Electricity Meter

Abstract

An electric meter is disclosed, comprising: a converter (19) configured to synchronously modulate a current measurement signal and a voltage measurement signal (12, 14) and output the synchronously modulated current measurement signal and the synchronously modulated voltage measurement signal (34, 35); and a measurement module (20) configured to receive the synchronously modulated current measurement signal and the synchronously modulated voltage measurement signal from the converter and process the synchronously modulated current measurement signal and the synchronously modulated voltage measurement signal.

Description

Technical Field

[0001] The present invention relates to an electricity meter, and in particular to an electricity meter capable of measuring direct current (DC) power. Background Art

[0002] The importance of electricity meters that can measure direct current (dc) power instead of alternating current (ac) power has grown as the focus on DC power has increased. However, the technology for DC meters that can be widely deployed is not as developed as that for AC meters. In addition, existing AC meters often perform poorly with DC. Summary of the invention

[0003] According to a first aspect of the invention, there is provided an electric meter comprising a converter configured to synchronously modulate a current measurement signal and a voltage measurement signal and output the synchronously modulated current measurement signal and the synchronously modulated voltage measurement signal. The electric meter further comprises a measurement module configured to receive the synchronously modulated current measurement signal and the synchronously modulated voltage measurement signal from the converter and process the synchronously modulated current measurement signal and the synchronously modulated voltage measurement signal (e.g., to determine power and / or another measurement result).

[0004] The measurement module may be a single integrated circuit (eg, in the form of a metering chip), or may include two or more integrated circuits (eg, an analog-to-digital converter integrated circuit and a digital processing integrated circuit such as a microcontroller or other ASIC or FPGA).

[0005] Preferably, the meter has zero offset (eg, < 0.1 μV). Preferably, the meter has a large dynamic range (eg, > 1000:1).

[0006] The synchronously modulated current measurement signal and the synchronously modulated voltage measurement signal can be sampled with a known, constant timing offset.

[0007] The current measurement signal and the voltage measurement signal may be a DC current measurement signal and a DC voltage measurement signal, an AC current measurement signal and an AC voltage measurement signal, or an AC current measurement signal and an AC voltage measurement signal with a fixed or varying DC offset, and / or a DC current measurement signal and a DC voltage measurement signal with an AC ripple. The meter is capable of generating a total power including any non-DC element.

[0008] The converter may include a source of a time-varying signal for synchronously modulating the current and DC voltage measurement signals. The time-varying signal may have at least one component with a fixed frequency. The time-varying signal may have at least one component with a varying frequency. The time-varying signal may be a spread spectrum signal. The source may be configured to output a pulse width modulated signal or a mixed signal. The time-varying signal may have only one component. The time-varying signal may include a square wave and / or a sine wave. The converter may be configured not to modulate at (or "avoid modulating at") a fundamental frequency or harmonic frequency of 16.7 Hz, 50 Hz, 60 Hz, or 400 Hz. The time-varying signal may scan through a range of frequencies, for example 40 Hz to 80 Hz. In that case, the converter may be configured to avoid modulation at (or "skip") fundamental frequencies (or harmonic frequencies) of 16.7 Hz, 50 Hz, 60 Hz, or 400 Hz, or if it does pass through those frequencies, it spends a very small proportion of the time at those frequencies on average (e.g., less than 1% or less than 0.1%). The converter may be configured to modulate at one or more frequencies between 1 Hz and 1 MHz. The converter may be configured to modulate at one or more frequencies between 51 Hz and 59 Hz, between 61 Hz and 65 Hz, and / or between 67 Hz and 390 Hz.

[0009] The source of the time-varying signal may be in the form of a crystal oscillator, a hardware timer, or a waveform generator, or may be a port for receiving a time-varying signal from an external source.

[0010] The electric meter, optionally the converter, may include a first modulator and a second modulator, the first modulator and the second modulator being configured to synchronously modulate the current measurement signal and the voltage measurement signal, respectively, and output the synchronously modulated current measurement signal and the synchronously modulated voltage measurement signal, respectively. The first modulator and the second modulator may include a first bus exchange switch and a second bus exchange switch, respectively. The first modulator and the second modulator may include a first group of switching devices and a second group of switching devices, respectively. The first modulator and the second modulator may include a first group of field effect transistors and a second group of field effect transistors, respectively. The first modulator and the second modulator may include a first group of analog switches and a second group of analog switches, respectively. The first modulator and the second modulator may include a first group of four-quadrant analog multipliers and a second group of four-quadrant analog multipliers, respectively.

[0011] The electric meter, optionally the measurement module, may include a first analog-to-digital converter and a second analog-to-digital converter for digitizing the synchronously modulated current measurement signal and the synchronously modulated voltage measurement signal, respectively, and outputting the digitized synchronously modulated current measurement signal and the digitized synchronously modulated voltage measurement signal. The first analog-to-digital converter and the second analog-to-digital converter may be included in a single integrated circuit.

[0012] The electric meter, optionally the measuring module, may include a digital computing unit for calculating a current value, a voltage value, a power value and / or an energy value. The digital computing unit may be configured to calculate the power value by multiplying a digitized synchronously modulated current measurement signal and a digitized synchronously modulated voltage measurement signal. The digital computing unit may include a microprocessor running a computer program to calculate the current value, the voltage value, the power value and / or the energy value. The digital computing unit may include hardware logic for calculating the current value, the voltage value, the power value and / or the energy value.

[0013] The electric meter, optionally the measuring module, may include at least one output device for providing a current value, a voltage value, a power value and / or an energy value. At least one output device may include a display for displaying the current value, the voltage value, the power value and / or the energy value. At least one output device may include a network interface for transmitting the current value, the voltage value, the power value and / or the energy value.

[0014] Preferably, the electric meter comprises a meter housing containing the converter and the measuring module.The converter and the measuring module may be supported on the same PCB or on respective ones of the PCBs which may be contained in the meter housing.

[0015] The electric meter may also include an input for receiving a current measurement signal from a remote current sensor. The remote current sensor may be internal or external to the meter housing.

[0016] The electric meter may also include a current sensor arranged to provide a current measurement signal. The current sensor may be coupled to a modulator (e.g., a first modulator) for modulating the current measurement signal by direct current (dc). The remote current sensor or current sensor may be a shunt. The electric meter may also include a first conductor and a second conductor for transferring power from a source to a load; wherein the remote current source or current source is configured to measure the current flowing through the first conductor. The shunt may be arranged in front of the load or behind the load. The second conductor may be a neutral conductor. The electric meter may also include a first connector and a second connector for providing a current measurement signal to the shunt, and a modulator (e.g., a first modulator) directly connected to the shunt via the first connection and the second connection. At least one of the first connection and the second connection between the shunt and the modulator includes the same material as the shunt. The shunt may include a metal alloy containing copper, nickel and manganese, optionally a manganese-nickel-copper alloy (Manganin, RTM), or an alloy containing 84% copper, 12% manganese and 4% nickel. The shunt may comprise a material having a temperature coefficient of resistance between 0 and 10×10 -6 / K or between 0 and -10×10 -6 / K or between 0 and 20×10 -6 / K or between 0 and -20×10 -6 / K. The remote current sensor or current sensor may be a Hall effect current sensor, a fluxgate current sensor, an anisotropic magnetoresistive current sensor, a giant magnetoresistive current sensor, or a tunneling magnetoresistive current sensor.

[0017] The electric meter may be a DC electric meter and / or a measurement module. The electric meter may comply with ANSI standards and / or IEC standards for electric meters.

[0018] According to a second aspect of the invention, there is provided a system comprising an electric power source, an output to a power sink, optionally a power sink; and an electric meter according to the first aspect of the invention interposed in an electrical path between the electric power source and the output to the power sink.

[0019] The system may be a photovoltaic system, and the power source may include a photovoltaic panel, and the power dissipator may include a distribution network, an energy storage device, or a load.

[0020] The system may be an electric vehicle charging system, and the power source may be a power distribution system, and the energy storage may be an electric vehicle energy storage device (eg, a battery or battery pack).

[0021] The system may be a DC grid system, and the power source may include an electrical power source or storage system, and the power dissipator is a load.

[0022] The system may also include a dc-dc converter placed in the electrical path between the power source and the electricity meter or between the electricity meter and the output to the power dissipator.

[0023] According to a third aspect of the present invention, there is provided a method comprising: performing current measurement and voltage measurement respectively to generate a current measurement signal and a voltage measurement signal, and synchronously modulating the current measurement signal and the voltage measurement signal in an electric meter and outputting the synchronously modulated current measurement signal and the synchronously modulated voltage measurement signal, and measuring the synchronously modulated current measurement signal and the synchronously modulated voltage measurement signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Certain embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, in which:

[0025] Figure 1 is a schematic block diagram of an electric meter;

[0026] Figure 2 is a flow chart of a method of capturing and processing signals in an electric meter;

[0027] Figure 3 is a schematic block diagram of a first modulator.

[0028] Figure 4 is a schematic block diagram of a second modulator.

[0029] Figure 5 is a schematic block diagram of a third modulator.

[0030] Figure 6 is a schematic block diagram of an electric meter including a current sensor in the form of a current shunt.

[0031] Figure 7a is a perspective view of a conductor and a first current diverter;

[0032] Figure 7b is a perspective view of the conductor and the second current shunt;

[0033] Figure 8 is a graph of DC meter error versus current;

[0034] Fig. 9 is a graph of the processing loss as a function of the cutoff frequency of a single-pole low-pass filter;

[0035] Fig.10 is a graph of the frequency response of the meter;

[0036] Fig.11aA graph showing a first set of input current signals and input voltage signals;

[0037] Fig.11b Shows from Fig.11a a graph of a first set of modulated current signals and modulated voltage signals obtained from a first set of input current signals and input voltage signals shown in FIG.

[0038] Fig.11c is through Fig.11b A graph of simulated measured power obtained by multiplying a first set of modulated current signals and modulated voltage signals as shown;

[0039] Fig.11d is through Fig.11a A graph of the calculated power obtained by multiplying the first set of current signals and voltage signals shown in ;

[0040] Fig.12a showing a second set of graphs of input current signals and input voltage signals;

[0041] Figure 12b Shows from Fig.12a a graph of a second group of modulated current signals and modulated voltage signals obtained from a second group of input current signals and input voltage signals shown in ;

[0042] Fig.12c is through Figure 12b A diagram of a simulated measured power obtained by multiplying a second set of modulated current signals and modulated voltage signals shown in;

[0043] Fig.12d is through Fig.12a A graph of the calculated power obtained by multiplying the second set of current signals and voltage signals shown in ;

[0044] Fig.13a showing a third set of graphs of input current signals and input voltage signals;

[0045] Fig.13b Shows from Fig.13a a graph of a third group of modulated current signals and modulated voltage signals obtained from a third group of input current signals and input voltage signals shown in FIG.

[0046] Fig.13c is through Fig.13b A diagram of a simulated measured power obtained by multiplying a third set of modulated current signals and modulated voltage signals shown in FIG.

[0047] Fig.13d is through Fig.13a A diagram of the calculated power obtained by multiplying the third set of current signals and voltage signals shown in ;

[0048] Fig.14 is a schematic block diagram of a photovoltaic system;

[0049] Fig.15 is a schematic block diagram of an electric vehicle charging system; and

[0050] Fig.16 It is a schematic block diagram of a DC grid system. DETAILED DESCRIPTION

[0051] The invention is based on the insight that a measurement module of an AC meter can be used to measure DC with low error (and still be able to measure AC) by synchronously modulating a current signal and a voltage signal in the AC meter and then demodulating the modulated current signal and the modulated voltage signal.

[0052] In the following, the same components are denoted by the same reference numerals.

[0053] refer to Figure 1 , shows an electric meter 1 together with a load 2, a power supply 3, and conductive paths 4, 5 connecting the load 2 and the power supply 3 to form a loop 6. The power supply 3 is in the form of a direct current supply. The load 2 may vary over time, resulting in an AC component of the current i. In addition, the power supply 3 may vary over time, resulting in an AC component of the current i.

[0054] The electric meter 1 comprises a current sensor 11 which generates a signal 12 proportional to the current i in the loop 6 (referred to herein as a “current measurement signal” or simply as a “current signal”).

[0055] The current sensor 11 is arranged on the lower side (i.e., the lower side relative to the load 2). Alternatively, an upper side current sensor 11′ may be used. The current sensor 11 is in the form of a resistive shunt. However, the current sensor 11 may be in the form of another sensor capable of sensing dc current, such as a fluxgate sensor, a Hall effect sensor, a giant magnetoresistance (GMR) sensor, or an anisotropic magnetoresistance (AMR) sensor. Preferably, the current sensor 11 is capable of generating a differential signal 12 that can help reduce electrical and magnetic interference. A current sensor 11 that generates a single-ended signal may be used.

[0056] The electricity meter 1 also includes a voltage sensor 13 that generates a signal 14 (referred to herein as a "voltage measurement signal" or simply "voltage signal"). Preferably, the voltage sensor 13 includes a pair of taps 15, 16 on either side of the load 2. Preferably, the taps 15, 16 are connected as close to the load as possible, preferably using a four-point ("Kelvin") arrangement to help reduce possible losses of the current measured as power in the load 3. Preferably, the voltage sensor 13 is capable of generating a differential signal 14 that can help reduce electrical and magnetic interference.

[0057] The electric meter 12 may include an attenuation circuit 17 for passively attenuating the voltage signal 14. The attenuation circuit 17 may take the form of a voltage divider.

[0058] The electric meter 1 comprises a sensor part 18 including a current sensor 11 and a voltage sensor 13, a converter part 19 (hereinafter referred to as a "converter") for synchronously modulating a current signal 12 and a voltage signal 14, and a measuring part 20. The parts 18, 19, 20 are generally contained in a meter housing 21.

[0059] Converter 19 includes first and second modulators 22 and 23 and a timing reference source 24 (also referred to herein as a “time-varying signal source”) that provides a timing reference 25 (referred to herein as a “time-varying signal”).

[0060] The modulators 22, 23 have respective signal input(s) 26, 27, timing reference input(s) 28, 29 and modulated signal output(s) 30, 31.

[0061] The first modulator 22 receives the current signal 12 at its input(s) 26 via signal path(s) 32, and the second modulator 23 receives the voltage signal 14 (which may be attenuated by the attenuation circuit 17) at its input 27 via signal path(s) 34. Any phase shift introduced by additional components (not shown) between the sensors 11, 13 and their respective modulators 22, 23 is matched between the inputs 26, 27. The signal paths 32, 33 may incorporate EMC protection, biasing and filtering passive components.

[0062] The timing reference source 24 may be in the form of a crystal oscillator, hardware timer or waveform generator or a port for receiving a signal from an external source. The timing reference 25 is provided to the modulators 22, 23 via inputs 28, 29. Additionally or alternatively, the timing reference 25 may be provided to a sampling system 31.

[0063] The modulators 22 , 23 synchronously modulate the current signal 12 and the voltage signal 14 respectively using the timing reference 25 and output synchronously modulated current signals 34 and voltage signals 35 respectively.

[0064] The measuring part 20 includes an analog-to-digital conversion unit 36 ​​(also referred to herein as a "sampling system"), which includes a first analog-to-digital converter 37 and a second analog-to-digital converter 38, and a data processing unit 39. The measuring part 20 may be in the form of an integrated circuit (e.g., a metering chip). However, the measuring part 20 may include two or more integrated circuits. For example, the analog-to-digital conversion unit 36 ​​may be in the form of an integrated circuit, while the data processing unit 39 may be in the form of another integrated circuit (e.g., a microcontroller, an ASIC, a DSP, an FPGA, or other suitable form of processing device).

[0065] The electricity meter 1 further comprises a display 40 and optionally a network interface 41 , such as a wireless network interface.

[0066] The analog-to-digital conversion unit 36 ​​receives the modulated current signal 34 via (one or more) signal paths 42 and receives the modulated voltage signal 35 via (one or more) signal paths 43. Any phase shift introduced by additional components (not shown) between the sensor modulators 22, 23 and the analog-to-digital conversion unit is matched. The signal paths 42, 43 may incorporate biasing, coupling, and filtering passive components. Preferably, the modulators 22, 23 generate respective differential signals 34, 35 to minimize electrical and magnetic interference.

[0067] Preferably, the modulated signals 34, 35 are sampled simultaneously by an analog-to-digital converter unit 36 ​​operating at a significantly higher rate than the timing reference 25 and converted into digital data streams 44, 45 representing the modulated signals. In some cases, the modulated signals 34, 35 may be sampled with a known, constant timing offset. Preferably, the digital data stream representing the modulated signals 34, 35 takes the form of paired voltage samples 44 and current samples 45.

[0068] The digital data streams 44, 45 are presented to the digital processing unit 36 ​​which demodulates the digital representations 44, 45 of the modulated signals by multiplying the pairs of current and voltage values ​​and performing filtering.

[0069] The digital processing unit 36 ​​may include a microprocessor (not shown) that runs software (not shown) and memory (not shown) and / or hardware logic configured to demodulate data in software and / or hardware.

[0070] Also refer to Figure 2 , showing signal capture and processing.

[0071] The voltage and current signals are measured continuously (step S1) and synchronously modulated (step S2). The modulated signals are sampled (step S3) and then demodulated (step S4), for example by multiplication or by using a timing reference. The resulting measurements, such as power and / or current, are output (step S5).

[0072] refer to Figure 3 , the modulators 22, 23 can be viewed as pairs of switches 51, 52 that alternately route input signals 12, 14 through pairs of multipliers 53, 54 (one multiplier having a multiplication factor of +1 and the other multiplier having a multiplication factor of -1) to produce modulated outputs 34, 35. The switches 51, 52 are synchronized with a common timing signal 55 derived from the timing reference 25 and generated by a control circuit 56.

[0073] The modulators 22, 23 can be implemented in several different ways. However, in general, similar multipliers tend to be expensive and unstable, so implementations using switches (eg MOSFETS and other forms of transistors) may be used.

[0074] refer to Figure 4 , shows a first example of a modulator 22 , 23 , which can process differential input signals 12 , 14 and output differential output signals 34 , 35 .

[0075] The modulators 22, 23 may be implemented by pairs of synchronized double pole double throw (DPDT) switches 57, 58. These may be implemented as discrete components or by groups of MOSFETs.

[0076] refer to Figure 5 , shows a second preferred example of modulators 22 , 23 , which can process differential input signals 12 , 14 and output differential output signals 34 , 35 .

[0077] Instead of using DPDT switches, the modulators 22, 23 may be implemented by synchronized, interleaved SPST switch pairs 59, 60 and subsequent SPST switch pairs 61, 62. The internal control circuit 56 is divided into two parts 56a, 56b, thereby providing first and second timing signals 55a, 55b in antiphase.

[0078] When the first timing signal 55a is enabled, the first switch 59 and the second switch 60 are closed, so that the first input terminal and the second output terminal and the second input terminal and the first output terminal are connected respectively. The second timing signal 55b is disabled, so the third switch 61 and the fourth switch 62 are opened.

[0079] When the second timing signal 55a is disabled, the first switch 59 and the second switch 60 are opened. The second timing signal 55b is enabled, so the third switch 61 and the fourth switch 62 are closed, so that the first input terminal and the first output terminal and the second input terminal and the second output terminal are connected respectively.

[0080] refer to Figure 6 , another example of an electric meter 1 ′ is shown.

[0081] In this example, the modulators 22, 23 take the form of bus switches which generate suitable level signals for direct connection to a metering chip 20 (eg, a Cirrus CS5484).

[0082] A low DC offset is preferred in high current applications because the low electromotive force (emf) drop at maximum current can help minimize heat dissipation, for example, 150 μΩ is typical for a 100A rated meter and 75 μΩ is typical for a 200A rated meter.

[0083] Since the shunt impedance is very low and the switch impedance is only a few ohms, good gain stability can be achieved for meter 1'. The modulation frequency may be between 1 Hz and 60 Hz, and therefore the phase shift in the 1 nF capacitor required for direct connection to some differential ADC inputs is small.

[0084] The meter 1 ' comprises two bus bars 105, 106, namely a live (or "hot") conductor 105 and a neutral bar 106. Clamp or blade connectors are provided to the supplies 107, 108 and the loads 109, 110. The resistive element 104 is arranged in the live bar, for example in the form of a manganese nickel copper alloy (RTM) welded to copper on both sides. A first connector 125 and a second connector 126 are provided to the switching element 22. This is, for example, a bus switching switch, for example one of the five switches in the IDTQS3383 bus switching chip. It is switched between two states by a control line 129.

[0085] In the first state, the first connector 125 is connected to the first bus switch output 127, and the second connector 126 is connected to the second bus switch output 128. In the second state, the first connector 125 is connected to the second bus switch output 128, and the second connector 126 is connected to the first bus switch output 127.

[0086] These signals are then fed to the differential current sense input 117 of the metering chip 114. A control line 129 is provided by the square wave oscillator 103. This is also used by the switch 102 to switch a voltage signal divided by the resistor chain 111, 112, with the resistor 113 being used to balance the impedance into the switch 102. A display 123 of the accumulated energy is provided, as well as an optional radio link 124 for remote reporting of consumption data.

[0087] Be careful when connecting the switching switch input to the shunt to avoid thermocouple electromotive force (emf). Thermocouple emf is caused by the temperature difference between dissimilar metal junctions, one of which is the shunt itself, such as a manganese nickel copper alloy (RTM) connection to copper. The thermocouple emf can be as low as 0.2μV / K. Further reduction can be made by minimizing the temperature difference between the ends of the shunt sensing resistor. This can be done by making the assembly symmetrical.

[0088] refer to Figure 7a and 7b Thermocouple emf can also be reduced by using an electrically insulating thermal bypass across the shunts 130 , 141 .

[0089] Thermocouple emf can be reduced by measuring the temperature difference across the shunt and compensating it using a design or per unit calibration coefficient.The temperature difference can be measured directly using thermoelectromotive force across the shunt from an additional pair of connecting wires 132, 133 made of different materials.

[0090] Other potential thermal EMF points before modulation are any connectors between the shunt and the terminals on the switch IC, and temperature gradients across the switch itself. These can be reduced by careful board layout, using direct soldering of copper wires 125, 126 to the shunt terminals.

[0091] To this end, minimizing interconnects may be advantageous. The switching switch may be an IC type device, for example, Texas Instruments CBT3383, ON Semiconductor 7WB383 or made of four discrete FETs or two dual FETs or FET arrays with out-of-phase gate drive differential pairs.

[0092] The ground for the electronics can be simply taken from the busbars on either side of the shunt, or from a pair of (e.g., 1 ohm) resistors 119, 120 that divide the emf across the shunt to minimize common mode emf. The resistors 119, 120 divert a small amount of current from the shunt, but will be taken into account in the normal meter calibration procedure.

[0093] In addition to thermal EMF, sources of input-referred DC offset include charge injection from the switch control signal onto the AC output, capacitive coupling of the switch control signal (or external magnetic or electric fields onto the output at the switching frequency), conversion of common-mode DC signals to the AC output, and coupling of switching switch Vcc noise to the output at the modulation frequency.

[0094] Thus, the meter uses direct modulation of the shunt output voltage up to the AC frequency so that DC current and / or power can be measured from the AC system. The voltage signal, which may be attenuated prior to analog-to-digital conversion, may also be modulated, either before sampling or after sampling if desired. The meter may use robust, low-cost components, such as bus-switched switches connected directly to the shunt output to reduce zero offset to extremely low levels (e.g., less than 0.1 μV), thereby allowing a wider dynamic range of current and power measurements to be performed with a given shunt (e.g., up to 1000 to 1), which is particularly useful in systems with high currents (e.g., 200A or 400A) where the maximum EMF across the shunt must be limited to control power dissipation and losses.

[0095] Existing AC metrology chips often have poor performance at DC. For example, although the Cirrus Logic CS5484 chip does not specify a DC offset in its datasheet, it specifies a typical stability of the DC offset of 4μV / K. This should be compared to Meter 1, which can measure at ±0.2μV over 80K, so the stability is better than 3nV / K, and the initial offset is less than 0.1μV. In another example, the Analog Devices ADE7753 specifies a maximum DC offset of ±13mV.

[0096] Normal (non-chopper-stabilized) ADCs typically rely on parameter matching between transistors for their DC stability, which limits the offset to (at best) 10-20μV, but can be worse. Even traditional chopper-stabilized amplifiers (or ADCs) typically have poor performance because of the high chopping frequency. For example, expensive high-stability amplifiers (e.g., ADA4522) have a typical offset of 0.7μV (5μV maximum).

[0097] The meters described in this article also tend to exhibit low or lower noise at low frequencies. Due to the 1 / f effect, the noise in some components increases at low frequencies. For example, the noise spectral density of the ADA 4622-x op amp shows an increased floor below the 1 / f corner. The meters described in this article allow for lower noise measurements at lower frequencies.

[0098] refer to Figure 8, which enables a DC power meter to have the same or better performance as, for example, a 0.2 ANSI power meter.

[0099] refer to Fig. 9 , shows the frequency response of a simulation of an electric meter. The response is for a meter using square wave modulation at 53.1 Hz and a high pass filter with a cutoff frequency of 0.1 Hz.

[0100] There is a hole in the response at the modulation frequency, in this case 53.1Hz, with a width equal to the bandwidth of the high-pass filter. There is a consistent error at low frequencies due to processing losses of the square wave modulation with finite bandwidth. The error increases with frequency due to finite bandwidth at high frequencies.

[0101] Although 55 Hz lies between the frequencies commonly used in power supplies (ie, 50 Hz and 60 Hz), it is preferably avoided because its 10th harmonic conflicts with the 11th harmonic of a 50 Hz supply, and the 12th harmonic conflicts with the 11th harmonic of a 60 Hz supply.

[0102] refer to Fig.10 , shows a numerical simulation of the loss of the output due to the finite bandwidth of the amplifier / ADC post-modulator.

[0103] The graph shows that the square wave modulator is more sensitive to overall bandwidth than the sine wave modulator. This is because a lot of the square wave modulator's energy ends up in the higher harmonics. This is acceptable as long as the bandwidth is sufficiently stable.

[0104] A range of different modulation signals can be used. The modulation signal can be a square wave, a sine wave, or any wave with zero mean. The modulation signal can be a frequency modulated square wave.

[0105] The modulator can be a linear feedback shift register (LFSR) based modulator or a maximum length sequence (MLS) based modulator. These types of modulators can provide a modulated signal with a wider, flatter bandwidth.

[0106] refer to Figures 11a to 11d , shows a first simulation of the effect of modulating an input current signal and an input voltage signal and obtaining power by multiplying the modulated current signal and the modulated voltage signal.

[0107] Fig.11a An input current signal and an input voltage signal are shown in the form of a DC current set to 1A and a DC voltage set to 300V. Fig.11b An input current signal and an input voltage signal modulated using a 53 Hz square wave are shown. Fig.11cThe result of multiplying the modulated current signal and the modulated voltage signal is shown, which has the effect of demodulating the modulated signal. The resulting power is typically constant at 300W. Spikes appear in the resulting power, which are caused by the limited bandwidth in the simulation. In a real meter, these spikes can be easily filtered out using an output filter. Such a filter is typically used to filter out the 2f component of the line power. For comparison, Fig.11d The result of directly multiplying the input current signal and the input voltage signal is shown, ie without modulation.

[0108] refer to Figures 12a to 12d , shows a second simulation of the effect of modulating the input current signal and the input voltage signal and obtaining power by multiplying the modulated current signal and the modulated voltage signal.

[0109] Fig.12a The input current signal and the input voltage signal are shown, which take the form of in-phase sinusoidal 60 Hz signals with zero DC offset and 1 A peak current, 300 V peak voltage. Figure 12b shows the input current signal and input voltage signal modulated using a 53Hz square wave, and Fig.12c The demodulated signal is shown. Although the modulated current signal and the modulated voltage signal appear to meander above zero and then below zero, once multiplied, the resulting sinusoidal power is Fig.12d Again, spikes appear in the resulting power, which is caused by the limited bandwidth of the simulation.

[0110] refer to Figures 13a to 13d , shows a third simulation of the effect of modulating the input current signal and the input voltage signal and obtaining power by multiplying the modulated current signal and the modulated voltage signal.

[0111] Fig.13a A 60 Hz sinusoidal voltage and a full wave rectified 60 Hz current are shown.

[0112] Again, Fig.13c The demodulated output shown in Fig.13d There is good agreement between the directly calculated powers shown in .

[0113] The electric meter described herein may be used in a variety of applications where it is necessary to measure the power produced or consumed.

[0114] refer to Fig.14 , a photovoltaic system 200 is shown.

[0115] The photovoltaic system 200 includes one or more photovoltaic panels 201, whose DC output is connected to an electricity meter 1. The electricity meter can be connected to a dc-dc converter 202 for changing the output voltage and provided to an output 203 to feed a dissipator 203, which can take the form of a power distribution system, an energy storage device (e.g., a battery or a load).

[0116] refer to Fig.15 , an electric vehicle charging system 300 is shown.

[0117] The dc-dc converter 302 receives power from the power distribution system 301 , which reduces the voltage level to a level suitable for charging. The power is fed through the meter 1 , which then provides power via the output 302 to charge the battery 304 in the electric vehicle 305 .

[0118] refer to Fig.16 , a DC grid system 400 is shown.

[0119] The grid system 400 comprises a DC grid 401 to which sources 402 and sinks 403 are connected. Each source 402 and sink 403 is connected to the DC grid 401 via an electricity meter 1 and a DC-DC converter 404.

[0120] Revise

[0121] It will be appreciated that many modifications may be made to the embodiments described above. Such modifications may include equivalent and other features known in the design, manufacture and use of electricity meters and component parts thereof, and may be used instead of or in addition to features already described herein. Features of one embodiment may be replaced or supplemented by features of another embodiment.

[0122] The meter can be modified so that it does not measure voltage but only current. One of the modulators can be omitted and one of the analog-to-digital converters can be omitted. The digital computing unit can be configured to measure and output current (not power).

[0123] Although claims have been made for specific combinations of features in this application, it should be understood that the disclosure scope of this application also includes any novel features or any novel combination of features disclosed herein explicitly or implicitly, or any generalization thereof, whether or not it relates to the same invention as the invention currently claimed in any claim and whether or not it solves any or all technical problems that are the same as the technical problems solved by the present invention. The applicant hereby draws attention that new claims may be made to these features and / or combinations of these features during the litigation process of this application or any further application derived therefrom.

Claims

1. An electric meter, comprising: A converter configured to synchronously modulate a current measurement signal and a voltage measurement signal and output the synchronously modulated current measurement signal and the synchronously modulated voltage measurement signal, wherein the converter comprises: a first modulator and a second modulator configured to synchronously modulate the current measurement signal and the voltage measurement signal, respectively, and output a synchronously modulated current measurement signal and a synchronously modulated voltage measurement signal, respectively; and a measurement module configured to receive the synchronously modulated current measurement signal and the synchronously modulated voltage measurement signal from the converter and process the synchronously modulated current measurement signal and the synchronously modulated voltage measurement signal, wherein the measurement module comprises: A first analog-to-digital converter and a second analog-to-digital converter are used to digitize the synchronously modulated current measurement signal and the synchronously modulated voltage measurement signal respectively and output a digitized synchronously modulated current measurement signal and a digitized synchronously modulated voltage measurement signal.

2. The electric meter according to claim 1, wherein: The converter comprises: A source of a time varying signal for synchronously modulating the current measurement signal and the voltage measurement signal.

3. The electric meter according to claim 2, wherein: The time-varying signal has at least one component with a fixed frequency.

4. The electric meter according to claim 2, wherein: The time-varying signal has at least one component that varies in frequency.

5. The electric meter according to claim 3, wherein: The time-varying signal has at least one component that varies in frequency.

6. The electric meter according to any one of claims 2 to 5, wherein: The time varying signal is a spread spectrum signal.

7. The electric meter according to any one of claims 1 to 5, wherein: The converter is configured to not modulate at a fundamental or harmonic frequency of 50 Hz, 60 Hz, or 16.667 Hz, or 400 Hz, or to modulate at a fundamental or harmonic frequency of 50 Hz, 60 Hz, or 16.667 Hz, or 400 Hz, less than 10% of the time on average.

8. The electric meter according to any one of claims 1 to 5, wherein: The converter is configured to modulate at one or more frequencies between 1 Hz and 1 MHz.

9. The electric meter according to any one of claims 1 to 5, wherein: The converter is configured to modulate at one or more frequencies between 51 Hz and 59 Hz, between 61 Hz and 65 Hz, and / or between 67 Hz and 390 Hz.

10. The electric meter according to claim 1, wherein: The first modulator and the second modulator include a first bus switch and a second bus switch, respectively.

11. The electric meter according to claim 1, wherein: The first modulator and the second modulator include a first set of switching devices and a second set of switching devices, respectively.

12. The electric meter according to claim 11, wherein: The first modulator and the second modulator include a first group of field effect transistors and a second group of field effect transistors, respectively.

13. The electric meter according to claim 11, wherein: The first modulator and the second modulator include a first set of analog switches and a second set of analog switches, respectively.

14. The electric meter according to claim 11, wherein: The first modulator and the second modulator include a first set of four-quadrant analog multipliers and a second set of four-quadrant analog multipliers, respectively.

15. The electric meter according to claim 1, wherein: The first analog-to-digital converter and the second analog-to-digital converter are included in a single integrated circuit.

16. The electric meter according to claim 1, wherein: The measurement module comprises: A digital calculation unit is used to calculate a current value, a voltage value, a power value and / or an energy value.

17. The electric meter according to claim 16, wherein: The digital calculation unit is configured to calculate the power value by multiplying the digitized synchronously modulated current measurement signal and the digitized synchronously modulated voltage measurement signal.

18. The electric meter according to claim 16 or 17, wherein: The digital calculation unit comprises a microprocessor running a computer program to calculate the current value, the voltage value, the power value and / or the energy value.

19. The electric meter according to claim 16 or 17, wherein: The digital calculation unit includes hardware logic for calculating the current value, the voltage value, the power value and / or the energy value.

20. The electric meter according to any one of claims 1 to 5, further comprising: At least one output device for providing a current value, a voltage value, a power value and / or an energy value.

21. The electric meter according to claim 20, further comprising: A display is used to display the current value, the voltage value, the power value and / or the energy value.

22. The electric meter according to claim 20, wherein: The at least one output device comprises: A network interface is used to transmit the current value, the voltage value, the power value and / or the energy value.

23. The electric meter of claim 1, further comprising: An input terminal is used to receive the current measurement signal from a remote current sensor.

24. The electric meter of claim 23, further comprising: A current sensor is arranged to provide said current measurement signal.

25. The electric meter of claim 24, wherein: The current sensor is DC coupled to a modulator for modulating the current measurement signal.

26. The electric meter of claim 24, wherein: The remote current sensor or current sensors are shunts.

27. The electric meter of claim 26, further comprising: a first conductor and a second conductor for transferring power from a source to a load; Therein, the remote current sensor or current sensor is configured to measure a current flowing through the first conductor.

28. The electric meter of claim 26, further comprising: a first connector and a second connector for providing the current measurement signal to the shunt; as well as A modulator is directly connected to the shunt via the first connector and the second connector.

29. The electric meter of claim 28, wherein: At least one of the first connector and the second connector between the shunt and the modulator comprises the same material as the shunt.

30. An electric meter according to any one of claims 26 to 29, wherein: The shunt includes a metal alloy including copper, nickel, and manganese.

31. An electric meter according to any one of claims 26 to 29, wherein: The shunt comprises a material having a temperature coefficient of resistance of: ·At 0 and 10×10 -6 / K or between 0 and –10×10 -6 / K, or ·At 0 and 20×10 -6 / K or between 0 and –20×10 -6 / K.

32. An electric meter according to any one of claims 26 to 29, wherein: The remote current sensor or current sensors are: Hall effect current sensor; Fluxgate current sensor; Anisotropic magnetoresistive current sensor; Giant magnetoresistance current sensor; or Tunneling magnetoresistive current sensor.

33. The electric meter according to any one of claims 1 to 5, being a direct current electric meter.

34. The electric meter according to any one of claims 1 to 5, being an AC electric meter.

35. The electric meter of any one of claims 1 to 5, the electric meter complying with the ANSI standard for electric meters.

36. An electricity meter as claimed in any one of claims 1 to 5, complying with IEC standards for electricity meters.

37. The electric meter of claim 1, wherein: The first modulator and the second modulator include: one or more inputs for one or more measurement signals; a corresponding timing reference input for receiving a timing reference; a respective switch arranged to switch synchronously using said timing reference in order to chop or invert said one or more measurement signals; and One or more modulation signal outputs, respectively, for the synchronously modulated one or more measurement signals.

38. An electric meter according to any one of claims 26 to 29, wherein: The shunt comprises manganese-nickel-copper RTM.

39. A system comprising: power supply; To the output of the power dissipator; the power dissipator; as well as An electric meter as claimed in any one of claims 1 to 38, positioned in the electrical path between the power supply and the output to the power dissipator.

40. The system of claim 39, wherein the system is a photovoltaic system, wherein: The power source comprises a photovoltaic panel, and the power dissipator comprises a power distribution network, an energy storage device, or a load.

41. The system of claim 39, wherein the system is an electric vehicle charging system, The power source is a power distribution system and the power dissipator is an electric vehicle energy storage device.

42. The system according to claim 39, wherein the system is a DC grid system, wherein: The power source comprises an electrical power source or storage system, and the power dissipator is a load.

43. The system of any one of claims 39 to 42, further comprising: A dc-dc converter is placed in the electrical path between the power source and the electricity meter or between the electricity meter and the output to the power dissipator.

44. A method for capturing and processing a signal, comprising: performing current measurement and voltage measurement to generate a current measurement signal and a voltage measurement signal, respectively; as well as In an electric meter according to any one of claims 1 to 38: synchronously modulating the current measurement signal and the voltage measurement signal, and outputting the synchronously modulated current measurement signal and the synchronously modulated voltage measurement signal; as well as The synchronously modulated current measurement signal and the synchronously modulated voltage measurement signal are measured.

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