電氣專業(yè)畢設(shè)英文文獻(xiàn)(格式已修改)(編輯修改稿)
2025-08-22 15:00 本頁面
【文章內(nèi)容簡(jiǎn)介】 rque and ?ux ripple. Their initial values can be set to approximately the ratio between nominal stator voltage and nominal stator ?ux modulus for Kψs, and the ratio between nominal stator voltage and nominal stator fluxFig. 2. Torque response characteristics for classical DTC with a twolevelVSI. Operating point: Γ= Nm. ωm = 200 r/min. modulus for Kψs, and the ratio between nominal stator voltage and nominal torque for KΓe.It can be seen in Fig. 1 that a feedforward action that pensates the BEMF term is added to the output of the torque controller to calculate the tangential ponent of the reference voltage vector. The BEMF term is obtained by multiplying the nominal stator ?ux modulus (ψsn) and the stator ?ux angular speed (ωs), which is previously ?ltered by means of a lowpass ?lter.The reference vector in x–y coordinates is then transformed to α–β ?xed coordinates. The novel controller developed synthesizes the reference voltage by choosing the nearest VSI vector to the reference voltage vector. The nearest vector is found by means of calculating the minimum distance of the voltage vectors that can be delivered by the VSI to the reference voltage vector. This calculation involves evaluating the modulus of the difference between vectors. The plexity of the system presented is increased when pared to classical DTC due to the use of proportional controllers instead of hysteresis parators, the x–y to α–β coordinate transformation and the method to ?nd the nearest vector. Finally, it should be noted that the balance of the neutral point voltage is one of the main issues associated with the control of the threelevel NPC VSI [11]. In the novel controller the balance is achieved by selecting the appropriate con?guration among the redundant possibilities that exist for some of the vectors delivered by the VSI.III. EXPERIMENTAL RESULTSThe practical implementation of the new controller is based on a dSpace DS1103 board that performs the control tasks. This board contains a PowerPC and a DSP. A threelevel NPC VSI utilizing IGBT devices is used to supply a 380/220V fourpole cagerotor induction motor. The dclink voltage employed is 200 V. Figs. 2 and3 show the steadystate torque responses at 200 r/min and nominal torque conditions ( Nm) for the classical DTC strategy with a twolevel VSI and the new control system employing a threelevel VSI described in this paper, respectively. The sample time used was 100 181。s in both systems.To assess the performance of both systems, the torque standard deviation (σΓe) is calculated for the torque ripple. Additionally, the ?ux standard deviation (σψs), the total harmonic distortion (THD) of the stator current THD_iS, and the mean switching frequency in the semiconductor devices (FSw) are calculated for both systems. From the experimental results shown in Figs. 2 and 3, it is apparent that the torque ripple for the new system utilizing a threelevel VSI is considerably reduced. The result
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