Fault Ride-Through Control Method for Wind Turbine Generator Based on Energy Storage and Wind Turbine Inertia Response

Abstract

The present invention relates to a fault ride-through control method for a wind turbine based on energy storage and wind turbine inertia response. Taking a doubly-fed wind turbine as the research object, based on the energy storage device (ES) and the inertia response of the wind turbine rotor, and considering the energy management strategy of the DC-side energy storage unit, a coordinated control strategy for the voltage fault ride-through of the wind turbine is proposed. The beneficial effects of the present invention are as follows: By using the inertia response of the wind turbine rotor in cooperation with the energy storage power response, the compensation power and capacity required by the energy storage device during the fault are reduced, and at the same time, the grid-connected voltage of the wind turbine during the fault is ensured to be maintained at a normal level, thereby improving the voltage fault ride-through ability of the wind turbine.

Description

Technical Field

[0001] The present invention belongs to the technical field of grid-connected wind power generation in a power system, and particularly relates to a fault ride-through control method for a wind turbine based on energy storage and wind turbine inertia response. Background Art

[0002] With the rapid development of new energy, the scale of wind farms connected to the grid is continuously increasing and the installed capacity ratio is continuously rising. Once a wind farm trips off the grid due to grid voltage fluctuations, it will cause a greater impact on the safe operation of the grid. Maintaining the non-disconnection of wind turbines during grid faults is an important issue for ensuring the safe and stable operation of the grid. Some countries with advanced wind power technologies have formulated corresponding wind power operation guidelines, among which the most important one is the low voltage ride-through ability, that is, it is required that wind turbines can still maintain grid-connected operation when the grid voltage drops and continuously transmit power to the grid.

[0003] When the wind turbine is operating normally, the wind energy is captured by the wind wheel and converted into electrical energy, and is fed into the grid via the stator and rotor of the wind turbine. When the grid voltage drops, the power output from the wind power generation system to the grid immediately decreases, while the mechanical power input by the wind blades cannot be immediately reduced, which will cause power imbalance inside the wind turbine and further lead to over-limits of the voltage and current of the generator and the converter. Doubly-fed wind turbines generally configure crowbar protection to divert the unbalanced power during faults. However, the crowbar protection has a series of disadvantages. One is that after the crowbar protection is started, the control of the rotor speed and reactive power of the wind turbine will be lost; the second is that the crowbar protection may fail due to overheating of the heat dissipation resistor during continuous multiple faults; the third is that the unbalanced power of the wind turbine will be consumed as heat energy and cannot be utilized. Summary of the Invention

[0004] The purpose of the present invention is to provide a fault ride-through control method for a wind turbine based on energy storage and wind turbine inertia response, adopting a coordinated control strategy for the wind turbine - energy storage device, using the energy storage response to cooperate with the wind turbine rotor inertia response to compensate for the unbalanced power of the wind turbine during faults, which can overcome the disadvantages of the crowbar protection, improve the voltage fault ride-through ability of the wind turbine, and at the same time reduce the demand for the energy storage power capacity.

[0005] To achieve the above object, the technical solution of the present invention is: a fault ride-through control method for a wind turbine based on energy storage and wind turbine inertia response. During a grid voltage fault, the coordinated control between the wind turbine and the energy storage device is started to achieve power balance between the wind turbine and the grid, and the energy storage device compensates the port voltage of the doubly-fed wind turbine; the energy storage device includes a DC-side energy storage unit, a grid-connected inverter unit, and an LC filter; the DC-side energy storage unit uses a supercapacitor for energy storage and is used for energy compensation during faults; the grid-connected inverter unit adopts a three-phase single-phase converter structure, which is beneficial for compensating zero-sequence components during asymmetric faults; the LC filter is connected to the grid in the way of a series transformer and compensates the port voltage of the doubly-fed wind turbine; the wind turbine is a doubly-fed wind turbine, including a wind wheel, a gearbox, an induction motor, a rotor-side converter RSC, a grid-side converter GSC, and corresponding control systems.

[0006] In an embodiment of the present invention, the method specifically includes the following steps:

[0007] S1. Detect the grid connection point voltage of the wind turbine to judge whether the grid has a fault; when the grid connection point voltage is normal, the rotor-side converter RSC of the wind turbine is used to achieve the maximum power tracking function of the wind turbine and the decoupling control of the active and reactive power output on the rotor side, and the grid-side converter GSC is used to achieve the stable control of the DC-side voltage and the decoupling control of the active and reactive power on the grid side, and the energy storage device does not operate; when the grid fault causes a voltage mutation, start the coordinated control strategy of the wind turbine - energy storage device, convert part of the wind energy captured by the wind turbine into the rotational kinetic energy of the rotor, thereby reducing the active power output at the port of the wind turbine, and thus reducing the power and capacity required by the energy storage device;

[0008] S2. According to the type of voltage fault ride-through, start the coordinated control strategy of the wind turbine - energy storage device:

[0009] When the grid fault causes the voltage to be too high, the input power of the wind turbine is less than the power output to the grid; to achieve the power balance of the wind turbine, the following coordinated control strategy is adopted: 1) Compensate the machine terminal voltage V of the wind turbine through the energy storage device s ; 2) Discharge the energy storage to compensate a part of the unbalanced power, denoted as P ES ; 3) Reduce the rotor speed through rotor control to compensate another part of the unbalanced power, denoted as P t ;

[0010] When the grid fault causes the voltage to drop, the input power of the wind turbine is greater than the power output to the grid; to achieve the power balance of the wind turbine, the following coordinated control strategy is adopted: 1) Compensate the machine terminal voltage V of the wind turbine through the energy storage device s ; 2) Charge the energy storage to absorb a part of the unbalanced power, denoted as PES ; 3) Control the rotor to increase the rotor speed to compensate for the other part of the unbalanced power, denoted as P t ;

[0011] In the above two cases, the ratio of the energy storage and the wind turbine rotor absorbing the unbalanced power is denoted as P ES : P t = 1:k;

[0012] S3. Calculate the proportional coefficient k in step S2 according to the maximum rotor speed constraint of the wind turbine, and obtain the energy storage response power during the fault and the reference value of the active power of the rotor side converter RSC in the wind turbine;

[0013] Through the above control strategy, the impact of the grid fault on the DFIG wind turbine is minimized, enabling the wind turbine to successfully achieve high / low voltage ride-through.

[0014] In an embodiment of the present invention, in step S2, P ES The specific calculation process is as follows:

[0015] After the grid fault occurs, assume that the input mechanical power of the wind turbine remains unchanged, denoted as P m ; P grid is the active power output to the grid, P ES is the active power absorbed / released by the energy storage, P t is the active power absorbed / released by the rotor inertia regulation, P gen is the output power of the wind turbine terminal; then during the fault process, the output power balance of the wind turbine is expressed as:

[0016] P m = P t + P ES + P grid

[0017] According to the characteristics of the energy storage type dynamic voltage regulator, assume that the per-unit value of the positive sequence component of the grid-connected voltage of the wind turbine after the fault is Then the energy storage power is as follows, where P gen is the output power of the wind turbine terminal;

[0018]

[0019] If the output power of the wind turbine remains unchanged during the fault, the unbalanced power between the output power of the wind turbine and the grid absorption is completely absorbed by the energy storage device, and the required power and capacity of the energy storage device are large, resulting in too high energy storage cost; considering that the rotor and blades of the wind turbine have large inertia, during the grid voltage fault, the rotational inertia of the wind turbine can be used to absorb / release part of the unbalanced power to reduce the energy storage demand; during the fault process, the change in the rotor angular velocity can be expressed as:

[0020]

[0021] Among them, P m is the maximum wind energy that can be captured by the wind turbine under the current wind speed; J is the moment of inertia; ω is the rotor rotational angular velocity; let P t be the rotor inertia regulation power of the wind turbine;

[0022] During the fault, the proportion of the unbalanced power diverted by the energy storage response and the rotor inertia response is k, that is:

[0023]

[0024] By combining equations (1)-(4), during the fault ride-through period, the energy storage power and the rotor absorption power of the wind turbine can be obtained respectively as:

[0025]

[0026] The above P ESk and P tk are the control reference values of the energy storage response power and the rotor inertia response power of the wind turbine during the fault ride-through period;

[0027] The power obtained from the above formula is fed back to the wind turbine, and the reference value of the active power output by the wind turbine during the fault period can be obtained as follows, where "1" represents the per-unit value of the rated power of the wind turbine;

[0028]

[0029] After determining the output power of the wind turbine during the fault period through the proportional coordination control strategy and the energy management strategy of the DC-side energy storage unit, ignoring the losses, the reference value P s * of the active power output on the stator side during the fault period can be obtained as:

[0030]

[0031] Among them, s is the slip of the wind turbine;

[0032] During the grid voltage fault period, the reference value P s * of the output power on the stator side is fed back to the grid-side converter RSC of the wind turbine to achieve coordinated control of the wind turbine - energy storage device; and when the grid voltage returns to normal, it switches to the original maximum power tracking control strategy on the grid-side converter RSC side.

[0033] In an embodiment of the present invention, the power distribution coefficient k of the energy storage device and the maximum power demand of the energy storage device in step S3 are determined by the following method:

[0034] According to the following formula

[0035]

[0036] it can be obtained that

[0037]

[0038] wherein, P m is the maximum wind energy that can be captured by the wind turbine under the current wind speed; J is the moment of inertia; ω is the angular velocity of the rotor rotation;

[0039] When the most serious fault occurs in the grid voltage, that is, when the three-phase symmetrical voltage of the grid drops to zero, the power that the grid can absorb drops to zero. At this time, the power absorbed by the energy storage device is the largest; at this time, there is

[0040] P ES = P gen

[0041] According to the limit speed ω m of the wind turbine rotor and the initial operating speed ω 0 and the inertia time constant with the constraint that the rotor speed of the wind turbine does not exceed ω m there is

[0042]

[0043] wherein, S is the rated apparent power and t is the zero-voltage crossing time. Then the maximum regulating power of the wind turbine rotor

[0044] Under the above conditions, the maximum power demand of the energy storage device is

[0045]

[0046] The ratio k of the unbalanced power absorbed by the energy storage and the wind turbine rotor is determined by the maximum regulating power P tmax of the wind turbine rotor and the maximum power P ESmax of the grid-connected inverter unit of the energy storage device

[0047]

[0048] If only the energy storage is used to compensate the unbalanced power, the maximum power demand of the energy storage is P m . After adopting this strategy, the maximum power demand of the DC-side energy storage unit is reduced by k / (1 + k)%.

[0049] In an embodiment of the present invention, the energy management strategy of the DC-side energy storage unit is specifically as follows: the reference value P ESkFurther adjust according to the energy storage state of charge, and the adjustment coefficient is denoted as k psc , that is, the actual regulated power of the energy storage is P' ESk = k psc P ESk ; Assume the maximum capacity of the energy storage is E SC_max , and the high and low charge state limits are E SC_up and E SC_down respectively; When the energy storage state of charge E SC_down ≤ E SC ≤ E SC_up , no power limit is imposed on the DC-side energy storage unit, and the adjustment coefficient k psc = 1; When E SC > E SC_up , due to the limitation of the DC-side energy storage unit capacity, the charging power of the DC-side energy storage unit is limited, that is, k psc is gradually reduced until k SC_max is reduced to 0 when the energy storage state of charge reaches the maximum capacity E psc ; When E SC < E SC_down , the discharging power of the DC-side energy storage unit is limited until k SC_min is reduced to 0 when the energy storage state of charge reaches the minimum capacity E psc ;

[0050] If during the fault, the DC-side energy storage unit has been charged to the maximum capacity E SC_max or discharged to the minimum capacity E SC_min , then the energy storage cannot be further charged or discharged; At this time, the maximum inertial regulation power P tmax of the wind turbine can be increased first, but it cannot exceed 1 p.u., and the reference value of the active power output by the wind turbine is determined by the energy management of the DC-side energy storage unit; If P tmax is increased or there is still unbalanced power after the rotor speed of the wind turbine reaches the upper / lower limit, then the crowbar protection of the wind turbine needs to be started.

[0051] Compared with the prior art, the present invention has the following beneficial effects: The present invention can formulate a coordinated control strategy method to meet the voltage fault ride-through of the wind turbine, reduce the required power and capacity during the fault of the energy storage type energy storage device, and enable the wind turbine to operate normally when a grid-connected voltage fault occurs, thereby improving the voltage fault ride-through ability of the wind turbine. Description of the Drawings

[0052] Figure 1 is a schematic diagram of the grid-connected structure of the wind turbine based on energy storage in the application example of the present invention;

[0053] Figure 2(a) is the overall flowchart of the coordinated control strategy for wind turbine voltage fault ride-through based on energy storage in the application example of the present invention; (b) is the schematic diagram of the coordinated control strategy;

[0054] Figure 3 is the schematic diagram of the energy management of the energy storage unit in the application example of the present invention;

[0055] Figure 4 is the simulation result diagram of the three-phase symmetrical voltage dip of the power grid in the application example of the present invention;

[0056] Figure 5 is the simulation result diagram of the three-phase asymmetrical voltage dip of the power grid in the application example of the present invention;

[0057] Figure 6 is the simulation result diagram of the high voltage ride-through of the power grid in the application example of the present invention. Detailed implementation manners

[0058] The technical solution of the present invention will be specifically described below with reference to the accompanying drawings.

[0059] A fault ride-through control method for a wind turbine based on energy storage and wind turbine inertia response of the present invention starts the coordinated control between the wind turbine and the energy storage device during the power grid voltage fault to achieve the power balance between the wind turbine and the power grid, and the energy storage device compensates the voltage at the doubly-fed wind turbine port; the energy storage device includes a DC-side energy storage unit, a grid-connected inverter unit, and an LC filter; the DC-side energy storage unit uses a supercapacitor for energy storage and is used for energy compensation during faults; the grid-connected inverter unit adopts a three-phase single-phase converter structure, which is beneficial to compensating the zero-sequence component during asymmetrical faults; the LC filter is connected to the power grid in a series transformer manner and compensates the voltage at the doubly-fed wind turbine port; the wind turbine is a doubly-fed wind turbine, including a wind wheel, a gearbox, an induction motor, a rotor-side converter RSC, a grid-side converter GSC, and corresponding control systems.

[0060] The following is the specific implementation process of the present invention.

[0061] As Figure 1As shown, in a preferred embodiment of the present invention, a coordinated control technology for a wind turbine voltage fault ride-through based on energy storage is provided. During a grid voltage fault, the coordinated control between the wind turbine and the energy storage device is initiated to achieve power balance between the wind turbine and the grid, and the energy storage device compensates the voltage at the doubly-fed wind turbine port. The energy storage device specifically includes a DC-side energy storage unit, a grid-connected inverter unit, and an LC filter. The energy storage unit uses a supercapacitor for energy storage to compensate for energy during faults; the grid-connected inverter unit adopts a three-phase single-phase converter structure, which is beneficial for compensating zero-sequence components during asymmetric faults; the LC filter is connected to the grid in series with a transformer and compensates the voltage at the wind turbine terminal. The wind turbine generator set is a doubly-fed wind turbine generator set, specifically including a wind wheel, a gearbox, an induction motor, a rotor-side converter (RSC), a grid-side converter (GSC), and corresponding control systems.

[0062] Combined with the attached Figure 2 (a) and 2(b) show the overall flowchart of the coordinated control strategy of the present invention to further elaborate and explain the present invention.

[0063] First, detect the current grid voltage to determine whether the grid has a fault. Under normal grid voltage conditions, the rotor-side converter of the wind turbine generator set is used to achieve the maximum power tracking function of the wind turbine and the decoupled control of active and reactive power output on the rotor side, and the grid-side converter is used to achieve the stable control of the DC-side voltage and the decoupled control of active and reactive power on the grid side, and the energy storage device does not operate. When the grid fault causes a voltage mutation, the coordinated control strategy of the wind turbine generator set - energy storage device is initiated, and part of the wind energy captured by the wind turbine is converted into rotor rotational kinetic energy, thereby reducing the active power output at the wind turbine port, thus reducing the power and capacity required by the energy storage device;

[0064] Secondly, according to the type of voltage fault ride-through, the coordinated control strategy of the wind turbine generator set - energy storage device is initiated.

[0065] When the grid fault causes the voltage to be too high, the input power of the wind turbine is less than the power output to the grid. To achieve power balance of the wind turbine, the following coordinated control strategy is adopted: 1) Compensate the wind turbine terminal voltage V by the energy storage device s ; 2) Discharge the energy storage to compensate a part of the unbalanced power, denoted as P ES ; 3) Reduce the rotor speed through rotor control to compensate another part of the unbalanced power, denoted as P t .

[0066] When the grid fault causes the voltage to drop, the input power of the wind turbine is greater than the power output to the grid. To achieve power balance of the wind turbine, the following coordinated control strategy is adopted: 1) Compensate the wind turbine terminal voltage V by the energy storage devices ; 2) Absorb a part of the unbalanced power through energy storage charging, denoted as P ES ; 3) Increase the rotor speed through rotor control to compensate for the other part of the unbalanced power, denoted as P t .

[0067] In the above two cases, the ratio of the unbalanced power absorbed by the energy storage and the wind turbine rotor is denoted as P ES : P t = 1:k.

[0068] Finally, calculate the power absorbed / released by the energy storage device, give the reference value of the active power in the RSC of the wind turbine during the fault, reduce the active power output at the wind turbine terminal, so as to reduce the power and capacity required by the energy storage device.

[0069] Through the above control process steps, the impact of the grid fault on the DFIG wind turbine is minimized, enabling the wind turbine to successfully complete the voltage fault ride-through.

[0070] Furthermore, the power P absorbed / released by the energy storage ES Adopts the following specific calculation process:

[0071] After the grid fault occurs, assume that the input mechanical power of the wind turbine remains unchanged, denoted as P m . P grid The active power output to the grid, P ES Is the active power absorbed / released by the energy storage, P t Is the active power absorbed / released by the rotor inertia regulation, P gen Is the output power at the wind turbine terminal. Then during the fault process, the power output balance of the wind turbine is expressed as:

[0072] P m = P t + P ES + P grid

[0073] According to the characteristics of the energy storage type dynamic voltage regulator, assume that the per-unit value of the positive sequence component of the voltage at the grid connection point of the wind turbine after the fault is Then the energy storage power is as follows, where P gen Is the output power at the wind turbine terminal.

[0074]

[0075] When the output power of the wind turbine remains constant during a fault, the unbalanced power between the output power of the wind turbine and the power absorbed by the grid is completely absorbed by the energy storage device. The required power and capacity of the energy storage device are large, resulting in too high energy storage costs. Considering that the wind turbine rotor and blades have a large inertia, during a grid voltage fault, the rotational inertia of the wind turbine can be used to absorb / release part of the unbalanced power to reduce the energy storage demand. During the fault process, the change in the rotor angular velocity can be expressed as:

[0076]

[0077] where, P m is the maximum wind energy that can be captured by the wind turbine at the current wind speed; J is the moment of inertia; ω is the rotor rotational angular velocity; let P t be the rotor inertia regulation power of the wind turbine generator set.

[0078] During the fault, the proportion of the unbalanced power diverted by the energy storage response and the rotor inertia response is k, that is:

[0079]

[0080] By combining equations (1)-(4), the energy storage power and the power absorbed by the wind turbine rotor during the fault ride-through can be obtained as follows:

[0081]

[0082] The above P ESk and P tk are the control reference values of the energy storage response power and the wind turbine rotor inertia response power during the fault ride-through.

[0083] The power obtained from formula (5) is fed back to the wind turbine generator set, and the reference value of the active power output by the wind turbine generator set during the fault can be obtained as follows. Where "1" represents the per-unit value of the rated power of the wind turbine.

[0084]

[0085] After determining the output power of the wind turbine generator set during the fault through the proportional coordination control strategy and the energy management strategy of the energy storage unit, ignoring the losses, the reference value of the active power output on the stator side during the fault P s * is:

[0086]

[0087] where, s is the slip of the wind turbine.

[0088] During the grid voltage fault, the reference value of the output power on the stator side P s *Feedback to the RSC of the wind turbine unit to achieve coordinated control of the wind turbine - energy storage device; when the grid voltage returns to normal, it switches to the original maximum power tracking control strategy on the RSC side.

[0089] Furthermore, the power distribution coefficient k of the energy storage device and the maximum power demand of the energy storage device are determined as follows:

[0090] According to

[0091]

[0092] It can be obtained that:

[0093]

[0094] Among them, P m is the maximum wind energy that can be captured by the wind turbine at the current wind speed; J is the moment of inertia; ω is the rotor rotational angular velocity.

[0095] When the most serious grid voltage fault occurs, that is, when the three - phase symmetrical grid voltage drops to zero, the power that the grid can absorb drops to zero, and at this time, the power absorbed by the energy storage device is the largest. At this time, there is:

[0096] P ES = P gen

[0097] According to the limit speed ω m of the wind turbine rotor, the initial operating speed ω 0 , the inertia time constant With the constraint that the wind turbine rotor speed does not exceed ω m , there is:

[0098]

[0099] Among them, S is the rated apparent power, and t is the zero - voltage crossing time. Then the maximum adjustable power of the wind turbine rotor

[0100] Under the above conditions, the maximum power demand of the energy storage device is:

[0101]

[0102] The proportion k of the unbalanced power absorbed by the energy storage and the wind turbine rotor is determined by the maximum adjustable power P tmax of the wind turbine rotor and the maximum power P ESmax of the grid - connected inverter unit of the energy storage device:

[0103]

[0104] If only the energy storage is used to compensate for the unbalanced power, the maximum power demand of the energy storage is equal to P mAfter adopting this strategy, the maximum power demand of the energy storage unit is reduced by k / (1 + k)%.

[0105] Furthermore, the energy management strategy of the energy storage unit is as follows: During the fault, the reference value of the energy storage power is P ESk which is further adjusted according to the state of charge of the energy storage, and the adjustment coefficient is denoted as k psc , that is, the actual regulated power of the energy storage is P' ESk = k psc P ESk . Suppose the maximum capacity of the energy storage is E SC_max , and the upper and lower charge state limits are E SC_up and E SC_down respectively. When the state of charge of the energy storage E SC_down ≤E SC ≤E SC_up , no power limiting is performed on the energy storage unit, and the adjustment coefficient k psc = 1. When E SC > E SC_up , due to the limitation of the energy storage unit capacity, the charging power of the energy storage unit is limited, that is, k is gradually reduced psc until k is reduced to 0 when the state of charge of the energy storage reaches the maximum capacity E SC_max . When E psc < E SC < E SC_down , the discharging power of the energy storage unit is limited until k is reduced to 0 when the state of charge of the energy storage reaches the minimum capacity E SC_min . psc

[0106] If during the fault, the energy storage unit has been charged to the maximum capacity E SC_max or discharged to the minimum capacity E SC_min , then the energy storage cannot be further charged or discharged. At this time, the maximum inertial regulation power P of the wind turbine can be increased first tmax (but not exceeding 1 p.u), and the reference value of the active power output by the wind turbine is determined by the energy management of the energy storage unit. If increasing P tmax or the rotor speed of the wind turbine reaches the upper / lower limit and there is still unbalanced power, then the crowbar protection of the wind turbine needs to be started.

[0107] To verify the effectiveness of the present invention, the above method is implemented using the relevant data of a doubly-fed wind turbine in the subsequent application example. The specific steps are not elaborated here, and mainly its technical effects and implementation details are given.

[0108] Application Example

[0109] In this case, the system described in the present invention is built using the MATLAB / Simulink software platform, and the implementation effect is demonstrated for the case data.

[0110] Operating environment:

[0111] Intel Core i3-10105 CPU 3.70 GHz, 16 GB of memory, Microsoft Windows 10 X64

[0112] MATLAB 2020b

[0113] Implementation results:

[0114] Figure 3 It reflects the simulation carried out in accordance with the low-voltage ride-through standard of the State Grid Corporation. The fault starts at 1 s, the grid voltage drops to 0.2 pu, lasts for 625 ms, and then starts to recover. The grid voltage recovers to 0.9 pu at 4 s. During the fault, the energy storage device fully compensates the voltage at the grid connection point, keeping the voltage at the generator terminal of the wind turbine at a normal level all the time. The unbalanced power between the active power output by the wind turbine generator set and the active power absorbed by the grid during the fault is absorbed by the energy storage device, and the reactive power is always 0. When the grid voltage recovers to 0.7 pu at 3.2 s, the doubly-fed wind turbine generator set resumes the maximum power tracking control under normal grid voltage conditions, and the rotational speed, pitch angle, etc. also start to recover. The variation law of the rotor current is similar to that of the active power output by the doubly-fed wind turbine generator set. It can be seen from the simulation waveforms that during the three-phase symmetrical voltage dip of the grid voltage, the doubly-fed wind turbine generator set is hardly affected by the fault through the coordinated compensation control of the energy storage device.

[0115] Figure 4 It reflects the simulation waveform diagram when the voltage of phase a changes in accordance with the low-voltage ride-through standard of the State Grid Corporation. Due to the relatively light fault level, the wind turbine generator set still conducts maximum power tracking control as when the grid voltage is normal to deliver as much active power to the grid as possible. The unbalanced power between the output at the generator terminal of the doubly-fed wind turbine and the absorption by the grid is absorbed by the energy storage device. The DC voltage, rotational speed, rotor current, and pitch angle also remain at the values under normal grid voltage conditions. The wind turbine generator set is not affected by the single-phase fault at all.

[0116] Figure 5 It reflects the simulation results when the voltage of the wind turbine generator set rises to 1.3 pu and lasts for 200 ms. The grid voltage rises to 1.3 pu at 0.3 s and lasts for 200 ms. Similar to the single-phase voltage dip fault, the wind turbine generator set still outputs active power according to the maximum power tracking. At this time, the power output by the energy storage device is 0.3 pu to meet the power balance on both sides. The wind turbine generator set is also not affected by the voltage rise fault at all.

[0117] Figure 6 It is the simulation result diagram of the high-voltage ride-through of the grid voltage in the application example.

[0118] According to the results of this case, it can be seen that during the grid voltage fault, the unbalanced power between the wind turbine and the grid is absorbed by the energy storage device. At the same time, considering the coordinated control strategy between the control of the wind turbine itself and the energy storage device, on the one hand, the power and capacity of the required energy storage device are reduced; on the other hand, when the energy storage device fully compensates the terminal voltage of the generator, the impact of the grid fault on the wind turbine is minimized.

[0119] It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. On the contrary, the present invention covers any alternatives, equivalent methods, and solutions defined by the claims within the scope of the present invention. Further, in order to enable the public to have a better understanding of the present invention, some specific details of the present invention are described in detail below. Those skilled in the art can fully understand the present invention without the description of these details.

Claims

1. A fault ride-through control method for a wind turbine based on energy storage and wind turbine inertia response, characterized in that, during a power grid voltage fault, the coordinated control between the wind turbine and the energy storage device is started to achieve the power balance between the wind turbine and the power grid, and the energy storage device compensates the port voltage of the doubly-fed wind turbine; the energy storage device includes a DC-side energy storage unit, a grid-connected inverter unit, and an LC filter; the DC-side energy storage unit uses a super capacitor for energy storage and is used for energy compensation during faults; the grid-connected inverter unit adopts a three-phase single-phase converter structure, which is beneficial to compensating the zero-sequence component during an asymmetric fault; the LC filter is connected to the power grid in a series transformer manner and compensates the port voltage of the doubly-fed wind turbine; the wind turbine is a doubly-fed wind turbine, including a wind wheel, a gearbox, an induction motor, a rotor-side converter RSC, a grid-side converter GSC, and corresponding control systems; the method specifically includes the following steps: S1. Detect the grid connection point voltage of the wind turbine to judge whether the power grid has a fault; under normal grid connection point voltage conditions, the rotor-side converter RSC of the wind turbine is used to achieve the maximum power tracking function of the wind turbine and the decoupled control of the active and reactive power output on the rotor side, and the grid-side converter GSC is used to achieve the stable control of the DC-side voltage and the decoupled control of the active and reactive power on the grid side, and the energy storage device does not act; when a voltage mutation is caused by a power grid fault, start the wind turbine-energy storage device coordinated control strategy to convert part of the wind energy captured by the wind turbine into the rotational kinetic energy of the rotor, thereby reducing the active power output at the port of the wind turbine, and thus reducing the power and capacity required by the energy storage device; S2. According to the type of voltage fault ride-through, start the wind turbine-energy storage device coordinated control strategy: When a fault occurs in the power grid resulting in too high voltage, the input power of the wind turbine is less than the power output to the power grid; to achieve the power balance of the wind turbine, the following coordinated control strategies are adopted: 1) Compensate the terminal voltage V of the wind turbine through the energy storage device s ; 2) Discharge the energy storage to compensate a part of the unbalanced power, denoted as P ES ; 3) Reduce the rotor speed through rotor control to compensate another part of the unbalanced power, denoted as P t ; When a fault occurs in the power grid, resulting in a voltage dip, the input power of the wind turbine is greater than the power output to the grid. To achieve power balance of the wind turbine, the following coordinated control strategies are adopted: 1) Compensate the terminal voltage V of the wind turbine through the energy storage device s ; 2) Absorb a part of the unbalanced power through energy storage charging, denoted as P ES ; 3) Increase the rotor speed through rotor control to compensate for another part of the unbalanced power, denoted as P t ; In the above two cases, the ratio of the energy storage and the wind turbine rotor absorbing the unbalanced power is denoted as P ES : P t = 1:k; S3. According to the maximum rotor speed constraint of the wind turbine, calculate the proportional coefficient k in step S2, and obtain the energy storage response power during the fault and the reference value of the active power of the rotor-side converter RSC in the wind turbine; Through the above control strategy, the influence of the power grid fault on the DFIG wind turbine is minimized to enable the wind turbine to successfully achieve high / low voltage fault ride-through.

2. The fault ride-through control method for a wind turbine based on energy storage and wind turbine inertia response according to claim 1, characterized in that, In step S2, P ES The specific calculation process is as follows: After a grid fault occurs, assuming that the input mechanical power of the wind turbine remains unchanged, denoted as P m ; P grid is the active power output to the grid, P ES is the active power absorbed / released by the energy storage, P t is the active power absorbed / released by the rotor inertia regulation, P gen is the output power at the machine terminal of the wind turbine; then during the fault process, the output power balance expression of the wind turbine is: P m = P t + P ES + P grid According to the characteristics of the energy storage type dynamic voltage regulator, assuming that the per-unit value of the positive-sequence component of the voltage at the grid connection point of the wind turbine after the fault is V g + , then the energy storage power is as follows, where P gen is the output power of the wind turbine at the machine terminal; if the output power of the wind turbine remains unchanged during the fault, the unbalanced power between the output power of the wind turbine and the absorption of the power grid is completely absorbed by the energy storage device; during a power grid voltage fault, the rotational inertia of the wind turbine is used to absorb / release part of the unbalanced power to reduce the energy storage demand; during the fault process, the change in the rotor angular velocity is expressed as: where P m is the maximum wind energy that can be captured by the wind turbine at the current wind speed; J is the moment of inertia; ω is the angular velocity of the rotor rotation; let P t be the rotor inertia regulation power of the wind turbine; During the fault, the proportion of the unbalanced power diverted by the energy storage response and the rotor inertia response is k, that is: The energy storage power and the power absorbed by the rotor of the wind turbine during the fault ride-through are obtained respectively: The above-mentioned P ESk and P tk are the energy storage power and the rotor absorption power of the wind turbine during the fault ride-through period; The power obtained from the above formula is fed back to the wind turbine, and the reference value of the active power output by the wind turbine during the fault is obtained as follows, where "1" represents the per-unit value of the rated power of the wind turbine; After determining the output power of the wind turbine during the fault through the proportional coordination control strategy and the energy management strategy of the DC-side energy storage unit, ignoring the losses, the reference value of the active power output on the stator side during the fault can be obtained It is as follows: where s is the slip of the wind turbine; During the grid voltage fault, the stator side output power reference value is fed back to the grid side converter RSC of the wind turbine to achieve coordinated control of the wind turbine - energy storage device; when the grid voltage returns to normal, it switches to the original maximum power tracking control strategy on the grid side converter RSC side.

3. The fault ride-through control method for a wind turbine based on energy storage and wind turbine inertia response according to claim 2, wherein, in step S3, the power distribution coefficient k of the energy storage device and the maximum power demand of the energy storage device are determined by the following method: According to the following formula it is obtained that: where, P m is the maximum wind energy that can be captured by the wind turbine at the current wind speed; J is the moment of inertia; ω is the angular velocity of the rotor rotation; when the most serious fault occurs in the grid voltage, that is, when the three-phase symmetrical voltage of the grid drops to zero, the power that the grid can absorb drops to zero, and at this time, the power absorbed by the energy storage device is the largest; at this time, there is: P ES = P gen According to the limit speed ω of the wind turbine rotor m , the initial operating speed ω 0 , and the inertia time constant With the constraint that the rotor speed of the wind turbine does not exceed ω m , there is: where S is the rated apparent power and t is the zero-voltage crossing time, then the maximum regulating power of the wind turbine rotor under the above conditions, the maximum power demand of the energy storage device is: The proportion k of the unbalanced power absorbed by the energy storage and the wind turbine rotor is determined by the maximum regulation power P of the wind turbine rotor tmax and the maximum power P of the grid-connected inverter unit of the energy storage device ESmax as follows: If only energy storage is used to compensate for unbalanced power, the maximum power demand of the energy storage is P m , after adopting this strategy, the maximum power demand of the energy storage unit on the DC side is reduced by k / (1 + k)%.

4. The fault ride-through control method for a wind turbine based on energy storage and wind turbine inertia response according to claim 1, wherein, The energy management strategy of the DC-side energy storage unit is as follows: During the fault, the reference value of the energy storage power P ESk is adjusted according to the state of charge of the energy storage, and the adjustment coefficient is denoted as k psc , that is, the actual regulated power of the energy storage is P' ESk = k psc P ESk ; Suppose The maximum energy storage capacity is E SC_max , and the high and low charging state limits are E SC_up and E SC_down respectively; when the energy storage state of charge E SC_down ≤ E SC ≤ E SC_up , the power of the energy storage unit on the DC side is not limited, and the adjustment coefficient k psc = 1; when E SC > E SC_up , due to the limitation of the capacity of the energy storage unit on the DC side, the charging power of the energy storage unit on the DC side is limited, that is, k psc is gradually reduced until the energy storage state of charge reaches the maximum capacity E SC_max when k psc is reduced to 0; when E SC < E SC_down , the discharging power of the energy storage unit on the DC side is limited until the energy storage state of charge reaches the minimum capacity E SC_min when k psc is reduced to 0; If during a fault, the DC-side energy storage unit has been charged to its maximum capacity E SC_max or discharged to its minimum capacity E SC_min , then the energy storage cannot be charged or discharged; at this time, first increase the maximum inertia regulation power P tmax of the wind turbine, but not exceeding 1 p.u., and the reference value of the active power output by the wind turbine is determined by the energy management of the DC-side energy storage unit; if increasing P tmax or there is still unbalanced power after the rotor speed of the wind turbine reaches the upper / lower limit, then the crowbar protection of the wind turbine needs to be started.

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