A collaborative mitigation method based on improved drooping virtual complex impedance

Abstract

This application provides a virtual complex impedance collaborative mitigation method based on improved droop, comprising: constructing a hybrid energy storage system model of a DC microgrid, including a bidirectional DC / DC converter for supercapacitors and battery circuits; setting virtual complex impedances matching the frequency domain characteristics of each side in the control circuits of the two circuits respectively; determining a virtual complex impedance adjustment strategy based on the current DC bus voltage fluctuation frequency band of the system to adjust the current shunting ratio of each converter; calculating the reference current peak value of each converter at preset intervals; and adjusting the proportional current limiting protection coefficient of the corresponding converter if the peak value exceeds the corresponding saturation current setting value. The method proposed in this application can effectively reduce the bus voltage deviation and fluctuation coefficient after the equipment reaches saturation, and improve the anti-saturation capability and overall fluctuation mitigation effect of the hybrid energy storage system.

Description

Technical Field

[0001] This application relates to the field of power quality control technology for DC microgrids, and in particular to a method for collaborative management of virtual complex impedance based on improved droop. Background Technology

[0002] With the development of microgrid technology, the development of distributed renewable energy sources such as solar and wind power has become an effective way to solve the energy crisis and environmental pollution. As the core of a controllable sub-network integrating distributed power sources, energy storage systems, and power loads, microgrids have become an important component of future smart power distribution systems. DC microgrids, with their advantages of simple structure, fewer energy conversion cycles, and high efficiency, and the elimination of concerns about frequency offset, phase synchronization, and reactive power compensation, have experienced rapid development in recent years.

[0003] In a multi-stage photovoltaic-storage DC microgrid, the intermittency of photovoltaic output, the randomness of load switching, and the switching disturbances of power electronic converters can all cause bus voltage fluctuations, and these fluctuations exhibit different frequency characteristics: slow changes at low frequencies and rapid changes at high frequencies. Batteries, with their large capacity and low power density, can meet the energy compensation needs of low-frequency fluctuations; while supercapacitors, with their high power density and fast charging and discharging capabilities, can quickly smooth out small-amplitude high-frequency fluctuations. To fully leverage the advantages of both, hybrid energy storage systems have emerged. During sudden load changes, hybrid energy storage systems can promptly perform peak shaving and valley filling, ensuring the reliability of the DC microgrid power supply. Traditional droop control is the main method of distributed control, providing not only "hot-swappable" functionality but also the necessary active damping.

[0004] Extensive research has focused on how to fully leverage the advantages of hybrid energy storage systems to achieve rational power allocation, reduce system operating costs, and extend the lifespan of energy storage components. While single-droop control technology for DC microgrids is relatively mature, it cannot achieve dynamic distribution of fluctuating power among different power supply units, and research on the coordinated control of hybrid energy storage systems remains insufficient. Summary of the Invention

[0005] This application provides a collaborative governance method for virtual complex impedance based on improved droop. To solve the above-mentioned technical problems, this application adopts the following technical methods: This application provides a collaborative governance method for virtual complex impedance based on improved droop, including: A hybrid energy storage system model for a DC microgrid is constructed; the hybrid energy storage system model includes a supercapacitor loop bidirectional BDC converter and a battery loop bidirectional BDC converter. In the control circuits of the bidirectional BDC converters in the battery circuit and the supercapacitor circuit respectively, virtual complex impedances that match the frequency domain characteristics of the energy storage unit on that side are set. Based on the frequency band of the current DC bus voltage fluctuation frequency of the system, the adjustment strategy for the virtual complex impedance is determined; Based on the adjusted virtual complex impedance, the current shunting ratio of each bidirectional BDC converter is determined. At preset intervals, calculate the current peak reference current corresponding to each bidirectional BDC converter; Determine whether the current reference current peak value exceeds the saturation current setting value corresponding to each bidirectional BDC converter; If so, adjust the proportional current limiting protection coefficient of each bidirectional BDC converter.

[0006] Optionally, in the control circuits of the bidirectional BDC converters in the battery circuit and the supercapacitor circuit respectively, a virtual complex impedance matching the frequency domain characteristics of the energy storage unit on that side is set; including: At the supercapacitor control circuit of the supercapacitor-based BDC converter, a second-order low-pass filter-type virtual complex impedance is designed: ; In the formula, This represents the virtual impedance of the supercapacitor control circuit. This is the virtual impedance cutoff frequency of the supercapacitor; k c ξ represents the droop factor of the supercapacitor with respect to the DC component; ξ is the critical damping ratio; s is a complex frequency domain variable; At the battery control circuit of the BDC converter in the battery circuit, a second-order high-pass filter type virtual complex impedance is designed: ; In the formula, This represents the virtual impedance of the battery control circuit. This is the lower limit frequency of the battery's virtual impedance. k b This represents the droop factor of the battery with respect to the DC component. k b2 This represents the droop factor of the battery for high-frequency components.

[0007] Optionally, determining the adjustment strategy for the virtual complex impedance based on the frequency band of the current DC bus voltage fluctuation frequency of the system includes: In the low-frequency band, when the fluctuation frequency of the current DC bus voltage of the system approaches zero, adjust the droop coefficient of the DC component corresponding to the second-order high-pass filter virtual complex impedance in the battery control circuit. In the high-frequency band, when the fluctuation frequency of the current DC bus voltage of the system exceeds the preset threshold, the droop coefficient of the DC component corresponding to the second-order low-pass filter virtual complex impedance in the supercapacitor control loop is adjusted.

[0008] Optionally, the step of calculating the current reference current peak value corresponding to each bidirectional BDC converter at preset time intervals includes: The output port currents of each bidirectional BDC converter in the hybrid energy storage system model were collected respectively. Based on the output port current, the current reference current peak value corresponding to each bidirectional DC / DC converter is calculated at preset intervals.

[0009] Optionally, the step of calculating the current reference current peak value corresponding to each bidirectional BDC converter at preset time intervals based on the output port current includes: Collect the output port voltage of each bidirectional BDC converter; Obtain the reference output port voltage and virtual complex impedance of each bidirectional BDC converter; Based on the output port voltage, the reference output port voltage, the output port current, and the virtual complex impedance, determine the reference current value corresponding to each bidirectional BDC converter; The reference current values ​​corresponding to each bidirectional BDC converter are stored in the corresponding sampling windows. At preset intervals, the current peak value of the reference current corresponding to each bidirectional BDC converter is calculated.

[0010] Optionally, determine whether the current reference current peak value exceeds the saturation current setting value corresponding to each bidirectional BDC converter; if so, adjust the proportional current limiting protection coefficient of each bidirectional BDC converter; including: Determine whether the peak value of the reference current of the supercapacitor exceeds the set value of the supercapacitor saturation current, and simultaneously determine whether the peak value of the reference current of the battery exceeds the set value of the battery saturation current. If the peak value of the reference current of the supercapacitor exceeds the set value of the supercapacitor saturation current, and the peak value of the reference current of the battery does not exceed the set value of the battery saturation current; Based on the amount by which the peak reference current of the supercapacitor exceeds the set value of the supercapacitor's saturation current, the reduction range of the proportional current limiting protection coefficient of the supercapacitor is determined. The amount of current reduction due to the reduction of the proportional current limiting protection coefficient is then adjusted by the proportional-integral controller and added to the reference current command of the bidirectional BDC converter in the battery circuit.

[0011] Optionally, the determination of whether the peak reference current of the supercapacitor exceeds the supercapacitor saturation current setting value and simultaneously determining whether the peak reference current of the battery exceeds the battery saturation current setting value includes the following: If the peak reference current of the battery exceeds the battery saturation current setting value, and the peak reference current of the supercapacitor does not exceed the supercapacitor saturation current setting value, the determination includes: If the peak value of the reference current of the battery exceeds the set value of the battery saturation current, and the peak value of the reference current of the supercapacitor does not exceed the set value of the supercapacitor saturation current; Based on the amount by which the peak reference current of the battery exceeds the set value of the battery saturation current, the reduction range of the proportional current limiting protection coefficient of the battery is determined. The amount of current reduction due to the reduction of the proportional current limiting protection coefficient is then adjusted by the proportional-integral controller and added to the reference current command of the bidirectional BDC converter of the supercapacitor circuit.

[0012] Optionally, the determination of whether the reference current peak of the supercapacitor exceeds the supercapacitor saturation current setting value and simultaneously whether the reference current peak of the battery exceeds the battery saturation current setting value includes the following: If the reference current peak of the battery does not exceed the battery saturation current setting value, and the reference current peak of the supercapacitor does not exceed the supercapacitor saturation current setting value, the determination includes: The reciprocal of the battery saturation current setting value is used as the increment step, which is added to the current proportional current limiting protection coefficient of the battery. The updated value is then compared with 1, and the smaller of the two values ​​is taken as the proportional current limiting protection coefficient of the battery. The reciprocal of the supercapacitor's saturation current setting value is used as the increment step and superimposed on the supercapacitor's current proportional current limiting protection coefficient. The updated value is then compared with 1, and the smaller of the two values ​​is taken as the supercapacitor's proportional current limiting protection coefficient.

[0013] This application has the following beneficial effects: The method proposed in this application can effectively reduce the bus voltage deviation and fluctuation coefficient after the equipment is saturated, thereby improving the anti-saturation capability and overall fluctuation control effect of the hybrid energy storage system. Attached Figure Description

[0014] Figure 1 A flowchart illustrating the improved drooping virtual complex impedance collaborative governance method provided in this application embodiment; Figure 2 A structural diagram of a hybrid energy storage system model provided in an embodiment of this application; Figure 3 The structural diagram of the hybrid energy storage system model provided in the embodiments of this application after adding virtual complex impedance; Figure 4 A flowchart illustrating the adaptive system control strategy for a hybrid energy storage system model provided in this application embodiment; Figure 5 A control block diagram of the adaptive cooperative control strategy for a hybrid energy storage system model provided in this application embodiment; Figure 6 This is a closed-loop output impedance ratio diagram provided in the embodiments of this application; Figure 7 This is a diagram showing the bus voltage variation under saturation conditions of a supercapacitor, provided in an embodiment of this application. Figure 8 The diagram showing the change in inductor current of the energy storage system under saturation conditions provided in the embodiments of this application; Figure 9 This is a graph showing the variation of the supercapacitor current limiting protection coefficient under saturation conditions, provided in an embodiment of this application. Figure 10 This is a diagram showing the bus voltage variation under battery saturation conditions provided in an embodiment of this application. Figure 11 This is a diagram showing the change in inductor current of an energy storage system under battery saturation conditions, provided in an embodiment of this application. Figure 12 The graph shows the variation of the battery current limiting protection coefficient under saturation conditions, as provided in the embodiments of this application. Detailed Implementation

[0015] To facilitate understanding by those skilled in the art, the present application will be further described below in conjunction with embodiments and accompanying drawings. The content mentioned in the embodiments is not intended to limit the present application.

[0016] To solve the above technical problems, such as Figure 1 As shown, this application proposes a collaborative governance method for virtual complex impedance based on improved droop, including: Step S101: Construct a hybrid energy storage system model of a DC microgrid; the hybrid energy storage system model includes a supercapacitor loop bidirectional BDC converter and a battery loop bidirectional BDC converter; like Figure 2 As shown, a hybrid energy storage system model of a DC microgrid is constructed, incorporating both supercapacitors and batteries. The supercapacitors and batteries are connected in parallel and then connected to the DC bus via a Buck / Boost bidirectional DC-DC converter, enabling bidirectional energy flow. The structure of the half-bridge bidirectional DC-DC converter (BDC) used in the energy storage unit is as follows. Figure 2 As shown in the figure. That is to say, this hybrid energy storage system model includes a supercapacitor loop bidirectional BDC converter and a battery loop bidirectional BDC converter.

[0017] in, These are the converter port voltage and port current, respectively. L j , R j These are the BDC inductance value and the inductor's equivalent resistance value, respectively. S j1 and S j2 Complementary switching transistors for the upper and lower bridge arms; Cj For the DC-side output port capacitor; R linej The output-side line impedance; R load This is the equivalent impedance of the DC-side load. v dcj and These are the output port voltages of the BDC converter. j The subscript number indicates either a storage battery (b) or a supercapacitor (c).

[0018] Step S102: In the control circuits of the bidirectional BDC converters in the battery circuit and the supercapacitor circuit respectively, set virtual complex impedances that match the frequency domain characteristics of the energy storage unit on that side. The droop control model is improved by directly acquiring the load-side voltage and incorporating the line impedance from the model. R linej This is converted into the converter output impedance, reducing the impact of line impedance on DC bus voltage deviation and power distribution.

[0019] At the same time, in order to further leverage the advantages of batteries and supercapacitors, such as Figure 3 As shown, second-order high-pass filter type virtual complex impedances and second-order low-pass filter type virtual complex impedances are designed in the control circuits of the bidirectional BDC converters in the battery circuit and supercapacitor circuit, respectively. This reduces the low-frequency impedance of the battery and increases its high-frequency impedance; it also increases the low-frequency impedance of the supercapacitor and decreases its high-frequency impedance, ultimately achieving the effect of frequency division and control of fluctuations. The virtual complex impedance can be expressed as: (1) (2)

[0020] in, and These are the virtual impedances of the battery control circuit and the supercapacitor control circuit, respectively. and These are the lower limit frequency of the virtual impedance of the battery and the cutoff frequency of the virtual impedance of the supercapacitor, respectively. k b This represents the droop factor of the battery with respect to the DC component. k b2 This represents the droop factor of the battery for high-frequency components. A higher droop factor can be added without changing the battery's original constant droop factor. k c This represents the droop factor of a supercapacitor with respect to the DC component. ξ This is the critical damping ratio.

[0021] Complex impedance droop compensation control strategy for hybrid energy storage system model as follows Figure 3As shown. and The droop coefficient is in complex form; the load is equivalent to an equivalent current source containing multiple fluctuating frequency components. d b Indicates the switching transistor S b1 duty cycle, G b1 , G c1 and G b2 , G c2 These represent the voltage transfer function and current transfer function of the energy storage unit converter, respectively, and are PI control elements.

[0022] The following analysis focuses on the complex impedance droop compensation control of the system, taking the branch of the bidirectional BDC converter in the battery circuit as an example. Figure 3 The state equations of the topology shown are established using the state-space averaging method: (3) In the formula, d b Duty cycle of the lower bridge arm switching transistor of the bidirectional BDC converter for the battery circuit; v dcb and These represent the output port voltage and current of the bidirectional BDC converter for the battery circuit, respectively.

[0023] Obtain the small signal model and transform it into s The domains include: (4) In the formula, D For steady-state duty cycle, U dcb yes v dcb steady-state components, I b yes steady-state components; , , , and They are respectively and The small signal component.

[0024] Solving for the transfer function between the variables according to equation (4) yields: (5) In the formula, G uu , Gud , G id , G ii These represent the transfer functions from output voltage disturbance to input voltage disturbance, output voltage disturbance to duty cycle disturbance, inductor current disturbance to duty cycle disturbance, and inductor current disturbance to output current disturbance in a bidirectional BDC converter with a battery circuit, respectively. G iu , Z out These are the open-loop input admittance and open-loop output impedance of the converter, respectively.

[0025] join in Figure 3 The voltage droop control shown derives the closed-loop output impedance of the bidirectional BDC converter in the battery circuit at this time. Z cb_out for: (6) In the formula, G bu The voltage outer loop transfer function, i.e. G b1 ; L lineb and R lineb The line impedance in the model; G ic The closed-loop transfer function of the BDC current loop is: (7) In the formula, G bi The transfer function of the inner current loop is, i.e. G b2 .

[0026] Similarly, the closed-loop output impedance of the bidirectional BDC converter with a supercapacitor circuit can be calculated. Z cc_out The ratio of the closed-loop output impedance of the two converters to the total impedance can be calculated from equation (6): (8) In the formula, k Zb This represents the percentage of the output impedance of the battery circuit. k Zc The output impedance ratio of the supercapacitor circuit; Z c | indicates the magnitude of the impedance.

[0027] Step S103: Based on the frequency band of the current DC bus voltage fluctuation frequency of the system, determine the adjustment strategy for the virtual complex impedance; The closed-loop output impedance ratio directly reflects the battery's and supercapacitor's ability to shunt fluctuations at different frequency bands. This can be achieved by adjusting the droop coefficient. k b , k c , k b2 This allows for frequency division management of fluctuations. In the low-frequency range, the fluctuation frequency of the current DC bus voltage in the system... s When the impedance approaches 0, the output impedance is approximately equal to the droop coefficient impedance. Adjusting the droop coefficient of the DC component corresponding to the second-order high-pass filter virtual complex impedance in the battery control circuit... k b Reducing the proportion of battery output impedance can improve the battery's ability to manage low-frequency fluctuations. In the high-frequency range, when the fluctuation frequency of the current DC bus voltage exceeds a preset threshold, it can be determined that the fluctuation frequency is too high. The battery's virtual impedance is constant, and the supercapacitor's virtual impedance also tends towards 0. Adjusting the droop coefficient of the DC component corresponding to the second-order low-pass filter-type virtual complex impedance in the supercapacitor control circuit... k c This makes the output impedance ratio of the supercapacitor lower, which can improve the supercapacitor's ability to manage high-frequency fluctuations.

[0028] Step S104: Determine the current shunting ratio of each bidirectional BDC converter based on the adjusted virtual complex impedance; After adjusting the droop coefficient of the corresponding bidirectional BDC converter, the corresponding virtual negative impedance will also change accordingly, thus affecting the total impedance of the system. Based on the proportion of the total impedance of each bidirectional BDC converter, the current shunting ratio of each bidirectional BDC converter is determined, and the first distribution of the fluctuation frequency is completed.

[0029] Step S105: Obtain the reference current value corresponding to each bidirectional BDC converter; In extreme situations, using the above-described single-stage allocation method to distribute fluctuating power may result in one energy storage device becoming saturated while another becomes redundant. The output port currents of each bidirectional BDC converter in the hybrid energy storage system model are then collected. and And to collect the output port voltage of each bidirectional BDC converter respectively. v dcc and v dcb Obtain the reference output port voltage of each bidirectional BDC converter. and virtual complex impedance and Based on the output port voltage, reference output port voltage, output port current, and virtual complex impedance, the reference current value corresponding to each bidirectional BDC converter can be obtained. and : (9) In the formula, and These are the reference current values ​​for the supercapacitor and the battery, respectively.

[0030] Step S106: Determine whether the reference current value exceeds the saturation current setting value corresponding to each bidirectional BDC converter; If so, adjust the proportional current limiting protection coefficient of each bidirectional BDC converter.

[0031] The energy storage device itself has an upper limit on output power, corresponding to the saturation current setting value. I max The control circuit is equipped with a limiting circuit to protect against overcurrent. If a single-stage distribution fluctuation causes a device to saturate, its current reference value... Exceeding the saturation current setting value I max The excess current will be cut off and then limited to its maximum value. Because the inductor current waveform is altered, the resulting harmonic components will reduce the effectiveness of fluctuation mitigation.

[0032] Considering the upper limit of the output power of the energy storage system, an adaptive optimization strategy of secondary allocation is proposed for the saturated state, based on the primary allocation of the fluctuation frequency.

[0033] Specifically, when a primary power distribution causes a device to saturate, an adaptive optimization strategy can be used to employ a proportional current-limiting control strategy for energy storage devices whose output current has reached its upper limit. Then, a portion of the fluctuating power is transferred to another redundant device, and the fluctuating power is distributed in a secondary manner: when the battery is close to saturation for low-frequency fluctuating power, the supercapacitor temporarily bears part of the low-frequency fluctuating power; when the supercapacitor is close to saturation for higher-frequency power fluctuations, the battery temporarily bears part of the high-frequency fluctuating power.

[0034] The specific current limiting method is to divide the upper limit of the output current by the calculated reference command current to obtain a coefficient, which is called the proportional current limiting protection coefficient. ε The new command current will be obtained by passing the original reference current and the current limiting protection factor. ε Multiplying them together yields the result. The specific expression is: (10) (11) In the formula, I max Indicates the saturation current setpoint, | I refmax| indicates the maximum absolute value of the current reference current. When the reference current is within the upper limit of the output, the current limiting protection coefficient is 1. Reference current values, including reference current values ​​corresponding to each bidirectional BDC converter. and , To correct the reference current value, this method can reduce the reference current proportionally to obtain a new reference current.

[0035] Accordingly, Figure 4 As shown, the reference current values ​​corresponding to each bidirectional BDC converter are... and As a basis for judgment, the reference current values ​​are stored in the corresponding sampling windows. X b , X c In the middle, every preset time t Calculate the current reference current peak value corresponding to each bidirectional BDC converter in the current array. I b and I c .

[0036] Determining the peak reference current of a supercapacitor I c Whether the supercapacitor's saturation current setting value is exceeded and simultaneously whether the battery's reference current peak value exceeds the battery's saturation current setting value; if the supercapacitor's reference current peak value exceeds the supercapacitor's saturation current setting value, and the battery's reference current peak value does not exceed the battery's saturation current setting value; based on the amount by which the supercapacitor's reference current peak value exceeds the supercapacitor's saturation current setting value, adjust the supercapacitor's proportional current limiting protection coefficient according to formula (10). ε c And the amount of current reduced due to lowering this proportional current limiting protection factor. via proportional-integral controller G c3 After adjustment, it is superimposed on the reference current command of the bidirectional BDC converter in the battery circuit.

[0037] If the reference current peak of the battery I b The current exceeds the battery saturation current setting value, but the reference current peak value of the supercapacitor does not exceed the supercapacitor saturation current setting value; based on the amount by which the reference current peak value of the battery exceeds the battery saturation current setting value, the proportional current limiting protection coefficient of the battery is adjusted downward according to formula (10). ε b And the amount of current reduced due to lowering this proportional current limiting protection factor. via proportional-integral controllerG b3 After adjustment, it is superimposed on the reference current command of the bidirectional BDC converter in the supercapacitor circuit.

[0038] If the peak reference current of the battery does not exceed the battery saturation current setting value, and the peak reference current of the supercapacitor does not exceed the supercapacitor saturation current setting value, the reciprocal of the battery saturation current setting value is used as the increment step, superimposed on the current proportional current limiting protection coefficient of the battery, and the updated value is compared with 1, taking the smaller of the two as the proportional current limiting protection coefficient of the battery; similarly, the reciprocal of the supercapacitor saturation current setting value is used as the increment step, superimposed on the current proportional current limiting protection coefficient of the supercapacitor, and the updated value is compared with 1, taking the smaller of the two as the proportional current limiting protection coefficient of the supercapacitor, as shown in the following formula: (12) Therefore, if the current reference current peak does not exceed the saturation current setting value corresponding to each bidirectional BDC converter, the proportional protection coefficient of each bidirectional BDC converter can be updated using formula (12). Finally, the overall control block diagram of the hybrid energy storage system model proposed in this application can be obtained as follows: Figure 5 As shown.

[0039] Simulation Experiment Building such Figure 3 The hybrid energy storage system topology shown has the virtual impedance cutoff frequencies of the battery and supercapacitor set. droop coefficient k b Take 0.1875, take k c = k b1 =1. The simulation parameters of the converter are as follows: L b =2mH, R b =0.002Ω, C o =500μF, v in =200V, v o =375V; Line impedance L lineb =80μH, R lineb= 8mΩ; The PI parameters of the supercapacitor branch converter are: k pv =1, k iv =0.1, k p i =5,k ii =20; The PI parameters of the battery branch converter are: k pv =0.1, k iv =10, k p i =0.18, k ii =24.15.

[0040] Figure 6 for k b =0.1875, k c =1, k b1 The output impedance ratio is 1. Below 10Hz, the battery's closed-loop output ratio is low, and its shunt capability is strong, so most low-frequency fluctuations are handled by the battery. In the 10Hz to 1000Hz frequency range, the supercapacitor's output impedance ratio is low, so most high-frequency fluctuations are handled by the supercapacitor, and it has a good mitigation effect.

[0041] Verification of supercapacitor saturation operation: The upper limit of battery current output was set to 16A, the upper limit of supercapacitor current output was set to 12A, the initial DC current requirement of the bus was set to 5A, and the fluctuating current frequency was set to 100Hz. At 2s, a fluctuating current of 14A was injected into the bus. At 3s, adaptive control was activated, adjusting the current limiting protection coefficient of the supercapacitor. At 6s, the fluctuating current was increased to 16A, and the current limiting protection coefficient of the supercapacitor was adjusted. ε c The current injection is reduced again, and the fluctuation current injection is cancelled at 8 seconds. The bus voltage change is as follows: Figure 7 As shown, the inductor currents of the battery and supercapacitor during the process are as follows: Figure 8 As shown, the current limiting protection coefficient of the supercapacitor ε c Changes such as Figure 9 As shown.

[0042] During the 2-3 second period, initial frequency allocation is performed based on equivalent impedance. At this time, most of the fluctuating power is borne by the supercapacitor, and the bus voltage fluctuation coefficient is 6.8%. During the 3-6 second period, adaptive cooperative control is activated. The supercapacitor current-limiting protection coefficient begins to decrease, the fluctuating current in the battery output inductor current increases, and the bus voltage fluctuation coefficient decreases to 6.3%, improving the mitigation effect by 7.4%. During the 6-8 second period, due to the increased bus voltage fluctuation, the supercapacitor current-limiting coefficient decreases again, transferring some of the fluctuating power to the battery. At this time, the bus voltage fluctuation coefficient is 6.8%, and the mitigation effect is 21% better than when adaptive control is not activated. These results confirm that this method can quickly adjust the supercapacitor current-limiting protection coefficient and enable the battery to quickly increase its output power, achieving a better high-frequency fluctuation mitigation effect.

[0043] Verification was performed under battery saturation conditions: The initial DC current demand was set to 5A. At 2 seconds, the bus DC current demand was set to 10A. Adaptive control was initiated at 3 seconds. At 6 seconds, the current demand was increased to 13A. At 8 seconds, the DC power demand was zero. The bus voltage change was as follows: Figure 10 As shown, the inductor currents of the battery and supercapacitor are as follows: Figure 11 As shown, the current limiting protection coefficient of the battery during the process ε b Changes such as Figure 12 As shown.

[0044] During the 2-3 second period, the DC current is distributed according to the equivalent impedance, mainly borne by the battery. During this period, the bus voltage deviation is 7.6V. From 3 to 6 seconds, the system initiates adaptive control, increasing the DC current output of the supercapacitor. With the combined effect of the supercapacitor and the battery, the bus voltage deviation decreases to 2.8V, improving the mitigation effect by 76.3%. From 6 to 8 seconds, due to the further increase in DC bus current demand, the battery output saturates, and the supercapacitor rapidly compensates. At this time, the bus voltage shows no significant change compared to before the 6th second, and the mitigation effect is approximately 86% higher than without adaptive control. These results confirm that this method has a good effect on low-frequency power compensation.

[0045] In summary, the method proposed in this application can effectively reduce the bus voltage deviation and fluctuation coefficient after the equipment reaches saturation, thereby improving the anti-saturation capability and overall fluctuation control effect of the hybrid energy storage system.

[0046] In some embodiments, this application also provides a computer system including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the steps in the above-described method embodiments.

[0047] This application also provides a computer-readable storage medium for storing a computer program. This computer-readable storage medium can be applied to a computer device, and the computer program causes the computer device to execute the corresponding processes in the methods described above in the embodiments of this application; for brevity, further details are omitted here.

[0048] The above embodiments are preferred implementations of this application. In addition, this application can be implemented in other ways. Any obvious substitutions without departing from the concept of this technical solution are within the protection scope of this application.

[0049] To facilitate understanding by those skilled in the art of the improvements made by this application compared to the prior art, some of the accompanying drawings and descriptions have been simplified, and for clarity, some other elements have been omitted from this application. Those skilled in the art should realize that these omitted elements may also constitute the content of this application.

Claims

1. A method for collaborative mitigation of virtual complex impedance based on improved droop, characterized in that, include: A hybrid energy storage system model for a DC microgrid is constructed; the hybrid energy storage system model includes a supercapacitor loop bidirectional BDC converter and a battery loop bidirectional BDC converter. In the control circuits of the bidirectional BDC converters in the battery circuit and the supercapacitor circuit respectively, virtual complex impedances that match the frequency domain characteristics of the energy storage unit on that side are set. Based on the frequency band of the current DC bus voltage fluctuation frequency of the system, the adjustment strategy for the virtual complex impedance is determined; Based on the adjusted virtual complex impedance, the current shunting ratio of each bidirectional BDC converter is determined. At preset intervals, calculate the current peak reference current corresponding to each bidirectional BDC converter; Determine whether the current reference current peak value exceeds the saturation current setting value corresponding to each bidirectional BDC converter; If so, adjust the proportional current limiting protection coefficient of each bidirectional BDC converter.

2. The method according to claim 1, characterized in that, The control circuits of the bidirectional BDC converters in the battery circuit and supercapacitor circuit respectively are configured with virtual complex impedances that match the frequency domain characteristics of the energy storage unit on that side; including: At the supercapacitor control circuit of the supercapacitor-based BDC converter, a second-order low-pass filter-type virtual complex impedance is designed: ； In the formula, The virtual impedance of the supercapacitor control circuit; This is the virtual impedance cutoff frequency of the supercapacitor; k c This represents the droop factor of a supercapacitor with respect to the DC component. ξ The critical damping ratio; s For complex frequency domain variables; At the battery control circuit of the BDC converter in the battery circuit, a second-order high-pass filter type virtual complex impedance is designed: ； In the formula, This represents the virtual impedance of the battery control circuit. This is the lower limit frequency of the battery's virtual impedance. k b This represents the droop factor of the battery with respect to the DC component. k b2 This represents the droop factor of the battery for high-frequency components.

3. The method according to claim 1, characterized in that, The method for determining the adjustment strategy for the virtual complex impedance based on the frequency band of the current DC bus voltage fluctuation frequency of the system includes: In the low-frequency band, when the fluctuation frequency of the current DC bus voltage of the system approaches zero, adjust the droop coefficient of the DC component corresponding to the second-order high-pass filter virtual complex impedance in the battery control circuit. In the high-frequency band, when the fluctuation frequency of the current DC bus voltage of the system exceeds the preset threshold, the droop coefficient of the DC component corresponding to the second-order low-pass filter virtual complex impedance in the supercapacitor control loop is adjusted.

4. The method according to claim 1, characterized in that, Before the step of calculating the current reference current peak value corresponding to each bidirectional DC / DC converter at preset time intervals, the following is included: The output port currents of each bidirectional BDC converter in the hybrid energy storage system model were collected respectively. Based on the output port current, the current reference current peak value corresponding to each bidirectional DC / DC converter is calculated at preset intervals.

5. The method according to claim 4, characterized in that, The step of calculating the current reference current peak value corresponding to each bidirectional BDC converter at preset time intervals based on the output port current includes: Collect the output port voltage of each bidirectional BDC converter; Obtain the reference output port voltage and virtual complex impedance of each bidirectional BDC converter; Based on the output port voltage, the reference output port voltage, the output port current, and the virtual complex impedance, determine the reference current value corresponding to each bidirectional BDC converter; The reference current values ​​corresponding to each bidirectional BDC converter are stored in the corresponding sampling windows. At preset intervals, the current peak value of the reference current corresponding to each bidirectional BDC converter is calculated.

6. The method according to claim 3, characterized in that, Determine whether the current reference current peak value exceeds the saturation current setting value corresponding to each bidirectional BDC converter; if so, adjust the proportional current limiting protection coefficient of each bidirectional BDC converter; including: Determine whether the peak value of the reference current of the supercapacitor exceeds the set value of the supercapacitor saturation current, and simultaneously determine whether the peak value of the reference current of the battery exceeds the set value of the battery saturation current. If the peak value of the reference current of the supercapacitor exceeds the set value of the supercapacitor saturation current, and the peak value of the reference current of the battery does not exceed the set value of the battery saturation current; Based on the amount by which the peak reference current of the supercapacitor exceeds the set value of the supercapacitor's saturation current, the reduction range of the proportional current limiting protection coefficient of the supercapacitor is determined. The amount of current reduction due to the reduction of the proportional current limiting protection coefficient is then adjusted by the proportional-integral controller and added to the reference current command of the bidirectional BDC converter in the battery circuit.

7. The method according to claim 6, characterized in that, The determination of whether the reference current peak of the supercapacitor exceeds the supercapacitor saturation current setting value and whether the reference current peak of the battery exceeds the battery saturation current setting value is as follows: If the reference current peak of the battery exceeds the battery saturation current setting value, and the reference current peak of the supercapacitor does not exceed the supercapacitor saturation current setting value, the determination includes: If the peak value of the reference current of the battery exceeds the set value of the battery saturation current, and the peak value of the reference current of the supercapacitor does not exceed the set value of the supercapacitor saturation current; Based on the amount by which the peak reference current of the battery exceeds the set value of the battery saturation current, the reduction range of the proportional current limiting protection coefficient of the battery is determined. The amount of current reduction due to the reduction of the proportional current limiting protection coefficient is then adjusted by the proportional-integral controller and added to the reference current command of the bidirectional BDC converter of the supercapacitor circuit.

8. The method according to claim 7, characterized in that, The determination of whether the reference current peak of the supercapacitor exceeds the supercapacitor saturation current setting value and whether the reference current peak of the battery exceeds the battery saturation current setting value is as follows: If the reference current peak of the battery does not exceed the battery saturation current setting value and the reference current peak of the supercapacitor does not exceed the supercapacitor saturation current setting value, it includes: The reciprocal of the battery saturation current setting value is used as the increment step, which is added to the current proportional current limiting protection coefficient of the battery. The updated value is then compared with 1, and the smaller of the two values ​​is taken as the proportional current limiting protection coefficient of the battery. The reciprocal of the supercapacitor's saturation current setting value is used as the increment step and superimposed on the supercapacitor's current proportional current limiting protection coefficient. The updated value is then compared with 1, and the smaller of the two values ​​is taken as the supercapacitor's proportional current limiting protection coefficient.

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