JP2009106131A - Voltage control method and voltage controller - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a voltage control method and a voltage controller which suppress steady strain and oscillation of a load voltage at self-sustaining operation, which are caused by disturbance near a resonance frequency of an AC filter. <P>SOLUTION: In the voltage controller in which an inverter 4 is connected to a load 5 side through the AC filter 3 constituted by an LC or an LCL using a coil L and a capacitor C, a value of an output current of the inverter 4 is detected as a detected current value of the inverter, the detected current value of the inverter is differentiated, a primary lag is applied to the detected current value of the inverter, and then the detected current value is added to a voltage command value. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a voltage control method and a voltage control apparatus.

  In general, in a power system, a parallel type voltage sag compensator is used as a voltage control device for the purpose of preventing equipment stoppage or malfunction due to an instantaneous voltage drop (instantaneous voltage drop) caused by a sudden load change or lightning strike. FIG. 8 is a diagram showing a system configuration example of a conventional voltage control apparatus. As shown in FIG. 9, the conventional voltage control apparatus supplies power from the system power supply 11 to the load 12 via the high-speed switch 10 in normal times when no sag occurs. The ACL 13 may be connected to the system side of the high speed switch 10.

  In general, an LC or LCL filter is installed as the AC filter 14 on the load side of the voltage control device. The voltage control device in which the AC filter 14 is installed normally puts the inverter 20 in a standby state or charges the electric double layer capacitor 21. In addition, in order to increase the functionality, the inverter 20 may be operated even when the system power supply 11 is connected to provide a function of compensating for harmonic current. When a voltage sag occurs, this voltage sag is detected, the high-speed switch 10 is shut off, the DC power stored in the electric double layer capacitor 21 is converted into AC power by the inverter 20, and no load is supplied to the load 12. Supply power with a momentary interruption.

FIG. 9 is a control block diagram of a conventional voltage control apparatus. As shown in FIG. 9, the control block 16 (see FIG. 8) generates a sine wave corresponding to the rated voltage synchronized with the system voltage V _S before the occurrence of the voltage sag, as a phase synchronization circuit (PLL) 17 and a sine wave generator. 18 and create. When a voltage sag is detected, the PLL 17 is disabled and a sine wave generator 18 'creates a sine wave having a rated frequency and outputs this as a voltage command value V ^* . The voltage command value V ^* is input to the PWM control unit 19 shown in FIG. 8, a gate signal is input from the PWM control unit 19 to the inverter 20, and load power supply is performed by the inverter 20.

In general, AVR control is used for voltage control, but for simplification of description, the voltage command value V _REF is included here for the sake of simplicity. In an actual voltage control device, feedback control is performed such that the voltage command value V _REF is corrected by matching a deviation from a detected value in order to perform constant voltage control.

  An example of the conventional voltage control apparatus as described above is disclosed in Patent Document 1 below. In the voltage control device disclosed in Patent Document 1 below, there is no description that the AC filter 14 is installed on the inverter output side, but in the actual device, the AC filter 14 is installed to remove harmonics.

JP-A-9-182316 Yasuchika Mori, “Control Engineering”, Corona, December 2001, p. 37-45

When the rectifier load 12 is connected to the above-described conventional voltage control device, when a voltage sag occurs in the system power supply 11, the conventional voltage control device detects this voltage sag, shuts off the high-speed switch 10, and the inverter 20 Power is supplied to the load 12. Such a state is called independent operation. Then, during the self-sustained operation, the voltage command value V _REF is created so that the load voltage becomes a sine wave, and the load is fed by the inverter 20.

  However, in the conventional voltage control device, when no resistor is connected in series with the capacitor C of the AC filter 14 for suppressing the carrier of the inverter output, or when the connected resistance value is small, the load voltage is controlled to a sine wave. There is a problem that steady distortion and oscillation occur. This problem occurs due to a disturbance near the resonance frequency of the AC filter 14.

  For this reason, the present invention provides a voltage control method and a voltage control device for suppressing steady distortion and oscillation of a load voltage during self-sustained operation, which are caused by disturbance near the resonance frequency of the AC filter 14. With the goal.

The voltage control method according to the first aspect of the present invention for solving the above problem is as follows:
In the voltage control apparatus in which the inverter is connected to the load side through an AC filter configured by LC or LCL using the coil L and the capacitor C.
The value of the output current of the inverter is detected as an inverter current detection value,
Differentiating the inverter current detection value,
A first-order lag is applied to the differentiated inverter current detection value and then added to the voltage command value.

A voltage control method according to a second invention for solving the above problem is the voltage control method according to the first invention.
Detecting the value of the current flowing through the capacitor in the AC filter as a capacitor current detection value;
The capacitor current detection value is multiplied by a proportional gain and added to the voltage command value.

A voltage control apparatus according to a third invention for solving the above-described problem is
In the voltage control apparatus in which the inverter is connected to the load side through an AC filter configured by LC or LCL using the coil L and the capacitor C.
Inverter current detection means for detecting the value of the output current of the inverter as an inverter current detection value;
Differentiating means for differentiating the inverter current detection value;
Minor loop means for adding a first order delay to the inverter current detection value differentiated by the differentiating means and adding to the voltage command value.

A voltage control method according to a fourth aspect of the invention for solving the above problem is the voltage control method according to the third aspect of the invention,
Capacitor current detection means for detecting the value of the current flowing through the capacitor in the AC filter as a capacitor current detection value;
Feedback means for adding the capacitor current detection value to the voltage command value after multiplying the capacitor current detection value by a proportional gain.

  According to the present invention, when a resistor is not connected in series with the capacitor of the AC filter for suppressing the carrier of the inverter output, or when the connected resistance value is small, the steady state caused by disturbance near the resonance frequency of the AC filter. Distortion and oscillation can be suppressed.

  Embodiments of a voltage control method and a voltage control apparatus according to the present invention will be described with reference to the drawings. 1 is a control block diagram of a voltage control method and a voltage control device according to the first embodiment of the present invention, and FIG. 2 is a transfer function of the voltage control method and the voltage control device according to the first embodiment of the present invention. FIG. 3 is a control block diagram of a voltage control method and a voltage control device according to a second embodiment of the present invention, and FIG. 4 is a voltage control method and a voltage control device according to the second embodiment of the present invention. FIG. 5 is a diagram showing a modification of the transfer function of the voltage control method and voltage control device according to the second embodiment of the present invention, FIG. 6 is a diagram showing an AC filter circuit, and FIG. 7 is a diagram showing a transfer function of a conventional voltage control apparatus.

  Hereinafter, a voltage control method and a voltage control device according to a first embodiment of the present invention will be described. The system configuration according to the present embodiment is the same as the conventional system configuration shown in FIG. 8, and thus detailed description thereof is omitted here.

First, the transfer function of the conventional voltage control apparatus will be described.
As shown in FIG. 6, in an AC filter 3 having an LC configuration located between an inverter 4 and a load 5, a conventional voltage control device having an input as an inverter voltage V _INV and an output as a load voltage _VL . The transfer function F _LC (s) can be expressed as a control block diagram shown in FIG. This is summarized as the following formula (1).

Therefore, the resonance frequency is expressed by the following formula (2).

FIG. 1 shows a control block diagram of a voltage control method and a voltage control apparatus according to this embodiment. The voltage control method and voltage control device according to the present embodiment have a configuration in which a first block 1 described later is added to the voltage command value V _REF of the conventional voltage control device. The first block 1 is installed at the subsequent stage of the sine wave generator 18 'shown in FIG.

In the first block 1, the inverter current detection value I _INV that is the value of the output current of the inverter 4 is differentiated, and further, a first-order lag is applied to the differentiated inverter current detection value I _INV to _{obtain the} voltage command value V _REF . A minor loop to be added is added. In the first block 1, since the differentiated and first-order-delayed inverter current detection value I _INV is targeted to a stable value (0 = no change), a match with “0” is performed. Yes.

Further, in other words, the voltage control apparatus according to the present embodiment includes an inverter current detecting means for detecting the value of the output current of the inverter 4 as an inverter current detection value I _INV, a differentiating means for differentiating the inverter current detection value I _INV Minor loop means for adding a first-order delay to the detected inverter current value I _INV differentiated by the differentiating means and adding it to the voltage command value V _REF is provided.

In consideration of this current minor loop, the transfer function when the input is the inverter voltage V _INV and the output is the load voltage V _L can be expressed as a block diagram as shown in FIG. When this is collectively F ′ _LC (s), the following equation (3) is obtained. Α represents a gain constant and β represents a time constant.

  Here, it is determined whether or not the system according to the present embodiment is stable by using the Rouss stability determination method. Note that the Rouss stability determination method is a generally well-known method as disclosed in Non-Patent Document 1, and thus detailed description thereof is omitted here.

  The above equation (1) representing the transfer function of the conventional voltage control device is not a positive value because the first-order term is “0”, and does not satisfy the necessary condition of the stability determination method of Rous. Is not stable. On the other hand, the above equation (3) according to the present embodiment satisfies the necessary condition of the Rouse stability determination method, and further, an appropriate gain constant α and By selecting the time constant β, the system can be stabilized.

  That is, the gain constant α is determined by the L value of the AC filter 3, but actually, a value of α smaller than the gain determined by the L value is selected in consideration of control delay and the like. As the time constant β, “1 + βs” is used as a low-pass filter, and a desired cutoff frequency is determined from the AC filter resonance frequency or the like.

Further, the gain constant α and the time constant β are selected so that the expression (3) is stable (a value that converges without divergence). At this time, “1 (0th-order term)”, “β · s (first-order term)”, “(LC + Cα) s ² (second-order term)” and “LCβ · s ³ (third-order term) in the denominator of the above formula (3). If the gain constant α and the time constant β are selected so that all of “)” are positive values, the above expression (3) satisfies the necessary and sufficient condition for stability.

  From the above, according to the voltage control method and the voltage control apparatus according to the present embodiment, steady distortion and oscillation of the load voltage during the self-sustained operation caused by disturbance near the resonance frequency of the AC filter 3 are caused. Can be suppressed.

Hereinafter, a voltage control method and a voltage control apparatus according to a second embodiment of the present invention will be described.
In the present embodiment, H (s) is defined as in the following formula (4) in the above formula (3) according to the first embodiment.

  FIG. 3 shows a control block diagram of the voltage control method and voltage control apparatus according to the present embodiment. This is a configuration in which a second block 2 is added to the control block diagram of the voltage control method and the voltage control apparatus according to the first embodiment shown in FIG. The first block 1 and the second block 2 to be described later are installed at the subsequent stage of the sine wave generator 18 'shown in FIG.

The second block 2 has a form in which feedback for adding the detected value of the current I _C flowing through the capacitor C in the AC filter 3 shown in FIG. 6 to the voltage command value V _REF by multiplying by a proportional gain K is added.

In other words, the voltage control apparatus according to the present embodiment includes a capacitor current detection unit that detects the value of the current I _C flowing through the capacitor C in the AC filter 3 as a capacitor current detection value, and the value of the current I _C as a proportional gain. Feedback means for adding the voltage command value _VREF to the voltage command value _VREF .

When the input function is V _INV and the output is V _L , the transfer function can be expressed as a block diagram as shown in FIG. Here, the output current I _OUT to the input, the transfer function when the output was V _L 'as _LC, F' F 'in order to obtain the'_'LC, modified as shown in FIG. 5 is a block diagram of FIG. 4 To do. From FIG. 8, the transfer function is summarized and F ″ _LC is expressed by the following equation (5).

  The above equation (5) satisfies the necessary conditions for the Rouse stability discrimination method, and can further stabilize the system by selecting an appropriate proportional gain K that satisfies the necessary and sufficient conditions for the Rouse stability discrimination method. . As a result, it is possible to suppress the steady distortion and oscillation of the load voltage during the self-sustained operation caused by disturbance near the resonance frequency of the AC filter 3.

  The present invention provides a voltage source for supplying a voltage to a load, a parallel type voltage sag compensator (including a main circuit configuration in which an ACL is installed on the system input side), an uninterruptible power supply and the like. The present invention can be used for a voltage control method and a voltage control apparatus that suppress steady distortion and oscillation.

1 is a control block diagram of a voltage control method and a voltage control apparatus according to a first embodiment of the present invention. It is the figure which showed the transfer function of the voltage control method and voltage control apparatus which concern on 1st Example of this invention. It is a control block diagram of the voltage control method and voltage control apparatus which concern on 2nd Example of this invention. It is the figure which showed the transfer function of the voltage control method and voltage control apparatus which concern on 2nd Example of this invention. It is the figure which showed the deformation | transformation of the transfer function of the voltage control method and voltage control apparatus which concern on 2nd Example of this invention. It is the figure which showed AC filter circuit. It is the figure which showed the transfer function of the conventional voltage control apparatus. It is the figure which showed the system configuration example of the conventional voltage control apparatus. It is a control block diagram of the conventional voltage control apparatus.

Explanation of symbols

1 1st block 2 2nd block 3 AC filter 4 Inverter 5 Load

Claims (4)

In the voltage control apparatus in which the inverter is connected to the load side through an AC filter configured by LC or LCL using the coil L and the capacitor C.
The value of the output current of the inverter is detected as an inverter current detection value,
Differentiating the inverter current detection value,
A voltage control method characterized by adding a first-order delay to the differentiated inverter current detection value and adding it to a voltage command value. The voltage control method according to claim 1,
Detecting the value of the current flowing through the capacitor in the AC filter as a capacitor current detection value;
A voltage control method characterized in that the capacitor current detection value is multiplied by a proportional gain and then added to the voltage command value. In the voltage control apparatus in which the inverter is connected to the load side through an AC filter configured by LC or LCL using the coil L and the capacitor C.
Inverter current detection means for detecting the value of the output current of the inverter as an inverter current detection value;
Differentiating means for differentiating the inverter current detection value;
A voltage control apparatus comprising: a minor loop means for adding a first order delay to the inverter current detection value differentiated by the differentiating means and adding the first delay to the voltage command value. The voltage control method according to claim 3, wherein
Capacitor current detection means for detecting the value of the current flowing through the capacitor in the AC filter as a capacitor current detection value;
A voltage control apparatus comprising: feedback means for multiplying the capacitor current detection value by a proportional gain and adding it to the voltage command value.

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