Power allocation method for multi-port photovoltaic-storage hybrid power generation system based on zero vector regulation

Abstract

The present invention discloses a power distribution method for a multi-port photovoltaic-storage hybrid power generation system based on zero vector regulation. On the DC side, a power module is used to monitor the states of a photovoltaic unit and an energy storage device, and a reference power of the photovoltaic unit is given to determine the current working mode of the photovoltaic-storage hybrid power generation system. Then, a closed-loop power distribution method is used to obtain a regulation factor of a redundant zero vector. On the AC side, a series of control loops are used to obtain a required synthesized reference voltage vector. In order to simplify the calculation, a multi-port inverter is equivalent to two virtual levels, and then the reference voltage vector is synthesized to obtain the residence time of the virtual vector. The residence time of the virtual redundant zero vector is adjusted by the regulation factor obtained by the closed-loop power distribution method. Finally, the residence time of the actual switch tube is obtained according to the volt-second balance principle, thereby realizing the power distribution of two DC ports.

Description

Technical Field

[0001] The present invention belongs to the technical field of photovoltaic-storage hybrid power generation system control, and more specifically, relates to a power distribution method for a multi-port photovoltaic-storage hybrid power generation system based on zero vector regulation. Background Art

[0002] In order to give full play to the advantages of the photovoltaic and storage hybrid power generation system, selecting a suitable topology to connect the photovoltaic and storage hybrid power generation system and providing a corresponding modulation method can reduce the loss of electric energy during transmission and achieve efficient energy transfer. At present, photovoltaic and storage hybrid power generation systems mostly adopt a two-stage structure, that is, the photovoltaic energy storage unit needs to be connected to the power grid through a two-stage converter, a DC-DC converter and a DC-AC inverter. Such a structure increases the weight and volume of the system and reduces the power density of the system. The single-stage multi-port inverter topology removes the DC-DC converter of the previous stage and directly connects the photovoltaic and storage hybrid power generation system to the DC port of the inverter, so that energy is directly transmitted from the DC end to the AC end through the inverter, which has the advantages of single energy conversion, small size and low cost.

[0003] The multi-port inverter system is derived from the multi-level inverter, providing multiple DC ports with significant advantages such as high working efficiency and high power density. However, since the photovoltaic and energy storage devices are directly connected to the DC port, the port voltage of the multi-port inverter is unbalanced, which makes it difficult to synthesize the reference voltage vector and cannot guarantee the power quality on the AC side. In addition, the high coupling of the multi-port inverter topology makes it difficult to simultaneously realize the power management of the photovoltaic and energy storage hybrid system when synthesizing the reference voltage vector, which limits the distribution of port power, making it impossible to adapt to complex working environments and unable to give full play to the advantages of the photovoltaic and energy storage hybrid power generation system.

[0004] The existing method of synthesizing reference voltage under unbalanced port voltage usually realizes port power control based on virtual vector, but this method bears a huge computational burden. In order to simplify the calculation and realize the distribution of port power, an improved space vector modulation strategy realizes ideal power distribution by specifying that the multi-port inverter always operates in two-level mode. However, the system always operates in two-level mode, which reduces the power quality. The coupling of port imbalance and port power of multi-port inverter brings difficulties to the modulation and control strategy of the system. At present, there is no simple and effective power distribution method to realize flexible power distribution between two ports of multi-port inverter. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a power distribution method for a multi-port photovoltaic and energy storage hybrid power generation system based on zero vector regulation, which can not only realize the synthesis of reference voltage vectors under the port voltage imbalance state, but also realize flexible power control of photovoltaic and energy storage devices at the same time, so that the multi-port photovoltaic and energy storage hybrid power generation system can work stably in multiple working modes and achieve good adaptability to complex working conditions.

[0006] To achieve the above-mentioned object of the invention, the present invention provides a power allocation method for a multi-port photovoltaic storage hybrid power generation system based on zero vector regulation, characterized in that it comprises the following steps:

[0007] (1) Obtain the adjustment factor of the redundant zero vector of the multi-port photovoltaic storage hybrid power generation system through a closed-loop power allocation method;

[0008] (1.1) The power management module monitors the status of the photovoltaic unit and the energy storage device. Given the reference power P output by the distributed photovoltaic unit in the multi-port photovoltaic storage hybrid power generation system, PVref ;

[0009] (1.2) According to the reference power P output by the distributed photovoltaic unit PVref , determine the current operation mode of the photovoltaic storage hybrid power generation system;

[0010] (1.3) Calculate the actual power P output by the distributed photovoltaic unit PV ;

[0011] (1.4) According to the current operation mode of the photovoltaic storage hybrid power generation system, P PVref and P PV , the adjustment factor K of the redundant zero vector of the multi-port photovoltaic storage hybrid power generation system is obtained through a closed-loop power allocation method;

[0012] (2) Calculate the reference voltage vector V on the AC side of the multi-port photovoltaic storage hybrid power generation system ref ;

[0013] (3) The multi-port inverter in the multi-port photovoltaic-storage hybrid power generation system is equivalent to a virtual two-level inverter, and then multiple virtual voltage vectors are synthesized under different switch state combinations according to the equivalent virtual two-level inverter, and finally the sectors are divided according to the distribution of the virtual voltage vectors in space;

[0014] (4) determining the sector where the synthesized reference voltage vector is located, selecting a virtual voltage vector for vector synthesis reference voltage from a plurality of virtual voltage vectors, and then calculating a virtual residence time of the required virtual voltage vector to synthesize the reference voltage vector;

[0015] (5) The residence time of the virtual redundant zero vector in the virtual voltage vector is rewritten according to the adjustment factor K of the redundant zero vector, and the residence time of the other virtual voltage vectors remains unchanged;

[0016] (6) Based on the principle that the volt-second value of a multi-port inverter is equal to that of an equivalent virtual two-level inverter, the actual allocated dwell time of the switch tube of each phase bridge arm is calculated.

[0017] The object of the invention of the present invention is achieved in this way:

[0018] The present invention discloses a power distribution method for a multi-port photovoltaic-storage hybrid power generation system based on zero vector regulation. On the DC side, a power module is used to monitor the states of a photovoltaic unit and an energy storage device, and a reference power of the photovoltaic unit is given to determine the current working mode of the photovoltaic-storage hybrid power generation system. Then, a closed-loop power distribution method is used to obtain a regulation factor of a redundant zero vector. On the AC side, a series of control loops are used to obtain a required synthesized reference voltage vector. In order to simplify the calculation, a multi-port inverter is equivalent to two virtual levels, and then a reference voltage vector is synthesized to obtain a residence time of the virtual vector. The residence time of the virtual redundant zero vector is adjusted by the regulation factor obtained by the closed-loop power distribution method. Finally, the residence time of the actual switch tube is obtained according to the volt-second balance principle, thereby realizing the power distribution of the two DC ports.

[0019] At the same time, the power allocation method of the multi-port photovoltaic storage hybrid power generation system based on zero vector regulation of the present invention also has the following beneficial effects:

[0020] (1) The present invention connects a multi-port inverter of a photovoltaic-storage hybrid power generation system. The power transmission between the DC side and the AC side only requires a single power conversion stage, which effectively reduces the system volume without increasing any hardware cost. At the same time, it can effectively improve the working efficiency of the hybrid system and meet the current requirements for small size, high power transmission efficiency and high reliability of photovoltaic-storage hybrid power generation systems.

[0021] (2) The present invention proposes a simple and effective power distribution method based on zero vector regulation in view of the inherent coupling characteristics of a multi-port inverter connected to a photovoltaic and energy storage hybrid power generation system. The method distributes power between two DC ports by adjusting the residence time of the redundant zero vector, thereby achieving ideal active power distribution between the photovoltaic unit and the energy storage device connected to the DC port.

[0022] (3) The power distribution method based on zero vector regulation of the present invention can effectively avoid complex calculation processes, not only ensuring the quality of the AC side current, but also solving the problem of voltage imbalance at the ports of the multi-port inverter. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1It is a structural topology diagram of a specific implementation method of a multi-port photovoltaic storage hybrid power generation system;

[0024] Figure 2 This is the topology diagram of the multi-port inverter structure.

[0025] Figure 3 It is a power distribution block diagram of a multi-port photovoltaic storage hybrid power generation system based on zero vector regulation of the present invention;

[0026] Figure 4 It is the power transmission pattern of the multi-port photovoltaic storage hybrid power generation system in four working modes;

[0027] Figure 5 is a schematic diagram of DC link voltage and spatial sector division of a multi-port inverter and an equivalent virtual two-level inverter;

[0028] Figure 6 Schematic diagram of the relationship between the vector residence time of the equivalent virtual two-level inverter and the residence time of the bridge arm switch tube of the multi-port inverter;

[0029] Figure 7 This is a diagram showing the steady-state performance of a multi-port photovoltaic and storage hybrid power generation system in different working modes;

[0030] Figure 8 It is a dynamic performance rendering of a multi-port photovoltaic storage hybrid power generation system when switching between different working modes. DETAILED DESCRIPTION

[0031] The specific implementation of the present invention is described below in conjunction with the accompanying drawings so that those skilled in the art can better understand the present invention. It should be 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.

[0032] Example

[0033] Figure 1 It is a structural topology diagram of a specific implementation method of a multi-port photovoltaic storage hybrid power generation system.

[0034] In this embodiment, if Figure 1 As shown, the multi-port photovoltaic storage hybrid power generation system is characterized by comprising: a distributed photovoltaic unit 1, an energy storage device 2, DC bus capacitors C1 and C25, a diode 6, an LC filter 4 and a multi-port inverter 3;

[0035] In this embodiment, if Figure 2As shown in FIG. 1 , the structure of the multi-port inverter is an improvement of the diode clamped (NPC) three-level inverter topology, with one power supply connected to the positive and negative poles, and another power supply connected between the neutral line and the ground line. A capacitor is connected between the neutral line and the ground line, and another capacitor is connected between the neutral line and the positive pole, while retaining the original three bridge arms of the inverter.

[0036] from Figure 2 It can be seen that the energy flow path from the two DC power sources to the AC side of the inverter reduces one DC bidirectional DC-DC unit compared with the traditional inverter of the same type, which can reduce the energy level conversion and improve the energy transmission efficiency of the system; in addition, the present invention treats the multi-port inverter as a virtual two-level inverter according to the needs under different working conditions, and further proposes a power allocation strategy for a multi-port photovoltaic storage hybrid power generation system based on zero vector regulation. The control block diagram is shown in FIG. Figure 3 As shown, the specific steps include:

[0037] S1. Obtaining the adjustment factor of the redundant zero vector of the multi-port photovoltaic storage hybrid power generation system through a closed-loop power allocation method;

[0038] S1.1. The power management module monitors the status of the photovoltaic unit and the energy storage device, and the reference power P output by the distributed photovoltaic unit in the multi-port photovoltaic storage hybrid power generation system is given. PVref ;

[0039] S1.2, according to the reference power P output by the distributed photovoltaic unit PVref , determine the current operating mode of the photovoltaic storage hybrid power generation system

[0040] S1.3. Calculate the actual power P output by the distributed photovoltaic unit PV ;

[0041]

[0042] Among them, V PV is the output voltage of the distributed photovoltaic unit, θ is the phase angle, i PV is the average current of the distributed photovoltaic unit in a switching cycle, i PV =d a1 i a +d b1 i b +d c1 i c , and For the switch tube S a1 , S b1 and S c1 The duty cycle, i a 、i b and i cis the three-phase current output by the multi-port inverter;

[0043] In this embodiment, if Figure 4 It can be seen that there are four working modes of the photovoltaic storage hybrid power generation system, mode 1: only the energy storage device supports the grid, mode 2: photovoltaic and energy storage device system support the grid together, mode 3: photovoltaic supports the grid and charges the energy storage device, mode 4: only photovoltaic supports the grid;

[0044] S1.4, based on the current operation mode of the photovoltaic storage hybrid power generation system, P PVref and P PV , the adjustment factor K of the redundant zero vector of the multi-port photovoltaic storage hybrid power generation system is obtained through a closed-loop power allocation method;

[0045] In this embodiment, the reference power P output by the distributed photovoltaic unit PVref The actual power P PV The difference is then passed through a closed-loop PI power control module to obtain the adjustment factor K of the redundant zero vector.

[0046] S2. Calculate the reference voltage vector V on the AC side of the multi-port photovoltaic storage hybrid power generation system ref ;

[0047] S2.1, given the reference active power P of the grid side of the multi-port photovoltaic storage hybrid power generation system ref , Reference reactive power Q ref , reference frequency f ref And the reference voltage U ref ;

[0048] S2.2, the current sampling module and the voltage sampling module in the multi-port photovoltaic storage hybrid power generation system read the grid-side current I2 and voltage U2 respectively, and then input the current I2 and voltage U2 into the power calculation module to calculate the active power P and reactive power Q outputted from the grid side;

[0049] S2.3, active power P, reactive power Q, reference active power P ref , Reference reactive power Q ref , reference frequency f ref , reference voltage U ref After the current I2 passes through the droop control module and the virtual impedance module, the grid side reference voltage is obtained.

[0050] S2.4, the grid side reference voltage After the cascade voltage and current dual PI control module, the reference voltage vector V on the multi-port inverter side is obtained. ref .

[0051] S3, the multi-port inverter in the multi-port photovoltaic storage hybrid power generation system is equivalent to a virtual two-level inverter, and then multiple virtual voltage vectors are synthesized under different switch state combinations according to the equivalent virtual two-level inverter, and finally the sectors are divided according to the distribution of the virtual voltage vectors in space;

[0052] In this embodiment, if Figure 5 As shown, the multi-port inverter in the photovoltaic storage hybrid power generation system with an upper port DC voltage of V1 and a lower port DC voltage of V2 is modeled as an equivalent virtual two-level inverter with a DC bus voltage of V1+V2.

[0053] S4, determining the sector where the synthesized reference voltage vector is located, selecting a virtual voltage vector for vector synthesis reference voltage from a plurality of virtual voltage vectors, and then calculating a virtual residence time of the required virtual voltage vector to synthesize the reference voltage vector;

[0054] In this embodiment, taking the first sector as an example, the virtual voltage vectors used to synthesize the reference voltage vector in the first sector are v1, v2 and v0, and the formula for synthesizing the reference voltage vector is,;

[0055]

[0056] Wherein, T1, T2 and T0 are the virtual residence times of virtual voltage vectors v1, v2 and v0 respectively, and the same is true for the other sectors;

[0057] S5. Rewrite the residence time of the virtual redundant zero vector in the virtual voltage vector according to the adjustment factor K of the redundant zero vector, and keep the residence time of other virtual voltage vectors unchanged;

[0058] Among them, the residence time of the virtual redundant zero vector is rewritten as:

[0059]

[0060] Among them, 0<K<1, t a ,t b ,t c It is the virtual switching time of each phase switch tube after rewriting.

[0061] S6. According to the principle that the volt-second value of the multi-port inverter is equal to that of the equivalent virtual two-level inverter, the dwell time actually allocated to the switch tube of each phase bridge arm is calculated;

[0062] The formula for calculating the actual allocated dwell time of the switch tube on each phase bridge arm can be divided into the following two cases:

[0063] like Figure 6 As shown, if T s V2<tx V PV , then the switch tube S on each phase bridge arm x1 , S x2 The residence time calculation formula is:

[0064]

[0065] If T s V2≥t x V PV , switch tube S x1 , S x2 The residence time calculation formula is:

[0066]

[0067] Among them, T s is the time required for a switching cycle, t x1 ,t x2 It is the switch tube S on the xth phase bridge arm. x1 , S x2 The actual allocated residence time, x = a, b, c.

[0068] like Figure 7 As shown, this embodiment carries out a multi-port photovoltaic storage hybrid power generation system and a power allocation method based on zero vector regulation. The results show that: using the power allocation method based on zero vector regulation, the multi-port photovoltaic storage hybrid power generation system can operate stably in multiple working modes and has good output current quality. The power allocation method based on zero vector regulation can not only achieve good static performance.

[0069] like Figure 8 As shown, the dynamic performance of the system is good when the photovoltaic storage switches between multiple working modes, and the output power can quickly track the reference power without large fluctuations. In addition, the multi-port photovoltaic storage hybrid power generation system of the present invention ensures the power transmission efficiency of the photovoltaic storage hybrid power generation system, and can achieve good port voltage quality under the condition of unbalanced port voltage while being able to distribute power between the two ports, making the system more flexible.

[0070] Although the above describes the illustrative specific embodiments of the present invention to facilitate the understanding of the present invention by those skilled in the art, 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 as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

Claims

1. A power allocation method for a multi-port photovoltaic storage hybrid power generation system based on zero vector regulation, characterized in that: The following steps are involved: (1) Obtain the adjustment factor of the redundant zero vector of the multi-port photovoltaic storage hybrid power generation system through a closed-loop power allocation method; (1.1) The power management module monitors the status of the photovoltaic unit and the energy storage device. Given the reference power P output by the distributed photovoltaic unit in the multi-port photovoltaic storage hybrid power generation system, PVref ; (1.2) According to the reference power P output by the distributed photovoltaic unit PVref , determine the current operation mode of the photovoltaic storage hybrid power generation system; (1.3) Calculate the actual power P output by the distributed photovoltaic unit PV ; (1.4) According to the current operation mode of the photovoltaic storage hybrid power generation system, P PVref and P PV , the adjustment factor K of the redundant zero vector of the multi-port photovoltaic storage hybrid power generation system is obtained through a closed-loop power allocation method; (2) Calculate the reference voltage vector V on the AC side of the multi-port photovoltaic storage hybrid power generation system ref ; (3) The multi-port inverter in the multi-port photovoltaic-storage hybrid power generation system is equivalent to a virtual two-level inverter, and then multiple virtual voltage vectors are synthesized under different switch state combinations according to the equivalent virtual two-level inverter, and finally the sectors are divided according to the distribution of the virtual voltage vectors in space; (4) determining the sector where the synthesized reference voltage vector is located, selecting a virtual voltage vector for vector synthesis reference voltage from a plurality of virtual voltage vectors, and then calculating a virtual residence time of the required virtual voltage vector to synthesize the reference voltage vector; (5) The residence time of the virtual redundant zero vector in the virtual voltage vector is rewritten according to the adjustment factor K of the redundant zero vector, and the residence time of the other virtual voltage vectors remains unchanged; (6) Based on the principle that the volt-second value of a multi-port inverter is equal to that of an equivalent virtual two-level inverter, the actual allocated dwell time of the switch tube of each phase bridge arm is calculated.

2. The power allocation method of a multi-port photovoltaic storage hybrid power generation system based on zero vector regulation according to claim 1 is characterized in that: The actual power P output by the distributed photovoltaic unit PV The calculation method is: Among them, V PV is the output voltage of the distributed photovoltaic unit, i PV is the average current of the distributed photovoltaic unit in one switching cycle, and θ is the phase angle.

3. The power allocation method of a multi-port photovoltaic storage hybrid power generation system based on zero vector regulation according to claim 1 is characterized in that: The calculation method of the adjustment factor K of the redundant zero vector is: The reference power P output by the distributed photovoltaic unit PVref The actual power P PV The difference is then passed through a closed-loop PI power control module to obtain the adjustment factor K of the redundant zero vector.

4. The power allocation method of a multi-port photovoltaic storage hybrid power generation system based on zero vector regulation according to claim 1 is characterized in that: The reference voltage vector V ref The calculation method is: S1, given the reference active power P of the grid side of the multi-port photovoltaic storage hybrid power generation system ref , Reference reactive power Q ref , reference frequency f ref And the reference voltage U ref ; S2, the current sampling module and the voltage sampling module in the multi-port photovoltaic storage hybrid power generation system read the grid-side current I2 and voltage U2 respectively, and then input the current I2 and voltage U2 into the power calculation module to calculate the active power P and reactive power Q output from the grid side; S3, active power P, reactive power Q, reference active power P ref , Reference reactive power Q ref , reference frequency f ref , reference voltage U ref After the current I2 passes through the droop control module and the virtual impedance module, the grid side reference voltage is obtained. S4, the grid side reference voltage After the cascade voltage and current dual PI control module, the reference voltage vector V on the multi-port inverter side is obtained. ref .

5. The power allocation method of a multi-port photovoltaic storage hybrid power generation system based on zero vector regulation according to claim 1 is characterized in that: The method for rewriting the residence time of the virtual redundant zero vector in the virtual voltage vector by the adjustment factor K of the redundant zero vector is: Among them, t a ,t b ,t c is the residence time of each phase of the virtual two-level inverter, and T1, T2 and T0 are the virtual residence times of the virtual voltage vectors v1, v2 and v0, respectively.

6. The power allocation method of a multi-port photovoltaic storage hybrid power generation system based on zero vector regulation according to claim 1 is characterized in that: The calculation method of the dwell time actually allocated to the switch tube on each phase bridge arm is: If T s V2<t x V PV , then the switch tube S on each phase bridge arm x1 , S x2 The residence time calculation formula is: If T s V2≥t x V PV , switch tube S x1 , S x2 The residence time calculation formula is: Among them, V1 and V2 are the DC voltages of the upper and lower ports of the photovoltaic and storage hybrid power generation system of the multi-port inverter, T s is the switching cycle time, t x1 ,t x2 It is the switch tube S on the x-phase bridge arm. x1 , S x2 The actual allocated residence time, x = a, b, c.

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