Power distribution network voltage sag compensation circuit and method based on super capacitor

Abstract

The invention discloses a power distribution network voltage sag compensation circuit and method based on a super capacitor. The power distribution network voltage sag compensation circuit comprises the super capacitor, a first three-phase inverter, a second three-phase inverter, a first transformer, a second transformer, a charging assembly and a control module. The input and output end of the super capacitor is electrically connected with the direct current side of the first three-phase inverter, the direct current side of the second three-phase inverter and the output end of the charging assembly at the same time, the power grid side of the first three-phase inverter is electrically connected with the low-voltage side of the first transformer, and 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 in series with a first alternating-current bus and a second alternating-current bus; the control module is electrically connected with the control end of the first three-phase inverter, the control end of the second three-phase inverter and the control end of the charging assembly. According to the invention, voltage fluctuation in the power grid can be quickly responded while equipment cost is controlled, and electric energy quality is guaranteed.

Description

Technical Field

[0001] The present invention relates to the field of power distribution technology, and in particular to a supercapacitor-based distribution network voltage sag compensation circuit and method. Background Art

[0002] In 10kV rural power grids, the voltage sag at the end of the line usually affects the stability of power supply and the safe operation of the rural power grid. This problem may be caused by a variety of factors and has a wide range of impacts. For example, there are usually large load fluctuations among rural power grid users. For example, the switching operation of electrical equipment such as irrigation and breeding will cause instantaneous load changes, especially during peak power consumption periods, which may cause a voltage sag at the end.

[0003] In this regard, most existing solutions are to achieve voltage compensation for a single feeder, and the commonly used equipment is a dynamic voltage restorer (DVR). When a voltage sag occurs in the system, the DVR injects an AC voltage with the same frequency as the system to offset the change in system voltage. The amplitude of the injected voltage is the difference between the normal voltage and the fault voltage. Although the use of DVR can achieve voltage sag compensation well, when voltage sag occurs on both feeders, the additional inverter will increase the investment cost.

[0004] In addition, the energy for the conventional DVR compensation voltage is provided by the DC side. Due to factors such as battery internal resistance and chemical reaction efficiency, traditional DC energy storage units may generate additional energy losses when providing power support, affecting the overall system efficiency. For occasions where voltage sags occur frequently, the battery charging speed may not be able to meet the needs of 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 rates and cannot provide enough current in a short period of time to cope with rapidly changing voltage requirements. Summary of the invention

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

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0007] A distribution network voltage sag compensation circuit based on a supercapacitor, comprising 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 ends of the supercapacitor are electrically connected to 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 at the same time; the grid side of the first three-phase inverter is electrically connected to the low-voltage side of the first transformer; 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 end of the charging component is used to connect the first AC bus;

[0009] The control module is electrically connected to the control end of the first three-phase inverter, the control end of the second three-phase inverter and the control end of the charging component respectively, and 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] In order to solve the above technical problems, another technical solution adopted by the present invention is:

[0011] A method for compensating for voltage sag in a distribution network based on a supercapacitor is applied to the above-mentioned voltage sag compensation circuit for a distribution network based on a supercapacitor, and comprises the following steps:

[0012] S1, obtaining and judging whether a voltage sag occurs on the first AC bus and / or the second AC bus according to the real-time voltage of the first AC bus and the second AC bus, and if so, executing step S2;

[0013] S2, controlling 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 the present invention are as follows: a distribution network voltage sag compensation circuit based on a supercapacitor is provided, a dual-fed line voltage sag compensation network connected between a first AC bus and a second AC bus is formed by a supercapacitor, a first three-phase inverter, a second three-phase inverter, a first transformer, and a second transformer. Combined with the characteristics of low internal resistance and high power density of the supercapacitor itself, when a voltage sag occurs at the end of the AC bus, the supercapacitor quickly releases the stored electric energy with a higher current through the three-phase inverter to compensate for the voltage drop. Two phase lines share a supercapacitor for compensation, which reduces equipment costs, can effectively respond to rapidly changing voltage demands, and ensure power quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1A circuit connection diagram of a supercapacitor-based distribution network voltage sag compensation circuit of the present invention;

[0017] Figure 2 A schematic diagram of the steps of a method for compensating for voltage sag in a distribution network based on supercapacitors according to the present invention;

[0018] Figure 3 A topological structure of a three-phase inverter and a control block diagram of an AC voltage stabilization dual closed-loop control strategy for a method for compensating for voltage sag in a distribution network based on supercapacitors according to the present invention;

[0019] Figure 4 The present invention provides a topological structure of a single-phase rectifier for a method for compensating for voltage sag in a distribution network based on supercapacitors and a control block diagram of a constant current single-loop charging strategy.

[0020] Description of labels:

[0021] AC1, the first AC bus; AC2, the second AC bus;

[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 DESCRIPTION

[0025] In order to explain the technical content, achieved objectives and effects of the present invention in detail, the following is an explanation in conjunction with the implementation modes and the accompanying drawings.

[0026] Please refer to Figure 1 , a distribution network voltage sag compensation circuit based on a super capacitor CP, comprising a super capacitor 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 ends of the supercapacitor CP are 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 end of the charging component at the same time. 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, and the input end of the charging component is used to connect the first AC bus AC1;

[0028] The control module is electrically connected to the control end of the first three-phase inverter U1, the control end of the second three-phase inverter U2 and the control end of the charging component respectively, and 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] From the above description, it can be seen that the beneficial effects of the present invention are: a dual-fed line voltage sag compensation network connected between the first AC bus AC1 and the second AC bus AC2 is formed by a supercapacitor CP, a first three-phase inverter U1, a second three-phase inverter U2, a first transformer T1, and a second transformer T2. Combined with the characteristics of low internal resistance and high power density of the supercapacitor CP itself, when a voltage sag occurs at the end of the AC bus, the supercapacitor CP quickly releases the stored electrical energy with a higher current through the three-phase inverter to compensate for the voltage drop. The two phase lines share a supercapacitor CP for compensation, which reduces equipment costs, can effectively respond to rapidly changing voltage requirements, and ensure power quality.

[0030] Further, 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 ends 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 end of the single-phase rectifier TB, and the control module is used to slowly charge the supercapacitor CP according to a preset low current through the single-phase rectifier TB.

[0033] From the above description, it can be seen that in the charging part of the supercapacitor CP, 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 achieve the purpose of reducing the power of the charging circuit, thereby reducing the burden of the charging equipment and the system cost, and realizing charging of the supercapacitor CP with little impact on the grid voltage, which is not easy to cause load imbalance problems.

[0034] Furthermore, the first three-phase inverter U1 and the second three-phase inverter U2 are both composed of a bridge inverter circuit, and the control module is electrically connected to the control end of the inverter switch tube of the bridge inverter circuit.

[0035] From the above description, it can be seen that the three-phase inverter part adopts a bridge inverter circuit composed of multiple inverter switching tubes, 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 end of the rectifier switch tube of the single-phase rectifier TB.

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

[0038] Please refer to Figures 2 to 4 A method for compensating for voltage sag in a distribution network based on a super capacitor CP is applied to the above-mentioned voltage sag compensation circuit for a distribution network based on a super capacitor CP, comprising the following steps:

[0039] S1, obtaining and judging whether a voltage sag occurs on the first AC bus AC1 and / or the second AC bus AC2 according to the real-time voltage of the first AC bus AC1 and the second AC bus AC2, and if so, executing step S2;

[0040] S2, controlling 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 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] From the above description, it can be seen that the beneficial effects of the present invention are: a dual-fed line voltage sag compensation network connected between the first AC bus AC1 and the second AC bus AC2 is formed by a supercapacitor CP, a first three-phase inverter U1, a second three-phase inverter U2, a first transformer T1, and a second transformer T2. Combined with the characteristics of low internal resistance and high power density of the supercapacitor CP itself, when a voltage sag occurs at the end of the AC bus, the supercapacitor CP quickly releases the stored electrical energy with a higher current through the three-phase inverter to compensate for the voltage drop. The two phase lines share a supercapacitor CP for compensation, which reduces equipment costs, can effectively respond to rapidly changing voltage requirements, and ensure power quality.

[0043] Furthermore, it also includes:

[0044] S4, obtaining and judging whether the loads of the first AC bus AC1 and the second AC bus AC2 are unbalanced according to the real-time load demands of the first AC bus AC1 and the second AC bus AC2, and if so, executing 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] From the above description, it can be seen that in addition to coping with the voltage sag process, when the terminal voltage of the first AC bus AC1 and the second AC bus AC2 decreases due to changes in their respective real-time load demands, voltage compensation can also be performed to ensure that the terminal voltage remains within the standard range and achieve load balance between the two circuits of the power grid.

[0047] Furthermore, the controlling the charging component to charge 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] From the above description, it can be seen that in the charging part of the supercapacitor CP, 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 achieve the purpose of reducing the power of the charging circuit, thereby reducing the burden of the charging equipment and the system cost, and realizing charging of the supercapacitor CP with little impact on the grid voltage, which is not easy to cause load imbalance problems.

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

[0051] Inputting a first control signal obtained by an AC voltage stabilization double closed-loop control strategy into a control end of an inverter switch tube 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] Preset expressions of the first three-phase inverter U1 and / or the second three-phase inverter U2 in the dq coordinate system:

[0054]

[0055] Where ω is the synchronous rotation angular frequency, u sd 、u sq is 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 is the Park transformation result of the output voltage of the first three-phase inverter U1 or the second three-phase inverter U2, i ld 、i lqis the Park transformation result of the output current of the first three-phase inverter U1 or the second three-phase inverter U2, N represents the transformer turns ratio, and L1 represents the grid-side equivalent inductance;

[0056] A reference value of an output voltage of the first three-phase inverter U1 and / or the second three-phase inverter U2 is preset:

[0057]

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

[0059] Set the voltage control as the outer loop and set 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] Taking current control as the inner loop and using a proportional controller, the current loop control strategy equation can be obtained as:

[0061]

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

[0063] will u * ld 、u * lq Park transformation and SPWM modulation are performed to obtain the first control signal.

[0064] From the above description, it can be seen that in the output control part of the three-phase inverter, an AC voltage stabilization dual closed-loop control strategy is used to control the inverter switch tube, so that the three-phase inverter has a stable and accurate output.

[0065] Furthermore, it also includes:

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

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

[0068]

[0069] Where ia is the output current of the current observer, sign(i a ) indicates i a The polarity of a >0, the output is 1, otherwise the output is -1, u dc is the input voltage of the first three-phase inverter U1 or the second three-phase inverter U2, t d is the dead time, T s is the switching cycle;

[0070] Feed-forward compensation is performed on 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] From the above description, we can see that the dead zone compensation is introduced into the AC voltage stabilization dual closed-loop control strategy to reduce the impact of output voltage imbalance or distortion caused by the switch dead time, and by adjusting the switch signal, the inverter output is ensured to be more accurate and stable. The dead zone compensation and dual closed-loop control work together to prevent the inverter from working when the line voltage deviation is not large, avoiding unnecessary losses and reducing the failure rate.

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

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

[0074] From the above description, it can be seen that in the supercapacitor CP charging part, a constant current single-loop charging strategy is adopted to maintain a constant current input through the current loop, thereby achieving the purpose of reducing the power of the charging circuit and reducing the burden of the charging equipment and the system cost.

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

[0076] A distribution network voltage sag compensation circuit based on supercapacitor CP, such as Figure 1As shown, it includes a super capacitor 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; the input and output ends of the super capacitor CP are 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 end of the charging component at the same time, the grid side of the first three-phase inverter U1 is electrically connected to the low-voltage side of the first transformer T1, 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, and the input end of the charging component is used to connect the first AC bus AC1; the control module is electrically connected to the control end of the first three-phase inverter U1, the control end of the second three-phase inverter U2 and the control end of the charging component, and the control module is used to control the super capacitor CP to perform voltage compensation on the first AC bus AC1 or / and the second AC bus AC2, wherein, u sa 、u sb 、u sc and i sa 、i sb 、i sc Indicates the grid-side voltage and current of the AC bus, u la 、u lb 、u lc and i la 、i lb 、i lc Indicates the load side voltage and current of the AC bus.

[0077] Among them, the charging component includes 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 ends 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; the control module is electrically connected to the control end of the single-phase rectifier TB, and the control module is used to slowly charge the supercapacitor CP through the single-phase rectifier TB according to a preset low current.

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

[0079] Please refer to Figures 2 to Figure 4 , Embodiment 2 of the present invention is:

[0080] A distribution network voltage sag compensation method based on a super capacitor CP is applied to a distribution network voltage sag compensation circuit based on a super capacitor CP in embodiment 1, comprising the following steps:

[0081] S1, obtaining and judging whether a voltage sag occurs on the first AC bus AC1 and / or the second AC bus AC2 according to the real-time voltage of the first AC bus AC1 and the second AC bus AC2, and if so, executing step S2;

[0082] S2, controlling 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 voltage sag compensation;

[0083] In this embodiment, a first control signal obtained by an AC voltage stabilization double closed-loop control strategy is input to the control end of the inverter switch tube of the first three-phase inverter U1 and / or the second three-phase inverter U2;

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

[0085] Preset expressions of 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 is 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 is the Park transformation result of the output voltage of the first three-phase inverter U1 or the second three-phase inverter U2, i ld 、i lq is the Park transformation result of the output current of the first three-phase inverter U1 or the second three-phase inverter U2, N represents the transformer turns ratio, and L1 represents the grid-side equivalent inductance;

[0088] The reference value of the output voltage of the first three-phase inverter U1 and / or the second three-phase inverter U2 is preset:

[0089]

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

[0091] Set the voltage control as the outer loop and set 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] Taking current control as the inner loop and using a proportional controller, the current loop control strategy equation can be obtained as:

[0093]

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

[0095] will u * ld 、u * lq Park transformation and SPWM modulation are performed to obtain a first control signal.

[0096] In addition, dead zone compensation is introduced into the AC voltage stabilization dual closed-loop control strategy. Dead zone compensation includes:

[0097] Calculate the average voltage error caused by the dead zone of the inverter switch tube in a switching cycle:

[0098]

[0099] Among them, i a is the output current of the current observer, sign(i a ) indicates i a The polarity of a >0, the output is 1, otherwise the output is -1, u dc is the input voltage of the first three-phase inverter U1 or the second three-phase inverter U2, t d is the dead time, T s is the switching cycle;

[0100] Feed-forward compensation is performed on 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, determining whether the real-time voltage of the first AC bus AC1 is equal to or greater than the real-time voltage requirement, and if so, controlling the charging component to charge the supercapacitor CP;

[0102] In this embodiment, the charging component is controlled to output 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 as a constant current is adopted to output a second control signal to the control end of the rectifier switch tube of the single-phase rectifier TB.

[0103] The constant current single-loop charging strategy adds the DQ decoupling link to achieve the slow charging and fast discharging mentioned in the solution, and the charging and discharging circuits are decoupled. The decoupling design can make the charging circuit unaffected by the discharge load, avoiding the adverse effects of battery current fluctuations on the charging quality during the charging process. At the same time, the high power output requirements for the battery during discharge will not reversely affect the charging process.

[0104] Combination Figure 4 As shown in the figure, the constant current single-loop charging strategy includes: the current stabilization loop charges the DC side detection current I dc With the specified value I * dc The comparison value is input into the PI regulator to provide an active reference current i for the current loop. * d , realize constant current I of super capacitor CP * dc Charging control. s 、i s is the grid-side voltage and current of the single-phase inverter, and u s Input the phase-locked loop to get the frequency and phase, and then s Input the SOGI phase-locked loop to obtain the signal i that is in phase and orthogonal to it. α 、i β To provide conditions for Park transformation, the expression of single-phase rectifier TB in dq coordinate system is:

[0105]

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

[0107]

[0108] Among them, k pi , k ii are the proportional and integral parameters of the current loop respectively; i *d 、i * q is the active current reference value. Substituting into:

[0109]

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

[0111] It should be noted that compared with traditional batteries, supercapacitor CP devices can provide extremely high charging and discharging power, but their energy density (stored energy) is relatively low, so they need to be slowly charged for a long time to store energy when the voltage is stable or higher than the system requirements. The working principle of slow charging is to control the charging current so that the supercapacitor CP device can be charged in a longer period of time, effectively avoiding the impact of high current shocks on the capacitor during the charging process on the power grid, and helping to reduce the load on other equipment in the power system (such as transformers, rectifiers, etc.), thereby improving the overall reliability and stability of the power system. At the same time, low-current slow charging has low power requirements, so a single-phase parallel rectifier can be used, which is not easy to cause load imbalance problems, and it is simple to control, simple to install, and has low equipment cost, which can reduce initial investment and has strong adaptability. It is especially suitable for areas without three-phase power grids or scenarios with small power demand.

[0112] S4, obtaining and judging whether the loads of the first AC bus AC1 and the second AC bus AC2 are unbalanced according to the real-time load demands of the first AC bus AC1 and the second AC bus AC2, and if so, executing step S5;

[0113] 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.

[0114] In summary, the present invention provides a distribution network voltage sag compensation circuit based on supercapacitors, which adopts supercapacitors, a first three-phase inverter, a second three-phase inverter, a first transformer, and a second transformer to form a dual-feed line voltage sag compensation network connected between a first AC bus and a second AC bus. Combined with the characteristics of low internal resistance and high power density of the supercapacitor itself, when a voltage sag occurs at the end of the AC bus, the supercapacitor quickly releases the stored electric energy with a higher current through the three-phase inverter to compensate for the voltage drop. Two phase lines share a supercapacitor for compensation, which reduces equipment costs, can effectively respond to rapidly changing voltage requirements, and ensure the quality of electric energy. An AC voltage stabilization dual closed-loop control strategy with dead zone compensation is introduced in the discharge part of the voltage compensation to reduce the impact of output voltage imbalance or distortion caused by the switch dead time, and by adjusting the switch signal, it is ensured that the output of the three-phase inverter is more accurate and stable. The dead zone compensation and dual closed-loop control work together to prevent the inverter from working when the line voltage deviation is not large, avoiding unnecessary losses and reducing the failure rate. A small current constant current single-loop charging strategy is adopted in the charging part to achieve the purpose of reducing the power of the charging circuit, reducing the burden on the charging equipment and the system cost.

[0115] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent transformations made using the contents of the present invention's specification and drawings, or directly or indirectly applied in related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A distribution network voltage sag compensation circuit based on supercapacitor, characterized in that: It 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; The input and output ends of the supercapacitor are electrically connected to 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 at the same time; the grid side of the first three-phase inverter is electrically connected to the low-voltage side of the first transformer; 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 end of the charging component is used to connect the first AC bus; The control module is electrically connected to the control end of the first three-phase inverter, the control end of the second three-phase inverter and the control end of the charging component respectively, and the control module is used to control the supercapacitor to perform voltage compensation on the first AC bus and / or the second AC bus.

2. A distribution network voltage sag compensation circuit based on supercapacitor according to claim 1, characterized in that: 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 ends 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 be connected in parallel with the first AC bus; The control module is electrically connected to the control end of the single-phase rectifier, and the control module is used to slowly charge the supercapacitor according to a preset low current through the single-phase rectifier.

3. The supercapacitor-based distribution network voltage sag compensation circuit according to claim 1, characterized in that: The first three-phase inverter and the second three-phase inverter are both composed of a bridge inverter circuit, and the control module is electrically connected to the control end of the inverter switch tube of the bridge inverter circuit.

4. A distribution network voltage sag compensation circuit based on supercapacitor according to claim 2, characterized in that: The single-phase rectifier is a bridge rectifier, and the control module is electrically connected to the control end of the rectifier switch tube of the single-phase rectifier.

5. A method for compensating for voltage sag in a distribution network based on supercapacitors, applied to a circuit for compensating voltage sag in a distribution network based on supercapacitors as claimed in any one of claims 1 to 4, characterized in that: The steps include: S1, obtaining and judging whether a voltage sag occurs on the first AC bus and / or the second AC bus according to the real-time voltage of the first AC bus and the second AC bus, and if so, executing step S2; S2, controlling 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.

6. A method for compensating for voltage sag in a distribution network based on supercapacitors according to claim 5, characterized in that: Also includes: S4, obtaining and judging whether the first AC bus and the second AC bus are load unbalanced according to the real-time load demand of the first AC bus and the second AC bus, and if so, executing 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.

7. A method for compensating voltage sag in a distribution network based on supercapacitors according to claim 5, characterized in that: The controlling the charging component to charge the supercapacitor specifically includes: The charging component is controlled to output a preset low current to the supercapacitor to complete low-current slow charging.

8. The method for compensating voltage sag in distribution network based on supercapacitor according to claim 5, characterized in that: The controlling the first three-phase inverter and / or the second three-phase inverter comprises: Inputting a first control signal obtained by an AC voltage stabilization double closed-loop control strategy into a control end of an inverter switch tube of the first three-phase inverter and / or the second three-phase inverter; The AC voltage stabilization dual closed-loop control strategy includes: Preset the expression of the first three-phase inverter and / or the second three-phase inverter in the dq coordinate system: Where ω is the synchronous rotation angular frequency, u sd 、u sq is 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 is the Park transformation result of the output voltage of the first three-phase inverter or the second three-phase inverter, i ld 、i lq is the Park transformation result of the output current of the first three-phase inverter or the second three-phase inverter, N represents the transformer turns ratio, and L1 represents the grid-side equivalent inductance; Presetting a reference value of an output voltage of the first three-phase inverter and / or the second three-phase inverter: Among them, u * d 、u * q is the reference value of the output voltage of the first three-phase inverter or the second three-phase inverter, u * ld is the load voltage reference value; Set the voltage control as the outer loop and set u * ld 、u sd and u * lq 、u sq The comparison value of the output current of the first three-phase inverter or the second three-phase inverter is obtained by the PI regulator. * ld 、i * lq ; Taking current control as the inner loop and using a proportional controller, the current loop control strategy equation can be obtained as: Among them, u rd 、u rq represents the d and q components of the current loop output voltage, K represents the multiplication coefficient, s represents the complex frequency domain variable, k iv represents the integral coefficient, k pv represents the proportionality coefficient; will u * ld 、u * lq Park transformation and SPWM modulation are performed to obtain the first control signal.

9. A method for compensating for voltage sag in a distribution network based on supercapacitors according to claim 8, characterized in that: Also includes: Dead zone compensation is introduced into the AC voltage stabilization dual closed-loop control strategy, and the dead zone compensation includes: Calculate the average voltage error of the inverter switch tube caused by the dead zone in one switching cycle: Among them, i a is the output current of the current observer, sgin(i a ) indicates i a The polarity of a >0, the output is 1, otherwise the output is -1, u dc is the input voltage of the first three-phase inverter or the second three-phase inverter, t d is the dead time, T s is the switching cycle; Feed-forward compensation is performed on the output voltage of the first three-phase inverter and / or the second three-phase inverter to offset the average voltage error.

10. A method for compensating for voltage sag in a distribution network based on supercapacitors according to claim 7, characterized in that: The controlling the charging component to output a preset low current to the supercapacitor is specifically as follows: A constant current single-loop charging strategy with the preset low current as a constant current is adopted to output a second control signal to the control end of the rectifier switch tube of the single-phase rectifier.

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