Power control method, power converter and photovoltaic power generation system

Abstract

The embodiment of the invention provides a power control method, a power converter and a photovoltaic power generation system.The power control method is partially applied to the photovoltaic power generation system, and the photovoltaic power generation system comprises the power converter and a plurality of photovoltaic power generation units connected to the first direct current input side of the power converter. The method comprises the following steps: when the total output power of a plurality of photovoltaic power generation units exceeds a preset total power limit value, determining the power limit priority of each photovoltaic power generation unit according to the respective photovoltaic voltage of the plurality of photovoltaic power generation units; wherein the lower the photovoltaic voltage is, the higher the power limit priority of the corresponding photovoltaic power generation unit is; and limiting the output power of the plurality of photovoltaic power generation units according to the power limiting priority until the limited total output power does not exceed the total power limiting value. According to the embodiment of the invention, the photovoltaic power generation unit with low photovoltaic voltage can be preferentially limited, the DC bus voltage is prevented from rising in power limitation, and the stress risk of the power converter is reduced.

Description

Power control methods, power converters and photovoltaic power generation systems Technical Field

[0001] This disclosure relates to the field of photovoltaic technology, specifically to a power control method, a power converter, and a photovoltaic power generation system. Background Technology

[0002] A photovoltaic (PV) power generation system typically includes a power converter and multiple PV units connected to the DC input side of the power converter. The PV units convert solar energy into electrical energy. The power converter then converts the electrical energy from the PV units into alternating current (AC) to supply power to the grid and loads.

[0003] A photovoltaic (PV) power generation system may experience power excess, meaning the total output power of the PV units exceeds the total power limit, also known as overpower. This power excess can lead to system malfunctions. Summary of the Invention

[0004] In view of the above problems, this disclosure provides a power control method, a power converter, and a photovoltaic power generation system to solve the above technical problems.

[0005] In a first aspect, embodiments of this disclosure provide a power control method applied to a photovoltaic power generation system. The photovoltaic power generation system includes a power converter and a plurality of photovoltaic power generation units connected to a first DC input side of the power converter. The power control method includes: when the total output power of the plurality of photovoltaic power generation units exceeds a preset total power limit value, determining a power limiting priority for each of the plurality of photovoltaic power generation units based on their respective photovoltaic voltages; wherein, the lower the photovoltaic voltage, the higher the power limiting priority of the corresponding photovoltaic power generation unit; and limiting the output power of the plurality of photovoltaic power generation units according to the power limiting priority until the total output power after limitation does not exceed the total power limit value.

[0006] Optionally, limiting the output power of the plurality of photovoltaic power generation units according to the power limiting priority until the total output power after limitation does not exceed the total power limit value includes: taking the photovoltaic power generation unit with the highest priority in the power limiting priority as the current target limiting unit; obtaining the power limiting value of the current target limiting unit, wherein the power limiting value of the current target limiting unit is the difference between the total power limit value and the output power of other photovoltaic power generation units; determining whether the power limiting value of the current target limiting unit is greater than or equal to zero; if yes, then limiting the output power of the current target limiting unit based on the power limiting value; if no, then limiting the output power of the current target limiting unit to zero, taking the next higher priority photovoltaic power generation unit as the new current target limiting unit in descending order of the power limiting priority, and returning to the step of obtaining the power limiting value of the current target limiting unit.

[0007] Optionally, the power control method further includes: when the total output power of the plurality of photovoltaic power generation units is less than the total power limit, determining the power recovery priority of each photovoltaic power generation unit based on the photovoltaic voltage of each of the plurality of photovoltaic power generation units; wherein, the higher the photovoltaic voltage, the higher the power recovery priority of the corresponding photovoltaic power generation unit; and restoring the output power of the plurality of photovoltaic power generation units according to the power recovery priority until the total output power reaches the total power limit or all photovoltaic power generation units have performed output power recovery.

[0008] Optionally, the output power recovery of the plurality of photovoltaic power generation units according to the power recovery priority includes: taking the photovoltaic power generation unit with the highest priority in the power recovery priority as the current target recovery unit; obtaining the power limit value of the current target recovery unit, wherein the power limit value of the current target recovery unit is the difference between the total power limit value and the output power of other photovoltaic power generation units; determining whether the power limit value of the current target recovery unit is greater than or equal to the single-path rated power of the current target recovery unit, or whether the actual output power of the current target recovery unit is less than or equal to the power limit value of the current target recovery unit; if yes, then the output power limit of the current target recovery unit is lifted, and the next higher priority photovoltaic power generation unit is taken as the new current target recovery unit in descending order of the power recovery priority, and the process returns to the step of obtaining the power limit value of the current target recovery unit; if no, then the output power recovery ends.

[0009] Optionally, limiting the output power of the current target limiting unit based on the power limit value includes: determining the total current limit value of the current target limiting unit based on the power limit value and photovoltaic voltage of the current target limiting unit; determining the target current limit value of the current target limiting unit according to the total current limit value, wherein the target current limit value is not greater than the total current limit value; and controlling the photovoltaic current of the current target limiting unit to be less than or equal to the target current limit value.

[0010] Optionally, limiting the output power of the current target limiting unit based on the power limit value further includes: determining the single-channel current limit value of the current target limiting unit based on the single-channel rated power and photovoltaic voltage of the current target limiting unit; wherein, determining the target current limit value of the current target limiting unit based on the total current limit value includes: determining the smaller value between the total current limit value and the single-channel current limit value, and using the smaller value as the target current limit value of the current target limiting unit.

[0011] Optionally, limiting the output power of the current target limiting unit based on the power limit value further includes: obtaining the maximum current of the current target limiting unit, wherein the maximum current is determined based on the hardware overcurrent capability of the current target limiting unit; wherein determining the target current limit value of the current target limiting unit according to the total current limit value includes: determining the minimum value among the total current limit value, the single-channel current limit value, and the maximum current, and using the minimum value as the target current limit value of the current target limiting unit.

[0012] Optionally, the power control method further includes: determining the total power limit value based on at least one of the acquired output power limit value, the total rated power of the first DC input side, and the over-temperature load limit value, wherein the output power limit value is determined based on the maximum output power of the power converter.

[0013] Optionally, the photovoltaic power generation system further includes an energy storage unit connected to the second DC input side of the power converter; the output power limit value is determined based on the sum of the maximum output power of the power converter and the maximum charging power of the energy storage unit.

[0014] Optionally, when the total output power of the plurality of photovoltaic power generation units exceeds the total power limit, the power control method further includes: when the photovoltaic voltage of any of the photovoltaic power generation units is greater than the DC bus voltage setpoint of the power converter, increasing the DC bus voltage setpoint of the power converter until the total output power of the plurality of photovoltaic power generation units does not exceed the total power limit.

[0015] Optionally, the photovoltaic power generation system further includes an energy storage unit connected to the second DC input side of the power converter; when the total output power of the plurality of photovoltaic power generation units exceeds the total power limit, the power control method further includes: when the photovoltaic voltage of any photovoltaic power generation unit is greater than the DC bus voltage setpoint of the energy storage unit or the power converter, simultaneously increasing the DC bus voltage setpoint of the energy storage unit and the power converter until the total output power of the plurality of photovoltaic power generation units does not exceed the total power limit.

[0016] Optionally, the step of simultaneously increasing the DC bus voltage setpoint of the energy storage unit and the power converter includes: determining the current difference of each of the plurality of photovoltaic power generation units, wherein the current difference of the photovoltaic power generation unit is the difference between its own target current limit value and the photovoltaic current; determining the minimum value among the current differences of the plurality of photovoltaic power generation units, determining a voltage adjustment value based on the minimum value and a preset automatic control strategy; and simultaneously increasing the DC bus voltage setpoint of the energy storage unit and the power converter based on the voltage adjustment value.

[0017] In a second aspect, embodiments of this disclosure provide a power converter, the power converter including a controller and a power conversion circuit, the controller being electrically connected to the power conversion circuit, and the controller being used to execute the method of the first aspect of this disclosure.

[0018] Optionally, the power converter is an inverter or a power conversion system (PCS).

[0019] Thirdly, embodiments of this disclosure provide a photovoltaic power generation system, including: a power converter, wherein the power converter is the power converter of the second aspect of this disclosure; and a plurality of photovoltaic power generation units, respectively connected to a first DC input side of the power converter.

[0020] The technical solution provided in this disclosure determines the power limiting priority of each photovoltaic power generation unit based on its photovoltaic voltage when the total output power of multiple photovoltaic power generation units exceeds a preset total power limit. The output power of multiple photovoltaic power generation units is limited according to the power limiting priority. The lower the photovoltaic voltage, the higher the power limiting priority of the corresponding photovoltaic power generation unit. This can preferentially limit the photovoltaic power generation units with lower photovoltaic voltage, avoid the photovoltaic voltage from rising after the output power of the photovoltaic power generation unit decreases, and avoid the DC bus voltage in the power converter from rising due to the photovoltaic voltage, thereby reducing the voltage stress risk of the power converter.

[0021] These or other aspects of this disclosure will become more apparent in the following description of embodiments. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of this disclosure, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this disclosure. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 shows a schematic diagram of a photovoltaic power generation system according to various exemplary embodiments of the present disclosure.

[0024] Figure 2 shows a flowchart of a power control method provided in an embodiment of the present disclosure.

[0025] Figure 3 shows a flowchart of output power limiting based on power limiting priority provided in an embodiment of the present disclosure.

[0026] Figure 4 shows a schematic diagram of the circuit structure of a photovoltaic power generation system provided in an embodiment of the present disclosure.

[0027] Figure 5 shows a flowchart of a power control method provided in another embodiment of this disclosure.

[0028] Figure 6 shows a flowchart of output power recovery based on power recovery priority provided in an embodiment of this disclosure. Detailed Implementation

[0029] Embodiments of this disclosure are described in detail below, with examples of embodiments shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this disclosure, and should not be construed as limiting this disclosure.

[0030] To enable those skilled in the art to better understand the solutions disclosed herein, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of this disclosure, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this disclosure without creative effort are within the scope of protection of this disclosure.

[0031] In this disclosure, it should be noted that relational terms such as first and second are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations.

[0032] Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0033] In the description of embodiments in this disclosure, terms such as "example" or "for example" are used to indicate exemplification, illustration, or description. Any embodiment or design described as "example" or "for example" in this disclosure is not to be construed as being more preferred or having more advantages than another embodiment or design. The use of terms such as "example" or "for example" is intended to present relative concepts in a clear manner.

[0034] Furthermore, in this disclosure, "multiple" refers to two or more. Therefore, in this disclosure, "multiple" can also be understood as "at least two." "At least one" can be understood as one or more, such as one, two, or more. For example, including at least one means including one, two, or more, and is not limited to which ones are included. For instance, including at least one of A, B, and C could mean including A, B, C, A and B, A and C, B and C, or A and B and C.

[0035] It should be noted that in this embodiment of the disclosure, "and / or" describes the relationship between associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. In addition, the character " / ", unless otherwise specified, generally indicates that the associated objects before and after it are in an "or" relationship.

[0036] It should be noted that in the embodiments of this disclosure, "connection" can be understood as electrical connection, and the connection between two electrical components can be a direct or indirect connection between the two electrical components. For example, the connection between A and B can be a direct connection between A and B, or an indirect connection between A and B through one or more other electrical components.

[0037] Figure 1 shows a schematic diagram of a photovoltaic power generation system according to various exemplary embodiments of the present disclosure. As shown in Figure 1, the photovoltaic power generation system 100 may include a plurality of photovoltaic power generation units 110 and a power converter 130.

[0038] In embodiments of this disclosure, each photovoltaic power generation unit 110 may include a photovoltaic string 111. The photovoltaic string 111 may include one or more photovoltaic modules connected in series and / or in parallel. Multiple photovoltaic power generation units 110 are connected to the first DC input side of a power converter 130. Exemplarily, the first DC input side of the power converter 130 includes multiple photovoltaic input interfaces (not shown), and the multiple photovoltaic power generation units 110 are connected one-to-one with each of the multiple photovoltaic input interfaces.

[0039] In embodiments of this disclosure, as shown in FIG1, the power converter 130 includes multiple DC-DC conversion circuits 112. Multiple photovoltaic power generation units 110 are connected via multiple photovoltaic input interfaces and are correspondingly connected to the multiple DC-DC conversion circuits. Each DC-DC conversion circuit 112 is used to convert the voltage output of the corresponding photovoltaic power generation unit 110 to control the output power of the photovoltaic power generation unit 110. For example, each DC-DC conversion circuit 112 performs Maximum Power Point Tracking (MPPT) on the corresponding photovoltaic power generation unit 110 to make the photovoltaic power generation unit 110 operate at its maximum power point. In some embodiments, the MPPT controller within the DC-DC conversion circuit 112 implements maximum power point tracking. The MPPT controller may include current and voltage sensors, as well as processing units such as MCUs (microcontroller units) or DSPs (digital signal processors). The current and voltage sensors of the MPPT controller can monitor the output voltage (referred to as photovoltaic voltage in this disclosure) and output current (referred to as photovoltaic current in this disclosure) of the photovoltaic string 111 in real time. The processing unit calculates the voltage and current values ​​that maximize the output power under the current conditions (i.e., the maximum power point), generates a PWM (pulse width modulation) signal, and controls the on and off time of the power switch in the DC-DC converter circuit 112 by changing the duty cycle. Through high-frequency switching action, it dynamically adjusts its equivalent impedance so that the operating point of the photovoltaic string 111 is pulled to the maximum power point.

[0040] In the various embodiments of this disclosure, the power switching transistor can be one or more combinations of semiconductor switching transistors such as bipolar junction transistor (BJT), metal-oxide-semiconductor field-effect transistor (MOSFET), and insulated-gate bipolar transistor (IGBT), and this application does not limit it.

[0041] In the embodiments disclosed herein, please continue to refer to FIG1. ​​The power converter 130 also includes a DC bus and a DC-AC conversion circuit 131. Multiple DC-DC conversion circuits 131 are connected in parallel to the DC bus. The DC terminal of the DC-AC conversion circuit 131 is connected to the DC bus, and the AC terminal is connected to the AC output side of the power converter 130 (not shown in FIG1). The AC output side can be connected to the power grid and / or a load (not shown in FIG1). The DC bus is a common power convergence point of the photovoltaic power generation system 100. In actual equipment, the DC bus can be a copper busbar, thick wire, or other conductors.

[0042] In some embodiments, when the photovoltaic power generation system 100 does not include energy storage, the power converter 130 can be an inverter (INV) that converts the DC output of the photovoltaic power generation unit 110 into AC power to supply power to the grid and / or loads.

[0043] In some embodiments, as shown in FIG1, the photovoltaic power generation system 100 may further include an energy storage unit 120, in which case the power converter 130 may be a power conversion system (PCS). The PCS can realize bidirectional power conversion. On the one hand, it can convert the DC output of the photovoltaic power generation unit 110 into AC power to supply power to at least one of the grid, load, or energy storage unit 120; on the other hand, it can convert the AC power from the grid into DC power to charge the energy storage unit 120. In a specific implementation, multiple photovoltaic power generation units 110 are connected to the DC bus through a multi-channel DC-DC conversion circuit 112 in the power converter 130, and the energy storage unit 120 is connected to the DC bus through the second DC input side of the power converter 130.

[0044] In embodiments of this disclosure, as shown in FIG1, the energy storage unit 120 may include a battery 121 and a bidirectional DC-DC converter 122. The battery 121 is connected to a DC bus via the bidirectional DC-DC converter 122. The battery 121 may be a battery pack composed of multiple battery cells connected in series and parallel. The bidirectional DC-DC converter 122 enables bidirectional and controllable energy flow between the battery 121 and the DC bus. During discharge, the bidirectional DC-DC converter 122 raises the voltage of the battery 121 to a voltage matching the DC bus. During charging, the bidirectional DC-DC converter 122 reduces the high voltage from the DC bus to a voltage level suitable for charging the battery 121. Referring to FIG1, the energy storage unit 120 may also include a battery management system 123. The battery management system 123 can monitor parameters such as voltage, current, and temperature of the battery 121, specifically monitoring the voltage of each battery cell, the total current of the battery pack, and the temperature of multiple key points. The battery management system 123 can dynamically estimate the performance parameters of the battery 121, such as SOC (State of Charge), SOH (State of Health), and power state. The battery management system 123 can provide safety protection for the battery 121, including but not limited to overcharge / over-discharge protection, overcurrent / short circuit protection, and over-temperature / low-temperature protection. In some embodiments, the DC-DC converter 122 and / or the battery management system 123 can be integrated into the power converter 130. In other embodiments, the energy storage unit 120 can be integrated into the power converter 130.

[0045] In the embodiments of this disclosure, the power converter 130 can operate in grid-connected mode and off-grid mode. In grid-connected mode, the power converter 130 can perform DC-AC conversion, using techniques such as Sinusoidal Pulse Width Modulation (SPWM) to convert the DC power on the DC bus into sinusoidal AC power with the same frequency and phase as the grid. The power converter 130 can control the output power to maintain the stability of the DC bus voltage. When the photovoltaic power generation exceeds the load requirement, the DC bus voltage tends to rise. The power converter 130 can increase the output power to feed the excess energy into the grid, thereby stabilizing the voltage. When the photovoltaic power generation is insufficient, the DC bus voltage tends to fall. The power converter 130 can reduce the output power (or draw power from the grid), at which time the energy storage unit 120 can discharge to supplement the deficit and stabilize the voltage.

[0046] In the embodiments of this disclosure, the power converter 130 may include a controller. The controller can send start / stop commands and power limiting instructions to the DC-DC converter circuit 112, and receive real-time power generation, operating voltage / current, and device status information from the DC-DC converter circuit 112. The controller can communicate with the battery management system 123 to obtain key parameters of the battery 121, such as state of charge (SOC), state of health (SOH), temperature, and voltage / current. Similarly, the controller can send corresponding instructions to the DC-AC converter circuit 131 to control the output power and operating status of the DC-AC converter circuit 131, which will not be elaborated upon in this application.

[0047] In the embodiments of this disclosure, each photovoltaic power generation unit 110 has a single-channel rated power. The single-channel rated power of the photovoltaic power generation unit 110 is determined by the rated power of its corresponding DC-DC converter circuit 112, that is, by the rated input power of the photovoltaic input interface corresponding to the power converter 130. The rated power of the DC-DC circuit 112 is determined by the specifications of its internal components, such as the current capacity of the power switch, the saturation current of the inductor, and the capacity of the heat dissipation system. The actual output power of each photovoltaic power generation unit 110 should be less than its own single-channel rated power, that is, the actual output power of one photovoltaic power generation unit 110 is less than the rated power of its corresponding DC-DC converter circuit 112. When the actual output power of the photovoltaic power generation unit 110 is greater than the rated power of its corresponding DC-DC converter circuit 112, overpower occurs. Long-term overpower can cause the power switch, inductor, diode, and other devices in the DC-DC converter circuit 112 to overheat and be damaged, or even burn out.

[0048] Based on the rated power of a single circuit of the photovoltaic power generation unit 110 and the photovoltaic voltage of the photovoltaic power generation unit 110, the single-circuit current limit value of the photovoltaic power generation unit 110 can be determined. The single-circuit current limit value is the maximum single-circuit current limited by the rated power of the single circuit. The single-circuit current limit value changes dynamically with the photovoltaic voltage of the photovoltaic power generation unit 110.

[0049] In this embodiment, each photovoltaic power generation unit 110 also has a maximum current, i.e., a single-channel maximum current limit. The maximum current of the photovoltaic power generation unit 110 is determined based on the hardware overcurrent capability of the photovoltaic power generation unit 110. In some embodiments, the actual photovoltaic current of the photovoltaic power generation unit 110 should not exceed its own maximum current. When the system needs to limit power, the controller in the power converter 130 can send a current limiting command to the DC-DC conversion circuit 112 to indicate the single-channel maximum current limit of the photovoltaic power generation unit 110. The MPPT controller in the DC-DC conversion circuit 112 controls the photovoltaic current of the corresponding photovoltaic power generation unit 110 to not exceed its own single-channel maximum current limit, thereby limiting the power of the photovoltaic power generation unit 110.

[0050] In this embodiment, the power converter 130 has a total rated power. The total rated power of the power converter 130 refers to the maximum photovoltaic (PV) input power that the DC side of the power converter 130 can accept. The total rated power mainly depends on the safe current-carrying capacity of the DC bus and related components, specifically the rated current of components such as the DC bus copper busbar, DC circuit breaker, fuse, and contactor. The total rated power on the DC side must not exceed the DC bus voltage multiplied by the maximum safe current of the DC bus. In some embodiments, the sum of the actual output power of multiple photovoltaic power generation units 110 (i.e., the total output power) should be less than or equal to the total rated power of the power converter 130. If the sum of the actual output power of the photovoltaic power generation units 110 exceeds the total rated power of the power converter 130, it will lead to overheating, insulation aging, and even fire in the DC bus, connectors, switches, etc.

[0051] In this embodiment, the energy storage unit 120 has a dynamic maximum charging power. The maximum charging power of the energy storage unit 120 is primarily determined by the maximum allowable charging voltage and maximum allowable charging current of the battery 121, which are determined by the battery's state of charge (SOC), temperature, state of health (SOH), and the battery's technical specifications. The battery management system 123 can determine the maximum charging power based on the real-time state of the battery 121 and send it to the controller within the power converter 130. In some implementations, the battery management system 123 can be integrated within the power converter 130, and the controller within the power converter 130 can implement the functions of the battery management system 123; this embodiment does not limit this approach.

[0052] In this embodiment, the power converter 130 has a dynamic maximum output power. The maximum output power of the power converter 130 determines the upper limit of energy drawn from the DC bus and converted to the AC side. For example, the maximum output power of the power converter 130 may depend on the inverter's rated power and derating factor, grid dispatch instructions, etc. The inverter's rated power is the absolute physical upper limit of the inverter design, determined by its internal power devices, heat dissipation system, magnetic components, etc. If the internal temperature of the inverter is too high, its control system will actively reduce the maximum output power (derating operation) to prevent overheating damage. In some operating conditions, such as grid-connected mode, the grid can limit the maximum output power of the power converter 130 through external commands; for example, a 50kW inverter may be required by the grid to output only 30kW. In grid-connected mode, the inverter output power is typically determined by photovoltaic power generation and grid dispatch instructions. In short, the maximum output power of the power converter 130 is mainly dynamically determined by its own rated power, its own temperature, grid dispatch instructions, etc. The sum of the actual output power of multiple photovoltaic power generation units 110 should generally not exceed the maximum output power of the power converter 130.

[0053] In some embodiments, when the photovoltaic power generation system 100 does not include energy storage, the sum of the actual output power of the multiple photovoltaic power generation units 110 does not exceed the maximum output power of the power converter 130. When the sum of the actual output power of the multiple photovoltaic power generation units 110 (PV input power) exceeds the maximum output power of the power converter 130, the excess power that cannot be absorbed will cause the DC bus capacitor to charge continuously, resulting in a sharp rise in the DC bus voltage. In some embodiments, when the photovoltaic power generation system 100 includes energy storage, the sum of the actual output power of the multiple photovoltaic power generation units 110 should not exceed the sum of the maximum charging power of the energy storage unit 120 and the maximum output power of the power converter 130. When the sum of the actual output power of the multiple photovoltaic power generation units 110 exceeds the sum of the maximum charging power of the energy storage unit 120 and the maximum output power of the power converter 130, the excess power that cannot be absorbed will cause the DC bus capacitor to charge continuously, resulting in a sharp rise in the DC bus voltage. This situation may trigger the system overvoltage protection, and in severe cases, may damage various components of the photovoltaic power generation system.

[0054] In related technologies, when the system has excess power, the maximum photovoltaic current of the photovoltaic power generation unit 110 is limited based on the DC bus voltage, thereby limiting the power of all photovoltaic power generation units 110. Specifically, when the system has excess power, the DC bus voltage increases, and the power converter 130 triggers a current limiting command to reduce the single-channel maximum current limit value of all photovoltaic power generation units 110. The DC-DC conversion circuit 112 within the power converter 130 controls the actual photovoltaic current of the photovoltaic power generation unit 110 to be less than its own single-channel maximum current limit.

[0055] Based on the characteristics of photovoltaic power generation, the typical power-voltage curve of a photovoltaic panel is an inverted U-shaped curve, with the point of highest power on the curve being the maximum power point. The MPPT controller continuously fine-tunes the photovoltaic voltage and current of the photovoltaic panel to keep them stable near the maximum power point, thereby maximizing power generation efficiency. If the power is reduced simply by lowering the single-channel maximum current limit of the photovoltaic power generation unit 110, due to the characteristics of the power-voltage curve, the actual photovoltaic voltage of the photovoltaic power generation unit 110 may increase after the power is reduced, which in turn may lead to an increase in the DC bus voltage, thereby increasing the voltage stress risk of the power converter 130.

[0056] Therefore, embodiments of this disclosure provide a power control method. Please refer to FIG2. The power control method of this disclosure can be applied to the photovoltaic power generation system shown in FIG1. ​​In a specific implementation, the method can be executed by the controller in the power converter 130. The method can include the following steps.

[0057] Step S201: When the total output power of multiple photovoltaic power generation units exceeds the preset total power limit value, the power limit priority of each photovoltaic power generation unit is determined according to the photovoltaic voltage of each of the multiple photovoltaic power generation units.

[0058] In the embodiments of this disclosure, in the photovoltaic power generation system 100 shown in FIG1, the power converter 130 can monitor the total output power of multiple photovoltaic power generation units 110 and compare the total output power with the total power limit value to determine whether the total output power of the multiple photovoltaic power generation units 110 exceeds the total power limit value.

[0059] In some embodiments, the power converter 130 may determine its total power limit based on at least one of the following: an output power limit, the total rated power of the power converter 130, and an over-temperature load power limit. As one embodiment, the total power limit may be the minimum of the output power limit, the total rated power of the power converter 130, and the over-temperature load power limit. Specifically, when the photovoltaic power generation system 100 does not include the energy storage unit 120, the output power limit is determined based on the maximum output power of the power converter 130. When the photovoltaic power generation system 100 includes the energy storage unit 120, the output power limit is determined based on the sum of the maximum charging power of the energy storage unit 120 and the maximum output power of the power converter 130. The over-temperature load power limit is used to prevent the modules from aging or being damaged more quickly due to exceeding their safe operating range at high temperatures; it may be determined based on the derating initiation temperature, the actual temperature of the photovoltaic modules, the total rated power, and the power temperature coefficient.

[0060] For example, the over-temperature power limit can be determined according to the following formula: Pderate = Ptspec * (Tpv - Tderate) * K where Pderate represents the over-temperature power limit, Ptspec represents the total rated power of the power converter 130, i.e., the total rated power on the DC side, Tpv represents the actual temperature of the photovoltaic module, K represents the power temperature coefficient, and Tderate represents the preset temperature limit. Typically, derating calculation is not enabled when Tpv ≤ Tderate.

[0061] When the total output power of multiple photovoltaic power generation units 110 exceeds the total power limit, the controller within the power converter 130 can acquire the photovoltaic voltage of each of the multiple photovoltaic power generation units 110, sort the multiple photovoltaic power generation units 110 according to the magnitude of the photovoltaic voltage, and thus determine the power limit priority. In the embodiments of this disclosure, the lower the photovoltaic voltage, the higher the power limit priority of the corresponding photovoltaic power generation unit, so that the photovoltaic power generation unit 110 with low photovoltaic voltage is preferentially reduced in power.

[0062] Step S202: Limit the output power of multiple photovoltaic power generation units according to the power limiting priority until the total output power after limiting does not exceed the total power limit value.

[0063] In the embodiments of this disclosure, the output power of multiple photovoltaic power generation units 110 is limited according to power limiting priority. The lower the photovoltaic voltage, the higher the power limiting priority of the corresponding photovoltaic power generation unit 110. Therefore, the photovoltaic power generation unit 110 with low photovoltaic voltage is given priority for power reduction. In the embodiments of this disclosure, the output power of the photovoltaic power generation units 110 can be reduced sequentially in descending order of power limiting priority until the total output power after limitation does not exceed the total power limit value. In specific implementations, the amount of output power to be reduced can be determined based on the difference between the total output power and the total power limit value. The output power of one or more photovoltaic power generation units 110 with low photovoltaic voltage can be reduced according to the amount of output power to be reduced. For example, if the difference between the total output power and the total power limit value is 2kW, the output power of the two photovoltaic power generation units 110 with the lowest photovoltaic voltage can be reduced, for example, by 1kW each. Alternatively, if the output power of the photovoltaic unit 110 with the lowest voltage is greater than 2kW, only the output power of that photovoltaic unit 110 can be reduced by 2kW.

[0064] In an embodiment of this disclosure, as shown in FIG3, step S202 may include the following steps.

[0065] Step S2021: Select the photovoltaic power generation unit with the highest priority in the power limitation priority as the current target limitation unit.

[0066] The photovoltaic power generation unit with the highest priority in the power limiting priority is the photovoltaic power generation unit that is first subject to output power limiting.

[0067] Step S2022: Obtain the power limit value of the current target limiting unit.

[0068] The current target limiting unit's power limit value is the difference between the total power limit value and the output power of other photovoltaic power generation units. Step S2023: Determine whether the current target limiting unit's power limit value is greater than or equal to zero. If yes, proceed to step S2024, limiting the output power of the current target limiting unit based on this power limit value, and then ending the current power limiting process. If not, proceed to step S2025.

[0069] When the difference between the total power limit and the output power of other photovoltaic (PV) power generation units is greater than or equal to zero, it indicates that the output power of the other PV power generation units is less than the total power limit. Reducing the output power of the current target limiting unit can prevent the total output power from exceeding the total power limit. When the difference between the total power limit and the output power of other PV power generation units is less than zero, it indicates that even if the output power of the current target limiting unit is limited to zero, the total output power still exceeds the total power limit. Therefore, it is necessary to reduce the output power of the other PV power generation units.

[0070] It is understandable that limiting the output power of the current target limiting unit based on this power limit value can be used to control the output power of the current target limiting unit to not exceed the power limit value.

[0071] Step S2025: Limit the output power of the current target limiting unit to zero. Then, select the next highest priority photovoltaic power generation unit as the new current target limiting unit, according to power limiting priority from highest to lowest. Return to step S2022 to obtain the power limiting value of the current target limiting unit.

[0072] When the output power of the current target limiting unit is limited to zero, the output power of the photovoltaic power generation unit is updated to 0 in a subsequent step.

[0073] For example, the photovoltaic (PV) power generation units are listed in descending order of power limiting priority: PV unit A, PV unit B, PV unit C, PV unit D, and PV unit E. First, PV unit A is selected as the current target limiting unit. The difference between the total power limit value and the output power of PV units B, C, D, and E is calculated, and this difference is used as the power limit value for PV unit A. If the current difference is greater than or equal to zero, it indicates that reducing the output power of PV unit A will ensure that the total output power does not exceed the total power limit value. Therefore, based on the current difference (i.e., the power limit value of PV unit A), the output power of PV unit A is limited to ensure that its output power does not exceed the current difference, and the current power limiting ends. In this case, limiting the output power of PV unit A ensures that the total output power does not exceed the total power limit value. If the current difference is less than zero, it indicates that even if the output power of photovoltaic power generation unit A is reduced to zero, the output power of photovoltaic power generation units B, C, D, and E is still greater than the total power limit. In this case, the output power of photovoltaic power generation unit A is limited to 0, and photovoltaic power generation unit B is designated as the new current limiting unit. The difference between the total power limit and the output power of photovoltaic power generation units C, D, and E is calculated to obtain the new current difference. If the new current difference is greater than or equal to zero, it indicates that reducing the output power of photovoltaic power generation unit B will ensure that the total output power does not exceed the total power limit. Therefore, based on the new current difference (i.e., the power limit of photovoltaic power generation unit B), the output power of photovoltaic power generation unit B is limited, ending the current power limiting. In this case, limiting the output power of photovoltaic power generation units A and B ensures that the total output power does not exceed the total power limit. If the new current difference is less than zero, it indicates that even if the output power of photovoltaic power generation unit B decreases to zero, the output power of photovoltaic power generation units C, D, and E is still greater than the total power limit. In this case, the output power of photovoltaic power generation units A and B is limited to 0, and photovoltaic power generation unit C is designated as the new current limiting unit. This process is repeated until the total output power does not exceed the total power limit.

[0074] In some embodiments of this disclosure, the output power of the photovoltaic power generation unit 110 can be limited by restricting the current of the photovoltaic power generation unit 110. An upper limit value (referred to as the target current limit value in this disclosure) of the output current of the photovoltaic power generation unit 110 is calculated and set based on the power limit value of the photovoltaic power generation unit 110, and the output current of the photovoltaic power generation unit 110 is made to be less than the target current limit value.

[0075] In some embodiments, limiting the output power of the current target limiting unit based on its power limit value includes the following steps: the power converter 130 determines the total current limit value of the current target limiting unit based on its power limit value and the photovoltaic voltage, and determines the target current limit value of the current target limiting unit based on the total current limit value. The photovoltaic current of the current target limiting unit is controlled to be less than or equal to the target current limit value.

[0076] For example, the target current limit value of the current target limiting unit is equal to the total current limit value of the current target limiting unit. The power converter 130 controls the photovoltaic current of the current target limiting unit to be less than or equal to its own target current limit value. The current target limiting unit can control its photovoltaic current to be less than or equal to its own target current limit value based on known methods, and this application does not limit it in this way.

[0077] In some implementations, limiting the output power of the current target limiting unit based on its power limit value further includes the following steps: determining the single-channel current limit value of the current target limiting unit based on its single-channel rated power and photovoltaic voltage. In this case, determining the target current limit value of the current target limiting unit based on the total current limit value includes: the power converter 130 determining the smaller of the total current limit value and the single-channel current limit value, and using this smaller value as the target current limit value of the current target limiting unit.

[0078] In some embodiments, the photovoltaic power generation unit 110 has a single-channel rated power, and limited by this single-channel rated power, the photovoltaic power generation unit 110 has a single-channel current limit value. To protect the single-channel photovoltaic power generation unit 110, the power converter 130 can acquire the photovoltaic voltage (real-time output voltage) of the photovoltaic power generation unit 110 and determine the single-channel current limit value of the photovoltaic power generation unit 110 based on the single-channel rated power and the photovoltaic voltage. Specifically, the single-channel current limit value can be the quotient of the single-channel rated power divided by the photovoltaic voltage. In this case, the target current limit value is determined by the smaller of the single-channel current limit value and the total current limit value. The power converter 130 controls the photovoltaic current of the photovoltaic power generation unit 110 to be less than or equal to its own target current limit value.

[0079] In some embodiments, limiting the output power of the current target limiting unit based on the power limiting value of the current target limiting unit further includes the following step: obtaining the maximum current of the current target limiting unit. In this case, determining the target current limiting value of the current target limiting unit based on the total current limiting value includes: the power converter 130 determining the minimum value among the total current limiting value, the single-channel current limiting value, and the maximum current, and using this minimum value as the target current limiting value of the current target limiting unit.

[0080] In some embodiments, the photovoltaic power generation unit 110 has a maximum current, which is based on the hardware overcurrent capability of the photovoltaic power generation unit 110. To protect a single photovoltaic power generation unit 110, a target current limit value is limited to be less than the maximum current of the photovoltaic power generation unit 110. In this case, the target current limit value is determined by the minimum of the single-channel current limit value, the total current limit value, and the maximum current. The power converter 130 controls the photovoltaic current of the current target-limited unit to be less than or equal to its own target current limit value.

[0081] In a typical implementation, the DC-DC converter circuit 112 corresponding to the photovoltaic power generation unit 110 can receive the target current limit value sent by the controller in the power converter 130, calculate the voltage and current values ​​that maximize the output power under the constraint of the target current limit value, generate a PWM (pulse width modulation) signal, control the on and off time of the power switch in its DC-DC converter circuit 112 by changing the duty cycle, and dynamically adjust its equivalent impedance through high-frequency switching action.

[0082] In some embodiments, if the photovoltaic voltage of the photovoltaic power generation unit 110 is greater than the given value of the bus voltage of the power converter 130 or the energy storage unit 120, and the photovoltaic voltage is greater than the DC bus voltage, then the total output power may still exceed the total power limit even after the PWM signal duty cycle is adjusted to 0. In this case, the output power control of the photovoltaic power generation unit 110 based on the target current limit value fails. Referring to the circuit diagram shown in Figure 4, when the PWM signal duty cycle is adjusted to 0, the power switch of the DC-DC converter circuit is turned off, and the photovoltaic power generation unit 110 is connected to the first DC input side of the power converter 130. Since the photovoltaic voltage is greater than the DC bus voltage, even if the PWM signal duty cycle of the switch of the DC-DC converter circuit is 0 and the DC-DC converter circuit is not working, the photovoltaic voltage can still be directly injected into the DC bus and output power to the DC bus. At this time, the DC bus voltage of the power converter 130 is less than or equal to the photovoltaic voltage of the photovoltaic power generation unit.

[0083] In some embodiments of this disclosure, when the photovoltaic power generation system does not include the energy storage unit 120, if the total output power of multiple photovoltaic power generation units 110 exceeds the total power limit, and the photovoltaic voltage of any photovoltaic power generation unit 110 is greater than the DC bus voltage setpoint of the power converter 130, the DC bus voltage setpoint of the power converter 130 is increased until the total output power of the multiple photovoltaic power generation units 110 does not exceed the total power limit. After increasing the DC bus voltage setpoint of the power converter 130, the power converter 130 can maintain the DC bus at this newly set, higher DC bus voltage, which can prevent the power of the photovoltaic power generation units 110 from being directly fed into the DC bus. Controlling the output power of the photovoltaic power generation units 110 based on the target current limit value still works, and the output power of the photovoltaic power generation units 110 is controlled.

[0084] In some embodiments of this disclosure, when the photovoltaic power generation system includes an energy storage unit 120, if the total output power of multiple photovoltaic power generation units 110 exceeds the total power limit, and the photovoltaic voltage of any photovoltaic power generation unit 110 is greater than the DC bus voltage setpoint of the energy storage unit 120 or the power converter 130, the DC bus voltage setpoint of the energy storage unit 120 and the DC bus voltage setpoint of the power converter 130 are simultaneously increased until the total output power of the multiple photovoltaic power generation units 110 does not exceed the total power limit. After simultaneously increasing the DC bus voltage setpoint of the energy storage unit 120 and the DC bus voltage setpoint of the power converter 130, the original power flow between the energy storage unit and the power converter 130 is not changed. At the same time, the DC bus voltage is increased, which can prevent uncontrolled direct input of photovoltaic power into the DC bus, allowing the power converter 130 to still limit the power of the photovoltaic power generation unit 110 through the DC-DC conversion circuit.

[0085] In some implementations, the DC bus voltage setpoints of the energy storage unit 120 and the power converter 130 can be increased synchronously in preset step sizes. For example, if the original DC bus voltage setpoints of the energy storage unit 120 and the power converter 130 are 410V and 380V respectively, and the photovoltaic voltage of a certain photovoltaic power generation unit 110 is 410V, then the DC bus voltage setpoints of the energy storage unit 120 and the power converter 130 can be increased synchronously in 10V steps, successively to 420V, 390V, 430V, 400V, 440V, 410V, etc., until the total output power of the photovoltaic power generation unit 110 is controlled by the current limit, that is, the total output power of multiple photovoltaic power generation units 110 does not exceed the total power limit value.

[0086] In some implementations, the voltage adjustment value can be determined based on the difference between the target current limit value of the photovoltaic power generation unit 110 and the photovoltaic current, and the DC bus voltage setpoint of the energy storage unit 120 and the DC bus voltage setpoint of the power converter 130 can be increased simultaneously based on the voltage adjustment value.

[0087] Specifically, the power converter 130 can determine the current difference value of each of the multiple photovoltaic power generation units 110, where the current difference value of each photovoltaic power generation unit 110 is the difference between its own target current limit value and the photovoltaic current. The power converter 130 determines the minimum value among the current differences of the multiple photovoltaic power generation units, and determines a voltage adjustment value based on the minimum value and a preset automatic control strategy. Based on the voltage adjustment value, the power converter 130 increases the bus voltage setpoint of the energy storage unit 120 and / or the power converter 130.

[0088] In a typical implementation, the power converter 130 increases the bus voltage setpoint of the energy storage unit 120 and the power converter 130 in steps with a voltage adjustment value, and the voltage adjustment value follows the change of the aforementioned current difference. The preset automatic control strategy can indeed be implemented using regulators such as proportional-integral (PI) regulators and proportional-integral-derivative (PI-DE) regulators, and this application does not impose any restrictions on this.

[0089] The technical solution provided in this disclosure determines the power limiting priority of each photovoltaic power generation unit based on its own photovoltaic voltage when the total output power of multiple photovoltaic power generation units exceeds the total power limit. The output power of multiple photovoltaic power generation units is limited according to the power limiting priority. The lower the photovoltaic voltage, the higher the power limiting priority of the corresponding photovoltaic power generation unit. The output power of the photovoltaic power generation unit with the lower photovoltaic voltage is limited first. This can avoid the photovoltaic voltage from rising after the output power of the photovoltaic power generation unit decreases, and avoid the DC bus voltage in the power converter from rising due to the rising photovoltaic voltage, thereby reducing the voltage stress risk of the power converter.

[0090] After output power limiting, if the total power limit value on the DC side increases, output power recovery can be performed to maximize the utilization of light energy. Referring to Figure 5, in addition to steps S201 and S202 in Figure 1, the power control method in this disclosure may further include the following steps in the embodiments.

[0091] Step S203: When the total output power of multiple photovoltaic power generation units is less than the total power limit, determine the power recovery priority of each photovoltaic power generation unit based on the photovoltaic voltage of each photovoltaic power generation unit.

[0092] In embodiments of this disclosure, in the photovoltaic power generation system 100 shown in FIG1, the power converter 130 can monitor the total output power of multiple photovoltaic power generation units 110 and compare the total output power with a total power limit value to determine whether the total output power of the multiple photovoltaic power generation units 110 exceeds the total power limit value. In some embodiments, the power converter 130 can determine the total power limit value based on at least one of the output power limit value, the total rated power of the power converter 130, and the over-temperature load power limit value. As one embodiment, the total power limit value can be the minimum value among the output power limit value, the total rated power of the power converter 130, and the over-temperature load power limit value.

[0093] When the total output power of multiple photovoltaic power generation units 110 is determined to be less than the total power limit, the power converter 130 can acquire the photovoltaic voltage of each of the multiple photovoltaic power generation units 110, sort the multiple photovoltaic power generation units 110 according to the magnitude of the photovoltaic voltage, and then determine the power recovery priority. In the embodiments of this disclosure, the higher the photovoltaic voltage, the higher the power recovery priority of the corresponding photovoltaic power generation unit.

[0094] Step S204: Perform output power restoration on multiple photovoltaic power generation units according to power restoration priority until the total output power reaches the total power limit or all photovoltaic power generation units have performed output power restoration.

[0095] In the embodiments of this disclosure, the output power of multiple photovoltaic power generation units 110 is restored according to power restoration priority. The higher the photovoltaic voltage, the higher the power restoration priority of the corresponding photovoltaic power generation unit 110. Therefore, the photovoltaic power generation unit 110 with high photovoltaic voltage is given priority for power restoration. In the embodiments of this disclosure, the output power of the photovoltaic power generation units 110 can be restored sequentially in descending order of power limit priority until the total output power does not exceed the total power limit value. In specific implementations, the amount of output power to be restored can be determined based on the difference between the total output power and the total power limit value. For example, the output power of one or more photovoltaic power generation units 110 with low photovoltaic voltage can be restored according to the amount of output power to be restored. For example, if the difference between the total output power and the total power limit value is 2kW, the two photovoltaic power generation units 110 with the highest photovoltaic voltage can be restored, for example, 1kW each.

[0096] In an embodiment of this disclosure, as shown in FIG6, step S204 may include the following steps.

[0097] Step S2041: Select the photovoltaic power generation unit with the highest priority in the power restoration priority as the current target restoration unit.

[0098] Step S2042: Obtain the power limit value of the current target recovery unit.

[0099] The power limit of the current target recovery unit is the difference between the total power limit and the output power of other photovoltaic power generation units. If the power limit of the current target recovery unit is greater than its single-channel rated power or if its actual output power is less than or equal to its power limit, then the current target recovery unit can output power according to its single-channel rated power. In this case, the total output power is still less than the total power limit, and power recovery can still be performed on other photovoltaic power generation units.

[0100] Step S2043: Determine whether the power limit value of the current target recovery unit is greater than or equal to the single-channel rated power of the current target recovery unit, or whether the actual output power of the current target recovery unit is less than or equal to the power limit value of the current target recovery unit. If yes, proceed to step S2045: Remove the output power limit on the current target recovery unit, select the next higher priority photovoltaic power generation unit as the new current target recovery unit according to the power recovery priority from high to low, and return to step S2042 to calculate the power limit value of the current target recovery unit. If no, proceed to step S2044: End the current output power recovery.

[0101] In this context, removing the output power limit on the current target recovery unit means not limiting the power output by the power limit value. The current target recovery unit can output power according to the actual photovoltaic power, for example, by operating at the maximum power point or by outputting power according to the single rated power.

[0102] The following examples illustrate the power limiting and power recovery processes of photovoltaic power generation units.

[0103] When the total output power of multiple photovoltaic power generation units exceeds the total power limit, the output power of the multiple photovoltaic power generation units is limited until the total output power does not exceed the total power limit. Specifically, the power limit value of each photovoltaic power generation unit 110 can be obtained according to the total power limit value Ptlimit. The power limit value of each photovoltaic power generation unit is the difference between the total power limit value Ptlimit and the output power of other photovoltaic power generation units. Taking three photovoltaic power generation units 110 as an example, it can be calculated according to the following formulas: Pt_1_max_limit = ((Ptlimit - (Ppv2+Ppv3) * K1)*L1); Pt_2_max_limit = ((Ptlimit - (Ppv1+Ppv3) * K2)*L2); Pt_3_max_limit = ((Ptlimit - (Ppv1+Ppv2) * K1)*L1); K3)*L3); where Vpv1, Vpv2, and Vpv3 ​​are the photovoltaic voltages of the three photovoltaic power generation units 110 respectively; Ppv1, Ppv2, and Ppv3 are the output power of the three photovoltaic power generation units 110 respectively; and Pt_1_max_limit, Pt_2_max_limit, and Pt_3_max_limit are the power limit values ​​of the three photovoltaic power generation units 110 respectively.

[0104] Where Kn = 0,1; Ln = 0,1; Kn represents whether to enable the power limit value of the photovoltaic power generation unit 110, enabling the power limit value means to limit the power of the photovoltaic power generation unit, and Ln represents whether to lock the limit value of the photovoltaic power generation unit 110 to 0, locking it to 0 means to control the output power of the photovoltaic power generation unit 110 to 0.

[0105] The specific logic for total power limiting is as follows: A. Compare the photovoltaic voltage of each path and sort them according to the photovoltaic voltage. The photovoltaic voltage with the smallest voltage is n, the second smallest voltage is n+1, and the largest voltage is n+2; B. Let Kn = 1; Kn+1 = 0, Kn+2 = 0; Ln = 1, Ln+1 = 1, Ln+2 = 1. At this time, calculate the power limit value of the photovoltaic power generation unit with the smallest photovoltaic voltage, that is, Pt_n_max_limit = ((Ptlimit - ( Ppvn+1 + Ppvn+2 )), and no limit is imposed on the other photovoltaic power generation units.

[0106] C. When Pt_n_max_limit is less than or equal to 0, if the total output power Ppv is greater than Ptlimit, then let Kn = 1; Kn+1 = 1; Kn+2 = 0; and simultaneously lock the power of n to 0, that is, let Ln = 0, Ln+1 = 1, Ln+2 = 1; that is, limit the output power of Kn to 0, and further limit Kn+1. At this time, calculate the power limit value of the photovoltaic power generation unit with the second smallest photovoltaic voltage, that is, Pt_n+1_max_limit = ((Ptlimit - (Ppvn + Ppvn+2)), where Ppvn = Pt_n_max_limit = 0, and Ppvn+2 is not limited.

[0107] D. When Pt_n_max_limit and Pt_n+1_max_limit are less than or equal to 0, if the total output power Ppv is greater than Ptlimit, then let Kn = 1; Kn+1 = 1, Kn+2 = 1; and simultaneously lock the power of n+1 to 0, i.e., let Ln = 0, Ln+1 = 0, Ln+2 = 1. That is, limit the output power of Kn and Kn+1 to 0, and further limit Kn+2. At this time, calculate the power limit value of the photovoltaic power generation unit with the third smallest photovoltaic voltage, i.e., Pt_n+2_max_limit = ((Ptlimit - (Ppvn + Ppvn+1)), where Ppvn = Pt_n_max_limit = 0, Ppvn+1 = Pt_n+2_max_limit = 0.

[0108] In this typical implementation, the output power of each photovoltaic (PV) power generation unit is limited by setting a target current limit value. Based on the power limit value and photovoltaic voltage of each PV power generation unit, the total current limit value of the PV power generation unit can be determined, specifically calculated using the following formulas: Ipt_1_max_limit = Pt_1_max_limit / Vpv1; Ipt_2_max_limit = Pt_2_max_limit / Vpv2; Ipt_3_max_limit = Pt_3_max_limit / Vpv3; where Ipt_1_max_limit, Ipt_2_max_limit, and Ipt_3_max_limit are the total current limit values ​​for the three PV power generation units respectively. Further, the target current limit value is determined based on the total current limit value of each PV power generation unit. The photovoltaic current of each PV power generation unit is limited to be less than or equal to its target current limit value.

[0109] When the total output power of multiple photovoltaic power generation units is less than the total power limit, the output power of multiple photovoltaic power generation units is restored until the total output power reaches the total power limit or all photovoltaic power generation units have had their output power restored. In the total power recovery process, the specific logic is as follows: A. Calculate the power limit value of the photovoltaic power generation unit with the largest photovoltaic voltage (i.e., n+2), using the formula: Pt_n+2_max_limit = ((Ptlimit - (Ppvn + Ppvn+1)). If Pt_n+2_max_limit is greater than its single-channel rated power or its single-channel actual output power is less than Pt_n+2_max_limit, then set Kn = 1; Kn+1 = 1; Kn+2 = 0; simultaneously unlock the power of n+2, setting Ln = 0, Ln+1 = 1, Ln+2 = 1. That is, n+2 can output power according to its single-channel rated power or actual output power. If the total output power of multiple photovoltaic power generation units is still less than the total power limit value, further recovery is performed on n+1. Calculate the power limit value of the photovoltaic power generation unit with the second largest photovoltaic voltage (i.e., n+1), using the formula: Pt_n+1_max_limit = ((Ptlimit - (Ppvn + Ppvn+1)). Ppvn+2 )).

[0110] B. If Pt_n+1_max_limit is greater than its single-channel rated power or its single-channel actual output power is less than Pt_n+1_max_limit, then let Kn = 1; Kn+1 = 0; Kn+2 = 0; and simultaneously release the power lock of n+1, that is, let Ln = 1, Ln+1 = 1, Ln+2 = 1. That is, n+1 can output power according to its single-channel rated power or actual output power. If the total output power of multiple photovoltaic power generation units is still less than the total power limit, n is further restored. The power limit value of the photovoltaic power generation unit with the smallest photovoltaic voltage (i.e., n) is calculated using the formula: Pt_n_max_limit = ((Ptlimit - (Ppvn+1 +Ppvn+2)).

[0111] C. If Pt_n_max_limit is greater than its single-channel rated power or the single-channel actual output power is less than Pt_n_max_limit, unlock the power lock of n.

[0112] It should be noted that although the steps of the method in this application are described in a specific order in the embodiments or accompanying drawings (such as flowcharts), this does not require or imply that these steps must be performed in that specific order, or that all the steps shown must be followed to achieve the desired result. Additionally or alternatively, certain steps may be omitted, multiple steps may be combined into one step, and / or one step may be broken down into multiple steps. Without conflicting with logical and technical effects, the execution order of these steps can be adjusted according to actual needs (e.g., interchanged), or multiple steps can be executed concurrently (simultaneously). Therefore, the order of steps in the flowcharts accompanying this application is merely an illustrative example and not a strict limitation on the scope of protection of this application.

[0113] This disclosure also provides a power converter applied to a photovoltaic power generation system, such as the photovoltaic power generation system 100 shown in FIG1. ​​The power converter includes a power conversion circuit and a controller, the controller being used to execute the power control method of this disclosure embodiment. The power converter can be the power converter 130 shown in FIG1.

[0114] In some implementations, the controller may include a core processing unit. The power converter may also include analog input interfaces, digital input / output interfaces, communication interfaces, human-machine interfaces, power modules, chassis, and heat dissipation. The core processing unit runs the operating system, control algorithms, and application software; the core processing unit can be an MCU, MPU, DSP, etc. The core processing unit executes the power control method. The analog input interfaces convert continuous analog signals from sensors into digital signals. Analog signals may include DC bus voltage, input voltages of each photovoltaic circuit, battery voltage, photovoltaic input current, battery current, grid-connected output current, heat sink temperature of key components, ambient temperature, and battery temperature. The digital input / output interfaces control the engagement and disengagement of relays and contactors, enabling grid-connected / off-grid switching and fault tripping. The communication interface enables the exchange of commands and data between the controller and internal subunits and external networks. The human-machine interface provides local operation and status display. The power module provides a stable and isolated power supply for the controller itself. The chassis and heat dissipation provide electromagnetic shielding, protection levels, and heat dissipation to ensure stable operation in harsh industrial environments.

[0115] This disclosure provides a photovoltaic power generation system, comprising: a power converter, which includes a power conversion circuit and a controller, the controller being used to execute the power control method of this disclosure embodiment; and a plurality of photovoltaic power generation units connected to the DC input side of the power converter. In some embodiments, the photovoltaic power generation system may be the photovoltaic power generation system 100 shown in FIG1.

[0116] The above are merely preferred embodiments of this disclosure and are not intended to limit this disclosure in any way. Although this disclosure has been disclosed above with reference to preferred embodiments, it is not intended to limit this disclosure. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the technical solution of this disclosure. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of this disclosure without departing from the content of the technical solution of this disclosure shall still fall within the scope of the technical solution of this disclosure.

Claims

1. A power control method applied to a photovoltaic power generation system, the photovoltaic power generation system comprising a power converter and a plurality of photovoltaic power generation units connected to a first DC input side of the power converter, characterized in that, The power control method includes: when the total output power of the plurality of photovoltaic power generation units exceeds a preset total power limit value, determining the power limit priority of each photovoltaic power generation unit according to the photovoltaic voltage of each of the plurality of photovoltaic power generation units; wherein, the lower the photovoltaic voltage, the higher the power limit priority of the corresponding photovoltaic power generation unit; and limiting the output power of the plurality of photovoltaic power generation units according to the power limit priority until the total output power after limitation does not exceed the total power limit value.

2. The power control method as described in claim 1, characterized in that, The output power of the plurality of photovoltaic power generation units is limited according to the power limiting priority until the total output power after limitation does not exceed the total power limit value. This includes: taking the photovoltaic power generation unit with the highest priority in the power limiting priority as the current target limiting unit; obtaining the power limiting value of the current target limiting unit, wherein the power limiting value of the current target limiting unit is the difference between the total power limit value and the output power of other photovoltaic power generation units; determining whether the power limiting value of the current target limiting unit is greater than or equal to zero; if yes, then limiting the output power of the current target limiting unit based on the power limiting value; if no, then limiting the output power of the current target limiting unit to zero, taking the next higher priority photovoltaic power generation unit as the new current target limiting unit in descending order of the power limiting priority, and returning to the step of obtaining the power limiting value of the current target limiting unit.

3. The power control method as described in claim 1, characterized in that, The power control method further includes: when the total output power of the plurality of photovoltaic power generation units is less than the total power limit, determining the power recovery priority of each photovoltaic power generation unit based on the photovoltaic voltage of each of the plurality of photovoltaic power generation units; wherein, the higher the photovoltaic voltage, the higher the power recovery priority of the corresponding photovoltaic power generation unit; and restoring the output power of the plurality of photovoltaic power generation units according to the power recovery priority until the total output power reaches the total power limit or all photovoltaic power generation units have been restored.

4. The power control method as described in claim 3, characterized in that, The output power of the plurality of photovoltaic power generation units is restored according to the power restoration priority, including: taking the photovoltaic power generation unit with the highest priority in the power restoration priority as the current target restoration unit; obtaining the power limit value of the current target restoration unit, wherein the power limit value of the current target restoration unit is the difference between the total power limit value and the output power of other photovoltaic power generation units; determining whether the power limit value of the current target restoration unit is greater than or equal to the single-channel rated power of the current target restoration unit, or whether the actual output power of the current target restoration unit is less than or equal to the power limit value of the current target restoration unit; if yes, then the output power limit of the current target restoration unit is lifted, and the next higher priority photovoltaic power generation unit is taken as the new current target restoration unit in descending order of the power restoration priority, and the step of obtaining the power limit value of the current target restoration unit is returned; if no, then the output power restoration ends.

5. The power control method as described in claim 2, characterized in that, The step of limiting the output power of the current target limiting unit based on the power limit value includes: determining the total current limit value of the current target limiting unit based on the power limit value and photovoltaic voltage of the current target limiting unit; determining the target current limit value of the current target limiting unit according to the total current limit value, wherein the target current limit value is not greater than the total current limit value; and controlling the photovoltaic current of the current target limiting unit to be less than or equal to the target current limit value.

6. The power control method as described in claim 5, characterized in that, The step of limiting the output power of the current target limiting unit based on the power limit value further includes: determining the single-channel current limit value of the current target limiting unit based on the single-channel rated power and photovoltaic voltage of the current target limiting unit; wherein, determining the target current limit value of the current target limiting unit based on the total current limit value includes: determining the smaller value between the total current limit value and the single-channel current limit value, and using the smaller value as the target current limit value of the current target limiting unit.

7. The power control method as described in claim 6, characterized in that, The step of limiting the output power of the current target limiting unit based on the power limit value further includes: obtaining the maximum current of the current target limiting unit, wherein the maximum current is determined based on the hardware overcurrent capability of the current target limiting unit; wherein, the step of determining the target current limit value of the current target limiting unit according to the total current limit value includes: determining the minimum value among the total current limit value, the single-channel current limit value and the maximum current, and using the minimum value as the target current limit value of the current target limiting unit.

8. The power control method according to any one of claims 1-7, characterized in that, The power control method further includes: determining the total power limit value based on at least one of the acquired output power limit value, the total rated power of the first DC input side, and the over-temperature load limit value, wherein the output power limit value is determined based on the maximum output power of the power converter.

9. The power control method as described in claim 8, characterized in that, The photovoltaic power generation system also includes an energy storage unit, which is connected to the second DC input side of the power converter; the output power limit value is determined based on the sum of the maximum output power of the power converter and the maximum charging power of the energy storage unit.

10. The power control method as described in claim 5, characterized in that, When the total output power of the plurality of photovoltaic power generation units exceeds the total power limit, the power control method further includes: when the photovoltaic voltage of any of the photovoltaic power generation units is greater than the DC bus voltage setpoint of the power converter, increasing the DC bus voltage setpoint of the power converter until the total output power of the plurality of photovoltaic power generation units does not exceed the total power limit.

11. The power control method as described in claim 5, characterized in that, The photovoltaic power generation system further includes an energy storage unit, which is connected to the second DC input side of the power converter. When the total output power of the plurality of photovoltaic power generation units exceeds the total power limit, the power control method further includes: when the photovoltaic voltage of any photovoltaic power generation unit is greater than the DC bus voltage setpoint of the energy storage unit or the power converter, simultaneously increasing the DC bus voltage setpoint of the energy storage unit and the power converter until the total output power of the plurality of photovoltaic power generation units does not exceed the total power limit.

12. The power control method as described in claim 11, characterized in that, The step of simultaneously increasing the DC bus voltage setpoint of the energy storage unit and the power converter includes: determining the current difference of each of the plurality of photovoltaic power generation units, wherein the current difference of the photovoltaic power generation unit is the difference between its own target current limit value and the photovoltaic current; determining the minimum value among the current differences of the plurality of photovoltaic power generation units, and determining a voltage adjustment value based on the minimum value and a preset automatic control strategy; and simultaneously increasing the DC bus voltage setpoint of the energy storage unit and the power converter based on the voltage adjustment value.

13. A power converter, characterized in that, The power converter includes a controller and a power conversion circuit, the controller being electrically connected to the power conversion circuit, and the controller being used to perform the method as described in any one of claims 1 to 12.

14. The power converter as described in claim 13, characterized in that, The power converter is an inverter or an energy storage converter.

15. A photovoltaic power generation system, characterized in that, include: A power converter, wherein the power converter is the power converter according to claim 13 or 14; a plurality of photovoltaic power generation units are respectively connected to the first DC input side of the power converter.

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