JP6729650B2 - Inverter control method, AC load power supply system, refrigeration circuit - Google Patents

Description

The present disclosure relates to technology for converting electric power.

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 parts.

JP-A-63-290193

The present disclosure suppresses heat generation of a converter that outputs a voltage input to an inverter.

A power supply system for an AC load according to the present disclosure includes an inverter (4) that applies a first AC voltage (V1) converted from a DC voltage (Vdc) to supply power (Po) to an AC load (5). , A converter (2) for converting the second AC voltage (V2) into the DC voltage (Vdc), and a control circuit (6).

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

And, the long the voltage value (Vac) is the first value (Vt1) or more, under the power of the first condition for reducing the power (S83, S84) is reduced (S85) .. If the voltage value is lower than the first value, under the power of the previous SL second condition for reducing the power that is more relaxed than the first condition (S82, S84) is reduced (S85) It

A second aspect of the power supply system to the AC load of the present disclosure is the first aspect thereof, wherein the voltage value (Vac) is less than the first value (Vt1), and the inverter (4) If the current (Iw) input to or output to the AC load (5) is equal to or greater than the first upper limit value (I3), droop control (S85) for the current is performed. The first upper limit is monotonically non-decreasing with respect to the increase in the voltage value.

A third aspect of the power supply system to the AC load of the present disclosure is the first aspect or the second aspect thereof, wherein the voltage value (Vac) is less than the first value (Vt1), If the current value (Ii) of the input current input to the converter (2) is not less than the second upper limit value, the droop control (S85) for the input current is performed. The second upper limit is monotonically non-decreasing with respect to the increase of the voltage value (Vac).

A fourth aspect of the power supply system to the AC load according to the present disclosure is the first aspect, the second aspect, or the third aspect thereof, in which the voltage value (Vac) is the first value (Vt1). If it is less than the predetermined second value (Vt2) lower than the above, the supply of the electric power (Po) to the AC load (5) is stopped (S73, S74).

A fifth aspect of the power supply system for an AC load of the present disclosure is the second aspect or the third aspect thereof, wherein the AC load (5) is a motor. The drooping control (S85) includes control for reducing the rotation speed of the motor.

A sixth aspect of the power supply system to the AC load of the present disclosure is the fifth aspect thereof, wherein the motor (5) drives the compressor (91) employed in the refrigeration circuit (9). It is either a motor, a fan used in an air conditioner, or a motor that drives a fan used in an air purifier.

A seventh aspect of the system for supplying power to an AC load according to the present disclosure is the fifth aspect thereof, wherein the motor (5) is a motor for driving a compressor (91) included in the refrigeration circuit (9). is there. The refrigeration circuit further comprises an expansion valve (93). The drooping control (S85) includes control for increasing the opening degree of the expansion valve.

An eighth aspect of the power supply system to the AC load of the present disclosure is any one of the first to seventh aspects thereof, wherein the voltage value (Vac) is less than the first value (Vt1). If so, 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 compressor (91) driven by a motor (5) and an expansion valve (93). The motor (5) is the AC load (5) supplied with power by the seventh aspect of the power supply system for the AC load of the present disclosure.

The control method of the inverter 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 DC voltage (Vdc) is obtained by converting the second AC voltage (V2) by the converter (2).

When the voltage value (Vac) of the second AC voltage is less than the predetermined first value (Vt1), the power is reduced (S85) and the power can be supplied (S8). If the voltage value (Vac) is equal to or higher than the first value (Vt1), the power is reduced (S85) under the first condition (S83, S84) for reducing the power. If the voltage value is less than the first value, the power is reduced (S85) under the second condition (S82, S84) for reducing the power that is relaxed compared to the first condition. ..

It is a block diagram which illustrates the composition of an alternating current load drive system. 7 is a flowchart illustrating a power reduction operation of the control circuit and an operation associated therewith. It is a graph which illustrates the dependence with respect to a voltage value of the function used as a current droop value. It is a block diagram which illustrates the structure of a refrigeration circuit.

FIG. 1 is a block diagram showing a configuration of an AC load driving system 100, in which the AC load driving 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 adopted. For example, the AC load 5 is an AC motor. For example, the AC motor drives a compressor used in the refrigeration circuit. Alternatively, for example, the AC motor drives a fan that blows air to the heat exchanger used in the refrigeration circuit. Alternatively, for example, the AC motor drives a fan used in an air cleaner.

The AC load drive system 100 includes an inverter 4. The inverter 4 converts the DC voltage Vdc input to itself into an AC voltage V1 and applies it to the AC load 5. The inverter 4 supplies the AC load 5 with electric power (hereinafter, “operating power”) Po for operating 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 includes a converter 2. The converter 2 converts the AC voltage V2 and outputs the DC voltage Vdc. The AC voltage V2 is output from the commercial power supply 1, which is an AC power supply, for example. An input current having a current value Ii is input from the commercial power supply 1 to the converter 2. Electric power Ps is supplied from the commercial power supply 1 to the AC load drive system 100.

For the converter 2, for example, a diode bridge rectifier circuit, a step-up converter, a step-down converter, or a step-up/down converter is adopted.

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

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

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

Therefore, the control circuit 6 changes 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.

The 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 for the rotation speed or the rotation torque of the motor 5. The value of the DC voltage Vdc may be input to the control circuit 6.

The voltage value Vac is obtained by using a known voltage sensor, and the current value Iw is obtained by using a known current sensor by a known method. 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. The 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, in order to improve the cooling performance, an increase in the rotation speed of the compressor can be adopted, and for example, the command value of the rotation speed indicated by the command data J increases.

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 rotation speed or the rotation 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 the operating power Po of a certain value, the current value Ii increases when the voltage value Vac decreases. This is because the input power Pi is proportional to the product of the voltage value Vac and the current value Ii when the power conversion efficiency of the converter 2 is considered to be constant, and the input power Pi is equal to the operating power Po when the loss in the inverter 4 is ignored. The increase in the current value Ii causes the diode or switching element forming the converter 2 to generate heat. The heat generation of the diode or the switching element lowers the efficiency and the performance of the element. Therefore, it is desired that the heat generation of the converter 2 be suppressed.

In the present 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 Vac decreases. Specifically, for example, the control circuit 6 changes the control signal G so that the inverter 4 performs the above operation. This is because the reduction of the operating power Po leads to the reduction of the input power Pi, and eventually the power Ps, and thereby alleviates or reduces the increase of the current value Ii.

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

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

It is not always necessary to reduce the operating power Po with respect to the decrease in the voltage value Vac. This is because the heat generated by the switching element and the like can be allowed up to a predetermined upper limit. For example, the upper limit of such tolerance depends on what is called allowable collector loss when a transistor is used as the switching element.

Therefore, as the technique proposed in the present embodiment, if the voltage value Vac is less than a predetermined threshold value (hereinafter referred to as “first value Vt1” for convenience), the voltage value Vac is equal to or more than the predetermined threshold value. A technique for making it easier to reduce the operating power Po supplied from the inverter 4 to the AC load 5 as compared with the above case will be given.

In terms of the operation of the control circuit 6, this is an operation of reducing the operating power Po when the voltage value Vac is less than the first value Vt1 and when the voltage value Vac is not less than the first value Vt1 (hereinafter also referred to as “power reducing operation”). The control method of supplying the operating power Po to the inverter 4 is performed by changing the condition for performing the operation. 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.

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 a 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 the operating power Po may be indirectly determined by determining the operating state of the AC load 5 (for example, the rotation speed and torque of the motor load). ..

After step S71, control is performed in step S72 to maintain the operating power Po and operate the inverter 4. 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.

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

In step S73, for example, the voltage value Vac is compared with the predetermined second value Vt2. The second value Vt2 is smaller than the first value Vt1. When voltage value Vac is less than second value Vt2 (that is, when Vac≧Vt2 is denied), 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 diode bridge rectifier circuit is adopted in the converter 2, the decrease in the voltage value Vac causes the decrease in the DC voltage Vdc. Step S73 may include a low voltage protection process for the DC voltage Vdc in such a case.

Here, the stop of the supply of the operating power Po is treated as a process different from the power reducing operation of supplying the operating power Po, although it is reduced.

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

At the beginning of the process of step S8, the first value Vt1 is compared with the voltage value Vac in step S81. As a result of the comparison, if the voltage value Vac is less than the first value Vt1 (that is, if Vac<Vt1 is affirmative), the process proceeds to step S82. If the voltage value Vac is greater than or equal to the first value Vt1 (that is, when Vac<Vt1 is denied), the process proceeds to step S83.

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

An example of drooping control is control in which the AC load 5 is a motor and the rotation speed of the motor is reduced. The reduction of the rotation speed of the motor is realized by the reduction of 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 the current flowing through the inverter 4, it can be measured as the current value Iw.

When Iw≧I3 is positive in step S84, the process proceeds to step S85 and the drooping control is performed. As a result, the current value Iw decreases. That is, in steps S84 and S85, the current droop value I3 functions as the upper limit value of the current value Iw.

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

Both steps S82 and S83 are processes for 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) is monotonically non-decreasing as the voltage value Vac increases. In step S83, the current droop value I3 is set to the predetermined value I31. For example, the predetermined value I31 is a value that does not depend on the voltage value Vac.

After steps S82 and S83 are executed, step S84 is executed. The process in step S84 in this case is a comparison between the current value Iw and the predetermined value I31. That is, steps S82, S83, S84, S85 are a set of steps for performing the drooping control so that the current value Iw does not exceed the predetermined value I31.

FIG. 3 is a graph exemplifying the dependency of the function f(Vac), which is the current droop value I3, on the voltage value Vac. In particular:
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 does not depend on 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 non-linear with respect to the voltage value Vac. For example, the function f(Vac) may change continuously or stepwise with respect to the change of 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 monotonically decreases as the voltage value Vac decreases.

By adopting the current droop value I3 set in this way, by executing steps S84 and S85, in the droop control for the current Iw, the lower the voltage value Vac is, the lower the current droop value I3 is, and the current Iw is set as the upper limit. Suppress. Therefore, as the voltage value Vac decreases, the operating power Po and eventually the power Ps decrease. Therefore, even if the voltage value Vac decreases, the current value Ii is suppressed from increasing, and the heat generation of the converter 2 is suppressed. The reduction of the operating power Po by steps S82, S84, S85 is an example of the above power reducing operation.

From the description of steps S82, S83, S84, it can be said that:
If the voltage value Vac is not less than the first value Vt1, the operating power Po is reduced and supplied under the first condition of I3=I31;
If the voltage value Vac is less than the first value Vt1, the operating power Po is reduced and supplied under the second condition of I3=f(Vac).

If Vac<Vt1, then f(Vac)<I31. Therefore, when the voltage value Vac is less than the first value Vt1, the operating power is higher than when the voltage value Vac is the first value Vt1 or more. Po is easily reduced. In other words, the second condition for reducing the operating power Po is relaxed more than the first condition.

Although the second condition is more relaxed than the first condition, the operating power Po is not necessarily reduced if Vac<Vt1. This is because if the determination in step S84 is negative, the process does not proceed to step S85 and the drooping control is not performed. Therefore, when Vac<Vt1, it can be said that the control circuit 6 enables the inverter 4 to reduce the power.

If the determination in step S73 is negative, step S74 is executed and the supply of the operating power Po is stopped. Therefore, when Vac<Vt2, the value of the function f(Vac) is not set. Good.

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

A first value Vt1′ that is larger than the first value Vt1 that determines the function f(Vac) may be introduced, and the first value Vt1 that is compared with the voltage value Vac in step S81 may be replaced with the first value Vt1′. .. In this case, when Vt1≤Vac≤Vt1', the current droop value I3 takes a predetermined value I31, and the droop control for the current Iw is performed with this value as the upper limit. That is, the function f(Vac) monotonously decreases with a decrease in the voltage value Vac, but there may be a region that does not depend on the voltage value Vac (monotone non-decreasing with respect to an increase in the voltage value Vac). ..

The reduction of the rotation speed of the motor exemplified as the drooping control directly reduces the current Iw. It is also considered in the drooping control that the operating power Po is indirectly reduced through the reduction of the rotation speed or the rotation torque of the motor by causing an event that causes the reduction of the rotation speed or the rotation torque of the motor. You can 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. 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 provided in the refrigeration circuit 9. The expansion valve 93 is a solenoid valve, and its opening degree is adjusted by a control signal L generated by the control circuit 6. For example, the opening 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 converter 2.

In step S85 (see FIG. 2), the opening degree of the expansion valve 93 is increased by the control signal L. As a result, the mechanical load of the compressor 91 is reduced, so the rotational torque required for the motor 5 that drives the compressor 91 is reduced, and the current Iw is reduced. Therefore, the process of increasing the opening degree of the expansion valve 93 can be included in the drooping control.

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

The storage device can be configured by one or more of various storage devices such as a ROM (Read Only Memory), a RAM (Random Access Memory), and a rewritable nonvolatile memory (EPROM (Erasable Programmable ROM), etc.). .. The storage device stores various kinds of information and data, stores a program executed by a 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, or realizes various functions corresponding to each processing step. Further, the control circuit 6 is not limited to this, and various procedures executed by the control circuit 6 or various means or various functions to be realized may be partially or entirely realized by hardware.

As described above, the present embodiment has proposed a technique of controlling the inverter 4 that converts the input DC voltage Vdc into the AC voltage V1 and applies the AC voltage V1 to the AC load 5. The DC voltage Vdc is obtained by converting the AC voltage V2 by the converter 2.

In the AC load driving system 100, when the voltage value Vac is less than the first value Vt1, the control circuit 6 allows the inverter 4 to reduce the operating power Po. As a result, operating power Po, and eventually power Ps, are reduced, and heat generation of converter 2 is suppressed. Such a technique can also be viewed as a control method of the inverter 4 that makes it possible to reduce and supply the operating power Po when the voltage value Vac is less than the first value Vt1.

If the voltage value Vac is the first value Vt1 or more, the operating power Po supplied from the inverter 4 to the AC load 5 is reduced (step S85) under the first condition (steps S83 and S84) to reduce the operating power Po. Supply. If the voltage value Vac is less than the first value Vt1, the operating power Po is reduced (step S85) under the second condition (steps S82 and S84) and the operating power Po is supplied. The second condition is more relaxed than the first condition.

For example, when the voltage value Vac is less than the first value 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 more than the upper limit current droop value I3. If so, the drooping control for the current is performed (step S85). The current droop value I3 is monotonically non-decreasing with respect to the increase of the voltage value Vac. As a result, the operating power Po supplied from the inverter 4 to the AC load 5 is reduced.

The drooping control on the current input to converter 2 may be performed. For example, if the voltage value Vac is less than the first value and the current value Ii is not less than the upper limit value, the drooping control for the current is performed. For example, the upper limit value can be set to be monotonically non-decreasing as the voltage value Vac increases. Specifically, for example, a flowchart in which the current value Iw is read as the current value Ii in step S84 (see FIG. 2) can be adopted. The upper limit value can be set independently of the above-mentioned current droop value I3.

If the voltage value Vac is less than the second value Vt2 that is 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 is a motor, and the drooping control may include control for reducing the rotation speed of the motor 5. This leads to a direct reduction of the operating power Po.

An example of the motor 5 may be a motor that drives a compressor 91 included in the refrigeration circuit 9. For example, the motor 5 drives the compressor 91 included in the refrigeration circuit 9 including the expansion valve 93. The refrigeration circuit 9 includes a compressor 91 driven by the motor 5 to which the operating power Po is supplied by the AC load driving system 100, and an expansion valve 93. The drooping control may include control for increasing the opening degree of the expansion valve 93. This leads to an indirect reduction of the operating power Po.

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

When a DC load driven by the DC voltage Vdc is provided, control for reducing the power supplied to the DC load may be performed. In this case, the input power Pi is the sum of the operating power Po and the power consumed by the DC power, and the reduction of the DC power contributes to the reduction of the power Ps. Such 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 as DC power from the capacitor 3, the expansion valve 93 operates when the voltage value Vac is less than the first value Vt1. You may stop.

It can be said that the AC load drive system 100 including the converter 2, the inverter 4, and the control circuit 6 that performs the power reduction operation is a power supply system to the AC load 5.

While 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 variants described above can be combined with one another.

2 Converter 4 Inverter 5 AC load (motor)
6 Control Circuit 9 Refrigeration Circuit 91 Compressor 93 DC Load (Expansion Valve)
100 AC load drive system (power supply system to AC load)

Claims (10)

An inverter (4) for applying a first AC voltage (V1) converted from a DC voltage (Vdc) to supply electric power (Po) to an AC load (5);
A converter (2) for converting a second AC voltage (V2) into the DC voltage (Vdc);
A control circuit (6) for allowing the inverter to reduce the 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 higher than the first value (Vt1), the power is reduced (S85) under the first condition (S83, S84) for reducing the power,
If the voltage value is less than the first value, the power under the second condition for reducing the power that is more relaxed than the first condition (S82, S84) is Ru is reduced (S85) , Power supply system to AC load. The voltage value (Vac) is less than the first value (Vt1), and the current (Iw) input to the inverter (4) or output to the AC load (5) has a first upper limit value ( If I3) or more, droop control (S85) for the current is performed,
The system according to claim 1, wherein the first upper limit is monotonically non-decreasing with respect to the increase in the voltage value. If the voltage value (Vac) is less than the first value (Vt1) and the current value (Ii) of the input current input to the converter (2) is not less than the second upper limit value, the input current Droop control (S85) is performed,
Said second upper limit value is monotonic non-decreasing, the power supply system of claim 1 to the AC load as defined in claim 2 with the rise of the voltage value (Vac). When the voltage value (Vac) is less than the predetermined second value (Vt2) lower than the first value (Vt1), the supply of the electric power (Po) to the AC load (5) is stopped ( S73, S74), The power supply system to the AC load according to any one of claims 1 to 3 . The AC load (5) is a motor,
The power supply system to the AC load according to claim 2 or 3 , wherein the drooping control (S85) includes control for reducing a rotation speed of the motor. The motor (5) is any one of a motor that drives a compressor (91) used in a refrigeration circuit (9), a fan that is used in an air conditioner, and a motor that drives a fan used in an air purifier. The power supply system for an AC load according to claim 5 , wherein: The motor (5) is a motor for driving a compressor (91) included in the refrigeration circuit (9),
The refrigeration circuit further comprises an expansion valve (93),
The power supply system to an AC load according to claim 5 , wherein the drooping control (S85) includes control for increasing an opening degree of the expansion valve. If it is less than the voltage value (Vac) is the first value (Vt1), the power supplied to the DC load (93) driven by the DC voltage is reduced, any of claims 1 to 7 The power supply system to the AC load according to one. A compressor (91) driven by the motor (5), which is the AC load (5) supplied with power by the AC load power supply system according to claim 7 .
A refrigeration circuit (9) comprising an expansion valve (93). A method for controlling an inverter (4) which converts an input DC voltage (Vdc) into a first AC voltage (V1) and supplies electric power to an AC load (5),
The DC voltage (Vdc) is obtained by converting the second AC voltage (V2) by the converter (2),
Voltage value of the second alternating voltage when (Vac) is smaller than the predetermined first value (Vt1), the power is reduced (S85) to allow the supply of the electric power (S8),
If the voltage value (Vac) is equal to or higher than the first value (Vt1), the power is reduced (S85) under the first condition (S83, S84) for reducing the power,
If the voltage value is less than the first value, the power is reduced (S85) under the second condition (S82, S84) for reducing the power that is relaxed compared to the first condition. , Inverter control method.

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