achieved.

[0004] To achieve the above purpose, the present invention adopts the following technical solution: A method for switching the operation system mode of multiple substations operating in parallel, where multiple substations are connected through a DC interconnected system to achieve parallel operation. The DC interconnected system includes an energy management system, a flexible converter FIC, and an energy storage system; the method for switching the operation system mode of multiple substations operating in parallel is deployed in the energy management system. The energy management system collects the operation status information of multiple substations and simultaneously controls the input and output power of the flexible converter FIC and the charge and discharge of the energy storage system.

[0005] In a preferred embodiment, it specifically includes the following steps:

[0006] Step SA1: Determine whether the DC interconnected system issues a fault alarm. If there is a fault, push the information to the energy management system and stop the parallel operation of multiple substations;

[0007] Step SA2: Determine whether the communication between the energy management system and the substation is abnormal. If there is an abnormality, push the information to the energy management system and stop the parallel operation of multiple substations;

[0008] Step SA3: Determine whether the transformer substation area has lost power. If the transformer substation area has not lost power, the parallel operation system enters the first power transfer mode; if the upstream power grid has lost power and not all the outgoing line switches of the transformer substation area have tripped, the parallel operation system enters the second power transfer mode; if the upstream power grid has lost power and all the outgoing line switches of the transformer substation area have tripped, push the information to the energy management system and stop the parallel operation of multiple transformer substation areas.

[0009] In a preferred embodiment, the first sub-mode of the first power transfer mode includes the following steps:

[0010] Step SB1: Determine the load rate ρ of each transformer substation area i whether it is greater than 0, where i = 1, 2, 3, …, N, and N is the number of transformer substation areas in parallel operation. If it is greater than 0, enter the first sub-mode;

[0011] Step SB2: Determine the load rate ρ of each transformer substation area i whether it is greater than the upper limit a1 of the load rate threshold, and calculate the FIC corresponding to the transformer substation area with a load rate greater than the threshold a1 m (1) Transfer-in power P FICm (1) and the power P to be transferred of all transformer substation areas to :

[0012] P FICm (1) = (ρ m - a2) · S m

[0013] P to = ∑P FICm (1)

[0014] In the formula, a2 is the lower limit of the load rate threshold, m = 1, 2, …, N m , N m 、S m 、ρ m are respectively the number of transformer substation areas with a load rate greater than the threshold a1, the distribution transformer capacity, and the load rate;

[0015] Calculate the FIC corresponding to the transformer substation area with a load rate less than the threshold a1 n (2) Transfer-out power P FICn (2) and the power P to be transferred of all transformer substation areas ti :

[0016] P FICn (2) = (a2 - ρ n ) · S n

[0017] P ti = ∑P FICn (2)

[0018] In the formula, n = 1, 2, …, N n , Nn 、S n 、ρ n are respectively the number of distribution transformer areas with a load rate less than the threshold a1, the capacity of distribution transformers, and the load rate;

[0019] Step SB3: Determine the magnitudes of P to and P ti . If P to is greater than P ti , P FICm (1) Perform power transfer according to the magnitude of P ti / n2, where n2 is the number of distribution transformer areas with remaining capacity; if P to is less than P ti , P FICn (2) Perform power transfer according to the magnitude of P to / n1, where n1 is the number of distribution transformer areas with a load rate exceeding the upper threshold a1.

[0020] In a preferred embodiment, the second sub - mode of the first power transfer mode includes the following steps:

[0021] Step SC1: Determine whether the load rate ρ i of each distribution transformer area is greater than 0. If it is less than 0, enter the second sub - mode;

[0022] Step SC2: Calculate the total power P i (+) of the distribution transformer areas without reactive power reverse flow and P i (-) of the distribution transformer areas with reactive power reverse flow: + 、P - :

[0023]

[0024] Step SC3: Determine the magnitudes of P + and P - . If P + is greater than P - , the outgoing power P FICi (+) of the FIC corresponding to the distribution transformer area without reactive power reverse flow is transferred according to the magnitude of P - / n3, where n3 is the number of distribution transformer areas without reactive power reverse flow; if P + is less than P - and the SOC of the energy storage system does not exceed the upper limit SOC max , the charging power P ES1 of the energy storage system is:

[0025] P ES1 = P - - P +

[0026] If P + is less than P -And the SOC of the energy storage system exceeds the upper limit SOC max , the FIC corresponding to the power reverse feeding area transfers to the power P FICi (-) Perform power transfer according to the size of P + / n4, where n4 is the number of power reverse feeding areas.

[0027] In a preferred embodiment, the second power transfer mode includes the following steps:

[0028] Step SD1: Determine the number of power outage areas N F Is it equal to the number of all parallel operation areas N?

[0029] Step SD2: If all parallel operation areas are powered off and the SOC of the energy storage system is less than the threshold SOC min , exit the power transfer mode 2; if all parallel operation areas are powered off and the SOC of the energy storage system is greater than the threshold SOC min , the energy storage system supplies power to all power outage areas and satisfies the following formula:

[0030] ∑P FICi (F) = P ES2

[0031] In the formula, ∑P FICi (F) is the total FIC power corresponding to the power outage areas, and P ES2 is the discharge power of the energy storage system.

[0032] Step SD3: If not all parallel operation areas are powered off, the normal areas and the energy storage system supply power to the power outage areas and satisfy the following formula:

[0033] ∑P FICi (F) = ∑P FICi (NF) + P ES2

[0034] In the formula, ∑P FICi (NF) is the total FIC power corresponding to the normal areas, and P ES2 is the discharge power of the energy storage system.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] 1) Solve the problem of distributed photovoltaic accommodation in low-voltage areas.

[0037] 2) Solve the problems of coexistence of heavy and light loads and emergency power supply in low-voltage areas.

[0038] 3) Dynamically improve the capacity of traditional areas and energy storage devices in the common DC interconnection system, improve the utilization rate of area equipment assets, and have obvious economic benefits. Description of the Drawings

[0039] Figure 1 Schematic diagram of the structure of a multi - substation parallel operation system according to a preferred embodiment of the present invention.

[0040] Figure 2 Main control strategy flowchart of a method for switching the mode of a multi - substation parallel operation system according to a preferred embodiment of the present invention.

[0041] Figure 3 Flowchart of the first power transfer mode according to a preferred embodiment of the present invention.

[0042] Figure 4 Flowchart of the second power transfer mode according to a preferred embodiment of the present invention. Detailed implementation manners

[0043] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0044] It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present application belongs.

[0045] It should be noted that the terms used herein are only for describing specific implementation manners and are not intended to limit the exemplary embodiments according to the present application; as used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0046] A method for switching the mode of a multi - substation parallel operation system, referring to Figures 1 to 4 , multiple substations are connected through a DC interconnection system to achieve parallel operation. The DC interconnection system includes an energy management system, a flexible inverter FIC, and an energy storage system; the method for switching the mode of the multi - substation parallel operation system is deployed in the energy management system. The energy management system collects the operation status information of multiple substations and simultaneously controls the input and output power of the flexible inverter FIC and the charge and discharge of the energy storage system.

[0047] Specifically, it includes the following steps:

[0048] Step SA1: Determine whether the DC interconnection system issues a fault alarm. If there is a fault, push the information to the energy management system and stop the parallel operation of multiple substations;

[0049] Step SA2: Determine whether the communication between the energy management system and the substations is abnormal. If there is an abnormality, push the information to the energy management system and stop the parallel operation of multiple substations;

[0050] Step SA3: Determine whether the substation area is powered off. If the substation area is not powered off, the parallel operation system enters the first power transfer mode; if the upstream power grid is powered off and not all the outgoing line switches of the substation area trip, the parallel operation system enters the second power transfer mode; if the upstream power grid is powered off and all the outgoing line switches of the substation area trip, push the information to the energy management system and stop the parallel operation of multiple substation areas.

[0051] The first sub-mode of the first power transfer mode includes the following steps:

[0052] Step SB1: Determine the load factor ρ of each substation area i whether it is greater than 0, where i = 1, 2, 3, …, N, and N is the number of substation areas in parallel operation. If it is greater than 0, enter the first sub-mode;

[0053] Step SB2: Determine the load factor ρ of each substation area i whether it is greater than the upper limit a1 of the load factor threshold, and calculate the FIC corresponding to the substation area with a load factor greater than the threshold a1 m (1) Transfer-in power P FICm (1) and the power P to be transferred of all substation areas to :

[0054] P FICm (1) = (ρ m - a2) · S m

[0055] P to = ∑P FICm (1)

[0056] In the formula, a2 is the lower limit of the load factor threshold, m = 1, 2, …, N m , N m 、S m 、ρ m are respectively the number of substation areas with a load factor greater than the threshold a1, the distribution transformer capacity, and the load factor;

[0057] Calculate the FIC corresponding to the substation area with a load factor less than the threshold a1 n (2) Transfer-out power P FICn (2) and the power P to be transferred of all substation areas ti :

[0058] P FICn (2) = (a2 - ρ n ) · S n

[0059] P ti = ∑P FICn (2)

[0060] In the formula, n = 1, 2, …, N n , N n, S n , ρ n are respectively the number of distribution transformer areas with a load rate less than the threshold a1, the distribution transformer capacity, and the load rate.

[0061] Step SB3: Judge P to and P ti . If P to is greater than P ti , P FICm (1) Perform power transfer according to the magnitude of P ti / n2, where n2 is the number of distribution transformer areas with remaining capacity; if P to is less than P ti , P FICn (2) Perform power transfer according to the magnitude of P to / n1, where n1 is the number of distribution transformer areas with a load rate exceeding the threshold upper limit a1.

[0062] The second sub - mode of the first mode of power transfer supply includes the following steps:

[0063] Step SC1: Judge whether the load rate ρ i of each distribution transformer area is greater than 0. If it is less than 0, enter the second sub - mode;

[0064] Step SC2: Calculate the total power P i (+) of the distribution transformer areas without reactive power reverse - flow and P i (-) of the distribution transformer areas with reactive power reverse - flow: + , P - :

[0065]

[0066] Step SC3: Judge the magnitudes of P + and P - . If P + is greater than P - , the outgoing power P FICi (+) of the FIC corresponding to the distribution transformer area without reactive power reverse - flow performs power transfer according to the magnitude of P - / n3, where n3 is the number of distribution transformer areas without reactive power reverse - flow; if P + is less than P - and the SOC of the energy storage system does not exceed the upper limit SOC max , the charging power P ES1 of the energy storage system is:

[0067] P ES1 =P - -P +

[0068] If P + is less than P - and the SOC of the energy storage system exceeds the upper limit SOCmax , the transferred power P of the FIC corresponding to the power reverse feed area FICi (-) Transfer power according to the magnitude of P + / n4, where n4 is the number of power reverse feed areas.

[0069] The second power transfer mode includes the following steps:

[0070] Step SD1: Determine the number N of power outage areas F Whether it is equal to the number N of all parallel operation areas;

[0071] Step SD2: If all parallel operation areas are powered off and the SOC of the energy storage system is less than the threshold SOC min , exit the power transfer mode 2; if all parallel operation areas are powered off and the SOC of the energy storage system is greater than the threshold SOC min , the energy storage system supplies power to all power outage areas and satisfies the following formula:

[0072] ∑P FICi (F) = P ES2

[0073] In the formula, ∑P FICi (F) is the total FIC power corresponding to the power outage areas, and P ES2 is the discharge power of the energy storage system.

[0074] Step SD3: If not all parallel operation areas are powered off, the normal areas and the energy storage system supply power to the power outage areas and satisfy the following formula:

[0075] ∑P FICi (F) = ∑P FICi (NF) + P ES2

[0076] In the formula, ∑P FICi (NF) is the total FIC power corresponding to the normal areas, and P ES2 is the discharge power of the energy storage system.

Claims

1. A method for switching system modes of multiple substation areas operating in parallel, characterized in that, Multiple substations are connected through a DC interconnection system to achieve parallel operation. The DC interconnection system includes an energy management system, a flexible inverter converter (FIC), and an energy storage system. The multi-substation parallel operation system mode switching method is deployed in the energy management system. The energy management system collects the operation status information of multiple substations, and at the same time controls the input and output power of the flexible inverter converter (FIC) and the charge and discharge of the energy storage system. Specifically, it includes the following steps: Step SA1: Determine whether the DC interconnection system issues a fault alarm. If there is a fault, push the information to the energy management system and stop the parallel operation of multiple substations. Step SA2: Determine whether the communication between the energy management system and the substations is abnormal. If there is an abnormality, push the information to the energy management system and stop the parallel operation of multiple substations. Step SA3: Determine whether the substations are de-energized. If the substations are not de-energized, the parallel operation system enters the first power transfer mode. If the upstream power grid is de-energized and not all the outgoing line switches of the substations are tripped, the parallel operation system enters the second power transfer mode. If the upstream power grid is de-energized and all the outgoing line switches of the substations are tripped, push the information to the energy management system and stop the parallel operation of multiple substations. The second power transfer mode includes the following steps: Step SD1: Determine whether the number N of power-off station areas F is equal to the number N of all parallel operating station areas; Step SD2: If all the parallel operating substations are de-energized and the SOC of the energy storage system is less than the threshold SOC min , exit power transfer mode 2; if all the parallel operating substations are de-energized and the SOC of the energy storage system is greater than the threshold SOC min , the energy storage system supplies power to all de-energized substations and satisfies the following formula: ∑P FICi (F) = P ES2 Where, ∑P FICi (F) is the total FIC power corresponding to the power outage area, and P ES2 is the discharge power of the energy storage system; Step SD3: If not all the substations in parallel operation are de-energized, the normal substations and the energy storage system supply power to the de-energized substations, and the following formula is satisfied: ∑P FICi (F) = ∑P FICi (NF) + P ES2 Where, ∑P FICi (NF) is the total FIC power corresponding to the normal power area, and P ES2 is the discharge power of the energy storage system.

2. The method for switching the operating system mode of a multi-substation parallel operation system according to claim 1, characterized in that, The first sub-mode of the first power transfer mode includes the following steps: Step SB1: Determine the load ratio ρ of each transformer substation area i Whether it is greater than 0, where i = 1, 2, 3, …, N, and N is the number of transformer substations operating in parallel. If it is greater than 0, enter the first sub-mode; Step SB2: Determine the load factor ρ of each substation area i Check if it is greater than the upper limit a1 of the load factor threshold, and calculate the FIC corresponding to the substation area where the load factor is greater than the threshold a1 m (1) Transfer-in power P FICm (1) and the power P to be transferred for all substation areas to : P FICm (1) = (ρ m - a2)·S m P to = ∑P FICm (1) where a2 is the lower limit of the load rate threshold, and m = 1, 2, …, N m , N m , S m , ρ m are respectively the number of distribution transformer areas with a load rate greater than the threshold a1, the distribution transformer capacity, and the load rate; Calculate the FIC corresponding to the distribution transformer area where the calculated load rate is less than the threshold a1 n (2) Transfer power P FICn (2) And the transferable power P of all distribution transformer areas ti : P FICn (2) = (a2 - ρ n )·S n P ti = ∑P FICn (2) where n = 1, 2, …, N n , N n , S n , ρ n are respectively the number of distribution transformer areas with load rate less than the threshold a1, the distribution transformer capacity, and the load rate; Step SB3: Determine P to and P ti in terms of magnitude. If P to is greater than P ti , P FICm (1) Perform power transfer according to the magnitude of P ti / n2, where n2 is the number of substations with remaining capacity; if P to is less than P ti , P FICn (2) Perform power transfer according to the magnitude of P to / n1, where n1 is the number of substations with a load rate exceeding the threshold upper limit a1.

3. A method for switching the operation system mode of multiple substations operating in parallel according to claim 2, characterized in that The second sub-mode of the first power transfer mode includes the following steps: Step SC1: Determine the load rate ρ of each substation area i Whether it is greater than 0. If it is less than 0, enter the second sub-mode; Step SC2: Calculate the total power P of the no-reactive-power reverse-feed transformer substation P i (+) and the total power P of the active-power reverse-feed transformer substation P i (-): + P - : Step SC3: Determine P + and P - in terms of magnitude. If P + is greater than P - , the outgoing power P FICi (+) of the FIC corresponding to the no-reactive-power-backflow substation area is transferred according to the magnitude of P - / n3, where n3 is the number of no-reactive-power-backflow substations. If P + is less than P- and the SOC of the energy storage system does not exceed the upper limit SOC max , the charging power P ES1 of the energy storage system is as follows: P ES1 = P - -P + If P + is less than P - and the SOC of the energy storage system exceeds the upper limit SOC max , the FIC corresponding to the power injection area transfers the power P FICi (-) performs power transfer according to the magnitude of P + / n4, where n4 is the number of power injection areas.

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