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A new flux estimation method of the direct torque control Ya Yuan, Tang Pu Hua, song Chang Lin

(numerical control research center, Sichuan Institute of technology, Chengdu 611744, China) abstract:in this paper, the flux oriented angle of stator-flux-oriented vector control (SFOVC) is deduced by the voltage vector space angle of the direct torque control (DTC), and mathematical model is set up based on the direct- and quadrature-axis component of the stator current. Thus, the flux estimation of the DTC is very simple to easily use, and the preciseness is very good. This paper gives the experimental results of the DTC for the 7.5kilowatt induction motor, and it verifies that theory analysis is right and practical.

KEY WORDS：direct torque control; stator-flux-oriented vector control; Introduction the research of direct torque control (DTC) of asynchronous motor has made great progress, but its application research needs to be further deepened. In this paper, a 7.5kW AC asynchronous motor DTC experimental device is established, and some problems in DTC are explored, in which a stator flux estimation method with high accuracy and easy implementation is developed

at present, in DTC, the estimation of stator flux linkage can be generally divided into two models with low noise and stable operation in the experimental process, one is U-I model, the other is I-N model [1]. It is difficult to choose the maximum range in the range jump when implementing these two methods

when the U-I model is adopted, the stator flux can be calculated according to the voltage and current measured at the stator end. The formula is as follows (1) Ψ S is the stator flux vector; Us is the voltage vector at the stator end; Is is the current vector at the stator end; RS is the stator resistance

although equation (1) is very simple, it is difficult to implement because there is a large error in voltage sampling. The switching time of inverter voltage in DTC will be very short, and the error of integral operation after sampling is very large, resulting in serious distortion of flux estimation

Another type of flux linkage estimation is I-N model. This method is based on the measured stator current and motor speed to calculate the stator flux, and its basic formula is in formula (2) Ψ R is the rotor flux vector; L σ Is leakage inductance; LS is the main stator inductancethis formula is not complicated, but it is obvious from formula (2) that the rotor flux vector must be determined first Ψ R can solve the stator flux linkage by equation (2). As we all know, determination Ψ R itself is a very complicated work. Therefore, it is quite difficult to estimate the stator flux according to the I-N model

there are also the combination of these two methods, or some other similar methods [2], but there are similar problems. In order to overcome these difficulties, the author proposes a new method, which combines the DTC method with the stator flux orientation method, and uses their characteristics to estimate the stator flux

in essence, DTC method is the same as stator flux oriented control. In DTC method, the function of closed-loop flux linkage is that no matter what happens to the torque, the stator flux linkage always keeps moving along a trajectory similar to a circle, and the speed of the flux linkage will also be dynamically adjusted to realize the decoupling of torque and flux linkage through a special closed-loop flux linkage. DTC can be regarded as a specific way of stator flux oriented control. Based on this understanding, the two methods can be combined to deal with the estimation of stator flux linkage. 2 stator flux estimation model figure 1 shows a stator flux orientation vector diagram. In the figure, ds-qs is the static coordinate, d-q is the coordinate rotating at the synchronous speed, and d axis and stator flux linkage Ψ S coincidence. The components of stator current is in ds-qs coordinate are ISDS and isqs respectively, and its components in d-q coordinate are IDs and IQs respectively. If a certain current model is used to estimate the stator flux linkage, the current components ISDS and isqs in ds-qs system and the current components IDs and IQs in d-q system can be used, but there is a great difference between the two. D-q system is a coordinate system used for stator flux orientation control. Considering the decoupling of d-axis and q-axis components, there are: Ψ ds＝ Ψ S; Ψ qs＝0。 This will make the current mode in the d-q system easier for the company to build a local production plant in Rhodes, which will bring great convenience to the estimation of stator flux. Figure 1 stator flux oriented vector diagram

fig.1 stator flux oriented vecto has a good strategy on the first day of M & A; In addition, to have a strict rule of conduct and an experienced M & a team r figure to adopt this flux estimation method, the first problem to be solved is how to determine the stator flux orientation angle (Figure 1 θ s)； The second problem to be solved is how to establish the flux estimation model. These two issues are analyzed below

2.1 stator flux orientation angle θ Determination of s

in the DTC method, the flux track tracking PWM method is adopted. This is by switching the switching logic of the inverter according to a certain law to make the flux linkage move according to a certain trajectory (similar to a circle). This voltage switching logic is known. I.e. motor setting

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