Hybrid distribution transformer fusing on-load tap changer and series-parallel converter and voltage control method

Abstract

The invention discloses a hybrid distribution transformer fusing an on-load tap changer and a series-parallel converter and a voltage control method, and belongs to the technical field of intelligent power distribution. The hybrid distribution transformer comprises 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 end of the secondary main winding, and compensation voltage is injected into the series side of the parallel converter through the secondary series winding. The voltage control is based on a voltage deviation and three-phase voltage unevenness hierarchical decision-making method, and the low-speed large-range voltage regulation of the on-load tap changer and the rapid and accurate compensation of the series-parallel converter are dynamically coordinated. The method has the high capacity advantage of an on-load tap changer and the quick response characteristic of a power electronic device, can synchronously solve the problems of long-term voltage deviation and instantaneous voltage fluctuation in the power distribution network, reduces the equipment cost and maintenance cost, and is suitable for voltage stabilization and electric energy quality optimization of the intelligent power distribution network.

Description

Technical Field

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

[0002] Traditional on-load tap-changing transformers adjust the transformer ratio through mechanical tap-changers to achieve rough voltage adjustment, but the response speed is slow (seconds), frequent operation can easily lead to mechanical wear, and it is difficult to cope with rapid voltage fluctuations (such as sudden changes in photovoltaic output and impact loads). Power electronic voltage regulators (such as DVR / SST) based on series-parallel converters of fully controlled devices (such as IGBT) can achieve millisecond-level dynamic compensation, but the capacity is limited, the cost is high, and it is difficult to take into account a wide range of voltage regulation needs when used alone. The on-load tap-changing transformer and power electronic devices operate independently and lack coordination, resulting in an inability to balance the adjustment range and response speed; a single device is difficult to solve the problems of long-term voltage offset and instantaneous voltage fluctuations at the same time; long-term full-load operation of power electronic devices leads to high losses and reduced reliability.

[0003] By integrating the on-load tap-changing switch 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, thereby reducing the overall cost and extending the 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 integrating an on-load tap-changing switch and a series-parallel converter, which has the high capacity advantage of the on-load tap-changing switch and the fast response characteristics of the power electronic device, can simultaneously solve the problems of long-term voltage deviation and instantaneous voltage fluctuation in the distribution network, and at the same time reduce equipment cost and maintenance cost, and is suitable for voltage stability and power quality optimization of smart distribution networks.

[0005] To achieve the above-mentioned purpose, the present invention adopts the following technical scheme: a hybrid distribution transformer integrating an on-load tap-changing switch and a series-parallel converter, which is composed of an original secondary winding, a series winding, an on-load tap-changing switch, 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 integrating an on-load tap-changer and a series-parallel converter. By using the hybrid distribution transformer integrating an on-load tap-changer and a series-parallel converter, slow and large-range voltage regulation is achieved by controlling the on-load tap-changer, 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: Step A1: If the three-phase voltages U i all exceed the set voltage upper limit U set1 , then step down the voltage, i = a , b , c ; Step A2: If the three-phase voltages U i all are lower than the set voltage lower limit U set2 , then step up the voltage, i = a , b , c ; Step A3: If two of the three-phase voltages U i exceed the upper limit and one is normal, calculate whether the voltage of the normal phase after stepping down is still normal. If it is normal, then step down the voltage; otherwise, do not act. Step A4: If two of the three-phase voltages U i are lower than the lower limit and one is normal, calculate whether the voltage of the normal phase after stepping up is still normal. If it is normal, then step up the voltage; otherwise, do not act. Step A5: If one of the three-phase voltages U i exceeds the upper limit and two are normal, calculate whether the voltages of the two normal phases after stepping down are still normal. If it is normal, then step down the voltage; otherwise, do not act. Step A6: If one of the three-phase voltages U i is lower than the lower limit and two are normal, calculate whether the voltages of the two normal phases after stepping up are still normal. If it is normal, then step up the voltage; otherwise, do not act. Step A7: Do not act in other cases.

[0009] In a preferred embodiment, U set is the voltage control target value, and the control method of the series-parallel converter includes: Step B1: Calculate the voltage unbalance degree of the input side, that is, Among them, 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 are respectively ; Step B2: > 2% If , the voltage regulation amount is ; If , the voltage regulation amount is ; If and , Case 1: if , the voltage regulation amount is , U i is the other two phases of the three-phase voltage U i except the maximum phase; Case 2: if , the voltage regulation amount is , U i is the other two phases of the three-phase voltage U i except the minimum phase; Step B3: < 2% If or , then adjust the voltage according to the target value U set ; If and , Case 1: if , the voltage regulation amount is , U i is the other two phases of the three-phase voltage U i except the maximum phase; Case 2: if , the voltage regulation amount is , U i is the three-phase voltageU i The other two phases except the smallest phase; Step B4: Adjust the voltage normally in other cases.

[0010] Compared with the prior art, the present invention has the following beneficial effects: (1) By integrating the structures, the system complexity and cost are reduced, while the advantages of the on-load tap-changer with large capacity and the fast response characteristics of power electronics are retained; (2) The coordinated control strategy reduces the operation times of the on-load tap-changer and prolongs the mechanical life; (3) The series-parallel converters can be compatible with the functions of reactive power compensation and harmonic suppression, improving the comprehensive power quality. Description of the Drawings

[0011] Figure 1 It is a schematic diagram of the equivalent circuit topology of the hybrid distribution transformer of the present invention.

[0012] Figure 2 It is a structural diagram of the hybrid distribution transformer of the present invention.

[0013] Figure 3 It is the voltage coordinated control method (1) of the present invention.

[0014] Figure 4 It is the voltage coordinated control method (2) of the present invention.

[0015] Figure 5 It is the voltage stability effect diagram under the condition that the voltage on the power supply side drops below the limit of the present invention.

[0016] Figure 6 It is the voltage stability effect diagram under the condition that the voltage on the power supply side exceeds the limit in both directions of the present invention. Detailed Embodiments

[0017] The present invention will be further described below in conjunction with the drawings and embodiments.

[0018] It should be noted that the following detailed description is illustrative and is intended to provide further description of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present application belongs.

[0019] 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. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0020] Figure 1It is a schematic diagram of the equivalent circuit topology of the hybrid distribution transformer integrating the on-load tap-changer and the series-parallel converter. Figure 2 It is a structural diagram. 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 terminal of the secondary main winding, and the series side injects a compensation voltage through the secondary series winding.

[0021] The unified coordination controller of the hybrid distribution transformer conducts hierarchical coordination control on the on-load tap-changer and the series-parallel converter. The voltage control is based on a hierarchical decision-making method of voltage deviation and three-phase voltage unbalance degree, dynamically coordinating the slow and large-range voltage regulation of the on-load tap-changer and the fast and precise compensation of the series-parallel converter.

[0022] In the hierarchical coordination control method, the upper-layer unified coordination controller determines the working modes of the on-load tap-changer and the series-parallel converter based on the load-side voltage amplitude and three-phase unbalance degree; in the lower-layer execution unit, the on-load tap-changer receives the tap adjustment instruction and executes the turns ratio switching, and the series-parallel converter adopts double-loop control.

[0023] Outer-loop voltage tracking: Among them, V ref_comp is the voltage reference signal, K p is the proportional coefficient, K i is the integral coefficient, V ref is the reference voltage, V load is the load-side voltage.

[0024] Inner-loop current hysteresis: Among them, I ref is the current reference signal of, T s is the sampling period, L f is the filter inductor, V dc is the DC voltage.

[0025] When the detected short-circuit current is greater than 2 times the rated value or the series-parallel converter fails, the on-load tap-changer is locked to prohibit tap switching; the series-parallel converter adopts dynamic threshold limiting, and the output current peak is limited to 1.2 times the rated value.

[0026] Such as Figure 3 、 4As shown, the control method of the on-load tap-changer includes: Step 1: If the three-phase voltages U i ( i = a , b , c ) all exceed the set upper voltage limit U set1 , then step down the voltage.

[0027] Step 2: If the three-phase voltages U i ( i = a , b , c ) all are lower than the set lower voltage limit U set2 , then step up the voltage.

[0028] Step 3: If two-phase voltages exceed the upper limit and one-phase voltage is normal, calculate whether the voltage of the normal one-phase after stepping down is still normal. If it is normal, then step down the voltage; otherwise, do not act.

[0029] Step 4: If two-phase voltages are lower than the lower limit and one-phase voltage is normal, calculate whether the voltage of the normal one-phase after stepping up is still normal. If it is normal, then step up the voltage; otherwise, do not act.

[0030] Step 5: If one-phase voltage exceeds the upper limit and two-phase voltages are normal, calculate whether the voltages of the two normal phases after stepping down are still normal. If it is normal, then step down the voltage; otherwise, do not act.

[0031] Step 6: If one-phase voltage is lower than the lower limit and two-phase voltages are normal, calculate whether the voltages of the two normal phases after stepping up are still normal. If it is normal, then step up the voltage; otherwise, do not act.

[0032] Step 7: Do not act in other cases.

[0033] As Figure 3 shown, U set For the voltage control target value, the control method of the series-parallel converter includes: Step 1: Calculate the voltage unbalance degree on the input side, that is Step 2: > 2% If , the voltage regulation amount is ; If , the voltage regulation amount is ; If and , Case 1: if , the voltage regulation amount is , U i is the three-phase voltage U i for the other two phases except the maximum phase in Case 2: if , the voltage regulation amount is , U i is the three-phase voltage U i for the other two phases except the minimum phase in

[0034] Step 3: <2% If or , then adjust the voltage according to the target value U set ; If and , Case 1: if , the voltage regulation amount is , U i is the three-phase voltage U i for the other two phases except the maximum phase in Case 2: if , the voltage regulation amount is , U i is the three-phase voltage U i for the other two phases except the minimum phase in Step B4: In other cases, adjust the voltage normally.

[0035] In this implementation, the design parameters of the hybrid distribution transformer are: 400 kVA, the voltage regulation range of the on-load tap-changer is 10 kV (4 ± 5%), and the series-parallel converter is 65 kW (voltage regulation range ±12 V). As Figure 5 、 6 shown, when the voltage exceeds the limit on the input side, the hybrid distribution transformer and voltage control method proposed by the present invention can effectively stabilize the output voltage.

[0036] The above is the preferred implementation of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications are also regarded as the protection scope of the present invention.

[0037] This patent is not limited to the above-mentioned best implementation mode. Anyone inspired by this patent can obtain various other forms of hybrid distribution transformers integrating on-load tap-changer and series-parallel converters, as well as voltage control methods. All equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope covered by this patent.

Claims

1. A hybrid distribution transformer integrating an on-load tap changer and a series-parallel converter, characterized in that It consists of an original secondary winding, a series winding, an on-load voltage regulating switch, 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.

2. A hybrid distribution transformer integrating an on-load tap changer and a series-parallel converter according to claim 1, characterized in that: 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.

3. A voltage control method for a hybrid distribution transformer integrating an on-load tap changer and a series-parallel converter, characterized in that: A hybrid distribution transformer integrating an on-load tap-changing switch and a series-parallel converter as described in claim 1 or 2 is used to achieve slow and wide-range voltage regulation by controlling the on-load tap-changing switch, and to achieve voltage compensation by the series-parallel converter.

4. The voltage control method of a hybrid distribution transformer integrating an on-load tap changer and a series-parallel converter according to claim 3, characterized in that: The control method of the on-load tap-changing switch includes: Step A1: If the three-phase voltage U i Exceeds 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 the voltage is increased, 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 voltage of the normal phase is still normal after the voltage reduction. If it is normal, reduce the voltage, otherwise do not act; 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 boosting. If it is normal, boost the voltage, otherwise do not act; 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 reduction. If it is normal, reduce the voltage, otherwise do not act; Step A6: If the three-phase voltage U i If the voltage of one phase exceeds the lower limit and the voltage of two phases is normal, calculate whether the voltage of the two phases is still normal after the voltage is boosted. If it is normal, boost the voltage, otherwise do not act; Step A7: No action is taken in other cases.

5. The voltage control method of a hybrid distribution transformer integrating an on-load tap changer and a series-parallel converter according to claim 4, characterized in that: U set To control the target voltage value, the control method of the series-parallel converter includes: Step B1: Calculate the input voltage imbalance ,Right now in, 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 ; Step B2: >2% like , the voltage regulation amount is ; like , the voltage regulation amount is ; like and , Case 1: if , the voltage regulation amount is , U i For three-phase voltage U i The other two phases except the largest phase; Case 2: if , the voltage regulation amount is , U i For three-phase voltage U i The other two phases except the smallest phase; Step B3: <2% like or , then according to the target value U set To regulate the voltage; like and , Case 1: if , the voltage regulation amount is , U i For three-phase voltage U i The other two phases except the largest phase; Case 2: if , the voltage regulation amount is , U i For three-phase voltage U i The other two phases except the smallest phase; Step B4: In other cases, the voltage is adjusted normally.

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