JP3212849B2 - Active filter digital control system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION When controlling an arithmetic operation by sampling an analog signal having a single specific frequency component and converting it into a digital signal, an accurate predicted value after one sampling of the signal of the specific frequency component is required. And sometimes.
The present invention has a single specific frequency as a component as described above.
From digital signals obtained by sampling analog signals
The present invention relates to a digital control system that controls an active filter by obtaining a predicted value after one sampling .

[0002]

2. Description of the Related Art In a digital control system, an operation amount for controlling an object to be controlled is obtained by digital operation, but the actual control is usually performed during a cycle after one sampling. Therefore, when an input signal or the like serving as a control variable is used for digital operation, an error occurs unless a value predicted after one sampling time is used. The input signal may be, for example, a sinusoidal waveform having a single specific frequency, and various linear approximation methods are conventionally used as a method for predicting a value of such a waveform after one sampling. Was.

[0003]

The above-described linear approximation method has a problem in accuracy, and it is difficult to accurately predict the value after one sampling. In particular, in the above-described active filter or the like that removes a harmonic of a specific frequency from an AC voltage / current, a value after one sampling of a harmonic of a specific frequency to be removed is predicted, and switching of the active filter is performed based on the predicted value. It is important to control the device. However, the above-mentioned linear approximation and the like cannot accurately predict the value after one sampling, and cannot perform highly accurate control.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above-mentioned problems of the prior art, and an object of the present invention is to sample an output of a band-pass filter that passes a harmonic of a specific frequency included in an AC power supply current. It is another object of the present invention to provide an active filter digital control system capable of performing highly accurate control by accurately predicting the instantaneous value of the harmonic of the specific frequency one sampling time after the sampling value.

[0005]

FIG. 1 is a diagram for explaining a prediction method according to the present invention. In the figure, time t1 is the start time of the current sampling period, and t0 is one sampling time T
The time before s, t2 is the time after one sampling time Ts. As described above, in the digital control system, the digital operation is performed during the current sampling period (t1 to t2), and the resulting control is executed in the subsequent sampling period. Therefore, for example, as shown in FIG. 1A, when digitally calculating a signal of a specific frequency (angular frequency = ω) during the current sampling period, the time t
The value i ^* at 2 must be used, and it becomes necessary to predict the value i ^* at time t2.

In the present invention, the above prediction is performed as follows. As shown in FIG. 1, the value i0 at time t0
, The value i1 at time t1, the value i ^{* at} time t2
Are three points on a sine wave of a specific frequency f, i0, i1
, I ^* are represented by the following equations (1) to (3). Im sin (ωt1−ωTs−θ) = i0 (1) Imsin (ωt1−θ) = i1 (2) Imsin (ωt1 + ωTs−θ) = i ^* (3) where Im is a specific frequency. The peak value of the component i, Ts is one sampling period, and θ is the phase of the specific frequency component.

From the above equations (1) and (2), the following equation (4) is obtained. i1 sin (ωt1−ωTs−θ) = i0 sin (ωt1−θ) (4) From the equation (4), the following equation (5) is obtained. cos (ωt1−θ) = ｛(i1cosωTs−i0) / (i1sinωTs)｝ sin (ωt1−θ) (5)

The following equation (6) is obtained from the equation (3). i ^* = Im sin (ωt1−θ) cos ωTs + Imcos (ωt1−θ) sin ωTs (6) From the equations (3), (5) and (6), the following equation (7) is obtained. ^{i * = 2i1 cos ωTs -i0 ...} (7) i.e., predict that before one sampling value i0 as shown in FIG. 1 (b), the value i ^* of after one sampling using the values i1 of the current sampling instant be able to.

[0009] To solve the above problems, the invention of claim 1 of the present invention, from the sampling values of the components of the specific frequencies before Symbol bandpass filter outputs, the (7) predicts the value after one sampling by formula and it is obtained by so as to remove harmonics of the specific frequency component included in the alternating current by using the prediction value, which makes it possible to perform high-precision control.

[0010]

[Embodiment of the Invention] Next active full embodiment of the present invention
The digital control system of the filter will be described . FIG.
FIG. 1 is a diagram illustrating an overall configuration of an active filter control system according to an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes an AC / DC converter including switching means SC1 to SC4 and a capacitor C1. The AC / DC converter 1 is subjected to PWM control by a control device (not shown), converts an AC voltage supplied from the power supply 3 through the three-winding transformer Tr to a DC voltage, and supplies the DC voltage to, for example, a load L of an electric vehicle or the like. .

During the operation of the AC / DC converter 1, a 1.8 kHz harmonic (angular frequency = ω) corresponding to the PWM control switching frequency (1.8 kHz in this embodiment) is output from the AC / DC converter 1. ) Occurs. The harmonics cause resonance with a distribution constant of a distribution line or the like, and have an adverse effect such as an abnormal increase in voltage. Reference numeral 2 denotes an active filter main circuit for removing the above harmonics,
The active filter main circuit is a bridge-connected S
A1 to SA4 switching means and a capacitor C2.
By performing the M control, the harmonics are removed.

Reference numeral 4 denotes an analog / active filter for detecting harmonics which selectively passes the harmonics of 1.8 kHz, and is an AC / DC detected by a current detector CT2.
Only the harmonic component ih is extracted from the inflow current iL into the converter 1 without phase delay. Reference numeral 5 denotes an analog-to-digital converter. The analog-to-digital converter 5 includes an output ih of the harmonic active analog active filter 4 and an input voltage VS of the active filter main circuit 2 detected by the voltage detecting transformer TR1. Inflow current i into active filter main circuit 2 detected by current detector CT1
c and the capacitor C2 detected by the voltage detector Vdt.
Is sampled and converted into a digital signal.

Reference numeral 6 denotes a digital signal processor (hereinafter D)
SP), and calculates a digital signal output from the analog-to-digital converter 5 to generate a control signal for performing PWM control on the switching means SA1 to SA4 of the active filter main circuit 2. The control output is a drive circuit 7 And the switching means SA1 to SA4 are controlled.

FIG. 3 is a block diagram showing the processing in the DSP 6, FIG. 4 is a diagram showing the configuration of the phase calculation means shown in FIG. 3, and FIG. 5 is a diagram showing the configuration of the prediction means 6a shown in FIG. 3, 4, and 5, the same components as those shown in FIG. 2 are denoted by the same reference numerals, 4 is the analog active filter for detecting harmonics, and 5 is the analog digital filter. A converter, 6 is a DSP, 7 is switching means SA1 to SA of the active filter main circuit 2.
4 is a driving circuit. In FIG. 4, reference numeral 61b denotes storage means for storing a value one sample before, and 62b denotes a sin which will be described later.
The calculation means for calculating (ωot + φ), 61a in FIG. 5 is a storage means for storing the value one sample before, and 62a is a calculation means for calculating the above equation (7).

Next, the control of the active filter in this embodiment will be described with reference to FIGS. 3, 4 and 5. FIG. The voltage Vdc across the capacitor C2 detected by the voltage detector Vdt, the harmonic current ih output from the harmonic active analog active filter 4, the voltage VS detected by the voltage detecting transformer TR1, and the voltage detected by the detector CT1. The current ic is sampled by the analog-to-digital converter 5, converted into a digital signal, and input to the DSP 6.

The voltage Vdc across the capacitor C2 and the reference voltage Vdc ^* input to the DSP 6 are given to a subtractor 6f.
The deviation is given to the proportional-plus-integral calculating means 6c. The proportional-plus-integral calculating means 6c performs a proportional / integral calculation on the deviation to obtain a peak value I of a current to flow into the active filter main circuit 2.
cor (peak value of the fundamental wave component current of the alternating current: for example, 50
Hz, angular frequency = ωo). On the other hand, the phase calculating means 6b calculates the voltage phase φ of the AC power supply 3 (angular frequency = ωo) from the voltage VS sampled and converted into a digital signal by the analog-to-digital converter 5, and sin (ω)
o t + φ) is output.

The above sin (ωot + φ) is calculated as follows. The voltage VS is a sine wave waveform, t1 is the current time,
t0 is the time before one sampling time Ts, V1 is the value of the current voltage VS, and V0 is the voltage V one sampling time before.
Assuming that the value of S, φ is the current phase of the signal V, and Ts is the sampling period, V0 and V1 are expressed by the following equation (8a) (8
b). V0 = Vm sin (ωo t1 + φ−ωTs) (8a) V1 = Vm sin (ωo t1 + φ) (8b)

Here, Vm is the peak value of the voltage VS, and ωo is the angular frequency of the AC voltage. From the above equations (8a) and (8b), the following equation (8c) is obtained. V0 / V1 = Vmsin (.omega.t1 + .phi .-. Omega.Ts) / Vmsin (.omega.t1 + .phi.) = Cos.omega.Ts- ｛sin.omega.Ts / tan (.omega.t1 + .phi.) (8c) From the above equation (8c), An expression is obtained. tan (ωo t1 + φ) = V1sinωo Ts / (V1cosωo Ts−V0) (8d)

Therefore, the following equation (8) is obtained from the equation (8d). sin (ωo t1 + φ) = sin [tan ^-1 {V1 sinωo Ts / (V1cosωo Ts−V0)}] (8) That is, as shown in FIG. The VS sampling value V0 is stored, and based on the current sampling value V1 and the sampling value V0 one sample before stored in the storage means 61b, the arithmetic means 62b calculates sin (ωot1 + φ) by the above equation (8). calculate.

The sin (ωo) output from the phase calculating means 6b
t1 + φ) is the peak value I output by the proportional-plus-integral calculating means 6c.
Cor is multiplied by the multiplier 6g to generate a command value icor ^* of the AC current flowing into the active filter main circuit 2. That is, the fundamental wave component of the AC current flowing into the active filter main circuit 2 is controlled so that the phase φ matches the phase of the power supply voltage VS, and the peak value Icor
Is controlled such that voltage Vdc = reference voltage Vdc ^* .

On the other hand, the prediction means 6a predicts the value ih ^* of the harmonic component ih after one sampling by the above-mentioned method. That is, as shown in FIG. 5, the prediction means 6a stores the sampling value of the harmonic component ih one sample before by the storage means 61a, and stores the sampling value i1 at the current time.
Based on the above and the sampling value before one sampling stored in the storage means 61a, the prediction value ih ^* after one sampling is obtained in the calculating means 62a by the above-mentioned equation (7).

The predicted value ih ^* of the harmonic component after one sampling obtained by the predicting means 6a is given to a subtractor 6h, and is subtracted from the command value icor ^* of the AC current.
The current command value icr (including the compensation of the harmonic component) is generated. That is, the predicted value ih ^* of the harmonic component (angular frequency = ω) is added to the command value icor ^* (angular frequency = ωo) of the alternating current ^.
(Corresponding to the compensation value of the harmonic component) is superimposed, and a current command value icr to flow into the active filter main circuit 2 is generated. The switching time calculating means 6d calculates the switching time based on the current command value icr as follows.

FIG. 6 is an equivalent circuit of the main circuit of the active filter in FIG. 2, and as shown in FIG.
The value of AF is L, the voltage on the input side of the active filter main circuit 2 is VS, the voltage on the AC side of the bridge circuit composed of the switching means SA1 to SA4 is Vi, and the capacitor C
1 is Vdc, the input current of the active filter main circuit 2 is ic, and the sampling cycle is Ts.
The following equations (9), (10), and (11) hold.

VS = Vi + L (di / dt) (9) di / dt = (1 / L) (VS-Vi) (10) Δic = (1 / L) (VS−Vi) ΔT (11) ) Where Δic = icr−ic, icr = icor ^* −ih ^* ,
ΔT = Ts = t1 + t2, Vi = Vdc.

From the above relationship, the switching means SA1 to SA1
The switching periods t1 and t2 of SA4 are the following (12)
It is calculated by equation (13). t1 = {VS Ts−L (icr−ic)} / Vdc (12) t2 = Ts−t1 (13) Switching periods t1, t calculated as described above
2 is supplied to the drive circuit 7 via the PWM signal generating means 6e, and the switching means SA1 to SA4 of the active filter main circuit 2 are controlled.

That is, as shown in FIG.
During a time tcal (for example, 10 μs) for calculating 1, t2, the switch means SA3 and SA1 are turned on. After this period has elapsed, if the period t1 is positive, the switch means SA1 and SA4 are turned on during the period t1, and
When the period t1 is negative, the switch means SA2 and SA3 are turned on during the period | t1 |.

When the period t1 elapses, the period t2
(= T2 '+ tcal), switch means SA3, SA
1 turns on. Switching means SA1 as described above
~ SA4, the harmonics of the specific frequency (1.8 kHz in this embodiment) superimposed on the power supply side are absorbed by the active filter, and the harmonics can be removed.

In the present embodiment, as described above, the active filter is controlled using the predicted value ih ^* of the harmonic component after one sampling, so that the high precision using the accurate predicted value is used. Control can be performed.

[0029]

As described above, the following effects can be obtained in the present invention. When removing a harmonic of a specific frequency using the active filter, a harmonic detection active filter for detecting the harmonic is provided, and the above (7) is obtained from the sampling value of the harmonic output by the harmonic detection active filter. ) predicts the value after one sampling by formula. Thus to remove harmonics of the specific frequency component included in the alternating current by using the predicted value, especially
1 sampling regardless of the size and phase of the constant frequency component
Later values can be predicted, and highly accurate control can be performed. Further, the above operation can be extremely easily processed by a processor unit such as a digital signal processor (DSP).

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a prediction method according to the present invention.

FIG. 2 is a diagram showing a configuration of an active filter control system according to an embodiment of the present invention.

FIG. 3 is a block diagram showing processing in a DSP 6 in FIG. 2;

FIG. 4 is a diagram showing a configuration of a phase calculating means 6b shown in FIG.

FIG. 5 is a diagram showing a configuration of a prediction unit 6a shown in FIG.

FIG. 6 is an equivalent circuit of the active filter main circuit shown in FIG. 2;

FIG. 7 is a diagram showing the operation of the switching means of the active filter.

[Explanation of symbols]

Reference Signs List 1 AC / DC converter 2 Active filter main circuit 3 Power supply 4 Analog / active filter for harmonic detection 5 Analog-to-digital converter 6 Digital signal processor (DS
P) 7 Drive circuit SC1 to SC4 Switching means SA1 to SA4 Switching means C1 Capacitor C2 Capacitor Tr Transformer L Load CT1 Current detector CT2 Current detector TR1 Voltage detecting transformer Vdt Voltage detector LAF, Lcon Reactor 6a Predicting means 6b Phase calculation Means 6c Proportional-integral calculating means 6d Switching time calculating means 6e PWM signal generating means 6f, 6h Subtracting means 6g Multiplier

────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Misi Abdallah 338-1 Kamisakuyanagi, Yamato-shi, Kanagawa Prefecture Toyo Electric Manufacturing Co., Ltd. (72) Inventor Katsuji Iida 338-1 Kamisakuyanagi, Yamato-shi, Kanagawa Toyo (56) References JP-A-48-38448 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01R 19/00 H02H 3/50-3 / 52 G06F 3/05 311

Claims (1)

(57) [Claims] 1. A bridge circuit comprising switching means connected in a bridge-like manner, and a capacitor connected to a DC side of the bridge circuit. The switching means is controlled to be supplied from an AC power supply. A digital control system for an active filter that removes a harmonic component of a specific frequency included in an alternating current, a bandpass filter that passes a harmonic component of a specific frequency included in an alternating current iL, and an output of the bandpass filter. The specific frequency component i
an analog-to-digital converter that samples and converts the instantaneous value of h, the instantaneous value of the AC power supply voltage VS, and the instantaneous value of the current ic flowing into the bridge circuit into a digital signal; Digital control means for controlling the switching means of the bridge circuit based on the sampling value of the AC power supply voltage VS, the digital control means calculates a phase φ of the power supply voltage, and the phase calculated by the phase calculation means A fundamental wave component icor ^* of the alternating current is generated based on φ, and a sampling value i1 of the component of the specific frequency sampled at the present time, a previous sampling value i0 of the component of the specific frequency, and an angle of the specific frequency. Frequency ω
And a sampling period Ts, the predicted value ih ^* of the signal of the specific frequency component after one sampling time is calculated as follows ^:
Equation ih ^* = 2 × i1 × cos (ωTs) −i0, the output ih ^{* of the} predicting means is subtracted from the fundamental wave component icor ^* of the alternating current, and the subtraction result, the power supply voltage VS and the current ic A digital control system for an active filter, wherein an open / close time of the switching means is calculated based on the following.