CN111541382B

CN111541382B - Control method for Vienna rectifier current distortion under heavy load condition

Info

Publication number: CN111541382B
Application number: CN202010366804.9A
Authority: CN
Inventors: 刘钊; 季嘉伟; 孔建寿; 余婕; 龚健
Original assignee: Nanjing University of Science and Technology
Current assignee: Nanjing University of Science and Technology
Priority date: 2020-04-30
Filing date: 2020-04-30
Publication date: 2022-06-21
Anticipated expiration: 2040-04-30
Also published as: CN111541382A

Abstract

The invention discloses a method for controlling the current distortion of a Vienna rectifier under the condition of heavy load, which obtains the modulation degree m of the Vienna rectifier according to the actual operation condition, and then obtains the modulation degree m of the Vienna rectifier according to m and theta_mTo obtain a corresponding maximum allowable lag angle theta_m(ii) a Calculating the actual lag angle theta and the maximum allowable lag angle theta_mComparing to determine whether to compensate for reactive power, if theta is less than or equal to theta_mNo compensation is required, if theta>θ_mReactive power needs to be compensated; and (5) completing the control of the Vienna rectifier by adopting a zero-sequence component injection method. The invention can not only improve the current distortion under the condition of large load, but also maximize the power factor angle.

Description

Control method for Vienna rectifier current distortion under heavy load condition

Technical Field

The invention relates to a power electronic technology, in particular to a control method for Vienna rectifier current distortion under a heavy load condition.

Background

For the Vienna rectifier, because an included angle exists between phase current and a reference voltage vector, a diode in the topology of the Vienna rectifier is forced to commutate when the three-phase current crosses zero, so that current distortion can be caused, and the current is deteriorated. Although the conventional zero-sequence component injection method can solve the current distortion problem under certain conditions, the method is limited by the modulation degree, so that the included angle between the phase current and the reference voltage vector is also limited, and therefore, when the load current is increased to exceed a certain limit, only the zero-sequence component injection method is not applicable any more, and the principle of the zero-sequence component injection method is explained in detail below.

Fig. 1 is a topology of a conventional three-phase three-wire system Vienna rectifier, the Vienna rectifier is a three-level converter, and fig. 2 is a three-level space vector diagram, which is divided into 6 sectors from sector i to sector vi according to three-phase voltage distribution. Reference voltage v due to voltage drop across inductance_refAnd current i_sWith a lag angle therebetween, as in fig. 2Sector I shows, assuming that v is set at a certain modulation_refRunning in the a area, the basic vector combination is [100 ]]，[10-1]，[00-1]，[0-1-1]. But when entering the b region, only [01-1 ] can be output due to the uncontrollable characteristic of the diode]Instead of [0-1]. Thus using a catalyst such as [000 ]]→[100]→[10-1]→[100]→[000]The five-section SVPWM can avoid current distortion. In other words, current distortion can be avoided as long as the switch is always on when the current commutates. Therefore, the analysis of the first sector is popularized to the rest sectors, and the analysis in SVPWM is equivalent to the calculation in SPWM, so that the zero-sequence component injection method can be obtained.

The conventional zero sequence component method is limited by the modulation degree m, such as the first sector space vector diagram of fig. 3, when v is_refWhen operating in

areas

1 and 2, it can be replaced by redundant vectors, and when entering area 3, only large vectors [1-1 ] can be used]And no redundant vector can be substituted, and 1-1]Since the current itself cannot be output during current commutation, once entering the region 3, if the modulation degree m exceeds a certain limit, the current will be distorted.

Disclosure of Invention

The invention aims to provide a control method for Vienna rectifier current distortion under a heavy load condition.

The technical solution for realizing the purpose of the invention is as follows: a method for controlling current distortion of a Vienna rectifier under a heavy load condition comprises the following steps:

step 1, obtaining a modulation degree m of the Vienna rectifier according to actual operation conditions, and obtaining the modulation degree m of the Vienna rectifier according to m and theta_mTo obtain a corresponding maximum allowable lag angle theta_m；

Step 2, calculating an actual lag angle theta and comparing the actual lag angle theta with the maximum allowable lag angle theta_mComparing to determine whether to compensate for reactive power, if theta is less than or equal to theta_mThen no compensation is required, if theta>θ_mReactive power needs to be compensated;

and 3, completing Vienna rectifier control by adopting a zero-sequence component injection method.

Further, in step 1, m and θ_mHas the relation of

Further, in step 2, the actual lag angle is calculated according to the formula

Wherein i_dAnd e_dRespectively active current and grid voltage, V_outFor the output voltage of the DC side, i_outTo output a current.

Further, in step 3, the reactive power to be compensated is

i_q ^*＝i_d ^*tanΔθ

Wherein Δ θ is obtained by the following formula

θ＝θ_v-Δθ

In the formula, theta_vIs a reference vector v_refTo the mains voltage e_dAngle of (i)_dActive current, omega is the angular frequency of the power grid, and L is the inductance value; with increasing reactive power of compensation, theta_vIt is also slightly increased, and therefore it is difficult to directly determine Δ θ so that the actual lag angle θ is equal to the maximum lag angle θ allowed by the current modulation_mAnd then the theta v and the delta theta can be obtained by solving the formula.

Compared with the prior art, the invention has the remarkable advantages that: the space vector diagram of the Vienna rectifier is analyzed, the application range of the traditional zero sequence component injection method is determined, the lag angle theta between the current and the reference voltage vector is reduced by compensating certain reactive power, and the lag angle theta is enabled to reach the use range of the zero sequence component method, so that the zero sequence component injection method is reused, the current distortion under the condition of large load can be improved, and the power factor angle can be maximized.

Drawings

Fig. 1 is a three-phase three-wire Vienna rectifier topology diagram.

Fig. 2 is a three-level spatial vector diagram. .

Fig. 3 is a first sector spatial vector diagram.

FIG. 4 shows modulation m and maximum allowable lag angle θ_mA graph of the relationship (c).

Figure 5 is a vector diagram of the operation of a unit power factor.

Fig. 6 is a schematic diagram of reactive power compensation.

FIG. 7 is θ_mAnd Δ θ and θ_vAnd Δ θ.

Fig. 8 is a graph of current simulation results.

Detailed Description

The following further describes embodiments of the present invention with reference to the drawings and specific examples.

Step 1, obtaining a modulation degree m of the Vienna rectifier according to actual operation conditions, and obtaining the modulation degree m of the Vienna rectifier according to m and theta_mTo obtain a corresponding maximum allowable lag angle theta_m。

In this step, the modulation degree m and the maximum allowable lag angle θ can be analyzed from the first sector space vector diagram of fig. 3_mThe relationship of (a) is as follows:

for convenience of description, normalization processing is adopted in the above formula, and it is assumed that the side length of the triangle is 2, the length of the reference vector is α, and the other side length is x.

M and theta can be obtained by simplification_mThe relation of (1):

from this relationship, a graph 4 can be drawn, from which it can be seen that the maximum allowable retardation angle θ increases as the modulation m increases_mIs gradually decreased. SelectingTheta corresponding to modulation degree m_mThe maximum allowable lag angle is obtained.

Step 2, calculating an actual lag angle theta and enabling the actual lag angle theta to be equal to the maximum allowable lag angle theta_mComparing to determine whether to compensate for reactive power, if theta is less than or equal to theta_mThen no compensation is required, if theta>θ_mThen reactive compensation is required.

The expression of the actual lag angle θ is as follows

Step 3, when theta>θ_mWhen needed to compensate the reactive power i_q ^*＝i_d ^*tan delta theta is solved by combining a zero sequence component injection method.

Referring to step 3 in detail, fig. 5 is a diagram of a running vector of the rectifier with a unit power factor, wherein a lag angle between a current and a reference vector reaches a maximum of θ_m. Increased load and output current i_outIncrease of i_dWill also increase when i_dWhen the angle of retardation θ increases as shown in FIG. 6>θ_mI is made by compensating a certain reactive power_dAnd v_refThe lag angle θ of (a) is reduced, and the compensated current is i as shown in fig. 6. Only need to compensate until when theta is equal to theta_mThe zero sequence component injection method is used, so that the power factor can be maximized, but it can be found from fig. 6 that the reference voltage vector v is obtained after certain reactive power is compensated_refTo the mains voltage e_dThe angle between them will also increase slightly, noted as θ_vThus making the specific value of the compensation reactive difficult to determine, but the lag angle theta and the compensation angles delta theta and theta can be obtained from fig. 6_vThe relation of (1):

θ＝θ_v-Δθ (4)

from the cosine theorem and the pythagorean theorem, one can obtain:

in the above formula u_LIs the inductor voltage, simplified to the following equation:

from figure 6, v can be seen very intuitively_refI.e. v after a certain reactive power has been compensated_refDecreases and thus the modulation m also decreases, the maximum allowable lag angle theta_mIn essence, is increased. In other words, by compensating for the reactive power, the original θ can be made>θ_mBecomes theta ≦ theta_mIn order to maximize the power factor angle, then only θ ═ θ needs to be satisfied_mThat is, the theta at that time is solved by using the formulas (4) and (6)_vAnd delta theta, wherein the delta theta is a reactive angle to be compensated, and the reactive instruction is

i_q ^*＝tanΔθ·i_d ^* (7)

Examples

To verify the validity of the inventive scheme, the following simulation experiment was performed.

An experimental simulation model is built in Matlab/Simulink, and system parameters are shown in Table 1. When the load increases to make i_dWhen the value is 12A, v at that time is calculated_refAnd a modulation degree m of 0.894, corresponding to θ_mBut the actual lag angle is 5.08 ° at 4 °, so the current distortion still exists by simply using the zero sequence component injection method. Therefore, by compensating for reactive power, θ is plotted_mAnd [ Delta ] theta and [ theta ]_vAnd Δ θ, as shown in FIG. 7, θ increases_vAnd (4) selecting corresponding delta theta when the increment is small, and obtaining the reactive current instruction of about 0.21A according to calculation.

TABLE 1 Vienna rectifier circuit parameters

Parameter(s)	Numerical value
		Electric network voltage (phase)	60V(50Hz)
Voltage on the direct current side	165V
		Filter inductance L	2mH
DC side capacitor C	2.05mF
		Switching frequency	30kHz

The simulation is shown in fig. 8, the current situation after only zero-sequence component injection is before 0.5s, the injection components are shown in table 2, and the current is improved after the compensation part is idle after 0.5 s.

TABLE 2 zero sequence component injection method

Sector area	Zero sequence component	Extent of implantation
			I	-V_b	V_a-2V_b+V_c>0,V_a-V_b<1,V_a-V_c>1
II	-V_a	2V_a-V_b-V_c>0,V_a-V_c<1,V_b-V_c>1
			III	-V_c	V_a+V_b-2V_c>0,V_a-V_b<-1,V_b-V_c<1
IV	-V_b	V_a-2V_b+V_c<0,V_a-V_b>-1,V_a-V_c<-1
			V	-V_a	2V_a-V_b-V_c<0,V_a-V_c>-1,V_b-V_c<-1
VI	-V_c	V_a+V_b-2V_c<0,V_a-V_b>1,V_b-V_c>-1

Claims

1. A method for controlling the current distortion of a Vienna rectifier under the condition of large load is characterized by comprising the following steps:

step 1, obtaining a modulation degree m of the Vienna rectifier according to actual operation conditions, and then obtaining the modulation degree m of the Vienna rectifier according to m and theta_mTo obtain a corresponding maximum allowable lag angle theta_m；

step 3, when reactive power is compensated, a zero sequence component injection method is adopted to complete Vienna rectifier control, and the reactive power required to be compensated is

i_q ^*＝i_d ^*tanΔθ

Wherein i_d ^*And i_q ^*Reference values for the active and reactive currents, respectively, Δ θ is obtained from the following equation

θ＝θ_v-Δθ

In the formula, theta_vIs a reference vector v_refTo the mains voltage e_dAngle of (ii) of_dActive current, omega, power grid voltage fundamental frequency and L, input side filter inductance; the actual lag angle theta is equal to the maximum lag angle theta allowed by the current modulation degree_mThen, the above formula is used to solve to obtain θ v and Δ θ.

2. The method for controlling the current distortion of the Vienna rectifier under the condition of large load as claimed in claim 1, wherein: in step 1, m and θ_mIs related to

3. The method for controlling distortion of a Vienna rectifier current under the condition of high load as claimed in claim 1, wherein: in step 2, the actual lag angle is calculated according to the formula

Wherein i_dAnd e_dRespectively active current and grid voltage, V_outFor the output voltage of the DC side, i_outFor the output current, ω is the fundamental frequency of the grid voltage and L is the input side filter inductance.