CN115498656A

CN115498656A - Virtual synchronous wind power plant cooperative photovoltaic power station additional damping control method and device

Info

Publication number: CN115498656A
Application number: CN202211180282.9A
Authority: CN
Inventors: 盛师贤; 乔平; 董彬政; 郭朝云; 张志鹏; 尹星; 吴炜; 黄珣; 王帅; 邹坤; 史永宏
Original assignee: State Grid Jibei Electric Power Co ltd Engineering Management Branch; PowerChina Hebei Electric Power Engineering Co Ltd
Current assignee: State Grid Jibei Electric Power Co ltd Engineering Management Branch; PowerChina Hebei Electric Power Engineering Co Ltd
Priority date: 2022-09-26
Filing date: 2022-09-26
Publication date: 2022-12-20

Abstract

The invention discloses a virtual synchronous wind power plant and photovoltaic power station cooperative additional damping control method and device, and belongs to the field of power systems. Aiming at the characteristics that in the existing additional damping control, the response speed of the variable pitch control of the fan in a rotating speed constant region is low and the oscillation suppression effect is not ideal, the photovoltaic power station is introduced, and the method for controlling the variable pitch control of the fan and the additional damping is provided. Designing additional damping controllers on an active control loop of the virtual synchronous wind power plant and a photovoltaic power plant controller, and putting the additional damping devices into the virtual synchronous wind power plant and the photovoltaic power plant to suppress low-frequency oscillation of a power grid when a fan runs in an MPPT (maximum power point tracking) area; when the fan operates in a constant rotating speed area, the wind power plant quits the additional damping control, and the VSG control and the photovoltaic power station jointly suppress the low-frequency oscillation of the power grid. The method can enable the double-fed fan and the photovoltaic power station to play a greater role in the field of power grid control.

Description

Virtual synchronous wind power plant and photovoltaic power station cooperative additional damping control method and device

Technical Field

The invention relates to the field of power electronics, in particular to a virtual synchronous wind power plant and photovoltaic power station additional damping control method and device.

Background

The low-frequency oscillation of the power system refers to that the synchronous generator sets running in parallel generate relative swing between generator rotors under the action of small interference due to insufficient damping torque, so that the line power and the bus voltage generate continuous oscillation of 0.1-2.5 Hz, and the continuous oscillation mainly occurs on a long-distance and heavy-load transmission line. The low-frequency oscillation of the power system mainly occurs on a long-distance and heavy-load transmission line, and the dynamic stability and the transmission capacity of a power grid are seriously influenced. The large-scale wind power plant and the photovoltaic power station are mainly distributed in remote areas far away from a load center, and the problem of low-frequency oscillation is more prominent due to large-scale wind-solar grid connection.

Power System Stabilizers (PSS) are widely used in suppressing regional low frequency oscillations. In addition to considering the instructions of the PSS, the conventional synchronization unit also needs to consider other control targets, so that the PSS cannot function alone. The control targets of the new energy unit are few, the control mode is flexible, and the ability of inhibiting low-frequency oscillation of the new energy unit is suitable to be increased by changing a control strategy in an area with high new energy permeability. The VSG control technology can obviously increase the inertia and the damping of the new energy unit, and has good development prospect in the field of new energy grid connection. However, research on the VSG control technology is mainly focused on using virtual inertia of a new energy source unit to participate in primary frequency modulation of a power grid, and research on participation of the new energy source unit in suppressing low-frequency oscillation of a power system based on VSG control is less. When the double-fed fan runs in a rotating speed constant region, the output power of the fan is changed by adjusting the pitch angle, and the damping of the power system is increased. However, the pitch angle control system is a mechanical system, the speed regulation is difficult to adapt to the oscillation change of the electromagnetic power, and the effect of inhibiting the low-frequency oscillation is not good.

Based on the above, a method for cooperatively controlling and inhibiting low-frequency oscillation of a power grid by using a wind power plant running in a virtual synchronization mode and other new energy units is needed, and the problem that in the prior art, in the process that the wind power plant inhibits the low-frequency oscillation of the power grid in a rotating speed constant region by using an additional damping control method, a pitch angle control system is low in adjustment speed, is difficult to adapt to the oscillation change of electromagnetic power, and further cannot inhibit the low-frequency oscillation phenomenon of the power grid is solved.

Disclosure of Invention

In order to overcome the defects, the application provides a virtual synchronous wind power plant and photovoltaic power station additional damping control method and device, and the method and device can be used for solving the problems that in the prior art, in the process that the wind power plant inhibits the low-frequency oscillation of a power grid in a constant rotating speed region by using an additional damping control method, a pitch angle control system is low in adjusting speed and is difficult to adapt to the oscillation change of electromagnetic power, and then the low-frequency oscillation phenomenon of the power grid cannot be inhibited.

In order to achieve the technical purpose, the technical scheme of the invention is as follows:

the virtual synchronous wind power plant and photovoltaic power plant cooperative additional damping control method comprises the following steps:

when the power grid generates a low-frequency oscillation phenomenon, the virtual synchronous wind power station and the photovoltaic power station receive the instruction active power sent by the additional damping controller;

and the virtual synchronous wind power plant and the photovoltaic power station adjust the respective current active power according to the instruction active power and the reserved active power of the double-fed fan.

The method is further improved in that: and S1, measuring the current wind speed according to the obtained measurement. If the Doubly-Fed wind turbine runs in a Maximum Power Point Tracking (MPPT) area, the Doubly-Fed Induction Generator (DFIG) reserves standby Power through overspeed load shedding, and the Virtual Synchronous Generator (VSG) is adopted to control and increase system damping. The photovoltaic power station operates in a maximum power tracking mode. When the DFIG operates in a constant rotating speed region, the DFIG reserves the reserve power through load shedding control of the pitch angle, and the other control modes are unchanged.

And S2, if the DFIG runs in the MPPT area, releasing standby power by the DFIG when low-frequency oscillation occurs, and respectively starting the additional damping control by the DFIG and the photovoltaic power station to output damping power.

And S3, if the DFIG operates in a constant rotating speed area, when low-frequency oscillation occurs, the photovoltaic power station outputs damping power, and the DFIG makes a contribution to system damping through VSG control.

The method is further improved in that: the additional damping controller of the virtual synchronous wind power plant specifically comprises the following components:

and S10, respectively reserving certain standby power for the DFIG in the MPPT area and the rotating speed constant area through overspeed load shedding control and pitch angle load shedding control.

And S11, adopting a VSG control technology for the DFIG based on the power backup, increasing the inertia and the damping of the double-fed fan, and reducing the weakening effect of the double-fed fan on the system damping.

And S12, taking the variable quantity of the active power at the grid-connected position of the DFIG as input, and designing an additional damping controller on an active control loop of the virtual synchronous wind power plant to enable the output power of the DFIG to respond to the variable quantity of the active power at the grid-connected position of the DFIG.

The method is further improved in that: the power standby obtained by the overspeed load shedding control and pitch angle load shedding control mode is determined by adopting the following method:

wind turbine captures wind energy through blades and converts the wind energy into mechanical energy P _m The expression of (a) is:

in the formula, P _b For the wind energy captured by the blade, rho is air density, R is the radius of the wind wheel blade, v is wind speed, lambda is blade tip speed ratio, and beta is pitch angle. C _p Is the coefficient of wind energy utilization, C _p Is a 2-membered function of λ and β.

When the DFIG operates in the MPPT area: the pitch angle of the fan is always 0 DEG C _P (λ,β)＝C _P (lambda). Assuming that the load shedding coefficient of the fan is d%, the wind energy utilization coefficient after load shedding is as follows:

C _Pdel (λ _del )＝(1-d％)C _p (λ,β)

in the formula, λ _de1 The corresponding tip speed ratio is obtained when the load is reduced at overspeed. The expression of the mechanical power captured by the wind turbine when the load is reduced by d% is as follows:

in the formula, P _mdel Representing mechanical power captured by the fan after load shedding, k _del Representing the sub-optimal power scaling factor.

Therefore, in the MPPT area, the standby power is obtained through the rotor overspeed control of the DFIG. The double-fed fan can store part of energy in the rotor through the overspeed load shedding of the rotor, and the effect similar to flywheel energy storage is achieved. When the system needs energy, the double-fed fan can release the energy by controlling the converter, and the system needs can be responded quickly. The energy stored after the control method is adopted is as follows:

in the formula, P _ew For the electromagnetic power output by the fan, J _w The equivalent moment of inertia of the fan rotor and the shafting system.

When the DFIG operates in a constant rotation speed region: omega ₁ ＝ω _max Tip speed ratio λ ₁ ＝ω _max *R/ν，C _P (λ,β)＝C _P And (. Beta.), the doubly-fed wind turbine can control the load shedding through the pitch angle. The wind energy utilization coefficient after load shedding is as follows:

C _Pdel (β)＝(1-d％)C _p (λ,β)

the initial value of the pitch angle corresponding to a specific load shedding factor can be obtained according to the above formula.

The method is further improved in that: the model of the additional damping control of the virtual synchronous wind power plant is as follows:

the DFIG active loop control equation based on VSG control is as follows:

in the formula, P _mdel 、P _e 、P _d Mechanical power, electromagnetic power, damping power, delta, of DFIG _VSG 、ω _VSG The power angle and the angular velocity omega of the VSG active loop output respectively ₀ Is the rated angular frequency, U, of the power grid _m Effective value of grid-connected point voltage, E ₀ The amplitude of the VSG reactive control output voltage, X is equivalent synchronous reactance, J is virtual moment of inertia of the double-fed fan, and a corresponding virtual inertia time constant H can be used for measuring the inertia of the generator set. The inertia time constant of the synchronous machine is a fixed value in a specific range under the limitation of self physical conditions; however, the virtual inertia time constant of the new energy source unit controlled by the VSG is more flexibly selected, and numerical values in a larger range can be obtained according to the needs of the power grid condition. D _p And (5) virtualizing a damping coefficient for the VSG active loop. The virtual damping coefficient can be adjusted to obtain small overshoot according to the concept of' optimal 2-order systemAnd a fast response speed, i.e.

The method is further improved in that: mechanical power P captured after fan overspeed load shedding control and pitch angle load shedding control _mdel As input for virtual synchronous active control of the DFIG. And the VSG control is replaced by the VSG control to obtain the VSG control of the double-fed fan based on power standby. The output of the active control loop determines the frequency and the phase angle of the potential in the VSG, and the output of the active control loop and the output of the reactive control loop jointly act on the DFIG rotor side converter as a modulation wave of PWM inversion.

The method is further improved in that: the additional damping control method of the virtual synchronous wind power plant comprises the following steps:

damping power P _d The capability of the DFIG based on VSG control for responding to the change of the voltage angular frequency of the grid-connected point and damping the low-frequency oscillation of the power system is reflected. The active power variable quantity at the DFIG grid-connected position is used as input, an additional damping controller is designed on a converter at the rotor side of the DFIG, and the output of the controller acts on a VSG active control loop. By varying the damping power P of the DFIG output based on VSG control _d The capacity of the virtual synchronous wind power plant for responding to power oscillation of the power system is enhanced, and the low-frequency oscillation phenomenon of the power system is restrained.

The method is further improved in that: the additional damping controller of the photovoltaic power station is designed by adopting the following method:

the photovoltaic grid-connected inverter generally adopts a voltage and current double-loop decoupling control strategy. The voltage outer loop keeps the voltage stability of the direct current side, the current inner loop tracks the voltage of the power grid, and the mathematical control equation of the inverter is as follows:

in the formula, x ₁ 、x ₂ And x ₃ Is an intermediate variable, e is a natural constant, Δ T, andΔ S is the amount of change in temperature and illumination intensity, respectively. k is a radical of _p1 、k _i1 Is a control parameter, k, of the outer loop of the voltage _p2 、k _i2 And k _p3 、k _i3 Are control parameters of d-axis and q-axis of the current inner loop, respectively. i.e. i _dg And i _qg D-and q-axis components, i, of the inverter output current, respectively _{dg_ref} And i _{qg_ref} For its reference value, i _{qg_ref} The magnitude of the voltage control unit controls the output active power of the photovoltaic power station. u. of _dg And u _qg Are respectively the voltage u of the grid-connected point of the photovoltaic power station _g The dq axis component of (c). U shape _dc And U _{dc_ref} Is the DC capacitor voltage and its reference value, U _m Is the photovoltaic array output voltage.

An additional damping controller is designed on a photovoltaic power station inverter by taking the active power variable quantity at the grid-connected position of the DFIG as input, and the intermediate variable x is changed ₁ Controlling d-axis component i of inverter output current _{dg_ref} And enabling the output power of the photovoltaic power station to respond to the active power change at the DFIG grid connection position.

The virtual synchronous wind power plant and photovoltaic power station cooperative additional damping control device is applied to the method and comprises the following steps:

a memory storing executable program code;

a processor coupled with the memory;

the processor calls the executable program codes stored in the memory for executing the steps of the virtual synchronous wind power plant and photovoltaic power station additional damping control method.

Due to the adoption of the technical scheme, the invention has the technical progress that: when the DFIG operates in the MPPT area, the virtual synchronous wind power plant and the photovoltaic power plant both participate in additional damping control. The wind power plant participates in restraining low-frequency oscillation of a power grid through VSG control and additional damping control. When the DFIG operates in a constant rotating speed area, the wind power plant does not participate in additional damping control any more, but participates in restraining low-frequency oscillation of a power grid through VSG control. The photovoltaic power station is switched between the MPPT mode and the additional damping control mode, and the photovoltaic power station outputs active power as much as possible in a mode of restraining low-frequency oscillation only in a half period. The cooperative control strategy can solve the problems that in the prior art, in the process that the wind power field utilizes an additional damping control method to inhibit the low-frequency oscillation of the power grid in a rotating speed constant region, the pitch angle control system is low in adjustment speed, is difficult to adapt to the oscillation change of electromagnetic power, and is not ideal in effect of inhibiting the low-frequency oscillation of the power grid.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without inventive exercise.

Fig. 1 is a control method for additional damping of a wind power plant cooperating with a photovoltaic power station, which is operated based on a virtual synchronization mode and provided by an embodiment of the present application;

FIG. 2 is a schematic flow chart illustrating the active power command from the additional damping controller according to an embodiment of the present disclosure;

fig. 3 is a control diagram of overspeed and deloading of a rotor of a doubly-fed fan in an MPPT region according to an embodiment of the present application;

fig. 4 is a virtual synchronization control diagram of a doubly-fed wind turbine based on power backup according to an embodiment of the present application;

fig. 5 is a diagram of an active ring control of a virtual synchronous machine according to an embodiment of the present application;

fig. 6 is a decoupling control diagram of a photovoltaic inverter provided in an embodiment of the present application;

FIG. 7a is a schematic diagram of additional damping control of a virtual synchronous wind farm provided by an embodiment of the present application;

FIG. 7b is a schematic diagram of additional damping control of a photovoltaic power plant according to an embodiment of the present disclosure;

fig. 8 is a schematic flowchart of determining a current active power according to an embodiment of the present application;

fig. 9 is a schematic structural diagram of a power grid system according to an embodiment of the present application;

fig. 10a is an active power output by a scene 1 additional damping control front-rear synchronizer G3 according to the embodiment of the present application;

fig. 10B is a diagram illustrating that the additional damping controls front and rear buses B9 of the scene 1 transmit active power according to the embodiment of the present application;

fig. 10c shows a difference in the rotational speed of the rotors of the front and rear synchronous machines controlled by additional damping in scenario 1 according to the embodiment of the present application;

fig. 10d is a diagram illustrating that the fan outputs active power and active power of the grid-connected monitoring point when the scene 1 has additional damping according to the embodiment of the present application;

fig. 10e is a view illustrating that the fan outputs active power and active power of the grid-connected monitoring point when the scene 1 has no additional damping according to the embodiment of the present application;

fig. 11a is an active power output by a scene 2 additional damping control front-back synchronous machine G3 provided in the embodiment of the present application;

fig. 11B is a diagram illustrating that active power is transmitted by the front and rear buses B9 under the additional damping control of the scenario 2 according to the embodiment of the present application;

fig. 11c is a rotation speed difference of rotors of a front and rear synchronous machines controlled by additional damping in scene 2 according to the embodiment of the present application;

fig. 11d is a diagram illustrating that the fan outputs active power and active power of a grid-connected monitoring point when additional damping is provided in scene 2 according to the embodiment of the present application;

fig. 11e is a view illustrating that the fan outputs active power and active power of a grid-connected monitoring point when no additional damping is provided in the scene 2 according to the embodiment of the present application;

fig. 12a is a comparison graph of active power Pe3 output by a synchronous machine G3 when a fan provided in the embodiment of the present application operates in a maximum power tracking region and a constant rotation speed region;

fig. 12b is a comparison graph of the difference between the rotation speeds of the rotors G2 and G3 of the synchronous machine when the fan operates in the maximum power tracking region and the constant rotation speed region according to the embodiment of the present application.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

When the power grid generates a low-frequency oscillation phenomenon, the virtual synchronous wind power plant and the photovoltaic power station receive the instruction active power sent by the additional damping controller.

Specifically, as shown in fig. 2, a schematic flow diagram for an additional damping controller to issue an instruction active power provided in an embodiment of the present application specifically includes:

step 201, obtaining a current wind speed.

Step 202, judging the operating area of the doubly-fed wind turbine according to the current wind speed, and performing different load shedding control on the doubly-fed wind turbine in different areas to reserve certain standby power.

Wind turbine captures wind energy through blades and converts the wind energy into mechanical energy P _m ：

In the formula, pb is wind energy captured by the blade, rho is air density, R is the radius of the wind wheel blade, v is wind speed, lambda is blade tip speed ratio, and beta is pitch angle. C _P Is a 2-element function of lambda and beta.

In the MPPT area, the doubly-fed fan obtains standby power through rotor overspeed control. As shown in fig. 3, a rotor overspeed load shedding control map of a doubly-fed wind turbine in the MPPT region is provided for the embodiment of the present application. Assuming that the wind speed is 9m/s, the load shedding power of the system is d%, the doubly-fed wind turbine is in load shedding operation at a point 2, and the output power is P _del . The point 1 corresponds to the maximum power P which can be output by the double-fed fan under the wind speed _opt The rotor speed corresponding to the point 3 is the maximum speed omega of the fan _max . When the system generates low-frequency oscillation, the double-fed fan operates between the point 1 and the point 3 according to the change of the power of the monitoring point in the system and the set control strategy. Assuming that the doubly-fed wind turbine operates to a balanced state at a point 4 when the oscillation disappears, and the output power of the doubly-fed wind turbine is P at the moment _w1 ＝P _del +ΔP _w 。

The pitch angle of the fan in the MPPT area is always 0 DEG C _P (λ,β)＝C _P (lambda). Assuming that the load shedding coefficient of the fan is d%, the wind energy utilization coefficient after load shedding is as follows:

C _Pdel (λ _del )＝(1-d％)C _p (λ,β)

in the formula of _de1 The corresponding tip speed ratio is obtained when the load is reduced at overspeed. According to the above formula and C _P The power expression at d% load shedding is shown in the-lambda curve:

in a rotating speed constant region, the double-fed fan obtains standby power through pitch angle control. At this time omega ₁ ＝ω _max Tip speed ratio λ ₁ ＝ω _max *R/ν，C _P (λ,β)＝C _P (β), the wind energy utilization coefficient after load shedding is:

C _Pdel (β)＝(1-d％)C _p (λ,β)

according to the above formula, the initial value of the pitch angle under the corresponding load shedding coefficient can be obtained.

And 203, controlling the doubly-fed wind turbine based on the power standby by adopting a virtual synchronous machine.

As shown in fig. 4, a virtual synchronization control diagram of a doubly-fed wind turbine based on power backup is provided in the embodiment of the present application.

The control part of the virtual synchronous control of the double-fed fan is mainly divided into active loop control and reactive control, and the output of the control part is used as a modulation wave of PWM inversion to act on a rotor side converter of the double-fed fan. As shown in fig. 5, a virtual synchronous machine active ring control diagram provided in the embodiment of the present application is shown. The active loop control of the VSG simulates a rotor second-order motion equation of the synchronous generator, and the output of the VSG determines the frequency and the phase angle of the potential in the VSG; the analogy to the rotor motion equation of the synchronous machine is that the rotor side virtual synchronous control active loop control equation of the doubly-fed wind turbine is as follows:

in the formula, J is the virtual moment of inertia of the doubly-fed wind turbine, and the corresponding virtual inertia time constant H can be used for measuring the inertia of the generator set. The inertia time constant of the synchronous machine is a fixed value in a specific range under the limitation of self physical conditions; however, the virtual inertia time constant of the new energy source unit controlled by the VSG is more flexibly selected, and numerical values in a larger range can be obtained according to the needs of the power grid condition. Of course, the value of the virtual inertia time constant of the new energy machine set is also limited by the inherent characteristics: the H values of the DFIG and the PMSG are generally in the second level, the H value of the photovoltaic power station is generally in the millisecond level, and the H values of the energy storage device are different due to different values of raw materials. Therefore, the wind turbine and the photovoltaic energy storage system VSG are generally controlled, and the photovoltaic power station VSG is not controlled independently. Delta _VSG For the power angle, omega, of a VSG inverter _VSG Is its angular velocity. Pm, pe and Pd are respectively the virtual mechanical power, the electromagnetic power and the damping power of the doubly-fed fan, and the calculation formula of each power is

Where equation 1 is the VSG simulated synchronous machine governor equation, P _ref Is the commanded active power of the VSG input. K _f The droop control coefficient is a droop control coefficient in a VSG active loop, and simulates a static frequency regulation effect coefficient of a speed regulation system of a synchronous machine. Omega ₁ Is the synchronous angular frequency E of the grid _VSG Is the VSG output voltage, um is the actual voltage of the power grid, XV is the equivalent synchronous reactance, and Dp is the damping coefficient.

And step 204, performing maximum power tracking control on the photovoltaic power station.

As shown in fig. 6, a decoupling control diagram for a photovoltaic inverter is provided in an embodiment of the present application.

The photovoltaic array converts light energy into electric energy, and the inverter inverts direct current output by the photovoltaic array into three-phase alternating current. The photovoltaic grid-connected inverter generally adopts a voltage and current double-loop decoupling control strategy. The voltage outer loop keeps the voltage stability of the direct current side, the current inner loop tracks the voltage of the power grid, and the mathematical control equation of the inverter is as follows:

in the formula, x ₁ 、x ₂ And x ₃ Is an intermediate variable, e is a natural constant, and Δ T and Δ S are temperature and illumination intensity variations, respectively. k is a radical of _p1 、k _i1 As a control parameter of the voltage outer loop, K _p2 、K _i2 And K _p3 、K _i3 Are control parameters of d-axis and q-axis of the current inner loop, respectively. i.e. i _dg And i _qg D-and q-axis components, i, of the inverter output current, respectively _{dg_ref} And i _{qg_ref} Is its reference value. u. of _dg And u _qg Respectively, the dq axis components of the grid-connected point voltage ug of the photovoltaic power station. U shape _dc And U _{dc_ref} Is the DC capacitor voltage and its reference value, U _m Is the photovoltaic array output voltage.

From the above equation and FIG. 6, it can be seen that the intermediate variable x can be varied ₁ Controlling d-axis component i of inverter output current _{dg_ref} And further, the purpose of controlling the output active power of the photovoltaic power station is achieved.

And step 205, determining control parameters of the additional damping controller according to the operation modes of the wind power plant and the photovoltaic power plant.

As shown in fig. 7a and b, schematic diagrams of additional damping control of a virtual synchronous wind farm and a photovoltaic power plant provided by the embodiment of the present application are shown. Specifically, the additional damping controller mainly comprises four links of filtering, term shifting, amplifying and amplitude limiting, namely delta P and delta P ₁ The feedback input signal and the output signal of the additional damping control link are respectively, N(s) and D(s) represent the numerator and denominator of the transfer function of the filtering link, T1 and T2 are phase-shifting link time constants, m is the number of the phase-shifting links, and K represents the gain coefficient of the amplifying link.

In the embodiment of the application, the maximum output power of the new energy unit is taken as the upper limit of the amplitude limiting link, and the standby power of the double-fed fan is completely put into use after oscillation occurs. The gain coefficient of the amplification link can be optimized by using a particle swarm algorithm in the feasibility analysis stage so as to obtain the optimal damping ratio. However, because the optimization algorithm consumes a long time, the gain of the controller can be determined by methods such as a phase compensation method and the like during an online application stage, and the problem of long consumed time is solved.

And step 206, according to the determined control parameters of the additional damping controller and the oscillation condition of the power grid, the additional damping controller sends out corresponding instruction active power.

Specifically, when the power grid oscillates, an oscillation analog quantity is input into the additional damping controller, control parameters of the additional damping controller are determined at the previous moment, command active power which the double-fed fan and the photovoltaic power station should output is obtained through calculation control of the additional damping controller, and the command active power is output to the double-fed fan and the photovoltaic power station.

And step 102, the virtual synchronous wind power plant and the photovoltaic power station adjust the current active power according to the instruction active power and the reserved active power of the double-fed fan.

As shown in step 102, if a situation occurs that requires adjustment of the current active power, the current active power needs to be determined first. When the power grid does not oscillate, the method provided by the embodiment of the application is adopted on the premise that the double-fed fan and the photovoltaic power station operate normally and stably, and the actual operating power which is not higher than the full-load power is not obtained after the reserved part of active power is not generated.

Fig. 8 is a schematic flowchart of a process for determining the current active power according to an embodiment of the present application.

Step 801, obtaining a current wind speed.

And step 802, determining full-load active power and active power which should be reserved under the current wind speed according to the current wind speed and a preset load shedding coefficient.

Specifically, the method for determining the reserved active power is consistent with step 202, and is not described herein again.

And 803, determining the current active power according to the current wind speed, the reserved active power and the full-load active power of the double-fed asynchronous wind driven generator at different wind speeds.

According to step 101, the commanded active power from the additional damping controller during grid oscillation can be obtained.

And when the power grid generates low-frequency oscillation, adjusting the current active power of the virtual synchronous wind power plant and the photovoltaic power station according to the instruction active power and the reserved active power. The suppression of the low-frequency oscillation of the power grid can be realized.

Specifically, if the instruction active power is greater than the current active power, the virtual synchronous wind power plant releases part of the reserved active power, and the current active power of the doubly-fed asynchronous wind power generator is increased to the instruction active power. The photovoltaic power station keeps the current output maximum power unchanged.

And if the instruction active power is smaller than the current active power, reducing the current active power of the virtual synchronous wind power plant and the photovoltaic power station to the instruction active power.

In order to demonstrate the effects of the embodiments of the present application, the following embodiments are further described.

Fig. 9 is a schematic diagram of a power grid system according to an embodiment of the present application. Specifically, in the system, G2 and G3 are two synchronous generators, and the capacities are 300MW and 150MW respectively; the wind power plant consists of 60 DFIGs of 1.5MW, and the DFIGs are controlled virtually and synchronously; PV is a 10MW equivalent photovoltaic plant. L is a radical of an alcohol _d1 ，L _d2 ，L _d3 Is an active load, wherein L _d1 And L _d2 For constant load, L _d3 Is an impact load. The power reference value on each bus is 100MW, and the voltage reference value is the rated voltage of each bus.

Firstly setting a scene 1, setting the wind speed to be 10m/s in the scene 1, operating a virtual synchronous wind power plant in an MPPT (maximum power point tracking) area, and participating in additional damping control in both the virtual synchronous wind power plant and a photovoltaic power station. When t =10s, a fault occurs in the bus B9. The effects of the embodiment of scenario 1 are shown in fig. 10 a-e. Fig. 10a to e are respectively the active power output by the additional damping control front and rear synchronous machines G3, the active power transmitted by the additional damping control front and rear busbars B9, the rotating speed difference of the rotors of the additional damping control front and rear synchronous machines, the active power output by the fan and the active power output by the grid-connected monitoring point when there is additional damping, and the active power output by the fan and the active power output by the grid-connected monitoring point when there is no additional damping in the scene 1. As can be seen from fig. 10a to e, the grid oscillation is rapidly suppressed by the method provided in the embodiment of the present application. According to the graphs of fig. 10a to e, the control strategy has a good inhibition effect on regional low-frequency oscillation and inter-regional low-frequency oscillation in the MPPT region, and the virtual synchronous wind power plant can respond to the active power change at the monitoring point before and after additional damping control.

Setting a scene 2 again, setting the wind speed in the scene 2 to be 13m/s, operating the virtual synchronous wind power plant in a constant rotating speed area, and enabling the virtual synchronous wind power plant not to participate in additional damping control any more. When t =10s, a fault occurs in the bus B9. The effects of the embodiment of scenario 2 are shown in fig. 11 a-e. Fig. 11a to e are respectively the active power output by the additional damping control front and rear synchronous machines G3, the active power transmitted by the additional damping control front and rear buses B9, the difference in the rotational speed of the rotors of the additional damping control front and rear synchronous machines, the active power output by the fan when there is additional damping and the active power output by the fan when there is no additional damping. As can be seen from fig. 11a to e, the grid oscillation is rapidly suppressed by the method provided in the embodiment of the present application. As can be seen from the graphs 11a to e, the control strategy has a good inhibition effect on regional low-frequency oscillation and inter-regional low-frequency oscillation in a rotating speed constant region, and the virtual synchronous wind power plants before and after additional damping control can respond to the active power change at the monitoring point. Because the capacity of the fan for outputting active power is stronger when the wind speed is higher, the photovoltaic power station occupies a smaller space in the system, and the virtual synchronous wind power station also plays a role in mainly inhibiting low-frequency oscillation in the scene.

Fig. 12a is a comparison graph of the output active power Pe3 of the synchronous machine G3 when the fan operates in the maximum power tracking area and the constant rotating speed area, and fig. 12b is a comparison graph of the rotating speed difference between the rotors G2 and G3 when the fan operates in different areas. As can be seen from fig. 12a and b, the control strategy according to the embodiment of the present application has an effect of suppressing local low-frequency oscillation in the rotation speed constant region and suppressing low-frequency oscillation between the regions close to the MPPT region as a whole. The time of local oscillation and the time of oscillation attenuation between areas are similar under different wind speeds, and the amplitude of the oscillation in the MPPT area is slightly lower than that in the constant rotating speed area. The effect of oscillation attenuation after additional damping in the MPPT area is obvious, the additional damping effect in the constant rotating speed area is not obvious enough, but the system oscillation before additional damping control is weaker than that in the MPPT area, and the overall control effects of the MPPT area and the system oscillation are equivalent. The virtual synchronous wind power station has more power reserve and stronger adjusting capacity in a rotating speed constant region, and can make more contribution to the damping of the system. Meanwhile, the capacity of the photovoltaic power station is small, the occupancy in the system is small, the additional damping control effect is not obvious enough, and the contribution of the virtual synchronous wind power station in the constant rotating speed area to the system damping is larger. By combining the analysis, the control strategy of the embodiment of the application has better inhibition effect on local low-frequency oscillation and inter-region low-frequency oscillation in the overall effect, and has stronger engineering practical value.

The invention may be described in the general context of computer-executable instructions, such as program modules, being executed by a computer. Generally, program modules include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types. The invention may also be practiced in distributed computing environments where tasks are performed by remote processing devices that are linked through a communications network. In a distributed computing environment, program modules may be located in both local and remote computer storage media including memory storage devices.

The principle and the implementation mode of the invention are explained by applying a specific example, and the description of the embodiment is only used for helping to understand the method and the core idea of the invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, the specific embodiments and the application range may be changed. In view of the above, the present disclosure should not be construed as limiting the invention.

Claims

1. The virtual synchronous wind power plant and photovoltaic power plant cooperative additional damping control method is characterized by comprising the following steps:

when the power grid generates a low-frequency oscillation phenomenon, the virtual synchronous wind power station and the photovoltaic power station receive instruction active power sent by respective additional damping controllers;

and the virtual synchronous wind power plant and the photovoltaic power station adjust the current active power of the virtual synchronous wind power plant and the photovoltaic power station according to the instruction active power and the reserved active power of the double-fed wind turbine.

2. The virtual synchronous wind farm collaborative photovoltaic power station additional damping control method according to claim 1, wherein the virtual synchronous wind farm and the photovoltaic power station adjust their respective current active power according to the instruction active power and the reserved active power of the doubly-fed wind turbine specifically:

s1, according to the obtained current wind speed, if a double-Fed wind driven Generator (DFIG) runs in a Maximum Power Point Tracking (MPPT) area, reserving standby Power through overspeed load shedding, and controlling and increasing system damping by adopting a Virtual Synchronous Generator (VSG); the photovoltaic power station operates in a maximum power tracking mode; when the DFIG operates in a constant rotating speed region, the DFIG reserves the reserve power through pitch angle load shedding control, and the other control modes are unchanged;

s2, if the DFIG operates in the MPPT area, the DFIG releases standby power when low-frequency oscillation occurs, and the virtual synchronous wind power plant and the photovoltaic power station respectively start additional damping control to output damping power;

and S3, if the DFIG operates in a constant rotating speed area, the DFIG makes a contribution to system damping through VSG control, and the photovoltaic power station outputs damping power when low-frequency oscillation occurs.

3. The virtual synchronous wind farm collaborative photovoltaic power station additional damping control method according to claim 1, wherein the virtual synchronous wind farm additional damping controller is specifically:

s10, reserving certain standby power for the DFIG in the MPPT area and the rotating speed constant area through overspeed load reduction control and pitch angle load reduction control respectively;

s11, adopting a VSG control technology for the DFIG based on the power backup, increasing inertia and damping of the double-fed fan, and reducing weakening effect of the double-fed fan on system damping;

and S12, taking the active power variation at the grid-connected position of the DFIG as input, and designing an additional damping controller on an active control loop of the virtual synchronous wind power plant to enable the output power of the DFIG to respond to the active power variation at the grid-connected position of the DFIG.

4. The virtual synchronous wind farm-coordinated photovoltaic power station additional damping control method according to claim 1, wherein the photovoltaic power station additional damping controller is specifically:

the control equation of the outer ring of the photovoltaic inverter voltage control is as follows:

wherein e is a natural constant, and Δ T and Δ S are variations in temperature and illumination intensity, respectively; u shape _dc And U _{dc_ref} Is the DC capacitor voltage and its reference value, U _m Outputting a voltage for the photovoltaic array; k is a radical of formula _p1 、k _i1 As a control parameter of the voltage outer loop, x ₁ Is an intermediate variable; i.e. i _{dg_ref} The reference value of the d-axis component of the output current of the inverter controls the output active power of the photovoltaic power station;

an additional damping controller is designed on a photovoltaic power station inverter by taking the active power variable quantity at the grid-connected position of the DFIG as input, and the intermediate variable x is changed ₁ Controlling d-axis component i of inverter output current _{dg_ref} And the output power of the photovoltaic power station responds to the change of active power at the DFIG grid-connected position.

5. The virtual synchronous wind farm collaborative photovoltaic power plant additional damping control method according to claim 2, wherein the overspeed load shedding control and pitch angle load shedding control are as follows:

wind turbine captures wind energy through blades and converts the wind energy into mechanical energy P _m The expression of (c) is:

in the formula, P _b For wind energy captured by the blades, rho is air density, R is the radius of the blades of the wind wheel, v is wind speed, lambda is blade tip speed ratio, and beta is pitch angle; c _P Is the coefficient of wind energy utilization, C _P Is a 2-membered function of λ and β;

when the DFIG operates in the MPPT area: the pitch angle of the fan is always 0 DEG C _P (λ,β)＝C _P (lambda); assuming that the load shedding coefficient of the fan is d%, the wind energy utilization coefficient after load shedding is as follows:

C _Pdel (λ _del )＝(1-d％)C _p (λ,β)

in the formula of lambda _de1 Corresponding tip speed ratio when overspeed load shedding is carried out; the expression of the mechanical power captured by the wind turbine when the load is reduced by d% is as follows:

in the formula P _mdel Representing mechanical power captured by the fan after load shedding, k _del Representing a suboptimal power scaling factor;

when the DFIG operates in a constant rotation speed region: omega ₁ ＝ω _max Tip speed ratio λ ₁ ＝ω _max *R/ν，C _P (λ,β)＝C _P (beta), the double-fed fan can control load shedding through the pitch angle; the wind energy utilization coefficient after load shedding is as follows:

C _Pdel (β)＝(1-d％)C _p (λ,β)

the initial value of the pitch angle corresponding to a specific deloading coefficient can be obtained according to the above formula.

6. The virtual synchronous wind farm collaborative photovoltaic power plant additional damping control method according to claim 2, wherein the model of the virtual synchronous wind farm additional damping control is:

the DFIG active loop control equation based on VSG control is as follows:

in the formula, P _mdel 、P _e 、P _d Mechanical power, electromagnetic power, damping power, delta, of DFIG _VSG 、ω _VSG The power angle and the angular velocity omega of the VSG active loop output respectively ₀ Is rated angular frequency, U, of the power grid _m Effective value of grid-connected point voltage, E ₀ Is the amplitude of the VSG reactive control output voltage, X is the equivalent synchronous reactance, J and D _p Respectively, the equivalent virtual moment of inertia of the VSG and the virtual damping coefficient of the active ring.

7. The virtual synchronous wind farm-photovoltaic power plant additional damping control method according to claim 5, characterized in that the mechanical power P captured after the wind turbine overspeed load shedding control and the pitch angle load shedding control _mdel As input for virtual synchronous active control of the DFIG; the VSG control is replaced by the current inner loop control of the double-fed fan double closed-loop control, and the VSG control of the double-fed fan based on power standby can be obtained; the output of the active control loop determines the frequency and the phase angle of the potential in the VSG, and the output of the active control loop and the output of the reactive control loop jointly act on the DFIG rotor side converter as a modulation wave of PWM inversion.

8. The virtual synchronous wind farm-photovoltaic power station-coordinated additional damping control method according to claim 6, characterized in that the virtual synchronous wind farm-coordinated additional damping control method is as follows:

the damping power P _d The capability of the DFIG based on VSG control for responding to the voltage angular frequency change of the grid-connected point and damping the low-frequency oscillation of the power system is reflected; the method comprises the following steps that the active power variable quantity at the DFIG grid-connected position is used as input, an additional damping controller is designed on a converter at the rotor side of the DFIG, and the output of the controller acts on a VSG active control loop; by changing the radicalDamping power P output by DFIG controlled by VSG _d The capacity of the virtual synchronous wind power plant for responding to power oscillation of the power system is enhanced, and the low-frequency oscillation phenomenon of the power system is restrained.

9. Virtual synchronous wind-powered electricity generation field is with photovoltaic power plant additional damping controlling means in coordination, its characterized in that includes:

a memory storing executable program code;

a processor coupled with the memory;

the processor invokes the executable program code stored in the memory to execute the steps of the virtual synchronous wind farm-coordinated photovoltaic power plant additional damping control method according to any one of claims 1-8.