Current transformer

Abstract

The application discloses a current transformer, which comprises a square wave voltage generating circuit, a first driving circuit and a plurality of direct current detection coils. The square wave voltage generating circuit comprises a first reference voltage source, a first inverter, a clock generating circuit and a multiplexer. The multiplexer receives a first reference voltage generated by the first reference voltage source, a second reference voltage generated by the first inverter and a reference clock signal generated by the clock generating circuit, and generates a square wave voltage with a predetermined clock frequency under the control of the reference clock signal. The first driving circuit is used for receiving the square wave voltage and generating a driving voltage following the square wave voltage. Each direct current detection coil in the plurality of direct current detection coils receives the driving voltage and senses a magnetic flux corresponding to a to-be-detected current passing through the direct current detection coil under the driving of the driving voltage.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electronic measurement, and more particularly, to a current transformer. BACKGROUND

[0002] With the wide use of various power systems in industrial production and daily life, there is a need for devices capable of accurately and conveniently measuring current to monitor the safe and effective operation of power systems. Traditional current transformers can only be used to measure alternating current and cannot measure direct current, and also produce large errors when measuring low-frequency alternating current.

[0003] A recently developed direct current transformer (DCCT) is a new type of current measuring device that can simultaneously measure direct current and alternating current in a non-contact manner. The DCCT mainly utilizes the nonlinearity and asymmetry of the core of a core coil when the core is magnetized by direct current and alternating current. By driving a feedback current to compensate for the effect of the primary current on the core coil, a zero magnetic flux state in the core coil is achieved, thereby achieving measurement of direct current. SUMMARY

[0004] One of the objects of the present application is to provide a current transformer that can suppress offset and gain drift and improve power supply rejection ratio.

[0005] According to one aspect of the present application, a current transformer is provided, which includes: a square wave voltage generating circuit including: a first reference voltage source for generating a first reference voltage; a first inverter for receiving the first reference voltage and inverting the first reference voltage to generate a second reference voltage; a clock generating circuit for generating a reference clock signal having a predetermined clock frequency; and a multiplexer for receiving the first reference voltage, the second reference voltage, and the reference clock signal, and alternately outputting the first reference voltage and the second reference voltage at the predetermined clock frequency in each clock cycle under the control of the reference clock signal, thereby generating a square wave voltage having the predetermined clock frequency; a first driving circuit for receiving the square wave voltage and generating a driving voltage following the square wave voltage, the first driving circuit including: a first operational amplifier, a first input terminal of the first operational amplifier for receiving the square wave voltage, a second input terminal of the first operational amplifier receiving the driving voltage fed back through a first feedback network, and an output terminal of the first operational amplifier outputting a first intermediate voltage; and a first push-pull output stage for receiving the first intermediate voltage and push-pull outputting the driving voltage; and a plurality of direct current detection coils, each of the direct current detection coils receiving the driving voltage and sensing a magnetic flux corresponding to a to-be-measured current passing through the direct current detection coil under the driving of the driving voltage.

[0006] In some embodiments, the plurality of DC detection coils includes a first DC detection coil and a second DC detection coil; and the current transformer further includes a second driving circuit configured to receive the driving voltage and invert the driving voltage to generate an inverted driving voltage, wherein the first DC detection coil receives the driving voltage and induces a first induced current based on a magnetic flux corresponding to the to-be-measured current passing through the first DC detection coil under driving of the driving voltage; the second DC detection coil receives the inverted driving voltage and induces a second induced current based on the magnetic flux corresponding to the to-be-measured current passing through the second DC detection coil under driving of the inverted driving voltage; and the current transformer determines the DC component related to the to-be-measured current based on the first induced current and the second induced current.

[0007] In some embodiments, the current transformer further includes a demodulation circuit configured to receive and demodulate a first induced voltage corresponding to the first induced current and a second induced voltage corresponding to the second induced current to remove AC components related to the driving voltage and the inverted driving voltage, thereby generating a demodulated voltage; and a low-pass filter configured to receive the demodulated voltage and perform low-pass filtering, thereby obtaining the DC component related to the to-be-measured current.

[0008] In some embodiments, the second driving circuit includes a second operational amplifier having a first input coupled to a reference voltage, a second input configured to receive the driving voltage and receive the inverted driving voltage through a second feedback network, and an output configured to output a second intermediate voltage; and a second push-pull output stage configured to receive the second intermediate voltage and push-pull output the inverted driving voltage.

[0009] In some embodiments, the current transformer includes a first voltage domain having a first supply voltage and a second voltage domain having a second supply voltage, the second voltage domain being generated by regulating the first supply voltage.

[0010] In some embodiments, the clock generation circuit and the multiplexer operate in the second voltage domain and are powered by the second supply voltage.

[0011] In some embodiments, the current transformer further includes a low-dropout regulator configured to receive an external supply voltage and generate the first supply voltage by regulating the external supply voltage; and a second reference voltage source configured to receive the first supply voltage and generate the second supply voltage based on the first supply voltage.

[0012] In some embodiments, the current transformer further includes an AC detection coil for sensing the magnetic flux passing through it corresponding to the current under test to determine an AC component associated with the current under test.

[0013] In some embodiments, the current transformer further includes: an integral drive circuit for receiving the DC component and the AC component related to the current under test and generating an integral drive current; a secondary coil for receiving the integral drive current, wherein the sum of the magnetic flux generated by the integral drive current through the secondary coil and the magnetic flux coupled to the current under test to the first DC detection coil, the second DC detection coil, the AC detection coil, and the secondary coil is equal to the sum of the magnetic flux generated by the first induced current, the second induced current, and the third induced current in the first DC detection coil, the second DC detection coil, and the AC detection coil, respectively; and a detection circuit for detecting the integral drive current flowing through the secondary coil.

[0014] The above is an overview of this application, and there may be simplifications, generalizations, and omissions of details. Therefore, those skilled in the art should recognize that this section is merely illustrative and not intended to limit the scope of this application in any way. This overview section is neither intended to identify the key or essential features of the claimed subject matter nor to serve as an aid in determining the scope of the claimed subject matter. Attached Figure Description

[0015] The above and other features of this application will become more fully apparent to those skilled in the art through the following detailed description in conjunction with the accompanying drawings and the appended claims. It is understood that these drawings and detailed descriptions depict only some exemplary embodiments of this application and should not be construed as limiting the scope of this application. The application will be more clearly and in more detail with reference to the accompanying drawings.

[0016] Figure 1 A schematic diagram of the current transformer 100 is shown.

[0017] Figure 2 A structural block diagram of a current transformer 200 according to some embodiments of this application is shown;

[0018] Figure 3 It shows Figure 2 Specific implementation methods of some modules in the current transformer 200;

[0019] Figure 4 A waveform diagram of a square wave voltage having a predetermined clock frequency is shown according to some embodiments of this application;

[0020] Figure 5 A structural diagram of a power supply generation circuit of a current transformer is shown according to some embodiments of the present application. DETAILED DESCRIPTION

[0021] In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments can be utilized, and other changes can be made, without departing from the spirit or scope of the subject matter presented herein. It will be readily understood that the aspects of the present application, as generally described herein, and illustrated in the Figures, can be arranged, substituted, combined, and designed in a wide variety of different configurations, all of which are explicitly contemplated and make part of this disclosure.

[0022] Reference Figure 1 , a structural diagram of a current transformer 100 capable of measuring a current to be measured is shown according to one embodiment of the present application. In some embodiments, the current to be measured has a direct current (DC) component and / or an alternating current (AC) component. The working principle of the current transformer 100 for measuring the current to be measured, i.e., a primary current I Figure 1 through a cable 110 is described below in conjunction with P

[0023] As shown in Figure 1 , the current transformer 100 includes a first toroidal core 121, a second toroidal core 122, and a third toroidal core 123, through which the cable 110 passes from the inner regions of the three toroidal cores 121, 122, and 123. A first winding W1, a second winding W2, and a third winding W3 are wound around the outside of the three toroidal cores 121, 122, and 123, respectively. In addition, the current transformer 100 also includes a fourth winding (or referred to as a secondary winding) W4, which is wound around the outside of all three toroidal cores 121, 122, and 123. The like-named ends of the four windings W1-W4 are marked with black dots in Figure 1 . In the circuit 100, the primary current I P flowing through the cable 110 to be measured generates magnetic flux in the three toroidal cores 121, 122, and 123, which can be offset by a secondary current I S in the secondary winding W4, and the remaining magnetic flux is induced by the three toroidal cores 121, 122, and 123 wound with the windings. Among them, the first core 121 and the second core 122 are used to induce the DC part of the remaining magnetic flux, and the third core 123 is used to induce the AC part of the remaining magnetic flux.

[0024] In addition, as shown in Figure 1 ​As shown, the current transformer 100 further comprises an oscillator 130 for generating an alternating driving voltage. The alternating driving voltage is coupled to the like end of the first coil W1 and the unlike end of the second coil W2 to drive the first core 121 and the second core 122 into or out of saturation state in opposite directions. If the primary current I P and the secondary current I S The DC component of the residual magnetic flux after the mutual cancellation of the magnetic fluxes generated in the three cores is 0, then the peak values of the two induced currents in the first coil W1 and the second coil W2 are equal; if the DC component of the residual magnetic flux is not 0, then the difference between the peak values of the two induced currents is proportional to the DC component of the residual magnetic flux.

[0025] The unlike end of the first coil W1 and the like end of the second coil W2 are respectively coupled to the first input end and the second input end of a peak detector 140, and the first input end and the second input end of the peak detector 140 are also respectively grounded through a resistor R1 and a resistor R2. The peak detector 140 is a double peak detector, which can measure the DC current component related to the primary current I P by comparing the peak values of the current in two directions.

[0026] The output end of the peak detector 140 is coupled to the first input end of a power amplifier 150 through a resistor. The first input end of the power amplifier 150 is also coupled to the like end of a third coil W3 through a resistor, and is also coupled to its output end through a capacitor. The second input end of the power amplifier 150 and the unlike end of the third coil W3 are respectively grounded. The output end of the power amplifier 150 is coupled to the like end of a secondary coil W4. Among them, the third core 123 is used to induce the alternating component in the primary current I P , and generate an induced current in the third coil W3; after the integral operation of the output of the peak detector 140 and the induced current through the power amplifier 150, the secondary current I S is generated.

[0027] The power amplifier 150 provides the secondary current I S to the secondary coil W4. Since the secondary current I S is a mirror current proportional to the primary current I P , the measurement of the secondary current I S can achieve the measurement of the primary current I P . Specifically, the unlike end of the secondary coil W4 is connected to a load resistor 160 to convert the current signal in the secondary coil W4 into a voltage. The two ends of the load resistor 160 are coupled to the two input ends of a precision amplifier 170 (for example, a differential amplifier) to generate an output voltage, which is proportional to the secondary current I Sis proportional to the primary current I in the cable under test, and thus can be used to characterize the primary current I in the cable under test P .

[0028] It should be noted that the structure diagram of the current transformer 100 given above is only for example, and those skilled in the art should understand that the DC current transformer based on the zero-flux principle can also have other implementations or variations.

[0029] The application provides a current transformer which can effectively suppress offset and gain drift and improve power supply rejection ratio (PSRR). The current transformer comprises a square wave voltage generating circuit, a first driving circuit and a plurality of DC detection coils. The square wave voltage generating circuit generates a square wave voltage with a predetermined clock frequency, and the square wave voltage is amplified by the first driving circuit and provided to the plurality of DC detection coils to drive each DC detection coil to sense the magnetic flux corresponding to the current to be measured passing through the DC detection coil.

[0030] The square wave voltage generating circuit comprises a first reference voltage source, a first inverter, a clock generating circuit and a multiplexer. The first reference voltage source is configured to generate a first reference voltage; the first inverter is configured to receive the first reference voltage and invert the first reference voltage to generate a second reference voltage; the clock generating circuit is configured to generate a reference clock signal with a predetermined clock frequency; and the multiplexer is configured to receive the first reference voltage, the second reference voltage and the reference clock signal, and alternately output the first reference voltage and the second reference voltage at a predetermined clock frequency in each clock cycle under the control of the reference clock signal, thereby generating a square wave voltage with a predetermined clock frequency. Since the frequency of the reference clock signal generated by the clock generating circuit can be accurately controlled, and the first reference voltage and the second reference voltage generated by the first reference voltage source and the first inverter can effectively isolate the power voltage drift, the square wave voltage generated by the square wave voltage generating circuit is more stable and accurate compared with the alternating current signal generated by the oscillator, which is conducive to improving the power supply rejection ratio of the current transformer.

[0031] The first driving circuit is configured to receive the square wave voltage and generate a driving voltage following the square wave voltage. The first driving circuit comprises a first operational amplifier and a first push-pull output stage. The first input terminal of the first operational amplifier is configured to receive the square wave voltage, the second input terminal receives the feedback driving voltage through a first feedback network, and the output terminal outputs a first intermediate voltage; and the first push-pull output stage is configured to receive the first intermediate voltage and push-pull output the driving voltage. In some embodiments, the first operational amplifier can be a high-precision low-drift operational amplifier, so that the driving voltage output via the first driving circuit effectively suppresses voltage drift and enhances driving capability, thereby suppressing offset and gain drift of the current transformer output when the DC detection coil is driven using the driving voltage.

[0032] The following is combined Figure 2 and Figure 3 The current transformer of this application is described in detail. Figure 2 A structural block diagram of a current transformer 200 according to some embodiments of this application is shown. Figure 3 Further details were provided Figure 2 Example implementation of some modules of the current transformer 200.

[0033] like Figure 2 and Figure 3 As shown, the current transformer 200 includes a square wave voltage generation circuit 210, a first drive circuit 220, and a second drive circuit 230. Specifically, the square wave voltage generation circuit 210 includes a first reference voltage source 212, a first inverter 214, a clock generation circuit 216, and a multiplexer 218. The first reference voltage source 212 is used to generate a first reference voltage +V. REF The first inverter 214 is used to receive the first reference voltage +V. REF and the first reference voltage +V REF Inverting to generate a second reference voltage -V REF Clock generation circuit 216 is used to generate a reference clock signal, the reference clock signal having a predetermined clock frequency f0; multiplexer 218 is used to receive a first reference voltage +V REF Second reference voltage -V REF And a reference clock signal, and under the control of the reference clock signal, alternately outputting the first reference voltage +V at a predetermined clock frequency f0 in each clock cycle. REF Second reference voltage -V REF This generates a square wave voltage V with a predetermined clock frequency f0. Square .

[0034] exist Figure 3 In the example, the first reference voltage source 212 is a series reference voltage source, which can output a stable reference voltage +V even when the power supply voltage varies over a large range. REF For example, the first reference voltage source 212 can receive a fluctuating +12V supply voltage and output a stable +5V or a reference voltage of other amplitudes. It is understood that the first reference voltage source 212 can employ any suitable reference voltage source circuit structure and can use commercially available chips.

[0035] In some embodiments, the inverter 214 is implemented based on an operational amplifier, which receives a first reference voltage +V. REF and the first reference voltage +V REF Inverting to generate a second reference voltage -V REFSpecifically, the inverting input of the operational amplifier in the inverter 214 receives a first reference voltage +V REF and receives a second reference voltage -V REF feedback from its output through a resistor; the non-inverting input of the operational amplifier is coupled to ground, and its output outputs the second reference voltage -V REF and is coupled to the multiplexer 218. In the example shown in Figure 3 , the current transformer further comprises a voltage follower 215 symmetrical to the inverter 214, which is also implemented based on an operational amplifier. Specifically, the non-inverting input of the operational amplifier in the voltage follower 215 receives the first reference voltage +V REF ; the inverting input receives a follower voltage +V REF feedback from its output through a resistor; the output outputs the follower voltage +V REF of the first reference voltage and is coupled to the multiplexer 218.

[0036] The clock generation circuit 216 comprises a high-stability reference clock circuit 2162 and a direct digital frequency synthesizer (DDS) 2164, wherein the direct digital frequency synthesizer 2164 generates a suitable reference clock signal based on the raw clock signal output by the high-stability reference clock circuit 2162. For example, the high-stability reference clock circuit 2162 can generate a raw clock signal of 30.72MHz, and after frequency synthesis by the direct digital frequency synthesizer 2164, a more suitable reference clock signal with a frequency of 44.7HZ can be generated to drive the direct current detection coil.

[0037] The first input of the multiplexer 218 receives the first reference voltage +V REF and the reference clock signal, and the second input receives the second reference voltage -V REF and the reference clock signal, and under the control of the reference clock signal, alternately outputs the first reference voltage +V REF and the second reference voltage -V REF at a predetermined clock frequency f0 in each clock period, so that the square wave voltage V Square with the predetermined clock frequency f0 as shown in Figure 4 is output at the output. For example, the multiplexer 218 can output the first reference voltage +V REF in the high level section of each clock period of the reference clock signal, and output the second reference voltage -V REF in the low level section; or the multiplexer 218 can also output the second reference voltage -V REF in the high level section of each clock period of the reference clock signal, and output the first reference voltage +V REFThis enables the multiplexer 218 to output a square wave voltage V with the same predetermined clock frequency f0 as the reference clock signal. Square The square wave voltage V Square It is then coupled to the first drive circuit 220 as the output of the square wave voltage generation circuit 210.

[0038] It should be noted that, Figure 3 The circuit structure and parameter selection of the first reference voltage source 212, first inverter 214, clock generation circuit 216, multiplexer 218, and the entire square wave voltage generation circuit 210 shown are for illustrative purposes only. Those skilled in the art can choose different implementation methods as needed to achieve the basic functions of the circuit without departing from the spirit and scope of this application.

[0039] Continue to refer to Figure 2 and Figure 3 As shown, the current transformer 200 also includes a first drive circuit 220, which is used to receive the square wave voltage V output by the square wave voltage generation circuit 210. Square And generate a following square wave voltage V Square Drive voltage V Drive This driving voltage is used to drive multiple DC sensing coils in the current transformer 200 to sense the magnetic flux corresponding to the current to be measured passing through each DC sensing coil, thus requiring strong driving capability.

[0040] Specifically, refer to Figure 3 The first driving circuit 220 includes a first operational amplifier AMP1 and a first push-pull output stage 224. The first input terminal of the first operational amplifier AMP1, i.e., the non-inverting input terminal, receives the square wave voltage V output by the square wave voltage generation circuit 210. Square The second input terminal, i.e., the inverting input terminal, receives the feedback drive voltage V through the first feedback network after the circuit is started. Drive The output terminal outputs the first intermediate voltage V. Interm1 The first push-pull output stage 224 is used to receive the first intermediate voltage V. Interm1 And push-pull output drive voltage V Drive For example, the first push-pull output stage 224 includes a first NPN bipolar junction transistor and a first PNP bipolar junction transistor. The collector of the first NPN bipolar junction transistor is connected to the positive power supply voltage, and the base is used to receive a first intermediate voltage V. Interm1 The emitter is coupled to the emitter of the first PNP bipolar junction transistor; the collector of the first PNP bipolar junction transistor is coupled to the negative power supply voltage, and the base is connected to the base of the first NPN bipolar junction transistor to receive the first intermediate voltage V. Interm1, the emitter of the first NPN bipolar junction transistor is coupled to the emitter of the second NPN bipolar junction transistor and used for outputting a driving voltage V Drive It should be noted that, as shown in Figure 3 , the input end and the output end of the first driving circuit 220, as well as the emitters of the first NPN bipolar junction transistor and the first PNP bipolar junction transistor are also coupled to a plurality of adaptive resistors, which will not be described one by one here. In addition, the first feedback network in the first driving circuit 220 feeds back the driving voltage V Drive output by the first push-pull output stage 224 to the second input end of the first operational amplifier AMP1 through a resistor. The first feedback network in the first driving circuit 220 can realize low drift of the output driving voltage V Drive relative to the input square wave voltage V Square , and the first push-pull output stage 224 can effectively improve the driving capability of the driving voltage V Drive .

[0041] It should be noted that, Figure 3 the implementation of the first operational amplifier AMP1, the first push-pull output stage 224, and the entire first driving circuit 220 shown in may be for example only. Those skilled in the art can understand that the driving circuit, the push-pull output stage, and other circuits can have many different implementations, so different circuit structures can be selected according to actual needs without departing from the spirit and protection scope of the present application. For example, in some other embodiments, the first push-pull output stage can be implemented based on MOSFET transistors instead of BJT transistors.

[0042] Figure 2 Continuing to refer to Figure 3 , the current transformer 200 includes two DC detection coils, i.e., a first DC detection coil W1 and a second DC detection coil W2; and the current transformer 200 further includes a second driving circuit 230 for receiving a driving voltage V Drive and inverting the driving voltage V Drive to generate an inverted driving voltage -V Drive . Although a separate second inverter 240 is shown in Figure 2 for inverting the driving voltage V Drive to generate the inverted driving voltage -V Drive , this inverting function can also be implemented via an input stage of the second driving circuit 230, thereby simplifying the circuit structure. At this time, the inverter with the inverting function and the driving circuit with the driving capability can be collectively referred to as the second driving circuit 230.

[0043] Specifically, as shown in Figure 3As shown, the second driving circuit 230 includes a second operational amplifier AMP2 and a second push-pull output stage 234. The first input terminal of the second operational amplifier AMP2, i.e., the non-inverting input terminal, is coupled to a third reference voltage. In this embodiment, the third reference voltage is ground. The second input terminal of the second operational amplifier AMP2, i.e., the inverting input terminal, is used to receive the driving voltage V from the first driving circuit 220. Drive And after the circuit starts up, it receives the inverted drive voltage -V through the second feedback network. Drive The output terminal is used to output the second intermediate voltage V. Interm2 The second push-pull output stage 234 is used to receive the second intermediate voltage V. Interm2 And push-pull output inverted drive voltage -V Drive The structure of the second drive circuit 230 and the second push-pull output stage 234 is similar to that of the first drive circuit 220 and the first push-pull output stage 224. Therefore, the description of the first drive circuit 220 and the first push-pull output stage 224 can be referred to, and will not be repeated here. The difference is that the second operational amplifier AMP2 in the second drive circuit 230 also realizes the control of the drive voltage V. Drive The inverse operation.

[0044] Next, the first DC detection coil W1 receives the driving voltage V. Drive And in the driving voltage V Drive Driven by the current, the magnetic flux corresponding to the current to be measured passing through the first DC detection coil W1 is induced to generate a first induced current I. Ind1 The second DC detection coil W2 receives the inverted drive voltage -V. Drive And in the inverted driving voltage -V Drive Driven by the magnetic flux passing through the second DC detection coil W2 corresponding to the current to be measured, a second induced current I is generated. Ind2 Based on the first induced current I Ind1 Second induced current I Ind2 The current transformer 200 can determine the DC component related to the current to be measured.

[0045] It should be noted that, although Figure 2 and Figure 3 The current transformer shown includes two DC detection coils, but other DC current transformers designed based on the zero-flux principle may include more than two DC detection coils. They can all be driven by the square wave voltage generated by the square wave voltage generation circuit of this application and the driving voltage generated by the first driving circuit, so as to sense the current to be measured.

[0046] refer to Figure 2The current transformer 200 also includes resistors R21 and R22, a demodulation circuit 250, and a low-pass filter 260. One end of resistor R21 is grounded, and the other end is coupled between the first DC detection coil W1 and the demodulation circuit 250, and the first induced current I... Ind1 After flowing through resistor R21, a first induced current I is generated at the non-grounded terminal of resistor R21. Ind1 The corresponding first induced voltage V Ind1 One end of resistor R22 is grounded, and the other end is coupled between the second DC detection coil W2 and the demodulation circuit 250. The second induced current I... Ind2 After flowing through resistor R22, a second induced current I is generated at the non-grounded terminal of resistor R22. Ind2 The corresponding second induced voltage V Ind2 The demodulation circuit 250 is used to receive and demodulate the first induced voltage V. Ind1 Second induced voltage V Ind2 To remove the components related to the driving voltage V Drive and the inverting drive voltage -V Drive The AC component is obtained, thus generating a demodulated voltage. A low-pass filter 260 receives the demodulated voltage and performs low-pass filtering to obtain a DC component related to the measured current. The current transformer 200 also includes an AC detection coil W3 and a resistor R23; wherein the AC detection coil W3 and the resistor R23 are connected in parallel, with one end of the parallel circuit grounded and the other end outputting the AC component related to the measured current. Specifically, the AC detection coil W3 is used to sense the magnetic flux passing through it corresponding to the measured current to generate a third induced current I. Ind3 The third induced current I Ind3 After flowing through resistor R23, a third induced current I is generated at the non-grounded terminal of resistor R23. Ind3 The corresponding third induced voltage V Ind3 The third induced voltage V Ind3 This represents the AC component related to the current being measured.

[0047] The current transformer 200 also includes an integrating drive circuit 270, a secondary coil W4, and a detection circuit 280. The integrating drive circuit 270 is used to receive the DC and AC components related to the current to be measured and generate an integrating drive current I. S The secondary coil W4 is used to receive the integrating drive current I. S Among them, the integral drive current I SThe magnetic flux generated by the secondary coil W4 is used to cancel the magnetic flux coupled to the first DC detection coil W1, the second DC detection coil W2, the AC detection coil W3, and the secondary coil by the current to be measured. The remaining magnetic flux is transmitted through the first sensing current I flowing through the first DC detection coil W1, the second DC detection coil W2, and the AC detection coil W3, respectively. Ind1 Second sensing current I Ind2 and the third sensing current I Ind3 To characterize it. That is, in absolute terms, the integral drive current I S The sum of the magnetic flux generated by the secondary coil W4 and coupled to the current to be measured through the first DC detection coil W1, the second DC detection coil W2, the AC detection coil W3, and the secondary coil W4 equals the first induced current I. Ind1 Second induced current I Ind2 and the third induced current I Ind3 The sum of the magnetic flux generated in the first DC detection coil W1, the second DC detection coil W2, and the AC detection coil W3, respectively. It can be seen that the integrating drive current I... S It has a proportional relationship with the current to be measured, and is obtained by integrating the drive current I. S The measurement can be performed to measure the current being measured. The detection circuit 270 includes a load resistor R. L and a voltage detection circuit (not shown), the voltage detection circuit being used to detect the integral drive current I. S Flow through load resistor R L The voltage generated during the measurement can be used to characterize the measured current.

[0048] exist Figure 2 The current transformer 200 shown also includes a follower 292 coupled between the low-pass filter 260 and the integrator drive circuit 270, a follower 294 coupled between the AC detection coil W3 and the integrator drive circuit 270, and a noise filter 296 coupled between the integrator drive circuit 270 and the secondary coil W4, which is used for signal buffering and noise filtering between the front and rear stages.

[0049] The specific implementation methods of the demodulation circuit 250, low-pass filter 260, integral drive circuit 270 and detection circuit 280 can be referred to the implementation methods of existing DC current transformers, and will not be elaborated here.

[0050] In some embodiments, in order to further improve the frequency stability and voltage stability of the square wave voltage generated by the square wave voltage generation circuit, a separate power supply is also provided for the clock generation circuit and the multiplexer in the square wave voltage generation circuit.

[0051] Specifically, refer to Figure 5, the current transformer can further include a low dropout regulator 510 and a second reference voltage source 520. The low dropout regulator 510 is configured to receive an external power supply voltage (V C , V S ) and generate a first power supply voltage (+V, -V) after voltage stabilization of the external power supply voltage. The second reference voltage source 520 is configured to receive the first power supply voltage and generate a second power supply voltage V REF based on the first power supply voltage (+V, -V). In some embodiments, the second reference voltage source 520 is a series reference voltage source, which can output a stable second power supply voltage V REF when the first power supply voltage (+V, -V) changes. In this way, the current transformer includes a first voltage domain with the first power supply voltage (+V, -V) and a second voltage domain with the second power supply voltage V REF , which is generated after voltage stabilization of the first power supply voltage (+V, -V). In some embodiments of the present application, the clock generation circuit and the multiplexer in the square wave voltage generation circuit operate in the second voltage domain, which is supplied by the more stable second power supply voltage V REF , thereby being able to provide a square wave voltage with more stable frequency and voltage, which is beneficial to improve the power supply rejection ratio of the current transformer. Other circuit modules operate in the first voltage domain. In other embodiments, some other circuits in the current transformer that require stable power supply voltage can also operate in the second voltage domain.

[0052] In some embodiments, the circuits (e.g., inverters, driver circuits, followers, integral driver circuits, power amplification circuits, and demodulation circuits) of the current transformer using operational amplifiers preferably use precision low drift operational amplifiers to more effectively suppress the offset and gain drift of the current transformer.

[0053] It should be noted that although several modules or sub-modules of the current transformer are mentioned in the foregoing detailed description, such division is merely exemplary and not mandatory. In fact, according to embodiments of the present application, the features and functions of two or more modules described above can be embodied in one module. Conversely, the features and functions of one module described above can be further divided into multiple modules.

[0054] Those of ordinary skill in the art can understand and implement other changes to the disclosed embodiments by studying the specification, the disclosed content, and the accompanying drawings and the appended claims. In the claims, the word "comprising" does not exclude other elements and steps, and the word "a" or "one" does not exclude a plurality. In the practical application of the present application, one part can perform the functions of multiple technical features cited in the claims. Any reference signs in the claims should not be understood as limiting the scope.

Claims

1. A current transformer, characterized in that, The current transformer includes: A square wave voltage generating circuit includes: A first reference voltage source is used to generate a first reference voltage; A first inverter is used to receive the first reference voltage and invert the first reference voltage to generate a second reference voltage; A clock generation circuit for generating a reference clock signal having a predetermined clock frequency; and A multiplexer is configured to receive a first reference voltage, a second reference voltage, and a reference clock signal, and under the control of the reference clock signal, alternately output the first reference voltage and the second reference voltage at a predetermined clock frequency in each clock cycle, thereby generating a square wave voltage having the predetermined clock frequency. A first driving circuit is configured to receive the square wave voltage and generate a driving voltage that follows the square wave voltage. The first driving circuit includes: A first operational amplifier, wherein a first input terminal of the first operational amplifier is used to receive the square wave voltage, a second input terminal of the first operational amplifier receives the feedback driving voltage through a first feedback network, and an output terminal of the first operational amplifier outputs a first intermediate voltage; and A first push-pull output stage, wherein the first push-pull output stage is configured to receive the first intermediate voltage and output the drive voltage in a push-pull manner; and A plurality of DC detection coils are provided, each of which receives the driving voltage and senses the magnetic flux corresponding to the current to be measured passing through the DC detection coil under the drive voltage; wherein the plurality of DC detection coils include a first DC detection coil and a second DC detection coil. A second driving circuit is configured to receive the driving voltage and invert the driving voltage to generate an inverted driving voltage. The first DC detection coil receives the driving voltage and, driven by the driving voltage, induces the magnetic flux corresponding to the current to be measured passing through the first DC detection coil to generate a first induced current; the second DC detection coil receives the reverse driving voltage and, driven by the reverse driving voltage, induces the magnetic flux corresponding to the current to be measured passing through the second DC detection coil to generate a second induced current; and the current transformer determines the DC component related to the current to be measured based on the first induced current and the second induced current. A demodulation circuit is used to receive and demodulate a first induced voltage corresponding to the first induced current and a second induced voltage corresponding to the second induced current, to remove the AC components related to the driving voltage and the inverted driving voltage, thereby generating a demodulated voltage; and A low-pass filter receives the demodulated voltage and performs low-pass filtering to obtain the DC component related to the current to be measured.

2. The current transformer according to claim 1, characterized in that, The second driving circuit includes: A second operational amplifier has its first input terminal coupled to a third reference voltage, its second input terminal receiving the driving voltage and receiving an inverted driving voltage via a second feedback network, and its output terminal outputting a second intermediate voltage. The second push-pull output stage is used to receive the second intermediate voltage and push-pull output the inverted drive voltage.

3. The current transformer according to claim 1, characterized in that, The current transformer includes a first voltage domain having a first power supply voltage and a second voltage domain having a second power supply voltage, the second voltage domain being generated by regulating the first power supply voltage.

4. The current transformer according to claim 3, characterized in that, The clock generation circuit and the multiplexer operate in the second voltage domain and are powered by the second power supply voltage.

5. The current transformer according to claim 3, characterized in that, The current transformer also includes: A low-dropout regulator, used to receive an external power supply voltage and regulate the external power supply voltage to generate the first power supply voltage; and A second reference voltage source is used to receive the first power supply voltage and generate the second power supply voltage based on the first power supply voltage.

6. The current transformer according to claim 1, characterized in that, The current transformer also includes: An AC detection coil is used to sense the magnetic flux passing through it corresponding to the current under test to generate a third induced current, and the current transformer determines the AC component associated with the current under test based on the third induced current.

7. The current transformer according to claim 6, characterized in that, The current transformer also includes: An integral drive circuit is used to receive the DC component and the AC component related to the current to be measured and generate an integral drive current. The secondary coil receives the integral drive current, wherein the sum of the magnetic flux generated by the integral drive current through the secondary coil and the magnetic flux coupled to the current under test to the first DC detection coil, the second DC detection coil, the AC detection coil, and the secondary coil is equal to the sum of the magnetic flux generated by the first induced current, the second induced current, and the third induced current in the first DC detection coil, the second DC detection coil, and the AC detection coil, respectively. A detection circuit is used to detect the integral drive current flowing through the secondary coil.

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