Wind and wave complementary power generation system based on switched reluctance motor

Abstract

The invention discloses a wind and wave complementary power generation system based on a switched reluctance motor. The overall architecture of the wind and wave complementary power generation system of the switched reluctance motor is introduced, the structural composition of the system is analyzed in detail, and a circuit design scheme of each part is provided. Based on the mutual relation among the generating power of a generator set, the charging and discharging power of a storage battery and the load power, the working modes of the system are scientifically divided into two types. In each mode, two different working conditions are further subdivided according to the limiting condition of the maximum charging and discharging power of the storage battery. Meanwhile, specific operation mechanisms of the system in four working states are deeply analyzed, and corresponding accurate control strategies are designed according to operation characteristics of all units of the system in different working states. A simulation model of the wind and wave complementary power generation system of the switched reluctance motor is built, simulation analysis is carried out on power generation conditions of wind power and wave energy under different working conditions, and effectiveness and feasibility of control strategies proposed by all parts of the system are verified. An experiment platform of the system is designed and built for experiments, and the effectiveness of a generator set maximum power tracking strategy and a storage battery charging and discharging strategy and the reliability of system power balance are verified.

Description

Technical Field

[0001] The invention relates to the field of switched reluctance motor power generation. Background Art

[0002] Switched reluctance motors (SRMs) are widely used in various industrial applications due to their simple structure, low cost, easy maintenance, high efficiency, and high reliability. With the growing global demand for renewable energy, the application of SRM technology in wind and wave power generation systems has become a promising technology.

[0003] Wind and wave energy play a crucial role in the ocean energy system, and their energy output characteristics differ significantly. Wind energy is more efficient in strong winds, while wave energy output is relatively stable, maintaining a stable energy supply even in weak winds. However, power generation systems based on a single energy source are often limited by energy instability and difficulty in accurate prediction. This is particularly true in extreme weather conditions or energy-scarce regions, where power generation efficiency and stability are often difficult to guarantee.

[0004] Therefore, it is particularly important to develop a wind-wave complementary power generation system, combining the advantages of switched reluctance motors (SRMs) in power regulation and efficient conversion. This system can utilize intelligent control strategies to adjust the power output of wind and wave energy in real time, optimizing the overall efficiency of energy utilization. When wind speeds are insufficient to drive wind turbines, wave generators can compensate for the energy shortage, and vice versa. This complementary energy configuration not only improves the overall efficiency and reliability of the power generation system, but also reduces environmental impact and enhances the system's adaptability to diverse natural conditions. This technology can more efficiently utilize ocean energy, bringing new development opportunities to the renewable energy sector. Summary of the Invention

[0005] The switched reluctance motor wind-wave complementary power generation system designed by the present invention adopts the following technical solutions:

[0006] The system structure of the present invention mainly consists of five parts: a switched reluctance generator unit; a switched reluctance linear generator unit; an energy storage unit; a DC bus; and a load.

[0007] The working mode of the present invention can be divided into the following four working states according to the relationship between the power generation power of the generator set, the charging and discharging power of the rechargeable battery and the load power:

[0008] Working mode 1: At this time, the generator set has sufficient power generation. After meeting the load power, it supplies power to the energy storage unit. Since the battery is limited by the maximum charging power, in this working mode, it can be divided into two working states:

[0009] Operating State 1.1: The load is heavy, absorbing a large amount of power from the generator sets. The remaining power flowing to the energy storage unit is small and not limited by the maximum charging power of the battery. Therefore, the generator sets can generate power at full power, and the system power is balanced.

[0010] Operating State 1.2: The load is light, absorbing only a small amount of generated power, with the remaining power flowing into the energy storage unit. Due to the maximum charging power limit of the battery, if the system power is to be balanced, the wind turbine should not generate power at full power. In other words, the wind turbine operating area should be offset from the maximum power point to maintain system power balance.

[0011] Working Mode 2: The load power required by the load is large, and the maximum output power of the generator after MPPT control is still not enough. The energy storage unit needs to jointly generate power to meet the power demand of the load. Since the battery has a maximum discharge power limit, this working mode can also be divided into two working states:

[0012] Working State 2.1: The power output by the generator set and energy storage unit can meet the power requirements of all loads. The generator is under MPPT control and the battery discharge power does not exceed the limit. At this time, the overall power of the system is balanced.

[0013] Operating State 2.2: The maximum discharge power of the generator set and battery still cannot meet all load requirements, and the system energy is not balanced. In this case, it is necessary to remove some loads to convert the system to another operating state.

[0014] In terms of control strategy, due to the randomness of wind energy in nature, it is necessary to use the MPPT method to achieve maximum wind energy capture. According to the Bates theorem, the mechanical energy that a wind turbine can convert from wind energy is:

[0015]

[0016] In formula (1), ρ is the air density; R is the radius of the wind turbine rotor; v is the wind speed; C p is the wind energy utilization coefficient, C p It is a function of the blade pitch angle β and the blade tip speed ratio λ.

[0017] λ=ω r R / v (2)

[0018] Where, ω r is the mechanical angular velocity of the wind turbine.

[0019] In order to improve the utilization efficiency of wind energy, it is necessary to perform MPPT control on the switched reluctance motor. At present, the main methods for tracking the maximum power of wind turbines include: hill climbing search method, three-point comparison method, wind speed tracking method and power feedback method.

[0020] During implementation, the three-point comparison method generates systematic errors due to the randomness of power point selection. This error makes it difficult to achieve ideal results when controlling large-inertia wind turbines. The wind speed tracking method requires additional wind speed measurement equipment to obtain wind speed data, which undoubtedly increases the system construction cost. The accuracy of the power feedback method is highly dependent on the precise mapping of the optimal power curve of the wind turbine, which places strict demands on data accuracy. The fixed search step size of the traditional hill climbing search method also has drawbacks: if the perturbation step size is set too small, the wind turbine will need to go through a large number of same-direction search processes from startup to tracking to the maximum power point, which significantly prolongs the system startup time. When the perturbation step size is too large, although it can speed up the startup speed, it will cause the system to oscillate continuously near the maximum power point, causing large fluctuations in the wind turbine output power. To address these problems, this paper innovatively proposes a step-by-step maximum power tracking control strategy, which effectively improves the system startup efficiency while ensuring the stability of power output.

[0021] Hill climbing methods can be categorized into two types, fixed-step and variable-step, depending on the perturbation step size. Fixed-step hill climbing methods are simple to use, but can easily lead to poor system control due to inappropriate step sizes. Furthermore, when the external wind speed fluctuates frequently, fixed-step hill climbing methods struggle to quickly return the wind turbine to its optimal power point. Setting the step size too long exacerbates speed fluctuations caused by wind speed fluctuations. Therefore, this paper employs a variable-step hill climbing method in the maximum power tracking region, rationally calculating the perturbation step size at the current moment. This increases the rapidity of the system's response and improves system stability.

[0022] Once the system enters the maximum power point tracking (MPPT) region, a variable-step hill-climbing search method is implemented. Since the wind turbine power characteristic curve at different speeds is approximately a downward-pointing parabola, the operating point is located on the right half of the curve when the system first enters the MPPT region. As the generator speed decreases, the curve shifts to the left. At this point, the slope of the curve—the change in generated power and speed (k = ΔP(t) / Δn(t))—gradually decreases to zero. At this point, the generator system is operating at its maximum power point for that wind speed.

[0023] Therefore, the characteristic that the ratio k gradually decreases to 0 when approaching the maximum power point can be used to perform variable step maximum power tracking control. The speed disturbance can be set to

[0024]

[0025] Where: m is the regulation coefficient (generally a number greater than 0), and P(t-1) is the system power at the previous moment.

[0026] In terms of wave energy generation systems, the surface coordinates in the cylindrical coordinate system (R, θ, z) are:

[0027]

[0028] The pressure distribution on the float surface can be expressed as:

[0029]

[0030] By using the Bessel function to approximate the equation (5), the vertical wave excitation force can be obtained as follows:

[0031]

[0032] Where C Z is the diffraction coefficient of the excitation force in the vertical direction; J0 is a first-order Bessel function. After simplification, the expression of the vertical wave excitation force is:

[0033]

[0034] Where F is the amplitude of the wave excitation force; ω is the frequency of the wave excitation force; is the initial phase of the wave excitation force.

[0035] The power generation device is mainly composed of components such as floats, traction links, generators and power converters. When the float in a free state is acted upon by waves, it will be subjected to forces from different directions at the same time. This complex force situation makes its dynamic modeling and analysis more difficult. In the switched reluctance wave energy linear generator system, since the float is connected to the traction link, its movement is limited to fluctuating up and down with the waves. Therefore, when performing a dynamic analysis of the float, it is only necessary to pay attention to its motion state in the vertical direction. In the simplified analysis process, the effects of fluid viscosity and friction resistance are not considered for the time being. According to Newton's second law, it can be obtained:

[0036]

[0037] Where, M is the mass of the float; is the acceleration; F exc The excitation force of the waves; F t is the radiation force; F b is the buoyancy of seawater; F pto is the electromagnetic force of the generator; G is the gravity acting on the float.

[0038] Radiation force F t It can be expressed as:

[0039]

[0040] Where m a is the additional mass; R a is the additional damping; For speed.

[0041] The buoyancy of the cylindrical float is:

[0042] F b =-ρgSx=-Kx (0)

[0043] Where ρ is the density, S is the bottom area of ​​the float, and K is the buoyancy coefficient. Combining equations (8), (9), and (10), the dynamic equation of the float under the excitation of regular ocean waves can be obtained as follows:

[0044]

[0045] Taking the position where the float is stationary in the water as the equilibrium position, equation (3-11) can be simplified to:

[0046]

[0047] Electromagnetic force equations of switched reluctance linear generator

[65] It can be expressed as:

[0048]

[0049] In the above formula, W m is the magnetic co-energy of the switched reluctance linear motor when single-phase power is applied. This magnetic co-energy is a static parameter of the motor, determined by the position of the rotor and the winding current. Finite element analysis was performed on the switched reluctance linear motor used in this article, revealing the relationship between the magnetic co-energy, the rotor position, and the winding current.

[0050] Substitute equation (3-13) into equation (3-12) to solve the differential equation. To facilitate the expression of the solution, define the expression D as:

[0051] D=K 2 -2K(M+m a )ω 2 +(M 2 +2Mm a +m a 2 )ω 4 +R 2 ω 2 (14)

[0052] After defining variables A and θ and ignoring the transient component, solving the above linear differential equation, we can obtain:

[0053] x=A·sin(ωt-θ) (15)

[0054] in:

[0055]

[0056] As can be seen from Equation (16), the sinusoidal motion of the float causes the output power of the switched reluctance wave energy linear generator to be non-constant. Analyzing the instantaneous power of the system is not very meaningful, so this paper studies the average output power within the wave cycle.

[0057] During one wave cycle, the average power of the system can be expressed as:

[0058]

[0059] In the above formula, P is used to determine the excitation current I k Derivative, when dP / dI k = 0, the power reaches its maximum value. When in a stable sea, the waves change very little within a few hours, so they can be treated as regular waves. According to formula (17), the maximum average power of the direct-drive wave energy generation system is determined by the unique excitation current I k Therefore, the control program can be set to find the only I corresponding to the maximum output power. k To achieve the maximum power output of the direct-drive wave energy power generation system.

[0060] This system adopts a single degree of freedom maximum power tracking control strategy to transmit the electric energy output by the direct-drive wave energy generator to the DC bus through an asymmetric half-bridge power converter and a DC / DC bidirectional converter. The bus voltage and the current flowing into the DC bus by the wave energy generator are measured by voltage sensors, current sensors, etc., and the control signal of the DC / DC bidirectional converter is obtained through the MPPT algorithm. k , tracking the maximum power point.

[0061] At present, the research on battery charging methods has made great progress. The conventional charging methods are mainly the following:

[0062] (1) Constant pressure method

[0063] The energy storage unit maintains a constant voltage throughout the charging process. While closed-loop control of voltage alone is convenient and quick to implement, it draws relatively high currents during the initial charging phase. This high current can damage the energy storage unit or even the entire system, impacting overall system reliability.

[0064] (2) Constant current method

[0065] The energy storage unit maintains a constant current throughout the charging process. Closed-loop control of current alone would save a lot of trouble, but because the voltage of the energy storage unit continues to rise during charging, the current may be too high relative to the maximum charge current, thus affecting the safety of the battery.

[0066] (3) Two-stage method

[0067] This strategy overcomes the shortcomings of both the constant voltage and constant current methods, combining the advantages of each at different stages. The two-stage method initially charges the battery using a constant current method. As charging progresses, the battery is then charged using a constant voltage method. This charging strategy uses a constant current method to maintain closed-loop current control during the startup phase, preventing the dangers of excessive current. After startup, closed-loop voltage control is implemented to avoid the potential for excessive voltage at the end of charging. Therefore, the energy storage unit designed in this paper utilizes a two-stage method to control the charging process.

[0068] Regarding the hardware system, this invention utilizes a three-phase 12 / 8 switched reluctance motor (SRM) as a wind turbine and a cylindrical switched reluctance linear motor as a wave generator, respectively. Both power converters employ an asymmetric half-bridge topology. Because the controller's output current is too low to directly drive the IGBTs in the power converters, this system utilizes a driver circuit based on the KA962F driver chip to enhance the controller's driving capability.

[0069] To ensure efficient system control response and reliable operation, the power converter's topside transistor uses Infineon's IRFP4668PBF switching transistor. With its high withstand voltage, low drive voltage, high switching frequency, compact size, and low cost, this switching transistor perfectly meets the system's requirements for fast switching, low energy loss, and high-efficiency conversion. The power converter's bottomside transistor utilizes the DSE1120-06A fast-recovery epitaxial diode. This device offers excellent reverse withstand voltage, short recovery time, high output current, and a compact footprint, providing strong support for stable system operation.

[0070] The DC bus voltage is set to 24 V. Since the power generated by the SRG is a DC pulse current, it is very important to filter the bus voltage. This paper adopts multiple filter capacitors in parallel to achieve the filtering effect and reduce the output voltage fluctuation.

[0071] The wind-wave hybrid power generation system needs to use a step-up / step-down circuit to increase the bus voltage U dc1 =24V converted to battery voltage U E=12V, the generator's energy can be safely stored in the battery. The power switches in the bidirectional half-bridge DC / DC converter are Infineon MOSFETs, model IRFP4668PBF. Compared to IGBT modules, MOSFET modules offer advantages such as high switching frequency, low cost, and small size. The freewheeling diode is the MUR6020 fast recovery diode from Silicon Lake. The driver chip is the EXB841 specialized module from Fuji.

[0072] To ensure proper operation of the buck-boost circuit, current continuity is usually necessary. Therefore, reliable inductor parameters must be selected when designing the circuit to filter the current to meet specified requirements. Since the inductor current fluctuates by approximately 20%, the required inductor value for the DC / DC converter can be calculated using the following formula:

[0073]

[0074] Substituting the parameters into the above equation, we can obtain that the inductance value should satisfy L ≥ 0.81mH. Therefore, the inductor with an inductance of 1mH is selected for the DC / DC converter designed in this article.

[0075] The control of switched reluctance motors (SRMs) and switched reluctance linear motors (SLRs) involves position and current control strategies, requiring real-time monitoring of analog quantities such as speed, position, current, and voltage. Therefore, this system utilizes the DSP TMS320F28335 chip. This chip, manufactured by Texas Instruments (TI), is a high-performance digital signal processor with high data processing capabilities and fast response speed, specifically designed to meet the requirements of high-speed and precise control. This chip enables precise control of SRGs and SRLGs, significantly improving the performance and efficiency of the motors.

[0076] Considering that the control requirements of the battery energy storage unit primarily focus on voltage and current detection, as well as two switching transistor signal outputs, this system selected Microchip's dsPIC30F2010 chip as the control core. This chip combines cost-effectiveness with stable performance. By applying a PI closed-loop control strategy, it effectively ensures efficient and stable operation of the battery energy storage unit under various operating conditions, thereby extending battery life and optimizing energy utilization efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0077] Figure 1 It is a schematic diagram of the system structure of the present invention.

[0078] Figure 2 It is a schematic diagram of the system working mode of the present invention.

[0079] Figure 3 It is a schematic diagram of the system working state conversion of the present invention.

[0080] Figure 4 It is a simulation waveform diagram of each part of the present invention under working condition 1.2.

[0081] Figure 5 It is a simulation waveform diagram of the power of the generator set of the present invention when the working conditions change.

[0082] Figure 6 It is the experimental platform built by the present invention.

[0083] Figure 7 It is the experimental waveform diagram of each part of the present invention under working condition 1.2.

[0084] Figure 8 It is an experimental waveform diagram of each part of the present invention when the working condition deteriorates.

[0085] Figure 9 It is the experimental waveform diagram of each part of the present invention when the working condition improves. DETAILED DESCRIPTION

[0086] The present invention will be further described below with reference to examples.

[0087] The structural diagram of the switched reluctance motor wind-wave hybrid power generation system studied in this paper is as follows: Figure 1 The system consists of five main components: a switched reluctance generator (SRG) unit, a switched reluctance linear generator (SLRG) unit, an energy storage unit, a DC bus, and a load. The SRG unit generates power from the rotation of the connected wind propeller, while the SRLG unit generates power from the force of waves on the connected float.

[0088] In this system, the four working states of the system are as follows: Figure 2 As shown. According to P G 、P L and P B The relationship between size and direction can be divided into the following four working states:

[0089] Working mode 1: At this time, the generator set has sufficient power generation. After meeting the load power, it supplies power to the energy storage unit. Since the battery is limited by the maximum charging power, in this working mode, it can be divided into two working states:

[0090] Operating State 1.1: The load is heavy, absorbing a large amount of power from the generator sets. The remaining power flowing to the energy storage unit is small and not limited by the maximum charging power of the battery. Therefore, the generator sets can generate power at full power, and the system power is balanced.

[0091] Operating State 1.2: The load is light, absorbing only a small amount of generated power, with the remaining power flowing into the energy storage unit. Due to the maximum charging power limit of the battery, if the system power is to be balanced, the wind turbine should not generate power at full power. In other words, the wind turbine operating area should be offset from the maximum power point to maintain system power balance.

[0092] Working Mode 2: The load power required by the load is large, and the maximum output power of the generator after MPPT control is still not enough. The energy storage unit needs to jointly generate power to meet the power demand of the load. Since the battery has a maximum discharge power limit, this working mode can also be divided into two working states:

[0093] Working State 2.1: The power output by the generator set and energy storage unit can meet the power requirements of all loads. The generator is under MPPT control and the battery discharge power does not exceed the limit. At this time, the overall power of the system is balanced.

[0094] Operating State 2.2: The maximum discharge power of the generator set and battery still cannot meet all load requirements, and the system energy is not balanced. In this case, it is necessary to remove some loads to convert the system to another operating state.

[0095] In summary, the system operates in two modes, depending on whether the generator set's power alone can meet the load's power consumption. In Mode 1, the system further operates depending on whether the battery exceeds its maximum charging power. When the battery charging power is less than the maximum charging power limit, the generator set performs MPPT control, and the system operates in Mode 1.1. If the power flowing into the battery exceeds the maximum charging power limit, the generator set must operate away from its maximum power point to maintain system energy balance. In Mode 2, the system also operates in two modes, depending on whether the battery exceeds its maximum discharge power. If the generator set and battery output power can meet the load's power consumption, the system energy balance is in Mode 2.1. If the generator set and battery maximum discharge power cannot meet the load's power consumption, some loads must be removed, shifting the system from Mode 2.2 to Mode 2.1, thus achieving system energy balance.

[0096] Based on the previous analysis of the power relationship among the wind-wave power generation unit, the energy storage unit, and the load, the system operating state is divided into four modes. If the method of measuring the voltage and current parameters of each part of the system in real time and then calculating and analyzing the power to achieve state switching is adopted, it will lead to heavy system calculation tasks, not only causing control response delays but also reducing the system operation stability. In contrast, using specific electrical characteristics during the actual operation process to distinguish the working state can more accurately and efficiently complete state differentiation, significantly reducing the program calculation amount and remarkably improving the system response speed. The schematic diagram of the working state conversion of the battery charge-discharge circuit is as shown in Figure 3 shown.

[0097] Analysis Figure 3 shows that when the wind-wave complementary power generation unit is simultaneously under MPPT control and the battery charging power does not exceed the limit, that is, the system is operating in state 1.1. If at this time there is I i ≥I im or U E >U E2 , it means that the battery charging power is limited at this time and the two-stage charging method is being used, that is, the system is operating in state 1.2. When U E <U E1 , it means that the system power balance is controlled by the battery charging power, that is, it is judged that the system returns to the working state 1.1 at this time. When the battery switches from the charging state to the discharging state, that is, U dc1 <U1, the working state of the system changes from 1.1 to state 2.1.

[0098] When the battery is in the discharging state, it is divided into two working states according to whether the charging power of the battery reaches the maximum discharge power. When I o >I om , that is, the discharge current exceeds the rated maximum discharge current; at this time, the system needs to cut off some loads and return to other working states.

[0099] Figure 4 Verify the voltage, current, and power waveforms of each part of the system when the wind-wave condition is good, that is, when the system is in working condition 1.2, the external wind speed is 10 m / s, and the wave energy excitation force is 1000sin(π / 2t) N. As shown in Figure 4 (a) and Figure 4 (b), it can be seen that when the wind speed is 10 m / s, the system starts MPPT tracking about 7 s after starting, and operates at the maximum power point about 9 s later. At this time, the rotational speed is about stable at 600 r / min, and the maximum power is about 200 W. The peak value of the phase current reaches about 18 A, and the bus voltage fluctuates around 24 V. Figure 4 (c) and Figure 4Figure (d) shows the voltage and current waveforms of the wave energy generator, as well as its output power, when the wave energy excitation force is 1000 sin(π / 2t)N. As shown in the figure, the wave energy generator reaches steady state after approximately 15 seconds of MPPT. At steady state, the output phase voltage is approximately 23V, the three-phase current peak is 12A, and the generator generates 196W of power. Figure 4 (e) and Figure 4 Figure (f) shows the battery voltage and current waveforms for operating condition 1.2. Analysis of the figure shows that for the first 3 seconds, the generator set is in MPPT mode, generating increasing power. During this time, the battery charging current stabilizes at around 2A, and the battery voltage rises from 10V to 12V, indicating constant-current charging. After 3 seconds, the battery voltage stabilizes at 12V, and the charging current decreases as the charging process progresses, indicating constant-voltage charging.

[0100] Figure 5 (a) and Figure 5 (b) shows the output power of the wind and wave power generation systems under varying operating conditions. For Condition 1.2, as described above, the wind speed is 10 m / s and the wave excitation is 1000 sin(π / 2t)N. For Condition 1.1, the wind speed is 7 m / s and the wave excitation is 800 sin(π / 2t)N. Analysis of the waveforms shows that the system's operating conditions change at 8 seconds, with power generation dropping rapidly, transitioning from Condition 1.2 to Condition 1.1. At 32 seconds, the operating conditions change again, with power generation rapidly increasing under the MPPT strategy, and the system switches from Condition 1.1 back to Condition 1.2.

[0101] Figure 6 (a) The system controller of the wind turbine generator unit includes: DSP28335 control board, voltage and current sensors, power supply module, drive circuit, power converter, etc. Figure 6 (b) shows the hardware experimental platform of the switched reluctance linear generator, which includes a DSP28335 controller, a power converter, a drive circuit, a voltage sampling circuit, a current sampling circuit, and a power module.

[0102] Figure 7 (a) shows the power and speed of the switched reluctance wind turbine during the entire power generation process under operating condition 1.2, as well as the bus voltage and phase B current when entering steady-state power generation; Figure 7 (b) The three-phase current, phase A voltage, and generated power of the switched reluctance wave energy generator during the reciprocating motion process under this operating condition are given; Figure 7 (c) The power and speed of the switched reluctance wind turbine during the entire power generation process under this operating condition, as well as the bus voltage and phase B current when entering steady-state power generation, are given; Figure 7(d) The three-phase current, phase A voltage, and generated power of the switched reluctance wave energy generator during the reciprocating motion under this operating condition are given;

[0103] Figure 8 The generated power of the wind turbine and wave energy generator as well as the voltage and current waveforms of the battery are given when the external wind speed is gradually reduced from 10m / s to 1m / s and the maximum set speed of the wave energy prime mover is reduced from 0.6m / s to 0.4m / s.

[0104] from Figure 8 Data analysis shows that when the external wind speed is 10m / s and the wave energy generator is at its maximum traction speed of 0.6m / s, the system operates in operating condition 1.2. At this point, the battery enters constant current charging mode with a maximum of 10A. Due to the constraints of the battery's maximum charging current, the wind turbine implements constant power generation control, steadily outputting 200W of power. As the wind speed continues to decrease, the wind turbine's power generation continues to decrease, and the battery charging current also decreases accordingly, causing the system to enter operating condition 1.1. In offshore scenarios, decreasing wind speeds are often accompanied by stabilization of waves. At this time, the maximum traction speed of the wave energy generator is adjusted to 0.4m / s, and the wave energy generator output power is 138W. If the wind speed decreases further, the generator set's power generation cannot meet the load demand. After the battery charging current returns to zero, it begins to discharge, and together with the generator set, it provides power to the load, and the system enters operating condition 2.1.

[0105] Figure 9 The results show the power generation of the wind turbine when the external wind speed changes from zero to 10 m / s; the power generation of the wave energy generator when the maximum set speed of the wave energy prime mover changes from 0.4 m / s to 0.6 m / s; and the voltage and current waveforms of the battery when the system gradually changes from operating condition 2.1 to operating condition 1.2.

[0106] analyze Figure 9 It can be seen that: when the external wind speed is 0m / s and the maximum traction speed of the wave energy prime mover is 0.4m / s, the power generation power of the wave energy generator is about 135W. The power generation power of the entire power generation system is insufficient to meet the load consumption, so the battery participates in the power supply of the load. At the beginning, the wind turbine does not participate in power generation, and the power shortage is large. The battery discharges at a constant current of 10A with the maximum discharge current. As the power generation power of the wind turbine gradually increases, the battery discharge current gradually decreases, and the discharge is carried out in a constant voltage manner; then the power generation power of the wind turbine further increases, and the increase in wind speed drives the maximum set speed of the wave energy generator to 0.6m / s. The power generated by the generator set is sufficient to meet the load consumption, and the battery switches to receiving electricity, and the system enters operating condition 1.1; when the wind speed continues to increase, the battery reaches the maximum charging current. In order to maintain the system power balance, the wind turbine exits the MPPT state at this time and enters a constant power output with a limit of 180W.

Claims

1. A wind-wave hybrid power generation system based on a switched reluctance motor, characterized by: A method for distinguishing working states based on the relationship between the powers of various parts of the system is proposed. Due to the instability of wind and wave conditions in nature, the power generation process exhibits significant randomness. In order to effectively improve the energy utilization efficiency and operational reliability of the system, it is necessary to implement a scientific energy management strategy. In the power generation system constructed by the present invention, the core task of the energy management system is to properly deal with power generation fluctuations caused by environmental factors such as wind speed fluctuations and wave intensity changes, and to ensure that the output power of the generator set, the charging and discharging power of the energy storage unit, and the load power always maintain a dynamic balance. Based on the relationship between the power generation power of the generator set, the charging and discharging power of the battery, and the load power, the present invention can finely divide the system operating state into the following four modes: Working mode 1: At this time, the generator set has sufficient power generation capacity, and after meeting the load power, it supplies power to the energy storage unit. Since the battery is limited by the maximum charging power, this working mode can be divided into two working states: Working state 1.1: The load is in a heavy load state, absorbing a large amount of power from the generator set. The remaining power flowing to the energy storage unit is small and is not limited by the maximum charging power of the battery. Therefore, the generator set can generate power at full power and the system power is balanced. Working state 1.2: The load is in a light load state, absorbing only a small amount of power generation, and the remaining large amount of power flows into the energy storage unit due to the maximum charging power limit of the battery. At this time, if the system power is to be balanced, the wind turbine should not generate power at full power, that is, the working area of ​​the wind turbine deviates from the maximum power point to maintain system power balance. Operating Mode 2: The load power required by the load is high, and the maximum output power of the generator after MPPT control is still insufficient. The energy storage unit must jointly generate power to meet the load's power demand. Because the battery has a maximum discharge power limit, this operating mode can also be divided into two operating states: Operating State 2.1: The power output of the generator set and energy storage unit can meet the power requirements of all loads. The generator is under MPPT control, and the battery discharge power does not exceed the limit. At this time, the overall power of the system is balanced. Operating State 2.2: The maximum discharge power of the generator set and battery still cannot meet all load requirements, and the system energy cannot be balanced. At this time, it is necessary to remove some loads to convert the system operating state to another operating state. In summary, the system is divided into two working modes according to whether the power generation power of the generator set can independently meet the power consumption of the load. When in working mode 1, it is further divided into two working states according to whether the battery exceeds the maximum charging power. When the battery charging power is less than the maximum charging power limit, the generator set performs MPPT control and the system is in working state 1.

1. If the power flowing into the battery exceeds the maximum charging power, the generator set should operate away from the maximum power point to maintain the energy balance of the system. When in working mode 2, it is also divided into two working states according to whether the battery exceeds the maximum discharge power. If the output power of the generator set and the battery can meet the power consumption of the load, the system energy balance is in working state 2.

1. If the maximum discharge power of the generator and the battery cannot meet the power consumption of the load, some loads should be cut off at this time to change the system from working state 2.2 to working state 2.1, so as to achieve the system energy balance.

2. In claim 1, the power relationship among the wind-wave generator set, the energy storage unit and the load is analyzed. Accordingly, the working state of the system is divided into four types. If the system state is switched by calculating and analyzing the power of each part after real-time measurement of the voltage and current parameters of each part during the operation of the system, this method will lead to a redundant system calculation amount, resulting in a delay in the control effect of the system and poor stability. However, some electrical characteristics in actual operation can more accurately and conveniently distinguish the working state, reduce the calculation amount in the program, and improve the rapidity of the system response. Therefore, the present invention proposes a method for changing the working state based on characteristic quantities. When the wind-wave complementary generator set is simultaneously under MPPT control and the battery charging power does not exceed the limit, that is, the system is operating in state 1.

1. If at this time Ii≥Iim or UE>UE2, it means that the battery charging power is limited at this time and the two-stage charging method is being used, that is, the system is operating in state 1.

2. When UE<UE1, it means that the system power balance is controlled by the battery charging power, that is, it is judged that the system returns to working state 1.1 at this time. When the battery changes from the charging state to the discharging state, that is, when Udc1<U1, the working state of the system changes from 1.1 to state 2.

1. When the battery is in the discharging state, it is divided into two working states according to whether the charging power of the battery reaches the maximum discharge power. When Io>Iom, that is, the discharge current exceeds the rated maximum discharge current; at this time, the system needs to cut off some loads and return to other working states.

3. The switched reluctance motor wind-wave complementary power generation system according to claim 1 is composed of multiple parts, including a wind turbine, a direct-drive wave energy generator, an energy storage unit, a DC bus, and a load. The power balance of each part of the system and the whole must be maintained at all times. Therefore, this paper proposes a control strategy that combines the maximum power tracking of the wind-wave complementary generator with the DC bus voltage closed loop to control the energy balance of the system. The switched reluctance motor wind-wave complementary power generation system is divided into two operating modes depending on whether the energy storage unit is in the charging state or the discharging state. Each operating mode is further divided into two operating states depending on whether the charge and discharge power of the battery exceeds the maximum charge and discharge power limit. When the system is in operating state 1.1, the wind turbine and the wave energy generator are both in the MPPT state, and the generated power flows into the battery and the load; when the load is light, the generated power will flow too much to the energy storage unit, and may even exceed the maximum charge power limit of the battery, and the system enters operating state 1.

2. At this time, the generator set should exit MPPT control and enter the complementary power generation state. This system consists of a 200W wind turbine and a 150W direct-drive wave energy generator. Since the wind turbine has a large adjustable power range, the maximum power point can be deviated by simply changing the excitation current to change the wind turbine speed. The deviation according to the optimal power curve makes the control of the wind turbine power reduction more precise, which is conducive to the stability of the DC bus voltage. Therefore, in the complementary power generation state, the wind turbine first exits the MPPT control state. When the battery enters the discharge phase, the system switches to Operating Mode 2. In this mode, if the energy storage unit's discharge power remains within the maximum discharge power limit, the system will operate stably in Operating State 2.

1. In this state, the generator set and energy storage unit work together to jointly supply power to the load, thereby ensuring a dynamic balance between the system's energy supply and demand. However, if the load demand exceeds a critical value and the combined output of the generator set and energy storage unit cannot meet the power load, the system will enter Operating State 2.

2. At this point, the system should remove some load to restore the system to another operating state.

4. The switched reluctance motor complementary power generation system according to claim 1, wherein a three-phase 12 / 8 switched reluctance motor and a cylindrical switched reluctance linear motor are used as the wind turbine and wave generator, respectively, and their power converters both employ an asymmetric half-bridge topology. Because the controller's output current is too low to directly drive the IGBT devices in the power converter, this system utilizes a driver circuit centered around the KA962F driver chip to enhance the controller's driving capability. To meet the requirements for rapid and reliable system control, the power converter's upper transistor uses Infineon's IRFP4668PBF. This switching transistor offers advantages such as high withstand voltage, low drive voltage, high switching frequency, compact size, and low cost, meeting the system's requirements for fast switching, low loss, and high efficiency. The lower transistor utilizes the fast-recovery epitaxial diode DSE1120-06A, which features high reverse withstand voltage, short recovery time, high output current, and compact size. The DC bus voltage is set to 24V. Since the electric energy generated by SRG is a DC pulse current, it is very important to filter the bus voltage. This paper adopts multiple filter capacitors in parallel to achieve the filtering effect and reduce the output voltage fluctuation. The wind-wave hybrid power generation system requires a buck-boost circuit to convert the bus voltage Udc1 = 24V to the battery voltage UE = 12V, allowing the generator's energy to be safely stored in the battery. The power switches in the bidirectional half-bridge DC / DC converter are Infineon's IRFP4668PBF MOSFETs. Compared to IGBT modules, MOSFET modules offer advantages such as high switching frequency, low cost, and small size. The freewheeling diode is the MUR6020 fast recovery diode from Silicon Lake. The driver chip is the dedicated EXB841 module from Fuji. To ensure the proper function of the buck-boost circuit, current continuity is generally required. Therefore, the circuit design requires reliable inductor parameters to filter the current to meet specified requirements. Since the inductor current fluctuates by approximately 20%, the required inductor value for the DC / DC converter can be calculated using the following formula: Substituting the parameters into the above equation, we can obtain that the inductance value should satisfy L ≥ 0.81mH. Therefore, the inductor with an inductance of 1mH is selected for the DC / DC converter designed in this article. A major advantage of digital controllers is their independent control capabilities. Within this system architecture, wind turbines, wave generators, and battery energy storage units can all be independently controlled using digital controllers. This independent control model significantly improves the overall system's flexibility and responsiveness, while also significantly enhancing its operational safety and reliability. If any unit in the system fails, the digital controller, leveraging its independent control capabilities, can quickly locate and isolate the faulty unit, effectively preventing the fault from spreading and ensuring continued stable system operation. Given that the control process for switched reluctance motors and switched reluctance linear motors involves multiple strategies, such as position and current control, and requires real-time monitoring of analog quantities such as speed, position, current, and voltage, this system uses the DSP TMS320F28335 chip as the core control component to meet precise control requirements. This chip, manufactured by Texas Instruments (TI), is a high-performance digital signal processor with high data processing capabilities and fast response speed, specifically designed to meet the demands of high-speed and precise control. This chip enables precise control of SRGs and SRLGs, significantly improving motor performance and efficiency. This system utilizes a TMS320F28335 control board. Voltage and current signals pass through the AD7606 sampling circuit and are then transmitted to the DSP via a sampling interface. Position signals converted from the Hall effect device are fed into the ECAP capture channel via a signal conditioning circuit based on a 40106 chip. After receiving the sensor signals, the DSP uses programmed calculations to generate control signals for the power converter's switches. These signals are processed by logic circuits and then transmitted to the drive isolation circuit, enabling precise control of the generator's operation. The control system for the battery energy storage unit (BESS) only involves voltage and current detection and two switching outputs. Therefore, the system uses a dsPIC30F2010 chip from Microchip. This chip offers high cost-effectiveness and reliable performance. By implementing a PI closed-loop control strategy, it ensures efficient and stable operation of the BESS under various operating conditions, thereby extending the battery's service life and improving energy efficiency. The control board connects to current and voltage sensors via an AD sampling interface to obtain bus voltage, battery terminal voltage, and battery charge and discharge current. The dsPIC30F6010 is programmed to generate control signals, which are then processed by digital chips 7404 and 40106 and optocoupler isolation chip 6N136 before being transmitted to the drive circuit to control the operation of the DC / DC converter.

5. The control strategy of the switched reluctance wind-wave complementary independent generator system described in claim 1 is completed by combining three parts: the MPPT control of the wind-wave generating set, the system energy balance strategy, and the charge-discharge protection control of the battery pack. The operating states of the generating set are distinguished according to the magnitude relationships of U1, U2, P1, and P2. When Udc1 < U1 and PG < P1, the switched reluctance wind-wave complementary independent generator conducts MPPT control to increase the energy conversion efficiency; when Udc1 > U2, the system conducts voltage closed-loop control to stabilize the bus voltage and ensure energy balance; when PG > P2, the wind-wave complementary power generation system of the switched reluctance motor adopts the complementary power generation mode, the wave energy generator conducts MPPT control, the wind turbine deviates from the maximum power point, and the power output is reduced to ensure system safety; when U1 < Udc1 < U2 and P1 < PG < P2, the system remains unchanged and waits to switch to a new control method. In the research process of the present invention, first, the power characteristics of the wind turbine are deeply analyzed, and four common maximum power tracking basic strategies, namely, the hill climbing search method, the three-point comparison method, the wind speed tracking method, and the power feedback method, are systematically elaborated. By organically integrating the technical advantages of the wind speed tracking method and the power feedback method, the step-by-step maximum power tracking strategy is innovatively proposed, effectively enhancing the control accuracy of the system. For the wave energy power generation part, based on the physical characteristics of the float, the vertical excitation force it receives under the action of sea waves is deeply studied, and then the dynamic model of the float under sea wave excitation is constructed. At the same time, the power generation operation principle of the switched reluctance linear motor is elaborated in detail, and on this basis, a single-degree-of-freedom maximum power tracking control method for the direct-drive switched reluctance wave power generation system is designed, significantly improving the capture and utilization efficiency of the system for wave energy. The present invention introduces three methods for charging the battery, and selects the two-stage method for charging the battery through comparison; controls the charge-discharge process of the battery by independently controlling the bidirectional half-bridge DC / DC converter; proposes a method to stabilize the system power by controlling the bus voltage. Finally, a system control scheme consisting of three parts, namely, the MPPT control of the wind-wave complementary generator system, the system energy balance strategy, and the charge-discharge protection control of the battery pack, is designed for the system.

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