WO2013140874A1

WO2013140874A1 - Power conversion device

Info

Publication number: WO2013140874A1
Application number: PCT/JP2013/052658
Authority: WO
Inventors: 敏井堀; 正宏平賀; 雅之広田; 祐介荒尾; 良田中
Original assignee: 株式会社日立産機システム
Priority date: 2012-03-23
Filing date: 2013-02-06
Publication date: 2013-09-26
Also published as: JP5814841B2; JP2013198383A; CN104081612A

Abstract

A power conversion device for outputting AC power having variable voltage and variable frequency, the power conversion device comprising: a forward converter for rectifying and converting AC voltage of an AC power source into DC voltage; a DC intermediate circuit having a smoothing capacitor for smoothing the DC voltage of the forward converter; a current-limiting circuit for suppressing a charge current to the smoothing capacitor of the DC intermediate circuit; a voltage detection circuit for detecting the voltage of the DC intermediate circuit; and a reverse converter for converting the DC voltage of the forward converter into AC voltage. A plurality of relays are connected in parallel to a resistor of the current-limiting circuit, and the plurality of relays are switched on when the rate of change of the voltage detection value of the DC intermediate circuit is equal to or less than a value set in advance.

Description

Power converter

The present invention relates to a power conversion device in which a plurality of relays of the same capacity are connected in parallel to an inrush prevention suppression circuit.

Power converters are widely used as speed control devices for motors in industry and home appliances. The voltage-type inverter, which is currently the mainstream power converter, converts AC voltage to DC with a forward converter, smoothes it with a large capacity electrolytic capacitor in the DC intermediate circuit, and then AC voltage with an arbitrary frequency again with an inverter. Convert to

An inrush prevention circuit is provided for the purpose of protecting the rectifier diode constituting the forward converter from the charging current from the large charging current to the electrolytic capacitor in the DC intermediate circuit. In general, the inrush prevention circuit includes a resistor for suppressing current and a relay connected in parallel to the resistor.

When turning on the power, the charging current to the electrolytic capacitor is suppressed by resistance, and the relay is turned on when the charging voltage of the electrolytic capacitor is fully charged. After the relay is turned on, no current flows through the resistor that suppresses the current, and all current flows through the relay. Therefore, the resistor that suppresses the current has a resistance loss until the relay is turned on. Become.

However, as the capacity of the power converter increases, the current flowing through the relay also increases in proportion to the capacity. As a result, the volume of the relay increases, the power converter increases in size, and a large bottleneck in terms of miniaturization. There was a problem of becoming.

In Patent Document 1, as a parallel contact abnormality detection device, solenoid coils that are depolarized from each other are connected in series with parallel connection points, and a contact detection signal that detects a voltage generated between each connection point is output. It is disclosed that the system can be safely stopped by detecting an abnormality in the parallel contact portion using an inrush current limiting relay.

Patent Document 2 detects the effective value of the voltage of the three-phase AC power input to the power converter and the DC voltage rectified by the rectifier circuit, and the DC voltage is calculated based on the effective value. A power conversion device is disclosed in which a switch is closed by a control circuit when a threshold value is exceeded.

Patent Document 3 discloses an inverter device characterized in that a plurality of semiconductor switching elements of an inrush prevention circuit are connected in parallel.

JP 2008-206280 JP 2011-87378 JP 2001-112265

In paragraph [0004] of Cited Document 1, the parallel contact abnormality detection device for the power conversion device according to the prior art is expensive because it is performed using the abnormality detection contact incorporated in the inrush current limiting relay. Also, it has been disclosed that the parallel use of inrush current limiting relay contacts that do not have an anomaly detection contact has the problem that if one of the contacts fails to open, the current concentrates on the other contact and burns out. Yes. In paragraph [0005], in view of such a problem, it is possible to detect the abnormality of the parallel contact portion at low cost by using an inrush current limiting relay having no abnormality detection contact, and to stop the system safely. It is disclosed that an object is to provide a power conversion device that can perform the operation, and detects the abnormality of a parallel contact, and the change rate of the voltage detection value of the DC intermediate circuit is set in advance for the ON timing of the relay. There is no disclosure of what to do when it falls below the stated value.

In addition, since a large current flowing through the DC circuit also flows through the solenoid coil, a large-sized coil is required, which is a major bottleneck for downsizing the inverter device.

In paragraph [0023] of the cited document 2, when Vdc> Vdc * −ΔV at t = t2, a command signal for turning on the switch from the command signal generator 12 to the switch 6 and maintaining the state is provided. It is output that the switch 6 is turned on.

Also, paragraph [0024] describes that the set value of ΔV is determined based on the allowable power of the rectifier circuit 2 in the power converter, the capacity of the smoothing capacitor 6, and the like. However, there is no disclosure about the point at which the switch is turned on when the rate of change in the voltage detection value of the DC intermediate circuit composed of the smoothing capacitor becomes equal to or less than a preset value.

Also, a transformer is required to detect the effective value of the voltage of the three-phase AC power input to the power converter, which again becomes a major bottleneck for downsizing the inverter device.

The paragraph [0006] of the cited document 3 has a problem that the characteristics change depending on the input frequency because the inverter device of the prior art 1 uses a coil for the relay of the inrush prevention circuit, the electromagnetic contactor, etc. It is described that there was a restriction on the received voltage of the inverter.

In paragraph [0025], after a predetermined time for the smooth C voltage to rise to a predetermined voltage has elapsed (t = a), the inrush prevention circuit controller 6 is operated to drive the inrush prevention drive circuit 30. Thus, it is disclosed to turn on the thyristor power supply voltage by turning on the thyristors 4a and 4b.

Furthermore, paragraph [0028] includes a load for reliably operating the thyristors 4a and 4b when the gate trigger current and the gate trigger voltage of the thyristors 4a and 4b with respect to the lower limit value of the operating temperature of the inverter device are IGT2 and VGT2, respectively. The line must pass through the shaded area in FIG. 3 without interruption. In other words, it is necessary for the semiconductor switching elements 4a and 4b to ignite within a predetermined ambient temperature range of the inverter device. If the power supply voltage of the DC power supply 5 dedicated to the inrush prevention circuit is Vs, the hatched portion is interrupted. It is disclosed that the load line passing through is within the range of the load line e and the load line f, the minimum value of the gate resistance 13 is obtained from the load line e, and the maximum value of the gate resistance is obtained from the load line f. Has been.

In actual circuit design, the power supply voltage value and the gate resistance value are determined in consideration of the fluctuation range of the power supply voltage and the variation in resistance value.

It is described that when a resistor is connected between the gate and cathode of the thyristor, it is necessary to take into account the current flowing through this resistor, and the gate trigger current depends on the operating temperature. The difficulty of gate control of thyristors, in which sigma changes greatly, is described. That is, in order to operate the thyristor accurately even at the minimum value of the specified operating temperature of the inverter device, it must be less than the minimum gate resistance value Rmin obtained from the load line e.

発生 Since the generated loss of gate resistance increases in proportion to (Vs * Vs) / Rmin, a resistor with a large allowable loss and a large physique is required, which is a bottleneck for downsizing the inverter device.

In paragraph [0023], the inrush prevention circuit DC power source 5 is a DC power source based on the cathode potentials of the thyristors 4a and 4b. Although this DC power supply 5 for the inrush prevention circuit is described as using a switching power supply or using a secondary battery such as a battery like other DC power supplies used inside the inverter device, it is described. An independent separate power supply must be prepared as the DC power supply 5 for the inrush prevention circuit, and this is also a bottleneck for downsizing the inverter device.

Further, paragraph [0009] clearly states that the semiconductor switching element can be applied to the inrush prevention circuit of the large-capacity inverter device, and the purpose is to obtain an inexpensive and highly reliable inverter device and motor drive device. However, it does not assume a small inverter device with a small capacity.

Further, Patent Document 3 does not disclose that the thyristors 4a and 4b connected in parallel are turned on when the rate of change in the voltage detection value of the DC intermediate circuit is equal to or lower than a preset value.

In Patent Document 1, Patent Document 2 and Patent Document 3, a plurality of relays of the same capacity are connected in parallel to the resistors constituting the inrush prevention circuit, and the plurality of relays connected in parallel are used to detect the voltage of the DC intermediate circuit. There is no disclosure of a point that turns on when the rate of change of the value is equal to or lower than a preset value.

Regarding the parallel driving of relays or thyristors described in Patent Document 1, Patent Document 2, and Patent Document 3, none of the elements can be turned on simultaneously in terms of timing.

同時に Even if a voltage is applied to the relay excitation circuit or thyristor gate circuit at the same time, it cannot be turned on simultaneously due to variations in the elements. There is always a time lag.

In this case, the current concentrates on the element that is turned on first in time, and ideally, the current is shared about half each when the other element is turned on with a time delay. Even in this case, if the impedances of the elements connected in parallel are not equal, the current concentrates on the element having the smaller impedance, and there is a risk of contact welding of the relay or destruction of the thyristor element, for example. For this reason, in Patent Document 1, it is possible to connect the solenoid coil in series with the parallel connection point of the relay, and to use the depolarization to make the shared current substantially uniform, but a coil that is a scroll is required. .

In Patent Document 2, the effective value of the voltage of the three-phase AC power source input to the power converter and the DC voltage rectified by the rectifier circuit are detected, and the DC voltage is calculated based on the effective value. Although it is disclosed that the switch is closed by the control circuit when the threshold ΔV or more is reached, in general, the capacitance value of the electrolytic capacitor for smoothing has a variation in the initial capacitance value with respect to the stated capacity of the component. Since the specification is ± 20%, even if the capacitance is 1000 μF, the capacitance value will be a barack from 800 μF to 1200 μF. In other words, the actual capacitance value is unknown even when looking at the capacitance value described in the actual product of the smoothing electrolytic capacitor.

For this reason, it is necessary to measure and store the initial capacitance value when it is mounted on the power converter, but this is not realistic. Furthermore, since the electrolytic capacitor has a limited life, it is necessary to measure and store the initial capacitance value when replacing with a new part. However, this point is not realistic.

In addition, the electrolytic capacitor for smoothing has a chemical reaction inside, and its lifetime is generally called the 10 ° C half law (Arrhenius's law). Has a characteristic that the life is doubled when the temperature drops by 10 ℃.

Generally, in the case of a general-purpose inverter that is a power conversion device, a smoothing electrolytic capacitor is defined as a life component, and it is difficult to accurately predict a capacity decrease due to aging.

In paragraph [0024], the set value of ΔV is determined based on the allowable power of the rectifier circuit 2 in the power converter, the capacity of the smoothing capacitor 6, and the like. The method of determining is not particularly specified, but it is described that it may be determined experimentally at the time of product design, for example, but the threshold voltage is considered in consideration of the initial variation of the capacitance value of the electrolytic capacitor and the capacitance decrease due to secular change. It is practically difficult to calculate ΔV in advance.

Furthermore, in Patent Document 3, it is described that the inrush prevention circuit control unit 6 is operated after a predetermined time when the smooth C voltage rises to the predetermined voltage (t = a). It is practically difficult to calculate the predetermined time in advance in consideration of the initial variation in the capacitance value of the electrolytic capacitor and the capacity decrease due to secular change.

Further, paragraph [0025] describes that the semiconductor switching element of the inverter unit 8 is driven to raise the motor frequency after a predetermined time (t = b) after turning on the thyristors 4a and 4b. In order to drive the motor after the smooth C voltage is established, it can be determined in the worst state considering the initial variation of the capacitance value of the electrolytic capacitor and the capacity decrease due to aging. Needs to be set when the predetermined time (t = b) is the longest, and there is a problem that the time from when the three-phase AC power input to the power converter is turned on until the power converter can be started is increased. .

An object of the present invention is to provide a power conversion device that is miniaturized as a whole device by connecting a plurality of relays having the same capacity in parallel with a resistor constituting an inrush prevention circuit.

In order to solve the above problems, a forward converter that rectifies an alternating voltage of an alternating current power source and converts it into a direct current voltage, a direct current intermediate circuit having a smoothing capacitor that smoothes the direct current voltage of the forward converter, and the direct current intermediate circuit A variable current circuit comprising: a current limiting circuit that suppresses a charging current to the smoothing capacitor; a voltage detection circuit that detects a voltage of the DC intermediate circuit; and an inverse converter that converts the DC voltage of the forward converter to an AC voltage. A power converter that outputs AC power having a voltage variable frequency, wherein a plurality of relays are connected in parallel to the resistance of the source circuit, and a rate of change of a voltage detection value of the DC intermediate circuit is preset. The configuration is such that the plurality of relays are turned on when the value becomes lower than the value.

According to the present invention, a plurality of relays connected in parallel to the resistance of the current-limiting circuit are turned on when the rate of change of the voltage detection value of the DC intermediate circuit is equal to or less than a preset value, Since the current flowing through each relay can be suppressed, and the current sharing ratio can be made substantially the same, a power conversion device that is downsized as a whole device can be provided.

It is a main circuit block diagram of a power converter device. It is an example of the components arrangement | positioning block diagram of a power converter device. It is a dimensional drawing of a relay with a rated current of 8A. It is a dimensional drawing of a relay with a rated current of 16A. It is an example of the DC voltage detection circuit block diagram of a DC intermediate circuit. It is an example of the transient characteristic figure of the charging voltage Vpn to a smoothing capacitor. It is an example of the copper foil pattern figure on a board | substrate. It is an example of the copper foil pattern figure on a board | substrate. It is another example of the copper foil pattern figure on a board | substrate. It is another example of the copper foil pattern figure on a board | substrate.

Hereinafter, the present invention will be described with reference to the drawings. In addition, the same reference number is attached | subjected about the common structure in each figure. Further, the present invention is not limited to the illustrated example.

FIG. 1 shows a main circuit configuration diagram of the power converter 12 according to the present embodiment. 1 is a forward converter that converts AC power into DC power, 2 is a smoothing capacitor, 3 is an inverse converter that converts DC power into AC power of an arbitrary frequency, and 4 is an AC motor. Reference numeral 6 denotes a cooling fan for cooling the power semiconductor module 11 including the forward converter 1 and the reverse converter 3.

7 is a digital operation panel that can set, change and display various control data of the power converter 12. The MCU, which is a microcomputer mounted on the control circuit 5, performs calculations based on information from the storage data of the storage unit in which various control data is stored, and generates various control data input from the digital operation panel 7. It is configured to perform necessary control processing accordingly. The digital operation panel 7 is configured to display an abnormality when an abnormality occurs.

5 is a control circuit that controls the switching element, which is a power semiconductor of the reverse converter, and also controls the power converter 12 as a whole, and is a control circuit equipped with a microcomputer MCU, which is input from the digital operation panel 7. It is configured so that necessary control processing can be performed according to various control data. A driver circuit 8 drives the switching element of the inverse converter.

9 is an inrush prevention circuit, which is composed of a resistor RB for suppressing the initial charging current to the smoothing capacitor 2 and relays RY1 and RY2 connected in parallel to the resistor.

RYS is the signal that turns on relays RY1 and RY2. Although the case where two relays are arranged in parallel is described, the number of relays arranged in parallel is not limited. Since the inverter which is the power converter 12 is a known technique, a detailed description thereof is omitted.

Figure 2 is an example of the main circuit component layout. Relays RY1 and RY2 having the same capacity with lead terminals are mounted in a soldered state on a substrate 8 on which a drive circuit is mounted.

A cooling fan 6 for cooling the cooling fin 6 (a dotted line portion in the figure) is mounted on the cooling fin 13 with the composite module 11 which is a collective power semiconductor in which the forward converter 1 and the reverse converter 3 are mounted in one module. ) Is a structure attached to the upper surface of the cooling fin. Since the composite module 11 configured as a collective power semiconductor generates a large loss, heat generated by this loss is conducted to the cooling fin 13 and the cooling fan 6 is used to cool the cooling fin 13. A resin module case 14 on which the control circuit 5 is mounted is attached to the cooling fin 13 so as to cover the drive circuit 8 and the power semiconductor 11.

FIG. 3 is an example of a dimensional diagram of the relay. (a) is a dimensional diagram of a relay with a rated current of 8A, and (b) is a dimensional diagram of a relay with a rated current of 16A. The volume of the relay in (a) is 10 * 20 * 15.6, and the volume of the relay in (b) is 15.7 * 30.1 * 23.3. Fig. 2 shows the case where two relays of (a) are installed, but comparing the occupied volume ratio in the inverter device with the case of installing one relay of (b), 2 * (10 * 20 * 15.6) / (15.7 * 30.1 * 23.3) * 100 ≒ 57%
Therefore, it can be said that connecting two relays with small rated currents in parallel reduces the occupied volume ratio and is suitable for a small-sized small inverter device with strict dimensions.

FIG. 4 is an example of a DC voltage detection circuit configuration diagram of the DC intermediate circuit.

The DC voltage Vpn of the DC intermediate circuit is divided by the resistors R1 and R2, the divided voltage is insulated by the insulated linear amplifier AMP, the insulated voltage is taken into the A / D converter of the microcomputer, and the rate of change of the DC voltage is calculated To do.

The DC voltage change rate ΔVpn can be calculated by the following formula.

ΔVpn = [Vpn {t (n + 1)}-Vpn {t (n)}] ------------- Equation (1)
here,
Vpn {t (n + 1)}: Detected DC voltage after elapse of time t (n + 1) Vpn (tn): Detected DC voltage after elapse of time (tn) ΔVpn: Time (tn) to time t (n + 1) Rate of change of DC voltage until the lapse of time The rate of change of DC voltage at each time from time tn to time t (n + 1) is calculated, and when this rate of change falls below a preset value, The relay excitation drive circuit 15 operates, and the RYS output signal causes a current to flow through an excitation circuit (not shown) of the relays RY1 and RY2 to turn on the relays RY1 and RY2.

It is well known that the charging voltage Vpn to the smoothing capacitor 2 that is the DC intermediate circuit in FIG. 1 is expressed by the following equation, where the effective value of the input power supply voltage to the power converter is V.

Vpn = √2 * V * [1-exp {-t / (C * R)}] ---------------------------- --------- Formula (2)
Here, t is time, C is the capacitance value of the smoothing capacitor 2, and R is the resistance value of the current limiting resistor RB.

From Equation (2), the charging voltage Vpn is determined uniquely by the effective value of the input power supply voltage Vrs by V, the capacitance value C of the smoothing capacitor 2, and the resistance value R of the current limiting resistor RB. τ = C * R is also uniquely determined. This eliminates the need to detect the effective value V of the input power supply voltage as disclosed in Patent Document 2, and includes all changes in capacitance due to changes in the effective value V of the input power supply voltage and changes over time of the smoothing capacitor 2. It is expressed as an equation (2) in an elliptical form.

For this reason, the change rate ΔVpn of the charging voltage Vpn to the smoothing capacitor 2 expressed by the equation (2) is calculated and detected, and when this change rate becomes a predetermined value or less, the excitation drive circuit 15 of the relay If the is operated, current flowing through the plurality of relays can be suppressed, and welding of the contact points of the relay due to charging overcurrent to the smoothing capacitor 2 when the relay is on can be prevented.

FIG. 5 is an example of a transient characteristic diagram of the charging voltage Vpn to the smoothing capacitor 2. The three-phase AC power input to the power converter at time to is turned on, and the charging voltage of the smoothing capacitor 2 rises according to the equation (2). What is important in this case is that the capacitance value C of the smoothing capacitor 2 and the resistance value R of the current limiting resistor RB are uniquely determined, and the charging time constant τ = C * R of the transient characteristic is also uniquely determined. This is the problem described in the problem to be solved by the invention, that is, the initial variation of the capacitance value of the electrolytic capacitor and the capacity decrease due to secular change show the behavior considered in the equation (2). That is.

If the charging voltage of the electrolytic capacitor according to the equation (2) is detected, it can be detected as information including the initial variation in the capacitance value of the electrolytic capacitor and the capacitance drop due to aging.

That is, no matter how much the capacitance value of the electrolytic capacitor varies due to initial variation or aging, the set value of ΔV disclosed in paragraph [0024] of Patent Document 2 is the rectifier circuit in the power converter. 2 is determined based on the allowable power of 2 and the capacity of the smoothing capacitor 6, for example, it may be determined experimentally during product design, but the voltage detection value of the DC intermediate circuit that is the voltage across the electrolytic capacitor By detecting the rate of change, it is possible to consider all initial variations in the capacitance value of the electrolytic capacitor and capacitance reduction due to aging, and it is not necessary to determine experimentally at the time of product design.

The voltage of the DC intermediate circuit is detected every predetermined detection time Δt, the change rate ΔVpn of the DC intermediate circuit at time tn and time t (n + 1) is calculated, and this change rate is a preset value ΔVd At time t (n + 1) when the following occurs, the excitation drive circuit 15 of the relay operates, and the RYS output signal causes a current to flow through the excitation circuit (not shown) of the relays RY1 and RY2 to turn on the relays RY1 and RY2. It is a configuration.

FIG. 6 is an example of a copper foil pattern diagram on the substrate.

(a) and (b) are enlarged parts where the relay is mounted among the components constituting the drive circuit 8, and the thick black line is a copper foil pattern wired on the substrate, A current flows through the copper foil pattern.

This is an example in which the lead terminals of relays RY1 and RY2 pass through through holes provided on the substrate and are soldered. Here, (a) is an example of a copper foil pattern in which the sharing of currents flowing through the relays RY1 and RY2 connected in parallel is unbalanced.

The current I flowing into the relays RY1 and RY2 is inversely proportional to the impedance from the inflow point to the outflow point, that is, the wiring length of the copper foil pattern. If the cross-sectional areas of the copper foil patterns are the same, the longer the wiring length, the higher the impedance and the smaller the current, and the shorter the wiring length, the smaller the impedance and the larger the current. In the copper foil pattern example (a), a large amount of current flows through the relay RY1 with a short copper foil pattern (0.7I: 70%), and a small current (0.3I: 30%) through the relay RY2 with a long copper foil pattern. As a result, current sharing between relays RY1 and RY2 becomes unbalanced. In this case, the inflowing current concentrates on the relay RY1, resulting in exceeding the rated current specification, which causes destruction such as contact welding of the relay RY1.

(B) An example of a copper foil pattern that eliminates the above-mentioned problems and balances the sharing of current flowing through relays RY1 and RY2 connected in parallel (0.5I: 50%) is (b).

The total impedance of the current inflow side copper foil pattern and the current outflow side copper foil pattern from the current inflow and outflow points to the lead electrode terminals of the relays RY1 and RY2 is approximately the same for each relay RY1 and RY2. If the mounting is performed in consideration of the copper foil pattern and the lead terminal arrangement of the relay, the sharing of the current flowing through the relays RY1 and RY2 connected in parallel can be made uniform.

That is, the ratings of relays RY1 and RY2 connected in parallel can be fully utilized. In the present embodiment, the case where there are two relays in parallel is described, but the number of relays in parallel is not limited.

FIG. 7 is another example of a copper foil pattern diagram on the substrate.

(A) and (b) are examples of copper foil patterns in which the sharing of the current flowing through the relays RY1 and RY2 connected in parallel is balanced.

(a) shows the pattern wiring length from the branch point of the current inflow side wiring to RY1 and RY2 connected in parallel to the current outflow connection point to RY2 and the branch point of the current inflow side of RY1 to RY1. This is the case of the copper foil pattern where the pattern wiring length to the current flow connection point is approximately the same. (B) is from the branch point of the current inflow side wiring to RY1 and RY2 connected in parallel to RY2. The ratio of the wiring length and cross-sectional area of the pattern up to the current outflow connection point and the ratio of the wiring length and cross-sectional area of the pattern from the branch point of the wiring on the current inflow side of RY1 to the current flow connection point to RY1 are substantially the same It is an example at the time of setting it as the copper foil pattern which becomes.

The impedance Z of the copper foil pattern is determined by Z = ρ * L / S, and ρ is the resistivity. This resistivity ρ is a constant uniquely determined by the material, for example, for copper: 1.72 × 10 ^ -6 ohm · cm, for silver: 1.62 × 10 ^ -6 ohm · cm. Therefore, once the material is determined, the impedance Z of the wiring pattern is determined by the ratio of the wiring length L and the cross-sectional area S (product of the pattern width and the pattern thickness), that is, Z∝L / S. That is, if the cross-sectional area S is doubled, the impedance Z becomes the same even if the wiring length is doubled.

For this reason, when the cross-sectional area S of the copper foil pattern is the same, if the wiring length L of the copper foil pattern is designed to be substantially the same, the impedance Z of the copper foil pattern can be made equal. An example is (a). Also, when the cross-sectional area S of the copper foil pattern is different, the impedance Z of the copper foil pattern can be made equal if the wiring length L of the copper foil pattern and the ratio of the cross-sectional area S are designed to be substantially the same. An example in this case is (b). Even in this case, the sharing of the current flowing through the relays RY1 and RY2 connected in parallel can be made uniform.

Of course, the copper foil pattern on the substrate can be provided on both the front surface and the back surface of the substrate. In this case, the ratio of the wiring length and cross-sectional area of the pattern provided on the front surface and the wiring length of the pattern provided on the back surface It may be considered that the ratio of the cross-sectional areas is parallel, and the same applies to the case where a pattern is provided on the inner layer of the substrate. (a) and (b) are one example and do not limit the copper foil pattern on the substrate.

That is, the ratings of relays RY1 and RY2 connected in parallel can be fully utilized.

This embodiment describes the case where there are two relays in parallel, but the number of relays in parallel is not limited.

1 ... Order converter, 2 ... Smoothing electrolytic capacitor, 3 ... Reverse converter, 4 ... AC motor, 5 ... Control circuit, 6 ... Cooling fan, 7 ... Digital operation panel, 8 ... Drive circuit, 9 ... Inrush prevention circuit , 10 ... connector, 11 ... power semiconductor, 12 ... power converter, 13 ... cooling fin, 14 ... resin molded case, 15 ... relay excitation drive circuit, RB ... current limiting resistor, RY1, RY2, RY3 ... relay, MCU ... microcomputer, Vpn ... DC intermediate circuit detection voltage with smoothing capacitor, RYS ... relay contact on signal, AMP ... isolated linear amplifier, AD ... A / D converter, *: multiplication factor, √ ... square root, ΔVd ... preset Change rate value, L ... copper foil pattern wiring length, S ... copper foil pattern cross-sectional area

Claims

A forward converter that rectifies the AC voltage of the AC power source and converts it into a DC voltage;
A DC intermediate circuit having a smoothing capacitor for smoothing the DC voltage of the forward converter;
A current limiting circuit for suppressing a charging current to the smoothing capacitor of the DC intermediate circuit;
A voltage detection circuit for detecting a voltage of the DC intermediate circuit;
An inverse converter that converts a DC voltage of the forward converter into an AC voltage;
A power conversion device that outputs AC power with variable voltage and variable frequency comprising:
A plurality of relays are connected in parallel to the resistance of the source circuit, and the plurality of relays are turned on when the rate of change in the voltage detection value of the DC intermediate circuit is equal to or less than a preset value. A power conversion device.
The power conversion device according to claim 1,
The power converter according to claim 1, wherein the relays connected in parallel are configured with relays having the same rated capacity.
The power conversion device according to claim 1,
The electrode terminals of the plurality of relays connected in parallel are such that the total impedance due to the current inflow side copper foil pattern and the current outflow side copper foil pattern to each relay electrode terminal is substantially the same for each relay. A power converter characterized by having a wiring pattern.
The power conversion device according to claim 1,
Pattern wiring length from the branch point of the current inflow side wiring to RY1 and RY2 connected in parallel to the current outflow connection point to RY2 and the current flow connection point from the branch point of the current inflow side of RY1 to RY1 A power conversion device characterized by having a wiring pattern in which the pattern wiring lengths up to are substantially the same.
The power conversion device according to claim 1,
The ratio of the pattern wiring length and cross-sectional area from the branch point of the current inflow side wiring to RY1 and RY2 connected in parallel to the current outflow connection point to RY2, and RY1 from the branch point of the current inflow side wiring of RY1 A power converter having a wiring pattern in which the ratio of the wiring length and the cross-sectional area of the pattern up to the current flow connection point is substantially the same.