Control method of grid-connected inverter

Abstract

The invention discloses a control method of a grid-connected inverter, which relates to the technical field of inverter control, and comprises the following steps: setting reference current output by the inverter through an initial control module, setting other control parameters, and monitoring a distribution and adjustment module under the strategy condition of filtering harmonic waves. And monitoring an output current value Dout of the inverter and an output current value Dadj (n) of the adjusted inverter n output by each inverter in real time, adjusting a control parameter of each inverter after introducing a power grid impedance parameter, distributing the output current of each inverter according to a preset proportion, and monitoring the voltage and frequency of the power grid in real time so as to track the adjusted voltage and frequency values. According to the grid-connected inverter control method, by improving the current control precision, optimization and innovation in the aspects of uniform distribution of current between parallel inverters, enhancement of voltage and frequency regulation capability, improvement of harmonic suppression capability and enhancement of weak power grid adaptability are achieved, and the operation performance and reliability of the grid-connected inverter are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of inverter control, and in particular to a control method for a grid-connected inverter. Background Art

[0002] With the rapid growth of global energy consumption and the increasing depletion of non-renewable energy, the energy crisis is becoming increasingly severe. Therefore, countries have stepped up their research and development of renewable energy to cope with the dual challenges of energy crisis and environmental pollution. Renewable energy such as photovoltaic power generation and wind power generation has become the key development direction of various countries due to its clean and renewable advantages. In the renewable energy power generation system, the grid-connected inverter is the key equipment that converts DC power into AC power and sends it to the power grid. Its performance and control method directly affect the efficiency and stability of the entire power generation system. Therefore, the research and optimization of the control method of the grid-connected inverter is of great significance.

[0003] Although grid-connected inverter control methods have made significant progress, there are still some shortcomings. In traditional grid-connected inverter control, current control often has problems such as slow response speed and low precision. Especially when the grid voltage fluctuates or the load changes, the inverter output current adjustment speed is slow, which makes it difficult to meet the high-precision grid connection requirements. In a system with multiple inverters running in parallel, if there is a lack of effective current distribution control strategy, the output current between the inverters will be unevenly distributed, resulting in some inverters being overloaded and other inverters being underloaded, affecting the overall efficiency and stability of the system. The ability to regulate the voltage and frequency of the power grid is crucial. However, the existing technology often has problems such as low regulation accuracy and slow response speed, which makes it difficult to meet the strict requirements of the power grid on voltage and frequency. The grid-connected inverter will generate harmonics during operation, causing pollution to the power grid. In the existing technology, the harmonic suppression technology is still imperfect and cannot effectively eliminate the harmonic components in the inverter output current. In addition, in a weak power grid environment, the grid impedance is large, which puts higher requirements on the control performance of the grid-connected inverter. However, the grid-connected inverter in the existing technology has poor adaptability in a weak power grid environment and is difficult to meet the requirements of stable grid connection. Summary of the invention

[0004] The purpose of the present invention is to provide a control method for a grid-connected inverter, which solves the problems raised in the above background technology.

[0005] To achieve the above object, the present invention provides the following technical solutions, and the specific control method is as follows:

[0006] According to the grid connection requirements and grid status, and through the initial control module, set the reference current of the inverter output and set other control parameters. The control parameters include the proportional gain value B p , integral gain value Bi , distribution coefficient α, voltage regulation coefficient γ, frequency regulation coefficient σ;

[0007] By monitoring the distribution and regulation module, under the condition of filtering harmonics, the inverter output current value D is monitored in real time. out And the adjusted inverter n output current value D of each inverter output adj(n) , and after introducing the grid impedance parameters, adjust the control parameters of each inverter, so that the output current of each inverter is distributed according to a preset ratio, monitor the voltage and frequency of the grid in real time, and adjust the output voltage and frequency of the inverter accordingly to track the adjusted voltage and frequency values. The monitoring distribution and adjustment module includes a single inverter current control unit, a current distribution control unit between parallel inverters, and a system voltage and frequency comprehensive adjustment unit;

[0008] Data upload: upload real-time detection data and control parameters to the data acquisition terminal;

[0009] The equipment used by the initial control module includes sensors, including current sensors, voltage sensors and frequency sensors, which are used to monitor the inverter output current, grid voltage and frequency parameters;

[0010] The equipment used in the monitoring distribution and regulation module includes a controller, a power switch tube, a resonant controller and an auxiliary circuit.

[0011] Optionally, the calculation formula of the single inverter current control unit is as follows:

[0012] D out =D ref +B p (D ref -D actual )+B i *D errorl ;

[0013] D errorl =f(D ref -D actual )dt;

[0014] in:

[0015] D out is the inverter output current value;

[0016] D ref is the current reference value;

[0017] B p is the proportional gain value, B i is the integral gain value, B p and B i Used to adjust the response speed and steady-state error of the controller;

[0018] D actual is the actual measured current value;

[0019] D errorl is the current error integral value;

[0020] f(D ref -D actual )dt represents the total current error accumulated over time from a certain moment to the current moment.

[0021] Optionally, the calculation formula of the current distribution control unit between the parallel inverters is as follows:

[0022]

[0023] in:

[0024] D adj(n) is the output current value of inverter n after adjustment;

[0025] α is the distribution coefficient, which is used to adjust the sensitivity of current distribution;

[0026] D total is the total system demand current value;

[0027] N is the total number of parallel inverters.

[0028] Optionally, the calculation formula of the system voltage and frequency comprehensive adjustment unit is as follows:

[0029]

[0030] in:

[0031] V ref is the voltage reference value;

[0032] V nom is the rated voltage value;

[0033] γ is the voltage regulation coefficient, which is used to adjust the voltage regulation intensity;

[0034] D reted is the rated current value of the inverter;

[0035] P ref is the frequency reference value;

[0036] P nom is the rated frequency value;

[0037] σ is the frequency adjustment coefficient, and σ is used to adjust the frequency adjustment intensity;

[0038] TD is the system capacitance value;

[0039] LF is the sampling period value;

[0040] LF nom It is the ideal charge and discharge cycle value.

[0041] Optionally, the voltage reference value V output by the system voltage and frequency comprehensive adjustment unit is ref and frequency reference value P ref , which changes the overall operating status of the system. The specific changes have the following impacts:

[0042] 1. Voltage reference value V ref Impact

[0043] S1, when the voltage reference value V ref When the voltage changes, the output voltage of the inverter will be adjusted accordingly. Since the inverter is usually designed to work within a specific voltage range, the voltage change affects the output current characteristics of the inverter, which include the maximum output current and efficiency.

[0044] S2. If the resulting voltage adjustment causes the inverter to approach its voltage limit, it is considered necessary to adjust the voltage reference value V ref To avoid overvoltage and undervoltage conditions;

[0045] 2. Frequency reference value P ref Impact

[0046] S1, when the frequency reference value P ref When it deviates from the rated value, the load demand and power factor of the system are considered to change;

[0047] S2. The above changes will indirectly affect the output current demand of the inverter. For example, if the frequency reference value P ref If the decrease leads to an increase in system load, it is considered necessary to increase the output current of the inverter to meet the load demand.

[0048] Optionally, the voltage reference value V ref and the frequency reference value P ref The changed operating state of the entire system is directly fed back to each part of the system, including the current control loop of the inverter. On the basis of maintaining system stability and power quality, it is considered necessary to adapt to changes in voltage and frequency by adjusting the current control strategy, including changing the parameters of the PI controller and introducing new control algorithms.

[0049] Optionally, the controller includes a digital signal processor and a field programmable gate array, which are used to implement the control algorithm and PWM modulation function;

[0050] The power switch tube includes an insulated gate bipolar transistor and a metal-oxide semiconductor field effect transistor, which are used for power conversion of the inverter;

[0051] The auxiliary circuit includes a filtering circuit, a protection circuit and a communication circuit.

[0052] Optionally, the single inverter current control unit introduces a PI controller, specifically a proportional-integral controller, in the control process to eliminate harmonics of a specific frequency;

[0053] The current distribution control unit between parallel inverters and the system voltage and frequency comprehensive adjustment unit affect and adjust control parameters due to the introduction of grid impedance parameters.

[0054] Compared with the prior art, the present invention has the following beneficial effects:

[0055] 1. The present invention adopts a single inverter current control unit to control the current, and realizes precise control of the inverter output current through the joint action of the proportional and integral links. This control method can quickly respond to grid voltage fluctuations and load changes, and improve the accuracy and stability of current control.

[0056] 2. The present invention controls the current distribution between parallel inverters through a current distribution control unit between parallel inverters, thereby realizing real-time monitoring of the output current of each inverter and dynamically adjusting the control parameters of each inverter according to the total current and the distribution error, thereby ensuring uniform distribution of the output current between the inverters and improving the overall efficiency and stability of the system.

[0057] 3. The present invention adopts a system voltage and frequency comprehensive adjustment unit to perform comprehensive adjustment of system voltage and frequency. The adjustment will dynamically calculate the adjustment amount of voltage and frequency according to the factors of inverter output current, system capacity and rated parameters, and accurately track the grid voltage and frequency by adjusting the output voltage and frequency of the inverter. This adjustment method improves the response speed and adjustment accuracy of the inverter to the grid voltage and frequency.

[0058] 4. The present invention introduces harmonic suppression strategies into the control algorithm, such as using a resonant controller to eliminate the harmonic components in the inverter output current. These methods can effectively reduce the pollution of harmonics to the power grid, thereby improving the operating quality and reliability of the grid-connected inverter.

[0059] 5. The present invention aims at solving the control problems in weak grid environment, optimizes the control algorithm and parameter settings, and improves the stability and adaptability of the inverter in weak grid environment. For example, by introducing grid impedance parameters into the control algorithm, the responsiveness of the inverter to changes in grid impedance is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 A method flow chart of the control method of the grid-connected inverter;

[0061] Figure 2 A schematic diagram of control parameters included in the control method of the grid-connected inverter;

[0062] Figure 3 This is a schematic diagram of the structure of the monitoring allocation and regulation module of the present invention;

[0063] Figure 4 It is a simplified flow diagram of the control and adjustment method under the influence of voltage and frequency of the present invention. DETAILED DESCRIPTION

[0064] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0065] The control method of the grid-connected inverter is different from the existing control method of the grid-connected inverter. The existing control method of the grid-connected inverter often has the problems of slow response speed and low precision of current control. In the system where multiple inverters operate in parallel, there is a lack of effective current distribution control strategy. As a result, some inverters are overloaded while other inverters are underloaded, affecting the overall efficiency and stability of the system. In addition, it is difficult to meet the strict requirements of the power grid on voltage and frequency. The grid-connected inverter will generate harmonics during operation, the grid impedance is large, and the adaptability is poor, making it difficult to meet the requirements of stable grid connection. The algorithm unit effectively solves the deficiencies in the prior art and improves the operating performance and reliability of the grid-connected inverter by improving the current control accuracy, achieving uniform current distribution between parallel inverters, enhancing the voltage and frequency regulation capabilities, improving the harmonic suppression capabilities, and enhancing the adaptability to weak power grids.

[0066] For example, see Figures 1 to 4 This embodiment provides a control method for a grid-connected inverter. The specific control method is as follows:

[0067] According to the grid connection requirements and grid status, and through the initial control module, set the reference current of the inverter output and set other control parameters. The control parameters include the proportional gain value B p , integral gain value B i , distribution coefficient α, voltage regulation coefficient γ, frequency regulation coefficient σ;

[0068] By monitoring the distribution and regulation module, under the condition of filtering harmonics, the inverter output current value D is monitored in real time.out And the adjusted inverter n output current value D of each inverter output adj(n) , and after introducing the grid impedance parameters, adjust the control parameters of each inverter, so that the output current of each inverter is distributed according to a preset ratio, monitor the voltage and frequency of the grid in real time, and adjust the output voltage and frequency of the inverter accordingly to track the adjusted voltage and frequency values. The monitoring distribution and adjustment module includes a single inverter current control unit, a current distribution control unit between parallel inverters, and a system voltage and frequency comprehensive adjustment unit;

[0069] Data upload: upload real-time detection data and control parameters to the data acquisition terminal;

[0070] The equipment used by the initial control module includes sensors, including current sensors, voltage sensors and frequency sensors, which are used to monitor the inverter output current, grid voltage and frequency parameters;

[0071] The equipment used in the monitoring distribution and regulation module includes a controller, a power switch tube, a resonant controller and an auxiliary circuit;

[0072] The controller includes a digital signal processor and a field programmable gate array to implement the control algorithm and PWM modulation function;

[0073] The power switch tubes include insulated gate bipolar transistors and metal-oxide semiconductor field effect transistors, which are used for power conversion of inverters;

[0074] The auxiliary circuit includes filtering circuit, protection circuit and communication circuit.

[0075] In this embodiment, the system realizes the precise control of the grid-connected inverter by the mutual cooperation of the three algorithm units, ensuring that the current, voltage and frequency output by the inverter are synchronized with the power grid. out , D adj(n) 、V ref and P ref The four calculation results can form a control method to achieve stable and efficient grid-connected operation, D out The output current value of the inverter. This unit is mainly used to achieve accurate control of the output current of a single grid-connected inverter. Its goal is to quickly and accurately adjust the actual output current of the inverter to the reference current to ensure that the inverter can supply power to the grid according to the predetermined current value. adj(n) To adjust the output current value of inverter n, this unit is used to achieve uniform distribution of output current between inverters in the parallel inverter system. Its goal is to dynamically adjust the control parameters of each inverter according to the total current and the actual output current of each inverter, so that the output current of each inverter can be distributed in a predetermined proportion or evenly. refis the voltage reference value, is the frequency reference value. This unit is mainly used to realize the comprehensive regulation of grid voltage and frequency by the grid-connected inverter system. Its goal is to dynamically adjust the output voltage and frequency of the inverter according to the output current of the inverter and the system parameters to track the voltage and frequency changes of the grid. ref and P ref The calculation results can also affect the feedback to D out and D adj(n) The calculation makes the three algorithms of this system have a high correlation and entanglement, so that the overall algorithm system can perform automatic feedback and optimization according to the actual situation to be closer to reality.

[0076] See also Figures 1 to 4 , the calculation formula of the single inverter current control unit is as follows:

[0077] D out =D ref +B p (D ref -D actual )+B i *D errorl ;

[0078] D errorl =f(D ref -D actual )dt;

[0079] in:

[0080] D out is the inverter output current value;

[0081] D ref is the current reference value;

[0082] B p is the proportional gain value, B i is the integral gain value, B p and B i Used to adjust the response speed and steady-state error of the controller;

[0083] D actual is the actual measured current value;

[0084] D errorl is the current error integral value;

[0085] f(D ref -D actual )dt represents the total current error accumulated over time from a certain moment to the current moment.

[0086] In this embodiment: First, in this algorithm unit, D refD is the current reference value, which is usually given by the upper control strategy or dispatch center of the system and is used to specify the current that the inverter should output. It is calculated based on system load forecast, energy management strategy and grid dispatch instructions. actual The actual measured current value is obtained by real-time measurement of the current sensor installed at the output end of the inverter, which reflects the current output current state of the inverter. p is the proportional gain value, B i is the integral gain value. These two parameters are the design parameters of the PI controller and are usually determined through system identification, simulation and experimental debugging. ref -D actual )dt is used to eliminate the steady-state error of the system, that is, when the system reaches a stable state, if there is still a small error, the integral term will continue to accumulate and adjust the control signal until the error is completely eliminated. Integral control helps to reduce or eliminate the steady-state error of the system and improve the control accuracy and stability of the system. Due to the response delay of the inverter and the inertia of the system itself, simple proportional control cannot quickly eliminate the error. Integral control helps to deal with these delays by accumulating errors and continuously adjusting the control signal. In addition, this algorithm unit uses a PI (proportional-integral) controller to adjust the inverter output current so that it can quickly and accurately track the given value, that is, the inverter output current value D out ;

[0087] This algorithm unit uses the proportional gain value B p The sum is the integral gain value B i The combined effect of the two links can effectively eliminate steady-state errors and improve the accuracy of the inverter output current. The proportional link can quickly respond to current deviations, while the integral link can gradually eliminate accumulated deviations. The combination of the two enables the inverter to quickly adjust the output current when the grid voltage fluctuates and the load changes to maintain system stability and enhance dynamic response. In addition, precise current control helps reduce the interaction between the inverter and the grid, reduce harmonic generation, and improve the overall stability of the system.

[0088] See also Figures 1 to 4 , the calculation formula of the current distribution control unit between parallel inverters is as follows:

[0089]

[0090] in:

[0091] D adj(n) is the output current value of inverter n after adjustment;

[0092] α is the distribution coefficient, which is used to adjust the sensitivity of current distribution;

[0093] D totalis the total system demand current value;

[0094] N is the total number of parallel inverters.

[0095] In this embodiment, first, D total is the total system demand current value, which is calculated by measuring the total current on the grid side and according to the system load forecast and dispatch instructions. N is the total number of parallel inverters, which is a fixed system parameter, indicating how many inverters are running in parallel. In other words, the control method of the grid-connected inverter is a device that feeds one network in parallel with two or more generators, converters and transformers. Under the distribution control of the current distribution sensitivity adjusted by the distribution coefficient α, this unit outputs the adjusted inverter n output current value D adj(n) ;

[0096] In a multi-inverter parallel system, it is necessary to calculate the current that each inverter should share. This is usually done by measuring the output current of other inverters, such as ∑m≠n D out (m) and is achieved by subtracting these currents from the total demand current;

[0097] This algorithm unit can ensure the uniform distribution of the output current of each inverter in the parallel inverter system through the distribution control of the current distribution control unit between parallel inverters, avoid the situation where some inverters are overloaded while other inverters are underloaded, improve the overall efficiency and stability of the system, and achieve balanced current distribution. When adding or reducing inverters in the system, the control strategy can automatically adjust the output current of each inverter without manual intervention, thereby improving the scalability and flexibility of the system. By optimizing the current distribution, it can reduce the redundant configuration of the inverter and reduce the system cost.

[0098] See also Figures 1 to 4 , the calculation formula of the system voltage and frequency comprehensive adjustment unit is as follows:

[0099]

[0100] in:

[0101] V ref is the voltage reference value;

[0102] V nom is the rated voltage value;

[0103] γ is the voltage regulation coefficient, which is used to adjust the voltage regulation intensity;

[0104] D reted is the rated current value of the inverter;

[0105] P ref is the frequency reference value;

[0106] Pnom is the rated frequency value;

[0107] σ is the frequency adjustment coefficient, and σ is used to adjust the frequency adjustment intensity;

[0108] TD is the system capacitance value;

[0109] LF is the sampling period value;

[0110] LF nom It is the ideal charge and discharge cycle value.

[0111] In this embodiment, the algorithm unit first calculates the rated voltage value V nom and inverter rated current D reted , which are the basic parameters of the power grid and are usually specified by the grid operator. The voltage reference value is adjusted according to the ratio of the inverter output current to the rated current to compensate for the voltage fluctuation caused by load changes. By comparing the difference between the actual charge and discharge cycle and the ideal cycle, the frequency reference value is adjusted to maintain the system frequency stability;

[0112] Although the system voltage and frequency integrated adjustment unit directly adjusts the reference values ​​of voltage and frequency, it indirectly affects the current control in the single inverter current control unit by affecting the operating status of the entire system, including load distribution and power factor. Specifically, when the voltage and frequency deviate from the rated values, the system's load characteristics and power requirements will change, which in turn affects the current that the inverter needs to output. This impact is indirect and dynamic, and involves the interaction of multiple control loops.

[0113] This algorithm unit monitors the output current and system parameters of the inverter in real time and dynamically adjusts the output voltage and frequency of the inverter, which can ensure the synchronization of the inverter output with the grid voltage and frequency, improve the stability and reliability of the system, and when the grid voltage and frequency fluctuate, the inverter can quickly respond and adjust the output voltage and frequency to maintain synchronous operation with the grid, enhance the inverter's adaptability to the grid, and optimize the inverter's operating efficiency, reduce energy loss, and improve the overall performance of the system by comprehensively adjusting the voltage and frequency. At the same time, it also helps to reduce harmonic generation and improve power quality.

[0114] See also Figures 1 to 4 , the voltage reference value V output by the system voltage and frequency comprehensive adjustment unit ref and frequency reference value P ref , which changes the overall operating status of the system. The specific changes have the following impacts:

[0115] 1. Voltage reference value V ref Impact

[0116] S1, when the voltage reference value V ref When the voltage changes, the output voltage of the inverter will be adjusted accordingly. Since the inverter is usually designed to work within a specific voltage range, the voltage change affects the output current characteristics of the inverter, which include the maximum output current and efficiency.

[0117] S2. If the resulting voltage adjustment causes the inverter to approach its voltage limit, it is considered necessary to adjust the voltage reference value V ref To avoid overvoltage and undervoltage conditions;

[0118] 2. Frequency reference value P ref Impact

[0119] S1, when the frequency reference value P ref When it deviates from the rated value, the load demand and power factor of the system are considered to change;

[0120] S2. The above changes will indirectly affect the output current demand of the inverter. For example, if the frequency reference value P ref If the decrease leads to an increase in system load, it is considered necessary to increase the output current of the inverter to meet the load demand.

[0121] In this embodiment, the algorithm unit is based on the voltage reference value V ref and frequency reference value P ref Adapt to changes and track the overall operating status of the system.

[0122] In the specific implementation process, the system voltage and frequency comprehensive adjustment unit adjusts the system voltage reference value V ref and frequency reference value P ref , so that the entire grid-connected inverter system can better adapt to changes in the power grid. When the grid voltage and frequency fluctuate, the system can quickly respond and adjust the output voltage and frequency to keep synchronization with the grid. This synchronization is crucial for a single inverter because it ensures the stability and controllability of the inverter output current. When the system voltage and frequency are stable, the current output of the single inverter under the control of the single inverter current control unit will also be more stable, reducing the current fluctuations and errors caused by grid fluctuations, thereby improving the overall stability of the system;

[0123] The voltage regulation part in the system voltage and frequency comprehensive adjustment unit is closely related to the inverter output current. By adjusting the reference value of the system voltage, the amplitude and phase of the inverter output current can be indirectly affected. This influence helps to optimize the current control process in the single inverter current control unit, making the inverter output current closer to the current reference value D. ref, thereby improving the accuracy of current control, especially when the load changes and the power grid fluctuates, the timely adjustment of the system voltage can ensure the rapid response and accurate tracking of the inverter output current, and reduce current errors and fluctuations.

[0124] The frequency regulation part in the system voltage and frequency comprehensive adjustment unit is closely related to the dynamic response capability of the system. By adjusting the reference value of the system frequency, the frequency and phase change speed of the inverter output current can be affected, thereby enhancing the dynamic response capability of the system. When the grid frequency changes and the system needs to respond quickly to load changes, timely adjustment of the system frequency can ensure rapid adjustment of the inverter output current and maintain synchronous operation with the grid. This rapid response capability is crucial to improving the stability and reliability of the system.

[0125] As a system-level comprehensive adjustment method, the system voltage and frequency comprehensive adjustment unit not only focuses on the current control performance of a single inverter, but also considers the voltage, frequency and power balance of the entire system. By comprehensively adjusting the reference values ​​of the system voltage and frequency, it can optimize the operating state of the entire system and improve the overall performance of the system. This overall performance improvement helps to reduce the system's energy loss, reduce harmonic content, and improve power quality and reliability. At the same time, it also helps to extend the service life of the inverter and the entire system.

[0126] For example 2, please refer to Figures 1 to 4 ,The single inverter current control unit introduces a PI controller in the control process, specifically a proportional-integral controller, which is used to eliminate harmonics of a specific frequency;

[0127] The current distribution control unit between parallel inverters and the system voltage and frequency comprehensive adjustment unit affect the adjustment of control parameters due to the introduction of grid impedance parameters.

[0128] In this embodiment, the single inverter current control unit introduces a PI controller in the calculation process in order to better eliminate harmonics of a specific frequency, including harmonics of integer multiples of the grid frequency, and the parallel inverter current distribution control unit and the system voltage and frequency comprehensive adjustment unit introduce grid impedance parameters in order to improve the inverter's ability to respond to changes in grid impedance. The estimated value of the grid impedance can be introduced into the control algorithm, and the control parameters can be adjusted accordingly. The control parameters include a proportional gain value B p , integral gain value B i , allocation coefficient α, voltage regulation coefficient γ, frequency regulation coefficient σ. This adjustment can be real-time or based on prediction and adaptive algorithms.

[0129] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A control method for a grid-connected inverter, characterized in that: The specific control method is as follows: According to the grid connection requirements and grid status, and through the initial control module, set the reference current of the inverter output and set other control parameters. The control parameters include the proportional gain value B p , integral gain value B i , distribution coefficient α, voltage regulation coefficient γ, frequency regulation coefficient σ; By monitoring the distribution and regulation module, under the condition of filtering harmonics, the inverter output current value D is monitored in real time. out And the adjusted inverter n output current value D of each inverter output adj(n) , and after introducing the grid impedance parameters, adjust the control parameters of each inverter, so that the output current of each inverter is distributed according to a preset ratio, monitor the voltage and frequency of the grid in real time, and adjust the output voltage and frequency of the inverter accordingly to track the adjusted voltage and frequency values. The monitoring distribution and adjustment module includes a single inverter current control unit, a current distribution control unit between parallel inverters, and a system voltage and frequency comprehensive adjustment unit; Data upload: upload real-time detection data and control parameters to the data acquisition terminal.

2. The control method of the grid-connected inverter according to claim 1, characterized in that: The equipment used by the initial control module includes sensors, including current sensors, voltage sensors and frequency sensors, which are used to monitor the inverter output current, grid voltage and frequency parameters; The equipment used in the monitoring distribution and regulation module includes a controller, a power switch tube, a resonant controller and an auxiliary circuit.

3. The control method of the grid-connected inverter according to claim 2, characterized in that: The calculation formula of the single inverter current control unit is as follows: D out =D ref +B p (D ref -D actual )+B i *D errorl ; D errorl =f(D ref -D actual )dt; in: D out is the inverter output current value; D ref is the current reference value; B p is the proportional gain value, B i is the integral gain value, B p and B i Used to adjust the response speed and steady-state error of the controller; D actual is the actual measured current value; D errorl is the current error integral value; f(D ref -D actual )dt represents the total current error accumulated over time from a certain moment to the current moment.

4. The control method of the grid-connected inverter according to claim 3, characterized in that: The calculation formula of the current distribution control unit between the parallel inverters is as follows: in: D adj(n) is the output current value of inverter n after adjustment; α is the distribution coefficient, which is used to adjust the sensitivity of current distribution; D total is the total system demand current value; N is the total number of parallel inverters.

5. The control method of the grid-connected inverter according to claim 4, characterized in that: The calculation formula of the system voltage and frequency comprehensive adjustment unit is as follows: in: V ref is the voltage reference value; V nom is the rated voltage value; γ is the voltage regulation coefficient, which is used to adjust the voltage regulation intensity; D reted is the rated current value of the inverter; P ref is the frequency reference value; P nom is the rated frequency value; σ is the frequency adjustment coefficient, and σ is used to adjust the frequency adjustment intensity; TD is the system capacitance value; LF is the sampling period value; LF nom It is the ideal charge and discharge cycle value.

6. The control method of the grid-connected inverter according to claim 5, characterized in that: The voltage reference value V output by the system voltage and frequency comprehensive adjustment unit ref and frequency reference value P ref , changing the overall operating state of the system; include: For voltage reference V ref Impact: When the voltage reference value V ref When the voltage changes, the output voltage of the inverter will be adjusted accordingly. Since the inverter is usually designed to work within a specific voltage range, the voltage change affects the output current characteristics of the inverter, which include the maximum output current and efficiency. If the resulting voltage regulation causes the inverter to approach its voltage limit, the voltage reference V ref To avoid overvoltage and undervoltage conditions; as well as, Frequency reference value P ref Impact: When the frequency reference value P ref When it deviates from the rated value, the load demand and power factor of the system are considered to change; The above changes will indirectly affect the output current demand of the inverter. If the frequency reference value P ref If the voltage drops and the system load increases, the output current of the inverter increases to meet the load demand.

7. The control method of the grid-connected inverter according to claim 6, characterized in that: The voltage reference value V ref and the frequency reference value P ref The changed operating state of the entire system is directly fed back to each part of the system, including the current control loop of the inverter. On the basis of maintaining system stability and power quality, it is considered necessary to adapt to changes in voltage and frequency by adjusting the current control strategy, including changing the parameters of the PI controller and introducing new control algorithms.

8. The control method of the grid-connected inverter according to claim 2, characterized in that: The controller includes a digital signal processor and a field programmable gate array, which are used to implement the control algorithm and PWM modulation function; The power switch tube includes an insulated gate bipolar transistor and a metal-oxide semiconductor field effect transistor, which are used for power conversion of the inverter; The auxiliary circuit includes a filtering circuit, a protection circuit and a communication circuit.

9. The control method of the grid-connected inverter according to claim 7, characterized in that: The single inverter current control unit introduces a PI controller, specifically a proportional-integral controller, in the control process to eliminate harmonics of a specific frequency; The current distribution control unit between parallel inverters and the system voltage and frequency comprehensive adjustment unit affect and adjust control parameters due to the introduction of grid impedance parameters.

Images