KR101804773B1 - Ac-dc converter circuit with ripple eliminating function - Google Patents

Abstract

An AC-DC converter circuit having a ripple eliminating function is disclosed. The AC-DC converter circuit having a ripple eliminating function according to an embodiment of the present invention includes a converter for converting the voltage of an AC input power source into a DC voltage, a DC link capacitor connected in parallel with the output terminal of the converter, a ripple eliminating part connected in parallel with the DC link capacitor and eliminating harmonic ripple generated in the DC link capacitor, a first controller for controlling the converter using pulse width modulation (PWM), and a second control part for controlling the ripple eliminating part such that the harmonic ripple is bypassed by the ripple eliminating part.

Description

[0001] AC-DC CONVERTER CIRCUIT WITH RIPPLE ELIMINATING FUNCTION WITH RIPPLE REMOVING FUNCTION [0002]

Embodiments of the present invention relate to techniques for removing ripples in an AC-DC converter.

The simplest AC-DC converter topology that supplies DC power is a full bridge diode rectifier, but it has drawbacks such as high harmonic generation of power supply current and low power factor.

To solve this problem, a power factor correction circuit is added. In order to reduce the volume of the ripple and the converter, a high switching frequency is required, thereby increasing the switching loss.

To improve this, a bridgeless power factor correction step-up converter consisting of two diodes and two power devices is used. However, there still exists a problem that a ripple component twice the fundamental frequency occurs in the process of converting the AC voltage into the DC voltage.

This causes electrical stress to the converter, which adversely affects the system. Although a large capacity electrolytic capacitor can be used as an energy buffer to remove such ripple components, there is a problem of a large volume, a large weight and a short life span.

Patent Document 10-2015-0117330 (Oct. 20, 2015)

Embodiments of the present invention provide a circuit in which harmonic ripple generated in an AC-DC converter using a pulse width modulation (PWM) technique is eliminated.

The AC-DC converter circuit according to an embodiment of the present invention includes a converter for converting a voltage of an AC input power source into a DC voltage, a DC link capacitor connected in parallel to an output terminal of the converter, a DC link capacitor connected in parallel with the DC link capacitor, A first controller for controlling the converter using ripple removal and pulse width modulation (PWM) techniques for eliminating harmonic ripple occurring in the capacitor, and a second controller for controlling the harmonics ripple to be bypassed by the ripple removal And a second control unit for controlling the ripple removing unit.

The DC link capacitor may be charged with the converted DC voltage and discharged in parallel with the load.

The converter may be a single-phase PWM converter.

The ripple removing unit includes a first switching device S3 connected in parallel to the DC link capacitor, a second switching device S4 connected in series to the first switching device, an inductor L _r connected in parallel to the second switching device, And a capacitor (C _r ) connected in series to the inductor.

The ripple rejection unit may be a buck-boost converter that operates as a buck converter when charging the capacitor and operates as a boost converter when discharging the capacitor.

The second control unit may control operations of the first switching device S3 and the second switching device S4 so that the capacitor _Cr is charged or discharged.

The second control unit, the second switching element (S4) and controls the in-off (off) state, using the PWM method of the first switching element (S1 by the harmonic ripple to charge the said capacitor (C _r) Can be controlled.

The second control unit may control the first switching device S3 to be in the off state so that the capacitor C _r is discharged and the operation of the second switching device S4 using the PWM technique.

The second control unit may calculate a duty ratio that is an on / off ratio of the operation of the first switching device (S3) and the second switching device (S4) to remove the harmonic ripple, 1 switching element S3 and the second switching element S4 can be controlled.

The second controller may calculate the duty ratio based on the compensation current (i _r ^* ) for removing the harmonic ripple, the voltage of the DC link capacitor, and the voltage (V _r ) of the capacitor (C _r ) have.

The second control unit may calculate the compensation current (i _r ^* ) based on the current (i _dc ) output from the converter and the voltage (V _r ) of the capacitor (C _r ).

The second control unit may calculate the current (i _dc ) output from the converter based on the current of the AC input power source, the gating time of the switch included in the converter, and the sampling time (Ts).

The DC link capacitor may be a film-type capacitor.

According to embodiments of the present invention, the harmonic components generated in the converter can be bypassed to the additional circuit capacitor of the bidirectional buck-boost converter, thereby removing harmonic ripple components generated in the converter.

Further, according to embodiments of the present invention, by replacing the harmonic ripple component generated in the converter with a small capacity film capacitor having excellent frequency characteristics, it is possible to improve the reliability and reduce the volume and weight of the entire system have.

1 is a circuit diagram of an AC-DC converter circuit having a ripple rejection function according to an embodiment of the present invention.
2 is a diagram illustrating a charging and discharging process of a DC link capacitor according to an embodiment of the present invention;
Figure 3 shows a switch control block diagram of the ripple removal
4 is a view showing a current waveform of the inductor included in the ripple removal.
5 to 12 are graphs showing experimental results of a converter circuit according to an embodiment of the present invention

Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. The following detailed description is provided to provide a comprehensive understanding of the methods, apparatus, and / or systems described herein. However, this is merely an example and the present invention is not limited thereto.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail. The following terms are defined in consideration of the functions of the present invention, and may be changed according to the intention or custom of the user, the operator, and the like. Therefore, the definition should be based on the contents throughout this specification. The terms used in the detailed description are intended only to describe embodiments of the invention and should in no way be limiting. Unless specifically stated otherwise, the singular form of a term includes plural forms of meaning. In this description, the expressions "comprising" or "comprising" are intended to indicate certain features, numbers, steps, operations, elements, parts or combinations thereof, Should not be construed to preclude the presence or possibility of other features, numbers, steps, operations, elements, portions or combinations thereof.

1 is a circuit diagram of an AC-DC converter circuit having a ripple rejection function according to an embodiment of the present invention.

1, an AC-DC converter circuit 100 according to an embodiment of the present invention includes a converter 110, a ripple removing unit 130, a DC link capacitor 150, a first controller 170, 2 < / RTI >

The converter 110 converts the voltage of the AC input power source into a DC voltage. Specifically, the converter 110 receives the AC voltage V _s and converts the AC voltage into a DC voltage under the control of the first controller 170 and outputs the DC voltage.

At this time, the converter 110 may be a single-phase pulse width modulation (PWM) converter.

The first controller 170 controls the converter 110 using the PWM technique. More specifically, the first controller 170 controls the operation of the switching elements S1 and S2 in the converter 110 using the PWM technique so that the voltage V _s of the AC input power input to the converter 110 is higher than the DC To a voltage (V _dc ).

Meanwhile, the DC link capacitor 150 is connected in parallel to the output terminal of the converter 110 and charged with the DC voltage V _dc converted from the converter 110. In addition, the charged DC link capacitor 150 may be discharged through a load connected in parallel with the DC link capacitor 150. At this time, the DC link capacitor 150 may be, for example, a film-type capacitor.

2 is a diagram illustrating a charging and discharging process of the DC link capacitor 150 according to an embodiment of the present invention.

2, converter 110 according to an embodiment of the present invention may operate in a charging mode (a) and (c) or a discharge mode (b) and (d). Specifically, the first controller 170 may control the converter 110 to the charge mode or the discharge mode using the PWM technique.

For example, referring to (a), when the voltage V _s of the AC input power source is a positive half period, the first control unit 170 controls the switch S1 to be on and the switch S2 to be off So that the converter 110 can be controlled. Accordingly, the current i _s flows through the diode D _s1 and the diode D2, and the DC link capacitor 150 can be charged.

Referring to (b), the voltage of the AC input power supply (V _s) is when the positive half cycle, the first controller 170 includes a converter 110, so that the switch S1 off (off), and the switch S2 turned on (on) Can be controlled. Accordingly, the current i _s flows through the switch S2 and the diode D2, and the DC link capacitor 150 can be discharged.

when the voltage V _s of the AC input power source is a negative half period, the first controller 170 controls the converter 110 such that the switch S1 is turned off and the switch S2 is turned on, Can be controlled. Accordingly, the current i _s flows through the diode D1 and the diode D _s2 , and the DC link capacitor 150 can be charged.

(d), when the voltage V _s of the AC input power source is a negative half period, the first control unit 170 can control the switch S1 to be on and the switch S2 to be off . Accordingly, the current i _s flows through the switch S1 and the diode D1, and the DC link capacitor 150 can be discharged.

Referring again to FIG. 1, the ripple removing unit 130 is connected in parallel with the DC link capacitor 150 to remove the harmonic ripple occurring in the DC link capacitor 150.

The ripple removing unit 130 includes a first switching device S3 connected in parallel to the DC link capacitor 150, a second switching device S4 connected in series to the first switching device S3, a second switching device S4 An inductor L _r in parallel with the inductor L _r and a capacitor C _r in series with the inductor L _r .

At this time, the ripple removing unit 130 has a capacitor (C _r) of the buck operating in the boost converter (boost converter) upon discharge of operating as a buck converter (buck converter) when fully charged, and the capacitor (C _r) - be a boost converter, have.

The second controller 190 controls the ripple removal unit 130 such that the harmonic ripple generated in the DC link capacitor 150 is bypassed to the ripple removal unit 130.

Specifically, the second controller 190 may control operations of the first switching device S3 and the second switching device S4 so that the capacitor C _r is charged or discharged.

If, when the harmonic ripple occurring in the DC link capacitor (150) to move from the DC link capacitor 150, a capacitor (C _r), ripple remover 130 is operating in the charging mode to charge the capacitor (C _r) can do.

On the other hand, when the harmonic ripple component moves from the capacitor C _r to the DC link capacitor 150, the ripple removal 130 can operate in a discharge mode for discharging the capacitor C _r .

For example, when the second control unit 190 controls the second switching device S4 to be in the on state and the operation of the first switching device S3 is controlled using the PWM technique, the ripple removal unit 130 May operate in the charging mode. At this time, the capacitor C _r included in the ripple removing unit 130 is charged by the harmonic ripple, and the bidirectional buck-boost converter can operate as a buck converter which is a voltage reduction converting circuit.

Specifically, when the second control unit 190 turns on the first switching device S3, the harmonic ripple component moves from the DC link capacitor 150 to the ripple removing unit 130, and the second control unit 190 The current i _r flowing in the inductor of the ripple removal unit 130 flows through the capacitor C _r included in the ripple removal unit 130 to the second And through a diode connected in parallel with the switching element S4.

If the second control unit 190 controls the first switching device S3 in an off state and controls the operation of the second switching device S4 using a PWM technique, the ripple removing unit 130 It can operate in the discharge mode. At this time, the capacitor C _r included in the ripple removal unit 130 is discharged, and the bidirectional buck-boost converter can operate as a boost converter, which is a boost converter.

Specifically, when the second control unit 190 turns on the second switching device S4, the harmonic ripple component flows from the capacitor C _r included in the ripple removal unit 130 to the ripple removal unit 130 The inductor L _r is stepped up while the second control unit 190 turns off the second switching device S 4 and the harmonic ripple component is supplied to the inductor L _r through the capacitor C _r , And the inductor (L _r ) to the DC link capacitor (150).

On the other hand, the second controller 190 is a converter (110, based on the gating time and sampling time (T _s) of the switch included in the converter 110, the AC input current of the power source (i _s) to be input to the converter 110, (I _dc ) output from the inverter circuit 20 can be calculated.

Specifically, the current (i _dc ) output from the converter 110 can be expressed by Equation (1) below.

[Equation 1]

Here, T _gs1 and T _gs2 represent the gating times of the switches S1 and S2 included in the converter 110, respectively.

The second control unit 190 also controls the output voltage of the DC link capacitor 150 based on the calculated output current i _dc and the voltage V _r of the capacitor C _r included in the ripple removal unit 130 It is possible to calculate the compensation current (i _r ^* ) for removing the harmonic ripple.

3 is a switch control block diagram of the ripple removal unit 130. As shown in FIG.

3, the compensation current i _r ^* for eliminating the harmonic ripple is calculated by the following equation: i _r1 ^* which is the harmonic component of the output current i _dc and the voltage of the capacitor C _r included in the ripple removing unit 130 V _r can be composed of the sum of i _r2 ^* , which is the component coming out of the PI controller.

At this time, i _r1 ^* is a component for removing the harmonic ripple, and can be calculated by applying a bandpass filter to the current i _dc .

Specifically, the harmonic ripple generated in the converter 110 may be a second harmonic ripple, and the transfer function of the band-pass filter may be expressed by Equation 2 below.

&Quot; (2) "

, f_c=120Hz, B=20일 수 있다.here,

, f _c = 120 Hz, B = 20.

On the other hand, i ^* _r2 is a component for preventing the overcharging of the capacitor C _r, can be calculated from the voltage V _r of the capacitor C _r.

Specifically, i _r2 ^* can be obtained as a result of the PI controller by inputting the difference between the voltage command value (V _r ^* ) of the preset capacitor C _r and the average value of the voltage V _r to the PI controller. Here, the average value of the voltage V _r is the low-pass filter with a voltage V _r to the cut-off frequency 10Hz; can be measured by using the (LPF Lowpass filter).

The second control unit 190 may control the compensation current i _r ^* to remove the harmonic ripple, the voltage V _r of the capacitor C _r included in the ripple removal unit 130 and the voltage V _{r of the} DC link capacitor The duty ratio which is the on / off ratio of the operation of the first switching device S3 and the second switching device S4 can be calculated based on the duty ratio V _dc .

4 is a graph showing a current waveform of the inductor included in the ripple removal unit 130. As shown in FIG.

(a), when the ripple removing unit 130 operates in the charge mode, the duty ratio D1 for the first switching device S3 can be calculated.

Specifically, when the first switching device S3 is turned on, the rising rate K _I1 of the current i _r flowing in the inductor L _r and the rising rate K _I1 of the current i _r flowing in the inductor L _r when the switch S 3 is off The falling rate K _D1 can be expressed by the following equations (3) and (4).

&Quot; (3) "

&Quot; (4) "

Here, V _dc is the voltage of the DC link capacitor 150, V _r is the voltage of the capacitor included in the ripple removal 130, and L _r is the inductance of the inductor included in the ripple removal 130.

Further, the compensation current (i _r ^* ) for removing the harmonic ripple must be equal to the magnitude of the average current, so that it can be expressed by the following equation (5).

&Quot; (5) "

Here, T _on1 is a time during which the first switching device S3 is maintained in an on state, T _off1 is a time during which the first switching device S3 is maintained in an off state, T _sw is a switching period to be.

In addition, the relationship between T _on1 and T _off1 in the charge mode can be expressed by Equation (6) below.

&Quot; (6) "

Therefore, the duty ratio D1 can be expressed by Equation (7) below.

&Quot; (7) "

Where f _sw is the inverse of T _sw as the switching frequency.

(b), when the ripple removing unit 130 operates in the discharge mode, the duty ratio D2 for the second switching device S4 can be calculated.

Specifically, the second switching device to the inductor L _r time (S4) is turned on (on) rate of increase in current i _r (K _I2) and a second switching element (S4) flowing through the inductor L _r When a is (off) off The falling rate K _D2 of the flowing current i _r can be expressed by the following equations (8) and (9).

&Quot; (8) "

&Quot; (9) "

In addition, since the compensation current (i _r ^* ) for removing the harmonic ripple has to be equal to the magnitude of the average current, it can be expressed by the following Equation (10).

&Quot; (10) "

Here, T _on2 is the time during which the second switching device S4 is held on and T _off2 is the time during which the second switching device S4 is maintained off.

In addition, the relationship between T _on2 and T _off2 in the discharge mode can be expressed by Equation (11) below.

&Quot; (11) "

Therefore, the duty ratio D2 can be expressed by the following equation (12).

&Quot; (12) "

Also, the second controller 190 may control the operation of the first switching device S3 and the second switching device S4 according to the calculated duty ratio. Specifically, the second controller can control the operation of the switch first switching device S3 included in the ripple removal unit 130 according to the duty ratio D1 of the step (190), and the ripple removal unit 130 The operation of the second switching element S4 included in the second switching element S4 can be controlled.

5 to 12 are diagrams showing experimental results of a converter circuit according to an embodiment of the present invention.

Meanwhile, the experimental parameters used to obtain the experimental results shown in Figs. 5 to 12 are shown in Table 1 below.

parameter value Power supply voltage (rms value) 220 [V] Power frequency 60 [Hz] Input inductance Ls 3 [mH] DC link capacitance Cdc 200 [uF] DC link capacitor voltage Vdc 350 [V] Output power 1.6 [kW] Ripple removal inductance Lr 100 [uH] Ripple removal capacitance Cr 150 [uF] Switching frequency 10 [kHz]

5 illustrates control performance when the converter circuit is in a steady state according to an embodiment of the present invention. (a), it can be seen that the voltage of the DC link capacitor 150 follows the set value 350v well. Also, referring to (b), it can be confirmed that the measured input current follows the command input current well. Also, (c) is the input voltage, and (b) and (c), it can be seen that the input current is controlled by the sinusoidal wave having the unit power factor.

6 is a graph illustrating a harmonic ripple voltage according to the presence or absence of the ripple removing unit 130 in a converter circuit according to an embodiment of the present invention. (a), it can be confirmed that the peak-to-peak value of the harmonic ripple voltage is up to 70 v when the ripple removing unit 130 is not present. On the other hand, referring to (b), when the ripple removing unit 130 is present, the peak-to-peak value of the harmonic ripple voltage is significantly reduced to 8V.

FIG. 7 shows a comparison of the harmonic ripple voltage according to the presence or absence of the ripple removing unit 130 in the converter circuit according to an embodiment of the present invention. (a) shows a harmonic ripple voltage when a DC link capacitor having a capacitance of 200 uF is used in a circuit in which the ripple removing unit 130 is present. (b) shows the harmonic ripple voltage when a DC link capacitor of 2000 uF capacitance is used in a circuit in which the ripple removing unit 130 is not present. (a) and (b), it can be seen that the harmonic ripple voltage of the two cases is similar. Therefore, by applying the ripple removing unit 130, the capacity of the DC link capacitor can be reduced.

8 shows the current and voltage of the capacitors included in the ripple removal 130 in the converter circuit according to an embodiment of the present invention. (a), the current of the capacitor included in the ripple removal unit 130 is discontinuously controlled, and it can be confirmed that the maximum value is 38 A and the effective value is 11 A. (b), it can be seen that the voltage of the capacitor included in the ripple removal unit 130 is controlled to have an average of 200 volts.

9 and 10 show the responses when the load decreases and when the load increases. (a), it can be seen that the harmonic ripple voltage is kept below 10% of the nominal value at the instant of load variation. (b), the control performance of the input current can be confirmed in the transient state, and it can be confirmed that the actual current follows the command current through the current control. (c), it can be confirmed that the voltage of the capacitor included in the ripple removal unit 130 is controlled by a sinusoidal wave. (d), it can be seen that the current of the capacitor included in the ripple removal unit 130 maintains a discontinuous operation.

Figure 11 shows the control performance when a 15% voltage drop occurs at the input voltage. (a), (b) and (c) show the input voltage, the voltage of the DC link capacitor, and the input current, respectively. Referring to FIG. 11, it can be seen that the fluctuation of the DC link capacitor voltage is controlled within 10% even with the variation of the input voltage.

12 shows the instantaneous power of the converter circuit according to an embodiment of the present invention.

(a) is the input power, and it can be seen that the input power consists of the DC component and the AC component which is twice the grid frequency. (b) is a power waveform of the capacitor included in the ripple removal unit 130, and it can be confirmed that the harmonic ripple component is bypassed by referring to the power waveform. (c) is the output power, and it can be confirmed that the output power is maintained at a constant value with reference thereto.

Thus, according to embodiments of the present invention, harmonic components generated in the converter can be bypassed with a bidirectional buck-boost converter to eliminate harmonic ripple components that adversely affect the converter and the DC link capacitors connected in parallel with the converter have. Further, according to embodiments of the present invention, by replacing the harmonic ripple component generated in the converter with a small capacity film capacitor having excellent frequency characteristics, it is possible to improve the reliability and reduce the volume and weight of the entire system have.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, I will understand. Therefore, the scope of the present invention should not be limited to the above-described embodiments, but should be determined by equivalents to the appended claims, as well as the appended claims.

100: AC-DC converter circuit
110: Converter
130: ripple removal
150: DC link capacitor
170:
190:

Claims (12)

A converter for converting a voltage of the AC input power source into a DC voltage;
A DC link capacitor connected in parallel with the output of the converter;
A ripple removing unit connected in parallel with the DC link capacitor to remove harmonic ripple generated in the DC link capacitor, and including at least one switching element and a capacitor (C _r );
A first controller for controlling the converter using a pulse width modulation (PWM) technique; And
And a second control unit for controlling the ripple removing unit such that the harmonic ripple is bypassed by the ripple removing unit,
Wherein the second control unit calculates a duty ratio that is an on / off ratio of the switching element operation based on a compensation current (i _r ^* ) for removing the harmonic ripple, and performs an operation of the switching element according to the duty ratio Control,
The compensation current i _r ^* is calculated by multiplying the harmonic component i _r1 ^* of the output current i _dc calculated by applying a bandpass filter to the output current i _dc of the converter, It said capacitor (C _r) the voltage command (V ^* _r) and the capacitor (C _r) the result input the difference between the average voltage in the PI controller a sum of the alternating current (i _r2 ^*) in the - DC converter circuit.
The method according to claim 1,
The converter is an AC-DC converter circuit that is a single-phase PWM converter.
The method of claim 2,
Wherein the ripple-
A first switching device (S3) connected in parallel with the DC link capacitor;
A second switching element S4 connected in series to the first switching element; And
And an inductor L _r connected in parallel to the second switching device,
And the capacitor (C _r ) is connected in series to the inductor (L _r ).
The method of claim 3,
Wherein the ripple-
Operates as a buck converter upon charging of the capacitor (C _r )
And an AC-DC converter circuit that is a buck-boost converter that operates as a boost converter when the capacitor (C _r ) discharges.
The method of claim 3,
The second control unit controls the operation of the first switching device (S3) and the second switching device (S4) so that the capacitor (C _r ) is charged or discharged.
The method of claim 5,
The second control unit, the second switching element (S4) and controls the in-off (off) state, using the PWM method of the first switching element (S1 by the harmonic ripple to charge the said capacitor (C _r) DC converter circuit for controlling the operation of the AC-DC converter circuit.
The method of claim 5,
The second control unit controls the first switching device S3 to be in an off state so that the capacitor C _r is discharged and controls the operation of the second switching device S4 using a PWM technique. DC converter circuit.
delete The method of claim 3,
Wherein the second control unit calculates the duty ratio based on the compensation current (i _r ^* ), the voltage of the DC link capacitor, and the voltage (V _r ) of the capacitor (C _r ).
delete The method of claim 9,
The second control unit calculates the output current (i _dc ) based on the current of the AC input power source, the gating time of the switch included in the converter, and the sampling time (Ts).
The method according to claim 1,
Wherein the DC link capacitor is a film-type capacitor.

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