Battery string energy storage system control method

Abstract

The application discloses a kind of group string type battery energy storage system control methods, the group string type battery energy storage system control method according to the voltage dynamic of each battery cluster adjusts DC / AC converter total DC bus voltage, realizes the charge balance of each battery cluster by distributing the given value of each battery cluster current, realizes the quick regulation of each battery cluster current by the method of feedforward plus feedback, the amplitude of output voltage is adjusted by the way of phase-shift control of primary side converter of isolated DC / DC converter, the voltage of isolated transformer secondary side bipolarity is rectified into unipolarity voltage by the rectification control of secondary side converter of isolated DC / DC converter, so as to control the voltage of battery cluster series inductance, thereby controlling inductance current.The control method presented in the application is simple and effective, and can effectively realize the whole machine power control of group string type battery energy storage system.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of battery energy storage system, in particular to a group string battery energy storage system and a control method thereof. BACKGROUND

[0002] Energy storage is a key technology to solve the stability problem of new power system dominated by renewable energy, and energy storage converter plays a role in converting DC power of energy storage system into AC power acceptable by power grid, and is a core component of energy conversion of energy storage system. The group string battery energy storage system uses a scheme that each cluster of batteries is controlled by an independent power converter, and the utilization rate of battery cluster is high. However, the DC / DC converter used in the commonly used group string energy storage system has a rated power not less than the battery cluster connected in parallel, and has high cost and low efficiency. SUMMARY

[0003] The present application aims to provide a group string battery energy storage system and a control method thereof to solve at least one technical problem in the background technology.

[0004] In order to achieve the above-mentioned purpose, the present application adopts the following technical scheme: the group string battery energy storage system is composed of a DC / AC converter and a plurality of energy storage branches, the AC side of the DC / AC converter is connected with the power grid, and the total DC bus of the DC / AC converter is connected in parallel with the plurality of energy storage branches; each energy storage branch is composed of a filter inductor, an isolation type DC / DC converter and a battery cluster; the filter inductor, the output end of the isolation type DC / DC converter and the battery cluster are connected in series and connected in parallel as a whole on the total DC bus of the DC / AC converter, and the input end of each isolation type DC / DC converter is connected in parallel with the total DC bus or one of the plurality of DC buses of the DC / AC converter; when the input end of the isolation type DC / DC converter is connected in parallel with one of the plurality of DC buses, the input end of each isolation type DC / DC converter is evenly connected in parallel on each DC bus to balance the input and output power of each DC bus.

[0005] The total DC bus voltage of the DC / AC converter is dynamically adjusted according to the voltage of the battery cluster of each energy storage branch, and the lower limit value of the given value of the total DC bus voltage of the DC / AC converter is the highest value of the voltage of the battery cluster in each energy storage branch, which can be expressed as: wherein U dc，min is the lower limit value of the given value of the total DC bus voltage of the DC / AC converter, n is the total number of energy storage branches (i.e. battery clusters), U be，i is the voltage of the i-th battery cluster, and U is the highest value of the voltage of the battery cluster in each energy storage branch; the upper limit value of the given value of the total DC bus voltage of the DC / AC converter is the lowest value of the voltage of the battery cluster in each energy storage branch plus the maximum output voltage of the isolation type DC / DC converter, which can be expressed as: wherein Uminis the minimum value of the voltage of the battery cluster in each energy storage branch, U o，max Umaxis the maximum output voltage of the isolated DC / DC converter. The given value of the total DC bus voltage of the DC / AC converter is between the lower limit value and the upper limit value of the given value of the total DC bus voltage of the DC / AC converter. In order to ensure reliable operation of the system, one method of selecting the given value of the total DC bus voltage of the DC / AC converter is to take the average of the lower limit value and the upper limit value of the given value of the total DC bus voltage of the DC / AC converter, that is: wherein U dc，ref Ugivis the given value of the total DC bus voltage of the DC / AC converter.

[0006] The controller of the isolated DC / DC converter includes three parts: 1, a total current given value generator, 2, a SOC balancing controller, and 3, a current inner loop controller.

[0007] The total current given value generator is used to generate the given value of the total DC bus current injected by each energy storage branch. The total DC bus voltage of the DC / AC converter can be controlled by the DC / AC converter or by the isolated DC / DC converter. When the total DC bus voltage of the DC / AC converter is controlled by the DC / AC converter, the given value of the total DC bus current injected by each energy storage branch is the given value of the total output power of the energy storage system divided by the given value or the measured value of the total DC bus voltage of the DC / AC converter, which can be expressed as wherein I ref Igis the given value of the total DC bus current injected by each energy storage branch, P ref Pgis the given value of the total output power of the energy storage system, U dc，ref Ugis the given value or the measured value of the total DC bus voltage of the DC / AC converter; when the total DC bus voltage of the DC / AC converter is controlled by the isolated DC / DC converter, the DC / AC converter outputs power according to the power instruction, and the total DC bus voltage of the DC / AC converter is controlled by a double closed loop control. The input of the outer loop controller is the difference between the given value and the measured value of the total DC bus voltage of the DC / AC converter, and the output is the given value Igof the total DC bus current injected by each energy storage branch. ref

[0008] The SOC balancing controller is used to control the battery cluster charge balancing of each energy storage branch. After the given value Igof the total DC bus current injected by each energy storage branch is obtained ref ​Afterwards, the given value of each energy storage branch current is distributed aiming at controlling the charge balance of each energy storage branch battery cluster. In the discharging state, the current is distributed to each energy storage branch in proportion to the state of charge of the battery cluster in each energy storage branch, so as to maintain the charge balance of the battery cluster in each energy storage branch. The given value of each energy storage branch current can be expressed as: wherein I ref is the given value of the total DC bus current injected into each energy storage branch, I ref，i is the given value of the i-th energy storage branch current, SOC i is the state of charge of the battery cluster in the i-th energy storage branch, and is the sum of the state of charge of all battery clusters; in the charging state, the current is distributed to each energy storage branch in proportion to the available charging capacity of the battery cluster in each energy storage branch, so as to maintain the charge balance of the battery cluster in each energy storage branch. The given value of each energy storage branch current in the charging state can be expressed as: wherein (1-SOC i ) is the available charging capacity of the battery cluster in the i-th energy storage branch, and is the sum of the available charging capacity of all battery clusters.

[0009] The current inner loop controller is used to control the current of each energy storage branch to be the same as the given value. The current inner loop controller of the isolated DC / DC converter adopts a scheme of feedforward control plus feedback control. The feedforward control quantity of the isolated DC / DC converter is the difference between the total DC bus voltage of the DC / AC converter and the voltage of the battery cluster connected to the isolated DC / DC converter. The input of the feedback controller is the difference between the given value and the measured value of the current of the energy storage branch where the isolated DC / DC converter is located, and the output is the feedback control voltage. The given value of the output voltage of the i-th isolated DC / DC converter can be expressed as: U o，i =(U dc -U be，i )+U fb，i , wherein (U dc -U be，i ) is the feedforward control quantity, U dc is the total DC bus voltage of the DC / AC converter, U be，i is the voltage of the battery cluster connected in series with the output end of the isolated DC / DC converter; and U fb，i is the feedback control voltage output by the feedback controller. The phase shift ratio of the converter connected to the primary side of the isolation transformer in the isolated DC / DC converter is the given value of the output voltage of the isolated DC / DC converter U o，i multiplied by the transformation ratio n of the primary and secondary sides of the isolation transformer and then divided by the DC bus voltage U p at the input end of the isolated DC / DC converter. The phase shift ratio of the i-th isolated DC / DC converter can be expressed as: wherein D in is the transformer ratio, U is the input voltage of the converter, V is the output voltage of the converter, and f is the frequency of the converter. p is the DC bus voltage at the input of the isolated DC / DC converter.

[0010] A two-level topology of the isolated DC / DC converter is as follows: the topology is formed by two full-bridge converters connected to each other through an isolation transformer. A first full-bridge converter F1 connected to a primary side of the isolation transformer is composed of a first half-bridge H1 and a second half-bridge H2, a first switch T1 and a second switch T2 form the first half-bridge H1, and a third switch T3 and a fourth switch T4 form the second half-bridge H2; a second full-bridge converter F2 connected to a secondary side of the isolation transformer is composed of a third half-bridge H3 and a fourth half-bridge H4, a fifth switch T5 and a sixth switch T6 form the third half-bridge H3, and a seventh switch T7 and an eighth switch T8 form the fourth half-bridge H4; a source of the first switch T1 and a drain of the second switch T2 are connected to each other to form a first alternating current connection point P1 of the primary side of the isolation transformer, and the first alternating current connection point P1 of the primary side of the isolation transformer is directly or in series with a capacitor connected to one end of the primary side of the isolation transformer; a source of the third switch T3 and a drain of the fourth switch T4 are connected to each other to form a second alternating current connection point P2 of the primary side of the isolation transformer, and the second alternating current connection point P2 of the primary side of the isolation transformer is directly or in series with a capacitor connected to the other end of the primary side of the isolation transformer; a source of the fifth switch T5 and a drain of the sixth switch T6 are connected to each other to form a first alternating current connection point S1 of the secondary side of the isolation transformer, and the first alternating current connection point S1 of the secondary side of the isolation transformer is directly or in series with a capacitor connected to one end of the secondary side of the isolation transformer; a source of the seventh switch T7 and a drain of the eighth switch T8 are connected to each other to form a second alternating current connection point S2 of the secondary side of the isolation transformer, and the second alternating current connection point S2 of the secondary side of the isolation transformer is directly or in series with a capacitor connected to the other end of the secondary side of the isolation transformer; a drain of the first switch T1 and a drain of the third switch T3 are connected to each other to form a first input point I1 of the isolated DC / DC converter, and a source of the second switch T2 and a source of the fourth switch T4 are connected to each other to form a second input point I2 of the isolated DC / DC converter; a drain of the fifth switch T5 and a drain of the seventh switch T7 are connected to each other to form a first output point O1 of the isolated DC / DC converter, and a source of the sixth switch T6 and a source of the eighth switch T8 are connected to each other to form a second output point O2 of the isolated DC / DC converter; a capacitor C connected in parallel between the first output point O1 and the second output point O2 of the isolated DC / DC converter is used for commutation. The switches T1, T2, T3, T4, T5, T6, T7 and T8 are metal oxide semiconductor field effect transistors (MOSFETs), insulated gate bipolar transistors (IGBTs) or other controllable switches with anti-parallel diodes.

[0011] The angle of each switch of the isolation type DC / DC converter is 360°, when the phase shift control is adopted, the first switch T1 and the second switch T2 of the first half bridge H1 are complementary on for 180° and dead zone is inserted to prevent through, the third switch T3 and the fourth switch T4 of the second half bridge H2 are complementary on for 180° and dead zone is inserted to prevent through, the fifth switch T5 and the sixth switch T6 of the third half bridge H3 are complementary on for 180° and dead zone is inserted to prevent through, the seventh switch T7 and the eighth switch T8 of the fourth half bridge H4 are complementary on for 180° and dead zone is inserted to prevent through;The first full bridge converter F1 adopts the mode of phase shift control to generate a bipolar alternating square wave voltage on the primary side of the isolation transformer, and the second full bridge converter F2 rectifies the bipolar alternating square wave voltage on the secondary side of the isolation transformer into a unipolar alternating square wave voltage.The phase shift angle between the first switch T1 and the third switch T3 is θ=180°*D, wherein θ is the phase shift angle, and D is the phase shift ratio. The falling edge of the third switch T3 lags behind the reference 0 point by 180° The falling edge of the fifth switch T5 and the eighth switch T8 leads the reference 0 point by 90°, and the falling edge of the sixth switch T6 and the seventh switch T7 lags behind the reference 0 point by 90°.

[0012] The present application has the advantages that: a novel string type battery energy storage system topology is adopted, compared with the topology structure of the full power DC / DC converter, the power of the isolation type DC / DC in the present application is only a small part of the power of the battery cluster, the loss generated is low, and therefore the present application has the advantages of low cost and high efficiency;The control method of the total DC bus voltage given value of the DC / AC converter proposed in the present application can adapt to various operating states of the battery cluster, and has the advantage of high adaptability;The control method of the isolation type DC / DC converter proposed in the present application can effectively control the total DC bus voltage of the whole machine power or the DC / AC converter, and can realize the state of charge equalization control of each battery cluster, and the current inner loop control method of feedforward plus feedback also has the advantage of fast response speed.

[0013] The advantages of the additional aspects of the present application will be more apparent from the following description part or will be understood through the practice of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0014] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiment description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creating laborious work.

[0015] Figure 1 is a structure diagram of a common battery energy storage system.

[0016] Figure 2 is a topological structure diagram of a DC / AC converter in a two-level battery energy storage system according to an embodiment of the present application.

[0017] Figure 3 is a topological structure diagram of a DC / AC converter in a three-level battery energy storage system according to an embodiment of the present application.

[0018] Figure 4 is a discharge control block diagram of an isolated DC / DC converter when a DC / AC converter controls a total DC bus voltage.

[0019] Figure 5 is a charge control block diagram of an isolated DC / DC converter when a DC / AC converter controls a total DC bus voltage.

[0020] Figure 6 is a discharge control block diagram of an isolated DC / DC converter when an isolated DC / DC converter controls a total DC bus voltage.

[0021] Figure 7 is a charge control block diagram of an isolated DC / DC converter when an isolated DC / DC converter controls a total DC bus voltage.

[0022] Figure 8 is a two-level isolated DC / DC converter topological structure according to an embodiment of the present application.

[0023] Figure 9 is a phase-shift modulation method of a two-level isolated DC / DC converter. DETAILED DESCRIPTION

[0024] Embodiments of the present application will be described in detail below with reference to the drawings, in which like reference numerals refer to like elements throughout. The embodiments described below are examples of the present application and are not intended to limit the present application.

[0025] Those skilled in the art can appreciate that unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0026] It should also be understood that terms such as those defined in a general dictionary are to be interpreted in the same way as they are interpreted in the context of the prior art, and are not to be interpreted in an idealized or overly formal sense unless otherwise defined as such.

[0027] It is to be understood that the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. It is further understood that the terms "comprise" and "comprising" and the like, when used in the specification, the claims and the like, signify the presence of stated features, integers, steps, operations, elements, and / or components but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0028] In the description of the present specification, the description of the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. In addition, the skilled person in the art can combine and combine the different embodiments or examples described in the specification and the features of the different embodiments or examples without contradiction.

[0029] In order to facilitate the understanding of the present application, the present application will be further explained and described in specific embodiments in connection with the accompanying drawings, and the specific embodiments do not constitute a limitation on the embodiments of the present application.

[0030] The skilled person in the art should understand that the drawings are only schematic views of the embodiments, and the components in the drawings are not necessarily necessary for the implementation of the present application.

[0031] The present application will be further described in connection with the accompanying drawings and specific embodiments.

[0032] The commonly used string battery energy storage system topology is shown in Figure 1 The system is composed of a DC / AC converter, a DC / DC converter and a battery cluster. The AC side of the DC / AC converter is connected to the power grid, the DC bus of the DC / AC converter is connected in parallel to the input end of the DC / DC converter, and the output end of the DC / DC converter is connected in parallel to the battery cluster. The power of the DC / DC converter is not less than the power of the battery cluster connected in parallel to its output end, and the DC / DC converter has high cost and low efficiency.

[0033] Embodiment 1

[0034] In this embodiment 1, a topology structure of a DC / AC converter in a string battery energy storage system is provided. Figure 2is a schematic diagram of the topology, the group string battery energy storage system is composed of two-level DC / AC converter and multiple energy storage branches, the AC side of the DC / AC converter is connected with the power grid, and the DC bus of the DC / AC converter is connected in parallel with the multiple energy storage branches; each energy storage branch is composed of a filter inductor, an isolated DC / DC converter and a battery cluster; the filter inductor, the output end of the isolated DC / DC converter and the battery cluster are connected in series with each other and then connected in parallel as a whole on the DC bus of the DC / AC converter; the capacitor C is a DC bus capacitor of the DC / AC converter and is connected in parallel on the DC bus; and the input end of each isolated DC / DC converter is connected in parallel on the DC bus of the DC / AC converter.

[0035] Embodiment 2

[0036] In this embodiment 2, a topology structure of a DC / AC converter in a group string battery energy storage system is provided, wherein the DC / AC converter is three-level. Figure 3 is a schematic diagram of the topology, the group string battery energy storage system is composed of two-level DC / AC converter and multiple energy storage branches, the AC side of the DC / AC converter is connected with the power grid, and the DC bus of the DC / AC converter is connected in parallel with the multiple energy storage branches; each energy storage branch is composed of a filter inductor, an isolated DC / DC converter and a battery cluster; the filter inductor, the output end of the isolated DC / DC converter and the battery cluster are connected in series with each other and then connected in parallel as a whole on the DC bus of the DC / AC converter; the capacitor C is a DC bus capacitor of the DC / AC converter and is connected in parallel on the DC bus; and the input end of each isolated DC / DC converter is connected in parallel on the DC bus of the DC / AC converter.

[0037] Embodiment 3

[0038] In this embodiment 3, a setting method of a given value of a total DC bus voltage of a DC / AC converter is provided, which comprises:

[0039] The total DC bus voltage of the DC / AC converter is dynamically adjusted according to the voltage of each battery cluster of each energy storage branch, and the lower limit value of the given value of the total DC bus voltage of the DC / AC converter is the highest value of the voltage of the battery cluster in each energy storage branch, which can be expressed as: wherein U dc，min is the lower limit value of the given value of the total DC bus voltage of the DC / AC converter, n is the total number of the energy storage branches (i.e. the battery clusters), and U be，iLet be the voltage of the i-th battery cluster. The maximum value of the battery cluster voltage in each energy storage branch; the upper limit of the DC / AC converter's total DC bus voltage setpoint is the minimum value of the battery cluster voltage in each energy storage branch plus the maximum output voltage of the isolated DC / DC converter, which can be expressed as: in U represents the minimum voltage of the battery clusters in each energy storage branch. o，max This represents the maximum output voltage of the isolated DC / DC converter. The total DC bus voltage setpoint of the DC / AC converter lies between its lower and upper limits. To ensure reliable system operation, one method for selecting the total DC bus voltage setpoint is to take the average of the lower and upper limits, which is: Among them U dc，ref This is the given value for the total DC bus voltage of the DC / AC converter.

[0040] Example 4

[0041] In this embodiment 4, a control method for an isolated DC / DC converter is provided, including:

[0042] like Figures 4-7 As shown, the controller of an isolated DC / DC converter consists of three parts: 1. a total current setpoint generator, 2. a SOC equalization controller, and 3. a current inner loop controller. In the diagram, L represents the inductance of the filter inductor in each energy storage branch, and C represents the equivalent capacitance on the DC bus of the DC / AC converter. I is the delay from the input control signal to the actual output of an isolated DC / DC converter. L，1 I L，2 , ...I L，n For the current of different energy storage branches, I L I is the sum of the currents in the energy storage branches. ref P is the given value of the sum of the DC bus currents of the DC / AC converters injected into each energy storage branch. ref U is the given value of the total output power of the energy storage system. dc，ref and U dc This refers to the given and measured values ​​of the total DC bus voltage of the DC / AC converter.

[0043] Figures 4-7The total current given value generator in the total current given value generator is used to generate the given value of the sum of the DC bus current injected by each energy storage branch. The total DC bus voltage of the DC / AC converter can be controlled by the DC / AC converter or by the isolated DC / DC converter. When the total DC bus voltage of the DC / AC converter is controlled by the DC / AC converter, the given value of the sum of the DC bus current injected by each energy storage branch is the given value of the total output power of the energy storage system divided by the given value or the measured value of the total DC bus voltage of the DC / AC converter, which can be expressed as When the total DC bus voltage of the DC / AC converter is controlled by the isolated DC / DC converter, the DC / AC converter outputs power according to the power instruction, and the total DC bus voltage of the DC / AC converter is controlled by a double closed loop. The outer loop controller uses a proportional-integral-derivative (PID) controller, the input of which is the difference between the given value U dc，ref and the measured value U dc of the total DC bus voltage of the DC / AC converter, and the output of which is the given value I ref of the sum of the DC bus current injected by each energy storage branch.

[0044] Figures 4-7 The SOC balancing controller in the SOC balancing controller is used to control the charge balance of the battery clusters in each energy storage branch. After obtaining the given value I ref of the sum of the DC bus current injected by each energy storage branch, the given value of the current of each energy storage branch is allocated to control the charge balance of the battery clusters in each energy storage branch; in the discharge state, the current of each energy storage branch is allocated in proportion to the state of charge of the battery clusters in each energy storage branch to maintain the charge balance of the battery clusters in each energy storage branch, and the given value of the current of each energy storage branch can be expressed as: where I ref is the given value of the sum of the DC bus current injected by each energy storage branch, I ref，i is the given value of the current of the i-th energy storage branch, SOC i is the state of charge of the battery clusters in the i-th energy storage branch, and the sum of the states of charge of all battery clusters; in the charging state, the current of each energy storage branch is allocated in proportion to the available charging capacity of the battery clusters in each energy storage branch to maintain the charge balance of the battery clusters in each energy storage branch, and the given value of the current of each energy storage branch in the charging state can be expressed as: where (1-SOC i ) is the available charging capacity of the battery clusters in the i-th energy storage branch, and the sum of the available charging capacities of all battery clusters.

[0045] Figures 4-7The inner current controller in the circuit is used to control the current of each energy storage branch, ensuring it matches its setpoint. The isolated DC / DC converter's inner current controller employs a feedforward control plus feedback control scheme. The feedforward control quantity is the difference between the total DC bus voltage of the DC / AC converter and the voltage of the battery cluster connected to the isolated DC / DC converter. The input to the feedback controller is the setpoint I of the current in the energy storage branch where the isolated DC / DC converter is located. ref，i and measured value I L，i The difference is used as the output feedback control voltage. The setpoint for the output voltage of the i-th isolated DC / DC converter can be expressed as: U o，i =(U dc -U be，i )+U fb，i , of which (U dc -U be，i U is the feedforward control variable. dc U is the total DC bus voltage of the DC / AC converter. be，i U is the voltage of the battery cluster connected in series with the output of the isolated DC / DC converter. fb，i This is the feedback control voltage output by the feedback controller. In an isolated DC / DC converter, the converter shift ratio connected to the primary side of the isolation transformer is the output voltage setpoint U of the isolated DC / DC converter. o，i Multiply by the turns ratio n of the isolation transformer's primary and secondary sides, then divide by the DC bus voltage U at the input of the isolation DC / DC converter. p The shift ratio of the i-th isolated DC / DC converter can be expressed as: Where D i To compare the turns ratio of the converter connected to the primary side of the isolation transformer, where n is the transformer turns ratio and U is the transformer ratio. p This is the DC bus voltage at the input of the isolated DC / DC converter.

[0046] Example 5

[0047] In this embodiment 5, a two-level topology of an isolated DC / DC converter is provided, including:

[0048] This topology consists of two full-bridge converters interconnected by an isolation transformer, such as... Figure 8As shown, the specific structure is: the first full-bridge converter F1 connected with the primary side of the isolation transformer is composed of the first half-bridge H1 and the second half-bridge H2, the first switch T1 and the second switch T2 constitute the first half-bridge H1, and the third switch T3 and the fourth switch T4 constitute the second half-bridge H2; the second full-bridge converter F2 connected with the secondary side of the isolation transformer is composed of the third half-bridge H3 and the fourth half-bridge H4, the fifth switch T5 and the sixth switch T6 constitute the third half-bridge H3, and the seventh switch T7 and the eighth switch T8 constitute the fourth half-bridge H4; the source of the first switch T1 and the drain of the second switch T2 constitute the first alternating current connection point P1 of the primary side of the isolation transformer, and the first alternating current connection point P1 of the primary side of the isolation transformer and one end of the primary side of the isolation transformer are connected with each other; the source of the third switch T3 and the drain of the fourth switch T4 are connected with each other, and constitute the second alternating current connection point P2 of the primary side of the isolation transformer, and the second alternating current connection point P2 of the primary side of the isolation transformer and the other end of the primary side of the isolation transformer are connected with each other; the source of the fifth switch T5 and the drain of the sixth switch T6 are connected with each other, and constitute the first alternating current connection point S1 of the secondary side of the isolation transformer, and the first alternating current connection point S1 of the secondary side of the isolation transformer and one end of the secondary side of the isolation transformer are connected with each other; the source of the seventh switch T7 and the drain of the eighth switch T8 are connected with each other, and constitute the second alternating current connection point S2 of the secondary side of the isolation transformer, and the second alternating current connection point S2 of the secondary side of the isolation transformer and the other end of the secondary side of the isolation transformer are connected with each other; the drain of the first switch T1 and the drain of the third switch T3 are connected with each other to constitute the first input point I1 of the isolation type DC / DC converter, and the source of the second switch T2 and the source of the fourth switch T4 are connected with each other to constitute the second input point I2 of the isolation type DC / DC converter; the drain of the fifth switch T5 and the drain of the seventh switch T7 are connected with each other to constitute the first output point O1 of the isolation type DC / DC converter, and the source of the sixth switch T6 and the source of the eighth switch T8 are connected with each other to constitute the second output point O2 of the isolation type DC / DC converter; the parallel capacitor C between the first output point O1 and the second output point O2 of the isolation type DC / DC converter is used for commutation.

[0049] Embodiment 6

[0050] In this embodiment 6, a phase-shift modulation method for a two-level isolation type DC / DC converter is provided, which comprises:

[0051] The angle of each switch of the isolation type DC / DC converter is 360° per cycle, as Figure 9As shown, when the phase-shift control is adopted, the first switch T1 and the second switch T2 of the first half-bridge H1 are complementary on for 180° and a dead zone is inserted to prevent shoot-through, the third switch T3 and the fourth switch T4 of the second half-bridge H2 are complementary on for 180° and a dead zone is inserted to prevent shoot-through, the fifth switch T5 and the sixth switch T6 of the third half-bridge H3 are complementary on for 180° and a dead zone is inserted to prevent shoot-through, and the seventh switch T7 and the eighth switch T8 of the fourth half-bridge H4 are complementary on for 180° and a dead zone is inserted to prevent shoot-through; the first full-bridge converter F1 adopts the phase-shift control mode to generate a bipolar AC square wave voltage Ut on the primary side of the isolation transformer, and the second full-bridge converter F2 rectifies the bipolar AC square wave voltage on the secondary side of the isolation transformer into a unipolar AC square wave voltage Uo. The falling edge of the third switch T3 lags behind the reference 0 point by 90° The falling edges of the fifth switch T5 and the eighth switch T8 lead the reference 0 point by 90°, and the falling edges of the sixth switch T6 and the seventh switch T7 lag behind the reference 0 point by 90°.

[0052] Although the above describes the specific embodiments of the present application in detail, so as to make the technical personnel in the art understand the present application, it should be clear that the present application is not limited to the scope of the specific embodiments, and for the ordinary technical personnel in the art, as long as various changes are within the spirit and scope of the present application defined and determined by the appended claims, all the application and creation using the concept of the present application are included in the protection.

Claims

1. A battery energy storage system, characterized in that the battery energy storage system is composed of a DC / AC converter and a plurality of energy storage branches, the AC side of the DC / AC converter is connected to a power grid, and the total DC bus of the DC / AC converter is connected in parallel with the plurality of energy storage branches; each energy storage branch is composed of a filter inductor, an isolated DC / DC converter, and a battery cluster; the filter inductor, the output of the isolated DC / DC converter, and the battery cluster are connected in series and then connected in parallel as a whole on the total DC bus of the DC / AC converter, and the input of each isolated DC / DC converter is connected in parallel with the total DC bus or one of the plurality of DC buses of the DC / AC converter; when the input of each isolated DC / DC converter is connected in parallel with one of the plurality of DC buses, the input of each isolated DC / DC converter is evenly connected in parallel on each DC bus to balance the input and output power of each DC bus. The DC / AC converter total DC bus voltage is adjusted according to the voltage dynamics of each energy storage branch battery cluster. The lower limit of the DC / AC converter total DC bus voltage given value is the highest value of the battery cluster voltage in each energy storage branch, which is expressed as: where U dc,min is the lower limit of the DC / AC converter total DC bus voltage given value, n is the total number of energy storage branches (i.e. battery clusters), U be,i is the voltage of the i-th battery cluster, is the highest value of the battery cluster voltage in each energy storage branch; the upper limit of the DC / AC converter total DC bus voltage given value is the lowest value of the battery cluster voltage in each energy storage branch plus the maximum output voltage of the isolated DC / DC converter, which is expressed as: where is the lowest value of the battery cluster voltage in each energy storage branch, U o,max is the maximum output voltage of the isolated DC / DC converter; the DC / AC converter total DC bus voltage given value is between the lower limit and the upper limit of the DC / AC converter total DC bus voltage given value. One method of selecting the DC / AC converter total DC bus voltage given value is to take the average of the lower limit and the upper limit of the DC / AC converter total DC bus voltage given value, i.e. where U dc,ref is the DC / AC converter total DC bus voltage given value.

2. The battery string system of claim 1, wherein, The DC / AC converter total DC bus voltage is controlled by a DC / AC converter or an isolated DC / DC converter; when the DC / AC converter total DC bus voltage is controlled by the DC / AC converter, the given value of the sum of the DC / AC converter total DC bus current injected by each energy storage branch is the given value of the total output power of the energy storage system divided by the given value or measured value of the DC / AC converter total DC bus voltage, expressed as where I ref is the given value of the sum of the DC / AC converter total DC bus current injected by each energy storage branch, P ref is the given value of the total output power of the energy storage system, U dc,ref is the given value or measured value of the DC / AC converter total DC bus voltage; when the DC / AC converter total DC bus voltage is controlled by the isolated DC / DC converter, the DC / AC converter outputs power according to the power instruction, the DC / AC converter total DC bus voltage adopts double closed loop control, the input of the outer loop controller is the difference between the given value and the measured value of the DC / AC converter total DC bus voltage, and the output is the given value I ref of the sum of the DC / AC converter total DC bus current injected by each energy storage branch.

3. The battery string system of claim 1, wherein, In the charging state, the given value of the total sum of the DC bus current injected by each energy storage branch is I ref After that, the given value of each energy storage branch current is allocated to control the charge balance of the battery cluster in each energy storage branch; in the discharging state, the state of charge of the battery cluster in each energy storage branch is proportional to the current allocated to each energy storage branch to maintain the charge balance of the battery cluster in each energy storage branch, and the given value of each energy storage branch current is represented as: Where I ref is the given value of the total sum of the DC bus current injected by each energy storage branch, I ref,i is the given value of the i-th energy storage branch current, SOC i is the state of charge of the battery cluster in the i-th energy storage branch, is the sum of the state of charge of all battery clusters; in the charging state, the available charging capacity of the battery cluster in each energy storage branch is proportional to the current allocated to each energy storage branch to maintain the charge balance of the battery cluster in each energy storage branch, and the given value of each energy storage branch current in the charging state is represented as: Where (1-SOC i ) is the available charging capacity of the battery cluster in the i-th energy storage branch, is the sum of the available charging capacity of all battery clusters.

4. The battery string system of claim 1, wherein, The current inner loop controller of the isolated DC / DC converter adopts a scheme of feedforward control plus feedback control, the feedforward control quantity of which is the difference between the total DC bus voltage of the DC / AC converter and the voltage of the battery cluster connected with the isolated DC / DC converter; the input of the feedback controller is the difference between the given value and the measured value of the current of the energy storage branch where the isolated DC / DC converter is located, and the output is the feedback control voltage; the given value of the output voltage of the i-th isolated DC / DC converter is represented as: U o,i =(U dc -U be,i )+U fb,i , wherein (U dc -U be,i ) is the feedforward control quantity, U dc is the total DC bus voltage of the DC / AC converter, U be,i is the voltage of the battery cluster connected in series with the output end of the isolated DC / DC converter, and U fb,i is the feedback control voltage output by the feedback controller; the phase shift ratio of the converter connected with the primary side of the isolation transformer in the isolated DC / DC converter is the given value U o,i of the output voltage of the isolated DC / DC converter multiplied by the transformation ratio n of the primary side and the secondary side of the isolation transformer and then divided by the DC bus voltage U p at the input end of the isolated DC / DC converter, and the phase shift ratio of the i-th isolated DC / DC converter is represented as: wherein D i is the phase shift ratio of the converter connected with the primary side of the isolation transformer, n is the transformation ratio of the transformer, and U p is the DC bus voltage at the input end of the isolated DC / DC converter.

5. The battery string system of claim 1, wherein, A two-level topology of the isolated DC / DC converter is as follows: the topology is composed of two full-bridge converters connected to each other through an isolation transformer, the first full-bridge converter F1 connected to the primary side of the isolation transformer is composed of a first half-bridge H1 and a second half-bridge H2, the first switch T1 and the second switch T2 constitute the first half-bridge H1, and the third switch T3 and the fourth switch T4 constitute the second half-bridge H2. The second full-bridge converter F2 connected with the secondary side of the isolation transformer is composed of the third half-bridge H3 and the fourth half-bridge H4, the fifth switch T5 and the sixth switch T6 constitute the third half-bridge H3, and the seventh switch T7 and the eighth switch T8 constitute the fourth half-bridge H4; the source of the first switch T1 and the drain of the second switch T2 are connected with each other to constitute the first alternating current connection point P1 of the primary side of the isolation transformer, and the first alternating current connection point P1 of the primary side of the isolation transformer is connected with one end of the primary side of the isolation transformer directly or after being connected with a capacitor in series; the source of the third switch T3 and the drain of the fourth switch T4 are connected with each other to constitute the second alternating current connection point P2 of the primary side of the isolation transformer, and the second alternating current connection point P2 of the primary side of the isolation transformer is connected with the other end of the primary side of the isolation transformer directly or after being connected with a capacitor in series; the source of the fifth switch T5 and the drain of the sixth switch T6 are connected with each other to constitute the first alternating current connection point S1 of the secondary side of the isolation transformer, and the first alternating current connection point S1 of the secondary side of the isolation transformer is connected with one end of the secondary side of the isolation transformer directly or after being connected with a capacitor in series; the source of the seventh switch T7 and the drain of the eighth switch T8 are connected with each other to constitute the second alternating current connection point S2 of the secondary side of the isolation transformer, and the second alternating current connection point S2 of the secondary side of the isolation transformer is connected with the other end of the secondary side of the isolation transformer directly or after being connected with a capacitor in series; the drain of the first switch T1 and the drain of the third switch T3 are connected with each other to constitute the first input point I1 of the isolation type DC / DC converter, and the source of the second switch T2 and the source of the fourth switch T4 are connected with each other to constitute the second input point I2 of the isolation type DC / DC converter; the drain of the fifth switch T5 and the drain of the seventh switch T7 are connected with each other to constitute the first output point O1 of the isolation type DC / DC converter, and the source of the sixth switch T6 and the source of the eighth switch T8 are connected with each other to constitute the second output point O2 of the isolation type DC / DC converter; the capacitor C connected in parallel between the first output point O1 and the second output point O2 of the isolation type DC / DC converter is used for commutation; wherein the switches T1, T2, T3, T4, T5, T6, T7 and T8 are controllable switches with anti-parallel diodes, and the controllable switches include metal oxide semiconductor field effect transistors and insulated gate bipolar transistors.

6. The battery string system of claim 5, wherein The method of phase-shift modulation of the isolated DC / DC converter with two-level topology structure suitable for the string battery energy storage system is as follows: the angle of each switch is 360° per cycle, the first switch tube T1 and the second switch tube T2 of the first half bridge H1 are complementary on for 180° and dead zone is inserted to prevent through, the third switch tube T3 and the fourth switch tube T4 of the second half bridge H2 are complementary on for 180° and dead zone is inserted to prevent through, the fifth switch tube T5 and the sixth switch tube T6 of the third half bridge H3 are complementary on for 180° and dead zone is inserted to prevent through, the seventh switch tube T7 and the eighth switch tube T8 of the fourth half bridge H4 are complementary on for 180° and dead zone is inserted to prevent through; the first full bridge converter F1 generates a bipolar alternating square wave voltage on the primary side of the isolation transformer in a phase-shift control mode, and the second full bridge converter F2 rectifies the bipolar alternating square wave voltage on the secondary side of the isolation transformer into a unipolar alternating square wave voltage; the phase-shift angle between the first switch tube T1 and the third switch tube T3 is θ=180°×D, wherein θ is the phase-shift angle and D is the phase-shift ratio; a reference 0 point is set, the falling edge of the first switch tube T1 leads the reference 0 point by 90° the falling edge of the third switch tube T3 lags the reference 0 point by 90° the falling edges of the fifth switch tube T5 and the eighth switch tube T8 lead the reference 0 point by 90°, and the falling edges of the sixth switch tube T6 and the seventh switch tube T7 lag the reference 0 point by 90°.

Images