KR20020074605A - Dc ripple voltage suppression device and method for a 3-phase buck-type diode rectifier - Google Patents

Abstract

PURPOSE: An apparatus and a method for lowering a DC riffle voltage for three phase step-down type diode rectifier are provided to improve efficiency of a rectifier and supply stably an output voltage by controlling a turning-on time and a turning-off time. CONSTITUTION: The low pass filter(209) receives a DC voltage(VDC) from a three phase step-down type diode rectifier and outputs the current without riffle of 360Hz. The current without riffle and DC current(iDC) of a rectifier according to the DC voltage(VDC) are applied to an output load calculator(208). The output load calculator(208) generates an output power to indicate the amount of output load and applies the output power to a low pass filter(204) of a preliminary switching frequency decision loop(A1) and a high pass filter(207) of a voltage riffle suppression loop(A2). The filtered output power is applied to a power/frequency function block(203). An auxiliary switching frequency(fff) is determined by a predetermined function value. The power/frequency function block(203) controls the auxiliary switching frequency(fff) according to the amount of output of the low pass filter(204). The high pass filter(207) extracts a desired riffle power signal by filtering the output load of the output load calculator(208). A riffle gain calculator(206) determines a frequency(fcomp) to indicate the variable amount of a final switching frequency(Fsw). A PI control loop(A3) controls an output voltage.

Description

DC RIPPLE VOLTAGE SUPPRESSION DEVICE AND METHOD FOR A 3-PHASE BUCK-TYPE DIODE RECTIFIER}

The present invention relates to a rectifier for converting an alternating current (AC) voltage into a direct current (DC) voltage, and more particularly, to an apparatus and method for reducing a low frequency ripple voltage of an output voltage generated in a three-phase step-down diode rectifier. It is about.

Three-phase AC-DC rectifiers are frequently required in applications requiring large output voltages at high input voltages, such as communication power systems. In such rectifiers, the isolation of input and output stages for safety, an increase in power factor for minimizing reactive power, weight reduction and miniaturization of devices through efficiency improvement are important issues.

In general, the output voltage of the rectifier has a low frequency ripple voltage according to the input power source, and thus a ripple current is generated. The ripple current flows through a DC-Link capacitor connected to the output side of the rectifier. This causes the operating temperature of the capacitor to rise, which causes a problem of shortening the electrical life of the capacitor. In addition, this low frequency ripple voltage is fed back to the voltage controller to cause waveform distortion of the input current.

As a method to solve this problem, a method of increasing the capacity of the capacitor of the rectifier or increasing the size of the output low-frequency LC filter has been used, but this method increases the cost and the overall size of the system including the rectifier. It was a cause.

In order to reduce the ripple voltage of the output voltage, a PWM (Pulse Width Modulation) method has been used in a conventional three-phase step-down diode rectifier. As is well known, this PWM method determines the turn-on time of the switch by the parameter of the resonant elements. In the above-described method, that is, the reduction of the duty ratio in the PWM method, the ratio of the on time and the off time of the switch is reduced. If the duty ratio is reduced, sufficient resonance may not occur, and thus, the switch may not operate with ZCS (Zero Current Switched), resulting in a reduction in the efficiency of the rectifier.

Accordingly, an object of the present invention is to improve the efficiency of the rectifier by appropriately controlling the turn-on time and off time, and low-frequency ripple for three-phase step-down rectifier that can provide an output voltage stably even when the load capacity changes. It is to provide a voltage reducing device and method.

According to one aspect of the present invention, in the low-frequency ripple voltage reduction device of a three-phase step-down diode rectifier, by using the DC voltage and current from the rectifier, the switching frequency is preliminarily determined, and the fineness of the previous final switching frequency is reduced. A first frequency generating means for obtaining a frequency representing a variable, and an output voltage of the rectifier based on a desired voltage not including ripple voltage as an ideal DC voltage required by the load system of the rectifier and an output DC voltage from the rectifier. A second frequency generating means for generating a frequency for controlling and a final switching frequency obtained by combining the frequencies generated by the first and second frequency generating means and modulating the final switching frequency to provide the rectifier to vary the previous final switching frequency. Three-phase step-down type comprising a third frequency generating means for A low frequency ripple voltage reduction device for a diode rectifier is provided.

1 is a circuit diagram of a three-phase step-down diode rectifier for use in explaining a low frequency ripple voltage reduction device and method for a three-phase step-down diode rectifier according to the present invention.

2 is a view used to explain a DC ripple voltage reduction method for a three-phase step-down diode rectifier of the present invention.

3 is a graph showing a relationship between a switching frequency and an output power used to describe a DC ripple voltage reduction method for a three-phase step-down diode rectifier according to the present invention.

4 is a graph showing a DC ripple power signal of a three-phase step-down diode rectifier according to the present invention.

5 is a graph showing the waveform of the output voltage over time used to explain the DC ripple voltage reduction method for a three-phase step-down diode rectifier of the present invention.

Fig. 6 is a graph showing waveforms of input voltage and current used to explain a DC ripple voltage reduction method for a three-phase step-down diode rectifier of the present invention.

<Explanation of symbols for the main parts of the drawings>

201: PI controller

203: P _out and f _ff functions

204, 209 low pass filter

206: Ripple Gain Calculator

207 high pass filter

208: Output Load Calculator

A1: preliminary switching frequency (f _ff ) decision loop

A2: voltage ripple suppression loop

A3: PI control loop

Referring to FIG. 1, FIG. 1 is a circuit diagram of a conventional three-phase step-down diode rectifier for explaining a low frequency ripple voltage reducing device and method according to the present invention. In the figure, V _a , V _b and V _c are the voltages of the three-phase input power supply. As shown in FIG. 1, the three-phase input power supply (V _a , V _b , V _c ) is composed of an inductor (L _a , L _b , L _c ) and a capacitor (Cr ₁ , Cr ₂ , Cr ₃ ), respectively. The resonant circuit is connected, and the resonant circuit is connected to six diodes D ₁ to D ₆ . The output current output through the _six diodes (D ₁ to D ₆ ) is one of the top diodes (D ₁ , D ₂ , D ₃ ) and one of the bottom diodes (D ₄ , D ₅ , D ₆ ) in the schematic. Will flow. That is, in the upper portion, the diode of the phase having the largest magnitude in the positive direction among the values in which each of the three-phase power supply passes the resonant circuit at any time is turned on and the other two diodes are reverse biased to maintain the off state. In the lower portion, the diode of the phase having the largest magnitude in the negative direction among the values of each of the three-phase power sources passing through the resonance circuit is turned on. Therefore, the diodes are turned on with a phase difference of 120 degrees, and the upper and lower diodes are turned on with a phase difference of 180 degrees. As described above, the output side of the diode is connected to one side of the switch S ₁ , and the other side of the inductor L _r connected in parallel with the diode D _d and the capacitor C _d connected in series with the output thereof. ) Is connected to a resonant circuit composed of an inductor (L _f ) and a capacitor (C _f ) again. The final output value of the three-phase step-down diode rectifier configured as described above includes a low frequency ripple voltage component that reduces the efficiency of the system.

Therefore, in the present invention, the apparatus and method for controlling the switching operation of the switch (S ₁ ) using the actual measured value obtained through the three-phase step-down diode rectifier and the desired value required to reduce the low frequency ripple voltage as an input. To provide.

The low frequency ripple voltage reduction method of the three-phase step-down diode rectifier of the present invention calculates the direct current output from the output voltage and the output current of the rectifier circuit, extracts the ripple output corresponding to the ripple voltage from the low frequency ripple component according to the present invention. By feeding forward to the reduction control loop, the low frequency ripple voltage can be efficiently reduced.

As described above, in order to effectively reduce the low frequency ripple voltage, it is necessary to obtain a stable output voltage against load changes. Here, in order to keep the output voltage constant, the operation of the switch must be controlled to increase the switching frequency when the output amount is increased and to reduce the switching frequency of the rectifier when the output amount is decreased.

Accordingly, the low frequency ripple voltage reduction method according to the present invention can reduce the low frequency ripple voltage by effectively controlling the operation of the single switch S ₁ in the circuit of the three-phase step-down diode rectifier.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Referring to Figure 2, using a pulse frequency modulation (PFM) modulation method, according to an embodiment of the present invention to effectively reduce the output ripple voltage by varying the switching frequency (F _sw ) of the switch (S ₁ ) A block diagram of a low frequency ripple voltage reduction device for a phase-down diode rectifier is shown.

As shown in FIG. 2, the low frequency ripple voltage reduction method for the three-phase step-down diode rectifier of the present invention, that is, a device for controlling the switch S ₁ is a preliminary switching to preliminarily determine the switching frequency f _ff . In the frequency f _ff determination loop A1, the voltage ripple suppression loop A2 that determines the frequency f _comp representing the microvariable of the final switching frequency F _sw , and the transient and normal characteristics of the DC voltage A PI control loop (A3) is provided that provides a frequency (f _volt ) for controlling the output voltage to ensure regulation of the output voltage. By such a configuration, the switching frequency of the switch S ₁ required to obtain a constant output voltage even with a change in load while reducing the low frequency ripple voltage component can be determined.

Specifically, the actual measured value of the AC / DC converted DC voltage (V _DC ) output from the three-phase step-down diode rectifier is passed through the low pass filter 209 to obtain a ripple free DC value of 360 Hz. Along with the current i _DC according to the / DC converted voltage V _DC is applied to the output load calculator 208.

As shown, the output load calculator 208 multiplies the ripple-free DC voltage (V ^′ _DC ) input from the low pass filter 209 by the DC current (i _DC ) from the rectifier to output power indicating the output load amount ( P _out ) is generated and provided to the low pass filter 204 of the preliminary switching frequency determination loop A1 and the high pass filter 207 of the voltage ripple suppression loop A2. The output amount filtered through the low pass filter 204 is applied to the power / frequency function block 203 and the preliminary switching frequency f _ff is determined based on a predetermined function value.

Power / frequency function block 203 increases the output quantity to be applied from the low-pass filter 204 and increasing the spare switching frequency (f _ff), if yield is decreased to control the frequency to reduce the pre-switching frequency (f _ff) .

Therefore, as shown in Fig. 3, as a result of the operation for obtaining a stable output voltage with respect to the load change on the output side, the relationship between the preliminary switching frequency f _ff of the required switch and the output power P _out is determined by the output power. It can be seen that the preliminary switching frequency f _ff changes almost linearly with the change in (P _out ).

Referring back to FIG. 2, the high pass filter 207 included in the voltage ripple suppression loop A2 performs high pass filtering on the output load input from the output load calculator 208 to extract a desired ripple power signal. The cutoff frequency of the high pass filter 207 is set so as to extract a ripple in a predetermined frequency band, for example, a ripple power signal of 360 kHz. The ripple gain calculator 206 then multiplies the ripple power signal passing through the high pass filter 207 with an appropriate gain to determine a frequency f _comp representing a small variable amount of the final switching frequency F _sw .

Finally, as described above, the PI control loop A3 is for controlling the output voltage in order to ensure regulation in the transient and normal characteristics of the DC voltage. In detail, first, the desired value of the DC voltage V _DC passing through the low pass filter 209 and the ideal DC output voltage, that is, the voltage V ^* _DC , is applied to the subtractor 203 to obtain an error signal. Here, the desired voltage is an ideal direct current voltage required by the load system of the rectifier and represents a voltage without ripple voltage. Then, when an error signal is provided to the PI controller 201, the PI controller 201 makes the error zero through integration control if the steady state error for the input is a nonzero constant. Therefore, the output frequency f _volt of the PI controller 201 maintains a large value in the transient state but converges to almost zero in the normal state.

The output frequencies f _ff , f _comp , f _volt of each of the three control loops A1, A2, A3 according to the present invention are applied to the adder 205 and added, and the added frequency is a pulse frequency modulator ( PFM) at PFM 210 to obtain the final switching frequency F _sw . The final switching frequency F _sw obtained according to the present invention is applied to the switch S ₁ shown in FIG. 1 to vary the switching frequency of the switch S ₁ , thereby reducing the low frequency ripple voltage component.

4 shows a case in which the output frequency f _volt of the PI controller is negligibly small in a steady state, so that the final switching frequency F _sw is composed only of the preliminary switching frequency f _ff and the small variable frequency f _comp . It is a figure for explaining the determination process of a final switching frequency. The graph ① shows a process in which the preliminary switching frequency f _ff is determined by the output load with the ripple component removed from the output load. On the other hand, the process of determining the micro variable frequency (f _comp ) by the ripple component of the output load is shown in the graph (3) → (2). As shown, the final switching frequency F _sw decreases in the portion where the ripple power waveform is positive while increases in the portion where the waveform is negative. The graph ① of FIG. 4 is the same as the relationship between the output power P _out and the preliminary switching frequency f _ff shown in FIG. 3, and the graph ② is the upper limit of the graph ① in order to realize negative gain. The graph (3) shows a low frequency ripple power component extracted through the high pass filter (207). Here, the slope of graph ② can be adjusted to an appropriate size in order to effectively reduce the voltage ripple.

Figure 5 shows the ripple magnitude of the output voltage before and after applying the new abatement method of the present invention based on 0.08 seconds. As shown, when the DC ripple voltage reduction algorithm of the present invention is not operated at a time within 0.08 seconds, the ripple magnitude of the output voltage is not reduced, and after 0.08 seconds, the new DC ripple voltage reduction control of the present invention is performed. According to the method, the output voltage ripple characteristics with reduced ripple are also shown.

Accordingly, it can be seen that when the new low frequency ripple voltage reduction method of the present invention is applied, the low frequency ripple voltage according to the input voltage is significantly reduced compared to the case where the ripple voltage reduction method is not applied.

6 illustrates input voltage and input current waveforms at the three-phase input stage of the three-phase step-down diode rectifier when the ripple voltage reduction method of the present invention is used. As shown, it can be seen that a power factor correction of almost perfect power factor 1 is achieved.

The above embodiments are described by way of example only, and the present invention is not limited to the above embodiments, and various modifications or substitutions may be easily made by those skilled in the art without departing from the scope of the present invention.

Therefore, according to the low frequency ripple voltage reduction device and method for a three-phase step-down diode rectifier of the present invention, it is possible to ideally improve the input characteristics such as the input current of the rectifier and the input power factor of the unit power factor, and to significantly reduce the low frequency output voltage ripple. As a result, the output characteristics of the three-phase step-down diode rectifier can be greatly improved.

Claims (17)

In the low frequency ripple voltage reduction device of a three-phase step-down diode rectifier, First frequency generating means for using the direct current voltage and current from said rectifier to preliminarily determine a switching frequency and obtain a frequency representing a microvariable of the final switching frequency; Second frequency generating means for generating a frequency for controlling the output voltage of the rectifier on the basis of a desired voltage including an ripple voltage as an ideal direct current voltage required by the load system of the rectifier and an output direct current voltage from the rectifier; , A three-phase step-down diode comprising a third frequency generating means for modulating a final switching frequency obtained by combining the frequencies generated by the first and second frequency generating means and providing it to the rectifier to vary the previous final switching frequency. Low frequency ripple voltage reduction device for rectifier. Means for filtering a direct current voltage from the rectifier; And a means for calculating an output load amount based on the filtered voltage and the direct current according to the direct current voltage and providing the output load to the first frequency generating means. The method of claim 1, Low frequency ripple voltage reduction device for a three-phase step-down diode rectifier is performed by the pulse frequency modulator in the third frequency generating means. The method of claim 2, The first frequency generating means, A low pass filter for filtering the output load; And a means for determining the preliminary switching frequency according to the output load amount so as to obtain a constant output voltage even with a load change of the output terminal of the rectifier. The method of claim 4, wherein The first frequency generating means, A high pass filter for filtering the output load and extracting a ripple power signal having a predetermined frequency; And a means for determining a microvariable value of the final switching frequency by multiplying the extracted ripple power signal of the predetermined frequency by the predetermined gain. The method of claim 5, A low frequency ripple voltage reduction device for a three-phase step-down diode rectifier having a cutoff frequency of the high pass filter is 360 Hz. The method of claim 4, wherein And the preliminary switching frequency determining means uses a function to determine the preliminary switching frequency in accordance with the output load. The method of claim 7, wherein The function for determining the preliminary switching frequency according to the output load amount is to maintain the output voltage of the rectifier constant, so that the preliminary switching frequency increases when the output load amount increases, and the preliminary switching frequency when the output load amount decreases. Low-frequency ripple voltage reduction device for three-phase step-down diode rectifier is also reduced. In the method for reducing the low frequency ripple voltage output from the three-phase step-down diode rectifier, A first frequency generation step of preliminarily determining a switching frequency and using the direct current voltage and current from the rectifier to obtain a frequency representing a microvariable of the final switching frequency; A second frequency generating step of generating a frequency for controlling the output voltage on the basis of a desired voltage having no ripple voltage as an ideal DC voltage required by the load system of the rectifier and a DC voltage from the rectifier; And a third frequency generating step of modulating a final switching frequency obtained by combining the frequencies generated by the first and second frequency generating means and providing the rectifier to the rectifier to vary the previous final switching frequency. Low frequency ripple voltage reduction method for rectifier. Filtering the DC voltage from the rectifier; And calculating the output load based on the filtered voltage and the DC current according to the DC voltage, and providing the output load to the first frequency generating means. The method of claim 9, Low frequency ripple voltage reduction method for a three-phase step-down diode rectifier in the third frequency generation step is performed by a pulse frequency modulator. The method of claim 9, The first frequency generating step, Low pass filtering the output load; And determining the preliminary switching frequency according to the output load amount so as to obtain a constant output voltage even with a load change of the output terminal of the rectifier. The method of claim 12, The first frequency generating step, A high pass filtering step of extracting a ripple power signal having a predetermined frequency by filtering the output load; And multiplying the extracted ripple power signal of the predetermined frequency by a predetermined gain to determine a microvariable value of the final switching frequency. The method of claim 9, The second frequency generation step, Obtaining a difference value between the desired voltage and an output voltage from the low pass filter; And controlling the difference value in order to ensure regulation in the transient state and the normal characteristic of the DC voltage. The method of claim 13, A low frequency ripple voltage reduction method for a three-phase step-down diode rectifier having a cutoff frequency of 360 Hz in the high pass filtering step. The method of claim 12, The determining of the preliminary switching frequency is a low frequency ripple voltage reduction method for a three-phase step-down diode rectifier using a function for determining the preliminary switching frequency according to the output load. The method of claim 16, The function for determining the preliminary switching frequency according to the output load amount is to maintain the output voltage of the rectifier constant, so that the preliminary switching frequency increases when the output load amount increases, and the preliminary switching frequency when the output load amount decreases. A low frequency ripple voltage reduction method for a three-phase step-down diode rectifier, which is also reduced.