JPH0417528A - Harmonic compensator - Google Patents

Abstract

PURPOSE:To compensate an aimed lower harmonic preferentially, to reduce a compensation current of a higher band and thereby to reduce the capacity of a device by inserting an appropriate low-pass filter in series into a current instruction generating means. CONSTITUTION:A harmonic compensator constructed of a reactor 3, a power converter 4 and a capacitor 5 as a main circuit is connected in parallel to a harmonic generating load 2, an output current iA of the harmonic compensator is generated so that the harmonic component thereof cancels the harmonic component of a load current iL, and thereby a supply current iS is made to have a sine waveform not containing the harmonic component. A fundamental wave component is removed from a load current detection signal iLUVW in a fundamental wave removing circuit 20A, a compensation current instruction signal iCO* is generated in a current instruction computing circuit 20B, a compensation current instruction signal iC* is obtained in a low-pass filter 25 by attenuating a higher band of the current instruction signal iCO*, and a control is made in a current control circuit 10 so that the harmonic component of an output current feedback signal iAF of the power converter 4 may accord with the signal iC*.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a harmonic compensation device that actively compensates for harmonic current in a power system in general industrial power equipment, etc.
In particular, the present invention relates to a harmonic compensation device that primarily compensates for relatively low-order harmonics.

(Prior art) To suppress harmonic currents in power systems, a passive harmonic suppressor consisting of a reactor and a capacitor C1 and a resistor R has been used, but recently self-excited power converters have been used. Active harmonic compensators, which have been around for some time, are now becoming widely used. -For boat fishing, active harmonic compensators are more flexible because they have more freedom in control, and they have many advantages in terms of performance, especially if high-order compensation areas are omitted.

An example of a passive harmonic suppression device is a frequency tuning type L
C filters and high-pass LCR filters are common,
In actual power supply systems, a combination of these is used. Note that the passive type filter is a well-known technology, so the details will be omitted.

Next, we will look at an example of an active harmonic compensator.In practical terms, there are two main methods for extracting harmonic signals (removing the fundamental wave). The overall configuration of the harmonic compensator including the following will be explained with reference to FIG.

In the figure, an AC power source 1 supplies power to a harmonic generating load 2, and a harmonic compensator comprising a reactor 3, a power converter 4, and a capacitor 5 as a main circuit is connected in parallel to this. . Here, by generating the harmonic component of the output current iA of the harmonic compensation bag device so as to cancel out the harmonic component of the load current LL, the power supply current ls is made into a sine waveform that does not include a harmonic component. I can do it. Regarding the control circuit, it can be roughly divided into three functions. That is, the load current detection signal i LU
A current command generation means 20 consisting of a fundamental wave removal circuit 2OA that removes a fundamental wave component from VW, inverts the polarity, and generates a compensation current command signal i, and a current command calculation circuit 20B;
A current control section that controls the harmonic components of the output current iA of the harmonic compensator to match the compensation current command signals l and 8, and a DC voltage V of the power converter 4. This is a voltage control section that controls the voltage.

First, the voltage control section receives the voltage command signal VD given by the voltage setter 12 and the voltage feedback signal V by the voltage detector 9.
DP- is compared in an adder 17, and the deviation e7. It is amplified by the voltage control circuit 13 to become the fundamental wave current command signal (DC value) i, +n, and is multiplied by the power supply voltage signal V5LIVW detected by the voltage detector 8 to become the fundamental wave current command signal (AC value) 1 plA. , the adder 15 obtains the compensation current command signal lc8.

That is, the DC voltage VD is controlled in a closed loop by manipulating the fundamental wave current that is in phase with or opposite to the AC power supply voltage.

Next, in the current control section, the output command signal lA and the output power feedback signal lAF detected by the current detector 7 are compared in an adder 16, and the deviation e,1 is amplified in the current control circuit IO. This becomes an output voltage command signal VA, and further becomes a drive signal BDS by the PWM control circuit 11, which drives the power converter 4. That is, the output voltage of the power converter 4 is manipulated based on the output current command signal iA8, and the output current iA as a harmonic compensator is controlled in a closed loop.

Next, regarding the current command generation means 20, there are two methods as described above.

First, the first method will be explained using FIG. 11. Prior to the explanation, the coordinate transformation formula used in this circuit will be shown. (
This conversion formula uses the method described in the reference document "Generalized theory of instantaneous reactive power and its applications" Electrical Engineering Theory 860, 483 (1982-7). ) Phase voltage detection signal V for each phase of U, V, and W. .

According to equation (3), V*v and ■SW are converted into two-phase voltage signals ■Sa+■BB by the three-phase/two-phase conversion circuit 21. Similarly, the load current detection signal 1I- for each phase of U, V, and W
U+ lLV+ iLW is a three-phase/
Two-phase load current signal iLa+iL is generated by two-phase conversion circuit 22.
j. Using these, the pq calculation circuit 23 performs conversion according to equation (4), and calculates an instantaneous real power signal p and an instantaneous imaginary power signal q. With this transformation, U,
The harmonic order on the V, W or α, β coordinates is (-1) order on the pq coordinate.

(For example, the fundamental wave component is converted to DC.) Bypass filters 24P and 24Q remove the DC component from the instantaneous real power signal p and the instantaneous imaginary power signal q, respectively, and convert the AC bone ph and instantaneous imaginary power signal into AC bone ph and instantaneous imaginary power signal. The AC power signal qh is obtained, and the polarity is inverted by the polarity inverting circuits 2BP and 26Q, respectively, and a compensated instantaneous actual power command signal p' is obtained.
and a compensated instantaneous imaginary power command signal q3. This is again converted according to equation (5) by the arithmetic circuit 27 using the two-phase voltage conversion signal vSa+"s4 to obtain the two-phase compensation current command signal ICa+IC," and further 2
The phase/three-phase conversion circuit 30 generates a three-phase compensation current command signal IC.
u + 1cvi (obtain w'.

Next, the second method will be explained using FIG. 12.

(There is no difference in the circuit other than the current command generation means, so only that part will be explained.) This equation does not convert into an instantaneous real power signal and an instantaneous imaginary power signal, but instead outputs the load current signal Lll+ of the real frequency. l For Ljl, a band eliminate filter 29α tuned directly to the fundamental frequency,
29β, the fundamental wave is removed and the harmonic component ILII□l pBh of the load current signal is obtained. The other configurations and operations of 3-phase/2-phase conversion, polarity reversal, and 2-phase/3-phase conversion are the same as in the first method.

(Problems to be Solved by the Invention) The passive type harmonic suppression device or the active type harmonic compensating device according to the prior art described above is generally applied in the following manner due to the characteristics of the operating principle. That is, in the high-order region, a passive type harmonic suppression device is used, which can easily obtain good performance, and can be realized in a small size and at low cost. An active harmonic compensator is used when irregular harmonics in a relatively low-order region are targeted. Depending on the configuration and control method of the self-commutated converter, active harmonic compensation devices currently have a practical compensation range of about 3rd to 13th harmonics.
Although it has many advantages in terms of function and performance, its biggest drawback is that it is more expensive than passive harmonic suppression devices.

This drawback is particularly noticeable in the following applications. In other words, this is the case when a passive harmonic suppressor or a phase advance capacitor is connected to a large-capacity, complex system that generates sidebands, such as a cycloconverter. At this time, the problem is that there is an anti-resonance point due to the inductive impedance on the power supply side and the capacitive impedance of the passive harmonic suppressor and phase advancing capacitor, and depending on the operating conditions of the cycloconverter, the sideband wave may reach the anti-resonance point. When tuned, the harmonic current is amplified and causes distortion in the grid voltage.

The second anti-resonance point is often about 2nd to 4th order in the low order range, depending on the general impedance of the system.

An active harmonic compensator is very effective in suppressing anti-resonance harmonics in such applications, but it is extremely difficult to use because it compensates for higher-order harmonics other than anti-resonance harmonics. It has a large capacity and is large and expensive.

Practical In order to achieve the above objectives, we constructed an economical system that is sufficient to compensate only the particularly harmful harmonics in the anti-resonant harmonic band using an active harmonic compensator, while compensating all harmonics. There are many requests.

The present invention aims to reduce capacity by focusing on compensating for low-order harmonics that adversely affect the power supply system and limiting compensation characteristics in the high-order range, and is a small and low-cost active harmonic compensation device. The purpose is to provide

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, a low-pass filter is provided to obtain a compensation current command signal with the high-order region attenuated,
The harmonic compensator of the present invention is a harmonic compensator connected in parallel to a system line connecting a power supply system and a harmonic generation load, and includes an electrical energy storage means and an electric power stored in the electrical energy storage means. a power converter that generates a desired instantaneous current and outputs it to the grid line; a current detector that detects the load current of the harmonic generation load; and a current command signal by removing the fundamental wave from the load current and reversing the polarity. a low-pass filter that is connected in series with the current command generation means and generates a compensation current command signal that attenuates the higher-order region of the current command signal; The power converter is equipped with current control means for controlling the output current of the power converter.

(Function) Among the above configurations, the function of the low-pass filter, which is the key point of the present invention that is different from the conventional technology explained in FIG. 10, will be explained using FIG. 2.

FIG. 2 schematically shows the frequency characteristics of the load current detected by the current detector passing through the current command generating means and the low-pass filter to generate the compensation current command signal. Figure (a) shows the amplitude characteristics, Figure (b) shows the phase characteristics, and the horizontal axis is ω/ω.

It is normalized by (ω: angular frequency, ω.: fundamental wave angular frequency) and is on a logarithmic scale. In the figure, 41 and 43 are the amplitude and phase characteristics of the fundamental wave removal circuit in the current command generation means, respectively, and 4
2.44 are the amplitude and phase characteristics of the low-pass filter, and 45 is the composite phase characteristic.

As can be seen from this amplitude characteristic, since the high-order components of the compensation current command signal are attenuated, the harmonic compensator has a characteristic that mainly compensates for the low-order range. Further, as shown in the phase characteristic, the frequency at which the composite phase characteristic 45 becomes zero shifts to the vicinity of the low-order region where compensation is to be focused, and compensation is performed most effectively in the vicinity of this frequency.

(Example) Embodiments of the present invention will be described below with reference to FIGS. 1 to 9.

FIG. 1 shows the overall configuration of a first embodiment of the present invention. In the figure, the minimum necessary components as a harmonic compensator are a capacitor 5 as an energy storage element, a self-commutated power converter 4, and an impedance between these mutual voltage sources in the main circuit section. The control circuit section includes a current detector 6 that detects a load current containing harmonics, and a load current detection signal LL.
Current command signal i from IVW. 0', a low-pass filter 25 that obtains a compensation current command signal ic' by attenuating the higher-order region of this current command signal ico', and the detector detected by the current detector 7. 7
A current control circuit IO controls the output current feedback signal i of the power converter 4 detected by the harmonics of the output current feedback signal iAF to match the compensation current command signal 1c8.

The other components of the practical device are the same as those explained in FIG. 10 as the prior art, and therefore will be omitted.

The difference between FIG. 1 and FIG. 10 is that in FIG. 10, a low-pass filter 25 is provided in series with the current command generating means 20, so parts related to the low-pass filter 25 will be described in detail below.

In the first embodiment, harmonic compensation is performed by inserting a robust filter into a compensation current command generating means using p (instantaneous actual power) and q (instantaneous imaginary power) conversion.

Figure 3 shows the current command generation means 2, which is the main point of this embodiment.
0 and the low-pass filter 25 are shown in detail. In the same figure, each component except the low-pass filters 25P and 25Q, each conversion operation, and the principle of operation are the same as the description of the prior art shown in FIG. 1J, so their description will be omitted. The low-pass filters 25P and 25Q are the bypass filter 24
For the AC component p5□ of the instantaneous actual power signal and the AC component Qh+ of the instantaneous actual power signal from which the DC component was removed (equivalent to fundamental wave removal) at P and 24Q, higher-order components are further attenuated to obtain phz and Qhz. Output. The signals obtained by inverting the polarity of these signals are the compensated instantaneous actual power command signal p7 and the compensated instantaneous imaginary power command signal 98.

Next, the operation of the first embodiment will be explained.

In explaining the operation of the first embodiment, we will explain the operation on the p, q coordinates and on the real frequency coordinates (U, V, W, or a.

Consider the correspondence with the above (β coordinate). Assuming ideal current control in the frequency range we are currently considering, the only difference that should be considered is that on the p and q coordinates, the order is (-1st order) on the actual frequency coordinates. For example, the frequency characteristics from the instantaneous actual power signal p to the compensated instantaneous actual power command signal p8 can be regarded as the frequency characteristics of the entire harmonic compensator, so the frequency characteristics on the p and q coordinates will be explained below.

FIG. 4 is a vector diagram of each signal representing instantaneous actual power on the p and q coordinates, and signals corresponding to those in FIG. 3 are given the same symbols. The instantaneous actual power signal p is passed through the bypass filter 2
4p causes a phase advance of ψ1, resulting in p, and this ph
Further, the low-pass filter 25p causes a phase delay of ψ2 with respect to l, resulting in ph2. Since the signal whose polarity is inverted by the polarity inversion circuit 26p is used as the compensation instantaneous actual power command signal p8, the instantaneous actual power vector p, which remains without being compensated, is expressed as the vector sum of p and p''. Ru.

(ψ is the phase difference between p and p.) The same applies to the instantaneous imaginary power.

From the second vector diagram, the frequency characteristics of the harmonic compensator will be explained by defining the harmonic survival rate ξ and the harmonic current output rate λ using the following equations. Set the transfer function of the bypass filter to 01. When the transfer function of the low-pass filter is 62, and the composite transfer function obtained by connecting G1 and 02 in series is GI2, it is expressed as follows. In order to achieve the above object, in the formula, for example, lpl indicates the absolute value of the vector p. Now, for the sake of simplicity, if we assume that G, , G2 are first-order filters shown in Fig. 5(a) and (b), then the series composite transfer function 61□ is shown in Fig. 5(c). The frequency characteristics of ξ and λ can be expressed by this transfer function G12. In the same figure, ω1. ω2 is the cut-off angular frequency of the bypass filter and the low-pass filter, respectively, and is ω1 and ω2. Further, S is a Laplace operator.

Here, numerical values are given to ω1 and ω2, and FIG. 6 shows an example of the frequency characteristic of the harmonic survival rate ξ, and FIG. 7 shows an example of the frequency characteristic of the harmonic number current output rate λ.

Figures 6 and 7 (a) are without a low-pass filter, ω
, -377 (rad/s), (b) figure with low-pass filter, ωl -377 (rad/s), ω2-
3017 (rad/s), (c) figure with low-pass filter, ω+ -377 (rad/s).

The comparison was made under the condition of ω2-1131 (rad/s).

From FIG. 6, it can be seen that the characteristic is focused on compensating for relatively low-order harmonics. Furthermore, from FIG. 7, it can be seen that the harmonic current output rate λ is attenuated in the high-order region when a low-pass filter is used. Since this harmonic current output rate λ means the weight of the compensation output current amplitude of the harmonic compensator with respect to the generated harmonic current amplitude, the compensation output current becomes small in a frequency region where this λ becomes small.

As described above, according to the first embodiment, by providing a low-pass filter on the pq coordinate in series with the current command generation means that performs p, q coordinate transformation, relatively low-order harmonics can be focused on. Compensating characteristics can be obtained, and the capacity of the device can be significantly reduced by reducing the compensation output current in the high-order region, making it possible to realize a harmonic compensation device that is small, lightweight, and inexpensive.

Furthermore, even in a system that uses a passive harmonic suppressor in a relatively high-order region, this embodiment can be used to appropriately share the burden of harmonic compensation.

Next, a second embodiment of the present invention will be described using FIG. 8. The present embodiment differs from the first embodiment only in the insertion positions of the low-pass filters 25α and 25β;
It is inserted between the c8 arithmetic circuit 27 and the 2-phase/3-phase conversion circuit 30. Other than this, each component, each conversion operation, and the operating principle are the same as in the first embodiment. Tatashi,
The cutoff angular frequency of the low-pass filter is a value on the actual frequency coordinates, and is a value equivalent to (+1st order) in order to obtain the same characteristics as the low-pass filter inserted on the p, q coordinates.

According to this embodiment, effects exactly similar to those of the first embodiment can be obtained. Furthermore, even if the low-pass filter is moved after the two-phase/three-phase conversion circuit 30, the same effect can of course be obtained. However, in this case, three low-pass filters are required.

A third embodiment of the present invention will be described using FIG. 9. This embodiment corresponds to the second method of the current command generation means explained using FIG. 12 in the section of the prior art, and includes a low-pass filter 25α.

25β is provided between band elimination filters 29α, 29β and polarity inversion circuits 26α, 26β. In this embodiment, the same effects as in the first and second embodiments can be obtained.

Above, we have shown examples of different insertion positions of low-pass filters for two typical types of current command generation means.Basically, if the low-pass filter is inserted in series between the load current detection signal and the compensation current command signal, Similar compensation characteristics can be obtained. but,
In practice, it is better to insert a low-pass filter after the fundamental wave removal function in terms of accuracy, and it is better to insert the low-pass filter in a two-phase circuit because of the required number of low-pass filters.

Further, although the harmonic compensator as a whole will be described using an example of a voltage type main circuit, the present invention can be applied in exactly the same way even if the main circuit is a current type in which the accelerator is an energy storage element. It goes without saying that reactor 3 or a transformer may be used.

[Effects of the Invention] According to the present invention, by inserting an appropriate low-pass filter in series with the current command generation means, target low-order harmonics are intensively compensated, and compensation current in the high-order region is reduced. By doing so, it is possible to reduce the capacity of the device and realize a small and inexpensive active harmonic compensator.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a harmonic compensation system using the present invention,
FIG. 2 is a frequency characteristic diagram of the compensation current generating means showing the effect of the present invention, FIG. 3 is a configuration diagram of the first embodiment of the present invention, and FIG. 4 is a hector diagram of instantaneous actual power in the first embodiment. FIG. 5 is a block diagram showing the transfer functions of the bypass filter and low-pass filter in the first embodiment, FIG. 6 is a frequency characteristic diagram of the harmonic survival rate ξ in the first embodiment, and FIG. 7 is a diagram showing the frequency characteristics of the harmonic survival rate ξ in the first embodiment. A frequency characteristic diagram of the harmonic current output rate λ in the example, FIG. 8 is a configuration diagram of the second embodiment, FIG. 9 is a configuration diagram of the third embodiment, and FIG. 10 is an example of a harmonic compensation system according to the prior art. FIG. 11 is a block diagram of a first method of extracting a harmonic signal according to the prior art, and FIG. 12 is a block diagram of a second method of extracting a harmonic signal according to the prior art. 1... AC power supply, 2... Harmonic generation load, 3... Reactor, 4... Power converter, 5... Capacitor, 6, 7... Current detector, 89... Voltage detection device, 10... current control circuit, 1
1... PWM control circuit, 12... Voltage setting device,
13. Voltage control circuit, 14. Multiplier, 15.
16.17・Adder, 20・Current command generation means,
20A...Fundamental wave removal circuit, 20B...Current command calculation circuit, 25...Low pass filter. Applicant's representative Patent attorney Takehiko Suzuhana, ph+ pll (=-ph2) 1) e (= I) + 1)") Figure 4 Figure 5 (a) LPF/J ω1 = 377) (b) LPF poly (ω1=37'7゜ω2=3α7) (C) LPF guess (ωdo377゜ω2=1131) Figure (a) LPFjJL (ω+=377) (b) LPF tomorrow (ω+=377°ω2= 3015) (C) LPF method 1) (ω+=377°ω2 =+131) Fig.

Claims (1)

[Claims] A harmonic compensator connected in parallel to a system line connecting a power supply system and a harmonic generation load includes an electric energy storage means and a desired instantaneous current generated from the electric power stored in the electric energy storage means. a power converter that outputs to the grid line, a current detector that detects the load current of the harmonic generation load, and a current command generation means that generates a current command signal by removing the fundamental wave and reversing the polarity from the load current; A low-pass filter is connected in series with the current command generating means and generates a compensation current command signal that attenuates the high-order region of the current command signal, and the output current of the power converter is adjusted to match the compensation current command signal. A harmonic compensator characterized by comprising a current control means for controlling.