阅读说明：本技术 使用Vienna整流器的12脉冲整流器DC-MPC电流矫正方法 (12-pulse rectifier DC-MPC current correction method using Vienna rectifier ) 是由 李彦 陈才学 欧阳港 杨旭涛 于 2021-06-24 设计创作，主要内容包括：本发明公开了一种使用Vienna整流器的12脉冲整流器DC-MPC电流矫正方法；所述整流器的电流矫正结构由三电平T型Vienna整流器并联12脉冲不控整流器构成。所述矫正方法首先通过功率占比反馈修正电压外环参考值从而获得无电流畸变的T型Vienna整流器参考有功功率。功率内环的占空比模型预测控制(DC-MPC)方法先筛选出利于控制中点电位平衡的备选矢量,接着通过滚动优化获得价值函数最优的第一矢量,最后针对第一矢量控制时间筛选出符合要求的第二矢量,最终得到占空比。DC-MPC方法提高了T型Vienna电流控制稳态下的控制精度,带功率占比控制的电压外环解决了电流畸变,从而提高了所述结构的电流矫正效果。(The invention discloses a current correction method for a 12-pulse rectifier DC-MPC (direct Current-Metal control Loop) by using a Vienna rectifier; the current correction structure of the rectifier is formed by connecting a three-level T-shaped Vienna rectifier with 12 pulse uncontrolled rectifiers in parallel. According to the correction method, firstly, a voltage outer ring reference value is corrected through power ratio feedback, so that the reference active power of the T-shaped Vienna rectifier without current distortion is obtained. The duty ratio model predictive control (DC-MPC) method of the power inner loop firstly screens out an alternative vector which is beneficial to controlling the neutral point potential balance, then a first vector with the optimal value function is obtained through rolling optimization, and finally a second vector which meets the requirement is screened out aiming at the control time of the first vector, and finally the duty ratio is obtained. The DC-MPC method improves the control precision of the T-shaped Vienna current control in a steady state, and the voltage outer ring with the power ratio control solves the current distortion, thereby improving the current correction effect of the structure.)

1. A12-pulse rectifier duty ratio model prediction current correction method using a Vienna rectifier is disclosed, wherein a rectifier current correction structure is formed by connecting a 12-pulse uncontrolled rectifier and a three-level T-shaped Vienna rectifier in parallel, and the control method mainly comprises the following steps:

the power distribution ratio voltage outer ring control method with no current distortion is applied to a current correction structure of a 12-pulse rectifier;

a duty ratio control model prediction current control method applied to a T-shaped Vienna rectifier.

2. According to the invention example application object and the control method in claim 1, the current distortion free power distribution ratio control method of the current correction structure of the 12-pulse rectifier is realized by correcting the reference value of the voltage outer ring, and then the reference power generated by the voltage outer ring is as follows:

。

3. the invention example application object and the control method in the claim 1, wherein the T-type Vienna rectifier DC-MPC current control method in the current rectification method comprises the following steps:

step 1: obtaining the instantaneous active power p at the moment k_kReactive power q_kIdeal active power p_refSector distribution N, midpoint potential dV_dc；

Step 2: screening out a vector beneficial to current midpoint potential balance as an alternative vector;

and step 3: traversing a calculation cost function, and taking an optimal vector as a first vector;

and 4, step 4: and traversing and calculating first vector control time by taking the zero vector and the residual alternative vectors as control sets, taking the vector conforming to the duty ratio control range as a second vector, wherein the first vector control time is as follows:

and 5: output duty cycle t_1i/T_s。

Technical Field

The invention relates to a power electronic converter and a control technology thereof, in particular to a method for predicting and controlling current rectification of a 12-pulse rectifier based on a duty ratio model.

Background

As power electronic devices are applied to more and more industrial fields, the harmonic problem of the power grid becomes more prominent. The realization of high power factor and low harmonic content of power electronic devices, especially rectifying devices, has become a hot problem of research. In high power applications, the requirements for a three-phase rectifier are: high efficiency, reliability, easy control and high quality of input current. The traditional three-phase diode uncontrollable rectifier has the characteristics of high reliability, simple topological structure, low cost and the like, and is widely applied to a rectification power supply, particularly a high-power occasion. However, the harmonic content of the input-side current of conventional diode rectifiers reaches approximately 30%, which does not comply with the international standard (IEC 61000-3-2/61000-3-4).

Compared with a traditional three-phase rectifier, the Vienna rectifier has the advantages that the number of switching tubes is less, a switching device only bears half of output voltage, the circuit topology is simple, current harmonic waves caused by dead time do not exist, and the Vienna rectifier becomes a research hotspot of scholars at home and abroad. The three-phase rectifier not only inherits the advantage of simple structure of the traditional three-phase rectifier, but also has the characteristics of high current quality, high power factor and the like.

The current correction method of the 12-pulse rectifier adopts a T-shaped Vienna rectifier as an active rectifier. In this current rectifying configuration, a passive rectifier provides a large amount of power to the dc-side load, and the Vienna rectifier suppresses the harmonics injected by the passive rectifier by actively filtering the 12-pulse rectifier input current. However, the Vienna rectifier is a unidirectional converter, so that a current smaller than zero cannot pass when the source voltage is larger than zero, which causes unnecessary current distortion, and the conventional control method of the Vienna rectifier has insufficient steady-state control accuracy, which affects the current correction effect.

Disclosure of Invention

In order to solve the problems, the invention provides a method for predicting and correcting current by using a 12-pulse rectifier duty ratio control model of a Vienna rectifier.

The model predictive control (DC-MPC) method based on duty ratio control is based on a T-shaped Vienna rectifier structure and is connected with a 12-pulse rectifier in parallel. The Vienna rectifier produces a difference between the uncontrolled rectifier portion and the ideal sinusoidal total input current without current distortion, thereby correcting the 12-pulse rectifier input current waveform.

In the application object, the correction structure control method of the embodiment of the invention is composed of a voltage outer ring with power ratio control for inhibiting current distortion and a power inner ring based on a DC-MPC, wherein the voltage outer ring output of the current correction structure of the 12-pulse rectifier is as follows:

the inner loop control method of the T-type Vienna rectifier in the current correction method is a DC-MPC control method, a second control vector is added into the MPC method of TVNR so as to generate a control duty ratio, and the control duty ratio comprises a first vector screening process, a second vector screening process and an action time rolling optimization calculation process.

Drawings

FIG. 1 is a diagram of a 12-pulse rectifier current rectification architecture;

FIG. 2 is a block diagram of a T-type Vienna rectifier;

FIG. 3 is a block diagram of a constant power ratio control strategy;

FIG. 4 is a schematic diagram of the ideal operating current for a 12-pulse rectifier configuration;

FIG. 5 is a block diagram of a 12-pulse rectifier DC-MPC current rectification system using a Vienna rectifier;

fig. 6 is a flow chart of duty ratio optimization control.

Detailed Description

For the convenience of understanding of the embodiments of the present invention, the following description will be made in terms of specific embodiments with reference to the accompanying drawings, which are not intended to limit the embodiments of the present invention.

In the present example, a 12-pulse uncontrolled rectifier corrects the input current to be sinusoidal by controlling the current of the TVNR in parallel with a T-type Vienna rectifier (TVNR) based on DC-MPC, as shown in fig. 1, which is the current correction topology of the 12-pulse rectifier proposed herein.

After the 12-pulse uncontrolled rectifying input current is correctedThe ideal operating current of (ii) is shown in FIG. 4_j＝i_jS+i_jTThe 12-pulse uncontrolled rectifying circuit and the T-shaped Vienna rectifier have different circuit structures, so that the current change rates of the two parts are different. The 12-pulse rectifier injects a 12k +1 subharmonic, and the TVNR in the 12-pulse rectifier input current correction structure provided herein provides an active filtering function for the input current of the 12-pulse rectifier; meanwhile, the bipolar direct current output voltage can be provided for specific application occasions; finally, it provides a portion of the load power, which may provide better harmonic mitigation.

The following describes the power distribution ratio voltage outer loop control method with current distortion or no current distortion for the current correction structure:

the active power associated with the vienna rectifier must be set to a certain ratio in order to be able to obtain an undistorted input current. This ratio can be determined according to a constant power ratio control strategy: in this strategy, the power ratio between the 12-pulse rectifier and the vienna rectifier remains constant under all operating conditions. Using this strategy requires an additional control loop to modify the dc link reference voltage at different operating points, i.e. control the dc side voltage to control the output power between the TVNR input power and the 12-pulse rectifier.

The expression of the active power reference value in the constant power ratio control strategy is as follows:

in the formula: d_pIs the power ratio

Thus, the output power ratio (defined as the ratio of the 12-pulse rectifier output power to the total output power) can be controlled by the output dc voltage control loop. Fig. 3 shows a block diagram of a control structure implementing this strategy.

The following describes the control method of TVNR power inner loop DC-MPC in corrective structure

Step 1: obtaining the instantaneous active power p at the moment k^kReactive power q^kIdeal active power p^refThe sector distribution N,Midpoint potential dV_dc；

Step 2: screening out a vector beneficial to current midpoint potential balance as an alternative vector; when vector screening is performed, the state of the midpoint potential on the dc side is determined, and the main sector 1 is taken as an example (the remaining sectors are similar), and if the midpoint potential is greater than zero, a short vector (poo) that can suppress the midpoint potential should be selected as a candidate vector. Therefore, if the optimal vector is a short vector, an appropriate short vector is selected according to the current state of the midpoint potential, and thus the balance control of the midpoint potential of the Vienna rectifier can be effectively realized.

And step 3: traversing a calculation cost function, and taking an optimal vector as a first vector;

the differential expression in the TVNR input current stationary coordinate system is:

direct side current i_oThe expression is as follows:

according to the instantaneous power theory, the instantaneous power change rate of the kth sampling period can be expressed as:

in the formula: u. of_m＝-e_αu_α-e_βu_β；u_n＝-e_βu_α+e_αu_β

Discretizing a TVNR power differential equation (3) according to a forward Euler formula to obtain predicted values of p and q at the k +1 moment as follows:

if the midpoint balance control is considered, discretizing the formula (2) to obtain the midpoint potential on the direct current side to obtain a prediction model as follows:

the value function J is expressed as:

however, after the vector beneficial to the midpoint balance control is screened, the cost function of the DC-MPC only needs to consider the power control, and the equation (6) can be rewritten as follows:

J＝(p^ref-p^k+1)²+(q^ref-q^k+1)² (7)

and (5) traversing the alternative vector by the calculation formula (7) to obtain a target first vector.

And 4, step 4: traversing and calculating the control time of a first vector by taking a zero vector and the residual alternative vectors as a control set, and taking a vector which conforms to the duty ratio control range as a second vector;

under the control of a single vector, a predicted value obtained after the action of the optimal vector has a larger difference from a specified reference value under certain conditions, and a control target has larger fluctuation, so that the current correction performance is influenced. In order to prevent the problem, the switching period is divided into 2 intervals, a second vector is introduced, the action time of the two vectors is distributed, the flexible regulation of the predicted value of the controlled quantity can be realized, and the reference value can be accurately tracked. In the control set, the zero vector in the main sector is selected as the second vector priority set to prevent the first vector action time t₁In the case of less than zero or an overflow switching period, the selection range of the second vector may be expanded, and the remaining candidate vectors in step 3 may be included in the control set. The rolling optimization screening second vector and action time calculation process is described below.

Assuming that the power slope remains constant for a relatively short period of time during the sampling period, the active and reactive power at the end of the control period may be expressed as:

in the formula: k is a radical of_p1And k_p2Active power slope, t, for optimum and zero vector action, respectively₂The second vector action time.

The error between the power prediction value and the reference value can be expressed in equation (8) as:

defining the cost function at minimum power, minimizing the cost function, i.e.

The optimal action time of the optimal vector is obtained by the equation (10):

the flow chart of duty cycle optimization is shown in FIG. 6

And 5: and outputting the duty ratio.

Calculate t₁Through t_1i/T_sThe PWM switching signal can be generated at a fixed switching frequency.