CN112262526B

CN112262526B - Power conversion device

Info

Publication number: CN112262526B
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: 2023-04-25
Anticipated expiration: 2039-07-11
Also published as: WO2020105219A1; CN112262526A; JP2020089027A; JP6925313B2

Abstract

The invention provides a power conversion device capable of properly performing overload protection even when the rotation speed of a cooling fan is reduced. The power conversion device includes: an inverter circuit (2) that converts a DC voltage into an AC voltage and energizes the motor (1) with the AC voltage; a current detector (5) for detecting 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). An overload protection unit (8) holds in advance a thermal time limit characteristic map for determining the correspondence relation between a load current (I1) and a continuously energizable time, corrects the thermal time limit characteristic map according to the rotation speed of a cooling fan (7), and issues an energization stop command (Con) when the continuously energizable time of the load current (I1) reaches the continuously energizable time based on the corrected thermal time limit characteristic map.

Description

Power conversion device

Technical Field

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

Background

Conventionally, as a protection system for supplying power to a load such as a motor, a system in which a current detection breaking device (thermal relay) is provided in a power supply line leading to the power conversion device is used as a protection system for overcurrent or overload. However, since this method simply compares the detected current value with the threshold value, the operation state such as the operation speed of the motor cannot be considered, and overload protection of the power conversion device and the motor may not be performed appropriately.

As a technique for solving such a problem, an inverter device shown in japanese patent publication No. 62-55379 (patent document 1) is given. The inverter device stores in advance a thermal time limit characteristic indicating a continuously 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 properly protect the motor from overload in consideration of the operating state of the motor. This approach is commonly referred to as an electronic thermal relay.

Prior art literature

Patent literature

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

Disclosure of Invention

Problems to be solved by the invention

In general, in motors and power conversion devices, miniaturization is required along with higher output. In order to eliminate the reduction in the heat radiation effect caused thereby, cooling fans are often mounted in motors and power conversion devices. In this case, the thermal time limit characteristic for the electronic thermal relay is determined on the premise that the cooling fan operates normally.

However, the cooling fan may have a rotation speed that decreases with, for example, a failure, aged deterioration, 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 properly perform overload protection with the electronic thermal relay. As a result, there is a risk of occurrence of burning, breakage, or the like of the motor or the power conversion device.

The present invention has been made in view of such 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 become apparent from the description and drawings of the present specification.

Means for solving the problems

The outline of a representative embodiment among the embodiments disclosed in the present application will be briefly described as follows.

The power conversion device according to an exemplary 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 a load; a cooling fan for cooling the inverter circuit or the load; and an overload protection portion that protects the inverter circuit or the load. The overload protection unit stores a thermal time limit characteristic map for determining a correspondence relation between a load current and a continuously energizable time, corrects the thermal time limit characteristic map according to the rotation speed of the cooling fan, and issues an energization stop command when the continuously energizable time of the load current reaches the continuously energizable time based on the corrected thermal time limit characteristic map.

ADVANTAGEOUS EFFECTS OF INVENTION

The effects obtained by the representative embodiments 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 external shape example of the periphery of the power conversion device 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 content of the thermal time limit characteristic map for addition in fig. 3.

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

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

Fig. 7 is a diagram showing an example of the actual holding content of the thermal time limit characteristic map for addition and subtraction in fig. 3.

Fig. 8 is a schematic diagram illustrating an example of the operation of the power conversion device of fig. 1.

Detailed Description

In the following embodiments, when the number of elements and the like (including the number, the numerical value, the amount, the range and the like) are mentioned, the number is not limited to the specific number, and may be more or less than the specific number, unless the case specifically mentioned and the case where the number is explicitly limited to the specific number and the like in principle. In the following embodiments, the constituent elements (including the constituent steps) are not necessarily required, except those specifically shown and those that are clearly considered to be necessary in principle. In the same manner, in the following embodiments, when reference is made to the shape, positional relationship, and the like of the constituent elements and the like, the shapes and the like substantially similar to or similar to the shapes and the like thereof are included, except for the case where the shapes and the positional relationship are specifically shown and the case where the shapes and the like are not regarded as such in principle. The same applies to the values and ranges described above.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In all the drawings for explaining the embodiments, the same reference numerals are given to the same components in principle, and repeated descriptions thereof are 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. In fig. 1, 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 from the power conversion device 10 is supplied are also shown. 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 the 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 a current sensor 9. In this example, the current detector 5 detects u-phase current Iu and w-phase current Iw via the current sensor 9, and converts its coordinates into d-axis current Id and 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 the target state. In this example, the controller 6 receives a speed command value Nref from the outside, and generates a three-phase voltage command value Vuref, vvref, vwref for rotating the motor 1 at a rotational speed based on the speed command value Nref using vector control without a position sensor.

Specifically, the controller 6 calculates the rotational speed of the motor 1 using, for example, an induced voltage observer, calculates the d-axis and q-axis current command values based on the error between the rotational speed and the speed command value Nref, and calculates the three-phase voltage command value Vuref, vvref, vwref based on the error between the current command values and the d-axis current Id and the q-axis current Iq. The inverter circuit 2 generates three-phase ac voltages Vu, vv, vw by performing switching operation in accordance with a PWM (Pulse Width Modulation) signal based on the three-phase voltage command value Vuref, vvref, vwref. In the case where the motor 1 includes a position detector, the rotational speed of the motor 1 may be derived from the time difference 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 provided with a rotation angle sensor such as a rotary encoder, for example, and is provided to one or both of the power conversion device 10 and the motor 1. The cooling fan 7 always rotates regardless of whether the inverter circuit 2 or the motor 1 is operated. In particular, such a cooling fan 7 is often mounted in the power conversion device 10 and the motor 1 that process kW-level electric 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 purge signal con_clr, and the preset electronic heat value (Electronic thermal level) Ith and the accumulation threshold Sth. The overload protection unit 8 uses these pieces of input information to reflect the rotation speed Nfan of the cooling fan 7 and determine whether the cooling fan is in an overload state or a non-overload state. When the overload protection unit 8 determines that the overload state is established, it issues a power-on stop command to the inverter circuit 2 by the operation enable signal Con. Accordingly, the inverter circuit 2 stops energizing the motor 1.

In fig. 1, the current detector 5, the controller 6, and the overload protection section 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 program processing on the detected u-phase current Iu and w-phase current Iw using an analog-to-digital converter. The controller 6 and the overload protection section 8 are also realized by program processing. However, a part or the whole of the circuit may be configured by a dedicated hardware circuit.

Fig. 2 is a schematic diagram showing an external shape example of the periphery of the power conversion device in fig. 1. The power conversion device 10 is constituted by, for example, a single housing having each module shown in fig. 1 mounted therein. The operation panel 11 and the like are also provided in the housing, for example. The cooling fan 7a is provided to cool the inside of the case, and particularly to cool 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, for example, heat generated by 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.

Summary of overload protection part

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 for storing therein thermal time limit

characteristic maps

801 and 802, an absolute value calculation unit 803, map data reading

processing units

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

The thermal time limit

characteristic maps

801 and 802 determine the correspondence between the load current I1 and the continuously-energized time. The correction unit 82 generates a corrected thermal time limit characteristic map by correcting the thermal time limit

characteristic maps

801 and 802 in accordance with the rotation speed Nfan of the cooling fan. The overload judging section 83 issues an energization stop command by the overload detection signal con_res when the continuous energization time of the load current I1 reaches the continuous energization time based on the corrected thermal time limit characteristic map.

Fig. 4 is a diagram conceptually showing the content of the thermal time limit characteristic map 801 for addition in fig. 3. Fig. 5 is a diagram conceptually showing the contents of the thermal time limit characteristic map 802 for subtraction in fig. 3. The addition operation time Δtp shown in fig. 4 represents a time added successively when the continuously energization time of the inverter circuit 2 is determined by using the integration method. The continuously-energizable time becomes longer as the addition operation time Δtp increases, and becomes shorter as the addition operation time Δtp decreases. Similarly, the subtraction operation time Δtm shown in fig. 5 represents a time obtained by subtracting the continuous energization time of the inverter circuit 2 successively when the continuous energization time is determined by the integration method. The continuous energization time is shorter as the subtraction operation time Δtm increases, and longer as the subtraction operation time Δtm decreases, contrary to the case of the addition operation time Δtp.

As shown in the characteristic (referred to as the reference characteristic 20 p) of the cooling fan in fig. 4 when the rotation speed Nfan is normal, the addition operation time Δtp is infinite when the load current I1 is the electron heat value Ith, and decreases as compared with the electron heat value Ith. This reduction characteristic is considered to be an nth power characteristic with respect to the load current I1, which accompanies heat generation of the load current I1. The electron heating value Ith represents a rated current, and represents a level at which no problem occurs even if a current is continuously flowing. The addition operation time Δtp is shifted in the decreasing direction as the rotation speed Nfan decreases, based on the reference characteristic 20p, as shown in the characteristic (referred to as the corrected characteristic 21 p) when the rotation speed Nfan of the cooling fan decreases in fig. 4.

On the other hand, as shown in the reference characteristic 20m in fig. 5, the subtraction operation time Δtm is infinite when the load current I1 is the electron heat value Ith, and decreases as compared with the electron heat value Ith, the n-th power characteristic with respect to the load current I1 decreases. As shown in the corrected characteristic 21m in fig. 5, the subtraction operation time Δtm is shifted in the increasing direction as the rotation speed Nfan of the cooling fan decreases, with reference to 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 corrected thermal time limit characteristic maps shown as corrected characteristics 21p and 21m in fig. 4 and 5.

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

In fig. 4 and 5, the load current I1 is in a state of the electron heating value Ith, and corresponds to a state in which the supply valve 16 and the discharge valve 17 are fully opened at the same time in fig. 6. In this state, the continuously-energized 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 from the electron heating value Ith and the addition operation time Δtp decreases, the supply valve 16 is controlled in the closing direction in accordance with the decrease amount. As a result, the continuously energization time Tz is controlled in the decreasing direction. When the rotation speed Nfan of the cooling fan decreases and the addition operation time Δtp is shifted in the decreasing direction, the supply valve 16 is changed in the closing direction, and the continuous energization time Tz can be controlled in the decreasing direction.

On the other hand, as shown in fig. 5, when the load current I1 decreases from the electron heating value Ith and the subtraction operation time Δtm decreases, the discharge valve 17 is controlled in the closing direction in accordance with the decrease amount. As a result, the continuously energization time Tz is controlled in the increasing direction. As described above, if the cooling fan 7 is continuously rotated, the cooling effect exceeds the heat generation effect in the case of "I1< Ith", and therefore, by setting the subtraction operation time Δtm, the continuously energization time Tz can be increased. When the rotation speed Nfan of the cooling fan decreases and the subtraction operation time Δtm is shifted in the increasing direction, the discharge valve 17 is changed in the opening direction, and the continuous energization time Tz can be controlled in the decreasing direction.

Details of overload protection

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

characteristic maps

801 and 802 for addition and subtraction in fig. 3. As shown in the reference characteristic 22p of fig. 7, the thermal time limit characteristic map 801 for addition actually determines the correspondence relationship between the load current I1 greater than the electron heating value Ith and the added value dth_p corresponding to the continuously energization time. As shown in the reference characteristic 22m of fig. 7, the thermal time limit characteristic map 802 for subtraction actually determines a correspondence relationship between a load current I1 smaller than the electronic heat value Ith and a subtraction value dth_m corresponding to the continuously energization time.

The reference characteristics 22p and 22m shown in fig. 7 are characteristics in which 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 in fig. 3 actually performs an operation of issuing an energization stop command to the inverter circuit 2 not when the water in the container 15 is lost but when the container 15 is filled with 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 continuously-energizable time Tz in a decreasing direction by opening the supply valve 16 as the added value dth_p increases, and controls the continuously-energizable time Tz in an increasing direction by opening the discharge valve 17 as the subtracted value dth_m increases.

In fig. 3, the absolute value operation unit 803 converts the load current I1 into a load current (absolute value) |i1|. The map data reading processing unit 804 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 performs correction by weighting the read added value dth_p by a coefficient proportional to the rotation speed Nfan of the cooling fan, and generates a corrected added value dth_p_cal. In this example, the correction unit 82 multiplies the added value dth_p by the inverse "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 reading 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 with the load current (absolute value) |i1|as the pointer value ath_m for each predetermined control cycle. The correction unit 82 performs correction by weighting the read subtraction value dth_m 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 multiplies the subtraction value dth_m by a value "nfan× Kfm" obtained by multiplying the rotation speed Nfan by a coefficient "Kfm" to generate a corrected subtraction value dth_m_cal.

In this way, the correction unit 82 corrects the read added value dth_p so that the rotation speed Nfan of the cooling fan increases as it decreases, thereby generating a corrected added value dth_p_cal. The correction unit 82 corrects the read subtraction value dth_m so that the rotation speed Nfan of the cooling fan decreases as it 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 judging unit 83 sequentially accumulates the corrected addition value dth_p_cal or the corrected subtraction value dth_m_cal corrected by the correcting 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 section 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|Σ or" | < 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 calculates an accumulation value Sint by accumulating the addition/subtraction value dth_cal that is successively input for each predetermined control period. The comparison processing unit 812 compares the accumulated value Sint with the accumulated threshold Sth. Then, the comparison processing unit 812 determines that the overload state is enabled (asserted) when "Sint is equal to or greater than Sth", and determines that the overload detection signal con_res is not in the overload state and maintains the overload detection signal con_res at the inactive level (adjacent level) when "Sint < Sth".

The latch processing unit 813 invalidates the operation permission signal Con (i.e., issues an energization stop command) when the overload detection signal con_res is active (i.e., in an overload state). The inverter circuit 2 performs the energization operation during the period in which the operation permission signal Con is at the active level, and stops the energization operation during the period in which the operation permission signal Con is at the inactive level. When receiving the clear signal con_clr, the latch processing unit 813 returns the operation permission signal Con to the active level (i.e., the permission power-on state).

Operation of Power conversion device

Fig. 8 is a schematic diagram illustrating an example of the operation of the power conversion device 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-state rotation period of the motor 1, and a period T3 corresponds to a deceleration period (a period during which the load current I1 in the opposite direction occurs) of the motor 1. In general, the load current (absolute value) |i1| occurring 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, there is a case where a load current (absolute value) |i1| larger than the electron heating value Ith flows in the acceleration period (period T1) and the deceleration period (period T3) of the motor 1. For example, even when a load current (absolute value) |i1| exceeding the electronic heat value Ith flows in this manner, it is advantageous to perform overload protection by using an integral method in order to continue the operation of the power conversion device 10 and the motor 1 without stopping.

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

On the other hand, when the rotation speed Nfan of the cooling fan decreases, as shown in the integration characteristic 26, the positive slope in the periods T1 and T3 increases as compared with the case of the integration characteristic 25 based on the corrected characteristic 23p of fig. 7. 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 continuously-energized time Tz when the rotation speed Nfan of the cooling fan is reduced is shortened as compared with the case when the rotation speed Nfan is normal.

Main Effect of the embodiment

As described above, by using the power conversion device 10 according to the embodiment, the continuous energization time Tz can be shortened in accordance with the amount of decrease in the rotation speed Nfan of the cooling fan 7, so that overload protection can be appropriately performed even when the rotation speed Nfan of the cooling fan 7 is decreased. As a result, the power conversion device 10 and the motor 1 can be prevented from being burned or damaged, and the reliability of the system can be improved.

Here, the case where the cooling fan 7 is provided in either the power conversion device 10 or the motor 1 is described as an example, and when the cooling fan 7 is provided in both of them, for example, 2 types of overload protection units 8 (for the power conversion device 10 and for the motor 1) shown in fig. 3 may be provided. Then, when a power-on 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 invention made by the present inventors has been specifically described based on the embodiments, but the invention is not limited to the above embodiments, and various modifications can be made without departing from the gist thereof. For example, the above-described embodiments are described in detail for the purpose of easily understanding the present invention, and are not limited to all the configurations that are required to be described. In addition, 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 structures may be added, deleted, or replaced for a part of the structures of the respective embodiments.

For example, the overload protection unit 8 according to the embodiment is applied to a motor system in which the motor 1 is a load, but the overload protection unit 8 is not particularly limited thereto, and can be similarly applied to various power systems in which heat generation is cooled by a cooling fan.

Description of the reference numerals

1. Motor with a motor housing having a motor housing with a motor housing

2. Inverter circuit

3. Three-phase power supply

4. Converter circuit

5. Current detector

6. Controller for controlling a power supply

7. Cooling fan

8. Overload protection part

9. Current sensor

10. Power conversion device

81. Storage unit

82. Correction part

83. Overload judging part

801. 802 thermal time limit characteristic mapping

804. 807 map data reading processing section

Con action enable signal

Dth_m subtraction value

Dth_p addition value

I1 Load current

Ith electronic heat value

Nfan rotational speed

Sint accumulated value

Sth accumulation threshold

Tz may be continuously energized for a time period.

Claims

1. A power conversion device, 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 for detecting a load current flowing in the load;

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

an overload protection section for protecting the inverter circuit or the load,

the overload protection part includes:

a storage unit that stores a thermal time limit characteristic map for determining a correspondence relation between the load current and a continuously energizable time;

a correction unit that corrects the thermal time limit characteristic map based on the rotation speed of the cooling fan to generate a corrected thermal time limit characteristic map; and

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

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

the correction unit weights the continuously-energized time based on the thermal time limit characteristic map by a coefficient proportional to the rotation speed of the cooling fan, and generates the corrected thermal time limit characteristic map.

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

the overload protection section further includes a map data reading processing section,

the memory unit stores a map of thermal time limit characteristics for addition for determining a correspondence relationship between the load current larger than an electronic heat value and an added value corresponding to the continuously-energized 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 period,

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

the overload judging unit calculates an accumulated value by accumulating the added value corrected by the correcting unit, and issues the energization stop command when the accumulated value exceeds a predetermined accumulation threshold.

4. A power conversion apparatus according to claim 3, wherein:

the correction unit corrects the addition value so as to increase as the rotation speed of the cooling fan decreases.

5. A power conversion apparatus according to claim 3, wherein:

the memory unit further stores a 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 predetermined control cycle,

the correction unit corrects the subtraction value read from the map data reading processing unit according to the rotation speed of the cooling fan,

the overload judging section calculates the accumulated value by accumulating the subtracted values corrected by the correcting section.

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

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

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

the power conversion device 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 section, the converter circuit and the controller are mounted in one housing,

the cooling fan is configured to cool the inside of the housing.

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

the load is a motor and the load is a motor,

the cooling fan is provided to the motor.

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

the cooling fan always performs a rotating action regardless of whether the inverter circuit or the load is operated.