JP6648577B2 - Power converter - Google Patents

Description

  The present invention relates to a power converter including a zero-phase core for suppressing electromagnetic noise.

A power conversion device that converts input power into predetermined power and outputs the power by performing high-speed switching of power semiconductor switching elements such as IGBTs and MOSFETs at several [kHz] to several hundred [kHz] has high efficiency, small size, Due to advantages such as weight reduction, the spread is rapidly expanding.
However, high-speed switching in the power converter causes electromagnetic noise, and electromagnetic noise disturbance to peripheral devices is a serious problem.

  In order to prevent this type of electromagnetic noise interference, power converters are generally provided with a noise filter and a common mode noise suppressing zero-phase core to reduce electromagnetic noise flowing to the outside. Furthermore, laws and regulations on electromagnetic noise that began in Europe have spread worldwide, and conducted noise (noise terminal voltage) and radiated noise (radiated electric field strength), which are subject to regulations, have been reduced in the usage environment of power converters. The level to be done is clear.

A noise filter applied to a power converter generally includes a reactor (common mode choke coil), a line capacitor, and a grounding capacitor. There is also a fault newly generated by adding a phase core).
For example, the leakage current is increased by the grounding capacitor that constitutes the noise filter and the leakage breaker responds, or these components become overheated due to excessive noise current flowing through the common mode choke coil and zero-phase core. There are cases where the device is damaged.

In particular, device damage due to overheating of the zero-phase core may occur in a variable speed motor drive system or the like.
FIG. 3 is a main circuit configuration diagram of the variable speed motor drive system. 3, reference numeral 10 denotes a three-phase AC power supply (power system), reference numeral 20 denotes a rectifier circuit including diodes 21 to 26, reference numeral 30 denotes a DC intermediate capacitor, reference numeral 40 denotes a three-phase inverter including semiconductor switching elements 41 to 46 such as IGBTs, 50 is an AC motor, 60 is a cooling fin, R, S, T are AC input terminals, E is a ground terminal, and U, V, W are AC output terminals.

In the above-described variable speed motor drive system, a common mode noise current flows along a path indicated by a solid arrow and a differential mode noise current flows along a path indicated by a broken arrow as the switching elements 41 to 46 are turned on and off.
Here, most of the electromagnetic interference is caused by a common mode noise current, that is, a high-frequency leakage current, which causes insulation breakdown of a motor winding and malfunctions of peripheral devices.

In order to reduce the common mode noise current, zero-phase cores 71 to 73 are used as shown in FIG. These zero-phase cores may be inserted in at least one place on the path of the common mode noise current. However, as shown in the illustrated zero-phase cores 71 and 73, the input cables of the AC power supply 10 are collectively connected, or When the output cables on the side of the electric motor 50 are collectively surrounded, they are often used as external components of the power converter. Further, a zero-phase core may be built in the power converter, and may be arranged in a DC intermediate circuit like the zero-phase core 72 in FIG.
In addition, for example, in Patent Document 1, a zero-phase core is arranged so as to enclose a three-phase input cable and a ground line on the AC power supply side or a three-phase output cable and the ground line on the motor side collectively. It is disclosed.

  Note that these zero-phase cores require fewer turns than a common mode choke coil, and are used in one turn (penetrating the wire through the core) or at most consist of several turns.

JP-A-2001-86734 (FIGS. 2 to 4 and the like)

When the inverter 40 is driven, the zero-phase cores 71 to 73 shown in FIG. 4 mainly output the output cable (hereinafter, “cable” and “electric wire” are synonymous) or the electric motor and the ground. It serves to reduce the common mode noise current flowing to the ground line via the stray capacitance formed therebetween.
Here, the longer the output cable or the larger the capacity of the motor, the larger the stray capacitance that is formed, and therefore the larger the common mode noise current. Therefore, the loss of the zero-phase core also increases, and the temperature rise due to overheating of the core becomes remarkable.

Generally, in a power converter such as an inverter, the capacity and drivable length of a drivable motor, the heat-resistant temperature, and the like are specified by the rating and specifications, and each power converter has a motor of an appropriate capacity. A zero-phase core having a specification suitable for the power conversion device is recommended on the assumption that a cable having an appropriate length is connected. In other words, as long as a proper motor or cable is used for the power converter, the zero-phase core is designed not to overheat.
However, in the field, an excessive common mode noise current exceeding the design value may flow through the zero-phase core due to a mistake in the capacity of the motor connected to the power converter or the length of the output cable, and as a result, There is a danger that the zero-phase core will overheat and damage the device.

Also, the temperature of the zero-phase core may rise to the Curie temperature of the core material when the generated loss is extremely large.
This type of zero-phase core is formed of a material such as ferrite, amorphous, and Finemet (registered trademark). The core material used for noise suppression is required to have a high initial magnetic permeability and a high Curie temperature. The Curie temperature of a core made of Finemet (registered trademark) having excellent characteristics is, for example, 570. It reaches [° C].

On the other hand, ferrites for EMC (electromagnetic compatibility) measures and ferrites for transformers and reactors of power converters have been actively developed for materials having a high initial permeability and capable of operating at high temperatures. This is because the application to semiconductor power converters that operate in a higher temperature environment than in the past, such as hybrid vehicles and electric vehicles, is in progress.
In other words, considering the future material development and the flow of applied equipment, the Curie temperature will increase further, and the zero-phase core will run away when used under unexpected conditions in equipment design, resulting in the incorporation of the zero-phase core. It is also assumed that the situation that the damaged device is damaged increases.

  Accordingly, an object of the present invention is to provide a power conversion device capable of preventing damage to the device due to overheating of a zero-phase core for suppressing common mode noise.

In order to solve the above problem, an invention according to claim 1 is a power converter that converts input power into predetermined power by a switching operation of a semiconductor switching element and outputs the converted power, wherein electromagnetic noise generated by the switching operation is provided. In a power converter including a zero-phase core for suppressing
The Curie temperature of the zero-phase core is set to be equal to or lower than the heat-resistant temperature of the electric wire around which the zero-phase core is wound.

An invention according to claim 2 is a power conversion device that converts input power to predetermined power by a switching operation of a semiconductor switching element and outputs the converted power, wherein a zero-phase power for suppressing electromagnetic noise generated by the switching operation is provided. In a power converter having a core,
The Curie temperature of the zero-phase core is set to be equal to or lower than an upper-limit use temperature of the zero-phase core determined by a standard to be satisfied by the power converter.

An invention according to claim 3 is a power conversion device that converts input power into predetermined power by a switching operation of a semiconductor switching element and outputs the converted power, wherein a zero-phase signal for suppressing electromagnetic noise generated by the switching operation is provided. In a power converter having a core,
The Curie temperature of the zero-phase core is set to be equal to or lower than the heat-resistant temperature of a recommended wire recommended as a wire to be connected to the power converter.

The invention according to claim 4 is the power converter according to any one of claims 1 to 3,
The power converter further includes a noise filter for suppressing noise generated due to a switching operation of the semiconductor switching element, wherein the noise filter includes at least one common mode choke coil and at least one ground capacitor. And the zero-phase core is wound around an electric wire such that the impedance of the common mode component is higher on the semiconductor switching element side than on the ground capacitor.

According to the present invention, the Curie temperature of the zero-phase core for suppressing electromagnetic noise provided in the power conversion device is equal to or lower than the heat-resistant temperature of the electric wire around which the zero-phase core is wound or the recommended electric wire of the power conversion device, or By setting the use of the zero-phase core below the upper limit value determined by the standards to be satisfied, even if a wire or load that is not appropriate for the power converter is connected, the zero-phase core can be prevented from overheating, and the zero-phase core and power conversion can be prevented. The device can be prevented from being damaged or the like.
Further, since the design and manufacture of the zero-phase core having the above-described characteristics are relatively easy, there is no possibility that the cost will be significantly increased.

It is the figure which showed the main circuit structure of the power converter which shows 4th Embodiment of this invention, along with the installation position of the noise filter, and the applicable range of the zero-phase core. FIG. 3 is a circuit diagram illustrating a configuration example of a noise filter. It is a main circuit block diagram of a variable speed motor drive system. FIG. 5 is a diagram illustrating an installation position of a zero-phase core in FIG. 4.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, ferrites for EMC measures and power converters are Mn-Zn based ferrites used for coils, transformers, AM frequency band noise measures, and Ni-Zn based ferrites used for FM frequency band noise measures. For example, according to the ferrite catalog of TDK Corporation, both Curie temperatures are generally 120 ° C. or higher. That is, the lower limit of the Curie temperature is specified as a standard for guaranteeing the quality of ferrite, and the upper limit is often not specified. This is considered to be because the main focus is on defining the operating range of the ferrite for the power converter as an inductor.

Strictly speaking, ferrites for EMC measures and power conversion devices are so-called soft ferrites, which are soft magnetic materials mainly composed of iron oxide.
Soft ferrite is also used in temperature-sensitive switches in addition to the above applications. The temperature-sensitive switch functions as a temperature sensor by utilizing the fact that the soft ferrite loses its properties as a magnetic material when the temperature exceeds the Curie temperature and the impedance rapidly decreases.
In the case of the soft ferrite used for the temperature-sensitive switch, the Curie temperature can be set in a range of about -10 [° C] to +130 [° C] depending on the application.

As described above, the use of the soft ferrite for the temperature-sensitive switch that can adjust the Curie temperature relatively freely can possibly prevent overheating of the zero-phase core and damage to the device.
On the other hand, when soft ferrite for EMC measures and power converters is used as it is for the zero-phase core, if the Curie temperature is lower than the heat resistance temperature of general electric wires (excluding heat-resistant wires), the zero-phase core Overheating etc.

Therefore, in the first embodiment corresponding to claim 1, the Curie temperature of the zero-phase core is set to be equal to or lower than the heat resistance temperature of the electric wire around which the zero-phase core is wound by using the same technology as the soft ferrite for the temperature-sensitive switch. By doing so, overheating and burning of the zero-phase core and breakage of the device are prevented.
As described above, since the technology for raising the Curie temperature of soft ferrite for power conversion devices is being developed, it is relatively easy to reduce the Curie temperature of soft ferrite.

Conventionally, when a zero-phase core is mounted inside a power converter, a high-heat-resistant wire is used assuming the worst case, and a design is made so that the device will not be damaged even if the zero-phase core generates heat. However, it is difficult to select an electric wire that does not melt even when the temperature rises to the Curie temperature of the core material.
In this regard, according to the present embodiment, it is only necessary to select an electric wire having heat resistance according to the low Curie temperature of the zero-phase core, so that the degree of freedom in design is improved.

Further, the second embodiment corresponding to claim 2 is based on the assumption that the zero-phase core is built in the power converter, and is equal to or lower than the upper-limit use temperature of the zero-phase core determined by the standard to be satisfied by the power converter. The Curie temperature of the zero-phase core is set so that
Here, the standards to be satisfied by the power conversion device include technical standards, UL standards, CSA standards, IEC standards, and the like in the Electrical Appliance and Material Safety Law. In these standards and standards, generally, a Curie temperature higher than a temperature range (maximum temperature) that can be used for elements such as a reactor, a transformer, and a core is set. This is presumed to be because the stable characteristics of each element can be guaranteed up to a temperature lower than the Curie temperature.

The upper-limit operating temperature of the zero-phase core (for example, 105 ° C. or 120 ° C.) determined by the standard to be satisfied by the power conversion device is usually determined for each element such as the reactor, transformer, and core. The temperature is set lower than the usable temperature.
For this reason, as described above, in the field, when the motor connected to the power converter is used with the wrong capacity or wiring length, an excessive common mode current exceeding the design value may flow through the zero-phase core. And may lead to overheating and breakage.

  In view of the above, in the second embodiment, the Curie temperature of the zero-phase core is set to be equal to or lower than the upper-limit use temperature of the zero-phase core determined by the standard to be satisfied by the power conversion device, so that the zero-phase core is overheated. And so on.

As described in the first embodiment, if soft ferrite is used as the zero-phase core, the technology applied to the temperature-sensitive switch can be used, and a range of about −10 ° C. to + 130 ° C. It is possible to set the Curie temperature with.
For soft ferrites for EMC measures and power converters, it is necessary to manage the manufacturing variation at the lowest temperature of the Curie temperature and to guarantee the temperature range in which the device operates properly. In this case, only the manufacturing variation of the upper limit of the Curie temperature needs to be managed, and it is possible to prevent the zero-phase core from being overheated to the use upper limit temperature or higher based on the required standard of the power converter.

Further, a third embodiment corresponding to claim 3 uses a soft ferrite or the like whose Curie temperature is set to be equal to or lower than the heat resistance temperature of the recommended electric wire described in an instruction manual of the power conversion device, and the like, and the zero-phase core is formed. To form.
This embodiment assumes a case where the zero-phase core and the power converter are provided in a packaging box when the zero-phase core is sold as an external component to the power converter.

  In such a case, since the zero-phase core is delivered to the customer as an external component of the power conversion device, at the delivery destination, an installation worker or a device user attaches the zero-phase core to a preselected wire. Will be. At that time, the instruction manual of the power converter usually describes the recommended maximum length and heat-resistant temperature of the electric wire.However, in the field where the power converter is installed, an electric wire with a length exceeding the maximum length is used. May be used.

As a result, an excessive common mode noise current flows through the zero-phase core, and the zero-phase core exceeds the heat-resistant temperature of the electric wire, and becomes overheated. The device is damaged (the electric wire melts, the output side of the device is short-circuited, and the (Eg, breakage).
If the zero-phase core is installed inside the power conversion device, it is possible to prevent damage to the device by using a high heat-resistant wire assuming the worst case. When shipping as an external part, since the electric wires used at the delivery destination cannot be managed, there is a high possibility that the accident described above will occur.

The third embodiment of the present invention is to solve the above-mentioned problem, and the third embodiment has a zero-phase core below a heat-resistant temperature of a recommended electric wire described in an instruction manual of a power converter. It is characterized by setting the Curie temperature.
This prevents the temperature of the zero-phase core from exceeding the heat-resistant temperature of the wires and prevents the device from being damaged, even when wires of an inappropriate length are connected to the power converter. can do. In addition, if the zero-phase core is used externally to the power converter, there is a risk that a user or an administrator may contact the overheated zero-phase core and cause burns. Since there is no risk of the phase core being overheated, burns and the like can be prevented.

Note that the zero-phase core has almost the same common mode noise reduction effect regardless of where it is installed in the zero-phase cores 71 to 73 shown in FIG. 4 when a noise filter is not used in the power converter. Obtainable.
That is, the common mode noise current generated by driving the inverter 40 is, as shown in FIG. 3, the inverter 40 → the output cable (AC output terminals U, V, W) → the motor 50 → the ground wire → the three-phase AC power supply 10 → Since the current flows in a loop of input cable (AC input terminals R, S, T) → rectifier circuit 20 → DC intermediate circuit → inverter 40, if any of zero-phase cores 71 to 73 is arranged on this route, a predetermined The common mode noise effect is obtained.

  On the other hand, in a power converter provided with a noise filter, an appropriate installation position of the zero-phase core is limited. Therefore, a fourth embodiment corresponding to claim 4 defines the installation position of the zero-phase core when the power converter is used in combination with the noise filter and the zero-phase core.

  FIG. 1 is a main circuit configuration diagram of a power converter according to a fourth embodiment, and shows an appropriate installation position of a zero-phase core according to a connection position of a noise filter. In FIG. 1, reference numeral 91 denotes an input cable, reference numeral 92 denotes an output cable, reference numeral 93 denotes a ground wire, and the other components are denoted by the same reference numerals as those in FIGS.

FIG. 1A shows an example in which a noise filter 80 is connected between an AC power supply 10 and a rectifier circuit 20. In this case, in a region A between the noise filter 80 and the motor 50, the zero-phase core is surrounded so as to surround any one of the input cable, the DC intermediate circuit (positive and negative wires), and the output cable 92 of the rectifier circuit 20. Just place them.
FIG. 1B shows an example in which a noise filter 80 is connected to a DC intermediate circuit. In this case, in the region B between the noise filter 80 and the electric motor 50, a zero-phase core may be arranged so as to surround either the DC intermediate circuit (positive or negative electric wire) or the output cable 92.

Here, a general configuration of the noise filter is, for example, as shown in FIG. In FIG. 2A, a noise filter 81 includes a capacitor (line-to-line capacitor) connected between AC input terminals R, S, T on the power supply side and AC output terminals R ′, S ′, T ′ on the load side. ) 81a, 81c, a ground capacitor 81d, and a common mode choke coil 81b.
Although not shown, even when the components of the noise filter are distributed and arranged such that the common mode choke coil is connected to the power supply side and the ground capacitor is connected to the DC intermediate circuit, the zero-phase core is connected to the ground. It is installed in the DC intermediate circuit or output cable on the inverter side (motor side) rather than the capacitor.

The grounding capacitor has a function of bypassing a common mode noise current generated by, for example, the inverter 40 of FIGS. 1A and 1B, and most of the common mode noise current is converted from the inverter 40 → the output cable 92 → the motor 50 → the ground. It flows on the route of line 93 → ground capacitor → power converter (input cable 91 or DC intermediate circuit) → inverter 40.
That is, the path through which most of the common mode noise current flows is included in the regions A and B shown in FIGS. 1A and 1B, that is, the application range of the zero-phase core.

  Here, the ground capacitors may be dispersedly arranged at a plurality of locations inside the power converter. For example, when a plurality of ground capacitors are connected in parallel one by one, or as shown in FIG. 2B, line capacitors 82a and 82c and ground capacitors 82e and 82d and a common mode choke coil 82b are used. This is the case where the π-type noise filter 82 is configured.

In this case, as a guide, the zero-phase core may be arranged closer to the inverter than a main ground capacitor having a capacitance of about 1/2 or more of the combined capacitance of the ground capacitors.
When the π-type noise filter 82 shown in FIG. 2B is used, if the capacitances of the ground capacitors 82e and 82d are C ₁ and C ₂ , respectively, generally, there is a case where C ₁ ≦ C _2. Therefore, the zero-phase core may be arranged closer to the inverter than the ground capacitor 82d.

  Each of the embodiments described above is directed to a three-phase power converter, but the present invention is applied to a single-phase or multi-phase power converter and a DC power converter used in various industrial fields. It is possible.

10: three-phase AC power supply 20: rectifier circuit 21-26: diode 30: DC intermediate capacitor 40: three-phase inverter 41-46: semiconductor switching element 50: three-phase AC motor 60: cooling fins 80, 81, 82: noise filter 81a, 81c: Line capacitor 81d: Ground capacitor 81b: Common mode choke coil 82a, 82c: Line capacitor 82d, 82e: Ground capacitor 82b: Common mode choke coil 91: Input cable 92: Output cable 93: Ground line R, S, T: AC input terminals R ', S', T ' : AC input terminals _{E, E', E in,} E out: ground terminal U, V, W: AC output terminal

Claims (4)

A power conversion device that converts input power to predetermined power by a switching operation of a semiconductor switching element and outputs the converted power, wherein the power conversion device includes a zero-phase core for suppressing electromagnetic noise generated by the switching operation. ,
A power converter wherein a Curie temperature of the zero-phase core is set to be equal to or lower than a heat-resistant temperature of an electric wire around which the zero-phase core is wound. A power conversion device that converts input power to predetermined power by a switching operation of a semiconductor switching element and outputs the converted power, wherein the power conversion device includes a zero-phase core for suppressing electromagnetic noise generated by the switching operation. ,
A power converter wherein a Curie temperature of the zero-phase core is set to be equal to or lower than an upper-limit use temperature of the zero-phase core determined by a standard to be satisfied by the power converter. A power conversion device that converts input power to predetermined power by a switching operation of a semiconductor switching element and outputs the converted power, wherein the power conversion device includes a zero-phase core for suppressing electromagnetic noise generated by the switching operation. ,
A power converter wherein a Curie temperature of the zero-phase core is set to be equal to or lower than a heat-resistant temperature of a recommended wire recommended as a wire to be connected to the power converter. The power converter according to any one of claims 1 to 3,
The power conversion device further includes a noise filter for suppressing noise generated due to a switching operation of the semiconductor switching element,
The noise filter has at least one common mode choke coil and at least one ground capacitor,
A power converter, wherein the zero-phase core is wound around an electric wire so that the impedance of a common mode component is larger on the semiconductor switching element side than the ground capacitor.

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