Background technology
Day by day under the complicated situation, corresponding monitoring equipment--electric energy quality monitoring system has obtained using widely, for electrical network detects big quantitative analysis data is provided, for power grid operation plays immeasurable effect in current operation of power networks.Along with the development of detection technique, more strict requirement has been proposed to how accurately catching the electrical network running parameter.Because electrical network contains a large amount of harmonic componentss usually, can be accompanied by situation such as voltage swells rapid drawdown, fluctuation, flickering, wink stream, lightning surge simultaneously.General high voltage power transmission signal is being the voltage signal of 100V through output rated voltage after measuring mutual inductor; Or civil power 220V signal; Under lightning surge and nonlinear-load shock effect; Voltage is changed, in the face of the signal of wide-voltage range like this, in the stable state and transient power quality parameter near guaranteeing to detect the range of nominal tension between-6KV~6KV in instantaneous (microsecond level); Also to capture the change in voltage of transient state, the voltage detecting of Power Quality Detection system has been proposed very high requirement.
In traditional high voltage detection range the inside, generally adopt the voltage transformer (VT) transformation to obtain being fit to the voltage that electronic equipment detects.Voltage transformer (VT) is actually a transformer that band is unshakable in one's determination, and it mainly is made up of first and second coil, iron core and insulating gel.When on a winding, applying an alternating voltage U1, in iron core, just produce a magnetic flux φ, according to the law of electromagnetic induction, then in Secondary Winding, just produce a secondary voltage U2.Voltage transformer (VT) is widely used in all kinds of high pressure in the low pressure transformation applications, and its voltage ratio can through regulating no-load voltage ratio, just can obtain required voltage according to once confirming with the turn ratio of Secondary Winding.But voltage transformer (VT) exists its intrinsic shortcoming: 1, the volume of voltage transformer (VT) is generally all bigger, and heavy, in electronic product, occupies very big space usually, just needs to be equipped with 3~4 voltage transformer (VT) in the three-phase system; 2, the voltage transformer secondary loop can not short circuit, otherwise can cause the excessive disastrous effect that causes of primary circuit electric current, and the electron device of secondary circuit is required than higher; 3, a large amount of harmonic componentss can cause the voltage transformer (VT) magnetic flux saturated, produce than higher voltage at secondary side, and waveform change, and circuit is impacted, and equipment for monitoring power quality need be monitored harmonic wave accurately; 4, voltage transformer (VT) causes the phase place time-delay, and the voltage transformer (VT) design is to design under the situation according to power frequency 50Hz; 5, wide-range voltage input, the requirement that has improved the dielectric strength of voltage transformer (VT), when guaranteeing that volume is little, the insulating Design of voltage transformer (VT) has become very big problem; Produce for avoiding and reducing the problems referred to above, voltage transformer (VT) need be by special technology manufacturing, and its cost also improves.And; When utilizing voltage transformer (VT) to detect; In the face of the input of the voltage signal of wide region, the insulating requirements of voltage transformer (VT) is also become very high, and contain under a large amount of harmonic components situation; Voltage transformer (VT) is easy to saturated, and the frequency analysis of paramount importance link that is electric energy quality monitoring system.
Because there is above-mentioned shortcoming in voltage transformer (VT); Therefore, people need seek a kind of replacement voltage transformer (VT) transformation mode, please referring to accompanying drawing 1; Realize voltage transitions through single-ended electric resistance partial pressure mode, obtain magnitude of voltage after the dividing potential drop after adopting the amplifier of high resistant input to isolate then.Adopt this mode, characteristics be input signal and system altogether, input voltage with the output voltage ratio is: Uo/Ui=R2/ (R1+R2), the value of adjustment R1 and R2 can obtain required lower magnitude of voltage, thereby play hypotensive effect.Amplifier U1A is characterized in the high impedance input as the buffering isolation network, and resistance pressure-dividing network is isolated, and avoids the rear end that the electric resistance partial pressure value is impacted.But; Owing to adopted input signal and system altogether in this mode; Can cause the earth potential of entire circuit plate to improve, when the external signal interference ratio was bigger, the ground wire current potential was also being followed and is being changed; The circuit accuracy test is impacted, and it is to cause signal can't measure important reasons accurately that earth potential changes.For the input of the voltage of wide region like this, obviously can cause earthy wide cut to change, cause the signal can't correct measurement.In addition, the insulating requirements that electrically isolates from other parts of high pressure ground wire also is the difficult point in the design, must increase the difficulty of structural design.
Summary of the invention
Realize that cost is high, exist and measure the inaccurate shortcoming that maybe can't measure to the above-mentioned voltage signal detection method of mentioning of the prior art; The present invention provides a kind of voltage signal detection method, circuit and application of equipment for monitoring power quality; It adopts differential type resistance pressure-dividing network isolating exterior signal; Adopt the multisection type dividing potential drop to reach different input range voltage detecting; Adopt high resistant input instrument amplifier to avoid influencing technology such as electric resistance partial pressure value, can the voltage of input wide region and the signal that contains a large amount of harmonic componentss be become the low voltage signal that the subset of can supplying power detects.
The technical scheme that technical solution problem of the present invention adopts is: a kind of voltage signal detection method of equipment for monitoring power quality; Detection method is to be provided with the above amplifier of one-level; Measured signal inputs to two input ends of first order amplifier respectively through the high-impedance resistors of series connection; All be connected with resistance pressure-dividing network between two high-impedance resistors and the first order amp.in, resistance pressure-dividing network is connected between first order amp.in and the signal ground, amplifier output measurement result.
A kind of circuit of realizing the voltage signal detection method of above-mentioned equipment for monitoring power quality; This circuit comprises the amplifier that one-level is above; Measured signal inputs to two input ends of first order amplifier respectively through the high-impedance resistors of series connection; All be connected with resistance pressure-dividing network between two high-impedance resistors and the first order amp.in, resistance pressure-dividing network is connected between first order amp.in and the signal ground, amplifier output measurement result.
A kind of as above-mentioned application of voltage signal detection method of equipment for monitoring power quality; This method is used to detect phase three-wire three or three-phase and four-line alternating current; When this method was used to detect the phase three-wire three alternating current, two phase lines were connected on the measured signal incoming line; When this method was used to detect the three-phase and four-line alternating current, a phase line was connected on the positive pole of measured signal incoming line, connects zero line on the negative pole of measured signal incoming line.
The technological means that the present invention adopts further comprises:
Describedly be provided with two when above when amplifier, resistance pressure-dividing network adopts the resistance that is connected in series more than two to form, and the partial pressure value of each resistance is introduced into the subsequent stages amplifier input terminal successively in the resistance pressure-dividing network.
Be connected with clamp diode on the described amplifier out.
Described amplifier is the amplifying circuit that the instrument amplifier of high resistant input, instrument amplifier, differential amplifier, triode or metal-oxide-semiconductor that three amplifiers are formed are formed.
Described high-impedance resistors adopts plastic packaging EE resistance or adopts several resistance series systems to realize.
Cross-over connection has voltage dependent resistor (VDR) or TVS pipe between described two measured signal lines.
The invention has the beneficial effects as follows: the present invention program can well solve high voltage signal and detect problem, satisfies the requirement to the input of external signal high resistant, is common to the occasion of various high-accuracy voltage input.The low-voltage signal that adopts the electric resistance partial pressure mode to obtain can well reduce input signal characteristics, reflected signal input situation of change truly; External signal and internal signal high impedance mode are isolated, and realize the output of high resistant input low-resistance, neither can impact external input signal, also simplify the internal circuitry senses entry method simultaneously; Adopt the multisection type dividing potential drop, can satisfy different input range voltage detecting.
Embodiment
Please referring to accompanying drawing 2, the circuit among the present invention mainly comprises the instrument amplifier and the catching diode of differential type resistance pressure-dividing network, multiterminal formula electric resistance partial pressure, high resistant input.In the present embodiment, be example, circuit of the present invention is specified with the two-stage amplifier; During practical implementation, also can select the above polystage amplifier of one-level amplifier or two-stage according to actual needs for use, in the present embodiment; Instrument amplifier U1 and instrument amplifier U2 adopt the instrument amplifier of high resistant input respectively; During practical implementation, instrument amplifier U1 and instrument amplifier U2 also can adopt alternate manner to realize, such as instrument amplifier or differential amplifier that three amplifiers are formed; The amplifiers that the high-impedance state that perhaps adopts triode or metal-oxide-semiconductor to constitute is imported etc. are so long as the amplifier circuit of high-impedance state input all is suitable for.In the present embodiment; Be connected with the differential type resistance pressure-dividing network on two input ends of instrument amplifier U1; Wherein, resistance R 1, resistance R 31 and resistance R 32 are formed one group of resistance pressure-dividing network, and resistance R 2, resistance R 41 and resistance R 42 are formed other one group of resistance pressure-dividing network; These two groups of resistance pressure-dividing networks constitute the differential type resistance pressure-dividing network; Resistance R 1 be a high resistance measurement with resistance R 2, can select generally that resistance is that R1=R2=20M Ω, precision are 0.1%, rated power 0.5W, temperature float the resistance for 25ppm, and resistance R 1 and resistance R 2 should possess characteristics such as high impedance, high withstand voltage, high precision and low temperature drift; Can select for use plastic packaging EE resistance to realize, external input signal and internal signal are isolated; Requiring lower-cost occasion, is not under the very high situation to accuracy requirement, can select to realize high impedances with several resistance series systems, high characteristic such as withstand voltage.External high pressure signal input Ui isolates back input instrument amplifier U1 through the resistance R 1 and the resistance R 2 of high value, by instrument amplifier U1 output testing result.In the present embodiment, the common node of resistance R 31 and resistance R 32, the common node of resistance R 41 and resistance R 42, these two nodes constitute other one group of partial pressure value, and in the input instrument amplifier U2, by instrument amplifier U2 output testing result.The resistance of resistance R 31, resistance R 32, resistance R 41 and resistance R 42 is lower; Generally can select resistance for use is that R31=R32=R41=R42 is that 5K, precision are 0.1%; Rated power 0.25W, temperature are floated the resistance for 25ppm, and the resistance value ratio of resistance R 31, resistance R 32, resistance R 41 and resistance R 42 is lower, so the superincumbent magnitude of voltage of stack is also lower; There is no need to select for use cost than higher high withstand voltage resistance, only need to guarantee that high precision and low temperature drift characteristic get final product.Above-mentioned resistance also should be noted that its power, specifically in side circuit, selects the resistance of suitable high or low power for use.In the present embodiment, resistance R 32 connects signal ground point as a reference with resistance R 42.
The present invention is through the dividing potential drop sampling of divider resistance R31, resistance R 32 and resistance R 41, resistance R 42; Generally speaking, get R1=R2, R31=R41; R32=R42; (R31+R32)=(R41+R42), the both sides input voltage obtains equilibrium partial pressure like this, and its current return is: R1 → R31 → R32 → R42 → R41 → R2.
Instrument amplifier U1 two differential input ends detect the pressure reduction of low resistance resistance R 31, resistance R 32 and resistance R 41, resistance R 42; Obtain magnitude of voltage: U1in=[(R31+R32)/(R1+R31+R32)] * Uin; Through regulating the no-load voltage ratio of resistance; Obtain being fit to the magnitude of voltage of U1 input range, the power supply power supply of instrument amplifier is provided by internal circuit.
The input voltage of instrument amplifier U2 is U2in=[R32/ (R31+R32)] * U1in.
For adapting to the wide-voltage range input, U1out possibly cause output voltage to exceed the scope of back-end circuit because enlargement factor is too high, thus adopt catching diode D1 clamped output voltage, in order to avoid damage the circuit of rear end.In the present embodiment, it is the catching diode of BAV99 that catching diode D1 selects model for use.
The output end signal U2out of instrument amplifier U1 output end signal U1out and instrument amplifier U2 is input among the analog to digital converter ADC through behind the signal condition, obtains digital signal and supplies DSP to handle, and this belongs to universal method, does not do detailed description among the present invention.Input signal is prevented surge, and anti-overvoltage protection can increase voltage dependent resistor (VDR) and TVS pipe at corresponding site (being external high pressure signal input part place).
When utilizing the present invention to carry out the detection of quality of power supply voltage signal; To obtain rated voltage behind the mutual inductor be that the ac voltage of 100V detects through measuring to the high-voltage signal of various grades such as 220KV, 110KV, 10KV in the present invention capable of using, is generally forms such as phase three-wire three alternating current or three-phase and four-line alternating current.When detecting the phase three-wire three alternating current, two phase lines are connected on the input end, as input signal Uin; When detecting the three-phase and four-line alternating current, the positive input of input signal Uin is A, B or C line, i.e. phase line, and the Uin negative input is the N line, promptly zero line adopts three groups of above-mentioned modules just can realize voltage transitions.
When utilizing the present invention for stable state and transient state accuracy detection; Because the change in voltage scope changes near rated voltage; For satisfying rear end ADC sample requirement, can select the smaller output that changes in a narrow margin of no-load voltage ratio, promptly through described instrument amplifier U1 channel signal output.
Utilize the present invention to detect for transient signal; Because of its voltage range from-6KV~+ change between the 6KV; If resistance pressure-dividing network is selected bigger no-load voltage ratio output for use; Possibly cause rear end testing circuit overvoltage saturated, need to select the value that no-load voltage ratio is smaller, can select said instrument amplifier U2 passage output for use.
Instrument amplifier U1 and instrument amplifier U2 detect input voltage signal with differential mode, have very high common-mode rejection ratio, play the effect of the common mode interference that suppresses two input signal cables.Simultaneously, because high impedance input characteristics of the present invention (can reach 109 Ω) prevents the electric resistance partial pressure value is impacted.At cost sensitivity and accuracy requirement is not very high occasion, can use three operational amplifiers to realize the instrument amplifier function, can adopt the input of other high impedance input method such as FET, operational amplifier homophase input mode to realize yet.
The present invention will be described with a concrete instance below, and selecting resistance R 1=R2 is 20M Ω, 0.1%, 0.5W, 25ppm, and resistance R 31=R32=R41=R42 is 5K, 0.1%; 0.25W, 25ppm; The voltage U 1i=0.00049975Ui of instrument amplifier U1 two input ends then, under rated voltage, U1i=0.049975V; The enlargement factor of instrument amplifier can be chosen as 10 times; For the analog to digital converter of 5V power supply, can support that the transient voltage more than 3 times detects, also can guarantee near the precision of the stable state parameter that rated voltage is simultaneously.
When transient voltage from-6KV~+ when changing between the 6KV, the input range of U2i for-1.49925V~+ change between the 1.49925V, can satisfy rear end ADC sampled voltage demand fully.
When voltage range changes than broad; The output voltage values of U1out has exceeded the sensing range of ADC; Because be stable state and Temporal Data passage, can not consider that excessive voltage range changes, at this moment; The catching diode D1 on the U1out voltage clamping on power supply VCC, avoid surpassing the input voltage range of ADC.
In the foregoing description; For satisfying the voltage detecting of different range; Divider resistance R3 adopts the series system of resistance R 31 and resistance R 32 to realize and divider resistance R4 adopts the series system of resistance R 41 and resistance R 42 to realize; Only divided two groups of different voltages with different in the foregoing description, can also select for use plural more resistance to realize divider resistance R3 and divider resistance R4 in the reality as required, drawn input signal between the corresponding resistance to corresponding instrument amplifier; Instrument amplifier also can be selected for use a plurality of, and the voltage ratio of multichannel different range is selected to measure.
The present invention program can well solve high voltage signal and detect problem, satisfies the requirement to the input of external signal high resistant, is common to the occasion of various high-accuracy voltage input.The low-voltage signal that adopts the electric resistance partial pressure mode to obtain can well reduce input signal characteristics, reflected signal input situation of change truly; External signal and internal signal high impedance mode are isolated, and realize the output of high resistant input low-resistance, neither can impact external input signal, also simplify the internal circuitry senses entry method simultaneously; Adopt the multisection type dividing potential drop, can satisfy different input range voltage detecting.