Grid-connected inverter control method and device

Abstract

This invention discloses a grid-connected inverter control method and apparatus. The method includes: acquiring a first parameter characterizing a grid fault state and a second parameter characterizing an inverter operating state; based on the first parameter, determining whether to control the inverter to switch to a first modulation algorithm with lower ripple current; if not, based on the second parameter, determining whether a preset threshold condition for modulation mode switching is met; if met, controlling the inverter to switch to either a second modulation algorithm with lower switching losses or a first modulation algorithm with lower ripple current. This invention establishes a hierarchical judgment logic based on the first parameter characterizing a grid fault state and the second parameter characterizing an inverter operating state, dynamically deciding and switching between the first modulation algorithm with lower ripple current and the second modulation algorithm with lower switching losses. This maximizes the high efficiency advantage of the second modulation algorithm while ensuring bus midpoint balance, thus balancing the economy and efficiency of system operation.

Description

Technical Field

[0001] This invention relates to the field of power electronic conversion technology, and in particular to a grid-connected inverter control method and device. Background Technology

[0002] Currently, in photovoltaic grid-connected inverter systems, discontinuous pulse width modulation (DPWM) is commonly used to improve the grid-connected output efficiency of the inverter. DPWM reduces switching losses by decreasing the number of switching operations, thus effectively improving the grid-connected output efficiency. However, in three-level topology inverter applications, DPWM can induce significant bus capacitor ripple current and, under certain reactive power output conditions, exacerbate the DC bus midpoint potential imbalance, thereby worsening the bus midpoint balance.

[0003] In existing technologies, to address the aforementioned negative impacts of DPWM waveform generation, additional hardware configuration for the bus capacitor is typically required, such as using capacitors with larger capacitance values ​​or stronger ripple current tolerance. However, this approach significantly increases the hardware cost and size of the inverter, failing to balance system economy with waveform generation efficiency optimization. Summary of the Invention

[0004] This invention provides a grid-connected inverter control method and apparatus to solve the technical problem in the prior art where additional bus capacitor hardware configuration is added to suppress the negative impact of DPWM waveform generation, resulting in increased hardware cost and size of the inverter, and failing to balance the optimization of system economy and waveform generation efficiency.

[0005] To address the aforementioned technical problems, firstly, a grid-connected inverter control method is provided, comprising: Obtain a first parameter used to characterize the grid fault state and a second parameter used to characterize the inverter operating state; Based on the first parameter, determine whether to control the inverter to switch to a first modulation algorithm with smaller ripple current; If not, based on the second parameter, determine whether the preset threshold condition for modulation mode switching is met. The preset threshold condition includes a preset exit threshold and an entry threshold. When the preset entry threshold or exit threshold is met, control the inverter to switch to the second modulation algorithm with lower switching losses or the first modulation algorithm with lower ripple current, respectively.

[0006] Secondly, a grid-connected inverter control device is provided, comprising: The parameter acquisition module is used to acquire a first parameter characterizing the grid fault state and a second parameter characterizing the inverter operating state. The decision control module is used to determine, based on the first parameter, whether to control the inverter to switch to the first modulation algorithm with lower ripple current; if not, based on the second parameter, whether the preset threshold condition for modulation mode switching is met, the preset threshold condition includes a preset exit threshold and an entry threshold; when the preset entry threshold or exit threshold is met, the inverter is controlled to switch to the second modulation algorithm with lower switching loss or the first modulation algorithm with lower ripple current, respectively. The drive output module is used to output a modulation signal corresponding to the first modulation algorithm or the second modulation algorithm according to the control of the decision control module, so as to drive the switching transistor of the inverter to work.

[0007] In the scheme implemented by the above-mentioned grid-connected inverter control method and device, a first parameter used to characterize the grid fault state is used to determine whether to control the inverter to switch to a first modulation algorithm with lower ripple current. If not, a second parameter characterizing the inverter's operating state is used to determine whether a preset threshold condition for modulation mode switching is met. If met, the inverter is controlled to switch to a second modulation algorithm with lower switching losses or a first modulation algorithm with lower ripple current. It can be seen that the present invention establishes hierarchical judgment logic based on the first parameter characterizing the grid fault state and the second parameter characterizing the inverter's operating state. Under grid fault conditions, the first modulation algorithm is preferentially controlled to operate, utilizing its lower ripple current. The system features include: ensuring small voltage deviations between positive and negative buses and balanced bus midpoints during fault ride-through, thus improving the success rate of fault ride-through; in non-fault conditions, further comprehensive judgment is made based on the second parameter. When the preset threshold condition for modulation mode switching is met, the system can switch to the second modulation algorithm with lower switching losses to reduce switching losses and improve the grid-connected output efficiency of the inverter, or switch to the first modulation algorithm to ensure bus midpoint balance. In other words, this invention can maximize the high efficiency advantage of the second modulation algorithm while ensuring bus midpoint balance through software algorithm. Compared with the traditional solution of adding additional bus capacitor hardware configuration, this reduces the overall cost of the inverter and takes into account the economy and efficiency of system operation. Attached Figure Description

[0008] Figure 1 This is a schematic diagram illustrating an application of the grid-connected inverter control method in one embodiment of the present invention.

[0009] Figure 2 This is a flowchart illustrating a grid-connected inverter control method in one embodiment of the present invention.

[0010] Figure 3 yes Figure 2 The diagram shows a flow chart of S10 in the grid-connected inverter control method.

[0011] Figure 4 yes Figure 2 Another flowchart of S10 in the grid-connected inverter control method shown.

[0012] Figure 5 yes Figure 2 The diagram shows the specific flow chart of S20 in the grid-connected inverter control method.

[0013] Figure 6 yes Figure 2 The flowchart of S30 in the grid-connected inverter control method is shown.

[0014] Figure 7 This is a schematic diagram of the structure of the grid-connected inverter control device provided in an embodiment of the present invention. Detailed Implementation

[0015] To better understand the technical content of this invention, the technical solution of this invention will be further introduced and explained below with reference to the schematic diagram, but it is not limited thereto.

[0016] The grid-connected inverter control method provided in this invention can be applied to inverters with multi-level topologies, which may include, but are not limited to, three-level NPC topologies, three-level ANPC topologies, or three-level T-type topologies. Figure 1 As shown, taking a photovoltaic grid-connected inverter as an example, the output terminal of the photovoltaic array is connected to the DC bus terminal of the inverter, and the AC output terminal of the inverter is directly connected to the public power grid in a three-phase three-wire configuration. When the control method of this invention is working, it uses software algorithms to monitor in real time the first parameter characterizing the grid fault state and the second parameter characterizing the inverter's operating state. Based on the first and second parameters, a hierarchical judgment logic is established to dynamically decide and switch between a first modulation algorithm with lower ripple current and a second modulation algorithm with lower switching losses. This maximizes the high efficiency of the second modulation algorithm while ensuring the balance of the bus midpoint, without increasing hardware costs, reducing the overall cost of the inverter, and balancing the economy and efficiency of system operation. The following section will combine... Figure 2 The specific workflow of the grid-connected inverter control method provided by this invention will be described in detail.

[0017] Please see Figure 2 As shown, Figure 2 This is a flowchart illustrating a grid-connected inverter control method provided in an embodiment of the present invention. In the embodiment shown in the figures, the grid-connected inverter control method includes the following steps: S10. Obtain the first parameter used to characterize the grid fault state and the second parameter used to characterize the inverter operating state.

[0018] In this invention, the inverter can be a photovoltaic grid-connected inverter, a wind power inverter, or an energy storage inverter, etc.

[0019] In this embodiment, the first parameter may include the grid voltage, while the second parameter may include at least one of the following: grid-connected active current, grid-connected reactive current, modulation index, and DC bus voltage deviation.

[0020] If the second parameter includes modulation, such as Figure 3 As shown, obtaining the second parameter used to characterize the inverter's operating state in step S10 may specifically include the following steps S11a-S13a: S11a. Obtain the effective values ​​of the three-phase line voltages and select the minimum value as the minimum effective value of the line voltage.

[0021] In this step, the instantaneous value of the inverter's DC bus voltage is collected. And the instantaneous voltage value between any two phase lines connected to the power grid. Specifically, the effective voltage values ​​of phase lines AB, BC, and CA can be calculated based on the instantaneous voltage values ​​of phase lines AB, BC, and CA, respectively, using the line voltage sampling method. , , Finally, according to the formula The smallest effective voltage value among the three effective voltage values ​​is selected as the minimum effective line voltage value. .

[0022] S12a. Calculate the minimum line voltage peak value based on the minimum line voltage RMS value.

[0023] In this step, the formula can be used. Minimum line voltage effective value Convert to minimum line voltage peak .

[0024] S13a. Calculate the ratio of the minimum line voltage peak value to the instantaneous value of the DC bus voltage to obtain the modulation index.

[0025] In this step, according to the formula The modulation index M is calculated.

[0026] In this embodiment, the minimum line voltage peak value is selected for modulation index calculation. This avoids repeated switching of the modulation algorithm near the switching threshold due to modulation index fluctuations when the three-phase grid voltage is unbalanced during actual grid connection, thus achieving a jitter-proofing effect. It is understood that in some other embodiments, arbitrary single-phase or average phase voltage can also be used to calculate the modulation index, which can also achieve the switching control of the inverter modulation algorithm.

[0027] If the second parameter includes DC bus voltage deviation, such as Figure 4As shown, the step S10 of obtaining the second parameter used to characterize the inverter's operating state may further include the following steps S11b-S12b: S11b: Obtain the instantaneous values ​​of the DC positive bus voltage and the DC negative bus voltage.

[0028] S12b. Calculate the difference between the instantaneous value of the DC positive bus voltage and the instantaneous value of the DC negative bus voltage to obtain the DC bus voltage deviation.

[0029] For steps S11b-S12b above, the DC positive bus voltage of the inverter is collected. and DC negative bus voltage According to the formula The DC bus voltage deviation was calculated. .

[0030] Furthermore, if the second parameter also includes grid-connected output active current and grid-connected output reactive current, the instantaneous current values ​​of phases A, B, and C in the inverter can be collected. The current quantities in the three-phase stationary coordinate system are transformed to the two-phase stationary αβ coordinate system using Clark transformation to obtain the α-axis and β-axis current components. Then, the current quantities in the two-phase stationary αβ coordinate system are transformed to the dq rotating coordinate system, which rotates synchronously with the grid voltage vector, using Park transformation to obtain the d-axis and q-axis current components. The grid voltage phase angle θ required for the Park transformation is obtained by performing a phase-locked loop operation on the three-phase grid voltage. Finally, the d-axis current component is used as the grid-connected output active current value. The ratio of the q-axis current component to the rated current is used as the grid-connected output reactive current. .

[0031] S20. Based on the first parameter, determine whether to control the inverter to switch to the first modulation algorithm with smaller ripple current; if not, proceed to step S30.

[0032] Preferably, in this step, the fault state includes a low-voltage ride-through fault state and a high-voltage ride-through fault state. For example... Figure 5 As shown, step S20 specifically includes the following steps S21-S22: S21. Determine whether the grid voltage is lower than the low voltage ride-through threshold or higher than the high voltage ride-through threshold. If yes, proceed to step S22; otherwise, proceed to step S30.

[0033] In this embodiment, the grid voltage refers to the voltage at the grid connection point, and the low voltage ride-through threshold can be set to 0.9U, and the high voltage ride-through threshold can be set to 1.1U, where U is the rated voltage of the inverter.

[0034] In this step, the grid connection point voltage is compared with the low voltage ride-through threshold or the high voltage ride-through threshold to detect whether the grid connection point voltage is lower than the low voltage ride-through threshold or higher than the high voltage ride-through threshold, thereby determining whether the inverter is currently in a low voltage ride-through fault state or a high voltage ride-through fault state.

[0035] S22. When the grid voltage is lower than the low voltage ride-through threshold or higher than the high voltage ride-through threshold, the inverter is determined to have entered a fault state, and the inverter is controlled to switch to the first modulation algorithm with a smaller ripple current.

[0036] In this embodiment, when the grid voltage is lower than the low voltage ride-through threshold, the low voltage ride-through flag can be set to 1, indicating that the inverter is in a low voltage ride-through fault state; while when the grid voltage is higher than the high voltage ride-through threshold, the high voltage ride-through flag can be set to 1, indicating that the inverter is in a high voltage ride-through fault state.

[0037] Preferably, the first modulation algorithm can be the SVPWM algorithm. When using the SVPWM algorithm, the switching losses of the inverter are relatively high, while the ripple current of the electrolytic capacitor is relatively small. Understandably, in some other embodiments, the first modulation algorithm may also include the SPWM (Sinusoidal Pulse Width Modulation) algorithm, which has a smaller ripple current.

[0038] In this step, when the low voltage ride-through flag or the high voltage ride-through flag is set to 1, the inverter is controlled to switch to run the SVPWM algorithm to ensure that the voltage deviation between the positive and negative buses is small and the bus midpoint is balanced during high and low voltage ride-through faults to ensure successful ride-through.

[0039] S30. Based on the second parameter, determine whether the preset threshold condition for modulation mode switching is met. If it is met, control the inverter to switch to the second modulation algorithm with lower switching loss or the first modulation algorithm with lower ripple current.

[0040] In this embodiment, the second parameters include the grid-connected output active current, the grid-connected output reactive current, the modulation index, and the DC bus voltage deviation. Preferably, the second modulation algorithm can be a DPWM algorithm. When using the DPWM algorithm, the inverter's switching losses are lower, while the electrolytic capacitor ripple current is larger. Understandably, in some other embodiments, the modulation algorithm may also include SHEPWM (Selected Harmonic Elimination Pulse Width Modulation) algorithm, which has lower switching losses.

[0041] In this step, the second parameter characterizing the inverter's operating state is combined with a preset threshold condition to determine whether to switch to the target modulation algorithm. The target modulation algorithm includes a first modulation algorithm and a second modulation algorithm.

[0042] In this embodiment, the preset threshold condition may include preset exit thresholds and preset entry thresholds. Specifically, as shown below... Figure 6 As shown, step S30 specifically includes the following steps S31-S33: S31. Determine whether at least one of the second parameters meets its preset exit threshold and continues to the set exit delay time; or, determine whether all parameters in the second parameters meet their preset entry threshold and continue to the preset entry delay time.

[0043] In this step, it is detected whether at least one of the second parameters meets its preset exit threshold, and if it does, it is detected whether the duration reaches its set exit delay time (e.g., 10ms). If it does, an exit flag is generated and the exit flag can be set to 1; or, it is detected whether all parameters in the second parameter meet their preset entry threshold, and if it does, it is detected whether the duration reaches the set entry delay time (e.g., 2S). If it does, an entry flag can be generated, or the exit flag can be set to 0.

[0044] Specifically, the exit flag and / or the entry flag can be generated through an independent timing mechanism. The timer increments when the corresponding condition is met and decrements when it is not met. The corresponding flag takes effect when the timer reaches a preset threshold. In this embodiment, the entry and exit timers are counted separately, incrementing when the condition is met and decrementing when it is not met. The exit timer is reset to zero when the entry delay time expires, and the entry timer is reset to zero when the exit delay time expires. For example, if any one of the second parameters meets the corresponding set exit threshold, the delay counter increments and decrements until the delay counter reaches the exit delay time, at which point the exit flag is set to 1 and the delay counter is reset to 0. If all four items in the second parameter meet the corresponding set entry threshold, the delay counter increments and decrements until the delay counter reaches the entry delay time, at which point the exit flag is set to 0 and the delay counter is reset to 0.

[0045] S32. When at least one of the second parameters meets its preset exit threshold and continues for its set exit delay time, control the inverter to switch to the first modulation algorithm with smaller ripple current.

[0046] In this embodiment, both the exit threshold and the entry threshold are set for the second modulation algorithm. Preferably, the grid-connected output active current... Grid-connected reactive current Regulation M and bus voltage deviation The corresponding exit threshold setting is shown in the following formula: ;in, Indicates the rated current.

[0047] In this step, when at least one of the second parameters meets its preset exit threshold and continues for its set exit delay, an SVPWM waveform mode command for controlling the switching of the SVPWM algorithm can be output.

[0048] S33. When all parameters in the second parameter meet their preset entry threshold and the set entry delay time is continuously applied, the inverter is controlled to switch to the second modulation algorithm with lower switching losses.

[0049] In this embodiment, the preset entry threshold and the preset exit threshold are preferably set to be non-continuous intervals. In this embodiment, the grid-connected output active current... Grid-connected reactive current Regulation M and bus voltage deviation The corresponding entry threshold setting is shown in the following formula: ;in, Indicates the rated current.

[0050] In this step, when all parameters in the second parameter meet their preset entry threshold and the continuously set entry delay time, a DPWM waveform mode command for controlling the switching of the DPWM algorithm can be output.

[0051] Preferably, in this embodiment, the entry delay time is greater than the exit delay time, so as to ensure that the high-efficiency modulation mode is entered only when the operating conditions are stable and good, and exits quickly when the operating conditions deteriorate slightly.

[0052] The aforementioned preset entry threshold and preset exit threshold are non-continuous intervals, forming a dead zone between the corresponding parameters. Furthermore, the grid-connected inverter control method may also include: when a parameter in the second parameter is between the preset exit threshold and the preset entry threshold, maintaining the currently running modulation algorithm. Based on this design, within the dead zone, the exit flag remains in its current state and does not activate, thereby avoiding frequent switching at threshold boundaries and achieving a de-jitter effect.

[0053] Understandably, in some other embodiments, it may also be possible to determine whether at least one of the second parameters meets its preset exit threshold, so as to switch to running the SVPWM algorithm when at least one of the parameters meets its preset exit threshold; or, it may be possible to determine whether all the parameters in the second parameter meet their preset entry threshold, so as to switch to running the DPWM algorithm when they are met.

[0054] As can be seen, the grid-connected inverter control method provided in the above embodiments is applied to the inverter. First, it can detect whether the grid voltage is lower than the low voltage ride-through threshold or higher than the high voltage ride-through threshold to determine whether it is a low voltage ride-through fault state or a high voltage ride-through fault state. If so, the SVPWM algorithm is switched to run, utilizing its characteristic of small ripple current to ensure small positive and negative bus voltage deviation and bus midpoint balance during fault ride-through, thereby improving the fault ride-through success rate. If not, that is, in a non-fault ride-through state, the active current value, reactive current value, bus voltage deviation value, and modulation index are monitored in real time. After any one of the above four parameters meets the corresponding set exit threshold, the delay timer increments automatically. When the detection... When the timer reaches the preset exit delay time, the exit flag is set to 1, and the SVPWM algorithm is switched to ensure the balance of the bus midpoint. At the same time, the delay timer is reset to zero. If the values ​​of the above four parameters meet the corresponding set entry thresholds, the delay timer increments. When the timer detects that it has reached the preset entry delay time, the exit flag is set to 0, and the DPWM algorithm is switched to reduce switching losses and improve the grid-connected output efficiency of the inverter. At the same time, the delay timer is reset to zero. This dynamic cyclic adjustment, compared with the control strategy that uses the fixed DPWM algorithm, can maximize the high efficiency advantage of the second modulation algorithm while ensuring the balance of the bus midpoint.

[0055] For example, if the inverter is a grid-connected photovoltaic inverter with a three-level NPC topology, the initial modulation algorithm during grid connection defaults to the DPWM algorithm. If a drop in the three-phase grid voltage to the low-voltage ride-through threshold is detected, a low-voltage ride-through fault is determined, the low-voltage ride-through flag is set to 1, and the SVPWM algorithm is switched to switch the waveform generation mode to SVPWM mode. Subsequently, the grid voltage recovers to the rated grid voltage, the low-voltage ride-through flag is set to 0, and at this time, if the active current... for reactive current for The modulation index M is 0.58, and the bus voltage deviation is... The voltage is 50V. Based on the exit threshold formula set above, the active current is... If the corresponding exit threshold is met, and the detection persists for 10ms, the exit flag is set to 1, and the SVPWM waveform transmission mode command is output, thus maintaining the SVPWM waveform transmission mode. As sunlight intensifies, the input power of the photovoltaic array increases, allowing the inverter to increase its output power and active current. Output to At this point, the bus voltage decreases due to the increased output power, the modulation index rises to 0.65, and the grid voltage is at its rated voltage. No reactive power output is needed to support the grid, and the reactive current drops to 0. The bus voltage deviation is 10V. Based on the aforementioned entry threshold, the active current at this point... reactive current Modulation system M bus voltage deviation If all four parameter values ​​meet their corresponding entry thresholds, the exit flag is set to 0 after 2 seconds of continuous detection. At this time, the DPWM waveform mode command is output to switch the DPWM algorithm to the DPWM waveform mode.

[0056] As can be seen, in the above-described scheme, the embodiments of the present invention establish hierarchical judgment logic based on a first parameter characterizing the grid fault state and a second parameter characterizing the inverter operating state. Under grid fault conditions, the inverter is preferentially controlled to run the first modulation algorithm, utilizing its low ripple current characteristic to ensure small voltage deviations between the positive and negative buses and balanced bus midpoints during fault ride-through, thereby improving the fault ride-through success rate. Under non-fault conditions, a comprehensive judgment is further performed based on the second parameter. When the preset threshold condition for modulation mode switching is met, the system can switch to the second modulation algorithm with lower switching losses to reduce switching losses and improve the inverter's grid-connected output efficiency, or switch back to the first modulation algorithm to ensure bus midpoint balance. Compared to traditional schemes that require additional bus capacitor hardware configuration, the present invention maximizes the high efficiency advantage of the second modulation algorithm while ensuring bus midpoint balance without increasing any hardware costs. Furthermore, this invention also creates a dead zone by setting entry and exit thresholds for discontinuous intervals, effectively avoiding frequent switching jitter at the threshold boundaries; it also sets asymmetrical entry and exit delay times to ensure that the high-efficiency modulation mode is only entered when the operating conditions are stable and good, and exits quickly when the operating conditions deteriorate slightly, thus balancing the stability and efficiency of the inverter system operation, while significantly reducing the overall cost of the inverter.

[0057] It should be understood that the above method embodiments are described as a series of actions for the sake of simplicity. However, those skilled in the art should know that the present invention is not limited by the described order of actions. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0058] Reference Figure 7 , Figure 7 A block diagram of the grid-connected inverter control device 300 provided in an embodiment of the present invention. Figure. Figure 7As shown, the grid-connected inverter control device 300 includes a parameter acquisition module 301, a decision control module 302, and a drive output module 303. Detailed descriptions of each functional module are as follows: The parameter acquisition module 301 is used to acquire a first parameter for characterizing the grid fault state and a second parameter for characterizing the inverter operating state. The decision control module 302 includes a switching judgment unit 3021 and a decision unit 3022. The switching judgment unit 3021 is used to determine, based on the first parameter, whether to control the inverter to switch to a first modulation algorithm with lower ripple current; if not, based on the second parameter, whether the preset threshold condition for modulation mode switching is met; the decision unit 3022 is used to control the inverter to switch to a first modulation algorithm with lower ripple current, and is also used to control the inverter to switch to a second modulation algorithm with lower switching loss or a first modulation algorithm with lower ripple current when the second parameter meets the preset threshold condition for modulation mode switching. The drive output module 303 is used to output a modulation signal corresponding to the first modulation algorithm or the second modulation algorithm according to the control of the decision control module 302, so as to drive the switching transistor of the inverter to work.

[0059] In some embodiments, the fault state includes a low-voltage ride-through fault state and a high-voltage ride-through fault state, wherein the first parameter includes the grid voltage; and wherein, The switching judgment unit 3021 is specifically used to determine whether the grid voltage is lower than the low voltage ride-through threshold or higher than the high voltage ride-through threshold; when the grid voltage is lower than the low voltage ride-through threshold or higher than the high voltage ride-through threshold, the inverter is determined to enter a fault state. The decision unit 3022 is specifically used to control the inverter to switch to a first modulation algorithm with smaller ripple current when it is determined that the inverter has entered a fault state.

[0060] In one embodiment, the second parameter includes at least one of grid-connected output active current, grid-connected output reactive current, modulation index, and DC bus voltage deviation.

[0061] In one embodiment, the preset threshold conditions include preset exit thresholds and entry thresholds; wherein, the switching judgment unit 3021 is further specifically used to determine whether at least one of the second parameters is... It satisfies its preset exit threshold; or, it determines whether all parameters in the second parameter satisfy its preset entry threshold. The decision unit 3022 is further configured to, when at least one of the second parameters satisfies its preset condition... When the exit threshold is reached, the inverter is controlled to switch to a first modulation algorithm with lower ripple current; when all parameters in the second parameter meet their preset entry thresholds, the inverter is controlled to switch to a second modulation algorithm with lower switching losses. Preferably, the switching judgment unit 3021 can output an SVPWM transmission mode command when it determines that at least one of the second parameters meets its preset exit threshold; and output a DPWM transmission mode command when all parameters in the second parameter meet their preset entry thresholds; the decision unit 3022 decides and calculates the modulation signal corresponding to the transmission mode based on the transmission mode command. The signal is output to the drive output module 303 so that the drive output module 303 outputs the modulation signal corresponding to SVPWM / DPWM, thereby driving the inverter's switching transistor to work and completing the modulation waveform switching.

[0062] In one embodiment, the switching determination unit 3021 is further configured to detect whether the duration for which at least one of the second parameters satisfies its preset exit threshold reaches a set exit delay time; or, to detect whether the duration for which all parameters in the second parameters satisfy their preset entry threshold reaches a set entry delay time. The decision unit 3022 is further configured to switch to run the first modulation algorithm when at least one of the second parameters meets its preset exit threshold and is continuously set for an exit delay time; or, to switch to run the second modulation algorithm when all the parameters in the second parameters meet their preset entry threshold and are continuously set for an entry delay time.

[0063] In one embodiment, the preset exit threshold and the preset entry threshold are non-contiguous intervals, and the decision unit 3022 is further configured to: When the parameter in the second parameter is between the preset exit threshold and the preset entry threshold, the currently running modulation algorithm is maintained.

[0064] In one embodiment, the second parameter includes modulation index, and the parameter acquisition module 301 is specifically used for: Obtain the effective values ​​of the three-phase line voltages, and select the minimum value as the minimum effective value of the line voltage. Calculate the minimum line voltage peak value based on the minimum line voltage RMS value; The modulation index is obtained by calculating the ratio of the minimum line voltage peak value to the instantaneous value of the DC bus voltage.

[0065] In one embodiment, the second parameter includes the DC bus voltage deviation, and the parameter acquisition module 301 is further specifically used for: Obtain the instantaneous values ​​of the DC positive bus voltage and the DC negative bus voltage; The difference between the instantaneous values ​​of the DC positive bus voltage and the DC negative bus voltage is calculated to obtain the DC bus voltage deviation.

[0066] In one embodiment, the first modulation algorithm is the SVPWM algorithm, and the second modulation algorithm is the DPWM algorithm.

[0067] This invention provides a grid-connected inverter control device 300. It establishes hierarchical judgment logic using a first parameter characterizing the grid fault state and a second parameter characterizing the inverter's operating state. Under grid fault conditions, the inverter is preferentially controlled to run a first modulation algorithm, utilizing its low ripple current characteristic to ensure small voltage deviations between positive and negative buses and balanced bus midpoints during fault ride-through, thus improving the fault ride-through success rate. Under non-fault conditions, further comprehensive judgment is made based on the second parameter. When the preset threshold condition for modulation mode switching is met, the device can switch to a second modulation algorithm with lower switching losses to reduce switching losses and improve the inverter's grid-connected output efficiency, or switch back to the first modulation algorithm to ensure bus midpoint balance. In other words, this invention, through software algorithms, maximizes the high efficiency of the second modulation algorithm while ensuring bus midpoint balance. Compared to traditional solutions that require additional bus capacitor hardware, this reduces the overall cost of the inverter and balances the economy and efficiency of system operation.

[0068] For specific limitations regarding the grid-connected inverter control device 300, please refer to the limitations on the grid-connected inverter control method mentioned above, which will not be repeated here. Each module in the aforementioned grid-connected inverter control device 300 can be implemented entirely or partially through software, hardware, or a combination thereof. These modules can be embedded in hardware or independently of the processor in a computer device, or stored in software in the memory of a computer device, so that the processor can call and execute the operations corresponding to each module.

[0069] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the above-described division of functional units and modules is used as an example. In practical applications, the above functions can be assigned to different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above.

[0070] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A grid-connected inverter control method, characterized in that, The grid-connected inverter control method includes: Acquire a first parameter for characterizing the grid fault state and a second parameter for characterizing the inverter operating state; the first parameter includes the grid voltage, and the fault state includes a low voltage ride-through fault state and a high voltage ride-through fault state; the second parameter includes at least one of the following: grid-connected output active current, grid-connected output reactive current, modulation index, and DC bus voltage deviation. Based on the first parameter, it is determined whether to control the inverter to switch to a first modulation algorithm with a smaller ripple current. The first modulation algorithm is either SVPWM algorithm or SPWM algorithm. If not, based on the second parameter, determine whether the preset threshold condition for modulation mode switching is met. The preset threshold condition includes a preset exit threshold and an entry threshold. When the preset entry threshold or exit threshold is met, control the inverter to switch to a second modulation algorithm with lower switching losses or a first modulation algorithm with lower ripple current, respectively. The second modulation algorithm is either a DPWM algorithm or a SHEPWM algorithm. Specifically, determining whether to control the inverter to switch to a first modulation algorithm with lower ripple current based on the first parameter includes: Determine whether the grid voltage is below the low voltage ride-through threshold or above the high voltage ride-through threshold; When the grid voltage is lower than the low voltage ride-through threshold or higher than the high voltage ride-through threshold, the inverter is determined to be in a fault state, and the inverter is controlled to switch to the first modulation algorithm with lower ripple current.

2. The grid-connected inverter control method as described in claim 1, characterized in that, Based on the second parameter, it is determined whether the preset threshold condition for modulation mode switching is met. When the preset entry threshold or exit threshold is met, the inverter is controlled to switch to either the second modulation algorithm with lower switching losses or the first modulation algorithm with lower ripple current, respectively. Specifically, this includes: Determine whether at least one of the second parameters meets its preset exit threshold; or, determine whether all of the second parameters meet their preset entry threshold. When at least one of the second parameters meets its preset exit threshold, the inverter is controlled to switch to the first modulation algorithm with a smaller ripple current. When all parameters in the second parameter meet their preset entry threshold, the inverter is controlled to switch to a second modulation algorithm with lower switching losses.

3. The grid-connected inverter control method as described in claim 2, characterized in that, After determining whether at least one of the second parameters meets its preset exit threshold, the method further includes: detecting whether the duration for which at least one of the second parameters meets its preset exit threshold reaches a set exit delay time, so as to switch the first modulation algorithm to run when at least one of the second parameters meets its preset exit threshold and continues for the set exit delay time; or, After determining whether all parameters in the second parameter meet their preset entry threshold, the method further includes: detecting whether the duration for which all parameters in the second parameter meet their preset entry threshold reaches a set entry delay time, so as to switch to running the second modulation algorithm when all parameters in the second parameter meet their preset entry threshold and continue for the set entry delay time.

4. The grid-connected inverter control method as described in claim 3, characterized in that, The entry delay time is greater than the exit delay time.

5. The grid-connected inverter control method as described in claim 2 or 3, characterized in that, The preset exit threshold and the preset entry threshold are in a non-continuous range, and the grid-connected inverter control method further includes: When the parameter in the second parameter is between the preset exit threshold and the preset entry threshold, the currently running modulation algorithm is maintained.

6. The grid-connected inverter control method as described in claim 1, characterized in that, The second parameter includes the modulation index, wherein obtaining the second parameter used to characterize the inverter's operating state specifically includes: Obtain the effective values ​​of the three-phase line voltages, and select the minimum value as the minimum effective value of the line voltage. Calculate the minimum line voltage peak value based on the minimum line voltage RMS value; The modulation index is obtained by calculating the ratio of the minimum line voltage peak value to the instantaneous value of the DC bus voltage.

7. The grid-connected inverter control method as described in claim 1, characterized in that, The second parameter includes the DC bus voltage deviation, wherein obtaining the second parameter used to characterize the inverter's operating state specifically includes: Obtain the instantaneous values ​​of the DC positive bus voltage and the DC negative bus voltage; The difference between the instantaneous values ​​of the DC positive bus voltage and the DC negative bus voltage is calculated to obtain the DC bus voltage deviation.

8. A grid-connected inverter control device, characterized in that, The grid-connected inverter control device includes: The parameter acquisition module is used to acquire a first parameter characterizing the grid fault state and a second parameter characterizing the inverter operating state; the first parameter includes the grid voltage, and the fault state includes a low voltage ride-through fault state and a high voltage ride-through fault state; the second parameter includes at least one of the following: grid-connected output active current, grid-connected output reactive current, modulation index, and DC bus voltage deviation. The decision control module is used to determine whether the grid voltage is lower than the low voltage ride-through threshold or higher than the high voltage ride-through threshold. When the grid voltage is lower than the low voltage ride-through threshold or higher than the high voltage ride-through threshold, the inverter is determined to have entered a fault state, and the inverter is controlled to switch to a first modulation algorithm with lower ripple current. If not, based on the second parameter, it is determined whether the preset threshold conditions for modulation mode switching are met. The preset threshold conditions include a preset exit threshold and an entry threshold. When the preset entry threshold or exit threshold is met, the inverter is controlled to switch to a second modulation algorithm with lower switching losses or a first modulation algorithm with lower ripple current, respectively. Wherein, the first modulation algorithm is an SVPWM algorithm or an SPWM algorithm, and the second modulation algorithm is a DPWM algorithm or a SHEPWM algorithm. The drive output module is used to output a modulation signal corresponding to the first modulation algorithm or the second modulation algorithm according to the control of the decision control module, so as to drive the switching transistor of the inverter to work.

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