KR20210046433A - Apparatus and Method for Controlling a Bi-directional Converter using battery and capacitor together - Google Patents

Abstract

Disclosed are a bi-directional converter control device using both a battery and a capacitor and a control method thereof. According to one aspect, the bi-directional converter control device comprises: an inductor; a first switch; and a second switch, wherein an input terminal is connected in parallel to the battery, and an output terminal is connected in parallel to the capacitor and a load. The bi-directional converter control device comprises: a disturbance observer which predicts a k-th state variable using a (k-1)-th estimated value of a load current, and derives a k-th estimated value of the load current using the predicted k-th state variable, a measured k-th state variable, and the (k-1)-th estimated value; and a control unit which operates the bi-directional converter as a boost converter or a buck converter according to the k-th estimated value, wherein the state variable includes an inductor current and a capacitor voltage. According to the present invention, an error between an actual load current and an estimated load current can be reduced.

Description

Apparatus and Method for Controlling a Bi-directional Converter using battery and capacitor together}

Embodiments of the present invention relate to a converter control device and a control method using a battery and a capacitor together, in particular, a converter control device and a control method for limiting the maximum current of the battery and charging and discharging the capacitor.

The content described in this section merely provides background information on the present invention and does not constitute prior art.

An electric vehicle refers to a vehicle that uses electric energy from batteries instead of fossil fuels to drive. As the demand for electric vehicles increases rapidly, the life of batteries is emerging for the efficiency of electric vehicles. Battery life is affected by temperature and C-rate (charge/discharge current rate). In particular, when the motor, which is a load, is accelerated, the discharge current of the battery increases, and when the discharge current of the battery increases, stress is applied to the battery and the battery life decreases.

In order to reduce the charge/discharge stress of the battery, a hybrid energy storage system (HESS) in which a battery and a super-capacitor are combined may be used. HESS can control the current of the battery and supercapacitor using switching of a converter so that the battery and supercapacitor can supply the current required for the load at an appropriate ratio. Specifically, when the load requires a lot of power, the HESS can reduce the current discharged from the battery using a DC-DC converter, and instead discharge the capacitor to supply power to the load.

The HESS needs to know the load current in order to determine the ratio of the current to the battery and supercapacitor. In general, HESS directly measures the load current or predicts the load current from the drive output of a motor (load). In the conventional HESS, the current of the load is determined by the above method, the current required for the load is divided by an appropriate ratio, and then the battery and the capacitor are controlled so that the current can be supplied according to the ratio.

When controlling the battery and capacitor after directly measuring the current of the load or predicting the load current from the driving output of the motor, there is a limit to reducing the error between the target current of the battery and the capacitor and the actual current. To reduce this limitation, a disturbance observer, a robust control technique that estimates and compensates for the uncertainty of the system model and the effect of the disturbance on the system can be used. After accurately predicting the magnitude and change of load current using a disturbance observer (DOB), it is necessary to precisely control the output current of the battery and capacitor.

On the other hand, when regenerative brake power generated during deceleration of the motor is stored only in the battery, there is a limit to shortening the time for storing the regenerative power in the battery. Specifically, since the battery has a larger time constant and a lower C-rate than that of a capacitor, it cannot efficiently store the current of the harmonic component included in the regenerative power for a short period of time. When regenerative power is stored in a battery within a short period of time, there is a problem of shortening the life of the battery due to a battery deterioration phenomenon. In contrast, the capacitor is suitable for rapid charging and discharging that can charge a lot of energy in a short time, and has a characteristic of a semi-permanent charging and discharging cycle life, so that regenerative braking power can be more efficiently received than a battery.

Accordingly, after predicting the current required by the load or the current supplied from the load, the battery and the capacitor are charged and discharged together by dividing the load current by an appropriate ratio. In particular, it is necessary to charge and discharge the capacitor more frequently than the battery.

Embodiments of the present invention are a converter control device and a control method for reducing an error between the actual load current and the predicted load current by predicting using a disturbance observer without directly measuring the current required for the load or the current supplied from the load. The main purpose is to provide.

An embodiment of the present invention is to limit the discharge current of the battery when the current required for the load is large, discharge the capacitor, and control the converter to extend the life of the battery by charging the capacitor from the battery when the current required for the load is low. One object is to provide an apparatus and a control method.

According to an embodiment of the present invention, the current of the load generated during regenerative braking of the motor is first stored in a capacitor, and when the voltage of the capacitor reaches a preset voltage, the capacitor energy and regenerative power are transferred to the battery, thereby It is an object of the present invention to provide a converter control device and a control method for extending the voltage.

According to an aspect of the present invention, there is provided a two-way converter control device including an inductor, a first switch, and a second switch, wherein an input terminal is connected to a battery in parallel, and an output terminal is connected to a capacitor and a load in parallel. , Predicting the k-th state variable using the k-1 estimated value of the load current, and the k-th estimated value of the load current using the predicted k-th state variable, the measured k-th state variable, and the k-1 th estimated value. Disturbance observer to derive; And a controller configured to operate the bidirectional converter as a boost converter or a buck converter according to the k-th estimated value, wherein the state variable includes an inductor current and a capacitor voltage.

According to another aspect of the present embodiment, in the control method of a bidirectional converter including an inductor, a first switch, and a second switch, the input terminal is connected in parallel to the battery, and the output terminal is connected in parallel to the capacitor and the load, Estimation of predicting the k-th state variable using the k-1 estimated value, and deriving the k-th estimated value of the load current using the predicted k-th state variable, the k-th state variable measured, and the k-1 th estimated value. process; And a control process of operating the bidirectional converter as a boost converter or a buck converter according to the k-th estimated value, wherein the state variable includes an inductor current and a capacitor voltage.

As described above, according to an embodiment of the present invention, an error between the actual load current and the predicted load current can be reduced by predicting the current required for the load or the current supplied from the load using the disturbance observer.

According to an embodiment of the present invention, the battery life can be extended by limiting the discharge current of the battery and discharging the capacitor when the current required for the load is large, and charging the capacitor from the battery when the current required for the load is low. .

According to an embodiment of the present invention, the current of the load generated during regenerative braking of the motor is first stored in the capacitor, and when the voltage of the capacitor reaches a preset voltage, the capacitor energy and the regenerative power are transferred to the battery. Life can be extended.

1 is a diagram for explaining a method of operating a conventional disturbance observer.
2 is a diagram illustrating an apparatus for controlling a bidirectional converter according to an embodiment of the present invention.
3 is a diagram illustrating a method of operating a disturbance observer and a control unit according to an embodiment of the present invention.
4 is a diagram for explaining a process in which a bidirectional converter operates as a boost converter according to an embodiment of the present invention.
5 is a diagram for explaining a process in which a bidirectional converter operates as a buck converter according to an embodiment of the present invention.
6 and 7 are graphs for explaining the performance of the bidirectional converter control apparatus according to an embodiment of the present invention.
8 is a flowchart illustrating a method of controlling a bidirectional converter according to an embodiment of the present invention.

Hereinafter, some embodiments of the present invention will be described in detail through exemplary drawings. In adding reference numerals to elements of each drawing, it should be noted that the same elements are assigned the same numerals as possible, even if they are indicated on different drawings. In addition, in describing the present invention, when it is determined that a detailed description of a related known configuration or function may obscure the subject matter of the present invention, a detailed description thereof will be omitted.

In addition, in describing the constituent elements of the present invention, terms such as first, second, A, B, (a) and (b) may be used. These terms are for distinguishing the constituent element from other constituent elements, and the nature, order, or order of the constituent element is not limited by the term. Throughout the specification, when a part'includes' or'includes' a certain element, it means that other elements may be further included rather than excluding other elements unless otherwise stated. . In addition, terms such as'~ unit' and'module' described in the specification mean a unit that processes at least one function or operation, which may be implemented as hardware or software, or a combination of hardware and software.

1 is a diagram for explaining the principle of a conventional disturbance observer.

Referring to FIG. 1, a controller 100, a system 110, an inverse system 120, and a Q-filter 130 for explaining the principle of a conventional disturbance observer are shown.

)를 시스템(110)에 인가할 때, 시스템(110)의 외부로부터 외란(disturbance)이 제어신호와 함께 인가된다. 제어신호와 외란이 시스템(110)에 함께 입력되는 경우, 시스템(110)의 출력값은 사용자가 의도한 출력값과 다르게 출력될 수 있다.In general, the control signal of the control unit 100 (

When) is applied to the system 110, a disturbance from the outside of the system 110 is applied together with a control signal. When the control signal and the disturbance are input to the system 110 together, the output value of the system 110 may be output differently from the output value intended by the user.

In order to output the output value of the system 110 equal to the output value intended by the user, it is necessary to remove the disturbance input to the system 110. Since it is difficult to measure the disturbance directly, the disturbance may be removed by extracting the disturbance from the output value of the system 110 and then canceling the actual disturbance using the extracted disturbance. This is called the disturbance observer theory.

)은 불안정한 모델이므로, 역시스템(120)에 Q-필터(Q-filter, 130)를 적용하여 역시스템(120)을 안정화할 수 있다. Referring to FIG. 1 again, when the output y of the system 110 is input to the inverse system 120, the inverse system 120 outputs a value in which the control signal and the disturbance are mixed. The disturbance is extracted by removing only the control signal from the mixed value of the control signal and the disturbance, and the extracted disturbance is estimated as the actual disturbance. At this time, when the system 110 has a stable model, the inverse model of the system 110 (

Since) is an unstable model, the inverse system 120 can be stabilized by applying a Q-filter 130 to the inverse system 120.

Accordingly, the disturbance observer theory is a theory that allows the system 110 to output an output value intended by the user by estimating the disturbance from the output of the system 110 and canceling the actual disturbance using the estimated disturbance.

2 is a diagram illustrating an apparatus for controlling a bidirectional converter according to an embodiment of the present invention.

Referring to FIG. 2, a bidirectional converter 200, a load 210, a disturbance observer 220, a control unit 230, a battery, and a capacitor are illustrated. The bidirectional converter control apparatus according to an embodiment of the present invention includes a disturbance tube 220 and a control unit 230.

The bidirectional converter 200 includes an inductor, a first switch, a second switch, a first diode and a second diode. The input terminal of the bidirectional converter 200 is connected in parallel to the battery, and the output terminal may be connected in parallel to the capacitor and the load 210, respectively.

The bidirectional converter 200 transfers the energy stored in the battery to the load 210 or the capacitor, transfers the energy stored in the battery and the capacitor to the load 210, or transfers the power produced by the load 210 to the capacitor or battery. Can be saved.

When the load 210 consumes power, the bidirectional converter 200 transfers the energy stored in the battery by the controller 230 to the load 210 or the capacitor, or transfers the energy stored in the battery and the capacitor to the load 210. It acts as a boost converter to deliver.

When the load 210 generates power, the bidirectional converter 200 operates as a buck converter that stores the power produced by the load 210 by the controller 230 in a capacitor or battery.

The load 210 may receive energy from a battery or a capacitor to consume power, or may generate energy to be stored in the battery or capacitor. For example, the load 210 is a motor of an electric vehicle, and consumes power during acceleration of the vehicle, and may generate power by regenerative brake of the motor during deceleration of the vehicle.

The disturbance observer 220 estimates the current of the load 210 using a battery voltage, a capacitor, a bidirectional converter 200, a battery, and a capacitor. The disturbance observer 220 may transmit the estimated load current to the controller 230. The process of estimating the load current by the disturbance observer 220 will be described in detail with reference to FIG. 3.

The controller 230 determines whether the load 210 consumes or produces power using the load current estimated by the disturbance observer 220, and boosts the bidirectional converter 200 when the load 210 consumes power. When operating as a converter and generating power, the bidirectional converter 200 is operated as a buck converter. The controller 230 sets the maximum value of the output current of the battery, and controls the switches of the bidirectional converter 200 so that the battery and the capacitor are charged and discharged accordingly.

Specifically, when the estimated value of the load current means a state in which the load 210 consumes power, and the estimated value is greater than the average current flowing through the output terminal of the bidirectional converter 200, the controller 230 determines that the energy stored in the battery and the capacitor is The second switch may be turned off and the first switch may be controlled to be transmitted to the load. Here, the average current flowing through the output terminal of the bi-directional converter 200 means a value obtained by multiplying the limit current value of the battery arbitrarily set by (1-D). Here, D denotes a switching duty ratio of the first switch in the boost converter.

When the estimated value of the load current refers to a state in which the load 210 consumes power, and the estimated value is less than the average current flowing through the output terminal of the bidirectional converter 200, the controller 230 regulates the energy of the battery to be charged in the capacitor. It can control 1 switch and 2nd switch. At this time, the controller 230 controls the bidirectional converter 200 so that the energy stored in the battery is charged to the capacitor and the energy stored in the battery is transferred to the load.

When the estimated value of the load current means a state in which the load 210 generates power, and the voltage of the capacitor is lower than the maximum voltage (saturated voltage), the controller 230 turns off the first switch and the second switch, The bidirectional converter 200 is controlled so that power generated from the load 210 can be delivered to the capacitor.

When the estimated value of the load current means the state in which the load 210 generates power, and the voltage of the capacitor is the maximum voltage, the controller 230 turns off the first switch so that the energy stored in the capacitor can be transferred to the battery. And the second switch is controlled according to the switching duty ratio.

3 is a diagram illustrating a method of operating a disturbance observer and a control unit according to an embodiment of the present invention.

), 양방향 컨버터(200), 커패시터(C), 부하(210,

), 외란 관측기(220) 및 제어부(230)이 도시되어 있다. 양방향 컨버터(200)는 인덕터(L), 제1스위치(Q1), 제2스위치(Q2), 제1다이오드(D1) 및 제2다이오드(D2)를 포함할 수 있다. 부하(210)는 가변저항으로 표시되어 있으나 가변저항으로 한정되는 것은 아니고, 전력을 생산하는 능동소자 또는 전력을 소비하는 수동소자로 동작할 수 있다.Referring to Figure 3, the battery, internal resistance of the battery (

), bidirectional converter 200, capacitor (C), load (210,

), a disturbance observer 220 and a control unit 230 are shown. The bidirectional converter 200 may include an inductor L, a first switch Q1, a second switch Q2, a first diode D1 and a second diode D2. The load 210 is indicated by a variable resistor, but is not limited to a variable resistor, and may operate as an active device that generates power or a passive device that consumes power.

Hereinafter, a process in which the disturbance observer 220 estimates a load current and the controller 230 controls the bidirectional converter 200 according to an embodiment of the present invention will be described.

1. The mathematical model of the circuit

는 이상적인 배터리 전압전원을 나타내고,

은 인덕터,

는 커패시터,

는 커패시터의 양단 전압,

은 부하 전류를 나타낸다. 부하는 가변저항일 수 있으며, 예를 들어 전기 자동차의 가속 또는 감속에 따라 저항 크기가 달라지는 모터를 의미할 수 있다. 부하 전류

은 가변저항의 크기에 따라 달라질 수 있다. 제1스위치 및 제2스위치의 온오프에 따라 회로로부터 수학식 1 내지 수학식 8을 도출할 수 있다.

Represents the ideal battery voltage power source,

Silver inductor,

Is the capacitor,

Is the voltage across the capacitor,

Represents the load current. The load may be a variable resistance, and for example, may refer to a motor whose resistance varies according to acceleration or deceleration of the electric vehicle. Load current

May vary depending on the size of the variable resistor. Equations 1 to 8 may be derived from the circuit according to the on/off of the first switch and the second switch.

Equations 1 to 9 are equations derived from a circuit when the bidirectional converter 200 operates as a boost converter. Equations 1 to 4 are equations derived from the circuit when the first switch is turned on and the second switch is turned off.

일 때, 수학식 3을 수학식 4와 같이 나타낼 수 있다.In Equation 3

When is, Equation 3 can be expressed as Equation 4.

Equations 5 to 8 are equations derived from the circuit when both the first switch and the second switch are turned off.

일 때, 수학식 7을 수학식 8과 같이 나타낼 수 있다.In Equation 7

When is, Equation 7 can be expressed as Equation 8.

When a switching duty ratio is applied to Equations 1 to 8 and expressed as an average model, it is as shown in Equation 9.

는 스텝 함수(step function)이다.In Equation 9

Is a step function.

일 때, 벅 컨버터의 수학 모델을 수학식 9와 동일하게 나타낼 수 있다.When the bidirectional converter 200 operates as a buck converter, a mathematical model of the circuit can be obtained using Equations 3 and 7. When the first switch is turned off and the second switch is turned on, the equation derived from the circuit is the same as in Equation 7, and when both the first switch and the second switch are turned off, the equation derived from the circuit is as in Equation 3.

When is, the mathematical model of the buck converter may be expressed in the same manner as in Equation 9.

와 벅 컨버터 동작에서

만 다를 뿐, 양방향 컨버터(200)의 수학 모델을 동작 모드와 상관없이 수학식 9와 같이 나타낼 수 있다.Therefore, in the boost converter operation of the bidirectional converter 200

And in buck converter operation

Only different, the mathematical model of the bidirectional converter 200 can be expressed as Equation 9 regardless of the operation mode.

일 때, 수학식 9를 수학식 10과 같이 나타낼 수 있다.To summarize Equation 9,

When is, Equation 9 can be expressed as Equation 10.

Equations 1 to 10 are equations using a continuous time model, and may be converted into discontinuous discrete time model equations by applying Euler approximation. When Equation 10 is converted to a discontinuous time model, it is as shown in Equation 11.

이고, h는 샘플링 시간(sampling time)이다.In Equation 11,

And h is the sampling time.

2. Disturbance Observer Model Design

The disturbance observer 220 measures the k-th state variable (inductor current and capacitor voltage), predicts the k-th state variable using the k-1 estimated value of the load current, and then predicts the k-th state variable. After subtracting the th state variable, a value obtained by multiplying the gain matrix and the sum of the k-1 th estimated value may be estimated as the load current.

Regarding the gain matrix, the state error is a matrix obtained by subtracting the measured k-th state variable from the state variable in the steady state, and the steady state operates based on the k-1 th switching duty ratio of the first switch or the second switch. When referring to a state, the gain matrix is a matrix calculated using a linear matrix inequality (LMI) so that the state error becomes zero.

는 부하전류의 k번째 추정값,

는 k-1번째 추정값,

는 측정한 k번째 상태변수,

는 예측한 k번째 상태변수, L은 이득행렬(gain matrix)일 때,

는 수학식 12로부터 추정될 수 있다.Explaining using the equation,

Is the kth estimated value of the load current,

Is the k-1th estimate,

Is the kth state variable measured,

Is the predicted k-th state variable, L is the gain matrix,

Can be estimated from Equation 12.

은 0 이거나 임의로 설정된 값일 수 있다.Meanwhile, in order to derive the first estimate of the load current

May be 0 or may be a randomly set value.

은 알려지지 않은 실제 부하 전류에 상수를 곱한 값을 의미하고, 이하에서는 부하전류를 추정하기 위해 외란

은

인 것으로 가정하여 설명한다. 이는, 부하전류가 수시로 변화하며 제어신호인 인덕터 전류기준치와 커패시터 전압기준치에 영향을 주기 때문이다.Referring to Equation 11 to specifically describe Equation 12,

Is the value obtained by multiplying the unknown actual load current by a constant. In the following, disturbances are used to estimate the load current.

silver

It is assumed that it is explained. This is because the load current changes from time to time and affects the inductor current reference value and the capacitor voltage reference value, which are control signals.

을 이용하여 수학식 13과 같이 표현될 수 있다.Meanwhile, Equation 11 is an expression including model uncertainty.

It can be expressed as Equation 13 by using.

인 경계값을 가진다.

은

으로써, 불확실성을 나타내는 u(k)를 포함하는 행렬이다. 즉,

은 최소값이

이고, 최대값이

이다. 이하에서는, 공칭 행렬(nominal matrix)

을

의 평균값으로 정의한다. 따라서, 수학식 13은 수학식 14와 같이 나타낼 수 있다.In Equation 13, u(k) denotes a switching duty ratio, and u(k) has a minimum value and a maximum value, respectively.

Has a threshold of

silver

As a result, it is a matrix including u(k) representing uncertainty. In other words,

Is the minimum value

And the maximum value is

to be. In the following, the nominal matrix

of

It is defined as the average value of. Therefore, Equation 13 can be expressed as Equation 14.

이다.In Equation 14

to be.

을 도출할 수 있다.In order to estimate d(k), which means an unknown load current, the disturbance observer 220 according to an embodiment of the present invention satisfies Equations 15 to 17.

Can be derived.

는 추정되는 럼프 외란(lump disturbance)이고, L은 대각선 이득 행렬(diagonal gain matrix)이다. 이득 행렬 L은

가 기하급수적인 형태로

에 수렴하도록 하는 행렬이다. 즉, 실제 외란과 추정된 외란 사이의 에러가 정상 상태(steady state)에서 0(zero)에 수렴하도록 L 행렬 내 원소 값이 결정된다. 정상 상태에서 시스템은 수학식 13 및 수학식 14로 표현될 수 있다. 이때, 수학식 13 및 수학식 14는 수학식 18 및 수학식 19를 만족해야 한다.here,

Is the estimated lump disturbance, and L is the diagonal gain matrix. The gain matrix L is

In exponential form

It is a matrix that converges to. That is, the values of the elements in the L matrix are determined so that the error between the actual disturbance and the estimated disturbance converges to 0 (zero) in a steady state. In the normal state, the system can be represented by Equations 13 and 14. At this time, Equations 13 and 14 must satisfy Equations 18 and 19.

Equation 20 may be derived by subtracting Equation 19 from Equation 18.

이 정상 상태에서의 스위칭 듀티비일 때, 외란

를 수학식 21과 같이 나타낼 수 있다.On the other hand, Equation 13 and Equation 20 are substituted into Equation 17,

When this is the switching duty ratio in the steady state, the disturbance

Can be expressed as in Equation 21.

이다. In Equation 21

to be.

Equation 22 can be derived by subtracting Equation 17 from Equation 12 and substituting Equation 19.

이다. In Equation 22

to be.

As a result, the model of the disturbance observer 220 according to an embodiment of the present invention may be expressed by Equations 21 and 22.

3. Calculation of the gain matrix L

이 안정적으로

에 수렴할 수 있도록 이득 행렬 L을 결정하는 방법을 설명한다.Hereinafter, using a linear matrix inequality (LMI), the k-th estimated value of the load current

This stably

A method of determining the gain matrix L so that it can converge on will be described.

Using Equation 21 and Equation 22, it can be expressed as Equation 23.

From this, it is necessary to determine the value of the gain matrix L so that the system can converge quickly while ensuring the stability of the system.

및

을 이용하여 수학식 24와 같이 표현될 수 있다. In the following, Equation 23 is a new variable

And

It can be expressed as Equation 24 by using.

이 임의의

에 대해 Hurwitz 기준을 만족해야 한다. 따라서, 행렬

이 Hurwitz 기준을 만족하도록 이득 행렬 L 값을 결정한다.In order for the system to be asymptotically stable, the matrix

This random

Must meet the Hurwitz criteria for Thus, the matrix

The gain matrix L value is determined to satisfy this Hurwitz criterion.

가 수학식 25를 만족하는 경우, 행렬

는 안정성을 보장할 수 있다. 여기서, 양 확정 행렬 P란, 0이 아닌 n 차원 벡터에 대해

를 만족하는 대칭행렬을 의미한다.Positive definite diagonal mtatrix

If is satisfies Equation 25, the matrix

Can guarantee stability. Here, the positive matrix P is for a non-zero n-dimensional vector

It means a symmetric matrix that satisfies.

,

,

을 만족한다.Equation 25 is

,

,

Is satisfied.

Meanwhile, Equation 25 may be expressed as Equation 26.

When Schur Decomposition is applied to Equation 26, Equation 26 can be expressed as Equation 27.

가

일 때, 수학식 27을 수학식 28과 같이 나타낼 수 있다.New variable

end

When is, Equation 27 can be expressed as Equation 28.

를 이용하여, 수학식 28에 대해 선형 행렬 부등식 LMI를 만족하는 행렬 L을 도출할 수 있다. 행렬 L은

에 의해 계산될 수 있다.The above definition

Using, it is possible to derive a matrix L that satisfies the linear matrix inequality LMI for Equation 28. Matrix L is

Can be calculated by

Hereinafter, a process of controlling the bidirectional converter 200 by using the estimated load current by the controller 230 according to an embodiment of the present invention will be described.

4. Control unit model design

The controller 230 sets the voltage reference value of the capacitor using the load current estimated by the disturbance observer 220 and the maximum current of the battery arbitrarily set, and then sets the current reference value of the inductor from the voltage reference value and the estimated load current. do. The controller 230 may determine the switching duty ratio from the set current reference value.

For example, when the estimated load current is greater than the average current flowing through the output terminal of the bidirectional converter 200 and the bidirectional converter 200 operates as a boost converter, the controller 230 first sets the maximum current of the battery to an arbitrary value. Can be set and the voltage reference value can be set. At this time, the average current flowing through the output terminal of the bidirectional converter 200 is a value obtained by multiplying the limit current value, which is the maximum current of the battery, by (1-D). Here, D is the on-off duty ratio of the first switch. The voltage reference value of the capacitor may be set by adding a value obtained by integrating a current measured voltage and a current value flowing through the capacitor. The current value flowing through the capacitor may be obtained from an estimated load current and an average current flowing through the output terminal of the bidirectional converter 200. The inductor current reference value and switching duty ratio can be obtained from the voltage reference value and the estimated load current.

이며,

는 인덕터 전류기준치이며,

는 커패시터의 전압기준치라고 할 때, 수학식 12를 수학식 29와 같이 나타낼 수 있다.Specifically, to describe the operation of the control unit 230, the switching duty ratio is a constant normal state,

Is,

Is the inductor current reference value,

When is the voltage reference value of the capacitor, Equation 12 can be expressed as Equation 29.

Equation 30 and Equation 31 can be derived from Equation 29.

에 대한 2차 방정식인 수학식 32를 도출할 수 있다.From Equation 30 and Equation 31,

Equation 32, which is a quadratic equation for, can be derived.

일 때,

에 대한 2차 방정식을 풀이하여 수학식 33을 도출할 수 있다.In Equation 32

when,

Equation 33 can be derived by solving the quadratic equation for.

는

및

에 의존한다. 즉, 전류기준치

는 설정된

와 추정된 부하전류

로부터 결정될 수 있다. When approximating that a and b are fixed values in Equation 33,

Is

And

Depends on In other words, the current reference value

Is set

And estimated load current

Can be determined from

을 이용하여 스위칭 듀티비를 결정한다. 제어부(230)는 양방향 컨버터(200)를 부스트 컨버터로 동작시킬 때 수학식 34와 같은 듀티비를 이용하여 제1스위치를 온오프시킬 수 있다. 제어부(230)는 양방향 컨버터(200)를 벅 컨버터로 동작시킬 때 수학식 35와 같은 듀티비를 이용하여 제1스위치를 온오프시킬 수 있다.The control unit 230 is a current reference value

The switching duty ratio is determined using. When operating the bidirectional converter 200 as a boost converter, the controller 230 may turn on and off the first switch using a duty ratio such as Equation 34. When operating the bidirectional converter 200 as a buck converter, the controller 230 may turn on and off the first switch using a duty ratio such as Equation 35.

4 is a diagram for explaining a process in which a bidirectional converter operates as a boost converter according to an embodiment of the present invention.

Referring to FIG. 4, when the bidirectional converter 200 operates as a boost converter, the flow of current and the flow of energy are illustrated. At this time, the second switch Q2 is always turned off.

은 제1스위치로 흐른다. 즉, 배터리, 배터리 내부저항(

), 인덕터(L) 및 제1스위치(Q1)가 폐회로를 구성한다. 배터리 전압이 인덕터에 인가되므로 인덕터 전류는 시간이 흐름에 따라 증가한다.When the first switch is turned on, the output current of the battery and the inductor current

Flows to the first switch. In other words, battery, battery internal resistance (

), the inductor L and the first switch Q1 constitute a closed circuit. Since the battery voltage is applied to the inductor, the inductor current increases over time.

)로 흐른다. 즉, 배터리, 배터리 내부저항, 인덕터, 제2다이오드, 커패시터 및 부하가 폐회로를 구성한다. 배터리로부터 출력된 전류는 커패시터 및 부하에 전달된다.When the first switch is turned off, the output current of the battery is transferred to the capacitor C and the load (

) Flows. That is, the battery, the internal resistance of the battery, the inductor, the second diode, the capacitor and the load constitute a closed circuit. The current output from the battery is delivered to the capacitor and the load.

By repeatedly turning on and off the first switch, the bidirectional converter 200 may operate as a boost converter.

5 is a diagram for explaining a process in which a bidirectional converter operates as a buck converter according to an embodiment of the present invention.

Referring to FIG. 5, when the bidirectional converter 200 operates as a buck converter, the flow of current and the flow of energy are illustrated. At this time, the first switch Q1 is always turned off.

When the second switch is turned off, power produced by the load is stored in the capacitor. Capacitors and loads form a closed circuit. As the capacitor charges over time, the voltage across the capacitor rises.

), 인덕터(L), 제2스위치(Q2), 커패시터 및 부하가 폐회로를 구성한다. When the second switch is turned on, energy stored in the capacitor is transferred to the battery. In other words, battery, battery internal resistance (

), the inductor (L), the second switch (Q2), the capacitor and the load constitute a closed circuit.

6 is a graph for explaining the performance of the bidirectional converter control apparatus according to an embodiment of the present invention.

6A shows a graph of the torque and rotational speed of the motor when the load is a motor, FIG. 6B is an actual measured load current and an estimated load current, FIG. 6C is a measured capacitor voltage and voltage reference value, and FIG. 6D is a measurement A graph of one battery current and a battery current (inductor current) reference value is shown.

Referring to FIG. 6A, the torque and rotation speed of the load are the discharge period (t1) of the battery and capacitor due to acceleration of the load (motor), the charging period (t2) of the capacitor, and the capacitor charging due to the regenerative braking of the load (motor). It is shown divided into section t3.

Referring to FIG. 6B, since a large load current is required in the load to increase the rotational speed of the motor in the period t1, the actual load current and the estimated load current increase. The load current hardly flows because the motor does not decelerate and accelerate in the t2 section. When the vehicle is decelerated in section t3, a negative current flows through the load due to the regenerative braking of the load. It can be seen from FIG. 6B that the load current graph estimated from the disturbance observer according to an embodiment of the present invention is very similar to the actually measured load current graph.

6C and 6D, since energy stored in the battery and the capacitor is transferred to the load in the period t1, the voltage of the capacitor decreases and the output current of the battery increases. It can be seen that the capacitor voltage increases as the energy stored in the battery is transferred to the capacitor in the period t2. In the period t3, the power produced from the load is transferred to the capacitor and the capacitor voltage increases.

6B, 6C, and 6D, the estimated load current is similar to the actual load current, and by using the capacitor voltage reference value and the inductor current reference value derived from the estimated load current, the battery and the capacitor are efficiently charged and discharged. You can see that you can do it.

7 is a graph for explaining the performance of the bidirectional converter control apparatus according to an embodiment of the present invention.

7A, 7B, 7C, and 7D, control according to a period in which the battery and capacitor are discharged (t1), a period in which the battery is discharged and the capacitor is charged (t2), and a period in which only the battery is discharged (t3). A graph of the operation of the device is shown.

Referring to FIG. 7A, the torque of the load (motor) increases in the period t1 and has a constant value in the period t2 and t3. Referring to FIG. 7B, the load current increases in the period t1 and has a constant positive value in the period t2 and t3.

Referring to FIG. 7C, since not only the battery but also the capacitor is discharged in the period t1, the voltage of the capacitor decreases, and in the period t2, the voltage increases because the capacitor is charged by the battery. In the period t3, all the power required for the load is supplied from the battery, so the voltage of the capacitor is kept constant.

Referring to FIG. 7D, the battery current (inductor current) has a positive value since the battery supplies a lot of load current or charges the capacitor in periods t1 and t2. In the period t3, the capacitor is not charged and discharged, and the load current is small, so the current of the battery in the period t3 has a smaller positive value than in the period t1 and t2.

7B, 7C, and 7D, the estimated load current is similar to the actual load current, and by using the capacitor voltage reference value and the inductor current reference value derived from the estimated load current, the battery and the capacitor are efficiently charged and discharged. You can see that you can do it.

8 is a flowchart illustrating a method of controlling a bidirectional converter according to an embodiment of the present invention.

The disturbance observer 220 according to an embodiment of the present invention may estimate the load current through the process described in FIG. 3 (S800).

The controller 230 determines whether the load is in a state of consuming power or generating power by using the load current estimated by the disturbance observer 220 (S802). For example, if the estimated load current is positive, the controller 230 may determine that the load consumes power, and if the estimated load current is negative, the load generates power.

When the load consumes power, the controller 230 determines whether the estimated load current is equal to or greater than a preset value (S804). Here, the preset value means an average current flowing through the output terminal of the bidirectional converter 200. The average current flowing through the output terminal of the bidirectional converter 200 is an average value of the current transferred from the battery to the load.

When the estimated load current is greater than or equal to a preset value, the output current of the battery is limited to an arbitrarily set value, and power required for the load may be supplied by discharging the capacitor (S806). That is, it is possible to supply power to the load by discharging the battery and the capacitor together. In this case, the output current of the battery may be limited.

When the estimated load current is less than the preset value, the battery charges the capacitor and supplies power to the load within the maximum current range of the battery (S808). That is, when the sum of the current required for the load and the current required to charge the capacitor is less than the limit current value of the battery, the battery can charge the capacitor and supply power to the load.

Meanwhile, when the load generates power, the controller 230 determines whether the voltage of the capacitor is a preset voltage (S810). Here, the preset voltage may be a maximum voltage (saturated voltage) of the capacitor or a randomly set value.

When the voltage of the capacitor is the maximum voltage, the controller 230 turns off both the first switch and the second switch to store the power generated from the load in the capacitor (S812).

When the voltage of the capacitor is less than the maximum voltage, the controller 230 controls the first switch and the second switch to prevent the capacitor from being saturated, and transfers the energy stored in the capacitor to the battery (S814).

In FIG. 8, steps S800 to S812 are described as sequentially executing, but this is merely illustrative of the technical idea of an embodiment of the present invention. In other words, if one of ordinary skill in the art to which an embodiment of the present invention pertains, within the range not departing from the essential characteristics of an embodiment of the present invention, the order shown in FIG. 8 is changed and executed, or one of the processes S800 to S812. Since the above processes are executed in parallel, various modifications and variations may be applied, and thus FIG. 8 is not limited to a time-series order.

Meanwhile, the processes shown in FIG. 8 can be implemented as computer-readable codes on a computer-readable recording medium. The computer-readable recording medium includes all types of recording devices that store data that can be read by a computer system. That is, the computer-readable recording medium includes storage media such as magnetic storage media (eg, ROM, floppy disk, hard disk, etc.) and optical reading media (eg, CD-ROM, DVD, etc.). In addition, the computer-readable recording medium can be distributed over a computer system connected through a network to store and execute computer-readable codes in a distributed manner.

The above description is merely illustrative of the technical idea of the present embodiment, and those of ordinary skill in the technical field to which the present embodiment belongs will be able to make various modifications and variations without departing from the essential characteristics of the present embodiment. Accordingly, the present embodiments are not intended to limit the technical idea of the present embodiment, but to explain the technical idea, and the scope of the technical idea of the present embodiment is not limited by these embodiments. The scope of protection of this embodiment should be interpreted by the following claims, and all technical ideas within the scope equivalent thereto should be construed as being included in the scope of the present embodiment.

200: bidirectional converter 210: load
220: disturbance observer 230: control unit

Claims (10)

Including an inductor, a first switch and a second switch, the input terminal is connected in parallel to the battery, and the output terminal controls a capacitor and a bi-directional converter connected in parallel to the load In the two-way converter control device,
Predict the k-th state of variables using the k-1 estimated value of the load current, and the load current using the predicted k-th state variable, the measured k-th state variable, and the k-1 estimated value. A disturbance observer that derives the k-th estimate of; And
And a control unit for operating the bidirectional converter as a boost converter or a buck converter according to the k-th estimated value,
The state variable is a bidirectional converter control device including an inductor current and a capacitor voltage. The method of claim 1,
The control unit,
When the k-th estimated value of the load current means a state in which the load consumes power, and the k-th estimated value is greater than the average current flowing through the output terminal of the bidirectional converter, the first switch and the first switch and the first switch are discharged so that the capacitor is discharged. A two-way converter control device for operating the two-way converter as a boost converter by controlling two switches. The method of claim 1,
The control unit,
When the k-th estimated value of the load current means a state in which the load consumes power, and the k-th estimated value is less than the average current flowing through the output terminal of the bidirectional converter, the first switch and the first switch and the capacitor are charged so that the capacitor is charged. A two-way converter control device for operating the two-way converter as a boost converter by controlling a second switch. The method of claim 1,
The control unit,
When the k-th estimated value of the load current means a state in which the load produces power, and the voltage of the capacitor is lower than the maximum voltage, the first switch and the second switch are turned off to charge the capacitor. Controlled bidirectional converter control. The method of claim 1,
The control unit,
When the k-th estimated value of the load current refers to a state in which the load produces power, and the voltage of the capacitor is the maximum voltage, the first switch and the second switch are configured so that the energy stored in the capacitor is transferred to the battery. By controlling, the bidirectional converter control device for operating the bidirectional converter as a buck converter. In the control method of a bidirectional converter comprising an inductor, a first switch and a second switch, an input terminal connected in parallel to a battery, and an output terminal connected in parallel to a capacitor and a load,
The k-th state variable is predicted by using the k-1 estimated value of the load current, and the k-th estimated value of the load current is calculated using the predicted k-th state variable, the k-th state variable measured, and the k-1 th estimated value. An estimation process to derive; And
A control process of operating the bidirectional converter as a boost converter or a buck converter according to the k-th estimated value,
The state variable is a control method of a bidirectional converter including an inductor current and a capacitor voltage. The method of claim 6,
The control process,
When the k-th estimated value of the load current means a state in which the load consumes power, and the k-th estimated value is greater than the average current flowing through the output terminal of the bidirectional converter, the first switch and the first switch and the first switch are discharged so that the capacitor is discharged. Two-way converter control method, which is a process of operating the two-way converter as a boost converter by controlling two switches. The method of claim 6,
The control process,
When the k-th estimated value of the load current means a state in which the load consumes power, and the k-th estimated value is less than the average current flowing through the output terminal of the bidirectional converter, the first switch and the first switch and the capacitor are charged so that the capacitor is charged. A method of controlling a bidirectional converter, which is a process of operating the bidirectional converter as a boost converter by controlling a second switch. The method of claim 6,
The control process,
When the k-th estimated value of the load current means a state in which the load produces power, and the voltage of the capacitor is lower than the maximum voltage, the first switch and the second switch are turned off to charge the capacitor. Two-way converter control method, which is the process of controlling. The method of claim 6,
The control process,
When the k-th estimated value of the load current refers to a state in which the load produces power, and the voltage of the capacitor is the maximum voltage, the first switch and the second switch are configured so that the energy stored in the capacitor is transferred to the battery. By controlling, the bidirectional converter control method is a process of operating the bidirectional converter as a buck converter.

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