CN112640283B - Inverter control method, power supply system for AC load, refrigeration circuit - Google Patents

Abstract

The heat generation of the inverter is suppressed. The inverter applies the AC voltage converted from the DC voltage to supply electric power to the AC load. When the voltage value (Vac) of the AC voltage converted into the DC voltage by the inverter is smaller than the first value (Vt1), the power can be reduced (steps S84 and S85).

Description

Inverter control method, power supply system for AC load, refrigeration circuit

technical field

The present invention relates to techniques for converting electric power.

Background technique

The following Patent Document 1 discloses that when the voltage input to the inverter is extremely reduced, the operation of the inverter is stopped, thereby preventing malfunction of the inverter and destruction of components.

prior art literature

Patent Literature

Patent Document 1: Japanese Patent Laid-Open No. 63-290193

SUMMARY OF THE INVENTION

The problem to be solved by the invention

The present invention suppresses the heat generation of the inverter which outputs the voltage input to the inverter.

means to solve the problem

The power supply system for an AC load of the present invention includes an inverter (4) that applies a first AC voltage (V1) converted from a DC voltage (Vdc) to supply power (Po) to the AC load (5); an inverter (2) which converts the second alternating current voltage (V2) into said direct current voltage (Vdc); and a control circuit (6).

In the first aspect, when the voltage value (Vac) of the second AC voltage is smaller than a predetermined first value (Vt1), the control circuit can cause the inverter to reduce the electric power (S85).

Then, if the voltage value (Vac) is equal to or greater than the first value (Vt1), the power is reduced (S85) based on the first conditions for reducing the power (S83, S84). If the voltage value is smaller than the first value, the power is reduced ( S85 ) based on a second condition ( S82 , S84 ) for reducing the power that is milder than the first condition.

In the second aspect of the power supply system to an AC load of the present invention, in the first aspect, if the voltage value (Vac) is smaller than the first value (Vt1) and input to the inverter (4) Or, when the current (Iw) output to the AC load (5) is equal to or greater than the first upper limit value (I3), droop control for the current is performed (S85). The first upper limit value is monotonically non-decreasing with respect to an increase in the voltage value.

According to the third aspect of the power supply system for an AC load of the present invention, in the first aspect or the second aspect, if the voltage value (Vac) is smaller than the first value (Vt1 ) and the inverter is sent to the inverter (2) When the current value (Ii) of the inputted input current is equal to or greater than the second upper limit value, the droop control for the input current is performed ( S85 ). The second upper limit value is monotonically non-decreasing with respect to an increase in the voltage value (Vac).

In the fourth aspect of the power supply system for an AC load according to the present invention, in the first aspect, the second aspect, or the third aspect, if the voltage value (Vac) is lower than the first value (Vt1) When the predetermined second value (Vt2) is reached, the supply of the electric power (Po) to the AC load (5) is stopped (S73, S74).

In the fifth aspect of the power supply system for an AC load of the present invention, in the second aspect or the third aspect, the AC load (5) is a motor. The droop control ( S85 ) includes control to reduce the rotational speed of the motor.

In a sixth aspect of the power supply system to an AC load of the present disclosure, in the fifth aspect, the motor (5) is a motor that drives a compressor (91) used in a refrigeration circuit (9), and drives an air conditioner. Any of the fans used and the motors that drive the fans used in the air purifier.

In a seventh aspect of the power supply system for an AC load of the present invention, in the fifth aspect, the motor (5) is a motor that drives a compressor (91) included in the refrigeration circuit (9). The refrigeration circuit also has an expansion valve (93). The droop control ( S85 ) includes control to increase the opening degree of the expansion valve.

In an eighth aspect of the power supply system for an AC load of the present invention, in any one of the first to seventh aspects, when the voltage value (Vac) is smaller than the first value (Vt1), The power supplied to the DC load (93) driven by the DC voltage is reduced.

The refrigeration circuit (9) of the present invention has a compressor (91) and an expansion valve (93) driven by a motor (5). The motor (5) is the AC load (5) supplied with electric power by the seventh aspect of the power supply system for an AC load of the present invention.

The inverter control method of the present invention controls an inverter (4) that converts an input DC voltage (Vdc) into a first AC voltage (V1) and supplies power to an AC load (5). The DC voltage (Vdc) is converted from the second AC voltage (V2) by the inverter (2).

Then, when the voltage value (Vac) of the second AC voltage is smaller than a predetermined first value (Vt1), the electric power can be reduced (S85) and the electric power can be supplied (S8).

If the voltage value (Vac) is equal to or greater than the first value (Vt1 ), the power is reduced based on the first conditions ( S83 , S84 ) for reducing the power ( S85 ). If the voltage value is smaller than the first value, the power is reduced ( S85 ) based on a second condition ( S82 , S84 ) for reducing the power that is milder than the first condition.

Description of drawings

FIG. 1 is a block diagram showing the configuration of an AC load drive system.

FIG. 2 is a flowchart showing a power reduction operation of a control circuit and an operation related thereto.

FIG. 3 is a graph showing the dependence on the voltage value as a function of the current droop value.

Fig. 4 is a block diagram showing the configuration of a refrigeration circuit.

Detailed ways

FIG. 1 is a block diagram showing the configuration of an AC load drive system 100 . Here, the AC load drive system 100 drives an AC load 5 . As the AC load 5, either a single-phase AC load or a multi-phase AC load can be used. For example, the AC load 5 is an AC motor. For example, the AC motor drives a compressor used in a refrigeration circuit. Alternatively, for example, the AC motor drives a fan that supplies air to the heat exchanger used in the refrigeration circuit. Or, for example, the AC motor drives a fan for an air cleaner.

The AC load drive system 100 has the inverter 4 . The inverter 4 converts the DC voltage Vdc input to itself into the AC voltage V1 and applies the AC voltage V1 to the AC load 5 . The inverter 4 supplies power (hereinafter referred to as “operating power”) Po for operating the AC load 5 to the AC load 5 . The number of phases of the AC voltage V1 corresponds to the number of phases of the AC load 5 .

The AC load drive system 100 has the inverter 2 . The inverter 2 converts the AC voltage V2 to output the DC voltage Vdc. The AC voltage V2 is output from, for example, the commercial power supply 1 which is an AC power supply. The input current of the current value Ii is input from the commercial power supply 1 to the inverter 2 . Power Ps is supplied from the commercial power supply 1 to the AC load drive system 100 .

The converter 2 is, for example, a diode bridge rectifier circuit, a boost converter, a buck converter, or a buck-boost converter.

FIG. 1 shows a case where the AC load drive system 100 further includes a filter 7 between the commercial power source 1 and the input side of the inverter 2 . In this case, the AC voltage V2 is applied from the commercial power source 1 to the inverter 2 via the filter 7 . For example, the filter 7 is a choke input type low-pass filter. The value of the current flowing from the commercial power supply 1 to the filter 7 can be used as the current value Ii. The voltage across the capacitor of the filter 7 can be understood as the AC voltage V2.

In FIG. 1 , the case where the AC load drive system 100 further has the capacitor 3 is shown. The capacitor 3 supports the DC voltage Vdc. The inverter 2 charges the capacitor 3 . The capacitor 3 is discharged, and the power (hereinafter referred to as "input power") Pi input to the inverter 4 is supplied alone or together with the inverter 2 . If the loss in the inverter 4 is ignored, the input power Pi is equal to the operating power Po.

The AC load drive system 100 has the control circuit 6 . The control circuit 6 controls the operation of the inverter 4 . For example, the inverter 4 converts the DC voltage Vdc into the AC voltage V1 by switching. The inverter 4 includes, for example, a switching element that performs the above-described switching operation.

The control circuit 6 generates a control signal G for controlling the switching operation, and outputs the control signal G to the inverter 4 . The AC voltage V1 varies depending on the switching operation of the inverter 4 . The fluctuation of the AC voltage V1 fluctuates the operating power Po. The fluctuation of the operating power Po changes the operation of the AC load 5 .

Therefore, the control circuit 6 changes the operating power Po under the control of the inverter 4 to drive the AC load 5 in various operations. A case where the AC load 5 is a three-phase motor will be described as an example.

Command data J, the voltage value Vac of the AC voltage V2, and the value of the current Iw flowing through the inverter 4 (hereinafter also referred to as "current value Iw") are input to the control circuit 6 . The command data J is, for example, a command value regarding the rotational speed or torque of the motor 5 . The value of the DC voltage Vdc can also be input to the control circuit 6 .

The voltage value Vac is obtained by a known method using a known voltage sensor, and the current value Iw is obtained by a known method using a known current sensor. The current value Iw can be obtained by measuring the current input to the inverter 4 .

The command data J is set according to the cooling performance of the refrigeration circuit using the compressor when the motor 5 drives the compressor, for example. This setting is, for example, a technique known as a control for driving a compressor of an air conditioner based on a temperature setting. For example, in order to improve the cooling performance, it is possible to increase the rotational speed of the compressor, for example, to increase the command value of the rotational speed indicated by the command data J.

The control circuit 6 uses the command data J, the voltage value Vac, and the current value Iw to determine the operating power Po. For example, when the command data J is a command value for the rotational speed or torque, an increase in the command value results in an increase in the operating power Po.

The control circuit 6 generates the control signal G so as to supply the operating power Po from the inverter 4 to the AC load 5 .

When the inverter 4 supplies the operating power Po of a certain value, when the voltage value Vac decreases, the current value Ii increases. This is because if the power conversion efficiency of the inverter 2 is considered constant, the input power Pi is proportional to the product of the voltage value Vac and the current value Ii, and if the loss in the inverter 4 is ignored, the input power Pi and The operating power Po is equal. An increase in the current value Ii causes heat generation of diodes and switching elements constituting the inverter 2 . The heat generation of the diodes or switching elements leads to a decrease in efficiency and a decrease in the performance of the elements. Therefore, it is desirable to suppress the heat generation of the inverter 2 .

In the present embodiment, as a technique for suppressing this heat generation, an inverter control method is proposed that causes the inverter 4 to perform an operation of reducing the operating power Po when the voltage value Vac decreases. Specifically, for example, the control circuit 6 fluctuates the control signal G so that the inverter 4 operates as described above. This is for reducing or reducing the increase in the current value Ii by reducing the input power Pi and further reducing the power Ps by reducing the operating power Po.

Thereby, the heat generation of the inverter 2 is suppressed. When the filter 7 is included, heat generation in the coil included in the filter 7 is also suppressed. In other words, heat generation on the side of the commercial power supply 1 including at least the inverter 2 in the AC load drive system 100 is suppressed.

When the inverter 2 increases or decreases the voltage value of the DC voltage Vdc by increasing or decreasing the voltage value Vac like a diode bridge rectifier circuit, the voltage value of the DC voltage Vdc decreases due to the decrease in the voltage value Vac. Therefore, regardless of the reduction in the operating power Po, the switching loss of the inverter 4 is reduced, and the heat generation of the inverter 4 is suppressed. Since the current value Iw also decreases when the operating power Po is decreased, the heat generation of the inverter 4 is further suppressed. For example, according to the function of the inverter 2, even if the voltage value of the DC voltage Vdc is not increased or decreased by the increase or decrease of the voltage value Vac, the heat generation of the inverter 4 can be suppressed when the operating power Po is decreased.

It is not necessary to always lower the operating power Po with respect to the lowering of the voltage value Vac. This is because heat generation of switching elements and the like can be tolerated up to a prescribed upper limit. For example, in the case where a transistor is used as the switching element, the upper limit of this tolerance depends on the so-called allowable collector loss.

Therefore, as a technique proposed in this embodiment, there is a technique in which, if the voltage value Vac is smaller than a predetermined threshold value (hereinafter, referred to as "first value Vt1" for convenience of description), the voltage value Vac becomes a predetermined threshold value Compared with the above case, the operating power Po supplied from the inverter 4 to the AC load 5 is easily reduced.

In view of the operation of the control circuit 6, this is a condition for performing the operation of reducing the operating power Po (hereinafter also referred to as “power reducing operation”) when the voltage value Vac is less than the first value Vt1 and when the voltage value Vac is greater than or equal to the first value Vt1 Otherwise, a control method for supplying the operating power Po to the inverter 4 is executed. For example, the control circuit 6 generates a control signal G for causing the inverter 4 to perform an operation of reducing the operating power Po, and outputs the control signal G to the inverter 4 .

FIG. 2 is a flowchart showing the power reduction operation of the control circuit 6 and the operation associated therewith. In step S71, the operating power Po is set. This setting is the determination of the operating power Po based on the command data J, the voltage value Vac, and the current value Iw, and is a process performed by a known technique. In step S71, not only the operating power Po is directly determined, but also the operating power Po can be indirectly determined by determining the operating state of the AC load 5 (eg, the rotational speed or torque of the motor load).

After step S71, in step S72, control is performed to operate the inverter 4 while maintaining the operating power Po. This control is a control for operating the inverter 4 while maintaining the operating power Po set in step S71, and is a process performed by a known technique.

After step S72, in step S73, when the voltage value Vac drops abnormally, a comparison for stopping the driving of the AC load 5 is performed.

In step S73, for example, the voltage value Vac is compared with a predetermined second value Vt2. The second value Vt2 is smaller than the first value Vt1. If the voltage value Vac is smaller than the second value Vt2 (ie, when Vac≧Vt2 is negative), the process proceeds to step S74.

In step S74, the supply of the operating power Po from the inverter 4 to the AC load 5 is stopped. For example, when the inverter 2 adopts a diode bridge rectifier circuit, a decrease in the voltage value Vac leads to a decrease in the DC voltage Vdc. Step S73 may include processing of low voltage protection of the DC voltage Vdc in this case.

Here, the stop of the supply of the operating power Po is handled as a different process from the power reduction operation in which the supply of the operating power Po is also performed.

If the voltage value Vac is equal to or greater than the second value Vt2 in step S73 (that is, when Vac≧Vt2 is affirmative), the process proceeds to step S8. In step S8, the control circuit 6 performs a power reduction operation. However, in step S8, the reduction of the operating power Po is not necessarily performed, as will be described later. Specifically, step S8 includes a plurality of steps of steps S81 to S85, and the process branches in step S84, and may exit from step S8 in the middle.

At the beginning of the process of step S8, a comparison between the first value Vt1 and the voltage value Vac is performed in step S81. As a result of this comparison, if the voltage value Vac is smaller than the first value Vt1 (ie, when Vac<Vt1 is affirmative), the process proceeds to step S82. If the voltage value Vac is equal to or greater than the first value Vt1 (that is, when Vac<Vt1 is negative), the process proceeds to step S83.

For convenience of description, steps S84 and S85 will be described before steps S82 and S83 are described. In step S85, so-called droop control is performed on the current Iw, and before step S85, it is determined in step S84 whether or not droop control is necessary.

As an example of the droop control, a control in which the rotation speed of the AC load 5 is reduced as a motor can be mentioned. The reduction of the rotational speed of the motor is achieved by the reduction of the current Iw, and contributes to the direct reduction of the operating power Po.

Whether or not to perform droop control is determined by comparing the current output from the inverter 4 to the AC load 5 and the current droop value I3. This current is the current flowing through the inverter 4, and thus can be measured as the current value Iw.

In step S84, when Iw≥I3 is affirmative, the process proceeds to step S85, and droop control is performed. Thereby, the current value Iw decreases. That is, through steps S84 and S85, the current droop value I3 functions as the upper limit value of the current value Iw.

When Iw≥I3 is negative in step S84 (that is, when Iw<I3), the process exits from step S8 and returns to step S72.

Steps S82 and S83 are both processes of determining the current droop value I3. In step S82, the current droop value I3 is set by the function f(Vac) of the voltage value Vac. Here, the function f(Vac) does not decrease monotonically with respect to the rise of the voltage value Vac. In step S83, the current droop value I3 is set to a predetermined value I31. For example, the predetermined value I31 is a value not related to the voltage value Vac.

After steps S82 and S83 are performed, step S84 is performed. The process in step S84 in this case is to compare the current value Iw with the predetermined value I31. That is, steps S82, S83, S84, and S85 are a set of steps for performing droop control so that the current value Iw does not exceed the predetermined value I31.

FIG. 3 is a graph showing the correlation with the voltage value Vac as a function f(Vac) of the current droop value I3. Specifically:

When Vac≥Vt1, f(Vac)=I31;

When Vac≤Vt2, f(Vac)=I32;

When Vt2≤Vac≤Vt1,

f(Vac)=I32+(Vac-Vt2)(I31-I32)/(Vt1-Vt2).

The predetermined value I32 is smaller than the predetermined value I31 and is not related to the voltage value Vac.

Of course, the above-mentioned function f(Vac) is an example, and when Vt2≤Vac≤Vt1, the function f(Vac) may be nonlinear with respect to the voltage value Vac. For example, the function f(Vac) may change continuously or stepwise with respect to the change in the voltage value Vac.

When step S81 is executed, since the determination in step S73 is affirmative, Vt2≤Vac is established. Therefore, in step S82, the current droop value I3 is set to a value that decreases monotonically with respect to the decrease in the voltage value Vac.

By using the current droop value I3 set in this way, and by executing steps S84 and S85, in the droop control for the current Iw, the lower the current droop value I3 as the lower voltage value Vac is as the upper limit, the current Iw is suppressed. Therefore, as the voltage value Vac decreases, the operating power Po decreases and the electric power Ps decreases. Therefore, even if the voltage value Vac decreases, the increase in the current value Ii is suppressed, and the heat generation of the inverter 2 is suppressed. The reduction of the operating power Po by such steps S82, S84, and S85 is an example of the above-described power reduction operation.

According to the description of steps S82, S83 and S84, it can be as follows:

If the voltage value Vac is equal to or greater than the first value Vt1, the supply operating power Po is reduced under the first condition of I3=I31;

If the voltage value Vac is smaller than the first value Vt1, the supply operating power Po is reduced under the second condition of I3=f(Vac).

If Vac<Vt1, f(Vac)<I31, therefore, when the voltage value Vac is less than the first value Vt1, it is easier to reduce the operating power Po than when the voltage value Vac is greater than or equal to the first value Vt1. In other words, the second condition for reducing the operating power Po is gentler than the first condition.

Although the second condition is milder than the first condition, even if Vac<Vt1, it is not always possible to reduce the operating power Po. This is because, when the determination in step S84 is negative, the process does not proceed to step S85 and the droop control is not performed. Therefore, when Vac<Vt1 , the control circuit 6 can reduce the power to the inverter 4 .

If the determination in step S73 is negative, step S74 is executed, and the value of the function f(Vac) may not be set when Vac<Vt2 in order to stop the supply of the operating power Po.

A second value Vt2' smaller than the second value Vt2 of the determination function f(Vac) may be introduced, and the second value Vt2 compared with the voltage value Vac may be replaced with the second value Vt2' in step S73. In this case, the supply of the operating power Po is stopped when Vac<Vt2', and the current droop value I3 takes the predetermined value I32 as the upper limit when Vt2'≤Vac≤Vt2, and performs droop control on the current Iw.

The first value Vt1' larger than the first value Vt1 of the determination function f(Vac) may be introduced, and the first value Vt1 compared with the voltage value Vac may be replaced with the first value Vt1' in step S81. In this case, when Vt1≤Vac≤Vt1', the current droop value I3 takes the predetermined value I31 as the upper limit, and the droop control with respect to the current Iw is performed. That is, the function f(Vac) decreases monotonically as the voltage value Vac decreases, but there may be a region uncorrelated with the voltage value Vac (it does not decrease monotonically as the voltage value Vac increases).

The reduction in the rotation speed of the motor exemplified as the droop control directly reduces the current Iw. A phenomenon that causes a reduction in the rotational speed or torque of the motor occurs, and the operating power Po is indirectly reduced via the reduction in the rotational speed or torque of the motor, which is also considered to be included in the droop control. Hereinafter, such control will be described.

FIG. 4 is a block diagram showing the configuration of the refrigeration circuit 9 . The refrigeration circuit 9 includes a compressor 91 , heat exchangers 92 and 94 , and an expansion valve 93 . The refrigerant (not shown) is compressed by the compressor 91 , evaporated by the heat exchanger 92 , expanded by the expansion valve 93 , and condensed by the heat exchanger 94 . The white arrows in the figure indicate the direction of refrigerant circulation.

The AC load 5 is a motor that drives the compressor 91 included in the refrigeration circuit 9 . The expansion valve 93 is a solenoid valve, and its opening degree is adjusted by the control signal L generated by the control circuit 6 . For example, the opening degree of the solenoid valve is determined by a stepping motor driven by the control signal L. For example, the operating power of the stepping motor can be obtained from the output of the inverter 2 .

In step S85 (see FIG. 2 ), the opening degree of the expansion valve 93 is increased in accordance with the control signal L. As a result, the mechanical load of the compressor 91 is reduced, the torque required to drive the motor 5 of the compressor 91 is reduced, and the current Iw is reduced. Therefore, it can be considered that the process of increasing the opening degree of the expansion valve 93 is included in the droop control.

As described above, the control circuit 6 that generates the control signal L and/or the control signal G may be configured to include a microcomputer and a storage device. The microcomputer executes the steps (in other words, the program) of each process described in the program. For example, the steps of FIG. 2 are executed by the microcomputer.

The above-mentioned storage device can be, for example, a ROM (Read Only Memory: read-only memory), a RAM (Random Access Memory: random access memory), a rewritable non-volatile memory (EPROM (Erasable Programmable ROM: Erasable Programmable ROM), etc. ) and one or more of various storage devices. The storage device stores various information, data, and the like, stores programs executed by the microcomputer, and provides a work area for executing the programs. The microcomputer can be understood as functioning as various means corresponding to each processing step described in the program, or as realizing various functions corresponding to each processing step. In addition, the control circuit 6 is not limited to this, and various steps executed by the control circuit 6 or a part or all of various units or various functions implemented by the control circuit 6 may be realized by hardware.

As described above, the present embodiment proposes a technique for controlling the inverter 4 that converts the input DC voltage Vdc into the AC voltage V1 and applies it to the AC load 5 . The DC voltage Vdc is converted from the AC voltage V2 by the inverter 2 .

In the AC load drive system 100, when the voltage value Vac is smaller than the first value Vt1, the control circuit 6 can cause the inverter 4 to reduce the operating power Po. As a result, the operating power Po is reduced, and further the power Ps is reduced, thereby suppressing the heat generation of the inverter 2 . This technique can also be regarded as a control method of the inverter 4, which can reduce the supply operation power Po when the voltage value Vac is smaller than the first value Vt1.

When the voltage value Vac is equal to or greater than the first value Vt1, the operating power Po supplied from the inverter 4 to the AC load 5 is reduced based on the first condition (steps S83, S84) (step S85) to supply the operating power Po. If the voltage value Vac is smaller than the first value Vt1, the operating power Po is reduced based on the second condition (steps S82, S84) (step S85), and the operating power Po is supplied. The second condition is milder than the first condition.

For example, if the voltage value Vac is smaller than the first value Vt1 and the input current (current value Ii) input to the inverter 4 or the current Iw output to the AC load 5 is equal to or greater than the current droop value I3 as the upper limit value, the Droop control for this current (step S85). The current droop value I3 does not decrease monotonically with respect to the increase of the voltage value Vac. Thereby, the operating power Po supplied from the inverter 4 to the AC load 5 is reduced.

It is also possible to perform droop control on the current input to the inverter 2 . For example, if the voltage value Vac is smaller than the first value Vt1 and the current value Ii is equal to or greater than the upper limit value, the droop control for the current is performed. For example, the upper limit value can be set so as not to decrease monotonically with respect to the increase of the voltage value Vac. Specifically, for example, a flowchart in which the current value Iw is replaced by the current value Ii in step S84 (see FIG. 2 ) can be employed. This upper limit value can be set independently of the above-described current droop value I3.

If the voltage value Vac is smaller than the second value Vt2 lower than the first value Vt1 , the supply of the operating power Po to the AC load 5 may be stopped.

For example, the AC load 5 may be a motor, and the droop control includes control to reduce the rotational speed of the motor 5 . This results in a direct reduction in the operating power Po.

As an example of the motor 5, a motor that drives the compressor 91 included in the refrigeration circuit 9 can be mentioned. For example, the motor 5 drives the compressor 91 provided in the refrigeration circuit 9 with the expansion valve 93 . The refrigeration circuit 9 includes a compressor 91 and an expansion valve 93 driven by the motor 5 supplied with the operating power Po from the AC load drive system 100 . The droop control may include control to increase the opening degree of the expansion valve 93 . This results in an indirect decrease in operating power Po.

The motor 5 can also be used as a motor for driving a fan used in an air conditioner and a fan used in an air cleaner.

In the case where a DC load driven by the DC voltage Vdc is provided, control to reduce the power supplied to the DC load can be performed. In this case, the input power Pi is the sum of the operating power Po and the power consumed by the DC load, and the reduction of the DC power contributes to the reduction of the power Ps. This control can be performed independently of the control of the inverter 4 .

For example, in the refrigeration circuit 9, when the expansion valve 93 is a DC load whose operating power is supplied from the capacitor 3 as DC power, the operation of the expansion valve 93 may be stopped when the voltage value Vac is smaller than the first value Vt1.

The AC load drive system 100 having the inverter 2 , the inverter 4 , and the control circuit 6 that performs the power reduction operation can be said to be a power supply system that supplies power to the AC load 5 .

As mentioned above, although embodiment was described, it can be understood that various changes in the form and details can be made without departing from the spirit and scope of the claims. The various embodiments and modifications described above can be combined with each other.

Claims (9)

1. A power supply system for an AC load, comprising:

an inverter (4) that supplies electric power (Po) to an AC load (5) by applying a first AC voltage (V1) converted from a DC voltage (Vdc);

an inverter (2) that converts a second alternating voltage (V2) into the direct voltage (Vdc); and

a control circuit (6) that can cause the inverter to reduce the electric power (S85) when the voltage value (Vac) of the second AC voltage is less than a predetermined first value (Vt1),

if the voltage value (Vac) is equal to or greater than the first value (Vt1), the power is reduced (S85) based on a first condition (S83, S84) for reducing the power, the first condition (S83, S84) being a condition that a current droop value (I3) acting as an upper limit value of a current (Iw) input to the inverter (4) or output to the AC load (5) in droop control (S84) for the current (Iw) takes a first predetermined value (I31),

reducing (S85) the power based on a second condition (S82, S84) for reducing the power, which is less than the first condition, if the voltage value is less than the first value, the second condition (S82, S84) being a condition that the current droop value (I3) takes a second prescribed value f (Vac),

The first prescribed value (I31) is greater than the second prescribed value f (Vac),

performing the droop control (S85) if the voltage value (Vac) is less than the first value (Vt1), is equal to or greater than a predetermined 2 nd value (Vt2) lower than the first value (Vt1), and the current (Iw) input to the inverter (4) or output to the AC load (5) is equal to or greater than the current droop value (I3),

the current droop value (I3) is monotonically non-decreasing with respect to the rise in the voltage value (Vac) and with the exception of a monotonic change.

2. The power supply system for an alternating-current load according to claim 1, wherein,

performing droop control (S85) for the input current if the voltage value (Vac) is less than the first value (Vt1) and is above the 2 nd value (Vt2) and a current value (Ii) of the input current input to the inverter (2) is above a second upper limit value,

the second upper limit value is monotonically non-decreasing with respect to a rise in the voltage value (Vac).

3. The power supply system for an alternating-current load according to claim 1, wherein,

if the voltage value (Vac) is less than a second predetermined value (Vt2) lower than the first value (Vt1), the supply of the electric power (Po) to the AC load (5) is stopped (S73, S74).

4. The power supply system for an alternating-current load according to claim 1,

the alternating current load (5) is an electric motor,

the droop control (S85) includes a control of reducing the rotation speed of the motor.

5. The power supply system for an alternating-current load according to claim 4, wherein,

the motor (5) is any one of a motor for driving a compressor (91) used in the refrigeration circuit (9), a fan used in an air conditioner, and a fan used in an air cleaner.

6. The power supply system for an alternating-current load according to claim 4, wherein,

the motor (5) is a motor for driving a compressor (91) provided in the refrigeration circuit (9),

the refrigeration circuit also has an expansion valve (93),

the droop control (S85) includes control for increasing the opening degree of the expansion valve.

7. The power supply system for an alternating-current load according to claim 1,

-if said voltage value (Vac) is lower than said first value (Vt1), reducing the power supplied to a dc load (93) driven by said dc voltage.

8. Refrigeration circuit (9), the refrigeration circuit (9) having:

a compressor (91) driven by the motor (5) as the alternating-current load (5) supplied with electric power by the electric power supply system for alternating-current loads according to claim 6; and

An expansion valve (93).

9. A method for controlling an inverter, which controls an inverter (4) that converts an input direct-current voltage (Vdc) into a first alternating-current voltage (V1) and supplies power to an alternating-current load (5),

the direct voltage (Vdc) is converted from a second alternating voltage (V2) by an inverter (2),

when the voltage value (Vac) of the second AC voltage is less than a predetermined first value (Vt1), the electric power can be supplied by reducing the electric power (S85) (S8),

if the voltage value (Vac) is equal to or greater than the first value (Vt1), the power is reduced (S85) based on a first condition (S83, S84) for reducing the power, the first condition (S83, S84) being a condition that a current droop value (I3) acting as an upper limit value of a current (Iw) input to the inverter (4) or output to the AC load (5) in droop control (S84) for the current (Iw) takes a first predetermined value (I31),

reducing (S85) the power based on a second condition (S82, S84) for reducing the power, which is less than the first condition, if the voltage value is less than the first value, the second condition (S82, S84) being a condition that the current droop value (I3) takes a second prescribed value f (Vac),

The first prescribed value (I31) is greater than the second prescribed value f (Vac),

performing the droop control (S85) if the voltage value (Vac) is less than the first value (Vt1), is equal to or greater than a predetermined 2 nd value (Vt2) lower than the first value (Vt1), and the current (Iw) input to the inverter (4) or output to the AC load (5) is equal to or greater than the current droop value (I3),

the current droop value (I3) is monotonically non-decreasing with respect to the rise in the voltage value (Vac) and with the exception of a monotonic change.

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