Maximum power tracking control method and system for grid-forming type photovoltaic inverter

Abstract

The invention provides a maximum power tracking control method and system for a grid-forming photovoltaic inverter, and the method comprises the steps: obtaining the change rate of the DC voltage of a grid-connected converter and the change rate of the output power of a photovoltaic panel in real time; according to the change rate of the DC voltage of the grid-connected converter and the change rate of the output power of the photovoltaic panel, determining a gain symbol of a power synchronization loop of the grid-forming type grid-connected converter; determining a modulation voltage phase of an output bridge arm of the grid-forming type grid-connected converter; determining the modulation voltage amplitude of an output bridge arm of the grid-forming type grid-connected converter; and according to the modulation voltage amplitude of the output bridge arm of the network construction type grid-connected converter and the modulation voltage phase of the output bridge arm of the network construction type grid-connected converter, determining the modulation voltage of the network construction type grid-connected converter. According to the method and the device, stable operation of the network construction type photovoltaic inverter on all the working points of the photovoltaic power-voltage curve is realized, the photovoltaic inverter always works at the maximum power point, and maximum power tracking stable control of the network construction type photovoltaic inverter is realized.

Description

Technical Field

[0001] The present application relates to the technical field of new energy power generation and grid connection. Specifically, it relates to a maximum power tracking control method and system for a grid-forming photovoltaic inverter. Background Art

[0002] In recent years, new energy power sources represented by wind power and photovoltaic power have developed rapidly, and the installed capacity has increased year by year. However, the current wind power and photovoltaic new energy show a grid-following characteristic of current source nature and do not show inertia to the power grid. The power system faces the problem of serious shortage of equivalent inertia, and the safety and stability of the power system are seriously threatened.

[0003] The grid-forming photovoltaic can automatically synchronize with the power grid and achieve real-time control of active power by adopting a virtual synchronous control method that simulates the rotor motion equation of a synchronous generator for its grid-connected inverter. By adopting a virtual excitation control method that simulates the excitation regulator of a synchronous generator, it can automatically adjust the voltage and achieve real-time control of reactive power. It shows an external characteristic similar to the active frequency regulation - reactive voltage regulation of a synchronous generator at the output port and has the ability to autonomously support the grid frequency and voltage.

[0004] In the patent "An Adaptive Virtual Synchronous Generator Impedance Tuning Method, Device and Medium" with the application number CN119134529A, it establishes an open-loop voltage control model to obtain a first voltage reference value and a second voltage reference value. When the current flowing through the grid-forming converter is less than the current limit, the voltage is adjusted to the first voltage reference value; otherwise, the voltage is adjusted to the second voltage reference value, and the resistance and inductance of the virtual impedance are controlled within a conservative feasible region. Since the virtual synchronous machine control method reduces the power control response speed of the photovoltaic inverter, and the power-voltage curve characteristic of the photovoltaic inverter causes it to easily transfer the operating point to the left area of the curve and have a stability problem during maximum power tracking, resulting in the photovoltaic inverter being unable to work properly. To solve this problem, the industrial community currently sets the operating point of the photovoltaic inverter at a place slightly smaller than the maximum power point, which leads to a reduction in the power generation of the photovoltaic inverter and causes an economic loss in power generation.

[0005] Therefore, aiming at the deficiencies of the existing technology, there is an urgent need in this field to propose a method capable of tracking and stabilizing the maximum power of a grid-forming photovoltaic inverter. Summary of the Invention

[0006] Aiming at the defects in the existing technology, the purpose of the present application is to provide a maximum power tracking control method and system for a grid-forming photovoltaic inverter.

[0007] In the first aspect of the present application, a maximum power tracking control method for a grid-forming photovoltaic inverter is provided, including:

[0008] Obtain the change rate of the DC voltage of the grid-connected converter and the change rate of the output power of the photovoltaic panel in real time;

[0009] Determine the gain sign of the power synchronization loop of the grid-forming grid-connected converter according to the change rate of the DC voltage of the grid-connected converter and the change rate of the output power of the photovoltaic panel;

[0010] Perform proportional control on the active power deviation of the grid-connected converter and add the grid frequency value to determine the phase of the modulation voltage of the output bridge arm of the grid-forming grid-connected converter;

[0011] Sum the proportional control output of the voltage deviation of the grid, the proportional control output of the reactive power deviation of the grid-connected converter, and the rated voltage value of the grid to determine the amplitude of the modulation voltage of the output bridge arm of the grid-forming grid-connected converter;

[0012] Determine the modulation voltage of the grid-forming grid-connected converter according to the amplitude of the modulation voltage of the output bridge arm of the grid-forming grid-connected converter and the phase of the modulation voltage of the output bridge arm of the grid-forming grid-connected converter.

[0013] Optionally, the determining the gain sign of the power synchronization loop of the grid-forming grid-connected converter according to the change rate of the DC voltage of the grid-connected converter and the change rate of the output power of the photovoltaic panel includes:

[0014] If the product of the change rate of the DC voltage of the grid-connected converter and the change rate of the output power of the photovoltaic panel is not less than zero, determine that the gain sign of the power synchronization loop of the grid-forming grid-connected converter is negative.

[0015] Optionally, the determining the gain sign of the power synchronization loop of the grid-forming grid-connected converter according to the change rate of the DC voltage of the grid-connected converter and the change rate of the output power of the photovoltaic panel further includes:

[0016] If the product of the change rate of the DC voltage of the grid-connected converter and the change rate of the output power of the photovoltaic panel is less than zero, determine that the gain sign of the power synchronization loop of the grid-forming grid-connected converter is positive.

[0017] Optionally, the method further includes:

[0018] Obtain the instantaneous value of the active power of the grid-connected converter;

[0019] Perform low-pass filtering on the instantaneous value of the active power of the grid-connected converter to determine the actual value of the active power of the grid-connected converter;

[0020] Subtract the actual value of the active power of the grid-connected converter from the set value of the active power of the grid-connected converter to determine the active power deviation of the grid-connected converter.

[0021] Optionally, performing proportional control on the active power deviation of the grid-connected converter and adding the grid frequency value to determine the output leg modulation voltage phase of the network-forming grid-connected converter includes:

[0022] Performing proportional control on the active power deviation of the grid-connected converter and adding the grid frequency value to determine the angular frequency of the control signal of the grid-connected converter;

[0023] Integrating the angular frequency of the control signal of the grid-connected converter to determine the output leg modulation voltage phase of the network-forming grid-connected converter.

[0024] Optionally, the method further includes:

[0025] A method for determining the proportional control output of the voltage deviation of the grid includes:

[0026] Subtracting the voltage set value of the grid from the actual voltage value to determine the voltage deviation of the grid;

[0027] Inputting the voltage deviation of the grid into a proportional controller for proportional control to determine the proportional control output of the voltage deviation of the grid;

[0028] A method for determining the proportional control output of the reactive power deviation of the grid-connected converter includes:

[0029] Subtracting the reactive power set value of the grid-connected converter from the actual reactive power value to determine the reactive power deviation of the grid-connected converter;

[0030] Inputting the reactive power deviation of the grid-connected converter into a proportional controller for proportional control to determine the proportional control output of the reactive power deviation of the grid-connected converter.

[0031] In a second aspect of the present application, a maximum power tracking control system for a network-forming photovoltaic inverter is provided, including:

[0032] Photovoltaic inverter grid-connected power generation system, grid-connected converter synchronous loop gain symbol control module, grid-connected converter synchronous angle phase control module, grid-connected converter AC voltage amplitude control module, grid-connected converter AC modulation voltage control module. The grid-connected converter synchronous loop gain symbol control module is used to control the gain symbol of the power synchronization loop of the grid-connected converter in the photovoltaic inverter grid-connected power generation system. The grid-connected converter synchronous angle phase control module is used to control the phase of the modulation voltage of the output bridge arm of the grid-connected converter in the photovoltaic inverter grid-connected power generation system. The grid-connected converter AC voltage amplitude control module is used to control the amplitude of the modulation voltage of the output bridge arm of the grid-connected converter in the photovoltaic inverter grid-connected power generation system. The grid-connected converter AC modulation voltage control module is used to control the modulation voltage of the grid-connected converter in the photovoltaic inverter grid-connected power generation system.

[0033] Optionally, the photovoltaic inverter grid-connected power generation system includes a photovoltaic panel, a DC capacitor bank, a grid-connected converter, an AC filter, and a power grid.

[0034] A maximum power tracking control method for a grid-forming photovoltaic inverter provided by this application. It controls the gain symbol of the power synchronization loop of the grid-forming grid-connected converter in real time by detecting the change rate of the DC voltage of the grid-connected converter and the output power of the photovoltaic panel in real time, and controls the modulation voltage of the grid-forming grid-connected converter by controlling the phase of the modulation voltage of the output bridge arm of the grid-forming grid-connected converter and the amplitude of the modulation voltage of the output bridge arm of the grid-forming grid-connected converter, so as to realize the control of the grid-connected power of the photovoltaic inverter, flexibly adjust the control strategy of the active power of the grid-connected converter, ensure that the grid-forming photovoltaic inverter always operates at the maximum power point, thereby realizing the stable control of the maximum power tracking of the grid-forming photovoltaic inverter in the power control mode, ensuring that the grid-forming photovoltaic inverter has the inertia response function, and realizing the stable control of the power of the grid-connected converter at each working point of the photovoltaic power-voltage characteristic curve, simplifying the control algorithm of the converter, reducing the control performance requirements for the digital controller, and effectively improving the power generation efficiency of the photovoltaic inverter grid-connected power generation system.

[0035] Other technical effects brought by the additional features will be further elaborated in the corresponding embodiments. Description of the Drawings

[0036] By reading the detailed description of the non-restrictive embodiments with reference to the following drawings, other features, objectives, and advantages of this application will become more apparent:

[0037] Figure 1 It is a flowchart of a maximum power tracking control method for a grid-forming photovoltaic inverter shown according to an exemplary embodiment.

[0038] Figure 2Schematic diagram of the strategy of a grid-forming PV inverter maximum power tracking control method shown according to an exemplary embodiment.

[0039] Figure 3 Schematic diagram of the gain symbol control strategy of the power synchronization loop of a grid-forming PV inverter shown according to an exemplary embodiment.

[0040] Figure 4 Schematic diagram of the phase angle control strategy of the grid-connected converter of a grid-forming PV inverter shown according to an exemplary embodiment.

[0041] Figure 5 Schematic diagram of the amplitude control strategy of the grid-connected converter of a grid-forming PV inverter shown according to an exemplary embodiment.

[0042] Figure 6 Schematic diagram of the instability effect of the maximum power tracking control of a grid-forming PV inverter shown according to an exemplary embodiment.

[0043] Figure 7 Schematic diagram of the stability effect of the maximum power tracking control of a grid-forming PV inverter shown according to an exemplary embodiment.

[0044] Figure 8 Schematic diagram of the overall structure of the maximum power tracking control system of a grid-forming PV inverter shown according to an exemplary embodiment. Detailed implementation mode

[0045] The present application will be described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present application, but do not limit the present application in any form. It should be noted that those of ordinary skill in the art can make several modifications and improvements without departing from the concept of the present application. These all belong to the protection scope of the present application.

[0046] The existing grid-forming PV uses the virtual synchronous machine control method, which reduces the power control response speed of the PV inverter, and the power-voltage curve characteristic of the PV inverter causes the operating point to shift to the left area of the curve during maximum power tracking, resulting in instability, making the PV inverter unable to work properly. In the industrial field, the operating point of the PV inverter is set near the maximum power point, but this method reduces the power generation of the PV inverter, causing economic losses in power generation. Based on the above problems, the embodiments of the present application provide a maximum power tracking control method for a grid-forming PV inverter to solve the above existing problems.

[0047] Figure 1 Flowchart of a maximum power tracking control method for a grid-forming PV inverter shown according to an exemplary embodiment. Figure 2Schematic diagram of a strategy for the maximum power tracking control method of a grid-forming photovoltaic inverter according to an exemplary embodiment.

[0048] Referring to Figure 1 、 Figure 2 As shown, in an embodiment of the present application, a maximum power tracking control method for a grid-forming photovoltaic inverter includes S11 to S15.

[0049] S11, obtain the change rate of the DC voltage of the grid-connected converter and the change rate of the output power of the photovoltaic panel in real time.

[0050] S12, determine the gain sign of the power synchronization loop of the grid-forming grid-connected converter according to the change rate of the DC voltage of the grid-connected converter and the change rate of the output power of the photovoltaic panel.

[0051] S13, perform proportional control on the active power deviation of the grid-connected converter and add the grid frequency value to determine the phase of the modulation voltage of the output bridge arm of the grid-forming grid-connected converter.

[0052] S14, sum the proportional control output of the voltage deviation of the grid, the proportional control output of the reactive power deviation of the grid-connected converter, and the rated voltage of the grid to determine the amplitude of the modulation voltage of the output bridge arm of the grid-forming grid-connected converter.

[0053] S15, determine the modulation voltage of the grid-forming grid-connected converter according to the amplitude of the modulation voltage of the output bridge arm of the grid-forming grid-connected converter and the phase of the modulation voltage of the output bridge arm of the grid-forming grid-connected converter.

[0054] In the above embodiment of the present application, by detecting the change rate of the DC voltage of the grid-connected converter and the output power of the photovoltaic panel in real time, the gain sign of the power synchronization loop of the grid-forming grid-connected converter is controlled in real time, and by controlling the phase of the modulation voltage of the output bridge arm of the grid-forming grid-connected converter and the amplitude of the modulation voltage of the output bridge arm of the grid-forming grid-connected converter, the modulation voltage of the grid-forming grid-connected converter is controlled, so as to realize the control of the grid-connected power of the photovoltaic inverter, flexibly adjust the control strategy of the active power of the grid-connected converter, ensure that the grid-forming photovoltaic inverter always operates at the maximum power point, thereby realizing the stable control of the maximum power tracking of the grid-forming photovoltaic inverter in the power control mode, ensuring that the grid-forming photovoltaic inverter has the inertia response function, and realizing the stable control of the grid-connected converter power at each working point of the photovoltaic power-voltage characteristic curve, simplifying the control algorithm of the converter, reducing the control performance requirements for the digital controller, and effectively improving the power generation efficiency of the photovoltaic inverter grid-connected power generation system.

[0055] Figure 3 Schematic diagram of a gain sign control strategy for the power synchronization loop of a grid-forming photovoltaic inverter according to an exemplary embodiment.

[0056] To determine the gain sign of the power synchronization loop of the network-forming grid-connected converter, refer to Figure 3 As shown in the following, in some specific embodiments of the present application, in S12, according to the change rate of the DC voltage of the grid-connected converter and the change rate of the output power of the photovoltaic panel, determine the gain sign of the power synchronization loop of the network-forming grid-connected converter, including S121 to S122.

[0057] S121, if the product of the change rate of the DC voltage of the grid-connected converter and the change rate of the output power of the photovoltaic panel is not less than zero, determine that the gain sign of the power synchronization loop of the network-forming grid-connected converter is negative.

[0058] S122, if the product of the change rate of the DC voltage of the grid-connected converter and the change rate of the output power of the photovoltaic panel is less than zero, determine that the gain sign of the power synchronization loop of the network-forming grid-connected converter is positive.

[0059] Exemplarily, the calculation formula for the gain sign of the power synchronization loop of the network-forming grid-connected converter is as follows:

[0060]

[0061] where, sg represents the gain sign of the power synchronization loop of the network-forming grid-connected converter, U dc represents the actual value of the DC voltage of the grid-connected converter, P pv represents the instantaneous value of the output power of the photovoltaic panel, represents the differential operation, represents the change rate of the DC voltage of the grid-connected converter, represents the change rate of the output power of the photovoltaic panel.

[0062] The change rate of the DC voltage of the grid-connected converter The calculation formula is as follows:

[0063]

[0064] where, T smp represents the sampling period of the DC voltage of the grid-connected converter, and k represents the sampling point sequence.

[0065] The change rate of the output power of the photovoltaic panel The calculation formula is as follows:

[0066]

[0067] In the above embodiments of the present application, according to the difference between the product of the conversion rate of the DC voltage of the grid-connected converter and the change rate of the output power of the photovoltaic panel on the left and right sides of the photovoltaic power-voltage characteristic curve, the gain sign of the power synchronization loop of the grid-forming grid-connected converter is adjusted in real time. Moreover, when the operating point of the grid-connected converter is on the left side of the photovoltaic power-voltage characteristic curve, stable control of the power of the grid-connected converter is achieved, ensuring that the photovoltaic inverter always operates at the maximum power point. Thus, the control algorithm of the converter is simplified, the control performance requirements for the digital controller are reduced, and at the same time, the power generation efficiency of the photovoltaic inverter grid-connected power generation system is effectively improved.

[0068] In an embodiment of the present application, a maximum power tracking control method for a grid-forming photovoltaic inverter may further include S16 to S18.

[0069] S16, obtaining the instantaneous value of the active power of the grid-connected converter.

[0070] S17, performing low-pass filtering on the instantaneous value of the active power of the grid-connected converter to determine the actual value of the active power of the grid-connected converter.

[0071] Specifically, the low-pass filtering process may employ an active power filter.

[0072] S18, subtracting the set value of the active power of the grid-connected converter from the actual value of the active power of the grid-connected converter to determine the active power deviation of the grid-connected converter.

[0073] Steps S16 to S18 of the present application are executed after step S12 and before step S13.

[0074] Exemplarily, based on steps S16 to S18, the formula for determining the actual value of the active power of the grid-connected converter is as follows:

[0075]

[0076] where P g represents the instantaneous value of the active power of the grid-connected converter, T p represents the filtering time constant of the active power filter, s represents the Laplace operator, and P fdbk represents the actual value of the active power of the grid-connected converter.

[0077] The active power deviation of the grid-connected converter is:

[0078] P ref -P fdbk

[0079] where P ref represents the set value of the active power of the grid-connected converter, and P fdbk represents the true value of the active power of the grid-connected converter.

[0080] Figure 4 Schematic diagram of the phase angle control strategy of a grid-forming PV inverter grid-connected converter shown according to an exemplary embodiment.

[0081] To determine the phase of the output leg modulation voltage of the grid-forming grid-connected converter, referring to Figure 4 shown, in some specific embodiments of the present application, S13, perform proportional control on the active power deviation of the grid-connected converter and add the grid frequency value to determine the phase of the output leg modulation voltage of the grid-forming grid-connected converter. S131 to S132 can be adopted.

[0082] S131, perform proportional control on the active power deviation of the grid-connected converter and add the grid frequency value to determine the angular frequency of the control signal of the grid-connected converter.

[0083] S132, integrate the angular frequency of the control signal of the grid-connected converter to determine the phase of the output leg modulation voltage of the grid-forming grid-connected converter.

[0084] The phase of the output leg modulation voltage of the grid-forming converter also represents the rotation angle of the control signal of the grid-connected converter.

[0085] Exemplarily, based on the above steps S131 to S132, calculate the angular frequency of the control signal of the grid-connected converter and the phase of the output leg modulation voltage of the grid-connected converter. The formulas are as follows:

[0086]

[0087] Where, ω gsc represents the angular frequency of the control signal of the grid-connected converter, ω g represents the grid frequency value, P ref represents the set value of the active power of the grid-connected converter, P fdbk represents the actual value of the active power of the grid-connected converter, K P represents the gain of the power control loop, θ gsc represents the phase of the output leg modulation voltage of the grid-connected converter, and s represents the Laplace operator.

[0088] Specifically, the grid frequency value ω g also represents the real-time angular frequency of the grid voltage, and K P also serves as the control coefficient for proportional control.

[0089] In the above embodiments of the present application, by performing proportional control on the active power deviation of the grid-connected converter and adding the grid frequency value to obtain the angular frequency of the control signal of the grid-connected converter, and then integrating according to the angular frequency of the control signal of the grid-connected converter, the modulation voltage phase of the output bridge arm of the grid-connected converter is obtained, so as to realize the control of the modulation voltage phase of the output bridge arm of the grid-forming grid-connected converter.

[0090] In an embodiment of the present application, a maximum power tracking control method for a grid-forming photovoltaic inverter may further include S19 to S20.

[0091] S19. A method for determining the proportional control output of the voltage deviation of the grid, including: S191 to S192.

[0092] S191. Subtract the actual voltage value of the grid from the set voltage value of the grid to determine the voltage deviation of the grid.

[0093] S192. Input the voltage deviation of the grid into a proportional controller for proportional control to determine the proportional control output of the voltage deviation of the grid.

[0094] Specifically, the proportional control output of the voltage deviation of the grid is the output after proportional control of the difference between the set voltage value and the actual voltage value of the grid voltage.

[0095] Exemplarily, based on the above steps S191 to S192, the proportional control output of the voltage deviation of the grid is:

[0096] (U sref -U fdbk )K V

[0097] Wherein, U sref represents the set voltage value of the grid, U fdbk represents the actual voltage value of the grid, and K V represents the proportional control coefficient of the voltage.

[0098] Specifically, the proportional control coefficient K V of the voltage also represents the droop coefficient of the AC voltage in the present application.

[0099] S20. A method for determining the proportional control output of the reactive power deviation of the grid-connected converter, including: S201 to S202.

[0100] S201. Subtract the actual reactive power value of the grid-connected converter from the set reactive power value of the grid-connected converter to determine the reactive power deviation of the grid-connected converter.

[0101] S202, perform proportional control on the reactive power deviation of the grid-connected converter in a proportional controller to determine the proportional control output of the reactive power deviation of the grid-connected converter.

[0102] Specifically, the reactive power deviation of the grid-connected converter represents the output after proportional control of the difference between the reactive power set value and the actual reactive power of the grid-connected converter.

[0103] Exemplarily, based on the above steps S201 to S202, the proportional control output of the reactive power deviation of the grid-connected converter is expressed as:

[0104] (Q sref -Q fdbk )K Q

[0105] where Q sref represents the reactive power set value of the grid-connected converter, Q fdbk represents the actual reactive power of the grid-connected converter, and K Q represents the proportional control coefficient of reactive power.

[0106] The above steps S19 to S20 are executed after step S13 and before step S14 in this application.

[0107] Figure 5 It is a schematic diagram of the amplitude control strategy of the grid-forming type photovoltaic inverter grid-connected converter shown according to an exemplary embodiment.

[0108] To determine the amplitude of the output bridge arm modulation voltage of the grid-forming type grid-connected converter, referring to Figure 5 shown, in some specific embodiments of this application, in S14, sum the proportional control output of the voltage deviation of the power grid, the proportional control output of the reactive power deviation of the grid-connected converter, and the rated voltage of the power grid to determine the amplitude of the output bridge arm modulation voltage of the grid-forming type grid-connected converter, which can be:

[0109] U s =(U sref -U fdbk )·K V +(Q sref -Q fdbk )·K Q +U gn

[0110] where U s represents the amplitude of the output bridge arm modulation voltage of the grid-forming type grid-connected converter, U sref represents the voltage set value of the power grid, U fdbk represents the actual voltage of the power grid, K V represents the droop coefficient of the AC voltage, Qsref Represents the reactive power set value of the grid-connected converter, Q fdbk Represents the actual reactive power value of the grid-connected converter K Q Represents the proportional control coefficient of the reactive power of the grid-connected converter, U gn Represents the rated voltage of the power grid

[0111] Specifically, K V Also represents the proportional control coefficient for proportional control of the voltage deviation of the power grid

[0112] Specifically, the actual voltage value U of the power grid fdbk Can be obtained by low-pass filtering the instantaneous value U of the phase voltage amplitude at the grid connection point of the grid-connected converter. Its expression is sm After low-pass filtering by a low-pass filter

[0113]

[0114] Among them, U fdbk Represents the actual voltage value of the power grid, U sm Represents the instantaneous value of the phase voltage amplitude at the grid connection point of the grid-connected converter, that is, the actual power grid voltage value, T u Represents the filtering time constant of the power grid phase voltage filter

[0115] In this embodiment, the low-pass filter for low-pass filtering the instantaneous value of the phase voltage amplitude at the grid connection point of the grid-connected converter can use the power grid phase voltage filter

[0116] The actual reactive power value of the grid-connected converter is obtained by low-pass filtering the instantaneous reactive power value of the grid-connected converter through a low-pass filter. Its expression is

[0117]

[0118] Among them, Q fdbk Represents the actual reactive power value of the grid-connected converter, T q Represents the filtering time constant of the reactive power filter of the grid-connected converter, Q g Represents the instantaneous reactive power value of the grid-connected converter

[0119] In this embodiment, the low-pass filter for low-pass filtering the instantaneous reactive power value of the grid-connected converter can use the reactive power filter

[0120] In the above embodiments of the present application, according to the proportional control output of the voltage deviation of the power grid, the proportional control quantity of the reactive power deviation of the grid-connected converter, and the rated voltage of the power grid, the control of the modulation voltage amplitude of the output bridge arm of the grid-forming grid-connected converter is realized

[0121] In some specific embodiments of the present application, the modulation voltage of the grid-forming grid-connected converter includes the modulation voltage of phase A, the modulation voltage of phase B, and the modulation voltage of phase C.

[0122] In some specific embodiments of the present application, to control the modulation voltage of the grid-forming grid-connected transformer, S15, according to the amplitude of the output bridge arm modulation voltage of the grid-forming grid-connected converter and the phase of the output bridge arm modulation voltage of the grid-forming grid-connected converter, the modulation voltage of the grid-forming grid-connected converter can be determined by using:

[0123]

[0124] where U ma represents the real-time value of the modulation voltage of phase A, U mb represents the real-time value of the modulation voltage of phase B, U mc represents the real-time value of the modulation voltage of phase C, U s represents the amplitude of the output bridge arm modulation voltage of the grid-forming grid-connected converter, and θ gsc represents the phase of the output bridge arm modulation voltage of the grid-connected converter.

[0125] In the above embodiments of the present application, the modulation voltage of the grid-connected converter is calculated in real time by using the mathematical relationship between the amplitude-phase and instantaneous value of the AC voltage, so as to realize the control of the modulation voltage of the grid-forming grid-connected converter, and further realize the stable control of the power of the grid-connected converter.

[0126] Figure 6 Fig. shows the schematic diagram of the instability effect of the maximum power tracking control of a grid-forming photovoltaic inverter according to an exemplary embodiment. Figure 7 Fig. shows the schematic diagram of the stable effect of the maximum power tracking control of a grid-forming photovoltaic inverter according to an exemplary embodiment.

[0127] Referring to Figure 6 As shown, when the maximum power tracking control method of a grid-forming photovoltaic inverter provided by the present application is not adopted, the active power fluctuates significantly at some operating points of the photovoltaic power-voltage characteristic curve of the photovoltaic inverter, and the maximum power of the photovoltaic inverter is unstable.

[0128] Referring to Figure 7 As shown, after adopting the maximum power tracking control method of a grid-forming photovoltaic inverter provided by the present application, the active power of the photovoltaic inverter operates stably at all operating points of the photovoltaic power-voltage characteristic curve, and it is ensured that the photovoltaic inverter always operates at the maximum power point. This shows that the maximum power tracking control method of a grid-forming photovoltaic inverter provided by the present application has reliability and effectiveness.

[0129] A maximum power point tracking control method for a grid-forming photovoltaic inverter provided by this application. By detecting the change rate of the DC voltage of the grid-connected converter and the change rate of the output power of the photovoltaic panel in real time, when the product of the change rate of the DC voltage and the change rate of the output power of the photovoltaic panel is less than or equal to zero, the gain sign of the active power control loop of the grid-connected converter is set to positive; when the product of the change rate of the DC voltage and the change rate of the output power of the photovoltaic panel is greater than zero, the gain sign of the active power control loop of the grid-connected converter is set to negative. The deviation of the active power is added to the grid frequency value through the output value of the proportional controller to obtain the synchronous angular frequency of the grid-connected converter. After integrating the synchronous angular frequency, the phase of the output modulation voltage of the grid-connected converter is obtained, and the grid-connected power of the photovoltaic inverter is adjusted to realize the stable operation of the working point of the photovoltaic inverter on all working points of the photovoltaic power-voltage characteristic curve, ensure that the photovoltaic inverter always operates at the maximum power point, realize the stable control of the maximum power point tracking of the grid-forming photovoltaic inverter, and ensure that the photovoltaic inverter has the inertia response function.

[0130] A maximum power point tracking control method for a grid-forming photovoltaic inverter provided by this application does not require complex switching operations, greatly simplifies the control algorithm of the converter, reduces the control performance requirements for the digital controller, and effectively improves the power generation efficiency of the photovoltaic inverter grid-connected power generation system.

[0131] Figure 8 It is a schematic diagram of the overall structure of a maximum power point tracking control system for a grid-forming photovoltaic inverter shown according to an exemplary embodiment.

[0132] Refer to Figure 8 As shown, in another embodiment of this application, a maximum power point tracking control system for a grid-forming photovoltaic inverter includes a photovoltaic inverter grid-connected power generation system, a grid-connected converter synchronous loop gain sign control module, a grid-connected converter synchronous angular phase control module, a grid-connected converter AC voltage amplitude control module, and a grid-connected converter AC modulation voltage control module.

[0133] The grid-connected converter synchronous loop gain sign control module is used to control the gain sign of the power synchronous loop of the grid-connected converter in the photovoltaic inverter grid-connected power generation system. The grid-connected converter synchronous angular phase control module is used to control the phase of the output bridge arm modulation voltage of the grid-connected converter in the photovoltaic inverter grid-connected power generation system. The grid-connected converter AC voltage amplitude control module is used to control the amplitude of the output bridge arm modulation voltage of the grid-connected converter in the photovoltaic inverter grid-connected power generation system. The grid-connected converter AC modulation voltage control module is used to control the modulation voltage of the grid-connected converter in the photovoltaic inverter grid-connected power generation system.

[0134] Specifically, the grid-connected converter synchronous loop gain symbol control module, the grid-connected converter synchronous angle phase control module, the grid-connected converter AC voltage amplitude control module, and the grid-connected converter AC modulation voltage control module jointly achieve the control of the active power of the grid-connected converter in the PV inverter grid-connected power generation system.

[0135] Among them, the output power P of the PV panel pv and the DC voltage signal U of the grid-connected converter dc are used as the input quantities of the grid-connected converter synchronous loop gain symbol control module. The output quantity of the grid-connected converter synchronous loop gain symbol control module is the gain symbol sg of the grid-connected converter synchronous loop. The gain symbol sg of the grid-connected converter synchronous loop is used as the input quantity of the grid-connected converter synchronous angle phase control module to control the gain change of its forward channel in real time. The output quantity of the grid-connected converter synchronous angle phase control module is the rotation angle θ gsc of the modulation voltage of the output bridge arm of the grid-connected converter, that is, the phase of the modulation voltage of the output bridge arm of the grid-connected converter. The set value Q of the grid-connected reactive power of the PV inverter sref , the instantaneous value Q of the reactive power of the grid-connected converter g , the set value U of the voltage of the power grid sref and the actual value U of the power grid voltage sm are used as the input quantities of the AC voltage amplitude control module. The output quantity of the AC voltage amplitude control module is the amplitude U s of the modulation voltage of the output bridge arm of the grid-connected converter. The output quantity of the grid-connected converter synchronous angle phase control module and the output quantity of the grid-connected converter AC voltage amplitude control module, that is, the rotation angle θ gsc of the modulation voltage of the output bridge arm of the grid-connected converter and the amplitude U s of the modulation voltage of the output bridge arm of the grid-connected converter are used as the input quantities of the grid-connected converter AC modulation voltage control module to obtain the three-phase modulation wave voltage of the grid-forming grid-connected converter and drive the grid-connected converter to operate through the PWM modulation module.

[0136] In some specific embodiments of the present application, the PV inverter grid-connected power generation system includes a PV panel, a DC capacitor bank, a grid-connected converter, an AC filter, and a power grid. Among them, the positive DC output terminal of the PV panel is connected to the positive terminal of the DC capacitor bank, the negative DC output terminal of the PV panel is connected to the negative terminal of the DC capacitor bank, the positive terminal of the DC capacitor bank is connected to the positive DC terminal of the grid-connected converter, the negative terminal of the DC capacitor bank is connected to the negative DC terminal of the grid-connected converter, the three-phase AC terminals of the grid-connected converter are respectively connected to the three-phase input AC terminals of the AC filter, and the three-phase output AC terminals of the AC filter are connected to the power grid through an electrical switch.

[0137] The photovoltaic panel is used to convert sunlight into electrical energy, the DC capacitor bank is used to stabilize the DC voltage, the grid-connected converter is used to invert the direct current into three-phase alternating current and send it into the grid, and the AC filter is used to filter out the current harmonics output by the grid-connected converter.

[0138] Specifically, the grid-connected converter can adopt a two-level converter or a three-level converter.

[0139] The specific embodiments of the present application have been described above. It should be understood that the present application is not limited to the above specific embodiments, and those skilled in the art can make various deformations or modifications within the scope of the claims, which do not affect the essence of the present application. The above preferred features can be used in any combination without conflict.

Claims

1. A maximum power point tracking control method for a grid-forming photovoltaic inverter, characterized in that, Including: Obtaining the change rate of the DC voltage of the grid-connected converter and the change rate of the output power of the photovoltaic panel in real time; Determining the gain sign of the power synchronization loop of the grid-forming grid-connected converter according to the change rate of the DC voltage of the grid-connected converter and the change rate of the output power of the photovoltaic panel; Performing proportional control on the active power deviation of the grid-connected converter and adding the grid frequency value to determine the phase of the modulation voltage of the output arm of the grid-forming grid-connected converter; Summing the proportional control output of the voltage deviation of the grid, the proportional control output of the reactive power deviation of the grid-connected converter, and the rated voltage value of the grid to determine the amplitude of the modulation voltage of the output arm of the grid-forming grid-connected converter; Determining the modulation voltage of the grid-forming grid-connected converter according to the amplitude of the modulation voltage of the output arm of the grid-forming grid-connected converter and the phase of the modulation voltage of the output arm of the grid-forming grid-connected converter.

2. The method according to claim 1, wherein The determining the gain sign of the power synchronization loop of the grid-forming grid-connected converter according to the change rate of the DC voltage of the grid-connected converter and the change rate of the output power of the photovoltaic panel includes: If the product of the change rate of the DC voltage of the grid-connected converter and the change rate of the output power of the photovoltaic panel is not less than zero, determining that the gain sign of the power synchronization loop of the grid-forming grid-connected converter is negative.

3. The method according to claim 2, characterized in that, The determining the gain sign of the power synchronization loop of the grid-forming grid-connected converter according to the change rate of the DC voltage of the grid-connected converter and the change rate of the output power of the photovoltaic panel further includes: If the product of the change rate of the DC voltage of the grid-connected converter and the change rate of the output power of the photovoltaic panel is less than zero, determining that the gain sign of the power synchronization loop of the grid-forming grid-connected converter is positive.

4. The method according to claim 1, wherein The method further includes: Obtaining the instantaneous value of the active power of the grid-connected converter; Performing low-pass filtering on the instantaneous value of the active power of the grid-connected converter to determine the actual value of the active power of the grid-connected converter; Subtracting the set value of the active power of the grid-connected converter from the actual value of the active power of the grid-connected converter to determine the active power deviation of the grid-connected converter.

5. The method according to claim 4, characterized in that The performing proportional control on the active power deviation of the grid-connected converter and adding the grid frequency value to determine the phase of the modulation voltage of the output arm of the grid-forming grid-connected converter includes: Performing proportional control on the active power deviation of the grid-connected converter and adding the grid frequency value to determine the angular frequency of the control signal of the grid-connected converter; Integrating the angular frequency of the control signal of the grid-connected converter to determine the phase of the modulation voltage of the output arm of the grid-forming grid-connected converter.

6. The method according to claim 1, wherein The method further includes: The method for determining the proportional control output of the voltage deviation of the grid includes: Subtracting the actual voltage value from the set voltage value of the grid to determine the voltage deviation of the grid; Inputting the voltage deviation of the grid into a proportional controller for proportional control to determine the proportional control output of the voltage deviation of the grid; The method for determining the proportional control output of the reactive power deviation of the grid-connected converter includes: Calculate the difference between the reactive power setpoint and the actual reactive power of the grid-connected converter to determine the reactive power deviation of the grid-connected converter; Input the reactive power deviation of the grid-connected converter into a proportional controller for proportional control to determine the proportional control output of the reactive power deviation of the grid-connected converter.

7. The method according to claim 6, wherein The step of summing the proportional control output of the voltage deviation of the power grid, the proportional control output of the reactive power deviation of the grid-connected converter, and the rated voltage of the power grid to determine the amplitude of the modulation voltage of the output bridge arm of the grid-forming grid-connected converter includes: U s = (U sref - U fdbk ) · K V + (Q sref - Q fdbk ) · K Q + U gn Among them, U s represents the amplitude of the modulation voltage of the output bridge arm of the grid-forming grid-connected converter, U sref represents the voltage set value of the power grid, U fdbk represents the actual voltage value of the power grid, K V represents the droop coefficient of the AC voltage, Q sref represents the reactive power set value of the grid-connected converter, Q fdbk represents the actual reactive power value of the grid-connected converter, K Q represents the proportional control coefficient of the reactive power of the grid-connected converter, U gn represents the rated voltage of the power grid.

8. The method according to claim 1, wherein The modulation voltage of the grid-forming grid-connected converter includes the modulation voltage of phase A, the modulation voltage of phase B, and the modulation voltage of phase C; The step of determining the modulation voltage of the grid-forming grid-connected converter according to the amplitude of the modulation voltage of the output bridge arm of the grid-forming grid-connected converter and the phase of the modulation voltage of the output bridge arm of the grid-forming grid-connected converter includes: Among them, U ma represents the real-time value of the modulation voltage of the A-phase, U mb represents the real-time value of the modulation voltage of the B-phase, U mc represents the real-time value of the modulation voltage of the C-phase, U s represents the amplitude of the modulation voltage of the output bridge arm of the grid-forming grid-connected converter, θ gsc represents the phase of the modulation voltage of the output bridge arm of the grid-connected converter.

9. A maximum power point tracking control system for a grid-forming photovoltaic inverter, characterized in that, including: A photovoltaic inverter grid-connected power generation system, a grid-connected converter synchronous loop gain sign control module, a grid-connected converter synchronous angle phase control module, a grid-connected converter AC voltage amplitude control module, and a grid-connected converter AC modulation voltage control module. The grid-connected converter synchronous loop gain sign control module is used to control the gain sign of the power synchronization loop of the grid-connected converter in the photovoltaic inverter grid-connected power generation system. The grid-connected converter synchronous angle phase control module is used to control the phase of the modulation voltage of the output bridge arm of the grid-connected converter in the photovoltaic inverter grid-connected power generation system. The grid-connected converter AC voltage amplitude control module is used to control the amplitude of the modulation voltage of the output bridge arm of the grid-connected converter in the photovoltaic inverter grid-connected power generation system. The grid-connected converter AC modulation voltage control module is used to control the modulation voltage of the grid-connected converter in the photovoltaic inverter grid-connected power generation system.

10. The maximum power point tracking control system of the grid-forming photovoltaic inverter according to claim 9, characterized in that, The photovoltaic inverter grid-connected power generation system includes a photovoltaic panel, a DC capacitor bank, a grid-connected converter, an AC filter, and a power grid. The positive DC output terminal of the photovoltaic panel is connected to the positive terminal of the DC capacitor bank. The negative DC output terminal of the photovoltaic panel is connected to the negative terminal of the DC capacitor bank. The positive terminal of the DC capacitor bank is connected to the positive DC terminal of the grid-connected converter. The negative terminal of the DC capacitor bank is connected to the negative DC terminal of the grid-connected converter. The three-phase AC terminals of the grid-connected converter are respectively connected to the three-phase input AC terminals of the AC filter. The three-phase output AC terminals of the AC filter are connected to the power grid through an electrical switch.

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