JP2013219985A - Power conversion device, compressor, blower, air conditioner, and refrigerator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a power conversion device capable of detecting variations in power source environments, such as voltage imbalance and voltage variation of an AC power source; a compressor; a blower; an air conditioner; and a refrigerator, each using the power conversion device.SOLUTION: On the basis of an output voltage, a reactor current and a command voltage of a converter part 10, a power conversion device finds a switching command value D according to a ratio of an output voltage of a rectifier to the command voltage. The power conversion device controls the driving of a switching element 12 of the converter part 10 on the basis of the switching command value D, and also detects a degree of variation in power source environments that is at least one of voltage imbalance and voltage variation of an AC power source on the basis of the switching command value D.

Description

  The present invention relates to a power converter, a compressor, a blower, an air conditioner, and a refrigerator using the power converter.

  In an air conditioner or a refrigerator, a power conversion system that drives a motor used for a compressor, a fan, or the like with an inverter has become the mainstream. According to this system, the motor can be operated with high efficiency by converting the alternating current into direct current with a rectifier and converting the direct current into alternating current with an arbitrary voltage and frequency with an inverter to drive the motor. , Can save energy. Furthermore, in recent years, in order to further save energy, a power converter is provided with a step-up or step-down converter (buck-boost converter) provided on the input side of the inverter, and the rectified output of the converter is stepped up or stepped down and input to the inverter. Has been proposed.

  In the power conversion device as described above, as a protection means for the switching element, for example, “the temperature of the switching element of the buck-boost converter and the inverter is detected, and the boost voltage is lowered based on the detected temperature. "Providing control means for performing control" has been proposed (see, for example, Patent Document 1).

JP 2011-066989 A (Claim 1)

In a power converter equipped with a converter on the input side of the inverter, even if there is a fluctuation in the power supply environment such as unbalance (unbalance) or fluctuations in the power supply voltage (voltage drop) in the interphase voltage of the three-phase power supply One of the merits is that by operating a converter capable of controlling current, voltage can be stably supplied to the inverter without being affected by the power supply environment.
However, if there is a fluctuation in the power supply environment such as unbalanced power supply or voltage drop more than expected on the power supply side, excessive stress is applied to the converter, leading to a reduction in the life of the switching element. Moreover, when the module temperature which comprises a power converter device rises by the fluctuation | variation of a power supply environment and reaches abnormality detection temperature, an air conditioning apparatus or a refrigerator may stop. For this reason, it is desired to detect a change in the power supply environment and to implement a protective measure for reducing the burden on the switching element.

  However, in a power converter provided with a converter on the input side of the inverter, the converter controls the voltage and current supplied to the inverter at a constant level. There was a problem that fluctuations in the power supply environment such as could not be easily detected. For this reason, there has been a problem that a protective measure for reducing the burden on the switching element cannot be implemented.

  According to Patent Document 1, the temperature of the switching element is detected and the countermeasure is implemented based on the detected temperature when the element is protected. However, when a sudden power imbalance occurs, countermeasures cannot be taken until the temperature of the element rises, and there is a concern that the period during which excessive stress is applied to the switching element becomes long and the life of the switching element is reduced. .

The present invention has been made to solve the above-described problems, and a power converter capable of detecting fluctuations in a power supply environment such as voltage imbalance or voltage fluctuation of an AC power supply and a compressor using the same , A blower, an air conditioner, and a refrigerator are obtained.
Moreover, the protection of a switching element is possible, and the power converter device which can fully ensure a required lifetime and can improve reliability, and a compressor, a fan, an air conditioning apparatus, and a refrigerator using the same are obtained.

  A power converter according to the present invention includes a rectifier that rectifies an AC voltage supplied from an AC power supply, a converter that includes a reactor, a switching element, and a backflow prevention element, and that varies an output voltage of the rectifier by chopping; A smoothing capacitor for smoothing the output of the converter unit, an inverter unit for converting the output of the converter unit smoothed by the smoothing capacitor into an AC voltage, a current detection unit for detecting a reactor current flowing in the reactor, and the converter An output voltage detection unit that detects an output voltage of the converter unit, and a control unit that controls a switching element of the converter unit so that the output voltage of the converter unit becomes a command voltage value, the control unit including the converter unit Output voltage, the reactor current, and the command voltage based on the command voltage A switching command value corresponding to a ratio of the output voltage of the rectifier is obtained, and based on the switching command value, the driving of the switching element of the converter unit is controlled, and on the basis of the switching command value, the voltage unbalance of the AC power supply And a degree of fluctuation of the power supply environment which is at least one of voltage fluctuations.

The present invention can detect fluctuations in the power supply environment such as voltage imbalance and voltage fluctuations of the AC power supply.
In addition, the switching element can be protected, and the required life can be sufficiently secured to improve the reliability.

It is a figure which shows the structure of the power converter device in Embodiment 1 of this invention. It is a figure which shows the structure of the converter part in Embodiment 1 of this invention. It is a figure which shows the mode of the change of the switching command by the power supply environment in Embodiment 1 of this invention. It is a figure which shows coping operation | movement at the time of the power supply environment change in Embodiment 1 of this invention. It is the figure which showed the structure of the air conditioning apparatus in Embodiment 2 of this invention. It is a figure which shows the structure of the refrigerator in Embodiment 3 of this invention.

Embodiment 1 FIG.
1 is a diagram showing a configuration of a power conversion device according to Embodiment 1 of the present invention.
In FIG. 1, 1 is a three-phase AC power source, and 2 is a three-phase rectifier that rectifies the AC voltage of the three-phase AC power source 1. The three-phase rectifier 2 has a configuration in which six rectifier diodes are bridge-connected. Reference numeral 10 denotes a converter unit. The converter unit 10 includes a reactor 11, a switching element 12 such as an IGBT (Insulated Gate Bipolar Transistor), and a backflow prevention element 13 such as a fast recovery diode. A smoothing capacitor 7 smoothes the output of the converter unit 10.
3 is a current detector for detecting the reactor current flowing in the reactor 11, 4 is an output voltage detector for detecting the output voltage of the converter 10 (voltage across the smoothing capacitor 7), and 20 is converter control means. Converter control means 20 generates a drive signal for operating switching element 12 from the output signals of current detector 3 and output voltage detector 4.
An inverter unit 8 drives the motor 9 by converting the voltage smoothed by the smoothing capacitor 7 into an AC voltage. The inverter unit 8 is configured by a switching element such as an IGBT. Reference numeral 30 denotes inverter control means. The inverter control means 30 generates a drive signal for operating the inverter unit 8.

The operation and action of the power converter configured as described above will be described.
First, the AC voltage of the three-phase AC power source 1 is rectified by the three-phase rectifier 2 to become a DC voltage. On / off of the switching element 12 of the converter unit 10 is controlled by the converter control means 20, and the DC voltage from the three-phase rectifier 2 is boosted or stepped down by the chopping.

  Here, in the converter unit 10, when the switching element 12 is turned on, the backflow prevention element 13 is prevented from conducting, and the voltage rectified by the three-phase rectifier 2 is applied to the reactor 11. On the other hand, when the switching element 12 is turned off, the backflow prevention element 13 becomes conductive, and a voltage in the opposite direction to that when the switching element 12 is on is induced in the reactor 11. At this time, from the viewpoint of energy, it can be seen that the energy accumulated in the reactor 11 when the switching element 12 is turned on is transferred to the inverter unit 8 which is a load when the switching element 12 is turned off. Therefore, the output voltage of the converter unit 10 can be controlled by controlling the on-duty of the switching element 12.

Next, the converter control means 20 that controls the output voltage of the converter unit 10 will be described.
FIG. 2 is a diagram showing a configuration of the converter according to Embodiment 1 of the present invention.
In FIG. 2, 21 is a voltage command calculating means. The voltage command calculation means 21 calculates a voltage command value from the command voltage value for the output voltage of the converter unit 10 and the output voltage detection value of the converter unit 10 detected by the output voltage detection unit 4. For example, the voltage command calculation means 21 performs proportional-integral control (PI control) with the difference between the command voltage value and the output voltage detection value as an input and the voltage command value as an operation amount.
Reference numeral 22 denotes current command calculation means. The current command calculation unit 22 calculates a switching command (on-duty command value) of the switching element 12 from the voltage command value calculated by the voltage command calculation unit 21 and the reactor current detected by the current detection unit 3. For example, the current command calculation means 22 performs proportional-integral-derivative control (PID control) using the difference between the voltage command value and the reactor current as an input and using the on-duty ratio of the switching element 12 as an operation amount.
Reference numeral 23 denotes drive pulse calculation means. Based on the switching command calculated by the current command calculating unit 22, the driving pulse calculating unit 23 generates a driving pulse (PWM command) in which the on-duty of the switching element 12 is set in synchronization with the carrier frequency.
Reference numeral 24 denotes power supply environment change degree calculation means. Based on the switching command calculated by the current command calculation means 22, the power supply environment change degree calculation means 24 detects the degree of fluctuation of the power supply environment such as voltage imbalance or voltage drop of the three-phase AC power supply 1. Details will be described later.
Reference numeral 25 denotes switching element protection means. The switching element protection means 25 executes a mitigation measure for power supply environment suppression control that reduces the load on the switching element 12 when the degree of fluctuation of the power supply environment detected by the power supply environment change degree calculation means 24 is not within a predetermined range. To do. Details will be described later.

  Next, the relationship between the change in the power supply environment such as voltage imbalance or voltage drop of the three-phase AC power supply 1 and the switching command will be described.

ここで、Ｅｄは昇降圧前の電圧であり、三相整流器２の出力電圧である。Ｅｏは指令電圧値である。つまり、スイッチング指令値Ｄは、指令電圧Ｅｏに対する三相整流器２の出力電圧Ｅｄの割合に応じた値として求めることができる。 When the voltage is stepped up / down by the converter unit 10, the switching command value D has the following relationship.

Here, Ed is a voltage before step-up / down, and is an output voltage of the three-phase rectifier 2. Eo is a command voltage value. That is, the switching command value D can be obtained as a value corresponding to the ratio of the output voltage Ed of the three-phase rectifier 2 to the command voltage Eo.

FIG. 3 is a diagram showing how the switching command changes due to the power supply environment in the first embodiment of the present invention.
In FIG. 3, the left side shows the case where there is no voltage unbalance and voltage drop in the three-phase AC power supply 1 (no power supply voltage fluctuation), and the center is the case where there is a voltage unbalance in the three-phase AC power supply 1 (there is a power supply voltage unbalance). The right side shows a case where the three-phase AC power supply 1 has a voltage drop (with a power supply voltage drop). The upper graph shows the voltage waveform of each phase of the three-phase AC power supply 1, the middle shows the output voltage Ed (voltage after rectification) of the three-phase rectifier 2, and the lower shows the switching command value D.

In the upper part of FIG. 3, when the power supply voltage of the three-phase AC power supply 1 is Vs and the power supply frequency is fs, as shown in the middle part of FIG. The maximum and minimum values are as follows.

  At this time, as shown in the lower part of FIG. 3, the switching command value D can be obtained as a value corresponding to the ratio of the output voltage Ed of the three-phase rectifier 2 to the command voltage Eo (constant in the short term). The value of the switching command value D also changes according to the voltage change of the voltage Ed.

When there is no power supply imbalance or power supply voltage drop, the output voltage Ed of the three-phase rectifier 2 changes within a predetermined range as shown in the middle stage on the left side of FIG. 3, and the voltage fluctuation range (difference between the maximum value and the minimum value) Is almost constant. Further, as shown in the lower left part of FIG. 3, the switching command value D also changes within a predetermined range with a constant change width (difference between the maximum value and the minimum value).
On the other hand, when the power supply is unbalanced, the voltage fluctuation range (difference between the maximum value and the minimum value) of the output voltage Ed of the three-phase rectifier 2 varies depending on the cycle, as shown in the middle middle part of FIG. As shown in FIG. 3, the change width (the difference between the maximum value and the minimum value) of the switching command value D increases.
For this reason, it is possible to detect the occurrence of the power supply unbalance by obtaining the change width of the switching command value D without directly detecting the voltage unbalance of the three-phase AC power supply 1.
Even when the voltage of the three-phase AC power source 1 fluctuates (decreases), the output voltage Ed of the three-phase rectifier 2 fluctuates outside a predetermined range, and accordingly, the change of the switching command value D is also outside the predetermined range. Will fluctuate. Therefore, by obtaining a change in the switching command value D, it is possible to detect a change in the power supply voltage.
Further, by using the above methods at the same time, it is possible to detect the power supply voltage imbalance and the power supply voltage drop from the change of the switching command value D even when the power supply imbalance and the power supply voltage drop are simultaneously.
In the present embodiment, the magnitude of at least one of voltage imbalance and voltage fluctuation of the three-phase AC power supply 1 is referred to as “degree of fluctuation in power supply environment”.

Next, the operation of the power supply environment change degree calculation means 24 will be described.
The power supply environment change degree calculation unit 24 acquires the switching command value D calculated by the current command calculation unit 22. Then, the degree of fluctuation of the power supply environment is detected from the difference between the maximum value of the switching command value D and the initial value in a predetermined period synchronized with the AC voltage cycle of the three-phase AC power supply 1. For example, the maximum value and the minimum value of the switching command value D in a predetermined period (for example, 6 fs period of the power supply) starting from the zero cross of the three-phase AC power supply 1 are detected, and the difference is obtained as the degree of fluctuation of the power supply environment.

  The method for detecting the degree of fluctuation of the power supply environment is not limited to this, and the fluctuation of the power supply environment is determined by the average value of the switching command value D in a predetermined period synchronized with the cycle of the AC voltage of the three-phase AC power supply 1. The degree may be detected.

Next, the mitigation measures for the power supply environment suppression control that reduces the load on the switching element 12 when the power supply environment fluctuates will be described.
FIG. 4 is a diagram showing a coping operation when the power supply environment fluctuates in Embodiment 1 of the present invention.
Hereinafter, a description will be given based on each step of FIG.

(S1)
The power supply environment change degree calculation unit 24 acquires the switching command value D calculated by the current command calculation unit 22.
(S2)
The power supply environment change degree calculation means 24 calculates the difference between the maximum value and the initial value of the switching command value D in a predetermined period synchronized with the cycle of the AC voltage of the three-phase AC power source 1 or the AC voltage of the three-phase AC power source 1. The degree of fluctuation of the power supply environment is detected from the average value of the switching command value D in a predetermined period synchronized with the cycle.
(S3)
The switching element protection unit 25 determines whether or not the degree of fluctuation of the power supply environment detected by the power supply environment change degree calculation unit 24 is within a predetermined range.
When the degree of fluctuation of the power supply environment is within the predetermined range, the process proceeds to step S4, and when the degree of fluctuation of the power supply environment is not within the predetermined range, the process is terminated.

As this predetermined range, for example, a range that exceeds the first threshold value and falls below the second threshold value (first threshold value <degree of fluctuation of power supply environment <second threshold value) is preset.
Here, the first threshold value is determined from the specifications of the switching element 12. The second threshold value is determined in consideration of the core temperature rise value due to the ripple current flowing into the smoothing capacitor 7, the element lifetime, and the like. In this way, by determining the first threshold value from the specification of the switching element 12 and determining the second threshold value from the allowable ripple current value of the smoothing capacitor 7, both the switching element 14 and the smoothing capacitor 7 can be protected. .
The present invention is not limited to this, and only one of the first threshold value and the second threshold value may be set.

(S4)
The switching element protection means 25 executes a mitigation measure for power supply environment suppression control that reduces the load on the switching element 14 of the converter unit 10.
This mitigation measure for the power supply environment suppression control is to suppress the operation of the converter unit 10. However, it should be noted that suppressing the operation of the converter unit 10 increases the influence of power supply imbalance and increases the ripple current of the smoothing capacitor 7.
For example, any one of the following (1) to (3) is implemented as a mitigation measure for the power supply environment suppression control.

(1) The boosting amount of the converter unit 10 is changed.
The switching element protection means 25 controls the switching element 14 of the converter unit 10 so that the output voltage of the converter unit 10 is lower than the command voltage value. Thus, the burden on the switching element can be reduced by changing the boost amount. However, if the boosting amount is changed significantly, the loss of the inverter unit 8 in the subsequent stage becomes large. Therefore, considering the inverter unit 8 side, the boosting value is set within an allowable range.

(2) The output frequency of the inverter unit 8 is reduced.
The switching element protection unit 25 outputs an instruction to lower the output frequency to the inverter control unit 30. The inverter control means 30 controls the switching element of the inverter unit 8 to reduce the output frequency of the inverter unit 8. Thereby, since the electric current which flows into the input of the converter part 10 falls, the burden concerning the switching element 12 of the converter part 10 reduces.

(3) Change the carrier frequency.
The switching element protection means 25 reduces the carrier frequency used when the drive pulse calculation means 23 generates a drive pulse (PWM command). As a result, when an element having an extremely large switching loss is used, the switching element can be lost by changing the carrier frequency, which can be greatly improved.

  Note that any one of the above (1) to (3) may be selected according to operating conditions. Thus, it goes without saying that the power supply environment suppression control can be relaxed by a method suitable for the application.

  With the above configuration, even when there is an unexpected change in the power supply environment, excessive stress applied to the switching element 12 is alleviated and the life of the switching element 12 is ensured, and control is performed before an abnormal stop. Priority can be given to continued operation as a container.

  Although the converter unit 10 of FIG. 1 is shown as a booster circuit, it goes without saying that the same effect can be obtained even if it is a step-down circuit.

  Note that at least one of the switching element 12 and the backflow prevention element 13 of the converter unit 10 may be formed of a wide band gap semiconductor. A wide band gap semiconductor is a general term for semiconductor elements having a larger band gap than silicon (Si) elements, and examples include silicon carbide (SiC) elements, gallium nitride (GaN), diamond elements, and the like. It is done.

  A switching element or a diode element formed of such a wide band gap semiconductor can perform high-speed switching. Further, since the withstand voltage is high and the allowable current density is also high, the switching element 12 and the backflow prevention element 13 can be downsized. By using the downsized switching element 12 and the backflow prevention element 13, It is possible to reduce the size of a semiconductor module incorporating the above element. Further, since the heat resistance is high, the heat radiation fins of the heat sink can be downsized and the water cooling part can be air cooled, so that the semiconductor module can be further downsized. Furthermore, since the power loss is low, the switching element 12 and the switching element 12 can be highly efficient, and further, the semiconductor module can be highly efficient.

As described above, in the present embodiment, the degree of fluctuation of the power supply environment that is at least one of voltage imbalance and voltage fluctuation of the AC power supply can be detected based on the switching command value D.
Thus, by calculating the degree of power supply unbalance or power supply voltage drop from the switching command value D of the converter unit 10, excessive stress is applied to the switching element 12 even when a sudden unbalance or voltage drop occurs. The element can be protected before being subjected to a long period of time, and a highly reliable power conversion device with a sufficient required life can be obtained.

Embodiment 2. FIG.
FIG. 5 is a diagram showing the configuration of the air-conditioning apparatus according to Embodiment 2 of the present invention. The air conditioner includes a compressor 100, a four-way valve 101, a heat exchanger (outdoor unit) 102, an expansion valve (decompression unit) 103, and a heat exchanger (indoor unit) 104, which are connected in a ring shape. A refrigerant circuit is configured. This refrigerant circuit constitutes a refrigeration cycle. And the power converter device which concerns on said Embodiment 1 is used as the drive control apparatus 110 of the motor (not shown) incorporated in the compressor 100. FIG. Moreover, the power converter device which concerns on said embodiment is used as the drive control apparatuses 111 and 112 of the air blowers 105 and 106 provided in order to ventilate the heat exchangers 102 and 104. FIG.
As described above, the air conditioner according to the second embodiment applies the power conversion device of the first embodiment to the compressor 100 and the fans 105 and 106 as control targets. Needless to say, the same effects as those of the first embodiment can be obtained.

Embodiment 3 FIG.
In addition, although said Embodiment 2 is an example of an air conditioning apparatus, this invention is applied similarly also in the drive control of the motor of a refrigerator or a freezer.
FIG. 6 is a diagram showing the configuration of the refrigerator according to Embodiment 3 of the present invention. The refrigerator 200 includes a refrigerant circuit similar to that shown in FIG. 5 (however, a four-way valve is not necessary), and the refrigerant circuit constitutes a refrigeration cycle. In the example of FIG. 6, the refrigerator 200 is used to send the cold air generated by the refrigerant compressor 201 that forms a part of the refrigeration cycle and the cooler 203 provided in the cooling chamber 202 to the refrigerator compartment, the freezer compartment, and the like. A blower 204 for circulating cold air is provided. The refrigerant compressor 201 and the cool air circulation fan 204 are driven by a motor controlled by the above-described power conversion device of the first embodiment. It goes without saying that the same effect as in the first embodiment can be obtained even if the motor is operated with such a configuration.

  While the present invention has been specifically described above based on the embodiments of the present invention, it is needless to say that the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.

  1 Three-phase AC power supply, 2 Three-phase rectifier, 3 Current detection unit, 4 Output voltage detection unit, 7 Smoothing capacitor, 8 Inverter unit, 9 Motor, 10 Converter unit, 11 Reactor, 12 Switching element, 13 Backflow prevention element, 14 Switching element, 20 Converter control means, 21 Voltage command calculation means, 22 Current command calculation means, 23 Drive pulse calculation means, 24 Power supply environment change degree calculation means, 25 Switching element protection means, 30 Inverter control means, 100 Compressor, 101 Four-way valve, 102 heat exchanger, 103 expansion valve, 104 heat exchanger, 105 blower, 106 blower, 110 drive control device, 111 drive control device, 112 drive control device, 200 refrigerator, 201 refrigerant compressor, 202 cooling chamber, 203 cooler, 204 blower.

Claims (13)

A rectifier that rectifies the AC voltage supplied from the AC power supply;
A converter unit having a reactor, a switching element, and a backflow prevention element, and varying the output voltage of the rectifier by chopping;
A smoothing capacitor for smoothing the output of the converter unit;
An inverter unit that converts the output of the converter unit smoothed by the smoothing capacitor into an AC voltage;
A current detector for detecting a reactor current flowing through the reactor;
An output voltage detection unit for detecting an output voltage of the converter unit;
Control means for controlling the switching element of the converter unit such that the output voltage of the converter unit becomes a command voltage value;
With
The control means includes
Based on the output voltage of the converter unit, the reactor current, and the command voltage, a switching command value corresponding to the ratio of the output voltage of the rectifier to the command voltage is obtained,
Based on the switching command value, controlling the driving of the switching element of the converter unit,
A power converter that detects a degree of fluctuation of a power supply environment that is at least one of voltage imbalance and voltage fluctuation of the AC power supply based on the switching command value. The control means includes
The degree of fluctuation of the power supply environment is detected based on a difference between a maximum value and an initial value of the switching command value in a predetermined period synchronized with an AC voltage cycle of the AC power supply. Power conversion device. The control means includes
The power conversion device according to claim 1, wherein a degree of fluctuation of the power supply environment is detected from an average value of the switching command values in a predetermined period synchronized with a cycle of the AC voltage of the AC power supply. The control means includes
The power supply environment suppression control mitigation measure for reducing the load on the switching element of the converter unit is executed when the degree of fluctuation of the power supply environment is not within a preset range. The power conversion device according to one item. The control means includes
As a mitigation measure for the power supply environment suppression control,
The power conversion device according to claim 4, wherein the switching element of the converter unit is controlled so that the output voltage of the converter unit is lower than the command voltage value. The control means includes
As a mitigation measure for the power supply environment suppression control,
The power conversion device according to claim 4, wherein a switching element of the inverter unit is controlled to reduce an output frequency of the inverter unit. The control means includes
Based on the switching command value, the on-duty of the switching element of the converter unit is controlled in synchronization with the carrier frequency,
The power converter according to claim 4, wherein the carrier frequency is lowered as a mitigation measure for the power supply environment suppression control. At least one of the switching element and the backflow prevention element is
The power conversion device according to any one of claims 1 to 7, wherein the power conversion device is formed of a wide band gap semiconductor. The wide band gap semiconductor is
9. The power converter according to claim 8, wherein the power converter is silicon carbide, gallium nitride-based material, or diamond. The power conversion device according to any one of claims 1 to 9,
And a motor driven by the power converter. The power conversion device according to any one of claims 1 to 9,
A blower comprising a motor driven by the power converter. An air conditioner comprising at least one of the compressor according to claim 10 and the blower according to claim 11. A refrigerator comprising at least one of the compressor according to claim 10 and the blower according to claim 11.

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