RU2689401C1 - Method of providing autonomous power supply - Google Patents

Abstract

FIELD: electrical engineering.SUBSTANCE: invention relates to electrical engineering and can be used in creation and operation of autonomous power supply systems of various objects, including during creation and operation of onboard power supply systems of spacecrafts. Method of autonomous power supply provision includes coordination of solar and accumulator battery operation with number of accumulators providing its minimum working discharge voltage exceeding voltage in working point at end of solar battery resource, wherein the nominal mode most optimal for the power supply system is stored during the entire service life of the solar and accumulator batteries by means of bypassing the failed battery in the accumulator battery by a bypass switch and then connecting one of the backup accumulators to the accumulator battery via a serial bypass switch.EFFECT: improving reliability and resource of operation of the power supply system of an object, while maintaining high energy characteristics and stabilizing voltage on the load.1 cl, 2 dwg

Description

Purpose

The invention relates to the electrical industry and can be used in the creation and operation of autonomous power supply systems of various objects, including the creation and operation of onboard power supply systems (BOT) spacecraft (SC).

The level of technology

Modern technology, among others, has set itself the task of increasing the duration of the active existence of the object being created with autonomous power supply. Spacecraft occupy a special place in a number of these objects. Today, the lifetime of a spacecraft, determined by the nominal time of operation, reaches 7-10 years and the task is to increase it to 15 years. Among the systems of modern spacecraft, in fact, determining the duration of active life of spacecraft, first of all, the ESS spacecraft. The design and characteristics of the BOT largely determine the structural appearance, the lifetime of the spacecraft in flight, its functionality, reliability, weight and size, and economic indicators, up to 25% of the mass, volume and cost of the spacecraft (see Tarasov BC active existence for a small spacecraft ". Specialty 05.09.03. Electrotechnical complexes and systems." National Research University "MEI", 2015). Therefore, the problem of improving the technical characteristics of the BOT KA is of current importance. In BOT modern spacecraft as the primary energy sources are used solar panels (SB), in which solar energy is converted into electrical energy by photoelectric converters, and allows you to provide power to all devices KA, as well as charging secondary power sources - electrical energy storage in the form of batteries (AB), which is one of the most critical link in the EPC. AB supplies power to spacecraft devices mainly in shadow areas arising due to periodic spacecraft passing shadow areas of the orbit shaded from the Sun by the Earth or areas partially shaded from the Sun by the Moon, as well as in emergency modes at the moment of loss of orientation to the Sun and in abnormal modes when there is a lack or absence of solar power to power all connected consumers, for example, when peak loads are turned on, when spacecraft maneuvers for orbit correction, at spacecraft inputs and outputs from orbit shadow segments .

A disadvantage of the known various methods and devices for powering a spacecraft from solar batteries and batteries, which stabilize the constant voltage on the load (see, for example, patent RF, No. 2396666), is the redundancy of the same type of functional units, which reduces the specific energy (power) characteristics of the power supply system and, in addition, they have a common drawback - they are not universal, as well as the lack of multifunctionality, which limits the scope of their use. It is known that the power supply system with a single DC power supply bus with one or two voltage ratings, for example, 27 V, or 27 V and 40 V, or 27 V and 100 V, is used to power various hardware of a specific spacecraft. on the other, the development of a new power supply system with cardinal processing of current sources - solar and rechargeable batteries and with corresponding time and financial costs is required.

For space technology, the most important tactical and technical characteristic of the BOT KA is the power density, i.e. the ratio of the power generated by the power supply system to its mass, which depends primarily on the specific mass characteristics of the current sources used, but also to a large extent on the adopted block diagram of the BOT, formed by the complex of electronic equipment of the BOT, which determines the operating modes of the sources and the efficiency of their use potential opportunities.

The closest to the proposed invention, in which there is a solution to the problems of universality and increasing the specific energy characteristics of the power supply system of the spacecraft, as well as solving the problem of optimizing the parameters of the SB and AB, is the "Power supply method of a spacecraft" (patent of the Russian Federation No. 2488911 from 02.10.2016 G.), taken by the authors for the prototype.

In this method of powering the spacecraft, the tasks are solved by powering the spacecraft from a primary source of limited power, a solar battery and secondary sources of electricity, batteries connected in parallel to the solar battery in the same polarity through a serial converter in the direction of discharge current flow, which is to stabilize the load voltage with several voltage ratings and coordination of the work of the primary and secondary electrical sources energy, the voltage of the primary and secondary sources of electricity are converted into AC and transformed into the required output voltage, without the need for switching on and off stabilized voltage converters and the presence of an individual stabilized voltage converter in the discharge circuit of the battery (one common stabilized voltage converter is used) , which allows to increase the specific energy characteristics of the power supply system of the spacecraft.

The common stabilized voltage converter is made in the form of a bridge inverter with a common transformer with n output windings, and the input of the charger is connected to one of the output windings of the transformer, while the other (n-1) output windings of the transformer are connected nominal output voltage, the solar battery is chosen with an output voltage at the operating point at the end of the resource based on the relationship:

Where

Usb - output voltage at the operating point at the end of the resource SB, V;

Uel is the voltage of one phototransducer at the working point at the end of the solar battery resource, V;

m is the number (permissible) of failed photovoltaic devices in one series circuit;

Δsusch - the magnitude of an insignificant reduction in voltage due to the failure of individual photovoltaic cells, any sequential circuit of photovoltaic cells relative to fully intact circuits,%.

A Lithium-based rechargeable battery is used, and the rechargeable battery is selected with the number of batteries in a series circuit based on the relationship:

Where

N is the number of batteries in the serial circuit AB;

Rteni - the maximum power consumption of the load during the period of passage of the “shadow” segment of the orbit, At⋅ h;

Sak - the capacity of the selected battery, ⋅h;

Uak cf - average discharge voltage of the battery, V;

w is the number (permissible) of failed batteries in a series of batteries of an AB battery, i.e. w is equal to the number of backup batteries in AB.

AB on the basis of Li, i.e. lithium-ion or lithium-polymer AB, differ from each other in the type of electrolyte used (hereinafter - lithium AB), which, unlike, for example, from nickel-hydrogen do not require special preventive autonomous work. Manufacturing technology of lithium AB are in development today and are constantly improving. Recently developed lithium batteries in a number of countries with a space program, compared with other types of batteries (for example, nickel-hydrogen, nickel-cadmium, nickel-metal hydride) have significant advantages in their specific energy characteristics (exceed them in 2- 3 times), high voltage on the element, low self-discharge, very good operation time and environmental cleanliness, as well as ease of charge and operation. The specific energy of lithium batteries can reach 130 or more Wh / kg, and the efficiency of energy - 95%.

For a lithium-ion battery (unit cell voltage) varies within the following limits (see "Power for a cold climate: cold-resistant lithium-polymer batteries from EEMB". Electronics News, No. 4, 2016):

- nominal voltage value - 3.6 ... 3.7 V;

- maximum (charged) - 4.2 V;

- minimum (taking into account the optimal allowable value) - 2.5 ... 3.0 V;

- the average discharge voltage of the battery Uakk cf = 3.1 V.

The power supply system of the prototype operates in the following main modes.

1. Power loads from SAT.

In the presence of solar power, exceeding the total power consumed by the loads, the stabilized voltage converter maintains a stable voltage on the load (electrical consumer). At the same time, a stable constant and alternating voltage is automatically maintained on the consumers of electric energy with regard to the transformation ratios of the windings. If it is necessary to charge an AB, the magnitude of its charging current is limited within the difference between the current power of the solar battery and the total power of the loads.

2. Food load from AB.

The mode is formed when there is a shortage or absence of power S to power all connected consumers, for example, when switching on peak loads, during spacecraft maneuvers for orbit correction, at spacecraft inputs and outputs from the shadow orbit areas or when the spacecraft is in the shadow orbit area.

In this mode, the voltage at the input of the stabilized voltage converter decreases to the operating point of the SAT at the end of the resource, and the power required for supplying the loads from the SAT is added by discharging the AB, which is connected in parallel to the solar battery through serial-type converters in the discharge current direction, and the discharge is AB carried out in two stages: first, the voltage at the output of the serial converters stabilizes, equal to the voltage at the operating point of the SAT at the end of the resource, and then this voltage is is formed into alternating and transformed into the required output voltage, while ABs are selected with a minimum discharge voltage not less than the voltage at the working point of the solar battery, and the discharge depth AB (minimum discharge voltage) is not allowed below the specified limit value (see patents, RF, No. 2510105, No. 2521538).

Optimization of SB by voltage, AB - by the number of batteries in a series circuit in accordance with expressions (1, 2) allows to increase the reliability of the BOT KA in the event of failure of m photoconverters in one series SB and / or w batteries in a series AB battery circuit, however In the prototype, there are drawbacks leading to a decrease in the reliability of operation of the solar electronic system and, as a result, to a decrease in the survivability of the spacecraft and its lifetime:

- w backup batteries in the battery’s sequential battery circuit are constantly “in working” condition when the battery is charged and discharged (the charging and discharge current of the battery flows through them), which significantly reduces their service life until they become main batteries (until the moment when the failed batteries are removed from the battery) );

- because in order to ensure the efficiency of the power transistor switch of a series-type converter, it is necessary to fulfill the condition under which the absolute value of the voltage at the operating point of the SB at the end of the resource | Ucb | must exceed the absolute value of the voltage AB | Uab |, i.e.

then due to the change in voltage of the battery (Uab) over a wide range from the maximum value in the presence of w backup batteries in the battery’s serial battery circuit to the nominal value at w = 0 (i.e. with the minimum required number of batteries in the battery), the voltage on the power transistor also changes in accordance with these changes, which leads to a decrease in the efficiency and reliability of the serial converter;

- the maximum value of Ua6 is limited by limiting the value of w, the reliability and life of the battery depend directly on the value of which is directly proportional.

The aim of the invention is to improve the reliability and lifetime of the autonomous power supply system.

DISCLOSURE OF INVENTION

The essence of the invention consists in the constant provision of the conditions of "minimum number of batteries", i.e. AB is chosen with the minimum permissible number of batteries, ensuring its minimum operating discharge voltage, higher than the voltage at the operating point at the end of the life of the SB, and this nominal mode is maintained for the entire lifetime of the SB and AB, which is the most "favorable" mode for the power transistor of the series the converter, at the same time the failed battery in the battery is eliminated by shunting bypass switch and then one of the backup batteries is connected to the battery through a serial buy a switch that causes:

- minimal redundancy of the reserve batteries is ensured due to their being in the energy-saving mode before switching on the AB batteries in the series circuit;

- increases the efficiency and reliability of the serial converter, since the number of series-connected batteries in the battery in the operating mode is constant and the voltage on the power transistor of the serial converter varies in a narrow range during the whole life cycle of the EPS;

- it provides the selection of the required number of backup batteries to achieve the required reliability of the BOT, not limited to the operating modes of the serial converter.

As a result, the reliability and service life of the BOT are increased and, as a result, the survivability and duration of its active existence.

The proposed method of providing an autonomous power supply, equipped with a primary source of limited power SAT and a secondary source of electric power AB, which consists in stabilizing the voltage on the load with several voltage ratings and coordinating the work of the SB and AB, and the voltage of the SB and AB is converted into AC through a common stabilized voltage converter and transform in the required output voltage, the charge of the battery is carried out from the output transformable voltage, while the battery is connected to the battery allelic SB in the same polarity through a serial converter in the direction of discharge current, and the discharge of the battery is carried out in two stages: first stabilize the voltage at the output of the serial converter, equal to the voltage at the operating point of the SB at the end of the resource, based on the relation (1), and then voltage is converted to AC and transformed into the required output voltage, the battery is chosen with the number of batteries, ensuring its minimum operating discharge voltage, the operating voltage at the end of the life of the solar battery, and this nominal optimal mode is maintained throughout the life of the solar and rechargeable batteries, by shunting the failed battery in the battery with a bypass switch and then replacing it with a backup battery battery through serial bypass switch.

Graphic Illustrations

The invention is illustrated by the graphic figures of FIG. 1 and FIG. 2

In the illustrated graph of FIG. 1 shows an example of a structural scheme for the implementation of the proposed method of providing an autonomous power supply containing components indicated by the positions:

1 - Solar;

2 - Stabilized voltage converter;

3 - Battery;

(3-1) - Series converter;

(3-2) - Power transistor switch of the serial converter;

(3-3) - Control device;

4 - Battery charger;

5 - Transformer;

(6-1, 6-2) - Local power modules for loads;

7 - Electricity consumers;

(8, 9, 10) - Sequential bypass switches (n pieces);

11 - BSHPP (Shunt Bypass Switch Unit);

12 - BKiV (Block of control and equalization of voltages and temperatures in AB);

13 - Microcomputer (local controller);

(14, 15, 16) - Output filter series converter on the choke 14, the capacitor 15 and the diode 16;

17 - Shunt Bypass Switch Keys

18 - Keys of consecutive bypass switches

19 - Backup batteries (19-1) - (19-n).

Description of the method of providing autonomous power supply

The stabilized voltage converter 2 is designed as a bridge inverter. Descriptions of bridge inverters are given, for example, in the following articles: “High-frequency voltage transducers with resonant switching”, by A.V. Lukin (Power Supply, Scientific and Technical Collection, Issue 1, edited by Yu.I. Konev. Power Supply Association, M., 1993), “The Series Connected Buck Boost Regulator For High Efficiency DC Voltage Regulation), by Arthur G. Birchenough (NASA Technical Memorandum 2003-212514, NASA Lewis Research Center, Cleveland, OH), as well as in the article “Block diagram and circuit solutions for automation and stabilization systems for unsealed geostationary spacecraft with electrical isolation of on-board equipment from solar and rechargeable batteries” authors: Polyakov S.A., Chernyshev A.I., Elman V.O., Kudryashov VS, see. “Electronic and elect. omehanicheskie systems and devices: Proceedings of the SPC "Pole." - Tomsk: IHP “RASKO” at the publishing house “Radio and Communication”, 2001.

The formation of an alternating voltage at the output of a stabilized voltage converter 2 is provided by its control device 2-1, which, according to a certain law, opens in pairs transistors 2-2, 2-5 and 2-3, 2-4, respectively.

The output of the stabilized voltage converter 2 is connected to the primary winding 5-1 of the transformer 5. The solar battery 1 is connected to the stabilized voltage converter 2 positive and negative busbars.

Charger 4 with its input is connected to the secondary winding 5-5 of transformer 5, one output - to the minus bus AB 3, and the second output - via the serial bypass switch 10 - to the positive bus n-th serially connected t reserve batteries 19, minus bus of the first the accumulator of which (19-1) is connected to the positive bus of the Nth (3.1-N) AB 3. The shunt bypass switches of the BSBP 11 are connected in parallel to the N batteries of the AB 3 and to the backup batteries 19 to bypass them, and the bypass switches 8, 9, 10 - succession for each of the t backup batteries 19 for their serial connection to the positive bus AB 3. The serial converter (3-1) consists of a power transistor switch (3-2), a control device (3-3), made on the basis of a pulse width modulator, the output filter on the inductor 14, the capacitor 15 and the diode 16 (see patent RF, №2521538).

The secondary windings (5-2), (5-3) of the transformer 5 are connected to the local load power modules (6-1), (6-2) with their nominal DC output voltage, output connected to the electricity consumers 7 (to the load) , in this case - to (7-1) and (7-2), respectively.

The secondary winding (5-4) of the transformer 5 is connected directly to the consumers of electricity AC (7-3).

One of the local load power modules is selected as the main one and voltage stabilization is carried out according to it. To this end, the local load power supply module (6-1) is feedback-connected to the control unit (2-1) of the stabilized voltage converter 2.

The power supply system operates in the following main modes.

1. Power supply of electricity consumers from SB 1.

In the presence of power SB 1, exceeding the total power consumed by the loads, the stabilized voltage converter 2, connected by feedback with the local module (6-1), maintains a stable voltage on the electricity consumers (7-1). At the same time, a stable constant and alternating voltage is automatically maintained at the consumers of electric power (7-2) and (7-3), taking into account the transformation ratios of the windings. If it is necessary to charge an AB 3, its charging current is limited within the difference between the current power of the SB 1 and the total power of the electricity consumers 7.

2. Power consumers 7 from batteries.

The mode is formed when there is a shortage or absence of the power of the SB 1 to power all connected electricity consumers 7, for example, when switching on peak loads, during spacecraft maneuvers for orbit correction, during spacecraft inputs and outputs from the shadow orbit or on the shadow orbit. In this mode, the voltage at the input of the stabilized voltage converter 2 decreases to the level of the operating point of the SB 1 at the end of the resource, and the power required for supplying electricity consumers 7 from the SB 1 is added due to the discharge of the AB 3.

SB 1 is chosen with an output voltage at the operating point at the end of the resource Ucb

based on the relation (1) given in the description above, namely:

AB 3 choose with the number of batteries in a series circuit N based on the ratio:

with the first addend

in expression (4) ensures that the condition is met in accordance with expression (3). Compliance with the conditions in accordance with the expression (3) means that the voltage at the terminal AB 3 connected to the transistor switch (3-2) must always be positive (or negative when the positive terminals SB 1 and AB 3 are combined and the pn- transistor is used p type) relative to the output voltage at the operating point at the end of the resource on the SB 1, thereby maintaining the power transistor switch (3-2) of the serial converter (3-3) in the open state when discharging the AB 3.

The second term 1 in expression (4) provides the number of batteries in AB 3 one more ("margin" in the form of one battery), and eliminates the "failures" in the operation of the EPC KA with the exception of the failed battery from AB 3. When AB 3 is discharged, the voltage at the output of the serial converter (3-1) is stabilized equal to the voltage at the operating point of the SB 1 at the end of the resource using a control device (3-3), made on the basis of a pulse-width modulator, power transistor switch (3-2 ) and the output filter made on the choke 14, the capacitor 15 and the diode 16, and then this voltage is converted to AC using a stabilized voltage converter 2 and transformed using a transformer 5 and local load power modules (6-1), (6-2) in required output voltage ratings for electricity consumers 7.

The voltage on AB 3 in the proposed device is formed by series-connected "minimum number" and "spare" batteries in accordance with expression (4), while the "minimum number of batteries" provides the minimum allowable voltage in the series circuit of batteries AB 3 in accordance with the expression (3 ). Nominal voltage Unom AB 3 in the form of the resultant value of the minimum allowable voltage and voltage of one battery (voltage "reserve") provides the nominal mode of the power transistor switch (3-2) and this nominal mode is maintained throughout the lifetime of the spacecraft.

Nominal mode is provided as follows. In the initial state, the voltage on the positive bus AB 3 corresponds to the nominal value Unom. This Unom through the closed keys of the serial bypass switches (8, 9, 10) is connected to the collector of the power transistor switch (3-2).

During operation, batteries AB 3, as well as backup batteries 19 using BKiV 12 and Micro COMPUTER 13 control and ensure the alignment of their voltages and temperatures (see, for example, patent RF, No. 2390478).

When a battery in AB 3 fails, a microcomputer signal 13 excludes the failed battery by shunting the BShPP 11 bypass switch (see, for example, RF patent No. 2415489) and then (at the stage of charge of AB 3) to the positive one. bus AB 3 connect the first (19-1) of the backup batteries 19 through the first serial bypass switch 8, while maintaining the condition of the expression (4).

When the next battery fails in AB 3, it is similarly bridged with keys of the bypass switch of BSBP 11 and then the second (19-2) of backup batteries 19 is connected to the bypass switch 8 sequentially via the second serial bypass switch 9, while maintaining the expression condition (4) etc. before connecting in the same way the n-th of the backup batteries 19.

Batteries AB 3 with a block shunt bypass switches BSHP 11 and backup batteries 19 with serial bypass switches (8, 9, 10) can be performed, for example, in the form of a structural diagram presented in figure 2, containing the components indicated by the positions:

11.1-1 - keys 17.1-1, 17.2-1 of the first shunt bypass switch 11;

11.2-1 - control element of the first shunt bypass switch 11;

11.1-2 - keys 17.1-2, 17.2-2 of the second shunt bypass switch 11;

11.2-2 - control element of the second shunt bypass switch 11;

11.1-N - keys 17.1 - N, 17.2-N of the Nth shunt bypass switch 11;

11.2-N - control element of the Nth shunt bypass switch 11;

8-1 - keys 18.1-1, 18.1-2 of the first serial bypass switch 8;

8-2 - control element of the first serial bypass switch 8;

9-1 - keys 18.2-1, 18.2-2 of the second serial bypass switch 9;

9-2 - control element of the second serial bypass switch 9;

10-1 - switches 18.n-1, 18.n-2 of the n-th serial bypass switch 10;

10-2 - control element of the n-th serial bypass switch 10.

In the initial state, the contacts of the keys 17.1-1, 17.1-2, 17.1-N of the shunt bypass switches 11 and the contacts of the keys 18.1-1, 18.2-1, 18.n-1 of the serial bypass switches 8, 9, 10 are closed and the supply voltage + Upit equals + Unom, which is equal to the sum of the voltages on the batteries (3.1-1 ÷ 3.1-N), i.e. - voltage AB 3. When one of the batteries (3.1-1 ÷ 3.1-N) fails, the open key of one of the bypass switches (11.1-1) ÷ (11.1-N) shunting the battery is closed, and the closed one is opened the signal from the Microcomputer 13 arriving at one of the control element (11.2-1 ÷ 11.2-N) of this shunt bypass switch (see, patent, RF, №2415489), thereby excluding the battery from the series circuit of batteries AB 3. Then , on a signal from Microcomputer 13, arriving at the first control element 8-2 of the first backup battery and 19-1, the key (8.1-1) of this battery is disconnected, and the key (8.2-1) is closed, thereby ensuring the serial connection of this backup battery to the serial circuit of the AB 3 batteries instead of the failed battery. In this case, the voltage + Uep keeps the same nominal value + Unom.

To eliminate failures in the operation of serial bypass switches 8, 9, 10, the positive power supply bus for control elements (8-2), (9-2), (10-2) should be connected directly to the + Unom point.

At the next battery outlet in the AB 3, it is shunted in the same way and the next second backup battery 19-2 is connected to the AB 3, and so on. before connecting the last backup battery 19-n.

It should be noted that the presence of a "spare" battery in AB 3 allows not to disturb the operation of the EPC IR when excluding a failed battery and connecting a backup battery to the AB battery 3 serial circuit. Shunt bypass switches 11 are also connected to backup batteries 19 with keys and control elements (not shown in Fig. 2), which provide shunting of a failed battery.

It should be noted that, in contrast to the prototype, backup batteries 19 in the proposed method of powering the spacecraft before connecting them to the series circuit of batteries AB 3 are in an energy-saving mode, as a result of which their service life increases. Under the energy-saving mode of AB it should be understood to maintain it in storage mode with periodic training in the form of cyclic charge-discharge.

It is known that the optimal storage condition for AB is charging up to 40% of the nominal capacity (see Fran Hoffard, "Proper operation can prolong the life of a lithium-ion battery", www.powerelectronics.com), therefore, in the proposed method of the invention periodic recharge of backup batteries 19 carried out at the stage of charge of the AB 3 (in view of the fact that the power supply of electricity consumers 7 in this mode is carried out from the SB 1) by alternately connecting them to the AB 3 (then disconnecting) using serial bypass switches 8, 9, 10. Moreover, when disconnected, the closed key of the serial bypass switches 8, 9, 10 of this battery is opened, and then the open key is closed. Similarly, if necessary, a periodic cyclic charge-discharge of backup batteries 19 is periodically held by alternately connecting and disconnecting to AB 3. Alternately connecting and disconnecting backup batteries to AB 3 allows it to keep its voltage in a narrow range.

Thus, the use of the proposed method of providing autonomous power allows you to increase the reliability and service life of the BOT due to:

- improving the efficiency and reliability of the serial converter by maintaining the nominal battery voltage and the voltage on the power transistor of the serial converter in a narrow range during the whole life cycle of the EPS;

- ensuring a minimum reduction in the resource of backup batteries due to their being in storage and training mode before being included in a series chain of AB batteries;

- selection of the required number of backup batteries to achieve the required reliability of the BES KA, not limited to the operating modes of the serial converter.

As a result of increasing the reliability and service life of the BOT, its survivability and the period of active existence increase.

Claims (1)

A method of providing autonomous power supply from the solar and from the rechargeable batteries, which consists in stabilizing the voltage on the load and coordinating the operation of the solar and rechargeable batteries, and their voltages are converted into AC via a common stabilized voltage converter and transformed into the required output voltage, while charging the battery from the output transformable voltage, and connect it in parallel to the solar battery in the same polarity through A serial converter in the direction of discharge current flow, which ensures the voltage stabilization at the working point at the end of the life of the selected solar battery when the battery is discharged, characterized in that the battery is chosen with the number of batteries providing its minimum working discharge voltage exceeding the voltage in operating point at the end of the solar battery life, and this nominal optimal mode is maintained throughout the life of the tion of solar and rechargeable batteries, by the fact that the shunt bypass switch failed battery into the battery and then return to it is connected to the battery one of the backup battery via the serial bypass switch.

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