Secondary side coil switching device of current transformer and control method thereof

Abstract

The invention relates to a secondary side coil switching device of a current transformer and a control method thereof, and relates to the technical field of power supply. The device comprises a current transformer, a secondary side coil switching module and a secondary side coil rectifying circuit, the current transformer comprises a primary side circuit and a secondary side coil, and the secondary side coil comprises N + 1 secondary side sub-coils; the number of the secondary side coil switching modules is N, and the secondary side coil switching modules are correspondingly connected with the standby sub-coils respectively and used for controlling connection or disconnection of the corresponding standby sub-coils so as to switch the effective number of turns of the secondary side coils connected to the current transformer. And the secondary side coil rectifying circuit is connected with a secondary side coil of the current transformer and the secondary side coil switching module, and is used for converting alternating current sensed by a primary side circuit of the current transformer into direct current voltage, and triggering the secondary side coil switching module to switch on or switch off the corresponding standby sub-coil through the direct current voltage. The device can improve the energy taking stability of the current transformer.

Description

Technical Field

[0001] The present application relates to the field of power supply technology, and in particular to a secondary coil switching device of a current transformer and a control method thereof. Background Art

[0002] With the vigorous construction of smart grids, real-time monitoring of the operating status of high-voltage transmission lines has received more and more attention. The monitoring equipment of high-voltage transmission lines usually works in ultra-high potential and strong magnetic environments. Since they are directly exposed to the wild, the line distance is long and the distribution range is wide, so a more stable and reliable power supply is the basis for the safe and stable operation of real-time monitoring equipment. Common power supply methods mainly include solar power supply, battery power supply, laser power supply and ultrasonic power supply. Due to problems such as volume, cost, output power, conversion efficiency, insulation, etc., the above methods have not been effectively utilized. Current transformer energy acquisition obtains energy in the magnetic field of the transmission line through the current transformer mounted on the AC transmission line. It has the advantages of easy installation and reliable operation. It has become one of the most suitable ways to supply power to online monitoring equipment for AC transmission lines.

[0003] When traditional current transformers are used to power online monitoring equipment, large fluctuations in the current of the transmission lines will not only lead to insufficient energy extraction by the current transformer at low currents, making it impossible for downstream equipment to work normally, but also cause the current transformer core to saturate at high currents, resulting in excessively high voltage spikes, resulting in poor stability in the energy extraction of the current transformer. Summary of the invention

[0004] Based on this, it is necessary to provide a secondary coil switching device of a current transformer and a control method thereof, which can improve the stability of energy extraction of the current transformer, in order to solve the above technical problems.

[0005] A secondary coil switching device for a current transformer, comprising:

[0006] A current transformer, wherein the current transformer comprises a primary side circuit and a secondary side coil, wherein the secondary side coil comprises N+1 secondary side sub-coils; wherein the first secondary side sub-coil is an initial sub-coil connected to the current transformer by default, and the remaining N secondary side sub-coils are optional spare sub-coils connected;

[0007] A secondary coil switching module, wherein the secondary coil switching modules are N in number and are respectively connected to each of the spare sub-coils of the current transformer, and are used to control the conduction or disconnection of the corresponding spare sub-coil to switch the effective number of turns of the secondary coil connected to the current transformer;

[0008] The secondary coil rectifier circuit is connected to the secondary coil of the current transformer and the secondary coil switching module, and is used to convert the AC current sensed by the primary side line of the current transformer into a DC voltage, and trigger the secondary coil switching module through the DC voltage to turn on or off the corresponding standby sub-coil.

[0009] In one embodiment, the secondary coil rectifier circuit includes:

[0010] P 01 Port, P 02 Port, P + Port and P - port;

[0011] Among them, the P 01 The port is connected to the upper tap of the initial sub-coil, and the P 02 The port is connected to the lower tap of the initial sub-coil, and the P + port and the P - The ports are respectively the positive terminal and the negative terminal of the secondary coil rectifier circuit for outputting a DC voltage, and are connected to an external load.

[0012] In one embodiment, the secondary coil rectifier circuit further includes:

[0013] Rectifier bridge and filter capacitor;

[0014] The two AC input terminals of the rectifier bridge are respectively connected to the corresponding P 01 port and the P 02 The rectifier bridge is used to convert the AC current sensed by the primary side line of the current transformer into a DC voltage; both ends of the filter capacitor are connected to the rectifier bridge, and the two ends of the filter capacitor are respectively the P + port and the P - port, and the filter capacitor is used to smooth the DC voltage.

[0015] In one embodiment, the secondary coil switching module includes:

[0016] P i3 Port and P () port;

[0017] The P i3 The port is connected to the next secondary side coil switching module adjacent to the secondary side coil switching module, and the P () The port is connected to the previous secondary side coil switching module adjacent to the secondary side coil switching module; the secondary side coil switching module is connected to the secondary side coil switching module adjacent to the secondary side coil switching module via the P 01The port is connected to the upper tap of the initial sub-coil, and the secondary coil switching module is connected to the upper tap of the initial sub-coil through the P + The port and the P-port are connected to the secondary side coil rectifier circuit.

[0018] In one embodiment, the secondary side coil switching module further includes:

[0019] A first trigger resistor, a second trigger resistor, a third trigger resistor, a first unidirectional thyristor, a second unidirectional thyristor and a bidirectional thyristor;

[0020] One main electrode of the bidirectional thyristor is connected to the lower tap of the corresponding standby sub-coil, and the other main electrode of the bidirectional thyristor is connected to the P i3 The gate of the bidirectional thyristor is connected to the third trigger resistor; the anode of the first unidirectional thyristor and the cathode of the second unidirectional thyristor are both connected to the gate of the bidirectional thyristor through the third trigger resistor, and the cathode of the first unidirectional thyristor and the anode of the second unidirectional thyristor are both connected to the P 01 port connection; one end of the first trigger resistor is connected to the gate of the first unidirectional thyristor, one end of the second trigger resistor is connected to the gate of the second unidirectional thyristor, and the other end of the first trigger resistor and the other end of the second trigger resistor are both connected to the P () Port connection.

[0021] In one embodiment, the resistance values ​​of the first trigger resistor, the second trigger resistor and the third trigger resistor are determined by:

[0022]

[0023] Among them, R i1 is the resistance value of the first trigger resistor, R i2 is the resistance value of the second trigger resistor, R i3 is the resistance value of the third trigger resistor, IG Si1 、VTM Si1 、VGT Si1 are respectively the on-state trigger current, on-state voltage drop and voltage drop between gate and main electrode of the first unidirectional thyristor, IG Si2 、VTM Si2 、VGT Si2 are respectively the conduction trigger current of the second unidirectional thyristor and the voltage drop between the gate and the main electrode; wherein, VTM Si =VTM Si1 =VTM Si2 , I.G. Si =IG Si1 =IG Si2 ; Udci is the DC voltage output by the secondary coil rectifier circuit, V R is the voltage drop of the rectifier bridge tube of the secondary side rectifier circuit, N i is the number of spare sub-coils connected, IG Di 、VTM Di-1 、VGT Di They are respectively the on-state trigger current, on-state voltage drop and the voltage drop between the gate electrode and the main electrode of the bidirectional thyristor.

[0024] In one embodiment, the secondary side coil switching module further includes:

[0025] A first rectifying capacitor and a second rectifying capacitor;

[0026] Wherein, the anode of the first rectifying capacitor and the cathode of the second rectifying capacitor are both connected to the bidirectional thyristor, and the cathode of the first rectifying capacitor is connected to the P + The anode of the second rectifier capacitor is connected to the P_ port.

[0027] In one embodiment, the principle of the secondary coil switching module includes:

[0028] The DC voltage output by the secondary coil rectifier circuit is applied to the first trigger resistor and the second trigger resistor to generate a first trigger current; when the first trigger current meets the conduction conditions of the first unidirectional thyristor and the second unidirectional thyristor, the first unidirectional thyristor and the second unidirectional thyristor are turned on; when the first unidirectional thyristor and the second unidirectional thyristor are turned on, the voltage between the upper tap and the lower tap of the corresponding standby sub-coil is applied to the third trigger resistor through the first unidirectional thyristor and the second unidirectional thyristor, so that the third trigger resistor generates a second trigger current; when the second trigger current meets the conduction conditions of the bidirectional thyristor, the bidirectional thyristor is turned on; when the bidirectional thyristor is turned on, a forward bias voltage is applied to the first rectifier diode and the second rectifier diode, and the first rectifier diode and the second rectifier diode are turned on, so that the corresponding standby sub-coil is connected to the current transformer.

[0029] A control method for a secondary side coil switching device of a current transformer, applied to the secondary side coil switching device of the current transformer described in the above embodiment, comprises:

[0030] The initial sub-coil included in the secondary side coil of the current transformer is connected to obtain energy, and the primary side circuit of the current transformer generates an alternating current;

[0031] The secondary coil rectifier circuit outputs a DC voltage according to the AC current. When the DC voltage meets the trigger condition corresponding to any secondary coil switching module, the secondary coil switching module is triggered to turn on or off the corresponding standby sub-coil to switch the effective number of turns of the secondary coil connected to the current transformer.

[0032] In one embodiment, the method described in the above embodiment further includes:

[0033] Obtaining a current value of an alternating current in a primary side circuit of the current transformer;

[0034] The current value is compared with a preset current threshold value, and when the time during which the current value is greater than the current threshold value exceeds a preset time threshold value, all the standby sub-coils are turned off and the time is reset.

[0035] The secondary coil switching device of the current transformer and the control method thereof, the secondary coil switching device of the current transformer is composed of a current transformer, a secondary coil switching module and a secondary coil rectifier circuit. Wherein, the current transformer includes a primary side circuit and a secondary side coil, and the secondary side coil includes N+1 secondary side sub-coils; wherein, the first secondary side sub-coil is the initial sub-coil connected by default to the current transformer, and the remaining N secondary side sub-coils are optional spare sub-coils. There are N secondary side coil switching modules, which are respectively connected to each of the spare sub-coils of the current transformer, and are used to control the conduction or disconnection of the corresponding spare sub-coil to switch the effective number of turns of the secondary side coil connected to the current transformer; the secondary side coil rectifier circuit is connected to the secondary side coil of the current transformer and the secondary side coil switching module, and is used to convert the AC current induced by the primary side circuit of the current transformer into a DC voltage, and trigger the secondary side coil switching module to conduct or disconnect the corresponding spare sub-coil through the DC voltage. Therefore, the secondary coil switching module is used to control the access of the secondary coil turns, so that the equivalent turns of the secondary coil increase with the increase of the primary current. This not only expands the working range of the current transformer energy acquisition system, but also keeps the secondary side voltage of the current transformer within a reasonable range, obtaining sufficient power to supply the subsequent circuits and load equipment, thereby improving the energy acquisition stability of the current transformer. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the conventional technology, the drawings required for use in the embodiments or the conventional technology descriptions are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0037] Figure 1 It is a schematic diagram of the structure of the current transformer energy extraction system in the related technology;

[0038] Figure 2 is a structural schematic diagram of a secondary side coil switching device of a current transformer in one embodiment;

[0039] Figure 3 is a schematic structural diagram of a secondary side coil rectifier circuit in one embodiment;

[0040] Figure 4 is a structural schematic diagram of a secondary side coil switching module in an embodiment;

[0041] Figure 5 It is a flow chart of a control method of a secondary coil switching device of a current transformer in one embodiment;

[0042] Figure 6 is a structural schematic diagram of a secondary side coil switching device of a current transformer in another embodiment;

[0043] Figure 7 1 is a secondary side current and load voltage waveform diagram when the primary side current is 6A in one embodiment;

[0044] Figure 8 1 is a secondary side current and load voltage waveform diagram when the primary side current is 150A in one embodiment;

[0045] Fig. 9 1 is a secondary side current and load voltage waveform diagram when the primary side current is 1250A in an embodiment. DETAILED DESCRIPTION

[0046] In order to facilitate understanding of the present application, the present application will be described more fully below with reference to the relevant drawings. Embodiments of the present application are provided in the drawings. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present application more thorough and comprehensive.

[0047] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0048] It can be understood that the terms "first", "second", etc. used in the present application can be used in this article to describe various elements, but these elements are not limited by these terms. These terms are only used to distinguish the first element from another element.

[0049] It should be noted that when an element is considered to be "connected" to another element, it can be directly connected to the other element, or connected to the other element through an intermediate element. In addition, the "connection" in the following embodiments should be understood as "electrical connection", "communication connection", etc. if there is transmission of electrical signals or data between the connected objects.

[0050] When used herein, the singular forms "a", "an", and "said / the" may also include plural forms, unless the context clearly indicates otherwise. It should also be understood that the terms "include / comprise" or "have" etc. specify the presence of stated features, wholes, steps, operations, components, parts or combinations thereof, but do not exclude the possibility of the presence or addition of one or more other features, wholes, steps, operations, components, parts or combinations thereof.

[0051] As described in the background technology, when the traditional current transformer supplies power to the online monitoring equipment, the large fluctuation of the transmission line current will not only lead to insufficient energy extraction of the current transformer at low current, making the downstream equipment unable to work normally, but also cause the current transformer core saturation to produce excessively high voltage spikes at high current, thus resulting in the problem of poor stability of the current transformer energy extraction. The inventors have found that the reason for this problem is obtained through the following analysis: the traditional current transformer energy extraction system is as follows: Figure 1 As shown in the figure, it consists of a current transformer core, a secondary coil, a rectifier filter module and a DC-DC module. The transmission line passes through the middle of the current transformer. The AC current in the transmission line is the primary current of the current transformer. The alternating magnetic field generated by the primary AC current generates an induced voltage in the secondary coil of the current transformer, which is then used by the back-end circuit or load after passing through the rectifier filter and DC-DC conversion circuit.

[0052] In the current transformer energy extraction device, the impedance, leakage reactance, core hysteresis loss and eddy current loss of the secondary coil are relatively small, and their influence can be ignored to simplify the circuit analysis. Let I1 be the primary line current, I2 be the current of the secondary coil, I mis the excitation current, E2 is the secondary induced electromotive force, U2 is the secondary voltage, N2 is the number of turns of the secondary coil, B is the magnetic induction intensity, μ is the magnetic permeability of the magnetic core, l is the magnetic path length, A e is the core cross-sectional area, and R is the equivalent resistance on the secondary side. Then the following relationship holds:

[0053] I m 2 +N2 2 I2 2 =I1 2 (1)

[0054]

[0055] Set coefficient Then the output voltage U2 is:

[0056]

[0057] It can be seen from formula (3) that when the primary side current I1 increases, the effective value of the secondary side coil output voltage will increase.

[0058] When the current on the primary side is too small, the induced voltage on the secondary side will also be very small. At this time, it is very likely that the starting voltage of the DC-DC circuit cannot be reached, the subsequent circuit cannot work normally, and the equipment cannot be used normally.

[0059] When the primary current is too large, the core enters the saturation zone for a period of time, that is, the magnetic flux enters the flat top zone, and the magnetic flux changes very slowly relative to the linear zone. At this time, the induced electromotive force is almost zero; but near the zero point of the primary current, the magnetic induction intensity in the core quickly reaches saturation, that is, the magnetic flux in the core changes very quickly, which will generate a spike voltage. Assume that the saturation magnetic induction intensity of the core is B S , the working point of the magnetization curve in each half cycle is -B S To B S , the integral of the secondary side induced electromotive force in half a cycle is:

[0060]

[0061] From formula (4), it can be seen that when the magnetic core works in the saturation state, the volt-second value of the secondary induced electromotive force in half a cycle is a constant and has nothing to do with the primary current. As the primary current amplitude increases, the saturation degree deepens, the proportion of the magnetic flux flat-top area in the half cycle increases, and the average value of the secondary induced electromotive force remains unchanged, so the waveform of the secondary induced electromotive force will become narrower and narrower, and the peak value will become higher and higher.

[0062] Normally, when the secondary side voltage exceeds the withstand voltage level of the back-end circuit, the discharge circuit will be controlled to be turned on (i.e., the secondary side is short-circuited), and the output power of the rectifier and filter circuit will be zero, thereby protecting the back-end circuit. That is, the working range of the CT energy extraction device is limited to a certain primary side current range.

[0063] Assuming the equivalent output impedance of the secondary side is pure resistance, when the magnetic core is not saturated, the output power of the secondary side is:

[0064]

[0065] It can be seen from the above formula that when the primary current and the secondary output impedance are constant and the magnetic core is not saturated, the fewer the secondary turns, the higher the output power.

[0066] From the above analysis, it can be seen that in order to widen the primary side current range, the CT secondary side coil needs to be switched to follow the primary side current size.

[0067] Based on the above reasons, the present invention provides a secondary coil switching device of a current transformer and a control method thereof, which can improve the energy extraction stability of the current transformer.

[0068] In one embodiment, Figure 2 As shown, a secondary side coil switching device of a current transformer is provided, comprising:

[0069] A current transformer 202, the current transformer 202 includes a primary side line 2022 and a secondary side coil 2024, the secondary side coil 2024 includes N+1 secondary side sub-coils; wherein the first secondary side sub-coil is an initial sub-coil connected to the current transformer 202 by default, and the remaining N secondary side sub-coils are optional spare sub-coils that can be connected;

[0070] A secondary coil switching module 204, wherein there are N secondary coil switching modules 204, which are respectively connected to each spare sub-coil of the current transformer 202, and are used to control the conduction or disconnection of the corresponding spare sub-coil to switch the effective number of turns of the secondary coil 2024 connected to the current transformer 202;

[0071] The secondary coil rectifier circuit 206 is connected to both the secondary coil 2024 of the current transformer 202 and the secondary coil switching module 204, and is used to convert the AC current sensed by the primary side line 2022 of the current transformer 202 into a DC voltage, and trigger the secondary coil switching module 204 through the DC voltage to turn on or off the corresponding standby sub-coil.

[0072] Exemplarily, the current transformer 202 further includes a magnetic core of an open ring structure, and the secondary coil 2024 of the current transformer 202 includes N+1 secondary sub-coils, and the number of turns of the secondary sub-coils may be the same or different.

[0073] The secondary coil switching device of the current transformer 202 is composed of a current transformer 202, a secondary coil switching module 204 and a secondary coil rectifier circuit 206. The current transformer 202 includes a primary circuit 2022 and a secondary coil 2024, and the secondary coil 2024 includes N+1 secondary sub-coils; the first secondary sub-coil is the initial sub-coil connected to the current transformer 202 by default, and the remaining N secondary sub-coils are optional spare sub-coils. There are N secondary coil switching modules 204, which are respectively connected to each spare sub-coil of the current transformer 202, and are used to control the conduction or shutdown of the corresponding spare sub-coil to switch the effective number of turns of the secondary coil 2024 connected to the current transformer 202; the secondary coil rectifier circuit 206 is connected to both the secondary coil 2024 of the current transformer 202 and the secondary coil switching module 204, and is used to convert the AC current sensed by the primary side line 2022 of the current transformer 202 into a DC voltage, and trigger the secondary coil switching module 204 to conduct or shut down the corresponding spare sub-coil through the DC voltage. Therefore, the secondary coil switching module 204 is used to control the access of the turns of the secondary coil 2024, so that the equivalent turns of the secondary coil 2024 increase with the increase of the primary current, which not only expands the working range of the current transformer 202 energy acquisition system, but also keeps the secondary side voltage of the current transformer 202 within a reasonable range, obtains sufficient power to supply the subsequent circuits and load equipment, thereby improving the energy acquisition stability of the current transformer 202.

[0074] In one embodiment, Figure 3 As shown, the secondary side coil rectifier circuit includes:

[0075] P 01 Port, P 02 Port, P + Port and P - port;

[0076] Among them, P 01 The port is connected to the upper tap of the initial sub-coil, P 02 The port is connected to the lower tap of the initial sub-coil, P + The positive terminal and the negative terminal of the secondary coil rectifier circuit for outputting a DC voltage are connected to an external load.

[0077] In this embodiment, the secondary coil rectifier circuit is connected to the initial sub-coil through the AC input terminal, so that the AC current output by the secondary coil can be rectified and converted into a DC voltage, and the DC voltage can be output to the external load through the positive terminal and the negative terminal, which can ensure that the external load obtains a stable voltage supply, which is conducive to the normal operation of the external circuit or equipment.

[0078] In one embodiment, Figure 3 As shown, the secondary side coil rectifier circuit also includes:

[0079] Rectifier bridge 302 and filter capacitor 304;

[0080] The two AC input terminals of the rectifier bridge 302 are respectively connected to the corresponding P 01 Port and P 02 Port, the rectifier bridge 302 is used to convert the AC current induced by the primary side line of the current transformer into a DC voltage; both ends of the filter capacitor 304 are connected to the rectifier bridge 302, and the two ends of the filter capacitor 304 are P + Port and P - Port, filter capacitor 304 is used to smooth the DC voltage.

[0081] In this embodiment, a rectifier bridge 302 and a filter capacitor 304 are provided in the secondary measuring coil rectifier circuit to convert the AC current induced by the primary side line into a DC voltage and smooth the output DC voltage, thereby further improving the stability of the output DC voltage.

[0082] In one embodiment, Figure 4 As shown, the secondary side coil switching module also includes:

[0083] The first trigger resistor Ri1, the second trigger resistor Ri2, the third trigger resistor Ri3, the first unidirectional thyristor T Si1 , the second unidirectional thyristor T Si2 And bidirectional thyristor T Di ;

[0084] Among them, the bidirectional thyristor T Di A main electrode MT1 is connected to the lower tap of the corresponding standby sub-coil, and the bidirectional thyristor T Di The other main electrode MT2 is connected to P i3 Port, bidirectional thyristor T Di The gate of the first unidirectional thyristor T Si1 The anode of the second unidirectional thyristor T Si2 The cathode of the bidirectional thyristor T is connected to the third trigger resistor Ri3 Di The gate of the first unidirectional thyristor T Si1 The cathode of the second unidirectional thyristor TSi2 The anode of P 01 Port connection; one end of the first trigger resistor Ri1 is connected to the first unidirectional thyristor T Si1 The gate of the second trigger resistor Ri2 is connected to one end of the second unidirectional thyristor T Si2 The other end of the first trigger resistor Ri1 and the other end of the second trigger resistor Ri2 are both connected to P () Port connection.

[0085] Exemplarily, each secondary coil switching module includes a first unidirectional thyristor T Si1 , the second unidirectional thyristor T Si2 And bidirectional thyristor T Di Different trigger currents are set, so that when the standby sub-coil is switched, the trigger conditions for each standby sub-coil to be turned on are different, and the standby sub-coil can be selectively turned on according to any trigger condition reached at this time. The first trigger resistor Ri1, the second trigger resistor Ri2 and the third trigger resistor Ri3 are configured according to the first unidirectional thyristor T Si1 , the second unidirectional thyristor T Si2 And bidirectional thyristor T Di The parameters correspond to the resistance value.

[0086] In this embodiment, by setting a first unidirectional thyristor T in the secondary side coil switching module Si1 , the second unidirectional thyristor T Si2 And bidirectional thyristor T Di , and correspondingly set the first trigger resistor Ri1, the second trigger resistor Ri2 and the third trigger resistor. The thyristor has unidirectional conductivity and controllability, and has only two states: on and off. When the trigger current generated by the corresponding trigger resistor meets the on condition of the thyristor, the thyristor automatically changes from off to on, so that the corresponding standby sub-coil is turned on and connected to the current transformer, thereby adjusting the effective number of turns of the secondary coil and improving the energy-taking stability of the current transformer.

[0087] In one embodiment, the resistance values ​​of the first trigger resistor, the second trigger resistor, and the third trigger resistor described in the above embodiment are determined by the following method:

[0088]

[0089] Among them, R i1 is the resistance value of the first trigger resistor, R i2 is the resistance value of the second trigger resistor, R i3 is the resistance value of the third trigger resistor, IG S-1 、VTM Si1 、VGT Si1are the conduction trigger current, on-state voltage drop and voltage drop between gate and main electrode of the first unidirectional thyristor, IG Si2 、VTM Si2 、VGT Si2 are the conduction trigger current of the second unidirectional thyristor and the voltage drop between the gate and the main electrode respectively; where VTM Si =VTM Si1 =VTM Si2 , I.G. Si =IG Si1 =IG Si2 ; U dci is the DC voltage output by the secondary coil rectifier circuit, V R is the voltage drop of the rectifier bridge tube, N i is the number of spare sub-coils connected, IG Di 、VTM Di-1 、VGT Di They are the turn-on trigger current, on-state voltage drop and voltage drop between gate and main electrode of the bidirectional thyristor respectively.

[0090] In one embodiment, Figure 4 As shown, the secondary side coil switching module also includes:

[0091] The first rectifier capacitor D i1 and the second rectifier capacitor D i2 ;

[0092] Among them, the first rectifier capacitor D i1 The anode and the second rectifier capacitor D i2 The cathodes of the two-way thyristor are connected to the first rectifier capacitor D i1 The cathode and P + Port connection, the second rectifier capacitor D i2 The anode of is connected to the P-port.

[0093] In this embodiment, by setting a first rectifier capacitor D in the secondary coil switching module i1 and the second rectifier capacitor D i2 When the DC voltage output by the secondary coil rectifier circuit reaches the conduction threshold of the i-th secondary coil switching module, the i-th secondary coil switching module is turned on. i1 and the second rectifier capacitor D i2 The unidirectional conductivity of the standby sub-coil is such that when the i-th secondary coil switching module is turned on, no current flows through the port connections corresponding to the subsequent Ni secondary coil switching modules connected to the i-th secondary coil switching module, and the ports are in the off state. This further improves the controllability of the on and off of the standby sub-coil.

[0094] In one embodiment, the principle of the secondary coil switching module included in the secondary coil switching device of the current transformer described in the above embodiment is:

[0095] The DC voltage output by the secondary coil rectifier circuit is applied to the first trigger resistor and the second trigger resistor to generate a first trigger current; when the first trigger current meets the conduction conditions of the first unidirectional thyristor and the second unidirectional thyristor, the first unidirectional thyristor and the second unidirectional thyristor are turned on; when the first unidirectional thyristor and the second unidirectional thyristor are turned on, the voltage between the upper tap and the lower tap of the corresponding standby sub-coil is applied to the third trigger resistor through the first unidirectional thyristor and the second unidirectional thyristor, so that the third trigger resistor generates a second trigger current; when the second trigger current meets the conduction conditions of the bidirectional thyristor, the bidirectional thyristor is turned on; when the bidirectional thyristor is turned on, a forward bias voltage is applied to the first rectifier diode and the second rectifier diode, and the first rectifier diode and the second rectifier diode are turned on, so that the corresponding standby sub-coil is connected to the current transformer.

[0096] Exemplarily, when the i-1th secondary coil switching module is working, the trigger current of the first unidirectional thyristor and the second unidirectional thyristor in the i-th secondary coil switching module is generated by applying the DC voltage output by the rectifier bridge of the secondary coil rectifier circuit to the first trigger resistor and the second trigger resistor. When the trigger current reaches the trigger current corresponding to the initial conduction of the first unidirectional thyristor or the second unidirectional thyristor, the first unidirectional thyristor or the second unidirectional thyristor automatically starts to conduct; after the first unidirectional thyristor and the second unidirectional thyristor are turned on, the voltage between the upper and lower taps of the initial sub-coil is applied to the third trigger resistor R through the first unidirectional thyristor and the second unidirectional thyristor. i3 The bidirectional thyristor T Di When the trigger current reaches the trigger current of the bidirectional thyristor T Di When the trigger current corresponding to the start conduction, the bidirectional thyristor T Di Automatically starts conducting; when the bidirectional thyristor T Di After being turned on, the first rectifier diode and the second rectifier diode are subjected to the forward bias voltage and turned on. At this time, the voltage U between the lower tap of the turned-on standby sub-coil and the upper tap of the initial sub-coil is Pi2-P01 =U dc +2V R +VTM Di , and the voltage between the upper tap of the conducting standby sub-coil and the upper tap of the initial sub-coil In the bidirectional thyristor T Di-1 , the first rectifier capacitor and the second rectifier capacitor are subjected to reverse voltage and are cut off, and then the voltage on the first trigger resistor and the second trigger resistor becomes 0, and the first unidirectional thyristor T Si1 and the second unidirectional thyristor T Si2The trigger current of the first unidirectional thyristor T Si1 and the second unidirectional thyristor T Si2 Cut-off, bidirectional thyristor T Di The trigger current of the bidirectional thyristor T Di The bidirectional thyristor T is turned on until the secondary coil current becomes 0. Di Thus, the effective number of turns of the secondary coil can be controlled and switched, which improves the stability of the current transformer energy extraction.

[0097] In one embodiment, Figure 5 As shown, a control method for a secondary side coil switching device of a current transformer is provided, which is applied to the secondary side coil switching device of the current transformer described in any one of the above embodiments, and the method includes:

[0098] Step S502: The initial sub-coil included in the secondary coil of the current transformer is connected to obtain energy, and the primary circuit of the current transformer generates an alternating current.

[0099] Exemplarily, the energy acquisition of the current transformer is initialized to set the trigger condition corresponding to each spare sub-coil, and the initial sub-coil included in the secondary side coil of the current transformer is connected to obtain energy. During the energy acquisition process, the primary side line of the current transformer generates an alternating current.

[0100] Step S504, the secondary coil rectifier circuit outputs a DC voltage according to the AC current. When the DC voltage meets the trigger condition corresponding to any secondary coil switching module, the secondary coil switching module is triggered to turn on or off the corresponding standby sub-coil to switch the effective number of turns of the secondary coil connected to the current transformer.

[0101] Exemplarily, the secondary coil rectifier circuit converts the AC current into a DC voltage, and the DC voltage is applied to the secondary coil switching module. When the DC voltage meets the triggering condition of any secondary coil switching module, the secondary coil switching module is triggered to turn on or off the corresponding standby sub-coil to switch the effective number of turns of the secondary coil connected to the current transformer. + , P-, the triggering conditions of each secondary coil switching module are U dc1 , U dc2 ,……,U dci ,……,U dcn There are n in total, and U dc1 ≤U dc2 ≤……≤U dci ≤……≤U dcn ; Determine the output voltage U of the secondary coil rectifier circuit dc Whether the set value U is reacheddc1 If the result is no, continue to maintain the judgment of process 2; if the result is yes, enter the next process. The first standby sub-coil is put into operation. At this time, N=N0+N1, U dc =U P12-P01 -2V R -VTM D1 . Determine the output voltage U of the secondary coil rectifier circuit dc Whether the set value U is reached dc2 If the result is no, continue the above judgment; if the result is yes, enter the next process. Add the second spare sub-coil to work, at this time N=N0+N1+N2, U dc =U P22-P01 -2V R -VTM D2 Continue to follow the above process, and the output voltage of the rectifier bridge continues to increase. Determine the output voltage U of the rectifier bridge dc Whether the set value U is reached dci When the result is no, continue to maintain the above judgment; when the result is yes, enter the next process. Add the nth spare sub-coil, at this time N=N0+N1+N2+…+N n , U dc =U Pn2-P01 -2V R -VTM Dn Among them, VTM Dn is the on-state voltage drop of the secondary coil switching module, U Pn2-P01 is the voltage between the lower tap of the connected standby sub-coil and the upper tap of the initial sub-coil, V R It is the voltage drop of the rectifier bridge tube in the secondary coil rectifier circuit.

[0102] In this embodiment, when the primary current of the current transformer is small, only the initial coil is put into operation, and the equivalent number of turns on the secondary side is N0. At this time, the number of turns of the secondary coil is small, so that a sufficiently high electric energy can be induced when the load impedance is constant; and when the primary current gradually increases, if the secondary coil is still the original number of turns N0, the secondary side will generate a high voltage spike due to the deep saturation of the magnetic core, causing damage to the equipment. It can be seen from formula (4) that the number of turns of the secondary coil needs to be increased to reduce the rate of change of the magnetic flux in the magnetic core so that the magnetic core exits deep saturation; when the primary current continues to increase, N1, N2, N3, ..., N i 、N i+1 ,……,N n The turns are connected in sequence, which effectively alleviates the saturation of the current transformer core and reduces the secondary side voltage spike under a wide range of primary side current conditions.

[0103] In one embodiment, the method described in the above embodiment further includes:

[0104] Obtain the current value of the AC current of the primary side line of the current transformer; compare the current value with a preset current threshold, and when the current value is greater than the current threshold for a period exceeding a preset time threshold, shut down all standby sub-coils and reset the time.

[0105] Exemplarily, when initializing the current transformer, the current threshold of the primary side circuit and the time to start energy extraction are set as the start time. During the energy extraction process, the current value of the primary side circuit is monitored, and the current value is compared with the preset current threshold. When the current value is greater than the current threshold for more than the preset time threshold, all the standby sub-coils of the secondary side coil are turned off and the start time is reset. Otherwise, the previously connected standby sub-coil is kept turned on.

[0106] In this embodiment, by monitoring the current value of the primary side line in real time, abnormal conditions can be discovered in time, and when the current overload time is too long, corresponding measures can be taken to ensure the safe operation of the equipment and system.

[0107] In one embodiment, Figure 6 As shown, another structural schematic diagram of a secondary coil switching device of a current transformer is provided, and the circuit principle includes:

[0108] The ring-shaped iron-based nanocrystalline material is selected as the core of the current transformer, with a relative magnetic permeability of 50000. The inner diameter of the core is 58mm, the outer diameter is 85mm, the height is 80mm, the magnetic path length is 224mm, and the core cross-sectional area is 1080mm 2 When the primary current is set to 6A, the expected output power is greater than 0.6W. Set the secondary equivalent output resistance to 27Ω.

[0109] The secondary winding coil of the current transformer is divided into three sections, one section is the initial sub-coil with 20 turns, one section is the first spare sub-coil with 130 turns, and one section is the second spare sub-coil with 150 turns. The number of turns of the initial sub-coil is N=N0=20 turns, and all connected are N=N0+N1+N2=20+130+150=300 turns. The primary current threshold is (6, 1250]A. When the output voltage of the rectifier bridge is set to 10V, it switches from 20 turns to 150 turns, and when it is 15V, it switches from 150 turns to 300 turns.

[0110] Bidirectional thyristor T D1 , T D2 The trigger currents for the initial conduction are IG D1 IG D2 , and IG D1 =IG D2 , unidirectional thyristor T S11 , T S12 , T S21 , TS22 The trigger currents for the initial conduction are IG s11 IG s12 IG s21 IG s22 , and IG S =IG s11 =IG s12 =IG s21 =IG s22 . T D1 , T D2 The on-state voltage drops are VTM D1 and VTM D2 , T S11 , T S12 , T S21 , T S22 The on-state voltage drop is VTM S11 、VTM S12 、VTM S21 、VTM S22 , VTM S =VTM S11 =VTM S12 =VTM S21 =VTM S22 ; T D1 , T D2 The voltage drop between the gate and the main electrode is VGT D1 、VGT D2 , T S11 , T S12 , T S21 , T S22 The gate-cathode voltage drops are VGT S11 、VGT S12 、VGT S21 、VGT S22 , VGT S =VGT S11 =VGT S12 =VGT S21 =VGT S22 ; Assume the voltage drop of the rectifier bridge is V R .

[0111] Assume that the output voltage of the rectifier bridge reaches U dc1 When the secondary coil is switched from 20 turns to 150 turns, the voltage of the 20-turn coil just before the switch is (U dc1 +2V R ), the voltage of the 150-turn coil is ((U dc1 +2V R )*150 / 20). When the output voltage of the rectifier bridge reaches U dc1 , that is, T S11 , TS12 The gate resistance R 11 , R 12 The voltage on the dc1 +2V R -VGT S ), the gate current reaches IG S11 IG S12 , T S11 , T S12 When T S11 , T S12 After the conduction, the voltage of the 150-turn coil is applied to R 13 Upper, R 13 The voltage on the dc1 +2V R )*150 / 20-VTM S -VGT D1 ).

[0112] When T D1 The gate current reaches IG D1 When T D1 The secondary coil is switched from 20 turns to 150 turns, and the voltage of the 150-turn coil immediately becomes (U dc1 +2V R +VTM D1 ); the voltage of the 20-turn coil immediately becomes (U dc1 +2V R +VTM D1 )*20 / 150, T S11 , T S12 The gate current is pulled down instantaneously, causing T S11 , T S12 Cut-off, T D1 The gate current becomes zero, but at this time T D1 It is turned on. T D1 The rectifier bridge output voltage U' corresponding to the moment before opening dc1 ≤U dc1 , so that T S11 , T S12 When conducting, T D1 The trigger current immediately reaches IG D1 , T D1 Immediately turn on; from T S11 , T S12 Turn-on time to T D1 The shorter the time period between the conduction moments, the greater the 13 The smaller the loss.

[0113] Assume that the output voltage of the rectifier bridge reaches U dc2When the secondary coil is switched from 150 turns to 300 turns, the voltage of the 150-turn coil just before the switch is (U dc2 +2V R +VTM D1 ), the voltage of the 300-turn coil is ((U dc2 +2V R +VTM D1 )*300 / 150). When reaching U dc2 , that is, T S21 , T S22 The gate resistance R 21 , R 22 The voltage on the dc2 +2V R -VGT S ), the gate current reaches IG S21 IG S22 , T S21 , T S22 When T S21 , T S22 After the conduction, the voltage of the 300-turn coil is applied to R 23 Upper, R 23 The voltage on the dc2 +2V R +VTM D1 )*300 / 150-VTM S -VGT D2 ).

[0114] When T D2 The gate current reaches IG D2 When T D2 The secondary coil is switched from 150 turns to 300 turns, and the voltage of the 300-turn coil immediately becomes (U dc2 +2V R +VTM D2 ); the voltage of the 150-turn coil immediately drops to (U dc2 +2V R +VTM D2 )*150 / 300, T S21 , T S22 The gate current is pulled down instantaneously, causing T S21 , T S22 Cut-off, T D2 The gate current becomes zero, but at this time T D2 It is turned on. T D2 The rectifier bridge output voltage U' corresponding to the moment before opening dc2 ≤U dc2 , so that T S21 , T S22 When conducting, T D2The trigger current immediately reaches IG D2 , T D2 Immediately turn on; from T S21 , T S22 Turn-on time to T D2 The shorter the time period between the conduction moments, the greater the 23 The smaller the loss.

[0115] In this embodiment, U dc1 =10V,U dc2 =15V.

[0116] When the primary current is 6A, the secondary current and load voltage are as follows: Figure 7 As shown in the figure, it can be seen that the load voltage is about 5V and the output power is close to 1W.

[0117] When the primary current is 150A, the secondary current and load voltage are as follows: Figure 8 It can be seen that the switching starts at about 10V load voltage, switching from 20 turns to 150 turns, the secondary current waveform changes from distortion to sine wave, and the magnetic core exits saturation.

[0118] When the primary current is 1250A, the secondary current and load voltage are as follows: Fig. 9 It can be seen that the switching starts at about 15V load voltage, from 150 turns to 300 turns, and the secondary current waveform is a sine wave.

[0119] In this embodiment, the secondary coil switching module is used to control the access of the secondary coil turns, so that the equivalent turns of the secondary coil increase with the increase of the primary current, which not only expands the working range of the CT energy acquisition system, but also keeps the secondary side voltage of the current transformer within a suitable range, thereby obtaining sufficient power to supply the subsequent circuits and load devices.

[0120] It should be understood that, although the various steps in the flowcharts involved in the above-mentioned embodiments are displayed in sequence according to the indication of the arrows, these steps are not necessarily executed in sequence according to the order indicated by the arrows. Unless there is a clear explanation in this article, the execution of these steps is not strictly limited in order, and these steps can be executed in other orders. Moreover, at least a part of the steps in the flowcharts involved in the above-mentioned embodiments can include multiple steps or multiple stages, and these steps or stages are not necessarily executed at the same time, but can be executed at different times, and the execution order of these steps or stages is not necessarily carried out in sequence, but can be executed in turn or alternately with other steps or at least a part of the steps or stages in other steps.

[0121] In the description of this specification, the description with reference to the terms "some embodiments", "other embodiments", "ideal embodiments", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic descriptions of the above terms do not necessarily refer to the same embodiment or example.

[0122] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0123] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.

Claims

1. A secondary coil switching device for a current transformer, characterized in that: include: A current transformer, wherein the current transformer comprises a primary side circuit and a secondary side coil, wherein the secondary side coil comprises N+1 secondary side sub-coils; wherein the first secondary side sub-coil is an initial sub-coil connected to the current transformer by default, and the remaining N secondary side sub-coils are optional spare sub-coils connected; A secondary coil switching module, wherein the secondary coil switching modules are N in number and are respectively connected to each of the spare sub-coils of the current transformer, and are used to control the conduction or disconnection of the corresponding spare sub-coil to switch the effective number of turns of the secondary coil connected to the current transformer; The secondary coil rectifier circuit is connected to the secondary coil of the current transformer and the secondary coil switching module, and is used to convert the AC current sensed by the primary side line of the current transformer into a DC voltage, and trigger the secondary coil switching module through the DC voltage to turn on or off the corresponding standby sub-coil.

2. The secondary coil switching device of the current transformer according to claim 1, characterized in that: The secondary coil rectifier circuit comprises: P 01 Port, P 02 Port, P + Port and P - port; Among them, the P 01 The port is connected to the upper tap of the initial sub-coil, and the P 02 The port is connected to the lower tap of the initial sub-coil, and the P + port and the P - The ports are respectively the positive terminal and the negative terminal of the secondary coil rectifier circuit for outputting a DC voltage, and are connected to an external load.

3. The secondary coil switching device of the current transformer according to claim 2, characterized in that: The secondary coil rectifier circuit also includes: Rectifier bridge and filter capacitor; The two AC input terminals of the rectifier bridge are respectively connected to the corresponding P 01 port and the P 02 The rectifier bridge is used to convert the AC current sensed by the primary side line of the current transformer into a DC voltage; both ends of the filter capacitor are connected to the rectifier bridge, and the two ends of the filter capacitor are respectively the P + port and the P - port, and the filter capacitor is used to smooth the DC voltage.

4. The secondary coil switching device of the current transformer according to claim 2, characterized in that: The secondary side coil switching module comprises: P i3 Port and P (i-1)3 port; The P i3 The port is connected to the next secondary side coil switching module adjacent to the secondary side coil switching module, and the P (i-1)3 The port is connected to the previous secondary side coil switching module adjacent to the secondary side coil switching module; the secondary side coil switching module is connected to the secondary side coil switching module adjacent to the secondary side coil switching module via the P 01 The port is connected to the upper tap of the initial sub-coil, and the secondary coil switching module is connected to the upper tap of the initial sub-coil through the P + port and the P - The port is connected to the secondary side coil rectifier circuit.

5. The secondary coil switching device of the current transformer according to claim 4, characterized in that: The secondary side coil switching module also includes: A first trigger resistor, a second trigger resistor, a third trigger resistor, a first unidirectional thyristor, a second unidirectional thyristor and a bidirectional thyristor; One main electrode of the bidirectional thyristor is connected to the lower tap of the corresponding standby sub-coil, and the other main electrode of the bidirectional thyristor is connected to the P i3 The gate of the bidirectional thyristor is connected to the third trigger resistor; the anode of the first unidirectional thyristor and the cathode of the second unidirectional thyristor are both connected to the gate of the bidirectional thyristor through the third trigger resistor, and the cathode of the first unidirectional thyristor and the anode of the second unidirectional thyristor are both connected to the P 01 port connection; one end of the first trigger resistor is connected to the gate of the first unidirectional thyristor, one end of the second trigger resistor is connected to the gate of the second unidirectional thyristor, and the other end of the first trigger resistor and the other end of the second trigger resistor are both connected to the P (i-1)3 Port connection.

6. The secondary coil switching device of the current transformer according to claim 5, characterized in that: The resistance values ​​of the first trigger resistor, the second trigger resistor and the third trigger resistor are determined by the following method: Among them, R i1 is the resistance value of the first trigger resistor, R i2 is the resistance value of the second trigger resistor, R i3 is the resistance value of the third trigger resistor, IG Si1 、VTM Si1 、VGT Si1 are respectively the on-state trigger current, on-state voltage drop and voltage drop between gate and main electrode of the first unidirectional thyristor, IG Si2 、VTM Si2 、VGT Si2 are respectively the conduction trigger current of the second unidirectional thyristor and the voltage drop between the gate and the main electrode; wherein, VTM Si =VTM sI1 =VTM Si2 , I.G. si =IG Si1 =IG Si2 ; U dci is the DC voltage output by the secondary coil rectifier circuit, V R is the voltage drop of the rectifier bridge tube of the secondary side rectifier circuit, N i is the number of spare sub-coils connected, IG Di 、VTM Di-1 、VGT Di They are respectively the on-state trigger current, on-state voltage drop and the voltage drop between the gate electrode and the main electrode of the bidirectional thyristor.

7. The secondary coil switching device of the current transformer according to claim 5, characterized in that: The secondary side coil switching module also includes: A first rectifying capacitor and a second rectifying capacitor; Wherein, the anode of the first rectifying capacitor and the cathode of the second rectifying capacitor are both connected to the bidirectional thyristor, and the cathode of the first rectifying capacitor is connected to the P + The anode of the second rectifier capacitor is connected to the P - Port connection.

8. The secondary coil switching device of the current transformer according to claim 7, characterized in that: The principle of the secondary coil switching module includes: The DC voltage output by the secondary coil rectifier circuit is applied to the first trigger resistor and the second trigger resistor to generate a first trigger current; when the first trigger current meets the conduction conditions of the first unidirectional thyristor and the second unidirectional thyristor, the first unidirectional thyristor and the second unidirectional thyristor are turned on; when the first unidirectional thyristor and the second unidirectional thyristor are turned on, the voltage between the upper tap and the lower tap of the corresponding standby sub-coil is applied to the third trigger resistor through the first unidirectional thyristor and the second unidirectional thyristor, so that the third trigger resistor generates a second trigger current; when the second trigger current meets the conduction conditions of the bidirectional thyristor, the bidirectional thyristor is turned on; when the bidirectional thyristor is turned on, a forward bias voltage is applied to the first rectifier diode and the second rectifier diode, and the first rectifier diode and the second rectifier diode are turned on, so that the corresponding standby sub-coil is connected to the current transformer.

9. A control method for a secondary coil switching device of a current transformer, applied to the secondary coil switching device of a current transformer according to any one of claims 1 to 8, characterized in that: include: The initial sub-coil included in the secondary side coil of the current transformer is connected to obtain energy, and the primary side circuit of the current transformer generates an alternating current; The secondary coil rectifier circuit outputs a DC voltage according to the AC current. When the DC voltage meets the trigger condition corresponding to any secondary coil switching module, the secondary coil switching module is triggered to turn on or off the corresponding standby sub-coil to switch the effective number of turns of the secondary coil connected to the current transformer.

10. The control method of the secondary coil switching device of the current transformer according to claim 8, characterized in that: The method further comprises: Obtaining a current value of an alternating current in a primary side circuit of the current transformer; The current value is compared with a preset current threshold value, and when the time during which the current value is greater than the current threshold value exceeds a preset time threshold value, all the standby sub-coils are turned off and the time is reset.

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