Boost inversion device of grid-following type offshore wind turbine generator and control method

Abstract

The invention relates to the technical field of power electronic devices, in particular to a boost inversion device of a following grid type offshore wind turbine generator and a control method. The three-phase rectifier bridge and the Boost chopper circuit are adopted to form the light topological boost rectifier module, an electrolytic capacitor for stabilizing direct current voltage is not needed, the topological structure of the boost rectifier module is simplified, the first control module adopting MPPT + PFC cooperative control is constructed, mutual cooperation is achieved in a capacitor-free scene, and the power supply efficiency is improved. Maximum power tracking and power factor correction functions are achieved, and the problems that in the prior art, a large-capacity electrolytic capacitor needs to be relied on to maintain voltage stability, and consequently the size of a system is increased, and the service life is shortened are solved. Moreover, the post-stage current source type inverter is directly connected to the power grid, and a single current loop tracking mode is utilized, so that the technical problem that the voltage endurance capability of a power device in the system is relatively high on the basis of relatively high direct current bus voltage in the prior art is solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power electronics, in particular to a boost inverter device and control method of a grid-connected offshore wind turbine. BACKGROUND

[0002] At present, the power system is transforming into a new type of power system with new energy as the core. The power generated by new energy needs to be efficiently connected to the power grid and fully utilized, which to a large extent relies on the precise regulation and control of power electronic conversion equipment. Among them, the grid-connected permanent magnet direct drive wind power system has become the core equipment for independent energy supply in remote islands and mountainous areas due to its significant advantages of flexible installation and convenient maintenance. At present, the implementation scheme of the power electronic conversion process of this type of wind power system mainly relies on a boost inverter device composed of a voltage source rectifier and a voltage source inverter. Specifically, it can be divided into two aspects. On the one hand, the voltage source rectifier in the front stage adopts maximum power point tracking (MPPT) control on the DC voltage, taking the DC bus voltage as the core object of regulation, relying on a large-capacity electrolytic capacitor to maintain voltage stability, and then realizing the approximation of the maximum power point. On the other hand, the voltage source inverter in the rear stage adopts a double-closed-loop dq decoupling control strategy to realize grid connection.

[0003] However, the above prior art needs to rely on a large number of electrolytic capacitors, resulting in a shortened system life and an increased volume, and it needs to be based on a higher DC bus voltage, which has a higher requirement for the voltage withstand capability of power devices in the system. SUMMARY

[0004] The present application provides a boost inverter device and control method of a grid-connected offshore wind turbine, which solves the technical problem that the prior art needs to rely on a large number of electrolytic capacitors, resulting in a shortened system life and an increased volume, and it needs to be based on a higher DC bus voltage, which has a higher requirement for the voltage withstand capability of power devices in the system.

[0005] In one aspect, the present application provides a boost inverter device of a grid-connected offshore wind turbine, comprising: a first control module, a second control module, and a cascaded wind turbine, a boost rectifier module, and a current source inverter; the boost rectifier module comprises a connected three-phase rectifier bridge and a Boost chopper circuit;

[0006] The first control module is connected with the boost rectifier module and is used to obtain and adjust the output current of the boost rectifier module according to the output current of the boost rectifier module, the first target reference current, the pulse voltage mapped from the AC voltage to the DC side, and the input side current;

[0007] The second control module is connected with the current source type inverter, and is configured to acquire and generate, according to synchronous phase angles corresponding to three-phase currents output by the current source type inverter and three-phase alternating current voltage signals on a load side, d-axis active currents and q-axis reactive currents in a synchronous rotating coordinate system; acquire a second target reference current; and adjust output currents of the current source type inverter according to the second target reference current, the d-axis active currents and the q-axis reactive currents.

[0008] Optionally, the acquiring and adjusting the output currents of the boost rectifier module according to the output currents of the boost rectifier module, the first target reference current, the pulse voltage mapped from the alternating current voltage to the direct current side and the input side current specifically comprises:

[0009] acquiring a current corresponding to the maximum power demand as the first target reference current;

[0010] generating an amplitude reference current according to the first target reference current and the output current by using a preset first PI controller;

[0011] multiplying the amplitude reference current and the pulse voltage mapped from the alternating current voltage to the direct current side to obtain a dynamic current reference value;

[0012] generating a first control signal according to the dynamic current reference value and the input side current by using a preset second PI controller, and outputting the first control signal to the Boost chopper circuit.

[0013] Optionally, the acquiring and generating, according to synchronous phase angles corresponding to three-phase currents output by the current source type inverter and three-phase alternating current voltage signals on a load side, d-axis active currents and q-axis reactive currents in a synchronous rotating coordinate system specifically comprises:

[0014] acquiring the synchronous phase angles corresponding to the three-phase currents output by the current source type inverter and the three-phase alternating current voltage signals on the load side;

[0015] converting the three-phase currents output by the current source type inverter into two-phase currents in a two-phase stationary coordinate system;

[0016] converting the two-phase currents to the d-axis active currents and the q-axis reactive currents in the synchronous rotating coordinate system by using Park transformation and the synchronous phase angles.

[0017] Optionally, the second target reference current comprises a d-axis current reference value and a q-axis current reference value, and the acquiring the second target reference current comprises:

[0018] acquiring and converting, to the synchronous rotating coordinate system, a current corresponding to the maximum power demand to obtain an initial target reference current;

[0019] The d-axis current component in the initial target reference current is used as the d-axis current reference value;

[0020] The q-axis current component in the initial target reference current is used as the q-axis current reference value.

[0021] Optionally, adjusting the output current of the current source inverter based on the second target reference current and the d-axis active current includes:

[0022] Using a preset third PI controller, a first voltage signal is generated based on the d-axis active current and the d-axis current reference value, and a second voltage signal is generated based on the q-axis reactive current and the q-axis current reference value. A second control signal is generated based on the first voltage signal and the second voltage signal, and the second control signal is output to the current source inverter.

[0023] Optionally, the Boost chopper circuit includes: a first IGBT switch, a freewheeling diode, and a high-frequency inductor;

[0024] The collector of the first IGBT switch is connected to one end of the high-frequency inductor and the anode of the freewheeling diode, respectively.

[0025] The emitter of the first IGBT switch is connected to the three-phase rectifier bridge and the current source inverter, respectively.

[0026] The gate of the first IGBT switch is connected to the first control module;

[0027] The other end of the high-frequency inductor is connected to the three-phase rectifier bridge;

[0028] The cathode of the freewheeling diode is connected to the current source inverter.

[0029] Optionally, the current source inverter includes: a three-phase full-bridge inverter module;

[0030] The DC side of the three-phase full-bridge inverter module is connected to one end of the smoothing inductor, and the other end of the smoothing inductor is connected to the cathode of the freewheeling diode.

[0031] The output side of the three-phase full-bridge inverter module is connected to the input end of the LC low-pass filter;

[0032] The output of the LC low-pass filter is connected to the three-phase load.

[0033] Optionally, the three-phase rectifier bridge is provided with three sets of bridge arms, and each set of bridge arms consists of two fast recovery diodes connected in series;

[0034] The wind turbine is connected to the connection point between the two fast recovery diodes of each group of bridge arms;

[0035] The two ends of each bridge arm are connected and connected to the Boost chopper circuit.

[0036] Optionally, the three-phase full-bridge inverter module is provided with three sets of branches, each set of branches consisting of two IGBTs connected in series;

[0037] The two ends of each branch are connected to each other and respectively connected to one end of the smoothing inductor and the emitter of the first IGBT switch.

[0038] The connection point of the two IGBT transistors in each branch is connected to the LC low-pass filter;

[0039] The gate of each IGBT is connected to the second control module.

[0040] In another aspect, the present invention provides a control method for a step-up inverter device of a grid-connected offshore wind turbine, applicable to any of the devices described above, the method comprising:

[0041] The first control module acquires and adjusts the output current of the boost rectifier module based on the output current of the boost rectifier module, the first target reference current, the pulse voltage mapped from the AC voltage to the DC side, and the input current.

[0042] The second control module acquires and generates the d-axis active current and q-axis reactive current in the synchronous rotating coordinate system based on the synchronous phase angles corresponding to the three-phase current output by the current source inverter and the three-phase AC voltage signal on the load side; acquires the second target reference current, and adjusts the output current of the current source inverter based on the second target reference current, the d-axis active current and the q-axis reactive current.

[0043] As can be seen from the above technical solutions, the present invention has the following advantages:

[0044] This invention provides a step-up inverter device for a grid-connected offshore wind turbine, comprising: a first control module, a second control module, and cascaded wind turbine, a step-up rectifier module, and a current source inverter; the step-up rectifier module includes a connected three-phase rectifier bridge and a Boost chopper circuit; the first control module is connected to the step-up rectifier module and is used to acquire and adjust the output current of the step-up rectifier module according to the output current of the step-up rectifier module, a first target reference current, a pulse voltage mapped from the AC voltage to the DC side, and the input current; the second control module is connected to the current source inverter and is used to acquire and generate d-axis active current and q-axis reactive current in a synchronous rotating coordinate system according to the three-phase current output by the current source inverter and the synchronous phase angle corresponding to the three-phase AC voltage signal on the load side; acquire a second target reference current, and adjust the output current of the current source inverter according to the second target reference current, the d-axis active current, and the q-axis reactive current.

[0045] In this invention, a lightweight boost rectifier module is constructed using a three-phase rectifier bridge and a Boost chopper circuit. This eliminates the need for electrolytic capacitors to stabilize the DC voltage, simplifying the topology of the boost rectifier module, reducing the size of the wind power system, and avoiding the problems of increased system size and shortened lifespan caused by existing technologies that rely on large-capacity electrolytic capacitors to maintain voltage stability. Furthermore, the first control module of this invention acquires and adjusts the output current of the boost rectifier module based on the output current, the first target reference current, the pulse voltage mapped from the AC voltage to the DC side, and the input current to correct the power factor and provide a stable current for the subsequent current source inverter. This breaks the conventional voltage tracking mode and directly drives power changes through current commands, eliminating the need for electrolytic capacitors. Furthermore, the second control module in this invention acquires and generates the d-axis active current and q-axis reactive current in a synchronous rotating coordinate system based on the synchronous phase angles corresponding to the three-phase current output by the current source inverter and the three-phase AC voltage signal on the load side; it acquires the second target reference current, and adjusts the output current of the current source inverter based on the second target reference current, the d-axis active current, and the q-axis reactive current, saving the dq decoupling calculation. This not only accelerates the dynamic response of the system, but also avoids the problem of existing technologies requiring a high DC bus voltage as a basis and placing high demands on the withstand voltage capability of power devices in the system. This significantly reduces the system's requirements for the withstand voltage level of power devices, while enhancing the system's adaptability and safety performance to wind speed fluctuations and fault conditions. Attached Figure Description

[0046] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0047] Figure 1 This is a structural schematic diagram of an offshore wind turbine provided in an embodiment of the present invention;

[0048] Figure 2 This is one of the structural schematic diagrams of a step-up inverter for a grid-connected offshore wind turbine provided in an embodiment of the present invention;

[0049] Figure 3 This is the second schematic diagram of the structure of a step-up inverter for a grid-connected offshore wind turbine provided in an embodiment of the present invention;

[0050] Figure 4 Control principle block diagrams of the first control module and the second control module provided in embodiments of the present invention;

[0051] Figure 5 This is a flowchart illustrating a control method for a grid-connected offshore wind turbine booster inverter, as provided in an embodiment of the present invention. Detailed Implementation

[0052] Existing traditional wind power systems use voltage-type MPPT control, which requires electrolytic capacitors to maintain voltage stability and regards DC bus voltage regulation as the core means of power point tracking. This mechanism inevitably relies on large-capacity electrolytic capacitors to maintain voltage stability, which will lead to increased system size and shortened lifespan. Furthermore, the inertia of the voltage loop itself will cause a significant delay in the power point tracking process. When there are sudden changes in sunlight or load fluctuations, the system will also exhibit structural problems such as slow response and voltage instability.

[0053] In addition, in order to maintain the AC voltage required for grid-connected operation, voltage source inverters usually require the DC bus voltage to be higher than the AC side voltage. That is, for a voltage source inverter to operate normally, it needs a higher DC bus voltage as a basis. This requirement not only limits the operating voltage range of the system and increases the boost pressure and energy consumption of the front-end circuit, but also increases the requirements for the voltage withstand capability of components. Ultimately, it affects the reliability and operating efficiency of the wind power system and limits its adaptability in low-voltage application scenarios.

[0054] The present invention provides a boost inverter device and control method for grid-connected offshore wind turbines. By simplifying the topology, utilizing direct current control to reduce capacitor limitations, and combining rate factor correction technology to improve power quality, this invention overcomes efficiency challenges through the integration of topology and control, achieving the design goal of a low-cost, high-reliability grid-connected wind power generation system. This invention offers advantages such as lightweight topology, wide voltage range adaptability, and strong adaptability, reducing construction costs, improving power supply reliability, and solving the technical problems of existing technologies that rely on a large number of electrolytic capacitors, leading to shortened system lifespan and increased size, and requiring a high DC bus voltage, which places high demands on the voltage withstand capability of power devices in the system.

[0055] To make the objectives, features, and advantages of this invention more apparent and understandable, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of this invention, and not all embodiments. 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.

[0056] Please see Figures 1 to 2 The present invention provides a step-up inverter device for a grid-connected offshore wind turbine, comprising: a first control module 1, a second control module 2, and cascaded wind turbine generator 3, a step-up rectifier module, and a current source inverter 6; the step-up rectifier module includes a three-phase rectifier bridge 4 and a Boost chopper circuit 5 connected together; the first control module 1 is connected to the step-up rectifier module and is used to acquire and adjust the output current of the step-up rectifier module according to the output current of the step-up rectifier module, a first target reference current, a pulse voltage mapped from the AC voltage to the DC side, and the input current; the second control module 2 is connected to the current source inverter 6 and is used to acquire and generate the d-axis active current and q-axis reactive current in a synchronous rotating coordinate system according to the three-phase current output by the current source inverter 6 and the synchronous phase angle corresponding to the three-phase AC voltage signal on the load side; acquire the second target reference current, and adjust the output current of the current source inverter 6 according to the second target reference current, the d-axis active current, and the q-axis reactive current.

[0057] It should be noted that the wind turbine generator 3 in this embodiment can be a permanent magnet direct-drive wind turbine generator 3, and the boost rectifier module adopts a lightweight topology without electrolytic capacitors, consisting of a three-phase rectifier bridge 4 and a boost chopper circuit 5. For example... Figure 1 As shown, the wind turbine generator 3, the boost rectifier module, and the current source inverter 6 are cascaded to form an offshore wind turbine unit.

[0058] The wind turbine generator 3 and the boost rectifier module together constitute the front-end energy conversion unit of the system. The wind turbine generator 3 employs a gearless architecture that directly connects the wind turbine and the permanent magnet synchronous generator, converting wind energy into three-phase alternating current whose frequency and amplitude vary with wind speed. The output of the wind turbine generator 3 is directly connected to the input of the boost rectifier module. In one example, the system uses a wide-adaptive speed control method for the permanent magnet direct-drive generator to achieve dynamic adjustment and control of energy input.

[0059] The core functions of the boost rectifier module are power factor correction and AC / DC conversion. Power factor refers to the ratio of active power to apparent power in an AC circuit. In the boost rectifier module, a high-frequency inductor performs energy conversion and buffering functions, and responds to the current direct control MPPT output by the first control module 1. This eliminates the need for electrolytic capacitors, thus completely removing the electrolytic capacitors used to stabilize DC voltage in existing technologies. This avoids the problems of relying on a large number of electrolytic capacitors, which leads to shortened system lifespan and increased size. Specifically, the three-phase rectifier bridge 4 converts the received AC power into a pulsating DC voltage containing AC side phase information. The Boost chopper circuit 5 incorporates a high-frequency inductor, which stores power fluctuations and regulates voltage boost. The overall topology is free of electrolytic capacitors, significantly reducing size and cost while improving reliability in high-humidity and high-salt-spray environments, meeting the requirements of offshore wind power applications.

[0060] The current source inverter 6 is used to respond to the control commands of the second control module 2, convert the received DC power into AC power, improve the quality of the AC power and output it, thereby maintaining the system power conservation and power quality stability without electrolytic capacitors.

[0061] In the absence of electrolytic capacitors and DC voltage pulsation, this embodiment controls the front-end energy conversion unit by controlling the current of the high-frequency inductor in the Boost chopper circuit 5 to track the maximum power point of the wind turbine. This avoids the voltage loop regulation scheme used in the prior art, which causes a significant delay in the power tracking process due to the inertia of the voltage loop itself. In the event of sudden changes in sunlight or load fluctuations, the system will also exhibit structural problems such as slow response and voltage instability.

[0062] Specifically, the first control module 1 acquires and adjusts the output current of the boost rectifier module based on the output current of the boost rectifier module, the first target reference current, the pulse voltage mapped from the AC voltage to the DC side, and the input current. The first target reference current is the maximum power demand corresponding to the system's maximum wind energy utilization, and this maximum power demand is converted into current. The output current of the boost rectifier module refers to the output current of the Boost chopper circuit 5, which is equal to the input current of the voltage source inverter.

[0063] In this embodiment, the first control module 1 is embedded with a PFC dual closed-loop control algorithm. This algorithm consists of an outer loop MPPT current control and an inner loop inductor current tracking. After acquiring the output current of the boost rectifier module, the first target reference current, the pulse voltage mapped from the AC voltage to the DC side, and the input current, it adjusts the current of the high-frequency inductor based on the embedded control algorithm so that the input current is in phase with the output voltage of the wind turbine generator 3, thereby achieving unity power factor (i.e., phase angle φ=0, cosφ=1) to complete the power factor correction and adjust the output current of the boost rectifier module, providing a stable current source for the subsequent current source inverter 6.

[0064] For the control of the downstream current source inverter 6, the second control module 2 adopts a phase-locked loop coordinate transformation and a single current loop architecture to achieve synchronization with the load voltage and precise control of the output current.

[0065] Specifically, the second control module 2 acquires and generates the d-axis active current and q-axis reactive current in a synchronous rotating coordinate system based on the synchronous phase angles corresponding to the three-phase current output by the current-source inverter 6 and the three-phase AC voltage signal on the load side; it acquires the second target reference current and adjusts the output current of the current-source inverter 6 based on the second target reference current, the d-axis active current, and the q-axis reactive current. The second target reference current is obtained by converting the maximum power demand output by the preceding MPTT stage to the d-axis. In this embodiment, the second target reference current and the d-axis active current are compared, and the d-axis active current is adjusted based on their deviation to ensure that the d-axis active current tracks the second target reference current, thus meeting the system's maximum power demand. In this process, this embodiment only performs closed-loop regulation on the d-axis active current. Based on this single current loop closed-loop regulation mode, the dq decoupling calculation is eliminated, which speeds up the dynamic response of the system. Moreover, it avoids the problem that the existing technology requires a high DC bus voltage as a basis and has high requirements for the withstand voltage of the power devices in the system. This greatly reduces the requirements of the system on the withstand voltage level of the power devices, while enhancing the system's adaptability to wind speed fluctuations and fault conditions and its safety performance.

[0066] Based on the above, this embodiment uses a three-phase rectifier bridge 4 and a Boost chopper circuit 5 to form a lightweight topology boost rectifier module. This eliminates the need for electrolytic capacitors to stabilize the DC voltage, simplifying the topology of the boost rectifier module, reducing the size of the wind power system, and avoiding the problems of increased size and shortened lifespan that existing technologies rely on large-capacity electrolytic capacitors to maintain voltage stability. Furthermore, the first control module 1 in this embodiment acquires and adjusts the output current of the boost rectifier module based on the output current of the boost rectifier module, the first target reference current, the pulse voltage mapped from the AC voltage to the DC side, and the input current to correct the power factor and provide a stable current for the subsequent current source inverter 6. This breaks the conventional voltage tracking mode and directly drives power changes through current commands, eliminating the need for electrolytic capacitors. Furthermore, in this embodiment, the second control module 2 acquires and generates the d-axis active current and q-axis reactive current in the synchronous rotating coordinate system based on the synchronous phase angle corresponding to the three-phase current output by the current source inverter 6 and the three-phase AC voltage signal on the load side; it acquires the second target reference current, and adjusts the output current of the current source inverter 6 based on the second target reference current, the d-axis active current, and the q-axis reactive current, thus saving the dq decoupling calculation. This not only accelerates the dynamic response of the system, but also avoids the problem that the existing technology requires a high DC bus voltage as a basis and has high requirements for the withstand voltage capability of the power devices in the system. It significantly reduces the system's requirements for the withstand voltage level of the power devices, while enhancing the system's adaptability and safety performance to wind speed fluctuations and fault conditions.

[0067] In one embodiment, see Figures 1 to 2 The three-phase rectifier bridge 4 is equipped with three sets of bridge arms, each set of bridge arms consisting of two fast recovery diodes connected in series;

[0068] The wind turbine 3 is connected to the connection point between the two fast recovery diodes of each bridge arm;

[0069] The two ends of each bridge arm are connected and connected to the Boost chopper circuit 5.

[0070] It should be noted that a fast recovery diode is a semiconductor device with fast reverse recovery characteristics. It uses a PIN structure design to reduce stored charge, which can shorten the reverse recovery time to tens to hundreds of nanoseconds.

[0071] In this system, the midpoint of each bridge arm (i.e., the connection point between the two fast recovery diodes connected in series on that bridge arm) serves as the input terminal of the three-phase rectifier bridge 4, which is connected to the three-phase output terminal of the wind turbine generator 3. This is used to convert the AC power output by the wind turbine generator 3 into pulsating DC power containing AC side phase information. The two ends of the rightmost bridge arm serve as the output terminals, which are connected to the high-frequency inductor and the first IGBT switch in the Boost chopper circuit 5, transmitting the pulsating DC power to the Boost chopper circuit 5.

[0072] In one embodiment, see Figures 1 to 3 The Boost chopper circuit 5 includes: a first IGBT switch Q1, a freewheeling diode D1, and a high-frequency inductor L. m ;

[0073] The collector of the first IGBT switch Q1 is connected to the high-frequency inductor L. m One end of the diode is connected to the anode of the freewheeling diode D1;

[0074] The emitter of the first IGBT switch Q1 is connected to the three-phase rectifier bridge 4 and the current source inverter 6, respectively.

[0075] The gate of the first IGBT switch Q1 is connected to the first control module 1;

[0076] High-frequency inductor L m The other end is connected to the three-phase rectifier bridge 4;

[0077] The cathode of the freewheeling diode D1 is connected to the current source inverter 6.

[0078] It should be noted that the Boost chopper circuit 5 is the core power conversion unit in the boost converter. High-frequency inductor L m It refers to an electromagnetic induction element composed of a frame, windings, magnetic core, etc. It is the only energy storage element in a boost device, and it uses the principle of magnetic energy storage to achieve the function of energy storage.

[0079] This embodiment is based on a high-frequency inductor L m It functions as an energy storage medium, achieving power buffering and voltage regulation. The specific working principle is as follows:

[0080] When the first IGBT switch Q1 turns on, the electrical energy output from the three-phase rectifier bridge 4 will flow to the high-frequency inductor L. m Provides charging current, high-frequency inductor L m The current rises linearly; when the first IGBT switch Q1 turns off under reverse voltage, the high-frequency inductor L... m Energy will be released into the current source inverter 6 during the IGBT turn-off process. Therefore, the first control module 1 controls the switching of the first IGBT switch Q1, thereby adjusting the high-frequency inductor L.m The current is adjusted to correct the power factor, thereby regulating the output current of the boost rectifier module and providing a stable current source for the subsequent current source inverter 6.

[0081] In one embodiment, see Figures 1 to 3 The current source inverter 6 includes: a three-phase full-bridge inverter module 61;

[0082] The DC side of the three-phase full-bridge inverter module 61 and the smoothing inductor L in One end is connected to the smoothing inductor L in The other end is connected to the cathode of the freewheeling diode D1;

[0083] The output side of the three-phase full-bridge inverter module 61 is connected to the input terminal of the LC low-pass filter 62;

[0084] The output of the LC low-pass filter 62 is connected to the three-phase load.

[0085] It should be noted that the three-phase full-bridge inverter module 61 is the main circuit in the current source inverter module 6, and its DC side is connected in series with a smoothing inductor L. in To maintain constant current characteristics. The smoothing inductor L... in Connected to the output of the pre-amplifier boost rectifier module, based on the smoothing inductor L in Its energy storage characteristics can stabilize the input current of the three-phase full-bridge inverter module 61, enabling the DC side of the three-phase full-bridge inverter to have the characteristics of a constant current source, thereby adapting to the front-end inductor current control mode.

[0086] The output side of the three-phase full-bridge inverter module 61 is connected to an LC low-pass filter 62 to suppress harmonics generated by the high-frequency operation of the switching transistors in the three-phase full-bridge inverter module 61, so that the output current waveform is close to a sine wave, thereby meeting the power quality requirements of the three-phase load.

[0087] In one example, the LC low-pass filter 62 includes a filter inductor L. g With filter capacitor C g .

[0088] In one embodiment, see Figures 1 to 3 The three-phase full-bridge inverter module 61 is equipped with three sets of branches, each set of branches consisting of two IGBTs connected in series;

[0089] The two ends of each branch are connected to each other and respectively connected to the smoothing inductor L. in One end is connected to the emitter of the first IGBT switch Q1;

[0090] The connection between the two IGBTs in each branch is connected to an LC low-pass filter 62.

[0091] The gate of each IGBT is connected to the second control module 2.

[0092] It should be noted that the IGBT transistors in the three-phase full-bridge inverter module 61 respond to the second control signal output by the second control module 2 and convert the received DC power into AC power output.

[0093] In one embodiment, the combination Figure 4 The specific process of acquiring and adjusting the output current of the boost rectifier module based on the output current of the boost rectifier module, the first target reference current, the pulse voltage mapped from the AC voltage to the DC side, and the input current in the first control module 1 is explained.

[0094] The process of acquiring and adjusting the output current of the boost rectifier module based on the output current of the boost rectifier module, the first target reference current, the pulse voltage mapped from the AC voltage to the DC side, and the input current includes:

[0095] Obtain the current corresponding to the maximum power demand as the first target reference current; use a preset first PI controller to generate an amplitude reference current based on the first target reference current and the output current; multiply the amplitude reference current and the pulse voltage mapped from the AC voltage to the DC side to obtain the dynamic current reference value; use a preset second PI controller to generate a first control signal based on the dynamic current reference value and the input current, and output the first control signal to the Boost chopper circuit 5.

[0096] It should be noted that, firstly, by dynamically adjusting the output power of the permanent magnet synchronous motor in the wind turbine generator 3, the system can always operate in a state of maximizing wind power utilization, thereby obtaining the maximum power demand. This maximum power demand is then converted into a reference command for the inductor current. This yields the first target reference current of this application, which enables current direct control maximum power point tracking (MPPT) control, providing a reference current for subsequent PFC dual closed-loop control.

[0097] The PFC dual-loop control includes an outer loop MPPT current control and an inner loop inductor current tracking. The outer loop MPPT current control (also known as the MPPT power outer loop) uses maximum power point tracking to output the amplitude of the inductor current as a reference current. Among them, the amplitude reference current This is a DC quantity. As shown in the figure, the amplitude reference current... The expression is as follows:

[0098]

[0099]

[0100] in, The first target reference current, This is the input current of the smoothing inductor, which is also the output current of the Boost chopper circuit 5. The ratio of the outer ring is the coefficient. Let be the integral coefficient of the outer ring. This is the differential operator in the Laplace transform.

[0101] The inner loop inductor current tracking maps the amplitude reference current and AC voltage of the outer loop output to the pulsating voltage V on the DC side. m (t) multiply to generate dynamic current command i mref This refers to the dynamic current reference value, which is expressed as follows:

[0102]

[0103] Then, PI control is used to make the actual inductor current track the dynamic current command i. mref To achieve power factor correction, the corresponding control expression is as follows:

[0104]

[0105] in,

[0106]

[0107] Among them, U m This is the reference value for the modulated wave. The proportionality coefficient of the inner ring. Let be the integral coefficient of the inner loop. This is the differential operator in the Laplace transform.

[0108] After obtaining the modulated wave reference value U m Then, PWM modulation is used, based on U m A corresponding first control signal is generated and input to the gate of the first IGBT transistor to drive the first IGBT transistor, thereby adjusting the high-frequency inductor L. m The current completes the operation of the high-frequency inductor L. m Tracking of current.

[0109] In one embodiment, the combination Figure 4 The process of acquiring and generating the d-axis active current and q-axis reactive current in the synchronous rotating coordinate system based on the synchronous phase angles corresponding to the three-phase current output by the current source inverter 6 and the three-phase AC voltage signal on the load side in the second control module 2 is explained.

[0110] The process of acquiring and generating the d-axis active current and q-axis reactive current in the synchronous rotating coordinate system based on the synchronous phase angles corresponding to the three-phase current output by the current source inverter 6 and the three-phase AC voltage signals on the load side includes:

[0111] Obtain the synchronous phase angles corresponding to the three-phase current output by the current source inverter 6 and the three-phase AC voltage signals on the load side; convert the three-phase current output by the current source inverter 6 into two-phase currents in a two-phase stationary coordinate system; use Park transformation and synchronous phase angle to convert the two-phase currents to synchronous rotating coordinates to obtain the d-axis active current and q-axis reactive current.

[0112] In one example, the second target reference current includes a d-axis current reference value and a q-axis current reference value. Obtaining the second target reference current includes:

[0113] Obtain and convert the current corresponding to the maximum power demand to the synchronous rotating coordinate system to obtain the initial target reference current; take the d-axis current component of the initial target reference current as the d-axis current reference value; take the q-axis current component of the initial target reference current as the q-axis current reference value.

[0114] In one example, adjusting the output current of the current source inverter 6 based on the second target reference current and the d-axis active current includes:

[0115] Using a preset third PI controller, a first voltage signal is generated based on the d-axis active current and the d-axis current reference value, and a second voltage signal is generated based on the q-axis reactive current and the q-axis current reference value. A second control signal is generated based on the first voltage signal and the second voltage signal, and the second control signal is output to the current source inverter 6.

[0116] It should be noted that, firstly, a phase-locked loop (PLL) is used to acquire the three-phase AC voltage signal on the load side, and the voltage phase and frequency are detected in real time to generate a synchronous phase angle, providing a reference for subsequent coordinate transformation. This synchronous phase angle is the synchronous phase angle corresponding to the three-phase AC voltage signal on the load side.

[0117] Simultaneously, the three-phase current output from the power source inverter is obtained. The three-phase current is converted through Clark transformation. Convert to a two-phase stationary coordinate system ( The current signal under the condition is used to obtain the two-phase current (i.e., shaft current and (axis current), specifically as follows:

[0118]

[0119] Among them, i g_a Let i be the phase A current. g_bLet i be the phase B current. g_c For phase C current, i α for shaft current, i β for Axis current.

[0120] Then, the synchronization phase angle output by the phase-locked loop (PLL) is combined with... The obtained two-phase currents are subjected to Park transformation to obtain the d-axis active current in the synchronous rotating coordinate system (dq). q-axis reactive current Its transformation expression is:

[0121]

[0122] In closed-loop control, the third PI controller only monitors the active current along the d-axis. Closed-loop regulation is performed by converting the power demand output from the preceding MPPT stage (i.e., the maximum power demand in the aforementioned embodiment) into a d-axis current reference value. It is understandable that by obtaining the current corresponding to the maximum power demand and transforming that current into a synchronous rotating coordinate system, an initial target reference current can be obtained. As mentioned earlier, the synchronous rotating coordinate system includes a d-axis and a q-axis. Based on this, the d-axis current component can be determined from the initial target reference current, and this d-axis current component is the d-axis current reference value. (i.e., the second target reference current). The q-axis current component in the initial target reference current is the q-axis current reference value i. gqref In this embodiment, i gqref Set to 0, so that i gq Tracking 0.

[0123] Next, the d-axis current reference value With actual d-axis current After comparison, a voltage command U in the dq coordinate system is generated by the third PI controller. d The instruction is as follows:

[0124]

[0125]

[0126] Use the q-axis current reference value i gqref With the actual q-axis current i gq After comparison, the voltage command Uq in the dq coordinate system is generated by the third PI controller, as shown below:

[0127]

[0128]

[0129] The voltage command U d U q The signal is converted into a three-phase voltage modulation signal through Park inverse transform and Clark inverse transform. The three-phase voltage modulation signal is compared with the triangular carrier wave to generate an SPWM drive signal, which is used to control the on / off state of each IGBT in the three-phase inverter module, thereby regulating the current of the current source inverter 6. The expression for the inverse transform is as follows:

[0130]

[0131]

[0132] Among them, U a U b U c It is a three-phase voltage modulation signal.

[0133] Please see Figure 5 This invention provides a control method for a step-up inverter for a grid-connected offshore wind turbine, applicable to the step-up inverter of any of the above embodiments, the method comprising:

[0134] 101. The first control module acquires and adjusts the output current of the boost rectifier module based on the output current of the boost rectifier module, the first target reference current, the pulse voltage mapped from the AC voltage to the DC side, and the input current.

[0135] 102. The second control module acquires and generates the d-axis active current and q-axis reactive current in the synchronous rotating coordinate system based on the synchronous phase angles corresponding to the three-phase current output by the current source inverter and the three-phase AC voltage signal on the load side; acquires the second target reference current, and adjusts the output current of the current source inverter based on the second target reference current, the d-axis active current and the q-axis reactive current.

[0136] In this embodiment of the invention, the first control module acquires and adjusts the output current of the boost rectifier module based on the output current of the boost rectifier module, the first target reference current, the pulse voltage mapped from the AC voltage to the DC side, and the input current. The second control module acquires and generates the d-axis active current and q-axis reactive current in a synchronous rotating coordinate system based on the three-phase current output by the current source inverter and the synchronous phase angle corresponding to the three-phase AC voltage signal on the load side. It also acquires the second target reference current and adjusts the output current of the current source inverter based on the second target reference current, the d-axis active current, and the q-axis reactive current. This solves the technical problems of existing technologies that rely on a large number of electrolytic capacitors, resulting in shortened system life and increased size, and that require a high DC bus voltage as a basis, placing high demands on the voltage withstand capability of the power devices in the system.

[0137] As described above, the boost inverter and control method for grid-connected offshore wind turbines provided by this invention break away from the conventional voltage tracking mode, remove the electrolytic capacitors in traditional PFC circuits, and directly drive the power conversion process through current commands, eliminating the need for electrolytic capacitors and greatly simplifying the system topology. Furthermore, by constructing a lightweight boost topology without electrolytic capacitors in the front stage and building a first control module employing MPPT+PFC collaborative control, they cooperate to achieve maximum power point tracking and power factor correction functions in capacitor-free scenarios. Moreover, the downstream current-source inverter in this invention is directly connected to the grid, and by using a single-current-loop SPWM tracking method, the dq decoupling calculation is eliminated, which not only accelerates the dynamic response speed but also solves the problem of existing wind turbines relying on high DC bus voltages, significantly reducing the system's requirements for the withstand voltage level of power devices, while enhancing the system's adaptability and safety performance to wind speed fluctuations and fault conditions.

[0138] In the several embodiments provided in this application, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of modules is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be an indirect coupling or communication connection between apparatuses or units through some interfaces, and may be electrical, mechanical, or other forms.

[0139] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0140] Furthermore, in the various embodiments of the present invention, the functional units can be integrated into one processing unit, or each functional unit can be a separate physical entity, or two or more functional units can be integrated into one processing unit. The integrated unit described above can be implemented in hardware or as a software functional unit.

[0141] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0142] The terms “first,” “second,” “third,” “fourth,” etc. (if present) in the specification and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented, for example, in orders other than those illustrated or described herein. Furthermore, the terms “comprising” and “having,” and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0143] It should also be noted that in the description of this invention, the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0144] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A step-up inverter for a grid-connected offshore wind turbine, characterized in that, include: The system comprises a first control module, a second control module, and a cascaded wind turbine generator, a boost rectifier module, and a current source inverter; the boost rectifier module includes a connected three-phase rectifier bridge and a Boost chopper circuit. The first control module is connected to the boost rectifier module and is used to acquire and adjust the output current of the boost rectifier module according to the output current of the boost rectifier module, the first target reference current, the pulse voltage mapped from the AC voltage to the DC side, and the input current. The second control module is connected to the current source inverter and is used to acquire and generate the d-axis active current and q-axis reactive current in the synchronous rotating coordinate system based on the synchronous phase angle corresponding to the three-phase current output by the current source inverter and the three-phase AC voltage signal on the load side; acquire the second target reference current, and adjust the output current of the current source inverter based on the second target reference current, the d-axis active current and the q-axis reactive current.

2. The boost inverter device according to claim 1, characterized in that, The step of acquiring and adjusting the output current of the boost rectifier module based on the output current of the boost rectifier module, the first target reference current, the pulse voltage mapped from the AC voltage to the DC side, and the input current specifically includes: Obtain the current corresponding to the maximum power demand as the first target reference current; Using a preset first PI controller, an amplitude reference current is generated based on the first target reference current and the output current; The dynamic current reference value is obtained by multiplying the amplitude reference current and the pulse voltage mapped from the AC voltage to the DC side. Using a preset second PI controller, a first control signal is generated based on the dynamic current reference value and the input current, and the first control signal is output to the Boost chopper circuit.

3. The boost inverter device according to claim 2, characterized in that, The step of acquiring and generating the d-axis active current and q-axis reactive current in the synchronous rotating coordinate system based on the synchronous phase angles corresponding to the three-phase current output by the current source inverter and the three-phase AC voltage signals on the load side includes: Obtain the synchronization phase angles corresponding to the three-phase current output by the current source inverter and the three-phase AC voltage signals on the load side; The three-phase current output by the current source inverter is converted into a two-phase current in a two-phase stationary coordinate system. Using the Park transformation and the synchronous phase angle, the two-phase currents are converted to synchronous rotating coordinates to obtain the d-axis active current and the q-axis reactive current.

4. The boost inverter device according to claim 3, characterized in that, The second target reference current includes a d-axis current reference value and a q-axis current reference value. Obtaining the second target reference current includes: The current corresponding to the maximum power requirement is acquired and converted to synchronous rotating coordinates to obtain the initial target reference current; The d-axis current component in the initial target reference current is used as the d-axis current reference value; The q-axis current component in the initial target reference current is used as the q-axis current reference value.

5. The boost inverter device according to claim 4, characterized in that, The step of adjusting the output current of the current source inverter based on the second target reference current, the d-axis active current, and the q-axis reactive current includes: Using a preset third PI controller, a first voltage signal is generated based on the d-axis active current and the d-axis current reference value, and a second voltage signal is generated based on the q-axis reactive current and the q-axis current reference value. A second control signal is generated based on the first voltage signal and the second voltage signal, and the second control signal is output to the current source inverter.

6. The boost inverter device according to claim 5, characterized in that, The Boost chopper circuit includes: a first IGBT switch, a freewheeling diode, and a high-frequency inductor; The collector of the first IGBT switch is connected to one end of the high-frequency inductor and the anode of the freewheeling diode, respectively. The emitter of the first IGBT switch is connected to the three-phase rectifier bridge and the current source inverter, respectively. The gate of the first IGBT switch is connected to the first control module; The other end of the high-frequency inductor is connected to the three-phase rectifier bridge; The cathode of the freewheeling diode is connected to the current source inverter.

7. The boost inverter device according to claim 6, characterized in that, The current source inverter includes: a three-phase full-bridge inverter module; The DC side of the three-phase full-bridge inverter module is connected to one end of the smoothing inductor, and the other end of the smoothing inductor is connected to the cathode of the freewheeling diode. The output side of the three-phase full-bridge inverter module is connected to the input end of the LC low-pass filter; The output of the LC low-pass filter is connected to the three-phase load.

8. The boost inverter device according to claim 7, characterized in that, The three-phase rectifier bridge is provided with three sets of bridge arms, and each set of bridge arms consists of two fast recovery diodes connected in series. The wind turbine is connected to the connection point between the two fast recovery diodes of each group of bridge arms; The two ends of each bridge arm are connected and connected to the Boost chopper circuit.

9. The boost inverter device according to claim 7, characterized in that, The three-phase full-bridge inverter module is equipped with three sets of branches, and each set of branches consists of two IGBT transistors connected in series. The two ends of each branch are connected to each other and respectively connected to one end of the smoothing inductor and the emitter of the first IGBT switch. The connection point of the two IGBT transistors in each branch is connected to the LC low-pass filter; The gate of each IGBT is connected to the second control module.

10. A control method for a step-up inverter of a grid-connected offshore wind turbine, characterized in that, Applied to the apparatus of any one of claims 1-9, the method comprises: The first control module acquires and adjusts the output current of the boost rectifier module based on the output current of the boost rectifier module, the first target reference current, the pulse voltage mapped from the AC voltage to the DC side, and the input current. The second control module acquires and generates the d-axis active current and q-axis reactive current in the synchronous rotating coordinate system based on the synchronous phase angles corresponding to the three-phase current output by the current source inverter and the three-phase AC voltage signal on the load side; acquires the second target reference current, and adjusts the output current of the current source inverter based on the second target reference current, the d-axis active current and the q-axis reactive current.

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