Self-synchronizing voltage source string type photovoltaic inverter system and control method

Abstract

The invention provides a self-synchronizing voltage source string type photovoltaic inverter system and a control method. The self-synchronizing voltage source string type photovoltaic inverter system comprises an internal potential frequency control module, a power angle rapid adjustment control module, an internal potential amplitude control module, a dual-mode parallel-competitive dominant control module, a bridge arm modulation voltage control module and an internal potential amplitude limiting control module. The dual-mode parallel-competitive dominant control module is respectively connected with the internal potential frequency control module, the power angle rapid adjustment control module and the bridge arm modulation voltage control module; 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. According to the invention, seamless smooth switching between a limited power working mode and a maximum power tracking working mode is realized, so that self-synchronizing voltage source control of the string type photovoltaic inverter is realized in a full operation mode.

Description

Technical Field

[0001] This invention belongs to the field of renewable energy grid connection technology, specifically relating to a self-synchronizing voltage source string photovoltaic inverter system and its control method. More specifically, it is a dual-mode parallel-competition-dominated self-synchronizing voltage source string photovoltaic inverter system and its method. Background Technology

[0002] In strong power grid environments, current source mode based on phase-locked loops is widely used due to its fast power control and stability; however, in weak power grids with a high proportion of renewable energy, its shortcomings are becoming increasingly apparent: phase-locked loops are sensitive to changes in grid impedance, are prone to unstable oscillations, and cannot provide voltage and frequency support to the grid.

[0003] To enhance system stability, voltage source mode, i.e., network configuration... type Control systems have emerged to address this issue. By simulating the characteristics of synchronous generators, they actively construct grid voltage and frequency to support system inertia. However, they suffer from problems such as slow dynamic response and limited maximum power point tracking efficiency.

[0004] In recent years, dual-mode hybrid control has become a research hotspot. By switching some current-source mode inverters to voltage-source mode, a hybrid grid-connected structure is formed, balancing stability and speed. However, existing dual-mode solutions rely on external dispatch commands to trigger mode switching, resulting in lag in dynamic response and insufficient support under transient faults, making it difficult to adapt to the complex operating conditions of large fluctuations in the grid short-circuit ratio in high-penetration scenarios.

[0005] The existing technology has key technical flaws.

[0006] First, traditional dual-mode control relies on centralized scheduling or external criteria to trigger mode switching. The switching process involves sudden power changes and phase angle jumps, leading to voltage oscillations at the grid connection point. Simultaneously, the intrinsic control objectives of the current source and voltage source modes are prone to conflict during transient processes, lacking an autonomous coordination mechanism. Secondly, although the voltage source mode has inertia support characteristics, there is no energy storage unit on the DC side of the photovoltaic inverter. During the fault, the DC voltage fluctuates violently, causing the internal potential amplitude to become unstable. The current limited amplitude control has a slow dynamic response, making it difficult to achieve active current support during fault ride-through. Third, in weak grids, phase-locked loops are susceptible to harmonic interference, and the frequency generation of the self-synchronization voltage source relies on only a single path, making it difficult to meet the dual requirements of MPPT and power-limited operation of photovoltaic systems, resulting in a decrease in synchronization stability after mode switching.

[0007] Patent document CN103259266A discloses a voltage vector stabilizer and control method based on self-frequency synchronization. However, this solution does not solve the technical problem that grid-type string photovoltaic inverters cannot seamlessly switch between power-limited operating mode and maximum power point tracking operating mode.

[0008] In conclusion, this problem urgently needs to be solved. Summary of the Invention

[0009] To address the shortcomings of existing technologies, the purpose of this invention is to provide a self-synchronizing voltage source string photovoltaic inverter system and its control method.

[0010] According to the present invention, a self-synchronizing voltage source string photovoltaic inverter system includes: an internal potential frequency control module, a power angle fast adjustment control module, an internal potential amplitude control module, a dual-mode parallel-competition-dominant control module, a bridge arm modulation voltage control module, and an 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; and the internal potential amplitude limiting control module is connected to the internal potential amplitude control module.

[0011] Preferably, the internal potential frequency control module includes: an internal potential first frequency control module and an internal potential second frequency control module.

[0012] Preferably, the internal potential first frequency control module can generate an internal potential first frequency value, the mathematical expression of which is:

[0013] 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. Signals in the frequency domain; Indicates the DC voltage control command value 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 DC voltage control of a photovoltaic inverter. Preferably, the mathematical expression for the power angle rapid adjustment control module 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.

[0014] Preferably, 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 obtain the internal potential rotation angle; the operating mode includes 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. .

[0015] 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 1 in the time domain; where, Indicates time; This represents the first frequency value of the internal potential output in the power control mode under time domain conditions. This represents the second frequency value of the internal potential output under voltage control mode in the time domain; The mathematical expression for the frequency value of Mode 2 is: ; in, This represents the frequency value of Mode 2 in the time domain.

[0016] 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.

[0017] Preferably, 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 for DC voltage stabilization control.

[0018] Preferably, the internal potential amplitude control module can provide internal potential amplitude data; the mathematical expression of 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.

[0019] Preferably, 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.

[0020] Preferably, 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 dominant 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 used by the photovoltaic inverter for transient current stabilization control in the time domain.

[0021] 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 in the time domain, respectively.

[0022] A control method for a self-synchronizing voltage source string photovoltaic inverter according to the present invention is implemented based on a self-synchronizing voltage source string photovoltaic inverter system, comprising: The internal potential frequency control module generates a first internal potential frequency value and a second internal potential frequency value; the first internal potential frequency value and the second internal potential frequency value are input into the dual-mode parallel-competition-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.

[0023] Compared with the prior art, the present invention has the following beneficial effects: 1. The dual-mode parallel-competition-dominant control module proposed in this invention realizes seamless and smooth switching between power-limited operation mode and maximum power point tracking operation mode of the grid-type string photovoltaic inverter, thereby realizing self-synchronizing voltage source control of the string photovoltaic inverter in all operating modes.

[0024] 2. The method in this invention can effectively solve the problem of DC bus over-limit protection during transient control. When the DC voltage of the grid-type string photovoltaic inverter exceeds the upward and downward limits, the power angle fast adjustment control module directly modulates the phase of the bridge arm voltage to achieve fast control of active power, thereby achieving fast power balance between the generator and the grid, and effectively avoiding inverter protection shutdown caused by DC voltage over-limit.

[0025] 3. This invention can effectively solve the overcurrent problem that occurs in grid-type string photovoltaic inverters during transient faults. 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 to which the phase current exceeds the limit current, thus providing reactive power support to the grid connection point while limiting the magnitude of the transient current.

[0026] 4. This invention enables the string photovoltaic inverter system to exhibit voltage source characteristics, improves the AC voltage control performance of the string photovoltaic inverter, enables it to autonomously synchronize with the grid for stable power generation, has autonomous inertia response and primary frequency regulation capability, can provide short-circuit current support during grid faults, has the ability to stably connect to the grid with load and switch to islanding, can autonomously establish voltage, has black start function, and can achieve zero-start voltage boost and external power supply. Attached Figure Description

[0027] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a schematic diagram of the string photovoltaic inverter topology provided by the present invention; Figure 2 This is a schematic block diagram of a string photovoltaic inverter control provided by the present invention; Figure 3 A schematic diagram of the internal potential first frequency control module provided by the present invention; Figure 4 A schematic diagram of the internal potential second frequency control module provided by the present invention; Figure 5 A schematic diagram of the power angle rapid adjustment control mode provided by the present invention; Figure 6 This is a schematic diagram of the dual-mode parallel-competition-dominated control module provided by the present invention; Figure 7 A schematic diagram of the control mode selection provided by the present invention; Figure 8 This is a schematic diagram of the internal potential amplitude control module provided by the present invention; Figure 9 A schematic diagram of the internal potential amplitude limiting control module provided by the present invention; Figure 10 This is a schematic diagram of the modulation voltage control module provided by the present invention. Detailed Implementation

[0028] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0029] This application proposes a dual-mode parallel-competition-dominated self-synchronizing voltage source control system and method for string photovoltaic inverters, referring to... Figure 1As shown, the self-synchronizing voltage source string photovoltaic inverter system includes a photovoltaic panel array, a DC / DC converter, a DC capacitor bank, a DC / AC grid-connected converter, an LC filter, a grid-connected switch, and a power grid. The photovoltaic panel array typically consists of multiple clusters of photovoltaic panels. The DC output terminal of each cluster is connected to the low-voltage side of the DC / DC converter. The positive and negative output terminals of the high-voltage side of each cluster of the DC / DC converter are connected together and then connected to the positive and negative output terminals of the DC capacitor bank. The positive and negative output terminals of the DC capacitor bank are connected to the positive and negative output terminals 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 a grid-connected electrical switch. The DC capacitor bank voltage signal of the real-time monitoring system is also included. U dc ( t Three-phase AC voltage signal u gabc ( t and three-phase alternating current signal i gabc ( t The active power of the grid-connected converter is obtained through signal calculation. p g ( t reactive power q g ( t and grid voltage amplitude signal u m ( t The power grid frequency signal is detected through a phase-locked loop (PLL). ω g ( 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 limitu 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.

[0030] 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: The first frequency of the internal potential (EPV) is generated by controlling the active power, and the second frequency is generated by controlling the DC voltage. These two frequencies are input to the dual-mode parallel-competitive-dominant module to generate the EPV frequency and phase angle. The EPV amplitude is generated through dual control of the grid connection point voltage and reactive power, and the EPV amplitude is adjusted by the EPV amplitude limiting control module to cope with grid transient faults. This control method allows the string photovoltaic inverter to freely and smoothly switch between two operating modes: power-limited control mode (control mode one) and maximum power point tracking control mode (control mode two). In all operating modes, it possesses voltage source characteristics such as autonomous grid synchronization, autonomous damping of grid frequency and voltage fluctuations, active support for transient fault lower limit current, and black start.

[0031] The present invention provides a self-synchronizing voltage source control method for a dual-mode parallel-competition-dominated string photovoltaic inverter, comprising 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-dominated control module, an internal potential amplitude control module, an internal potential amplitude limiting control module, and a modulation voltage control module. The data communication relationships between the control modules are as follows: Figure 2 As shown.

[0032] The specific descriptions of each control module are as follows: 1) The internal potential first frequency control module controls the first command value of active power in the frequency domain. Second command value of active power Actual value of active power Grid connection point frequency command value Actual value of grid connection frequency The active power error value is obtained through mathematical calculations. The first frequency controller of the internal potential first frequency control module calculates the error value between the active power command and the actual active power value. and the actual angular frequency of the grid connection point voltage The first frequency data, i.e., the first frequency value of the internal potential, is obtained through mathematical calculation. This is then sent to the internal potential phase angle generation unit; The calculation formula for the first frequency control module of internal potential is shown below: ; in, This indicates the error between the active power command and the actual active power value. The signal in the frequency domain; where, Represents the Laplace operator; 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. This represents the angular frequency deviation between the output voltage of the photovoltaic inverter and the grid connection point voltage in the frequency domain. The rated angular frequency of the grid connection point voltage. Signals in the frequency domain; This represents the frequency regulation coefficient 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. The symbol “·” represents the inertial time constant of the photovoltaic inverter, and the symbol “·” represents the multiplication operation.

[0033] The transformation formula from a time-domain signal to a frequency-domain signal is: ; in, This represents the expression of the signal in the time domain. t Indicates time; Represents time-domain signal The expression in the frequency domain, s Represents the Laplace algorithm; The Laplace operation, or Laplace transform, represents the conversion of a time-domain signal to a frequency-domain signal. This represents the Laplace operation from a frequency domain signal to a time domain signal, i.e., the inverse Laplace transform.

[0034] 2) The internal potential second frequency control module controls the DC voltage of the photovoltaic inverter in the frequency domain. The actual value of the DC voltage of the photovoltaic inverter The deviation is input to the first-order lead-lag element and connected to the grid point frequency rating. Subtracting the output of the first-order lead-lag element yields the second frequency data, i.e., the second frequency value of the internal potential. It is then sent to the internal potential phase angle generating unit; The calculation formula for the second frequency control module of internal potential is shown below: ; in, This represents the second frequency value of the internal potential output in voltage control mode. The signal in the frequency domain is referred to as the second frequency value of the internal potential. This 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 DC voltage control of a photovoltaic inverter. This represents the Laplace operator.

[0035] The implementation block diagram of the internal potential first frequency control module is as follows: Figure 4 As shown: 3) Power angle rapid adjustment control module, including a power angle compensation calculation unit and a switch mode selection unit; the power angle compensation calculation unit calculates the deviation between the actual DC voltage value and the high threshold DC voltage value through a first voltage deviation controller. The first compensated power angle is obtained after the DC voltage exceeds the high voltage threshold. The deviation between the actual DC voltage value and the low threshold DC voltage is processed by a second voltage deviation controller. The second compensated power angle is obtained after the DC voltage is below the low voltage threshold. The switch mode selection unit outputs a value based on the actual DC voltage, the high threshold DC voltage, and the low threshold DC voltage. When the actual DC voltage is greater than the high threshold, the switch mode selection unit outputs 1; when the actual DC voltage is less than the low threshold DC voltage, 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 rapid adjustment control module outputs 0; when the switch mode selection unit outputs 1, the power angle rapid adjustment control module outputs the first compensation power angle. When the switch mode selection unit outputs 2, the power angle rapid adjustment control module outputs the second compensation power angle. The compensated power angle data is sent to the dual-mode parallel-competition-dominated control module.

[0036] First voltage deviation controller The expression is shown in the following formula: ; in, 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.

[0037] First compensating angle The calculation formula is shown below: ; in, Indicates the upper limit of DC voltage protection for photovoltaic inverters. Signals in the frequency domain.

[0038] The expression for voltage deviation controller 2 is shown in the following equation: ; in, This represents the proportional coefficient of the DC voltage lower limit protection control circuit in a photovoltaic inverter. This represents the integral coefficient of the DC voltage lower limit protection control loop of the photovoltaic inverter.

[0039] Second compensation angle The calculation formula is shown below: ; in, This indicates the lower protection limit of the DC voltage of the photovoltaic inverter in the frequency domain. Signals in the frequency domain; The calculation formula for the power angle rapid adjustment control module is shown below: ; in, This refers to the compensation angle used by the photovoltaic inverter for DC voltage stabilization control, also known as the compensation power angle data. This indicates the first compensated power angle after the DC voltage exceeds the high voltage threshold. In the time domain, this is referred to as the compensation power angle 1. This indicates the second compensation power angle after the DC voltage falls below the low voltage threshold. In the time domain, this is referred to as the compensation power angle 1. This indicates the upper limit of the DC voltage protection value for the photovoltaic inverter; This indicates the lower protection limit of the DC voltage of the photovoltaic inverter.

[0040] In other words, the mathematical expression for the power angle rapid adjustment control module 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; Indicates the upper limit of DC voltage protection for photovoltaic inverters. Signals in the frequency domain; Indicates the lower protection limit of the DC voltage of the photovoltaic inverter. 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.

[0041] 4) Dual-mode parallel-competition-dominated control module, including 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 calculates the internal potential frequency based on the first frequency data in the time domain, i.e., the first internal potential frequency value. Second frequency data, i.e., the second frequency value of the internal potential. and set time Calculations show that when the system mode changes from operating mode one to operating mode two, the frequency value of mode one is calculated using the following formula: ; in, This indicates the transition time between operating mode one and mode two, also known as the set time. This represents the frequency value of mode one; When the system mode changes from operating mode 2 to operating mode 1, the frequency value of mode 2 is calculated using the following formula: ; in, This represents the frequency value of mode two.

[0042] The internal potential frequency selection unit calculates based on the first frequency data, the second frequency data, and a preset frequency deviation value. The system defaults to operating in mode one. In mode one, when the second frequency data... Greater than the first frequency data Deviation value from preset frequency When the sum is equal, the operating mode is selected as 2, i.e., mode two; otherwise, the operating mode is selected as 1, i.e., mode one. In mode two, when the first frequency data... Greater than the second frequency data Deviation value from preset frequency When the sum is equal to the sum, the operating mode is selected as 1, i.e., mode one; otherwise, the operating mode is selected as 2, i.e., mode two. When the operating mode is selected as 1, i.e., mode one, the internal potential frequency is selected as the frequency value of mode one; when the operating mode is selected as 2, i.e., mode two, the internal potential frequency is selected as the frequency value of mode two.

[0043] The internal potential rotation angle is obtained by integrating the output of the internal potential frequency selection unit (i.e., the angular frequency value of the photovoltaic inverter's internal potential) and adding the compensation angle used for DC voltage stabilization control of the photovoltaic inverter. The mathematical expression for the internal potential rotation angle of the photovoltaic inverter is as follows: ; 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.

[0044] The implementation block diagram of the dual-mode parallel-competition-dominated control module is as follows: Figure 6 As shown; where, sel This indicates the selection signal for the multiplexer; n represents the sampling time; "&&" represents logical AND; "·" represents multiplication. 4) Internal potential amplitude control module, including: reactive power deviation control unit, grid connection point voltage deviation control unit, and internal potential amplitude control unit; the reactive power deviation control unit controls the deviation between the commanded value and the actual value of reactive power of the photovoltaic inverter to obtain the control quantity Δ reflecting the reactive power deviation. u sq ( t ); The grid connection point voltage deviation control unit controls the deviation between the grid connection point voltage command value and the actual grid connection point voltage value to obtain a control quantity Δ reflecting the grid connection point voltage deviation. u 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. The formula for calculating the internal potential amplitude data is shown below: ; 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.

[0045] 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; 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. .

[0046] The calculation formula for the internal potential amplitude limiting control module is shown below: ; 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; 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. 6) The bridge arm modulation voltage control module obtains the bridge arm voltage data in the rotating coordinate system through polar coordinate to rotating coordinate transformation based on the bridge arm voltage amplitude data, internal potential phase angle data and internal potential phase angle compensation data, and then obtains the modulation wave voltage of the three-phase bridge arm through Park inverse transformation.

[0047] 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 formula for calculating the modulation wave voltage of the three-phase bridge arm is as follows: ; 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. The implementation block diagram of the three-phase bridge arm modulation voltage control module is as follows: Figure 10 As shown; where, dq Represents a two-phase rotating coordinate system; This represents the amplitude-phase polar coordinate system.

[0048] Those skilled in the art will understand that, besides implementing the system and its various devices, modules, and units provided by this invention in the form of purely computer-readable program code, the same functions can be achieved entirely through logical programming of the method steps, making the system and its various devices, modules, and units of this invention function in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers. Therefore, the system and its various devices, modules, and units provided by this invention can be considered as a hardware component, and the devices, modules, and units included therein for implementing various functions can also be considered as structures within the hardware component; alternatively, the devices, modules, and units for implementing various functions can be considered as both software modules implementing the method and structures within the hardware component.

[0049] In the description of this application, it should be understood that the terms "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0050] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

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; and the internal potential amplitude limiting control module is connected to the internal potential amplitude control module.

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 This 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 3, characterized in that, 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, with the internal potential frequency... 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.

6. 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.

7. 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.

8. The self-synchronizing voltage source string photovoltaic inverter system according to claim 7, 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.

9. 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 in the time domain, respectively.

10. 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 9, 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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