CN103916037A - Three-level current transformer space vector modulation scheme based on gh coordinate system - Google Patents

Abstract

The invention discloses a three-level current transformer space vector modulation scheme based on a gh coordinate system and belongs to a three-level current transformer pulse width modulation scheme. According to the modulation scheme, first, three-phase reference voltages v<a>, v<b> and v<c> are transformed into the gh coordinate system, and the intermediate variables s, q and w are calculated through the components of reference voltage vectors on the g axis and the h axis; second, through the intermediate variables s, q and w, a large area where the reference vectors are located is determined, and coordinate correction is performed on the reference vectors; third, the intermediate variables x, y and z are calculated through the corrected coordinates, and a triangular area where the reference vectors are located is judged; fourth, the base vectors of the reference vectors and the acting time of the base vectors are determined according to the judgment results in the second step and the third step; fifth, according to the results, a switching device of a current transformer is switched, so that the output voltage of the three-level current transformer is equivalent to the reference voltage. The modulation scheme is logical and clear in achievement process, easy to achieve, high in calculation precision and small in calculation workload.

Description

Three-level current transformer space vector modulation scheme based on gh coordinate system

Technical field

The present invention relates to a kind of three-level current transformer space vector modulation scheme, particularly a kind of three-level current transformer space vector modulation scheme based on gh coordinate system.

Background technology

In existing method for controlling three-phase converter, SVPWM (SVPWM) technology has higher direct voltage utilance with respect to SPWM modulation technique, and the waveform quality producing is high, harmonic content is few, be convenient to the advantages such as digital signal processor control in real time, is used widely.

Be applied to the SVPWM method of three-level current transformer because on off state is many, modulated process complexity.Tradition three level SVPWM methods are first by reference to voltage vector V _refcoordinate relation under α β coordinate system obtains V through twice decision process _refresiding position on α β plane, by with V _refthree adjoining base vector synthesized reference voltage vectors, base vector action time according to weber equilibrium principle obtain.Tradition three level SVPWM methods are judged in the process of reference vector positions that amount of calculation is large and are related to radical sign computing, the accuracy that impact is calculated; While calculating base vector action time, computational process is loaded down with trivial details, the real-time that impact is controlled.

Summary of the invention

The object of this invention is to provide a kind of three-level current transformer space vector modulation scheme based on gh coordinate system, solve Traditional Space modulator approach amount of calculation large, computational efficiency is low, affects the problem of realtime control.

For achieving the above object, this scheme is achieved through the following technical solutions:

Step 1, establish three-level current transformer a, b, c three-phase reference voltage is respectively v _a, v _b, v _c, convert it in gh coordinate system, obtain reference voltage vector coordinate (v _g, v _h), by v _g, v _hcarry out linear operation, obtain intermediate variable s, q, w;

Step 2, by intermediate variable s, q, w, judge large region, reference voltage vector place, and according to result of determination, the coordinate of reference voltage vector revised, obtain revising rear coordinate (v _g', v _h');

Step 3, to v _g', v _h' carry out linear operation and obtain intermediate variable x, y, z, judge the little delta-shaped region in reference voltage vector place by x, y, z;

Step 4, according to the judged result of step 3 and DC voltage V _dc, two basic vector V that computing reference voltage vector is adjacent ₂, V ₃t action time ₂, t ₃;

Step 5, the above result of basis, switch converter switches device, makes three-level current transformer output voltage and reference voltage equivalence;

In described step 1, three-phase reference voltage is transformed to gh coordinate system, through type:

$\left[\begin{array}{c}{v}_g\\ v_h\end{array}\right]=\frac{2}{3}\left[\begin{array}{ccc}1& -1& 0\\ 0& 1& -1\end{array}\right]\left[\begin{array}{c}{v}_a\\ v_b\\ v_c\end{array}\right]$

Obtain the coordinate of reference voltage vector in gh coordinate system;

To v _g, v _hcarry out linear operation, through type:

$\left\{\begin{array}{c}s(v_g,v_h)=v_g-v_h\\ q(v_g,v_h)=v_g+{2v}_h\\ w(v_g,v_h)=v_g+v_h/2\end{array}\right.$

Obtain s, q, tri-intermediate variables of w;

In step 2, reference voltage vector coordinate is revised, by showing:

Large region	v g′	v h'
			Ⅰ	v g-V dc/3	v h
Ⅱ	v g	v h-V dc/3
			Ⅲ	v g+V dc/3	v h-V dc/3
Ⅳ	v g+V dc/3	v h
			Ⅴ	v g	v h+V dc/3
Ⅵ	v g-V dc/3	v h+V dc/3

Obtain revising the coordinate of rear reference voltage vector, wherein, V _dcfor DC voltage;

In step 3, to v _g', v _h' carry out linear operation, through type:

$\left\{\begin{array}{c}x(v_g,v_h)={{3v}_g}^{\&prime;}\\ y(v_g,v_h)={{3v}_h}^{\&prime;}\\ z(v_g,v_h)=3({v_g}^{\&prime;}+{v_h}^{\&prime;})\end{array}\right.$

Obtain three intermediate variables of x, y, z;

Take reference voltage vector in large region I, little triangle 1 as example, in described step 4, through type:

$\left\{\begin{array}{c}{t}_2=\frac{x}{V_{\mathrm{dc}}}{T}_s\\ t_3=\frac{y}{V_{\mathrm{dc}}}{T}_s\end{array}\right.$

Obtain t action time of two basic voltage vectors adjacent with reference voltage vector ₂, t ₃, wherein, T _sfor switch periods.

Beneficial effect: owing to taking such scheme, reference vector revised coordinate in gh coordinate system is carried out to linear transformation and ask for intermediate variable, judge reference vector region according to the feature of intermediate variable, directly select intermediate variable as base vector action time.Modulator approach step is clear, realizes simply, has solved the problem that traditional SVPWM method operand is large, process is complicated, has reached object of the present invention.

Advantage is embodied in:

1, the method realizes based on gh coordinate system, and base vector coordinate is integer, and the acquisition process of intermediate variable does not exist radical sign computing, has improved computing accuracy, has reduced the complexity of arithmetical operation;

2, the method can judge reference vector position fast, and reference vector makeover process is simple, explicit physical meaning;

3, the action time of adjacent base vector can be directly selected from intermediate variable, save the computational process of action time, reduced amount of calculation.

Accompanying drawing explanation

Fig. 1 is diode clamping tri-level converter circuit schematic diagram;

Fig. 2 is diode clamping tri-level current transformer space vector of voltage distribution map;

Fig. 3 is the large regional determination figure in reference vector place;

Fig. 4 is Delta Region, reference vector place process decision chart;

Fig. 5 be reference voltage while being three phase sine three-level current transformer output three-phase phase voltage through filtered waveform.

Embodiment

Further illustrate the present invention below in conjunction with the drawings and specific embodiments.

Fig. 1 is diode clamp (NPC) three-level current transformer circuit theory diagrams, and this circuit is divided into three level with the electric capacity of two series connection by DC bus-bar voltage.Each brachium pontis in it is connected with four switching devices, and with pair of series clamping diode and the parallel connection of inner switch pipe, its centre cap is connected with the 3rd level, realizes neutral point clamp.Current transformer has 27 kinds of on off states, and wherein 24 is non-zero vector, and 3 is zero vector.

Fig. 2 is the distribution map of three-level current transformer voltage vector in gh coordinate system.

As shown in Figure 3 and Figure 4, the three-level current transformer space vector modulation scheme based on gh coordinate system, step is as follows:

In step 1, Fig. 1, set three-phase in three-level current transformer a, b, c three-phase and be respectively v with reference to phase voltage _a, v _b, v _c, switch periods is set as T _s, DC side is that voltage is V _dc, according to three-phase reference voltage, pass through formula:

$\left[\begin{array}{c}{v}_g\\ v_h\end{array}\right]=\frac{2}{3}\left[\begin{array}{ccc}1& -1& 0\\ 0& 1& -1\end{array}\right]\left[\begin{array}{c}{v}_a\\ v_b\\ v_c\end{array}\right]---\left(1\right)$

To gh coordinate system, obtain reference vector coordinate (v with reference to vector _g, v _h).

In Fig. 3, pass through formula:

$\left\{\begin{array}{c}s(v_g,v_h)=v_g-v_h\\ q(v_g,v_h)=v_g+{2v}_h\\ w(v_g,v_h)=v_g+v_h/2\end{array}\right.---\left(2\right)$

To v _g, v _hcarry out linear transformation, obtain intermediate variable s, q, w.

Step 2, judge large region, reference vector place according to intermediate variable s, q, w, decision procedure as shown in Figure 3.According to result of determination, reference vector is carried out to coordinate modification, its correcting mode is as shown in table 1.

Table 1 reference vector coordinate modification mode

Large region	v g′	v h'
			Ⅰ	v g-V dc/3	v h
Ⅱ	v g	v h-V dc/3
			Ⅲ	v g+V dc/3	v h-V dc/3
Ⅳ	v g+V dc/3	v h
			Ⅴ	v g	v h+V dc/3
Ⅵ	v g-V dc/3	v h+V dc/3

Step 3, according to the revised coordinate (v of reference vector _g', v _h'), pass through formula:

$\left\{\begin{array}{c}x(v_g,v_h)={{3v}_g}^{\&prime;}\\ y(v_g,v_h)={{3v}_h}^{\&prime;}\\ z(v_g,v_h)=3({v_g}^{\&prime;}+{v_h}^{\&prime;})\end{array}---\left(3\right)\right.$

Obtain intermediate variable x, y, z.And judge Delta Region, reference vector place according to the characteristic of x, y, z, decision procedure is as shown in Figure 4.

Step 4, according to the result of determination of step 2 and step 3, determine the base vector of synthesized reference vector, and when synthesized reference vector, base vector action time can be by intermediate variable direct representation.If the base vector of synthesized reference vector is respectively V ₁, V ₂, V ₃, be respectively t its action time ₁, t ₂, t ₃, adjacent base vector action time when having provided reference vector in table 2 and being arranged in ⅠNei Delta Region, large region, wherein, each brachium pontis represents V with on off state 2 _x1, V _x2conducting, V _x3, V _x4turn-off; On off state 1 represents V _x2, V _x3conducting, V _x1, V _x4turn-off; On off state 0 represents V _x3, V _x4conducting, V _x1, V _x2turn-off (wherein, x=a, b, c).

When reference vector is positioned at the Delta Region in other large region, the expression formula of base vector action time is identical with expression formula action time of corresponding Delta Region in table 2.Can, by intermediate variable direct representation, reduce operand the action time of the adjacent base vector of reference vector, is also one of innovative point of the present invention.

Base vector action time when table 2 reference vector is arranged in ⅠNei Delta Region, large region

Step 5, employing symmetric modulation method, can draw the switching time of power device, Fig. 5 is that three-phase output phase voltage is through the filtered waveform of 600Hz low pass filter, as seen from the figure, switch combination makes three-level current transformer output voltage and reference voltage equivalence, thereby has verified correctness of the present invention and validity.

Claims (1)

1. the space vector modulation scheme based on gh coordinate system three-level current transformer, is characterized in that:

Step 1, establish three-level current transformer a, b, c three-phase reference voltage is respectively v _a, v _b, v _c, convert it in gh coordinate system, obtain reference voltage vector coordinate (v _g, v _h), by v _g, v _hcarry out linear operation, obtain intermediate variable s, q, w;

Step 2, by intermediate variable s, q, w, judge large region, reference voltage vector place, and according to result of determination, the coordinate of reference voltage vector revised, obtain revising rear coordinate (v _g', v _h');

Step 3, to v _g', v _h' carry out linear operation and obtain intermediate variable x, y, z, judge the little delta-shaped region in reference voltage vector place by x, y, z;

Step 4, according to the judged result of step 3 and DC voltage V _dc, two basic vector V that computing reference voltage vector is adjacent ₂, V ₃t action time ₂, t ₃;

Step 5, the above result of basis, switch converter switches device, makes three-level current transformer output voltage and reference voltage equivalence;

In described step 1, three-phase reference voltage is transformed to gh coordinate system, through type:

$\left[\begin{array}{c}{v}_g\\ v_h\end{array}\right]=\frac{2}{3}\left[\begin{array}{ccc}1& -1& 0\\ 0& 1& -1\end{array}\right]\left[\begin{array}{c}{v}_a\\ v_b\\ v_c\end{array}\right]$

Obtain the coordinate of reference voltage vector in gh coordinate system;

To v _g, v _hcarry out linear operation, through type:

$\left\{\begin{array}{c}s(v_g,v_h)=v_g-v_h\\ q(v_g,v_h)=v_g+{2v}_h\\ w(v_g,v_h)=v_g+v_h/2\end{array}\right.$

Obtain s, q, tri-intermediate variables of w;

In step 2, reference voltage vector coordinate is revised, by showing:

Large region v _g′ v _h' Ⅰ v _g-V _dc/3 v _h Ⅱ v _g v _h-V _dc/3 Ⅲ v _g+V _dc/3 v _h-V _dc/3 Ⅳ v _g+V _dc/3 v _h Ⅴ v _g v _h+V _dc/3 Ⅵ v _g-V _dc/3 v _h+V _dc/3

Obtain revising the coordinate of rear reference voltage vector, wherein, V _dcfor DC voltage;

In step 3, to v _g', v _h' carry out linear operation, through type:

$\left\{\begin{array}{c}x(v_g,v_h)={{3v}_g}^{\&prime;}\\ y(v_g,v_h)={{3v}_h}^{\&prime;}\\ z(v_g,v_h)=3({v_g}^{\&prime;}+{v_h}^{\&prime;})\end{array}\right.$

Obtain three intermediate variables of x, y, z;

Take reference voltage vector in large region I, little triangle 1 as example, in described step 4, through type:

$\left\{\begin{array}{c}{t}_2=\frac{x}{V_{\mathrm{dc}}}{T}_s\\ t_3=\frac{y}{V_{\mathrm{dc}}}{T}_s\end{array}\right.$

Obtain t action time of two basic voltage vectors adjacent with reference voltage vector ₂, t ₃, wherein, T _sfor switch periods.