Claims
- 1. An apparatus for regulating an AC line voltage, comprising:
- an input port for connection to a source of input AC voltage;
- an output port for delivering a regulated voltage to a load;
- transformer means for regulating the output voltage, comprising a buck/boost winding connected between the input and output port, a primary winding split into two oppositely wound portions each having a greater number of turns than the buck/boost winding, each primary winding portion being split into at least two winding parts and a common transformer core about which both windings are wound;
- switch means for controlling the connection of the primary winding in circuit with the buck/boost winding, including means for selectively connecting the primary winding in different configurations in the circuit the switch means comprising first switch means for controlling connection of the two parts of one of the primary winding portions in series in the circuit in a first, boost configuration, and second switch means for controlling connection of the two parts of the other winding portion in series in the circuit in a second, buck configuration;
- voltage sensing means for detecting the magnitude of the line voltage and for producing corresponding control signals when the line voltage varies outside predetermined limits; and
- switch controlling means responsive to the voltage sensing means control signals for closing said first switch means if the voltage is below the predetermined limits and closing said second switch means if the voltage is aboe the predetermined limits, the transformer means comprising a step up transformer in the first configuration and a step down transformer in the second configuration; and
- energy proportional current and voltage limiting means for limiting the current and voltage across the primary winding.
- 2. The apparatus as claimed in claim 1, wherein the energy proportional current and voltage limiting means comprises a multi-level conduction energy proportional clamping means connected across one winding part of each of the primary winding portions for limiting the voltage and power across the primary winding to below several predetermined values.
- 3. The apparatus as claimed in claim 2, wherein the energy proportional clamping means comprises a network, the network comprising a varistor in series with a resistor, and a thyristor connected in parallel with the varistor and resistor which is triggered from the common varistor and resistor node.
- 4. The apparatus as claimed in claim 1, including a circuit common line having an input port for connection to a neutral power input;
- the first and second switch means comprising first and second pairs of switches, and
- the switch controlling means comprising means for closing the first pair of switches in response to a voltage below the predetermined limits, means for closing the second pair of switches in response to a voltage above the predetermined limits, and means for closing one switch of each pair to terminate one part of each of the winding portions to each other in response to voltages within the predetermined limits.
- 5. The apparatus as claimed in claim 4, wherein the voltage sensing means includes error sensing means for providing an up or down condition signal when the line voltage varies by a given magnitude up or down from a set voltage to be regulated,
- zero crossing detector means for producing output signals at half cycle zero crossings of the line voltage, and
- gate circuit means responsive to both the error sensing means and zero crossing detector means for providing a corresponding up or down switch signal comprising said control signals to said switch controlling means at each zero crossing when the line voltage has varied up or down from the given magnitude.
- 6. The apparatus as claimed in claim 5, wherein the switch controlling means comprises counter means having successive low, mid and high stages, the counter means being responsive to up switch signals to advance from one stage to the next between the low and high stage and being responsive to down switch signals to step back between stages in the opposite direction,
- each of the stages having control outputs for controlling actuation of the switches, the low stage having control output means for controlling actuation of the first pair of switches, the high stage having control output means for controlling actuation of the second pair of switches, and the mid stage having control output means for controlling actuation of one switch of each pair.
- 7. The apparatus as claimed in claim 4, including a line to which all four switches are terminated.
- 8. The apparatus as claimed in claim 1, wherein one end of each of the winding portions is connected to the same circuit point relative to the buck/boost winding, the circuit including a common line for connection to a neutral power input, the opposite end of each winding portion being connected to the common line.
- 9. The apparatus as claimed in claim 1, wherein the energy proportional current and voltage limiting means comprises a multi-level conduction, energy proportional clamping device connected across one part of each of the primary winding portions.
- 10. The apparatus as claimed in claim 1, wherein the switch means is connected to the buck boost winding via fuse means for removing operating power from the circuit in response to predetermined circuit malfunctions.
- 11. The apparatus as claimed in claim 1, wherein the buck/boost winding has an intermediate tap point, and three connector points connected to the input port, the switch means, and the output port, respectively, one of the connector points being connected to the tap point with the other two connector points connected to respective opposite ends of the buck/boost winding.
- 12. The apparatus as claimed in claim 1, wherein a further winding wound around the common transformer core is connected between the buck/boost winding and switch means, the further winding having a first portion wound in the same direction as the buck boost winding and a second portion wound in the opposite direction to the first portion.
- 13. The apparatus as claimed in claim 12, wherein the second portion of the further winding has a greater number of turns to the first portion.
- 14. The apparatus as claimed in claim 12, wherein the second portion of the further winding has less turns than the first portion.
- 15. The apparatus as claimed in claim 12, wherein the first and second portions of the further winding have an equal number of turns.
- 16. An apparatus for regulating an AC voltage comprising:
- an input port for connection to a source of input AC voltage;
- an output port for delivering a regulated voltage to a load;
- a neutral line;
- transformer means connected between the input and output port for controlling the output voltage level, comprising a buck/boost winding, a primary winding having more turns than the buck/boost winding, and a common transformer core about which both of the windings are wound, the buck/boost winding being connected between the input and output port;
- switch means for controlling the connection of the primary winding in circuit with the buck/boost winding, comprising a first pair of switches for selectively connecting opposite ends of the primary winding to the buck/boost winding, and a second pair of switches for selectively connecting opposite ends of the primary winding to the neutral line;
- voltage sensing means for sensing the voltage level at a chosen point in the apparatus;
- switch controlling means responsive to the voltage sensing means for controlling said switches, comprising means for closing one of said first pair of switches and the opposite one of said second pair of switches in response to voltages below a first predetermined level so that said transformer means acts as a step up transformer, means for closing the other one of said first pair of switches and the other one of said second pair of switches in response to voltages above a second predetermined level so that said transformer means acts as a step down transformer, and means for closing both of said second pair of switches in response to voltages intermediate said two predetermined levels, and a further winding connecting between the buck/boost winding and the first pair of switches, the further winding being wound on the common transformer core and having a first portion wound in the same direction as the buck/boost winding and a second portion wound in the opposite direction to the first portion.
- 17. The apparatus as claimed in claim 16, including energy proportional clamping means connected in parallel across the primary winding for limiting the voltage across the primary winding to an energy dependent maximum value.
- 18. The apparatus as claimed in claim 17, wherein said clamping means includes a transient surge suppressor.
- 19. The apparatus as claimed in claim 18, wherein said clamping means comprises a triac having common and high terminals connected to opposite ends of the primary winding, and a transient suppressor, the triac having a gate and the transient suppressor being connected between the gate and high terminal of the triac.
- 20. The apparatus as claimed in claim 16, including impedance means connected between the input line and the switch means for limiting the maximum possible current which can flow through the switches to a predetermined safe value.
- 21. An apparatus for regulating an AC line voltage, comprising:
- an input port for connection to a source of input AC voltage;
- an output port for delivering a regulated voltage to a load;
- a buck/boost winding connected between the input and output port;
- a circuit common line with a neutral input port for connection to a neutral power input;
- a primary winding assembly for selective connection in a plurality of different possible configurations to a connecting point between the input and output port, the configurations including a boost configuration in which the assembly is connected in circuit with the buck/boost winding to provide a step up transformer, a buck configuration in which the assembly is connected to provide a step down transformer, and a straight through configuration in which the primary winding assembly is terminated itself;
- the primary winding assembly comprising a first, boost portion and a second, oppositely wound buck portion, each portion being split into at least two parts, one end of each of the winding portions being connected to said buck/boost winding connecting point, and switch means comprising a first pair of switches connecting the two parts of the boost portion, a second pair of switches connecting the two parts of the buck portion, and a common line connecting all the switches together;
- voltage sensing means for detecting the magnitude of the input line voltage and for producing corresponding control signals when the voltage varies outside predetermined limits; and
- switch controlling means responsive to the voltage sensing means for controlling the switch means to connect the primary winding means in the boost configuration if the voltage is below the predetermined limits, to connect the primary winding means in the buck configuration if the voltage is above the predetermined limits, and to connect the primary winding means in the straight through configuration if the voltage is within the predetermined limits, the switch controlling means comprising means for closing the first pair of switches in response to voltages below the predetermined limits, closing the second pair of switches in response to voltages above the predetermined limits, and closing one switch of each pair to terminate one part of each of the winding portions to each other in response to voltages within the predetermined limits.
BACKGROUND OF THE INVENTION
This is a continuation-in-part of Application Ser. No. 805,829 of the same Applicant, filed Dec. 6, 1985 and entitled "AC LINE VOLTAGE REGULATOR," now abandoned.
The present invention relates generally to the control of AC line voltage, and more specifically to AC voltage regulation apparatus of the transformer switching type.
Ever since AC power has been used to operate critical electronic equipment there has been a need to regulate the power in order to protect the equipment against voltage sags and destructive surges. Electronic equipment has become more sophisticated over the years, and now includes computers with high speed logic circuits which are extremely sensitive to variations in the power supply level. Thus there are now many types of apparatus available for AC power regulation.
One of the solid state devices which has been available for many years and which is recognized as one of the highest performance power protection devices is known in the art as the Multi Primary Switching (MPS) Line Conditioner. Such a device is described in my U.S. Pat. No. 3,970,918.
The MPS technique utilizes several primary windings on a common magnetic transformer core, as well as a very low impedance buck/boost winding on the same core which is conncted between the input and output of the apparatus so that a regulated voltage appears at the output. Each of the primary windings has a designed-in turns ratio and winding direction so that buck, or boost, or straight through operating modes can be achieved by selectively terminating a corresponding primary winding. Buck or boost modes are achieved by terminating the corresponding primary winding to the AC power via switching devices. Straight-through operation is achieved by terminating one of the primary windings to itself, i.e. by using the mutual inductance of transformer windings to reflect a short circuit in the buck/boost winding. Input or output voltage detection techniques which are well known in the art are used to activate the appropriate switches.
The MPS line conditioner can achieve outstanding performance, and has inherent current protection under momentary latch up conditions which can occur when two switches are conducting simultaneously. This is because the total resistance in the primary winding is reflected into the buck/boost winding by the impedance ratio of the windings. The impedance ratio is the square of the turns ratio, and this would be 100:1 if the turns ratio is 10:1. Thus the winding resistance has only an insignificant effect on the output regulation of the device while it provides substantial protection for the switches or switching devices. This means that the MPS line regulator has inherent protective features in other types of regulators during tap changing or ranging steps.
In spite of the inherent current protection in this type of regulator, there are two types of failure which can occur as the result of the transformer turns and impedance ratios. The first type of failure can occur at the instant power is turned on while electric equipment is already connected at the output. The second type of failure can occur while power is already on, at the instant an extremely large load at the output is turned on.
The first type of failure results from the fact that in solid state devices all circuits, including switches, are initially inoperative for a brief moment when power is first turned on, or restored following a power cut. If the power is turned on at a peak in the input power sine wave, the peak line voltage is impressed on the buck/boost winding. If the turns ratio is 10:1, ten times this voltage will appear across the three open switches, which may easily cause destruction of the semiconductor switches.
The second type of failure occurs when the regulator is operating in any one of its normal modes at the time when a heavy equipment load is being connected to its output. It can happen that the initial surge current causes a current flow through the buck/boost winding which opposes the current flowing through the particular connected primary winding at that instant. This opposing current can be so large that the switching device is destroyed.
According to the present invention an AC voltage regulating apparatus is provided having an input port for connection to a voltage source and an output port for connection to a load. The apparatus comprises a transformer assembly including a buck/boost winding and a primary winding wound on a common transformer core, with the buck/boost winding connected between the input and output port. A switch assembly is provided for controlling the connection of the primary winding in circuit with the buck/boost winding in accordance with the magnitude of the line voltage. The switch assembly connects the primary winding in a first direction when the voltage is above a first predetermined level so that the transformer assembly comprises a step down transformer for reducing the voltage, and connects the primary winding in the opposite direction in response to voltages below a second predetermined level so that the transformer assembly comprises a step up transformer for boosting or increasing the voltage. The switch assembly is preferably arranged to terminate the primary winding to itself when the voltage is within predetermined limits so that the transformer assembly operates in a straight-through mode. An energy proportional current and voltage limiting circuit is provided for limiting the voltage and power across the primary winding.
Thus a primary switching transformer is provided which requires only a single primary winding, significantly reducing the size, weight and materials cost of the apparatus while being of equivalent efficiency to larger scale voltage regulators.
An energy proportional clamping circuit is preferably connected in parallel across the primary winding for limiting the maximum possible voltage which may develop across the winding when all the switches of the switching assembly are open.
Instead of connecting a single primary winding in opposite directions, the primary winding may comprise two oppositely wound portions, with the switch assembly arranged to connect the opposite portions selectively in the circuit.
According to one embodiment of the invention, the switching assembly comprises a first pair of switches for selectively connecting opposite ends of the primary winding to a common tap point on the primary winding, and a second pair of switches for selectively connecting opposite ends of the primary winding to a common line, which may be the circuit neutral line. A suitable control assembly is provided to control the closing of respective switches, and the control assembly is responsive to the line voltage level, measured at the circuit input or output, to control the mode of operation of the apparatus. The control assembly is arranged to close one switch of the first pair and the opposite end switch of the second pair connected to the opposite end of the primary winding in response to voltages above the first predetermined level, with the primary winding direction being such that the apparatus operates in the buck, or voltage reducing mode, when these switches are closed. The control assembly is arranged to closed the other switch of each pair in response to voltages below the second predetermined level so that the apparatus operates in the boost mode, and to close both switches of the second pair while the voltage is between these values to terminate the primary winding to itself so that the apparatus operates in a straight-through mode, i.e. input voltage is equal to output voltage.
The common tap point may be an intermediate point on the buck/boost winding, or either end of the winding, with the input and output ports being connected to the respective opposite ends of the winding in the first case and either to the intermediate point and unconnected end of the winding, respectively, or vice versa, in the second case. Alternatively, the switch assembly may be connected to the buck/boost winding via a further winding having a first portion wound in one direction and second portion with more turns than the first wound in the opposite direction. This avoids the necessity of providing a tap on the buck/boost winding.
According to another, preferred embodiment of the invention, the primary winding comprises two oppositely wound portions, and the switch assembly comprises a series of switches for selectively connecting one portion of the primary winding between the buck/boost winding and a circuit common line, or connecting the oppositely would portion between the buck/boost winding and the common line, which may be the circuit neutral line. In this arrangement, the energy proportional clamping circuit is connected between the two primary winding portions. The switches are preferably connected in pairs, one pair controlling the series connection of two parts of the first winding portion, and the other pair controlling the series connection of two parts of the oppositely wound portion. The switches are terminated to the same line, and in the straight through mode one switch of each pair is closed to terminate the primary winding to itself.
US Referenced Citations (8)
Foreign Referenced Citations (2)
| Number |
Date |
Country |
| 257838 |
Mar 1928 |
ITX |
| 534742 |
Mar 1977 |
SUX |
Continuation in Parts (1)
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Number |
Date |
Country |
| Parent |
805829 |
Dec 1985 |
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Patent Grant
4716357
