阅读说明：本技术 一种预测直接功率控制方法 (Predictive direct power control method ) 是由 孟文新 张杭 张爱民 孙丰瑞 于 2020-05-18 设计创作，主要内容包括：本申请属于整流器控制技术领域,特别是涉及一种预测直接功率控制方法。常见的电流控制位基于前馈解耦的电压定向电流控制,需要进行PARK变换和PLL计算,计算复杂,且PI控制器的参数整定困难,受系统参数影响大。本申请提供了一种预测直接功率控制方法,建立整流器在两相静止坐标系的数学模型,获取所述整流器在两相静止坐标系的瞬时有功功率和瞬时无功功率；以瞬时有功功率和所述瞬时无功功率误差最小为原则设计指标函数,再以电网电压矢量作为基本控制矢量,推导出整流器参考电压矢量计算公式；采用空间矢量调制实现固定开关频率控制；同时采用内模控制对所述瞬时有功功率和所述瞬时无功功率进行修正。提高稳态时的输出波形质量。(The application belongs to the technical field of rectifier control, and particularly relates to a prediction direct power control method. The common current control bit is based on voltage-oriented current control of feedforward decoupling, PARK conversion and PLL calculation are needed, the calculation is complex, and parameter setting of a PI controller is difficult and is greatly influenced by system parameters. The application provides a direct power prediction control method, which comprises the steps of establishing a mathematical model of a rectifier in a two-phase static coordinate system, and obtaining instantaneous active power and instantaneous reactive power of the rectifier in the two-phase static coordinate system; designing an index function by using the minimum error of instantaneous active power and the instantaneous reactive power as a principle, and then using a power grid voltage vector as a basic control vector to deduce a rectifier reference voltage vector calculation formula; space vector modulation is adopted to realize fixed switching frequency control; and simultaneously correcting the instantaneous active power and the instantaneous reactive power by adopting internal model control. And the quality of an output waveform in a steady state is improved.)

1. A predictive direct power control method, characterized by: the method comprises the following steps:

step 1): establishing a mathematical model of a rectifier in a two-phase static coordinate system, and acquiring instantaneous active power and instantaneous reactive power of the rectifier in the two-phase static coordinate system;

step 2): designing an index function by using the minimum error of the instantaneous active power and the instantaneous reactive power as a principle, and then using a power grid voltage vector as a basic control vector to deduce a rectifier reference voltage vector calculation formula;

step 3): model prediction direct power control is realized by adopting space vector modulation; and simultaneously correcting the instantaneous active power and the instantaneous reactive power by adopting internal model control.

2. The predictive direct power control method of claim 1, wherein: and in the step 1), the instantaneous active power and the instantaneous reactive power of the rectifier in the two-phase static coordinate system are obtained according to an instantaneous power principle.

3. The predictive direct power control method of claim 2, wherein: the mathematical model in the step 1) is as follows:

wherein L is an inductance value on the AC side; c₁，C₂Capacitance values of an upper capacitor and a lower capacitor on a direct current side are respectively; r is the line impedance; i.e. i_α，i_βRespectively are alternating currents under a two-phase static coordinate system; e.g. of the type_α，e_βRespectively are alternating voltages under a two-phase static coordinate system; u shape_dc1，U_dc2The voltages at two ends of the direct current side capacitor C1 and the capacitor C2 respectively; r_LIs a load resistor; s_αp，S_αn，S_βp，S_βnRespectively, the switch state quantities in the two-phase static coordinate system.

4. The predictive direct power control method of claim 3, wherein: the mathematical model of the alternating current side current of the rectifier is as follows:

wherein L is an inductance value on the AC side; r is the line impedance; i.e. i_α，i_βRespectively are alternating currents under a two-phase static coordinate system; e.g. of the type_α，e_βRespectively are alternating voltages under a two-phase static coordinate system; u shape_dc1，U_dc2The voltages at two ends of the direct current side capacitor C1 and the capacitor C2 respectively; s_αp，S_αn，S_βp，S_βnRespectively, the switch state quantities in the two-phase static coordinate system.

5. The predictive direct power control method of claim 1, wherein: and 2) designing an index function by adopting a prediction model in the step 2) and taking the minimum error of the instantaneous active power and the instantaneous reactive power as a principle.

6. The predictive direct power control method of claim 1, wherein: the index function in the step 2) is as follows: f ═ p_ref-p(k+1)]²+[q_ref-q(k+1)]²

In the formula p_refGiven value of instantaneous active power, q_refThe value is a given value of instantaneous reactive power, and p (k +1) is a predicted value of active power before correction; q (k +1) is a predicted value of the reactive power before correction; k is the kth sampling period.

7. The predictive direct power control method of claim 1, wherein: the step 3) comprises delay compensation control.

8. The predictive direct power control method of claim 6, wherein: the step 3) of adopting the internal model control comprises adding the sum of the errors of the previous k sampling periods and the predicted value of the (k +1) th time, so as to correct the predicted value and obtain a new predicted value.

9. The predictive direct power control method of claim 1, wherein: the internal model control formula is as follows:

wherein m is an adjustment coefficient; p is a radical of^*(k +1) is a predicted value of the active power after the internal model correction; q. q.s^*(k +1) is the predicted value of reactive power after internal model correction, p (k +1) is the predicted value of active power before correction, q (k +1) is the predicted value of reactive power before correction, ξ_pξ is the difference between the given value and the predicted value of the active power_qThe difference between the given value of the reactive power and the predicted value is obtained; k is the kth sampling period.

10. The method of predictive direct power control according to any of claims 1 to 9, wherein: the rectifier is a VIENNA rectifier.

Technical Field

The application belongs to the technical field of rectifier control, and particularly relates to a prediction direct power control method.

Background

Compared with the traditional two-point flat PWM rectifier, the VIENNA rectifier has the advantages of high power density, low device stress, low input current harmonic content and the like as a three-level PWM (pulse width modulation) rectifier, and compared with the traditional diode clamping type and flying capacitor clamping type three-level rectifiers, the three-level PWM rectifier has the advantages of simpler topological structure, less required power devices, no bridge arm direct connection risk and no dead time. Therefore, in some high power, high density applications, the VIENNA rectifier is a very desirable topology. Therefore, the charging device is widely applied to the fields of electric automobile charging stations, charging pile systems, aerospace power supplies and the like in recent years. With the diversification of the application occasions of the VIENNA rectifier, the requirements on the static and dynamic performances of the VIENNA rectifier are higher and higher, and new requirements are provided for the control strategy of the VIENNA rectifier

At present, the control methods applied to the VIENNA rectifier mainly include hysteresis control, SVPWM-based PI control, single-cycle control, sliding mode variable structure control, and the like. Hysteresis control has the advantages of high speed, good robustness and the like, but the hysteresis control has the defects of unfixed switching frequency, mutual influence of current between lines, influence of load change on the switching frequency and the like. The PI control method based on SVPWM has the defects of slow response speed, overshoot and the like.

Disclosure of Invention

1. Technical problem to be solved

The method for predicting the direct power control is based on the problems that the power static difference is large when the direct power control is predicted to have a steady state, the actual control effect is poor when the steady state is caused, the harmonic content of the input current on the network side is large, and the power factor of a system is low.

2. Technical scheme

In order to achieve the above object, the present application provides a predictive direct power control method, comprising the steps of:

step 1): establishing a mathematical model of a rectifier in a two-phase static coordinate system, and acquiring instantaneous active power and instantaneous reactive power of the rectifier in the two-phase static coordinate system;

step 2): designing an index function by using the minimum error of the instantaneous active power and the instantaneous reactive power as a principle, and then using a power grid voltage vector as a basic control vector to deduce a rectifier reference voltage vector calculation formula;

step 3): model prediction direct power control is realized by adopting space vector modulation; and simultaneously correcting the instantaneous active power and the instantaneous reactive power by adopting internal model control.

Another embodiment provided by the present application is: and in the step 1), the instantaneous active power and the instantaneous reactive power of the rectifier in the two-phase static coordinate system are obtained according to an instantaneous power principle.

Another embodiment provided by the present application is: the mathematical model in the step 1) is as follows:

another embodiment provided by the present application is: the mathematical model of the alternating current side current of the rectifier is as follows:

another embodiment provided by the present application is: and 2) designing an index function by adopting a prediction model in the step 2) and taking the minimum error of the instantaneous active power and the instantaneous reactive power as a principle.

Another embodiment provided by the present application is: the index function in the step 2) is as follows: f ═ p_ref-p(k+1)]²+[q_ref-q(k+1)]²

In the formula p_refGiven value of instantaneous active power, q_refThe value is a given value of instantaneous reactive power, and p (k +1) is a predicted value of active power before correction; q (k +1) is a predicted value of the reactive power before correction; k is the kth sampling period.

Another embodiment provided by the present application is: the step 3) comprises delay compensation control.

Another embodiment provided by the present application is: the step 3) of adopting the internal model control comprises adding the sum of the errors of the previous k sampling periods and the predicted value of the (k +1) th time, so as to correct the predicted value and obtain a new predicted value.

Another embodiment provided by the present application is: the internal model control formula is as follows:

wherein m is an adjustment coefficient.

Another embodiment provided by the present application is: the rectifier is a VIENNA rectifier.

3. Advantageous effects

Compared with the prior art, the method for predicting the direct power control has the advantages that:

the application provides a direct power control method by prediction, and provides a direct power control method by model prediction with internal model control.

The application provides a direct power control method for predicting, and provides a direct power control strategy for a three-phase VIENNA rectification model with internal model control.

According to the prediction direct power control method, the controller design is carried out in the two-phase static coordinate system by adopting model prediction direct power control, the PARK transformation and PLL calculation are not needed, the design of the controller is not influenced by system parameters, and the dynamic and static performance is better.

According to the prediction direct power control method, internal model control is introduced, and the problem that power tracking errors are large when the model predicts the stable state of direct power control is solved. The introduction of the two-step prediction method solves the problem of control error caused by control delay in an actual system.

The prediction direct power control method provided by the application does not need synchronous rotating coordinate transformation and a phase-locked loop technology, independent control is carried out on active power and reactive power of a rectifier under a two-phase static coordinate system, a good control effect can be kept under the condition that a power grid is unbalanced, distorted and high in harmonic content, and due to the introduction of internal model control, when a steady state is ensured, power can be tracked without static error, and the steady state effect is better.

Drawings

FIG. 1 is a schematic diagram of a three-phase VIENNA rectifier topology of the present application;

FIG. 2 is an equivalent circuit diagram of a three-phase VIENNA rectifier of the present application;

FIG. 3 is a modified block diagram of the active power internal model of the present application;

fig. 4 is a block diagram of model predictive direct power control based on in-model control optimization according to the present application.

Detailed Description

Hereinafter, specific embodiments of the present application will be described in detail with reference to the accompanying drawings, and it will be apparent to those skilled in the art from this detailed description that the present application can be practiced. Features from different embodiments may be combined to yield new embodiments, or certain features may be substituted for certain embodiments to yield yet further preferred embodiments, without departing from the principles of the present application.

Referring to fig. 1 to 4, the present application provides a predictive direct power control method, including the steps of:

step 1): establishing a mathematical model of a rectifier in a two-phase static coordinate system, and acquiring instantaneous active power and instantaneous reactive power of the rectifier in the two-phase static coordinate system;

step 2): designing an index function by using the minimum error of the instantaneous active power and the instantaneous reactive power as a principle, and then using a power grid voltage vector as a basic control vector to deduce a rectifier reference voltage vector calculation formula;

step 3): model prediction direct power control is realized by adopting space vector modulation; and simultaneously correcting the instantaneous active power and the instantaneous reactive power by adopting internal model control.

Further, in the step 1), instantaneous active power and instantaneous reactive power of the rectifier in a two-phase static coordinate system are obtained according to an instantaneous power principle.

Further, the mathematical model in step 1) is:

the topology of the three-phase VIENNA rectifier is shown in figure 1. E in FIG. 1_k、i_k、L_k、R_k(k ═ a, b, c) are three-phase symmetrical grid phase voltage, three-phase current, grid side filter inductance and equivalent line impedance respectively; d_kp、D_kn(k ═ a, b, c) is a fast recovery diode; s_k1、S_k2(k ═ a, b, c) is a semiconductor power switching tube, and S is_k1、S_k2A bidirectional power switch tube is formed, and bidirectional flow of current can be realized; c₁、C₂Is a DC bus filter capacitor; r_LIs a load resistor on the direct current side. The bidirectional power switch tube in fig. 1 can be equivalent to a three-switch selector, and fig. 2 is an equivalent circuit diagram thereof.

For analyzing the on and off of the switching tube, a switching function Si, S is introduced here_iIndicating the switching state of the phase I, the switching function S_iIs represented as follows:

where I is A, B, C, I is a, B, C, and the switching state is related to three basic state quantities S in the equivalent circuit diagram_ip、S_io、S_inTaken together, are:

wherein S_ip、S_io、S_inThe following relationship is satisfied:

wherein j is p, o, n.

From Kirchhoff's Voltage Law (KVL) and fig. 4, a voltage equation 4 for each phase loop can be obtained.

In the formula of U_AO、U_BO、U_COThe voltage from a bridge arm of a rectifier bridge to the midpoint of a direct-current side capacitor is obtained; u shape_ONIs the voltage from the midpoint of the capacitor to the neutral point of the grid. Modifications to formula (4) may result:

under the condition of three-phase balance of the power supply at the alternating current side, the sum of three-phase voltages is 0, and the sum of three-phase currents is 0, namely:

by adding the three equations of equation (5), the following can be obtained:

as can also be seen from fig. 2:

then it is possible to obtain:

from equations (8) and (9), it is possible to obtain:

according to kirchhoff's current law, the p point of the direct current bus is analyzed to obtain:

the same analysis of n points gives:

the following formulae (11) and (12) can be obtained by arranging:

the mathematical model of the Vienna rectifier under an abc three-phase static coordinate system can be obtained by arranging the formulas

The standard matrix equation is arranged as the formula:

wherein A ═ diag [ L, L, L, C₁,C₂]

X＝diag[i_a,i_b,i_c,U_dc1,U_dc2]

C＝diag[1,1,1,0,0]

E＝diag[e_a,e_b,e_c,0,0]

The mathematical model is established under a three-phase static coordinate system, and the mathematical model of the three-phase VIENNA rectifier under the two-phase static coordinate system can be obtained through CLARK conversion, and comprises the following steps:

the mathematical model of the alternating side current is as follows:

let the component of the AC side voltage α axis of the rectifier be u_α＝S_αpU_dc1-S_αnU_dc2β Axis component is u_β＝S_βpU_dc1-S_{β n}U_dc2Then equation (17) can be simplified as:

according to the instantaneous power theory, the instantaneous active and reactive power on the ac side of the system can be expressed as:

by taking the derivative of equation (19), the instantaneous power change rate can be obtained as:

under ideal grid voltage conditions, the instantaneous rate of change of voltage is:

further, the mathematical model of the alternating-current side current of the rectifier is as follows:

further, a prediction model is adopted in the step 2), and an index function is designed on the basis of the principle that the error of the instantaneous active power and the instantaneous reactive power is minimum.

Further, the index function in step 2) is: f ═ p_ref-p(k+1)]²+[q_ref-q(k+1)]²In the formula p_refGiven value of instantaneous active power, q_refThe value is a given value of instantaneous reactive power, and p (k +1) is a predicted value of active power before correction; q (k +1) is a predicted value of the reactive power before correction; k is the kth sampling period.

Model prediction direct power principle

The formula (18) and the formula (21) are substituted into the formula (20) to obtain the final product

Suppose that in the kth sampling period, the active and reactive derivative values are A and B, i.e.

Substituting linear first-order equation for inverse derivative equation in equation (23) can obtain the predicted values of active and reactive power at the end of each switching period, i.e.

The control algorithm aims to obtain more accurate output voltage vector (u) of the AC side of the rectifier_α、u_β). To achieve this goal, according to the model predictive control principle, i.e. the error of the active and reactive power at the end of each control cycle is minimal, the design index function is:

F＝[p_ref-p(k+1)]²+[q_ref-q(k+1)]²(25)

in the formula p_ref、q_refRespectively are given values of active power and reactive power. p (k +1) is a predicted value of the active power before correction; q (k +1) is a predicted value of the reactive power before correction; q. q.s_refIn generalAre directly given as 0, p_refAnd the output of the rectifier direct-current voltage PI controller is determined.

Further, the step 3) includes a delay compensation control.

In an actual system, a sampling and control algorithm of the system cannot be completed instantaneously, and a control delay of one sampling period exists, that is, a voltage vector in k periods is used in a k +1 period. Although the delay time is generally short, the control effect of the system is still greatly reduced if the delay time is not compensated. To eliminate this delay, a two-step prediction method is introduced here, i.e. the values in equation (25) should be p (k +2), q (k +2) instead of p (k +1), q (k +1), so the objective function should be changed to:

F＝[p_ref-p(k+2)]²+[q_ref-q(k+2)]²(26)

by substituting formula (24) for formula (26), the compound

F＝[p_ref-p(k+1)-AT]²+[q_ref-q(k+1)-AT]²(27)

According to algebraic knowledge, in order to obtain the minimum power error, i.e. the minimum index function, the rectifier AC output voltage u in equation (27) should be ordered_α、u_βThe partial derivative of (c) is simultaneously 0.

By making each equation in equation (28) 0, the equations can be arranged to derive the rectifier AC side output voltage vector (u)_α、u_β) Comprises the following steps:

formula (III) ξ_p＝p_ref-p(k+1)，ξ_q＝q_ref-q (k + 1). Each variable is a predicted value of the kth sampling moment to the kth +1 moment. Besides the active power and the reactive power, the rest of the predicted values can be calculated by a second-order Taylor series expansion formula, and the e at the k +1 sampling moment is used as the text_aFor example, the following steps are carried out:

e_α(k+1)＝1.75e_α(k)-e_α(k-1)+0.25e_α(k-2) (30)

further, the step 3) of adopting the internal model control includes adding the sum of the errors of the previous k sampling periods to the predicted value of the (k +1) th time, so as to correct the predicted value and obtain a new predicted value.

Further, the internal model control formula is as follows:

wherein m is an adjustment coefficient.

Internal model control

When the system reaches steady state, p (k +1) ═ p_ref、q(k+1)＝q_ref. As can be seen from equations (27) and (29), when the power deviation is equal to 0, the controller cannot accurately calculate the target voltage vector, so that the existence of the power error is a necessary condition for the controller to operate efficiently. The principle of the internal model control is that the sum of the errors of the previous k sampling periods is added with the predicted value of the (k +1) th time, so that the predicted value is corrected, a new predicted value is obtained, the calculation process is similar to a quasi-integral effect, and therefore the effect of reducing the active power and the reactive power static difference is achieved, and the power tracking effect in the steady state is improved. The internal model control formula obtained according to the above principle is:

in the formula, m is an adjustment coefficient, and is usually 0.05. The internal model modified block diagram of the active power obtained by the formula (31) is shown in fig. 3. Through the above formula, a control block diagram of model predictive direct power control is obtained as fig. 4.

Further, the rectifier is a VIENNA rectifier.

The control method of the VIENNA rectifier can be divided into current control and power control according to different control objects, common current control bits are based on voltage-oriented current control of feedforward decoupling, PARK conversion and PLL calculation are needed in the method, the calculation is complex, parameter setting of a PI controller is difficult, and the method is greatly influenced by system parameters.

The MATLAB/SIMULINK simulation proves that the control method has excellent dynamic and static performances and can effectively reduce the power tracking static difference in a steady state.

Although the present application has been described above with reference to specific embodiments, those skilled in the art will recognize that many changes may be made in the configuration and details of the present application within the principles and scope of the present application. The scope of protection of the application is determined by the appended claims, and all changes that come within the meaning and range of equivalency of the technical features are intended to be embraced therein.