A design method for magnetic control transformer

Abstract

The present invention proposes a design method for a magnetic control transformer, comprising the following steps: S1, selecting the type of magnetic control transformer; S2, constructing a mathematical model of the magnetic control transformer according to the type of the magnetic control transformer; S3, setting the magnetic flux density, line load and reactive power that the magnetic control transformer needs to output as input values, inputting the input values ​​into the mathematical model of the magnetic control transformer, and obtaining the design parameters of the magnetic control transformer; S4, using simulation software to establish a magnetic circuit simulation model of the magnetic control transformer, inputting the design parameters of the magnetic control transformer for verification, and when the simulated reactive power output by the magnetic circuit simulation model and the output reactive power error are within the set range, the calculated design parameters of the magnetic control transformer are valid. The magnetic control transformer of the present invention realizes the adjustment of the excitation reactance by controlling the magnetic saturation of the iron core, which can realize both the excitation reactance adjustment function and the boost function.

Description

Technical Field

[0001] The invention relates to the technical field of high voltage, and in particular to a design method of a magnetically controlled transformer. Background Art

[0002] At present, a large number of cables are used for power supply in urban power grid construction, which increases the capacitive reactive charging power in the power system. When the load is light, there is excessive redundant capacitive reactive power. At this time, inductive reactive compensation equipment is urgently needed to compensate for the capacitive reactive power. Traditional reactive compensation schemes usually use controllable reactors, thyristor-controlled reactors, magnetically controlled reactors, etc. or active compensation devices based on power electronic equipment. However, the common problems of power electronic equipment are: low reliability, inability to work in harsh environments, high operation and maintenance costs, and electromagnetic interference generated by high-frequency switches will also affect the electromagnetic environment of the city. The other method of external controllable reactors requires an additional large area, which is not suitable for urban distribution stations with limited space. Therefore, a reliable, low-cost, flexible control, and compact inductive reactive compensation device is needed to adapt to the current construction of urban distribution networks. Summary of the invention

[0003] The present invention solves the problems of low reliability and high cost of traditional reactive power compensation devices, and proposes a design method for a magnetically controlled transformer. The magnetically controlled transformer adjusts the excitation reactance by controlling the magnetic saturation of the iron core, which can achieve both the excitation reactance adjustment function and the voltage boost function.

[0004] In order to achieve the above objectives, the following technical solutions are proposed:

[0005] A design method for a magnetically controlled transformer comprises the following steps:

[0006] S1, select the type of magnetron transformer;

[0007] S2, constructing a mathematical model of the magnetic control transformer according to the type of the magnetic control transformer;

[0008] S3, setting the magnetic flux density, line load and reactive power that the magnetic control transformer needs to output as input values, inputting the input values ​​into the mathematical model of the magnetic control transformer, and obtaining the design parameters of the magnetic control transformer;

[0009] S4, using simulation software to establish a magnetic circuit simulation model of the magnetic control transformer, input the design parameters of the magnetic control transformer for verification, when the simulated reactive power output by the magnetic circuit simulation model and the output reactive power error are within the set range, the calculated design parameters of the magnetic control transformer are valid.

[0010] Preferably, the type of magnetically controlled transformer selected in S1 is a single-phase split-core transformer, which is provided with an iron core I, an iron core II and a side yoke from left to right, and the outer sides of the iron core I and the iron core II are wound with a low-voltage primary winding with a number of turns N1 and a high-voltage secondary winding with a number of turns N2, and four identical turns N are provided. k / 2 The DC excitation control windings are wound on the iron core I and the iron core II respectively. The input voltage of the low voltage primary winding is U1, and the output voltage of the high voltage secondary winding is U2. The DC excitation control windings are cross-connected and connected to an external DC voltage source U k The iron core I and the iron core II are both provided with magnetic valves.

[0011] Preferably, the simulation software includes ANSYS and SIMULINK.

[0012] Preferably, the magnetic flux density and line load are set according to the required voltage level, capacity and volume.

[0013] Preferably, the error range between the simulated reactive power output by the magnetic circuit simulation model and the output reactive power is 0%-1%.

[0014] Preferably, the S2 specifically comprises the following steps:

[0015] S201, set the excitation inductance L m :

[0016]

[0017] Where: μ is the magnetic permeability of the core, l is the height of the coil along the core column, N represents the number of turns, and A is the cross-sectional area of ​​the core;

[0018] S202, when the rated voltage is in no-load operation state, the magnetic valve is in a critical saturation state, satisfying the formula:

[0019]

[0020] Among them: U 1m is the AC power supply voltage, A b is the cross-sectional area of ​​the core, B t is the magnetic induction intensity of the magnetic valve, ω0 is the phase of the industrial frequency AC power supply;

[0021] S203, calculate the capacity S of each phase or each column of the core column r :

[0022]

[0023] Where: I N is the rated phase current, E0 is the rated phase voltage;

[0024] S204, calculate the primary-secondary voltage ratio:

[0025]

[0026] S205, taking into account the national standard for voltage loss, the formulas from S201 to S204 are combined as the mathematical model of the magnetic control transformer.

[0027] The beneficial effects of the present invention are:

[0028] (1) Magnetron transformer has the application prospect of replacing traditional transformers and has multiple functions such as voltage transformation, reactive power regulation and voltage stabilization.

[0029] (2) The new parameter design calculation method based on intelligent magnetically controlled distribution network transformer can use analytical calculation and multiple optimization algorithms to combine to determine the values ​​of key parameters of the transformer.

[0030] (3) While compensating for reactive power, the impact of secondary side voltage drop on the power grid is taken into consideration, so that the designed magnetically controlled transformer can operate more safely and stably. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is a structural diagram of a magnetic control transformer of an embodiment;

[0032] Figure 2 is a small slope ideal BH curve model of the embodiment;

[0033] Figure 3 It is a magnetic circuit and circuit diagram of a magnetic control transformer of an embodiment;

[0034] Figure 4 is a schematic diagram of magnetic saturation of a magnetron transformer of an embodiment;

[0035] Figure 5 1 is a single-phase circuit diagram of a magnetron transformer according to an embodiment of the present invention. DETAILED DESCRIPTION

[0036] Example:

[0037] This embodiment proposes a design method for a magnetically controlled transformer, wherein the design of the magnetically controlled transformer adopts a single-phase split-core transformer structure, the two columns on the left are the iron core, the low-voltage primary winding, the high-voltage secondary winding and the DC excitation control winding are all wound on the iron core, and the column on the right is a side yoke, which provides a circuit for the excitation flux.

[0038] In addition, there is a small cross-section section in each of the two cores, which is called a magnetic valve.

[0039] In particular, the low voltage primary winding and the high voltage secondary winding are directly wound on the outside of the two cores, with the number of turns being N1 and N2 respectively.

[0040] Four identical DC excitation control windings are wound on each core column, and their number of turns is N. k / 2. The input voltage of the low-voltage primary winding is U1, the output voltage of the high-voltage secondary winding is U2, and the DC excitation control winding is cross-connected, with an external DC voltage source U k .

[0041] The excitation inductance adjustment mechanism of the magnetic control transformer is based on the nonlinear saturation characteristics of the magnetization curve of the soft magnetic material. When the magnetic saturation of the iron core increases, the magnetic permeability μ of the iron core will also decrease. l is the height of the coil along the direction of the iron core column, and N represents the number of turns. According to the circuit principle, the excitation inductance L of the iron core reactor m satisfy:

[0042]

[0043] By changing the size of the DC current in the DC excitation control winding, that is, changing the magnetic saturation degree of the small cross-section section of the iron core (i.e., the magnetic valve), the magnetic permeability of the iron core in the reactor can be continuously adjusted. The higher the magnetic permeability of the iron core, the greater the equivalent excitation inductance of the magnetic control transformer; conversely, the lower the magnetic permeability of the iron core, the smaller the equivalent excitation inductance. By adjusting the size of the DC excitation current, the equivalent excitation inductance of the magnetic control transformer can be smoothly adjusted.

[0044] It is well known that the magnetic properties of the core of a magnetic component determine the static and dynamic properties of the component. The magnetic properties of the core not only depend on the performance of the core magnetic material, but also have a great relationship with the core structure, size, excitation method, etc. In engineering, the measured dynamic basic magnetization curve (BH curve) of the core is often used to represent the magnetic properties of the core, and the complex DC excitation process is reflected as the change of the core working point on the BH curve. A large number of literatures have conducted sufficient research on the mathematical model of the BH magnetization curve of conventional magnetic materials and achieved relatively accurate research results, but these studies are mostly based on the magnetization characteristics of the core of the voltage transformer and voltage transformer during normal operation, when the magnetic induction intensity of the core is lower than the magnetic induction intensity at saturation. When the magnetic control transformer is running, the magnetic valve is in the saturation zone of the core, which has a higher working magnetic induction intensity. Therefore, the mathematical model of the BH magnetization curve of conventional magnetic materials is not suitable for the analysis of the magnetization characteristic curve of the magnetic control transformer.

[0045] In order to simulate the magnetization characteristics of the magnetic control transformer working in the magnetic saturation stage, this paper adopts a simplified magnetization curve model of piecewise linear permeability, which ignores the hysteresis effect and eddy current effect of ferromagnetic materials and assumes that the instantaneous value of the permeability of the core is equal to the air permeability when the core is saturated. Its simplified core magnetic induction intensity curve H = f (B) is as follows Figure 2 shown.

[0046] Figure 2Middle, B S is the magnetic induction intensity when the core is critically saturated, μ1 is the magnetic permeability of the core in the unsaturated region, and μ0 is the magnetic permeability of air.

[0047] According to the flux continuity theorem, the magnetic induction intensity of the magnetic valve section and the magnetic induction intensity of the iron core satisfy the following relationship:

[0048] BA b =B0(A b -A b1 )+B t A b1 (1.2)

[0049] In the formula, B is the magnetic induction intensity of the iron core, A b is the cross-sectional area of ​​the core, B0 is the magnetic induction intensity of the air next to the magnetic valve, B t is the magnetic induction intensity of the magnetic valve, A b1 is the cross-sectional area of ​​the magnetic valve.

[0050] Where B0=μ0H t Therefore, the magnetic field intensity Ht of the magnetic valve section and the magnetic induction intensity B of the iron core can be obtained and satisfy the following relationship:

[0051]

[0052] In the formula B t =mB S , B t1 It is the magnetic induction intensity value of the iron core when the magnetic valve is critically saturated.

[0053] according to Figure 1 , draw the magnetic circuit and circuit diagram of the magnetron transformer as shown Figure 3 As shown, (a) is a schematic diagram of the magnetic circuit of the magnetic control transformer, and (b) is a circuit diagram of the magnetic control transformer;

[0054] Taking magnetic flux Φ1 and Φ2 as variables, when a capacitor is connected to the secondary side of the magnetic control transformer, the corresponding circuit equation is as follows:

[0055]

[0056]

[0057]

[0058] When the magnetron transformer is working normally, the main core and the side yoke always maintain an unsaturated state, so the side yoke and the core l 11 and l 12 The magnetic field strength of the segment can be ignored, so the magnetic circuit equation of the magnetic control transformer is written as follows:

[0059] N1i1+N2i2=f(B1)(ll t1 )+f(B t1 ) t1 -N k i k (1.7)

[0060] N1i1+N2i2=f(B2)(ll t1 )+f(B t2 ) t1 +N k i k (1.8)

[0061] Where B1 is the magnetic induction intensity of the main core in core I, B2 is the magnetic induction intensity of the main core in core II, B t1 is the magnetic induction intensity of the magnetic valve in the core I, B t2 is the magnetic induction intensity of the magnetic valve in the core II, and f(B) is the corresponding magnetic field intensity.

[0062] The primary side of the magnetron transformer is connected to the industrial frequency AC power supply, so there is

[0063] U1=U 1m sin(ωt) (1.9)

[0064] Among them: U 1m is the AC power supply voltage value.

[0065] Depend on Figure 3 It can be seen that the DC magnetic flux of core I and core II is equal in magnitude and opposite in direction. The Fourier decomposition of magnetic flux Φ1 and Φ2 gives

[0066] Φ1=B1A b =a0+a k sin(ω k t)+b k cos(ω k t) (1.10)

[0067] Φ2=B2A b =-a0+c k sin(ω k t)+d k cos(ω k t) (1.11)

[0068] Substituting equations (1.12) and (1.13) into equations (1.6) to (1.8), we can obtain

[0069] a k =c k =b k =d k=0,k=2,3,4,…… (1.11)

[0070]

[0071] In order to reduce the cost of the core, the magnetic valve is usually designed to be in a critical saturation state when operating at rated voltage and no-load.

[0072]

[0073] According to formula (1.12) to formula (1.16), we can get

[0074]

[0075] Where Bd is the DC component of the magnetic induction intensity generated by the DC excitation control voltage in the main iron core.

[0076] It can be seen from equations (1.16) and (1.17) that under rated voltage, when the DC excitation current is 0, the magnetic valve is in a critical saturation state, such as Figure 4 As shown by the dashed line in the middle; when the DC excitation current is not 0, the maximum value of the core magnetic induction intensity B1 is greater than B t ,like Figure 4 As shown by the solid line in the middle, at this time, the magnetic valve section will have a magnetic saturation interval β within a power frequency cycle. This magnetic saturation interval β is defined as the magnetic saturation of the magnetic valve, and its calculation formula is expressed as follows:

[0077]

[0078] Depend on Figure 2 It can be seen that when the magnetic induction intensity of the magnetic valve section is in the magnetic saturation range, the magnetic field intensity H is much greater than its value in the unsaturated range, so the excitation reactance decreases sharply when magnetic saturation occurs.

[0079] The capacity of a transformer generally refers to the passing capacity under stable operation, that is:

[0080] S n =mU N I N ×10 -3 (kVA) (1.16) In the formula, m is the number of phases, U N Rated phase voltage (V), I N Rated phase current (A).

[0081] For the case of sinusoidal stable operation, we have:

[0082]

[0083] Where, f is the grid frequency; W is the number of turns of each phase winding in series, that is, the number of turns of each phase wound on the core column; φ m is the magnetic flux connected to the W-turn winding, that is, the magnetic flux passing through the core column.

[0084] The capacity per phase or column can be written as:

[0085]

[0086] If l represents the height of the coil along the core column, that is, the length of the core column, the ampere-turns per unit length are defined as the line load or electrical load, that is:

[0087]

[0088] When designing a device, the magnetic flux density B and the line load A S It is chosen by the designer himself. For devices with the same frequency and the same electromagnetic load, a large capacity will inevitably require a large volume.

[0089] When the magnetic control transformer enters the saturation region, the secondary voltage will drop. Figure 5 As shown, ignoring L2, the primary and secondary voltage ratio can be deduced as:

[0090]

[0091] The specific operation process of this embodiment is as follows:

[0092] Step 1: Select the appropriate magnetic flux density B and line load A according to the required voltage level, capacity and volume. s ;

[0093] Step 2: Determine the reactive power to be output. Considering the national standard for voltage loss, combine equations (1.1), (1.20) with (1.13), (1.18);

[0094] Step 3: Obtain the design parameters of the magnetic control transformer;

[0095] Step 4: Use simulation software such as ANSYS or SIMULINK to establish a magnetic circuit simulation model of the magnetic control transformer and verify the parameters obtained in the above calculation steps.

Claims

1. A design method for a magnetically controlled transformer, characterized in that: The following steps are involved: S1, select the type of magnetron transformer; S2, constructing a mathematical model of the magnetic control transformer according to the type of the magnetic control transformer; S3, setting the magnetic flux density, line load and reactive power that the magnetic control transformer needs to output as input values, inputting the input values ​​into the mathematical model of the magnetic control transformer, and obtaining the design parameters of the magnetic control transformer; S4, using simulation software to establish a magnetic circuit simulation model of the magnetic control transformer, input the design parameters of the magnetic control transformer for verification, when the simulated reactive power output by the magnetic circuit simulation model and the output reactive power error are within the set range, the calculated design parameters of the magnetic control transformer are valid.

2. The design method of a magnetically controlled transformer according to claim 1, characterized in that: The type of magnetically controlled transformer selected in S1 is a single-phase split-core transformer, which is provided with an iron core I, an iron core II and a side yoke from left to right. The outer sides of the iron core I and the iron core II are wound with a low-voltage primary winding with a number of turns N1 and a high-voltage secondary winding with a number of turns N2. At the same time, there are 4 identical turns N k / 2 DC excitation control windings are wound on core I and core II respectively. The input voltage of the low voltage primary winding is U1, and the output voltage of the high voltage secondary winding is U2. The DC excitation control windings are cross-connected and connected to an external DC voltage source U k The iron core I and the iron core II are both provided with magnetic valves.

3. The design method of a magnetically controlled transformer according to claim 1 is characterized in that: The simulation software includes ANSYS and SIMULINK.

4. The design method of a magnetically controlled transformer according to claim 1, characterized in that: The magnetic flux density and line load are set according to the required voltage level, capacity and volume.

5. The design method of a magnetically controlled transformer according to claim 1, characterized in that: The error range between the simulated reactive power output by the magnetic circuit simulation model and the output reactive power is 0%-1%.

6. The design method of a magnetically controlled transformer according to claim 1, characterized in that: The S2 specifically includes the following steps: S201, set the excitation inductance L m : Where: μ is the magnetic permeability of the core, l is the height of the coil along the core column, N represents the number of turns, and A is the cross-sectional area of ​​the core; S202, when the rated voltage is in no-load operation state, the magnetic valve is in a critical saturation state, satisfying the formula: Among them: U 1m is the AC power supply voltage, A b is the cross-sectional area of ​​the core, B t is the magnetic induction intensity of the magnetic valve, ω0 is the phase of the industrial frequency AC power supply; S203, calculate the capacity S of each phase or each column of the core column r : Where: I N is the rated phase current, E0 is the rated phase voltage; S204, calculate the primary-secondary voltage ratio: S205, taking into account the national standard for voltage loss, the formulas from S201 to S204 are combined as the mathematical model of the magnetic control transformer.

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