JP2010161900A - Switching power supply and motor system using same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a switching power supply not depending on a motor cable length and a load condition and a motor system using the switching power supply as a motor driver. <P>SOLUTION: Common mode choke coils 41 and 15 disposed on the input side/output side of the switching power supply 40 are provided with a third coil L3, to which a resistance 42 and a diode switch 43 are connected. Only when a common mode current value become equal to or higher than a given value, a current is caused to flow through the resistance 42. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a switching power supply for driving a motor and the like and a motor system using the switching power supply, and more particularly to a switching power supply capable of reducing high-frequency leakage current and a motor system using the switching power supply.

  The switching power supply generates alternating current of any frequency by switching the input direct current or alternating current, and transforms and rectifies this alternating current to generate direct current of arbitrary voltage. Used for DC voltage conversion.

  Such a switching power supply generates a high-frequency leakage current to turn on and off the input power supply. The high-frequency current resulting from this high-frequency leakage current leaks outside, adversely affects other devices, and causes electromagnetic interference (EMI).

  FIG. 5 shows a configuration of a switching power supply used in a drive unit of a motor that drives the scanner stage. In FIG. 5, 10 and 11 are DC power supplies, and 12 is a switching power supply used as a motor driver. The DC power supplies 10 and 11 are connected to terminals S1 and S2 of the switching power supply 12. A motor (not shown) is connected to the terminals U, V, and W of the switching power supply 12.

  The switching power supply 12 includes a switching unit 13 and common mode choke coils 14 and 15. The switching unit 13 generates a three-phase alternating current by turning on and off the internal switching element 13a. This three-phase alternating current is supplied to the motor via terminals U, V, and W.

  As described above, high-frequency noise is generated when the switching element is turned on and off. Common mode choke coils 14 and 15 are used in order not to leak the high frequency noise to the outside.

  A common mode choke coil is a coil in which a plurality of windings are wound around one core in opposite directions. When a common mode current flows, magnetic flux is added inside the core, and a large impedance is generated. This impedance allows normal mode current to pass and blocks only common mode current that is leakage current.

  The common mode choke coil 14 has a configuration in which two windings L1 and L2 are wound around one core in opposite directions. One ends of the coils L1 and L2 are connected to the terminals S1 and S2, respectively, and the other ends are connected to the input terminals of the switching unit 13.

  The common mode choke coil 15 has the same configuration, except that three coils are wound around one core in opposite directions. One end of these coils is connected to the output terminal of the switching unit 13, and the other end is connected to the terminals U, V, and W, respectively.

  These common mode choke coils 14 and 15 prevent high frequency noise generated in the switching unit 13 from leaking to the outside.

  FIG. 6 shows an image of a common mode current that is a leakage current. In FIG. 6, 20 is a motor driver, and the switching power supply 12 of FIG. 5 is used. 21 is a motor, 22 and 23 are motor drivers 20, and stray capacitance between the motor 21 and the frame ground FG.

  The normal mode current is a current for driving the motor 21 and flows through 24 paths. On the other hand, the common mode current, which is a leakage current, flows through the stray capacitances 21 and 22 through 25 paths between the common potential point of the motor driver 20 and the motor 21 and the frame ground FG. Since the switching power supply switches the input voltage, this common mode current becomes a high-frequency leakage current containing a lot of high-frequency components.

  FIG. 7 shows a configuration of a motor system represented by a scanner stage. In addition, the same code | symbol is attached | subjected to the same element as FIG. 6, and description is abbreviate | omitted. In FIG. 7, reference numeral 26 denotes a motor cable that connects the motor driver 20 and the motor 21. 27 to 29 are stray capacitances between the motor driver 20 and the frame ground FG, between the motor cable 26 and the frame ground FG, and between the motor 21 and the frame ground FG, respectively.

  As described in FIG. 6, the common mode current flows via the stray capacitance. In the scanner stage, it is often necessary to connect the motor driver 20 and the motor 21 with a long cable 26. As the length of the motor cable 26 increases, the capacitance value of the stray capacitance 28 increases and a large common mode current flows.

  Patent Document 1 describes an invention of a solar power generation device that can reduce a leakage current due to a stray capacitance and reduce a noise level of a common mode coil. The outline of the present invention will be described below with reference to FIG.

  In FIG. 8, the output power of the solar cell 30 is input to the DC-DC converter 32 via the noise filter 31 and boosted. The boosted direct current is converted into alternating current by the inverter 33 and output to the alternating current power system 35 through the noise filter 34.

  The noise filters 31 and 34 are used to suppress high-frequency leakage current generated by the DC-DC converter 32 and the inverter 33. The common mode transformer T1 and capacitors C1 and C2 connected to the input / output side of the common mode transformer T1 are used. Consists of.

  The common mode transformer T1 has a configuration in which a tertiary winding is provided in addition to the coil for suppressing the common mode current, and a resistor R1 is connected to the tertiary winding. When a common mode current flows through the common mode transformer T1, a voltage is induced in the tertiary winding. Since the induced voltage is consumed by the resistor R1, the vibration of the common mode transformer T1 is suppressed, and the noise level can be reduced.

JP 2002-369543 A

  However, such a switching power supply has the following problems. As described above, in a motor system in which the motor driver 20 and the motor 21 are separated from each other, such as a scanner stage, and a long motor cable 26 must be connected between them, the stray capacitance of the motor cable 26 is large. Thus, the common mode current increases. For this reason, the core in the common mode choke coils 14 and 15 inserted symptomatically becomes magnetically saturated, and there is a problem that the effect of suppressing the common mode current is reduced.

  In the invention described in Patent Document 1, a resistor is directly connected to the tertiary winding of the common mode transformer T1, and all the induced voltages are applied to the resistor R1, so that a large loss occurs and the resistor R1 However, there is a problem that an expensive large resistor must be used.

  Accordingly, an object of the present invention is to provide a switching power supply that does not depend on the length of the motor cable and load conditions, and a motor system using the switching power supply as a motor driver.

In order to solve such a problem, the invention according to claim 1 of the present invention,
A switching unit that includes a switching element, processes the input voltage by controlling on and off of the switching element, and outputs the voltage;
A common mode choke coil that is disposed on the input side and / or output side of the switching unit and has a third winding that suppresses the common mode current and outputs a voltage related to the common mode current;
A resistor connected in series with the third winding;
Turns on when the output voltage of the third winding is input to one end and a predetermined constant voltage is input to the other end and the output voltage of the third winding becomes larger than the predetermined constant voltage. And the diode part
Is provided. High frequency leakage current is reduced and no heat is generated.

The invention according to claim 2 is the invention according to claim 1,
According to the impedance characteristic of the common mode current, the number of turns of the third winding is changed. The impedance characteristics of the common mode current can be adjusted.

The invention according to claim 3 is the invention according to claim 1 or 2,
The diode part is
A first diode to which a first constant voltage is applied to the cathode;
The cathode is connected to the anode of the first diode, the second constant voltage is applied to the anode, and the output voltage of the third winding is input to the connection point with the first diode. A second diode
Is provided. Configuration is simplified.

The invention according to claim 4 is the invention according to any one of claims 1 to 3,
The predetermined constant voltage is used as an output voltage of a DC power supply that supplies power to the switching unit. Since a constant voltage source is not necessary, the configuration is simplified.

The invention according to claim 5 is the invention according to any one of claims 1 to 4,
A direct current is input to the switching unit, and an alternating current is generated from the direct current. It is suitable for use in a driver such as a motor.

The invention described in claim 6
A switching power supply according to any one of claims 1 to 5,
A motor supplied with electric power from the switching power supply;
A cable connecting the switching power supply and the motor;
Is provided. Regardless of the length of the cable, high-frequency leakage current can be suppressed stably.

As is apparent from the above description, the present invention has the following effects.
According to the first, second, third, fourth, fifth and sixth aspects of the present invention, there is provided a switching power supply that includes a switching element, processes the input voltage by controlling on / off of the switching element, and outputs the processed voltage. A third winding is provided in the common mode choke coil disposed on the input side and / or the output side of the switching power source, and a resistor and a diode portion are connected to the third winding, so that the third winding Only when the output voltage exceeds a certain value, a current is allowed to flow through the resistor. Moreover, this switching power supply was applied to the motor system.

  Only when the common mode current exceeds a certain value, the current is passed through the resistor to consume the power, so the core of the common mode choke coil is not saturated and the power consumed by the resistor can be reduced. Therefore, there is an effect that high-frequency leakage current can be suppressed and an inexpensive small resistor can be used.

  Further, the damping characteristic of the common mode current can be adjusted by changing the number of turns of the third winding. For this reason, there is an effect that stable impedance characteristics can be obtained by changing the number of turns according to the impedance characteristics of the common mode current.

It is a block diagram which shows one Example of this invention. 1 is an equivalent circuit of the embodiment in FIG. 1. 2 is an impedance characteristic of the equivalent circuit. It is a characteristic view which shows the effect of FIG. 1 Example. It is a block diagram of the conventional switching power supply. It is a figure which shows the path | route of a common mode electric current. It is a block diagram of a scanner stage. It is a block diagram of the conventional solar power generation device.

  Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a switching power supply according to the present invention. Note that the same reference numerals are given to the same elements as those in FIG.

  In FIG. 1, the output voltage of the DC power supplies 10 and 11 is Vs. The output voltage Vs of the DC power supplies 10 and 11 is input to the switching unit 13 from the terminals S1 and S2. Therefore, a voltage of ± Vs is input to the switching unit 13 with reference to the frame ground FG.

  The switching unit 13 controls on / off of the internal switching element 13a to convert the input direct current into a three-phase alternating current. This three-phase alternating current is supplied to a motor (not shown) through a common mode choke coil 15 and terminals U, V, and W.

  Reference numeral 41 denotes a common mode choke coil having a configuration in which three coils L1 to L3 are wound around one core. The coils L1 and L2 are wound in opposite directions, one end of which is connected to the terminals S1 and S2, and the other end is connected to the input terminal of the switching unit 13.

  The common mode choke coil 41 has a configuration in which a coil L3 is added to the common mode choke coil 14. Coils L1 and L2 have the same number of turns and are wound in opposite directions. The coil L3 is wound around the same core as the coils L1 and L2. The number of turns and the winding direction of the coil L3 are arbitrary. For example, when the number of turns of the coils L1 and L2 is N, the number of turns of the coil L3 is 2N.

  The coil L3 has the same function as the coil to which the resistor R1 is connected in the common mode transformer T1, which is a component of the conventional example of FIG. 8, and when a common mode current flows through the coils L1 and L2, A voltage proportional to the common mode current is induced across the coil L3.

  Reference numeral 42 denotes a resistor, one end of which is connected to one end of the coil L3. Reference numeral 43 denotes a diode portion, which includes four diodes D1 to D4. Diodes D1 and D2 correspond to the first diode, and diodes D3 and D4 correspond to the second diode. The positive output voltage of the DC power supply 10 corresponds to a first constant voltage, and the negative output voltage of the DC power supply 11 corresponds to a second constant voltage.

  The cathodes of the diodes D1 and D2 are connected to the terminal S1, and the anodes of the diodes D3 and D4 are connected to the terminal S2. The anode of the diode D1 and the cathode of the diode D3 are connected to the other end of the coil L3, and the anode of the diode D2 and the cathode of the diode D4 are connected to the other end of the resistor 42.

  In such a configuration, when the voltage induced in the coil L3 is smaller than the output voltage ± Vs of the DC power supplies 10 and 11, all of the diodes D1 to D4 are turned off and no current flows through the resistor 42.

  When the voltage induced in the coil L3 exceeds ± Vs, the diodes D1 and D3 or D2 and D4 are turned on, and a current flows through the resistor 42. When power is consumed by the resistor 42, the impedance of the common mode choke coil 41 increases and the common mode current is suppressed. For this reason, the core in the common mode choke coil 41 is not magnetically saturated.

  That is, the diodes D1 to D4 function as diode clamps that clamp the common mode current only when the common mode current increases. The value of the common mode current to be clamped can be adjusted by changing the number of turns of the coil L3.

  In the conventional example of FIG. 8, current flows through the resistor R1 regardless of the magnitude of the voltage induced in the tertiary winding. That is, all the electric power induced in the tertiary winding is consumed by the resistor R1. Therefore, there is a problem that a large loss occurs and R1 generates heat.

  In this embodiment, a current flows through the resistor 42 only when the voltage induced in the coil L3 exceeds the output voltage of the DC power supplies 10 and 11. Since the voltage induced in the coil L3 can be adjusted by the number of turns of the coil L3, the current can be passed through the resistor 42 only when high-frequency noise leaks to the outside. For this reason, the power consumed by the resistor 42 is very small, and even if a resistor having a small shape is used as the resistor 42, no heat is generated.

  FIG. 2 shows an equivalent circuit for the common mode component of the embodiment of FIG. In addition, the same code | symbol is attached | subjected to the same element as FIG. 1, and description is abbreviate | omitted. In FIG. 2, 50 is the stray capacitance with respect to the frame ground FG, 51 is the resistance of the cable connecting the switching power supply 40 and the motor, 52 is the inductance of the cable, 53 is the capacitance of the cable, and 54 is the capacitance of the motor.

  FIG. 2A is an equivalent circuit when the diodes D <b> 1 to D <b> 4 are turned on and a current flows through the resistor 42, and the resistor 42 is connected to the secondary side of the common mode choke coil 41.

  FIG. 2B shows the resistance 42 connected to the secondary side of the common mode choke coil 41 as a resistance component 55. The value of the resistance component 55 can be adjusted by changing the number of turns of the coil L3 in the common mode choke coil 41.

  As can be seen from FIG. 2, since the common mode component is basically composed of an inductance and a capacitor, it has a characteristic of easily having a resonance point. As can be seen from FIG. 2B, the resistor 42 connected to the coil L3 of the common mode choke coil 41 is represented as a resistance component 55 inserted in series with the common mode choke coils 15 and 41 or the inductance of the cable. Can do. The resistance component 55 functions as a damping element, and the resonance point can be suppressed.

  FIG. 3 is a graph showing impedance characteristics calculated from the equivalent circuit shown in FIG. 2B, where the horizontal axis represents frequency and the vertical axis represents impedance.

  FIG. 3A is a graph showing a change in impedance characteristics with and without the resistance component 55, and 60 is a characteristic when the resistance component 55 is present and 61 is not (short-circuited). 61 having no resistance component 55 has a point with extremely low impedance, as in 62, and high-frequency leakage current is generated at this point. However, 60 having resistance component 55 has a point with extremely low impedance. Therefore, stable impedance characteristics can be obtained in the entire frequency band. For this reason, high frequency leakage current does not occur.

  As described above, the value of the resistance component 55 can be varied depending on the number of turns of the coil L3. By adjusting the number of turns of the coil L3 so that the impedance characteristic of the equivalent circuit shown in FIG. 2 has a flat characteristic such as 60, a stable impedance can be achieved even when the cable length between the switching power supply and the motor becomes long. Characteristics can be realized.

  FIG. 3B shows impedance characteristics when the cable length between the switching power supply 40 and the motor is changed. 63 is an impedance when the cable length is short, 64 is an intermediate cable length, and 65 is an impedance when the cable length is long. It is a characteristic. A stable impedance characteristic is obtained regardless of the length of the cable, that is, the cable capacity.

  FIG. 4 is a waveform of a common mode current flowing from the switching power supply 40 to a load such as a motor, where the horizontal axis represents time and the vertical axis represents current. (A) is a current waveform when there is no resistance component 55, and a high-frequency component appears remarkably. (B) is a current waveform in the case where there is a resistance component 55, in which a high-frequency component is removed and only a switching component is obtained.

  Thus, by providing the common mode choke coil 41 with the coil L3 and connecting the resistor 42 to the coil L3, the resonance point can be removed and the high frequency component of the output current can be greatly reduced. Further, the power consumption of the resistor 42 can be reduced by causing the current to flow through the resistor 42 only when the common mode current is large by the diode portion 43.

  Although the coil L3 is provided in the input-side common mode choke coil 41 and the resistor 42 is connected to the coil L3 in the embodiment of FIG. 1, the present invention can also be applied to the output-side common mode choke coil 15. That is, the present invention can be applied to either or both of the input-side and output-side common mode choke coils depending on the situation.

  In addition, the switching power supply that generates the three-phase alternating current that drives the motor has been described, but a single-phase alternating current or a power supply that outputs direct current may be used. The input power supply may be an alternating current. In short, any power source may be used as long as it has a built-in switching element and controls on / off of the switching element to extract desired power.

  Furthermore, the diode unit 43 is connected to the DC power sources 10 and 11 that supply power to the switching power source 40, but may be connected to other power sources as long as the voltage is stable.

DESCRIPTION OF SYMBOLS 10, 11 DC power supply 13 Switching part 40 Switching power supply 15, 41 Common mode choke coil 42 Resistance 43 Diode part 51 Cable resistance 52 Cable inductance 53 Cable capacity 54 Motor capacity 55 Resistance component S1, S2, U, V, W Terminal L1- L3 Coil D1-D4 Diode

Claims (6)

A switching unit that includes a switching element, processes the input voltage by controlling on and off of the switching element, and outputs the voltage;
A common mode choke coil that is disposed on the input side and / or output side of the switching unit and has a third winding that suppresses the common mode current and outputs a voltage related to the common mode current;
A resistor connected in series with the third winding;
Turns on when the output voltage of the third winding is input to one end and a predetermined constant voltage is input to the other end and the output voltage of the third winding becomes larger than the predetermined constant voltage. And the diode part
A switching power supply comprising:   2. The switching power supply according to claim 1, wherein the number of turns of the third winding is changed in accordance with impedance characteristics of a common mode current. The diode part is
A first diode to which a first constant voltage is applied to the cathode;
The cathode is connected to the anode of the first diode, the second constant voltage is applied to the anode, and the output voltage of the third winding is input to the connection point with the first diode. A second diode
The switching power supply according to claim 1 or 2, further comprising:   The switching power supply according to any one of claims 1 to 3, wherein the predetermined constant voltage is an output voltage of a DC power supply that supplies power to the switching unit.   5. The switching power supply according to claim 1, wherein a direct current is input to the switching unit, and an alternating current is generated from the direct current. 6. A switching power supply according to any one of claims 1 to 5,
A motor supplied with electric power from the switching power supply;
A cable connecting the switching power supply and the motor;
A motor system comprising: