Pavement photovoltaic three-level layered direct current micro-grid system and power smooth control method thereof

Abstract

The invention discloses a pavement photovoltaic three-level layered direct current micro-grid system and a power smooth control method thereof, a virtual impedance I-V droop control technology is simultaneously applied to a hybrid energy storage control link and an inverter control link, and the implementation difficulty and the calculation pressure of the system are greatly reduced due to the characteristic that communication is not needed. Meanwhile, automatic absorption of steady-state components in road surface photovoltaic power can be achieved, the hybrid energy storage characteristic is exerted, frequency division absorption of high-frequency and low-frequency components in fluctuation power is achieved, the electric energy quality of the system is effectively improved, and smooth control over photovoltaic power fluctuation is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of road surface photovoltaic power generation, and more specifically, to a three-level hierarchical DC microgrid system for road surface photovoltaic power generation and its power smoothing control method. Background Art

[0002] In recent years, countries around the world have been actively promoting the low-carbon transformation of the energy system. The power industry is the main force in carbon emission reduction. In the future, the proportion of new energy power generation will continue to increase. New energy sources represented by wind energy and solar energy will occupy a larger proportion in the power system.

[0003] Road surface photovoltaic power generation technology is an engineering practice application of intelligent roads. Although it can efficiently utilize land resources and achieve better environmental and economic benefits, it also brings new challenges. In the field of road traffic, problems such as the volatility and uncertainty of photovoltaic power generation are further amplified. Compared with the multi-peak problem of traditional photovoltaic caused by cloud shading, the vehicle shadow with strong random and fast-changing characteristics makes the road surface photovoltaic array not only have multi-peak characteristics, but also its P-V characteristic changes rapidly, further increasing the difficulty of implementing maximum power tracking, making the fluctuation characteristics of photovoltaic power more complex, and thus making photovoltaic power smoothing control more difficult.

[0004] Distributed control strategies have better control accuracy and lower implementation and operation difficulties in the field of power smoothing control due to advantages such as no communication and low latency, and are more suitable for the road surface photovoltaic usage scenarios under shadow disturbances. However, the existing distributed control strategies only consider the power distribution inside the hybrid energy storage, and do not fully consider the inverter control link. The inverter control link usually adopts a voltage-current double closed-loop control strategy to deliver all photovoltaic power to the grid by controlling the stability of the DC bus voltage. And the virtual impedance droop control adopted by the energy storage system also takes the DC bus voltage as the control object. When the two work simultaneously, the output of the hybrid energy storage will be interfered by the inverter, and smooth control cannot be achieved. The inverter cannot absorb all the steady-state components of the photovoltaic power either, resulting in incorrect power flow. Summary of the Invention

[0005] One of the objectives of the present invention is to provide a three-level hierarchical DC microgrid system for road surface photovoltaic power generation to achieve smooth control of photovoltaic power fluctuations; the second objective of the present invention is to provide a three-level hierarchical power smoothing control method for road surface photovoltaic power generation.

[0006] To solve the above technical problems, the technical solutions of the present invention are as follows:

[0007] The first aspect of the present invention provides a three-level hierarchical DC microgrid system for road surface photovoltaic power generation, including a DC bus, an energy storage subsystem, a photovoltaic subsystem, and an inverter branch, where:

[0008] One end of the DC bus is connected to the power grid, and the energy storage subsystem, the photovoltaic subsystem, and the inverter branch are respectively connected to the DC bus;

[0009] Both the energy storage subsystem and the inverter branch adopt the virtual impedance droop control strategy.

[0010] Further, the energy storage subsystem includes a battery branch and a supercapacitor branch. The battery branch and the supercapacitor branch are respectively connected to the DC bus, and the battery branch and the supercapacitor branch respectively adopt the virtual impedance droop control strategy.

[0011] Further, the battery branch and the supercapacitor branch are respectively connected to the DC bus through a converter.

[0012] The second aspect of the present invention provides a road surface photovoltaic three - level hierarchical power smoothing control method, which is characterized in that the control method is applied to the road surface photovoltaic three - level hierarchical DC micro - grid system, and the control method includes the following steps:

[0013] Apply the I - V droop control strategy to the converter control link and the inverter control link, and respectively construct a small - signal model of the I - V droop control DC converter based on virtual impedance;

[0014] According to the I - V droop control characteristics, respectively calculate the current relationship between the energy storage subsystem and the inverter branch input to the DC bus, and obtain the second - order current filters of the energy storage subsystem and the inverter branch;

[0015] According to the second - order current filters of the energy storage subsystem and the inverter branch, respectively obtain the transfer function and the equivalent impedance of the small - signal model of the I - V droop control DC converter;

[0016] According to the equivalent impedances of the energy storage subsystem and the inverter branch, calculate the current distribution characteristics of the energy storage subsystem and the inverter branch, obtain the virtual impedance parameters in the energy storage subsystem and the inverter branch, and realize three - level hierarchical power smoothing control.

[0017] Further, the internal transformation relationship of the small - signal model of the I - V droop control DC converter based on virtual impedance is:

[0018]

[0019] In the formula, I o represents the high - voltage - side current, U o represents the high - voltage - side voltage, L represents the filter inductor, C represents the high - voltage - side filter capacitor, s represents the complex variable, D p represents the duty cycle of the converter at steady state, G il_d represents the partial transfer function of the inductor current to the duty cycle, Gil_io represents the local transfer function of the inductor current to the high - voltage - side current, G il_uin represents the local transfer function of the inductor current to the low - voltage - side voltage, G uo_il represents the local transfer function of the high - voltage - side voltage to the inductor current, G uo_io represents the local transfer function of the high - voltage - side voltage to the high - voltage - side current, G uo_uin represents the local transfer function of the high - voltage - side voltage to the low - voltage - side voltage.

[0020] Furthermore, calculate the current relationships of the energy - storage subsystem and the input DC bus of the inverter branch respectively, including:

[0021]

[0022] In the formula, the energy - storage subsystem includes a battery branch and a super - capacitor branch, i o_inv_ref represents the current reference value of the inverter flowing into the DC bus, i o_bat_ref represents the current reference value of the battery injecting into the DC bus, i o_SC_ref represents the current reference value of the super - capacitor injecting into the DC bus, U dc_ref represents the DC - bus voltage reference value, u dc represents the bus voltage, L inv represents the virtual inductor introduced in the inverter droop controller, L bat represents the virtual inductor introduced in the battery droop controller, R bat represents the virtual resistor introduced in the battery droop controller, R SC represents the virtual resistor introduced in the super - capacitor droop controller.

[0023] Furthermore, obtain the second - order current filters of the energy - storage subsystem and the inverter branch, including:

[0024]

[0025] In the formula, i o_inv represents the current of the inverter flowing into the DC bus, i o_bat represents the current of the battery injecting into the DC bus, i o_SC represents the current of the super - capacitor injecting into the DC bus, i o represents the total actual current of each branch flowing into the DC bus.

[0026] Furthermore, the I - V droop - controlled DC - converter small - signal model corresponding to the inverter branch includes a voltage outer loop and a current inner loop. Among them, the outer loop is the bus - voltage droop - control loop, which outputs the inductor - current command value required by the inner loop; the inner loop realizes the converter control by tracking the inductor - current command value, where the closed - loop transfer function T of the inner loop c1 and the closed - loop transfer function T of the outer loopc2 and the equivalent impedance Z of the energy storage branch oc is:

[0027]

[0028]

[0029] In the formula, Z v represents the introduced virtual impedance, and G pi represents the transfer function of the proportional-integral controller.

[0030] Furthermore, it also includes improving the voltage-current double closed-loop control strategy for the small-signal model of the I-V droop control DC converter corresponding to the inverter branch, including:

[0031] Using the I-V droop control structure to replace the voltage outer loop, keeping the current inner loop control structure unchanged, and the control object is still the d-axis current;

[0032] In the dq coordinate system, making the initial position of the d-axis coincide with the A phase to ensure that the q-axis component of the AC voltage is always 0;

[0033] Obtaining the equivalent control block diagram of the inverter under the virtual impedance I-V droop control, and after simplification, the current inner loop transfer function T c_id and the voltage outer loop transfer function T v_udc of the inverter branch and the equivalent impedance Z oc_inv of the inverter branch are:

[0034]

[0035] In the formula, U d is the d-axis component of the grid-side voltage, Z v_inv is the virtual impedance introduced in the inverter droop control, U dc is the DC component of the bus voltage, and K PWM represents the pulse-width modulation (PWM) gain coefficient.

[0036] Furthermore, calculating the current distribution characteristics of the energy storage subsystem and the inverter branch, including:

[0037]

[0038] In the formula, K inv , K bat , K SC are the current distribution characteristics of the inverter branch, the battery branch, and the supercapacitor branch respectively, and Z oc_inv , Z oc_bat , Z oc_SC are the equivalent impedances corresponding to the inverter branch, the battery branch, and the supercapacitor branch respectively.

[0039] Compared with the prior art, the beneficial effects of the technical solution of the present invention are as follows:

[0040] A three-level hierarchical power smoothing control strategy for road surface photovoltaic proposed by the present invention, its feature of not requiring communication greatly reduces the implementation difficulty and the computational pressure of the system. At the same time, this strategy can automatically absorb the steady-state component in the road surface photovoltaic power, and utilize the characteristics of hybrid energy storage to achieve the frequency-divided absorption of the high- and low-frequency components in the fluctuating power, effectively improving the power quality of the system. Description of the Drawings

[0041] Figure 1 Schematic diagram of the DC microgrid structure provided by an embodiment of the present invention;

[0042] Figure 2 Schematic diagram of the flow of a three-level hierarchical power smoothing control method for road surface photovoltaic provided by an embodiment of the present invention;

[0043] Figure 3 System block diagram of a three-level hierarchical smoothing control strategy based on a virtual impedance frequency division mechanism provided by an embodiment of the present invention;

[0044] Figure 4 Schematic diagram of the small-signal model structure of a DC converter with I-V droop control based on virtual impedance provided by an embodiment of the present invention;

[0045] Figure 5 Schematic diagram of the structure of a bidirectional Buck-Boost DC converter provided by an embodiment of the present invention;

[0046] Figure 6 Equivalent control block diagram of an inverter with I-V droop control based on virtual impedance provided by an embodiment of the present invention;

[0047] Figure 7 Bode diagram of the branch impedance characteristic after phase correction provided by an embodiment of the present invention. Detailed Embodiments

[0048] The drawings are only for illustrative purposes and should not be construed as a limitation to this patent;

[0049] To better illustrate this embodiment, some components in the drawings are omitted, enlarged or reduced, and do not represent the dimensions of the actual product;

[0050] For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0051] The technical solution of the present invention will be further described below with reference to the drawings and embodiments.

[0052] Embodiment 1

[0053] An embodiment of the present invention provides a three - level hierarchical DC micro - grid system for road surface photovoltaics, as Figure 1 shown, which includes a DC bus, an energy storage subsystem, a photovoltaic subsystem, and an inverter branch, where:

[0054] One end of the DC bus is connected to the grid, and the energy storage subsystem, the photovoltaic subsystem, and the inverter branch are respectively connected to the DC bus;

[0055] Both the energy storage subsystem and the inverter branch adopt a virtual impedance droop control strategy.

[0056] In this embodiment, the photovoltaic power source and the AC grid are connected through the DC bus. Given the volatility of photovoltaic power, an energy storage device is usually added to maintain the stability of the system power. The energy storage device adopts a hybrid energy storage system composed of a battery and a supercapacitor.

[0057] In a further embodiment, the energy storage subsystem includes a battery branch and a supercapacitor branch. The battery branch and the supercapacitor branch are respectively connected to the DC bus, and the battery branch and the supercapacitor branch respectively adopt a virtual impedance droop control strategy.

[0058] In a further embodiment, the battery branch and the supercapacitor branch are respectively connected to the DC bus through a converter.

[0059] Embodiment 2

[0060] This embodiment provides a three - level hierarchical power smoothing control method for road surface photovoltaics, as Figure 2 shown. The control method is applied to the three - level hierarchical DC micro - grid system for road surface photovoltaics described in Embodiment 1. The control method includes the following steps:

[0061] Apply the I - V droop control strategy to the converter control link and the inverter control link, and respectively construct a small - signal model of the I - V droop control DC converter based on virtual impedance;

[0062] According to the I - V droop control characteristics, respectively calculate the current relationship between the energy storage subsystem and the inverter branch input to the DC bus, and obtain the second - order current filters of the energy storage subsystem and the inverter branch;

[0063] According to the second - order current filters of the energy storage subsystem and the inverter branch, respectively obtain the transfer function and equivalent impedance of the small - signal model of the I - V droop control DC converter;

[0064] According to the equivalent impedances of the energy storage subsystem and the inverter branch, calculate the current distribution characteristics of the energy storage subsystem and the inverter branch, obtain the virtual impedance parameters in the energy storage subsystem and the inverter branch, and realize the three-level hierarchical power smoothing control.

[0065] Embodiment 3

[0066] On the basis of Embodiment 2, this embodiment further discloses a three-level hierarchical smoothing control strategy based on the virtual impedance frequency division mechanism, specifically:

[0067] Figure 3 It is a system block diagram of a three-level hierarchical smoothing control strategy based on the virtual impedance frequency division mechanism, in which the battery, the supercapacitor, and the inverter all adopt virtual impedance droop control. By introducing appropriate virtual impedances, the impedance characteristics of the three are adjusted to achieve three-level hierarchical control.

[0068] In a further embodiment, as Figure 3 and Figure 4 shown, the internal transformation relationship of the small-signal model of the I-V droop control DC converter based on virtual impedance is:

[0069]

[0070] In the formula, I o represents the high-side current, U o represents the high-side voltage, L represents the filter inductor, C represents the high-side filter capacitor, s represents the complex variable, D p represents the duty cycle of the converter at steady state, G il_d represents the local transfer function of the inductor current to the duty cycle, G il_io represents the local transfer function of the inductor current to the high-side current, G il_uin represents the local transfer function of the inductor current to the low-side voltage, G uo_il represents the local transfer function of the high-side voltage to the inductor current, G uo_io represents the local transfer function of the high-side voltage to the high-side current, G uo_uin represents the local transfer function of the high-side voltage to the low-side voltage

[0071] In a further embodiment, calculate the current relationship of the input DC bus of the energy storage subsystem and the inverter branch respectively, including:

[0072]

[0073] In the formula, the energy storage subsystem includes a battery branch and a supercapacitor branch, i o_inv_ref represents the reference value of the current flowing from the inverter into the DC bus, i o_bat_ref represents the reference value of the current injected by the battery into the DC bus, io_SC_ref represents the current reference value of the supercapacitor injected into the DC bus, U dc_ref represents the DC bus voltage reference value, u dc represents the bus voltage, L inv represents the virtual inductor introduced in the inverter droop controller, L bat represents the virtual inductor introduced in the battery droop controller, R bat represents the virtual resistance introduced in the battery droop controller, R SC represents the virtual resistance introduced in the supercapacitor droop controller.

[0074] In a further embodiment, a second-order current filter for the energy storage subsystem and the inverter branch is obtained, including:

[0075]

[0076] where, i o_inv represents the current of the inverter flowing into the DC bus, i o_bat represents the current of the battery injected into the DC bus, i o_SC represents the current of the supercapacitor injected into the DC bus, i o represents the total actual current of each branch flowing into the DC bus.

[0077] In a further embodiment, before obtaining the transfer functions of the voltage outer loop and the current inner loop and the equivalent impedance respectively, the following steps are further included:

[0078] Draw a small-signal model of the I-V droop control DC converter based on the virtual impedance, as Figure 3 shown.

[0079] In a further embodiment, the I-V droop control DC converter small-signal model corresponding to the inverter branch includes a voltage outer loop and a current inner loop, where the outer loop is a bus voltage droop control loop, and outputs the inductor current command value required by the inner loop; the inner loop realizes the converter control by tracking the inductor current command value, where the closed-loop transfer function T c1 of the inner loop and the closed-loop transfer function T c2 of the outer loop and the equivalent impedance Z oc of the energy storage branch are:

[0080]

[0081] where, Z v represents the introduced virtual impedance, G pi represents the transfer function of the proportional-integral controller.

[0082] In a further embodiment, it further includes improving the voltage-current double closed-loop control strategy for the small-signal model of the I-V droop control DC converter corresponding to the inverter branch, including:

[0083] Replace the voltage outer loop with the I-V droop control structure, keep the current inner loop control structure unchanged, and the control object is still the d-axis current;

[0084] In the dq coordinate system, make the initial position of the d-axis coincide with the A phase to ensure that the q-axis component of the AC voltage is always 0;

[0085] Obtain the equivalent control block diagram of the inverter under the virtual impedance I-V droop control. After simplification, the current inner loop transfer function T c_id and the voltage outer loop transfer function T v_udc as well as the equivalent impedance Z oc_inv of the inverter branch are:

[0086]

[0087] In the formula, U d is the d-axis component of the grid-side voltage, Z v_inv is the virtual impedance introduced in the inverter droop control, U dc is the DC component of the bus voltage, and K PWM represents the pulse width modulation gain coefficient.

[0088] In a further embodiment, the impedance characteristics of the battery branch and the supercapacitor branch can be calculated by the above calculation method of the equivalent impedance of the inverter branch to obtain the equivalent impedances of the battery branch and the supercapacitor branch.

[0089] Analyze the impedance characteristics of the battery branch, the supercapacitor branch and the inverter branch, as Figure 6 shown. In the ultra-low frequency region, the parallel impedance characteristic Z sum is dominated by the inverter branch impedance Z oc_inv ; in the mid-low frequency region, the parallel impedance characteristic Z sum is dominated by the battery branch impedance Z oc_bat ; in the high frequency region, the parallel impedance characteristic Z sum is dominated by the supercapacitor branch impedance Z oc_SC Taking the dominant role means that the bus current in this frequency range will mainly flow to this branch;

[0090] In a further embodiment, calculating the current distribution characteristics of the energy storage subsystem and the inverter branch includes:

[0091]

[0092] In the formula, Kinv 、K bat 、K SC are the current distribution characteristics of the inverter branch, the battery branch, and the supercapacitor branch respectively. Z oc_inv 、Z oc_bat 、Z oc_SC are the equivalent impedances corresponding to the inverter branch, the battery branch, and the supercapacitor branch respectively.

[0093] The control variable method is used to analyze each virtual impedance parameter in the droop controller in turn. Through the continuous change of the parameters, the influence trend of the parameter on the current distribution characteristics of each branch is explored, and the following conclusions are obtained:

[0094] When discussing the influence of the virtual inductor L inv of the inverter droop controller on the current frequency division characteristics, as the virtual inductor L inv increases, more low-frequency current transfers from the inverter branch to the battery branch, which will make the power of the inverter branch smoother, while the battery branch has to bear more low-frequency components;

[0095] When discussing the influence of the virtual inductor L bat and the virtual resistor R bat of the battery droop controller on the current distribution characteristics, as the virtual inductor L bat increases, more medium and low-frequency components are gradually included in the absorption range of the supercapacitor branch. As the virtual resistor R bat increases, more and more medium and low-frequency components transfer from the battery branch to the inverter branch;

[0096] When discussing the influence of the virtual resistor R SC of the supercapacitor droop controller on the current distribution characteristics, the virtual resistor R SC acts on both side boundaries of the high-frequency interval at the same time. As its virtual resistance value R SC increases, both side boundaries of the high-frequency interval where the supercapacitor branch plays a dominant role are shrinking, and the absorption range of this branch for high-frequency components is gradually decreasing.

[0097] A three-level hierarchical power smoothing control strategy for road surface photovoltaic proposed in the embodiment of the present invention applies the virtual impedance droop control technology to a two-stage road surface photovoltaic power generation system and combines it with a hybrid energy storage system. By constructing the impedance characteristics of the system, the frequency division absorption characteristics of three parallel branches are realized. Without communication, the automatic absorption of the steady-state component in the road surface photovoltaic power can be achieved, and the characteristics of the hybrid energy storage can be utilized to realize the frequency division absorption of the high and low-frequency components in the fluctuating power.

[0098] The same or similar reference numerals correspond to the same or similar components;

[0099] The terms used to describe the positional relationship in the drawings are for illustrative purposes only and should not be construed as a limitation of this patent;

[0100] Obviously, the above embodiments of the present invention are merely examples given to clearly illustrate the present invention and are not limitations on the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation manners here. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the claims of the present invention.

Claims

1. A three - level hierarchical DC micro - grid system for road - surface photovoltaic, characterized in that, It includes a DC bus, an energy storage subsystem, a photovoltaic subsystem, and an inverter branch, where: One end of the DC bus is connected to the power grid, and the energy storage subsystem, the photovoltaic subsystem, and the inverter branch are respectively connected to the DC bus; Both the energy storage subsystem and the inverter branch adopt a virtual impedance droop control strategy.

2. The road surface photovoltaic three - level hierarchical DC microgrid system according to claim 1, wherein, The energy storage subsystem includes a battery branch and a supercapacitor branch. The battery branch and the supercapacitor branch are respectively connected to the DC bus, and the battery branch and the supercapacitor branch respectively adopt a virtual impedance droop control strategy.

3. The pavement photovoltaic three - level hierarchical DC micro - grid system according to claim 2, characterized in that, The battery branch and the supercapacitor branch are respectively connected to the DC bus through a converter.

4. A three - level hierarchical power smoothing control method for road surface photovoltaic systems, characterized in that, The control method is applied to the road surface photovoltaic three-level hierarchical DC microgrid system according to any one of claims 1 to 3. The control method includes the following steps: Apply the I-V droop control strategy to the converter control link and the inverter control link, and respectively construct a small-signal model of the I-V droop control DC converter based on virtual impedance; According to the I-V droop control characteristics, calculate the current relationship between the energy storage subsystem and the inverter branch input to the DC bus respectively, and obtain the second-order current filters of the energy storage subsystem and the inverter branch; According to the second-order current filters of the energy storage subsystem and the inverter branch, obtain the transfer function and equivalent impedance of the small-signal model of the I-V droop control DC converter respectively; According to the equivalent impedances of the energy storage subsystem and the inverter branch, calculate the current distribution characteristics of the energy storage subsystem and the inverter branch, obtain the virtual impedance parameters in the energy storage subsystem and the inverter branch, and realize three-level hierarchical power smoothing control.

5. The method for three - level hierarchical power smoothing control of road surface photovoltaic according to claim 4, wherein The internal transformation relationship of the small-signal model of the I-V droop control DC converter based on virtual impedance is: where, I o represents the high - voltage - side current, U o represents the high - voltage - side voltage, L represents the filter inductor, C represents the high - voltage - side filter capacitor, s represents the complex variable, D p represents the duty cycle of the converter in the steady state, G il_d represents the local transfer function of the inductor current to the duty cycle, G il_io represents the local transfer function of the inductor current to the high - voltage - side current, G il_uin represents the local transfer function of the inductor current to the low - voltage - side voltage, G uo_il represents the local transfer function of the high - voltage - side voltage to the inductor current, G uo_io represents the local transfer function of the high - voltage - side voltage to the high - voltage - side current, G uo_uin represents the local transfer function of the high - voltage - side voltage to the low - voltage - side voltage.

6. The method for three - level hierarchical power smoothing control of road surface photovoltaic according to claim 5, wherein Calculate the current relationship between the energy storage subsystem and the inverter branch input to the DC bus respectively, including: In the formula, the energy storage subsystem includes a battery branch and a supercapacitor branch, i o_inv_ref represents the current reference value of the inverter flowing into the DC bus, i o_bat_ref represents the current reference value of the battery injecting into the DC bus, i o_SC_ref represents the current reference value of the supercapacitor injecting into the DC bus, U dc_ref represents the DC bus voltage reference value, u dc represents the bus voltage, L inv represents the virtual inductor introduced in the inverter droop controller, L bat represents the virtual inductor introduced in the battery droop controller, R bat represents the virtual resistance introduced in the battery droop controller, R SC represents the virtual resistance introduced in the supercapacitor droop controller.

7. The method for three - level hierarchical power smoothing control of road surface photovoltaic according to claim 6, characterized in that, Obtain the second-order current filters of the energy storage subsystem and the inverter branch, including: Where, i o_inv represents the current flowing from the inverter into the DC bus, i o_bat represents the current injected from the battery into the DC bus, i o_SC represents the current injected from the super capacitor into the DC bus, i o represents the total actual current flowing from each branch into the DC bus.

8. The method for three - level hierarchical power smoothing control of road surface photovoltaic according to claim 7, wherein, The small-signal model of the I-V droop control DC converter corresponding to the inverter branch includes a voltage outer loop and a current inner loop. The outer loop is the bus voltage droop control loop, which outputs the inductor current command value required by the inner loop. The inner loop realizes the converter control by tracking the inductor current command value, where the closed-loop transfer function T c1 of the inner loop and the closed-loop transfer function T c2 of the outer loop, as well as the equivalent impedance Z oc of the energy storage branch are as follows: where Z v represents the introduced virtual impedance, and G pi represents the transfer function of the proportional-integral controller.

9. The method for three - level hierarchical power smoothing control of road surface photovoltaic according to claim 8, wherein, It also includes improving the voltage-current double closed-loop control strategy of the small-signal model of the I-V droop control DC converter corresponding to the inverter branch, including: Use the I-V droop control structure to replace the voltage outer loop, keep the current inner loop control structure unchanged, and the control object is still the d-axis current; In the dq coordinate system, make the initial position of the d-axis coincide with the A phase to ensure that the q-axis component of the AC voltage is always 0; The equivalent control block diagram of the inverter under virtual impedance I-V droop control is obtained. After simplification, the current inner-loop transfer function T of the inverter branch can be obtained. c_id And the voltage outer-loop transfer function T v_udc As well as the equivalent impedance Z of the inverter branch oc_inv Are as follows: where, U d is the d-axis component of the grid-side voltage, Z v_inv is the virtual impedance introduced in the droop control of the inverter, U dc is the DC component of the bus voltage, and K PWM represents the pulse-width modulation gain coefficient.

10. The method for controlling the power smoothing of a three-level pavement photovoltaic hierarchical layer according to claim 9, characterized in that, Calculate the current distribution characteristics of the energy storage subsystem and the inverter branch, including: Wherein, K inv , K bat , K SC are respectively the current distribution characteristics of the inverter branch, the battery branch, and the supercapacitor branch, and Z oc_inv , Z oc_bat , Z oc_SC are respectively the equivalent impedances corresponding to the inverter branch, the battery branch, and the supercapacitor branch.

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