A DC current measurement device and method

Abstract

The present application provides a DC current measurement device and method. Since the DC current causes the two current transformers to reach the magnetic saturation state, and the auxiliary voltage module applies an AC voltage with positive and negative periodic changes to the connection module, demagnetizes the first current transformer and magnetizes the second current transformer during the positive cycle, and magnetizes the first current transformer and demagnetizes the second current transformer during the negative cycle, the two current transformers are alternately demagnetized; and since the connection module uses the larger secondary current on the two current transformers as the measurement result of the DC current measurement device, the ratio of the output measurement result to the DC current on the primary line is equal to the turn ratio of the primary winding and the secondary winding of the two current transformers, that is, the DC current measurement device realizes the measurement of the DC current on the primary line; the DC current measurement device is only based on the two current transformers, the connection module, and the auxiliary voltage module, so the measurement cost of the DC current measurement device is reduced.

Description

Technical Field

[0001] The present invention relates to the field of power electronics technology, and particularly to a DC current measurement device and method. Background Art

[0002] Currently, DC power transmission is usually achieved by a DC power transmission system; in the DC power transmission system, a DC current transformer is usually arranged at an important position to monitor the DC current at the important position and provide control signals for the safe and stable operation of the DC power transmission system.

[0003] In the prior art, DC current transformers can be divided into: zero-flux DC current transformers, fiber-optic DC current transformers, Hall current sensors, and optoelectronic DC transformers. According to their different structures and working principles, they can realize the measurement of DC currents at different positions.

[0004] However, the cost of measuring DC current by the above-mentioned DC current transformers is relatively high, which is an urgent problem to be solved at present. Summary of the Invention

[0005] In view of this, the present invention provides a DC current measurement device and method to reduce the cost of measuring DC current.

[0006] To achieve the above object, the embodiments of the present invention provide the following technical solutions:

[0007] On the one hand, the present application provides a DC current measurement device, including: a connection branch, an auxiliary voltage module, and a first transformer and a second transformer with the same parameters and opposite polarities; wherein:

[0008] The primary windings of the two transformers are used to sample the DC current on the primary line; the DC current causes the two transformers to reach the magnetic saturation state;

[0009] The connection module is used to establish the connection between the first ends of the secondary windings of the two transformers and the connection between the second ends, and use the larger secondary current on the two transformers as the measurement result of the DC current measurement device;

[0010] The auxiliary voltage module is used to apply an AC voltage with positive and negative periodic changes to the connection module, demagnetize the first transformer and magnetize the second transformer during the positive cycle, and magnetize the first transformer and demagnetize the second transformer during the negative cycle.

[0011] Optionally, the connection module includes: a first unidirectional conduction branch, a second unidirectional conduction branch, a third unidirectional conduction branch, and an auxiliary resistor, and a measurement resistor or a current sensor; wherein:

[0012] The input end of the first unidirectional conduction branch is connected to the second end of the secondary winding of the first transformer, and the output end of the first unidirectional conduction branch is connected to the second end of the secondary winding of the second transformer;

[0013] The input end of the second unidirectional conduction branch is connected to the first end of the secondary winding of the first transformer, and the output end of the first unidirectional conduction branch is connected to the first end of the secondary winding of the second transformer;

[0014] An internal connection point of the first unidirectional conduction branch and an internal connection point of the second unidirectional conduction branch are respectively connected to two poles of the auxiliary voltage module;

[0015] The input end of the third unidirectional conduction branch is connected to the second end of the secondary winding of the second transformer, and the output end of the third unidirectional conduction branch is connected to the second end of the secondary winding of the first transformer through the measuring resistor or the current sensor;

[0016] The auxiliary resistor is connected in parallel between two ends of the second unidirectional conduction branch;

[0017] The measuring resistor is used to convert the larger secondary current on the two transformers into the voltage across its own two ends and use it as the measurement result of the DC current measuring device;

[0018] The current sensor is used to measure the larger secondary current on the two transformers and use its own measurement result as the measurement result of the DC current measuring device.

[0019] Optionally, both the first unidirectional conduction branch and the second unidirectional conduction branch include: at least two first diodes; in the first unidirectional conduction branch and the second unidirectional conduction branch:

[0020] All the first diodes are connected end to end, and the positive pole of the formed connection branch is used as the input end of the corresponding unidirectional conduction branch, and the negative pole is used as the output end of the corresponding unidirectional conduction branch;

[0021] The connection point of any two adjacent first diodes is used as an internal connection point of the corresponding unidirectional conduction branch.

[0022] Optionally, the third unidirectional conduction branch includes: at least one second diode; among them:

[0023] If the number of the second diodes is greater than 1, all the second diodes are connected end to end, and the positive pole of the formed connection branch is used as the input end of the third unidirectional conduction branch, and the negative pole is used as the output end of the third unidirectional conduction branch.

[0024] Optionally, the AC periodic voltage is a sinusoidal AC signal.

[0025] Optionally, the auxiliary voltage module includes: an auxiliary control circuit, a switching switch, and an isolation transformer with an auxiliary winding having multiple taps; wherein:

[0026] One end of the auxiliary voltage module is connected to one end of the isolation transformer, the other end of the auxiliary voltage module is connected to the first end of the switching switch, and the primary winding of the isolation transformer receives the power frequency voltage;

[0027] The output end of the auxiliary control circuit is connected to the control end of the switching switch, and is used to control the second end of the switching switch to be connected to the initial tap of the auxiliary winding of the isolation transformer to output the AC voltage, and also control the second end of the switching switch to be connected to the corresponding tap of the auxiliary winding of the isolation transformer according to the measurement result to adjust the amplitude of the AC voltage.

[0028] On the other hand, the present application provides a DC current measurement method, which is characterized in that it is applied to a controller and is used to control the DC current measurement device as described in any one of the previous aspects of the present application; the DC current measurement method includes:

[0029] Controlling the auxiliary voltage module in the DC current measurement device to output an AC voltage with a preset amplitude that changes periodically between positive and negative;

[0030] Calculating the DC current on the primary line according to the measurement result output by the DC current measurement device.

[0031] Optionally, if the connection branch in the DC current measurement device includes a measurement resistor, then the step of calculating the DC current on the primary line according to the measurement result output by the DC current measurement device includes:

[0032] Calculating the current flowing through the measurement resistor according to the measurement result and the resistance value of the measurement resistor;

[0033] Calculating the DC current on the primary line according to the turns ratio of the primary winding and the secondary winding of the current transformer and the current flowing through the measurement resistor.

[0034] Optionally, if the connection branch includes a current sensor, then the step of calculating the DC current on the primary line according to the measurement result output by the DC current measurement device includes:

[0035] Calculating the DC current according to the measurement result and the turns ratio of the primary winding and the secondary winding of the current transformer.

[0036] Optionally, after the step of calculating the DC current on the primary line based on the measurement result output by the DC current measurement device, the method further includes:

[0037] Controlling the auxiliary voltage module to adjust the amplitude of the AC voltage according to the measurement result.

[0038] Optionally, the step of controlling the auxiliary voltage module to adjust the amplitude of the AC voltage according to the measurement result includes:

[0039] If the measurement result is within a preset range among multiple preset ranges, the amplitude of the AC periodic voltage is adjusted to the corresponding voltage value.

[0040] As can be seen from the above technical solution, the present invention provides a DC current measurement device, including: a connection module, an auxiliary voltage module, and a first transformer and a second transformer with the same parameters and opposite polarities. The primary windings of the two transformers sample the DC current on the primary line. Since the DC current causes the two transformers to reach the magnetic saturation state, and the auxiliary voltage module applies an AC voltage with positive and negative periodic changes to the connection module, demagnetizing the first transformer and magnetizing the second transformer in the positive period, and magnetizing the first transformer and demagnetizing the second transformer in the negative period, the two transformers alternately release magnetic saturation; and because the connection module uses the larger secondary current on the two transformers as the measurement result of the DC current measurement device, the ratio of the output measurement result to the DC current on the primary line is equal to the turn ratio of the primary winding and the secondary winding of the two transformers, that is, the DC current measurement device realizes the measurement of the DC current on the primary line; the DC current measurement device is only based on two magnetic saturation transformers with consistent parameters and opposite polarities, as well as a connection module and an auxiliary voltage module, so the DC current measurement device has a simple structure and a reliable measurement method. Therefore, the measurement cost of measuring the DC current is reduced. Description of the Drawings

[0041] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained according to the provided drawings without creative efforts.

[0042] Figure 1 It is a schematic structural diagram of the DC current measurement device provided by the embodiment of the present application;

[0043] Figure 2Schematic waveform diagrams of the secondary current of the second current transformer TB when the first current transformer TA is disconnected, the secondary current of the first current transformer TA when the second current transformer TB is disconnected, and the measurement results of the DC current measurement device under a sinusoidal AC voltage;

[0044] Figures 3 - 6 Structural schematic diagrams of four DC current measurement devices provided by embodiments of the present application;

[0045] Figures 7 - 9 Flow schematic diagrams of three DC current measurement methods provided by embodiments of the present application. Detailed implementation manners

[0046] Next, the technical solutions in the embodiments of the present application will be clearly and completely described with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present application.

[0047] In the present application, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or sequence between these entities or operations. Moreover, the terms "include", "comprise" or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "including a..." does not exclude the existence of additional identical elements in the process, method, article or device including the said element.

[0048] As can be seen from the background art, DC current transformers can be divided into: zero-flux DC current transformers, fiber-optic DC current transformers, Hall current sensors, and optoelectronic DC transformers. Specifically:

[0049] The zero-flux DC current transformer is composed of a basic magnetic integrator and a magnetic modulator, based on the principle of a magnetic potential self-balancing comparator, and is a transformer based on the principle of a closed-loop system formed by a magnetic modulator and electronic feedback; however, the zero-flux DC current transformer is provided with a two-stage negative feedback system, which makes its own structure and algorithm relatively complex, and thus its own cost is relatively high.

[0050] The fiber optic DC current transformer is a passive current sensor based on the Faraday effect, Sagnac interference principle, and Ampere's circuital law. Although the passive current sensor is passive, its cost is extremely high, and the measurement accuracy is not high at small currents.

[0051] The Hall DC current transformer is made according to the Hall effect principle and applies Ampere's law, that is, a magnetic field proportional to the current is generated around the current-carrying conductor, and the magnitude of the current in the current-carrying conductor is indirectly measured by measuring the magnitude of the Hall electromotive force. However, the cost of the closed-loop type of the Hall DC current transformer is relatively high, and the accuracy of the open-loop type is not high.

[0052] The optoelectronic DC transformer obtains a voltage signal proportional to the current to be measured through a sampling coil at the high potential end, and then converts it into an electrical pulse signal through an analog-to-digital converter to drive a light-emitting device to output a light pulse signal. After the light pulse signal is transmitted back to the ground potential end through the optical fiber, it is first converted into an electrical pulse signal by an optoelectronic device, and then amplified and converted from digital to analog to correctly reflect the current signal to be measured. However, in the optoelectronic current transformer, the analog-to-digital conversion collector for measuring the voltage at the high potential end needs to be powered, and it is difficult to supply power to the high potential end, that is, both insulation and energy supply need to be ensured. Therefore, laser power supply or isolation transformer power supply is mostly used, resulting in a relatively high cost of the optoelectronic DC transformer.

[0053] In order to overcome the problem of the relatively high cost of the above current sensors for measuring DC current, the embodiment of the present application provides a DC current measurement device, and its specific structure is as Figure 1 shown, including: a connection module 10, an auxiliary voltage module 20, and a first transformer TA and a second transformer TB with the same parameters and opposite polarities.

[0054] The primary windings of the first transformer TA and the second transformer TB are used to sample the DC current on the primary line, and the DC current causes the first transformer TA and the second transformer TB to reach the magnetic saturation state.

[0055] It should be noted that the magnetic saturation state is a physical property of magnetic materials, which means that due to the limitation of the physical structure of the magnetic conductive material, the magnetic flux passing through it cannot increase infinitely and thus remains in a certain amount.

[0056] The connection module 10 can establish the connection between the first ends of the secondary windings of the first transformer TA and the second transformer TB and the connection between the second ends, and use the larger secondary current on the first transformer TA and the second transformer TB as the measurement result of the DC current measurement device; usually, the measurement and protection equipment of the DC transmission system receives the measurement result of the DC current measurement device.

[0057] The auxiliary voltage module 20 can apply an AC voltage with positive and negative cycle changes to the connection module 10, demagnetize the first current transformer TA during the positive cycle, and magnetize the second current transformer TB, and magnetize the first current transformer TA and demagnetize the second current transformer TB during the negative cycle.

[0058] Preferably, the AC cycle signal is a sinusoidal AC voltage; in practical applications, including but not limited to the above preferred embodiments, specific limitations are not made here and can be determined according to specific circumstances, all within the protection scope of this application.

[0059] Take, for example, the sinusoidal AC voltage shown in (1) of Figure 2 . If the first current transformer TA is disconnected, that is, the connection between the secondary winding of the first current transformer TA and the connection module 10 is disconnected, then when the sinusoidal AC voltage is not applied, the second current transformer TB reaches the magnetic saturation state under the DC current.

[0060] After applying the sinusoidal AC voltage, when the sinusoidal AC voltage is in the negative half-cycle, the second current transformer TB is demagnetized. Since the second current transformer TB is in the magnetic saturation state at this time, that is, its magnetic flux hardly changes, the current in the secondary winding of the second current transformer TB changes following the sinusoidal AC voltage, that is, the secondary current I2 flowing through the second current transformer TB changes following the sinusoidal AC voltage.

[0061] When the secondary current I2 flowing through the secondary winding of the second current transformer TB reaches the maximum, it demagnetizes itself, that is, its own magnetic flux begins to change following the sinusoidal AC voltage; if the iron core of the second current transformer TB conforms to the ideal hysteresis loop, its own magnetic flux decreases sharply, making the induced electromotive force in its own secondary winding balance with the sinusoidal AC voltage, so that the secondary current I2 flowing through itself remains unchanged and is still the maximum value, that is, I2 = (Id + Im) × W1 / W2; where Im is the exciting current of the secondary winding of the second current transformer TB, and W1 / W2 is the turns ratio of the secondary winding to the primary winding of the second current transformer TB.

[0062] When the sinusoidal AC voltage is in the positive half-cycle, the second current transformer TB is magnetized, and at this time, the secondary current I2 flowing through the second current transformer TB becomes: I2 = (Id - Im) × W1 / W2; since the magnetic flux in the iron core of the second current transformer TB increases rapidly at this time, the induced electromotive force in the secondary winding of the second current transformer TB also balances with the sinusoidal AC voltage, that is, in the positive half-cycle, the secondary current I2 flowing through the second current transformer TB remains unchanged until the secondary current I2 flowing through the second current transformer TB makes the iron core of the second current transformer TB reach the magnetic saturation state, the direction of the secondary current I2 flowing through the second current transformer TB changes and follows the sinusoidal AC voltage. Therefore, when the first current transformer TA is disconnected, under the action of the sinusoidal AC voltage, the waveform diagram of the secondary current I2 flowing through the second current transformer TB is as shown in Figure 2as shown in (3) in

[0063] Similarly, when the second current transformer TB is disconnected, the change process of the secondary current I2' flowing through the first current transformer TA is similar to the above, and it can be deduced that it will not be elaborated here; its waveform diagram is as shown in Figure 2 as shown in (3) in

[0064] When neither the first current transformer TA nor the second current transformer TB is disconnected, since the larger secondary currents on the first current transformer TA and the second current transformer TB are used as the measurement result of the DC current measuring device, the measurement result of the DC current measuring device is as shown in Figure 2 as shown in (4) in , almost all is (Id + Im)×W1 / W2; in practical applications, since Im is much smaller than Id, the measurement result of the DC current measuring device is Id×W1 / W2.

[0065] In summary, since the DC current causes the two current transformers to reach the magnetic saturation state, and the auxiliary voltage module 20 applies an AC voltage with positive and negative periodic changes to the connection module 10, demagnetizing the first current transformer TA and magnetizing the second current transformer TB during the positive cycle, and magnetizing the first current transformer TA and demagnetizing the second current transformer TB during the negative cycle, the two current transformers are alternately demagnetized; and since the connection module 10 uses the larger secondary currents on the two current transformers as the measurement result of the DC current measuring device, the ratio of the output measurement result to the DC current on the primary line is equal to the turn ratio of the primary winding and the secondary winding of the two current transformers, that is, the DC current measuring device realizes the measurement of the DC current on the primary line; the DC current measuring device is only based on two magnetic saturation current transformers with consistent parameters and opposite polarities, as well as the connection module 10 and the auxiliary voltage module 20, so the DC current measuring device has a simple structure and a reliable measurement method. Therefore, the measurement cost of measuring the DC current is reduced.

[0066] In practical applications, the auxiliary voltage module 20 can be an isolation transformer, including but not limited to this embodiment, and no specific limitation is made here, which can be determined according to specific circumstances, and all are within the protection scope of this application.

[0067] It should be noted that, compared with the zero-flux DC current transformer, the DC current measuring device provided by this application has one less negative feedback system, so that the structure and algorithm of the DC current measuring device are simpler, and at the same time the cost is relatively lower; compared with the Hall DC current transformer, the DC current measuring device provided by this application has a simple structure itself, does not require secondary power supply, and can achieve high-precision measurement at a relatively low cost.

[0068] This application provides a specific implementation manner of the connection module 10, such as Figure 3 orFigure 4 As shown in the figure, it includes: a first unidirectional conduction branch 11, a second unidirectional conduction branch 12, a third unidirectional conduction branch 13, an auxiliary resistor Rf, and a measuring resistor Rfz or a current sensor I.

[0069] The input end of the first unidirectional conduction branch 11 is connected to the second end of the secondary winding of the first current transformer TA, and the output end of the first unidirectional conduction branch 11 is connected to the second end of the secondary winding of the second current transformer TB; the input end of the second unidirectional conduction branch 12 is connected to the first end of the secondary winding of the first current transformer TA, and the output end of the first unidirectional conduction branch 11 is connected to the first end of the secondary winding of the second current transformer TB.

[0070] The two poles of the auxiliary voltage module 20 are respectively connected to an internal connection point of the first unidirectional conduction branch 11 and an internal connection point of the second unidirectional conduction branch 12; the auxiliary resistor Rf is connected in parallel between the two ends of the second unidirectional conduction branch 12.

[0071] The input end of the third unidirectional conduction branch 13 is connected to the second end of the secondary winding of the second current transformer TB, and the output end of the third unidirectional conduction branch 13 is connected to the second end of the secondary winding of the first current transformer TA through a measuring resistor Rfz (as shown in Figure 3 the figure) or a current sensor I (as shown in Figure 4 the figure).

[0072] It should be noted that the positive and negative periodic alternating voltage output by the auxiliary voltage module 20 can, through the above structure, demagnetize the first current transformer TA and magnetize the second current transformer TB during the positive cycle, and magnetize the first current transformer TA and demagnetize the second current transformer TB during the negative cycle; and, through the above structure, the larger secondary current on the first current transformer TA and the second current transformer TB can flow through the measuring resistor Rfz or the current sensor I.

[0073] Among them, the measuring resistor Rfz is used to convert the larger secondary current on the two current transformers into the voltage across its own two ends and use it as the measurement result of the DC current measuring device; the current sensor I is used to measure the larger secondary current on the two current transformers and use its own measurement result as the measurement result of the DC current measuring device.

[0074] Specifically, for the structures of the first unidirectional conduction branch 11 and the second unidirectional conduction branch 12, reference can be made to Figure 5 which both include: at least two first diodes Z1.

[0075] All the first diodes Z1 are connected end to end. The positive pole of the formed connection branch is used as the input end of the corresponding unidirectional conduction branch, and the negative pole is used as the output end of the corresponding unidirectional conduction branch. The connection point of any two adjacent first diodes Z1 serves as an internal connection point of the corresponding unidirectional conduction branch.

[0076] Specifically, for the structure of the third unidirectional conduction branch 13, reference can be made to Figure 5 , all of which include: at least one second diode Z2.

[0077] If the number of second diodes Z2 is greater than 1, all the second diodes Z2 are connected end to end. The positive pole of the formed connection branch is used as the input end of the third unidirectional conduction branch 13, and the negative pole is used as the output end of the third unidirectional conduction branch 13.

[0078] The above is only a specific implementation manner of the connection module 10. In practical applications, it includes but is not limited to the above implementation manner. No specific limitation is made here and it can be determined according to the specific structure, and all are within the protection scope of this application.

[0079] Another embodiment of this application provides an implementation manner of the auxiliary voltage module 20, and its specific structure is as Figure 6 shown, including: an auxiliary control circuit FK, a switching switch K, and an isolation transformer T with an auxiliary winding having multiple taps.

[0080] One end of the auxiliary voltage module 20 is connected to one end of the isolation transformer T, the other end of the auxiliary voltage module 20 is connected to the first end of the switching switch K, and the primary winding of the isolation transformer T receives the power frequency voltage AC.

[0081] The output end of the auxiliary control circuit FK is connected to the control end of the switching switch K, and is used to control the second end of the switching switch K to be connected to the initial tap of the auxiliary winding of the isolation transformer T to output an alternating voltage, and also control the second end of the switching switch K to be connected to the corresponding tap of the auxiliary winding of the isolation transformer T according to the measurement result of the DC measurement device to adjust the amplitude of the alternating voltage.

[0082] It should be noted that the auxiliary control circuit FK adjusts the AC periodic voltage according to the measurement result of the DC measurement device, which can improve the measurement accuracy of the measurement result of the DC measurement device, that is, can improve the measurement accuracy of the DC current.

[0083] The above is only a specific implementation manner of the auxiliary voltage module 20. In practical applications, it includes but is not limited to the above implementation manner. No specific limitation is made here and it can be determined according to the specific structure, and all are within the protection scope of this application.

[0084] The present application provides a method for measuring direct current, which is applied to a controller and used to control the direct current measuring device in the above embodiment; the specific process of the direct current measuring method is as follows Figure 7 shown, and includes the following steps:

[0085] S110. Control the auxiliary voltage module in the direct current measuring device to output an alternating voltage with a preset amplitude and positive and negative periodic changes.

[0086] S120. Calculate the direct current on the primary line according to the measurement result output by the direct current measuring device.

[0087] If the connection branch in the direct current measuring device includes a measuring resistor, as Figure 3 shown, then step S120 includes the following steps, as Figure 8 shown:

[0088] S210. Calculate the current flowing through the measuring resistor according to the measurement result of the direct current measuring device and the resistance value of the measuring resistor.

[0089] S220. Calculate the direct current on the primary line according to the turns ratio of the primary winding and the secondary winding of the current transformer and the current flowing through the measuring resistor.

[0090] For example, if the measurement result of the direct current measuring device is 50V and the resistance value of the measuring resistor Rfz is 5 ohms, then the current flowing through the measuring resistor Rfz is 10A; and the turns ratio of the primary winding and the secondary winding of the current transformer is 100:1, so the direct current on the primary line is 1000A.

[0091] If the connection branch in the direct current measuring device includes a current sensor I, as Figure 4 shown, then step S120 is specifically: calculate the direct current on the primary line according to the measurement result of the direct current measuring device and the turns ratio of the primary winding and the secondary winding of the current transformer.

[0092] For example, if the measurement result of the direct current measuring device is 10A and the turns ratio of the primary winding and the secondary winding of the current transformer is 100:1, then the direct current on the primary line is 1000A.

[0093] It should be noted that the reason why the current flowing through the measuring resistor Rfz is proportional to the direct current has been described in detail in the above embodiment, and will not be elaborated here one by one.

[0094] This embodiment also provides another implementation manner of the direct current measuring method, and its specific process is as Figure 9 shown, and on this basis, it further includes:

[0095] S130. Control the auxiliary voltage module to adjust the amplitude of the AC voltage according to the measurement result of the DC current measurement device.

[0096] Specifically, step S130 specifically includes the following steps:

[0097] Judge whether the measurement result of the DC current measurement device is within a preset voltage range among multiple preset ranges. If the measurement result of the DC current measurement device is within one of the preset ranges, then adjust the amplitude of the AC periodic voltage to the corresponding voltage value.

[0098] For example, taking Figure 3 as an example, if the voltage across the measurement resistor Rfz is 50V and is between 48V - 52V, then the auxiliary control circuit FK adjusts the amplitude of the AC periodic voltage to 100V; if the voltage across the measurement resistor Rfz is 55V and is between 52V - 56V, then the auxiliary control circuit FK adjusts the amplitude of the AC periodic voltage to 120V.

[0099] In practical applications, the number of preset voltage ranges stored in the auxiliary control circuit FK, and the size of each preset voltage range, can both be set according to actual adjustment requirements. There is no specific limitation here and they are all within the protection scope of this application.

[0100] Regarding the above description of the disclosed embodiments, the features described in each embodiment in this specification can be mutually replaced or combined, enabling those skilled in the art to implement or use this application. The above is only a preferred embodiment of the present invention and does not impose any form of limitation on the present invention. Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can, without departing from the scope of the technical solution of the present invention, make many possible changes and modifications to the technical solution of the present invention by using the methods and technical contents disclosed above, or modify it into equivalent embodiments with equivalent changes. Therefore, any simple modification, equivalent change, and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A DC current measurement device, characterized in that, Comprising: A connection branch, an auxiliary voltage module, and a first transformer and a second transformer with the same parameters and opposite polarities; wherein: The primary windings of the two transformers are used to sample the DC current on the primary line; the DC current causes the two transformers to reach the magnetic saturation state; The connection module is used to establish the connection between the first ends of the secondary windings of the two transformers and the connection between the second ends, and use the larger secondary current on the two transformers as the measurement result of the DC current measuring device; The auxiliary voltage module is used to apply an AC voltage with positive and negative periodic changes to the connection module, demagnetize the first transformer and magnetize the second transformer during the positive cycle, and magnetize the first transformer and demagnetize the second transformer during the negative cycle; The connection module includes: a first unidirectional conduction branch, a second unidirectional conduction branch, a third unidirectional conduction branch, and an auxiliary resistor, and a measuring resistor or a current sensor; wherein: The input end of the first unidirectional conduction branch is connected to the second end of the secondary winding of the first transformer, and the output end of the first unidirectional conduction branch is connected to the second end of the secondary winding of the second transformer; The input end of the second unidirectional conduction branch is connected to the first end of the secondary winding of the first transformer, and the output end of the first unidirectional conduction branch is connected to the first end of the secondary winding of the second transformer; An internal connection point of the first unidirectional conduction branch and an internal connection point of the second unidirectional conduction branch are respectively connected to the two poles of the auxiliary voltage module; The input end of the third unidirectional conduction branch is connected to the second end of the secondary winding of the second transformer, and the output end of the third unidirectional conduction branch is connected to the second end of the secondary winding of the first transformer through the measuring resistor or the current sensor; The auxiliary resistor is connected in parallel between the two ends of the second unidirectional conduction branch; The measuring resistor is used to convert the larger secondary current on the two transformers into the voltage across its own two ends and use it as the measurement result of the DC current measuring device; The current sensor is used to measure the larger secondary current on the two transformers and use its own measurement result as the measurement result of the DC current measuring device.

2. The DC current measuring device according to claim 1, characterized in that, The first unidirectional conduction branch and the second unidirectional conduction branch both include: at least two first diodes; in the first unidirectional conduction branch and the second unidirectional conduction branch: All the first diodes are connected end to end, and the positive pole of the formed connection branch is used as the input end of the corresponding unidirectional conduction branch, and the negative pole is used as the output end of the corresponding unidirectional conduction branch; The connection point of any two adjacent first diodes is used as an internal connection point of the corresponding unidirectional conduction branch.

3. The DC current measuring device according to claim 1, characterized in that, The third unidirectional conduction branch includes: at least one second diode; wherein: If the number of the second diodes is greater than 1, all the second diodes are connected end to end, and the positive pole of the formed connection branch is used as the input end of the third unidirectional conduction branch, and the negative pole is used as the output end of the third unidirectional conduction branch.

4. The DC current measuring device according to any one of claims 1-3, characterized in that, The AC periodic voltage is a sinusoidal AC signal.

5. The DC current measurement device according to any one of claims 1-3, characterized in that, The auxiliary voltage module includes: an auxiliary control circuit, a switching switch, and an isolation transformer with an auxiliary winding having multiple taps; where: One end of the auxiliary voltage module is connected to one end of the isolation transformer, the other end of the auxiliary voltage module is connected to the first end of the switching switch, and the primary winding of the isolation transformer receives the power frequency voltage; The output end of the auxiliary control circuit is connected to the control end of the switching switch, and is used to control the second end of the switching switch to be connected to the initial tap of the auxiliary winding of the isolation transformer to output the AC voltage, and further control the second end of the switching switch to be connected to the corresponding tap of the auxiliary winding of the isolation transformer according to the measurement result to adjust the amplitude of the AC voltage.

6. A method for measuring direct current, characterized in that, Applied to a controller for controlling the DC current measuring device according to any one of claims 1-5; The DC current measuring method includes: Controlling the auxiliary voltage module in the DC current measuring device to output an AC voltage with a preset amplitude that varies periodically between positive and negative; Calculating the DC current on the primary line according to the measurement result output by the DC current measuring device.

7. The DC current measurement method according to claim 6, wherein If the connection branch in the DC current measuring device includes a measuring resistor, then the step of calculating the DC current on the primary line according to the measurement result output by the DC current measuring device includes: Calculating the current flowing through the measuring resistor according to the measurement result and the resistance value of the measuring resistor; Calculating the DC current on the primary line according to the turns ratio of the primary winding and the secondary winding of the current transformer and the current flowing through the measuring resistor.

8. The DC current measurement method according to claim 6, characterized in that, If the connection branch includes a current sensor, then the step of calculating the DC current on the primary line according to the measurement result output by the DC current measuring device includes: Calculating the DC current according to the measurement result and the turns ratio of the primary winding and the secondary winding of the current transformer.

9. The DC current measurement method according to any one of claims 6-8, characterized in that, After the step of calculating the DC current on the primary line according to the measurement result output by the DC current measuring device, it further includes: Controlling the auxiliary voltage module to adjust the amplitude of the AC voltage according to the measurement result.

10. The DC current measurement method according to claim 9, characterized in that, The step of controlling the auxiliary voltage module to adjust the amplitude of the AC voltage according to the measurement result includes: If the measurement result is within a preset range among multiple preset ranges, then adjusting the amplitude of the AC periodic voltage to the corresponding voltage value.

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