A direct current collection networking system of a large wave energy power generation device and a control method thereof

Abstract

The application provides a direct current collection networking system of a large wave energy power generation device and a control method thereof, the method comprising: identifying the type and signal interface of the wave energy power generation device and its rectifier connected to each sub-module; when the type of the sub-module is uncontrolled rectification, generating a first modulation signal according to a control strategy to control the switch tube in the sub-module; when the type of the sub-module is PWM rectification or load, generating a second modulation signal according to a control strategy to control the switch tube in the sub-module. The direct current collection system and the loop switching control strategy thereof can identify the form and interface type of the wave energy power generation device and its rectifier circuit, adapt to different types of wave energy power generation device and its rectification form, realize low-voltage side series voltage stabilizing control, wave energy generator speed control and duty cycle signal decoupling function, the control loop is simpler, and the overall performance is better.

Description

Technical Field

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

[0002] Wave energy is a renewable and clean energy source with high energy flux density, large energy reserves, wide distribution, and safe and stable supply. Moreover, my country has abundant coastal resources, so wave energy can be an important development target for my country to promote the construction of a new energy structure.

[0003] Due to the characteristics of large-scale array float-type wave energy generation devices—dispersed arrays, multiple generator sets, and continuous and uniform energy transmission—energy conversion and collection in large-scale array float-type wave energy generation and collection systems are relatively complex. The overall system's anti-interference capability is weak, and there are difficulties in standardizing the types and interfaces of wave energy generator sets and their rectifiers. Therefore, the design of DC collection systems needs to enhance system anti-interference capabilities, ensure voltage balance and stability on the low-voltage side of the DC collection system under operating conditions, and further address the complexity of control strategies caused by the different types and interfaces of wave energy generator sets and their rectifiers.

[0004] Firstly, to efficiently utilize wave energy, a comprehensive wave energy transmission network is needed. Nearshore wave energy generation typically employs an AC generation-AC collection-AC transmission method. However, this method suffers from high construction costs, significant losses, and overvoltage issues, making it suitable only for small-capacity wave energy generation devices located close to shore. Typical wave energy generation devices struggle to meet these requirements. Therefore, some researchers have proposed a hybrid AC / DC transmission scheme. Existing technical solutions offer a hybrid AC / DC transmission system for wave energy generator groups based on modular multilevel converters. The AC power generated by the wave energy generator is transmitted through two AC-DC-DC power conversion systems before being input to the high-voltage DC bus side for long-distance grid connection. This scheme also proposes a dual-current inner-loop control method to control the generator speed. The back-to-back high-voltage DC system provided by this scheme easily forms multi-terminal transmission, fitting the wide and dispersed distribution characteristics of wave energy generator groups. However, this control scheme only maintains the low-voltage side port voltage stability by changing the modulation signal duty cycle and does not propose a solution to the series port voltage coupling problem.

[0005] Secondly, 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 distributed wave energy generators generating electricity, which is then converted into DC power by rectifiers. The converted DC power is then collected and its voltage boosted by a DC collector system before being output as boosted DC power to a high-voltage DC bus. In this DC grid, the research on the DC collector system is a key technology for wave energy transmission. Existing technology proposes a multi-port bidirectional Buck-Boost converter, capable of bidirectional energy flow and DC voltage boosting, which has some feasibility for application in wave energy power generation DC collector systems. However, its hardware costs are high, and it does not consider port voltage equalization control. Existing technology proposes a control strategy for a four-switch Buck-Boost converter, reducing the impact of disturbances on the system. However, when applied to the field of wave energy power generation DC collector systems, it is necessary to consider the need to design different control strategies due to differences in the types and interfaces of wave energy generators and their rectifiers.

[0006] However, existing large-scale array float-type wave energy generation devices typically distribute a series of power generation devices 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 transferred to a collection system. However, different energy collection systems currently suffer from the following drawbacks:

[0007] (1) The AC collection system has a multi-stage power conversion structure, which leads to a complex structural design, often accompanied by high construction costs and large equipment size. It also has a weak ability to resist various interferences (such as modulation signal duty cycle fluctuations and voltage amplitude fluctuations). Due to the characteristics of AC power itself, it is very difficult to design a suitable control scheme to eliminate the influence of interference.

[0008] (2) Compared to AC energy collection systems, DC energy collection systems have a simpler circuit topology and fewer energy conversions, resulting in higher energy transmission efficiency. However, technical challenges remain: DC parallel energy collection systems connect the boosted DC voltage in parallel to a high-voltage DC bus, requiring a significant voltage boost. However, due to hardware limitations, multiple cascaded DC-DC converters are typically needed to meet the voltage boosting requirements. This not only makes circuit construction difficult in practical applications but also reduces system stability, hindering stable wave energy transmission. Furthermore, the large number of cascaded transformers makes it difficult to design control schemes that regulate generator power based on output.

[0009] (3) A DC-DC series energy collection system only requires a single DC-DC converter to boost the DC voltage. However, each sub-module in its circuit topology needs to have an independent inductor for power transmission, which greatly increases the hardware cost in the case of large wave energy generator sets. Furthermore, connecting the output voltages of multiple DC collector modules in series can lead to serious coupling problems between the voltages of the sub-modules.

[0010] It is evident that the existing control schemes only maintain the low-voltage side port voltage stability by changing the modulation signal duty cycle, without addressing the series port voltage coupling problem. Furthermore, these schemes aim to control the power transmission of the wave energy generator by stabilizing the low-voltage side port voltage. However, in practical applications, wave energy generators and their rectification schemes often exhibit various characteristics (e.g., uncontrolled rectification and PWM rectification), resulting in inconsistent power output under different rectification schemes, requiring analysis based on specific circumstances. While this multi-port bidirectional Buck-Boost converter is feasible for wave energy DC collector systems, its hardware costs are high, and it does not consider port voltage equalization control. Moreover, when applied to wave energy DC collector systems, the design of different control strategies due to variations in the types and interfaces of wave energy generators and their rectifiers must be considered.

[0011] Therefore, it is crucial to design appropriate control schemes to solve the series port voltage coupling problem, achieve low-voltage side port voltage balancing and generator maximum power point tracking, and improve the stability of DC collector systems. Summary of the Invention

[0012] In order to overcome the shortcomings of the prior art, the purpose of this invention is to provide a DC collection and networking system and method for a large wave energy power generation device. This system and method can solve the problems of the prior art that only regards the wave energy generator and its rectifier module as a low-voltage DC port, without taking into account the different types and interface types of generator sets and rectifier modules.

[0013] To solve the above problems, the technical solution adopted by the present invention is as follows:

[0014] A DC collection and networking system for a large-scale wave energy power generation device includes:

[0015] Multiple sets of wave energy generation devices and a DC current collection system are provided. Each sub-module of the DC current collection system is distributed and connected to each set of wave energy generation devices through a low-voltage side. Each set of wave energy generators is connected to the DC current collection system with a rectifier module. The rectifier module is used to convert the AC power generated by the wave energy generation device into a low-voltage DC power signal, and then boost the low-voltage DC power signal through the DC current collection system and transmit it to the high-voltage DC bus side.

[0016] The DC current collector system includes multiple DC current collector modules that correspond one-to-one with the wave energy generation device. Each DC current collector module adopts a four-switch DC-DC converter circuit. Each DC current collector module includes a low-voltage side capacitor and a high-voltage side capacitor, and two DC current collector modules are connected by a coupling inductor.

[0017] A further embodiment is that the four-switch 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.

[0018] A control method for a DC collection grid system of a large-scale wave energy power generation device, the method being applied to control the aforementioned DC collection grid system of a large-scale wave energy power generation device, the method comprising the following steps:

[0019] Each sub-module of the DC collector system is distributed and connected to each group of wave energy generation devices through the low-voltage side.

[0020] The type and signal interface of the wave energy generation device and its rectifier connected to each sub-module are identified, and a control strategy is selected based on the identification results.

[0021] When the submodule is connected to an uncontrolled rectifier wave energy generation device, the first modulation signal is generated based on the collected generator speed, low-voltage side port voltage and inductor current, according to the control strategy, to control the switching transistors in the submodule.

[0022] When the submodule is connected to a wave energy generation device of type PWM rectification or load, a second modulation signal is generated based on the collected low-voltage side port voltage and inductor current, and the switching transistor in the submodule is controlled according to the control strategy.

[0023] According to the control method of the DC collection grid system of a large wave energy power generation device provided by the present invention, it is assumed that the DC collection system is connected to n wave energy generator sets and rectifier modules, and V is defined. si The low-voltage DC side voltage for each submodule, V i The voltage is the high-voltage side voltage of the submodule. Since the generator sets on the distributed side are connected in series on the high-voltage side through the DC collector submodule, the high-voltage DC bus voltage is the sum of the high-voltage side voltages of each submodule.

[0024] Define C siL i and C i These are the low-voltage side capacitor, coupling inductor, and high-voltage side capacitor of the i-th submodule, respectively. To represent the inductor coupling effect between each 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 on that submodule.

[0025] According to the control method of the DC collection grid system of a large wave energy power generation device provided by the present invention, when each sub-module of the DC collection system is distributed to each group of wave energy power generation devices through the low-voltage side, the voltage matrix expression applied to the inductor of each sub-module is as follows:

[0026]

[0027] Among them, V Li (i = 1, 2, ..., n) represents the voltage applied to the inductor of the i-th submodule, L ii M is the self-inductance coefficient of the inductor. im (i = 1, 2, ..., n; m = 1, 2, ..., n; i ≠ m) represents the mutual inductance coefficient between the i-th and m-th submodules, i Li Let be the current flowing through the coupled inductor of the i-th submodule.

[0028] According to the control method of the DC collection network system of a large wave energy power generation device provided by the present invention, taking a DC collection system with two sub-modules (n=2) as an example, the working mode of the DC collection system is divided into buck mode and boost mode according to the modulation strategy.

[0029] In buck mode, the small-signal modeling equations for the inductor current and the low-voltage side output voltage are expressed as Equation (2):

[0030]

[0031] in,

[0032] In boost mode, the small-signal modeling equations for inductor current and output voltage are expressed as formula (3):

[0033]

[0034] in,

[0035] According to the present invention, a control method for a DC collection grid system of a large wave energy power generation device is provided. The control strategy includes: when the submodule is connected to an uncontrolled rectifier, an uncontrolled rectifier control strategy is adopted, and the control strategy is switched to a low-voltage side port voltage control loop or a generator speed control loop as needed.

[0036] When switching to the low-voltage side port voltage control loop, the low-voltage side port voltage V of the acquisition submodule is... si and the reference voltage value V ref Weighting;

[0037] When switching to the generator speed control loop, the generator speed ω is collected. i With reference value of rotational speed ω ref The weighted values ​​are then passed through a PI controller to obtain the inductor current reference value i. ref With the sampled inductor current value i Li The signal is weighted, and the weighted result is used by a PI controller to obtain the duty cycle d of the modulation signal before correction. i * The duty cycle d of the first modulation signal is obtained through a coupled inductor decoupling network. i .

[0038] According to the present invention, a control method for a DC collection grid system of a large wave energy power generation device is provided, wherein the control strategy includes: when the submodule is connected to a PWM rectification type or the submodule is connected to a load on the low-voltage side, a PWM rectification control strategy is adopted.

[0039] The low-voltage side port voltage V of the acquisition submodule si and the reference voltage value V ref In comparison, the comparison result is used by a PI controller to obtain the inductor current reference value i. ref With the sampled inductor current value i Li The signal is weighted, and the weighted result is used by a PI controller to obtain the duty cycle d of the modulation signal before correction. i * The duty cycle d of the modulation signal is obtained through a coupled inductor decoupling network. i .

[0040] According to the control method of the DC collection grid system of a large wave energy power generation device provided by the present invention, for a PWM rectified wave energy power generation device, when analyzing disturbances, the control strategy eliminates the influence of disturbances and inductive coupling on the coupled inductor current, and converts the control object into the coupled inductor current.

[0041] According to the control method of the DC collection grid system of a large wave energy power generation device provided by the present invention, when a load is connected to the low-voltage side of the sub-module of the DC collection system, the sub-module of the DC collection system needs to stabilize the low-voltage side port voltage V. si Furthermore, since the current flowing through the load and the voltage applied to the load are linearly related, it is only necessary to eliminate the influence of disturbances and inductive coupling on the load voltage through control strategies.

[0042] In practical applications, the voltage applied across the load, i.e. the voltage across the low-voltage side capacitor, converts the controlled object into the low-voltage side port voltage.

[0043] Therefore, compared with existing technologies, this invention proposes a systematic control loop switching scheme to address different types of wave energy generator sets and their rectification and conversion methods, and considering the case of loads connected to the low-voltage side of the DC current collection system. This scheme can automatically identify the connected signals to determine the loop control scheme, providing diverse control structures and controlled object services without increasing the number of control loops. These include high-voltage side series voltage balancing, wave energy generator speed control, and submodule decoupling functions. Thus, this invention not only ensures optimal power control of the wave energy generator set and stable high-voltage DC voltage, but also greatly simplifies the control loop of the DC current collection system and optimizes the overall performance of the control loop.

[0044] Therefore, the DC power collection system and its loop switching control strategy proposed in this invention can identify the form and interface type of wave energy generator sets and their rectifier circuits, and adapt to different types of wave energy generator sets and their rectification forms. It can realize low-voltage side series voltage regulation control, wave energy generator speed control and duty cycle signal decoupling functions. Compared with other DC power collection systems and their control schemes, it has a simpler control loop and better overall performance.

[0045] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0046] Figure 1 This is a circuit diagram of an embodiment of a DC collection and networking system for a large wave energy power generation device according to the present invention.

[0047] Figure 2 This is a circuit diagram of the DC collection system in an embodiment of a DC collection network system for a large wave energy power generation device according to the present invention.

[0048] Figure 3 This is a control principle diagram of the control strategy in an embodiment of the control method for a DC collection and networking system of a large wave energy power generation device according to the present invention.

[0049] Figure 4 This is a control principle diagram of the uncontrolled rectifier control strategy in an embodiment of the control method for a DC collection and networking system of a large wave energy power generation device according to the present invention.

[0050] Figure 5 This is a control principle diagram of the PWM rectification control strategy in an embodiment of the control method for a DC collection and networking system of a large wave energy power generation device according to the present invention.

[0051] Figure 6This is a flowchart of the control strategy in an embodiment of the control method for a DC collection and networking system of a large wave energy power generation device according to the present invention.

[0052] Figure 7 This is a diagram showing the port voltage waveforms of two sub-modules on the high-voltage side in an embodiment of the control method for a DC collection network system of a large wave energy power generation device according to the present invention.

[0053] Figure 8 This is a voltage waveform diagram observed at two low-voltage side ports in an embodiment of the control method of a DC collection network system for a large wave energy power generation device according to the present invention.

[0054] Figure 9 This is a current waveform diagram of the inductors of two sub-modules in an embodiment of the control method of a DC collection network system for a large wave energy power generation device of the present invention.

[0055] Figure 10 This is a rotational speed diagram of a wave energy power generation device using uncontrolled rectification, as shown in an embodiment of the control method for a DC collection network system of a large wave energy power generation device according to the present invention. Detailed Implementation

[0056] 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.

[0057] An example of a DC collection and networking system for a large-scale wave energy power generation device:

[0058] See Figure 1 The present invention provides a DC collection and networking system for a large wave energy power generation device, comprising: multiple sets of wave energy power generation devices and a DC collection system. Each sub-module of the DC collection system is distributed and connected to each set of wave energy power generation devices through a low-voltage side. Each set of wave energy generators is connected to the DC collection system by a rectifier module. The rectifier module is used to convert the AC power generated by the wave energy power generation device into a low-voltage DC power signal, and then boost the low-voltage DC power signal through the DC collection system and transmit it to the high-voltage DC bus side.

[0059] The DC current collector system includes multiple DC current collector modules that correspond one-to-one with the wave energy generation device. Each DC current collector module adopts a four-switch DC-DC converter circuit. Each DC current collector module includes a low-voltage side capacitor and a high-voltage side capacitor, and two DC current collector modules are connected by a coupling inductor.

[0060] In this embodiment, the four-switch DC-DC converter circuit includes four switching structures consisting of field-effect transistors and diodes connected in anti-parallel, with 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 high-voltage side bridge arm and its high-voltage side capacitor C i Parallel connection to form a high-voltage side half-bridge module; switching transistor S 3i The drain and switching transistor S 4i The source terminals are connected in series, and the two switching structures together form the low-voltage side bridge arm. This low-voltage side bridge arm is connected to the low-voltage side capacitor C. si They are connected in parallel to form a low-voltage side half-bridge module.

[0061] In practical applications, the wave energy generation device in this embodiment is a wave energy generator. Since the generator set cannot operate under no-load conditions, a permanent magnet synchronous motor (PMSM) is commonly used to form the wave energy generator set. The AC power generated by the generator set is converted to DC power by a rectifier (generally an uncontrolled rectifier or a PWM rectifier). Then, the low-voltage DC power is boosted and transmitted to the high-voltage DC bus side through a DC collector system. The multi-port DC collector system uses a four-switch DC-DC converter circuit, which can realize DC power collection and boost transmission functions for different types of wave energy generator sets. In addition, by adding a coupling inductor, the dynamic response performance of the circuit topology is improved, the hardware construction cost and size are reduced, and the influence of the coupling inductor on other sub-modules is eliminated by optimizing the control strategy, thus achieving decoupling.

[0062] Specifically, assuming the DC current collector system connects to n wave energy generator sets and their rectifier modules, its topology is as follows: Figure 2 As shown. Define V si Low-voltage DC side voltage for each submodule, V i This is the high-voltage side voltage of the submodule. Since the generator sets on the distributed side are connected in series on the high-voltage side through the DC collector submodule, the high-voltage DC bus voltage is the sum of the high-voltage side voltages of each submodule.

[0063] 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 inductive 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. Where M... im(i = 1, 2, ..., n, m = 1, 2, ..., n, i ≠ m) are the mutual inductance coefficients, i ’ Lm This indicates the rate of change of inductor current on other DC collector device submodules.

[0064] Each submodule also contains four switching structures consisting of anti-parallel connections of field-effect transistors and diodes, with 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 The drain and switching transistor S 4i The sources of the transistors are connected in series, and the two switching transistors together 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 4i The series terminal is led out and connected to a high-frequency coupled inductor.

[0065] An embodiment of a control method for a DC collection grid system of a large wave energy power generation device:

[0066] A control method for a DC collection network system of a large-scale wave energy power generation device is disclosed. This method is applied to the control of the aforementioned DC collection network system of a large-scale wave energy power generation device. Figure 6 As shown. The method includes the following steps:

[0067] Each sub-module of the DC collector system is distributed and connected to each group of wave energy generation devices through the low-voltage side.

[0068] The type and signal interface of the wave energy generation device and its rectifier connected to each sub-module are identified, and a control strategy is selected based on the identification results.

[0069] When the submodule is connected to an uncontrolled rectifier wave energy generation device, the first modulation signal is generated based on the collected generator speed, low-voltage side port voltage and inductor current, according to the control strategy, to control the switching transistors in the submodule.

[0070] When the submodule is connected to a wave energy generation device of type PWM rectification or load, a second modulation signal is generated based on the collected low-voltage side port voltage and inductor current, and the switching transistor in the submodule is controlled according to the control strategy.

[0071] In this embodiment, it is assumed that the DC current collector system is connected to n wave energy generators and rectifier modules, and V is defined as follows: si The low-voltage DC side voltage for each submodule, V i The voltage is the high-voltage side voltage of the submodule. Since the generator sets on the distributed side are connected in series on the high-voltage side through the DC collector submodule, the high-voltage DC bus voltage is the sum of the high-voltage side voltages of each submodule.

[0072] Then, define 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. To represent the inductor coupling effect between each 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 on that submodule.

[0073] In this embodiment, when the various sub-modules of the DC collector system are distributed to each group of wave energy generation devices through the low-voltage side, the voltage matrix expression applied to the inductor of each sub-module is formula (1):

[0074]

[0075] Among them, V Li (i = 1, 2, ..., n) represents the voltage applied to the inductor of the i-th submodule, L ii M is the self-inductance coefficient of the inductor. im (i = 1, 2, ..., n; m = 1, 2, ..., n; i ≠ m) represents the mutual inductance coefficient between the i-th and m-th submodules, i Li Let be the current flowing through the coupled inductor of the i-th submodule.

[0076] In this embodiment, taking a DC collector system with two sub-modules (n=2) as an example, the operating modes of the DC collector system are divided into buck mode and boost mode according to the modulation strategy.

[0077] In buck mode, the small-signal modeling equations for the inductor current and the low-voltage side output voltage are expressed as Equation (2):

[0078]

[0079] in,

[0080] In boost mode, the small-signal modeling equations for inductor current and output voltage are expressed as equation (3):

[0081]

[0082] in,

[0083] Specifically, the control strategy in this embodiment includes: when the submodule is connected to an uncontrolled rectifier, an uncontrolled rectifier control strategy is adopted, and the control strategy is switched to a low-voltage side port voltage control loop or a generator speed control loop as needed.

[0084] When switching to the low-voltage side port voltage control loop, the low-voltage side port voltage V of the acquisition submodule is... si and the reference voltage value V ref Weighting is applied.

[0085] When switching to the generator speed control loop, the generator speed ω is collected. i With reference value of rotational speed ω ref The weighted values ​​are then passed through a PI controller to obtain the inductor current reference value i. ref With the sampled inductor current value i Li The signal is weighted, and the weighted result is used by a PI controller to obtain the duty cycle d of the modulation signal before correction. i * The duty cycle d of the first modulation signal is obtained through a coupled inductor decoupling network. i .

[0086] Specifically, the control strategy in this embodiment also includes: when the submodule is connected to a PWM rectifier or the submodule is connected to a load on the low-voltage side, a PWM rectifier control strategy is adopted;

[0087] The low-voltage side port voltage V of the acquisition submodule si and the reference voltage value V ref In comparison, the comparison result is used by a PI controller to obtain the inductor current reference value i. ref With the sampled inductor current value i Li The signal is weighted, and the weighted result is used by a PI controller to obtain the duty cycle d of the modulation signal before correction. i * The duty cycle d of the modulation signal is obtained through a coupled inductor decoupling network. i .

[0088] For PWM rectified wave energy generation devices, when analyzing disturbances, the influence of disturbances and inductive coupling on the coupled inductor current is eliminated through control strategies, and the controlled object is converted into the coupled inductor current.

[0089] When a load is connected to the low-voltage side of a DC collector system submodule, the submodule needs to stabilize the low-voltage side port voltage V. si Furthermore, since the current flowing through the load and the voltage applied to the load are linearly related, it is only necessary to eliminate the influence of disturbances and inductive coupling on the load voltage through the control strategy. In practical applications, the voltage applied across the load is the voltage across the low-voltage side capacitor, which converts the controlled object into the low-voltage side port voltage.

[0090] In practical applications, the sub-modules of the DC collection network system of the wave energy power generation device proposed in this embodiment are distributed to each generator set through the low-voltage side, which can avoid mutual influence between their port voltages, thus ensuring the independent operation of the wave energy generator. The voltage matrix applied to the inductors of the n sub-modules is expressed as shown in Equation (1) above.

[0091] Based on the modulation strategy, the operating modes of the DC collector system proposed in this embodiment are divided into two types: buck mode and boost mode. In buck mode, the small-signal modeling equations for inductor current and low-voltage side output voltage are Equation (2); in boost mode, the small-signal modeling equations for inductor current and output voltage are Equation (3).

[0092] According to the small-signal modeling equation, the expressions for the low-voltage side port voltage and inductor current of the DC collector system are related to the duty cycle of the modulation signal, the high-voltage side port voltage, and the inductor current of other sub-modules. To eliminate the adverse effects of minor disturbances other than the duty cycle on the output, this embodiment incorporates a decoupling network into the control strategy. Through the decoupling network, the influence of the high-voltage side series voltage, the low-voltage side current, and coupling effects on the output can be eliminated, ultimately yielding a duty cycle signal expression free of interference, so that the output is only related to the duty cycle of the modulation signal.

[0093] In this embodiment, the generator set of the large-scale array float-type wave energy power generation device converts AC power into DC power through a rectifier connection and connects to the low-voltage side DC collector system. The rectifier type is generally uncontrolled rectifier or PWM rectifier. In addition, there are also cases where the DC collector system submodules are connected to loads on the low-voltage side. The control scheme of the DC collector network structure proposed in this invention can identify the connected objects on the low-voltage side and determine the interface type of the generator set rectifier. It then selects different control strategies based on the generator set's rectification scheme to eliminate the interference of minor disturbances on the output, and utilizes the mutual inductance of coupled inductors to ensure the stable operation of each DC collector system submodule.

[0094] For the PWM rectification scheme: Since it operates with unity power factor, it can achieve maximum power point tracking control of the high-voltage DC bus voltage for the wave energy generator. Therefore, the DC collector system submodule only needs to stabilize the low-voltage side port voltage V. siThis ensures stable system operation. When analyzing disturbances, control strategies are needed to eliminate the impact of disturbances and inductive coupling on the low-voltage side port voltage. When the low-voltage side port voltage remains stable, the fan speed control and power output can also remain stable.

[0095] For the uncontrolled rectification scheme: the wave generator speed, maximum power point, and high-voltage DC bus voltage are all uncontrolled. Therefore, the DC collector system submodule needs to stabilize the low-voltage side port voltage V. si Furthermore, it is necessary to achieve the generator's maximum power point tracking function. When analyzing disturbances, it is necessary to eliminate the influence of disturbances and inductive coupling on the current of the uncontrolled rectifier on the low-voltage side through control strategies. In practical applications, it can be assumed that the current flowing through the uncontrolled rectifier is equal to the coupled inductor current, so the control object is converted into the coupled inductor current.

[0096] For DC collector system submodules with loads connected to the low-voltage side: The DC collector system submodules need to stabilize the low-voltage side port voltage V. si Since the current flowing through the load and the voltage applied to the load are linearly related, it is only necessary to eliminate the influence of disturbances and inductive coupling on the load voltage through control strategies. In practical applications, the voltage applied across the load is the voltage across the low-voltage side capacitor, so the controlled object is converted to the low-voltage side port voltage.

[0097] Therefore, addressing issues such as inductor coupling between submodules in a DC current collector system and differences in low-voltage side access objects, this embodiment proposes an anti-interference loop switching control strategy for a wave energy DC current collector system, such as... Figure 3 As shown.

[0098] The control strategy proposed in this embodiment is implemented by four control loops, which are: (1) low-voltage side port voltage control loop (low-voltage side voltage loop); (2) uncontrolled rectifier generator speed control loop (speed control loop); (3) inductor current control loop (inductor current inner loop); and (4) coupled inductor decoupling network.

[0099] When the generator set rectification scheme is uncontrolled rectification, an uncontrolled rectification control strategy is used. This strategy incorporates a generator speed control loop and switches between a low-voltage side port voltage control loop and a generator speed control loop as needed. When switching to the low-voltage side port voltage control loop, the low-voltage side port voltage V of the submodule is collected. si (i = 1, 2, 3), and compared with the reference voltage value V ref Weighting is performed; when switching to the uncontrolled rectifier generator speed control loop, the generator speed ω is collected. i With reference value of rotational speed ω ref The weighted average is then used to obtain the inductor current reference value i via a PI controller. refWith the sampled inductor current value i Li The weighted values ​​are then used to calculate the duty cycle d of the modulation signal before correction, which is obtained through a PI controller. i * Finally, the duty cycle d of the modulation signal is obtained through a coupled inductor decoupling network. i The system and its control strategy ensure the stability of the high-voltage side series voltage through a high-voltage side series voltage control loop, improve the generator's operation through a generator speed control loop to enable it to track the maximum power point, and enhance system stability by eliminating the impact of disturbances and coupling on the inductor current through a coupled inductor decoupling network. The uncontrolled rectifier control strategy is as follows: Figure 4 As shown.

[0100] When the rectification scheme is PWM rectification or the load is connected to the low-voltage side of the submodule, the generator set's power is directly reflected in the low-voltage side port voltage. Therefore, no additional speed control system is needed; instead, the low-voltage side port voltage of the submodule is adjusted. Thus, a PWM rectification control strategy is adopted. First, the low-voltage side port voltage V of the submodule is collected. si i = 1, 2, 3… and the reference voltage value V ref In comparison, the obtained result is used by a PI controller to derive the inductor current reference value i. ref With the sampled inductor current value i Li The weighted values ​​are then used to calculate the duty cycle d of the modulation signal before correction, which is obtained through a PI controller. i * Finally, the duty cycle d of the modulation signal is obtained through a coupled inductor decoupling network. i The system and its control strategy ensure low-voltage side voltage stability, while eliminating the adverse effects of disturbances and inductive coupling on the DC collector system through a decoupling network. The PWM rectification control strategy is as follows: Figure 5 As shown.

[0101] In practical applications, taking a three-port DC current collector system as an example, two wave energy generators are connected to the low-voltage side of the DC current collector system, while the high-voltage side is connected in series to a high-voltage DC bus equivalent to a 600V voltage source. For example... Figure 7 and 8 As shown, Figure 7 The diagram shows the port voltage waveforms of the two sub-modules on the high-voltage side. Figure 8 This is a diagram showing the voltage waveforms observed at the two low-voltage side ports. Figure 7 and Figure 8It can be seen that the high-voltage side port voltage of each submodule is stable at 300V with an error controlled within 1%, proving that the DC collection network structure achieves voltage balance of the high-voltage side port of each submodule under steady state. Furthermore, through the proposed DC collection system, the port voltage of the wave energy generator and its rectifier module can be stabilized at 150V with an error controlled within 1%, verifying the effectiveness and feasibility of the voltage control loop.

[0102] See Figure 9 , Figure 9 The current waveforms flowing through the inductors of the two sub-modules are shown below. Figure 9 It can be seen that the inductor current control loop stabilizes the current amplitude flowing through the coupled inductor within -20 to 20A, verifying the effectiveness and feasibility of the inductor current control loop.

[0103] When the wave energy generator set uses uncontrolled rectification, a speed control circuit is also required. For example... Figure 10 As shown, Figure 10 The rotational speed diagram of a wave energy generator using uncontrolled rectification is provided by... Figure 10 It can be seen that the generator speed control loop stabilized the generator speed at 45 rad / s with an error controlled within 1%, verifying the effectiveness and feasibility of the generator speed control loop.

[0104] Therefore, the DC power collection system and its loop switching control strategy proposed in this invention can identify the form and interface type of wave energy generator sets and their rectifier circuits, and adapt to different types of wave energy generator sets and their rectification forms. It can realize low-voltage side series voltage regulation control, wave energy generator speed control and duty cycle signal decoupling functions. Compared with other DC power collection systems and their control schemes, it has a simpler control loop and better overall performance.

[0105] 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.

[0106] 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 DC collection grid system of a large-scale wave energy power generation device, characterized in that, The DC aggregation network system includes: Multiple sets of wave energy generation devices and a DC current collection system are provided. Each sub-module of the DC current collection system is distributed and connected to each set of wave energy generation devices through a low-voltage side. Each set of wave energy generators is connected to the DC current collection system with a rectifier module. The rectifier module is used to convert the AC power generated by the wave energy generation device into a low-voltage DC power signal, and then boost the low-voltage DC power signal through the DC current collection system and transmit it to the high-voltage DC bus side. The DC collector system includes multiple DC collector modules that correspond one-to-one with the wave energy generation device. Each DC collector module adopts a four-switch DC-DC converter circuit. Each DC collector module includes a low-voltage side capacitor and a high-voltage side capacitor, and two DC collector modules are connected by a coupling inductor. The method includes the following steps: Each sub-module of the DC collector system is distributed and connected to each group of wave energy generation devices through the low-voltage side. The type and signal interface of the wave energy generation device and its rectifier connected to each sub-module are identified, and a control strategy is selected based on the identification results. When the submodule is connected to an uncontrolled rectifier wave energy generation device, the first modulation signal is generated based on the collected generator speed, low-voltage side port voltage and inductor current, according to the control strategy, to control the switching transistors in the submodule. When the submodule is connected to a wave energy generation device of type PWM rectification or load, a second modulation signal is generated based on the collected low-voltage side port voltage and inductor current, and the switching transistor in the submodule is controlled according to the control strategy. Assuming a DC power collection system connects to n wave energy generators and rectifier modules, define V si The low-voltage DC side voltage for each submodule, V i The voltage is the high-voltage side voltage of the submodule. Since the generator sets on the distributed side are connected in series on the high-voltage side through the DC collector submodule, the high-voltage DC bus voltage is the sum of the high-voltage side voltages of each submodule. Define 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. To represent the inductor coupling effect between each 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 on that submodule. Taking a DC collector system with two sub-modules (n=2) as an example, 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 small-signal modeling equations for the inductor current and the low-voltage side output voltage are expressed as Equation (2): in, ; In boost mode, the small-signal modeling equations for inductor current and output voltage are expressed as formula (3): in, .

2. The method according to claim 1, characterized in that: The four-switch 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.

3. The method according to claim 1, characterized in that: When the various sub-modules of the DC collector system are distributed and connected to each group of wave energy generation devices through the low-voltage side, the voltage matrix expression applied to the inductor of each sub-module is given by formula (1): （1） Among them, V Li (i=1,2,…,n) represents the voltage applied to the inductor of the i-th submodule, L ii M is the self-inductance coefficient of the inductor. im (i=1,2,…,n; m=1,2,…,n; i≠m) represents the mutual inductance coefficient between the i-th and m-th submodules, i Li Let be the current flowing through the coupled inductor of the i-th submodule.

4. The method according to claim 1, characterized in that: The control strategy includes: when the submodule is connected to an uncontrolled rectifier, an uncontrolled rectifier control strategy is adopted, and the low-voltage side port voltage control loop or generator speed control loop is switched as needed. When switching to the low-voltage side port voltage control loop, the low-voltage side port voltage V of the acquisition submodule is... si and the reference voltage value V ref Weighting; When switching to the generator speed control loop, the generator speed ω is collected. i With reference value of rotational speed ω ref The weighted values ​​are then passed through a PI controller to obtain the inductor current reference value i. ref With the sampled inductor current value i Li The signal is weighted, and the weighted result is used by a PI controller to obtain the duty cycle d of the modulation signal before correction. i The duty cycle d of the first modulation signal is obtained through a coupled inductor decoupling network. i .

5. The method according to claim 1, characterized in that: The control strategy includes: when the submodule is connected to a PWM rectifier or the submodule is connected to a load on the low-voltage side, a PWM rectifier control strategy is adopted; The low-voltage side port voltage V of the acquisition submodule si and the reference voltage value V ref In comparison, the comparison result is used by a PI controller to obtain the inductor current reference value i. ref With the sampled inductor current value i Li The signal is weighted, and the weighted result is used by a PI controller to obtain the duty cycle d of the modulation signal before correction. i The duty cycle d of the modulation signal is obtained through a coupled inductor decoupling network. i .

6. The method according to claim 5, characterized in that: For PWM rectified wave energy generation devices, when analyzing disturbances, the influence of disturbances and inductive coupling on the coupled inductor current is eliminated through control strategies, and the controlled object is converted into the coupled inductor current.

7. The method according to claim 5, characterized in that: When a load is connected to the low-voltage side of a DC collector system submodule, the submodule needs to stabilize the low-voltage side port voltage V. si Furthermore, since the current flowing through the load and the voltage applied to the load are linearly related, it is only necessary to eliminate the influence of disturbances and inductive coupling on the load voltage through control strategies. In practical applications, the voltage applied across the load, i.e. the voltage across the low-voltage side capacitor, converts the controlled object into the low-voltage side port voltage.

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