WO2011092774A1

WO2011092774A1 - Boost dc-to-dc converter and power converter powered by the same

Info

Publication number: WO2011092774A1
Application number: PCT/JP2010/006674
Authority: WO
Inventors: Shouichi Tanaka
Original assignee: Three Eye Co., Ltd.
Priority date: 2010-02-01
Filing date: 2010-11-12
Publication date: 2011-08-04
Also published as: WO2011092774A9

Abstract

An object of the invention is to provide a boost DC-to-DC converter capable of changing a boost ratio between an input voltage and an output voltage smoothly. Another object of the invention is to provide a simple power converter for driving a five-phase switched reluctance motor. Two pairs of one reactor and one DC power resource are connected in series with a series switch. Moreover the two pairs are connected in parallel via two parallel switches. Each of the two pairs is short-circuited via the series switch by each of the parallel switches. The five-phase power converter applying five phase voltages to five phase windings of a switched reluctance motor has at least six transistors and six freewheeling diodes. two phase windings of five phase windings having a star connection configuration is turned on simultaneously and turned off simultaneously. One of the two phase windings is connected to a high potential line and the other one of the two phase windings is connected to a low potential line, when two transistors are turned on simultaneously.

Description

BOOST DC-TO-DC CONVERTER AND POWER CONVERTER POWERED BY THE SAME

Cross-Reference to Related Application

This application claims benefit, for example under 35 U.S.C.119, from PCT/JP2010/003748 filed on Jun/04/2010 and PCT/JP2010/004724 filed on July/23/2010, the entire content of which is incorporated herein reference. Moreover, the contents of the above application should be used to consider this application.

Background of Invention

1. Field of the Invention
The present invention relates to a boost DC-to-DC converter and a power converter for driving a five-phase switched reluctance motor. In particular, the invention discloses a novel DC-to-DC converter for applying a variable boost voltage and a novel power converter for driving a five-phase switched reluctance motor.

2. Description of the Related Art
It is desirable to change a DC link voltage applied to a motor-driving circuit for driving a traction motor of a battery vehicle and so on, because the traction motor has a variable speed and a variable current in a wide range. The motor-driving circuit includes an inverter for driving a synchronous motor or an induction motor and also includes a power converter for driving a switched reluctance motor.

Japan Unexamined Patent Publication JPA 2004/234476 shows one method for changing the DC link voltage Vx applied to a motor-driving circuit 300 for driving a motor, as shown in Figure 1. A DC link voltage Vx is changed by a DC-to-DC converter 600, which is called the boost converter briefly. In Figure 1, boost converter 600 has two boost choppers, which have reverse-switching phases to each other. The first boost chopper consists of a reactor 601, a lower transistor 603 and an upper transistor 605. The second boost chopper consists of a reactor 602, a lower transistor 604 and an upper transistor 606. Two boost choppers apply two boost voltages to the motor-driving circuit 300 alternately. Ripple of the current flowing between a battery 100 and motor-driving circuit 300 is reduced by employing two boost choppers. However, a conventional boost converter including the dual-chopper-type boost chopper type can not output high power at a high boost ratio, because turning-on periods of lower transistors 603 and 604 are extended.

United Patent No. 6,140,799 and 6,674,180 shows another known method for change DC link voltage Vx as shown in Figure 2. A series-parallel-changing circuit 500 consisting of three switches 501-503 has two modes. In the series mode, two

batteries

101 and 102 are connected in series to each other by a series switch 501. In the parallel mode, two

batteries

101 and 102 are connected in parallel to each other by two

parallel switches

502 and 503. However, the single-parallel-changing circuit 500 only outputs one of two values of DC link voltage Vx. Moreover, mechanical shock and electrical shock of changing the connection become large.

U. S. Patent. No. 6,528, 964 proposes a current regulator for changing an input current of the power converter for driving the SRM, in accordance with a required torque and a detected angular speed. However, 964' patent does not disclose to employ the boost converter in order to shorten a current-decreasing period when a freewheeling phase current of the SRM is reduced.

U. S. Patent. No. 5,111,095 invented by Hendershot shows a five-phase 10/8 SRM with two kinds of rotor pole pitches disposed alternately. However, the five-phase SRM requires a complicated power converter with many switching elements including transistors and freewheeling diodes. For example, a conventional five-phase power converter needs ten transistors and ten freewheeling diodes.

U. S. Patent. No. 6,140,799 U. S. Patent. No. 6,674,180 U. S. Patent. No. 6,528, 964 U. S. Patent. No. 5,111,095

An object of the invention is to provide a boost DC-to-DC converter capable of changing a boost ratio between an input voltage and an output voltage smoothly. Another object of the invention is to provide a simple power converter for driving a five-phase switched reluctance motor.

As for a first aspect of the invention, a boost chopper type DC-to-DC converter (1) has two pairs consisting of a reactor and a DC power source each. A series switch connects the two pairs in series to each other. Two parallel switches connect the two pairs in parallel to each other. Each of the two pairs is short-circuited via the series switch by turning-on of each of the two parallel switches. Accordingly, the boost converter can apply two constant values of the DC voltage without switching. Furthermore, the boost DC-to-DC converter can change a variable DC voltage smoothly in the wide range with less switching loss.

According to a preferred embodiment, the boost converter has a series connection stage (A), a parallel connection stage (B) and a short-circuit stage (C, D and E). The stage (A) has the turned-on series switch (110) and the turned-off parallel switches (120) and (130). The stage (B) has the turned-off series switch (110) and the turned-on parallel switches (120) and (130). The short-circuit stage (C, D and E) has at least one of the short-circuited first pair and the short-circuited second pair. Accordingly, a plurality of the boost mode can be executed by selecting of the above stages.

According to another preferred embodiment, the series stage (A) and the short-circuit stage (C, D and E) are executed alternately. As the result, the boost converter can apply a high boost voltage with less switching loss. According to another preferred embodiment, the parallel stage (B) and the short-circuit stage (C, D and E) are executed alternately. As the result, the boost converter can apply a low boost voltage with less switching loss.

According to another preferred embodiment, the boost converter applies a boosted DC voltage (Vx) to a power converter (2) for driving a switched reluctance motor (60). The power converter (2) has a plurality of transistors (201-206), which control phase currents flowing through a plurality of phase windings (401-405) of the switched reluctance motor (60). The power converter (2) has a transient period (Pt) while a freewheeling current of the phase windings (401-405) flows by means of turning-off of at least one of the transistors (201-206). The DC-to-DC converter (1) increases the boosted DC voltage (Vx) in the transient period (Pt). Accordingly, the freewheeling current is decreased quickly.

According to another preferred embodiment, a first winding (151) of the first reactor (150) and a second winding (161) of the second reactor (160) are wound on a common core (8) consisting of a closed magnetic circuit. The first winding (151) wound on a first core leg (81) of the common core (8) excites a first magnetic flux. The second winding (161) wound on a second core leg (82) of the common core (8) excites a second magnetic flux. The common core has a bypass core leg (85) flowing difference component of the first magnetic flux and the second magnetic flux, of which flowing directions are same to each other. The bypass core leg (85) has smaller cross-section than each of the first and the second core legs (81, 82). Accordingly, the reactors (150, 160) of the boost converter (1) become small and can reduce a weight.

According to another preferred embodiment and another aspect of the invention, a five-phase switched reluctance motor (60) has five phase windings (401-405) wound on five stator poles of a stator core respectively. One ends of the five phase windings (401-405) are connected to a neutral point (N). A power converter (2) has at least six transistors (201-206) and six freewheeling diodes (301-306). A first and a third phase windings (401, 403) are connected to the high potential line (6) via the transistors (201, 203) and are connected to the low potential line (7) via the freewheeling diodes (301, 303). A second and a fourth phase windings (402, 404) are connected to the low potential line (7) via the transistors (202, 204) and are connected to the high potential line (6) via the freewheeling diodes (302, 304). A fifth phase windings (405) is connected to the high potential line (6) via the transistor (205) and the freewheeling diode (306), and is connected to the low potential line (7) via the transistor (206) and the freewheeling diode (305). One of the transistors (201, 203 and 205) connected to the high potential line (6) and another one of the transistors (202, 204 and 206) connected to the low potential line (7) are turned on and turned off simultaneously. Accordingly, the five-phase SRM can be driven by the five-phase power converter with simple structure.

According to another preferred embodiment and another aspect of the invention, a five-phase switched reluctance motor (60) has five phase windings (401-405) wound on five stator poles of a stator core respectively. One ends of the five phase windings (401-405) are connected to a neutral point (N). The power converter (2) has five half bridges having a pair of an upper transistor and a lower transistor. Each of half bridge is connected to the other ends of the five phase windings (401-405) respectively. The upper transistor connects the phase winding to a high potential line (6). The lower transistor connects the phase winding to a low potential line (7). One of the upper transistors and one of the lower transistors are turned on and turned off simultaneously. Accordingly, the five-phase SRM can be driven by the five-phase power converter with simple structure.

Figure 1 is a circuit diagram showing a conventional dual chopper type DC-to-DC boost converter for driving a motor-driving circuit. Figure 2 is a circuit diagram showing a conventional series-parallel-changing circuit of two batteries for driving a motor-driving circuit. Figure 3 is a circuit topology showing a motor-driving-apparatus having the boost converter with dual boost choppers. Figure 4 is a circuit diagram showing a series stage of the boost converter shown in Figure 3. Figure 5 is a circuit diagram showing a short-circuited stage of the boost converter shown in Figure 3. Figure 6 is a circuit diagram showing a parallel stage of the boost converter shown in Figure 3. Figure 7 is a circuit diagram showing an open stage of the boost converter shown in Figure 3. Figure 8 is a circuit diagram showing one partial short-circuited stage of the boost converter shown in Figure 3. Figure 8 is a circuit diagram showing another partial short-circuited stage of the boost converter shown in Figure 3. Figure 10 is a timing chart showing a DC link voltage applied by the boost converter shown in Figure 3. Figure 11 is a timing chart showing a DC link voltage applied by the conventional boost converter shown in Figure 1. Figure 12 is a timing chart showing a DC link voltage applied by the conventional series-parallel connection circuit shown in Figure 2. Figure 13 is a circuit topology for showing an electrical energy accumulator employing two EDLCs. Figure 14 is a block diagram showing a power conditioner for solar cells. Figure 15 is a cross-section showing a common reactor consisting of two reactors employed by the boost converter shown in Figure 3. Figure 16 is a cross-section showing a common reactor consisting of two reactors employed by the boost converter shown in Figure 3. Figure 17 is a circuit topology showing a first example of a five-phase power converter for driving a five-phase switched reluctance motor. Figure 18 is a schematic diagram for showing magnetic polarities of five stator poles in five rotor angular periods of the five-phase SRM of the first example... Figure 19 is a schematic cross-section showing five-phase SRM with four U-shaped rotor poles at a first angular position. Figure 20 is a schematic cross-section showing five-phase SRM with four U-shaped rotor poles at a second angular position. Figure 21 is a schematic cross-section showing five-phase SRM with four U-shaped rotor poles at a third angular position. Figure 22 is a schematic cross-section showing five-phase SRM with four U-shaped rotor poles at a fourth angular position. Figure 23 is a schematic cross-section showing five-phase SRM with four U-shaped rotor poles at a fifth angular position. Figure 24 is a schematic diagram for showing magnetic polarities of five stator poles in five rotor angular periods of the five-phase SRM of a second example. Figure 25 is a circuit topology showing the second example of a five-phase power converter for driving a five-phase switched reluctance motor. Figure 26 is a schematic diagram for showing magnetic polarities of five stator poles in five rotor angular periods of the five-phase SRM of a third example. Figure 27 is a circuit topology showing the third example of a five-phase power converter for driving a five-phase switched reluctance motor. Figure 28 is a timing chart for showing a boosted DC link voltage applied to the five-phase power converter. Figure 29 is a schematic axial cross-section of a disc-shaped inner-rotor-radial-gap type SRM capable of reducing radial vibration. Figure 30 is a schematic radial cross-section of one half of an inner-rotor-radial-gap type SRM capable of reducing radial vibration.

Detailed Description of Preferred Embodiment

(Structure)
Figure 3 shows a circuit topology of a motor-driving apparatus of an embodiment. The motor-driving apparatus drives a motor 60, for example a switched reluctance motor-generator (SRMG). The motor-driving apparatus consists of a boost chopper type DC-to-DC converter 1, a motor-driving circuit 2 and a smoothing capacitor 3. The motor-driving circuit 2 consists of a power converter for driving the switched reluctance motor. Motor-driving circuit 2 can consist of an inverter for driving a synchronous motor or an induction motor. The boost chopper type DC-to-DC converter 1 called the boost converter boosts battery voltages Vb of two

batteries

4 and 5, and applies a DC link voltage Vx to power converter 2 and smoothing capacitor 3. Power converter 2 applies a multi-phase voltage to a motor 60.

Boost converter 1 has two boost choppers consisting of a series switch 110,

parallel switches

120 and 130 and an output switch 140. The boost converter 1 has a first reactor 150 and a second reactor 160. The first boost chopper consists of the reactor 150 and the

switches

110, 120 and 140. The second boost chopper consists of the reactor 160 and the

switch

110, 130 and 140. As well-known, boost converter 1 can employ a diode instead of the output switch 140, when the boost converter 1 is one directional type. Boost converter 1 outputs a DC link voltage Vx to power converter 2 and smoothing capacitor 3 via a pair of

DC link lines

6 and 7 consisting of a high potential line 6 and a low potential line 7.

(Operation)
Operation of boost converter 1 is explained referring to Figures 4-9. Figures 4-9 show six connection states of the boost converter 1.

Batteries

4 and 5 have 125V each. Figure 4 shows a series connection state A. In the state A,

parallel switches

120 and 130 are turned off, and series switch 110 is turned on. Output switch 140 should be turned on. DC link voltage Vx becomes 250 V or more than 250V, because

reactors

150 and 160 connected in series to each other have magnetic energies and output voltages each.

Figure 5 shows a full short-circuit state C. In the state C, three

switches

110, 120 and 130 are turned on. The output switch 140 is turned off. Currents of the

reactors

150 and 160 are increased, and

reactors

150 and 160 accumulate magnetic energies. Figure 6 shows a parallel connection state B. In the state B,

parallel switches

120 and 130 are turned on, and series switch 110 is turned off. Output switch 140 should be turned on. DC link voltage Vx becomes 125V or more than 125V, because

reactors

150 and 160 connected in parallel to each other has magnetic energies and has voltages each.

Figure 7 shows an open connection state D. In the state D, three switches 110-130 are turned off. By the turning-off of three switches 110-130 and the output switch 140, the battery voltage is separated safely. Figure 8 shows a first half short-circuit connection state E. In the state E, parallel switch 120 and series switch 110 are turned on, and parallel switch 130 is turned off. Output switch 140 can be turned on. DC link voltage Vx becomes 125V or more than 125V by reactor 160 and battery 5. Reactor 150 accumulates magnetic energy. It is important that magnetizing of reactor 150 and demagnetizing of reactor 160 are executed simultaneously. Moreover, a freewheeling current of battery 4 and a boost current of battery 5 have opposite directions to each other in parallel switch 120, when the boost converter outputs the boost current. As the result, the resistive loss of parallel switch 120 is reduced.

Figure 9 shows a second half short-circuit connection state F. In the state F, parallel switch 130 and series switch 110 are turned on, and parallel switch 120 is turned off. DC link voltage Vx becomes 125V or more than 125V by reactor 150 and battery 5. Reactor 160 accumulates magnetic energy. It is important that magnetizing of reactor 160 and demagnetizing of reactor 150 are executed simultaneously. Moreover, a freewheeling current of battery 5 and a boost current of battery 4 have opposite directions to each other in parallel switch 130, when the boost converter outputs the current. As the result, the resistive loss of parallel switch 130 becomes is reduced.

A plurality of the states selected in the states A-F can be executed alternately or in turn for operating a selected one of boost modes. In one high boost mode, the states A and C are operated alternately with a predetermined career frequency. A boost ratio is controlled by changing a period ratio, a PWM duty ratio, between the states A and C. In one low boost mode, the states B and C are operated alternately with a predetermined career frequency. The boost ratio is controlled by changing a period ratio, a PWM duty ratio, between the states B and C.

In another high boost mode, the states E, A, F and A are operated in turn with a predetermined career frequency. In another low boost mode, the states E, B, F and B are operated in turn with a predetermined career frequency. In the states E and F, the current ripple is reduced, because one reactor accumulates the magnetic energy, and another reactor consumes the magnetic energy. The boost ratio can be controlled by changing the duty ratio.

Figure 10 is a timing chart showing DC link voltage Vx changed by changing the modes or the states. In a period T1 employing the parallel connection state B, DC link voltage Vx becomes 125V. In a period T3 employing the series connection state A, the DC link voltage Vx is 250V. In a period T2 between the periods T1 and T3, the low boost mode is employed. DC link voltage Vx becomes an intermediate value between 125V and 250V. In a period T4, the high boost mode is employed. DC link voltage Vx becomes more than 250V.

Figure 11 is a timing chart showing DC link voltage Vx applied by the conventional boost converter shown in Figure 1. Figure 12 is a timing chart showing the voltage Vx applied by the conventional series-parallel-changing circuit shown in Figure 2. Consequently, the boost converter 1 shown in Figure 3 can apply either one of two constant values 125V and 250V of the DC link voltage Vx without switching of boost converter 1. Furthermore, boost converter 1 can change DC link voltage Vx smoothly and widely. Switching loss and current ripple of the boost converter 1 are reduced by means of selecting the best boost mode of the boost converter 1 in accordance with a value of DC link voltage Vx. For example, resistive power loss of the boost converter becomes 25% in the parallel state B, because the boost currents flow in parallel.

Figures 13 shows one arranged design of boost converter 1 shown in Figure 3. In Figure 13, an electrical energy accumulator 1A employs two

EDLCs

4A and 5A, which are electric double layer capacitors. The accumulator 1A has the circuit topology shown in Figure 3. Moreover, it is well-known that the boost chopper can be used as a step-down converter, when a current flows to opposite directions to each other. Accordingly, accumulator 1A accumulates the magnetic energy and outputs the electrical current. When voltages of

EDLCs

4A and 5A are small, the states A and C can be executed alternately. When the voltages of

EDLCs

4A and 5A is large, the states B and C can be executed alternately.

Reactors

150 and 160 become small, when windings of

reactors

150 and 160 are wound on a common magnetic core.

Figures 14 shows another arranged design of boost converter 1 shown in Figure 3 Figure 14 shows a power conditioner for solar cells 4B and 5B. The power conditioner has boost converter 1, smoothing capacitor 3 and a three-phase inverter 2. Boost converter 1 has the circuit topology shown in Figure 3 or Figure 13. The three-phase inverter 2 outputs a three-phase voltage with predetermined amplitude to a three-phase grid network 700. Figures 15 and 16 are schematic cross-sections showing a preferred example of a common reactor consisting of

reactors

150 and 160 shown in Figure 3. The common reactor has two

windings

151 and 161 wound on a common core 8. The winding 151 of reactor 150 is wound around a first core leg 81 of the common core 8. The winding 161 of reactor 160 is wound around a second core leg 82 of the common core 8. The

core legs

81 and 82 are magnetically connected by

core yokes

83 and 84 for forming a closed magnetic circuit. Moreover, the core yokes 83 and 84 are magnetically connected by an intermediate core leg 85 having smaller cross-section than

core legs

81 and 82. The magnetic flux excited by winding 151 has same direction as the magnetic flux excited by winding 161. The intermediate core leg 85 can only flow the difference of the two magnetic fluxes. As the result,

reactor

150 and 160 can become small.

(A first example of a five-phase power converter 2)
The first example of the five-phase power converter 2 for driving a five-phase SRM is explained referring to Figures 17 and 18. Figure 17 shows a circuit topology of five-phase power converter 2 for driving a five-phase switched reluctance motor shown in Figures 3 and 19-23. Figure 18 shows a timing chart showing magnetic polarities of each stator poles A-E of the five-phase SRM shown in Figures 19-23. Figures 19-23 are schematic diagrams for showing five angular positions of the five-phase 10/8 SRM with four U-shaped rotor poles.

As shown in Figure 19, the SRM being similar to the Hendershot's five-phase 10/8 SRM has two rotor pitches alternately in a circumferential direction of a rotor 10. In Figures 19-23, the five-phase SRM has two sets of five phase windings 401-405 constituting a stator winding. Each of five phase windings 401-405 is wound on each of stator poles A-E of the stator 201 in turn. In Figure 17, five-phase power converter 2 consists of six transistors 201-206 and six freewheeling diodes 301-306. The

upper transistors

201, 203 and 205 connect the high potential line 6 and the

phase windings

401, 403 and 405 respectively. The

lower transistors

202, 204 and 206 connect the low potential line 7 and the

phase windings

402, 404 and 405 respectively. Other ends of phase windings 401-405 are connected to a neutral line N. Namely, five phase windings 401-405 has a star configuration connection.

The lower

freewheeling diodes

301, 303 and 305 are connected to one ends of

phase windings

401, 403 and 405 respectively. The upper

freewheeling diodes

302, 304 and 306 are connected to one ends of

phase windings

402, 404 and 406 respectively. Each of transistors switched synchronously can be connected to each of freewheeling diodes 301-306 in parallel due to reduce the known diode voltage drop. Boost converter 1 shown in Figure 3 applies boosted DC link voltage Vx to power converter 2. [0033]
In Figure 19, five-phase 10/8 SRM has a stator 9 and a rotor core 10. The stator 9 has two sets of five stator poles A-E connected magnetically to each other with a cylinder-shaped stator core back 90. The rotor core 10 has four U-shaped rotor pole cores 101-104 fixed on an outer circumferential surface of a nonmagnetic cylinder portion 10A press-fixed on an axis 11. Each of U-shaped rotor pole cores 101-104 having two rotor poles 105 each are disposed with a constant circumferential pitch on the outer surface of the rotor core back 10A. Arrangement of ten rotor poles 105 is same as it of the Hendershot's five-phase 10/8 SRM.

Rotor 10 has two kinds of circumferential rotor pole gaps, which are four narrow gaps and four wide gaps. The narrow gap and the wide gap are disposed alternately between adjacent two rotor poles 105. A circumferential width of the wide rotor pole gap between adjacent two U-shaped rotor poles is about 150% of a circumferential width of the narrow rotor pole gap between adjacent two rotor poles of one U-shaped rotor pole. Each angular position of the rotor 10 at each time t1, t2, t3, t4 and t5 is shown in Figures 19-23.

In Figure 19,

transistors

205 and 204 are turned on in a period from t3 to t4. A phase currents Ied is supplied to the phase winding 405 and 404. In Figure 20,

transistors

203 and 202 are turned on in a period from t4 to t5. A phase currents Icb is supplied to the

phase windings

403 and 402. In Figure 21,

transistors

201 and 206 are turned on in a period from t5 to t1. A phase currents Iae is supplied to the

phase windings

401 and 405. In Figure 22,

transistors

203 and 204 are turned on in a period from t1 to t2. A phase current Icd is supplied to the

phase windings

403 and 404. In Figure 23,

transistors

201 and 202 are turned on in a period from t2 to t3. A phase currents Iab is supplied to the phase winding 401 and 402. It should be considered that the phase current Iae in the period from t5 to t1 flows toward an opposite direction to the phase current Ied in the period from t3 to t4.

Furthermore, as considered in Figures 17, one of

upper transistors

201, 203 and 205 and one of

lower transistors

202, 204 and 206 are turned on at one time and turned off at one time. As the result, an electric potential of the neutral line N is not changed by the turning-on and the turning-off of the two transistors at one time. It means that the single-switch-per-phase power converter 2 shown in Figure 17 does not needs well-known two split capacitors which are required in a conventional split voltage type converter with the single-switch-per-phase topology.

In Figures 19-23, dotted lines show the magnetic flux flowing in long paths of stator core back 90. Real lines show the magnetic flux flowing in short paths. Iron loss of the core back 90 is reduced by the magnetic flux in the long paths of stator core back 90.

(A second example of a five-phase power converter 2)
The second example of the power converter 2 for driving a five-phase SRM is explained referring to Figures 24 and 25. Figure 24 shows timing chart showing magnetic polarities of stator poles A-E of the five-phase SRM of the second example. Figure 25 shows a circuit topology of a five-phase power converter 2 for driving a five-phase SRAM of the second example. The five-phase SRAM of the second example has the same structure as the SRM shown in Figure 19-23 except the magnetic polarities of two sets of stator poles A-E. In the other words, the phase currents of five phase windings 401-405 have different flow direction from the phase currents shown in Figure 17.

The magnetic polarities of the second example shown in Figure 24 are different from the magnetic polarities of the first example shown in Figure 18. The magnetic polarities of stator poles A, C in Figure 24 are changed alternately. Accordingly, the power converter 2 shown in Figure 25 has additional transistors 201' and 203' instead of the

freewheeling diodes

301 and 303 shown in Figure 17.

In the period t1-t2 shown in Figure 22, transistors 204' and 203' are turned on. The freewheeling current flows via the transistor 203 and the diode 304. In the period t2-t3 shown in Figure 23,

transistors

201 and 202 are turned on. The freewheeling current flows via the transistor 201' and the diode 302. In the period t3-t4 shown in Figure 19, transistors 204' and 206 are turned on. The freewheeling current flows via the transistor 205 and the diode 304. In the period t4-t5 shown in Figure 20,

transistors

203 and 202 are turned on. The freewheeling current flows via the transistor 203' and the diode 302. In the period t5-t1 shown in Figure 21, transistors 205 and 201' are turned on. The freewheeling current flows via the

transistor

201 and 206.

According to the above-explained second example, the five-phase power converter 2 needs eight transistors and two freewheeling diodes. Moreover, the iron loss of the stator core back is reduced, because changing of the magnetic flux in the long paths is reduced. Furthermore, one of upper transistors and one of lower transistors are turned on at one time and turned off at one time, too. As the result, an electric potential of the neutral line N is not changed by the turning-on and the turning-off of two transistors at one time.

(A third example of a five-phase power converter 2)
The third example of the power converter 2 for driving a five-phase SRM is explained referring to Figures 26 and 27. Figure 26 shows a timing-chart showing magnetic polarities of stator poles A-E of the five-phase SRM of the third example. Figure 27 shows a circuit topology of a five-phase power converter 2 for driving a five-phase SRAM of the third example. The five-phase SRAM of the third example has the same structure as the SRM shown in Figure 19-23 except the magnetic polarities of two sets of stator poles A-E. In the other words, the phase currents of five phase windings 401-405 have different flow direction from the phase currents shown in Figure 17.

The magnetic polarities of the third example shown in Figure 26 are different from the magnetic polarities of the first and the second examples shown in Figures 18 and 24. The magnetic polarities of stator poles A-E in Figure 26 are changed alternately. Accordingly, power converter 2 shown in Figure 27 has additional transistors 201', 202', 203' and 204' instead of the

freewheeling diodes

301, 302, 303 and 304 shown in Figure 17.

In the period t1-t2 shown in Figure 22,

transistors

203 and 204 are turned on. The freewheeling current flows via the transistor 203' and the transistors 204'. In the period t2-t3 shown in Figure 23,

transistors

201 and 202 are turned on. The freewheeling current flows via the transistor 201' and the transistor 202'. In the period t3-t4 shown in Figure 19, transistors 204' and 206 are turned on. The freewheeling current flows via the transistor 204 and the transistor 205. In the period t4-t5 shown in Figure 20, transistors 202' and 203' are turned on. The freewheeling current flows via the transistor 202 and the transistor 203. In the period t5-t1 shown in Figure 21, transistors 205 and 201' are turned on. The freewheeling current flows via the

transistor

206 and 201.

According to the above-explained third example, five-phase power converter 2 needs ten transistors. The five phase currents and five freewheeling currents flow through the ten transistors. As the result, current concentration is reduced. Furthermore, one of upper transistors and one of lower transistors are turned on at one time and turned off at one time, too. As the result, an electric potential of the neutral line N is not changed by the turning-on and the turning-off of two transistors at one time.

(Waveform of DC link voltage Vx)
The boost converter 1 shown in Figures 3 and 17 applies DC link voltage Vx to five-phase power converter 2 shown in Figure 17. Figure 28 is a timing chart showing schematic waveforms of five phase voltages Va, Vb, Vc, Vd and Ve and five phase currents Iab, Icb, Icd, Ied and Iae. The phase voltage Va is applied to phase winding 401. The phase voltage Vb is applied to phase winding 402. The phase voltage Vc is applied to phase winding 403. The phase voltage Vd is applied to phase winding 404. The phase voltage Ve is applied to phase winding 405. The five phase currents Iab, Icb, Icd, Ied and Iae are shown in Figure 17.

In Figure 28, boost converter 1A boosts DC link voltage Vx during each of transient periods Pt. The transient period Pt means a period when a phase current rises up mostly and a freewheeling current falls down mostly. Each of phase voltages Va, Vb, Vc, Vd and Ve is applied in each pair of the transient period Pt and a constant-current period Pc. Each of phase voltages Va, Vb, Vc, Vd and Ve is increased in each transient period Pt, which is a predetermined period just after when the previous phase switch is turned off and just after the present switch was turned on. The freewheeling current of the previous phase charges the battery in the transient period Pt. A present phase current increases in the transient period Pt. As the result, rising-up of the phase current of the present phase becomes quickly, and the freewheeling current is decreased quickly, because the phase voltages Va, Vb, Vc, Vd and Ve are increased in the transient period Pt by means of boosting DC link voltage Vx.

For example, each phase current keeps a predetermined constant value in a constant-current period Pc. Consequently, the transient period Pt is shortened by means of applying the increased phase voltage in the transient period Pt, because quick increasing of the phase current and quick decreasing of the freewheeling current are realized by means of increasing of DC link voltage Vx in the transient period Pt.

It is possible to separate smoothing capacitor 3 from high potential line 6 during transient period Pt by means of employing a separating transistor connected to smoothing capacitor 3 in series to each other. By turning-off of the separating transistor, changing of the voltage Vx becomes rapidly. Furthermore, boost converter 1 can change amplitude of the DC link voltage Vx in accordance with a required value of the motor torque, too.

According to a preferred embodiment, either one of one turned-on upper transistor and one turned-on lower transistor of the five-phase power converter 2 is switched with a PWM method in the constant-current period Pc in order to keep the phase current constant in the constant-current period Pc. For example, transistors 203 is switched with a PWM method in the constant-current period Pc of the period from the time t1 to time t2. Accordingly, a freewheeling current circulates diode 303, phase winding 403, phase winding 404, turned-on transistors 204, when transistor 203 is turned off.

It is possible to switch the lower transistor 204 with the PWM method instead of switching of transistor 203. A freewheeling current circulates diode 304, turned-on transistors 203, phase winding 403, phase winding 404, when transistor 204 is turned off. Moreover,

transistors

203 and 204 can be switched with the PWM method alternately in order to decrease heating of

transistors

203 and 204. This freewheeling of the phase current reduces a current ripple of boost converter 1 and

batteries

4 and 5.

(Another discussion 1)
Another discussion 1 is described hereinafter. DC link voltage Vx applied to power converter 2 in the transient period Pt should be changed in accordance with a rotating speed and a torque instruction value. The DC link voltage Vx should be increased at a high value of the rotating speed in order to rise the phase current and to reduce the freewheeling current (regenerative current) quickly, because an absolute time of the transient period Pt is reduced. Moreover, DC link voltage Vx should be increased at a high value of the torque in order to rise the phase current and to reduce the freewheeling current (regenerative current) quickly, because the value of the phase current in the constant-current period Pc must be high. A starting time point of the constant-current period Pc can be delayed at a high value of phase current. A ending time point of the constant-current period Pc can be started earlier at a high value of phase current.
Furthermore, the rising rate of the rising current and the falling rate of the freewheeling current in the transient period Pt can be controlled in accordance with the rotating speed and the torque instruction value.

(Another discussion 2)
Another discussion 2 is described hereinafter. A pair of one upper transistor and one lower transistor should be turned on earlier than the boosting of the DC link voltage Vx at in order to apply the phase voltage to the phase winding. Accordingly, switching loss of the switches 201-206 of power converter 2 can be decreased.

(Another discussion 3)
Another discussion 3 is described hereinafter. The switched reluctance motor should have a large diameter and a short axial length for reducing acoustic noise. Main component of the acoustic noise is generated by a cylinder-shaped wall portion of a motor housing of which an inner surface is fixed to a stator core of the SRM. Accordingly, the cylinder-shaped wall portion of a motor housing vibrates toward the radius direction. However, the radial vibration of the cylinder-shaped wall portion is reduced, because the cylinder-shaped wall portion supported by both of side walls of the motor housing in the axial direction.

The SRM with the large diameter and the short axial length is preferable to an in-wheel motor of an EV. Moreover, it is preferable for the SRM with the large diameter and the short axial length to have a large number of stator poles. Because, many stator poles generate radial magnetic forces. For example, a five-phase SRM with the U-shaped rotor poles has eight stator poles magnetized simultaneously, when the SRM has twenty stator poles. Moreover, an axial length of the stator pole should have mostly equal to a circumferential width of the stator pole in order to reduce a resistive power loss of the phase winding.

Figure 29 shows one example of the SRM with a large diameter and a short axial length. Figure 29 is a schematic axial cross-section of a disc-shaped SRM. A stator core 4001 is sandwiched by a front disc portion 5001 and a rear disc portion 5002 of a motor housing. Each of the

disc portions

5001 and 5002 has two cylinder-shaped

portions

5005 and 5006 extending from outer portions of

disc portions

5001 and 5002 each. The inner cylinder-shaped portions 5005 come into contact with an outer circumferential surface of stator core 4001. The outer cylinder-shaped portions 5006 are apart radial outwardly from the cylinder-shaped portions 5005 with the predetermined distance. Both top portions of cylinder-shaped portions 5005 come into contact to each other. Both top portions of cylinder-shaped portions 5006 come into contact to each other.

Accordingly, a cylinder-shaped space 6000 is formed between two cylinder-shaped

portions

5005 and 5006. Cooling fluid circulates into a cooling fluid passage consisting of the cylinder-shaped space 6000 accommodating a V-character-shaped beam 1000. Two top portions of the V-character-shaped beam 1000 are joined to two root portions of the outer cylinder-shaped portions 5006. A center portion of V-character-shaped beam 1000 is joined to the top portions of inner cylinder-shaped portions 5005. As the result, radial component of magnetic vibration of inner cylinder-shaped portions 5005 caused by the stator core 4001 is reduced by the V-character-shaped beam 1000 effectively. Consequently, vibration of outer cylinder-shaped portions 5006 is decreased largely. In the other words, the V-character-shaped beam 1000 extending diagonally from the axial direction and the radial direction restrains the vibration of the outer cylinder-shaped portions 5006.

The above V-character-shaped beam 1000 extending diagonally in the cylinder-shaped space 6000 surrounding the stator core 4001 has superior benefits for the motor, in particular the SRM. The summary of the beam is described as bellow.

A motor having a cylinder-shaped stator core 4001 sandwiched by a front disc portion 5001 and a rear disc portion 5002 of a motor housing having a cylinder-shaped space 6000 surrounding the stator core 4001;
wherein the motor housing has a V-character-shaped beam 1000 extending diagonally in the cylinder-shaped space 6000 surrounded by an inner cylinder-shaped portion 5005 and an outer cylinder-shaped portion 5006 of the front disc portion 5001 and the rear disc portion 5002;
two top portions of the beam 1000 come into contact with two root portions of the outer cylinder-shaped portion 5006; and
an axial center portion of the beam 1000 come into contact with an axial center portion of the stator core 4001 across the inner cylinder-shaped portion 5005.

Figure 30 shows another vibration reduction example of the five-phase SRM with ten stator poles. Figure 30 is a schematic radial cross-section of one half of an inner-rotor-radial-gap type SRM. A stator core 7000 having ten stator poles (not shown) surrounds a rotor core 8000 having eight rotor poles (not shown), which is already explained. The rotor core 8000 is press-fixed to a rotating axis 8001. An outer circumferential surface of the cylinder-shaped stator core 7000 with a stator winding (not shown) faces an inner circumferential surface of a cylinder-shaped portion 9000 of motor housing across a cylinder-shaped cooling fluid passage 9001 with a predetermined small radial length.

A ring-shaped spring plate 9002 having corrugated shape is accommodated in the cylinder-shaped cooling fluid passage 9001. Ten outer bending portions 9003 come into contact with the inner circumferential surface of cylinder-shaped portion 9000 of the motor housing. Ten inner bending portions 9004 come into contact with the outer circumferential surface of stator core 7000. An angle between the outer bending portion 9003 and the inner bending portion 9004 being adjacent to each other is equal to an angle between two stator poles being adjacent to each other.

Each of inner bending portions 9004 is adjacent to each of the stator poles across a cylinder-shaped stator yoke of the stator core 7000 in the radial direction. As the result, radial vibration of cylinder-shaped portion 9000 of the motor housing is reduced largely by elastic deformation of the ring-shaped spring plate 9002 having corrugated shape, because ring-shaped spring plate 9002 is deformed elastically by the radial magnetic vibration of stator core 7000. Furthermore, the bending

portions

9003 and 9004 can slide on the circumferential surfaces of stator core 7000 and cylinder-shaped portion 9000 of the motor housing in the circumferential direction. In the other words, bended ring-shaped spring plate 9002 having bended corrugate shape changes directions of the radial magnetic vibration of stator core 7000.

The circumferential distance between the inner bending portion 9003 and the outer bending portion 9004 can be decided according to the vibration pattern of stator core 4001. Similarly, disposed positions of inner bending portion 9003 and outer bending portion 9004 can be decided according to the vibration pattern of the motor. Preferably, inner bending portion 9004 should come into contact with circumferential portions having less radial vibration. A plurality of bended ring-shaped spring plates 9002 arranged in the axial direction of the stator core 4001 can have different wave pattern to each other. The cooling fluid can consume the vibration force of the bended ring-shaped spring plates 9002. It means reduction of the mechanical resonance.

The above bended ring-shaped spring plate 9002 disposed between stator core 7000 and cylinder-shaped portion 9000 of the motor housing has superior benefits for reducing of the motor, in particular the SRM. The summary of the ring-shaped spring plate 9002 is described as bellow.

A motor having a cylinder-shaped stator core 7000 of which an outer circumferential surface faces an inner circumferential surface of a cylinder-shaped portion 9000 of a motor housing across a cylinder-shaped gap 9001;
wherein a bended ring-shaped spring plate 9002 with bended corrugate shape disposed in the cylinder-shaped gap 900b surrounds the stator core 7000;
the bended ring-shaped spring plate 9002 has a plurality of outer bending portions 9003, which come into contact with the inner circumferential surface of the cylinder-shaped portion 9000 of the motor housing;
the bended ring-shaped spring plate 9002 has a plurality of inner bending portions 9004, which come into contact with the outer circumferential surface of the stator core 7000; and
the inner bending portion 9003 and the outer bending portion 9004 are disposed alternately in the circumferential direction.

Claims

A boost chopper type DC-to-DC converter (1) comprising:
a first pair of a first reactor (150) and a first DC power source (4) connected in series to each other;
a second pair of a second reactor (160) and a second DC power source (5) connected in series to each other;
a series switch (110) connected the first pair and the second pair in series;
a first parallel switch (120) short-circuiting the first pair via the series switch (110);
a second parallel switch (130) short-circuiting the second pair via the series switch (110);
an output switch (140) for outputting a boosted DC voltage (Vx) to an electrical load (2); and
one end of the output switch (140) is connected to the first pair and the first parallel switch (120).
The boost chopper type DC-to-DC converter (1) according to claim 1, wherein the DC-to-DC converter has a series connection stage (A), a parallel connection stage (B) and a short-circuit stage (C, D and E);
the stage (A) has the turned-on series switch (110) and the turned-off parallel switches (120) and (130);
the stage (B) has the turned-off series switch (110) and the turned-on parallel switches (120) and (130); and
the short-circuit stage (C, D and E) has at least one of the short-circuited first pair and the short-circuited second pair.
The boost chopper type DC-to-DC converter (1) according to claim 2, wherein the series stage (A) and the short-circuit stage (C, D and E) are executed alternately.
The boost chopper type DC-to-DC converter (1) according to claim 2, wherein the parallel stage (B) and the short-circuit stage (C, D and E) are executed alternately.
The boost chopper type DC-to-DC converter (1) according to claim 1, wherein the DC-to-DC converter (1) applies a boosted DC voltage (Vx) to a power converter (2) for driving a switched reluctance motor (60);
the power converter (2) has a plurality of transistors (201-206), which control phase currents flowing through a plurality of phase windings (401-405) of the switched reluctance motor (60);
the power converter (2) has a transient period (Pt) while a freewheeling current of the phase windings (401-405) flows by means of turning-off of at least one of the transistors (201-206); and
the DC-to-DC converter (1) increases the boosted DC voltage (Vx) in the transient period (Pt).
The boost chopper type DC-to-DC converter (1) according to claim 1, wherein a first winding (151) of the first reactor (150) and a second winding (161) of the second reactor (160) are wound on a common core (8) consisting of a closed magnetic circuit;
the first winding (151) wound on a first core leg (81) of the common core (8) excites a first magnetic flux;
the second winding (161) wound on a second core leg (82) of the common core (8) excites a second magnetic flux;
the common core has a bypass core leg (85) flowing difference component of the first magnetic flux and the second magnetic flux, of which flowing directions are same to each other; and
the bypass core leg (85) has smaller cross-section than each of the first and the second core legs (81, 82).
The boost chopper type DC-to-DC converter (1) according to claim 1, wherein the DC-to-DC converter (1) applies a boosted DC voltage (Vx) to a power converter (2) for driving a five-phase switched reluctance motor (60);
the five-phase switched reluctance motor (60) has five phase windings (401-405) wound on five stator poles of a stator core respectively;
one ends of the five phase windings (401-405) are connected to a neutral point (N);
the power converter (2) has at least six transistors (201-206) and six freewheeling diodes (301-306);
a first and a third phase windings (401, 403) are connected to the high potential line (6) via the transistors (201, 203) and are connected to the low potential line (7) via the freewheeling diodes (301, 303);
a second and a fourth phase windings (402, 404) are connected to the low potential line (7) via the transistors (202, 204) and are connected to the high potential line (6) via the freewheeling diodes (302, 304); and
a fifth phase windings (405) is connected to the high potential line (6) via the transistor (205) and the freewheeling diode (306), and is connected to the low potential line (7) via the transistor (206) and the freewheeling diode (305).
The boost chopper type DC-to-DC converter (1) according to claim 1, wherein the DC-to-DC converter (1) applies a boosted DC voltage (Vx) to a power converter (2) for driving a five-phase switched reluctance motor (60);
the five-phase switched reluctance motor (60) has five phase windings (401-405) wound on five stator poles of a stator core respectively;
one ends of the five phase windings (401-405) are connected to a neutral point (N);
the power converter (2) has five half bridges having a pair of an upper transistor and a lower transistor each;
each of half bridges is connected to the other ends of the five phase windings (401-405) respectively;
the upper transistor connects the phase winding to a high potential line (6); and
the lower transistor connects the phase winding to a low potential line (7).
A power converter (2) for applying a five-phase voltage to a five-phase switched reluctance motor (60), wherein the five-phase switched reluctance motor (60) has five phase windings (401-405) wound on five stator poles of a stator core respectively;
one ends of the five phase windings (401-405) are connected to a neutral point (N);
the power converter (2) has at least six transistors (201-206) and six freewheeling diodes (301-306);
a first and a third phase windings (401, 403) are connected to the high potential line (6) via the transistors (201, 203) and are connected to the low potential line (7) via the freewheeling diodes (301, 303);
a second and a fourth phase windings (402, 404) are connected to the low potential line (7) via the transistors (202, 204) and are connected to the high potential line (6) via the freewheeling diodes (302, 304);
a fifth phase windings (405) is connected to the high potential line (6) via the transistor (205) and the freewheeling diode (306), and is connected to the low potential line (7) via the transistor (206) and the freewheeling diode (305); and
wherein one of the transistors (201, 203, and 205) connected to the high potential line (6) and another one of the transistors (202, 204, and 206) connected to the low potential line (7) are turned on and turned off simultaneously.
A power converter (2) for applying a five-phase voltage to a five-phase switched reluctance motor (60), wherein the five-phase switched reluctance motor (60) has five phase windings (401-405) wound on five stator poles of a stator core respectively;
one ends of the five phase windings (401-405) are connected to a neutral point (N);
the power converter (2) has five half bridges having a pair of an upper transistor and a lower transistor each;
each of half bridges is connected to the other ends of the five phase windings (401-405) respectively;
the upper transistor connects the phase winding to a high potential line (6); and
the lower transistor connects the phase winding to a low potential line (7).