[Nut-upsdev] [PATCH 3/3] OpenUPS: fix current calculations
Russell King
rmk at armlinux.org.uk
Sun Feb 4 00:19:56 UTC 2018
Monitoring the input and output currents reported through upsc for an
OpenUPS device suggests that it is an energy creation device - the
power out is greater than the power into the system once the battery
is fully charged.
Analysis and measurement reveals several issues:
1. "UPS.PowerStatus.Output.Current" is scaled for NUTs "output.current"
value, which should be the output current from the UPS.
However, the value reported for "UPS.PowerStatus.Output.Current" is
not the output from the UPS terminals to the load, but is the
current into the LTC3780 buck-boost converter on the output. The
evidence for this is that with a known constant load, the current
reported is dependent on whether we are using battery voltage or
input voltage, and varies as one would expect if it were reporting
the current supplied to the LTC3780.
2. "UPS.PowerStatus.Input.Current" is scaled for NUTs "input.current"
value, which should be the input current to the UPS.
The value reported for "UPS.PowerStatus.Input.Current" follows and
matches the current supplied to the battery while charging is taking
place, whether bulk charging or floating.
In order to fix these issues, the general principle of switch mode
power conversion is employed:
Power out = Power in * Efficiency (where Efficiency is between 0..1)
The fix for "output.current" involves knowing whether the UPS was
powered from the battery or the input voltage (which is the voltage
fed to the LTC3780), calculating the power into the LTC3780 converter,
and using the above equation to refer it to the output.
Fixing "input.current" requires a similar process, except in reverse.
We calculate the power being supplied into the battery, and refer that
back to the input terminals, remembering to sum the current draw from
the LTC3780.
---
drivers/openups-hid.c | 100 ++++++++++++++++++++++++++++++++++++--------------
1 file changed, 73 insertions(+), 27 deletions(-)
diff --git a/drivers/openups-hid.c b/drivers/openups-hid.c
index 6bd00b6..30e9f26 100644
--- a/drivers/openups-hid.c
+++ b/drivers/openups-hid.c
@@ -42,6 +42,8 @@ static double vin_scale = 1;
static double vout_scale= 1;
static double ccharge_scale = 1;
static double cdischarge_scale = 1;
+static double v_in, v_bat, v_out, i_ltc;
+static int on_input;
static char openups_scratch_buf[20];
@@ -129,9 +131,9 @@ static const char *openups_off_fun(double value);
static const char *openups_scale_vin_fun(double value);
static const char *openups_scale_vout_fun(double value);
-/* static const char *openups_scale_vbat_fun(double value); */
-static const char *openups_scale_ccharge_fun(double value);
-static const char *openups_scale_cdischarge_fun(double value);
+static const char *openups_scale_vbat_fun(double value);
+static const char *openups_scale_input_current_fun(double value);
+static const char *openups_scale_output_current_fun(double value);
static const char *openups_temperature_fun(double value);
static info_lkp_t openups_charging_info[] = {
@@ -162,16 +164,16 @@ static info_lkp_t openups_vout_info[] = {
{0, NULL, openups_scale_vout_fun}
};
-/* static info_lkp_t openups_vbat_info[] = {
+static info_lkp_t openups_vbat_info[] = {
{0, NULL, openups_scale_vbat_fun}
-};*/
+};
-static info_lkp_t openups_ccharge_info[] = {
- {0, NULL, openups_scale_ccharge_fun}
+static info_lkp_t openups_input_current_info[] = {
+ {0, NULL, openups_scale_input_current_fun}
};
-static info_lkp_t openups_cdischarge_info[] = {
- {0, NULL, openups_scale_cdischarge_fun}
+static info_lkp_t openups_output_current_info[] = {
+ {0, NULL, openups_scale_output_current_fun}
};
static info_lkp_t openups_temperature_info[] = {
@@ -190,6 +192,8 @@ static const char *openups_discharging_fun(double value)
static const char *openups_online_fun(double value)
{
+ /* Save charging status for input current calculation */
+ on_input = value != 0;
return value ? "online" : "!online";
}
@@ -205,31 +209,65 @@ static const char *openups_off_fun(double value)
static const char *openups_scale_vin_fun(double value)
{
- snprintf(openups_scratch_buf, sizeof(openups_scratch_buf), "%.2f", value * vin_scale);
+ /* Save v_in for input current calculation */
+ v_in = value * vin_scale;
+ snprintf(openups_scratch_buf, sizeof(openups_scratch_buf), "%.2f", v_in);
return openups_scratch_buf;
}
static const char *openups_scale_vout_fun(double value)
{
- snprintf(openups_scratch_buf, sizeof(openups_scratch_buf), "%.2f", value * vout_scale);
+ v_out = value * vout_scale;
+ snprintf(openups_scratch_buf, sizeof(openups_scratch_buf), "%.2f", v_out);
return openups_scratch_buf;
}
-/* static const char *openups_scale_vbat_fun(double value)
+static const char *openups_scale_vbat_fun(double value)
{
- snprintf(openups_scratch_buf, sizeof(openups_scratch_buf), "%.2f", value * vbat_scale);
+ /* Save v_bat for input current calculation */
+ v_bat = value;
+ snprintf(openups_scratch_buf, sizeof(openups_scratch_buf), "%.2f", value);
return openups_scratch_buf;
-}*/
+}
-static const char *openups_scale_ccharge_fun(double value)
+/* Input.Current is not the line in current but seems to be the charge
+ * current into the battery terminals. The real line input current is
+ * determined from the charger power plus the current fed to the LTC3780
+ * buck/boost.
+ */
+static const char *openups_scale_input_current_fun(double value)
{
- snprintf(openups_scratch_buf, sizeof(openups_scratch_buf), "%.3f", value * ccharge_scale);
+ double i_in;
+
+ if (on_input && v_in != 0)
+ i_in = (v_bat * value * ccharge_scale) / (v_in * .9) + i_ltc;
+ else
+ i_in = 0;
+
+ snprintf(openups_scratch_buf, sizeof(openups_scratch_buf), "%.3f", i_in);
return openups_scratch_buf;
}
-static const char *openups_scale_cdischarge_fun(double value)
+/* Output.Current is not the current flowing out of the terminals of the
+ * board, but is the current flowing into the LTC3780 buck/boost converter.
+ * Hence, in order to calculate the output current, we need to calculate the
+ * power into the LTC3780, take account of its efficiency, and then calculate
+ * the output current.
+ */
+static const char *openups_scale_output_current_fun(double value)
{
- snprintf(openups_scratch_buf, sizeof(openups_scratch_buf), "%.3f", value * cdischarge_scale);
+ double v_ltc, i_out;
+
+ /* Voltage supplied to the LTC3780 */
+ v_ltc = on_input ? v_in : v_bat;
+
+ /* Current drawn by the LTC3780, save for input current calculation */
+ i_ltc = value * cdischarge_scale;
+
+ /* Output current = Power-in * Efficiency / Vout */
+ i_out = v_ltc * i_ltc * .965 / v_out;
+
+ snprintf(openups_scratch_buf, sizeof(openups_scratch_buf), "%.3f", i_out);
return openups_scratch_buf;
}
@@ -304,7 +342,7 @@ static hid_info_t openups_hid2nut[] = {
/* Battery */
{"battery.type", 0, 0, "UPS.PowerSummary.iDeviceChemistry", NULL, "%s", HU_FLAG_STATIC, stringid_conversion},
{"battery.mfr.date", 0, 0, "UPS.PowerSummary.iOEMInformation", NULL, "%s", HU_FLAG_STATIC, stringid_conversion},
- {"battery.voltage", 0, 0, "UPS.PowerSummary.Voltage", NULL, "%.2f", HU_FLAG_QUICK_POLL, NULL},
+ {"battery.voltage", 0, 0, "UPS.PowerSummary.Voltage", NULL, NULL, HU_FLAG_QUICK_POLL, openups_vbat_info },
/* { "battery.voltage.nominal", 0, 0, "UPS.PowerSummary.ConfigVoltage", NULL, NULL, HU_FLAG_QUICK_POLL, openups_vbat_info }, */
{"battery.current", 0, 0, "UPS.PowerSummary.Current", NULL, "%.3f", HU_FLAG_QUICK_POLL, NULL},
{"battery.capacity", 0, 0, "UPS.PowerSummary.DesignCapacity", NULL, "%.0f", HU_FLAG_STATIC, NULL},
@@ -320,14 +358,6 @@ static hid_info_t openups_hid2nut[] = {
{"battery.cell5.voltage", 0, 0, "UPS.PowerSummary.Battery.Cell5", NULL, NULL, HU_FLAG_QUICK_POLL, openups_vbat_info},
{"battery.cell6.voltage", 0, 0, "UPS.PowerSummary.Battery.Cell6", NULL, NULL, HU_FLAG_QUICK_POLL, openups_vbat_info},
*/
- /* Output */
- {"output.voltage", 0, 0, "UPS.PowerSummary.Output.Voltage", NULL, NULL, HU_FLAG_QUICK_POLL, openups_vout_info},
- {"output.current", 0, 0, "UPS.PowerSummary.Output.Current", NULL, NULL, HU_FLAG_QUICK_POLL, openups_cdischarge_info},
-
- /* Input */
- {"input.voltage", 0, 0, "UPS.PowerSummary.Input.Voltage", NULL, NULL, HU_FLAG_QUICK_POLL, openups_vin_info},
- {"input.current", 0, 0, "UPS.PowerSummary.Input.Current", NULL, NULL, HU_FLAG_QUICK_POLL, openups_ccharge_info},
-
/* Status */
{"BOOL", 0, 0, "UPS.PowerSummary.PresentStatus.Good", NULL, NULL, HU_FLAG_QUICK_POLL, openups_off_info},
{"BOOL", 0, 0, "UPS.PowerSummary.PresentStatus.InternalFailure", NULL, NULL, HU_FLAG_QUICK_POLL, commfault_info},
@@ -342,6 +372,22 @@ static hid_info_t openups_hid2nut[] = {
{"BOOL", 0, 0, "UPS.PowerSummary.PresentStatus.ACPresent", NULL, NULL, HU_FLAG_QUICK_POLL, openups_online_info},
{"BOOL", 0, 0, "UPS.PowerSummary.PresentStatus.BatteryPresent", NULL, NULL, HU_FLAG_QUICK_POLL, openups_nobattery_info},
+ /* Output/Input voltages */
+ {"output.voltage", 0, 0, "UPS.PowerSummary.Output.Voltage", NULL, NULL, HU_FLAG_QUICK_POLL, openups_vout_info},
+ {"input.voltage", 0, 0, "UPS.PowerSummary.Input.Voltage", NULL, NULL, HU_FLAG_QUICK_POLL, openups_vin_info},
+
+
+ /* Output/Input currents */
+ /* UPS.PowerSummary.PresentStatus.ACPresent, UPS.PowerSummary.Voltage,
+ * and UPS.PowerSummary.Output.Voltage must precede this.
+ */
+ {"output.current", 0, 0, "UPS.PowerSummary.Output.Current", NULL, NULL, HU_FLAG_QUICK_POLL, openups_output_current_info},
+ /* UPS.PowerSummary.PresentStatus.ACPresent, UPS.PowerSummary.Voltage,
+ * UPS.PowerSummary.Output.Current, and
+ * UPS.PowerSummary.Input.Voltage must precede this.
+ */
+ {"input.current", 0, 0, "UPS.PowerSummary.Input.Current", NULL, NULL, HU_FLAG_QUICK_POLL, openups_input_current_info},
+
/* end of structure. */
{NULL, 0, 0, NULL, NULL, NULL, 0, NULL}
};
--
2.7.4
--
Russell King
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