KR101562848B1 - Method for uninterruptible power supply system control by using active damping control scheme and repeat control techniques - Google Patents

Abstract

An uninterruptible power supply system according to the present invention comprises: a rectifying unit to convert an AC voltage inputted from a system into a DC voltage to supply the DC voltage to a DC link end; an inverter to convert the DC voltage supplied by a battery and the rectifying unit into an AC voltage to supply the AC voltage to a load; a positive feedback control unit to provide a positive feedback on the voltage or a current outputted from the inverter in order to stabilize power supplied to the load to calculate a command value of the inverter; and a repetition control unit to generate a frequency signal if a higher-order harmonic current is generated from the positive feedback control unit to compensate for a voltage of a harmonic component. According to the present invention, even when a nonlinear load is connected to generate a higher-order harmonic current for which the positive feedback control unit cannot compensate, the repetition control unit can compensate for a voltage drop of a higher-order harmonic to cancel out a distortion of an output voltage, and thus a stable voltage can be supplied.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method of controlling an uninterruptible power supply using an active damping-based repetitive control technique,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an uninterruptible power supply system, and more particularly, to an uninterruptible power supply system capable of applying a sinusoidal wave without distortion even when a non-linear load is connected to the system.

An uninterruptible power system (UPS) is an equipment that is installed to supply normal power to the equipment in use when there is an unexpected power outage or an excessive voltage drop due to an accident in an AC power source .

The use of uninterruptible power supplies is essential because advanced digital information processing equipment, such as industrial-grade equipment, medical equipment, and financial equipment, sensitive to power outages and voltage fluctuations of commercial power sources, require stable power supply even in the case of power outages or voltage irregularities.

Uninterruptible power supplies are divided into Pass-Standby, Line-Interactive and Double-Conversion depending on the dependency of input voltage and output voltage. The double-conversion method operates both the rectifier and the inverter to supply the constant voltage and the constant voltage to the load even when the normal input voltage is supplied. When the input voltage is abnormal, the battery is operated to supply the power. This has advantages in terms of reliability.

In recent years, the use of non-linear loads has been increasing as the use of sophisticated digital information processing equipment has increased. In a conventional uninterruptible power supply, when a nonlinear load is used, harmonics are contained in the UPS output voltage, resulting in non-sinusoidal distortion. In this case, there is a problem that the load equipment sensitive to the distortion of the output waveform may fail. Accordingly, there is a demand for an uninterruptible power supply device capable of supplying a stable output voltage without disturbance even when a large load variation or a nonlinear load is connected.

Korean Patent No. 1318960

The present invention provides an uninterruptible power supply system capable of stably supplying power to a load even when a large load variation or a nonlinear load is connected.

According to an aspect of the present invention, there is provided an uninterruptible power supply system comprising: a rectifier for converting an AC voltage input from a system into a DC voltage and supplying the DC voltage to a DC link stage; An inverter for converting a DC voltage supplied from the rectifying unit into AC and supplying the DC voltage to the load; A feedback controller for calculating a command value of the inverter by positively feedbacking the voltage or current output from the inverter to stabilize the power supplied to the load; And a repetition control unit for generating a periodic signal to compensate for a voltage of a harmonic component when a current of a harmonic order is generated from the feedback control unit.

Preferably, the feedback controller according to the present invention may include a current controller that calculates a voltage command value of the inverter that feeds back the current output from the inverter to cancel the disturbance generated in the current.

Preferably, the feedback controller according to the present invention may further include a voltage controller for calculating a voltage command value of the inverter that feedbacks the voltage output from the inverter to cancel the disturbance generated in the voltage.

Preferably, the repetition control unit according to the present invention is connected in parallel with the voltage controller to compensate for the voltage drop of the harmonic component output from the voltage controller.

Preferably, the repetition control unit according to the present invention can calculate a control signal for compensating the voltage command value of the inverter calculated by the voltage controller according to the following equation.

[Mathematical Expression]

는 제어 신호,

는 시스템 상수,

은 전기각 한 주기의 샘플링 횟수,

은 샘플링 데이터들을 기본 위상각 대비 진상시키기 위한 상수,

는 제어가 불가능한 고차 고조파 성분들의 불필요한 제어를 방지하기 위한 필터링 변수를 의미한다.here

A control signal,

Is a system constant,

The number of sampling times of one cycle of electricity,

A constant for advancing the sampling data to the basic phase angle,

Means a filtering parameter for preventing unnecessary control of the uncontrollable higher harmonic components.

Preferably, the uninterruptible power supply system according to the present invention further includes an LC filter connected in series with the inverter, and further includes an active damping control unit for improving the stability margin of the repetitive control unit by lowering the resonance point of the LC filter.

Preferably, the active damping controller according to the present invention can subtract the value obtained by multiplying the current value output from the inverter by the active damping gain from the output value of the feedback controller.

Preferably, the uninterruptible power supply system according to the present invention may further include a forward gain control unit for removing the influence of disturbance generated from the load.

Preferably, the forward gain control unit according to the present invention may add a value obtained by multiplying the voltage value output from the inverter by the forward control gain to the output value of the feedback control unit.

According to the present invention, even if a nonlinear load is connected and a harmonic-order current can not be compensated by the feedback control unit, the repetitive control unit compensates the voltage drop of the harmonic order to cancel the distortion of the output voltage, have.

The present invention is advantageous in that the active damping control unit controls the resistance component of the LC filter to lower the resonance point so that the effective gain of the repetitive control unit is prevented from being limited and the stability can be improved.

Further, the present invention is advantageous in that the forward gain control unit eliminates the delay caused by integration and signal delay of the feedback control unit, thereby improving the inertia of the uninterruptible power supply unit.

1 is a block diagram of an uninterruptible power supply system according to an embodiment of the present invention.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to or limited by the exemplary embodiments. Like reference numerals in the drawings denote members performing substantially the same function.

The objects and effects of the present invention can be understood or clarified naturally by the following description, and the purpose and effect of the present invention are not limited by the following description. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail.

1 is a block diagram of an uninterruptible power supply system according to an embodiment of the present invention. 1, the uninterruptible power supply system includes a rectifying unit 101, a battery, a battery charge / discharge unit 106, an inverter 103, an LC filter 108, a bypass switch 109, a feedback control unit 105, A control unit 107, an active damping control unit 1055, and a forward gain control unit 1057.

The uninterruptible power supply system according to this embodiment can be provided to a double conversion type UPS. The double conversion system is a double conversion system in which the inverter 103 receives the power of the battery and supplies the power to the load 13 in the case of a power failure, and has a double conversion structure for operating the uninterruptible power supply through the inverter 103, And the system power source 11 is directly supplied to the load stage 13 with the high-efficiency mode.

Since the uninterruptible power supply apparatus according to the present embodiment operates the bypass switch 109 at a normal system power supply (commercial power supply) 11 to supply power directly to the load 13 at the bypass line, . This offline operation is also referred to as a high efficiency mode. In the high-efficiency mode alone, a switching time takes place in the operation switching from normal operation to battery operation in the case of power failure, which may cause a momentary power failure situation in the load 13 even though it is a short time.

In this high efficiency mode, since the commercial power supply 11 is directly supplied to the lower stage 13, the unstable input voltage can be transmitted as it is. Therefore, it is not suitable for the load requiring stable output voltage and frequency, so the double conversion type UPS structure can be merged.

1 includes a rectifying part 101, a battery, a battery charge / discharge device 106, an inverter 103 and an LC filter 108 between the system 11 and the lower stage 13 .

The rectifying unit 101 can convert the AC voltage inputted from the system 11 into a DC voltage and supply it to the DC link stage. The DC link stage can be understood as an input terminal of the inverter 103 as a terminal to which the following inverter 103 is connected. A PWM rectifier, a three-level boost converter, or the like may be used as the rectifying part 101. The inverter 103 may be a two-level inverter, a three-level NPC (Neutral Point Clamp) inverter, a TNPC Can be used.

The power source of the system 11 is converted into a DC voltage through the PWM rectifier 101 and this voltage is again converted into an AC voltage through the inverter 103 and supplied to the load 13. The inverter 103 can convert the DC voltage supplied from the battery and the rectifying part 101 into AC and supply the DC voltage to the load 13.

The battery and the battery charge / discharge unit 106 are connected between the rectification unit 101 and the inverter 103. During the power failure, the battery power is converted to AC through the inverter 103 and supplied to the load 13 stage. With this structure, the uninterruptible power supply unit can perform the power unmotor switching to the load 13 at the time of the power failure, and at the time of the normal operation, the used power is double converted and supplied to the load 13, It is possible to supply the high-quality power of the load 13 to the load 13.

However, when a nonlinear load is connected to the load 13, harmonics are contained in the output voltage of the uninterruptible power supply. Conventional UPS control methods can not eliminate sinusoidal distortions caused by harmonics contained. The uninterruptible power supply system according to the present embodiment can eliminate sinusoidal distortion of harmonics through the feedback control unit 105 and the repetitive control unit 107 in the control of the UPS.

The feedback control unit 105 may calculate the command value of the inverter 103 by feedbacking the voltage or current output from the inverter 103 in order to stabilize the power supplied to the load 13. [ The feedback control section 105 may include a voltage controller 1051 or a current controller 1053. [

)를 궤환하여 인버터(103)의 전압 지령값(

)을 산출할 수 있다. 전류 제어기(1053)는 외란에 대한 동특성을 결정할 수 있다. The current controller 1053 outputs the current (" 0 ") output from the inverter 103 to cancel the disturbance generated in the output current

And outputs the voltage command value of the inverter 103

) Can be calculated. The current controller 1053 can determine the dynamic characteristics of the disturbance.

를 산출할 수 있다. 전류 제어기(1053)로는 P 제어기, PI 제어기, PID 제어기, PR 제어기가 사용될 수 있다.The LC filter 108 may be connected in series with the inverter 103. The current controller 1053 measures the output current value of the capacitor C side of the LC filter 108 and compares it with a reference value or set value that it desires to calculate an error. Using this error value,

Can be calculated. As the current controller 1053, a P controller, a PI controller, a PID controller, and a PR controller can be used.

)를 제어하여 부하(13)가 갑자기 변하거나 부하의 용량이 증가하거나 감소할 때에도 안정적으로 동작하게 하는 역할을 한다. 전류 제어기(1053)에는 후술하게 될 능동 댐핑 제어부(1055) 및 전향 이득 제어부(1057)가 추가적으로 연계될 수 있다.The current controller 1053 controls the capacitor current

So as to stably operate the load 13 even when the load suddenly changes or the load capacity increases or decreases. The current controller 1053 may additionally have an active damping controller 1055 and a forward gain controller 1057 to be described later.

)을 궤환하여 인버터(103)의 전압 지령값(

)을 산출할 수 있다. 전압 제어기(1051)로는 P 제어기, PI 제어기, PID 제어기, PR 제어기가 사용될 수 있다. The voltage controller 1051 adjusts the voltage output from the inverter 103 to cancel the disturbance generated in the output voltage

And outputs the voltage command value of the inverter 103

) Can be calculated. As the voltage controller 1051, a P controller, a PI controller, a PID controller, and a PR controller can be used.

When the voltage controller 1051 and the current controller 1053 are provided as a PI controller, the PI controller can remain in a normal state in size and phase error because the command is sinusoidal. In order to solve this problem, it is preferable to apply a proportional-resonance (PR) controller, which has been applied to the stationary coordinate system AC current controller of the three-phase AC motor, to the external voltage control loop. The proportional-resonance controller can increase the gain at the control frequency to zero the steady state error.

In this embodiment, the feedback control section 105 may be provided only with the voltage controller 1051 without the current controller 1053 or with the current controller 1053 without the voltage controller 1051. [

When a harmonic order current is generated from the feedback controller 105, the repetitive control unit 107 generates a periodic signal to compensate for the voltage of the harmonic component. The repetitive control unit 107 is connected in parallel or plug-in manner with the voltage controller 1051 to compensate for the voltage drop of the harmonic component output from the voltage controller 1051. [

When the nonlinear load 13 is connected to the uninterruptible power supply according to the present embodiment, a harmonic-order current that can not be compensated by the feedback controller 105 can be generated. When such a harmonic current is output, a voltage drop of harmonic order is generated by the output terminal impedance component of the LC filter 108. This results in distortion in the output voltage. These voltage distortions appear repeatedly at 50 Hz or 60 Hz in one cycle. The repetition control unit 107 compensates for this.

The repetition control unit 107 can compensate for one entire period of each electrical period. In this case, the repetitive control unit 107 can calculate a control signal for compensating the voltage command value of the inverter unit 103 calculated by the voltage controller 1051 according to the following equation (1).

[Equation 1]

는 제어 신호,

는 시스템 상수,

은 전기각 한 주기의 샘플링 횟수,

은 샘플링 데이터들을 기본 위상각 대비 진상시키기 위한 상수,

는 제어가 불가능한 고차 고조파 성분들의 불필요한 제어를 방지하기 위한 필터링 변수를 의미한다.here

A control signal,

Is a system constant,

The number of sampling times of one cycle of electricity,

A constant for advancing the sampling data to the basic phase angle,

Means a filtering parameter for preventing unnecessary control of the uncontrollable higher harmonic components.

The repetitive control unit 107 may be provided as an odd harmonic repetitive controller or an even harmonic repetitive controller that compensates only odd or even harmonics. In this case, the repetitive control unit 107 can calculate the control signal for compensating the voltage command value of the inverter unit 103 calculated by the voltage controller 1051 according to the following equation (2).

&Quot; (2) "

Each variable is as described in Equation (1).

은 진상되는 각이 전기각 주기의 1~3% 미만이 되도록 값이 설정될 수 있다.

는 제어가 불가능한 고차 고조파 성분들의 불필요한 제어를 방지하기 위하여 설정되는 것으로 일반적으로 1 보다 작은 상수 또는 하기의 [수학식 3]과 같이 위상지연이 없는 저역통과필터(LPF : low pass filter)의 형태로 구현될 수 있다. In equations (1) and (2)

May be set so that the angle at which the phase advances is less than 1 to 3% of the period of each electrical period.

Is generally set to a constant of less than 1 or in the form of a low pass filter (LPF) with no phase delay as in Equation (3): " (3) " Can be implemented.

&Quot; (3) "

는 필터링 상수이다. 반복 제어부(107)는 전압 제어기(1051) 도는 전류 제어기(1053)에 연결될 수 있으나 60Hz의 전원 주파수가 고정되는 전압 제어기(1051)에 연결되는 것이 보다 바람직하다. 이 경우, 60Hz에 대한 오차만 존재한다고 가정할 수 있고, 이의 고조파 성분에서 시스템 게인 이득을 상승시킴으로써 고조파의 전압 강하에 대한 출력 전압의 왜곡을 보상한다.here

Is a filtering constant. It is more preferable that the repetitive control unit 107 is connected to the voltage controller 1051 or the voltage controller 1051 which can be connected to the current controller 1053 but is fixed at a power frequency of 60 Hz. In this case, it can be assumed that there is only an error with respect to 60 Hz, and the distortion of the output voltage with respect to the voltage drop of the harmonic is compensated by raising the system gain gain at the harmonic component thereof.

The active damping control unit 1055 can improve the stability margin of the repetitive control unit 107 by lowering the resonance point of the LC filter 108. [ The active damping control unit 1055 relaxes the unstable elements of the controllers 1051 and 1053 by the resonance of the LC sensor 108.

The active damping control unit 1055 can lower the resonance point of the LC filter 108 by subtracting the value obtained by multiplying the current value output from the inverter 103 by the active damping gain from the output value of the feedback control unit 105. When the repetitive control unit 107 is added to the voltage controller 1051, the effective gain of the repetitive control unit 107 is limited by the resonance point of the LC filter 108. [ In this case, a lot of tuning work is required for the high performance of the controllers 1051 and 1053, and there is a problem that the controllers 1051 and 1053 become unstable even if the frequency is slightly changed.

The active damping control unit 1055 can control the resistance component capable of damping to suppress the resonance of the LC filter 108 to lower the resonance point of the LC filter 108. [ In this case, the stability margin of the voltage controller 1051 and the repetitive control unit 107 can be improved. When the stability margin is improved, the effective gain of the repetition control unit 107 is increased. If the effective gain of the repetitive control unit 107 is increased, the steady-state error can be removed more effectively, thereby improving the performance and stability of the entire control system.

)을 궤환할 수 있다. The forward gain control unit 1057 can eliminate the influence of the disturbance generated from the load 13. [ The forward gain control unit 1057 can compensate the load current, the capacitor current command of the LC filter 108, the output voltage, and the like in order to eliminate the influence of the load 13. In this embodiment, the forward gain control unit 1057 controls the output voltage (i.e., the output voltage) to minimize the integration or display open element of the feedback control unit 105

Can be fed back.

에 전향 제어 이득을 곱한 값을 궤환 제어부(105)의 출력값에 더함으로써 부하(13)에서 발생되는 외란의 영향을 최소화할 수 있다.The forward gain control unit 1057 receives the output voltage of the inverter

By adding the value obtained by multiplying the forward control gain by the forward control gain to the output value of the feedback control section 105, the influence of the disturbance generated in the load 13 can be minimized.

The control factors of the feedback controller 105 including the repetitive controller 107, the active damping controller 1055, and the forward gain controller 1057 can be calculated as follows.

&Quot; (4) "

는 전압 제어기(1051)의 전달함수,

는 전압 제어 시스템의 개루프 전달함수를 나타낸다.here,

The transfer function of the voltage controller 1051,

Represents the open loop transfer function of the voltage control system.

The error equation of the voltage control system including the repetitive control section 107 can be calculated by the following equation (5).

&Quot; (5) "

의 오른쪽항의

,

식이 안정해야 한다.

는 반복 제어부(107)를 포함하지 않은 궤환 제어 시스템의 전달함수로 볼 수 있다.

가 안정하려면 분모항(

)이 안정해야 한다.

항이 안정하기 위해서는 모든 근이 좌표명면에서 단위원(unit circle)안에 들어와야 한다. 또한,

이 안정하기 위해서는 분모항 구성 성분의 반복 제어부(107)와 관련된 전달함수(

)가 안정해야 한다. In order for the error equation of the voltage control system to be stable

Right of protest

,

The diet should be stable.

Can be regarded as a transfer function of the feedback control system that does not include the repetition control unit 107.

To be stable,

) Should be stable.

In order for the term to be stable, all roots must be within the unit circle in the coordinate plane. Also,

The transfer function related to the repetition control unit 107 of the demarcation term component

) Should be stable.

)가 안정하기 위해서는 small gain theorem에 의해서

조건이 만족되어야 한다. 따라서, 궤환 제어부(105)의 제어 인자들은

이 만족되도록 선정이 되어야 한다.The transfer function associated with the iterative control unit 107

) Is stabilized by the small gain theorem

The condition must be satisfied. Therefore, the control factors of the feedback control section 105

Should be satisfied.

The uninterruptible power supply system according to the present embodiment can eliminate the harmonic distortion generated in the nonlinear load 13 when the dual conversion type UPS is controlled. Accordingly, the total harmonic distortion (THD) can be reduced as compared with the conventional UPS, and a clean sinusoidal wave can be supplied to the load (13).

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. will be. Therefore, the scope of the present invention should not be limited to the above-described embodiments, but should be determined by all changes or modifications derived from the scope of the appended claims and equivalents of the following claims.

11: System 13: Load
101: rectification part 103: inverter
105: feedback control unit 106: battery charge /
107: Repetition control section 108: Filter section
109: Bypass switch 1051: Voltage controller
1053: current controller 1055: active damping control unit
1057: Forward gain control section

Claims (9)

A rectifier for converting an AC voltage input from the system into a DC voltage and supplying the DC voltage to the DC link stage;
An inverter for converting a DC voltage supplied from the rectifying unit into AC and supplying the DC voltage to the load;
A feedback control unit for calculating a command value of the inverter by positively feedbacking the voltage or current output from the inverter to stabilize power supplied to the load;
A repetition control unit for generating a periodic signal and compensating for a voltage of a harmonic component when a harmonic-order current is generated from the feedback control unit;
An LC filter connected in series with the inverter; And
And an active damping control unit for improving the stability margin of the repetitive control unit by lowering the resonance point of the LC filter.
The method according to claim 1,
The feedback control unit,
And a current controller for calculating a voltage command value of the inverter by feeding back the current output from the inverter to cancel the disturbance generated in the output current.
The method according to claim 1,
The feedback control unit,
And a voltage controller for calculating a voltage command value of the inverter by feeding back the voltage output from the inverter to cancel a disturbance generated in the output voltage.
The method of claim 3,
Wherein the repetition control unit comprises:
And the voltage controller is connected in parallel with the voltage controller to compensate for the voltage drop of the harmonic component output from the voltage controller.
The method of claim 3,
The repetition control unit,
Wherein a control signal for compensating the voltage command value of the inverter calculated by the voltage controller is calculated according to the following equation.
[Mathematical Expression]

here

A control signal,

Is a system constant,

The number of sampling times of one cycle of electricity,

A constant for advancing the sampling data to the basic phase angle,

Means a filtering parameter for preventing unnecessary control of the uncontrollable higher harmonic components.
delete The method according to claim 1,
The active damping control unit,
Wherein a value obtained by multiplying a current value output from the inverter by an active damping gain is subtracted from an output value of the feedback control section.
The method according to claim 1,
Further comprising a forward gain control unit for eliminating the influence of disturbance generated from the load.
9. The method of claim 8,
The forward gain control unit includes:
And a value obtained by multiplying a voltage value output from the inverter by a forward control gain is added to an output value of the feedback control section.

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