CN115133798A

CN115133798A - Discrete space vector modulation three-level inverter low common mode prediction control method

Info

Publication number: CN115133798A
Application number: CN202210645137.7A
Authority: CN
Inventors: 邢相洋; 景萌萌; 温创平; 张承慧
Original assignee: Shandong University
Current assignee: Shandong University
Priority date: 2022-06-09
Filing date: 2022-06-09
Publication date: 2022-09-30

Abstract

The invention provides a discrete space vector modulation three-level inverter low common mode prediction control method, which can effectively reduce the system cost, reduce the common mode voltage and reduce the current ripple. The method specifically comprises the following steps: sampling the voltage of the power grid side and the output current of the inverter side, and predicting the voltage value at the next moment based on a current prediction model and dead-beat control; judging the sector based on the predicted voltage value and carrying out sector conversion, wherein the obtained conversion result is used as a reference voltage vector; synthesizing virtual vectors based on discrete space vector modulation, taking three virtual vectors closest to a reference voltage vector as candidate vectors, and judging the optimal vector by a current tracking value function; selecting an optimal small vector and action time through a midpoint balance value function, obtaining an optimal vector sequence and action time based on a volt-second balance principle, and equivalently synthesizing an optimal virtual vector; and obtaining the switching pulse sequence and the acting time of the auxiliary bridge arm and the three-phase half-bridge structure of the converter based on the optimal vector sequence, the acting time and the sector number.

Description

Discrete space vector modulation three-level inverter low common mode prediction control method

Technical Field

The invention belongs to the technical field of three-level eight-switch converters, and particularly relates to a discrete space vector modulation three-level inverter low common mode prediction control method and system.

Background

The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

The three-phase multi-level converter is widely applied to the fields of medium-high voltage power generation, electric transmission and the like in industry. The most mature multilevel topology is a three-level neutral point clamped converter, using 12 active power switches and 6 diodes as auxiliary devices. Furthermore, the T-type three-level inverter adopts the anti-parallel active switch, so that 6 clamping diodes are further saved, and the T-type three-level inverter is widely applied to photovoltaic power generation.

In order to further reduce the cost, the current three-level eight-switch converter system with low common-mode voltage only adopts 8 active switches and 2 clamping diodes to realize three-level output, and has higher reliability due to the reduction of the common-mode voltage. However, due to the absence of the medium vector and the elimination of the high common mode vector, only 13 voltage vectors are available, which results in large output current ripple. The inherent midpoint voltage oscillation of a three-level inverter also increases the voltage stress on the device and increases the ripple in the output current.

However, the conventional modulation algorithm is difficult to be directly applied to a three-level eight-switch converter system, because different from the conventional three-level converter, part of the switching tubes of the eight-switch converter are three-phase coupled, so that three-phase voltages only have two levels at the same time, and medium vectors are lost.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention provides a discrete space vector modulation three-level inverter low common mode prediction control method, which can reduce the system cost, effectively realize the reduction of common mode voltage, the control of midpoint potential balance, the fixation of switching frequency, quick dynamic response and low current ripple and obviously improve the system performance.

In order to achieve the above object, one or more embodiments of the present invention provide the following technical solutions:

in a first aspect, a discrete space vector modulated three-level inverter low-common mode prediction control method is disclosed, which includes:

sampling three-phase output current of a power grid side and an inverter side, and predicting a voltage value at the next moment based on a current prediction model and dead-beat control;

judging the sector based on the predicted voltage value, and performing sector conversion, wherein the obtained conversion result is used as a reference voltage vector;

synthesizing virtual vectors based on discrete space vector modulation, taking three virtual vectors closest to a reference voltage vector as candidate vectors, and selecting an optimal virtual vector through a current tracking cost function;

selecting an optimal small vector and the acting time thereof through a midpoint balance value function, and obtaining a low common-mode vector sequence and the acting time based on a volt-second balance principle to equivalently synthesize an optimal virtual vector;

and obtaining the switching pulse sequence and the acting time of the auxiliary bridge arm and the three-phase half-bridge structure of the converter based on the optimal vector sequence, the acting time and the sector number.

As a further technical solution, the current prediction model is:

wherein e is _x Is the grid voltage u _x Is the output voltage of the inverter, i _x For three-phase output current, L and R are filter inductance and resistance.

As a further technical solution, the sampled voltage on the grid side and the sampled current on the inverter side are subjected to coordinate transformation:

obtaining a sampling value e under a 60-degree coordinate system _α (k)，e _β (k)，i _g (k)，i _h (k) And drawing of the meridiansGlantian extrapolation to obtain a current value

As a further technical scheme, according to the dead-beat control, a current prediction model formula is discretized to obtain a voltage value V which enables a current error to be zero at the next moment _g (k +1) and V _h (k+1)：

RL filter circuit, R is filter resistance value, L is filter inductance value, T _s Is the time of the sampling, and,

as a further technical scheme, a space vector diagram of the inverter is divided into six sectors, each sector occupies 60 degrees, and a sector S where a reference voltage is located is divided by V _g (k +1) and V _h And (k +1) is obtained by judgment.

As a further technical scheme, the reference voltages are all rotated to the sector I through sector conversion to simplify calculation, and the conversion result is used as a reference voltage vector V _ref 。

As a further technical scheme, based on discrete space vector modulation, the sampling period T is adjusted _s Dividing the voltage vector into N equal intervals, filling a preset time interval with a plurality of voltage vectors to synthesize a virtual voltage vector, and expressing the virtual voltage vector as follows:

wherein t is _j Is the actual voltage vector V _j The action time of (d) is an integral multiple of the preset interval. In the method, the virtual vectors are uniformly distributed in a triangular vertex form, and the total number of (N +1) (N +2)/2 virtual vectors is。

As a further approach, the coordinates of the reference voltage vector are divided by V _dc Normalizing by/2, and multiplying by N, namely:

the coordinates of the reference voltage vector are then rounded down and are denoted h, respectively ₁ ,h ₂ And h ₃ ：

When h is generated ₁ +h ₂ Is equal to h ₃ When the reference voltage vector falls in the lower triangle, the candidate vector is V ₁ (h ₁ +1,h ₂ ),V ₂ (h ₁ ,h ₂ +1),V ₃ (h ₁ ,h ₂ ) (ii) a When h is ₁ +h ₂ Is equal to h ₃ +1, the reference voltage vector falls in the upper triangle, and the candidate vector is V ₁ (h ₁ +1,h ₂ ),V ₂ (h ₁ ,h ₂ +1),V ₃ (h ₁ +1,h ₂ +1)。

As a further scheme, three candidate vectors are used as variables, and an optimal virtual vector V is selected through a current tracking cost function _opt Expressed as:

as a further scheme, a switching pulse sequence and action time of an auxiliary bridge arm are determined according to the midpoint potential; and determining the switching pulse sequence and the action time of the three-phase half-bridge structure according to the midpoint potential and the sector.

In a second aspect, a discrete space vector modulated low common mode predictive control system is disclosed, comprising:

a data prediction module configured to: sampling three-phase output current of a power grid side and an inverter side, and predicting a voltage value at the next moment based on a current prediction model and dead-beat control;

a conversion module configured to: judging the sector based on the predicted voltage value and carrying out sector conversion, wherein the obtained conversion result is used as a reference voltage vector;

a candidate vector module configured to: synthesizing virtual vectors based on discrete space vector modulation, taking three virtual vectors closest to a reference voltage vector as candidate vectors, and selecting an optimal virtual vector through a current tracking cost function;

an optimal virtual vector module configured to: selecting an optimal small vector and action time thereof through a midpoint balance value function, and obtaining an optimal vector sequence and action time based on a volt-second balance principle to equivalently synthesize an optimal virtual vector;

a control module configured to: and obtaining the switching pulse sequence and the acting time of the auxiliary bridge arm and the three-phase half-bridge structure of the converter based on the optimal vector sequence, the acting time and the sector number.

The above one or more technical solutions have the following beneficial effects:

the invention uses the three-level inverter low common mode prediction control method of discrete space vector modulation, reduces the common mode voltage, and improves the system stability; the concept of virtual vectors is introduced, the predicted reference voltage is fitted by using multiple vectors, the current ripple is reduced, and the electric energy quality of output current is improved; selecting an optimal small vector and the acting time thereof by adopting a value function to realize midpoint potential balance; a switching sequence is ingeniously designed, so that fixed switching frequency is realized, and high-efficiency filtering of current harmonic waves is facilitated; the hierarchical algorithm under the 60-degree coordinate system realizes rolling optimization through simple algebraic operation, avoids complex trigonometric function calculation and greatly reduces the calculation pressure.

Compared with a three-level neutral point clamping converter, the method reduces 1/3 the number of power switches and reduces the system cost; the method realizes high-reliability high-performance control, is simple to realize, is easy to expand to a multi-level converter system, and has strong practicability; the method has wide application prospect in the industrial fields of photovoltaic power generation, electric vehicles, motor drive and the like.

Advantages of additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention and together with the description serve to explain the invention and not to limit the invention.

Fig. 1 is a structural diagram of a three-level eight-switch grid-connected inverter system;

FIG. 2 is a basic space vector diagram of a three-level eight-switch low-common mode grid-connected inverter system;

fig. 3 is a control block diagram of the three-level eight-switch low-common mode grid-connected inverter system according to the present invention;

4(a) -4 (b) are vector sequences of the three-level eight-switch low common mode grid-connected inverter system of the present invention;

5(a) -5 (b) are switching sequences of auxiliary bridge arms of the three-level eight-switch low-common mode grid-connected inverter system according to the invention;

fig. 6(a) -6 (b) are switching sequences of a three-phase half-bridge structure of the three-level eight-switch low common mode grid-connected inverter system according to the present invention;

fig. 7(a) -7 (c) show the dc side capacitor voltage, the line voltage, the output current and the common mode voltage of the three-level eight-switch grid-connected inverter system according to the present invention, which is controlled by single vector model prediction, double vector model prediction, and discrete space vector modulation low common mode prediction.

Fig. 8(a) -8 (c) are Fast Fourier Transform (FFT) analyses of the three-level eight-switch grid-connected inverter system according to the present invention, which uses single-vector model predictive control, double-vector model predictive control, and discrete space vector modulation for low common-mode predictive control.

Fig. 9(a) -9 (c) are dynamic response waveforms of the current of the three-level eight-switch grid-connected inverter system adopting single vector model predictive control, double vector model predictive control and discrete space vector modulation low common mode predictive control.

Detailed Description

It is to be understood that the following detailed description is exemplary and is intended to provide further explanation of the invention as claimed. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the invention.

The embodiments and features of the embodiments of the invention may be combined with each other without conflict.

Example one

The embodiment discloses a discrete space vector modulation three-level inverter low common mode prediction control method for realizing control over a three-level eight-switch converter. The method of the present invention is applicable to both DC-AC and AC-DC, and is specifically described below by taking DC-AC as an example, and further explained with reference to the accompanying drawings and examples.

In one or more embodiments, a control object targeted by the discrete space vector modulated three-level inverter low-common mode prediction control method is a three-level eight-switch converter system, referring to fig. 1, fig. 1 is a topology structure of an eight-switch three-level inverter, and is formed by connecting an auxiliary bridge arm and a three-phase half-bridge structure, where the auxiliary bridge arm includes one active switch, two clamping diodes, and one active switch that are sequentially connected in series, and a midpoint of the two clamping diodes is connected with a midpoint of a dc-side capacitor; the three-phase half-bridge structure comprises three-phase bridge arms connected in parallel, each phase of bridge arm comprises two active switches connected in series, six active switches are formed in total, and the middle point of each phase of bridge arm is connected with an alternating current load through a filter.

Through different switch combinations, the auxiliary bridge arm generates three levels through a direct-current voltage source and a capacitor, one level is selected through switching of an upper bridge arm and a lower bridge arm of a three-phase half-bridge structure, and then the level is used as an output level of an alternating-current side.

The three levels are specifically

0、

Respectively marked as P, O and N; wherein, V _dc The value of the power supply voltage on the direct current side.

DC power supply V under ideal condition _dc Equally divided by two capacitors. With the neutral point O connecting the two capacitors as a zero reference potential, the capacitor C ₁ At a voltage of V _dc /2, and capacitor C ₂ At a voltage of-V _dc /2. Switch S ₁ Whether or not to turn on determines the voltage V _H Is V _dc The/2 is again clamped to zero level via a diode. Similarly, S ₂ Determining V _M Is equal to-V _dc And/2 is also 0. Therefore, the operating principle of the auxiliary bridge arm can also be expressed as:

therefore, the auxiliary bridge arm can generate three levels V _dc /2、0、-V _dc And/2, labeled "P", "O", and "N", respectively. In addition, the auxiliary arm is connected via V _H And V _M Connected to a three-phase half-bridge configuration. Each phase bridge arm of the three-phase half-bridge structure is provided with two IGBTs which are connected with an output filter and a load through the midpoint of each phase bridge arm. The three-phase output voltage is represented as:

wherein the content of the first and second substances,

V _lo and (l) denotes a phase voltage. Thereby, according to the conversion formula

The 21 voltage vectors of the topology are obtained, representing the relationship between different switch combinations and output voltage vectors, and recorded in table 1.

TABLE 1

In order to suppress the common mode voltage, the amplitude of which exceeds V, and enhance the stability of the system _dc The voltage vector of/6 is discarded, i.e., the partial redundant small and zero vectors shown in bold in Table 1. Furthermore, there is no medium vector because the three-phase output voltage of the half-bridge configuration is only selected between two levels at a time. So that the three-level eight-switch low-common mode inverter system has only 13 available voltage vectors. The active switch is an IGBT.

The common mode voltage of a three-phase eight-switch converter can be expressed as:

thus, the common mode voltage of the 21 voltage vectors is at V _dc 6 amplitude variation with maximum amplitude V _dc And/2, as shown in Table 1.

Fig. 2 is a basic space vector diagram of a three-level eight-switch low-common mode grid-connected inverter system. In order to suppress the common mode voltage, the amplitude of which exceeds V, and enhance the stability of the system _dc The voltage vector of/6 is discarded, i.e., the partial redundant small and zero vectors shown in bold in Table 1. Furthermore, there is no medium vector because the three-phase output voltage of the half-bridge configuration is only selected between two levels at a time. Thus three-level eight-switch low common mode inverter systemThere are only 13 voltage vectors available.

Fig. 3 is a control block diagram of the three-level eight-switch low-common mode grid-connected inverter system, and the control block diagram is divided into steps of prediction model, rolling optimization, switching pulse and the like.

A step of predicting a model: and sampling the three-phase output current of the grid side and the inverter side, predicting the voltage value at the next moment based on a current prediction model and dead-beat control of the system, judging the sector where the voltage value is located, performing sector conversion, and taking the conversion result as a reference voltage vector.

The current prediction model of the three-phase eight-switch converter system is as follows:

wherein e is _x Is the grid voltage u _x Is the output voltage of the inverter, i _x And L and R are filter inductance and resistance. Coordinate transformation of sampled voltage on grid side and sampled current on inverter side

Wherein, [ x ] _a x _b x _c ] ^T To the mains voltage e _x Or an output current i on the AC side _x Coordinates under an abc three-phase coordinate system; [ x ] of _g x _h ] ^T To the mains voltage e _x Or sampling the current i _x Obtaining the current value by the Lagrange extrapolation method according to the coordinate under the 60-degree coordinate system

According to the dead-beat control and discretization of a current prediction model formula, a voltage value V which can enable a current error to be zero at the next moment is obtained _g (k +1) and V _h (k+1)：

Wherein, the system adopts RL filter circuit, R is filter resistance value, L is filter inductance value, and T is _s Is the sampling time.

The spatial vector map is divided into six sectors, each sector occupying 60 degrees. The sector S in which the reference voltage is located can be via V _g (k +1) and V _h The sign of (k +1) is judged as shown in table 2:

TABLE 2

Sector S

I

II

III

IV

V

VI

V _g (k+1)

+

-

+

V _h (k+1)

+

-

V _g (k+1)+V _h (k+1)

Arbitrary

+

-

Arbitrary

-

+

Further, the sector switching rotates both reference voltages to sector I to simplify the calculation. Converting the result as a reference voltage vector V _ref Coordinates in a 60 degree coordinate system

The coordinate transformation is shown in table 3:

TABLE 3

The rolling optimization algorithm is realized in two layers under a 60-degree coordinate system so as to improve the calculation efficiency: the first layer, based on discrete space vector modulation, may synthesize a large number of virtual vectors, with three virtual vectors closest to a reference voltage vector as candidate vectors, and select a virtual vector with the best current tracking performance via a cost function.

After the prediction model of the controlled system is established, the MPC can solve the optimal control vector again when each sampling period comes, namely, the MPC is on-line optimization. The optimization process is an on-line calculation of the loop body at each control period.

Based on discrete space vector modulation, the sampling period T is adjusted _s The virtual voltage vector is synthesized by dividing into N equal intervals and filling a preset time interval with a plurality of voltage vectors, and can be expressed by the formula:

wherein t is _j Is the actual voltage vector V _j The action time of (d) is an integral multiple of the preset interval. In the method, the virtual vectors are uniformly distributed in a triangular vertex mode, and the total number of the virtual vectors is (N +1) (N + 2)/2.

Coordinates of the reference voltage vector divided by V _dc Normalizing by/2, and multiplying by N, namely:

When h is generated ₁ +h ₂ Is equal to h ₃ When the reference voltage vector falls in the lower triangle, the candidate vector is V ₁ (h ₁ +1,h ₂ ),V ₂ (h ₁ ,h ₂ +1),V ₃ (h ₁ ,h ₂ ) (ii) a When h is generated ₁ +h ₂ Is equal to h ₃ +1, the reference voltage vector falls in the upper triangle, and the candidate vector is V ₁ (h ₁ +1,h ₂ ),V ₂ (h ₁ ,h ₂ +1),V ₃ (h ₁ +1,h ₂ +1). Selecting an optimal virtual vector V via a current tracking cost function with three candidate vectors as variables _opt Expressed as:

the second layer selects the optimal small vector and its action time via the midpoint balance cost function. Neutral-point balanced state, i.e. the value of the capacitor voltage V on the DC side _P Equal to the lower capacitor voltage value V _N . Therefore, to achieve midpoint voltage balance, when V _P >V _N Selecting P type small vector, discharging capacitance, V _P Decrease; when V is _P <V _N When N-type small vector is selected, the lower capacitor is discharged, V _N And decreases. The optimal action time of the small vector is based on a midpoint balance value function g _v (V _j ) It is determined that,

k＝min g _v (k),k∈Z, (16)

wherein C is the capacitance of the DC side, T _s For a sampling period, T _s The division into N equal intervals, k being the number of time intervals over which the selected small vector acts. i all right angle _o Midpoint current i being a small vector _o Recorded in table 4 below:

TABLE 4

Vector

V ₇ [POO]

V ₉ [OPO]

V ₁₁ [OOP]

V ₁₄ [OON]

V ₁₆ [NOO]

V ₁₈ [ONO]

i ₀

i _b +i _c

i _a +i _c

i _a +i _b

-i _a -i _b

-i _b -i _c

-i _a -i _c

And then designing an optimal vector sequence and action time based on a volt-second balance principle so as to equivalently synthesize an optimal virtual vector. Two large vectors V _B1 And V _B2 Zero vector V _Z And a small vector V _S Acting to synthesize an optimal virtual vector. Will switch for a period T _s Equally dividing into N time intervals; the action time is indicated by the interval n. Determining the action time of each vector based on the volt-second balance principle:

furthermore, the switching pulse part determines the switching pulse sequence and the action time of the auxiliary bridge arm according to the midpoint balance; and determining the switching pulse and the acting time of the three-phase half-bridge structure according to the midpoint balance and the sector number.

Fig. 4(a) - (b) are vector sequences (taking sector I as an example) of the three-level eight-switch low-common mode grid-connected inverter system according to the present invention. Abandoning high common-mode vector, controlling the amplitude of common-mode voltage at V _dc Within/6, reduced by half

When V is _P Greater than V _N When the action vector is V ₀ 、V ₁ 、V ₂ And V ₇ . Based on equations (15) - (17), the action times of the four vectors are:

when V is _P Less than V _N When the action vector is V ₀ 、V ₁ 、V ₂ And V ₁₄ . Based on equations (15) - (17), the action times of the four vectors are:

fig. 5(a) - (b) are switching sequences of an auxiliary bridge arm of the three-level eight-switch low-common mode grid-connected inverter system according to the present invention. The auxiliary bridge arm determines the vector type and outputs V _H And V _M And is also the input of the three-phase half-bridge configuration. When S is ₁ V of auxiliary bridge arm when switching on _H P, otherwise O; when S is ₂ When switched on, V _M Is O, otherwise is N. The levels are therefore used to describe the switching states of the auxiliary legs. For example, "PO" represents S ₁ Opening, S ₂ Off, V _H And V _M P and O respectively, and the three-phase output level is P or O. Obviously, the auxiliary leg is independent of the sector rotation.

Thus, V _P Greater than V _N Then, the switching sequence of the auxiliary bridge arm is always as follows: OO-PO-PN-PO-OO is divided into five sections. The action time is expressed as:

thus, V _P Less than V _N And meanwhile, the switching sequence of the auxiliary bridge arm is always as follows: OO-ON-PN-ON-OO, divided into five sections. The action time is expressed as:

fig. 6(a) - (b) are switching sequences of a three-phase half-bridge structure of the three-level eight-switch low common mode grid-connected inverter system according to the present invention. The three-phase half-bridge structure, i.e. the two-level topology, determines the three-phase voltage situation, which is related to the sector rotation. "1" or "0" is used to indicate the switching state of the bridge arm. For example, "100" indicates that the upper arm of the a phase is on and the lower arms of the B phase and the C phase are on.

When V is _P Greater than V _N The sequence of the three-phase half-bridge structure of the first sector is: 100-110-100, the action time is as follows:

the sequence of the three-phase half-bridge structure in the other sectors and so on is summarized in fig. 6 (a).

When V is _P Less than V _N The sequence of the three-phase half-bridge structure of the first sector is: 110-100-110, the action time is:

the three-phase half-bridge structure is analogized to the sequence of the other sectors, summarized in fig. 6 (b).

The pulse sequence and the action time of all switches are summarized in table 5.

TABLE 5

Fig. 7(a) - (c) show the dc side capacitor voltage, the line voltage, the output current and the common mode voltage of the three-level eight-switch inverter system according to the present invention, which is controlled by single vector model prediction, double vector model prediction, and discrete space vector modulation low common mode prediction. And the THD of the three methods were 10.44%, 3.76% and 2.97%, respectively. Obviously, compared with the existing method, the method greatly reduces the current ripple and improves the current quality; meanwhile, the common-mode voltage is reduced to half of that of the traditional model predictive control method by the method, so that the system stability is improved; the method selects proper vector action to realize the balance of the midpoint voltage.

Fig. 8(a) - (c) are Fast Fourier Transform (FFT) analyses of the three-level eight-switch inverter system of the present invention using single vector model predictive control, dual vector model predictive control, and low common mode predictive control with discrete space vector modulation. Compared with the existing method, the current harmonic of the proposed method is smaller and more intensively distributed at integral multiples of the switching frequency, which is beneficial to designing a filter to filter out the harmonic more efficiently.

Fig. 9(a) - (c) are dynamic response waveforms of current of the three-level eight-switch inverter system according to the present invention, which are controlled by single vector model prediction, dual vector model prediction, and discrete space vector modulation low common mode prediction. As can be seen from the waveforms, the proposed method achieves a fast and stable dynamic response while maintaining a low current ripple.

Therefore, the three-level eight-switch converter system uses the three-level inverter low common mode prediction control method of discrete space vector modulation, so that the common mode voltage can be reduced, and the system stability is improved; the concept of virtual vectors is introduced, the predicted reference voltage is fitted by using multiple vectors, the current ripple is reduced, and the electric energy quality of output current is improved; selecting an optimal small vector and the acting time thereof by adopting a value function to realize midpoint potential balance; a switching sequence is ingeniously designed, so that fixed switching frequency is realized, and high-efficiency filtering of current harmonic waves is facilitated; the hierarchical algorithm under the 60-degree coordinate system realizes rolling optimization through simple algebraic operation, avoids complex trigonometric function calculation and greatly reduces the calculation pressure. Compared with a three-level neutral point clamping converter, the number of power switches is reduced by 1/3, and the system cost is reduced; the method realizes high-reliability and high-performance control, is simple to realize, is easy to expand to a multi-level converter system, and has strong practicability; the method has wide application prospect in the industrial fields of photovoltaic power generation, electric automobiles, motor drive and the like.

Example two

The present embodiment is directed to a computer device, which includes a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the steps of the method when executing the computer program.

EXAMPLE III

An object of the present embodiment is to provide a computer-readable storage medium.

A computer-readable storage medium, on which a computer program is stored which, when being executed by a processor, carries out the steps of the above-mentioned method.

Example four

The present embodiment aims to provide a discrete space vector modulated low common mode predictive control system, which includes:

a conversion module configured to: judging the sector based on the predicted voltage value, and performing sector conversion, wherein the obtained conversion result is used as a reference voltage vector;

an optimal virtual vector module configured to: selecting an optimal small vector and the acting time thereof through a midpoint balance value function, and obtaining an optimal vector sequence and the acting time based on a volt-second balance principle to equivalently synthesize an optimal virtual vector;

Compared with a three-level neutral point clamping converter, the number of power switches is reduced by 1/3, and the system cost is reduced; the common-mode voltage is reduced, and the system stability is improved; current ripples are reduced, and the electric energy quality of output current is improved; the balance of the midpoint voltage and the fixation of the switching frequency are realized, and the current harmonic wave is conveniently and efficiently filtered; and the simple algebraic operation replaces the complex trigonometric function calculation, so that the calculation pressure is reduced.

The steps involved in the apparatuses of the above second, third and fourth embodiments correspond to the first embodiment of the method, and the detailed description thereof can be found in the relevant description of the first embodiment. The term "computer-readable storage medium" should be taken to include a single medium or multiple media containing one or more sets of instructions; it should also be understood to include any medium that is capable of storing, encoding or carrying a set of instructions for execution by a processor and that cause the processor to perform any of the methods of the present invention.

Those skilled in the art will appreciate that the modules or steps of the present invention described above can be implemented using general purpose computer means, or alternatively, they can be implemented using program code that is executable by computing means, such that they are stored in memory means for execution by the computing means, or they are separately fabricated into individual integrated circuit modules, or multiple modules or steps of them are fabricated into a single integrated circuit module. The present invention is not limited to any specific combination of hardware and software.

Although the embodiments of the present invention have been described with reference to the accompanying drawings, it is not intended to limit the scope of the present invention, and it should be understood by those skilled in the art that various modifications and variations can be made without inventive efforts by those skilled in the art based on the technical solution of the present invention.

Claims

1. The three-level inverter low common mode prediction control method based on discrete space vector modulation is characterized by being applicable to a three-level eight-switch converter and comprising the following steps of:

judging the sector based on the predicted voltage value and carrying out sector conversion, wherein the obtained conversion result is used as a reference voltage vector;

selecting an optimal small vector and action time thereof through a midpoint balance value function, and obtaining a low common-mode vector sequence and action time based on a volt-second balance principle to equivalently synthesize an optimal virtual vector;

2. The discrete space vector modulated three-level inverter low-common mode prediction control method according to claim 1, wherein the current prediction model is:

3. The discrete space vector modulated low common mode model predictive control method of claim 1, wherein the grid side sampled voltage and the inverter side sampled current are coordinate transformed:

obtaining a sampling value e under a 60-degree coordinate system _α (k)，e _β (k)，i _g (k)，i _h (k) And obtaining the current value by Lagrange extrapolation

4. The discrete space vector modulated three-level inverter low-common mode predictive control method of claim 1, wherein a voltage value V for making a current error zero at the next moment is obtained by discretizing a current predictive model formula according to dead-beat control _g (k +1) and V _h (k+1)：

RL filter circuit, R is filter resistance value, L is filter inductance value, T _s Is the sampling time.

5. The discrete space vector modulated three-level inverter low common mode predictive control method according to claim 1, wherein the space vector diagram of the inverter is divided into six sectors, each sector occupies 60 degrees, and the sector S in which the reference voltage is located is divided by V _g (k +1) and V _h The sign of (k +1) is judged.

6. As claimed in claim 1The three-level inverter low common mode prediction control method of discrete space vector modulation is characterized in that reference voltages are all rotated to a sector I through sector conversion to simplify calculation, and the conversion result is used as a reference voltage vector V _ref ；

Based on discrete space vector modulation, the sampling period T is adjusted _s Dividing the voltage vector into N equal intervals, filling a preset time interval with a plurality of voltage vectors to synthesize a virtual voltage vector, and expressing the virtual voltage vector as follows:

7. The discrete space vector modulated three-level inverter low common mode predictive control method of claim 1, wherein the coordinates of the reference voltage vector are divided by V _dc Normalizing by/2, and multiplying by N, namely:

When h is generated ₁ +h ₂ Is equal to h ₃ When the reference voltage vector falls in the lower triangle, the candidate vector is V ₁ (h ₁ +1,h ₂ ),V ₂ (h ₁ ,h ₂ +1),V ₃ (h ₁ ,h ₂ ) (ii) a When h is generated ₁ +h ₂ Is equal to h ₃ +1, the reference voltage vector falls in the upper triangle, and the candidate vector is V ₁ (h ₁ +1,h ₂ ),V ₂ (h ₁ ,h ₂ +1),V ₃ (h ₁ +1,h ₂ +1)；

Selecting an optimal virtual vector V via a current tracking cost function with three candidate vectors as variables _opt Expressed as:

8. the low common mode predictive control system of the discrete space vector modulation is characterized by comprising the following components:

9. A computer arrangement comprising a memory, a processor and a computer program stored on the memory and executable on the processor, wherein the steps of the method as claimed in any one of claims 1 to 7 are performed by the processor when executing the program.

10. A computer-readable storage medium, on which a computer program is stored which, when being executed by a processor, is adapted to carry out the steps of the method according to any one of the preceding claims 1 to 7.