Power supply arrangement having a boost circuit for an electricity meter

A power supply arrangement for an electricity meter includes an input, a full wave rectifier, and a voltage doubler circuit. The input is configured to receive a periodical input signal. The full wave rectifier is coupled to the input and has a first output. The first output is coupled to a first load of the electricity meter. The voltage doubler circuit is coupled to the input and has a second output coupled to a second load of the electricity meter. The voltage doubler is configured to prevent the flow of current from the second output to the input.

FIELD OF THE INVENTION

The present invention relates to electricity meters, and in particular, to arrangements for providing power within an electricity meter.

BACKGROUND

Electricity meters are meters that, among other things, measure electrical energy flowing to a load, or at least through a conductor that feeds one or more loads. Electricity meters are often located at domestic residences for the purpose of measuring consumption of electricity by a residence for billing purposes. Electricity meters are also located on larger commercial and industrial structures for similar reasons. Electricity meters are often used for additional purposes, such as tracking energy usage trends, and/or load control.

With respect to load control, electricity meters sometimes include disconnect switches that automatically disconnect and reconnect a load to the utility power lines. Disconnect switches can be used for prepaid electricity services, as well as for load shedding. In prepaid electrical service situations, the disconnect switch automatically disconnects the load from the power lines once the customer has consumed the prepaid amount of energy. When additional energy is purchased, the disconnect switch reconnects the load to the power line. Because disconnect switches connect an entire customer load (such as a residence) to the power lines, the disconnect switch must be able to handle a significant amount of current, such as, for example 200 amperes. Mechanical switches are well-suited for switching currents of this magnitude.

In order to actuate the mechanical switches, an actuator such as a solenoid or motor typically must be used. In one example, the meter assembly includes an actuator in the form of a small motor that actuates the disconnect switch. Linear power supplies have been used to provide the motor driver circuit with power.

A problem has arisen with a residential electricity meter employing a linear power supply and a motor driver circuit. In particular, in one example, the motor driver circuit includes a capacitor that is discharged through a small motor to open or close the 200 ampere switch. The capacitor is then allowed to charge to the maximum level before a subsequent operation is performed. The capacitor provides a reserve of energy that is used to reduce the stress on the linear power supply during the relatively infrequent operation of the switch.

Charging the capacitor to the level of the power supply unregulated voltage Vurcreates a problem in that under conditions of heavily loading the power supply with optional circuitry and under conditions of low line voltage the capacitor is charged to a voltage level insufficient to reliability operate the motor. To overcome this problem a transformer with a higher secondary voltage could be used. However, to maintain proper regulation, the capacity of the transformer would have to be increased proportionally. This would result in a physically larger transformer and higher cost. In general, electricity meters do not include excessive space to accommodate larger components, and cost is always a concern. Moreover, using a larger transformer would result in higher losses which reduces efficiency and increases internal heating.

One potential solution involves the use of a switched-mode supply. Use of switched-mode technology in place of a linear power supply is undesirable due to the increased complexity and cost and the potential for reduced reliability. Moreover, use of a higher secondary voltage transformer in conjunction with a switch mode DC regulator is also considered undesirable for reasons of complexity, cost, and the impact of accommodating the higher electrical noise associated with switched-mode typology.

There is a need, therefore, for low cost means to provide a larger voltage for the purposes of charging a motor drive circuit.

SUMMARY OF THE INVENTION

At least some embodiments of the invention address the above stated need, as well as others, by employing a power supply arrangement for an electricity meter that includes two outputs, including one that provides a boosted voltage. The boosted voltage may be used to charge a capacitor that provides excess power to an actuator circuit such as a motor that operates a switch.

A first embodiment of the invention is a power supply arrangement for an electricity meter that includes an input, a full wave rectifier, and a voltage doubler circuit. The input is configured to receive a periodical input signal. The full wave rectifier is coupled to the input and has a first output. The first output is coupled to a first load of the electricity meter. The voltage doubler circuit is coupled to the input and has a second output coupled to a second load of the electricity meter. The voltage doubler is configured to prevent the flow of current from the second output to the input.

The above-described features and advantages, as well as others, will become apparent to those of ordinary skill in the art by reference to the following detailed description and accompanying drawings.

DESCRIPTION

FIG. 1shows a block diagram of a first embodiment of an arrangement according an exemplary embodiment of the invention.FIG. 1shows an electricity meter102coupled to a power line104. The power line104delivers electrical power from a source, which may be a utility “mains” power line, to a load, which may be an electrical system of a residence, commercial building or industrial building. It is noted that the power line104shown in representative form only as a single conductor. It will be appreciated that those of ordinary skill in the art may readily adapt the elements of the electricity meter102for single phase or polyphase metering systems using any known metering form.

The electricity meter102includes sensor circuitry106,108, a metrology circuit110, a display112, and a communication circuit114. The electricity meter102also includes a disconnect switch116. The disconnect switch116is configured to controllably break and make the connection through the power line104. The disconnect switch116may thus be used to disconnect the load (or in some cases portions thereof) from the source. As discussed above, disconnect switch116may be operated in a situation in which prepaid electricity services have been expended.

The disconnect switch116must make and break a connection in a conductor carrying significant electrical power. To this end, the disconnect switch116may suitably be a 200 ampere switch. To operate such a switch, an actuator118is provided.

In accordance with an embodiment of the invention, the meter102includes a power supply arrangement that includes a linear power supply120and a voltage boost circuit122. The linear power supply120is operably coupled to provide electrical power to the metrology circuit110, the display112and the communication circuit114, while the voltage boost circuit122is connect to provide electrical power at least indirectly to the actuator118. The voltage boost circuit122provides an output voltage that exceeds that of the linear power supply120. In some embodiments, the voltage boost circuit122comprises what is known in the art as a voltage doubler or voltage multiplier circuit.

In the general configuration of the meter102, the sensor circuitry106,108includes a voltage sensor106and a current sensor108. In polyphase meters, the sensor circuitry106,108will include multiple voltage sensors and multiple current sensors, as is known in the art. Referring again to the example ofFIG. 1, the voltage sensor106is operably coupled to sense the voltage on the power line104. To this end, the voltage sensor106is any suitable circuit, including any of a plurality of well-known forms, that generates a signal that is representative of the voltage and/or voltage waveform on the power line104. By way of example, the voltage sensor106may comprise a resistive voltage divider that generates a scaled-down version of the power line voltage waveform as an output. Similar to the voltage sensor106, the current sensor108is operably coupled to sense the current on the power line104. To this end, the current sensor108is any suitable circuit, including any of a plurality of well-known forms, that generates a signal that is representative of the current and/or current waveform on the power line104. By way of example, the current sensor108is a toroid device having a center opening through which the power line104passes.

The metrology circuit110is operably coupled to receive voltage and current measurement signals from the sensors106,108. The metrology circuit110is configured to, among other things, determine and communicate information regarding power or energy consumption of the load. For example, the metrology circuit110may generate metering information in the form of kilowatt-hours, peak demand, I2hours, apparent energy, reactive energy or other known quantities. Metrology circuits capable of generating such metering information are well known in the art. By way of example, it is well known to digitally sample the voltage and current waveform signals (such as those provided by the sensors106,108), multiple contemporaneous voltage and current samples together, and accumulate the multiplied products over time to generate watt-hour information. It is likewise known to calculate apparent power by generating RMS voltage and RMS current values using the voltage and current waveform signals provided by the sensors106,108, and then multiplying the RMS voltage by the RMS current. Other methods of generating such values, as well as other useful metering values, using sampling of voltage and current measurement signals, are well known in the art.

The metrology circuit110also will typically include a meter controller, such as a processor circuit or microcontroller circuit, that controls the overall operations of the meter102including control over display and communication operations. Such meter architectures are known in the art.

The display circuit112is preferably an LCD display and associated driving circuitry. The display circuit112is operably coupled to the metrology circuit110. The display circuit112is suitably configured to provide a visual indication of information regarding the metering values generated by the metrology circuit110. Suitable display circuits are well known in the art and may include various other features.

The communication circuit114is a device that facilitates communication of information between the metrology circuit and an external computer or other device. To this end, the communication circuit114may include an optical port or other port that facilitates local communication. The communication circuit114may instead, or in addition, include a modem that facilitates communication to a remote location over a communication medium. By way of example, the communication circuit114may include a power line modem that facilitates communication with a remote, centralized facility over the power line104. In another example, the communication circuit114includes an RF modem that facilitates communications using RF signals and a wireless network.

In one embodiment, the communication circuit114is configured to be able to receive a signal from a remote device that includes a command to open (and optionally to close) the switch116. The communication circuit114is further configured to communicate that information to the actuator118directly, or through the intervention of the control circuit within the metrology circuit110.

The switch116, as discussed above, is operably connected to controllably break or make a connection in the power line104. To this end, the switch116has at least one mechanically movable contact that may be moved to close or break the connection in the power line104. The open or closed position of the switch116is controlled by the actuator118, which may suitably be a motor, not shown. The actuator118causes the switch116to open or close in response to control signals, for example, received from the metrology circuit110, the communication circuit114or any other circuit that includes control logic.

The power supply120is preferably a linear supply. The power supply120is operably connected provide power to various circuits of the meter102include the metrology circuit110, the display112, and the communication circuit114. The power supply120is preferably coupled to obtain power from the power line104via a transformer124. The voltage boost circuit122is operably connected to the power supply120and is configured to provide a voltage that is higher than the output voltage of the power supply120.

The voltage boost circuit122is operably coupled to provide the increased output voltage to an energy storage unit126within the meter102. The energy storage unit126, which may suitably be one or more capacitors, is capable of storing a voltage that is higher than the output voltage of the power supply120. The energy storage unit126is operably coupled to provide the stored higher voltage to the actuator118to provide the power necessary to operate the actuator118, at least on a temporary basis. In particular, when the actuator118is not operating, which is most of the time, the energy storage unit126is charged to the charge voltage (which exceeds the output voltage of the power supply120) by the voltage boost circuit122. When the actuator118operates to open (or close) the switch116, the energy storage unit126discharges its stored charge to the actuator118. The actuator118converts the electrical energy from the energy storage unit126to motive energy to operate the switch116. After the actuator118opens or closes the switch116, the boost circuit122recharges the energy storage unit126.

As discussed above, it is noted that the boost circuit122may suitably include or comprise a voltage doubler circuit. It will be appreciated that the phrase “voltage doubler” circuit as used herein means a circuit that is configured to boost a voltage from an AC source, and does not necessarily require an exact “doubling” of an input voltage. The phrase “voltage doubler” refers to the fact that circuit has the general architecture to substantially double the input voltage. The phrase “voltage doubler” circuit should also be considered to incorporate similar voltage multipliers that include more than one doubler stage.

An advantage of the above described embodiment is that increase voltage may be provided to the actuator118on a periodic basis without requiring a higher voltage linear power supply120. Instead, the voltage boost circuit122allows a higher voltage to be stored in the energy storage unit126, which in turn may be used on a temporary basis to provide relatively high power to the actuator118.

FIG. 2shows an exemplary embodiment of the power supply arrangement ofFIG. 1including some of the context from the meter102. More specifically,FIG. 2shows a power supply arrangement200for an electricity meter that includes an input202configured to receive a periodical input signal. The arrangement200also includes a full wave rectifier204and a voltage boost circuit206. The full wave rectifier204is coupled to the input202and has a first output208. The first output208is coupled to a first load210of an electricity meter. By way of example, the first load210includes the metrology, communication and/or display circuits of the meter.

The voltage boost circuit206is coupled to the input202and has a second output212coupled to a second load214of the electricity meter. The voltage boost circuit206includes a rectifying element and/or is otherwise configured to prevent the flow of current from the second output212to the input202.

In further detail, the input202may suitably comprise a terminal of a secondary winding of a power supply transformer220. The power supply transformer220may suitably be an embodiment of the transformer124ofFIG. 1. The power supply transformer220converts the voltage from the power line (e.g. power line104ofFIG. 1) to a lower voltage that is employed by the rectifier circuit204to generate a suitable power supply voltage for the circuits of the first load210, which may include metrology, communication, control and display circuits. The power supply transformer220does not, however, provide voltage that would be, when converted to DC by a rectifier circuit, sufficient for the second load214.

In any event, the rectifier circuit204comprises all or part of a full-wave linear power supply that generates a first output voltage VUR at the output208. To this end, the rectifier circuit204includes a diode bridge222and a smoothing capacitor224. The voltage VUR is provided to the first load210. The voltage VUR is unregulated in the full wave linear power supply formed by the rectifier circuit204. Thus, the load210may include, in addition to metrology, control, communication, and/or display circuits, voltage regulator devices that receive the voltage VUR and generate regulated output voltages.

The voltage boost circuit206includes a capacitor226, a rectifying device228, and a source of current230. The capacitor226and the rectifying device228are series coupled between the input202and the second output212. The current source230is coupled between the capacitor226and the rectifying device228. The current source230typically will also include a rectifier, not shown. Further detail regarding examples of suitable boost circuits are provided below in connection withFIGS. 3 to 5.

In general, the voltage boost circuit206in several embodiments is configured as a voltage doubler that operates to increase the voltage from the AC input voltage received at the input202.

The second load214in this embodiment is an energy storage circuit, such as the energy storage circuit126ofFIG. 1. The second load214in any event requires or employs a voltage that exceeds that of the voltage VUR. In the embodiment, which corresponds to the embodiment ofFIG. 1, the energy storage element of the second load214is coupled to an actuator234. The actuator234may suitably be the actuator118ofFIG. 1.

Thus,FIG. 2provides in further detail an exemplary embodiment of the power supply arrangement shown inFIG. 1.FIGS. 3 to 5show specific examples of the power supply arrangement ofFIG. 2. InFIGS. 3 to 5, the transformer220ofFIG. 2is represented by its equivalent circuit of a voltage source V1and a resistor R3. The voltage source V1is the voltage provided by the secondary winding of the transformer220and the resistor R3is used to model the transformer's impedance. V1has a typical range of 11.7 VRMS minimum to 17.5 RMS maximum.

Referring now to the embodiment ofFIG. 3, diodes D1-D4in conjunction with C1form the linear DC supply. Resistor R1represents the first load, i.e. the first load210ofFIG. 2, which may include metrology, communication and/or display circuitry of a meter. At minimum input voltage and maximum load current, the voltage on C1(Vur) can be as low as approximately 9 volts in this embodiment. The capacitor C2in this embodiment represents the storage element or second load214ofFIG. 2. The capacitor C2is used as a motor drive capacitor that needs to be charged to a voltage of approximately 16 volts. Consequently, if Vuris used to charge capacitor C2the needed voltage of 16 volts will not necessarily be achieved under varying operating conditions.

InFIG. 3, capacitor C3and diodes D5, D6, and D7, make up the voltage boost circuit used to charge C2to a maximum of approximately 2 times Vur. This is accomplished similar to the operation of a typical voltage doubler circuit. A difference between the present invention and a typical voltage doubler circuit is that voltage doubling operation of this device is achieved in conjunction with a full wave bridge circuit. The full wave bridge is used to provide DC power (Vur) to the first load (represented by R1), and the voltage doubler charges the motor drive capacitor C2to approximately 2 times Vur.

Under normal operation, capacitor C2charges to full voltage of at least 16 volts. As discussed above in connection withFIG. 1, this may occur during normal operation of the meter102, when there is no command to change the state of the switch116. However, when a command is given to either open or close the switch, the capacitor C2is electrically connected directly, via a switch, not shown, to the motor, also not shown inFIG. 3. The capacitor C2discharges down to about 2 volts, which is the forward voltage drop of a solid state switch (not shown). Once discharged, the capacitor C2is disconnected from the motor and allowed to charge up to maximum voltage before a subsequent operation is performed.

InFIG. 3, the capacitor C2charges from both the voltage doubler circuit and from the full wave bridge Vuruntil the voltage reaches Vurminus the voltage drop across D5. Then the voltage across C2continues to increase to approximately 2 times Vurfrom the voltage doubler operation. Thus, the embodiment ofFIG. 1employs both the unregulated rectified voltage output Vurand a voltage doubler (C3, D5, D6, D7) to charge the capacitor C2. The time to charge from 0 volts up to Vuris typically much shorter than the time required to charge from Vurto 2 times Vurbecause more current can be supplied from the full wave bridge compared to the current supplied through C3. However, current through C3can be increased by increasing the value of C3.

In another embodiment, the diode D5is removed from the circuit ofFIG. 3. In this embodiment, the circuit performs almost the same as the circuit ofFIG. 3. The difference is that during the first portion of the charging cycle C2only charges to Vurminus the voltage drop across both D6and D7. Then the voltage across C2continues to increase to approximately 2 times Vurbecause of the voltage doubler circuit.

It is possible, however, in these embodiments, that Vurcan droop somewhat during the first stage where C2is being charged directly by Vur. This temporary drop in Vurmay be undesirable with respect to other elements in the circuit, such as those that receive power from Vur.

Other alternative embodiments of the arrangement ofFIG. 2address this issue. In particular,FIG. 4shows an embodiment that tends to minimize the droop in Vurwhen C2is being charged. Droop is reduced by charging C2only from the voltage boost circuit comprising C3and not directly from Vur. To this end, a transistor Q6replaces the diode D7. The transistor Q6is controlled such that C3is charged from Vurduring ½ cycle of the 60 Hertz input power. During the next half cycle the charge on C3is transferred to C2. After several cycles C2will be charged to approximately 2 times Vur. During the half cycle C3is being charged from Vurdiode D6is forward biased and transistor Q6is not conducting and therefore no current is flowing into C2. During the next half cycle the emitter voltage of Q6increases above Vurand transistor Q6turns on and charge is transferred to C2. In this way current never flows directly from Vurinto C2.

FIG. 5shows a slight variation of the above described embodiment. In the above-described embodiment ofFIG. 4, wherein the transistor Q6replaces D7ofFIG. 3, and D5ofFIG. 3is eliminated, the capacitor C3is charged from current flowing from Vur. The additional current needed to charge C3flowing through the bridge rectifier increases the voltage drop across the bridge rectifier resulting in a larger droop of Vur. To reduce this droop, the circuit ofFIG. 5uses the current that comes directly from the bridge input to charge C3. Consequently, no additional voltage drop is produced across the bridge rectifiers, thereby minimizing the droop of Vur. Ideally Q6would have a relatively high gain such as 100 so that the base current needed to turn on Q6is minimized. Current flowing through the base of Q6is in a sense wasted because it does not transfer to C2and therefore does not contribute to charging C2. The circuit ofFIG. 4minimizes the time it takes to charge the motor drive capacitor while minimizing the droop in Vurduring the charging cycle.

It will be appreciated that the above described embodiments are merely exemplary, and that those of ordinary skill in the art may readily devise their own modifications and implementations that incorporate the principles of the present invention and fall within the spirit and scope thereof.