JPH11122950A - Inverter power device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inverter power device, in which inverter output capacitance is reduced by canceling capacitor phase-advancing reactive power. SOLUTION: This inverter power device has an inverter 3 for converting a DC input into an AC having fixed frequency and outputting it, a low-pass filter 4, in which a capacitor Cb is connected in parallel with an output from the inverter 3 via a series reactor La and which removes a higher harmonics component excepting fundamental wave contained in the output from the inverter 3 and a transformer Tc, in which the primary sides are connected at both ends of the capacitor Cb. In this case, the gap of a transformer core is set so that the exciting impedance Zo' of the transformer Tc mode is equal to the impedance Zc of the capacitor Cb in fundamental frequency, and reactive power flowing through into the capacitor Cb is canceled by reactive power which flows into the exciting impedance Zo'.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter power supply, and more particularly to an inverter power supply in which a low-pass filter for removing harmonic components other than a fundamental wave and a transformer are connected to an inverter output.

[0002]

2. Description of the Related Art As an inverter, for example, a PWM inverter generates a positive / negative pulse train having a predetermined width and period from a DC input by an ON / OFF switching operation, which becomes a sinusoidal waveform with a fundamental wave (effective value) and a predetermined frequency (Fb). )
It outputs the alternating current. Actually, a carrier harmonic component near the switching frequency (Fc) and a noise harmonic component near an integer multiple thereof (2Fc ± Fn, etc.) are added to the sine waveform of the fundamental wave (frequency Fb), and the inverter output waveform is Instead of a regular sine waveform, it becomes a slightly distorted sine waveform.

Therefore, a power supply device using an inverter removes harmonic components (each harmonic component of a carrier and noise) other than a fundamental wave included in an inverter output in most products except for a general-purpose inverter for motor control. A low-pass filter (carrier removal filter) for extracting a normal sine waveform is provided, and an example thereof will be described below with reference to FIGS. 2 (a) and 2 (b). In the inverter power supply device (1) shown in FIG. 2A, (2) is a DC power supply unit, (3) is an inverter, (4) is a low-pass filter, (Ta) is an insulating transformer, and (5) is a load. It is.

The DC power supply section (2) is connected to a commercial AC power supply (V
s) is transformed and rectified by the transformer (Tb) and the rectifier (6), and the capacitor (Ca) is DC-charged. The inverter (3) converts a DC voltage input from the DC power supply unit (2) into an AC voltage having a predetermined frequency and outputs the AC voltage. The low-pass filter (4) has a capacitor (Cb) connected in parallel to the inverter output via a series reactor (La), and removes harmonic components other than the fundamental wave included in the inverter output. The insulating transformer (Ta) has a primary side connected to both ends of the capacitor (Cb) and a load (5) connected to the secondary side, has an almost infinite exciting impedance (Zo), and has an external noise reduction function. Cut off.

According to the above configuration, in the inverter output waveform, the fundamental frequency (Fb) in a lower frequency region than the resonance frequency (Fo) of the low-pass filter (4) passes through the low-pass filter (4), and Carriers and noise harmonic components in a higher frequency range than the frequency (Fo) are cut off and removed by the low-pass filter (4).

As shown in FIG. 2B, the equivalent circuit of the inverter power supply device (1) transforms a capacitor (Cb) connected in parallel to the inverter equivalent power supply (3 ') via a series reactor (La). The circuit (Ta ′) and the load (5) are sequentially connected. The transformer circuit (Ta ') has a resistor (R) connected to one end of the capacitor (Cb).
a) and a series impedance (Za) composed of a reactor (Lb) and a series impedance (Zb) composed of a resistor (Rb) and a reactor (Lc) are sequentially connected in series,
A parallel impedance (excitation impedance Zo) composed of a resistor (Rc) and a reactor (Ld) is inserted between a connection point (M) of both impedances (Za) and (Zb) and the other end of the capacitor (Cb). is there.

Then, the series impedance (Za) (Z
b) is substantially zero, the excitation impedance (Zo) is substantially infinite, and the fundamental power (current) (Wb) is changed from the output of the inverter equivalent power supply (3 ') to the low-pass filter (4) and the impedance (Za) ( Flow through Zb) to the load (5). On the other hand, harmonic component power (current) other than the fundamental power (Wb)
(Qn) is blocked and removed by the low-pass filter (4).

[0008]

According to the above-described inverter power supply (1), the capacitor (Cb) of the low-pass filter (4) is connected in parallel to the inverter output.
The fundamental wave power (Wb) flows not only into the load side but also into the capacitor (Cb), and a current which is advanced in voltage flows through the capacitor (Cb) to increase the apparent power of the inverter (3). In particular, when the resonance frequency (Fo) of the low-pass filter (4) is close to or has to be close to the fundamental frequency (Fb), the above-described leading current easily flows.

For example, in a resistive load, the output capacity of the inverter (3) is (Pi), the active power consumed by the load (5) is (WL), and the advanced reactive power flowing through the capacitor (Cb) is (Qc). If other losses are ignored, Pi = √ (WL ² + Qc ² ), and the inverter output capacity (Pi) increases. For this reason, there is a problem that the size of the apparatus is increased and the cost is increased.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an inverter power supply device capable of canceling a capacitor leading reactive power and reducing an inverter output capacity.

[0011]

According to the present invention, there is provided an inverter for converting a DC input into an AC having a predetermined frequency and outputting the AC, and a capacitor connected in parallel to the inverter output via a series reactor, so that the inverter output other than the fundamental wave included in the inverter output is output. In an inverter power supply device including a low-pass filter for removing a harmonic component and a transformer having a primary side connected to both ends of the capacitor and a load connected to a secondary side, an excitation impedance of the transformer is a fundamental frequency. Set the gap of the transformer core to be equal to the impedance of the above capacitor,
The reactive power flowing through the capacitor is canceled by the reactive power flowing through the excitation impedance of the transformer.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an inverter power supply according to the present invention will be described below with reference to FIGS. FIGS. 1A and 1B show a circuit diagram of an inverter power supply device according to the present invention and an equivalent circuit diagram thereof, respectively.
Parts that are the same as the parts shown in (b) are given the same reference numerals, and descriptions thereof are omitted. However, in FIG. 1A, only the capacitor (Ca) is shown in the DC power supply section (2). The difference is that the excitation impedance (Z
At o ′), as shown in FIG. 1B, in the present invention, the excitation impedance (Zo ′) is set equal to the impedance (Zc) of the capacitor (Cb) at the fundamental frequency (Fb).

For example, if a gap is provided in an iron core around which the coil of the transformer (Tc) is wound, the magnetic hysteresis (△ B / △ H) fluctuates, and the inductance (excitation impedance Zo ′) of the coil also changes. fluctuate. Therefore, the gap length is determined by the excitation impedance (Zo ').
Is set to be equal to the impedance (Zc) of the capacitor (Cb) at the fundamental frequency (Fb). Further, the gap number may be set to a predetermined number instead of the gap length, or both the gap length and the gap number may be set to predetermined values. Further, the material of the transformer core may be set so that the excitation impedance (Zo ′) becomes equal to the impedance (Zc) at the fundamental frequency (Fb).

According to the above configuration, as shown in FIG. 1B, the fundamental wave power (Wb) flows through the capacitors (impedance Zc) and (Cb), and the phase leading reactive power (90 ° phase leading current) (Qc ), The reactor is a slow load, so that the fundamental wave power (Wb) flows through the exciting impedance (Zo ′), and the slow reactive power (90 ° slow exciting current) (Qt) is generated. Then, since the impedance (Zc) is equal to the excitation impedance (Zo '), the reactive powers (Qc) and (Qt) are equal and opposite in phase, and the reactive power (Qc) is canceled by the reactive power (Qt).

For example, in a resistive load, if the output capacity of the inverter (3) is (Pi) and the active power consumed by the load (5) is (WL), when other losses and the like are ignored, Pi = √ (WL) ² + Qc ² -Qt ² ) where Qc:
The leading reactive power of the capacitor (Cb) becomes Qt: the retarding reactive power of the exciting impedance (Zo '). here,
Qc = Qt, and the reactive power (Q
Since c) is canceled by the reactive power (Qt), P
i = √ (WL ² ) = WL (kVA).

[0016]

According to the present invention, in an inverter power supply device in which a transformer is connected to a low-pass filter in which a capacitor is connected in parallel via a series reactor to an inverter output, the exciting impedance of the transformer is a capacitor at a fundamental frequency. Since the gap of the transformer core is set to be equal to the impedance of the transformer, the reactive power flowing through the capacitor is canceled by the reactive power flowing through the exciting impedance, and the apparent power of the inverter is prevented from increasing, so that the inverter capacity can be reduced.

[Brief description of the drawings]

FIGS. 1A and 1B are a circuit diagram and an equivalent circuit diagram showing an embodiment of an inverter power supply device according to the present invention.

2A and 2B are a circuit diagram showing a conventional example of an inverter power supply device and an equivalent circuit diagram thereof.

[Explanation of symbols]

 Reference Signs List 3 inverter 4 low-pass filter Tc transformer 5 load La series reactor Cb capacitor Zo 'exciting impedance Zc capacitor impedance

Claims (1)

[Claims] An inverter for converting a DC input into an AC having a predetermined frequency and outputting the same, and a capacitor connected in parallel to the inverter output via a series reactor to remove a harmonic component other than a fundamental wave contained in the inverter output. In an inverter power supply device including a filter and a transformer having a primary side connected to both ends of the capacitor and a load connected to a secondary side, an exciting impedance of the transformer is equal to an impedance of the capacitor at a fundamental frequency. An inverter power supply device in which a gap between transformer cores is set as described above, and reactive power flowing through a capacitor is canceled by reactive power flowing through an exciting impedance of the transformer.