CN104601083A - Negative sequence inhibiting device and method for asynchronous motor under unbalanced voltage condition - Google Patents

Abstract

The invention relates to negative sequence inhibiting device and method for an asynchronous motor under an unbalanced voltage condition. The device is characterized in three phases of a positive/ negative sequence voltage current detecting module are respectively correspondingly connected with three phases at the asynchronous motor; the input side of a negative sequence inhibiting wave generation module is connected to a power grid through a voltage regulator; a power supply module is connected with the power grid. According to the technical scheme, the device has the advantages that the positive and negative sequence components and unbalance factor of the asynchronous motor end of the motor in running are acquired on real time; the microcomputer is used for calculating and processing, a corresponding control instruction is sent to the negative sequence inhibitor to generate voltage waveform for inhibiting the negative sequence component of the asynchronous motor, so as to reduce the adverse influence of the negative sequence component on the asynchronous motor; in addition, when detecting that the voltage unbalance factor of the asynchronous motor end and the stator single-phase maximum current exceed the extreme safety operation range, an alarming signal is sent, a power supply of the asynchronous motor is cut off, and therefore, the safety operation of the asynchronous motor is ensured.

Description

Asynchronous machine negative phase-sequence inhibitor under a kind of Voltage unbalance condition and implementation method

Technical field

The present invention relates to a kind of negative phase-sequence inhibitor and its implementation, specifically relate to the asynchronous machine negative phase-sequence inhibitor under a kind of Voltage unbalance condition and implementation method.

Background technology

Unbalanced source voltage caused primarily of single-phase load three-phase skewness in electrical network, now there is certain negative sequence component in electric power system, and negative phase-sequence is very harmful to electric power system, threatens safety and the economical operation of electric power system.The operation of negative-sequence current to generating, transmission of electricity, power transformation, distribution and power consumption equipment all can bring larger harm, is mainly reflected in:

1) increase synchronous generator supplementary load loss and rotor heating, and cause extraneous vibration;

2) make with the relay protection misoperation that negative sequence component starts in electric power system, when negative-sequence current action time is longer, conventional distance protection will proceed to blocking, make the quick acting section of distance protection in a period of time out of service;

3) negative-sequence current causes three-phase current unbalance, thus the rated output making to have a phase current maximum in power transformer three-phase current and limit transformer, reduce its effective rate of utilization, in addition, also cause stray transformer flux to increase and local overheating;

4) during Voltage unbalance, will inevitably occur that certain phase voltage is too high or too low, therefore single-phase electric devices overvoltage or under voltage can be caused to run, if three phase electric equipment, such as most typical threephase asynchronous, there will be fan-out capability reduction, loss increase, the harmful effects such as serious and vibration of generating heat, all causes waste of energy, also have influence on the safe operation of power consumption equipment, even cause industry park plan to interrupt and heavy economic losses.

As the motor of the various device drives devices such as blower fan, pump, compressor, lathe, transport tape, being widely used in multiple industry and the fields such as metallurgy, petrochemical industry, chemical industry, coal, building materials, public utility, is the maximum current consuming apparatus of power consumption.According to statistics, China's motor consume that electric energy accounts for whole society's total electricity consumption more than 60%.And asynchronous motor is because it is cheap and superior performance, be used widely in industrial every field.If there is imbalance of three-phase voltage phenomenon in line voltage, can cause the adverse effects such as energy consumption increase, temperature rise aggravation, service life reduction, entail dangers to motor safe operation under serious conditions, impact is normally produced.

Summary of the invention

For the deficiencies in the prior art, the object of this invention is to provide the asynchronous machine negative phase-sequence inhibitor under a kind of Voltage unbalance condition and implementation method, technical scheme provided by the invention is by gathering asynchronous machine winding three-phase voltage, electric current, and calculate positive and negative sequence voltage and electric current fast, calculate voltage unbalance factor.Then utilize power electronic technology, produce and be used for the voltage waveform that can cancel out each other with negative sequence component, reach the object suppressing negative sequence component in electrical network, thus when eliminating Voltage unbalance negative sequence component to the adverse effect of asynchronous machine.

The object of the invention is to adopt following technical proposals to realize:

The present invention also provides the inhibitor of the asynchronous machine negative phase-sequence under a kind of Voltage unbalance condition, and its improvements are, described negative phase-sequence inhibitor comprises interconnective positive-negative sequence measure voltage & current module and negative phase-sequence suppresses waveform generation module; The three-phase of described positive-negative sequence measure voltage & current module is corresponding to be respectively connected with three of asynchronous machine machine end; Described negative phase-sequence suppresses the outlet side of waveform generation module by access asynchronous machine power input in parallel; Described positive-negative sequence measure voltage & current module suppresses the comparing element in waveform generation module to be connected with negative phase-sequence; The power supply of described negative phase-sequence inhibitor is provided by electrical network.

Further, described positive-negative sequence measure voltage & current module comprises the first control module, for controlling the closed of asynchronous machine power supply K switch and opening;

Described positive-negative sequence measure voltage & current module utilizes coordinate transform and least square method to calculate positive-negative sequence component amplitude and the phase place of asynchronous machine machine end three-phase voltage;

Described negative phase-sequence suppresses waveform generation module to comprise the commutation inversion module, comparing element and the second control module that connect successively; Described commutation inversion module comprises rectification link, filtering link and inversion link; Capacitor in described rectification link, filtering link and the parallel connection of inversion link;

Described negative phase-sequence suppresses waveform generation module according to the negative sequence voltage amplitude detected and phase place, and utilizes commutation inversion module to produce three-phase negative/positive suppression voltage waveform.

Further, described rectification link is made up of the submodule of three-phase cascade; Often all be parallel with Diode series branch road mutually;

Described filtering link comprises reactor and capacitor; The two ends of described reactor are connected with one end of a phase in one end of capacitor and inversion link respectively;

Described inversion link is made up of three-phase diode series arm; Described Diode series props up the diode composition of route series connection.

Further, described power supply comprises: adopt electric network source and super capacitor energy storage device to obtain.

Further, the protection act mechanism of described negative phase-sequence inhibitor is: when asynchronous machine power supply non-equilibrium among three phase voltages is between 0 ~ 5%, negative phase-sequence inhibitor normally works, and produces the three-phase voltage waveform for suppressing negative sequence component in asynchronous machine power supply; When asynchronous machine power supply non-equilibrium among three phase voltages is greater than 5% and the maximum monophase current I of stator _max>I _ntime, the first control module then sends early warning signal, and cuts off asynchronous machine power supply K switch, I simultaneously _max=max{I _a, I _b, I _c, wherein I _a, I _b, I _cbe respectively asynchronous machine stator three-phase current effective value; If I _max≤ I _ntime, then negative phase-sequence inhibitor normally works, and continues monitoring asynchronous machine power supply non-equilibrium among three phase voltages and the single-phase lowest high-current value of stator.

The present invention also provides the implementation method of the asynchronous machine negative phase-sequence inhibitor under a kind of Voltage unbalance condition, and its improvements are, described method comprises the steps:

1. asynchronous machine positive-negative sequence voltage magnitude and the single-phase maximum current of phase place, voltage unbalance factor and stator is obtained;

2. negative phase-sequence inhibitor produces the three-phase voltage waveform suppressing asynchronous machine negative sequence component.

Further, described step 1. in, positive-negative sequence measure voltage & current module Real-time Collection asynchronous machine machine end three-phase windings voltage magnitude and phase place, and utilize the detection algorithm based on multiple least square to try to achieve negative sequence component amplitude and the phase place of winding voltage, calculate voltage unbalance factor, obtain the single-phase maximum current of asynchronous machine stator.

Further, in electric power system, asynchronous machine machine end is expressed as following discrete form without the unbalanced threephase voltage of zero-sequence component:

In formula, ω represents power supply angular frequency; U _m ⁺, U _m ^-represent the amplitude of voltage positive-negative sequence component; represent the initial phase angle of voltage positive-negative sequence component; Δ T represents the sampling interval; K represents sampled instantaneous value; ε _a(k), ε _b(k), ε _ck () represents the combination in any of random noise and high order harmonic component; The component of supply voltage under α β coordinate system is:

$\left(\begin{array}{c}{U}_{\mathrm{\α}}\left(k\right)\\ U_{\mathrm{\β}}\left(k\right)\end{array}\right)=\frac{2}{3}\left(\begin{array}{ccc}1& -\frac{1}{2}& -\frac{1}{2}\\ 0& \frac{\sqrt{3}}{2}& -\frac{\sqrt{3}}{2}\end{array}\right)\left(\begin{array}{c}{U}_a\left(k\right)\\ U_b\left(k\right)\\ U_c\left(k\right)\end{array}\right)---\left(2\right);$

Complex voltage vector is obtained according to above formula (2):

In formula, Section 1 and Section 2 represent the positive and negative sequence phasor of supply voltage respectively, and Section 3 represents random noise and the high order harmonic component composite phasor after coordinate transform;

Suppose that supply frequency is known, above formula (3) be expressed as:

$U\left(k\right)=e^{\mathrm{j\ωk\ΔT}}{U}_{\mathrm{dq}}^{+}+e^{-\mathrm{j\ωk\ΔT}}{U}_{\mathrm{dq}}^{-}+\mathrm{\η}\left(k\right)---\left(4\right);$

In formula:

The variable of subscript d and q representative under synchronous rotating frame, becomes matrix form by the three-phase imbalance voltage transformation that formula (4) represents:

U(k)＝h ^Tθ+η(k) (6)；

In formula:

Adopt the multiple least-squares algorithm of the recursion of band forgetting factor, Optional Value function is:

$J\left[\mathrm{\θ}\left(k\right)\right]=\underset{j=0}{\overset{k}{\mathrm{\Σ}}}{\mathrm{\λ}}^{k-j}{(U\left(j\right)-h^T\left(j\right)\mathrm{\θ}\left(j\right))}^{*T}(U\left(j\right)-h^T\left(j\right)\mathrm{\θ}\left(j\right))---\left(8\right);$

In formula, λ is forgetting factor, λ ∈ (0,1]; Subscript " * " and " T " represent conjugation and the transposition of complex matrix respectively.Try to achieve and make the minimized θ of cost function, use the least square method of recursion of the band forgetting factor shown in formula (9):

$\left\{\begin{array}{c}\widehat{\mathrm{\θ}}\left(k\right)=\widehat{\mathrm{\θ}}(k-1)+K\left(k\right)[U\left(k\right)-h^T\left(k\right)\widehat{\mathrm{\θ}}(k-1)]\\ K\left(k\right)=P(k-1)h\left(k\right){[h^T\left(k\right)P(k-1)h\left(k\right)+\mathrm{\λ}]}^{-1}\\ P\left(k\right)={\mathrm{\λ}}^{-1}[I-\frac{P(k-1)h\left(k\right)h^T\left(k\right)}{h^T\left(k\right)P(k-1)h\left(k\right)+\mathrm{\λ}}]P(k-1)\end{array}\right.---\left(9\right);$

Initial parameter is taken as:

$\left\{\begin{array}{c}\widehat{\mathrm{\θ}}\left(0\right)=\left(\begin{array}{c}0\\ 0\end{array}\right)\\ P\left(0\right)={\mathrm{\π}}_{0}I\end{array}\right.---\left(10\right);$

In formula, π ₀for initial error covariance constant, π ₀>0; I is unit matrix; The relation of positive sequence dq axle component and negative phase-sequence dq axle component is as follows:

Evaluated error covariance resetting technique is adopted to prevent evaluated error covariance matrix P (k) from going to zero: first definite threshold, when evaluated error covariance matrix P (k) resets to initial value π ₀i; When each supply voltage is undergone mutation, positive-negative sequence measure voltage & current module all has initial capability for correcting;

Adopt stagnant chain rate compared with method determine the moment that resets, hysteresis band is determined by the harmonic wave contained in voltage and noise;

Described positive-negative sequence detection module uses the definition of IEC voltage unbalance factor, and its computing formula is as follows:

$\mathrm{VUF}=\frac{\left|U_N\right|}{\left|U_P\right|}---\left(12\right);$

In formula: U _n-negative sequence voltage vector form,

U _p-positive sequence voltage vector form, $U_P=\frac{1}{3}(U_a+a{U}_b+a^2{U}_c);$

A-coefficient,

U _a, U _b, U _c-asynchronous machine stator winding three-phase voltage vector form.

Further, described step 2. in, negative phase-sequence suppresses waveform generation module by computer control commutation inversion module, makes negative phase-sequence inhibitor produce the three-phase voltage waveform suppressing asynchronous machine negative sequence component; Comprise the steps:

1) commutation inversion module input side supplies three phase mains by electrical network through voltage regulator, regulates three-phase input voltage value according to demand;

2) three-phase exported by commutation inversion module suppresses voltage waveform, after voltage magnitude and phase-detection, exports and suppresses waveform voltage amplitude U _–and phase place

3) by comparing element to U _–, with U _m–, compare, and export negative sequence voltage amplitude error e _uand phase error

4) by negative sequence voltage amplitude error e _uand phase error be delivered to the second control module, second control module sends control command according to error amount, in adjustment commutation inversion module, power electronic device opens and the turn-off time, then again export revised three-phase voltage negative phase-sequence and suppress waveform, with this reciprocation cycle, enable produced negative phase-sequence suppress waveform to offset negative sequence component in asynchronous machine stator winding, reduce the supplementary load loss caused by it, make asynchronous machine safe operation.

Compared with immediate prior art, the excellent effect that technical scheme provided by the invention has is:

1, the asynchronous machine negative phase-sequence inhibitor under Voltage unbalance condition provided by the invention and implementation method, mainly through gathering asynchronous machine winding three-phase voltage, electric current, and calculating positive and negative sequence voltage and electric current fast, calculating voltage unbalance factor.Then power electronic technology is utilized, automatic adjustment its voltage amplitude, phase place, produce the three-phase voltage waveform for offsetting the negative sequence component in asynchronous machine power supply, reach the object suppressing negative sequence component in electrical network, thus when eliminating Voltage unbalance, negative sequence component, to the adverse effect of asynchronous machine, reaches reduction energy consumption of electrical machinery, extends motor useful life, safeguard the object that motor safety runs, to China's propulsion energy-saving reduction of discharging plan, there is important practical usage.

2, this negative phase-sequence inhibitor can in real time negative sequence voltage amplitude, phase place in accurate measurements to asynchronous electric electromechanical source online, and calculates voltage unbalance factor, obtains the maximum single-phase electricity flow valuve of stator.

3, this negative phase-sequence inhibitor utilizes bank of super capacitors as stand-by power supply, reduces the impact on the electrical network quality of power supply to a certain extent.

4, in addition, the present invention in conjunction with in motor trade national standard to the limit value requirement of voltage unbalance factor, meet the protection demand within the scope of this, make asynchronous machine under Voltage unbalance condition highly effective and safe run.

Accompanying drawing explanation

Fig. 1 be negative phase-sequence inhibitor provided by the invention and with asynchronous machine syndeton schematic diagram;

Fig. 2 is that negative phase-sequence provided by the invention suppresses waveform generation process schematic diagram;

Fig. 3 is negative phase-sequence inhibitor action mechanism schematic diagram provided by the invention;

Fig. 4 is three-phase imbalance voltage, current waveform figure when not adopting negative phase-sequence inhibitor of the present invention, and wherein (a) is three-phase imbalance voltage oscillogram; Wherein (b) is three phase unbalance current oscillogram;

Fig. 5 adopts three-phase voltage, the current waveform figure in the present invention after negative phase-sequence inhibitor; Wherein (a) adopts the three-phase imbalance voltage oscillogram in the present invention after negative phase-sequence inhibitor; Wherein (b) adopts the three phase unbalance current oscillogram in the present invention after negative phase-sequence inhibitor.

Embodiment

Below in conjunction with accompanying drawing, the specific embodiment of the present invention is described in further detail.

The present invention obtains set end voltage positive and negative sequence component and degree of unbalance when motor runs by Real-time Collection; By Microcomputer Calculation process, sending corresponding control command to negative phase-sequence inhibitor, producing the voltage waveform for suppressing asynchronous machine negative sequence component, thus reduce negative sequence component to the adverse effect of asynchronous machine.In addition, if detect that set end voltage degree of unbalance and the single-phase maximum current of stator exceed safety margins range of operation, then send alarm signal, cut off asynchronous machine power supply, guarantee that motor safety runs.

Negative phase-sequence inhibitor provided by the invention has positive-negative sequence measure voltage & current module and negative phase-sequence suppresses waveform generation module, wherein positive-negative sequence electric current and voltage module mainly utilizes coordinate transform and least-squares algorithm to calculate positive-negative sequence component amplitude and the phase place of asynchronous machine machine end three-phase voltage, negative phase-sequence suppresses waveform generation module then according to the negative sequence voltage amplitude detected and phase place, and utilizes rectification, filtering and inversion link to produce three-phase negative/positive suppression voltage waveform.Negative phase-sequence inhibitor and asynchronous machine johning knot composition are as shown in Figure 1.The three-phase of positive-negative sequence measure voltage & current module is corresponding to be respectively connected with three of asynchronous machine machine end; Described negative phase-sequence suppresses the input side of waveform generation module to access electrical network by voltage regulator; Described positive-negative sequence measure voltage & current module suppresses the comparing element in waveform generation module to be connected with negative phase-sequence; The power supply of described negative phase-sequence inhibitor is provided by electrical network.

Described positive-negative sequence measure voltage & current module comprises the first control module, for controlling the closed of asynchronous machine power supply K switch and opening; Described negative phase-sequence suppresses waveform generation module to comprise the commutation inversion module, comparing element and the second control module that connect successively; Described commutation inversion module comprises rectification link, filtering link and inversion link; Capacitor in described rectification link, filtering link and the parallel connection of inversion link;

Described rectification link is made up of the submodule of three-phase cascade; Often all be parallel with Diode series branch road mutually; Described filtering link comprises reactor and bank of super capacitors; The two ends of described reactor are connected with one end of a phase in one end of bank of super capacitors and inversion link respectively; Described inversion link is made up of three-phase diode series arm; Described Diode series props up the diode composition of route series connection.

The present invention also provides the implementation method of the asynchronous machine negative phase-sequence inhibitor under a kind of Voltage unbalance condition, comprises the steps:

1. asynchronous machine positive-negative sequence voltage, voltage unbalance factor and the single-phase maximum current of stator is obtained;

In negative phase-sequence inhibitor and with in asynchronous machine johning knot patterned basic, select to gather three-phase windings voltage, electric current at asynchronous machine machine end, comprise amplitude and phase place, then a kind of detection algorithm based on multiple least square is utilized, this algorithm when containing high order harmonic component and random noise, can detect amplitude and the phase angle of the positive-negative sequence component of set end voltage quickly and accurately.

In electric power system, only considering three-phase three-line system, is there is not zero-sequence component, so zero-sequence component can be ignored.Unbalanced threephase voltage without zero-sequence component can be expressed as following discrete form:

In formula, ω represents power supply angular frequency; U _m ⁺, U _m ^-represent the amplitude of voltage positive-negative sequence component; represent the initial phase angle of voltage positive-negative sequence component; Δ T represents the sampling interval; K represents sampled instantaneous value; ε _a(k), ε _b(k), ε _ck () represents the combination in any of random noise and high order harmonic component.The component of supply voltage under α β coordinate system is:

$\left(\begin{array}{c}{U}_{\mathrm{\α}}\left(k\right)\\ U_{\mathrm{\β}}\left(k\right)\end{array}\right)=\frac{2}{3}\left(\begin{array}{ccc}1& -\frac{1}{2}& -\frac{1}{2}\\ 0& \frac{\sqrt{3}}{2}& -\frac{\sqrt{3}}{2}\end{array}\right)\left(\begin{array}{c}{U}_a\left(k\right)\\ U_b\left(k\right)\\ U_c\left(k\right)\end{array}\right)---\left(2\right);$

A complex voltage vector can be obtained according to above formula

In formula, Section 1 and Section 2 represent the positive and negative sequence phasor of supply voltage respectively, and Section 3 represents random noise and the high order harmonic component composite phasor after coordinate transform.

Suppose that supply frequency is known, formula (3) is expressed as

$U\left(k\right)=e^{\mathrm{j\ωk\ΔT}}{U}_{\mathrm{dq}}^{+}+e^{-\mathrm{j\ωk\ΔT}}{U}_{\mathrm{dq}}^{-}+\mathrm{\η}\left(k\right)---\left(4\right);$

In formula

The variable of subscript d and q representative under synchronous rotating frame, becomes matrix form by the three-phase imbalance voltage transformation that formula (4) represents:

U(k)＝h ^Tθ+η(k) (6)；

In formula:

If wushu (6) regards observational equation as, then h ^tθ is the complex voltage estimated, and is the row phasor of known plural form, is parameter phasor to be estimated.In actual applications, complex voltage must be obtained by observation, and often containing high order harmonic component and noise in observation information.So what observe can only be containing noisy complex voltage U (k).In order to obtain the estimated value of parameter, can adopt the multiple least-squares algorithm of the recursion of band forgetting factor, Optional Value function is:

$J\left[\mathrm{\θ}\left(k\right)\right]=\underset{j=0}{\overset{k}{\mathrm{\Σ}}}{\mathrm{\λ}}^{k-j}{(U\left(j\right)-h^T\left(j\right)\mathrm{\θ}\left(j\right))}^{*T}(U\left(j\right)-h^T\left(j\right)\mathrm{\θ}\left(j\right))---\left(8\right);$

In formula, λ is forgetting factor, λ ∈ (0,1]; Subscript " * " and " T " represent conjugation and the transposition of a complex matrix respectively.Making the minimized θ of cost function to try to achieve, using the least square method of recursion of the band forgetting factor shown in formula (9).

$\left\{\begin{array}{c}\widehat{\mathrm{\θ}}\left(k\right)=\widehat{\mathrm{\θ}}(k-1)+K\left(k\right)[U\left(k\right)-h^T\left(k\right)\widehat{\mathrm{\θ}}(k-1)]\\ K\left(k\right)=P(k-1)h\left(k\right){[h^T\left(k\right)P(k-1)h\left(k\right)+\mathrm{\λ}]}^{-1}\\ P\left(k\right)={\mathrm{\λ}}^{-1}[I-\frac{P(k-1)h\left(k\right)h^T\left(k\right)}{h^T\left(k\right)P(k-1)h\left(k\right)+\mathrm{\λ}}]P(k-1)\end{array}\right.---\left(9\right);$

In time-varying system, in order to can continuous corrected parameter, must prevent evaluated error covariance matrix P (k) from decaying to zero, the renewal process of P (k) is many as seen from the above equation λ ^-1one.As 0< λ <1, can P (k) be effectively stoped to go to zero.λ is less, and the impact of legacy data on estimated value is less, thus it is stronger to follow the tracks of the ability of time-varying parameter, but stable state accuracy can corresponding reduction, and estimated value is easily subject to noise jamming and error is strengthened.λ is larger, and the confidence level of legacy data is also larger, and accuracy of detection improves thereupon, have certain robustness, but dynamic response is slack-off to noise.In practical application, compromise in dynamic response and stable state accuracy two is needed to consider.Recursive algorithm wants work, must arrange initial parameter value.Common way is exactly directly initial parameter to be taken as:

$\left\{\begin{array}{c}\widehat{\mathrm{\&theta;}}\left(0\right)=\left(\begin{array}{c}0\\ 0\end{array}\right)\\ P\left(0\right)={\mathrm{\&pi;}}_{0}I\end{array}\right.---\left(10\right);$

In formula, π ₀for initial error covariance constant, π ₀>0; I is unit matrix.The estimated value of θ can be tried to achieve by iteration, also i.e. the amplitude of the positive-negative sequence component of line voltage and initial phase angle, but sometimes positive sequence dq axle component and negative phase-sequence dq axle component more conventional.Relational expression by both is derived mutually.Both relations are as follows:

After changing recursive algorithm first time convergence, estimated parameter trends towards actual value, and at this moment, the element value in evaluated error covariance matrix P (k) can become very little.If supply voltage is undergone mutation again, correction term will lose original capability for correcting, thus recursive algorithm is restrained slowly, even occur dispersing.In order to accelerate the tracking velocity of algorithm, making it have continuous print capability for correcting, being employed herein evaluated error covariance resetting technique.General principle prevents evaluated error covariance matrix P (k) from going to zero exactly.Specific practice is: first determine a threshold value, when evaluated error covariance matrix P (k) resets to initial value π ₀i.Like this, when each supply voltage is undergone mutation, algorithm all has initial capability for correcting.

The present invention adopt stagnant chain rate compared with method decide the moment that resets, hysteresis band is determined by the harmonic wave contained in voltage and noise.If the content of such as interference noise is 10% of fundametal compoment, then can elects the width of stagnant ring 30% of fundamental voltage amplitude as, the frequent recovery of covariance matrix can be prevented like this.E _h, e _lbe respectively the threshold value of reset and set covariance matrix, when evaluated error is greater than e _htime, then covariance matrix is reset to initial value, until evaluated error is less than e _ltime, just stop resetting, the object introducing stagnant ring is exactly the stable operation ensureing filter.The method under the prerequisite containing high order harmonic component and random noise, can detect amplitude and the phase angle of the positive-negative sequence component of asynchronous machine machine end supply voltage rapidly and accurately.

Positive-negative sequence detection module of the present invention uses IEC voltage unbalance factor definition (VUF-Voltage Unbalance Factor), and its computing formula is as follows:

$\mathrm{VUF}=\frac{\left|U_N\right|}{\left|U_P\right|}---\left(12\right);$

In formula: U _n-negative sequence voltage vector form,

U _p-positive sequence voltage vector form, $U_P=\frac{1}{3}(U_a+a{U}_b+a^2{U}_c);$

A-coefficient,

U _a, U _b, U _c-asynchronous machine stator winding three-phase voltage vector form.

2. negative phase-sequence inhibitor produces the three-phase voltage waveform suppressing asynchronous machine negative sequence component.

By under the theoretical known Voltage unbalance state of Electrical Motor, there is negative sequence field in asynchronous machine inside, its direction of rotation is contrary with rotor direction of rotation, and the relative rotation speed of itself and rotor is (2-s) n ₁, n ₁for synchronous speed, because during actual motion, slip s is very little, therefore (2-s) ≈ 2.To suppress or eliminate the impact of this negative sequence component, identical with it, that direction of rotation is contrary with it magnetic field of amplitude is needed to offset with it, the effect of negative phase-sequence inhibitor is just the three-phase voltage waveform producing this function, and negative phase-sequence suppresses waveform generation flow process as shown in Figure 2.

Negative phase-sequence suppresses waveform generation module operation principle as described below:

1) commutation inversion module input side supplies three phase mains by electrical network through voltage regulator, can regulate three-phase input voltage value according to demand;

2) three-phase exported by commutation inversion module suppresses voltage waveform, after voltage magnitude and phase-detection, exports and suppresses waveform voltage amplitude U _–and phase place

3) by comparing element to U _–, with U _m–, compare, then export negative sequence voltage amplitude error e _uand phase error

4) by negative sequence voltage amplitude error e _uand phase error be delivered to the second control module, second control module sends control command according to error amount, in adjustment commutation inversion module, power electronic device opens and the turn-off time, then again export revised three-phase voltage negative phase-sequence and suppress waveform, with this reciprocation cycle, enable produced negative phase-sequence suppress waveform to balance out negative sequence component in asynchronous machine stator winding as far as possible, reduce the supplementary load loss caused by it, motor safety is run efficiently.

Negative phase-sequence inhibitor power supply module proposed by the invention is directly powered through three-phase regulator by electrical network, in the process, can be the bank of super capacitors shown in Fig. 2 simultaneously and carry out quick charge, when the electrical network quality of power supply is poor, voltage regulator output voltage can be adjusted to zero, transfer to and use bank of super capacitors to suppress waveform generation module to be powered for negative phase-sequence, to reduce in negative phase-sequence inhibitor power electronic device thus to the impact of the electrical network quality of power supply.Finally reach the object namely suppressing asynchronous machine set end voltage negative sequence component, reduce the impact on the electrical network quality of power supply in the negative phase-sequence inhibitor course of work simultaneously to a certain extent.

The present invention is with reference to " when suggestion asynchronous machine runs, voltage unbalance factor is no more than 5% " in GB 22713-2008 " unbalance voltage is on the impact of three-phase cage induction motor performance ", by in negative phase-sequence inhibitor response limiting system, 5% is set to the action upper limit of voltage unbalance factor, protection act mechanism and scope can be applicable to the voltage unbalance factor scope being no more than 5%, automatically anticipation can be made to running status, when exceeding the safe operation limit, send early warning and drive protection act, guaranteeing that motor safety runs; Being specially: when asynchronous machine power supply non-equilibrium among three phase voltages is between 0 ~ 5%, negative phase-sequence inhibitor normally works, producing the three-phase voltage waveform for suppressing negative sequence component in asynchronous machine power supply; When voltage unbalance factor is greater than 5% and the maximum monophase current I of stator _max>I _ntime, the first control module then sends early warning signal, and cuts off asynchronous machine power supply K switch simultaneously, guarantees man-machine safety, I _max=max{I _a, I _b, I _c, wherein I _a, I _b, I _cbe respectively stator three-phase current effective value, in addition, if I _max≤ I _ntime, then negative phase-sequence inhibitor normally works, and continues monitoring voltage degree of unbalance and the single-phase lowest high-current value of stator, the first control module of negative phase-sequence inhibitor with this reciprocation cycle, to ensure that asynchronous machine can safe operation in Voltage unbalance situation.Negative phase-sequence inhibitor action mechanism as shown in Figure 3.

Embodiment

For one, laboratory 5.5kW squirrel cage asynchronous motor, carried out inhibition checking to negative phase-sequence inhibitor proposed by the invention, asynchronous machine installs three-phase voltage before and after negative phase-sequence inhibitor, practical measurement of current waveform additional respectively as shown in Fig. 4 (a) and (b) and Fig. 5 (a) He (b).In Fig. 4 (a), non-equilibrium among three phase voltages is 2.14%, and in (b), three-phase current unbalance degree is 15.55%; And non-equilibrium among three phase voltages is close to 0% in Fig. 5 (a), in (b), three-phase current unbalance degree is 0.91%, and therefrom can find out, the inhibition of negative phase-sequence inhibitor proposed by the invention is comparatively obvious.

Finally should be noted that: above embodiment is only in order to illustrate that technical scheme of the present invention is not intended to limit; although with reference to above-described embodiment to invention has been detailed description; those of ordinary skill in the field still can modify to the specific embodiment of the present invention or equivalent replacement; these do not depart from any amendment of spirit and scope of the invention or equivalent replacement, are all applying within the claims of the present invention awaited the reply.

Claims (9)

1. the asynchronous machine negative phase-sequence inhibitor under Voltage unbalance condition, is characterized in that, described negative phase-sequence inhibitor comprises interconnective positive-negative sequence measure voltage & current module and negative phase-sequence suppresses waveform generation module; The three-phase of described positive-negative sequence measure voltage & current module is corresponding to be respectively connected with three of asynchronous machine machine end; Described negative phase-sequence suppresses the outlet side of waveform generation module by access asynchronous machine power input in parallel; Described positive-negative sequence measure voltage & current module suppresses the comparing element in waveform generation module to be connected with negative phase-sequence; The power supply of described negative phase-sequence inhibitor is provided by electrical network.

2. asynchronous machine negative phase-sequence inhibitor as claimed in claim 1, is characterized in that, described positive-negative sequence measure voltage & current module comprises for the first control module controlling the closed of asynchronous machine power supply K switch and open;

Described positive-negative sequence measure voltage & current module utilizes coordinate transform and least square method to calculate positive-negative sequence component amplitude and the phase place of asynchronous machine machine end three-phase voltage;

Described negative phase-sequence suppresses waveform generation module to comprise the commutation inversion module, comparing element and the second control module that connect successively; Described commutation inversion module comprises rectification link, filtering link and inversion link; Capacitor in described rectification link, filtering link and the parallel connection of inversion link;

Described negative phase-sequence suppresses waveform generation module according to the negative sequence voltage amplitude detected and phase place, and utilizes commutation inversion module to produce three-phase negative/positive suppression voltage waveform.

3. asynchronous machine negative phase-sequence inhibitor as claimed in claim 1, it is characterized in that, described rectification link is made up of the submodule of three-phase cascade; Often all be parallel with Diode series branch road mutually;

Described filtering link comprises reactor and capacitor; The two ends of described reactor are connected with one end of a phase in one end of capacitor and inversion link respectively;

Described inversion link is made up of three-phase diode series arm; Described Diode series props up the diode composition of route series connection.

4. asynchronous machine negative phase-sequence inhibitor as claimed in claim 1, it is characterized in that, described power supply comprises: adopt electric network source and super capacitor energy storage device to obtain.

5. asynchronous machine negative phase-sequence inhibitor as described in any of claims 1, it is characterized in that, the protection act mechanism of described negative phase-sequence inhibitor is: when asynchronous machine power supply non-equilibrium among three phase voltages is between 0 ~ 5%, negative phase-sequence inhibitor normally works, and produces the three-phase voltage waveform for suppressing negative sequence component in asynchronous machine power supply; When asynchronous machine power supply non-equilibrium among three phase voltages is greater than 5% and the maximum monophase current I of stator _max>I _ntime, the first control module then sends early warning signal, and cuts off asynchronous machine power supply K switch, I simultaneously _max=max{I _a, I _b, I _c, wherein I _a, I _b, I _cbe respectively asynchronous machine stator three-phase current effective value; If I _max≤ I _ntime, then negative phase-sequence inhibitor normally works, and continues monitoring asynchronous machine power supply non-equilibrium among three phase voltages and the single-phase lowest high-current value of stator.

6. an implementation method for the asynchronous machine negative phase-sequence inhibitor under the Voltage unbalance condition according to any one of claim 1-5, it is characterized in that, described method comprises the steps:

1. asynchronous machine positive-negative sequence voltage magnitude and the single-phase maximum current of phase place, voltage unbalance factor and stator is obtained;

2. negative phase-sequence inhibitor produces the three-phase voltage waveform suppressing asynchronous machine negative sequence component.

7. implementation method as claimed in claim 6, it is characterized in that, described step 1. in, positive-negative sequence measure voltage & current module Real-time Collection asynchronous machine machine end three-phase windings voltage magnitude and phase place, and utilize the detection algorithm based on multiple least square to try to achieve negative sequence component amplitude and the phase place of winding voltage, calculate voltage unbalance factor, obtain the single-phase maximum current of asynchronous machine stator.

8. implementation method as claimed in claim 7, it is characterized in that, in electric power system, asynchronous machine machine end is expressed as following discrete form without the unbalanced threephase voltage of zero-sequence component:

In formula, ω represents power supply angular frequency; U _m ⁺, U _m ^-represent the amplitude of voltage positive-negative sequence component; represent the initial phase angle of voltage positive-negative sequence component; Δ T represents the sampling interval; K represents sampled instantaneous value; ε _a(k), ε _b(k), ε _ck () represents the combination in any of random noise and high order harmonic component; The component of supply voltage under α β coordinate system is:

$\left(\begin{array}{c}{U}_{\mathrm{\&alpha;}}\left(k\right)\\ U_{\mathrm{\&beta;}}\left(k\right)\end{array}\right)=\frac{2}{3}\left(\begin{array}{ccc}1& -\frac{1}{2}& -\frac{1}{2}\\ 0& \frac{\sqrt{3}}{2}& -\frac{\sqrt{3}}{2}\end{array}\right)\left(\begin{array}{c}{U}_a\left(k\right)\\ U_b\left(k\right)\\ U_c\left(k\right)\end{array}\right)---\left(2\right);$

Complex voltage vector is obtained according to above formula (2):

In formula, Section 1 and Section 2 represent the positive and negative sequence phasor of supply voltage respectively, and Section 3 represents random noise and the high order harmonic component composite phasor after coordinate transform;

Suppose that supply frequency is known, above formula (3) be expressed as:

$U\left(k\right)=e^{\mathrm{j\&omega;k\&Delta;T}}{U}_{\mathrm{dq}}^{+}+e^{-\mathrm{j\&omega;k\&Delta;T}}{U}_{\mathrm{dq}}^{-}+\mathrm{\&eta;}\left(k\right)---\left(4\right);$

In formula:

The variable of subscript d and q representative under synchronous rotating frame, becomes matrix form by the three-phase imbalance voltage transformation that formula (4) represents:

U(k)＝h ^Tθ+η(k) (6)；

In formula:

Adopt the multiple least-squares algorithm of the recursion of band forgetting factor, Optional Value function is:

$J\left[\mathrm{\&theta;}\left(k\right)\right]=\underset{j=0}{\overset{k}{\mathrm{\&Sigma;}}}{\mathrm{\&lambda;}}^{k-j}{(U\left(j\right)-h^T\left(j\right)\mathrm{\&theta;}\left(j\right))}^{*T}(U\left(j\right)-h^T\left(j\right)\mathrm{\&theta;}\left(j\right))---\left(8\right);$

In formula, λ is forgetting factor, λ ∈ (0,1]; Subscript " * " and " T " represent conjugation and the transposition of complex matrix respectively.Try to achieve and make the minimized θ of cost function, use the least square method of recursion of the band forgetting factor shown in formula (9):

$\left\{\begin{array}{c}\widehat{\mathrm{\&theta;}}\left(k\right)=\widehat{\mathrm{\&theta;}}(k-1)+K\left(k\right)[U\left(k\right)-h^T\left(k\right)\widehat{\mathrm{\&theta;}}(k-1)]\\ K\left(k\right)=P(k-1)h\left(k\right){[h^T\left(k\right)P(k-1)h\left(k\right)+\mathrm{\&lambda;}]}^{-1}\\ P\left(k\right)={\mathrm{\&lambda;}}^{-1}[I-\frac{P(k-1)h\left(k\right)h^T\left(k\right)}{h^T\left(k\right)P(k-1)h\left(k\right)+\mathrm{\&lambda;}}]P(k-1)\end{array}\right.---\left(9\right);$

Initial parameter is taken as:

$\left\{\begin{array}{c}\widehat{\mathrm{\&theta;}}\left(0\right)=\left(\begin{array}{c}0\\ 0\end{array}\right)\\ P\left(0\right)={\mathrm{\&pi;}}_{0}I\end{array}\right.---\left(10\right);$

In formula, π ₀for initial error covariance constant, π ₀>0; I is unit matrix; The relation of positive sequence dq axle component and negative phase-sequence dq axle component is as follows:

Evaluated error covariance resetting technique is adopted to prevent evaluated error covariance matrix P (k) from going to zero: first definite threshold, when evaluated error covariance matrix P (k) resets to initial value π ₀i; When each supply voltage is undergone mutation, positive-negative sequence measure voltage & current module all has initial capability for correcting;

Adopt stagnant chain rate compared with method determine the moment that resets, hysteresis band is determined by the harmonic wave contained in voltage and noise;

Described positive-negative sequence detection module uses the definition of IEC voltage unbalance factor, and its computing formula is as follows:

$\mathrm{VUF}=\frac{\left|U_N\right|}{\left|U_P\right|}---\left(12\right);$

In formula: U _n-negative sequence voltage vector form, $U_N=\frac{1}{3}(U_a+a^2{U}_b+a{U}_c);$

U _p-positive sequence voltage vector form, $U_P=\frac{1}{3}(U_a+a{U}_b+a^2{U}_c);$

A-coefficient,

U _a, U _b, U _c-asynchronous machine stator winding three-phase voltage vector form.

9. implementation method as claimed in claim 6, is characterized in that, described step 2. in, negative phase-sequence suppresses waveform generation module by computer control commutation inversion module, makes negative phase-sequence inhibitor produce the three-phase voltage waveform suppressing asynchronous machine negative sequence component; Comprise the steps:

1) commutation inversion module input side supplies three phase mains by electrical network through voltage regulator, regulates three-phase input voltage value according to demand;

2) three-phase exported by commutation inversion module suppresses voltage waveform, after voltage magnitude and phase-detection, exports and suppresses waveform voltage amplitude U ^–and phase place

3) by comparing element to U ^–, with U _m ^–, compare, and export negative sequence voltage amplitude error e _uand phase error

4) by negative sequence voltage amplitude error e _uand phase error be delivered to the second control module, second control module sends control command according to error amount, in adjustment commutation inversion module, power electronic device opens and the turn-off time, then again export revised three-phase voltage negative phase-sequence and suppress waveform, with this reciprocation cycle, enable produced negative phase-sequence suppress waveform to offset negative sequence component in asynchronous machine stator winding, reduce the supplementary load loss caused by it, make asynchronous machine safe operation.