Off-grid and grid-connected smooth cut-in control method and device

Abstract

The invention discloses an off-grid and grid-connected smooth cut-in control method and device. The method comprises the following steps: acquiring a first power grid signal of a power grid side circuit, and acquiring a first inversion signal of a direct current side circuit; extracting a feedback signal source and a power grid harmonic signal according to the first power grid signal, and generating a first compensation harmonic signal according to the power grid harmonic signal; based on preset input power, feedback adjustment is carried out on the preset input power according to a feedback signal source, setting adjustment is carried out in combination with the first compensation harmonic signal, and a first inner ring adjustment signal is generated; extracting an inversion harmonic signal according to the first inversion signal, and generating a second compensation harmonic signal according to the inversion harmonic signal; and performing harmonic suppression according to the first compensation harmonic signal and the second compensation harmonic signal, controlling the off-grid and grid-connected change-over switch to be closed, and controlling the output power of the direct current side circuit to the power grid side circuit according to the first inner ring adjusting signal. Harmonic waves in the grid connection process are effectively suppressed, and smooth grid connection of the direct-current power supply can be ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of smart grids, and particularly to a smooth switching-in control method and device for grid-connected and off-grid operations. Background Art

[0002] With the rapid development of renewable energy, the grid-connected and off-grid technologies of DC power supplies play an important role in distributed generation systems, especially in the applications of solar and wind power generation, significantly improving the energy utilization efficiency.

[0003] In the prior art, an inverter converts the DC power supplied by a solar panel or a battery pack, etc. into alternating current and needs to operate in modes such as off-grid operation or grid-connected operation. However, there is an islanding effect in the inverter. When the power grid is disconnected, the inverter will still continue to supply power to the load, resulting in severe fluctuations in voltage and frequency. When the islanding effect occurs, that is, when the power grid is disconnected, it will cause changes in the load of the grid-connected inverter, and more power needs to be provided to meet the load operation. At the same time, it also increases the voltage harmonic content, affecting the safe and stable operation of the power grid. Summary of the Invention

[0004] The present invention provides a smooth switching-in control method and device for grid-connected and off-grid operations, which solves the problem that the existing grid-connected and off-grid circuits have a large amount of harmonic content, affecting the safe and stable operation of the power grid, so as to suppress the harmonics when the DC power supply is grid-connected to the power grid and improve the smoothness of the grid-connected operation of the DC power supply.

[0005] According to one aspect of the present invention, there is provided a smooth switching-in control method for a grid-connected and off-grid switching circuit. The grid-connected and off-grid switching circuit includes: a DC side circuit, a grid side circuit, and a grid-connected and off-grid switching switch connected between the DC side circuit and the grid side circuit. The smooth switching-in control method for grid-connected and off-grid operations includes:

[0006] In the grid-connected mode, obtain a first grid signal of the grid side circuit and a first inverter signal of the DC side circuit;

[0007] Extract a feedback signal source and a grid harmonic signal according to the first grid signal, and generate a first compensation harmonic signal according to the grid harmonic signal; based on a preset input power, perform feedback adjustment on the preset input power according to the feedback signal source, and perform tuning adjustment in combination with the first compensation harmonic signal to generate a first inner loop adjustment signal;

[0008] Extract an inverter harmonic signal according to the first inverter signal, and generate a second compensation harmonic signal according to the inverter harmonic signal;

[0009] Perform harmonic suppression based on the first compensation harmonic signal and the second compensation harmonic signal, control the grid-connected and off-grid switching switch to close, and control the output power of the DC-side circuit to the grid-side circuit according to the first inner-loop regulation signal.

[0010] According to another aspect of the present invention, there is provided a grid-connected and off-grid smooth switching control device, which includes:

[0011] A sampling module for acquiring a first grid signal on the grid side and acquiring a first inverter signal of the DC-side circuit;

[0012] A first compensation harmonic signal acquisition module for extracting a feedback signal source and a grid harmonic signal according to the first grid signal, and generating a first compensation harmonic signal according to the grid harmonic signal;

[0013] A first inner-loop regulation signal acquisition module for performing feedback regulation on the preset input power according to the feedback signal source based on the preset input power, and performing tuning regulation in combination with the first compensation harmonic signal to generate a first inner-loop regulation signal;

[0014] A second compensation harmonic signal acquisition module for extracting an inverter harmonic signal according to the first inverter signal, and generating a second compensation harmonic signal according to the inverter harmonic signal;

[0015] An output power determination module for performing harmonic suppression according to the first compensation harmonic signal and the second compensation harmonic signal, controlling the grid-connected and off-grid switching switch to close, and controlling the output power of the DC-side circuit to the grid-side circuit according to the first inner-loop regulation signal.

[0016] The technical solution of the embodiment of the present invention compensates for grid harmonic signals and inverter harmonic signals to obtain a first compensation harmonic signal and a second compensation harmonic signal, and then controls the grid-connected and off-grid switching switch to close according to the first compensation harmonic signal and the second compensation harmonic signal, so that the DC-side circuit can smoothly switch into the grid. That is, the present invention effectively reduces the harmonic influence during the grid connection process and ensures the smooth grid connection of the DC power supply.

[0017] It should be understood that the content described in this part is not intended to identify the key or important features of the embodiments of the present invention, nor is it used to limit the scope of the present invention. Other features of the present invention will become easily understood through the following description. Description of the Drawings

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the accompanying drawings required for the description of the embodiments. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can be obtained based on these drawings.

[0019] Figure 1 It is a flowchart of a grid-connected and off-grid smooth switching-in control method provided by an embodiment of the present invention;

[0020] Figure 2 It is a structural schematic diagram of a grid-connected and off-grid switching circuit provided by an embodiment of the present invention;

[0021] Figure 3 It is a flowchart of another grid-connected and off-grid smooth switching-in control method provided by an embodiment of the present invention;

[0022] Figure 4 It is a flowchart of a smooth switching-in control method in the grid-connected mode provided by an embodiment of the present invention;

[0023] Figure 5 It is a flowchart of another grid-connected and off-grid smooth switching-in control method provided by an embodiment of the present invention;

[0024] Figure 6 It is a flowchart of a control method in the off-grid mode provided by an embodiment of the present invention. Detailed implementation manners

[0025] In order to enable those skilled in the art to better understand the solutions of the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0026] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above accompanying drawings are used to distinguish similar objects, and do not necessarily need to describe a specific order or sequence. It should be understood that such used data can be interchanged under appropriate circumstances so that the embodiments of the present invention described here can be implemented in an order other than those illustrated or described here. In addition, the terms "including" and "having" and any of their deformations are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device including a series of steps or units does not necessarily need to be limited to those clearly listed steps or units, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0027] Figure 1 This is a flowchart of a grid-connected and off-grid smooth switching control method provided by an embodiment of the present invention. This embodiment is applicable to the grid connection of a DC power supply and the grid. This grid-connected and off-grid smooth switching control method can be executed by a grid-connected and off-grid smooth switching control device, and this grid-connected and off-grid smooth switching control device can be implemented in the form of hardware and / or software. As Figure 1 shown, the method includes:

[0028] S110. In the grid-connected mode, obtain a first grid signal of the grid-side circuit and a first inverter signal of the DC-side circuit.

[0029] Specifically, the grid-connected mode refers to the state where the DC-side circuit is connected to the grid-side circuit and operates synchronously. In the grid-connected mode, the inverter converts the DC power supply into alternating current and exchanges energy with the grid. The first grid signal refers to parameter signals such as voltage, current, or frequency obtained from the grid-side circuit in the grid-connected mode, which are used to monitor the state and operation of the grid. The first inverter signal refers to the AC signal output by the inverter obtained from the DC-side circuit in the grid-connected mode, which can reflect the working state and output characteristics of the inverter.

[0030] In the embodiment of the present invention, obtaining the first grid signal and the first inverter signal can monitor the grid state and the inverter output characteristics, enabling the control module to identify potential faults or unstable factors and take measures in advance, thereby ensuring safe and reliable grid-connected operation.

[0031] S120. Extract a feedback signal source and a grid harmonic signal according to the first grid signal, and generate a first compensation harmonic signal according to the grid harmonic signal; based on a preset input power, perform feedback adjustment on the preset input power according to the feedback signal source, and perform tuning adjustment in combination with the first compensation harmonic signal to generate a first inner-loop adjustment signal.

[0032] Specifically, the feedback signal source refers to the information source extracted from the first grid signal, which reflects the actual operating state of the grid. Exemplarily, the feedback signal source may include parameters such as grid voltage and grid current. Grid power can be calculated based on the grid voltage and grid current. The grid harmonic signal refers to the non-linear waveform components extracted from the first grid signal, usually caused by non-linear loads, which may lead to power quality problems. Exemplarily, the grid harmonic signal may include parameters such as the harmonic components of grid current and the harmonic components of grid voltage. The first compensation harmonic signal can be calculated based on the harmonic components of grid current and the harmonic components of grid voltage. Exemplarily, the harmonic components in the first grid signal may include the third harmonic, the fifth harmonic, and the seventh harmonic, etc. The first compensation harmonic signal refers to the compensation signal generated based on the grid harmonic signal, which can cancel the harmonic influence in the grid and improve the power quality. The preset input power refers to the expected power output value set during the design of the DC power supply in the DC side circuit, which is used to guide the power regulation of the DC power supply. The first inner-loop regulation signal refers to the signal generated after the preset input power is regulated by the feedback of the feedback signal source and harmonic compensation calculation, which is used to control the output power of the DC side circuit and achieve dynamic regulation.

[0033] In the embodiment of the present invention, the actual operating state of the grid and its harmonic components are obtained from the first grid signal, and the first compensation harmonic signal is generated based on the grid harmonic signal. The first compensation harmonic signal is used to cancel the influence of the harmonic components in the first grid signal and increase the smoothness of the grid connection process. Secondly, by adjusting the preset input power according to the feedback signal source, it can ensure that the power output from the DC side matches the grid demand, thereby enhancing the flexibility and response ability of the DC side circuit during the grid connection operation.

[0034] S130. Extract the inverter harmonic signal according to the first inverter signal, and generate the second compensation harmonic signal according to the inverter harmonic signal.

[0035] Specifically, the inverter harmonic signal refers to the harmonic components extracted from the inverter signal, usually caused by the non-linear characteristics of the inverter. Exemplarily, the inverter harmonic signal includes the harmonic components of the inverter voltage and the harmonic components of the inverter current, and these harmonic components may include the third harmonic, the fifth harmonic, and the seventh harmonic, etc. The second harmonic compensation signal refers to the compensation signal generated based on the inverter harmonic signal, which is used to cancel the harmonic components in the inverter output, thereby improving the power quality and system performance.

[0036] In the embodiment of the present invention, the second harmonic compensation signal can reduce the harmonic interference caused by the characteristics of the inverter and improve the output power quality.

[0037] S140. Perform harmonic suppression based on the first compensated harmonic signal and the second compensated harmonic signal, control the closing of the grid-connected and off-grid switching switch, and control the output power of the DC-side circuit to the grid-side circuit according to the first inner-loop regulation signal.

[0038] Specifically, harmonic suppression refers to the process of reducing or eliminating harmonic components in the power system through various technical means. Reducing harmonics can ensure the smooth connection of the DC-side circuit during the grid connection process. In the embodiments of the present invention, harmonic compensation is used to reduce the harmonic components in the DC-side circuit and the grid-side circuit.

[0039] In the embodiments of the present invention, the first compensated harmonic signal and the second compensated harmonic signal are combined to cancel each other out and perform harmonic suppression, which can ensure the smoothness of the grid connection process and reduce the impact of harmonics on the grid. After the grid-connected and off-grid switching switch is closed, the DC-side circuit operates in parallel with the grid. The power output from the DC side to the grid side after grid connection is adjusted according to the first inner-loop regulation signal to ensure that the DC power supply on the DC side can automatically adapt to changes in grid demand, thereby improving the overall efficiency and reliability of the system.

[0040] The technical solution of the embodiments of the present invention performs harmonic compensation on the grid harmonic signal and the inverter harmonic signal to obtain the first compensated harmonic signal and the second compensated harmonic signal, and then controls the closing of the grid-connected and off-grid switching switch according to the first compensated harmonic signal and the second compensated harmonic signal, so that the DC-side circuit can smoothly connect to the grid. That is, the present invention effectively reduces the harmonic impact during the grid connection process and ensures the smooth grid connection of the DC power supply.

[0041] Figure 2 This is a schematic structural diagram of a grid-connected and off-grid switching circuit provided by an embodiment of the present invention. As Figure 2 shown, the grid-connected and off-grid switching circuit includes: a DC-side circuit, a grid-side circuit, and a grid-connected and off-grid switching switch 140 connected between the DC-side circuit and the grid-side circuit. The DC-side circuit includes an inverter module 120 and a filter 130. The filter 130 is connected between the inverter module 120 and the first end of the off-grid switch. The grid-side circuit includes an isolation transformer module 150. The isolation transformer module 150 is connected between the second end of the off-grid switch and the grid 160.

[0042] Specifically, the grid-connected and off-grid switching circuit refers to a circuit used to control the connection and disconnection between the DC power supply 110 and the power grid 160. The DC side circuit refers to the circuit part connected to the DC power supply 110 such as a solar panel or a battery pack, which is responsible for receiving and processing DC electrical energy and converting the DC electrical energy into AC electrical energy. The filter 130 refers to an electrical device used to selectively pass or block signals of specific frequencies. The filter 130 usually includes high-order filters such as an inductor-capacitor filter (LC) and an inductor-capacitor-inductor filter (LCL). Exemplarily, the battery or other forms of DC power supply 110 provides a DC input signal, and then the inverter module 120 converts the DC input signal into a bidirectional pulse signal. The filter 130 filters the double-pulse signal to obtain a fundamental component sinusoidal signal. In the embodiment of the present invention, the inverter module 120 refers to a unidirectional inverter module, which may include structures such as an H-bridge and a dual-BUCK, and is usually controlled by a pulse width modulation signal.

[0043] The grid-connected and off-grid switching switch 140 refers to a control switch connected between the DC side circuit and the grid side circuit, which is used to realize the switching between the AC electrical energy generated by the inverter and the power grid. The grid-connected and off-grid switching switch 140 provides a hardware channel for the whole machine state switching, and is driven by the controller 170 of the grid-connected and off-grid switching switch. The controller 170 of the grid-connected and off-grid switching switch controls the relay by using an electronic driver composed of MOS transistors, so as to realize the switching of the grid-connected and off-grid hardware channel.

[0044] The grid side circuit refers to the circuit part connected to the power grid. The isolation transformer module 150 refers to an electrical device used to convert the input voltage into different output voltages, which has an electrical isolation function. Collecting the first grid signal before the isolation transformer module 150 can protect the measuring device from the high voltage or noise on the grid side and ensure the safety of the signal collection process. The power grid 160 refers to a power transmission and distribution system responsible for delivering the electrical energy generated by the power plant to users.

[0045] The sampling module 180 refers to a device used to monitor and collect electrical signals in the grid side circuit and the DC side circuit in real time. The sampling module 180 uploads the collected electrical signals to the control module 190. The sampling module 180 may include a voltage sensor and a current sensor composed of Hall sensors, and may also include an operational amplifier, etc. The control module 190 refers to the core module that can execute the grid-connected and off-grid smooth switching control method provided by any embodiment of the present invention. Exemplarily, the control module can send a switching signal to the controller 170 of the grid-connected and off-grid switching switch, or send a pulse width modulation signal to the inverter module 120.

[0046] In an embodiment of the present invention, a first inverter signal is obtained at the first end of the grid-connected and off-grid switching switch 110, that is, the output end of the filter 130; a first grid signal is obtained at the second end of the grid-connected and off-grid switching switch 110, that is, the input end of the isolation transformer module 150.

[0047] Figure 3 As shown in the flowchart of another grid-connected and off-grid smooth switching control method provided by the embodiment of the present invention. Based on the above embodiments, Figure 3 as shown, the method includes:

[0048] S210. Obtain the harmonic components of the grid voltage, the harmonic components of the grid current, the grid current, the grid voltage, and the phase signal at the second end of the grid-connected and off-grid switching switch of the grid-side circuit.

[0049] Specifically, the harmonic components of the grid voltage refer to the non-fundamental frequency components existing in the grid voltage, usually caused by non-linear loads, which will affect the smoothness of the grid-connected process. The harmonic components of the grid current refer to the non-fundamental frequency components existing in the grid current, reflecting the distortion of the current signal, usually also caused by non-linear loads, and will also affect the smoothness of the grid-connected process. The grid current refers to the current flowing through the grid-side circuit. The grid voltage refers to the magnitude and direction of the voltage at the second end of the grid-connected and off-grid switching switch, which affects the power transmission and the operation of the equipment. The phase signal refers to the phase information between the grid voltage and the grid current.

[0050] In an embodiment of the present invention, the first grid signal includes the harmonic components of the grid voltage, the harmonic components of the grid current, the grid current, the grid voltage, and the phase signal. Analyzing the harmonic components of the grid voltage and the harmonic components of the grid current can judge the power quality on the grid side and avoid the potential impact of harmonics on the grid-connected process. Analyzing the grid current, the grid signal, and the phase signal can timely understand the operating state of the grid, provide a reference for the DC-side circuit, and ensure that the DC-side circuit can maintain a good synchronization state with the grid after grid connection.

[0051] S220. Obtain the harmonic components of the inverter voltage, the harmonic components of the inverter current, the inverter current, and the inverter voltage at the first end of the grid-connected and off-grid switching switch of the DC-side circuit.

[0052] Specifically, the harmonic components of the inverter voltage refer to the non-fundamental frequency components existing in the voltage signal output by the inverter. These harmonic components may be caused by the switching process of the inverter and will affect the smoothness of the grid-connected process. The harmonic components of the inverter current refer to the non-fundamental frequency components existing in the current signal output by the inverter, usually also caused by the working characteristics and load characteristics of the inverter, and will also affect the smoothness of the grid-connected process. The inverter current refers to the current output by the inverter to the load or the grid. The inverter voltage refers to the AC voltage output by the inverter.

[0053] In an embodiment of the present invention, the first inverter signal includes harmonic components of the inverter voltage, harmonic components of the inverter current, the inverter current, and the inverter voltage. Analyzing the harmonic components of the inverter voltage and the harmonic components of the inverter current can determine the power quality of the electrical energy after inversion by the inverter module on the DC side, and avoid potential impacts of harmonics on the grid connection process. Analyzing the inverter current and the inverter voltage can timely understand the operating state of the inverter side and make timely adjustments to ensure that the DC side circuit can maintain a good synchronization state with the power grid after grid connection.

[0054] S230. Extract a feedback signal source from the first grid signal, and through an outer loop controller, based on a preset input power, perform feedback adjustment on the preset input power according to the feedback signal source to generate a first power signal; the feedback signal source includes grid current and grid voltage.

[0055] Specifically, the outer loop controller refers to a control system component that is responsible for receiving information from the feedback signal source and adjusting parameters according to the preset input power to achieve the output of the first power signal. The first power signal refers to the power signal generated after feedback adjustment by the outer loop controller.

[0056] In an embodiment of the present invention, using the grid signal and the current signal in the first grid signal as the feedback signal source, together with the feedback quantity and the preset input power, are given to the outer loop controller for adjustment, thereby improving the accuracy of power output.

[0057] S240. Extract a grid harmonic signal from the first grid signal, and through a pre-grid connection harmonic controller, generate a first compensated harmonic signal according to the grid harmonic signal; the grid harmonic signal includes harmonic components of the grid current and harmonic components of the grid voltage.

[0058] Specifically, the pre-grid connection harmonic controller refers to a control device that is responsible for analyzing and processing the extracted grid harmonic signal before grid connection of the power grid to generate a first compensated harmonic signal and reduce the impact of harmonics on power quality. The pre-grid connection harmonic controller usually includes active components such as operational amplifiers and microcontrollers, and these active components enable the pre-grid connection harmonic controller to effectively analyze grid harmonics and implement dynamic compensation, thereby improving power quality and system stability.

[0059] Exemplarily, the pre-grid connection harmonic controller can extract harmonic components from the first grid signal, analyze these signals through algorithms such as Fourier transform, identify the frequency and amplitude of the harmonics. According to the analysis results, the pre-grid connection harmonic controller calculates the required compensated harmonic signal to cancel the harmonic components in the power grid, generates a first compensated harmonic signal, and further reduces the impact of harmonics on the grid connection process.

[0060] S250. Through the inner loop controller, perform tuning adjustment according to the first compensated harmonic signal and the first power signal to generate a first inner loop adjustment signal.

[0061] Specifically, the inner loop controller refers to a component mainly responsible for quickly responding to system changes in a short time. It outputs the first inner loop adjustment signal by monitoring the first compensated harmonic signal and the first power signal in real time. The first inner loop adjustment signal refers to the adjustment signal generated by the inner loop controller according to the input first compensated harmonic signal and first power signal. The first inner loop adjustment signal is used to adjust the output of the inverter module to achieve dynamic compensation for power and harmonics.

[0062] In the embodiment of the present invention, the inner loop controller generates the first inner loop adjustment signal, which can quickly respond to changes in harmonics and power in the power grid and ensure real-time adjustment of the system.

[0063] S260. Extract the inverter harmonic signal from the first inverter signal. Through the off-grid harmonic controller, generate a second compensated harmonic signal according to the inverter harmonic signal; the inverter harmonic signal includes the harmonic components of the inverter voltage and the inverter current.

[0064] Specifically, the off-grid harmonic controller refers to a control device responsible for analyzing and processing the extracted inverter harmonic signal to generate a second compensated harmonic signal and reduce the impact of harmonics on the power quality. The off-grid harmonic controller usually includes active components such as operational amplifiers and microcontrollers. These active components enable the off-grid harmonic controller to effectively analyze the harmonics in the DC side circuit and implement dynamic compensation, thereby improving the power quality and system stability.

[0065] Exemplarily, the off-grid harmonic controller can extract the inverter harmonic signal from the first inverter signal and analyze these signals through algorithms such as Fourier transform to identify the frequency and amplitude of the harmonics. According to the analysis results, the off-grid harmonic controller calculates the required compensated harmonic signal to cancel the harmonic components in the DC side circuit, generates the second compensated harmonic signal, and further reduces the impact of DC side harmonics on the grid connection process.

[0066] S270. When the phase signal of the power grid circuit is in phase with the phase signal of the inverter circuit, if the first compensated harmonic signal and the second compensated harmonic signal are synchronized and cancel each other out, then issue a first switching signal; the first switching signal is used to control the controller of the off-grid / grid-connected switching switch to switch to the grid-connected mode.

[0067] Specifically, the first switching signal refers to the signal sent by the control module for indicating the action of the controller of the grid-connected and off-grid switching switch. The first switching signal realizes the control of the strong electricity by the weak electricity. The controller of the grid-connected and off-grid switching switch controls the grid-connected and off-grid switching switch to close according to the first switching signal, that is, to switch to the grid-connected mode, so that the DC power supply of the DC side circuit can provide the grid-connected power input. That the first harmonic compensation signal and the second harmonic compensation signal are synchronized means that the phases of the two signals are the same, the frequencies are the same, and synchronous adjustment can be achieved.

[0068] In the embodiment of the present invention, the in-phase of the phase signal of the grid circuit and the phase signal of the inverter circuit is the most basic condition for the inverter to be grid-connected, which ensures that the alternating current output by the inverter is in phase with the alternating current of the grid, and avoids the impact current at the moment of grid connection. By keeping the first harmonic compensation signal and the second harmonic compensation signal synchronized and canceling each other out, the harmonic components in the output current of the inverter can be further suppressed, and the power quality can be improved.

[0069] S280. In the grid-connected mode, the first inner-loop regulation signal is calibrated by the second harmonic compensation signal, the pulse width modulation signal of the inverter module of the DC side circuit is adjusted, and the output power of the inverter module to the grid side circuit is controlled according to the adjusted pulse width modulation signal.

[0070] Specifically, the pulse width modulation signal refers to a modulation method that controls the signal by changing the pulse width. In the embodiment of the present invention, adjusting the pulse width modulation signal according to the first inner-loop regulation signal and the second harmonic compensation signal can enable the inverter module to adjust the output power according to the states of the grid side and the DC side after being grid-connected, ensuring that the inverter module can respond to the changes of the grid in real time, thereby optimizing the energy transmission efficiency. In addition, the first inner-loop regulation signal is obtained according to the first harmonic compensation signal, and together with the second harmonic compensation signal, it can enhance the effect of harmonic suppression.

[0071] The technical solution of the embodiment of the present invention closes the grid-connected and off-grid switching switch according to the first harmonic compensation signal and the second harmonic compensation signal, so that the grid-connected and off-grid switching circuit enters the grid-connected mode, effectively reducing the influence of harmonics on the grid connection process and increasing the smoothness of the grid connection process. In addition, through the feedback regulation of the inner-loop controller and the outer-loop controller together, the conduction mode of the inverter module is controlled to ensure the stability of the output power and the effective compensation of harmonics. The synergistic effect of these two-level control strategies improves the reliability and stability of the grid during grid-connected operation.

[0072] Optionally, in the grid-connected mode, before adjusting the first inner-loop regulation signal with the second compensating harmonic signal to regulate the pulse-width modulation signal of the inverter module in the DC-side circuit and controlling the output power of the inverter module to the grid-side circuit according to the adjusted pulse-width modulation signal, it further includes: generating a feedforward signal through a feedforward controller according to the grid voltage and phase signal of the first grid signal; adjusting the first inner-loop regulation signal according to the feedforward signal and the second compensating harmonic signal to generate an adjusted pulse-width modulation signal.

[0073] Specifically, the feedforward controller refers to a control system component whose main function is to predict the behavior of the grid side based on the grid current, grid voltage, and phase signal and make pre-adjustments. The feedforward signal refers to the control signal generated by the feedforward controller. By making adjustments before a deviation occurs in the grid-connected and off-grid switching circuit, the feedforward signal can significantly improve the response speed of the control module and reduce delays.

[0074] The technical solution of the embodiment of the present invention generates a pulse-width modulation signal according to the feedforward signal, controls the inverter module to make adjustments before a deviation occurs in the grid-connected and off-grid switching circuit, so as to ensure that the DC-side circuit responds to changes in the grid side in a timely manner, can optimize the output power of the DC side, and improve the quality of the output electric energy. At the same time, this method can effectively suppress harmonics and improve the overall stability and reliability during the grid-connected operation of the grid-connected and off-grid switching circuit.

[0075] Optionally, after controlling the output power of the inverter module to the grid-side circuit according to the adjusted pulse-width modulation signal in the grid-connected mode, it further includes: filtering the output power of the inverter module in the grid-connected mode through a filtering module to generate a filtered grid-connected mode output power; the filtered grid-connected mode output power is used to be transmitted to the isolation transformer module of the grid-side circuit through the turned-on grid-connected and off-grid switching switch.

[0076] Specifically, the filtered grid-connected mode output power refers to the power signal obtained after the output power generated by the inverter module is processed by the filtering module. Since the power output by the inverter module usually contains some harmonic components and noise, these harmonics and noises will affect the power quality of the grid. The filtering module can filter out these unwanted harmonics and noises, making the output power smoother and more stable, and more in line with the requirements of the grid.

[0077] In the embodiment of the present invention, filtering through the filtering module can significantly reduce the harmonic content of the inverter output, further suppress harmonics, and make the power quality in the grid-connected mode more in line with the grid standards.

[0078] Figure 4 It is a flowchart of a smooth switching-in control method in the grid-connected mode provided by the embodiment of the present invention. As Figure 4As shown in the figure, the grid connection process is as follows: The sampling module 180 samples the first grid signal at the second end of the off-grid / grid-connected switching switch 140, and the pre-grid connection harmonic controller 195 generates a first harmonic compensation signal based on the first grid signal. At the same time, the sampling module 180 samples the first inverter signal at the first end of the off-grid / grid-connected switching switch 140, and the off-grid harmonic controller 194 generates a second harmonic compensation signal based on the first inverter signal. The control module issues a first switching signal to control the closing of the off-grid / grid-connected switching switch 140 according to the relationship between the first harmonic compensation signal and the second harmonic compensation signal. After the off-grid / grid-connected switching switch 140 is closed, the outer loop controller 191 generates a first power signal based on the first grid signal and the preset input power; the inner loop controller 192 generates a first inner loop adjustment signal based on the first power signal and the first harmonic compensation signal; the feed-forward controller 193 generates a feed-forward signal based on the first grid signal, and the control module generates a pulse width modulation signal according to the first harmonic compensation signal, the second harmonic compensation signal, the first inner loop adjustment signal and the feed-forward signal to control the conduction mode of the inverter module 120. The inverter module 120 can achieve power regulation and harmonic suppression, and the output waveform is transmitted to the off-grid / grid-connected switching switch 140 through the filter 130, and then input into the power grid through the isolation transformer module 150. In the embodiment of the present invention, the control module may include an outer loop controller 191, an inner loop controller 192, a feed-forward controller 193, an off-grid harmonic controller 194 and a pre-grid connection harmonic controller 195, and the types of these controllers may include PI controllers, sliding mode controllers and repetitive controllers, etc.

[0079] Figure 5 It is a flowchart of another off-grid / grid-connected smooth switching-in control method provided by the embodiment of the present invention. On the basis of the above embodiments, optionally, the off-grid / grid-connected smooth switching-in control method further includes:

[0080] S310. In the off-grid mode, obtain the second inverter signal of the DC side circuit.

[0081] Specifically, the off-grid mode refers to the working mode in which the DC side circuit operates independently when it is disconnected from the grid side circuit. The second inverter signal refers to the AC signal output by the inverter obtained from the DC side circuit in the off-grid mode, which can reflect the working state and output characteristics of the inverter.

[0082] In the embodiment of the present invention, obtaining the second inverter signal of the DC side circuit can monitor the output characteristics of the inverter in the off-grid mode, enabling the control module to identify potential faults or unstable factors, thereby ensuring safe and reliable grid connection operation.

[0083] S320. Extract the inverter feedback signal source from the second inverter signal. The inverter feedback signal source includes inverter current and inverter voltage. Based on the preset input power, perform feedback adjustment on the preset input power according to the inverter feedback signal source, and generate a second inner-loop adjustment signal through the inner-loop controller.

[0084] Specifically, the inverter feedback signal source refers to the feedback signal extracted from the first inverter signal, which is used to reflect the actual output situation of the inverter for adjustment. The second inner-loop adjustment signal refers to the signal generated according to the feedback adjustment, which is used to further control the output of the DC-side power supply to ensure it is close to the preset value.

[0085] S330. Extract the inverter harmonic signal from the second inverter signal. Generate a second compensation harmonic signal according to the inverter harmonic signal through the off-grid harmonic controller. The inverter harmonic signal includes the harmonic components of the inverter voltage and the inverter current.

[0086] Specifically, the inverter harmonic signal is usually caused by the non-linear characteristics of the inverter. Exemplarily, the inverter harmonic signal includes the harmonic components of the inverter voltage and the inverter current, and these harmonic components can include the third harmonic, the fifth harmonic, and the seventh harmonic, etc.

[0087] In the embodiment of the present invention, the second compensation harmonic signal can cancel or reduce the harmonics in the inverter output by generating a signal with the same magnitude and opposite phase as the inverter harmonic signal, thereby suppressing the harmonics in the DC-side circuit in the off-grid mode.

[0088] S340. Perform harmonic suppression on the second inner-loop adjustment signal according to the second compensation harmonic signal to generate a pulse width modulation signal in the off-grid mode. The pulse width modulation signal in the off-grid mode is used to control the output power of the inverter module on the DC-side circuit to the load side.

[0089] In the embodiment of the present invention, the pulse width modulation signal in the off-grid mode can control the inverter module on the DC-side circuit, thereby controlling the magnitude and waveform of the output power of the inverter module to the load side.

[0090] Optionally, after performing harmonic suppression on the second inner-loop adjustment signal according to the second compensation harmonic signal to generate a pulse width modulation signal in the off-grid mode, it further includes: generating an off-grid mode output power through the inverter module according to the pulse width modulation signal in the off-grid mode; filtering the off-grid mode output power through the filter module to generate a filtered off-grid mode output power; the filtered off-grid mode output power is used to drive the load to operate in the off-grid mode.

[0091] In the embodiment of the present invention, the filtering module filters the output power in the off-grid mode, which can effectively filter out harmonics and noise, and then provide a stable and reliable power supply for the load, ensuring its normal operation in the off-grid mode, and improving the operation efficiency and extending the service life.

[0092] The technical solution of the embodiment of the present invention adjusts the pulse width modulation signal of the inverter module in the off-grid mode through the second inner loop adjustment signal and the second compensated harmonic signal, realizes the precise control of the output power, reduces the influence of harmonics on the DC-side circuit when working in the off-grid mode, so as to ensure that the load can obtain a stable power supply in the off-grid mode.

[0093] Figure 6 It is a flowchart of a control method in the off-grid mode provided by the embodiment of the present invention. As Figure 6 shown, the control process in the off-grid mode is as follows: The sampling module 180 samples the first inverter signal at the output end of the filter 130, and the inner loop controller 192 generates a second inner loop adjustment signal according to the first inverter signal and the preset input power. At the same time, the off-grid harmonic controller 194 generates a second harmonic compensation signal according to the first inverter signal, and the control module generates a pulse width modulation signal according to the second inner loop adjustment signal and the second harmonic compensation signal to control the conduction state of the inverter module 120. The AC power output by the inverter module 120 is filtered by the filter 130 and then supplies power to the load 100.

[0094] The embodiment of the present invention also provides an off-grid and grid-connected smooth switching control device. The device includes:

[0095] A signal acquisition module, configured to acquire a first grid signal on the grid side and acquire a first inverter signal of the DC-side circuit.

[0096] A first compensated harmonic signal acquisition module, configured to extract a feedback signal source and a grid harmonic signal according to the first grid signal, and generate a first compensated harmonic signal according to the grid harmonic signal.

[0097] A first inner loop adjustment signal acquisition module, configured to perform feedback adjustment on the preset input power according to the feedback signal source based on the preset input power, and perform tuning adjustment in combination with the first compensated harmonic signal to generate a first inner loop adjustment signal.

[0098] A second compensated harmonic signal acquisition module, configured to extract an inverter harmonic signal according to the first inverter signal and generate a second compensated harmonic signal according to the inverter harmonic signal.

[0099] An output power determination module, configured to perform harmonic suppression according to the first compensated harmonic signal and the second compensated harmonic signal, control the off-grid and grid-connected switching switch to close, and control the output power of the DC-side circuit to the grid-side circuit according to the first inner loop adjustment signal.

[0100] Optionally, the grid-connected and off-grid smooth switching-in control further includes:

[0101] A first power signal acquisition module, configured to extract a feedback signal source according to a first grid signal, and through an outer-loop controller, based on a preset input power, perform feedback adjustment on the preset input power according to the feedback signal source to generate a first power signal.

[0102] A feedforward signal acquisition module, configured to generate a feedforward signal through a feedforward controller according to the grid voltage and phase signal of the first grid signal.

[0103] The grid-connected and off-grid smooth switching-in control device provided by the embodiment of the present invention can execute the grid-connected and off-grid smooth switching-in control method provided by any embodiment of the present invention, and has corresponding functional modules and beneficial effects for executing the method.

[0104] It should be understood that various forms of the processes shown above can be used, steps can be reordered, added, or deleted. For example, the steps described in the present invention can be executed in parallel, sequentially, or in different orders, as long as the desired results of the technical solution of the present invention can be achieved, and no limitation is made herein.

[0105] The above specific implementation manners do not constitute a limitation on the protection scope of the present invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A grid-connected and off-grid smooth switching control method, characterized in that, For an off-grid and grid-connected switching circuit, the off-grid and grid-connected switching circuit includes: a DC side circuit and a grid side circuit, and an off-grid and grid-connected switching switch connected between the DC side circuit and the grid side circuit; the off-grid and grid-connected smooth switching-in control method includes: In the grid-connected mode, obtain the first grid signal of the grid side circuit and the first inverter signal of the DC side circuit; Extract the feedback signal source and the grid harmonic signal according to the first grid signal, and generate the first compensation harmonic signal according to the grid harmonic signal; based on the preset input power, perform feedback adjustment on the preset input power according to the feedback signal source, and perform tuning adjustment in combination with the first compensation harmonic signal to generate the first inner loop adjustment signal; Extract the inverter harmonic signal according to the first inverter signal, and generate the second compensation harmonic signal according to the inverter harmonic signal; Perform harmonic suppression according to the first compensation harmonic signal and the second compensation harmonic signal, control the off-grid and grid-connected switching switch to close, and control the output power of the DC side circuit to the grid side circuit according to the first inner loop adjustment signal.

2. The grid-connected and off-grid smooth switching control method according to claim 1, wherein The DC side circuit includes an inverter module and a filter, the filter is connected between the inverter module and the first end of the off-grid and grid-connected switch, the grid side circuit includes an isolation transformer module, and the isolation transformer module is connected between the second end of the off-grid and grid-connected switch and the grid; The obtaining the first grid signal of the grid side circuit and the first inverter signal of the DC side circuit includes: Obtain the harmonic components of the grid voltage, the harmonic components of the grid current, the grid current, the grid voltage and the phase signal at the second end of the off-grid and grid-connected switch of the grid side circuit; the first grid signal includes the harmonic components of the grid voltage, the harmonic components of the grid current, the grid current, the grid voltage and the phase signal; Obtain the harmonic components of the inverter voltage, the harmonic components of the inverter current, the inverter current and the inverter voltage at the first end of the off-grid and grid-connected switch of the DC side circuit; the first inverter signal includes the harmonic components of the inverter voltage, the harmonic components of the inverter current, the inverter current and the inverter voltage.

3. The grid-connected and off-grid smooth switching-in control method according to claim 2, wherein The extracting the feedback signal source and the grid harmonic signal according to the first grid signal, and generating the first compensation harmonic signal according to the grid harmonic signal; Based on the preset input power, performing feedback adjustment on the preset input power according to the feedback signal source, and performing tuning adjustment in combination with the first compensation harmonic signal to generate the first inner loop adjustment signal, includes: Extract the feedback signal source according to the first grid signal, and through the outer loop controller, based on the preset input power, perform feedback adjustment on the preset input power according to the feedback signal source to generate the first power signal; the feedback signal source includes the grid current and the grid voltage; Extract the grid harmonic signal according to the first grid signal, and through the pre-grid connection harmonic controller, generate the first compensation harmonic signal according to the grid harmonic signal; the grid harmonic signal includes the harmonic components of the grid current and the harmonic components of the grid voltage; Through the inner loop controller, tuning adjustment is performed according to the first compensated harmonic signal and the first power signal to generate a first inner loop adjustment signal.

4. The grid-connected and off-grid smooth switching control method according to claim 2, wherein The extracting an inverter harmonic signal according to the first inverter signal and generating a second compensated harmonic signal according to the inverter harmonic signal includes: Extracting an inverter harmonic signal according to the first inverter signal, and generating a second compensated harmonic signal according to the inverter harmonic signal through an off-grid harmonic controller; the inverter harmonic signal includes harmonic components of the inverter voltage and harmonic components of the inverter current.

5. The grid-connected and off-grid smooth switching control method according to claim 2, wherein The performing harmonic suppression according to the first compensated harmonic signal and the second compensated harmonic signal, controlling the off-grid / grid connection switch to close, and controlling the output power of the DC side circuit to the grid side circuit according to the first inner loop adjustment signal includes: When the phase signal of the grid circuit is in phase with the phase signal of the inverter circuit, if the first compensated harmonic signal and the second compensated harmonic signal are synchronized and cancel each other out, a first switching signal is issued; the first switching signal is used to control the controller of the off-grid / grid connection switch to switch to the grid-connected mode; In the grid-connected mode, the first inner loop adjustment signal is tuned by the second compensated harmonic signal, the pulse width modulation signal of the inverter module of the DC side circuit is adjusted, and the output power of the inverter module to the grid side circuit is controlled according to the adjusted pulse width modulation signal.

6. The grid-connected and off-grid smooth switching control method according to claim 5, wherein Before tuning the first inner loop adjustment signal by the second compensated harmonic signal, adjusting the pulse width modulation signal of the inverter module of the DC side circuit, and controlling the output power of the inverter module to the grid side circuit according to the adjusted pulse width modulation signal in the grid-connected mode, it further includes: Generating a feedforward signal through a feedforward controller according to the grid voltage and phase signal of the first grid signal; Adjusting the first inner loop adjustment signal according to the feedforward signal and the second compensated harmonic signal to generate an adjusted pulse width modulation signal.

7. The grid-connected and off-grid smooth switching control method according to claim 6, wherein After controlling the output power of the inverter module to the grid side circuit according to the adjusted pulse width modulation signal in the grid-connected mode, it further includes: Filtering the output power of the inverter module in the grid-connected mode through a filtering module to generate a filtered grid-connected mode output power; the filtered grid-connected mode output power is used to be transmitted to the isolation transformer module of the grid side circuit through the closed off-grid / grid connection switch.

8. The grid-connected and off-grid smooth switching control method according to claim 1, wherein The off-grid / grid connection smooth switching control method further includes: In the off-grid mode, obtaining a second inverter signal of the DC side circuit; Extracting an inverter feedback signal source according to the second inverter signal, the inverter feedback signal source includes inverter current and inverter voltage; based on a preset input power, performing feedback adjustment on the preset input power according to the inverter feedback signal source, and generating a second inner loop adjustment signal through an inner loop controller; Extracting an inverter harmonic signal according to the second inverter signal; generating a second compensated harmonic signal according to the inverter harmonic signal through an off-grid harmonic controller; the inverter harmonic signal includes harmonic components of the inverter voltage and harmonic components of the inverter current; Harmonic suppression is performed on the second inner-loop regulation signal according to the second compensation harmonic signal to generate a pulse-width modulation signal in the off-grid mode; the pulse-width modulation signal in the off-grid mode is used to control the output power of the inverter module of the DC side circuit to the load side.

9. The grid-connected and off-grid smooth switching control method according to claim 8, characterized in that After performing harmonic suppression on the second inner-loop regulation signal according to the second compensation harmonic signal to generate a pulse-width modulation signal in the off-grid mode, it further includes: The inverter module generates an off-grid mode output power according to the pulse-width modulation signal in the off-grid mode; The filter module filters the off-grid mode output power to generate a filtered off-grid mode output power; the filtered off-grid mode output power is used to drive the load to operate in the off-grid mode.

10. A grid-connected and off-grid smooth switching control device, characterized in that, The off-grid / grid-connected smooth switching control device includes: A signal acquisition module, configured to acquire a first grid signal on the grid side and a first inverter signal of the DC side circuit; A first compensation harmonic signal acquisition module, configured to extract a feedback signal source and a grid harmonic signal according to the first grid signal, and generate a first compensation harmonic signal according to the grid harmonic signal; A first inner-loop regulation signal acquisition module, configured to perform feedback regulation on the preset input power according to the feedback signal source based on a preset input power, and perform tuning regulation in combination with the first compensation harmonic signal to generate a first inner-loop regulation signal; A second compensation harmonic signal acquisition module, configured to extract an inverter harmonic signal according to the first inverter signal, and generate a second compensation harmonic signal according to the inverter harmonic signal; An output power determination module, configured to perform harmonic suppression according to the first compensation harmonic signal and the second compensation harmonic signal, control the off-grid / grid-connected switching switch to close, and control the output power of the DC side circuit to the grid side circuit according to the first inner-loop regulation signal.

Images