CN112262526A

CN112262526A - Power conversion device

Info

Publication number: CN112262526A
Application number: CN201980038355.0A
Authority: CN
Inventors: 高野裕理; 高田英人; 梁田哲男; 松本丰; 上井雄介
Original assignee: Hitachi Industrial Equipment Systems Co Ltd
Current assignee: Hitachi Industrial Equipment Systems Co Ltd
Priority date: 2018-11-22
Filing date: 2019-07-11
Publication date: 2021-01-22
Anticipated expiration: 2039-07-11
Also published as: WO2020105219A1; CN112262526B; JP6925313B2; JP2020089027A

Abstract

The invention provides a power conversion device capable of properly performing overload protection even when the rotating speed of a cooling fan is reduced. The power conversion device includes: an inverter circuit (2) that converts a direct-current voltage into an alternating-current voltage and energizes the motor (1) with the alternating-current voltage; a current detector (5) that detects a load current (I1) flowing through the motor (1); a cooling fan (7) for cooling the inverter circuit (2) or the motor (1); and an overload protection unit (8) for protecting the inverter circuit (2) or the motor (1). The overload protection unit (8) stores in advance a thermal time-limit characteristic map for determining the correspondence relationship between the load current (I1) and the continuous energization time, corrects the thermal time-limit characteristic map in accordance with the rotation speed of the cooling fan (7), and issues an energization stop command (Con) when the continuous energization time of the load current (I1) reaches the continuous energization time based on the corrected thermal time-limit characteristic map.

Description

Power conversion device

Technical Field

The present invention relates to a power conversion apparatus, and for example, to an overload protection technique in a power conversion apparatus that supplies power to a load.

Background

Conventionally, in a power converter that supplies power to a load such as a motor, as a protection method at the time of overcurrent or overload, a method of providing a current detection breaking device (thermal relay) in a power supply line leading to the power converter has been used. However, since this method simply compares the detected current value with a threshold value, there is a case where overload protection of the power converter and the motor cannot be appropriately performed in consideration of an operating state such as an operating speed of the motor.

As a technique for solving such a problem, an inverter device shown in japanese patent publication No. 62-55379 (patent document 1) can be cited. The inverter device stores in advance a thermal time-limit characteristic indicating a continuous operable time in consideration of a cooling effect inherent to the motor, and compares the thermal time-limit characteristic with a thermal history analog value (integrated value) calculated from a current value supplied to the motor. This makes it possible to appropriately perform overload protection in consideration of the operating state of the motor. This approach is commonly referred to as an electronic thermal relay.

Documents of the prior art

Patent document

Patent document 1: japanese examined patent publication No. 62-55379

Disclosure of Invention

Problems to be solved by the invention

In general, in motors and power conversion devices, there is a demand for miniaturization together with higher output. In order to eliminate the reduction in the heat radiation effect, a cooling fan is often mounted on the motor and the power conversion device. In this case, the thermal time limit characteristic for the electronic thermal relay is determined on the premise that the cooling fan is normally operated.

However, the cooling fan may have a reduced rotation speed due to, for example, a failure, deterioration with age, or contamination. In this way, in a situation where the cooling effect is reduced as the rotation speed of the cooling fan is reduced, it may become difficult to appropriately perform the overload protection with the electronic thermal relay. As a result, there is a risk of occurrence of burnout, breakage, or the like of the motor or the power conversion device.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a power conversion device capable of appropriately performing overload protection even when the rotation speed of a cooling fan is reduced.

The above and other objects and novel features of the present invention will be apparent from the description of the specification and the accompanying drawings.

Means for solving the problems

A brief description will be given of an outline of a representative embodiment among embodiments disclosed in the present application, as follows.

The power conversion device according to a representative embodiment of the present invention includes: an inverter circuit that converts a direct-current voltage into an alternating-current voltage and energizes a load with the alternating-current voltage; a current detector that detects a load current flowing in the load; a cooling fan that cools the inverter circuit or the load; and an overload protection section that protects the inverter circuit or the load. The overload protection unit stores a thermal time-limit characteristic map for determining a correspondence relationship between the load current and the continuous energization time, corrects the thermal time-limit characteristic map in accordance with the rotation speed of the cooling fan, and issues an energization stop command when the continuous energization time of the load current reaches the continuous energization time based on the corrected thermal time-limit characteristic map.

ADVANTAGEOUS EFFECTS OF INVENTION

The effect obtained by the representative embodiment of the invention disclosed in the present application will be briefly described, and overload protection can be appropriately performed even when the rotation speed of the cooling fan is reduced.

Drawings

Fig. 1 is a block diagram showing a configuration example of the periphery of a power conversion device according to an embodiment of the present invention.

Fig. 2 is a schematic diagram showing an example of the external shape of the periphery of the power converter shown in fig. 1.

Fig. 3 is a block diagram showing a detailed configuration example of the overload protection unit in fig. 1.

Fig. 4 is a diagram conceptually showing the contents of the hot time limit characteristic map for addition in fig. 3.

Fig. 5 is a diagram conceptually showing the contents of the hot time limit characteristic map for subtraction in fig. 3.

Fig. 6 is a conceptual diagram illustrating a schematic operation example of the integration method.

Fig. 7 is a diagram showing an example of actual holding contents of the addition and subtraction thermal time-limit characteristic maps in fig. 3.

Fig. 8 is a schematic diagram showing an operation example of the power converter of fig. 1.

Detailed Description

In the following embodiments, when the number of elements or the like (including the number, numerical value, amount, range, and the like) is referred to, the number is not limited to a specific number unless otherwise specified or clearly limited to a specific number in principle, and may be equal to or larger than or smaller than the specific number. In the following embodiments, the constituent elements (including element steps) are not essential except for those explicitly shown in particular and those explicitly considered essential in principle. Similarly, in the following embodiments, when referring to the shape, positional relationship, and the like of the constituent elements and the like, the shapes substantially similar to or similar to the shapes and the like are included except for cases where they are specifically shown and cases where they are not considered to be the same in principle. The same applies to the above values and ranges.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In all the drawings for describing the embodiments, the same components are denoted by the same reference numerals in principle, and repeated description thereof will be omitted.

Structure around Power conversion device

Fig. 1 is a block diagram showing a configuration example of the periphery of a power conversion device according to an embodiment of the present invention. Fig. 1 also shows, in addition to the power conversion device 10, a three-phase power supply 3 that supplies power to the power conversion device 10, and a load to which power is supplied from the power conversion device 10. The load is, for example, a motor (three-phase motor) 1 or the like. The power conversion device 10 includes an inverter circuit 2, a converter circuit 4, a current detector 5, a controller 6, an overload protection unit 8, and a current sensor 9.

The converter circuit 4 converts an ac voltage from the external three-phase power supply 3 into a dc voltage Vdc and supplies the dc voltage Vdc to the inverter circuit 2. The inverter circuit 2 converts the dc voltage Vdc into ac voltages (three-phase ac voltages Vu, Vv, Vw), and energizes the motor 1 with the three-phase ac voltages Vu, Vv, Vw. The current sensor 9 is provided on a supply line of the three-phase ac voltages Vu, Vv, Vw. The current detector 5 detects a load current flowing in the motor 1 via the current sensor 9. In this example, the current detector 5 detects the u-phase current Iu and the w-phase current Iw via the current sensor 9, and converts the coordinates thereof into the d-axis current Id and the q-axis current Iq. Then, the current detector 5 detects the load current I1 by vector-synthesizing the d-axis current Id and the q-axis current Iq.

The controller 6 controls the inverter circuit 2 so that the operating state of the motor 1 approaches a target state. In this example, the controller 6 receives an external speed command value Nref, and generates three-phase voltage command values Vuref, Vvref, and Vwref for rotating the motor 1 at a rotation speed based on the speed command value Nref by using position sensorless vector control.

Specifically, the controller 6 estimates the rotation speed of the electric motor 1 using, for example, an induced voltage observer or the like, calculates current command values for the d-axis and the q-axis based on an error between the rotation speed and a speed command value Nref, and calculates three-phase voltage command values Vuref, Vvref, Vwref based on an error between the current command values and a d-axis current Id and a q-axis current Iq. The inverter circuit 2 performs a switching operation in accordance with a pwm (pulse Width modulation) signal based on the three-phase voltage command values Vuref, Vvref, Vwref, thereby generating three-phase ac voltages Vu, Vv, Vw. When the motor 1 is provided with a position detector or the like, the rotation speed of the motor 1 may be derived from the time difference result output from the position detector and input to the controller 6.

Here, the power conversion device 10 or the motor 1 is provided with a cooling fan 7 for cooling the power conversion device 10 (particularly, the inverter circuit 2) or the motor 1. The cooling fan 7 is mounted with a rotation angle sensor such as a rotary encoder, for example, and is provided for one or both of the power converter 10 and the motor 1. The cooling fan 7 is rotated at all times regardless of whether the inverter circuit 2 or the motor 1 is operated. In particular, the cooling fan 7 is often mounted on the power converter 10 and the motor 1 that handle kW-class power.

The overload protection section 8 protects the inverter circuit 2 or the motor 1 from an overload. The overload protection unit 8 receives the rotation speed Nfan obtained from the rotation angle sensor of the cooling fan 7, the load current I1 from the current detector 5, the clear signal Con _ clr, the preset Electronic thermal level Ith, and the cumulative threshold Sth. The overload protection unit 8 uses these input information to determine whether the cooling fan 7 is in an overload state or a non-overload state while reflecting the rotation speed Nfan. When determining that the overload state is present, the overload protection unit 8 issues an energization stop command to the inverter circuit 2 by the operation permission signal Con. In response to this, the inverter circuit 2 stops the energization of the motor 1.

In fig. 1, the current detector 5, the controller 6, and the overload protection unit 8 are typically constituted by a microcontroller or the like. In this case, the current detector 5 calculates the load current I1, the d-axis current Id, and the q-axis current Id by performing a program process on the detected u-phase current Iu and w-phase current Iw using an analog-digital converter. The controller 6 and the overload protection section 8 are also realized by program processing. However, it is needless to say that a part or all of the circuit can be configured by a dedicated hardware circuit.

Fig. 2 is a schematic diagram showing an example of the external shape of the periphery of the power converter shown in fig. 1. The power converter 10 is configured by, for example, one case in which each module shown in fig. 1 is mounted. The casing is also provided with, for example, an operation panel 11. The cooling fan 7a is provided to cool the inside of the case, and particularly, cools heat generated by the transistors of the inverter circuit 2. The overload protection unit 8 detects the rotation speed Nfan _ a of the cooling fan 7a based on the rotation angle sensor of the cooling fan 7 a. The cooling fan 7b is provided in the motor 1, and cools heat generated by, for example, a coil (parasitic resistance thereof) of the motor 1. The overload protection unit 8 detects the rotation speed Nfan _ b of the cooling fan 7b based on the rotation angle sensor of the cooling fan 7 b.

Overview of the overload protection section

Fig. 3 is a block diagram showing a detailed configuration example of the overload protection unit in fig. 1. The overload protection unit 8 shown in fig. 3 includes a storage unit 81 that stores thermal time-limit

characteristic maps

801 and 802 in advance, an absolute value calculation unit 803, map data read

processing units

804 and 807, a correction unit 82, an overload determination unit 83, and a latch processing unit 813. First, assuming that the cooling fan 7 is provided in either the power conversion device 10 or the motor 1, the conceptual processing content of the overload protection unit 8 will be described.

The thermal time-limit

characteristic maps

801 and 802 determine the correspondence relationship between the load current I1 and the continuous energization time. The correction unit 82 generates a corrected thermal time characteristic map by correcting the thermal time

characteristic maps

801 and 802 in accordance with the rotation speed Nfan of the cooling fan. When the continuous energization time of the load current I1 reaches the continuous energization time based on the corrected thermal time-limit characteristic map, the overload determination unit 83 issues an energization stop command by the overload detection signal Con _ res.

Fig. 4 is a diagram conceptually showing the contents of the hot time limit characteristic map 801 for addition in fig. 3. Fig. 5 is a diagram conceptually showing the contents of the hot time limit characteristic map 802 for subtraction in fig. 3. The addition operation time Δ Tp shown in fig. 4 represents a time that is sequentially added when the continuous energization time of the inverter circuit 2 is determined by the integration method. The continuous energization time becomes longer as the addition operation time Δ Tp increases, and becomes shorter as the addition operation time Δ Tp decreases. Similarly, the subtraction time Δ Tm shown in fig. 5 represents a time that is sequentially subtracted when the continuous energization time of the inverter circuit 2 is determined by the integral method. In contrast to the case of the addition operation time Δ Tp, the continuous energization time is shorter as the subtraction operation time Δ Tm increases, and is longer as the subtraction operation time Δ Tm decreases.

As shown in the characteristic (referred to as reference characteristic 20p) of fig. 4 when the rotation speed Nfan of the cooling fan is normal, the added operation time Δ Tp is infinite when the load current I1 is the electronic heat value Ith, and decreases as the load current increases compared to the electronic heat value Ith. The reduction characteristic is an nth power characteristic with respect to the load current I1, taking into account heat generation accompanying the load current I1. The electronic heat value Ith represents a rated current, and represents a level at which no problem occurs even if a current is continuously flown. As shown in a characteristic (referred to as a characteristic after correction 21p) of fig. 4 when the rotation speed Nfan of the cooling fan is reduced, the additive operation time Δ Tp is shifted in a reduction direction as the rotation speed Nfan is reduced with reference to the reference characteristic 20 p.

On the other hand, as shown in the reference characteristic 20m in fig. 5, the subtraction time Δ Tm is infinite when the load current I1 is the electronic heat value Ith, and decreases with decreasing electronic heat value Ith as the characteristic decreases to the nth power with respect to the load current I1. As shown in the corrected characteristic 21m in fig. 5, the subtraction time Δ Tm is shifted in the increasing direction as the rotation speed Nfan of the cooling fan decreases, based on the reference characteristic 20 m. In this way, the correction unit 82 corrects the reference characteristics 20p and 20m (i.e., the thermal time-limit

characteristic maps

801 and 802 in fig. 3) in fig. 4 and 5 in accordance with the rotation speed Nfan of the cooling fan 7, thereby generating a corrected thermal time-limit characteristic map as shown by the corrected characteristics 21p and 21m in fig. 4 and 5.

Fig. 6 is a conceptual diagram illustrating a schematic operation example of the integration method. The overload protection unit 8 controls the continuous energization time Tz by using, for example, an integration method as shown in fig. 6. The continuously energizable time Tz corresponds to the water in the tank 15. The water in the container 15 is controlled by a supply valve 16 and a discharge valve 17. The overload determination unit 83 in fig. 3 issues an operation stop command to the inverter circuit 2 when, for example, water in the tank 15 disappears.

In fig. 4 and 5, the load current I1 is the state of the electronic heat value Ith, and corresponds to the state where the supply valve 16 and the discharge valve 17 are fully opened at the same time in fig. 6. In this state, the continuous energization time Tz does not increase or decrease, and the inverter circuit 2 can continuously flow the load current I1. Here, as shown in fig. 4, when the load current I1 increases compared to the electronic heat value Ith and the addition operation time Δ Tp decreases, the supply valve 16 is controlled in the closing direction in accordance with the amount of decrease. As a result, the continuously energizable time Tz is controlled in the decreasing direction. When the rotational speed Nfan of the cooling fan is decreased and the added operation time Δ Tp is shifted in the decreasing direction, the supply valve 16 is changed in the closing direction, and the continuous energization time Tz is controlled in the decreasing direction.

On the other hand, as shown in fig. 5, when the load current I1 decreases compared to the electronic heat value Ith and the subtraction time Δ Tm decreases, the discharge valve 17 is controlled in the closing direction according to the amount of decrease. As a result, the continuously energizable time Tz is controlled in the increasing direction. As described above, on the premise that the cooling fan 7 is constantly rotating, since the cooling effect exceeds the heat generation effect in the case of "I1 < Ith", the continuously operable energization time Tz can be increased by providing such a subtraction time Δ Tm. When the rotation speed Nfan of the cooling fan is decreased and the subtraction time Δ Tm is shifted in the increasing direction, the discharge valve 17 is changed in the opening direction, and the continuous energization time Tz is controlled in the decreasing direction.

Details of the overload protection section

Next, the detailed processing contents of the overload protection unit 8 in fig. 3 will be described. Fig. 7 is a diagram showing an example of actual holding contents of the addition and subtraction thermal time-limit

characteristic maps

801 and 802 in fig. 3. The thermal time-limit characteristic map 801 for addition actually determines the correspondence relationship between the load current I1 larger than the electronic heat value Ith and the added value Dth _ p corresponding to the continuous energization time, as shown in the reference characteristic 22p of fig. 7. The thermal time-limit characteristic map 802 for subtraction actually determines the correspondence relationship between the load current I1 smaller than the electronic heat value Ith and the subtraction value Dth _ m corresponding to the continuous energization time, as shown in the reference characteristic 22m of fig. 7.

The reference characteristics 22p and 22m shown in fig. 7 are characteristics in which the polarities of the reference characteristics 20p and 20m shown in fig. 4 and 5 are inverted, respectively. In fig. 6, the overload protection unit 8 of fig. 3 actually performs an operation of issuing an energization stop command to the inverter circuit 2 not when the water in the tank 15 is lost but when the tank 15 is full of water. In this case, the continuous energization time Tz corresponds to the remaining capacity in the container 15. The overload protection unit 8 controls the supply valve 16 to be opened more and the continuous energization time Tz to be decreased as the addition value Dth _ p increases, and controls the discharge valve 17 to be opened more and the continuous energization time Tz to be increased as the subtraction value Dth _ m increases.

In fig. 3, the absolute value calculation unit 803 converts the load current I1 into a load current (absolute value) | I1 |. The map data read processing unit 804 for addition reads the addition value Dth _ p corresponding to the load current I1 from the thermal time-limit characteristic map 801 for addition, with the load current (absolute value) | I1| as the pointer value Ath _ p for each predetermined control cycle. The correction unit 82 corrects the read addition value Dth _ p by weighting it by a coefficient proportional to the rotation speed Nfan of the cooling fan, and generates a corrected addition value Dth _ p _ cal. In this example, the correction unit 82 multiplies the added value Dth _ p by the reciprocal "1/(Nfan × Kfp)" of the value obtained by multiplying the rotation speed Nfan by the coefficient "Kfp" to generate a corrected added value Dth _ p _ cal.

The map data read processing unit 807 for subtraction reads a subtraction value Dth _ m corresponding to the load current I1 from the thermal time-limit characteristic map 802 for subtraction using the load current (absolute value) | I1| as a pointer value Ath _ m for each predetermined control cycle. The correction unit 82 corrects the read subtraction value Dth _ m by weighting it by a coefficient proportional to the rotation speed Nfan of the cooling fan, and generates a corrected subtraction value Dth _ m _ cal. In this example, the correction unit 82 generates a corrected subtraction value Dth _ m _ cal by multiplying the subtraction value Dth _ m by a value "Nfan × Kfm" obtained by multiplying the rotation speed Nfan by a coefficient "Kfm".

In this way, the correction unit 82 corrects the read added value Dth _ p so as to increase as the rotation speed Nfan of the cooling fan decreases, thereby generating a corrected added value Dth _ p _ cal. The correction unit 82 corrects the read subtraction value Dth _ m so as to decrease as the rotation speed Nfan of the cooling fan decreases, thereby generating a corrected subtraction value Dth _ m _ cal. As a result, the corrected addition value Dth _ p _ cal is a characteristic that shifts the reference characteristic 22p in the increasing direction as shown in the corrected characteristic 23p of fig. 7, and the corrected subtraction value Dth _ m _ cal is a characteristic that shifts the reference characteristic 22m in the decreasing direction as shown in the corrected characteristic 23m of fig. 7.

The overload determination unit 83 sequentially accumulates the corrected added value Dth _ p _ cal or the corrected subtracted value Dth _ m _ cal corrected by the correction unit 82, and issues an energization stop command when the accumulated value exceeds a predetermined accumulation threshold Sth. Specifically, the overload determination unit 83 includes an addition/subtraction switching unit 810, an accumulation unit 811, and a comparison unit 812. The addition/subtraction switching processing unit 810 compares the load current (absolute value) | I1| with the electronic heat value Ith. Then, the addition/subtraction switching processing unit 810 selects the corrected addition value Dth _ p _ cal in the case of "| I1| ≧ Ith", and selects the corrected subtraction value Dth _ m _ cal in the case of "| I1| < Ith" as the output addition/subtraction value Dth _ cal.

The accumulation processing unit 811 accumulates the addition subtraction value Dth _ cal sequentially input for each predetermined control cycle, thereby calculating an accumulated value Sint. The comparison processing section 812 compares the accumulation value Sint with an accumulation threshold value Sth. Then, the comparison processing unit 812 determines that the overload state is the overload state and the overload detection signal Con _ res is enabled (alert) when "Sint ≧ Sth", and determines that the overload state is the non-overload state and the overload detection signal Con _ res is maintained at the disable level (negate level) when "Sint < Sth".

When the overload detection signal Con _ res is active (that is, in an overload state), the latch processing unit 813 deactivates the operation permission signal Con (that is, issues the energization stop command). The inverter circuit 2 performs an energization operation while the operation permission signal Con is at the active level, and stops the energization operation while the operation permission signal Con is at the inactive level. Further, the latch processing unit 813 returns the operation permission signal Con to the active level (i.e., permits the power-on state) when receiving the clear signal Con _ clr.

Action of Power conversion device

Fig. 8 is a schematic diagram showing an operation example of the power converter of fig. 1. In fig. 8, for example, a period T1 corresponds to an acceleration period of the motor 1, a period T2 corresponds to a steady rotation period of the motor 1, and a period T3 corresponds to a deceleration period of the motor 1 (a generation period of the load current I1 in the reverse direction). Normally, the load current (absolute value) | I1| generated during the steady-state rotation of the motor 1 (period T2) is set to be equal to or less than the electronic heat value Ith.

On the other hand, in actual use, a load current (absolute value) | I1| larger than the electronic heat value Ith may flow in the acceleration period (period T1) and the deceleration period (period T3) of the motor 1. For example, in order to continue the operation of the power conversion device 10 and the motor 1 without stopping even when the load current (absolute value) | I1| exceeding the electronic heat value Ith flows in this way, it is advantageous to perform the overload protection using the integral method.

In fig. 8, in the integration characteristic 25 in the case where the rotation speed Nfan of the cooling fan is normal, the addition value Dth _ p is determined based on the reference characteristic 22p in fig. 7 in the period T1, and the accumulation value Sint increases with a positive slope corresponding to the addition value Dth _ p. In the period T2, the subtraction value Dth _ m is determined based on the reference characteristic 22m in fig. 7, and the accumulated value Sint decreases with a negative slope corresponding to the subtraction value Dth _ m. In the period T3, an addition value Dth _ p larger than that in the case of the period T1 is determined based on the reference characteristic 22p in fig. 7, and the accumulated value Sint increases with a positive slope according to the addition value Dth _ p. In this example, the accumulated value Sint exceeds the accumulated threshold value Sth at time (tn) within the period T3. Accordingly, the operation permission signal Con is shifted from the active level to the inactive level.

On the other hand, when the rotation speed Nfan of the cooling fan is decreased, as shown in the integral characteristic 26, the positive slope in the periods T1 and T3 is increased based on the corrected characteristic 23p in fig. 7, as compared with the case of the integral characteristic 25. The negative slope in the period T2 is smaller than that in the case of the integration characteristic 25 based on the corrected characteristic 23m in fig. 7. Accordingly, the accumulated value Sint exceeds the accumulation threshold Sth at a time (tc) earlier than the time (tn) within the period T3. As a result, the continuous energization time Tz when the rotation speed Nfan of the cooling fan is reduced is shorter than that when the rotation speed Nfan is normal.

Main effects of embodiment

As described above, by using the power converter 10 of the embodiment, the continuous energization time Tz can be shortened in accordance with the reduction amount of the rotation speed Nfan of the cooling fan 7, and therefore, the overload protection can be appropriately performed even when the rotation speed Nfan of the cooling fan 7 is reduced. As a result, burnout, damage, and the like of the power conversion device 10 and the motor 1 can be prevented, and the reliability of the system can be improved.

Here, the case where the cooling fan 7 is provided in either the power converter 10 or the motor 1 is described as an example, and in the case where the cooling fan 7 is provided in both the power converter 10 and the motor 1, for example, 2 types of the overload protection units 8 (for the power converter 10 and the motor 1) shown in fig. 3 may be provided. Then, when an energization stop command is issued from at least one of the 2 types of overload protection units 8, the operation of the inverter circuit 2 may be stopped.

The present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the invention. For example, the above embodiments are described in detail to explain the present invention easily and understandably, and are not limited to having all the configurations described. Further, a part of the structure of one embodiment may be replaced with the structure of another embodiment, and the structure of another embodiment may be added to the structure of one embodiment. In addition, other configurations can be added, deleted, and replaced for a part of the configurations of the embodiments.

For example, here, the case where the overload protection unit 8 of the embodiment is applied to a motor system that uses the motor 1 as a load is taken as an example, but the overload protection unit 8 is not particularly limited thereto, and can be similarly applied to various power systems that cool heat generated by a cooling fan.

Description of the reference numerals

1 electric motor

2 inverter circuit

3 three-phase power supply

4 converter circuit

5 Current detector

6 controller

7 Cooling fan

8 overload protection part

9 Current sensor

10 power conversion device

81 storage unit

82 correcting part

83 overload judging part

801. 802 thermal time-limited feature mapping

804. 807 mapping data reading processing part

Con action enable signal

Dth _ m subtracted value

Dth _ p added value

I1 load current

Ith electronic heating value

Nfan rotational speed

Sint accumulated value

Sth cumulative threshold

Tz may be continuous power on time.

Claims

1. A power conversion apparatus, characterized by comprising:

an inverter circuit that converts a direct-current voltage into an alternating-current voltage and energizes a load with the alternating-current voltage;

a current detector that detects a load current flowing in the load;

a cooling fan that cools the inverter circuit or the load; and

an overload protection section that protects the inverter circuit or the load,

the overload protection portion includes:

a storage unit that stores a thermal time-limit characteristic map for determining a correspondence relationship between the load current and a continuous energization time;

a correction unit that corrects the thermal time-limit characteristic map in accordance with the rotation speed of the cooling fan and generates a corrected thermal time-limit characteristic map; and

and an overload determination unit that issues an energization stop command when a continuous energization time of the load current reaches the continuous energization time based on the corrected thermal time-limit characteristic map.

2. The power conversion apparatus according to claim 1, characterized in that:

the correction unit generates the corrected thermal time-limit characteristic map by weighting the continuous energization time based on the thermal time-limit characteristic map by a coefficient proportional to the rotation speed of the cooling fan.

3. The power conversion apparatus according to claim 1, characterized in that:

the overload protection section further includes a mapping data read processing section,

the storage unit stores the thermal time-limit characteristic map for addition for determining a correspondence relationship between the load current larger than an electronic heat value and an added value corresponding to the continuous energization time,

the map data reading processing unit reads the addition value corresponding to the load current from the thermal time-limit characteristic map for addition for each predetermined control cycle,

the correction section corrects the added value read from the map data read processing section in accordance with the rotation speed of the cooling fan,

the overload determination unit adds the added values corrected by the correction unit to calculate an added value, and issues the energization stop command when the added value exceeds a predetermined added threshold value.

4. The power conversion apparatus according to claim 3, characterized in that:

the correction unit corrects the added value so that the added value increases as the rotation speed of the cooling fan decreases.

5. The power conversion apparatus according to claim 3, characterized in that:

the storage unit further holds the thermal time-limit characteristic map for subtraction for determining a correspondence relationship between the load current smaller than the electronic heat value and a subtraction value corresponding to the continuously energizable time,

the map data reading processing unit reads the subtraction value corresponding to the load current from the thermal time-limit characteristic map for subtraction for each of the predetermined control cycles,

the correction section corrects the subtraction value read from the map data read processing section in accordance with the rotation speed of the cooling fan,

the overload determination unit adds the subtraction values corrected by the correction unit to calculate the addition value.

6. The power conversion apparatus according to claim 5, characterized in that:

the correction unit corrects the subtraction value so that the subtraction value decreases as the rotation speed of the cooling fan decreases.

7. The power conversion apparatus according to claim 1, characterized in that:

the power conversion apparatus further includes:

a converter circuit for converting an external ac voltage into the dc voltage and supplying the dc voltage to the inverter circuit; and

a controller that controls the inverter circuit in such a manner that an operating state of the load approaches a target state,

the inverter circuit, the current detector, the overload protection unit, the converter circuit, and the controller are mounted in a single case,

the cooling fan is arranged to cool the inside of the case.

8. The power conversion apparatus according to claim 1, characterized in that:

the load is a motor that is driven by a motor,

the cooling fan is provided to the motor.

9. The power conversion apparatus according to claim 1, characterized in that:

the cooling fan is rotated at all times regardless of whether the inverter circuit or the load is operated.