0熊志鹏 外文翻译 6.5版本

外文资料翻译资料来源：文章名：A novel sensorless control method for brushless DC motor书刊名：IET Electric Power Applications作 者：H.-B. Wang H.-P. Liu出版社：重庆大学出版社，2008章 节：1.3 Principle of the proposed Method页 码：P4P20文 章 译 名：一种新颖的无传感器控制的无 刷直流电机 姓 名： 熊志鹏 学 号： 1002150325 指导教师(职称)： 李艳红（讲师） 专 业： 自动化 班 级： 03 所 在 学 院： 机电学部 Abstract The authors present the theory and implementation of a novel sensorless control method for theinterior permanent magnet (IPM) brushless DC motor (BLDCM). The proposed new sensorless technique canaccurately detect the zero-cross point (ZCP) of back electromotive force (BEMF), which is based on acomparison of the terminal voltage of the unconducting phase during the first and second part of a pulsewidth modulation (PWM) cycle. Compared with the conventional BEMF sensorless approach, the proposednew sensorless method solves the problem of the sensorless BLDCM drives at very low speeds. Experimentalresults confirm the validity of the new method.1 Introduction Brushless DC motor (BLDCM) can be broadly categorisedinto interior permanent magnet (IPM) motors and surface-mounted permanent magnet (SPM) motors. Comparedwith SPM motors, IPM motors have a mechanically robustand solid structure, because the magnets are physicallycontained and protected. In addition, because of their reluctance to torque production, the IPM motors are more suitable for traction applications, which require constant power output at high speeds over a wide range. So, IPM motors are more practical than SMP motors in various industrial and other applications. The drive for the BLDCM requires a position sensor for providing proper commutation sequence to turn on the power devices in the inverter bridge. Position sensor not only increases the cost and encumbrance of the overall drive system but also reduces its control robustness and reliability. Furthermore, it might be difficult to install and maintain a position sensor because of the limited assembly space and rigid working environment with severe vibration and/or high temperature. Therefore various sensorless control schemes have been developed for the estimation of rotor position and speed 17. Schemes based on back electromotive force (BEMF) have been shown to be successful at medium- and high-rotor speeds; however, they fail at very low speeds because the amplitude of BEMF is zero at rest and proportional to the rotor speed. So, position sensing using inductance variation and signal injection methods are very popular in BLDCM applications. Such schemes have the important advantage that they are useful at very low speeds where there is little BEMF. AnINFORMmethodwasproposedbySchroedl8,which was based on the real-time inductance measurements using saliency and saturation effects. During a short-time interval, the complex INFORM reactance was calculated for estimating the flux angle. Kulkarni and Ehsani 9 proposed a method for calculating the effective phase inductance from the behaviour of the hysteresis current controller for an excited phase. Corley and Lorenz 10 used voltage injection at a carrier frequency of 2 kHz. The corresponding frequency component of current was modulated by the rotor position variation of the phase inductance. Information about the rotor position was extracted by making a comparison with a set of signals at the same carrier frequency and modulated by an estimated rotor position, which was derived from a simple motion estimator. A similar approach has been reported by Noguchi and Kohno 11, who used a 4 kHz carrier frequency. Although these techniques allow for very low-speed operation,drawbacks are very obvious. All these methods require high-precision and high-bandwidth (fast) measurement and fast signal-processing capability, which inevitably increase the complexity and cost of control system and lead to acoustic noise, torque ripple andincreased losses. This study presents a novel sensorless position detection technique for IPM BLDCM that can detect equal self- inductance of the energised phases by using measurements of the instantaneous voltage across the unconducting phase. Moreover, the rotor position of equal self-inductance is just the zero-cross point (ZCP) of BEMF of the unconducting phase. Compensating 308 offset, the required commutation positions can be determined. This method is very simple and easy to implement and also allows for very low-speed operation.2 Model of inductance of IPM BLDCM Generally, BLDCM is driven by a three-phase inverter with what is called a six-step commutation. Each conducting phase is called one step. The conducting interval for Each phase is 120 electrical degrees. Therefore only two of the three phases are excited at any instant, and a phase remains open in BLDCM. Fig. 1 shows an equivalent circuit of BLDCM and invertersystem. The amplitude of BEMF is proportional to rotor speed, but the ZCP of the unconducting phase is invariant. In a BLDCM, the BEMF induced by the rotary permanent magnet excitation field is approximately trapezoidal, as shown in Fig. 2. The BEMF is a function of rotorposition. Therefore with the speed command and rotor position, the symmetric three-phase BEMF waveforms can be generated at every operating speed. Equation (1) gives relationship between the A-phase BEMF and rotor position. Similar equations can be found for the B-phase and the C-phaseFigure 1 Inverter topology and equivalent circuit of the BLDCMFigure 2 BEMF waveforms BEMF.(1)where v is the mechanical speed of a motor, keis the BEMF constant. The IPM BLDCM can be modelled like a salient pole synchronous motor 12, 13. The winding inductance varies significantly with the rotor position. The stator self-inductances of IPM motor can be approximately expressed as(2)The m stator-to-stator utual inductances are(3) where u is the electrical rotor angle; Laa0the component of the self-inductance caused by the space fundamental air- gap flux; Lal the additional component caused by the armature leakage flux and Lg2is the component of the self- inductance caused by rotor position dependent flux. The ZCP of BEMF of a particular phase occurs 30 electrical degrees before that phase is energised. But the ZCP of a phase winding also coincides with the alignment of the magnetic axis of that winding with the d-axis of the rotor. Clearly at that position, the self-inductance of that phase is a maximum, whereas the inductances of the two other phases will, because of geometric symmetry, be equal to each other. In other words, wherever the rotor d-axis aligns with the magnetic axis of the A-phase winding, Eais equal to zero and lbb lcc. Similar statements can be made about the B-phase winding and the C-phase winding. Therefore the positions of equal inductance of the energised phases, just like the ZCP of BEMF of the unconducting phase, occur 30 electrical degrees before the next commutation position. Equation (4) gives exact relationships among rotor positions, self-inductances,mutual inductances and BEMF.(4) It is shown from (4) that the rotor position where the rotor reaches the equal self-inductance position coincides with the ZCP of BEMF of the unconducting phase. Therefore some schemes that can detect the equal self-inductance of energised phases in real time can determine the ZCP of BEMF of the unconducting phase. After compensating for 308 offset, commutation position of BLDCM can be Determined.3 Principle of the proposed Method Regarding the three-phase inverter pulse width modulation (PWM) control scheme is widely applied to control the speed and current of BLDCM. The PWM scheme that is used in this study is H_PWM-L_PWM. Fig. 3 illustrates the gating sequence of the electronic switches waveforms in this typical PWM strategy in which both the active switches in the lower half bridge and upper half bridge are modulated simultaneously The selected interval for subsequent analysis shown in Fig. 4 corresponds to the instant when the current is beginning to switch from A-phase to B-phase, whereas thecurrent of C-phase is assumed to have already decayed to zero. During the interval switches, T Aand T Bare the only two active switches. When the switches T A and T B are switched off, as shown in Fig. 5, the inductive motor phase current is circulating through freewheeling diodesD Band D? A. The dashed line in Figs. 4 and 5 illustrates the real loop current direction.Figure 3 Timing diagram of H_PWM-L_PWM control SignalsThe circuit equations of Fig. 4 are(5)(6)where Vs is the inverter switch on-state voltage drop. Substituting (6) and (7) into (5) gives(7)if the BEMF assumes constant in the PWM cycle. From (4), it is found that laais equal to lbb, Eais equal to ?Eb, lbcisFigure 4 Equivalent circuit during the PWM on timeFigure 5 Equivalent circuit during the PWM off timeequal to lac, where u is at 608 or 2408. So the potential of C-phase is(8)The circuit equations of Fig. 5 are(9)(10)where VD is the inverter diode on-state voltage drop. Substituting (11) and (12) into (10) gives(11)where u is at 608 or 2408. Substituting (4) into (13), the potential of C-phase, v0ccan be represented as(12)Comparing (9) with (14) gives(13) Analysing (4), it is known that Ecis equal to zero when u is equal to 608 or 2408. Therefore the ZCP of BME of C-phase can be estimated by computing the differences of terminal voltage of C-phase according to (15). Moreover, these are similar statements about the A-phase winding and the B- phase winding when rotor position u is at 1208, 1808, 3008 and 3608.4 Analysis of the sensitivity of the proposed method When the rotor is at any position and under the assumption that the current of C-phase has decayed to zero, A-phase and B-phase are modulated simultaneously as shown in Figs. 4 and 5. Fig. 6 shows the A-phase current waveform in a H_PWM-L_PWM cycle, in which T is the PWM period and t is the switch on-state time. According to Fig. 4, combining (5), (6) and (7), we get(14)According to Fig. 5, combining (10), (11) and (12), we get(15)According to similar triangle principle, Fig. 6 can give Approximately(16)The voltage difference Dvc(T) between vc(t=2) and v0 c(t T)=2) can be represented as(17)Figure 6 The A-phase current waveform in a H_PWM- L_PWM periodSubstituting (8), (13), (16), (17), (18) into (19) gives(18)From (2), we have(19)If the difference of VS? VDis ignored, substituting (21) into(20) gives(20)The direct and the quadrature axis inductance are(21)(22)(23)Substituting (26) into (20) gives(24)Similarly, when A-phase is open, we get(25)When B-phase is open, we obtain(26)From (27), (28) and (29), it is clear that comparing the first and second difference of the terminal voltage of the unconducting phase can determine its ZCP of the BEMF.Moreover, this difference depends only on quadrature inductance Lq, direct inductance Ldand DC bus voltage, which are constant in the circuit. Therefore this method is robust to the speed of BLDCM. Theoretically, it can operate at any low speeds, even at zero speed.5Experimental results Fig. 7 shows the prototype of the proposed sensorless driveand the adopted BLDC machine (five poles, rated power3 kW and rated speed 2600 rpm). To ascertain the effectiveness of the technique, there are two commutation methods in Fig. 7. So, we can compare the commutation signals from the proposed technique and the Hall sensor. Unlike conventional solutions, analog filter circuit and the phase shift circuit are not required in the proposed method. It can be seen that only six additional resistors have been included for the proposed control method. The entire drivesystem is controlled by a low-cost, fixed-point digital signal processor (DSP), Dspic6010. Fig. 8 shows the waveform of three-phase terminal voltage with H_PWM-L_PWM modulation and HALL commutation signal. From Fig. 8, we can find that the DC bus voltage is 20 V. Fig. 9 illustrates how to detect the ZCP of theunconducting phase. The sampling instants of voltage in Fig. 9 are the t/2 and (T t)/2, which are the mid-pointFigure 7 Block diagram representation showing the implementation of the proposed systemFigure 8 Three-phase terminal voltage and HALL commutation signal during PWM on time and mid-point during PWM off time shown in Fig. 6. According to (27), (28) and (29), based on a comparison of the terminal voltage of the unconducting phase during the first and second part in a PWM cycle, the range of the ZCP can be estimated, which is implemented by the software. Fig. 10 illustrates sensorless operation at 58 rpm (from top to bottom: A and B phase terminal voltages, the ZCP signal and commutation signal obtained with the proposed approach). It is clear that each trigger edge of ZCP signal corresponds to 608, 1208, 1808, 2408, 3008 and 3608 rotor position of the terminal voltage of the unconducting phase. This is in agreement with result of (4). Fig. 11 shows the terminal voltage for A-phase and B- phase, the commutation signal from Hall sensor and the commutation signal obtained using the proposed method in which the motor speed is only 58 rpm, which is less than 3% rated speed. It can be seen that there is a little error between the commutation signal from Hall sensor and the estimated commutation signal from the proposed strategy.Figure 9 The process of estimating ZCP of unconducting PhaseFigure 10 A- and B-phase terminal voltages, the ZCP and estimated commutation signalFigure 11 A-and B-phase terminal voltages, the commutation signal from Hall sensor and the estimated commutation signal In Fig. 12, experimental results show the real A-phase current waveform and that corresponding to the PWM waveform. The experimental waveform of A-phase shows a good agreement with the waveform of theoretical analysis shown in Fig. 6.Figure 12 The real A-phase current waveform and corresponded PWM waveform6 Conclusion A novel approach to the position-sensor elimination of an IPM BLDCM is presented in this paper. Both theoretical analysis and experimental results verify that satisfactoryperformance can be achieved with the proposed sensorless commutationmethod. When compared with the conventional solutions, the proposed method has several advantages and disadvantages, including the following.1. This method does not depend on the BEMF, and so it can be operated at very low speeds. DC bus voltage Ud, quadrature inductance Lq, direct inductance Ld andcomponent of the self-inductance Lg2are very important to the sensitivity of the proposed method.2. The process of estimating ZCP is implemented by the software, and so this method does not need any sensor. Moreover, the parameter in the software is important tocommutation error.3. This method does not need to know the exact parameter of the motor, such as self-inductance, mutual inductance and its inertia, because it only needs to knowwhen self-inductances of energised phases are equal.4. The motor in the method should be a salient motor, because this method requires that quadrature inductance Lq is not equal to direct inductance Ld.5. The special PWM scheme, H_PWM-L_PWM, is used in this method, which will result in higher switch losses when compared with the conventional PWM modulation scheme.6. Torque ripple in this method is bigger than that in the conventional method in which PWM scheme is H_PWM- L_ON or L_PWM-H_ON. To overcome the disadvantage of the proposed method, a new approach is under process that the proposed sensorless method will be transferred to the BEMF method when themotor speed is above a certain speed.7 References1 ACARNLEY P.P., JOHN F.: Review of position sensorless operation of brushless permanent magnet machines, IEEE Trans. Ind. Electr., 2006, 53, (2), pp. 3523622 JOHNSON J.P., EHSANI M., GUZELGUNLER Y.: Review of sensorless methods for brushless DC. Industry Applications Conference, 1999, 34th IAS Annual Meeting. Conference Record of the 1999 IEEE 1999, vol. 1, pp. 1431503 CHEN C.-H., CHENG M.-Y.: A new sensorless control scheme for brushless DC motors without phase shift circuit. Proc.6th IEEE Int. Conf. Power Electronics and Drive Systems, KL, Malaysia, 2005, pp. 108410894 IIZUKA K., UZUHASHI H., KANO M., ENDO T., MOHRI K., IIZUKA, ET AL.: Microcomputer control for sensorless brushless motor, IEEE Trans. Ind. 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