CN103236815B - Method for modulating space vector impulse width of frequency converter - Google Patents

Abstract

The invention provides a method for modulating the space vector impulse width of a frequency converter. The method comprises the following steps of: A, sampling the three-phase current of an electric motor by the frequency converter, and performing coordinate conversion on the current from three phases to two phases; B, calculating a current vector angle according to a current value under a two-phase coordinate system; C, determining a space vector conversion angle through the current vector angle and a power factor angle; and D, generating a modulating signal of the space vector impulse width. The deal zone influence of five-segment type SVPWM (Space Vector Pulse Width Modulation) during the conversion process is balanced through correlation of the power factor angle and the space vector conversion angle, so that the problem of current waveform distortion is solved. The method effectively eliminates the current waveform distortion of the five-segment type SVPWM at the moment of conversion, and has good effect in practical application. The method has novel effectiveness, and is technical innovation of frequency converters during application process.

Description

The method of the space vector pulse width modulation of frequency converter

Technical field

The present invention relates to Frequency Converter Control technical field, specifically, the present invention relates to a kind of method of space vector pulse width modulation of frequency converter.

Background technology

Modulation system most usage space vector pulse width modulation-SVPWM of frequency converter.Wherein, the modulation system of five-part form SVPWM due to its switching loss little, voltage utilization is high, is widely used in frequency convertor system.In the process using five-part form SVPWM modulation, in order to the balance of upper and lower bridge arm, need to insert different zero vectors in same sector, but under such pattern, the impact of Dead Time is different.This impact can cause voltage waveform saltus step distortion, current waveform distortion simultaneously.Although effective compensation can be carried out by dead area compensation to clamper phenomenon at zero point, because dead band impact is in different modes inconsistent, cause the poor effect of dead area compensation.

1: under the prerequisite that the phase place and amplitude that ensure voltage vector are constant, five-part form SVPWM has multiple implementation.

Fig. 1 is the space vector distribution map of a kind of five-part form SVPWM modulation system of the prior art, and for sector 1, sector 1 voltage vector u is made up of 100 and 110 vectors.

The first synthesis model schematic diagram that Fig. 2 is the space vector distribution map shown in Fig. 1.The first synthesis model: in sector 1, failing vector only has 000 vector, and whole sector is made up of PWM ripple below, and failing vector 000 is on the both sides of carrier cycle.

The second synthesis model schematic diagram that Fig. 3 is the space vector distribution map shown in Fig. 1.The second synthesis model: in sector 1, failing vector only has 111 vectors, and whole sector is made up of PWM ripple below, and failing vector 111 is in the centre of carrier cycle.

The third synthesis model schematic diagram that Fig. 4 is the space vector distribution map shown in Fig. 1.The third synthesis model: two kinds of patterns switch mutually, such as in sector 1, switches the synthesis mode of vector at 30 ° of points.This pattern has many good qualities, and not only ensures the switch balance of upper and lower bridge arm, is also convenient to the current sample under single resistance mode, mostly uses this pattern in actual applications.

2: the impact of dead band on different PWM mode is different.

Ideally, as long as ensure amplitude and the phase invariant of voltage vector, when 0 vector is inserting and the form of 0 vector all can not form impact to voltage vector.But in actual applications, in order to prevent the straight-through of upper and lower bridge arm, Dead Time can be inserted in each PWM cycle, and the impact in dead band is distinguishing in different modes.

Fig. 5-1 is a kind of space vector distribution map inserting Dead Time in the SVPWM cycle of the prior art; Fig. 5-2 is the synthesis model schematic diagram after the space vector distribution map insertion Dead Time shown in Fig. 5-1.The impact in what above-mentioned Fig. 5-1 and Fig. 5-2 illustrated is dead band under the PWM mode of insertion 000 vector.

As can be seen from Fig. 5-1 and Fig. 5-2, after inserting Dead Time Td, in a carrier cycle, the amplitude of 100 vectors remains unchanged, and is u1; And the width of 110 vectors decreases time Td, u2 amplitude reduces.Add Td the action time of 0 vector simultaneously.Actual voltage vector is the u3 vector in figure, and amplitude and phase place all can depart from desired value u.

Fig. 6-1 is that another kind of the prior art inserts the space vector distribution map of Dead Time in the SVPWM cycle; Fig. 6-2 is the synthesis model schematic diagram after the space vector distribution map insertion Dead Time shown in Fig. 6-1.The impact in what above-mentioned Fig. 6-1 and Fig. 6-2 illustrated is dead band under the PWM mode of insertion 111 vector.

As can be seen from Fig. 6-1 and Fig. 6-2, after 0 vector of insertion 111, the action time of 100 vectors can broaden the change of Td, u1 amplitude greatly.And the action time of 110 vectors remains unchanged, u2 remains unchanged.The action time of 0 vector is shortened.The voltage vector of final synthesis, as shown in u4 in figure, has obvious difference with the u3 of actual value u and front a kind of PWM mode.

3: current five-part form pattern switches have been put all in a sector.

Switching point $\mathrm{\θ}=\frac{\mathrm{\π}}{6}+(n-1)*\frac{\mathrm{\π}}{3},$ N is sector number.

When switching, the voltage vector of reality from u3 kick to u4, can have larger amplitude of variation, and this amplitude is relevant with Dead Time, can cause voltage current waveform distortion.

Summary of the invention

Technical problem to be solved by this invention is to provide a kind of method of space vector pulse width modulation of frequency converter, can associating by power-factor angle and space vector commuting angle, the impact in balance five-part form SVPWM dead band in handoff procedure, solves current waveform problem of dtmf distortion DTMF.

For solving the problems of the technologies described above, the invention provides a kind of method of space vector pulse width modulation of frequency converter, comprising step:

A. the three-phase current of described frequency converter to a motor is sampled, and described electric current is carried out the coordinate transform from three-phase to two-phase;

B. according to the current value calculating current azimuth under two phase coordinate systems;

C. by described current vector angle and power factor angle, the commuting angle of space vector is determined;

D. span vector pulse width modulating signal.

Alternatively, described frequency converter is sampled by the three-phase current of AD sample mode to described motor in step.

Alternatively, after sampling obtains described three-phase current, the current value under clerk conversion obtains α β coordinate system.

Alternatively, described current vector angle is calculated by following formula in stepb:

${\mathrm{\θ}}_i=\arctan \frac{I_{\mathrm{\β}}}{I_{\mathrm{\α}}}$

Wherein, θ _ifor described current vector angle, I _α, I _βfor the described current value under described α β coordinate system.

Alternatively, be as the criterion with described current vector angle, the commuting angle of described space vector is:

${\mathrm{\θ}}_i=\frac{\mathrm{\π}}{6}+(n-1)*\frac{\mathrm{\π}}{3}$

Wherein, n is sector number.

Alternatively, in whole current cycle, the commuting angle of described space vector is:

${\mathrm{\θ}}_i=\frac{\mathrm{\π}}{6}+(n-1)*\frac{\mathrm{\π}}{3}$

Wherein, θ is described commuting angle, for described power factor angle, n is sector number.

Compared with prior art, the present invention has following characteristics and advantage:

1: according to the change of power-factor angle, capture current vector angle in real time, change the switching time of zero vector flexibly, the impact of dead band saltus step is dropped to minimum;

2: effectively improve current waveform.

In a word, the present invention effectively eliminates the current waveform distortion phenomenon of five-part form SVPWM switching instant, achieves good effect in actual applications.The method has novel effective, is technological innovation in application of frequency converter process.

Accompanying drawing explanation

The above and other features of the present invention, character and advantage become more obvious by passing through below in conjunction with the description of drawings and Examples, wherein:

Fig. 1 is the space vector distribution map of a kind of five-part form SVPWM modulation system of the prior art;

The first synthesis model schematic diagram that Fig. 2 is the space vector distribution map shown in Fig. 1;

The second synthesis model schematic diagram that Fig. 3 is the space vector distribution map shown in Fig. 1;

The third synthesis model schematic diagram that Fig. 4 is the space vector distribution map shown in Fig. 1;

Fig. 5-1 is a kind of space vector distribution map inserting Dead Time in the SVPWM cycle of the prior art;

Fig. 5-2 is the synthesis model schematic diagram after the space vector distribution map insertion Dead Time shown in Fig. 5-1;

Fig. 6-1 is that another kind of the prior art inserts the space vector distribution map of Dead Time in the SVPWM cycle;

Fig. 6-2 is the synthesis model schematic diagram after the space vector distribution map insertion Dead Time shown in Fig. 6-1;

Fig. 7 is the method flow diagram of the space vector pulse width modulation of the frequency converter of one embodiment of the invention;

Fig. 8 is the schematic diagram of the current value of three-phase current under clerk conversion obtains α β coordinate system of one embodiment of the invention;

Fig. 9 is the relation correlation curve figure within the whole cycle between current actual value and current variation value of one embodiment of the invention;

Figure 10 is the schematic diagram of the angle of voltage vector leading current vector when space vector switches of one embodiment of the invention;

Figure 11 is the PWM oscillogram of five-part form SVPWM modulation system in two sectors of one embodiment of the invention;

Figure 12 is a kind of frequency converter bringing onto load current waveform figure when not adjusting commuting angle of the prior art;

Figure 13 is the frequency converter bringing onto load current waveform figure after the adjustment commuting angle of one embodiment of the invention.

Embodiment

Below in conjunction with specific embodiments and the drawings, the invention will be further described; set forth more details in the following description so that fully understand the present invention; but the present invention obviously can implement with multiple this alternate manner described that is different from; those skilled in the art can when doing similar popularization, deduction without prejudice to when intension of the present invention according to practical situations, therefore should with content constraints protection scope of the present invention of this specific embodiment.

Usually, during frequency converter use five-part form space vector, in various modes handoff procedure, the impact in dead band causes voltage current waveform distortion.The present invention is by selecting have clear improvement to current waveform distortion rational switching time.

Fig. 7 is the method flow diagram of the space vector pulse width modulation of the frequency converter of one embodiment of the invention.As shown in Figure 7, this SVPWM method can comprise:

Perform step S701, the three-phase current of frequency converter to motor is sampled, and electric current is carried out the coordinate transform from three-phase to two-phase.

In above-mentioned steps S701, three-phase current feedback is the necessary condition realizing frequency converter control system, after obtaining three-phase current by AD sampling, and the current value under clerk conversion can obtain α β two phase coordinate system.Fig. 8 is the schematic diagram of the current value of three-phase current under clerk conversion obtains α β coordinate system of one embodiment of the invention, and this current value can be written as:

$\left[\begin{array}{c}{I}_{\mathrm{\α}}\\ I_{\mathrm{\β}}\end{array}\right]=\sqrt{\frac{2}{3}}\left[\begin{array}{ccc}1& -\frac{1}{2}& -\frac{1}{2}\\ 0& \frac{\sqrt{3}}{2}& \frac{\sqrt{3}}{2}\end{array}\right]\left[\begin{array}{c}{I}_a\\ I_b\\ I_c\end{array}\right]$

Then, this SVPWM method can comprise:

Perform step S702, according to the Current calculation current vector angle under two phase coordinate systems.

Wherein, the electric current I under α β coordinate system is calculated above _α, I _β, after arc tangent, obtain current vector angle θ under α β coordinate system _i:

${\mathrm{\θ}}_i=\arctan \frac{I_{\mathrm{\β}}}{I_{\mathrm{\α}}}$

Then, this SVPWM method continues to comprise:

Perform step S703, by current vector angle and power factor (PF), determine the commuting angle of space vector.

This step is crucial to this technical problem of solution, in three-phase static coordinate system, according to motor stator voltage formula:

$L\stackrel{\·}{I}+\mathrm{RI}+E=U$

For A phase current:

I=I _m*cosθ _i

This is the sinusoidal representation of current phasor.

$\stackrel{\·}{I}=-I_m*\sin {\mathrm{\θ}}_i$

$\stackrel{\·\·}{I}=-I_m*\cos {\mathrm{\θ}}_i$

Wherein, when voltage suddenlys change in two carrier cycles, ignore the change of back electromotive force E, variable quantity be about-I _m* cos θ _i.When voltage vector u is from u3 kick to u4, the change of electric current can be expressed from the next:

$\mathrm{\ΔI}=\frac{\mathrm{\ΔU}-L*\mathrm{\Δ}\stackrel{\·}{I}}{R}\≈\frac{\mathrm{\ΔU}+L*I_m*\cos {\mathrm{\θ}}_i*\mathrm{\ΔT}}{R}$

In the positive half cycle of electric current, it is △ U on voltage magnitude impact that PWM mode switches the dead band saltus step brought.Work as current vector angle time, △ I amplitude is minimum, for as current vector angle θ _iwhen=0, △ I amplitude maximum, for $\frac{\mathrm{\ΔU}+L*I_m*\mathrm{\ΔT}}{R}.$

In like manner, in electric current negative half period, the affect amplitude of dead band saltus step on voltage vector is △ U.Work as current vector angle time, | △ I| amplitude is minimum, for as current vector angle θ _iduring=π, | △ I| amplitude maximum, for $\frac{\left|\mathrm{\ΔU}\right|+L*I_m*\mathrm{\ΔT}}{R}.$

Therefore, within the whole cycle, the variable quantity of current phasor amplitude can be expressed from the next:

$\left|\mathrm{\ΔI}\right|=\frac{\left|\mathrm{\ΔU}\right|+|L*I_m*\cos {\mathrm{\θ}}_i*\mathrm{\ΔT}|}{R}$

Fig. 9 is the relation correlation curve figure within the whole cycle between current actual value and current variation value of one embodiment of the invention.

Therefore, when space vector switches, need to consider current phasor, avoid, at current phasor peak value place switched voltage vector, switching point being put into the less place of current phasor amplitude as much as possible.Work as θ _i=0, during π, A phase current magnitude is maximum; When time, A phase current magnitude is minimum; When time, B phase current magnitude is maximum; When time, B phase current magnitude is minimum; When time, C phase current magnitude is maximum; When time, C phase current magnitude is minimum.Therefore, be as the criterion with current vector angle, select switching point n is sector number.Due to transducer drive inductive load, power factor is necessarily delayed.The angle of voltage vector leading current vector is power-factor angle be the schematic diagram of the angle of voltage vector leading current vector when space vector switches of one embodiment of the invention as shown in Figure 10.

Within the whole cycle, PWM switching point is by before n is that sector number is revised as: ${\mathrm{\θ}}_i=\frac{\mathrm{\π}}{6}+(n-1)*\frac{\mathrm{\π}}{3},$ N is sector number.

Finally, this SVPWM method comprises:

Perform step S704, span vector pulse width modulation (SVPWM) signal.

After determining voltage vector commuting angle θ, five-part form SVPWM just can switch according to this rule in sector.Figure 11 is the PWM oscillogram of five-part form SVPWM modulation system in two sectors of one embodiment of the invention, and in two sectors, PWM waveform just as shown in figure 11.

Figure 12 is a kind of frequency converter bringing onto load current waveform figure when not adjusting commuting angle of the prior art; Figure 13 is the frequency converter bringing onto load current waveform figure after the adjustment commuting angle of one embodiment of the invention.Visible by contrasting, after space vector modulation mode adjusts, the load-carrying current waveform of frequency converter has clear improvement, and plays very important effect in actual applications.

Compared with prior art, the present invention has following characteristics and advantage:

1: according to the change of power-factor angle, capture current vector angle in real time, change the switching time of zero vector flexibly, the impact of dead band saltus step is dropped to minimum;

2: effectively improve current waveform.

In a word, the present invention effectively eliminates the current waveform distortion phenomenon of five-part form SVPWM switching instant, achieves good effect in actual applications.The method has novel effective, is technological innovation in application of frequency converter process.

Although the present invention with preferred embodiment openly as above, it is not that any those skilled in the art without departing from the spirit and scope of the present invention, can make possible variation and amendment for limiting the present invention.Therefore, every content not departing from technical solution of the present invention, any amendment done above embodiment according to technical spirit of the present invention, equivalent variations and modification, all fall within protection range that the claims in the present invention define.

Claims (2)

1. a method for the space vector pulse width modulation of frequency converter, comprises step:

A. the three-phase current of described frequency converter to a motor is sampled, and after sampling obtains described three-phase current, described three-phase current is carried out clark conversion, realizes the coordinate transform from three-phase to two-phase, obtain the current value under α β coordinate system;

B. according to the described current value calculating current azimuth under two phase coordinate systems;

Described current vector angle is calculated by following formula:

${\mathrm{\θ}}_i=\arctan \frac{I_{\mathrm{\β}}}{I_{\mathrm{\α}}}$

Wherein, θ _ifor described current vector angle, I _α, I _βfor the described current value under described α β coordinate system;

C. by described current vector angle and power factor angle, determine the commuting angle of space vector, described power factor angle is the angle of described space vector voltage vector leading current vector when switching;

Be as the criterion with described current vector angle, the commuting angle without the described space vector before described power factor angle correction is:

${\mathrm{\θ}}_i=\frac{\mathrm{\π}}{6}+(n-1)*\frac{\mathrm{\π}}{3}$

In above formula, n is sector number;

In whole current cycle, after revising, the commuting angle of determined described space vector is:

In above formula, θ is the commuting angle of determined described space vector in this step, for described power factor angle, n is sector number;

D. span vector pulse width modulating signal.

2. method according to claim 1, is characterized in that, described frequency converter is sampled by the three-phase current of AD sample mode to described motor in step.