KR20190007338A - Method and apparatus for resonance point following operation of a power conversion device - Google Patents

Abstract

The present invention relates to a method for a resonance frequency following operation of a power converter and an apparatus thereof for stably operating a power converter system by operating at a frequency close to the resonance point following an impedance variation of a load side at the power converter that performs the resonance frequency following operation. The method for a resonance frequency following operation of a power converter comprises the steps of: detecting a phase difference of a voltage and a current supplied to the load to perform the efficient resonance following operation at the power converter; checking whether the detected phase difference is smaller than a minimum phase difference allowable value; setting a capacitor connecting required plug if a time, for which the detected phase difference is smaller than the minimum phase difference allowable value, is longer than a predetermined time; and connecting a resonance capacitor and a first capacitor in parallel after a stop of the power converter based on a set value of the capacitor connecting required plug.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a resonant frequency-

The present disclosure relates to a method and apparatus for adaptively connecting capacitors on the power conversion system side to facilitate resonant point following movement when there is a variation in the impedance of the lower side of the power conversion system.

This disclosure is derived from a study conducted as part of the development of the intelligent energy power semiconductor IC for the 60kW class energy storage system of Korea Industrial Technology Evaluation and Management Institute. (Project number: 10048822, Title: Development of intelligent energy power semiconductor IC for 60kW class energy storage system)

When performing resonant operation by resonance of inductance and capacitance in a power converter, it is desirable that the operating frequency should be operated as close as possible to the resonance point while staying in a capacitive load operating region.

If the operating frequency exceeds the inductive operation area, which is the left side of the resonance point, the switching element performs hard switching during the current flow in the element, and the spike voltage due to the stray inductance of the bus connected to the switching element Lt; / RTI > Such a spike voltage is a risk factor that may lead to burnout of the switching element.

On the load side, the load impedance changes depending on the type of load and the operating condition. In consideration of the change in the load impedance, a resonance follow-up operation method is required to enable the resonance point following operation to be adaptively performed on the power converter side.

There is a need for a method and an apparatus for controlling the power converter system so that the power converter system operates stably at a frequency close to the resonance point in accordance with the impedance change of the load side in the power converter performing resonance following operation.

A step of detecting a phase difference between a voltage and a current supplied to a load side in a power converter performing a resonance following operation, and checking whether the detected phase difference is smaller than a minimum phase difference allowable value; Setting a capacitor connection necessity flag when the detected phase difference is less than the minimum phase difference allowable value for a predetermined time or longer; And connecting the resonance capacitor and the first capacitor in parallel after the stop of the power converter based on the set value of the capacitor connection necessity flag.

Preferably, the step of connecting the first capacitor controls the opening and closing of a first switch element connected in series with the first capacitor to connect the first capacitor.

Preferably, the step of checking whether the detected phase difference is less than the minimum phase difference allowable value comprises the step of operating in a power down mode for decreasing the output power of the power converter if the detected phase difference is smaller than the minimum phase difference allowable value And further comprising:

Preferably, the method further comprises the step of resetting the capacitor connection necessity flag after connecting the first capacitor in parallel.

According to another aspect of the present invention, there is provided a power converter apparatus for resonance-following operation, the apparatus comprising: a phase detector for detecting a phase difference between a voltage and a current supplied to a load; A first capacitor connected in parallel with the resonant capacitor; And a first switch element connected in parallel to the first capacitor, wherein the controller determines that a capacitor connection necessity flag is set when the time when the detected phase difference is less than the predetermined minimum phase difference allowable value is longer than a predetermined time And turns on the first switch element to connect the first capacitor in parallel with the resonance capacitor after the operation stop based on the set value of the capacitor connection necessity flag.

Preferably, the controller operates in a power down mode in which the output power of the power converter is reduced when the phase difference detected by the phase detector is smaller than a predetermined minimum phase difference allowable value.

Preferably, the controller resets the capacitor connection necessity flag after turning on the first switch element.

According to another aspect of the present invention, there is provided a power converter device for resonance-following operation, comprising: a phase detector for detecting a phase difference between a voltage and a current supplied to a load; a phase difference detector A first capacitor connected in parallel with the resonant capacitor; And a first switch element connected in parallel to the first capacitor, wherein the controller determines that a capacitor disconnecting necessity flag is set when the detected phase difference is longer than a predetermined maximum phase difference allowable value for a predetermined time or longer And turns off the first switch element to disconnect the first capacitor connected in parallel with the resonance capacitor after the operation stop based on the set value of the capacitor disconnection necessity flag.

Even if the load impedance varies depending on the operating conditions and the characteristics of the load through the power converter according to the above-mentioned problem solution, the capacitor connected in parallel with the resonance capacitor is adaptively turned on so that the resonance capacitor is operated in the capacitive range, Or turning off the power converter, thereby enabling the power converter to perform a stable resonance point following operation.

1 shows a power conversion system according to an embodiment of the present disclosure;
2 is a graph for explaining a resonance point following operation according to an embodiment of the present disclosure.
3 is a frequency-voltage gain curve for explaining a resonance point following operation according to one embodiment of the present disclosure.
4 is a flowchart of a method for performing a resonance point following operation by regulating switch opening / closing connected in series with a capacitor connected in parallel with a resonator according to an embodiment of the present disclosure.

Hereinafter, embodiments according to the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments described herein but may be embodied in other forms. Rather, the embodiments disclosed herein are provided so that the disclosure can be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like reference numerals designate like elements throughout the specification. It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. In the present specification, the singular form includes plural forms unless otherwise specified in the specification.

Applications for high frequency high voltage power conversion are becoming more and more diverse in the industry. Induction heaters, ozone generators, and plasma generators are power conversion applications that require high frequencies from 100kHz to 220kHz and high voltage outputs from 0 to 5,000V. The input power level for such a high-frequency high-voltage power conversion application is slightly different for each device, but an input power level of about 5 kW is often required. In the industry, there is a high demand for a high frequency high voltage power conversion application device which can operate stably even if the impedance varies greatly depending on the type of load and the environment.

Apparent power, which is the sum of active power and reactive power, is delivered to the load side of high-frequency high-voltage power conversion application equipment. Approximately 40 kVar to 80 kVar of reactive power can flow to the load side. Therefore, when the effective power of 5 kW is taken into consideration, To the load side.

In an inverter stage (or converter) for converting power from a high-frequency high-power power converter to a load, a FET is used as a switching device for high-frequency switching. In this specification, the switching element can be reversibly replaced with the term switching element.

In the above embodiment, the switching element is the FET, but any switch device for high frequency switching is possible. For example, high-frequency switching devices such as IGBTs, GTOs, and high-speed transistors can be used instead of FETs. Throughout this specification, the power converter and the power conversion system are used interchangeably in the same sense.

FIG. 1 illustrates a power conversion system 100 in accordance with one embodiment of the present disclosure.

It is assumed that the input power source 110 of the power conversion system 100 according to FIG. 1 uses a three-phase power source. Mainly considering that the three-phase 220V is a general input power source in the industry. Although a three-phase power source is used in the embodiment according to FIG. 1, it is only an embodiment. However, a single phase power source may be used as an apparatus for implementing the resonance point following operation method according to the present disclosure.

The three-phase power source from the input power source 110 is rectified by the rectification unit 120 and is established as a DC power source by the DC link 130 capacitor. The rectifying unit 120 is generally composed of six diodes 121, 122, 123, 124, 125, and 126 when the input power is three-phase. In general, the input power is rectified by four diodes as well as when the input power is single-phase.

The DC voltage established on the DC link 130 is converted into a desired high frequency high voltage output by the inverter section 140 comprising the switching elements 141, 142, 143 and 144. The capacitor 145 at the point connected to the output removes the DC component of the output.

The high-speed switching elements 141, 142, 143, and 144 of the inverter unit 140 can use a high-breakdown-voltage semiconductor device capable of high-speed switching. Of course, depending on the application, IGBT or GTO is also possible. Any other semiconductor device capable of high-speed switching can be used to implement the power converter according to the embodiment of the present disclosure.

Typically, the power conversion system 100 provides power to the controller 190 via an SMPS 180 (a switched mode power supply) that receives a DC link voltage 130. The controller controls the resonance following operation of the power conversion system 100 and controls the gate signal output of the switching elements 141, 142, 143, and 144 of the inverter unit 140. The second controller for controlling the output of the gate signals of the switching elements 141, 142, 143 and 144 of the inverter unit 140 separately from the controller 190 for controlling the resonance following operation can be controlled independently .

The output is transformed by the transformer 150, is insulated, and is transmitted to the load 170 via the resonator 160. When the input power source 110 is 220 V, the voltage established by the DC link is usually 380 V, but the magnitude of the voltage transmitted to the load side by the transformer 150 can be adjusted. The resonant circuit of the transformer 150 output stage usually includes an inductor 164 and a capacitor 162. By the resonance between the inductor and the capacitor, the power converter according to the embodiment of the present disclosure performs the resonance following operation. The resonance frequency is calculated as follows.

(수식 1)

(Equation 1)

The resonance frequency is a frequency value under the condition that the impedance due to the inductor 164 of the resonator 160 and the impedance due to the capacitor 162 become equal to each other.

The power conversion system 100 according to an embodiment of the present disclosure supplies active power to the load 170 side through the high speed switching of the switching elements 141, 142, 143, and 144 and is provided at the output terminal of the transformer 150 And supplies the reactive power to the load 170 side through resonance in the LC tank (inductor 164, L) and the capacitor 162 (C) tank of the resonance unit 160.

It is preferable to perform the LC resonance point following operation when the inverter is operated by switching the inverter unit 140 including the switching elements 141, 142, 143, and 144 in the power conversion system 100 as described above. The operation state is established. This is because an operation close to the resonance point results in an efficient operation in which the power factor is the best.

2 is a graph for explaining a resonance point following operation according to an embodiment of the present invention.

In the embodiment according to FIG. 2, the resonance frequency is about 142 KHz. In the graph, the right side (right side) on the basis of the resonance point is the capacitive operation region 201 and the left side (left side) of the resonance point is the inductive operation region 203. As described above, it is preferable that the power conversion system is operated near the resonance point so that the operation is performed near the resonance point so that the power factor is improved and the efficiency is improved.

Among them, it is preferable to operate the power conversion system in the capacitive operation region 201, for the following reason. When the load is applied to the power conversion system and the operation is performed in the inductive operation region 203 (for example, point A) beyond the resonance point, the switching elements 141, 142, 143, and 144 of the inverter unit 140 of FIG. A hard switching is performed in which a current flows in the device at the time of switching. At this time, the stray inductance Ls on the bus, which is an electric conduction path connected to the switching element of the power conversion system, and the extremely high spike voltage Vspike = Ls * di / dt, which can threaten the switching withstand voltage, . Depending on the switching speed, the magnitude of the strain inductance (Ls), and the breakdown voltage level of the switching element, some switching elements may be damaged depending on the system.

On the other hand, if the power converter is operated in the capacitive operation region 201 but is operated at a point far from the resonance point, for example, at the point B, the reactive power supplied to the load side is relatively increased. Conventional products should take measures to immerse transformers or reactors in oil in order to cool the heat generated by the load side transformer or reactor when the apparent power operation is large.

Considering the above, it can be seen that the power conversion system operates in the capacitive operation region 201 on the right side of the resonance point, and more preferable soft switching operation is performed as the operation frequency is closer to the resonance point. Therefore, the power conversion system operating frequency is maximized in the active operation region 201 by operating in the capacitive operation region 201 as close to the resonance point as possible without moving to the inductive operation region 203 to the left of the resonance point (power factor is improved ) As a result, it is necessary to control so that the efficiency of the system is maximized.

1, when the L and C values of the resonance unit 160 are fixed in the power conversion system 100, the inverter unit 140 is controlled to be operated in the capacitive operation region 201 while being close to the resonance point You can do it. However, a problem that arises in practical applications is that the capacitance component on the side of the load 170 affects the value of the resonant capacitor 162. In addition, if the impedance component on the side of the load 170 is not fixed but fluctuates according to the situation, the resonance point following operation may be further difficult.

In FIG. 1, the load 170 may be slightly different in size, but R (resistance), L (inductor), and C (capacitor) components are slightly present in the load 170. For example, there is a capacitor component in the case of a plasma generator, which is a kind of load, and the size of the capacitor component varies depending on the operating conditions during operation. When the gas passes between the plasma reactors or the temperature of the electrode plate of the plasma reactor rises, a change in the load side capacitance value occurs and the load impedance fluctuation occurs.

In the case of induction generators and other loads as well as plasma generators, the situation where the load side impedance changes frequently depends on the situation. If the load impedance varies from time to time, the user may not be able to follow the resonance follow-up operation.

If the load impedance increases, the power converter is operated by lowering the operating frequency in order to increase the output. If the operating frequency is lowered according to the higher output, the operation region can move to the inductive region, which is the region beyond the resonance point. Therefore, it is necessary to stop the system in order to avoid the operation of the power converter in the inductive region since the resonance-point-based operation frequency moves to the left side.

Referring back to FIG. 1, in the power conversion system 100, the phase detector 195 detects the phase difference of the voltage current supplied to the load 170 side. Usually a capacitive load will cause the voltage to be delayed in phase relative to the current. The phase difference between voltage and current can be found by calculating the difference between the voltage and the current passing through the zero point as a counter. A counter for detecting a phase difference usually uses a phase lock loop (PLL).

The output of the phase detector 195 may be the phase of the voltage and the current itself or may be the phase difference between the voltage and the current. The controller 190 checks whether the phase difference detected by the phase detector 195 is out of a predetermined range due to impedance variation on the load 170 side.

If the load capacitor 171 becomes larger under a certain environment or operating condition as in the above example, the resonance point is shifted by adding it to the resonance capacitor 1610. In this case, the resonance frequency becomes small, and the power conversion system 100, which originally operated in the C region of FIG. 2, deviates from the C region and deviates to the right side capacitive region 201 in the B direction. That is, the voltage is delayed more than before the current, which appears as a larger phase difference. Conversely, if the load capacitor 171 component value decreases under a specific condition, the operation frequency of the power conversion system 100, which was operating in the C region of FIG. 2, is gradually shifted to the left side of the C region 210, It comes close. As another situation, if the impedance of the load 170 increases, the operating frequency may be lowered to increase the output of the power conversion system 100, in which case the operating frequency may approach the resonance point.

If the phase difference detected by the phase detector 195 is smaller than the minimum phase difference allowable value, the power conversion system 100 operates in a power down mode for lowering the output . In this case, the operating frequency will be higher, so it will move to the right side near the resonance point. If the duration of the phase difference detected by the phase detector 195 is less than the minimum phase difference allowable value for a predetermined period of time or more, the controller 190 sets the resonance capacitor 1610 in parallel with the resonance capacitor 1610 It is determined that a capacitor connection is required. That is, it is determined that the resonance point frequency value itself needs to be lowered by increasing the capacitor value.

In one embodiment, if the duration of the phase difference detected by the phase detector 195 is less than the minimum phase difference allowable value for a predetermined period of time or longer, the controller 190 sets the capacitor connection required flag to 1 The power converter system is ready to turn on the first switch 1611 of FIG. 1 to connect the first capacitor 1621 in parallel with the resonant capacitor 1610.

In one embodiment, the power conversion system 100 checks the capacitor connection necessity flag during operation or after the operation of the power conversion system is checked, and after the operation of the power conversion system is stopped based on the value of the capacitor connection necessity flag, 1 switch 1611 is turned on to connect the first capacitor 1621 in parallel with the resonant capacitor 1610. Since the value of the resonance capacitor is now increased as a whole, the resonance frequency value becomes smaller, and therefore, the resonance point moves to the left side from the voltage gain curve in comparison with the previous operation.

3 is a frequency-voltage gain curve for explaining a resonance point following operation according to one embodiment of the present disclosure.

According to FIG. 3, the power conversion system 100 exhibits the same voltage gain curve as the first 310, and the power conversion system 100 checks the capacitor connection necessity flag immediately before the power conversion system 100 is stopped as in the previous embodiment, When the first switch 1611 is turned on and the first capacitor 1621 is connected in parallel to the resonant capacitor 1610 based on the connection required flag value, the voltage gain curve at the restart of the power conversion system 100 is 320 and And the operation is performed according to the same voltage gain curve. That is, the resonance point shifts to the left, and more stable capacitive operation can be ensured for the 150K to 160KHz region compared to the voltage gain curve of 320. The power conversion system 100 resets the capacitor connection necessity flag when the first switch 1611 is turned on and the first capacitor 1621 is connected in parallel with the resonance capacitor 1610 when the operation is stopped.

The reason for connecting the capacitors connected in parallel with the resonance capacitor 1610 after the power conversion system 100 stops operation is that when a capacitor connected in parallel with the resonance capacitor 1610 is connected during operation, This is because there is a possibility of occurrence. However, according to the present disclosure, it is also possible to connect the capacitors connected in parallel with the resonant capacitor 1610 during operation of the power conversion system 100 according to the user's selection as long as the trip is prevented.

If the duration that the re-detected phase difference becomes smaller than the minimum phase difference allowable value during the operation of the power conversion system 100 in the state where the voltage gain curve is 320 continues for a certain period of time or more, the power conversion system 100 again controls the capacitor connection The controller 190 turns on the second switch 1612 after the power conversion system 100 is stopped and connects the second capacitor 1622 with the resonant capacitor 1610 in parallel . The controller 190 resets (flag = 0) the capacitor connection necessity flag after turning on or turning on the second switch 1612.

The first and second capacitors 1621 and 1622 are connected in parallel with the resonant capacitor 1610 when the power conversion system 100 is in operation and the power conversion system 100 is restarted and operated, And the power conversion system 100 will be operated in the state of the voltage gain curve 330. [

Usually, the minimum phase difference allowable value can be selected according to the user's design selection at 5 to 15 degrees, and the predetermined time for checking whether the detected phase difference is less than the minimum phase difference allowable value lasts for a predetermined time is 1 second ~ 10 seconds depending on your design choice. Of course, this is an embodiment only, and the minimum retardation value and the predetermined time can be selected in various ways.

Conversely, if the duration during which the phase difference detected by the phase detector 195 is greater than the maximum phase difference allowable value continues for a predetermined period of time or more, the power conversion system 100 is operated in a state in which a large amount of reactive power is supplied It is necessary to release the connection of the existing second capacitor 1622 and move the resonance point to the right side. Accordingly, the controller releases the second capacitor connection by setting the capacitor disconnection necessity flag (flag '= 1) and turning off the second switch 1612 after the power conversion system 100 stops. Then, the capacitor disconnection necessity flag is reset (flag '= 0). The voltage gain curve has shifted from the 330 state to the 320 state and when the resonance point still needs to be shifted to the right side, that is, when the phase difference detected by the phase detector 195 is greater than the maximum phase difference allowable value, The first capacitor 1621 is disconnected in the same manner. As described above, the first and second capacitors may be disconnected during the operation of the power conversion system 100, but in order to ensure the safety of the entire system, the capacitors connected in parallel with the resonant capacitor are disconnected .

The maximum retardation allowable value may be a predetermined value depending on the user's selection, and may be appropriately set between about 40 to 60 degrees.

4 is a flowchart of a method for performing a resonance point following operation by regulating switch opening / closing connected in series with a capacitor connected in parallel with a resonator according to an embodiment of the present disclosure.

First, the phase detector 195 on the power converter detects the phase difference between the voltage and the current supplied to the load side (S410). The controller 190 checks whether the detected phase difference is smaller than a predetermined minimum phase difference allowable value. If it is determined that the detected phase difference is smaller than the minimum phase difference allowable value (S430), the controller 190 determines that a capacitor connection is required in parallel with the resonant capacitor and sets a capacitor connection flag flag = 1) (S440). Then, the operation of the power converter is stopped (S450). The controller 190 connects capacitors connected in parallel with the resonant capacitor (S460). Then, the controller 190 resets the capacitor connection flag (flag = 0) (S470) and restarts the power converter operation (S480). When the power converter is restarted and operated, the resonance point due to the voltage gain curve moves to the left side to enable a more stable resonance point following operation.

In the above embodiment, the capacitor is connected in parallel with the resonance capacitor at the time of stopping the power converter. However, if the requirement or condition of the power conversion system is satisfied, the detected phase difference is smaller than the minimum phase difference allowable value duration is longer than a predetermined time, it is possible to connect a capacitor connected in parallel with the resonance capacitor directly on-line during operation based on the determination.

As described above, embodiments of the present invention have been disclosed through detailed description and drawings. The terms are used only for the purpose of describing the present invention and are not used to limit the scope of the present invention described in the meaning or the claims. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. Accordingly, the true scope of the present invention should be determined by the technical idea of the appended claims.

110; Input power
120; Rectifying part
130; DC link
140; Inverter section
150; Transformer
160; Resonance portion
170; Load
180; SMPS
190; controller
195; The phase-
171; Load capacitor

Claims (8)

Detecting a phase difference between a voltage and a current supplied from the power converter to the load side;
Checking whether the detected phase difference is smaller than a minimum phase difference allowable value;
Setting a capacitor connection necessity flag when the detected phase difference is less than the minimum phase difference allowable value for a predetermined time or longer; And
And connecting the resonance capacitor and the first capacitor in parallel after the stop of the power converter based on the set value of the capacitor connection necessity flag. 2. The power converter according to claim 1, wherein the step of connecting the first capacitor controls the opening and closing of a first switch element connected in series with the first capacitor to connect the first capacitor. Way. 2. The method of claim 1, wherein the step of checking whether the detected phase difference is smaller than the minimum phase difference allowable value comprises the steps of operating in a power down mode for reducing the output power of the power converter if the detected phase difference is smaller than the minimum phase difference allowable value Wherein the resonant frequency-follower operation method of the power converter further comprises: 2. The method of claim 1, further comprising the step of resetting the capacitor connection necessity flag after connecting the first capacitor in parallel. A phase detector for detecting a phase difference between a voltage and a current supplied to the load side;
A controller for checking whether the phase difference detected by the phase detector is smaller than a predetermined minimum phase difference allowable value;
A first capacitor connected in parallel with the resonant capacitor; And
And a first switch element connected in parallel with the first capacitor,
Wherein the controller sets a capacitor connection necessity flag when the detected phase difference is less than the predetermined minimum phase difference allowable value for a predetermined time or more as a result of the check, And turns on the first switch element to connect the first capacitor in parallel with the resonant capacitor. 6. The power converter according to claim 5, wherein the controller is configured to operate in a power down mode to reduce the power converter output power when the phase difference detected by the phase detector is smaller than a predetermined minimum phase difference allowable value. 6. The power converter according to claim 5, wherein the controller resets the capacitor connection necessity flag after turning on the first switch element. A phase detector for detecting a phase difference between a voltage and a current supplied to the load side;
A controller for checking whether the phase difference detected by the phase detector is larger than a predetermined maximum phase difference allowable value;
A first capacitor connected in parallel with the resonant capacitor; And
And a first switch element connected in parallel with the first capacitor,
Wherein the controller sets a capacitor disconnecting necessity flag when the detected phase difference is greater than the predetermined maximum phase difference allowable value for a predetermined time or more as a result of the check, And turns off the first switch element to disconnect the first capacitor connected in parallel with the resonant capacitor.

Images