Summary of the invention
In order to overcome the deficiency of the residual current waveform distortion that sampling unit picks up, the invention provides a kind of zero sequence current mutual inductor break detection circuit and residual current detection circuit.
The technical solution adopted in the present invention is: a kind of zero sequence current mutual inductor break detection circuit and residual current detection circuit, and it comprises constant current source unit, for steady current is provided, amplifying unit, for amplifying input signal, sampling unit, in order to convert current signal to voltage signal, the two ends of sampling unit respectively with amplifying unit just, negative input end is corresponding to be connected, it is characterized in that: after described constant current source unit is in parallel with sampling unit, be connected on the input end of amplifying unit, between constant current source unit and sampling unit, be provided with switch element, also comprise control module, for judging that the residual electricity flow valuve detecting is zero output signal actuating switch unit, thereby detect the duty of zero sequence current mutual inductor to judge whether to need warning, or residual electricity flow valuve is output signal cut-off switch unit of non-zero, with the size of comparison residual electricity flow valuve and standard value to judge whether to need warning.
Described amplifying unit comprises the first operational amplifier U1B, capacitor C 3, resistance R 4/R5/R6/R7/R8/R9, the positive input terminal 5 of the first operational amplifier U1B is by resistance R 8 ground connection, positive input terminal 5 is connected with bias voltage output terminal by resistance R 9, output terminal 7 by resistance R 6 and R7 as signal output residual, after the capacitance-resistance filter of the signal of output terminal 7 by R6 and C3 composition, after R7 current limliting, be connected with control module as signal output residual, output terminal 7 is connected with negative input end 6 by R4 again.
Described constant current source unit comprises the second operational amplifier U1A, resistance R 1/R2, voltage reference diode U3 and a N channel field-effect pipe Q1, one end ground connection after resistance R 2 and voltage reference diode U3 series connection, one termination VCC, on node between negative input end 2 connecting resistance R2 and the voltage reference diode U3 of the second operational amplifier U1A, positive input terminal 3 meets VCC by resistance R 1, the gate pole 1 of the one N channel field-effect pipe Q1 is connected with the output terminal 1 of the second operational amplifier U1A, drain electrode 2 is connected with positive input terminal 3, and source electrode 3 is connected with switch element.
Described switch element comprises the 2nd N channel field-effect pipe Q2 and resistance R 3, the gate pole 1 of the 2nd N channel field-effect pipe Q2 meets signal input AD_CTL to control break-make through resistance R 3, drain electrode 2 is connected with the source electrode 3 of a N channel field-effect pipe Q1, and source electrode 3 connects the negative input end 6 of the first operational amplifier U1B by resistance R 5.
Described sampling unit comprises zero sequence current mutual inductor in parallel and resistance R S1, and one end of sampling unit is connected with the negative input end 6 of the first operational amplifier U1B by resistance R 5, the other end ground connection of sampling unit.
Described control module adopts single-chip microcomputer, and described single-chip microcomputer is connected with the signal output residual of amplifying unit, is connected with the signal input AD_CTL of switch element.
Also comprise the voltage follower as bias voltage, the output terminal of described voltage follower is connected with the positive input terminal of amplifying unit by resistance R 9.
Described resistance R 5/R8 value is identical, and described resistance R 4/R9 value is identical.
Described sampling unit also comprises the capacitor C in parallel with resistance R S1 2.
Described sampling unit also comprises the clamping circuit in parallel with resistance R S1, and this clamping circuit is made up of two diode D1/D2 parallel connection of a positive and a negative.
The invention has the beneficial effects as follows: this zero sequence current mutual inductor break detection circuit and residual current detection circuit adopt being switched on or switched off of switch element control constant current source unit, adopt control module to judge that the residual electricity flow valuve detecting is zero output signal actuating switch unit, thereby detect the duty of zero sequence current mutual inductor to judge whether to need warning, or residual electricity flow valuve is output signal cut-off switch unit of non-zero, with the size of comparison residual electricity flow valuve and standard value to judge whether to need warning, so do not need in real time to the logical steady current of zero sequence current mutual inductor, avoid the impact of steady current on zero sequence current mutual inductor, make it occur the problem of residual current waveform distortion, can detect exactly residual electricity flow valuve, thereby this circuit does not propose special requirement to zero sequence current mutual inductor, there is practicality widely.
Embodiment
Below in conjunction with accompanying drawing, embodiments of the present invention is further illustrated:
As shown in Figure 1 and Figure 2,, a kind of zero sequence current mutual inductor break detection circuit and residual current detection circuit, it comprises that it comprises constant current source unit, for steady current is provided, amplifying unit, for amplifying input voltage, sampling unit, in order to convert current signal to voltage signal, the two ends of sampling unit respectively with amplifying unit just, negative input end is corresponding to be connected, after described constant current source unit is in parallel with sampling unit, be connected on the input end of amplifying unit, between constant current source unit and sampling unit, be provided with switch element, also comprise control module, for judging that the residual electricity flow valuve detecting is zero output signal actuating switch unit, thereby detect the duty of zero sequence current mutual inductor to judge whether to need warning, or residual electricity flow valuve is output signal cut-off switch unit of non-zero, with the size of comparison residual electricity flow valuve and standard value to judge whether to need warning.Control constant current source unit place in circuit or be disconnected from the circuit by the break-make of switch element, whether conducting connects normally to detect zero sequence current mutual inductor, disconnect the size to detect residual electricity flow valuve, by constant current source signal and residual current signal, the current signal after superimposed converts voltage signal to described sampling unit, the given circuit of the present invention does not need in real time to the logical steady current of zero sequence current mutual inductor, avoid the impact of steady current on zero sequence current mutual inductor, make it occur the problem of residual current waveform distortion, thereby zero sequence current mutual inductor is not proposed to special requirement, there is practicality widely.
Described control module adopts the PIC18F series monolithic of Microchip company, its operating voltage is by 5V voltage signal gained after the filtering of π type, certainly, the single-chip microcomputer of selecting other series but can realize technical scheme of the present invention is all fine, adopt single-chip microcomputer can detect exactly residual electricity flow valuve, and judge that whether residual electricity flow valuve is normal.
Circuit for alarming comprises the relay trip unit, audible alarm unit and the light warning unit that are connected with single-chip microcomputer respectively, if detect, zero sequence current mutual inductor does not connect or residual electricity flow valuve exceedes 1000mA, can relay trip unit, audible alarm unit and light warning unit be moved respectively by single-chip microcomputer, to make warning.
Described control module also can adopt comparer, and its operating voltage is 5V voltage signal.Default first standard signal that magnitude of voltage is 0 in the first comparer; be used for judging whether zero sequence current mutual inductor connects normally; default second standard signal that magnitude of voltage is corresponding with the residual current standard value of protective device in the second comparer; to adopt the circuit voltage signal and the second standard signal that collect to compare with the second comparer, thereby judge that whether residual electricity flow valuve is normal.
Described amplifying unit comprises the first operational amplifier U1B, capacitor C 3, resistance R 4/R5/R6/R7/R8/R9, the positive input terminal 5 of the first operational amplifier U1B is by resistance R 8 ground connection, positive input terminal 5 is connected with bias voltage output terminal by resistance R 9, output terminal 7 by resistance R 6 and R7 as signal output residual, after the capacitance-resistance filter of the signal of output terminal 7 by R6 and C3 composition, after R7 current limliting, be connected with control module as signal output residual, output terminal 7 is connected with negative input end 6 by R4 again; Described sampling unit comprises zero sequence current mutual inductor in parallel and resistance R S1, one end of sampling unit is connected with the negative input end 6 of the first operational amplifier U1B by resistance R 5, the other end ground connection of sampling unit, resistance after the internal resistance of sampling unit by resistance R S1 or zero sequence current mutual inductor is in parallel with resistance R S1, constant current source signal and residual current signal are thought to the current signal after stack converts voltage signal to, again after the first operational amplifier U1B amplifies, offer single-chip microcomputer, to judge duty and the residual electricity flow valuve of zero sequence current mutual inductor.
Described constant current source unit comprises the second operational amplifier U1A, resistance R 1/R2, voltage reference diode U3 and a N channel field-effect pipe Q1, one end ground connection after resistance R 2 and voltage reference diode U3 series connection, one termination VCC, on node between negative input end 2 connecting resistance R2 and the voltage reference diode U3 of the second operational amplifier U1A, positive input terminal 3 meets VCC by resistance R 1, the gate pole 1 of the one N channel field-effect pipe Q1 is connected with the output terminal 1 of the second operational amplifier U1A, drain electrode 2 is connected with positive input terminal 3, source electrode 3 is connected with switch element, from the source electrode 3 output current Is of a N channel field-effect pipe Q1.
Described switch element comprises the 2nd N channel field-effect pipe Q2 and resistance R 3, the gate pole 1 of the 2nd N channel field-effect pipe Q2 meets signal input AD_CTL to control break-make through resistance R 3, this signal input AD_CTL connects the common IO mouth of single-chip microcomputer, drain electrode 2 is connected with the source electrode 3 of a N channel field-effect pipe Q2, source electrode 3 connects the negative input end 6 of the first operational amplifier U1B by resistance R 5, export high level signal to gate pole 1 by single-chip microcomputer in good time, to control the break-make of the 2nd N channel field-effect pipe Q2, make switch element control constant current source unit whether access sampling unit, to realize the duty and the switching that detects residual electricity flow valuve function of electric circuit inspection zero sequence current mutual inductor.
Also comprise the voltage follower as bias voltage, described voltage follower comprises the 3rd operational amplifier U1C and resistance R 10/R11, one end ground connection after R10 and R11 series connection, one termination VCC, the positive input terminal 10 of the 3rd operational amplifier U1C is connected on the node between resistance R 10 and R11, negative input end 9 is connected with output terminal 8, output terminal 8 is bias voltage output terminal, output terminal 8 is connected with the positive input terminal 5 of the first operational amplifier U1B by resistance R 9, output terminal 8 output voltages of the 3rd operational amplifier U1C are Vref=1/2VCC, this output voltage is again after resistance R 8 and R9 dividing potential drop, give 5 one bias voltages of positive input terminal of the first operational amplifier U1B, the sine wave of residual current signal is moved on the whole, make it all within the scope of positive voltage, to solve because residual current signal is sinusoidal wave, the problem that negative voltage can not be identified by most of single-chip microcomputer, this bias voltage need be according to the difference of single-chip microcomputer operating voltage or AD reference voltage and difference.
Described sampling unit also comprises the capacitor C in parallel with resistance R S1 2; 4 pin of described the second operational amplifier U1A meet VCC, 11 pin ground connection, and connect capacitor C 1 between 4 pin and 11 pin, and capacitor C 1 is decoupling capacitor, has decoupling effect, capacitor C 2 is shunt capacitances, has filter action.
Described sampling unit also comprises the clamping circuit in parallel with resistance R S1; this clamping circuit is made up of two diode D1/D2 parallel connection of a positive and a negative; once can only there is a diode current flow; and another is in cut-off state; its forward and reverse pressure drop will be clamped at below the 0.5-0.7 of diode forward conduction voltage drop so, thereby plays the object of holding circuit.
Principle analysis:
The internal resistance of supposing zero sequence current mutual inductor is R=100 Ω, RS1=100 Ω, and R1=1k Ω, VCC=5V, the burning voltage of voltage reference diode U3 is 2.5V, constant current source electric current is Is=(VCC-2.5)/R1=2.5mA.
Get R5=R8=10k Ω, R4=R9=100k Ω, R10=R11=1k Ω, the output voltage of voltage follower is Vref=2.5V.
If residual electricity flow valuve Iresi=0mA that 1 single-chip microcomputer detects, now AD_CTL is high level, and the 2nd N channel field-effect pipe Q2 keeps on-state.
If a) zero sequence current mutual inductor connects normal, R // RS1=50 Ω, the voltage of R5 and C2 tie point is Vin=(R // RS1) * Is=50*2.5=125mV, the voltage of the output terminal 7 of the first operational amplifier U1B is Vout1=Vref – Vin* (R4/R5)=2.5V-1.25V=1.25V, and now single-chip microcomputer can detect that zero sequence current mutual inductor connects normally.
If b) zero sequence current mutual inductor does not connect, Vin=RS1*2.5=250mV, Vout2=Vref – Vin* (R4/R5)=2.5V-2.5V=0V.
C) analyze two kinds of situations above, their output voltage V out1 and Vout2 have obvious difference, and single-chip microcomputer can distinguish that whether zero sequence current mutual inductor connects normally, has completed broken string measuring ability according to this type of difference.
If d) single-chip microcomputer detects that mutual inductor connects normally, AD_CTL is low level, start to detect residual electricity flow valuve, if residual electricity flow valuve is greater than 0mA, continue to detect residual electricity flow valuve, if residual electricity flow valuve is 0mA, AD_CTL is high level, whether the 2nd N channel field-effect pipe Q2 keeps on-state, start to detect zero sequence current mutual inductor and connect.
If the residual electricity flow valuve Iresi > 0mA that 2 single-chip microcomputers detect, now AD_CTL is low level, the 2nd N channel field-effect pipe Q2 is in off-state, suppose that residual electricity flow valuve is 1A, coil ratio is 2000:1, the input current of circuit is 0.5mA, Vin=0.5*50=25mV, Vout=Vref – Vin* (R4/R5)=2.5V-0.25V=2.25V after amplifying.Gather aftertreatment through Chip Microcomputer A/D again; can obtain real residual electricity flow valuve, the residual current setting value of this residual electricity flow valuve and protective device be compared, if exceed setting value; should be judged as leak current fault, protective device should send chimes of doom or provide trip signal.
Relative, circuit involved in the present invention, if the voltage signal after sampling unit conversion is connected with the positive input terminal 5 of the first operational amplifier U1B, the negative input end 6 of the first operational amplifier U1B has two kinds of connections:
The first
As shown in Figure 3, voltage follower is connected with the negative input end 6 of the first operational amplifier U1B, so connect, the reference point of constant current source signal is to remain ground, and the reference point of sampling unit has become the output voltage V ref of voltage follower, this will cause electric current can not form loop, occur circuit mistake.
The second
As shown in Figure 4, do not access voltage follower, the negative input end 6 of the first operational amplifier U1B is by resistance R 57 ground connection, connect output terminal by resistance R 54, so connect, bias voltage using the voltage signal after sampling unit conversion as the first operational amplifier U1B, but this bias voltage just needs always in access state, otherwise just can only detect half-wave, and always in access state, long-time running like this, steady current will exert an influence to zero sequence current mutual inductor, make it occur the problem of residual current waveform distortion, can not detect exactly residual electricity flow valuve, unless ensured that zero sequence current mutual inductor performance used is good especially, but select the zero sequence current mutual inductor that performance is good can affect production cost and restrict the practical application of this circuit.
Below described embodiment is only the preferred embodiment of the present invention by reference to the accompanying drawings, and the not restriction to protection scope of the present invention, any improvement of doing based on spirit of the present invention all ought to be within protection domain of the present invention.