CN107994758B - Space vector modulation method for nine-switch power converter - Google Patents

Abstract

The present invention provides a space vector modulation method for a nine-switch converter. The method includes the steps of determining the hexagon where two reference voltage vectors are located by using the original value of the upper and lower AC terminal reference voltages; the two reference voltage vectors and the hexagon where they are located. The difference between the center vectors of the two reference voltage vectors is converted from the nine-switch converter voltage space vector plane to the six-switch converter voltage vector space plane, the equivalent voltage vector of the six-switch converter is selected, and the effect of the equivalent voltage vector is determined. Time; the six-switch converter voltage vector is mapped to the nine-switch converter voltage vector plane, and the action time of the six-switch converter voltage vector is converted into the nine-switch converter voltage vector action time. The beneficial effect is that the method is easy to understand, simplifies the complexity of the modulation method of the nine-switch converter, and facilitates digital implementation. It is helpful to understand the working mechanism of the nine-switch converter, and has important practical value for the application of the nine-switch converter.

Description

Space vector modulation method for nine-switch power converter

technical field

The invention relates to a voltage space vector modulation method of a nine-switch power converter.

Background technique

With the continuous development of miniaturization, high reliability and low power consumption of power converters, scholars from all over the world have done a lot of work on the improvement of the topology structure of power converters, and achieved a lot of results. The nine-switch converter can realize independent control of two three-phase AC terminals. Compared with the traditional 12-switch back-to-back power converter, the topology structure reduces switching devices and corresponding driving circuits, reduces the volume, and reduces system power consumption. The voltage space vector plane partition of the nine-switch converter is shown in Figure 1.

The nine-switch converter can also have two-way three-phase AC output, which can realize independent control of two-phase AC loads. Its operation mode can be divided into two types: same-frequency operation and different-frequency operation.

The space vector modulation strategy has been widely used in the control of power converters. The space vector modulation strategy can be used to realize the control of different types of power converters. However, the space vector modulation strategies of power converters with different topologies are different. The vector modulation method determines the working state of the switching device through the voltage vectors of the upper and lower AC output terminals, instead of determining the switching state of the switching device by a single voltage vector in the traditional sense. Similarly, the modulation method of the nine-switch converter is also different from that of other power converters.

SUMMARY OF THE INVENTION

Aiming at the working characteristics of the nine-switch converter, the present invention proposes a space vector modulation method and a control system for the nine-switch converter.

In order to realize the control of the nine-switch converter in the same frequency and different frequency working modes, the present invention provides a voltage space vector modulation method for the nine-switch converter, and the method includes the following steps:

①Using the original value of the reference voltage at the upper and lower AC terminals to determine the hexagon where the two reference voltage vectors are located;

② The difference between the two reference voltage vectors and the central voltage vector Vdc/3 of the hexagon where they are located is made respectively, and the two reference voltage vectors are converted from the voltage space vector plane of the nine-switch converter to the voltage vector space plane of the six-switch converter. Select The equivalent voltage vector of the six-switch converter is determined, and the action time of the equivalent voltage vector is determined.

③ Map the voltage vector of the six-switch converter to the voltage vector plane of the nine-switch converter, and convert the action time of the voltage vector of the six-switch converter into the action time of the voltage vector of the nine-switch converter.

The invention has the beneficial effects that the voltage space vector of the nine-switch converter is converted into the voltage space vector of the six-switch converter, the algorithm is easy to understand, the complexity of the modulation method of the nine-switch converter is greatly simplified, and the digital realization is convenient. The method is helpful for understanding the working mechanism of the nine-switch converter, and has important reference value for the modulation of the multi-AC terminal converter, and has important practical value for the application of the nine-switch converter.

Description of drawings

Fig. 1 is the plane division of voltage space vector of nine-switch converter;

Fig. 2 is the equivalent voltage space vector plane when two reference voltage vectors of the present invention are in the same sector;

Fig. 3 is that two reference voltage vectors of the present invention are in the equivalent voltage space vector plane of adjacent sectors;

Fig. 4 is that two reference voltage vectors of the present invention are in the equivalent voltage space vector plane of non-adjacent sectors;

Detailed ways

The voltage space vector modulation method of the nine-switch converter of the present invention will be described with reference to the accompanying drawings. It should be noted here that the description of these embodiments is used to help understand the present invention, but does not constitute a limitation of the present invention.

The voltage space vector modulation method of the nine-switch converter of the present invention includes the following steps:

①Using the original value of the upper and lower reference voltages to determine the hexagon where the two reference voltage vectors are located. Divide the voltage vector space plane of the nine-switch converter into 6 sectors, each sector corresponds to a hexagon, the hexagon contains six voltage vectors, and can be equivalent to the voltage vector of the six-switch converter; At the same time, the sectors in which the two reference voltages are located are determined.

② The difference between the two reference voltage vectors and the center vector of the hexagon where they are located is made respectively, and the two reference voltage vectors are converted from the voltage space vector plane of the nine-switch converter to the voltage vector space plane of the six-switch converter, and the six-switch converter is selected. Equivalent voltage vector, and determine the equivalent voltage vector action time. When the two reference voltage vectors are in the same sector, the length of all voltage vectors in the nine-switch voltage space vector plane is reduced to 1/2 of the original voltage vector length, and the two reference voltage vectors remain unchanged;

Subtract the central voltage vector V _dc /3 in the hexagon where the two reference voltage vectors are located to obtain the voltage vector under the voltage space vector plane of the nine-switch converter converted to the voltage vector under the voltage space vector plane of the six-switch converter ;

When the two reference voltage vectors are in different sectors, the length of all voltage vectors in the nine-switch voltage space vector plane is reduced to 1/4 of the original voltage vector length, and the two reference voltage vectors remain unchanged;

Subtract the central voltage vector V _dc /6 in the hexagon where the two reference voltage vectors are located to obtain the voltage vector under the voltage space vector plane of the nine-switch converter converted to the voltage vector under the voltage space vector plane of the six-switch converter. .

③ Map the voltage vector of the six-switch converter to the voltage vector plane of the nine-switch converter, and convert the action time of the voltage vector of the six-switch converter into the action time of the voltage vector of the nine-switch converter.

The function of the voltage space vector modulation method of the nine-switch converter of the present invention is realized as follows:

In the voltage space vector modulation method of the nine-switch converter of the present invention, the DC bus voltage is set as V _dc in the topology structure of the nine-switch converter, and there are three bridge arms, namely bridge arm A, bridge arm B and bridge arm C. For Any bridge arm has three working states. From this topology of the nine-switch converter, 27 voltage space vectors of the nine-switch converter can be obtained. According to the comparison table of the voltage space vector of the nine-switch converter and the six-switch converter, the voltage vector of the nine-switch converter can be converted into two six-switch converters. The combination of the voltage vector of the device.

1. Divide the voltage space vector plane of the nine-switch converter into 6 sectors, as shown in Figure 1, L1, L2 and L3 divide the voltage space vector plane of the nine-switch converter into 6 sectors, which are: I, II, III, IV, V and VI; each sector corresponds to a hexagon, and the voltage vector corresponding to each hexagon is consistent with the voltage space vector of the six-switch converter. The voltage space vector comparison table of the nine-switch converter and the six-switch converter disclosed in the present invention is shown in the following table.

2. When the two reference voltage vectors are in the same sector, reduce the voltage space vector plane of the nine-switch converter to 1/2 of the original voltage space vector plane, as shown in Figure 2; the two reference voltage vectors V _U ^* and V _L ^* Difference with the voltage vector OO ₁ ′ (V _dc /3), respectively, to obtain the equivalent vectors V _U ^*' and _VL ^*' which are equivalent to the voltage space vector plane of the nine-switch converter to the voltage vector plane of the six-switch converter ; Utilize the voltage space vector modulation method of the six-switch converter to obtain the equivalent synthetic vector of V _U ^*' and V _L ^*' , namely V _U ^*' =T _u2 *V2+T _u3 *V3 and V _L ^*' =T _l1 *V1+T _l2 *V2, wherein V2 and V3 can synthesize V _U ^*' , and the action time is T _u2 and T _u3 respectively; V1 and V2 can synthesize _VL ^*' , and the action time is T _l1 and T respectively _l2 .

Mapping the voltage vector of the six-switch converter to the voltage vector plane of the nine-switch converter, the voltage vector of the nine-switch converter may be V30, V22, V71, V72 or V20. If T _u2 >T _l2 , the corresponding nine-switch converter voltage The vectors are V30, V22, V71, V20, and the corresponding nine-switch converter voltage vector action time is _Tu3 , _Tl2 , _Tl1 , _Tu2 - _Tl2 ; otherwise, the corresponding nine-switch converter voltage vector is V30, V22, V71, V72, and the corresponding nine-switch converter voltage vector action time is _Tu3 , _Tu2 , _Tl1 , _Tl2 - _Tu2 .

When the two reference voltage vectors are in different sectors, the voltage space vector plane of the nine-switch converter is reduced to 1/4 of the original voltage space vector plane, which can be divided into the following two cases:

(1) If the sectors where the two reference voltage vectors are located are adjacent, as shown in FIG. 3 , make the difference between the reference voltage vector V _U ^* and the voltage vector OO ₂ ′ (V _dc /6), and V _L ^* and the voltage The vector OO ₁ ′(V _dc /6) is subtracted to obtain the equivalent vectors V _U ^*' and _VL ^*' which are equivalent to the voltage space vector plane of the nine-switch converter to the voltage vector plane of the six-switch converter; using the six-switch converter The converter voltage space vector modulation method can obtain the equivalent composite vector of V _U ^*' and V _L ^*' , namely V _U ^*' =T _u3 *V3+T _u4 *V4 and V _L ^*' =T _l2 *V2+ _T13 *V3, wherein V3 and V4 can synthesize VU ^*' , and the action time is _Tu3 and _Tu4 respectively; V2 and V3 can synthesize _VL ^*' , and the action time is _T12 and _{T13 respectively} .

Mapping the voltage vector of the six-switch converter to the voltage space vector plane of the nine-switch converter, the voltage vector of the nine-switch converter may be V40, V33, V72, V73 or V30. If T _u3 >T _l3 , the corresponding nine-switch converter The voltage vectors are V40, V33, V72, V30, and the corresponding nine-switch converter voltage vector action time is _Tu4 , _Tl3 , _Tl2 , _Tu3 - _Tl3 ; otherwise, the corresponding nine-switch converter voltage vector is V40 , V33, V72, V73, and the corresponding nine-switch converter voltage vector action time is T _u4 , T _u3 , T _l2 , T _l3 -T _u3 .

(2) If the sectors where the two reference voltage vectors are located are not adjacent, as shown in FIG. 4 , make the difference between the reference voltage vector V _U ^* and the voltage vector OO ₃ ′, and make the difference between _VL ^* and the voltage vector OO ₁ ′ difference, obtain the equivalent vectors V _U ^*' and V _L ^*' which are equivalent to the voltage space vector plane of the nine-switch converter to the voltage vector plane of the six-switch converter; using the six-switch converter voltage space vector modulation method, obtain V _U The equivalent composite vector of ^*' and _VL ^*' , namely V _U ^*' =T _u4 *V4+T _u5 *V5 and _VL ^*' =T _l2 *V2+T _l3 *V3, where V4 and V5 can be composited V _U ^*' , and the action times are T _u4 and T _u5 respectively; V2 and V3 can synthesize _VL ^*' , and the action times are T _l2 and T _l3 respectively. Mapping the voltage vector of the six-switch converter to the voltage vector plane of the nine-switch converter, the voltage vectors of the nine-switch converter are V40, V50, V72, V73, and the corresponding action times of the nine-switch converter voltage vector are _Tu4 , _Tu5 , T _l2 , T _l3 .

3. According to 2, the voltage vector of the nine-switch converter represented by the combination of the two six-switch vectors and the corresponding action time of the nine-switch converter voltage vector are obtained, and the vector selection is carried out according to the vector order formulated according to the principle of the least change state, and the nine-switch converter is converted. The switching state corresponding to each bridge arm of the converter is decoded to finally obtain the driving waveform of the switching device of the nine-switch converter.

Claims (1)

1. a nine-switch converter voltage space vector modulation method, it is characterized in that: this nine-switch converter is used for dragging independent dual loads, and the nine-switch converter voltage space vector plane is divided into 6 sectors, six sectors. Corresponding to a small hexagon respectively, the small hexagon corresponding to each sector contains six voltage vectors, which can be equivalent to the voltage vector of the six-switch converter with constraints; Drag the sector where the two reference voltage vectors of the upper and lower AC terminals of the independent double load are located, and convert the voltage space vector plane of the nine-switch converter into the voltage space vector plane of the three-phase six-switch converter; the specific method is: transform the nine-switch converter into a voltage space vector plane. Convert the sector where the two reference voltage vectors of the upper and lower AC terminals of the independent dual load dragged by the converter are located to the three-phase six-switch converter voltage space vector plane. Select the equivalent voltage vector of the three-phase six-switch converter, and determine the three-phase six-switch converter. The equivalent voltage vector action time under the switching converter space vector; when the two reference voltage vectors are in the same sector, the length of all voltage vectors in the nine-switch voltage space vector plane is reduced to 1/2 of the original voltage vector length, and the two reference voltage vectors are in the same sector. The voltage vector remains unchanged; the central voltage vector Vdc/3 in the hexagon where it is located is respectively subtracted from the two reference voltage vectors, which is 1/3 of the DC bus voltage Vdc, and the voltage under the voltage space vector plane of the nine-switch converter is obtained. The vector is converted to the voltage vector under the voltage space vector plane of the three-phase six-switch converter; when the two reference voltage vectors are in different sectors, the length of all voltage vectors in the nine-switch voltage space vector plane is reduced to 1/the length of the original voltage vector 4. The two reference voltage vectors remain unchanged; the central voltage vector Vdc/6 in the hexagon where they are located is respectively subtracted from the two reference voltage vectors, which is 1/6 of the DC bus voltage Vdc, and the voltage of the nine-switch converter is obtained. The voltage vector under the space vector plane is converted to the voltage vector under the voltage space vector plane of the three-phase six-switch converter; finally, the voltage vector of the three-phase six-switch converter is mapped to the voltage space vector plane of the nine-switch converter, and the three-phase six-switch converter is converted into the voltage space vector plane. The switching converter voltage vector action time is converted into the nine-switch converter voltage vector action time.

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