JPH0739253U - Active filter current detection circuit - Google Patents

Abstract

(57) [Summary] [Purpose] In a distribution system in which a phase-advancing capacitor 4 is installed, a current that expands due to harmonics while resonating with the wiring inductance of the system, the leakage inductance of the transformer, and the capacitance of the phase-advancing capacitor. The present invention provides a current detection circuit of an active filter that can sufficiently suppress the above without applying an active filter having a capacity larger than necessary. [Structure] Phase advancing capacitor equipment and active filter 5
A current detection unit 12 'that detects a power supply current on the power supply side from the point where and are connected, and a control device that calculates a compensation command of the active filter according to the output signal and controls the active filter according to the compensation command. 54, an active filter comprising: a first resistor 122 for detecting a current signal, a second resistor 124, and a second resistor 124, which are connected in series to the output terminal of the current detector, and connected in parallel to the second resistor. Reactor
123, wherein the voltage across the signal detection resistors connected in series is used as a detection signal for a compensation command.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention is intended to increase the harmonic current due to resonance between the phase-advancing capacitor installed to improve the power factor of the power distribution system and the impedance of the power distribution system. The present invention relates to the improvement of the current detection circuit of the active filter that prevents the harmonic interference of the system.

[0002]

[Prior art]

 With the widespread use of various converters for semiconductor applications in recent years, the influence of harmonics on other devices installed in the system due to the harmonic current generated from these devices is increasing. As a compensator that suppresses the harmonic currents flowing out to these distribution systems, the current flowing out is a high-speed, high-performance inverter that injects the harmonic current that is out of phase with the current flowing out, and is controlled so as to cancel it. The application examples of active filters are increasing.

However, in these distribution systems, generally, a distribution transformer of a substation or a receiving transformer of a customer branches to a plurality of loads to supply power, so that harmonics of a specific load are compensated for. However, if a phase-advancing capacitor is connected to another branch circuit, the harmonics will expand, and the countermeasures may not be sufficient if only partial circuit harmonics countermeasures are taken.

Further, generally, a power-advance phase-advancing capacitor facility for perfect power factor is installed at the power receiving end of the load to be compensated, and if the system voltage supplied to the power receiving end has waveform distortion, Similarly, a specific harmonic may expand and sufficient harmonic countermeasures may not be achieved.

FIG. 2 shows an equivalent circuit of a conventional system in which a current on the load side is detected and harmonics are compensated by the active filter 5. A system power supply 1 having a power system impedance 2 is connected in parallel with a load 3 including a rectifying device that generates harmonics, a phase-advancing capacitor 4, and an active filter 5 for suppressing harmonics. . In this case, a combined load current flowing through the phase-advancing capacitor 4 that may expand harmonics by resonance with the power supply system impedance 2 and the load 3 including a rectifying device that generates harmonics is detected by the current detecting unit 12. The active filter 5 injects a current having a phase opposite to the harmonic component (I _C + I _L ) of the combined load current.

Now, if attention is paid to the harmonic component, the following equation is established.

[Equation 1]

[Equation 2]

Here, V _S is the harmonic voltage included in the system voltage, Z _S is the system impedance, and Z _C is the impedance of the phase-advancing capacitor. Now, if the load current including the phase-advancing capacitor is detected and the active filter current I _AF is controlled so as to cancel this harmonic current,

[Equation 3]

Substituting equation (3) into equation (1) and equation (2), the power supply current I _S flowing through the power system side is

[Equation 4] However, when the system inductance and the phase-advancing capacitor resonate at a specific harmonic order,

[Equation 5] Becomes

In this state, if the power supply system voltage is distorted and the harmonic voltage V _S exists or the harmonic component exists on the load side, the active filter is also supplied with a current expanded by resonance when the active filter is turned on. Flowing. In general, this expanded current reaches 5 to 10 times the harmonic current of the load, so it is necessary to install an active filter with an excessive capacity.

[0010]

[Problems to be solved by the device]

 The present invention has been made in view of the above points, and an object thereof is to improve the wiring inductance of the system and the leakage inductance of the transformer in the distribution system in which the phase advancing capacitor is installed. To provide a current detection circuit for an active filter that can sufficiently suppress the current that expands due to harmonics when it resonates with the electrostatic capacitance of the phase capacitor without applying an active filter with an unnecessarily large capacitance. is there.

[0011]

[Means for Solving the Problems]

 Therefore, the current detection circuit of the active filter according to the present invention is an active filter that is provided in parallel with the phase advancing capacitor equipment provided in the distribution system to suppress the expanded harmonics of the system due to resonance. A current detection unit that detects the power supply current on the power supply system side from the point where the capacitor equipment and the active filter are connected, and a compensation command that calculates the compensation command of the active filter according to the output signal of the current detection unit. And a control device for controlling the active filter according to the first filter, the first resistor and the second resistor for detecting a current signal, which are connected in series to the output terminal of the current detector, and the second resistor. It is equipped with a reactor connected in parallel to the second resistor, and the voltage across the resistor for signal detection connected in series is used as the detection signal for the compensation command. It is characterized in that the.

That is, the current on the power supply side from the connection point of the active filter through which the resonance current flows, including the phase-advancing capacitor, is detected by a current transformer, and a current signal proportional to the detected current is detected in the detection circuit. A resistor to obtain and a reactor that obtains a signal obtained by differentiating the detected current in series are provided to form a series body of these, and the voltage across the series body is used as a current detection signal to detect the active filter by the detection signal. Compensation current of is calculated and controlled.

[0013]

[Action]

FIG. 1 shows an equivalent circuit of a system in which a current detecting unit 12 'according to the present invention is used to suppress harmonics by an active filter. The same reference numerals as those in FIG. 2 indicate the same parts. In this case, the active filter 5 detects the power supply current including the resonance current in the current detection unit 12 ', and the harmonic component I _S of this power supply current is used to calculate the current I _{AF of the} active filter as follows.

[Equation 6] Controlled by.

For simplification, FIG. 1 will be considered by dividing it into the first term and the second term of the equation (6) as shown in FIGS. 3A and 3B.

FIG. 3A shows that the current I _L of the harmonic component flowing on the load side is detected on the power supply side from the point where the active filter is connected, and the active filter 5 is controlled so as to cancel it. is there. Here, the relationship between the power source current I _S after compensation, the load current I _L, and the active filter current I _AF is

[Equation 7]

In the compensated power supply current, the current of the harmonic component should be considerably compensated and should hardly flow. Therefore, if the harmonic current contained in the detected power supply current is increased K times to compensate by increasing the control gain of the active filter,

[Equation 8]

Substituting this relationship into equation (7) and rearranging

[Equation 9] Becomes

That is, when controlling so as to cancel the harmonic current that is simply calculated from the detected power supply current as in the case of the conventional load current detection, K = 1, so the power supply current after compensation is obtained. Harmonic component of

[Equation 10] Therefore, if it is left as it is, it can be suppressed to only half of the harmonic component of the load current.

Here, if the control gain is K = 10,

[Equation 11] Therefore, the harmonic current component flowing on the power supply side can be reduced to about 1/10 of the harmonic current component flowing on the load side.

FIG. 3 (b) shows the system configuration in the case of suppressing the harmonics flowing into the phase advance capacitor 4 from the system side. The power supply current I _S at this time is

[Equation 12]

Here, the active filter 5 controls the detected power supply current by the following equation.

[Equation 13]

G (S) in the above expression is a transfer constant representing a control constant having a differential characteristic, and the harmonic current component I _S of the detected power supply current is differentiated and multiplied by G, and A reverse polarity current is supplied by the active filter 5. That is, i _AF and i _S are respectively represented by the instantaneous values of I _AF and I _S , which can be expressed once by replacing them in the time domain.

[Equation 14] Here, n is the harmonic order at the time of resonance, and the active filter is controlled by the current i _AF which is the derivative of the time-varying current at the speed n times the angular velocity ω of the fundamental wave.

If this is displayed as a vector of n-th order component,

[Equation 15]

Substituting this relational expression into Expression (12) and rearranging

[Equation 16]

Here, at the time of resonance, the impedance Z _S on the system side and the impedance Z _{C of the} phase advancing capacitor

[Equation 17] However, in equation (15)

[Equation 18] And the relationship between the capacitance C of the phase advancing capacitor and the impedance Z _C

[Formula 19] Since there is a relation of

[Equation 20] Is obtained.

That is, if Z _S + Z _C = 0 at the time of resonance of the nth-order component, in the conventional active filter detection method on the load current side, resonance occurs, for example, as shown in the above equation (4). Even if the capacitor current I _C is detected, it cannot be suppressed and the harmonic is expanded. However, by configuring the control circuit as shown in equation (6), the impedance against voltage distortion is maintained even at resonance. It becomes the action of resistance of Z = G / C, and resonance can be suppressed.

[0027]

【Example】

An embodiment of the present invention will be described below in detail with reference to the drawings. FIG. 4 is a diagram showing a specific element configuration of a current detection unit 12 'which is input to a control circuit of an active filter to which the present invention is applied. FIG. 5 shows an example of the main circuit configuration of the active filter 5 using the current detection circuit of the active filter according to the present invention. FIG. 6 shows a main circuit configuration of a conventional active filter device. 5 and 6, 1 is a system power supply, 2 is a power system impedance (Z _S ), 3 is a load composed of a rectifying device that generates harmonics, and 4 is connected in parallel with the load for power factor improvement. The phase advancing capacitor (impedance is Z _C ) installed, and 5 is an active filter for suppressing harmonics.

The active filter 5 has an inverter 52 composed of a high-speed switching element, a DC capacitor 53 connected to the DC side of the inverter 52, and a control circuit 54 for controlling the compensation current I _AF by the inverter. The AC side is connected to the system power supply 1 via the AC reactor 51, and a high frequency filter 55 is connected in parallel with the reactor 51 to absorb the switching ripple of the inverter 52. A current detector 12 'for detecting a combined current flowing through the load 3, the phase-advancing capacitor 4, and the active filter 5 is provided, and a current detector 11 for detecting an alternating current of the inverter 52 is provided. .

A harmonic current is calculated and detected based on the current i _S detected by the current detector 12 ′, and a compensation current command value for suppressing the harmonic current and the active filter current i detected by the current detector 11 are detected. The current of the inverter 52 is controlled so that it becomes equal to _AF .

FIG. 4 is a diagram showing the details of the current detector 12 ′ used in the current detection circuit of the active filter according to the present invention, which detects the combined current flowing through the load 3, the phase advance capacitor 4, and the active filter 5. To the output terminal of the current detector 121, a circuit composed of a first resistor 122 and a second resistor 124 connected in series and a reactor 123 connected in parallel to the second resistor 124 is connected to detect the current. A current including a harmonic component of the current detected by the device 121 is supplied to the control circuit 54 as a detection signal i _S.

In the conventional system configuration in which the detection circuit 12 is provided on the load side with respect to the connection point of the active filter 5 as shown in FIG. 6, an attempt is made to compensate the current expanded by resonance, so An active filter with a matching capacity was needed, but the current detector 12 'detects the combined current flowing through the load 3, the phase advance capacitor 4, and the active filter 5, and the harmonics on the load side In addition to the detection by the resistor 122 of Fig. 4, by adding a differentiation circuit consisting of the reactor 123 and the resistor 124 as shown in Fig. 4, it is possible to suppress the expansion of resonance by giving the system a braking resistance effect. it can.

[0032]

[Effect of device]

 As described above, according to the current detection circuit of the active filter of the present invention, the current detector 12 'is configured on the system side of the active filter 5 even if the phase advancing capacitor 4 resonates with the impedance of the power system side. In addition to detecting harmonics of the conventional load on the power supply side, adding a differentiating circuit to the current detector makes it possible to suppress the expansion of the resonance current by acting as a braking resistor. Therefore, it is possible to aggravate the voltage distortion of the system and suppress harmonic interference that affects other electric devices installed in the system.

[Brief description of drawings]

FIG. 1 shows an equivalent circuit of a system in which harmonics are suppressed by an active filter using a current detector according to the present invention.

FIG. 2 shows an equivalent circuit of a conventional system in which a load side current is detected and harmonics are compensated by an active filter.

FIG. 3 is a schematic representation of FIG. 1 for ease of understanding the equations.
It is the figure which divided and showed two of the 1st term and 2nd term of Formula (6) like (a) and (b).

FIG. 4 is a diagram showing a specific element configuration of a current detection unit input to a control circuit of an active filter to which the present invention is applied.

FIG. 5 shows an example of a main circuit configuration of an active filter using the current detection circuit of the active filter according to the present invention.

FIG. 6 shows a main circuit configuration of a conventional active filter device.

[Explanation of symbols]

 1 system power supply 2 power system impedance 3 load that generates harmonics 4 phase capacitors 5 active filters 12, 12 'current detector 51 AC reactor 52 inverter 53 DC capacitor 54 control circuit 55 high frequency filter 121 current detector 122 first Resistance 123 Reactor 124 Second resistance

Claims (1)

[Scope of utility model registration request] 1. An active filter which is provided in parallel with a phase advancing capacitor facility provided in a power distribution system and suppresses expanded harmonics of the system due to resonance, wherein the phase advancing capacitor facility and the active filter are connected. The current detection unit that detects the power supply current on the power supply system side from the above point, and the control that calculates the compensation command of the active filter according to the output signal of the current detection unit and controls the active filter according to the compensation command And a first resistor and a second resistor for current signal detection connected in series to the output terminal of the current detection unit, and a reactor connected in parallel to the second resistor. A current detection circuit for an active filter, wherein the voltage across the signal detection resistors connected in series is used as a detection signal for a compensation command.