Control method of grid-forming type direct-drive wave energy power generation system suitable for weak power grid condition

Abstract

The invention relates to a network construction type direct-drive wave energy power generation system control method suitable for a weak power grid condition, and the method comprises a machine side control strategy for a main circuit of a power generation system and a network side control strategy for the main circuit, and the main circuit comprises a machine side wave energy linear permanent magnet generator and a machine side converter at the machine side. And a grid-side converter and a low-pass filter. Compared with the prior art, the method has the advantages of improving the weak power grid stability of the direct-drive wave energy generator set and the like.

Description

Technical Field

[0001] The present invention relates to the field of grid-building inverters, and in particular to a control method for a grid-building direct-drive wave energy power generation system suitable for weak grid conditions. Background Art

[0002] As a renewable energy source, wave energy is attracting more and more attention due to its advantages such as high energy density, predictability, and environmental friendliness. Among the developed wave energy conversion devices, the Archimedes wave pendulum is the first wave energy conversion device that uses direct drive power output technology. It uses a linear permanent magnet generator to convert wave energy into electrical energy. Since the amplitude and frequency of the induced voltage and stator current of the linear permanent magnet generator change with the mover, which is different from traditional AC generators such as synchronous generators and induction generators, the dynamic characteristics of its output power are different and have extremely strong volatility.

[0003] The large-scale grid connection of wave power generation projects will bring great challenges to the stable operation of traditional power grids. At present, the traditional mainstream solution is to implement a grid-following control strategy through a grid-connected voltage source converter. This strategy relies on a phase-locked loop and a vector controller to synchronize the converter with the grid. However, when the grid becomes weak, due to the interactive dynamics between the phase-locked loop and the grid impedance, the system will produce serious dynamic instability. In order to improve stability, it is usually necessary to limit the active power output of the converter. Summary of the invention

[0004] The purpose of the present invention is to avoid the risk of system instability caused by the coupling of the phase-locked loop and the grid impedance, thereby improving the weak grid stability of the direct-drive wave energy generator set and providing a control method for a grid-connected direct-drive wave energy power generation system suitable for weak grid conditions.

[0005] The purpose of the present invention can be achieved by the following technical solutions:

[0006] A control method for a grid-connected direct-drive wave energy power generation system suitable for weak grid conditions, the method comprising a machine-side control strategy for a main circuit of the power generation system and a grid-side control strategy for the main circuit, the main circuit comprising a wave energy linear permanent magnet generator and a machine-side converter on the machine side, as well as a grid-side converter and a low-pass filter, the machine-side control strategy specifically comprising the following steps:

[0007] S1, obtaining the current of the generator stator at the maximum power generation working point of the wave energy linear permanent magnet generator;

[0008] The three-phase current output by S2 and the linear permanent magnet generator is transformed into Park coordinates to obtain the d-axis output current and the q-axis output current. At the same time, the stator current of S1 is used as the q-axis current reference value in the current control loop of the machine-side converter;

[0009] S3, based on the deviation between the q-axis current reference value and the q-axis output current, obtain the q-axis voltage reference value of the machine-side converter through the PI controller;

[0010] S4, the d-axis current reference value of the machine-side converter is 0, and based on the deviation between the d-axis current reference value and the d-axis output current, the d-axis voltage reference value of the machine-side converter is obtained through the PI controller;

[0011] S5, performing an inverse Park coordinate transformation on the d-axis and q-axis voltage reference values ​​of the machine-side converter, and inputting the generated modulation signal into the PWM controller to generate a control signal of the machine-side converter, thereby controlling the machine-side converter;

[0012] The grid-side control strategy specifically includes the following steps:

[0013] S6. Obtaining the active power reference value required by the grid side;

[0014] S7, measure the current and voltage of the grid connection point, obtain the current and voltage of the d and q axes after Park coordinate transformation, and obtain the actual value P of the output active power through power calculation;

[0015] S8, calculating the deviation between the active power reference value and the active power actual value P, and outputting the phase angle by simulating the inertial damping characteristics and droop characteristics in the synchronous machine;

[0016] S9, based on the current and voltage of the d and q axes, the actual value of the output reactive power Q is obtained through power calculation;

[0017] S10, calculating the deviation between the reactive power reference value and the reactive power actual value Q, and outputting the voltage amplitude by simulating the inertial damping characteristics and droop characteristics in the synchronous machine;

[0018] S11, obtaining a reference voltage based on the voltage amplitude and the phase angle, and decomposing the reference voltage into a grid-connected point d-axis reference voltage and a grid-connected point q-axis reference voltage;

[0019] S12, calculating the deviation between the grid-connected point d-axis reference voltage and the actual value of the grid-connected point d-axis voltage, and obtaining the grid-side converter d-axis reference current after considering the voltage control link coupled with the grid-connected point q-axis voltage;

[0020] S13, calculating the deviation between the grid-connected point q-axis reference voltage and the actual value of the grid-connected point q-axis voltage, and obtaining the grid-side converter q-axis reference current after considering the voltage control link coupled with the grid-connected point d-axis voltage;

[0021] S14, calculating the deviation between the grid-side converter d-axis reference current and the actual value of the grid-side converter d-axis current, and outputting the grid-side d-axis voltage reference value after considering the current control link coupled with the grid-side converter q-axis current;

[0022] S15, calculating the deviation between the grid-side converter q-axis reference current and the actual value of the grid-side converter q-axis current, and outputting the grid-side q-axis voltage reference value after considering the current control link coupled with the grid-side converter d-axis current;

[0023] S16, performing Park inverse transformation on the grid-side d-axis voltage reference value and the grid-side q-axis voltage reference value, and inputting the generated modulation signal into the PWM controller to generate a control signal of the grid-side converter, so as to control the grid-side converter.

[0024] Furthermore, the q-axis current reference value in the current control loop of the generator-side converter is:

[0025]

[0026] Where, the mass of the wave above the linear generator and the float is m tot , the hydrodynamic damping coefficient of the float is β w , the elastic coefficient of the generator is k s , ψ PM represents the permanent magnet flux of the mover, v represents the float speed, t represents the time, λ represents the pole pitch of the linear generator, and x represents the displacement of the generator float.

[0027] Furthermore, the reference values ​​of the d-axis and q-axis voltages of the machine-side converter are:

[0028]

[0029] Among them, i d-ref represents the d-axis current reference value in the current control loop of the machine-side converter, i d and i q represents the d-axis output current and the q-axis output current, are the proportional coefficient and integral coefficient of the PI controller respectively, are the d-axis and q-axis voltage reference values ​​of the machine-side converter respectively, and s is the Laplace operator.

[0030] Furthermore, the modulation signal obtained by performing inverse Park coordinate transformation on the d-axis and q-axis voltage reference values ​​of the machine-side converter is a three-phase control signal and

[0031] Further, the phase angle is:

[0032]

[0033] Among them, s is the Laplace operator, K p is the droop gain of active power control, w p is the cutoff frequency of the low-pass filter, wo represents the steady-state value of frequency, P represents the actual value of active power on the grid side, w represents the frequency, θ is the phase angle, P * Indicates the active power reference value on the grid side.

[0034] Furthermore, the active power reference value is:

[0035]

[0036] Where, the mass of the wave above the linear generator and the float is m tot , the hydrodynamic damping coefficient of the float is β w , the elastic coefficient of the generator is k s , v represents the float velocity, t represents the time, λ represents the pole pitch of the linear generator, and x represents the displacement of the generator float.

[0037] Furthermore, the voltage amplitude is:

[0038]

[0039] Among them, Q * It represents the reactive power reference value on the grid side, Q is the actual reactive power value on the grid side, and w q is the cutoff frequency of the low-pass filter, K q is the droop gain of reactive power control, u o Indicates the voltage amplitude, Represents the steady-state value of the voltage amplitude.

[0040] Furthermore, the grid-side converter d-axis and q-axis reference currents and grid-side d-axis and q-axis voltage reference values ​​are:

[0041]

[0042] Among them, G o (s), G i (s) are all PI controllers, Respectively represent the d-axis and q-axis reference voltages at the grid connection point, u od 、u oq Represent the actual values ​​of the d-axis and q-axis voltages at the grid connection point, respectively. od 、i oq Respectively represent the actual values ​​of the d-axis and q-axis currents at the grid connection point, Respectively represent the d-axis and q-axis reference currents of the grid-side converter, i gd 、i gq Respectively represent the actual value of the d-axis and q-axis current of the grid-side converter, They represent the grid-side d and q axis voltage reference values ​​respectively.

[0043] Furthermore, the droop characteristic of S8 is a Pf droop characteristic, where f represents frequency, and the droop characteristic of S10 is a QV characteristic, where V represents voltage.

[0044] Furthermore, the current of the generator stator at the maximum power generation operating point of the wave energy linear permanent magnet generator is calculated based on the measured displacement x and speed v of the float connected to the mover of the wave energy linear permanent magnet generator.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] The present invention adopts a grid-type control strategy. By constructing active-frequency equations and reactive-voltage equations similar to those of synchronous motors, it can effectively simulate the operation of synchronous generators, provide inertia and damping, and provide voltage and frequency support to the power grid. At the same time, the present invention proposes a grid-side inverter grid-connected control method that does not rely on grid sampling and has a phase-locked loop structure, taking into account the transient characteristics of waves on the machine side of a large-scale direct-drive wave energy power generation system. Under weak grid conditions, compared with the traditional phase-locked loop synchronization solution, it can avoid the risk of system instability caused by the coupling of the phase-locked loop and the grid impedance, thereby improving the weak grid stability of the direct-drive wave energy generator set. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 It is a block diagram of the overall method of the present invention;

[0048] Figure 2 This is a flow chart of the machine-side control method of a grid-type direct-drive wave energy power generation system;

[0049] Figure 3 The present invention is a flow chart of the grid-side control method of a grid-type direct-drive wave energy power generation system. DETAILED DESCRIPTION

[0050] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0051] The present invention proposes a control method for a grid-connected direct-drive wave energy power generation system suitable for weak grid conditions. The block diagram of the method is as follows: Figure 1 The flow chart of the machine side control method is shown in Figure 2 As shown, the flow chart of the grid side control method is as follows Figure 3As shown. The main circuit of the present invention includes a wave energy linear permanent magnet generator, a machine-side converter, a grid-side converter, and a low-pass filter. The control method is divided into two parts: the machine side and the grid side. The machine-side converter control method includes the following links: active power calculation, Park coordinate transformation, current control loop, and PWM controller. The grid-side converter control method includes the following links: power calculation, current and voltage measurement, Park coordinate transformation, PWM controller, voltage and current control loop, and virtual synchronous machine control loop.

[0052] The generator-side converter control method fully considers the dynamic characteristics of the float connected to the linear permanent magnet generator rotor, including its speed and displacement, and includes the following steps:

[0053] Step S1: measuring the displacement and velocity of a float connected to a wave energy linear permanent magnet generator rotor, and calculating the current of the generator stator at its maximum power generation operating point;

[0054] Step S2: measuring the three-phase current output by the linear permanent magnet generator, and performing Park coordinate transformation to obtain the d-axis output current and the q-axis output current, and at the same time allocating the stator current of the maximum power generation operating point as the q-axis current reference value in the current control loop of the machine-side converter;

[0055] Step S3: Based on the deviation between the q-axis current reference value and the q-axis output current, a q-axis voltage reference value of the machine-side converter is obtained through a PI controller;

[0056] Step S4: setting the d-axis reference value to 0, and obtaining the d-axis voltage reference value of the generator-side converter through a PI controller based on the deviation between the d-axis current reference value and the d-axis output current;

[0057] Step S5: Perform an inverse Park coordinate transformation on the d-axis and q-axis voltage reference values ​​of the generator-side converter, and input the generated modulation signal into the PWM controller to generate a control signal for the generator-side converter.

[0058] The active power-phase angle synchronous control loop in the grid-side converter control method fully considers the maximum power point tracking dynamics on the machine side. The active power-phase angle synchronous control loop includes the following steps:

[0059] Step S6: Calculate the active power reference value required on the grid side according to the displacement and speed of the float connected to the mover in the linear permanent magnet generator;

[0060] Step S7: measuring the current and voltage of the grid connection point, obtaining the current and voltage of the d and q axes after Park coordinate transformation, and obtaining the actual value of the output active power through power calculation;

[0061] Step S8: Calculate the deviation between the active power reference value and the active power, and output the phase angle by simulating the inertial damping characteristics in the synchronous machine and combining the Pf droop characteristics.

[0062] In the experimental example, the reactive power-voltage amplitude control loop includes the following steps:

[0063] Step S9: measuring the current and voltage of the grid connection point, obtaining the current and voltage of the d and q axes after Park coordinate transformation, and obtaining the actual value of the output reactive power through power calculation;

[0064] Step S10: According to the reactive power reference value and the reactive power deviation, the voltage amplitude is output by simulating the inertial damping characteristics in the synchronous machine and combining the QV droop characteristics.

[0065] In the experimental example, the voltage control loop in the dq coordinate system includes the following steps:

[0066] Step S11: After processing the phase angle and the amplitude, a reference voltage is obtained, and the reference voltage is decomposed into a grid-connected point d-axis reference voltage and a grid-connected point q-axis reference voltage;

[0067] Step S12: Calculate the deviation between the grid-connected point d-axis reference voltage and the actual value of the grid-connected point d-axis voltage, and obtain the grid-side converter d-axis reference current after considering the voltage control link coupled with the grid-connected point q-axis voltage;

[0068] Step S13: Calculate the deviation between the grid-connected point q-axis reference voltage and the actual value of the grid-connected point q-axis voltage, and obtain the grid-side converter q-axis reference current after considering the voltage control link coupled with the grid-connected point d-axis voltage.

[0069] In the experimental example, the current control loop in the dq coordinate system includes the following steps:

[0070] Step S14: Calculate the deviation between the grid-side converter d-axis reference current and the actual value of the grid-side converter d-axis current, and output a d-axis voltage reference value after taking into account the current control link coupled with the grid-side converter q-axis current;

[0071] Step S15: Calculate the deviation between the grid-side converter q-axis reference current and the actual value of the grid-side converter q-axis current, and output the q-axis voltage reference value after considering the current control link coupled with the grid-side converter d-axis current;

[0072] Step S16: Perform Park inverse transformation on the output d-axis and q-axis voltage reference values, and the generated modulation signal is input into the PWM controller to generate a control signal for the grid-side converter.

[0073] In the experimental example, the d and q axis current reference values ​​i d-ref 、i q-ref The settings are as follows:

[0074] To reduce the power loss of the stator, set i d-ref=0, considering the maximum power point tracking dynamics on the generator side, the q-axis current reference value is set as shown in formula (1):

[0075]

[0076] The mass of the wave above the linear generator and the float is m tot , the hydrodynamic damping coefficient of the float is β w , the elastic coefficient of the generator is k s , ψ PM represents the permanent magnet flux of the mover, and v represents the float speed.

[0077] will i d 、i q Substituting into equation (2), we can obtain the d-axis and q-axis voltage reference values ​​of the generator-side converter.

[0078]

[0079] in are the d-axis and q-axis voltage reference values ​​of the machine-side converter respectively, are the proportional coefficient and integral coefficient of the PI controller respectively.

[0080] Then through Park's inverse transformation, we get The input is sent to the PWM controller to generate the control signal for the machine-side converter.

[0081] In the experimental example, the specific formula of the phase angle θ in the active power-phase angle synchronous control loop during the grid-side converter control process is as follows:

[0082]

[0083] s is the Laplace operator, K p is the droop gain of active power control, w p is the cutoff frequency of the low-pass filter, the superscript “o” indicates the steady-state value of the variable, P represents the actual value of the grid-side active power, and the grid-side active power reference value P * The calculation formula is as follows:

[0084]

[0085] In the experimental example, the amplitude u in the reactive power-voltage amplitude control loop o The specific formula is as follows:

[0086]

[0087] K q is the droop gain of reactive power control, w q is the cut-off frequency of the low-pass filter, Q is the actual value of the grid-side reactive power, Q *It is the grid-side reactive power reference value.

[0088] In the experimental example, the voltage and current control loop formula in the dq coordinate system is as follows:

[0089]

[0090] Where G o (s), G i (s) are all PI controllers, Respectively represent the d-axis and q-axis reference voltages at the grid connection point, u od 、u oq Represent the actual values ​​of the d-axis and q-axis voltages at the grid connection point, respectively. od 、i oq Respectively represent the actual values ​​of the d-axis and q-axis currents at the grid connection point, Respectively represent the d-axis and q-axis reference currents of the grid-side converter, i gd 、i gq Respectively represent the actual value of the d-axis and q-axis current of the grid-side converter, Represent the output d and q axis voltage reference values ​​respectively.

[0091] The present invention proposes a grid-side inverter control method that does not rely on grid sampling and has no phase-locked loop structure, while taking into account the transient characteristics of the waves on the machine side of a large-scale direct-drive wave energy power generation system. Under weak grid conditions, compared with the traditional phase-locked loop synchronization solution, it can avoid the risk of system instability caused by the coupling of the phase-locked loop and the grid impedance, thereby improving the weak grid stability of the direct-drive wave energy generator set.

[0092] The present invention relates to a control method for a grid-type direct-drive wave energy power generation system suitable for weak power grid conditions. The control method for a grid-type direct-drive wave energy power generation system includes machine-side converter control and grid-side converter control. The control process of the machine-side converter includes: obtaining a machine-side current reference value according to the control requirements of maximum power extraction and low loss on the machine side; the current deviation value is used to obtain a voltage and generate a modulation signal through a PI controller, and a control signal is generated through PWM to achieve control of the machine-side current and output power; the control process of the grid-side converter includes: forming an active power-phase angle synchronization control loop according to the deviation value of the machine-side active power and the grid-side active power, forming a reactive power-voltage amplitude control loop and a voltage and current control loop in a dq coordinate system according to the reactive power deviation value on the grid side, and generating a control signal through PWM to achieve control of the active and reactive power on the grid side. In the present invention, the wave energy power generation system does not rely on a phase-locked loop for synchronization during operation, thereby improving its stability under a weak power grid.

[0093] The present invention has the following beneficial effects:

[0094] (1) The present invention proposes a control method for large-scale direct-drive wave energy generation system grid-connected scenarios. By constructing active-frequency equations and reactive-voltage equations similar to those of synchronous motors, the inertia and damping of synchronous generators can be effectively simulated to provide voltage and frequency support for the power grid.

[0095] (2) The present invention proposes a grid-side inverter grid-connected control method that does not rely on grid sampling and has no phase-locked loop structure, while taking into account the transient characteristics of the waves on the machine side of a large-scale direct-drive wave energy power generation system. Under weak grid conditions, compared with the traditional phase-locked loop synchronization solution, it can avoid the risk of system instability caused by the coupling of the phase-locked loop and the grid impedance, thereby improving the weak grid stability of the direct-drive wave energy generator set.

[0096] The preferred specific embodiments of the present invention are described in detail above. It should be understood that a person skilled in the art can make many modifications and changes based on the concept of the present invention without creative work. Therefore, any technical solution that can be obtained by a person skilled in the art through logical analysis, reasoning or limited experiments based on the concept of the present invention on the basis of the prior art should be within the scope of protection determined by the claims.

Claims

1. A control method for a grid-building direct-drive wave energy power generation system suitable for weak grid conditions, characterized in that: The method includes a machine-side control strategy for a main circuit of a power generation system and a grid-side control strategy for the main circuit. The main circuit includes a wave energy linear permanent magnet generator and a machine-side converter on the machine side, as well as a grid-side converter and a low-pass filter. The machine-side control strategy specifically includes the following steps: S1, obtaining the current of the generator stator at the maximum power generation working point of the wave energy linear permanent magnet generator; The three-phase current output by S2 and the linear permanent magnet generator is transformed into Park coordinates to obtain the d-axis output current and the q-axis output current. At the same time, the stator current of S1 is used as the q-axis current reference value in the current control loop of the machine-side converter; S3, based on the deviation between the q-axis current reference value and the q-axis output current, obtain the q-axis voltage reference value of the machine-side converter through the PI controller; S4, the d-axis current reference value of the machine-side converter is 0, and based on the deviation between the d-axis current reference value and the d-axis output current, the d-axis voltage reference value of the machine-side converter is obtained through the PI controller; S5, performing an inverse Park coordinate transformation on the d-axis and q-axis voltage reference values ​​of the machine-side converter, and inputting the generated modulation signal into the PWM controller to generate a control signal of the machine-side converter, thereby controlling the machine-side converter; The grid-side control strategy specifically includes the following steps: S6. Obtaining the active power reference value required by the grid side; S7, measure the current and voltage of the grid connection point, obtain the current and voltage of the d and q axes after Park coordinate transformation, and obtain the actual value P of the output active power through power calculation; S8, calculating the deviation between the active power reference value and the active power actual value P, and outputting the phase angle by simulating the inertial damping characteristics and droop characteristics in the synchronous machine; S9, based on the current and voltage of the d and q axes, the actual value of the output reactive power Q is obtained through power calculation; S10, calculating the deviation between the reactive power reference value and the reactive power actual value Q, and outputting the voltage amplitude by simulating the inertial damping characteristics and droop characteristics in the synchronous machine; S11, obtaining a reference voltage based on the voltage amplitude and the phase angle, and decomposing the reference voltage into a grid-connected point d-axis reference voltage and a grid-connected point q-axis reference voltage; S12, calculating the deviation between the grid-connected point d-axis reference voltage and the actual value of the grid-connected point d-axis voltage, and obtaining the grid-side converter d-axis reference current after considering the voltage control link coupled with the grid-connected point q-axis voltage; S13, calculating the deviation between the grid-connected point q-axis reference voltage and the actual value of the grid-connected point q-axis voltage, and obtaining the grid-side converter q-axis reference current after considering the voltage control link coupled with the grid-connected point d-axis voltage; S14, calculating the deviation between the grid-side converter d-axis reference current and the actual value of the grid-side converter d-axis current, and outputting the grid-side d-axis voltage reference value after considering the current control link coupled with the grid-side converter q-axis current; S15, calculating the deviation between the grid-side converter q-axis reference current and the actual value of the grid-side converter q-axis current, and outputting the grid-side q-axis voltage reference value after considering the current control link coupled with the grid-side converter d-axis current; S16, performing Park inverse transformation on the grid-side d-axis voltage reference value and the grid-side q-axis voltage reference value, and inputting the generated modulation signal into the PWM controller to generate a control signal of the grid-side converter, so as to control the grid-side converter.

2. A control method for a grid-forming direct-drive wave energy power generation system suitable for weak grid conditions according to claim 1, characterized in that: The q-axis current reference value in the current control loop of the generator-side converter is: Where, the mass of the wave above the linear generator and the float is m tot , the hydrodynamic damping coefficient of the float is β w , the elastic coefficient of the generator is k s , ψ PM represents the permanent magnet flux of the mover, v represents the float speed, t represents the time, λ represents the pole pitch of the linear generator, and x represents the displacement of the generator float.

3. A control method for a grid-building type direct-drive wave energy power generation system suitable for weak grid conditions according to claim 1, characterized in that: The reference values ​​of the d and q axis voltages of the machine-side converter are: Among them, i d-ref represents the d-axis current reference value in the current control loop of the machine-side converter, i d and i q represents the d-axis output current and the q-axis output current, are the proportional coefficient and integral coefficient of the PI controller respectively, are the d-axis and q-axis voltage reference values ​​of the machine-side converter respectively, and s is the Laplace operator.

4. A control method for a grid-building direct-drive wave energy power generation system suitable for weak grid conditions according to claim 1, characterized in that: The modulation signal obtained by performing inverse Park coordinate transformation on the d-axis and q-axis voltage reference values ​​of the machine-side converter is a three-phase control signal and 5. The control method of a grid-building type direct-drive wave energy power generation system suitable for weak grid conditions according to claim 1, characterized in that: The phase angle is: Among them, s is the Laplace operator, K p is the droop gain of active power control, w p is the cutoff frequency of the low-pass filter, w o represents the steady-state value of frequency, P represents the actual value of active power on the grid side, w represents the frequency, θ is the phase angle, P * Indicates the active power reference value on the grid side.

6. A control method for a grid-building type direct-drive wave energy power generation system suitable for weak grid conditions according to claim 5, characterized in that: The active power reference value is: Where, the mass of the wave above the linear generator and the float is m tot , the hydrodynamic damping coefficient of the float is β w , the elastic coefficient of the generator is k s , v represents the float velocity, t represents the time, λ represents the pole pitch of the linear generator, and x represents the displacement of the generator float.

7. A control method for a grid-building type direct-drive wave energy power generation system suitable for weak grid conditions according to claim 1, characterized in that: The voltage amplitude is: Among them, Q * It represents the reactive power reference value on the grid side, Q is the actual reactive power value on the grid side, and w q is the cutoff frequency of the low-pass filter, K q is the droop gain of reactive power control, u o Indicates the voltage amplitude, Represents the steady-state value of the voltage amplitude.

8. The control method of a grid-building type direct-drive wave energy power generation system suitable for weak grid conditions according to claim 1, characterized in that: The grid-side converter d-axis and q-axis reference current and grid-side d-axis and q-axis voltage reference values ​​are: Among them, G o (s), G i (s) are all PI controllers, Respectively represent the d-axis and q-axis reference voltages at the grid connection point, u od 、u oq Represent the actual values ​​of the d-axis and q-axis voltages at the grid connection point, respectively. od 、i oq Respectively represent the actual values ​​of the d-axis and q-axis currents at the grid connection point, Respectively represent the d-axis and q-axis reference currents of the grid-side converter, i gd 、i gq Respectively represent the actual value of the d-axis and q-axis current of the grid-side converter, They represent the grid-side d and q axis voltage reference values ​​respectively.

9. A control method for a grid-building type direct-drive wave energy power generation system suitable for weak grid conditions according to claim 1, characterized in that: The droop characteristic of S8 is a Pf droop characteristic, where f represents frequency, and the droop characteristic of S10 is a QV characteristic, where V represents voltage.

10. The control method of a grid-building type direct-drive wave energy power generation system suitable for weak grid conditions according to claim 1, characterized in that: The current of the generator stator at the maximum power generation operating point of the wave energy linear permanent magnet generator is calculated based on the measured displacement x and speed v of the float connected to the mover of the wave energy linear permanent magnet generator.

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