A super capacitor-based power distribution network voltage sag compensation circuit and method

Abstract

The application discloses a power distribution network voltage sag compensation circuit and method based on a super capacitor, comprising a super capacitor, a first three-phase inverter, a second three-phase inverter, a first transformer, a second transformer, a charging component and a control module; the input and output ends of the super capacitor are electrically connected with the DC side of the first three-phase inverter, the DC side of the second three-phase inverter and the output end of the charging component; the power grid side of the first three-phase inverter is electrically connected with the low-voltage side of the first transformer; the power grid side of the second three-phase inverter is electrically connected with the low-voltage side of the second transformer; the first transformer and the second transformer are respectively connected with a first AC bus and a second AC bus in series; and the control module is electrically connected with the control ends of the first three-phase inverter and the second three-phase inverter and the control end of the charging component. The application can quickly respond to voltage fluctuation in the power grid while controlling the cost of the equipment and guaranteeing power quality.

Description

Technical Field

[0001] This invention relates to the field of power distribution technology, and in particular to a voltage sag compensation circuit and method for power distribution networks based on supercapacitors. Background Technology

[0002] In 10kV rural power grids, voltage dips at the line ends typically affect the stability of power supply and the safe operation of the grid. This problem can be caused by a variety of factors and has a wide impact. For example, rural grid users often experience significant load fluctuations; switching operations on irrigation, aquaculture, and other electrical equipment can cause instantaneous load changes, especially during peak electricity consumption periods, which may lead to voltage dips at the line ends.

[0003] Existing solutions mostly address voltage sag compensation for individual feeders, with a common device being a dynamic voltage restorer (DVR). When a voltage dip occurs in the system, the DVR injects an AC voltage at the same frequency as the system voltage to offset the change. The amplitude of the injected voltage is the difference between the normal voltage and the fault voltage. While DVRs can effectively compensate for voltage dips, the additional inverter equipment increases costs when both feeders experience voltage dips.

[0004] Furthermore, the energy for the compensation voltage in a conventional DVR is provided by the DC side. Traditional DC energy storage units, due to factors such as battery internal resistance and chemical reaction efficiency, may incur additional energy losses when providing power support, affecting the overall system efficiency. In situations where voltage dips occur frequently, the battery charging speed may not be sufficient to meet the demands for rapid recovery. Although some high-performance batteries (such as lithium batteries) have good discharge rates, traditional lead-acid batteries and some other types of batteries perform poorly in terms of discharge rate and cannot provide sufficient current to cope with rapidly changing voltage demands in a short period of time. Summary of the Invention

[0005] The technical problem to be solved by this invention is to provide a voltage sag compensation circuit and method for power distribution networks based on supercapacitors, which can quickly respond to voltage fluctuations in the power grid while controlling equipment costs and ensuring power quality.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0007] A voltage sag compensation circuit for power distribution networks based on supercapacitors includes a supercapacitor, a first three-phase inverter, a second three-phase inverter, a first transformer, a second transformer, a charging component, and a control module.

[0008] The input and output terminals of the supercapacitor are simultaneously electrically connected to the DC side of the first three-phase inverter, the DC side of the second three-phase inverter, and the output terminal of the charging component. The grid side of the first three-phase inverter is electrically connected to the low-voltage side of the first transformer, and the grid side of the second three-phase inverter is electrically connected to the low-voltage side of the second transformer. The high-voltage side of the first transformer and the high-voltage side of the second transformer are respectively used to connect the first AC bus and the second AC bus in series. The input terminal of the charging component is used to connect to the first AC bus.

[0009] The control module is electrically connected to the control terminal of the first three-phase inverter, the control terminal of the second three-phase inverter, and the control terminal of the charging component, respectively. The control module is used to control the supercapacitor to perform voltage compensation on the first AC bus and / or the second AC bus.

[0010] To solve the above-mentioned technical problems, another technical solution adopted by the present invention is as follows:

[0011] A method for voltage sag compensation in distribution networks based on supercapacitors, applied to the aforementioned voltage sag compensation circuit for distribution networks based on supercapacitors, includes the following steps:

[0012] S1. Obtain and determine whether a voltage dip occurs on the first AC bus and / or the second AC bus based on the real-time voltage magnitude of the first AC bus and the second AC bus. If so, proceed to step S2.

[0013] S2. Control the first three-phase inverter and / or the second three-phase inverter so that the voltage of the supercapacitor is output to the first AC bus and / or the second AC bus to complete voltage sag compensation.

[0014] S3. Determine whether the real-time voltage of the first AC bus is equal to or greater than the real-time voltage requirement. If so, control the charging component to charge the supercapacitor.

[0015] The beneficial effects of this invention are as follows: It provides a voltage sag compensation circuit for power distribution networks based on supercapacitors. The circuit consists of a supercapacitor, a first three-phase inverter, a second three-phase inverter, a first transformer, and a second transformer, forming a dual-feed voltage sag compensation network connected between the first AC bus and the second AC bus. Combining the characteristics of supercapacitors—low internal resistance and high power density—when a voltage sag occurs at the end of the AC bus, the supercapacitor rapidly releases its stored energy through the three-phase inverter with a high current to compensate for the voltage drop. Two phase lines share one supercapacitor for compensation, reducing equipment costs and effectively coping with rapidly changing voltage demands, thus ensuring power quality. Attached Figure Description

[0016] Figure 1This is a circuit connection diagram of a distribution network voltage sag compensation circuit based on a supercapacitor according to the present invention.

[0017] Figure 2 This is a schematic diagram illustrating the steps of a distribution network voltage sag compensation method based on supercapacitors according to the present invention.

[0018] Figure 3 The topology of a three-phase inverter and the control block diagram of an AC voltage regulation dual closed-loop control strategy for a distribution network voltage sag compensation method based on supercapacitors according to the present invention are shown below.

[0019] Figure 4 This is a topology of a single-phase rectifier and a control block diagram of a constant current single-loop charging strategy for a distribution network voltage sag compensation method based on supercapacitors, according to the present invention.

[0020] Label Explanation:

[0021] AC1, First AC busbar; AC2, Second AC busbar;

[0022] CP, supercapacitor;

[0023] T1, First Transformer; T2, Second Transformer; T3, Third Transformer; TB, Single-phase Rectifier;

[0024] U1, the first three-phase inverter; U2, the second three-phase inverter. Detailed Implementation

[0025] To explain in detail the technical content, objectives, and effects of the present invention, the following description is provided in conjunction with the embodiments and accompanying drawings.

[0026] Please refer to Figure 1 A voltage sag compensation circuit for power distribution networks based on a supercapacitor CP includes a supercapacitor CP, a first three-phase inverter U1, a second three-phase inverter U2, a first transformer T1, a second transformer T2, a charging component, and a control module.

[0027] The input and output terminals of the supercapacitor CP are simultaneously electrically connected to the DC side of the first three-phase inverter U1, the DC side of the second three-phase inverter U2, and the output terminal of the charging component. The grid side of the first three-phase inverter U1 is electrically connected to the low-voltage side of the first transformer T1, and the grid side of the second three-phase inverter U2 is electrically connected to the low-voltage side of the second transformer T2. The high-voltage side of the first transformer T1 and the high-voltage side of the second transformer T2 are respectively used to connect the first AC bus AC1 and the second AC bus AC2 in series. The input terminal of the charging component is used to connect to the first AC bus AC1.

[0028] The control module is electrically connected to the control terminal of the first three-phase inverter U1, the control terminal of the second three-phase inverter U2, and the control terminal of the charging component, respectively. The control module is used to control the supercapacitor CP to perform voltage compensation on the first AC bus AC1 and / or the second AC bus AC2.

[0029] As can be seen from the above description, the beneficial effects of the present invention are as follows: a dual-feed voltage sag compensation network is formed by using a supercapacitor CP, a first three-phase inverter U1, a second three-phase inverter U2, a first transformer T1, and a second transformer T2 connected between the first AC bus AC1 and the second AC bus AC2. Combining the characteristics of the supercapacitor CP itself, which has low internal resistance and high power density, when a voltage sag occurs at the end of the AC bus, the supercapacitor CP can quickly release the stored electrical energy through the three-phase inverter with a high current to compensate for the voltage drop. The two phase lines share one supercapacitor CP for compensation, reducing equipment costs and effectively coping with rapidly changing voltage demands, thus ensuring power quality.

[0030] Furthermore, the charging assembly includes a single-phase rectifier TB and a third transformer T3;

[0031] The DC side of the single-phase rectifier TB is electrically connected to the input and output terminals of the supercapacitor CP, the grid side of the single-phase rectifier TB is electrically connected to the low-voltage side of the third transformer T3, and the high-voltage side of the third transformer T3 is used to connect the first AC bus AC1 in parallel.

[0032] The control module is electrically connected to the control terminal of the single-phase rectifier TB. The control module is used to slowly charge the supercapacitor CP through the single-phase rectifier TB at a preset low current.

[0033] As can be seen from the above description, in the supercapacitor CP charging section, a slow charging circuit composed of a single-phase rectifier TB and a third transformer T3 is adopted. The output current of the single-phase rectifier TB is controlled by the control module to reduce the power of the charging circuit, thereby reducing the burden on the charging equipment and the system cost. This allows the supercapacitor CP to be charged with minimal impact on the grid voltage, and it is less likely to cause load imbalance problems.

[0034] Furthermore, both the first three-phase inverter U1 and the second three-phase inverter U2 are composed of bridge inverter circuits, and the control module is electrically connected to the control terminal of the inverter switching transistor of the bridge inverter circuit.

[0035] As can be seen from the above description, the three-phase inverter section adopts a bridge inverter circuit composed of multiple inverter switching transistors, which has the advantages of high efficiency, simple structure, stability and reliability, and shows good adaptability to changes in grid load.

[0036] Furthermore, the single-phase rectifier TB is a bridge rectifier, and the control module is electrically connected to the control terminal of the rectifier switching tube of the single-phase rectifier TB.

[0037] As can be seen from the above description, the single-phase rectifier TB is a bridge rectifier, which has high rectification efficiency, simple structure and low cost.

[0038] Please refer to Figures 2 to 4 A voltage sag compensation method for distribution networks based on supercapacitor CP, applied to the aforementioned voltage sag compensation circuit for distribution networks based on supercapacitor CP, includes the following steps:

[0039] S1. Obtain and determine whether a voltage dip occurs in the first AC bus AC1 and / or the second AC bus AC2 based on the real-time voltage magnitude of the first AC bus AC1 and the second AC bus AC2. If so, proceed to step S2.

[0040] S2. Control the first three-phase inverter U1 and / or the second three-phase inverter U2 so that the voltage of the supercapacitor CP is output to the first AC bus AC1 and / or the second AC bus AC2 to complete the voltage sag compensation.

[0041] S3. Determine whether the real-time voltage of the first AC bus AC1 is equal to or greater than the real-time voltage requirement. If so, control the charging component to charge the supercapacitor CP.

[0042] As can be seen from the above description, the beneficial effects of the present invention are as follows: a dual-feed voltage sag compensation network is formed by using a supercapacitor CP, a first three-phase inverter U1, a second three-phase inverter U2, a first transformer T1, and a second transformer T2 connected between the first AC bus AC1 and the second AC bus AC2. Combining the characteristics of the supercapacitor CP itself, which has low internal resistance and high power density, when a voltage sag occurs at the end of the AC bus, the supercapacitor CP can quickly release the stored electrical energy through the three-phase inverter with a high current to compensate for the voltage drop. The two phase lines share one supercapacitor CP for compensation, reducing equipment costs and effectively coping with rapidly changing voltage demands, thus ensuring power quality.

[0043] Furthermore, it also includes:

[0044] S4. Obtain and determine whether the first AC bus AC1 and the second AC bus AC2 are unbalanced based on the real-time load demand of the first AC bus AC1 and the second AC bus AC2. If so, proceed to step S5.

[0045] S5. Control the first three-phase inverter U1 and the second three-phase inverter U2 so that the voltage of the supercapacitor CP is output to the first AC bus AC1 or the second AC bus AC2 to achieve load balance.

[0046] As can be seen from the above description, in addition to dealing with voltage dips, voltage compensation can also be performed when the voltage at the end of the first AC bus AC1 and the second AC bus AC2 drops due to changes in their respective real-time load demands, ensuring that the voltage at the end remains within the standard range and achieving load balance between the two circuits of the power grid.

[0047] Furthermore, the control charging component for charging the supercapacitor CP specifically includes:

[0048] The charging component is controlled to output a preset low current to the supercapacitor CP to complete low-current slow charging.

[0049] As can be seen from the above description, in the supercapacitor CP charging section, a slow charging circuit composed of a single-phase rectifier TB and a third transformer T3 is adopted. The output current of the single-phase rectifier TB is controlled by the control module to reduce the power of the charging circuit, thereby reducing the burden on the charging equipment and the system cost. This allows the supercapacitor CP to be charged with minimal impact on the grid voltage, and it is less likely to cause load imbalance problems.

[0050] Further, controlling the first three-phase inverter U1 and / or the second three-phase inverter U2 includes:

[0051] The first control signal obtained by the AC voltage regulation dual closed-loop control strategy is input at the control terminal of the inverter switching transistor of the first three-phase inverter U1 and / or the second three-phase inverter U2;

[0052] The AC voltage stabilization dual closed-loop control strategy includes:

[0053] The expressions for the first three-phase inverter U1 and / or the second three-phase inverter U2 in the dq coordinate system are preset as follows:

[0054]

[0055] Where ω is the synchronous rotation angular frequency, u sd u sq The Park transformation result of the power supply voltage of the first three-phase inverter U1 or the second three-phase inverter U2, u ld u lq i is the Park transformation result of the output voltage of the first three-phase inverter U1 or the second three-phase inverter U2. ld i lqThe output current of the first three-phase inverter U1 or the second three-phase inverter U2 is represented by the Park transformation result, where N represents the transformer turns ratio and L1 represents the grid-side equivalent inductance.

[0056] Preset reference values ​​for the output voltages of the first three-phase inverter U1 and / or the second three-phase inverter U2:

[0057]

[0058] Among them, u * d u * q u is a reference value for the output voltage of either the first three-phase inverter U1 or the second three-phase inverter U2. * ld This is the reference value for the load voltage;

[0059] With voltage control set as the outer loop, u * ld u sd and u * lq u sq The comparison value is used to obtain the reference value i of the output current of the first three-phase inverter U1 or the second three-phase inverter U2 through the PI regulator. * ld i * lq ;

[0060] Using current control as the inner loop and employing a proportional controller, the current loop control strategy equation can be obtained as follows:

[0061]

[0062] Among them, u rd u rq The output voltage d and q components of the current loop are represented, K represents the multiplication coefficient, s represents the complex frequency domain variable, and k iv k represents the integral coefficient. pv Indicates the proportionality coefficient;

[0063] will u * ld u * lq The first control signal is obtained by performing Park transformation and SPWM modulation.

[0064] As can be seen from the above description, in the output control section of the three-phase inverter, an AC voltage regulation dual closed-loop control strategy is adopted to control the inverter switching transistors, so that the three-phase inverter has a stable and accurate output.

[0065] Furthermore, it also includes:

[0066] Dead-time compensation is introduced into the AC voltage regulation dual closed-loop control strategy, and the dead-time compensation includes:

[0067] Calculate the average voltage error caused by the dead zone of the inverter switch over one switching cycle:

[0068]

[0069] Where ia is the output current of the current observer, sign(i a ) represents i a The polarity of i a When the value is greater than 0, the output is 1; otherwise, the output is -1. dc t is the input voltage of either the first three-phase inverter U1 or the second three-phase inverter U2. d For dead time, T s For switching cycles;

[0070] Feedforward compensation is applied to the output voltage of the first three-phase inverter U1 and / or the second three-phase inverter U2 to offset the average voltage error.

[0071] As described above, the AC voltage regulator dual-loop control strategy incorporates dead-time compensation to reduce the impact of output voltage imbalance or distortion caused by switching dead time. By adjusting the switching signal, it ensures a more accurate and stable inverter output. The combined effect of dead-time compensation and dual-loop control allows the inverter to remain inactive when the line voltage deviation is small, avoiding unnecessary losses and reducing the failure rate.

[0072] Furthermore, controlling the charging component to output a preset low current to the supercapacitor CP specifically involves:

[0073] A constant current single-loop charging strategy with the preset low current as the constant current is adopted, and a second control signal is output to the control terminal of the rectifier switching tube of the single-phase rectifier TB.

[0074] As can be seen from the above description, in the supercapacitor CP charging section, a constant current single-loop charging strategy is adopted. The current loop is used to maintain a constant current input, thereby reducing the power of the charging circuit and reducing the burden on the charging equipment and system cost.

[0075] Please refer to Figure 1 Embodiment 1 of the present invention is as follows:

[0076] A voltage sag compensation circuit for distribution networks based on a supercapacitor CP, such as Figure 1As shown, the system includes a supercapacitor CP, a first three-phase inverter U1, a second three-phase inverter U2, a first transformer T1, a second transformer T2, a charging assembly, and a control module. The input and output terminals of the supercapacitor CP are simultaneously electrically connected to the DC side of the first three-phase inverter U1, the DC side of the second three-phase inverter U2, and the output terminal of the charging assembly. The grid side of the first three-phase inverter U1 is electrically connected to the low-voltage side of the first transformer T1, and the grid side of the second three-phase inverter U2 is electrically connected to the low-voltage side of the second transformer T2. The high-voltage side of the first transformer T1 and the high-voltage side of the second transformer T2 are respectively used to connect the first AC bus AC1 and the second AC bus AC2 in series. The input terminal of the charging assembly is used to connect to the first AC bus AC1. The control module is electrically connected to the control terminals of the first three-phase inverter U1, the second three-phase inverter U2, and the charging assembly. The control module is used to control the supercapacitor CP to perform voltage compensation on the first AC bus AC1 and / or the second AC bus AC2. sa u sb u sc and i sa i sb i sc u represents the grid-side voltage and current of the AC bus. la u lb u lc and i la i lb i lc This indicates the load-side voltage and current of the AC bus.

[0077] The charging components include a single-phase rectifier TB and a third transformer T3. The DC side of the single-phase rectifier TB is electrically connected to the input and output terminals of the supercapacitor CP, and the grid side of the single-phase rectifier TB is electrically connected to the low-voltage side of the third transformer T3. The high-voltage side of the third transformer T3 is used to connect the first AC bus AC1 in parallel. The control module is electrically connected to the control terminal of the single-phase rectifier TB. The control module is used to slowly charge the supercapacitor CP through the single-phase rectifier TB at a preset low current.

[0078] Preferably, both the first three-phase inverter U1 and the second three-phase inverter U2 are composed of bridge inverter circuits, and the control module is electrically connected to the control terminal of the inverter switching transistor of the bridge inverter circuit. The single-phase rectifier TB is a bridge rectifier, and the control module is electrically connected to the control terminal of the rectifier switching transistor of the single-phase rectifier TB.

[0079] Please refer to Figures 2 through 3. Figure 4 Embodiment two of the present invention is as follows:

[0080] A voltage sag compensation method for distribution networks based on a supercapacitor CP, applied to a voltage sag compensation circuit for distribution networks based on a supercapacitor CP in Embodiment 1, includes the following steps:

[0081] S1. Obtain and determine whether a voltage dip occurs in the first AC bus AC1 and / or the second AC bus AC2 based on the real-time voltage magnitude of the first AC bus AC1 and the second AC bus AC2. If so, proceed to step S2.

[0082] S2. Control the first three-phase inverter U1 and / or the second three-phase inverter U2 so that the voltage of the supercapacitor CP is output to the first AC bus AC1 and / or the second AC bus AC2 to complete the voltage sag compensation.

[0083] In this embodiment, a first control signal obtained by the AC voltage regulation dual closed-loop control strategy is input to the control terminal of the inverter switching transistor of the first three-phase inverter U1 and / or the second three-phase inverter U2.

[0084] Combination Figure 3 As shown, the AC voltage regulator dual closed-loop control strategy includes:

[0085] Preset the expressions for the first three-phase inverter U1 and / or the second three-phase inverter U2 in the dq coordinate system:

[0086]

[0087] Where ω is the synchronous rotation angular frequency, u sd u sq The Park transformation result of the power supply voltage of either the first three-phase inverter U1 or the second three-phase inverter U2, u ld u lq i represents the Park transformation result of the output voltage of either the first three-phase inverter U1 or the second three-phase inverter U2. ld i lq The Park transformation result is the output current of the first three-phase inverter U1 or the second three-phase inverter U2, where N represents the transformer turns ratio and L1 represents the grid-side equivalent inductance.

[0088] Preset reference values ​​for the output voltages of the first three-phase inverter U1 and / or the second three-phase inverter U2:

[0089]

[0090] Among them, u * d u * q U is the reference value for the output voltage U2 of either the first three-phase inverter U1 or the second three-phase inverter. * ldThis is the reference value for the load voltage;

[0091] With voltage control set as the outer loop, u * ld u sd and u * ld u sq The comparison value is used to obtain the reference value i of the output current of the first three-phase inverter U1 or the second three-phase inverter U2 through the PI regulator. * ld i * lq ;

[0092] Using current control as the inner loop and employing a proportional controller, the current loop control strategy equation can be obtained as follows:

[0093]

[0094] Among them, u rd u rq The output voltage d and q components of the current loop are represented, K represents the multiplication coefficient, s represents the complex frequency domain variable, and k iv k represents the integral coefficient. pv Indicates the proportionality coefficient;

[0095] will u * ld u * lq The first control signal is obtained by performing Park transformation and SPWM modulation.

[0096] Furthermore, dead-time compensation is introduced into the AC voltage regulation dual closed-loop control strategy. Dead-time compensation includes:

[0097] Calculate the average voltage error caused by the dead zone of the inverter switch over one switching cycle:

[0098]

[0099] Among them, i a Let sign(i) be the output current of the current observer. a ) represents i a The polarity of i a When the value is greater than 0, the output is 1; otherwise, the output is -1. dc t is the input voltage of either the first three-phase inverter U1 or the second three-phase inverter U2. d For dead time, T s For switching cycles;

[0100] Feedforward compensation is applied to the output voltage of the first three-phase inverter U1 and / or the second three-phase inverter U2 to offset the average voltage error.

[0101] S3. Determine whether the real-time voltage of the first AC bus AC1 is equal to or greater than the real-time voltage requirement. If so, control the charging component to charge the supercapacitor CP.

[0102] In this embodiment, the charging component outputs a preset low current to the supercapacitor CP to complete low-current slow charging. Specifically, a constant current single-loop charging strategy with the preset low current being a constant current is adopted, and a second control signal is output to the control terminal of the rectifier switch of the single-phase rectifier TB.

[0103] The constant current single-loop charging strategy incorporates a DQ decoupling stage to achieve the slow charging and fast discharging mentioned in the solution, decoupling the charging and discharging circuits. This decoupling design ensures the charging circuit is unaffected by the discharge load, preventing current fluctuations during charging from negatively impacting charging quality. Simultaneously, the high power output requirements of the battery during discharge do not conversely affect the charging process.

[0104] Combination Figure 4 As shown, the constant current single-loop charging strategy includes: the current-stabilizing loop detects the DC side current I during charging. dc With the specified value I * dc The comparison value is input to the PI regulator to provide the active reference current i for the current loop. * d To achieve constant current IC for supercapacitors CP * dc Charging control. s i s For the grid-side voltage and current of the single-phase inverter, u s The input phase-locked loop obtains the frequency and phase, and then i s Inputting the SOGI phase-locked loop yields signals i that are in phase and quadrature with it. α i β To provide the conditions for the Park transformation, the expression for the single-phase rectifier TB in the dq coordinate system is:

[0105]

[0106] Among them, u sd u sq This is obtained by performing a Park transformation on the grid-side constant voltage of a single-phase inverter. R represents the grid-side equivalent resistance, and L2 represents the grid-side equivalent inductance. The above expression is decoupled using feedforward, assuming:

[0107]

[0108] Where, k pi k ii These are the proportional and integral parameters of the current loop, respectively; i *d i * q This is the reference value for active current. Substituting it, we get:

[0109]

[0110] Therefore, i d with i q Complete decoupling and complete symmetry are achieved; the current loops in the dq coordinate system can be designed independently and are completely identical. Finally, the second control signal for the rectifier switching transistor is obtained through Clarke transformation and SPWM modulation.

[0111] It should be noted that compared to traditional batteries, supercapacitor converters (CPs) can provide extremely high charging and discharging power, but their energy density (stored energy) is relatively low. Therefore, they need to be slowly charged for extended periods when the voltage is stable or higher than the system requirements for energy storage. The working principle of slow charging is to control the charging current so that the supercapacitor CP can complete charging over a longer time, effectively avoiding the impact of high current surges on the power grid during the charging process. This helps reduce the load on other equipment in the power system (such as transformers and rectifiers), thereby improving the overall reliability and stability of the power system. At the same time, low-current slow charging has low power requirements, so single-phase parallel rectifiers can be used, which is less likely to cause load imbalance problems. Furthermore, it is simple to control and install, has low equipment costs, reduces initial investment, and is highly adaptable, especially suitable for areas without three-phase power grids or scenarios with low power demand.

[0112] S4. Obtain and determine whether the load of the first AC bus AC1 and the second AC bus AC2 is unbalanced based on the real-time load demand of the first AC bus AC1 and the second AC bus AC2. If so, proceed to step S5.

[0113] S5 controls the first three-phase inverter U1 and the second three-phase inverter U2, so that the voltage of the supercapacitor CP is output to the first AC bus AC1 or the second AC bus AC2 to achieve load balance.

[0114] In summary, this invention provides a voltage sag compensation circuit for power distribution networks based on supercapacitors. It employs a supercapacitor, a first three-phase inverter, a second three-phase inverter, a first transformer, and a second transformer to form a dual-feed voltage sag compensation network connected between the first and second AC buses. Leveraging the low internal resistance and high power density of supercapacitors, when a voltage sag occurs at the end of the AC bus, the supercapacitor rapidly releases its stored energy through the three-phase inverter with a high current to compensate for the voltage drop. Two phases share a single supercapacitor for compensation, reducing equipment costs and effectively addressing rapidly changing voltage demands while ensuring power quality. The discharge section of the voltage compensation incorporates a dual closed-loop control strategy for AC voltage regulation with dead-time compensation, reducing the impact of output voltage imbalance or distortion caused by switching dead time. By adjusting the switching signals, the output of the three-phase inverter is ensured to be more accurate and stable. The combined effect of dead zone compensation and dual closed-loop control allows the inverter to remain inactive when the line voltage deviation is small, avoiding unnecessary losses and reducing the failure rate. In the charging section, a low-current constant-current single-loop charging strategy is adopted to reduce the power of the charging circuit, thereby reducing the burden on the charging equipment and the system cost.

[0115] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent modifications made based on the content of the present invention specification and drawings, or direct or indirect applications in related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A voltage sag compensation circuit for power distribution networks based on supercapacitors, characterized in that, It includes a supercapacitor, a first three-phase inverter, a second three-phase inverter, a first transformer, a second transformer, charging components, and a control module; The input and output terminals of the supercapacitor are simultaneously electrically connected to the DC side of the first three-phase inverter, the DC side of the second three-phase inverter, and the output terminal of the charging component. The grid side of the first three-phase inverter is electrically connected to the low-voltage side of the first transformer, and the grid side of the second three-phase inverter is electrically connected to the low-voltage side of the second transformer. The high-voltage side of the first transformer and the high-voltage side of the second transformer are respectively used to connect the first AC bus and the second AC bus in series. The input terminal of the charging component is used to connect to the first AC bus. The control module is electrically connected to the control terminal of the first three-phase inverter, the control terminal of the second three-phase inverter, and the control terminal of the charging component, respectively. The control module is used to control the supercapacitor to perform voltage compensation on the first AC bus and / or the second AC bus. The charging assembly includes a single-phase rectifier and a third transformer; The DC side of the single-phase rectifier is electrically connected to the input and output terminals of the supercapacitor, the grid side of the single-phase rectifier is electrically connected to the low-voltage side of the third transformer, and the high-voltage side of the third transformer is used to connect in parallel to the first AC bus. The control module is electrically connected to the control terminal of the single-phase rectifier. The control module is used to slowly charge the supercapacitor using the single-phase rectifier at a preset low current.

2. The voltage sag compensation circuit for power distribution networks based on supercapacitors according to claim 1, characterized in that, Both the first three-phase inverter and the second three-phase inverter are composed of bridge inverter circuits, and the control module is electrically connected to the control terminal of the inverter switching transistor of the bridge inverter circuit.

3. The voltage sag compensation circuit for power distribution networks based on supercapacitors according to claim 1, characterized in that, The single-phase rectifier is a bridge rectifier, and the control module is electrically connected to the control terminal of the rectifier switch tube of the single-phase rectifier.

4. A method for voltage sag compensation in a distribution network based on a supercapacitor, applied to a voltage sag compensation circuit for a distribution network based on a supercapacitor as described in any one of claims 1 to 3, characterized in that, Includes the following steps: S1. Obtain and determine whether a voltage dip occurs on the first AC bus and / or the second AC bus based on the real-time voltage magnitude of the first AC bus and the second AC bus. If so, proceed to step S2. S2. Control the first three-phase inverter and / or the second three-phase inverter so that the voltage of the supercapacitor is output to the first AC bus and / or the second AC bus to complete voltage sag compensation. S3. Determine whether the real-time voltage of the first AC bus is equal to or greater than the real-time voltage requirement. If so, control the charging component to charge the supercapacitor.

5. A method for compensating for voltage sags in a distribution network based on a supercapacitor, as described in claim 4, is characterized in that... Also includes: S4. Obtain and determine whether the load of the first AC bus and the second AC bus is unbalanced based on the real-time load demand of the first AC bus and the second AC bus. If so, proceed to step S5. S5. Control the first three-phase inverter and the second three-phase inverter so that the voltage of the supercapacitor is output to the first AC bus or the second AC bus to achieve load balance.

6. A method for compensating for voltage sags in a distribution network based on a supercapacitor, as described in claim 4, is characterized in that... The charging control component specifically includes the following steps for charging the supercapacitor: The charging component is controlled to output a preset low current to the supercapacitor to complete low-current slow charging.

7. A method for compensating for voltage sags in a distribution network based on a supercapacitor, as described in claim 4, is characterized in that... The control of the first three-phase inverter and / or the second three-phase inverter includes: The first control signal obtained by the AC voltage regulation dual closed-loop control strategy is input at the control terminal of the inverter switching transistor of the first three-phase inverter and / or the second three-phase inverter. The AC voltage stabilization dual closed-loop control strategy includes: The expressions for the first three-phase inverter and / or the second three-phase inverter in the dq coordinate system are preset as follows: ； in, To synchronize the rotational angular frequency, u sd u sq The Park transformation result of the power supply voltage of the first three-phase inverter or the second three-phase inverter, u ld u lq i is the Park transformation result of the output voltage of the first three-phase inverter or the second three-phase inverter. ld i lq The output current of the first three-phase inverter or the second three-phase inverter is the Park transformation result, where N represents the transformer turns ratio and L1 represents the grid-side equivalent inductance. Preset reference values ​​for the output voltages of the first three-phase inverter and / or the second three-phase inverter: ； in, , This is a reference value for the output voltage of either the first three-phase inverter or the second three-phase inverter. This is the reference value for the load voltage; With voltage control set as the outer loop, as well as The comparison value is used to obtain a reference value for the output current of either the first three-phase inverter or the second three-phase inverter through a PI regulator. ; Using current control as the inner loop and employing a proportional controller, the current loop control strategy equation can be obtained as follows: ； ； Among them, u rd u rq The output voltage d and q components of the current loop are represented, K represents the multiplication coefficient, s represents the complex frequency domain variable, and k iv k represents the integral coefficient. pv Indicates the proportionality coefficient; Will The first control signal is obtained by performing Park transformation and SPWM modulation.

8. A method for compensating for voltage sags in a distribution network based on a supercapacitor, as described in claim 7, is characterized in that... Also includes: Dead-time compensation is introduced into the AC voltage regulation dual closed-loop control strategy, and the dead-time compensation includes: Calculate the average voltage error caused by the dead zone of the inverter switch over one switching cycle: ; Among them, i a The output current of the current observer is used. express The polarity, when When the value is greater than 0, the output is 1; otherwise, the output is -1. dc t is the input voltage of either the first three-phase inverter or the second three-phase inverter. d For dead time, T s For switching cycles; Feedforward compensation is applied to the output voltage of the first three-phase inverter and / or the second three-phase inverter to offset the average voltage error.

9. A method for compensating for voltage sags in a distribution network based on a supercapacitor, as described in claim 6, is characterized in that... The specific steps of controlling the charging component to output a preset low current to the supercapacitor are as follows: A constant current single-loop charging strategy with the preset low current as the constant current is adopted, and a second control signal is output to the control terminal of the rectifier switch of the single-phase rectifier.

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