AN4121
Application note
Poly-phase demonstration kit with the STPMC1 and STPMS2
Introduction
This application note describes the poly-phase demonstration kit with the STPMC1 and
STPMS2.
The STPMC1 is a metering ASSP implemented in an advanced 0.35 µm BCD6 technology.
The STPMC1 device works as an energy calculator in power line systems utilizing a
Rogowski coil, current transformer, shunt or Hall current sensors. Used in combination with
one or more STPMS2 ICs, it implements all the functions needed in a 1-, 2- or 3-phase
energy meter, providing effective measurement of active and reactive energies, V
RMS
, I
RMS
,
instantaneous voltage and current per phase in 1-, 2- or 3-phase wye and delta services,
from 2 to 4 wires.
In a standalone configuration, the STPMC1 outputs a pulse train signal having a frequency
proportional to the cumulative active power, and it can directly drive a stepper motor,
therefore implementing a simple active energy meter.
This device can also be coupled with a microprocessor for multifunction energy meters. In
this case, measured data are read at a fixed time interval from the device internal registers
by the microcontroller through an SPI interface.
The STPMS2 is an ASSP designed to be the building block for single or multiphase energy
meters. It consists of a preamplifier and two 2
nd
order
Δ∑
modulators, band-gap voltage
reference, a low-drop voltage regulator and DC buffers in its analog section and clock
generator and output multiplexer in its digital section.
The demonstration kit is made up of a main board with the STPMC1 onboard (STEVAL-
IPE0010V1), and it can be coupled with up to 5 daughterboards, each having an STPMS2
onboard to sense the voltage and current of each phase (STEVAL-IPE0014V1).
Figure 1.
Demonstration kit block diagram
AM12798v1
N
RST
Cur r ent
S ens or
Vol t a ge
S ens or
S T PMS 2
DAS
DAR
VCC
DAR
DAS
VOT P
MON
MOP
L ED
S CS
S YN- NP
S T PMS 2
M
DAT
DAT
DAN
DAH
S T PMC1
XT AL 1
XT AL 2
VS S
S CL - NC
S DA- T D
VDD
VS S A
P1
S T PMS 2
M
November 2012
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AN4121
Contents
Contents
1
2
Application description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Circuit description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1
2.2
Motherboard circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Daughterboard circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2.1
2.2.2
2.2.3
2.2.4
Current sensing circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Anti-aliasing filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Voltage sensing circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Jumper settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.3
2.4
Clock management network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Communication with microprocessor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3
Board layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.1
3.2
3.3
Layout rules for three-phase systems design . . . . . . . . . . . . . . . . . . . . . . . 9
Motherboard layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Daughterboard layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4
Experimental results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
4.1
Three-phase energy measurement accuracy . . . . . . . . . . . . . . . . . . . . . . 12
4.1.1
4.1.2
Test with symmetrical voltages and balanced load at PF = 1 . . . . . . . . 12
Test with symmetrical voltages and balanced load at PF = 0.5
inductive and PF = 0.8 capacitive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
4.2
Typical phase energy measurement accuracy . . . . . . . . . . . . . . . . . . . . . 15
4.2.1
Test with symmetrical voltages and only one phase load at PF = 1
and PF = 0,5 inductive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Appendix A Three-phase systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
A.1
A.2
Power in three-phase AC circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Power measurement techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
A.2.1
A.2.2
A.2.3
Two-wattmeter method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Three-wattmeter method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
One-wattmeter method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Appendix B BOM list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
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Contents
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Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
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AN4121
Application description
1
Application description
Poly-phase systems, and particularly three-phase meters, are most commonly used in
practical industrial applications, and in a few cases also for domestic use.
The purpose of the STEVAL-IPE0010V1 + STEVAL-IPE0014V1 is STPMC1 and STPMS2
device demonstration but it can also be used as a starting point to design a Class 0.2
accuracy meter for power line systems from 2- to 4-wire delta or wye service.
Each phase is monitored from an independent daughterboard, in which an autonomous
power supply provides the supply to the board itself and, once it is connected, also to the
motherboard.
In this board, the STPMS2 device senses the phase current through a CT sensor, and the
phase voltage through a voltage divider. The presence of a dedicated network reduces, for a
large amount, the sampling (aliasing) noise, therefore increasing the meter precision. The
STPMS2 outputs a sigma-delta stream sent, together with supply voltage, to the STPMC1
through a card edge connector.
The motherboard receives from the daughterboards the sigma-delta streams that are further
elaborated by the STPMC1. This device, from a 4.194 MHz crystal oscillator, provides a
common clock with programmable frequency to all the daughterboards.
The motherboard, through a 10-pin flat cable connector (P1 in
Figure 2),
can be interfaced
to a microprocessor board to implement advanced metering features (multi-tariff, data
management and storage, communication…). It also has stepper motor connectors for a
simple energy meter implementation (W2, W5 in
Figure 2).
The STPMC1 board can also be interfaced to a dedicated GUI through the STPMxx parallel
programmer/reader released with the application.
Table 1.
Operating conditions
Condition
V
NOM
I
NOM
I
MAX
f
LIN
T
OP
Value
230
CT: I
NOM
= 1
CT: I
MAX
= 30
50/60 ± 10%
- 40 / +
85
Unit
V
RMS
A
RMS
A
RMS
Hz
°C
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AN4121
Circuit description
2
2.1
Circuit description
Motherboard circuit
The motherboard consists of the following sections:
●
●
STPMC1 circuitry
Connectors.
The schematic of the board is shown in
Figure 2
and in
Figure 3.
Figure 2.
VCC
STPMC1 circuitry schematics
VCC
VCC
D12
D9
D10
D11
R 60
4.7K
R 61
4.7K
R 62
4.7K
P1
2
4
6
8
10
1
3
5
7
9
R 63
4.7K
C64
10n
U8
TP2
20
19
18
17
16
15
R64
1M1%
Y1
4194.304KHz
CLK
CLK
DAN 100
DAN
DAT 100
DAT
R55
11
R56
12
14
13
LED
SDATD
SCLNLC
CLKOUT
CLKIN
SYN
VSSA
CLK
DAN
DAT
STPMC1
C61
15p
C62
15p
MON
MOP
SCS
VDD
VSS
VCC
VOTP
DAH
DAR
DAS
1
2
W2 MON
D7
3
W5 MOP
4
5
6
7
8
9
10
R16
R15
R35
100 DAH
100 DAR
100 DAS
DAH
DAR
DAS
VCC
C63
1µ
U9A
W8
GND
VCC
W34
C65
100n
1
D8
2
+
C66
1000u
ST_m74hc14
AM12744v1
CLK
1
2 NCLK
ST_m74hc14
VCC
U9G
7
14
VCC
GND
VCC
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