A control method of a coupled inductance type DC collector system

Abstract

The application provides a control method of a coupled inductance type direct current collection system, which comprises the following steps: connecting each sub-module of the coupled inductance type direct current collection system to each group of wave energy generation devices through a low-voltage side dispersion connection, and connecting a high-voltage side of each group of wave energy generation devices to a high-voltage direct current bus in series; connecting n-1 controlled voltage sources with the coupled inductance in series in each sub-module, eliminating the influence of the high-voltage side series voltage, the low-voltage side current and the inductive coupling effect on the output quantity by establishing a coupled inductance decoupling network, obtaining a modulation signal duty ratio without interference quantity, and controlling the switch tube in the sub-module. In the control method, a current control loop is added, and the adverse influence of the inductive coupling effect on the duty ratio signal when the disturbance exists is eliminated through a feedforward correction loop, so that the stability of the direct current collection system is enhanced.

Description

Technical Field

[0001] This invention relates to the field of renewable energy power generation and grid connection technology, specifically to a coupled inductive DC current collection system suitable for large-scale wave energy power generation devices and a control method for using this system. Background Technology

[0002] my country is a large coastal country with abundant coastal energy reserves. Wave energy, as a renewable and clean energy source with high energy density, large energy reserves, wide distribution, and safe and stable supply, is very suitable to become an important development goal for my country's new energy structure construction.

[0003] Currently, nearshore wave energy generation generally adopts an AC generation-AC collection-AC transmission method. However, this method suffers from high construction costs, significant reactive charging current during current transmission, and overvoltage issues, making it suitable only for small-capacity wave energy power plants near the shore. Most wave energy generator sets do not meet these requirements. In the similar field of offshore wind power, existing technologies have proposed a hybrid AC / DC wave energy transmission method, further proposing a dual-current inner-loop control method to control generator speed. This scheme provides a back-to-back high-voltage DC system that easily forms multi-terminal transmission, fitting the wide and dispersed distribution of wave energy generator groups. However, this control scheme does not address inductive coupling and inductor current instability. Although the topology of the hybrid AC / DC transmission method is constantly improving, it still suffers from numerous energy conversion cycles and difficulties in designing control methods.

[0004] Therefore, in large-scale wave energy power generation in the open ocean, a DC generation-DC collection-DC transmission method is often adopted. This transmission method typically involves individual generators producing wave energy, which is then converted from AC to DC by rectifiers for easy transmission. The converted DC then passes through a DC collector system to collect the dispersed wave energy and boost its voltage, finally outputting the boosted DC power to the high-voltage DC bus. In this DC grid, the research on the DC collector system is a key technology for wave energy transmission. Existing technical solutions provide a large-scale generator grid-connected system and its control method. However, this system suffers from uncertain, temporary DC faults. By proposing an additional control scheme, combined with a converter station lockout restart control method, DC fault ride-through can be achieved, improving system stability.

[0005] It is evident that the power conversion and transmission of wave energy generation devices are relatively complex and have weak anti-interference capabilities. Therefore, the design of DC current collector systems must enhance the system's anti-interference capabilities and ensure the stability of the DC current and generator transmission power under operating conditions.

[0006] Existing large-scale array float-type wave energy generation devices typically distribute a series of power generation units with energy output systems within a certain sea area. Energy is transferred to the power generation system via an intermediate conversion platform, primarily using a hydraulic energy storage system, and then the generated electricity is transmitted to a collection system. However, current DC collection systems still have the following drawbacks: (1) The DC parallel energy collection system connects the boosted DC voltage in parallel to the high-voltage DC bus, requiring a large boost amplitude. However, due to hardware limitations, multiple DC-DC voltage converters usually need to be cascaded to meet the voltage boost requirement. This not only makes circuit construction difficult in practical applications, but also reduces the stability of the system, which is not conducive to the stable transmission of wave energy. Due to the large number of cascaded transformers, it is also difficult to design a control scheme to control the generator power according to the output. (2) A DC-DC series energy collection system only requires a single DC-DC converter to complete the DC voltage boosting. However, it requires the voltage output of multiple DC collector modules to be connected in series, which leads to a serious coupling problem between the voltages of each sub-module.

[0007] The existing control scheme proposes an additional control method, combined with the converter station's lockout and restart control method, to achieve DC fault ride-through and improve system stability. However, it does not consider the voltage coupling problem at the series ports. This control scheme aims to control the generator's power transmission through lockout and restart techniques. However, in practical applications, wave energy generators often use uncontrolled rectification to convert AC to DC for transmission, in which case the generator cannot track the maximum power point. Therefore, designing an appropriate control scheme to solve the voltage coupling problem at the series ports, achieve stable DC current control and maximum power point tracking of the generator, and improve the stability of the DC collector system is crucial. Summary of the Invention

[0008] In order to overcome the shortcomings of the prior art, the present invention aims to provide a DC collection grid system and method for a large wave energy power generation device. The system and method can solve various shortcomings of the prior art. By using a feedforward correction circuit, the adverse effects of inductive coupling on the duty cycle signal when disturbances are present are eliminated, thereby enhancing the stability of the DC collection system.

[0009] To solve the above problems, the technical solution adopted by the present invention is as follows: A control method for a coupled inductive DC current collector system, applied to a coupled inductive DC current collector system of a wave energy power generation device, the method comprising the following steps: Each sub-module of the coupled inductive DC collector system is distributed and connected to each group of wave energy generation devices through the low-voltage side, and its high-voltage side is connected in series to the high-voltage DC bus. Define V si The low-side voltage of each submodule, V i The high-voltage side voltage of the submodule is defined as C. si L i and C i These are the low-voltage side capacitor, coupling inductor, and high-voltage side capacitor of the i-th submodule, respectively. In each submodule, n-1 controlled voltage sources are connected in series with coupled inductors. By establishing a coupled inductor decoupling network, the effects of high-voltage side series voltage, low-voltage side current, and inductor coupling on the output are eliminated, and the duty cycle of the modulation signal without interference is obtained to control the switching transistors in the submodule.

[0010] According to the present invention, a control method for a coupled inductor-type DC collector system includes adding n-1 controlled voltage sources connected in series with the coupled inductor to each submodule, comprising: The high-voltage side bridge arm is composed of two switching structures in each submodule, and this high-voltage side bridge arm is connected to the high-voltage side capacitor C. i The high-voltage side half-bridge module is formed by connecting the capacitors in parallel, and the high-voltage side capacitor C is defined. i The voltage across the terminals is V i It is led out from the series terminal of the first and second switching transistors, connected in series with the controlled voltage source and the high-frequency coupled inductor, and then connected to the low-voltage side bridge arm; The low-voltage side bridge arm is formed by two switching structures in each submodule, and then connected to the low-voltage side capacitor C. si The capacitors are connected in parallel to form a low-voltage side half-bridge module, and the voltage across the low-voltage side capacitor is defined as V. si It is led out from the series terminal of the third and fourth switching transistors and connected to the high-frequency coupling inductor.

[0011] According to the control method of the coupled inductor-type DC collector system provided by the present invention, when analyzing the transmission of the low-voltage side voltage rise of the submodule to the high-voltage side within one cycle, the port connected to the wave energy generation device on the low-voltage side of the submodule can be regarded as a power source. The magnitude of the current flowing through the low-voltage side capacitor is related to the inductor current i. Li equal; Taking a DC collector system with two sub-modules (n=2) as an example, the low-voltage side and high-voltage side bridge arms of the two sub-modules are connected by a high-frequency coupling inductor L. i Connected, assuming the self-inductance coefficients of the inductors are L and L respectively. 11 L 22 The currents flowing through the high-frequency coupled inductor are i L1 i L2 ; The coupling effect of the inductance between the two sub-modules is equivalent to a controlled voltage source connected in series with the coupled inductor.

[0012] According to the control method of the coupled inductor type DC collector system provided by the present invention, the working mode of the DC collector system is divided into buck mode and boost mode according to the modulation strategy. In buck mode, the expressions for inductor current and low-side output voltage are given by formula (1): (1) in, .

[0013] In boost mode, the expressions for inductor current and output voltage are given by formula (2): (2) Where M is the mutual inductance coefficient, .

[0014] According to the control method of the coupled inductor type DC collector system provided by the present invention, the general formula for expressing the output quantity with respect to the duty cycle of the modulation signal of the submodule is formula (3): (3) Among them, G i11 G i12 G i13 G i21 G i22 G i23 G v11 G v12 G v13 G v21 G v22 G v2 The coefficients before each variable are given, and the duty cycle of the sampled submodule modulation signal is defined as follows: d1 , d2 Its corrected output value is d1、 d2.

[0015] According to the control method of the coupled inductor type DC collector system provided by the present invention, in the step-down mode, the functional expression of the feedforward compensation device is obtained as formula (4): (4) After introducing the decoupling network, the output quantity is related to the duty cycle of the modulation signal of the submodule. d1 , d2 The expression is formula (5): (5) According to the control method of the coupled inductor type DC collector system provided by the present invention, in boost mode, the functional expression of the feedforward compensation device is obtained as formula (6): (6) After introducing the decoupling network, the output quantity is related to the duty cycle of the modulation signal of the submodule. d1 , d2 The expression is formula (7): (7).

[0016] According to the control method of the coupled inductor type DC collector system provided by the present invention, when the rectification scheme of the wave energy generator is uncontrolled rectification, it switches to the generator speed control loop as needed, and controls the speed of the wave energy generator by adjusting the low-voltage side port current, that is, controlling and adjusting the current flowing through the high-frequency coupled inductor, including: The measured rotational speed ω of the wave energy generator i With reference value of rotational speed ω ref The comparison result is used by a PI controller to obtain the reference current i. ref ;change i ref With the measured inductor current value i Li The weighted values ​​are then used to obtain the duty cycle d of the modulation signal before correction via a PI controller. i The duty cycle d of the modulation signal is obtained through a coupled inductor decoupling network. i .

[0017] According to the present invention, a control method for a coupled inductor-type DC current collector system includes multiple multi-port DC current collectors corresponding one-to-one with the wave energy power generation device. Two multi-port DC current collectors are connected through a high-frequency coupled inductor. Each multi-port DC current collector uses a switching DC-DC converter circuit to distribute the low-voltage side to the wave energy power generation device to ensure that each generator set operates independently. The DC voltage is then boosted and energy is collected before being connected in series to the high-voltage side high-voltage DC bus.

[0018] According to a control method for a coupled inductor-type DC collector system provided by the present invention, the switching DC-DC converter circuit includes four switching structures formed by anti-parallel connection of field-effect transistors and diodes. The source of the first switching transistor and the drain of the second switching transistor are connected in series, and the two switching structures together form a high-voltage side bridge arm. The high-voltage side bridge arm and its high-voltage side capacitor are connected in parallel to form a high-voltage side half-bridge module. The drain of the third switching transistor and the source of the fourth switching transistor are connected in series, and the two switching structures together form a low-voltage side bridge arm. The low-voltage side bridge arm and its low-voltage side capacitor are connected in parallel to form a low-voltage side half-bridge module.

[0019] Therefore, in order to eliminate the adverse effects of inductor coupling between various DC collector system submodules in the prior art, this invention proposes a coupled inductor type DC collector system and its control method suitable for wave energy generator sets. The proposed decoupling network eliminates the coupling effect between inductors after adding a feedback loop for feedforward correction, and can effectively suppress the high voltage DC voltage oscillation caused by the current and power fluctuations of the wave energy generator set. It can also effectively resist the influence of the duty cycle disturbance of the modulation signal on the inductor current, making the DC collector system more stable.

[0020] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0021] Figure 1 This is a flowchart of an embodiment of a control method for a coupled inductor-type DC collector system according to the present invention.

[0022] Figure 2 This is a schematic diagram of the first circuit of the coupled inductive DC collector system in an embodiment of the control method for a coupled inductive DC collector system of the present invention.

[0023] Figure 3 This is a second circuit schematic diagram of the coupled inductive DC collector system in an embodiment of the control method for a coupled inductive DC collector system of the present invention.

[0024] Figure 4 This is a control principle diagram of the modulation strategy in an embodiment of the control method for a coupled inductor-type DC collector system of the present invention.

[0025] Figure 5 This is a first circuit diagram of a dual-module coupled inductive DC collector system circuit in an embodiment of the control method for a coupled inductive DC collector system of the present invention.

[0026] Figure 6 This is a second circuit diagram of a dual-module coupled inductive DC collector system circuit in an embodiment of the control method for a coupled inductive DC collector system of the present invention.

[0027] Figure 7 This is a block diagram of the interference removal control obtained for different output quantities in an embodiment of the control method for a coupled inductor type DC collector system of the present invention.

[0028] Figure 8 This is a schematic diagram of the current control strategy of a coupled inductive DC collector system in an embodiment of the control method of a coupled inductive DC collector system according to the present invention.

[0029] Figure 9 This is a current waveform diagram in the open-loop state of an embodiment of the control method for a coupled inductor-type DC collector system according to the present invention.

[0030] Figure 10 This is a current waveform diagram with a current control loop added in an embodiment of the control method for a coupled inductor-type DC collector system of the present invention.

[0031] Figure 11 This is a motor speed diagram of a permanent magnet synchronous motor in an embodiment of the control method for a coupled inductor-type DC collector system of the present invention. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0033] See Figure 1 This invention provides a control method for a coupled inductive DC current collector system, which is applied to a coupled inductive DC current collector system of a wave energy power generation device. The method includes the following steps: Step S1: Connect each sub-module of the coupled inductive DC collector system to each group of wave energy generation devices through the low-voltage side, and connect its high-voltage side in series to the high-voltage DC bus. Step S2, define V si The low-side voltage of each submodule, V i The high-voltage side voltage of the submodule is defined as C. si L i and C i These are the low-voltage side capacitor, coupling inductor, and high-voltage side capacitor of the i-th submodule, respectively. Step S3: Add n-1 controlled voltage sources to each submodule and connect them in series with the coupled inductor. By establishing a coupled inductor decoupling network, the influence of high-voltage side series voltage, low-voltage side current and inductor coupling effect on the output is eliminated, and the duty cycle of the modulation signal without interference is obtained to control the switching transistors in the submodule.

[0034] In step S3 above, n-1 controlled voltage sources are added to each submodule and connected in series with the coupled inductor, including: The high-voltage side bridge arm is composed of two switching structures in each submodule, and this high-voltage side bridge arm is connected to the high-voltage side capacitor C. i The high-voltage side half-bridge module is formed by connecting the capacitors in parallel, and the high-voltage side capacitor C is defined. i The voltage across the terminals is V i It is led out from the series terminal of the first and second switching transistors, connected in series with the controlled voltage source and the high-frequency coupled inductor, and then connected to the low-voltage side bridge arm; The low-voltage side bridge arm is formed by two switching structures in each submodule, and then connected to the low-voltage side capacitor C. si The capacitors are connected in parallel to form a low-voltage side half-bridge module, and the voltage across the low-voltage side capacitor is defined as V. si It is led out from the series terminal of the third and fourth switching transistors and connected to the high-frequency coupling inductor.

[0035] When analyzing the transmission of the low-voltage side voltage rise of the submodule to the high-voltage side within a cycle, the port connecting the low-voltage side of the submodule to the wave energy generation device can be considered as a power source. The magnitude of the current flowing through the low-voltage side capacitor is related to the inductor current i. Li equal.

[0036] Taking a DC collector system with two sub-modules (n=2) as an example, the low-voltage side and high-voltage side bridge arms of the two sub-modules are connected by a high-frequency coupling inductor L. i Connected, assuming the self-inductance coefficients of the inductors are L and L respectively. 11 L 22 The currents flowing through the high-frequency coupled inductor are i L1 i L2 .

[0037] The coupling effect of the inductance between the two sub-modules is equivalent to a controlled voltage source connected in series with the coupled inductor.

[0038] In this embodiment, the operating modes of the DC collector system are divided into buck mode and boost mode according to the modulation strategy. In buck mode, the expressions for inductor current and low-side output voltage are given by formula (1): (1) Where M is the mutual inductance coefficient, .

[0039] In boost mode, the expressions for inductor current and output voltage are given by formula (2): (2) in, .

[0040] In this embodiment, the general formula for expressing the output quantity with respect to the duty cycle of the modulation signal of the submodule is formula (3): (3) Among them, G i11 G i12 G i13 G i21 G i22 G i23 G v11 G v12 G v13 G v21 G v22 G v2 The coefficients before each variable are given, and the duty cycle of the sampled submodule modulation signal is defined as follows: d1 , d2 Its corrected output value is d1、 d2.

[0041] In step-down mode, the functional expression of the feedforward compensation device is given by formula (4): (4) After introducing the decoupling network, the output quantity is related to the duty cycle of the modulation signal of the submodule. d1 , d2 The expression is formula (5): (5) In boost mode, the functional expression of the feedforward compensation device is given by formula (6): (6) After introducing the decoupling network, the output quantity is related to the duty cycle of the modulation signal of the submodule. d1 , d2 The expression is formula (7): (7).

[0042] In this embodiment, when the rectification scheme of the wave energy power generation device is uncontrolled rectification, it is switched to a generator speed control loop as needed, and the speed of the wave energy power generation device is controlled by adjusting the current at the low-voltage side port, that is, controlling and adjusting the current flowing through the high-frequency coupling inductor, including: The measured rotational speed ω of the wave energy generator i With reference value of rotational speed ω ref The comparison result is used by a PI controller to obtain the reference current i. ref ;change i ref With the measured inductor current value i Li The weighted values ​​are then used to obtain the duty cycle d of the modulation signal before correction via a PI controller. i The duty cycle d of the modulation signal is obtained through a coupled inductor decoupling network. i .

[0043] In this embodiment, the coupled inductor-type DC current collector system includes multiple multi-port DC current collectors that correspond one-to-one with the wave energy power generation device. Two multi-port DC current collectors are connected through a high-frequency coupled inductor. Each multi-port DC current collector uses a switching DC-DC converter circuit to distribute the low-voltage side to the wave energy power generation device to ensure that each generator set operates independently. The DC voltage is then boosted and energy is collected before being connected in series to the high-voltage side high-voltage DC bus.

[0044] The switching DC-DC converter circuit includes four switching structures formed by anti-parallel connection of field-effect transistors and diodes. The source of the first switching transistor and the drain of the second switching transistor are connected in series, and the two switching structures together form a high-voltage side bridge arm. This high-voltage side bridge arm and its high-voltage side capacitor are connected in parallel to form a high-voltage side half-bridge module. The drain of the third switching transistor and the source of the fourth switching transistor are connected in series, and the two switching structures together form a low-voltage side bridge arm. This low-voltage side bridge arm and its low-voltage side capacitor are connected in parallel to form a low-voltage side half-bridge module.

[0045] In summary, this invention proposes a coupled inductive DC collector system and its current control method suitable for wave energy generator sets. The proposed control method incorporates a feedforward correction loop to eliminate the adverse effects of inductive coupling on the duty cycle signal when disturbances are present, thereby enhancing the stability of the DC collector system. The proposed control method also incorporates a current control loop to ensure the stability of the port current of the distributed wave energy generator sets and their uncontrolled rectifier modules.

[0046] Specifically, this invention proposes a coupled inductive DC collector system suitable for wave energy generators. The circuit topology of the proposed coupled inductive DC collector system is as follows: Figure 2 and Figure 3As shown, the multi-port DC current collector employs a four-switch DC-DC converter circuit. The low-voltage side is distributed to the wave energy generator sets to ensure independent operation of each generator set. The DC voltage is then boosted and energy collected before being connected in series to the high-voltage side high-voltage DC bus. Furthermore, this embodiment incorporates a coupling inductor. On one hand, the inductive coupling improves the dynamic response performance of the circuit topology, reducing hardware construction costs and size. On the other hand, optimized control strategies eliminate the influence of the coupling inductor on other sub-modules and maintain a stable current flowing through the coupling inductor.

[0047] exist Figure 2 and Figure 3 In the example of the low-voltage side port connected to the i-th (i = 1, 2, …n) wave energy generator, V is defined as follows. si Low-voltage DC side voltage for each submodule, V i This represents the high-voltage side voltage of the submodule. Since the distributed generator sets are connected in series on the high-voltage side via DC collector submodules, the high-voltage DC bus voltage is the sum of the high-voltage side voltages of all submodules. C si L i , and C i These represent the low-voltage side capacitor, coupling inductor (coupled with the inductors of other submodules), and high-voltage side capacitor of the i-th submodule, respectively. To represent the inductor coupling effect between a submodule and the other (n-1) submodules, (n-1) controlled voltage sources are added to each submodule and connected in series with the coupling inductor L1. The direction of their voltage reference is shown in the figure. Wherein, M... im (i = 1, 2, 3…, m = 1, 2, 3…, i ≠ m) represents the mutual inductance coefficient; each submodule also contains four switching structures consisting of anti-parallel connections of field-effect transistors and diodes, for example, the switching transistor S… 1i The source and switch S 2i The drains are connected in series, and the two switching structures together form the high-voltage side bridge arm. This bridge arm is connected to the high-voltage side capacitor C. i The capacitors are connected in parallel to form a high-voltage side half-bridge module, and the voltage across the high-voltage side capacitor is defined as V. i It originates from the switching transistor S 1i and switching transistor S 2i The series terminal is led out and connected in series with the controlled voltage source and the high-frequency coupled inductor, and then connected to the low-voltage side bridge arm. In the low-voltage side bridge arm, the switching transistor S... 3i Drain and switching transistor S 4i The two switching transistors are connected in series at their sources to form the low-voltage side bridge arm, which is then connected to the low-voltage side capacitor C. si The capacitors are connected in parallel to form a low-voltage side half-bridge module, and the voltage across the low-voltage side capacitor is defined as V. si From the switching transistor S 3i and switching transistor S 4iThe series terminal is led out and connected to a high-frequency coupled inductor.

[0048] Taking a dual-wave energy generator set (n=2) as an example, the operating modes of the DC collector system are explained in detail: First, the modulation strategy of the sub-module is introduced, and its modulation strategy waveform diagram within one cycle is shown in the figure. Figure 4 As shown. First, by comparing carrier V c1 and V c2 With modulated wave V r The voltage amplitude controls the drive signal of the switching transistor in the submodule; V m1 and V m3 S 1n and S 3n The drive signal, S 2n and S 4n drive signal V m2 and V m4 V m1 and V m3 The voltage is inverted. In one cycle, when V... r Completely below V c2 At that time, S 3n As of now, S 4n On, S i1 and S i2 Alternating conduction, the submodule operates in buck mode; when V r Completely higher than V c1 At that time, S 2n As of now, S 1n On, S 3n and S 4n The submodules operate alternately, with the submodules operating in boost mode.

[0049] The topology of the DC collector system consisting of two sub-modules is as follows: Figure 5 and 6 As shown, two sub-modules are distributed on the low-voltage side to each generator set, and on the high-voltage side, they are connected in series to the high-voltage DC bus. When analyzing the voltage rise on the low-voltage side and its transmission to the high-voltage side within one cycle, the port connecting the low-voltage side to the wave energy generator set can be considered as a power source, and the current flowing through the low-voltage side capacitor is defined as i. csi Its amplitude is related to the inductor current i Li Equal, the reference direction has been marked in the figure; due to the high-frequency coupling inductor L between the low-voltage and high-voltage bridge arms of each submodule. i Let i=1 and 2 be connected, and let the self-inductance coefficients of the inductors be L and L respectively. 11 L 22 The currents flowing through the coupled inductors are i L1 i L2To facilitate a more intuitive analysis of the effect of inductive coupling, the inductive coupling between the two submodules is equivalent to a controlled voltage source connected in series with the coupled inductor. The reference direction is shown in the diagram. M is the mutual inductance coefficient, and i... ’ L1 i ’ L2 These represent the rate of change of inductor current on another DC collector module.

[0050] In buck mode, the inductor current and the low-voltage side output voltage are expressed by formula (1).

[0051] In boost mode, the expressions for inductor current and output voltage are given by formula (2).

[0052] In practical applications, it is necessary to consider the type of wave energy generator set and its rectifier interface. Taking permanent magnet synchronous motor and uncontrolled rectifier as an example. Since the four-switch DC-DC converter circuit has a symmetrical topology, bidirectional power flow, and a proportional relationship between inductor current and port voltage, taking the dual-submodule DC collector system as an example, the simplified expression of the output quantity (i.e., inductor current or low-voltage side port voltage) with respect to the duty cycle of the modulation signal can be obtained as formula (3). The expression also varies depending on the working mode of the submodule. In order to eliminate the influence of disturbance on the control quantity, this invention adopts the method of adding feedforward correction to realize the duty cycle disturbance control loop, and defines the duty cycle of the sampled submodule modulation signal as d1 , d2 Its corrected output value is d1、 d2. By establishing a feedforward correction decoupling network, the adverse effects of inductive coupling and other interference on the duty cycle are eliminated. For different output quantities, the resulting interference removal control block diagram is as follows: Figure 7 As shown.

[0053] In buck mode, the function expression of the feedforward compensation device can be obtained as formula (4). After introducing the decoupling network, the output quantity is related to the duty cycle of the submodule modulation signal. d1 , d2 The expression is given by formula (5); in boost mode, the function expression of the feedforward compensation device is given by formula (6). After introducing the decoupling network, the output quantity is related to the duty cycle of the submodule modulation signal. d1 , d2 The expression is given by formula (7). It can be seen that by using a decoupling network, the effects of high-voltage side series voltage, low-voltage side current and coupling effect on the output can be eliminated, and finally the expression of the duty cycle signal without interference can be obtained, so that the inductor current is only related to the duty cycle of the modulation signal.

[0054] In practical applications, the generator set of a large-scale array float-type wave energy power generation device converts AC power into DC power via a rectifier and connects it to a low-voltage side DC collector system. Taking an uncontrolled rectifier as an example, its generator speed, maximum power point, and low-voltage DC bus voltage are all uncontrolled. Therefore, the DC collector system needs to stabilize the low-voltage side port voltage V. si This enables the generator to achieve maximum power point tracking, while also eliminating the adverse effects of disturbances and inductive coupling on the duty cycle signal through control strategies.

[0055] Therefore, to address the inductive coupling and inductor current stability issues of DC collector system submodules, this embodiment proposes a current control strategy for wave energy DC collector systems, such as... Figure 8 As shown.

[0056] The control strategy proposed in this embodiment consists of three control loops: (1) generator speed control loop; (2) inductor current control loop; and (3) coupled inductor decoupling network. When the generator set rectification scheme is uncontrolled rectification, a generator speed control loop needs to be added, and the generator speed is controlled by adjusting the low-voltage side port current. In practical applications, this means controlling and adjusting the current flowing through the coupled inductor. First, the wave energy generator speed ω is measured. i and the reference value of rotational speed ω ref The value is compared, and the reference current i is obtained through the PI controller. ref ;change i ref With the measured inductor current value i Li The weighted result is used to obtain the duty cycle d of the modulation signal before correction via a PI controller. i Finally, the duty cycle d of the modulation signal is obtained through a coupled inductor decoupling network. i It is evident that the system and its control strategy improve the generator's operation through the generator speed control loop, enabling it to track the maximum power point; ensure the stability of the port current of the distributed wave energy generator set and rectifier module through the inductor current control loop; and enhance the system's stability by eliminating the influence of disturbances and coupling on the duty cycle signal through the coupled inductor decoupling network.

[0057] Take the twin-module DC collector system as an example. Figure 9 and Figure 10 The waveforms of the inductor current flowing through submodule 1 are observed in the open-loop state and after incorporating the control scheme proposed in this invention. Figure 9and Figure 10 It can be seen that, in the open-loop state, the current flowing through the coupled inductor fluctuates significantly with large amplitude differences. After adding the current control loop proposed in this invention, the inductor current control loop stabilizes the current amplitude flowing through the coupled inductor within -20~20A. This verifies the effectiveness and feasibility of the inductor current control loop proposed in this invention.

[0058] Figure 11 This is a graph showing the motor speed of the permanent magnet synchronous machine after incorporating the control scheme proposed in this invention. Figure 11 It can be seen that the generator speed control loop stabilized the generator speed at 45 rad / s, with the error controlled within 1%. This verifies the effectiveness and feasibility of the generator speed control loop proposed in this invention.

[0059] Therefore, in order to eliminate the adverse effects of inductor coupling between various DC collector system submodules in the prior art, this invention proposes a coupled inductor type DC collector system and its control method suitable for wave energy generator sets. The proposed decoupling network eliminates the coupling effect between inductors after adding a feedback loop for feedforward correction, and can effectively suppress the high voltage DC voltage oscillation caused by the current and power fluctuations of the wave energy generator set. It can also effectively resist the influence of the duty cycle disturbance of the modulation signal on the inductor current, making the DC collector system more stable.

[0060] The technical features of the above embodiments can be combined in any way. For the sake of brevity, 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.

[0061] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. A control method for a coupled inductor-type DC collector system, characterized in that, This method is applied to a coupled inductive DC current collector system of a wave energy power generation device, and the method includes the following steps: Each sub-module of the coupled inductive DC collector system is distributed and connected to each group of wave energy generation devices through the low-voltage side, and its high-voltage side is connected in series to the high-voltage DC bus. Define V si The low-side voltage of each submodule, V i The high-voltage side voltage of the submodule is defined as C. si L i and C i These are the low-voltage side capacitor, coupling inductor, and high-voltage side capacitor of the i-th submodule, respectively. In each submodule, n-1 controlled voltage sources are connected in series with a coupled inductor, including: a high-voltage side bridge arm composed of two switching structures from each submodule, which is connected to the high-voltage side capacitor C. i The high-voltage side half-bridge module is formed by connecting the capacitors in parallel, and the high-voltage side capacitor C is defined. i The voltage across the terminals is V i It is led out from the series terminals of the first and second switching transistors, connected in series with the controlled voltage source and the high-frequency coupling inductor, and then connected to the low-voltage side bridge arm; the low-voltage side bridge arm is composed of two switching structures from each submodule, and then connected to the low-voltage side capacitor C. si The capacitors are connected in parallel to form a low-voltage side half-bridge module, and the voltage across the low-voltage side capacitor is defined as V. si It is led out from the series terminal of the third and fourth switching transistors and connected to the high-frequency coupling inductor; By establishing a coupled inductor decoupling network, the effects of high-voltage side series voltage, low-voltage side current, and inductive coupling on the output are eliminated, and the duty cycle of the modulation signal without interference is obtained to control the switching transistors in the submodule.

2. The method according to claim 1, characterized in that: When analyzing the transmission of the low-voltage side voltage rise of the submodule to the high-voltage side within a cycle, the port connecting the low-voltage side of the submodule to the wave energy generation device can be considered as a power source. The magnitude of the current flowing through the low-voltage side capacitor is related to the inductor current i. Li equal; If the two submodules are DC collector systems, the low-voltage and high-voltage bridge arms of the two submodules are connected by a high-frequency coupling inductor L. i Connected, assuming the self-inductance coefficients of the inductors are L and L respectively. 11 L 22 The currents flowing through the high-frequency coupled inductor are i L1 i L2 ; The coupling effect of the inductance between the two sub-modules is equivalent to a controlled voltage source connected in series with the coupled inductor.

3. The method according to claim 2, characterized in that: Based on the modulation strategy, the operating modes of DC collector systems are divided into buck mode and boost mode; In buck mode, the expressions for inductor current and low-side output voltage are given by formula (1): （1） in, , The duty cycle of the modulation signal. , =1,2; In boost mode, the expressions for inductor current and output voltage are given by formula (2): （2） Where M is the mutual inductance coefficient, , =1, 2.

4. The method according to claim 3, characterized in that: The general formula for expressing the output quantity with respect to the duty cycle of the modulation signal of the submodule is formula (3): （3） Among them, G i11 G i12 G i13 G i21 G i22 G i23 G v11 G v12 G v13 G v21 G v22 G v2 The coefficients before each variable are given, and the duty cycle of the sampled submodule modulation signal is defined as follows: d1 , d2 Its corrected output value is d1、 d2.

5. The method according to claim 4, characterized in that: In step-down mode, the functional expression of the feedforward compensation device is given by formula (4): （4） After introducing the decoupling network, the output quantity is related to the duty cycle of the modulation signal of the submodule. d1 , d2 The expression is formula (5): （5）。 6. The method according to claim 5, characterized in that: In boost mode, the functional expression of the feedforward compensation device is given by formula (6): （6） After introducing the decoupling network, the output quantity is related to the duty cycle of the modulation signal of the submodule. d1 , d2 The expression is formula (7): （7）。 7. The method according to claim 1, characterized in that: When the rectification scheme of the wave energy generator is uncontrolled rectification, it can be switched to a generator speed control loop as needed, and the speed of the wave energy generator can be controlled by adjusting the current at the low-voltage side port. This means controlling and regulating the current flowing through the high-frequency coupling inductor, including: The measured rotational speed ω of the wave energy generator i With reference value of rotational speed ω ref The comparison result is used by a PI controller to obtain the reference current i. ref ;change i ref With the measured inductor current value i Li The weighted values ​​are then used to obtain the duty cycle d of the modulation signal before correction via a PI controller. i The duty cycle d of the modulation signal is obtained through a coupled inductor decoupling network. i .

8. The method according to claim 1, characterized in that: The coupled inductor-type DC current collector system includes multiple multi-port DC current collectors that correspond one-to-one with the wave energy power generation device. Two multi-port DC current collectors are connected through a high-frequency coupled inductor. Each multi-port DC current collector uses a switching DC-DC converter circuit to distribute the low-voltage side to the wave energy power generation device to ensure that each generator set operates independently. The DC voltage is then boosted and energy is collected before being connected in series to the high-voltage side high-voltage DC bus.

9. The method according to claim 8, characterized in that: The switching DC-DC converter circuit includes four switching structures formed by anti-parallel connection of field-effect transistors and diodes. The source of the first switching transistor and the drain of the second switching transistor are connected in series, and the two switching structures together form a high-voltage side bridge arm. This high-voltage side bridge arm and its high-voltage side capacitor are connected in parallel to form a high-voltage side half-bridge module. The drain of the third switching transistor and the source of the fourth switching transistor are connected in series, and the two switching structures together form a low-voltage side bridge arm. This low-voltage side bridge arm and its low-voltage side capacitor are connected in parallel to form a low-voltage side half-bridge module.

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