System using power converter, microsurge suppressor and microsurge suppression method

A motor driving system includes an AC power supply 1, an AC reactor 2, a power converter 3 and a motor 4. A microsurge suppressor 5 is inserted on a power supply line from the power converter 3 to the motor 4 and the similar microsurge suppressor 6 is inserted on a power supply line from the AC reactor 2 to the power converter 3. The microsurge suppressor 5 includes a multi-layer printed wiring board having two terminals connected to the power converter 3 and the motor 4 and a capacitor for bypassing a surge, and the terminal 4 on the side of the motor of the multi-layer printed wiring board is directly connected to a terminal of the motor 4. The capacitor for bypassing a surge is connected between the terminal of the motor 4 and the end on the side of a second terminal of second wiring.

BACKGROUND OF THE INVENTION

The present invention relates to a system using a power converter controlled by switching, for example, a system that drives various loads such as a motor by the output of a power converter.

A power converter controlled by switching is used for driving various equipment such as a motor and is also utilized in fields of household electrical appliances, transportation equipment, an uninterruptible power system, a solar generator and a fuel cell. To realize required performance, the improvement of the switching characteristics of power elements forming the power converter is required to be promoted, switching speed for pulse width control is 10 to 100 ns and is considerably fast.

When pulse voltage having an abrupt waveform and generated because of high speed PWM (Pulse Width Modulation) control is applied to equipment connected to the power converter, for example, an AC reactor connected to the side of a converter (the side of an alternating-current power supply) and a load (a motor and others) connected to the side of an inverter, the pulse voltage is reflected at each terminal of the AC reactor and the load and an oscillatory microsurge is caused. The terminal voltage of the AC reactor and the load rises because of the constant of wiring between the power converter and the AC reactor or the load.

When the microsurge is caused, the insulation of equipment forming a system is deteriorated, and the reliability and the life are deteriorated. Besides, in case common mode current via the stray capacitor of the equipment is caused because of surge voltage and a load is a motor, shaft current that flows on the side of the shaft of the motor is caused. The generation of the shaft current particularly comes into question in case an applied object is an electric railcar, an iron and steel plant and others. Further, as strong radiation noise is caused in the vicinity of the power supply terminal of the load, electromagnetic interference is caused in near electronic equipment and a near information communication device. Particularly, as most objects that utilize a recent power converter use information equipment, the effect is serious. Besides, the effect upon wireless LAN being popularized and networked home by wireless to be expected in future is also serious.

FIG. 11shows the schematic configuration of a motor driving system which is one example of a system using a power converter controlled by switching. The motor driving system shown inFIG. 11includes an AC power supply1, an AC reactor2, a power converter3and a motor4. The AC reactor2, a frame (not shown) of the motor4and the earth line (not shown) of the power converter3are grounded. The frame denotes structure which supports equipment and which covers the whole equipment with a conductor in a state in which the structure is electrically insulated from a current-carrying part of the equipment.

The power converter3receives power supplied from the AC power supply1via the AC reactor2and converts it to power of an arbitrary frequency and arbitrary voltage. The power converter3basically includes a converter (a power rectifier)31that converts input ac power to dc voltage, a smoothing capacitor32that smoothes dc voltage output from the converter31and an inverter (a power inverter)33that converts the smoothed dc voltage to ac voltage, these components are mounted on a wiring board (not shown), and the converter31and the inverter33are connected via dc main circuit conductors30n,30pformed on the wiring board. A cooling fin (not shown) is attached to each element case including the converter31and the inverter33. The cooling fin is provided to suppress the temperature rise of the elements and is electrically connected to an earth line (not shown) of the wiring board.

In such a system, pulse voltage having an abrupt waveform and generated at the terminal of the inverter33because of high speed PWM (Pulse Width Modulation) control is propagated to the terminal of the motor4via a cable34and is reflected at the terminal of the motor4because the impedance is unconformable. Therefore, at the terminal of the motor4, a microsurge is caused. Similarly, pulse voltage having an abrupt waveform and generated at the terminal of the converter31is propagated to the terminal of the AC reactor2via a cable35, is reflected at the terminal of the AC reactor2because the impedance is mismatched, and a microsurge is also caused at the terminal of the AC reactor.

FIGS. 12A to 12Eshow voltage waveforms at the terminals of the inverter33and the motor4.FIG. 12Ashows a voltage waveform at the terminal of the inverter33andFIG. 12Bshows an enlarged waveform of a part.FIG. 12Cshows a voltage waveform at the terminal of the motor4andFIG. 12Dshows an enlarged waveform of a part.FIG. 12Eshows a measured example of the voltage waveform at the terminal of the motor4. As shown inFIGS. 12A to 12E, a microsurge is remarkable on the side of the terminal of the motor4, and it is known that the surge becomes large as the cable34is extended.

FIGS. 13A to 13Eshow voltage waveforms at the terminals of the converter31and the AC reactor2. As inFIGS. 12A to 12E,FIG. 13Ashows a voltage waveform at the terminal of the converter31andFIG. 13Bshows an enlarged waveform of a part.FIG. 13Cshows a voltage waveform at the terminal of the AC reactor2andFIG. 13Dshows an enlarged waveform of a part.FIG. 13Eshows a measured example of the voltage waveform at the terminal of the AC reactor2. As shown inFIGS. 13Ato13E, a microsurge is also remarkable on the side of the terminal of the AC reactor2.

For a measure against the deterioration of the reliability and the life by the microsurge, there is a method of increasing the withstand voltage of the motor. For a method of suppressing a microsurge, there are a method of using a microsurge suppression filter (refer to a patent document 1), a method of equalizing the impedance of the motor and the cable (refer to a non-patent document 1), a method of inserting a damping circuit at the terminal of the motor (refer to a non-patent document 2) and a method of inserting a high-tension circuit into a control system of the power converter and delaying a leading edge of voltage (refer to a non-patent document 3).

However, as the proper performance of the power converter may be deteriorated by the addition of these means for the measures, countermeasures in which wavelike effect upon the whole system including the power converter is fully examined are required. Besides, as countermeasures in which the characteristics of the cables and the input impedance and others of the motor and others are fully grasped are required, measurement requiring labor and intricate computing are required and improvement is required in terms of flexibility.

Further, when anew component is added for a measure against a microsurge, the induction of common mode current from the component and the generation of radiation noise cannot be avoided. Besides, when the capacity of the power converter is increased, the large-sizing of the component for a countermeasure which is made of iron and which includes winding structure and the increase of the weight cannot be avoided and the cost is increased.

SUMMARY OF THE INVENTION

The invention is made in view of the above-mentioned situation and the object is to suppress a surge generated at the terminal of equipment connected to a power converter without depending upon a condition of a component such as the length of a cable and the capacity of the power converter and to simultaneously suppress radiation noise and current (shaft current) that flows on its shaft in case a load is a motor.

A system according to the invention uses the power converter controlled by switching, is provided with a microsurge suppressor on the side of the load inserted on a power supply line from the power converter to the load, the microsurge suppressor on the side of the load includes a multi-layer printed wiring board on the side of the load provided with a first terminal on the side of the power converter and a second terminal on the side of the load and a capacitative element for bypassing a surge on the side of the load, a first power wiring and a second power wiring respectively capacitively coupled are formed on a first wiring layer and a second wiring layer of the multi-layer printed wiring board on the side of the load, the first terminal and the second terminal are connected via the first power wiring, the second terminal and a terminal of the load are directly connected, and the capacitative element for bypassing a surge on the side of the load is directly connected to the second terminal and the end on the side of the second terminal of the second power wiring.

According to the invention, an oscillatory component propagated to the terminal of the load can be made to flow to the second power wiring52by capacitive coupling via the capacitor for bypassing a surge and a microsurge can be effectively suppressed. Besides, radiation noise can be reduced by suppressing a microsurge at the terminal of the load.

The system according to the invention includes the capacitative element for bypassing a surge on the side of the load having larger capacity than capacitance between the terminals of the load. According to the invention, high-frequency current from the terminal of the load to the load can be securely bypassed and shaft current in case the load is a motor can be suppressed.

The system according to the invention includes the first power wiring and the second power wiring respectively geometrically symmetrical. According to the invention, reflected current can be reversed and electromagnetic noise by first reflection at the terminal of the load can be effectively suppressed.

The system according to the invention includes a damping resistor connected to the end on the side of the first terminal of the second power wiring. According to the invention, a reflected wave induced onto the second power wiring can be effectively suppressed.

The system according to the invention includes the multi-layer printed wiring board including a third power wiring to be a virtual grounding conductor formed on a third layer and a damping resistor connected between the end on the side of the first terminal of the second power wiring and the third power wiring. According to the invention, an unbalanced component of each phase output from an inverter can be absorbed, the variation of potential is suppressed and a leak can be effectively prevented.

The system according to the invention is further provided with a microsurge suppressor on the input side inserted on a power supply line from the AC reactor on the side of an AC power supply to the power converter, the microsurge suppressor on the input side includes a multi-layer printed wiring board on the input side provided with a third terminal and a fourth terminal and a capacitative element for bypassing a surge on the input side, a fourth power wiring and a fifth power wiring respectively capacitively coupled are formed on a first wiring layer and a second wiring layer of the multi-layer printed wiring board on the input side, the third terminal and the fourth terminal are connected via the fourth power wiring, the fourth terminal and a terminal of the AC reactor are directly connected, and the capacitative element for bypassing a surge on the input side is directly connected to the fourth terminal and the end on the side of the fourth terminal of the fifth power wiring.

The system according to the invention includes the capacitative element for bypassing a surge on the input side having larger capacity than capacitance between the terminals of the AC reactor.

The system according to the invention includes the fourth power wiring and the fifth power wiring respectively geometrically symmetrical.

The system according to the invention includes a damping resistor connected to the end on the side of the third terminal of the fifth power wiring.

The system according to the invention includes the multi-layer printed wiring board including a sixth power wiring to be a virtual grounding conductor formed on a third layer and provided with a damping resistor connected between the end on the side of the third terminal of the fifth power wiring and the sixth power wiring.

A microsurge suppressor according to the invention is provided to suppress the generation of a microsurge in the system using the power converter controlled by switching, is provided with a multi-layer printed wiring board having a first terminal on the side of the power converter and a second terminal on the side of another equipment and a capacitative element for bypassing a surge, a first power wiring and a second power wiring respectively capacitively coupled are formed on a first wiring layer and a second wiring layer of the multi-layer printed wiring board, the first terminal and the second terminal are connected via the first power wiring, the second terminal and a terminal of the other equipment are directly connected, and the capacitative element for bypassing a surge is directly connected to the second terminal and the end on the side of the second terminal of the second power wiring.

The microsurge suppressor according to the invention includes the capacitative element for bypassing a surge having larger capacity than capacitance between the terminals of another equipment.

The microsurge suppressor according to the invention includes the first power wiring and the second power wiring respectively geometrically symmetrical.

The microsurge suppressor according to the invention is provided with a damping resistor connected to the end on the side of the first terminal of the second power wiring.

The microsurge suppressor according to the invention includes the multi-layer printed wiring board including a third power wiring to be a virtual grounding conductor formed on a third layer and a damping resistor connected between the end on the side of the first terminal of the second power wiring and the third power wiring.

The microsurge suppressor according to the invention includes the other equipment as a load driven by the power converter.

The microsurge suppressor according to the invention includes the other equipment as an AC reactor connected to the side of an AC power supply for supplying to the power converter.

A microsurge suppression method according to the invention is a way to generate a microsurge at an intermediate terminal except a terminal of an equipment between the power converter and the equipment connected to the power converter and to control the generated microsurge between the intermediate terminal and the terminal of the equipment in the system using the power converter controlled by switching.

According to the invention, a surge generated at the terminal of the equipment (the load connected to the output side such as the motor, the AC reactor connected to the input side) connected to the power converter is suppressed without depending upon a condition such as the length of the cable and the capacity of the power converter and simultaneously, radiation noise and current (shaft current) that flows, on its shaft in case the load is the motor) can be suppressed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings, embodiments of the invention will be described below.FIG. 1shows a motor driving system using a power converter controlled by switching, and an AC power supply1, an AC reactor2, the power converter3and a motor4are the same as those in the system shown inFIG. 11. The motor driving system according to the invention is different from the system shown inFIG. 11in that a microsurge suppressor5is inserted on a power supply line from the power converter3to the motor4and the similar microsurge suppressor6is inserted on a power supply line from the AC reactor2to the power converter3. However, the microsurge suppressor6is not essential and can be omitted. As shown inFIGS. 12 and 13, as surge voltage at the terminal of the AC reactor2is smaller than surge voltage at the terminal of the motor4and further, the length of a cable can be also shortened, the microsurge suppressor6may be also omitted depending upon the magnitude of the surge voltage.

The microsurge suppressors5,6are provided with a multi-layer printed wiring board having two terminals connected to the power converter3and the motor4or the AC reactor2and a capacitor for bypassing a surge, and the terminal on the side of the motor4or on the side of the AC reactor2of the multi-layer printed wiring board is directly connected to the terminal of the motor4or the AC reactor2. The multi-layer printed wiring board is provided with at least two wiring layers and wiring formed on the first and second wiring layers is capacitively coupled. The capacitor for bypassing a surge is connected between the terminal on the side of the motor4or on the side of the AC reactor2and the end on the side of a second terminal of the second wiring.

FIG. 2shows the schematic configuration of the microsurge suppressor5. The microsurge suppressor5shown inFIG. 2includes a three-layer printed wiring board50, the capacitors for bypassing a surge57U,57V,57W (may be merely described as the capacitor for bypassing a surge57) and damping resistors58U,58V,58W (may be merely described as a damping resistor58). The printed wiring board50is provided with a first wiring layer501, a second wiring layer502, a third wiring layer503and dielectric boards54arranged between the wiring layers501to503. On the first wiring layer501, first power wiring51U,51V,51W for transmitting power (may be merely described as first power wiring51) is formed, and at both ends of the first power wiring51U,51V,51W, machine screws55U,55V,55W forming a first terminal (may be merely described as the first terminal55) and machine screws56U,56V,56W forming a second terminal (may be merely described as the second terminal56) are provided.

Besides, on the second wiring layer502, second power wiring52U,52V,52W for suppressing an oscillatory component by a reflected wave (may be merely described as second power wiring52) is formed, and on the third wiring layer503, third power wiring53to be a virtual grounding layer is formed. The first power wiring51and the second power wiring52are capacitively coupled by substantially equally patterning. The patterns of the first power wiring51and the second power wiring52are made symmetrical.

The first terminal55is connected to a cable34(34U,34V,34W) and the second terminal56is directly connected to the terminal40(40U,40V,40W) of the motor. The capacitor for bypassing a surge57is connected between the second terminal56and the end on the side of the second terminal of the second power wiring and the damping resistor58is connected between the other end (the end on the side of the first terminal) of the second power wiring and the third power wiring.

FIG. 3shows the schematic section of the microsurge suppressor5shown inFIG. 2. InFIG. 3, distributed capacitance.59distributed to the first power wiring51and the second power wiring52is schematically shown by a broken line, however, the distributed capacitance59bypasses a high-frequency surge component propagated on the first power wiring51to the second power wiring52as described later. The high-frequency surge component that cannot be bypassed to the capacitor59is propagated to the second terminal56and is bypassed to the second power wiring52via the capacitor for bypassing a surge57connected to the second terminal56. Therefore, the capacity of the capacitor for bypassing a surge57is set to a value larger than capacitance between the motor terminals40.

As the high-frequency surge component propagated on the first power wiring51is bypassed to the second power wiring52via the distributed capacitance59and the capacitor for bypassing a surge57as described above, shaft current that flows to the side of the shaft of the motor4is suppressed.

FIG. 4shows a state in which the microsurge suppressor5shown inFIG. 2is attached to the motor4. As clear fromFIG. 4, the microsurge suppressor can be easily built in a terminal box of the motor4.

The microsurge suppressor6inserted on the power supply line from the AC reactor2to the power converter3is also provided with the similar configuration to that of the microsurge suppressor5.FIG. 5shows a state in which the microsurge suppressor6is attached to the AC reactor2. The microsurge suppressor6includes a three-layer printed wiring board60, a capacitor for bypassing a surge67(67R,67S,67T) and a damping resistor (not shown). The printed wiring board60is provided with the similar configuration to that of the printed wiring board50of the microsurge suppressor5, a third terminal65(65R,65S,65T) is connected to a cable35(35R,35S,35T), and a fourth terminal66(66R,66S,66T) is directly connected to a terminal (not shown) of the AC reactor2.

In the above description, the printed boards50,60forming the microsurge suppressors5,6are respectively a three-layer board, however, they may be also respectively a two-layer board in which the third wiring layer is omitted.FIG. 6shows the schematic section of another example of the microsurge suppressor5.FIG. 6is different fromFIGS. 2 and 3in that the third wiring layer503and the dielectric board54between the second wiring layer502and the third wiring layer503are omitted and a damping resistor58is provided to the second wiring layer502.

Next, referring toFIG. 6, microsurge suppression operation will be described. In case direct current E is caused at the terminal of an inverter by the switching of the inverter33, a voltage wave is propagated to the terminal of the motor via the cable34together with a current wave. When the voltage wave and the current wave reach the terminal40of the motor, they are reflected on the terminal40of the motor and advance toward the terminal of the inverter because the impedance of the cable and the motor is not matched. In case no measure is particularly taken, they are repeatedly reflected between the terminal of the inverter and the terminal40of the motor, being attenuated because of loss on the cable.

When the microsurge suppressor5shown inFIG. 6is directly connected to the terminal40of the motor, voltage E including an oscillatory component by the mismatch of impedance at the first terminal55is propagated toward the terminal40of the motor on the first power wiring51. As the first power wiring51and the second power wiring52of the printed wiring board50are capacitively coupled, a high-frequency component of the voltage E is attenuated as it is propagated toward the terminal40of the motor because distributed capacitance59flows on the second power wiring52. The high-frequency component that is not attenuated flows on the second power wiring52via the capacitor for bypassing a surge57. As a surge component by reflection at the terminal40of the motor similarly flows on the second power wiring52via the capacitor for bypassing a surge57and distributed capacitance59, the repeat of reflection is suppressed and the generation of surge voltage at the terminal40of the motor is suppressed. A microsurge at the terminal40of the motor can be suppressed by generating the microsurge not at the terminal40of the motor but at the first terminal55of the microsurge suppressor5and controlling the generated microsurge by the distributed capacitance59between the first terminal55and the second terminal56and the capacitor for bypassing a surge57as described above.

The damping resistor58is provided to suppress a reflected wave induced onto the second power wiring52, however, in case a reflected wave can be suppressed by the resistance of the second power wiring52, the damping resistor may be also omitted. The capacitive coupling of the printed wiring board50and the damping resistor58will be supplemented below. The capacitive coupling of the first power wiring51and the second power wiring52is approximately 1.4 nF. As the capacitive coupling is not large as described above, only current of 1 A momentarily flows in the damping resistor58and the damping resistor of approximately 10 W fully plays a role. Therefore, the printed wiring board50can be miniaturized to an extent that it can be housed in the terminal box of the motor4.

When the printed wiring board50includes three layers and the damping resistor is connected to the third power wiring53to be a floating virtual grounding layer as shown inFIGS. 2 and 3, an unbalanced component of each phase output from the inverter can be absorbed, the variation of potential is suppressed and a leak can be effectively prevented.

Next, it will be described that the microsurge suppressor5has effect to reduce electromagnetic noise. As current flows being attenuated in two ways by reflection at the terminal40of the motor and at the terminal of the inverter, that is, high-frequency current flows on the cable34in case no microsurge is suppressed, high-frequency noise is radiated from the cable34. In the meantime, when the microsurge suppressor5is inserted, current reflected at the terminal40of the motor flows onto the second power wiring52and is suppressed, and therefore, bidirectional current flows only when the current is first reflected at the terminal40of the motor. Therefore, the radiation of high-frequency noise is greatly suppressed.

Further, as in the microsurge suppressor5, current distribution concentrates on only the first wiring layer501and the inside of the second wiring layer and current flows mutually in reverse directions, a magnetic field on the surface of the board is negated. Therefore, noise radiated by current first reflected at the terminal40of the motor can be also suppressed. Suppression effect is further enhanced by making the first power wiring51and the second power wiring52symmetrical.

Next, an example in which a microsurge, motor shaft current and radiation noise are measured will be described.

FIGS. 7A and 7Bshow the example of the measurement of a microsurge at the terminal40of the motor.FIG. 7Ashows the hourly variation of motor terminal voltage andFIG. 7Bshows its frequency spectrum. “A” inFIGS. 7A and 7Bdenotes the result of measurement when the microsurge suppressor5is used and “N” denotes the result of measurement when no microsurge suppressor5is used (“A” and “N” show the similar result of measurement inFIGS. 8 and 9). As clear fromFIGS. 7A and 7B, when the microsurge suppressor5is used, a high-frequency oscillatory component is suppressed.

FIGS. 8A and 8Bshow an example of the measurement of motor shaft current.FIG. 8Ashows the hourly variation of motor shaft current andFIG. 8Bshows its frequency spectrum. When motor shaft current is measured, a motor in which a motor frame and a bearing frame are insulated is used and the measurement is made by short-circuiting these two frames. As current (shaft current) that flows in a short-circuited location flows through a path of the shaft—a bearing—the motor frame, shaft current is measured.FIGS. 8A and 8Bshow that as the peak value of voltage at a leading edge is suppressed by suppressing the peak value of a microsurge, shaft current is also suppressed.

FIG. 9shows an example of the measurement of a magnetic field showing radiation noise in the vicinity of the terminal of the motor.FIG. 9shows its frequency spectrum and radiation noise is clearly suppressed by the microsurge suppressor5.

FIGS. 10A and 10Bshow an example of the measurement of a microsurge at the terminal on the side of the power converter of the AC reactor.FIG. 10Ashows the hourly variation of terminal voltage andFIG. 10Bshows its frequency spectrum. “A” inFIGS. 10A and 10Bshows the result of measurement when the microsurge suppressor6is used and “N” shows the result of measurement when no microsurge suppressor6is used. As clear fromFIGS. 10A and 10B, when the microsurge suppressor6is used, a high-frequency oscillatory component is suppressed.