WO2005034351A2

WO2005034351A2 - Ac voltage controller

Info

Publication number: WO2005034351A2
Application number: PCT/US2004/032150
Authority: WO
Inventors: Adrian F. Ionescu
Original assignee: Power Control Technologies, Inc.
Priority date: 2003-09-30
Filing date: 2004-09-30
Publication date: 2005-04-14
Also published as: WO2005034351A3

Abstract

An AC voltage controller for frequencies of 50 Hz or 60 Hz controls the current through a load from a high frequency AC source 10 to a variable energy transfer transformer 20 including a main magnetic core 21, a saturable magnetic shunt core 21, a saturable magnetic shunt core 22, primary 23, secondary 26 and two controlling windings 24 and 25. DC current flowing through the two controlling windings 24 and 25 may saturate the magnetic shunt 22, therefore decreasing the amount of AC high frequency magnetic flux generated by the primary 23 which is diverted from the secondary 26 by the magnetic shunt 22. The secondary voltage is dependent on the amount of magnetic flux and on its rate of change (or dF/dt). The result of saturating the magnetic shunt is therefore an increase of the output voltage measured across the secondary for a given load 70.

Description

BACKGROUND

[0001] This disclosure relates to alternating current voltage controllers, more particularly to controllers for varying or regulating the AC voltage applied to a large variety of loads.

[0002] The need for a variable or constant output AC voltage controller of small size and weight that does not dissipate a significant amount of heat is not new. A multiple tap transformer and its associated array of switches, connecting various taps to the output for obtaining the desired output voltage is one of the first forms of AC modifiable AC voltage controllers. As its name clearly describes, its main disadvantage of not being able to provide a continuous adjustment of the output voltage, the variable autotransformer (often known in the industry by the trade-name "Variac") appeared many years ago for use where a continuous range of voltages lower or higher than the input AC line voltage is needed. In systems where remote or automatic output voltage control is needed, a small electric motor is used to turn the wiper in order to obtain the desired output voltage.

[0003] Another controlling device widely used is the magnetic amplifier. However, compared to the multiple-tap transformer or to the "Variac", the magnetic amplifier consists of a series controllable reactance that shifts the phase of the output voltage compared to the AC input line voltage. In many applications, this device's high impedance at lower output voltages makes it a less than ideal voltage source.

[0004] Later, several electronic high frequency switching AC voltage controllers have been devised. US patent 5,018,058 teaches how to obtain a pure sinusoidal output voltage waveform from the AC line voltage using switchmode electronic circuitry. Furthermore, US Patents 5,714,847, 5,500,575 and 6,604,515 present other methods of obtaining a variable AC output voltage of sinusoidal waveform.

[0005] Although electronic high frequency switchmode AC voltage controllers have several major advantages, such as a small size and weight and a relatively low manufacturing cost, their main disadvantage is the high degree of electromagnetic radiation and high frequency noise induced in the AC input lines and output conductors. SUMMARY

[0006] This disclosure discusses a variable AC or constant regulated AC voltage source which overcomes the disadvantages of previous AC voltage controllers. One embodiment of the invention includes a variable energy transfer transformer for controlling the amplitude of the controller output voltage by variable energy transfer from the AC high frequency voltage source. A DC current source controls the amount of saturation of the magnetic shunt, thereby controlling the amount of energy transferred from the primary to the secondary, and further controlling, therefore, the output voltage for a given load condition.

[0007] In one embodiment, an AC voltage controller includes a 50 or 60 Hz AC reference voltage connected to an input; a high frequency voltage generator coupled to the AC reference voltage, wherein the AC reference voltage modulates an output of the high frequency voltage generator; a primary winding arranged on a main magnetic core and coupled to the modulated output of the high frequency voltage generator; a secondary winding magnetically coupled to the primary winding through the main magnetic core; a saturable magnetic shunt core arranged within the main magnetic core so as to align a plane containing a shunt core magnetic flux perpendicularly with respect to a plane containing a magnetic flux axis of the main magnetic core; primary and secondary control windings operatively coupled to the saturable magnetic shunt core and to a controlled DC current source; an AC forming circuit coupled between the secondary winding and an output load terminal, the AC forming circuit smoothing a train of amplitude modulated high frequency voltage pulses received from the secondary winding based upon a detected phase of the AC reference voltage, the AC forming circuit matching a frequency, a waveform, and a phase of an output voltage applied to the output load terminal with corresponding characteristics of the AC reference voltage; and an error amplifier connected between the AC reference voltage and the output voltage and generating a control signal applied to the controlled DC current source, wherein the control signal controls a DC current applied to the primary and secondary control windings, wherein the DC current controls an amplitude of the output voltage by at least partially saturating a magnetic flux in the saturable magnetic shunt core.

[0008] In another aspect of the invention, an AC voltage controller includes an AC reference voltage connected to a high frequency pulsed voltage generator, wherein the AC reference voltage modulates an output of the high frequency pulsed voltage generator; a transformer arranged to magnetically couple the modulated output of the high frequency voltage generator from a primary winding to a signal conditioning circuit connected between a secondary winding and an output terminal of the controller; saturable magnetic shunt means operatively arranged within the transformer for controllably diverting at least a portion of a main magnetic flux of the transformer from a main magnetic core to a shunt magnetic core in response to a DC control current provided by a controlled DC current source connected to the saturable magnetic shunt means, wherein the control DC control current establishes a magnetic flux in the shunt magnetic core which controls an output voltage applied to the output terminal.

[0009] In another embodiment of the invention, a method of controlling an AC voltage includes modulating a high frequency pulsed voltage source with a 50 or 60 Hz AC reference voltage; coupling the modulated high frequency pulsed voltage to a main magnetic path; providing a saturable magnetic flux shunt path arranged essentially perpendicular to the main magnetic path; filtering the coupled modulated high frequency pulsed voltage received through the main magnetic path to essentially remove high frequency components and to provide an output voltage, wherein said filtering includes matching a phase, waveform, and frequency of the output voltage with corresponding characteristics of the AC reference voltage; and controlling an amplitude of the output voltage by controlling a magnetic flux saturation level in the saturable magnetic flux shunt path.

[0010] Further scope and applicability of the present disclosure will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the disclosure will become apparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] This disclosure is described in more detail with reference to the attached drawings in which:

[0012] Fig. 1 is a block diagram of an embodiment of the invention; [0013] Fig. 2 shows an embodiment of the variable energy transfer transformer 20;

[0014] Fig. 3 shows another embodiment 20' of the variable energy transfer transformer;

[0015] Fig. 4 depicts one embodiment of the internal circuit structure of AC forming block 60 representing a standard AC synchronized, non-isolated forward converter;

[0016] Fig. 5 describes another embodiment 60' of the internal circuit structure of the AC forming block representing another version of a standard AC synchronized, non- isolated forward converter; and

[0017] Fig. 6 describes another embodiment 60"of the internal circuit structure of the AC forming block representing a full wave rectification version of a standard AC synchronized, non-isolated forward converter. *

DETAILED DESCRIPTION

[0018] An embodiment of the invention is described below with reference to the drawings. Fig. 1 describes the operating block diagram showing its principal elements. A high frequency input voltage source 10, energized from a frequency (50 or 60 Hz) AC voltage source 100, supplies energy via lines 101 and 102 to the primary of the variable energy transfer transformer 20. Transformer 20 includes main magnetic circuit 21 for transferring the energy from the primary 23 to the secondary 26. Saturable magnetic shunt core 22 also contains the anti-series controlling windings 24 and 25. High Frequency Input Voltage Source 10 may be constituted individually, or along with the primary 23 of a half or full-wave bridge switching circuit topology operating at 50% duty cycle, in non-resonant or resonant mode. All of these terms are well known in the industry, therefore no description of their operation mode should be necessary.

[0019] Controlling windings 24 and 25 are connected together via line 103. Secondary 26 is connected via lines 106 and 107 to AC Forming Block 60, more fully described below. The resulting AC output voltage is applied via lines 108 and 107 to load 70. [0020] When no DC current flows through controlling windings 24 and 25 via lines 104 and 105, most of the magnetic AC flux generated by the primary 23 current by-passes the section of the main magnetic circuit where the secondary 26 is located, by being diverted via the magnetic shunt core 22.

[0021] The magnetic circuit of the diverted AC magnetic flux is closed as the AC magnetic flux returns to the section of the main magnetic circuit where the primary is located. In this case, a small part of the magnetic flux, generated by the primary 23 current, flows through the section of the main magnetic circuit where the secondary 26 is located. This will cause a relatively low output DC voltage applied via lines 108 and 107 to a given load 70. As the DC current through controlling windings 24 and 25 increases, magnetic shunt core 22 approaches its saturation point, thereby decreasing the effectiveness of the magnetic shunt. In this case, less of the magnetic flux generated by the primary 23 is diverted from the secondary 26, and the output voltage applied to a given load 70 via lines 108 and 107 increases.

[0022] When the magnetic shunt core 22 reaches full saturation, no magnetic flux is diverted from the secondary 26, and the DC output voltage measured on lines 108 and 107 reaches its maximum value. The output voltage is applied to error amplifier 40 via line 110 for comparison with the reference signal applied to the error amplifier 40 by variable AC , reference 30, through line 109.

[0023] The variable AC reference scales-down the 50 or 60 Hz AC voltage source 100 via line 112 to obtain the desired amplitude of the reference AC signal, which is applied to error amplifier 40 through line 109. Error amplifier 40 controls DC controllable current source 50 via line 111 to determine the proper amount of current to be injected via lines 104 and 105 into the controlling windings 24 and 25, respectively, to determine the amount of saturation of magnetic shunt core 22.

[0024] AC forming block 60 re-converts the train of high frequency pulses, amplitude modulated by the waveform of the 50 or 60 Hz AC voltage source 100, and obtained at the secondary 26, into a variably controlled AC voltage measured on lines 108 and 107, and applied to load 70. This AC voltage measured on lines 108 and 107 has the same frequency, waveform and phase as compared to the AC voltage source 100. The phase of the 50 or 60 Hz AC voltage source 100 is detected via line 113 by AC forming block 60 for determining the proper phase of the AC voltage on lines 108 and 107, as more fully described below.

[0025] Fig. 2 shows one embodiment of the variable energy transfer transformer. As shown, it includes primary 23 connected by lines 101 and 102, secondary 26 connected by lines 106 and 107, controlling windings 24 and 25, connected in series via line 103, and connected via lines 104 and 105, main magnetic circuit core 21 and saturable magnetic shunt core 22. As shown, main magnetic circuit core 21 may include two U-type ferrite cores, while the saturable magnetic shunt core may include two I-type ferrite cores, mounted as shown. While ferrite material has the advantage of a low saturation point under relatively low DC bias current, other high frequency magnetic materials, such as molypermaloy, iron powder, etc. may be used.

[0026] Fig. 3 shows an alternative embodiment 20' of the core system of the variable energy transfer transformer. Saturable magnetic shunt core 22 includes two sets of laminated "I-cores" 22a and 22b. This configuration may be used where the effect of the insulation coating of each lamination is relatively thin, and the effect of the saturable magnetic shunt may only provide a lower secondary voltage reduction.

[0027] Fig. 4 presents an embodiment of the circuit structure of the AC forming block 60, operating in half-wave rectification mode. Secondary 26 applies a train of high frequency pulses via line 106 to the positive rectification circuit including diodes 61 and 64, and to the negative rectification circuit including diodes 62 and 63. On lines 601 and 602, respectively, are trains of positive and negative high frequency pulses which are amplitude modulated by the waveform of the 50 or 60 Hz AC voltage source 100, with an amplitude determined by the amount of saturation of the magnetic shunt core 22.

[0028] AC synchronizer circuit 600 turns on transistors (power MOSFETS with integral diodes in this example) 65 and 66 via lines 604 and 603 for conducting during the entire duration of their respective positive or negative half cycle of the 50 or 60 Hz AC voltage source 100. Inductor 67 filters out the high frequency pulses applied via line 605, along with capacitor 68, while diodes 63 and 64 discharge energy stored in the inductor 67 during the OFF cycle, or during the time period when no pulsed current is applied by the rectification circuits via either transistor 65 or 66.

[0029] The filtered AC voltage of the same waveform, frequency and phase as the 50 or 60 Hz AC voltage source 100, but of an amplitude determined by the amount of saturation of the magnetic shunt core 22, is measured on line 108.

[0030] Fig. 5 presents another embodiment of the circuit structure 60' of the AC forming block which uses half-wave rectification using the integral diodes of MOSFETS 61, 62, 63 and 64. Secondary 26 applies a train of high frequency pulses via line 106 to the half- wave rectification circuit including transistors 61, 62, 63 and 64. In this case, AC synchronizer 600 will turn on transistors 61 and 63 during the positive AC half cycle of the 50 or 60 Hz AC voltage source 100 via lines 601 and 603, transistors 62 and 64 via lines 602 and 604, respectively, during the negative AC half cycle of the 50 or 60 Hz AC voltage source 100.

[0031] For the positive half cycle of the 50 or 60 Hz AC voltage source 100, the high frequency pulsed positive current flows via transistor 61 and forward biased integral diode of transistor 62, while the energy stored in the filter inductor 67 is discharged via transistor 63 and the forward biased integral diode of transistor 64. For the negative half cycle of the 50 or 60 Hz AC voltage source 100, the high frequency pulsed negative current flows via transistor 62 and forward biased integral diode of transistor 61, while the energy stored in the filter inductor 67 is discharged via transistor 64 and the forward biased integral diode of transistor 63.

[0032] Line 605 supplies the train of high frequency positive or negative pulses to filter inductor 67 and filter capacitor 68 for obtaining, on line 108, an AC voltage of the same waveform, frequency and phase as the 50 or 60 Hz AC voltage source 100, but of an amplitude determined by the amount of saturation of the magnetic shunt core 22, as measured on line 108.

[0033] Fig. 6 depicts an alternative embodiment 60' ' of the AC forming block which uses a full-wave rectification operating mode of the circuit described in Fig. 4 above. In this case, the secondary 26 has a center tap 'C\ while diodes 61a, 61b, 62a and 62b comprise a standard rectifier bridge. Diodes 63 and 64 are not absolutely necessary, but they may be useful for avoiding any high voltage transients measured on lines 601 and 605, in the event of an accidental circuit interruption, as the energy stored in the filter inductor 67 cannot find another discharge path.

[0034] Fig. 7 further explains the mode of operation of the variable energy transfer transformer 20. It is known that primary 23 connected to an AC high frequency voltage source via lines 101 and 102 produces an AC high frequency magnetic flux in the main magnetic circuit core 21. Secondary 26 converts the AC high frequency magnetic flux generated by the primary 23 into an AC high frequency voltage. The controlling windings 24 and 25 produce a DC flux in each branch 22a and 22b of the saturable magnetic shunt core 22, shown as 121 and 122, respectively.

[0035] In the event that the DC magnetic fluxes 123 and 124 generated by the respective controlling winding 24 and 25 travel through the main magnetic circuit core 21, the main magnetic circuit core will not saturate, as fluxes are of opposite signs and cancel each other. AC voltages induced in each controlling winding by the AC magnetic flux generated by primary 23 are equal and of opposite signs, therefore these AC voltages will cancel each other, and no AC voltage will be measured on the input of the controlling windings.

INDUSTRIAL APPLICABILITY

[0036] This disclosure has broad industrial applicability to power control of various processes and devices by controlling the AC voltage applied to a large variety of loads.

[0037] It will be obvious that implementation of this disclosure may be carried out in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the disclosure, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims. The breadth and scope of the present disclosure is therefore limited only by the scope of the appended claims and their equivalents.

Claims

CLAIMSWhat is claimed as new and desired to be protected by Letters Patent of the United States is:

1. An AC voltage controller, comprising: a 50 or 60 Hz AC reference voltage connected to an input; a high frequency voltage generator coupled to the AC reference voltage, wherein the AC reference voltage modulates an output of the high frequency voltage generator; a primary winding arranged on a main magnetic core and coupled to the modulated output of the high frequency voltage generator; a secondary winding magnetically coupled to the primary winding through the main magnetic core; a saturablt magnetic shunt core arranged within the main magnetic core so as to align a plane containing a shunt core magnetic flux perpendicularly with respect to a plane containing a magnetic flux axis of the main magnetic core; primary and secondary control windings operatively coupled to the saturable magnetic shunt core and to a controlled DC current source; an AC forming circuit coupled between the secondary winding and an output load terminal, the AC forming circuit smoothing a train of amplitude modulated high frequency voltage pulses received from the secondary winding based upon a detected phase of the AC reference voltage, the AC forming circuit matching a frequency, a waveform, and a phase of an output voltage applied to the output load terminal with corresponding characteristics of the AC reference voltage; and an error amplifier connected between the AC reference voltage and the output voltage and generating a control signal applied to the controlled DC current source, wherein the control signal controls a DC current applied to the primary and secondary control windings, wherein the DC current controls an amplitude of the output voltage by at least partially saturating a magnetic flux in the saturable magnetic shunt core.

2. An AC voltage controller, comprising: an AC reference voltage connected to a high frequency pulsed voltage generator, wherein the AC reference voltage modulates an output of the high frequency pulsed voltage generator; a transformer arranged to magnetically couple the modulated output of the high frequency voltage generator from a primary winding to a signal conditioning circuit connected between a secondary winding and an output terminal of the controller; saturable magnetic shunt means operatively arranged within the transformer for controUably diverting at least a portion of a main magnetic flux of the transformer from a main magnetic core to a shunt magnetic core in response to a DC control current provided by a controlled DC current source connected to the saturable magnetic shunt means, wherein the control DC control current establishes a magnetic flux in the shunt magnetic core which controls an output voltage applied to the output terminal.

3. The AC voltage controller of claim 2, wherein the signal conditioning circuit comprises means for smoothing a train of amplitude modulated high frequency voltage pulses received from the secondary winding and means for matching a frequency, a waveform, and a phase of the output voltage with corresponding characteristics of the AC reference voltage.

4. The AC voltage controller of claim 2, further comprising an error amplifier connected between the AC reference voltage and the output voltage, wherein the error amplifier generates a control signal applied to the controlled DC current source.

5. The AC voltage controller of claim 4, wherein the control signal controls a DC current applied to primary and secondary control windings of the saturable magnetic shunt means.

6. The AC voltage controller of claim 2, wherein the DC control current controls an amplitude of the output voltage by at least partially saturating a magnetic flux in the saturable magnetic shunt core.

. A method of controlling an AC voltage, the method comprising: modulating a high frequency pulsed voltage source with a 50 or 60 Hz AC reference voltage; coupling the modulated high frequency pulsed voltage to a main magnetic path; providing a saturable magnetic flux shunt path arranged essentially perpendicular to the main magnetic path; filtering the coupled modulated high frequency pulsed voltage received through the main magnetic path to essentially remove high frequency components and to provide an output voltage, wherein said filtering includes matching a phase, waveform, and frequency of the output voltage with corresponding characteristics of the AC reference voltage; and controlling an amplitude of the output voltage by controlling a magnetic flux saturation level in the saturable magnetic flux shunt path.

8. The method of claim 7, wherein said controlling a magnetic flux saturation level in the saturable magnetic flux shunt path is accomplished by applying a DC control current to a control winding interfacing with the saturable magnetic flux shunt path.