JPS63220767A - Power factor improving circuit - Google Patents

Abstract

PURPOSE:To stabilize the ON-time of a switching element, by controlling the phase of reference sine wave so that the phase difference of input current against AC power voltage may be made approximate to zero. CONSTITUTION:To an AC power source 1, a full-wave rectification circuit 4 consisting of a diode bridge is connected via a reactor 3, and to a space between the output terminals, a load 8 is connected via a smoothing capacitor 6 and the like. This power factor improving circuit is provided with an input current detecting circuit 11, the voltage waveform detecting circuit 12 of the AC power source 1, and a CPU 17, and the CPU 17 is composed of a zero-cross detecting means 13, a phase difference arithmetic means 14, a reference sine wave producing means 15, and a sine wave approximating PWM waveform producing means 16. Then, from an input current value I0, a phase difference phibetween both end voltage v1 and AC power voltage v0 of a switching element 9 is computed, and reference sine wave vk is delayed by the phase difference phi. from the reference sine wave vk, control signal S1 is produced, and the output is directed to the switching element 9, and both end voltage for the smoothing capacitor 6 is kept constant.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention provides a full-wave rectifier circuit connected between AC power supply terminals and a backflow prevention diode connected between the output terminals of this full-wave rectifier circuit. (a capacitor input type rectifier circuit is constructed with the above), a reactor connected in series to the input side or output side of the full-wave rectifier circuit, and the output terminal of the full-wave rectifier circuit in parallel. The present invention relates to a power factor correction circuit that is configured to maintain a high power factor by utilizing the energy storage effect of a reactor by switching the switching element using a sinusoidal approximation control signal and having a switching element connected thereto.

<Conventional technology> In recent years, with the development of large-capacity semiconductor devices, inverters that operate AC motors at variable speeds are rapidly becoming popular, but capacitor input rectifier circuits are generally used as DC power supplies for inverters. ing.

Capacitor input rectifier circuits have a high fundamental wave power factor, but because the input current is an inrush current with a high harmonic content, the waveform distortion is large, the overall power factor is low, and harmonics can cause damage to the surrounding area. In order to generate electric power, it also has the disadvantage of causing serious disturbances to the electric power system.

For this reason, a technology has been proposed that improves the input current waveform to a sine wave with low distortion and improves the overall power factor by adding a reactor and a switching element to a capacitor input rectifier circuit. There is (
For example, see IEEJ Transactions B t041, No. 2) (February 1980), pp. 33-40, "Method for Improving Rectified Power Supply Input Current Waveforms Using Bidirectional Switches" (authors: Kazuki Sasaki, Yoshifumi Amemiya □).

This document is for a three-phase AC power source, but if the contents disclosed in this document are applied to a single-layer AC power source, the following results will be obtained.

As shown in FIG. 5, the voltage of an AC power supply 31 is full-wave rectified by a full-wave rectifier circuit 32 consisting of a diode bridge, and the rectified voltage is smoothed by a smoothing capacitor 33 to obtain a DC voltage, which is supplied to a load 34. . On the other hand, a reactor 35 is inserted in series at the front stage of the full-wave rectifier circuit 32, and a switching element 36 is inserted in parallel at the next stage of the full-wave rectifier circuit 32, and the switching element 36 is turned on by a sine wave approximation PWM signal S. - By appropriately controlling the off time, the input current flowing through the reactor 35 can be reduced to 1. The power factor is improved by improving the waveform to a sine wave. Note that 37 is a diode for preventing backflow.

FIG. 6 shows an equivalent circuit of the circuit in FIG.
It is assumed that the power supply voltage by 31 is V61, the voltage across the switching element 36 is VI, the inductance of the reactor 35 is 10, and the input current is 10.

The phase difference between the voltage V across the switching element 36 and the power supply voltage v, = V@sinω[ is φ, the input current i,
Letting the phase difference of (B) is the power supply voltage of 9° and the voltage across the switching element 36! FIG. 7 is a vector diagram when the magnitude of <Il is increased compared to the case of FIG. From the relationship that the voltage jωL1° across the reactor 35 is always orthogonal to the input current 10,! By increasing the magnitude of (φ is constant), the power supply voltage t.

It is possible to reduce the phase difference δ of the input current to with respect to the input current to.

Voltage across switching element 36! In order to increase the magnitude of , it is sufficient to shorten the on time of the switching element 36 based on the sine wave approximation PWM signal S1, thereby changing the phase of the input current 10 to the power supply voltage ! . (δ→0), the fundamental wave power factor can be improved.

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

Voltage across the switching element 369. In order to increase the size of the switching element 36, the ON time of the switching element 36 is shortened. Voltage V+
Since the magnitude of V+ depends on the DC voltage VDC, the magnitude of the voltage V+ across the switching element 36 cannot be increased.

As shown by the broken line in FIG. 4(B), the switching element 3
When only the magnitude (■) of the voltage v1 across the switching element 9 is controlled while the phase difference φ between the voltage V across the switching element 9 and the power supply voltage v0 of the AC power source 31 is held constant, the input current value 1. As shown by the broken line in FIG. 4(A), the characteristics of the power factor with respect to changes in are not very good.

Furthermore, it is not at all preferable that the DC voltage Vile, which should originally be constant, decreases, and from this point of view as well, controllability becomes poor.

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

<Means for Solving the Problems> In order to achieve the above object, the present invention has the following configuration.

That is, the power factor correction circuit of the present invention includes a full-wave rectifier circuit (4) connected between the AC power supply terminals (2a, 2b) and a backflow prevention circuit between the output terminal of this full-wave rectifier circuit (4). a smoothing capacitor (6) connected via a diode (5), and a reactor (3) connected in series to the input side or output side of the full-wave rectifier circuit (4);
A power factor correction circuit comprising a switching element (9) connected in parallel between the output terminals of the full-wave rectifier circuit (4), the input current (1°) to the full-wave rectifier circuit (4)
an input current detection circuit (II) that detects the zero voltage phase of the AC power supply voltage (v0), a zero cross detection means (13) that detects the zero voltage phase of the AC power supply voltage (v0), and an input current value (
10), the phase difference (
a phase difference calculation means (14) for calculating the phase difference (φ); and a reference sine wave (vx '') based on the zero voltage phase detected by the zero cross detection means (]3) based on the calculated phase difference (φ). Reference sine wave creation means (15)
A sine wave approximation control signal (Sl) that approximates the waveform of the voltage (vl) across the switching element (9) to a sine wave is created based on the reference sine wave (VK) and applied to the switching element (9). Near the given sine wave (hereinafter referred to as control waveform creation means)
16) It is equipped with the following.

Effect〉 The effects of the configuration of the present invention are as follows.

That is, the phase difference calculation means (14) calculates the phase difference (φ) of the voltage (vl) across the switching element (9) with respect to the AC power supply voltage (v0) based on the input current value (■.),
The reference sine wave creation means (15) creates a reference sine wave (v6) by delaying the zero cross timing of the AC power supply voltage (v0) by a phase difference (φ), and the sine wave approximation control waveform creation means (16) creates the reference sine wave (v6). A sine wave approximation control signal (Sl) is created based on the sine wave (vK) and the switching element (9)
Output to.

When the switching element (9) is controlled in this way, the voltage (V,) across the switching element (9) and the input current (1,) become sinusoidal, and the AC power supply voltage (
The phase difference (δ) of the input current (10) with respect to v0) approaches zero.

To bring the phase difference (δ) close to zero, the reference sine wave (v0
Since the phase (φ) of ) is changed, the duty ratio of the sine wave approximation control signal (S, ) is kept constant, the on-time of the switching element (9) is stabilized, and the energy generated by the reactor (3) is The cumulative effect remains unchanged. As a result, the DC voltage (VD
. ) will be held constant.

<Example> Hereinafter, an example of the present invention will be described in detail based on the drawings.

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

An aftereffect rectifier circuit 4 consisting of a diode bridge is connected between AC power supply terminals 2a and 2b to which the AC power supply 1 is connected via a reactor 3 such as a chiller 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 an output terminal 7a of the smoothing capacitor 6.

A load 8 is connected between 7b and 7b. This load 8 may be an inverter circuit in an inverter-driven air conditioner, a switching regulator, or a power transistor or a power MO between the output terminals of the full-wave rectifier circuit 4.
Switching elements 9 such as 3-FETs are connected in parallel.

Further, a current transformer CT provided in the power line connecting the AC power supply l and the full-wave rectifier circuit 4 is connected to the t-V conversion circuit 10, so that the input current to the full-wave rectifier circuit 4 is 1. It constitutes an input current detection circuit 11 that detects. The IV conversion circuit 10 calculates the average value I of the AC input current i picked up by the current transformer CT.

It converts the voltage into a direct current voltage (2), and is composed of a diode bridge DB, , a resistor R, and a capacitor C3.

12 is a t-source voltage waveform detection circuit that detects the waveform of the power supply voltage V of the AC power supply 1, and includes a step-down transformer 71% diode bridge DB connected between the AC power supply terminals 2a and 2b.
, and a resistor R.

13 is a power supply voltage V detected by the power supply voltage waveform detection circuit 12;

This is a zero cross detection means for detecting the zero voltage phase of the voltage.

14 is the voltage v across the switching element 9 and the AC type i1! based on the DC voltage ■ from the i-v conversion circuit 10.
The zero phase difference φ, which is a phase difference calculation means for calculating the phase difference φ between X1 and the power supply voltage V, is expressed as follows, where the function symbols are g and h, φ= g (VP) = h (T o ) ・
It can be expressed as ・・・・・・・・・・・・■.

15 is based on the modulation degree H (constant) and the phase difference φ, with the zero voltage phase detected by the zero cross detection means 13 as a reference,
The reference sine waves V and I are expressed as: v8,000Hsin (θ-φ) ・・・・・・・・・
...This is a reference sine wave creation means created according to ■.

θ in equation (2) is the phase of the power supply voltage v0 of the AC power supply 1, and when the power supply frequency is F, it is θ−2πFt.

From formulas ■ and ■, Vw - Hsin (θ-h (1°))...
...■.

The modulation degree H is determined to be a predetermined constant value in order to keep the necessary DC voltage VB to be supplied to the load 8 constant. Therefore,
The reference sine wave vg is, after all, the detected input current value ■. It will be created based on.

16 is a near sine wave 4fJ PWM signal S for on/off control of the switching element 9, which is a reference sine wave vK.
This is a sine wave approximation PWM waveform creation means that is created based on. The sine wave approximation PWM signal S1 is transmitted through the switching element 9
This is a signal for switching the switching element 9 so that the voltage V across the input current l becomes a voltage that makes the waveform of the input current l approach a sine wave.

The aforementioned zero cross detection means 13, phase difference calculation means 14,
The reference sine wave creation means 15 and the sine wave near-pwM waveform creation means 16 are realized by software processing by the CPU 17 of the microcomputer.

Next, the principle of operation will be explained. For convenience of explanation, the input current is expressed as io (θ).

Since the phase of the basic voltage distribution of the voltage v1 across the switching element 9 is delayed by φ with respect to the power supply voltage v0, Vow, rV, Sinθ V+−rVlsjn(θ−φ) is obtained. The voltage equation is dθ5 (V, sinθ-V, 5in(θ-φ))...
・・・・・・・・・・・・■ If we integrate both sides of the 0 formula ■ to find the input current 10(θ), we get T to (θ)−□×ωL V, sfnφ V, sinφ ・・・・・・・・・・・・■ is obtained. However, the input current io (θ) with respect to the power supply voltage v0, which is ωL...
If the phase difference of is δ, then from equation (■), the input current i, (θ) and the power supply voltage V, which are V, sinφ, are in phase,
That is, when δ−〇, from the formula ■, v, v, cosφ
≠0 ・・−・・−・−Medium bar−・■. Also, the magnitude Io of the input current 10 (θ) at this time is:
Substituting the formula ■ into the formula ■, 1, = −sinφ
・・・・・・・・・・・・■ωL From 2〇, cosφ−V6/Vl ・・・・・・・・・
...From the [stock] formula ■, sinφ=ωL-ro /V+ ...
・・・・・・■゛ Therefore, tanφ−ωL・■. /v, ・・・・・・・・・
...[Phase] From the above, any input current 10 (
Regarding θ), the condition for the phase difference φ between the voltage v1 across the switching element 9 in order to bring the phase of the input current to (θ) and the phase of the power supply voltage v0 into the same phase (δ−〇) is as follows from ゐ〇: O It is.

That is, if the phase difference φ between the voltage v across the switching element 9 is controlled so as to satisfy the condition of Equation 0, the input current to
(θ) can be made in phase with the power supply voltage v0. Assuming that ωL,,Vo are known, the input current i6
(θ) size 1. By detecting , the phase difference φ between the voltage V across the switching element 9 and the power supply voltage V can be determined.

The phase difference φ between the voltage V across the switching element 9 is controlled as described above by the CPU 1, which controls the switching element 9 on and off based on the sine wave approximation PWM signal S.
It is 7.

Now, the magnitude of the input current to (θ) picked up by the current transformer CT is 1. is converted into a DC voltage v7 by the IV conversion circuit IO, and then read into the CPU 17. Further, the zero cross detection means 13 detects the zero voltage phase of the AC power supply voltage V, and outputs it to the CPU 17.

The CPU 17 calculates the magnitude vo of the power supply voltage V, the reactance ωL of the reactor 3, and the read input terminal value Is.
(that is, VF), the phase difference φ is calculated based on equation 0.

Then, a sine wave near the sine wave whose on/off duty is determined based on the reference sine wave vK so that the voltage v1 across the switching element 9 has a waveform delayed by the phase difference φ from the zero-cross point with respect to the power supply voltage v0. (The luPWM signal S1 is output to the switching element 9.

When the switching element 9 is switched in this way,
The input current io (θ) is finally given by 2〇, ■, i, (θ) #I'T1. sin θ, the input terminal is (θ) can have a waveform approximating a sine wave, and the input current i.

The fundamental wave power factor can be set to 1 by setting the phase difference δ between the power supply voltage V of the AC power source 1111 to zero.

On the other hand, since the harmonic components become reactive power, it is desirable to reduce this as much as possible.For this purpose, the switching frequency of the switching element 9 is increased to perform high-speed switching, thereby reducing the reactive power due to the harmonic components. suppress.

The synergy of the above factors improves the overall power factor as a whole.

FIG. 2 shows an example of the sine wave approximation PWM signal S1 that is output from the CPU 17 and switches the switching element 9.

The reference sine wave VK −Hsin (θ−φ) is the power supply voltage V
, the phase is delayed by φ. This reference sine wave VK
The sine wave approximation PWM signal S, created based on , is a rectangular wave. When the switching element 9 is switched by this sine wave approximation PWM signal SL, the voltage V- across the switching element 90 becomes a rectified waveform whose phase is delayed by φ with respect to the power supply voltage V.

By the way, the OF of the sine wave approximation P W M (?r S,
The longer the F deity, the greater the modulation degree H, and the OF
As the F deity becomes shorter, the modulation degree H decreases.

In this way, the sine wave approximation PWM signal S.

Since the OFF duty and the modulation degree H have a one-to-one relationship, the modulation degree H, that is, the magnitude vl of the voltage Vl across the switching element 9 can be controlled by adjusting the OFF duty. In this way, the modulation degree H (that is, the voltage v
In the conventional example described above, the phase difference δ between the input current i and the power supply voltage V of the AC power supply 1 is made zero by controlling the magnitude V1) of .

However, in this embodiment, the modulation degree H is fixed constant, and the voltage V across the switching element 9 and the power supply voltage V of the AC power supply 1 are
・The input current value is the phase difference φ! . The phase difference δ between the input current 10 and the power supply voltage v0 of the AC power supply 1 is made to be zero by controlling according to the following.

The phase difference calculation means 14 by the CPU 17 calculates the phase difference φ between the voltage v1 across the switching element 9 and the power supply voltage V of the AC power supply l based on the read input current value I0, and the reference sine wave creation means 15 , zero cross detection means 13
is delayed by a phase difference φ from the timing at which the zero-crossing phase of the power supply voltage Ve of the AC current [1] is detected, and then the reference sine wave v
Create K-Hsin (θ-φ) and perform sine wave approximation PWM
The waveform creation means 16 creates a sine wave approximation PWM signal Sl based on the reference sine wave V and a carrier wave (triangular wave), and controls the switching of the switching element 9 based on the sine wave approximation PWM signal S1.

By controlling in this way, the input current i.

can be made into a sinusoidal waveform, and the phase difference δ between the input current 50 and the power supply voltage v0 of the AC power supply 1 can be brought close to zero, and the fundamental wave power factor can be brought close to 1.

As mentioned above, the average value of input current 10 is ■. By controlling the phase difference φ according to the sine wave approximation PWM signal S
While creating the reference sine wave v1 that is the basis for creating l,
Since the modulation degree H is kept constant, the smoothing capacitor 6
Fluctuations in the DC voltage V·C output from the converter can be suppressed. This point will be explained based on the vector diagram shown in FIG.

The magnitude V of the voltage V+ across the switching element 9.

Keep the power supply voltage constant! . When the phase difference φ between the voltage 9I across the switching element 9 and the voltage 9I across the switching element 9 is decreased (Figures (A) and (B)), the voltage across the reactor 3 jωL! . From the relationship that is always orthogonal to the input current 10, the power supply voltage! . Input current for! , the phase difference δ can be reduced. Then, -Hsin (θ-φ) is created in the reference sine wave V so that this phase difference δ becomes zero, and the voltage across the switching element 9 is reduced! Since the phase φ of 1.1 is controlled, the input current 1. can be brought close to being in phase with the power supply voltage t, and the fundamental wave power factor can be improved.

In this case, the magnitude 1 of the voltage Vl across the switching element 9 is kept constant by only changing the phase φ of the reference sine wave vK, so the duty ratio during the off period of the sine wave approximation PWM signal S+ remains constant. The on-time of the switching element 9 is maintained.

remains unchanged, so there is no change in the energy storage effect of the reactor 3. As a result, the DC voltage VIIC across the smoothing capacitor 6 is held constant, resulting in good controllability.

As shown by the solid line in FIG. 4 CB), the switching element 9
With the voltage across the terminals V, the magnitude ■1 held constant,
Voltage V across switching element 9.

When only the phase difference φ between and the power supply voltage v0 of the AC power supply 1 is controlled, the input current value ■. As shown by the solid line in FIG. 4(A), the characteristics of the power factor with respect to changes in are improved over those of the conventional example (broken la).

In addition, in the above embodiment, the reactor 3 is a full-wave I-wave circuit 4.
However, the reactor 3 may be inserted between the output terminal of the full-wave rectifier circuit 4 and the anode of the diode 5.

<Effect of the invention> According to the present invention, the following effects are achieved.

The reference sine wave (v0) is used to bring the phase difference (δ) between the input terminal (i.
) to control the phase (φ) of the sine wave approximation control signal (
By keeping the duty ratio of S+) constant, the on-time of the switching element (9) can be stabilized.

That is, while effectively utilizing the energy storage effect of the reactor (3), the waveform of the input current (10) can be improved to a sinusoidal waveform, and the phase difference (δ) of the input current (i, ) with respect to the AC power supply voltage (v0) can be improved. It is possible to improve the power factor by bringing it closer to zero.

[Brief explanation of the drawing]

Figures 1 to 4 relate to embodiments of the present invention, where Figure 1 is a circuit diagram of a power factor correction circuit, Figure 2 is a waveform diagram for explaining operation, Figure 3 is a vector diagram, and Figure 4 is a diagram of a power factor correction circuit. It is a characteristic diagram. Fifth
7 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 rectifier circuit 5... Backflow prevention diode 6... Smoothing capacitor 9... Switching element 11. ... Input current detection circuit 13 ... Zero cross detection means 14 ... Phase difference calculation means 15 ... Reference sine wave creation means 16 ... Sine wave approximation control waveform creation means ■, ... AC power supply voltage i ,...input current ■,...input current value v,...phase difference V of vl with respect to voltage φ...V across the switching element...reference sine wave

Claims (1)

[Claims] (1) A full-wave rectifier circuit (4) connected between AC power supply terminals (2a, 2b) and a backflow prevention diode (5) connected between the output terminal of this full-wave rectifier circuit (4). a smoothing capacitor (6), and a reactor (3) connected in series to the input side or output side of the full-wave rectifier circuit (4);
A power factor correction circuit comprising a switching element (9) connected in parallel between the output terminals of the full-wave rectifier circuit (4), which detects an input current (i_0) to the full-wave rectifier circuit (4). an input current detection circuit (11) that detects the zero voltage phase of the AC power supply voltage (v_0); and a zero cross detection means (13) that detects the zero voltage phase of the AC power supply voltage (v_0);
a phase difference calculating means (14) for calculating a phase difference (φ) between the voltage (v_1) across the switching element (9) and the AC power supply voltage (v_0) based on the calculated phase difference (φ); ); and a reference sine wave generating means (15) for generating a reference sine wave (v_K) based on the zero voltage phase detected by the zero-cross detecting means (13); Sine wave approximation control signal (S_1) that approximates the waveform to a sine wave
a sine wave approximation control waveform creation means (16) for creating a sine wave approximate control waveform based on the reference sine wave (v_K) and applying it to the switching element (9).