Implementation of the Three-Phase Switched ... - IEEE Xplore

IEEE/ASME TRANSACTIONS ON MECHATRONICS, VOL. 15, NO. 3, JUNE 2010

421

Implementation of the Three-Phase Switched Reluctance Machine System for Motors and Generators Hao Chen, Senior Member, IEEE, and Jason J. Gu, Senior Member, IEEE

Abstract—This paper presents two three-phase switched reluctance machine systems. One is the dual motors drive for the electric locomotive traction; the other is the variable-speed generator system for wind power applications. The principles of the switched reluctance machine system operated at four quadrants, the scheme of the symmetrical traction at quadrant I and quadrant III, and the scheme of the symmetrical regenerative braking control at quadrant II and quadrant IV, are given. The transient phase current analysis and the energy analysis of the switched reluctance machine system at the operational state of braking or generating are evaluated, and the rotor position and the peak value of the phase current at three different conditions are given. The closedloop rotor speed control of the main motor, synchronization of the rotor speed, and balance distribution of loads between the main motor and the subordinate motor have been implemented by the fuzzy logic algorithm. The closed-loop output power control of the switched reluctance wind power generator system implemented by regulating the turn-ON angle of the main switches with fuzzy logic algorithm and fixed turn-OFF angle of the main switches is also presented. The major components of the two prototypes are explained in detail. The experimental results of the dual 7.5-kW three-phase 6/4 structure switched reluctance motors (SRMs) parallel drive system prototype are included. It is shown that the maximum difference in the output torque of the two motors at the same given rotor speeds is within 10.00% and the maximum difference in the practical rotor speed of the two motors is within 5.00%. The tested results of three-phase 12/8 structure switched reluctance variablespeed wind power generator system show that the error of the closed-loop output power control is within 2.2%, while the rotor speed range is close to the ratio of 1:3 with the low rotor speed 405 r/min. The average dc line current of the power converter can be utilized as a feedback signal for the actual output torque of SRM drive or a feedback signal for the actual output power of switched reluctance generator system. Index Terms—Four quadrants, fuzzy logic, generator control, motor control, pulsewidth modulation (PWM), switched reluctance.

Manuscript received January 6, 2009; revised April 24, 2009. First published August 21, 2009; current version published April 2, 2010. Recommended by Technical Editor M. Benbouzid. This work was supported in part by the International S&T Cooperation Program of China under Grant 2008DFA61870, in part by the Natural Science Foundation of Jiangsu Province under Grant BK2007039, in part by the Specialized Research Fund for the Doctoral Program of Higher Education of China under Grant 20070290504, in part by the Six Talent Flood Tide Project of Jiangsu Province under Grant 07-D-024, and in part by the 333 Engineering Project of Jiangsu Province under Grant 2007-71. H. Chen is with the School of Information and Electrical Engineering, China University of Mining and Technology, Xuzhou 221116, China (e-mail: [email protected]). J. J. Gu is with the Department of Electrical and Computer Engineering, Dalhousie University, Halifax, NS B3J 2X4, Canada (e-mail: [email protected]). Digital Object Identifier 10.1109/TMECH.2009.2027901

I. INTRODUCTION HE SWITCHED reluctance machine system is a mechatronic device that has been developed for many years [1]. The iron core of the stator and the rotor in the switched reluctance machine are laminated by the magnetic sheet steels, which are the structure of the salient pole. There is a centralized coil in each stator pole. The machine is supplied with the unipolar current by the unipolar power converter. It has the advantages of a firm structure of the machine without brushes on the rotor and the firm structure of the unidirectional power converter without the “direct-short circuit” fault in the bidirectional power converter [2]. It also has an advantage in the implementation of the fault-tolerant control. The system has a good ability for fault-tolerant control with independence on the magnetic flux paths of the machine and on the main circuit of the power converter [3]. The reliability of the switched reluctance machine system is higher than that of other types of the machine system. It had been applied as a motor in many situations, such as in coal mines [4], in electric vehicles, in high-speed drives, in small domestic appliances, in fans, and in pumps. The control theory and the systematical design method of the switched reluctance motor (SRM) drive have been researched in some literatures [5]–[10]. SRMs had been used for high-bandwidth actuator applications; since the torque control is sufficiently fast, high-performance motion control, four-quadrant operation, high-bandwidth speed and position control, low- and zero-speed operation can be implemented [11]. Those performances in SRMs are better than those in the permanent-magnet synchronous motor with the hysteresis direct torque control [12]. The new technique for multidimensional performance optimization of SRM drives with optimum firing turn-ON and turn-OFF angles for achieving high drive efficiency and lowest torque ripple had been conducted on the drive for an electric vehicle [13]. The key technologies for enhancement of efficiency, elimination of position sensors and reduction of torque pulsation contribute to the switched reluctance drive for automotive applications [14]. Approximately 6% improvement in efficiency is observed for the motor made from the amorphous alloy material [15]. A piezoelectric washer has been designed and incorporated into an SRM drive system to sense harmonics of torque-ripple-induced vibrations [16] and a closed-loop feedback-based control technique for torque harmonic mitigation has been established using a simple PI control strategy [17]. For a very long period of time, the series dc motors have been used as the drive system of the storage battery electric locomotive in coal mines. With the modernized level of coal mining

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enhanced, it is necessary to improve the transport vehicle in the aspects of performance, safety, reliability, and maintenance cost. The SRM drive has advantages in flammable and explosive environmental adaptability of coal mining. It could be operated in four quadrants so that the regenerative braking operation of the electric locomotive could be implemented. The SRM drive has a great advantage in electric locomotive traction application of coal mining. The parallel drive system of the dual motors has the advantages of arranging the space and placing the motors rationally, improving the attractive properties of the drive with composition of the two motors. The whole inertia movement of the parallel drive system of the dual motors is smaller than that of the drive system of the single motor with the same output. It contributes to the reduction of loss of the electric energy in the course of starting. Comparing with the electric locomotive drawn by one motor, the locomotive drawn by paralleling dual motors has higher reliability. If there are some malfunctions in one motor, the parallel drive system could be operated continuously on the condition of reducing the tractive power by removing the broken motor. It is important for the parallel drive system with two SRMs to balance the distribution of the loads at the operational state of traction. There is a difference in the mechanical properties of the two motors because of the difference in the manufacturing of the two motors. The mechanical properties [18] of the two motors are soft at the high rotor speed range with the fixed-angle pulsewidth modulation (PWM) control strategy or the angle position control strategy; the mechanical properties of the two motors are soft with the phase current chopping control strategy, so that the difference in the average electromagnetic torque of the two motors at the same rotor speeds is small. The soft mechanical properties of the SRM drive contribute to paralleling the dual SRMs drive with balanced distribution of loads at the operational state of traction. The switched reluctance machine can be operated as an autonomous ac generator [19], the applications of hybrid vehicles [20], starter/alternator in automotive applications [21], and for more electric cars [22]. The numerical model of the switched reluctance generator for calculating the dynamic behavior has been developed with the electric circuit and magnetic circuit being coupled [23]. The 8/6 structure switched reluctance generator excited by the suppression resistor converter has a simple circuit configuration and low cost, including the gate circuit [24]. With the increasing demands of the electric power, the importance of environmental protection and the development of the regenerative energy, the wind power generating electricity has been developed rapidly over the past decade. There are different wind power generator systems, such as the doubly fed induction generator system [25], synchronous generator, the induction generator, and the permanent-magnet generator. The switched reluctance machine system could also be operated as a wind power generator system [26], [27]. The required starting torque of the switched reluctance generator is small because of its small rotor inertia without the windings, the magnet, and the brushes on the rotor. This way the wind power generator system with a switched reluctance generator requires low starting wind velocity and is able to generate electrical power with low wind velocity. It contributes to extend the efficient time of the


Fig. 1.

Diagram of phase inductance and phase current.

generated electricity and increases the utilized ratio of the wind power. The advantage in the high system efficiency within wide rotor speed ranges contributes to enhance the transformed ratio of wind/electrical energy. The strong capability of fault tolerance of the switched reluctance generator system extends the overall lifetime of the wind power generator system. In case, one of the generator phases is broken down, the commutation control signals of the damaged phase can be blocked and the excitation of the damaged phase will be stopped so that the switched reluctance generator can continue to generate electrical power. All this contributes to reducing the costs of wind power electricity when the switched reluctance generator is used in a wind power generator system. There are some developed novel mechatronics system [28]–[30]. This paper presents 2 three-phase switched reluctance machine systems. One is the dual motors drive for the electric locomotive traction; the other is the variable-speed generator system for wind power applications. II. OPERATIONAL PRINCIPLES The relationship between the phase inductance, the rotor position θ, and the phase current i at four quadrants is shown in Fig. 1, where, Lm in is the minimum value of the phase inductance, and Lm ax is the maximum value of the phase inductance. The main switches of the power converter are turned on at θ1k (turn-ON angle), and turned off at θ2k (turn-OFF angle) (k = I, II, III, IV). While the phase current is at the ascending region of the phase inductance (∂L/∂θ > 0), the direction of electromagnetic torque is the same as the rotational direction of the rotor; the machine operates in traction mode. While the phase current is at the descending region of the phase inductance (∂L/∂θ < 0), the direction of electromagnetic torque is in the opposite direction of the rotational direction of the rotor, the machine operates in braking mode or in generating mode. While the phase current is at the rotor position where the axis of the

CHEN AND GU: IMPLEMENTATION OF THE THREE-PHASE SWITCHED RELUCTANCE MACHINE SYSTEM FOR MOTORS AND GENERATORS

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switches of the power converter are turned on at the turn-ON angle θ1 , turned off at the turn-OFF angle θ2 , and the commutation is finished at commutation angle θ3 . The following can be derived based on (1):  di   > 0, θ1 ≤ θ < θ2 dθ . (2)   di < 0, θ < θ ≤ θ b 3 dθ It is shown that the peak value of the phase current is in the range θ2 ≤ θ ≤ θb . For that interval, the voltage equation of the phase winding is as follows: Fig. 2.

−U2 = ωL

Analysis of the phase inductance and the phase current.

rotor pole is aligned with the axis of the stator pole (there is the maximum value of the phase inductance in the rotor position), or at the rotor position where the axis of the rotor slot is aligned with the axis of the stator pole (there is the minimum value of the phase inductance in the rotor position), the electromagnetic torque is zero because ∂L/∂θ is zero. While the switched reluctance machine is operated at quadrant I and quadrant III, the greater part of the phase current is at the ascending region of the phase inductance. The direction of the average electromagnetic torque of the machine is the same as the rotational direction of the rotor, so that it is the operational state of traction. While the switched reluctance machine is operated at quadrant II and quadrant IV, the greater part of the phase current is at the descending region of the phase inductance. The direction of the average electromagnetic torque of the motor is in the opposite direction of the rotational direction of the rotor, so that it is the operational state of braking or generating. If the leakage flux of the switched reluctance machine is neglected, the phase inductance L(θ) has the form shown in Fig. 2, where Lm in is the minimum value of the phase inductance, Lm ax is the maximum value of the phase inductance, θr is one rotor period, θm is the maximum phase inductance rotor position, θa and θb are related to the stator and the rotor pole-face factor. If the resistance of the phase windings, the voltage drop of the main switches and the ON-state voltage drop of the flywheel diodes are neglected, the transient phase current of the switched reluctance machine shown in Fig. 2 could be expressed as follows: i= i= i=

ω[Lm in

U (θ − θ1 ) , + (∂L/∂θ)(θ − θa )]

U (θ − θ1 ) , ωLm ax ω[Lm ax

θ1 ≤ θ ≤ θm

i=

U (θ2 − θ1 ) − U2 (θ − θ2 ) , ω[Lm ax + (∂L/∂θ)(θ − θm )]

i=

U (θ2 − θ1 ) − U2 (θ − θ2 ) , ωLm in

−iω

∂L > U2 ∂θ

(4)

so that di > 0. dθ

(5)

The peak value of the phase current is at rotor position θ = θb , and the peak value of the phase current is given by im ax =

1 U (θ2 − θ1 ) − U2 (θb − θ2 ) · . ω Lm in

(6)

If the rotational EMF is equal to the commutation voltage of the machine, then −iω

∂L = U2 ∂θ

(7)

so that di = 0. dθ

(8)

There exists a flathead phase current in the interval [θ2 , θb ], and the flathead value of the phase current is given by im ax =

U2 1 · . ω −(∂L/∂θ) |θ =θ 2

(9)

If the rotational EMF is smaller than the commutation voltage of the machine, then −iω

θm ≤ θ ≤ θ2

∂L < U2 ∂θ

(10)

so that di < 0. dθ

θ2 < θ ≤ θb θb ≤ θ ≤ θ 3

(3)

If the rotational electromotive force (EMF) is bigger than the commutation voltage of the machine, then

θ = θm

U (θ − θ1 ) , + (∂L/∂θ)(θ − θm )]

∂L di + iω . dθ ∂θ

(1)

where U is the phase excitation voltage, U2 is the commutation voltage of the machine, ω is the rotor angular speed, the main

(11)

The peak value of the phase current is at rotor position θ = θ2 , and the peak value of the phase current is given by im ax =

U (θ2 − θ1 ) 1 . ω Lm ax + (θ2 − θm )(∂L/∂θ) |θ =θ 2

(12)

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1) During the Excitation Period: In the region of increasing inductance (θ1 ≤ θ < θm ), a part of the electrical energy supplied by the excitation power supply is transformed into stored magnetic energy of the switched reluctance machine; the remaining part of the electrical energy is converted to mechanical energy with the aid of the magnetic field of the machine. At the rotor position of maximum inductance (θ = θm ), the whole excitation energy is transformed into a stored magnetic energy of the machine, and there is no mechanical energy output or input. In the region of decreasing inductance (θm ≤ θ ≤ θ2 ): 1) when operated as the motor, the electrical energy provided by the power supply and the mechanical energy of the motor with loads are all converted into the stored magnetic energy of the motor and 2) when operated as the generator, the electrical energy provided by the power supply and the input mechanical energy supplied by the prime mover are all converted into the stored magnetic energy of the generator. 2) During the Commutation Period: In the region of decreasing inductance (θ2 ≤ θ ≤ θb ): 1) when operated as the motor, the mechanical energy of the motor with loads and the stored magnetic energy of the motor are all changed into the electrical energy and fed to power supply by the aid of the magnetic field of the motor with the continuing current and 2) when operated as the generator, the input mechanical energy supplied by the prime mover and the stored magnetic energy of the generator are all changed into the electrical energy and supplied to the electrical load by the aid of the magnetic field of the generator with the continuing current. In the region of minimum inductance (θb ≤ θ ≤ θ3 ≤ θr + θa ) (while a, which is the rotational EMF, is bigger than the commutation voltage of the machine system, or b, which is the rotational EMF, is equal to the commutation voltage of the machine), only the stored magnetic energy of the machine is changed into the electrical energy and fed to the power supply or supplied to the electrical load with the continuing current, and there is no mechanical energy output or input. If the continuing current enters into the inductance-increasing region (θ3 > θr + θa ) again, the stored magnetic energy of the machine is transformed into mechanical energy output: 1) when operated as the motor, it causes the decreasing of the braking torque during one period and 2) when operated as the generator, it causes the decreasing of the ratio of mechanical energy supplied by the prime mover to electrical energy during one period. This situation should be avoided by regulating the control parameters θ1 , θ2 , and U, with θ2 +

U (θ2 − θ1 ) ≤ θr + θa . U2

At the operational state of traction, the triggering signals of the main switches at quadrant I (θ1I , θ2I ) are advanced as follows: θf 1 = θ1I + θ2I .

These could be used as the triggering signals of the main switches at quadrant III (θ1III , θ2III )

Although there can be some mechanical energy output in the range θ1 ≤ θ < θm : 1) when operated as the motor, the mechanical energy of the motor with loads is small partly transformed into electrical energy and fed to power supply during one period, θr and 2) when operated as the generator, the mechanical energy supplied by the prime mover is small partly transformed into electrical energy and supplied to the electrical load during one period θr .

θ1III = θf 1 − θ2I

(15)

θ2III = θf 1 − θ1I

(16)

so, the symmetrical traction at quadrant I and quadrant III could be implemented. At the state of regenerative braking or at the state of generating, the triggering signals of the main switches at quadrant II (θ1II , θ2II ) are advanced as follows: θf 2 = θ1II + θ2II .

(17)

These could be used as the triggering signals of the main switches at quadrant IV (θ1IV , θ2IV ) θ1IV = θf 2 − θ2II

(18)

θ2IV = θf 2 − θ1II

(19)

so, the symmetrical regenerative braking control or the symmetrical generating control at quadrant II and quadrant IV could be implemented. The output power of the SRM drive system is as follows: P2 = K · U1 · I1

(20)

where K (0 < K < 1) is related to the loss of the system, such as the power converter loss, the copper loss of the motor, the iron loss of the motor, the mechanical loss of the motor and the stray loss of the motor, U1 is the dc line voltage of the power converter, I1 is the average dc line current of the power converter that is as follows: 1 θr I1 = i1 dθ (21) θr 0 where θ is the rotor position, θr is one rotor period, i1 is the dc line current of the power converter. The output torque of SRM drive is as follows: P2 (22) Ω where the rotor angular velocity, Ω, has the relationship with the rotor speed, n, as follows: T2 =

2πn (in radians per second) (23) 60 so that the average dc line current of the power converter could be used as the feedback signal of the output torque of SRM drive. The phase current chopping control strategy could be adopted at the low rotor speed range in order to balance the distribution of the loads of the two SRMs in the parallel drive system. The fixed-angle PWM control strategy is adopted for the adjustable speed control at the high rotor speed range and the regenerative braking control of the drive. The turn-ON angle and the turn-OFF angle of the main switches in the power converter are fixed. Ω=

(13)

(14)


Fig. 3.

425

Block diagram of the switched reluctance dual motors parallel drive system.

The triggering signals of the main switches are modulated by the PWM signal. The phase winding average voltage could be adjusted by regulating the duty ratio of the PWM signal. So, the output torque and the rotor speed of the motor are adjustable at the operational state of traction, and the braking torque is adjustable at the operational state of regenerative braking, by regulating the phase winding average voltage. In the dual SRMs parallel drive system, one motor is the main motor, and the other is the subordinate motor. The block diagram of the switched reluctance dual motors parallel drive system is shown in Fig. 3. The main motor could be controlled with the closed-loop rotor speed control implemented by the fixedangle PWM control strategy and the phase current chopping control strategy with fuzzy logic algorithm. The subordinate motor could be controlled with the balanced distribution of loads control implemented by the fixed-angle PWM control strategy and the phase current chopping control strategy with fuzzy logic algorithm. In the main motor, there are two input control parameters, there is the deviation of the rotor speed between the given rotor speed and the feedback rotor speed, the variation from the deviation of the rotor speed. The output control parameter is the increment of the duty ratio of the PWM signal of the main motor at the high rotor speed range, and the output control parameter is the increment of the phase current chopping limitation of the main motor at the low rotor speed range. In the subordinate motor, there are also two input control parameters; they are the deviation of the rotor speed between the main motor and the

subordinate motor, and the deviation of the average dc line current of the power converter between the main motor and the subordinate motor. The output control parameter is the increment of the duty ratio of the PWM signal of the subordinate motor at the high rotor speed range, and the output control parameter is the increment of the phase current chopping limitation of the subordinate motor at the low rotor speed range. The fuzzy logic algorithm for the closed-loop rotor speed control of the main motor could be expressed as follows: if then

˜=E ˜i E ˜ ˜ U = Uij

and

i = 1, 2, . . . , m,

˜ = EC ˜ j EC j = 1, 2, . . . , n (24)

˜ is the fuzzy set of the deviation of the rotor speed of where E ˜ is the fuzzy set of the variation from the the main motor, EC ˜ is the deviation of the rotor speed of the main motor, and U fuzzy set of the increment of the duty ratio of the PWM signal of the main motor or the fuzzy set of the increment of the phase current chopping limitation of the main motor. The fuzzy logic algorithm for the balanced distribution of loads control between the main motor and the subordinate motor could be expressed as follows: if then

˜1i ˜1 = E E ˜ ˜ U2 = U2ij

and

i = 1, 2, . . . , m,

˜2 = E ˜2j E j = 1, 2, . . . , n (25)

426


˜1 is the fuzzy set of the deviation of the rotor speed where E ˜2 is the between the main motor and the subordinate motor, E fuzzy set of the deviation of the average dc line current of the power converter between the main motor and the subordinate ˜2 is the fuzzy set of the increment of the duty ratio motor; and U of the PWM signal of the subordinate motor or the fuzzy set of the increment of the phase current chopping limitation of the subordinate motor. The output power of the switched reluctance generator system is as follows: P2 = U2 · I2

(26)

where U2 is the dc line voltage of the power converter and I2 is the average dc line current of the power converter. The average dc line current of the power converter could be used as a feedback signal of the actual output power of the system. The turn-OFF angle of the main switches was fixed at the optimized value. The comparison between the desired output power and the actual output power is made. The closed-loop output power control of the switched reluctance wind power generator system can be implemented by regulating the turnON angle of the main switches with the aid of a fuzzy logic algorithm. There are two input control parameters in the fuzzy logic algorithm, such as the deviation of the average dc line current and the variation of the deviation of the average dc line current. The deviation of the average dc line current at the time moment of ti time is as follows: ei = Iavg − Iavi

(27)

where Iavg is the desired average dc line current, Iavi is the actual average dc line current at the moment of ti . The variation from the deviation of the average dc line current at the moment of ti time is as follows: e˙ i = ei − e(i−1)

(28)

where e(i−1) is the deviation of the average dc line current at ti −1 . The output control parameter in the fuzzy logic algorithm is the increment of the turn-ON angle of the main switches, ∆θ1i , and θ1i = θ1(i−1) + ∆θ1i

(29)

where θ1i is the turn-ON angle of the main switches at the moment of ti , and θ1(i−1) is the turn-ON angle of the main switches at the moment of ti −1 . The fuzzy logic algorithm for the closed-loop output power control of the switched reluctance wind power generator system can be expressed as follows: ˜3 = E ˜3i ˜ = ED ˜ j if E and ED then V˜ = V˜ij i = 1, 2, . . . , m,

j = 1, 2 , . . . , n (30)

˜3 is the fuzzy set of the deviation of the average dc line where E ˜ is the fuzzy set of the variation of the deviation current, ED of the average dc line current, and V˜ is the fuzzy set of the increment of the turn-ON angle of the main switches.

Fig. 4.

Motor. (a) Rotor. (b) Stator.

Fig. 5.

Two motors on the chassis of the locomotive.

III. ELEMENTS OF SYSTEM The three-phase 6/4 structure SRM drive was developed for the adhesion weight of 5 ton of electric locomotive in coal mines, which is drawn by the parallel drive system of the dual 7.5-kW SRMs. The rotor and the stator of the motor are shown in Fig. 4(a) and (b), respectively. The two motors are applied to draw the front wheel and the rear wheel of the locomotive by the two gear boxes, respectively, which are installed on the chassis of the locomotive, as shown in Fig. 5. The motors have the rated output 7.5 kW at the rated speed of 1110 r/min, and the adjustable rotor speed ranges between 200 and 2220 r/min. The rotor position detectors installed on the no shaft extension of the motors, respectively, consists of three photoelectric transducers and a slotted disk. The three photoelectric transducers SP , SQ , and SR , are fixed to the end shield of the SRM. The corresponding slotted disk coaxial with the rotor has four teeth with 50◦ width, four slots with 40◦ width structure, and the three photoelectric transducers, SP , SQ , and SR , are to be installed with a 30◦ interval successively. The schematic diagram of the rotor position detector is shown in Fig. 6. The two three-phase asymmetric bridge power converters in parallel were used in the drive system. The main circuit is shown in Fig. 7. Four VDMOSFETs are adopted in parallel as one main switch unit, two fast recovery diodes (FRDs) are adopted in parallel as one flywheel diode unit, which are shown in Fig. 8, while the VDMOSFETs would share well both static and dynamic states with no snubber. The Intel 8XC196KC single chip microprocessor is adopted as the controller. While the rotor of the motor is rotated, the three photoelectric transducers could provide the square-wave signals


427

TABLE I DISTRIBUTION OF THE BASIC TRIGGERING SIGNALS OF THE MAIN SWITCHES

Fig. 6.

Schematic diagram of the rotor position detector.

Fig. 7.

Main circuit of power converter.

Fig. 8. FRDs.

Parallel circuits of power switches. (a) Four VDMOSFETs. (b) Two

P, Q, and R, with 30◦ intervals, which represent the information of the rotor position. P, Q, and R signals could be used as the basic triggering signals of the main switches of A, B, and C phases, respectively. By regulating the rotor position detector, the turn-ON angle of the main switches in the power converter is fixed at −5.0◦ (θ = 0◦ is defined as the rotor position while the axis the rotor slot is aligned with that of the stator pole of the conducted phase), while the motor is operated at quadrant I. The distribution of the basic triggering signals of the main switches at four quadrants is shown in Table I. The SRM drive system could be operated conveniently at four quadrants with traction

Fig. 9. Flameproof enclosure control box installed with the power converter and the controller.

at quadrant I and quadrant III symmetrically, with regenerative braking at quadrant II and quadrant IV symmetrically, based on Table I. The power converters and the controller are integrated in the flameproof enclosure control box fixed in the driver’s cab. Fig. 9 shows the photograph of the flameproof enclosure control box with the power converters and the controller. There is a control stick in the top of the flameproof enclosure control box. The decision form of the fuzzy logic algorithm I is for the closed-loop rotor speed control of the main motor, the decision form II is for the balanced distribution of loads control between the main motor and the subordinate motor, which could be attained by scattering the continuous input control parameters and continuing the discrete output control parameter. The two decision forms of the fuzzy logic algorithm are stored in the programmed storage cell of the controller. While the practical rotor speed of the main motor could be measured, the closedloop rotor speed control of the main motor could be implemented by the decision form I. The rotor speed of the main motor could be adjusted by regulating the duty ratio of the PWM signal or the phase current chopping limitation of the main motor, so that the deviation of the rotor speed of the main motor could be reduced. While the deviation of rotor speeds between the main motor and the subordinate motor is presented, and the deviation of the average dc line current of the power converter

428


Fig. 10. Developed switched reluctance variable-speed wind power generator system prototype.

Fig. 12. Cross section of the three-phase 12/8 structure switched reluctance generator.

Fig. 11.

Block diagram of the switched reluctance generator system.

between the main motor and the subordinate motor could be measured, the balanced distribution of loads control between the main motor and the subordinate motor could be implemented by the decision form II. The rotor speed and the output torque of the subordinate motor could be adjusted by regulating the duty ratio of the PWM signal or the phase current chopping limitation of the subordinate motor, so that the deviation of the rotor speed between the main motor and the subordinate motor could be reduced and the loads could be tended to the balanced distribution between the main motor and the subordinate motor. The other three-phase switched reluctance machine system was developed for the variable-speed wind power generator system, which consists of a three-phase 12/8 structure switched reluctance generator, a rotor position detector, a power converter, and a controller. The photograph of the prototype is shown in Fig. 10. The control equipment box includes the power converter and the digital controller. The block diagram of the system is shown in Fig. 11. The cross section of the switched reluctance generator is shown in Fig. 12. It has 12-tooth poles in the stator and 8-tooth poles in the rotor. There is a centralized coil wound on each stator tooth, and there are four coils in each phase, so that the A phase winding could be made up of the coils “1,” “4,” “7,” and “10,” the B phase winding could be made up of the coils “2,” “5,” “8,” and “11,” and the C phase winding could be made up of the coils “3,” “6,” “9,” and “12.” By taking A phase winding as an example, the four coils—“1,” “4,” “7,” and “10,” could be connected in a series to form the winding of the phase A, which is shown in Fig. 13. The four coils in

Fig. 13.

Patterns of the structure of one phase winding.

Fig. 14.

Rotor position detector.

phases B and C could also be connected in a series. There are no brushes, no magnets, and no windings on the rotor. The rotor position detector is installed at the point where there is no shaft extension of the generator, which is shown in Fig. 14. It is made up of three photoelectric transducers and a slotted disk. There are eight teeth with 22.5◦ widths per tooth and eight slots with


Fig. 15.

Fig. 16.

Control board.

Fig. 17.

Mechanical properties of one motor drive system.

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Power converter.

22.5◦ widths per slot on the slotted disk, which is fixed on the same shaft of the rotor. The three photoelectric transducers, SP , SQ , and SR , are fixed on the end shield of the generator in a 60◦ interval. When the rotor of the generator rotates, the three photoelectric transducers produce square wave signals, which represent the rotor position information. It can be used as a rotor position feedback for the excitation controller that is used to turn the main switches of the power converter on and off. The three-phase asymmetric bridge power converter shown in Fig. 11 is used in the system. When two main switches for one phase are turned on, the generator is excited. When the two main switches are turned off, and the two flywheel diodes for one phase are in conducting stage, the electrical energy is supplied by the generator through the flywheel diodes. In the case of the initial excitation, K2 is turned off and K1 is turned on, and the generator is excited by the storage battery. In the case of the operational excitation, K2 is turned on and K1 is turned off, so that the generator is excited by the electrolytic capacitor C2 . RL is the load. The photograph of the power converter is shown in Fig. 15. The MOSFETs were chosen as main power switches of the exciting power converter. The starting excitation control, the excitation commutating control, the constant-power output control, the overspeed protection, the overvoltage protection, the overcurrent protection, the undervoltage protection, and also the displaying of some information are all implemented in the controller, which are based on the digital hardware and software. The decision form of the fuzzy logic algorithm for the closedloop output power control can be obtained, which is then stored in the program memory of the controller. If the actual average dc line current is measured, the actual output power can be adjusted by controlling the turn-ON angle of the main switches based on the decision form, so that the deviation between the desired output power and the actual output power can be reduced. The photograph of the control board is shown in Fig. 16. IV. TEST RESULTS Experiments have been carried out to obtain the mechanical properties of the developed switched reluctance single motor

drive system prototype at four quadrants with the different duty ratio of the PWM signal, D, and rotor speed curves of the two motors, which are shown in Figs. 17 and 18. Fig. 18(a) represents the starting course from 0 to 1110 r/min given rotor speed with 2 × 64.6 N·m and Fig. 18(b) represents the braking course from 800 to 0 r/min. The tested phase current waveforms of the two motors are shown in Fig. 19, while the two motors are from traction state with 938 r/min and 2 × 64.6 N·m to braking state. The synchronization of the two motors in the dynamic rotor speed and in the state conversion is achieved. Table II gives the experimental results of the steady rotor speed and the output torque, where nm is the practical rotor speed of the main motor, ns is the practical rotor speed of the subordinate motor, T2m is the output torque of the main motor, T2s is the output torque of the subordinate motor, en is the relative deviation of the rotor speed of the subordinate motor, eT is the relative deviation of

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Fig. 19. Tested phase current waveforms. Abscissa: 10.0 ms/division, ordinate: 190.0 A/division. TABLE II TESTS RESULTS OF THE STEADY ROTOR SPEED AND THE OUTPUT TORQUE

Fig. 18. Tested rotor speed curves. (a) Starting course. (b) Braking course. Abscissa: 500.0 ms/division, ordinate: 505 r/min/division.

the output torque of the subordinate motor, and ns − nm en = × 100% nm eT =

T2s − T2m × 100%. T2m

(31) Fig. 20.

Developed electric locomotive.

(32)

The tested maximum difference in the output torque of the two motors at the same given rotor speeds is within 10.00%, and the tested maximum difference in the practical rotor speed of the two motors is within 5.00%. The proposed electric locomotive in coal mines drawn by the switched reluctance dual motors parallel drive system is fully tested. The tractive force of the electric locomotive at the scale of hour is 7.1 kN, and the tractive force at the scale of long time is 5.0 kN. The velocity of the electric locomotive at the scale of hour is 7.0 km/h, and the maximum velocity of the locomotive is 10.0 km/h. The

maximum braking distance is 14.0 m. The developed electric locomotive is shown in Fig. 20. The power supply source is a group of storage batteries installed in the power sources box carried on the electric locomotive. The rated supplied voltage is 88 V dc, and the rated capacity is 330 Ah. The dc output voltage of the developed switched reluctance variable-speed wind power generator system prototype is 24 V. The rated output power is 500 W at 405–1200 r/min. The turnOFF angle of the main switches of the power converter is fixed at 34◦ (θ = 0◦ is the rotor position where the axis of the rotor


431

TABLE III TEST RESULTS OF THE PROTOTYPE

the larger the copper loss of the generator and the switch loss of the power converter, and the lower the system efficiency. V. CONCLUSION

Fig. 21. Measured phase current waveforms. (a) Abscissa: 5.0 ms/division, ordinate: 70.0 A/division. (b) Abscissa: 10.0 ms/division, ordinate: 70.0 A/division.

slot is aligned with that of the stator pole of the conducted phase). The initial power supply is the storage battery with a nominal dc voltage of 24 V. The closed-loop output power control is implemented by regulating the turn-ON angle of the main switches with the fuzzy logic algorithm at a desired power value of 500 W. The measured phase current waveforms are shown in Fig. 21: (a) the rotor speed is 405 r/min and the output power is 507 W and (b) the rotor speed is 580 r/min and the output power is 510 W. Test results for the output power, the average dc line current, the phase current peak value, and the system efficiency at a given rotor speed are shown in Table III. It is shown that the error of the closed-loop output power control is within 2.2% while the rotor speed range is close to the ratio of 1:3 with the low rotor speed of 405 r/min. The system efficiency is low, especially within the low rotor speed range, as the voltage of the system is low and the current is high, so that the copper loss of the generator and the switch loss of the power converter are high. At a constant-output-power operation, the lower the rotor speed, the higher the phase current peak value,

The average dc line current of the power converter can be utilized as a feedback signal for the actual output torque of a SRM drive or a feedback signal for the actual output power of a switched reluctance generator system. The switched reluctance dual motors parallel drive system is very reliable. While one of the dual SRMs has broken down, the other SRM could be operated at the reduced loads. The switched reluctance dual motors parallel drive system implemented by the fixed-angle PWM control strategy at high rotor speed range and the phase current chopping control strategy at the low rotor speed range with fuzzy logic algorithm contribute to synchronize the rotor speed and balance distribution of loads. The test results of the 5-ton electric locomotive in coal mines, drawn by the developed three-phase 6/4 structure switched reluctance dual motors parallel drive system, show that the two motors in the dynamic rotor speed and in the state conversion are synchronized. The maximum difference in the output torque of the two motors at the same given rotor speeds is within 10.00%, and the maximum difference in the practical rotor speed of the two motors is within 5.00%. The reliability of the electric locomotive in a coal mine could be enhanced. The regenerative braking operation of the electric locomotive could be implemented easily so that electric energy could be saved. All this contributes to reduce the utilization cost of the electric locomotive per ton kilometer. The closed-loop output power control realized by regulating the turn-ON angle of the main switches with the aid of the fuzzy algorithm and the fixing of the turn-OFF angle at the optimized value, contributes to the implementation of a high-efficiency wind power controller for a switched reluctance wind power generator. Increasing the voltage of the system leads to improvement of system efficiency. The switched reluctance generator has very good prospects for implementation in small wind power generator systems that are driven directly by the wind turbine without a gear box. This is due to the advantages of firm structure and the ability for fault-tolerant control. The sufficiency of low starting wind velocity leads to reduction in the costs of the electricity that is produced by the wind power generators. A 500-W three-phase 12/8 structure switched reluctance variable-speed wind power generator system prototype has been built. Optimization of the structure and the control parameters, improvement of the system efficiency and the transformed ratio of wind energy/electrical energy, and implementation of the

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Hao Chen (SM’08) received the B.S. and Ph.D. degrees from the Department of Automatic Control, Nanjing University of Aeronautics and Astronautics, Nanjing, China, in 1991 and 1996, respectively. In 1998, he became an Associate Professor in the School of Information and Electrical Engineering, China University of Mining and Technology, Xuzhou, China, where he has been a Professor since 2001. From 2002 to 2003, he was a Visiting Professor at Kyungsung University, Busan, Korea. Since 2008, he has also been an Adjunct Professor at the University of Western Australia, Perth, Australia. He is the author of one book, and has also authored or coauthored more than 150 papers. His current research interests include motor control, electric vehicles, electric traction, servo drives, and wind power generator control. Dr. Chen won the Prize of Science and Technology of Chinese Youth in 2004 and the Prize of the Fok Ying Tong Education Foundation for Youth Teachers.

Jason J. Gu (SM’06) received the Bachelor’s degree in electrical engineering and information science from the University of Science and Technology of China, Hefei, China, in 1992, the Master’s degree in biomedical engineering from Shanghai Jiaotong University, Shanghai, China, in 1995, and the Ph.D. degree from the University of Alberta, Edmonton, AB, Canada, in 2001. He is currently an Associate Professor of electrical and computer engineering at Dalhousie University, Halifax, NS, Canada. He is also a Cross-Appointed Professor in the School of Biomedical Engineering and a member of the Faculty of Computer Science for his multidisciplinary research work. His current research interests include robotics and teleoperation, biomedical engineering, rehabilitation engineering, neural networks, and control. Dr. Gu was a recipient of the Best Paper Award at the International Conference on Computer Science and Engineering (ICCSE) 2003. He was also awarded the Faculty of Engineering Teaching Award in 2003, the Outstanding IEEE Student Branch Councilor Award in 2004, Discovery Award of the Province of Nova Scotia in Canada in 2005, and the Faculty of Engineering Research Award in 2006. He is a member of the American Society of Engineering Education and a Senior Member of the Institution of Electrical Engineers (IEE), U.K.