CN1177404C - Dead-zone compensation method of frequency converter - Google Patents

Abstract

The present invention discloses a dead zone compensation method for frequency converters, which is characterized in that a composite compensation method of the combination of current feedforward and current feedback of synchronous arrangement in a coordinate system is adopted. Effective compensation is carried out by properly analyzing current space, the instability of traditional feedforward compensation is effectively solved, and the distortion of actual output currents of the frequency converter is reduced. The waveform distortion of output currents is reduced, and the drive characteristic of the frequency converter is enhanced. The method has the advantages of simplicity, practicality, high reliability and stability.

Description

The dead-zone compensation method of frequency converter

The present invention relates to the dead-zone compensation method of frequency converter, relate in particular to and effectively to solve the compound compensation method that conventional feed forward compensates existing instability problem.

Existing typical universal frequency converter system configuration, as shown in Figure 1, this system adopts the VVVF control mode based on an amount of modulation of voltage space, its basic principle is described below: three-phase alternating current is through rectifier bridge rectification and bus capacitor filtering, for the inverter bridge of being made up of IGBT Q1-Q6 provides DC power supply.DSP or MCU controller are by detecting biphase current.The synthetic setting frequency is carried out pulse-width modulation, produces the PWM drive signal of three-phase six pipes, controls each phase upper and lower bridge arm and regulates inverter output voltage in turn, and then regulate the actual input voltage of motor, thereby reach the purpose of variable voltage variable frequency speed governing.

As seen from Figure 1, each phase brachium pontis is two pipe alternate conduction up and down, because the switch of power electronic device needs the time, if do not take measures, a certain arm one side pipe of very possible appearance turn-offs as yet fully, and another side pipe is open-minded, forms so-called " leading directly to " phenomenon.Therefore, in actual applications, be to prevent two pipe conductings simultaneously up and down, both open and cut-off signals between introduce " Dead Time ", two Guan Jun are in the reliable turn-off state in this time.

But, the introducing of " Dead Time ", make and produce error between frequency converter actual output voltage and instruction voltage, form so-called " dead time effect ", as shown in Figure 2: Fig. 2 a be that to generate simplified model, Fig. 2 b be Dead Time in the dead band to actual output pulse width influence, Fig. 2 c dead time effect influences the output average voltage, this effect is particularly evident when the motor low-frequency operation, causes the current of electric distortion, has a strong impact on the drive characteristic of frequency converter.How " dead time effect " effectively compensated, become the key subject that must solve in the high-performance drive system.From present Development Technology, the method for dead area compensation mainly is divided into following two big classes:

1, based on the compensation method of Voltage Feedback, this method is regulated the PWM pulsewidth by comparing the error of frequency converter actual output voltage and setting voltage, reaches the compensation purpose.This method is direct, but to voltage sample and isolate distant high requirement, must do interference, the strong and weak electricity isolation etc. of system carefully be designed during design, the hardware relative complex, so this kind compensation scheme is actually rare at present.

2, based on the compensation method of current feed-forward.This method is by detecting the polarity of frequency converter output current, regulate the PWM pulsewidth, reach the compensation purpose, because current driving control system, how to obey to drive and wait until in the control system, therefore current detecting has become essential important step, under the prerequisite that does not increase hardware cost, has obtained a large amount of application based on the dead-zone compensation method of current feed-forward in Driving Scheme.In principle, as long as can correctly detect three-phase current polarity, adopt the current feed-forward mode to carry out full remuneration to " dead time effect ", Fig. 3 shows conventional current feedforward compensation algorithm structure.

SIGN is a sign function among the figure, and satisfies following condition:

SIGN(X)

Vdead is the error voltage that " dead time effect " introduced, and its size satisfies:

$\mathrm{Vdead}=\frac{\mathrm{Td}}{\mathrm{Tpwn}}\mathrm{Udc}----\left(2\right)$

(2) Td is a Dead Time in the formula, and Tpwm is PWM period of wave, and Udc is a busbar voltage.

Be not difficult to find out that by Fig. 3 conventional feedforward compensation method adopts the method that directly detects each phase current polarity to compensate, its realization is very simple, but has a vital problem when specific implementation, i.e. the accurate detection of frequency converter output current polarity.And very unfortunately, in the PWM drive system, owing to have certain ripple and PWM noise in the actual output current, the influence of the factors such as hysteresis of current filtering introducing in addition, near the current polarity the current over-zero accurately detects very difficult.The polarity of mistake is judged, compensating error voltage not only, make error voltage magnify on the contrary, thereby cause the further deterioration of current waveform, and form so-called " clamp current " (Clamping Current) at zero cross near, make compensation further carry out, make the mis-behave of drive system on the contrary toward wrong direction.Therefore, Chang Gui feedforward current compensation method has bigger limitation in actual applications.

The object of the present invention is to provide a kind of dead-zone compensation method of frequency converter, solve the output error voltage that causes because of Dead Time and carry out real-Time Compensation, thereby significantly reduce the output current wave distortion, improve the drive characteristic of frequency converter.

The objective of the invention is to be achieved through the following technical solutions: a kind of dead-zone compensation method of frequency converter, it is characterized in that, adopt and place the compound compensation method that current feed-forward combines with current feedback under the coordinate system synchronously, by analyzing in right amount between current hollow, effectively compensate, effectively solve the unsteadiness that the conventional feed forward compensation exists, reduce the distortion of frequency converter actual output current.

Dead-zone compensation method according to frequency converter provided by the invention, it is characterized in that, in the VVVF system, adopt space vector voltage modulated method, during steady operation, space vector of voltage is to rotate with leg speed, and its direction of rotation has determined the real-world operation direction of drive motors; Correspondingly, three-phase resultant current space vector also will rotate with identical speed with equidirectional, but fall behind space vector of voltage on phase place.

Dead-zone compensation method according to frequency converter provided by the invention, it is characterized in that, because the reference voltage space vector is all the time with fixing rapid-result synchronously rotation during steady operation, and phase place is controlled fully, therefore if know the size of power-factor angle, just can derive the position angle of reference current space vector fully by the position of space vector of voltage, thereby determine current polarity with reference to three-phase current.

Dead-zone compensation method according to frequency converter provided by the invention is characterized in that, power-factor angle can obtain after the phase angle filtering by actual feedback currents vector in the synchronous rotating frame of space vector of voltage orientation.

Dead-zone compensation method according to frequency converter provided by the invention is characterized in that, the power-factor angle process inertia filtering with calculating can obtain reference current vector position angle, thereby obtain three-phase reference current polarity, and participate in feedforward compensation with this.

Dead-zone compensation method according to frequency converter provided by the invention is characterized in that, by the detection of power-factor angle, the polarity of indirect detection three-phase reference current has reduced the requirement of system to current detection accuracy and speed effectively.

Implement the dead-zone compensation method of frequency converter of the present invention, its advantage is: adopt a kind of improved software algorithm that the output error voltage that causes because of Dead Time is carried out real-Time Compensation, thereby significantly reduce the output current wave distortion, improve the drive characteristic of frequency converter, this algorithm is simple and practical, has higher reliability and stability.

Below in conjunction with drawings and Examples, the present invention is further illustrated, in the accompanying drawing:

Fig. 1 is a universal frequency converter typical case VVVF control system structure principle chart in the prior art;

Fig. 2 is " dead time effect " schematic diagram in the prior art;

Fig. 3 is conventional current feedforward compensation algorithm structure figure in the prior art;

Fig. 4 is a compound dead area compensation algorithm structure block diagram in the technical solution of the present invention;

Fig. 5 is a phase voltage modulating wave of the present invention and concerns oscillogram with current phase;

Fig. 6 is space vector of voltage of the present invention and current space vector phase diagram;

Fig. 7 is the actual measurement compensation after-current oscillogram of the present invention under different service conditionss;

Fig. 8 is the realization flow block diagram of dead area compensation algorithm of the present invention.

As shown in Figure 4, adopt and place the compound compensation method that current feed-forward combines with current feedback under the coordinate system synchronously,, effectively compensate by analyzing in right amount between current hollow, effectively solve the unsteadiness that the conventional feed forward compensation exists, reduce the distortion of frequency converter actual output current.

To be example below, and it be realized doing one set forth with conventional open loop VVVF voltage open form drive system.We have adopted space vector voltage Chinese system of weights method in the VVVF system, and during steady operation, space vector of voltage is with not fast rotation together, and its direction of rotation has determined the actual compensation direction of drive motors; Correspondingly, three-phase resultant current space vector also will rotate with identical speed with equidirectional, but fall behind space vector of voltage on phase place, and Fig. 5 shows the phase relation that a phase voltage PWM involves phase hydraulic pressure electric current.

By last figure as can be seen, reference voltage is ahead of this phase current, and phase difference is a power-factor angle therebetween, can further release thus, and current space vector lags behind space vector of voltage equally, and size also is power factor and angle, as shown in Figure 6.Because the reference voltage space vector is all the time with fixing rapid-result synchronously rotation during steady operation, and phase place is controlled fully, therefore if know the size of power-factor angle, just can derive the position angle of reference current space vector fully by the position of space vector of voltage, thereby determine current polarity with reference to three-phase current.

Can see by Fig. 6, power-factor angle can obtain after the phase angle filtering by actual feedback currents vector in the synchronous rotating frame of space vector of voltage orientation, this rotation with the leg speed coordinate system under, current phasor D-Q component can make things convenient for calculating by following formula:

$\left[\begin{array}{c}{I}_d\\ I_q\end{array}\right]=\left[\begin{array}{c}\sin (2/3\·\mathrm{\π}-\mathrm{\θ})\sin \mathrm{\θ}\\ -\mathrm{Cos}(2/3\·\mathrm{\π}-\mathrm{\θ})\mathrm{Cos\θ}\end{array}\right]\left[\begin{array}{c}{I}_u\\ I_v\end{array}\right]----\left(3\right)$

${\mathrm{\Φ}}_{\mathrm{pf}}=\arctan \frac{I_q}{I_d}----\left(4\right)$

Because system adopts DSP as controller, therefore above computing implements very simple.Power-factor angle process inertia filtering with calculating can obtain reference current vector position angle, thereby obtain three-phase reference current polarity, and participate in feedforward compensation with this.Also can find out thus, this compound dead-zone compensation method comes down to detect by power-factor angle, the polarity of indirect detection three-phase reference current, this based on the compound backoff algorithm under the synchronous coordinate system, reduced the requirement of system to current detection accuracy and speed effectively, a large amount of experiments has also proved this point.

Fig. 7 shows the actual measurement compensation after-current waveform under the different service conditionss, and Fig. 7 a carrier frequency is 10K, the current waveform of f=0.5Hz; Fig. 7 b carrier frequency is 10K, the current waveform of f=1.0Hz; Fig. 7 c carrier frequency is 6K, the current waveform of f=0.2Hz; Fig. 7 d carrier frequency is 6K, the current waveform of f=0.5Hz; Fig. 7 e carrier frequency is 1K, the current waveform of f=0.1Hz; Fig. 7 f carrier frequency is 1K, the current waveform of f=0.2Hz.

By seeing as the figure experimental waveform, motor low-frequency operation electric current has kept good sinusoidal degree, has proved absolutely the validity of this dead band backoff algorithm.

Fig. 8 has provided the realization block diagram that the algorithm Semi-polarity detects, each link effect and signal flow relation is as follows: at first motor U, V biphase current are sampled, and to be tied to the diaxon that the coordinate transformation method under the synchronous rotating frame calculates under the synchronous coordinate system according to static coordinate on this basis be electric current I d, Iq; After calculating Id, Iq, it is carried out low-pass filtering, be easy to calculate the amplitude and the phase place thereof of resultant current vector under the D-Q coordinate system according to Id, Iq value after the filtering; The low-pass filter ripple is carried out at the current phasor phase angle that calculates, can adopt one order inertia filtering commonly used, and with the phase angle of filtered phase angle as the reference current phasor; According to the reference current vector phase angle that obtains, can conveniently release it and specifically be in which sector, and further determine the three-phase current combinations of polarities; After obtaining three-phase polarity, can according to each phase current polarity, on the basis of reference voltage, add or deduct dead zone error voltage, as new reference voltage input instruction according to the method for routine compensation.

Based on the core of the compound backoff algorithm under the synchronous coordinate system be calculate estimation rate factor angle by feedback current under the synchronous coordinate system, thereby further release reference current space resultant vector position angle indirectly by the space vector of voltage angle, and determine three-phase current polarity with this, dead time effect is carried out real-Time Compensation.

Claims (2)

1, a kind of dead-zone compensation method of frequency converter is characterized in that, adopts the compound compensation method that current feed-forward combines with current feedback under the voltage oriented synchronous coordinate system, and the output error voltage that causes because of Dead Time is carried out real-time effective compensation, wherein:

By the coordinate transform of feedback current under the voltage oriented synchronous coordinate system, rated output factor angle specifically may further comprise the steps earlier:

(1) motor U, V biphase current are sampled;

(2) be tied to coordinate transformation method under the synchronous rotating frame according to static coordinate, calculate diaxon electric current I d, Iq under the voltage oriented synchronous coordinate system;

(3) Id, Iq are carried out low-pass filtering;

(4), calculate the amplitude and the phase angle thereof of resultant current vector under the D-Q coordinate system according to filtered Id, Iq value;

(5) with above-mentioned phase angle as power-factor angle;

Release reference current space resultant vector position angle indirectly by the space vector of voltage angle again, determine three-phase current polarity, real-Time Compensation is carried out in the dead band, specifically may further comprise the steps with this:

(6) power-factor angle that calculates is carried out the low-pass filtering of one order inertia filtering;

(7) the voltage vector position angle is deducted the phase angle of filtered power-factor angle as the reference current phasor;

(8) according to the reference current vector phase angle that obtains, release it and specifically be in which sector, and further determine the three-phase current combinations of polarities;

(9), according to the current polarity of each phase in the three-phase, on the basis of reference voltage, add or deduct dead zone error voltage, as new reference voltage input instruction according to conventional feedforward compensation method.

2, according to the dead-zone compensation method of the described frequency converter of claim 1, it is characterized in that, in described (4) step, the amplitude and the phase angle thereof of calculating resultant current vector under the D-Q coordinate system according to following formula:

$\left[\begin{array}{c}\mathrm{Id}\\ \mathrm{Iq}\end{array}\right]=\left[\begin{array}{c}\sin (2/3\·\mathrm{\π}-\mathrm{\θ})\sin \mathrm{\θ}\\ -\mathrm{Cos}(2/3\·\mathrm{\π}-\mathrm{\θ})\mathrm{Cos\θ}\end{array}\right]\left[\begin{array}{c}\mathrm{Iu}\\ \mathrm{Iv}\end{array}\right]---\left(3\right)$

${\mathrm{\Φ}}_{\mathrm{pf}}=\arctan \frac{\mathrm{Iq}}{\mathrm{Id}}----\left(4\right)$

Images