CN105490604B - A kind of forecast Control Algorithm of the inductive switching motor variable speed system of three-phase four - Google Patents

Abstract

The invention discloses a predictive control method for a frequency conversion speed regulation system of a three-phase four-switch induction motor, comprising: A. respectively measuring the three-phase current, two DC side Capacitor voltage and motor speed; B. Calculate the voltage vector corresponding to the four switch combinations (00, 01, 11, 10) through the measured DC capacitor voltage; C. Estimate the stator and rotor of the induction motor based on the measured phase current and speed Flux linkage; D. Predict the absolute value of the four voltage vectors corresponding to the stator flux linkage, the predicted torque and the predicted DC voltage; E. Calculate the cost function of the four voltage vectors: subtract the predicted value from the reference value and then take the absolute value, each Items are multiplied by weight coefficients and added. F. Apply the switch state corresponding to the voltage vector that minimizes the cost function to the inverter. This method is suitable for various frequency conversion speed regulation systems driven by three-phase four switches.

Description

A predictive control method for frequency conversion speed regulation system of three-phase four-switch induction motor

technical field

The invention belongs to the field of frequency conversion speed regulation of induction motors, and more specifically relates to a predictive control method for induction motor frequency conversion speed regulation systems under the topology of a three-phase four-switch power converter.

Background technique

Frequency conversion speed regulation systems based on induction motors have been widely used in aerospace, military, industrial and other fields, and their power converters are composed of six-switch three-phase full-control power electronic devices. Among them, the energy density of the converter is high, and the power electronic devices are relatively "fragile". Once an open circuit or short circuit fault occurs in a power tube of the converter, the entire system will lose the ability to work normally, and even catastrophic consequences will occur.

As the requirements for the safety and reliability of frequency conversion speed control systems are getting higher and higher, real-time fault-tolerant control is highly valued. However, most frequency conversion speed control systems are not equipped with redundant backup, which makes the three-phase four-switch without redundant backup Topology has received greater attention. In many patents and literatures on the control strategy of the three-phase four-switch frequency conversion speed regulation system, the general methods are divided into two categories: one is to assume that the DC capacitor voltage is constant, and design the control algorithm on this basis. One phase of the capacitor is directly connected to the neutral point of the capacitor, and the flow of the phase current will cause the fluctuation and drift of the capacitor voltage, so this method cannot be used in the actual system; the other is to design a control algorithm for the capacitor voltage fluctuation and drift, but This algorithm is generally an open-loop control strategy, and the dynamic performance of the speed control system is poor.

Contents of the invention

In order to overcome the deficiency of the control strategy of the existing three-phase four-switch frequency conversion speed regulation system, the present invention proposes a predictive control method under the topology of the three-phase four-switch power converter. The method can realize high-performance flux linkage and torque closed-loop control under the condition of capacitor voltage fluctuation, and can also suppress the drift of capacitor voltage, without the need of pulse width modulator and coordinate transformation. This method is suitable for various frequency conversion speed regulation systems driven by three-phase four switches.

In order to achieve the above object, the present invention provides a predictive control method for an induction motor frequency conversion speed regulation system under the topology of a three-phase four-switch power converter, the method comprising:

(1) The three-phase currents i _a ^k , i _b ^k , _ick ^k are respectively measured by the existing current hall sensor, voltage hall sensor and photoelectric encoder speed sensor in the induction motor drive system, and the two DC side capacitors Voltage U _C1 ^k , U _C2 ^k and motor speed ω;

(2) Calculate the current moment values of the voltage vectors V ₁ , V ₂ , V ₃ , and V ₄ corresponding to the four switch combinations through the measured two DC side capacitor voltages U _C1 ^k , U _C2 ^k , and according to the measured three-phase current i _a ^k , i _b ^k , i _c ^k signals to calculate current vector The value of , the four switch combinations are 00,10,11,01;

(3) By measuring the motor speed ω and the current vector Estimating stator flux linkage and rotor flux linkage

(4) Predict all voltage vectors V ₁ , V ₂ , V ₃ , and V ₄ corresponding to capacitor voltages according to the motor model and inverter model Stator flux linkage and electromagnetic torque

(5) Use the predicted capacitor voltages corresponding to each voltage vector V ₁ , V ₂ , V ₃ , V ₄ Stator flux linkage and electromagnetic torque Calculate the cost function, and take the voltage vector that minimizes the cost function as the optimal voltage vector;

(6) Applying the switch signal corresponding to the optimal voltage vector, wherein the corresponding relationship between the voltage vector and the switch signal is the same as in step (2).

The advantage of the present invention is that, through the accurate modeling of the motor model, in the case of capacitor voltage fluctuations, the closed-loop high-performance control of the magnetic field, torque and rotational speed of the induction motor can be realized, and at the same time, it realizes the Balanced control of three-phase current in converter topology. In order to ensure the reliability of the system, the present invention suppresses the drift of the capacitor voltage. The invention directly outputs the switch signal without the need of a pulse width modulator. All variables are completed under the stator coordinate system, no coordinate transformation is required. The control structure is simple and easy to understand and easy to implement physically.

Description of drawings

Fig. 1 is the applicable induction motor drive system of the inventive method and basic structural diagram thereof;

Fig. 2 is the control principle block diagram of the inventive method;

Fig. 3 is a control flow chart of the model predictive control method of the induction motor driven by three-phase four switches according to the present invention.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not constitute a conflict with each other.

As shown in Fig. 1, what the present invention relates to is the power converter structure of the frequency conversion speed regulation system of the induction motor and the connection model of the induction motor. Two of the three phases of the motor are connected to the normal switching bridge arm, and the third phase is connected to the neutral point of the capacitor on the DC side.

As shown in Figure 2, the control block diagram involved in the present invention, and the connection block diagram with the induction motor system driven by three-phase four switches, in conjunction with accompanying drawing 2 illustrate the principle of the technical solution adopted by the present invention:

In order to realize a high-performance closed-loop control strategy, the speed outer loop control adopts the traditional proportional integral controller to obtain the given value of the torque, and the current inner loop control adopts the model predictive controller. This scheme includes flux linkage estimation, torque, flux linkage And capacitor voltage prediction, cost function optimization in three steps.

First, the induction motor current model is used to estimate the current stator and rotor flux linkage of the induction motor. The fluctuation of the capacitor voltage will cause the voltage vector of the inverter to fluctuate in phase angle and amplitude. This fluctuation will cause a huge error in the flux linkage estimation algorithm based on the voltage model, resulting in inaccurate flux linkage estimation. This scheme uses a current-based The flux linkage estimation algorithm of the model can measure and estimate the current stator and rotor flux linkage by using the speed and phase current, and overcome the influence of capacitor voltage fluctuation on the flux linkage estimation.

Secondly, use the voltage sensor to measure the real-time voltage of the capacitor and calculate the accurate value of the current voltage vector. Then, use the mathematical model of the induction motor to put the four voltage vectors corresponding to the current four switch states into the model one by one, and predict different The stator flux linkage, stator current, electromagnetic torque, and capacitor voltage of the next sampling period under the voltage vector.

Finally, the predicted absolute value of flux linkage, electromagnetic torque, and capacitor voltage are different from the reference value, and their absolute values are calculated, multiplied by the corresponding weight coefficients, and added to obtain the cost function. The four voltage vectors correspond to four The cost function takes a value, and the switch signal corresponding to the minimum voltage vector of the cost function is applied to the inverter.

The three-phase current of the motor is obtained from the motor through the Hall sensor, and the speed signal is measured from the photoelectric encoder speed sensor. From the power converter, the capacitor voltage is obtained through the voltage Hall sensor. The above variables participate in the system control as the input quantity of the control system. The control system directly outputs discrete switching signals, which simplifies the control structure. The control system is divided into inner and outer control loops: the outer loop is a traditional PI regulator, which realizes the closed-loop control of the speed, and generates a given torque through the speed regulator; the inner loop is a model predictive controller, which realizes the motor torque and magnetic The closed-loop control of the chain, and the inner loop also realizes the suppression of the capacitor voltage drift.

As shown in Figure 3, it is a control flow chart of the induction motor model predictive control method driven by three-phase four switches of the present invention, as shown in the figure, the method includes:

1. Initialization Initialize the cost function g to a sufficiently large value.

2. Measure the three-phase current i _a ^k , i _b ^k , _ick ^k and the two DC side capacitor voltages respectively through the existing current hall sensor, voltage hall sensor and photoelectric encoder speed sensor in the induction motor drive system U _C1 ^k , U _C2 ^k and motor speed ω;

3. Calculate the current moment values of the voltage vectors V ₁ , V ₂ , V ₃ , and V ₄ corresponding to the four switch combinations through the measured two DC side capacitor voltages U _C1 ^k and U _C2 ^k , and according to the measured three-phase current i _a ^k , i _b ^k , _ick ^k signal to calculate current vector The value of the four switch combinations are 00, 10, 11, 01; the calculation method of the voltage vector is shown in Table 1.

Table 1

The calculation method of the current vector is as follows:

where the superscript k is the sampling time.

4. The measured motor speed ω and current vector Estimating stator flux linkage and rotor flux linkage

Among them, L _s , L _m , L _r are stator inductance, excitation inductance and rotor inductance respectively, R _s R _r are rotor resistance and stator resistance respectively. T _s is the sampling time, k _r ＝L _m /L _r is the rotor mutual inductance coefficient, is the flux leakage coefficient, and τ _r =L _r /R _r is the rotor time constant.

5. Predict all voltage vectors V ₁ , V ₂ , V ₃ , and V ₄ corresponding to capacitor voltages according to the motor model and inverter model Stator flux linkage and electromagnetic torque

The predicted current vector at the next moment as follows:

in, is the equivalent resistance, L _σ =σL _s is the leakage inductance of the motor, τ _σ =σL _s /R _σ , represents the voltage vector,

Stator flux linkage and electromagnetic torque are predicted from the predicted current vectors.

Among them, p is the number of pole pairs of the induction motor, and the symbol of Im means taking the imaginary part of the complex number.

For the four-switch three-phase topology, since the upper and lower tubes cannot be connected directly, the switch combination S _b S _c can only take values of 00, 10, 01, 11, and the values of the capacitor currents i _dc1 and i _dc2 are as follows

i _dc1 ^k ＝i _b ^k S _b +i _c ^k S _c (0.7)

i _dc2 ^k ＝i _b ^k ·(1-S _b )+ _ic ^k ·(1-S _c )

The predicted value of capacitor voltage U _C1 (k+1), U _C2 (k+1) is

(0.8)

6. Use the predicted capacitor voltages corresponding to each voltage vector V ₁ , V ₂ , V ₃ , V ₄ Stator flux linkage and electromagnetic torque Calculate the cost function, and take the voltage vector that minimizes the cost function as the optimal voltage vector;

The designed cost function control rate g _i is as follows:

in are the rated torque and rated flux linkage of the induction motor, respectively, is torque given, The absolute value of the flux linkage is given, the symbol |·| is the absolute value of the solution, and ||·|| is the absolute value of the complex quantity solution, which is obtained according to the parameters on the motor nameplate. Both λ ₀ and λ _dc are adjustable parameters, and the parameters are obtained by trial and error to optimize the overall performance of the system. The subscript i respectively represents the parameters calculated from the four voltage vectors.

7. Apply the switching signal corresponding to the optimal voltage vector. The corresponding relationship between the voltage vector and the switch signal is the same as in step (2). The voltage vector of g _i that minimizes the cost function is considered to be the optimal voltage vector among the four voltage vectors, and the switch combination corresponding to the optimal voltage vector is applied, and its corresponding relationship is shown in Table 1 to achieve the optimal control of the system.

8. Repeat 1-7 at the next moment to obtain the optimal voltage vector at the next moment.

It is easy for those skilled in the art to understand that the above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention, All should be included within the protection scope of the present invention.

Claims (7)

1. A predictive control method for a variable-frequency speed control system of an induction motor under a three-phase four-switch power converter topology is characterized by comprising the following steps:

(1) three-phase current i is respectively measured by the existing current Hall sensor, voltage Hall sensor and photoelectric coded disc speed sensor in the induction motor driving system_a ^k,i_b ^k,i_c ^kTwo DC side capacitor voltages U_C1 ^k,U_C2 ^kAnd motor speed ω;

(2) by measuring two DC-side capacitor voltages U_C1 ^k,U_C2 ^kCalculating voltage vectors V corresponding to four switch combinations₁,V₂,V₃,V₄Value at the present moment and based on the measured three-phase currents i_a ^k,i_b ^k,i_c ^kSignal calculation of current vectorWherein the four switch combinations are 00,10,11, 01;

(3) by measuring motor speed omega and current vectorEstimating stator flux linkageAnd rotor flux linkage

(4) Predicting all voltage vectors V from a motor model and an inverter model₁,V₂,V₃,V₄Corresponding capacitor voltageStator flux linkageAnd electromagnetic torque

(5) Using predicted individual voltage vectors V₁,V₂,V₃,V₄Corresponding capacitor voltageStator flux linkageAnd electromagnetic torqueCalculating a cost function, and taking a voltage vector which minimizes the cost function as an optimal voltage vector;

(6) and (3) applying a switching signal corresponding to the optimal voltage vector, wherein the corresponding relation between the voltage vector and the switching signal is the same as that in the step (2).

2. The method of claim 1, wherein step (2) is performed by measuring the capacitance voltage U_C1 ^k,U_C2 ^kCalculating voltage vectors V corresponding to four switch combinations₁,V₂,V₃,V₄The current time value is specifically:

voltage vector V corresponding to switch combination 00₁＝2·U_C2 ^k/3；

Voltage vector corresponding to switch combination 10

Voltage vector corresponding to switch combination 11

Voltage vector V corresponding to switch combination 01₄＝-2·U_C1 ^k/3。

3. A method according to claim 1 or 2, characterized in that in step (2) the measured three-phase currents i are used as a basis_a ^k,i_b ^k,i_c ^kSignal calculation of current vectorValue of (2), concrete rootCalculated according to the following formula:

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4. a method according to claim 1 or 2, characterized in that step (3) is performed by measuring the motor speed ω and the current vectorEstimating stator flux linkageAnd rotor flux linkageThe method specifically comprises the following steps:

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wherein L is_s，L_m，L_rRespectively stator inductance, excitation inductance and rotor inductance, R_r、R_sRespectively rotor resistance and stator resistance, T_sIs the sampling time, k_r＝L_m/L_rIs the mutual inductance coefficient of the rotor,is the magnetic leakage coefficient, τ_r＝L_r/R_rIs the rotor time constant.

5. The method according to claim 4, wherein all the voltage vectors V are predicted in the step (4) based on the motor model and the inverter model₁,V₂,V₃,V₄Corresponding capacitor voltage The method specifically comprises the following steps:

predicted value of capacitor voltage Is composed of

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Wherein the capacitance current i_dc1,i_dc2Is taken as follows

i_dc1 ^k＝i_b ^k·S_b+i_c ^k·S_c

i_dc2 ^k＝i_b ^k·(1-S_b)+i_c ^k·(1-S_c)，

S_b,S_cIndicating the switch state.

6. The method according to claim 4, wherein all the voltage vectors V are predicted in the step (4) based on the motor model and the inverter model₁,V₂,V₃,V₄Corresponding stator flux linkageAnd electromagnetic torqueThe method specifically comprises the following steps:

predicting a current vector at a next time instantThe following were used:

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wherein,is the equivalent resistance, L_σ＝σL_sIs the leakage inductance, tau, of the motor_σ＝σL_s/R_σ，Which represents a vector of voltages that is,

predicting stator flux linkage based on predicted current vectorAnd electromagnetic torque

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Wherein p is the induction machine pole pair number, and Im is represented by the imaginary part of a complex number.

7. The method of claim 1 or 2, wherein the step (5) is performed by using predictionEach voltage vector V of₁,V₂,V₃,V₄Corresponding capacitor voltageStator flux linkageAnd electromagnetic torqueCalculating a cost function, specifically:

g according to a cost function_iCalculating each voltage vector V separately₁,V₂,V₃,V₄The value of the corresponding cost function is determined,

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wherein Respectively the rated torque and the rated flux linkage of the induction machine,for the purpose of the torque giving,for the given absolute value of the flux linkage, | - | symbol is the solving absolute value, | | | - | is the solving absolute value of the complex quantity, obtained according to the motor nameplate parameter, λ₀，λ_dcAll the parameters are adjustable parameters, the parameters are obtained by a trial-and-error method, the overall performance of the system is optimal, and the index i is dividedRespectively, parameters calculated from the four voltage vectors.