JPH07322496A - Current source active filter for power distribution - Google Patents

Abstract

(57) [Summary] [Purpose] In the current source active filter, the sideband wave
The frequency can be increased and the band rejection filter coil
Module and capacitor can be made small, and the circuit structure is simple.
Remove sidebands [Structure] The power variation that constitutes the current source active filter
The inverter 7 of the converter A has a plurality of switching elements.
All transistors T_u ⁺, T^- _u, T⁺ _v, T^- _v, T
⁺ _w, T^- _w, Diodes D1 to D6
There is. A predetermined current (reactor current) is applied to the DC terminal of the inverter 7.
Toll current) I_dReactor 9 for supplying
It Transistor T_u ⁺, T^- _u, T⁺ _v, T^- _v, T
⁺ _w, T^- _wIs controlled by the control circuit 8 so that the 3
Enter one finger so that each of them is always on.
I i_i ^*(_i=_{u, v, w}) Equal to that of PW
M control, that is, sawtooth wave modulation is performed. Converter is 1/2 turn
Using a sawtooth carrier that is phase-shifted only
Therefore, the output currents from the converters A and B are combined.
The combined current is output to the LC filter 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power distribution active filter, and more particularly to a current source active filter.

[0002]

2. Description of the Related Art A power distribution active filter compensates a harmonic current generated by a load of an electric device or the like using a power semiconductor element so that a sinusoidal current flows through a system.

A voltage type active filter and a current type active filter are known as the active power distribution filters. The current source active filter controls the current of the DC reactor as a DC current source to a specified value, and by changing the polarity of the power switching element by turning it on and off, it creates the same current waveform as the harmonic current. It is a filter. Further, the voltage type active filter is a filter of a type which forms the same current waveform as a harmonic current by charging / discharging a capacitor as a DC voltage source and turning on / off a high power switching element.

Compared with a voltage type active filter, a current type active filter can sufficiently cope with a low speed switching element such as a bipolar transistor, a control circuit and a control calculation of a compensation current are simple, and an operation of a current source is essentially required. Therefore, there is an advantage that interference with the system (resonance phenomenon etc.) is small.

The conventional current source active filter compares the size of a harmonic waveform with a triangular waveform called a carrier wave,
This is performed by turning on / off the switching element of the power converter.

The current source active filter is operated by connecting multiple power converters. For example, FIG. 1 shows an active filter that operates by connecting two current source converters A and B. The output current of each converter A, B has a PWM (pulse width modulation) controlled waveform as shown in FIG. 3, and in addition to the current (i _i ^* ) to be supplied to the distribution line, a large amount of PWM High frequency component caused (hereinafter referred to as sideband)
Is included. According to the literature, i _i ^* is a single frequency f
Harmonic current with _h, and PWM carrier frequency f
if _{c, f = mf c + nf} h m = 1,2,3 ..., n = ± 1, ± 2, are known to have a sideband with ± 3 ... frequency components.

It is known that when the power converters are multiplexed, sidebands with odd m are canceled out, and only components with even m remain.

[0008]

However, conventionally, when the PWM control is performed by the triangular wave carrier and the power converters are multiplexed, the result is as shown in FIG. 8 (b). Figure 8 (b)
Is the frequency spectrum when the converter is operated to output a sinusoidal current of f _h = 500 Hz. The triangular wave carrier frequency f _c is 2.5 kHz. In FIG. 8B, the components of I _{2, -1} and I _2,1 remain, and a band elimination filter circuit is required to remove these components, but a complicated circuit is essential. further,
If the frequency f of the sideband is increased, the coils and capacitors forming the band elimination filter can be reduced, but there is a limit to increasing the PWM carrier frequency f ₀ .

The object of the present invention is to solve the problems of the prior art and to increase the frequency of the sideband, thereby simplifying the filter for removing the sideband and significantly improving the performance as compared with the triangular wave carrier. An object is to provide a current source active filter that can be improved.

[0010]

In order to achieve the above object, the invention of claim 1 is a detection for detecting a load current in which a fault current generated from a load is superimposed on a system current flowing through a distribution line. Means, a calculating means for calculating a fault current based on the detection result of the detecting means, and a plurality of switching elements, and ON / OFF of the switching element by a pulse width modulation method based on the calculation result of the calculating means. In the distribution active filter including a plurality of compensation current generating means for generating a compensation current equivalent to the fault current by performing the compensation current and supplying the compensation current to the distribution line, the compensation current generating means uses a pulse width modulation method. A sawtooth wave is used as the carrier wave to be used, and the compensation current is output by turning on / off the switching element based on the comparison of the sawtooth wave and the fault current waveform. It is the gist.

The invention of claim 2 is, in addition to the structure of the invention of claim 1, characterized in that the compensating current generating means is connected to a distribution line through a band elimination filter. The gist of the invention of claim 3 is that in the invention of claim 2, the band elimination filter is an LC filter.

[0012]

According to the first aspect of the invention, the detecting means detects the load current in which the fault current generated from the load is superimposed on the system current flowing through the distribution line. The calculating means calculates the fault current based on the detection result of the detecting means. Compensation current generating means, based on the magnitude comparison of the sawtooth wave and the fault current waveform based on the calculation result of the calculating means, by performing pulse width modulation control to turn on and off the switching element,
Outputs compensation current.

According to the invention of claim 2, in addition to the operation of claim 1, the compensating current generating means is connected to the distribution line through a band elimination filter, so that the harmonics caused by the pulse width modulation control are band eliminated. It is removed by the filter and the compensation current is output to the distribution line.

According to the third aspect of the invention, the LC filter removes the harmonics caused by the pulse width modulation control by the band elimination filter.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. As shown in FIG. 1, a load 2 is connected to a three-phase distribution line 1, and a current source active filter (hereinafter, simply referred to as active filter) 3 is connected to the load 2 in parallel.

The active filter 3 will be described in detail. The active filter 3 is a detection means and a fault current detection device 4 as a calculation means, a compensation current generation device 5 as a compensation current generation means, and an L as a band elimination filter.
And a C filter 6. The fault current detection device 4 is composed of an electronic circuit. The fault current detector 4 is connected to each phase of the distribution line 1 via a current transformer CT,
Input the load current flowing in each phase.

The fault current detector 4 has a fault current i _i ^* (superimposed on the system currents _isu , _isv , and _isw that flow from the grid.
_i = _{u, v, w} ) is detected. Fault current i
_i ^* is a harmonic current, a reverse phase current (unbalanced component), or the like generated by the load 2 such as an electric device using the power semiconductor element. The fault current detector 4 detects the fault current as follows.

[0018] the system current i _su, i _sv, the _{i sw, i su = I S} sinω s t i sv = I S sin (ω s t-2π / 3) i sw = I S sin (ω s t + 2π / 3 ) Ω _s : The angular frequency of the power supply. If the load currents i _Lu , i _Lv , and i _Lw are set, the compensation current i _ci = i _i ^* (also referred to as a command value to the converters A and B described later) to be compensated by the active filter 3 is i _i ^* = i. _Li- i _Si ( _i = _{u, v, w} ). In this embodiment, the fault current detection device 4 issues a command from the load current i _Li detected by the current transformer CT and i _Si generated based on the angular frequency ω _s of the power supply supplied from the distribution line 1 inside the circuit. The value i _i ^* is calculated, and this command value i _i ^*
Is input to the converters A and B.

I _S is the amplitude of i _Si . This I _S
Is obtained by performing feedback control so that the reactor current I _d becomes I _d ^* . That is,
The fault current detection device 4 is provided with a PI compensator (not shown), the deviation of the reactor current i _d is fed back through the PI compensator, and I _S = (K _p + K _I / P) (I _d ^* −I _d In the formula, P = d / dt, (differential operator, 1 / P means integral ∫dt) K _p , K _I : Gain of PI compensator. Note that I _S converges to an appropriate value I _S0 by the feedback control. For example, when I _S > I _S0 , active power more than the load 2 needs is supplied from the power supply. If the line voltage does not change, the electric power of the load 2 is constant, and thus excess energy is stored in the reactor 9 described later to increase I _d . When I _S <I _S0 , power is supplied from the reactor 9 to the load 2 to reduce I _d .

As a result, I _S can be made I _S0 by the above feedback control. The reactor current I _d (= I _d ^* ) is the command value i _{i at} any instant.
^It must be greater than ^* ( _i = _{u, v, w} ). Therefore,
In this embodiment, the fault current detection device 4 uses i _u ^{* to} i _w ^*.
Of which the absolute value is the maximum (| i ^* | _max ),
_Id ^* = 1.2 | i ^* | _max is calculated. Considering the copper loss of the reactor 9, it is preferable that I _d ^* be as small as possible.

Next, the compensation current generator 5 will be described. As shown in FIG. 1, a compensating current generator 5 is a pair of power converters connected in a multiplexed manner (hereinafter, simply referred to as a converter).
It is composed of A and B and a reactor 9.

FIG. 2 is a connection diagram of the converter A. In addition,
Since the converter B has the same structure as the converter A, the converter A will be explained.
The description of the converter B will be omitted. Moreover, in FIG.
For convenience of explanation, only one converter A has an LC filter.
The filter 6 is not connected, but the LC filter 6 is
As shown, connect the AC terminals of converters A and B in common.
There is. As shown in the figure, converter A is a current source PWM inverter.
(Hereinafter referred to as an inverter) 7 and a control circuit 8
Is made. The inverter 7 has a plurality of switching elements.
Bipolar transistor as a child (hereinafter Transis
T)_U ⁺, T_U ^-, T_V ⁺, T_V ^-, T_w ⁺，
T_w ^-, And diodes D1 to D6.
A predetermined current (reactor voltage) is applied to the DC terminal of the inverter 7.
Flow) I_dIs connected to the reactor 9. Na
The reactor 9 connected to both converters A and B is a common iron.
Keep the phase between reactors (current balance) and smoothing
It is designed to combine.

[0023] The transistor _{^{T U +, T U -,}} T V +, T
_V ⁻ , T _w ⁺ , and T _w ⁻ are controlled by the control circuit 8 so that one of each of the + side and the − side is always on. This control is performed as follows. The control circuit 8 of the converters A and B divides the time axis into minute times T equally as shown in FIG. 3, and outputs the average value of the current i _i at each minute time from the fault current detecting device 4 as a command value. i _i ^* ( _i = _{u, v, w} )
The PWM control is performed so that it becomes equal to that. That is, sawtooth wave modulation is performed.

[0024] ^{_{i u * -i v * ≡i uv}} * i v * -i w * ≡i Vw * i w * -i u * ≡i wu * to define, the signal wave i _uv ^* ~i _wu ^* and A transistor to be turned on is uniquely determined as shown in FIG. 4A from the magnitude relationship with the sawtooth wave i _s having an amplitude of 1.5I _d .

For example, during the period of i _wu ^* <i _s ≦ i _Vw ^* , T _U ⁺ and T _W ^- are turned on. ^{_{i Vw * <i s ≦ i}} uv * of T in the period _U ^+, T _V ^- turning on. Also, i _s ≤ i _wu
^{When *} and i _uv ^* <i _s , T _U ⁺ and T _U ⁻ are turned on.

When controlled in this way, the current i for a minute time
_i mean the micro period t = 0 to T is substantially equal to the command value i _i ^* for. That is, in the case of t = τ _{1 to} τ ₃ in FIG. 4A, i _u = I _d , and i _u = 0 in the remaining time. Therefore, the average value i _u = (τ ₃ −τ ₁ ) I _{d ^{/ T ≒ (i uv * -i}} wu *) becomes the _{I d / 3I d = i u} *.

[0027] Similarly, the t = τ ₂ ~τ ₃ in i _v = -I
_d , and the average value i _v ≈i _v ^* . Further, in the three-phase circuit, since i _u + i _v + i _w = 0, the average value i _w ≈i
_w ^*

Further, in this embodiment, the converters A and B use sawtooth wave carriers which are phase-shifted from each other by 1/2 cycle as shown in FIG. Since the converters are multiplexed, the output currents from the converters A and B are combined and the combined current is output to the LC filter 6.

Therefore, by this multiplexing, each converter A,
The combined current output from B and combined as shown in FIG.
I_u= I_uA+ I_uB, Note that i in the left brackets_uIs each
I output from the converter_uis not. Also, i shown in FIG.
_uAIs the output current i from converter A_uSay i_uBIs strange
Output current i from converter B_uSay. In other phases
i _v, I_wIs the same as for () frequency spectrum
The frame is as shown in FIG. With this multiplexing,
The output current of the inverter 7 is an even sideband (2f_c± m
f_h, M = ± 1, ± 2 ...) remains.

Next, the LC filter 6 will be described.
The LC filter 6 is connected to the AC terminals of the converters A and B, and the output terminal is connected to the distribution line 1 of each phase. The LC filter 6 with a capacitor C between the respective phases are connected, it is constituted by a coil L is connected to each phase, when the upper limit frequency of the harmonic to be removed and f _0, a f ₀ or more components It is designed to have a characteristic that almost all components are removed and components below f ₀ pass through without attenuation.

Therefore, the LC filter 6 supplies the component of f <f ₀ of the inverter output current to the distribution line side with almost no attenuation. In addition, most of the 2f _c sidebands caused by PWM flow sideways into the capacitor C, and only a very small current flows through the distribution line 1.

In the active filter 3 configured as described above, the fault current detector 4 loads the load currents i _Lu , i _Lv , which flow in each phase of the distribution line 1 through the current transformer CT into each phase.
Enter i _Lw respectively. Then, the fault current detection device 4
Detects the fault current i _i ^* superimposed on the system currents _isu , _isv , and _isw flowing from the grid.

Then, the fault current detection device 4 is operated by the fault current i.
_i ^* is output to each converter A and B as a command value. As shown in FIG. 5, the converters A and B perform PWM control, that is, sawtooth modulation, by using sawtooth carriers that are phase-shifted from each other by ½ period so as to be equal to that of the command value i _i ^* .

Incidentally, with this converter alone, the frequency spectrum as shown in FIG. 7A is obtained (FIG. 7A).
Then, for convenience of explanation, f _h = 500 Hz, T = 0.5 m
s, the spectrum of the output current i _u when the amplitude ratio α = I _h / I _d = 0.5 (this corresponds to a sawtooth frequency of 5.0 Hz). Note that I _h is a command current, that is, a current to be supplied to the distribution line. ). 7 and 8, the vertical axis represents | I _{m, n} / I _d |.

In this embodiment, two converters are multiplexed.
I when converted_uThe spectrum of (combined current) is shown in Fig. 8.
It shows in (a). This is because T and α are the same as those in FIG.
But f _h= 1.2 kHz.

Then, the LC filter 6 supplies the component of f <f ₀ of the inverter output current to the distribution line side with almost no attenuation. Now, for comparison, a case will be described in which only carriers are different and other configurations perform PWM control with the same active filter as in the above-described embodiment.

The triangular wave carrier shown in FIG.
When M control is performed, the signal wave i_uv ^*~ I _wu ^*And 1.5I_dof
Triangular wave with amplitude i_tDepending on the size relationship with
Determine the randista. In this case, the commutation turn in one minute period
The number (the number of times of on / off) is as shown in FIG.
The same three times as in the case of sawtooth.

As a result, the sawtooth wave carrier can have a frequency twice that of the triangular wave carrier. From this, the frequency f of the sideband becomes high, and the coil L and the capacitor C of the LC filter can be made small.

Further, FIG. 7B shows the converter f shown in FIG.
₄ shows the frequency spectrum of the current i _u when operated so as to output a sine wave current of _h = 500 Hz.
The carrier frequency (triangular wave frequency) is 2.5 kHz. Comparing FIGS. 7A and 7B, m =
1 sidebands are the most, whereas triangular waves are m = 2
There are a lot of it.

If a triangular wave carrier is used for the converters A and B,
F when duplicated_h= Synthetic current at 1.2 kHz
The spectrum of (combined current) is shown in FIG. Cat
The rear frequency (triangular wave frequency) is 2.5 kHz. Figure
8 (a) sawtooth I_{2, -2}, I _{2, -1}, I_2,1, I_2,2But
Conspicuously, these frequencies are I_hSeveral times
The inflow to these distribution lines 1 is a simple LC filter.
It is possible to prevent it. Note that f_h= 1.2 kHz
Corresponds to the 19th frequency of the commercial power supply (60 Hz). triangle
In case of waves, I_{2, -1}, I_2,1Is I_hIs in close proximity and this
It is necessary to load a band elimination filter to attenuate the
is there. In addition, it is difficult to design a filter with such characteristics.
It is difficult.

The present invention is not limited to the above-mentioned embodiments, but can be implemented by appropriately modifying a part of the structure without departing from the spirit of the invention. (1) Although the LC filter is used in the above-mentioned embodiment, it may be configured with other filters.

[0042]

As described above in detail, according to the first aspect of the present invention, the frequency of the sideband can be increased, which simplifies the filter for removing the sideband and improves the performance of the triangular wave carrier. It can be greatly improved in comparison.

According to the second aspect of the present invention, the harmonics caused by the pulse width modulation control are removed by the band elimination filter, and the compensation current can be reliably output to the distribution line. According to the invention of claim 3, the coil and the capacitor can be downsized by the LC filter.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a current source active filter of an embodiment embodying the present invention.

FIG. 2 is a circuit diagram of a converter which also constitutes a current source active filter.

FIG. 3 is an explanatory diagram showing an output current waveform of a current source converter.

FIG. 4A shows P of a current source converter in the case of sawtooth wave modulation.
FIG. 3B is an explanatory diagram of a WM control pattern, and FIG. 6B is an explanatory diagram of a PWM control pattern of the current source converter in the case of triangular wave modulation.

FIG. 5 is an explanatory diagram of carriers when multiplexed in the case of sawtooth wave modulation.

FIG. 6 is an explanatory diagram of carriers when multiplexed in the case of triangular wave modulation.

7A is a frequency spectrum of a converter output current in the case of sawtooth modulation, and FIG. 7B is a frequency spectrum of a converter output current in the case of triangular wave modulation.

FIG. 8A is a frequency spectrum of a converter output current in the case of sawtooth modulation by multiplexing the converter, and FIG. 8B is a frequency spectrum of a converter output current in the case of triangular wave modulation by multiplexing the converter. Is.

[Explanation of symbols]

1 ... Distribution line, 2 ... Load, 3 ... Active filter, 4 ...
Fault current detection device as detection means and calculation means, 5 ... Compensation current generation device as compensation current generation means, 6 ... LC filter, 7 ... Inverter, 8 ... Control circuit, 9 ... Reactor, CT ... Current transformer, A , B ... Power converter.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Naoki Yamamura, No. 204, Otani-cho, Tsu City, Mie Prefecture 4 (72) Shinya Matsunami, 15 Minamihonjo, Nijo-dori, Gifu City, Gifu Prefecture

Claims (3)

[Claims] 1. A detection unit for detecting a load current in which a fault current generated from a load is superimposed on a system current flowing through a distribution line, and a calculation unit for calculating the fault current based on a detection result of the detection unit. , Including a plurality of switching elements,
A plurality of compensating current generating means for generating a compensating current equivalent to the fault current by turning on / off the switching element by a pulse width modulation method based on the calculation result of the calculating means and supplying the compensating current to the distribution line. In the active filter for power distribution, the compensation current generating means uses a sawtooth wave as a carrier wave used in the pulse width modulation method, and based on the magnitude comparison between the sawtooth wave and the fault current waveform, the switching element is A current source active filter for distribution that turns on and off to output a compensation current. 2. The current source active filter for distribution according to claim 1, wherein the compensation current generating means is connected to the distribution line via a band elimination filter. 3. The current source active filter for distribution according to claim 2, wherein the band elimination filter is an LC filter.