CN105490572B

CN105490572B - A kind of neutral balance strategy process based on dynamic control parameter

Info

Publication number: CN105490572B
Application number: CN201510838853.7A
Authority: CN
Inventors: 易灵芝; 陈宇; 黄鹤; 刘仲范; 林舒; 任旭亮
Original assignee: Xiangtan University
Current assignee: Xiangtan University
Priority date: 2015-11-27
Filing date: 2015-11-27
Publication date: 2018-03-30
Anticipated expiration: 2035-11-27
Also published as: CN105490572A

Abstract

The present invention discloses a kind of harmonic wave observer algorithm of the neutral balance strategy applied to distributed new in grid-connected.It comprises the following steps：Inversion output capacitance voltage u is measured by voltage-current sensor_CInput capacitance voltage U_c1,U_c2With output current i_out;By u_CIt is passed through harmonic voltage observation module;Harmonic voltage is observed into module results and i_LInput neutral point voltage balance module obtains dynamic control parameterλ;WillλGoing out to input SVPWM modules control control power circuit makes neutral point voltage balance.The technical effects of the invention are that：It has studied a kind of single-phase full bridge Conergy NPC neutral balance strategies of the harmonic wave observer algorithm theoretical based on Luenberger state observations.Reduce by an inductive current sensor, cost reduces.Inverter side electric current can be accurately estimated in real time, solve single-phase full bridge ConergyNPC midpoint potential imbalance problems.

Description

dynamic control parameter-based midpoint balance strategy method

Technical Field

The invention relates to a harmonic observer algorithm applied to a midpoint balance strategy in distributed new energy grid connection, in particular to the midpoint balance strategy and the harmonic observer algorithm.

Background

The three-level inverter (NPC) has the advantages of low output voltage harmonic content, small EMI (electro-magnetic interference), small switching loss, small filter inductance and the like. Since the conventional diode-type NPC uses a clamp diode, loss and cost increase; the loss degrees of the inner and outer switching tubes of the single-phase bridge arm are different, the heating of devices is not uniform, the integration and miniaturization are difficult, and the single-phase bridge arm is not suitable for low-voltage, low-power, high-efficiency and low-cost occasions of distributed energy. In single-phase grid-connected application, power calculation and current loop control are realized on a grid side and an inverter side through current sensors, and cost is increased and reliability is influenced by excessive sensors. According to the node current law, the information of the inverter side current is synthesized by the network side current and the filter capacitor current, harmonic information in the filter capacitor is obtained, and the inverter side current can be estimated.

Disclosure of Invention

In order to solve the problems of frequency spectrum leakage and barrier effect existing in a single harmonic component fast Fourier transform algorithm, the real-time response performance is poor, the accuracy requirements of a Kelman filter and a least square algorithm on a mathematical model are high, and the calculated amount is large. The improved digital phase-locked loop needs to be stabilized through a plurality of periodic phase-locked loops, dynamic performance is affected, and the like, and a single-phase full-bridge Conergy NPC neutral-point balance strategy based on dynamic control parameters is researched; and then, a harmonic observer algorithm based on a Luenberger state observation theory is introduced in detail, the current at the side of the inverter is accurately estimated in real time, and the harmonic observer algorithm is used for solving the problem of neutral point potential imbalance of the single-phase full-bridge ConergyNPC.

The technical scheme for solving the technical problems is as follows: measuring inversion output capacitance voltage U by voltage and current sensor_CInput capacitor voltage U_c1,U_c2And an output current i_outWill U is_CThe harmonic voltage observation module is introduced to obtain output voltage Ud, and the output voltages Ud and i of the harmonic voltage observation module are used_LObtaining dynamic control parameters by an input midpoint voltage balancing moduleλAnd controlling the power circuit by the control parameter lambda through a single-phase SVPWM (space vector pulse width modulation) strategy so as to realize midpoint voltage balance.

The invention has the technical effects that: a single-phase full-bridge Conergy NPC midpoint balance strategy based on a harmonic observer algorithm of a Luenberger state observation theory is researched. And one inductive current sensor is omitted, so that the cost is reduced. The inverter side current can be accurately estimated in real time, and the problem of point potential imbalance of the single-phase full-bridge ConergyNPC is solved.

Drawings

Fig. 1 is a simplified single-phase full-bridge energy NPC control model according to the present invention.

Fig. 2 is a single-phase full-bridge energy NPC switching model.

FIG. 3 is a drawing of a division of the α - β coordinate system.

Fig. 4 shows the SVPWM synthesis rule.

Detailed Description

The invention will be described in further detail below with reference to the accompanying drawings: as shown in FIG. 1, the output capacitor voltage U is first sampled_CInput capacitor voltage U_c1,U_c2And an output current i_outIs a step of;

SVPWM modulation strategy: defining the switching vector as (A) as shown in FIG. 2S _a, S _b) Which are distributed in 5 fixed positions on α coordinate axes of α - β coordinate system, and the whole coordinate system is divided into 4 regions (see fig. 3), whereinV _refFor the inverter input voltage reference vector, the phase angle is theta, and the dashed circle representsV _refA trajectory along a counterclockwise rotation within the α - β coordinate system;V _inis composed ofV _refProjection on α coordinate axis (see FIG. 4), in order to reduce fluctuation of midpoint potential, switching vectors (1,0) and (0, -1) have the same action time, switching vectors (0,1) and (-1,0) have the same action time, and S is prohibited in the same switching period_xSwitching directly between 1 and-1. The SVPWM strategy adopts a 5-vector synthesis method, and the vector time corresponding to the 5-vector synthesis sequence isThe vector synthesis is accomplished by the switching function in table 1.

In practical application, balance capacitor(U_c1、U_c2Voltage of dc side capacitor C1, C2), midpoint potential fluctuationThe switching function and the output phase current of the two bridge arms are determined:

(1)

the switching vectors (1,0) and (0, -1) are a pair of complementary vectors which have a sum of the times of action T in a switching cycle_a. Let T be the acting time of vectors (1,0) and (0,1)_a+=T_aAnd/2, setting the action time of vectors (0, -1) and (-1,0) as T_a-=T_a/2. According to the characteristics of 4 switching vectors in the table 1 and the formula (1), dynamic control parameters are introducedλAnd neutral point potential balance is realized. The relation between the action time and the switching vector is as follows:

(2)

reference value for fluctuation of midpoint potentialSubstituting equation (2) for equation (1) to estimate T in the next switching period_aTime allocation of (2):

(3)

samplingC ₁、C ₂Upper voltage and inverter side output currenti _aCan accurately estimateλ：

(4)

Will be provided withλThe parameter is substituted into the formula (2), and the unbalance of the midpoint potential at the moment is compensated through single-phase SVPWM modulation.

The estimation of the dynamic control parameter lambda needs to obtain the current i of the output side of the inverter in real time_aNumerical values. In FIG. 1, i_a(t) can be expressed as:

(5)

in the formula (5)Can not be directly obtained, a harmonic observer algorithm is designed in the text, the harmonic information in each order in the input signal is observed in real time, the orthogonal signal of each harmonic is generated at the same time, and i is finished_a(t) observation.

When the inverter works in a steady state, the voltage u of the output capacitor_c(t) can be decomposed into the following formula (6) by Fourier series, wherein u_cm(t) represents m times of fundamental waveIs given (m =0,1,2,3, …)），

a_mExpressed as magnitude of component signal

(6)。

According to the characteristics of the signal to be observed, the spatial state expression of ucm (t) is set as the formula

(7) Xm (t) is a state vector, where xm1(t) = ucm (t),(ii) a ym (t) is an output value, the space vector model of ucm (t) meets the visual condition, Am is a system matrix, Cm is an output matrix,

(7)

discretizing the formula (7) according to a formula (8) to obtain a discrete model ucm (kT) of ucm (T), wherein the formula (9) is shown, and the sampling period is T.

(8)

(9)。

According to the formulas (5) and (9), uc (kT) can be formed by overlapping ucm (kT) models, the spatial expression of the uc (kT) models is shown as a formula (10), x (kT) is a state vector and consists of N xm (kT), and the size of the state vector is shown as(ii) a y (kT) is an output value; ad a system matrix of uc (kT) of sizeC is an output matrix of size

(10)。

According to the observer design principle, the corresponding observer of equation (6)The expression of the spatial state is shown as formula (11),is a feedback matrix;is a state estimate of xm (kt),as an estimate of ucm (kt),is an estimate of the ucm (kT) quadrature value;is an output value

(11)。

Discrete observer for input signal uc (t) according to design idea of progressive observationDesigned as a closed-loop observer of which N areSub-modules for estimation of harmonics, feedback values thereofHarmonic waves in the input signalThe sum of the estimated values is then calculated,is defined as formula (12). In the formulaFor the feedback matrix, it is composed of NComposition is carried out;a state estimate of x (kT);as an estimate of the input value uc (kT)

(12)。

Wherein,to progressive errorIs shown asInA progressive speed approaching ucm (t); according to the pole arrangement theory, to satisfyThe ideal pole of the characteristic equation is defined asWhereinFor the distance of the ideal pole from the center circle of the z-domainThe parameters of (3) adjust the convergence speed, observation bandwidth and precision of the observer.Is the equation (13)

(13)

The characteristic equation of the formula (15) in the Z domain is the formula (14), where E isZ isThe number of z is 2N,(14)

the desired characteristic polynomial is defined as:

(15)

the coefficients of equation (14) and equation (15) are equal, and a matrix is determinedThe parameter (c) of (c).

TABLE 15 vector-synthesized single-phase SVPWM strategy

Table1five vector single-phase SVPWM strategy

Description of the tables:

region 1: dividing rules:

the synthesis sequence is as follows:

the synthesis time is as follows:

region 2: dividing rules:

the synthesis sequence is as follows:

the synthesis time is as follows:

region 3: dividing rules:

the synthesis sequence is as follows:

the synthesis time is as follows:

region 4: dividing rules:

the synthesis sequence is as follows:

the synthesis time is as follows:

Claims

1. A midpoint balance strategy method based on dynamic control parameters comprises the following steps:

a detection module for measuring the voltage U of the inverter output capacitor via a voltage/current sensor_CInput capacitor voltage U_c1、U_c2And an output current i_out；

Will measure the voltage U_CThe harmonic observer is led in to obtain an inductive current i_a；

Will input the capacitor voltage U_c1、U_c2Output current i_outHarmonic observer inductanceStream i_aAfter the input signal is input to a midpoint voltage balancing module, a dynamic control parameter lambda is obtained through calculation;

controlling a power circuit by the control parameter lambda through a single-phase SVPWM (space vector pulse width modulation) strategy so as to realize midpoint voltage balance;

implementing i by the harmonic observer_a(t) the method of observation is as follows:

observer design principle, single-phase full-bridge Conergy NPC mathematical model corresponding observerThe expression of space state is shown as formula (1) < CHEM >_mIs a feedback matrix;is x_m(kT) of the estimated value of the state,is u_cm(kT) of the estimated value of (kT),is u_cm(kT) an estimate of the quadrature value;is an output value;

<mrow> <mfenced open = "{" close = ""> <mtable> <mtr> <mtd> <mrow> <mover> <mi>x</mi> <mo>^</mo> </mover> <mrow> <mo>(</mo> <mo>(</mo> <mrow> <mi>k</mi> <mo>+</mo> <mn>1</mn> </mrow> <mo>)</mo> <mi>T</mi> <mo>)</mo> </mrow> <mo>=</mo> <msub> <mi>A</mi> <mrow> <mi>m</mi> <mi>d</mi> </mrow> </msub> <msub> <mover> <mi>x</mi> <mo>^</mo> </mover> <mi>m</mi> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mi>T</mi> <mo>)</mo> </mrow> <mo>+</mo> <msub> <mi>l</mi> <mi>m</mi> </msub> <mrow> <mo>(</mo> <mi>C</mi> <mi>x</mi> <mo>(</mo> <mrow> <mi>k</mi> <mi>T</mi> </mrow> <mo>)</mo> <mo>-</mo> <mi>C</mi> <munderover> <mo>&Sigma;</mo> <mrow> <mi>m</mi> <mo>=</mo> <mn>0</mn> </mrow> <mi>&infin;</mi> </munderover> <msub> <mover> <mi>x</mi> <mo>^</mo> </mover> <mi>m</mi> </msub> <mo>(</mo> <mrow> <mi>k</mi> <mi>T</mi> </mrow> <mo>)</mo> <mo>)</mo> </mrow> </mrow> </mtd> </mtr> <mtr> <mtd> <mrow> <mo>=</mo> <msub> <mi>A</mi> <mrow> <mi>m</mi> <mi>d</mi> </mrow> </msub> <mfenced open = "[" close = "]"> <mtable> <mtr> <mtd> <mrow> <msub> <mover> <mi>x</mi> <mo>^</mo> </mover> <mrow> <mi>m</mi> <mn>1</mn> </mrow> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mi>T</mi> <mo>)</mo> </mrow> </mrow> </mtd> </mtr> <mtr> <mtd> <mrow> <msub> <mover> <mi>x</mi> <mo>^</mo> </mover> <mrow> <mi>m</mi> <mn>2</mn> </mrow> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mi>T</mi> <mo>)</mo> </mrow> </mrow> </mtd> </mtr> </mtable> </mfenced> <mo>+</mo> <msup> <mrow> <mo>&lsqb;</mo> <msub> <mi>b</mi> <mrow> <mi>m</mi> <mn>1</mn> </mrow> </msub> <mo>,</mo> <msub> <mi>b</mi> <mrow> <mi>m</mi> <mn>2</mn> </mrow> </msub> <mo>&rsqb;</mo> </mrow> <mi>T</mi> </msup> <mi>C</mi> <mrow> <mo>(</mo> <mi>y</mi> <mo>(</mo> <mrow> <mi>k</mi> <mi>T</mi> </mrow> <mo>)</mo> <mo>-</mo> <munderover> <mo>&Sigma;</mo> <mrow> <mi>m</mi> <mo>=</mo> <mn>0</mn> </mrow> <mi>&infin;</mi> </munderover> <msub> <mover> <mi>x</mi> <mo>^</mo> </mover> <mrow> <mi>m</mi> <mn>1</mn> </mrow> </msub> <mo>(</mo> <mrow> <mi>k</mi> <mi>T</mi> </mrow> <mo>)</mo> <mo>)</mo> </mrow> </mrow> </mtd> </mtr> <mtr> <mtd> <mrow> <msub> <mover> <mi>y</mi> <mo>^</mo> </mover> <mi>m</mi> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mi>T</mi> <mo>)</mo> </mrow> <mo>=</mo> <mi>C</mi> <msub> <mover> <mi>x</mi> <mo>^</mo> </mover> <mi>m</mi> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mi>T</mi> <mo>)</mo> </mrow> </mrow> </mtd> </mtr> </mtable> </mfenced> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>1</mn> <mo>)</mo> </mrow> </mrow>

wherein C is an output matrix with the size of 1 × 2N; a. the_mdIs a system matrix;

according to the design idea of progressive observation, input signal u_c(t) discrete observerDesigned as a kind of closed-loop observer,is defined as formula (2), wherein l is a feedback matrix consisting of N l_mComposition is carried out;a state estimate of x (kT);is an estimate of the input value uc (kT);

<mrow> <mfenced open = "{" close = ""> <mtable> <mtr> <mtd> <mrow> <mover> <mi>x</mi> <mo>^</mo> </mover> <mrow> <mo>(</mo> <mo>(</mo> <mrow> <mi>k</mi> <mo>+</mo> <mn>1</mn> </mrow> <mo>)</mo> <mi>T</mi> <mo>)</mo> </mrow> <mo>=</mo> <msub> <mi>A</mi> <mi>a</mi> </msub> <mover> <mi>x</mi> <mo>^</mo> </mover> <mrow> <mo>(</mo> <mi>k</mi> <mi>T</mi> <mo>)</mo> </mrow> <mo>+</mo> <mi>l</mi> <mrow> <mo>(</mo> <mi>y</mi> <mo>&lsqb;</mo> <mi>k</mi> <mi>T</mi> <mo>&rsqb;</mo> <mo>-</mo> <munderover> <mo>&Sigma;</mo> <mrow> <mi>m</mi> <mo>=</mo> <mn>0</mn> </mrow> <mi>&infin;</mi> </munderover> <msub> <mover> <mi>x</mi> <mo>^</mo> </mover> <mrow> <mi>m</mi> <mn>1</mn> </mrow> </msub> <mo>(</mo> <mrow> <mi>k</mi> <mi>T</mi> </mrow> <mo>)</mo> <mo>)</mo> </mrow> </mrow> </mtd> </mtr> <mtr> <mtd> <mrow> <mo>=</mo> <msub> <mi>A</mi> <mi>d</mi> </msub> <msup> <mfenced open = "[" close = "]"> <mtable> <mtr> <mtd> <mrow> <msub> <mover> <mi>x</mi> <mo>^</mo> </mover> <mn>0</mn> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mi>T</mi> <mo>)</mo> </mrow> </mrow> </mtd> <mtd> <mrow> <msub> <mover> <mi>x</mi> <mo>^</mo> </mover> <mn>1</mn> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mi>T</mi> <mo>)</mo> </mrow> </mrow> </mtd> <mtd> <mrow> <msub> <mover> <mi>x</mi> <mo>^</mo> </mover> <mn>2</mn> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mi>T</mi> <mo>)</mo> </mrow> </mrow> </mtd> <mtd> <mn>...</mn> </mtd> <mtd> <mrow> <msub> <mover> <mi>x</mi> <mo>^</mo> </mover> <mi>N</mi> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mi>T</mi> <mo>)</mo> </mrow> </mrow> </mtd> </mtr> </mtable> </mfenced> <mi>T</mi> </msup> <mo>+</mo> <msup> <mfenced open = "[" close = "]"> <mtable> <mtr> <mtd> <msub> <mi>l</mi> <mn>0</mn> </msub> </mtd> <mtd> <msub> <mi>l</mi> <mn>1</mn> </msub> </mtd> <mtd> <mn>...</mn> </mtd> <mtd> <msub> <mi>l</mi> <mi>N</mi> </msub> </mtd> </mtr> </mtable> </mfenced> <mi>T</mi> </msup> <mrow> <mo>(</mo> <mi>y</mi> <mo>(</mo> <mrow> <mi>k</mi> <mi>T</mi> </mrow> <mo>)</mo> <mo>-</mo> <munderover> <mo>&Sigma;</mo> <mrow> <mi>m</mi> <mo>=</mo> <mn>0</mn> </mrow> <mi>&infin;</mi> </munderover> <msub> <mover> <mi>x</mi> <mo>^</mo> </mover> <mrow> <mi>m</mi> <mn>1</mn> </mrow> </msub> <mo>(</mo> <mrow> <mi>k</mi> <mi>T</mi> </mrow> <mo>)</mo> <mo>)</mo> </mrow> </mrow> </mtd> </mtr> <mtr> <mtd> <mrow> <mover> <mi>y</mi> <mo>^</mo> </mover> <mrow> <mo>(</mo> <mi>k</mi> <mi>T</mi> <mo>)</mo> </mrow> <mo>=</mo> <mi>C</mi> <mover> <mi>x</mi> <mo>^</mo> </mover> <mrow> <mo>(</mo> <mi>k</mi> <mi>T</mi> <mo>)</mo> </mrow> <mo>=</mo> <mfenced open = "[" close = "]"> <mtable> <mtr> <mtd> <mrow> <mo>&lsqb;</mo> <mn>1</mn> <mo>,</mo> <mn>0</mn> <mo>&rsqb;</mo> </mrow> </mtd> <mtd> <mrow> <mo>&lsqb;</mo> <mn>1</mn> <mo>,</mo> <mn>0</mn> <mo>&rsqb;</mo> </mrow> </mtd> <mtd> <mrow> <mo>&lsqb;</mo> <mn>1</mn> <mo>,</mo> <mn>0</mn> <mo>&rsqb;</mo> </mrow> </mtd> <mtd> <mn>...</mn> </mtd> <mtd> <mrow> <mo>&lsqb;</mo> <mn>1</mn> <mo>,</mo> <mn>0</mn> <mo>&rsqb;</mo> </mrow> </mtd> </mtr> </mtable> </mfenced> <msup> <mfenced open = "[" close = "]"> <mtable> <mtr> <mtd> <mrow> <msub> <mover> <mi>x</mi> <mo>^</mo> </mover> <mn>0</mn> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mi>T</mi> <mo>)</mo> </mrow> </mrow> </mtd> <mtd> <mrow> <msub> <mover> <mi>x</mi> <mo>^</mo> </mover> <mn>1</mn> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mi>T</mi> <mo>)</mo> </mrow> </mrow> </mtd> <mtd> <mrow> <msub> <mover> <mi>x</mi> <mo>^</mo> </mover> <mn>2</mn> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mi>T</mi> <mo>)</mo> </mrow> </mrow> </mtd> <mtd> <mn>...</mn> </mtd> <mtd> <mrow> <msub> <mover> <mi>x</mi> <mo>^</mo> </mover> <mi>N</mi> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mi>T</mi> <mo>)</mo> </mrow> </mrow> </mtd> </mtr> </mtable> </mfenced> <mi>T</mi> </msup> </mrow> </mtd> </mtr> </mtable> </mfenced> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>2</mn> <mo>)</mo> </mrow> </mrow>

wherein A is_dUc (kT) system matrix;to progressive errorWhich is represented asInApproaches to u_cm(t) a progressive speed; according to the pole arrangement theory, to satisfyThe ideal pole of the characteristic equation is defined asWherein a is_mT is the distance between the ideal pole and the center circle of the z-domain, and a is controlled_mThe parameter of T adjusts the convergence speed, observation bandwidth and precision of the observer,is the equation (3):

<mrow> <mover> <mi>x</mi> <mo>~</mo> </mover> <mrow> <mo>(</mo> <mo>(</mo> <mrow> <mi>k</mi> <mo>+</mo> <mn>1</mn> </mrow> <mo>)</mo> <mi>T</mi> <mo>)</mo> </mrow> <mo>=</mo> <mrow> <mo>(</mo> <msub> <mi>A</mi> <mi>d</mi> </msub> <mo>-</mo> <mi>l</mi> <mo>&CenterDot;</mo> <mi>C</mi> <mo>)</mo> </mrow> <mover> <mi>x</mi> <mo>~</mo> </mover> <mrow> <mo>(</mo> <mi>k</mi> <mi>T</mi> <mo>)</mo> </mrow> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>3</mn> <mo>)</mo> </mrow> </mrow>

the characteristic equation of the formula (5) in the Z domain is the formula (4), wherein E is a 2N × 2N identity matrix, and Z isThe number of z is 2N:

f_d(z)＝|zE-A_d+l·C| (4)

the desired characteristic polynomial is defined as:

the coefficients of equation (4) and equation (5) are equal, so that the parameter of l can be determined, and the inductor current i can be completed by equation (6)_a(t) observation;

the relation between the lambda and the action time of the switching vector is as follows:

<mrow> <mfenced open = "{" close = ""> <mtable> <mtr> <mtd> <mrow> <msub> <mi>T</mi> <mrow> <mi>a</mi> <mo>+</mo> </mrow> </msub> <mo>=</mo> <mrow> <mo>(</mo> <mi>&lambda;</mi> <mo>+</mo> <mn>1</mn> <mo>)</mo> </mrow> <msub> <mi>T</mi> <mi>a</mi> </msub> <mo>/</mo> <mn>2</mn> </mrow> </mtd> </mtr> <mtr> <mtd> <mrow> <msub> <mi>T</mi> <mrow> <mi>a</mi> <mo>-</mo> </mrow> </msub> <mo>=</mo> <mrow> <mo>(</mo> <mn>1</mn> <mo>-</mo> <mi>&lambda;</mi> <mo>)</mo> </mrow> <msub> <mi>T</mi> <mi>a</mi> </msub> <mo>/</mo> <mn>2</mn> </mrow> </mtd> </mtr> </mtable> </mfenced> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>7</mn> <mo>)</mo> </mrow> </mrow>

wherein the action time of the vectors (1,0) and (0,1) is T_a+The vectors (0, -1) and (-1,0) have a duration of action T_a-；

In the next switching cycle T_aTime allocation of (2):

<mrow> <mfenced open = "{" close = ""> <mtable> <mtr> <mtd> <mrow> <msup> <mi>&Delta;U</mi> <mo>*</mo> </msup> <mo>-</mo> <mi>&Delta;</mi> <mi>U</mi> <mo>=</mo> <msup> <mi>&Delta;U</mi> <mo>*</mo> </msup> <mo>-</mo> <mfrac> <mn>1</mn> <mi>C</mi> </mfrac> <mo>&Integral;</mo> <mrow> <mo>(</mo> <msup> <msub> <mi>S</mi> <mi>a</mi> </msub> <mn>2</mn> </msup> <mo>-</mo> <msup> <msub> <mi>S</mi> <mi>b</mi> </msub> <mn>2</mn> </msup> <mo>)</mo> </mrow> <msub> <mi>i</mi> <mi>a</mi> </msub> <mo>=</mo> <msup> <mi>&Delta;U</mi> <mo>*</mo> </msup> <mo>-</mo> <mfrac> <mn>1</mn> <mi>C</mi> </mfrac> <mrow> <mo>(</mo> <msub> <mi>T</mi> <mrow> <mi>a</mi> <mo>+</mo> </mrow> </msub> <mo>-</mo> <msub> <mi>T</mi> <mrow> <mi>a</mi> <mo>-</mo> </mrow> </msub> <mo>)</mo> </mrow> <mo>&times;</mo> <msub> <mi>i</mi> <mi>a</mi> </msub> </mrow> </mtd> </mtr> <mtr> <mtd> <mrow> <msub> <mi>T</mi> <mi>a</mi> </msub> <mo>=</mo> <msub> <mi>T</mi> <mrow> <mi>a</mi> <mo>-</mo> </mrow> </msub> <mo>+</mo> <msub> <mi>T</mi> <mrow> <mi>a</mi> <mo>-</mo> </mrow> </msub> <mo>=</mo> <mrow> <mo>(</mo> <mi>&lambda;</mi> <mo>+</mo> <mn>1</mn> <mo>)</mo> </mrow> <msub> <mi>T</mi> <mi>a</mi> </msub> <mo>/</mo> <mn>2</mn> <mo>+</mo> <mrow> <mo>(</mo> <mn>1</mn> <mo>-</mo> <mi>&lambda;</mi> <mo>)</mo> </mrow> <msub> <mi>T</mi> <mi>a</mi> </msub> <mo>/</mo> <mn>2</mn> </mrow> </mtd> </mtr> </mtable> </mfenced> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>8</mn> <mo>)</mo> </mrow> </mrow>

wherein (S)_a，S_b) As a switching vector, Δ U^*Is a midpoint potential fluctuation reference value, and delta U is a midpoint potential fluctuation value which is only formed by switching functions of two bridge arms and an output phase current i_aDetermining:

<mrow> <mi>&Delta;</mi> <mi>U</mi> <mo>=</mo> <msub> <mi>U</mi> <mrow> <mi>c</mi> <mn>1</mn> </mrow> </msub> <mo>-</mo> <msub> <mi>U</mi> <mrow> <mi>c</mi> <mn>2</mn> </mrow> </msub> <mo>=</mo> <mfrac> <mn>1</mn> <mi>C</mi> </mfrac> <mo>&Integral;</mo> <mrow> <mo>(</mo> <msup> <msub> <mi>S</mi> <mi>a</mi> </msub> <mn>2</mn> </msup> <mo>-</mo> <msup> <msub> <mi>S</mi> <mi>b</mi> </msub> <mn>2</mn> </msup> <mo>)</mo> </mrow> <msub> <mi>i</mi> <mi>a</mi> </msub> <mi>d</mi> <mi>t</mi> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>9</mn> <mo>)</mo> </mrow> </mrow>

wherein U is_c1、U_c2Is the voltage of the DC side capacitors C1 and C2, balance the capacitor C₁＝C₂＝C；

<mrow> <mi>&lambda;</mi> <mo>=</mo> <mfrac> <mrow> <mo>-</mo> <mi>C</mi> <mo>&times;</mo> <mrow> <mo>(</mo> <msup> <mi>&Delta;U</mi> <mo>*</mo> </msup> <mo>-</mo> <mi>&Delta;</mi> <mi>U</mi> <mo>)</mo> </mrow> </mrow> <mrow> <msub> <mi>T</mi> <mi>a</mi> </msub> <mo>&times;</mo> <msub> <mi>i</mi> <mi>a</mi> </msub> </mrow> </mfrac> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>10</mn> <mo>)</mo> </mrow> </mrow>

Sample C₁、C₂Upper voltage and harmonic observer inductive current i_aThe lambda value can be accurately estimated through the formula (10), and the unbalance of the midpoint potential at the moment is compensated through single-phase SVPWM modulation.

2. The method of claim 1, wherein the SVPWM modulation scheme is implemented as follows:

when U is turned_dc/2＜U_in≤U_dcThe synthesis sequence is (1,0) → (1, -1) → (0, -1) → (1, -1) → (1,0), and the synthesis time is

T_a＝(2(U_dc-V_in)/U_dc)*T_s

T_b＝T_s-T；

When 0 < U_in≤U_dcAt the time of/2, the synthesis sequence is (1,0) → (0,0) → (0, -1) → (0,0) → (1,0), and the synthesis time is

T_a＝(2*V_in/U_dc)*T_s

T_b＝T_s-T_a；

when-U_dc/2＜U_inThe synthesis sequence is (0,1) → (0,0) → (-1,0) → (0,0) → (0,1) at a time of ≤ 0, and the synthesis time is

T_a＝(-2*V_in/U_dc)*T_s

T_b＝T_s-T_a；

when-U_dc≤U_in≤-U_dcAt the time of/2, the synthesis sequence is (0,1) → (-1,1) → (-1,0) → (-1,1) → (0,1), and the synthesis time is

T_a＝(2*(V_in+U_dc)/U_dc)*T_s

T_b＝T_s-T_a。