Circuit for realizing high-frequency detection and low-frequency reconstruction of inverter phase current based on CT

Abstract

The application discloses a kind of based on CT realizes inverter phase current high frequency detection and algorithm realizes low frequency reconstruction circuit, comprising: high frequency detection unit connects signal conditioning unit;High frequency detection unit provides high frequency signal to signal conditioning unit;Signal conditioning unit connects low frequency reconstruction unit;Low frequency reconstruction unit connects high frequency detection unit;Signal conditioning unit processes high frequency signal, obtains for positive half-wave signal;Low frequency reconstruction unit restores positive half-wave signal, obtains inverter actual phase current.The application detects current by using current transformer, without designing additional isolation circuit, reduces cost;By adjusting the installation position of current transformer, the problem that traditional current transformer cannot accurately detect inverter low frequency current is solved;The application is simple in design, and circuit is reliable.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic induction technology and relates to a circuit based on CT to realize high-frequency detection and low-frequency reconstruction of inverter phase current. Background Technology

[0002] Permanent magnet synchronous motors (PMSMs) offer advantages such as high power density, high performance, and high reliability, making them widely used in industrial applications. To reduce the size of PMSMs, sensorless control methods are typically employed, with current closed-loop control implemented by a DSP and inverter. Therefore, the accuracy of inverter phase current sampling determines the quality of control performance, leading to the development of various current sensing technologies.

[0003] Traditional inverter phase current detection methods can be categorized into three types: sampling resistor detection, Hall sensor detection, and conventional current transformer (CT) detection. Sampling resistor detection is suitable for low-power PMSMs, but for high-power PMSMs, the sampling resistor consumes power and requires additional isolation design. Hall sensor detection is expensive, bulky, and suffers from temperature drift. Conventional CT detection cannot detect the low-frequency current during motor startup. Therefore, a circuit capable of high-frequency detection and low-frequency reconfiguration of inverter phase current is urgently needed. Summary of the Invention

[0004] The purpose of this invention is to solve the problems of the inability to detect the low-frequency current during inverter startup and the safety isolation of the power conversion circuit in the prior art when performing inverter phase current detection, and to provide a circuit based on CT to realize high-frequency detection and low-frequency reconstruction of inverter phase current.

[0005] To achieve the above objectives, the present invention employs the following technical solution:

[0006] A circuit based on CT to realize high-frequency detection and low-frequency reconstruction of inverter phase current includes: a high-frequency detection unit, a signal conditioning unit, and a low-frequency reconstruction unit.

[0007] The high-frequency detection unit is connected to the signal conditioning unit; the high-frequency detection unit is used to provide high-frequency signals to the signal conditioning unit; the signal conditioning unit is connected to the low-frequency reconstruction unit; the low-frequency reconstruction unit is connected to the high-frequency detection unit; the signal conditioning unit conditions the high-frequency signal to obtain a positive half-cycle signal; the low-frequency reconstruction unit restores the positive half-cycle signal to obtain the actual phase current of the inverter.

[0008] A further improvement of the present invention is that:

[0009] The high-frequency detection unit includes a current transformer and an inverter;

[0010] The inverter includes three inverter top transistors (S). up and three inverter down transistors S dnInverter upper transistor S up and inverter lower transistor S dn Two pairs form a group; the current transformers are in three groups; one group of inverter upper transistor S up and inverter lower transistor S dn A corresponding set of current transformers;

[0011] The primary winding of the current transformer is connected in series with the inverter's upper transistor S. up and inverter lower transistor S dn middle;

[0012] Inverter upper transistor S up One end is connected to an external voltage source U DC Inverter upper transistor S up The other end is connected to the primary side of the current transformer;

[0013] Inverter lower transistor S dn One end is connected to the primary side of the current transformer; the lower transistor S of the inverter dn The other end is grounded.

[0014] The turns ratio of the primary and secondary windings of the current transformer is 2:2N, where 2N is the number of turns in the secondary winding.

[0015] The primary winding of the current transformer has two turns.

[0016] The secondary side of the current transformer consists of several turns of enameled wire coil with a center tap, wherein the center tap is grounded.

[0017] The signal conditioning unit consists of three groups; the signal conditioning unit includes a full-bridge rectifier circuit, a self-integrating resistor Rs, and a low-pass filter circuit.

[0018] The full-bridge rectifier circuit is connected to the secondary side of the current transformer to convert the high-frequency signal into a positive half-cycle signal. The full-bridge rectifier circuit is connected to the self-integrating resistor Rs to restore the positive half-cycle signal and obtain a signal proportional to the primary current of the current transformer. The self-integrating resistor Rs is connected to the low-pass filter circuit. The low-pass filter circuit filters out high-frequency interference in the restored positive half-cycle signal.

[0019] The full-bridge rectifier circuit includes diodes D1, D2, D3, and D4; the low-pass filter circuit includes an operational amplifier, resistors R1, R2, R3, R4, and R5, and capacitors C1, C2, and C3.

[0020] One end of the secondary side of the current transformer is connected to the anode of diode D1 and the cathode of diode D3, and the other end of the secondary side of the current transformer is connected to the anode of diode D2 and the cathode of diode D4. The cathode of diode D2 is connected to the cathode of diode D1, one end of resistor R1, and one end of resistor Rs. The anode of diode D4 is connected to the anode of diode D3, the other end of resistor Rs, one end of capacitor C1, one end of capacitor C2, and one end of resistor R4. The other end of resistor R1 is connected to the other end of capacitor C1 and one end of resistor R2. The other end of resistor R2 is connected to one end of resistor R3 and one end of capacitor C3. The other end of resistor R3 is connected to the other end of capacitor C2 and the non-inverting input of operational amplifier op amp. The other end of resistor R4 is connected to the inverting input of operational amplifier op amp and one end of resistor R5. The other end of resistor R5 is connected to the other end of capacitor C3 and the output of operational amplifier op amp.

[0021] The low-frequency reconstruction unit consists of three groups, each using a DSP28335. The output of the operational amplifier (op-amp) is connected to the DSP28335. The DSP28335 controls the inverter's upper transistor S. up and inverter lower transistor S dn .

[0022] Diodes D1, D2, D3, and D4 are all Schottky diodes.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] This invention connects a high-frequency detection unit to a signal conditioning unit, which in turn connects to a low-frequency reconstruction unit. The low-frequency reconstruction unit is then connected to the high-frequency detection unit. The high-frequency detection unit provides a high-frequency signal, which the signal conditioning unit conditions to produce a positive half-cycle signal. The low-frequency reconstruction unit restores the positive half-cycle signal to obtain the actual phase current of the inverter. This invention uses a current transformer for current detection without requiring additional isolation circuitry, thus reducing costs. By adjusting the installation position of the current transformer, the problem of traditional current transformers failing to accurately detect low-frequency inverter current is solved. This invention is simple in design and reliable in circuitry. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1This is a connection diagram of the high-frequency detection unit, the low-frequency reconstruction unit, and the full-bridge rectifier circuit.

[0027] Figure 2 This is a circuit diagram of the signal conditioning unit;

[0028] Figure 3 For i up i dn and i a Relationship diagram;

[0029] Figure 4 For u cur_a u cur_b and u cur_c Relationship diagram;

[0030] Figure 5 This is a schematic diagram of the secondary output signal of the high-frequency detection unit;

[0031] Figure 6 A schematic diagram illustrating the correspondence between reconstructed sectors and phase currents;

[0032] Figure 7 The phase current is reconstructed according to the reconstruction algorithm;

[0033] Figure 8 This refers to the phase current detected by a current sensor.

[0034] Among them, 1-high frequency detection unit, 2-signal conditioning unit, 3-low frequency reconstruction unit, 4-current transformer, 5-full bridge rectifier circuit, and 6-low pass filter circuit. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0036] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0037] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0038] In the description of the embodiments of the present invention, it should be noted that if terms such as "upper," "lower," "horizontal," or "inner" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of the invention is in use, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. Furthermore, terms such as "first" and "second" are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0039] Furthermore, the use of the term "horizontal" does not imply that the component must be absolutely horizontal, but rather that it can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal than "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0040] In the description of the embodiments of the present invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in the present invention according to the specific circumstances.

[0041] The present invention will now be described in further detail with reference to the accompanying drawings:

[0042] See Figure 1 and Figure 2 This invention discloses a circuit based on CT to realize high-frequency detection and low-frequency reconstruction of inverter phase current, including: high-frequency detection unit 1, signal conditioning unit 2 and low-frequency reconstruction unit 3;

[0043] The high-frequency detection unit 1 is connected to the signal conditioning unit 2; the high-frequency detection unit 1 provides a high-frequency signal to the signal conditioning unit 2; the signal conditioning unit 2 is connected to the low-frequency reconstruction unit 3; the low-frequency reconstruction unit 3 is connected to the high-frequency detection unit 1; the signal conditioning unit 2 is used to adjust the high-frequency signal to obtain a positive half-cycle signal; the low-frequency reconstruction unit 3 restores the positive half-cycle signal to obtain the actual phase current of the inverter.

[0044] The high-frequency detection unit 1 includes a current transformer 4 and an inverter;

[0045] The inverter includes three inverter top transistors (S). up and three inverter down transistors S dn Inverter upper transistor S up and inverter lower transistor S dnTwo pairs form a group; current transformers 4 form three groups; one group of inverter upper transistor S up and inverter lower transistor S dn This corresponds to a set of current transformers 4.

[0046] The primary winding of current transformer 4 is connected in series with transistor S on the inverter. up and inverter lower transistor S dn middle;

[0047] Inverter upper transistor S up One end is connected to an external voltage source U DC Inverter upper transistor S up The other end is connected to the primary side of current transformer 4;

[0048] Inverter lower transistor S dn One end is connected to the primary side of current transformer 4; the lower inverter transistor S dn The other end is grounded.

[0049] The turns ratio of the primary and secondary sides of current transformer 4 is 2:2N, where N is the number of turns in the secondary winding.

[0050] The primary winding of current transformer 4 is a 2-turn coil.

[0051] The secondary side of current transformer 4 consists of several turns of enameled wire coil with a center tap, wherein the center tap is grounded.

[0052] Signal conditioning unit 2 consists of three groups; signal conditioning unit 2 includes a full-bridge rectifier circuit 5, a self-integrating resistor Rs, and a low-pass filter circuit 6;

[0053] The full-bridge rectifier circuit 5 is connected to the secondary side of the current transformer 4, converting the high-frequency signal into a positive half-cycle signal; the full-bridge rectifier circuit 5 is connected to the self-integrating resistor Rs, which is used to restore the positive half-cycle signal to obtain a signal proportional to the primary current of the current transformer 4; the self-integrating resistor Rs is connected to the low-pass filter circuit 6; the low-pass filter circuit 6 filters the high-frequency interference in the restored positive half-cycle signal.

[0054] The full-bridge rectifier circuit 5 includes diodes D1, D2, D3, and D4; the low-pass filter circuit 6 includes an operational amplifier, resistors R1, R2, R3, R4, and R5, and capacitors C1, C2, and C3.

[0055] One end of the secondary side of current transformer 4 is connected to the anode of diode D1 and the cathode of diode D3, and the other end of the secondary side of current transformer 4 is connected to the anode of diode D2 and the cathode of diode D4. The cathode of diode D2 is connected to the cathode of diode D1, one end of resistor R1, and one end of resistor Rs. The anode of diode D4 is connected to the anode of diode D3, the other end of resistor Rs, one end of capacitor C1, one end of capacitor C2, and one end of resistor R4. The other end of resistor R1 is connected to the other end of capacitor C1 and one end of resistor R2. The other end of resistor R2 is connected to one end of resistor R3 and one end of capacitor C3. The other end of resistor R3 is connected to the other end of capacitor C2 and the non-inverting input of operational amplifier op amp. The other end of resistor R4 is connected to the inverting input of operational amplifier op amp and one end of resistor R5. The other end of resistor R5 is connected to the other end of capacitor C3 and the output of operational amplifier op amp.

[0056] Low-frequency reconstruction unit 3 consists of three groups, each using a DSP28335. The output of the operational amplifier (op amp) is connected to the DSP28335. The DSP28335 controls the upper transistor S of the inverter. up and inverter lower transistor S dn .

[0057] Diodes D1, D2, D3, and D4 are all Schottky diodes.

[0058] like Figure 1 and Figure 2 As shown, the high-frequency detection unit 1 and part of the signal conditioning unit 2, the turns ratio of the primary and secondary sides of the current transformer 4 is 2:2N, where N is the number of turns in the secondary winding. The primary side of the current transformer 4 has 2 turns and is connected in series with the inverter's upper transistor S. up and inverter lower transistor S dn In the middle, the secondary center tap of current transformer 4 is grounded. The inverter includes three sets of inverter upper transistors S. up and inverter lower transistor S dn S on each group of inverters up and inverter lower transistor S dn All are connected in series with the primary side of current transformer 4; the inverter upper transistor S of each group up and inverter lower transistor S dn Each generates a single-phase current; this can be denoted as i. a i b and i c With current i a For example, under the action of signal conditioning unit 2, the output current signal is rectified by a full-bridge rectifier and then passed through resistor R. s Generate voltage signal u cur_a Assuming the stator inductance of the PMSM is sufficiently large, i aIt is continuous, and the positive direction of the current is as follows: Figure 1 As shown. When the phase a current is positive, when the inverter's upper transistor S... up Turn on, inverter down transistor S dn When shut down, i up The current gradually increases; diode D1 connected to the secondary side of current transformer 4 turns on while diode D2 turns off; at this time, the induced current on the secondary side of current transformer 4 flows through resistor R. s Voltage drop u cur_a Subsequently, the inverter's upper transistor S... up Turn off, i up i becomes 0 dn When freewheeling begins, diode D2 turns on while diode D1 turns off, resulting in a voltage drop u. cur_a When the phase current is negative, the voltage drop u can be deduced similarly. cur_a The process of its generation. The process is as follows: Figure 5 As shown. In resistor R s Under the self-integration effect, the signal conditioning unit output is restored to a positive half-cycle signal proportional to the primary current.

[0059] The low-frequency reconstruction unit is a DSP28335, and its core is the reconstruction algorithm; since the motor stator windings are star-connected, according to Kirchhoff's Current Law (KCL), we have i a +i b +i c =0, therefore, the DSP only needs to sample two-phase currents, while the third-phase current can be calculated. For example... Figure 6 As shown, with the positive zero-crossing of the phase a current as the time zero point, and with an interval of π / 3, 360° is divided into 6 reconstruction sectors, denoted as I to VI. In sector I, the phase a current is u. cur_a The current in phase b is -u cur_b The current in phase c is u cur_b -u cur_a In sector II, the phase a current is u. cur_a The current in phase c is -u cur_c The current in phase b is u cur_c -u cur_a The relationship between sectors and current is shown in Table 3. Therefore, the current of each phase can be reconstructed from Table 3. Since only the signal near the peak value of each phase current at 120° is used, its minimum value is about half of the peak value, thus avoiding the use of data near the current zero crossing point and reducing the impact of the inverter dead time, thereby improving the accuracy of current reconstruction. Figure 7 u in rec_a It is the phase current obtained after reconstruction. Figure 8The phase current is detected by a current sensor. Due to the per-unit processing used in the control, the two values ​​are not equal. However, it can be seen that the waveform trends of the two are consistent, which shows that the reconstruction algorithm is accurate.

[0060] The specific working steps of this embodiment are as follows:

[0061] 1. Connect the two-turn coil, which is connected in series between the upper and lower transistors of the inverter, to the primary side of the current transformer of the high-frequency detection unit.

[0062] 2. The high-frequency switching current will generate a magnetic field, which will induce a current on the secondary side of the current transformer.

[0063] 3. The induced current generated on the secondary side is rectified into a positive half-cycle signal by a full-wave rectifier.

[0064] 4. The positive half-cycle signal in step 3 passes through resistor R. s It is converted into a voltage signal.

[0065] 5. The voltage signal in step 4 is restored to a signal proportional to the primary current by the self-integrating circuit.

[0066] 6. The signal in step 5 is filtered out for high-frequency noise by a low-pass filter circuit.

[0067] 7. The DSP28335 acquires the signal within 120° of the peak value of each cycle in step 6 via ADC.

[0068] 8. Reconstruct the signals from step 6 into phase currents according to the current reconstruction algorithm of the low-frequency reconstruction unit.

[0069] Taking the current reconstruction algorithm as an example, we will analyze the current in phase A, where the current direction is as follows: Figure 1 As shown, i A =i up -i dn At the same time, i up and i dn One of them is always 0, and within a certain time range, the two currents have opposite polarities, such as... Figure 3 As shown. Therefore, at a certain moment, the instantaneous value of the current in phase A is i. A =i up Or i A =-i dn . The original side has the same name as Figure 1 As shown, the magnetic fields generated by the upper and lower turns of the coil are in the same direction, so at a certain moment the current induced in the secondary side is i = Ki. up Or i = Ki dn K is the proportionality coefficient. After full-bridge rectification, the current induced on the secondary side is i = |Ki| up |i=|Ki dn|, i.e. u cur_a That is, K|i A The goal of the reconstruction algorithm is to restore it to Ki. A Assuming the A-phase current i A =Isinωt, then the currents in phases B and C are When θ = 0, we have i A =sinωt=0, Similarly, in When, we can obtain θ and i A i B i C The relationship is shown in Table 1. θ is the electrical angle.

[0070]

[0071]

[0072] Therefore, the regulations are as shown in Table 2:

[0073]

[0074] The reconstruction algorithm is shown in Table 3:

[0075]

[0076]

[0077] This invention solves the safety isolation problem of control and power conversion circuits by using a current transformer (CT) to detect the phase current of the inverter; by changing the installation position of the CT, it solves the problem that traditional CTs cannot detect low-frequency current during motor startup; and by designing a reasonable reconstruction algorithm, it avoids using data near the current zero-crossing point, thus reducing the impact of the inverter dead time.

[0078] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A circuit for high-frequency detection and low-frequency reconstruction of inverter phase current based on CT, characterized in that, include: High-frequency detection unit (1), signal conditioning unit (2) and low-frequency reconstruction unit (3); The high-frequency detection unit (1) is connected to the signal conditioning unit (2); the high-frequency detection unit (1) is used to provide a high-frequency signal to the signal conditioning unit (2); the signal conditioning unit (2) is connected to the low-frequency reconstruction unit (3); the low-frequency reconstruction unit (3) is connected to the high-frequency detection unit (1); the signal conditioning unit (2) conditions the high-frequency signal to obtain a positive half-cycle signal; the signal conditioning unit (2) consists of three groups; the signal conditioning unit (2) includes a full-bridge rectifier circuit (5), a self-integrating resistor Rs, and a low-pass filter circuit (6). The full-bridge rectifier circuit (5) is connected to the secondary side of the current transformer (4) to convert the high-frequency signal into a positive half-cycle signal; the full-bridge rectifier circuit (5) is connected to the self-integrating resistor Rs to restore the positive half-cycle signal and obtain a signal proportional to the primary current of the current transformer (4); the self-integrating resistor Rs is connected to the low-pass filter circuit (6); the low-pass filter circuit (6) filters out high-frequency interference in the restored positive half-cycle signal; The low-frequency reconfiguration unit (3) is used to reconfigure the inverter phase current.

2. The circuit for high-frequency detection and low-frequency reconstruction of inverter phase current based on CT according to claim 1, characterized in that, The high-frequency detection unit (1) includes a current transformer (4) and an inverter; The inverter includes three inverter top transistors. and three inverter down diodes The inverter upper tube and inverter lower tube Two are grouped together; the current transformers (4) are in three groups; one group is the inverter upper tube and inverter lower tube A corresponding set of current transformers (4); The primary side of the current transformer (4) is connected in series with the inverter. and inverter lower tube middle; The inverter upper tube One end is connected to an external voltage source The inverter upper tube The other end is connected to the primary side of the current transformer (4); The inverter lower transistor One end is connected to the primary side of the current transformer (4); the lower tube of the inverter The other end is grounded.

3. The circuit for high-frequency detection and low-frequency reconstruction of inverter phase current based on CT according to claim 2, characterized in that, The turns ratio of the primary side to the secondary side of the current transformer (4) is 2:2N, where 2N is the number of turns in the secondary winding.

4. The circuit for high-frequency detection and low-frequency reconstruction of inverter phase current based on CT according to claim 3, characterized in that, The primary winding of the current transformer (4) is a 2-turn coil.

5. The circuit for high-frequency detection and low-frequency reconstruction of inverter phase current based on CT according to claim 4, characterized in that, The secondary side of the current transformer (4) consists of several turns of enameled wire coil with a center tap, wherein the center tap is grounded.

6. The circuit for high-frequency detection and low-frequency reconstruction of inverter phase current based on CT according to claim 5, characterized in that, The full-bridge rectifier circuit (5) includes diodes D1, D2, D3 and D4; the low-pass filter circuit (6) includes an operational amplifier, resistors R1, R2, R3, R4 and R5, and capacitors C1, C2 and C3. One end of the secondary side of the current transformer (4) is connected to the positive terminal of diode D1 and the negative terminal of diode D3, and the other end of the secondary side of the current transformer (4) is connected to the positive terminal of diode D2 and the negative terminal of diode D4; the negative terminal of diode D2 is connected to the negative terminal of diode D1, one end of resistor R1 and one end of resistor Rs; the positive terminal of diode D4 is connected to the positive terminal of diode D3, the other end of resistor Rs, one end of capacitor C1, one end of capacitor C2 and one end of resistor R4; the other end of resistor R1 is connected to the other end of capacitor C1 and one end of resistor R2; the other end of resistor R2 is connected to one end of resistor R3 and one end of capacitor C3, the other end of resistor R3 is connected to the other end of capacitor C2 and the non-inverting input terminal of operational amplifier op amp; the other end of resistor R4 is connected to the inverting input terminal of operational amplifier op amp and one end of resistor R5, the other end of resistor R5 is connected to the other end of capacitor C3 and the output terminal of operational amplifier op amp.

7. The circuit for high-frequency detection and low-frequency reconstruction of inverter phase current based on CT according to claim 6, characterized in that, The low-frequency reconstruction unit (3) consists of three groups, and each low-frequency reconstruction unit (3) is a DSP28335. The output terminal of the operational amplifier (op amp) is connected to the DSP28335. The DSP28335 controls the upper transistor of the inverter. and inverter lower tube .

8. The circuit for high-frequency detection and low-frequency reconstruction of inverter phase current based on CT according to claim 7, characterized in that, Diodes D1, D2, D3, and D4 are all Schottky diodes.

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