JP5840514B2 - Leakage current suppression circuit - Google Patents

Description

  Embodiments described herein relate generally to a leakage current suppressing circuit.

  A power converter represented by an inverter performs power conversion by a switching operation of a semiconductor switching element. Taking a three-phase PWM inverter for driving a motor as an example, a command value of a voltage to be output is compared with a carrier such as a triangular wave, and semiconductor elements of each phase are switched based on the comparison result. At this time, on the principle, the common mode voltage indicating the average value of the three-phase UVW phase output voltages is not zero, and a large voltage is generated in synchronization with the carrier. This common mode voltage causes a leakage current (high-frequency noise) that flows to the ground via the stray capacitance of the motor. Since leakage current causes problems such as causing trouble to other devices, countermeasures against leakage current are indispensable. As an effective countermeasure, a filter circuit composed of passive elements such as coils and capacitors may be provided.

  2. Description of the Related Art Conventionally, in a power conversion device that has taken measures against leakage current, an inductance element having high impedance with respect to high-frequency leakage current, such as a common mode choke coil, is inserted on the input line from the three-phase AC power supply to the converter.

  The converter converts three-phase power into DC power, and this DC voltage is smoothed by a smoothing capacitor. The smoothing capacitor is connected between the lines of the main circuit wiring between the converter and the inverter. The inverter converts the smoothed DC voltage into a three-phase AC voltage having a desired magnitude and frequency and supplies it to the motor.

  Further, a leakage current bypass circuit including a capacitor and a low impedance element such as a common mode current extraction circuit is provided in a loop including the inductance element and the switching element of the inverter that is a source of the common mode voltage. The common mode current extraction circuit includes three pairs of a capacitor and a single phase reactor.

  The filter circuit, for example, has a common mode choke coil with high impedance characteristics to suppress the flow of common mode current, which is a leakage current, and the leakage current that cannot be suppressed still is a bypass circuit formed by a capacitor and a common mode current extraction circuit. Flowing. Therefore, such a circuit configuration is very effective in suppressing leakage current, and other similar filter circuits have been proposed.

Japanese Patent No. 4351916 Japanese Patent No. 3596694

  However, in the filter circuit described above, the bypass circuit becomes large, for example, the common mode current extraction circuit includes three single-phase reactors, which leads to an increase in the size of the entire filter circuit.

  Then, embodiment of this invention aims at providing the leakage current suppression circuit which suppresses a leakage current effectively, without enlarging.

  According to the embodiment, an inverter including a converter that outputs a DC voltage, and an inverter that has a plurality of switching elements and that converts the DC voltage output from the converter into an AC voltage by switching the plurality of switching elements. A leakage current suppression circuit for use in an apparatus, comprising: a first switching element pair including two switching elements connected in series; and a first capacitor set including a plurality of capacitors connected in series, wherein the first switching element pair includes: A first arm connected in parallel to an intermediate capacitor of the plurality of capacitors, a second switching element pair including two switching elements connected in series, and a second capacitor set including a plurality of capacitors connected in series, The second switching element pair is connected in parallel to the intermediate capacitor of the plurality of capacitors. The second arm, the main winding connected in series at the front stage or the rear stage of the inverter and connected to the wiring of each phase, the connection point of the first switching element pair and the connection point of the second switching element pair And a common mode transformer including a core around which the main winding and the auxiliary winding are wound, wherein the first arm and the second arm are the inverter device. The ratio of the voltage of the intermediate capacitor of the first capacitor set and the voltage of the intermediate capacitor of the second capacitor set is 2 to 1, and the number of turns of the main winding of the common mode transformer is A leakage current suppressing circuit is provided in which the ratio of the number of turns of the auxiliary winding is a ratio of the DC voltage of the inverter to three times the voltage of the intermediate capacitor of the first capacitor set.

FIG. 1 is a diagram schematically illustrating an example of a configuration of a leakage current suppression circuit of the power conversion device according to the first embodiment. FIG. 2 is a diagram schematically illustrating an example of a configuration of a leakage current suppression circuit of the power conversion device according to the second embodiment. FIG. 3 is a diagram illustrating a switching state of the first and second arms in the leakage current suppressing circuit of the power conversion device according to the second embodiment. FIG. 4 is a diagram schematically illustrating an example of a configuration of a leakage current suppression circuit of the power conversion device according to the third embodiment. FIG. 5 is a diagram illustrating a switching state of the first and second arms in the leakage current suppression circuit of the power conversion device according to the third embodiment. FIG. 6 is a diagram schematically illustrating an example of a configuration of a leakage current suppression circuit of the power conversion device according to the fourth embodiment.

Hereinafter, the leakage current suppression circuit of the embodiment will be described with reference to the drawings.
FIG. 1 is a diagram schematically illustrating a configuration example of a leakage current suppression circuit in the power conversion device according to the first embodiment. The leakage current suppression circuit of the present embodiment includes a converter that outputs DC power, and an inverter that has a plurality of switching elements and converts the DC power output from the converter into AC power by switching the plurality of switching elements. It is a leakage current suppression circuit used for an inverter apparatus.

  The power conversion device of this embodiment includes a converter 1, an inverter 2, a smoothing capacitor 3, a first arm 20, a second arm 23, a common mode transformer 26, and a controller 30.

  Converter 1 is connected to power supply 5 via common mode transformer 26. Converter 1 converts the three-phase power supplied from power supply 5 into DC power. The DC voltage output from the converter 1 is smoothed by the smoothing capacitor 3.

  Smoothing capacitor 3 is connected to a DC power line connected between converter 1 and inverter 2.

  The inverter 2 converts the DC voltage smoothed by the smoothing capacitor 3 into a three-phase AC voltage having a desired magnitude and frequency and outputs the converted voltage. That is, each output phase of the inverter 2 includes two switching elements and constitutes three phases of U, V, and W. In the present embodiment, a motor 4 is connected to the inverter 2 as a load, and the three-phase AC voltage output from the inverter 2 is supplied to the motor 4.

  The first arm 20 is connected to the DC power line of the inverter 2. The first arm 20 is connected in parallel to three capacitors (first capacitor sets) 21a, 21b, 21c connected in series and a middle capacitor (intermediate capacitor) 21b, and two switching elements (first switching) connected in series to each other. Element pair) 22a and 22b. As the switching elements 22a and 22b, for example, a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor), an IGBT (Insulated Gate Bipolar Transistor), or the like can be employed.

  The second arm 23 includes two switching elements (second switching element pairs) 25a connected in series to a middle capacitor (intermediate capacitor) 24b of three capacitors (second capacitor sets) 24a, 24b, and 24c connected in series. 25b is connected in parallel. As the switching elements 25a and 25b, for example, MOSFET, IGBT or the like can be adopted.

  Based on the switching state of the inverter 2, the controller 30 switches the switching of the switching elements 22 a and 22 b of the first arm 20 and the switching elements 25 a and 25 b of the second arm 23. The controller 30 may be included in the leakage current suppression circuit, or may be included in the inverter device.

In the present embodiment, the capacities of the capacitors of the first arm 20 and the second arm 23 are selected to be the same as 21a and 21c and 24a and 24c, respectively. Further, when the potential at both ends of the capacitor 21b is defined as + E1 / 2 and -E1 / 2 and the potential at both ends of the capacitor 24b is defined as + E2 / 2 and -E2 / 2 with respect to the intermediate potential of the inverter DC section,
E1 = 2 × E2 (1)
The capacitance of each capacitor is selected so as to satisfy the relationship.

  In the common mode transformer 26, a main winding 26A connected to each phase wiring extending from the power source 5, an auxiliary winding 26B connected to a leakage current suppression circuit, a main winding 26A and an auxiliary winding 26B are wound. And a core. In this embodiment, the direction in which the main winding 26A and the auxiliary winding 26B are wound around the core is the same.

The auxiliary winding 26B of the common mode transformer 26 is connected to a connection point between the switching elements 22a and 22b of the first arm 20 and a connection point between the switching elements 25a and 25b of the second arm 23. The ratio of the number of turns N1 of the main winding 26A and the number of turns N2 of the auxiliary winding 26B of the common mode transformer 26 is such that the positive side potential and the negative side potential of the DC line of the converter 1 and the inverter 2 are + E / 2, − If it is E / 2, it is selected so as to satisfy the following condition.
N1: N2 = E: 3/2 × E1 (2)
The common mode voltage of the inverter 2 that is a source of leakage current is expressed by the average of the three phases of the output, and + E / 2, + E / 6, -E / 6, -E / 2 depending on the switching pattern of each phase. The following four voltage levels can be taken.

  On the other hand, the two arms 20 and 23 have + E1 / 2 and -E1 / 2 from the first arm 20 and + E1 / 4 and -E1 / 4 from the second arm 23 depending on which of the upper and lower elements is conducted. Since any voltage is output, four voltage levels of + 3E1 / 4, + E1 / 4, −E1 / 4, and −3E1 / 4 can be generated in the auxiliary winding 26B of the common mode transformer 26.

  If the number of turns of the main winding 26 </ b> A and the auxiliary winding 26 </ b> B of the common mode transformer 26 is the ratio of the expression (2), the same voltage as the common mode voltage of the inverter 2 can be applied via the common mode transformer 26. For this reason, it becomes possible to cancel a common mode voltage and to suppress a leakage current.

  As described above, in the power conversion device of the present embodiment, the leakage current suppression circuit can be configured by the switching element and the capacitor, and there is no need to provide a large filter circuit. Therefore, according to the present embodiment, it is possible to provide a leakage current suppressing circuit that effectively suppresses the leakage current without increasing the size.

  Here, a circuit configuration in which a common mode transformer 26 is provided between the power source 5 and the converter 1 is shown. However, for example, a DC line between the converter 1 and the inverter 2 or a power source on the output side of the inverter 2 The same effect can be obtained when the common mode transformer 26 is provided in the line.

  Next, a leakage current suppression circuit of the power conversion device according to the second embodiment will be described with reference to the drawings. In the following description, the same components as those in the first embodiment described above are denoted by the same reference numerals and description thereof is omitted.

  FIG. 2 is a diagram schematically showing a configuration example of a leakage current suppression circuit in the power conversion device of the present embodiment.

  The first arm 20 has two switching elements 22 a and 22 b in series with each other, and these switching elements 22 a and 22 b are directly connected to the DC section of the inverter 2.

  Further, the ratio of the capacitances of the three capacitors 24a, 24b, 24c of the second arm 23 is 2: 1: 2. In this case, the voltages of the auxiliary winding 26B of the common mode transformer 26 output by the first arm 20 and the second arm 23 are four voltages of + 3E / 4, + 1E / 4, -1E / 4, and -3E / 4. By setting the ratio of the number of turns of the main winding 26A and the number of turns of the auxiliary winding 26B to 2: 3, the common mode voltage of the inverter 2 can be canceled as in the power converter of the first embodiment. It becomes possible.

  FIG. 3 shows the first arm 20 and the second arm when the voltage of the main winding 26A of the common mode transformer 26 is V1 and the voltage of the auxiliary winding 26B is V2 in the power converter shown in FIGS. It is a figure which shows an example of the connection state of 23 switching elements.

  In the following description, the upper element in each phase of the inverter is a switching element that switches the connection between the positive side of the DC voltage power line of the inverter 2 and the motor 4, and the lower element in each phase of the inverter is the inverter 2 This switching element switches the connection between the negative electrode side of the DC voltage line and the motor 4.

  In the following description, the upper element of the first arm 20 is the switching element 22a connected to the positive side of the DC voltage line of the inverter 2, and the lower element of the first arm 20 is the DC of the inverter 2. The switching element 22b is connected to the negative side of the voltage line. The upper element of the second arm 23 is a switching element 25a connected to the positive side of the DC voltage line of the inverter 2, and the lower element of the second arm 23 is connected to the negative side of the DC voltage line of the inverter 2. Switching element 25b.

  When the upper elements are all conductive in the three phases of the inverter 2, the common mode voltage of the inverter 2 is + E / 2. At this time, if the upper element 22a of the first arm 20 and the lower element 25b of the second arm 23 are made conductive, the auxiliary winding 26B of the common mode transformer 26 is applied with a voltage V2 of + 3E / 4. : The voltage V1 of + E / 2 which is the same as the common mode voltage is applied to the main winding 26A of the common mode transformer 26 in accordance with 3, and the direction in which the main winding 26A and the auxiliary winding 26B are wound around the core is the same. This cancels the common mode voltage.

  Similarly, when two phases of the three phases of the inverter 2 are conductive with the upper element and one phase with the lower element, a common mode voltage of + E / 6 is generated. At this time, if the upper element 22a of the first arm 20 and the upper element 25a of the second arm 23 are made conductive, a voltage V2 of + E / 4 is applied to the auxiliary winding 26B of the common mode transformer 26. 3, the voltage V1 of + E / 6, which is the same as the common mode voltage, is applied to the main winding 26A of the common mode transformer 26, and the direction in which the main winding 26A and the auxiliary winding 26B are wound around the core is the same. This cancels the common mode voltage.

  Of the three phases of the inverter, when one phase is conductive with the upper element and two phases with the lower element, a common mode voltage of -E / 6 is generated. At this time, if the lower element 22b of the first arm 20 and the lower element 25b of the second arm 23 are made conductive, a voltage V2 of −E / 4 is applied to the auxiliary winding 26B of the common mode transformer 26. According to 2: 3, the voltage V1 of −E / 6 is applied to the main winding 26A of the common mode transformer 26, and the direction in which the main winding 26A and the auxiliary winding 26B are wound around the core is the same. Common mode voltage is canceled.

  In all three phases of the inverter, when the lower element is conductive, a common mode voltage of −E / 2 is generated. At this time, if the lower element 22b of the first arm 20 and the upper element 25a of the second arm 23 are made conductive, the auxiliary winding 26B of the common mode transformer 26 is applied with a voltage V2 of −3E / 4. According to 2: 3, a voltage V1 of −E / 2 is applied to the main winding 26A of the common mode transformer 26, and the direction in which the main winding 26A and the auxiliary winding 26B are wound around the core is the same. Common mode voltage is canceled.

  Thus, by switching the switching of the first arm 20 and the second arm 23 in accordance with the switching state of the inverter 2, the common mode voltage can be canceled and the leakage current is greatly reduced.

  As described above, in the power conversion device of the present embodiment, the leakage current suppression circuit can be configured by the switching element and the capacitor, and there is no need to provide a large filter circuit. Moreover, since the number of parts can be reduced as compared with the first embodiment, the size can be further reduced and the manufacturing cost can be reduced. Therefore, according to the present embodiment, it is possible to provide a leakage current suppressing circuit that effectively suppresses the leakage current without increasing the size.

Next, a leakage current suppression circuit of the power conversion device according to the third embodiment will be described with reference to the drawings.
FIG. 4 is a diagram schematically illustrating a configuration example of a leakage current suppression circuit in the power conversion device of the present embodiment. The leakage current suppression circuit of the present embodiment differs from the leakage current suppression circuit of the second embodiment in the configuration of the common mode transformer 26.

  In the present embodiment, the winding direction of the main winding 26A of the common mode transformer 26 and the winding direction of the auxiliary winding 26B are opposite to each other. 4 shows a configuration in which the winding direction of the common mode transformer 26 is replaced in the power converter of the second embodiment, the winding direction of the common mode transformer 26 in the power converter of the first embodiment. It is the same even if they are replaced.

  FIG. 5 shows the switching of the first arm 20 and the second arm 23 when the voltage of the main winding 26A of the common mode transformer 26 is V1 and the voltage of the auxiliary winding 26B is V2 in the power converter shown in FIG. It is a figure which shows an example of the connection state of an element.

  When the upper elements are all conductive in the three phases of the inverter 2, the common mode voltage of the inverter 2 is + E / 2. At this time, if the lower element 22b of the first arm 20 and the upper element 25a of the second arm 23 are made conductive, the auxiliary winding 26B of the common mode transformer 26 is applied with a voltage V2 of −3E / 4. In response to 2: 3, a voltage V1 of + E / 2 which is the same as the common mode voltage is applied to the main winding 26A of the common mode transformer 26, and the directions of the main winding 26A and the auxiliary winding 26B are reversed. The common mode voltage is canceled out.

  Similarly, when two phases of the three phases of the inverter 2 are conductive with the upper element and one phase with the lower element, a common mode voltage of + E / 6 is generated. At this time, if the lower element 22b of the first arm 20 and the lower element 25b of the second arm 23 are made conductive, a voltage V2 of −E / 4 is applied to the auxiliary winding 26B of the common mode transformer 26. : The voltage V1 of + E / 6, which is the same as the common mode voltage, is applied to the main winding 26A of the common mode transformer 26 in accordance with 3, and the direction in which the main winding 26A and the auxiliary winding 26B are wound around the core is reversed. This cancels the common mode voltage.

  Of the three phases of the inverter 2, when one phase is conducted by the upper element and the second phase is conducted by the lower element, a common mode voltage of −E / 6 is generated. At this time, when the upper element 22a of the first arm 20 and the upper element 25a of the second arm 23 are made conductive, the voltage V2 of + E / 4 is applied to the auxiliary winding 26B of the common mode transformer 26. : A voltage V1 of −E / 6 is applied to the main winding 26A of the common mode transformer 26 in accordance with 3, and the direction in which the main winding 26A and the auxiliary winding 26B are wound around the core is reversed. Common mode voltage is canceled.

  When the lower element is conductive in all three phases of the inverter 2, a common mode voltage of -E / 2 is generated. At this time, if the upper element 22a of the first arm 20 and the lower element 25b of the second arm 23 are made conductive, the auxiliary winding 26B of the common mode transformer 26 is applied with a voltage V2 of + 3E / 4. : A voltage V1 of −E / 2 is applied to the main winding 26A of the common mode transformer 26 in accordance with 3, and the direction in which the main winding 26A and the auxiliary winding 26B are wound around the core is reversed. Common mode voltage is canceled.

  Thus, by switching the switching of the first arm 20 and the second arm 23 in accordance with the switching state of the inverter 2, the common mode voltage can be canceled and the leakage current is greatly reduced.

  As described above, according to the present embodiment, it is possible to provide a power conversion device that effectively suppresses leakage current without increasing the size, as in the first and second embodiments described above.

Next, a leakage current suppression circuit of the power conversion device according to the fourth embodiment will be described with reference to the drawings.
FIG. 6 is a diagram schematically illustrating a configuration example of a leakage current suppression circuit in the power conversion device of the present embodiment. The power converter of this embodiment is different from the power converter of the second embodiment in that a common mode choke coil is connected to the front stage of the common mode transformer 26.

  In the power conversion device of this embodiment, the configuration of the first arm 20 and the second arm 23 and the orientation of the main winding 26A and the auxiliary winding 26B of the common mode transformer 26 are the same as those of the second embodiment described above. As shown in FIG. 3, by switching the switching of the first arm 20 and the second arm 23 in accordance with the switching of the inverter 2, the generated common mode voltage can be canceled and the leakage current can be reduced. To do.

  In the power converter of this embodiment, the common mode choke coil 27 is connected to the power supply line. In the state where either the upper element or the lower element is conductive in each phase of the inverter 2, switching between the first arm 20 and the second arm 23 is switched as shown in the second embodiment and the third embodiment. Thus, the common mode voltage of the inverter 2 can be canceled.

  However, in any phase of the inverter 2, during the so-called dead time period in which the element to be conducted is switched between the upper element and the lower element, the voltage of that phase is not uniquely determined. The common mode voltage cannot be canceled accurately, and a slight common mode current flows. Since the common mode choke coil 27 acts as a large impedance with respect to the common mode current, it is possible to reduce the leakage current that cannot be suppressed by switching the switching between the first arm 20 and the second arm 23.

  As described above, according to the present embodiment, a leakage current suppression circuit for a power converter that effectively suppresses leakage current without increasing the size is provided, as in the first to third embodiments described above. It is possible to reduce leakage current that cannot be suppressed by switching switching between the first arm 20 and the second arm 23.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 1 ... Converter, 2 ... Inverter, 3 ... Smoothing capacitor, 20 ... 1st arm, 21a, 21b, 21c ... Capacitor, 22a ... Switching element (upper element), 22b ... Switching element (lower element), 23 ... 2nd arm 24a, 24b, 24c ... capacitor, 25a ... switching element (upper element), 25b ... switching element (lower element), 26 ... common mode transformer, 26A ... main winding, 26B ... auxiliary winding, 27 ... common mode choke coil.

Claims (5)

Leakage current suppression for use in an inverter device comprising: a converter that outputs a DC voltage; and an inverter that has a plurality of switching elements and that converts the DC voltage output from the converter into an AC voltage by switching the plurality of switching elements. A circuit,
A first switching element pair including two switching elements connected in series and a first capacitor set including a plurality of capacitors connected in series, wherein the first switching element pair is connected in parallel to an intermediate capacitor of the plurality of capacitors The first arm
A second switching element pair including two switching elements connected in series and a second capacitor set including a plurality of capacitors connected in series, wherein the second switching element pair is connected in parallel to an intermediate capacitor of the plurality of capacitors The second arm
A main winding connected in series at the front stage or rear stage of the inverter and connected to the wiring of each phase, and the auxiliary winding connected to the connection point of the first switching element pair and the connection point of the second switching element pair And a common mode transformer with
The first arm and the second arm are connected to a DC line of the inverter device,
The ratio of the voltage of the intermediate capacitor of the first capacitor set to the voltage of the intermediate capacitor of the second capacitor set is 2: 1.
The ratio of the number of turns of the main winding and the number of turns of the auxiliary winding of the common mode transformer is a ratio of the DC voltage of the inverter and three times the voltage of the intermediate capacitor of the first capacitor set. Leakage current suppression circuit. Leakage current suppression for use in an inverter device comprising: a converter that outputs a DC voltage; and an inverter that has a plurality of switching elements and that converts the DC voltage output from the converter into an AC voltage by switching the plurality of switching elements. A circuit,
A first arm including a first switching element pair including two switching elements connected in series;
A second switching element pair including two switching elements connected in series and a second capacitor set including three capacitors connected in series, wherein the second switching element pair is connected in parallel to an intermediate capacitor of the three capacitors The second arm
A main winding connected in series at the front stage or rear stage of the inverter and connected to the wiring of each phase, and the auxiliary winding connected to the connection point of the first switching element pair and the connection point of the second switching element pair And a common mode transformer with
The first arm and the second arm are connected to a DC line of the inverter device,
The capacity ratio between the intermediate capacitor and each of the other two capacitors is 1: 2.
The leakage current suppression circuit according to claim 1, wherein a ratio of the number of turns of the main winding and the number of turns of the auxiliary winding of the common mode transformer is 2 to 3. The inverter is a three-phase output inverter having a first switching element connected to the positive electrode side and a second switching element connected to the negative electrode side for each output phase,
When all the first switching elements of the output three phases are conducted, the switching element on the positive side of the first arm and the switching element on the negative side of the second arm are conducted,
Two of the three output phases of the inverter device are the first switching element, and one is the switching element on the positive side of the first arm and the positive side of the second arm when the second switching element is conductive. The element is conducting,
When one of the three phases of the output of the inverter device is a first switching element and two are conducting a second switching element, the switching element on the negative side of the first arm and the switching on the negative side of the second arm The element is conducting,
When the second switching element is conducted in all three phases of the output of the inverter device, the switching element on the negative side of the first arm and the switching element on the positive side of the second arm are conducted,
The leakage current suppression circuit according to claim 1, wherein the main winding and the auxiliary winding are wound in the same direction. The inverter is a three-phase output inverter having a first switching element connected to the positive electrode side and a second switching element connected to the negative electrode side for each output phase,
When all the first switching elements of the output three phases are conducted, the switching element on the negative side of the first arm and the switching element on the positive side of the second arm are conducted,
When one of the three output phases is the first switching element and one is the second switching element, the negative-side switching element of the first arm and the negative-side switching element of the second arm are conductive. ,
When one of the three output phases is the first switching element and two are the second switching element, the positive-side switching element of the first arm and the positive-side switching element of the second arm Conducting,
When the second switching element conducts in all three output phases, the switching element on the positive side of the first arm and the switching element on the negative side of the second arm conduct,
The leakage current suppression circuit according to claim 1, wherein the main winding and the auxiliary winding are wound in opposite directions.   The leakage current suppression circuit according to any one of claims 1 to 4, wherein a common mode choke coil is disposed on a power supply line of the inverter device.

Images