The vector control that emerged in the 1970s greatly improved the control performance of asynchronous motors. Accurately estimating (or observing) the magnitude and angle of the rotor flux in the indirect field oriented vector control is the key to the problem. Traditional flux estimators are available in both voltage and current versions. Voltage-type flux estimators rely on stator resistance, while current-type flux estimators rely on rotor resistance. During the operation of the motor, the stator and rotor resistance will change with the temperature rise (and the skin effect of the wire, etc.), which has a great influence on the estimation accuracy. In recent years, many scholars have proposed a method to reduce the influence of stator-rotor resistance perturbation on the estimation of flux linkage. For example, use two estimators together, or improve the pure integral of the voltage-type estimator, and so on. However, these improved flux estimators still contain stator rotor resistance parameters.
In this paper, a rotor flux estimator that does not contain stator rotor resistance parameters is proposed. In other words, the perturbation of stator rotor resistance has little effect on the accuracy of the flux estimator. Based on the basic equations of asynchronous motor in the new coordinate system, the rotor flux estimator based on stator current vector orientation is derived. Through digital simulation, it is proved that the estimator can maintain high precision when the stator rotor resistance is greatly perturbed. Finally, the application of indirect magnetic field oriented vector control is discussed. It is considered that this method can be used in high performance control of asynchronous motors.
2 Rotor flux estimator based on stator current vector orientation In the static (c) coordinate system, the basic voltage equation and flux equation of asynchronous motor written in vector form are the sub-resistance and inductance of China Electrical Engineering Journal; iV and Vr are rotor Voltage vector, current vector and flux vector; for rotor and rotor mutual inductance; called the motor speed.
The rotation speed of the stator current vector is recorded as 1. Select a "1-2 coordinate system" whose 1 axis coincides with 4 and lags behind the 2 axis p/2, and makes the rotation speed of the coordinate system equal to å¦«. Hereinafter, the following target 1 is used to distinguish the projection of each vector on the 1 axis and the 2 axis.
In this coordinate system, the basic voltage and flux linkage equation of the asynchronous motor in vector form is oriented on the stator current vector is due to one axis of the 1-2 coordinate system (as shown), so: U=|is|, 7s2=. According to this, the basic equations (3) and (4) are expanded, and it can be seen that in addition to the first formula in the equation (5), the remaining seven equations in the equations (5) and (6) Rs is not included, only the 7 equations are used in the following derivation, so the derived flux estimator must not contain enough.
Using equations (5) and (6), after simple derivation, you can multiply both sides of equation (7) by LmW! , respectively, and the two sides of the equation (9), to obtain the differential equation of the rotor flux 2 axis differential assumption Â¥ v20, then you can divide the formula (8) by the formula (10), get! After that, the differential equation of the one-axis component of the rotor flux is obtained or written as Â¥r2=0, which is a singular point of the system, but only in very rare cases (such as starting). In simulation and actual engineering, a small number can be used instead of the zero crossing of Â¥r2 without introducing too much error.
By the simultaneous equations (11) and (13), the differential equations of the rotor flux linkage in the 1-2 coordinate system after the stator current vector orientation can be obtained, which can be succinctly expressed as the stator current based on the 1-2 coordinate system. The vector oriented rotor flux linkage rash is referred to hereinafter as the new flux estimator "), and its block diagram is shown.
Different from the traditional voltage type and current type estimator, the new flux estimator composed of equation (15) introduces the parameter W1.W1 is the rotation speed of the stator current vector. When it is steady state, it is equal to the angular frequency of the power source; In the dynamic process, the expression of W1 is the use of Hall sensor to obtain the stator current value with high precision. The new flux estimator current type estimator + new flux estimator can be seen from the current type flux estimator Depending on the rotor resistance, when the motor rotor resistance is perturbed, the estimation results show a large transient and steady-state error. The new flux estimator does not contain the rotor resistance parameter, so the estimation result is almost unaffected and the estimation error is close to zero.
When the motor increases the stator resistance by 50% in the open loop of the power frequency, the estimation error of the new flux estimator and the voltage flux estimator is as shown in the sum.
The amplitude estimation error of the new flux estimator and the voltage flux estimator. The angle estimation error of the new flux estimator and the voltage flux estimator can be seen as the voltage type flux estimator depends on the stator resistance. Therefore, when the stator resistance of the motor is perturbed, the estimation result shows a large transient and steady-state error. The new flux estimator does not contain the stator resistance parameter, so the estimation result is almost unaffected and the estimation error is close to zero.
4 Application of rotor flux estimator based on stator current vector orientation in vector control As mentioned above, rotor flux estimator based on stator current vector orientation (new flux estimator) has superior performance in open loop operation. . The main purpose of verifying its open-loop performance is to use it in a closed-loop controlled asynchronous motor speed control system.
The mathematical model of the asynchronous motor speed control system is established in Matlab/Simulink, and the digital simulation is carried out. The motor parameters are as described above.
In the simulation, the traditional indirect magnetic field oriented vector control is used to control the amplitude estimation error of the new flux estimator and the current flux estimator. When the current signal is not loud, the differentiator sub-signal is tracked. Therefore, the so-called can be calculated by measuring the sub-current.
It is worth noting that in the derivation process, the stator current vector orientation avoids the parameter Rs, and by stripping the Rr-containing term, the Rr. finally obtained new flux estimator, the expression of Vr1 is slightly complicated. However, in this way, the stator rotor resistance parameter can be eliminated. The introduction of the new parameter 1 implies the effect of the fixed rotor resistance on the estimator, so that the estimator does not contain the stator rotor resistance parameter, thereby greatly reducing the influence of parameter perturbation on the estimation accuracy.
3 Digital Simulation and Results In Matlab/Simulink, the motor and flux estimator model was established. Among them, the motor parameters are: Rs is the rated load. The initial conditions of the simulation are: t=0, the current and flux linkage of the motor are all 0. The motor runs open-loop under the power frequency, and the rotor flux resistance increases by 100%, the new flux estimator and current-type flux estimator The estimated error is as shown in and .
The angle estimation error of the new flux estimator and the current flux estimator is the Chinese motor engineering program, the flux amplitude amplitude command is 1Wb, the rotational speed command is 100prad/s. The stator and rotor resistance are simultaneously perturbed, and the perturbation amplitude is Mx=50%, MfIOO%. In the simulation, using the same PI controller, in the feedback link of the rotor flux linkage, the voltage flux estimator, the current flux estimator and the new flux estimator are used successively.
The error between the estimated and true values â€‹â€‹of the three flux estimators is shown as the sum.
Voltage-type flux estimator New flux estimator current-type flux estimator rotor flux amplitude estimation error This is not the main problem to be solved in this paper, so there is no in-depth discussion on this, but through research, the inductance parameter perturbation and The new flux estimator still maintains good performance when the rotational speed measurement error is small. If appropriate corrections are added, the effects of these disturbances can be better suppressed.
The stator flux vector estimator based on stator current vector orientation proposed in this paper does not contain stator rotor resistance parameters, except for a few singular points, which can maintain a fairly high precision. Whether open loop or closed loop operation, the estimator performance is almost unaffected when the stator rotor resistance changes significantly. Compared with the traditional flux estimator, the new flux estimator has obvious advantages in anti-disturbance. With the accurate estimation of the rotor flux linkage as the basis, the key problems of asynchronous motor vector control are solved, and various control strategies can play a better role, thus achieving high-performance control and operation of the asynchronous motor speed control system.
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