Offshore multi-energy direct-current series collection system and coordination control method

Abstract

The invention discloses an offshore multi-energy direct current series collection system and a coordination control method, and belongs to the technical field of power electronics. The system comprises a plurality of collection modules, a voltage-sharing conversion module and a receiving end flexible direct current conversion module; the collection module comprises a plurality of renewable energy power generation units which are connected in parallel; the voltage-sharing current conversion module comprises a plurality of voltage source current converters, the direct current sides of the voltage source current converters are connected with the collecting module in parallel and then connected with the receiving end flexible direct current current conversion module in series, and the alternating current sides of all the voltage source current converters are connected with an alternating current bus; the collection module is used for collecting the renewable energy units and providing corresponding fault removal and energy consumption functions; the voltage-sharing conversion module is used for carrying out voltage-sharing control on the direct-current voltage output by each collection module; and the receiving end flexible direct current conversion module is used for controlling the direct current voltage of the high-voltage side to be constant, so that the problem that the direct current voltage cannot be constant in the prior art can be solved.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, and in particular to a marine multi-energy DC series collection system and a coordinated control method. Background Technology

[0002] The development of offshore renewable energy has effectively alleviated the limitations of onshore energy development and contributed to the goal of "carbon peaking and carbon neutrality." Currently, offshore wind power has been developed on a large scale, but at present, it mainly relies on AC aggregation. With the gradual increase in wind turbine capacity and the continuous expansion of AC aggregation systems, large-scale offshore wind power aggregation in weak AC systems carries the risk of instability. DC series aggregation can overcome the risk of synchronous instability under weak AC system connections, and can simultaneously aggregate multiple types of renewable energy such as wind and solar power. In particular, it can be considered for the simultaneous deployment of wind, solar, and wave power in the same sea area, thereby achieving high power density aggregation in a single sea area.

[0003] However, the current DC series aggregation topology for multiple energy sources at sea is not yet mature. The current technology is limited to the full DC grid control technology for offshore wind power. Under the DC series aggregation of wind power, the voltage of each series unit is determined by the output power and DC current, which cannot achieve constant DC voltage and cannot achieve full DC voltage equalization aggregation of multiple energy sources in a specific sea area. Summary of the Invention

[0004] This invention provides a multi-energy DC series collection system and coordinated control method for marine applications, which can solve the problem that in the prior art, the voltage of each series unit in the wind power DC series collection system is determined by the output power and DC current, making it impossible to achieve constant DC voltage and achieve multi-energy full DC voltage equalization collection in a specific sea area.

[0005] To address the aforementioned technical problems, embodiments of the present invention provide a marine multi-energy DC series collection system, comprising: several collection modules, a voltage equalization converter module, and a receiving-end flexible DC converter module;

[0006] The aggregation module includes several renewable energy power generation units, and the renewable energy power generation units within the same aggregation module are connected in parallel;

[0007] The voltage equalization converter module includes several voltage source converters. The DC side of each voltage source converter is connected in parallel with a collection module, and the AC side of all voltage source converters is connected to the AC bus.

[0008] After the DC side of the voltage source converter is connected in parallel with the collection module, it is connected in series with the receiving-end flexible DC converter module through a submarine cable;

[0009] The collection module is used to connect and collect renewable energy power generation units in parallel and output the corresponding DC voltage;

[0010] The voltage equalization converter module is used to perform voltage equalization control on the DC voltage output by each collection module according to the voltage source converter and the preset voltage equalization control strategy.

[0011] The receiving-end flexible DC converter module is used to control the DC voltage on the high-voltage side to remain constant.

[0012] As a preferred embodiment, the voltage equalization control strategy includes: a DC voltage synchronization control strategy, a grid-based DC voltage droop control strategy, and a DC voltage droop control strategy based on virtual oscillation.

[0013] As a preferred embodiment, when the voltage equalization control strategy is a DC voltage synchronization control strategy, the voltage equalization control of the DC voltage output by each collection module includes:

[0014] The corresponding frequency phase is generated based on the DC voltage synchronization control loop;

[0015] The first equalizing converter modulation coefficient is generated based on the frequency phase and voltage-current inner loop, and then the DC voltage output by each collection module is equalized based on the first equalizing converter modulation coefficient.

[0016] As a preferred embodiment, the frequency phase is generated in the following manner:

[0017]

[0018] Where, k dch k dc and τ dc These represent the high-pass gain, steady-state gain, and time constant of the voltage synchronization controller, respectively; k uq With τ uq They are respectively hybrid synchronous controller G uq Steady-state gain and time constant; u dc and u dcref These represent the actual DC voltage value and the DC voltage reference value, respectively; s is the Laplace operator; θ s For the generated frequency phase; u dref u d and u q These represent the d-axis voltage reference, the actual d-axis voltage value, and the actual q-axis voltage value, respectively.

[0019] As a preferred embodiment, when the voltage equalization control strategy is a grid-based DC voltage droop control strategy, the voltage equalization control of the DC voltage output by each collecting module includes:

[0020] A corresponding DC voltage deviation reference value is generated based on the frequency deviation of the phase-locked loop;

[0021] Based on the DC voltage deviation reference value, the DC voltage outer loop, and the AC voltage amplitude outer loop, a corresponding current reference is generated;

[0022] Based on the current reference and the phase-locked loop phase, a corresponding second voltage equalization converter modulation coefficient is generated, and then the DC voltage output by each collection module is controlled for voltage equalization based on the second voltage equalization converter modulation coefficient.

[0023] As a preferred embodiment, the DC voltage reference deviation value is generated in the following manner:

[0024]

[0025] Where, τ dc Δω is the time constant; Δω is the frequency deviation of the phase-locked loop; Δu dcref This is the reference deviation value for DC voltage.

[0026] As a preferred embodiment, when the voltage equalization control strategy is a DC voltage droop control strategy based on virtual oscillation, the voltage equalization control of the DC voltage output by each collection module includes:

[0027] Based on the output AC current of the voltage equalization converter and the virtual oscillation controller, the corresponding virtual inductor current and virtual capacitor voltage are generated.

[0028] Based on the virtual inductor current and virtual capacitor voltage, a corresponding third voltage equalization converter modulation coefficient is generated, and then the DC voltage output by each collection module is controlled by the third voltage equalization converter modulation coefficient.

[0029] As a preferred embodiment, the output voltage of the virtual oscillation controller is generated in the following manner:

[0030]

[0031] Where, k pac and k iac These are the voltage amplitudes PI ac The proportional and integral coefficients of the controller; U ref and U mag These are the voltage amplitude reference and the actual voltage amplitude, respectively; v c and i L These represent the capacitor voltage and the inductor current, respectively; k i ∠φ and ∠φ are respectively the current i of the converter filter inductor. Labc The feedback gain and phase; e is the output voltage of the virtual oscillation controller; C is the transformation matrix from two-phase stationary coordinates to three-phase stationary coordinates (abc); V k is the oscillation frequency. v This is the output gain.

[0032] As a preferred embodiment, the renewable energy power generation unit includes: a DC wind turbine power generation unit, a photovoltaic power generation unit, and a wave energy power generation unit;

[0033] The DC wind turbine power generation unit, photovoltaic power generation unit, and wave energy power generation unit are connected in parallel.

[0034] Based on the above embodiments, another embodiment of the present invention provides a coordinated control method for multi-energy DC series aggregation at sea, applicable to the multi-energy DC series aggregation system described in the above embodiments;

[0035] The marine multi-energy DC series collection system includes: several collection modules, a voltage equalization converter module, and a receiving-end flexible DC converter module;

[0036] The aggregation module includes several renewable energy power generation units, and the renewable energy power generation units within the same aggregation module are connected in parallel;

[0037] The voltage equalization converter module includes several voltage source converters. The DC side of each voltage source converter is connected in parallel with a collection module, and the AC side of all voltage source converters is connected to the AC bus.

[0038] After the DC side of the voltage source converter is connected in parallel with the collection module, it is connected in series with the receiving-end flexible DC converter module through a submarine cable;

[0039] The aforementioned multi-energy DC series collection and coordinated control method for marine applications includes:

[0040] The collection module connects and aggregates renewable energy power generation units in parallel to output the corresponding DC voltage.

[0041] Through the voltage equalization converter module, the DC voltage output by each collection module is controlled to be equalized according to the voltage source converter and the preset voltage equalization control strategy.

[0042] The DC voltage on the high-voltage side is kept constant by controlling the receiving-end flexible DC converter module.

[0043] Compared with the prior art, the embodiments of the present invention have the following beneficial effects:

[0044] This invention provides a marine multi-energy DC series collection system, comprising: several collection modules, a voltage equalization converter module, and a receiving-end flexible DC converter module; each collection module includes several renewable energy power generation units, which are connected in parallel within the same collection module; each voltage equalization converter module includes several voltage source converters, with the DC side of each voltage source converter connected in parallel with a collection module, and the AC side of all voltage source converters connected to an AC bus; after the DC side of the voltage source converters is connected in parallel with the collection module, it is connected in series with the receiving-end flexible DC converter module via a submarine cable; the collection module is used to collect the renewable energy power generation units in parallel and output corresponding DC voltages; the voltage equalization converter module is used to perform voltage equalization control on the DC voltage output by each collection module according to the voltage source converters and a preset voltage equalization control strategy; the receiving-end flexible DC converter module is used to control the DC voltage on the high-voltage side to be constant. As can be seen, by setting up a voltage equalization converter module to control the DC voltage output by each collection module, the present invention can achieve constant DC voltage and realize multi-energy full DC voltage equalization collection in a specific sea area. Attached Figure Description

[0045] Figure 1 This is a schematic diagram of the structure of a marine multi-energy DC series collection system provided in an embodiment of the present invention;

[0046] Figure 2 This is a control diagram illustrating three coordinated pressure equalization control strategies;

[0047] Figure 3 This is a schematic diagram of a simulation model of three collection modules connected in DC series;

[0048] Figure 4 It is a simulation waveform diagram of three DC-DC series-connected modules;

[0049] Figure 5 This is a schematic flowchart of a multi-energy DC series collection and coordinated control method for marine applications, provided by an embodiment of the present invention. Detailed Implementation

[0050] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0051] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0052] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0053] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0054] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0055] In the description of the embodiments of this application, the terms "multiple" and "several" refer to two or more (including two), similarly, "multiple groups" refer to two or more (including two groups), and "multiple pieces" refer to two or more (including two pieces).

[0056] In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0057] Example 1

[0058] Please refer to Figure 1To address the problem that in existing technologies, the voltage of each series unit in a wind power DC series aggregation system is determined by the output power and DC current, making it impossible to achieve constant DC voltage and achieve multi-energy DC voltage equalization aggregation for specific sea areas, an embodiment of the present invention provides a structural schematic diagram of a marine multi-energy DC series aggregation system, including: several aggregation modules, a voltage equalization converter module, and a receiving-end flexible DC converter module.

[0059] The aggregation module includes several renewable energy power generation units, and the renewable energy power generation units within the same aggregation module are connected in parallel;

[0060] The voltage equalization converter module includes several voltage source converters. The DC side of each voltage source converter is connected in parallel with a collection module, and the AC side of all voltage source converters is connected to the AC bus.

[0061] After the DC side of the voltage source converter is connected in parallel with the collection module, it is connected in series with the receiving-end flexible DC converter module through a submarine cable;

[0062] The collection module is used to connect and collect renewable energy power generation units in parallel and output the corresponding DC voltage;

[0063] The voltage equalization converter module is used to perform voltage equalization control on the DC voltage output by each collection module according to the voltage source converter and the preset voltage equalization control strategy.

[0064] The receiving-end flexible DC converter module is used to control the DC voltage on the high-voltage side to remain constant.

[0065] Preferably, the voltage equalization control strategy includes: a DC voltage synchronization control strategy, a grid-based DC voltage droop control strategy, and a DC voltage droop control strategy based on virtual oscillation.

[0066] Preferably, when the voltage equalization control strategy is a DC voltage synchronization control strategy, the step of equalizing the DC voltage output by each aggregation module includes: generating a corresponding frequency phase according to the DC voltage synchronization control loop; generating a corresponding first voltage equalization converter modulation coefficient according to the frequency phase and the voltage and current inner loop; and then equalizing the DC voltage output by each aggregation module according to the first voltage equalization converter modulation coefficient.

[0067] Preferably, the frequency phase is generated in the following manner:

[0068]

[0069] Where, k dch k dc and τ dc These represent the high-pass gain, steady-state gain, and time constant of the voltage synchronization controller, respectively; k uq With τuq They are respectively hybrid synchronous controller G uq Steady-state gain and time constant; u dc and u dcref These represent the actual DC voltage value and the DC voltage reference value, respectively; s is the Laplace operator; θ s For the generated frequency phase; u dref u d and u q These represent the d-axis voltage reference, the actual d-axis voltage value, and the actual q-axis voltage value, respectively.

[0070] Preferably, when the voltage equalization control strategy is a grid-based DC voltage droop control strategy, the voltage equalization control of the DC voltage output by each collection module includes: generating a corresponding DC voltage deviation reference value based on the frequency deviation of the phase-locked loop; generating a corresponding current reference based on the DC voltage deviation reference value, the DC voltage outer loop, and the AC voltage amplitude outer loop; generating a corresponding second voltage equalization converter modulation coefficient based on the current reference and the phase-locked loop phase; and then performing voltage equalization control on the DC voltage output by each collection module based on the second voltage equalization converter modulation coefficient.

[0071] Preferably, the DC voltage reference deviation value is generated in the following manner:

[0072]

[0073] Where, τ dc Δω is the time constant; Δω is the frequency deviation of the phase-locked loop; Δu dcref This is the reference deviation value for DC voltage.

[0074] Preferably, when the voltage equalization control strategy is a DC voltage droop control strategy based on virtual oscillation, the voltage equalization control of the DC voltage output by each collection module includes: generating corresponding virtual inductor current and virtual capacitor voltage based on the output AC current of the voltage equalization converter and the virtual oscillation controller; generating corresponding third voltage equalization converter modulation coefficient based on the virtual inductor current and virtual capacitor voltage; and then performing voltage equalization control on the DC voltage output by each collection module based on the third voltage equalization converter modulation coefficient.

[0075] Preferably, the output voltage of the virtual oscillation controller is generated in the following manner:

[0076]

[0077] Where, k pac and k iac These are the voltage amplitudes PI ac The proportional and integral coefficients of the controller; U ref and Umag These are the voltage amplitude reference and the actual voltage amplitude, respectively; v c and i L These represent the capacitor voltage and the inductor current, respectively; k i ∠φ and ∠φ are respectively the current i of the converter filter inductor. Labc The feedback gain and phase; e is the output voltage of the virtual oscillation controller; C is the transformation matrix from two-phase stationary coordinates to three-phase stationary coordinates (abc); V k is the oscillation frequency. v This is the output gain.

[0078] Preferably, the renewable energy power generation unit includes: a DC wind turbine power generation unit, a photovoltaic power generation unit, and a wave energy power generation unit; the DC wind turbine power generation unit, the photovoltaic power generation unit, and the wave energy power generation unit are connected in parallel.

[0079] Specifically, offshore wind power and solar power are combined in the same sea area to form a high-power-density energy harvesting system. For example... Figure 1 As shown, the collection module collects renewable energy sources such as wind and solar power, and is equipped with fault isolation switches and energy dissipation devices. The collection module is stepped up to high voltage through a series connection and transmitted to the onshore receiving-end converter station via a line. To achieve constant voltage control at the collection module ports, unaffected by power consumption, a series collection voltage equalization topology is introduced. Each unit's DC side is connected in parallel with the collection module, and their AC sides share an AC bus. The AC power is used to transfer power from the overvoltage collection module to the undervoltage collection module, thus achieving voltage equalization control of the DC voltage of each collection module.

[0080] Figure 1 The topology consists of three parts. The first part is the aggregation module, which comprises all CSMs connected in series. In parallel with the DC-side capacitors are distributed energy consumption units, DC wind turbines, photovoltaic power generation units, and their disconnect switches. Multiple power generation units can be connected in parallel to form an aggregation module. With this aggregation module topology, voltage boosting can be achieved through series aggregation. Multiple aggregation modules connected in series achieve a voltage boosting effect, thus realizing DC series aggregation of renewable energy sources such as wind turbines and photovoltaics.

[0081] The second part is the voltage equalization converter module, which proposes a multi-port converter voltage equalization topology based on voltage source converters. Internally, it consists of multiple AC-DC converters connected in parallel. The AC side is connected to the AC bus through transformers with appropriate turns ratios, and the DC side is connected in parallel to the corresponding collection module.

[0082] The third part is the receiving-end flexible DC converter module, which is used to control the DC voltage on the high-voltage side (the side after the collection module is connected in series) to be constant. After the DC series is collected, it is transmitted to the receiving-end converter station through the DC submarine cable line, thereby realizing the DC series transmission of the multi-energy system at sea.

[0083] With the upper control topology established, the following section of this invention will focus on the coordinated voltage equalization control of the series voltage equalization topology and its operation mode:

[0084] 1. Regarding the sub-module aggregation, existing power capture control strategies are adopted for renewable energy sources such as DC wind turbines and photovoltaic power generation. The control strategies for various sources are relatively mature at this stage, so this invention will not elaborate further. The main consideration is the voltage equalization control of the aggregation module.

[0085] 2. The receiving-end converter station adopts a constant DC voltage control method, which can be either grid-following control or grid-connected control, which will not be elaborated here.

[0086] 3. This invention focuses on the coordinated control strategy of the voltage equalization converter, and mainly includes three control methods. Please refer to [the relevant documentation]. Figure 2 This is a control diagram illustrating three coordinated pressure equalization control strategies.

[0087] (1) The first control strategy adopts a master-slave control mode, with one part of the converters using DC voltage synchronous control as the master control and another part of the converters using grid-following droop control. The specific control strategy is as follows:

[0088] For DC voltage synchronization control, the following control strategy is used to generate frequency and phase:

[0089]

[0090] Where k dch k dc , τ dc These represent the high-pass gain, steady-state gain, and time constant of the voltage synchronization controller, respectively. uq With τ uq These are the hybrid synchronous controller G uq Steady-state gain and time constant. dc with u dcref These represent the actual and reference values ​​of the DC voltage, respectively. s is the Laplace operator, and θ... s To generate phase, u dref u d with u q The reference voltage is shown for the d-axis, the actual d-axis voltage, and the actual q-axis voltage. The inner loop can employ dual closed-loop control of voltage and current. DC voltage synchronization control is primarily used for voltage frequency droop control, generating phase, which, in conjunction with the voltage and current inner loop, generates voltage modulation coefficients to achieve power control of the voltage-equalizing converter, thereby achieving DC voltage equalization in the collection module.

[0091] Secondly, the mesh control uses a traditional phase-locked loop to obtain the phase, such as... Figure 2As shown, the outer loop uses both a DC voltage outer loop and an AC voltage amplitude outer loop. Specifically, a droop control element is introduced here, as detailed below:

[0092]

[0093] Where τ dc Let Δω and Δu be the filtering time constants. dcref These represent the frequency deviation and voltage reference deviation values ​​of the phase-locked loop (PLL). The grid-type control uses an outer loop for DC voltage and an outer loop for AC voltage amplitude to generate a current reference for the inner loop. This current inner loop, in conjunction with the PLL phase, generates the corresponding modulation coefficients for the voltage-equalizing converter, thereby achieving DC voltage balancing for the corresponding parallel aggregation modules.

[0094] (2) The second control method adopts DC voltage synchronous control and does not adopt grid-type control.

[0095] (3) The third control method mainly adopts voltage droop control based on virtual oscillation. It primarily introduces DC voltage droop control to control the oscillation frequency of the virtual oscillation circuit. The specific expression is as follows:

[0096]

[0097] AC voltage amplitude control is mainly achieved by adjusting the output gain k. v The specific expression is as follows:

[0098]

[0099] Where k pac k iac These are the proportional and integral coefficients of the voltage amplitude PIac controller, respectively. ref with U mag This serves as a reference for the voltage amplitude and the actual voltage amplitude. (v in the figure) c with i L These represent the capacitor voltage and the inductor current, respectively, k i ∠φ and ∠φ are respectively the current i of the converter filter inductor. Labc Feedback gain and phase. The expression for a voltage-controlled current source is as follows:

[0100]

[0101] Where α is the gain coefficient;

[0102]

[0103] The output voltage e of the virtual oscillation controller can be used as a reference for the voltage-current dual closed-loop control or directly applied to the modulation coefficient of the controlled voltage-equalizing converter to achieve voltage equalization control of the parallel aggregation module of the voltage-equalizing converter. Let k be the transformation matrix from two-phase stationary coordinates to three-phase stationary coordinates (abc). v This is the output gain.

[0104] Theoretically, all three types of coordinated control can be adopted. Since voltage-equalizing converters are used to exchange unbalanced power through the AC system to achieve voltage-equalizing control of parallel aggregation modules, when the aggregation modules are far apart, interconnected weak AC systems can easily cause instability risks in grid-connected control. Therefore, in cases of weak connections, DC voltage synchronization coordinated control and voltage-equalizing coordinated control based on virtual oscillation are preferred. Furthermore, in master-slave coordinated control, if the grid-connected control (DC voltage synchronization control) voltage-equalizing converter fails and exits, the grid-connected control converter cannot form a grid with voltage equalizing AC systems.

[0105] To verify the effectiveness of the above control strategy, three collection modules are connected in series. To simplify system analysis, the offshore multi-energy system collection system is equivalent to a power source. The specific control strategy and method for the voltage equalization converter submodule are detailed below. To achieve voltage equalization control of the series submodule, a two-electric voltage equalization converter is used as an example for analysis, employing virtual oscillation control to achieve voltage equalization of the three collection modules in series. The control parameters are shown in Table 1 below:

[0106]

[0107] Table 1 Control Parameters

[0108] Taking three DC-connected pooling modules in series as an example, the effectiveness of the above control strategy is verified. With three pooling modules connected in series, the equivalent DC power supply voltage is 4.5kV, and the voltage of each series-connected pooling module is 1.5kV. Please refer to... Figure 3 This is a schematic diagram of a simulation model of three collection modules connected in DC series.

[0109] Please refer to Figure 4 The simulation waveforms are shown below for the three merging modules connected in DC series. The simulation results are as follows: Figure 4 As shown, the power of the collecting module is initially 0. At 2s, a step jump occurs, and the output power of sub-module 1 is at its maximum, resulting in a significant voltage rise. At this time, AC power flows from the voltage equalization converter VSC1 to sub-modules 2 and 3, thus achieving voltage equalization. Similarly, at 4s, the output power of collecting module 2 also experiences a step jump, and the voltage of the sub-modules quickly balances due to the presence of the voltage equalization converter.

[0110] Therefore, this invention provides a multi-energy DC series collection system for marine applications. By incorporating a voltage-equalizing converter module, it controls the DC voltage output from each collection module to maintain a constant DC voltage within a reasonable range, enabling full DC voltage equalization collection of multiple energy sources in a specific sea area. In summary, this invention provides a detailed analysis of the voltage-equalizing topology and control strategy for marine multi-energy systems. Compared to traditional voltage-equalizing converters that require a central controller, this invention draws inspiration from the topology of autotransformers and proposes a plug-and-play marine full DC series voltage-equalizing topology. This achieves voltage-equalizing control without communication and exhibits strong scalability.

[0111] Example 2

[0112] Please refer to Figure 5 This is a flowchart illustrating a coordinated control method for multi-energy DC series aggregation at sea, provided in an embodiment of the present invention. It is applicable to the multi-energy DC series aggregation system at sea described in the above embodiment.

[0113] The marine multi-energy DC series collection system includes: several collection modules, a voltage equalization converter module, and a receiving-end flexible DC converter module;

[0114] The aggregation module includes several renewable energy power generation units, and the renewable energy power generation units within the same aggregation module are connected in parallel;

[0115] The voltage equalization converter module includes several voltage source converters. The DC side of each voltage source converter is connected in parallel with a collection module, and the AC side of all voltage source converters is connected to the AC bus.

[0116] After the DC side of the voltage source converter is connected in parallel with the collection module, it is connected in series with the receiving-end flexible DC converter module through a submarine cable;

[0117] The aforementioned multi-energy DC series collection and coordinated control method for marine applications includes:

[0118] The collection module connects and aggregates renewable energy power generation units in parallel to output the corresponding DC voltage.

[0119] Through the voltage equalization converter module, the DC voltage output by each collection module is controlled to be equalized according to the voltage source converter and the preset voltage equalization control strategy.

[0120] The DC voltage on the high-voltage side is kept constant by controlling the receiving-end flexible DC converter module.

[0121] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A marine multi-energy DC series collection system, characterized in that, include: Several collection modules, voltage equalization converter modules, and receiving-end flexible DC converter modules; The aggregation module includes several renewable energy power generation units, and the renewable energy power generation units within the same aggregation module are connected in parallel; The voltage equalization converter module includes several voltage source converters. The DC side of each voltage source converter is connected in parallel with a collection module, and the AC side of all voltage source converters is connected to the AC bus. After the DC side of the voltage source converter is connected in parallel with the collection module, it is connected in series with the receiving-end flexible DC converter module through a submarine cable; The collection module is used to connect and collect renewable energy power generation units in parallel and output the corresponding DC voltage; The voltage equalization converter module is used to perform voltage equalization control on the DC voltage output by each collection module according to the voltage source converter and the preset voltage equalization control strategy. The receiving-end flexible DC converter module is used to control the DC voltage on the high-voltage side to remain constant.

2. The marine multi-energy DC series collection system as described in claim 1, characterized in that, The voltage equalization control strategies include: DC voltage synchronization control strategy, grid-based DC voltage droop control strategy, and DC voltage droop control strategy based on virtual oscillation.

3. The marine multi-energy DC series collection system as described in claim 2, characterized in that, When the voltage equalization control strategy is a DC voltage synchronization control strategy, the voltage equalization control of the DC voltage output by each collection module includes: The corresponding frequency phase is generated based on the DC voltage synchronization control loop; The first equalizing converter modulation coefficient is generated based on the frequency phase and voltage-current inner loop, and then the DC voltage output by each collection module is equalized based on the first equalizing converter modulation coefficient.

4. The marine multi-energy DC series collection system as described in claim 3, characterized in that, The frequency phase is generated in the following manner: Where, k dch k dc and τ dc These represent the high-pass gain, steady-state gain, and time constant of the voltage synchronization controller, respectively; k uq With τ uq These are the hybrid synchronous controllers G uq Steady-state gain and time constant; u dc and u dcref These represent the actual DC voltage value and the DC voltage reference value, respectively; s is the Laplace operator; θ s For the generated frequency phase; u dref u d and u q These represent the d-axis voltage reference, the actual d-axis voltage value, and the actual q-axis voltage value, respectively.

5. The marine multi-energy DC series collection system as described in claim 4, characterized in that, When the voltage equalization control strategy is a grid-based DC voltage droop control strategy, the voltage equalization control of the DC voltage output by each collection module includes: A corresponding DC voltage deviation reference value is generated based on the frequency deviation of the phase-locked loop; Based on the DC voltage deviation reference value, the DC voltage outer loop, and the AC voltage amplitude outer loop, a corresponding current reference is generated; Based on the current reference and the phase-locked loop phase, a corresponding second voltage equalization converter modulation coefficient is generated, and then the DC voltage output by each collection module is controlled for voltage equalization based on the second voltage equalization converter modulation coefficient.

6. The marine multi-energy DC series collection system as described in claim 5, characterized in that, The DC voltage reference deviation value is generated in the following manner: Where, τ dc Δω is the time constant; Δω is the frequency deviation of the phase-locked loop; Δu dcref This is the reference deviation value for DC voltage.

7. The marine multi-energy DC series collection system as described in claim 6, characterized in that, When the voltage equalization control strategy is a DC voltage droop control strategy based on virtual oscillation, the voltage equalization control of the DC voltage output by each collection module includes: Based on the output AC current of the voltage equalization converter and the virtual oscillation controller, the corresponding virtual inductor current and virtual capacitor voltage are generated. Based on the virtual inductor current and virtual capacitor voltage, a corresponding third voltage equalization converter modulation coefficient is generated, and then the DC voltage output by each collection module is controlled for voltage equalization based on the third voltage equalization converter modulation coefficient.

8. The marine multi-energy DC series collection system as described in claim 7, characterized in that, The output voltage of the virtual oscillation controller is generated in the following manner: Where, k pac and k iac These are the voltage amplitudes PI ac The proportional and integral coefficients of the controller; U ref and U mag These are the voltage amplitude reference and the actual voltage amplitude, respectively; v c and i L These represent the capacitor voltage and the inductor current, respectively; k i ∠φ and ∠φ are respectively the current i of the converter filter inductor. Labc The feedback gain and phase; e is the output voltage of the virtual oscillation controller; C is the transformation matrix from two-phase stationary coordinates to three-phase stationary coordinates (abc); V k is the oscillation frequency. v This is the output gain.

9. The marine multi-energy DC series collection system as described in claim 1, characterized in that, The renewable energy power generation unit includes: a DC wind turbine power generation unit, a photovoltaic power generation unit, and a wave energy power generation unit; The DC wind turbine power generation unit, photovoltaic power generation unit, and wave energy power generation unit are connected in parallel.

10. A method for coordinated control of multi-energy DC series collection at sea, characterized in that, Applicable to the marine multi-energy DC series collection system as described in any one of claims 1-9; The marine multi-energy DC series collection system includes: several collection modules, a voltage equalization converter module, and a receiving-end flexible DC converter module; The aggregation module includes several renewable energy power generation units, and the renewable energy power generation units within the same aggregation module are connected in parallel; The voltage equalization converter module includes several voltage source converters. The DC side of each voltage source converter is connected in parallel with a collection module, and the AC side of all voltage source converters is connected to the AC bus. After the DC side of the voltage source converter is connected in parallel with the collection module, it is connected in series with the receiving-end flexible DC converter module through a submarine cable; The aforementioned multi-energy DC series collection and coordinated control method for marine applications includes: The collection module connects and aggregates renewable energy power generation units in parallel to output the corresponding DC voltage. Through the voltage equalization converter module, the DC voltage output by each collection module is controlled to be equalized according to the voltage source converter and the preset voltage equalization control strategy. The DC voltage on the high-voltage side is kept constant by controlling the receiving-end flexible DC converter module.

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