KR20080109543A - Power converter system - Google Patents

Abstract

A power source converter system is provided to reduce harmonic as the number of diode stack is not increased and the pulse number of the power converter is increased. A power source converter system(100) produces the output voltage of the direct current by rectifying 3 phase input voltage of a alternating current. The power source converter system comprises a transformer(10), a first rectifier, a second rectifier, a pulse number transforming unit(40) and a zero phase current cut-off section(50). The transformer converts the input voltage into a first output voltage and a second output voltage. The first rectifier produces the first rectifying voltage by rectifying a first output voltage. The second rectifier produces the second rectifying voltage by rectifying the second output voltage. The pulse number transform unit produces the rectifying voltage which is greater than the first pulse number of the secondary pulse number after the first rectifying voltage and the second rectifying voltage which is the respective first pulse number are input. The zero phase current cut-off section blocks the current of the zero phase component of the first rectifying voltage and the second rectifying voltage after the first rectifying voltage and the second rectifying voltage are input.

Description

Power converter system

1 is a circuit diagram schematically showing a power converter system according to the present invention.

FIG. 2 is a diagram schematically illustrating a three-phase single winding transformer according to an embodiment of the transformer of FIG. 1.

3 is a diagram schematically illustrating a phase-reactor in an embodiment of the pulse number converter of FIG. 1.

4 is a diagram schematically illustrating an image current blocking transformer according to an embodiment of the image current blocking unit of FIG. 1.

5 is a graph schematically illustrating a 24 pulse output voltage with respect to 6 pulse rectified voltages by the power converter system of FIG. 1.

<Description of Symbols for Main Parts of Drawings>

100: power converter system, 10: transformer,

20: first diode bridge, 30: third diode bridge,

40: pulse number conversion section, 50: video current blocking section,

60: smooth part.

The present invention relates to a power converter system, and more particularly, a power converter system that can be utilized in an input power quality improvement system of a large-capacity power converter that converts AC power of several tens of KW or more into DC power or DC power into AC power. It is about.

In a power converter system that converts AC power to DC power, a diode is used to convert AC power to DC power. At this time, harmonics associated with the number of pulses of the converter are generated with respect to the input current due to the switching operation of the diode.

Harmonics are physical quantities that are integer multiples of the fundamental frequency. These harmonics are a distortion of a stable sinusoidal wave, which may cause malfunctions of various relays, malfunctions of precision electronic devices, equipment damage, and overheating.

Therefore, the Institute of Electrical and Electronics Engineers (IEEE) 519 regulates voltage and current distortion. In this case, the distortion wave may be expressed as the sum of the fundamental wave and the harmonic, and the total harmonic distortion (THD) corresponds to the ratio of the effective value of the total harmonic component to the effective value of the fundamental wave component.

On the other hand, if the number of pulses of the converter is P in a power converter system using a diode, harmonics of P × n ± 1 (n is a positive integer) are generated. Therefore, as a method of reducing harmonics, a method of inserting an additional harmonic filter into an AC power supply unit with a pulse number of 12 pulses by a diode in consideration of economical efficiency may be used. However, when the number of pulses caused by the diode is 12 pulses or more, harmonics are reduced and the capacity of the harmonic filter is reduced.

In addition, in the conventional 12 pulse converter, it is common to use a 6 pulse diode stack and additionally use a transformer. In this method, the 5th and 7th harmonics of the input power line can be eliminated, but the total current distortion (THD) is still about 14%, which is still high and cannot satisfy the IEEE 519 standard. In addition, in this method, two pairs of a diode stack and a transformer are required in order to increase the number of pulses, thereby increasing the cost and the size of the system.

It is an object of the present invention to provide a power converter system capable of reducing harmonics and lowering current distortion by increasing the number of pulses of a power converter without increasing the number of diode stacks.

The present invention includes a transformer for rectifying a three-phase input voltage of an alternating current to generate a direct current output voltage, and converting the input voltage into a first output voltage and a second output voltage; A first rectifier configured to rectify the first output voltage to generate a first rectified voltage; A second rectifier configured to rectify the second output voltage to generate a second rectified voltage; A pulse number converter configured to receive the first rectified voltage and the second rectified voltage as first pulse numbers, respectively, and generate a rectified voltage having a second pulse number greater than the first pulse number; And an image current blocking unit configured to receive the first rectified voltage and the second rectified voltage and cut off currents of the image components of the first rectified voltage and the second rectified voltage.

Preferably, the first output voltage and the second output voltage are three-phase AC voltages, and the first output voltage and the second output voltage are higher than the input voltage.

It is preferable that the transformer is a three-phase single winding transformer.

Preferably, the transformer changes the phase to advance or slow the input voltage by 15 degrees to produce the first output voltage and the second output voltage.

It is preferable that the said 1st pulse number is 6 pulses, and the said 2nd pulse number is 24 pulses.

Wherein the pulse number converter comprises: an interphase reactor having a first tab and a second tab formed between both terminals, a first diode connected to form a current path from the first tab toward the smoothing part, and from the second tab It is preferable to include a second diode connected to form a current path in the direction of the smooth portion.

Preferably, positive terminals of the output terminals of each of the first rectifying unit and the second rectifying unit are connected to both terminals of the interphase reactor, respectively.

Preferably, the magnitude of the current flowing from the first rectifier to the interphase reactor is substantially the same as the magnitude of the current flowing from the second rectifier to the interphase reactor.

The image current interrupting unit electrically disconnects the positive and negative terminals of the first isolation transformer and the output terminal of the second rectifying unit electrically blocking the positive and negative terminals of the output terminal of the first rectifying unit. And a second insulation transformer, wherein the first insulation transformer and the second insulation transformer are electrically connected to each other.

The first isolation transformer has a primary side connected to the positive terminal of the output terminal of the first rectifying section, the secondary side is connected to a negative terminal of the output terminal of the first rectifying section, and the second insulation transformer is the primary side. Preferably, the second rectifier is connected to the positive terminal of the output terminal and the secondary side is connected to the negative terminal of the output terminal of the second rectifier.

It is preferable to further include a smoothing unit for receiving the rectified voltage to generate the output voltage.

The smoothing unit may include a capacitor connected between the pulse number converting unit and the image current blocking unit.

According to the present invention, by increasing the number of pulses of the power converter without increasing the number of diode stacks, harmonics can be reduced to lower the current distortion rate.

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

1 is a circuit diagram schematically showing a power converter system according to the present invention. FIG. 2 is a diagram schematically illustrating a three-phase single winding transformer according to an embodiment of the transformer of FIG. 1.

3 is a diagram schematically illustrating a phase-reactor in an embodiment of the pulse number converter of FIG. 1. 4 is a diagram schematically illustrating an image current blocking transformer according to an embodiment of the image current blocking unit of FIG. 1.

Referring to the drawings, the power converter system 100 is to rectify the three-phase input voltage (Va, Vb, Vc) of the alternating current to generate an output voltage (Vo) of direct current, transformer 10; First rectifier 20; A second rectifier 30; A pulse number converter 40; Image current blocking unit 50; And a smoothing part 60.

Transformer 10 converts input voltages Va, Vb, and Vc into first output voltages Va1, Vb1, and Vc1 and second output voltages Va2, Vb2, and Vc2. The first rectifier 20 rectifies the first output voltages Va1, Vb1, and Vc1 to generate the first rectified voltage V1. The second rectifier 30 rectifies the second output voltages Va2, Vb2, and Vc2 to generate the second rectified voltage V2.

The pulse number converter 40 receives the first rectified voltage V1 and the second rectified voltage V2, which are first pulse numbers, respectively, and generates a rectified voltage of a second pulse number greater than the first pulse number. The image current blocking unit 50 receives the first rectified voltage V1 and the second rectified voltage V2 and cuts off currents of the image components of the first rectified voltage V1 and the second rectified voltage V2. The smoothing unit 60 receives the rectified voltage and generates an output voltage Vo.

The transformer 10 converts input voltages Va, Vb, and Vc into first output voltages Va1, Vb1, and Vc1 and second output voltages Va2, Vb2, and Vc2. At this time, the input voltage Va, Vb, Vc corresponding to the input and output of the transformer 10, the first output voltage Va1, Vb1, Vc1 and the second output voltage Va2, Vb2, Vc2 are alternating in three phases. Voltage.

That is, the transformer 10 converts phases and magnitudes of the input voltages Va, Vb, and Vc, which are three-phase alternating voltages, according to a topology as shown in FIG. 2. As shown in FIG. 2, the transformer 10 according to the present embodiment may be a three-phase single winding transformer. Accordingly, the first output voltage Va1, Vb1, Vc1 and the second output are changed by changing the phase to advance or slow the input voltage Va, Vb, Vc by 15 degrees according to the topology shown in FIG. Generate voltages Va2, Vb2, and Vc2.

In this case, the transformer 10 shown in FIG. 2 has an extended delta connection structure and is configured to supply a three-phase balanced voltage while maintaining a phase difference of 30 degrees. That is, the three-phase voltages of which the phases are changed by 15 degrees and the first output voltage Va1, Vb1, Vc1 and the second output voltage Va2, Vb2, Vc2 pass through two rectifier modules 20 and 30, respectively, and are each pulsed. Rectified voltage is made.

In addition, the transformer 10 shown in FIG. 2 is configured to be capable of stepping up and / or depressurizing the number of turns, so that the first output voltage Va1, Vb1, Vc1 and the second output voltage Va2, Vb2. , Vc2 may be higher or lower than the input voltages Va, Vb, and Vc.

For example, when the transformer 10 shown in FIG. 2 has an input line voltage Vab of 380V, the winding ratio k1: k2: k3 of the transformer 10 is set such that the output line voltage Va1b1 becomes 440V. Can be adjusted. That is, in the present invention, the boosted transformer 10 is applied, so that a stable direct current output voltage Vo of 594V can be supplied even with a low input line voltage Vab of 380V.

On the other hand, in the conventional power converter system, there is a problem in that the capacity of the transformer becomes larger than the load capacity by using a transformer of a lottery type as a transformer. However, in the power converter system 100 according to the present invention, by using an autotransformer, which is a single winding transformer, as shown in FIG. Can be as low as 30%. Therefore, the power converter system 100 according to the present invention has the effect of innovatively reducing the manufacturing cost and the size of the system.

The first rectifier 20 and the second rectifier 30 rectify the first output voltages Va1, Vb1, and Vc1 and the second output voltages Va2, Vb2, and Vc2, respectively, to form the first rectified voltage V1 and the second rectifier. 2 Generate the rectified voltage (V2). To this end, each of the first rectifier 20 and the second rectifier 30 may be a diode pulse of 6 pulses. That is, two three-phase voltages Va1, Vb1, Vc1, Va2, Vb2, and Vc2, each of which has a phase shifted by 15 degrees, pass through the first rectifying unit 20 and the second rectifying unit 30, respectively. (V1, V2) are made.

The pulse number converter 40 receives the first rectified voltage V1 and the second rectified voltage V2, which are first pulse numbers, respectively, and generates a rectified voltage of a second pulse number greater than the first pulse number. In this case, the first pulse number is 6 pulses, the second pulse number is preferably 24 pulses.

That is, the rectified voltage of 12 pulses having a phase difference of 30 degrees is generated by the first rectifying unit 20 and the second rectifying unit 30, and the pulse number converter 40 changes the number of pulses to rectify 24 pulses. Generate a voltage. To this end, the pulse number converter 40 includes an interphase reactor (IR), a first diode D1, and a second diode D2.

The interphase reactor IR is connected between the first rectifying unit 20 and the second rectifying unit 30, and a first tab T1 and a second tab T2 are formed between both terminals. At this time, both terminals are connected to positive terminals p1 and q1 of the output terminals of each of the first rectifying unit 20 and the second rectifying unit 30.

The first diode D1 is connected to form a current path from the first tab T1 toward the smooth portion 60. The second diode D2 is connected to form a current path from the second tab T2 toward the smooth portion 60.

At this time, when the first rectified voltage V1 is greater than the second rectified voltage V2, the first diode D1 is turned on, and the current I1 flowing from the first rectifier 20 to the phase reactor IR is increased. The current Io2 flowing from the second rectifier 30 to the interphase reactor IR is reduced. On the contrary, when the second rectified voltage V2 is greater than the first rectified voltage V1, the second diode D2 is turned on, and the current Io2 flowing from the second rectifier 30 to the phase reactor IR is increased. The current Io1 flowing from the first rectifier 20 to the interphase reactor IR is reduced.

That is, in the interphase reactor IR, the first diode D1 and the second diode D2 are connected to the interphase reactor IR from the first rectifier 20 by using the first tap T1 and the second tap T2. The first rectified voltage of 6 pulses having a 30 degree phase difference by automatically turning on / off the current Io1 flowing in the furnace and the current Io2 flowing from the second rectifying unit 30 to the phase reactor IR. V1 and the second rectified voltage V2 are modulated with 24 pulses.

In general, in order to operate the 12-pulse converter with 24 pulses, the first rectifying unit 20 and the second rectifying unit 30 should be balanced, and the magnitudes of the rectified output currents Io1 and Io2 should be substantially the same. To this end, in the secondary connection of the transformer 10, the first rectifying unit 20 and the second rectifying unit 30 should have the same leakage reactance.

In a typical 12-pulse Δ-Δ-Y transformer, the number of turns of the secondary connection is different so that the leakage reactance is not the same, which may lead to current imbalance. However, in the present invention, since the transformer 10 has a symmetric extended delta structure as shown in FIGS. 1 and 2, the imbalance problem caused by the asymmetry of the Δ-Y winding of the transformer in the conventional power converter system is solved. I can solve it.

In addition, in the power converter system 100 according to the present invention, an interphase reactor IR having two intermediate tabs of a first tap T1 and a second tap T2, a first rectifying part 20, and a second rectifying part By including two rectifiers of 30, since the lowest harmonic is 23rd in operation with 24 pulses, the 1st, 7, 11, 17, 19th orders are compared with the conventional power converter system operating with 6 pulses or 12 pulses. Harmonics can be removed. Therefore, in devices connected to the power converter system 100, problems such as malfunctions of various relays, malfunctions of precision electronic devices, device damage, and overheating may be reduced.

In addition, the power converter system 100 according to the present invention can reduce the current distortion (THD) to 6% or less to satisfy the IEEE 519 standard.

The image current blocking unit 50 receives the first rectified voltage V1 and the second rectified voltage V2 and cuts off currents of the image components of the first rectified voltage V1 and the second rectified voltage V2. The image current blocking unit 50 includes a first isolation transformer Ti1 and a second isolation transformer Ti2.

The first isolation transformer Ti1 electrically cuts the positive terminal and the negative terminal of the output terminal of the first rectifying unit 20. That is, the first insulation transformer Ti1 has a primary side connected to the positive terminal of the output terminal of the first rectifying unit 20, and the secondary side connected to the negative terminal of the output terminal of the first rectifying unit 20. .

The second isolation transformer Ti2 electrically cuts the positive terminal and the negative terminal of the output terminal of the second rectifying unit 30. The second insulation transformer Ti2 has a primary side connected to the positive terminal of the output terminal of the second rectifier 30, and a secondary side connected to the negative terminal of the output terminal of the second rectifier 30.

That is, the image current blocking unit 50 is electrically connected to the first isolation transformer Ti1 and the second isolation transformer Ti2, and cuts off the current of an image component having the same magnitude and phase among specific harmonics. A Zero-Sequence Blocking Transformer (ZSBT) is formed.

The transformer 10 is provided with respective input terminals a, b, and c corresponding to three phases, and each of the first output terminals a1, b1 and c1 and the second output terminal corresponding to three phases ( a2, b2, c2) are provided. The currents flowing through the first output terminals a1, b1 and c1 and the second output terminals a2, b2 and c2 contain a lot of harmonics.

In the current containing a lot of harmonics, a current of an image component having the same magnitude and phase among specific harmonics is generated. Due to the current of the image component, an error may occur when the first rectifier 20 and the second rectifier 30 operate independently.

To prevent this, the image current blocking unit 50 may insert an image current blocking transformer (ZSBT) to cut off the current of the image component so that two completely independent modules such as an isolation transformer may be normally operated.

One terminal of the output terminal is connected to the pulse number converter 40, the other terminal is connected to the image current blocking unit 50, and a smoothing unit 60 corresponding to the capacitor Co is provided between the terminals. Is inserted. Accordingly, the output voltage Vo is converted into 24 pulses through the pulse number converter 40 and the outputs from the first rectifier 20 and the second rectifier 30 are converted into an image through the image current cutoff unit 50. The current of the component is cut off and output through the output terminal.

The output voltage Vo receives a rectified voltage and generates and outputs a DC voltage smoothed by the capacitor Co of the smoothing unit 60. In this case, the capacitor Co is connected between the pulse number converter 40 and the image current blocking unit 50. Here, the output terminal is connected to an alternating current (AC) motor driver through a pulse width modulation (PWM) inverter, so that a part of the driving circuit for driving the AC motor by the power converter system 100 according to the present invention is provided. Can be.

5 is a graph schematically illustrating a 24 pulse output voltage with respect to 6 pulse rectified voltages by the power converter system of FIG. 1.

Referring to the figure, an output voltage Vo of 24 pulses can be obtained with respect to an input voltage of three-phase alternating current by the power converter system (100 in FIG. 1). To this end, first, the input voltage of the three-phase alternating current is converted into six pulses of the first rectified voltage V1 and the second rectified voltage V2 through the first rectifying unit 20 and the second rectifying unit 30.

Next, the first rectified voltage V1 and the second rectified voltage V2 of 6 pulses are converted into 24 pulse rectified currents by the pulse number converter 40, and the image is captured by the associative current breaker 50. The current of the component is cut off, producing an output voltage Vo.

Since the lowest harmonic is 23rd as the 24th pulse is operated by the power converter system (100 in FIG. 1) of the present invention, 1, 7, 11, and 6 are compared with the conventional power converter system operating with 6 pulses or 12 pulses. 17th and 19th harmonics can be removed. Therefore, in devices connected to the power converter system 100, problems such as malfunctions of various relays, malfunctions of precision electronic devices, device damage, and overheating may be reduced.

In addition, the power converter system 100 according to the present invention can reduce the current distortion (THD) to 6% or less to satisfy the IEEE 519 standard. That is, by increasing the number of pulses of the power converter without increasing the number of diode stacks, harmonics can be reduced to lower the current distortion rate.

According to the power converter system according to the present invention, by increasing the number of pulses of the power converter without increasing the number of diode stacks, it is possible to reduce harmonics and lower the current distortion rate.

Although the present invention has been described with reference to one embodiment shown in the accompanying drawings, it is merely an example, and those skilled in the art may realize various modifications and equivalent other embodiments therefrom. I can understand. Accordingly, the true scope of protection of the invention should be defined only by the appended claims.

Claims (15)

By rectifying three-phase input voltage of AC to generate DC output voltage, A transformer for converting the input voltage to a first output voltage and a second output voltage; A first rectifier configured to rectify the first output voltage to generate a first rectified voltage; A second rectifier configured to rectify the second output voltage to generate a second rectified voltage; A pulse number converter configured to receive the first rectified voltage and the second rectified voltage as first pulse numbers, respectively, and generate a rectified voltage having a second pulse number greater than the first pulse number; And And a video current blocking unit configured to receive the first rectified voltage and the second rectified voltage and cut off a current of an image component of the first rectified voltage and the second rectified voltage. The method of claim 1, And the first output voltage and the second output voltage are three-phase AC voltages. The method of claim 1, And the first output voltage and the second output voltage are higher or lower than the input voltage. The method of claim 1, And the transformer is a three-phase single winding transformer. The method of claim 4, wherein A power supply system for generating the first output voltage and the second output voltage by changing a phase such that the transformer advances or slows the input voltage by 15 degrees. The method of claim 5, And the first rectified voltage and the second rectified voltage are six pulse rectified voltages, respectively. The method of claim 6, And a first pulse number of 6 pulses and a second pulse number of 24 pulses. The method of claim 1, The pulse number converter, An interphase reactor having a first tab and a second tab formed between both terminals, A first diode connected to form a current path from the first tab toward the smoothing part, and And a second diode coupled to form a current path from the second tab in the direction of the smooth portion. The method of claim 8, And a positive terminal of an output terminal of each of the first rectifying unit and the second rectifying unit is connected to both terminals of the phase-phase reactor, respectively. The method of claim 9, And a magnitude of current flowing from the first rectifier to the interphase reactor is substantially equal to a magnitude of current flowing from the second rectifier to the interphase reactor. The method of claim 1, The image current interrupting unit may electrically connect a first isolation transformer electrically blocking a positive terminal and a negative terminal of an output terminal of the first rectifying unit, and a positive terminal and a negative terminal of an output terminal of the second rectifying unit. A second isolation transformer for disconnecting, And the first isolation transformer and the second isolation transformer are electrically interconnected. The method of claim 1, The first isolation transformer has a primary side connected to the positive terminal of the output terminal of the first rectifying section, the secondary side is connected to a negative terminal of the output terminal of the first rectifying section, and the second insulation transformer is the primary side. And a secondary side of which is connected to a negative terminal of an output terminal of the second rectifying unit, and a secondary side of which is connected to a negative terminal of an output terminal of the second rectifying unit. The method of claim 1, And each of the first and second rectifiers comprises a diode bridge. The method of claim 1, And a smoothing unit configured to receive the rectified voltage and generate the output voltage. The method of claim 14, And a smoothing unit connected to the pulse number converting unit and the image current blocking unit.

Images