JP2001178141A - Power converter unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress fault current at the time of a short-circuited load while maintaining the power factor of a voltage inverter. SOLUTION: The power converter unit comprises a power converter 1 comprising a voltage inverter 2 and an inductive impedance 3, and a capacitive impedance load 4. The inductive impedance 3 comprises the capacitive impedance 4 and a resonance circuit. The voltage inverter 2 generates a voltage having a frequency close to the resonance frequency of the resonance circuit. Consequently, the resonance circuit resonates and reactive power circulates between the inductive impedance 3 and the capacitive impedance 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a power converter for supplying power to a load having a capacitive impedance, such as a discharge tube for a silent discharge device such as an ozone generator.

[0002]

2. Description of the Related Art Since a silent discharge tube for an ozonizer is a load having a capacitive impedance, the following two power supply systems are employed. One is a current source converter that controls the current by flowing a current into the load, and the other is a current source converter disclosed in Japanese Patent Application Laid-Open No. 7-1777.
In this system, a voltage is supplied by a voltage-type inverter disclosed in Japanese Patent Publication No. 49, and a reactor is installed in parallel with a discharge tube to improve a load power factor as viewed from the inverter. JP-A-7-1
FIG. 12 shows an embodiment of 77749. In the power supply device shown in FIG. 12, a reactor is provided in parallel with the discharge tube, and a parallel resonance is generated between the capacitor of the discharge tube and the reactor, and operation is performed to improve the power factor as viewed from the power supply. .

[0003]

An ozone generator using a silent discharge tube, as described in FIG.
This can be expressed as an equivalent circuit in which the capacitance C and the resistor R are connected in parallel. An ozone generator is a device that generates ozone from a raw material gas by applying a high-frequency high voltage between a high-voltage electrode and a ground electrode of a silent discharge tube to generate a discharge.
The failure mode is a short-circuit failure. In the power converter shown in FIG. 12, when the load is short-circuited, the only factor that suppresses the rise of the current of the voltage-source inverter is the leakage impedance of the step-up transformer, and an excessive current flows. was there. The present invention has been made in order to solve the above-described problem, and relates to a power conversion device that supplies power to a load having a capacitive impedance such as a discharge tube for a silent discharge device such as an ozonizer. The purpose of the present invention is to also suppress the fault current at the time of load short circuit while maintaining the power factor of.

[0004]

In order to achieve the above object, the present invention is directed to a voltage type inverter, a capacitive impedance, and an induction connected in series with the voltage type inverter and the capacitive impedance. It is characterized by having an inductive impedance, thereby generating a series resonance with the capacitive impedance and the inductive impedance, thereby improving the power factor of the voltage source inverter, and the inductive impedance as a load. Even when the impedance is short-circuited, no overcurrent occurs. The invention according to claim 2 is characterized in that a transformer is provided at the output of the voltage-type inverter. As a result, the voltage of the voltage type inverter is converted into the voltage required for the load, and the voltage and current rating of the voltage type inverter can be most economically selected, and the load and the inverter can be insulated. The invention according to claim 3 is characterized in that a transformer connected in series between the inductive impedance and the capacitive impedance is provided. As a result, the voltage of the voltage-type inverter can be converted to the voltage required for the load, and the voltage and current rating of the voltage-type inverter can be most economically selected.
Insulation between the load and the inverter can be achieved. Further, by installing the inductive impedance on the inverter side of the transformer, for example, the inductive impedance serves as an inductive impedance for balancing when two voltage source inverters are configured in parallel and an inductive impedance for series resonance. be able to.

Further, the invention according to claim 4 is characterized in that the voltage type inverter outputs a rectangular wave voltage. Thereby, by applying a rectangular wave voltage, a series resonance is generated by the capacitive impedance and the inductive impedance,
The power factor of the voltage type inverter is good, and the overcurrent can be suppressed by the inductive impedance even when the capacitive impedance as the load is short-circuited. According to a fifth aspect of the present invention, there is provided a current detector for detecting an output current of a voltage type inverter or an output current of a power conversion device, a voltage detector for detecting an output voltage of the voltage type inverter, A reactive power calculation circuit for obtaining a voltage source inverter output reactive power from an output voltage; and a reactive power control circuit for adjusting an output frequency of the voltage source inverter so that the voltage source inverter output reactive power is minimized. . As a result, even when the inductive impedance and the capacitive impedance of the load fluctuate, the series resonance state is maintained, the power factor of the voltage-source inverter is improved, and the capacitive impedance of the load is reduced by the inductive impedance. Even when a short circuit occurs, a fault current can be suppressed. Further, according to the present invention, a current detector for detecting an output current of a voltage type inverter or an output current of a power converter, and a reactive power calculation signal delayed by 90 degrees from the output voltage of the voltage type inverter are provided. A generated signal generator, a reactive power calculation circuit for obtaining an output reactive power from the output current and the reactive power calculation signal, and an invalidity adjusting an output frequency of the voltage type inverter so that the output reactive power of the voltage type inverter is minimized. And a power control circuit. Thereby, even when the inductive impedance and the capacitive impedance of the load fluctuate, the series resonance state is maintained, the power factor of the voltage-type inverter is improved, and
Due to the inductive impedance, the fault current can be suppressed even when the capacitive impedance as the load is short-circuited. Also,
By using the signal generator instead of the voltage detection value to calculate the reactive power, the detector can be omitted and it is economical.

According to a seventh aspect of the present invention, there is provided a current detector for detecting an output current of a voltage type inverter or a power converter, an output of a voltage type inverter, an AC winding of a transformer, or an output of a power converter. A voltage detector for detecting voltage, an active power calculation circuit for obtaining an output active power from the output current and the output voltage, and an active power control for adjusting an inverter output voltage so that the output active power becomes equal to the output active power command value. And a circuit.
This minimizes the reactive power of the inverter, and
The output active power can be controlled, and the fault current at the time of load short-circuit can be suppressed. The invention according to claim 8 is a current detector for detecting an output current of a voltage type inverter or a power converter, a signal generator for generating a signal for active power calculation synchronized with an output voltage of the voltage type inverter, An active power calculation circuit for obtaining an output active power from the output current and the active power calculation signal, and an active power control circuit for adjusting an inverter output voltage so that the output active power is equal to the output active power command value. Features. This allows
The reactive power of the inverter can be minimized, the output active power can be controlled, and the fault current at the time of load short-circuit can be suppressed.
Further, by detecting the active power by the signal generator, the voltage detector can be omitted, which is economical.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) FIG. 1 is a schematic configuration diagram showing a first embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a power conversion device including a voltage source inverter 2 and an inductive impedance 3, and 4 denotes a capacitive impedance load.
Reference numeral 4 denotes resistance in parallel so as to be an equivalent circuit of an ozone generator which is a typical capacitive load. The inductive impedance 3 and the capacitive impedance 4 constitute a resonance circuit. The voltage source inverter 2 generates a voltage having a frequency close to the resonance frequency of the resonance circuit. This allows
The resonance circuit resonates and the reactive power circulates between the inductive impedance and the capacitive impedance. The voltage-source inverter 2 only needs to supply, for example, the active power consumed by the resistance in parallel with the capacitive impedance, and the power output of the inverter can be increased. In addition, the resonance makes it possible to apply a voltage up to twice the voltage output from the voltage source inverter 2 to the capacitive impedance. Also,
Voltage source inverter 2 and inductive impedance 3 are loaded 4
Are connected in series, the fault current can be suppressed even when the capacitive impedance is short-circuited.

In the present embodiment, the load is made capacitive and resonance is generated by providing an inductive impedance in the power converter, but when the load is inductive,
It is clear that resonance may be provided by providing a capacitive impedance in the power converter. (Second Embodiment) FIG. 2 is a schematic configuration diagram showing a second embodiment of the present invention. In FIG. 2, reference numeral 5 denotes a transformer. By installing a transformer, the current rating and voltage rating of the voltage-type inverter can be selected to suit the rating of the semiconductor used in the voltage-type inverter, regardless of the voltage required on the load side. A conversion device can be provided. Also, by inserting a transformer, insulation from the load can be achieved. Normally, an ozone generator having a capacitive impedance needs to apply a voltage of about several kV to 10 kV. On the other hand, the ON / OFF negative control element currently used as a medium- and small-capacity voltage-source inverter is mainly an IGBT, and has a voltage rating of several hundreds to several hundreds of volts. Therefore, in the ozone generator, the transformer in FIG. 2 is a step-up transformer. In the circuit shown in FIG. 2, since a transformer is inserted in series with the inductive impedance 3, the leakage impedance of the transformer is added to the inductive impedance.

(Third Embodiment) FIG. 3 is a schematic configuration diagram showing a third embodiment of the present invention. In this embodiment, the transformer 5 is installed between the inductive impedance 3 and the capacitive impedance 4, and the inductive impedance is installed on the DC winding side of the transformer. In the case of an ozone generator, the transformer 5 is a step-up transformer as described above. Therefore, if the inductive impedance 3 is installed on the DC winding side of the transformer, the voltage may be low, and the whole may be economical and small. Further, as shown in FIG. 4, the output capacity of the power supply is increased, and a plurality of power supplies (in FIG.
When the voltage type inverters are connected in parallel, a reactor may be required for the parallel connection, but the reactor may also serve as an inductive impedance for resonance. (Fourth Embodiment) FIG. 5 is a schematic configuration diagram showing a fourth embodiment of the present invention. In FIG. 5, reference numeral 6 denotes a voltage detector for detecting the output voltage of the voltage-type inverter, 7 denotes a current detector for detecting the output current of the voltage-type inverter, and 60 denotes a voltage-type inverter based on the voltage detector 6 and the current detector 7. A reactive power detection circuit for detecting the output reactive power 61, and a reactive power control circuit 50 for controlling the output frequency command value 51 of the voltage type inverter so as to minimize the detected reactive power 61.

As mentioned above, the capacitive impedance 4
When the resonance circuit formed by the inductive impedance 3 and the leakage impedance of the transformer 5 resonates, the power factor of the voltage-source inverter increases. However, the resonance frequency fluctuates due to fluctuations in the capacitive impedance, manufacturing errors in the inductive impedance, and the like. Despite these fluctuations, in order to always reduce the reactive power of the voltage-type inverter and to increase the power factor, the output reactive power of the voltage-type inverter is detected, and the voltage-type inverter 2 is controlled to minimize the reactive power. To control the output frequency. In the present embodiment, the current detector 7 is installed on the DC winding side of the transformer 5, but is installed on the AC winding side of the transformer 5 or on the output of the power converter 1. Needless to say, the same effect can be obtained. Also, as shown in FIG. 6, even if the voltage detector 6 is installed on the AC winding side of the transformer 5, the same effect can be obtained when the leakage impedance of the transformer is smaller than the inductive impedance. (Fifth Embodiment) FIG. 7 is a schematic configuration diagram showing a fifth embodiment of the present invention. In FIG. 7, reference numeral 70 denotes a signal generator for calculating a reactive power. In order to calculate the reactive power from the output current, it is necessary to obtain a voltage waveform shifted by 90 degrees from the inverter output voltage. A signal generator 70 outputs a voltage waveform shifted by 90 degrees.

The operation of the signal generator 70 will be described.
In the description, FIG. 8 shows a detailed circuit diagram of the voltage source inverter 2 and FIG. 9 shows an operation waveform thereof. Q1 to Q4 are on / off control elements constituting the voltage source inverter. Since it is a voltage type inverter, Q1, Q2 connected in series
And Q3 and Q4 are controlled not to be turned on at the same time. Q
During the period when 1 and Q4 are on, the output voltage (Vinv) of the voltage source inverter has a positive polarity DC voltage (VDC).
Appear during the period in which Q2 and Q3 are on, with a negative polarity. As a method of obtaining a voltage waveform shifted by 90 degrees, instead of detecting the actual voltage, the voltage waveform is obtained from the phase difference and frequency between Q1 and Q3 known in advance by the control device. For example, a signal having a pulse width corresponding to the phase difference may be output with a delay of 1/4 cycle of the frequency command value. still,
The reactive power control circuit does not have to control the reactive power to a constant value, but only has to operate so as to minimize the reactive power, and the detection of the reactive power does not need to be accurate as an absolute amount. Therefore, there is no problem even if the signal does not reflect the pulse width as shown by VQ in FIG. As shown in FIG. 7, if the voltage-source inverter output voltage for detecting the reactive power is obtained from the control signal, the voltage detector can be omitted, and an economical power converter can be provided.

(Sixth Embodiment) FIG. 10 is a schematic configuration diagram showing a sixth embodiment of the present invention. As shown in FIG. 10, reference numeral 80 denotes an active power detection circuit for detecting active power from the voltage detector 6 and the current detector 7, and reference numeral 90 denotes a voltage-source inverter for converting the detected active power 81 to the active power set value 92. Is an active power control circuit for controlling the pulse width command value 93. In FIG. 10, an active power detection circuit 80 detects an output active power 81 by multiplying an output current and an output voltage. When the output is of a single phase, the amount of ripple is large, so a filter 82 is provided at the subsequent stage. The active power control circuit 90 controls the pulse width of the voltage source inverter, that is, the phase difference φ of the operation waveform in FIG. 9 so that the detected active power 81 matches the active power set value 92. The reactive power of the voltage source inverter is the same as that of FIG. In FIG. 10, as in the case of active power detection, a filter for removing ripples is provided because the output is a single-phase output. As shown in FIG. 10, the output active power is controlled by controlling the frequency of the voltage source inverter so as to reduce the reactive power, and controlling the pulse width of the voltage source inverter so that the active power matches the set value. , The power factor of the voltage source inverter can always be operated at a high level, the capacity of the voltage source inverter and the capacity of the step-up transformer can be reduced, and an economical power converter can be provided.

Further, by providing the inductive impedance in series, even when the capacitive load is short-circuited, the rise of the fault current can be suppressed, and the overcurrent can be protected. In FIG. 10, the current detector detects the current on the DC winding side of the transformer 5, but it is apparent that the same effect can be obtained by detecting the current on the AC winding side of the transformer. (Seventh Embodiment) FIG. 11 is a schematic configuration diagram showing a seventh embodiment of the present invention. In FIG. 11, reference numeral 71 denotes a signal generator that outputs a voltage signal for detecting active power. The output voltage of the voltage source inverter is as described in the operation explanatory diagram of FIG. 9, and can be calculated from the gate waveform applied to the voltage source inverter. 71 is Vin in FIG.
v is calculated and output. The active power calculated based on the output voltage waveform of the voltage type inverter and the active power at the output point of the power converter differ from each other by the loss of the transformer 5 and the inductive impedance 3. The loss is usually 3% or less, and if it can be neglected in the whole control, it is possible to control by detecting the active power by the signal generator. With the configuration as shown in FIG. 11, when the output is high as in an ozone generator-like power supply, a high-voltage detector can be omitted, and an economical power converter can be provided.

[0014]

As described above, according to the present invention,
A voltage-source inverter, and an inductive impedance connected in series with the capacitive impedance, and a reactive power control circuit that adjusts the frequency so as to minimize the output reactive power of the voltage-source inverter; The active power control circuit that adjusts the output pulse width of the voltage-source inverter to match the output power factor allows the output of the voltage-source inverter to have a high power factor even if the output changes or the load constant changes. is there. As a result, the required capacity of the voltage-type inverter or the transformer is reduced, and an economical power converter can be provided. In addition, since the inductive impedance is connected in series with the voltage type inverter, even if a short circuit occurs due to the capacitive impedance, the rise of the short circuit current can be suppressed and protection can be performed.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a first embodiment of the present invention.

FIG. 2 is a schematic configuration diagram showing a second embodiment of the present invention.

FIG. 3 is a schematic configuration diagram showing a third embodiment of the present invention.

FIG. 4 is a schematic configuration diagram showing a modified example of the third embodiment of the present invention shown in FIG.

FIG. 5 is a schematic configuration diagram showing a fourth embodiment of the present invention.

FIG. 6 is a schematic configuration diagram showing a modified example of the fourth embodiment of the present invention shown in FIG.

FIG. 7 is a schematic configuration diagram showing a fifth embodiment of the present invention.

FIG. 8 is a detailed circuit diagram showing a voltage source inverter applied to the fifth embodiment of the present invention shown in FIG. 7;

FIG. 9 is a diagram showing the operation of the voltage source inverter shown in FIG.

FIG. 10 is a schematic configuration diagram showing a sixth embodiment of the present invention.

FIG. 11 is a schematic configuration diagram showing a seventh embodiment of the present invention.

FIG. 12 is a schematic configuration diagram showing a conventional power converter for a silent discharge device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Power conversion device, 2 ... Voltage source inverter, 3 ... Inductive impedance, 4 ... Capacitive impedance, 5 ... Transformer, 6 ... Voltage detector, 7 ... Current detector, 50 ... Reactive power control circuit, 51 ... Frequency command value, 60: reactive power detection circuit, 61: reactive power detection value, 62: filter, 70: reactive power detection signal generator, Q1 to Q4: on / off control element, 80: active power detection circuit, 81: active Power detection value,
82: filter, 90: active power control circuit, 91: active power set value

Continued on the front page (72) Inventor Ryutaro Makise 1-1-1, Shibaura, Minato-ku, Tokyo F-term in Toshiba head office (reference) 5H007 AA02 BB00 CA01 CB02 CB05 CB22 CC05 CC32 DA03 DC02 DC05 EA08 FA03 FA14 FA18

Claims (8)

[Claims] 1. A power converter, comprising: a voltage-source inverter; a capacitive impedance; and an inductive impedance connected in series with the voltage-source inverter and the capacitive impedance. 2. The power converter according to claim 1, further comprising a transformer at an output of the voltage source inverter. 3. The power conversion device according to claim 1, further comprising a transformer connected in series between the inductive impedance and the capacitive impedance. 4. The power converter according to claim 1, wherein the voltage-source inverter outputs a rectangular wave voltage. 5. A current detector for detecting an output current of the voltage type inverter or an output current of the power converter, a voltage detector for detecting an output voltage of the voltage type inverter, the current detector, and the voltage detection. Reactive power calculation circuit for obtaining the output reactive power of the voltage source inverter from the output signal from the power supply, and a reactive power control circuit for adjusting the output frequency of the voltage source inverter so that the output reactive power of the voltage source inverter is minimized The power converter according to any one of claims 1 to 4, comprising: 6. A current detector for detecting an output current of the voltage source inverter or an output current of the power converter, and a signal for generating a reactive power calculation signal delayed by 90 degrees from the output voltage of the voltage source inverter. A generator, a reactive power calculation circuit for obtaining an output reactive power based on output signals from the current detector and the signal generator, and the voltage source inverter such that the output reactive power from the reactive power calculation circuit is minimized. The power converter according to any one of claims 1 to 4, further comprising: a reactive power control circuit that adjusts an output frequency of the power converter. 7. A current detector for detecting an output current of the voltage-source inverter or the power converter, and a voltage for detecting an output of the voltage-source inverter or an AC winding of the transformer or an output voltage of the power converter. A detector, an active power calculation circuit for obtaining an output active power based on output signals from the current detector and the voltage detector, and an output active power from the active power calculation circuit being equal to an output active power command value. The power converter according to any one of claims 1 to 6, further comprising: an active power control circuit that adjusts an output voltage of the voltage source inverter. 8. A current detector for detecting an output current of the voltage-type inverter or the power converter, a signal generator for generating a signal for calculating an active power synchronized with an output voltage of the voltage-type inverter, and the current detection Active power calculation circuit for obtaining an output active power based on an output signal from the signal generator and the signal generator; and an output of the voltage source inverter such that the output active power from the active power calculation circuit becomes equal to the output active power command value. The power converter according to any one of claims 1 to 6, further comprising: an active power control circuit that adjusts a voltage.