Self-synchronous voltage source group string photovoltaic inverter system and control method

Abstract

The application provides a self-synchronous voltage source group string photovoltaic inverter system and a control method, which comprises an internal potential frequency control module, a power angle quick adjustment control module, an internal potential amplitude control module, a double-mode parallel-competition dominant control module, a bridge arm modulation voltage control module and an internal potential amplitude limiting control module; the double-mode parallel-competition dominant control module is connected with the internal potential frequency control module, the power angle quick adjustment control module and the bridge arm modulation voltage control module respectively; the bridge arm modulation voltage control module is connected with the internal potential amplitude limiting control module; and the internal potential amplitude limiting control module is connected with the internal potential amplitude control module. The application realizes the seamless smooth switching of the limited power working mode and the maximum power tracking working mode, so as to realize the self-synchronous voltage source control of the group string photovoltaic inverter in the full operation mode.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of renewable energy grid connection, and particularly relates to a self-synchronous voltage source group string type photovoltaic inverter system and a control method. BACKGROUND

[0002] Under a strong power grid environment, a current source mode based on a phase-locked loop is widely used due to its power control rapidity and stability; however, in a weak power grid with a high proportion of new energy access, its defects are increasingly prominent: the phase-locked loop is sensitive to changes in power grid impedance, is easy to cause unstable oscillation, and cannot provide voltage and frequency support for the power grid.

[0003] In order to enhance the stability of the system, a voltage source mode, that is, a grid-forming type control, is born, which actively builds the grid voltage and frequency by simulating the characteristics of a synchronous generator, supports the system inertia, but has problems such as slow dynamic response and limited maximum power point tracking efficiency.

[0004] In recent years, a dual-mode hybrid control has become a research hotspot, which forms a hybrid grid connection structure by switching part of the current source mode inverter to the voltage source mode, and takes into account stability and rapidity. However, the existing dual-mode scheme relies on external scheduling instructions to trigger mode switching, the dynamic response is lagging, and the support capacity is insufficient under transient faults, and it is difficult to adapt to the complex working conditions of the large fluctuation of the power grid short-circuit ratio in the high penetration rate scenario.

[0005] The existing technology has key technical defects.

[0006] Firstly, the traditional dual-mode control relies on centralized scheduling or external criteria to trigger mode switching, and there is a power jump and phase angle jump in the switching process, which leads to voltage oscillation at the grid connection point. At the same time, the endogenous control targets of the current source and the voltage source mode are easy to conflict in the transient process, and lack of autonomous coordination mechanism;

[0007] Secondly, although the voltage source mode has inertia support characteristics, there is no energy storage unit on the direct current side of the photovoltaic inverter, and the internal potential amplitude is unstable due to the severe fluctuation of the direct current voltage during the fault period. The dynamic response of the existing amplitude control is slow, and it is difficult to realize active current support during fault ride-through;

[0008] Thirdly, the phase-locked loop is easy to be disturbed by harmonics under a weak power grid, and the frequency generation of the self-synchronous voltage source only relies on a single path, which is difficult to meet the dual requirements of MPPT and limited power operation of the photovoltaic system, resulting in a decrease in synchronization stability after mode switching.

[0009] The patent document CN103259266A discloses a voltage vector stabilizer and a control method based on self-frequency synchronization. However, the scheme does not solve the technical problem that the grid-connected type string photovoltaic inverter cannot be seamlessly and smoothly switched between the limited power working mode and the maximum power tracking working mode.

[0010] Therefore, the problem needs to be solved. SUMMARY

[0011] In view of the defects in the prior art, the purpose of the present application is to provide a self-synchronous voltage source string photovoltaic inverter system and a control method.

[0012] The self-synchronous voltage source string photovoltaic inverter system according to the present application comprises an internal potential frequency control module, a power angle fast adjustment control module, an internal potential amplitude control module, a double-mode parallel-competition dominant control module, a bridge arm modulation voltage control module and an internal potential amplitude limiting control module.

[0013] The double-mode parallel-competition dominant control module is connected to the internal potential frequency control module, the power angle fast adjustment control module and the bridge arm modulation voltage control module, respectively. The bridge arm modulation voltage control module is connected to the internal potential amplitude limiting control module. The internal potential amplitude limiting control module is connected to the internal potential amplitude control module.

[0014] Preferably, the internal potential frequency control module comprises an internal potential first frequency control module and an internal potential second frequency control module.

[0015] Preferably, the internal potential first frequency control module can generate an internal potential first frequency value, and the mathematical expression is as follows:

[0016]

[0017] wherein, represents the angular frequency deviation of the photovoltaic inverter output voltage and the grid-connected point voltage in the frequency domain; wherein, represents the Laplace operator; represents the rated angular frequency of the grid-connected point voltage a signal in the frequency domain; wherein, represents time; represents the frequency modulation coefficient of the photovoltaic inverter; represents the active power instruction value given by the station controller a signal in the frequency domain; represents the maximum active power value captured at the front end of the photovoltaic inverter a signal in the frequency domain; represents the actual value of the photovoltaic inverter output active power a signal in the frequency domain; Filtering time constant of the first order low pass filter representing the active power output of the photovoltaic inverter; Actual angular frequency of the grid point voltage Signal in the frequency domain; First frequency value of the internal potential output in the power control mode Signal in the frequency domain, referred to as the first frequency value of the internal potential; Damping coefficient of the power control mode; Inertial time constant of the photovoltaic inverter, the symbol “·” represents multiplication operation;

[0018] The internal potential second frequency control module can generate the second frequency value of the internal potential, and the mathematical expression is:

[0019] ;

[0020] Wherein, Second frequency value of the internal potential output in the voltage control mode Signal in the frequency domain; DC voltage control instruction value of the photovoltaic inverter Signal in the frequency domain; Actual value of the DC voltage of the photovoltaic inverter in the frequency domain Signal in the frequency domain; Proportional coefficient of the DC voltage controller; Time constant of the lead element of the lead-lag element for DC voltage control of the photovoltaic inverter; Time constant of the lag element of the lead-lag element for DC voltage control of the photovoltaic inverter;

[0021] Preferably, the mathematical expression of the power angle rapid adjustment control module is:

[0022] ;

[0023] Wherein, Compensation angle of the photovoltaic inverter for DC voltage stability control; DC voltage of the photovoltaic inverter Signal in the frequency domain; Upper limit value of the DC voltage protection of the photovoltaic inverter Signal in the frequency domain; Lower limit value of the DC voltage protection of the photovoltaic inverter in the frequency domain Signal in the frequency domain; a Proportional coefficient of the upper limit protection control element of the DC voltage of the photovoltaic inverter; b Integral coefficient of the upper limit protection control element of the DC voltage of the photovoltaic inverter; ca proportional coefficient representing a lower limit protection control link of a DC voltage of a photovoltaic inverter; d an integral coefficient representing a lower limit protection control link of a DC voltage of a photovoltaic inverter; represents a Laplace inverse transform.

[0024] Preferably, the dual-mode parallel-competition dominant control module can adjust the operation mode of the system to obtain the potential angle frequency of the photovoltaic inverter and then obtain the internal potential rotation angle; the operation mode includes mode one and mode two.

[0025] The dual-mode parallel-competition dominant control module defaults the system to work in mode one, and the internal potential frequency selects the output of mode one ; in the case of mode one operation, it is judged whether the sum of the internal potential frequency and the preset frequency deviation value is greater than the sum, and the result is yes, the operation mode is selected as mode two, and the internal potential frequency selects the output of mode one ; the result is no, the operation mode is selected as mode one, and the internal potential frequency selects the output of mode one ; ;

[0026] In the case of operation of the mode two, it is judged whether the sum of the internal potential frequency and the preset frequency deviation value is greater than the sum, and the result is yes, the operation mode is selected as mode one, and the internal potential frequency selects the output of mode one ; the result is no, the operation mode is selected as mode two, and the internal potential frequency selects the output of mode one ; wherein, when the operation mode is selected as mode one, the internal potential frequency is selected as the mode one frequency value; when the operation mode is selected as mode two, the internal potential frequency is selected as the mode two frequency value; the internal potential frequency is input to the integrator and the compensation power angle data is added to obtain the internal potential phase angle data .

[0027] The mathematical expression of the mode one frequency value is:

[0028] ;

[0029] wherein, represents the conversion time between the operation mode one and the mode two; represents the frequency value of mode one in the time domain; wherein, represents time; ​represents the first frequency value of the internal potential output in the time domain under the power control mode; represents the second frequency value of the internal potential output in the time domain under the voltage control mode;

[0030] The mathematical expression of the mode two frequency value is:

[0031] ;

[0032] wherein, represents the frequency value of mode two in the time domain.

[0033] The mathematical expression of the internal potential rotation angle of the photovoltaic inverter is:

[0034] ;

[0035] wherein, represents the internal potential rotation angle of the photovoltaic inverter; represents the integral operator; represents the internal potential angle frequency of the photovoltaic inverter.

[0036] Preferably, the power angle fast adjustment control module outputs the compensation angle of the photovoltaic inverter for direct current voltage stability control to the dual-mode parallel-competition dominant control module; the dual-mode parallel-competition dominant control module comprises an internal potential phase angle generator and an internal potential frequency calculation unit; the internal potential phase angle generator can generate internal potential phase angle data according to the internal potential frequency provided by the internal potential frequency calculation unit and the compensation angle of the photovoltaic inverter for direct current voltage stability control.

[0037] Preferably, the internal potential amplitude control module can provide internal potential amplitude data; the mathematical expression of the internal potential amplitude data is:

[0038] ;

[0039] wherein, represents the internal potential amplitude of the photovoltaic inverter signal in the frequency domain; represents the rated voltage amplitude of the grid-connected point in the frequency domain signal in the frequency domain; represents the proportional coefficient of the photovoltaic inverter reactive power control; represents the instruction value of the photovoltaic inverter reactive power signal in the frequency domain; represents the time constant of the filter for the actual value of the photovoltaic inverter reactive power represents the actual value of the photovoltaic inverter reactive power signal in the frequency domain; represents the proportional coefficient of the photovoltaic inverter grid-connected point voltage control; command value of the grid-connected point voltage of the photovoltaic inverter a signal in the frequency domain; a time constant of a filter for representing an actual value of the grid-connected point voltage of the photovoltaic inverter an actual value of the grid-connected point voltage of the photovoltaic inverter a signal in the frequency domain.

[0040] Preferably, the internal potential amplitude data is subtracted by internal potential amplitude compensation data provided by the internal potential amplitude limiting control module to obtain bridge arm voltage amplitude data;

[0041] The mathematical expression of the internal potential amplitude limiting control module is as follows:

[0042] ;

[0043] wherein, represents the maximum value of the absolute value of the three-phase current of the photovoltaic inverter in the time domain; represents the real-time value of the grid-connected current of the photovoltaic inverter in phase a in the time domain; represents the real-time value of the grid-connected current of the photovoltaic inverter in phase b in the time domain; represents the real-time value of the grid-connected current of the photovoltaic inverter in phase c in the time domain; represents the current value for transient control of the photovoltaic inverter in the time domain; represents the amplitude of the maximum output current of the photovoltaic inverter in the time domain; represents the transient current suppression control value of the photovoltaic inverter in the time domain; represents the d-axis component of the transient control compensation voltage of the photovoltaic inverter in the time domain; represents the q-axis component of the transient control compensation voltage of the photovoltaic inverter in the time domain; represents the resistance value of the virtual impedance for transient control of the photovoltaic inverter; represents the reactance value of the virtual impedance for transient control of the photovoltaic inverter; represents an exponential function; represents the amplitude of the bridge arm modulation voltage of the photovoltaic inverter in the time domain, i.e., bridge arm voltage amplitude data.

[0044] Preferably, the bridge arm modulation voltage control module can obtain the rotating coordinate system component data of the three-phase bridge arm voltage according to the bridge arm voltage amplitude data provided by the internal potential amplitude limiting control module, the internal potential phase angle data provided by the dual-mode parallel-competition dominant control module, and the compensation angle of the photovoltaic inverter for direct-current voltage stability control provided by the power angle rapid adjustment control module, and further obtain the modulation wave voltage of the three-phase bridge arm.

[0045] The calculation formula of the rotating coordinate system component data of the three-phase bridge arm voltage is as follows:

[0046]

[0047] wherein, represents the d-axis component of the bridge arm modulation voltage of the photovoltaic inverter in time domain; represents the d-axis component of the bridge arm modulation voltage of the photovoltaic inverter in time domain; represents the amplitude of the bridge arm modulation voltage of the photovoltaic inverter in time domain; represents the compensation angle of the photovoltaic inverter for transient current stability control in time domain.

[0048] The mathematical expression of the modulation wave voltage of the three-phase bridge arm is:

[0049]

[0050] wherein, and represent the modulation voltage of the a-phase bridge arm of the photovoltaic inverter, the modulation voltage of the b-phase bridge arm of the photovoltaic inverter and the modulation voltage of the c-phase bridge arm of the photovoltaic inverter in time domain, respectively.

[0051] According to the self-synchronous voltage source group string photovoltaic inverter control method provided by the application, based on the self-synchronous voltage source group string photovoltaic inverter system, the method comprises the steps of:

[0052] The internal potential frequency control module generates an internal potential first frequency value and an internal potential second frequency value; the internal potential first frequency value and the internal potential second frequency value are input into the double-mode parallel-competition dominant control module, and then an internal potential phase angle and an internal potential frequency are generated; and then the bridge arm modulation voltage control module combines the bridge arm voltage amplitude data provided by the internal potential amplitude limiting control module and the compensation angle of the photovoltaic inverter for direct-current voltage stability control provided by the power angle rapid adjustment control module to generate the modulation wave voltage of the three-phase bridge arm.

[0053] Compared with the prior art, the application has the beneficial effects as follows:

[0054] 1. The double-mode parallel-competition dominant control module proposed in the application realizes seamless and smooth switching of the grid-constructed group string photovoltaic inverter in the limited power working mode and the maximum power tracking working mode, so that the self-synchronous voltage source control of the group string photovoltaic inverter is realized in the full operation mode.

[0055] ​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​2、The method can solve the problem of over-limit protection of the DC bus in transient control, when the DC voltage of the grid-connected group string type photovoltaic inverter is over-limited upward and downward, the phase of the bridge arm voltage is directly modulated by the power angle fast adjustment control module to realize fast control of active power, thereby realizing fast balance of machine-grid side power, and effectively avoiding the problem of inverter protection shutdown caused by DC voltage over-limit.

[0056] 3、The application can effectively solve the problem of over-current of the grid-connected group string type photovoltaic inverter in transient fault, the designed internal potential amplitude limiting control module can quickly reduce the amplitude of the bridge arm voltage and adjust the phase of the bridge arm voltage according to the degree of exceeding the limit current of the phase current, thereby limiting the size of the transient current and providing reactive power support for the grid connection point.

[0057] 4、The application realizes that the group string type photovoltaic inverter system presents voltage source characteristics, improves the AC voltage control performance of the group string type photovoltaic inverter, and makes it can independently synchronize the grid stable power generation operation, has independent inertia response and primary frequency modulation capability, can provide short-circuit current support when the grid fails, has stable grid operation capability of grid-connected islanding with load, can independently establish voltage, has black start function, realizes zero rise voltage and supplies power to the outside. BRIEF DESCRIPTION OF DRAWINGS

[0058] Other features, objects and advantages of the application will become more apparent from the following detailed description of non-limiting embodiments, made with reference to the accompanying drawings:

[0059] Figure 1 A group string type photovoltaic inverter topology schematic diagram provided by the application;

[0060] Figure 2 A group string type photovoltaic inverter control schematic diagram provided by the application;

[0061] Figure 3 An internal potential first frequency control module schematic diagram provided by the application;

[0062] Figure 4 An internal potential second frequency control module schematic diagram provided by the application;

[0063] Figure 5 A power angle fast adjustment control mode schematic diagram provided by the application;

[0064] Figure 6 A double-mode parallel-competition dominant control module schematic diagram provided by the application;

[0065] Figure 7 A control mode selection schematic diagram provided by the application;

[0066] Figure 8An internal potential amplitude control module schematic diagram provided by the present application;

[0067] Figure 9 An internal potential amplitude limiting control module schematic diagram provided by the present application;

[0068] Figure 10 A modulated voltage control module schematic diagram provided by the present application. DETAILED DESCRIPTION

[0069] The present application will be described in detail below with specific embodiments. The following examples 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 for those skilled in the art, without departing from the concept of the present application, a number of changes and improvements can be made. These are within the scope of the present application.

[0070] The present application provides a dual-mode parallel-competition dominant self-synchronous voltage source control system and method for a string-type photovoltaic inverter, as shown in Figure 1 The self-synchronous voltage source string-type photovoltaic inverter system includes a photovoltaic panel array, a DC / DC direct current converter, a direct current capacitor bank, a DC / AC grid-connected converter, an LC filter, a grid-connected switch, and a power grid. The photovoltaic panel array is generally composed of multiple clusters of photovoltaic panels. The direct current output terminals of each cluster of photovoltaic panels are connected in direct current to the low-voltage side of the DC / DC direct current converter. The high-voltage side positive and negative output terminals of each cluster of DC / DC direct current converters are connected together and connected to the positive and negative output terminals of the direct current capacitor bank. The positive and negative output terminals of the direct current capacitor bank are connected to the positive and negative output terminals of the grid-connected converter. The three-phase alternating current terminals of the grid-connected converter are respectively connected to the three-phase input alternating current terminals of the alternating current filter. The three-phase output alternating current terminals of the alternating current filter are connected to the power grid through the grid-connected electrical switch. The direct current capacitor bank voltage signal U dc ( t ) of the system, the three-phase alternating current voltage signal u gabc ( t ) and the three-phase alternating current signal i gabc ( t ) of the system are detected in real time. The active power p g ( t ), the reactive power q g ( t ) and the grid voltage amplitude signal u m ( t ) of the grid-connected converter are calculated through signal calculation. The grid frequency signal ωg ( t The aforementioned detection signal, serving as the operating status signal of the grid-connected converter, is sent to the self-synchronizing voltage source control module of the string photovoltaic inverter; the first command value of active power is then... p g1 ( t ), second command value of active power p g2 ( t ), reactive power command value q g1 ( t AC voltage amplitude DC value u mr ( t DC voltage command value u dcr ( t DC voltage protection upper limit u dch ( t DC voltage protection upper limit u dcl ( t The maximum allowable output current amplitude of the AC current is sent as a command control signal to the self-synchronizing voltage source control module of the string photovoltaic inverter. The self-synchronizing voltage source control module of the string photovoltaic inverter executes the dual-mode parallel-competition-dominated self-synchronizing voltage source control algorithm to output the modulated voltage of the three bridge arms of the photovoltaic inverter. u ma ( t ), u mb ( t )and u mc ( t The PWM unit generates drive pulses to control the operation of the photovoltaic grid-connected converter.

[0071] Figure 1 The self-synchronizing voltage source control module of the string photovoltaic inverter shown includes: an internal potential phase control module based on dual-mode parallel-competition-dominated, an internal potential amplitude control module, a grid-connected current reference value control module, and a grid-connected current real-time control module. The data communication relationship between each control module is shown below:

[0072] The first frequency of the internal potential is generated by controlling the active power, the second frequency of the internal potential is generated by controlling the DC voltage, the first frequency and the second frequency of the internal potential are input to the dual-mode parallel-competition dominant module to generate the internal potential frequency and the phase angle; the internal potential amplitude is generated by double control of the grid-connected point voltage and the reactive power, and the internal potential amplitude adjustment is realized by the internal potential amplitude limiting control module to cope with the power grid transient fault. The control method can make the string type photovoltaic inverter freely and smoothly switch between the limited power control mode, i.e. control mode one, and the maximum power tracking control mode, i.e. control mode two, and the voltage source characteristics such as independent synchronous grid, independent damping of grid frequency and voltage fluctuation, active support of limited current under transient fault and black start are possessed in the full operation mode.

[0073] According to the application, a dual-mode parallel-competition dominant string type photovoltaic inverter self-synchronous voltage source control method is provided, which comprises an internal potential first frequency control module, an internal potential second frequency control module, a power angle fast adjustment control module, a dual-mode parallel-competition dominant control module, an internal potential amplitude control module, an internal potential amplitude limiting control module and a modulation voltage control module, and the data connection relationship of each control module is shown as Figure 2 .

[0074] The specific description of each control module is as follows:

[0075] 1) The internal potential first frequency control module obtains the active power error value through mathematical operation of the first instruction value of the active power , the second instruction value of the active power , the actual value of the active power , the grid-connected point frequency instruction value and the actual value of the grid-connected point frequency , the first frequency controller of the internal potential first frequency control module obtains the error value of the active power instruction and the actual value of the active power and the actual angular frequency of the grid-connected point voltage through mathematical calculation to obtain the first frequency data, i.e. the internal potential first frequency value , and then send to the internal potential phase angle generating unit;

[0076] The calculation formula of the internal potential first frequency control module is shown as follows:

[0077] ;

[0078] wherein, represents the error value of the active power instruction and the actual value of the active power , which is the signal in the frequency domain; wherein, represents the Laplace operator; represents the active power instruction value given by the field controller signal in the frequency domain; represents the maximum active power value captured by the front end of the photovoltaic inverter signal in the frequency domain; represents the actual value of the active power output by the photovoltaic inverter signal in the frequency domain; represents the filter time constant of the first order low pass filter for the active power output by the photovoltaic inverter represents the angular frequency deviation of the photovoltaic inverter output voltage from the grid point voltage in the frequency domain represents the rated angular frequency of the grid point voltage signal in the frequency domain; represents the frequency modulation coefficient of the photovoltaic inverter represents the actual angular frequency of the grid point voltage signal in the frequency domain; represents the first frequency value of the internal potential output in the power control mode signal in the frequency domain, abbreviated as the first frequency value of the internal potential represents the damping coefficient of the power control mode represents the inertia time constant of the photovoltaic inverter, and the symbol “·” represents multiplication.

[0079] The transformation formula for transforming the time domain signal into the frequency domain signal is:

[0080] ;

[0081] wherein, represents the expression of the signal in the time domain, t represents time; represents the time domain signal expression in the frequency domain, s represents the Laplace algorithm; represents the Laplace operation from the time domain signal to the frequency domain signal, i.e. the Laplace transformation; represents the Laplace operation from the frequency domain signal to the time domain signal, i.e. the inverse Laplace transformation.

[0082] 2) The internal potential second frequency control module inputs the deviation between the instruction value of the photovoltaic inverter DC voltage control in the frequency domain and the actual value of the photovoltaic inverter DC voltage to a first order lead-lag element, and the rated value of the grid point frequency Subtract the output of the first order lead-lag element to obtain the second frequency data, i.e. the internal potential second frequency value , which is sent to the internal potential phase angle generation unit;

[0083] The calculation formula of the internal potential second frequency control module is shown in the following formula:

[0084] ;

[0085] wherein, represents the internal potential second frequency value output in the voltage control mode a signal in the frequency domain, simply referred to as the internal potential second frequency value; represents the command value of the photovoltaic inverter direct current voltage control a signal in the frequency domain; represents the actual value of the photovoltaic inverter direct current voltage in the frequency domain a signal in the frequency domain; represents the proportional coefficient of the direct current voltage controller; represents the time constant of the lead element of the lead-lag element for the photovoltaic inverter direct current voltage control; represents the time constant of the lag element of the lead-lag element for the photovoltaic inverter direct current voltage control; represents the Laplace operator.

[0086] The implementation block diagram of the internal potential first frequency control module is as shown in Figure 4 :

[0087] 3) The power angle fast adjustment control module includes a compensation power angle calculation unit and a switch mode selection unit; the compensation power angle calculation unit obtains the first compensation power angle after the direct current voltage exceeds the high voltage threshold value through the first voltage deviation controller from the deviation of the direct current voltage actual value and the direct current voltage high threshold value; The second compensation power angle after the direct current voltage is lower than the low voltage threshold value is obtained through the second voltage deviation controller from the deviation of the direct current voltage actual value and the direct current voltage low threshold value; The switch mode selection unit gives according to the direct current voltage actual value, the direct current voltage high threshold value and the direct current voltage low threshold value, when the direct current voltage actual value is greater than the direct current voltage high threshold value, the switch mode selection unit outputs 1; when the direct current voltage actual value is less than the direct current voltage low threshold value, the switch mode selection unit outputs 2; otherwise, the switch mode selection unit outputs 0; when the switch mode selection unit outputs 0, the power angle fast adjustment control module outputs 0; when the switch mode selection unit outputs 1, the power angle fast adjustment control module outputs the first compensation power angle ; when the switch mode selection unit outputs 2, the power angle fast adjustment control module outputs the second compensation power angle . The compensation power angle data is sent to the dual-mode parallel-competition dominant control module.

[0088] The expression of the first voltage deviation controller is as shown in the following formula:

[0089] ;

[0090] wherein, a represents the proportional coefficient of the upper limit protection control link of the DC voltage of the photovoltaic inverter; b represents the integral coefficient of the upper limit protection control link of the DC voltage of the photovoltaic inverter.

[0091] the first compensation power angle The calculation formula is as follows:

[0092] ;

[0093] wherein, represents the upper limit protection value of the DC voltage of the photovoltaic inverter in the frequency domain.

[0094] The expression of the voltage deviation controller 2 is as follows:

[0095] ;

[0096] wherein, represents the proportional coefficient of the lower limit protection control link of the DC voltage of the photovoltaic inverter; represents the integral coefficient of the lower limit protection control link of the DC voltage of the photovoltaic inverter.

[0097] the second compensation power angle The calculation formula is as follows:

[0098] ;

[0099] wherein, represents the lower limit protection value of the DC voltage of the photovoltaic inverter in the frequency domain in the frequency domain;

[0100] The calculation formula of the power angle fast adjustment control module is as follows:

[0101] ;

[0102] wherein, represents the compensation angle of the photovoltaic inverter for DC voltage stability control, referred to as compensation power angle data; represents the first compensation power angle after the DC voltage exceeds the high voltage threshold in the time domain, referred to as compensation power angle 1; represents the second compensation power angle after the DC voltage is lower than the low voltage threshold in the time domain, referred to as compensation power angle 1; represents the upper limit protection value of the DC voltage of the photovoltaic inverter; A lower limit value of the DC voltage of the photovoltaic inverter.

[0103] In other words, the mathematical expression of the power angle fast adjustment control module is:

[0104] ;

[0105] wherein, represents a compensation angle of the photovoltaic inverter for DC voltage stability control; represents a lower limit value of the DC voltage of the photovoltaic inverter in the frequency domain; represents an upper limit value of the DC voltage of the photovoltaic inverter in the frequency domain; represents an upper limit value of the DC voltage of the photovoltaic inverter in the frequency domain; represents a lower limit value of the DC voltage of the photovoltaic inverter in the frequency domain; a represents a proportional coefficient of the upper limit protection control link of the DC voltage of the photovoltaic inverter; b represents an integral coefficient of the upper limit protection control link of the DC voltage of the photovoltaic inverter; c represents a proportional coefficient of the lower limit protection control link of the DC voltage of the photovoltaic inverter; d represents an integral coefficient of the lower limit protection control link of the DC voltage of the photovoltaic inverter.

[0106] 4) A dual-mode parallel-competition dominant control module, comprising an internal potential frequency selection unit, an internal potential frequency calculation unit, and an internal potential phase angle generator; the internal potential frequency calculation unit is calculated according to the time domain first frequency data, i.e., the internal potential first frequency value , the second frequency data, i.e., the internal potential second frequency value , and the set time When the system mode changes from operation mode one to operation mode two, the mode one frequency value is calculated, and the calculation formula is as follows:

[0107] ;

[0108] wherein, represents a conversion time between operation mode one and mode two, simply referred to as a set time; represents a frequency value of mode one;

[0109] When the system mode changes from operation mode two to operation mode one, the mode two frequency value is calculated, and the calculation formula is as follows:

[0110] ;

[0111] wherein, represents the mode two frequency value.

[0112] The inner potential frequency selection unit calculates according to the first frequency data, the second frequency data and the preset frequency deviation value, and the default system starts to work in mode one; in the mode one operation condition, when the second frequency data is greater than the first frequency data and the sum of the preset frequency deviation value , the operation mode selection is 2, that is, mode two; otherwise, the operation mode selection is 1, that is, mode one; in the mode two operation condition, when the first frequency data is greater than the second frequency data and the sum of the preset frequency deviation value , the operation mode selection is 1, that is, mode one; otherwise, the operation mode selection is 2, that is, mode two; when the operation mode selection is 1, that is, mode one, the inner potential frequency selection is the mode one frequency value; when the operation mode selection is 2, that is, mode two, the inner potential frequency selection is the mode two frequency value.

[0113] The output of the inner potential frequency selection unit, that is, the photovoltaic inverter inner potential angle frequency value, is integrated and added with a compensation angle used for the direct current voltage stability control of the photovoltaic inverter to obtain an inner potential rotation angle, and the mathematical expression of the photovoltaic inverter inner potential rotation angle is:

[0114] ;

[0115] wherein, represents the photovoltaic inverter inner potential rotation angle; represents an integral operator; represents the photovoltaic inverter inner potential angle frequency.

[0116] The implementation block diagram of the double-mode parallel-competition dominant control module is shown in Figure 6 ; wherein, sel represents the selection signal of the multiplexer; n represents the sampling time; "&&" represents the logical and; and "·" represents the multiplication operation.

[0117] 4) The inner potential amplitude control module, comprising: a reactive power deviation control unit, a grid-connected point voltage deviation control unit and an inner potential amplitude control unit; the reactive power deviation control unit controls the deviation between the instruction value and the actual value of the reactive power of the photovoltaic inverter to obtain the control quantity Δ u sq ( t ) reflecting the reactive power deviation;

[0118] The grid-connected point voltage deviation control unit controls the deviation between the instruction value and the actual value of the grid-connected point voltage to obtain the control quantity Δu sv ( t The internal potential amplitude control unit will reflect the control quantity Δ that reflects the reactive power deviation. u sq ( t ) and the control quantity Δ that reflects the voltage deviation at the grid connection point u sv ( t The summation of these values ​​is used to obtain the internal potential amplitude data via an integrator.

[0119] The formula for calculating the internal potential amplitude data is shown below:

[0120] ;

[0121] in, Indicates the amplitude of the internal potential of the photovoltaic inverter The signal in the frequency domain, i.e., the internal potential amplitude data; Indicates the rated voltage amplitude at the grid connection point in the frequency domain. Signals in the frequency domain; This represents the control quantity that reflects the voltage deviation at the grid connection point in the frequency domain; This represents the control quantity reflecting reactive power deviation in the frequency domain; This represents the proportional coefficient for reactive power control in a photovoltaic inverter. Indicates the command value of reactive power of photovoltaic inverter Signals in the frequency domain; The time constant of the filter represents the actual value of the reactive power of the photovoltaic inverter; This represents the actual value of the reactive power of the photovoltaic inverter. Signals in the frequency domain; The proportional coefficient representing the voltage control at the grid connection point of the photovoltaic inverter; Indicates the command value of the grid connection point voltage of the photovoltaic inverter. Signals in the frequency domain; The time constant of the filter is used to represent the actual value of the grid-connected voltage of the photovoltaic inverter. This represents the actual value of the grid connection point voltage of the photovoltaic inverter. Signals in the frequency domain.

[0122] The flowchart for calculating the internal potential amplitude data, i.e., the schematic diagram of the internal potential amplitude control module, is shown below. Figure 8 As shown; the square electrical symbol with double arrows in the figure represents the limiting circuit;

[0123] 6) Internal potential amplitude limiting control module, including a phase current nonlinear controller and an internal potential adjustment module. The phase current nonlinear controller detects the maximum absolute value of the three-phase current of the photovoltaic inverter in real time. , to the maximum value With transient current limiting amplitude The transient current suppression control value is obtained by nonlinear calculation of the difference. ; Set the transient current suppression control value Multiply by virtual resistance respectively Z R and virtual resistance Z L Obtain the compensation voltage in the rotating coordinate system and The internal potential amplitude compensation data is obtained by transforming the coordinates from rotation to polar coordinates. Internal potential phase angle compensation data Internal potential amplitude data Subtract internal potential amplitude compensation data The amplitude of the bridge arm modulation voltage is obtained. .

[0124] The calculation formula for the internal potential amplitude limiting control module is shown below:

[0125] ;

[0126] in, This represents the maximum absolute value of the three-phase current of the photovoltaic inverter in the time domain. This represents the real-time value of the grid-connected current of phase a of the photovoltaic inverter in the time domain; This represents the real-time value of the grid-connected current of phase b of the photovoltaic inverter in the time domain; This represents the real-time value of the grid-connected current of phase c of the photovoltaic inverter in the time domain; This represents the current value used for transient control of the photovoltaic inverter in the time domain; This represents the amplitude of the maximum output current of the photovoltaic inverter in the time domain; This represents the transient current suppression control value of the photovoltaic inverter in the time domain; This represents the d-axis component of the transient control compensation voltage of the photovoltaic inverter in the time domain. Represents the q-axis component of the transient control compensation voltage of the photovoltaic inverter in the time domain; The resistance value representing the virtual impedance of the transient control of the photovoltaic inverter; This represents the reactance value of the transient control virtual impedance of the photovoltaic inverter. Represents an exponential function; This represents the amplitude of the modulated voltage of the photovoltaic inverter bridge arm in the time domain, i.e., the bridge arm voltage amplitude data;

[0127] The implementation block diagram of the internal potential amplitude limiting control module is as follows: Figure 9 As shown; This represents the function that takes the absolute value.

[0128] 6) Bridge arm modulation voltage control module, according to bridge arm voltage amplitude data, inner potential phase angle data and inner potential phase angle compensation data, through polar coordinate to rotating coordinate transformation, the data of bridge arm voltage in rotating coordinate system is obtained, and then through park inverse transformation, the modulation wave voltage of three-phase bridge arm is obtained.

[0129] The calculation formula of three-phase bridge arm voltage in rotating coordinate system component data is as follows:

[0130] ;

[0131] Among them, represents the d-axis component of the bridge arm modulation voltage of the photovoltaic inverter in the time domain; represents the d-axis component of the bridge arm modulation voltage of the photovoltaic inverter in the time domain; represents the amplitude of the bridge arm modulation voltage of the photovoltaic inverter in the time domain; represents the compensation angle of the photovoltaic inverter for transient current stability control in the time domain;

[0132] The calculation formula of the modulation wave voltage of the three-phase bridge arm is as follows:

[0133] ;

[0134] Among them, , and respectively represent the modulation voltage of the a-phase bridge arm of the photovoltaic inverter, the modulation voltage of the b-phase bridge arm of the photovoltaic inverter and the modulation voltage of the c-phase bridge arm of the photovoltaic inverter in the time domain;

[0135] The implementation block diagram of the three-phase bridge arm modulation voltage control module is shown in Figure 10 ; Among them, dq represents a two-phase rotating coordinate system; represents an amplitude-phase polar coordinate system.

[0136] Those skilled in the art know that in addition to implementing the system provided by the present application and each device, module, unit thereof in a pure computer readable program code manner, the same function can also be realized by logically programming the method steps to make the system provided by the present application and each device, module, unit thereof in the form of logic gate, switch, application specific integrated circuit, programmable logic controller and embedded microcontroller. Therefore, the system provided by the present application and each device, module, unit thereof can be considered as a hardware component, and the devices, modules, units included therein for realizing various functions can also be considered as structures within the hardware component; the devices, modules, units for realizing various functions can also be considered as both software modules realizing the method and structures within the hardware component.

[0137] In the description of the present application, it should be understood that the terms "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like refer to the orientation or positional relationship shown in the drawings, and are only intended to facilitate the description of the present application and simplify the description, and are not intended to indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.

[0138] The specific embodiments of the present application are described above. It should be understood that the present application is not limited to the above specific embodiments, and various changes or modifications can be made by those skilled in the art within the scope of the claims, which do not affect the essential content of the present application. The embodiments of the present application and the features in the embodiments can be arbitrarily combined with each other without conflict, provided that they do not conflict.

Claims

1. A self-synchronizing voltage source string photovoltaic inverter system, characterized in that, include: Internal potential frequency control module, power angle fast adjustment control module, internal potential amplitude control module, dual-mode parallel-competition-dominated control module, bridge arm modulation voltage control module and internal potential amplitude limiting control module; The dual-mode parallel-competitive dominant control module is connected to the internal potential frequency control module, the power angle fast adjustment control module, and the bridge arm modulation voltage control module, respectively; the bridge arm modulation voltage control module is connected to the internal potential amplitude limiting control module; the internal potential amplitude limiting control module is connected to the internal potential amplitude control module. The dual-mode parallel-competitive-dominant control module can adjust the system's operating mode to obtain the internal potential angular frequency of the photovoltaic inverter and thus the internal potential rotation angle; the operating modes include mode one and mode two. The dual-mode parallel-competition-dominated control module defaults to operating in mode one, with the internal potential frequency... Select output mode 1 ; In the case of running in mode one, determine Is it greater than Deviation value from preset frequency If the sum is true, then the operating mode is selected as mode two, and the internal potential frequency is... Select output mode 1 If the result is negative, then the operating mode is selected as Mode 1, and the internal potential frequency is [not specified]. Select output mode 1 ; Under the operating conditions of the second mode, determine Is it greater than Deviation value from preset frequency If the sum of these values ​​is true, then the operating mode is Mode 1, and the internal potential frequency is... Select output mode 1 If the result is negative, then the operating mode is selected as Mode 2, and the internal potential frequency is [not specified]. Select output mode 1 Specifically, when the operating mode is selected as Mode 1, the internal potential frequency is selected as the Mode 1 frequency value; when the operating mode is selected as Mode 2, the internal potential frequency is selected as the Mode 2 frequency value; the internal potential frequency... The internal potential phase angle data is obtained by inputting the data into the integrator and adding the compensated power angle data. ; The mathematical expression for the frequency value of Mode 1 is: ； in, Indicates the transition time between operating mode one and mode two; This represents the frequency value of mode one; The mathematical expression for the frequency value of Mode 2 is: ； in, This represents the frequency value of mode two; The mathematical expression for the rotation angle of the internal potential of the photovoltaic inverter is: ； in, This indicates the rotation angle of the internal potential of the photovoltaic inverter. Indicates the integration operator; This indicates the angular frequency of the internal potential of the photovoltaic inverter.

2. The self-synchronizing voltage source string photovoltaic inverter system according to claim 1, characterized in that, The internal potential frequency control module includes: an internal potential first frequency control module and an internal potential second frequency control module.

3. The self-synchronizing voltage source string photovoltaic inverter system according to claim 2, characterized in that, The internal potential first frequency control module can generate the internal potential first frequency value, the mathematical expression of which is: in, This represents the angular frequency deviation between the output voltage of the photovoltaic inverter and the grid connection point voltage in the frequency domain; where, Represents the Laplace operator; The rated angular frequency of the grid connection point voltage. The signal in the frequency domain; where, Indicates time; This represents the frequency regulation coefficient of a photovoltaic inverter; This indicates the active power command value given by the station controller. Signals in the frequency domain; This indicates the maximum active power captured by the front end of the photovoltaic inverter. Signals in the frequency domain; This represents the actual value of the active power output of the photovoltaic inverter. Signals in the frequency domain; The filtering time constant of a first-order low-pass filter represents the output active power of a photovoltaic inverter. The actual angular frequency of the grid connection point voltage. Signals in the frequency domain; This represents the first frequency value of the internal potential output in power control mode. The signal in the frequency domain is referred to as the first frequency value of the internal potential. The damping coefficient represents the power control mode. This represents the inertial time constant of the photovoltaic inverter, and the symbol "·" indicates a multiplication operation. The internal potential second frequency control module can generate the internal potential second frequency value, the mathematical expression of which is: ； in, This represents the second frequency value of the internal potential output in voltage control mode. Signal in the frequency domain Indicates the command value for DC voltage control of the photovoltaic inverter. Signals in the frequency domain; This represents the actual value of the DC voltage of the photovoltaic inverter in the frequency domain. Signals in the frequency domain; This represents the proportional gain of the DC voltage controller; The time constant of the lead element represents the lead-lag element used in the DC voltage control of a photovoltaic inverter. This represents the time constant of the lead-lag element used in the DC voltage control of a photovoltaic inverter.

4. The self-synchronizing voltage source string photovoltaic inverter system according to claim 1, characterized in that, The mathematical expression for the rapid adjustment control module of the power angle is: ； in, This indicates the compensation angle used by the photovoltaic inverter for DC voltage stabilization control; Indicates the DC voltage of the photovoltaic inverter Signals in the frequency domain; Indicates the upper limit of DC voltage protection for photovoltaic inverters. Signals in the frequency domain; This indicates the lower protection limit of the DC voltage of the photovoltaic inverter in the frequency domain. Signals in the frequency domain; a This represents the proportional coefficient of the DC voltage upper limit protection control circuit in a photovoltaic inverter. b This represents the integral coefficient of the DC voltage upper limit protection control loop of the photovoltaic inverter; c This represents the proportional coefficient of the DC voltage lower limit protection control circuit in a photovoltaic inverter. d This represents the integral coefficient of the DC voltage lower limit protection control loop of the photovoltaic inverter; This represents the inverse Laplace transform.

5. The self-synchronizing voltage source string photovoltaic inverter system according to claim 4, characterized in that, The power angle rapid adjustment control module outputs the compensation angle of the photovoltaic inverter for DC voltage stabilization control to the dual-mode parallel-competitive dominant control module; The dual-mode parallel-competitive dominant control module includes: an internal potential phase angle generator and an internal potential frequency calculation unit; the internal potential phase angle generator can generate internal potential phase angle data based on the internal potential frequency provided by the internal potential frequency calculation unit and the compensation angle of the photovoltaic inverter used for DC voltage stabilization control.

6. The self-synchronizing voltage source string photovoltaic inverter system according to claim 1, characterized in that, The internal potential amplitude control module can provide internal potential amplitude data; the mathematical expression for the internal potential amplitude data is: ； in, Indicates the amplitude of the internal potential of the photovoltaic inverter Signals in the frequency domain; Indicates the rated voltage amplitude at the grid connection point in the frequency domain. Signals in the frequency domain; This represents the proportional coefficient for reactive power control in a photovoltaic inverter. Indicates the command value of reactive power of photovoltaic inverter Signals in the frequency domain; The time constant of the filter represents the actual value of the reactive power of the photovoltaic inverter; This represents the actual value of the reactive power of the photovoltaic inverter. Signals in the frequency domain; The proportional coefficient representing the voltage control at the grid connection point of the photovoltaic inverter; Indicates the command value of the grid connection point voltage of the photovoltaic inverter. Signals in the frequency domain; The time constant of the filter is used to represent the actual value of the grid-connected voltage of the photovoltaic inverter. This represents the actual value of the grid connection point voltage of the photovoltaic inverter. Signals in the frequency domain.

7. The self-synchronizing voltage source string photovoltaic inverter system according to claim 6, characterized in that, The bridge arm voltage amplitude data is obtained by subtracting the internal potential amplitude compensation data provided by the internal potential amplitude limiting control module from the internal potential amplitude data. The mathematical expression for the internal potential amplitude limiting control module is: ； in, This represents the maximum absolute value of the three-phase current of the photovoltaic inverter in the time domain. This represents the real-time value of the grid-connected current of phase a of the photovoltaic inverter in the time domain; This represents the real-time value of the grid-connected current of phase b of the photovoltaic inverter in the time domain; This represents the real-time value of the grid-connected current of phase c of the photovoltaic inverter in the time domain; This represents the current value used for transient control of the photovoltaic inverter in the time domain; This represents the amplitude of the maximum output current of the photovoltaic inverter in the time domain; This represents the transient current suppression control value of the photovoltaic inverter in the time domain; This represents the d-axis component of the transient control compensation voltage of the photovoltaic inverter in the time domain. Represents the q-axis component of the transient control compensation voltage of the photovoltaic inverter in the time domain; The resistance value representing the virtual impedance of the transient control of the photovoltaic inverter; This represents the reactance value of the transient control virtual impedance of the photovoltaic inverter. Represents an exponential function; This represents the amplitude of the modulated voltage of the photovoltaic inverter bridge arm in the time domain, i.e., the bridge arm voltage amplitude data; This represents the compensation angle used by the photovoltaic inverter for transient current stabilization control in the time domain.

8. The self-synchronizing voltage source string photovoltaic inverter system according to claim 1, characterized in that, The bridge arm modulation voltage control module can obtain the three-phase bridge arm voltage component data in the rotating coordinate system based on the bridge arm voltage amplitude data provided by the internal potential amplitude limiting control module, the internal potential phase angle data provided by the dual-mode parallel-competitive dominance control module, and the compensation angle of the photovoltaic inverter for DC voltage stabilization control provided by the power angle fast adjustment control module, and thus obtain the modulation wave voltage of the three-phase bridge arm. The formula for calculating the component data of the three-phase bridge arm voltage in the rotating coordinate system is as follows: ； in, Represents the d-axis component of the modulation voltage of the photovoltaic inverter bridge arm in the time domain; Represents the d-axis component of the modulation voltage of the photovoltaic inverter bridge arm in the time domain; This represents the amplitude of the modulation voltage of the photovoltaic inverter bridge arm in the time domain; This represents the compensation angle of a photovoltaic inverter used for transient current stabilization control in the time domain. The mathematical expression for the modulation wave voltage of the three-phase bridge arm is: ； in, , and These represent the modulation voltages of the a-phase bridge arm, b-phase bridge arm, and c-phase bridge arm of the photovoltaic inverter, respectively, in the time domain. This indicates the rotation angle of the internal potential of the photovoltaic inverter.

9. A control method for a self-synchronizing voltage source string photovoltaic inverter, implemented based on the self-synchronizing voltage source string photovoltaic inverter system according to any one of claims 1 to 8, characterized in that, include: The internal potential frequency control module generates a first internal potential frequency value and a second internal potential frequency value. The first and second internal potential frequencies are input into the dual-mode parallel-competitive dominant control module to generate the internal potential phase angle and internal potential frequency. Then, the bridge arm modulation voltage control module combines the bridge arm voltage amplitude data provided by the internal potential amplitude limiting control module with the compensation angle of the photovoltaic inverter for DC voltage stabilization control provided by the power angle fast adjustment control module to generate the modulation wave voltage of the three-phase bridge arm.

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