Power Management System and Method for String Solar Inverters

Abstract

A system includes a maximum power point tracker (MPPT), an energy storage device, and an inverter. The MPPT is coupled between a first solar panel string and a DC voltage bus, wherein the MPPT includes a first DC / DC converter and is configured to implement an MPPT control scheme on the first DC / DC converter. The energy storage device is coupled between a second solar panel string and the DC voltage bus, wherein the energy storage device includes a second DC / DC converter. The inverter is coupled between the DC voltage bus and the grid, wherein the inverter is configured to operate in multiple modes, including a grid-connected mode and a grid-following mode, and wherein in the grid-connected mode, the second DC / DC converter is configured to regulate the voltage on the DC voltage bus.

Description

Technical Field

[0001] This case relates to a photovoltaic energy conversion system, and more particularly to a power management and control method for a string solar inverter that provides grid-forming (GFM) functionality. Background Technology

[0002] With the continued increase in global renewable energy penetration, power systems face new stability challenges. Traditional power grids rely heavily on synchronous generators, whose rotating mass provides inertia and damping, helping to maintain grid frequency stability. However, inverter-based renewable energy sources, such as photovoltaic systems, typically employ grid-following (GFL) control, where the inverter acts as a current source and synchronizes with the grid via a phase-locked loop (PLL). Due to the limited internal energy storage capacity of GFL inverters and the fact that their control mechanisms are not designed to mimic the behavior of synchronous generators, they cannot establish grid voltage or frequency, nor can they provide effective inertia.

[0003] Recent research has focused on grid-forming (GFM) inverter technology, which enables inverters to act as voltage sources, setting grid voltage and frequency, supporting islanded operation, and providing synthetic inertia and damping. GFM inverters can provide critical stability services, including frequency response and black-start capability. These technologies have been successfully applied to battery storage systems where the inverter's DC side has a significant amount of available energy. However, conventional solar inverters struggle to achieve GFM control because they typically operate each photovoltaic string at its maximum power point (MPP), leaving insufficient power margin to provide inertia.

[0004] Two methods have been proposed to enable solar inverters to be grid-connected: (1) adding a dedicated energy storage device to the DC side of the inverter; and (2) operating the photovoltaic string off its maximum power point to provide a margin when grid support is needed. The first approach increases system cost and complexity, while the second approach requires fine coordination of the DC / DC conversion stage to ensure sufficient backup power without affecting the overall system performance.

[0005] In conventional inverter architectures, the DC bus is regulated by the inverter, and each DC / DC converter independently executes a maximum power point tracking (MPPT) algorithm. However, in grid-mode (GFM) architecture, the power flowing into and out of the DC bus is controlled by separate, unrelated control objectives, which can lead to DC bus instability. Without direct coordination, unwanted voltage fluctuations may occur on the DC bus, limiting the feasibility of GFM in photovoltaic energy conversion systems. Therefore, an improved string solar inverter power management architecture is needed to achieve stable grid control without the addition of external energy storage. This project aims to meet this requirement. Summary of the Invention

[0006] The embodiments disclosed in this application typically solve or circumvent these and other problems, and generally offer technical advantages. This application provides a power management and control method for string solar inverters.

[0007] According to an embodiment of the present invention, a system is provided comprising a maximum power point tracker, an energy storage device, and an inverter. The maximum power point tracker is coupled between a first solar panel string and a DC voltage bus, wherein the maximum power point tracker includes a first DC / DC converter and is configured to implement a maximum power point tracking control scheme on the first DC / DC converter. The energy storage device is coupled between a second solar panel string and the DC voltage bus, wherein the energy storage device includes a second DC / DC converter. The inverter is coupled between the DC voltage bus and the grid, wherein the inverter is configured to operate in multiple modes, including a grid-connected mode and a grid-following mode, and wherein in the grid-connected mode, the second DC / DC converter is configured to regulate the voltage on the DC voltage bus.

[0008] According to an embodiment of the present invention, a method is provided, comprising configuring a maximum power point tracker to implement a maximum power point tracking control scheme on a first DC / DC converter, wherein the first DC / DC converter is coupled between a first solar panel string and the DC voltage bus of a string inverter power system; configuring the inverter to operate in multiple modes including grid-connected mode and grid-following mode, wherein the inverter is coupled between the DC voltage bus and the grid; and configuring a second DC / DC converter within an energy storage unit to regulate the voltage on the DC voltage bus when the inverter is configured to operate in grid-connected mode, and configuring the inverter to regulate the voltage on the DC voltage bus when the inverter is configured to operate in grid-following mode, wherein the second DC / DC converter is coupled between a second solar panel string and the DC voltage bus.

[0009] According to an embodiment of the present invention, a system is provided comprising N DC / DC converters, an inverter, and control circuitry. The N DC / DC converters are respectively coupled between N solar panel strings and a DC voltage bus. The inverter is coupled between the DC voltage bus and the power grid, and is configured to operate in multiple modes, including a grid-connected mode and a grid-following mode. The control circuitry is configured to assign one of the N DC / DC converters as a maximum power point tracker (MPPT) and operate the assigned DC / DC converter according to a MPT control scheme; and to use the remaining N DC / DC converters as multiple energy storage converters, wherein in the grid-connected mode, the multiple energy storage converters are configured to regulate the voltage on the DC voltage bus.

[0010] The foregoing outlines the features and technical advantages of this application to better understand the detailed description thereof below. Other features and advantages of this application, which constitute the subject matter of the claims, will be described below. Those skilled in the art will understand that the concept and specific implementation of this application can be readily used as the basis for modifying or designing other structures or processes to achieve the same purpose. Those skilled in the art will also recognize that such equivalent structures do not depart from the spirit and scope of this application as set forth in the appended claims. Attached Figure Description

[0011] To gain a more comprehensive understanding of this case and its advantages, the following description will be provided in conjunction with the accompanying drawings:

[0012] Figure 1 A block diagram of a string inverter power system according to various embodiments of the present invention is shown.

[0013] Figure 2 Various embodiments according to this case are shown. Figure 1 The circuit diagram shown is a first embodiment of the string inverter power system.

[0014] Figure 3 Various embodiments according to this case are shown. Figure 2 The diagram shows the control block diagram of the string inverter power system operating in grid mode.

[0015] Figure 4 Various embodiments according to this case are shown. Figure 2 The diagram shows the control block diagram of the string inverter power system operating in grid-connected mode.

[0016] Figure 5 Various embodiments according to this case are shown. Figure 1 The circuit diagram shown is a second embodiment of the string inverter power system.

[0017] Figure 6 Various embodiments according to this case are shown. Figure 5 The diagram shows the control block diagram of the string inverter power system.

[0018] Figure 7 This is a flowchart illustrating a method for initiating according to various embodiments of this case. Figure 1 The control method for the string inverter power system is shown.

[0019] Figure 8 This is a flowchart illustrating various embodiments of the present invention for operation. Figure 1 The control method for the string inverter power system is shown.

[0020] Unless otherwise stated, the corresponding numbers and symbols in the drawings generally refer to the corresponding parts. These drawings are drawn to clearly illustrate relevant aspects of various embodiments and are not necessarily drawn to scale.

[0021] List of reference numerals

[0022] 10: First DC / DC converter group

[0023] 11: First solar panel string

[0024] 101, 103: Maximum Power Point Tracker

[0025] 102, 104: Energy storage device

[0026] 112: First solar panel string

[0027] 114: First DC / DC converter

[0028] 122: Second solar panel string

[0029] 124: Second DC / DC converter

[0030] 132: Third solar panel string

[0031] 134: Third DC / DC converter

[0032] 142: Fourth solar panel string

[0033] 144: Fourth DC / DC converter

[0034] 154, 30: Inverter

[0035] 20: Second DC / DC converter group

[0036] 21: Second solar panel string

[0037] 310, 320, 330: Multiplication Unit

[0038] 311, 321, 331: MPPT units

[0039] 312, 322, 332, 342, 352: Voltage controllers

[0040] 313: MPPT PWM Generator

[0041] 314, 324, 334, 344, 354: Current controllers

[0042] 315: Double-pole single-throw switch

[0043] 323: PWM Generator

[0044] 345: Average or maximum unit

[0045] 350: Power Manager

[0046] 351: Network configuration unit

[0047] 353: Inverter PWM Generator

[0048] 702, 704, 706, 708, 710, 712, 714, 802, 804, 806: Steps

[0049] C1, Cf1, Cf2: Capacitors

[0050] IPv: Current

[0051] I ABCINV I PVPR I PVTRACKER : Measuring current

[0052] Lf, Lg: Inductors

[0053] P INVREF Power setpoint

[0054] P MPP Maximum power

[0055] S1: Circuit breaker

[0056] V ABCINV Output voltage

[0057] Vdc: DC voltage bus

[0058] V DCREF : Reservation Reference

[0059] Vpvm, Vpvp: Voltage

[0060] V PVTRACKER : Measuring voltage

[0061] VPVREF V PVREF1 V PVREF2 V PVREF3 Reference panel voltage

[0062] GRID: power grid Detailed Implementation

[0063] Some typical embodiments that embody the features and advantages of this invention will be described in detail in the following description. It should be understood that this invention can have various variations in different forms, all of which do not depart from the scope of this invention, and the descriptions and drawings therein are for illustrative purposes only and not for limiting this invention.

[0064] This invention will be described in the specific context of providing a power management and control method for string solar inverters with grid-connected GFM functionality, using some embodiments. However, the content of this invention can also be applied to various power conversion systems. Various embodiments will be described in detail below with reference to the accompanying drawings.

[0065] Figure 1 A block diagram of a string inverter power system according to various embodiments of the present invention is shown. The string inverter power system includes multiple solar panel strings divided into two functional groups, namely a first solar panel string group 11 and a second solar panel string group 21. The string inverter power system further includes N DC / DC converters divided into two functional groups. The first DC / DC converter group 10 includes M DC / DC converters, each DC / DC converter in the first DC / DC converter group 10 being connected to a solar panel string in the corresponding first solar panel string group 11. The second DC / DC converter group 20 includes the remaining (NM) DC / DC converters, each DC / DC converter being connected to a solar panel string in the corresponding second solar panel string group 21.

[0066] In the illustrated embodiment, the first DC / DC converter group 10 is coupled between the first solar panel string group 11 and the DC voltage bus Vdc, and the second DC / DC converter group 20 is coupled between the second solar panel string group 21 and the DC voltage bus Vdc. The inverter 30 is further coupled between the DC voltage bus Vdc and the external power grid. The inverter 30 converts the voltage on the DC voltage bus to an AC output and operates in multiple modes, including grid-connected mode and grid-linked mode, as will be described in detail below. The DC / DC converters of the first and second DC / DC converter groups 10 and 20 jointly manage the extracted power from the solar panel strings and the voltage regulation on the DC voltage bus.

[0067] exist Figure 1During the startup procedure of the string inverter power system shown, all DC / DC converters in the first DC / DC converter group 10 and the second DC / DC converter group 20 initially operate in DC bus regulation mode to establish the voltage on the DC voltage bus at a predetermined rated value. A pre-charge operation is initially performed to charge the DC bus capacitors to a safe level, followed by a soft-start procedure in which the voltage on the DC voltage bus is gradually increased to its rated operating voltage. After the DC voltage bus voltage stabilizes, the inverter 30 enters a pre-synchronization mode, in which the voltage on the output filter capacitor of the inverter 30 is synchronized with the grid voltage. The inverter 30 then shuts off its AC side circuit breaker to enter grid-connected mode. Once the inverter 30 is operating stably, one of the N DC / DC converters (typically one of the DC / DC converters in the first DC / DC converter group 10) is assigned as a maximum power point tracker to begin maximum power point tracking ramp-up, while the remaining DC / DC converters continue to regulate the voltage on the DC voltage bus as energy storage. There is no available reserve power in the maximum power point tracking ramp-up range.

[0068] After completing the startup procedure, inverter 30 operates in either grid-connected or grid-following mode based on the relationship between the grid demand power and the maximum available power of the DC / DC converter. Specifically, when the output power demand of the string inverter power system is less than or equal to the available power that the string inverter power system can provide under the maximum power point tracking control scheme, inverter 30 is configured to operate in grid-connected mode. On the other hand, when the output power demand of the string inverter power system is greater than the available power that the string inverter power system can provide under the maximum power point tracking control scheme, inverter 30 is configured to operate in grid-following mode.

[0069] In grid-connected mode, inverter 30 acts as a voltage source, maintaining the grid voltage and frequency. The DC / DC converters in the second DC / DC converter group 20 regulate the voltage on the DC voltage bus, simultaneously ensuring that their corresponding solar panel strings operate at a voltage higher than their maximum power point voltage to maintain reserve power. Reserve power (ΔP) represents the additional active power that the string inverter power system can provide relative to its current operating point. Specifically, reserve power (ΔP) represents the additional active power that can be provided by reducing the operating voltage of the solar panel strings in the second solar panel string group 21 towards their respective maximum power points.

[0070] Operationally, when the grid experiences frequency reduction or requires additional active power, inverter 30 releases the required additional power by releasing its reserve power. During this process, the DC / DC converters in the second DC / DC converter group 20 reduce the operating voltage of their associated solar panel strings towards their respective maximum power point voltages to extract the additional power. If the grid power demand exceeds the maximum deliverable power from the DC / DC converters of DC / DC converter groups 10 and 20 (defined by the maximum power point tracking limit), inverter 30 transitions from grid-connected mode to grid-following mode. In this mode, inverter 30 acts as a current source synchronized with the grid voltage and regulates the voltage on the DC voltage bus, while simultaneously delivering the maximum available power from the solar panel strings. Therefore, coordinated grid-connected / grid-following operation and controlled utilization of reserve power enable inverter 30 to provide inertial response, frequency support, and stable power delivery under varying grid conditions.

[0071] Figure 2 Various embodiments according to this case are shown. Figure 1 The circuit diagram shown is a first embodiment of a string inverter power system. Figure 2 As shown, the string inverter power system includes a maximum power point tracker 101, an energy storage device 102, a capacitor C1, an inverter 154, a first filter composed of an inductor Lf and a capacitor Cf1, a circuit breaker S1, and a second filter composed of a capacitor Cf2 and an inductor Lg.

[0072] Maximum power point tracker 101 includes a first DC / DC converter 114 and associated control circuitry (not shown). The first DC / DC converter 114 is coupled between a first solar panel string 112 and a DC voltage bus Vdc. The first solar panel string 112 provides power to the first DC / DC converter 114, which is configured to operate with a maximum power point tracking control scheme. Energy storage device 102 includes a second DC / DC converter 124 and associated control circuitry (not shown). The second DC / DC converter 124 is coupled between a second solar panel string 122 and a DC voltage bus Vdc. The second solar panel string 122 provides power to the second DC / DC converter 124, and the second DC / DC converter 124 is configured to regulate the voltage on the DC voltage bus.

[0073] In practice, string inverter power systems can include multiple solar panel strings and DC / DC converters. Depending on application and design requirements, string inverter power systems may include additional maximum power point trackers (MPPTs), each containing a DC / DC converter, and may also include additional energy storage devices constructed in the same manner. To more clearly illustrate the innovation of this case, Figure 2The embodiment is one with only a single maximum power point tracker and a single energy storage device. Those skilled in the art will recognize that the operating principles described herein are equally applicable to systems with any suitable number of maximum power point trackers and energy storage devices.

[0074] like Figure 2 As shown, capacitor C1 is connected between the inputs of inverter 154. The first filter, consisting of inductor Lf and capacitor Cf1, is connected to the output of inverter 154. The second filter, consisting of capacitor Cf2 and inductor Lg, is connected to the output of the first filter via circuit breaker S1. Figure 2 As shown, circuit breaker S1 is connected between the common electrode of inductor Lf and capacitor Cf1 and the common electrode of capacitor Cf2 and inductor Lg. The output of the second filter is connected to the power grid.

[0075] In some embodiments, Figure 2 The first and second DC / DC converters 114 and 124 shown are implemented as buck-boost converters; in other embodiments, Figure 2 The first and second DC / DC converters 114 and 124 shown are implemented as boost converters, respectively. However, other suitable converter topologies may be used depending on system requirements, including, but not limited to, boost converters, interleaved boost converters, or stacked dual boost converters. Similarly, inverter 154 may be implemented as a single-phase inverter or a three-phase inverter, or any other inverter architecture suitable for the intended grid connection and power level.

[0076] Operationally, the first DC / DC converter 114 is controlled to implement maximum power point tracking, while the second DC / DC converter 124 operates as an energy storage device that regulates the voltage on the DC voltage bus and provides reserve power when needed. When the inverter 154 is configured to operate in grid-connected mode, the second DC / DC converter 124 is configured to control the output voltage of the second solar panel string 122 to be greater than the maximum power point voltage of the first solar panel string 112. In the inertial response operation of the grid-connected mode of the string inverter power system, the second DC / DC converter 124 configures the second solar panel string 122 to provide additional power by reducing the output voltage of the second solar panel string 122 until the output voltage of the second solar panel string 122 reaches its maximum power point voltage.

[0077] Figure 3 Various embodiments according to this case are shown. Figure 2The diagram shows the control block diagram of a string inverter power system operating in grid-connected mode. The control circuit includes an MPPT unit 311, a power manager 350, an MPPT PWM generator 313, an energy storage PWM generator 323, and an inverter PWM generator 353. The MPPT PWM generator 313 includes a voltage controller 312 and a current controller 314. The energy storage PWM generator 323 includes a voltage controller 322 and a current controller 324. The inverter PWM generator 353 includes a grid-connected mode unit 351, a voltage controller 352, and a current controller 354.

[0078] Please see Figure 2 The MPPT PWM generator 313 is designed to generate PWM signals for controlling the operation of the first DC / DC converter 114. TRACKER The energy storage PWM generator 323 is designed to generate PWM signals for controlling the operation of the second DC / DC converter 124. RESERVOIR The inverter PWM generator 353 is designed to generate PWM signals for controlling the inverter 154. INVERTER .

[0079] like Figure 3 The MPPT unit 311 shown is configured to receive the measurement current I of the first solar panel string 112. PVTRACKER and the first solar panel string 112 at the output measured voltage V PVTRACKER MPPT unit 311 uses two measurements to evaluate the instantaneous operating point on the IV and PV curves of the first solar panel string 112. Based on these measurements, well-known MPPT algorithms (such as the perturbation observation algorithm and the incremental electric directive algorithm) calculate the reference panel voltage V at the maximum power point. PVREF .

[0080] When inverter 154 operates in grid mode, and the first DC / DC converter 114 and its associated first solar panel string 112 are configured as a maximum power point tracker, the bipolar single-throw switch 315 switches from low to high. Reference panel voltage V PVREF It is input to the MPPT PWM generator 313.

[0081] The MPPT PWM generator 313 comprises two loops: an external voltage loop and an internal current loop. Voltage controller 312 represents the external voltage loop of the MPPT PWM generator 313. Current controller 314 represents the internal current loop of the MPPT PWM generator 313. The external voltage loop and internal current loop are well-known in the art and will not be described further here.

[0082] In operation, the reference panel voltage VPVREF It is in the voltage controller 312 that the measured voltage V PVTRACKER A comparison is made to determine the current reference transmitted to the current controller 314. The current reference is compared with the measured current I in the current controller 314. PVTRACKER The comparison determines the PWM signal used to control the operation of the first DC / DC converter 114. TRACKER .

[0083] The energy storage PWM generator 323 includes two loops: an external voltage loop and an internal current loop. Voltage controller 322 represents the external voltage loop of the energy storage PWM generator 323. Current controller 324 represents the internal current loop of the energy storage PWM generator 323. The external voltage loop and internal current loop are well known in the art and will not be described further here.

[0084] like Figure 3 As shown, the predetermined reference V DCREF It is transmitted to the energy storage PWM generator 323. In some embodiments, a predetermined reference V is used. DCREF This is a reference value for the voltage on the DC voltage bus, generated by the DC voltage bus controller (not shown). Predetermined reference V DCREF This is determined by the desired AC output voltage of inverter 154. Predetermined reference V DCREF It is greater than ×Vo and additional design margins can be selected to accommodate modulation index limitations. Vo is the root mean square value of the AC output voltage.

[0085] In terms of operation, refer to V. DCREF The voltage controller 322 compares the current with Vdc to determine the current reference transmitted to the current controller 324. The current reference is the measured current I of the second solar panel string 122 in the current controller 324. PVPR The comparison is used to determine the PWM signal (PWM signal) for controlling the operation of the second DC / DC converter 124. RESERVOIR .

[0086] like Figure 3 As shown, the measured voltage V PVTRACKER and measuring current I PVTRACKER The maximum power P transmitted to the multiplication unit 310 from the maximum power point tracker 101 is... MPP It is generated in multiplication unit 310. Power manager 350 is architecture designed to receive maximum power P. MPP Depending on the operating mode, the power manager 350 generates different power setpoints for the inverter 154. Specifically, when the inverter 154 is configured to operate in grid-connected mode, the power setpoint P... INVREF It is equal to N×PMP Subtract the predetermined reserve power ΔP. On the other hand, when the inverter 154 is configured to operate in grid-connected mode, the power setpoint P... INVREF It is equal to the power demanded by the power grid or limited by the total maximum available power N×P MPP .

[0087] The inverter PWM generator 353 includes a grid mode unit 351, a voltage controller 352, and a current controller 354. The inverter PWM generator 353 is configured to receive power setpoint P. INVREF And generate a PWM signal (PWM signal) for controlling the operation of inverter 154. INVERTER .

[0088] The network configuration unit 351 implements a network control scheme, which includes virtual inertia and damping parameters, respectively... J and D This indicates that, in this configuration, J A virtual inertial component, representing the inertial behavior of a simulated synchronous generator, is used to start inverter 154 to limit the rate of frequency change and provide stability support during grid disturbances. Parameters D This represents the damping coefficient that produces the damping torque effect, which suppresses oscillations and enhances system stability after faults or abrupt changes in operating conditions. In typical implementations, such as droop control or virtual synchronous generator (VSG) control, the grid-mode unit 351 uses parameters in its own power loop. J and D The grid mode unit 351 simulates the dynamic response of a synchronous generator and generates corresponding reference voltage and frequency signals for the inverter 154. By establishing these reference signals, the grid mode unit 351 enables the inverter 154 to synthesize grid-supporting characteristics, maintain stable voltage and frequency, and contribute to the overall grid resilience of renewable energy-rich power systems.

[0089] The inverter PWM generator 353 comprises two loops: an external voltage loop and an internal current loop. Voltage controller 352 represents the external voltage loop of the inverter PWM generator 353. Current controller 354 represents the internal current loop of the inverter PWM generator 353. The external voltage loop and internal current loop are well-known in the art and will not be described further here.

[0090] In operation, the reference voltage signal generated by the network mode unit 351 is compared with V in the voltage controller 352. ABCINV A comparison is made to determine the current reference transmitted to the current controller 354. In some embodiments, V ABCINVThis is the output voltage of inverter 154. The current reference generated by voltage controller 352 is the measured current I of inverter 154 in current controller 354. ABCINV The comparison determines the PWM signal that controls the operation of inverter 154. INVERTER In some embodiments, I ABCINV This is the output current flowing through inverter 154.

[0091] Figure 4 Various embodiments according to this case are shown. Figure 2 The diagram shows a control block diagram of a string inverter power system operating in grid-following mode. Control block diagrams of conventional GFL control schemes are well-known in the art. However, in this case, this control block diagram is used as an operating mode for the string inverter power system. In this grid-following mode, inverter 154 acts as a current source synchronized with the grid voltage via a phase-locked loop (PLL) and injects active and reactive currents according to a specified setpoint. Operationally, when the available reserve power ΔP is insufficient to support grid-following operation, inverter 154 transitions from grid-following mode to the well-known grid-following operation mode, thereby allowing inverter 154 to regulate the voltage on the DC voltage bus and track the grid voltage waveform. In this configuration, inverter 154 no longer establishes its own voltage or frequency. Instead, inverter 154 tracks the grid voltage and delivers the maximum power that all solar panel strings can collectively provide.

[0092] like Figure 4 As shown, the grid-connected control scheme regulates the voltage on the DC voltage bus by adjusting the current injection of the inverter, ensuring that the inverter 154 can safely deliver the maximum available solar power generation when grid support cannot be maintained, while maintaining synchronization with the grid.

[0093] Figure 5 Various embodiments according to this case are shown. Figure 1 The circuit diagram shown is a second embodiment of the string inverter power system. Figure 5 The string inverter power system in the middle is related to Figure 2 Similar to [previous case], except that it includes M maximum power point trackers and (NM) energy storage devices. M and N are both positive integers. N is greater than M. To more clearly illustrate the innovation of this case, Figure 5 The embodiment is one of three of M maximum power point trackers and one of (NM) energy storage devices. Those skilled in the art will recognize that the operating principles described herein are equally applicable to systems with any suitable number of maximum power point trackers and energy storage devices.

[0094] like Figure 5As shown, the maximum power point tracker 101 includes a first DC / DC converter 114 and associated control circuitry (not shown). The first DC / DC converter 114 is coupled between the first solar panel string 112 and the DC voltage bus Vdc. The first solar panel string 112 provides power to the first DC / DC converter 114, which is configured to operate with a maximum power point tracking control scheme.

[0095] The maximum power point tracker 102 includes a second DC / DC converter 124 and associated control circuitry (not shown). The second DC / DC converter 124 is coupled between the second solar panel string 122 and the DC voltage bus Vdc. The second solar panel string 122 provides power to the second DC / DC converter 124, and the second DC / DC converter 124 is configured to operate with a maximum power point tracking control scheme.

[0096] The maximum power point tracker 103 includes a third DC / DC converter 134 and associated control circuitry (not shown). The third DC / DC converter 134 is coupled between the third solar panel string 132 and the DC voltage bus Vdc. The third solar panel string 132 provides power to the third DC / DC converter 134, and the third DC / DC converter 134 is configured to operate with a maximum power point tracking control scheme.

[0097] Energy storage 104 includes a fourth DC / DC converter 144 and associated control circuitry (not shown). The fourth DC / DC converter 144 is coupled between the fourth solar panel string 142 and the DC voltage bus Vdc. The fourth solar panel string 142 provides power to the fourth DC / DC converter 144, and the fourth DC / DC converter 144 is configured to regulate the voltage Vdc on the DC voltage bus.

[0098] Figure 6 Various embodiments according to this case are shown. Figure 5 The diagram shows the control block diagram of the string inverter power system. Figure 6 The control implementation shown is with Figure 3 The configuration shown is similar, except that it includes two additional MPPT units. Figure 6 In one embodiment, the MPPT unit 311 generates a reference panel voltage V for the first solar panel string 112. PVREF1 The PWM signal used for the first DC / DC converter 114 is based on the reference panel voltage V. PVREF1 The MPPT unit 321 generates a reference panel voltage V for the second solar panel string 122. PVREF2 The PWM signal used for the second DC / DC converter 124 is based on the reference panel voltage V. PVREF2The MPPT unit 331 generates a reference panel voltage V for the third solar panel string 132. PVREF3 The PWM signal used for the third DC / DC converter 134 is based on the reference panel voltage V. PVREF3 Therefore, three MPPT units 311, 321, and 331 are provided through three maximum power point trackers 101, 102, and 103 in the string inverter power system. Each MPPT PWM generator includes a corresponding voltage control loop and a current control loop, and the operation of these loops is similar to that described above for... Figure 3 The PWM control loops described above are identical.

[0099] In some embodiments, when multiple MPPT units are as follows Figure 6 As shown, string inverter power systems can dynamically rotate the role of the maximum power point tracker among these DC / DC converters. For example, the controller can select M DC / DC converters from multiple converters coupled to multiple solar panel strings, and run a maximum power point tracking control scheme on one or more of these selected DC / DC converters, making them the maximum power point trackers. The assignment of the active maximum power point tracker among the M converters can be periodically rotated according to changes in solar radiation, shading modes, or other corresponding solar panel string operating conditions. This rotating assignment method allows string inverter power systems to more accurately identify the maximum available power of different strings over time and enhances overall power estimation and reserve power allocation under non-uniform environmental conditions.

[0100] like Figure 6 As shown, the power output obtained from the three MPPT units is supplied to the average or maximum unit 345, which, depending on design requirements, generates the average or maximum value of the output from the three MPPT units. The resulting value P... MPP This is then supplied to the power manager 350, which determines the inverter's power setpoint P. INVREF And the inverter PWM generator is similar to Figure 3 It runs in the following way. For example... Figure 6 As shown, this multi-tracker configuration is better able to estimate available solar energy when using multiple solar panel strings under different environmental conditions.

[0101] Figure 7 This is a flowchart illustrating various embodiments of the present invention for starting up. Figure 1 The control method for the string inverter power system is shown. Figure 7 The flowchart shown is merely an example and should not unduly limit the scope of the claims. Those skilled in the art will be able to identify many variations, alternatives, and modifications. For example, Figure 7The steps shown can be added, deleted, replaced, rearranged, and repeated.

[0102] In step 702, the startup procedure of the string inverter power system begins with pre-charging the capacitor coupled between the DC voltage bus and ground.

[0103] In step 704, during the soft-start procedure, the capacitor is further charged to bring the voltage on the DC voltage bus to a predetermined voltage.

[0104] In step 706, the multiple DC / DC converters in the string inverter power system are configured to regulate the voltage on the DC voltage bus. The inverter then begins its startup sequence by entering a pre-synchronization mode, in which the voltage across the inverter's output filter capacitor is synchronized with the grid voltage. After synchronization is achieved, the inverter shuts off the circuit breaker to enter grid-connected mode.

[0105] In step 708, the output power of the string inverter power system is gradually increased by implementing a maximum power point tracking control scheme on the first DC / DC converter, while maintaining the voltage on the DC voltage bus of the remaining DC / DC converters.

[0106] In step 710, the initial power output setpoint of the inverter is provided based on the output power of the first DC / DC converter.

[0107] In step 712, it is determined whether the output power demand is less than or equal to the available power under the maximum power point tracking control scheme. If the condition is met, proceed to step 714; otherwise, proceed to step 716.

[0108] In step 714, the inverter is configured to operate in grid-connected mode.

[0109] In step 716, the inverter is configured to operate in grid-connected mode.

[0110] Under normal operating conditions, the inverter is configured to operate in grid-connected mode. When the grid suddenly loses its generating capacity or experiences a significant load increase, the grid frequency may drop rapidly. To cope with such load transients, the synthetic inertia function of grid-connected mode control enables the inverter to release additional active power by driving the operating voltage of the energy storage solar panels from a higher voltage (e.g., their open-circuit voltage) to their respective maximum power point voltage. As the system frequency begins to stabilize, the inverter's droop control function adjusts the active and reactive power setpoints to continue supporting grid recovery.

[0111] The droop control method is a distributed strategy that simulates the natural behavior of a synchronous generator by introducing an inverse linear relationship between frequency and active power (i.e., the frequency decreases slightly when the inverter outputs more active power) and an inverse linear relationship between voltage and reactive power (i.e., the voltage decreases slightly when the inverter outputs more reactive power). In this embodiment, the frequency decreases slightly when the inverter outputs active power, and the terminal voltage decreases slightly when it outputs reactive power, allowing the inverter to self-regulate and stably share power with other distributed resources without communication. Once the grid reaches a new steady-state frequency, the inverter's output power and the operating voltage of the solar storage panels will stabilize at the corresponding steady-state values ​​determined by the droop control settings.

[0112] While grid-connected mode can maintain stable operation under typical disturbances, in some cases, the available reserve power is insufficient to sustain grid control. In such situations, if the grid frequency deviates from an acceptable range, or weather changes reduce available power to the point that the reserve power is insufficient to maintain grid functionality, the inverter will transition from grid-connected mode to grid-following mode. In grid-following mode, the inverter regulates the DC voltage and tracks the grid voltage waveform, delivering the maximum available power from the solar panel strings according to a known grid-following control scheme.

[0113] Figure 8 This is a flowchart illustrating various embodiments of the present invention for operation. Figure 1 The control method for the string inverter power system is shown. Figure 8 The flowchart shown is merely an example and should not unduly limit the scope of the claims. Those skilled in the art will be able to identify many variations, alternatives, and modifications. For example, Figure 8 The steps shown can be added, deleted, replaced, rearranged, and repeated.

[0114] In step 802, the maximum power point tracker is configured to implement a maximum power point tracking control scheme on the first DC / DC converter, wherein the first DC / DC converter is coupled between the first solar panel string and the DC voltage bus of the string inverter power system.

[0115] In step 804, the inverter is configured to operate between multiple modes, including grid-connected mode and grid-linked mode, wherein the inverter is coupled between the DC voltage bus and the grid.

[0116] In step 806, when the inverter is configured to operate in grid-connected mode, the second DC / DC converter in the energy storage is configured to regulate the voltage on the DC voltage bus, and when the inverter is configured to operate in grid-connected mode, the inverter is configured to regulate the voltage on the DC voltage bus, wherein the second DC / DC converter is coupled between the second solar panel string and the DC voltage bus.

[0117] The method further includes, in the startup procedure of the string inverter power system, pre-charging the capacitor coupled between the DC voltage bus and ground. In the soft-start procedure, the capacitor is charged to bring the voltage on the DC voltage bus to a predetermined voltage. The DC / DC converters in the string inverter power system are configured to regulate the voltage on the DC voltage bus. By implementing a maximum power point tracking control scheme on the first DC / DC converter, the output power of the string inverter power system is gradually increased while maintaining the remaining DC / DC converters to continue regulating the voltage on the DC voltage bus. The initial power output setpoint of the inverter is provided based on the output power of the first DC / DC converter.

[0118] The method further includes, after completing the startup procedure, configuring the inverter architecture to enter grid-connected mode and providing the inverter's operating power output setpoint based on the output power and reserve power of the first DC / DC converter.

[0119] The method further includes configuring the inverter to operate in grid-connected mode when the output power demand of the string inverter power system is less than or equal to the available power that the string inverter power system can provide under the maximum power point tracking control scheme, and configuring the inverter to operate in grid-following mode when the output power demand of the string inverter power system is greater than the available power that the string inverter power system can provide under the maximum power point tracking control scheme.

[0120] The method further includes, in grid configuration mode, configuring the inverter as a voltage source that maintains the voltage and frequency of the AC grid by releasing additional power to the AC grid, and in grid-connected mode, configuring the inverter as a current source that injects power to the AC grid.

[0121] The method further includes selecting M DC / DC converters from among a plurality of DC / DC converters autocoupled between the corresponding plurality of solar panel strings and the DC voltage bus, and implementing a maximum power point tracking control scheme on at least one of the M DC / DC converters to configure at least one of the M DC / DC converters as a maximum power point tracker, and periodically rotating the role of the maximum power point tracker among the M DC / DC converters according to changes in solar radiation or the operating conditions of the plurality of solar panel strings.

[0122] The method is further incorporated into the grid configuration, which architectures the inverter to provide inertia, damping, and primary frequency response.

[0123] The method further includes, in the grid configuration mode, controlling the second DC / DC converter to set the output voltage of the second solar panel string to be greater than the maximum power point voltage of the first solar panel string, and in the inertial response operation of the grid configuration mode of the string inverter power system, controlling the second DC / DC converter to reduce the output voltage of the second solar panel string until the output voltage of the second solar panel string reaches the maximum power point voltage of the second solar panel string, so as to configure the second solar panel string to provide additional power.

[0124] This case may be modified in various ways by those skilled in the art, but all of them shall not deviate from the protection sought by the appended claims.

[0125] Furthermore, the scope of this application is not intended to be limited to the specific embodiments of the methods, machines, manufacturing processes, material compositions, apparatuses, methods, and steps described in the specification. Those skilled in the art will understand from the content of this application that, according to this application, existing or future methods, machines, manufacturing processes, material compositions, apparatuses, methods, or steps capable of performing substantially the same function or achieving substantially the same results as the corresponding embodiments described herein can be used. Therefore, the appended claims are intended to cover such methods, machines, manufacturing processes, material compositions, apparatuses, methods, or steps.

Claims

1. A system comprising: A maximum power point tracker is coupled between a first solar panel string and a DC voltage bus, wherein the maximum power point tracker includes a first DC / DC converter and is configured to implement a maximum power point tracking control scheme on the first DC / DC converter; An energy storage device coupled between a second solar panel string and the DC voltage bus, wherein the energy storage device includes a second DC / DC converter; and An inverter is coupled between a DC voltage bus and a power grid, wherein the inverter is configured to operate between multiple modes including a grid-connected mode and a grid-following mode, and wherein in the grid-connected mode, the second DC / DC converter is configured to regulate a voltage on the DC voltage bus.

2. The system as claimed in claim 1, wherein: In this grid configuration, the inverter is designed to provide inertia, damping, and primary frequency response.

3. The system of claim 1, further comprising: Multiple maximum power point DC / DC converters, wherein each maximum power point DC / DC converter is located in a corresponding maximum power point tracker coupled between at least one solar panel string and the DC voltage bus; and Multiple energy storage DC / DC converters, wherein each of the energy storage DC / DC converters is coupled between at least one solar panel string and the DC voltage bus.

4. The system as claimed in claim 1, wherein: The inverter is configured to operate in this grid configuration when the system's output power demand is less than or equal to the available power that the system can provide under the maximum power point tracking control scheme; and When the output power demand of the system is greater than the available power that the system can provide under the maximum power point tracking control scheme, the inverter is configured to operate in grid-connected mode.

5. The system of claim 4, wherein: In this grid configuration, the inverter is structured as a voltage source that maintains a voltage and a frequency for a power grid by releasing additional power to it; and In this grid-connected mode, the inverter is configured as a current source that injects power into the grid.

6. The system of claim 1, wherein: When the inverter is configured to operate in grid-connected mode, the inverter is configured to regulate the voltage on the DC voltage bus.

7. The system of claim 1, wherein: In this grid configuration, the second DC / DC converter is configured to control the output voltage of the second solar panel string to be greater than the maximum power point voltage of the first solar panel string. In an inertial response operation in this grid configuration of the system, the second DC / DC converter reduces the output voltage of the second solar panel string until the output voltage of the second solar panel string reaches the maximum power point voltage of the second solar panel string, thereby configuring the second solar panel string to provide additional power.

8. The system of claim 1, wherein: The first DC / DC converter is a first buck-boost converter; and The second DC / DC converter is a second buck-boost converter.

9. A method comprising: A maximum power point tracker is configured to implement a maximum power point tracking control scheme on a first DC / DC converter, wherein the first DC / DC converter is coupled between a first solar panel string and a DC voltage bus of a set of string inverter power systems; An inverter is configured to operate in multiple modes, including a grid-connected mode and a grid-following mode, wherein the inverter is coupled between the DC voltage bus and a power grid; and When the inverter is configured to operate in the grid-connected mode, a second DC / DC converter within an energy storage device is configured to regulate a voltage on the DC voltage bus. When the inverter is configured to operate in the grid-connected mode, the inverter is configured to regulate the voltage on the DC voltage bus. The second DC / DC converter is coupled between a second solar panel string and the DC voltage bus.

10. The method of claim 9, further comprising: In a startup procedure of the string inverter power system, a capacitor is pre-charged between the DC voltage bus and a ground. In a soft-start procedure, the capacitor is charged so that the voltage on the DC voltage bus reaches a predetermined voltage. The multiple DC / DC converters in the string inverter power system are configured to regulate the voltage on the DC voltage bus; By implementing the maximum power point tracking (MPPT) scheme on the first DC / DC converter, the output power of the string inverter power system is gradually increased, while maintaining the remaining DC / DC converters to continue regulating the voltage on the DC voltage bus; and An initial power output setpoint for the inverter is provided based on the output power of the first DC / DC converter.

11. The method of claim 10, further comprising: After completing the startup procedure, configure the inverter architecture to enter this grid configuration mode; and The inverter's operating power output setpoint is provided based on the output power of the first DC / DC converter and a reserve power.

12. The method of claim 9, further comprising: When the output power demand of the string inverter power system is less than or equal to the available power that the string inverter power system can provide under the maximum power point tracking control scheme, the inverter architecture is configured to operate in this grid configuration mode; and When the output power demand of the string inverter power system is greater than the available power that the string inverter power system can provide under the maximum power point tracking control scheme, the inverter architecture is configured to operate in the grid-connected mode.

13. The method of claim 9, further comprising: In this grid configuration, the inverter is structured as a voltage source that maintains a voltage and a frequency of the AC grid by releasing additional power to it; and In this grid-connected mode, the inverter is configured as a current source that injects power into the AC grid.

14. The method of claim 9, further comprising: Among the multiple DC / DC converters that are autocoupled between the corresponding multiple solar panel strings and the DC voltage bus, M DC / DC converters are selected. By implementing the maximum power point tracking control scheme on at least one of the M DC / DC converters, at least one of the M DC / DC converters is configured as a maximum power point tracker; and The role of the maximum power point tracker is periodically rotated among the M DC / DC converters based on changes in solar radiation or the operating conditions of the multiple solar panel strings.

15. The method of claim 9, further comprising: In this network configuration, the inverter is designed to provide inertia, damping, and primary frequency response.

16. The method of claim 15, further comprising: In this grid configuration, the second DC / DC converter is controlled to set an output voltage of the second solar panel string to be greater than a maximum power point voltage of the first solar panel string; and In an inertial response operation of the grid configuration mode of the string inverter power system, the second DC / DC converter is controlled to provide additional power by reducing the output voltage of the second solar panel string until the output voltage of the second solar panel string reaches the maximum power point voltage of the second solar panel string.

17. A system comprising: N DC / DC converters are respectively coupled between N solar panel strings and a DC voltage bus; An inverter, coupled between the DC voltage bus and a power grid, is configured to operate in multiple modes, including a grid-connected mode and a grid-following mode; and A control circuit, with the following architecture: Assign one of the N DC / DC converters as a maximum power point tracker, and operate the assigned DC / DC converter according to a maximum power point tracking control scheme; and The remaining DC / DC converters among the N DC / DC converters are configured as multiple energy storage converters, wherein in this network configuration, the multiple energy storage converters are structured to regulate a voltage on the DC voltage bus.

18. The system of claim 17, wherein: The control circuit is further structured to periodically rotate the assigned maximum power point tracker among the N DC / DC converters based on changes in solar radiation or the operating conditions of the multiple solar panel strings.

19. The system of claim 18, wherein: The control circuit is further structured to assign M of the DC / DC converters as multiple maximum power point trackers by implementing multiple maximum power point tracking control schemes, and to use the remaining DC / DC converters as multiple energy storage converters, where M is greater than 1 and M is less than N.

20. The system of claim 17, wherein: During a progressive increase cycle in which the assigned maximum power point tracker increases the output power in the maximum power point tracking control scheme, the remaining DC / DC converter does not provide reserve power. as well as After the gradual increase cycle is completed, the multiple energy storage converters adjust the DC voltage bus to the grid configuration mode based on a reserve power that can be obtained from the corresponding multiple solar panel strings.

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