INTERNATIONAL TRANSACTIONS ON ELECTRICAL ENERGY SYSTEMS Int. Trans. Electr. Energ. Syst. 2015; 25:1083–1099 Published online 19 February 2014 in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/etep.1893
Application and simulation of dual-mechanical-port machine in hybrid electric vehicles Mohammad Ghanaatian*,† and Ahmad Radan Power Electronics LAB, Faculty of Electrical and Computer Engineering, K.N. Toosi University of Technology, Seyed Khandan Bridge, 1431714191 Tehran, Iran
SUMMARY There are growing interests in electric and hybrid electric vehicles (HEVs) because of environmental concerns. Recent efforts are directed toward developing an improved propulsion system for electric and HEVs applications. In a conventional series–parallel HEV, a planetary gear is used to integrate the power of internal combustion engine and two electric machines into the drive train so that the engine can always operate with the highest efficiency while the vehicle runs at any desired speed and torque. However, two electric machines and associated power inverters along with a planetary gear make the HEV drive train much more complicated and bulky in size. Dual-mechanical-port electrical machine (DMPM) is a new breed of energy conversion device with more compact and integrated structure that can potentially realize an efficient electrical variable transmission for HEV applications. This machine can replace the planetary gear and two electric machines of conventional structure in order to make their structures much simpler. Applying a proper power management and control strategy to have a good driving performance for a series–parallel HEV based on DMPM are the main contributions of this paper. Because Toyota Prius II (Toyota Motor Sales, U.S.A., Inc., Torrance, CA, USA) is a well-known series–parallel HEV, the parameters of this vehicle are chosen as a practical example in simulation results. Copyright © 2014 John Wiley & Sons, Ltd. key words:
dual mechanical ports; speed; torque; control; power management
1. INTRODUCTION Concerns over fluctuating gas prices and global climate change have made a lot of interest toward new automotive technology. Hybrid electric vehicles (HEVs) are proposed to replace the conventional vehicles, because of their advantages of zero pollutant emissions, high-efficiency, and multi-energy sources. In order to optimize the configuration and the functionality of HEVs, much effort has been done. In HEVs, the internal combustion engine (ICE) is required to operate within a very narrow region for the highest fuel efficiency regardless of the vehicle speed. Under such a constraint, a continuous variable transmission (CVT) is needed in HEV applications. Two types of CVT have been developed; the first one is a mechanical version of CVT and called the planetary gear set [1]. It is a mechanical device that has some drawbacks such as decreasing vehicle efficiency and also increasing the car’s overall cost. The second type of CVT is the so-called electrical variable transmission (EVT) [2,1]. Recently, dual-mechanical-port electrical machine (DMPM), as a new generation of electrical machines, has been demonstrated to be a very promising candidate for EVTs [3,4] to apply in series–parallel HEVs. When the DMP machine is used to drive a HEV, it replaces the two electric machines and the planetary gear set in a conventional HEV. In this paper, a new control strategy providing an optimal function for series–parallel HEV based on DMPM is introduced in detail. The purpose of this paper is to evaluate the performance of the series–
*Correspondence to: Mohammad Ghanaatian, Power Electronics LAB, Faculty of Electrical and Computer Engineering, K.N. Toosi University of Technology, Seyed Khandan Bridge,1431714191 Tehran, Iran. † E-mail:
[email protected] Copyright © 2014 John Wiley & Sons, Ltd.
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parallel HEV based on DMPM under a proper power management and control strategy so that for a given driver demand and vehicle operation conditions, the vehicle has the desired economical functionality. The remaining parts of the paper are organized as follows: In Section 2, principle concepts of DMP machine are discussed. An overview of the conventional HEV and novel structure of HEV based on DMPM are presented in Section 3. Different components of the vehicle are modeled in Section 4, along with a full description on the applied power management and control strategy. A series–parallel HEV based on DMPM is simulated in Section 5, and the results are given. Finally, conclusion is presented in Section 6.
2. PRINCIPLE CONCEPTS OF DMPM DMPM is a new generation of electrical machine consisting of a stator and two rotors. The inner rotor is fed with a three-phase winding through slip rings. The stator is also fed with a three-phase winding. Permanent magnets are mounted on the outer rotor. It is more similar to the structure of a double fed induction generator (DFIG) with an extra outer rotor, making it more flexible and controllable [5]. This machine has two electrical ports on the stator and inner rotor and two mechanical ports on both rotor axes. In fact it is a compact machine playing the role of two machines: an inner machine consisting of the inner and outer rotors and an outer machine consisting of the outer rotor and stator. These two machines can function as either motor or generator. Depending on motor or generator functions, different modes of operation are possible for DMPM. Figure 1 shows the different parts of a DMPM.
3. HYBRID ELECTRIC VEHICLE CONFIGURATION The most successful hybrid configuration currently utilized by various vehicle manufacturers consists of a diesel or gasoline engine, coupled with a motor and a generator linked to a battery pack. An HEV adds an electric power path to the conventional power train. Some noticeable advantages of HEVs upon conventional vehicles are as follows: • Compared with ICEs, electric machines provide torque more quickly, especially at low speed. • With the electric drive assistance, the engine can be controlled to operate in an optimal region regardless of the road load. • While the vehicle is decelerating, the electric machine can capture major parts of the vehicle’s kinetic energy and recharge the battery. With regard to different structures, HEVs are classified into three groups, namely, series hybrid, parallel hybrid, and series–parallel hybrid. Despite having more complex structure, series–parallel HEVs combine the advantages of both series and parallel hybrids. The structure and characteristics of series hybrid and parallel hybrid types are well described in [6–10]. Because this work mainly focuses on the series–parallel type of HEVs, there is a brief explanation on this type in the following section. 3.1. Series–parallel hybrid This type of HEVs combines the parallel and series configuration features by the use of a planetary gear set. In the series–parallel configurations, the vehicle can operate as a series hybrid, a parallel
Figure 1. Different parts of a dual-mechanical-port electrical machine. Copyright © 2014 John Wiley & Sons, Ltd.
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hybrid, or a combination of both. With a proper control strategy, it can be designed to take the advantages of both parallel and series types and avoid their drawbacks. Because there are more energy flow paths and operating modes compared with other configurations, the power management and the control strategy become more complicated. Toyota Prius is the most well-known series–parallel HEV [6,7,9,10]. A planetary gear is composed of three parts: sun gear, carrier gear, and ring gear. The mechanical connections between the engine and the electric machines are usually accomplished by planetary gear. In Toyota Prius’ configuration, the sun gear is connected to the engine, the ring gear is connected to the motor, and the carrier gear is connected to the generator. Design of the planetary gear decouples the engine speed from the vehicle speed and allows the engine to operate near its optimal condition most of the time. Figure 2 shows a planetary gear set [7,9,10,2,1]. 3.2. HEV based on DMPM Two electric machines and a planetary gear box make the series–parallel HEV drive train much more complicated and bulky in size. A DMP machine replaces the planetary gear box and the two electric machines in the conventional series–parallel HEV and makes their structures simpler. In this structure, the mechanical loss of planetary gear is also omitted. Figure 3 shows the applied strategy in HEVs based on DMP machine. As it is shown, both the stator and inner rotor windings are energized by connecting the windings to a common direct current (DC) bus through two DC/alternating current inverters. The mechanical shaft of the inner rotor is coupled to the ICE, and the mechanical shaft of the outer rotor is coupled to the differential trans-axis. Because the ICE speed is decoupled from the vehicle speed in this structure, with a proper power management and control strategy, the ICE can be applied at its maximum efficiency during all driving conditions.
Figure 2. Planetary gear set.
Figure 3. Hybrid electric vehicle based on dual mechanical port. Copyright © 2014 John Wiley & Sons, Ltd.
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4. VEHICLE COMPONENTS MODELING In this section, the different parts of a series–parallel HEV based on DMPM and the way they are modeled in the simulation are well discussed. 4.1. DMPM dynamic model Dynamic equations of a DMP machine can be given in the outer rotor reference frame with the d-axis in the direction of outer rotor magnet poles and the q-axis 90 electrical degree leads relative to the d-axis as follows [5,3,4,11–13]. dλqs þ ωλds dt dλds V ds ¼ ids r s þ ωλqs dt dλqr þ ðω ωr Þλdr V qr ¼ iqr r r þ dt dλdr ðω ωr Þλqr V dr ¼ idr r r þ dt λqs ¼ Ls iqs þ Lm iqr V qs ¼ iqs r s þ
(1) (2) (3) (4) (5)
λds ¼ λm1 þ Ls ids þ Lm idr
(6)
λqr ¼ Lr iqr þ Lm iqs
(7)
λdr ¼ λm2 þ Lr idr þ Lm ids rffiffiffi 3 3 3 iqs λm1 þ iqr λm2 þ Lsd Lsq ids iqs þ 7 6 2 2 7 T out ¼ p6 4 3 5 3 Lrd Lrq idr iqr þ Lmd Lmq ids iqr þ iqs idr 2 2 "rffiffiffi # 3 3 3 3 λm2 iqr þ Lmd ids iqr Lmq iqs idr Lrq Lrd idr iqr T in ¼ p 2 2 2 2
(8)
2
(9)
(10)
Equations (1)–(4) are the voltage equations for the stator and inner rotor windings. rs and rr are the stator and inner rotor winding resistance respectively. Equations (5)–(8) are the flux linkage equations for the stator and rotor windings. Ls and Lr are the self-inductance of the stator and rotor windings respectively. Lm is the mutual inductance between the inner rotor winding and the stator winding. λm1 and λm2 are the flux linkages produced by the PM-rotor in the outer and inner machines respectively. p is the number of pole pairs. Tout and Tin are the outer rotor torque and the inner rotor torque respectively. According to the aforementioned equations, inner and outer machines are not independent and have interaction with each other. In order to analyze the DMPM dynamics, a DMPM with the following characteristics is simulated without any closed-loop controller. This machine has two pole pairs (Table I). In this test, three-phase voltages are injected to the stator and inner rotor windings as the inputs of the system. Inner rotor speed and outer rotor speed are measured as the outputs of the system. Because the outer rotor is a permanent magnet (PM), it cannot be started, similar to a permanent-magnet synchronous motor (PMSM), so a V/f control is applied to start the machine. When exciting the stator winding with a frequency increase in a ramp shape, the outer rotor accelerates same as a PMSM machine. Rotating PMs on outer rotor provides rotating flux for inner rotor. In case its winding is opened, no rotating torque will impose on the inner rotor; when it is shorted, it acts as an induction motor, and when inner rotor winding is excited with a certain frequency, its mechanical angular velocity is determined in the same way as in a DFIG. Variations of the stator and inner rotor voltages are shown in Figure 4. While the outer rotor speed and the inner rotor speed are up to 60 and 40 rad/second respectively, the frequency and amplitude of input voltage are kept unchanged. This happens at t = 40 seconds. Moreover, a Copyright © 2014 John Wiley & Sons, Ltd.
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Table I. Parameters of dual mechanical port [12,13]. Parameter
Unit
λm1 λm2 R Ld/Lq Ldm/Lqm J
Wb Wb Ω mH mH kg/m2
Inner rotor 0.15 – 0.2 3/4.5 – 0.16
Inner rotor and stator interaction
Stator
Outer rotor
– – – – 0.5/1.5 –
– – 0.35 9/15 – –
– 0.2 – – – 0.1
Figure 4. (a) Inner rotor voltage frequency (rad/second), (b) inner rotor voltage, (c) stator voltage frequency (rad/second), and (d) stator voltage.
torque of 100 N.m is loaded to both the outer and inner rotor shafts at t = 44 and t = 68 seconds respectively. As the measurement shows (Figure 5), the electrical speed of the outer rotor is the synchronous speed determined by the stator voltage frequency and two pole pairs (p = 2). In other words, the stator and the outer rotor can be considered as a PMSM and have the same functionality. As stated previously, the structure of a DMPM is more similar to the structure of a DFIG with an extra outer rotor, so the electrical angular velocity of the inner rotor is equal to the difference between the stator and inner rotor voltage angular velocity. The measurements in Figure 5 confirm this expectation. In such conditions, inner rotor field, outer rotor field, and stator field all rotate with the same angular velocity determined by the electrical angular velocity of the outer rotor. Moreover, the electromagnetic torque produced in each rotor during the time is shown in Figure 6. In the next step, DMPM is simulated in a closed-loop test and with a proportional integrator (PI) controller. The control algorithm is shown in Figure 7. In this test, speed references and mechanical load torques of both rotors are the inputs of the system. In this control strategy, in order to have the maximum torque-to-current ratio and minimum losses, ids and idr are considered equal to zero, so Equations (9) and (10) are simplified as follows: "rffiffiffi # 3 λm2 iqr (11) T in ¼ p 2
T out
Copyright © 2014 John Wiley & Sons, Ltd.
"rffiffiffi # 3 ¼p iqs λm1 þ iqr λm2 2
(12)
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Figure 5. Outer rotor and inner rotor speed.
Figure 6. Outer rotor and inner rotor torque.
In Equation (11), as the PM flux is supposed unchanged in the outer air gap, λm2 is constant. As a result, Tin depends on iqr, and there is a linear relation between them. So, the value of iqr is determined by Tin, which is equal to the inner rotor load torque. On the other hand, because the values of λm1 and λm2 are constant because of the unchanged PM flux in the air gaps and iqr is determined according to the value of Tin, the value of Tout is only dependent on iqs in Equation (12). Mechanical dynamic equations of the machine are as follows: dωout þ Bωout (13) dt dωin þ Bωin T in T loadinner ¼ J in (14) dt In these equations, J, B, and ω are the moment of inertia, friction coefficient, and mechanical speed of the rotor respectively. As Tload, J, and B are constant for both rotors, Tout and Tin are proportional to ωout and ωin respectively. As a result, ωout and ωin are proportional to iqs and iqr respectively. So, applying a PI controller in this control strategy is reasonable. Figure 8 shows variations of the inputs. T out T loadouter ¼ J out
Copyright © 2014 John Wiley & Sons, Ltd.
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Figure 7. Control diagram.
Figure 8. System inputs.
Inner rotor speed, outer rotor speed, inner rotor current, and stator current are considered as the output variables of the system. As the simulation results show, speed of both rotors track their reference value (Figure 9). According to Figure 10, stator current frequency is equal to the outer rotor electrical speed. Inner rotor current frequency is also equal to the difference between the outer rotor electrical speed and the inner rotor electrical speed. It can also be seen that changes in speed and torque of each rotor affects speed and torque of the other rotor. This result shows that the outer and inner machines are not independent and have interaction with each other.
4.2. ICE model In the ICE block diagram, according to the ICE speed feedback, the maximum available torque via the ICE is determined. The throttle command, which is a number between (0,1), is multiplied with the maximum torque, and the result shows the fraction of the maximum torque must be produced via the ICE. Figure 11 is an ICE block diagram. Copyright © 2014 John Wiley & Sons, Ltd.
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Figure 9. Inner rotor and outer rotor speed.
Figure 10. Stator and inner rotor current.
4.3. Battery model The battery electrical model is an internal resistance and a dependent voltage source. The voltage source is dependent on the integral of the battery current. This model is explained in [14,15]. The battery model is shown in Figure 12. In Figure 12, the internal voltage is independent of the battery current. On the other hand, the external voltage depends on the battery current and shows more fluctuations than the internal voltage. Figure 13 shows the battery internal voltage versus the battery state of charge (SOC). As it is shown, the battery internal voltage is relatively constant while the SOC is between (0.4,0.8), and it changes suddenly out of this interval. So, having a good battery operation in the DC link, the battery SOC must be kept between (0.4,0.8). The DC link is composed of a battery and a DC/DC chopper. The battery nominal voltage is 200 V. In order to control the motor in high speed, the DC/DC chopper increases the battery voltage from 200 to 800 V. 4.4. Power management unit The applied power management and control strategy aim to satisfy a number of goals for HEVs such as maximum fuel economy, minimum emissions, minimum system cost, and a good driving Copyright © 2014 John Wiley & Sons, Ltd.
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Figure 11. Internal combustion engine block diagram.
Figure 12. Battery model [15].
Figure 13. Typical charge characteristics [17].
performance. In this paper, the vehicle operation is divided into five modes, which are starting, acceleration, regenerative braking, battery charging, and normal. These modes are based on vehicle speed, requested power, battery SOC, and accelerator command, which are described as follows: • Starting mode: in this mode of operation, motor speed is low, and the ICE would not have a good efficiency if applied. So, it becomes off, and the vehicle is energized just from the battery. This mode of operation is also named as pure electric mode. • Acceleration mode: in this mode of operation, the requested power is as high that both the battery and the ICE are used to propel the vehicle. • Normal mode: in this mode of operation, the ICE speed is increased enough that it is working in its optimal region and providing the requested power by itself. Copyright © 2014 John Wiley & Sons, Ltd.
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• Regenerative braking mode: in this mode of operation, the vehicle kinetic energy is converted into electricity and charges the battery. As a result, the vehicle speed is decreased. • Battery charging mode: in this mode of operation, the battery needs to be charged because its SOC is decreased to its marginal level. So, the ICE has to charge the battery in addition to propelling the vehicle. In case the ICE needs to deliver different power demands, there is an optimal operating point corresponding to each power. These points constitute an optimal operating line. Figure 14 shows a typical optimal operating line of an ICE [6]. The required torque is commanded by the driver. If the torque is positive, it is requested with the accelerator command, and if negative, it is requested with the brake command. Accelerator command and brake command are supposed to be a number between (0,1) and (1,0) respectively. These commands are multiplied by the maximum available torque of DMP machine at the machine speed, which is determined according to the torque versus speed characteristics of the machine. The result is the requested torque. This value of torque must be transmitted to the wheels through the outer rotor. The requested power could also be determined by multiplying the requested torque and the outer rotor angular speed. 4.5. DMPM modeling and power flow path Outer rotor torque is composed of two components. One is supplied from the stator (outer machine), and the other is supplied from the inner rotor (inner machine). Equations (15) and (16) show these two components respectively: "rffiffiffi # 3 3 3 3 λm1 iqs þ Lmd iqs idr Lmq ids iqr Lsq Lsd ids iqs (15) T stator ¼ p 2 2 2 2 "rffiffiffi # 3 3 3 3 λm2 iqr þ Lmd ids iqr Lmq iqs idr Lrq Lrd idr iqr T in ¼ p 2 2 2 2
(16)
Furthermore, the output power is also supplied from two sources: the battery and the ICE. A part of the ICE power is directly transferred to the outer rotor from the inner air gap (Pdirect), and the remaining power is going to the battery path (Pindirect). In other words, a part of the requested power is supplied from the ICE (inner rotor) through the inner air gap. The remaining of the requested power is supplied from the battery (stator) through the outer air gap. These power components are shown in the following equations [11]:
Figure 14. Typical optimal operating line [6]. Copyright © 2014 John Wiley & Sons, Ltd.
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T outerrotor ¼ T ICE þ T stator
(17)
Pouterrotor ¼ PICE þ Pstator
(18)
Pdirect ¼ T ICE ðωouterrotor Þ
(19)
Pindirect ¼ T ICE ðωinnerrotor ωouterrotor Þ
(20)
Pstator ¼ ðT outerrotor T ICE Þωouterrotor
(21)
If the battery voltage and the battery current are multiplied, the power extracted from the battery is obtained. So, the remaining of the requested power must be supplied from the ICE. According to the ICE power, the optimum ICE torque and speed are estimated, on the basis of its optimum operating line characteristics. In the next step, it is tried to make the ICE work on its optimum operating line. As it is mentioned before, the ICE axis is connected to the inner rotor. Therefore, the inner rotor reference torque is the optimum ICE torque but in the opposite direction. In fact, the inner rotor causes a reaction torque for the ICE. Because in the applied strategy, the optimum speed is considered as a reference speed for the ICE, in such conditions, the ICE has to produce the optimum torque (inner rotor torque) in order to rotate with its reference speed (optimum speed). So, the ICE is set on its optimum operating line. Figure 15 shows the ICE and inner rotor connection. The remaining of the requested torque and power must be supplied from the stator. Depending on the positive or negative values of these parameters, the outer motor of the DMPM will have to operate in a motor mode or in a generator mode respectively. 4.6. Control unit The reference values that are estimated in the power management unit are the ICE speed, the inner rotor torque, and the stator torque. The values of these parameters are the reference values for the control unit. In the control unit, the ICE reference speed is compared with the measured ICE speed as shown in Figure 16. Through a PI controller, the throttle value is determined. As it is shown in Figure 17, the stator and inner rotor torques are compared with their references. The output of the PI controller is the reference value of iq. On the other hand, the measured values of the stator and inner rotor current are transferred to dq reference frame with the d-axis in the direction of the outer rotor magnet poles and the q-axis is 90 electrical degree lead relative to the d-axis. The measured iq values are compared with their references. In this case, the output of the PI controller shows the reference value of vq.
Figure 15. Internal combustion engine (ICE) and inner rotor connection.
Figure 16. Internal combustion engine (ICE) speed control. Copyright © 2014 John Wiley & Sons, Ltd.
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Figure 17. Inner rotor and stator control strategy.
While the outer rotor speed is below the nominal speed (constant torque region), ids is considered to be zero. In such condition, the stator torque depends only on iqs component, and the maximum torque per current amps and the minimum copper loss happened. While the outer rotor is in its nominal speed, the maximum back electro motive force (EMF) is produced in the stator. Because of the limitation of the DC link, speed control of the outer rotor is not possible above the nominal speed. Flux weakening is a strategy applied to control the machine in a higher speed range [16]. So, in the speed above the nominal speed, a negative value of ids is injected to the stator causing the flux weakening. ids must be determined in a way that the condition qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi I sn ≥ i2ds þ i2qs is satisfied where Isn is the nominal current of the stator. The following equation is used in this paper to obtain ids : ids ¼
qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ðaccelerator * I sn Þ2 i2qs
(22)
In order to have a simple and linear control, idr is considered to be zero. As mentioned previously, in braking mode, the ICE turns off. In other words, the ICE torque becomes zero. So, the inner rotor torque must be zero too. In such condition, because of the ICE friction, the ICE speed becomes zero, and all the kinetic energy saved in the ICE shaft is lost. Curve 1 in Figure 18 shows the variation of the ICE speed in this condition (braking is happened at t = 5 seconds). In order to prevent losses and restore the ICE energy in braking mode, a zero reference speed replaced the zero reference torque. So, by the speed control of the inner rotor, the ICE kinetic energy will be restored into the battery. Curve 2 in Figure 18 shows the variation of the ICE speed while the inner rotor is in speed control mode (braking happened at t = 5 seconds).
Figure 18. Internal combustion engine (ICE) speed variation in braking mode. Copyright © 2014 John Wiley & Sons, Ltd.
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5. SIMULATION In this section, a DMP machine is simulated in a series–parallel HEV, and the simulation results are presented. First, the driver requests a value of torque and power through the accelerator command. According to the vehicle speed, the state of the battery charge, the requested torque, and the accelerator
Figure 19. (a) Accelerator command, (b) maximum available torque (N.m), (c) requested torque, and (d) requested power (Kw).
Figure 20. (a) Inner rotor torque (N.m), (b) internal combustion engine speed (rpm), (c) throttle command, and (d) internal combustion engine torque (N.m). Copyright © 2014 John Wiley & Sons, Ltd.
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command, the vehicle operation mode is determined. Consequently, inner rotor torque reference, stator torque reference, and ICE speed reference are estimated in the power management unit. Figure 19a and b indicates the accelerator command and the maximum available torque respectively. As it is shown in Figure 19b, at about t = 5 seconds, the constant torque region is finished, and the machine goes into the field weakening region. Figure 19c and d shows the requested torque and power respectively. The negative value of power shown in Figure 19d shows the regenerative power that is restored into the battery in the braking mode of operation. Figure 20a shows the inner rotor torque. As it is expected, its value is negative. During the time interval [10–12 seconds], the vehicle is in braking mode. In this situation, a zero speed reference is applied to the inner rotor instead of a zero torque reference. In order to have a maximum dynamic response, the maximum negative torque is applied to the inner rotor in this time interval. Figure 20b indicates the ICE speed and its reference. As it is shown, while the ICE is off, its speed is zero. The throttle position command is the result of the ICE speed control through a PI controller. Figure 20c shows the throttle command. While the ICE is off, the throttle command is zero. In some intervals, in order to have the maximum dynamic response, the throttle command is equal to one. Figure 20d
Figure 21. Outer rotor torque (N.m).
Figure 22. Vehicle speed (Km/hour).
Figure 23. (a) Stator current and (b) inner rotor current. Copyright © 2014 John Wiley & Sons, Ltd.
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shows the ICE torque. This torque is in the opposite direction of the inner rotor torque. As the ICE has low efficiency at lower speed, it turns off at start time, and the vehicle is supported only by the battery. Figure 21 shows the outer rotor torque. This torque tracks the requested torque, shown in Figure 19c, properly. Region 1 in Figure 21 is the point in which the ICE starts. Region 2 is the point in which the ICE speed becomes zero in braking. Figure 22 shows the variation of the vehicle speed. As it is indicated in this figure, the higher the requested torque is, the more rapidly the vehicle speed will increase. In the interval [10–12 seconds], the vehicle speed reduces because of braking. Figure 23a and b indicates the variation of the stator and inner rotor currents respectively. Figure 24 shows the battery SOC, the battery current, the battery external voltage, and the battery internal voltage. While the battery is charging, its current is negative and the SOC increases. While
Figure 24. Battery operation characteristics.
Figure 25. Power distribution. Copyright © 2014 John Wiley & Sons, Ltd.
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the battery supplies the load power, the SOC decreases and current is positive. In the cases where the battery is not used, the current is zero and the SOC remains constant. Figure 25 shows the load power distribution between the ICE and the battery. In addition, the outer rotor power satisfies the requested power. As it is shown in Figure 25, a large amount of power is requested in the time interval [7–10 seconds]. In such condition, if the battery had enough charging, both the battery and the ICE would provide the requested power. But as it is shown in Figure 24a, the battery SOC is going below the low marginal region (0.4). As a result, the ICE should produce more energy to charge the battery besides satisfying the requested power. In Figure 25, the ICE produces more energy to charge the battery and satisfy the requested power.
6. CONCLUSION Dual-mechanical-port machine is an integration of two electrical machines with two separate mechanical axes beside the two electrical ports providing manifold modes of operation and high flexibility for this machine when compared with usual machines. In this paper, the structure and dynamic performances of DMP machine are scrutinized and tested by simulation. While a new series–parallel HEV topology based on DMP is introduced and dynamically modeled and simulated in MATLAB SIMULINK (MAtlab toolbox, The MathWorks, Inc., Natick, MA, USA), a new control strategy and a proper power management for this novel concept are introduced in detail. The control strategy leads the engine to run in its high-efficiency operating regions. Feasibility of the control system is further validated by MATLAB SIMULINK. Simulation results show that the DMP machine can fully realize the functions of motor, generator, and planetary gear set and can be well considered as a replacement for these three discrete units. In this new concept of HEVs, there are two rotors and only one stator resulting in a more compact structure that reduces the overall volume and weight of the vehicle and makes the fuel economy more beneficial. 7. LIST OF ABBREVIATIONS AND SYMBOLS HEV DMPM ICE CVT EVT DFIG DC PM PMSM SOC PI rs rr Ls Lr Lm λm1 λm2 p 1D447out Tout J B P
Hybrid Electric Vehicle Dual Mechanical Port Machine Internal Combustion Engine Continuous Variable Transmission Electrical Variable Transmission Double Fed Induction Generator Direct Current Permanent Magnet Permanent Magnet Synchronous Motor State Of Charge Proportional Integrator Stator winding resistance Inner rotor winding resistance Self-inductance of the stator Self-inductance of the rotor winding Mutual inductance between the inner rotor winding and the stator winding Flux linkage produced by the PM-rotor in the outer machine Flux linkages produced by the PM-rotor in the inner machine Number of pole pairs Outer rotor torque Inner rotor torque Moment of inertia of the rotor Friction coefficient of the rotor Power
Copyright © 2014 John Wiley & Sons, Ltd.
Int. Trans. Electr. Energ. Syst. 2015; 25:1083–1099 DOI: 10.1002/etep
DMPM APPLICATION IN HYBRID ELECTRIC VEHICLES
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Copyright © 2014 John Wiley & Sons, Ltd.
Int. Trans. Electr. Energ. Syst. 2015; 25:1083–1099 DOI: 10.1002/etep
