Networking inverter control method for improving transient stability performance

Abstract

The invention discloses a network construction inverter control method for improving transient stability performance, and the method comprises the steps: comparing the current state data, monitored in real time, of a network construction inverter grid-connected system with a state data threshold value, and adjusting the virtual parameters of an active ring in a network construction inverter after determining that the grid-connected system is in a non-ideal power grid state. The method comprises the following steps of: performing amplitude limiting processing on the adjusting current through a current amplitude limiter, and generating a corresponding modulation signal according to the obtained modulation current to be input into the grid-forming inverter grid-connected system so as to keep the grid-forming inverter grid-connected system stable. Through adjustment of virtual parameters in the active ring, limitation of output angular frequency overshoot of the active ring is realized, the recovery efficiency of the active ring is improved, and the transient stability of the grid-forming inverter and the efficiency of the grid-forming inverter for rapidly recovering from a non-ideal power grid state are indirectly improved; and the operation reliability and safety of the grid-forming inverter are improved through the current amplitude limiter.

Description

Technical Field

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

[0002] As energy and environmental pollution problems become increasingly serious, traditional fossil energy has gradually been unable to meet the needs of industrial applications. At this time, renewable energy, mainly wind and solar power, has received widespread attention. Today, the AC power transmission and distribution system is in a transition period from centralized power generation to distributed power generation, and more and more traditional generators are being replaced by distributed energy. However, since the distributed power generation system does not have the inertia and damping inherent in traditional synchronous machines, the system's ability to respond to external interference and fluctuations has been greatly reduced, and its own stability will also be significantly reduced.

[0003] To this end, a grid-forming inverter (GFI) based on virtual synchronous generator (VSG) control came into being. By adopting VSG control, GFI has a certain damping and inertia, thereby improving the inverter's own power oscillation and frequency fluctuation suppression capabilities, thereby improving system stability. However, although GFI realizes the simulation of traditional synchronous machines through VSG, it also inevitably inherits its shortcomings, causing the inverter to be more prone to transient instability and overcurrent shock when abnormal conditions occur in the system. Especially under extreme non-ideal grid conditions, these problems may seriously affect the safe and stable operation of GFI, and even cause great damage to the stability performance of the entire system. Although some technical studies in the prior art have introduced virtual resistors in VSG to solve the overcurrent problem during the grid voltage sag, the introduction of virtual resistors can easily cause power oscillations in the system after the grid resumes normal operation, greatly reducing the transient stability performance of the system. Summary of the invention

[0004] The present invention provides a grid-connected inverter control method for improving transient stability performance, so as to achieve the technical effect of improving the fault ride-through capability of a grid-connected system under non-ideal conditions and the transient stability performance of the system itself.

[0005] In order to solve the above technical problems, an embodiment of the present invention provides a grid-connected inverter control method for improving transient stability performance, comprising the following steps:

[0006] Real-time monitoring and acquisition of current state data of the grid-connected inverter system, comparison of the current state data with a preset state data threshold, and determination of whether the grid-connected inverter system is in a non-ideal grid state based on the comparison result;

[0007] If it is determined according to the comparison result that the grid-connected system is in a non-ideal grid state, the virtual parameters of the active loop in the preset grid-connected inverter are numerically adjusted so that the angular frequency output by the adjusted active loop adjusts the reference current output by the voltage loop accordingly to obtain the adjusted current;

[0008] The adjustment current is limited and adjusted by a current limiter to obtain a corresponding modulation current, and a corresponding modulation signal is generated according to the modulation current and input into the grid-connected inverter system to keep the grid-connected inverter system stable.

[0009] The grid-connected inverter control method for improving transient stability performance provided by the present invention monitors the current state data of the grid-connected inverter system in real time, and compares it with the state data threshold, and then determines whether the grid-connected inverter system is in a non-ideal grid state according to the judgment result, that is, determines whether the grid-connected inverter system needs to perform fault ride-through control. Only when it is determined that the grid-connected inverter system is in a non-ideal grid state, the system starts the fault ride-through control of the grid-connected inverter.

[0010] If it is determined that the grid-connected system of the grid-connected inverter is in a non-ideal grid state, the system will numerically adjust the virtual parameters in the active loop in the grid-connected inverter, i.e., the grid-connected controller, and thereby adjust the output angular frequency of the active loop, thereby adjusting the reference current value output by the voltage loop accordingly. Since the grid-connected system is in a non-ideal state, the common point voltage between it and the grid-connected inverter will drop significantly, so both the active loop and the reactive loop in the grid-connected inverter will collapse. Therefore, the system can limit the overshoot of the active loop output angular frequency by timely adjusting the virtual parameters in the active loop, ensuring that the fluctuation of the active loop output angular frequency will be strongly constrained, and then further improving the efficiency of the active loop to resume normal operation, and also ensuring the system's fault ride-through control capability when the grid-connected system is in a non-ideal state, and improving the grid-connected inverter's transient stability performance for the grid-connected system and itself, as well as the efficiency of rapid recovery from non-ideal grid states.

[0011] After adjusting the reference current output by the voltage loop through the angular frequency output after the active loop parameters are adjusted, the system will also limit the adjusted current through the current limiter to avoid the overcurrent shock that may occur during the fault ride-through control and cause the grid inverter system to be burned, thereby improving the operating reliability and safety of the grid inverter.

[0012] The modulated current obtained after the current limiting processing is converted into a corresponding modulation signal, and transmitted to the grid-connected inverter system, so as to ensure the balance of transmission power and transmission voltage between the grid-connected inverter system and the grid-connected inverter, provide voltage source support for the grid-connected inverter system throughout the whole process, improve the stability of the voltage and frequency of the power system, and also improve the new energy absorption capacity and power supply quality of the grid-connected inverter system.

[0013] As a preferred example, the current state data is compared with a preset state data threshold, and judging whether the grid-connected inverter system is in a non-ideal grid state according to the comparison result, specifically includes:

[0014] Comparing the current voltage amplitude in the current state data with the lower limit of the voltage fluctuation range to obtain a first comparison result;

[0015] When the first comparison result is that the current voltage amplitude is less than the lower limit of the voltage fluctuation range, it is determined that the grid-connected system of the grid-connecting inverter is in an abnormal state, and further parameters and state judgment are performed on the grid-connecting inverter.

[0016] In order to improve the accuracy of judging the current state of the grid-connected inverter system, the system first compares the current voltage amplitude of the grid-connected inverter system with the lower limit of the voltage fluctuation range of the grid-connected inverter system, and judges the current state of the grid-connected inverter system based on the comparison result, that is, judges whether the current voltage amplitude fluctuation value of the grid-connected inverter system is within the allowable fluctuation range.

[0017] If the comparison result shows that the current voltage amplitude is less than the lower limit of the voltage fluctuation range, it means that the current voltage amplitude of the grid-connected system of the grid-connected inverter is no longer within the allowable range of voltage fluctuation, which means that the voltage fluctuation value of the grid-connected system is already in an abnormal state. It is necessary to further collect parameters and judge the state of the grid-connected inverter to determine whether the grid-connected system is in a non-ideal grid state, that is, whether the system needs to enable fault ride-through control of the grid-connected inverter.

[0018] As a preferred example, the current state data is compared with a preset state data threshold, and judging whether the grid-connected inverter system is in a non-ideal grid state according to the comparison result, further includes:

[0019] When the first comparison result is that the current voltage amplitude is greater than or equal to the lower limit of the voltage fluctuation range, it is determined that the grid-connected inverter system is in a normal operating state.

[0020] If the comparison result shows that the current voltage amplitude is greater than or equal to the lower limit of the fluctuation range, it means that the current voltage amplitude of the grid-connected system of the grid-connected inverter is still within the allowable range of voltage fluctuation, which means that the voltage fluctuation of the grid-connected system is in normal operation. No further operations are required and the current operating state can be maintained.

[0021] As a preferred example, the further performing of parameter collection and status judgment on the grid-connected inverter is specifically as follows:

[0022] Acquiring a current output angular frequency of the active loop in the grid-connected inverter, and comparing the current output angular frequency with a preset angular frequency threshold to obtain a second comparison result;

[0023] When the second comparison result is that the current output angular frequency is greater than the angular frequency threshold, it is determined that the grid-connected inverter system is in a non-ideal grid state.

[0024] In order to further ensure the accuracy of the system's judgment on the current state of the grid-connected system, after determining that the amplitude of the current voltage fluctuation of the grid-connected system is greater than the allowable range of voltage fluctuation, the system will further judge the current output angular frequency of the active loop in the grid-connected inverter to determine whether it has exceeded the threshold of the output angular frequency of the active loop.

[0025] If the result of the judgment is that the current output angular frequency of the active loop is greater than the angular frequency threshold, it means that the active loop has changed to positive feedback operation, and according to the normal operation logic of the grid-connected inverter, it can be determined that when the active loop continues to operate, the modulation angle of its output will be continuously integrated, which will cause the active loop to collapse. Therefore, in order to avoid the continuous integration of the modulation angle output by the active loop, which will cause the active loop to collapse and affect the operation of the grid-connected system, after the system detects and determines that the angular frequency of the active loop output has reached the angular frequency threshold, it determines that the grid-connected system of the grid-connected inverter is in a non-ideal grid state, and needs to turn on the fault ride-through function to stabilize the operation of the grid-connected system as soon as possible.

[0026] As a preferred example, the further performing parameter collection and status judgment on the grid-connected inverter further includes:

[0027] When the second comparison result is that the current output angular frequency is less than or equal to the angular frequency threshold, it is determined that the grid-connected inverter system is in an abnormal voltage state, and a corresponding abnormal voltage alarm is triggered.

[0028] If the second comparison result shows that the current output angular frequency of the active loop is less than or equal to the angular frequency threshold, it means that the active loop has not yet entered the positive feedback operation, that is, the grid-connected inverter grid-connected system has not completely entered the non-ideal grid state, but only the voltage of the grid-connected system is in an abnormal state. Therefore, the system will trigger a voltage abnormality alarm prompt to remind the maintenance personnel of the grid-connected system to troubleshoot the voltage problem of the grid-connected system, thereby improving the voltage fault maintenance efficiency of the system and also improving the accuracy of system fault judgment.

[0029] As a preferred example, the numerical adjustment of the virtual parameters of the active loop in the preset grid-connected inverter specifically includes:

[0030] The virtual inertia and virtual damping of the active loop in the grid-connected inverter are numerically adjusted by using a preset virtual damping amplification factor and a virtual inertia amplification factor, so that the adjusted values ​​of the virtual damping and the virtual inertia are amplified, and the integrator in the active loop is reset.

[0031] In order to stabilize the operation state of the grid-connected system as quickly as possible and improve the transient stability performance of the system, the fault ride-through control method provided by the present invention realizes the function of limiting the overshoot of the output angular frequency of the active loop by increasing the specific values ​​of the virtual parameters including virtual damping and virtual inertia in the active loop of the grid-connected inverter. Resetting the integrator in the active loop also improves the effect of limiting the overshoot of the output angular frequency of the active loop.

[0032] As a preferred example, the current limiter is used to limit the adjustment current, specifically:

[0033] Performing square sum calculation on the adjusted current to obtain a calculation result, and comparing the calculation result with a preset current limiting threshold to obtain a corresponding comparison result;

[0034] When the comparison result is that the calculation result is greater than or equal to the current limiting threshold, the adjustment current is adjusted according to the current limiting threshold to obtain the modulation current.

[0035] In order to avoid the situation where the overcurrent shock that may exist during the fault ride-through control process of the grid-connected inverter may cause the circuit to burn out, the fault ride-through control method provided by the present invention uses a current limiter to limit the calculation result of the square sum of the adjusted current, that is, compare the calculation result with the current limiting threshold of the current limiter to determine whether the calculation result exceeds the current limiting threshold of the current limiter.

[0036] If it is determined that the calculation result exceeds the current limiting threshold of the current limiter, it is necessary to limit the adjustment current, that is, adjust the adjustment current according to the current limiting threshold. By directly adjusting the current amplitude of the adjustment current, it is ensured that the modulation current output by the grid-connected inverter to the grid-connected system will not cause damage to the circuit, thereby improving the current limiting accuracy of the current limiter.

[0037] As a preferred example, the limiting adjustment of the adjustment current by a current limiter further includes:

[0038] When the comparison result is that the calculation result is less than the current limiting threshold, the adjustment current is adjusted according to the calculation result of the adjustment current to obtain the modulation current.

[0039] If the calculated result does not exceed the current limiting threshold, there is no need to enable the current limiter to limit the adjusted current, and the adjusted current can be directly output as the modulation current.

[0040] Accordingly, an embodiment of the present invention further provides a grid-connected inverter control device for improving transient stability performance, wherein the fault ride-through control device includes a grid-connected data monitoring module, a model parameter adjustment module, and a modulation current output module;

[0041] The grid-connected data monitoring module is used to monitor and obtain the current state data of the grid-connected inverter system in real time, compare the current state data with a preset state data threshold, and determine whether the grid-connected inverter system is in a non-ideal grid state according to the comparison result;

[0042] The model parameter adjustment module is used to adjust the virtual parameters of the active loop in the preset grid-connected inverter numerically if it is determined according to the comparison result that the grid-connected system is in a non-ideal grid state, so that the angular frequency output by the adjusted active loop adjusts the reference current value output by the voltage loop accordingly to obtain the adjusted current;

[0043] The modulation current output module is used to limit the adjustment current through a current limiter to obtain a corresponding modulation current, and generate a corresponding modulation signal according to the modulation current and input it into the grid-connected inverter system to keep the grid-connected inverter system stable.

[0044] As a preferred example, the grid-connected data monitoring module compares the current state data with a preset state data threshold, and determines whether the grid-connected inverter grid-connected system is in a non-ideal grid state according to the comparison result, specifically including:

[0045] Comparing the current voltage amplitude in the current state data with the lower limit of the voltage fluctuation range to obtain a first comparison result;

[0046] If the first comparison result is that the current voltage amplitude is less than the lower limit of the voltage fluctuation range, it is determined that the grid-connected system of the grid-connected inverter is in an abnormal state, and further parameters are collected and the state is determined for the grid-connected inverter;

[0047] If the first comparison result is that the current voltage amplitude is greater than or equal to the lower limit of the voltage fluctuation range, it is determined that the grid-connected inverter system is in normal operation.

[0048] As a preferred example, the grid-connected data monitoring module further performs parameter collection and status judgment on the grid-connected inverter, specifically:

[0049] Acquiring a current output angular frequency of the active loop in the grid-connected inverter, and comparing the current output angular frequency with a preset angular frequency threshold to obtain a second comparison result;

[0050] If the second comparison result is that the current output angular frequency is greater than the angular frequency threshold, it is determined that the grid-connected inverter system is in a non-ideal grid state;

[0051] If the second comparison result is that the current output angular frequency is less than or equal to the angular frequency threshold, it is determined that the grid-connected inverter system is in an abnormal voltage state, and a corresponding abnormal voltage alarm is triggered.

[0052] As a preferred example, the model parameter adjustment module numerically adjusts the virtual parameters of the active loop in the preset grid-connected inverter, specifically including:

[0053] The virtual inertia and virtual damping of the active loop in the grid-connected inverter are numerically adjusted by using a preset virtual damping amplification factor and a virtual inertia amplification factor, so that the adjusted values ​​of the virtual damping and the virtual inertia are amplified, and the integrator in the active loop is reset.

[0054] As a preferred example, the modulation current output module performs amplitude limiting adjustment on the adjustment current through a current limiter, specifically:

[0055] Performing square sum calculation on the adjusted current to obtain a calculation result, and comparing the calculation result with a preset current limiting threshold to obtain a corresponding comparison result;

[0056] If the comparison result is that the calculation result is greater than or equal to the current limiting threshold, adjusting the adjustment current according to the current limiting threshold to obtain the modulation current;

[0057] If the comparison result is that the calculation result is less than the current limiting threshold, the adjustment current is adjusted according to the calculation result of the adjustment current to obtain the modulation current. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 : A flow chart of an embodiment of a grid-connected inverter control method for improving transient stability performance provided by the present invention;

[0059] Figure 2 : A structural diagram of an embodiment of a grid-connected inverter control device for improving transient stability performance provided by the present invention;

[0060] Figure 3 : A flow chart of another embodiment of the grid-connected inverter control method provided by the present invention;

[0061] Figure 4 : A control structure diagram of a grid-connected inverter when the grid-connected system provided by the present invention is in an ideal state;

[0062] Figure 5 : A control structure diagram of a grid-connected inverter when the grid-connected system provided by the present invention is in a non-ideal state. DETAILED DESCRIPTION

[0063] 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.

[0064] Embodiment 1

[0065] Please refer to Figure 1 , which is a flow chart of an embodiment of a grid-connected inverter control method for improving transient stability performance provided by the present invention, including steps 101 to 103, each of which is specifically as follows:

[0066] Step 101: Real-time monitoring and acquisition of current status data of a grid-connected inverter system, comparison of the current status data with a preset status data threshold, and determination of whether the grid-connected inverter system is in a non-ideal grid state based on the comparison result.

[0067] The grid-connected inverter control method for improving transient stability performance provided by the embodiment of the present invention will monitor the current state data of the grid-connected inverter system in real time, and judge it with the state data threshold, and then determine whether the grid-connected inverter system is in a non-ideal grid state according to the judgment result, that is, determine whether the grid-connected inverter system needs to perform fault ride-through control. Only when it is determined that the grid-connected inverter system is in a non-ideal grid state, the system will start the fault ride-through control of the grid-connected inverter.

[0068] Specifically, the current state data is compared with a preset state data threshold in this embodiment, and judging whether the grid-connected inverter system is in a non-ideal grid state according to the comparison result specifically includes:

[0069] Comparing the current voltage amplitude in the current state data with the lower limit of the voltage fluctuation range to obtain a first comparison result;

[0070] When the first comparison result is that the current voltage amplitude is less than the lower limit of the voltage fluctuation range, it is determined that the grid-connected system of the grid-connecting inverter is in an abnormal state, and further parameters and state judgment are performed on the grid-connecting inverter.

[0071] In order to improve the accuracy of judging the current state of the grid-connected inverter system, the system first compares the current voltage amplitude of the grid-connected inverter system with the lower limit of the voltage fluctuation range of the grid-connected inverter system, and judges the current state of the grid-connected inverter system based on the comparison result, that is, judges whether the current voltage amplitude fluctuation value of the grid-connected inverter system is within the allowable fluctuation range.

[0072] If the comparison result shows that the current voltage amplitude is less than the lower limit of the voltage fluctuation range, it means that the current voltage amplitude of the grid-connected system of the grid-connected inverter is no longer within the allowable range of voltage fluctuation, which means that the voltage fluctuation value of the grid-connected system is already in an abnormal state. It is necessary to further collect parameters and judge the state of the grid-connected inverter to determine whether the grid-connected system is in a non-ideal grid state, that is, whether the system needs to enable fault ride-through control of the grid-connected inverter.

[0073] Furthermore, the current state data is compared with a preset state data threshold value in this embodiment, and judging whether the grid-connected inverter grid-connected system is in a non-ideal grid state according to the comparison result, further includes:

[0074] When the first comparison result is that the current voltage amplitude is greater than or equal to the lower limit of the voltage fluctuation range, it is determined that the grid-connected inverter system is in a normal operating state.

[0075] If the comparison result shows that the current voltage amplitude is greater than or equal to the lower limit of the fluctuation range, it means that the current voltage amplitude of the grid-connected system of the grid-connected inverter is still within the allowable range of voltage fluctuation, which means that the voltage fluctuation of the grid-connected system is in normal operation. No further operations are required and the current operating state can be maintained.

[0076] Furthermore, the present embodiment further performs parameter collection and status judgment on the grid-connected inverter, specifically:

[0077] Acquiring a current output angular frequency of the active loop in the grid-connected inverter, and comparing the current output angular frequency with a preset angular frequency threshold to obtain a second comparison result;

[0078] When the second comparison result is that the current output angular frequency is greater than the angular frequency threshold, it is determined that the grid-connected inverter system is in a non-ideal grid state.

[0079] In order to further ensure the accuracy of the system's judgment on the current state of the grid-connected system, after determining that the amplitude of the current voltage fluctuation of the grid-connected system is greater than the allowable range of voltage fluctuation, the system will further judge the current output angular frequency of the active loop in the grid-connected inverter to determine whether it has exceeded the threshold of the output angular frequency of the active loop.

[0080] If the result of the judgment is that the current output angular frequency of the active loop is greater than the angular frequency threshold, it means that the active loop has changed to positive feedback operation, and according to the normal operation logic of the grid-connected inverter, it can be determined that when the active loop continues to operate, the modulation angle of its output will be continuously integrated, which will cause the active loop to collapse. Therefore, in order to avoid the continuous integration of the modulation angle output by the active loop, which will cause the active loop to collapse and affect the operation of the grid-connected system, after the system detects and determines that the angular frequency of the active loop output has reached the angular frequency threshold, it determines that the grid-connected system of the grid-connected inverter is in a non-ideal grid state, and needs to turn on the fault ride-through function to stabilize the operation of the grid-connected system as soon as possible.

[0081] Furthermore, the further parameter collection and status judgment of the grid-connected inverter described in this embodiment also includes:

[0082] When the second comparison result is that the current output angular frequency is less than or equal to the angular frequency threshold, it is determined that the grid-connected inverter system is in an abnormal voltage state, and a corresponding abnormal voltage alarm is triggered.

[0083] If the second comparison result shows that the current output angular frequency of the active loop is less than or equal to the angular frequency threshold, it means that the active loop has not yet entered the positive feedback operation, that is, the grid-connected inverter grid-connected system has not completely entered the non-ideal grid state, but only the voltage of the grid-connected system is in an abnormal state. Therefore, the system will trigger a voltage abnormality alarm prompt to remind the maintenance personnel of the grid-connected system to troubleshoot the voltage problem of the grid-connected system, thereby improving the voltage fault maintenance efficiency of the system and also improving the accuracy of system fault judgment.

[0084] Step 102: If it is determined according to the comparison result that the grid-connected system is in a non-ideal grid state, the virtual parameters of the active loop in the preset grid-connected inverter are numerically adjusted so that the angular frequency of the adjusted active loop outputs a corresponding adjustment to the reference current output by the voltage loop to obtain the adjusted current.

[0085] If it is determined that the grid-connected system of the grid-connected inverter is in a non-ideal grid state, the system will numerically adjust the virtual parameters in the active loop in the grid-connected inverter, i.e., the grid-connected controller, and thereby adjust the output angular frequency of the active loop, thereby adjusting the reference current value output by the voltage loop accordingly. Since the grid-connected system is in a non-ideal state, the common point voltage between it and the grid-connected inverter will drop significantly, so both the active loop and the reactive loop in the grid-connected inverter will collapse. Therefore, the system can limit the overshoot of the active loop output angular frequency by timely adjusting the virtual parameters in the active loop, ensuring that the fluctuation of the active loop output angular frequency will be strongly constrained, and then further improving the efficiency of the active loop to resume normal operation, and also ensuring the system's fault ride-through control capability when the grid-connected system is in a non-ideal state, and improving the grid-connected inverter's transient stability performance for the grid-connected system and itself, as well as the efficiency of rapid recovery from non-ideal grid states.

[0086] Specifically, the numerical adjustment of the virtual parameters of the active loop in the preset grid-connecting inverter described in this embodiment specifically includes:

[0087] The virtual inertia and virtual damping of the active loop in the grid-connected inverter are numerically adjusted by using a preset virtual damping amplification factor and a virtual inertia amplification factor, so that the adjusted values ​​of the virtual damping and the virtual inertia are amplified, and the integrator in the active loop is reset.

[0088] In order to stabilize the operation state of the grid-connected system as quickly as possible and improve the transient stability performance of the system, the fault ride-through control method provided by the present invention realizes the function of limiting the overshoot of the output angular frequency of the active loop by increasing the specific values ​​of the virtual parameters including virtual damping and virtual inertia in the active loop of the grid-connected inverter. Resetting the integrator in the active loop also improves the effect of limiting the overshoot of the output angular frequency of the active loop.

[0089] Step 103: The adjustment current is limited and adjusted by a current limiter to obtain a corresponding modulation current, and a corresponding modulation signal is generated according to the modulation current and input into the grid-connected inverter system to keep the grid-connected inverter system stable.

[0090] After adjusting the reference current output by the voltage loop through the angular frequency output after the active loop parameters are adjusted, the system will also limit the adjusted current through the current limiter to avoid the overcurrent shock that may occur during the fault ride-through control and cause the grid inverter system to be burned, thereby improving the operating reliability and safety of the grid inverter.

[0091] The modulated current obtained after the current limiting processing is converted into a corresponding modulation signal, and transmitted to the grid-connected inverter system, so as to ensure the balance of transmission power and transmission voltage between the grid-connected inverter system and the grid-connected inverter, provide voltage source support for the grid-connected inverter system throughout the whole process, improve the stability of the voltage and frequency of the power system, and also improve the new energy absorption capacity and power supply quality of the grid-connected inverter system.

[0092] Specifically, in this embodiment, the current limiter is used to limit the adjustment current, specifically:

[0093] Performing square sum calculation on the adjusted current to obtain a calculation result, and comparing the calculation result with a preset current limiting threshold to obtain a corresponding comparison result;

[0094] When the comparison result is that the calculation result is greater than or equal to the current limiting threshold, the adjustment current is adjusted according to the current limiting threshold to obtain the modulation current.

[0095] In order to avoid the situation where the overcurrent shock that may exist during the fault ride-through control process of the grid-connected inverter may cause the circuit to burn out, the fault ride-through control method provided by the present invention uses a current limiter to limit the calculation result of the square sum of the adjusted current, that is, compare the calculation result with the current limiting threshold of the current limiter to determine whether the calculation result exceeds the current limiting threshold of the current limiter.

[0096] If it is determined that the calculation result exceeds the current limiting threshold of the current limiter, it is necessary to limit the adjustment current, that is, adjust the adjustment current according to the current limiting threshold. By directly adjusting the current amplitude of the adjustment current, it is ensured that the modulation current output by the grid-connected inverter to the grid-connected system will not cause damage to the circuit, thereby improving the current limiting accuracy of the current limiter.

[0097] Furthermore, the method of limiting the adjustment current by using a current limiter in this embodiment further includes:

[0098] When the comparison result is that the calculation result is less than the current limiting threshold, the adjustment current is adjusted according to the calculation result of the adjustment current to obtain the modulation current.

[0099] If the calculated result does not exceed the current limiting threshold, there is no need to enable the current limiter to limit the adjusted current, and the adjusted current can be directly output as the modulation current.

[0100] Embodiment 2

[0101] See also Figure 3 , Figure 3 A flow chart of another embodiment of the grid-connected inverter control method provided by the present invention.

[0102] like Figure 3 As shown, Figure 3 The method shown first needs to establish the GFI structure based on VSG control under ideal grid conditions. It can be determined that when the grid is in an ideal state, Figure 3 The grid-building inverter will execute the grid-building control technology based on VSG control. Since VSG mainly includes mechanical equations and electromagnetic equations based on traditional synchronous generators, the grid-building control technology based on VSG control mainly realizes the simulation of the synchronous machine by the grid-building inverter through control. The rotor motion equation equivalently obtained by the above method is as follows:

[0103]

[0104] Among them, J is the virtual inertia, ω and ω n are the synchronous machine angular velocity and the grid angular velocity, T m and T e are virtual mechanical torque and virtual electromagnetic torque respectively, D p is virtual damping.

[0105] From the above motion equation, it can be seen that by introducing virtual damping, the frequency response can be made smoother, thereby preventing drastic frequency fluctuations and maintaining the stability of the system. The mechanical torque and electromagnetic torque in the inverter are obtained from the active power command and the active power output of the inverter, respectively. The specific expressions are as follows:

[0106]

[0107] Among them, P m and P eThey are respectively the active power command and the active power output by the inverter. Similar to the synchronous generator, the grid-connected inverter also adjusts the active power actually output by the inverter by controlling the virtual mechanical torque, and on this basis, responds to the grid frequency deviation through the speed regulator to better maintain the system frequency stability. Through the above mechanism, the inverter can increase the active power output when the grid frequency decreases, and reduce the active power output when the grid frequency increases, so as to help the grid stabilize the frequency fluctuation as soon as possible. At the same time, the grid-connected inverter will also adjust the virtual potential of its own output by simulating the excitation system of the traditional synchronous generator. Therefore, when the output virtual potential, that is, the grid connection point voltage, deviates from the set value, the grid-connected inverter will adjust the output of reactive power to restore the voltage to the set value. Among them, the relevant expression of the virtual potential inside the grid-connected inverter is as follows:

[0108]

[0109] Among them, K and K q are the voltage regulation coefficient and the damping coefficient of the reactive loop, E is the virtual potential, Q m and Q e are the reactive power command and the reactive power output by the inverter, U o and U n It is the output value and command value of the inverter terminal voltage.

[0110] For details, see Figure 4 , Figure 4 The control structure diagram of the grid inverter provided by the present invention is in an ideal state. Figure 4 As shown, L f and C f are filter inductor and filter capacitor respectively, R g and L g are the equivalent resistance and equivalent inductance on the grid side, v abc and i abc are the three-phase voltage and three-phase current output by the inverter in real time. θ is the modulation angle, which is mainly used to generate the three-phase modulation wave and obtain the switching signal of the IGBT in the grid inverter after intersecting with the carrier in the pulse width modulation (PWM).

[0111] Depend on Figure 4It can be seen that VSG forms the main grid controller part of GFI, and is composed of two parts: active loop and reactive loop. Among them, the active loop mainly simulates the inertia and damping of the synchronous machine, and has a primary frequency regulation characteristic, which is used to cope with the frequency fluctuation on the grid side; the reactive loop simulates the primary voltage regulation characteristic of the synchronous machine, which is used to control the reactive power and terminal voltage output of the grid inverter, and provide certain support in the event of a grid failure. Among them, the real-time active power and reactive power output of the inverter in VSG can be obtained through instantaneous power theory calculation, and its specific expression is as follows:

[0112]

[0113] After establishing the GFI structure based on VSG control under the ideal grid, the system will set the evaluation criteria for determining the non-ideal grid state. Because the voltage of the grid changes little under the ideal grid state, its fluctuation range will not exceed the preset fluctuation range threshold, that is, the voltage fluctuates only within the allowable range. When the grid is in a non-ideal state, that is, the grid voltage drops due to a short circuit fault, or the grid frequency fluctuates greatly due to the imbalance of power load and power generation, the grid inverter will take certain measures to achieve ride-through control during the fault period and provide certain support capabilities to the grid to ensure the transient stability performance of the system.

[0114] Therefore, in order to improve the transient stability performance of GFI, the system sets the grid state evaluation criteria to facilitate the fault ride-through control of the grid inverter. In this embodiment, when the grid voltage amplitude and the active loop output angular frequency meet the following conditions, it can be determined that the grid has a fault and a certain fault ride-through control is required to ensure the safe and stable operation of the system. The conditional formula is as follows:

[0115]

[0116] Among them, v g and ω p are the real-time amplitude of the grid voltage and the angular frequency of the active loop output, v g_low and ω p_up They are respectively the lower limit of the range of allowable fluctuations in the grid voltage and the upper limit of the angular frequency allowed to be output by the active loop.

[0117] Furthermore, after determining the criteria for judging non-ideal grid conditions, the system will further design a GFI control structure that has the ability to improve transient stability performance under non-ideal grid conditions. Similar to traditional synchronous machines, the essential reason for VSG transient instability is that the active power between input and output cannot be balanced. Therefore, when the active power output of the grid-forming inverter is less than the active power command value, and the active power transmitted by the inverter reaches the transient peak value, the active loop will become a positive feedback operation. Figure 1It can be seen that when the active loop changes to positive feedback operation, the modulation angle θ will continue to integrate and eventually lead to the collapse of the active loop.

[0118] Therefore, in order to improve the transient stability performance of GFI and overcome the problem of active loop instability under power grid fault, this embodiment provides a network control method based on VSG control under non-ideal power grid state, and its specific structure is as follows: Figure 5 As shown, Figure 5 A control structure diagram of a grid-connected inverter provided by the present invention when the grid is in a non-ideal state.

[0119] See also Figure 5 It can be obtained that k D and k J are the magnification factors of virtual damping and virtual inertia respectively (k D >1,k J >1), I dref1 and I qref1 are the dq axis reference current values ​​output by the voltage loop, I dref2 and I qref2 I dref1 and I qref1 The dq axis reference current value after the limiter is applied. Figure 5 Compared with the traditional grid-building inverter, the structure of the grid-building inverter shown can flexibly change the virtual inertia and virtual damping in the active loop under the conditions of grid fault and its own abnormality. The specific implementation expression for the active loop is as follows:

[0120]

[0121] like Figure 5 As shown, when the grid-forming inverter is connected to an ideal grid, the switches S1 and S2 inside the active loop are both placed at position 1; and when the grid voltage or grid frequency is lower than the lower limit of the fluctuation range under the ideal grid state, the switches S1 and S2 inside the active loop will be adjusted to position 2, and the virtual damping and virtual inertia of the active loop will be amplified. The grid-forming inverter provided in this embodiment will reset the integrator in the active loop circuit while amplifying the virtual inertia and damping, so as to further improve the recovery rate of the active loop output angular frequency.

[0122] At the same time, the grid-forming inverter provided in this embodiment also adds a voltage and current double closed loop, which further ensures the quality of the power output by the grid-forming inverter and improves the response speed of the internal signal. The current limiter added to the voltage loop and the current loop can suppress the overcurrent shock that may be generated when the grid voltage drops, thereby avoiding the overcurrent shock from burning the core switch components inside the inverter. Among them, the current limiting expression inside the voltage and current loop is as follows:

[0123]

[0124] Among them, I max is the output current value of the limiter, and the specific expression is as follows:

[0125]

[0126] Among them, I m is the current limiting threshold of the limiter.

[0127] It can be seen from the above two formulas that the grid-connected inverter provided in this embodiment will only start the current limiting function of the current limiter when the inverter has an overcurrent, thereby limiting the maximum overcurrent to ensure that the inverter is not burned and improve the transient stability performance of the system. At the same time, since the limiter acts on the synthesized dq current amplitude, it is not directly applied to I dref1 and I qref1 Therefore, it provides a more accurate and effective current limiting for the inverter and improves the current limiting accuracy of the current limiter.

[0128] After completing the above preparations, the system can monitor the grid voltage amplitude and the active loop output angular frequency in real time, and when it is determined that the grid voltage amplitude and the active loop output angular frequency are not within the system's allowable fluctuation range, the system determines that the grid is in a non-ideal state. When the grid is in a non-ideal state, the common point voltage between the GFI and the grid will drop significantly. At this time, the active loop and reactive loop inside the inverter will lose their functions, and the angular frequency output by the active loop and the virtual potential output by the reactive loop will quickly reach saturation. Therefore, if Figure 5 As shown, the switches S1 and S2 of the active loop in the grid-forming inverter provided in this embodiment will be adjusted to position 2, the virtual damping and virtual inertia of the active loop will be rapidly amplified, and at the same time the internal integrator of the active loop will be reset to limit the overshoot of the output angular frequency of the active loop. At this time, the change rate and deviation expression of the angular frequency of the active loop are as follows:

[0129]

[0130] Through the above two formulas, the significant increase of virtual damping and virtual inertia under non-ideal grid conditions greatly limits the rate of change and deviation of the active loop angular frequency after reset, resulting in strong constraints on the angular frequency fluctuation of the inverter output under non-ideal grid conditions, thereby ensuring that the output angular frequency of the active loop itself can recover to the rated value at a higher rate. The reset of the integrator inside the active loop and the rapid increase of virtual damping and virtual inertia will ensure that the GFI can recover the synchronization with the grid angular frequency as soon as possible without the internal phase-locked loop of the grid-following inverter, so that the grid-connected inverter can quickly recover from non-ideal grid conditions when connected to the grid, improving the transient stability performance of itself and the grid system.

[0131] At the same time, the introduction of the voltage and current dual closed loop and limiter effectively ensures that the GFI will not be burned due to possible overcurrent shock during the ride-through control, further improving the operating reliability and safety of the grid-connected inverter.

[0132] In this embodiment, the system will continuously repeat the monitoring process of the grid voltage amplitude and the active loop output angular frequency to determine whether the grid has recovered stability, that is, whether the grid inverter needs to exit fault ride-through control. If it is determined that the grid voltage amplitude and the active loop output angular frequency inside the inverter are still not within the system allowable fluctuation range, it indicates that the grid is still in a non-ideal state, and the GFI needs to continue to execute the non-ideal state control structure of the grid inverter; if it is determined that the grid voltage amplitude and the active loop output angular frequency inside the inverter are already within the system allowable fluctuation range, it indicates that the grid can be approximately regarded as an ideal grid state, the limiter will return to normal state, and the switches S1 and S2 of the active loop inside the GFI will return to position 1, and continue to return to the ideal operation state of the grid.

[0133] In order to better illustrate the working principle and step flow of a grid-connected inverter control method and device for improving transient stability performance of the present invention, reference may be made to, but is not limited to, the relevant records above.

[0134] Accordingly, see Figure 2 , Figure 2 This is a structural diagram of an embodiment of a grid-connected inverter control device for improving transient stability performance provided by the present invention. Figure 2 As shown, the fault ride-through control device includes a grid-connected data monitoring module 201 , a model parameter adjustment module 202 and a modulation current output module 203 .

[0135] Among them, the grid-connected data monitoring module 201 is used to monitor and obtain the current status data of the grid-connected inverter system in real time, compare the current status data with a preset status data threshold, and determine whether the grid-connected inverter system is in a non-ideal grid state based on the comparison result.

[0136] Further, the grid-connected data monitoring module 201 compares the current state data with a preset state data threshold, and determines whether the grid-connected inverter system is in a non-ideal grid state according to the comparison result, specifically including:

[0137] Comparing the current voltage amplitude in the current state data with the lower limit of the voltage fluctuation range to obtain a first comparison result;

[0138] If the first comparison result is that the current voltage amplitude is less than the lower limit value of the voltage fluctuation range, it is determined that the grid-connected system of the grid-connected inverter is in an abnormal state, and further parameters and status judgment are performed on the grid-connected inverter; if the first comparison result is that the current voltage amplitude is greater than or equal to the lower limit value of the voltage fluctuation range, it is determined that the grid-connected system of the grid-connected inverter is in a normal operating state.

[0139] Furthermore, the grid-connected data monitoring module 201 further performs parameter collection and status judgment on the grid-connected inverter, specifically:

[0140] Acquiring a current output angular frequency of the active loop in the grid-connected inverter, and comparing the current output angular frequency with a preset angular frequency threshold to obtain a second comparison result;

[0141] If the second comparison result is that the current output angular frequency is greater than the angular frequency threshold, it is determined that the grid-connected inverter system is in a non-ideal grid state; if the second comparison result is that the current output angular frequency is less than or equal to the angular frequency threshold, it is determined that the grid-connected inverter system is in an abnormal voltage state, and a corresponding abnormal voltage alarm is triggered.

[0142] The model parameter adjustment module 202 is used to numerically adjust the virtual parameters of the active loop in the preset grid-connected inverter if it is determined according to the comparison result that the grid-connected system is in a non-ideal grid state, so that the angular frequency of the adjusted active loop outputs the reference current value of the voltage loop output accordingly to obtain the adjusted current.

[0143] Furthermore, the model parameter adjustment module 202 numerically adjusts the virtual parameters of the active loop in the preset grid-connected inverter, specifically including:

[0144] The virtual inertia and virtual damping of the active loop in the grid-connected inverter are numerically adjusted by using a preset virtual damping amplification factor and a virtual inertia amplification factor, so that the adjusted values ​​of the virtual damping and the virtual inertia are amplified, and the integrator in the active loop is reset.

[0145] The modulation current output module 203 is used to limit the adjustment current through a current limiter to obtain a corresponding modulation current, and generate a corresponding modulation signal according to the modulation current and input it into the grid-connected inverter system to keep the grid-connected inverter system stable.

[0146] Furthermore, the modulation current output module 203 performs amplitude limiting adjustment on the adjustment current through a current limiter, specifically:

[0147] Performing square sum calculation on the adjusted current to obtain a calculation result, and comparing the calculation result with a preset current limiting threshold to obtain a corresponding comparison result;

[0148] If the comparison result is that the calculation result is greater than or equal to the current limiting threshold, the adjustment current is adjusted according to the current limiting threshold to obtain the modulation current; if the comparison result is that the calculation result is less than the current limiting threshold, the adjustment current is adjusted according to the calculation result of the adjustment current to obtain the modulation current.

[0149] In summary, the embodiment of the present invention provides a control method for a grid-connected inverter that improves transient stability performance. By comparing the current state data of the grid-connected system of the grid-connected inverter with the state data threshold value, after determining that the grid-connected system is in a non-ideal grid state, the virtual parameters of the active loop in the grid-connected inverter are adjusted so that the angular frequency of its output is adjusted accordingly, and then the adjusted current is obtained. The adjusted current is limited by the current limiter to obtain the corresponding modulation current, and the corresponding modulation signal is generated according to the modulation current and input to the grid-connected system of the grid-connected inverter to keep it stable. By adjusting the virtual parameters in the active loop, the overshoot of the output angular frequency of the active loop is limited, the efficiency of the active loop restoring normal operation is improved, the fault ride-through capability of the system is ensured, and the transient stability performance of the grid-connected inverter itself and the efficiency of rapid recovery from non-ideal grid states are indirectly improved; the operation reliability and safety of the grid-connected inverter are improved by the current limiter.

[0150] The specific embodiments described above further illustrate the purpose, technical solutions and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. It is particularly pointed out that for those skilled in the art, any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the scope of protection of the present invention.

Claims

1. A grid-connected inverter control method for improving transient stability performance, characterized in that: The following steps are involved: Real-time monitoring and acquisition of current state data of the grid-connected inverter system, comparison of the current state data with a preset state data threshold, and determination of whether the grid-connected inverter system is in a non-ideal grid state based on the comparison result; If it is determined according to the comparison result that the grid-connected system is in a non-ideal grid state, the virtual parameters of the active loop in the preset grid-connected inverter are numerically adjusted so that the angular frequency output by the adjusted active loop adjusts the reference current output by the voltage loop accordingly to obtain the adjusted current; The adjustment current is limited and adjusted by a current limiter to obtain a corresponding modulation current, and a corresponding modulation signal is generated according to the modulation current and input into the grid-connected inverter system to keep the grid-connected inverter system stable.

2. A grid-connected inverter control method for improving transient stability performance according to claim 1, characterized in that: The current state data is compared with a preset state data threshold, and whether the grid-connected inverter system is in a non-ideal grid state is determined according to the comparison result, specifically: Comparing the current voltage amplitude in the current state data with the lower limit of the voltage fluctuation range to obtain a first comparison result; When the first comparison result is that the current voltage amplitude is less than the lower limit of the voltage fluctuation range, it is determined that the grid-connected system of the grid-connecting inverter is in an abnormal state, and further parameters and state judgment are performed on the grid-connecting inverter.

3. A grid-connected inverter control method for improving transient stability performance as claimed in claim 2, characterized in that: The step of comparing the current state data with a preset state data threshold, and judging whether the grid-connected inverter system is in a non-ideal grid state according to the comparison result, further includes: When the first comparison result is that the current voltage amplitude is greater than or equal to the lower limit of the voltage fluctuation range, it is determined that the grid-connected inverter system is in a normal operating state.

4. A grid-connected inverter control method for improving transient stability performance according to any one of claims 2-3, characterized in that: The further performing of parameter collection and status judgment on the grid-connected inverter is specifically as follows: Acquiring a current output angular frequency of the active loop in the grid-connected inverter, and comparing the current output angular frequency with a preset angular frequency threshold to obtain a second comparison result; When the second comparison result is that the current output angular frequency is greater than the angular frequency threshold, it is determined that the grid-connected inverter system is in a non-ideal grid state.

5. A grid-connected inverter control method for improving transient stability performance as claimed in claim 4, characterized in that: The further performing parameter collection and status judgment on the grid-connected inverter further includes: When the second comparison result is that the current output angular frequency is less than or equal to the angular frequency threshold, it is determined that the grid-connected inverter system is in an abnormal voltage state, and a corresponding abnormal voltage alarm is triggered.

6. A grid-connected inverter control method for improving transient stability performance according to any one of claims 1 to 5, characterized in that: The numerical adjustment of the virtual parameters of the active loop in the preset grid-connected inverter specifically includes: The virtual inertia and virtual damping of the active loop in the grid-connected inverter are numerically adjusted by using a preset virtual damping amplification factor and a virtual inertia amplification factor, so that the adjusted values ​​of the virtual damping and the virtual inertia are amplified, and the integrator in the active loop is reset.

7. A grid-connected inverter control method for improving transient stability performance according to any one of claims 1 to 6, characterized in that: The current limiting adjustment is performed on the adjustment current by a current limiter, specifically: Performing square sum calculation on the adjusted current to obtain a calculation result, and comparing the calculation result with a preset current limiting threshold to obtain a corresponding comparison result; When the comparison result is that the calculation result is greater than or equal to the current limiting threshold, the adjustment current is adjusted according to the current limiting threshold to obtain the modulation current.

8. A grid-connected inverter control method for improving transient stability performance as claimed in claim 7, characterized in that: The step of limiting the adjustment current by using a current limiter further includes: When the comparison result is that the calculation result is less than the current limiting threshold, the adjustment current is adjusted according to the calculation result of the adjustment current to obtain the modulation current.

Images