WO2021258508A1

WO2021258508A1 - Low-voltage ride-through control method and system for wind turbine generator

Info

Publication number: WO2021258508A1
Application number: PCT/CN2020/106881
Authority: WO
Inventors: 张祯滨; 韩明昊; 王瑞琪; 李昱; 李�真
Original assignee: 山东大学
Priority date: 2020-06-22
Filing date: 2020-08-04
Publication date: 2021-12-30
Also published as: AU2020455056A1; CN111682587B; CN111682587A; AU2020455056B2

Abstract

Disclosed is a low-voltage ride-through control method for a wind turbine generator. The method comprises the following steps: receiving real-time voltage monitoring data of a power grid, and active power currently emitted by a wind turbine generator; and according to the voltage data, determining whether a voltage drop occurs in the power grid, involving: if a voltage drop occurs, further determining whether the voltage drop is within a set range, and if the voltage drop exceeds the set range, cutting off the wind turbine generator; if the voltage drop is within the set range, calculating reactive power that can be currently provided, and determining whether a reactive power demand can be met while the current active power is maintained; and if so, continuing to run until a fault is recovered or the wind turbine generator is cut off when a specified time is reached, otherwise, gradually modifying active and reactive given values. In the technical solution, by means of a control policy, the reactive output capability of a system is improved when a voltage drop occurs in a power grid, such that low-voltage ride-through is realized, without the need to additionally provide a hardware protection circuit.

Description

Low voltage ride-through control method and system of wind power generator

Technical field

The invention belongs to the technical field of low voltage ride through for wind power generation systems, and in particular relates to a method and system for controlling low voltage ride through of a wind power generator.

Background technique

The statements in this section merely provide background technical information related to the present disclosure, and do not necessarily constitute prior art.

Since the wind power system is sensitive to changes in grid voltage, when a voltage drop occurs in the grid, the imbalance of mechanical and electrical power in this transient process will affect the stable operation of the wind turbine, and the resulting overcurrent and additional torque of the generator may be Damage the device. In addition, a short-term failure of the power grid may cause the wind turbine to be disconnected from the grid, and the disconnection of the wind turbine will bring about changes in the power distribution and the stability of the entire system. Therefore, with the gradual increase in the proportion of wind power generation systems in renewable energy, phenomena such as wind curtailment and energy limitation have appeared. In order to ensure the stability of the grid connected to wind power, my country has stipulated the industry standard for low voltage ride-through of wind power, that is, the wind power unit maintains continuous operation without off-grid within the voltage time range specified by the curve as shown in Figure 5. After the voltage returns to normal, the wind power The active power output of the unit recovers quickly, and the wind turbine should have the ability to inject reactive current. Among them, the reactive current injection response time is not more than 75ms, the injection duration is not less than 550ms, and the injection effective value I _T ≥1.5×(0.9-U _TP )I _n , where I _T is the reactive current injection effective value; I _n It is the rated current of the wind turbine; U _TP is the unit value of the voltage at the test point.

Traditional wind turbines rely on the addition of additional hardware protection circuits, such as Crowbar protection circuits, and the use of DC support capacitors to achieve low voltage ride through. The traditional method of adding additional hardware protection circuits can effectively adjust the active power balance of the power system and protect the excitation converter and rotor windings in the event of a grid failure, but it will cause the wind farm to lose control in a short period of time. The switching operation of the Crowbar circuit will cause a transient impact in the system. At this time, the induction motor will absorb a large amount of reactive power from the system, and it is difficult to reach the low voltage ride through standard specified by our country.

Since wind power generation systems are often based on maximum power point tracking control, these protection strategies that use additional hardware often ignore the reactive power regulation capabilities of the converter itself, and it is difficult to use the idle capacity of the converter. Therefore, in the actual project, in order to ensure that the low voltage ride through standard is met, a reactive power compensator will be added at the same time as the protection circuit is added to provide reactive power to help the grid voltage recovery. Such a low voltage ride through mechanism requires a large number of additional hardware devices and ignores the reactive power output capability of the wind power system, which undoubtedly leads to an increase in system cost and a decrease in work efficiency, and it is difficult to obtain an economic low voltage ride through effect. Secondly, the wind power system is a typical multi-time scale dynamic system. The addition of hardware devices also increases the difficulty of design and control. In addition, the Crowbar circuit used will consume a lot of active power when the voltage drops, causing energy loss.

Summary of the invention

In order to overcome the above-mentioned shortcomings of the prior art, the present invention provides a low voltage ride through control method for a wind generator. Through the control strategy, the reactive power output capability of the system is improved when the grid voltage drops, and low voltage ride-through is realized, without the need to add a hardware protection circuit.

To achieve the foregoing objective, one or more embodiments of the present invention provide the following technical solutions:

A wind power generator low voltage ride through control method includes the following steps:

Receive real-time monitoring data of the grid voltage and the active power currently emitted by the wind turbine;

According to the voltage data, judge whether the power grid has voltage sag:

If there is a voltage drop, further judge whether the voltage drop is within the set range, if it exceeds the set range, cut off the wind turbine; if it is within the set range, calculate the current reactive power that can be provided to determine whether the current can be maintained In the case of active power, the demand for reactive power is met. If it can, continue to operate until the fault is restored or the wind turbine is cut off within the specified time; otherwise, the given value of active and reactive power is gradually corrected.

One or more embodiments provide a wind turbine low voltage ride through control system, including:

Voltage real-time monitoring module, which receives real-time monitoring data of grid voltage and active power currently emitted by wind turbines;

The voltage sag judgment module judges whether the power grid has a voltage sag based on the voltage data;

Voltage sag control module, if a voltage sag occurs, it will further determine whether the voltage sag is within the set range, if it exceeds the set range, cut off the wind turbine; if it is within the set range, calculate the current reactive power that can be provided to determine Whether it can meet the reactive power demand while maintaining the current active power, if so, continue to operate until the fault is restored or the wind turbine is cut off within the specified time; otherwise, gradually correct the given value of active and reactive power.

One or more embodiments provide an electronic device, including a memory, a processor, and a computer program stored in the memory and running on the processor, and the processor implements low voltage ride-through of a wind turbine when the program is executed. Control Method.

One or more embodiments provide a computer-readable storage medium having a computer program stored thereon, and when the program is executed by a processor, a wind turbine low voltage ride through control method is implemented.

One or more embodiments provide a converter, which is characterized in that a computer program is stored thereon, and when the program is executed by a processor, the wind turbine low voltage ride through control method is realized.

The above one or more technical solutions have the following beneficial effects:

The invention only changes the control strategy without adding a hardware protection circuit, improves the reactive power output capability of the wind turbine during low voltage ride through, effectively overcomes the transient impact and energy loss problems caused by the addition of hardware circuits, and reduces the system cost at the same time. Improve the power conversion efficiency of the system.

Description of the drawings

The accompanying drawings of the specification constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and the description thereof are used to explain the present invention, and do not constitute an improper limitation of the present invention.

Figure 1 is the relationship curve between wind energy utilization coefficient and pitch angle and blade tip speed ratio;

Figure 2 shows the relationship curve between wind turbine speed and power;

Figure 3 shows the equivalent circuit of a wind power grid-connected converter;

Figure 4 shows the adjustment interval of reactive power;

Figure 5 shows the low voltage ride through standard;

Fig. 6 is a flow chart of a low voltage ride through control strategy provided by an embodiment of the present invention.

detailed description

It should be pointed out that the following detailed descriptions are all exemplary and are intended to provide further description of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

It should be noted that the terms used here are only for describing specific embodiments, and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should also be understood that when the terms "comprising" and/or "including" are used in this specification, they indicate There are features, steps, operations, devices, components, and/or combinations thereof.

In the case of no conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other.

Maximum power point tracking is the basic principle of wind turbine control and an important means to improve wind energy utilization. The purpose of the maximum power point tracking control is to make the wind turbine output its maximum power at different wind speeds. When the wind turbine is in normal operation, its output mechanical power P is:

In the formula: C _P is the wind energy utilization coefficient, ρ is the air density, A is the flow surface area, and v is the wind speed. The wind energy utilization coefficient C _P is a function of the pitch angle β and the tip speed ratio λ. The relationship between C _P and β and λ, that is, the performance curve of the wind turbine is shown in Figure 1. Obviously, when the pitch angle is fixed, there is a certain λ under the same wind speed to maximize C _P , and from this, the relationship curves of different wind speeds, rotation speeds and power are obtained, as shown in Figure 2.

The reactive power support of the wind generator needs to be realized through a converter. The main function of the converter between the wind turbine and the grid is to transfer active power from the wind turbine to the grid. However, when the active power is lower than the apparent power of the converter, the converter can also provide reactive power support to the AC grid by controlling the power factor of the integrated wind power into the grid. Therefore, the essence of the reactive power output capability of a wind power generation system is the power exchange between three phases, and is limited by its own apparent power. The increase of active power will reduce the output of reactive power. Wind power converter equivalent circuit shown in Figure 3, where U is the converter output voltage, E _N is the network voltage and, x is the equivalent inductance, [alpha] is the output voltage of the converter and the network with Angle difference, according to the equivalent circuit to derive the expression of active power and reactive power:

And get the adjustment interval of active power and reactive power as shown in Figure 4. The adjustment interval is the area enclosed by ABCD, P _max represents the active power obtained when the maximum power tracking is achieved, and the shaded part is the area where Q is a negative value. Reactive power can be emitted in this area. In addition to the above derivation range, the influence of converter capacity on reactive power output needs to be considered.

Example one

This embodiment discloses a low voltage ride-through control method for wind turbines. The core point is based on the maximum power point tracking strategy and optimization, which improves the power quality of the system during normal operation, and improves the reactive power output capacity of the system when the grid voltage drops, and then Achieve low voltage ride through. Specifically, the

Step 1: The controller receives the real-time monitoring data E of the grid voltage and the active power P _pre currently emitted by the wind turbine;

Step 2: Determine whether the grid is operating normally, if yes, go to step 3; if not, first determine whether the drop is within the set range, if it exceeds the set range, cut off the wind turbine, if it is within the set range, calculate the current The maximum apparent power S _max and the reactive power Q that can be provided, go to step 4;

In this embodiment, if the voltage E≥0.9E _N, represents a drop has not occurred, the normal operation of the power grid; if E <0.9E _N, further determines whether a voltage drop within a predetermined range, if 0.2E _{_N} ≤E _{<0.9E N,} Calculate the current maximum apparent power S _max and the reactive power Q that can be provided.

In order to ensure that the low voltage ride-through does not cause the protection to operate, the generator should be cut off, and the output current of the converter should be within 1.1 times of its rated current. The maximum apparent power can be calculated as Smax=3E _N *1.1I _N , where E _N is the voltage value of the grid connection point (see Figure 3), I _N is the rated current of the converter

Step 3: Obtain voltage optimization control parameters based on the maximum power point tracking control strategy;

Step 4: Maintain the current active power and send out the reactive power that needs to be issued, that is, according to the instantaneous maximum apparent power limit condition, judge whether the switching reactive power demand can be met without changing the active power. If so, continue to operate until The fault is restored or the wind turbine is cut off within the specified time; otherwise, the active and reactive power setpoints are gradually corrected according to the soft control strategy. Specifically, if the maximum reactive power that can be provided by the converter calculated in step 2 is greater than the required reactive power Q _set , the required reactive power Q _set can be simply calculated according to the power grid regulations as

Among them, S is the converter capacity, and ΔE is the difference between the grid-connected point voltage before and after the fault.

When the voltage recovery at the grid-connected point is detected, it switches to the maximum power point tracking control strategy operation. If the voltage does not recover for a long time or the voltage drops below 20% of the rated value, the fan will be cut off in a quick response.

The softening control strategy is

In the formula, α is a variable in the interval [0,1], and its value is adjusted in real time according to the amplitude of the voltage drop and the change of the rate of change, and P _pre is the output of the active power when the voltage change is detected.

Generally speaking, when the wind power generation system adopts the maximum power point tracking control strategy, the reactive power setting is set to zero when the wind power generation system is connected to the grid. Scheduling. This has resulted in the actual situation that a hardware protection circuit must be matched to achieve the low voltage ride through requirement in the event of a faulty voltage drop. Therefore, in order to adjust the reactive power from the control strategy, the original maximum power point tracking mode must be changed to form an optimized control strategy that does not pursue the maximum power generation efficiency and sacrifices a part of the active power to generate reactive power.

When a voltage drop is detected, according to the low voltage ride-through standard and considering the possible noise influence, when the grid voltage drops below 90% of the rated value, the original maximum power point tracking operation mode is switched, and the original reactive power is no longer used The given value of the current active power is kept unchanged, and the reactive power that needs to be issued is sent out.

Ensure that it does not have a severe impact on the control of active power, and then determine whether the reactive power demand for switching can be met without changing the active power according to the instantaneous maximum apparent power limit condition. If the generated reactive power can reach the low voltage ride-through standard, continue to run until the fault is restored or the wind turbine is cut off within the specified time; otherwise, follow the

The soft control strategy is used to gradually correct the given values of active and reactive power to avoid severe impact on the system, and to achieve the demand for active and reactive power changes during the low voltage ride through process, where α is on the interval [0,1] The variable of, its value changes according to the amplitude and rate of change of the voltage drop for real-time adjustment, and P _pre is the output of the active power when the voltage change is detected. When the controller detects that the grid-connected point voltage has recovered, it switches to the maximum power point tracking control strategy operation. If the voltage does not recover for a long time or the voltage drops below 20% of the rated value, it quickly responds and cuts off the fan. The above specific process is shown in Figure 6.

For wind turbines in normal operation, this power adjustment strategy can also be used to improve the reactive power adjustment capability of wind power. After the maximum apparent power is calculated, the current active power set value can be kept unchanged, and Reactive power that needs to be issued

Provide reactive power support to the grid when the power generation can meet user needs, improve the power quality of the system, increase the efficiency of wind power generation, reduce the degree of dependence on other power generation methods, and reduce the demand for reactive power compensation hardware.

This embodiment is based on the maximum power point tracking strategy and the power characteristics of the converter, and makes full use of the idle capacity of the converter to improve the power quality of the system during normal operation; detect voltage changes when the grid voltage drops, and adjust the active power and The given value of reactive power to ensure that the reactive output of the system can meet the requirements of low voltage ride through without the need for additional hardware protection circuits. It effectively overcomes the transient impact and energy loss problems caused by the addition of hardware circuits, while reducing the system cost and improving the power conversion efficiency of the system.

The invention is based on the maximum power point tracking control strategy often adopted by wind turbines. Due to the non-linear characteristics of the wind generator, the maximum power point of the operation output will change with the change of the wind power. In order to ensure the maximum output of active power, the active power output is controlled by adjusting the torque component of the wind turbine rotor converter to ensure that the wind turbine runs on the best power curve. When the power generation is sufficient to support the demand of the load, it adjusts its own output power to output a certain amount of reactive power to the grid, thereby improving the power quality of the system.

In the power system of inductive lines, the occurrence of voltage drop indicates insufficient reactive power. Capacitive reactive power should be provided to reduce the degree of voltage distortion caused by inductive reactive power disturbance during voltage drop and prevent further voltage drop. At this time, the original control strategy must be adjusted in accordance with my country's low voltage ride through standard, while ensuring the maximum power point tracking, the idle capacity of the converter is used to output reactive power as much as possible to support the voltage. When a serious fault occurs, it can flexibly reduce the output of active power, meet the low voltage ride-through reactive current output standard, convert more reactive power, and help the grid voltage to recover. When the grid voltage is restored, the active output will be gradually increased to Rated power to improve low voltage ride through capability.

Example two

The purpose of this embodiment is to provide a low voltage ride through control system for a wind turbine, which includes:

Example three

The purpose of this embodiment is to provide an electronic device.

An electronic device including a memory, a processor, and a computer program stored on the memory and capable of running on the processor. The processor implements the low voltage ride-through control of a wind turbine as described in the embodiment when the processor executes the program method.

Embodiment four

The purpose of this embodiment is to provide a computer-readable storage medium. A computer program is stored thereon, and when the program is executed by the processor, the wind turbine low voltage ride through control method as described in the embodiment is realized.

Embodiment five

The purpose of this embodiment is to provide a converter which is configured to be able to store a computer program, which when executed by a processor realizes the wind turbine low voltage ride through control method as described in the embodiment.

The steps involved in the above embodiments two to five correspond to the method embodiment 1, and the specific implementation manner can refer to the relevant description part of the embodiment 1. The term "computer-readable storage medium" should be understood to include a single medium or multiple media including one or more instruction sets; it should also be understood to include any medium that can store, encode, or carry for use by a processor The set of executed instructions and causes the processor to execute any method in the present invention.

Those skilled in the art should understand that the above-mentioned modules or steps of the present invention can be implemented by a general-purpose computer device. Alternatively, they can be implemented by a program code executable by the computing device, so that they can be stored in a storage device. The device is executed by a computing device, or they are separately fabricated into individual integrated circuit modules, or multiple modules or steps in them are fabricated into a single integrated circuit module for implementation. The present invention is not limited to any specific combination of hardware and software.

The above descriptions are only preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Although the specific embodiments of the present invention are described above in conjunction with the accompanying drawings, they are not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that on the basis of the technical solutions of the present invention, those skilled in the art do not need to make creative efforts. Various modifications or variations that can be made are still within the protection scope of the present invention.

Claims

A wind power generator low voltage ride through control method is characterized in that it comprises the following steps:

Receive real-time monitoring data of the grid voltage and the active power currently emitted by the wind turbine;

According to the voltage data, judge whether the power grid has voltage sag:

If there is a voltage drop, further judge whether the voltage drop is within the set range, if it exceeds the set range, cut off the wind turbine; if it is within the set range, calculate the current reactive power that can be provided to determine whether the current can be maintained In the case of active power, the demand for reactive power is met. If it can, continue to run until the fault is restored or the wind turbine is cut off within the specified time; otherwise, the set values of active and reactive power are gradually corrected.
The low voltage ride through control method of a wind power generator according to claim 1, wherein:

If there is no voltage drop, the output voltage is optimized based on the maximum power point tracking control strategy.
The low voltage ride-through control method of a wind turbine according to claim 1, wherein when the voltage drop is within the set range, the current maximum apparent power is also calculated, and the current maximum apparent power is determined according to the instantaneous maximum apparent power limit condition. Whether it can meet the reactive power demand while maintaining the current active power.
The low voltage ride-through control method for wind turbines according to claim 3, characterized in that, if the reactive power demand cannot be met while maintaining the current active power, the active and reactive power supply is gradually corrected according to the soft control strategy. Value.
The low voltage ride-through control method of a wind turbine according to claim 4, wherein the softening control strategy is:

In the formula, α is a variable in the interval [0,1], and its value is adjusted in real time according to the magnitude and rate of change of the voltage drop. S max is the current maximum apparent power, and P pre is the value of the active power when the voltage change is detected. Output.
The wind turbine low voltage ride through control method according to claim 2, wherein the real-time monitoring data of the grid voltage is continuously received, and when the voltage is restored, the maximum power point tracking control strategy is switched to optimize the control of the output voltage.
A wind power generator low voltage ride through control system, which is characterized in that it comprises:

Voltage real-time monitoring module, which receives real-time monitoring data of grid voltage and active power currently emitted by wind turbines;

The voltage sag judgment module judges whether the power grid has a voltage sag based on the voltage data;

Voltage sag control module, if a voltage sag occurs, it will further determine whether the voltage sag is within the set range, if it exceeds the set range, cut off the wind turbine; if it is within the set range, calculate the current reactive power that can be provided to determine Whether it can meet the reactive power demand while maintaining the current active power, if so, continue to operate until the fault is restored or the wind turbine is cut off within the specified time; otherwise, gradually correct the given value of active and reactive power.
An electronic device comprising a memory, a processor, and a computer program stored on the memory and running on the processor, wherein the processor executes the program as described in any one of claims 1 to 6 The wind power generator low voltage ride through control method is described.
A computer-readable storage medium with a computer program stored thereon, which, when executed by a processor, realizes the low voltage ride-through control method of a wind power generator according to any one of claims 1-6.
A converter, characterized in that a computer program is stored thereon, and when the program is executed by a processor, the wind power generator low voltage ride through control method according to any one of claims 1-6 is realized.