JPH1198825A - Power-factor improvement circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To properly perform the reduction of loss when a 100 VAC system is used, the arbitrary setting of output voltage when a 200 VAC system is used, and overcurrent protection when there is a short circuit current to a load or a power supply is started. SOLUTION: A first inverter 2 of step-down type and a second inverter 5 of step-up type are series-connected to the output of a full-wave rectifying circuit which is fed with alternating-current signals and outputs full-wave rectified signal. A control circuit 14 of power-factor improvement type controls a direct-current output voltage to a constant voltage and the switching of the first inverter 5, so that the waveform of alternating-current input current is made similar to the waveform of alternating-current input voltage, thereby improving the power factor. A switching control circuit 20 holds the switching element of the first inverter 2 in the on state when the 100 VAC system is used and the alternating-current input current is below a specified overcurrent protection value, and thus allow only the second inverter 5 to perform voltage increasing operation. If the 200 VAC system is used or the alternating-current input current is equal to or above the specified overcurrent protection value, the first inverter 2 is synchronized with the second inverter 5 to exercise switching control, thereby causing voltage increasing and decreasing operation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power factor improving circuit for controlling a switching of an AC input current waveform so as to be similar to an AC input voltage waveform to reduce harmonic distortion.

[0002]

2. Description of the Related Art In recent years, even in a switching regulator known as a power supply for a computer in accordance with the regulation of the total amount of power supply harmonic distortion of electronic equipment, a power factor improving circuit is provided in an input circuit stage of a commercial AC power supply to the switching regulator. Provided. Conventionally, this type of power factor correction circuit
For example, FIG. The power factor improving circuit of FIG. 2 comprises a main circuit including an input rectifier diode 1, a choke coil 4, and a boost inverter 50 using a boost chopper, and a power factor improving control circuit 14 is provided for the main circuit. The step-up inverter 50 includes a MOSFET 5a, a diode 6, and an output smoothing capacitor 7.

A power factor improving control circuit 14 inputs a detection voltage detected by an input current detection resistor 8 to an input terminal 9 for input current detection, and outputs an output voltage Eo to an input terminal 10 for output voltage detection.
, And the full-wave rectified waveform of the input rectifier diode bridge 1 is input to the input terminal 11 for input voltage waveform detection as the input voltage Ei. From the inverter signal output terminal 12 of the power factor improvement control circuit 14, a switching signal subjected to PWM control is output in accordance with the error voltage between the reference voltage and the output voltage, and the output voltage is controlled by on / off control of the boost inverter 5. The power factor is stabilized by controlling the switching of the input current waveform so that it is similar to the full-wave rectified waveform obtained by multiplying the output voltage and the input voltage, and bringing the input current waveform closer to the sine waveform in phase with the input voltage. It is improved to reduce harmonic distortion.

[0004]

[Problems to be solved by the invention] However, FIG.
In the conventional power factor correction circuit shown in FIG. First, since the boosting inverter 50 can only perform the boosting operation, for example, when an effective value of 264 volts AC is input, D
Even if an output voltage of 300 volts is required, the output voltage becomes 370 volts or more due to the boosting operation, and the expected 300 volts of DC cannot be obtained.

Second, in the step-up inverter 50, the duty of the switching control signal is zero, that is, the MOSF is activated when the overcurrent protection circuit built in the power factor correction control circuit 14 operates.
When ET5a is fixed in the off state, MOSFET5
The current flowing through a can be made zero, but the current to the load cannot be limited even if the MOSFET 5a is turned off. For this reason,
Even if an overcurrent condition occurs due to a load short circuit, etc.
In addition, it is not possible to limit the inrush current at the time of starting the power supply, and a dedicated circuit for limiting the inrush current is required.

In order to solve the problem of the power factor improving circuit shown in FIG. 2, a step-down inverter 20 is added in front of the boost inverter 50 as shown in FIG. A switching signal from the control circuit 12 is supplied to the MOSFET 2a via the drive circuit 19,
Step-down inverter 20 in synchronization with step-up inverter 50
A power factor improving circuit that realizes a buck-boost type inverter operation by controlling switching of a power factor has been considered.

According to this power factor improvement circuit, the input AC
By operating a 264 volt buck-boost inverter,
The required output voltage of DC 300 volts can be obtained. Further, when the overcurrent protection circuit built in the power factor correction control circuit 14 operates to reduce the duty of the switching control signal and finally reduce the duty to zero, the MOSFET 2a of the step-down inverter 20 is turned off. can do.

However, the MOSF of the step-down inverter 20
When the duty of the switching control signal is, for example, 50%, the current flowing through the ET 2a is twice the peak value of the current flowing through the MOSFET 5a of the boost inverter 50. For this reason, there is a problem that the ON loss of the inverter becomes large, and the choke coil 4 must be designed so as not to be saturated.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has been made to reduce loss when using an AC 100 volt system, arbitrarily set an output voltage when using an AC 200 volt system, and to provide a short-circuit current to a load and the like. An object of the present invention is to provide a power factor improvement circuit capable of appropriately protecting an overcurrent against an inrush current due to rapid charging of an output capacitor at the time of starting a power supply.

[0010]

In order to achieve this object, the present invention is configured as follows. The power factor correction circuit according to the present invention includes, as a main circuit, a full-wave rectifier circuit that inputs an AC signal and outputs a full-wave rectified signal, a first step-down inverter connected in series to an output of the full-wave rectifier circuit, and A booster-type second inverter connected in series to the output of the first inverter; The first inverter is constantly driven by switching control. That is, the power factor improvement control circuit controls the DC output voltage at a constant voltage and performs switching control of the first inverter so as to make the AC input current waveform similar to the AC input voltage waveform, thereby improving the power factor.

Further, a switching control circuit is provided. When the AC input voltage is within a predetermined low voltage range and the AC input current is less than a predetermined overcurrent protection value, the switching control circuit fixes the switching element of the first inverter to the ON state and sets the second inverter to the second state.
Only the boosting operation by the inverter is performed. Further, the switching control circuit raises and lowers by performing switching control of the first inverter in synchronization with the second inverter when the AC input voltage is within a predetermined high voltage range or the AC input current is equal to or higher than a predetermined overcurrent protection value. Pressure operation.

A switching control circuit for detecting an effective value of the AC input voltage, detecting that the effective value is within a predetermined high voltage range, and outputting a high voltage detection signal; An overcurrent detection circuit that outputs an overcurrent detection signal when the overcurrent setting value is exceeded, an OR circuit that takes the logical sum of the detection outputs of the input voltage detection circuit and the overcurrent detection circuit,
A voltage source that outputs a control voltage for fixing the switching element of the first inverter to the ON state, and a control voltage of the voltage source is selected when neither the high voltage detection signal nor the overcurrent detection signal can be obtained via the OR circuit. The switching element of the first inverter is controlled to be in an ON state, and when at least one of the high voltage detection signal and the overcurrent detection signal is obtained via the OR circuit, the signal is output from the power factor improvement control circuit. A switching circuit that selects a switching control signal and controls switching of the switching element of the first inverter;

Specifically, the switching control circuit fixes the switching element of the first inverter to the ON state when the AC input voltage is within a voltage range of a 100 volt system and the AC input current is less than a predetermined overcurrent protection value. The first inverter is synchronized with the second inverter only when the AC input voltage is within the range of 200 volts or the AC input current is equal to or higher than a predetermined overcurrent protection value. The switching control is performed to perform the step-up / step-down operation.

Here, the voltage range of the 100 volt system detected for the switching control of the switching control circuit is in the range of 85 volts to 135 volts in the effective value, and the voltage range of the 200 volt system is 170 volts in the effective value. It ranges from volts to 264 volts. As described above, according to the present invention, the AC input voltage is 100 VAC (for example, 85 VAC to 132 VAC).
Volts) and if the AC input current is less than the overcurrent set value, only the second inverter is driven to perform the boosting operation. At this time, since the step-down operation of the first inverter is stopped to function simply as a conduction switch, a large current does not flow through the first inverter by the synchronous drive with the second inverter of the boost type, and the ON loss of the inverter does not flow. And the choke coil 4 is not saturated, so that the size can be reduced.

If the AC input voltage is an AC 200 volt system (for example, AC 170 volts to 264 volts) or the AC input current is equal to or more than an overcurrent value, the first inverter and the second inverter are driven synchronously to perform a step-up / step-down operation. The output voltage can be arbitrarily set in a range from a voltage lower than the input voltage to a higher voltage by the step-up / step-down operation for the input AC voltage. In addition, by limiting the current flowing through the step-down type first inverter, an overcurrent protection operation for the load can be performed. In addition, a rapid charging current (rush current) to the output capacitor 7 at the time of starting the power supply can be limited by performing the overcurrent protection operation.

[0016]

FIG. 1 is a circuit block diagram of an embodiment of a power factor correction circuit according to the present invention. In FIG.
First, the main circuit connects an input rectifier diode bridge 1 for inputting an AC input and outputting a full-wave rectified signal, followed by a step-down first inverter 2, and further following the first inverter 2, a step-up second inverter 5. Are connected.

The first inverter 2 includes a MOSFET 2a, a flywheel diode 3, a choke coil 4 and a second
An elevating chopper is configured by synchronizing the MOSFET 5a of the inverter 5 with the MOSFET 2a and the MOSFET 5a.
A step-up / step-down operation that can be arbitrarily set from the step-down range in which the input / output voltage conversion rate is 1 or less to the step-up range in which the input / output voltage conversion rate is 1 or more is performed by the on / off control of a. The flywheel diode 3 of the first inverter 2 forms a path for flowing a current from the choke coil 4 to the load side when the MOSFET 2a is turned off.

The second inverter 5 includes a MOSFET 5a,
The choke coil 4, the diode 6, and the output smoothing capacitor 7 constitute a step-up inverter using a step-up chopper, and perform a step-up operation in which an input / output voltage conversion ratio becomes 1 or more. The diode 6 of the second inverter 5 is
When T5a is turned off, the diode becomes a diode that supplies a current to the load side by the energy stored in the choke coil 4.

A power factor improving control circuit 14 is provided for the first inverter 2 and the second inverter 5 provided in such a main circuit.
And a switching control circuit 20. The power factor correction type control circuit 14 has an input terminal 9 for input current detection, an input terminal 10 for output voltage detection, and an input terminal 11 for input voltage waveform detection, and an input current detection resistor provided on the second inverter 5 side. 8, the AC input current Ii, the output voltage Eo at the output side of the diode 6 of the second inverter 5, and the AC input voltage Ei which is a full-wave rectified signal of the input rectifier diode bridge 1 are input.

The power factor improving control circuit 14 outputs a switching signal subjected to PWM control from the inverter signal output terminal 12 in accordance with an error voltage ΔE between a reference voltage Er for determining a preset output voltage and an output voltage Eo. Then, the MOSFET 5a of the fixedly connected second inverter 5 is turned on / off by a switching signal to stabilize the output voltage.

At the same time, the power factor improving control circuit 14 performs switching control of the input current Ii so as to be similar to a full-wave rectified waveform obtained by multiplying the output voltage Eo and the input voltage Ei, and inputs the input current waveform. The power factor is improved by approaching a sine waveform in phase with the voltage waveform to reduce harmonic distortion. Further, the power factor improving control circuit 14 includes the overcurrent detection circuit 1
3a is built in. The overcurrent detection circuit 13a detects an overcurrent at the overcurrent detection output terminal 13 when the detected input current Ii to the input current detection input terminal 9 becomes equal to or greater than a preset overcurrent limit value. Signal E2
Is output.

The switching control circuit 20 includes an input voltage detecting circuit 1
5, OR circuit 16, voltage source 17, and switch circuit 1
8 are provided. The input voltage detection circuit 15 detects an effective value of the AC input by inputting an AC input signal Ei output as a full-wave rectified signal from the input current ion bridge 1, and the effective value is a predetermined low value for an AC 100 volt system. A voltage range of, for example, AC 85 volts to 132 volts, or a high voltage range of AC 200 volts, for example, AC1
It detects whether it is in the range of 70 volts to 264 volts.

In this embodiment, the input voltage detecting circuit 15 is set to 200 volts which becomes H level when the effective value of the AC input voltage is in a range of 170 VAC to 264 volts which is a high voltage range of 200 volts AC. A system voltage detection signal E3 is output. Therefore, when a voltage of 85 to 132 VAC, which is a constant voltage range of 100 VAC, is detected, the 200 volt voltage detection signal E3 is at the L level.

The overcurrent detection signal E2 from the overcurrent detection output terminal 13 of the overcurrent detection circuit 13a provided in the power factor improvement control circuit 14 and the 200 volt system voltage detection signal E3 from the input voltage detection circuit 15 are: The logical sum is input to the OR circuit 16 and calculated. Therefore, the OR circuit 16 outputs the H level signal when the overcurrent detection signal E2 is obtained from the power factor improvement control circuit 14 side or when the 200 volt system voltage detection signal E3 is obtained from the input voltage detection circuit 15. Is output to the changeover switch circuit 18.

The changeover switch circuit 18 has changeover terminals A and B. The changeover terminal A is connected to the inverter signal output terminal 12 of the power factor improvement control circuit 14 to input a switching signal. Is connected to a voltage source 17. The output of the changeover switch circuit 18 is
To the gate of the MOSFET 2 a of the first inverter 2.

The changeover switch circuit 20 is controlled by the output of the OR circuit 16. That is, the OR circuit 16 generates an H level output when the overcurrent detection signal E2 is at the H level or the 200 volt detection signal E3 is at the H level, and switches to the switching terminal A side of the switching circuit 18 as shown in FIG. The switching signal output from the inverter signal output terminal 12 of the power factor correction type control circuit 14 is transmitted to the drive circuit 1
9 to the gate of the MOSFET 2a of the first inverter.

Therefore, when the switching switch 20 is switched to the switching terminal A, the MOSFETs 2a and 5a of the first inverter 2 and the second inverter 5 are synchronized by the switching signal from the power factor improving control circuit 14. On / off control is performed, so that the step-down operation of the first inverter 2 and the second
The step-up operation of the inverter 5 is performed simultaneously. On the other hand, when the output of the OR circuit 16 becomes L level, the changeover switch circuit 18 switches to the changeover terminal B side, and supplies the DC voltage from the voltage source 17 to the MOSFET 2a of the first inverter 2 via the drive circuit 19, The MOSFET 2a is fixedly turned on. Therefore, the first inverter 2 stops the step-down operation, functions as a mere conduction switch, and only the second inverter 5 performs the step-up operation.

The switching state of the switching terminal B of the changeover switch circuit 18 at which the output of the OR circuit 16 becomes L level is detected by the input voltage detection circuit 15 when the input voltage detection circuit 15 detects AC voltage of 85 volts to 132 volts which is in a low voltage range of 100 VAC. And 200
This is when the volt-system voltage detection signal E3 is at the L level, and when the AC input current Ii is less than the overcurrent set value in the overcurrent detection circuit 13a provided in the power factor improvement control circuit 14.

Next, the operation of the embodiment shown in FIG. 1 will be described. First, it is assumed that the AC input is performed from an AC 200 volt system. An AC input voltage E1 that is input from the AC 200 volt system and is a full-wave rectifier of the input rectifier diode bridge 1
The input voltage detection circuit 15 detects the effective value of 264 volts, sets the 200 volt system voltage detection signal E3 to the H level, and switches the changeover switch circuit 18 to the changeover terminal A side via the OR circuit 16 as shown.

Therefore, the switching signal from the inverter signal output terminal 12 of the power factor improving control circuit 14 is fixedly supplied to the MOSFET 5a of the second inverter 5, and at the same time, through the changeover switch circuit 18 and the drive circuit 19. The power supply is also supplied to the MOSFET 2a of the first inverter 2, and the first inverter 2 and the second inverter 5 are turned on / off in synchronization with the switching signal E1 from the power factor improvement control circuit 14.

As a result, the first inverter 2 and the second inverter 5 perform a step-up / step-down operation with respect to 264 VAC to lower the output voltage as compared with the case where only the voltage is boosted. Output voltage D by setting
C300 volts can be obtained. Next, AC input is A
Assuming that the AC voltage is 100 volts, the input voltage detection circuit 15 outputs
5 to 132 volts input AC voltage is detected and 20
The 0 volt system voltage detection signal E3 is set to L level. At this time, assuming that the overcurrent detection circuit 13a provided in the power factor correction control circuit 14 has not performed overcurrent detection, the overcurrent detection signal E2 is also at the L level.

Therefore, the output of the OR circuit 16 becomes L level, the switch circuit 18 is switched to the switch terminal B side, and the DC voltage of the voltage source 17 is supplied to the MOSFET 2a of the first inverter 2 via the drive circuit 19. , MO
The SFET 2a is fixed in the ON state. First inverter 2
Stops the step-down operation and functions as a mere conduction switch, and only the second inverter 5 performs the step-up operation. Therefore, the input of the AC 100 volt system is boosted by the second inverter 5, and a boosted output of DC 300 volt determined according to the reference voltage of the power factor improvement control circuit 14 can be obtained.

Next, the overcurrent protection operation will be described. AC20
In the operation state by the input of the 0 volt system, the first inverter 2 and the second inverter 5 are controlled to be turned on / off synchronously. In the detection circuit 13a, the AC input current I
When i exceeds the overcurrent limit value, the overcurrent detection signal E2 is changed from the L level to the H level.

However, since the output of the OR circuit 16 is at the H level upon the detection of the AC 200 volt system and has been switched to the switching terminal A, no switching operation is performed. On the other hand, with the detection of the overcurrent by the overcurrent detection circuit 13a, the duty of the switching signal from the inverter signal output terminal 12 of the power factor improvement control circuit 14 is reduced for overcurrent control and finally becomes zero, Therefore, the first
The MOSFET 2a of the inverter 2 limits the current flowing to the load. At the same time, the MOSFET 5a of the second inverter 5
Also limit the current flowing through the

On the other hand, in the operation state when the AC input is a 100 volt system, the output of the OR circuit 16 becomes L level and switches to the switching terminal B side of the changeover switch circuit 18, and MO of the first inverter 2 by voltage
The SFET 2a is fixedly turned on, and only the second inverter 5 performs the boosting operation. In this state, when the current flowing to the load increases and exceeds the overcurrent protection value in the overcurrent detection circuit 13a, the overcurrent detection signal E2 becomes H level and is supplied to the changeover switch circuit 18 via the OR circuit 16. To switch to the switching terminal A side. Power factor improving control circuit 14
The switching signal E1 from the switching switch circuit 18,
MOSF of the first inverter 2 via the drive circuit 19
The first inverter 2 and the second inverter 5 are supplied to the ET 2a, and are turned on and off in synchronization with the detection of the overcurrent. The overcurrent protection operation is performed by reducing the on-duty of the switching control signal E1.

Further, even when a rapid charging current (rush current) flows into the output smoothing capacitor 7 at the time of starting the power supply,
Similarly, overcurrent protection operation can be performed to limit. In the above embodiment, the first inverter 2
And MOS as a switching element of the second inverter 5
Although the MOSFETs 2a and 5a are used, a switching element such as a bipolar transistor or an IGBT may be used as another embodiment.

The input current is detected by the input current detecting resistor 8.
However, an appropriate current detecting element such as a current transformer or a Hall element can be used. Further, the changeover switch circuit 18 can be realized by an arbitrary changeover switch element such as a semiconductor switch or a relay. Further, the above embodiment is
Although a 100 volt system and a 200 volt system are taken as examples of the AC input, a form corresponding to an arbitrary AC system can be adopted as necessary.

[0038]

As described above, according to the present invention, if the AC input is, for example, an AC 100 volt system and the AC input current is less than the overcurrent set value, only the boost type second inverter is driven. The step-up operation is performed, and at this time, the operation of the step-down type first inverter is stopped to function simply as a conduction switch, and the large current of the step-down type first inverter is synchronized with the step-up type second inverter. Does not flow, lowers the on-loss of the first inverter,
Also, the choke coil can be made compact because it does not saturate.

When the AC input is, for example, an AC 200 volt system or the AC input current is equal to or higher than the overcurrent set value, the step-down type first inverter and the step-up type second inverter are synchronously driven to switch to step-up / step-down operation. The main DC voltage with respect to the input AC voltage can be arbitrarily set in a range from a voltage lower than the input voltage to a higher voltage. Further, since the current flowing through the step-down first inverter can be limited, an overcurrent protection operation for the load can be reliably performed. In addition, a rapid charging current (rush current) to the output smoothing capacitor at the time of starting the power supply can be limited by performing the overcurrent protection operation.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram showing an embodiment of the present invention.

FIG. 2 is a circuit block diagram of a conventional circuit using a boost inverter.

FIG. 3 is a circuit block diagram of a conventional circuit using a buck-boost inverter.

[Explanation of symbols]

 1: input rectifier diode bridge (full-wave rectifier circuit) 2: first inverter (step-down type) 2a, 5a: MOSFET 3: flywheel diode 4: choke coil 5: second inverter (step-up type) 6: diode 7: output Smoothing capacitor 8: Input current detection resistor 9: Input current detection input terminal 10: Output voltage detection input terminal 11: Input voltage waveform detection input terminal 12: Inverter signal output terminal 13: Overcurrent detection output terminal 14: Force Ratio improvement control circuit 15: Input voltage detection circuit 16: OR circuit 17: Voltage source 18: Changeover switch (switching circuit) 19: Drive circuit 20: Switching control circuit

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI H02J 3/18 H02J 3/18 D H02M 1/12 H02M 1/12 7/217 7/217

Claims (4)

[Claims] 1. A full-wave rectifier circuit for inputting an AC signal and outputting a full-wave rectified signal, and a first step-down rectifier connected in series to an output of the full-wave rectifier circuit.
An inverter; a step-up type second inverter connected in series to an output of the first inverter; and a first inverter that controls a DC output voltage at a constant voltage and makes an AC input current waveform similar to an AC input voltage waveform. A power factor improving control circuit for improving a power factor by performing switching control; and when the AC input voltage is within a predetermined low voltage range and the AC input current is less than a predetermined overcurrent protection value, the first
When the switching element of the inverter is fixed to the ON state and only the boosting operation by the second inverter is performed, and the AC input voltage is within a predetermined high voltage range or the AC input current is equal to or higher than a predetermined overcurrent protection value. And a switching control circuit for performing a step-up / step-down operation by performing switching control of the first inverter in synchronization with the second inverter. 2. The power factor improving circuit according to claim 1, wherein the switching control circuit detects an effective value of the AC input voltage and detects that the effective value is within a predetermined high voltage range. An input voltage detection circuit that outputs a high voltage detection signal to the input voltage detection circuit; an overcurrent detection circuit that outputs an overcurrent detection signal when the AC input current exceeds a predetermined overcurrent set value; An OR circuit for extracting a logical sum of detection outputs of the current detection circuit, a voltage source for outputting a control voltage for fixing a switching element of the first inverter to an ON state, and the high voltage detection signal and the When none of the current detection signals is obtained, the control voltage of the voltage source is selected to control the switching element of the first inverter to an on state, and the high voltage detection signal or overcurrent detection is performed via the OR circuit. A switching circuit that selects a switching control signal output from the power factor correction control circuit when at least one of the signals is obtained, and controls switching of a switching element of the first inverter. Characteristic power factor correction circuit. 3. The power factor improving circuit according to claim 1, wherein the switching control circuit is configured such that the AC input voltage is within a voltage range of a 100 volt system and the AC input current is less than a predetermined overcurrent protection value. At this time, the switching element of the first inverter is fixed to the ON state, and only the boosting operation by the second inverter is performed, and the AC input voltage is within a range of 200 volts or the AC input current is a predetermined value. A power factor improving circuit for performing a step-up / step-down operation by performing switching control of the first inverter in synchronization with a second inverter when an overcurrent protection value is exceeded. 4. The power factor improving circuit according to claim 3, wherein the 100 volt system voltage range is an effective value in a range of 85 volts to 135 volts, and the 200 volt system voltage range is an effective value. A power factor improving circuit having a value in a range from 170 volts to 264 volts.