New energy flexible direct current output system

Abstract

The invention discloses a new energy flexible direct current output system, which comprises a power generation end, an energy storage unit, a sending end converter and a receiving end converter, and is characterized in that the energy storage unit is composed of a plurality of sub-modules, and each sub-module comprises a half-bridge unit and an energy storage element; the transmitting-end converter comprises an alternating-current end and a direct-current end, the alternating-current end is connected with the first alternating-current line, and the direct-current end is connected with the receiving-end converter through the direct-current line; the receiving-end current converter is connected with a receiving-end power grid through a second alternating-current line, and the receiving-end current converter is used for receiving the direct current output by the sending-end current converter, converting the direct current into alternating current and sending the alternating current to the receiving-end power grid; the power generation end is connected with the first alternating current line, and the power generation end and the sending end converter or the receiving end converter are respectively connected with the energy storage unit. According to the system, energy storage is configured in the system, so that wind and light output fluctuation can be effectively smoothed, the new energy utilization rate is improved, and the stable operation interval of the system can be effectively improved on the basis of ensuring safe access of wind, light and the like and system stability.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible direct current (DC) in power systems, and in particular to a new energy flexible DC output system. Background Art

[0002] my country has begun to vigorously promote the use of new energy sources such as solar energy and onshore wind power, and actively develop offshore wind power. However, new energy power generation is often unpredictable, has small flow, and is relatively scattered. Especially for offshore wind power, offshore wind farms are far away from the land, and the loss is too large using ordinary transmission methods. Although there are many of them, they are small in scale, mostly in the millions of megawatts level. Therefore, flexible direct current transmission is the best way to connect offshore wind farms to the grid. Flexible direct current transmission technology has large transmission capacity, low loss, long service life, and basically no transmission distance restrictions on submarine cable lines. It can effectively solve the problem of large-capacity and long-distance transmission of offshore wind farms, and is of great significance to the future development and construction of concentrated and contiguous offshore wind power and large-capacity offshore wind power in my country.

[0003] Flexible direct current with access to new energy is an important means and development direction for building a new type of power system in the future. New energy sources such as wind and solar energy are geographically unevenly distributed and difficult to dispatch flexibly. In addition, the power generation is random and volatile. A high proportion of new energy access will pose a major challenge to the safe and stable operation of the power grid. There are the following technical difficulties in the flexible direct current system with access to new energy: 1) The power volatility and randomness of new energy are serious, making it difficult to meet the power system's demand for stable output; 2) When the AC access system fails, the power channel is blocked, causing serious temporary power surplus problems, resulting in a high risk of system failure; 3) When the new energy field fails, the connected AC system faces serious power shocks, endangering system stability. Summary of the invention

[0004] In order to solve the above technical problems, an embodiment of the present invention provides a new energy flexible direct current output system. By configuring an energy storage unit, it can effectively smooth out the fluctuations in wind and solar power output and improve the utilization rate of new energy. On the basis of ensuring the safe access of wind, light, etc. and the stability of the system, it can effectively improve the stable operation range of the system.

[0005] The embodiment of the present invention provides a new energy flexible direct current output system, including a power generation end, an energy storage unit, a sending-end converter and a receiving-end converter, wherein:

[0006] The energy storage unit is composed of multiple sub-modules, which include a half-bridge unit and an energy storage element;

[0007] The sending-end converter includes an AC end and a DC end, the AC end is connected to the first AC line, and the DC end is connected to the receiving-end converter through the DC line. The sending-end converter is used to receive the AC power output by the generating end, and convert the AC power into DC power and send it to the receiving-end converter;

[0008] The receiving-end converter is connected to the receiving-end power grid through the second AC line, and the receiving-end converter is used to receive the DC power output by the sending-end converter, and convert the DC power into AC power and send it to the receiving-end power grid;

[0009] The power generation end is connected to the first AC line, and the power generation end, the sending end converter or the receiving end converter are respectively connected to the energy storage unit.

[0010] In a possible implementation of this embodiment, the half-bridge unit includes a first power switch device and a second power switch device;

[0011] The half-bridge unit is connected to the energy storage element, and is used to output the energy in the energy storage element by controlling the on and off of the first power switch device and the second power switch device.

[0012] In a possible implementation of this embodiment, the submodules are connected in series.

[0013] In a possible implementation of this embodiment, controlling the on and off of the first power switch device and the second power switch device includes:

[0014] When the first power switch device is turned on and the second power switch device is turned off, the submodule is in the on state;

[0015] When the first power switch device is turned off and the second power switch device is turned on, the submodule is in a cut-off state;

[0016] When the first power switch device is turned off and the second power switch device is turned off, the submodule is in a locked state.

[0017] In a possible implementation of this embodiment, the power generation end, the sending end converter or the receiving end converter are respectively connected to the energy storage unit, including:

[0018] The energy storage unit is connected to the power generation end through the first AC line, and is used to realize independent exchange of active power and reactive power of the receiving end power grid through PQ decoupling control;

[0019] Or the energy storage unit is connected to the DC terminal of the sending-end converter through a DC line to realize direct collection and direct control of the DC power output by the sending-end converter;

[0020] Or the energy storage unit is connected to the receiving-end converter through the DC side bus to improve the fault ride-through capability of the new energy through the flexible DC output system.

[0021] In a possible implementation of this embodiment, the energy storage unit is connected to the DC end of the sending-end converter via a DC line, and is also used to input the stored power resources into the receiving-end power grid during peak power consumption hours;

[0022] In a possible implementation of this embodiment, the energy storage unit is connected to the DC end of the sending-end converter via a DC line, and is also used to achieve active support, reactive support, and frequency and voltage regulation.

[0023] In a possible implementation of this embodiment, the energy storage unit is connected to the DC end of the sending-end converter through a DC line, and is also used to achieve peak shaving and valley filling, active power support, reactive power support, and frequency and voltage regulation.

[0024] In a possible implementation of this embodiment, the energy storage element is a battery or a capacitor.

[0025] In a possible implementation of this embodiment, the power generation end is a new energy power generation group.

[0026] Compared with the prior art, the beneficial effects of the present invention are:

[0027] The new energy flexible direct current output system provided by the embodiment of the present invention includes a power generation end, an energy storage unit, a sending end converter, a receiving end converter and a receiving end power grid, the energy storage unit is composed of multiple submodules, and the submodules include a half-bridge unit and an energy storage element; the sending end converter includes an AC end and a DC end, the AC end is connected to the first AC line, the DC end is connected to the receiving end converter through the DC line, the sending end converter is used to receive the AC power output by the power generation end, and convert the AC power into DC power and send it to the receiving end converter; the receiving end converter is connected to the receiving end power grid through the second AC line, and the receiving end converter is used to receive the DC power output by the sending end converter, and convert the DC power into AC power and send it to the receiving end power grid; the power generation end is connected to the first AC line, and the power generation end, the sending end converter or the receiving end converter are respectively connected to the energy storage unit. The above system can effectively smooth the fluctuation of wind and solar power output and improve the utilization rate of new energy by configuring energy storage in the system. On the basis of ensuring the safe access of wind, light and other sources and the stability of the system, it can effectively improve the stable operation range of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 A schematic diagram of system topology of an embodiment of a new energy flexible direct current output system provided by the present invention;

[0029] Figure 2 A topological diagram of an energy storage unit of an embodiment of a new energy flexible direct current output system provided by the present invention;

[0030] Figure 3 A first system topology diagram of an embodiment of a new energy flexible direct current output system provided by the present invention;

[0031] Figure 4 A second system topology diagram of an embodiment of a new energy flexible direct current output system provided by the present invention;

[0032] Figure 5 This is a third system topology diagram of an embodiment of the new energy flexible direct current output system provided by the present invention. DETAILED DESCRIPTION

[0033] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] It should be understood that the step numbers used in this document are only for convenience of description and are not intended to limit the order in which the steps are executed.

[0035] It should be understood that the terms used in the present specification are only for the purpose of describing specific embodiments and are not intended to limit the present invention. As used in the present specification and the appended claims, unless the context clearly indicates otherwise, the singular forms "a", "an" and "the" are intended to include plural forms.

[0036] The terms “include” and “comprising” indicate the presence of described features, integers, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or combinations thereof.

[0037] The term "and / or" means and includes any and all possible combinations of one or more of the associated listed items.

[0038] See also Figure 1 A certain embodiment of the present invention provides a new energy flexible direct current output system. Figure 1 As shown, it includes a power generation end, an energy storage unit, a sending-end converter and a receiving-end converter, wherein:

[0039] The energy storage unit is composed of multiple sub-modules, which include a half-bridge unit and an energy storage element;

[0040] The sending-end converter includes an AC end and a DC end, the AC end is connected to the first AC line, and the DC end is connected to the receiving-end converter through the DC line. The sending-end converter is used to receive the AC power output by the generating end, and convert the AC power into DC power and send it to the receiving-end converter;

[0041] The receiving-end converter is connected to the receiving-end power grid through the second AC line, and the receiving-end converter is used to receive the DC power output by the sending-end converter, and convert the DC power into AC power and send it to the receiving-end power grid;

[0042] The power generation end is connected to the first AC line, and the power generation end, the sending end converter or the receiving end converter are respectively connected to the energy storage unit.

[0043] In this embodiment, if Figure 1 As shown, the system includes a power generation end, an energy storage unit, a sending-end flexible DC converter, a receiving-end flexible DC converter and a receiving-end power grid, wherein the energy storage unit is composed of multiple sub-modules, each of which includes a half-bridge unit and an energy storage element, such as Figure 2 shown.

[0044] The sending-end converter is the sending-end flexible DC converter. The sending-end flexible DC converter includes an AC end and a DC end. The AC end is connected to the AC line, and the DC end is connected to the receiving-end flexible DC converter through the DC line. The sending-end flexible DC converter is used to receive the AC power output by the power generation end, and convert the AC power into DC power and send it to the receiving-end flexible DC converter.

[0045] The receiving-end flexible DC converter is connected to the receiving-end AC grid through an AC line. The receiving-end flexible DC converter is used to receive the DC power output by the sending-end flexible DC converter and convert the DC power into AC power and send it to the receiving-end grid. The generating end is connected to the first AC line, and the generating end, the sending-end flexible DC converter or the receiving-end flexible DC converter can be connected to the energy storage unit respectively.

[0046] It should be noted that the sending-end converter is the sending-end flexible DC converter; the receiving-end AC power grid is the receiving-end power grid; and the receiving-end converter is the receiving-end flexible DC converter.

[0047] In one embodiment, the half-bridge unit includes a first power switch device and a second power switch device;

[0048] The half-bridge unit is connected to the energy storage element, and is used to output the energy in the energy storage element by controlling the on and off of the first power switch device and the second power switch device.

[0049] In one embodiment, the submodules are connected in series.

[0050] In one embodiment, controlling the on and off of the first power switch device and the second power switch device includes:

[0051] When the first power switch device is turned on and the second power switch device is turned off, the submodule is in the on state;

[0052] When the first power switch device is turned off and the second power switch device is turned on, the submodule is in a cut-off state;

[0053] When the first power switch device is turned off and the second power switch device is turned off, the submodule is in a locked state.

[0054] In one embodiment, the energy storage element is a battery or a capacitor.

[0055] In this embodiment, if Figure 2 , Figure 2 The topology diagram of the energy storage unit. The unit is composed of N submodules connected in series. Each submodule consists of a half-bridge power unit and an energy storage element. The energy storage element can be a capacitor, battery or other element with energy storage capacity. According to the conduction state of the upper and lower tubes of the half-bridge power unit, the energy storage unit submodule can have three operating states: when the upper tube is turned on and the lower tube is turned off, the submodule is in the on state; when the upper tube is turned off and the lower tube is turned on, the submodule is in the off state; when both the upper tube and the lower tube are turned off, the submodule is in the locked state. The switching of the submodules in the energy storage unit can be controlled by the system operating state to quickly respond to changes in system power, so as to improve the stable operation range of the system.

[0056] It should be noted that the upper and lower tubes refer to power switching devices. The drain (D) of the upper tube is connected to the positive pole of the power supply (Vcc), the source (S) is connected to the drain of the lower tube, and the source of the lower tube is connected to the negative pole of the power supply (ground, GND). The upper and lower tubes are alternately turned on to achieve the output of alternating current.

[0057] In one embodiment, the power generation end, the sending end converter or the receiving end converter are respectively connected to the energy storage unit, including:

[0058] The energy storage unit is connected to the power generation end through the first AC line, and is used to realize independent exchange of active power and reactive power of the receiving end power grid through PQ decoupling control;

[0059] Or the energy storage unit is connected to the DC terminal of the sending-end converter through a DC line to realize direct collection and direct control of the DC power output by the sending-end converter;

[0060] Or the energy storage unit is connected to the receiving-end converter through the DC side bus to improve the fault ride-through capability of the new energy through the flexible DC output system.

[0061] In one embodiment, the power generation end is a new energy power generation group.

[0062] In this embodiment, if Figure 3 As shown, Figure 3This is the first system topology diagram of the output of new energy via flexible DC. The new energy generator set is connected to the AC line, the energy storage unit is connected to the AC line, the AC end of the sending-end flexible DC converter is connected to the AC line, the DC end is connected to the receiving-end flexible DC converter through the DC line, and the receiving-end flexible DC converter is connected to the AC grid through the AC bus to send out the new energy power. In this topology, the energy storage unit is directly connected to the AC bus / line, and the resulting AC energy storage unit adopts PQ decoupling control, which can realize independent exchange of active and reactive power with the grid.

[0063] like Figure 4 As shown, Figure 4 This is the second system topology diagram of new energy output via flexible DC. The new energy generator set is connected to the AC line, the AC end of the flexible DC converter at the sending end is connected to the AC line, the DC end is connected to the DC energy storage unit through the DC line, and then the flexible DC converter at the receiving end is connected to the AC grid through the AC bus to send out the new energy power. In this topology, all controls are DC quantities, which can achieve direct acquisition and direct control without the need for phase-locked loops and other links. The flexible DC converter connected to the DC bus can achieve functions including peak shaving and valley filling, active / reactive support, and frequency and voltage regulation.

[0064] like Figure 5 As shown, Figure 5 This is the third system topology diagram of the output of new energy via flexible DC. The new energy generator set is connected to the AC line, the AC end of the sending-end flexible DC converter is connected to the AC line, the DC end is connected to the receiving-end flexible DC converter through the DC line, the DC energy storage unit is connected to the DC side bus of the receiving-end flexible DC converter, and the receiving-end flexible DC converter is connected to the AC grid through the AC bus to send out the new energy power. Connecting the energy storage unit to the receiving-end flexible DC converter can improve the fault ride-through capability of the flexible DC system with large-scale new energy access, and effectively improve the economic efficiency of the flexible DC transmission project with offshore wind power and photovoltaic access.

[0065] It should be noted that the power generation end is a new energy generator set, which is a combination of equipment that converts renewable energy or new energy into electrical energy, such as wind generator sets, solar generator sets, biomass generator sets, etc.

[0066] In one embodiment, the energy storage unit is connected to the DC end of the sending-end converter via a DC line, and is also used to achieve active support, reactive support, and frequency and voltage regulation.

[0067] In one embodiment, the energy storage unit is connected to the DC end of the sending-end converter via a DC line, and is also used to achieve peak shaving and valley filling, active power support, reactive power support, and frequency and voltage regulation.

[0068] In the second system topology of the flexible direct current output of new energy in this embodiment, by connecting the energy storage unit to the DC end of the flexible direct current converter at the sending end, the control is all DC quantity, which can realize direct acquisition and direct control without the need for phase-locked loop and other links. In conjunction with the flexible direct current converter of the connected DC bus, it can realize functions including peak shaving and valley filling, active / reactive support, and frequency and voltage regulation.

[0069] The present invention provides a new energy flexible direct current output system, which can effectively smooth out wind and solar power output fluctuations by optimizing the system topology. Photovoltaic, wind turbine and other new energy sources experience output power fluctuations as the environment changes. The new energy flexible direct current transmission system containing energy storage can adaptively output or absorb power, smooth out wind and solar power output fluctuations, and improve the stable operation range of the system. It has great practical value and broad application prospects in the field of offshore wind, solar, energy storage and flexible direct current transmission.

[0070] Energy storage technology is the key technology support point for the construction of new power systems in the future. It can effectively solve the intermittent and volatile problems of renewable energy power generation, realize frequency and peak regulation of large power grids, friendly grid connection of wind and solar power sources, support microgrid operation and user demand-side response, which has far-reaching significance. The use of energy storage technology in the new energy via flexible DC output system can effectively realize the friendly access and coordinated control of renewable energy. Energy storage technology mainly studies the use of energy storage systems to convert electrical energy into chemical energy, potential energy, electromagnetic energy and other forms for storage, and reconverts it into electrical energy for release when needed. By configuring energy storage in the new energy via flexible DC transmission system, the fluctuation of wind and solar output can be effectively smoothed, the utilization rate of new energy can be improved, and the stable operation range of the system can be effectively improved on the basis of ensuring the safe access of wind, light and other sources and the stability of the system. Therefore, energy storage has broad application prospects in the scenario of new energy via flexible DC transmission.

[0071] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0072] The specific embodiments described above further describe the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. It is particularly pointed out that for those skilled in the art, any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the scope of protection of the present invention.

Claims

1. A new energy flexible direct current output system, characterized in that: It includes a power generation end, an energy storage unit, a sending-end converter and a receiving-end converter, among which: The energy storage unit is composed of a plurality of submodules, each of which includes a half-bridge unit and an energy storage element; The sending-end converter includes an AC end and a DC end, wherein the AC end is connected to a first AC line, and the DC end is connected to a receiving-end converter via a DC line. The sending-end converter is used to receive the AC power output by the generating end, and convert the AC power into DC power and send it to the receiving-end converter; The receiving-end converter is connected to the receiving-end power grid via a second AC line, and the receiving-end converter is used to receive the DC power output by the sending-end converter, and convert the DC power into AC power and send it to the receiving-end power grid; The power generation end is connected to the first AC line, and the power generation end, the sending-end converter or the receiving-end converter are respectively connected to the energy storage unit.

2. The new energy flexible direct current output system according to claim 1, characterized in that: The half-bridge unit includes a first power switch device and a second power switch device; The half-bridge unit is connected to the energy storage element, and is used to output the energy in the energy storage element by controlling the on and off of the first power switch device and the second power switch device.

3. The new energy flexible direct current output system according to claim 1, characterized in that: The submodules are connected in series.

4. The new energy flexible direct current output system as claimed in claim 2, characterized in that: The controlling the on and off of the first power switch device and the second power switch device comprises: When the first power switch device is turned on and the second power switch device is turned off, the submodule is in an on state; When the first power switch device is turned off and the second power switch device is turned on, the submodule is in a cut-off state; When the first power switch device is turned off and the second power switch device is turned off, the submodule is in a locked state.

5. The new energy flexible direct current output system according to claim 1, characterized in that: The power generation end, the sending end converter or the receiving end converter are respectively connected to the energy storage unit, including: The energy storage unit is connected to the power generation end through the first AC line, and is used to realize independent exchange of active power and reactive power of the receiving-end power grid through PQ decoupling control; Or the energy storage unit is connected to the DC terminal of the sending-end converter through a DC line, so as to directly collect and directly control the DC power output by the sending-end converter; Or the energy storage unit is connected to the receiving-end converter via a DC side bus, so as to improve the fault ride-through capability of the new energy through the flexible DC output system.

6. The new energy flexible direct current output system as claimed in claim 5, characterized in that: Also includes: The energy storage unit is connected to the DC end of the sending-end converter via a DC line, and is also used to input the stored power resources into the receiving-end power grid during peak power consumption hours.

7. The new energy flexible direct current output system as claimed in claim 5, characterized in that: Also includes: The energy storage unit is connected to the DC end of the sending-end converter via a DC line, and is also used to achieve active support, reactive support, and frequency and voltage regulation.

8. The new energy flexible direct current output system as claimed in claim 5, characterized in that: Also includes: The energy storage unit is connected to the DC end of the sending-end converter via a DC line, and is also used to achieve peak shaving and valley filling, active power support, reactive power support, and frequency and voltage regulation.

9. The new energy flexible direct current output system according to claim 1, characterized in that: The energy storage element is a battery or a capacitor.

10. The new energy flexible direct current output system according to claim 1, characterized in that: The power generation end is a new energy power generation group.

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