Three-phase AC input power supply zero-cross detection circuit and detection method

Abstract

The invention discloses a three-phase AC input power supply zero-cross detection circuit and detection method, and the circuit comprises a three-phase AC input power supply, and also comprises a step-down rectification circuit connected with the three-phase AC input power supply, a control unit circuit electrically connected with the step-down rectification circuit, and an optical coupler isolation output circuit connected with the control unit circuit. The optocoupler isolation output circuit is used for outputting a current signal so as to conveniently detect the zero-crossing moment of the current, and the control unit circuit is used for enabling the current signal output by the optocoupler isolation output circuit to be matched with the voltage signal output by the step-down rectifying circuit. According to the three-phase AC input power supply zero-crossing detection circuit and detection method provided by the invention, zero-crossing detection can be realized through a simple structure, and the change of a power supply signal can be adapted through an adaptive filtering algorithm, so that a zero-crossing point can be accurately detected.

Description

Technical Field

[0001] The invention belongs to the technical field of electronic circuits, and in particular relates to a three-phase AC input power zero-crossing detection circuit and a detection method. Background Art

[0002] Zero-crossing detection in circuits is a detection technology used to identify the moment when an alternating current (AC) signal or voltage waveform passes through zero. In AC, the voltage will periodically change from a positive value through zero to a negative value, or from a negative value through zero to a positive value. The zero-crossing detection circuit detects these zero-crossing events. Zero-crossing detection can be used to control the switching moment of switching devices, thereby optimizing the waveform and reducing electromagnetic interference caused by switching operations. In power systems, zero-crossing detection can help monitor the stability of the power grid and promptly detect abnormal fluctuations in voltage or current. Therefore, zero-crossing detection circuits play an important role in circuit systems.

[0003] Taking electric actuators as an example, the zero-crossing detection of the three-phase input power supply of existing electric actuators is usually implemented by hardware, such as a zero-crossing comparator. However, the comparator requires dual power supplies to work, which brings difficulty to the design of the power supply. At the same time, although there is also a solution using an isolation transformer, that is, the three-phase AC input power supply is converted into a low voltage through an isolation transformer, and then the zero-crossing moment is judged by collecting the low voltage, the overall hardware cost of this circuit is high, and it is not suitable for occasions with too many structural size restrictions. Therefore, a zero-crossing detection circuit with a simple structure is needed. The present invention solves this technical problem. Summary of the invention

[0004] The present invention provides a three-phase AC input power zero-crossing detection circuit and detection method, which can not only realize zero-crossing detection through a simple structure, but also adapt to the change of power supply signal through an adaptive filtering algorithm, so as to accurately detect the zero-crossing point.

[0005] A three-phase AC input power zero-crossing detection circuit comprises a three-phase AC input power supply, a buck rectifier circuit connected to the three-phase AC input power supply, a control unit circuit electrically connected to the buck rectifier circuit, and an optocoupler isolation output circuit connected to the control unit circuit, wherein the optocoupler isolation output circuit is used to output a current signal to facilitate detection of the zero-crossing moment of the current, and the control unit circuit is used to match the current signal output by the optocoupler isolation output circuit with the voltage signal output by the buck rectifier circuit.

[0006] Furthermore, the step-down rectifier circuit includes a first step-down resistor and a second step-down resistor connected to the three-phase AC input power supply, and a rectifier bridge connected to the first step-down resistor and the second step-down resistor, and the rectifier bridge is connected to the control unit circuit.

[0007] Further, the control unit circuit includes a first diode connected to the rectifier bridge, and a first transistor connected to the first diode, and an anode of the first diode is connected to an output end of the rectifier bridge;

[0008] The emitter of the first transistor is connected to the cathode of the first diode, the base of the first transistor is connected to the output end of the rectifier bridge, and the collector of the first transistor is connected to the input end of the optocoupler isolation output circuit.

[0009] Furthermore, the optocoupler isolation output circuit includes an optocoupler whose anode is connected to the collector of the first transistor, a pull-up resistor electrically connected to the collector of the optocoupler, the cathode of the optocoupler is connected to the output end of the rectifier bridge, and the collector is connected to the reference end.

[0010] A three-phase AC input power zero-crossing detection method, based on the above three-phase AC input power zero-crossing detection circuit, comprises the following steps:

[0011] S1, converting AC signal into DC signal through step-down rectifier circuit;

[0012] S2, connecting the adaptive filter to the step-down rectifier circuit and the control unit circuit, and removing the noise in the rectified DC signal through an adaptive filtering algorithm;

[0013] S3, by controlling the control unit circuit, the current signal output by the optocoupler isolation output circuit is matched with the voltage signal output by the step-down rectifier circuit;

[0014] S4, the optocoupler isolation output circuit outputs the corresponding current signal for detecting the zero-crossing moment.

[0015] Furthermore, the specific content of step S2 is as follows:

[0016] In S21 and LMS algorithm, the calculation method of the output signal is expressed as:

[0017]

[0018] Where y(n) represents the output signal of the nth iteration of the filter, W T (n) represents the transpose of the coefficient vector W(n) of the nth iteration of the filter, X(n) represents the input signal vector of the nth iteration of the filter, M represents the order of the filter, that is, the number of coefficients, w(i) represents the i-th coefficient of the filter, and x(M-1) represents the value of the input signal at time (M-1);

[0019] The output error is expressed as:

[0020] e(n)=d(n)-y(n);

[0021] Where, e(n) represents the error signal of the nth iteration, and d(n) represents the expected output signal of the nth iteration;

[0022] w(n+1)=w(n)+μe(n)*x(n);

[0023] Among them, w(n+1) represents the filter coefficient vector of the n+1th iteration updated after the nth iteration; w(n) represents the filter coefficient vector at the nth iteration; μ is the learning rate, that is, the step size, which determines the step size of the coefficient update and has an important influence on the convergence speed and stability of the algorithm; x(n) represents X(n) after multiplication with w(n);

[0024] S22, selecting a hyperbolic tangent function as a step factor improvement function to make μ variable, so as to improve convergence speed and accuracy;

[0025] S23. Introduce an adjustment function to further improve the convergence accuracy and reduce the error.

[0026] Furthermore, the specific content of step S22 is as follows:

[0027] S221, the hyperbolic tangent function Improvement function as a step size factor;

[0028] S222. Introduce parameters α and β to jointly control the change of the step factor curve, and obtain the relationship between the step size and the error as follows:

[0029]

[0030] Furthermore, the specific content of step S23 is as follows:

[0031] S231, introduce adjustment function

[0032]

[0033] Among them, y represents the adjustment factor, a≥1;

[0034] S232. The improved functional relationship of μ(n) with respect to e(n) is:

[0035]

[0036] The above contents can be used to improve the speed and accuracy of convergence and reduce errors.

[0037] The technical effects of the present invention are as follows:

[0038] (1) This solution uses a step-down rectifier circuit to step down and rectify the input signal of the three-phase AC input power supply, and through the cooperation of the control unit circuit and the optocoupler isolation output circuit, the optocoupler isolation output circuit can output a corresponding current signal, so that the entire circuit can accurately detect the zero-crossing moment of the three-phase AC output power supply, and the circuit components used are relatively small;

[0039] (2) In the present solution, the first diode in the control unit is used to provide a working voltage to the first transistor, that is, to ensure that the voltage of the base of the first transistor is higher than the voltage of the emitter by a voltage drop of a diode, so that the first transistor is in a common base amplification state, so that the emitter current and the collector current of the first transistor are the same, and the voltage output by the rectifier bridge is a half-wave rectified waveform, so that the current flowing through the anode of the first optical coupler is also a half-wave waveform, thereby causing the first optical coupler to work in an intermittent state of on and off, which is convenient for outputting a corresponding signal to detect the zero-crossing moment;

[0040] (3) In this scheme, an adaptive filter can be used to remove noise from the rectified DC signal, which is specifically achieved through a corresponding adaptive filtering algorithm. The adaptive filtering algorithm in this scheme can change the step size μ in the LMS algorithm. The hyperbolic tangent function is used as the step size factor improvement function to help improve the step size convergence speed. In order to avoid the step size convergence speed affecting the convergence accuracy due to the fast convergence speed, this scheme introduces an adjustment function to help improve the convergence accuracy. By combining the two functions, the convergence speed can be improved while the convergence accuracy can be improved, thereby reducing the error. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is a schematic diagram of the structure of Example 1 of the present invention.

[0042] Figure 2 This is a connection block diagram of embodiment 1 of the present invention.

[0043] Figure 3 This is a flow chart of Example 2 of the present invention.

[0044] Figure 4 The relationship between the step size factor and the error in Example 2 of the present invention is Figure 1 .

[0045] Figure 5 The relationship between the step size factor and the error in Example 2 of the present invention is Figure 2 .

[0046] Figure 6 The relationship between the step size factor and the error in Example 2 of the present invention is Figure 3 .

[0047] Among them, the accompanying drawings are marked as: R142, the first step-down resistor; R145, the second step-down resistor; R144, the third resistor; R143, the pull-up resistor; C99, the first filter capacitor; C100, the second capacitor; C101, the third capacitor; D33, the rectifier bridge; D34, the voltage-stabilizing diode; S32, the first diode; Q4, the first transistor; PC13, the optocoupler. DETAILED DESCRIPTION

[0048] The technical solution of the present invention will be described in detail below in conjunction with specific embodiments and drawings.

[0049] Example 1

[0050] See also Figure 1 , Figure 2 A three-phase AC input power zero-crossing detection circuit includes a three-phase AC input power supply, a buck rectifier circuit connected to the three-phase AC input power supply, a control unit circuit electrically connected to the buck rectifier circuit, and an optocoupler isolation output circuit connected to the control unit circuit. The optocoupler isolation output circuit is used to output a current signal to facilitate detection of the zero-crossing moment of the current. The control unit circuit is used to match the current signal output by the optocoupler isolation output circuit with the voltage signal output by the buck rectifier circuit.

[0051] Further, the step-down rectifier circuit includes a first step-down resistor R142 and a second step-down resistor R145 connected to the three-phase AC input power supply, a rectifier bridge D33 connected to the first step-down resistor R142 and the second step-down resistor R145, and the rectifier bridge D33 is connected to the control unit circuit. Preferably, a first filter capacitor C99 is connected between the first step-down resistor R142 and the second step-down resistor R145 in this embodiment.

[0052] Further, the control unit circuit includes a first diode S32 connected to the rectifier bridge D33, a first transistor Q4 connected to the first diode S32, and an anode of the first diode S32 is connected to the output end of the rectifier bridge D33;

[0053] The emitter of the first transistor Q4 is connected to the cathode of the first diode, the base of the first transistor Q4 is connected to the output end of the rectifier bridge D33, and the collector of the first transistor Q4 is connected to the input end of the optocoupler isolation output circuit.

[0054] Furthermore, the optocoupler isolation output circuit includes an optocoupler PC13 whose anode is connected to the collector of the first transistor Q4, a pull-up resistor electrically connected to the collector of the optocoupler PC13, a cathode of the optocoupler PC13 connected to the output end of the rectifier bridge D33, and a collector connected to the reference end GND.

[0055] Preferably, the output end of the rectifier bridge D33 in this embodiment is also connected to the voltage stabilizing diode D34, the third resistor R144, and the second capacitor C100, and the pull-up resistor R143 in this embodiment is connected to the reference end GND through the third capacitor C101.

[0056] The working principle of this embodiment 1 is as follows:

[0057] The current of the AC power source passes through the first voltage-dropping resistor and the second voltage-dropping resistor and then enters the first rectifier bridge. The first voltage-dropping resistor and the second voltage-dropping resistor are used to step down the voltage of the AC power. The stepped-down AC power is rectified through the rectifier bridge to obtain a half-wave rectified waveform.

[0058] The first diode S32 is used to provide a working voltage to the first transistor Q4, that is, to ensure that the base voltage of the first transistor Q4 is higher than the emitter voltage by a voltage drop of a diode, so that the first transistor Q4 is in a common base amplification state. The first transistor Q4 is in a common base amplification state so that the emitter current and the collector current of the first transistor Q4 are the same; the voltage output by the first rectifier bridge D33 is a half-wave rectified waveform, so that the current flowing through the anode of the first optical coupler PC13 is also a half-wave waveform, thereby causing the first optical coupler PC13 to work in a discontinuous state such as on and off;

[0059] Furthermore, the waveform outputted by the collector of the first optical coupler PC13 is a square wave waveform;

[0060] When the AC input power source passes through zero, the voltage is 0, so that a voltage valley appears in the half-wave waveform output by the first rectifier bridge D33, and the current in the circuit is 0. Furthermore, the first optical coupler PC13 is in the off state, and the collector of the first optical coupler PC13 outputs a high level.

[0061] When the AC input power supply voltage is non-zero, the current in the circuit increases, which further causes the first optocoupler PC13 to be in an on state, and the collector of the first optocoupler PC13 outputs a low level; thereby, the entire circuit can accurately detect the zero-crossing moment of the AC input power supply, and the staff can observe the zero-crossing moment through the output signal. In addition, the circuit components of this scheme are few, the topology is simple, and it is easy to implement.

[0062] Example 2

[0063] See also Figure 3-Figure 6 In order to make the detection result more accurate, the present solution also provides a three-phase AC input power zero-crossing detection method, based on the above three-phase AC input power zero-crossing detection circuit, comprising the following steps:

[0064] S1, converting AC signal into DC signal through step-down rectifier circuit;

[0065] S2, connecting the adaptive filter to the step-down rectifier circuit and the control unit circuit, and removing the noise in the rectified DC signal through an adaptive filtering algorithm;

[0066] S3, by controlling the control unit circuit, the current signal output by the optocoupler isolation output circuit is matched with the voltage signal output by the step-down rectifier circuit;

[0067] S4, the optocoupler isolation output circuit outputs the corresponding current signal for detecting the zero-crossing moment.

[0068] The connection method of the adaptive filter is an existing technology known to those skilled in the art and will not be described in detail here. The adaptive filter can remove noise in the DC signal to make subsequent results more accurate.

[0069] Furthermore, the specific content of step S2 is as follows:

[0070] In S21 and LMS algorithm, the calculation method of the output signal is expressed as:

[0071]

[0072] Where y(n) represents the output signal of the nth iteration of the filter, W T (n) represents the transpose of the coefficient vector W(n) of the nth iteration of the filter, X(n) represents the input signal vector of the nth iteration of the filter, M represents the order of the filter, that is, the number of coefficients, w(i) represents the i-th coefficient of the filter, and x(M-1) represents the value of the input signal at time (M-1);

[0073] The output error is expressed as:

[0074] e(n)=d(n)-y(n);

[0075] Wherein, e(n) represents the error signal of the nth iteration, and d(n) represents the expected output signal of the nth iteration;

[0076] w(n+1)=w(n)+μe(n)*x(n);

[0077] Among them, w(n+1) represents the filter coefficient vector of the n+1th iteration updated after the nth iteration; w(n) represents the filter coefficient vector at the nth iteration; μ is the learning rate, that is, the step size, which determines the step size of the coefficient update and has an important influence on the convergence speed and stability of the algorithm; x(n) represents X(n) after multiplication with w(n);

[0078] S22, selecting a hyperbolic tangent function as a step factor improvement function to make μ variable, so as to improve convergence speed and accuracy;

[0079] S23. Introduce an adjustment function to further improve the convergence accuracy and reduce the error.

[0080] Furthermore, the specific content of step S22 is as follows:

[0081] S221, the hyperbolic tangent function Improvement function as a step size factor;

[0082] S222. Introduce parameters α and β to jointly control the change of the step factor curve, and obtain the relationship between the step size and the error as follows:

[0083]

[0084] Where exp represents the natural exponential function e x . e is the base of natural logarithms.

[0085] See also Figure 4 After using the hyperbolic tangent function as the step factor improvement function, the relationship between the step factor and the error is shown in the figure. The convergence speed is too fast, and it is easy to be misaligned, and there are still defects in accuracy.

[0086] Furthermore, the specific content of step S23 is as follows:

[0087] S231, introduce adjustment function

[0088]

[0089] Among them, y represents the adjustment factor, a≥1;

[0090] See also Figure 5 ,In the adjustment function, the relationship between the step factor and the error is shown in the figure. When the error is large, the convergence speed will increase, and when the error is small, the convergence speed will decrease;

[0091] S232. The improved functional relationship of μ(n) with respect to e(n) is:

[0092]

[0093] The above contents can be used to improve the speed and accuracy of convergence and reduce errors.

[0094] See also Figure 6 After combining the hyperbolic tangent function with the adjustment function, the relationship between the step size factor and the error is shown in the figure. When the error is large, the convergence speed will increase. When the error is small, there will still be a faster convergence speed, but not too fast, which helps to ensure the convergence accuracy.

[0095] The above description is only an exemplary embodiment of the present invention, and does not limit the patent scope of the present invention. All equivalent structural changes made by using the contents of the present invention specification and drawings under the technical concept of the present invention, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A three-phase AC input power zero-crossing detection circuit, comprising a three-phase AC input power supply, characterized in that: It also includes a step-down rectifier circuit connected to the three-phase AC input power supply, a control unit circuit electrically connected to the step-down rectifier circuit, and an optocoupler isolation output circuit connected to the control unit circuit. The optocoupler isolation output circuit is used to output a current signal to facilitate the detection of the zero-crossing moment of the current, and the control unit circuit is used to match the current signal output by the optocoupler isolation output circuit with the voltage signal output by the step-down rectifier circuit.

2. The three-phase AC input power zero-crossing detection circuit according to claim 1, characterized in that: The step-down rectifier circuit comprises a first step-down resistor (R142) and a second step-down resistor (R145) connected to the three-phase AC input power supply, and a rectifier bridge (D33) connected to the first step-down resistor (R142) and the second step-down resistor (R145), and the rectifier bridge (D33) is connected to the control unit circuit.

3. The three-phase AC input power zero-crossing detection circuit according to claim 2, characterized in that: The control unit circuit comprises a first diode (S32) connected to the rectifier bridge (D33), and a first transistor (Q4) connected to the first diode (S32), wherein the anode of the first diode (S32) is connected to the output end of the rectifier bridge (D33); The emitter of the first transistor (Q4) is connected to the cathode of the first diode, the base of the first transistor (Q4) is connected to the output end of the rectifier bridge (D33), and the collector of the first transistor (Q4) is connected to the input end of the optical coupling isolation output circuit.

4. The three-phase AC input power zero-crossing detection circuit according to claim 3, characterized in that: The optocoupler isolation output circuit comprises an optocoupler (PC13) whose anode is connected to the collector of the first transistor (Q4), a pull-up resistor (R143) electrically connected to the collector of the optocoupler (PC13), a cathode of the optocoupler (PC13) connected to the output end of the rectifier bridge (D33), and a collector connected to a reference end.

5. A three-phase AC input power zero-crossing detection method, based on the three-phase AC input power zero-crossing detection circuit as claimed in claim 1, characterized in that: The following steps are involved: S1, converting AC signal into DC signal through step-down rectifier circuit; S2, connecting the adaptive filter to the step-down rectifier circuit and the control unit circuit, and removing the noise in the rectified DC signal through an adaptive filtering algorithm; S3, by controlling the control unit circuit, the current signal output by the optocoupler isolation output circuit is matched with the voltage signal output by the step-down rectifier circuit; S4, the optocoupler isolation output circuit outputs the corresponding current signal for detecting the zero-crossing moment.

6. The three-phase AC input power zero-crossing detection method according to claim 5, characterized in that: The specific content of step S2 is as follows: In S21 and LMS algorithm, the calculation method of the output signal is expressed as: Where y(n) represents the output signal of the nth iteration of the filter, W T (n) represents the transpose of the coefficient vector W(n) of the nth iteration of the filter, X(n) represents the input signal vector of the nth iteration of the filter, M represents the order of the filter, that is, the number of coefficients, w(i) represents the i-th coefficient of the filter, and x(M-1) represents the value of the input signal at time (M-1); The output error is expressed as: e(n)=d(n)-y(n); Wherein, e(n) represents the error signal of the nth iteration, and d(n) represents the expected output signal of the nth iteration; w(n+1)=w(n)+μe(n)*x(n); Among them, w(n+1) represents the filter coefficient vector of the n+1th iteration updated after the nth iteration; w(n) represents the filter coefficient vector at the nth iteration; μ is the learning rate, that is, the step size, which determines the step size of the coefficient update and has an important influence on the convergence speed and stability of the algorithm; x(n) represents X(n) after multiplication with w(n); S22, selecting a hyperbolic tangent function as a step factor improvement function to make μ variable, so as to improve convergence speed and accuracy; S23. Introduce an adjustment function to further improve the convergence accuracy and reduce the error.

7. The three-phase AC input power zero-crossing detection method according to claim 6, characterized in that: The specific content of step S22 is as follows: S221, the hyperbolic tangent function Improvement function as a step size factor; S222. Introduce parameters α and β to jointly control the change of the step factor curve, and obtain the relationship between the step size and the error as follows:

8. The three-phase AC input power zero-crossing detection method according to claim 7, characterized in that: The specific content of step S23 is as follows: S231, introduce adjustment function Among them, y represents the adjustment factor, a≥1; S232. The improved functional relationship of μ(n) with respect to e(n) is: The above contents can be used to improve the speed and accuracy of convergence and reduce errors.

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