WO2011051096A2

WO2011051096A2 - An ac-dc converter and an inverter

Info

Publication number: WO2011051096A2
Application number: PCT/EP2010/065064
Authority: WO
Inventors: Ji Long Yao; Jing KE; Ying Hua Song; Xue Zhi Wu; Yan Feng Zhao
Original assignee: Siemens AG; Siemens Corp
Current assignee: Siemens AG; Siemens Corp
Priority date: 2009-10-30
Filing date: 2010-10-08
Publication date: 2011-05-05
Anticipated expiration: 2012-04-30
Also published as: WO2011051096A3; CN102055354A; CN102055354B

Abstract

The present invention discloses an AC-DC converter comprising: a three-phase thyristor based converter, a simplified insulated gate bipolar transistor (IGBT) based full-bridge converter, and an inductor connected between them; in the driving mode, the three-phase thyristor based converter works as an AC-DC rectifier, and the simplified IGBT based full-bridge converter works as a boost chopper circuit, and controls the inductor to suppress the current harmonic of the power supply network, so as to increase the power factor; in the regeneration braking mode, the three- phase thyristor based converter feeds the regenerated energy back to the power supply system for energy recovery. The present invention also discloses an inverter. Use of said solution of the present invention can not only increase the power factor, but can also achieve energy recovery at a lower cost.

Description

An AC-DC Converter and an Inverter

Technical field

The present invention relates to electronic and circuit technology, and more particularly to an AC-DC converter and an inverter comprising the AC-DC converter.

Background art

Currently, the variable frequency and speed motor (inverter) has been widely used in various industrial fields mainly for accurate speed control or energy saving. Due to a simple structure and a relatively lower cost, a diode bridge rectifier is used for most inverters to perform the

conversion from alternating current (AC) to direct current (DC) . Figure 1 is a schematic digram illustrating the structure of a existing common inverter. As shown in Figure 1, the diode bridge rectifier is used for processing the conversion from AC to DC, and an insulated gate bipolar transistor (IGBT) based inverter is used for processing the conversion from DC to AC. However, the diode bridge rectifier has its own limitations. Firstly, it is a non-controllable device, and its inputted current (current in the power supply network) comprises significant harmonic waves (low power factor) , which bring extra reactive power and voltage stress to the power supply system; in addition, the diode bridge rectifier is a

unidirectional device, and as such, it cannot perform energy recovery during the regeneration braking process.

In order to increase the power factor, the reactor was adopted as a common solution in the prior art. Figure 2 is a schematic diagram showing the structure of a prior inverter with a reactor. As shown in Figure 2, the reactor can be connected to the DC side, so that the power factor can be increased with the intrinsic harmonic filtering function of the reactor. The method is simple to implement, but a reactor is typically larger in size, which leads to a bigger, heavier inverter and significantly increased cost. It has also been proposed in the prior art that the power factor may be increased by using an active filter (connected to the R, S and T terminals, as shown in Figure 1), and in a particular embodiment, a plurality of active power filters connected in series or in parallel may be used. This method may implement the unit power factor but also increase the cost due to the fact that the active filter costs almost the same as the inverter does.

For the regenerated energy produced during the regeneration braking process, it is common to use a braking resistor to consume the regenerated energy. Figure 3 illustrates the structure of a prior inverter with a braking resistor.

However, the braking resistor is usually larger in size, which leads to a bigger, heavier inverter and the problem of heat generation. In addition, considering energy saving, the regenerated energy may also be returned to the power supply system with the auxiliary equipment; however, this is also a high cost method. Currently, research is again focused on the IGBT based rectifier, which does its rectification work by means of pulse width modulation (PWM) . Figure 4 illustrates the structure of a prior inverter with an IGBT based rectifier. The intrinsic characteristics of the PWM rectification mode, i.e. the characteristics of bidirectional energy flow and effect of a high-frequency switch can ensure the structure shown in Figure 4 not only achieves the purpose of increasing the power factor, but also achieves energy recovery. However, the rectifier is composed of a three-phase IGBT bridge and a three-phase inductor, and needs to use a complicated control algorithm to generate the driving signal for the IGBT;

therefore, its cost can be very high. The object of the present invention is to provide an AC-DC converter, which can not only achieve the goal of increasing the power factor, but also implement energy recovery at a lower cost.

Another object of the present invention is to provide an inverter, which can not only achieve the goal of increasing the power factor, but also implement energy recovery at a lower cost.

In order to achieve these objects, the technical solution of the present invention is implemented as follows: an AC-DC converter, which comprises: a three-phase thyristor based converter, a simplified IGBT based full-bridge

converter, and an inductor connected between said three-phase thyristor based converter and said simplified IGBT based full-bridge converter; wherein: said three-phase thyristor based converter is used for working as an AC-DC rectifier when used in the driving mode, and feeding the regenerated energy back to the power supply system when in the regeneration braking mode;

said simplified IGBT based full-bridge converter is used for working as a boost chopper circuit when used in the driving mode, and working as a buck chopper circuit when in the regeneration braking mode;

said inductor is used for suppressing the current harmonic of the power supply network under the control of said simplified IGBT based full-bridge converter.

An inverter, which comprises: an AC-DC converter, a capacitor and an IGBT based inverter; said AC-DC converter comprises: a three-phase thyristor based converter, a simplified IGBT based full-bridge converter, and an inductor connected between said three-phase thyristor based converter and said simplified IGBT based full-bridge converter; wherein: said three-phase thyristor based converter is used for working as an AC-DC rectifier when used in the driving mode, and feeding the regenerated energy back to the power supply system when in the regeneration braking mode;

It can be seen clearly that in the technical solution of the present invention, in the driving mode, the three-phase thyristor based converter works as an AC-DC rectifier, and the simplified IGBT based full-bridge converter works as a boost chopper circuit, so as to control the inductor to suppress the current harmonic of the power supply network, such that the power factor is increased; in the regeneration braking mode, the three-phase thyristor based converter can be controlled to feed the regenerated energy back to the power supply system to implement energy recovery, and, at the same time, the simplified IGBT based full-bridge converter can be controlled to work as a buck chopper circuit, so as to control the inductor to suppress the current harmonic of the power supply network such that the power factor can be ensured during the energy recovery process. In addition, compared with the prior art, the AC-DC converter in said solution of the present invention is only composed of two IGBTs and a thyristor converter, hence has a lower cost.

Brief description of the Drawings

The following will give a further description of the

preferred embodiments of the present invention by referring to the drawings, so as to make those of ordinary skill in the art more clearly understand the abovementioned and other features and benefits of the present invention, and in the drawings :

Figure 1 is a schematic diagram showing the structure of a prior common inverter;

Figure 2 is a schematic diagram showing the structure of a prior inverter with a reactor;

Figure 3 is a schematic diagram showing the structure of a prior inverter with a braking resistor;

Figure 4 is a schematic diagram showing the structure of a prior inverter with an IGBT based rectifier;

Figure 5 is a schematic diagram showing the structure of the inverter comprising said AC-DC converter of the present invention ;

Figure 6 is a schematic diagram illustrating the way in which the AC-DC converter shown in Figure 5 works in the driving mode ;

Figure 7 is a schematic diagram illustrating the way in which the AC-DC converter shown in Figure 5 works in the

regeneration braking mode;

Figure 8 shows schematic diagrams of the current waveform and frequency spectrum of the power supply network after using the prior inverter with a diode bridge rectifier; wherein, Figure 8 (A) is the schematic diagram of the current

waveform, and Figure 8 (B) is the schematic diagram of the frequency spectrum;

Figure 9 shows the schematic diagrams of the current waveform and frequency spectrum of the power supply network after using the prior inverter with a reactor; wherein, Figure 9 (A) is the schematic diagram of the current waveform, and Figure 9 (B) is the schematic diagram of the frequency spectrum;

Figure 10 shows the schematic diagrams of the current waveform and frequency spectrum of the power supply network after using the inverter comprising said AC-DC converter of the present invention; wherein, Figure 10 (A) is the

schematic diagram of the current waveform, and Figure 10 (B) is the schematic diagram of the frequency spectrum; Figure 11 is a schematic diagram showing the simulation results after using said AC-DC converter of the present invention in the regeneration braking mode; wherein, Figure 11 (A) is the schematic diagram of the voltage waveform of the power supply network, and Figure 11 (B) is the schematic diagram of the current waveform of the power supply network.

Exemplary Embodiments The present invention proposes a completely new AC-DC

converter structure to address the problems in the prior art, and is a low-cost solution that can increase the power factor while having the energy recovery function. In order to make the technical solution and benefits of the present invention clearer, the following will further explain the present invention in combination with the drawings and embodiments. It should be understood that the embodiments described herein are used only for explaining rather than limiting the present invention.

Figure 5 is a schematic diagram illustrating the structure of the inverter comprising said AC-DC converter of the present invention. As shown in Figure 5, the inverter is mainly composed of an AC-DC converter, a capacitor and an IGBT based inverter, wherein the functions of the capacitor and the IGBT based inverter are the same as those used in prior art, hence will not be further described herein. The AC-DC converter mainly comprises: a three-phase thyristor based converter 51, a simplified IGBT based full-bridge converter 52, and an inductor 53 connected between the three- phase thyristor based converter 51 and the simplified IGBT based full-bridge converter 52.

Since the full-bridge converter is composed of 4 IGBTs, and only 2 IGBTs are needed in the present embodiment, i.e., the IGBT 522 and the IGBT 524, the full-bridge converter shown in Figure 5 can be called a simplified IGBT based full-bridge converter. It can be seen that, the simplified IGBT based full-bridge converter also comprises two bridge arms but, compared with the traditional full-bridge converter, each bridge arm has an IGBT replaced by a rectifier diode 521 or 523. The two output terminals of the three-phase thyristor based converter 51 are respectively connected with the two bridge arms. It should also be noted that Figure 5 is used only for illustration purposes, and in actual applications, the inductor 53 can be either connected to the output

terminal of the three-phase thyristor based converter 51 as shown in Figure 5, or connected to another output terminal, or connected to both output terminals. The three-phase thyristor based converter 51 works as an AC- DC rectifier when used in the driving mode, and feeds the regenerated energy back to the power supply system when in the regeneration braking mode. The simplified IGBT based full-bridge converter 52 works as a boost chopper circuit when used in the driving mode, and works as a buck chopper circuit when in the regeneration braking mode. The inductor 53 suppresses the current harmonic of the power supply network under the control of the simplified IGBT based full-bridge converter 52.

For convenience, the three-phase thyristor based converter 51 and the simplified IGBT based full-bridge converter 52 are hereafter referred to as the thyristor converter 51 and the full-bridge converter 52.

The following will give a further description of said

solution of the present invention in combination with

specific drawings: Figure 6 is a schematic diagram showing the way in which the AC-DC converter shown in Figure 5 works in the driving mode. To simplify the drawing, the designations of the components are omitted in Figure 6, and this is the same for Figure 7 that follows.

In the driving mode, the energy is delivered from the power supply system to the electric motor, and the thyristor converter 51 is caused to work as an AC-DC rectifier by controlling the conduction angle of the thyristor converter 51.

At this point, the full-bridge converter 52 works as a boost chopper circuit, that is, it works as a DC-DC chopper converter. In particular, the IGBT 524 is controlled to the cut-off state, and the current flow direction is switched between path 1 and path 2 as shown in Figure 6 by controlling the IGBT 522 to be in conducting or cut-off state, i.e. the cut-off state corresponds to the path 1, and the conducting state corresponds to the path 2, and thereby controls the current waveform for the inductor 53.

The current waveform corresponding to the inductor 53 has an optimal value, i.e. optimal waveform. In the optimal

waveform, the harmonic of the inputted current (i.e. the current harmonic of the power supply network) can be reduced to the greatest extent, that is, the harmonic of the inputted current can be the lowest, so that the power factor is increased. In actual applications, the optimal value may be achieved through controlling the IGBT 522 so as to change the current waveform for the inductor 53.

The above control modes for the thyristor converter 51, the IGBT 524 and the IGBT 522 are well known in the art, hence will not be repeated herein. Figure 7 is a schematic diagram illustrating the way in which the AC-DC converter shown in Figure 5 works in the

regeneration braking mode. In the regeneration braking mode, relying on the intrinsic characteristics of the thyristor converter 51, the

regenerated energy can be fed back to the power supply system by controlling the conduction angle of the thyristor

converter 51. Only when the thyristor converter 51 is in the reverse conducting state can it feed the regenerated energy back to the power supply system, and in order to keep the thyristor converter 51 in the reverse conducting state, the conduction angle should be limited to a certain range. At this moment, the full-bridge converter 52 will work as a buck chopper circuit. In particular, the IGBT 522 is

controlled to be in the conducting state, and the current flow direction can be switched between the path 1 and path 2 as shown in Figure 7 by controlling the IGBT 524 to be in the conducting or cut-off state, i.e., the cut-off state

corresponds to the path 1, and the conducting state

corresponds to the path 2, thereby controlling the current waveform for the inductor 53 and causing the current waveform for the inductor 53 to be in the optimal state, so as to ensure the power factor during the energy recovery process.

Similarly, the above control methods for the thyristor converter 51, IGBT 524 and IGBT 522 are well known in the art and therefore will not be repeated herein.

It can be seen that, the adoption of said solution of the present invention not only increases the power factor, but also implements energy recovery. The following will describe the advantages of said solution of the present invention when compared to the prior art in conjunction with the simulation results: 1) Increase of power factor

Figure 8 is a schematic diagram illustrating the current waveform and frequency spectrum of the power supply network after using the prior inverter with a diode bridge rectifier, wherein, Figure 8 (A) is the schematic diagram of the current waveform, and Figure 8 (B) is the schematic diagram of the frequency spectrum. It can be seen that, the peak value of the current is around 35 A, and there is a significant harmonic component observed in the current.

Figure 9 is the schematic diagram of the current waveform and frequency spectrum of the power supply network after using the prior inverter with a reactor (2mH DC reactor) , wherein Figure 9 (A) is the schematic diagram of the current

waveform, and Figure 9 (B) is the schematic diagram of the frequency spectrum. It can be seen that, compared with Figure 8, the 11^th and the 13^th (550 Hz and 650 Hz) harmonics are significantly reduced, but the 5^th and the 7^th (250 Hz and 350 Hz) harmonics are still significant; in addition, the peak value of the current is reduced to around 9A. It can be predicted that, if a reactor with a larger inductance value is adopted, the harmonics may be further reduced, but the inverter will become heavier and larger, and its cost will increase as well.

Figure 10 is a schematic diagram of the current waveform and frequency spectrum of the power supply network after using the inverter with said AC-DC converter of the present

invention, wherein Figure 10 (A) is the schematic diagram of the current waveform, and Figure 10 (B) is the schematic diagram of the frequency spectrum. It can be seen that, the efficacy has been significantly improved, that is, almost all the harmonics have been reduced. 2) Implementation of energy recovery

Figure 11 is a schematic diagram of simulation results after using said AC-DC converter of the present invention in the regeneration braking mode, wherein Figure 11 (A) is the schematic diagram of the voltage waveform of the power supply network, and Figure 11 (B) is the schematic diagram of the current waveform of the power supply network. It can be seen that, the energy is flowing from the electric motor to the electric network (because the voltage and the current are different in phase) , which means energy recovery has been achieved. In addition, it can be understood from the earlier description that the power factor during the energy recovery process can be ensured.

3) Lower cost

As shown in Figure 4, the IGBT based rectifier (works as PWM rectification) is composed of a three-phase IGBT bridge and a three-phase inductor, and in said solution of the present invention solution in Figure 5, the AC-DC converter is mainly composed of two IGBTs, an inductor and a thyristor converter. Since the cost of the thyristor is significantly lower than that of the IGBT, the overall cost of said solution of the present invention is lower than that of the IGBT based rectifier.

4) Full control of the DC voltage

For a traditional inverter with a diode bridge rectifier, the DC voltage is uncontrollable; therefore, the inverter may easily break down when the voltage on the power supply network fluctuates. For the IGBT based rectifier which in fact functions as a boost chopper circuit, the DC bus voltage is higher, which may cause damage to the IGBT when the voltage on the power supply network is relatively high.

However, for said AC-DC converter of the present invention, since there are two DC voltage control stages, i.e., when the full-bridge converter works as a boost chopper circuit, if the DC voltage has been increased, the thyristor converter can reduce the DC voltage by controlling the conduction angle, and vice versa. As a result, the DC voltage can be fully controlled, and the likelihood of malfunctions caused by the voltage fluctuation of the power supply network will be reduced. It should be noted that the above embodiments are used only for illustration, and are not intended to limit the technical solution of the present invention. Any amendments, equivalent substitutions and improvements made within the spirit and principle of the present invention should be encompassed within the protective scope of the present invention.

Claims

1. An AC-DC converter, characterized in that it comprises: a three-phase thyristor based converter (51), a simplified IGBT based full-bridge converter (52), and an inductor (53) connected between said three-phase thyristor based converter

(51) and said simplified IGBT based full-bridge converter

(52 ) ; wherein :

said three-phase thyristor based converter (51) is used for working as an AC-DC rectifier when used in the driving mode, and feeding the regenerated energy back to the power supply system when in the regeneration braking mode;

said simplified IGBT based full-bridge converter (52) is used for working as a boost chopper circuit when used in the driving mode, and working as a buck chopper circuit when in the regeneration braking mode;

said inductor (53) is used for suppressing the current harmonic of the power supply network under the control of said simplified IGBT based full-bridge converter (52).

2. The AC-DC converter as claimed in claim 1, characterized in that said simplified IGBT based full-bridge converter (52) comprises two bridge arms;

each bridge arm comprises a rectifier diode (521, 523) and an IGBT (522, 524) connected in series with said rectifier diode (521, 523) .

3. The AC-DC converter as claimed in claim 2, characterized in that two output terminals of said three-phase thyristor based converter (51) are separately connected with said two bridge arms; said inductor (53) is connected with an output terminal, or, both output terminals are connected with said inductor (53) .

4. An inverter, which comprises: an AC-DC converter, a capacitor and an IGBT based inverter; characterized in that said AC-DC converter comprises: a three-phase thyristor based converter (51), a simplified IGBT based full-bridge converter (52) , and an inductor (53) connected between said three-phase thyristor based converter (51) and said simplified IGBT based full-bridge converter (52); wherein:

5. The inverter as claimed in claim 4, characterized in that said simplified IGBT based full-bridge converter (52) comprises two bridge arms;

6. The inverter as claimed in claim 5, characterized in that two output terminals of said three-phase thyristor based converter (51) are separately connected with said two bridge arms; said inductor (53) is connected with a output terminal, or, both output terminals are connected with said inductor

(53) .