A Low-Voltage Management Method for Distribution Networks Based on Single-Phase and Three-Phase Hybrid Topology

Abstract

This invention discloses a low-voltage management method for distribution networks based on a hybrid single-phase and three-phase topology. A voltage regulation circuit consisting of a three-phase inverter unit and a single-phase rectifier unit is connected in series on the grid side of the AC bus. A phase selection circuit connects the single-phase rectifier unit to the load side of the AC bus. The phase selection circuit connects the AC side of the single-phase rectifier unit to the target phase line on the load side of the AC bus. According to a preset control strategy, the single-phase rectifier unit obtains active power from the target phase line and transmits it to the grid side of the AC bus through the three-phase inverter unit, thereby boosting the AC bus voltage. This invention obtains active power from a target phase line on the load side of the AC bus, converts it into AC voltage after passing through the single-phase rectifier unit and the three-phase inverter unit, and injects it into the AC bus, thus boosting the bus voltage. Compared to the UPQC structure, the equipment used is less expensive and provides a simple and effective solution to the low-voltage problem in the distribution network.

Description

Technical Field

[0001] This invention relates to the field of power distribution technology, and in particular to a low-voltage management method for power distribution networks based on a single-phase and three-phase hybrid topology. Background Technology

[0002] In some remote areas, the power supply radius of the distribution network lines is large and the wire diameter is small, which can cause voltage dips, seriously affecting users' normal power consumption and causing economic losses and waste of resources.

[0003] Currently, the low-voltage management of distribution networks proposes the use of a unified power quality conditioner (UPQC) to address the problem of prolonged voltage dips. However, in actual distribution networks, the UPQC structure and control system are complex, costly, and have high installation and maintenance costs. To save costs, corresponding UPQC control schemes can only be designed for specific problems. Summary of the Invention

[0004] The technical problem to be solved by this invention is to provide a method for managing low voltage in distribution networks based on a single-phase and three-phase hybrid topology, which can reduce equipment investment costs while simply and effectively solving the low voltage problem in distribution networks.

[0005] A method for low-voltage management of distribution networks based on single-phase and three-phase hybrid topology includes the following steps:

[0006] S1. A voltage regulation circuit consisting of a three-phase inverter unit and a single-phase rectifier unit is connected in series on the grid side of the AC bus, and the single-phase rectifier unit is connected to the load side of the AC bus through a phase line selection circuit.

[0007] S2. Control the phase selection circuit to connect the AC side of the single-phase rectifier unit to the phase line of the load side of the AC bus.

[0008] S3. According to the preset control strategy, control the single-phase rectifier unit to obtain active power from the target phase line and transmit it to the grid side of the AC bus through the three-phase inverter unit to increase the voltage of the AC bus.

[0009] The beneficial effects of this invention are as follows: It provides a low-voltage management method for distribution networks based on a hybrid single-phase and three-phase topology. A voltage regulation circuit composed of a three-phase inverter unit and a single-phase rectifier unit is connected between the load side and the grid side of the AC bus. When a voltage dip occurs on the AC bus, the single-phase rectifier unit is controlled by a preset control strategy to obtain active power from a target phase line on the load side of the AC bus. After being converted into AC voltage by the single-phase rectifier unit and the three-phase inverter unit, the AC voltage is injected into the AC bus, thereby raising the bus voltage. Compared with the UPQC structure, the equipment used has a lower cost and solves the low-voltage phenomenon in the distribution network simply and effectively. Attached Figure Description

[0010] Figure 1 This is a schematic diagram illustrating the steps of a low-voltage management method for a distribution network based on a single-phase and three-phase hybrid topology according to the present invention.

[0011] Figure 2 This is a circuit connection diagram of a voltage regulation circuit for a low-voltage management method for distribution networks based on a single-phase and three-phase hybrid topology according to the present invention.

[0012] Figure 3 This is a control block diagram of a single-phase rectifier in a low-voltage management method for distribution networks based on a single-phase / three-phase hybrid topology according to the present invention.

[0013] Figure 4 This is a control block diagram of a three-phase inverter for a low-voltage management method of a distribution network based on a single-phase and three-phase hybrid topology according to the present invention.

[0014] Figure 5 This is an equivalent current-voltage vector diagram of a low-voltage management method for distribution networks based on a single-phase and three-phase hybrid topology according to the present invention. Detailed Implementation

[0015] 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.

[0016] Please refer to Figures 1 to 5 A low-voltage management method for distribution networks based on a single-phase and three-phase hybrid topology includes the following steps:

[0017] S1. A voltage regulation circuit consisting of a three-phase inverter unit and a single-phase rectifier unit is connected in series on the grid side of the AC bus, and the single-phase rectifier unit is connected to the load side of the AC bus through a phase line selection circuit.

[0018] S2. Control the phase selection circuit to connect the AC side of the single-phase rectifier unit to the phase line of the load side of the AC bus.

[0019] S3. According to the preset control strategy, control the single-phase rectifier unit to obtain active power from the target phase line and transmit it to the grid side of the AC bus through the three-phase inverter unit to increase the voltage of the AC bus.

[0020] As can be seen from the above description, the beneficial effects of the present invention are as follows: a voltage regulation circuit composed of a three-phase inverter unit and a single-phase rectifier unit is connected between the load side and the grid side of the AC bus. When a voltage dip occurs on the AC bus, the single-phase rectifier unit is controlled by a preset control strategy to obtain active power from a target phase line on the load side of the AC bus. After being converted by the single-phase rectifier unit and the three-phase inverter unit, the AC voltage is injected into the AC bus, thereby raising the bus voltage. Compared with the UPQC structure, the equipment used has a lower cost and solves the low voltage phenomenon of the distribution network simply and effectively.

[0021] Further, the target phase line includes the phase line with the lowest voltage and the phase line with the highest voltage, and step S2 specifically includes:

[0022] The phase selection circuit controls the AC side of the single-phase rectifier to connect the highest voltage phase line and the lowest voltage phase line of the AC bus, respectively.

[0023] Step S3 specifically includes:

[0024] The single-phase rectifier unit is controlled to absorb the active power of the highest voltage phase line and the lowest voltage phase line, absorb the reactive power of the highest voltage phase line and inject reactive power into the lowest voltage phase line.

[0025] As can be seen from the above description, the target phase lines are selected as the phase lines with the lowest voltage and the phase lines with the highest voltage. While solving the problem of bus voltage sag, this can alleviate the problem of voltage imbalance to a certain extent and ensure the stable operation of the distribution network.

[0026] Furthermore, the preset control strategy specifically includes:

[0027] A preset switching control signal is input to the control terminal of the switching transistor in the single-phase rectifier unit to control the on / off state of the switching transistor.

[0028] As can be seen from the above description, by using a preset control strategy, the power transmission process is transformed into a switching control process, thereby achieving automated and precise control of the operation of the single-phase rectifier unit and reasonably controlling the voltage compensation process.

[0029] Furthermore, step S3 also includes:

[0030] S31. Using the single-phase rectifier unit as an equivalent resistor to connect the phase line with the highest voltage and the phase line with the lowest voltage respectively, the equivalent voltage across the equivalent resistor and the equivalent current flowing through the equivalent resistor are obtained.

[0031] S32. Based on the equivalent voltage and the equivalent current, obtain the preset switching control signal.

[0032] Further, step S32 specifically includes:

[0033] S321. Obtain the phase difference between the phase line with the highest voltage and the phase line with the lowest voltage;

[0034] S322. Orthogonally decompose the equivalent current and combine it with the phase difference to perform coordinate transformation to obtain the active component and reactive component of the current.

[0035] S323. Based on the active current component, the reactive current component and their corresponding control reference values, the preset switching transistor control signal is obtained.

[0036] Further, step S321 specifically includes:

[0037] The phase difference is obtained by tracking the equivalent voltage via a phase-locked loop.

[0038] As can be seen from the above description, phase-locked loops are used to achieve automated closed-loop tracking, thereby accurately measuring the phase difference.

[0039] Further, step S2 specifically includes:

[0040] Close the selection switch in the phase selection circuit that connects the AC side of the single-phase rectifier unit to the target phase line, and disconnect the selection switches that connect the AC side of the single-phase rectifier unit to the remaining phase lines of the AC bus.

[0041] As can be seen from the above description, by switching the on and off states of the selector switch at different positions, the target phase line can be flexibly connected. The circuit composition is simple and the control is convenient.

[0042] Please refer to Figures 1 to 5 Embodiment 1 of the present invention is as follows:

[0043] A method for low-voltage management of distribution networks based on single-phase and three-phase hybrid topology, such as... Figure 1 As shown, it includes the following steps:

[0044] S1. A voltage regulation circuit consisting of a three-phase inverter unit and a single-phase rectifier unit is connected in series on the grid side of the AC bus, and the single-phase rectifier unit and the load side of the AC bus are connected through a phase line selection circuit.

[0045] like Figure 2As shown, the single-phase rectifier unit consists of a rectifier, a transformer, and a DC bus filter capacitor. The AC side of the rectifier is connected to the phase selection circuit via the transformer, while the DC side of the rectifier is connected to the DC side of the three-phase inverter unit via the DC bus filter capacitor. The AC side of the three-phase inverter is connected to the grid side of the AC bus via the transformer. During voltage regulation circuit operation, DC voltage is obtained from the grid through the single-phase rectifier. This DC voltage is connected to the DC bus filter capacitor, and then passed through the three-phase inverter to obtain AC voltage. This AC voltage is then connected in series with the three-phase inverter and connected to the grid voltage, thus achieving the function of boosting the grid voltage.

[0046] S2. The phase selection circuit controls the AC side of the single-phase rectifier unit to connect the target phase line of the load side of the AC bus.

[0047] In this embodiment, the target phase lines include the lowest voltage phase line and the highest voltage phase line. When selecting phase line connections, the phase line selection circuit connects the AC side of the single-phase rectifier to the highest voltage and lowest voltage phase lines of the AC bus, respectively; specifically as follows... Figure 2 As shown, the phase selection circuit has three selection switches at each end of the single-phase rectifier, one for connecting the lowest voltage phase and the other for connecting the highest voltage phase. These three switches correspond to phases A, B, and C of the AC bus, respectively. After determining the current lowest and highest voltage phases, the corresponding selection switches are closed, while the other selection switch is opened.

[0048] S3. According to the preset control strategy, control the single-phase rectifier unit to obtain active power from the target phase line and transmit it to the grid side of the AC bus through the three-phase inverter unit to increase the voltage of the AC bus.

[0049] In this embodiment, step S3 specifically includes: achieving a power factor of 1, the single-phase rectifier only transmitting active power, controlling the single-phase rectifier unit to absorb the active power of the phase line with the highest voltage and the phase line with the lowest voltage, absorbing the reactive power of the phase line with the highest voltage and injecting reactive power into the phase line with the lowest voltage, as illustrated in the following example:

[0050] On the AC side of a single-phase rectifier, such as Figure 2 As shown, when the voltage of phase A is higher and the voltage of phase C is lower, the single-phase rectifier is connected to both phases A and C (target phase lines). From the perspective of the grid port, since the power factor of the single-phase rectifier is 1, the single-phase rectifier is equivalent to an equivalent resistance R. eq The current flowing through the equivalent resistance is I. ac The voltage across the equivalent resistance is U. ac From phase A, I ac Decomposed into U a I in phase ac2 , and with Ua Orthogonal I ac1 I ac1 Lag U a ,I ac2 I absorbs active power from the power grid. ac1 Reactive power is absorbed from the power grid. Similarly, from the perspective of phase C, I ca2 I absorbs active power from the power grid. ca2 Reactive power is injected into the power grid. In summary, when the voltage of phase A is high, the inductive load of phase A is increased, thus lowering the voltage of phase A; when the voltage of phase C is low, the inductive load of phase C is reduced, thus raising the voltage of phase C.

[0051] In this embodiment, in order to achieve the above-mentioned power transmission process, the preset control strategy is as follows: a preset switching control signal is input to the control terminal of the switching transistor of the single-phase rectifier unit to control the on / off state of the switching transistor, as follows:

[0052] S31. Using a single-phase rectifier unit as an equivalent resistor connected to the phase line with the highest voltage and the phase line with the lowest voltage respectively, the equivalent voltage across the equivalent resistor and the equivalent current flowing through the equivalent resistor are obtained.

[0053] S32. Based on the equivalent voltage and equivalent current, obtain the preset switching control signal.

[0054] In this embodiment, step S32 specifically includes:

[0055] S321. Track the equivalent voltage via a phase-locked loop to obtain the phase difference;

[0056] S322. Orthogonally decompose the equivalent current and combine it with the phase difference to perform coordinate transformation to obtain the active and reactive components of the current.

[0057] S323. Based on the active current component, the reactive current component and their corresponding control reference values, obtain the preset switching transistor control signal.

[0058] Combination Figure 3 and Figure 5 As shown, in the control section of a single-phase rectifier, u ac The phase difference φ between the AC phases is obtained through PLL tracking. ac After orthogonal decomposition and the information obtained from phase φ, αβ / d q Transformation to obtain i d and i q This represents the grid-side information for a single-phase rectifier. U dc * represents the target control voltage given on the DC side of the rectifier, U dc The current DC side voltage is compared with the current DC side voltage by a comparator to obtain offset information, which is then processed by P. I1Tracking yields the target control difference I. d *. I d * indicates the active component control target, I q * indicates the reactive component control target. I d * and i d After comparison, through P I2 Track the difference to obtain d d ;I q *As the target control value, it is set to 0, indicating that the reactive power component is 0. q * and i q After comparison, through P I3 By tracking the difference, d is obtained. q Using the obtained d d d q The information of sinφ and cosφ, after d q The duty cycle information of the PWM rectifier is obtained by transforming and adding the αβ values. After obtaining the PWM rectified wave, the diagonal switches of the rectifier are controlled to turn on and off simultaneously, and the upper and lower bridge arms are turned on with a phase difference of 180°.

[0059] Combination Figure 4 As shown, through the above control process, DC voltage is obtained by conversion on the DC side of the single-phase rectifier. After passing through the filter capacitor, the DC voltage is controlled to convert the DC voltage into an AC voltage that is compatible with the bus and inject it into the AC bus to achieve voltage boost.

[0060] In summary, this invention discloses a low-voltage management method for distribution networks based on a hybrid single-phase and three-phase topology. A voltage regulation circuit consisting of a three-phase inverter unit and a single-phase rectifier unit is connected between the load side and the grid side of the AC bus. When a voltage dip occurs on the AC bus, a preset control strategy controls the single-phase rectifier unit to obtain active power from a target phase line on the load side of the AC bus. This active power is then converted into AC voltage by the single-phase rectifier unit and the three-phase inverter unit and injected into the AC bus, thereby boosting the bus voltage. Compared to the UPQC structure, the equipment used has lower costs and provides a simple and effective solution to the low-voltage phenomenon in the distribution network.

[0061] 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 method for low-voltage management of distribution networks based on single-phase and three-phase hybrid topology, characterized in that, Includes the following steps: S1. A voltage regulation circuit consisting of a three-phase inverter unit and a single-phase rectifier unit is connected in series on the grid side of the AC bus, and the single-phase rectifier unit is connected to the load side of the AC bus through a phase line selection circuit. S2. Control the phase selection circuit to connect the AC side of the single-phase rectifier unit to the target phase line of the load side of the AC bus. S3. According to the preset control strategy, control the single-phase rectifier unit to obtain active power from the target phase line and transmit it to the grid side of the AC bus through the three-phase inverter unit to increase the voltage of the AC bus. The target phase lines include the phase line with the lowest voltage and the phase line with the highest voltage. Step S2 specifically involves: The phase selection circuit controls the AC side of the single-phase rectifier unit to connect to the highest voltage phase line and the lowest voltage phase line of the AC bus, respectively. Step S3 specifically includes: The single-phase rectifier unit is controlled to absorb the active power of the highest voltage phase line and the lowest voltage phase line, absorb the reactive power of the highest voltage phase line and inject reactive power into the lowest voltage phase line; The preset control strategy is specifically as follows: A preset switching control signal is input to the control terminal of the switching transistor in the single-phase rectifier unit to control the on / off state of the switching transistor. Step S3 also includes: S31. Using the single-phase rectifier unit as an equivalent resistor to connect the phase line with the highest voltage and the phase line with the lowest voltage respectively, the equivalent voltage across the equivalent resistor and the equivalent current flowing through the equivalent resistor are obtained. S32. Obtain the preset switching control signal based on the equivalent voltage and the equivalent current; Step S32 specifically includes: S321. Obtain the phase difference between the phase line with the highest voltage and the phase line with the lowest voltage; S322. Orthogonally decompose the equivalent current and combine it with the phase difference to perform coordinate transformation to obtain the active component and reactive component of the current. S323. Based on the active current component, the reactive current component and their corresponding control reference values, the preset switching transistor control signal is obtained.

2. The low-voltage management method for distribution networks based on a single-phase / three-phase hybrid topology according to claim 1, characterized in that, Step S321 specifically involves: The phase difference is obtained by tracking the equivalent voltage via a phase-locked loop.

3. The low-voltage management method for distribution networks based on a single-phase / three-phase hybrid topology according to claim 1, characterized in that, Step S2 specifically involves: Close the selection switch in the phase selection circuit that connects the AC side of the single-phase rectifier unit to the target phase line, and disconnect the selection switches that connect the AC side of the single-phase rectifier unit to the remaining phase lines of the AC bus.

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