A control method, device and storage medium for a medium and low voltage DC power distribution system

Abstract

The present invention discloses a control method, device, and storage medium for a medium- and low-voltage DC power distribution system. The low-voltage DC power distribution system includes a photovoltaic power station, an energy storage device, and a medium- and low-voltage DC bus. The control method includes determining different control modes based on the absolute value of the deviation between the actual value and the rated value of the medium-voltage DC bus voltage. The control strategy for the master converter station includes a constant voltage or power-limited control strategy, the control strategy for the slave converter station includes a constant power or power-limited control strategy, the control strategy for the photovoltaic power station includes a maximum power point or power-limited control strategy, and the control strategy for the energy storage device includes a constant power or droop control strategy. Embodiments of the invention can fully utilize the adjustability of the power devices within the system, improve the power balance and voltage stability of the medium-voltage DC bus, and can be widely applied in the field of DC power distribution technology.

Description

Technical Field

[0001] The present invention relates to the field of direct current (DC) power distribution technology, and in particular to a control method, device, and storage medium for a medium- and low-voltage DC power distribution system. Background Art

[0002] DC distribution systems are intelligent distribution systems that provide DC power using voltage source converters and feature advanced energy management systems. DC distribution networks have attracted extensive attention and research due to their advantages, including low line losses, large transmission capacity, flexible power supply methods, and convenient integration of renewable energy sources. However, with the increasing penetration of new energy sources such as wind and solar power, and the continued development of power electronics in DC distribution networks, DC power distribution and utilization systems that incorporate photovoltaics and energy storage systems have experienced variable power flow characteristics and complex operating modes. These issues have seriously impacted the power supply quality and reliability of DC distribution networks.

[0003] Due to the particularity of DC power, namely that DC distribution systems only contain active power and no reactive power, the system's active power flow is closely related to the magnitude of the DC voltage. Therefore, the system's power flow can be controlled by simply controlling the voltage of the distribution network. The DC system exhibits weak inertia and low damping, making it no less difficult to control than the AC system. Therefore, a reasonable and effective voltage control method is needed to ensure the stability of the DC distribution network under various operating modes. Current research mainly focuses on coordinated control between multi-terminal converter stations. DC voltage regulation mainly relies on the voltage regulation performance of a single converter station, with a small regulation range. It also fails to fully utilize the sources, loads, and storage within the DC distribution network to participate in bus power regulation to maintain voltage stability. Summary of the Invention

[0004] In view of this, the purpose of the embodiments of the present invention is to provide a control method, device and storage medium for a medium and low voltage DC power distribution system, which can determine the control strategy of the converter station, photovoltaic power station and energy storage device according to the deviation of the medium voltage DC bus voltage and the transmission power, make full use of the adjustability of the power devices in the system, and improve the power balance and voltage stability of the medium voltage DC bus.

[0005] In a first aspect, an embodiment of the present invention provides a control method for a medium- and low-voltage DC power distribution and utilization system, wherein the medium- and low-voltage DC power distribution and utilization system includes at least two DC buses of different voltage levels. Of the two DC buses of adjacent voltage levels, the DC bus with a higher voltage is called a medium-voltage DC bus, and the DC bus with a lower voltage level is called a low-voltage DC bus. The medium-voltage DC bus is connected to a photovoltaic power station, an energy storage device, a first load, and the low-voltage DC bus through a transformer. The low-voltage DC bus is connected to a second load. Both ends of the medium-voltage DC bus are connected to an AC main grid through converter stations, and the two converter stations are respectively a master converter station or a slave converter station.

[0006] The control method comprises:

[0007] When the absolute value of the deviation between the actual value of the medium voltage DC bus voltage and the rated value is less than the first value, the master converter station is determined to adopt a constant voltage control strategy, the slave converter station is determined to adopt a constant power control strategy, the photovoltaic power station is determined to adopt a maximum power point control strategy, and the energy storage device is determined to adopt a constant power control strategy;

[0008] When the absolute value of the deviation between the actual value and the rated value of the medium voltage DC bus voltage is between the first value and the second value, determining that the master converter station adopts a constant voltage or power limit control strategy according to the transmission power of the master converter station, determining that the slave converter station adopts a droop or power limit control strategy according to the transmission power of the slave converter station, determining that the photovoltaic power station adopts a maximum power point control strategy, and determining that the energy storage device adopts a constant power control strategy;

[0009] When the absolute value of the deviation between the actual value of the medium voltage DC bus voltage and the rated value is greater than the second value, the main converter station is determined to adopt a constant voltage or power limit control strategy according to the transmission power of the main converter station, the slave converter station is determined to adopt a droop or power limit control strategy according to the transmission power of the slave converter station, the photovoltaic power station is determined to adopt a power limit or maximum power point control strategy according to the deviation of the medium voltage DC bus, and the energy storage device is determined to adopt a droop control strategy.

[0010] Optionally, when the absolute value of the deviation between the actual value and the rated value of the medium voltage DC bus voltage is between a first value and a second value, determining whether the main converter station adopts a constant voltage or power limiting control strategy according to the transmission power of the main converter station specifically includes:

[0011] If the transmission power of the main converter station is within the first capacity limit range, it is determined that the main converter station adopts a constant voltage control strategy;

[0012] If the transmission power of the main converter station reaches the first capacity limit, it is determined that the main converter station adopts a power limit control strategy.

[0013] Optionally, when the absolute value of the deviation between the actual value and the rated value of the medium voltage DC bus voltage is between a first value and a second value, determining whether to adopt a droop or power limiting control strategy at the slave converter station according to the transmission power of the slave converter station specifically includes:

[0014] If the transmission power of the slave converter station is within the second capacity limit, determining that the slave converter station adopts a droop control strategy;

[0015] If the transmission power of the slave converter station reaches the second capacity limit, it is determined that the slave converter station adopts a power limiting control strategy.

[0016] Optionally, when the absolute value of the deviation between the actual value of the medium voltage DC bus voltage and the rated value is greater than a second value, determining whether the main converter station adopts a constant voltage or power limit control strategy according to the transmission power of the main converter station specifically includes:

[0017] If the transmission power of the main converter station is less than the first capacity limit, determining that the main converter station adopts a constant voltage control strategy;

[0018] If the transmission power of the main converter station reaches the first capacity limit, it is determined that the main converter station adopts a power limit control strategy.

[0019] Optionally, when the absolute value of the deviation between the actual value of the medium voltage DC bus voltage and the rated value is greater than a second value, determining whether the slave converter station adopts a droop or power limiting control strategy according to the transmission power of the slave converter station specifically includes:

[0020] If the transmission power of the slave converter station is less than the second capacity limit, determining to adopt a droop control strategy at the slave converter station;

[0021] If the transmission power of the slave converter station reaches the second capacity limit, it is determined that the slave converter station adopts a power limiting control strategy.

[0022] Optionally, when the absolute value of the deviation between the actual value of the medium voltage DC bus voltage and the rated value is greater than a second value, determining, based on the deviation of the medium voltage DC bus, that the photovoltaic power station adopts a power limiting or maximum power point control strategy specifically includes:

[0023] If the actual value of the medium voltage DC bus is greater than the rated value, the photovoltaic power station is determined to adopt a power limiting control strategy;

[0024] If the actual value of the medium voltage DC bus is less than the rated value, it is determined that the photovoltaic power station adopts the maximum power point control strategy.

[0025] Optionally, the droop control curve of the slave converter station satisfies the following relationship:

[0026]

[0027] Among them, P 2max represents the upper limit of the second capacity limit of the transmission power from the converter station, P 2min Indicates the lower limit of the second capacity limit of the power transmitted from the converter station, U dcLmin Indicates the voltage value of the medium voltage DC bus when the deviation is the negative first value, U dcLmax Indicates the voltage value of the medium voltage DC bus when the deviation is the first positive value, U dcHmin Indicates the voltage value of the medium voltage DC bus when the deviation is the negative second value, U dcHmax Indicates the voltage value of the medium voltage DC bus when the deviation is the second positive value, P2 is the actual transmission power from the converter station; P 2refis the reference transmission power from the converter station; U is the actual value of the medium voltage DC bus voltage.

[0028] Optionally, the droop coefficient of the energy storage device satisfies the following relationship:

[0029]

[0030] Among them, k B Indicates the droop coefficient of the energy storage device, P ref_BES is the reference value of the energy storage device power; P B is the actual transmission value of the energy storage device power, U dcHmin Indicates the voltage value of the medium voltage DC bus when the deviation is the negative second value, U dcHmax The deviation of the medium-voltage DC bus is the second positive value, and U is the actual value of the medium-voltage DC bus voltage.

[0031] In a second aspect, an embodiment of the present invention provides a control device for a medium and low voltage DC power distribution system, comprising:

[0032] at least one processor;

[0033] at least one memory for storing at least one program;

[0034] When the at least one program is executed by the at least one processor, the at least one processor implements the above method.

[0035] In a third aspect, an embodiment of the present invention provides a computer-readable storage medium storing a program executable by a processor, wherein the program executable by the processor executes the above method.

[0036] The implementation of the embodiment of the present invention includes the following beneficial effects: In this embodiment, different control modes are determined according to the deviation between the actual value and the rated value of the medium-voltage DC bus voltage and the transmission power. The control strategies of the converter station photovoltaic power station and the energy storage device are different under different control modes. The control strategy of the main converter station includes a constant voltage or a power limit control strategy, the control strategy of the slave converter station includes a constant power or a power limit control strategy, the control strategy of the photovoltaic power station includes a maximum power point or a power limit control strategy, and the control strategy of the energy storage device includes a constant power or a droop control strategy, thereby fully utilizing the adjustability of the power devices in the system, improving the power balance and voltage stability of the medium-voltage DC bus, and realizing smooth switching of the control mode of the DC power distribution system with access to the photovoltaic power station and the energy storage device. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a structural block diagram of a medium and low voltage DC power distribution system provided by an embodiment of the present invention;

[0038] Figure 2 This is a schematic flow chart of the steps of a control method for a medium and low voltage DC power distribution system provided by an embodiment of the present invention;

[0039] Figure 3 This is an operation curve diagram of various parts of a medium and low voltage DC power distribution system provided by an embodiment of the present invention;

[0040] Figure 4 This is a simulation result of the system operating state when the source and load of a medium and low voltage DC power distribution system continuously fluctuate, provided by an embodiment of the present invention;

[0041] Figure 5 This is a simulation result of the system operating status when the master station exits in a medium and low voltage DC power distribution system provided by an embodiment of the present invention;

[0042] Figure 6 This is a structural block diagram of a control device for a medium and low voltage DC power distribution system provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0043] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The step numbers in the following embodiments are provided for ease of description only and do not limit the order of the steps. The order of execution of the steps in the embodiments can be adaptively adjusted based on the understanding of those skilled in the art.

[0044] In the following description, reference is made to “some embodiments”, which describes a subset of all possible embodiments, but it will be understood that “some embodiments” may be the same subset or different subsets of all possible embodiments and may be combined with each other without conflict.

[0045] In the following description, the terms "first\second\third" are merely used to distinguish similar objects and do not represent a specific ordering of the objects. It is understandable that "first\second\third" can be interchanged with a specific order or sequence where permitted, so that the embodiments of the present invention described herein can be implemented in an order other than that illustrated or described herein.

[0046] Unless otherwise defined, all technical and scientific terms used in the embodiments of the present invention have the same meanings as those commonly understood by those skilled in the art to which the present invention pertains. The terms used in the embodiments of the present invention are for the purpose of describing the embodiments of the present invention only and are not intended to limit the present invention.

[0047] Before further explaining the embodiments of the present invention in detail, the nouns and terms involved in the embodiments of the present invention are explained. The nouns and terms involved in the embodiments of the present invention are subject to the following interpretations.

[0048] In this embodiment, a medium- and low-voltage DC power distribution system includes at least two DC buses of different voltage levels. Among the two DC buses of adjacent voltage levels, the DC bus with a higher voltage is called a medium-voltage DC bus, and the DC bus with a lower voltage level is called a low-voltage DC bus. The medium-voltage DC bus is connected to a photovoltaic power station, an energy storage device, a first load and the low-voltage DC bus through a transformer. The low-voltage DC bus is connected to a second load. Both ends of the medium-voltage DC bus are connected to the AC main grid through converter stations, and the two converter stations are respectively a master converter station or a slave converter station.

[0049] Specifically, see Figure 1 The medium and low voltage DC power distribution and utilization system adopts a two-terminal DC distribution network topology. When one of the converter stations stops operating due to a fault, the other end can continue to supply power without causing all loads to lose power. The medium voltage level is ±10kV and the low voltage level is 750V. The medium and low voltage DC power distribution and utilization system also includes photovoltaic power stations and battery energy storage devices. The photovoltaic array is connected to the medium voltage DC bus through a step-up full-bridge isolation transformer, and the battery energy storage device is connected to the medium voltage DC bus through a Buck-Boost converter to achieve bidirectional power transmission. The first load includes charging pile loads and commercial loads, and the second load includes industrial loads. The converter station includes voltage source converter stations (VSC), namely VSC1 and VSC2. The AC main grid realizes energy supply and transmission with the DC power distribution and utilization system through the VSC converter station.

[0050] See Figure 2 The embodiment of the present invention provides a control method for a medium and low voltage DC power distribution system, comprising the steps of:

[0051] S100: When the absolute value of the deviation between the actual value and the rated value of the medium-voltage DC bus voltage is less than a first value, determine that the master converter station adopts a constant voltage control strategy, determine that the slave converter station adopts a constant power control strategy, determine that the photovoltaic power station adopts a maximum power point control strategy, and determine that the energy storage device adopts a constant power control strategy.

[0052] S200. When the absolute value of the deviation between the actual value and the rated value of the medium-voltage DC bus voltage is between the first value and the second value, determine whether the master converter station adopts a constant voltage or power limit control strategy according to the transmission power of the master converter station, determine whether the slave converter station adopts a droop or power limit control strategy according to the transmission power of the slave converter station, determine whether the photovoltaic power station adopts a maximum power point control strategy, and determine whether the energy storage device adopts a constant power control strategy.

[0053] S300. When the absolute value of the deviation between the actual value and the rated value of the medium-voltage DC bus voltage is greater than a second value, determine whether the master converter station adopts a constant voltage or power limit control strategy according to the transmission power of the master converter station, determine whether the slave converter station adopts a droop or power limit control strategy according to the transmission power of the slave converter station, determine whether the photovoltaic power station adopts a power limit or maximum power point control strategy according to the deviation of the medium-voltage DC bus, and determine whether the energy storage device adopts a droop control strategy.

[0054] Specifically, the calculation formula for the deviation between the actual value and the rated value of the medium voltage DC bus voltage is as follows: Δ=(UU dc ) / U dc , where U represents the actual value of the medium voltage DC bus voltage, U dc represents the rated value of the medium-voltage DC bus voltage, and Δ represents the deviation of the medium-voltage DC bus voltage.

[0055] It should be noted that the specific values ​​of the first value and the second value are determined according to actual applications and are not specifically limited in this embodiment. For example, in this embodiment, the first value is 1% and the second value is 2.5%.

[0056] Specifically, referring to Table 1, different control modes are determined based on the absolute value of the deviation between the actual and rated medium-voltage DC bus voltages, as well as the converter station's transmission power capacity limitations. The two converter stations utilize a master-slave control scheme. In this embodiment, VSC1 serves as the master station, and VSC2 serves as the slave station.

[0057] Table 1

[0058]

[0059] See Figure 3 , Figure 3 (a) represents the system operation characteristics of VSC1, Figure 3 (b) represents the system operation characteristics of VSC2, Figure 3 (c) represents the system operation characteristics of the photovoltaic power station, Figure 3 (d) represents the system operation characteristics of the energy storage device.

[0060] When the system is in control mode 1, the deviation between the actual value of the medium voltage DC bus voltage and the rated value is less than 1%, that is, U is [U dcLmin , U dcLmax ] range, VSC1 and VSC2 adopt the master-slave control method. Among them, VSC1 is the master station, adopts the fixed voltage control strategy, and assumes the voltage regulation role. The reference voltage is the rated value of the medium voltage bus voltage U ref =U dcVSC2 is a slave station and uses a constant power control strategy. The PV power station uses a maximum power point tracking (MPPT) control strategy and operates at the maximum power point of the PV PU curve. The energy storage device uses a constant power control strategy with a power reference value of 0, indicating an idle state.

[0061] When in control mode 2, the deviation between the actual value of the medium voltage DC bus voltage and the rated value is less than 2.5% and greater than 1%, that is, U is [U dcHmin , U dcLmin ] or [U dcLmax , U dcHmax ] range, VSC1 selects a control mode based on whether its own transmission power exceeds its own capacity limit, and VSC2 selects a control mode based on whether its own transmission power exceeds its own capacity limit; the photovoltaic power station adopts the MPPT control strategy; the energy storage device adopts the fixed power control strategy and is in an idle state.

[0062] When in control mode 3, the deviation between the actual value of the medium voltage DC bus voltage and the rated value is greater than 2.5%, that is, U dcHmin orU>U dcHmax ,VSC1 selects the control mode according to whether its own transmission power exceeds its own capacity limit, VSC2 selects the control mode according to whether its own transmission power exceeds its own capacity limit, the photovoltaic power station selects the control mode according to the voltage deviation state, and the energy storage device uniformly adopts the droop control strategy.

[0063] Optionally, when the absolute value of the deviation between the actual value and the rated value of the medium voltage DC bus voltage is between a first value and a second value, determining whether the main converter station adopts a constant voltage or power limiting control strategy according to the transmission power of the main converter station specifically includes:

[0064] S210: If the transmission power of the main converter station is within the first capacity limit range, determine that the main converter station adopts a constant voltage control strategy;

[0065] S220: If the transmission power of the main converter station reaches a first capacity limit, determine that the main converter station adopts a power limit control strategy.

[0066] Specifically, see Figure 3 , if the transmission power P1 of the main converter station is within the capacity range [P 1min , P 1max ], the constant voltage control strategy is adopted; if the transmission power reaches the capacity limit P 1min or P 1max , the power limit control strategy is adopted and the system operates at the power limit P 1min or P 1max .

[0067] ​Optionally, when the absolute value of the deviation between the actual value and the rated value of the medium voltage DC bus voltage is between a first value and a second value, determining whether to adopt a droop or power limiting control strategy at the slave converter station according to the transmission power of the slave converter station specifically includes:

[0068] S230: If the transmission power of the slave converter station is within the second capacity limit, determine that the slave converter station adopts a droop control strategy;

[0069] S240: If the transmission power of the slave converter station reaches a second capacity limit, determine to adopt a power limit control strategy for the slave converter station.

[0070] Specifically, see Figure 3 , if the transmission power P2 from the converter station is within the capacity limit [P 2min , P 2max ], the droop control strategy is adopted to take on the task of controlling the DC voltage; if the transmission power P2 from the converter station reaches the capacity limit, the power limit control strategy is adopted to operate at the power limit P 2min / P 2max .

[0071] Optionally, when the absolute value of the deviation between the actual value of the medium voltage DC bus voltage and the rated value is greater than a second value, determining whether the main converter station adopts a constant voltage or power limit control strategy according to the transmission power of the main converter station specifically includes:

[0072] S310: If the transmission power of the main converter station is less than the first capacity limit, determine that the main converter station adopts a constant voltage control strategy;

[0073] S320: If the transmission power of the main converter station reaches a first capacity limit, determine that the main converter station adopts a power limit control strategy.

[0074] Specifically, see Figure 3 If the transmission power P1 of the main converter station is less than the capacity limit, the constant voltage control strategy is adopted; if the transmission power P1 of the main converter station reaches the capacity limit, the limited power control strategy is adopted and operates at the power limit.

[0075] Optionally, when the absolute value of the deviation between the actual value of the medium voltage DC bus voltage and the rated value is greater than a second value, determining whether the slave converter station adopts a droop or power limiting control strategy according to the transmission power of the slave converter station specifically includes:

[0076] S330: If the transmission power of the slave converter station is less than the second capacity limit, determine that the slave converter station adopts a droop control strategy;

[0077] S340: If the transmission power of the slave converter station reaches a second capacity limit, determine to adopt a power limit control strategy for the slave converter station.

[0078] Specifically, see Figure 3 If the transmission power P2 from the converter station is less than the capacity limit, the droop control strategy is adopted; if the transmission power P2 from the converter station reaches the capacity limit, the power limit control strategy is adopted and operates at the power limit.

[0079] Optionally, when the absolute value of the deviation between the actual value of the medium voltage DC bus voltage and the rated value is greater than a second value, determining, based on the deviation of the medium voltage DC bus, that the photovoltaic power station adopts a power limiting or maximum power point control strategy specifically includes:

[0080] S350: If the actual value of the medium voltage DC bus is greater than the rated value, determine that the photovoltaic power station adopts a power limiting control strategy;

[0081] S360: If the actual value of the medium voltage DC bus is less than the rated value, determine that the photovoltaic power station adopts a maximum power point control strategy.

[0082] Specifically, see Figure 3 If the actual value of the DC bus voltage is greater than the rated value, that is, U>U dc , the power limit control strategy is adopted to limit the photovoltaic output power to P PL , no longer operates at the maximum power point; if the actual value of the DC bus voltage is less than the rated value, the MPPT control strategy is adopted.

[0083] Optionally, the droop control curve of the slave converter station satisfies the following relationship:

[0084]

[0085] Among them, P 2max represents the upper limit of the second capacity limit of the transmission power from the converter station, P 2min Indicates the lower limit of the second capacity limit of the power transmitted from the converter station, U dcLmin Indicates the voltage value of the medium voltage DC bus when the deviation is the negative first value, U dcLmax Indicates the voltage value of the medium voltage DC bus when the deviation is the first positive value, U dcHmin Indicates the voltage value of the medium voltage DC bus when the deviation is the negative second value, U dcHmax Indicates the voltage value of the medium voltage DC bus when the deviation is the second positive value, P2 is the actual transmission power from the converter station; P 2ref is the reference transmission power from the converter station; U is the actual value of the medium voltage DC bus voltage.

[0086] When the converter station VSC2 operates at the power reference value P 2ref When the power supply voltage of the converter station VSC2 is close to the power limit, the droop coefficient is relatively large, and the droop control focuses on reducing voltage fluctuations. ... 2min / P 2max, making the droop coefficient smaller, and the droop control focuses on the power distribution between converter stations.

[0087] Then the droop coefficient is:

[0088]

[0089] Optionally, the droop coefficient of the energy storage device satisfies the following relationship:

[0090]

[0091] Among them, k B Indicates the droop coefficient of the energy storage device, P ref_BES is the reference value of the energy storage device power; P B is the actual transmission value of the energy storage device power, U dcHmin Indicates the voltage value of the medium voltage DC bus when the deviation is the negative second value, U dcHmax The deviation of the medium-voltage DC bus is the second positive value, and U is the actual value of the medium-voltage DC bus voltage.

[0092] In order to verify the effectiveness of the coordinated control method of the embodiment of the present invention, the attached Figure 1 The electromagnetic transient simulation model of the two-terminal flexible DC power distribution system shown in FIG2 has simulation parameters as shown in Appendix 2.

[0093] Table 2

[0094]

[0095] See Figure 4 , Figure 4 The simulation results of the system operation state when the source and load fluctuate continuously in the example application of the present invention are as follows: Figure 4 (a) is the DC bus voltage, Figure 4 (b) is the photovoltaic output, Figure 4 (c) is the output of VSC1, Figure 4 (d) VSC2 is the output. When t=0.6s, the light intensity of the photovoltaic power station changes from 1000W / m2 to 500W / m 2 , recover to 1000W / m at t=1s 2At t=1.3s, the DC load increases by 1.2MW, and at t=1.5s, a 2MW DC load is added. The simulation results show that when the irradiation intensity decreases at t=0.6s, the photovoltaic output drops from 2MW to 1.05MW under the action of MPPT control, causing a slight drop in the bus voltage. At this time, VSC1, as the main converter station, adopts the constant voltage control mode and increases the input power from 1.84MW to 2.71MW to stabilize the DC bus voltage. When the irradiation intensity recovers, the output of the photovoltaic power station and VSC1 also returns to the rated value. When the system adds 1.2MW load at t=1.3s, VSC1 generates 1.2MW of active power to make up for the active power shortage. When the system adds 2MW load at t=1.5s, VSC1 first exerts the constant voltage control effect to increase power, but because the power exceeds the set margin value P 1max =5MW, VSC1 switches to constant power control. At this time, VSC2 switches to droop control, adding 1MW power to maintain bus voltage stability. During the whole process, due to the deviation of DC bus voltage |Δ|≤1%, in [U dcLmin ,U dcLmax ], the energy storage unit does not participate in coordinated control.

[0096] See Figure 5 , Figure 5 This is the simulation result of the system operation status when the master station exits in the example application of the present invention. Figure 5 (a) is the DC bus voltage, Figure 5 (b) output power for the energy storage device, Figure 5 (c) is the output of VSC1, Figure 5 (d) is the output of VSC2, set at t = 1s. VSC1, due to the tripping of the AC-side circuit breaker, ceases power exchange with the AC mains and ceases operation. The simulation results show that VSC1 ceases operation at t = 1s, and its output power drops to zero at t = 1.04s. At this point, the system is connected to the AC grid only by VSC2. At t = 1.02s, the DC voltage drops to 19.5kV, and the converter station's control strategy switches to droop control. Its active power output begins to increase after oscillations. The energy storage unit also switches to droop control, transferring power to the bus. As the energy storage unit's output power increases, the DC voltage drops to a minimum of 18.69kV at t = 1.07s and then gradually recovers. Because the DC bus voltage reaches 19.5kV again at t = 1.21s, the battery energy storage switches back to constant power control. The output power from the converter station continues to increase, eventually stabilizing at 6.8MW. Under the droop control of the converter station, the DC bus voltage steady-state deviation was 0.28 kV. The voltage varied smoothly throughout the coordinated control process, preventing large transient shocks in the system and enabling smooth switching between modes.

[0097] The implementation of the embodiment of the present invention includes the following beneficial effects: In this embodiment, different control modes are determined according to the deviation between the actual value and the rated value of the medium-voltage DC bus voltage and the transmission power. The control strategies of the converter station photovoltaic power station and the energy storage device are different under different control modes. The control strategy of the main converter station includes a constant voltage or a power limit control strategy, the control strategy of the slave converter station includes a constant power or a power limit control strategy, the control strategy of the photovoltaic power station includes a maximum power point or a power limit control strategy, and the control strategy of the energy storage device includes a constant power or a droop control strategy, thereby fully utilizing the adjustability of the power devices in the system, improving the power balance and voltage stability of the medium-voltage DC bus, and realizing smooth switching of the control mode of the DC power distribution system with access to the photovoltaic power station and the energy storage device.

[0098] See Figure 6 The embodiment of the present invention provides a control device for a medium and low voltage DC power distribution system, comprising:

[0099] at least one processor;

[0100] at least one memory for storing at least one program;

[0101] When the at least one program is executed by the at least one processor, the at least one processor implements the above method.

[0102] Among them, the memory is a non-transient computer-readable storage medium that can be used to store non-transient software programs and non-transient computer executable programs. The memory may include a high-speed random access memory and may also include a non-transient memory, such as at least one disk storage device, a flash memory device, or other non-transient solid-state storage device. In some embodiments, the memory optionally includes a remote memory remotely arranged relative to the processor, and these remote memories can be connected to the processor via a network. Examples of the above-mentioned network include but are not limited to the Internet, an intranet, a local area network, a mobile communication network and a combination thereof.

[0103] It can be seen that the contents of the above method embodiments are all applicable to the present device embodiments. The functions specifically implemented by the present device embodiments are the same as those of the above method embodiments, and the beneficial effects achieved are also the same as those achieved by the above method embodiments.

[0104] In addition, the embodiments of the present application further disclose a computer program product or computer program, which is stored in a computer-readable storage medium. The processor of a computer device can read the computer program from the computer-readable storage medium, and the processor executes the computer program, so that the computer device performs the above-mentioned method. Similarly, the contents of the above-mentioned method embodiment are all applicable to the present storage medium embodiment, and the functions specifically implemented by the present storage medium embodiment are the same as those of the above-mentioned method embodiment, and the beneficial effects achieved are also the same as those achieved by the above-mentioned method embodiment.

[0105] It is understood that all or some steps, systems in the disclosed method above can be implemented as software, firmware, hardware and appropriate combinations thereof. Some physical components or all physical components can be implemented as software by a processor, such as a central processing unit, a digital signal processor or a microprocessor, or implemented as hardware, or implemented as an integrated circuit, such as an application specific integrated circuit. Such software can be distributed on a computer-readable medium, and the computer-readable medium can include computer storage media (or non-transitory media) and communication media (or temporary media). As known to those of ordinary skill in the art, the term computer storage medium is included in any method or technology for storing information (such as computer-readable instructions, data structures, program modules or other data) and is volatile and non-volatile, removable and non-removable media. Computer storage media includes but is not limited to RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disk (DVD) or other optical disk storage, magnetic cassette, magnetic tape, disk storage or other magnetic storage device, or can be used to store desired information and any other medium that can be accessed by a computer. Furthermore, as is well known to those skilled in the art, communication media typically embodies computer-readable instructions, data structures, program modules, or other data in a modulated data signal such as a carrier wave or other transport mechanism, and may include any information delivery media.

[0106] The above is a specific description of the preferred implementation of the present invention, but the invention is not limited to the embodiments. Those skilled in the art can make various equivalent modifications or substitutions without violating the spirit of the present invention. These equivalent modifications or substitutions are all included in the scope defined by the claims of this application.

Claims

1. A control method for a medium and low voltage DC power distribution system, characterized in that: The medium- and low-voltage DC power distribution system includes at least two DC buses of different voltage levels. Among the two DC buses of adjacent voltage levels, the high-voltage DC bus is called the medium-voltage DC bus, and the low-voltage DC bus is called the low-voltage DC bus. The medium-voltage DC bus is connected to the photovoltaic power station, the energy storage device, the first load, and the low-voltage DC bus through a transformer. The low-voltage DC bus is connected to the second load. Both ends of the medium-voltage DC bus are connected to the AC main grid through converter stations. The two converter stations are respectively the master converter station or the slave converter station. The control method comprises: When the absolute value of the deviation between the actual value of the medium voltage DC bus voltage and the rated value is less than the first value, the master converter station is determined to adopt a constant voltage control strategy, the slave converter station is determined to adopt a constant power control strategy, the photovoltaic power station is determined to adopt a maximum power point control strategy, and the energy storage device is determined to adopt a constant power control strategy; When the absolute value of the deviation between the actual value and the rated value of the medium voltage DC bus voltage is between the first value and the second value, determining that the master converter station adopts a constant voltage or power limit control strategy according to the transmission power of the master converter station, determining that the slave converter station adopts a droop or power limit control strategy according to the transmission power of the slave converter station, determining that the photovoltaic power station adopts a maximum power point control strategy, and determining that the energy storage device adopts a constant power control strategy; When the absolute value of the deviation between the actual value and the rated value of the medium voltage DC bus voltage is greater than a second value, determining that the master converter station adopts a constant voltage or power limit control strategy based on the transmission power of the master converter station, determining that the slave converter station adopts a droop or power limit control strategy based on the transmission power of the slave converter station, determining that the photovoltaic power station adopts a power limit or maximum power point control strategy based on the deviation of the medium voltage DC bus, and determining that the energy storage device adopts a droop control strategy; The droop control curve of the converter station satisfies the following relationship: Among them, P 2max represents the upper limit of the second capacity limit of the transmission power from the converter station, P 2min Indicates the lower limit of the second capacity limit of the power transmitted from the converter station, U dcLmin Indicates the voltage value of the medium voltage DC bus when the deviation is the negative first value, U dcLmax Indicates the voltage value of the medium voltage DC bus when the deviation is the first positive value, U dcHmin Indicates the voltage value of the medium voltage DC bus when the deviation is the negative second value, U dcHmax Indicates the voltage value of the medium voltage DC bus when the deviation is the second positive value, P2 is the actual transmission power from the converter station; P 2ref is the reference transmission power from the converter station; U is the actual value of the medium voltage DC bus voltage.

2. The control method according to claim 1, characterized in that: When the absolute value of the deviation between the actual value and the rated value of the medium voltage DC bus voltage is between the first value and the second value, determining whether the main converter station adopts a constant voltage or power limit control strategy according to the transmission power of the main converter station specifically includes: If the transmission power of the main converter station is within the first capacity limit range, it is determined that the main converter station adopts a constant voltage control strategy; If the transmission power of the main converter station reaches the first capacity limit, it is determined that the main converter station adopts a power limit control strategy.

3. The control method according to claim 1, wherein: When the absolute value of the deviation between the actual value and the rated value of the medium voltage DC bus voltage is between the first value and the second value, determining whether the slave converter station adopts a droop or power limit control strategy according to the transmission power of the slave converter station specifically includes: If the transmission power of the slave converter station is within the second capacity limit, determining that the slave converter station adopts a droop control strategy; If the transmission power of the slave converter station reaches the second capacity limit, it is determined that the slave converter station adopts a power limiting control strategy.

4. The control method according to claim 1, wherein: When the absolute value of the deviation between the actual value of the medium voltage DC bus voltage and the rated value is greater than the second value, determining whether the main converter station adopts a constant voltage or power limit control strategy according to the transmission power of the main converter station specifically includes: If the transmission power of the main converter station is less than the first capacity limit, determining that the main converter station adopts a constant voltage control strategy; If the transmission power of the main converter station reaches the first capacity limit, it is determined that the main converter station adopts a power limit control strategy.

5. The control method according to claim 1, characterized in that: When the absolute value of the deviation between the actual value of the medium voltage DC bus voltage and the rated value is greater than the second value, determining whether the slave converter station adopts a droop or power limit control strategy according to the transmission power of the slave converter station, specifically including: If the transmission power of the slave converter station is less than the second capacity limit, determining to adopt a droop control strategy at the slave converter station; If the transmission power of the slave converter station reaches the second capacity limit, it is determined that the slave converter station adopts a power limiting control strategy.

6. The control method according to claim 1, characterized in that: When the absolute value of the deviation between the actual value of the medium-voltage DC bus voltage and the rated value is greater than the second value, determining whether the photovoltaic power station adopts a power limiting or maximum power point control strategy based on the deviation of the medium-voltage DC bus, specifically including: If the actual value of the medium voltage DC bus is greater than the rated value, the photovoltaic power station is determined to adopt a power limiting control strategy; If the actual value of the medium voltage DC bus is less than the rated value, it is determined that the photovoltaic power station adopts the maximum power point control strategy.

7. The control method according to claim 1, characterized in that: The droop coefficient of the energy storage device satisfies the following relationship: Among them, k B Indicates the droop coefficient of the energy storage device, P ref_BES is the reference value of the energy storage device power; P B is the actual transmission value of the energy storage device power, U dcHmin Indicates the voltage value of the medium voltage DC bus when the deviation is the negative second value, U dcHmax The deviation of the medium-voltage DC bus is the second positive value, and U is the actual value of the medium-voltage DC bus voltage.

8. A control device for a medium and low voltage DC power distribution system, characterized in that: include: at least one processor; at least one memory for storing at least one program; When the at least one program is executed by the at least one processor, the at least one processor implements the method according to any one of claims 1 to 7.

9. A computer-readable storage medium storing a program executable by a processor, characterized in that: The processor-executable program is used to perform the method according to any one of claims 1 to 7 when executed by the processor.

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