Chaotic control method for grid-connected inverter of wind power system

Abstract

The invention provides a chaos control method of a wind power system grid-connected inverter, which comprises the following steps: establishing a wind power system grid-connected inverter mathematical model which comprises dynamic characteristics of a wind driven generator, an inverter and a power grid, and designing a chaos controller based on a physical law and a circuit theory, the chaos controller generates a control signal through chaos mapping and a feedback control strategy in a chaos theory, design and establishment of the chaos controller are related to nonlinearity and uncertainty of the system, the chaos controller is controlled through the grid-connected inverter, the control signal generated by the chaos controller is applied to the grid-connected inverter, and the grid-connected inverter is controlled to control the grid-connected inverter. The output voltage and the output current of the grid-connected inverter are adjusted, and the output of the inverter is kept to be matched with the frequency and the voltage level of the power grid; according to the method, the change of parameters in the wind power system is tracked and detected in real time through the established grid-connected inverter, the chaos phenomenon is identified, and the harmful chaos oscillation phenomenon of the wind power system is avoided.

Description

Technical Field

[0001] The present invention relates to the field of wind power systems, and particularly to a chaotic control method for a grid-connected inverter of a wind power system. Background Art

[0002] With the gradual expansion of the scale of wind power systems and their tendency to operate in parallel with the grid, as well as the intervention of modern power electronic devices, their dynamic characteristics have become increasingly complex. Some nonlinear singular phenomena often occur in the system, and the chaotic phenomenon is a very complex phenomenon caused by the interaction of various parameters in a nonlinear system. Its occurrence will be accompanied by non-periodic, seemingly irregular, sudden or intermittent electromechanical oscillations in the system. In severe cases, it will lead to the large-scale disintegration of the system and large-scale power outages. Since the wind power system is a typical large-scale complex nonlinear system, chaotic phenomena will also occur under certain conditions. Chaos will affect the stable operation of the wind power system. Therefore, in order to ensure the safety of the wind power system.

[0003] In the existing document 201910257741.0 for the actually operating wind power system, an accurate model of the system has not been obtained. Coupled with the influence of various disturbances during the operation process and the change of parameters in the model, the chaotic criterion based on the continuous system model has limitations when detecting and discriminating chaotic phenomena in the wind power system. Therefore, the present invention proposes a chaotic control method for a grid-connected inverter of a wind power system to solve the problems existing in the prior art. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the present invention proposes a chaotic control method for a grid-connected inverter of a wind power system. This chaotic control method for a grid-connected inverter of a wind power system can track and detect the changes of parameters in the wind power system in real time through the established grid-connected inverter, identify chaotic phenomena, avoid harmful chaotic oscillation phenomena in the wind power system, with simple design and easy-to-understand software programming. The control signal generated by the chaotic controller is applied to the grid-connected inverter for chaotic detection of the wind power system, overcoming the difficulties of the complex mathematical model, complex system, and uncertainty of the wind power system.

[0005] The technical solution of the present invention is realized as follows: A chaotic control method for a grid-connected inverter of a wind power system, comprising the following steps:

[0006] Step 1: Establish a mathematical model of the grid-connected inverter of the wind power system. This mathematical model includes the dynamic characteristics of the wind turbine, inverter, and power grid. The establishment of the model is based on physical laws and circuit theories;

[0007] Step 2: Design a chaotic controller. The chaotic controller generates a control signal through the chaotic mapping and feedback control strategy in chaos theory. The design of the chaotic controller is based on the nonlinearity and uncertainty of the system, and the chaotic controller is controlled through the grid-connected inverter;

[0008] Step 3: Apply the control signal generated by the chaos controller to the grid-connected inverter to adjust the output voltage and output current of the grid-connected inverter, and keep the output of the inverter matched with the frequency and voltage levels of the power grid;

[0009] Step 4: Set the normal range of the grid frequency and determine the rated wind speed of the wind turbine;

[0010] Step 5: Detect the change of the grid component frequency over a period of time and compare it with the normal range of the grid frequency, detect the wind speed of the grid component and compare it with the rated wind speed;

[0011] Step 6: Monitor the output of the grid-connected inverter in real time to complete the control of the wind power system.

[0012] The further improvement lies in: In Step 1, the grid-connected inverter of the wind power system controls the DC bus voltage by controlling the active power and conducts unity power factor grid connection by controlling the reactive power

[0013] The further improvement lies in: In Step 1, the mathematical model of the wind turbine includes an aerodynamic model, a mechanical model and an electromagnetic model. The aerodynamic model calculates the torque exerted by the wind on the wind turbine using the Betz theory and the blade element momentum theory. The mechanical model includes the dynamic behaviors of the wind turbine, gearbox and generator shafting, including inertia, damping and elastic effects. The electromagnetic model utilizes the electrical characteristics of the generator, including the relationships between voltage, current, magnetic flux and torque, and uses the motor equations and Kirchhoff's laws. The inverter model includes the behaviors and control strategies of the power switching devices, and the grid model includes voltage, frequency and impedance.

[0014] The further improvement lies in: In Step 2, select the chaotic map Logistic map. The output of the chaotic map provides the randomness and complexity of the control signal. The system state is adjusted by controlling the signal through a feedback control strategy. Sliding mode control is used to handle the uncertainties in the system. After the chaos controller is generated, the effectiveness of the chaos controller is verified through simulation and experiments, and the performance of the controller is tested.

[0015] The further improvement lies in: In Step 3, analyze the control signal generated by the chaos controller, convert it into a control instruction for the inverter, adjust the switching mode of the inverter according to the control signal generated by the chaos controller through pulse width modulation technology, thereby controlling the waveform and frequency of the inverter output voltage. Design a current control loop to adjust the output current of the inverter, and design a voltage control loop to adjust the output voltage of the inverter, so as to keep the output of the inverter matched with the frequency and voltage levels of the power grid.

[0016] A further improvement lies in: in step four, the normal range of the grid frequency is set to 50 Hz. For a system with a grid capacity of 3 million kilowatts or more, the frequency deviation does not exceed ±0.2 Hz, and the rated wind speed range of the wind turbine is between 10 and 12 m / s.

[0017] A further improvement lies in: in step five, the grid components include a wind turbine and a storage battery. Within the normal range of the grid frequency, when the wind speed exceeds the rated wind speed and the output power is smooth, the storage battery is in a charging state. When the grid frequency drops and exceeds the normal range of the grid frequency, part of the rotational kinetic energy of the wind turbine rotor is released to support the grid frequency for a short time. When the grid frequency is lower than the normal range of the grid frequency, the rotor inertia control module is cut off to prevent the wind turbine from releasing too much kinetic energy and possibly causing shutdown. At the same time, the discharge power of the storage battery is increased to participate in the primary frequency regulation of the grid. When the grid frequency is lower than the normal range of the grid frequency after a certain time delay, the discharge power of the storage battery is increased to participate in the secondary frequency regulation of the grid. When the grid frequency exceeds the normal range of the grid frequency, a part of the wind energy is sent into the storage battery to perform frequency regulation on the grid again. When the grid frequency exceeds the normal range of the grid frequency after a certain time delay, with the cooperation of the storage battery, the wind turbine reduces the wind energy capture coefficient, and finally performs primary frequency regulation on the grid.

[0018] A further improvement lies in: in step six, a voltage sensor and a current sensor are installed at the output end of the inverter to monitor the output voltage and current of the inverter, collect the data of the voltage sensor and the current sensor, and transmit it to the wind power system. At the same time, the frequency of the inverter output is monitored, and the output power of the inverter is calculated using the collected voltage and current data.

[0019] A further improvement lies in: the voltage sensor and the current sensor convert all input signals into standard voltage signals of 5V, and the voltage sensor and the current sensor are connected in a conventional electrical connection.

[0020] Compared with the prior art, the present invention has the following advantages: This application detects the changes in parameters in the wind power system in real time through the established grid-connected inverter, identifies chaotic phenomena, and avoids harmful chaotic oscillation phenomena in the wind power system. The design is simple, and the software programming is easy to understand. The control signal generated by the chaos controller is applied to the grid-connected inverter for chaotic detection of the wind power system, overcoming the difficulties of complex mathematical models, complex systems, and uncertainties in the wind power system, and having universality and being applicable to all wind power systems. The data storage circuit has the function of automatically protecting data after power failure, ensuring the uninterrupted real-time detection of chaos and improving the reliability of detection. Utilizing the high-speed data calculation and data processing capabilities of the computer, the real-time reliability of the detection system is greatly improved. Description of the Drawings

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0022] Figure 1 This is the step diagram of the present invention. Specific embodiments

[0023] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0024] In Document 201910257741.0, by improving the completeness and accuracy of information extraction, according to the DBN-ELM significant fault diagnosis model, the diagnosis accuracy of significant faults is improved, and the complexity of identifying unknown fault types is reduced. If the chaos criterion of the system model cannot be used when detecting and discriminating the chaotic phenomenon of the wind power system, in this application, by establishing multiple inverter models, the chaotic phenomenon occurring inside the wind power system is controlled and tracked to detect the change of parameters in the wind power system and identify the chaotic phenomenon, so as to avoid the occurrence of harmful chaotic oscillation phenomena in the wind power system.

[0025] Embodiment 1

[0026] See Figure 1 , the embodiment of the present invention discloses a chaotic control method for a grid-connected inverter of a wind power system, including the following steps:

[0027] Step 1: Establish a mathematical model of the grid-connected inverter of the wind power system. This mathematical model includes the dynamic characteristics of the wind turbine, the inverter, and the power grid. The establishment of the model is based on physical laws and circuit theories;

[0028] Step 2: Design a chaos controller. The chaos controller generates a control signal through the chaos mapping and feedback control strategy in chaos theory. The design of the chaos controller is based on the nonlinearity and uncertainty of the system, and the chaos controller is controlled through the grid-connected inverter;

[0029] Step 3: Apply the control signal generated by the chaos controller to the grid-connected inverter, adjust the output voltage and output current of the grid-connected inverter, and keep the output of the inverter matched with the frequency and voltage levels of the power grid;

[0030] Step 4: Set the normal range of the grid frequency and determine the rated wind speed of the wind turbine.

[0031] Step 5: Detect the change of the grid component frequency over a period of time and compare it with the normal range of the grid frequency, detect the wind speed of the grid component and compare it with the rated wind speed.

[0032] Step 6: Monitor the output of the grid-connected inverter in real time to complete the control of the wind power system.

[0033] In Step 1, the grid-connected inverter of the wind power system controls the DC bus voltage by controlling the active power and conducts grid connection with a unity power factor by controlling the reactive power.

[0034] In Step 1, when establishing the mathematical model of the grid-connected inverter of the wind power system, the dynamic characteristics of the wind turbine, inverter and grid need to be considered. The mathematical model of the wind turbine includes an aerodynamic model, a mechanical model and an electromagnetic model. The aerodynamic model calculates the torque acting on the wind turbine by the wind force using the Betz theory and the blade element momentum theory. The mechanical model includes the dynamic behaviors of the wind turbine, gearbox and generator shafting, including inertia, damping and elastic effects. The electromagnetic model utilizes the electrical characteristics of the generator, including the relationships between voltage, current, magnetic flux and torque, and uses the motor equations and Kirchhoff's laws. The inverter model includes the behaviors of the power switching devices and the control strategy. The grid model includes voltage, frequency and impedance. Among them, the power switching device model controls the switching of other semiconductor devices. The overall model combines the models of the wind turbine, inverter and grid to form a complete system model, which defines the state of the system at specific time and space points, and establishes a mathematical model of the grid-connected inverter of the wind power system. This model can reflect the dynamic behavior of the system and provide a basis for the design and simulation of the chaos control method.

[0035] In Step 2, select the chaotic map Logistic map. When selecting the chaotic map, it is judged by the size and stability of the chaotic region. The output of the chaotic map provides the randomness and complexity of the control signal. The system state is adjusted by the control signal through the feedback control strategy, and sliding mode control is used to handle the uncertainties in the system. After the chaotic controller is generated, the effectiveness of the chaotic controller is verified through simulation and experiments. When testing the performance of the controller, the output of the chaotic map provides the randomness and complexity of the control signal, and the feedback control strategy ensures that the control signal can effectively adjust the system state. The setting of the chaotic controller allows real-time monitoring of the system state and adjustment of the control strategy according to the monitoring results.

[0036] In step three, the control signal generated by the chaos controller is analyzed and converted into a control instruction for the inverter. The switching mode of the inverter is adjusted according to the control signal generated by the chaos controller through pulse-width modulation (PWM) technology. PWM can precisely control the waveform and frequency of the inverter output voltage to control the waveform and frequency of the inverter output voltage. The phase-locked loop (PLL) technology is used to synchronize the output of the inverter with the frequency and phase of the power grid. The PLL can monitor the frequency and phase of the power grid in real time and adjust the output of the inverter to maintain synchronization. By designing a current control loop to regulate the output current of the inverter and a voltage control loop to regulate the output voltage of the inverter, the output of the inverter is made to match the frequency and voltage level of the power grid to achieve stable grid connection operation.

[0037] In step four, the normal range of the power grid frequency is set to 50 Hz. For systems with a power grid capacity of 3 million kilowatts or more, the frequency deviation does not exceed ±0.2 Hz. Therefore, the power grid frequency should fluctuate between 49.8 Hz and 50.2 Hz. The rated wind speed range of the wind turbine is between 10 and 12 m / s, the cut-in wind speed is usually between 3 and 5 m / s, and the cut-out wind speed is generally between 25 and 30 m / s. The setting of these parameters ensures that the wind turbine can operate within a safe wind speed range and protects the unit from damage under extreme wind speed conditions.

[0038] In step five, the power grid components include a wind turbine and a storage battery. When the wind speed exceeds the rated wind speed within the normal range of the power grid frequency, the output power is smooth and the storage battery is in a charging state. When the power grid frequency drops and exceeds the normal range of the power grid frequency, part of the rotational kinetic energy of the wind turbine rotor is released to support the power grid frequency for a short time. When the power grid frequency is lower than the normal range of the power grid frequency, the rotor inertia control module is cut off to prevent the wind turbine from releasing too much kinetic energy, which may cause shutdown. At the same time, the discharge power of the storage battery is increased to participate in the primary frequency modulation of the power grid. When the power grid frequency is lower than the normal range of the power grid frequency after a certain time delay, the discharge power of the storage battery is increased to participate in the secondary frequency modulation of the power grid. When the power grid frequency exceeds the normal range of the power grid frequency, a part of the wind energy is sent into the storage battery to perform frequency modulation on the power grid again. When the power grid frequency exceeds the normal range of the power grid frequency after a certain time delay, with the cooperation of the storage battery, the wind turbine reduces the wind energy capture coefficient and finally performs primary frequency modulation on the power grid.

[0039] In Step 6, a voltage sensor and a current sensor are installed at the output end of the inverter to monitor the output voltage and current of the inverter, collect the data of the voltage sensor and the current sensor, and transmit it to the wind power system. Using the SCADA system, the monitoring personnel can observe the output status of the inverter in real time and monitor the output frequency of the inverter. Calculate the output power of the inverter using the collected voltage and current data. At the same time, according to the changes in wind speed and grid demand, optimize the scheduling of the wind power generation system, adjust the output power of the inverter to improve the overall efficiency and stability, and use historical data and real-time monitoring data to predict potential equipment failures and performance degradation, and perform maintenance in advance to avoid unexpected shutdowns.

[0040] The voltage sensor and the current sensor convert all input signals into standard voltage signals of 5V. The voltage sensor and the current sensor are connected in a conventional electrical connection, and overload protection and short-circuit protection components are installed to ensure that the connection between the inverter and the grid can be quickly cut off in case of abnormalities, protecting the safety of equipment and personnel.

[0041] Embodiment 2

[0042] When detecting the wind speed of the grid components and comparing it with the rated wind speed in Step 5 above, when the grid frequency is normal and the wind speed is less than the rated wind speed, the wind turbine operates in the MPPT mode, and the active power output of the grid-connected connection line of the wind energy storage unit is smooth. When the wind speed exceeds the rated wind speed and the grid frequency is normal, the upper control unit starts the fan pitch angle control module of the lower control unit to control the variable pitch and limit the wind power output. The output power of the grid-connected bus of the wind energy storage unit is smooth. At this time, the energy storage battery is in the charging state. When the grid frequency drops and exceeds the normal range, release part of the rotational kinetic energy of the wind turbine rotor to support the grid frequency for a short time. If the grid frequency is still low and not restored, the rotational speed of the rotor drops to 0.7ω ref Prevent the wind turbine from releasing too much kinetic energy, which may cause shutdown, and at the same time increase the discharge power of the energy storage battery to participate in the primary frequency modulation of the grid. When the grid frequency drops and exceeds the normal range, ω < 0.8ω ref , the energy storage battery increases the discharge power to participate in the primary frequency modulation of the grid. When the grid frequency is low, after a period of delay, the energy storage battery increases the discharge power to participate in the secondary frequency modulation of the grid. When the grid frequency is high and exceeds the normal range, part of the wind energy is sent into the energy storage battery to participate in the primary frequency modulation of the grid. When the grid frequency is high, after a period of delay, with the cooperation of the energy storage battery, the variable pitch control of the wind turbine starts to reduce the wind energy capture coefficient and participate in the primary frequency modulation of the grid.

[0043] When the chaotic control method of the grid-connected inverter of this wind power system is used, the evolution of any state variable of the system contains the information of other variables. Therefore, the information of all state variables can be analyzed and discovered from the measurement data of one variable, so as to obtain the operation state information of the whole system. The state phase space of the system is reconstructed by measuring the time series of any state variable of the wind power system. On this basis, the chaotic operation state of the system is judged and detected by qualitatively observing the geometric structure characteristics of the attractor in the reconstructed phase space or calculating the eigenvalues of the system.

[0044] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for controlling chaos in a grid-connected inverter of a wind power system, characterized in that: The following steps are involved: Step 1: Establish a mathematical model of the grid-connected inverter of the wind power system, which includes the dynamic characteristics of the wind turbine generator, inverter and power grid; Step 2: Design a chaos controller. The chaos controller generates a control signal through the chaos map and feedback control strategy in chaos theory. The establishment of the chaos controller controls the nonlinearity and uncertainty in the system, and operates the chaos controller through the grid-connected inverter. Step 3: Apply the control signal generated by the chaos controller to the grid-connected inverter to adjust the output voltage and output current of the grid-connected inverter, and match the frequency and voltage levels of the power grid to each other by maintaining the output of the inverter; Step 4: Set the normal range of the grid frequency and determine the rated wind speed of the wind turbine; Step 5: Install the grid components and detect the change of the grid component frequency over a period of time and compare it with the normal range of the grid frequency, detect the wind speed of the grid components and compare it with the rated wind speed; Step 6: Monitor the output of the grid-connected inverter in real time and use the inverter to control the wind power system.

2. The method for controlling chaos of a grid-connected inverter of a wind power system according to claim 1, characterized in that: In step 1, the grid-connected inverter of the wind power system controls the DC bus voltage by controlling the active power, and controls the reactive power to achieve unity power factor grid connection.

3. The method for controlling chaos of a grid-connected inverter of a wind power system according to claim 1, characterized in that: In step one, the mathematical model of the wind turbine includes an aerodynamic model, a mechanical model and an electromagnetic model. The aerodynamic model calculates the torque exerted by wind on the wind rotor using Betz theory and blade element momentum theory. The mechanical model includes the dynamic behavior of the wind rotor, gearbox and generator shaft system including inertia, damping and elastic effects. The electromagnetic model utilizes the electrical characteristics of the generator including the relationship between voltage, current, flux and torque, using motor equations and Kirchhoff's laws. The inverter model includes the behavior and control strategy of the power switching device. The grid model includes voltage, frequency and impedance.

4. The method for controlling chaos of a grid-connected inverter of a wind power system according to claim 1, characterized in that: In step 2, the chaotic mapping Logistic mapping is selected, the system state is adjusted by the feedback control strategy control signal, and the sliding mode control is used to deal with the uncertainty in the system. After the chaotic controller is generated, the effectiveness of the chaotic controller is verified through simulation and experiments, and the performance of the controller is tested.

5. The method for controlling chaos of a grid-connected inverter of a wind power system according to claim 1, characterized in that: In step three, the control signal generated by the chaos controller is analyzed and converted into the control instruction of the inverter. The switching mode of the inverter is adjusted according to the control signal generated by the chaos controller through pulse width modulation technology to control the waveform and frequency of the inverter output voltage. The output current of the inverter is adjusted by designing a current control loop, and the output voltage of the inverter is adjusted by designing a voltage control loop to keep the output of the inverter matching the frequency and voltage level of the power grid.

6. The method for controlling chaos of a grid-connected inverter of a wind power system according to claim 1, characterized in that: In step 4, the normal range of the grid frequency is set to 50 Hz, and the rated wind speed range of the wind turbine is between 10 and 12 m / s.

7. The method for controlling chaos of a grid-connected inverter of a wind power system according to claim 1, characterized in that: In step five, the grid components include wind turbines and energy storage batteries. Within the normal range of grid frequency, the wind speed exceeds the rated wind speed and the output power is smooth. When the grid frequency drops and exceeds the normal range of grid frequency, part of the wind turbine's wind wheel rotational kinetic energy is released. When the grid frequency is lower than the normal range of grid frequency, the rotor inertia control module is cut off, and at the same time, the discharge power of the energy storage battery is increased to participate in the primary frequency modulation of the grid. When the grid frequency is lower than the normal range of grid frequency after a delay, the discharge power of the energy storage battery is increased to participate in the secondary frequency modulation of the grid. When the grid frequency exceeds the normal range of grid frequency, part of the wind energy is sent to the energy storage battery to modulate the grid again. When the grid frequency exceeds the normal range of grid frequency after a delay, with the cooperation of the energy storage battery, the wind turbine reduces the wind energy capture coefficient and finally modulates the grid once.

8. The method for controlling chaos of a grid-connected inverter of a wind power system according to claim 1, characterized in that: In step six, a voltage sensor and a current sensor are installed at the output end of the inverter to monitor the output voltage and current of the inverter, and data of the voltage sensor and the current sensor are collected and transmitted to the wind power system, while the frequency of the inverter output is monitored.

9. The method for controlling chaos of a grid-connected inverter of a wind power system according to claim 8, characterized in that: The voltage sensor and the current sensor convert all input signals into standard voltage signals of 5V, and the voltage sensor and the current sensor are connected in a conventional electrical manner.

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