CN114914894A - Multi-input direct-current power balancer and photovoltaic system - Google Patents

Multi-input direct-current power balancer and photovoltaic system Download PDF

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CN114914894A
CN114914894A CN202210694604.5A CN202210694604A CN114914894A CN 114914894 A CN114914894 A CN 114914894A CN 202210694604 A CN202210694604 A CN 202210694604A CN 114914894 A CN114914894 A CN 114914894A
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current power
controllable switch
input
power balancer
balancer
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汪洪亮
邱晓东
朱晓楠
唐伟
邓孝军
康迪
罗安
岳秀梅
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Hunan University
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J1/00—Circuit arrangements for dc mains or dc distribution networks
    • H02J1/10—Parallel operation of dc sources
    • H02J1/106—Parallel operation of dc sources for load balancing, symmetrisation, or sharing
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/4207—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells for several batteries or cells simultaneously or sequentially
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/425—Structural combination with electronic components, e.g. electronic circuits integrated to the outside of the casing
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/425—Structural combination with electronic components, e.g. electronic circuits integrated to the outside of the casing
    • H01M10/4264—Structural combination with electronic components, e.g. electronic circuits integrated to the outside of the casing with capacitors
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
    • H02J7/0013—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries acting upon several batteries simultaneously or sequentially
    • H02J7/0014—Circuits for equalisation of charge between batteries
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
    • H02J7/0013—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries acting upon several batteries simultaneously or sequentially
    • H02J7/0014—Circuits for equalisation of charge between batteries
    • H02J7/0019—Circuits for equalisation of charge between batteries using switched or multiplexed charge circuits
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02S—GENERATION OF ELECTRIC POWER BY CONVERSION OF INFRARED RADIATION, VISIBLE LIGHT OR ULTRAVIOLET LIGHT, e.g. USING PHOTOVOLTAIC [PV] MODULES
    • H02S40/00—Components or accessories in combination with PV modules, not provided for in groups H02S10/00 - H02S30/00
    • H02S40/30—Electrical components
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/425—Structural combination with electronic components, e.g. electronic circuits integrated to the outside of the casing
    • H01M2010/4271—Battery management systems including electronic circuits, e.g. control of current or voltage to keep battery in healthy state, cell balancing
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
    • H02J2300/20—The dispersed energy generation being of renewable origin
    • H02J2300/22—The renewable source being solar energy
    • H02J2300/24—The renewable source being solar energy of photovoltaic origin
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
    • H02J2300/20—The dispersed energy generation being of renewable origin
    • H02J2300/22—The renewable source being solar energy
    • H02J2300/24—The renewable source being solar energy of photovoltaic origin
    • H02J2300/26—The renewable source being solar energy of photovoltaic origin involving maximum power point tracking control for photovoltaic sources
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E70/00—Other energy conversion or management systems reducing GHG emissions
    • Y02E70/30—Systems combining energy storage with energy generation of non-fossil origin

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Manufacturing & Machinery (AREA)
  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Control Of Electrical Variables (AREA)

Abstract

The invention relates to a multi-input direct-current power balancer and a photovoltaic system, and relates to the field of direct-current parallel current sharing, wherein N input ends of the multi-input direct-current power balancer are connected with positive ends of N direct-current power supplies in a one-to-one correspondence manner, and the multi-input direct-current power balancer comprises a controller, an inductor, N bypass capacitors and N controllable switch units; one end of each of the N controllable switch units is simultaneously connected with the positive ends of the N direct-current power supplies and one end of each of the N bypass capacitors in a one-to-one correspondence manner, the other ends of the N controllable switch units are connected with one end of the inductor, and the other ends of the N bypass capacitors are connected with the other end of the inductor; the N controllable switch units are connected with the controller, and the controller is used for controlling the on-off and time of the controllable switch units so as to control the voltage of each direct current power supply. The invention can solve the problems of parallel current sharing and power mismatch of the direct current power supply.

Description

Multi-input direct-current power balancer and photovoltaic system
Technical Field
The invention relates to the field of direct current parallel current sharing, in particular to a multi-input direct current power balancer and a photovoltaic system.
Background
In recent years, social problems caused by greenhouse effects such as global warming and sea level rise gradually develop into a survival crisis of human beings, and batteries are a core part of industries promoting carbon emission reduction, such as electric automobiles and energy storage systems. In order to achieve capacity expansion of power, batteries are generally connected in series and in parallel to form a battery pack. For example, the electric automobile is provided with the series-parallel connection of the ternary lithium batteries, and the data center power supply is provided with the lithium iron phosphate batteries which are connected in series and then in parallel.
Because the characteristics of the batteries when leaving the factory have the influence of differences, the difference of aging degrees after use, temperature and other external environments, after the single batteries or the batteries are connected in series and in parallel, a serious non-uniform current phenomenon, particularly the discharge tail end, can be generated in the charge-discharge process, the service life of each battery is further influenced differently, and the service life and the reliability of a system are reduced.
The basic equivalent circuit of the battery comprises an open-circuit voltage source and a series resistor, wherein the voltage of the open-circuit voltage source is the open-circuit voltage of the battery. For different cells, both parameters differ. Fig. 1 is a schematic diagram of parallel connection of N-way batteries, and fig. 2 is an equivalent circuit. As shown in fig. 1 and 2, the open circuit voltage V 1 ′～V N ' Difference, series resistance R s1 ～R sN Also differently, when the external output voltage is V o Then each battery current I N Comprises the following steps:
Figure BDA0003701868700000011
as can be seen from the above formula, the difference of the parameters leads each path of battery current I N It is difficult to be the same. In addition, an open circuit voltage V 1 ′～V N ' the voltage difference present is much smaller than the open circuit voltage itself.
In the literature, "parallel battery pack charge-discharge equalizer and equalization strategy research", by controlling the equalizer, when a single battery reaches a set voltage during charging, the single battery is isolated from a charging circuit; and during discharging, the energy is supplemented to the single battery with the lowest energy through the Cuk chopper circuit, so that energy balance in the charging and discharging process is realized. Patent CN206313501U provides a charging and discharging management device for parallel batteries, which provides a control strategy for the differential pressure processing of battery packs in the existing battery cell technology and grouping technology, and during the discharging process, when the total pressure is greater than a set value, a single group is cut off, and when the total pressure is less than the set value, the parallel connection works, so that the problem of long charging time of a large-capacity battery pack is solved.
In addition, in the photovoltaic system, due to the factors such as factory-leaving inconsistency of the photovoltaic modules, different aging attenuation degrees of the photovoltaic cells, shadow shielding and the like, the voltages of the maximum power points of the photovoltaic cells are different, the power mismatch problem is generated after the photovoltaic cells are directly connected in parallel, each path of the photovoltaic cells cannot output respective maximum power, and the power generation amount of the photovoltaic cells is reduced. Patent CN 108512244 discloses a series photovoltaic optimizer system and a control method thereof. The series photovoltaic optimizer enables each photovoltaic cell to achieve maximum power output by converting unmatched energy from parallel to series. Patent CN 103095181 discloses a single-inductance photovoltaic module and a control method thereof, which ensure that all photovoltaic battery packs operate at the maximum output power point.
The defects of the prior art are as follows:
due to the difference of battery parameters, the battery monomers are connected in parallel or connected in parallel after being connected in series, and the phenomenon of monomer non-uniform current or battery string non-uniform current exists in the charging and discharging process, so that the charging and discharging depth of each battery is different, the service life of the battery is affected differently, and the service life and reliability of the system are reduced.
Existing current sharing schemes include two categories: passive current sharing and active current sharing. The passive current sharing scheme is to change the current of the battery with larger current by connecting the resistors in series, but extra power loss is generated on the resistors in series, and the generated heat can influence the temperature of the battery body and the safety; according to the active current sharing scheme, energy transfer is achieved through a DC/DC converter, when a certain battery is not current-shared, the converter connected with the battery pack is started, and energy of the battery pack is transmitted to the battery to achieve current sharing. If the N batteries are equalized, N DC/DC converters are needed to be configured, and the cost is high.
For a photovoltaic system, a method for solving the problem of power mismatch caused by direct parallel connection of photovoltaic cells mainly comprises the steps of configuring a DC/DC converter for each path of photovoltaic cell, respectively controlling the voltage of each path of photovoltaic cell, realizing distributed maximum power point tracking and enabling each path of photovoltaic cell to output respective maximum power. Similarly, the plurality of DC/DC converters leads to an increase in cost and insufficient practicality.
Disclosure of Invention
The invention aims to provide a multi-input direct-current power balancer and a photovoltaic system, which can solve the problem of parallel current sharing of direct-current power supplies (including batteries) and the problem of parallel power mismatch of photovoltaic batteries based on a novel circuit topology.
In order to achieve the purpose, the invention provides the following scheme:
a multi-input direct-current power balancer is characterized in that N input ends of the multi-input direct-current power balancer are connected with positive ends of N batteries in a one-to-one correspondence mode, and the multi-input direct-current power balancer comprises a controller, an inductor, N bypass capacitors and N controllable switch units;
one end of each of the N controllable switch units is simultaneously connected with the positive ends of the N batteries and one end of each of the N capacitors in a one-to-one correspondence manner, the other ends of the N controllable switch units are connected with one end of the inductor, and the other ends of the N capacitors are connected with the other end of the inductor and led out to serve as one output end of the multi-input direct-current power balancer; the negative ends of the N batteries are connected together and led out to be used as the other output end of the multi-input direct-current power balancer;
the N controllable switch units are all connected with the controller, and the controller is used for controlling the on-off and time of the controllable switch units, so that one specific unit in the N controllable switch units is switched on, and the rest N-1 controllable switch units are switched off.
Optionally, each of the controllable switch units comprises a bidirectional controllable switch.
Optionally, the bidirectional controllable switch is composed of two controllable switch elements arranged in a vertex-to-vertex manner.
Optionally, the controllable switching element is a MOSFET or an IGBT.
Optionally, the dc power source is a chargeable and dischargeable battery.
Optionally, each of the controllable switch units comprises a unidirectional controllable switch.
Optionally, the unidirectional controllable switch is formed by connecting a diode in series with the MOSFET or connecting a diode in series with the IGBT.
Optionally, the dc power supply is a photovoltaic cell.
Optionally, a voltage stabilizing capacitor is connected in parallel between the two output ends of the multiple-input dc power balancer.
Optionally, the inductor of the multiple-input dc power balancer has two operation modes: inductor current is continuous and inductor current is discontinuous.
A photovoltaic system including the multiple-input dc power balancer, the photovoltaic system comprising: the photovoltaic cell, the multi-input direct-current power balancer and the photovoltaic inverter, wherein the positive electrode of the photovoltaic cell is correspondingly connected with the input end of the multi-input direct-current power balancer, and the two output ends of the multi-input direct-current power balancer are correspondingly connected with the two input ends of the photovoltaic inverter.
According to the specific embodiment provided by the invention, the following technical effects are realized:
the novel circuit topology provided by the invention is correspondingly connected to the output end of the battery, and replaces the original direct parallel connection scheme. The topology can provide compensation voltage on the basis of the original voltage, realize the respective control of the voltage of each path of battery, and further solve the current equalization problem when the batteries are connected in parallel. In addition, the problem of mismatch of parallel power in a photovoltaic system can be solved.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without inventive exercise.
FIG. 1 is a schematic diagram of a parallel connection of N batteries in the prior art;
FIG. 2 is a schematic diagram of an equivalent parallel circuit of N batteries in the prior art;
FIG. 3 is a schematic diagram of a circuit structure of an N-input power balancer applied to a parallel current-sharing system of batteries according to the present invention;
FIG. 4 is a diagram of the topology of the N input power balancer circuit of the present invention;
FIG. 5 is a circuit topology structure diagram of the two-input power balancer applied to parallel current sharing of the battery according to the embodiment of the present invention;
FIG. 6 is a schematic diagram of a first circuit mode when two input power balancers according to the present invention are applied to parallel current sharing of batteries;
FIG. 7 is a schematic diagram of a second circuit mode when the two-input power balancer is applied to parallel current sharing of batteries according to the present invention;
FIG. 8 is a diagram illustrating simulation results of a parallel current sharing of batteries with a two-input power balancer according to the present invention;
FIG. 9 is a schematic diagram of a power balancer of the present invention applied to a photovoltaic system;
FIG. 10 is a diagram of a circuit topology for a photovoltaic system with a power balancer of the present invention;
FIG. 11 is a schematic diagram of a first circuit mode of the power balancer of the present invention applied in a photovoltaic system;
FIG. 12 is a schematic diagram of a second circuit mode of the power balancer of the present invention applied to a photovoltaic system;
FIG. 13 is a schematic diagram of a PV curve for a power balancer for implementing power boost in a photovoltaic system according to the present invention;
FIG. 14 is a schematic diagram of Matlab/Simulink simulation results for a two-input photovoltaic power balancer of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The invention aims to provide a multi-input direct-current power balancer and a photovoltaic system, which have the following advantages:
(1) the problem of parallel current sharing of the direct-current power supply can be solved. A novel circuit topology is provided, namely a direct current power balancer, which is connected to the output end of a direct current power supply to replace the original direct parallel connection scheme. The topology can correspondingly provide N paths of compensation voltage on the basis of the original direct current power supply voltage in the direct parallel connection, and realizes the respective regulation of each path of direct current power supply voltage so as to realize the current regulation.
(2) The proposed new topology has the feature of low cost. The circuit topology of the proposed dc power balancer is shown in fig. 4. On one hand, the proposed topology belongs to a multi-input single-output topology circuit, and compared with a scheme using a plurality of DC/DC converters, the topology has the advantages of fewer elements and lower cost; on the other hand, the voltage difference between the direct current power supplies is processed, so that the voltage stress of the internal switching element is small, the realization of higher switching frequency is facilitated, the capacity of the energy storage element is further reduced, the volume of the energy storage element is smaller, and the whole circuit has the advantages of low cost and small volume.
(3) The control idea of the proposed novel topology is simple. The current-sharing control method is simple and convenient to implement, one path of current in the multiple paths of direct current power supplies is selected as the given current of each path of direct current power supply to carry out closed-loop control, and the current of each path of direct current power supply can be controlled by adjusting the duty ratio and further adjusting the voltage of the direct current power supplies.
(4) In addition, the topology can also solve the problem of power mismatch caused by direct parallel connection of photovoltaic cells in a photovoltaic system, is connected to the positive terminal of the photovoltaic cell, provides compensation voltage on the basis of the original voltage, and realizes respective control of the voltage of each photovoltaic cell to enable the voltage to reach respective maximum power point. Scheme as shown in fig. 9, the power balancer is applied to the photovoltaic system to replace the original direct parallel scheme.
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in further detail below.
For convenience of description, a battery is used as a representative dc power supply in the embodiment of the present invention, but the dc power supply in the embodiment of the present invention is not limited to the battery. The description will be made by taking a battery as an example.
Fig. 3 is a schematic diagram of a circuit structure of an N-input dc power balancer applied to a battery parallel current-sharing system according to the present invention. V N ' is the voltage of the Nth cell at the time of open circuit, R sN Is an equivalent series resistance. And setting the switching period as T, and changing the working time of each path of battery in real time according to the control requirement, wherein the working time is mainly determined by the turn-on time of the corresponding path of controllable switching unit in the direct-current power balancer. The on and off time of the controllable switch unit is determined by a controller closed-loop control algorithm.
The direct current power balancer controls the power supply time of the corresponding path of battery for the load by controlling the on-off time of the corresponding controllable switch unit, so that the voltage of the corresponding path of battery is controlled. Meanwhile, the on-off of the controllable switch unit can control the relative length of the charging and discharging time of the corresponding bypass capacitor in the direct-current power balancer, and further adjust the voltage V of the corresponding bypass capacitor CN . And the final currents of all the paths of battery voltages after the voltage compensation of the bypass capacitor tend to be consistent, so that the current equalization is realized. Namely that
Figure BDA0003701868700000061
Fig. 4 shows an N-input dc power balancer, which includes a controller, an inductor L, N bypass capacitors C, and N controllable switch units K. One end of each of the N controllable switch units is simultaneously connected with the positive electrode ends of the N batteries and one end of each of the N bypass capacitors in a one-to-one correspondence manner, the other ends of the N controllable switch units are connected with one end of each of the inductors, and the other ends of the N bypass capacitors are connected with the other end of each of the inductors and led out to serve as one output end of the multi-input direct-current power balancer; the negative ends of the N batteries are connected together and led out to be used as the other output end of the multi-input direct-current power balancer;
preferably, a voltage stabilizing capacitor is connected in parallel between two output ends of the multi-input direct-current power balancer;
the N controllable switch units are all connected with the controller, and the controller is used for controlling the on-off and time of the controllable switch units, so that one specific unit in the N controllable switch units is switched on, and the rest N-1 controllable switch units are switched off.
The controllable switch unit K may be formed by a plurality of or a single commonly used power device in series and parallel, such as MOSFET, IGBT, diode, etc. The material of the controllable switch unit K may be SiC, GaN, Si. The bypass capacitor C may provide a different compensation voltage for each cell.
The controllable switch unit K may comprise a bidirectional controllable switch or a unidirectional controllable switch.
The bidirectional controllable switch can be composed of two controllable switch elements arranged in a butting mode, and the controllable switch elements can be MOSFETs or IGBTs. Correspondingly, the energy of the N batteries can flow in both directions, i.e., the N batteries can be both discharged and charged.
The unidirectional controllable switch can be formed by connecting a diode with a MOSFET in series or connecting a diode with an IGBT in series. Correspondingly, the energy of the N batteries can only flow in a single direction, namely the N batteries can only discharge and cannot be charged.
The controller is used for controlling the conduction of a preset path of controllable switch unit K to control the connection of a corresponding path of battery and the inductor so as to supply power to the load.
The N DC power supplies share the inductor L, so that the number of inductive elements is greatly reduced. Each path of direct current power supply corresponds to a bypass capacitor C and a controllable switch unit K.
K n When the circuit is disconnected, the corresponding battery passes through the bypass capacitor C n And the following load form a current loop, the bypass capacitor C n Charging, K n When closed, the corresponding path battery passes through K n And the following load form a current loop, the bypass capacitor C n And (4) discharging. By controlling K n Can control the power supply time of the corresponding circuit of battery and the bypass capacitor C according to the opening and closing of the capacitor and the relative length of the time n The voltage of (c).
Note that: bypass capacitor C here n For K n By-passing the capacitor C when switched off n The withstand voltage value of (2) is low, so that the circuit cost is reduced, and a capacitor with a smaller capacitance value can be further selected.
Example 1:
taking two-way battery current sharing as an example, the circuit topology is a two-input dc power balancer, as shown in fig. 5. C o Representing the post-stage regulation capacitance. Each path of battery corresponds to a bypass capacitor C and two opposite bidirectional controllable switches S. Each bi-directionally controllable switch is composed of a MOSFET. The two batteries share one inductor L. Let two paths of battery voltage be V respectively 1 And V 2 The output currents are respectively I 1 And I 2 The current flowing through the bypass capacitor is I C1 And I C2 。
According to the energy flow direction, the working mode of the circuit can be divided into a battery charging process and a battery discharging process, and is controlled by the on-off of the bidirectional controllable switch. S 1 Antiparallel diode conducting and S 2 The switch is on, or 3 Antiparallel diode conducting and S 4 The battery discharging process is carried out when the switch is conducted; s 2 Antiparallel diode conducting and S 1 The switch is on, or 4 Antiparallel diode conducting and S 3 The switch is turned on to perform a charging process.
The operation principle of the circuit is described by taking the discharging process as an example.
FIG. 6 shows a bidirectional controllable switch S 1 Antiparallel diode conducting and S 2 Switch on, S 3 、S 4 Turning off; FIG. 7 is S 1 、S 2 Off, S 3 Antiparallel diode conducting and S 4 The switch is turned on.
The drive pulses of the bidirectional controllable switches in the two paths are complementary. Assuming that the magnitude relation of two battery voltages is V when the circuit is in a steady state 1 >V 2 From the circuit principle, it can be deduced that:
V 2 ＜V o ＜V 1
i.e. in steady state, the output voltage is between the two input voltages. Capacitor C 1 Voltage V of C1 Is (V) 1 -V o )>0V, capacitance C 2 Voltage V of C2 Is (V) 2 -V o )<0V. Therefore, the maximum voltage of the bypass capacitor is the difference value of the voltage of the battery, and the voltage difference value is far smaller than the normal voltage of the battery, so that the voltage stress of the bypass capacitor is very small, and the circuit cost is reduced.
As shown in fig. 6, the first mode of operation: s 1 Antiparallel diode conducting and S 2 Switch on, S 3 、S 4 And closing. Batteries 1, S 1 、S 2 Inductor L and voltage-stabilizing capacitor C O Forming a loop. At this point, the battery 1 supplies power to the following load, so that the battery 1 discharges, V 1 And decreases. Due to (V) 1 -V o )>0, so the inductor current rises. Due to V C1 And V C2 Is a very small voltage, so the capacitance C 1 、C 2 Is very small and is ignored here, so V 2 Remain unchanged. At this time, two opposite top MOSFETs are S 3 And S 4 Has a voltage of (V) 1 -V 2 )。
As shown in fig. 7, the second mode of operation: s 1 、S 2 Off, S 3 Antiparallel diode conducting and S 4 The switch is turned on. Batteries 2, S 3 、S 4 Inductor L and voltage-stabilizing capacitor C O Forming a loop. At this time, the battery 2 supplies power to a load at the rear, and thus the battery 2 is dischargedElectricity, V 2 And decreases. Due to (V) 2 -V o )<0 and thus the inductor current drops. V 1 Remain unchanged. At this time, two opposite top MOSFETs are S 1 And S 2 Has a voltage of (V) 2 -V 1 )。
Before the two battery currents are completely equal, the first working mode and the second working mode periodically and circularly work alternately. By controlling two-way bidirectional controllable switches (S) 1 、S 2 And S 3 、S 4 ) The time of conduction, i.e. the duty cycle D, the bypass capacitance C 1 、C 2 The voltage of the two batteries is controlled, and the output currents of the two batteries are the same.
The charging and discharging processes of the batteries 1 and 2 are similar in principle, except that energy flows from the load (e.g. the grid) side to the batteries via the bidirectional controllable switch, and will not be described in detail herein.
From the above analysis, the voltage stress of the bidirectional controllable switch is the difference of the battery voltage, which is very small and much smaller than the normal voltage of the battery. Therefore, the bidirectional controllable switch can select a switching device with small voltage stress, and the cost is reduced.
The power balancer with bidirectional energy flow can be applied to an energy storage system without limitation.
In order to achieve the aim of current sharing, a closed-loop control algorithm of the controller collects one path of current in the multiple paths of batteries as given current of other paths of batteries, and performs closed-loop control to enable the currents of the multiple paths of batteries to be consistent. Taking the current of the battery 1 as an example, the current of the battery 2 is closed-loop controlled. Detecting the output current I of the battery 1 1 As I 2 Given value of (S), regulating the switching tube S 2 And S 4 D, finally I 2 Tend to be I 1 And the two batteries realize current sharing.
Matlab/Simulink software is used for building simulation models when two paths of batteries are input, the output result is shown in FIG. 8, and current sharing is achieved by two paths of battery currents after current sharing control.
When the photovoltaic system is applied, two paths of photovoltaic cells are taken as an example, and the schematic diagram of the system is shown in the figureFig. 9 shows a circuit topology of the system circuit and the power balancer as shown in fig. 10. Since energy flows in one direction only from the photovoltaic cell to the output side, a diode is connected in series with the MOSFET. The operation mode is shown in fig. 11 and fig. 12, the operation process and principle are the same as the discharge process of the dc power balancer with bidirectional energy flow, and details are not repeated here. In contrast, the control target in the cell current equalizing process is the cell current, and when applied to a photovoltaic system, the control target is the voltage of the photovoltaic cell. The voltage value of the maximum power point of the photovoltaic cell can be obtained by using the existing method, the voltage value is used as the given voltage of the closed-loop control algorithm of the controller to carry out closed-loop control, and the switching tube S is controlled 1 And S 2 The circuit can work alternatively under two circuit modes of fig. 11 and fig. 12 by adjusting the bypass capacitor C 1 、C 2 The actual voltage of the photovoltaic cells finally approaches to the maximum power point voltage, and the two photovoltaic cells reach respective maximum power points, so that the generated energy of the photovoltaic system is improved. As shown in FIG. 11, when two photovoltaic cells are directly connected in parallel, the voltage is V MPP Due to the difference of the two paths of photovoltaic cells, the generated energy cannot reach the maximum at the moment; bypass capacitor C of two-input power balancer 1 、C 2 Providing a compensation voltage of Δ V 1 And Δ V 2 After voltage compensation, the voltage of the two photovoltaic cells reaches the voltage V of the maximum power point of each photovoltaic cell from the original VMPP 1m And V 2m And maximum power is output respectively, so that the integral promotion of the generated energy is realized.
The key points of the invention are as follows:
(1) the concept of a "dc power balancer" is presented. The compensation voltage is provided on the basis of the voltage of the direct current power supply in the original direct parallel connection, and the voltage of each path of battery can be respectively controlled, so that the output current of each path of battery is the same, and the problem of parallel connection and non-uniform current of the batteries is solved.
(2) A novel circuit topology for a dc power balancer is presented. And processing the voltage difference between the multiple batteries. The voltage difference of the battery is small, so that the voltage stress of the switching element and the capacitor element of the topology is small, and the cost is reduced and higher switching frequency is realized.
(3) The current-sharing control method of the direct-current power balancer is provided, one path of current in multiple paths of batteries is used as given current of each path of battery to carry out closed-loop control, and the current of each path of battery can be controlled by adjusting the duty ratio and further adjusting the voltage of the battery.
(4) The circuit structure of the direct current power balancer is a multi-path input single-path output, and the input is connected with a battery. If N batteries are input, the DC power balancer has N power inputs and only 1 output.
(5) In the circuit topology of the direct current power balancer, a bypass capacitor is connected between a battery and an output, and the voltage of the bypass capacitor is small compensation voltage, so that the capacitor with a small capacitance value can be selected.
The invention has the following beneficial effects:
(1) the problem of battery non-uniform current is solved. The concept of a direct current power balancer is provided, the direct current power balancer is connected to the output of the batteries, the original direct parallel scheme is replaced, and the voltage of each path of batteries can be controlled respectively, so that the parallel current sharing of the multiple paths of batteries is realized.
(2) The switching element of the proposed new circuit topology has low voltage stress, which is only the difference between the voltages of the batteries of the various paths. The voltage difference of the battery is small, so the voltage stress of the internal switch element and the capacitor element is small, which is beneficial to reducing the cost and realizing higher switching frequency, and has good competitiveness of low cost, high efficiency and high power density.
(3) The control method for realizing current sharing by the topology is simple and easy to realize, one path of current in multiple paths of batteries is used as the given current of each path of battery to carry out closed-loop control, and the current of each path of battery can be controlled by adjusting the duty ratio and further adjusting the voltage of the battery.
(4) Matlab/Simulink software is used for controlling two paths of batteries with parameter difference, two input direct current power balancers are used for simulation, and a simulation result is shown in figure 8 and shows the current equalizing effect of the system after the power balancers are used.
(5) When applied to a photovoltaic system, a schematic diagram of the PV curve for achieving the effect is shown in fig. 13. The simulation result is shown in fig. 14, taking two parallel photovoltaic cells as an example, the photovoltaic cells are directly connected in parallel before the power balancer is used, the voltages of the photovoltaic cells are not completely the same, and after the two input power balancers are used, the photovoltaic cells independently work to respective maximum power points, so that the total generated energy is improved.
The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other.
The principles and embodiments of the present invention have been described herein using specific examples, which are provided only to help understand the method and the core concept of the present invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, the specific embodiments and the application range may be changed. In view of the above, the present disclosure should not be construed as limiting the invention.

Claims (10)

1. A multi-input direct-current power balancer is characterized in that N input ends of the multi-input direct-current power balancer are connected with positive ends of N direct-current power supplies in a one-to-one correspondence mode, and the multi-input direct-current power balancer comprises a controller, an inductor, N bypass capacitors and N controllable switch units;
one end of each of the N controllable switch units is simultaneously connected with the positive ends of the N direct-current power supplies and one end of each of the N bypass capacitors in a one-to-one correspondence manner, the other ends of the N controllable switch units are connected with one end of the inductor, and the other ends of the N bypass capacitors are connected with the other end of the inductor and led out to serve as one output end of the multi-input direct-current power balancer; the negative ends of the N direct current power supplies are connected together and led out to be used as the other output end of the multi-input direct current power balancer;
the N controllable switch units are all connected with the controller, and the controller is used for controlling the on-off and time of the controllable switch units, so that one specific unit in the N controllable switch units is switched on, and the rest N-1 controllable switch units are switched off.
2. The multiple-input direct current power balancer of claim 1, wherein each of the controllable switch cells comprises a bidirectional controllable switch.
3. The multiple-input direct current power balancer of claim 2, wherein the bidirectional controllable switch is composed of two controllable switching elements disposed opposite each other.
4. The multiple-input direct current power balancer of claim 3, wherein the controllable switching elements are MOSFETs or IGBTs.
5. The multiple-input direct current power balancer of any one of claims 1-4, wherein the direct current power source is a chargeable and dischargeable battery.
6. The multiple-input direct current power balancer of claim 1, wherein each of the controllable switch cells comprises a unidirectional controllable switch.
7. The multiple-input direct current power balancer of claim 5, wherein the unidirectional controllable switch is composed of one diode in series with a MOSFET or one diode in series with an IGBT.
8. The multiple-input direct current power balancer of claim 6 or 7, wherein the direct current power source is a photovoltaic cell.
9. The multiple-input dc power balancer of any one of claims 1-8, wherein a voltage stabilizing capacitor is connected in parallel between the two output terminals of the multiple-input dc power balancer.
10. A photovoltaic system employing the multiple-input dc power balancer of any one of claims 1-9, the photovoltaic system comprising: the photovoltaic cell, the multi-input direct-current power balancer and the photovoltaic inverter, wherein the positive electrode of the photovoltaic cell is correspondingly connected with the input end of the multi-input direct-current power balancer, and the two output ends of the multi-input direct-current power balancer are correspondingly connected with the two input ends of the photovoltaic inverter.
CN202210694604.5A 2022-06-20 2022-06-20 Multi-input direct-current power balancer and photovoltaic system Pending CN114914894A (en)

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