KR102136982B1 - Solar streetlight apparatus and method using bidrectional buck converter - Google Patents

Abstract

The present technology discloses a solar street light device and method using a bidirectional buck converter. According to a specific example of the present invention, as battery charging and lighting control are performed with energy stored in one inductor, the number of inductors can be reduced to reduce the total number of parts of the buck converter, thereby reducing the load to increase the response speed of the buck converter. Can decrease.

Description

SOLAR STREETLIGHT APPARATUS AND METHOD USING BIDRECTIONAL BUCK CONVERTER}

The present invention relates to a solar street light device and a control method using a bidirectional buck converter, and more specifically, to reduce the number of components of the bidirectional buck converter by performing battery charging and lighting with battery energy stored in one inductor. It's about technology.

Recently, due to the prevention of global warming and the ease of installation, the construction of a power grid using solar energy, the next-generation energy source, has attracted attention.

A typical system using a battery and LED lighting is a stand-alone solar LED street light system. That is, the feature of the stand-alone solar LED street light is a system that stores energy generated by the solar module in the daytime in a battery and releases energy with LED lighting at night. It can manage battery charging and power supply for driving the LED lighting. A bi-directional buck converter of a power converter is essential, and high reliability at low cost is required.

The present invention reduces the number of parts of the buck converter by reducing the number of inductors by performing battery charging and lighting control with energy stored in one inductor, thereby reducing the load, thereby improving the response speed of the buck converter by bidirectional buck The object is to provide a solar street light device and method using a converter.

The object of the present invention is not limited to the above-mentioned object, other objects and advantages of the present invention that are not mentioned can be understood by the following description, and will be more clearly understood by embodiments of the present invention. In addition, it will be readily appreciated that the objects and advantages of the present invention can be realized by means of the appended claims and combinations thereof.

The present invention provides a solar street light device using a bi-directional buck converter for charging a light output voltage of a solar panel to a battery and controlling lighting with a charged battery voltage, wherein the bi-directional buck converter uses energy stored in one inductor. It is characterized in that it is provided to perform the battery charging and lighting control.

Preferably, the bi-directional buck converter includes a battery charging circuit connected between both ends of the solar panel to charge the light output voltage of the solar panel to the battery,

The battery charging circuit,

A first main switching unit having a first diode connected in series to the output terminal of the solar panel, a second diode connected to the output terminal of the first diode, and a first switching element connected in parallel;

A resonant circuit unit comprising an inductor connected to the output terminal of the first main switching unit, a first capacitor connected to the output terminal of the inductor and the other terminal of the battery, and positioned between one end of the first main switching unit and one end of the battery; And

A charging unit located at an output terminal of the inductor and configured to include a first resistor and a battery connected in parallel with the first capacitor to charge energy stored in the inductor to the battery; And

It may include a first reflux unit for transferring the output current of the first capacitor to the inductor when a third diode is positioned at the other end of the battery and the output terminal of the first main switching to cut off the supply of the light output voltage of the solar panel. .

Preferably, the bidirectional buck converter,

Located between the front end of the inductor and the other end of the first capacitor includes a lighting circuit that is turned on or off based on the battery voltage,

The lighting circuit

A second main switching part which positions a second switching element and a fourth diode in parallel on the other end of the battery;

A DC unit connected to an output terminal of the second switching element and a front end of the inductor to charge a battery voltage;

A lighting unit connected to the DC unit in parallel to turn on or off a lighting element; And

It may be configured as a fifth diode, and may include a second reflux unit connected to the output terminal of the lighting unit and the other end of the inductor to reflux the output current of the capacitor to the inductor when the battery voltage supply is blocked.

Preferably, the bidirectional buck converter,

Further comprising a control unit for generating a first switching signal and a second switching signal for controlling the on or off of the first switching element and the second switching element,

The control unit,

An illumination reference current deriving unit for deriving an illumination reference current from the battery voltage;

A battery reference current deriving unit that derives a battery reference current based on a predetermined duty cycle, an inductor current, and a light output voltage of the solar panel; And

A switching signal for selecting one of the lighting reference current and the battery reference current based on the light output voltage, generating a first switching signal based on the selected battery reference current, and generating a second switching signal based on the selected lighting reference current It may include a generator.

Preferably, the battery reference current deriving unit,

Deriving the delivered power based on the duty cycle, the inductor current, and the light output voltage of the solar panel,

A maximum power point tracking (MPPT) algorithm is performed on the derived transfer power to derive an optical reference voltage to the light output voltage of the solar panel,

The derived reference voltage may be provided to derive a battery reference voltage by performing PI (Proportional Integral) control.

Preferably, the lighting circuit,

When the second switching element is switched to the on state by the second switching signal of the control unit to supply the battery voltage

The output current of the battery may be provided to the second capacitor via the second switching element and may be provided to light the lighting element as the output current of the second capacitor is transmitted to the second resistor and the light emitting diode.

Preferably, the lighting circuit is when the second switch element is switched to the off state based on the second switching signal of the control unit to cut off the supply of the battery voltage,

The second capacitor may include transmitting the output current of the second capacitor to the second resistor and the light emitting diode to maintain the lighting state of the lighting element and returning the output current of the second capacitor to the inductor through reflux through the fifth diode. .

Another aspect of the invention,

It includes a battery charging circuit connected between both ends of the solar panel to charge the light output voltage of the solar panel, the battery charging circuit of the first diode and the first diode connected in series to the output terminal of the solar panel A first main switching unit having a second diode connected to the output terminal and a first switching element connected in parallel; A resonant circuit unit consisting of an inductor connected to the output terminal of the one-person switching unit and a first capacitor connected to the output terminal of the inductor and the other terminal of the battery, positioned between one end of the first main switching unit and one end of the battery; A charging unit which is located in the output terminal of the inductor and which is connected in series with the first capacitor and the battery in series to charge energy stored in the inductor to the battery; And a first reflux unit that positions a third diode at the other end of the battery and the output terminal of the first main switching to transfer the output current of the first capacitor to the inductor when the supply of the solar panel's optical output voltage is blocked.

A lighting circuit positioned between the front end of the inductor and the other end of the first capacitor to be turned on or off based on a battery voltage, wherein the lighting circuit includes a second switching element and a fourth diode located in parallel at the output terminal of the battery in parallel. A second main switching unit connected; A DC unit connected to an output terminal of the second switching element and a front end of the inductor to charge a battery voltage; A lighting unit connected to the DC unit in parallel to turn on or off a lighting element; And a second reflux unit composed of a fifth diode and connected to the output terminal of the lighting unit and the other end of the inductor to reflux the output current of the capacitor to the inductor when the battery voltage supply is cut off.

Further comprising a control unit for generating a first switching signal and a second switching signal for controlling the on or off of the first switching element and the second switching element, the control unit, deriving the lighting reference current from the output voltage of the battery An illumination reference current derivation unit; A battery reference current deriving unit that derives a battery reference current based on a predetermined duty cycle, an inductor current, and a light output voltage of the solar panel; And selecting one of the lighting reference current and the battery reference current based on the light output voltage, generating a first switching signal based on the selected battery reference current, and generating a second switching signal based on the selected lighting reference current. Another feature is to include a signal generator.

In another aspect of the present invention, in a solar street light method using a bi-directional buck converter for charging a battery at daytime with a light output voltage of a solar panel and controlling lighting with a battery voltage at night, the light output of the solar panel A data receiving step of receiving voltage and current, battery voltage and current, and inductor current; A mode setting step of setting a day mode or a night mode based on a result of comparing the light output voltage of the solar panel with a predetermined threshold voltage;

When the day mode is set, the maximum power operating point tracking algorithm is performed based on the comparison result of the light output voltage, the battery voltage, and the maximum battery voltage to derive the light reference voltage, and PI control is performed on the derived light reference voltage and light output voltage To derive a battery reference current, derive a battery reference current by performing PI control based on the derived battery reference current and the battery current, generate the first switching signal with the derived battery reference current, and generate the generated first Another feature is a battery charging step of controlling the on/off of the first switching element with a switching signal to charge the light output voltage to the battery.

Preferably, when the night mode is set in the mode setting step, if the counting value of the counter does not result in a set value, a battery voltage is provided to derive an illumination reference current and generate a second switching signal based on the derived illumination reference current. 2 may further include an illumination control step of transmitting to the switching element and controlling the lighting of the lighting element with a battery voltage based on the on/off control of the second switching element.

According to the present invention having the above-described configuration, as battery charging and lighting control are performed with energy stored in one inductor, the number of inductors can be reduced to reduce the number of parts of the overall buck converter, and the load is reduced to thereby respond to the buck converter. Speed can be reduced.

The following drawings attached in this specification are intended to illustrate preferred embodiments of the present invention, and serve to further understand the technical idea of the present invention together with the detailed description of the invention described below, and thus the present invention is described in such drawings. It is not limited to interpretation.
1 is a block diagram of a buck converter according to an embodiment of the present invention.
2 is a partial PV characteristic diagram of a solar panel according to an embodiment of the present invention.
3 is a conceptual explanatory diagram of an MPPT algorithm according to an embodiment of the present invention.
4 and 5 are battery charging circuit diagrams according to an embodiment of the present invention.
6 and 7 is a lighting control circuit diagram according to an embodiment of the present invention.
8 is a flowchart for lighting control according to another embodiment of the present invention.
9 is a waveform diagram when charging a battery according to an embodiment of the present invention.
10 is a waveform diagram when discharging a battery according to an embodiment of the present invention.
11 is a comparative waveform diagram of an MPPT algorithm according to an embodiment of the present invention.

It should be noted that the technical terms used in this specification are only used to describe specific embodiments and are not intended to limit the present invention. In addition, technical terms used in this specification should be interpreted as meanings generally understood by a person having ordinary knowledge in the technical field to which the present invention belongs, unless defined otherwise. It should not be interpreted as a meaning or an excessively reduced meaning. In addition, when the technical term used in this specification is a wrong technical term that does not accurately represent the spirit of the present invention, it should be understood as being replaced by a technical term that can be correctly understood by those skilled in the art. In addition, the general terms used in the present invention should be interpreted as defined in the dictionary or in context before and after, and should not be interpreted as an excessively reduced meaning.

In addition, a singular expression used in this specification includes a plural expression unless the context clearly indicates otherwise. In the present application, the terms "consisting of" or "comprising" should not be construed as including the various components, or various steps described in the specification, among which some components or some steps are It may not be included, or it should be construed to further include additional components or steps.

Further, terms including ordinal numbers such as first and second used in the present specification may be used to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from other components. For example, the first component may be referred to as a second component without departing from the scope of the present invention, and similarly, the second component may be referred to as a first component.

When an element is said to be "connected" or "connected" to another component, it may be directly connected to or connected to the other component, but other components may exist in the middle. On the other hand, when a component is said to be "directly connected" or "directly connected" to another component, it should be understood that no other component exists in the middle.

Hereinafter, preferred embodiments according to the present invention will be described in detail with reference to the accompanying drawings, but the same or similar elements will be given the same reference numbers regardless of the reference numerals, and redundant descriptions thereof will be omitted. In addition, in the description of the present invention, when it is determined that detailed descriptions of related known technologies may obscure the subject matter of the present invention, detailed descriptions thereof will be omitted. In addition, it should be noted that the accompanying drawings are only for easy understanding of the spirit of the present invention and should not be interpreted as limiting the spirit of the present invention by the accompanying drawings. The spirit of the present invention should be interpreted to extend to all changes, equivalents, and substitutes in addition to the accompanying drawings.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

1 is a circuit diagram showing the configuration of a bidirectional buck converter according to an embodiment of the present invention. Referring to FIG. 1, the bidirectional buck converter of an embodiment of the present invention includes a battery charging circuit 100, a lighting circuit 200, and a control unit. 300.

Battery charging circuit 100 includes a diode (D ₁₎ (D ₂₎ and the switch element and the main switching section (110) consisting of (Q _1), the inductor resonant circuit 120 is composed of (L) and a capacitor (C ₁₎ And, it may include a charging unit 130 composed of a resistor (R _Bat ) and a battery (Bat), and a reflux unit 140 composed of a diode (D ₃ ).

Here, the main switch 110 is positioned between one end and the resonance circuit 120 of the solar cell panel 10, connected to the diode (D ₁₎ to one end of the solar cell panel 10, and a diode (D ₁₎ Connect the switch element (Q ₁ ) to the output terminal. A diode D ₂ is connected to both ends of the switch element Q- ₁ .

The resonant circuit unit 120 places the inductor L at _one end of the switch element Q ₁ and the capacitor C ₂ in parallel between the inductor 121 and the charging unit 130.

And the charging unit 130 is located between one end of the capacitor (C ₂ ) and the other end of the solar panel 10, the resistor (R _Bat ) and the battery (Bat) of the charging unit 130 on both ends of the capacitor (C ₂ ) Connect in series.

In addition, the reflux unit 140 is positioned between the output terminal of the switching element Q ₁ and the front end of the inductor L and connects the diode D ₃ in parallel with the capacitor C ₂ .

When the switching element Q ₁ is turned on based on the switching signal Q1_sw of the control unit 300, the light output voltage V _cell of the solar panel is a diode D ₁ and a switching element of the main switching unit 110. It is transmitted to the resonance circuit unit 120 via (Q ₁ ), the resonance circuit unit 120 transmits the resonance current to the capacitor (C ₂ ) as the resonance current generated in the inductor (L) flows to the capacitor (C ₂ ) Charged to, and the output current of the charged capacitor (C ₂ ) is transferred to the battery (Bat) via the resistor (R _Bat ) of the charging unit 130. Accordingly, the light output voltage V _cell supplied based on the solar panel 10 is buck converted and charged in the battery Bat.

In addition, when the switching element Q ₁ is turned off based on the switching signal Q1_sw of the control unit 300, the current flowing through the capacitor C ₂ flows through the reflux unit 140 to the inductor L, and thus the sun In the state in which the supply of the output voltage of the battery panel 10 is cut off, the energy stored in the inductor L is supplied to the capacitor C ₂ .

Meanwhile, the lighting circuit 200 includes a main switching unit 210 composed of a switching element Q ₂ and a diode D ₄ , a DC unit 220 composed of a capacitor C ₁ , and a resistor R _Led . And a lighting unit 230 formed of a light emitting diode (Led) and a reflux unit 240 formed of a diode (D ₅ ).

The main switching unit 210 places the switching element Q ₂ at the output terminal of the battery Bat and connects the diode D ₄ in parallel between both ends of the switching element Q ₂ .

And the DC unit 220 connects the capacitor C ₁ between the output terminal of the switch element Q ₂ and the front end of the inductor L.

On the other hand, the lighting unit 230 is positioned in series between the resistor (R _Led ) and the light emitting diode (Led) between the other end of the capacitor (C ₁ ) and the other end of the switching element (Q ₂ ).

And reflux 240 is located a diode (D ₅₎ between one end of the capacitor (C ₂₎ and the output terminal of the switching element (Q ₂₎ and the resonant circuit 120.

Accordingly, when the switching element Q ₂ of the main switching unit 210 is turned on based on the switching signal Q2_sw of the control unit 300, the current transmitted from the battery Bat passes through the switching element Q ₂ supplied to the capacitor (C ₁₎ of the DC unit 220, and a capacitor (C ₁₎ is charged with providing the received electric current delivered from the battery (Bat). The lighting element (not shown) is turned on due to the resistance of the lighting unit 230 (R _Led ) and the current of the DC unit 220 flowing through the LED.

In addition, when the switching element Q ₂ is turned off based on the switching signal Q2_sw of the control unit 300, the current output from the capacitor C ₁ passes through the lighting unit 230 and the reflux unit 240 to inductor L. As it is refluxed, the light emitting diode (Led) is continuously lit and the energy stored in the inductor (L) is supplied to the capacitor (C ₁ ).

), 태양 전지 패널의 광 출력 전압(V_cell), 및 인덕터 전류(i_L)를 토대로 배터리 충전회로(100)의 스위칭 신호(Q1_sw)와 조명회로(200)의 스위칭 신호(Q2_sw)를 생성하는 구성을 갖춘다.On the other hand, the control unit 300 is a battery voltage (

), generating a switching signal (Q1_sw) of the battery charging circuit 100 and a switching signal (Q2_sw) of the lighting circuit 200 based on the light output voltage (V _cell ) of the solar panel, and the inductor current (i _L ) It has a configuration.

Here, the controller 300 may include an illumination reference current derivation unit 310, a battery reference current derivation unit 320, and a switching signal generation unit 330.

)을 전달받아 조명 기준 전류(i_{ref_led})를 도출하고 도출된 조명 기준 전류(i_{ref _led})를 스위칭 신호 생성부(330)로 전달하도록 포함할 수 있다.That is, the illumination reference current deriving unit 310 is a battery voltage (

) To derive the illumination reference current i _{ref_led} and deliver the derived illumination reference current i _{ref _led} to the switching signal generator 330.

In addition, the battery reference current deriving unit 320 based on the light output voltage (V _cell ) of the solar panel 10, the inductor current (i _L ) and a predetermined PWM duty value (Duty), the battery reference current (i _{ref_bat)} ) And derive the derived battery reference current (i _{ref _bat} ) to the switching signal generator 330.

In addition, the switching signal generation unit 330 is based on the lighting reference current (i _{red _led} ), the battery reference current (i _{ref_bat} ), and the light output voltage (V _cell ) of the solar panel 10, the switching signal (Q1_sw) It is provided to generate (Q2_sw), respectively.

)을 토대로 조명 기준 전류(i_{ref_led})을 도출하는 일련의 과정은 본 발명의 실시 예와 관련된 기술분야에서 통상의 지식을 가진 자라면 이해할 수 있다.Battery voltage in an embodiment of the present invention (

), a series of processes for deriving the illumination reference current i _{ref_led} can be understood by those skilled in the art related to the embodiment of the present invention.

In addition, the battery reference current deriving unit 320 performs an MPPT (Maximum Power Point Tracking) algorithm to reduce power loss due to the light output voltage (V _cell ) of the solar panel 10 that fluctuates according to changes in the external environment. The light reference voltage V _{ref _cell} of the solar panel 10 can be derived.

Referring to the drawings below, the MPPT algorithm is performed to derive the light reference voltage (V _{ref _cell} ) of the solar panel 10 that is fluctuated by the external environment to extract the maximum power operating point (MPOP). The sequence is explained.

That is, the voltage (V)/current (I) curve of the solar panel 10 fluctuates according to the amount of insolation as shown in (a), where the delivered power (P) is derived from P=VI and the voltage (V) And the transmission power (P) characteristic curve is as shown in (b).

For example, the maximum power operating point (MPOP), which is the point at which the maximum power is transmitted, is tracked based on the light output voltage (V _cell ) and the transmission power (P _out ) characteristic curve of the solar panel 10 according to the solar radiation. The maximum power operating point (MPOP) varies depending on external environmental conditions such as solar radiation and temperature. That is, although the power of solar energy from which solar radiation is produced increases, the temperature of the solar panel increases, and when the temperature of the solar panel increases, the power production efficiency decreases. Accordingly, the maximum power operation point that is tracked according to external environmental conditions such as temperature and solar radiation should be performed at a high speed.

2 is a conceptual diagram of a maximum power tracking (MPPT) algorithm based on a partial PV characteristic curve of the battery reference current derivation unit 320, and FIG. 3 is a process of estimating a maximum power operating point from the partial PV characteristic curve shown in FIG. It is a diagram for explaining, and the MPPT algorithm will be described in detail with reference to FIGS. 2 and 3.

The MPPT algorithm is performed for each mode divided into three regions, assuming that it is currently controlled by the light output voltage (V _cell ) of the solar panel 10.

(1) Mode 1: (section t1-t2)

In the section of mode 1, the first following voltage is set to a value obtained by subtracting the variable voltage (ΔV) from the light output voltage (V _cell ) of the solar panel 10, and at t1 the light output voltage of the solar panel 10 ( Vcell) starts tracking to the first estimated voltage. At this time, the energy accumulated in the solar panel is rapidly transferred to the battery (Bat) side. Then, the mode 1 is terminated at a time t2 when the output voltage V _cell of the solar panel 10 reaches the first tracking voltage.

(2) Mode 2: (t2-t3 section)

The second tracking voltage is adjusted by adding 2ΔV to the first tracking voltage value reached at the starting point t2 of the section of mode 2, and thus the light output voltage V _cell of the solar panel 10 is adjusted. 2 Following voltage is reached. At this time, the energy accumulated in the solar panel 10 transferred to the battery (Bat) side is rapidly reduced. And the maximum value of the light output voltage (V _cell ) and the transmission power (P) of the solar panel 10 at the time when the transmission power (P) reaches the maximum value is extracted. In addition, the mode 2 is terminated at a time t3 when the light output voltage V _cell of the solar panel 10 reaches the second tracking voltage.

In addition, the maximum value (Pmax(k-2)) of the delivered power P and the output voltage from the partial solar PV characteristic curve for the variation of the variable voltage ΔV estimated based on the previously estimated maximum power operating point (Vmax(k-2)) is measured.

(3) Mode 3: (t3-t4 section)

The output voltage Vmax(k-2) at which the maximum value Pmax(k-2) of the transmitted power P measured in mode 2 is generated is set as the third following voltage. The holding time (T2: time constant) of this section is determined by the charging characteristic of the battery (Bat) and the MPPT time constant, and the output voltage (Vmax(k-) at which the maximum value of the transmitted power (Pmax(k-2)) occurs If 2)) exists within intrinsic V based on the current voltage, the output voltage (Vmax(k-2)) should be minimized to shorten the MPPT estimation time constant.

In the same way, Pmax(k-1) and Vmax(k-1) and Pmax(k) and Vmax(k) are sequentially measured, and the partial solar PV characteristic curve shows the transfer power of the solar panel 10 ( P) and the voltage V are moved to the maximum power operating point MPOP having the maximum value.

The size of the variable voltage value V is set by the user considering the partial solar PV characteristic curve and the following speed.

For example, if the following speed is desired, the size of V can be set to a large value, but it is difficult to accurately follow the maximum power. If the maximum speed is more accurate than the following speed, the variable voltage value (V) has a small value. Must be entered.

Therefore, the output voltage that can be moved by a specific power (W) on the partial solar PV characteristic curve and the MPPT characteristic curve can be determined as a variable transmission power value.

The partial solar PV characteristic curve of the solar panel 10 can be measured as a partial solar PV curve corresponding to the intrinsic V of the reference voltage of the MPOP derived from the previous partial solar PV characteristic curve.

In addition, even if the partial solar PV characteristic curve indicated by a solid line by the amount of solar radiation before one step changes to the partial solar PV characteristic curve of the current dotted line due to the change in solar intensity, the output voltage with the maximum transmission power on the current partial solar PV characteristic curve If it is within this variable voltage (V), it will operate at full power operating point without delay. In addition, even if the maximum power generation voltage on the PV curve currently exists only in V, it is followed by the maximum power voltage after a few steps.

Accordingly, an embodiment of the present invention can perform a correction for the maximum power operating point that varies depending on the external environment through an MPPT algorithm, thereby reducing the derivation time of the optical reference voltage (V _{ref _cell} ) and the overall response time of the buck converter. Can be reduced.

In addition, the battery reference current deriving unit 320 derives the battery reference current i _{ref _bat} by performing PI control on the light reference voltage v _{ref _cell} derived through the high-speed MPPT algorithm described above. The derived battery reference current i _{ref _bat} is transferred to the switching signal generator 330.

In addition, the switching signal generator 330 selects one of the battery reference current i _{ref _bat} and the lighting reference current i _{ref _led} according to the light output voltage V _cell of the solar panel 10 and selects the selected battery A series of processes for generating the switching signal Q1_sw or the switching signal Q2_sw and generating the switching signal Q1_sw (Q2_sw) based on the reference current i _{ref _bat} and the illumination reference current i _{ref _led} Those of ordinary skill in the art related to the embodiments of the can be understood.

The operation process of the bidirectional buck converter according to the embodiment of the present invention having the above-described configuration will be described with reference to FIGS. 4 to 7 as follows.

4 and 5 are views for explaining the battery charging process of the buck converter. Referring to FIG. 4, the switching element Q ₁ of the main switching unit 110 is connected to the switching signal Q1_sw of the control unit 300. Switched to the on-state, and thus the light output voltage (V _cell ) of the solar panel 10 is provided to the inductor (L) of the resonant circuit unit 120 via the diode (D ₁ ) and the switching element (Q ₁ ) do. The inductor L stores energy of the solar panel.

And the stored energy is supplied to the capacitor C ₂ of the resonant circuit unit 120 and charged. The output current of the capacitor C ₂ is charged to the battery Bat via a resistor R _Bat .

At this time, since the battery (Bat) is a nonlinear device, the equivalent circuit modeled with input and output characteristics is as follows.

The equivalent circuit for this model satisfies the following equations 1 and 2.

.. 식 1

.. Photos

.. 식 2

.. Photos

는 전압원이고,

저항이며,

,

는 충전 또는 방전 시 배터리 과도 응답이며,

는

를 지나가는 전압이고

는

로 유입되는 전류이다.here,

Is a voltage source,

Resistance,

,

Is the battery transient response when charging or discharging,

The

Is the voltage passing through

The

It is the current flowing into.

Summarizing the expressions 1 and 2 with respect to the continuous time (k, k+1), they are represented by the following expressions 3 and 4.

.. 식 3

.. Photos

.. 식 4

.. Photos

는 샘플링 시간이고,

는 OTC 시간 상수이고

는 전압 소스로 SOC(state of charge) 함수로 나타낸다.here,

Is the sampling time,

Is the OTC time constant

Is a voltage source and is expressed as a SOC (state of charge) function.

)의 충전 전압이 매우 작거나 배터리 작동 시간이 매우 짧은 경우

,

는 무시할 수 있고, 이에 하나의 시간 상수에 대한 모델(OTC)의 등가 회로는 다음과 같다.Also capacitor(

) The charging voltage is very small or the battery operating time is very short

,

Is negligible, and the equivalent circuit of the model (OTC) for one time constant is as follows.

) 및 전압 소스(

)는 SOC(state of charge), SOH (State of Health) 및 온도 함수로 정해지며,

는 방전 시 양의 값을 가지고 충전 시 음의 값을 가지는 배터리 전류이고,

는 배터리 전압이다. Where resistance(

) And voltage source (

) Is determined by SOC (state of charge), SOH (State of Health) and temperature functions,

Is a battery current that has a positive value during discharge and a negative value during charging,

Is the battery voltage.

)은 다음 식 5로 나타낸다.Also, the battery voltage for one time constant (

) Is represented by the following equation 5.

.. 식 5

.. Photos

)는 듀티 사이클(d)와 태양 전지 패널의 충전 전압(

)으로부터 결정되고 다음 식 6으로 나타낸다. 여기서,

는 태양 전지 패널의 광 출력 전압(

)으로 배터리 개방 회로의 전압이다. 이에 모드 1에서 배터리 전압(

)과 인덕터 전류(

)은 다음 식 7 및 8에 의해 결정된다.5 is a view showing the relationship between the current (I _L ) flowing through the inductor (L) and the duty cycle (D), the current (I _L ) flowing through the inductor (L) rapidly increases (d) is mode 1 (CCM) and Mode 2 (DCM) are important duty cycles, and the light output voltage (

) Is the duty cycle (d) and the charging voltage of the solar panel (

) And is represented by the following equation (6). here,

Is the solar panel light output voltage (

) Is the voltage of the battery open circuit. Therefore, the battery voltage in mode 1

) And inductor current (

) Is determined by the following equations 7 and 8.

.. 식 6

.. Photos

.. 식 7

.. Photos

.. 식 8

.. Photos

6 is a view showing the flow of the inductor current I _L when the switching element Q ₁ is turned off by the first switching signal Q1_sw. Referring to FIG. 6, the capacitor when the switching element Q ₁ is turned off The charging current of (C ₂ ) is continuously supplied to the inductor L as it is transferred to the inductor L via the diode D ₃ of the reflux unit 140.

)은 스위칭 소자(Q₂)를 경유하여 캐패시터(C₁)에 공급되어 충전되고, 캐패시터(C₁)의 출력 전류는 인덕터(L)에 공급됨과 동시에 조명부(220)의 저항(R_Led) 및 발광 다이오드(Led)에 흐르게 되고, 이에 조명 소자(미도시됨)가 점등된다.7 is a view showing an operating state of the lighting circuit 200 of the bi-directional buck converter shown in FIG. 1. Referring to FIG. 7, when the switching element Q ₂ is turned on based on the switching signal Q2_sw of the controller 300, the battery voltage (

) Is supplied and charged to the capacitor C ₁ via the switching element Q ₂ , and the output current of the capacitor C ₁ is supplied to the inductor L and at the same time the resistance (R _Led ) of the lighting unit 220 and The light-emitting diode (Led) flows, and the lighting element (not shown) is turned on.

At this time, since the input/output characteristics of the light emitting diode Led are also nonlinear, the modeled equivalent circuit of the light emitting diode Led is as follows.

) 및 전압(

)은 다음 식 9를 만족한다.According to this equivalent circuit, the positive operating current (

) And voltage (

) Satisfies Expression 9 below.

.. 식 9

.. Photos

는 역전 포화 전류이고, q는 전자 전하로 1.602X10^{- 19}C 이며,

는 Boltzmann 상수로 1.381X10^-23 J/K이다.here,

And the reverse saturation current, q is an electronic charge 1.602X10 ^- and C ^19,

Is the Boltzmann constant of 1.381X10 ^-23 J/K.

) 보다 낮으면 발광 다이오드(Led)는 소등되고, 이때 전류(I)는 피크 반복 역전압(

) 보다 높아질 때까지 작은 값으로 유지됨을 확인할 수 있다.At this time, the characteristic curve of the operating current (I) vs. the voltage (U) of the light emitting diode (Led) is as follows, and according to the I/U characteristic curve of the light emitting diode, the voltage (U) to light up the light emitting diode (Led) Set threshold voltage (

If it is lower than ), the light emitting diode (Led) turns off, and the current (I) is the peak repetitive reverse voltage (

It can be seen that it is kept at a small value until higher.

) 보다 높아지면 전류(I)는 급격하게 증가됨을 확인할 수 있고, 이때 발광 다이오드(Led)가 정상적으로 동작되어 조명소자는 점등된다.And, the voltage U is the threshold voltage (

It can be seen that when it is higher than the current (I) is rapidly increased, the light emitting diode (Led) is operating normally, the lighting element is turned on.

)이 임계 전압(

) 보다 높아질 때 조명 소자가 정상적으로 점등된다. According to the characteristic curve of the light emitting diode (Led), the operating voltage of the lighting unit 220 (

) Is the threshold voltage (

), the lighting element turns on normally.

)과 인덕터(L)에 흐르는 전류(I_L)는 다음 식 10으로부터 도출될 수 있다.At this time, the operating voltage of the light emitting diode (Led) (

) And the current I _L flowing through the inductor L can be derived from the following equation (10).

.. 식 10

.. Photos

.. 식 11

.. Photos

)이 임계 전압(

)에 도달되는 듀티 사이클이다.Where d is the operating voltage (

) Is the threshold voltage (

).

Meanwhile, FIG. 8 is a diagram showing an operating state when the switching element Q ₂ is turned off based on the switching signal Q2_sw of the control unit 300. Referring to FIG. 8, the current of the capacitor C ₁ is a reflux unit. It is transmitted to the inductor L via the diode D ₆ of 240.

Accordingly, as the buck converter is designed so that the energy stored in the inductor L is shared between the battery charging circuit 100 and the lighting circuit 200, the light emitting diodes of the lighting circuit 200 with solar energy stored in the inductor L ( Led) can be turned on, thereby reducing the total number of parts of the buck converter and reducing the manufacturing cost.

8 is a flowchart illustrating a lighting control method using a buck converter according to another embodiment of the present invention. Referring to FIG. 8, the lighting control method of another embodiment of the present invention includes a data receiving step 410 and a mode setting step. 420, a battery charging step 430, and a lighting control step 440.

) 및 발광다이오드 전류(i_led)를 수신하고 수신된 광 출력 전압(V_cell)은 모드 설정 단계(420)로 전달되며, 모드 설정 단계(420)는 수신된 광 출력 전압(V_cell)과 정해진 임계 전압(k)을 토대로 조명이 소등되는 주간 모드와 조명이 점등되는 야간 모드를 설정한다.First, the data receiving step 410 includes the photovoltaic output voltage (V _cell ), battery current (i _bat ), and battery voltage (

) And the light emitting diode current (i _led ), the received light output voltage (V _cell ) is transferred to the mode setting step 420, and the mode setting step 420 is determined with the received light output voltage (V _cell ). Based on the threshold voltage k, a day mode in which the light is turned off and a night mode in which the light is turned on are set.

)보다 크고 배터리 전압(

)이 배터리 전압(

)의 최대값(V_{bat_max})보다 작은 경우 배터리 충전 단계(430)는 MPPT 알고리즘을 통해 태양 전지 패널(10)의 광 기준 전압(V_{ref _cell})을 도출하고, 도출된 광 기준 전압(V_{ref _cell})과 수신된 광 출력 전압(V_cell)을 기반으로 전압에 대한 PI(Proportional Integral) 제어를 수행하여 배터리 기준 전류(i_{ref _bat})를 도출하며, 도출된 배터리 기준 전류(i_{ref_bat}) 및 배터리 전류(i_bat)를 기반으로 전류에 대한 PI 제어를 수행하여 듀티 사이클(d)을 설정한다.In addition, the battery charging step 430 charges the battery bat with the light output voltage V _cell of the solar panel 10 in the daytime mode. That is, the light output voltage (V _cell ) of the solar panel 10 is the battery voltage (

) And battery voltage (

) This battery voltage (

) The maximum value (V _{bat_max)} than the small-charge phase battery 430 derives the optical reference voltage (V _{ref _cell)} of the solar panel 10 through the MPPT algorithm, and deriving an optical reference voltage (V _{ref _cell} of ) And PI (Proportional Integral) control of the voltage based on the received light output voltage (V _cell ) to derive the battery reference current (i _{ref _bat} ), and the derived battery reference current (i _{ref_bat} ) and battery current The duty cycle (d) is set by performing PI control on the current based on (i _bat ).

In addition, the battery charging step 430 generates a switching signal Q1_sw having a duty cycle d. The light output voltage V _cell of the solar panel 10 is charged to the battery Bat according to the on/off state of the switching element Q ₁ according to the generated switching signal Q1_sw.

On the other hand, when the night mode is set in the mode setting step 420, the lighting control step 440 is performed.

)을 토대로 조명 기준 전류(i_{ref_led})를 도출한다. The lighting control step 440 starts the counting operation of the timer and when the counting value of the timer does not reach the set value, the battery voltage (

) To derive the illumination reference current (i _{ref_led} ).

For the derived illumination reference current i _{ref _led} and illumination current i _led , the lighting control step 440 performs PI control to generate the switching signal Q2_sw and the duty cycle of the generated switching signal Q2_sw According to the lighting control.

Accordingly, as battery charging and lighting control are performed with energy stored in one inductor, the number of components can be reduced to reduce the load, and thus, the response speed of the bidirectional buck converter can be reduced.

<Example>

) 은 12V로 각각 설정한다.9 is an output waveform diagram of a bidirectional buck converter when charging the battery by storing energy in the inductor, and FIG. 10 is a diagram showing output waveforms of each part when discharging energy stored in the inductor, and an embodiment of the present invention sets the DC gain to 0.01 And set the time constant to 1 msec, the inductor (L) is 500 ?H, the capacitors (C1) (C2) are all 100?F, the light output voltage V _in is 18V, and the battery voltage (

) Is set to 12V each.

), 및 듀티 사이클(Duty) 각각에 대한 시뮬레이션 결과와 실체 측정치를 비교하면, 실제 인덕터 전류의 측정치가 배터리 기준 전류와 동일함을 확인할 수 있다.Accordingly, as shown in FIG. 9 when storing the energy of the inductor, the inductor current IL, battery current ibat, and battery voltage (

), and comparing the simulation result and the actual measurement value for each of the duty cycle (Duty), it can be confirmed that the actual inductor current measurement is the same as the battery reference current.

FIG. 10 is a view showing an output waveform when the stored energy of the inductor is discharged, that is, when the battery is discharged. Referring to FIG. 10, the measured value of the inductor current and the battery reference current are equal to -1A after 70 msec during the stored energy discharge of the inductor. Can be seen.

11 is a waveform diagram showing simulation results of a high speed MPPT algorithm in an embodiment of the present invention. The fast MPPT algorithm measures the reference voltage by changing the variable voltage value (V) at a fixed time corresponding to the maximum power, estimates the maximum delivered power value based on the measured lighting reference voltage, and then changes the constant lighting reference voltage (V) without change. _{ref _led} ) is obtained. Accordingly, referring to FIG. 11, it can be seen that when compared with the existing MPPT algorithm simulation results, the MPPT efficiency is improved by 99%, and the response time is significantly improved within 70 msec.

In the above, it has been described with reference to preferred embodiments of the present invention, but those skilled in the art may variously modify and change the present invention without departing from the spirit and scope of the present invention described in the following claims. You will understand that you can.

100: battery charging circuit
110, 210: main switching unit
120: resonant circuit unit
130: charging unit
140, 240: reflux
220: DC unit
230: lighting unit
200: lighting circuit
300: control unit
310: lighting reference current derivation unit
320: battery reference current deriving unit
330: switching signal generator
410: data receiving step
420: mode setting step
430: battery charging stage
440: lighting control stage

Claims (10)

delete In the solar street light device using a bi-directional buck converter for charging the light output voltage of the solar panel to the battery and controlling the lighting with the charged battery voltage,
The bidirectional buck converter,
It is provided to perform the battery charging and lighting control with the energy stored in one inductor,
The bidirectional buck converter,
It includes a battery charging circuit connected between both ends of the solar panel to charge the light output voltage of the solar panel to the battery,
The battery charging circuit,
A first main switching unit having a first diode connected in series to the output terminal of the solar panel, a second diode connected to the output terminal of the first diode, and a first switching element connected in parallel;
A resonant circuit unit comprising an inductor connected to the output terminal of the first main switching unit, a first capacitor connected to the output terminal of the inductor and the other terminal of the battery, and positioned between one end of the first main switching unit and one end of the battery; And
A charging unit located at an output terminal of the inductor and configured to include a first resistor and a battery connected in parallel with the first capacitor to charge energy stored in the inductor to the battery; And
And a first reflux unit for transferring the output current of the first capacitor to the inductor when a third diode is positioned at the other end of the battery and the output terminal of the first main switching to cut off the supply of the light output voltage of the solar panel. Solar street light device using a bi-directional buck converter. According to claim 2, The bi-directional buck converter,
Located between the front end of the inductor and the other end of the first capacitor includes a lighting circuit that is turned on or off based on the battery voltage,
The lighting circuit
A second main switching part which positions a second switching element and a fourth diode in parallel on the other end of the battery;
A DC unit connected to an output terminal of the second switching element and a front end of the inductor to charge a battery voltage;
A lighting unit connected to the DC unit in parallel to turn on or off a lighting element; And
It is composed of a fifth diode, and is connected to the output terminal of the lighting unit and the other end of the inductor, and includes a second reflux unit for refluxing the output current of the capacitor to the inductor when the battery voltage supply is cut off. Solar street light device. The bidirectional buck converter of claim 3,
Further comprising a control unit for generating a first switching signal and a second switching signal for controlling the on or off of the first switching element and the second switching element,
The control unit,
An illumination reference current deriving unit for deriving an illumination reference current from the battery voltage;
A battery reference current deriving unit that derives a battery reference current based on a predetermined duty cycle, an inductor current, and a light output voltage of the solar panel; And
A switching signal for selecting one of the lighting reference current and the battery reference current based on the light output voltage, generating a first switching signal based on the selected battery reference current, and generating a second switching signal based on the selected lighting reference current Solar street light device using a bi-directional buck converter, characterized in that it comprises a generator. The method of claim 4, wherein the battery reference current derivation unit,
Deriving the delivered power based on the duty cycle, the inductor current, and the light output voltage of the solar panel,
A maximum power point tracking (MPPT) algorithm is performed on the derived transfer power to derive an optical reference voltage to the light output voltage of the solar panel,
A solar street light device using a bi-directional buck converter, characterized in that it is provided to derive a battery reference voltage by performing PI (Proportional Integral) control on the derived light reference voltage. The method of claim 5, wherein the lighting circuit,
When the second switching element is switched to the on state by the second switching signal of the control unit to supply the battery voltage
Bi-directional buck, characterized in that it is provided to light the lighting element as the output current of the battery is transmitted to the second capacitor via the second switching element and the output current of the second capacitor is transmitted to the second resistor and the light emitting diode. Solar street light device using converter. The method of claim 6, wherein the lighting circuit
When the second switch element is switched to the off state according to the second switching signal of the control unit, the supply of the battery voltage is cut off,
The output current of the second capacitor is transmitted to a second resistor and a light emitting diode to maintain the lighting state of the lighting element, and the output current of the second capacitor is refluxed through the fifth diode to be delivered to the inductor. Solar street light device using a bi-directional buck converter. It includes a battery charging circuit connected between both ends of the solar panel to charge the light output voltage of the solar panel, the battery charging circuit of the first diode and the first diode connected in series to the output terminal of the solar panel A first main switching unit having a second diode connected to the output terminal and a first switching element connected in parallel; A resonant circuit unit comprising an inductor connected to the output terminal of the first main switching unit, a first capacitor connected to the output terminal of the inductor and the other terminal of the battery, and positioned between one end of the first main switching unit and one end of the battery; A charging unit which is located in the output terminal of the inductor and which is connected in series with the first capacitor and the battery in series to charge energy stored in the inductor to the battery; And a first reflux unit that positions a third diode at the other end of the battery and the output terminal of the first main switching to transfer the output current of the first capacitor to the inductor when the supply of the solar panel's optical output voltage is blocked.
A lighting circuit positioned between the front end of the inductor and the other end of the first capacitor to be turned on or off based on a battery voltage, wherein the lighting circuit includes a second switching element and a fourth diode located in parallel at the output terminal of the battery in parallel. A second main switching unit connected; A DC unit connected to an output terminal of the second switching element and a front end of the inductor to charge a battery voltage; A lighting unit connected to the DC unit in parallel to turn on or off a lighting element; And a second reflux unit configured as a fifth diode and connected to the output terminal of the lighting unit and the other end of the inductor to reflux the output current of the capacitor to the inductor when the battery voltage supply is cut off.
Further comprising a control unit for generating a first switching signal and a second switching signal for controlling the on or off of the first switching element and the second switching element, the control unit, deriving the lighting reference current from the output voltage of the battery An illumination reference current derivation unit; A battery reference current deriving unit that derives a battery reference current based on a predetermined duty cycle, an inductor current, and a light output voltage of the solar panel; And selecting one of the lighting reference current and the battery reference current based on the light output voltage, generating a first switching signal based on the selected battery reference current, and generating a second switching signal based on the selected lighting reference current. Solar street light device using a bi-directional buck converter, characterized in that it comprises a signal generator. In the solar street light control method using a bi-directional buck converter for charging the battery at daytime with the light output voltage of the solar panel and controlling the lighting with the battery voltage at night,
A data receiving step of receiving the light output voltage and current, battery voltage and current, and inductor current of the solar panel; A mode setting step of setting a day mode or a night mode based on a result of comparing the light output voltage of the solar panel with a predetermined threshold voltage;
When the day mode is set, the maximum power operating point tracking algorithm is performed based on the comparison result of the light output voltage, the battery voltage, and the maximum battery voltage to derive the light reference voltage, and PI control is performed on the derived light reference voltage and light output voltage To derive the battery reference current, perform PI control based on the derived battery reference current and battery current to derive the battery reference current, generate a first switching signal with the derived battery reference current, and generate the first switching And controlling the on/off of the first switching element with a signal to charge the light output voltage to the battery, the method of controlling a solar street light using a bi-directional buck converter. The method of claim 9, wherein in the mode setting step
When setting the night mode, if the counting value of the counter does not result in the set value, the battery voltage is supplied to derive the lighting reference current, and the second switching signal is generated based on the derived lighting reference current and transmitted to the second switching element.
The control method of the solar street light using a bi-directional buck converter further comprises a lighting control step of controlling the lighting of the lighting element with a battery voltage based on the on/off control of the second switching element.

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