WO2013072908A1

WO2013072908A1 - Method and converter for converting high voltage dc to pulsating ac voltage

Info

Publication number: WO2013072908A1
Application number: PCT/IL2012/000371
Authority: WO
Inventors: Yefim Riskin
Original assignee: Ionics - Ionic Systems Ltd.
Priority date: 2011-11-17
Filing date: 2012-11-08
Publication date: 2013-05-23
Also published as: IL216425A0

Abstract

Method of conversion of high DC voltage to pulsating AC voltage and a converter using the method, wherein AC voltage is generated by a high frequency fixed generator, the voltage is transmitted by capacitive coupling (11, 12, 13, 14) to at least one voltage multiplier (10a, 10b) which rotates relative to an AC voltage generator (15), wherein alternating transmission of opposite polarity voltages from the voltage multiplier outputs to the output AC terminals is realized via at least two corona discharge zones (2, 3, 8, 9).

Description

Method and converter for converting high voltage DC to pulsating AC voltage

FIELD OF THE INVENTION

This invention relates to the conversion of HV DC to pulsating AC voltage.

BACKGROUND OF THE INVENTION

Devices for converting high DC voltages to pulsating AC voltage are disclosed in JP 2002216994, JP 2004039352 and JP 2008123912.

JP 2002216994 discloses a pulse AC type static eliminator, wherein a first Zener diode is provided between the positive output terminal of a high-voltage generating circuit, and a common conductor, and a second Zener diode is similarly provided between the negative output terminal of the high- voltage generating circuit, and the common conductor. The sum of the breakdown voltage of the first and second Zener diodes is larger than the voltage at the positive output terminal.

JP2004039352 discloses a static eliminator comprising high-voltage electric power source circuits for generating a high voltage; a needle electrode impressed with the high voltages supplied from the high- voltage electric power source circuits to generate an ion by corona discharge; the grounding electrode provided in the vicinity of the needle electrode; and a control part for conducting On/Off control for the high- voltage electric power source circuits, for sampling a current flowing in the grounding electrode while synchronized with the On/Off control, and for finding a value corresponding to the ion generating amount, based on a sampling value.; The eliminator is also provided with thermistor temperature correcting circuits for changing a voltage of an input side in each of the high-voltage electric power source circuits using a thermistor to compensate the fluctuation in the sampling value generated by change with respect to a temperature of a floating capacity between a high-voltage wiring circuit for supplying the high voltage to the needle electrode and the grounding electrode. JP 2008123912 discloses a static eliminator having a circuit structure capable of holding down the output of a high voltage generating circuit to the minimum voltage. Two high voltage generating circuits have respective secondary switches that are opened for the high voltage generating circuits which are not yet in operation, and the circuits are controlled in a high impedance state. Thereby, the high voltage generating circuits which are not yet operated can be separated from the high voltage generating circuits in operation. The output voltage of the high voltage generating circuits in operation is conveyed as is to a discharge electrode.

The disadvantage of these devices is their complexity resulting from the use because of two AC voltage generators, two opposite polarity voltage multipliers and a device for alternately switching on the generators.

JP 2010218750 discloses a similar device having a single AC voltage generator, a generator controller, single polarity voltage multiplier and a means for generating a reverse polarity pulse. High voltage from a high voltage generating circuit is divided in resistance by a resistance dividing circuit, and in a period when impressing positive high voltage on the discharge needle at a divided midpoint, electric charge is accumulated in a capacitor, and when the high voltage generating circuit stops operation, the accumulated electric charge of the capacitor is discharged in reverse polarity, and is divided in the resistance by the resistance dividing circuit, and negative high voltage is impressed on the discharge needle at the divided midpoint.

The above approaches are prone to the following drawbacks:

1. Notable difference in the shape and duration of the AC pulses at the device output. The positive pulses are rectangular in shape and their duration can be changed by adjusting the voltage multiplier turn-on time, while the negative pulses are always triangular since a capacitor discharges across a pair of resistors connected in series) and have constant duration which depends only on the nominal values of the capacitor and the resistors.

2. Failure to generate intervals between the reverse polarity pulses as required in static eliminators since a negative pulse is generated immediately after the positive pulse is ended.

One of the common disadvantages of the all the above approaches resides in their low efficiency of 50% of converting the high DC voltage to pulsating AC voltage. Indeed, in order to obtain voltage of ± 10 kV at the converter output the total value of the DC voltage in the known circuits must be 20 kV.

Another common disadvantage of the known devices is an imbalance of amplitudes of the reverse polarity pulses at the converter output which stems from many reasons, the major one being the failure to actually provide equal DC voltages at the respective output of each of the single polarity tracks, comprising an AC generator and a voltage multiplier.

Deviations of AC generator parameters and multipliers necessitate inclusion of an additional amplitude balancing means or additional balancing operations. SUMMARY OF THE INVENTION

An objective of the present invention is to reduce or eliminate the disadvantages of known technical solutions.

The above objective is achieved by a method and apparatus for converting high DC voltage to pulsating AC voltage having the features of the respective independent claims.

The method is based on rotating at least one voltage multiplier relative to a fixed high frequency AC voltage generator and also relative to at least two fixed electrodes designed for alternating transmission of opposite polarity voltage from the voltage multiplier output to the converter output.

The opposite polarity voltage transmission to fixed electrodes is effected through at least two corona discharge zones generated between the fixed electrodes and at least two electrodes rotating together with the voltage multiplier, the rotating electrodes being connected to the opposite polarity outputs of the above voltage multiplier.

The fixed electrodes may be ionizing, in which case the rotating electrodes must be nonionizing. Alternatively, the fixed electrodes may be nonionizing, in which case the rotating electrodes must be ionizing.

In order for corona discharge to develop between the moving and the fixed electrodes, the fixed electrodes are placed in immediate proximity to the fixed ones (2 ÷ 6 mm). The distance between the electrodes determines the voltage drop in the corona discharge zone; in this case it will be in range of 1 ÷ 2 kV.

In the proposed method the high AC voltage is transmitted by capacitive coupling from a fixed AC generator to a rotating voltage multiplier where it is converted to high DC voltage.

If only two ionizing electrodes are used, the maximal converter current does not exceed 100 μΑ, which is sufficient for most applications.

The reason for the level limitation to 100 μΑ is that crossing this current value for one ionizing electrode would result in the "quiet corona" transition to a sharp breakdown of the discharge gap; thus should an increase of the output current of the converter be required the number of ionizing electrodes must be increased.

The frequency of the AC pulses at the converter output is controlled by adjusting the number of revolutions per unit time of the voltage multiplier.

The ratio between the duration of the reverse polarity pulses at the converter output and the interval between them is controlled by adjusting the length of the nonionizing electrodes relative to half of the circle's perimeter described by the electrodes during rotation.

The method provides for automatic balancing of the amplitudes of the pulsating AC voltage at the converter output since only one AC voltage generator and one voltage multiplier is used.

The converter based on the proposed method comprises the following elements: a body, an electric motor and a high voltage AC generator fixed on the body. Moreover, the converter has at least two nonionizing electrodes and at least one voltage multiplier which are mounted on the rotor fastened to the electric motor axis which rotates the elements relative to the body.

Also, the converter contains elements used to provide capacitive coupling between the high potential and the low potential outputs of the AC generator and the voltage multiplier inputs.

The above elements formed as air capacitor plates face each other both on the body and the rotor.

Further the converter has terminals for connecting to an external power supply and output terminals for load connection. BRIEF DESCRIPTION OF THE DRAWINGS

In order to understand the invention and to see how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

Fig. 1 is a schematic representation of an AC-DC converter according to an embodiment of the invention; and

Fig. 2 shows an elevation in the direction of arrow "A" in Fig. 1.

DETAILED DESCRIPTION OF EMBODIMENTS

Fig. 1 shows schematically the construction of a converter according to an embodiment of the invention having a body 1, ionizing electrodes 2 and 3, output converter terminals 4, an electric motor 5 having an axis 6 coupled to a rotor 7. Nonionizing electrodes 8 and 9, a pair of voltage multipliers 10a, 10b and concentric rotor plates 1 land 12 are mounted on the rotor 7. The rotor plate 11 is annular and surrounds the plate 12, which is disc-shaped. Stator plates 13 and 14 are mounted on the body 1 so as to face the rotor plates Hand 12 while being spatially separated therefrom, thereby forming a pair of air-spaced capacitors.

A high voltage AC voltage generator 15 is connected to an external AC power supply (not shown) via terminals 16 and feed AC power to the air-spaced capacitors of the converter via the stator plates 13 and 14. The ionizing electrodes 2 and 3 are connected to the output terminals 4 and the nonionizing electrodes 8 and 9 are respectively connected to the opposite polarity outputs of the respective voltage multiplier 10a, 10b whose inputs are connected to the rotor plates 1 1 and 12. The electric motor 5 is likewise connected to the terminals 16 for receiving power from the external AC power supply.

With reference to Fig. 2 operation of the converter will now be described. When power is supplied from the external AC power source to the terminals 16, the electric motor 5 is energized and the rotor 6 rotates, thereby rotating the rotor plates 11 and 12. Consequently, the AC voltage generator 15 becomes connected to the voltage multipliers 10a, 10b via the rotor plates 11 and 12 and the stator plates 13 and 14 of the air capacitors. The multipliers 10a, 10b convert AC voltage from the generator 15 to high DC voltage which is applied to the nonionizing electrodes 8 and 9. During their rotation, the nonionizing electrodes 8 and 9 alternately pass near ionizing electrodes 2 and 3 and two corona discharge zones are generated between the respective electrodes. The opposite polarity voltages from the outputs of the respective multipliers 10a, 10b alternately propagate through these zones and appear at the output terminals 4 of the converter. The corona discharge zone constitutes a nonlinear resistance in which each two-fold current increase results merely in a 10% increase of voltage drop in the corona discharge zone, which enables the output voltage of the converter to be maintained nearly constant over a wide range of changes in the load current.

The converter according to the invention has the following advantages in comparison with the state-of-the art devices.

a. High conversion efficiency. Indeed, when the voltage at the voltage multiplier output is -13 kV and the voltage loss in two corona discharge zones is -3 kV the output voltage is equal to ±10 kV which corresponds to 77% efficiency.

b. Simplicity due to there being only one AC generator and one voltage multiplier in the design; a smaller number of voltage multiplication cascades is required owing to the efficiency of DC/ AC conversion and this is achieved without the need for separate control of the two channels of high DC voltage generation.

c. Automatic balancing of the reverse polarity pulse amplitudes at the converter output.

A converter which the following specifications was designed based on the technical solutions implemented in the present invention.

AC voltage at the output ±10 kV

Output current 1.0 ÷ 100 μΑ

AC pulses frequency 10 ÷ 100 Hz

Conversion efficiency 77%

Converter dimensions (mm) 70 x70 x 20

Claims

CLAIMS:

1. Method of conversion of high DC voltage to pulsating AC voltage, which includes AC voltage generation by means of high frequency fixed generator, this voltage transmission by capacitive coupling to a voltage multiplier and this multiplier rotation relative to AC voltage generator, wherein alternating transmission of opposite polarity voltages from the voltage multiplier outputs to the output AC terminals is realized via at least two corona discharge zones.

2. Method of conversion of high DC voltage to pulsating AC voltage, which includes AC voltage generation according to claim 1, wherein the corona discharge zones are generated due to at least two fixed ionizing electrodes which are placed at immediate proximity to at least two electrodes rotating together with the voltage multiplier, the rotating electrodes being connected to the opposite polarity outputs of the above voltage multiplier.

3. Method of conversion of high DC voltage to pulsating AC voltage, which includes AC voltage generation according to claim 1, wherein the frequency of the output pulsing AC voltage is controlled by adjusting the rotation velocity of the voltage multiplier.

4. Method of conversion of high DC voltage to pulsating AC voltage, which includes AC voltage generation according to claim 1, wherein the ratio between the duration of the reverse polarity pulses and the interval between them is controlled by adjusting the length of the nonionizing electrodes relative to the half of the circle's perimeter described by the electrodes during rotation.

5. Converter including an electric motor (5) having a rotor (6), fixed high frequency AC voltage generator (15), at least one voltage multiplier (10a, 10b) mounted on the rotor (6) of the electric motor, means for capacitive coupling (11, 12, 13, 14) between the outputs of the AC voltage generator and the inputs of the at least one voltage multiplier, wherein the alternating transmission of opposite polarity voltages from the multiplier outputs to the output converter terminals is realized via at least two corona discharge zones.

6. Converter according to claim 5, wherein the corona discharge zones are generated owing to at least two fixed ionizing electrodes (2, 3) mounted in immediate proximity to at least two nonionizing electrodes (8, 9) mounted on the rotor and connected to the opposite polarity outputs of the voltage multiplier.

7. Converter according to claim 5, wherein the frequency of the output AC voltage is controlled by adjusting the rate of rotation of the electric motor.

8. Converter according to claim 5, wherein the ratio between the duration of the reverse polarity pulses at the converter output and the interval between the above pulses is controlled by adjusting the length of the arc of the nonionizing electrode relative to a half of the circuit described by the electrodes during rotation.