Light storage VSG control method and system for coordinating power maximum output and energy storage

Abstract

The invention relates to the technical field of photovoltaic power generation energy storage grid connection, and discloses an optical storage VSG control method and system for coordinating power maximum output and energy storage, and the method comprises the steps: building an output power-angular frequency model between the output power of an inverter and the angular frequency of a VSG virtual rotor based on a VSG control principle; establishing a direct current capacitor voltage-output power model; establishing a control model of the proportional relation between the direct current side voltage and the output frequency deviation; simulating droop control between the input power and the rotor speed in the synchronous generator, associating the battery power with the direct current side voltage, establishing a battery droop control strategy, and transferring the battery power change response demand to a direct current side capacitor; active-power control in a traditional photovoltaic energy storage power generation system control principle is optimized, and a battery droop control strategy is established, so that battery power change response demands are transferred to a direct current side capacitor, more photovoltaic energy is utilized, and demands and adverse effects on photovoltaic power generation absorbed by a local battery are reduced.

Description

Technical Field

[0001] The present application relates to the technical field of photovoltaic power generation, energy storage and grid connection, and in particular to a photovoltaic storage VSG control method and system for coordinating maximum power output and energy storage. Background Art

[0002] Virtual Synchronous Generator (VSG for short), in the power system, VSG is a power electronic device or control system that can simulate the characteristics of a traditional synchronous generator. It can make distributed power sources (such as solar power generation, wind power generation, etc.) show inertia and damping characteristics similar to those of synchronous generators through control algorithms, thus contributing to the stable operation and frequency regulation of the power system.

[0003] In recent years, due to the decline in the cost of power electronic components and renewable energy technologies, new energy power generation, especially photovoltaic power generation, has been widely studied and applied, and the power energy system is facing new technical challenges. From the perspective of power system operation, there are two main challenges to the high penetration of photovoltaic power sources. First, photovoltaic power generation is random and volatile, and their output will change with changes in the environment, which leads to challenges to the balance of the power system and resource adequacy during peak power demand periods. Secondly, photovoltaic power generation is connected to the power grid through power electronic converters and does not have mechanical inertia and damping characteristics. As traditional synchronous generators are replaced by distributed power electronic equipment in large quantities, the entire power system presents low inertia characteristics, and the reliability and stability of the power grid are also reduced.

[0004] In order to solve the low inertia problem of new energy, the concept of virtual synchronous generator is proposed. By simulating the main model, active frequency regulation, reactive voltage regulation and other characteristics of the synchronous generator in the control strategy of the grid-connected inverter, the new energy power generation containing power electronic equipment can be similar to the conventional synchronous motor in terms of operation mechanism and external characteristics, and the new energy power generation system is equivalent to a synchronous generator. However, most of the existing VSG control strategies use infinite power to equalize distributed power and energy storage elements, without considering the impact of its real output capacity on the VSG virtual inertia adaptive control effect, which hinders the practical application of new energy power generation systems. In response to this, the photovoltaic system will be equipped with battery energy storage to enhance the controllability of photovoltaic output power. The intermittent and fluctuating photovoltaic power is completely handled by the battery, which will lead to frequent charging and discharging and premature aging of the battery. In addition, since this method is prone to premature exhaustion of battery capacity, in order to avoid overvoltage on the DC side, it is easy to cause photovoltaic power unloading, reducing the utilization rate of photovoltaic power.

[0005] When the power grid is in operation, it is hoped that renewable energy will respond to the power flow changes of the power grid, rather than prohibiting renewable energy from outputting fluctuating power. All units in the power grid with frequency regulation capabilities can collectively absorb the fluctuating power of renewable energy. Therefore, it is more economically valuable to flexibly deliver the fluctuating photovoltaic power to the grid, rather than storing it entirely in the battery. Allowing the DC side voltage to fluctuate to reflect the changes in photovoltaic power can achieve adaptive delivery of maximum photovoltaic power. In addition to battery-free photovoltaic power generation systems, this idea has also been applied to wind power generation systems, grid-connected energy storage systems, and high-voltage direct current transmission systems. However, due to the complex connection between the DC side voltage and power balance of the photovoltaic storage VSG system, existing studies have not applied this idea to the VSG control strategy of the photovoltaic storage system. Summary of the invention

[0006] In order to flexibly transmit fluctuating photovoltaic power to the grid instead of storing it completely in the battery, so as to achieve maximum power output and reduce battery operating pressure, the present application provides a photovoltaic storage VSG control method and system that coordinates maximum power output and energy storage.

[0007] In the first aspect, the present application provides a method for controlling a photovoltaic storage VSG that coordinates maximum power output and energy storage, using the following technical solutions:

[0008] A method for controlling a photovoltaic storage VSG that coordinates maximum power output and energy storage, comprising:

[0009] Based on the VSG control principle, an output power-angular frequency model between the inverter output power and the VSG virtual rotor angular frequency is established;

[0010] Establishing a DC capacitor voltage-output power model between the DC side voltage and the inverter output power;

[0011] According to the correlation between the DC side voltage change and the VSG virtual rotor angular frequency change, a control model for the proportional relationship between the DC side voltage and the output frequency deviation is established;

[0012] The droop control between input power and rotor speed in synchronous generator is simulated, the battery power is related to the DC side voltage, and the battery droop control strategy is established so that the battery power variation is transferred to the DC side capacitor in response to demand.

[0013] Optionally, the method for establishing an output power-angular frequency model between the inverter output power and the VSG virtual rotor angular frequency based on the VSG control principle includes:

[0014]

[0015]

[0016]

[0017] in, is the virtual inertia of VSG, is the virtual damping, and are the actual angular frequency and rated angular frequency of the VSG virtual rotor, is the virtual damping coefficient, and are the mechanical power and actual output power of the inverter respectively; For a given reference power, is the adjustment parameter of the prime mover, and are the inverter output voltage and grid-side voltage respectively, is the impedance between the inverter and the grid.

[0018] Optionally, the method for establishing a DC capacitor voltage-output power model between the DC side voltage and the inverter output power includes:

[0019]

[0020] in, and Respectively represent the rated capacitance and rated voltage of the inverter DC side, Indicates the actual DC side voltage of the inverter.

[0021] Optionally, the method for establishing a control model of the proportional relationship between the DC side voltage and the output frequency deviation according to the correlation between the DC side voltage change and the VSG virtual rotor angular frequency change includes:

[0022] The correlation between the DC side voltage change and the VSG virtual rotor angular frequency change is:

[0023]

[0024]

[0025] in, is the angular frequency change, is the correlation coefficient, is the voltage change on the DC side.

[0026] Optionally, the method of associating the battery power with the DC side voltage to establish a battery droop control strategy includes:

[0027] According to the battery current control model, a small signal model of system power balance under input change and a small signal model of system power balance under load change are obtained.

[0028] Optionally, the battery current control model includes:

[0029]

[0030]

[0031] in, is the change in battery current, is the change in battery power, is the battery voltage; is the droop coefficient between frequency and battery power, which varies from the maximum power The maximum angular frequency deviation allowed under Decide.

[0032] Optionally, the small signal model of system power balance under the input change includes:

[0033]

[0034]

[0035]

[0036] in, is the photovoltaic power change, is the damping ratio.

[0037] Optionally, the small signal model of system power balance under load change,

[0038]

[0039]

[0040]

[0041] in, is the output power change, is the capacitance power change.

[0042] Optionally, a working mode control strategy between the DC side voltage and the DC / DC converter is established:

[0043] When the DC voltage When in the normal voltage range, the DC / DC converter remains in the MPPT control mode;

[0044] When the DC voltage When the specified voltage threshold is exceeded, the DC / DC converter is controlled to switch to the photovoltaic load reduction control mode to reduce the photovoltaic output power;

[0045] When the photovoltaic output power naturally decreases to a specified photovoltaic power threshold or the load power increases to a specified load power threshold, the photovoltaic DC / DC converter is controlled to switch to the MPPT working mode.

[0046] In a second aspect, the present application provides a photovoltaic storage VSG control system for coordinating maximum power output and energy storage, including a processor, in which a program of a photovoltaic storage VSG control method and system for coordinating maximum power output and energy storage as described above is run.

[0047] In summary, the present application includes at least one of the following beneficial technical effects:

[0048] 1. Compared with the traditional VSG, the photovoltaic storage VSG control method of the present invention uses an analog synchronous control link to replace the active power control in the control principle of the traditional photovoltaic energy storage power generation system, and simulates the droop control between the input power and the rotor speed in the synchronous generator, associates the battery power with the DC side voltage, and establishes a battery droop control strategy to replace the bidirectional Buck-Boost control link in the control principle of the traditional photovoltaic energy storage power generation system, so that the battery power change response demand is transferred to the DC side capacitor, so that more photovoltaic energy can be utilized, and at the same time, the demand for local batteries to absorb photovoltaic power generation is reduced, thereby greatly reducing the demand for battery power and reducing the impact on the battery. At the same time, it provides the same output power as the traditional VSG, and can achieve higher photovoltaic power transmission without damaging the frequency regulation function of the power grid, fully improve the photovoltaic power utilization rate, avoid unnecessary charging and discharging of the battery, and significantly improve the battery life;

[0049] 2. In order to ensure that the DC side voltage is within a reasonable range when the system is working normally, the present invention establishes a working mode control strategy between the DC side voltage and the DC / DC converter as an additional control scheme, gives priority to the safety of the system, changes the maximum output of the photovoltaic power to retain active standby control, and makes the operating point of the photovoltaic array deviate from the maximum power point, thereby reserving a part of the active power. There is no need to provide the high operating and maintenance costs required by the additional energy storage unit, which reduces the complexity of the system. Within the normal power fluctuation range, compared with the use of additional energy storage units, the photovoltaic load reduction control method is more economical and reliable. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 It is the existing photovoltaic storage VSG control method and the grid-connected structure diagram of the related photovoltaic energy storage power generation system;

[0051] Figure 2 It is a schematic diagram of the analog synchronous control link of an embodiment of the present invention;

[0052] Figure 3is a control principle diagram of a bidirectional Buck-Boost converter according to an embodiment of the present invention;

[0053] Figure 4 A grid-connected structure diagram of a photovoltaic storage VSG control method and a related photovoltaic energy storage power generation system according to an embodiment of the present invention;

[0054] Figure 5 It is a curve diagram showing the battery power change response under photovoltaic power change according to an embodiment of the present invention;

[0055] Figure 6 It is a response curve diagram of inverter output power change under photovoltaic power change according to an embodiment of the present invention;

[0056] Figure 7 is a response curve diagram of battery power under load changes according to an embodiment of the present invention;

[0057] Figure 8 A curve diagram of DC capacitor power response under load changes according to an embodiment of the present invention;

[0058] Fig. 9 This is a schematic diagram of photovoltaic load reduction control according to an embodiment of the present invention;

[0059] Fig.10 This is a DC side voltage over-high adjustment control diagram of a photovoltaic DC / DC according to an embodiment of the present invention;

[0060] Fig.11 This is a control diagram for adjusting the DC side voltage of the inverter in an embodiment of the present invention;

[0061] Fig.12 A topological structure diagram of a dual-photovoltaic power supply simulation system according to an embodiment of the present invention;

[0062] Fig.13 A comparison diagram of power-related parameters changing over time under the change of photovoltaic power is simulated by using the photovoltaic storage VSG control method in the embodiment of the present invention;

[0063] Fig.14 To adopt the existing VSG control strategy, the power-related parameters under the change of photovoltaic power are simulated and compared with time;

[0064] Fig.15 It is a graph of each response curve of the improved control under the photovoltaic power change of the embodiment of the present invention;

[0065] Fig.16 In order to adopt the photovoltaic storage VSG control method in the embodiment of the present invention, a comparison diagram of power-related parameters changing with time under load power changes is simulated;

[0066] Fig.17To adopt the existing VSG control strategy, the power-related parameters under load power changes are simulated and compared with time;

[0067] Fig.18 It is a response curve diagram of the embodiment of the present invention under the change of power grid frequency. DETAILED DESCRIPTION

[0068] Embodiments of the present application are described in detail below, examples of which are shown in the accompanying drawings.

[0069] In the description of this specification, the description with reference to the terms "certain embodiments", "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples" or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiments or examples are included in at least one embodiment or example of the present application. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0070] like Figure 1 The figure shows the grid-connected structure and detailed control schematic diagram of the traditional photovoltaic energy storage power generation system. It adopts a two-stage structure. The front stage adopts the Boost circuit to achieve photovoltaic maximum power tracking, and the rear stage inverter adopts the voltage source virtual synchronous machine control strategy to support the grid voltage and frequency. Since the power difference between photovoltaic input and output needs to be buffered in the middle when the VSG technology is used for frequency and voltage regulation, the system is equipped with an energy storage device at the DC bus, and the energy storage device is used to maintain the DC side voltage constant, so as to achieve the effect of power decoupling between the front and rear stages, so that the VSG can output power according to the power command and its own response, without changing the power to match the stability of the DC side voltage.

[0071] In the present invention, in order to flexibly output the fluctuating photovoltaic power to the grid instead of absorbing all of it into the energy storage battery, the embodiment of the present application discloses a photovoltaic storage VSG control method for coordinating the maximum power output and energy storage, referring to Figure 2-Figure 4 As shown, including:

[0072] Based on the VSG control principle, an output power-angular frequency model between the inverter output power and the VSG virtual rotor angular frequency is established; the establishment process of the output power-angular frequency model is as follows:

[0073]

[0074]

[0075]

[0076] in, is the virtual inertia of VSG, is the virtual damping, and are the actual angular frequency and rated angular frequency of the VSG virtual rotor, is the virtual damping coefficient, and are the mechanical power and actual output power of the inverter respectively; For a given reference power, is the adjustment parameter of the prime mover, and are the inverter output voltage and grid-side voltage respectively, is the impedance between the inverter and the grid.

[0077] Among them, PV Panel refers to photovoltaic panels or solar panels, which are key equipment that can convert solar energy into electrical energy; Sine Wave Generator refers to a sine wave generator; Grid refers to the Electrical Grid; Pulse refers to the pulse signal generated by SPWM modulation.

[0078] Establishing a DC capacitor voltage-output power model between the DC side voltage and the inverter output power; the method of the DC capacitor voltage-output power model includes:

[0079]

[0080] in, and Respectively represent the rated capacitance and rated voltage of the inverter DC side, Indicates the actual DC side voltage of the inverter.

[0081] According to the correlation between the DC side voltage change and the VSG virtual rotor angular frequency change, a control model of the proportional relationship between the DC side voltage and the output frequency deviation is established; the droop control between the input power and the rotor speed in the synchronous generator is simulated, the battery power is associated with the DC side voltage, and a battery droop control strategy is established to replace the bidirectional Buck-Boost control link in the control principle of the traditional photovoltaic energy storage power generation system, so that the battery power change response demand is transferred to the DC side capacitor.

[0082] The control model of the DC side voltage and the output frequency deviation ratio in this embodiment includes an analog synchronous control link for controlling the output frequency according to the DC side voltage (see Figure 2 and Figure 4), this embodiment uses the analog synchronous control link to replace the active power control links in the control principle of the traditional photovoltaic energy storage power generation system. and After the correlation between the DC voltage change and the VSG virtual rotor angular frequency change, the DC voltage can be regarded as the virtual rotor speed.

[0083]

[0084]

[0085] in, is the angular frequency change, is the correlation coefficient, is the voltage change on the DC side.

[0086] In this embodiment, in order to simulate the droop control between the input power and the rotor speed in the synchronous generator, the battery power is associated with the DC side voltage, and the control principle of the battery DC-DC converter is as follows: Figure 3 As shown in FIG. 1 , the method for establishing a battery droop control strategy includes:

[0087] According to the battery current control model, a small signal model of system power balance under input change and a small signal model of system power balance under load change are obtained.

[0088] Optionally, the battery current control model includes:

[0089]

[0090]

[0091] in, is the change in battery current, is the change in battery power, is the battery voltage; is the droop coefficient between frequency and battery power, which varies from the maximum power The maximum angular frequency deviation allowed under Decide.

[0092] Optionally, the small signal model of system power balance under the input change includes:

[0093]

[0094]

[0095]

[0096] in, is the photovoltaic power change, is the damping ratio, Figure 5 , 7 In It is the preset battery power change.

[0097] Optionally, the small signal model of system power balance under load change,

[0098]

[0099]

[0100]

[0101] in, is the output power change, is the capacitance power change, Figure 6 , 8 In Preset reference amount for output power change.

[0102] To verify the feasibility of this embodiment of the present invention, Figure 5 and Figure 6 As shown in the figure, the theoretical response curves of battery power and inverter output power change under different damping ratios. Figure 5 and Figure 6 It can be seen that the battery only helps buffer the additional photovoltaic power during the transient process. When the system reaches a stable state, the additional photovoltaic power will be fully output to the grid. Therefore, compared with the traditional VSG, the photovoltaic storage VSG control method of the present invention enables more photovoltaic energy to be utilized, while reducing the demand for local batteries to absorb photovoltaic power generation, thereby greatly reducing the demand for battery power.

[0103] Figure 7 and Figure 8 The theoretical response curves of battery power and capacitor power under different damping ratios and the same other parameters are shown respectively. In this case, the battery power only needs to increase smoothly, while the rapidly changing power is provided by the DC side capacitor. This means that the proposed strategy can reduce the impact on the battery while providing the same output power as the traditional VSG. Therefore, the photovoltaic storage VSG control method proposed in this embodiment of the present invention is significantly superior to the traditional VSG control because it can achieve higher photovoltaic power transmission without compromising the frequency regulation function of the power grid, fully improve the photovoltaic power utilization rate, avoid unnecessary charging and discharging of the battery, and significantly improve the battery life.

[0104] In addition, another embodiment of the present invention provides an additional control scheme included in the photovoltaic storage VSG control method, the purpose of which is to ensure that the DC side voltage is within a reasonable range when the system is working normally, and to establish a working mode control strategy between the DC side voltage and the DC / DC converter:

[0105] When the DC voltage When in the normal voltage range, the DC / DC converter remains in the MPPT control mode;

[0106] When the DC voltage When the specified voltage threshold is exceeded, the DC / DC converter is controlled to switch to the photovoltaic load reduction control mode to reduce the photovoltaic output power;

[0107] When the photovoltaic output power naturally decreases to a specified photovoltaic power threshold or the load power increases to a specified load power threshold, the photovoltaic DC / DC converter is controlled to switch to the MPPT working mode.

[0108] In practical applications, when the DC voltage exceeds the maximum limit, the maximum PV power is likely to exceed the absorption capacity of the grid and the battery. Therefore, the safety of the system should be given priority at this time, rather than continuing to maintain the maximum power output. In this case, the maximum output of the photovoltaic power needs to be changed to retain active backup control, so that the operating point of the photovoltaic array deviates from the maximum power point, thereby reserving a part of the active power. The schematic diagram is as follows Fig. 9 As shown, To reserve active power reserves; the disadvantage of this method is that it requires the loss of a portion of the captured light energy, which reduces the energy utilization efficiency, but it does not require the high operation and maintenance costs required for additional energy storage units, reducing the complexity of the system. Within the normal power fluctuation range, the photovoltaic load reduction control method is more economical and reliable than the use of additional energy storage units.

[0109] When the DC side voltage is too high, the control strategy is as follows Fig.10 As shown, the DC / DC converter connected to the photovoltaic system is controlled to work in the MPPT control mode within the normal voltage range. When the DC side voltage is detected to be too high, it is immediately switched to the photovoltaic load reduction control mode to reduce the photovoltaic output power to achieve stable DC voltage control. When the photovoltaic output power decreases naturally or the load power increases, the photovoltaic DC / DC converter will automatically switch to the MPPT working mode.

[0110] When the DC side voltage is too low, the control principle diagram is as follows Fig.11 As shown, when Above a specified voltage threshold, will be limited to zero, and the virtual synchronous controller will work normally; When the voltage threshold is lower than the specified value, the output frequency of the virtual synchronous controller The corresponding deviation will be subtracted , thereby reducing the output power to maintain When the power demand of the grid decreases or the light irradiance increases, will naturally be higher than the specified voltage threshold, will be restored to zero and the PV storage system will seamlessly switch to normal control mode.

[0111] In this embodiment of the present invention, the MPPT working mode includes a power generation status monitoring mode. By monitoring the real-time light intensity and ambient temperature received by the photovoltaic power generation component and the power generation status data, based on the historical experimental data of the photovoltaic power generation component, the power generation status is monitored and warned, and timely warnings can be given when potential power generation failures are found in the photovoltaic power generation component.

[0112] Power generation status monitoring modes include:

[0113] Acquire real-time environmental data and power generation data of the photovoltaic power generation assembly and key position temperature; the real-time environmental data includes real-time light intensity and real-time ambient temperature;

[0114] According to the model information of the photovoltaic power generation component and the real-time environmental data, the corresponding conversion rate attenuation reference curve is retrieved from the historical experimental data. ; It should be noted that the conversion rate attenuation reference curve changes with the total working time of the corresponding photovoltaic power generation component and is classified according to the environmental reference data; wherein the environmental reference data includes the environmental reference data and the reference ambient temperature; for example, the reference light intensity is 10000Lux / m 2 A complete conversion rate attenuation reference curve corresponding to the reference ambient temperature of 5 degrees to 25 degrees.

[0115] Draw the real-time conversion rate attenuation curve corresponding to the photovoltaic power generation component based on the power generation data , the real-time conversion rate attenuation curve Reference curve of conversion rate decay Compare and calculate the abnormal evaluation value of photovoltaic power generation components by combining the temperature of key positions;

[0116] The abnormal evaluation value is compared with the preset threshold to provide an early warning of potential power generation failure.

[0117] Specifically, the process of retrieving the corresponding conversion rate attenuation reference curve from the historical experimental data is as follows: obtain the daily average light intensity, the maximum temperature of the day and the minimum temperature of the day corresponding to the photovoltaic power generation component. If the daily average light intensity is 10000Lux / m 2, the maximum temperature of the day is 25 degrees, and the minimum temperature of the day is 5 degrees, then the conversion rate attenuation reference curve A is selected from the historical experimental data as the corresponding conversion rate attenuation reference curve.

[0118] The method for obtaining the abnormal evaluation value is:

[0119]

[0120] in, is the abnormal evaluation value, is the total working time, is the real-time conversion rate decay curve Reference curve of conversion rate decay The number of intersections, is the temperature at the key position, It is the reference temperature of key positions.

[0121] when hour, The preset threshold can be used to determine whether there is a potential power generation failure in the photovoltaic power generation component and that an early warning is needed.

[0122] In order to verify the advantages of the solar storage VSG control method proposed in this invention, the following Fig.12 The simulation system of dual photovoltaic power supply and storage power supply shown in the figure works in an off-grid state, wherein the photovoltaic storage system No. 1 and the photovoltaic storage system No. 2 are both controlled by the photovoltaic storage VSG control method proposed in the present invention, the line impedance configuration of the load to each photovoltaic storage power supply is the same, and the topological structure of each photovoltaic storage power supply is the same. Figure 4 The same means that the PV-storage system No. 1 and the PV-storage system No. 2 are the same except that they may receive different light or ambient temperature. The specific main parameters are shown in Table 1. In addition, in order to facilitate the comparative analysis of the experiment, a simulation system of dual PV-storage power supply connected with traditional VSG control and the same parameters is built. The single-machine control structure is as follows Figure 1 shown.

[0123]

[0124] like Fig.13 As shown in the figure, the two photovoltaic power outputs are set to 75kW in 0-2s, and the power load is 100kW, then the two inverters output 50kW of power respectively, and the two batteries absorb 25kW of power respectively. The photovoltaic power is set to change in 2s, the photovoltaic power of the No. 1 photovoltaic storage system unit increases to 95kW, and the photovoltaic power of the No. 2 photovoltaic storage system unit decreases to 25kW. The load remains unchanged. As the input photovoltaic power increases, the output power of the No. 1 photovoltaic storage system inverter increases to 85kW, and as the input photovoltaic power decreases, the output power of the No. 2 photovoltaic storage system inverter also decreases to 15kW. At this time, both batteries absorb 10kW of power.

[0125] To facilitate comparative analysis, the same working conditions are set in the traditional VSG control system. Fig.14 As shown, at 2s, since the load did not change, the output power of the two inverters did not change either. However, due to the increase in the photovoltaic power of the inverter of the No. 1 photovoltaic storage system, the extra 45kW of power was completely absorbed by the battery, while the photovoltaic power of the inverter of the No. 2 photovoltaic storage system decreased, and the battery needed to output an additional 25kW of power.

[0126] Under the condition of constant load, the photovoltaic output of the two photovoltaic power sources changes respectively, resulting in the change of output power. The extra power in the improved system can be absorbed by each battery on average. Fig.13 It can be seen that the battery power provides energy that fluctuates during the transient process. In traditional VSG control, photovoltaic power waste and excessive battery charging and discharging will inevitably occur. By comparison, it can be seen that the photovoltaic storage VSG control method proposed in the present invention has the ability to share battery power and photovoltaic power in the microgrid compared to traditional VSG control. This also verifies that the control scheme can flexibly achieve the maximum output of photovoltaic power and avoid frequent battery charging and discharging.

[0127] In the above working conditions, the active power, reactive power, frequency and DC side voltage changes of the common coupling point of the photovoltaic storage VSG control method of the present invention are as follows: Fig.15 As shown, the active power is 100kW, and the output is relatively stable throughout the process. The reactive power is 10kVar, and the output is stable throughout the process. The DC voltage is maintained at 720V in 0-2s, and it is maintained at around 700V after the photovoltaic power drops. There are slight fluctuations, which are within a reasonable range. The frequency is basically maintained at 50Hz throughout the process, which can verify that the frequency stability meets the design requirements.

[0128] like Fig.16 As shown, based on the photovoltaic mutation in the above experiment, the load change is set at 2s, and the load increases to 120kW, which is equal to the sum of the photovoltaic powers of the two units. The inverter of the No. 1 photovoltaic storage system outputs 95kW of power, and the inverter of the No. 2 photovoltaic storage system outputs 25kw of power. The battery power output is maintained at 0kW. At this time, the two inverters realize the full output of the photovoltaic power.

[0129] When the load changes, the photovoltaic storage VSG control method of the present invention can quickly adjust the output power of the inverter to respond to the load change, while maximizing the use of the fluctuating photovoltaic power and reducing the charging and discharging of the battery. Fig.17In traditional VSG control, the battery of photovoltaic storage system No. 1 absorbs 35kW, while the battery of photovoltaic storage system No. 2 generates an additional 35kW of power. Setting the active power command value according to the load will cause a waste of photovoltaic power and additional battery charging and discharging. In order to achieve the effect of battery power sharing, traditional VSG control needs to frequently optimize the power command value, which reduces the flexibility and stability of the system.

[0130] The comparative analysis of the two scenarios shows that, regardless of the change in input photovoltaic power or load power, the photovoltaic storage VSG control method provided by the present invention can achieve global sharing and utilization of photovoltaic power in the entire multi-machine system by outputting the changed photovoltaic power. Under the control of the photovoltaic storage VSG control method of the present invention, the opposite changes in power of different photovoltaic power sources can offset each other. Therefore, compared with the traditional VSG strategy, the photovoltaic storage VSG control method of the present invention can make full use of the volatility of photovoltaic power sources, output real-time photovoltaic power to the greatest extent, and reduce dependence on batteries.

[0131] In addition, by Fig.16 and Fig.17 It can be seen that due to the constant capacitance voltage control used in the traditional control, the output curve of the battery power fluctuates greatly, which will undoubtedly cause great pressure on the battery. However, the improved control method of the photovoltaic storage VSG of the present invention has an extremely smooth control battery power output curve. In addition, the battery power response speed in the improved control is faster, the time before reaching stability is very short, and the dynamic performance of the system is greatly improved. It can be seen that the improved photovoltaic storage VSG control has significant advantages in terms of improving the economy of battery life and maximizing the use of photovoltaic power, as well as improving the dynamic performance of the system.

[0132] In order to verify the grid support capability of the photovoltaic storage VSG control method proposed in this invention, a simulation model is constructed in matlab / simulink as follows: Figure 4 The system shown is a single photovoltaic storage inverter connected in parallel with a large power grid.

[0133] like Fig.18 As shown, the grid frequency is set to decrease by 0.1Hz in 2s. Under the action of inertial support, the frequency curve does not drop immediately, but slowly drops to 49.9Hz. As the frequency decreases, the active power emitted by the inverter also increases by 16kW, verifying that the control strategy has the ability of primary frequency regulation. At the same time, in order to maintain the stability of the system voltage, the inverter increases a part of the reactive power. At this time, since the photovoltaic power remains unchanged, the DC side voltage also drops by 25V within the allowable range to adapt to the change in power. It can be seen that the photovoltaic storage VSG control method proposed in the present invention can meet the requirements of providing grid frequency support capabilities, give play to the characteristics of the virtual synchronous generator, and provide inertial support and primary frequency regulation functions.

[0134] In a second aspect, the present application provides a photovoltaic storage VSG control system that coordinates maximum power output and energy storage, and the system runs a photovoltaic storage VSG control method and system program for coordinating maximum power output and energy storage as described in any one of the above.

[0135] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations on the present application. Ordinary technicians in this field can change, modify, replace and modify the above embodiments within the scope of the present application.

Claims

1. A photovoltaic storage VSG control method for coordinating maximum power output and energy storage, It is characterized in that include: Based on the VSG control principle, an output power-angular frequency model between the inverter output power and the VSG virtual rotor angular frequency is established; Establishing a DC capacitor voltage-output power model between the DC side voltage and the inverter output power; According to the correlation between the DC side voltage change and the VSG virtual rotor angular frequency change, a control model for the proportional relationship between the DC side voltage and the output frequency deviation is established; The droop control between input power and rotor speed in synchronous generator is simulated, the battery power is related to the DC side voltage, and the battery droop control strategy is established so that the battery power variation is transferred to the DC side capacitor in response to demand.

2. The photovoltaic storage VSG control method for coordinating maximum power output and energy storage according to claim 1, It is characterized in that The method for establishing an output power-angular frequency model between the inverter output power and the VSG virtual rotor angular frequency based on the VSG control principle includes: in, is the virtual inertia of VSG, is the virtual damping, and are the actual angular frequency and rated angular frequency of the VSG virtual rotor, is the virtual damping coefficient, and are the mechanical power and actual output power of the inverter respectively; For a given reference power, is the adjustment parameter of the prime mover, and are the inverter output voltage and grid-side voltage respectively, is the impedance between the inverter and the grid.

3. The photovoltaic storage VSG control method for coordinating maximum power output and energy storage according to claim 2, It is characterized in that The method for establishing a DC capacitor voltage-output power model between the DC side voltage and the inverter output power comprises: in, and Respectively represent the rated capacitance and rated voltage of the inverter DC side, Indicates the actual DC side voltage of the inverter.

4. The photovoltaic storage VSG control method for coordinating maximum power output and energy storage according to claim 3, It is characterized in that The method for establishing a control model for the proportional relationship between the DC side voltage and the output frequency deviation according to the correlation between the DC side voltage change and the VSG virtual rotor angular frequency change includes: The correlation between the DC side voltage change and the VSG virtual rotor angular frequency change is: in, is the angular frequency change, is the correlation coefficient, is the voltage change on the DC side.

5. The photovoltaic storage VSG control method for coordinating maximum power output and energy storage according to claim 4, It is characterized in that The method of associating the battery power with the DC side voltage and establishing a battery droop control strategy includes: According to the battery current control model, a small signal model of system power balance under input change and a small signal model of system power balance under load change are obtained.

6. The photovoltaic storage VSG control method for coordinating maximum power output and energy storage according to claim 5, It is characterized in that The battery current control model includes: in, is the change in battery current, is the change in battery power, is the battery voltage; is the droop coefficient between frequency and battery power, which varies from the maximum power The maximum angular frequency deviation allowed under Decide.

7. The photovoltaic storage VSG control method for coordinating maximum power output and energy storage according to claim 6, It is characterized in that The small signal model of system power balance under the input change includes: in, is the photovoltaic power change, is the damping ratio.

8. The photovoltaic storage VSG control method for coordinating maximum power output and energy storage according to claim 6, It is characterized in that The small signal model of system power balance under the load change, in, is the output power change, is the capacitance power change.

9. The photovoltaic storage VSG control method for coordinating maximum power output and energy storage according to claim 1, It is characterized in that Establish the working mode control strategy between the DC side voltage and the DC / DC converter: When the DC voltage When in the normal voltage range, the DC / DC converter remains in the MPPT control mode; When the DC voltage When the specified voltage threshold is exceeded, the DC / DC converter is controlled to switch to the photovoltaic load reduction control mode to reduce the photovoltaic output power; When the photovoltaic output power naturally decreases to a specified photovoltaic power threshold or the load power increases to a specified load power threshold, the photovoltaic DC / DC converter is controlled to switch to the MPPT working mode.

10. A photovoltaic storage VSG control system that coordinates maximum power output and energy storage, It is characterized in that A program is running that implements the photovoltaic storage VSG control method for coordinating maximum power output and energy storage as described in any one of claims 1 to 9.

Images