KR102046920B1 - Apparattus for monitoring of power system - Google Patents

Abstract

According to an embodiment of the present invention, a conversion unit for calculating the d +, q +, d-, q-4 parameters by dq conversion of the output current of the distributed power inverter or PCS (Power Conditioning System); A comparison unit comparing the four parameters with a reference parameter value to determine whether there is a change; A failure type determination unit classifying a failure type according to whether four parameters change; And a control unit for outputting a compensation command corresponding to the categorized failure type.

Description

Power system monitoring device {APPARATTUS FOR MONITORING OF POWER SYSTEM}

One embodiment of the present invention relates to a power system monitoring apparatus, and more particularly, to a power system monitoring apparatus applicable to a renewable energy source, an inverter installed for energy storage, a power conditioning system (PCS), and the like.

Converters for converting alternating current to direct current and switching inverters for direct current using alternating current technology have been used in various fields in various fields. Uninterruptible power supply that provides stable power at all times against unexpected power failures (outages and voltage / frequency fluctuations), solar inverters that convert the DC output of solar cells into alternating current, and power in light or midnight All of the PCS for ESS that is stored and then supplied when needed are products using this converter and inverter technology.

Therefore, power conversion efficiency of converters and inverters used in many fields is very important from the energy management level, and various methods for improving efficiency have been researched and developed.

In the medium / low voltage field, a two-level method using two equivalent switching elements has been mainly used for a converter converting alternating current to direct current or an inverter converting direct current to alternating current.

In the two-level method, the DC voltage is controlled to only two kinds of (+) and (-) during PWM operation, so the switching device configuration is simple and easy to control. However, there are many disadvantages due to the generation of harmonics and the high voltage stress of the switching device.

Recently, the application of multi-level power conversion technology has been studied as an issue for improving the efficiency. According to research and experiment results, the three-level method is known to be effective in improving the efficiency in the medium / low voltage field.

In developed countries (US, Europe, Japan), products using the 3-level method are already commercialized. The three-level method uses four equivalent switching elements to control the DC voltage in three ways (+), 0, and (-) during PWM operation.

Therefore, the harmonic generation and the voltage stress of the switching element are less than half by the conventional two-level method, so that the loss in the switching element and the filter circuit can be substantially reduced, thereby improving efficiency.

The three-level method can be classified into two types, a NPC (Neutral Point Clamped) method and a T-type Neutral Point Clamped (TNPC) method, depending on the configuration of the switching element.

Currently, the three-level method applied to some commercially available UPS and PCS is mainly an NPC method, but the recently proposed TNPC method is more effective in improving efficiency because it can reduce the conduction loss of the switching device.

However, since NPC and TNPC methods must control four equivalent switching elements, the switching element configuration is complicated and difficult to control.

On the other hand, the control method which is conventionally applied to the three-phase converter which converts alternating current into direct current, and the three-phase inverter which converts direct current into alternating current is vector control. In vector control, control is performed after converting three-phase voltage and current values of the ABC coordinate axis that change over time into a DQ coordinate axis rotating at the same speed as the angular velocity of the power frequency.

In the vector control, the active and reactive powers are distinguished in the coordinate transformation process, so the active power and the reactive power can be controlled independently, and since the voltage and current values become DC components that do not change with time, the steady state error of the PI controller is increased. There is an advantage that does not occur.

However, in the case of controlling a three-phase three-level converter or an inverter using a DSP (Digital Signal Processor), which is currently used for general purposes by a conventional vector control method, a PWM value comparison method according to a phase change of each phase and a control switching device Selection problem, PWM output problem for control of each equivalent 4 switching elements with 3 level operation sequence requires separate 3 phase 3 level vector controller design with complicated algorithm and addition of complex additional circuit There is.

The technical problem to be achieved by the present invention is to provide a power system monitoring device that can quickly and accurately classify the type of system failure.

According to an embodiment of the present invention, a conversion unit for calculating the d +, q +, d-, q-4 parameters by dq conversion of the output current of the distributed power inverter or PCS (Power Conditioning System); A comparison unit comparing the four parameters with a reference parameter value to determine whether there is a change; A failure type determination unit classifying a failure type according to whether four parameters change; And a control unit for outputting a compensation command corresponding to the categorized failure type.

The comparison unit may determine whether the values of Δq + and d− are 0, and determine whether the values of the d + and q− parameters are 0 and whether they are negative or positive.

The failure type determination unit may determine that the values of Δq + and q− are 0 to be in a normal state.

The failure type determination unit may determine that distortion occurs when Δq + is 0 and q− is not zero.

The failure type determination unit may determine that a disturbance occurs in phase C when the signs of q− and d + are the same, and may determine that a disturbance occurs in phase B when the signs of q− and d + are different.

The failure type determination unit may determine that phase balance has occurred when Δq + is not 0 and d + and d− are 0.

The failure type determination unit may determine that a voltage drop occurs when Δq + and d− are not 0 and d + is 0.

The failure type determination unit may determine that voltage drop and distortion occur when Δq + and d + are not zero.

The failure type determination unit may determine that a voltage drop and a disturbance occur in phase C when the signs of q− and d + are the same, and may determine that a voltage drop and a disturbance occur in phase B when the signs of q− and d + are different. .

The controller may include two PI controllers.

The apparatus may further include a dq inverse converter configured to inversely convert a control command of the controller to a three-phase signal and output the inverted signal to the inverter or the PCS.

The power system monitoring device of the present invention can quickly and accurately classify the type of system failure.

In addition, compensation control according to the failure type can be systematically performed.

1 is a diagram of a power conversion system schematic diagram according to an embodiment of the present invention,
2 is a configuration diagram of a power system monitoring apparatus according to an embodiment of the present invention;
3 and 4 are views for explaining the operation of the power system monitoring apparatus according to an embodiment of the present invention.

As the invention allows for various changes and numerous embodiments, particular embodiments will be illustrated and described in the drawings. However, this is not intended to limit the present invention to specific embodiments, it should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention.

Terms including ordinal numbers, such as second and first, may be used to describe various components, but the components are not limited by the terms. The terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the second component may be referred to as the first component, and similarly, the first component may also be referred to as the second component. The term and / or includes a combination of a plurality of related items or any item of a plurality of related items.

When a component is referred to as being "connected" or "connected" to another component, it may be directly connected to or connected to that other component, but it may be understood that other components may be present in between. Should be. On the other hand, when a component is said to be "directly connected" or "directly connected" to another component, it should be understood that there is no other component in between.

The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting of the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this application, the terms "comprise" or "have" are intended to indicate that there is a feature, number, step, operation, component, part, or combination thereof described in the specification, and one or more other features. It is to be understood that the present invention does not exclude the possibility of the presence or the addition of numbers, steps, operations, components, components, or a combination thereof.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art. Terms such as those defined in the commonly used dictionaries should be construed as having meanings consistent with the meanings in the context of the related art and shall not be construed in ideal or excessively formal meanings unless expressly defined in this application. Do not.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments will be described in detail with reference to the accompanying drawings, and the same or corresponding components will be given the same reference numerals regardless of the reference numerals, and redundant description thereof will be omitted.

1 is a diagram of a power conversion system schematic diagram according to an embodiment of the present invention.

Referring to FIG. 1, a power conversion system schematic diagram according to an embodiment of the present invention includes a distributed power supply device 10, a power system 20, and a power system monitoring device 100, and supplies power to a load (not shown). Supply system.

The distributed power supply 10 includes, for example, a photovoltaic device 11 as a first power supply source and a battery energy storage system (ESS) 12, and a three-phase inverter 13 and a PCS (Powe). Conditioning System 14.

In addition, the power system 20 includes a second power supply grid 21 and a transformer 22.

The first power supply source generates power independently of the power system, and a wind power generation device may be included in the first power supply source in addition to the solar power generation device.

The three-phase inverter 13 and the PCD 14 regulate power signals output from the first power supply to supply power to the load.

Here, the power output from the three-phase inverter 13 and the PCS 14 may be supplied to the load through a harmonic filter (not shown). The harmonic filter may be composed of, for example, a filter resistor Rf and a filter inductor Lf.

The power system monitoring apparatus 100 generates an inverter control signal for controlling the three-phase inverter 13 or the PCS 14, and applies the inverter control signal to the three-phase inverter 13 or the PCS 14. Thus, the three-phase inverter or PCS 14 supplies power to the load based on the inverter control signal. In the following embodiment of the present invention will be described based on the three-phase inverter, it is also possible to generate a control signal in the PCS 14 according to the same principle.

In this case, the inverter control signal controls the three-phase inverter 13 to output the normal current signal and the reverse phase current signal. Accordingly, the three-phase inverter 13 outputs both the normal current signal and the reverse phase current signal. .

Here, the meaning of "reverse phase" means a component that corresponds to "normal phase" and in which the order of the original voltage and the phase is reversed in the three-phase circuit. For example, if the phase of the voltage supplied to the three-phase circuit has 0 degrees, 120 degrees, and 240 degrees in the clockwise direction, the reverse phase voltage signal component is a voltage component having a phase of 0 degrees, 120 degrees and 240 degrees in the counterclockwise order. Means.

2 is a block diagram of a power system monitoring device 100 according to an embodiment of the present invention. 2, the power system monitoring apparatus 100 according to an embodiment of the present invention is the conversion unit 110, the comparison unit 120, the failure type determination unit 130, the control unit 140 and the inverse conversion unit 150 It may be configured to include).

The converter 110 may calculate d +, q +, d−, and q−4 parameters by performing dq conversion on the output current value of the inverter of the distributed power supply. For example, the converter 110 may calculate d + and q + according to Equation 1 below. In Equation 1, Vd + means d + parameter, and Vq + means q + parameter. In Equation 1, Va, Vb, and Vc denote voltages of phases, and w denotes angular velocity.

[Equation 1]

In the case of the forward dq conversion according to Equation 1, the direct current value can be obtained by measuring the angular velocity in the same direction as the three phases, while when the angular velocity is set in the opposite direction and the measurement is performed, an AC value of twice the fundamental frequency is obtained as the dq value. You can get In this case, by removing the double frequency value, the values generated by the accident can be obtained as dc values, and the reverse dq conversion information can be utilized. The converter 110 may calculate d- and q- according to, for example, Equation 2 below. In Equation 2, Vd- means a d-parameter, and Vq- means a q-parameter. In Equation 2, Va, Vb, and Vc mean voltage magnitudes for each phase, and w means angular velocity.

[Equation 2]

The comparator 120 may determine the change by comparing the four parameters calculated by the converter 110 with the reference parameter values. The reference parameter refers to d +, q +, d −, and q − values in a steady state, and may be set as shown in Equation 3 below.

[Equation 3]

The comparator 120 determines whether the values of q + and d- of the four parameters have changed, and determines whether the values of d + and q- have changed and whether the sign is negative or positive. That is, the comparator 120 determines whether the values of Δq + and d− are 0, and determines whether the values of the d + and q− parameters are 0 and whether they are negative or positive.

The failure type determination unit 130 may classify the failure type according to whether four parameters change. 3 and 4 are views for explaining the operation of the power system monitoring apparatus according to an embodiment of the present invention, Table 1 below shows the four parameters (d +, q +, d-, q-) according to an embodiment The failure types are classified according to the change and the sign.

Δq + q- d + d- normal 0 0 B leading 0 + - C leading 0 - - Trailing B 0 - + C trailing 0 + + Splay ≠ 0 - 0 0 Narrow ≠ 0 + 0 0 Voltage drop ≠ 0 0 ≠ 0 Voltage drop C leading ≠ 0 - - Voltage drop B leading ≠ 0 + - Voltage drop Trailing B ≠ 0 - + Voltage drop C trailing ≠ 0 + +

Referring to FIGS. 1 and 3 to 4 and Table 1, the failure type determination unit 130 may determine that the values of Δq + and q− are 0 to be in a normal state. The failure type determination unit 130 may determine that the system is normal without determining whether the d + or d− changes when the values of Δq + and q− are all zero.

The failure type determination unit 130 may determine that distortion occurs when Δq + is 0 and q− is not zero. The failure type determination unit 130 may determine that a disturbance occurs in phase C when the signs of q− and d + are the same, and may determine that a disturbance occurs in phase B when the signs of q− and d + are different.

More specifically, the failure type determination unit 130 determines that phase B is leading when q− is positive and d + is negative, and phase B is lagging when q− is negative and d + is positive. Can be judged. Alternatively, the failure type determination unit 130 may determine that phase C is trailing when both q- and d + are positive, and phase C trails when both q- and d + are negative.

The failure type determination unit 130 may determine that the phase balance has occurred when Δq + is not zero and d + and d− are zero.

More specifically, the failure type determination unit 130 has a phase difference of phase B and phase C exceeding 120 degrees when Δq + is not 0 and d + and d− are 0, and q− is negative. If it is determined that a phase splay has occurred, and q- is positive, it can be determined that a phase balance with a phase difference of less than 120 degrees occurs between B phase and C phase.

The failure type determination unit 130 may determine that a voltage drop occurs in any one of A phase, B phase, and C phase when Δq + and d− are not 0, and d + is 0.

The failure type determination unit 130 may determine that voltage drop and distortion occur when Δq + and d + are not zero. The failure type determination unit 130 determines that a voltage drop and a disturbance occur in phase C when the signs of q- and d + are the same, and may determine that a voltage drop and a disturbance occur in phase B when the signs of q- and d + are different. have.

More specifically, when Δq + and d + are not zero, the failure type determination unit 130 determines that a voltage drop and a phase C leading occurs when q- and d + are negative, and q- and d + are If both are positive, it can be determined that voltage drop and C-phase trailing have occurred. In addition, when Δq + and d + is not 0, the failure type determination unit 130 determines that a voltage drop and a phase B lead occurs when q− is positive and d + is negative, and q− is negative. If d + is positive, it can be determined that voltage drop and B-phase trailing have occurred.

Referring back to FIG. 2, the controller 140 may output a compensation command corresponding to the classified failure type. The controller 140 may include, for example, two PI controllers (not shown). The two PI controllers can be designed to output a compensation command for forward dq and a compensation command for reverse dq, respectively.

The inverse converter 150 may invert the control command of the controller into a three-phase signal and output the inverted signal to the inverter.

The term '~ part' used in the present embodiment refers to software or a hardware component such as a field-programmable gate array (FPGA) or an ASIC, and the '~ part' performs certain roles. However, '~' is not meant to be limited to software or hardware. '~ Unit' may be configured to reside in an addressable storage medium or may be configured to play one or more processors. Thus, as an example, '~' means components such as software components, object-oriented software components, class components, and task components, and processes, functions, properties, procedures, and the like. Subroutines, segments of program code, drivers, firmware, microcode, circuits, data, databases, data structures, tables, arrays, and variables. Functions provided within components and 'parts' may be combined into a smaller number of components and 'parts' or further separated into additional components and 'parts'. In addition, the components and '~' may be implemented to play one or more CPUs in the device or secure multimedia card.

Although described above with reference to a preferred embodiment of the present invention, those skilled in the art will be variously modified and changed within the scope of the invention without departing from the spirit and scope of the invention described in the claims below I can understand that you can.

100: power system monitoring device
110: converter
120: comparison unit
130: failure type determination unit
140: control unit
150: inverse transform unit

Claims (11)

A conversion unit configured to perform dq conversion on an output current value of an inverter of a distributed power supply or a power conditioning system (PCS) to calculate d +, q +, d−, and q− 4 parameters according to Equation 1 below;
A comparison unit comparing the four parameters with a reference parameter value to determine whether there is a change;
A failure type determination unit classifying a failure type of the inverter or the PCS of the distributed power supply according to whether four parameters change; And
It includes a control unit for outputting a compensation command corresponding to the categorized failure type,
The comparison unit determines whether the values of Δq + and d-, which are change values of q +, are 0, and determine whether the values of the d + and q- parameters are 0 and are negative or positive,
The determining unit determines whether the values of Δq + and d- are 0, whether the values of the d + and q- parameters are 0 and whether they are negative or positive. State, C phase trailing state, phase balanced (splay or narrow) state, voltage drop state, voltage drop C phase lead state, voltage drop C phase lead state, voltage drop B phase lead state, voltage drop B phase trailing state and voltage drop Power system monitoring device to classify C-phase trailing conditions.
[Equation 1]
d + = 2/3 * (Va * sin (ωt) + Vb * sin (ωt-2π / 3) + Vc * sin (ωt + 2π / 3))
q + = 2/3 * (Va * cos (ωt) + Vb * cos (ωt-2π / 3) + Vc * cos (ωt + 2π / 3)
d- = 2/3 * (Va * sin (-ωt) + Vb * sin (-ωt-2π / 3) + Vc * sin (-ωt + 2π / 3))
q- = 2/3 * (Va * cos (-ωt) + Vb * cos (-ωt-2π / 3) + Vc * cos (-ωt + 2π / 3))
(Equation 1, Va, Vb, Vc means the voltage magnitude of each phase, ω means the angular velocity)
delete The method of claim 1,
And the failure type determination unit determines that the state is normal when all values of Δq + and q− are zero.
The method of claim 1,
The failure type determination unit Δq + is 0, q- is a non-zero power system monitoring device for determining that the distortion (distortion) has occurred.
The method of claim 4, wherein
The failure type determination unit determines that a disturbance occurs in phase C when the signs of q- and d + are the same, and determines that a disturbance occurs in phase B when the signs of q- and d + are different.
The method of claim 1,
The failure type determining unit determines that a phase balance has occurred when Δq + is not 0 and d + and d− are 0.
The method of claim 1,
The failure type determining unit determines that a voltage drop has occurred when Δq + and d− are not 0 and d + is 0.
The method of claim 1,
The failure type determining unit determines that the voltage drop and the disturbance occurs when Δq + and d + is not 0.
The method of claim 8,
The failure type determination unit determines that the voltage drop and the disturbance occurred in phase C when the signs of q- and d + are the same, and the power system determines that the voltage drop and the disturbance occurred in phase B when the signs of q- and d + are different. monitor.
The method of claim 1,
The control unit includes a power system monitoring device including two PI controller.
The method of claim 1,
And a dq inverse converting unit converting the control command of the control unit into a three-phase signal and outputting the inverse to the inverter or the PCS.

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