CN112636617B - Control method of Vienna rectifier - Google Patents

Abstract

The invention relates to a control method of a Vienna rectifier, belonging to the technical field of power electronics. The control method includes: obtaining the current positive sequence modulation degree of the Vienna rectifier, as well as the current and voltage of the current grid side; calculating the unbalance degree of the current grid according to the current and voltage of the current grid side; determining the current grid under the current positive sequence modulation degree, the current grid If the unbalance degree of the current grid is in the first range under the current positive sequence modulation system, the current control is performed according to the first current command; if under the current positive sequence modulation system, the current grid If the unbalance degree of the side is in the second range, the current control is performed according to the second current command; the first range is:

The second range is:

r is the unbalance degree; _mp is the positive sequence modulation degree. The invention is suitable for the situation that the power grid is seriously unbalanced, and expands the normal working range of the Vienna rectifier.

Description

A kind of control method of Vienna rectifier

technical field

The invention relates to a control method of a Vienna rectifier, belonging to the technical field of power electronics.

Background technique

Vienna rectifiers have excellent characteristics such as low harmonic distortion, high power factor, and unidirectional energy flow, so they are widely used in electric vehicle charging piles and wind power generation systems. Compared with the traditional two-level PWM rectifier, the voltage stress of the switch tube of the Vienna rectifier is smaller, and there is no need to set dead time, so it is more suitable for high-voltage and high-power applications, and the control is simple and reliable.

However, as shown in Figure 1, due to the characteristics of the bridge arm diode of the Vienna rectifier, there is a current distortion problem, so it is limited by the working range under normal power grids. However, in practical applications, due to load asymmetry and other reasons. The unbalanced three-phase grid voltage of the 3-phase grid also occurs frequently. In this case, the current distortion problem of the Vienna rectifier will be more serious, which will cause the Vienna rectifier to work outside the stable range.

Most of the existing control methods of Vienna rectifiers are controlled with the goal of keeping the DC side voltage stable and obtaining unity power factor, which are suitable for minor grid imbalance, that is, the range of the normal grid, and thus do not exceed the stable working range of the Vienna rectifier. However, the existing control methods cannot control the serious unbalance phenomenon on the grid side, so it is necessary to propose a control scheme suitable for the serious unbalance on the grid side.

SUMMARY OF THE INVENTION

The purpose of this application is to provide a Vienna rectifier control method to solve the problem that the existing control method cannot be applied to the serious imbalance on the grid side.

In order to achieve the above purpose, the present application proposes a technical solution for a control method of a Vienna rectifier, comprising the following steps:

1) Obtain the current positive sequence modulation degree of the Vienna rectifier, as well as the current and voltage on the current grid side;

2) Calculate the unbalance degree of the current grid according to the current and voltage on the current grid side;

3) Determine the range of the current unbalance degree of the power grid under the current positive sequence modulation system;

4) If the unbalance degree of the current power grid is in the first range under the current positive sequence modulation system, the current control is performed according to the first current command; In the second range, the current control is performed according to the second current command;

The first range is:

The second range is:

Among them, r is the unbalance degree; _mp is the positive sequence modulation degree.

The beneficial effects of the technical scheme of the control method of the Vienna rectifier of the present invention are: the present invention determines the first range of the unbalance degree by studying the working range of the Vienna rectifier under the normal power grid, and determines the unbalance degree through the constraint of the space vector boundary In the second range, the Vienna rectifier is controlled by different current commands in different ranges of the unbalance degree, which is suitable for the serious unbalance of the power grid and expands the normal working range of the Vienna rectifier.

Further, the first current command is:

Among them, P ₀ is the active power; e _α ^p is the positive sequence component of the grid voltage α axis; e _α ⁿ is the negative sequence component of the grid voltage α axis; e _β ^p is the positive sequence component of the grid voltage β axis; e _β ⁿ is the grid voltage β axis negative sequence component; i _α ^p is the grid current α axis positive sequence component; i _β ^p is the grid current β axis positive sequence component; i _α ⁿ is the grid current α axis negative sequence component; i _β ⁿ is the grid current β axis Negative sequence component.

Further, the second current command is:

Among them, P ₀ is the active power; e _α ^p is the positive sequence component of the grid voltage α axis; e _α ⁿ is the negative sequence component of the grid voltage α axis; e _β ^p is the positive sequence component of the grid voltage β axis; e _β ⁿ is the grid voltage β axis negative sequence component; i _α ^p is the grid current α axis positive sequence component; i _β ^p is the grid current β axis positive sequence component; i _α ⁿ is the grid current α axis negative sequence component; i _β ⁿ is the grid current β axis Negative sequence component.

Further, the calculation process of the imbalance degree is as follows:

r= _Vn / _Vp ;

Among them: V _p is the positive sequence voltage; V _n is the negative sequence voltage.

Description of drawings

Fig. 1 is the structure topology diagram of Vienna rectifier in the prior art;

Fig. 2 is the T/4 delay method separation positive and negative sequence principle diagram of the present invention;

Fig. 3 is the control principle diagram of the control method of Vienna rectifier of the present invention

4a is a schematic diagram of the lower boundary of the stable working range of the Vienna rectifier in the first sector of the present invention;

4b is a schematic diagram of the upper boundary of the stable working range of the Vienna rectifier in the first sector of the present invention;

Fig. 5 is the relation curve of the maximum angle θ _m between the modulation factor m and the voltage and the current vector when the Vienna rectifier of the present invention works stably;

Fig. 6 is the relation diagram of the voltage vector and the current vector when the power grid is unbalanced in the αβ coordinate system of the present invention;

Fig. 7 is the first critical curve of unbalance degree r and positive sequence modulation degree _mp of the present invention;

Fig. 8 is the operating range limit diagram of Vienna rectifier when the voltage and current of the present invention are in the same phase;

9 is the second critical curve of the unbalance degree r and the positive sequence modulation degree _mp when the voltage and current are in the same phase of the present invention;

Fig. 10 is the simulation result diagram of three-phase current and DC side voltage of the control method of Vienna rectifier of the present invention;

FIG. 11 is a simulation result diagram of the b-phase current and voltage of the control method of the Vienna rectifier of the present invention.

Detailed ways

Example of control method of Vienna rectifier:

The main idea of the control method of Vienna rectifier is that, based on the fact that the existing control method cannot be applied to the situation of serious unbalance on the grid side, the first range of unbalance degree is determined by studying the working range of Vienna rectifier under normal grid; The boundary constraint determines the second range of unbalance degree, which expands the range of unbalance degree on the grid side when the Vienna rectifier is working normally, so that the Vienna rectifier can work normally when the grid side is seriously unbalanced.

The control method of the Vienna rectifier includes the following steps:

1) Obtain the current and voltage on the grid side, and calculate the current unbalance on the grid side.

As shown in Figure 2, the power grid in the αβ coordinate system is:

为正序分量初相角；V_n为负序电压；

为负序分量初相角；e_β为电网电压β轴电压；e_β ^p为电网电压β轴正序分量；e_β ⁿ为电网电压β轴负序分量。where e _α is the grid voltage α axis voltage; e _α ^p is the grid voltage α axis positive sequence component; e _α ⁿ is the grid voltage α axis negative sequence component; V _p is the positive sequence voltage; ω is the grid angular velocity; t is the time ;

is the initial phase angle of the positive sequence component; V _n is the negative sequence voltage;

is the initial phase angle of the negative sequence component; e _β is the grid voltage β axis voltage; e _β ^p is the grid voltage β axis positive sequence component; e _β ⁿ is the grid voltage β axis negative sequence component.

Delay T/4, that is, after 90°, you can get:

Among them, e _α ⊥ is the voltage after e _α is delayed by 90°; e _β ⊥ is the voltage after e _β is delayed by 90°.

And then get the positive and negative sequence voltage and current:

Among them, i _α is the grid current α axis current; i _β is the grid current β axis current; i _α ^p is the grid current α axis positive sequence component; i _β ^p is the grid current β axis positive sequence component; i _α ⁿ is the grid current α-axis negative sequence component; i _β ⁿ is the grid current β-axis negative sequence component, i _α ⊥ is the voltage after i _α is delayed by 90°; i _β ⊥ is the current after i _β is delayed by 90°.

The calculation process of the imbalance degree r is as follows:

r=V _n /V _p ; where V _p and V _n are obtained from the above e _α ^p , e _β ^p , e _α ⁿ , and e _β ⁿ , and the unbalance degree r is obtained.

2) Obtain the current positive-sequence modulation degree of the Vienna rectifier, and determine the range of the current unbalance degree on the grid side under the current positive-sequence modulation degree:

As shown in FIG. 3 , if the current unbalance degree on the grid side is in the first range under the current positive sequence modulation degree, the current control is performed according to the first current command.

The first range is:

Among them, _mp is the positive sequence modulation degree.

The first current command is:

Among them, P ₀ is the active power command, obtained by multiplying the voltage outer loop by the reference voltage, M=[(e _α ^p ) ² +(e _β ^p ) ² ]-[(e _α ⁿ ) ² +(e _β ⁿ ) ² ], where M≠0. Then transfer it to the dq coordinate system to obtain the current command in the dq coordinate system.

If the current unbalance degree on the grid side is in the second range under the current positive sequence modulation degree, the current control is performed according to the second current command.

The second range is:

The second current command is:

Wherein, N=[(e _α ^p ) ² +(e _β ^p ) ² +(e _α ⁿ ) ² +(e _β ⁿ ) ² ].

The above-mentioned second current command is the current command when the control is optimal. As another embodiment, the second current command may also be in the form of the first current command, which is not limited in the present invention.

If the current unbalance on the grid side exceeds the second range under the current positive sequence modulation, the Vienna rectifier will not be able to control.

In the above embodiment, the first range is determined according to the working range of the Vienna rectifier under the normal power grid, and the specific determination process is as follows:

The lower boundary of the stable working range of the Vienna rectifier in the first sector is shown in Figure 4a, and the upper boundary of the stable working range of the Vienna rectifier in the first sector is shown in Figure 4b, so the stable operation of the Vienna rectifier in the first sector is shown in Figure 4b. The range satisfies the relation shown in Figure 5:

Among them, m is the modulation degree, m=v _ref , v _ref is the reference voltage vector; θ _m is the maximum value of the angle θ between the current vector and the voltage vector, that is, the maximum allowable angle. It can be seen from this relation that as m changes, θ _m also changes. When m decreases, θ _m increases gradually, but when m < 0.577, θ _m is the largest, which is

The description of the grid in the αβ coordinate system is equivalent to another form:

其中，

为负序电压初相角。

in,

is the initial phase angle of the negative sequence voltage.

According to the definition of imbalance degree r, the above formula is normalized to get:

其中，e′_α为归一化后的电网电压α轴分量；e′_β为归一化后的电网电压β轴分量。

Among them, e' _α is the normalized grid voltage α-axis component; e' _β is the normalized grid voltage β-axis component.

According to the general requirements of unbalanced grid control, it is necessary to eliminate the active double frequency and ensure the unity power factor, so the first current command is used for control, and in order to facilitate the observation of the relationship between the current vector and the voltage vector, the first current command is assigned to One gets:

其中，i′_α为归一化后的电网电流α轴分量；i′_β为归一化后的电网电压β轴分量。

Among them, i' _α is the normalized grid current α-axis component; i' _β is the normalized grid voltage β-axis component.

并不影响矢量运行轨迹，只会改变其初相位，因此可以在分析中统一为

在不平衡电网的条件下电流矢量和电压矢量关系如图6所示。那么根据图6中关系可以得知：because

It does not affect the vector running trajectory, but only changes its initial phase, so it can be unified in the analysis as

Under the condition of unbalanced grid, the relationship between current vector and voltage vector is shown in Figure 6. Then according to the relationship in Figure 6, we can know:

为参考电压矢量；V_o为直流侧电压；V_p为正序电压；m_p为正序调制度。在不平衡电网的工况下，只有当θ小于等于当前工况下m所对应的θ_m时，才能保证Vienna整流器的稳定运行，因此结合θ_m的公式可以得到如图7所示的不平衡度r与正序调制度m_p的关系曲线，该关系曲线通过一系列的点进行拟合得到：Among them, θ is the angle between the current vector and the voltage vector (the actual angle between the current vector and the voltage vector, which is related to the unbalance degree r);

is the reference voltage vector; V _o is the DC side voltage; V _p is the positive sequence voltage; _mp is the positive sequence modulation degree. Under the condition of unbalanced power grid, the stable operation of Vienna rectifier can be guaranteed only when θ is less than or equal to θ _m corresponding to m in the current working condition. Therefore, the unbalance as shown in Figure 7 can be obtained by combining the formula of θ _m The relationship between the degree r and the positive sequence modulation degree _mp is obtained by fitting a series of points:

The above relationship curve is the first critical curve of the first range, so the first range is:

The first range is essentially a situation where the unbalance of the power grid is small, and belongs to the range of the normal power grid. Therefore, the first range is obtained through the working range of the Vienna rectifier under the normal power grid. However, once the unbalance degree exceeds the first range, the first current command will be invalid. Therefore, when it exceeds the first range, the current and voltage are directly controlled to be in the same phase to ensure that the angle between the current vector and the voltage vector is 0 and will not exceed θ _m .

That is, the second current command is:

After normalization we get:

Since the angle between the current vector and the voltage vector is 0, the unbalance degree is not limited by the first range, and should be constrained by the space _vector boundary. The vector should not exceed its boundary. Once it exceeds, the Vienna rectifier will not work, and the second critical curve of the unbalance degree as shown in Figure 9 will be obtained:

So the second range is:

The effectiveness of the present invention is verified by simulating the present invention below:

The experimental simulation model is built in Matlab/Simulink, and the actual parameters of the system are shown in Table 1:

Table 1. Actual parameters of the system

For the convenience of analysis, the fixed positive sequence voltage V _p =110V is selected, so the positive sequence modulation degree _mp =0.75, and then the negative sequence voltage V _n is changed to verify the effectiveness of the present invention. From the relationship of the first critical curve, when r was 9.3% at _mp = 0.75, so this control scheme was tested by changing _Vn such that r = 7% and 14%.

The simulation results are shown in Figure 10 and Figure 11. It can be seen from Figure 10 that when the unbalance degree suddenly changes from r=7% to r=14%, the three-phase current after segment control (the darker color in Figure 10) is used. The solid line is the c-phase current ic, the lighter solid line is the a-phase current ia, and the dashed line is the b-phase current ib) There is no distortion all the time, which proves that the Vienna rectifier works within the stable range. The DC side voltage can guarantee to eliminate the double frequency fluctuation when r=7%, but when the second current command control is used after the upper limit of 9.3%, the double frequency fluctuation cannot be eliminated, which also proves the above analysis. It can be found from the b-phase voltage eb (solid line) and current ib (dotted line) in Fig. 11 that the unit power factor can be guaranteed regardless of whether r=7% or 14%, so the segmented control proposed by the present invention is effective .

It can be seen from the above simulation results that when the unbalance degree of the power grid suddenly changes from the first range to the second range, using the segmented control scheme of the present invention, the three-phase current is not distorted, and when the unbalance degree is in the first range , using the first current command for control can eliminate the double frequency fluctuation of the DC side voltage and ensure the unity power factor; when the unbalance is in the second range, the second current command is used for control, although the DC side voltage double frequency Fluctuations cannot be eliminated, but unity power factor is guaranteed. The control on the power grid side when the power grid is seriously unbalanced can meet the basic requirements, and the invention greatly expands the working range of the Vienna rectifier under the unbalanced power grid by adopting the segmented control.

Claims (1)

1. a control method of Vienna rectifier, is characterized in that, comprises the following steps: 1) Obtain the current positive sequence modulation degree of the Vienna rectifier, as well as the current and voltage on the current grid side; 2) Calculate the unbalance degree of the current grid according to the current and voltage of the current grid side; 3) Determine the range of the current unbalance degree of the power grid under the current positive sequence modulation system; 4) If the unbalance degree of the current power grid is in the first range under the current positive sequence modulation system, the current control is performed according to the first current command; In the second range, the current control is performed according to the second current command; The first range is:

The second range is:

Among them, r is the unbalance degree; _mp is the positive sequence modulation degree; The first current command is:

The second current command is:

Among them, P ₀ is the active power; e _α ^p is the positive sequence component of the grid voltage α axis; e _α ⁿ is the negative sequence component of the grid voltage α axis; e _β ^p is the positive sequence component of the grid voltage β axis; e _β ⁿ is the grid voltage β axis negative sequence component; i _α ^p is the grid current α axis positive sequence component; i _β ^p is the grid current β axis positive sequence component; i _α ⁿ is the grid current α axis negative sequence component; i _β ⁿ is the grid current β axis Negative sequence component; the calculation process of unbalance degree is: r= _Vn / _Vp ; Among them: V _p is the positive sequence voltage; V _n is the negative sequence voltage.

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