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Changes for page 3.4 Battery parameters

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61 61  
62 62  The SOC calculation algorithm “Current and voltage (enhanced)” differs from the simplified algorithm by online correction of effective capacitance. When using this algorithm, it is necessary to fine tune the tabular dependence Uocv = Uocv (SOC, t °C).
63 63  
64 -== 3.4.3 SOC correction ==
64 +== 3.4.3 Cell resistance estimation ==
65 65  
66 +Calculation of the resistance of cells is carried out in two ways. The first method is used when the battery passes from a relaxation state to a charge or discharge state, wherein the cell resistance value
67 +
68 +R = (U-Uocv) / Istable,
69 +
70 +where U is the cell voltage measured in the charge or discharge state, V; Uocv is the cell voltage measured in the state of relaxation (before switching to the state of charge or discharge); Istable – stabilized current through the cell in the state of charge or discharge.
71 +
72 +The second method is used for a stepwise change in the current through the cell, while the value of the cell resistance:
73 +
74 +R = (U,,2,,-U,,1,,) / (I,,stable2,,-I,,stable1,,) provided that | I,,stable2,,-I,,stable1,, | > 0.2 × Q,,max,,
75 +
76 +(Q,,max,, is the maximum cell capacity),
77 +
78 +where U,,2,, is the voltage on the cell at the moment when the stabilized current I,,stable2,, is flowing through it; U,,1,, – the voltage on the cell at the moment when the stabilized current I,,stable1,, flowing through it.
79 +
80 +The stabilized current I,,stable,, = I, if during the stabilization time the instantaneous current I is in the range from 0.95 × I to 1.05 × I.
81 +
82 +To change parameters of the algorithm for calculating the cell resistance, select the menu "Cells → Cell resistance estimation":
83 +
84 +[[Cell resistance estimation settings>>image:1732207338609-903.png||data-xwiki-image-style-alignment="center" height="187" width="337"]]
85 +
86 +In this section:
87 +
88 +* Current stabilization time, second;
89 +* Maximum estimation period – maximum time between resistance measurements. If more time has elapsed since the last determination of the stabilized current Istable than is determined in this field, the resistance calculation is not performed, second;
90 +* Maximum resistance factor – the coefficient of calculation of the maximum acceptable resistance of the cell;
91 +* Minimum SOC – minimum cell SOC value for resistance calculation;
92 +* Maximum SOC – maximum cell SOC value for resistance calculation.
93 +
94 +The calculated resistance is accepted by the system as valid (and therefore updated) if its value is in the range from Resistance/2 to “Maximum resistance factor” × Resistance, where "Resistance" is the nominal resistance of the cell (see section Cell defaults). If the calculated resistance value is greater than the value (Maximum resistance factor × Resistance), the updated resistance value will be equal to the value (Maximum resistance factor × Resistance).
95 +
96 +== 3.4.4 Cell balancing ==
97 +
98 +The BMS Main 2.x supports two cell balancing algorithms:
99 +
100 +* balancing stacks individually;
101 +* balancing the entire battery (used by default).
102 +
103 +Balancing stacks individually balances the voltage within a group of cells that are connected to the same BMS Logic board. **It is not recommended to use this algorithm in typical battery designs**.
104 +
105 +Balancing the entire battery makes the voltage of all cells be equal to the minimum cell voltage.
106 +
107 +The following balancing rules are supported:
108 +
109 +* only when the battery is charging (current I > 0);
110 +* when the battery is charging (current I > 0) or when the battery is in a state of relaxation;
111 +* always (regardless of battery state).
112 +
113 +A balancing resistor is connected to the cell if:
114 +
115 +* the voltage on the cell is higher than the starting voltage of the balancing;
116 +* the difference between the cell voltage and the minimum voltage among the cells of the battery is greater than the balancing threshold.
117 +
118 +If the BMS Logic board overheats, then the balancing of the cells connected to this board will not be performed (see Logic high temperature protection).
119 +
120 +To change the cell balancing parameters, select the menu "Cell → Cell balancing":
121 +
122 +[[Cell balancing settings>>image:1732207485773-804.png||data-xwiki-image-style-alignment="center" height="264" width="387"]]
123 +
124 +In this section:
125 +
126 +* Enable – a flag to enable cell balancing;
127 +* Algorithm – a balancing algorithm:
128 +** Balancing stacks individually;
129 +** Balancing the entire battery;
130 +* Constrain (rule):
131 +** Charging;
132 +** Charging or relaxed;
133 +** Always (regardless of battery state);
134 +* Minimum cell voltage to start balancing, V;
135 +* Balancing threshold, V;
136 +* Start cell discharging – a command to start forced balancing of all battery cells (used for service purposes);
137 +* Stop cell discharging – a command to stop forced balancing of all battery cells (used for service purposes).
138 +
139 +== 3.4.5 Series balancing ==
140 +
141 +The BMS Main 2.x board supports work with two independent (galvanically unrelated) cell series. To monitor the status of two series, two current sensors are used: primary and secondary (AUX). A series of cells must be equivalent: they must have the same number of cells and the same capacity.
142 +
143 +Since the series of cells can operate at different loads, they must be balanced. For this, the BMS Main 2.x provides two relays: “Balancing series 1” and “Balancing series 2” (see section Configuration of output discrete signals and relays), as well as a combined algorithm that considers both the voltage of each series and the charge that these series gave load. “Balancing series 1” and “Balancing series 2” relays are used to connect high-power balancing resistors in parallel with cells series 1 and 2.
144 +
145 +When charging the battery, balancing is performed based on the voltage of the series. A balancing resistor is connected to the cell series if:
146 +
147 +* the series voltage is higher than the starting voltage of the balancing;
148 +* the difference between the voltage of a series of cells and the minimum voltage among the battery series is greater than the balancing threshold.
149 +
150 +When the battery is discharging (work on load), balancing is turned on if one of the series gives the load a charge (Ah), which is more by the amount Qthr of the charge given off by another series.
151 +
152 +To change the series balancing parameters, select the menu "Cell → Series balancing":
153 +
154 +[[Series balancing settings>>image:1732207584941-447.png||data-xwiki-image-style-alignment="center" height="258" width="438"]]
155 +
156 +In this section:
157 +
158 +* Enable – a flag to enable series balancing;
159 +* Number of BMS Logic boards in a series;
160 +* Minimum series voltage to start balancing, V;
161 +* Balancing threshold, V;
162 +* Coulomb threshold – the difference of the charges Qthr, given by a series of cells, above which balancing to be started, Ah;
163 +* Period – period to reset of charge counters for each series (to avoid accumulation of error), second.
164 +
165 +== 3.4.6 Cell analysis ==
166 +
167 +Discharge characteristics of the battery – the dependence Uocv = Uocv (DOD) – is used to determine the tabular dependence Uocv = Uocv (SOC, t °C) (see section Calculating the state of charge (SOC)), which is necessary for calculating the state of charge of the battery.
168 +
169 +The BMS Main 2.x board can automatically determine the battery discharge characteristic.
170 +
171 +Before starting the process of determining the discharge characteristic, it is necessary to prepare a BMS:
172 +
173 +1. Charge the battery.
174 +1. Connect a contactor to the discharging relay which switches the resistive load to the battery.
175 +1. Connect a resistive load to the contactor, which will provide a discharge current of 0.5C (where C is the cell capacitance).
176 +
177 +To configure parameters for determining the discharge characteristic of the battery, select the menu "Cells → Cell analysis":
178 +
179 +[[Cell analysis section>>image:1732207696322-587.png||data-xwiki-image-style-alignment="center" height="213" width="258"]]
180 +
181 +== SOC correction ==
182 +
66 66  The BMS Main 2.x board can recalculate the battery SOC after long-term storage or after long-term working in the case when the battery was not charged fully or discharged totally. Recalculation is done based on the tabular dependency Uocv = Uocv (SOC, t) (see section Calculating the state of charge (SOC)).
67 67  
68 68  To configure parameters for periodically correcting the battery state of charge, select the menu "Cells → SOC correction":
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69 69  
70 70  [[SOC correction settings>>image:1732206262509-786.png||data-xwiki-image-style-alignment="center" height="291" width="298"]]
71 71  
189 + In this section:
190 +
191 +* Enable – a flag to enable SOC correction;
192 +* Shutdown period – a time the battery is off, day. If the BMS detects on its startup that it was off during the “Shutdown period” time, the BMS recalculates the battery state of charge base on the tabular dependency Uocv = Uocv (SOC, t);
193 +* Correction period – a period of correcting the battery SOC, day. If the BMS detects that the last correction was more than the “Correction period” ago, the BMS recalculates the battery state of charge base on the tabular dependency Uocv = Uocv (SOC, t) and tunes it gradually during the “SOC change time”;
194 +* SOC change time – a duration of the linear changing the battery SOC to the value calculated by the correction algorithm, minute.
195 +
72 72  
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