阅读说明：本技术 一种消除vienna整流器电流过零点畸变的方法 (Method for eliminating VIENNA rectifier current zero crossing distortion ) 是由 孙鑫祥 于 2020-12-10 设计创作，主要内容包括：本发明涉及一种消除VIENNA整流器电流过零点畸变的方法,包括以下步骤：采集电网电压信息；通过整流器进行能量分析,根据整流器直流侧提供给负载的有功功率计算d轴网侧电流分量；分析基于输入未知的q轴网侧电流分量时电网电压向量、网侧输入电流向量和整流器输出电压向量之间的几何关系；根据电流过零点的临界条件和步骤S3中获取的几何关系来计算注入特定的q轴网侧电流分量；根据整流器输出电压向量确定开关管的开关序列。该方法使得VIENNA整流器在电流过零点运行时,可以完全消除输出电压畸变,与整流器输出电压定向电流消除电流过零点畸变方法相比,提高了功率因数。(The invention relates to a method for eliminating VIENNA rectifier current zero crossing distortion, which comprises the following steps: collecting power grid voltage information; performing energy analysis through a rectifier, and calculating a current component of a d-axis network side according to active power provided to a load by a direct current side of the rectifier; analyzing a geometrical relationship among a grid voltage vector, a grid side input current vector and a rectifier output voltage vector when unknown q-axis grid side current components are input; calculating a current component injected into a specific q-axis network side according to the critical condition of the current zero crossing point and the geometric relation obtained in the step S3; and determining the switching sequence of the switching tube according to the vector of the output voltage of the rectifier. The method can completely eliminate the distortion of the output voltage when the VIENNA rectifier operates at the zero crossing point of the current, and compared with the method for eliminating the distortion of the zero crossing point of the current by the directional current of the output voltage of the rectifier, the power factor is improved.)

1. A method for eliminating distortion at zero crossings of VIENNA rectifier current, comprising the steps of:

s1, collecting power grid voltage information q;

s2, determining active power provided by the direct current side of the rectifier to the load according to the power grid voltage information, and determining a d-axis network side current component I based on the active power provided by the direct current side of the rectifier to the load_d；

S3, analyzing the unknown q-axis network side current component I based on input_qThe geometric relationship among the time power grid voltage vector E, the grid side input current vector I and the rectifier output voltage vector U;

s4, calculating the current component I injected into the specific q-axis network side according to the critical condition of the current zero crossing point and the geometric relation obtained in the step S3_qAnd a rectifier output voltage vector U;

and S5, determining a switching sequence of the switching tube according to the rectifier output voltage vector U obtained in the step S4.

2. The method for eliminating distortion of zero-crossing points of VIENNA rectifier current in claim 1, wherein the d-axis network side current component I in step S2_dThe calculation formula of (2) is as follows:

I_d＝P/E (1)

where P is the active power supplied to the load by the dc side of the rectifier and E is the collected grid voltage.

3. The method of claim 1, wherein the distortion of VIENNA rectifier current zero crossings is eliminated by: in the step S3, the grid-side input current vector I lags the grid voltage vector E and leads the rectifier output voltage vector U, and the angle of the grid-side input current vector I lags the grid voltage vector E is the power factor of the grid sideThe rectifier output voltage vector U is on the boundary line of the modulatable region and the non-modulatable region.

4. The method of claim 1, wherein the q-axis net side current component I specified in step S4 is used to eliminate distortion at zero crossing point of VIENNA rectifier current_qThe calculation formula of (2) is as follows:

wherein U is_dAnd U_qFor the decomposition vector of the rectifier output voltage vector in dq coordinate system, I_dAnd I_qThe grid voltage vector E is a decomposition vector of the grid side input current vector I in a dq coordinate system and is coincident with the d axis.

5. The method of claim 4, wherein the distortion of VIENNA rectifier current zero crossings is eliminated by: according to U_dAnd U_qA switching sequence is determined.

Technical Field

The invention belongs to the field of power electronic technology application, and particularly relates to a method for eliminating VIENNA rectifier current zero crossing distortion.

Background

In recent years, three-level converters have received much attention. Compared with the traditional two-level converter, the three-level converter has the advantages of lower total harmonic distortion rate, lower device voltage stress and higher energy conversion efficiency. Among a plurality of three-level converters, the VIENNA rectifier is widely applied to medium-voltage and high-voltage high-power occasions such as wind driven generators, electric automobiles and the like by virtue of high power factor and simple control.

The VIENNA rectifier current zero crossing distortion problem is mainly caused by the fact that a traditional control method works on a network side unit power factor, namely that a power grid voltage and a network side input current are caused in the same phase. When the VIENNA rectifier operates at the current zero crossing point, it appears that the modulated voltage does not coincide with the phase current sign, which is the root cause of distortion in the current zero crossing.

To eliminate the VIENNA rectifier current zero crossing distortion problem, the essential solution is to make the net side input current and the rectifier output voltage in phase. But this approach sacrifices power factor. And high power factor is one of the superior performances of VIENNA rectifiers. Therefore, a VIENNA rectifier control method that eliminates current zero crossing distortion and improves power factor is needed.

Disclosure of Invention

The invention aims to solve the problem, and provides a method for eliminating the distortion of the zero crossing point of the VIENNA rectifier current, which solves the problem of the distortion of the zero crossing point of the current by injecting a specific q-axis network side input current component. Meanwhile, the problem of power factor reduction caused by eliminating current zero crossing distortion is solved.

The invention realizes the purpose through the following technical scheme:

a method of eliminating VIENNA rectifier current zero crossing distortion comprising the steps of:

s1, collecting power grid voltage information q;

s2, determining active power provided by the direct current side of the rectifier to the load according to the power grid voltage information, and determining a d-axis network side current component I based on the active power provided by the direct current side of the rectifier to the load_d；

S3, analyzing the unknown q-axis network side current component I based on input_qThe geometric relationship among the time power grid voltage vector E, the grid side input current vector I and the rectifier output voltage vector U;

s4, according to the critical condition and step of the current zero crossing pointThe geometry obtained in step S3 is used to calculate the current component I injected into the specific q-axis network side_qAnd a rectifier output voltage vector U;

and S5, determining a switching sequence of the switching tube according to the rectifier output voltage vector U obtained in the step S4.

As a further optimization scheme of the present invention, the d-axis network side current component I in the step S2_dThe calculation formula of (2) is as follows:

I_d＝P/E (1)

where P is the active power supplied to the load by the dc side of the rectifier and E is the collected grid voltage.

As a further optimization scheme of the present invention, in step S3, the grid-side input current vector I lags the grid voltage vector E and leads the rectifier output voltage vector U, and the angle of the grid-side input current vector I lags the grid voltage vector E is the power factor of the grid sideThe rectifier output voltage vector U is on the boundary line of the modulatable region and the non-modulatable region.

As a further optimization of the present invention, the q-axis network side current component I specified in step S4_qThe calculation formula of (2) is as follows:

wherein U is_dAnd U_qFor the decomposition vector of the rectifier output voltage vector in dq coordinate system, I_dAnd I_qThe grid voltage vector E is a decomposition vector of the grid side input current vector I in a dq coordinate system and is coincident with the d axis.

As a further optimization of the invention, according to U_dAnd U_qA switching sequence is determined.

The invention has the beneficial effects that:

1) according to the invention, by injecting a specific q-axis network side input current component, the relation among a power grid voltage vector, a network side input current vector and a rectifier output voltage vector is adjusted, so that the problem of current zero crossing distortion is eliminated;

2) compared with the method of outputting voltage directional current by adopting a rectifier, the method improves the power factor of the power grid side.

Drawings

FIG. 1 is a flow chart of the present invention for eliminating distortion of VIENNA rectifier current zero crossings;

FIG. 2 is a topology of a VIENNA rectifier;

FIG. 3 is a space vector diagram of a VIENNA rectifier;

FIG. 4 is a modulatable local space vector diagram of a VIENNA rectifier;

FIG. 5 is a non-modulatable local spatial vector diagram of a VIENNA rectifier;

FIG. 6 is a vector diagram in dq axes;

FIG. 7 is I_dAnda graph of (a).

Detailed Description

The present application will now be described in further detail with reference to the drawings, it should be noted that the following detailed description is given for illustrative purposes only and is not to be construed as limiting the scope of the present application, as those skilled in the art will be able to make numerous insubstantial modifications and adaptations to the present application based on the above disclosure.

Example 1

The embodiment provides a control method for eliminating distortion of a VIENNA rectifier current zero crossing point, as shown in fig. 1, including the following steps:

the topology of the VIENNA rectifier is shown in fig. 2. For the sake of analysis, it can be considered that the values and directions of the three-phase currents are almost constant in one carrier cycle. R_LIs a load; c₁、C₂The capacitor is a direct current side upper and lower capacitor; s is a switching tube; d is an uncontrolled diode; l is_sAnd R_sThe inductance value and the resistance value of the three-phase alternating current side input inductor are respectively; e.g. of the type_x(x ═ a, b, c) are three-phase ac mains phase voltages; i.e. i_xInputting current for the network side; u. of_xAnd outputting voltage for a bridge arm of the rectifier.

Defining a switching function S_x(x ═ a, b, c) represents the state of the inner tube. When the inner tube is conducted, S_x1 is ═ 1; when the inner tube is turned off, S_x0. When S is_xWhen the current is positive or negative at 1, the x-phase output of the rectifier is connected to point O, defining this state as a 0 level. At S_xWhen the current is positive, the current passes through the diode Dx when 0 is satisfied₁Connecting with the positive bus, defining the state as 1 level; when the current is negative, the current passes through the diode D_x2In connection with the negative bus, this state is defined as-1 level, the specific relationship of which is shown in table 1 below.

TABLE 1

Since each state of the three phases can determine a vector, e.g., vector [1, -1, -1] indicates that phase a outputs a 1 level and phase B and phase C both output a-1 level. A space vector diagram of a VIENNA rectifier can be obtained as shown in fig. 3. The presence of certain vectors in the figure is conditional in view of the above constraints. In actual operation, the rectifier output voltage lags the net side input current θ. Taking the zero-crossing point of the phase-B current from negative to positive as an example, at this time, the local space vector diagram of the VIENNA rectifier is shown in fig. 4, where u and i represent the output voltage vector of the bridge arm of the rectifier and the input current vector of the network side, respectively.

When the phase B current has just completed zero crossing from negative to positive, ia >0, ib >0 and ic <0, the following constraints must be satisfied: the a and B phases cannot output-1 level, the C phase cannot output 1 level, and vectors [0, -1, -1] and [1, -1, -1] cannot be output in fig. 4. Considering only the case where the modulation degree is high (m >0.5) and θ < π/6, when u is located in sector A2, u can be modulated by vector synthesis of [1, 1, 0], [1, 0, -1] and [0, 0, -1] voltages; when u is located in sector a3, only the [1, 0, 0] and [1, 0, -1] voltage vectors are present, and u cannot be synthesized and is therefore unmodulatable. The line segment of the same portion of the a2 and A3 sectors is the boundary between the modulatable region and the non-modulatable region.

Step S1, sampling power grid voltage information;

step S2, under the energy analysis of the rectifier, determining the current component of the d-axis network side through the active power provided to the load by the direct current side of the rectifier;

d-axis network-side input current component I_dThe method specifically comprises the following steps:

I_d＝P/E (1)

where P is the active power supplied to the load by the dc side of the rectifier and E is the sampled grid voltage, both of which are known.

Step S3, analyzing the relation among the grid voltage vector, the grid side input current vector and the rectifier output voltage vector on the basis of injecting unknown q-axis grid side current components;

injecting an unknown q-axis net-side input current component I_qThe requirements are as follows:

injecting an unknown q-axis net-side input current component I_qThe grid voltage vector E, the grid-side input current vector I, and the rectifier output voltage vector U need to satisfy the following relationship, as shown in fig. 6:

the grid side input current vector I will lag the grid voltage vector E while the rectifier output voltage vector U will lead. The angle of the lag of the grid-side input current vector I and the grid voltage vector E is recorded asThe physical meaning is the power factor on the grid side. At this time, the range of the q-axis network side input current component is denoted as [ I ]_q，min，0]In which I_q，min<0。

When I is_q<I_qWhen the current vector I is input to the network side, the output voltage vector U of the rectifier is lagged, and the VIENNA rectifier still has the problem of output voltage distortion at the current zero-crossing point; when Iq is>When the current vector I is 0, the grid side input current vector I leads the grid voltage vector E, and the included angle theta between the grid side current and the rectifier input voltage is increased, so that the current zero crossing point distortion area is increased.

Injecting an unknown q-axis net-side input current component I_qThe rectifier output voltage vector U is always located on the boundary line between the modulatable region and the non-modulatable region.

Taking the sector A as an example, when the phase B current is equal to zero, if the reactive current I is injected_qThe rectifier input voltage is then in sector a2, representing the injected reactive current I_qLarge, the rectifier is not operating at maximum power factor; if injecting reactive current I_qThe input voltage of the rectifier is then in sector a3, representing the injected reactive current I_qOn the small side, the rectifier still has output voltage distortion at the current zero crossing.

Step S4, solving the current component injected into the specific q-axis network side according to the critical condition of current zero-crossing distortion and the geometrical relationship between the vectors;

based on the FIG. 6 analysis, rectifier output voltage vector U is decomposed into U in dq coordinate system_dAnd U_qComponent, net-side input current vector I is decomposed into I in dq coordinate system_dAnd I_qThe component, grid voltage vector E, coincides with the d-axis. The vector composition relation satisfied under dq axis system is as follows:

wherein, U_d、U_qAnd I_qIs unknown quantity(ii) a E and I_dIn known amounts.

The parallel line passing through the point C and the parallel line passing through the point A and the point Q is parallel to the point B, and the line segments BC and AB are parallel and perpendicular to the axis D. In triangle ABC, the delta angle and power factor are knownThe relationship of (A) is as follows:if the input voltage of the rectifier is located at the boundary between the sectors a2 and A3, the geometrical relationship of the following equation must be satisfied:

simultaneously, the method also comprises the following steps:

as can be seen from the formulae (2), (3) and (4), U_d、U_q、I_qAndfor the unknowns, with four equations at the same time, a particular q-axis net side input current component can be solved.

Formula (5) gives_dAndbut solving with this equationThe analytic solution of (2) is difficult, and a search method can be adopted according to I_dAnddetermining the unknown quantityThereby obtaining an input current component I injected into a specific q-axis network side_q. Under the calculation of normalization, FIG. 7 is I_dAndin which only the graphs givenWithin the interval of 0-15 DEG, omega L_sI_dAndthe graph of (1), U obtained from equation 2_dAnd U_qThe switching sequence of the switching tube can be determined.

The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention.