CN102938615A - Method for controlling five-level frequency converter - Google Patents

Abstract

The invention discloses a method for controlling a five-level frequency converter and belongs to the field of five-level frequency converters. The control method comprises the steps of changing coordinates, determining coordinate values of three vertexes of a triangle, and calculating action time corresponding to three vertexes; determining all different switch states corresponding to each of the vectors; defining an output switch sequence, and achieving different control targets; and generating a control pulse of the frequency converter. The method has the advantages that functions of the five-level frequency converter can be implemented, control methods of the five-level frequency converter can be simplified by the control method, simultaneously, the redundant switch state is used for achieving balance control of a midpoint level, and a new method for controlling a voltage space vector pulse width modulation algorithm of frequency converters of high level numbers is provided.

Description

A kind of five-level converter control method

Technical field

The present invention relates to a kind of five-level converter control method, belong to the five-level converter field.

Background technology

Along with the development of power electronic technology, computer technology and modern control theory, the multi-level frequency conversion device is just becoming one of research direction the most popular in the applications such as power power-supply, motor-driven and electric power system unsteady flow.Multi-level frequency conversion device output level number increases, and is conducive to realize the sine of output voltage waveforms, reduces harmonic component, reduces du/dt and di/dt, thereby has improved system's reliability of operation.

Pulse-width modulation (PWM) control algolithm that realizes the output waveform of transformer sineization is one of core algorithm of frequency convertor system control.PWM algorithm commonly used has particular harmonic null method (SHEPWM), hysteresis current control method (CFPWM), carrier modulation method and space vector of voltage (SVPWM) etc.SVPWM becomes the control algolithm that frequency converter nowadays mainly adopts with advantages such as its higher direct voltage utilance, low switching frequencies.But adopt traditional control algolithm, the SVPWM amount of calculation of many level is difficult to be applied on the multi-level frequency conversion device equipment along with the rapid increase of increasing of level number, and this has also limited the development of multi-level frequency conversion device.

Summary of the invention

Problem for above-mentioned prior art existence, the invention provides a kind of five-level converter control method, this control method can be simplified the five-level converter control method, utilize simultaneously the Redundanter schalter state to realize the balance control of midpoint potential, for realizing that more the control of the Realization of pulse width modulation based on voltage space vector algorithm of the frequency converter of high level number provides a kind of new method.

To achieve these goals, the technical solution used in the present invention is: a kind of five-level converter, comprise three-phase alternating-current supply, AC reactor, five level rectifying devices, five level inverters, motor, voltage sensor, current sensor, AD conversion chip and digital processing unit, three-phase alternating-current supply is connected by the input of AC reactor with five level rectifying devices, the output of five level rectifying devices is connected with five level inverters, five level inverters are connected with motor, motor is connected with current sensor with voltage sensor respectively, and voltage sensor is connected the AD conversion chip and is connected with digital processing unit with current sensor, digital processing unit and five level rectifying devices, five level inverters be connected the AD conversion chip and connect.

Based on above-mentioned frequency converter, the step of its control method is as follows:

(1), space vector is carried out coordinate transform from three traditional phase coordinate systems;

(2), determine the coordinate figure on a place Atria summit according to the value of reference vector terminal point coordinate, namely the coordinate of three basic vector calculates three action times that the summit is corresponding again;

(3), according to determining the three basic vector, determine all different on off states that each vector is corresponding;

(4), the on off state of Sequential output is the output switch sequence in definition sampling period, then whole Redundanter schalter states of three vectors can form some groups of output switch sequences, by selecting different on off sequences, realize different control targets;

(5), according to the action time of calculating gained and selected on off sequence generating the Frequency Converter Control pulse.

The invention has the beneficial effects as follows: this control method only need be passed through simple coordinate transform, determines the coordinate figure on a place Atria summit, calculates three action times that the summit is corresponding again; Determine all different on off states that each vector is corresponding; Definition output switch sequence realizes different control targets; Just can generate the Frequency Converter Control pulse, simplified the control method of existing five-level converter, utilize simultaneously the Redundanter schalter state to realize the balance control of midpoint potential, for realizing that more the control of the Realization of pulse width modulation based on voltage space vector algorithm of the frequency converter of high level number provides a kind of new method.

Description of drawings

Fig. 1 is the control schematic diagram of five-level converter of the present invention;

Fig. 2 is the flow chart of five-level converter control method of the present invention;

Fig. 3 is three kinds of coordinate systems on the plane;

Fig. 4 is five level space vector figure under the imaginary coordinate;

Fig. 5 is the little triangle of a class corresponding to reference voltage vector;

Fig. 6 is another kind of little triangle corresponding to reference voltage vector.

Embodiment

The invention will be further described below in conjunction with accompanying drawing.

As shown in Figure 1, a kind of five-level converter, comprise three-phase alternating-current supply, AC reactor, five level rectifying devices, five level inverters, motor, voltage sensor, current sensor, AD conversion chip and digital processing unit, three-phase alternating-current supply is connected by the input of AC reactor with five level rectifying devices, the output of five level rectifying devices is connected with five level inverters, five level inverters are connected with motor, motor is connected with current sensor with voltage sensor respectively, and voltage sensor is connected the AD conversion chip and is connected with digital processing unit with current sensor, digital processing unit and five level rectifying devices, five level inverters be connected the AD conversion chip and connect.

As shown in Figure 2, the step of the control method of this five-level converter is as follows:

(1), space vector is carried out coordinate transform from three traditional phase coordinate systems;

(2), determine the coordinate figure on a place Atria summit according to the value of reference vector terminal point coordinate, namely the coordinate of three basic vector calculates three action times that the summit is corresponding again;

(3), according to determining the three basic vector, determine all different on off states that each vector is corresponding;

(4), the on off state of Sequential output is the output switch sequence in definition sampling period, then whole Redundanter schalter states of three vectors can form some groups of output switch sequences, by selecting different on off sequences, realize different control targets;

(5), according to the action time of calculating gained and selected on off sequence generating the Frequency Converter Control pulse.

The below is the detailed description to committed step:

(1) principle of coordinate transform: new coordinate system is to be rotated counterclockwise 90 ° at traditional coordinate system to obtain, and postrotational coordinate system Vja, Vjb, Vjc represent, as shown in Figure 3.If use Vja, Vjb, Vjc and Va, Vb, Vc represent respectively the variable under ja-jb-jc and the a-b-c coordinate system, and the transformational relation that then is tied to the new coordinate system of ja-jb-jc from the a-b-c coordinate is

$\left[\begin{array}{c}\mathrm{Vja}\\ \mathrm{Vjb}\\ \mathrm{Vjc}\end{array}\right]=\left[\begin{array}{ccc}0& 1& -1\\ -1& 0& 1\\ 1& -1& 0\end{array}\right]\left[\begin{array}{c}\mathrm{Va}\\ \mathrm{Vb}\\ \mathrm{Vc}\end{array}\right]---\left(1\right);$

Wherein: Va, Vb, Vc are the magnitude of voltage under traditional coordinate system; Vja, Vjb, Vjc are the new value under the new coordinate system after the conversion.

As shown in Figure 4, be that five level space vector figure under the new coordinate are arrived in a coordinate transform.

Through after the new coordinate transform, it will be appreciated that no matter be the resultant vector of judging reference vector in the analysis below, or vector all simplified corresponding action time greatly, and is general to multi-level converter, also reached the purpose that non-zero sequence vector and zero sequence vector are controlled respectively simultaneously.

(2) by new coordinate transform, under the ja-jb-jc coordinate system, determine coordinate and the corresponding action time of resultant vector according to reference vector.In multi-level converter, in order to prevent output voltage too high saltus step is arranged, the nearest three basic vector of general selection and reference vector synthesizes, i.e. little leg-of-mutton three summits, its terminal point place.Within a sampling period, by the three-phase reference voltage level under the new coordinate system is rounded and gets its fractional part, weber equilibrium principle according to Space vector modulation, at first determined the coordinate figure on three summits at place by reference vector terminal point coordinate value, calculate again three action times that the summit is corresponding, i.e. duty ratios.

(3) determine little leg-of-mutton three summits

For the n level converter, little leg-of-mutton three summits of establishing a certain reference vector place are P _A, P _B, P _C, then the little triangle in the three dimensional vector diagram may have equilateral triangle and two kinds of situations of del.As shown in Figure 4, Fig. 5 represents equilateral triangle, Fig. 6 represents del.

The below determines the coordinate on lower three summits of different situations.At first, to reference vector coordinate Vrja, Vrjb, Vrjc rounds, and can get $\left\{\begin{array}{c}\underset{\‾}{V_{\mathrm{rja}}}=\mathrm{floor}\left(V_{\mathrm{rja}}\right)\\ \underset{\‾}{V_{\mathrm{rjb}}}=\mathrm{floor}\left(V_{\mathrm{rjb}}\right)\\ \underset{\‾}{V_{\mathrm{rjc}}}=\mathrm{floor}\left(V_{\mathrm{rjc}}\right)\end{array}\right.---\left(2\right);$

Wherein floor () expression rounds downwards;

If Vrja+Vrjb+Vrjc=1, the Vref terminal point drops in the equilateral triangle so, and an Atria apex coordinate is:

$\left\{\begin{array}{c}{P}_A:(\underset{\‾}{V_{\mathrm{rja}}}+1,\underset{\‾}{V_{\mathrm{rjb}}},\underset{\‾}{V_{\mathrm{rjc}}})\\ P_B:(\underset{\‾}{V_{\mathrm{rja}}},\underset{\‾}{V_{\mathrm{rjb}}}+1,\underset{\‾}{V_{\mathrm{rjc}}})\\ P_C:(\underset{\‾}{V_{\mathrm{rja}}},\underset{\‾}{V_{\mathrm{rjb}}},\underset{\‾}{V_{\mathrm{rjc}}}+1)\end{array}\right.---\left(3\right);$

If Vrja+Vrjb+Vrjc=-2, the Vref terminal point drops in the del so, and an Atria apex coordinate is:

$\left\{\begin{array}{c}{P}_A:(\underset{\‾}{V_{\mathrm{rja}}},\underset{\‾}{V_{\mathrm{rjb}}}+1,\underset{\‾}{V_{\mathrm{rjc}}}+1)\\ P_B:(\underset{\‾}{V_{\mathrm{rja}}}+1,\underset{\‾}{V_{\mathrm{rjb}}},\underset{\‾}{V_{\mathrm{rjc}}}+1)\\ P_C:(\underset{\‾}{V_{\mathrm{rja}}}+1,\underset{\‾}{V_{\mathrm{rjb}}}+1,\underset{\‾}{V_{\mathrm{rjc}}})\end{array}\right.---\left(4\right).$

(4) computed duty cycle

According to the weber equilibrium principle, with the synthetic target vector of vector of an Atria summit representative.If the duty ratio of three vectors is respectively d _PA, d _PB, d _PC, according to the geometrical relationship among Fig. 5, can obtain

d _PA=h _PA

d _PB=h _PB （5）；

d _PC=h _PC

H wherein _PA, h _PB, h _PCThe reference vector terminal point to around the distance on three limits, their value all greater than zero less than 1.Two kinds of situations of corresponding diagram 4 can have

Under the ja-jb-jc coordinate system, only need to be divided into integer and two parts of decimal with reference to the coordinate figure of vector terminal point, integer part is carried out the coordinate that simple calculations can obtain nearest three basic vector; And need hardly computing can directly obtain the action time of three output points to fractional part.

(5) determine whole Redundanter schalter states of basic vector

Be located under the new coordinate system, the coordinate of basic vector is V _s(V _Sia, V _Sib, V _Sic), the output switch state representation that this vector is corresponding is (V _Sa, V _Sb, V _Sc), can be got by formula (1)

$\left\{\begin{array}{c}{V}_{\mathrm{sa}}=V_{\mathrm{sa}}\\ V_{\mathrm{sb}}=V_{\mathrm{sa}}-V_{\mathrm{sjc}}\\ V_{\mathrm{sc}}=V_{\mathrm{sa}}+V_{\mathrm{sjb}}\end{array}\right.---\left(7\right);$

Wherein, V _Sa, V _Sb, V _ScBe integer, and 0≤V _Sa≤ n-1,0≤V _Sb≤ n-1,0≤V _Sc≤ n-1.N is the Maximum Output Level number, can obtain whole Redundanter schalter states corresponding to any basic vector under the new coordinate system by formula (7).

(6) selection of different on off sequences

Select suitable Redundanter schalter state by the impact of calculating different Redundanter schalter state alignment current potentials, thereby reach the purpose of control midpoint potential balance.

(7) control impuls of output frequency converter

Control impuls according to the action time of calculating gained and selected on off sequence generation frequency converter.

Only need through simple coordinate transform, determine the coordinate figure on a place Atria summit, calculate again three action times that the summit is corresponding; Determine all different on off states that each vector is corresponding; Definition output switch sequence realizes different control targets; Just can generate the Frequency Converter Control pulse, simplified the control method of existing five-level converter, utilize simultaneously the Redundanter schalter state to realize the balance control of midpoint potential, for realizing that more the control of the Realization of pulse width modulation based on voltage space vector algorithm of the frequency converter of high level number provides a kind of new method.

Claims (8)

1. a five-level converter control method is characterized in that, the concrete steps of control method are:

(1), space vector is carried out coordinate transform from three traditional phase coordinate systems;

(2), determine the coordinate figure on a place Atria summit according to the value of reference vector terminal point coordinate, namely the coordinate of three basic vector calculates three action times that the summit is corresponding again;

(3), according to determining the three basic vector, determine all different on off states that each vector is corresponding;

(4), the on off state of Sequential output is the output switch sequence in definition sampling period, then whole Redundanter schalter states of three vectors can form some groups of output switch sequences, by selecting different on off sequences, realize different control targets;

(5), according to the action time of calculating gained and selected on off sequence generating the Frequency Converter Control pulse.

2. the control method of a kind of five-level converter according to claim 1 is characterized in that, the coordinate transform in the described step (1), and its rule of conversion is as follows:

New coordinate system is to be rotated counterclockwise 90 ° at traditional coordinate system to obtain, postrotational coordinate system Vja, Vjb, Vjc represents, if use Vja, Vjb, Vjc and Va, Vb, Vc represent respectively the variable under ja-jb-jc and the a-b-c coordinate system, and the transformational relation that then is tied to the new coordinate system of ja-jb-jc from the a-b-c coordinate is:

$\left[\begin{array}{c}\mathrm{Vja}\\ \mathrm{Vjb}\\ \mathrm{Vjc}\end{array}\right]=\left[\begin{array}{ccc}0& 1& -1\\ -1& 0& 1\\ 1& -1& 0\end{array}\right]\left[\begin{array}{c}\mathrm{Va}\\ \mathrm{Vb}\\ \mathrm{Vc}\end{array}\right]---\left(1\right);$

Wherein: Va, Vb, Vc are the magnitude of voltage under traditional coordinate system; Vja, Vjb, Vjc are the new value under the new coordinate system after the conversion.

3. the control method of a kind of five-level converter according to claim 2 is characterized in that, described step (2): by new coordinate transform, under the ja-jb-jc coordinate system, determine coordinate and the corresponding action time of resultant vector according to reference vector; In multi-level converter, in order to prevent output voltage too high saltus step is arranged, the nearest three basic vector of general selection and reference vector synthesizes, i.e. little leg-of-mutton three summits, its terminal point place; Within a sampling period, by the three-phase reference voltage level under the new coordinate system is rounded and gets its fractional part, weber equilibrium principle according to Space vector modulation, at first determined the coordinate figure on three summits at place by reference vector terminal point coordinate value, calculate again three action times that the summit is corresponding, i.e. duty ratios.

4. the control method of a kind of five-level converter according to claim 3 is characterized in that, described definite little leg-of-mutton three summits, and for the n level converter, little leg-of-mutton three summits of establishing a certain reference vector place are P _A, P _B, P _C, then the little triangle in the three dimensional vector diagram may have equilateral triangle and two kinds of situations of del;

The below determines the coordinate on lower three summits of different situations, at first, to reference vector coordinate Vrja, Vrjb, Vrjc rounds, and can get

$\left\{\begin{array}{c}\underset{\‾}{V_{\mathrm{rja}}}=\mathrm{floor}\left(V_{\mathrm{rja}}\right)\\ \underset{\‾}{V_{\mathrm{rjb}}}=\mathrm{floor}\left(V_{\mathrm{rjb}}\right)\\ \underset{\‾}{V_{\mathrm{rjc}}}=\mathrm{floor}\left(V_{\mathrm{rjc}}\right)\end{array}\right.---\left(2\right);$

Wherein floor () expression rounds downwards;

If Vrja+Vrjb+Vrjc=1, the Vref terminal point drops in the equilateral triangle so, and an Atria apex coordinate is:

$\left\{\begin{array}{c}{P}_A:(\underset{\‾}{V_{\mathrm{rja}}}+1,\underset{\‾}{V_{\mathrm{rjb}}},\underset{\‾}{V_{\mathrm{rjc}}})\\ P_B:(\underset{\‾}{V_{\mathrm{rja}}},\underset{\‾}{V_{\mathrm{rjb}}}+1,\underset{\‾}{V_{\mathrm{rjc}}})\\ P_C:(\underset{\‾}{V_{\mathrm{rja}}},\underset{\‾}{V_{\mathrm{rjb}}},\underset{\‾}{V_{\mathrm{rjc}}}+1)\end{array}\right.---\left(3\right);$

If Vrja+Vrjb+Vrjc=-2, the Vref terminal point drops in the del so, and an Atria apex coordinate is:

$\left\{\begin{array}{c}{P}_A:(\underset{\‾}{V_{\mathrm{rja}}},\underset{\‾}{V_{\mathrm{rjb}}}+1,\underset{\‾}{V_{\mathrm{rjc}}}+1)\\ P_B:(\underset{\‾}{V_{\mathrm{rja}}}+1,\underset{\‾}{V_{\mathrm{rjb}}},\underset{\‾}{V_{\mathrm{rjc}}}+1)\\ P_C:(\underset{\‾}{V_{\mathrm{rja}}}+1,\underset{\‾}{V_{\mathrm{rjb}}}+1,\underset{\‾}{V_{\mathrm{rjc}}})\end{array}\right.---\left(4\right).$

5. the control method of a kind of five-level converter according to claim 4 is characterized in that, described computed duty cycle is according to the weber equilibrium principle, and with the synthetic target vector of vector of an Atria summit representative, the duty ratio of establishing three vectors is respectively d _PA, d _PB, d _PC, can obtain:

d _PA=h _PA

d _PB=h _PB （5）；

d _PC=h _PC

H wherein _PA, h _PB, h _PCBe the distance on three limits around the reference vector terminal point arrives, can have

6. the control method of a kind of five-level converter according to claim 5 is characterized in that, the concrete grammar of whole Redundanter schalter states of described definite basic vector is:

Be located under the new coordinate system, the coordinate of basic vector is V _s(V _Sia, V _Sib, V _Sic), the output switch state representation that this vector is corresponding is (V _Sa, V _Sb, V _Sc), can be got by formula (1)

$\left\{\begin{array}{c}{V}_{\mathrm{sa}}=V_{\mathrm{sa}}\\ V_{\mathrm{sb}}=V_{\mathrm{sa}}-V_{\mathrm{sjc}}\\ V_{\mathrm{sc}}=V_{\mathrm{sa}}+V_{\mathrm{sjb}}\end{array}\right.---\left(7\right);$

Wherein, V _Sa, V _Sb, V _ScBe integer, and 0≤V _Sa≤ n-1,0≤V _Sb≤ n-1,0≤V _Sc≤ n-1; N is the Maximum Output Level number, can obtain whole Redundanter schalter states corresponding to any basic vector under the new coordinate system by formula (7).

7. the control method of a kind of five-level converter according to claim 6, it is characterized in that, the selection of described different on off sequences is selected suitable Redundanter schalter state by the impact of calculating different Redundanter schalter state alignment current potentials, thereby reaches the purpose of control midpoint potential balance.

8. five-level converter control method according to claim 7 is characterized in that, the control impuls of described output frequency converter is the control impuls according to the action time of calculating gained and selected on off sequence generation frequency converter.

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