Bias current detection circuit of single-phase industrial frequency transformer

Abstract

The invention discloses a bias current detection circuit for a single-phase industrial frequency transformer. The bias current detection circuit is used for detecting bias current of the single-phase industrial frequency transformer. The magnetic bias current detection circuit of the single-phase industrial frequency transformer comprises a sampling mutual inductor, a current sampling circuit and an amplifying circuit which are connected in sequence, the sampling mutual inductor is provided with a first winding Np, a second winding Ns and a sampling winding N1, the winding directions of the first winding Np and the second winding Ns are opposite, the winding directions of the first winding Np and the sampling winding N1 are the same, the first winding Np is connected in a primary side loop of the single-phase industrial frequency transformer in series, and the second winding Ns is connected in a secondary side loop of the single-phase industrial frequency transformer in series. The current sampling circuit is connected with two ends of the sampling winding N1. The bias current detection circuit of the single-phase industrial frequency transformer has the advantages of being low in cost and capable of accurately detecting the bias current.

Description

Technical Field

[0001] The invention relates to the field of power frequency transformers, in particular to a bias current detection circuit for a single-phase power frequency transformer. Background Art

[0002] Single-phase power frequency transformer is a core component widely used in power conversion equipment. In addition to voltage conversion and energy transmission, single-phase power frequency transformer also has the advantages of fault isolation and load impact resistance. It is a necessary component in inverters, uninterruptible power supplies, and converter products.

[0003] Products with single-phase power frequency transformers (such as inverters) will inevitably have bias problems in actual use. At present, the main method for detecting the bias current of a single-phase power frequency transformer is to collect the primary current and secondary current of the single-phase power frequency transformer, and then use software algorithms to calculate the current bias current. However, in high-power inverters, the primary current of a single-phase power frequency transformer is as high as several hundred amperes, so the overcurrent specifications of the Hall current sensor required to collect the primary current are high and expensive; and the bias current is calculated through the software algorithm in the MCU processor, resulting in a certain deviation between the calculated bias current and the actual bias current, which makes it difficult to completely eliminate the bias current even after subsequent software control.

[0004] In view of the existence of the above problems, it is necessary to study a single-phase power frequency transformer bias current detection circuit, which has low cost and can accurately detect the bias current. Summary of the invention

[0005] The object of the present invention is to provide a single-phase power frequency transformer bias current detection circuit, which has low cost and can accurately detect the bias current.

[0006] In order to achieve the above object, the solution of the present invention is: A single-phase power frequency transformer bias current detection circuit is used to detect the bias current of the single-phase power frequency transformer. The single-phase power frequency transformer bias current detection circuit comprises a sampling transformer, a current sampling circuit and an amplifier circuit connected in sequence; the sampling transformer comprises a first winding Np, a second winding Ns and a sampling winding N1, the first winding Np and the second winding Ns are wound in opposite directions, the first winding Np and the sampling winding N1 are wound in the same direction, the first winding Np is connected in series in the primary loop of the single-phase power frequency transformer, the second winding Ns is connected in series in the secondary loop of the single-phase power frequency transformer, and the current sampling circuit is connected to both ends of the sampling winding N1.

[0007] The current sampling circuit includes a resistor R1, and the two ends of the resistor R1 are respectively connected to the first connection end and the second connection end of the current sampling circuit, and the first connection end and the second connection end of the current sampling circuit are respectively connected to the two ends of the sampling winding N1; the amplifier circuit is a differential amplifier circuit, and the in-phase input end and the inverting input end of the amplifier circuit are respectively connected to the first connection end and the second connection end of the current sampling circuit.

[0008] The current sampling circuit further includes a resistor R2, and two ends of the resistor R2 are respectively connected to a first connection end and a second connection end of the current sampling circuit.

[0009] The single-phase power frequency transformer bias current detection circuit also includes a DC bias circuit, which is connected to the output end of the amplifier circuit.

[0010] The DC bias circuit includes a resistor R8 and a capacitor C4, a first end of the resistor R8 and a first end of the capacitor C4 are connected to the output end of the amplifier circuit, a second end of the resistor R8 is connected to a bias power supply VREF, and a second end of the capacitor C4 is grounded.

[0011] The amplifier circuit includes resistor R3, resistor R4, resistor R5, resistor R6, resistor R7 and operational amplifier U1; the first end of resistor R3 is connected to the non-inverting input end of the amplifier circuit, the second end of resistor R3 and the first end of resistor R5 are connected to the non-inverting input end of operational amplifier U1, the first end of resistor R4 is connected to the inverting input end of the amplifier circuit, the second end of resistor R4 and the first end of resistor R6 are connected to the inverting input end of operational amplifier U1, the second end of resistor R5 and the output end of operational amplifier U1 are connected to the output end of the amplifier circuit, the power supply end of operational amplifier U1 is connected to the positive power supply VCC+, and the ground end of operational amplifier U1 and the second end of resistor R6 are grounded.

[0012] The amplifier circuit further includes a capacitor C2 connected in parallel with the resistor R5.

[0013] The amplifier circuit also includes a capacitor C1 and a capacitor C3. The two ends of the capacitor C1 are respectively connected to the in-phase input terminal and the inverting input terminal of the operational amplifier U1. The first end of the capacitor C3 is connected to the inverting input terminal of the operational amplifier U1. The second end of the capacitor C3 is grounded.

[0014] The single-phase power frequency transformer bias current detection circuit also includes a first clamp circuit and a second clamp circuit. The first clamp circuit is connected to the non-inverting input terminal of the operational amplifier U1, and the second clamp circuit is connected to the inverting input terminal of the operational amplifier U1.

[0015] The first clamping circuit includes a diode D1 and a diode D2, wherein the positive electrode of the diode D1 is connected to the negative power supply VCC-, the negative electrode of the diode D2 is connected to the positive power supply VCC+, and the positive electrode of the diode D2 and the negative electrode of the diode D1 are connected to the non-inverting input terminal of the operational amplifier U1; the second clamping circuit includes a diode D3 and a diode D4, wherein the positive electrode of the diode D3 is connected to the negative power supply VCC-, the negative electrode of the diode D4 is connected to the positive power supply VCC+, and the positive electrode of the diode D4 and the negative electrode of the diode D3 are connected to the non-inverting input terminal of the operational amplifier U1; the voltages of the positive power supply VCC+ and the negative power supply VCC- are opposite.

[0016] After adopting the above scheme, the working principle of the present invention is: Since the first winding Np and the second winding Ns of the sampling transformer are wound in opposite directions, the current direction of the first winding Np and the current direction of the second winding Ns are opposite, and thus the magnetic flux of the magnetic field generated by the first winding Np and the magnetic flux of the magnetic field generated by the second winding Ns have the characteristic of opposite directions; When the single-phase power frequency transformer has no bias magnetism, the current magnitude of the first winding Np is the same as the current magnitude of the second winding Ns (that is, the primary loop current and the secondary loop current of the single-phase power frequency transformer are the same). At this time, the magnetic flux of the magnetic field generated by the first winding Np and the magnetic flux of the magnetic field generated by the second winding Ns have the characteristics of the same magnetic flux magnitude and opposite magnetic flux direction, so that the magnetic flux of the magnetic field generated by the first winding Np and the magnetic flux of the magnetic field generated by the second winding Ns cancel each other out. At this time, the sampling winding N1 has no induced magnetic flux, so that the current of the sampling winding N1 is zero; When the single-phase power frequency transformer is biased, the current magnitude of the first winding Np is different from the current magnitude of the second winding Ns (that is, the primary loop current and the secondary loop current of the single-phase power frequency transformer are different). At this time, the magnetic flux of the magnetic field generated by the first winding Np and the magnetic flux of the magnetic field generated by the second winding Ns have the characteristics of different flux magnitudes and opposite flux directions. In this way, after the magnetic flux that does not belong to the bias part is offset, the remaining magnetic flux causes the sampling winding N1 to form an induced current. The magnitude of the induced current is the magnitude of the bias current to be detected. In this way, the bias current detection circuit of the single-phase power frequency transformer of the present invention samples and amplifies the induced current of the sampling winding N1 through the current sampling circuit and the amplifier circuit, and then obtains a bias current detection signal corresponding to the induced current of the sampling winding N1. The bias current detection signal is input into the MCU processor, so that the MCU processor can obtain the magnitude of the bias current to be detected.

[0017] From the above, it can be seen that the present invention does not need to use a Hall current sensor to detect the bias current, which has lower costs; moreover, the present invention directly collects the induced current with the same magnitude as the bias current, so that the bias current can be detected more accurately. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the present invention. DETAILED DESCRIPTION

[0019] In order to further explain the technical solution of the present invention, the present invention is described in detail below through specific embodiments.

[0020] like Figure 1 As shown, the present invention discloses a single-phase power frequency transformer bias current detection circuit, which is used to detect the bias current of the single-phase power frequency transformer; the single-phase power frequency transformer bias current detection circuit includes a sampling transformer, a current sampling circuit and an amplifier circuit connected in sequence; the sampling transformer has a first winding Np, a second winding Ns and a sampling winding N1, the first winding Np and the second winding Ns are wound in opposite directions, the first winding Np and the sampling winding N1 are wound in the same direction, the first winding Np is connected in series in the primary circuit of the single-phase power frequency transformer, the second winding Ns is connected in series in the secondary circuit of the single-phase power frequency transformer, and the current sampling circuit is connected to both ends of the sampling winding N1.

[0021] The working principle of the present invention is: Since the first winding Np and the second winding Ns of the sampling transformer are wound in opposite directions, the current direction of the first winding Np and the current direction of the second winding Ns are opposite, and thus the magnetic flux of the magnetic field generated by the first winding Np and the magnetic flux of the magnetic field generated by the second winding Ns have the characteristic of opposite directions; When the single-phase power frequency transformer has no bias magnetism, the current magnitude of the first winding Np is the same as the current magnitude of the second winding Ns (that is, the primary loop current and the secondary loop current of the single-phase power frequency transformer are the same). At this time, the magnetic flux of the magnetic field generated by the first winding Np and the magnetic flux of the magnetic field generated by the second winding Ns have the characteristics of the same magnetic flux magnitude and opposite magnetic flux direction, so that the magnetic flux of the magnetic field generated by the first winding Np and the magnetic flux of the magnetic field generated by the second winding Ns cancel each other out. At this time, the sampling winding N1 has no induced magnetic flux, so that the current of the sampling winding N1 is zero; When the single-phase power frequency transformer is biased, the current magnitude of the first winding Np is different from the current magnitude of the second winding Ns (that is, the primary loop current and the secondary loop current of the single-phase power frequency transformer are different). At this time, the magnetic flux of the magnetic field generated by the first winding Np and the magnetic flux of the magnetic field generated by the second winding Ns have the characteristics of different flux magnitudes and opposite flux directions. In this way, after the magnetic flux that does not belong to the bias part is offset, the remaining magnetic flux causes the sampling winding N1 to form an induced current. The magnitude of the induced current is the magnitude of the bias current to be detected. In this way, the bias current detection circuit of the single-phase power frequency transformer of the present invention samples and amplifies the induced current of the sampling winding N1 through the current sampling circuit and the amplifier circuit, and then obtains a bias current detection signal corresponding to the induced current of the sampling winding N1. The bias current detection signal is input into the MCU processor, so that the MCU processor can obtain the magnitude of the bias current to be detected.

[0022] From the above, it can be seen that the present invention does not need to use a Hall current sensor to detect the bias current, which has lower costs; moreover, the present invention directly collects the induced current with the same magnitude as the bias current, so that the bias current can be detected more accurately.

[0023] In an embodiment of the present invention, the current sampling circuit includes a resistor R1, the two ends of the resistor R1 are respectively connected to the first connection end and the second connection end of the current sampling circuit, the first connection end and the second connection end of the current sampling circuit are respectively connected to the two ends of the sampling winding N1, the current sampling circuit can form a loop with the sampling winding N1 so that the sampling winding N1 can form an induced current; and the amplifier circuit is a differential amplifier circuit, the in-phase input end and the inverting input end of the amplifier circuit are respectively connected to the first connection end and the second connection end of the current sampling circuit. Further, the current sampling circuit also includes a resistor R2, the two ends of the resistor R2 are respectively connected to the first connection end and the second connection end of the current sampling circuit, and the resistor R2 is in parallel with the resistor R1, so that the sampling winding N1 can be prevented from being open when one of the resistors R2 and R1 is damaged.

[0024] In an embodiment of the present invention, the amplifier circuit includes a resistor R3, a resistor R4, a resistor R5, a resistor R6, a resistor R7 and an operational amplifier U1; wherein, a first end of the resistor R3 is connected to a non-inverting input end of the amplifier circuit, a second end of the resistor R3 and a first end of the resistor R5 are connected to a non-inverting input end of the operational amplifier U1, a first end of the resistor R4 is connected to an inverting input end of the amplifier circuit, a second end of the resistor R4 and a first end of the resistor R6 are connected to an inverting input end of the operational amplifier U1, a second end of the resistor R5 and an output end of the operational amplifier U1 are connected to an output end of the amplifier circuit, a power supply end of the operational amplifier U1 is connected to a positive power supply VCC+, and a ground end of the operational amplifier U1 and a second end of the resistor R6 are grounded.

[0025] In an embodiment of the present invention, the amplifier circuit further includes a capacitor C2 connected in parallel with the resistor R5. The capacitor C2 can improve the stability of the amplifier circuit.

[0026] In an embodiment of the present invention, the amplifier circuit also includes a capacitor C1 and a capacitor C3, the two ends of the capacitor C1 are respectively connected to the non-inverting input terminal and the inverting input terminal of the operational amplifier U1, the first end of the capacitor C3 is connected to the inverting input terminal of the operational amplifier U1, and the second end of the capacitor C3 is grounded. The capacitors C1 and C3 can also improve the stability of the amplifier circuit.

[0027] In an embodiment of the present invention, the single-phase industrial frequency transformer bias current detection circuit of the present invention also includes a first clamping circuit and a second clamping circuit. The first clamping circuit is connected to the non-inverting input terminal of the operational amplifier U1, and the second clamping circuit is connected to the inverting input terminal of the operational amplifier U1. The first clamping circuit and the second clamping circuit can respectively clamp the voltages of the non-inverting input terminal and the inverting input terminal of the operational amplifier U1 to prevent the voltages of the non-inverting input terminal and the inverting input terminal of the operational amplifier U1 from being too large, thereby causing damage to the operational amplifier U1. Specifically, the first clamping circuit includes a diode D1 and a diode D2, the positive electrode of the diode D1 is connected to the negative power supply VCC-, the negative electrode of the diode D2 is connected to the positive power supply VCC+, the positive electrode of the diode D2 and the negative electrode of the diode D1 are connected to the non-inverting input terminal of the operational amplifier U1; the second clamping circuit includes a diode D3 and a diode D4, the positive electrode of the diode D3 is connected to the negative power supply VCC-, the negative electrode of the diode D4 is connected to the positive power supply VCC+, the positive electrode of the diode D4 and the negative electrode of the diode D3 are connected to the non-inverting input terminal of the operational amplifier U1; the voltages of the positive power supply VCC+ and the negative power supply VCC- are opposite.

[0028] In an embodiment of the present invention, the single-phase power frequency transformer bias current detection circuit of the present invention also includes a DC bias circuit, the DC bias circuit is connected to the output end of the amplifier circuit, and the output end of the amplifier circuit is connected to the MCU processor; the DC bias circuit can ensure that the output signal of the amplifier circuit is a positive voltage signal to meet the signal reception requirements of the MCU processor. Specifically, the DC bias circuit includes a resistor R8 and a capacitor C4, the resistor R8 acts as a pull-up resistor, the first end of the resistor R8 and the first end of the capacitor C4 are connected to the output end of the amplifier circuit, the second end of the resistor R8 is connected to the bias power supply VREF, and the second end of the capacitor C4 is grounded.

[0029] The above embodiments and drawings do not limit the product form and style of the present invention. Any appropriate changes or modifications made by ordinary technicians in the relevant technical field should be deemed to be within the patent scope of the present invention.

Claims

1. A single-phase power frequency transformer bias current detection circuit, which is used to detect the bias current of a single-phase power frequency transformer, characterized in that: The single-phase power frequency transformer bias current detection circuit comprises a sampling transformer, a current sampling circuit and an amplifying circuit which are connected in sequence; the sampling transformer comprises a first winding Np, a second winding Ns and a sampling winding N1, the first winding Np and the second winding Ns are wound in opposite directions, the first winding Np and the sampling winding N1 are wound in the same direction, the first winding Np is connected in series in the primary loop of the single-phase power frequency transformer, the second winding Ns is connected in series in the secondary loop of the single-phase power frequency transformer, and the current sampling circuit is connected to both ends of the sampling winding N1.

2. The single-phase power frequency transformer bias current detection circuit as claimed in claim 1, characterized in that: The current sampling circuit comprises a resistor R1, two ends of the resistor R1 are respectively connected to a first connection end and a second connection end of the current sampling circuit, and the first connection end and the second connection end of the current sampling circuit are respectively connected to two ends of the sampling winding N1; The amplifier circuit is a differential amplifier circuit, and the in-phase input terminal and the inverting input terminal of the amplifier circuit are respectively connected to the first connection terminal and the second connection terminal of the current sampling circuit.

3. The single-phase power frequency transformer bias current detection circuit as claimed in claim 2, characterized in that: The current sampling circuit further includes a resistor R2, and two ends of the resistor R2 are respectively connected to a first connection end and a second connection end of the current sampling circuit.

4. The single-phase power frequency transformer bias current detection circuit as claimed in claim 2, characterized in that: The invention also comprises a direct current bias circuit, which is connected to the output end of the amplifier circuit.

5. The single-phase power frequency transformer bias current detection circuit as claimed in claim 4, characterized in that: The DC bias circuit includes a resistor R8 and a capacitor C4, a first end of the resistor R8 and a first end of the capacitor C4 are connected to the output end of the amplifier circuit, a second end of the resistor R8 is connected to a bias power supply VREF, and a second end of the capacitor C4 is grounded.

6. The single-phase power frequency transformer bias current detection circuit as claimed in claim 2 or 4, characterized in that: The amplifying circuit includes a resistor R3, a resistor R4, a resistor R5, a resistor R6, a resistor R7 and an operational amplifier U1; The first end of the resistor R3 is connected to the non-inverting input terminal of the amplifier circuit, the second end of the resistor R3 and the first end of the resistor R5 are connected to the non-inverting input terminal of the operational amplifier U1, the first end of the resistor R4 is connected to the inverting input terminal of the amplifier circuit, the second end of the resistor R4 and the first end of the resistor R6 are connected to the inverting input terminal of the operational amplifier U1, the second end of the resistor R5 and the output terminal of the operational amplifier U1 are connected to the output terminal of the amplifier circuit, the power supply terminal of the operational amplifier U1 is connected to the positive power supply VCC+, and the ground terminal of the operational amplifier U1 and the second end of the resistor R6 are grounded.

7. The single-phase power frequency transformer bias current detection circuit as claimed in claim 6, characterized in that: The amplifier circuit further includes a capacitor C2 connected in parallel with the resistor R5.

8. The single-phase power frequency transformer bias current detection circuit as claimed in claim 6, characterized in that: The amplifier circuit also includes a capacitor C1 and a capacitor C3. The two ends of the capacitor C1 are respectively connected to the in-phase input terminal and the inverting input terminal of the operational amplifier U1. The first end of the capacitor C3 is connected to the inverting input terminal of the operational amplifier U1. The second end of the capacitor C3 is grounded.

9. The single-phase power frequency transformer bias current detection circuit as claimed in claim 6, characterized in that: It also includes a first clamping circuit and a second clamping circuit. The first clamping circuit is connected to the non-inverting input terminal of the operational amplifier U1, and the second clamping circuit is connected to the inverting input terminal of the operational amplifier U1.

10. The single-phase power frequency transformer bias current detection circuit as claimed in claim 9, characterized in that: The first clamping circuit includes a diode D1 and a diode D2, wherein the positive electrode of the diode D1 is connected to the negative power supply VCC-, the negative electrode of the diode D2 is connected to the positive power supply VCC+, and the positive electrode of the diode D2 and the negative electrode of the diode D1 are connected to the non-inverting input terminal of the operational amplifier U1; The second clamping circuit includes a diode D3 and a diode D4, the positive electrode of the diode D3 is connected to the negative power supply VCC-, the negative electrode of the diode D4 is connected to the positive power supply VCC+, and the positive electrode of the diode D4 and the negative electrode of the diode D3 are connected to the non-inverting input terminal of the operational amplifier U1; The voltages of the positive power supply VCC+ and the negative power supply VCC- are opposite.

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