JPH088772B2 - Power factor correction circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a full-wave rectifier circuit connected between AC power supply terminals and a backflow prevention diode between output terminals of the full-wave rectifier circuit. Smoothing capacitor (the capacitor input type rectifying circuit is configured by the above), a reactor serially connected to the input side or the output side of the full-wave rectifying circuit, and a parallel connection between the output terminals of the full-wave rectifying circuit. By switching the switching element by the sine wave approximation control signal,
The present invention relates to a power factor correction circuit configured to maintain a high power factor by utilizing the energy storage effect of a reactor.

<Prior Art> In recent years, with the development of large-capacity semiconductor elements, inverters that perform variable-speed operation of AC motors are rapidly becoming popular.
A capacitor input type rectifier circuit is generally used as a DC power source for the inverter.

The capacitor input type rectifier circuit has a high fundamental wave power factor, but since the input current is an inrush current having a high harmonic content rate, the waveform distortion is large and the total power factor is low. In addition, there is a disadvantage that the power system is seriously damaged because of the generation of fault power to the surroundings due to harmonics.

For this reason, by adding a reactor and a switching element to the capacitor input type rectifier circuit, a technique has been proposed that improves the input current waveform to a sinusoidal waveform with a small distortion factor and also improves the total power factor. (For example, “Journal of the Institute of Electrical Engineers of Japan, Volume B 104, No. 2” (Showa 59, 2
Mon.) pp. 33-40, "Improving the input current waveform of a rectified power source with a bidirectional switch" Author: Ichiro Sasaki, Yoshifumi Amamiya-).

This document is for the case where the power supply is a three-phase AC power supply, but the contents disclosed in this document are considered as follows when applied to a single-phase AC power supply.

As shown in FIG. 5, the voltage of the AC power supply 31 is full-wave rectified by the full-wave rectification circuit 32 composed of a diode bridge, and the rectified voltage is smoothed by the smoothing capacitor 33 to obtain a DC voltage and supplied to the load 34. . On the other hand, while inserting the reactor 35 in series in the front stage of the full-wave rectifier circuit 32 and inserting the switching element 36 in parallel in the next stage of the full-wave rectifier circuit 32,
By appropriately controlling the on / off time of the switching element 36 by the M signal S ₁ , the waveform of the input current i ₀ flowing through the reactor 35 is improved into a sinusoidal shape to improve the power factor.
Reference numeral 37 is a backflow prevention diode.

FIG. 6 shows an equivalent circuit of the circuit of FIG. AC source
The power supply voltage from 31 is v ₀ , the voltage across switching element 36 is v ₁ , the inductance of reactor 35 is L, and the input current is
i ₀ .

Switching element 36 for power supply voltage v ₀ = V ₀ sin ωt
Let φ be the phase difference of the voltage v ₁ between both ends of V and δ be the phase difference of the input current i ₀ , then v ₁ = V ₁ sin (ωt−φ) i ₀ = I ₀ sin (ωt−δ) Then, it becomes as shown in FIG. FIG. 7B is a vector diagram when the phase difference φ between the power supply voltage ₀ and the voltage ₁ across the switching element 36 is constant and the magnitude of ₁ is increased as compared with the case of FIG. 7A. . From the relationship of the voltage across j.omega.L ₀ of the reactor 35 is always perpendicular to the input current _{0, 1}
Power supply voltage by increasing the size of (φ is constant)
A phase difference δ of the input current ₀ for ₀ can be reduced.

To increase the size of the voltage across the _first switching element 36 may be shortened ON time of the switching element 36 based on the sine wave approximation PWM signal S _1, thereby, the power supply voltage the phase of the input current _{0 The} fundamental wave power factor can be improved by approaching the phase of ₀ (δ → 0).

<Problems to be Solved by the Invention> However, the conventional example having such a configuration has the following problems.

When the ON time of the switching element 36 is shortened in order to increase the magnitude of the voltage ₁ across the switching element 36,
The stored energy in the reactor 35 decreases, and the DC voltage V _DC across the smoothing capacitor 33 decreases. However, since the magnitude of the voltage ₁ across the switching element 36 depends on the DC voltage V _DC , in the end, the switching element 3
The magnitude of voltage ₁ across 6 cannot be increased.

As indicated by the fourth (B) broken line, the switching element 36
Of the switching element 9 while maintaining a constant phase difference φ between the voltage v ₁ between the two ends and the power supply voltage v ₀ of the AC power supply 31.
v when controlling only the magnitude V ₁ of the _1, the characteristics of the power factor with respect to the change of the input current value I ₀ is as shown by the dashed line in Figure No. 4 (A), not in the very good characteristics.

Further, it is not preferable that the DC voltage V _DC , which should be originally constant, be lowered, and the controllability is also poor in this respect as well.

The present invention has been made in view of such circumstances, and an object thereof is to effectively utilize the energy storage effect of a reactor to improve the degree of improvement in power factor and controllability.

<Means for Solving Problems> The present invention has the following configuration in order to achieve such an object.

That is, the power factor correction circuit of the present invention comprises a full-wave rectification circuit (4) connected between AC power supply terminals (2a, 2b) and a backflow prevention diode between the output terminals of this full-wave rectification circuit (4). A smoothing capacitor (6) connected via (5), a reactor (3) serially connected to the input side or output side of the full-wave rectifier circuit (4), and the full-wave rectifier circuit (4). A power factor correction circuit comprising a switching element (9) connected in parallel between output terminals, the input current detection circuit (11) detecting an input current (i ₀ ) to the full-wave rectification circuit (4). A zero cross detection means (13) for detecting a zero voltage phase of the AC power supply voltage (v ₀ ), and the switching element (9) based on the input current value (I ₀ ) detected by the input current detection circuit (11). voltage across (v ₁₎ of) the phase difference with respect to the AC power supply voltage (v ₀₎ φ)
And a reference sine wave that creates a reference sine wave (v _K ) with reference to the zero voltage phase by the zero cross detection means (13) based on the calculated phase difference (φ) A sine wave approximation control signal (S ₁ ) for approximating the waveform of the voltage (v ₁ ) across the switching element (9) to a sine wave based on the reference sine wave (v _K ). A sine wave approximate control wave forming means (16) for giving to the switching element (9).

<Operation> The operation of the configuration of the present invention is as follows.

That is, the phase difference calculating means (14) calculates the phase difference (φ) of the voltage across the switching element (9) (v ₁ ) with respect to the AC power supply voltage (v ₀ ) based on the input current value (I ₀ ), The reference sine wave creation means (15) creates a reference sine wave (v _K ) by delaying the phase difference (φ) from the zero cross timing of the AC power supply voltage (v ₀ ) and creates the approximate sine wave control waveform creation means (16). Is a sine wave approximation control signal (S ₁ ) based on the reference sine wave (v _K ).
Is generated and output to the switching element (9).

When the switching element (9) is controlled in this manner, the voltage (v ₁ ) across the switching element (9) and thus the input current (i ₀ ) becomes sinusoidal, and the input current (i ₀ ) for the AC power supply voltage (v ₀ ) changes. The phase difference (δ) of ₀ ) approaches zero.

In order to bring the phase difference (δ) close to zero, the phase (φ) of the reference sine wave (v _K ) is changed.
The duty ratio of the sine wave approximation control signal (S ₁ ) is kept constant and the ON time of the switching element (9) is stabilized, and the energy storage effect of the reactor (3) does not change.
As a result, the DC voltage (V
_DC ) will be held constant.

<Example> Hereinafter, an example of the present invention is described in detail based on a field.

 FIG. 1 is a circuit diagram of a power factor correction circuit according to an embodiment.

A full-wave rectifier circuit 4 composed of a diode bridge is connected between AC power supply terminals 2a and 2b connecting the AC power supply 1 via a reactor 3 such as a choke coil. A smoothing capacitor 6 is connected between the output terminals of the full-wave rectifier circuit 4 via a diode 5 for preventing backflow, and a load 8 is connected between the output terminals 7a and 7b of the smoothing capacitor 6. The load 8 may be a switching regulator as well as an inverter circuit in an inverter-driven air conditioner. A switching element 9 such as a power transistor or a power MOS • FET is connected in parallel between the output terminals of the full-wave rectifier circuit 4.

Further, a current transformer CT provided on a power supply line connecting the AC power supply 1 and the full-wave rectification circuit 4 is connected to the IV conversion circuit 10 to detect an input current i ₀ to the full-wave rectification circuit 4. It constitutes a current detection circuit 11. IV conversion circuit 10
Is for converting the average value I ₀ of the AC input current i ₀ picked up by the current transformer CT into a DC voltage V _P , and is composed of a diode bridge DB ₁ , a resistor R ₁ and a capacitor C ₁ .

Reference numeral 12 is a power supply voltage waveform detection circuit for detecting the waveform of the power supply voltage v ₀ of the AC power supply 1, which is composed of a step-down transformer T ₁ connected between the AC power supply terminals 2a and 2b, a diode bridge DB ₂ and a resistor R _2. ing.

Reference numeral 13 is a zero-crossing detecting means for detecting the zero voltage phase of the power supply voltage v ₀ by the power supply voltage waveform detection circuit 12.

14 is based on the DC voltage V _P from the IV conversion circuit 10,
It is a phase difference calculation means for calculating the phase difference φ between the voltage v ₁ across the switching element 9 and the power supply voltage v ₀ of the AC power supply 1. The phase difference φ can be represented by φ = g (V _P ) = h (I ₀ ) ..., Where the function symbols are g and h.

15 based on the phase difference phi between the modulation degree H (constant), based on the zero-voltage phase based on a zero-cross detecting means 13, a reference sine wave v _K, the _{formula, v K = H sin (θ} -φ) ...... It is a standard sine wave creating means created according to.

In the equation, θ is the phase of the power supply voltage v ₀ of the AC power supply 1, and when the power supply frequency is F, θ = 2πFt.

From the equation, v _K = H sin (θ−h (I ₀ )) ………….

The modulation factor H is the required DC voltage V _DC to be supplied to the load 8.
Is set to a predetermined constant value in order to make constant. Therefore, the reference sine wave v _K is eventually created based on the detected input current value I ₀ .

Reference numeral 16 is a sine wave approximate PWM waveform creating means for creating the sine wave approximate PWM signal S ₁ for controlling the switching element 9 on / off based on the reference sine wave v _K. In the sine wave approximate PWM signal S ₁ , the voltage v ₁ across the switching element 9 is the input current i ₀
Is a signal for switching the switching element 9 so that the voltage of the waveform becomes close to a sine wave.

The above-mentioned zero-cross detecting means 13, phase difference calculating means 14, reference sine wave creating means 15 and sine wave approximate PWM waveform creating means 1
6 is realized by software processing by the CPU 17 of the microcomputer.

Next, the operation principle will be described. For convenience of explanation, the input current is represented by i ₀ (θ).

Since the phase of the fundamental wave of the voltage v ₁ across the switching element 9 is delayed by φ with respect to the power supply voltage v ₀ , Becomes The voltage equation at this time is Can be expressed as When the input current i ₀ (θ) is calculated by integrating both sides of the equation, Is obtained. However, Is. If the phase difference of the input current i ₀ (θ) with respect to the electrode voltage v ₀ is δ, Is. When the input current i ₀ (θ) and the power supply voltage v ₀ are in phase, that is, when δ = 0, from the equation, V ₀ −V ₁ cos φ = 0. Further, the magnitude I ₀ of the input current i ₀ (θ) at this time
Substitutes the expression into the expression, Becomes From the formula, cosφ = V ₀ / V ₁ ………… From the formula, sinφ ＝ ωL.I ₀ / V ₁ ………… () Therefore, tanφ = ωL · I ₀ / V ₀ ………… Therefore, for any input current i ₀ (θ),
Voltage across the switching element 9 for making the phase of the input current i ₀ (θ) and the phase of the power supply voltage v ₀ in phase (δ = 0)
The condition for the phase difference φ of v ₁ is Is.

That is, the switching element 9 so that the condition of the equation is satisfied.
By controlling the phase difference φ of the voltage v ₁ across
It is possible to make it in phase with the power supply voltage v ₀ of ₀ (θ).
If ωL, V ₀ is known, the phase difference φ of the voltage v ₁ across the switching element 9 with respect to the power supply voltage v ₀ can be known by detecting the magnitude I ₀ of the input current i ₀ (θ).

The phase difference φ of the voltage v ₁ across the switching element 9 is controlled as described above by approximating the switching element 9 by a sine wave.
The CPU 17 performs on / off control based on the PWM signal S ₁ .

Now, the input current picked up by the current transformer CT
The magnitude I ₀ of i ₀ (θ) is converted into the DC voltage V _P by the IV conversion circuit 10 and then read into the CPU 17. Further, the zero-cross detection means 13 detects the zero voltage phase of the power supply voltage v ₀ of the AC power supply 1 and outputs it to the CPU 17.

The CPU 17 determines the magnitude V ₀ of the power supply voltage v ₀ , the reactance ωL of the reactor 3, and the read input current value I ₀ (that is,
V _P ) and the phase difference φ is calculated based on the equation.

The voltage v ₁ across the switching element 9 is the power supply voltage.
The sine wave approximate PWM signal S ₁ whose on / off duty is determined based on the reference sine wave v _K is applied to the switching element 9 so that the waveform has a phase difference φ delayed from v _{0 with} respect to v ₀ . Output to.

When the switching element 9 is switched in this way, the input current i ₀ (θ) is eventually calculated from the equation Therefore, the input current i ₀ (θ) can be approximated to a sine wave, and the phase difference δ between the input current i ₀ and the power supply voltage v ₀ of the AC power supply 1 is set to zero to set the fundamental wave power factor. It can be 1.

On the other hand, since the harmonic component becomes reactive power, it is desirable to make it as small as possible. Therefore, by increasing the switching frequency for the switching element 9 and performing high-speed switching, the reactive power due to the harmonic component is reduced. suppress.

Through the above synergies, the overall power factor is improved as a whole.

An example of the approximate sine wave PWM signal S ₁ output from the CPU 17 and switching the switching element 9 is shown in FIG.

The phase of the reference sine wave v _K = H sin (θ−φ) lags the power supply voltage v ₀ by φ. The sine wave approximation PWM signal S ₁ created based on this reference sine wave v _K is a rectangular wave. The voltage across switching element 9 when switching element 9 is switched by this sine wave approximate PWM signal S ₁ .
v ₁ is a rectified waveform whose phase is delayed by φ with respect to the power supply voltage v ₀ .

By the way, the modulation degree H increases as the OFF duty of the sine wave approximation PWM signal S ₁ increases, and the modulation degree H decreases as the OFF duty decreases. Thus the sinusoidal approximation
Since the OFF duty of the PWM signal S ₁ and the modulation degree H have a one-to-one relationship, the modulation degree H, that is, the magnitude V ₁ of the voltage v ₁ across the switching element 9 can be controlled by adjusting the OFF duty. . Thus, the modulation degree H (that is, the voltage v ₁
The phase difference δ between the input current i ₀ and the power supply voltage v ₀ of the AC power supply 1 is set to _zero by controlling the magnitude v ₁ ) of
This is the case of the conventional example already described.

However, in this embodiment, the modulation degree H is fixed and the voltage v ₁ across the switching element 9 and the power supply voltage v _{0 of the} AC power supply 1 are fixed.
Phase difference between the phase difference by controlling in accordance with the input current value I ₀ and phi, the input current i ₀ and the power supply voltage v ₀ of the AC power supply 1 and δ
Is set to zero.

The phase difference calculating means 14 by the CPU 17 calculates the phase difference φ between the voltage v ₁ across the switching element 9 and the power source voltage v ₀ of the AC power source 1 based on the read input current value I ₀ , and the reference sine wave creating means Reference numeral 15 denotes a reference sine wave v _K = H sin (θ −, which is delayed by a phase difference φ from the timing at which the zero-cross detection means 13 detects the zero-cross phase of the power supply voltage V ₀ of the AC power supply 1.
φ), and the sine wave approximation PWM waveform forming means 16 creates a sine wave approximation PWM signal S ₁ based on the reference sine wave v _K and the carrier wave (triangular wave), and the sine wave approximation PWM signal S ₁ The switching element 9 is switching-controlled based on

By controlling in this way, the input current i ₀ can be made sinusoidal, and the input current i ₀ and the power supply voltage of the AC power supply 1 can be changed.
The phase difference δ with v ₀ can be brought close to zero to bring the fundamental wave power factor close to 1.

As described above, by controlling the phase difference φ according to the average value I ₀ of the input current i ₀ , while creating the reference sine wave v _K that is the basis for creating the approximate sine wave PWM signal S ₁ , Modulation degree H
Since it is kept constant, the fluctuation of the DC voltage V _DC output from the smoothing capacitor 6 can be suppressed. This point will be described based on the vector diagram shown in FIG.

And the magnitude V ₁ of the voltage across the _first switching element 9 constant supply voltage ₀ and the voltage across the switching element 9
_When the phase difference φ with respect to ₁ is decreased (Fig. (A) → Fig. (B)), the voltage jωL ₀ across the reactor 3 is always orthogonal to the input current ₀ , and therefore the power supply voltage
A phase difference δ of the input current ₀ for ₀ can be reduced. Then, so that this phase difference δ becomes zero,
Since the reference sine wave v _K = H sin (θ−φ) is created and the phase φ of the voltage ₁ across the switching element 9 is controlled, the input current ₀ can be brought closer to the same phase with respect to the power supply voltage ₀ . The wave power factor can be improved.

In this case, the magnitude of the voltage v ₁ across the switching element 9 is held constant only by changing the phase φ of the reference sine wave v _K , so the duty ratio of the off period in the sine wave approximation PWM signal S ₁ is constant. Held by the switching element 9
Since the on time of is invariable, the energy storage effect by the reactor 3 remains unchanged. As a result, the DC voltage V _DC across the calming capacitor 6 is kept constant, and the controllability is also good.

Fourth, as shown by the solid line in Figure (B), while maintaining the magnitude V ₁ of the voltage across v ₁ of the switching device 9 at a constant voltage across v ₁ and the AC power supply 1 of the power supply voltage of the switching element 9
When only the phase difference φ with v ₀ is controlled, the power factor characteristics with respect to changes in the input current value I ₀ are improved as compared with the case of the conventional example (broken line), as shown by the solid line in FIG. 4 (A). ing.

Although the reactor 3 is inserted in the preceding stage of the full-wave rectifier circuit 4 in the above embodiment, the reactor 3 is replaced with the full-wave rectifier circuit 4.
It may be inserted between the output terminal of and the anode of the diode 5.

<Effects of the Invention> According to the present invention, the following effects are exhibited.

In order to bring the phase difference (δ) of the input current (i ₀ ) with respect to the AC power supply voltage (v ₀ ) close to zero, in order to control the phase (φ) of the reference sine wave (v _K ), the sine wave approximation control signal ( The on-time of the switching element (9) can be stabilized by keeping the duty ratio of S ₁ ) constant.

That is, while effectively utilizing the energy storage effect of the reactor (3), the waveform of the input current (i ₀ ) can be improved to a sine wave shape, and the phase difference of the input current (i ₀ ) with respect to the AC power supply voltage (v ₀ ) ( The power factor can be improved by making δ) close to zero.

[Brief description of drawings]

1 to 4 relate to an embodiment of the present invention. FIG. 1 is a circuit diagram of a power factor correction circuit, FIG. 2 is a waveform diagram for explaining the operation, FIG. 3 is a vector diagram, and FIG. It is a characteristic diagram. Fifth
FIGS. 1 to 7 relate to a conventional example, FIG. 5 is a circuit diagram of a power factor correction circuit, FIG. 6 is an equivalent circuit diagram of FIG. 5, and FIG. 7 is a vector diagram. 1 ... AC power supply 2a, 2b ... AC power supply terminal 3 ... Reactor 4 ... Full wave rectification circuit 5 ... Reverse current prevention diode 6 ... Smoothing capacitor 9 ... Switching element 11 ... Input current detection circuit 13 ... … Zero cross detecting means 14 …… Phase difference calculating means 15 …… Reference sine wave creating means 16 …… Sine wave approximate control waveform creating means v ₀ …… AC power supply voltage i ₀ …… Input current I ₀ …… Input current value v ₁ ...... Voltage across switching element φ …… Phase difference of v ₁ with respect to v ₀ v _K …… Reference sine wave S ₁ …… Approximate sine wave PWM signal

Claims (1)

[Claims] 1. A full-wave rectifier circuit (4) connected between AC power supply terminals (2a, 2b) and a backflow prevention diode (5) between the output terminals of this full-wave rectifier circuit (4). The connected smoothing capacitor (6) and the reactor (3) serially connected to the input side or the output side of the full-wave rectification circuit (4).
And a switching element (9) connected in parallel between the output terminals of the full-wave rectification circuit (4), the input current (i ₀ ), An input current detection circuit (11), a zero cross detection means (13) for detecting the zero voltage phase of the AC power supply voltage (V ₀ ), and an input current value (1) detected by the input current detection circuit (1). Based on I ₀ ), the phase difference (φ) of the voltage (v ₁ ) across the switching element (9) with respect to the AC power supply voltage (v ₀ ).
And a reference sine wave that creates a reference sine wave (v _K ) with reference to the zero voltage phase by the zero cross detection means (13) based on the calculated phase difference (φ) A sine wave approximation control signal (S ₁ ) for approximating the waveform of the voltage (v ₁ ) across the switching element (9) to a sine wave based on the reference sine wave (v _K ). A power factor correction circuit comprising: a sine wave approximate control waveform creating means (16) for giving to the switching element (9).