Multi-stage cascaded converter for management and control among battery clusters

Abstract

The invention relates to a multi-stage cascaded converter for management and control among battery clusters, which comprises multi-stage cascaded DC converters capable of bidirectionally flowing power, the DC converter arranged at the first stage is an isolated DC converter, and the DC converters arranged at the other stages are non-isolated DC converters; the isolated direct-current converter comprises one or two sub power conversion circuits, and the non-isolated direct-current converter comprises one or more sub non-isolated power conversion circuits which are connected in parallel; the cascade converter is connected in series on the battery cluster and takes electricity from the battery cluster, and the control of the charging current and the discharging current of the parallel battery cluster can be realized by changing the series compensation voltage. Compared with the prior art, the multi-stage cascaded converter has an isolation function and a wide-range voltage regulation capability, the stress meets the port voltage and charging and discharging current requirements of a battery cluster, the multi-stage cascaded converter has a stable voltage source capability adapting to rapid change of a large-current load, and has a coordinated control capability on cost, efficiency and power density.

Description

Technical Field

[0001] The present invention relates to the field of power electronics technology and battery energy storage systems, and in particular to a multi-stage cascade converter for battery cluster control. Background Art

[0002] The smallest basic unit of the electrochemical energy storage system is the battery cell. The system architecture is that several battery cells are connected in series to form a battery module, several battery modules are connected in series to form a battery cluster, and several battery clusters are connected in parallel to form an energy storage unit. The energy storage unit is connected to the power grid through an energy storage inverter and a step-up transformer.

[0003] Due to the inconsistency of battery cells in manufacturing, working environment, and aging, the open circuit voltage and equivalent series impedance of each battery cell are inconsistent. During the charge and discharge cycle of the energy storage system, the state of charge of different battery cells is different, and the port voltage of different battery cells is different. Since the battery module is composed of several battery cells connected in series, the port voltage of different battery modules is different. Since the battery cluster is composed of several battery modules connected in series, the port voltage of different battery clusters is different.

[0004] In the energy storage unit of the electrochemical energy storage system, several battery clusters with different port voltages are connected in parallel. The voltage difference between the battery clusters acts on the line impedance between the parallel battery clusters to generate current, which is defined as the circulating current between the parallel battery clusters. The circulating current consumes electrical energy through the line impedance, generates heat dissipation, causes losses, and reduces the overall charge and discharge cycle efficiency of the energy storage system.

[0005] In order to suppress the circulation between battery clusters and improve the system efficiency, it is necessary to manage the battery clusters in a refined manner. For example, the prior art patent CN114204647B provides a parallel battery cluster state management system solution, the structure of which is as follows: Figure 1 As shown, R Bat is the impedance of the battery cluster itself, U OCVis the open circuit voltage. Each battery cluster is connected in series with a voltage source and then in parallel with other battery clusters to form a common DC bus. The voltage difference between battery clusters caused by the inconsistency of battery cells can be compensated by controlling the voltage of the voltage source, which suppresses the formation of circulation between battery clusters. The power of the voltage source is much smaller than the power of the battery cluster, and the proportion of the voltage source power is the ratio of the rated compensation voltage of the voltage source to the rated voltage of the battery cluster. The voltage source is composed of a DC / DC converter. The maximum voltage specification of the DC / DC converter input is the same as the maximum voltage of the battery cluster, and the maximum current specification of the output is the same as the maximum charge and discharge current allowed by the battery cluster. The maximum compensation voltage specification of the output is determined by the maximum difference in the voltage of the parallel battery cluster ports, and a certain adjustment margin is reserved. The DC / DC converter has the following application requirements: it needs to have an isolation structure, meet high voltage input, large current output, bidirectional power flow, adapt to the voltage source control mode with rapid changes in load current, and an ultra-wide gain voltage adjustment range.

[0006] Therefore, how to realize a power converter that meets the above application requirements is currently an urgent need. Summary of the invention

[0007] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and provide a multi-stage cascade converter for battery cluster control.

[0008] The purpose of the present invention can be achieved by the following technical solutions:

[0009] A multi-stage cascade converter for inter-cluster battery management, comprising a multi-stage cascaded DC converter capable of bidirectional power flow, wherein the first stage is an isolated DC converter, and the remaining stages are non-isolated DC converters; the isolated DC converter comprises one or two sub-power conversion circuits, and the non-isolated DC converter comprises one or more parallel sub-non-isolated power conversion circuits; the cascade converter is connected in series to a battery cluster and draws power from the battery cluster, and controls the charging current and discharging current of the parallel battery cluster by changing the series compensation voltage.

[0010] Preferably, the method for selecting the number of sub-power conversion circuits inside the isolated DC converter includes: using one sub-power conversion circuit when the primary switch voltage stress specification of the sub-power conversion circuit meets the usage stress, otherwise using two sub-power conversion circuits.

[0011] Preferably, the sub-power conversion circuit includes a transformer, a primary circuit and a secondary circuit, the primary circuit includes a first primary capacitor, a second primary capacitor, a first primary switch, a second primary switch, a resonant inductor and a resonant capacitor, and the secondary circuit includes a first secondary switch, a second secondary switch, a third secondary switch, a fourth secondary switch and a secondary capacitor; the first primary capacitor is connected between the positive input terminal of the sub-power conversion circuit and the positive end of the second primary capacitor, the negative end of the second primary capacitor is connected to the negative input terminal of the sub-power conversion circuit, the first primary switch is connected between the positive end of the first primary capacitor and the first end of the second primary switch, and the second end of the second primary switch is connected to the first primary capacitor. The negative end of the second primary capacitor, the resonant inductor is connected between the first end of the second primary switch and the first end of the primary winding of the transformer, and the resonant capacitor is connected between the second end of the primary winding of the transformer and the positive end of the second primary capacitor; the first secondary switch is connected between the positive end of the secondary capacitor and the first end of the second secondary switch, the second end of the second secondary switch is connected to the negative end of the secondary capacitor, the third secondary switch is connected between the positive end of the secondary capacitor and the first end of the fourth secondary switch, the second end of the fourth secondary switch is connected to the negative end of the secondary capacitor, the first end of the secondary winding of the transformer is connected to the first end of the second secondary switch, and the second end of the secondary winding of the transformer is connected to the first end of the fourth secondary switch.

[0012] Preferably, when the isolated DC converter includes two sub-power conversion circuits, the two sub-power conversion circuits are connected in series on the DC side of the primary circuit, connected in parallel on the DC side of the secondary circuit, and share a secondary capacitor.

[0013] Preferably, the sub-non-isolated power conversion circuit includes an input capacitor, an output capacitor, an energy storage inductor, a first switch and a second switch; the first switch is connected between the positive end of the input capacitor and the first end of the second switch, the second end of the second switch is connected to the negative end of the input capacitor, the energy storage inductor is connected between the first end of the second switch and the positive end of the output capacitor, and the negative end of the output capacitor is connected to the negative end of the input capacitor.

[0014] Preferably, when the non-isolated DC converters are cascaded, their input capacitors are also the output capacitors of the previous-stage DC converters, and their output capacitors are also the input capacitors of the next-stage DC converters.

[0015] Preferably, the method for selecting the number of parallel sub-non-isolated power conversion circuits inside the non-isolated DC converter includes: selecting the minimum parallel number that meets thermal stress conditions and reliability conditions based on the thermal stress specifications and current stress of the first switch and the second switch of the sub-non-isolated power conversion circuit and on the premise of meeting the current range of the battery cluster.

[0016] Preferably, the method for selecting the cascade number of the non-isolated DC converter includes:

[0017] The gain range that a single-stage non-isolated DC converter can handle is determined based on the processing capability of the digital signal processor for the gain range. The input voltage and output voltage ranges of the converter are then determined based on the compensation voltage range and the output voltage range of the first-stage isolated DC converter. Finally, the optimal number of cascades is determined for cost, efficiency and power density.

[0018] Preferably, the cascade converter is applied to a battery cluster with a voltage in the range of 1000V-1500V, and the compensation voltage range is set to 1V-40V.

[0019] Preferably, the cascade converter is specifically three-stage, the isolated DC converter arranged at the first stage has a fixed gain ratio of 20, the non-isolated DC converter arranged at the second stage has a gain between 0.1-0.9, and the non-isolated DC converter arranged at the third stage has a gain between 0.1-0.9.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] 1. The present invention is a multi-stage cascade converter, which controls the charging current and discharging current of a parallel battery cluster by changing the series compensation voltage. The converter has an isolation function and a wide range of voltage adjustment capability, which can meet the port voltage and charging and discharging current requirements of the battery cluster and has the ability to provide a stable voltage source that can adapt to rapid changes in large current loads.

[0022] 2. The first-stage compensation voltage source converter is an isolated DC converter that can meet the isolation requirements, battery cluster voltage stress requirements, and load change dynamic response requirements, and can achieve the functions of fixed gain step-down, isolation and bidirectional power flow.

[0023] 3. The multi-stage non-isolated DC converter after the second stage can meet the voltage regulation capability, battery cluster current stress requirements, and load change dynamic response requirements, and can realize the functions of variable gain step-down and bidirectional power flow. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of a battery cluster voltage compensation system in the prior art;

[0025] Figure 2 A topological cascade structure diagram of a multi-stage cascade converter of the present invention;

[0026] Figure 3 It is a connection diagram of the converter of the present invention in a parallel battery cluster management system;

[0027] Figure 4 Schematic diagram of the structure of a three-stage cascade converter according to an embodiment of the present invention;

[0028] Figure 5Schematic diagram of the distribution of voltage conversion functions of each stage of a three-stage cascade converter according to an embodiment of the present invention. DETAILED DESCRIPTION

[0029] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0030] In view of the problems existing in the prior art, the present invention provides a voltage source converter for battery cluster control, specifically a multi-stage cascade converter for battery cluster control, such as Figure 2 As shown, it includes a multi-stage cascaded DC converter capable of bidirectional power flow, wherein the first stage is an isolated DC converter, and the remaining stages are non-isolated DC converters. Figure 3 As shown, the cascade converter of the present invention is connected in series to the battery cluster and draws power from the battery cluster. By changing the series compensation voltage, the charging current and discharging current of the parallel battery cluster can be controlled. For example, when the system is in a charging state and the SOC (state of charge) of the first battery cluster is higher than the SOC of other battery clusters, the output voltage of the cascade converter 1 is controlled so that the output voltage of the cascade converter 1 increases, thereby reducing the charging current of the first battery cluster, that is, the increase of the SOC of the first battery cluster slows down, and finally the SOC of each battery cluster is consistent; when the system is in a discharging state and the SOC of the first battery cluster is higher than the SOC of other battery clusters, the output voltage of the cascade converter 1 is controlled so that the output voltage of the cascade converter 1 increases, thereby increasing the discharge current of the first battery cluster, that is, the decrease of the SOC of the first battery cluster is accelerated, and finally the SOC of each battery cluster is consistent.

[0031] The first-stage isolated DC converter provides isolation, the ability to stabilize the input voltage of the subsequent non-isolated DC converter when the load changes rapidly, and fixed high-gain conversion capability. The subsequent non-isolated DC converter of the cascade converter provides wide-range voltage regulation capability and stable compensation voltage capability for rapid changes in large current loads.

[0032] Figure 2 In this embodiment, the first influencing factor for selecting the number of non-isolated DC converter cascades is the compensation voltage U CThe second influencing factor is the range of the voltage at the output end of the first-stage isolated DC converter, and the third influencing factor is the processing capability of the digital signal processor for the gain range. The method for selecting the number of cascaded non-isolated DC converters includes: determining the gain range that a single-stage non-isolated DC converter can handle according to the processing capability of the digital signal processor for the gain range, and then determining its own input voltage and output voltage range according to the compensation voltage range and the voltage range at the output end of the first-stage isolated DC converter, and finally determining the number of cascades with the best combination of cost, efficiency and power density.

[0033] The isolated DC converter includes one or two sub-power conversion circuits, and the non-isolated DC converter includes one or more parallel-connected sub-non-isolated power conversion circuits.

[0034] The sub-power conversion circuit includes a transformer, a primary circuit and a secondary circuit. The primary circuit includes a first primary capacitor, a second primary capacitor, a first primary switch, a second primary switch, a resonant inductor and a resonant capacitor. The secondary circuit includes a first secondary switch, a second secondary switch, a third secondary switch, a fourth secondary switch and a secondary capacitor. The first primary capacitor is connected between the positive input end of the sub-power conversion circuit and the positive end of the second primary capacitor, the negative end of the second primary capacitor is connected to the negative input end of the sub-power conversion circuit, the first primary switch is connected between the positive end of the first primary capacitor and the first end of the second primary switch, the second end of the second primary switch is connected to the negative end of the second primary capacitor, the resonant inductor is connected between the first end of the second primary switch and the first end of the primary winding of the transformer, and the resonant capacitor is connected between the second end of the primary winding of the transformer and the positive end of the second primary capacitor. The first secondary switch is connected between the positive end of the secondary capacitor and the first end of the second secondary switch, the second end of the second secondary switch is connected to the negative end of the secondary capacitor, the third secondary switch is connected between the positive end of the secondary capacitor and the first end of the fourth secondary switch, the second end of the fourth secondary switch is connected to the negative end of the secondary capacitor, the first end of the secondary winding of the transformer is connected to the first end of the second secondary switch, and the second end of the secondary winding of the transformer is connected to the first end of the fourth secondary switch.

[0035] The first influencing factor for the selection of the number of sub-power conversion circuits in the isolated DC converter is the battery cluster voltage U Bat , the second influencing factor is the primary switch voltage stress specification. The selection method includes: when the primary switch voltage stress specification of the sub-power conversion circuit meets the use stress, one sub-power conversion circuit is used, otherwise two sub-power conversion circuits are used, so that the cost, efficiency and power density are optimal. When the isolated DC converter includes two sub-power conversion circuits, the two sub-power conversion circuits are connected in series on the DC side of the primary circuit, in parallel on the DC side of the secondary circuit, and share a secondary capacitor.

[0036] The sub-non-isolated power conversion circuit includes an input capacitor, an output capacitor, an energy storage inductor, a first switch, and a second switch. The first switch is connected between the positive end of the input capacitor and the first end of the second switch, the second end of the second switch is connected to the negative end of the input capacitor, the energy storage inductor is connected between the first end of the second switch and the positive end of the output capacitor, and the negative end of the output capacitor is connected to the negative end of the input capacitor.

[0037] When non-isolated DC converters are cascaded, their input capacitors are also the output capacitors of the previous DC converter, and their output capacitors are also the input capacitors of the next DC converter.

[0038] The first influencing factor for selecting the number of parallel sub-non-isolated power conversion circuits in the non-isolated DC converter is the battery cluster current I Bat The second influencing factor is the thermal stress specification and current stress of the first switch and the second switch of the sub-non-isolated power conversion circuit. If a single switch does not meet the first influencing factor, the condition can be met by connecting switches in parallel. The method for selecting the number of sub-non-isolated power conversion circuits in parallel includes: selecting the minimum number of parallel connections that meet the thermal stress condition and the reliability condition based on the thermal stress specification and current stress of the first switch and the second switch of the sub-non-isolated power conversion circuit and on the premise of meeting the current range of the battery cluster.

[0039] Example

[0040] Figure 4 It is a specific structural diagram of a three-stage cascade converter provided in this embodiment.

[0041] In this embodiment, the first-stage isolation converter includes two sub-power conversion circuits, the input is U Bat The DC sides of the primary circuits of the two sub-power conversion circuits are connected in series, and the DC sides of the secondary circuits are connected in parallel and connected to a common secondary capacitor C. 12 .

[0042] The sub-power conversion circuit 1 includes a first primary capacitor C1, a second primary capacitor C2, a first primary switch Q1, a second primary switch Q2, a resonant capacitor C r1 , resonant inductor L r1 , transformer T1, first secondary switch S1, second secondary switch S2, third secondary switch S3, fourth secondary switch S4 and secondary capacitor C 12 The first primary capacitor C1 is electrically connected to the positive input terminal of the sub-power conversion circuit, namely U Bat The first primary switch Q1 is electrically connected between the positive end of the first primary capacitor C1 and the positive end of the second primary capacitor C2; the second primary capacitor C2 is electrically connected between the negative end of the first primary capacitor C1 and the negative input end of the sub-power conversion circuit 1 (i.e., the positive input end of the sub-power conversion circuit 2); the first primary switch Q1 is electrically connected between the positive end of the first primary capacitor C1 and the first end of the second primary switch Q2; the resonant inductor Lr1 The resonant capacitor C is electrically connected between the first end of the second primary switch Q2 and the first end of the primary winding of the transformer T1; r1 The first secondary switch S1 is electrically connected between the second end of the primary winding of the transformer T1 and the positive end of the second primary capacitor C2; the second end of the second primary switch Q2 is electrically connected to the negative end of the second primary capacitor C2. 12 The second end of the second secondary switch S2 is electrically connected to the secondary capacitor C 12 The third secondary switch S3 is electrically connected to the secondary capacitor C 12 The second end of the fourth secondary switch S4 is electrically connected to the secondary capacitor C 12 a first end of the secondary winding of the transformer T1 is electrically connected to a first end of the second secondary switch S2, and a second end of the secondary winding is electrically connected to a first end of the fourth secondary switch S4.

[0043] The second sub-power conversion circuit includes a first primary capacitor C3, a second primary capacitor C4, a first primary switch Q3, a second primary switch Q4, a resonant capacitor C r2 , resonant inductor L r2 , transformer T2, first secondary switch S5, second secondary switch S6, third secondary switch S7, fourth secondary switch S8, and a sub-power conversion circuit share a secondary capacitor C 12 The first primary capacitor C3 is electrically connected between the positive input terminal of the second sub-power conversion circuit (i.e., the negative input terminal of the first sub-power conversion circuit) and the positive terminal of the second primary capacitor C4; the second primary capacitor C4 is electrically connected between the negative terminal of the first primary capacitor C3 and the negative input terminal of the second sub-power conversion circuit (i.e., the negative input terminal of the first sub-power conversion circuit). Bat The first primary switch Q3 is electrically connected between the positive end of the first primary capacitor C3 and the first end of the second primary switch Q4; the resonant inductor L r2 The resonant capacitor C is electrically connected between the first end of the second primary switch Q4 and the first end of the primary winding of the transformer T2; r2 The first secondary switch S5 is electrically connected between the second end of the primary winding of the transformer T2 and the positive end of the second primary capacitor C4; the second end of the second primary switch Q4 is electrically connected to the negative end of the second primary capacitor C4; the first secondary switch S5 is electrically connected to the secondary capacitor C 12 The second end of the second secondary switch S6 is electrically connected to the secondary capacitor C 12 The third secondary switch S7 is electrically connected to the secondary capacitor C 12 The second end of the fourth secondary switch S8 is electrically connected to the secondary capacitor C 12a first end of the secondary winding of the transformer T2 is electrically connected to a first end of the second secondary switch S6, and a second end of the secondary winding is electrically connected to a first end of the fourth secondary switch S8.

[0044] The second-stage non-isolated DC converter includes four sub-non-isolated power conversion circuits. The inputs of the four sub-non-isolated power conversion circuits are connected in parallel, and the common input capacitor is the common secondary capacitor C of the isolated DC converter. 12 , the output is connected in parallel, and the common output capacitor C 23 .

[0045] The non-isolated power conversion circuit includes an energy storage inductor L 21 , the first switch S 21 , the second switch S 22 . The first switch S 21 Electrically connected to the input capacitor C 12 The positive terminal of the second switch S 22 The first end of the second switch S 22 The second end is electrically connected to the input capacitor C 12 The negative terminal; energy storage inductor L 21 Electrically connected to the first switch S 21 The second terminal of the output capacitor C 23 Between the positive terminals, the output capacitor C 23 The negative terminal of the input capacitor C 12 The non-isolated power conversion circuit 2 includes an energy storage inductor L 22 , the first switch S 23 , the second switch S 24 . The first switch S 23 Electrically connected to the input capacitor C 12 The positive terminal of the second switch S 24 The first end of the second switch S 24 The second end is electrically connected to the input capacitor C 12 The negative terminal; energy storage inductor L 22 Electrically connected to the first switch S 23 The second terminal of the output capacitor C 23 The non-isolated power conversion circuit 3 includes an energy storage inductor L 23 , the first switch S 25 , the second switch S 26 . The first switch S 25 Electrically connected to the input capacitor C 12 The positive terminal of the second switch S 26 The first end of the second switch S 25 The second end is electrically connected to the input capacitor C 12 The negative terminal; energy storage inductor L 23 Electrically connected to the first switch S 25The second terminal of the output capacitor C 23 The non-isolated power conversion circuit 4 includes an energy storage inductor L 24 , the first switch S 27 , the second switch S 28 . The first switch S 27 Electrically connected to the input capacitor C 12 The positive terminal of the second switch S 28 The first end of the second switch S 28 The second end is electrically connected to the input capacitor C 12 The negative terminal; energy storage inductor L 24 Electrically connected to the first switch S 27 The second terminal of the output capacitor C 23 between the positive ends.

[0046] The third-stage non-isolated DC converter includes six sub-non-isolated power conversion circuits. The inputs of the six sub-non-isolated power conversion circuits are connected in parallel, and the common input capacitor is the common output capacitor C of the second-stage non-isolated DC converter. 23 , the output is connected in parallel, and the common output capacitor is C5, which is the output compensation voltage U of the entire cascade converter. c .

[0047] The non-isolated power conversion circuit 5 includes an energy storage inductor L 31 , the first switch S 31 , the second switch S 32 . The first switch S 31 Electrically connected to the input capacitor C 23 The positive terminal of the second switch S 32 The first end of the second switch S 32 The second end is electrically connected to the input capacitor C 23 The negative terminal; energy storage inductor L 31 Electrically connected to the first switch S 31 The second end of the output capacitor C5 is connected to the positive end of the output capacitor C5, and the negative end of the output capacitor C5 is connected to the input capacitor C 23 The non-isolated power conversion circuit 6 includes an energy storage inductor L 32 , the first switch S 33 , the second switch S 34 . The first switch S 33 Electrically connected to the input capacitor C 23 The positive terminal of the second switch S 34 The first end of the second switch S 34 The second end is electrically connected to the input capacitor C 23 The negative terminal; energy storage inductor L 32 Electrically connected to the first switch S 33The non-isolated power conversion circuit 7 includes an energy storage inductor L 33 , the first switch S 35 , the second switch S 36 . The first switch S 35 Electrically connected to the input capacitor C 23 The positive terminal of the second switch S 36 The first end of the second switch S 36 The second end is electrically connected to the input capacitor C 23 The negative terminal; energy storage inductor L 33 Electrically connected to the first switch S 35 The non-isolated power conversion circuit eight includes an energy storage inductor L 34 , the first switch S 37 , the second switch S 38 . The first switch S 37 Electrically connected to the input capacitor C 23 The positive terminal of the second switch S 38 The first end of the second switch S 38 The second end is electrically connected to the input capacitor C 23 The negative terminal; energy storage inductor L 34 Electrically connected to the first switch S 37 The non-isolated power conversion circuit 9 includes an energy storage inductor L 35 , the first switch S 39 , the second switch S 310 . The first switch S 39 Electrically connected to the input capacitor C 23 The positive terminal of the second switch S 310 The first end of the second switch S 310 The second end is electrically connected to the input capacitor C 23 The negative terminal; energy storage inductor L 35 Electrically connected to the first switch S 39 The non-isolated power conversion circuit comprises an energy storage inductor L 36 , the first switch S 311 , the second switch S 312 . The first switch S 311 Electrically connected to the input capacitor C 23 The positive terminal of the second switch S 312 The first end of the second switch S 312 The second end is electrically connected to the input capacitor C 23 The negative terminal; energy storage inductor L 36 Electrically connected to the first switch S 311 between the second end of and the positive end of the output capacitor C5.

[0048] Figure 5 This is a schematic diagram of the voltage conversion function distribution of each level of the three-level cascade converter in this embodiment. Based on the application function and implementation perspective of the multi-level cascade converter, the cascade converter for inter-cluster control is applied to the battery cluster U with a minimum voltage of around 1000V and a maximum voltage of around 1500V. Bat , compensation voltage U C The range is set to 1V-40V, and the battery cluster current I Bat The absolute maximum value is 200A.

[0049] The fixed gain ratio of the first-stage isolated DC converter is 20. 12 The power direction can be from the primary side to the secondary side of the isolated DC converter, or from the secondary side to the primary side, depending on the effect on C 12 The load conditions on the

[0050] The gain of the second-stage non-isolated DC converter is between 0.1 and 0.9, which will act on the input capacitor C 12 The 50V-75V voltage is converted into 7.5V-40V, which meets the gain range that can be achieved under the digital processing controller. According to the capabilities of the digital processing controller, the gain range of 0.1-0.9 can be expanded or reduced. The power direction can be determined from the input capacitor C 12 To the output capacitor C 23 , or from the output capacitor C 23 To the input capacitor C 12 , according to the effect on C 23 The load conditions on the

[0051] The gain of the third-stage non-isolated DC converter is between 0.1 and 0.9, which will act on the input capacitor C 23 The 7.5V-9.4V voltage is converted into 1V-7.5V, which meets the gain range that can be achieved under the digital processing controller. According to the capabilities of the digital processing controller, the gain range of 0.1-0.9 can be expanded or reduced. The power direction can be obtained from the input capacitor C 23 To the output capacitor C5, or from the output capacitor C5 to the input capacitor C 23 , which is transformed according to the load conditions acting on C5.

[0052] The first influencing factor for the selection of the number of sub-power conversion circuits of the isolated DC converter is the battery cluster voltage U Bat In this embodiment, U BatThe range is 1000-1500V, and the second influencing factor is the primary switch voltage stress specification. Without loss of generality, for example, when the primary switch voltage stress is 1200V, two sub-power conversion circuits are used in series on the primary side; when the primary switch voltage stress is 2000V, one sub-power conversion circuit is used.

[0053] In the application of inter-cluster battery control, the multi-stage cascade converter has clear division of labor for each stage of the converter, and the control accuracy of the compensation voltage is within 0.3V difference, and the ripple peak value is within 0.3V. In addition, the design of the converter has coordinated control of cost, efficiency and power density. According to the application conditions, current switch technology conditions and digital control processor technology conditions, the optimal solution design of the multi-stage cascade converter for inter-cluster battery control is realized.

[0054] In the description of the present invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0055] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0056] The preferred specific embodiments of the present invention are described in detail above. It should be understood that a person skilled in the art can make many modifications and changes based on the concept of the present invention without creative work. Therefore, any technical solution that can be obtained by a person skilled in the art through logical analysis, reasoning or limited experiments based on the concept of the present invention on the basis of the prior art should be within the scope of protection determined by the claims.

Claims

1. A multi-level cascade converter for battery cluster control, characterized in that: A multi-stage cascaded DC converter capable of bidirectional power flow, wherein the first stage is an isolated DC converter and the remaining stages are non-isolated DC converters; the isolated DC converter includes one or two sub-power conversion circuits, and the non-isolated DC converter includes one or more parallel sub-non-isolated power conversion circuits; the cascaded converter is connected in series to a battery cluster and draws power from the battery cluster, and controls the charging current and discharging current of the parallel battery cluster by changing the series compensation voltage.

2. A multi-level cascade converter for battery cluster control according to claim 1, characterized in that: The method for selecting the number of sub-power conversion circuits inside the isolated DC converter includes: when the primary switch voltage stress specification of the sub-power conversion circuit meets the use stress, one sub-power conversion circuit is used, otherwise two sub-power conversion circuits are used.

3. A multi-level cascade converter for battery cluster control according to claim 1, characterized in that: The sub-power conversion circuit includes a transformer, a primary circuit and a secondary circuit, the primary circuit includes a first primary capacitor, a second primary capacitor, a first primary switch, a second primary switch, a resonant inductor and a resonant capacitor, and the secondary circuit includes a first secondary switch, a second secondary switch, a third secondary switch, a fourth secondary switch and a secondary capacitor; the first primary capacitor is connected between the positive input terminal of the sub-power conversion circuit and the positive terminal of the second primary capacitor, the negative terminal of the second primary capacitor is connected to the negative input terminal of the sub-power conversion circuit, the first primary switch is connected between the positive terminal of the first primary capacitor and the first terminal of the second primary switch, and the second terminal of the second primary switch is connected to the positive terminal of the second primary capacitor. The negative end of the secondary capacitor, the resonant inductor is connected between the first end of the second primary switch and the first end of the primary winding of the transformer, and the resonant capacitor is connected between the second end of the primary winding of the transformer and the positive end of the second primary capacitor; the first secondary switch is connected between the positive end of the secondary capacitor and the first end of the second secondary switch, the second end of the second secondary switch is connected to the negative end of the secondary capacitor, the third secondary switch is connected between the positive end of the secondary capacitor and the first end of the fourth secondary switch, the second end of the fourth secondary switch is connected to the negative end of the secondary capacitor, the first end of the secondary winding of the transformer is connected to the first end of the second secondary switch, and the second end of the secondary winding of the transformer is connected to the first end of the fourth secondary switch.

4. A multi-level cascade converter for battery cluster control according to claim 3, characterized in that: When the isolated DC converter includes two sub-power conversion circuits, the two sub-power conversion circuits are connected in series on the DC side of the primary circuit, connected in parallel on the DC side of the secondary circuit, and share a secondary capacitor.

5. The multi-level cascade converter for battery cluster control according to claim 1, characterized in that: The sub-non-isolated power conversion circuit includes an input capacitor, an output capacitor, an energy storage inductor, a first switch and a second switch; the first switch is connected between the positive end of the input capacitor and the first end of the second switch, the second end of the second switch is connected to the negative end of the input capacitor, the energy storage inductor is connected between the first end of the second switch and the positive end of the output capacitor, and the negative end of the output capacitor is connected to the negative end of the input capacitor.

6. A multi-level cascade converter for battery cluster control according to claim 5, characterized in that: When the non-isolated DC converters are cascaded, their input capacitors are simultaneously the output capacitors of the previous DC converter, and their output capacitors are simultaneously the input capacitors of the next DC converter.

7. A multi-level cascade converter for battery cluster control according to claim 5, characterized in that: The method for selecting the number of parallel sub-non-isolated power conversion circuits inside the non-isolated DC converter includes: selecting the minimum parallel number that meets thermal stress conditions and reliability conditions based on the thermal stress specifications and current stress of the first switch and the second switch of the sub-non-isolated power conversion circuit and on the premise of meeting the battery cluster current range.

8. The multi-level cascade converter for battery cluster control according to claim 1, characterized in that: The method for selecting the number of cascades of the non-isolated DC converter comprises: The gain range that a single-stage non-isolated DC converter can handle is determined based on the processing capability of the digital signal processor for the gain range. The input voltage and output voltage ranges of the converter are then determined based on the compensation voltage range and the output voltage range of the first-stage isolated DC converter. Finally, the optimal number of cascades is determined for cost, efficiency and power density.

9. The multi-level cascade converter for battery cluster control according to claim 1, characterized in that: The cascade converter is applied to a battery cluster with a voltage in the range of 1000V-1500V, and the compensation voltage range is set to 1V-40V.

10. A multi-level cascade converter for battery cluster control according to claim 9, characterized in that: The cascade converter specifically has three stages, the isolated DC converter at the first stage has a fixed gain ratio of 20, the non-isolated DC converter at the second stage has a gain between 0.1-0.9, and the non-isolated DC converter at the third stage has a gain between 0.1-0.9.

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