A hybrid distribution transformer integrating on-load tap-changer and series-parallel converter and voltage control method

Abstract

The present invention discloses a hybrid distribution transformer and voltage control method that integrates an on-load tap-changer and a series-parallel converter, and belongs to the field of intelligent power distribution technology. The hybrid distribution transformer includes a primary winding, a secondary main winding, a secondary series winding, an on-load tap-changer, a series-parallel converter, and a unified coordination controller, wherein the parallel side of the parallel converter is connected to the output end of the secondary main winding, and the series side injects a compensation voltage through the secondary series winding. The voltage control is based on a hierarchical decision-making method based on voltage deviation and three-phase voltage unevenness, and dynamically coordinates the slow and large-scale voltage regulation of the on-load tap-changer and the fast and accurate compensation of the series-parallel converter. The present invention combines the high capacity advantage of the on-load tap-changer and the fast response characteristics of the power electronic device, and can simultaneously solve the problems of medium- and long-term voltage offset and instantaneous voltage fluctuation in the distribution network, while reducing equipment cost and maintenance costs. It is suitable for voltage stability and power quality optimization of intelligent distribution networks.

Description

Technical Field

[0001] The present invention relates to the field of intelligent power distribution technology, and in particular to a hybrid distribution transformer integrating an on-load tap-changer and a series-parallel converter, and a voltage control method. Background Art

[0002] Traditional on-load tap-changing transformers use mechanical tap-changers to adjust the transformer ratio for coarse voltage regulation. However, these transformers have slow response times (in seconds), frequent operation can easily lead to mechanical wear, and they struggle to cope with rapid voltage fluctuations (such as sudden changes in photovoltaic output and impact loads). Power electronic voltage regulators (such as DVRs / SSTs) utilize series-parallel converters with fully controlled devices (such as IGBTs) to achieve millisecond-level dynamic compensation. However, these devices are limited in capacity, expensive, and struggle to meet wide-ranging voltage regulation requirements when used alone. The on-load tap-changing transformer and power electronic devices operate independently, lacking coordination, resulting in a compromise between regulation range and response speed. A single device cannot simultaneously address both long-term voltage excursions and transient voltage fluctuations. Long-term full-load operation of power electronic devices leads to high losses and reduced reliability.

[0003] By integrating the on-load tap-changer and the series-parallel converter into the same transformer body and designing a hierarchical collaborative control method, the unification of large-scale efficient voltage regulation and dynamic and precise compensation is achieved, reducing overall costs and extending equipment life. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a hybrid distribution transformer and voltage control method that integrates an on-load tap-changer and a series-parallel converter. The method combines the high capacity advantage of the on-load tap-changer with the fast response characteristics of the power electronic device, can simultaneously solve the problems of long-term voltage offset and instantaneous voltage fluctuation in the distribution network, and at the same time reduce equipment costs and maintenance expenses. The method is suitable for voltage stability and power quality optimization of smart distribution networks.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a hybrid distribution transformer integrating an on-load tap-changer and a series-parallel converter, comprising a primary-secondary winding, a series winding, an on-load tap-changer, a series-parallel converter, and a unified coordination controller; the parallel side of the series-parallel converter is connected to the output end of the secondary main winding, and the series side of the series-parallel converter injects a compensation voltage through the secondary series winding.

[0006] In a preferred embodiment, the series-parallel converter is composed of two power electronic converters, and the parallel-side converter of the series-parallel converter maintains the DC bus voltage.

[0007] The present invention also provides a voltage control method for a hybrid distribution transformer that integrates an on-load tap-changing switch and a series-parallel converter. By using the hybrid distribution transformer that integrates an on-load tap-changing switch and a series-parallel converter, slow and large-range voltage regulation is achieved by controlling the on-load tap-changing switch, and voltage compensation is achieved by the series-parallel converter.

[0008] In a preferred embodiment, the control method of the on-load tap-changer includes:

[0009] Step A1: If the three-phase voltage U i Both exceed the set voltage upper limit U set1 , then the blood pressure drops, i = a , b , c ;

[0010] Step A2: If the three-phase voltage U i Both are lower than the set voltage lower limit U set2 , then the voltage is increased, i = a , b , c ;

[0011] Step A3: If the three-phase voltage U i If the two-phase voltage exceeds the upper limit and one phase voltage is normal, calculate whether the normal voltage of one phase is still normal after the voltage is reduced. If it is normal, reduce the voltage, otherwise do not operate;

[0012] Step A4: If the three-phase voltage U i If the two-phase voltage exceeds the lower limit and one phase voltage is normal, calculate whether the normal voltage of one phase is still normal after the boost. If it is normal, boost the voltage, otherwise do not operate.

[0013] Step A5: If the three-phase voltage U i If the voltage of one phase exceeds the upper limit and the voltage of two phases is normal, calculate whether the voltage of the two phases is still normal after the voltage is reduced. If it is normal, reduce the voltage, otherwise do not take action;

[0014] Step A6: If the three-phase voltage U i If the voltage of one phase exceeds the lower limit and the voltages of the two phases are normal, calculate whether the voltages of the two phases are still normal after the voltage boost. If they are normal, boost the voltage, otherwise do not operate.

[0015] Step A7: No action is taken in other cases.

[0016] In a preferred embodiment,U set To control the target voltage value, the control method of the series-parallel converter includes:

[0017] Step B1: Calculate the input voltage imbalance ,Right now

[0018]

[0019] in, U max Is the maximum voltage among the three-phase voltages, U min Is the minimum voltage among the three-phase voltages, U a 、 U b 、 U c They are ;

[0020] Step B2: >2%

[0021] like , the voltage regulation amount is ;

[0022] like , the voltage regulation amount is ;

[0023] like and ,

[0024] Case 1: if , the voltage regulation amount is , U i Three-phase voltage U i The other two phases except the largest phase;

[0025] Case 2: if , the voltage regulation amount is , U i Three-phase voltage U i The other two phases except the smallest phase;

[0026] Step B3: <2%

[0027] like or , then according to the target value U set Perform voltage regulation;

[0028] like and ,

[0029] Case 1: if , the voltage regulation amount is , U i Three-phase voltage U i The other two phases except the largest phase;

[0030] Case 2: if , the voltage regulation amount is , U i Three-phase voltage U i The other two phases except the smallest phase;

[0031] Step B4: In other cases, adjust the voltage normally.

[0032] Compared with the existing technology, the present invention has the following beneficial effects: (1) the system complexity and cost are reduced through structural fusion, while retaining the large capacity advantage of the on-load tap-changer and the fast response characteristics of power electronics; (2) the collaborative control strategy reduces the number of on-load tap-changer operations and extends the mechanical life; (3) the series-parallel converter is compatible with reactive power compensation and harmonic suppression functions, thereby improving the overall power quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a topological diagram of the equivalent circuit of the hybrid distribution transformer of the present invention.

[0034] Figure 2 This is a structural diagram of the hybrid distribution transformer of the present invention.

[0035] Figure 3 This is the voltage coordinated control method (1) of the present invention.

[0036] Figure 4 This is the voltage coordinated control method (II) of the present invention.

[0037] Figure 5 This is a diagram showing the voltage stabilization effect when the power supply side voltage exceeds the limit downward.

[0038] Figure 6 This is a diagram showing the voltage stabilization effect when the power supply side voltage exceeds the limit in both directions according to the present invention. DETAILED DESCRIPTION

[0039] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0040] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present application belongs.

[0041] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application; as used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form, and it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or their combinations.

[0042] Figure 1 The equivalent circuit topology diagram of the proposed hybrid distribution transformer integrating on-load tap-changer and series-parallel converter is shown in Figure 2. Figure 2 The hybrid distribution transformer consists of a primary winding, a secondary main winding, a secondary series winding, an on-load tap changer, a series-parallel converter, and a unified coordination controller. The parallel side of the parallel converter is connected to the output of the secondary main winding, while the series side injects a compensation voltage through the secondary series winding.

[0043] The unified coordination controller of the hybrid distribution transformer performs hierarchical coordinated control of the on-load tap-changer and series-parallel converters. The voltage control is based on a hierarchical decision-making method based on voltage deviation and three-phase voltage imbalance, dynamically coordinating the slow and large-range voltage regulation of the on-load tap-changer with the fast and accurate compensation of the series-parallel converters.

[0044] In the hierarchical coordinated control method, the upper-level unified coordinated controller decides the working mode of the on-load tap-changer and the series-parallel converter based on the load-side voltage amplitude and three-phase imbalance; in the lower-level execution unit, the on-load tap-changer receives the tap adjustment instruction and executes the ratio switching, and the series-parallel converter adopts double closed-loop control.

[0045] Outer loop voltage tracking:

[0046]

[0047] in, V ref_comp is the voltage reference signal, K p is the proportionality coefficient, K i is the integration coefficient, V ref is the reference voltage, V load is the load side voltage.

[0048] Inner loop current hysteresis:

[0049]

[0050] in, I ref The current reference signal, T s is the sampling period, L f is the filter inductor, V dc is a DC voltage.

[0051] When a short-circuit current greater than twice the rated value or a series-parallel converter fault is detected, the on-load tap changer is locked and tap switching is prohibited; the series-parallel converter adopts dynamic threshold limiting, and the output current peak is limited to 1.2 times the rated value.

[0052] like Figure 3 、 4 As shown, the control method of the on-load tap-changing switch includes:

[0053] Step 1: If the three-phase voltage U i ( i = a , b , c ) exceeds the set voltage upper limit U set1 , then the blood pressure will drop.

[0054] Step 2: If the three-phase voltage U i ( i = a , b , c ) are lower than the set voltage lower limit U set2 , then the voltage is increased.

[0055] Step 3: If the voltage of two phases exceeds the upper limit and the voltage of one phase is normal, calculate whether the voltage of the normal phase is still normal after the voltage is reduced. If it is normal, reduce the voltage; otherwise, do not take any action.

[0056] Step 4: If the two-phase voltage exceeds the lower limit and the voltage of one phase is normal, calculate whether the voltage of the normal phase is still normal after the boost. If it is normal, boost the voltage; otherwise, do nothing.

[0057] Step 5: If one phase voltage exceeds the upper limit and the two phase voltages are normal, calculate whether the two phase voltages are still normal after the voltage reduction. If they are normal, reduce the voltage; otherwise, do nothing.

[0058] Step 6: If one phase voltage exceeds the lower limit and the two phase voltages are normal, calculate whether the normal two phase voltages are still normal after the voltage boost. If they are normal, boost the voltage; otherwise, do nothing.

[0059] Step 7: No action is taken in other cases.

[0060] like Figure 3 As shown, U set To control the target voltage value, the control method of the series-parallel converter includes:

[0061] Step 1: Calculate the voltage imbalance on the input side, that is

[0062]

[0063] Step 2: >2%

[0064] like , the voltage regulation amount is ;

[0065] like , the voltage regulation amount is ;

[0066] like and ,

[0067] Case 1: if , the voltage regulation amount is , U i Three-phase voltage U i The other two phases except the largest phase;

[0068] Case 2: if , the voltage regulation amount is , U i Three-phase voltage U i The other two phases except the smallest phase.

[0069] Step 3: <2%

[0070] like or , then according to the target value U set Perform voltage regulation;

[0071] like and ,

[0072] Case 1: if , the voltage regulation amount is , U iThree-phase voltage U i The other two phases except the largest phase;

[0073] Case 2: if , the voltage regulation amount is , U i Three-phase voltage U i The other two phases except the smallest phase;

[0074] Step B4: In other cases, adjust the voltage normally.

[0075] In this implementation plan, the design parameters of the hybrid distribution transformer are: 400kVA, the voltage regulation range of the on-load tap changer is 10kV (4±5%), and the series-parallel converter is 65kW (voltage regulation range ±12V). Figure 5 、 6 As shown, when the voltage exceeds the limit on the input side, the hybrid distribution transformer and voltage control method proposed in the present invention can effectively stabilize the output voltage.

[0076] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications are also considered to be within the scope of protection of the present invention.

[0077] This patent is not limited to the above-mentioned optimal implementation mode. Anyone can derive various other forms of hybrid distribution transformers and voltage control methods that integrate on-load tap-changing switches and series-parallel converters based on the inspiration of this patent. All equivalent changes and modifications made within the scope of the patent application of this invention should fall within the scope of this patent.

Claims

1. A voltage control method for a hybrid distribution transformer integrating an on-load tap changer and a series-parallel converter, characterized in that: The hybrid distribution transformer integrating an on-load tap-changer and a series-parallel converter consists of a primary-secondary winding, a series winding, an on-load tap-changer, a series-parallel converter, and a unified coordination controller; the parallel side of the series-parallel converter is connected to the output end of the secondary main winding, and the series side of the series-parallel converter injects a compensation voltage through the secondary series winding; The series-parallel converter is composed of two power electronic converters, and the parallel-side converter of the series-parallel converter maintains the DC bus voltage; By controlling the on-load tap-changer, slow and wide-range voltage regulation is achieved, and the series-parallel converter realizes voltage compensation; The control methods of the on-load tap changer include: Step A1: If the three-phase voltage U i Both exceed the set voltage upper limit U set1 , then the pressure drops, i=a,b,c; Step A2: If the three-phase voltage U i Both are lower than the set voltage lower limit U set2 , then boost, i=a,b,c; Step A3: If the three-phase voltage U i If the two-phase voltage exceeds the upper limit and one-phase voltage is normal, calculate whether the normal voltage of one phase is still normal after the voltage is reduced. If it is normal, reduce the voltage, otherwise do not operate; Step A4: If the three-phase voltage U i If the two-phase voltage exceeds the lower limit and one-phase voltage is normal, calculate whether the normal voltage of the one-phase is still normal after the voltage is boosted. If it is normal, boost the voltage, otherwise do not operate. Step A5: If the three-phase voltage U i If the voltage of one phase exceeds the upper limit and the voltages of the two phases are normal, calculate whether the voltages of the two phases are still normal after the voltage reduction. If they are normal, reduce the voltage, otherwise do not operate. Step A6: If the three-phase voltage U i If the voltage of one phase exceeds the lower limit and the voltages of the two phases are normal, calculate whether the voltages of the two phases are still normal after the voltage boost. If they are normal, boost the voltage, otherwise do not operate. Step A7: No action is taken in other cases; U set To control the target voltage value, the control method of the series-parallel converter includes: Step B1: Calculate the input side voltage imbalance ε, that is Among them, U max Is the maximum voltage among the three-phase voltages, U min It is the minimum voltage among the three-phase voltages, U a 、U b 、U c They are voltage of item a, voltage of item b, and voltage of item c respectively; Step B2: If ε>2% like The voltage regulation is ΔU=U max -U i ; like The voltage regulation is ΔU=U i -U min ; like and Case 1:if(U set -U min )>(U max -U set ), the voltage regulation amount is ΔU=U max -U i , U i is the three-phase voltage U i The other two phases except the largest phase; Case 2:if(U set -U min )<(U max -U set ), the voltage regulation amount is ΔU=U i -U min , U i is the three-phase voltage U i The other two phases except the smallest phase; If ε<2% like or According to the target value U set Perform voltage regulation; like and Case 1:if(U set -U min )>(U max -U set ), the voltage regulation amount is ΔU=U max -U i , U i is the three-phase voltage U i The other two phases except the largest phase; Case 2:if(U set -U min )<(U max -U set ), the voltage regulation amount is ΔU=U i -U min , U i is the three-phase voltage U i The other two phases except the smallest phase; Step B3: In other cases, adjust the voltage normally.

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