Dual-mode parallel competition dominant self-synchronous voltage source type photovoltaic power generation unit

Abstract

The application provides a dual-mode parallel competition dominant self-synchronous voltage source type photovoltaic power generation unit, comprising: a photovoltaic array composed of photovoltaic components, used for converting light into electric energy; a direct current / alternating current converter composed of power electronic converters, used for converting direct current generated by the front-end photovoltaic array into alternating current; a self-synchronous voltage source generation control composed of a dual-mode parallel competition dominant control module, a modulated voltage control module and a synchronous phase angle control module, used for autonomously establishing voltage, autonomously synchronizing with a power grid, supporting transient frequency and voltage of the power grid; and according to direct current bus voltage fluctuation characteristics and power flow characteristics, through state maintenance and competition dominance of two voltage source control modes, self-synchronous voltage source characteristics of the photovoltaic power generation unit under multiple operating conditions such as light mutation and power grid failure are maintained, and direct current bus voltage stability under no direct current pry bar is realized. The application is suitable for string type and centralized photovoltaic, including control, equipment and system.

Description

Technical Field

[0001] This invention relates to the technical field of power electronic control of photovoltaic power generation units, and more specifically, to a self-synchronizing voltage source photovoltaic power generation unit dominated by dual-mode parallel competition. Background Technology

[0002] Photovoltaic (PV) power generation, as an important form of clean energy, has become one of the most promising renewable energy sources globally. With the increasing proportion of PV power generation, the grid's capacity to absorb new energy sources faces severe challenges, especially given the increasingly stringent requirements for frequency regulation and voltage stability in low-inertia grids. Currently, there are two main grid-connection methods for PV power generation: grid following (GFL) and grid forming (GFM) control. Traditional grid following control relies on the grid's frequency and voltage signals to synchronously control the output of the PV inverter. This method is prone to problems such as wide-frequency oscillations and transient instability when the proportion of new energy is high. Especially when the grid inertia is low or grid fluctuations are large, traditional grid following control cannot effectively cope with rapid frequency changes, limiting grid stability and the ability to absorb new energy. To address the problems caused by high-proportion new energy grid connection, grid forming control technology has emerged. Grid forming control, by simulating the external characteristics of a synchronous generator, enables the PV system to possess voltage source characteristics similar to a traditional generator, providing the grid with the necessary autonomous voltage construction, inertia support, and active frequency regulation functions. This control method can still provide necessary voltage support when the photovoltaic system is disconnected from the grid, thereby ensuring the stability of the grid.

[0003] Patent document CN115986816A discloses a two-stage photovoltaic grid-connected architecture and its control method based on a synchronous machine interface. The architecture includes: a DC boost circuit for tracking the maximum power point of the photovoltaic power generation unit; a three-phase inverter circuit for controlling the transmission power of the new energy synchronous machine system downstream of the three-phase inverter circuit; and a controller for controlling the DC boost circuit and the three-phase inverter circuit. This controller ensures that when the output power of the photovoltaic power generation unit fluctuates, causing fluctuations in the DC voltage on the input side of the photovoltaic power generation unit, the fluctuating DC voltage is converted into a change in the frequency of the output AC voltage to adjust the power angle of the new energy synchronous machine system, thereby changing the transmission power of the unit to actively follow the power changes of the photovoltaic power generation unit. Although grid-connected control technology has significant advantages, it still faces some challenges in practical applications. Existing grid-connected control technologies typically require energy storage systems (such as batteries) to provide inertia support and frequency regulation. However, the configuration of energy storage systems not only increases the cost of the photovoltaic system but also places higher demands on its operational reliability and economy. Therefore, how to achieve efficient inertia support and frequency regulation through the photovoltaic array itself without relying on energy storage systems has become an urgent problem to be solved in current photovoltaic power generation systems. Furthermore, in practical applications, the power output of photovoltaic power generation systems is usually affected by changes in sunlight conditions, temperature, and grid load, which necessitates flexible control capabilities when the system is connected to the grid. While traditional grid-based control methods can cope with grid frequency variations, they cannot simultaneously achieve maximum power output and frequency response, especially in the absence of energy storage. Optimizing power output and responding to grid frequency changes remains a technical challenge. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the purpose of this invention is to provide a self-synchronizing voltage source photovoltaic power generation unit dominated by dual-mode parallel competition.

[0005] According to the present invention, a dual-mode parallel competition-dominated self-synchronizing voltage source photovoltaic power generation unit includes: a photovoltaic array, a DC / AC conversion unit, and a self-synchronizing voltage source generation and control unit;

[0006] The photovoltaic array is used to convert light energy into electrical energy; the DC / AC conversion unit is used to convert DC power into AC power; the self-synchronizing voltage source generation and control unit includes a dual-mode parallel competition-dominant control module, a modulation voltage control module, and a synchronization phase angle control module, which are used to autonomously establish voltage, autonomously achieve grid synchronization, and support grid transient frequency and voltage.

[0007] The dual-mode parallel competition-dominant control module maintains the state of two voltage source control modes in parallel, including a first mode and a second mode. In the first mode, the DC bus voltage is maintained constant by itself, while in the second mode, the DC bus voltage is maintained constant by external means. Based on the DC bus voltage fluctuation and power flow characteristics, the competitive dominance of the two modes maintains the self-synchronizing voltage source characteristics of the photovoltaic power generation unit under conditions of sudden changes in sunlight or grid faults, and achieves DC bus transient voltage stability without DC crowbar circuit.

[0008] Preferably, the photovoltaic array includes multiple photovoltaic module strings, and the photovoltaic module strings are connected in parallel to form a photovoltaic sub-array. The photovoltaic sub-array is connected to the power conversion unit via a DC combiner box. The photovoltaic module is composed of photovoltaic cells, and the photovoltaic cells include silicon-based cells or non-silicon-based cells.

[0009] Preferably, the DC / AC conversion unit is a string structure, including multiple DC-DC converters and a DC-AC converter; each DC-DC converter is connected to a photovoltaic array for regulating the operating status of the photovoltaic array; the multiple DC-DC converters are connected in parallel via a common DC bus to the DC-AC converter for regulating the DC bus voltage and AC output power; the self-synchronizing voltage source generation and control unit enables the DC-AC converter to have autonomous voltage build-up, autonomous synchronization, and grid support capabilities; the AC side is connected to the grid via an LC filter.

[0010] Preferably, the DC / AC conversion unit is a centralized structure, including a DC-AC converter; multiple photovoltaic sub-arrays are connected in parallel via a common DC bus and directly connected to the DC-AC converter, used to simultaneously regulate the operating status of the photovoltaic arrays, the DC bus voltage, and the AC output power; the AC side is connected to the power grid via an LC filter.

[0011] Preferably, the self-synchronizing voltage source generation and control unit includes: a front-end DC-DC control section, a grid-side DC-AC control section, and a dual-mode contention command control section;

[0012] The front-end DC-DC control section has an MPPT working mode and a constant voltage control mode; the grid-side DC-AC control section includes a modulation voltage control module and a synchronization phase angle control module; the dual-mode competition command control section is used to realize the competition switching between the first mode and the second mode according to the DC bus voltage and active power.

[0013] In the first mode, the DC-DC converter operates in MPPT mode, and the DC-AC converter maintains a constant DC bus voltage;

[0014] In the second mode, the DC-DC converter operates in constant voltage mode, and the DC-AC converter controls the AC output power to a set reference value.

[0015] Preferably, the self-synchronizing voltage source generation and control unit includes: a grid-side DC-AC control section and a dual-mode competition command control section;

[0016] The grid-side DC-AC control section includes a modulation voltage control module and a synchronization phase angle control module; the dual-mode competition command control section is used to realize the competitive switching between the first mode and the second mode according to the DC bus voltage and active power.

[0017] In the first mode, the DC-AC converter maintains a constant DC bus voltage and outputs maximum power;

[0018] In the second mode, the DC-AC converter controls the AC output power to a set reference value.

[0019] Preferably, the control logic of the dual-mode contention command control section includes:

[0020] When the DC bus voltage exceeds the upper limit threshold, the system switches from the first mode to the second mode and controls the AC output power to the set value.

[0021] When the DC bus voltage is lower than the lower threshold, the system switches from the second mode to the first mode to maintain a constant DC bus voltage and balance the AC output power with the photovoltaic output power.

[0022] Preferably, for the string structure, in the first mode the photovoltaic DC voltage is lower than the maximum power point voltage, the maximum power output is controlled by DC-DC and the bus voltage is controlled by DC-AC; in the second mode the photovoltaic DC voltage is higher than the maximum power point voltage, the bus voltage is controlled by DC-DC and the active power is controlled by DC-AC and responds to the grid frequency.

[0023] For a centralized structure, in the first mode the photovoltaic DC voltage is lower than the maximum power point voltage, the DC-AC controls the bus voltage and outputs the maximum power; in the second mode the photovoltaic DC voltage is higher than the maximum power point voltage, the DC-AC controls the active power and responds to the grid frequency.

[0024] Preferably, when a grid fault causes an AC voltage drop, for a string structure, the DC bus voltage is controlled to not exceed the limit by mode switching, and an active power output reference is set according to the available active power capacity and active power limit.

[0025] Preferably, when a grid fault causes an AC voltage drop, for a centralized structure, active power output is controlled by mode switching, and an active power output reference is set according to the available active power capacity and active power limit.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. This invention proposes a dual-mode competitive dominance mechanism of "external DC voltage maintenance - internal DC voltage maintenance", which can maintain the self-synchronization voltage source control characteristics of photovoltaic units under various operating conditions such as sudden changes in sunlight and grid faults. It solves the problem of smooth switching between the two states of maximum active power tracking and bus voltage maintenance, so that the photovoltaic power generation unit has the ability of autonomous grid synchronization, autonomous voltage establishment and frequency regulation in both steady state and transient state.

[0028] 2. This invention is applicable to photovoltaic power generation unit topologies without DC crowbars on the DC side, and can achieve DC bus unloading and transient voltage stabilization without relying on external equipment (such as DC crowbars) during transient processes, thereby reducing hardware costs.

[0029] 3. This invention is applicable to both string photovoltaic topologies and centralized photovoltaic topologies. Attached Figure Description

[0030] 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:

[0031] Figure 1 This is a schematic diagram of a self-synchronizing voltage source type string photovoltaic circuit model in an embodiment of the present invention;

[0032] Figure 2 This is a schematic diagram of a self-synchronizing voltage source type centralized photovoltaic circuit model in an embodiment of the present invention;

[0033] Figure 3 This is a schematic diagram of the string photovoltaic self-synchronization voltage source control structure in an embodiment of the present invention;

[0034] Figure 4 This is a schematic diagram of the centralized photovoltaic self-synchronization voltage source control structure in an embodiment of the present invention;

[0035] Figure 5 This is a schematic diagram of the dual-mode parallel competition-dominated control logic in an embodiment of the present invention;

[0036] Figure 6 This is a schematic diagram illustrating the effect of dual-mode parallel competition-dominated self-synchronizing voltage source control under varying illumination conditions in an embodiment of the present invention.

[0037] Figure 7 This is a schematic diagram of the process of the present invention. Detailed Implementation

[0038] 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 scope of protection of the present invention.

[0039] Example 1:

[0040] Reference Figure 1 and Figure 2 According to the present invention, a dual-mode parallel competition-dominated self-synchronizing voltage source photovoltaic power generation unit includes: a photovoltaic array, a DC / AC conversion unit, and a self-synchronizing voltage source generation control unit; the photovoltaic array is used to convert light energy into electrical energy; the DC / AC conversion unit is used to convert DC power into AC power; the self-synchronizing voltage source generation control unit includes a dual-mode parallel competition-dominated control module, a modulation voltage control module, and a synchronization phase angle control module, used to autonomously establish voltage, autonomously achieve grid synchronization, and support grid transient frequency and voltage; the dual-mode parallel competition-dominated control module maintains the state of two voltage source control modes in parallel, including a first mode and a second mode, wherein the DC bus voltage of the first mode is maintained constant by itself, and the DC bus voltage of the second mode is maintained constant by external means; based on the DC bus voltage fluctuation and power flow characteristics, the self-synchronizing voltage source characteristics of the photovoltaic power generation unit under sudden changes in light intensity or grid fault conditions are maintained through the competition-dominated nature of the two modes, and the DC bus transient voltage stability is achieved without a DC crowbar circuit.

[0041] The photovoltaic array includes multiple photovoltaic module strings, which are connected in parallel to form a photovoltaic subarray. The photovoltaic subarray is connected to the power conversion unit via a DC combiner box. The photovoltaic module is composed of photovoltaic cells, which may be silicon-based or non-silicon-based.

[0042] Reference Figure 3 and Figure 4 The DC / AC conversion unit is a string structure, including multiple DC-DC converters and DC-AC converters. Each DC-DC converter is connected to a photovoltaic array to regulate the operation of the photovoltaic array. The multiple DC-DC converters are connected in parallel to the DC-AC converter via a common DC bus to regulate the DC bus voltage and AC output power. The self-synchronizing voltage source generation and control unit enables the DC-AC converter to have autonomous voltage build-up, autonomous synchronization, and grid support capabilities. The AC side is connected to the grid via an LC filter.

[0043] The DC / AC conversion unit has a centralized structure, including a DC-AC converter; multiple photovoltaic sub-arrays are connected in parallel via a common DC bus and then directly connected to the DC-AC converter, which is used to simultaneously regulate the operating status of the photovoltaic arrays, the DC bus voltage, and the AC output power; the AC side is connected to the power grid via an LC filter.

[0044] The self-synchronizing voltage source generation and control unit includes: a front-end DC-DC control section, a grid-side DC-AC control section, and a dual-mode competition command control section; the front-end DC-DC control section has an MPPT operating mode and a constant voltage control mode; the grid-side DC-AC control section includes a modulation voltage control module and a synchronization phase angle control module; the dual-mode competition command control section is used to realize the competition switching between the first mode and the second mode according to the DC bus voltage and active power; in the first mode, the DC-DC converter operates in MPPT mode, and the DC-AC converter maintains a constant DC bus voltage; in the second mode, the DC-DC converter operates in constant voltage mode, and the DC-AC converter controls the AC output power to a set reference value.

[0045] The self-synchronizing voltage source generation control unit includes: a grid-side DC-AC control section and a dual-mode competition command control section; the grid-side DC-AC control section includes a modulation voltage control module and a synchronization phase angle control module; the dual-mode competition command control section is used to realize the competition switching between the first mode and the second mode according to the DC bus voltage and active power; in the first mode, the DC-AC converter maintains the DC bus voltage constant and outputs maximum power; in the second mode, the DC-AC converter controls the AC output power to a set reference value.

[0046] The control logic of the dual-mode competition command control section includes: when the DC bus voltage exceeds the upper limit threshold, switching from the first mode to the second mode to control the AC output power to the set value; when the DC bus voltage is lower than the lower limit threshold, switching from the second mode to the first mode to maintain the DC bus voltage constant and balance the AC output power with the photovoltaic output power.

[0047] For string structures, in the first mode, the photovoltaic DC voltage is lower than the maximum power point voltage, and the maximum power output is controlled by a DC-DC converter, while the bus voltage is controlled by a DC-AC converter. In the second mode, the photovoltaic DC voltage is higher than the maximum power point voltage, and the bus voltage is controlled by a DC-DC converter, while the active power is controlled by a DC-AC converter and the grid frequency is responded to. For centralized structures, in the first mode, the photovoltaic DC voltage is lower than the maximum power point voltage, and the bus voltage is controlled by a DC-AC converter and the maximum power output is achieved. In the second mode, the photovoltaic DC voltage is higher than the maximum power point voltage, and the active power is controlled by a DC-AC converter and the grid frequency is responded to.

[0048] When a grid fault causes an AC voltage drop, for string-type structures, mode switching is used to control the DC bus voltage to prevent it from exceeding limits, and an active power output reference is set based on available active power capacity and active power limit. For centralized structures, mode switching is used to control active power output, and an active power output reference is set based on available active power capacity and active power limit.

[0049] Example 2:

[0050] Reference Figure 5 and Figure 6 This invention provides a dual-mode parallel competition-dominated self-synchronizing voltage source photovoltaic power generation unit, comprising: a photovoltaic array, composed of photovoltaic modules, for converting sunlight into electrical energy; a DC / AC converter, composed of power electronic converters, for converting the DC power generated by the front-end photovoltaic array into AC power; and a self-synchronizing voltage source generation and control system, composed of a dual-mode parallel competition-dominated control module, a modulation voltage control module, and a synchronization phase angle control module, for autonomously establishing voltage, autonomously synchronizing with the grid, and supporting the transient frequency and voltage of the grid; and, based on the DC bus voltage fluctuation characteristics and power flow characteristics, maintaining the self-synchronizing voltage source characteristics of the photovoltaic power generation unit under multiple operating conditions such as sudden changes in sunlight and grid faults through state maintenance and competition dominance of two voltage source control modes, thereby achieving stable transient voltage of the bus without a DC crowbar on the DC side. This invention is applicable to string and centralized photovoltaic systems, including control, equipment, and systems.

[0051] Reference Figure 7 A dual-mode parallel competition-dominated self-synchronizing voltage source photovoltaic power generation unit includes: a photovoltaic array, composed of photovoltaic modules connected in series and parallel, used to convert sunlight into electrical energy; a DC / AC converter, composed of DC-DC or DC-AC power electronic converters, used to convert the DC power generated by the front-end photovoltaic array into AC power; and a self-synchronizing voltage source generation control, composed of a dual-mode parallel competition-dominated control module, a modulation voltage control module, and a synchronization phase angle control module, used to autonomously establish voltage, autonomously synchronize with the grid, and support the transient frequency and voltage of the grid. The dual-mode parallel competition selection control module maintains the state of two voltage source control modes in parallel, including: mode 1 where the DC bus voltage is maintained constant by itself, and mode 2 where the DC bus voltage is maintained constant externally. Based on the DC bus voltage fluctuation characteristics and power flow characteristics, the self-synchronizing voltage source control characteristics of the photovoltaic power generation unit are maintained under various operating conditions such as sudden changes in sunlight and grid faults through the state maintenance and competition-dominated operation of the two voltage source control modes, and the transient voltage stability of the bus without a DC crowbar on the DC side is achieved.

[0052] A photovoltaic (PV) array consists of several PV modules connected in series to form a PV module string, and several PV module strings connected in parallel to form a PV subarray. The PV subarray is connected to a power conversion unit via a DC combiner box. PV modules are composed of PV cells assembled, laminated, and framed. PV cells include silicon-based cells and non-silicon cells.

[0053] For string photovoltaic systems, the DC / AC conversion mainly consists of back-to-back DC-DC and DC-AC power electronic converters, forming a two-stage structure. The front end contains multiple DC-DC converters, each connected to a photovoltaic array, responsible for regulating the operation of the photovoltaic array. The multiple DC-DC converters are connected in parallel to the DC-AC converter via a common DC bus. The DC-AC converter is mainly responsible for regulating the DC bus voltage and AC output power. Through the self-synchronizing voltage source control unit, it can autonomously establish voltage, autonomously synchronize with the grid, and support the transient frequency and voltage characteristics of the grid. The AC side uses an LC filter to connect to the grid.

[0054] For centralized photovoltaic systems, DC / AC conversion is achieved by a DC-AC converter, i.e., a single-stage structure. Multiple photovoltaic sub-arrays at the front end are directly connected to the DC-AC converter in parallel via a common DC bus. The converter is responsible for simultaneously regulating the operating status of the photovoltaic arrays, as well as the DC bus voltage and AC output power. Its AC side can also use an LC filter to connect to the grid.

[0055] For string photovoltaic systems, self-synchronizing voltage source generation control includes a front-end DC-DC control section, a grid-side DC-AC control section, and a dual-mode competition command control section. The DC-DC control section includes two control modes: one is the MPPT (Multi-Level Photovoltaic Power) mode, where the active power control reference value is corrected by the primary frequency regulation control module, and the result is input to the MPPT control module to calculate the corresponding DC voltage reference for the photovoltaic modules, which is then input to the photovoltaic module voltage control module to obtain the modulation wave; the other is the constant voltage control mode, which maintains a constant DC bus voltage based on the set bus voltage reference value through DC bus voltage control. The grid-side DC-AC control section consists of a modulation voltage control module and a synchronization phase angle control module. The synchronization phase angle control module includes two modes: Mode 1, where the DC bus voltage is maintained constant by itself, and Mode 2, where the DC bus voltage is maintained constant by external means. The former is used to maintain a constant DC bus voltage, while the latter is used to control the AC output power to the set reference value. The modulation voltage control module is responsible for generating the modulation voltage, and the reactive power control module generates an internal potential reference, which is input to the virtual admittance module to generate a current reference (in transient conditions, the output current is controlled by current limiting), and after passing through the inner current loop, the modulation voltage is generated. The dual-mode competitive selection control module achieves dual-mode competitive selection based on DC bus voltage and AC active power. In mode 1, the front-end DC-DC converter operates in MPPT mode, while the grid-side DC-AC converter maintains a constant DC bus voltage. In mode 2, the front-end DC-DC converter operates in constant DC voltage mode, while the grid-side DC-AC controls the AC output power to the reference value (in transient conditions, the output active power is controlled by active power limiting).

[0056] For centralized photovoltaic systems, self-synchronizing voltage source generation control includes a grid-side DC-AC control section and a dual-mode competition command control section. The grid-side DC-AC control section consists of a modulation voltage control module and a synchronization phase angle control module. The synchronization phase angle control module includes two modes: Mode 1, where the DC bus voltage is maintained constant by itself; and Mode 2, where the DC bus voltage is maintained constant externally. The former, based on the DC bus voltage reference output from the primary frequency regulation and MPPT control modules (which is also the DC voltage of the photovoltaic array), controls the DC bus voltage to remain constant while also regulating the AC power to maximize the AC output power. The latter, based on the active power reference setting corrected by the primary frequency regulation, regulates the AC power. The modulation voltage control module consists of reactive power control, virtual admittance, current limiting, and an inner current loop. The dual-mode competitive selection control module achieves dual-mode competitive selection based on DC bus voltage and AC active power. In mode 1, the grid-side DC-AC converter maintains a constant DC bus voltage, while in mode 2, the grid-side DC-AC converter controls the AC output power to the reference value (the output active power is controlled by active power limiting in transient conditions).

[0057] The control logic of the dual-mode competition decision control section is as follows: 1) When the DC bus voltage exceeds the upper limit of the set threshold range, the output power of the front-end photovoltaic is higher than the output power of the grid side, resulting in a power surplus that causes the bus voltage to rise further. At this time, mode 1 cannot maintain the bus voltage at the set value and needs to switch to mode 2. The excess active power will raise the DC bus voltage to a higher steady-state value and then stabilize. The grid side AC side outputs the constant active power level set by mode 2. 2) When the DC bus voltage exceeds the lower limit of the set threshold range, the output power of the front-end photovoltaic is lower than the output power of the grid side, resulting in a power shortage that causes the bus voltage to drop further. At this time, mode 2 cannot maintain the actual output power at the set value and needs to switch to mode 1. At this time, the DC bus voltage is kept constant so that the AC side output power and the front-end photovoltaic output power reach a balanced state. The AC side outputs the maximum active power level of the front-end photovoltaic under the current irradiance.

[0058] The steady-state control characteristics of the dual-mode competitive decision control principle corresponding to the specific photovoltaic topology are as follows: 1) For string photovoltaic, mode 1 is mainly for the operating area where the photovoltaic DC voltage is lower than the voltage corresponding to the maximum power point. The front-end DC-DC is responsible for the maximum active power control, and the grid-side DC-AC is responsible for maintaining the DC bus voltage constant. At this time, the DC voltage of the photovoltaic array is controlled and is given and controlled by the maximum power control module of the front-end DC-DC. Mode 2 is mainly for the operating area where the photovoltaic DC voltage is higher than the voltage corresponding to the maximum power point. The front-end DC-DC is responsible for maintaining the DC bus voltage constant, and the grid-side DC-AC controls the active power and responds to the grid frequency change. At this time, the DC voltage of the photovoltaic array is not controlled and is determined by the steady-state DC voltage of the photovoltaic array IV characteristic curve at the current active power output level. 2) For centralized photovoltaic systems, Mode 1 is mainly for operating areas where the photovoltaic DC voltage is lower than the voltage corresponding to the maximum power point. The grid-side DC-AC is responsible for optimizing and controlling the DC bus voltage to the maximum power point, while maintaining a constant bus voltage and maximum power output. At this time, the DC voltage of the photovoltaic array is the bus voltage. Mode 2 is mainly for operating areas where the photovoltaic DC voltage is higher than the voltage corresponding to the maximum power point. The grid-side DC-AC controls the active power and responds to changes in grid frequency. At this time, the DC voltage of the photovoltaic array is not controlled and is determined by the steady-state DC voltage of the photovoltaic array under the current active power output level by the IV characteristic curve.

[0059] The transient control characteristics corresponding to specific photovoltaic topologies under the dual-mode competitive selection control principle are as follows: 1) For string photovoltaic systems, when a grid fault causes a drop in AC voltage, the active power transmission is obstructed, leading to an increase in DC bus voltage. Dual-mode competitive selection control enables a smooth switch from mode 1 to mode 2. In this case, the DC bus voltage is controlled by the front-end DC-DC converter to prevent overshooting. The active power output reference command set for mode 2 should be set based on the available active power capacity (calculated based on the reactive current required to support transient voltage) and the active power limit (set based on the DC bus voltage range). 2) For centralized photovoltaic systems, when a grid fault causes a drop in AC voltage, the active power transmission is obstructed, leading to an increase in DC bus voltage. Dual-mode competitive selection control enables a smooth switch from mode 1 to mode 2. In this case, the DC bus voltage is not controlled. The active power output reference command set for mode 2 should be set based on the available active power capacity (calculated based on the reactive current required to support transient voltage) and the active power limit (set based on the DC bus voltage range and the photovoltaic array IV characteristic curve).

[0060] An electronic device includes: a processor; and a memory storing a computer program that, when executed by the processor, causes the processor to perform a control method for a self-synchronizing voltage source photovoltaic power generation unit.

[0061] A non-transitory computer-readable storage medium storing computer-readable instructions that, when executed by a processor, cause the processor to perform a control method for a self-synchronizing voltage source photovoltaic power generation unit.

[0062] by Figure 2 Taking the centralized photovoltaic system shown as an example, consider the following: Figure 6 The example shown is a simulation of light intensity changes. In the example, the active power reference value is Pref = 0.8 pu. The illuminance decreases from 1000 W / m2 (1 pu) and then increases again. It can be seen that the control mode switches from the initial voltage source control mode 2 (surplus front-end power, DC bus voltage is maintained by external means), to voltage source control mode 1 (insufficient front-end power, DC bus voltage is maintained by itself), and then back to voltage source control mode 2.

[0063] In voltage source control mode 2, because the photovoltaic system can respond to changes in grid frequency, it exhibits significant inertia during power fluctuations. This characteristic effectively balances grid frequency fluctuations, ensuring stable photovoltaic power output. In voltage source control mode 1, however, the system adjusts its photovoltaic power output according to changes in illuminance. The photovoltaic system's power output closely follows these changes and does not exhibit inertia. In this mode, the system's control objective is to maintain maximum power output while ensuring the stability of the DC bus voltage.

[0064] Those skilled in the art can understand this embodiment as a more specific description of Embodiment 1.

[0065] 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.

[0066] 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 photovoltaic power generation unit dominated by dual-mode parallel competition, characterized in that, include: Photovoltaic array, DC / AC converter unit, and self-synchronizing voltage source generation and control unit; The photovoltaic array is used to convert light energy into electrical energy; the DC / AC conversion unit is used to convert DC power into AC power; the self-synchronizing voltage source generation and control unit includes a dual-mode parallel competition-dominant control module, a modulation voltage control module, and a synchronization phase angle control module, which are used to autonomously establish voltage, autonomously achieve grid synchronization, and support grid transient frequency and voltage. The dual-mode parallel competition-dominant control module maintains the state of two voltage source control modes in parallel, including a first mode and a second mode. In the first mode, the DC bus voltage is maintained constant by itself, while in the second mode, the DC bus voltage is maintained constant by external means. Based on the DC bus voltage fluctuation and power flow characteristics, the competitive dominance of the two modes maintains the self-synchronizing voltage source characteristics of the photovoltaic power generation unit under conditions of sudden changes in sunlight or grid faults, and achieves DC bus transient voltage stability without DC crowbar circuit. The DC / AC conversion unit is either a string structure or a centralized structure; When the DC / AC converter unit is a string structure, the self-synchronizing voltage source generation and control unit includes: a front-end DC-DC control section, a grid-side DC-AC control section, and a dual-mode competition command control section; the front-end DC-DC control section has an MPPT operating mode and a constant voltage control mode; the grid-side DC-AC control section includes a modulation voltage control module and a synchronization phase angle control module; the dual-mode competition command control section is used to realize the competition switching between the first mode and the second mode according to the DC bus voltage and active power; in the first mode, the DC-DC converter operates in MPPT mode, and the DC-AC converter maintains a constant DC bus voltage; in the second mode, the DC-DC converter operates in constant voltage mode, and the DC-AC converter controls the AC output power to a set reference value; When the DC / AC conversion unit is a centralized structure, the self-synchronizing voltage source generation and control unit includes: a grid-side DC-AC control section and a dual-mode competition command control section; the grid-side DC-AC control section includes a modulation voltage control module and a synchronization phase angle control module; the dual-mode competition command control section is used to realize the competition switching between the first mode and the second mode according to the DC bus voltage and active power; in the first mode, the DC-AC converter maintains the DC bus voltage constant and outputs maximum power; in the second mode, the DC-AC converter controls the AC output power to a set reference value.

2. The dual-mode parallel competition-dominated self-synchronizing voltage source photovoltaic power generation unit according to claim 1, characterized in that, The photovoltaic array includes multiple photovoltaic module strings, which are connected in parallel to form a photovoltaic sub-array. The photovoltaic sub-array is connected to the power conversion unit via a DC combiner box. The photovoltaic modules are composed of photovoltaic cells, which include silicon-based cells or non-silicon-based cells.

3. The dual-mode parallel competition-dominated self-synchronizing voltage source photovoltaic power generation unit according to claim 1, characterized in that, The DC / AC conversion unit is a string structure, including multiple DC-DC converters and a DC-AC converter. Each DC-DC converter is connected to a photovoltaic array to regulate the operating status of the photovoltaic array. The multiple DC-DC converters are connected in parallel to the DC-AC converter via a common DC bus to regulate the DC bus voltage and AC output power. The self-synchronizing voltage source generation and control unit enables the DC-AC converter to have autonomous voltage build-up, autonomous synchronization, and grid support capabilities. The AC side is connected to the grid via an LC filter.

4. The dual-mode parallel competition-dominated self-synchronizing voltage source photovoltaic power generation unit according to claim 1, characterized in that, The DC / AC conversion unit has a centralized structure, including a DC-AC converter; multiple photovoltaic sub-arrays are connected in parallel via a common DC bus and then directly connected to the DC-AC converter, which is used to simultaneously regulate the operating status of the photovoltaic arrays, the DC bus voltage, and the AC output power; the AC side is connected to the power grid via an LC filter.

5. The dual-mode parallel competition-dominated self-synchronizing voltage source photovoltaic power generation unit according to claim 1, characterized in that, The control logic of the dual-mode contention command control section includes: When the DC bus voltage exceeds the upper limit threshold, the system switches from the first mode to the second mode and controls the AC output power to the set value. When the DC bus voltage is lower than the lower threshold, the system switches from the second mode to the first mode to maintain a constant DC bus voltage and balance the AC output power with the photovoltaic output power.

6. The dual-mode parallel competition-dominated self-synchronizing voltage source photovoltaic power generation unit according to claim 5, characterized in that, For string structures, in the first mode, the photovoltaic DC voltage is lower than the maximum power point voltage, the maximum power output is controlled by DC-DC converter, and the bus voltage is controlled by DC-AC converter; in the second mode, the photovoltaic DC voltage is higher than the maximum power point voltage, the bus voltage is controlled by DC-DC converter, and the active power is controlled by DC-AC converter and the grid frequency is responded to. For a centralized structure, in the first mode the photovoltaic DC voltage is lower than the maximum power point voltage, the DC-AC controls the bus voltage and outputs the maximum power; in the second mode the photovoltaic DC voltage is higher than the maximum power point voltage, the DC-AC controls the active power and responds to the grid frequency.

7. The dual-mode parallel competition-dominated self-synchronizing voltage source photovoltaic power generation unit according to claim 5, characterized in that, When a grid fault causes an AC voltage drop, for string structures, the DC bus voltage is controlled to remain within limits by mode switching, and the active power output reference is set according to the available active power capacity and active power limit.

8. The dual-mode parallel competition-dominated self-synchronizing voltage source photovoltaic power generation unit according to claim 5, characterized in that, When a grid fault causes an AC voltage drop, for a centralized structure, active power output is controlled by mode switching, and an active power output reference is set according to the available active power capacity and active power limit.

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