MPPT (Maximum Power Point Tracking) and frequency support control method of multi-port optical storage power generation system

Abstract

The invention discloses an MPPT and frequency support control method for a multi-port optical storage power generation system, and the method comprises the steps: firstly, building a virtual power generation synchronous machine model, and describing the power and frequency of an AC side; then, the reference voltage of the inverter is calculated through a cascade proportional-integral controller, and the output power of the energy storage port is determined according to the power compensation value of the power buffer; then, through unified power feedback control, control over photovoltaic array MPPT and frequency adjustment is achieved at the same time; and finally, six duty ratios are generated by using a zero vector modulation method, and an inverter switch is driven, so that the on-off of each phase of bridge arm is controlled.

Description

Technical Field

[0001] The present invention belongs to the technical field of integrated photovoltaic and energy storage power generation, and more specifically, relates to a MPPT and frequency support control method for a multi-port photovoltaic and energy storage power generation system. Background Art

[0002] Photovoltaic power generation technology has become an important solution to alleviate energy crisis and environmental pollution problems due to its advantages of cleanness, sustainability and low cost. Since the efficiency of a photovoltaic power generation system is affected by various uncontrollable natural factors, it is usually necessary to supplement with an energy storage unit on the basis of a maximum power point tracking algorithm to ensure the stability and maximization of photovoltaic output power. Integrating a photovoltaic array and an energy storage unit in an integrated photovoltaic and energy storage power generation system by using a single-stage multi-port inverter helps to improve the power density and energy conversion efficiency of the system and effectively reduce the system cost.

[0003] Since the integrated photovoltaic and energy storage power generation system lacks the mechanical inertia of a traditional synchronous generator, when the AC power grid undergoes load changes or sudden disturbances, the system cannot respond quickly and provide the necessary frequency stabilizing effect, resulting in increased system frequency fluctuations and further increasing the risk of instability of the power generation system. Although the introduction of virtual synchronous generator technology can simulate the inertia characteristics of a synchronous generator and provide the necessary frequency support for the integrated photovoltaic and energy storage power generation system, it usually requires sacrificing the maximum power point tracking efficiency of the photovoltaic array. This makes it difficult for the system to achieve the tracking and stable output of the maximum power point of the photovoltaic array while providing frequency support, thus restricting the overall efficiency of the power generation system.

[0004] Existing control strategies usually design control strategies for a single converter in a two-stage topology to achieve maximum photovoltaic power point tracking and AC power grid frequency support. However, these strategies cannot be directly applied to a single-stage multi-port inverter with multiple input ports. Although multi-port inverters provide more degrees of freedom compared to traditional power converters, no scheme applicable to single-stage multi-port inverters has been proposed that can simultaneously achieve photovoltaic MPPT (Maximum PowerPoint Tracking) and frequency regulation control. Therefore, there is an urgent need to design an effective unified coordination control method for it. Summary of the Invention

[0005] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a MPPT and frequency support control method for a multi-port photovoltaic and energy storage power generation system. By designing two independent power buffers to conduct unified coordination control on the multi-port photovoltaic and energy storage power generation system, it can simultaneously achieve maximum power point tracking of the photovoltaic array on the DC side and frequency support of the AC side power grid on the premise of ensuring system stability, thereby effectively improving the energy utilization efficiency and operation stability of the integrated photovoltaic and energy storage power generation system.

[0006] To achieve the above-mentioned invention objective, a MPPT and frequency support control method for a multi-port photovoltaic and energy storage power generation system of the present invention is characterized by including the following steps:

[0007] (1) Collect the three-phase current i 2x (t) and three-phase voltage u 2x (t), the voltage and current V PV (t), i PV (t) of the photovoltaic array, and the voltage V ESS (t) and actual output power P ESS (t) of the energy storage port, where x = a, b, c represents the three phases of the power grid;

[0008] (2) Obtain the reference voltage vector V ref (t) on the output side of the single-stage multi-port inverter;

[0009] (3) Obtain the power compensation value ΔP1(s) of the photovoltaic MPPT power buffer;

[0010] (4) Obtain the power compensation value ΔP2(s) of the frequency support power buffer;

[0011] (5) Obtain the total power P ESSref (s) to be compensated at the energy storage port = ΔP1(s) + ΔP2(s);

[0012] (6) According to the reference voltage vector V ref (t) and the total power P ESS ref(s) to be compensated, use the power distribution method of the multi-port photovoltaic and energy storage hybrid power generation system based on zero vector regulation to calculate the duty cycles d 1x and d 2x of the first and second switching tubes on each phase leg, where x = a, b, c represents the three-phase legs of the single-stage multi-port inverter;

[0013] (7) Within one switching period, compare the six duty cycles d 1a , d 2a , d 1b , d 2b , d 1c , d 2c with the amplitude of the triangular carrier wave respectively to generate six driving signals G a1 , G a2 , G b1 , G b2 , G c1 , G c2 for driving the single-stage multi-port inverter, and then use the driving signal G x1 to control the switching tube S1x , the driving signal G x1 's complementary signal controls the switching transistor The driving signal G x2 controls the switching transistor S 2x , the driving signal G x2 's complementary signal controls the switching transistor Among them, S 1x , S 2x , are respectively the first switching transistor, the second switching transistor, the third switching transistor, and the fourth switching transistor corresponding to each bridge arm.

[0014] The invention purpose of the present invention is realized as follows:

[0015] A MPPT and frequency support control method for a multi-port photovoltaic and energy storage power generation system of the present invention. First, a virtual generator synchronous machine model is established to describe the AC-side power and frequency. Then, the reference voltage of the inverter is calculated through a cascaded proportional-integral controller, and the output power of the energy storage port is determined according to the power compensation value of the power buffer. Through unified power feedback control, the control of MPPT of the photovoltaic array and frequency regulation is achieved simultaneously. Finally, six duty ratios are generated by using the zero-vector modulation method to drive the inverter switches, thereby controlling the on-off of each phase bridge arm.

[0016] At the same time, a MPPT and frequency support control method for a multi-port photovoltaic and energy storage power generation system of the present invention also has the following beneficial effects:

[0017] (1), The present invention can be effectively applied to the photovoltaic and energy storage combined power generation system under the condition of variable DC port voltage of the multi-port inverter. Even when the DC link voltage is unbalanced and time-varying, the fluctuation of the grid frequency change rate under disturbance can still be effectively reduced.

[0018] (2), The present invention directly integrates the photovoltaic array and the energy storage port and designs a unified coordinated control strategy for them, avoiding the use of an additional DC-DC converter. Compared with the traditional two-stage scheme, the system efficiency is increased by 2% on the basis of ensuring the stable operation of the system;

[0019] (3), The present invention proposes a MPPT and frequency support coordinated control method for a multi-port photovoltaic and energy storage combined power generation system. While achieving accurate tracking of the maximum power point of the photovoltaic array, this method can provide reliable frequency support for the AC-side power grid. Brief Description of the Drawings

[0021] Figure 1 is the structure diagram of a photovoltaic and energy storage combined power generation system connected by a single-stage multi-port inverter;

[0022] Figure 2It is a control block diagram of a multi-port photovoltaic energy storage combined power generation system frequency support method based on unified coordinated control;

[0023] Figure 3 It is a flowchart of the MPPT and frequency support control method of a multi-port photovoltaic energy storage power generation system of the present invention;

[0024] Figure 4 It is a schematic diagram of the steady-state waveform of photovoltaic maximum power point tracking realized by the multi-port photovoltaic energy storage combined power generation system according to the present invention under different illumination amplitudes;

[0025] Figure 5 It is a schematic diagram of the dynamic waveform of photovoltaic maximum power point tracking of the multi-port photovoltaic energy storage combined power generation system according to the present invention under variable illumination amplitude conditions;

[0026] Figure 6 It is a schematic diagram of the dynamic waveform of photovoltaic maximum power point tracking of the multi-port photovoltaic energy storage combined power generation system according to the present invention under variable AC active power conditions;

[0027] Figure 7 It is a comparison waveform diagram between a traditional photovoltaic energy storage combined power generation system without frequency support function and the one realized according to the present invention under different virtual inertia conditions;

[0028] Figure 8 It is a comparison diagram of the power generation system efficiency between a photovoltaic energy storage combined power generation system based on a two-stage DC coupling topology and the one realized according to the present invention under different illumination amplitude conditions. Specific Embodiments

[0029] The following describes the specific embodiments of the present invention with reference to the accompanying drawings so that those skilled in the art can better understand the present invention. It should be particularly noted that in the following description, when the detailed description of known functions and designs may dilute the main content of the present invention, these descriptions will be omitted here.

[0030] Embodiment

[0031] Figure 1 It is a structural diagram of a photovoltaic energy storage combined power generation system connected by a single-stage multi-port inverter.

[0032] In this embodiment, as Figure 1 shown, the multi-port photovoltaic energy storage combined power generation system includes: a first DC voltage source 1, a second DC voltage source 2, DC side capacitors C1, C23, a diode 4, and a single-stage multi-port inverter 5;

[0033] The single-stage multi-port inverter includes two independent DC voltage sources, two DC side capacitors, and three bridge arms, where the two DC voltage sources are respectively denoted as the first voltage source v h , the second voltage source v l; The two DC-side capacitors are denoted as the first DC capacitor C1 and the second DC capacitor C2; the three bridge arms are respectively denoted as the first bridge arm, the second bridge arm, and the third bridge arm; each bridge arm includes four switching tubes and two diodes, and the two center switching tubes and the two diode output terminals are all connected to the neutral point of the DC link. Among them, the first bridge arm includes the first switching tube S 1a 、the second switching tube S 2a 、the third switching tube and the fourth switching tube The second switching tube S 2a 、the third switching tube are the center switching tubes of the first bridge arm; the second bridge arm includes the fifth switching tube S 1b 、the sixth switching tube S 2b 、the seventh switching tube and the eighth switching tube The sixth switching tube S 2b 、the seventh switching tube are the center switching tubes of the second bridge arm; the third bridge arm includes the ninth switching tube S 1c 、the tenth switching tube S 2c 、the eleventh switching tube and the twelfth switching tube The tenth switching tube S 2c 、the eleventh switching tube are the center switching tubes of the third bridge arm;

[0034] One plate of the first DC capacitor C1, the collector of the first switching tube, the collector of the fifth switching tube, and the collector of the ninth switching tube are all connected to the positive terminal of the first DC voltage source;

[0035] The other plate of the first DC capacitor C1, one plate of the second DC capacitor C2, the midpoint of the clamping diodes of the first bridge arm, the midpoint of the clamping diodes of the second bridge arm, and the midpoint of the clamping diodes of the third bridge arm are all connected to the positive terminal of the second DC voltage source;;

[0036] The diode is connected between the positive terminal of the photovoltaic array and the collectors of the first switching tube, the fifth switching tube, and the ninth switching tube;

[0037] It should be noted that the first DC power supply and the second DC voltage source are used to provide direct current to the system. As Figure 1 shown, the single-stage multi-port inverter 5 provides a direct power flow from the DC side to the AC side, and has the advantages of small volume and low cost. The diode 4 is used to prevent the reverse flow of energy in the circuit and protect other devices from damage. The DC capacitors C1 and C2 are used to stabilize the DC-side voltage and absorb high-frequency harmonics. For the first bridge arm to the third bridge arm, 1 indicates that the switching tubes of the bridge arm are conducting, and 0 indicates that the switching tubes of the bridge arm are disconnected.

[0038] Control block diagram of a frequency support method for a multi-port photovoltaic and energy storage combined power generation system based on unified coordinated control, as Figure 2 shown. Next, we will combine Figure 2 to elaborate on the present invention in detail, as Figure 3 shown, which specifically includes the following steps:

[0039] (1), Collect the three-phase current i 2x (t) and three-phase voltage u 2x (t) on the grid side of the multi-port photovoltaic and energy storage combined power generation system, the voltage and current V PV (t), i PV (t) of the photovoltaic array, and the voltage V ESS (t) and actual output power P ESS (t) of the energy storage port, where x = a, b, c represent the three phases of the grid;

[0040] (2), Obtain the reference voltage vector V ref (t) on the output side of the multi-port photovoltaic and energy storage inverter;

[0041] (2.1), Given the reference voltage amplitude V n (t) and frequency ω n (t), reference active power P ref (t) and reactive power Q ref (t) that are expected to be obtained on the AC grid side of the photovoltaic and energy storage power generation system;

[0042] (2.2), Input the three-phase current i 2x (t) and three-phase voltage u 2x (t) on the grid side into the power calculation module to obtain the actual active power P(t) and reactive power Q(t) on the grid side of the photovoltaic and energy storage combined power generation system;

[0043] (2.3), Obtain the reference active power P in (t) and the amplitude E gref (t) of the grid-side reference voltage vector according to the virtual synchronous generator control equation with droop characteristics;

[0044]

[0045] Among them, k ω , k q are the given droop control coefficients, k ω (ω m (t) - ω n (t)) = ΔP droop (t) is the active power deviation of the virtual synchronous generator caused by the frequency deviation, ω m (t) is the angular frequency of the virtual synchronous generator, and the initial value is the fundamental frequency of the grid-side AC voltage.

[0046] (2.4) Obtain the angular frequency ω of the virtual synchronous generator according to the rotor motion equation of the synchronous generator m (t):

[0047]

[0048] where J is the virtual inertia coefficient, which alleviates frequency fluctuations and delays frequency deviation by increasing the inertia of the system, enabling the system to have more time for regulation; D is the virtual damping coefficient, which is mainly used to control the oscillation behavior and dynamic stability of the system. Both need to be given according to the actual requirements of the photovoltaic and energy storage combined power generation system.

[0049] (2.5) Integrate the angular frequency ω of the virtual synchronous generator m (t) to obtain the phase angle θ of the grid-side reference voltage vector gref (t).

[0050] (2.6) Input the three-phase current i 2x (t) and the three-phase voltage u 2x (t), the amplitude Egref(t) and the phase angle θ of the reference voltage vector gref (t) into the cascaded proportional-integral controller to obtain the reference voltage vector V of the output side of the single-stage multi-port inverter ref (t).

[0051] (3) Calculate the power compensation value ΔP1(s) of the photovoltaic MPPT power buffer;

[0052] (3.1) Use the perturbation and observation method to obtain the output voltage and current V of the photovoltaic array at the maximum power point PVref (t), i PVref (t), and the reference output power of the photovoltaic array can be calculated as follows:

[0053] P PVref (t) = V PVref (t)i PVref (t) (3)

[0054] (3.2) Calculate the difference between the reference active power on the grid side and the reference output power of the photovoltaic array as the power compensation value that the photovoltaic power buffer needs to provide to achieve maximum power point tracking of the photovoltaic:

[0055] ΔP1(t) = P ref (t) - P PVref (t) (4)

[0056] (3.3) Perform Laplace transformation on the power compensation value ΔP1(t) of the photovoltaic MPPT power buffer to obtain the representation ΔP1(s) in the s domain.

[0057] (4) Calculate the power compensation value ΔP2(s) of the frequency support power buffer;

[0058] (4.1) Perform Laplace transform on the rotor motion equation of the virtual synchronous generator shown in Equation (5) to obtain its expression in the s-domain, as shown in Equation (6):

[0059]

[0060] ΔP VSG (s) = (D + Jω n (s)s)Δω(s) (6)

[0061] Among them, ΔP VSG (s) = P in (s) - P(s) is the active power deviation of the virtual synchronous generator caused by virtual inertia and damping, and Δω(s) = ω m (s) - ω n (s) is the angular frequency change;

[0062] (4.2) Obtain ΔP VSG (s) through the following proportional derivative controller;

[0063]

[0064] Among them, k p1 and k d are the proportional coefficient and derivative coefficient of the proportional derivative controller respectively.

[0065] (4.3) Calculate ΔP droop (s) according to the droop control characteristic equation;

[0066] ΔP droop (s) = k ω Δω(s) (9)

[0067] Among them, ΔP droop represents the value of the AC active power drop caused by the frequency deviation.

[0068] (4.4) Combine the power deviation ΔP VSG (s) caused by virtual inertia / damping and the power deviation ΔP droop (s) caused by frequency deviation to calculate the power compensation value ΔP2(s) of the frequency support power buffer:

[0069] ΔP2(s) = -ΔP VSG (s) - ΔP droop (s) (10)

[0070] (5) Sum the power compensation value of the photovoltaic MPPT power buffer and the power compensation values ΔP1(s) and ΔP2(s) of the frequency support buffer to obtain the total power P ESSref (s) to be compensated at the energy storage port;

[0071] P ESSref (s) = ΔP1(s) + ΔP2(s) (11)

[0072] Among them, ΔP1(s) is the power compensation value required to achieve the maximum power point tracking of the photovoltaic, and ΔP2(s) is the power compensation value required to achieve the AC side frequency support. The energy storage port serves as a power buffer source, providing power compensation for the maximum power point tracking and necessary power support for the frequency support, thus realizing the unified and coordinated control between the two.

[0073] (6) Output the duty cycles d 1a , d 2a , d 1b , d 2b , d 1c , d 2c ;

[0074] (6.1) Calculate the difference between the total power required to be compensated at the energy storage port and the actual output power, design a proportional-integral controller based on the difference, and obtain the zero vector regulation parameter k;

[0075] k = G PI (s)(P ESSref (s) - P ESS (s)) (12)

[0076]

[0077] Among them, P ESS (s) is the representation of P ESS (t) in the s domain after Laplace transformation, and k p2 and k i are the proportional parameter and integral parameter of the proportional-integral controller respectively;

[0078] (6.2) Determine the sector H where it is located according to the phase angle of the reference voltage vector V ref (t);

[0079]

[0080] Among them, the six non-zero vectors v j (j = 1, 2,..., 6) that make up the six sectors can be calculated by the following formula:

[0081]

[0082] (6.3), Substitute the reference voltage vector V ref (t) to calculate the dwell times T1, T2, and T0 of two adjacent non-zero vectors V1, V2 and the zero vector V0 that make up sector H within one switching period:

[0083]

[0084] where, T s is the switching period, and T1, T2, and T0 are the dwell times corresponding to V1, V2, and V0 respectively;

[0085] (6.4), Substitute the zero vector adjustment parameter k to obtain the dwell times t x (x = a, b, c) of each phase of the single-stage multi-port inverter;

[0086]

[0087] (6.5), Judge the quantitative relationship between T s V ESS and t x V PV and substitute the dwell times t x of each phase to calculate the three-phase duty cycles d 1x , d 2x ;

[0088] Judge the quantitative relationship between T s V ESS (t) and t x V PV (t) and substitute the dwell times t x of each phase to calculate the three-phase duty cycles d 1x , d 2x ;

[0089]

[0090] (7), Within one switching period, compare the six duty cycles d 1a , d 2a , d 1b , d 2b , d 1c , d 2c with the triangular carrier amplitude respectively to generate six drive signals G a1 , G a2 , G b1 , G b2 , G c1 , G c2 for driving the multi-port inverter, and then use the drive signal G x1 to control the switching tube S1x , the driving signal G x1 's complementary signal controls the switching tube The driving signal G x2 controls the switching tube S 2x , the driving signal G x2 's complementary signal controls the switching tube Among them, S 1x , S 2x , are respectively the first switching tube, the second switching tube, the third switching tube, and the fourth switching tube corresponding to each arm.

[0091] Finally, the generated switching signal is input into the single-stage multi-port inverter to control the inverter switching tubes of each arm to perform switching actions.

[0092] Figure 3 The figure shows the flow chart of the proposed unified coordinated control strategy. On the DC side, the energy storage unit is used to balance the power between photovoltaic power generation and the AC side demand. On the AC side, the energy storage unit is used to simulate a virtual synchronous generator with droop characteristics to provide necessary frequency support for the system. Two power buffers independently generate the required power compensation values, which are regulated by unified power feedback control.

[0093] Figure 4 The figure shows the schematic diagram of the steady-state waveform of the maximum power point tracking of the photovoltaic in the multi-port photovoltaic and energy storage combined power generation system implemented according to the present invention under different irradiation conditions: (a) γ < 0.5, (b) γ < 0.5, (c) γ < 0.5, where γ = V ESS / V PV . From top to bottom, the waveforms are the grid-side voltage / current u 2a / i 2a , the DC port power P PV / P ESS and the line voltage V ab . In Figure 4 (b), only the photovoltaic array is used to support the AC grid. In Figure 4 (c), the energy storage unit is used to absorb the excess power of the photovoltaic array. Although the DC port voltage ratios are different, the same grid voltage / current can be obtained. Therefore, the proposed solution is effective for unbalanced DC port voltage conditions.

[0094] Figure 5 , 6 are respectively the schematic diagrams of the dynamic waveforms of the maximum power point tracking of the photovoltaic in the multi-port photovoltaic and energy storage combined power generation system according to the present invention under variable light intensity conditions and variable AC side active power conditions: Figure 5 The dynamic results under variable irradiance conditions are given: (a) from E1 W / m 2 to E2 W / m2 , (b) from E2 W / m 2 to E3 W / m 2 , (c) from E3 W / m 2 to E1 W / m 2 . Among them, when E1 W / m 2 the condition is met, P PV = 800 W, when E2 W / m 2 the condition is met, P PV = 1000 W, when E3 W / m 2 the condition is met, P PV = 1200 W. From top to bottom, the waveforms are the AC grid power P, the AC grid frequency f, the DC port power P PV / P ESS and the AC grid current i 2a . Since there is no frequency deviation, the energy storage unit only needs to balance the power difference between the photovoltaic power generation and the AC grid. It can be concluded from Figure 5 that the power P ESS of the energy storage unit will automatically change with the change of the power output by the photovoltaic array to achieve smooth and rapid power distribution. Figure 6 gives the dynamic results under variable AC power conditions: (a) from 1000 W to 1250 W, (b) from 1000 W to 750 W. From top to bottom, the waveforms are the AC grid power P, the AC grid frequency f, the DC port power P PV / P ESS and the AC grid current i 2a . In Figure 6 (a), when the AC power increases, the output power of the energy storage unit changes from 0 W to 250 W, and the grid frequency changes from 50 Hz to 49.9 Hz. In Figure 6 (b), when the AC power decreases, the output power of the energy storage unit changes from 0 W to -250 W, and the grid frequency changes from 50 Hz to 50.1 Hz. The energy storage unit is used to compensate for power when P PV < P, and absorb excess power when P PV > P. Flexible power flow among the photovoltaic array, the energy storage unit and the AC grid is achieved.

[0095] Figure 7 gives the comparison with the traditional strategy under different virtual inertia constants. (a) The traditional strategy without virtual inertia, (b) The unified coordinated control scheme when the virtual inertia constant J = 0.064 kg·m 2 , (c) The unified coordinated control scheme when the virtual inertia constant J = 0.128 kg·m 2 . From top to bottom, the waveforms are the grid frequency f and the rate of change of frequency (RoCoF). In addition, the transient response time t r of the frequency is also given. FromFigure 7 As can be seen from the waveforms shown, as the virtual inertia constant increases, the frequency decreases more slowly, and the lowest point of the RoCoF also moves up accordingly. Under the condition of no virtual inertia, the grid frequency changes rapidly from 50 Hz to 49.9 Hz (about 0.04 s). And the RoCoF exceeds the ideal threshold of 1 Hz·s determined according to the grid code and tolerance requirements. -1 . In Figure 7 (b), the RoCoF is near the required threshold, and the virtual inertia J = 0.064 kg·m 2 . In Fig. 7(c), the RoCoF reaches -0.5 Hz·s -1 , within the selected threshold range. Figure 7 The results show that the proposed solution has effective grid frequency support capabilities.

[0096] Figure 8 Fig. shows a comparison diagram of the efficiency of the integrated photovoltaic and energy storage power generation system based on the two-stage DC coupling topology and the power generation system implemented according to the present invention under different light intensity conditions. Among them, the dashed line represents the system efficiency based on the two-stage DC coupling topology, and the solid line represents the system efficiency based on the single-stage multi-port inverter. (a) Under the light intensity of E1 W / m 2 , (b) Under the light intensity of E3 W / m 2 . It can be concluded from Figure 8 that the efficiency of the integrated photovoltaic and energy storage power generation system based on the single-stage multi-port topology is increased by about 2% compared with that based on the two-stage DC coupling topology. Due to the removal of the DC-DC converter, the proposed control method provides a more efficient solution for the integration of the photovoltaic array and the energy storage port.

[0097] Although the above describes the illustrative specific embodiments of the present invention for the convenience of those skilled in the art to understand the present invention, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention defined and determined by the appended claims, these changes are obvious, and all inventions made using the concept of the present invention are within the scope of protection.

Claims

1. A MPPT and frequency support control method for a multi-port photovoltaic and energy storage power generation system, characterized in that Including the following steps: (1) Collect the three-phase current \(i_{x}(t)\) and three-phase voltage \(u_{x}(t)\) on the grid side of the multi-port photovoltaic and energy storage integrated power generation system, the voltage and current \(V(t)\), \(i(t)\) of the photovoltaic array, and the voltage \(V(t)\) and actual output power \(P(t)\) of the energy storage port, where \(t\) represents the sampling moment and \(x = a, b, c\) represents the three phases of the power grid; 2x (t) and three-phase voltage u 2x (t), the voltage and current of the photovoltaic array V PV (t), i PV (t), and the energy storage port voltage V ESS (t) and the actual output power P ESS (t), where t represents the sampling moment and x = a, b, c represents the three phases of the power grid; (2) Obtain the reference voltage vector V ref (t) on the output side of the single-stage multi-port inverter; (3), obtaining the power compensation value ΔP1(s) of the photovoltaic MPPT power buffer; (4), obtaining the power compensation value ΔP2(s) of the frequency support power buffer; (5) Obtain the total power P to be compensated at the energy storage port ESSref (s) = ΔP1(s) + ΔP2(s); (6) According to the reference voltage vector V ref (t) and the total power P ESS ref(s) to be compensated, the duty cycles d 1x and d 2x of the first and second switching tubes on each phase bridge arm are calculated by using the power distribution method of the multi-port optical storage hybrid power generation system based on zero vector regulation, where x = a, b, c represents the three-phase bridge arms of the single-stage multi-port inverter; (7) During a switching period, compare the six duty cycles d 1a 、d 2a 、d 1b 、d 2b 、d 1c 、d 2c with the amplitude of the triangular carrier respectively to generate six driving signals G a1 、G a2 、G b1 、G b2 、G c1 、G c2 for driving the single-stage multi-port inverter. Then, use the driving signal G x1 to control the switching transistor S 1x , and use the complementary signal of the driving signal G x1 to control the switching transistor The driving signal G x2 controls the switching transistor S 2x , and the complementary signal of the driving signal G x2 controls the switching transistor Among them, S 1x 、S 2x 、 are the first switching transistor, the second switching transistor, the third switching transistor, and the fourth switching transistor corresponding to each bridge arm respectively; (7) During a switching cycle, compare the six duty cycles d 1a 、d 2a 、d 1b 、d 2b 、d 1c 、d 2c with the amplitude of the triangular carrier wave respectively to generate six driving signals G a1 、G a2 、G b1 、G b2 、G c1 、G c2 for driving the single-stage multi-port inverter. Then, use the driving signal G x1 to control the switching tube S 1x , and use the complementary signal of the driving signal G x1 to control the switching tube The driving signal G x2 controls the switching tube S 2x , and the complementary signal of the driving signal G x2 controls the switching tube where S 1x 、S 2x 、 are respectively the first switching tube, the second switching tube, the third switching tube, and the fourth switching tube corresponding to each bridge arm.

2. The MPPT and frequency support control method for a multi-port photovoltaic and energy storage power generation system according to claim 1, characterized in that, The acquisition method of the reference voltage vector V ref (t) is as follows: (2.1) Given the reference voltage amplitude V n (t) and frequency ω n (t), reference active power P ref (t) and reactive power Q ref (t); (2.2), The three-phase current i 2x (t) and the three-phase voltage u 2x (t) are sent to the power calculation module to obtain the actual active power P(t) and reactive power Q(t) of the grid side of the photovoltaic and energy storage combined power generation system; (2.3) Obtain the reference active power P in (t) and the amplitude E gref (t) of the grid-side reference voltage vector; where k ω and k q are given droop control coefficients, and ω m (t) is the angular frequency of the virtual synchronous generator; (2.4) Obtain the angular frequency ω of the virtual synchronous generator according to the swing equation of the virtual synchronous generator m (t): wherein, J and D are virtual inertia coefficients and virtual damping coefficients given according to the actual requirements of the photovoltaic and energy storage combined power generation system; (2.5) Integrate the angular frequency ω of the virtual synchronous generator m (t) to obtain the phase angle θ of the grid-side reference voltage vector gref (t); (2.6), input the three-phase current \(i\) 2x (t) and the three-phase voltage \(u\) 2x (t), the amplitude \(E_{gref}(t)\) and phase angle \(\theta\) gref (t) of the reference voltage vector into the cascaded proportional-integral controller to obtain the reference voltage vector \(V\) ref (t) on the output side of the single-stage multi-port inverter.

3. The MPPT and frequency support control method for a multi-port photovoltaic and energy storage power generation system according to claim 1, characterized in that, The method for obtaining the power compensation value ΔP1(s) of the photovoltaic MPPT power buffer is as follows: (3.1) Obtain the output voltage and current V PVref (t), i PVref (t) of the photovoltaic array at the maximum power point by using the perturbation and observation method. The reference output power of the photovoltaic array can be calculated as follows: P PVref (t) = V PVref (t)i PVref (t) (3.2), calculating the difference between the grid-side reference active power and the photovoltaic array reference output power as the power compensation value that the photovoltaic power buffer needs to provide to achieve the maximum power point tracking of the photovoltaic: ΔP1(t) = P ref (t) - P PVref (t) (3.3), performing Laplace transformation on the power compensation value ΔP1(t) of the photovoltaic MPPT power buffer to obtain the expression of ΔP1(s) in the s domain.

4. The MPPT and frequency support control method for a multi-port photovoltaic and energy storage power generation system according to claim 1, characterized in that The method for obtaining the power compensation value ΔP2(s) of the frequency support power buffer is as follows: (4.1), performing Laplace transformation on the swing equation of the virtual synchronous generator to obtain its expression in the s domain as follows: ΔP VSG (s) = (D + Jω n (s)s)Δω(s) where, ΔP VSG (s) represents the power deviation, Δω(s) is the representation of Δω(t) in the s-domain, and Δω(s) = ω m (s) - ω n (s) is the angular frequency change; (4.2) Obtain the power deviation ΔP through a proportional derivative controller VSG (s): where k p1 and k d are the proportional coefficient and the derivative coefficient of the proportional derivative controller, respectively; (4.3) Calculate ΔP according to the droop control characteristic equation droop (s); ΔP droop (s) = k ω Δω(s) (4.4), Combine the power deviation ΔP VSG caused by virtual inertia / damping (s) and the power deviation ΔP droop caused by frequency deviation (s), and calculate the power compensation value ΔP2(s) of the frequency support power buffer: ΔP2(s) = -ΔP VSG (s) - ΔP droop (s).

5. The MPPT and frequency support control method for a multi-port photovoltaic and energy storage power generation system according to claim 1, characterized in that The method for obtaining the duty cycles d 1x 1x and d 2x 2x of the first and second switching tubes on each phase leg by using the power distribution method of the multi-port optical storage hybrid power generation system based on zero vector regulation is as follows: (5.1) Calculate the difference between the total power to be compensated at the energy storage port and the actual output power, and then design a proportional-integral controller G PI (s) to obtain the zero-vector regulation parameter k; k = G PI (s)(P ESSref (s)-P ESS (s)) where P ESS (s) is the representation in the s-domain after the Laplace transform of P ESS (t), and k p2 and k i are the proportional parameter and the integral parameter of the proportional-integral controller, respectively; (5.2) Determine the sector H where it is located according to the phase angle of the reference voltage vector V ref (t); Among them, the six non-zero vectors v that form six sectors j , where j = 1, 2, …, 6, are obtained by calculation using the following formula: (5.3), Substitute the reference voltage vector V ref (t) to calculate the dwell times T1, T2, and T0 of two adjacent non-zero vectors V1 and V2 and the zero vector V0 that make up sector H within one switching period: where T s is the switching period, and T1, T2, and T0 are the dwell times corresponding to V1, V2, and V0 respectively; (5.4), Substitute the zero vector adjustment parameter k to obtain the dwell time t of each phase of the single-stage multi-port inverter, where x = a, b, c; x , x = a, b, c; (5.5), Determine T s V ESS (t) and t x V PV (t), and substitute the dwell time t of each phase x Calculate the three-phase duty cycle d 1x and d 2x ;

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