Low jitter pulse output for power meter
There is provided an energy consumption meter device comprising including a processor arranged to receive input data from the sampling unit. The processor calculates at a calculation step [n] an energy contribution value using ΔE using a sampled voltage value and a sampled current value. The processor will calculate an energy value E[n] using a reminder value which was calculated at a previous calculation step [n−1]. The processor will then calculate a relative delay Td′ using the threshold value, the reminder value and the energy value, and generate an output pulse at an output time tpulse which is delayed for the relative delay Td′ with respect to the calculation time step[n]. By delaying the output pulse with a value which is a closest proximity of Td, the cycle-by-cycle jitter is less or equal to the clock frequency of the timer tclk.
1. An energy consumption meter device, said device comprising:
a sampling unit arranged to sample, at a sampling frequency fout, a measured voltage value and a measured current value; and
a processor arranged to repeatedly perform on each of a plurality of calculation steps [ . . . , n−1, n, n+1, . . . ] and with a time period Tc equal to 1/fout, the following actions:
receive a sampled voltage value UAC and a sampled current value IL from said sampling unit,
calculate an energy contribution value ΔE using formula:
Δ E=UAC*IL* 1/ Tc,
calculate an energy value E[n] using formula:
E[n]=E[n− 1]+Δ E,
with E[n−1] being a reminder value which was calculated at a previous calculation step,
test if said energy value E[n], is lower than −1*Th or if said energy value E[n] is higher than +1*Th, with Th being a positive constant threshold value equal to a difference between two predefined adjacent energy levels, and if so:
calculate a relative delay Td′ using said threshold value, said reminder value and said energy value,
generate an output pulse at an output time tpulse which is delayed for said relative delay Td′ with respect to a present calculation step [n], and
update said reminder value E[n−1] as follows:
E[n− 1]= E[n]+Th , if E[n]<− 1* Th , or a)
E[n− 1]= E[n]−Th , if E[n]>+ 1* Th; b)
and if not so:
set said reminder value E[n−1] to said energy value E[n],
wherein the processor is further arranged to:
initiate a timer value at said present calculation step [n],
increment said timer value with a timer clock frequency fclk which is larger than said sampling frequency fout, and
generate said output pulse once said timer value is equal or higher than Td′/Tclk.
2. An energy consumption meter device according to claim 1 , wherein said timer clock frequency fclk is larger than 100 times said sampling frequency fout.
3. An energy consumption meter device according to claim 2 , wherein said timer clock frequency fclk is larger than 1000 times said sampling frequency fout.
4. An energy consumption meter device according to claim 1 , wherein said processor ( 8 ) is arranged to calculate said relative delay Td′ using an approximation or interpolation method based on k+1 state variables obtained in previous k+1 calculation steps: [n] . . . [n−k], with n, k being integer values.
5. An energy consumption meter device according to claim 1 , wherein said processor is arranged to calculate the relative delay Td′ using a first-order linear approximation method and wherein
Td
′
=
T
c
Th
-
E
[
n
-
1
]
E
[
n
]
-
E
[
n
-
1
]
with
Td′ being said relative delay,
Tc being said calculation time period,
Th being said threshold value,
E[n−1] being said reminder value,
E[n] being the energy value in step [n].
6. An energy consumption meter device according to claim 1 , wherein said processor comprises:
a first pulse generator arranged to:
receive said sampled voltage value UAC and said sampled current value IL from said sampling unit;
calculate said energy contribution value ΔE using said sampled voltage value and said sampled current value;
calculate said energy value E[n] by adding said energy contribution value ΔE to said reminder value E[n−1], said reminder value being calculated in a previous calculation step;
create a trigger if said energy value E[n] is either smaller than −1*Th or higher than +1*Th, with Th being a positive constant threshold value equal to a difference between two predefined adjacent energy levels;
a time difference extractor arranged to:
receive said trigger from said first pulse generator;
receive said threshold value, said reminder value and said energy value from said first pulse generator;
calculate a relative delay Td′ using said threshold value, said reminder value and said energy value;
a second pulse generator arranged to:
receive said trigger from said first pulse generator;
receive said relative delay Td′ from said time difference extractor;
generate said output pulse which is delayed relative to a receipt time of the trigger for a time period equal to said relative delay Td′.
7. Method of a generating a pulse, said pulse being indicative for an amount of energy consumption, said method comprising:
receiving a sampled voltage value UAC and a sampled current value IL from a sampling unit at a sampling frequency fout, in which a time period Tc equals 1/fout;
calculating an energy contribution value ΔE using formula:
Δ E=UAC*IL* 1/ Tc;
calculating an energy value E[n] using formula:
E[n]=E[n− 1]+Δ E,
with E[n−1] being a reminder value which was calculated at a previous calculation step;
testing if said energy value E[n], is lower than −1*Th or if said energy value E[n] is higher than +1*Th, with Th being a positive constant threshold value equal to a difference between two predefined adjacent energy levels, and if so:
calculating a relative delay Td′ using said threshold value, said reminder value and said energy value, and
generating an output pulse at an output time tpulse which is delayed for said relative delay Td′ with respect to a present calculation step [n], and
updating said reminder value E[n−1] as follows:
E[n− 1]= E[n]+Th , if E[n]<− 1* Th , or a)
E[n− 1]= E[n]−Th , if E[n]>+ 1* Th; b)
and if not so:
setting said reminder value E[n−1] to said energy value E[n],
wherein the method further comprises:
initiating a timer value at said present calculation step [n];
incrementing said timer value with a timer clock frequency fclk which is larger than said sampling frequency fout;
generating said output pulse once said timer value is equal or higher than Td′/Tclk.
8. Method of a generating a pulse according to claim 7 , wherein said timer clock frequency fclk is larger than 100 times said sampling frequency fout.
9. Method of a generating a pulse according to claim 7 , wherein said timer clock frequency fclk is larger than 1000 times said sampling frequency fout.
10. Method of a generating a pulse according to claim 7 , wherein said calculating of said relative delay Td′ comprises using an approximation or interpolation method based on k+1 state variables obtained in previous k+1 calculation steps: [n] . . . [n−k], with n, k being integer values.
11. Method of a generating a pulse according to claim 7 , wherein said calculating of said relative delay Td′ is performed by using a first-order linear approximation method and wherein
Td
′
=
T
c
Th
-
E
[
n
-
1
]
E
[
n
]
-
E
[
n
-
1
]
with
Td′ being said relative delay,
Tc being said calculation time period,
Th being said threshold value,
E[n−1] being said reminder value,
E[n] being the energy value in step [n].