JPH0584146U - Active filter - Google Patents

Abstract

(57) [Abstract] [Purpose] To reduce the circuit elements of the filter circuit and the phase advancing capacitor circuit. In an active filter for compensating reactive power of a power system by connecting a PWM-controlled inverter 3 and a phase-advancing capacitor circuit 4 in parallel, the phase-advancing capacitor C of the phase-advancing capacitor circuit is connected to a higher harmonic of the inverter. Also serves as the capacitor of the removal filter. The filter is composed of a reactor L ₁ , a capacitor C and a vibration suppressing resistor R.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to an active filter for compensating reactive power in a power system.

[0002]

[Prior Art]

 As shown in FIG. 2, an active filter of this type has a configuration in which an inverter 1 is used as a current phase control means and is combined with a phase advancing capacitor circuit 2 in order to have both a lead and a delay reactive power compensation function. By controlling the output current phase of the inverter 1 and the lead current of the capacitor 2, it is possible to continuously change from the advanced power to the delayed power.

Particularly, if the capacities of the phase advancing capacitor circuit 2 and the inverter 1 are made equal, it is possible to output the maximum value of the advanced power from zero to the sum of the capacitor capacity and the inverter capacity.

The inverter 1 has a main circuit configuration of a self-extinguishing type semiconductor switch such as a transistor, and outputs a voltage and a current close to a sine wave by the high frequency PWM control thereof. Since this output contains high-order harmonics due to the PWM waveform, a filter circuit 1A composed of LCR (resistor R is for vibration suppression) is provided at the output stage.

The phase advancing capacitor circuit 2 is provided with a reactor L corresponding to 6 to 8% of the capacity of the phase advancing capacitor C in series so as not to cause resonance with the power system. ..

[0006]

[Problems to be solved by the device]

 In the conventional active filter, the output stage of the inverter 1 is provided with a harmonic elimination filter circuit 1A for PWM control, and the phase advancing capacitor circuit 2 is provided with a resonance suppressing reactor L. The circuit elements of the reactor L and the filter 1A have large current capacity and power capacity for compensating the reactive power to the power system, and require a large size together with the inverter main circuit and the phase advancing capacitor C, This was a factor in increasing the facility cost and installation space of the active filter.

An object of the present invention is to provide an active filter capable of reducing the circuit elements of the filter circuit and the phase advancing capacitor circuit.

[0008]

[Means for Solving the Problems]

 In order to solve the above problems, the present invention provides an active filter for compensating reactive power of a power system by connecting a PWM controlled inverter and a phase advancing capacitor circuit in parallel. The phase-advancing capacitor is provided with a resonance preventing reactor in series and a vibration suppressing resistor in parallel with the reactor. A filter at the output stage of the inverter is composed of the actuator, the resistor, and the capacitor for phase advance.

[0009]

[Action]

 By using the phase-advancing capacitor also as the capacitor of the inverter's high-order harmonics removal filter circuit, the number of capacitors can be reduced, and the high-order harmonics removal reactor can be made smaller.

[0010]

【Example】

FIG. 1 is a circuit diagram showing an embodiment of the present invention. The inverter 3 has a bridge circuit of power transistors Tru to Trz as a self-extinguishing type semiconductor switch as a main circuit, and obtains a three-phase pulse output approximate to a sine wave by its PWM control. At this output stage, reactors L _{1 which} are reactor elements of a filter for removing higher harmonics are provided in series with each phase.

In the phase advancing capacitor circuit 4, a reactor L ₂ that serves as a resonance suppressing reactor element is provided in series with a capacitor C that serves as a phase advancing and filter element. The reactor L ₂ has a value of about 6% of the capacity of the capacitor C. A resistor R that serves as a higher harmonic elimination element is provided in parallel with the reactor L ₂ of each phase.

In the above configuration, the phase advancing capacitor circuit 4 includes the capacitor C and the reactor L. ₂ A phase advance and a resonance suppression circuit are constituted by. The filter for removing the higher harmonics of PWM control included in the output of the inverter 3 is a reactor L.₁And resistor R and capacitor C.

That is, the capacitor C is used not only for phase advancing, but also as a capacitor element of a harmonic elimination filter of the inverter, and the value of the reactor L ₁ becomes a cutoff frequency for eliminating harmonics. Is determined from the time constant with the capacitor C.

According to the present embodiment, the phase advancing capacitor C is also used as the filter capacitor. As a result, three filter capacitors are omitted in the device configuration of the active filter, and it becomes the same as the configuration in which the inductance of the reactor L ₁ is reduced. Can be made compact and cost can be reduced.

[0015]

[Effect of the device]

 As described above, according to the present invention, since the phase-advancing capacitor of the phase-advancing capacitor circuit is also used as the capacitor of the high-order harmonics removing filter circuit of the inverter, the device configuration of the active filter has a relatively large capacity. The number of large capacitors can be reduced, and the reactor for removing higher harmonics can be downsized to reduce the cost and size of the equipment.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a conventional circuit diagram.

[Explanation of symbols]

3 ... Inverter 4 ... Phase advancing capacitor circuit C ... Phase advancing capacitor L ₁ ... Reactor for removing higher harmonics L ₂ ... Reactor for suppressing resonance R ... Resistor for suppressing vibration

Claims (1)

[Scope of utility model registration request] 1. An active filter for compensating reactive power of a power system by connecting a PWM controlled inverter and a phase advancing capacitor circuit in parallel, wherein the phase advancing capacitor circuit resonates in series with a phase advancing capacitor of each phase. A prevention reactor and a vibration suppression resistor in parallel with the reactor are provided, the inverter is provided with a high order harmonic removal reactor in an output stage, and the high order harmonic removal reactor and a resistor and a phase advancing capacitor form an inverter. An active filter comprising a filter of an output stage.