CN113037110B - Five-level inverter midpoint voltage control method - Google Patents
Five-level inverter midpoint voltage control method Download PDFInfo
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- CN113037110B CN113037110B CN202110210594.9A CN202110210594A CN113037110B CN 113037110 B CN113037110 B CN 113037110B CN 202110210594 A CN202110210594 A CN 202110210594A CN 113037110 B CN113037110 B CN 113037110B
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/483—Converters with outputs that each can have more than two voltages levels
- H02M7/487—Neutral point clamped inverters
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Abstract
The invention provides a method for controlling the midpoint voltage of a five-level inverter, which carries out virtual synthesis on vectors influencing the midpoint voltage balance again to obtain a virtual vectorNewly defining partial cells, and effectively solving the problem of vector V through the redundancy characteristic of the vector (20‑2) Generating a midpoint current i b The problem that the midpoint voltage balance control cannot be realized in partial cells is caused, and the midpoint voltage balance control of the whole region of the space vector diagram is realized. The method solves the problem that the traditional space vector modulation strategy of the ANPC five-level converter has an area in which the midpoint voltage cannot be balanced and controlled, and virtually synthesizes vectors in partial areas in the traditional space vector diagram, so that the midpoint voltage balance control is realized.
Description
Technical Field
The invention relates to the technical field of converter voltage control, in particular to the field of five-level inverters, and specifically relates to a midpoint voltage control method of an ANPC five-level inverter.
Background
In 2005, an Active Neutral Point Clamped (ANPC) multilevel topology was first proposed, which can overcome the disadvantage of loss imbalance of the conventional diode-clamped topology. The ANPC five-level converter has the advantages of smaller stress of a switching device and less harmonic content of output current, and is widely concerned in the field of high-voltage frequency conversion and new energy conversion. The balance of the midpoint voltage of the ANPC five-level converter is a necessary condition for stable operation of the whole converter system, and the space vector modulation has the advantages of good output current waveform, high direct-current side voltage utilization rate and the like, so that the research on the balance control of the midpoint voltage under the space vector modulation has important significance.
The five-level space vector diagram one has 125 basic vectors, and some vectors also have redundant states, so the five-level SVPWM control strategy is more complex compared with the three-level SVPWM control strategy. The national scholars Han dazzling et al put forward a three-level-based five-level simplification algorithm in patent books, which considers a five-level space vector diagram as 6 three-level vector diagrams, divides three-level sectors, and achieves the control effect of five levels according to the calculation and distribution of the action time of basic vectors. The control strategy is intuitive and effective, the details of an original five-level space vector are retained, the stability is good, but the problem of partial three-level space vector modulation is brought into the five-level space vector modulation, the studied object of the patent is a diode clamping type five-level inverter, the application field of topology is narrow, and the increase of neutral points caused by the increase of direct-current bus capacitance can possibly influence the proposed simplified control strategy.
In the prior art of neutral point voltage control of the ANPC five-level inverter, a domestic scholars perform balance control by injecting zero-sequence current, but the method can effectively balance neutral point voltage only under specific power factor and proper modulation degree. The domestic scholars of Thankage propose a midpoint potential balance control strategy based on a virtual space vector, and introduce a regulating factor to solve the midpoint voltage balance problem of a three-level converter, and some scholars also propose a similar dynamic regulating factor to control the midpoint voltage of an ANPC five-level inverter, but the methods not only increase the complexity of the control strategy, but also the problem of the midpoint current generated by a basic vector is not fundamentally solved.
Fig. 1 is a three-phase ANPC five-level converter topology, the switching states of which are shown in table 1. The topology has five levels of +2E, + E, 0, -E and-2E, and the levels of +/-E and 0 respectively have a redundant switch state, so that the five-level converter ANPC has 8 switch states, the load current direction in fig. 1 is taken as a positive direction, table 1 lists the influence of various switch states ON the midpoint voltage, and it can be seen that 4 switch states (N1N, ON, OP and P1N) influencing the midpoint voltage exist, and the 2E and-2E level states cannot influence the midpoint voltage.
TABLE 1 ANPC five-level switch State Table
As can be seen from table 1, the E, 0 and-E states output by the ANPC five-level converter correspond to two redundant switch states respectively, where the P1P and N1P switch states have no influence ON the midpoint voltage, and the switch states having influence ON the midpoint voltage have four kinds, and the current paths thereof are P1N, OP, ON and N1N, respectively, as shown in fig. 2. The current paths for these four switching states are specifically analyzed below.
The current path diagram shown in fig. 2: fig. 2 (a) is a current path diagram of the P1N switching state, in which the current flows through the switching tubes S3, S6, and S7 in the P1N operating mode, and the current flows through the neutral point, thereby affecting the neutral voltage. When the current direction is positive, the capacitor C1 on the upper side of the direct current is charged, and the capacitor C2 is discharged; when the current direction is negative, the capacitor C1 on the upper side of the direct current discharges, and the capacitor C2 charges; fig. 2 (b) is a current path diagram in the OP switch state, in which the output voltage level is 0, and the current only passes through the neutral point, so that the current only affects the neutral point voltage, and the effect of the direction of the current on the neutral point voltage is the same as that in the P1N state; similarly, the influence ON the midpoint voltage in the N1N, ON state is the same as in the P1N state.
A traditional neutral point voltage control strategy of the ANPC five-level converter is to realize neutral point voltage balance control by researching neutral point currents generated by space vectors in different switching states. FIG. 3 is a five-level space vector diagram, in which 2, 1, 0, -1 and-2 represent +2E, + E, 0, -E and-2E levels, respectively.
In the traditional ANPC five-level midpoint voltage control, some vectors not only have one or more redundant vectors, but also have different influences on the midpoint voltage under different switching states of each phase, so that different switching sequences can be combined to complete the balance control on the midpoint voltage. In the following, the a large area is taken as an example, the principle of other large areas is similar, and table 2 shows the influence of different switches of partial cell vectors on the midpoint voltage.
TABLE 2 mid-point currents for different switch combinations
By redundant vector V (21-1) 、V (10-2) For example, the load current is assumed to be positive. When vector V (21-1) When in use: b. when the phases c respectively adopt a P1P/N1N switching state, the generated midpoint current is i c (ii) a When the phases b and c respectively select a P1P/N1P switch state, the generated midpoint current is 0; when vector V (10-2) When in use: when the phase a selects the P1P (including P1P/N1N and P1P/N1P) switch state, the generated midpoint current is i b (ii) a When the switch state of the phase a is selected to be P1N (including P1N/N1N and P1N/N1P), the generated midpoint current is-i c . After the above analysis, when the vector V is (21-1) The P1P/N1N switch state is selected (the generated midpoint current is i) c ) Vector V (10-2) Selecting the P1N switch state (producing a midpoint current of-i) c ) Assuming that the current in a switching period is constant, C is the capacitance value of the upper and lower direct current buses, the action time of two vectors is t, and when V is in a switching period (21-1) And V (10-2) The acting time of the vector redundancy switch is the same, and the variation delta U of the midpoint voltage is the same np Comprises the following steps:
from the above equation, it can be seen that some cells can perform balancing control on the midpoint voltage through their own redundancy vectors.
While vectors in other cells do not have redundant vectors, e.g. vector V in cell A10 in FIG. 3 (b) (2-1-2) The midpoint current cannot be eliminated by the redundancy vector, but the vector itself has a different switching state, vector V when N1P (including P1P/N1P and P1N/N1P) states are selected (2-1-2) The generated midpoint current is 0, so that the influence on the midpoint voltage can be eliminated. But in the A large region, vector V (20-2) The midpoint current generated in each switching state combination is i b And the vector V, the vector without redundancy and the redundancy state are mutually adjusted to realize the midpoint voltage balance control (20-2) Midpoint voltage offset generated in the PWM switching sequence of the a12, a13, a14 regions:
wherein t1 is V (20-2) Time of action, hence the prior art vector V (20-2) The generated midpoint current cannot be eliminated, the midpoint voltage in the cells A12, A13 and A14 cannot realize balance control, and other large areas are similar.
The prior art has the following disadvantages: within the large region of the space vector diagram A, the vector V (20-2) The generated midpoint current is i b And the vector has no redundant vector and redundant state to eliminate the midpoint current, so that the midpoint voltage balance control can not be realized in the areas A12, A13 and A14, and the other large areas are similar.
Disclosure of Invention
The technical problems to be solved by the invention are as follows: in order to solve the problem that a traditional space vector modulation strategy of a five-level converter has a region in which neutral point voltage cannot be controlled in a balanced mode, a novel space vector modulation method is provided, vectors in partial regions in a traditional space vector diagram are subjected to virtual synthesis, and therefore neutral point voltage balance control is achieved.
The technical scheme adopted by the invention is as follows: a method for controlling the midpoint voltage of a five-level inverter comprises the following steps: in the A large area, the current generating the midpoint is selected to be i a Vector V of (1-1-2) And generating a midpoint current of i c Vector V of (21-1) And vector V (20-2) Performing virtual synthesis to solve the vector V (20-2) Generated midpoint current i b The problem that the midpoint voltage balance cannot be performed in the regions A12, A13 and A14, vector V (20-2) The generated midpoint current is i b So that the selected midpoint current is generated as i a Vector V of (1-1-2) And generating a midpoint current of i c Vector V of (21-1) And V (20-2) Participating in synthesizing a virtual vector;
let a virtual space vector V VSM By vector V (1-1-2) 、V (21-1) Sum vector V (20-2) Synthesizing according to the formula (3),
then V VSM The resulting midpoint current is:
therefore, the virtual vector V when the sum of the output three-phase currents is zero VSM The synthesis of the virtual space vector enables the original three cells A12, A13 and A14 to be divided into new four cells without influencing the midpoint voltage.
Virtual vector V VSM Dividing the previous three cells into four cells A12, A13, A14 and A15, and adopting a virtual space vector V when the reference vector is positioned in a new cell VSM And two adjacent basic vectors, the vector used in the A14 region being V (1-1-2) 、V (21-1) 、V (20-2) 、V (21-2) And V (2-1-2) When the method is used in the new synthesis area, the factor V is avoided (20-2) Vector-generated non-cancelled midpoint current i b In this case, the control of the midpoint voltage in each cell of the a-large cell is also realized.
Similarly, the virtual vector synthesis method is applied to other large areas.
The technical scheme of the invention has the following beneficial effects:
the method provided by the invention carries out virtual synthesis again on the vector influencing the midpoint voltage balance, redefines partial cells, and effectively solves the problem of the vector V through the redundancy characteristic of the vector (20-2) Generating a midpoint current i b The problem that the midpoint voltage balance control cannot be realized in partial cells is caused, and the midpoint voltage balance control of the whole region of the space vector diagram is realized.
Drawings
FIG. 1 is a schematic diagram of a three-phase ANPC five-level converter topology;
FIG. 2 is a diagram of current paths having an effect ON a midpoint voltage, wherein FIG. 2 (a) is a P1N switch state, FIG. 2 (b) is an OP switch state, FIG. 2 (c) is an N1N switch state, and FIG. 2 (d) is an ON switch state;
fig. 3 is a five-level space vector diagram, wherein fig. 3 (a) is a space vector diagram of each large area of five levels, and fig. 3 (b) is a space vector diagram of a large area;
fig. 4 shows a partial region vector virtual lower a partition.
Detailed Description
The invention is further described with reference to the following figures and detailed description.
The invention mainly provides a method for controlling the midpoint voltage of a five-level inverter, so that the midpoint voltage control is effectively realized. For example, in the A large region, the current generating the midpoint is selected to be i a Vector V of (1-1-2) And generating a midpoint current of i c Vector V of (21-1) And vector V (20-2) Performing virtual synthesis to solve the vector V (20-2) Generated midpoint current i b The problem of midpoint voltage balance cannot be performed in the regions a12, a13, and a14, and the other large regions are similar.
Because of the vector V (20-2) The generated midpoint current is i b So that the selected midpoint current is generated as i a Vector V of (1-1-2) And generating a midpoint current of i c Vector V of (21-1) And V (20-2) Participate in the synthesis of the virtual vector.
Let a virtual space vector V VSM By vector V (1-1-2) 、V (21-1) Sum vector V (20-2) Synthesizing according to the formula (3).
Then V VSM The midpoint current generated is
Therefore, the virtual vector V when the sum of the output three-phase currents is zero VSM There is no effect on the midpoint voltage. The composition of the virtual space vectors causes the original three cells a12, a13, a14 to be divided into new four cells as shown in fig. 4.
Virtual vector V VSM The former three cells are divided into four cells a12, a13, a14, a 15. When the reference vector is located in a new cell, a virtual space vector V is adopted VSM And two neighboring basis vectors. For example, the vector used in the A14 region is V (1-1-2) 、V (21-1) 、V (20-2) 、V (21-2) And V (2-1-2) Wherein the vector V (1-1-2) And V (21-1) The P1N/N1P and P1P/N1N switch states are selected, respectively, so that the vector V (20-2) 、V (1-1-2) 、V (21-1) The sum of the generated midpoint currents is 0; vector V (2-1-2) 、V (21-2) The midpoint currents corresponding to the switch states of N1P and P1P are also selected to be 0, so that the sum of the currents generated by the cell basic vector is 0. The control method of the A12, A13 and A15 cells is similar, and other cells adopt the traditional method to control the midpoint current, so that the midpoint voltage of each cell can be effectively controlled. When the method is used in the new synthesis area, the factor V is avoided (20-2) Vector-generated non-cancelled midpoint current i b In this case, the control of the midpoint voltage in each cell of the a-large cell is also realized. Similarly, the virtual vector synthesis method is applied to other large areas.
Claims (3)
1. A method for controlling a midpoint voltage of a five-level inverter is characterized by comprising the following steps: in the A large area, the current generating the midpoint is selected to be i a Vector V of (1-1-2) And generating a midpoint current of i c Vector V of (21-1) And vector V (20-2) The virtual synthesis is carried out, and the virtual synthesis,solving for vector V (20-2) Generated midpoint current i b The problem that the midpoint voltage balance cannot be performed in the regions A12, A13 and A14, vector V (20-2) The generated midpoint current is i b So that the selected midpoint current is generated as i a Vector V of (1-1-2) And generating a midpoint current of i c Vector V of (21-1) And V (20-2) Participating in synthesizing a virtual vector;
let a virtual space vector V VSM By vector V (1-1-2) 、V (21-1) Sum vector V (20-2) Synthesizing according to the formula (3),
then V VSM The resulting midpoint current is:
therefore, the virtual vector V when the sum of the output three-phase currents is zero VSM The synthesis of the virtual space vector has no influence on the midpoint voltage, so that the original three cells A12, A13 and A14 are divided into new four cells.
2. The method for controlling the midpoint voltage of the five-level inverter according to claim 1, wherein: virtual vector V VSM Dividing the previous three cells into four cells A12, A13, A14 and A15, and adopting a virtual space vector V when the reference vector is positioned in a new cell VSM And the adjacent two basic vectors are combined, and the vector used in the A14 area is V (1-1-2) 、V (21-1) 、V (20-2) 、V (21-2) And V (2-1-2) When the method is used in the new synthesis area, the factor V is avoided (20-2) Vector-generated non-cancelled midpoint current i b In this case, the control of the midpoint voltage in each cell of the a-large cell is also realized.
3. The method for controlling the midpoint voltage of the five-level inverter according to claim 1, wherein: similarly, the virtual vector synthesis method is applied to other large areas.
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| US8934276B2 (en) * | 2012-08-16 | 2015-01-13 | Mitsubishi Electric Research Laboratories, Inc. | DC-link voltage balancing control for multilevel inverters |
| US20160352251A1 (en) * | 2015-05-31 | 2016-12-01 | Abb Technology Ag | Active Neutral-Point-Clamped (ANPC) Converters and Operating Methods Thereof |
| KR101695091B1 (en) * | 2015-06-02 | 2017-01-10 | 영남대학교 산학협력단 | SVPWM scheme for common-mode voltage reduction in five-level ANPC inverters |
| CN105978374B (en) * | 2016-06-16 | 2018-12-25 | 江苏东润智联科技有限公司 | The method that three-level inverter neutral point voltage balance and common-mode voltage inhibit |
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| CN106533230A (en) * | 2016-12-15 | 2017-03-22 | 东南大学 | Three-level virtual space vector voltage equalizing modulation method based on simplified balance factor |
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