Circuit with both voltage control and three-phase unbalance control

Abstract

The present invention provides a circuit that combines voltage management and three-phase imbalance management, and relates to the technical field of power distribution networks. The circuit of the present invention includes a three-phase AC to single-phase AC module and a jumper capacitor, wherein the three-phase AC to single-phase AC module includes a front-stage three-phase AC unit and a rear-stage single-phase AC unit, and the front-stage three-phase AC unit and the rear-stage single-phase AC unit both include a number of switch tubes; by controlling the on and off of the switch tube in the front-stage three-phase AC unit, the three-phase power balance is achieved; by controlling the on and off duty cycle of the switch tube in the rear-stage single-phase AC unit, the amplitude of the output voltage is adjusted to achieve high and low voltage management. Compared with traditional UPQC equipment, the circuit proposed by the present invention does not require the use of a transformer, and reduces the system cost while achieving the management of low and high voltage problems, effectively reducing the system volume and improving the power density.

Description

Technical Field

[0001] The present invention relates to the technical field of power distribution networks, and in particular to a circuit that combines voltage control and three-phase imbalance control. Background Art

[0002] As the part of the power system that directly interacts with users, the low-voltage distribution network undertakes the important task of power distribution, and its power supply quality directly affects the user's power experience. In the low-voltage distribution network, the transformer transmits the power flow to the user through a three-phase four-wire feeder. The single-phase load accounts for the majority in the substation (referring to the power supply area of ​​a distribution transformer), and the more developed the economy, the greater the proportion of single-phase users. The power consumption patterns of these loads are affected by multiple factors such as season, weather, and time, and have strong random characteristics, resulting in uneven distribution of three-phase power flows in the substation, which in turn causes three-phase imbalance in the distribution network. In addition, with the rapid development of industrial production in recent years, factors such as the increase in nonlinear loads in the substation, the increase in charging and discharging of electric vehicles, the access of distributed power generation to the grid, and the frequent start and stop of high-power equipment have exacerbated the three-phase imbalance problem of the low-voltage distribution network. Due to the incomplete consideration of early planning in some distribution substations, and the limitations of geographical location and economic costs, the three-phase imbalance problem is difficult to control and the means of control are lacking. At the same time, the high and low voltage problems in the distribution network substation will also lead to problems such as increased grid line loss, equipment failure, and power outages, affecting the production and life of users. In some power supply areas, the transformer outlet voltage is in a low voltage state due to seasonal and intermittent fluctuations in loads, and the voltage fluctuations are aggravated by impact loads. When there is a large load at the end of the line, the end power supply voltage will also be low. Especially in mountainous and remote areas, some substations have a long power supply radius, poor power quality at the end, and low power supply reliability, so that the power supply voltage is often too high or too low compared to the standard voltage (220V); too high or too low voltage will cause the user's electrical equipment to not work properly, which has a great impact on the regional economy.

[0003] However, there is no circuit in the prior art that takes into account both voltage control and three-phase imbalance control. These two problems in the distribution network are usually controlled by different control methods. The existing control method for three-phase imbalance in the distribution network is load phase switching power supply, which has a long construction period and requires continuous phase switching adjustment according to the operating conditions of the distribution network. The existing voltage control scheme generally adopts the following methods: Figure 1 The UPQC device shown in FIG. 1 is complex in structure and high in cost. As can be seen from the above description, the existing control circuit cannot take into account both voltage control and three-phase unbalance control, and is also costly. Summary of the invention

[0004] 1. Technical issues to be resolved

[0005] In view of the shortcomings of the prior art, the present invention provides a circuit that combines voltage control and three-phase imbalance control, which solves the technical problems that the existing control circuit cannot take into account both voltage control and three-phase imbalance control and has high cost.

[0006] (II) Technical solution

[0007] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0008] In a first aspect, the present invention provides a circuit for both voltage management and three-phase imbalance management, including a three-phase AC to single-phase AC module and a jumper capacitor;

[0009] Among them, the three input terminals of the three-phase AC to single-phase AC module are connected to the three-phase distribution lines A, B, and C respectively;

[0010] The single-phase output terminal of the three-phase AC to single-phase AC module is connected to the first terminal of the single-phase load, and the common terminal of the single-phase output terminal and the single-phase load is connected to any one-phase distribution line of the three-phase distribution line via a jumper capacitor;

[0011] The second end of the single-phase load is connected to the neutral line of the power distribution network;

[0012] Among them, the three-phase AC to single-phase AC module includes a front-stage three-phase AC unit and a rear-stage single-phase AC unit, and the front-stage three-phase AC unit and the rear-stage single-phase AC unit both include a number of switching tubes; by controlling the conduction and disconnection of the switching tube in the front-stage three-phase AC unit, the three-phase power balance is achieved; by controlling the conduction and disconnection duty cycle of the switching tube in the rear-stage single-phase AC unit, the amplitude of the output voltage is adjusted to achieve high and low voltage management.

[0013] Preferably, the three-phase AC to single-phase AC module includes a primary conversion circuit module or a secondary conversion circuit module;

[0014] Among them, in the first-stage conversion circuit module, the front-stage three-phase AC unit is a three-phase AC circuit, and the rear-stage single-phase AC unit is a single-phase AC circuit;

[0015] In the two-stage conversion circuit module, the front three-phase AC unit is a three-phase AC / DC circuit, and the rear three-phase AC unit is a single-phase DC / AC circuit, wherein a first capacitor group is connected between the three-phase AC / DC circuit and the single-phase DC / AC circuit.

[0016] Preferably, the three-phase AC / DC circuit includes a three-phase PWM rectifier circuit, and the on and off of the switch tubes in the three-phase PWM rectifier circuit are controlled by a power factor correction control algorithm to achieve three-phase power balance.

[0017] Preferably, the single-phase DC / AC circuit includes a seventh switch tube, an eighth switch tube and an inductor, wherein the first end of the seventh switch tube is connected to the first output end of the three-phase AC / DC circuit; the second end of the seventh switch tube is connected to the first end of the eighth switch tube, and the connection end thereof is connected to the connection end of the jumper capacitor and the single-phase load via the inductor; the second end of the eighth switch tube is connected to the second output end of the three-phase AC / DC circuit;

[0018] The third end of the seventh switch tube and the third end of the eighth switch tube are both control ends, and the control ends are used to connect control signals. The amplitude of the output voltage is adjusted by adjusting the on / off duty cycle of the seventh switch tube and the eighth switch tube through the control signal to achieve high and low voltage management.

[0019] Preferably, the jumper capacitor is a film capacitor.

[0020] In a second aspect, the present invention provides a circuit for both voltage management and three-phase unbalance management, including a three-phase AC to single-phase AC module and a jumper capacitor;

[0021] Among them, the three input terminals of the three-phase AC to single-phase AC module are connected to the three-phase distribution lines A, B, and C respectively;

[0022] The three-phase AC to single-phase AC module is electrically connected to the neutral line of the power distribution network;

[0023] The single-phase output terminal of the three-phase AC to single-phase AC module is connected to the first terminal of the single-phase load, and the common terminal of the single-phase output terminal and the single-phase load is connected to any one-phase distribution line of the three-phase distribution line via a jumper capacitor;

[0024] The second end of the single-phase load is connected to the neutral line of the power distribution network;

[0025] Among them, the three-phase AC to single-phase AC module includes a front-stage three-phase AC unit and a rear-stage single-phase AC unit, and the front-stage three-phase AC unit and the rear-stage single-phase AC unit both include a number of switching tubes; by controlling the conduction and disconnection of the switching tube in the front-stage three-phase AC unit, the three-phase power balance is achieved; by controlling the conduction and disconnection duty cycle of the switching tube in the rear-stage single-phase AC unit, the amplitude of the output voltage is adjusted to achieve high and low voltage management.

[0026] Preferably, the three-phase AC to single-phase AC module includes a primary conversion circuit module or a secondary conversion circuit module;

[0027] Among them, in the first-stage conversion circuit module, the front-stage three-phase AC unit is a three-phase AC circuit, and the rear-stage single-phase AC unit is a single-phase AC circuit;

[0028] In the two-stage conversion circuit module, the front-stage three-phase AC unit is a three-phase AC / DC circuit, and the rear-stage three-phase AC unit is a single-phase DC / AC circuit, wherein a first capacitor group and a second capacitor group are connected between the three-phase AC / DC circuit and the single-phase DC / AC circuit, wherein the capacitance values ​​of the first capacitor group and the second capacitor group are equal;

[0029] A midpoint connection point is arranged between the first capacitor group and the second capacitor group, and the midpoint connection point is electrically connected to a neutral line of the power distribution network.

[0030] Preferably, the three-phase AC / DC circuit includes a three-phase PWM rectifier circuit, and the on and off of the switch tubes in the three-phase PWM rectifier circuit are controlled by a power factor correction control algorithm to achieve three-phase power balance.

[0031] Preferably, the single-phase DC / AC circuit includes a seventh switch tube, an eighth switch tube and an inductor, wherein the first end of the seventh switch tube is connected to the first output end of the three-phase AC / DC circuit; the second end of the seventh switch tube is connected to the first end of the eighth switch tube, and the connection end thereof is connected to the connection end of the jumper capacitor and the single-phase load via the inductor; the second end of the eighth switch tube is connected to the second output end of the three-phase AC / DC circuit;

[0032] The third end of the seventh switch tube and the third end of the eighth switch tube are both control ends, and the control ends are used to connect control signals. The amplitude of the output voltage is adjusted by adjusting the on / off duty cycle of the seventh switch tube and the eighth switch tube through the control signal to achieve high and low voltage management.

[0033] Preferably, the jumper capacitor is a film capacitor.

[0034] (III) Beneficial effects

[0035] The present invention provides a circuit that combines voltage management and three-phase imbalance management. Compared with the prior art, it has the following beneficial effects:

[0036] The present invention provides a circuit with both voltage control and three-phase imbalance control, comprising a three-phase AC to single-phase AC module and a jumper capacitor, wherein the three input ends of the three-phase AC to single-phase AC module are respectively connected to three-phase distribution lines A, B, and C; the single-phase output end of the three-phase AC to single-phase AC module is connected to the first end of the single-phase load, the single-phase output end and the common end of the single-phase load are connected to any one-phase distribution line in the three-phase distribution line via the jumper capacitor, and the second end of the single-phase load is connected to the neutral line of the distribution network; wherein the three-phase AC to single-phase AC module comprises a front-stage three-phase AC unit and a rear-stage single-phase AC unit, wherein the front-stage three-phase AC unit and the rear-stage single-phase AC unit both comprise a plurality of switch tubes; by controlling the on and off of the switch tube in the front-stage three-phase AC unit, the three-phase power balance is achieved; by controlling the on and off duty ratio of the switch tube in the rear-stage single-phase AC unit, the amplitude of the output voltage is adjusted to achieve high and low voltage control. Compared with the traditional UPQC equipment, the circuit proposed by the present invention does not need to use a transformer. While achieving the problem of too low and too high voltage, it reduces the system cost, effectively reduces the system volume and improves the power density. At the same time, a jumper capacitor is connected between the distribution line and the load, forming a constant closed-loop path of one point of a certain phase distribution line → jumper capacitor → load → point N of the distribution line, and there is no switching device to perform switching action, which reduces the impact of power grid fluctuations on the load and does not damage the power carrier communication between the distribution network and the user. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0038] Figure 1 It is the architecture diagram of the existing UPQC device;

[0039] Figure 2 This is a schematic diagram of a circuit for voltage control and three-phase imbalance control in Example 1;

[0040] Figure 3 For Example 1 Figure 2 A typical circuit of the architecture diagram shown;

[0041] Figure 4 for Figure 3 A schematic diagram of the working mode 1 of the rear stage inverter circuit in the circuit shown;

[0042] Figure 5 for Figure 3A schematic diagram of the working mode 2 of the rear stage inverter circuit in the circuit shown;

[0043] Figure 6 It is a schematic diagram of a circuit for voltage control and three-phase imbalance control in Embodiment 2;

[0044] Figure 7 For Example 2 Figure 6 A typical circuit of the architecture diagram shown;

[0045] Figure 8 for Figure 7 A schematic diagram of the working mode 1 of the rear stage inverter circuit in the circuit shown;

[0046] Fig. 9 for Figure 7 Schematic diagram of working mode 2 of the subsequent inverter circuit in the circuit shown. DETAILED DESCRIPTION

[0047] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are 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.

[0048] It should be noted that, for the convenience of description, the switch MOSFET is used to represent the controllable (on and off) switch tube in the embodiment of the present invention, but the switch tube in the present invention is not limited to MOSFET. Take MOSFET as an example for explanation. The first end of the MOSFET refers to the drain, the second end refers to the source, and the control end refers to the gate. A drive control signal is applied to the control end of each switch tube in the embodiment of the present invention. For the sake of brevity, it will not be repeated later. The power switch tube in the embodiment of the present invention can also be implemented by other controllable switch tube devices other than MOSFET, such as IGBT. At the same time, in order to ensure the normal operation of each switch device in the embodiment of the present invention, a freewheeling diode needs to be connected in parallel to each switch device. The parallel direction of the freewheeling diode is related to the type of the switch device. The technician can set it according to the type of the switch device, which is not limited here. If not specified, the switch device defaults to including a freewheeling diode, which will be pointed out in this embodiment in special cases.

[0049] The embodiments of the present application provide a circuit that combines voltage control and three-phase imbalance control, thereby solving the technical problems that the existing control circuits cannot take into account both voltage control and three-phase imbalance control and have high costs, thereby achieving three-phase power supply for single-phase loads, taking into account both voltage control and three-phase imbalance control, and reducing system cost and volume.

[0050] The technical solution in the embodiment of the present application is to solve the above technical problems, and the overall idea is as follows:

[0051] To address the three-phase imbalance problem, the traditional method for managing the three-phase imbalance in the distribution network of the substation is load phase-changing power supply. This method has high labor costs and a long construction period, and can only temporarily improve the three-phase imbalance problem. Phase-changing adjustments must be made continuously according to the operating conditions of the distribution network of the substation.

[0052] In order to solve the problem of too low or too high power supply voltage at the distribution transformer or line end, the traditional solution is to use UPQC device for treatment. Figure 1 As shown. Figure 1 It can be seen that the UPQC device first connects a rectifier in parallel at the grid end to generate a DC voltage, and then converts the DC voltage into AC through an inverter. This AC is added to the grid through a coupling transformer connected in series to the grid, so that the load side voltage is superimposed on the grid voltage by an AC voltage generated by the inverter, thereby adjusting the grid voltage. When the grid voltage is too low, the voltage can be raised by adding a voltage in the same phase as the grid voltage using UPQC; when the grid voltage is too high, the voltage can be reduced by adding a voltage in the opposite phase to the grid voltage using UPQC, so that the load voltage returns to the standard voltage (220V).

[0053] From the above analysis, it can be seen that the architecture of UPQC is relatively complex. It adopts a two-stage structure of rectification followed by inversion, and requires a coupling transformer to be connected in series with the power grid, resulting in low device efficiency, large size and high cost.

[0054] In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0055] It should be noted that in the following embodiments, the capacitors involved, such as the jumper capacitor, the first capacitor, the second capacitor, etc., may be a capacitor group composed of multiple capacitors. In the embodiments of the present application, one capacitor is used as a representative for description.

[0056] Embodiment 1:

[0057] This embodiment provides a circuit that combines voltage management and three-phase imbalance management. The circuit structure is as follows: Figure 2 As shown, it includes a three-phase AC to single-phase AC module and a cross-connect capacitor C c , wherein the three input terminals of the three-phase AC to single-phase AC module are respectively connected to the three-phase distribution lines A, B, and C; the single-phase output terminal of the three-phase AC to single-phase AC module is connected to the first terminal of the single-phase load, and the common terminal of the single-phase output terminal and the single-phase load is connected via a jumper capacitor C cIt is connected to any one phase of the three-phase distribution circuit, and in this embodiment, it is connected to the C phase distribution circuit. The second end of the single-phase load is connected to the neutral line of the distribution network. The three-phase AC to single-phase AC module includes a front-stage three-phase AC unit and a rear-stage single-phase AC unit, and the front-stage three-phase AC unit and the rear-stage single-phase AC unit each include a plurality of switch tubes; by controlling the on and off of the switch tube in the front-stage three-phase AC unit, the three-phase power balance is achieved; by controlling the on and off duty cycle of the switch tube in the rear-stage single-phase AC unit, the amplitude of the output voltage is adjusted to achieve high and low voltage management.

[0058] In the specific implementation process, the internal circuit of the three-phase AC to single-phase AC module can adopt the traditional AC / AC one-stage conversion, or the AC / DC+DC / AC two-stage conversion, etc. The specific circuit of the module can be selected according to different application scenarios.

[0059] Figure 2 A typical circuit of the architecture shown is Figure 3 As shown, the circuit adopts an AC / DC+DC / AC two-stage conversion circuit, a first capacitor C1 is connected between the two-stage conversion circuit, and the front-stage AC / DC of the circuit adopts a three-phase PWM rectifier circuit, including L 1. L 2. L 3. Q1, Q2, Q3, Q4, Q5, and Q6 can achieve three-phase power balance through control algorithms such as power factor correction (PFC), thereby solving the problem of three-phase load imbalance.

[0060] The single-phase inverter circuit of the latter stage includes Q7, Q8, L 4. Supply power to the single-phase load of the distribution network in the substation area. The latter stage can adjust the amplitude of the output voltage by adjusting the duty cycle of the conduction and shutdown of Q7 and Q8, thereby achieving high and low voltage management. At the same time, because it is through the first capacitor C 1 The output voltage obtained by inverting the stored DC voltage is less affected by grid voltage fluctuations, harmonics, etc., which can improve the power supply quality of users.

[0061] superior Figure 3 Given the crossover capacitance C c It is connected to the C-phase distribution line of the power grid. Theoretically, it is feasible to connect it to any of the three-phase distribution lines of A, B, and C. It can be selected according to the actual construction conditions.

[0062] Since there is a distribution line C→C c → load → distribution line N point constant closed loop path, there is no switching device in the meantime to perform switching action, so the access of this circuit will not destroy the power carrier communication between the distribution network and the user, which is beneficial to the management of the distribution network.

[0063] At the same time, due to C c The voltage it withstands is the voltage difference between point C of the distribution line and the load. Under normal circumstances, this voltage is relatively small. Only when the distribution line has low voltage or high voltage will there be a higher voltage, usually only tens of volts. At the same time, the capacitor uses alternating current and does not serve as an energy storage device. Therefore, film capacitors can be used, which are very low in cost.

[0064] The front-stage three-phase PWM rectification circuit is a mature technology, and its working principle will not be described here.

[0065] The working principle of the subsequent single-phase inverter circuit is as follows:

[0066] Switching devices Q7 and Q8 form a bridge arm, and this topology has two operating modes. The states of the switching devices in each mode are shown in the attached table.

[0067] Working mode 1: Figure 4 As shown, the switch tube Q7 is turned off and Q8 is turned on. The current has two flow paths, specifically: three-phase power grid → front-stage three-phase PWM rectifier circuit → C 1→Q8→ L 4→Load, distribution line point C→ C c → load, the inductor current decreases (assuming L 4 The current is positive from left to right, the same below)

[0068] Working mode 2: Figure 5 As shown, the switch tube Q8 is turned off, Q7 is turned on, and the current has two flow paths, specifically: three-phase power grid → front-stage three-phase PWM rectifier circuit → C 1→Q7→ L 4→Load, distribution line point C→ C c →Load, at this time the inductor current increases.

[0069] Cross-over capacitor C c The voltage is the same or opposite to the phase C voltage of the distribution network. CN ) is too low, C c Voltage V Cc With V CN In phase, the output load voltage Vo is raised. When V CN When the voltage V Cc With V CN The phases are opposite, achieving a reduction in the output load voltage Vo.

[0070] It should be noted that no matter whether the grid is boosted or bucked, the working conditions of the circuit are similar. The output voltage Vo can be controlled by controlling the duty cycle of the upper and lower tubes (Q7 and Q8) of the inverter part of the circuit. When the duty cycle is set to make the output voltage higher than the grid voltage Vo, the voltage can be boosted. When the duty cycle is set to make the output voltage lower than the grid voltage Vo, the voltage can be bucked.

[0071] Embodiment 2:

[0072] This embodiment provides a circuit that combines voltage management and three-phase imbalance management. The circuit structure is as follows: Figure 6 As shown, it includes a three-phase AC to single-phase AC module and a cross-connect capacitor C c , wherein the three input terminals of the three-phase AC to single-phase AC module are respectively connected to the three-phase distribution lines A, B, and C; the three-phase AC to single-phase AC module is electrically connected to the neutral line of the distribution network; the single-phase output terminal of the three-phase AC to single-phase AC module is connected to the first terminal of the single-phase load, and the common terminal of the single-phase output terminal and the single-phase load is connected via a jumper capacitor C c It is connected to any one phase of the three-phase distribution circuit, and in this embodiment, it is connected to the C phase distribution circuit. The second end of the single-phase load is connected to the neutral line of the distribution network. The three-phase AC to single-phase AC module includes a front-stage three-phase AC unit and a rear-stage single-phase AC unit, and the front-stage three-phase AC unit and the rear-stage single-phase AC unit each include a plurality of switch tubes; by controlling the on and off of the switch tube in the front-stage three-phase AC unit, the three-phase power balance is achieved; by controlling the on and off duty cycle of the switch tube in the rear-stage single-phase AC unit, the amplitude of the output voltage is adjusted to achieve high and low voltage management.

[0073] In the specific implementation process, the internal circuit in the three-phase AC to single-phase AC module can adopt traditional AC / AC one-stage conversion, or AC / DC+DC / AC two-stage conversion, etc. The specific circuit of the module can be selected according to different application scenarios.

[0074] Figure 6 A typical circuit of the architecture shown is Figure 7 As shown, the circuit adopts the AC / DC+DC / AC two-stage conversion circuit mode, and the first capacitor C1 and the second capacitor C2 are connected between the two-stage conversion circuit, wherein the capacitance values ​​of the first capacitor C1 and the second capacitor C2 are equal; a midpoint connection point is set between the first capacitor C1 and the second capacitor C2, and the midpoint connection point is electrically connected to the neutral line of the power distribution network. The front-stage AC / DC of the circuit adopts a three-phase PWM rectifier circuit, including L 1. L 2. L3. Q1, Q2, Q3, Q4, Q5, and Q6 can achieve three-phase power balance through control algorithms such as power factor correction (PFC), thereby solving the problem of three-phase load imbalance.

[0075] The single-phase inverter circuit of the latter stage includes Q7, Q8, L 4. Supply power to the single-phase load of the distribution network in the substation area. The latter stage can adjust the amplitude of the output voltage by adjusting the on-off duty cycle of Q7 and Q8, thereby achieving high and low voltage management. C 1 and C 2 The output voltage obtained by inverting the stored DC voltage is less affected by grid voltage fluctuations, harmonics, etc., which can improve the power supply quality of users.

[0076] The figure above shows C c It is connected to the C-phase distribution line of the power grid. Theoretically, it is feasible to connect it to any of the three-phase distribution lines of A, B, and C. It can be selected according to the actual construction conditions.

[0077] Since there is a distribution line C → C c → load → closed-loop path of point N in the distribution line. The access of the new circuit will not destroy the power carrier communication between the distribution network and the user, which is beneficial to the management of the distribution network.

[0078] The front-stage three-phase PWM rectification circuit is a mature technology, and its working principle will not be described here.

[0079] The working principle of the subsequent single-phase inverter circuit is as follows:

[0080] Switching devices Q7 and Q8 form a bridge arm, and this topology has two operating modes. The states of the switching devices in each mode are shown in the attached table.

[0081] Working mode 1: Figure 8 As shown, the switch tube Q7 is turned off, Q8 is turned on, and the current flow path is C 2→Q8→ L 4→Load, distribution line point C→ C c → load, the inductor current decreases (assuming L 4 The current is positive from left to right, the same below).

[0082] Working mode 2: Fig. 9 As shown, the switch tube Q8 is turned off, Q7 is turned on, and the current flow path is C 1→Q7→ L 4→Load, distribution line point C→ C c →Load, at this time the inductor current increases.

[0083] C c The voltage is the same or opposite to the phase C voltage of the distribution network. CN ) is too low, C c Voltage V Cc With V CN In phase, the output load voltage Vo is raised. When V CN When the voltage V Cc With V CN The phases are opposite, achieving a reduction in the output load voltage Vo.

[0084] It should be noted that no matter whether the grid is boosted or bucked, the working conditions of the circuit are similar. The output voltage Vo can be controlled by controlling the duty cycle of the upper and lower tubes (Q7 and Q8) of the inverter part of the circuit. When the duty cycle is set to make the output voltage higher than the grid voltage Vo, the voltage can be boosted. When the duty cycle is set to make the output voltage lower than the grid voltage Vo, the voltage can be bucked.

[0085] In summary, compared with the prior art, the present invention has the following beneficial effects:

[0086] The circuit with both voltage control and three-phase imbalance control proposed in the embodiment of the present invention can realize three-phase power supply for single-phase load and solve the three-phase imbalance problem. The latter stage can adjust the amplitude of the output voltage by adjusting the on / off duty cycle of Q7 and Q8, thereby realizing high and low voltage control. Compared with the traditional UPQC equipment, there is no need to use a transformer. While achieving the control of low and high voltage problems, the system cost is reduced, the system volume is effectively reduced, and the power density is improved. At the same time, a jumper capacitor is connected between the distribution line and the load to form a distribution line C point → C c → load → distribution line N points constant closed loop path, during which no switching device performs switching action, reducing the impact of grid fluctuations on the load and will not damage the power carrier communication between the distribution network and the user.

[0087] 2. A capacitor is set in the three-phase AC to single-phase AC module C 1. By C 1 The output voltage obtained by inverting the stored DC voltage is less affected by grid voltage fluctuations, harmonics, etc., which can improve the power supply quality of users.

[0088] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0089] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A circuit with both voltage control and three-phase imbalance control, characterized in that: Includes a three-phase AC to single-phase AC module and a jumper capacitor; Among them, the three input terminals of the three-phase AC to single-phase AC module are connected to the three-phase distribution lines A, B, and C respectively; The single-phase output terminal of the three-phase AC to single-phase AC module is connected to the first terminal of the single-phase load, and the common terminal of the single-phase output terminal and the single-phase load is connected to any one-phase distribution line of the three-phase distribution line via a jumper capacitor; The second end of the single-phase load is connected to the neutral line of the power distribution network; Among them, the three-phase AC to single-phase AC module includes a front-stage three-phase AC unit and a rear-stage single-phase AC unit, and the front-stage three-phase AC unit and the rear-stage single-phase AC unit both include a number of switching tubes; by controlling the conduction and disconnection of the switching tube in the front-stage three-phase AC unit, the three-phase power balance is achieved; by controlling the conduction and disconnection duty cycle of the switching tube in the rear-stage single-phase AC unit, the amplitude of the output voltage is adjusted to achieve high and low voltage management.

2. The circuit for voltage control and three-phase unbalance control as claimed in claim 1, characterized in that: The three-phase AC to single-phase AC module includes a primary conversion circuit module or a secondary conversion circuit module; Among them, in the first-stage conversion circuit module, the front-stage three-phase AC unit is a three-phase AC circuit, and the rear-stage single-phase AC unit is a single-phase AC circuit; In the two-stage conversion circuit module, the front three-phase AC unit is a three-phase AC / DC circuit, and the rear three-phase AC unit is a single-phase DC / AC circuit, wherein a first capacitor group is connected between the three-phase AC / DC circuit and the single-phase DC / AC circuit.

3. The circuit for voltage control and three-phase unbalance control as claimed in claim 2, characterized in that: The three-phase AC / DC circuit includes a three-phase PWM rectifier circuit, and the on and off of the switch tube in the three-phase PWM rectifier circuit is controlled by a power factor correction control algorithm to achieve three-phase power balance.

4. The circuit for voltage control and three-phase unbalance control as claimed in claim 2, characterized in that: The single-phase DC / AC circuit includes a seventh switch tube, an eighth switch tube and an inductor, wherein a first end of the seventh switch tube is connected to a first output end of the three-phase AC / DC circuit; a second end of the seventh switch tube is connected to a first end of the eighth switch tube, and a connection end thereof is connected to a connection end of a jumper capacitor and a single-phase load via an inductor; a second end of the eighth switch tube is connected to a second output end of the three-phase AC / DC circuit; The third end of the seventh switch tube and the third end of the eighth switch tube are both control ends, and the control ends are used to connect control signals. The amplitude of the output voltage is adjusted by adjusting the on / off duty cycle of the seventh switch tube and the eighth switch tube through the control signal to achieve high and low voltage management.

5. The circuit for voltage control and three-phase imbalance control as claimed in any one of claims 1 to 4, characterized in that: The cross-over capacitor is a film capacitor.

6. A circuit with both voltage control and three-phase imbalance control, characterized in that: Includes a three-phase AC to single-phase AC module and a jumper capacitor; Among them, the three input terminals of the three-phase AC to single-phase AC module are connected to the three-phase distribution lines A, B, and C respectively; The three-phase AC to single-phase AC module is electrically connected to the neutral line of the power distribution network; The single-phase output terminal of the three-phase AC to single-phase AC module is connected to the first terminal of the single-phase load, and the common terminal of the single-phase output terminal and the single-phase load is connected to any one-phase distribution line of the three-phase distribution line via a jumper capacitor; The second end of the single-phase load is connected to the neutral line of the power distribution network; Among them, the three-phase AC to single-phase AC module includes a front-stage three-phase AC unit and a rear-stage single-phase AC unit, and the front-stage three-phase AC unit and the rear-stage single-phase AC unit both include a number of switching tubes; by controlling the conduction and disconnection of the switching tube in the front-stage three-phase AC unit, the three-phase power balance is achieved; by controlling the conduction and disconnection duty cycle of the switching tube in the rear-stage single-phase AC unit, the amplitude of the output voltage is adjusted to achieve high and low voltage management.

7. The circuit for voltage control and three-phase unbalance control as claimed in claim 6, characterized in that: The three-phase AC to single-phase AC module includes a primary conversion circuit module or a secondary conversion circuit module; Among them, in the first-stage conversion circuit module, the front-stage three-phase AC unit is a three-phase AC circuit, and the rear-stage single-phase AC unit is a single-phase AC circuit; In the two-stage conversion circuit module, the front-stage three-phase AC unit is a three-phase AC / DC circuit, and the rear-stage three-phase AC unit is a single-phase DC / AC circuit, wherein a first capacitor group and a second capacitor group are connected between the three-phase AC / DC circuit and the single-phase DC / AC circuit, wherein the capacitance values ​​of the first capacitor group and the second capacitor group are equal; A midpoint connection point is arranged between the first capacitor group and the second capacitor group, and the midpoint connection point is electrically connected to a neutral line of the power distribution network.

8. The circuit for voltage control and three-phase unbalance control as claimed in claim 7, characterized in that: The three-phase AC / DC circuit includes a three-phase PWM rectifier circuit, and the on and off of the switch tube in the three-phase PWM rectifier circuit is controlled by a power factor correction control algorithm to achieve three-phase power balance.

9. The circuit for voltage control and three-phase unbalance control as claimed in claim 7, characterized in that: The single-phase DC / AC circuit includes a seventh switch tube, an eighth switch tube and an inductor, wherein a first end of the seventh switch tube is connected to a first output end of the three-phase AC / DC circuit; a second end of the seventh switch tube is connected to a first end of the eighth switch tube, and a connection end thereof is connected to a connection end of a jumper capacitor and a single-phase load via an inductor; a second end of the eighth switch tube is connected to a second output end of the three-phase AC / DC circuit; The third end of the seventh switch tube and the third end of the eighth switch tube are both control ends, and the control ends are used to connect control signals. The amplitude of the output voltage is adjusted by adjusting the on / off duty cycle of the seventh switch tube and the eighth switch tube through the control signal to achieve high and low voltage management.

10. The circuit for voltage control and three-phase unbalance control as claimed in any one of claims 6 to 9, characterized in that: The cross-over capacitor is a film capacitor.

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