CN103227605A - Control method for preventing overvoltage of high-voltage frequency converter with fan load during speed reduction process - Google Patents

Abstract

The invention discloses a control method for preventing overvoltage of a high-voltage frequency converter with fan load during the speed reduction process. The control method comprises the steps as follows: three-phase current and/or two-phase current are/is sampled; the three-phase current is decomposed into torque current and field current; the detected three-phase current is expressed in a spacial position coordinate system, and the three-phase current is converted to the coordinate system dq that rotates at a synchronous speed, so that current components id and iq on the axle dq are obtained; the state of a motor can be judged based on positive and negative of the iq, the active power that is input to the high-voltage frequency converter by the motor is calculated, and the energy that is input to the high-voltage frequency converter can be calculated according to the active power; and in addition, the energy that is input to the high-voltage frequency converter is compared with the energy that can be borne by cells of the high-voltage frequency converter, the rotational speed is increased when the overvoltage threshold value is reached, and the operation is carried out according to a normal speed reduction curve conversely. The control method has the benefits as follows: shortest and optimal speed reduction time of a system can be ensured, and the danger that a direct current cell side of the high-voltage frequency converter warns about overvoltage fault can also be avoided.

Description

A kind of control method that is used for the anti-overvoltage of high voltage converter band fans load reduction of speed

Technical field

The present invention relates to a kind of control method, relate in particular to a kind of control method that is used for the anti-overvoltage of high voltage converter band fans load reduction of speed.

Background technology

Transform problem of frequency converter ubiquity for fan-type load, in reduction of speed, tend to cause frequency converter unit direct current overvoltage fault exactly, this is because the direct load of high voltage converter is a motor, and the direct load of motor is a blower fan, if and motor is in generating state in the reduction of speed process, be equivalent to motor and exporting energy to the unit, and the unit is the pattern of full-bridge rectification owing to what adopt, energy can only one-way flow, be the unit the power transfer of electrical network to motor, and the energy that can't feed back motor is given electrical network.And for fan-type load, frequent lifting speed is that working condition is required, and each producer has only employing that the mode of deceleration time lengthening is prevented the generation of stop element overvoltage fault now.Also can solve this problem in theory with the mode of feedback, but owing to cost height, technical difficulty apply to greatly and not in the middle of the practical application of high voltage converter.

Summary of the invention

The object of the present invention is to provide a kind of control method that is used for the anti-overvoltage of high voltage converter band fans load reduction of speed, in the reduction of speed process, gather the torque current of motor and do control automatically, thereby prevent fault in the overvoltage of reduction of speed process mesohigh frequency converter generating unit, assurance system and equipment is operation stably normally, solves the shortcoming that prior art exists.

The present invention adopts following technical scheme to realize:

A kind of control method that is used for the anti-overvoltage of high voltage converter band fans load reduction of speed is characterized in that, comprises the steps:

1) three-phase and/or biphase current are sampled;

2) under rotating coordinate system, three-phase current is decomposed into torque current and exciting current;

3) positive and negative according to torque current is detected three-phase current i _A, i _B, i _COn the coordinate system of locus, show, three-phase current is transformed to the coordinate system d that rotates with synchronous speed by three or two conversion and rotation transformation _qOn, thereby obtain d _qCurrent component i on the axle _d, i _q

4) utilize i _qThe positive and negative state of judging motor, and calculate the active power size of motor to high voltage converter input, according to watt level, calculate the energy that is input to high voltage converter;

5) relatively be input to the energy of high voltage converter and the energy that the high voltage converter unit can bear, arrive the overvoltage threshold values, just promote rotating speed, otherwise by normal reduction of speed curve motion.

Further, in step 4): work as i _qWhen negative, calculate active power P _o, work as P _oCalculate this moment motor when negative and be input to the meritorious energy W of high voltage converter _o

In step 5): work as W _oAbsolute value soon reach and set the needed threshold values W of pressure point _gThe time, increase given frequency at once, make the motor speedup, allow it be in motoring condition, make P _oJust be output as.

The useful technique effect that the present invention possesses is: can guarantee the deceleration time of fast optimum of system, also can avoid the danger of high voltage converter direct current cell side newspaper overvoltage fault.

Description of drawings

Fig. 1 is the reduction of speed curve chart of high voltagehigh frequency device.

Fig. 2 is the entire block diagram of vector control.

The three-phase current i that Fig. 3 representation space position coordinates is fastened _A, i _B, i _C

Embodiment

Main thought of the present invention; be to intend adopting a kind of Current Feedback Control to eliminate the danger of this direct current overvoltage; the normal reliable ground operation of assurance equipment; by following description to embodiment; to help public understanding the present invention more; but can't the specific embodiment that the applicant is given be considered as restriction to technical solution of the present invention, any definition to parts or technical characterictic change and/or to overall structure do form but not the conversion of essence all should be considered as the protection range that technical scheme of the present invention limits.

As shown in Figure 1, curve 1 is the reduction of speed curve of high voltage converter, has the reduction of speed curve of a more than slope certainly in the real system, here only with a slope curve, be convenient to analyze, and for the reduction of speed curve of many slopes, can be by that analogy; Curve 1 is that blower fan is from the free reduction of speed curve of rated frequency, as can be seen when high voltage converter according to curve A from the rated frequency reduction of speed, motor is owing to the reason of blower fan reduction of speed curve 1, the initial time motor still is in motoring condition, when high voltage converter according to curve 1 fall-back to the A point, motor speed (being rotation speed of fan) is ω ₁So if disconnect high voltage converter this moment, the free reduction of speed curve of blower fan should be a curve 3 just so, is the equal of curve 1 rotational speed omega ₁Following reduction of speed curve is not difficult to draw drawing a conclusion thus, and when the absolute value of the reduction of speed slope of high voltage converter was lower than the absolute value of the blower fan reduction of speed slope of curve, motor just was in motoring condition so, otherwise then is in the dynamic brake state.So confirmable is that motor will be exported energy towards high voltage converter when the reduction of speed slope of curve absolute value of high voltage converter is higher than the blower fan reduction of speed slope of curve, thereby causes the unit direct current to be pressed with the danger of overvoltage.The direct current overvoltage not only can cause the shutdown of equipment, and regular overvoltage meeting useful life of causing dc bus capacitor.

We know that electric system is when steady operation, and the fundametal compoment of threephase stator electric current shows as DC component in synchronous rotating frame.If three-phase alternating current all is under the situation of perfect sinusoidal, excitation component that then embodies in synchronous rotating frame and torque component all are stable direct currents.No matter motor is in electronic or generating state, and excitation component all is stable, and torque component just has the difference of matter.When motor was in motoring condition, high voltage converter output this moment energy was so torque component is at this moment for just; When motor is in generating state, torque component is for negative.Core part of the present invention utilizes this specific character to control motor exactly, in the hope of find perfect meeting point between the quickest and overvoltage fault.

The technical scheme that is adopted in the present embodiment is:

A kind of control method that is used for the anti-overvoltage of high voltage converter band fans load reduction of speed is characterized in that, comprises the steps:

1) three-phase and/or biphase current are sampled;

2) under rotating coordinate system, three-phase current is decomposed into torque current and exciting current;

3) positive and negative according to torque current is detected three-phase current i _A, i _B, i _COn the coordinate system of locus, show, three-phase current is transformed to the coordinate system d that rotates with synchronous speed by three or two conversion and rotation transformation _qOn, thereby obtain d _qCurrent component i on the axle _d, i _q

4) utilize i _qThe positive and negative state of judging motor, and go out to calculate the active power size of motor to high voltage converter input, according to watt level, calculate the energy that is input to high voltage converter;

5) relatively be input to the energy of high voltage converter and the energy that the high voltage converter unit can bear, arrive the overvoltage threshold values, just promote rotating speed, otherwise by normal reduction of speed curve motion.

Wherein: in step 4): work as i _qWhen negative, calculate active power P _o, work as P _oCalculate this moment motor when negative and be input to the meritorious energy W of high voltage converter _o

In step 5): work as W _oAbsolute value soon reach and set the needed threshold values W of pressure point _gThe time, increase given frequency at once, make the motor speedup, allow it be in motoring condition, make P _oJust be output as.

As shown in Figures 2 and 3, control method of the present invention is to add on the basis of vector control, and main modular is current transformation module and the simulation of given adjuster among Fig. 2, below two modules is specifically described:

Three-phase current can be transformed to the coordinate system d that rotates with synchronous speed by three or two conversion and rotation transformation _qOn, thereby obtain d _qCurrent component i on the axle _d, i _q, be shown below:

$\left\{\begin{array}{c}{i}_{\mathrm{\α}}=\sqrt{\frac{3}{2}}{i}_A\\ i_{\mathrm{\β}}=\frac{\sqrt{2}}{2}{i}_A+\sqrt{2}{i}_B\end{array}\right.---\left(1\right)$

$\left\{\begin{array}{c}{i}_d=i_{\mathrm{\α}}\cos \mathrm{\θ}+i_{\mathrm{\β}}\sin \mathrm{\θ}\\ i_q=-i_{\mathrm{\α}}\sin \mathrm{\θ}+i_{\mathrm{\β}}\cos \mathrm{\θ}\end{array}\right.---\left(2\right)$

Initial value for angle θ can be arbitrarily, as long as its vector control orientation accurately can guarantee the correctness and the reasonability of its Current Decomposition, what adopt here is the angle of rotor flux linkage orientation.

The i that after the current transformation module is finished conversion is gone out _dAnd i _qBe input in the given adjustor module.The module theme of given adjuster is utilized i exactly _qThe positive and negative state of judging motor this moment, by before introduction, work as i _qFor negative the time, motor is in generating state, again by the calculating of power, calculates this moment to the size of motor to the energy of high voltage converter output, more given frequency needs is carried out corresponding adjusting according to this, and concrete control method is as follows.

Derivation of energy formula on the electric capacity is formula (3):

$W=\frac{1}{2}{\mathrm{CU}}^2---\left(3\right)$

C is the appearance value of electric capacity in the formula, and U is the voltage on the electric capacity.Supposition high-tension transformer unit DC side normal voltage value is U now _o, the appearance value is C _o, the pressure point excessively of DC side is U _gSo arriving the pressure point energy needed is formula (4):

$W_g=\frac{1}{2}{C}_o({U_g}^2-{U_o}^2)---\left(4\right)$

Because the problem of motor model is worked as i _qMotor is in generating state when negative, but the active power that see away from the high voltage converter output port this moment is formula (5):

$P=U_d*i_d+U_q*i_q---\left(5\right)$

When meritorious power for negative the time, this moment, just expression had energy to import in high voltage converter.

The concrete method of given adjustor module is exactly to work as i _qWhen negative, through type (5) is calculated active power P _O, work as P _OThrough type (6) calculates this moment motor and is input to the meritorious energy of high voltage converter when negative.

$W_o=P_o*t---\left(6\right)$

Work as W _oAbsolute value soon reach and set the needed threshold values W of pressure point _gThe time, increase given frequency at once, make the motor speedup, allow it be in motoring condition, make P _OJust be output as, the voltage of DC side accumulation this moment can bleed off with meritorious form again.When dc voltage recovers normal value, recover normal reduction of speed curve.

Certainly; the present invention can also have other various embodiments; under the situation that does not deviate from spirit of the present invention and essence thereof; those of ordinary skill in the art can make various corresponding changes and distortion according to the present invention, but these corresponding changes and distortion all should belong to the protection range of the appended claim of the present invention.

Claims (2)

1. a control method that is used for the anti-overvoltage of high voltage converter band fans load reduction of speed is characterized in that, comprises the steps:

1) three-phase and/or biphase current are sampled;

2) under rotating coordinate system, three-phase current is decomposed into torque current and exciting current;

3) positive and negative according to torque current is detected three-phase current i _A, i _B, i _COn the coordinate system of locus, show, three-phase current is transformed to the coordinate system d that rotates with synchronous speed by three or two conversion and rotation transformation _qOn, thereby obtain d _qCurrent component i on the axle _d, i _q

4) utilize i _qThe positive and negative state of judging motor, and calculate the active power size of motor to high voltage converter input, according to watt level, calculate the energy that is input to high voltage converter;

5) relatively be input to the energy of high voltage converter and the energy that the high voltage converter unit can bear, arrive the overvoltage threshold values, just promote rotating speed, otherwise by normal reduction of speed curve motion.

2. the control method that is used for the anti-overvoltage of high voltage converter band fans load reduction of speed according to claim 1 is characterized in that, in step 4): work as i _qWhen negative, calculate active power P _o, work as P _oCalculate this moment motor when negative and be input to the meritorious energy W of high voltage converter _o

In step 5): work as W _oAbsolute value soon reach and set the needed threshold values W of pressure point _gThe time, increase given frequency at once, make the motor speedup, allow it be in motoring condition, make P _oJust be output as.

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