CN103701333A - Circulating current suppression method for cascade parallel high-voltage frequency converter - Google Patents

Abstract

The invention discloses a circulating current suppression method for a cascade parallel high-voltage frequency converter. The method comprises the following steps of sampling and calculating an actual output voltage value and an actual output current value of each phase; calculating difference values between a given voltage value and the actual voltage values, and performing proportional-integral regulation to obtain current regulating variables of cascade branch circuits; calculating an average value of the actual current value of the cascade branch circuit of each phase, calculating difference values between the average value and the actual current values, and performing proportional-integral regulation to obtain offset regulating variables of modulated waves of x cascade branch circuits; adding the offset regulating variables to sinusoidal modulated waves to generate modulated waves required by the cascade branch circuits respectively; comparing the modulated waves with preset carriers in power units in parallel branch circuits to generate PWM (pulse width modulation) triggering signals of the power units respectively. According to the method, a voltage and current dual-closed loop control mode is adopted for controlling circulating current generated between the parallel cascade branch circuits, so that the aim of balancing the current of the parallel cascade branch circuits is fulfilled, and the circulating current in the parallel cascade branch circuits is eliminated.

Description

A kind of cascade parallel high voltage frequency converter circulation inhibition method

Technical field

The present invention relates to a kind of control method of cascade parallel high voltage frequency converter, especially relate to the control method that a kind of cascade parallel high voltage frequency converter suppresses circulation.

Background technology

In national Eleventh Five-Year Plan, " 12 ", encourage continuously enterprise to carry out under the policy guide of energy-saving and emission-reduction, numerous iron and steel, metallurgical mining, petrochemical industry, generating, cement production enterprise drive and carry out reducing energy consumption the large-size machine in production link.Under this market demand, the frequency inverter capacity limit constantly refreshes to seize vast capacity high voltage converter market in domestic manufacturer.

Traditional high voltage converter generally adopts the topological structure of cascade full bridge unit, adopt the high voltage converter of cascade topological structure in parallel, can improve output voltage grade by increasing power cell progression on the one hand, can improve current flowing ability by increasing a way of cascade in parallel on the other hand.This compares with conventional high-tension frequency converter, in the situation that output voltage grade is identical, the ability of its On current increases along with the increase of cascade branch road number in parallel, improved the space that high voltage converter capacity promotes, when the cascade branch road of a certain parallel connection breaks down, by this branch road of bypass, make high voltage converter can continue normal operation simultaneously, strengthened high voltage converter reliability of operation.Yet the cascade branch road in cascade parallel high voltage frequency converter, due to the difference of circuit parameter, output voltage waveforms, causes having circulation in the cascade branch road between parallel connection.The existence of circulation not only can affect the useful life of device, also can affect the energy-saving efficiency of equipment.

Summary of the invention

The object of this invention is to provide a kind of cascade parallel high voltage frequency converter circulation inhibition method, the method is by the form of the two closed-loop controls of voltage and current, the circulation producing between cascade branch road in parallel is controlled, reach the object of cascade branch current balance in parallel, eliminate the circulation in the cascade branch road between parallel connection.

The present invention adopts following technical scheme: a kind of cascade parallel high voltage frequency converter circulation inhibition method, described cascade parallel high voltage frequency converter comprises frequency converter, master controller and A, B, C three-phase converter module, line voltage access frequency converter primary side, frequency converter secondary side connects respectively A, B, C three-phase converter module, it is that x, cascaseded power cell number are y that way is propped up in the cascade being often in parallel in A, B, C three-phase converter module, the x bar cascade branch road of every phase is in parallel, and master controller is by producing PWM triggering signal to control the work of each power cell inverter circuit; Described circulation inhibition method comprises the following steps:

1) the voltage actual value that sampling, calculating A export mutually and the current actual value of A phase x bar cascade branch road;

2) calculate the difference of A phase voltage set-point and voltage actual value, to step 2) difference calculated carries out the electric current regulated quantity that proportional integral adjusting obtains A phase x bar cascade branch road;

3) calculate the mean value of A phase x bar cascade branch current actual value, calculate again the difference of this mean value and mutually every cascade branch current actual value of A, to step 2) carry out proportional integral adjusting after the difference calculated with step 3) respectively of described electric current regulated quantity, obtain the offset amount of x bar cascade branch road modulating wave;

4) the modulating wave offset amount described in step 3) is added with the mutually preset sinusoidal modulation wave of A respectively, produces the required modulating wave of A phase x bar cascade branch road;

5) modulating wave step 4) being obtained respectively with A mutually the preset carrier wave in each parallel branch internal power unit compare, produce the PWM triggering signal of each power cell;

6) adopt the control procedure mutually identical with A to obtain B, the C PWM triggering signal of each power cell mutually simultaneously.

In step 1), the calculating of voltage actual value and current actual value is to ask for by carrying out the method for discrete Fourier transform calculating first-harmonic effective value after the magnitude of voltage in one-period, current value sampling.

The preset carrier wave in each parallel branch internal power unit described in step 5) is bipolarity triangular carrier, the carrier phase of power cell that is in same one-level in x bar cascade branch road is consistent, and the carrier phase of the power cell of different progression differs 1/2y carrier cycle successively.

Inhibition principle of the present invention can be summarized as follows: first sample, calculate each voltage actual value and current actual value of output mutually; The difference of calculating voltage set-point and voltage actual value, and carry out the electric current regulated quantity that proportional integral adjusting obtains cascade branch road; Calculate the mean value of each phase cascade branch current actual value, then calculate the difference of this mean value and current actual value, then carry out proportional integral adjusting, obtain the offset amount of x bar cascade branch road modulating wave; Offset amount is added with sinusoidal modulation wave respectively, produces the required modulating wave of cascade branch road; Modulating wave is compared with the preset carrier wave in each parallel branch internal power unit respectively, produce the PWM triggering signal of each power cell.

Compared with prior art, cascade parallel high voltage frequency converter circulation inhibition method of the present invention, can obtain following technique effect: be applied in cascade parallel high voltage frequency converter, every phase voltage closed-loop control makes output voltage tracing preset voltage, simultaneously the current closed-loop of each cascade branch road of every phase control balancedly distribute same mutually in the output current of every cascade branch road, controller in each cycle period to voltage, electric current carries out two closed-loop controls, regulate the PWM triggering signal of each power cell, suppress the generation of circulation between cascade branch road in parallel, improved the energy-saving efficiency of high voltage converter.

Accompanying drawing explanation

Below in conjunction with accompanying drawing and specific implementation method, the invention will be further described, in accompanying drawing:

Fig. 1 is embodiment of the present invention cascade parallel high voltage frequency converter topological structure schematic diagram;

Fig. 2 is power cell topological structure schematic diagram;

Fig. 3 is single-phase pair of closed-loop control schematic diagram of cascade parallel high voltage frequency converter;

Fig. 4 is cascade parallel high voltage frequency converter Single-phase SPWM modulation schematic diagram.

Embodiment

Below in conjunction with embodiment and accompanying drawing, the present invention is described in further detail, but embodiments of the present invention are not limited to this.

Embodiment

The present embodiment be take 2 grades of parallel connections, 5 grades of cascade high voltage transformers as example describes, and is also that way x=2 is propped up in cascade, and cascaseded power cell is counted y=5.As Figure 1-4, in 2 grades of parallel connections, 5 grades of cascade high voltage transformer topological structures, primary side is that wye connection, secondary side are triangular form connection, and secondary side is many group windings, and every group of winding output voltage amplitude, phase place are identical.A bit concrete, line voltage access frequency converter primary side, frequency converter secondary side meets respectively power cell A11 to the input of power cell C52.After the output series connection of power cell A11 to A51, formed two ends connect respectively AC reactor to form the first cascade branch road of A phase, and after the output series connection of power cell A12 to A52, formed two ends connect respectively AC reactor to form the second cascade branch road of A phase; The first cascade branch road of A phase and the second cascade branch circuit parallel connection of A phase, as the output A phase of high voltage converter.And the output B phase of high voltage converter, output C phase structure are all mutually the same with A.A, the B of output, C three-phase adopt wye connection, and master controller transmits PWM triggering signal with the work of power ratio control unit by optical fiber, make high voltage converter realize variable voltage variable frequency output.

Wherein, the topological structure of the power cell of A, B, C three-phase is all identical.That is to say, power cell forms by rectifier diode, filter capacitor and H inverter bridge, and its structural representation as shown in Figure 2.Filter capacitor is connected in parallel on after the output of rectifier diode, is connected with H bridge inverter.

The above-mentioned AC reactor being arranged in cascade branch road for absorbing the high order harmonic component composition of high voltage converter output voltage, is used for limiting the impulse current that may occur when electric motor starting.

A kind of cascade parallel high voltage frequency converter circulation inhibition method provided by the invention, specifically comprises the following steps:

1) the voltage actual value u that sampling, calculating A export mutually _aand the current actual value i of A phase the first cascade branch road _a1, the A current actual value i of the second cascade branch road mutually _a2.What voltage actual value and current actual value calculated is the first-harmonic effective value in one-period.

In the voltage actual value described in step 1) and the computational methods of current actual value, be specially:

(1) the sinusoidal sequence value sintable[32 of preset 32 respectively in master controller] and cosine sequences value costable[32], the sinusoidal sequence value sintable[32 of described 32] and cosine sequences value costable[32] just form sinusoidal centrifugal pump and the cosine centrifugal pump of one-period;

(2) in one-period, carry out 32 voltage or current sample, to sampled value saxple[i] by following formula, carry out the effective value validvalue of DFT transformation calculations fundamental voltage or electric current, described formula is,

$\mathrm{validvalue}=\sqrt{{\left[\underset{i=0}{\overset{31}{\mathrm{\Σ}}}\left(\mathrm{sample}\right[i]\×\sin \mathrm{table}[i\left]\right)\right]}^2+{\left[\underset{i=0}{\overset{31}{\mathrm{\Σ}}}\left(\mathrm{sample}\right[i]\×\cos \mathrm{table}[i\left]\right)\right]}^2},(i=\mathrm{0,1},...,31)$

2) calculate A phase voltage set-point u _arefwith voltage actual value u described in step 1) _adifference, this difference is carried out to proportional integral and regulates and to obtain the A electric current regulated quantity of the first cascade branch road, the second cascade branch road (being A 2 cascade branch roads mutually) mutually;

Described voltage given value u _areffor master controller is calculated the corresponding magnitude of voltage of high voltage converter running frequency by preset V/F opisometer.

3) calculation procedure 1) described in the A mean value of the current actual value of the first cascade branch road and the current actual value of the second cascade branch road mutually calculate again this average

value and mutually every cascade branch current actual value i of A _a1, i _a2difference, to step 2) described electric current regulated quantity carries out proportional integral adjusting respectively with after this difference, obtains the A offset amount of the first cascade branch road, the second cascade branch road (being A 2 cascade branch roads mutually) modulating wave mutually.

Step 2) proportional integral and described in step 3) regulates and is calculated as follows:

u(n)=u(n-1)+k _p×[e(n)-e(n-1)]+k _i×e(n),n=1,2,...

U in formula (n), u (n-1) are respectively current proportional and integral controller output variable, a front proportional and integral controller output variable, e (n), e (n-1) are respectively current proportional and integral controller output variable, a front proportional and integral controller input variable, k _p, k _ibe respectively proportionality coefficient, integral coefficient.

4) the modulating wave offset amount described in step 3) is added with the mutually preset sinusoidal modulation wave of A respectively, produces A the first cascade branch road, the required modulating wave of the second cascade branch road (being A 2 cascade branch roads mutually) mutually;

5) modulating wave step 4) being obtained respectively with A mutually the preset carrier wave in each parallel branch internal power unit compare, produce the A PWM triggering signal of each power cell mutually.

The described preset carrier wave of each power cell is bipolarity triangular carrier, and carrier frequency is 800Hz, and the carrier phase of power cell that is in same one-level in 2 cascade branch roads is consistent, and the carrier phase of the power cell of different progression differs 1/10 carrier cycle successively.

6) adopt the control procedure mutually identical with A to obtain B, the C PWM triggering signal of each power cell mutually simultaneously.

The above is described a kind of embodiment of the present invention, but is not limited in the scope of embodiments of x=2 of the invention process, y=5.Any those of ordinary skill in the art, in any modification, replacement and the equivalent variations that do not depart from essence of the present invention and make, all belong in the scope of protection of the invention.

Claims (6)

1. a cascade parallel high voltage frequency converter circulation inhibition method, described cascade parallel high voltage frequency converter comprises frequency converter, master controller and A, B, C three-phase converter module, line voltage access frequency converter primary side, frequency converter secondary side connects respectively A, B, C three-phase converter module, it is that x, cascaseded power cell number are y that way is propped up in the cascade being often in parallel in A, B, C three-phase converter module, the x level cascade branch road of every phase is in parallel, and master controller is by producing PWM triggering signal to control each power cell; It is characterized in that, described circulation inhibition method comprises the following steps:

1) the voltage actual value that sampling, calculating A export mutually and the current actual value of A phase x bar cascade branch road;

2) calculate the difference of A phase voltage set-point and voltage actual value, to step 2) difference calculated carries out the electric current regulated quantity that proportional integral adjusting obtains A phase x bar cascade branch road;

3) calculate the mean value of A phase x bar cascade branch current actual value, calculate again the difference of this mean value and mutually every cascade branch current actual value of A, to step 2) carry out proportional integral adjusting after the difference calculated with step 3) respectively of described electric current regulated quantity, obtain the offset amount of x bar cascade branch road modulating wave;

4) the modulating wave offset amount described in step 3) is added with the mutually preset sinusoidal modulation wave of A respectively, produces the required modulating wave of A phase x bar cascade branch road;

5) modulating wave step 4) being obtained respectively with A mutually the preset carrier wave in each parallel branch internal power unit compare, produce the PWM triggering signal of each power cell;

6) adopt the control procedure mutually identical with A to obtain B, the C PWM triggering signal of each power cell mutually simultaneously.

2. circulation inhibition method according to claim 1, it is characterized in that, in step 1), the calculating of voltage actual value and current actual value is to ask for by carrying out the method for discrete Fourier transform calculating first-harmonic effective value after the magnitude of voltage in one-period, current value sampling.

3. circulation inhibition method according to claim 1, it is characterized in that, the preset carrier wave in each parallel branch internal power unit described in step 5) is bipolarity triangular carrier, the carrier phase of power cell that is in same one-level in x bar cascade branch road is consistent, and the carrier phase of the power cell of different progression differs 1/2y carrier cycle successively.

4. circulation inhibition method according to claim 1, is characterized in that, in the computational methods of the voltage actual value described in step 1) and current actual value, is:

(1) the sinusoidal sequence value sintable[32 of preset 32 respectively in master controller] and cosine sequences value costable[32], the sinusoidal sequence value sintable[32 of described 32] and cosine sequences value costable[32] sinusoidal centrifugal pump and the cosine centrifugal pump of formation one-period;

(2) in one-period, carry out 32 voltage or current sample, to sampled value saxple[i] by following formula, carry out the effective value validvalue that fundamental voltage or electric current are calculated in discrete Fourier transform:

$\mathrm{validvalue}=\sqrt{{\left[\underset{i=0}{\overset{31}{\mathrm{\Σ}}}\left(\mathrm{sample}\right[i]\×\sin \mathrm{table}[i\left]\right)\right]}^2+{\left[\underset{i=0}{\overset{31}{\mathrm{\Σ}}}\left(\mathrm{sample}\right[i]\×\cos \mathrm{table}[i\left]\right)\right]}^2},i=\mathrm{0,1},...,31.$

5. circulation inhibition method according to claim 1, is characterized in that step 2) and step 3) described in proportional integral regulate and to be calculated as follows:

u(n)=u(n-1)+k _p×[e(n)-e(n-1)]+k _i×e(n),n=1,2,...

U in formula (n), u (n-1) are respectively current proportional and integral controller output variable, a front proportional and integral controller output variable, e (n), e (n-1) are respectively current proportional and integral controller output variable, a front proportional and integral controller input variable, k _p, k _ibe respectively proportionality coefficient, integral coefficient.

6. circulation inhibition method according to claim 1, is characterized in that, described x=2, y=5.

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