WO2019150727A1

WO2019150727A1 - Inverter control method, alternating current load drive system, and refrigeration circuit

Info

Publication number: WO2019150727A1
Application number: PCT/JP2018/043670
Authority: WO
Inventors: 雄希中島
Original assignee: ダイキン工業株式会社
Priority date: 2018-01-31
Filing date: 2018-11-28
Publication date: 2019-08-08
Also published as: JP2019134601A; CN111630765A; CN111630765B; AU2018407010B2; AU2018407010A1; JP6638746B2; MY185112A

Abstract

The present invention suppresses heat generation of a switching element of an inverter. An alternating current load drive system (100) has: a converter (2) that converts an alternating current voltage (V2) outputted from a commercial power supply (1) into a direct current voltage (Vdc); and an inverter (4), which converts the direct current voltage (Vdc) into an alternating current voltage (V1), and supplies an alternating current load (5) with operating power (Po). The control circuit (6) detects the direct current voltage (Vdc), and if the direct current voltage (Vdc) is lower than a predetermined first value, the control circuit reduces the power (Po) to be supplied to the alternating current load (5) from the inverter (4).

Description

Inverter control method, AC load drive system, refrigeration circuit

This disclosure relates to a power converter.

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 component destruction.

Japanese Unexamined Patent Publication No. 63-290193

This disclosure suppresses heat generation of the inverter.

An AC load driving system (100) of the present disclosure includes an inverter (4) that converts an input DC voltage (Vdc) into a first AC voltage (V1) and applies the first AC voltage (V1) to an AC load (5), and a control circuit (6 ).

In the first aspect, the control circuit reduces the power (Po) supplied from the inverter to the AC load when the voltage value (Vdc) of the DC voltage is less than a predetermined first value (Vt1) ( S84) is made possible (S84). Reduction of electric power (Po) suppresses heat generation of the inverter.

The second aspect of the AC load drive system (100) of the present disclosure is the first aspect, and if the voltage value (Vdc) is equal to or greater than the first value (Vt1), the power is the first. If the voltage value (Vdc) is reduced (S84) under the condition (S74, S83) and less than the first value, the second condition (S82, S83) that is more relaxed than the first condition. Originally reduced.

A third aspect of the AC load drive system (100) of the present disclosure is the first aspect or the second aspect, wherein the voltage value (Vdc) is less than the first value (Vt1), A current (Iw) that is greater than or equal to a predetermined second value (Vt2) lower than the first value (Vt1) and that is input to the inverter (4) or output to the AC load (5) is a first value. If it is equal to or greater than the upper limit (I3) (S83), the drooping control (S84) for the current is performed. The first upper limit value is monotonously non-decreasing with respect to the increase in the voltage value.

A fourth aspect of the AC load driving system (100) of the present disclosure is the first aspect or the second aspect, wherein the voltage value (Vdc) is lower than the first value (Vt1). If it is less than the second value (Vt2), the supply of the electric power (Po) to the AC load (5) is stopped (S81, S75).

The fifth aspect of the AC load drive system (100) of the present disclosure is the third aspect, in which the AC load (5) is a motor. The drooping control (S84) includes control for reducing the rotational speed of the motor.

A sixth aspect of the AC load drive system (100) of the present disclosure is the fifth aspect, and the motor (5) drives a compressor (91) employed in the refrigeration circuit (9). Either a motor, a fan employed in an air conditioner, or a motor driving a fan employed in an air purifier.

A seventh aspect of the AC load drive system (100) of the present disclosure is the fifth aspect thereof, and the motor (5) drives a compressor (91) employed in the refrigeration circuit (9). It is a motor. The refrigeration circuit includes an expansion valve (93). The drooping control (S84) includes control for increasing the opening degree of the expansion valve.

An eighth aspect of the AC load drive system (100) of the present disclosure is any one of the first to seventh aspects, wherein the DC voltage (Vdc) is converted into a second AC voltage ( Obtained by conversion from V2). The DC voltage decreases due to a decrease in the second AC voltage (V2).

The ninth aspect of the AC load drive system (100) of the present disclosure is the eighth aspect, and if the input current (Ii) input to the converter (2) is equal to or greater than the second upper limit value, Droop control (S84) is performed on the input current. The second upper limit value is monotonously non-decreasing with respect to the increase in the voltage value (Vdc).

A tenth aspect of the AC load drive system (100) of the present disclosure is any one of the first to ninth aspects, wherein the voltage value (Vdc) is less than the first value (Vt1). For example, the power supplied to the DC load (93) driven by the DC voltage is reduced.

The refrigeration circuit (9) of the present disclosure includes a compression driven by the motor that is the AC load supplied with power by the AC load drive system (100) of the seventh aspect of the AC load drive system (100) of the present disclosure. A machine (91) and an expansion valve (93).

The inverter control method of the present disclosure is a method of controlling the inverter (4) that converts the input DC voltage (Vdc) into the first AC voltage (V1) and applies it to the AC load (5). The control method enables reduction in operating power (Po) supplied from the inverter (4) to the AC load 5 when the voltage value (Vdc) is less than the first value (Vt1).

It is a block diagram which shows the structure of the system (henceforth an "AC load drive system") which drives AC load. It is a flowchart which shows the electric power reduction operation | movement of a control circuit, and the operation | movement accompanying this. It is a graph which illustrates the dependence with respect to a voltage value of the function used as a drooping current value. 4 is a block diagram illustrating the configuration of a refrigeration circuit 9. FIG.

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

AC load drive system 100 includes an inverter 4. The inverter 4 converts the DC voltage Vdc input to itself into an AC voltage V 1 and applies it to the AC load 5. The inverter 4 supplies power to operate the AC load 5 (hereinafter “operating power”) Po 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.

AC load drive system 100 includes a control circuit 6. The control circuit 6 controls the operation of the inverter 4. For example, inverter 4 performs a switching operation to convert DC voltage Vdc into AC voltage V1. 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 it to the inverter 4. The AC voltage V1 varies depending on the switching operation of the inverter 4. The change in the AC voltage V1 changes the operating power Po. The change in the operating power Po changes the operation of the AC load 5.

The control circuit 6 varies the operating power Po through the control of the inverter 4 and thereby drives 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 value of DC voltage Vdc (hereinafter also referred to as “voltage value Vdc”), and the value of current Iw flowing through inverter 4 (hereinafter also referred to as “current value Iw”) are input to control circuit 6. . The command data J is, for example, a command value for the rotational speed or rotational torque of the motor 5.

The voltage value Vdc 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 depending on the cooling performance of the refrigeration circuit using the compressor when the motor 5 drives the compressor, for example. This setting is a well-known technique as control for driving a compressor based on a temperature setting in an air conditioner, for example. For example, to increase the cooling performance, an increase in the rotational speed of the compressor can be employed. For example, the rotational speed command value indicated by the command data J increases.

The control circuit 6 determines the operating power Po using the command data J, the voltage value Vdc, and the current value Iw. For example, when the command data J is a command value for rotational speed or rotational torque, an increase in the command value causes an increase in the operating power Po.

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

When the inverter 4 supplies a certain value of operating power Po, the current value Iw increases when the voltage value Vdc decreases. This is because the operating power Po is proportional to the product of the voltage value Vdc and the current value Iw, assuming that the power conversion efficiency of the inverter 4 is constant in order to briefly explain the reason. The increase in the current value Iw causes heat generation of the switching elements constituting the inverter 4. The heat generation of the switching element leads to a decrease in efficiency and a decrease in element performance. It is desirable to suppress the heat generation of the switching element.

In this embodiment, as a technique for suppressing such heat generation, an inverter control method is proposed in which the inverter 4 is caused to perform an operation of reducing the operating power Po when the voltage value Vdc is lowered. Specifically, for example, the control circuit 6 changes the control signal G so that the inverter 4 performs the above operation.

However, it is not always necessary to reduce the operating power Po with respect to the decrease in the voltage value Vdc. This is because heat generation of the switching element or the like can be allowed up to a predetermined upper limit. For example, such an upper limit of tolerance depends on so-called allowable collector loss when a transistor is employed as the switching element.

As a technique proposed in the present embodiment, if the voltage value Vdc is less than a predetermined threshold value (hereinafter referred to as “first value” for convenience), the operating power Po supplied from the inverter 4 to the AC load 5 is A technique for reducing and supplying operating power Po will be listed. In view of the operation of the control circuit 6, this is the execution of a control method for causing the inverter 4 to perform an operation of reducing the operating power Po (hereinafter also referred to as “power reducing operation”) when the voltage value Vdc is equal to or lower than the first value. It is. For example, the control circuit 6 generates a control signal G that causes the inverter 4 to perform an operation of reducing the operating power Po, and outputs the control signal G to the inverter 4.

According to such a technique, for example, even if the voltage value Vdc decreases, heat generation of the inverter 4, for example, heat generation due to an increase in the current Iw is suppressed.

FIG. 1 illustrates a case where the AC load driving system 100 further includes a converter 2 and a capacitor 3. Capacitor 3 supports DC voltage Vdc. Converter 2 charges capacitor 3. Capacitor 3 discharges and supplies electric power (hereinafter referred to as “input electric power”) Pi input to inverter 4 alone or together with converter 2. If the loss in the inverter 4 is ignored, the input power Pi is equal to the operating power Po.

The AC voltage V2 is applied to the converter 2. The AC voltage V2 is output from, for example, a commercial power source 1 that is an AC power source. The DC voltage Vdc is converted from the AC voltage V2 by the converter 2. For example, a diode bridge rectifier circuit, a step-up converter, a step-down converter, and a step-up / step-down converter are employed for the converter 2. The DC voltage Vdc can be reduced by at least one of a decrease in the value of the AC voltage V2 and an operation of the converter 2.

For example, when a diode bridge rectifier circuit is employed for the converter 2, the DC voltage Vdc decreases due to a decrease in the value of the AC voltage V2. 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. The power reduction operation of the control circuit 6 is also effective for a decrease in the voltage value Vdc caused by a decrease in the value of the AC voltage V2. The power reduction operation further suppresses the heat generation of the inverter 4 with respect to a failure including a reduction in performance of the commercial power supply 1. When the AC voltage V2 decreases, the input current Ii input to the converter 2 also increases, and the loss of the converter 2 also increases. This power reduction operation is also useful for suppressing heat generation of the components constituting the converter 2.

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. The setting is determination of the operating power Po based on the command data J, the voltage value Vdc, 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 is determined indirectly by determining the operating state of the AC load 5 (for example, the rotational speed or rotational torque of the motor load). Good.

In step S72, control is performed to operate the inverter 4 while maintaining the operating power Po. The control is 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.

In step S73, the first value Vt1 is compared with the voltage value Vdc. As a result of the comparison, if the voltage value Vdc is less than the first value Vt1 (that is, when Vdc <Vt1 is affirmed), the process proceeds to step S8, and the control circuit 6 enables the power reduction operation.

Step S8 includes, for example, step S81. In step S81, a comparison is made to determine whether so-called low voltage protection is necessary.

In step S81, for example, the voltage value Vdc is compared with a predetermined second value Vt2. However, the second value Vt2 is lower than the first value Vt1. If voltage value Vdc is less than second value Vt2 (that is, if Vdc ≧ Vt2 is denied), the process proceeds to step S75.

In step S75, the supply of the operating power Po from the inverter 4 to the AC load 5 is stopped. This is a process corresponding to so-called low voltage protection. Stopping the supply of the operating power Po is different from the power reduction operation of reducing the supply of the operating power Po, although it is reduced.

For convenience of description, steps S83 and S84 will be described before step S82. In step S84, so-called drooping control is performed on the current Iw. In step S83, whether drooping control is necessary is determined prior to step S84.

As an example of the drooping control, the AC load 5 is a motor, and the rotation speed can be reduced. Reduction of the rotation speed of the motor is realized by reducing the current Iw, and contributes to the direct reduction of the operating power Po.

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

When it is affirmed in step S83 that Iw ≧ I3, the process proceeds to step S84, and the drooping control is performed. As a result, the current value Iw decreases. That is, the current droop value I3 functions as the upper limit value of the current value Iw by steps S83 and S84.

When Iw ≧ I3 is negative in step S83 (that is, when Iw <I3), the process exits from step S8 and returns to step S72.

Steps S74 and S82 are processes for determining the current droop value I3. If voltage value Vdc is greater than or equal to first value Vt1 in step S73 (that is, if Vdc <Vt1 is negative), the process proceeds to step S74, and current droop value I3 is set to a predetermined value I31. For example, a value that does not depend on the voltage value Vdc is adopted as the predetermined value I31.

After step S74 is executed, step S83 is executed. The process in step S83 in this case is a comparison between the current value Iw and the predetermined value I31. That is, steps S74, S83, and S84 are a set of steps for performing drooping control so that the current value Iw does not exceed the predetermined value I31.

If voltage value Vdc is greater than or equal to second value Vt2 in step S81 (that is, when Vdc ≧ Vt2 is affirmed), the process proceeds to step S82, and current droop value I3 is set as a function f (Vdc) of voltage value Vdc. The Here, the function f (Vdc) is monotonously non-decreasing with respect to the increase of the voltage value Vdc.

FIG. 3 is a graph illustrating the dependence of the function f (Vdc), which is the current droop value I3, on the voltage value Vdc. In particular:
When Vdc ≧ Vt1, f (Vdc) = I31;
When Vdc ≦ Vt2, f (Vdc) = I32;
When Vt2 ≦ Vdc ≦ Vt1,
f (Vdc) = I32 + (Vdc−Vt2) (I31−I32) / (Vt1−Vt2);
It is. However, the predetermined value I32 is smaller than the predetermined value I31 and does not depend on the voltage value Vdc.

The above function f (Vdc) is an example, and when Vt2 ≦ Vdc ≦ Vt1, the function f (Vdc) may be nonlinear with respect to the voltage value Vdc. For example, the function f (Vdc) may change continuously with respect to the change of the voltage value Vdc, or may change stepwise.

If the determination in step S81 is negative, step S75 is executed, and in view of the fact that the supply of operating power Po is stopped, when Vdc <Vt2, the value of the function f (Vdc) is not set. Also good.

A second value Vt2 ′ smaller than the second value Vt2 that determines the function f (Vdc) may be introduced, and the second value Vt2 compared with the voltage value Vdc in step S81 may be replaced with the second value Vt2 ′. . In this case, supply of the operating power Po is stopped when Vdc <Vt2 ′, and when Vt2 ′ ≦ Vdc ≦ Vt2, the current drooping value I3 takes a predetermined value I32, and the drooping control for the current Iw is performed with this as the upper limit.

A first value Vt1 ′ larger than the first value Vt1 for determining the function f (Vdc) may be introduced, and the first value Vt1 compared with the voltage value Vdc in step S73 may be replaced with the first value Vt1 ′. . In this case, when Vt1 ≦ Vdc ≦ Vt1 ′, the current droop value I3 takes a predetermined value I31, and the droop control for the current Iw is performed with this as the upper limit. That is, the function f (Vdc) decreases monotonously with a decrease in the voltage value Vdc, but there may be a region that does not depend on the voltage value Vdc (is monotonously non-decreasing with respect to an increase in the voltage value Vdc). .

Step S81 is executed when the determination in step S73 is affirmative. If the determination in step S81 is affirmative, Vt2 <Vdc <Vt1 is established. In step S82, the current droop value I3 is set to a value that decreases monotonously with respect to the decrease in the voltage value Vdc.

By adopting the current droop value I3 set in this way, the droop control for the current value Iw is performed with the lower current droop value I3 as the upper limit as the voltage value Vdc decreases by executing steps S83 and S84. Suppress. As the voltage value Vdc decreases, the operating power Po decreases, and even if the voltage value Vdc decreases, the current Iw is suppressed from increasing, and the heat generation of the inverter 4 is suppressed. Such reduction of the operating power Po in steps S82, S83, and S84 is an example of the above-described power reduction operation.

From the description of steps S74, S82, and S83, the following can be said:
If the voltage value Vdc is greater than or equal to the first value Vt1, the operating power Po is reduced and supplied under the first condition of I3 = I31;
If the voltage value Vdc is less than the first value Vt1, the operating power Po is reduced and supplied under the second condition of I3 = f (Vdc).

If Vdc <Vt1, f (Vdc) <I31. When the voltage value Vdc is less than the first value Vt1, the operating power Po is more likely to be reduced than when the voltage value Vdc is greater than or equal to the first value Vt1. In other words, the second condition for reducing the operating power Po is more relaxed than the first condition.

Although the second condition is more relaxed than the first condition, the operating power Po is not necessarily reduced if Vdc <Vt1. This is because when the determination in step S83 is negative, the process does not proceed to step S84 and the drooping control is not performed. When Vdc <Vt1, it can be said that the control circuit 6 enables the inverter 4 to reduce power.

If there is no processing in steps S81 and S82, step S75 is executed when the determination result in step S73 is affirmative (that is, Vdc <Vt1). If steps S81 and S82 are provided, the frequency of low-voltage protection in step S75 is reduced by performing the power reduction operation. In other words, the power reduction operation facilitates avoiding a situation where the AC load 5 stops due to low voltage protection.

After the voltage value Vdc has decreased, the voltage value Vdc may increase. For example, when the AC voltage V2 is lowered due to a failure of the commercial power supply 1 and the voltage value Vdc is lowered due to this, or when the voltage value Vdc is lowered due to insufficient storage amount of the capacitor 3, When the reduction operation is performed, the voltage value Vdc may increase.

Reduction of the rotation speed of the motor exemplified as the drooping control directly reduces the current Iw. However, it is also possible to reduce the operating power Po indirectly by reducing the rotational speed and / or rotational torque of the motor by generating an event that causes a reduction in the rotational speed and / or rotational torque of the motor. It can be included in the control. Hereinafter, such control will be described.

FIG. 4 is a block diagram illustrating 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. A 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 in which the refrigerant circulates.

The AC load 5 is a motor that drives a compressor 91 employed in the refrigeration circuit 9. The expansion valve 93 is an electromagnetic valve, and its opening degree is adjusted by a control signal L generated by the control circuit 6. For example, the opening degree of the electromagnetic 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 converter 2.

In step S84 (see FIG. 2), the opening degree of the expansion valve 93 is increased by the control signal L. Thereby, since the mechanical load of the compressor 91 is reduced, the rotational torque required for the motor 5 that drives the compressor 91 is reduced, and the current Iw is reduced. The process of increasing the opening degree of the expansion valve 93 can be included in the drooping control.

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

The storage device can be composed of one or more of various storage devices such as ROM (Read Only Memory), RAM (Random Access Memory), and rewritable nonvolatile memory (EPROM (Erasable Programmable ROM), etc.). . The storage device stores various information, data, and the like, stores a program executed by the microcomputer, and provides a work area for executing the program. It can be understood that the microcomputer functions as various means corresponding to each processing step described in the program and can realize that various functions corresponding to each processing step are realized. The control circuit 6 is not limited to this, and various procedures executed by the control circuit 6, various means to be realized, or some or all of various functions may be realized by hardware.

As described above, in this embodiment, the AC load drive system 100 including the inverter 4 and the control circuit 6 has been proposed. It can be said that the AC load drive system 100 is an AC load drive system that drives the AC load 5. The inverter 4 converts the input DC voltage Vdc into an AC voltage V 1 and applies it to the AC load 5. The control circuit 6 makes it possible to reduce the operating power Po supplied from the inverter 4 to the AC load 5 when the voltage value Vdc is less than the first value Vt1. Reduction of the operating power Po suppresses the heat generation of the inverter 4.

If the voltage value Vdc is equal to or higher than the first value Vt1, the operating power Po is reduced under the first condition. If the voltage value Vdc is less than the first value Vt1, the operating power Po is reduced under the second condition that is more relaxed than the first condition.

The voltage value Vdc is less than the first value Vt1, and is equal to or higher than the second value Vt2 lower than the first value Vt1, and the current input to the inverter 4 or the current output to the AC load 5 is the upper limit value. If the current droop value is equal to or greater than I3, the droop control for the current is performed. The current drooping value I3 is monotonously non-decreasing with respect to the increase of the voltage value Vdc. Thereby, the operating power Po supplied from the inverter 4 to the AC load 5 is reduced.

If the voltage value Vdc is less 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. This provides low voltage protection. The power reduction operation facilitates avoiding a situation where the AC load 5 is stopped due to the low voltage protection.

For example, the AC load 5 is a motor, and the drooping control may include control for reducing the rotational speed of the motor 5. This leads to a direct reduction in operating power Po.

Examples of the motor 5 include a motor that drives a compressor 91 that is employed in the refrigeration circuit 9. For example, the motor 5 drives a compressor 91 that is employed in the refrigeration circuit 9 including the expansion valve 93. In this case, the drooping control may include control for increasing the opening degree of the expansion valve 93. This leads to an indirect reduction in operating power Po.

The motor 5 can also be employed as a fan for driving a fan employed in an air conditioner or a fan employed in an air purifier.

The DC voltage Vdc is obtained by converting from the AC voltage V2 by the converter 2, for example. In this case, for example, the DC voltage Vdc decreases due to the decrease in the AC voltage V2. The drooping control may be performed on the input current Ii input by the converter 2. For example, if the input current Ii is not less than the upper limit value, the drooping control is performed for the input current Ii. For example, the upper limit value can be set monotonically non-decreasing with respect to the increase of the DC voltage Vdc. Specifically, for example, a flowchart in which the current Iw is replaced with the input current Ii in step S83 (see FIG. 2) can be employed. The upper limit value can be set independently of the above-described current droop value I3.

When the decrease in the DC voltage Vdc is caused by, for example, a shortage of the charged amount of the capacitor 3, the power supplied to the DC load driven by the DC voltage Vdc may be reduced. This can be performed independently of the control of the inverter 4.

For example, in the refrigeration circuit 9, when the operating power of the expansion valve 93 is a DC load supplied as DC power from the capacitor 3, the operation of the expansion valve 93 is stopped when the DC voltage Vdc is less than the first value Vt1. May be. As a result, the shortage of the charged amount of the capacitor 3 is resolved, and the decrease in the voltage value Vdc is reduced.

A method for controlling the inverter 4 has also been proposed in this embodiment. This control method makes it possible to reduce the operating power Po supplied from the inverter 4 to the AC load 5 when the voltage value Vdc is less than the first value Vt1.

Although the embodiments have been described above, it will be understood that various changes in 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

An inverter (4) for converting the input DC voltage (Vdc) to the first AC voltage (V1) and applying it to the AC load (5);
A control circuit (6) that enables reduction (S84) of power (Po) supplied from the inverter to the AC load when the voltage value (Vdc) of the DC voltage is less than a predetermined first value (Vt1); An AC load drive system (100) comprising:
If the voltage value (Vdc) is greater than or equal to the first value (Vt1), the power is reduced (S84) under the first condition (S74, S83),
The AC load drive system according to claim 1, wherein if the voltage value (Vdc) is less than the first value, the voltage value is reduced under a second condition (S82, S83) that is relaxed than the first condition. (100).
The voltage value (Vdc) is less than the first value (Vt1) and greater than or equal to a predetermined second value (Vt2) lower than the first value (Vt1), and is input to the inverter (4). Alternatively, if the current (Iw) output to the AC load (5) is greater than or equal to the first upper limit value (I3) (S83), the drooping control (S84) for the current is performed,
The AC load drive system (100) according to claim 1 or 2, wherein the first upper limit value is monotonously non-decreasing with respect to the increase in the voltage value.
If the voltage value (Vdc) is less than a predetermined second value (Vt2) lower than the first value (Vt1), the supply of the electric power (Po) to the AC load (5) is stopped ( S81, S75), AC load drive system (100) according to claim 1 or claim 2.
The AC load (5) is a motor,
The AC load drive system (100) according to claim 3, wherein the drooping control (S84) includes a control for reducing a rotation speed of the motor.
The motor (5) is one of a motor for driving a compressor (91) employed in the refrigeration circuit (9), a fan employed in an air conditioner, and a motor driving a fan employed in an air purifier. The AC load drive system (100) according to claim 5, wherein:
The motor (5) is a motor for driving a compressor (91) employed in the refrigeration circuit (9),
The refrigeration circuit includes an expansion valve (93),
The AC load drive system (100) according to claim 5, wherein the drooping control (S84) includes a control for increasing an opening degree of the expansion valve.
The DC voltage (Vdc) is obtained by converting the second AC voltage (V2) by the converter (2).
The AC load drive system (100) according to any one of claims 1 to 7, wherein the DC voltage decreases due to a decrease in the second AC voltage (V2).
If the input current (Ii) input to the converter (2) is greater than or equal to the second upper limit value, the drooping control (S84) for the input current is performed,
The AC load drive system (100) according to claim 8, wherein the second upper limit value is monotonously non-decreasing with respect to the increase in the voltage value (Vdc).
The power supplied to the DC load (93) driven by the DC voltage is reduced if the voltage value (Vdc) is less than the first value (Vt1). The AC load drive system (100) according to one.
A compressor (91) driven by the motor as the AC load to which power is supplied by the AC load drive system (100) according to claim 7;
A refrigeration circuit (9) comprising an expansion valve (93).
A method of controlling an inverter (4) that converts an input DC voltage (Vdc) into a first AC voltage (V1) and applies it to an AC load (5),
An inverter control method that enables reduction (S84) of electric power (Po) supplied from the inverter to the AC load when a voltage value (Vdc) of the DC voltage is less than a predetermined first value (Vt1).