CZ306211B6 - Transformer unit with controlled change of output voltage magnitude - Google Patents

Abstract

In particular, the output voltage controlled voltage transformer unit, intended in particular for supplying light signaling devices, comprises a transformer with a single secondary winding and multiple primary windings with taps, a microprocessor, a measuring circuit and a set of switching elements. The individual taps (2.apst.) Of the primary winding (2) of the transformer (1) are connected to the electronic switching elements (3) whose control circuits are connected to the outputs of the microprocessor (4) while the control inputs (4) are supplied a signal of the transformer unit output voltage change programmer (5) and, on the other hand, an output signal of the transformer unit input voltage amplitude detection voltage measurement circuit (6). The amplitude input voltage measurement circuit of the transformer unit is a dual differential measuring circuit consisting of an instrument amplifier and an analog-to-digital converter.

Description

Transformer unit with controlled change of output voltage

Field of technology

The invention relates to a transformer unit with a controlled change in the magnitude of the output voltage, intended in particular for supplying light signaling devices - as part of a light signaling device controller for controlling traffic lights of these devices with the possibility of varying their luminosity (dimming) depending on their supply voltage.

Prior art

The AC output voltage of the transformer can be varied by switching the winding taps on either the primary or secondary side.

Switching taps on the secondary side brings, especially at higher outputs, considerable complications associated with large current surges when connecting to another tap. Elimination of these problems brings high technical demands and necessarily associated increased costs.

These problems do not occur when switching taps on the primary side - we work with significantly lower currents. On the other hand, there is a short-term disconnection of the transformer from the mains and, as a result, a loss of saturation of the transformer core.

Existing solutions related to transformer control (in order to change the output voltage or current flowing through the transformer's secondary winding) are specifically focused on specific areas of application.

E.g. U.S. Pat. No. 5,726,561 solves a specific task, the so-called automatic voltage regulation (AVR) of a supply network. The exact task is to provide one fixed constant voltage at the output from any input changing voltage. Thus, its purpose differs from the application of the power supply of the light signaling devices of the present design, where two switchable different voltages on the secondary side are primarily required. According to the described function, in the solution described here, the individual work steps are performed in the 50 msec mode, which is a longer time than required by the input for the power supply of the light signaling devices.

U.S. Pat. No. 6,351,105 is directed to controlling electric heating by switching taps on the secondary side of a transformer, the transformer used having only one primary coil. Therefore, switching on the secondary side is used here and the switching time is not solved.

European patent 0 637 122 specifically addresses the control of an autotransformer. The task is to stabilize the supply voltage for appliances, while the input is the fluctuating voltage of the supply (distribution) network.

International patent application PCT WO 2006/045 948 addresses the switching of taps of the primary winding of a transformer. However, the solution is for powering industrial electric furnaces, where the output voltage of the transformer is very small (10V) and the required current is very high. There is no short-term power failure on the secondary side, but the need to control the switching of taps so that the supply network is not loaded with harmonic frequencies. The method of selecting the type of tap-changers and the method of controlling the tap-changers is specific for this purpose.

U.S. Pat. No. 5,289,110, in turn, addresses the power supply of airport lighting, which is equipped with light bulbs, so as to guarantee a constant current through the flowing light bulb. To do this, it uses a transformer with taps, but regulates it so that the goal is not to set the specified output voltage of the transformer, but to maintain the prescribed constant current flowing through the secondary circuit. Patented

- 1 CZ 306211 B6 the solution also allows the selection of the current at the output, depending on the current flowing through the input supply circuit, the change of which is to regulate the output current in a certain way.

The solution according to the international patent application PCT WO 97/05356 uses a transformer with a primary winding with taps and with one secondary winding. In terms of application, this solution is focused on energy and distribution networks, where the goal is to replace the original mechanical regulation of the distribution network voltage with a mechanical tap changer. The main focus is therefore the regulation of voltage in the network within the specified limits, other possible uses mentioned in the application relate to the reduction of harmonic voltages and currents in the network and possible applications of phase and pulse-width load control are mentioned.

The British patent 2,220,088 specifically addresses the power supply of HID lamps (high-brightness discharge lamps). The task is to ensure a constant supply of the lamp during voltage changes in the supply network. For this purpose, a modified choke is used, which has taps on its single winding.

Japanese Patent Application 5,913,555 addresses the optimization of the input power to the power supply circuit on the secondary side of the transformer. Because said supply circuit operates efficiently only within a specified range, and the transformer that supplies it is connected to a fluctuating supply network, it is not initially guaranteed that in the event of large voltage fluctuations in the supply network, the secondary winding of the transformer supplying said circuit to the required extent. For this purpose, the solution introduces feedback, where the voltage on the secondary side of the transformer is measured, and based on the deviations, the voltage supply is switched to specific taps on the primary side of the transformer.

German patent 3,331,614 addresses the switching of taps on the secondary side of a transformer, the switching time being much longer than that required for powering light signaling devices.

From the above overview, it is clear that the known patent documents also describe various ways to achieve the desired goal, but none of the above solutions describes a procedure which for the types of transformers used to power light signaling devices (i.e. toroidal transformer 500). VA to 2000 VA) achieves a guaranteed tap switching time, without affecting the transformer fuses (ie without surge currents).

The essence of the invention

The transformer unit with controlled change of the output voltage according to the invention, comprising in particular a transformer with one secondary winding and multiple primary windings with taps, a microprocessor, a measuring circuit and a system of switching elements, contributes to this elimination to a large extent.

The essence of the invention lies in the fact that the individual taps of the primary winding of the transformer are connected to electronic switching elements, the control circuits of which are connected to the outputs of the microprocessor. The control signal of the transformer unit output voltage change programmer 45 and the output signal of the transformer unit input voltage amplitude detection measuring circuit are fed to the inputs of the microprocessor. The measuring circuit for detecting the amplitude of the input voltage of the transformer unit is a double differential measuring circuit consisting of an instrument amplifier and an analog-to-digital converter.

The solution of the transformer unit according to the invention allows the above-mentioned specific control of taps on the primary side to change the output voltage in a very short time interval of up to 50 ms without disconnecting the transformer from the mains when replacing taps on the primary winding.

-2EN 306211 B6

Although some known solutions offer a fundamentally similar set of elements, ie by microprocessor control switching elements controlling transformer taps. However, the invention is based on a specific method of controlling these elements. If, for example, human forces were to manually switch the voltage on the given taps according to a given principle, the same result would be achieved. This principle is based on maintaining a DC balance between the half-periods of the supplied mains voltage, which is a requirement in the operation of the transformer. If a slight deviation in the timing of this procedure is made for a given input while performing the above switching procedure, the transformer reacts almost immediately with the surge current (DC balance is disturbed). Because it is not enough to simply switch the branches between each other (albeit "at the right time"), it was necessary to create the specific principle described here, ie the solution to this problem.

As mentioned, other known patents address in particular the arrangement of electronic components or address switching procedures but with completely different objectives from the present invention, where these objectives are different from the current needs of light signaling devices and where said procedures are clearly not applicable to address these needs. they do not lead to the completion of such a solution - which is based on the gradual, suitable for the transformer and accepted by the transformer, transfer of power between the taps and stabilization of the transformer operation to a new tap, without any surge current.

Explanation of the drawing

To further elucidate the essence of the invention, the attached drawing serves, where Fig. 1 is a block diagram of a transformer unit according to the invention in an exemplary embodiment intended for powering light signaling devices;

Fig. 2 - schematic representation of the time course of the switching cycle.

Example of an embodiment of the invention

The transformer unit with controlled change of the output voltage in an exemplary embodiment intended to supply light signaling devices (see Fig. 1) comprises a transformer 1 with one secondary winding and multiple primary windings 2 with taps 2 ', microprocessor 4, measuring circuit 6 and a set of switching elements 3.

The supply transformer 1 has one secondary winding, dimensioned for the appropriate current consumption, with a no-load voltage corresponding to the highest operating voltage of the connected device (lights of the light signaling device). In the initial state, ie when they are not muted, this voltage is on the secondary winding.

The primary winding 2 is ready for operation on the mains supply voltage, which will be available at the destination. The individual taps 2 'of the primary winding 2 are connected to separate electronic (non-contact) switching elements 3 (triac), the control circuits of which are connected to the outputs of the microprocessor 4. the output signal of the transformer unit input voltage amplitude detection measuring circuit 6.

The measuring circuit 6 for detecting the amplitude of the input voltage of the transformer unit is a double differential measuring circuit, consisting of an instrument amplifier and an analog-to-digital converter. By sampling (analog-to-digital conversions) the obtained differential values of the voltage applied to the inputs of these instrument amplifiers are read. Appropriate connection of a specific voltage to specific inputs provides an accurate overview of the state of the power supply network, and thanks to resampling, also a sufficiently accurate time position for the current voltage level of the power supply network.

- 3 CZ 306211 B6

The connection is realized in such a way that certain inputs of both instrument amplifiers are connected to a common neutral conductor of the supply network and a certain input of one of the amplifiers is connected via a correctly dimensioned phase voltage resistor divider; the other input of the second amplifier is connected to the neutral conductor (thus three neutral points and one phase are connected). This connection of the amplifiers at its output, i.e. at the input of the analog-to-digital converter, provides an adjusted voltage proportional to the voltage on the phase and neutral conductor, any variations in component parameters being projected into both of these output voltages simultaneously and equally.

The mathematical operation on the digital side, ie by subtracting the samples from the phase voltage channel and the neutral sample sample, obtains the exact instantaneous value of the phase voltage, and also obtains information on whether this voltage is in the positive or negative half-wave. - whether the digital value of the phase voltage sample is less than the digital value of the sample for the neutral conductor and vice versa. If both samples are identical, it is the passage of the mains voltage to zero. This is detected in two ways - by an internal comparator, which can cause a program interruption in the event of a match, depending on the implementation of the operation of the analog-to-digital converter by direct comparison of digital samples. This solution allows delayed synchronization with the voltage state in the supply network, which is necessary for further action.

At the moment when it is necessary to make a voltage change on the secondary side, the device receives a dedicated command from the programmer 5 changes the output voltage of the transformer unit. The start of the switching cycle is synchronized with the nearest zero-level mains voltage pass. At that point, the time constants for the individual steps of the algorithm are determined.

For a period of one to two periods, the transformer is prepared for new operating conditions (powered by another tap), while the transformer does not remain without power supply (it is not disconnected from the mains) in any period of the mains voltage. After the second preparation period, only the new branch is permanently used.

The following characteristic points (cycle moments) are shown in the schematic representation of the time course of the switching cycle (see Fig. 2):

(a) the moment when the device receives the changeover command. This moment has no time relationship with the current amplitude of the mains voltage (ie it can come at any time).

b) Waiting for the nearest zero crossing due to total synchronization. The duration from time b) to g) is 45 milliseconds.

c) The moment when the control state of all taps of the transformer changes before the next pass of voltage through the maximum amplitude.

d) The moment when in the opposite half-wave the control of the triac of the new tap changes (there was no switching off and on again, this would occur only if one whole period was omitted; energy is still stored in the transformer, when it is on the winding a voltage of opposite polarity is induced to maintain the direction of the current, therefore it is switched to another branch from point c) to point d)).

e) Moment of zero current by inductive load.

f) Change in triac control at the location of the highest voltage amplitude.

g) Moment of full use of the new branch.

Note: the invention does not address the initial power-up of the power transformer, using an existing commercially available, external element.

Claims (1)

PATENT CLAIMS A transformer unit with a controlled change in the magnitude of the output voltage, in particular for supplying light signaling devices, comprising in particular a transformer with one secondary winding and multiple primary windings with taps, a microprocessor, a measuring circuit and a set of switching elements, characterized in that the individual taps ( 2 ') of the primary winding (2) of the transformer (1) are connected to electronic switching elements (3), whose control circuits are connected to the outputs of the microprocessor (4), while the control signal of the programmer (5) is fed to the inputs of the microprocessor (4). changes in the output voltage of the transformer unit and on the one hand the output signal of the transformer unit input voltage amplitude detection measuring circuit (6), said transformer unit input voltage amplitude detection measuring circuit (6) being a dual differential measuring circuit consisting of an instrument amplifier and an analog-to-digital converter.