Design of a Calibration Board Integrated in a Smart Electrical Energy Meter

Abstract

We present in this paper, the design of a calibration board integrated into a Smart Electrical Energy Meter (SEEM). Indeed, we proposed a method to calibrate remotely and onsite the SEEM, where the meter is self-calibrated based on a current reference value and a voltage reference value. These references should be generated by an integrated power source. So we included in the calibration board a converter and an AC load. The converter is used to convert the voltage coming from the electrical network, which can vary, to a reference voltage which is stable and known, while the AC load is used to set the current value. The designed converter is an AC-DC-AC type, called indirect converter. To control the DC-AC block switches we used a digital technique based on the feed-forward technique. Our design of the AC-AC converter is validated by a simulation on MATLAB where we show for a variable input voltage around a nominal value, the output voltage remains stable with a very low Total Harmonic Distortion (THD).

Existing System

Advanced instrument for field calibration of electrical energy meters.

Proposed System

The smart meters are more and more in developing. The researchers implement more options and functionalities in this kind of instruments, in order to facilitate some processes or to resolve some problems. In our case we attempt to integrate the calibration process, and perform it remotely from the central. The aim issue was to have a reference for the calibration of the smart meter, because when we want to calibrate the meter we cannot know exactly how much is voltage value of the electrical line, and if we use this voltage as reference we cannot be sure that the value measured by the meter corresponds to the reference value. For this reason, we developed a calibration board integrated in the smart electrical energy meter. In this board the main elements are the ACAC converter and the AC load. In this paper we detailed the study to design the AC-AC converter. This element is an indirect converter which is based on an AC-DC converter in cascade with Voltage Source Inverter. The AC-AC converter aim is to generate a stable AC voltage at the output, used as reference, regardless the variation of the voltage electrical line. To compensate the variations of the AC voltage input we used a digital control based on the feed-forward technique. This controller must generate the PWM signal based on the unipolar PWM technique, taking into account the variations of the AC voltage input. For the AC load, we used a linear inductive load that consumes a known current which is used as reference and create a delay between the current and the voltage, in order to compensate the phase shift added by the measurement system. The converter is verified by a simulation on MATLAB Simulink. As results, we have proved that even if the AC voltage input vary the AC voltage output reach stable. Moreover, the low THD prove that the waveforms of the current and the voltage are almost sinusoidal. The structure of the smart electrical energy meter is presented. We added a calibration board into the meter to calibrate it remotely. The calibration board structure is shown in figure 2. It contains several elements, which we quote: (i) The AC-AC converter: With this element we generate a known and stable AC voltage. (ii) The AC load: This element is used to consumes a known AC current and create a phase shift between the voltage and the current. This phase shift is necessary to compensate the phase shit that can be added by the system of measure. (iii) Two relays: These elements used to switch the signal. The operation of the calibration board as well as the calibration method are detailed in the paper.

Architecture

Block diagram of the SEEM

Block diagram of the AC-AC converter

Design of the AC-AC converter