KR101590442B1 - Device for Detecting Aging of DC Link Capacitor in Bi-directional Hybrid Solar Power Conditioning System - Google Patents

Abstract

The present invention relates to a device for diagnosing the aging of a DC link capacitor in a bi-directional hybrid solar power conditioning system capable of preventing degradation of efficiency by diagnosing the aging of a DC link capacitor where DC current is temporarily stored. The device includes: a solar power generation unit which generates DC current from solar light; a maximum power point tracking converter which receives supply of the DC current generated by the solar power generation unit and performs maximum power point tracking (MPPT) control to track the maximum; a DC link capacitor which receives the DC current MPPT-controlled by the maximum power point tracking converter and temporarily stores the current; a bi-directional DC/AC inverter which receives the DC current stored in the DC link capacitor as input, converts the current into AC current, and outputs the AC current; an EMI filter which filters the AC current outputted by the bi-directional DC/AC inverter and supplies the filtered current to a power system or load; a battery in which the DC current generated by the solar power generation unit is stored; a battery management unit which manages the DC current stored in the battery; a bi-directional DC/DC converter which adjusts the level of the DC current outputted by the battery management unit and outputs the result; and an energy management unit which monitors and controls the maximum power point tracking converter, battery management unit, bi-directional DC/DC converter, and bi-directional DC/AC inverter and diagnoses the aging of the DC link capacitor.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a device for detecting aging of a DC link capacitor in a bidirectional hybrid photovoltaic PCS (Bi-directional Hybrid Solar Power Conditioning System)

The present invention relates to an aging diagnostic apparatus for a DC link capacitor in a bidirectional hybrid solar PCS, and more particularly, to an aging diagnosis apparatus for aging a DC link capacitor in a bidirectional hybrid solar PCS in which deterioration of conversion efficiency is prevented, Diagnostic apparatus.

In recent years, most electric load facilities have been replaced by power conversion systems that depend on power switching devices. As a result, there is a tendency that an inverter (ASD) and an uninterruptible power supply (UPS) And DC / DC converters for SMPS are widely used.

Such power conversion devices generally use aluminum electrolytic capacitors in the DC bus portion of the power converter for the purpose of voltage regulation, temporary storage of energy, and reduction of switching ripple current.

The reason why the electrolytic capacitor is used in this way is that it is relatively inexpensive and has a relatively large capacity and is capable of high breakdown voltage as compared with other capacitors.

However, since the increase in the use time of such capacitors is a major risk factor for an accident that causes the vaporization and explosion of the electrolyte due to the gradual deterioration, it is necessary to perform parameter analysis within the capacitor A fault diagnosis is required.

Methods for following the C value of the capacitor, measuring an equivalent series resistor (ESR), estimating the life of the capacitor by calculating the amount of electrolyte, and other methods for estimating the life of the capacitor core And the like.

However, most of the follow - up methods are favored by ESR follow - up methods because of the constraints of experimental setup, online implementation, and tolerance. The on-line method is becoming a major concern because the ESR follow-up technique can measure the capacitor without separating it from the system even when the power converter is in operation.

The ESR follow-up technique studies the pulsating voltage and the current component of a capacitor, passes it through a specific bandpass filter, analyzes the magnitude of each frequency component, and then follows the ESR, In this paper, we propose a method to follow the ESR by using adaptive signal processing (LMS) technique from the effective voltage and current of the capacitor.

However, the proposed techniques depend on the complex computation process and the signal processing algorithm using the DSP board, which is disadvantageous in terms of implementation and cost.

SUMMARY OF THE INVENTION The present invention provides an aging diagnostic apparatus for a DC link capacitor in a bidirectional hybrid solar PCS in which efficiency deterioration due to aging diagnosis of a DC link capacitor temporarily storing a DC current is prevented in advance It has its purpose.

According to another aspect of the present invention, there is provided an apparatus for diagnosing the aging of a DC link capacitor in a bidirectional hybrid solar PCS, comprising: a solar power generator for generating a DC current from sunlight; A DC link capacitor for receiving a DC current controlled by MPPT through the maximum power point tracking converter and temporarily storing the DC current, and a DC link capacitor A bidirectional DC / AC inverter for converting a DC current into an AC current and outputting the AC current; an EMI filter for filtering the AC current output from the DC / AC bidirectional inverter and supplying the AC current to a power system or a load; A battery for storing a generated DC current; a battery management unit for managing a DC current stored in the battery; DC bidirectional converter for controlling the level of the DC current outputted through the DC / DC converter and outputting the level of the DC current outputted through the DC / DC bidirectional converter, a DC / DC bidirectional converter and a DC / DC bidirectional inverter, And an energy management unit for diagnosing the aging of the link capacitor.

The apparatus for diagnosing the aging of DC link capacitors in bidirectional hybrid solar PCS according to the present invention has the following effects.

That is, efficiency deterioration due to the aging diagnosis of the DC link capacitor temporarily storing the DC current can be prevented in advance.

1 is a block diagram schematically showing an apparatus for diagnosing the aging of a DC link capacitor in a bidirectional hybrid solar PCS according to the present invention
FIG. 2 is a circuit diagram schematically showing an apparatus for diagnosing the aging of a DC link capacitor in a bi-directional hybrid solar PCS,
3 is a view for explaining the occurrence of efficiency deterioration due to ripple occurring in the DC link capacitor
4 is a graph showing a ripple change according to a DC link capacitor
5 is a graph showing the relationship between ESR and Vripple
FIG. 6 is a graph showing ripple change with ESR aging

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. It should be noted that the drawings denoted by the same reference numerals in the drawings denote the same reference numerals whenever possible, in other drawings.

In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear. And certain features shown in the drawings are to be enlarged or reduced or simplified for ease of explanation, and the drawings and their components are not necessarily drawn to scale. However, those skilled in the art will readily understand these details.

FIG. 1 is a block diagram schematically showing an apparatus for diagnosing the aging of a DC link capacitor in a bidirectional hybrid solar PCS according to the present invention, and FIG. 2 is a schematic diagram of a system for diagnosing aging of a DC link capacitor in a bidirectional hybrid solar PCS, Fig.

As shown in FIGS. 1 and 2, the apparatus for diagnosing the aging of a DC link capacitor in a bidirectional hybrid solar PCS according to the present invention includes a solar power generator 110 for generating a DC current from solar light, A maximum power point tracking converter 120 for performing MPPT control to follow a maximum value by receiving a DC current generated from the DC power source 110 and receiving a DC current controlled by MPPT through the maximum power point tracking converter 120 A DC / AC bidirectional inverter 140 for receiving a DC current stored in the DC link capacitor 130 and converting the DC current into an AC current and outputting the AC current, and a DC / AC bidirectional inverter An EMI filter 150 for filtering the AC current output from the photovoltaic power generation unit 140 and supplying the filtered AC current to a power system or a load; a battery 160 for storing a DC current generated from the solar power generation unit 110; DC current stored in A DC / DC bidirectional converter 180 for adjusting and outputting a level of a DC current output through the battery management unit 170, and a DC / An energy management unit EMS for monitoring and controlling the converter 120, the battery management unit 170 and the DC / DC bidirectional converter 180 and the DC / AC bidirectional inverter 140 and diagnosing the aging of the DC link capacitor 130; (Energy Management System) 190.

Meanwhile, the AC current output through the EMI filter 150 is supplied to the power system or the load, respectively. When the photovoltaic power generation unit 110 does not generate electricity and requires a power source as a load, the photovoltaic power generation unit 110 uses the DC current stored in the battery 160 and uses it.

In addition, when the DC current produced by the solar power generation unit 110 is used for the load and remains, the battery 160 is charged. If the load is not operated, the solar power generation unit 110 The generated DC current is stored in the battery 160 or sold through the power system.

Here, the solar power generation unit 110 includes a plurality of solar cells connected to receive external solar energy to produce electric energy. The solar cell can be used anywhere as long as a proper amount of sunshine is ensured , Power generation capacity and facility size are directly proportional to each other. Therefore, when a small capacity demand such as home use is used, it is possible to produce electric power by installing an electric panel with a small area on a building roof.

Such a solar cell is based on the principle of semiconductors. When a pn-junction semiconductor is irradiated with light having a certain energy level or higher, the electrons of the semiconductor are excited as a free electron capable of moving, and electrons and holes pair is generated. The generated electrons and ions move to the electrode located on the opposite side to generate electromotive force.

The solar cell is a silicon solar cell in which a p-type semiconductor is formed by doping an impurity (B) on a silicon substrate and then doping another impurity (P) thereon to convert a part of the layer into an n- Lt; / RTI >

The solar cell may be a thin film solar cell or a CIGS solar cell. The CIGS solar cell may include copper (Cu), indium (In), germanium (Ge) , And CIGS compound semiconductors including selenium (Se).

Since the semiconductor contains three or four elements, the width of the bandgap can be controlled by controlling the content of the element, thereby increasing the energy conversion efficiency. Occasionally, selenium (Se) is replaced with sulfur (S) or selenium (Se) with sulfur (S).

The maximum power point tracking converter 120 receives the DC current generated by the solar power generator 110 and adjusts the level of the DC signal. In one embodiment, the maximum power point tracking converter 120 may include a flyback converter circuit and may convert an input DC signal having a high voltage level of several hundreds V or more to a low voltage level.

When the maximum power point tracking converter 120 operates, the internal resistance of the battery 160 and the DC link capacitor 130 are electrically connected. The converter may include an inductor, a switching FET, and an input capacitor, which is a DC link capacitor 130, and an output capacitor. These converters serve to improve rectification and control characteristics by using capacitors on the input and output.

The DC / DC bidirectional converter 180 may convert a DC current within a certain range when the DC current output from the battery 160 is not constant. In one embodiment, the DC / DC bidirectional converter 180 may include a flyback converter circuit and may convert an input DC signal having a high voltage level of several hundreds V or more to a low voltage level.

The DC / AC bidirectional inverter 140 includes bridge circuits each of which is connected in parallel to the DC link capacitor 130 and includes four switching elements. The switching elements are switching elements such as MOSFETs (Metal Oxide Semiconductor Field Effect Transistor), IGBT (Insulated Gate Bipolar Transistor), and the like. The switching elements are turned on according to driving signals, - Turned on or off.

And the duty ratio of the driving signal switching elements. The free-wheeling elements may be connected to the respective switching elements. Freewheeling elements are connected in parallel to the switching elements, respectively, to form current paths when turned off by switching to consume the residual current.

Also, although not shown in detail, the control unit (not shown) of the power conversion device is connected to the connection portion of the gate electrode of the IGBT switching device of the switching unit. The control unit controls the switching operation of the switching unit to control the size and shape of the output voltage of the load.

The switching elements in the DC / AC bidirectional inverter 140 are turned on / off based on an inverter switching control signal from a controller (not shown). As a result, AC power having a predetermined frequency is output. Preferably, it has a frequency (approximately 60 Hz or 50 Hz) that is equal to the alternating frequency of the grid.

The EMI filter 150 performs low pass filtering to smooth the AC power output from the DC / AC bidirectional inverter 140. To this end, in the figure, an inductor is exemplified, but various examples are possible.

The output signal of the maximum power point tracking converter 120 is input to the DC / AC bidirectional inverter 140 via the DC link capacitor 130. The DC / AC bidirectional inverter 140 can convert a DC signal whose level is adjusted by the maximum power point tracking converter 120 into an AC synchronized with the commercial power system.

Meanwhile, an EMI filter 150 may be connected to an output terminal of the DC / AC bidirectional inverter 140. The EMI filter 150 may include a capacitor and an inductor. The high-frequency current delivered to the secondary side of the transformer of the flyback converter circuit included in the maximum power offset converter 120 may be a frequency It plays a role of smoothing with low frequency (50 ~ 60Hz) current.

As described above, the maximum output point tracking converter 120 converts the DC input signal transmitted through the input stage capacitor from the solar cell module to a DC output signal of a relatively low level and outputs the DC output signal. At this time, the maximum power magnitude (maximum power point) of the signal generated from the solar cell module and the conditions for generating the maximum power vary depending on the environment such as the temperature and the solar radiation amount of the periphery where the solar cell module operates.

The battery 160 is not limited to a lithium ion battery, but may be a nickel metal hydride battery (NiMH). In addition, a separate overcharge protection circuit (not shown) may be mounted to prevent the battery 160 from over-charging.

The battery management unit 170 is for ensuring safety in addition to high efficiency charging and discharging through battery control. The battery management technique can be roughly divided into two types.

First, it can be divided into heat management control which enables equal performance of the weak battery by uniform cooling and second state of charge (SOC) control which determines the state of the battery and operates at the optimum efficiency point.

3 is a view for explaining the occurrence of efficiency deterioration due to ripple occurring in the DC link capacitor.

As shown in FIG. 3, Vripple occurs in the DC link portion by the PWM operation, and a capacitor is additionally used to reduce the Vripple generated in the DC link portion. However, since the DC link capacitor generally has poor durability, ripple occurs in the PWM operation of the IGBT, and MPPT accuracy is degraded, resulting in an overall reduction in efficiency.

4 is a graph showing ripple change according to a DC link capacitor.

As shown in FIG. 4, the capacitance is remarkably lowered according to ripple change of the capacitor.

FIG. 5 is a graph showing the relationship between ESR and Vripple. As shown in FIG. 5, it can be seen that the ripple change according to the ESR rises sharply from 0.1 OMEGA.

6 is a graph showing ripple change with ESR aging.

As shown in FIG. 6, the capacity of the capacitor deteriorates depending on the use time. When the capacitance of the capacitor starts to decrease from about 10% to about 40% to 50% or more, . In addition, regarding the ESR rise, when the value is about twice or more than the normal value and about 1.3 times or more as compared with the initial value, it is generally judged that the abnormality is started and applied to the fault diagnosis algorithm.

The aging diagnosis of the DC link capacitor 130 using the ripple value is performed in the energy managing unit 190 as shown in Equation 1 below.

Here, the follow-up of the capacitor value (Cdc) of the DC link capacitor (130) follows the equation (1) by using the value of? Vdc_link obtained when the battery (160) is charged and stores it in the energy management unit (190) every day. At this time, the energy manager 190 stores the capacitor value (Cdc) of the DC link capacitor 130 obtained in Equation (1) in a graph form.

The value of Vdc_link_avg is used as the average value of Vdc_link, and the value of Vdc_link_avg is calculated by cumulatively comparing the instantaneous values of Vdc_link for a predetermined time to calculate the difference between the maximum value and the minimum value of Vdc_link.

P _battery represents the charge capacity of the battery, K represents a proportional constant for reflecting the Vdc_link measurement error, and Wf is a constant for reflecting the system ripple effect when the battery is charged.

The maximum power point tracking converter 120, the DC / AC bidirectional inverter 140, and the DC / DC bidirectional converter 180 when the capacitor value Cdc of the tracked DC link capacitor 130 decreases by a certain percentage or more of the initial value, Resulting in a reduction in the efficiency of the apparatus. Also, since the fire risk due to the temperature rise of the DC / AC bidirectional inverter 140 increases, the energy management unit notifies the user of an alarm for replacement and inspection of the DC link capacitor 130.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention as defined in the appended claims. It will be understood that the invention may be varied and varied without departing from the scope of the invention.

110: Solar power generating part 120: Maximum power point tracking converter
130: DC link capacitor 140: DC / AC bidirectional inverter
150: EMI filter 160: Battery
170: Battery management unit 180: DC / DC bidirectional converter
190: Energy Management Department

Claims (5)

A solar photovoltaic portion for generating a DC current from sunlight;
A maximum power point tracking converter for performing MPPT control to follow a maximum value by receiving a DC current generated from the solar power generation unit;
A DC / AC bidirectional inverter for receiving a DC current stored in the DC link capacitor and converting the received DC current into an AC current and outputting the DC current;
An EMI filter for filtering the AC current output from the DC / AC bidirectional inverter and supplying the filtered AC current to a power system or a load;
A battery for storing the DC current generated from the solar power generation unit;
A battery management unit for managing a DC current stored in the battery,
A DC / DC bidirectional converter for adjusting and outputting a level of a DC current output through the battery management unit,
And an energy management unit monitoring and controlling the maximum power point tracking converter, the battery management unit, the DC / DC bidirectional converter and the DC / AC bidirectional inverter, and diagnosing the aging of the DC link capacitor,
The deterioration of the DC link capacitor detects a ripple value through a change,
Wherein the aging diagnosis of the DC link capacitor using the ripple value is performed by the energy management unit as follows: < EMI ID = 1.0 >
[Equation 1]

(Here, the follow-up of the capacitor value (Cdc) of the DC link capacitor follows the equation (1) using the value of? Vdc_link obtained when the battery is charged, and is stored in the energy management unit every day. The value of Vdc_link_avg is the average value of Vdc_link The value of DELTA Vdc_link_avg is obtained by cumulatively comparing the instantaneous value of Vdc_link for a predetermined period of time to calculate a difference between the maximum value and the minimum value of Vdc_link. The value of P _Battery represents the charge capacity of the battery, and K represents the value of Vdc_link Is a proportional constant to reflect the measurement error, and Wf is a constant to reflect the system ripple effect when charging the battery.) 2. The bidirectional hybrid solar PCS as claimed in claim 1, wherein the DC / AC bidirectional inverter comprises a bridge circuit connected in parallel to the DC link capacitor and including four switching elements. Aging diagnostic device. delete delete The apparatus of claim 1, wherein the energy management unit stores a capacitor value (Cdc) of the DC link capacitor obtained in Equation (1) in a graphical form.

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