JP2022119584A - Power factor improvement circuit, air conditioner, control method, and program for power factor improvement circuit - Google Patents

Abstract

To provide a power factor reduction circuit capable of sufficiently reducing energy loss in a light load state in which a load is smaller than a predetermined load state.SOLUTION: In a power factor improvement circuit, a switching element is operated at a reference switching frequency in a reference load state, and the switching element is operated at a light load switching frequency lower than the reference switching frequency in a light load state in which the load is smaller than the reference load state. When an ON time of the switching element, which is set to be equal to or less than an allowable ripple current amplitude value in the reference load state, is a reference On time, and an On time of the switching element, which is set to be equal to or less than the allowable ripple current amplitude value in the light load state is an ON time at light load, the switching frequency at the light load is set on the basis of the reference switching frequency, the reference ON time, and the ON time at light load.SELECTED DRAWING: Figure 1

Description

The present invention relates to a power factor correction circuit used, for example, in an air conditioner or the like.

For example, a power factor correction circuit used in a compressor of an air conditioner is driven in a continuous current mode because of its heavy load. In such a power factor correction circuit, the switching frequency for operating the switching element is kept constant regardless of changes in the state of the connected load. Therefore, the switching loss that occurs in each switching cycle is almost constant regardless of the state of the load.

On the other hand, the ripple current flowing in the coil of the power factor correction circuit varies depending on the state of the connected load. As shown in FIG. As shown in FIG. 6, the ripple current amplitude is reduced.

Since ripple current causes EMI noise, such a power factor correction circuit also requires a filter circuit for removing EMI noise. In addition, in the smoothing circuit provided on the downstream side of the power factor correction circuit, the capacitor for removing and smoothing the ripple of the input current requires a certain ripple resistance. Filter circuits and capacitors are designed to correspond to the maximum value of ripple current that occurs at maximum load.

Japanese Patent Application Laid-Open No. 8-19259

However, the filter circuits and capacitors described above are designed to accommodate the maximum value of ripple current, so they have a margin when the load is light.

In particular, in applications such as air conditioners, where light load conditions last longer than maximum load conditions, the performance of filter circuits and capacitors can be fully utilized to reduce energy loss during light load conditions. Hard to say.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a power factor reduction circuit capable of sufficiently reducing energy loss in a light load state in which the load is smaller than a predetermined load state. and

That is, the power factor correction circuit according to the present invention includes a rectifier circuit that rectifies an AC voltage to a DC voltage, a coil connected in series to one output terminal of the rectifier circuit, and the coil connected to the other output terminal of the rectifier circuit. a switching element that short-circuits or opens between an output terminal and a chopper circuit configured by a closed circuit in which a diode and a smoothing capacitor are connected in series; In addition, in a light load state in which the load is smaller than the reference load state, the switching element is operated at a light load switching frequency lower than the reference switching frequency. The ON time of the switching element set to be equal to or less than the allowable ripple current amplitude value is the reference ON time, and the ON time of the switching element is set to be equal to or less than the allowable ripple current amplitude value in the light load state. When the light load ON time is set, the light load switching frequency is set based on the reference switching frequency, the reference ON time, and the light load ON time.

With such a structure, the switching element operates at the light-load switching frequency lower than the reference switching frequency used in the reference load state in the light-load state, thereby reducing the switching loss in the light-load state. can. In addition, since the switching frequency at light load is set based on the reference switching frequency, the reference ON time, and the ON time at light load, the ON time at light load is less than the reference ON time. The switching loss can be reduced while making full use of the performance of the filter circuit for removing EMI noise and the performance of the capacitor. In addition, the ripple current at the timing when the switching element is turned on can be made smaller than when the frequency is kept constant, so the reverse recovery loss in the diode at this time can also be reduced.

In order to maximize the performance of the filter circuit and the capacitor and reduce the switching loss under light load conditions, the reference load condition is the maximum load condition and the allowable ripple current amplitude value is the maximum. Any value may be used as long as it is the amplitude value of the ripple current generated in the load state.

As a specific setting example for setting the switching frequency at light load within the range of the allowable ripple current amplitude value, the reference ON time is set so as to achieve the allowable ripple current amplitude value under the reference load state. and the ON time during light load is set so as to achieve the allowable ripple current amplitude value in the light load state.

In order to appropriately set the switching frequency at light load, which can always respond to changes in the state of the load and realize the function as a power factor correction circuit and the effect of reducing switching loss, the switching frequency at light load may be set in conjunction with the cycle of the AC voltage.

As a specific mode for making the ON time during light load as close as possible to the reference ON time, the coil current detector for detecting the current flowing through the coil is further provided, and the ON time during light load is: It may be set to the time from when the switching element is turned on until the ripple current amplitude value flowing through the coil detected by the coil current detector reaches the maximum value.

Further comprising an input voltage detector for detecting an instantaneous value of the AC voltage input to the rectifier circuit, the voltage detected by the input voltage detector at a timing a predetermined time before the peak of the AC voltage, the A switching element is operated at the reference switching frequency, and the time required for the ripple current detected by the coil current detector to change from the minimum value to the maximum value is set as the light load ON time.

A preferable application example of the power factor correction circuit according to the present invention is an air conditioner provided with a compressor to which the output of the power factor correction circuit is input. With such a configuration, switching loss at light load is reduced compared to the conventional one, and highly efficient operation becomes possible.

As a method of controlling a power factor correction circuit according to the present invention that can sufficiently reduce switching loss in a light load state, a rectifier circuit that rectifies an AC voltage to a DC voltage and a rectifier circuit that is connected in series to one output terminal of the rectifier circuit are connected. a coil, a switching element that short-circuits or opens the coil with the other output terminal of the rectifier circuit, and a chopper circuit configured by a closed circuit in which a diode and a smoothing capacitor are connected in series. A control method for a power factor correction circuit, comprising operating the switching element at a reference switching frequency under a reference load condition, and operating the switching element at the reference switching frequency under a light load condition in which the load is smaller than the reference load condition The ON time of the switching element set to be equal to or less than the allowable ripple current amplitude value in the reference load state is set to the reference ON time and the allowable ripple in the light load state. When the ON time of the switching element set to be equal to or less than the current amplitude value is the ON time at light load, based on the reference switching frequency, the reference ON time, and the ON time at light load, It is characterized in that the switching frequency at light load is set.

In addition, in order to sufficiently reduce the switching loss in the light load state by rewriting the program in the existing power factor correction circuit, a rectification circuit that rectifies the AC voltage to the DC voltage and one output of the rectification circuit A chopper composed of a coil connected in series at one end, a switching element that short-circuits or opens the coil with the other output end of the rectifier circuit, and a closed circuit in which a diode and a smoothing capacitor are connected in series. and a program for operating the switching element at a reference switching frequency in a reference load state, and in a light load state in which the load is smaller than the reference load state, the The computer functions as a switching controller that operates the switching element at a switching frequency at light load that is lower than the reference switching frequency. When the ON time of the switching element set to be the reference ON time and the ON time of the switching element set so as to be equal to or less than the allowable ripple current amplitude value in the light load state, A power factor correction circuit program may be used in which the switching frequency at light load is set based on the reference switching frequency, the reference ON time, and the ON time at light load.

The power factor correction circuit program may be electronically distributed, or may be recorded on a program recording medium such as a CD, DVD, or flash memory.

As described above, according to the power factor correction circuit according to the present invention, the performance of the filter circuit and the capacitor designed according to the ripple current generated in the reference state where the load is relatively large can be sufficiently exhibited even at the time of light load. Therefore, the switching frequency for operating the switching element can be reduced at the time of light load. Therefore, in applications where the operation time is longer in the light load state than in the reference load state, the energy loss can be reduced as a whole, enabling efficient operation. Moreover, since the ripple current itself that flows in the light load state can be reduced, the reverse recovery loss in the diode can also be reduced.

1 is a circuit diagram showing a power factor correction circuit in one embodiment of the present invention; FIG. 5 is a graph showing how switching frequency is determined in one embodiment of the present invention. 4 is a graph showing signal waveforms at maximum load in the same embodiment; 4 is a graph showing signal waveforms at light load in the same embodiment; 7 is a graph showing signal waveforms in a maximum load state in a conventional power factor correction circuit; 7 is a graph showing signal waveforms in a light load state in a conventional power factor correction circuit;

<Configuration of Power Factor Correction Circuit 100>

A power factor correction circuit 100 according to an embodiment of the present invention will be described with reference to each drawing.

The power factor correction circuit 100 of this embodiment is used, for example, to improve the power factor of electric power supplied to a compressor (not shown) in an air conditioner. provided between the circuits.

This power factor correction circuit 100, as shown in FIG. , a switching element M1 that short-circuits or opens the coil L1 with the other output end of the rectifier circuit 1, and a chopper circuit 3 configured by a closed circuit in which a diode D5 and a smoothing capacitor are connected in series. It is a thing. A compressor as a load is connected to the output end of the chopper circuit 3 via an inverter circuit. Further, the power factor correction circuit 100 of this embodiment is provided with a filter circuit F for removing EMI noise between the AC power supply and the rectifier circuit 1 . Furthermore, the power factor correction circuit 100 includes an input voltage detector (not shown) that detects the output voltage of the AC power supply, that is, the instantaneous value of the AC voltage that is input to the rectifier circuit 1, and a coil that detects the current flowing through the coil L1. A current detector 2 and a switching controller 4 for controlling ON/OFF of the switching element M1 are provided.

Each part will be described in detail.

The filter circuit F is configured so as to prevent EMI noise from being generated by the ripple current flowing through the coil L1 and not to affect the AC power supply side. This filter circuit F is designed to allow the maximum ripple current that occurs at maximum load. That is, the filter circuit F is configured based on the allowable ripple current amplitude value. Therefore, when the switching frequency is fixed as in the conventional art, the ripple current becomes small when the load is light, and the filter circuit F has a margin.

The rectifier circuit 1 is configured such that four diodes D1, D2, D3, and D4 are connected to form a bridge, and full-wave rectification of AC is performed to output DC.

The coil L1 is a boost coil, and a main winding that constitutes the coil L1 and an auxiliary winding for current detection are wound around the core, so that the current flowing through the coil L1 can be detected. . When a current flows through the main winding, a voltage is generated in the auxiliary winding in proportion to it. Based on the voltage generated in this auxiliary winding, the magnitude of the ripple current flowing through the coil L1 is detected. . That is, the auxiliary winding constitutes the coil current detector 2 described above. Note that the coil current detector 2 is not limited to the auxiliary winding. It may be configured to detect the voltage applied to the coil L1 to detect the amount of current flowing through the coil L1.

For example, a MOSFET or the like can be used as the switching element M1. The switching element M1 is controlled in a current continuous mode so that the current flowing through the coil L1 continues to flow continuously. Then, ON/OFF of the switching element M1 is switched so that the power supply current has a waveform similar to that of the power supply. Electric energy is accumulated in the coil L1 while the switching element M1 is ON. Further, in this embodiment, the switching frequency for operating the switching element M1 is changed according to the state of the load. The details of the operation of the switching element M1 will be described later together with the switching control section 4. FIG.

Diode D5 is a fast recovery diode, and electric energy accumulated in coil L1 is supplied to the load via diode D5 while switching element M1 is OFF.

Capacitor C1 acts as a smoothing capacitor, removes ripple contained in the current flowing through coil L1 when switching element M1 is ON/OFF, and supplies the current to the load. The characteristics of the capacitor C1 are set based on the maximum amplitude of ripple current that occurs at maximum load. That is, the characteristics of the capacitor C1 are set according to the allowable ripple current amplitude value.

The functions of the switching control unit 4 are realized by a microcomputer having, for example, a CPU, a memory, an A/D converter, a D/A converter, and various input/output means. That is, the function of the switching control unit 4 is realized by executing the power factor correction circuit program stored in the memory.

The switching control unit 4 operates the switching element M1 at a reference switching frequency predetermined as a fixed value when the load is maximum, which is the reference load state. It is configured to operate the switching element M1 at a light-load switching frequency that is lower than the reference switching frequency. More specifically, the switching control unit 4 sets the light-load switching frequency for operating the switching element M1 in the light-load state and the length of the ON time during the light-load period in one cycle based on a predetermined algorithm. do.

Here, fixed values are set in advance for the reference switching frequency and the reference ON time, which is the ON time in one cycle, which is used at the time of maximum load, which is the reference load state. The reference ON time is set so that when the maximum ripple current amplitude occurs at maximum load, it is equal to or less than the allowable ripple current amplitude value.

Specifically, as shown in FIG. 2(a), the amplitude of the ripple current flowing through the coil L1 becomes maximum at the timing when the AC voltage takes a peak value. The reference ON time t0 is set so that the current amplitude value becomes the allowable ripple current amplitude value. Further, in this embodiment, the period 1/f0, which is the reciprocal of the reference switching frequency f0, is set to be approximately twice the reference ON time t0. These values are always fixed values. Based on these values and the light load ON time t1 which is set to be as close as possible to the reference ON time t0 at light load, the switching control unit 4 calculates and sets the light load switching frequency f1 used at light load. do.

A concrete algorithm is as follows.

First, the switching control unit 4 sets the switching frequency to the reference switching frequency f0 before the instantaneous value of the AC voltage reaches its peak. In this embodiment, for example, when the AC power supply voltage detected by the input voltage detector reaches 95% of the peak value, the switching element M1 is operated at the reference switching frequency f0 and the reference ON time t0.

Here, as shown in FIG. 2(c), the maximum ripple current appears when the instantaneous value of the AC power supply voltage reaches its peak, so the switching controller 4 stores the timing. Further, as shown in FIG. 2(d), the coil current detected by the coil current detector 2 detects the time during which the full amplitude of the ripple current at the timing described above appears, and sets that time when the load is light. It is detected as ON time t1 at light load.

The switching control unit 4 calculates the switching frequency at light load by f1=t1/t0·f0 based on the detected ON time t1 at light load, reference ON time t0, and reference switching frequency f0. By using the light-load switching frequency f1 and the light-load ON time t1 set in this way, it is possible to generate a ripple current value as large as possible within the allowable ripple current amplitude value, and at a frequency lower than the reference switching frequency f0. can set the switching frequency at light load. The switching frequency f1 during light load and the ON time during light load are executed for each voltage cycle of the AC power supply.

<Effect of Power Factor Correction Circuit 100>

With the power factor correction circuit 100 of the present embodiment configured as described above, in the light load state, the switching frequency f1 at light load, which is lower than the reference switching frequency f0 used in the reference load state which is the maximum load state, is used. The switching element M1 can be operated. Therefore, it is possible to reduce the switching loss at the time of light load.

In addition, the light load ON time t1 set at light load is set as close as possible to the reference ON time t0 set at maximum load. and the performance of the capacitor C1 can be fully utilized to reduce the switching loss.

In addition, the ripple current at the timing when the switching element M1 is turned ON can be made smaller than when the frequency is kept constant, so the reverse recovery loss in the diode D5 can also be reduced.

In other words, as shown in the signal waveform at maximum load in FIG. 3 and the signal waveform at light load in FIG. Therefore, the switching frequency can be reduced by increasing the ripple current when the load is light compared to the conventional case. For example, in the case of air conditioners, where the operating time at maximum load is short and the operating time at light load accounts for most of the time, the effect of reducing switching loss at light load increases overall energy efficiency. be able to.

Other embodiments will be described.

In the above embodiment, the light load ON time t1 and the light load switching frequency f1 are switched for each load state in each power supply voltage cycle. Alternatively, fixed t1 and f1 may be used. In this case, the power factor correction circuit may be configured without using various detectors.

The reference load state is not limited to the maximum load state, and a relatively large load state may be used as the reference load state. In addition, the application for which the power factor correction circuit is used is not limited to the air conditioner, and it may be used for various applications such as a washing machine.

In addition, as long as it does not contradict the gist of the present invention, various modifications of the embodiments and parts of the embodiments may be combined.

100 Power factor correction circuit 1 Rectifier circuit L1 Coil M1 Switching element D5 Diode C1 Capacitor 3 Chopper circuit F Filter circuit 4・Switching controller

Claims (9)

a rectifier circuit that rectifies an AC voltage to a DC voltage;
a coil connected in series to one output terminal of the rectifier circuit;
a switching element that short-circuits or opens the coil with the other output end of the rectifier circuit;
a chopper circuit configured by a closed circuit in which a diode and a smoothing capacitor are connected in series;
The switching element is operated at a reference switching frequency in a reference load state, and the switching element is operated at a light load switching frequency lower than the reference switching frequency in a light load state in which the load is smaller than the reference load state. is configured as
The ON time of the switching element is set to be equal to or less than the allowable ripple current amplitude value in the reference load state, and the reference ON time is set to be equal to or less than the allowable ripple current amplitude value in the light load state. When the ON time of the switching element is the ON time at light load,
A power factor correction circuit, wherein the switching frequency at light load is set based on the reference switching frequency, the reference ON time, and the ON time at light load. the reference load state is a maximum load state;
2. A power factor correction circuit according to claim 1, wherein said allowable ripple current amplitude value is the amplitude value of ripple current generated in said maximum load condition. the reference ON time is set so as to achieve the allowable ripple current amplitude value in the reference load state;
3. The power factor correction circuit according to claim 1, wherein said light load ON time is set so as to achieve said allowable ripple current amplitude value in said light load state. 4. The power factor correction circuit according to claim 1, wherein said light load switching frequency is set in conjunction with a period of said AC voltage. Further comprising a coil current detector that detects the current flowing through the coil,
2. The light load ON time is set to a time from when the switching element is turned ON to when the ripple current amplitude value flowing through the coil detected by the coil current detector reaches a maximum value. 5. The power factor correction circuit according to any one of 4. Further comprising an input voltage detector that detects an instantaneous value of the AC voltage input to the rectifier circuit,
operating the switching element at the reference switching frequency at a timing a predetermined time before the peak of the AC voltage of the voltage detected by the input voltage detector;
6. The power factor correction circuit according to claim 5, wherein the ON time at light load is set to the time required for the ripple current detected by the coil current detector to change from the minimum value to the maximum value. A power factor correction circuit according to any one of claims 1 to 6;
and a compressor to which the output of the power factor correction circuit is input. A rectifying circuit that rectifies an AC voltage to a DC voltage, a coil that is connected in series to one output terminal of the rectifying circuit, and a switching element that shorts or opens the coil to the other output terminal of the rectifying circuit. and a chopper circuit configured by a closed circuit in which a diode and a smoothing capacitor are connected in series, wherein
The switching element is operated at a reference switching frequency in a reference load state, and the switching element is operated at a light load switching frequency lower than the reference switching frequency in a light load state in which the load is smaller than the reference load state. ,
The ON time of the switching element is set to be equal to or less than the allowable ripple current amplitude value in the reference load state, and the reference ON time is set to be equal to or less than the allowable ripple current amplitude value in the light load state. When the ON time of the switching element is the ON time at light load,
A control method, wherein the switching frequency at light load is set based on the reference switching frequency, the reference ON time, and the ON time at light load. A rectifying circuit that rectifies an AC voltage to a DC voltage, a coil that is connected in series to one output terminal of the rectifying circuit, and a switching element that shorts or opens the coil to the other output terminal of the rectifying circuit. and a chopper circuit configured by a closed circuit in which a diode and a smoothing capacitor are connected in series, and a program used in a power factor correction circuit comprising:
The switching element is operated at a reference switching frequency in a reference load state, and the switching element is operated at a light load switching frequency lower than the reference switching frequency in a light load state in which the load is smaller than the reference load state. It makes the computer demonstrate the function as a switching control unit,
The ON time of the switching element is set to be equal to or less than the allowable ripple current amplitude value in the reference load state, and the reference ON time is set to be equal to or less than the allowable ripple current amplitude value in the light load state. When the ON time of the switching element is the ON time at light load,
A program for a power factor correction circuit, wherein the switching frequency at light load is set based on the reference switching frequency, the reference ON time, and the ON time at light load.

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