WO2012123984A1 - Electric propulsion system - Google Patents

Abstract

An object of the present invention is to provide an electric propulsion system capable of reducing a weight and a power loss. A generator connected to an engine supplies a generator voltage to the motor directly. The system has a torque-speed map having a balance area, a low torque area and a high torque area, a low speed area and a high speed area. The engine is controlled in order to a generator voltage accords with a multi-phase motor voltage, when the engine can stay in a predetermined high efficiency area. Both of the generator and the motor are capable of pole-changing and/or turn-changing. The system has a first engine-generator and a second engine/generator. The second engine-generator is stopped a required generation current is less than a predetermined value. Accordingly, The engine can stay in the high efficiency area, even though the motor speed is changed widely by means of the pole-number-changing and/or the turn-number-changing and/or the engine-generator-dividing. In the other words, the above common voltage operation can be adopted in wider motor speed range by means of the changing and/or the dividing.

Description

ELECTRIC PROPULSION SYSTEM Cross-Reference to related application

This application claims benefit under 35 U.S.C.119 of:
PCT/JP2010/073883 filed on Dec/24/2010, the title of MOTOR-DRIVING APPARATUS FOR DRIVING THREE-PHASE MOTOR OF VARIABLE SPEED TYPE; PCT/JP2011/000305 filed on JAN/21/2011, the title of THREE-PHASE INVERTER FOR DRIVING VARIABLE-SPEED ELECTRIC MACHINE; and PCT/JP2011/000669 filed on Feb/07/2011, the title of TRANSVERSE FLUX MACHINE; of which the entire content are incorporated herein reference.

Background of Invention

1. Field of the Invention
The present invention relates to an electric propulsion system, more particularly to the electric propulsion system for a series-hybrid system and a pure electric vehicle.

2. Description of the Related Art
A pure electric vehicle and a series-hybrid vehicle have an excellent for saving fuel consumption and for earth atmosphere. It is known that the electric propulsion system of the series-hybrid vehicle and the electric vehicle needs to reduce a weight, a power loss and a production cost. However, it is really hard for vehicle application to improve the weight, the power loss and the production cost of the electric propulsion system. Size of the electric machine decreases a copper loss and an iron loss, but the weight and the cost are increased.

Japan Patent No. 3,337,126 describes about a series-hybrid system having an emergency bypass circuit for connecting the generator to the motor directly at a time when a power switching apparatus is broken or troubled. The bypass circuit of 126' patent must have four groups of three switches for connecting two three-phase machines. The first and the second groups of the three switches connect a three-phase generator to a three-phase motor. The third group of the three switches connects the generator to a three-phase rectifier. The fourth group of the three switches connects a three-phase inverter to the motor. Furthermore, 126' patent employs the permanent magnet synchronous generator (PMSG) and the permanent magnet synchronous motor (PMSM). However, synchronization of rotations of the PMSG and the PMSM is not easy, because rotation speeds and phases of PMSG and PMSM must be synchronized equivalently for the direct-connecting.

A dual-engine with two engines is proposed for fuel-saving. One engine of the dual-engine is stopped when a vehicle needs a small torque. Two engines of the dual engine can be arranged in parallel or in series. Each engine torque is transmitted via each mechanical clutch and a gear system. However, the prior dual engine must have complicated mechanical structure with the two clutches and the gear system. U. S. Patent Unexamined Publication No. 2009/284,228 proposes a hybrid system having the parallel-arranged dual engine. A first engine of the dual engine drives wheels mechanically, and a second engine of the dual engine drives a generator. However, 228' Publication has the limit that the first engine cannot drive the generator, and the second engine cannot drive the wheels.

PTL 1: Japan Patent No. 3,337,126
PTL 2: U. S. Patent Unexamined Publication No. 2009/284,228

An object of the invention is to reduce a power loss and a production cost of an electric propulsion system. Another object of the invention is to reduce a weight and the production cost of the electric propulsion system. Another object of the invention is to reduce the weight, the power loss and the production cost of the electric propulsion system.

As for the first aspect of the invention, a torque-speed map of a motor is divided to a balance area (A), a low torque area (B) and a high torque area (C), a low speed area (D) and a high speed area (E). The balance area (A), the low torque area (B) and the high torque area (C) are disposed in a middle speed area between the low speed area (D) and a high speed area (E). The balance area (A) is disposed a middle torque area between the low torque area (B) and the high torque area (C). The motor stays in the balance area (A), when an engine stays in a predetermined high frequency area.

Especially, a multi-phase generator voltage accords with a multi-phase motor voltage by means of controlling an engine torque and an engine speed in a limit that the engine stay in the high efficiency are. Accordingly, In the other words, a common multi-phase voltage is applied to both of the generator and the motor connected via a DC link of the electric propulsion system, if the engine for driving the generator can stay in the high efficiency area (A), which is equivalent that the motor can stay in the balance area (A), the low speed area (B) and the high speed area (C).

As the result, control of the rectifier and the inverter becomes simple. Voltage ripples on the DC link are reduced, because the rectified voltage of the rectifier in synchronization with the switching of the inverter. It is not required to provide a large smoothing capacitor connected to the DC link. For example, a three-phase full-wave rectified voltage applied from the rectifier to the inverter is preferable for the inverter applying the three-phase voltage with the same frequency and the same phases. A DC energy apparatus is charged when the motor is operated in the charge area (B), and is discharged when the motor is operated in the discharge area (C).

According to a preferred embodiment, each phase terminal of the generator is connected to each phase terminal of the motor via each bypass switch. Each bypass switch is closed in the balance area (A), the low torque area (B) and the high torque area (C) and is opened in the low speed area (D) and the high speed area (E). Accordingly, power switching losses of the rectifier and the inverter can be ignored, when the motor is driven in the areas (A), (B) and (C).

According to another preferred embodiment, a current of the bypass switch consisting of a relay is reduced by means of switching the rectifier and the inverter just before turning-off the relay. In the other words, the current between the generator and the motor flows via the rectifier and the inverter until the bypass switch is turned off completely. Accordingly, the sparking of the relay is reduced.

According to another preferred embodiment, the engine is driven in the high efficiency area (A), when the motor stays in either the low speed area (D) or the high speed area (E), even though the charging level of the DC energy apparatus (7) is lower than a predetermined value. Furthermore, the engine is stopped, when the motor stays in either one of the low speed area (D) and the high speed area (E), if the charging level of the DC energy apparatus is higher than a predetermined value. In the other words, the pair of the generator and the rectifier is operated independently from a pair of the motor and the inverter, when the DC energy apparatus is not charged enough.

According to another embodiment, the single-phase switching method (the SPSM) described in PCT/JP2010/073883 applied by the inventor is employed, when the motor and the generator are operated with the common three-phase voltage in the areas (A, B and C). In the SPSM, only one leg of the three-phase inverter is PWM-switched, and another two legs of the three-phase inverter are not PWM-switched. As the result, the power loss of the inverter is decreased largely. The three-phase full-wave rectified voltage is applied to the inverter by a boost DC-to-DC converter in order to producing the three-phase voltage. In the other words, the SPSM mentioned above can be operated by the electric propulsion system, when the rectifier and the motor employ the common three-phase voltage.

According to another preferred embodiment, the generator and/or the motor consist of a three-phase induction machine. Because of the slip of the induction motor, the driving of the generator and the motor with the common voltage becomes easy, even though the motor speed is changed rapidly and transiently.

According to another preferred embodiment, at least one of the generator and the motor is capable of changing at least one of a pole-number and/or a turn number by means of changing connection of at least one of the multi-phase inverters consisting of the rectifier and the inverter by means of switching the multi-phase inverter. Accordingly, the system efficiency is improved, and the generator and the motor can become compact, because the balance area, which is equivalent to the high efficiency area of the engine, is widened.

According to another preferred embodiment, both of the generator and the motor are capable of changing at least one of a pole-number and/or a turn number by means of changing connection of both of the rectifier and the inverter by means of switching the multi-phase inverter. Accordingly, the system efficiency is further improved, and the generator and the motor can become further compact, because the balance area (A), which is equivalent to the high efficiency area of the engine, is further widened.

According to another preferred embodiment, the rectifier and/or the inverter consists of a nine-switch three-phase inverter of which each leg consists of an upper switch, a middle switch and a lower switch, which are connected in series to each other, Each connecting point between the upper switch and the middle switch is connected to each phase winding of a first three-phase winding of the generator and/or the motor, Each connecting point between the middle switch and the lower switch is connected to each phase winding of a second three-phase winding of the generator and/or the motor. The first and the second three-phase windings are connected in series to each other in the series mode, and the first and the second three-phase windings are connected in parallel to each other in the parallel mode.

In the other words, two three-phase windings are connected in parallel or in series by means of employing the simple nine-switch inverter. Accordingly, the balance area (A) is equivalently widened by changing the connection of the two three-phase windings.

According to another preferred embodiment, the first three-phase winding is wound in a left three-phase induction machine for driving a left wheel. The second three-phase winding is wound in a right three-phase induction machine for driving a right wheel. Accordingly, the torque-speed curve of motor can be changed without employing a motor having six terminals.

According to another preferred embodiment, each same phase winding of the first three-phase winding and the second three-phase winding is wound on each same stator poles of the generator and/or the motor. For example, the first U-phase stator winding and the two U-phase winding are wound on one U-stator poles. The nine-switch inverter can select one of the series mode and the parallel mode easily. The torque-curve of the electric propulsion system can be changed. After all, the motor becomes compact. Preferably, the series connection is employed in a low speed range, and the parallel connection is employed in a high speed range.

According to another preferred embodiment, the generator and /or the motor consist of a three-phase induction machine. Each phase winding of the first three-phase winding and each phase winding of the second three-phase winding are wound alternately in a circumferential direction of the three-phase induction machine. Both of the pole number and the turn number of the three-phase induction machine is changed by means of switching the nine-phase inverter. As the result, the torque curve is changed largely, because a pole number and a turn number of the electric machine are changed spontaneously.

According to another preferred embodiment, the controller further has at least one single mode in which the supplying of the current to one three-phase winding is stopped. Accordingly, the torque-speed curve can be changed largely.

According to another preferred embodiment, the multi-phase motor-generator consists of a plurality of single-phase transverse flux machines arranged in tandem. Each single-phase transverse flux machine has a squirrel-cage conductor surrounds each rotor salient of the single-phase transverse flux machine having stator salient. The three-phase induction machine is started as a reluctance motor. Accordingly, the generator and/or the motor can become compact.

According to another preferred embodiment, each single-phase squirrel-cage induction transverse flux machine has double-sided structure with a rotor disposed between two stators in a radial direction. The rotor has rotor teeth made of laminated flat steel plates laminated to an axial direction. Accordingly, the rotor structure becomes simple.

According to another preferred embodiment, a first generator is driven by a first engine. A second generator is driven by a second engine. The rectifier rectifies the generator currents from the two generators. The second engine is stopped, when a required generator current value is less than a predetermined value. Accordingly, the common-voltage-driving mode having a common voltage applied to the motor and the generator can be widened.

According to another preferred embodiment, the controller starts the stopped second engine again, when the required generator current value becomes larger than the predetermined value. The controller drives both of the first engine and the second engine at an equal rotating speed after the starting of the second engine again.

According to another preferred embodiment, the first engine and the second engine share a common cylinder-block. A first crankshaft of the first engine and a second crankshaft of the second engine are extended to an opposite end to each other. Accordingly, the dual-engine/dual-generator system becomes compact.

According to another preferred embodiment, the first engine is larger than the second engine. Accordingly, the high efficiency area of the engine is widened in the torque range largely. The smaller engine is driven, when the required torque is small. The larger engine is driven instead of the smaller engine, when the required torque is increased. Both of two engines are driven, when the required torque is further increased.

As for the second aspect of the invention, both of the generator and the motor are capable of changing at least one of a pole-number and/or a turn number by means of changing connection of both of the multi-phase inverters consisting of the rectifier and the inverter. Accordingly, the generator and the motor can become compact. Further the engine can be operated in the high efficiency area of the engine, even though the motor speed and the motor torque are changed by means of changing the pole-number and/or the turn number of both of the generator and the motor equivalently.

As for the third aspect of the invention, a first engine drives a first generator, and a second engine drives a second generator. Generated power of two generators is rectified by the rectifier. The two engines or either one of the two engines are driven in accordance with the required torque. As the result, the high efficiency area of the engine is widened in the torque range.

Figure 1 is a block diagram showing a series-hybrid system of the first embodiment. Figure 2 is a torque-speed diagram showing torque-curves of a motor, a generator and an engine shown in Figure 1. Figure 3 is a flow-chart showing an area-selection routine. Figure 4 is a circuit topology configuration showing the electric propulsion system shown in Figure 1. Figure 5 is a switching-pattern-configuration showing the changing of the switching patterns of the inverter driven with the single-phase-switching-method. Figure 6 is a switching-pattern-configuration chart showing the switching states of six switches of the inverter shown in Figure 4. Figure 7 is a timing chart showing waveforms of a three-phase sinusoidal voltage. Figure 8 is a timing chart showing waveforms of a biggest inter--phase voltage and a smaller inter-phase voltage. Figure 9 is a circuit topology configuration showing the electric propulsion system of the second embodiment. Figure 10 is a circuit topology configuration showing a series mode of the inverter shown in Figure 9. Figure 11 is a circuit topology configuration showing a series mode of the inverter shown in Figure 9. Figure 12 is a circuit topology configuration showing a series mode of the inverter shown in Figure 9. Figure 13 is a circuit topology configuration showing a series mode of the inverter shown in Figure 9. Figure 14 is a circuit topology configuration showing a series mode of the inverter shown in Figure 9. Figure 15 is a circuit topology configuration showing a series mode of the inverter shown in Figure 9. Figure 16 is a circuit topology configuration showing a series mode of the inverter shown in Figure 9. Figure 17 is a circuit topology configuration showing a series mode of the inverter shown in Figure 9. Figure 18 is a circuit topology configuration showing a series mode of the inverter shown in Figure 9. Figure 19 is a circuit topology configuration showing a series mode of the inverter shown in Figure 9. Figure 20 is a circuit topology configuration showing a series mode of the inverter shown in Figure 9. Figure 21 is a circuit topology configuration showing a series mode of the inverter shown in Figure 9. Figure 22 is a circuit topology configuration showing a parallel mode of the inverter shown in Figure 9. Figure 23 is a circuit topology configuration showing a parallel mode of the inverter shown in Figure 9. Figure 24 is a circuit topology configuration showing a parallel mode of the inverter shown in Figure 9. Figure 25 is a circuit topology configuration showing a parallel mode of the inverter shown in Figure 9. Figure 26 is a circuit topology configuration showing a parallel mode of the inverter shown in Figure 9. Figure 27 is a circuit topology configuration showing a parallel mode of the inverter shown in Figure 9. Figure 28 is a circuit topology configuration showing a parallel mode of the inverter shown in Figure 9. Figure 29 is a circuit topology configuration showing a parallel mode of the inverter shown in Figure 9. Figure 30 is a circuit topology configuration showing a parallel mode of the inverter shown in Figure 9. Figure 31 is a circuit topology configuration showing a parallel mode of the inverter shown in Figure 9. Figure 32 is a circuit topology configuration showing a parallel mode of the inverter shown in Figure 9. Figure 33 is a circuit topology configuration showing a parallel mode of the inverter shown in Figure 9. Figure 34 is a circuit topology configuration showing an upper-switch-on mode of the inverter shown in Figure 9. Figure 35 is a circuit topology configuration showing an upper-switch-on mode of the inverter shown in Figure 9. Figure 36 is a circuit topology configuration showing a lower-switch-on mode of the inverter shown in Figure 9. Figure 37 is a circuit topology configuration showing a lower-switch-on mode of the inverter shown in Figure 9. Figure 38 is a schematic development of stator poles, which shows a series connection with doubled poles and turn numbers of the three-phase induction motor in the second embodiment. Figure 39 is a schematic development of stator poles, which shows a parallel connection of the three-phase induction motor in the second embodiment. Figure 40 is a schematic development of stator poles showing the third embodiment having stator poles on which two phase windings connected in series are wound. Figure 41 is a schematic development of stator poles showing the third embodiment having stator poles on which the first phase windings is energized. Figure 42 is a schematic development of stator poles showing the third embodiment having stator poles on which the second phase windings is energized. Figure 43 is a schematic development of stator poles showing the third embodiment having stator poles on which two phase windings connected in parallel are wound. Figure 44 is a block diagram showing a series-hybrid system of the fourth embodiment having two in-wheel motor capable of connected in series or in parallel. Figure 45 is a circuit topology configuration showing an inverter shown in Figure 44. Figure 46 is a schematic diagram showing torque-speed curves of induction motor. Figure 47 is a flow-chart showing a control routine for reducing mechanical shock at the changing the connection of two three-phase windings shown in Figure 44. Figure 48 is an axial cross-section showing a three-phase induction TFM of the sixth embodiment. Figure 49 is an axial cross-section showing two laminated soft steel plates and one soft steel plate being laminating now. Figure 50 is a partial side view of stator shown in Figure 48. Figure 51 is a partial plan view of stator shown in Figures 48 and 50. Figure 52 is an axial cross-section showing a three-phase induction TFM of a first arranged embodiment. Figure 53 is a partial development showing a rotor surface of the three-phase induction TFM shown in Figure 52. Figure 54 is a partial development showing a stator surface of the three-phase induction TFM shown in Figure 52. Figure 55 is an axial cross-section showing a three-phase induction TFM of a second arranged embodiment. Figure 56 is a schematic side view showing a part of one soft flat steel sheet of left rotor teeth shown in Figure 55. Figure 57 is a flow-chart showing the starting of single-phase induction TFM. Figure 58 is a part of an axial cross-section showing a three-phase induction TFM of a third arranged embodiment. Figure 59 is a block diagram showing a three-phase induction linear transverse flux generator of a fourth arranged embodiment. Figure 60 is a cross-section showing the three-phase induction linear transverse flux generator shown in Figure 59. Figure 61 is a block circuit diagram showing an electric propulsion system of the seventh embodiment. Figure 62 is a flow chart showing selection of the combination of the driven engine or the driven engines in Figure 61.

Detailed Description of the Preferred Embodiment

Preferred embodiments of the electric propulsion system are explained referring an example of the series hybrid system having a three-phase induction machine. However, a part of the embodiment can be employed for a pure electric vehicle.
(The first embodiment)
Figure 1 is a block diagram showing a series-hybrid system of the first embodiment. A generator 1 consisting of a three-phase induction motor-generator supplies a generator current I5 to a three-phase rectifier 4 consisting of a three-phase inverter. An axis of the generator 1 is jointed to a cranking shaft of an internal combustion engine 2. The rectifier 4 connected to a three-phase inverter 5 via a DC link 6 supplies a rectified current I3 to the DC link 6.

The inverter 5 supplies an inverter current I1 to a motor 3 consisting of a three-phase induction motor-generator. A DC energy apparatus 7 consists of a Li-ion battery 71 and a boost DC-to-DC converter 72. The converter 72 connecting the battery 71 to the DC link 6 applies a boosted voltage across the DC link 6. Three terminals of a three-phase stator winding of generator 1 are connected to three terminals of a three-phase stator winding of motor 3 via three bypass switches 8 consisting of a relay. A controller 9 controls the engine 2, rectifier 4, the inverter 5 and the converter 72. The largest value of engine 2 is smaller than the largest torque of motor 3.

Figure 2 shows a torque-speed curve 'Tmmax' of motor 3, a torque-speed curve 'Tgmax' of generator 1 and a torque-speed curve 'Temax' of engine 2 in a torque-speed dimensions. A transverse axis shows a speed 'N' of an engine. The transverse axis shows frequencies of generator 1 and motor 3 under the condition that a common three-phase voltage with a common frequency is applied to generator 1 and motor 3, too. It should be understood that the rotor axis of the generator 1 is jointed directly to the axis of the engine 2. A vertical axis shows a torque of generator 1, engine 2 and motor 3.

The torque-speed area in which motor 3 can be driven is divided to a balance area (A), a low torque area (B) and a discharge are (C), a low speed area (D) and a high speed area (E). The balance area (A), the low torque area (B) and the discharge are (C) are in a middle speed area between the low speed area (D) and a high speed area (E). The balance area (A) is in a middle torque area between the low torque area (B) and the discharge are (C).

The balance area (A) is equal to a predetermined high efficiency area of the engine 2, when a three-phase generator voltages applied from rectifier 4 to generator 1 is equal to a three-phase motor voltage applied from inverter 5 to motor 3. In the other words, the balance area (A) means the high efficiency area of the engine 2, if a common three-phase voltage is applied to generator 1 and motor 3. The lowest frequency value (fL) of the common three-phase voltage in the balance area (A) is equal equivalently to the lowest speed value (NL) of engine 2 in the high efficiency area. The highest frequency value (fH) of the common three-phase voltage in the balance area (A) is equal equivalently to the highest speed value (NH) of engine 2 in the high efficiency area.

Operations of the electric propulsion system in the areas (A)-(E) are explained as follows. In the middle speed areas (A), (B) and (C), the bypass switches 8 connects three terminals of generator 1 to three terminals of motor 3. Rectifier 4 and/or inverter 5 supplies the common three-phase voltage to both three-phase stator windings of generator 1 and motor 3, which consist of three-phase induction machines, when motor 3 stays in the areas (A), (B) and (C). A rotor speed of generator 1 does not accord with a rotor speed of motor 3, because generator 1 and motor 3 are three-phase induction machines each.

The common three-phase voltage has a frequency, which is changed in accordance with the motor speed. Furthermore, the engine speed is changed in order that a slip rate of generator 1 and a slip rate of motor 3 stay in an allowable range. The slip rates of generator 1 and motor 3 should be adjusted to accord with the best efficiency slip value by means of controlling the engine speed and the frequency of the common three-phase voltage. The best efficiency slip value means that a total loss of generator 1 and motor 3 becomes the smallest value. In the transient period, the slip rates of generator 1 and motor 3 can be apart from the best efficiency slip value. In the high efficiency area (A), almost motor power is supplied to motor 3 via bypass switches 8 made of a relay with three pairs of contact points.

In the low torque area (B), a generator current is larger than a motor current. A remaining generator current is supplied to battery 71 via rectifier 4 and boost DC-to-DC converter 72. The battery-charging can be controlled easily by means of PWM-switching of boost DC-to-DC converter 72. Engine 2 is stopped, when battery 71 is charged enough, and the battery power is supplied to motor 3 rotating in the area (B). After the charging level of battery 71 is dropped under a predetermined level, engine 2 is start again. In the high torque area (C), the inverter current of battery 71 and generator current are supplied to motor 3. Accordingly, motor 3 produces larger torque than a torque produced by generator 1. When the charging level of battery 71 reaches to a predetermined lowest level by the battery-discharging, motor 3 is only driven with the generator power.

In the low speed area (D) and the high speed area (E), engine 2 is stopped, and motor 3 produces a traction torque with using the battery power, because the engine efficiency is bad. In the areas (D) and (E), bypass switches are opened. Engine 2 is driven in the area (A), when the battery level drops under the predetermined low level. The generator frequency is independent from the inverter frequency in order to drive the motor in the high efficiency are (A).

When engine 2 is started, the battery power is supplied to generator 1 via rectifier 4, which is the three-phase inverter. When the vehicle is braking, a kinetic energy of the vehicle is absorbed by battery 71 via inverter 5 and DC-to-DC converter 72. Inverter rectifies the three-phase motor current. DC-to-DC converter 72 controls the regenerative current of inverter 5.

An area-selection routine is shown in Figure 3. At first, a torque instruction value, the motor torque, the motor speed, the engine speed and the engine torque are detected at the step S100. Then, the area which should be selected is decided at the step S102 in accordance with the detected parameters. At next, the engine 2, rectifier 4, inverter 5 and DC-to-DC converter are controlled in accordance with the decided area and the parameters.

Figure 4 shows a circuit topology of the electric propulsion system shown in Figure 1. Three-phase inverter 5 has a U-leg with an upper switch 11 and a lower switch 12, a V-leg with an upper switch 21 and a lower switch 22 and a W-leg with an upper switch 31 and a lower switch 32. Rectifier 4 has a U-leg with an upper switch 11A and a lower switch 12A, a V-leg with an upper switch 21A and a lower switch 22A and a W-leg with an upper switch 31A and a lower switch 32A. Each switch consists of an IGBT and a free-wheeling diode connected in parallel to each other.

The preferable switching method of inverter 5 is explained referring Figures 5-8. This switching method is called the single-phase switching method, the SPSM. The boost DC-to-DC converter 7 shown in Figure 1 outputs a boosted voltage Vx to inverter 5 via DC link 6. The voltage Vx has the three-phase full-wave rectified waveform as shown in Figure 8. A transverse axis in Figure 8 shows electric angle of motor 3. A vertical axis in Figure 8 shows amplitude of the boosted voltage Vx, which is equal to the DC link voltage. It is important that the rotor angle does not need to detect, because motor 3 is the induction motor.

Inverter 5 applies three phase sinusoidal voltages Vu, Vv and Vw shown in Figure 7 to three-phase induction motor 3. An electric angle range of 360 degrees is divided to six stages A-F having sixty degrees each. The biggest inter-phase voltage among three phase voltages Vu, Vv and Vw has the three-phase full-wave rectified waveform as shown in Figure 7. Accordingly, it is understood that DC-to-DC converter 7 outputs the biggest inter-phase voltage Vx.

Inverter 5 has six switching patterns as shown in Figure 5 in order to produce another inter-phase voltage called the smaller inter-phase voltage Vy. Each switching pattern is operated in each of six stages A-F. The biggest inter-phase voltage Vx and the smaller inter-phase voltage Vy are voltages on a potential of a lowest phase voltage with the lowest amplitude. Waveform of the smaller inter-phase voltage Vy is similar or equal to the single-phase full-wave rectified waveform as shown in Figure 8.

The largest amplitude of the smaller inter-phase voltage Vy is equal to the smallest amplitude of the biggest inter-phase voltage Vx. Furthermore, the two inter-phase voltages Vx and Vy have a phase difference. As the result, inverter 5 outputs the three-phase sinusoidal voltage shown in Figure 7, when inverter 5 outputs the two inter-phase voltages Vx and Vy and the lowest DC voltage value. It is preferable to employ a potential of a negative terminal of battery 71 as the lowest DC voltage value.

In each of stages A-F, two legs of inverter 5 are not PWM-switched and only one leg of inverter 5 is PWM-switched. The PWM-switch-less legs are called the fixed legs. It is important that one of two fixed legs has a turned-on upper switch of one fixed leg and a turned-on lower switch of the other fixed leg. The biggest inter-phase voltage Vx is applied across two fixed legs, because converter 72 outputs the biggest inter-phase voltage Vx via two fixed legs. The PWM-switched leg is called the switched leg. The smaller inter-phase voltage Vy is applied from the switched leg, because one of two fixed leg outputs the low battery potential via the turned-on lower switch.

The biggest inter-phase voltage Vx is changed in each electrical angle of 60 degrees as shown in Figure 7 in turn. In the stage A from 30 degrees to 90 degrees, the biggest inter-phase voltage Vx is the inter-phase voltage Vu-Vw. In the stage B from 90 degrees to 150 degrees, the biggest inter-phase voltage Vx is the inter-phase voltage Vu-Vv. In the stage C from 150 degrees to 210 degree, the biggest inter-phase voltage Vx is the inter-phase voltage Vw-Vv. In the stage D from 210 degrees to 270 degrees, the biggest inter-phase voltage Vx is the inter-phase voltage Vw-Vu. In the stage E from 270 degrees to 330 degrees, the biggest inter-phase voltage Vx is the inter-phase voltage Vv-Vu. In the stage F from 330 degrees to 30 degrees, the biggest inter-phase voltage Vx is the inter-phase voltage Vv-Vw.

In the stage A from 30 degrees to 90 degrees and in the stage D from 210 degrees to 270 degrees, V-phase leg is PWM-switched. The U-phase leg and the W-phase leg are the fixed legs.
In the stage B from 90 degrees to 150 degrees and in the stage E from 270 degrees to 330 degrees, W-phase leg is PWM-switched. The U-phase leg and the V-phase leg are the fixed legs.
In the stage C from 150 degrees to 210 degrees and in the stage F from 33 degrees to 30 degrees, U-phase leg is PWM-switched. The V-phase leg and the W-phase leg are the fixed legs. Figure 6 shows operations of six switches 11, 12, 21, 22, 31 and 32.

One of two switches of the switched leg has the duty ratio changing from 0% to 100% in the period of 60 degrees excessively. The other one of two switches of the switched leg has the duty ratio changing from 100% to 0% in the period of the above 60 degrees excessively. Amplitude of the smaller inter-phase voltage Vy with the single-phase full-wave rectified waveform is controlled by means of controlling a PWM duty ratio of the switched leg. The amplitude of the biggest inter-phase voltage should be considered.

The amplitude of the biggest inter-phase voltage Vx is 1.5-1.73, when the biggest amplitude of one phase-voltage is 1. A boost ratio of converter 72 becomes 75-86.5% of the boost ratio of the conventional motor-driving apparatus with a converter and an inverter. As the result, the upper switch of converter 72 can have higher duty ratio than the conventional motor-driving apparatus. For example, the converter of the conventional motor-driving apparatus outputs a boost voltage of 700 V, when a battery voltage Vb is 250V. The boost ratio becomes 2.8. On the other hand, the converter of the motor-driving apparatus of the embodiment outputs only 525-605V.

Both of the apparatuses can apply an equal biggest inter-phase voltage Vx to the inverter 4. The boost voltage of converter 72 is reduced largely. Rectifier 4 can be switched in synchronization with inverter 5, when the areas A-C shown in Figure 2. Converter 72 can apply the biggest inter-phase voltage Vx, even though generator outputs a three-phase voltage with a different frequency from the frequency of the inverter.

(The second embodiment)
The second embodiment of the electric propulsion system is explained referring to Figures 9-43. The second embodiment is essentially same as the first embodiment showing in Figures 1-8. However, rectifier 4 and inverter 5 of the second embodiment consist of a nine-switch inverter each as shown in Figure 9. Moreover, induction generator 1 has a first three-phase stator winding 1A and a second three-phase stator winding 1B. Induction motor 3 has a first three-phase stator winding 3A and a second three-phase stator winding 3B, too.

In Figure 9, rectifier 4 has a upper switch group X, a middle switch group Y and a lower switch group Z. Rectifier 4 has three upper switches 11A, 21A and 31A of the upper switch group X, three lower switches 12A, 22A and 32A of the middle switch group Y and three middle switches 13A, 23A and 33A of lower switch group Z. The U-phase leg of rectifier 4 consists of switches 11A, 13A and 12A connected in series to each other. The V-phase leg of rectifier 4 consists of switches 21A, 23A and 22A connected in series to each other. The W-phase leg of rectifier 4 consists of switches 31A, 33A and 32A connected in series to each other. Each phase winding of the first three-phase winding 1A is connected to each contact point between each upper switch and each middle switch of rectifier 4. Each phase winding of the second three-phase winding 1B is connected to each contact point between each middle switch and each lower switch of rectifier 4.

Inverter 5 has a upper switch group X, a middle switch group Y and a lower switch group Z. Inverter 5 has three upper switches 11, 21 and 31 of the upper switch group X, three lower switches 12, 22 and 32 of the middle switch group Y and three middle switches 13, 23 and 33 of lower switch group Z. The U-phase leg of inverter 5 consists of switches 11, 13 and 12 connected in series to each other. The V-phase leg of inverter 5 consists of switches 21, 23 and 22 connected in series to each other. The W-phase leg of inverter 5 consists of switches 31, 33 and 32 connected in series to each other.

Each phase winding of the first three-phase winding 3A is connected to each contact point between each upper switch and each middle switch of inverter 5. Each phase winding of the second three-phase winding 3B is connected to each contact point between each middle switch and each lower switch of inverter 5. Each phase winding of the first three-phase winding 1A with the same phase is connected to each phase winding of the first three-phase winding 3A with the same phase via each bypass switch 8 respectively. In the other words, rectifier 4 and inverter 5 employ the nine-switch inverter each. Each upper switch of same phase windings of the first and the second three-phase windings 1A and 3A are connected by each bypass switch 8. The bypass switches 8 are turned on, when rectifier 4 is operated in synchronization with inverter 5 as described in the first embodiment.

The first three-phase winding 3A consists of a U-phase winding U1, a V-phase winding V1 and a W-phase winding W1. The second three-phase winding 3B consists of a U-phase winding U2, a V-phase winding V2 and a W-phase winding W2. A U-phase current IU1 flows through the U-phase winding U1. A V-phase current IV1 flows through the V-phase winding V1. A W-phase current IW1 flows through the W-phase winding W1. A U-phase current IU2 flows through the U-phase winding U2. A V-phase current IV2 flows through the V-phase winding V2. A W-phase current IW2 flows through the W-phase winding W2.

Each of two nine- switch inverters 4 and 5 have a parallel mode, a series mode, an upper-switch-on mode and a lower-switch-on mode each. In the series mode, the first three-phase winding and the second three-phase winding are connected in series to each other. In the parallel mode, the first three-phase winding and the second three-phase winding are connected in parallel to each other. In the upper-switch-on mode, only the first three-phase winding is driven, and the second three-phase winding is stopped. In the lower-switch-on mode, only the second three-phase winding is driven, and the first three-phase winding is stopped. In the above four mode, the single-phase-switching-method, the SPSM, can be driven in order to reduce the switching loss.

The series mode of inverter 5 is explained referring to Figures 10-21. The series mode of rectifier 4 is essentially same as the series mode of inverter 5. In the series mode, a pair of the upper switch and the lower switch of the same leg shown in Figures 10-21 is regarded as the upper switch of the same leg of the six-switch inverter shown in Figure 5.

In any one leg shown in Figures 10-21, the lower switch is turned on when the upper switch is turned on, and the lower switch is turned off when the upper switch is turned off. Switching patterns of upper switches 11, 21 and 31 and lower switches 12, 22 and 32 of the nine-switch inverter shown in Figures 10-21 are same as the switching patterns of upper switches 11, 21 and 33 of six-switch inverter 5 shown in Figure 5. Switching patterns of middle switches 13, 23 and 33 of the nine-switch inverter shown in Figures 10-21 are same as the switching patterns of lower switches 12, 22 and 32 of six-switch inverter 5 shown in Figure 5. In Figures 10-21, the single-phase-switching method (the SPSM) is operated.

Figures 10 and 11 show the switching pattern in the stage (A) shown in Figure 7. The U-phase leg and the W-phase leg are the fixed legs, and the V-phase leg is the switched leg. Figure 10 shows a PWM-on state when the switches 21 and 22 are turned on. Figure 11 shows a PWM-off state when the switch 23 is turned on. The PWM-on state and the PWM-off state are changed in each PWM carrier interval.

Figures 12 and 13 show the switching pattern in the stage (B) shown in Figure 7. The U-phase leg and the V-phase leg are the fixed legs, and the W-phase leg is the switched leg. Figure 12 shows a PWM-on state when the switches 31 and 32 are turned on. Figure 13 shows the PWM-off state when the switch 33 is turned on. The PWM-on state and the PWM-off state are changed in each PWM carrier interval.

Figures 14 and 15 show the switching pattern in the stage (C) shown in Figure 7. The V-phase leg and the W-phase leg are the fixed legs, and the U-phase leg is the switched leg. Figure 14 shows a PWM-on state when the switches 11 and 12 are turned on. Figure 15 shows the PWM-off state when the switch 13 is turned on. The PWM-on state and the PWM-off state are changed in each PWM carrier interval.

Figures 16 and 17 show the switching pattern in the stage (D) shown in Figure 7. The U-phase leg and the W-phase leg are the fixed legs, and the V-phase leg is the switched leg. Figure 16 shows a PWM-on state when the switches 21 and 22 are turned on. Figure 17 shows the PWM-off state when the switch 23 is turned on. The PWM-on state and the PWM-off state are changed in each PWM carrier interval.

Figures 18 and 19 show the switching pattern in the stage (E) shown in Figure 7. The U-phase leg and the V-phase leg are the fixed legs, and the W-phase leg is the switched leg. Figure 18 shows a PWM-on state when the switches 31 and 32 are turned on. Figure 19 shows the PWM-off state when the switch 33 is turned on. The PWM-on state and the PWM-off state are changed in each PWM carrier interval.

Figures 20 and 21 show the switching pattern in the stage (F) shown in Figure 7. The V-phase leg and the W-phase leg are the fixed legs, and the U-phase leg is the switched leg. Figure 20 shows a PWM-on state when the switches 11 and 12 are turned on. Figure 21 shows the PWM-off state when the switch 13 is turned on. The PWM-on state and the PWM-off state are changed in each PWM carrier interval. After all, the first three-phase winding 3A and the second three phase winding 3B are connected in series as explained above.

The parallel mode of inverter 5 is explained referring to Figures 22-33. The parallel mode of rectifier 4 is essentially same as the parallel mode of inverter 5. In the parallel mode, the middle switches 13, 23 and 33 are always turned on. The upper switches 11, 21 and 31 of the nine-switch inverter shown in Figures 22-33 has the same switching states as the upper switches 11, 21 and 31 of the six-switch inverter shown in Figure 5. The lower switches 12, 22 and 32 of the nine-switch inverter shown in Figures 22-33 has the same switching states as the lower switches 12, 22 and 32 of the six-switch inverter shown in Figure 5. In Figures 22-32, the single-phase-switching method, the SPSM, is operated.

Figures 22 and 23 show the switching pattern in the stage (A) shown in Figure 7. The U-phase leg and the W-phase leg are the fixed legs, and the V-phase leg is the switched leg. Figure 22 shows a PWM-on state when the switch 21 is turned on. Figure 23 shows a PWM-off state when the switch 22 is turned on. The PWM-on state and the PWM-off state are changed in each PWM carrier interval.

Figures 24 and 25 show the switching pattern in the stage (B) shown in Figure 7. The U-phase leg and the V-phase leg are the fixed legs, and the W-phase leg is the switched leg. Figure 24 shows a PWM-on state when the switch 31 is turned on. Figure 25 shows the PWM-off state when the switch 32 is turned on. The PWM-on state and the PWM-off state are changed in each PWM carrier interval.

Figures 26 and 27 show the switching pattern in the stage (C) shown in Figure 7. The V-phase leg and the W-phase leg are the fixed legs, and the U-phase leg is the switched leg. Figure 26 shows a PWM-on state when the switch 11 is turned on. Figure 27 shows the PWM-off state when the switch 12 is turned on. The PWM-on state and the PWM-off state are changed in each PWM carrier interval.

Figures 28 and 29 show the switching pattern in the stage (D) shown in Figure 7. The U-phase leg and the W-phase leg are the fixed legs, and the V-phase leg is the switched leg. Figure 28 shows a PWM-on state when the switch 21 is turned on. Figure 29 shows the PWM-off state when the switch 22 is turned on. The PWM-on state and the PWM-off state are changed in each PWM carrier interval.

Figures 30 and 31 show the switching pattern in the stage (E) shown in Figure 7. The U-phase leg and the V-phase leg are the fixed legs, and the W-phase leg is the switched leg. Figure 30 shows a PWM-on state when the switch 31 is turned on. Figure 31 shows the PWM-off state when the switch 32 is turned on. The PWM-on state and the PWM-off state are changed in each PWM carrier interval.

Figures 32 and 33 show the switching pattern in the stage (F) shown in Figure 7. The V-phase leg and the W-phase leg are the fixed legs, and the U-phase leg is the switched leg. Figure 32 shows a PWM-on state when the switch 11 is turned on. Figure 33 shows the PWM-off state when the switch 12 is turned on. The PWM-on state and the PWM-off state are changed in each PWM carrier interval. After all, the first three-phase winding 3A and the second three phase winding 3B are connected in parallel as explained above.

The upper-switch-on mode when only the first three-phase winding 3A is driven is explained referring to Figure 34 and 35. Figure 34 shows the stage (A) shown in Figure 7. Figure 35 shows the stage (D) shown in Figure 7. In the upper-switch-on mode, three lower switches 12, 22 and 32 are always turned on. Three middle switches 13, 23 and 33 of the nine-switch inverter shown in Figures 34 and 35 are operated as the three lower switches 12, 22 and 32 of the six-switch inverter shown in Figure 5. The SPSM is operated. In Figure 34, the U-leg and the W-leg are the fixed leg, and the V-phase leg is the switched leg. The upper switch 21 and the middle switch 23 are PWM-switched complementarily. In Figure 35, the U-leg and the W-leg are the fixed leg, and the V-phase leg is the switched leg. The upper switch 21 and the middle switch 23 are PWM-switched complementarily.

The lower-switch-on mode when only the second first three-phase winding 3B is driven is explained referring to Figure 36 and 37. Figure 36 shows the stage (A) shown in Figure 7. Figure 37 shows the stage (D) shown in Figure 7. In the lower-switch-on mode, three upper switches 11, 21 and 31 are always turned on. Three middle switches 13, 23 and 33 of the nine-switch inverter shown in Figures 36 and 37 are operated as the three upper switches 11, 21 and 31 of the six-switch inverter shown in Figure 5. The SPSM is operated. In Figure 36, the U-leg and the W-leg are the fixed leg, and the V-phase leg is the switched leg. The middle switch 23 and the lower switch 22 are PWM-switched complementarily. In Figure 37, the U-leg and the W-leg are the fixed leg, and the V-phase leg is the switched leg. The middle switch 23 and the lower switch 22 are PWM-switched complementarily.

One application of the four modes explained above is explained referring to Figures 38 and 39. Figures 38 and 39 are schematic circuit configurations for showing a pole-turn-changing method of a three-phase induction motor. Figures 38 and 39 show six stator poles 1001U1, 1001V2, 1001W1, 1001U2, 1001V1 and 1001W2, which are arranged to the circumferential direction around the rotor axis. Each one of the three phase windings U1, W1 and V1 of the first three-phase winding 3A and each one of the three phase windings V2, U2 and W2 of the second three-phase winding 3B are arranged alternately. Accordingly, six phase windings U1, V2, W1, U2, V1 and W2 are wound on six stator poles 1001U1, 1001V2, 1001W1, 1001U2, 1001V1 and 1001W2 respectively.

Each of the six phase windings can be wound with the distributed winding method, even though Figures 38 and 39 show the concentrated winding configurations. The U-phase currents IU1 and IU2 of U-phase windings U1 and U2 excite a U-phase magnet flux each. The V-phase currents IV1 and IV2 of V-phase windings V1 and V2 excite a V-phase magnet flux each. The W-phase currents IW1 and IW2 of W-phase windings W1 and W2 excite a W-phase magnet flux each.

Figure 38 is a schematic configuration showing a stator-pole arrangement of three-phase induction motor 3 with three-phase winding 3A and 3B, which are connected in series by means of employing the series parallel mode. A phase angle difference between the U-phase currents IU1 and IU2 and the V-phase currents IV1 and IV2 is 120 degrees. A phase angle difference between the V-phase currents IV1 and IV2 and the W-phase currents IW1 and IW2 is 120 degrees. A phase angle difference between the W-phase currents IW1 and IW2 and the U-phase currents IU1 and IU2 is 120 degrees. As the result, the six stator poles 1001U1, 1001V2, 1001W1, 1001U2, 1001V1 and 1001W2, which are arranged in 720 electric degrees makes four magnet poles, because one magnet poles of the stator core needs 180 degrees.

Figure 39 is a schematic configuration showing a stator-pole arrangement of three-phase induction motor 3 with three-phase winding 3A and 3B, which are connected in parallel by means of employing the parallel mode. As shown in Figures 38 and 39, directions of three phase currents IU2, IV2 and IW2 shown in Figure 39 are opposite in comparison with directions of three phase currents IU2, IV2 and IW2 shown in Figure 38.

In the other words, it means that each phase angle of three phase currents IU2, IV2 and IW2 shifts 180 electric degrees by changing the mode between the series mode and the parallel mode. As the result, the six stator poles 1001U1, 1001V2, 1001W1, 1001U2, 1001V1 and 1001W2 are arranged in 360 electric degrees in Figure 39. After all, the pole number in the parallel mode becomes half of the pole number in the series mode. Furthermore, a turn number of the parallel mode shown in Figure 39 becomes half of the turn number of the series mode shown in Figure 38. As the result, three-phase induction motor 3 produces a large torque by having the series mode, and can rotate in a high speed range. The high frequency area A shown in Figure 2 is widened equivalently by means of changing the mode. When either one of the upper-switch-on mode and the upper-switch-on mode is employed, the turn number of the three-phase induction motor 3 becomes half, when each phase winding of the first and second three-phase windings has an equal turn number to each other.

Rectifier 4 can have the series mode and the parallel mode, too. The series mode of the rectifier 4 is preferable for generator 1, when generator 1 is rotating in the low speed range. The parallel mode of the rectifier 4 is preferable for generator 1, when generator 1 is rotating in the high speed range. After all, the high efficiency area A can be widened by means of changing the mode of rectifier 4 and inverter 5.

(An arranged embodiment)
In the above explanation, by selecting one in the four mode of the inverter 5, three-phase induction motor 3 can have the four operation mode. However, a reluctance motor including a synchronous reluctance motor and a switched reluctance motor can have the four operation mode by means of selecting one in the four mode of the inverter 5, because a torque of the reluctance motor does have a relation to the current direction.

(The third embodiment)
The third embodiment of the electric propulsion system is explained referring to Figures 40-43. The system of the third embodiment is essentially same as the second embodiment employing the nine-switch inverter 5 and two three-phase winding 3A and 3B. However, each pair of two phase windings with the same phase in the first and second three-phase winding are wound each same stator pole of the stator core in Figures 40-43. The distributed winding can be employed instead of the concentrated winding shown in Figures 40-43. U-phase windings U1 and U2 are wound on U-phase stator pole 10001U. V-phase windings V1 and V2 are wound on V-phase stator pole 10001V. W-phase windings W1 and W2 are wound on W-phase stator pole 10001W.

Accordingly, in the series mode, the turn number of each phase winding of motor 3 becomes double totally, when each phase winding of the first and the second three- phase windings 3A and 3B is equal to each other. In the parallel mode, the turn number of each phase winding of motor 3 becomes zero totally, when each phase winding of the first and the second three- phase windings 3A and 3B is equal to each other. In the upper-switch-on mode or the upper-switch-on mode, the turn number of each phase winding of motor 3 becomes half, when each phase winding of the first and the second three- phase windings 3A and 3B is equal to each other.

(An arranged embodiment)
An arranged embodiment is explained referring to Figures 40-43. In this arranged embodiment, each phase winding of the first three-phase winding 3A has a different turn number from each phase winding of the second three-phase winding 3B. For example, each phase winding of the first three-phase winding 3A has 50 turns each. Each phase winding of the second three-phase winding 3B has 30 turn numbers each. As the result, each phase winding of motor 3 has 80 turn numbers totally in the series mode. Each phase winding of motor 3 has 20 turn numbers totally in the parallel mode. Each phase winding of motor 3 has 50 turn numbers totally in the upper-switch-on mode. Each phase winding of motor 3 has 30 turn numbers totally in the lower-switch-on mode. By changing the turn number of motor 3, the torque-speed curve of motor 3 can be changed step by step.

(The fourth embodiment)
The fourth embodiment of the electric propulsion system is explained referring to Figures 44-47. The system of the fourth embodiment is essentially same as the second embodiment employing the nine-switch inverter 5 and two three-phase winding 3A and 3B. However, a pair of a left motor 30A and a right motor 30B, which are a three-phase induction motor each, are employed instead of the one three-phase induction motor 3 of the second embodiment. The left motor 30A has the first three-phase winding 3A explained above. The right motor 30B has the second three-phase winding 3A explained above. Each phase winding of the first and second three-phase winding 3A and 3B has an equal turn number to each other. An axis of left motor 30A is jointed directly to an axis of a left wheel motor 300A. An axis of right motor 30B is jointed directly to an axis of a right wheel motor 300B.

Inverter 5 consists of the nine-switch inverter shown in Figure 45, which is the same as the nine-switch inverter 5 shown in Figure 9. Accordingly, the three-phase winding 3A of the left motor 30A is connected to three-phase winding 1A of generator 1 via the bypass switches 8. The three-phase winding 3B of the left motor 30B is connected to three contact points between the three-middle switches 13, 23 and 33 and three lower switches 12, 22 and 32 of the nine-switch inverter 5.

Nine-switch inverter 5 has the series mode and the parallel mode. Two three- phase windings 3A and 3B are connected in series by means of employing the series mode, when a wheel speed is in a low speed range. Two three- phase windings 3A and 3B are connected in parallel by means of employing the series mode, when a wheel speed is in a low speed range. As the result, the direct-driven wheels 300A and 300B can have a preferable torque-speed curve.

One important problem of this embodiment is the well-known wheel rotation difference which occurs in a period when the vehicle is curved along a curved roadway. However, this problem may be solved easily by the prior art called 'the single inverter differential induction machine method'. The single inverter differential induction machine method is explained referring to Figures 46 and 47. An induction motor has a torque-frequency curve shown in Figure 46. A rotor rotates at a best efficiency point of the rotor frequency value 'fr', which is proportional to a rotor speed, when the synchronous frequency 'fs1' is applied from inverter 5 to the induction motor.

The slip rate is '(fs1-fr)/fs1'. When the vehicle rotates, the left motor 30A has the rotor frequency value 'frl', and the right motor 30B has the rotor frequency value 'frr'. As the result, two induction motors 30A and 30B has different slip rates to each other. Accordingly, torques of two motors 30A and 30B become different to each other largely as shown in Figure 46.

However, the torque difference of two motors 30A and 30B are changed easily, when the synchronous frequency is changed from 'fs1' to 'fs2' and a motor current is changed. In Figure 46, the torque of left motor 30A at the rotor frequency 'frl' becomes 'Tl', and the torque of right motor 30B at the rotor frequency 'frr' becomes 'Tr'. The torque difference between the torque values 'Tl' and 'Tr' can become very small or a preferable value, when the synchronous frequency becomes 'fs2'. In the other words, the wheel rotation difference can be absorbed by means of changing the synchronous frequency and motor current value supplied from the inverter to the induction motor. By employing this method, the direct-drive system of the fourth embodiment is solved the wheel rotation difference between two induction motors 30A and 30B.

Figure 47 shows a schematic flow-chart for absorbing the wheel rotation difference. At first, parameters, for example the vehicle speed, the steering angle, the synchronized frequency, the motor current, are detected at the step S200. Then, it is judged whether or not the vehicle should rotate, at step S200. Then, the synchronous frequency value 'f' and the motor current value 'I' are calculated in accordance with the vehicle speed and the steering angle and so on, at step S202.

(An arranged embodiment)
An arranged embodiment is explained referring to Figures 47. In this arranged embodiment, the routine shown in Figure 47 is employed for absorbing the torque shock which occurs at the pole-changing and/or the turn-number-changing described above.
In the other words, the torque difference before and after the pole-changing and/or the turn-number changing is reduced by means of changing of the synchronous frequency and the motor current.

(The fifth embodiment)
The fifth embodiment of the electric propulsion system is explained referring to Figure 1. The feature of the fifth embodiment is a motor compressor system. The DC power is supplied to a sub inverter 500 from the DC link 6. The sub inverter 500 supplies the three-phase voltage to a three-phase motor 501 of driving the compressor 502. It is important that the DC link voltage Vx has the three-phase-full-wave rectified waveform. The sub inverter 500 has two operation modes. In the first operation mode, the sub inverter 500 is operated with the single-phase-switching method, the SPSM for driving the motor 3. In the second operation mode, A PWM-duty ratio of the six-switch sub inverter 500 is controlled in order to cancel the periodical changing of the amplitude of the DC link voltage Vx.

For example, the PWM-duty ratio of the sub inverter 500 is decreased, when the amplitude of the DC link voltage Vx is large. The PWM-duty ratio of the sub inverter 500 is increased, when the amplitude of the DC link voltage Vx is small. As the result, the ripples of the motor 501 and the compressor 502 are reduced easily even though the DC link voltage Vx applied to the sub inverter 500 includes the large ripples.

(The sixth embodiment)
The sixth embodiment is explained referring to Figures 48-60. The feature of the sixth embodiment is in structure of generator 1 and motor 3, 3A and 3B explained above. A weight, a power loss and a production cost of generator 1 and motor 3, 3A and 3B are essentially important for constructing the above electric propulsion system, because the above electric propulsion system needs to transmit the engine power via a long pathway consisting of generator 1, rectifier 4, inverter 5 and motor 3.

It is required that the electric propulsion system has higher efficiency than the conventional mechanical propulsion system. It is known that a transverse flux machine, (the TFM), which has a transverse flux path, has very higher values of the torque/weight ratio and the large power/torque ratio. As the result, the above electric propulsion system employing the TFMs has higher performance on the weight, the loss and the cost than the prior electrical and mechanical propulsion system of the vehicle. However, a known prior TFM has a lot of problems, for example the complex structure, yet. Novel TFMs being preferable for generator 1 and motor 3, 3A and 3B of the above electric propulsion system are explained as follows. However, numbers written in Figures 48-60 are independent from the numbers written in Figures 1-47.

Figure 48 schematically shows an axial cross-section showing a three-phase induction TFM consisting of three single-phase induction TFMs arranged in tandem to the axial direction AX. A stator 1 of the three-phase TFM has a ring-shaped U-phase stator 1U, a ring-shaped V-phase stator 1V and a ring-shaped W-phase stator 1W, which are adjacent to each other to the axial direction AX. The U-phase stator 1U consists of a ring-shaped stator core 2U and a ring-shaped U-phase windings U1 and U2. The V-phase stator 1V consists of a ring-shaped stator core 2V and a ring-shaped V-phase windings V1 and V2. The W-phase stator 1W consists of a ring-shaped stator core 2W and a ring-shaped W-phase windings W1 and W2.

Each of stator cores 2U, 2V and 2W, which is made of laminated soft steel plates, consists of left stator teeth 21L, right stator teeth 21R, a ring-shaped yoke portion 24, left diagonal portions 25L and right diagonal portions 25R. Each of stator teeth 21L and 21R projects inward in the radial direction RA. Each yoke portion 24 extends to the circumferential direction PH. The left stator teeth 21L, the right stator tooth 21R, the left diagonal portion 25L and the right diagonal portion 25R are arranged to the circumferential direction PH each. Each left diagonal portion 25L joins each left stator tooth 21L and yoke portion 24. Each right diagonal portion 25R joins each right stator tooth 21R and yoke portion 24.

The left diagonal portion 25L extends diagonally from yoke portion 24 forward and inward. The right diagonal portion 25R extends diagonally from yoke portion 24 backward and inward. Left stator teeth 21L and right stator teeth 21R of U-phase stator core 2U are adjacent to each other in the axial direction AX across the ring-shaped U-phase windings U1 and U2. Left stator teeth 21L and right stator teeth 21R of V-phase stator core 2V are adjacent to each other in the axial direction AX across the ring-shaped V-phase windings V1 and V2. Left stator teeth 21L and right stator teeth 21R of W-phase stator core 2W are adjacent to each other in the axial direction AX across the ring-shaped W-phase winding W1 and W2.

A rotor 4 of the three-phase TFM has a ring-shaped U-phase rotor core 4U, a ring-shaped V-phase rotor core 4V and a ring-shaped W-phase rotor core 4W, which are adjacent to each other in the axial direction AX. Each of the rotor cores 4U, 4V and 4W, which is made of laminated soft steel plates, consists of left rotor teeth 41L, right rotor teeth 41R, a ring-shaped yoke portion 44, left diagonal portions 45L and right diagonal portions 45R each. The left rotor teeth 41L and the right rotor teeth 41R project outward in the radial direction RA. Each yoke portion 44 extends to the circumferential direction PH.

Left rotor teeth 41L, right rotor teeth 41R, left diagonal portions 45L and right diagonal portions 45R are arranged to the circumferential direction PH each. Each left diagonal portion 45L joins each left rotor tooth 41L and yoke portion 44. Each right diagonal portion 45R joins each right rotor tooth 41R and yoke portion 44. The left diagonal portion 45L extends diagonally from yoke portion 44 forward and outward. The right diagonal portion 45R extends diagonally from yoke portion 44 backward and outward. Left rotor teeth 41L can face left stator teeth 21L with the same phase. Right rotor teeth 41R can face the right stator teeth 21R with the same phase.

Left rotor teeth 41L and right rotor teeth 41R of U-phase rotor core 4U are adjacent to each other in the axial direction AX across one ring-shaped secondary coil 60 made from copper. Left rotor teeth 41L and right rotor teeth 41R of V-phase rotor core 4V are adjacent to each other in the axial direction AX across another coil 60. Left rotor teeth 41L and right rotor teeth 41R of W-phase rotor core 4W are adjacent to each other in the axial direction AX across another coil 60. Each ring-shaped secondary coil 60 consists of a short-circuited secondary coil of each squirrel-cage single-phase induction motor.

Each of stator cores 2U, 2V, 2W and rotor cores 4U, 4V and 4W is constructed with a plurality of ring-plate-shaped soft steel plates 7 laminated to the axial direction AX as shown in Figures 49. Figure 49 shows two laminated soft steel plates 7 and one soft steel plate 7 being laminating now. Each of soft steel plates 7 consists of left teeth 71L, right teeth 71R, a ring-shaped yoke portion 74, left diagonal portions 75L and right diagonal portions 75R. The left teeth 71L and the right teeth 71R project radial inward. The yoke portion 74 extends to the circumferential direction AX. Each left diagonal portion 75L extending diagonally joins yoke portion 74 and each one of left teeth 71L. Each right diagonal portion 75R extending diagonally joins yoke portion 74 and each one of right teeth 71R.

Consequently, each of stator cores 2U, 2V and 2W is constructed by predetermined number of the laminated soft steel plates 7. A spirally-laminated soft steel plate can be employed instead of a plurality of laminated soft steel plates 7. Laminated amorphous iron plates 7 or spirally-laminated amorphous iron plate can be employed instead of laminated soft steel plates 7 or the spirally-laminated soft steel plate.

Similarly, each of rotor cores 4U, 4V and 4W is constructed by predetermined number of laminated soft steel plates. Left diagonal portions 75L and right diagonal portions 75R of one plate are formed by means of pressing a flat steel plate. Each of ring-shaped non-magnetic spacers 80 having triangle-shaped cross-section is inserted between left stator teeth 21L and right stator teeth 21R as shown in Figure 48.

Figure 50 is a partial side view of U-phase stator 1U. Figure 51 is a circumferential development showing the ring-shaped U-phase stator core 2U partially. Left stator teeth 21L and left diagonal portions 25L are arranged to the circumferential direction PH. Right stator teeth 21R and right diagonal portions 25R are arranged to the circumferential direction PH. Each non-magnetic spacer 8 is further disposed between a pair of left stator teeth 21L and left diagonal portion 25L and a pair of right stator teeth 21R and right diagonal portion 25R, which are adjacent to each other in the circumferential direction PH.

In Figure 50, left stator teeth 21L and left diagonal portions 25L are illustrated, but right stator teeth 21R and right diagonal portions 25R are hidden by non-magnetic spacers 8. Left diagonal portion 25L and right diagonal portion 25R are arranged alternately in the circumferential direction PH.

The rotor 4 with U-phase rotor core 4U, V-phase rotor core 4V and W-phase rotor core 4W are constructed with the essentially same method for constructing stator cores 2U, 2V and 2W. The U-phase single-phase induction TFM consists of stator 1U and rotor 4U. The V-phase single-phase induction TFM consists of stator 1V and rotor 4V. The W-phase single-phase induction TFM consists of stator 1W and rotor 4W.

The first three-phase winding 3A shown in Figure 9 consists of U-phase winding U1, V-phase winding V1 and W-phase winding W1, which has the star connection shown in Figure 9. The second three-phase winding 3B shown in Figure 9 consists of U-phase winding U2, V-phase winding V2 and W-phase winding W2, which has the star connection shown in Figure 9. Inverter shown in Figure 9 applies the three-phase sinusoidal voltage to the first and the second three- phase windings 3A and 3B. Accordingly, a torque-speed curve of three-phase induction TFM shown in Figure 49 can be changed by means of selecting either one of the series connection and the parallel-connection of the first three-phase windings and the second three-phase windings.

(A first arranged embodiment)
The first arranged embodiment is explained referring to Figure 52 showing the three-phase induction TFM schematically. The TFM shown in Figure 52 is essentially same as the TFM shown in Figure 49. The different points are explained as follows. In Figure 52, the rotor 4 of the known outer rotor type TFM has three rotor cores 4U, 4V and 4W, which are fixed to a cylinder-shaped rotor base 700 made of die-casting with aluminum including a lot of copper powder. The cylinder-shaped rotor base 700 may be made with die-casting with copper, too. The cylinder-shaped rotor base 700 has a ring-shaped portion 700R extending to the circumferential direction between the left diagonal portion 45L and the right diagonal portion 45R.

The cylinder-shaped rotor base 700 serves as the short-circuited secondary coil of the each single-phase induction TFMs. In the other words, the ring-shaped portion 700R performs as the secondary one turn coil of the induction motor. The left diagonal portion 45L serves as the left rotor teeth 41L shown in Figure 49. The right diagonal portion 45R serves as the right rotor teeth 41R shown in Figure 49. Accordingly, each of diagonal portions 45L and 45R are surrounded with rotor base 700. Furthermore, a radial width of rotor base 700 can be reduced. Motor torque of the TFM shown in Figure 52 is increased, because the short-circuited secondary coil of the induction TFM can have a low electric resistance value.

Three stator cores 1U, 1V and 1W are buried at outer peripheral surface of a disc-shaped housing 600 made of aluminum without near top portions of the teeth. U-phase windings U1 and U2 are accommodated in U-phase stator core 1U. V-phase windings V1 and V2 are accommodated in V-phase stator core 1V. W-phase windings W1 and W2 are accommodated in W-phase stator core 1W. The star-connected first three-phase winding consisting of three phase windings U1, V1 and W1 are connected in series or in parallel to the star-connected second three-phase winding consisting of three phase windings U2, V2 and W2. Either one of the series connection and the parallel connection is selected in accordance with the detected motor parameter and instructions.

Figure 53 is a schematic development showing a part of an inner peripheral surface of the rotor 4 shown in Figure 52. Figure 54 is a schematic development showing a part of an outer peripheral surface of the stator shown in Figure 52.

(A second arranged embodiment)
The second arranged embodiment is explained referring to Figure 55 showing the three-phase induction TFM with double-sided radial gap structure. Six stator cores 1U0, 1V0, 1W0, 1UI, 1VI and 1WI of the three-phase double-sided induction TFM are fixed to the housing 600 made from aluminum. U-phase stator core 1UO has the ring-shaped U-phase winding U1. U-phase stator core 1UI has the ring-shaped U-phase winding U2. V-phase stator core 1VO has the ring-shaped V-phase winding V1. V-phase stator core 1VI has the ring-shaped V-phase winding V2. W-phase stator core 1WO has the ring-shaped W-phase winding W1. W-phase stator core 1WI has the ring-shaped W-phase winding W2.

A rotor 700 has a cylinder portion 702 made from die-casted copper metal. The cylinder portion 702 fixed to an axis 800 via a disc 701 of the rotor 700 has three pairs of left rotor teeth 41L and the right rotor teeth 41R. The rotor 700 is disposed between outer stator cores 1UO, 1VO and 1WO and inner stator cores 1UI, 1VI and 1WI. The three pairs of the left rotor teeth 41L and the right rotor teeth 41R are adjacent to each other in the axial direction AX.

Left rotor teeth 41L and right rotor teeth 41R are made of soft flat steel sheets laminated to the axial direction AX. In the other words, left rotor teeth 41L and right rotor teeth 41R are not bent for making the diagonal portions explained above. Instead of the bending, the double-sided structure is employed. U-phase magnet flux circulates around stator cores 1UO and 1UI and rotor teeth 41L and 41R. Similarly, V-phase magnet flux circulates around stator cores 1VO and 1VI and rotor teeth 41L and 41R. W-phase magnet flux circulates around stator cores 1WO and 1WI and rotor teeth 41L and 41R. Consequently, rotor structure becomes very simple, because rotor teeth 41L and 41R can employ the laminated flat steel plates. The motor torque is increased, and the iron loss and the weight are decreased.

A part of one soft flat steel sheet 2000 of left rotor teeth 41L is shown in Figure 56. The soft flat steel sheet 2000 has left rotor teeth 41L and joint portions 2001. Each joint portion 2001 connects two left rotor teeth 41L adjacent to each other in the circumferential direction PH. As the result, the laminating of the rotor teeth 41L becomes easy.

Operation of the above three-phase induction TFM is explained referring to Figure 57. The three-phase induction TFMs shown in Figures 48, 52 and 54 are driven by nine-switch-inverter 5 shown in Figure 9. However, each single-phase induction motor cannot produce a starting torque as known well. In order to the starting, inverter 5 applies a three-phase synchronous current to the three-phase induction TFM. The three-phase synchronous current has a synchronized frequency and phases of the three-phase current. Each reluctance value of each phase winding of the three-phase induction TFM changes in accordance with rotor angle, because the above three single-phase induction TFMs has rotor teeth 41L and 41R and stator teeth 21L and 21R consisting of salient.

The reluctance becomes the largest, when stator teeth 21L and 21R face rotor teeth portions 41L and 41R perfectly. The reluctance becomes the smallest, when stator teeth 21L and 21R do not face rotor teeth portions 41L and 41R perfectly. Accordingly, each of three single-phase squirrel-cage induction TFMs can perform as a synchronous reluctance motor and a switched reluctance motor by means of changing the three-phase voltage in accordance with the detected rotor angle. After the starting, the three-phase TFM can be driven as the three single-phase induction motor. Furthermore, the three single-phase induction motor can be driven as the reluctance motor by means of applying the three-phase voltage with the synchronous frequency. In the other words, the above salient type three TFMs can perform as either one of a single-phase induction machine and a single-phase reluctance machine by means of selecting the frequency of the applied voltage.

Typical starting process of the three-phase induction TFM is explained referring to Figure 57. At first, it is judged whether or not the TFM should be started (S300). At the step S302, the three-phase synchronous voltage with the synchronous frequency is applied to the TFM, if the answer is 'Yes'. At the step S304, it is judged whether or not the starting is success. Next, the three-phase voltage with the frequency, which is different from the synchronous frequency, is applied to the three-phase TFM at the step S406.

(A third arranged embodiment)
The third arranged embodiment is explained referring to Figure 58 showing a schematic axial cross-section of the three-phase induction TFM with six pairs of stator cores 101-106 and rotor cores 401-406. The six stator cores 101-106 are adjacent to each other in the axial direction AX. Similarly, the six rotor cores 401-406 are adjacent to each other in the axial direction AX. U-phase winding U1 is accommodated in U-phase stator core 101. V-phase winding V1 is accommodated in V-phase stator core 102. W-phase winding W1 is accommodated in W-phase stator core 103. The first three-phase winding consists of three phase windings U1, V1 and W1.

U-phase winding U2 is accommodated in U-phase stator core 104. V-phase winding V2 is accommodated in V-phase stator core 105. W-phase winding W2 is accommodated in W-phase stator core 106. The second three-phase winding consists of three phase windings U2, V2 and W2. The first and the second three-phase windings are connected in series or in parallel by means of switching the nine-switch inverter.

(A fourth arranged embodiment)
The fourth arranged embodiment is explained referring to Figure 59 and 60. Figure 59 is a block diagram showing a linear generator 1 driven by a pair of internal combustion engines 3000. Figure 60 is a cross-section of the linear generator 1. Linear generator 1 has a housing 4001 to which twenty four linear stator cores 3002 are fixed. Each of twenty four stator windings 3003 are accommodated in each of twenty four stator cores 3002. Linear generator 1 has two movers 3004 and 3005. Both ends of two movers 3004 and 3005 are connected to two engines 3000. Each of two movers 3004 and 305 has six pairs of left rotor teeth 41L and right rotor teeth 41R each. Left rotor teeth 41L and right rotor teeth 41R are fixed to a flat rotor base 3006 made from non-magnetic metal. The linear TFM with the double-sided structure is essentially equal to the double-sided induction TFM shown in Figure 55.

In the above embodiments, the three-phase induction TFM is explained. However, another-phase induction TFM or the reluctance TFM or a magnet synchronous TFM or a wound rotor synchronous TFM can be employed as generator 1 or motor 3 instead of the above induction TFM.

(The seventh embodiment)
The seventh embodiment is explained referring to Figures 61-62. Figure 61 is a block diagram showing the electric propulsion apparatus for driving a bus of a truck. Figure 62 is a flow chart showing selection of the combination of the driven engine or the driven engines in Figure 61. The feature of the seventh embodiment is in structure of generator 1 and engine 2 explained above. The problem of the common voltage method is that the common voltage method applying the common voltage to generator 1 and motor 3 can be adopted in a narrow range of the motor range. Because the high efficiency area of engine 2 is not wide. The common voltage method explained above can be employed in wider area, if the high efficiency area of the engine is wide.

In Figure 61, the engine consists of a first engine 211 and a second engine 212. The first engine 211 has a plurality of cylinders (not shown). The second engine 212 has a plurality of cylinders (not shown). The first engine 211 is smaller than the second engine 212. Two engines 211 and 212 share a common cylinder-block 230. A first crankshaft 213 of the first engine 211 and a second crankshaft 214 of the second engine 212 are extended along a common axis line. An axis of first generator 111 is connected to an outer end portion of the first crankshaft 213 projecting out of one end surface of the common cylinder-block 230.
The second generator 112 is connected to an outer end portion of the second crankshaft 214 projecting out of the opposite other end surface of the common cylinder-block 230.

Three phase terminals of the first generator 111 and three phase terminals of the second generator 112 are connected to rectifier 4 having six legs. The first generator 111 is smaller than second generator 112. The other circuit structure is same as the circuit configuration shown in Figure 44. Rectifier 4 can consist of the nine-switch inverter having a series-connection mode, the parallel-connection mode, the first-generator-driving mode and the second-generator-driving mode. Rectifier 4 can consist of two six-switch three-phase inverter or two nine-switch three-phase inverter.

Operation of the electric propulsion system, in particular to select the driven engine is explained referring to Figure 62. At first, it is decided whether or not the engine should be driven as S400. If it is 'Yes', it is judged whether or not an instruction value of a required torque is smaller than a predetermined small value at step 402. If it is 'Yes', the first engine 211, which is smaller engine, is started by the generator 111 at step 403. If it is 'No' at step 402, it is judged whether or not an instruction value of a required torque is smaller than a predetermined middle value at step 404. If it is 'Yes', the second engine 212, which is larger engine, is started by the generator 112 at step 405. If it is 'No' at step 404, it is judged whether or not an instruction value of a required torque is smaller than a predetermined large value at step 406. If it is 'Yes', the first engine 311 and the second engine 212 are started by the generators 111 and 112 at step 407.

A rotation speed of the started engine reaches a rotation speed of the rotating other engine, rectifier 4 applies a common three-phase voltage to the first generator 111 and the second three-phase generator 112.

(The eighth embodiment)
The eighth embodiment is explained referring to Figures 59-61. A feature of this embodiment is to employ the linear-engine-linear-generator structure shown in Figure 59 and 60, as the pair of the engine-generators shown in Figure 61. Figure 59 is a plan view. The first engine 211, which consists of a linear engine, has a left cylinder-block and a right cylinder-block, as shown in Figure 59. Similarly, the second engine 212, which consists of a linear engine, has a left cylinder-block, and a right cylinder-block, as shown in Figure 59. A pair of the left cylinder-blocks of the first engine 211 and the second engine 212 form a left common cylinder-block 3000. A pair of the right cylinder-blocks of the first engine 211 and the second engine 212 form a right common cylinder-block 3000. The first engine 211 has a left piston (not shown) in the left common cylinder-block 3000 and a right piston (not shown) in the right cylinder-block 3000. The second engine 212 has a left piston (not shown) in the left common cylinder-block 3000 and a right piston (not shown) in the right cylinder-block 3000, too.

The left piston of the fist engine 211 is connected to the left end portion of the linear mover 3004 shown in Figures 60-61. The right piston of the fist engine 211 is connected to the right end portion of the linear mover 3004 shown in Figures 60-61. Similarly, the left piston of the second engine 212 is connected to the left end portion of the linear mover 3005 shown in Figures 60-61. The right piston of the second engine 212 is connected to the right end portion of the linear mover 3005 shown in Figures 60-61.

The linear mover 3004 and the linear mover 3005 are reciprocated in a longitudinal direction independently to each other. In the other words, the first engine 211 and the second engine 212 can be driven independently to each other. Accordingly, the first engine 211 drives the linear mover 3004 at the low torque range. The first engine 211 and the second engine 212 drive the linear movers 3004-3005 at the high torque range. It is capable driving the larger second engine 212 at the middle torque range.
Consequently, the high efficiency area of the engine can be widened.

Claims (31)

1. An electric propulsion system comprising:
   a generator (1) consisting of a multi-phase motor-generator driven by an internal combustion engine (2);
   a motor (3) consisting of a multi-phase motor-generator for driving a propulsion apparatus;
   a rectifier (4) consisting of a multi-phase inverter for rectifying a multi-phase generator current supplied from the generator;
   an inverter (5) consisting of a multi-phase inverter for supplying a multi-phase motor current to the motor (3);
   a DC energy apparatus (7) connecting to the rectifier (4) and the inverter (5) via a DC link (6) connecting between the rectifier (4) and the inverter (5); and
   a controller (9) for controlling the generator (1), the engine (2) and the motor (3);
   wherein the controller (9) has a motor torque-speed map (1000) including a balance area (A), a low torque area (B) and a high torque area (C), a low speed area (D) and a high speed area (E);
   the balance area (A), the low torque area (B) and the high torque area (C) are disposed in a middle speed area between the low speed area (D) and a high speed area (E);
   the balance area (A) is disposed in a middle torque area between the low torque area (B) and the high torque area (C);
   the motor stays in the balance area (A), when the engine (2) stays in a predetermined high frequency area;
   the DC energy apparatus (7) is charged when the motor (3) is operated in the low torque area (B), and is discharged when the motor (3) is operated in the high torque area (C); and
   the controller (9) controls a speed and a torque of the engine in order to keep a condition that a generator voltage essentially accords with a motor voltage, when the motor (3) stays in the balance area (A), the low torque area (B) and the high torque area (C).
2. The electric propulsion system according to claim 1, wherein each phase terminal of the generator (1) is connected to each phase terminal of the motor (3) via each bypass switch (8); and
   each bypass switch (8) is closed in the balance area (A), the low torque area (B) and the high torque area (C) and is opened in the low speed area (D) and the high speed area (E).
3. The electric propulsion system according to claim 2, wherein the bypass switches (8) consists of a relay apparatus; and
   each phase current of the relay apparatus is reduced by means of switching the rectifier (4) and the inverter (5) just before turning-off the relay apparatus.
4. The electric propulsion system according to claim 1, wherein the DC energy apparatus (7) has a battery (71) and a boost DC-to-DC converter (72) applied a boosted voltage to the DC link (6);
   the rectifier (4) and the inverter (5) consist of a three-phase inverter each;
   the converter (72) applies the boosted voltage with three-phase full-wave rectified waveform to the DC link (6), when the motor (3) stays in the balance area (A), the low torque area (B) and the high torque area (C);
   one leg of the inverter (5) is PWM-switched, when the motor (3) stays in the balance area, the low torque area (B) and the high torque area (C); and
   another two legs of the inverter (5) is not PWM-switched, but periodically switched, when the motor (3) stays in the balance area, the low torque area (B) and the high torque area (C).
5. The electric propulsion system according to claim 4, wherein the one leg of the inverter (5), which is PWM-switched applies a smaller inter-phase voltage (Vy) having single-phase full-wave rectified waveform.
6. The electric propulsion system according to claim 1, wherein the generator (1) and/or the motor (2) consists of a three-phase induction machine.
7. The electric propulsion system according to claim 1, wherein at least one of the generator (1) and the motor (3) is capable of changing at least one of a pole-number and/or a turn number by means of changing connection of at least one of the multi-phase inverters consisting of the rectifier (4) and the inverter (5) by means of switching the multi-phase inverter.
8. The electric propulsion system according to claim 7, wherein both of the generator (1) and the motor (3) are capable of changing at least one of a pole-number and/or a turn number by means of changing connection of both of the multi-phase inverters consisting of the rectifier (4) and the inverter (5) by means of switching the multi-phase inverter.
9. The electric propulsion system according to claim 7, wherein the multi-phase inverter consists of a nine-switch three-phase inverter of which each leg consists of an upper switch, a middle switch and a lower switch, which are connected in series to each other;
   each connecting point between the upper switch and the middle switch is connected to each phase winding of a first three-phase winding of the multi-phase motor-generator;
   each connecting point between the middle switch and the lower switch is connected to each phase winding of a second three-phase winding of the motor-generator;
   the controller has a series mode and a parallel mode for switching the nine-switch inverter;
   the first and the second three-phase windings are connected in series to each other in the series mode; and
   the first and the second three-phase windings are connected in parallel to each other in the parallel mode.
10. The electric propulsion system according to claim 9, wherein the first three-phase winding is wound in a left three-phase induction machine for driving a left wheel; and
    the second three-phase winding is wound in a right three-phase induction machine for driving a right wheel.
11. The electric propulsion system according to claim 9, wherein each same phase winding of the first three-phase winding and the second three-phase winding is wound on each same stator poles of the motor-generator.
12. The electric propulsion system according to claim 9, wherein the multi-phase motor-generator consists of a three-phase induction machine;
    each phase winding of the first three-phase winding and each phase winding of the second three-phase winding are wound alternately in a circumferential direction of the three-phase induction machine; and
    both of the pole number and the turn number of the three-phase induction machine is changed by means of switching the nine-phase inverter.
13. The electric propulsion system according to claim 9, wherein the controller further has at least one single mode in order to stop to supply the motor current to either one of the first and the second three-phase windings.
14. The electric propulsion system according to claim 1, wherein the multi-phase motor-generator consists of a plurality of single-phase transverse flux machines arranged in tandem;
    each single-phase transverse flux machine has a squirrel-cage conductor surrounds each rotor salient of the single-phase transverse flux machine having stator salient; and
    the three-phase induction machine is started as a reluctance motor.
15. The electric propulsion system according to claim 14, wherein each single-phase transverse flux machine has double-sided structure with a rotor disposed between two stators in a radial direction; and
    the rotor has rotor teeth made of laminated flat steel plates laminated to an axial direction.
16. The electric propulsion system according to claim 1, wherein the internal combustion engine (2) consists of a pair of a first engine (211) and a second engine (212), which can rotate independently to each other;
    the generator (1) consists of a pair of a first generator (111) and a second generator (112);
    the first generator (111) is driven by the first engine (211), and the second generator (112) is driven by the second engine (212);
    the rectifier (4) rectifies the generator currents supplied from both of the first generator (111) and the second generator (112); and
    the controller (9) drives both of the first and the second engines (211 and 212) when a required generator current value is larger than a predetermined value, and drives only either one of the first and the second engines (211 and 212) when the required generator current value is less than the predetermined value.
17. The electric propulsion system according to claim 16, wherein the controller (9) starts the stopped second engine (211) again, when the required generator current value becomes larger than the predetermined value; and
    the controller (9) drives both of the first engine (211) and the second engine (212) at an equal rotating speed after the starting of the second engine (212) again.
18. The electric propulsion system according to claim 16, wherein the first engine (211) and the second engine (212) share a common cylinder-block (230);
    a first crankshaft (213) of the first engine (211) and a second crankshaft (214) of the second engine (212) are extended along a common axis line;
    the first generator (111) is connected to an outer end portion of the first crankshaft (213) projecting out of one end surface of the common cylinder-block (230);
    the second generator (112) is connected to an outer end portion of the second crankshaft (214) projecting out of the opposite other end surface of the common cylinder-block (230).
19. The electric propulsion system according to claim 16, wherein the first engine (211) is larger than the second engine (212);
    the controller (9) selects either one or both of the first and the second engines (211 and 212) in accordance with the required generator current value.
20. An electric propulsion system comprising:
    a generator (1) consisting of a multi-phase motor-generator driven by an internal combustion engine (2);
    a motor (3) consisting of a multi-phase motor-generator for driving a propulsion apparatus;
    a rectifier (4) consisting of a multi-phase inverter for rectifying a multi-phase generator current supplied from the generator;
    an inverter (5) consisting of a multi-phase inverter for supplying a multi-phase motor current to the motor (3);
    a DC energy apparatus (7) connecting to the rectifier (4) and the inverter (5) via a DC link (6) connecting between the rectifier (4) and the inverter (5); and
    a controller (9) for controlling the generator (1), the engine (2) and the motor (3);
    wherein both of the generator (1) and the motor (3) are capable of changing at least one of a pole-number and/or a turn number by means of changing connection of both of the multi-phase inverters consisting of the rectifier (4) and the inverter (5).
21. The electric propulsion system according to claim 20, wherein the multi-phase inverter consists of a nine-switch three-phase inverter of which each leg consists of an upper switch, a middle switch and a lower switch, which are connected in series to each other;
    each connecting point between the upper switch and the middle switch is connected to each phase winding of a first three-phase winding of the multi-phase motor-generator;
    each connecting point between the middle switch and the lower switch is connected to each phase winding of a second three-phase winding of the multi-phase motor-generator;
    the controller has a series mode and a parallel mode for switching the nine-switch inverter;
    the first and the second three-phase windings are connected in series to each other in the series mode; and
    the first and the second three-phase windings are connected in parallel to each other in the parallel mode.
22. The electric propulsion system according to claim 21, wherein the first three-phase winding is wound in a left three-phase induction machine for driving a left wheel; and
    the second three-phase winding is wound in a right three-phase induction machine for driving a right wheel.
23. The electric propulsion system according to claim 21, wherein each same phase winding of the first three-phase winding and the second three-phase winding is wound on each same stator poles of the motor-generator.
24. The electric propulsion system according to claim 21, wherein the motor-generator consists of a three-phase induction machine;
    each phase winding of the first three-phase winding and each phase winding of the second three-phase winding are wound alternately in a circumferential direction of the three-phase induction machine; and
    both of the pole number and the turn number of the three-phase induction machine is changed by means of switching the nine-phase inverter.
25. The electric propulsion system according to claim 21, wherein the controller further has at least one single mode in order to stop to supply the motor current to either one of the first and the second three-phase windings.
26. An electric propulsion system comprising:
    a generator (1) consisting of a multi-phase motor-generator driven by an internal combustion engine (2);
    a motor (3) consisting of a multi-phase motor-generator for driving a propulsion apparatus;
    a rectifier (4) consisting of a multi-phase inverter for rectifying a multi-phase generator current supplied from the generator;
    an inverter (5) consisting of a multi-phase inverter for supplying a multi-phase motor current to the motor (3);
    a DC energy apparatus (7) connecting to the rectifier (4) and the inverter (5) via a DC link (6) connecting between the rectifier (4) and the inverter (5); and
    a controller (9) for controlling the generator (1), the engine (2) and the motor (3);
    wherein the internal combustion engine (2) consists of a pair of a first engine (211) and a second engine (212), which can be can be driven independently to each other;
    the generator (1) consists of a pair of a first generator (111) and a second generator (112);
    the first generator (111) is driven by the first engine (211), and the second generator (112) is driven by the second engine (212);
    the rectifier (4) rectifies the generator currents supplied from both of the first generator (111) and the second generator (112); and
    the controller (9) drives both of the first and the second engines (211 and 212) when a required generator current value is larger than a predetermined value, and drives only either one of the first and the second engines (211 and 212) when the required generator current value is less than the predetermined value.
27. The electric propulsion system according to claim 26, wherein the controller (9) starts the stopped second engine (212) again, when the required generator current value becomes larger than the predetermined value; and
    the controller (9) drives both of the first engine (211) and the second engine (212) at an equal rotating speed after the starting of the second engine (212) again.
28. The electric propulsion system according to claim 26, wherein the first engine (211) and the second engine (212) share a common cylinder-block (230);
    a first crankshaft (213) of the first engine (211) and a second crankshaft (214) of the second engine (212) are extended along a common axis line;
    the first generator (111) is connected to an outer end portion of the first crankshaft (213) projecting out of one end surface of the common cylinder-block (230);
    the second generator (112) is connected to an outer end portion of the second crankshaft (214) projecting out of the opposite other end surface of the common cylinder-block (230).
29. The electric propulsion system according to claim 26, wherein the first engine (211) is larger than the second engine (212);
    the controller (9) selects either one or both of the first and the second engines (211 and 212) in accordance with the required generator current value.
30. The electric propulsion system according to claim 26, wherein the first engine (211) has two cylinder-blocks, which are disposed between the first generator (111) consisting of the first linear transverse flux machine; the second engine (212) has two cylinder-blocks, which are disposed between the second generator (112) consisting of the second linear transverse flux machine; the first generator (111) has a first mover (3004) of which each end portion is connected to each piston accommodated in each cylinder-block of the first engine (211); and the second generator (112) has a second mover (3005) of which each end portion is connected to each piston accommodated in each cylinder-block of the second engine (212).
31. The electric propulsion system according to claim 26, wherein the first generator (111) and the second generator (112) are adjacent to each other; the first mover (3004) and the second mover (3005) are arranged in parallel to each other; one of the two cylinder-blocks of the first engine (211) and one of the two cylinder-blocks of the second engine (212) consist of a left common cylinder-block; and the other one of the two cylinder-blocks of the first engine (211) and the other one of the two cylinder-blocks of the second engine (212) consists of a right common cylinder-block.

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