An energy control method for an island distributed wind / storage power supply load

Abstract

The present invention relates to the technical field of new energy power generation system control, and particularly to an energy control method for an island distributed wind / storage power supply load, comprising the following steps: First, determine the droop coefficient of the relationship between the power change amount and the DC bus voltage change amount; then, in combination with the external voltage and internal current control strategy, achieve the charge and discharge energy control of the energy storage battery, and further achieve the dynamic balance of supply and demand energy. The present invention can enable the energy storage device to timely supplement or absorb power, realizes stable power supply of the wind power generation system in the off-grid mode and efficient operation of the energy storage device, and ensures the stable operation of the system. At the same time, the present invention enables the effective utilization and consumption of wind energy, ensures the effective tracking of load demand, can adapt to various complex working conditions, and improves the safety of the system.

Description

Technical Field

[0001] The present invention relates to the technical field of new energy power generation system control, and particularly to an island distributed wind / storage power supply load energy control method. Background Art

[0002] With the continuous increase in the global demand for clean energy, wind power generation, as a renewable energy source, has received extensive attention and application. In a wind power generation system, a doubly-fed induction generator (DFIG) has become the mainstream choice of modern wind power generation technology due to its high efficiency and stability. The doubly-fed induction generator can operate in both grid-connected and off-grid modes. In the off-grid mode, the system needs to supply power independently to meet the needs of local loads.

[0003] In the off-grid operation mode, due to the intermittency and randomness of wind power generation, the wind power has large fluctuations. It is difficult to ensure stable power supply to the load solely relying on wind power generation. Therefore, it is necessary to introduce an energy storage device to regulate and control the power to make up for the deficiencies of wind power generation and ensure stable power supply of the system under different loads and different wind speeds.

[0004] However, in practical applications, how to efficiently control the energy flow on the energy storage side of the doubly-fed motor has become an urgent problem to be solved. The existing energy storage control methods still have deficiencies in response speed and regulation accuracy when dealing with rapidly changing wind speeds and complex load changes, and the load tracking is not accurate enough. Summary of the Invention

[0005] The purpose of the present invention is to solve the drawbacks existing in the prior art, and to propose an island distributed wind / storage power supply load energy control method. By the energy storage device, the power can be supplemented or absorbed in a timely manner, realizing stable power supply of the wind power generation system in the off-grid mode and efficient operation of the energy storage device, and ensuring stable operation of the system.

[0006] To achieve the above purpose, the present invention adopts the following technical solutions:

[0007] An island distributed wind / storage power supply load energy control method includes the following steps:

[0008] Step 1: Real-time detect the wind speed v, the load side voltage u 1abc , the current i 1abc , the battery voltage u v , the current i v .

[0009] Step 2: Calculate the real-time maximum power P m , the load consumption power P load .

[0010] Step 3: Calculate the relationship between the formula-derived power ΔP and the DC-side voltage Δu, and determine the droop coefficient. dc

[0011] Step 4: Connect an energy storage device to the DC side of the doubly-fed wind generator. By controlling the charging and discharging process of the energy storage device, use a PI regulator to adjust the current, and achieve the control of the battery charging and discharging process through a PWM control circuit, thereby realizing stable power supply to the load.

[0012] Preferably, in Steps 2 and 3, the following steps are specifically included:

[0013] An energy storage device is connected to the DC bus of the doubly-fed wind generator, and the load is connected to the AC side. For the rotor and grid-side converters of the doubly-fed wind generator, a direct power control method based on virtual flux is adopted. The rotor side uses direct power control based on maximum power tracking to make the stator side output maximum power, and the grid-side control is used to stabilize the DC-side voltage.

[0014] According to the Betz theory, the maximum input mechanical power P of the doubly-fed wind power generation is obtained. m , and the power consumed by the load side: P load = u 1α i 1α + u 1β i 1β , where i 1α , i 1β are the α and β axis components of the load current, and u 1α , u 1β are the α and β axis components of the load voltage. P load is the power to be consumed by the load.

[0015] Without considering the power loss of the doubly-fed wind generator, during the operation of the load powered by the doubly-fed wind generator, the DC-side voltage fluctuation reflects the power imbalance between the input and output.

[0016]

[0017] Among them, C dc and U dc are the capacitance and rated voltage of the DC side respectively, and u dc is the actual DC-side voltage. Combining with the motion equation of the doubly-fed wind generator:

[0018]

[0019] Among them, J m is the inertia of the doubly-fed wind generator, ω r is the rotor angular velocity, and ω is the rated angular velocity.

[0020]

[0021] where Δω is the rotational speed change, and Δu dc is the DC side voltage change;

[0022] By associating the reference given value of the battery charge and discharge power ΔP with the DC side voltage, we can obtain:

[0023] ΔP = u bat Δi

[0024]

[0025] where Δi is the battery current change, and u bat is the battery voltage, and k is the droop coefficient between the frequency and the battery power, which is determined by the maximum angular frequency allowed under the maximum power change.

[0026] Preferably, in step 4, it specifically includes the following steps:

[0027] Subtract the maximum power generated by the wind turbine from the power consumed by the load to obtain the battery reference power. Subtract the battery reference power from the actual battery power to obtain the battery power change, and use its value for droop control to obtain the voltage change. Use the voltage change as the input of the voltage outer loop PI control to obtain the reference current of the current inner loop. Then compare the reference current with the actually measured battery current, calculate the current error, and generate a control signal after processing by the PI controller. Finally, obtain the signal through the PWM controller.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. Under the conditions of wind speed and load changes, the present invention can timely supplement or absorb power through the energy storage device, realizing stable power supply of the wind power generation system in the off-grid mode and efficient storage and release of the energy storage device, ensuring the stable operation of the system.

[0030] 2. The present invention makes full use of wind energy, reduces power waste, ensures effective tracking of the load, and can adapt to various complex working conditions, improving the safety and adaptability of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is the topology structure diagram of the wind / storage system of the present invention;

[0032] Figure 2 is the control diagram of the energy storage battery of the present invention;

[0033] Figure 3 is the diagram of the power fluctuation of each part of the system of the present invention under the condition of wind speed fluctuation and constant load;

[0034] Figure 4This is a diagram showing the power fluctuations of various parts of the system of the present invention under the condition of constant wind speed and randomly varying load;

[0035] Figure 5 This is a diagram showing the power fluctuations of various parts of the system of the present invention under the condition of fluctuating wind speed and randomly varying load. Detailed implementation manner

[0036] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings, so that those skilled in the art can better understand the advantages and features of the present invention, and thus more clearly define the protection scope of the present invention. The embodiments described in the present invention are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0037] Figure 1 is a topological structure diagram of a wind / storage system. As Figure 1 shown, the doubly-fed wind turbine is off-grid, and the energy storage device is connected to the DC bus.

[0038] Figure 2 is a control diagram of the energy storage battery. This control method is sequentially implemented on the topological structure diagram of the Figure 1 doubly-fed wind turbine according to the following steps:

[0039] An energy control method for an island distributed wind / storage power supply load includes the following steps:

[0040] Step 1: Data acquisition

[0041] Detect the wind speed v, the voltage u 1abc and current i 1abc on the load side, the battery voltage u v and current i v .

[0042] Step 2: Calculate power

[0043] According to the Betz theory, when the mechanical losses of the wind turbine are not considered, the actual mechanical power output by the wind turbine can be expressed as:

[0044]

[0045] where C p is the wind energy utilization coefficient; ρ is the air density; S is the swept area of the wind turbine impeller; v is the wind speed upstream of the wind turbine. According to the Betz theory, the maximum wind energy utilization coefficient C pmax of the wind turbine is 0.593.

[0046] Power consumed on the load side:

[0047] P load = u 1α i 1α + u 1β i 1β

[0048] where i 1α , i 1β are the α, β-axis components of the load current, and u 1α , u 1β are the α, β-axis components of the load voltage, and P load is the power consumed by the load.

[0049] Step 3: Calculate the relationship between the power change and the DC-side voltage change

[0050] For a doubly-fed induction generator (DFIG) without considering losses, the following formula can be obtained from the law of conservation of energy:

[0051] P m = P load + P V

[0052] where P m is the mechanical energy generated by the DFIG, and P V is the battery power.

[0053]

[0054] where C dc and U dc are the DC-side capacitor and the rated voltage respectively, and u dc is the actual DC-side voltage.

[0055] In a DFIG, the DC-side voltage reflects the power imbalance between the input and output, and its formula is as follows:

[0056]

[0057] Combined with the DFIG motion equation, it can be obtained:

[0058]

[0059] where J m is the inertia of the DFIG, ω r is the rotor angular velocity, and ω is the rated angular velocity.

[0060] From the above formula, it can be obtained:

[0061]

[0062] where Δω is the change in rotational speed, and Δu dcis the change in DC - side voltage;

[0063] By correlating the battery power with the DC - side voltage, we can obtain:

[0064] ΔP = u bat Δi

[0065]

[0066] where Δi is the change in battery current, u bat is the battery voltage, and k is the droop coefficient between the frequency and the battery power, which is determined by the maximum angular frequency allowed under the maximum power change.

[0067] Step 4:

[0068] Subtract the maximum power generated by the wind turbine from the power consumed by the load to obtain the battery reference power. Subtract the battery reference power from the actual battery power to obtain the battery power change. Use droop control on its value to obtain the voltage change. Use the voltage change as the input of the outer - loop voltage PI control to obtain the reference current of the inner - loop current. Then compare the reference current with the actually measured battery current, calculate the current error, generate a control signal after processing by the PI controller, and finally obtain the signal through the PWM controller.

[0069] For the rotor and grid - side converters of the doubly - fed wind turbine, a direct power control method based on virtual flux is adopted. The rotor - side uses direct power control based on maximum power tracking to make the stator - side output maximum power, and the grid - side control is used to stabilize the DC - side voltage.

[0070] As Figure 2 shown in the structure, a simulation model is built in the MATLAB / Simulink environment. The parameters used in the simulation are as follows: the rated power of the doubly - fed wind turbine is 30KA, the rated speed is 1500r / min, the rated frequency is 50Hz, the number of motor pole pairs is 2, the DC - bus voltage is 750V, the grid voltage is 380V, and the frequency is 50Hz. The stator resistance and inductance are 0.235Ω and 0.002H respectively, the rotor resistance and inductance are 0.02Ω and 0.001H respectively, the grid - side resistance and inductance are 0.01Ω and 0.004H respectively, and the mutual inductance is 0.018H.

[0071] Figure 3 shows the power change of each part under the condition of system wind - speed fluctuation and constant load when the control method of the present invention is adopted. Figure 3 (a) represents the output power of the wind turbine at maximum power; Figure 3 (b) represents the power output of the energy storage device. When the power is positive, it means the energy storage device outputs power, and when the power is negative, it means the energy storage device absorbs power; Figure 3(c) represents the power consumption of the load. As can be seen from the figure, the wind speed changes at 1 s and 1.5 s, and the maximum output power of the wind turbine increases accordingly, while the power consumption of the load remains basically constant at 3000 W. During the period from 0 to 1.5 s, the output power of the wind turbine is not sufficient to support the power consumed by the load, and at this time the energy storage device generates power; after 1.5 s, the output power of the wind turbine is greater than the power consumed by the load, and at this time the energy storage absorbs the excess power.

[0072] Figure 4 Shows the power changes of each part under the condition that the system wind speed is constant and the load changes randomly by adopting the control method of the present invention; Figure 4 (a) represents the output power of the wind turbine at the maximum power; Figure 4 (b) represents the power output of the energy storage device; Figure 4 (c) represents the power consumption of the load. As can be seen from the figure, at this time the wind speed remains unchanged, and the wind turbine generates a constant power; the load is a random load, and the power fluctuates randomly. From Figure 4 (b)(c), it can be seen that the energy storage power fluctuates with the load power and can absorb the excess power in time.

[0073] Figure 5 Shows the power changes of each part under the condition that the system wind speed fluctuates and the load changes randomly by adopting the control method of the present invention; Figure 5 (a) represents the output power of the wind turbine at the maximum power; Figure 5 (b) represents the power output of the energy storage device; Figure 5 (c) represents the power consumption of the load. As can be seen from the figure, the wind speed changes at 1 s and 1.5 s, and the maximum output power of the wind turbine increases accordingly. The load is a random load, and the power fluctuates randomly. The output power of the wind turbine is greater than the power consumed by the load. At this time, the energy storage absorbs the excess power, and the power fluctuation of the energy storage device matches the power fluctuation of the load and wind speed.

[0074] In summary, under the conditions of wind speed and load changes, the present invention can timely supplement or absorb power through the energy storage device, realizing stable power supply of the wind power generation system in the off-grid mode and efficient storage and release of the energy storage device, ensuring the stable operation of the system. The present invention makes full use of wind energy, reduces energy waste, ensures effective tracking of the load, can adapt to a variety of complex working conditions, and improves the safety and adaptability of the system.

[0075] The descriptions and practices disclosed in the present invention are easy to think and understand for those of ordinary skill in the art. Without departing from the principle of the present invention, several improvements and refinements can also be made. Therefore, the modifications or improvements made without departing from the spirit of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A method for controlling energy of isolated island distributed wind / storage power supply load, characterized in that: The steps include: Step 1: Real-time detection of wind speed v and load side voltage u 1abc 、Current i 1abc , battery voltage u v 、Current i v ; Step 2: Calculate the maximum mechanical power P generated by the real-time fan m , load power consumption P load ; Step 3: Calculate the battery power change ΔP and DC side voltage change Δu using the formula dc Relationship, determine the droop coefficient; Step 4: Connect an energy storage device to the DC side of the doubly-fed wind turbine generator, control the charging and discharging process of the energy storage device, use a PI regulator to adjust the current, and control the battery charging and discharging process through a PWM control circuit, thereby achieving stable power supply to the load; In steps 2 and 3, the following steps are specifically included: The energy storage device is connected to the DC bus of the doubly-fed wind turbine generator, and the load is connected to the AC side. For the rotor and grid-side converter of the doubly-fed wind turbine generator, a direct power control method based on virtual flux linkage is adopted. The rotor side adopts direct power control based on maximum power tracking to make the stator side output maximum power, and the grid-side control is used to stabilize the DC side voltage. According to Betz theory, the maximum mechanical power P generated by the fan is m , load side power consumption: P load =u 1α i 1α +u 1β i 1β , where i 1α ,i 1β is the α,β axis component of the load current, u 1α ,u 1β are the α,β axis components of the load voltage; Without considering the power loss of the doubly-fed wind turbine generator, the DC side voltage fluctuation reflects the power imbalance between input and output during the operation of the doubly-fed wind turbine generator power supply load; Among them C dc and U dc are the capacitance and rated voltage of the DC side, u dc is the actual DC side voltage; combined with the motion equation of the doubly fed wind turbine generator: Among them J m is the inertia of the doubly-fed wind turbine generator, ω r is the rotor angular velocity, ω is the rated angular velocity; Where Δω is the speed change, Δu dc is the voltage change on the DC side; The battery power change ΔP is referenced to the given value and the DC side voltage change Δu dc Related, we can get: ΔP=u v Δi Where Δi is the change in battery current, u v is the battery voltage, k is the droop coefficient of the frequency and battery power, which is determined by the maximum angular frequency allowed under the maximum power change.

2. The method for controlling the energy of an isolated island distributed wind / storage power supply load according to claim 1, characterized in that: Step 4 specifically includes the following steps: The maximum mechanical power generated by the fan is subtracted from the power consumed by the load to obtain the battery reference power; the battery reference power is subtracted from the actual battery power to obtain the battery power change, and its value is used for droop control to obtain the DC side voltage change; The DC side voltage change is used as the input of the voltage outer loop PI control to obtain the reference current of the current inner loop; then the reference current is compared with the actual measured current of the battery, the current error is calculated, and the control signal is generated after being processed by the PI controller, and finally the signal is obtained through the PWM controller.

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