Frequency-converter control method for suppressing open-loop system oscillation and apparatus therefor
Technical field
The present invention relates to the Frequency Converter Control technology, be specifically related to a kind of frequency converter control method and device that can suppress the vibration under zero load or the underloading situation in VVVF (variable voltage variable frequency) open cycle system.
Background technology
The VVVF system is a current the most widely used Frequency Converter Control system, and it can realize frequency-conversion voltage-varying speed according to the V/F characteristic that the user selects.Although shortcomings such as there is low speed moment deficiency in this type of open cycle system, dynamic response is not good enough need not depend on the parameter of electric machine during owing to use, therefore, use simply, can realize conveniently that multimachine drags, therefore application is very extensive in blower fan, the driving of pump class.Fig. 1 is typical universal frequency converter VVVF control system.There is inherent instability in such open cycle system simultaneously, near (20Hz~30Hz), be prone to persistent oscillation some operation frequency range, particularly half fundamental frequency to tripping operation.Under sky, light running situation, this problem is particularly outstanding, has limited the operation speed adjustable range of this type of open cycle system.Studies show that the oscillating characteristic in the VVVF system is relevant with the size of motor stator resistance, transient state leakage reactance, and have confidential relation with the dead band time setting of inversion circuit.Conventional VSI drives in the VVVF system, and a phase upper and lower bridge arm all is in off state in the Dead Time, and the load-side energy is to the feedback of major loop capacitive side, so still has the fluctuation of meritorious and quadergy during stable operation.This fluctuation causes torque ripple and motor speed fluctuation, under the lighter situation of dampings such as empty underloading, excites the rotor persistent oscillation, and the frequency converter output current significantly vibrates, and causes tripping operation then, therefore must take measures to suppress vibration.When the known motor parameter, it is easy that introducing speed ring or electric current loop suppress vibration; But the universal frequency converter driving number of poles of VVVF control and the induction machine that capacity has nothing in common with each other, without any the adjuster that depends on the parameter of electric machine, it is then comparatively difficult to suppress vibration this moment.
From present Development Technology, need not the parameter of electric machine in the universal frequency converter, under the condition of not introducing any associated rotating speed, current regulator, the method that vibration is suppressed mainly contains following several: 1) inverter direct-flow side current detecting, its theory diagram as shown in Figure 2.Judge according to the DC side sense of current whether vibration exists, and, quadergy meritorious by the frequency adjustment ACTIVE CONTROL flows and suppresses vibration.Therefore this method must be connected in series sampling resistor in DC side owing to need to detect the DC side electric current, increases corresponding vibration discriminator circuit simultaneously.This scheme can't realize in the frequency converter that directly detects the AC side output current usually.2) directly change, carry out frequency adjustment, the inhibition of vibrating according to this by differential negative feedback control according to frequency converter AC side output current amplitude.This method is based on following understanding: the fluctuation of a definite form appearred in current phasor relative voltage vector phase angle when vibration took place, and therefore suppressed the variation of current phasor phase place by the disturbance of voltage vector position angle.This method lacks strict theoretical proof, and can't guarantee all can be effective when driving the motor of different capacity and number of pole-pairs.The inventor has also proved this point to the experimental result of different capacity motor.The analysis showed that, during motor operation vibration, output side transducer current amplitude and phase place all present fluctuation, therefore if can carry out suitable FEEDBACK CONTROL to current amplitude and phase place, that is the coordination control by frequency converter output voltage, frequency, just can effectively suppress to vibrate.
Summary of the invention
But the technical problem to be solved in the present invention is the control method that a kind of divided ring system oscillation suppresses, in implementing this vibration process of inhibition, need not use the parameter of electric machine, rotating speed that need not be common and current regulator, just can realize differential negative feedback voltage vector phase place, amplitude coordination control, make this control have practicality widely.
The above-mentioned technical problem of the present invention solves like this, constructs a kind of frequency converter control method that suppresses the open cycle system vibration, may further comprise the steps: produce reference frequency; Detect the amplitude and the phase place of inverter output terminal electric current; Produce correction quantity of frequency; Reference frequency and correction quantity of frequency stack are obtained corrected frequency; Utilize the phase place of corrected frequency control pulse width modulated wave; Control described frequency converter by above-mentioned pulse width modulated wave; It is characterized in that, produce correction quantity of frequency and may further comprise the steps: in voltage oriented coordinate system, decompose current amplitude and phase place that above-mentioned detection obtains, obtain d-axis, quadrature axis component; To obtain the active current component after direct axis component and the quadrature axis component single order low-pass filtering; Described active current component is made ratio one differential transform, obtain correction quantity of frequency.
Above-mentioned according to the frequency converter control method that suppresses open cycle system vibration of the present invention in, also comprise: the step that produces the voltage of the described pulse-width modulation wave amplitude of control by described reference frequency.
Above-mentioned according to the frequency converter control method that suppresses open cycle system vibration of the present invention in, described active current component is made ratio-differential transform, comprise with K
P1For proportionality factor, with τ
1For time constant to described active current component i
dCarry out low-pass filtering and obtain the step of first regulated quantity; With K
P2For proportionality factor, with τ
2For time constant to described active current component i
dLow-pass filtering obtains the step of second regulated quantity; First and second regulated quantitys are synthesized, obtain correction quantity of frequency.
Above-mentioned according to the frequency converter control method that suppresses open cycle system vibration of the present invention in, τ
1>>τ
2, K
P2=K
P1
Another technical problem of the present invention solves like this, constructs a kind of frequency changer controller that suppresses the open cycle system vibration, comprising: the reference frequency generation device; The sampling apparatus that is used for sampling frequency converter output end current amplitude and phase place; Output current signal to sampling apparatus carries out the adjusting device that computing obtains correction quantity of frequency; Be used for adder with reference frequency and correction quantity of frequency stack; According to the pulse width modulator of corrected frequency control inverter, described adjusting device comprises: in voltage oriented coordinate system, above-mentioned output current signal is decomposed, obtain the coordinate decomposer of direct axis component and quadrature axis component; The low-pass filter of output active current component; Behind active current component proportion differential transform, the frequency correcting device of output frequency correction.
Above-mentioned according to the frequency changer controller that suppresses open cycle system vibration provided by the invention in, also comprise: receive reference frequency signal, produce the voltage conversion device of control pulse width modulator control voltage.
Above-mentioned according to the frequency changer controller that suppresses open cycle system vibration provided by the invention in, described frequency correcting device comprises: receive the active current component signal, carry out the low-pass filtering conversion of two different time constants respectively, and export the first frequency correcting device and the second frequency correcting device of first frequency correction, second frequency correction; With first frequency correction and the addition of second frequency correction, the second adder of output frequency correction.
Above-mentioned according to the frequency changer controller that suppresses open cycle system vibration provided by the invention in, the time coefficient of low-pass filtering link is respectively τ in described first, second frequency correcting device
1And τ
2, the proportionality coefficient of proportional component is respectively K
P1And K
P2, τ wherein
1>>τ
2, K
P1=K
P2
Implement frequency converter control method and the device that suppresses the open cycle system vibration provided by the invention, because need not the parameter of electric machine, just by the coordination control of voltage vector phase place, amplitude, the oscillation problem when very having solved the zero load that exists in the VVVF control system or underloading effectively.Because do not adopt conventional electric current, speed regulator, make that the realization of system is very simple, strong robustness can adapt to different types of induction machine, and theory analysis and practice show that all the method that above-mentioned vibration suppresses is simple and practical.
Description of drawings
Fig. 1 is the logical construction schematic diagram of typical general frequency converter VVVF control system;
Fig. 2 is that the schematic diagram of prior art sampling inverter output end current amplitude is represented;
Fig. 3 is the voltage oriented coordinate system schematic diagram that the present invention uses;
Fig. 4 is the schematic diagram of explanation oscillation suppression method of the present invention and device;
Fig. 5 is the structured flowchart that describes an embodiment who realizes Fig. 4 block diagram in detail;
Fig. 6 is a schematic flow sheet of realizing oscillation suppression method of the present invention;
Fig. 7 is that the frequency converter carrier frequency is under the 6K situation, and empty load of motor operates in the current waveform figure of 24.70Hz;
Fig. 8 is that the frequency converter carrier frequency is under the 6K situation after employing the inventive method, and empty load of motor operates in the current waveform figure of 24.70Hz.
Embodiment
In conjunction with the accompanying drawings and embodiments, principle, realization and the effect of the inventive method being done one elaborates.As previously mentioned, the inventive method and analysis thereof are based on that the coordinate system of voltage vector orientation carries out, and as shown in Figure 3, in this coordinate system, the angle of current phasor and voltage vector is a power-factor angle.Current phasor is the motor active current in the projection of voltage vector direction, and projection in vertical direction is the motor reactive current.When running frequency was higher, the motor active current had promptly reflected the size of motor torque electric current.Because under the VVVF mode, therefore the motor oscillates operating point, can think during analysis that the d axle component of current phasor has reflected motor instantaneous torque electric current usually greater than 5Hz, detect the fluctuation situation of the variation of this component with regard to the indirect detection electromagnetic torque of energy.Dynamo-electric equilibrium equation according to motor:
(1)
T
e=K
1i
sd (2)
Can get by (2):
ΔT
e=K
1Δi
sd (3)
Here suppose that load is constant, T
eBe electromagnetic torque, T
lBe load torque, ω
rBe motor rotor speed, i
SdBe direct-axis current, K
1Be the relevant constant of the parameter of electric machine, comprehensive (1) and (3), adopt small-signal analysis can obtain near the stable operation balance point, having:
(4)
That is:
(5)
Obviously, if running frequency is constant, then have:
(6)
ω in the formula
sBe instantaneous slippage angular frequency.
On the other hand, motor rotor speed is:
ω
r=ω
1-ω
s (7)
ω in the formula
1Be stator electric angle frequency.
Stable for guaranteeing motor speed, obviously have:
(8)
(8) the formula derivation result in fact can make an explanation by following physical significance:
Because in the coordinate system control system of voltage vector orientation, the approximate variation that has reflected motor torque of the fluctuation of direct-axis current, the fluctuation of speed is caused by the variation of electromagnetic torque under the oscillatory regime, and therefore the detection according to torque ripple can obtain current motor speed situation of change.Near balance point, when direct-axis current increases, mean that electromagnetic torque increases, motor speed increases, and needs to reduce the increase that the stator running frequency suppresses rotating speed this moment; On the contrary, when direct-axis current reduces, mean that the motor electromagnetic torque reduces, motor speed reduces, and needs to improve the stator running frequency this moment and suppresses reducing of motor speed.By this differential negative feedback control, effectively suppressed the fluctuation of motor speed, thereby avoided the irregular operation state under the light Light Condition.Under the stable state, direct-axis current remains unchanged, electromagnetic torque all the time with the load torque balance, frequency adjustment is inoperative.More than the control basic thought is to control motor rotor speed to stablize, and final simultaneously control stator voltage, current phasor relative phase are stablized.
Fig. 4 shows the principle structure schematic diagram of the new control method that forms based on above thought, as shown in the drawing, two-phase sample rate current U and V are mapped as d-axis, quadrature axis component (Fig. 3) in voltage oriented coordinate system, LPF is a single order low-pass filtering link, obtain current phasor direct axis component id through after the low-pass filtering, i.e. motor operation active current component.Consider The noise when directly differentiating, system adopts two different low-pass filtering links of time constant to handle the synthetic frequency regulating amount that obtains in back.During actual system design, K
P1=K
P2, τ
1>>τ
2It is to be noted, system is in frequency adjustment, do not change the command voltage value, this mainly is based on following consideration: when meritorious electric current increased, according to above control strategy, the motor running frequency descended, and command voltage does not become, the motor magnetic flux increases, and helps the decline of active current, plays degenerative effect; Vice versa.In the schematic diagram shown in Fig. 4, reference frequency generation device 401, signal synthesizer 402, PWM PDM keyer 403, inverter 404, V/F unit 405, inverter 406, load 407, sampling apparatus 408, coordinate decomposer 409, low-pass filter 410 and frequency regulation arrangement 411 are arranged, wherein, reference frequency generation device 401 is used to produce reference frequency; Sampling apparatus 408 is used to detect the amplitude and the phase place of inverter output terminal electric current; Coordinate decomposer 409 is used for decomposing current amplitude and the phase place that above-mentioned detection obtains at directed coordinate system, obtains d-axis, quadrature axis component; Low-pass filter 410 is used for and will obtains the active current component after direct axis component and the quadrature axis component single order low-pass filtering; Frequency regulation arrangement 411 is used for described active current component is made ratio-differential transform, obtains the first frequency correction.Signal synthesizer 402 is used for reference frequency and correction quantity of frequency stack are obtained corrected frequency; PWM PDM keyer 403 is utilized the phase place of corrected frequency control pulse width modulated wave, controls described frequency converter 406 by above-mentioned pulse width modulated wave, and the output of inverter 406 drives load 407.
Realize in the structured flowchart of an embodiment of Fig. 4 block diagram in the detailed description shown in Fig. 5, comprise reference signal generating unit 501, signal synthesizer 502, PWM control unit 503, V/F unit 504, VSI inversion unit 505, load 506, coordinate resolving cell 507, LPF unit 508, proportion differential unit 509 and 510 and signal synthesis unit 511.Wherein, reference signal generating unit 501 is used to produce reference frequency; Coordinate resolving cell 507 is used for amplitude and the phase place with detected frequency converter 505 output end currents, is decomposed in directed coordinate system; LPF unit 508 is used for and will obtains the active current component after direct axis component and the quadrature axis component single order low-pass filtering; Proportion differential unit 510 is used for K
P1For proportionality factor, with τ
1For time constant to active current component i
dCarry out the low-pass filtering conversion and obtain first regulated quantity, proportion differential unit 509 is used for K
P2For proportionality factor, with τ
2For time constant to active current component i
dCarry out the low-pass filtering conversion and obtain second regulated quantity, signal synthesis unit 511 is used for first and second regulated quantitys are synthesized, and obtains correction quantity of frequency.As an example, can select τ
1>>τ
2, K
P2=K
P1
The software of the above-mentioned control method of the present invention is realized very convenient, and Fig. 6 shows the software flow pattern of specific implementation.As shown in the figure, start from frame 601, in frame 602, calculate id (k), in frame 603, carry out differentiation element and handle; In frame 604, carry out the frequency regulating amount amplitude limit, in frame 605, calculate id (k) → id (k-1); In frame 606, current running frequency is upgraded, return at frame 607 at last.
Adopt such scheme driving of the present invention and control a variable-frequency motor, this parameter of electric machine is as follows: rated voltage: 380V, rated current: 24A, rated power: 7.5KW, rated speed: 1165rpm, specified running frequency 60HZ.If no any vibration braking measure, this motor rotation of VVVF system drive shakes easily at 20 ~ 30HZ under the empty load of motor situation, and Fig. 7 is under the 6K situation for the frequency converter carrier frequency, empty load of motor operates in the current waveform of 24.70HZ, and the lattice among the figure are represented the 10A electric current.Adopt the frequency converter drive motors running of the control method of above-mentioned vibration inhibition of the present invention, operate steadily at 1 ~ 60HZ under the empty load of motor situation, Fig. 8 is under the 6K situation for the frequency converter carrier frequency, and empty load of motor operates in the current waveform of 24.70HZ, and the lattice among the figure are represented the 10A electric current.To recently, method of the present invention has fine inhibition effect to vibration from two figure, the unsteadiness when having suppressed this type systematic sky, light running effectively.