A multi-input DC power balancer and photovoltaic system

Abstract

The present invention relates to a multi-input DC power balancer and a photovoltaic system, and relates to the field of DC parallel current sharing, wherein the N input terminals of the multi-input DC power balancer are connected one-to-one with the positive terminals of N DC power supplies, and the multi-input DC power balancer includes a controller, an inductor, N bypass capacitors and N controllable switch units; one end of the N controllable switch units is simultaneously connected one-to-one with the positive terminals of the N DC power supplies and one end of the N bypass capacitors, the other ends of the N controllable switch units are connected to one end of the inductor, and the other ends of the N bypass capacitors are connected to the other end of the inductor; the N controllable switch units are all connected to the controller, and the controller is used to control the on and off of the controllable switch units and their time, thereby controlling the voltage of each DC power supply. The present invention can solve the problems of parallel current sharing and power mismatch of DC power supplies.

Description

Technical Field

[0001] The present invention relates to the field of DC parallel current sharing, and in particular to a multi-input DC power balancer and a photovoltaic system. Background Art

[0002] In recent years, social problems caused by greenhouse effects such as global warming and sea level rise have gradually evolved into a crisis of human survival. In many industries that promote carbon emission reduction, such as electric vehicles and energy storage systems, batteries are the core parts. In order to achieve power expansion, batteries are usually connected in series and parallel to form a battery pack. For example, electric vehicles have ternary lithium batteries connected in series and parallel, and data center power supplies have lithium iron phosphate batteries connected in series and then in parallel.

[0003] Due to the differences in battery characteristics before leaving the factory, differences in the degree of aging after use, and the influence of external environments such as temperature, after battery cells or batteries are connected in series and parallel, the charging and discharging process will produce serious uneven current, especially at the end of discharge, which will have different impacts on the life of each battery and reduce the system life and reliability.

[0004] The basic equivalent circuit of a battery includes an open-circuit voltage source and a series resistor. The voltage of the open-circuit voltage source is the open-circuit voltage of the battery. For different batteries, both parameters vary. Figure 1 This is a schematic diagram of N batteries connected in parallel. Figure 2 is an equivalent circuit. Figure 1 and Figure 2 , open circuit voltage V 1 ′~V N 'There is a difference, the series resistance R s1 ~R sN Also different, when the external output voltage is V o When each battery current I N for:

[0005]

[0006] From the above formula, it can be seen that the difference in parameters makes each battery current I N In addition, the open circuit voltage V 1 ′~V N 'The voltage difference that exists is much smaller than the open circuit voltage itself.

[0007] The document "Research on Charge and Discharge Equalizer and Equalization Strategy of Parallel Battery Packs" controls the equalizer to isolate the single cell from the charging circuit after it reaches the set voltage during charging; during discharge, the Cuk chopper circuit replenishes energy to the single cell with the lowest energy, achieving energy balance during the charge and discharge process. Patent CN206313501U provides a charge and discharge management device for parallel batteries, which provides a control strategy for battery pack pressure difference processing based on existing battery cell technology and grouping technology. When the total pressure is greater than the set value during the discharge process, the single group is cut off, and when it is less than the set value, it works in parallel, solving the problem of long charging time for large-capacity battery packs.

[0008] In addition, in the photovoltaic system, due to the inconsistency of photovoltaic components leaving the factory, the different degrees of aging and attenuation of photovoltaic cells, and shadow occlusion and other factors, the voltage at the maximum power point of the photovoltaic cells will be different, and a power mismatch problem will occur after direct parallel connection. Each photovoltaic cell cannot output its own maximum power, reducing the power generation of the photovoltaic cell. Patent CN108512244 discloses a series photovoltaic optimizer system and its control method. The series photovoltaic optimizer converts the unmatched energy from parallel to series connection so that each photovoltaic cell can achieve maximum power output. Patent CN103095181 discloses a single-inductor photovoltaic module and control method to ensure that all photovoltaic battery groups operate at the maximum output power point.

[0009] The defects of the original technology are as follows:

[0010] Due to the differences in battery parameters, when battery cells are connected in parallel or in series and then in parallel, there is uneven current flow in the cells or in the battery strings during the charge and discharge process, which makes the charge and discharge depth of each battery different, has different effects on the battery life, and reduces the system life and reliability.

[0011] There are two types of current balancing solutions: passive current balancing and active current balancing. The passive current balancing solution is to connect a resistor in series with the battery with a larger current to change the current, but this will cause additional power loss in the series resistor, and the heat generated will affect the temperature of the battery body and affect the safety; the active current balancing solution uses a DC / DC converter to achieve energy transfer. When a battery does not balance the current, the converter connected to the battery pack is started to transfer the energy of the battery pack to the battery to achieve current balancing. If N batteries are to be current balanced, N DC / DC converters need to be configured, which is costly.

[0012] For photovoltaic systems, the solution to the power mismatch problem caused by direct parallel connection of photovoltaic cells is to configure a DC / DC converter for each photovoltaic cell, control the voltage of each photovoltaic cell separately, and implement distributed maximum power point tracking so that each photovoltaic cell outputs its own maximum power. Similarly, multiple DC / DC converters lead to increased costs and insufficient practicality. Summary of the invention

[0013] The purpose of the present invention is to provide a multi-input DC power balancer and a photovoltaic system, which, based on the novel circuit topology, can solve the problem of parallel current sharing of DC power sources (including batteries) and can also solve the power mismatch problem of parallel photovoltaic cells.

[0014] To achieve the above object, the present invention provides the following solutions:

[0015] A multi-input DC power balancer, wherein N input terminals of the multi-input DC power balancer are connected one-to-one with positive terminals of N batteries, and the multi-input DC power balancer comprises a controller, an inductor, N bypass capacitors and N controllable switch units;

[0016] One end of the N controllable switch units is simultaneously connected to the positive ends of the N batteries and one end of the N capacitors in a one-to-one correspondence, the other ends of the N controllable switch units are connected to one end of the inductor, and the other ends of the N capacitors are connected to the other end of the inductor and are led out as an output end of the multi-input DC power balancer; the negative ends of the N batteries are connected together and led out as another output end of the multi-input DC power balancer;

[0017] The N controllable switch units are all connected to the controller, and the controller is used to control the on and off of the controllable switch units and their time, so that a specific unit among the N controllable switch units is turned on, and the remaining N-1 units are all turned off.

[0018] Optionally, each of the controllable switch units includes a bidirectional controllable switch.

[0019] Optionally, the bidirectional controllable switch consists of two controllable switch elements arranged opposite to each other.

[0020] Optionally, the controllable switching element is MOSFET or IGBT.

[0021] Optionally, the DC power source is a rechargeable and dischargeable battery.

[0022] Optionally, each of the controllable switch units includes a unidirectional controllable switch.

[0023] Optionally, the unidirectional controllable switch is composed of a diode connected in series with a MOSFET or a diode connected in series with an IGBT.

[0024] Optionally, the DC power supply is a photovoltaic cell.

[0025] Optionally, a voltage stabilizing capacitor is connected in parallel between two output ends of the multi-input DC power balancer.

[0026] Optionally, the inductor of the multi-input DC power balancer has two operating modes: continuous inductor current and discontinuous inductor current.

[0027] A photovoltaic system, comprising the multi-input DC power balancer, comprising: a photovoltaic cell, a multi-input DC power balancer and a photovoltaic inverter, wherein the positive pole of the photovoltaic cell is connected to the input end of the multi-input DC power balancer correspondingly, and the two output ends of the multi-input DC power balancer are connected to the two input ends of the photovoltaic inverter correspondingly.

[0028] According to the specific embodiments provided by the present invention, the present invention achieves the following technical effects:

[0029] The new circuit topology proposed in the present invention is connected to the output end of the battery, replacing the original direct parallel connection scheme. This topology can provide a compensation voltage based on the original voltage, realize the separate control of each battery voltage, and thus solve the current equalization problem when the batteries are connected in parallel. In addition, it can also solve the problem of parallel power mismatch in photovoltaic systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0031] Figure 1 A schematic diagram of N batteries connected in parallel in the prior art;

[0032] Figure 2 It is a schematic diagram of an equivalent circuit of N batteries connected in parallel in the prior art;

[0033] Figure 3 This is a schematic diagram of the circuit structure of the N-input power balancer of the present invention applied to a battery parallel current sharing system;

[0034] Figure 4 This is a topological structure diagram of the N-input power balancer circuit of the present invention;

[0035] Figure 5 This is a circuit topology diagram of an embodiment of the present invention in which two input power balancers are applied to batteries for current balancing in parallel;

[0036] Figure 6 It is a schematic diagram of a first circuit mode when two input power balancers of the present invention are applied to batteries connected in parallel for current balancing;

[0037] Figure 7A schematic diagram of a second circuit mode when two input power balancers of the present invention are applied to batteries connected in parallel for current balancing;

[0038] Figure 8 It is a schematic diagram of simulation results of two-input power balancer of the present invention applied to parallel current sharing of batteries;

[0039] Fig. 9 This is a schematic diagram of the power balancer of the present invention applied to a photovoltaic system;

[0040] Fig.10 This is a circuit topology diagram of the power balancer of the present invention applied to a photovoltaic system;

[0041] Fig.11 It is a schematic diagram of a first circuit mode when the power balancer of the present invention is applied to a photovoltaic system;

[0042] Fig.12 A schematic diagram of a second circuit mode when the power balancer of the present invention is applied to a photovoltaic system;

[0043] Fig.13 A schematic diagram of a PV curve showing that the power balancer of the present invention is applied to a photovoltaic system to achieve power enhancement;

[0044] Fig.14 It is a schematic diagram of Matlab / Simulink simulation results of the two-input photovoltaic power balancer of the present invention. DETAILED DESCRIPTION

[0045] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0046] The object of the present invention is to provide a multi-input DC power balancer and a photovoltaic system, which have the following advantages:

[0047] (1) It can solve the problem of current balancing in parallel connection of DC power supplies. A new circuit topology, called a DC power balancer, is proposed, which is connected to the output end of the DC power supply to replace the original direct parallel connection solution. This topology can provide N compensation voltages corresponding to the DC power supply voltage in the original direct parallel connection, so that each DC power supply voltage can be adjusted separately, thereby realizing current regulation.

[0048] (2) The proposed new topology has the characteristics of low cost. The circuit topology of the proposed DC power balancer is as follows Figure 4As shown. On the one hand, the proposed topology belongs to a multi-input single-output topology circuit. Compared with the solution using multiple DC / DC converters, it has fewer components and lower costs. On the other hand, the voltage difference between the DC power supplies is processed, so the voltage stress of the internal switching elements is small, which is conducive to achieving a higher switching frequency, thereby reducing the capacity of the energy storage element, and the energy storage element is smaller, so that the entire circuit has the advantages of low cost and small size.

[0049] (3) The control idea of ​​the proposed new topology is simple. The proposed current sharing control method is simple and easy to implement. One current from multiple DC power supplies is selected as the given current of each DC power supply for closed-loop control. The current of each DC power supply can be controlled by adjusting the duty cycle and then adjusting the DC power supply voltage.

[0050] (4) In addition, this topology can also solve the power mismatch problem caused by direct parallel connection of photovoltaic cells in the photovoltaic system. By connecting to the positive terminal of the photovoltaic cell, a compensation voltage is provided on the basis of the original voltage, so that the voltage of each photovoltaic cell can be controlled separately so that they can reach their respective maximum power points. Fig. 9 As shown, a power balancer is applied to a photovoltaic system to replace the original direct parallel solution.

[0051] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0052] It should be noted that, for the convenience of description, a battery is used to represent the DC power source in the embodiment of the present invention, but the DC power source in the embodiment of the present invention is not limited to a battery. The battery is used as an example for description.

[0053] like Figure 3 The figure shows the circuit structure diagram of the N-input DC power balancer of the present invention applied to the battery parallel current sharing system. N ′ is the voltage of the Nth battery when it is open circuit, R sN is the equivalent series resistance. Assuming the switching period is T, the working time of each battery changes in real time according to the control requirements, which mainly depends on the opening time of the corresponding controllable switch unit in the DC power balancer. The opening and disconnecting time of the controllable switch unit is determined by the closed-loop control algorithm of the controller.

[0054] The DC power balancer controls the time that the corresponding battery supplies power to the load by controlling the opening and closing time of the corresponding controllable switch unit, thereby controlling the voltage of the corresponding battery. At the same time, the opening and closing of the controllable switch unit can control the relative length of the charging and discharging time of the corresponding bypass capacitor in the DC power balancer, thereby adjusting the corresponding bypass capacitor voltage V CN After the voltage of all the batteries is compensated by the bypass capacitor voltage, the final current tends to be consistent, achieving current sharing.

[0055]

[0056] like Figure 4 The figure shows a DC power balancer with N inputs, including a controller, an inductor L, N bypass capacitors C and N controllable switch units K. One end of the N controllable switch units is simultaneously connected to the positive ends of N batteries and one end of N bypass capacitors in a one-to-one correspondence, the other ends of the N controllable switch units are all connected to one end of the inductor, the other ends of the N bypass capacitors are all connected to the other end of the inductor and are led out as an output end of the multi-input DC power balancer; the negative ends of the N batteries are connected together and led out as another output end of the multi-input DC power balancer;

[0057] Preferably, a voltage stabilizing capacitor is connected in parallel between the two output terminals of the multi-input DC power balancer;

[0058] N controllable switch units are all connected to the controller, and the controller is used to control the on and off of the controllable switch units and their time, so that a specific unit among the N controllable switch units is turned on, and the remaining N-1 units are all turned off.

[0059] The controllable switch unit K can be composed of multiple or a single commonly used power devices in series and parallel, such as MOSFET, IGBT, diode, etc. The manufacturing material of the controllable switch unit K can be SiC, GaN, Si. The bypass capacitor C can provide different compensation voltages for each battery.

[0060] The controllable switch unit K may include a bidirectional controllable switch or a unidirectional controllable switch.

[0061] The bidirectional controllable switch can be composed of two controllable switch elements arranged on top of each other, and the controllable switch elements can be MOSFET or IGBT. Correspondingly, the energy of N batteries can flow in both directions, that is, the N batteries can be discharged or charged.

[0062] The unidirectional controllable switch can be composed of a diode connected in series with a MOSFET or a diode connected in series with an IGBT. Correspondingly, the energy of the N batteries can only flow in one direction, that is, the N batteries can only be discharged but not charged.

[0063] The controller is used to control a predetermined controllable switch unit K to be turned on to control the corresponding battery to be connected to the inductor so as to supply power to the load.

[0064] N DC power supplies share the inductor L, which greatly reduces the number of inductor components. Each DC power supply corresponds to a bypass capacitor C and a controllable switch unit K.

[0065] K n If the corresponding path is disconnected, the battery will be bypassed by the bypass capacitor Cn The load behind it forms a current loop, and the bypass capacitor C n Charging, K n If closed, the corresponding battery passes K n The load behind it forms a current loop, and the bypass capacitor C n Discharge. By controlling K n The opening and closing of the circuit and the relative length of time can control the battery power supply time and bypass capacitor C of the corresponding circuit. n voltage.

[0066] Note: The bypass capacitor C n For K n Provide bypass when disconnected, bypass capacitor C n The withstand voltage is low, thus reducing the circuit cost, and further, capacitors with smaller capacitance values ​​can be selected.

[0067] Embodiment 1:

[0068] Taking two battery current equalization as an example, the circuit topology is a two-input DC power balancer, such as Figure 5 As shown. o Represents the post-stage voltage stabilizing capacitor. Each battery corresponds to a bypass capacitor C and two bidirectional controllable switches S. Each bidirectional controllable switch is composed of a MOSFET. The two batteries share an inductor L. Assume that the voltages of the two batteries are V 1 and V 2 , the output current is I 1 and I 2 , the current flowing through the bypass capacitor is I C1 and I C2 .

[0069] According to the direction of energy flow, the circuit operation mode can be divided into battery charging process and discharging process, which are controlled by the on-off of the bidirectional controllable switch. 1 The anti-parallel diode is conducting and S 2 The switch is on, or S 3 The anti-parallel diode is conducting and S 4 When the switch is turned on, it is the battery discharge process; S 2 The anti-parallel diode is conducting and S 1 The switch is on, or S 4 The anti-parallel diode is conducting and S 3 The charging process occurs when the switch is turned on.

[0070] The working principle of the circuit is introduced using the discharge process as an example.

[0071] Figure 6 is a bidirectional controllable switch S 1 The anti-parallel diode is conducting and S 2 Switch on, S3 , S 4 Shut down; Figure 7 For S 1 , S 2 Shutdown, S 3 The anti-parallel diode is conducting and S 4 The switch is on.

[0072] The bidirectional controllable switch driving pulses in the two paths are complementary. Assume that the magnitude relationship of the two battery voltages in the steady state of the circuit is V 1 >V 2 , it can be deduced from the circuit principle:

[0073] V 2 <V o <V 1

[0074] That is, in steady state, the output voltage is between the two input voltages. Capacitor C 1 The voltage V C1 is (V 1 -V o )>0V, capacitor C 2 The voltage V C2 is (V 2 -V o )<0V. Therefore, the maximum voltage of the bypass capacitor is the difference of the battery voltage, which is much smaller than the normal voltage of the battery. Therefore, the voltage stress of the bypass capacitor is very small, which reduces the circuit cost.

[0075] like Figure 6 As shown, the first working mode: S 1 The anti-parallel diode is conducting and S 2 Switch on, S 3 , S 4 Off. Battery 1, S 1 , S 2 , inductor L and stabilizing capacitor C O At this time, battery 1 supplies power to the load behind it, so battery 1 discharges, V 1 Decreases. Since (V 1 -V o )>0, so the inductor current increases. C1 and V C2 is a very small voltage, so the capacitor C 1 , C 2 The current is very small and can be ignored here, so V 2 At this time, the two MOSFETs facing each other, namely S 3 With S 4 The voltage is (V 1 -V 2 ).

[0076] like Figure 7 As shown, the second working mode: S 1 , S 2 Shutdown, S 3 The anti-parallel diode is conducting and S 4 The switch is on. Battery 2, S 3 , S 4 , inductor L and stabilizing capacitor C O At this time, battery 2 supplies power to the load behind it, so battery 2 discharges, V 2 Decreases. Since (V 2 -V o )<0, so the inductor current decreases. V 1 At this time, the two MOSFETs facing each other, namely S 1 With S 2 The voltage is (V 2 -V 1 ).

[0077] Before the two battery currents are completely equal, the first working mode and the second working mode work alternately in a periodic cycle. 1 , S 2 and S 3 , S 4 ) conduction time, that is, adjust the duty cycle D and adjust the bypass capacitor C 1 , C 2 The voltage of the two batteries is controlled, thereby achieving the same output current of the two batteries.

[0078] The charging and discharging processes and principles of battery 1 and battery 2 are similar, except that energy flows from the load (such as the power grid) side to the battery through a bidirectional controllable switch, which will not be repeated here.

[0079] From the above analysis, it can be seen that the voltage stress of the bidirectional controllable switch is the difference in battery voltage, which is very small and much smaller than the normal voltage of the battery. Therefore, the bidirectional controllable switch can select a switch device with small voltage stress, which reduces the cost.

[0080] The above-mentioned power balancer with bidirectional energy flow can be applied to, but is not limited to, energy storage systems.

[0081] To achieve the goal of current sharing, the closed-loop control algorithm of the controller collects the current of one of the multiple batteries as the given current of the other batteries, and performs closed-loop control to make the currents of the multiple batteries tend to be consistent. Taking the current of sampled battery 1 as an example, the current of battery 2 is closed-loop controlled. Detect the output current I of battery 1 1 As I 2 The given value of the switch tube S 2 With S4 The duty cycle D eventually makes I 2 Tend to I 1 , the two batteries achieve current sharing.

[0082] Use Matlab / Simulink software to build a simulation model with two battery inputs, and the output results are as follows: Figure 8 As shown in FIG. 1 , after the current sharing control, the currents of the two batteries are shared.

[0083] When applied to photovoltaic systems, taking two photovoltaic cells as an example, the system diagram is as follows: Fig. 9 As shown, the system circuit and the circuit topology of the power balancer are as follows Fig.10 As shown. Since energy flows in one direction, only from the photovoltaic cell to the output side, a diode and MOSFET are connected in series. Fig.11 and Fig.12 As shown in the figure, the working process and principle are the same as the discharge process of the DC power balancer with bidirectional energy flow, which will not be repeated here. The difference is that the control target in the battery current sharing process is the battery current, while when applied to the photovoltaic system, the control target is the voltage of the photovoltaic cell. The voltage value at the maximum power point of the photovoltaic cell can be obtained by using the existing method, and this value is used as the given voltage of the closed-loop control algorithm of the controller for closed-loop control. By controlling the switch tube S 1 With S 2 The circuit will be turned on and off. Fig.11 and Fig.12 The two circuit modes work alternately by adjusting the bypass capacitor C 1 , C 2 The voltage of the photovoltaic cell eventually makes the actual voltage of the photovoltaic cell approach the maximum power point voltage, and the two photovoltaic cells reach their respective maximum power points, thus achieving an increase in the power generation of the photovoltaic system. Fig.11 As shown, when two photovoltaic cells are directly connected in parallel, the voltage is V MPP Due to the difference between the two photovoltaic cells, the power generation cannot reach the maximum at this time; the bypass capacitor C of the two input power balancers 1 , C 2 The compensation voltage provided is ΔV 1 and ΔV 2 After voltage compensation, the voltage of the two photovoltaic cells increases from the original VMPP to their respective maximum power point voltage V 1m and V 2m , each outputs maximum power, achieving an overall increase in power generation.

[0084] The key points of the present invention are as follows:

[0085] (1) The concept of "DC power balancer" is proposed. It is connected to the output of the battery to replace the original direct parallel connection scheme. A compensation voltage is provided based on the DC power supply voltage in the original direct parallel connection. The voltage of each battery can be controlled separately to achieve the same output current of each battery, thus solving the problem of uneven current in parallel connection of batteries.

[0086] (2) A new circuit topology for DC power balancer is proposed. The voltage difference between multiple batteries is processed. The battery voltage difference is generally small, so the voltage stress of the switch elements and capacitor elements of this topology is small, which is conducive to reducing costs and achieving higher switching frequency.

[0087] (3) A current equalization control method for a DC power balancer is proposed. The current of one of the multiple batteries is used as the given current of each battery for closed-loop control. The current of each battery can be controlled by adjusting the duty cycle and then the battery voltage.

[0088] (4) The proposed DC power balancer circuit structure is multi-input and single output, and the input is connected to the battery. If N batteries are input, the DC power balancer has N power inputs and only 1 output.

[0089] (5) In the circuit topology of the DC power balancer, the bypass capacitor is connected between the battery and the output, and its voltage is a very small compensation voltage, so a capacitor with a very small capacitance can be selected.

[0090] The beneficial effects of the present invention are as follows:

[0091] (1) The problem of uneven current flow in batteries is solved. The concept of a DC power balancer is proposed, which is connected to the output of the battery to replace the original direct parallel connection solution. The voltage of each battery can be controlled separately to achieve parallel current flow of multiple batteries.

[0092] (2) The voltage stress of the switch elements of the proposed new circuit topology is low, which is only the difference between the battery voltages. The battery voltage difference is generally very small, so the voltage stress of the internal switch elements and capacitor elements is small, which is conducive to reducing costs and achieving higher switching frequencies. It has good competitiveness in low cost, high efficiency, and high power density.

[0093] (3) The proposed topology is simple and easy to implement in achieving current balancing. The current of one of the multiple batteries is used as the given current of each battery for closed-loop control. The current of each battery can be controlled by adjusting the duty cycle and then the battery voltage.

[0094] (4) Using Matlab / Simulink software, two batteries with different parameters are controlled and simulated using a two-input DC power balancer. Figure 8 The simulation results are presented, showing the current sharing effect of the system after the use of the power balancer.

[0095] (5) When applied to a photovoltaic system, the PV curve diagram of the achieved effect is as follows Fig.13 The simulation results are shown in Fig.14 As shown, taking two photovoltaic cells in parallel as an example, before using the power balancer, the photovoltaic cells are directly connected in parallel, and the voltages of the photovoltaic cells are not exactly the same. After using the two-input power balancer, the photovoltaic cells work independently to their respective maximum power points, and the total power generation is improved.

[0096] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0097] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A multi-input DC power balancer, characterized in that: The N input terminals of the multi-input DC power balancer are connected to the positive terminals of the N DC power supplies in a one-to-one correspondence, and the multi-input DC power balancer includes a controller, an inductor, N bypass capacitors and N controllable switch units; One end of the N controllable switch units is simultaneously connected to the positive ends of the N DC power supplies and one end of the N bypass capacitors in a one-to-one correspondence, the other ends of the N controllable switch units are connected to one end of the inductor, and the other ends of the N bypass capacitors are connected to the other end of the inductor and are led out as an output end of the multi-input DC power balancer; the negative ends of the N DC power supplies are connected together and led out as another output end of the multi-input DC power balancer; The N controllable switch units are all connected to the controller, and the controller is used to control the on and off of the controllable switch units and their time, so that a specific unit among the N controllable switch units is turned on, and the remaining N-1 units are all turned off.

2. The multi-input DC power balancer according to claim 1, characterized in that: Each of the controllable switch units includes a bidirectional controllable switch.

3. The multi-input DC power balancer according to claim 2, characterized in that: The bidirectional controllable switch is composed of two controllable switch elements arranged opposite to each other.

4. The multi-input DC power balancer according to claim 3, characterized in that: The controllable switch element is MOSFET or IGBT.

5. The multi-input DC power balancer according to any one of claims 1 to 4, characterized in that: The DC power source is a chargeable and dischargeable battery.

6. The multi-input DC power balancer according to claim 1, characterized in that: Each of the controllable switch units includes a unidirectional controllable switch.

7. The multi-input DC power balancer according to claim 6, characterized in that: The unidirectional controllable switch is composed of a diode connected in series with a MOSFET or a diode connected in series with an IGBT.

8. The multi-input DC power balancer according to claim 6 or 7, characterized in that: The DC power source is a photovoltaic cell.

9. The multi-input DC power balancer according to claim 1, characterized in that: A voltage stabilizing capacitor is connected in parallel between the two output ends of the multi-input DC power balancer.

10. A photovoltaic system, characterized in that: The photovoltaic system applies the multi-input DC power balancer described in any one of claims 1 to 9, and the photovoltaic system includes: a photovoltaic cell, a multi-input DC power balancer and a photovoltaic inverter, the positive pole of the photovoltaic cell is correspondingly connected to the input end of the multi-input DC power balancer, and the two output ends of the multi-input DC power balancer are correspondingly connected to the two input ends of the photovoltaic inverter.

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