Patent Description:
Mains electricity delivered to homes and offices is typically higher then specified. For example, in Australia, the mains electricity is specified as having a voltage of 220Vac, but typically the mains electricity is delivered at a voltage of 255Vac. The higher voltage leads to a higher current at an appliance (i.e., a load), which ultimately results in a higher power being dissipated by the appliance.

There are two major impacts resulting from the higher voltage. First, the higher voltage and current put electrical stress on appliances and reduces the lifespan of the appliances. Second, the increased power equates to an increase in power consumption and costs.

Conventional voltage reduction methods involve significant modification to the input voltage and often lead to significant energy losses. Therefore, such conventional methods are not suitable in reducing the voltage of mains electricity.

Therefore, there is a need to provide a voltage reduction technique that is highly efficiency (i.e., minimal loss of energy during regulation).

A voltage regulator for the mains voltage comprising a transformer with a single primary winding and a single secondary winding and four switches configured to modify the output voltage is proposed in <CIT>.

Disclosed are arrangements which seek to provide a voltage reduction with high efficiency (i.e., minimal energy loss).

An aspect of the present disclosure provides a voltage regulation circuit that is capable of reducing the voltage of mains electricity by a certain voltage (e.g., 30Vac) using a non-isolated series transformer.

The invention is defined by the features of claim <NUM>. The dependent claims recite advantageous embodiments of the invention.

At least one embodiment of the present invention will now be described with reference to the drawings, in which:.

Where reference is made in any one or more of the accompanying drawings to steps and/or features, which have the same reference numerals, those steps and/or features have for the purposes of this description the same function(s) or operation(s), unless the contrary intention appears.

<FIG> shows a voltage regulation transformer circuit <NUM> having an input filter <NUM>, an output filter <NUM>, a series transformer <NUM>, a first switch <NUM>, and a second switch <NUM>. An input voltage of the voltage regulation transformer circuit <NUM> is applied to an input node <NUM> and a neutral node <NUM>. An output voltage of the voltage regulation transformer circuit <NUM> is provided between an output node <NUM> and the neutral node <NUM>.

The series transformer <NUM> includes a primary winding <NUM>, a first secondary winding <NUM>, and a second secondary winding <NUM>. As indicated by the dots, the winding polarities of the primary winding <NUM> and the first secondary winding <NUM> are <NUM>° out-of-phase. Also indicated by the dots, the winding polarities of the primary winding <NUM> and the second secondary winding <NUM> are in-phase (i.e., a phase shift of <NUM>°).

The secondary voltage at the first secondary winding <NUM> (which is induced by the primary voltage of the primary winding <NUM>) depends on the ratio of the windings between the primary winding <NUM> and the first secondary winding <NUM>. The ratio between the primary winding <NUM> and the first secondary winding <NUM> can be adjusted by varying the number of turns in the first secondary winding <NUM>. The number of turns in the first secondary winding <NUM> can be varied using a tap (not illustrated).

Other components such as switch protection devices, diode bridges, and the like have been omitted for clarity purposes.

The input node <NUM> is connected to the filter <NUM>. The filter <NUM> is a low pass filter to remove high frequency components of the input voltage that might affect the voltage regulation transformer circuit <NUM>. The cutoff frequency of the low pass filter <NUM> can be set at a value to ensure that noise at the input node <NUM> has minimal effects to the circuit <NUM>. The input filter <NUM> has a switch capacitance to allow its characteristics to be changed as required during active regulation. In one arrangement, the input is the mains electricity. The filter <NUM> in turn is connected to a first end (marked by the dot) 132A of the primary winding <NUM>. A second end 132B of the primary winding <NUM> is connected to the output filter <NUM>, which in turn is connected to the output node <NUM>. The output filter <NUM> is a low pass filter to smooth the output voltage and remove unwanted high frequency components resulting from the voltage regulation transformer circuit <NUM>. The cutoff frequency of the low pass filter <NUM> can be set at above <NUM>/<NUM> to remove the effects of the control signals <NUM> and <NUM> (described hereinafter in relation to <FIG>). A first end (marked by the dot) 134A of the first secondary winding <NUM> is connected to the neutral node <NUM>. A second end 134B of the first secondary winding <NUM> is connected to the switch <NUM>. The switch <NUM> is in turn connected to the second end 132B of the primary winding <NUM>.

When the switch <NUM> is closed (i.e., connected), the second end 134B of the first secondary winding <NUM> is connected to the second end 132B of the primary winding <NUM>. The switch <NUM> must be open (i.e., disconnected) at this stage. If the switch <NUM> is closed at the same time as the switch <NUM> is closed, there is effectively a short circuit across the primary winding <NUM> and the first secondary winding <NUM>. In other words, when the switches <NUM> and <NUM> are closed at the same time, there is a short circuit across the input node <NUM> and the neutral node <NUM>.

<FIG> shows an equivalent circuit of the connection between the primary winding <NUM> and the first secondary winding <NUM> when the switch <NUM> is closed and the switch <NUM> is open. As seen in <FIG>, when the switch <NUM> is closed and the switch <NUM> is open, then the voltage at the second end 132B is the secondary voltage of the first secondary winding <NUM> and the output voltage at the output node <NUM> is the secondary voltage of the first secondary winding <NUM> that is filtered by the output filter <NUM>.

When the switch <NUM> is closed and the switch <NUM> is open, current flows in the primary winding <NUM> generating a first flux in the core of the transformer <NUM>. The first flux then induces current to flow in the first secondary winding <NUM>, which generates a second flux that is opposite to the first flux. As the first flux and the second flux are opposite, the net result in a reduction in the flux in the core of the transformer <NUM>, which means that the primary voltage across the primary winding <NUM> is reduced.

When the switch <NUM> is open (i.e., disconnected), the second end 134B of the first secondary winding <NUM> is disconnected from the second end 132B of the primary winding <NUM>. The switch <NUM> can be either closed or open at this stage. This configuration results in an open circuit for the first secondary winding <NUM>, which means the secondary voltage across the first secondary winding <NUM> is not generated.

<FIG> shows an equivalent circuit of the connection between the primary winding <NUM> and the first secondary winding <NUM> when the switches <NUM> and <NUM> are open. As seen in <FIG>, when the switch <NUM> is open, then the output voltage at the output node <NUM> is effectively the input voltage reduced by voltage drops across the input filter <NUM>, the primary winding <NUM>, and the output filter <NUM>. The situation where both <NUM> and <NUM> are open is not ideal and only happens during transition of the alternate closing of the switches <NUM> and <NUM>.

The connection between the primary winding <NUM> and the second secondary winding <NUM> is now described. A first end (marked by the dot) 136A of the second secondary winding <NUM> is connected to the neutral node <NUM>. A second end 136B of the second secondary winding <NUM> is connected to the switch <NUM>. The switch <NUM> is in turn connected to the neutral node <NUM>.

When the switch <NUM> is closed (i.e., connected) while the switch <NUM> is open, the second end 136B of the second secondary winding <NUM> is connected to the neutral node <NUM>. This configuration results in a short circuit in the second secondary winding <NUM>. The impedance in the short-circuited second secondary winding <NUM> is then reflected to the primary winding <NUM>. This results in the primary winding having a nominal impedance of zero due to the reflected impedance from the short-circuited second secondary winding <NUM>. The voltage at the second end <NUM> is effectively the input voltage, while the output voltage at the output node <NUM> is then effectively the input voltage at the input node <NUM> that is filtered by the output filter <NUM>. When the switch <NUM> is closed, the switch <NUM> must be open to prevent creating a short circuit across the primary winding <NUM> and the first secondary winding <NUM> as described hereinbefore.

<FIG> shows an equivalent circuit of the connection between the primary winding <NUM> and the second secondary winding <NUM> when the switch <NUM> is closed and the switch <NUM> is open. As seen in <FIG>, the output voltage is effectively the input voltage at the input node <NUM>.

Table <NUM> below shows the relationships between the input voltage applied at the input node <NUM>, the output voltage at the output node <NUM>, and the state of the switches <NUM> and <NUM>:.

In one example, an input voltage of 250Vac is applied at the input node <NUM> and the neutral node <NUM>. The ratio of the windings between the primary winding <NUM> and the first secondary winding <NUM> is calculated to deliver the required voltage drop, and then the out-of-phase secondary voltage of the first secondary winding <NUM> induced by the primary winding <NUM> is a ratio of the turns, of the primary voltage. As an example, if the ratio of the windings between the primary winding <NUM> and the first secondary winding <NUM> is <NUM> to <NUM>, then the out-of-phase secondary voltage of the first secondary winding <NUM> induced by the primary winding <NUM> is <NUM>/<NUM>th of the primary voltage. Therefore, the out-of-phase secondary voltage of the first secondary winding <NUM> in this example is 225Vac.

When the switch <NUM> is closed and the switch <NUM> is open, the voltage at the second end 132B is 225Vac (i.e., the secondary voltage of the first secondary winding <NUM>. When the switch <NUM> is open and the switch <NUM> is closed, the voltage at the second end 132B is 250Vac (assuming the voltage drops across the filter <NUM> and the primary winding <NUM> are negligible). When the switch <NUM> is open and the switch <NUM> is open, the voltage at the second end 132B is 250Vac (assuming the voltage drops across the filter <NUM> and the primary winding <NUM> are negligible). As described hereinafter, the switches <NUM> and <NUM> are alternately closed, thereby changing the voltage at the second end 132B. In this example, the voltage at the second end 132B alternates between 225Vac (when the switch <NUM> is closed and the switch <NUM> is open) and 250Vac (when the switch <NUM> is open and the switch <NUM> is closed). The output voltage at the node <NUM> is therefore the average voltage at the second end <NUM>, where the average voltage depends on the duration of the respective voltages of 225Vac and 250Vac at the second end 132B and the output filter <NUM>.

As described hereinbefore, the switches <NUM> and <NUM> are never closed at the same time.

<FIG> shows the output voltage waveform at the second end 132B when the switches <NUM> and <NUM> are being switched in an closed/open sequence (which are associated with the control signals shown in <FIG> shows an enlarged view of the voltage waveform shown in <FIG>. The voltage at the level indicated by the reference numeral <NUM> is effectively the input voltage at the input node <NUM>. When the switch <NUM> is closed, the voltage drops to the level indicated by the reference numeral <NUM>.

<FIG> shows two control signals <NUM> and <NUM> where a first control signal <NUM> controls the switching of the switch <NUM> and a second control signal <NUM> controls the switching of the switch <NUM>. When the first control signal <NUM> is high, then the switch <NUM> is closed. The switch <NUM> is open when the first control signal <NUM> is low. When the second control signal <NUM> is high, then the switch <NUM> is closed. The switch <NUM> is open when the second control signal <NUM> is low.

The first and second control signals <NUM> and <NUM> are pulse width modulated signals. A pulse width <NUM> of the first control signal <NUM> corresponds to the duration that the switch <NUM> is closed. Therefore, the voltage drop at the second end 132B is regulated by the pulse width <NUM> of the first control signal <NUM>.

The closing of the switch <NUM> by the first control signal <NUM> may cause inrush currents and voltage spikes. To minimise such inrush currents and voltage spikes, the first control signal <NUM> is pulsed at the beginning of the pulse width <NUM>, as shown by the pulses <NUM>, before the first control signal <NUM> is held at the high level.

The pulses <NUM> of the first control signal <NUM> are load adaptive, as the number of pulses <NUM>, the width of each pulse <NUM>, and the frequency of the pulses <NUM> are varied dependent on the load of the voltage regulation circuit <NUM>. The number of pulses <NUM>, the width of each pulse <NUM>, and the frequency of the pulses <NUM> also determine the power efficiency of the voltage regulation circuit <NUM>. The number of pulses <NUM> is increased when the output voltage of the circuit <NUM> is being used by higher loads.

The power factor of the voltage regulation circuit <NUM> can also be varied by varying the pulse width <NUM>. The pulse width <NUM> effectively alters the output voltage waveform.

The switching of the control signals <NUM> and <NUM> is controlled by a processor or a Complex Programmable Logic Device (CPLD) (not shown). Changes in the duty cycle of the control signals <NUM> and <NUM> are used to control the output voltage.

The control signals <NUM> and <NUM> typically operate at <NUM>, which would be removed by the low pass filters <NUM> and <NUM>. The control signals <NUM> and <NUM>, however, can operate at different switching frequencies.

In one arrangement, the voltage regulation circuit <NUM> and the associated components are limited to a maximum current. In the event that the current exceeds the maximum current, then the voltage regulation circuit <NUM> is shut down and a bypass relay (not shown) is activated to bypass the voltage regulation circuit <NUM>. This ensures the voltage regulation transformer circuit <NUM> is protected and not over stressed.

As described hereinbefore, and in particular in Table <NUM>, the switches <NUM> and <NUM> must not be closed at the same time. Therefore, when transitioning from the closing-to-opening of the switch <NUM> to the opening-to-closing of the switch <NUM>, the second control signal <NUM> goes to the low level (i.e., opening the switch <NUM>) in advance of the first control signal <NUM> going high (i.e., closing the switch <NUM>). A pre-determined period <NUM>, where both control signals <NUM> and <NUM> are held at the low position, is maintained between the second control signal <NUM> going low and the first control signal <NUM> going high to ensure that both switches <NUM> and <NUM> never close at the same time. Further, the transition period of when both of the control signals <NUM> and <NUM> are low provide a relaxation time to allow the switching transients to decay.

Similarly, when transitioning between the closing-to-opening of the switch <NUM> to the opening-to-closing of the switch <NUM>, the first control signal <NUM> goes to the low level (i.e., opening the switch <NUM>) in advance of the second control signal <NUM> going high (i.e., closing the switch <NUM>). A pre-determined period <NUM>, where both control signals <NUM> and <NUM> are held at the low position, is maintained between the first control signal <NUM> going low and the second control signal <NUM> going high to ensure that both switches <NUM> and <NUM> never close at the same time.

As described hereinbefore, the output voltage <NUM> is the average of the output voltage waveform at the second end 132B as determined by the output filter <NUM> and the duration of the respective voltages <NUM> and <NUM> as determined by the control signals <NUM> and <NUM>.

The arrangements described are applicable to voltage regulation.

The foregoing describes only some embodiments of the present invention, and modifications and/or changes can be made thereto within the scope of the appended claims.

Claim 1:
A voltage regulation circuit (<NUM>) comprising:
a transformer (<NUM>) having a primary winding (<NUM>) having a first end (132A) and a second end (132B), and a first secondary winding (<NUM>) having a first end (134A) and a second end (134B), wherein the first end (132A) of the primary winding (<NUM>) and a neutral node (<NUM>) are configured to receive an input voltage and the second end (132B) of the primary winding (<NUM>) and the neutral node (<NUM>) are configured to produce an output voltage, wherein the first end (134A) of the first secondary winding (<NUM>) is connected to the neutral node (<NUM>), wherein the primary winding (<NUM>) produces a primary voltage based on the input voltage, and wherein a secondary voltage of the first secondary winding (<NUM>) is out-of-phase to the primary voltage of the primary winding (<NUM>); and
a first switch (<NUM>) configured to connect the second end (134B) of the first secondary winding (<NUM>) with the second end (132B) of the primary winding (<NUM>), wherein, when the first switch is connected, the output voltage is the secondary voltage,
wherein the transformer further comprises a second secondary winding (<NUM>), having a first end (136A) and a second end (136B), wherein the first end (136A) of the second secondary winding (<NUM>) is connected to the neutral node (<NUM>),
and wherein the voltage regulation circuit further comprises a second switch (<NUM>) configured to connect the second end (136B) of the second secondary winding (<NUM>) to the neutral node (<NUM>),
wherein, when the second switch (<NUM>) is closed and the first switch (<NUM>) is open, the output voltage is effectively the input voltage reduced by voltage drops across the primary winding (<NUM>), and
wherein, when the second switch (<NUM>) is open and the first switch (<NUM>) is closed, the output voltage is the secondary voltage, as defined by a ratio of the windings between the primary winding (<NUM>) and the first secondary winding (<NUM>);
the voltage regulation circuit being configured to
alternately close the switches (<NUM>) and (<NUM>), thereby changing the average voltage at the second end (132B) of the primary winding (<NUM>), wherein the average voltage depends on the duration of the respective voltages at the second end (132B) of the primary winding (<NUM>); and wherein the switches (<NUM>) and (<NUM>) are never closed at the same time.