KR101735071B1

KR101735071B1 - Limited current apparatus for 3phase load

Info

Publication number: KR101735071B1
Application number: KR1020150051174A
Authority: KR
Inventors: 김명호
Original assignee: 삼성중공업 주식회사
Priority date: 2015-04-10
Filing date: 2015-04-10
Publication date: 2017-05-12
Also published as: KR20160121314A

Abstract

The present invention relates to a current control device of a three-phase load, in which a plurality of inverters are connected in parallel to one three-phase load to control the entire circulating current generated among a plurality of inverters. The three upper-side current control devices are connected in parallel with each other in a three-phase load, and a plurality of inverters, which distribute and supply three-phase control currents for controlling the load, and a control current supplied from a plurality of inverters, A plurality of coordinate converters for converting the control currents fed back from the plurality of inverters into a plurality of inverters, A cross circulating current controller for inputting a cyclic current and following a zero value by proportional integral control, and a video circulating current controller for inputting a video circulation current and performing proportional integral control to follow the zero value A three-phase load current control device comprising a circulating current controller.

Description

TECHNICAL FIELD [0001] The present invention relates to a current control apparatus for a three-

The present invention relates to a three-phase load current control device, and more particularly, to a three-phase load current control device in which a plurality of inverters are connected in parallel to one three-phase load to control the entire circulating current generated among a plurality of inverters And a control device.

Inverter is a power conversion device, and is generally used for general purpose in industry such as field of wind power generator and various electric devices. The inverter combines the AC voltage of the desired voltage and frequency with the PWM (Pulse Width Modulation) method through the switching operation of the semiconductor switch, and supplies the AC voltage to the load, thereby precisely controlling the load driving.

When a load is driven by using such an inverter, a plurality of inverters are connected in parallel to one load in order to cope with the limit of the output current capacity of the inverter and the failure of the inverter.

However, when a plurality of inverters are connected to one load in this way, a plurality of inverters may not be able to apply a balanced current to one load due to a delay in the operation of the semiconductor switch and a delay in the PWM signal , The inverter is damaged due to overloading of the specific inverter.

Therefore, development and research have been actively carried out so that a uniform current can be supplied to a load from a plurality of inverters at present. However, most of the advanced development devices and researches are controlling the current supplied to the load in the inverter, but do not provide a method for controlling the circulating current generated between the inverters.

Korean Patent Publication No. 10-2009-0096841 (2009.09.15)

SUMMARY OF THE INVENTION The present invention provides a three-phase load current control device capable of controlling the entire circulating current flowing in a current path formed between a plurality of inverters connected to a single load will be.

The problems to be solved by the present invention are not limited to the above-mentioned problems, and other problems not mentioned can be clearly understood by those skilled in the art from the following description.

According to an aspect of the present invention, there is provided a three-phase load current control apparatus including: a plurality of inverters connected in parallel to a three-phase load to supply and distribute three-phase control currents for controlling the loads, A plurality of coordinate converters for converting the control current supplied from the coordinate converter into a component of a synchronous coordinate system and feeding back the control current to the plurality of inverters; A circulation current controller for extracting an image circulation current circulating between circulating cross circulating currents and between identical phases of a plurality of different inverters, a cross circulation current controller for receiving the cross circulation current and performing proportional integral control to follow the zero value And the image circulation current is input and subjected to proportional integral control to obtain zero The current controller includes a circular image that follow.

The circulation current controller extracts the cross circulation current in proportion to the difference value between the d-axis components of the different control current and the difference between the q-axis components respectively coordinate-converted from the different coordinate transducers, It is possible to extract the image circulating current in proportion to the image circulation current.

The cross circulation current controller receives the cross circulation current and outputs a command cross voltage, and the image circulation current controller receives the image circulation current and outputs a command image circulation voltage.

Further comprising a load current controller connected to the plurality of inverters to adjust the control current on the synchronous coordinate system, and at least a part of the output value of the cross circulating current controller may be fed back to the output value of the load current controller.

And an inverse coordinate transformer that receives the output value of the load current controller and the output value of the image circulation current controller and inversely converts the output of the inverter into a component in a three-axis stationary coordinate system and provides the component to the inverter.

The three-phase load current control device according to the present invention can prevent the overload from being applied to any one of the semiconductor switches constituting the inverter by distributing the current in a balanced manner among a plurality of inverter units in one load, It is possible to prevent breakage of the semiconductor switch and further breakage of the inverter circuit.

1 is an inverter circuit to which a three-phase load current control device according to an embodiment of the present invention is connected.
Fig. 2 is a structural diagram of the current control device of the three-phase load of Fig. 1;
3 is a structural diagram of a cross-circulating current controller and a video current controller.
4 is a diagram showing a path of a cross circulating current circulating in the inverter circuit of FIG.
5 is a view showing a path of image circulation current circulating in the inverter circuit of FIG.

Brief Description of the Drawings The advantages and features of the present invention and methods of achieving them can be made clear with reference to the embodiments described below in detail with reference to the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the invention to those skilled in the art. To fully disclose the scope of invention to a person skilled in the art, and the invention is only defined by the claims. Like reference numerals refer to like elements throughout the specification.

Hereinafter, an inverter circuit to which a three-phase load current control device according to an embodiment of the present invention is connected will be described in detail with reference to FIG.

1 is an inverter circuit to which a three-phase load current control device according to an embodiment of the present invention is connected.

The inverter circuit 1 having the three-phase load current control device 50 connected in parallel is connected to a plurality of inverters 60 connected to one three-phase load 80 and controls the circulating current flowing between the inverters 60 do. Thus, the inverter circuit 1 equally distributes the same-sized current to one three-phase load 80.

For convenience of description, the inverter circuit 1 is connected in parallel to two inverters in one load, and the value multiplied by the current component is halved so as to be described. However, this is merely an example, the number of inverters connected to one load must be limited to two, the value multiplied by the current component is not limited to 1/2, and three inverters, four inverters A plurality of inverters may be connected in parallel so that the value multiplied by the current component can also be changed.

The inverter circuit 1 includes an AC power supply 10, a power inductor unit 20 connected to the AC power supply 10, a rectifying unit 30 for rectifying an AC current supplied from the power inductor unit 20, a rectifying unit 30, A capacitor unit 40 connected in parallel with the three-phase load, a three-phase load current control unit 50 including a load current controller 51 and a circulation current controller 52, and a current control unit 50 of a three- An inverter 60 for supplying a balanced current to the three-phase load 80, and the like.

Hereinafter, each component included in the inverter circuit 1 will be described in more detail.

The AC power source 10 is a three-phase power source capable of outputting voltages on a phase, b phase, and c phase having different phases, that is, phase differences of 120 degrees. So that an alternating current of a predetermined magnitude is formed. A power inductor unit 20 composed of a plurality of inductors L _s1 to L _s6 is connected to one side of the AC power source 10 to remove a noise component unnecessarily mixed with AC output from the AC power source 10, 30).

Thus, the rectifying unit 30 composed of the plurality of diodes D1 to D12 rectifies the alternating current of each phase applied from the alternating-current power supply 10 to the pulsating component and applies it to the capacitor unit 40. [

The capacitor unit 40 stores electric energy corresponding to the rectified current in the rectifying unit 30 and is discharged by supplying current to the inverter 60 connected to the current control unit 50 of the three- When discharging the charged electricity, the capacitor unit 40 converts the output of the capacitor unit 40 into a waveform close to the direct current, and outputs the waveform to the inverter 60 so that a constant voltage can be applied.

The three-phase load current control device 50 suppresses the current circulating in the current path formed between the inverters 60, that is, the circulating current, so that the currents output from the plurality of inverters 60 are equal to each other, (61) and the second inverter (62). The three-phase load current control device 50 includes a load current controller 51 for controlling the load current generated in the inverter 60, a d-axis cross circulation current controller (for controlling the cross circulating current and the image circulating current) 2), a q-axis cross-circulating current controller 52q (see Fig. 2) and an image circulation current controller 52o (see Fig. 2). The structure and operation of the three-phase load current control device 50 will be described later in detail.

The inverter 60 is connected to a single three-phase load 80 by a first inverter 61 and a second inverter 62 in parallel so that a three-phase control current required in one three- And distribute it to each other. The inverter 60 may be composed of semiconductor switches S1 to S12 for controlling the flow of the input signal, that is, a voltage or a current, and a diode connected in anti-parallel to the semiconductor switches S1 to S12.

The structure of the inverter 60 will be described in more detail by taking the first inverter 61 as an example. The first inverter 61 includes a pair of the first semiconductor switch S1 and the second semiconductor switch S2 A first power semiconductor set connected in series and having a first diode and a second diode connected in anti-parallel to each of the first semiconductor switch S1 and the second semiconductor switch S2, a third semiconductor switch S3, A second power semiconductor set in which a pair of semiconductor switches S4 are connected in series and a third diode and a fourth diode are connected in anti-parallel to each of the third semiconductor switch S3 and the fourth semiconductor switch S4, The fifth switch S 5 and the sixth semiconductor switch S 6 are connected in series and the fifth and sixth semiconductor switches S 5 and S 6 are connected in series to each other in a state where the fifth diode and the sixth diode are connected in anti- Power semiconductor sets are connected in parallel with each other.

The first semiconductor switch S1 to the sixth semiconductor switch S6 may be elements having the same electrical characteristics, and the first semiconductor switch S1 to the sixth semiconductor switch S6 may be a current path (IGBTs), GTOs (Gate Gates), and the like, which form a current path, that is, an IGBT (Insulated Gate Bipolar Mode Transistor), a MOSFET (Metal Oxide Silicon Field Effect Transistor), a Symmetric Gate Commutated Thyristor (SGCT) Turn-off thyristor).

However, in this specification, an IGBT which is simple to drive and has high efficiency at high voltage and large current will be described as an example of semiconductor switches S1 to S6.

The IGBT has a gate, an emitter and a collector terminal, and a PWM controller can be installed at a gate terminal. The PWM controller determines a signal to be inputted to the gate terminal by comparing the reference signal and the carrier signal, That is, while the semiconductor switches S1 to S12 are switched by the magnitude comparison between the reference signal and the carrier signal, the semiconductor switch (S1 counterpart S12) can output a square wave having an average value similar to the reference signal.

The second inverter 62 is formed in the same structure as the first inverter 61 described above and can output a square wave like the first inverter 61. The square wave from which the circulating current output from the first inverter 61 and the second inverter 62 is removed is transformed into a sinusoidal wave through the load inductor unit 70 and supplied to the three-phase load 80, .

Hereinafter, the structure of the three-phase load current control device will be described with reference to FIG.

Fig. 2 is a structural diagram of the current control device of the three-phase load of Fig. 1;

The three-phase load current control device 50 removes the current circulating in the current path formed between the first inverter 61 and the second inverter 62 and outputs the current to the first inverter 61 and the second inverter 62, So that a current of the same magnitude can be output.

The three-phase load current controller 50 includes a load current controller 51 for controlling the load current, a controller 60 for converting the control current supplied from the inverter 60 to a synchronous reference frame, A plurality of coordinate transducers 54a and 54b which feed back from the output side to the input side of the inverter 60 and a cross circulating current circulating between different phases of different inverters 60 from the coordinate transformed control currents by the coordinate transducers 54a and 54b

), Image circulation currents circulating between identical phases of different inverters 60

And a plurality of adders AD1 to AD14 for calculating the inputted plurality of values.

Here, the synchronous coordinate system represents a coordinate system having a d axis in which excitation flux exists, a q axis perpendicular to the d axis, and an n axis as an image divisor.

The load current controller 51 is connected to the first inverter 61 and the second inverter 62 and outputs a current for controlling the load on the synchronous coordinate system.

) And d-axis load current (

) D load current controller 51d that controls the q-axis command load current (

) And q-axis load current (

And a q load current controller 51q for controlling the q load current controller 51q.

Here, the d load current controller 51d compares the command current component that is subtracted by the first adder AD1, that is, the command load current of the d axis (

) Of the d-axis obtained from the first inverter (61) and the second inverter (62) through the synchronous coordinate system

) And the command load voltage of d axis (

Can be output. The q load current controller 51q receives the q-axis command load current (< RTI ID = 0.0 >

) And the q-axis load current (obtained through the synchronous coordinate system from the first inverter 61 and the second inverter 62

) To calculate the q-axis command load voltage (

Can be output.

At this time, the d-axis load current (

) Of the d-axis output from the first coordinate converter 54a through the tenth adder AD10

And the second current component of the d-axis output from the second coordinate converter 54b

). And the q-axis load current (

) Of the q-axis output from the first coordinate converter 54a through the eleventh adder AD11

And the second current component of the q-axis output from the second coordinate converter 54b

) Can be obtained by summing.

The circulating current controller 52 proportionally integrates the command load current and the circulating current to follow the circulating current with a zero value. The circulation current controller 52 controls the d-axis cross-

A d-cross circulating current controller 52d for controlling the q-axis cross current

A q-cross circulating current controller 52q that controls the image circulation current

And an image circulation current controller 52o for controlling the image circulation current controller 52o.

The d-cross circulating current controller 52d compares the command current subtracted by the third adder AD3 with the d-cross circulating current

) To calculate the command cross voltage (d) of the d axis

), And the q-cross circulating current controller 52q can output the command current subtracted by the fourth adder AD4 and the q-cross circulating current

) Is processed to calculate the command cross-talk voltage of the q-axis

Can be output.

At this time, the d-cross circulating current

) Of the d-axis output from the first coordinate converter 54a through the twelfth adder AD12

) Can be a value obtained by multiplying the added or subtracted current component by 1/2, and the q-cross circulating current (

) Of the q-axis output from the first coordinate converter 54a through the thirteenth adder AD13

) Multiplied by 1/2.

The voltage component output from the d-cross circulating current controller 52d is multiplied by 1/2 and then fed back to the sixth adder AD6 and the seventh adder AD7 and the voltage output from the q-cross circulating current controller 52q Component is multiplied by 1/2 and then fed back to the eighth adder AD8 and the ninth adder AD9 and can be calculated with the output value of the load current controller 51. [ That is, the voltage components output from the cross-circulation current controllers 52d and 52q can be calculated by being fed back to the output value of the load current controller 51. [

Here, the sixth adder AD6 adds the command load voltage (d) of the d-axis output from the load current controller 51

) D multiplied by d command crossing voltage (

, And the seventh adder AD7 subtracts the first command voltage (d) of the d axis

) And the d-axis second command voltage (

To be input to the first inverse coordinate transformer 53a and the second inverse coordinate transformer 53b.

The eighth adder AD8 adds the q-axis command load voltage (

) And the q command cross voltage multiplied by 1/2 (

And the ninth adder AD9 subtracts the first command voltage component of the q-axis from the first command voltage component

) And the second command voltage component of the q-axis (

To be input to the first inverse coordinate transformer 54a and the second inverse coordinate transformer 53b.

On the other hand, the image circulation current controller 52o outputs the command image circulation current (< RTI ID = 0.0 >

) And a value that is a difference value between the image circulating current components coordinate-converted in the first coordinate converter 54a and the second coordinate converter 54b, that is, the image circulation current (

) To process the command image circulation voltage (

), And the outputted command image circulation voltage (

) Is multiplied by 1/2, then input to the first inverse coordinate transformer 53a, and the command image circulation voltage (

) To -1/2, and then input to the second inverse coordinate transformer 53b.

At this time, the image circulation current (

) Of the d-axis output from the first coordinate converter 54a through the fourteenth adder AD14,

And the second image circulation current component of the d-axis output from the second coordinate converter 54b

) By a factor of 1/2.

The first inverse coordinate transformer 53a receives the output value of the sixth adder AD6, the eighth adder AD8, and the first image circulation current component (

Axis coordinate system, that is, the three-phase coordinate components of the a-axis, the b-axis, and the c-axis, to the first inverter 61 and the second inverse coordinate transformer 53b receives the inverse- AD7), the output value of the ninth adder AD9 and the first image circulation current component (

), And inversely converts the component into a component in the three-axis stationary coordinate system, and provides it to the second inverter 62.

In other words, the first inverse-coordinate transformer 53a transforms the three-phase coordinate system component, that is, the first a-phase command voltage component (

), The first b-phase command voltage component (

) And the first c-phase command voltage component (

) To the first inverter (61), and the second inverse coordinate transformer (53b) supplies the second a-phase command voltage component

), The second b-phase command voltage component (

) And the second c-phase command voltage component (

And provides it to the second inverter 62.

Thus, finally, the voltage output from the first inverter 61 is multiplied by the d-axis command crossing voltage (

), q-axis command crossing voltage (

) And command image circulation voltage (

) Is added, that is,

And the voltage output from the second inverter 62 is finally multiplied by the command load voltage of the d axis and the q axis by -1/2, and the d axis command crossing voltage (

), q-axis command crossing voltage (

) And command image circulation voltage (

) Is added, that is,

.

When the equations of voltages output from the first inverter 61 and the second inverter 62 are concatenated, the cross-circulating voltage component circulating between the first inverter 61 and the second inverter 62 and the image circulation voltage component Can be removed. In other words, the cross-circulating voltage circulating between the first inverter 61 and the second inverter 62

) And the image circulation voltage (

Are removed from each other by the voltages output from the first inverter 61 and the second inverter 62 so that the first inverter 61 and the second inverter 62 output the command load voltage value to the three- As shown in FIG.

Hereinafter, with reference to FIG. 3, the structure of the circulating current controller will be described in more detail.

(a) shows a d-cross current controller, (b) shows a q-cross current controller, and (c) shows a zero current controller.

The d-cross circulating current controller 52d, the q-cross circulating current controller 52q and the image circulating current controller 52o calculate the command cross-circulating current of the d-axis

), command cross circulating current of q axis (

) And the command image circulation current component (

), The d-axis cross-circulating current (

), the q-axis cross-circulating current (

) And the image circulation current (

) Is calculated in parallel with the proportional operation and the integral operation so that the d-axis command cross voltage

), the q-axis command cross voltage (

) And command image voltage (

). At this time, the gains Kp and Ki used in the proportional and integral calculations can be set to various values. The gains (Kp, Ki) of the respective controllers may be set to different values. Each of the voltage components outputted through the first and second coordinate

converters

53a and 53b is converted into a command voltage component of a coordinate system of three phases.

Hereinafter, the circulating current circulating through the inverter circuit will be described in detail with reference to Figs. 4 and 5. Fig. The circulation current occurs when there is a difference between the output voltages of the first inverter 61 and the second inverter 62. In FIGS. 4 and 5, A case where there is a difference in the switching pattern of the inverter will be described as an example.

FIG. 4 is a view showing a path of a cross-circulating current circulating in the inverter circuit of FIG. 1, and FIG. 5 is a diagram showing a path of a video circulating current circulating in the inverter circuit of FIG.

The circulating current indicates a current circulating in the current path between the first inverter 61 and the second inverter 62 and this circulating current is defined as the output current difference between the first inverter 61 and the second inverter 62 .

This circulating current is generated by circulating the path of the semiconductor switch for controlling the current circulation current circulating in the path of the semiconductor switch controlling the current components of different phases among the inverters 61 and 62 and the current component of the same phase And can be divided into a circulating current.

For example, first, the circular cross-currents from the point p1 of the capacitor section 40, as S1-> L _L1 shown in Figure _{4 -> L L6 -> S8-} >S10->L5->S4-> n1- gt; p1. < / RTI > In other words, the cross circulating current circulates the path of the semiconductor switch controlling the current components of different phases.

This cross-circulating current may also occur particularly when the rectifying portions of a plurality of inverters are insulated and the capacitor portions 40 connected to the respective inverters are not connected to each other.

Next, the image circulating current is the one phase of the AC power supply 10, as that is, U _L1 from Ls1->D1->p1->S1-> L L1 shown in Fig. _{5 -> L L6 -> S8-} > can be cycled to the path of n2->D12->Ls4-> U _L3 -> U _L1 . In other words, the image circulating current circulates the path of the semiconductor switch controlling the current component of the same phase.

These cross circulation currents and image circulation currents flow only between two inverters and do not affect the load. Therefore, they are preferably not present and can be suppressed through the above-described cross-circulating current controller and image current controller.

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 exemplary embodiments or constructions. It can be understood that It is therefore to be understood that the above-described embodiments are illustrative and non-restrictive in every respect.

1: inverter circuit 10: AC power source
20: power inductor section 30: rectifying section
40: capacitor section 50: current control device for three-phase load current
60: inverter 61: first inverter
62: second inverter 70: load inductor section
80: Three-phase load D: Diode
S: Semiconductor switch

Claims

A plurality of inverters connected in parallel with each other to supply a three-phase control current for controlling the load;
A plurality of coordinate transformers for coordinate-converting the control current supplied from the plurality of inverters into components of a synchronous coordinate system and feeding back the control current to the plurality of inverters;
A circulation current for circulating between different phases of a plurality of different inverters from the control current converted by the coordinate converter and a circulation current for circulating between the same phases of a plurality of different inverters is extracted Current controller;
A cross circulating current controller for receiving the cross circulating current and performing proportional integral control to follow the zero value;
And an image circulation current controller for receiving the image circulation current and performing proportional integral control to follow the zero value,
Wherein the circulation current controller extracts the cross circulation current in proportion to the difference value between the d-axis components and the q-axis components of the different control currents coordinate-converted from the different coordinate transducers, And the image circulation current is extracted in proportion to the value of the current.

delete

The image display apparatus according to claim 1, wherein the cross circulation current controller receives the cross circulation current and outputs the cross circulation current as a command cross voltage, and the image circulation current controller receives the image circulation current and outputs it as a command image circulation voltage Current control device.

The apparatus according to claim 1, further comprising: a load current controller connected to the plurality of inverters to adjust the control current on the synchronous coordinate system, wherein at least a part of the output value of the cross circulating current controller is fed back to the output value of the load current controller A current control device of a three-phase load.

5. The apparatus as claimed in claim 4, further comprising an inverse coordinate converter for receiving an output value of the load current controller and an output value of the image circulation current controller and inversely converting the component into a component in a three-axis stationary coordinate system, Control device.