All-electric helicopter energy storage SOC balance control method based on fine tuning virtual resistor

Abstract

The invention discloses an all-electric helicopter energy storage SOC equalization control method based on a fine-tuning virtual resistor, and belongs to the technical field of energy storage system control, and the method comprises the following steps: S1, calculating an equalization factor; s2, calculating virtual impedance; s3, calculating to obtain an adjusted droop coefficient according to the calculated equalization factor and the virtual impedance; s4, calculating the reference voltage of the converter according to the reference voltage of the bus, the adjusted droop coefficient and the output current of the converter; and S5, tracking the reference voltage of the converter by adopting voltage and current double-closed-loop control. According to the all-electric helicopter energy storage SOC balance control method based on the fine-tuning virtual resistor, fine tuning is performed on the virtual resistor through a feedback mechanism to ensure that the SoC of each energy storage unit can be kept consistent in the charging and discharging process, the energy storage balance performance is remarkably improved, and meanwhile, the SoC difference caused by line impedance mismatching is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of energy storage system control, and in particular to a method for balancing energy storage SOC of an all-electric helicopter based on fine-tuning virtual resistance. Background Art

[0002] The energy storage system (ESS) is a key component of the DC architecture of an all-electric helicopter. Connected to the DC microgrid via a bidirectional DC / DC converter, it plays a vital role in maintaining the microgrid's power and voltage stability. However, in actual operation, if the state of charge (SoC) of the distributed energy storage units is not balanced, continued operation may cause the energy storage units to overcharge or overdischarge, significantly reducing the service life of the ESS. Therefore, to prevent damage to the energy storage units due to excessive charging and discharging, coordinated control of the ESS's SoC is necessary to achieve balanced SoC.

[0003] In DC systems, traditional droop control is a commonly used power distribution method, but it has obvious limitations. Traditional droop control can only distribute load power or current to each distributed energy storage unit according to a fixed ratio. If the droop coefficients are inconsistent, the SoC of the energy storage units will be different; even if the droop coefficients remain consistent, the SoC will still be inconsistent due to differences in the characteristics of the energy storage units themselves. To overcome this shortcoming of traditional droop control, adaptive droop control of microgrid systems has emerged. This method can achieve good voltage recovery and stable operation of the microgrid by adaptively adjusting state variables such as bus voltage and energy storage system SoC, effectively solving the problem of inconsistent energy storage SoC caused by traditional droop control.

[0004] In the current practical application scenarios of all-electric helicopters, line impedance mismatch is common due to the unique layout of energy storage systems. However, most existing research has not fully considered the impact of line impedance mismatch on energy storage SoC balance. This can result in the SoC of energy storage units not being completely aligned, thus affecting the stable operation of the all-electric helicopter DC architecture and the service life of the energy storage system. Therefore, further in-depth research on the SoC balance control of energy storage systems in all-electric helicopter DC architectures is needed to resolve the line impedance mismatch issue and achieve precise SoC balance of energy storage units. Summary of the Invention

[0005] The purpose of the present invention is to provide an all-electric helicopter energy storage SOC balancing control method based on fine-tuning virtual resistance, which can effectively compensate for the influence of line impedance mismatch and achieve zero-error balancing of the SoC of the energy storage unit.

[0006] To achieve the above objectives, the present invention provides a method for balancing the energy storage SOC of an all-electric helicopter based on fine-tuning virtual resistance, comprising the following steps:

[0007] S1. Calculate the equilibrium factor;

[0008] S2. Calculate virtual impedance;

[0009] S3. Calculate the adjusted droop coefficient based on the calculated equalization factor and virtual impedance;

[0010] S4. Calculating a reference voltage of the converter according to the reference voltage of the bus, the adjusted droop coefficient, and the output current of the converter;

[0011] S5. Use voltage and current dual closed-loop control to track the reference voltage of the converter.

[0012] Preferably, in S1, the calculation formula of the balance factor is:

[0013]

[0014] Among them, q is the equilibrium factor; n is the acceleration factor; SOC i is the current charge of the i-th energy storage; DOD i =1-SOC i , is the amount of charge used; SOC ave is the average charge of each energy storage unit; DOD ave It is the average charge used by each energy storage unit.

[0015] Preferably, in S2, the calculation formula of the virtual impedance is:

[0016]

[0017] Among them, R m,i is the virtual impedance; k p is the proportional coefficient; k o is the integral coefficient; λ i is the droop voltage drop of the i-th converter, including λ1 and λ2; λ ave is the average value of the droop voltage drop of each converter;

[0018]

[0019] Where λ1 is the droop voltage drop of the first converter, λ2 is the droop voltage drop of the second converter, is the reference voltage of the bus, u dc is the actual voltage of the bus, I o1 is the output current of the first converter, I o2is the output current of the second converter, R1 is the resistance of the line between the first converter and the bus, R2 is the resistance of the line between the second converter and the bus, R v1 is the droop coefficient of the first converter, R v2 is the droop coefficient of the second converter.

[0020] Preferably, in S3, the calculation formula of the adjusted droop coefficient is:

[0021] R' v,i =qR Vi +R m,i ;

[0022] Among them, R' v,i is the droop coefficient of the i-th converter after adjustment, R Vi is the droop coefficient of the i-th converter.

[0023] Preferably, in S4, the calculation formula of the reference voltage of the converter is:

[0024]

[0025] Among them, U ref,i is the reference voltage of the i-th converter, is the reference voltage of the bus, I oi is the output current of the i-th converter.

[0026] Preferably, in S5, for the i-th converter, its reference voltage U ref,i With the output voltage u C Make a difference and get the voltage error, then input the voltage error into the PI controller to output the reference current of the inductor current Set the inductor current reference current and the inductor current i L The current error is obtained by taking the difference, and then the current error is input into the PI controller to output the duty cycle; the duty cycle is input into the PWM module to obtain the switching signal S1; if the converter is a unidirectional converter, only one switching signal is required, and the switch is driven by the switching signal S1; if the converter is a bidirectional converter, two switching signals are required, namely S1 and the inverse signal S2 of S1.

[0027] Therefore, the present invention adopts the above-mentioned all-electric helicopter energy storage SOC balancing control method based on fine-tuning virtual resistance, which significantly improves the balancing performance of energy storage and reduces the SoC difference caused by line impedance mismatch.

[0028] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a simplified diagram of the two distributed energy storage all-electric helicopter systems;

[0030] Figure 2 This is a control principle diagram of a method for balancing energy storage SOC of an all-electric helicopter based on fine-tuning virtual resistance according to the present invention;

[0031] Figure 3 This is a flow chart of a method for balancing energy storage SOC of an all-electric helicopter based on fine-tuning virtual resistance according to the present invention;

[0032] Figure 4 This is a control logic diagram of a voltage-current dual closed-loop control method for an all-electric helicopter energy storage SOC balancing control method based on fine-tuning virtual resistance according to the present invention;

[0033] Figure 5 1 is a diagram showing the SOC balancing effect when the load is not disturbed in an embodiment of the present invention;

[0034] Figure 6 1 is a diagram of the output current of the DC / DC converter in the case of no load disturbance in an embodiment of the present invention;

[0035] Figure 7 1 is a fine-tuning virtual impedance diagram under the condition of no load disturbance in an embodiment of the present invention;

[0036] Figure 8 is a bus voltage diagram under the condition of no load disturbance in an embodiment of the present invention;

[0037] Figure 9 1 is a diagram showing the SOC balancing effect when the load is disturbed in an embodiment of the present invention;

[0038] Figure 10 is a diagram of the output current of the DC / DC converter when the load is disturbed in an embodiment of the present invention;

[0039] Figure 11 is a load power diagram in the case where the load is disturbed in an embodiment of the present invention;

[0040] Figure 12 3 is a bus voltage diagram when the load power is disturbed in an embodiment of the present invention. DETAILED DESCRIPTION

[0041] The technical solution of the present invention is further described below with reference to the accompanying drawings and embodiments.

[0042] Unless otherwise defined, the technical or scientific terms used in the present invention shall have the usual meanings understood by persons of ordinary skill in the field to which the present invention belongs. The words "first", "second" and similar terms used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. Words such as "include" or "comprise" mean that the elements or objects preceding the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. Words such as "connect" or "connected" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the object being described changes, the relative positional relationship may also change accordingly.

[0043] Example 1

[0044] The present invention provides a method for controlling the energy storage SOC balance of an all-electric helicopter based on fine-tuning virtual resistance, which can realize the following Figure 1 The energy storage control of the two distributed energy storage all-electric helicopter systems shown in the figure is as follows: Figure 2 As shown (wherein, LPF is a low-pass filter and PI represents a PI controller).

[0045] Specific control methods such as Figure 3 As shown, the following steps are included:

[0046] S1. Calculate the equilibrium factor.

[0047] The calculation formula of the balance factor is:

[0048]

[0049] Among them, q is the equilibrium factor; n is the acceleration factor; SOC i is the current charge of the i-th energy storage; DOD i =1-SOC i , is the amount of charge used; SOC ave is the average charge of each energy storage unit; DOD ave It is the average charge used by each energy storage unit.

[0050] S2. Calculate the virtual impedance.

[0051] The calculation formula of virtual impedance is:

[0052]

[0053] Among them, R m,i is the virtual impedance; k p is the proportional coefficient; k ois the integral coefficient; λ i is the droop voltage drop of the i-th converter, including λ1 and λ2; λ ave is the average droop voltage drop of each converter.

[0054]

[0055] Where λ1 is the droop voltage drop of the first converter, λ2 is the droop voltage drop of the second converter, is the reference voltage of the bus, u dc is the actual voltage of the bus, I o1 is the output current of the first converter, I o2 is the output current of the second converter, R1 is the resistance of the line between the first converter and the bus, R2 is the resistance of the line between the second converter and the bus, R v1 is the droop coefficient of the first converter, R v2 is the droop coefficient of the second converter.

[0056] S3. Calculate the adjusted droop coefficient based on the calculated equalization factor and virtual impedance.

[0057] The calculation formula for the adjusted droop coefficient is:

[0058] R' v,i =qR Vi +R m,i

[0059] Among them, R' v,i is the droop coefficient of the i-th converter after adjustment, R Vi is the droop coefficient of the i-th converter.

[0060] S4. Calculate the reference voltage of the converter according to the reference voltage of the bus, the adjusted droop coefficient, and the output current of the converter.

[0061] The calculation formula of the converter reference voltage is:

[0062]

[0063] Among them, U ref,i is the reference voltage of the i-th converter, is the reference voltage of the bus, I oi is the output current of the i-th converter.

[0064] S5. Use voltage and current dual closed-loop control to track the reference voltage of the converter.

[0065] like Figure 4 As shown, for the i-th converter, its reference voltage U ref,iWith the output voltage u C Make a difference and get the voltage error, then input the voltage error into the PI controller to output the reference current of the inductor current Set the inductor current reference current and the inductor current i L The current error is obtained by taking the difference, and then the current error is input into the PI controller to output the duty cycle; the duty cycle is input into the PWM module to obtain the switching signal S1; if the converter is a unidirectional converter, only one switching signal is required, and the switch is driven by the switching signal S1; if the converter is a bidirectional converter, two switching signals are required, namely S1 and the inverse signal S2 of S1.

[0066] In this embodiment, the following Figure 1 The model shown is used to verify the energy storage SOC balancing control method. The relevant parameters are shown in Table 1:

[0067] Table 1 Simulation related parameters

[0068]

[0069]

[0070] ①When the load is not disturbed:

[0071] The three energy storage units are in a discharge state, with an initial state of charge of 70%. No control is performed for the first 0-3 seconds. Due to the inconsistency of the line resistance, the state of charge of the three energy storage units will differ after 3 seconds. At this time, energy storage unit balancing control is added, and the state of charge of the three energy storage units finally converges to the same state. The results of MATLAB / Simulink simulation are as follows: Figure 5-8 shown.

[0072] Depend on Figure 5 It can be seen that the above energy storage SOC balancing control method is effective; it can be seen from Figure 6 that the SOC with a smaller energy storage outputs a lower current through the DC / DC converter, and the SOC with a larger energy storage outputs a higher current through the DC / DC converter; Figure 7 It can be seen that the virtual impedance corresponding to the lower line resistance is larger, and the virtual impedance corresponding to the larger line resistance is smaller; Figure 8 It can be seen that the bus voltage is stable.

[0073] ②When the load is disturbed:

[0074] The three energy storage units are in the discharge state, and the initial state of charge is 70%. No control is performed for the first 0-3 seconds. After 3 seconds, the energy storage unit balance control is added. The results of the simulation through MATLAB / Simulink are as follows: Figure 9-12 shown.

[0075] Depend on Figure 9 It can be seen that the above energy storage SOC balancing control method is still effective in the presence of disturbances; it can be seen from 10 that the presence of disturbances causes a sudden change in the output current of the energy storage unit; Figure 11 It can be seen that impact loads appeared at 5s, 7s, and 9s; Figure 12 It can be seen that the bus voltage remains stable when there is an impact load.

[0076] Therefore, the present invention adopts the above-mentioned all-electric helicopter energy storage SOC balancing control method based on fine-tuning virtual resistance, and fine-tunes the virtual resistance through a feedback mechanism to ensure that the SoC of each energy storage unit can remain consistent during the charging and discharging process, significantly improving the balancing performance of energy storage, while reducing the SoC difference caused by line impedance mismatch.

[0077] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for balancing the energy storage SOC of an all-electric helicopter based on fine-tuning virtual resistance, characterized in that: The following steps are involved: S1. Calculate the equilibrium factor; S2. Calculate virtual impedance; S3. Calculate the adjusted droop coefficient based on the calculated equalization factor and virtual impedance; S4. Calculating a reference voltage of the converter according to the reference voltage of the bus, the adjusted droop coefficient, and the output current of the converter; S5. Use voltage and current dual closed-loop control to track the reference voltage of the converter.

2. The method for controlling energy storage SOC balance of an all-electric helicopter based on fine-tuning virtual resistance according to claim 1, characterized in that: In S1, the calculation formula of the balance factor is: Among them, q is the equilibrium factor; n is the acceleration factor; SOC i is the current charge of the i-th energy storage; DOD i =1-SOC i , is the amount of charge used; SOC ave is the average charge of each energy storage unit; DOD ave It is the average charge used by each energy storage unit.

3. The method for controlling energy storage SOC balance of an all-electric helicopter based on fine-tuning virtual resistance according to claim 2, characterized in that: In S2, the calculation formula of virtual impedance is: Among them, R m,i is the virtual impedance; k p is the proportional coefficient; k o is the integral coefficient; λ i is the droop voltage drop of the i-th converter, including λ1 and λ2; λ ave is the average value of the droop voltage drop of each converter; Where λ1 is the droop voltage drop of the first converter, λ2 is the droop voltage drop of the second converter, is the reference voltage of the bus, u dc is the actual voltage of the bus, I o1 is the output current of the first converter, I o2 is the output current of the second converter, R1 is the resistance of the line between the first converter and the bus, R2 is the resistance of the line between the second converter and the bus, R v1 is the droop coefficient of the first converter, R v2 is the droop coefficient of the second converter.

4. The method for controlling energy storage SOC balance of an all-electric helicopter based on fine-tuning virtual resistance according to claim 3 is characterized in that: In S3, the calculation formula for the adjusted droop coefficient is: R′ v,i =qR Vi +R m,i ; Among them, R′ v,i is the droop coefficient of the i-th converter after adjustment, R Vi is the droop coefficient of the i-th converter.

5. The method for controlling energy storage SOC balance of an all-electric helicopter based on fine-tuning virtual resistance according to claim 4 is characterized in that: In S4, the calculation formula of the converter reference voltage is: Among them, U ref,i is the reference voltage of the i-th converter, is the reference voltage of the bus, I oi is the output current of the i-th converter.

6. The method for controlling energy storage SOC balance of an all-electric helicopter based on fine-tuning virtual resistance according to claim 1, characterized in that: In S5, for the i-th converter, its reference voltage U ref,i With the output voltage u C Make a difference and get the voltage error, then input the voltage error into the PI controller to output the reference current of the inductor current Set the inductor current reference current and the inductor current i L The current error is obtained by performing a subtraction, and then the current error is input into the PI controller to output the duty cycle. The duty cycle is input into the PWM module to obtain the switching signal S1. If the converter is a unidirectional converter, only one switching signal is required. In this case, the switch is driven by the switching signal S1. If the converter is a bidirectional converter, two switching signals are required, namely S1 and the inverse signal S2 of S1 .

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