Topological structure and modulation method of partial power control type energy storage system

Abstract

The invention discloses a topological structure of a partial power control type energy storage system and a modulation method. The topological structure of a second full-bridge converter in an existing isolated DC / DC converter is improved, the dead time of a switching tube in the second full-bridge converter is improved into the overlapping conduction time of the switching tube, and in the time, upper and lower switches of a half bridge are conducted at the same time, so that the switching efficiency is improved. A follow current path is always provided for the charging and discharging current of the energy storage system during the alternating conduction period of the second full-bridge converter switch tube; according to the characteristic that the overall phase shift of the isolated DC / DC converter driving signals on the energy storage branches can cause the ripple current of the filter inductor to have the same phase shift angle, the overall phase shift angle of the isolated DC / DC converter driving signals on each energy storage branch is adjusted; the occurrence moments of the current peak value or valley value of the filter inductor of each energy storage branch are distributed in the switching period Ts at equal time intervals, so that the cancellation of the current peak and trough between the energy storage branches is realized, and the current ripple of the direct current bus is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of energy storage system control, and in particular to a topological structure and a modulation method of a partial power control type energy storage system. Background Art

[0002] Under the background of "dual carbon", my country is accelerating the construction of a new power system with renewable energy as the main body. With the continuous increase in the penetration rate of new energy, the randomness, volatility and intermittency of wind and solar output characteristics have an increasingly greater impact on the safe, stable and efficient operation of the power system. Energy storage is a key technology to solve the above problems. The energy storage system can not only effectively reduce the volatility caused by the large-scale access of new energy to the power grid, promote the balance of power supply and load in the operation of the power system, but also enhance the peak-shaving capacity of the distribution network, reduce the impact on the distribution network, and promote the efficient local consumption of distributed new energy.

[0003] The existing partial power control energy storage system consists of multiple energy storage branches and DC / AC converters. Figure 1 As shown, each energy storage branch is composed of a battery cluster, an isolated DC / DC converter and a filter inductor. The filter inductor, the output end of the isolated DC / DC converter and the battery cluster are connected in series. Multiple energy storage branches are connected in parallel to form a common DC bus of the energy storage system. The common DC bus serves as the input of the isolated DC / DC converters in multiple energy storage branches and realizes the grid-connected operation of the energy storage system through a DC / AC converter. The energy storage system uses an isolated DC / DC converter as a partial power controller. The partial power controller has the advantages of simple modulation method and topology, high stability and low system cost. However, the existing partial power control type energy storage system needs to rely on the output capacitor C of the partial power controller to provide a freewheeling path for the charging and discharging current of the energy storage system. Figure 2 As shown, there are problems of high cost and high component stress. At the same time, the common DC bus energy storage system often uses multiple energy storage branches in parallel to increase the power level. The DC bus current has the problem of doubling the peak-to-peak value of the DC bus current due to the overlap of the peaks and troughs of the currents of multiple energy storage branches. The DC bus current has a large ripple, resulting in a large DC bus voltage ripple. To suppress the DC bus voltage ripple, it is necessary to increase the energy storage branch filter inductance or the DC bus capacitance, which is costly. Summary of the invention

[0004] The partial power control type energy storage system applicable to the present invention is composed of a DC / AC converter and multiple energy storage branches. The AC side of the DC / AC converter is connected to the power grid, and the total DC bus of the DC / AC converter is connected in parallel with 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 to the total DC bus of the DC / AC converter, and each isolated DC / DC converter input end is connected in parallel with the total DC bus of the DC / AC converter or one of the multiple DC buses; when each isolated DC / DC converter input end is connected in parallel with one of the multiple DC buses, each isolated DC / DC converter input end is evenly connected in parallel with each DC bus to balance the input and output power of each DC bus.

[0005] The present invention proposes an isolated DC / DC converter topology structure for a partial power control energy storage system with a unipolar output voltage. Figure 3As shown. This topology is formed by 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 consists 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 to the secondary side of the isolation transformer consists of a third half-bridge H3 and a 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 to each other, forming the first half-bridge H1 of the primary side of the isolation transformer. an AC connection point P1, the first AC connection point P1 of the primary side of the isolation transformer is directly connected to one end of the primary side of the isolation transformer or connected in series with a capacitor; the source of the third switch T3 and the drain of the fourth switch T4 are connected to each other to form a second AC connection point P2 of the primary side of the isolation transformer, the second AC connection point P2 of the primary side of the isolation transformer is directly connected to the other end of the primary side of the isolation transformer or connected in series with a capacitor; the source of the fifth switch T5 and the drain of the sixth switch T6 are connected to each other to form a third AC connection point S3 of the secondary side of the isolation transformer, the third AC connection point S3 of the secondary side of the isolation transformer is directly connected to the other end of the primary side of the isolation transformer or connected in series with a capacitor; The source of the seventh switch T7 and the drain of the eighth switch T8 are connected to each other to form a fourth AC connection point S4 of the secondary side of the isolation transformer, and the fourth AC connection point S4 of the secondary side of the isolation transformer is directly or serially connected to the other end of the secondary side of the isolation transformer; the drain of the first switch T1 and the 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 the source of the second switch T2 and the source of the fourth switch T4 are connected to each other to form a second input point I2 of the isolated DC / DC converter; the fifth switch The drain of the seventh switch T5 and the drain of the seventh switch T7 are connected to each other to form the first output point O1 of the isolated DC / DC converter, and the source of the sixth switch T6 and the source of the eighth switch T8 are connected to each other to form the second output point O2 of the isolated DC / DC converter; wherein the first switch T1, the second switch T2, the third switch T3, the fourth switch T4, the fifth switch T5, the sixth switch T6, the seventh switch T7 and the eighth switch T8 are controllable switches with anti-parallel diodes such as metal oxide semiconductor field effect transistors (MOSFETs) and insulated gate bipolar transistors (IGBTs). The charge and discharge modulation method for the isolated DC / DC converter is as follows: Figure 4As shown, the angle of each switch cycle of the isolated DC / DC converter is 2*π, the first switch tube T1 and the second switch tube T2 of the first half-bridge H1 are complementary to each other at an angle of π, and a dead zone is inserted to prevent direct conduction, the third switch tube T3 and the fourth switch tube T4 of the second half-bridge H2 are complementary to each other at an angle of π, and a dead zone is inserted to prevent direct conduction, the fifth switch tube T5 and the sixth switch tube T6 of the third half-bridge H3 are complementary to each other at an angle of π, and an overlapping conduction time is inserted to ensure the freewheeling path of the charging and discharging current of the energy storage system, the seventh switch tube T7 and the eighth switch tube T8 of the fourth half-bridge H4 are complementary to each other at an angle of π, and an overlapping conduction time is inserted to ensure the freewheeling path of the charging and discharging current of the energy storage system; the first full-bridge converter F1 generates a bipolar AC square wave voltage Ut on the primary side of the isolation transformer by a phase-shift control method, 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 phase shift angle between the first switch tube T1 and the third switch tube T3 is θ=Y*π, where θ is the phase shift angle, Y is the phase shift ratio, and the phase shift ratio is a value between 0 and 1. The reference 0 point of the driving signal is set, the falling edge of the first switch tube T1 leads the reference 0 point of the driving signal by θ / 2, the falling edge of the third switch tube T3 lags behind the reference 0 point of the driving signal by θ / 2, the falling edges of the fifth switch tube T5 and the eighth switch tube T8 lead the reference 0 point of the driving signal by π / 2, and the falling edges of the sixth switch tube T6 and the seventh switch tube T7 lag behind the reference 0 point of the driving signal by π / 2. Compared with the existing isolated DC / DC topology, the present invention eliminates the freewheeling capacitor C connected in parallel between the first output point O1 and the second output point O2 of the isolated DC / DC converter, thereby saving system cost; compared with the existing modulation method, the present invention improves the switch tube dead time Td in the second full-bridge converter modulation method to the switch tube overlapping conduction time To, during which the fifth switch T5 and the sixth switch T6 are turned on at the same time, and the seventh switch T7 and the eighth switch T8 are turned on at the same time, thereby ensuring that a freewheeling path is always provided for the charging and discharging current of the energy storage system during the alternating conduction of the switch tubes of the second full-bridge converter. Compared with the existing modulation method of the partial power control type energy storage system, the significant difference is that the use of the freewheeling capacitor C at the output end of the isolated DC / DC converter is avoided, further reducing the system cost and component stress.

[0006] The first isolated DC / DC converter topology structure for partial power control energy storage system and bipolar output voltage proposed by the present invention is as follows: Figure 5As shown. The topology is formed by 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 consists 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 to the secondary side of the isolation transformer consists of a third half-bridge H3 and a fourth half-bridge H4. The fifth switch T5, the sixth switch T6, the seventh switch T7 and the eighth switch T8 constitute the third half-bridge H3, and the ninth switch T9, the tenth switch T10, the eleventh switch T11 and the tenth switch T12 constitute the third half-bridge H3. The second switch T12 forms a fourth half bridge H4; the source of the first switch T1 and the drain of the second switch T2 are connected to each other to form a first AC connection point P1 of the primary side of the isolation transformer, and the first AC connection point P1 of the primary side of the isolation transformer is directly connected to one end of the primary side of the isolation transformer or connected in series with a capacitor; the source of the third switch T3 and the drain of the fourth switch T4 are connected to each other to form a second AC connection point P2 of the primary side of the isolation transformer, and the second AC connection point P2 of the primary side of the isolation transformer is directly connected to the other end of the primary side of the isolation transformer or connected in series with a capacitor; the drain of the fifth switch T5 is connected to the drain of the sixth switch T6, and the seventh switch T7 is connected to the drain of the sixth switch T8. The source of the ninth switch T9 is connected to the source of the tenth switch T10, the source of the eleventh switch T11 is connected to the source of the twelfth switch T12, the source of the ninth switch T9 is connected to the drain of the eleventh switch T11, and the source of the ninth switch T9 is connected to the drain of the eleventh switch T11, forming a fourth AC connection point S4 on the secondary side of the isolation transformer. The fourth AC connection point S4 on the secondary side of the isolation transformer is connected to the drain of the tenth switch T10, the source of the eleventh switch T11 is connected to the source of the twelfth switch T12, and the source of the ninth switch T9 is connected to the drain of the eleventh switch T11, forming a fourth AC connection point S4 on the secondary side of the isolation transformer. Point S4 is connected to the other end of the secondary side of the isolation transformer directly or in series with a capacitor; the drain of the first switch T1 and the drain of the third switch T3 are connected to each other to form a first input point I1 of the isolated DC / DC converter, the source of the second switch T2 and the source of the fourth switch T4 are connected to each other to form a second input point I2 of the isolated DC / DC converter; the source of the sixth switch T6 and the source of the tenth switch T10 are connected to each other to form a first output point O1 of the isolated DC / DC converter, and the drain of the eighth switch T8 and the drain of the twelfth switch T12 are connected to each other to form a second output point O2 of the isolated DC / DC converter;The first switch T1, the second switch T2, the third switch T3, the fourth switch T4, the fifth switch T5, the sixth switch T6, the seventh switch T7, the eighth switch T8, the ninth switch T9, the tenth switch T10, the eleventh switch T11 and the twelfth switch T12 are controllable switches with anti-parallel diodes such as metal oxide semiconductor field effect transistors (MOSFETs) and insulated gate bipolar transistors (IGBTs), wherein the fifth switch T5 and the sixth switch T6 are connected in series in reverse directions and can be exchanged, the seventh switch T7 and the eighth switch T8 are connected in series in reverse directions and can be exchanged, the ninth switch T9 and the tenth switch T10 are connected in series in reverse directions and can be exchanged, and the eleventh switch T11 and the twelfth switch T12 are connected in series in reverse directions and can be exchanged. The bipolar isolated DC / DC converter structure has the advantages of simple modulation method, high stability, bipolar output voltage and wide adjustment range. ;

[0007] The second isolated DC / DC converter topology structure for partial power control energy storage system and bipolar output voltage proposed by the present invention is as follows: Figure 6As shown. The topology is formed by 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 consists 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 to the secondary side of the isolation transformer consists of a third half-bridge H3 and a fourth half-bridge H4. The fifth switch T5, the sixth switch T6, the first diode D1, the second diode D2, the seventh switch T7, the eighth switch T8, the third diode D3 and the fourth diode D4 constitute the third half-bridge H3, the ninth switch T9, the tenth switch T10, the fifth diode D5, the sixth diode D6, the eleventh switch T11, the eighth switch T12, the eighth diode D13 and the eighth diode D14 constitute the third half-bridge H3, the ninth switch T9, the tenth switch T11, the fifth diode D5, the sixth diode D6, the eleventh switch T12, the eighth switch T13, the eighth diode D14 and the eighth diode D15 constitute the third half-bridge H3. The switch T11, the twelfth switch T12, the seventh diode D7 and the eighth diode D8 constitute a fourth half bridge H4; the source of the first switch T1 and the drain of the second switch T2 are connected to each other to form a first AC connection point P1 of the primary side of the isolation transformer, and the first AC connection point P1 of the primary side of the isolation transformer is directly connected to one end of the primary side of the isolation transformer or connected in series with a capacitor; the source of the third switch T3 and the drain of the fourth switch T4 are connected to each other to form a second AC connection point P2 of the primary side of the isolation transformer, and the second AC connection point P2 of the primary side of the isolation transformer is directly connected to the other end of the primary side of the isolation transformer or connected in series with a capacitor; the source of the fifth switch T5 is connected to the drain of the sixth switch T6, and the cathode of the first diode D1 is connected to the drain of the fifth switch T5 , the anode of the second diode D2 is connected to the source of the sixth switch T6, the drain of the seventh switch T7 is connected to the source of the eighth switch T8, the anode of the third diode D3 is connected to the source of the seventh switch T7, the cathode of the fourth diode D4 is connected to the drain of the eighth switch T8, the source of the fifth switch T5 is connected to the drain of the seventh switch T7, and the third AC connection point S3 of the secondary side of the isolation transformer is connected to one end of the secondary side of the isolation transformer directly or in series with a capacitor; the source of the ninth switch T9 is connected to the drain of the tenth switch T10, the cathode of the fifth diode D5 is connected to the drain of the ninth switch T9, the anode of the sixth diode D6 is connected to the source of the tenth switch T10, and the eleventh The drain of the switch T11 is connected to the source of the twelfth switch T12, the anode of the seventh diode D7 is connected to the source of the eleventh switch T11, the cathode of the eighth diode D8 is connected to the drain of the twelfth switch T12, the source of the ninth switch T9 is connected to the drain of the eleventh switch T11, forming a fourth AC connection point S4 of the secondary side of the isolation transformer, and the fourth AC connection point S4 of the secondary side of the isolation transformer is directly connected to the other end of the secondary side of the isolation transformer or connected in series with a capacitor; the drain of the first switch T1 and the 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 the source of the second switch T2 and the source of the fourth switch T4 are connected to each other to form a second input point I2 of the isolated DC / DC converter;The anode of the first diode D1 is connected to the cathode of the second diode D2, the anode of the fifth diode D5 is connected to the cathode of the sixth diode D6, the anode of the first diode D1 and the anode of the fifth diode D5 are connected to each other to form a first output point O1 of the isolated DC / DC converter, the cathode of the third diode D3 is connected to the anode of the fourth diode D4, the cathode of the seventh diode D7 is connected to the anode of the eighth diode D8, the cathode of the third diode D3 and the cathode of the seventh diode D7 are connected to each other to form a second output point O2 of the isolated DC / DC converter, wherein the first switch T1, the second switch T2, the third switch T3, the fourth switch T4, the fifth switch T5, the sixth switch T6, the seventh switch T7, the eighth switch T8, the ninth switch T9, the tenth switch T10 are connected to each other. The switch T10, the eleventh switch T11 and the twelfth switch T12 are controllable switches with anti-parallel diodes such as metal oxide semiconductor field effect transistors (MOSFETs) and insulated gate bipolar transistors (IGBTs), wherein the fifth switch T5 is connected in series with the first diode D1 and can be interchanged, the sixth switch T6 is connected in series with the second diode D2 and can be interchanged, the seventh switch T7 is connected in series with the third diode D3 and can be interchanged, the eighth switch T8 is connected in series with the fourth diode D4 and can be interchanged, the ninth switch T9 is connected in series with the fifth diode D5 and can be interchanged, the tenth switch T10 is connected in series with the sixth diode D6 and can be interchanged, the eleventh switch T11 is connected in series with the seventh diode D7 and can be interchanged, and the twelfth switch T12 is connected in series with the eighth diode D8 and can be interchanged. The bipolar isolated DC / DC converter structure has the advantages of simple modulation method, high stability, bipolar output voltage and wide adjustment range. ;

[0008] The present invention is applicable to Figure 5 , Figure 6 The charge and discharge modulation method of the isolated DC / DC converter topology with bipolar output voltage is shown in FIG. Figure 7As shown, the improved modulation method is: the improved modulation method applicable to the topological structure is: the angle of each switch cycle of the isolated DC / DC converter is 2*π, the first switch tube T1 and the second switch tube T2 of the first half bridge H1 are complementary conduction angles π, and a dead zone is inserted to prevent direct conduction, the third switch tube T3 and the fourth switch tube T4 of the second half bridge H2 are complementary conduction angles π, and a dead zone is inserted to prevent direct conduction, the fifth switch tube T5 and the sixth switch tube T6 of the third half bridge H3 are switched at the same time, the seventh switch tube T7 and the eighth switch tube T8 are switched at the same time, the fifth switch tube T5, the sixth switch tube T6 and the seventh switch tube T7, the eighth switch tube T8 are complementary conduction angles π, and overlapping conduction time is inserted to ensure the freewheeling path of the charging and discharging current of the energy storage system, and the fourth half bridge H4 The ninth switch tube T9 and the tenth switch tube T10 are switched on simultaneously, the eleventh switch tube T11 and the twelfth switch tube T12 are switched on simultaneously, the ninth switch tube T9, the tenth switch tube T10 and the eleventh switch tube T11, the twelfth switch tube T12 are complementary to each other at a conduction angle π, and overlapping conduction time is inserted to ensure the freewheeling path of the charging and discharging current of the energy storage system; the first full-bridge converter F1 generates a bipolar AC square wave voltage Ut on the primary side of the isolation transformer by a phase shift control method, 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, and the phase shift angle between the first switch tube T1 and the third switch tube T3 is θ=Y*π, where θ is the phase shift angle, Y is the phase shift ratio, and the phase shift ratio is a value between -1 and 1. The reference 0 point of the driving signal is set, the falling edge of the first switch tube T1 leads the reference 0 point of the driving signal by θ / 2, the falling edge of the third switch tube T3 lags the reference 0 point of the driving signal by θ / 2, the falling edges of the fifth switch tube T5, the sixth switch tube T6, the eleventh switch tube T11, and the twelfth switch tube T12 lead the reference 0 point of the driving signal by π / 2, and the falling edges of the seventh switch tube T7, the eighth switch tube T8, the ninth switch tube T9, and the tenth switch tube T10 lag the reference 0 point of the driving signal by π / 2.

[0009] The third topology of the isolated DC / DC converter with bipolar output voltage for partial power control energy storage system proposed by the present invention is as follows: Figure 8As shown, the topology is formed by 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 consists 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 to the secondary side of the isolation transformer consists of a third half-bridge H3 and a 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 to each other, forming the first AC connection point of the primary side of the isolation transformer. P1, the first AC connection point P1 of the primary side of the isolation transformer is directly connected to one end of the primary side of the isolation transformer or connected in series with a capacitor; the source of the third switch T3 and the drain of the fourth switch T4 are connected to each other to form a second AC connection point P2 of the primary side of the isolation transformer, and the second AC connection point P2 of the primary side of the isolation transformer is directly connected to the other end of the primary side of the isolation transformer or connected in series with a capacitor; the source of the fifth switch T5 and the drain of the sixth switch T6 are connected to each other to form a third AC connection point S3 of the secondary side of the isolation transformer, and the third AC connection point S3 of the secondary side of the isolation transformer is directly connected to the secondary side of the isolation transformer or connected in series with a capacitor. The source of the seventh switch T7 and the drain of the eighth switch T8 are connected to each other to form a fourth AC connection point S4 of the secondary side of the isolation transformer, and the fourth AC connection point S4 of the secondary side of the isolation transformer is directly connected to the other end of the secondary side of the isolation transformer or connected in series with a capacitor; the drain of the first switch T1 and the 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 the source of the second switch T2 and the source of the fourth switch T4 are connected to each other to form a second input point I2 of the isolated DC / DC converter; the drain of the fifth switch T5 and the drain of the seventh switch T7 are connected to each other The first output point O1 of the isolated DC / DC converter is formed by connecting the source of the sixth switch T6 and the source of the eighth switch T8 to each other to form the second output point O2 of the isolated DC / DC converter; wherein the first switch T1, the second switch T2, the third switch T3 and the fourth switch T4 are controllable switches with anti-parallel diodes such as metal oxide semiconductor field effect transistors (MOSFETs) and insulated gate bipolar transistors (IGBTs), and the fifth switch T5, the sixth switch T6, the seventh switch T7 and the eighth switch T8 are controllable switches without anti-parallel diodes and supporting bidirectional current flow. The output voltage bipolar isolated DC / DC converter structure has the advantages of simple modulation method and topological structure, high stability and low system cost.

[0010] The present invention is applicable to Figure 8 The charge and discharge modulation method of the isolated DC / DC converter topology with bipolar output voltage is shown in FIG. Figure 4As shown, the improved modulation method is as follows: the angle of each switch cycle of the isolated DC / DC converter is 2*π, the first switch tube T1 and the second switch tube T2 of the first half bridge H1 are complementary conduction angles π, and a dead zone is inserted to prevent direct conduction, the third switch tube T3 and the fourth switch tube T4 of the second half bridge H2 are complementary conduction angles π, and a dead zone is inserted to prevent direct conduction, the fifth switch tube T5 and the sixth switch tube T6 of the third half bridge H3 are complementary conduction angles π, and an overlapping conduction time is inserted to ensure the freewheeling path of the charging and discharging current of the energy storage system, the seventh switch tube T7 and the eighth switch tube T8 of the fourth half bridge H4 are complementary conduction angles π, and an overlapping conduction time is inserted to ensure the freewheeling path of the charging and discharging current of the energy storage system; the first full-bridge converter F1 adopts a phase shift control method to control the phase shift control of the isolation transformer. The primary side generates a bipolar AC square wave voltage Ut, 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 phase shift angle between the first switch tube T1 and the third switch tube T3 is θ=Y*π, where θ is the phase shift angle, Y is the phase shift ratio, and the phase shift ratio is a value between -1 and 1; the reference 0 point of the drive signal is set, the falling edge of the first switch tube T1 leads the reference 0 point of the drive signal by θ / 2, the falling edge of the third switch tube T3 lags behind the reference 0 point of the drive signal by θ / 2, the falling edges of the fifth switch tube T5 and the eighth switch tube T8 lead the reference 0 point of the drive signal by π / 2, and the falling edges of the sixth switch tube T6 and the seventh switch tube T7 lag behind the reference 0 point of the drive signal by π / 2.

[0011] The overlapping conduction of the upper and lower bridge switches of the second full-bridge converter of the partial power control energy storage system is achieved by using a driving signal duty cycle D greater than 0.5. The overlapping conduction time of the second full-bridge converter switch is set by adjusting the size of the duty cycle exceeding 0.5. Assume that To is the overlapping conduction time, D is the duty cycle of the second full-bridge converter drive signal, Ts is the switch period of the switch tube, fs is the switch frequency of the switch tube, and T s =1 / f s , Db is the base duty cycle of the switch tube, which is equal to 0.5, Do is the part of the switch tube duty cycle exceeding 0.5, which corresponds to the overlapped conduction time To, D = D b +D o , adjusting the size of Do can realize the adjustment of the overlapping conduction time To. According to the above, the calculation formula of the overlapping conduction time To can be expressed as: T o =D o ×T s. This improved modulation method can always provide a freewheeling path for the charging and discharging current of the energy storage system during the commutation of the isolated DC / DC converter. Compared with the modulation method of the existing partial power control type energy storage system, it avoids the use of freewheeling capacitors at the output end of the partial power controller, further reduces the cost of the system, reduces the stress of components, and improves the reliability of the system.

[0012] In the partial power control energy storage system using the first, second and third output voltage bipolar isolated DC / DC converters, the total DC bus voltage of the DC / AC converter is adjusted dynamically according to the voltage of the battery clusters in each energy storage branch. The lower limit of the given value of the total DC bus voltage of the DC / AC converter is the maximum value of the battery cluster voltage in each energy storage branch minus the amplitude of the voltage between the first output point O1 and the second output point O2 of the isolated DC / DC converter, which can be expressed as: Among them U dc,min is the lower limit 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 ith battery cluster, is the maximum value of the battery cluster voltage in each energy storage branch, U o，m is the amplitude of the voltage between the first output point O1 and the second output point O2 of the isolated DC / DC converter; the upper limit of the given value of the total DC bus voltage of the DC / AC converter is the minimum value of the battery cluster voltage in each energy storage branch plus the amplitude of the voltage between the first output point O1 and the second output point O2 of the isolated DC / DC converter, which can be expressed as: in is the minimum value of the battery cluster voltage in each energy storage branch. The total DC bus voltage set value of the DC / AC converter is between the lower limit and upper limit of the total DC bus voltage set value of the DC / AC converter. In order to ensure the reliable operation of the system, one method for selecting the total DC bus voltage set value of the DC / AC converter is to take the average value of the lower limit and upper limit of the total DC bus voltage set value of the DC / AC converter, that is: Among them U dc，ref is the given value of the total DC bus voltage of the DC / AC converter.

[0013] The present invention proposes a method suitable for a partial power control type energy storage system and adopts Figure 2 , Figure 3 and Figure 8 The bus current ripple suppression modulation method of the isolated DC / DC converter is as follows: Fig. 9As shown. This modulation method utilizes the characteristic that the overall phase shift of the isolated DC / DC converter driving signal on the energy storage branch will cause the filter inductor ripple current to have the same phase shift angle as the ripple current. The driving signals of the first switch T1, the second switch T2, the third switch T3, the fourth switch T4, the fifth switch T5, the sixth switch T6, the seventh switch T7, and the eighth switch T8 of the isolated DC / DC converter are overall phase shifted to change the time when the peak and valley of the filter inductor current appear in the switching cycle Ts period. By adjusting the overall phase shift angle of the isolated DC / DC converter driving signal on each energy storage branch, the time intervals of the peak or valley of the current of the filter inductor of each energy storage branch are distributed in the switching cycle Ts period. When the number of energy storage branches connected in parallel to the common DC bus is n, the angle of each switch cycle of the isolated DC / DC converter is 2*π, then the energy storage branch The reference 0 point of the isolated DC / DC converter drive signal in energy storage branch 2 is phase-shifted by 1 / n*π relative to the reference 0 point of the isolated DC / DC converter drive signal in energy storage branch 1, the reference 0 point of the isolated DC / DC converter drive signal in energy storage branch 3 is phase-shifted by 2 / n*π relative to the reference 0 point of the isolated DC / DC converter drive signal in energy storage branch 1, the reference 0 point of the isolated DC / DC converter drive signal in energy storage branch 4 is phase-shifted by 3 / n*π relative to the reference 0 point of the isolated DC / DC converter drive signal in energy storage branch 1, and so on, the reference 0 point of the isolated DC / DC converter drive signal in energy storage branch n is phase-shifted by (n-1) / n*π relative to the reference 0 point of the isolated DC / DC converter drive signal in energy storage branch 1. The modulation method can achieve the cancellation of current peaks and troughs between energy storage branches and suppress the current ripple of the common DC bus. The problem of doubling of the peak-to-peak value of the DC bus current and large ripple caused by overlapping current peaks and troughs of multiple energy storage branches in the DC bus current is solved, and the volume of the energy storage branch filter inductor is significantly reduced, thereby reducing the cost of the energy storage system.

[0014] The present invention proposes a method suitable for a partial power control type energy storage system and adopts Figure 5 and Figure 6 The bus current ripple suppression modulation method of the isolated DC / DC converter is as follows: Fig.10As shown, the modulation method utilizes the characteristic that the overall phase shift of the isolated DC / DC converter driving signal on the energy storage branch will cause the filter inductor ripple current to have the same phase shift angle as the ripple current, and the overall phase shift of the driving signals of the first switch T1, the second switch T2, the third switch T3, the fourth switch T4, the fifth switch T5, the sixth switch T6, the seventh switch T7, the eighth switch T8, the ninth switch T9, the tenth switch T10, the eleventh switch T11, and the twelfth switch T12 of the isolated DC / DC converter is performed to change the time when the peak and valley of the filter inductor current appear in the switching cycle Ts period. By adjusting the overall phase shift angle of the isolated DC / DC converter driving signal on each energy storage branch, the time intervals of the peak or valley of the current of the filter inductor of each energy storage branch are distributed in the switching cycle Ts period. When the number of energy storage branches connected in parallel to the common DC bus is n, each switch of the isolated DC / DC converter The angle of one cycle is 2*π, then the reference 0 point of the isolated DC / DC converter drive signal in energy storage branch 2 is phase-shifted by 1 / n*π relative to the reference 0 point of the isolated DC / DC converter drive signal in energy storage branch 1, the reference 0 point of the isolated DC / DC converter drive signal in energy storage branch 3 is phase-shifted by 2 / n*π relative to the reference 0 point of the isolated DC / DC converter drive signal in energy storage branch 1, the reference 0 point of the isolated DC / DC converter drive signal in energy storage branch 4 is phase-shifted by 3 / n*π relative to the reference 0 point of the isolated DC / DC converter drive signal in energy storage branch 1, and so on, the reference 0 point of the isolated DC / DC converter drive signal in energy storage branch n is phase-shifted by (n-1) / n*π relative to the reference 0 point of the isolated DC / DC converter drive signal in energy storage branch 1. Through this modulation method, the current peaks and troughs between the energy storage branches can be eliminated, and the current ripple of the common DC bus can be suppressed. The problem of doubling of the peak-to-peak value of the DC bus current and large ripple caused by overlapping current peaks and troughs of multiple energy storage branches in the DC bus current is solved, and the volume of the energy storage branch filter inductor is significantly reduced, thereby reducing the cost of the energy storage system.

[0015] Additional advantages of the present invention will be more clearly given in the following description or learned through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0017] Figure 1 It is a topology structure of a partial power control type energy storage system according to an embodiment of the present invention;

[0018] Figure 2 It is an existing isolated DC / DC converter topology;

[0019] Figure 3 It is an output voltage unipolar isolated DC / DC converter topology structure of an embodiment of the present invention;

[0020] Figure 4 A modulation method of a single isolated DC / DC converter according to an embodiment of the present invention;

[0021] Figure 5 It is an output voltage bipolar isolated DC / DC converter topology structure according to an embodiment of the present invention;

[0022] Figure 6 It is an output voltage bipolar isolated DC / DC converter topology structure according to an embodiment of the present invention;

[0023] Figure 7 A modulation method of a single isolated DC / DC converter according to an embodiment of the present invention;

[0024] Figure 8 It is an output voltage bipolar isolated DC / DC converter topology structure according to an embodiment of the present invention;

[0025] Fig. 9 It is an overall modulation method of a partial power control type energy storage system containing four battery clusters according to an embodiment of the present invention;

[0026] Fig.10 It is an overall modulation method of a partial power control type energy storage system containing four battery clusters according to an embodiment of the present invention;

[0027] Fig.11 It is the DC bus ripple current of the partial power control type energy storage system containing four battery clusters after adopting the overall modulation method of the present invention;

[0028] Fig.12 It is the DC bus ripple current of a partial power controlled energy storage system containing four battery clusters after adopting the existing modulation method. DETAILED DESCRIPTION

[0029] The embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements with the same or similar functions. The embodiments described below by the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be interpreted as limiting the present invention.

[0030] It should be understood by those skilled in the art that unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by those skilled in the art to which this invention belongs.

[0031] It should also be understood that terms, such as those defined in commonly used dictionaries, should be understood to have a meaning consistent with that in the context of the prior art and will not be interpreted in an idealized or overly formal sense unless as defined herein.

[0032] Those skilled in the art will appreciate that, unless otherwise stated, the singular forms "a", "an", "said" and "the" used herein may also include plural forms. It should be further understood that the term "comprising" used in the specification of the present invention refers to the presence of the features, integers, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements and / or groups thereof.

[0033] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine different embodiments or examples described in this specification and the features of different embodiments or examples, unless they are contradictory.

[0034] To facilitate understanding of the present invention, the present invention is further explained below with reference to specific embodiments in conjunction with the accompanying drawings, and the specific embodiments do not constitute a limitation on the embodiments of the present invention.

[0035] Those skilled in the art should understand that the drawings are merely schematic diagrams of embodiments, and the components in the drawings are not necessarily necessary for implementing the present invention.

[0036] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0037] Embodiment 1: A partial power control type energy storage system according to an embodiment of the present invention is as follows Figure 1As shown in the figure, the energy storage system consists of multiple energy storage branches and DC / AC converters. Each energy storage branch consists of a battery cluster, an isolated DC / DC converter and a filter inductor. The filter inductor, the output end of the isolated DC / DC converter and the battery cluster are connected in series. Multiple energy storage branches are connected in parallel to form a common DC bus of the energy storage system. The common DC bus constructs a positive and negative DC bus through two split capacitors. The positive or negative DC bus is staggered as the input of the isolated DC / DC converter in multiple energy storage branches. The common DC bus realizes the grid-connected operation of the energy storage system through the DC / AC converter. A topological structure of an isolated DC / DC converter with a unipolar output voltage in the energy storage system is shown in the figure. Figure 3As shown, the topology consists of two full-bridge converters connected to each other via 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 to the secondary side of the isolation transformer is composed of a third half-bridge H3 and a 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 to each other to form a first AC connection point P1 of the primary side of the isolation transformer, and the first AC connection point P1 of the primary side of the isolation transformer is directly connected to one end of the primary side of the isolation transformer or connected in series with a capacitor; the source of the third switch T3 and the drain of the fourth switch T4 are connected to each other to form a second AC connection point P2 of the primary side of the isolation transformer, and the second AC connection point P2 of the primary side of the isolation transformer is directly connected to the other end of the primary side of the isolation transformer or connected in series with a capacitor; the source of the fifth switch T5 The drains of the first switch T1 and the sixth switch T6 are connected to each other to form a third AC connection point S3 of the secondary side of the isolation transformer, and the third AC connection point S3 of the secondary side of the isolation transformer is connected to one end of the secondary side of the isolation transformer directly or in series with a capacitor; the source of the seventh switch T7 and the drain of the eighth switch T8 are connected to each other to form a fourth AC connection point S4 of the secondary side of the isolation transformer, and the fourth AC connection point S4 of the secondary side of the isolation transformer is connected to the other end of the secondary side of the isolation transformer directly or in series with a capacitor; the drain of the first switch T1 and the 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 the source of the second switch T2 and the source of the fourth switch T4 are connected to each other to form a second input point I2 of the isolated DC / DC converter; the drain of the fifth switch T5 and the 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 the source of the sixth switch T6 and the source of the eighth switch T8 are connected to each other to form a second output point O2 of the isolated DC / DC converter. The first switch T1, the second switch T2, the third switch T3, the fourth switch T4, the fifth switch T5, the sixth switch T6, the seventh switch T7 and the eighth switch T8 are controllable switches with anti-parallel diodes such as metal oxide semiconductor field effect transistors (MOSFETs) and insulated gate bipolar transistors (IGBTs). The unipolar isolated DC / DC converter structure has the advantages of simple modulation method and topological structure, high stability and low system cost.

[0038] Embodiment 2: A modulation method for a single isolated DC / DC converter with a unipolar output voltage suitable for the partial power control energy storage system described in Embodiment 1 Figure 4As shown, the improved modulation method is as follows: the angle of each switch cycle of the isolated DC / DC converter is 2*π, the first switch tube T1 and the second switch tube T2 of the first half bridge H1 are complementary conduction angles π, and a dead zone is inserted to prevent direct conduction, the third switch tube T3 and the fourth switch tube T4 of the second half bridge H2 are complementary conduction angles π, and a dead zone is inserted to prevent direct conduction, the fifth switch tube T5 and the sixth switch tube T6 of the third half bridge H3 are complementary conduction angles π, and an overlapping conduction time is inserted to ensure the freewheeling path of the charge and discharge current, the seventh switch tube T7 and the eighth switch tube T8 of the fourth half bridge H4 are complementary conduction angles π, and an overlapping conduction time is inserted to ensure the freewheeling path of the charge and discharge current; the first full-bridge converter F1 generates a bipolar AC square wave voltage Ut on the primary side of the isolation transformer by a phase shift control method, 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 phase shift angle between the first switch tube T1 and the third switch tube T3 is θ=Y*π, where θ is the phase shift angle, Y is the phase shift ratio, and the phase shift ratio varies from 0 to 1. The reference 0 point of the driving signal is set, the falling edge of the first switch tube T1 is ahead of the reference 0 point of the driving signal by θ / 2, the falling edge of the third switch tube T3 is behind the reference 0 point of the driving signal by θ / 2, the falling edges of the fifth switch tube T5 and the eighth switch tube T8 are ahead of the reference 0 point of the driving signal by π / 2, and the falling edges of the sixth switch tube T6 and the seventh switch tube T7 are behind the reference 0 point of the driving signal by π / 2. The present invention improves the modulation method of the second full-bridge converter F2 of the isolated DC / DC converter, and improves the switch tube dead time Td in the existing second full-bridge converter F2 modulation method to the switch tube overlapping conduction time To. During this time, the fifth switch T5 and the sixth switch T6 are turned on at the same time, and the seventh switch T7 and the eighth switch T8 are turned on at the same time, thereby ensuring that a freewheeling path is always provided for the charging and discharging current of the energy storage system during the alternating conduction of the switch tubes of the second full-bridge converter. Compared with the existing energy storage system charging and discharging modulation method, the present invention significantly differs in that the use of the freewheeling capacitor C at the output end of the partial power controller, i.e., the isolated DC / DC converter, is avoided, thereby further reducing the system cost and component stress.

[0039] Embodiment 3: According to the partial power control type energy storage system described in Embodiment 1, a two-level, bipolar output voltage topology structure of the isolated DC / DC converter in the energy storage system is as follows: Figure 5As shown, the topology structure is formed by 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 to the secondary side of the isolation transformer is composed of a third half-bridge H3 and a fourth half-bridge H4, the fifth switch T5, the sixth switch T6, the seventh switch T7 and the eighth switch T8 constitute the third half-bridge H3, the ninth switch T9, the tenth switch T10, the eleventh switch T11 and The twelfth switch T12 forms the fourth half bridge H4; the source of the first switch T1 and the drain of the second switch T2 are connected to each other to form the first AC connection point P1 of the primary side of the isolation transformer, and the first AC connection point P1 of the primary side of the isolation transformer is directly connected to one end of the primary side of the isolation transformer or connected in series with a capacitor; the source of the third switch T3 and the drain of the fourth switch T4 are connected to each other to form the second AC connection point P2 of the primary side of the isolation transformer, and the second AC connection point P2 of the primary side of the isolation transformer is directly connected to the other end of the primary side of the isolation transformer or connected in series with a capacitor; the drain of the fifth switch T5 is connected to the drain of the sixth switch T6, and the seventh switch T8 is connected to the drain of the sixth switch T9. The source of the eighth switch T7 is connected to the source of the eighth switch T8, the source of the fifth switch T5 is connected to the drain of the seventh switch T7, forming a third AC connection point S3 of the secondary side of the isolation transformer, and the third AC connection point S3 of the secondary side of the isolation transformer is directly connected to one end of the secondary side of the isolation transformer or connected in series with a capacitor; the drain of the ninth switch T9 is connected to the drain of the tenth switch T10, the source of the eleventh switch T11 is connected to the source of the twelfth switch T12, and the source of the ninth switch T9 is connected to the drain of the eleventh switch T11, forming a fourth AC connection point S4 of the secondary side of the isolation transformer, and the fourth AC connection point S5 of the secondary side of the isolation transformer is connected to the drain of the eleventh switch T12. The contact S4 is connected to the other end of the secondary side of the isolation transformer directly or in series with a capacitor; the drain of the first switch T1 and the drain of the third switch T3 are connected to each other to form a first input point I1 of the isolated DC / DC converter, the source of the second switch T2 and the source of the fourth switch T4 are connected to each other to form a second input point I2 of the isolated DC / DC converter; the source of the sixth switch T6 and the source of the tenth switch T10 are connected to each other to form a first output point O1 of the isolated DC / DC converter, and the drain of the eighth switch T8 and the drain of the twelfth switch T12 are connected to each other to form a second output point O2 of the isolated DC / DC converter;The first switch T1, the second switch T2, the third switch T3, the fourth switch T4, the fifth switch T5, the sixth switch T6, the seventh switch T7, the eighth switch T8, the ninth switch T9, the tenth switch T10, the eleventh switch T11 and the twelfth switch T12 are controllable switches with anti-parallel diodes such as metal oxide semiconductor field effect transistors (MOSFETs) and insulated gate bipolar transistors (IGBTs), wherein the fifth switch T5 and the sixth switch T6 are connected in series in reverse directions and can be exchanged, the seventh switch T7 and the eighth switch T8 are connected in series in reverse directions and can be exchanged, the ninth switch T9 and the tenth switch T10 are connected in series in reverse directions and can be exchanged, and the eleventh switch T11 and the twelfth switch T12 are connected in series in reverse directions and can be exchanged. The bipolar isolated DC / DC converter structure has the advantages of simple modulation method, high stability, bipolar output voltage and wide adjustment range. ;

[0040] Embodiment 4: According to the partial power control type energy storage system described in Embodiment 1, a two-level, bipolar output voltage topology structure of the isolated DC / DC converter in the energy storage system is as follows: Figure 6As shown, the topology is formed by 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 to the secondary side of the isolation transformer is composed of a third half-bridge H3 and a fourth half-bridge H4. The fifth switch T5, the sixth switch T6, the first diode D1, the second diode D2, the seventh switch T7, the eighth switch T8, the third diode D3 and the fourth diode D4 constitute the third half-bridge H3, the ninth switch T9, the tenth switch T10, the fifth diode D5, the sixth diode D6, the third diode D7 and the fourth diode D8 constitute the third half-bridge H3. The eleventh switch T11, the twelfth switch T12, the seventh diode D7 and the eighth diode D8 constitute a fourth half bridge H4; the source of the first switch T1 and the drain of the second switch T2 are connected to each other to form a first AC connection point P1 of the primary side of the isolation transformer, and the first AC connection point P1 of the primary side of the isolation transformer is directly connected to one end of the primary side of the isolation transformer or connected in series with a capacitor; the source of the third switch T3 and the drain of the fourth switch T4 are connected to each other to form a second AC connection point P2 of the primary side of the isolation transformer, and the second AC connection point P2 of the primary side of the isolation transformer is directly connected to the other end of the primary side of the isolation transformer or connected in series with a capacitor; the source of the fifth switch T5 is connected to the drain of the sixth switch T6, and the cathode of the first diode D1 is connected to the drain of the fifth switch T5. The anode of the second diode D2 is connected to the source of the sixth switch T6, the drain of the seventh switch T7 is connected to the source of the eighth switch T8, the anode of the third diode D3 is connected to the source of the seventh switch T7, the cathode of the fourth diode D4 is connected to the drain of the eighth switch T8, the source of the fifth switch T5 is connected to the drain of the seventh switch T7, and the third AC connection point S3 of the secondary side of the isolation transformer is connected to the third AC connection point S3 of the secondary side of the isolation transformer. The third AC connection point S3 of the secondary side of the isolation transformer is directly connected to one end of the secondary side of the isolation transformer or connected in series with a capacitor; the source of the ninth switch T9 is connected to the drain of the tenth switch T10, the cathode of the fifth diode D5 is connected to the drain of the ninth switch T9, the anode of the sixth diode D6 is connected to the source of the tenth switch T10, and the tenth The drain of the first switch T11 is connected to the source of the twelfth switch T12, the anode of the seventh diode D7 is connected to the source of the eleventh switch T11, the cathode of the eighth diode D8 is connected to the drain of the twelfth switch T12, the source of the ninth switch T9 is connected to the drain of the eleventh switch T11, forming a fourth AC connection point S4 of the secondary side of the isolation transformer, and the fourth AC connection point S4 of the secondary side of the isolation transformer is directly connected to the other end of the secondary side of the isolation transformer or connected in series with a capacitor; the drain of the first switch T1 and the 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 the source of the second switch T2 and the source of the fourth switch T4 are connected to each other to form a second input point I2 of the isolated DC / DC converter;The anode of the first diode D1 is connected to the cathode of the second diode D2, the anode of the fifth diode D5 is connected to the cathode of the sixth diode D6, the anode of the first diode D1 and the anode of the fifth diode D5 are connected to each other to form a first output point O1 of the isolated DC / DC converter, the cathode of the third diode D3 is connected to the anode of the fourth diode D4, the cathode of the seventh diode D7 is connected to the anode of the eighth diode D8, the cathode of the third diode D3 and the cathode of the seventh diode D7 are connected to each other to form a second output point O2 of the isolated DC / DC converter, wherein the first switch T1, the second switch T2, the third switch T3, the fourth switch T4, the fifth switch T5, the sixth switch T6, the seventh switch T7, the eighth switch T8, the ninth switch T9, the tenth switch T10 are connected to each other. The switch T10, the eleventh switch T11 and the twelfth switch T12 are controllable switches with anti-parallel diodes such as metal oxide semiconductor field effect transistors (MOSFETs) and insulated gate bipolar transistors (IGBTs), wherein the fifth switch T5 is connected in series with the first diode D1 and can be interchanged, the sixth switch T6 is connected in series with the second diode D2 and can be interchanged, the seventh switch T7 is connected in series with the third diode D3 and can be interchanged, the eighth switch T8 is connected in series with the fourth diode D4 and can be interchanged, the ninth switch T9 is connected in series with the fifth diode D5 and can be interchanged, the tenth switch T10 is connected in series with the sixth diode D6 and can be interchanged, the eleventh switch T11 is connected in series with the seventh diode D7 and can be interchanged, and the twelfth switch T12 is connected in series with the eighth diode D8 and can be interchanged. The bipolar isolated DC / DC converter structure has the advantages of simple modulation method, high stability, bipolar output voltage and wide adjustment range. ;

[0041] Embodiment 5: An improved modulation method for a single isolated DC / DC converter with bipolar output voltage applicable to the partial power control type energy storage system described in Embodiment 3 and Embodiment 4 Figure 7As shown, the improved modulation method is: the improved modulation method applicable to the topological structure is: the angle of each switch cycle of the isolated DC / DC converter is 2*π, the first switch tube T1 and the second switch tube T2 of the first half bridge H1 are complementary conduction angles π, and a dead zone is inserted to prevent direct conduction, the third switch tube T3 and the fourth switch tube T4 of the second half bridge H2 are complementary conduction angles π, and a dead zone is inserted to prevent direct conduction, the fifth switch tube T5 and the sixth switch tube T6 of the third half bridge H3 are switched at the same time, the seventh switch tube T7 and the eighth switch tube T8 are switched at the same time, the fifth switch tube T5, the sixth switch tube T6 and the seventh switch tube T7, the eighth switch tube T8 are complementary conduction angles π, and overlapping conduction time is inserted to ensure the freewheeling path of the charging and discharging current of the energy storage system, and the fourth half bridge H4 The ninth switch tube T9 and the tenth switch tube T10 are switched on simultaneously, the eleventh switch tube T11 and the twelfth switch tube T12 are switched on simultaneously, the ninth switch tube T9, the tenth switch tube T10 and the eleventh switch tube T11, the twelfth switch tube T12 are complementary to each other at a conduction angle π, and overlapping conduction time is inserted to ensure the freewheeling path of the charging and discharging current of the energy storage system; the first full-bridge converter F1 generates a bipolar AC square wave voltage Ut on the primary side of the isolation transformer by a phase shift control method, 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 phase shift angle between the first switch tube T1 and the third switch tube T3 is θ=Y*π, where θ is the phase shift angle, Y is the phase shift ratio, and the phase shift ratio is a value between -1 and 1. The reference 0 point of the driving signal is set, the falling edge of the first switch tube T1 leads the reference 0 point of the driving signal by θ / 2, the falling edge of the third switch tube T3 lags the reference 0 point of the driving signal by θ / 2, the falling edges of the fifth switch tube T5, the sixth switch tube T6, the eleventh switch tube T11, and the twelfth switch tube T12 lead the reference 0 point of the driving signal by π / 2, and the falling edges of the seventh switch tube T7, the eighth switch tube T8, the ninth switch tube T9, and the tenth switch tube T10 lag the reference 0 point of the driving signal by π / 2.

[0042] Embodiment 6: According to the partial power control type energy storage system described in Embodiment 1, a two-level, bipolar output voltage topology structure of the isolated DC / DC converter in the energy storage system is as follows: Figure 8As shown, the topology is formed by 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 to the secondary side of the isolation transformer is composed of a third half-bridge H3 and a 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 to each other, forming the first AC connection point of the primary side of the isolation transformer. P1, the first AC connection point P1 of the primary side of the isolation transformer is directly connected to one end of the primary side of the isolation transformer or connected in series with a capacitor; the source of the third switch T3 and the drain of the fourth switch T4 are connected to each other to form a second AC connection point P2 of the primary side of the isolation transformer, and the second AC connection point P2 of the primary side of the isolation transformer is directly connected to the other end of the primary side of the isolation transformer or connected in series with a capacitor; the source of the fifth switch T5 and the drain of the sixth switch T6 are connected to each other to form a third AC connection point S3 of the secondary side of the isolation transformer, and the third AC connection point S3 of the secondary side of the isolation transformer is directly connected to the secondary side of the isolation transformer or connected in series with a capacitor. The source of the seventh switch T7 and the drain of the eighth switch T8 are connected to each other to form a fourth AC connection point S4 of the secondary side of the isolation transformer, and the fourth AC connection point S4 of the secondary side of the isolation transformer is directly connected to the other end of the secondary side of the isolation transformer or connected in series with a capacitor; the drain of the first switch T1 and the 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 the source of the second switch T2 and the source of the fourth switch T4 are connected to each other to form a second input point I2 of the isolated DC / DC converter; the drain of the fifth switch T5 and the drain of the seventh switch T7 are connected to each other The first output point O1 of the isolated DC / DC converter is formed by connecting the source of the sixth switch T6 and the source of the eighth switch T8 to each other to form the second output point O2 of the isolated DC / DC converter; wherein the first switch T1, the second switch T2, the third switch T3 and the fourth switch T4 are controllable switches with anti-parallel diodes such as metal oxide semiconductor field effect transistors (MOSFETs) and insulated gate bipolar transistors (IGBTs), and the fifth switch T5, the sixth switch T6, the seventh switch T7 and the eighth switch T8 are controllable switches without anti-parallel diodes and supporting bidirectional current flow. The output voltage bipolar isolated DC / DC converter structure has the advantages of simple modulation method and topological structure, high stability and low system cost.

[0043] Embodiment 7: An improved modulation method for a single isolated DC / DC converter with bipolar output voltage as described in Embodiment 6 Figure 4As shown, the improved modulation method is as follows: the angle of each switch cycle of the isolated DC / DC converter is 2*π, the first switch tube T1 and the second switch tube T2 of the first half bridge H1 are complementary conduction angles π, and a dead zone is inserted to prevent direct conduction, the third switch tube T3 and the fourth switch tube T4 of the second half bridge H2 are complementary conduction angles π, and a dead zone is inserted to prevent direct conduction, the fifth switch tube T5 and the sixth switch tube T6 of the third half bridge H3 are complementary conduction angles π, and an overlapping conduction time is inserted to ensure the freewheeling path of the charge and discharge current, the seventh switch tube T7 and the eighth switch tube T8 of the fourth half bridge H4 are complementary conduction angles π, and an overlapping conduction time is inserted to ensure the freewheeling path of the charge and discharge current; the first full-bridge converter F1 generates a bipolar AC square wave voltage Ut on the primary side of the isolation transformer by a phase shift control method, 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 phase shift angle between the first switch tube T1 and the third switch tube T3 is θ=Y*π, where θ is the phase shift angle, Y is the phase shift ratio, and the phase shift ratio varies from -1 to 1. The reference 0 point of the driving signal is set, the falling edge of the first switch tube T1 is ahead of the reference 0 point of the driving signal by θ / 2, the falling edge of the third switch tube T3 is behind the reference 0 point of the driving signal by θ / 2, the falling edges of the fifth switch tube T5 and the eighth switch tube T8 are ahead of the reference 0 point of the driving signal by π / 2, and the falling edges of the sixth switch tube T6 and the seventh switch tube T7 are behind the reference 0 point of the driving signal by π / 2.

[0044] Embodiment 8: The overlapping conduction of the upper and lower bridge switches of the second full-bridge converter of the partial power control type energy storage system is realized by using a driving signal duty cycle D greater than 0.5. The overlapping conduction time of the second full-bridge converter switch is set by adjusting the size of the duty cycle exceeding 0.5. Assume that To is the overlapping conduction time, D is the duty cycle of the second full-bridge converter drive signal, Ts is the switch period of the switch tube, fs is the switch frequency of the switch tube, T s =1 / f s , Db is the base duty cycle of the switch tube, which is equal to 0.5, Do is the part of the switch tube duty cycle exceeding 0.5, which corresponds to the overlapped conduction time To, D = D b +D o , adjusting the size of Do can realize the adjustment of the overlapping conduction time To. According to the above, the calculation formula of the overlapping conduction time To can be expressed as: T o =D o ×T s . This improved modulation method can always provide a freewheeling path for the charging and discharging current of the energy storage system during the commutation of the isolated DC / DC converter. Compared with the modulation method of the existing partial power control type energy storage system, it avoids the use of freewheeling capacitors at the output end of the partial power controller, further reduces the cost of the system, reduces the stress of components, and improves the reliability of the system.

[0045] Embodiment 9: Using Figure 5 , Figure 6 and Figure 8 The output voltage is a bipolar isolated DC / DC converter and the overall structure is as shown in Figure 1 In the partial power control energy storage system shown in FIG. 1 , the total DC bus voltage of the DC / AC converter is adjusted dynamically according to the voltage of the battery clusters in each energy storage branch. The lower limit of the given value of the total DC bus voltage of the DC / AC converter is the maximum value of the battery cluster voltage in each energy storage branch minus the amplitude of the voltage between the first output point O1 and the second output point O2 of the isolated DC / DC converter, which can be expressed as: Among them U dc,min is the lower limit 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 ith battery cluster, is the maximum value of the battery cluster voltage in each energy storage branch, U o,m is the amplitude of the voltage between the first output point O1 and the second output point O2 of the isolated DC / DC converter; the upper limit of the given value of the total DC bus voltage of the DC / AC converter is the minimum value of the battery cluster voltage in each energy storage branch plus the amplitude of the voltage between the first output point O1 and the second output point O2 of the isolated DC / DC converter, which can be expressed as: in is the minimum value of the battery cluster voltage in each energy storage branch. The total DC bus voltage set value of the DC / AC converter is between the lower limit and upper limit of the total DC bus voltage set value of the DC / AC converter. In order to ensure the reliable operation of the system, one method for selecting the total DC bus voltage set value of the DC / AC converter is to take the average value of the lower limit and upper limit of the total DC bus voltage set value of the DC / AC converter, that is: Among them U dc,ref is the given value of the total DC bus voltage of the DC / AC converter.

[0046] Embodiment 10: An embodiment of the present invention is applicable to a battery cluster having four batteries and using Figure 2 , Figure 3 and Figure 8 The overall modulation method of the partial power control type energy storage system of the isolated DC / DC converter is as follows Fig. 9As shown. In this embodiment, the number of energy storage branches is 4, and the angle of each switch cycle of the isolated DC / DC converter is 2*π. Then, the reference 0 point of the isolated DC / DC converter drive signal in energy storage branch 2 is phase-shifted by 1 / 4*π relative to the reference 0 point of the isolated DC / DC converter drive signal in energy storage branch 1, the reference 0 point of the isolated DC / DC converter drive signal in energy storage branch 3 is phase-shifted by 1 / 2*π relative to the reference 0 point of the isolated DC / DC converter drive signal in energy storage branch 1, and the reference 0 point of the isolated DC / DC converter drive signal in energy storage branch 4 is phase-shifted by 3 / 4*π relative to the reference 0 point of the isolated DC / DC converter drive signal in energy storage branch 1. By means of this modulation method, the current peaks and valleys between the energy storage branches can be eliminated, and the current ripple of the common DC bus can be suppressed. The problem of the peak-to-peak value of the DC bus current doubling and the large ripple caused by the overlapping of the current peaks and troughs of multiple energy storage branches in the DC bus current is solved, and the energy storage branch filter inductance and DC bus filter capacitance are significantly reduced, thereby reducing the cost of the energy storage system. In this embodiment, there are 4 energy storage branches, and the reference 0 point of the isolated DC / DC converter drive signal in energy storage branch 2, energy storage branch 3, and energy storage branch 4 is 1 / 4*π, 1 / 2*π, and 3 / 4*π, respectively, relative to the reference 0 point of the isolated DC / DC converter drive signal in energy storage branch 1. The DC bus current ripple after using this modulation method is as follows: Fig.11 As shown in FIG. 1 , the current peaks and valleys between the four energy storage branches cancel each other out, thus suppressing the current ripple of the common DC bus. The DC bus ripple current using the existing modulation method is as follows: Fig.12 As shown, the peak-to-peak value of the DC bus current ripple caused by the overlapping of the current peaks and troughs of the four energy storage branches is four times that of a single energy storage branch. Therefore, the modulation method proposed in the present invention realizes the cancellation of the current peaks and troughs between the energy storage branches, which can significantly reduce the filter inductance of the energy storage branch and the filter capacitance of the DC bus, thereby reducing the cost of the energy storage system.

[0047] Embodiment 11: An embodiment of the present invention is suitable for a battery cluster having four batteries and using Figure 5 and Figure 6 The overall modulation method of the partial power control type energy storage system of the isolated DC / DC converter is as follows Fig.10As shown. In this embodiment, the number of energy storage branches is 4, and the angle of each switch cycle of the isolated DC / DC converter is 2*π, then the reference 0 point of the isolated DC / DC converter drive signal in energy storage branch 2 is phase-shifted by 1 / 4*π relative to the reference 0 point of the isolated DC / DC converter drive signal in energy storage branch 1, the reference 0 point of the isolated DC / DC converter drive signal in energy storage branch 3 is phase-shifted by 1 / 2*π relative to the reference 0 point of the isolated DC / DC converter drive signal in energy storage branch 1, and the reference 0 point of the isolated DC / DC converter drive signal in energy storage branch 4 is phase-shifted by 3 / 4*π relative to the reference 0 point of the isolated DC / DC converter drive signal in energy storage branch 1. By using this improved modulation method, the current peaks and valleys between the energy storage branches can be eliminated, and the current ripple of the common DC bus can be suppressed. The problem of the peak-to-peak value of the DC bus current doubling and the large ripple caused by the overlapping of the current peaks and troughs of multiple energy storage branches in the DC bus current is solved, and the energy storage branch filter inductance and DC bus filter capacitance are significantly reduced, thereby reducing the cost of the energy storage system. In this embodiment, there are 4 energy storage branches, and the reference 0 point of the isolated DC / DC converter drive signal in energy storage branch 2, energy storage branch 3, and energy storage branch 4 is 1 / 4*π, 1 / 2*π, and 3 / 4*π, respectively, relative to the reference 0 point of the isolated DC / DC converter drive signal in energy storage branch 1. The DC bus current ripple after using this modulation method is as follows: Fig.11 As shown in FIG. 1 , the current peaks and valleys between the four energy storage branches cancel each other out, thus suppressing the current ripple of the common DC bus. The DC bus ripple current using the existing modulation method is as follows: Fig.12 As shown, the peak-to-peak value of the DC bus current ripple caused by the overlapping of the current peaks and troughs of the four energy storage branches is four times that of a single energy storage branch. Therefore, the modulation method proposed in the present invention realizes the cancellation of the current peaks and troughs between the energy storage branches, which can significantly reduce the filter inductance of the energy storage branch and the filter capacitance of the DC bus, thereby reducing the cost of the energy storage system.

[0048] Although the above describes the illustrative specific embodiments of the present invention to facilitate those skilled in the art to understand the present invention, and it should be clear that the present invention is not limited to the scope of the specific embodiments, for those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations using the concept of the present invention are protected.

Claims

1. A topological structure and modulation method for a partially power controlled energy storage system, wherein the topological structure of the partially power controlled energy storage system is composed of a DC / AC converter and multiple energy storage branches, wherein the AC side of the DC / AC converter is connected to the power grid, and the total DC bus of the DC / AC converter is connected in parallel with 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 to the total DC bus of the DC / AC converter, and the input end of each isolated DC / DC converter is connected to the total DC bus of the DC / AC converter or one of the multiple DC buses; When each isolated DC / DC converter input end is connected in parallel with one of the multiple DC buses, each isolated DC / DC converter input end is evenly connected in parallel with each DC bus to balance the input and output power of each DC bus; wherein a two-level, unipolar output voltage topology of the isolated DC / DC converter is: the topology is formed by 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 to the secondary side of the isolation transformer is composed of a third half-bridge H3 and a 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 to each other to form a first AC connection point P1 of the primary side of the isolation transformer, and the first AC connection point P1 of the primary side of the isolation transformer is directly connected to one end of the primary side of the isolation transformer or connected in series with a capacitor; the source of the third switch T3 and the drain of the fourth switch T4 are connected to each other to form a second AC connection point P2 of the primary side of the isolation transformer, and the second AC connection point P2 of the primary side of the isolation transformer is directly connected to the other end of the primary side of the isolation transformer or connected in series with a capacitor; the source of the fifth switch T5 and the drain of the sixth switch T6 are connected to each other to form a third AC connection point S3 of the secondary side of the isolation transformer, and the secondary side of the isolation transformer The third AC connection point S3 of the secondary side is connected to one end of the secondary side of the isolation transformer directly or in series with a capacitor; the source of the seventh switch T7 and the drain of the eighth switch T8 are connected to each other to form a fourth AC connection point S4 of the secondary side of the isolation transformer, and the fourth AC connection point S4 of the secondary side of the isolation transformer is connected to the other end of the secondary side of the isolation transformer directly or in series with a capacitor; the drain of the first switch T1 and the 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 the source of the second switch T2 and the source of the fourth switch T4 are connected to each other to form a second input point I2 of the isolated DC / DC converter; the drain of the fifth switch T5 and the 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 the source of the sixth switch T6 and the source of the eighth switch T8 are connected to each other to form a second output point O2 of the isolated DC / DC converter; The first switch T1, the second switch T2, the third switch T3, the fourth switch T4, the fifth switch T5, the sixth switch T6, the seventh switch T7 and the eighth switch T8 are controllable switches with anti-parallel diodes such as metal oxide semiconductor field effect transistors (MOSFETs) and insulated gate bipolar transistors (IGBTs). The improved modulation method applicable to the topological structure is as follows: the angle of each switch cycle of the isolated DC / DC converter is 2*π, the first switch tube T1 and the second switch tube T2 of the first half bridge H1 are complementary conduction angles π, and a dead zone is inserted to prevent direct conduction, the third switch tube T3 and the fourth switch tube T4 of the second half bridge H2 are complementary conduction angles π, and a dead zone is inserted to prevent direct conduction, the fifth switch tube T5 and the sixth switch tube T6 of the third half bridge H3 are complementary conduction angles π, and an overlapping conduction time is inserted to ensure the freewheeling path of the charging and discharging current of the energy storage system, and the The seventh switch tube T7 and the eighth switch tube T8 of the quad half-bridge H4 are complementary to each other at an angle π, and the overlapping conduction time is inserted to ensure the freewheeling path of the charging and discharging current of the energy storage system; the first full-bridge converter F1 generates a bipolar AC square wave voltage Ut on the primary side of the isolation transformer by means of phase shift control, 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 phase shift angle between the first switch tube T1 and the third switch tube T3 is θ=Y*π, where θ is the phase shift angle, Y is the phase shift ratio, and Compared to a value between 0 and 1; setting a reference 0 point of the driving signal, the falling edge of the first switch tube T1 leads the reference 0 point of the driving signal by θ / 2, the falling edge of the third switch tube T3 lags behind the reference 0 point of the driving signal by θ / 2, the falling edges of the fifth switch tube T5 and the eighth switch tube T8 lead the reference 0 point of the driving signal by π / 2, and the falling edges of the sixth switch tube T6 and the seventh switch tube T7 lag behind the reference 0 point of the driving signal by π / 2; the present invention is similar to the existing charge and discharge modulation method of the partial power control type energy storage system The technical feature is that the dead time Td of the switch tube in the existing modulation method of the second full-bridge converter is improved to the overlapping conduction time To of the switch tube. During the overlapping conduction time, the fifth switch T5 and the sixth switch T6 are turned on at the same time, and the seventh switch T7 and the eighth switch T8 are turned on at the same time, thereby ensuring that a freewheeling path is always provided for the charging and discharging current of the energy storage system during the alternating conduction of the switch tube of the second full-bridge converter, thereby eliminating the need to connect a freewheeling capacitor C in parallel between the first output terminal O1 and the second output terminal O2, further reducing system cost and component stress.

2. The partial power control energy storage system according to claim 1, wherein a two-level, bipolar output voltage topology of the isolated DC / DC converter is: the topology is formed by 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 to the secondary side of the isolation transformer is composed of a third half-bridge H3 and a fourth half-bridge H4. The fifth switch T5, the sixth switch T6, the seventh switch T7 and the eighth switch T8 constitute the third half-bridge H3, and the ninth switch T9, the tenth switch T10, the eleventh switch T11 and the twelfth switch T12 constitute the fourth half-bridge H4. The source of the first switch T1 and the drain of the second switch T2 are connected to each other to form a first AC connection point P1 on the primary side of the isolation transformer. The first AC connection point P1 on the primary side of the isolation transformer is directly or serially connected to a capacitor. The source of the third switch T3 and the drain of the fourth switch T4 are connected to each other to form a second AC connection point P2 of the primary side of the isolation transformer, and the second AC connection point P2 of the primary side of the isolation transformer is directly connected to the other end of the primary side of the isolation transformer or connected in series with a capacitor; the drain of the fifth switch T5 is connected to the drain of the sixth switch T6, the source of the seventh switch T7 is connected to the source of the eighth switch T8, and the source of the fifth switch T5 and the drain of the seventh switch T7 are connected to each other to form a third AC connection point P2 of the secondary side of the isolation transformer. The third AC connection point S3 of the secondary side of the isolation transformer is directly connected to one end of the secondary side of the isolation transformer or connected in series with a capacitor; the drain of the ninth switch T9 is connected to the drain of the tenth switch T10, the source of the eleventh switch T11 is connected to the source of the twelfth switch T12, and the source of the ninth switch T9 is connected to the drain of the eleventh switch T11, forming a fourth AC connection point S4 of the secondary side of the isolation transformer, and the fourth AC connection point S4 of the secondary side of the isolation transformer is directly connected to the other end of the secondary side of the isolation transformer or connected in series with a capacitor; The drain of the first switch T1 and the drain of the third switch T3 are connected to each other to form a first input point I1 of the isolated DC / DC converter, the source of the second switch T2 and the source of the fourth switch T4 are connected to each other to form a second input point I2 of the isolated DC / DC converter; the source of the sixth switch T6 and the source of the tenth switch T10 are connected to each other to form a first output point O1 of the isolated DC / DC converter, and the drain of the eighth switch T8 and the drain of the twelfth switch T12 are connected to each other to form a second output point O2 of the isolated DC / DC converter; The first switch T1, the second switch T2, the third switch T3, the fourth switch T4, the fifth switch T5, the sixth switch T6, the seventh switch T7, the eighth switch T8, the ninth switch T9, the tenth switch T10, the eleventh switch T11 and the twelfth switch T12 are controllable switches with anti-parallel diodes such as metal oxide semiconductor field effect transistors (MOSFETs) and insulated gate bipolar transistors (IGBTs), wherein the fifth switch T5 and the sixth switch T6 are connected in series in opposite directions and can be exchanged, the seventh switch T7 and the eighth switch T8 are connected in series in opposite directions and can be exchanged, the ninth switch T9 and the tenth switch T10 are connected in series in opposite directions and can be exchanged, and the eleventh switch T11 and the twelfth switch T12 are connected in series in opposite directions and can be exchanged; The improved modulation method applicable to the topological structure is as follows: the angle of each switching cycle of the isolated DC / DC converter is 2*π, the first switch tube T1 and the second switch tube T2 of the first half bridge H1 are complementary to each other at an angle of π, and a dead zone is inserted to prevent direct conduction, the third switch tube T3 and the fourth switch tube T4 of the second half bridge H2 are complementary to each other at an angle of π, and a dead zone is inserted to prevent direct conduction, the fifth switch tube T5 and the sixth switch tube T6 of the third half bridge H3 are switched at the same time, the seventh switch tube T7 and the eighth switch tube T8 are switched at the same time, the fifth switch tube T5, the sixth switch tube T6 and the seventh switch tube T7, the eighth switch tube T8 are complementary to each other at an angle of π, and an overlapping conduction time is inserted to ensure the freewheeling path of the charging and discharging current of the energy storage system, the ninth switch tube T9 and the tenth switch T10 of the fourth half bridge H4 are switched at the same time, the eleventh switch tube T11 and the twelfth switch tube T12 are switched at the same time, the ninth switch tube T9, the tenth switch tube T10 and the eleventh switch tube T11, the twelfth switch tube T12 are complementary to each other at an angle of π, and an overlapping conduction time is inserted to ensure the freewheeling path of the charging and discharging current of the energy storage system The time ensures the freewheeling path of the charging and discharging current of the energy storage system; the first full-bridge converter F1 uses a phase-shift control method 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 phase shift angle between the first switch tube T1 and the third switch tube T3 is θ=Y*π, where θ is the phase shift angle, Y is the phase shift ratio, and the phase shift ratio is a value between -1 and 1; set the reference 0 point of the drive signal, The falling edge of the first switch tube T1 leads the reference 0 point of the drive signal by θ / 2, the falling edge of the third switch tube T3 lags behind the reference 0 point of the drive signal by θ / 2, the falling edges of the fifth switch tube T5, the sixth switch tube T6, the eleventh switch tube T11 and the twelfth switch tube T12 lead the reference 0 point of the drive signal by π / 2, and the falling edges of the seventh switch tube T7, the eighth switch tube T8, the ninth switch tube T9 and the tenth switch tube T10 lag behind the reference 0 point of the drive signal by π / 2.

3. The partial power control energy storage system according to claim 1, wherein a two-level, output voltage bipolar topology structure of the isolated DC / DC converter is: the topology structure is formed by 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 to the secondary side of the isolation transformer is composed of a third half-bridge H3 and a fourth half-bridge H4, a fifth switch T5, a sixth switch T6, a first diode D1, a second diode D2, a seventh switch T7, The eighth switch T8, the third diode D3 and the fourth diode D4 constitute a third half-bridge H3, the ninth switch T9, the tenth switch T10, the fifth diode D5, the sixth diode D6, the eleventh switch T11, the twelfth switch T12, the seventh diode D7 and the eighth diode D8 constitute a fourth half-bridge H4; the source of the first switch T1 and the drain of the second switch T2 are connected to each other to form a first AC connection point P1 of the primary side of the isolation transformer, and the first AC connection point P1 of the primary side of the isolation transformer is directly connected to one end of the primary side of the isolation transformer or connected in series with a capacitor; the source of the third switch T3 and the drain of the fourth switch T4 are connected to each other to form a second AC connection point P2 of the primary side of the isolation transformer, and the second AC connection point P2 of the primary side of the isolation transformer is connected to the first AC connection point P1 of the primary side of the isolation transformer. The current connection point P2 is connected to the other end of the primary side of the isolation transformer directly or in series with a capacitor; the source of the fifth switch T5 is connected to the drain of the sixth switch T6, the cathode of the first diode D1 is connected to the drain of the fifth switch T5, the anode of the second diode D2 is connected to the source of the sixth switch T6, the drain of the seventh switch T7 is connected to the source of the eighth switch T8, the anode of the third diode D3 is connected to the source of the seventh switch T7, the cathode of the fourth diode D4 is connected to the drain of the eighth switch T8, the source of the fifth switch T5 and the drain of the seventh switch T7 are connected to each other, forming a third AC connection point S3 of the secondary side of the isolation transformer, and the third AC connection point S3 of the secondary side of the isolation transformer is connected to the isolation transformer directly or in series with a capacitor. The source of the ninth switch T9 is connected to the drain of the tenth switch T10, the cathode of the fifth diode D5 is connected to the drain of the ninth switch T9, the anode of the sixth diode D6 is connected to the source of the tenth switch T10, the drain of the eleventh switch T11 is connected to the source of the twelfth switch T12, the anode of the seventh diode D7 is connected to the source of the eleventh switch T11, the cathode of the eighth diode D8 is connected to the drain of the twelfth switch T12, the source of the ninth switch T9 is connected to the drain of the eleventh switch T11, and the fourth AC connection point S4 of the secondary side of the isolation transformer is connected to the other end of the secondary side of the isolation transformer directly or in series with a capacitor;The drain of the first switch T1 and the drain of the third switch T3 are connected to each other to form a first input point I1 of the isolated DC / DC converter, the source of the second switch T2 and the source of the fourth switch T4 are connected to each other to form a second input point I2 of the isolated DC / DC converter; the anode of the first diode D1 is connected to the cathode of the second diode D2, the anode of the fifth diode D5 is connected to the cathode of the sixth diode D6, the anode of the first diode D1 and the anode of the fifth diode D5 are connected to each other to form a first output point O1 of the isolated DC / DC converter, the cathode of the third diode D3 is connected to the anode of the fourth diode D4, the cathode of the seventh diode D7 is connected to the anode of the eighth diode D8, and the cathode of the third diode D3 is connected to the anode of the eighth diode D9. The cathode of the first switch T1 is connected to the cathode of the seventh diode D7 to form a second output point O2 of the isolated DC / DC converter, wherein the first switch T1, the second switch T2, the third switch T3, the fourth switch T4, the fifth switch T5, the sixth switch T6, the seventh switch T7, the eighth switch T8, the ninth switch T9, the tenth switch T10, the eleventh switch T11 and the twelfth switch T12 are controllable switches with anti-parallel diodes such as metal oxide semiconductor field effect transistors (MOSFET) and insulated gate bipolar transistors (IGBT), wherein the fifth switch T5 is connected in series with the first diode D1 and can be exchanged in position, the sixth switch T6 is connected in series with the second diode D2 and can be exchanged in position, and the seventh switch T7 is connected in series with the third diode D 3 are connected in series and can be exchanged, the eighth switch T8 is connected in series and can be exchanged, the ninth switch T9 is connected in series and can be exchanged, the tenth switch T10 is connected in series and can be exchanged, the eleventh switch T11 is connected in series and can be exchanged, the twelfth switch T12 is connected in series and can be exchanged; the improved modulation method applicable to the topological structure is: the angle of each switch cycle of the isolated DC / DC converter is 2*π, the first switch tube T1 and the second switch tube T2 of the first half bridge H1 are complementary to each other at an angle of π, and a dead zone is inserted to prevent direct conduction, the third switch tube T3 and the fourth switch tube T4 of the second half bridge H2 are complementary to each other at an angle of π, and an insertion The dead zone prevents direct conduction. The fifth switch tube T5 and the sixth switch tube T6 of the third half bridge H3 are switched on at the same time, and the seventh switch tube T7 and the eighth switch tube T8 are switched on at the same time. The fifth switch tube T5, the sixth switch tube T6 and the seventh switch tube T7, the eighth switch tube T8 are complementary to each other at a conduction angle of π, and an overlapping conduction time is inserted to ensure the freewheeling path of the charging and discharging current of the energy storage system. The ninth switch tube T9 and the tenth switch tube T10 of the fourth half bridge H4 are switched on at the same time, and the eleventh switch tube T11 and the twelfth switch tube T12 are switched on at the same time. The ninth switch tube T9, the tenth switch tube T10 and the eleventh switch tube T11, the twelfth switch tube T12 are complementary to each other at a conduction angle of π, and an overlapping conduction time is inserted to ensure the freewheeling path of the charging and discharging current of the energy storage system.The first full-bridge converter F1 generates a bipolar AC square wave voltage Ut on the primary side of the isolation transformer by phase shift control, 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 phase shift angle between the first switch tube T1 and the third switch tube T3 is θ=Y*π, where θ is the phase shift angle, Y is the phase shift ratio, and the phase shift ratio is a value between -1 and 1; the reference 0 point of the drive signal is set, the falling edge of the first switch tube T1 is θ / 2 ahead of the reference 0 point of the drive signal, the falling edge of the third switch tube T3 is θ / 2 behind the reference 0 point of the drive signal, the falling edge of the fifth switch tube T5, the sixth switch tube T6, the eleventh switch tube T11, and the twelfth switch tube T12 is π / 2 ahead of the reference 0 point of the drive signal, and the falling edge of the seventh switch tube T7, the eighth switch tube T8, the ninth switch tube T9, and the tenth switch tube T10 is π / 2 behind the reference 0 point of the drive signal. ; 4. The partial power control type energy storage system according to claim 1, wherein a two-level, output voltage bipolar topology structure of the isolated DC / DC converter is: the topology structure is formed by 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 to the secondary side of the isolation transformer is composed of a third half-bridge H3 and a 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 to each other to form a first AC connection point P1 of the primary side of the isolation transformer, and the first AC connection point P1 of the primary side of the isolation transformer is directly connected to one end of the primary side of the isolation transformer or connected in series with a capacitor; the source of the third switch T3 and the drain of the fourth switch T4 are connected to each other to form a second AC connection point P2 of the primary side of the isolation transformer, and the second AC connection point P2 of the primary side of the isolation transformer is directly connected to the other end of the primary side of the isolation transformer or connected in series with a capacitor; the source of the fifth switch T5 and the drain of the sixth switch T6 are connected to each other to form a third AC connection point S3 of the secondary side of the isolation transformer, and the secondary side of the isolation transformer The third AC connection point S3 of the secondary side is connected to one end of the secondary side of the isolation transformer directly or in series with a capacitor; the source of the seventh switch T7 and the drain of the eighth switch T8 are connected to each other to form a fourth AC connection point S4 of the secondary side of the isolation transformer, and the fourth AC connection point S4 of the secondary side of the isolation transformer is connected to the other end of the secondary side of the isolation transformer directly or in series with a capacitor; the drain of the first switch T1 and the 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 the source of the second switch T2 and the source of the fourth switch T4 are connected to each other to form a second input point I2 of the isolated DC / DC converter; the drain of the fifth switch T5 and the 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 the source of the sixth switch T6 and the source of the eighth switch T8 are connected to each other to form a second output point O2 of the isolated DC / DC converter; The first switch T1, the second switch T2, the third switch T3 and the fourth switch T4 are controllable switches with anti-parallel diodes such as metal oxide semiconductor field effect transistors (MOSFETs) and insulated gate bipolar transistors (IGBTs), and the fifth switch T5, the sixth switch T6, the seventh switch T7 and the eighth switch T8 are controllable switches without anti-parallel diodes and supporting bidirectional current flow; The improved modulation method applicable to the topological structure is as follows: the angle of each switch cycle of the isolated DC / DC converter is 2*π, the first switch tube T1 and the second switch tube T2 of the first half-bridge H1 are complementary conduction angles π, and a dead zone is inserted to prevent direct conduction, the third switch tube T3 and the fourth switch tube T4 of the second half-bridge H2 are complementary conduction angles π, and a dead zone is inserted to prevent direct conduction, the fifth switch tube T5 and the sixth switch tube T6 of the third half-bridge H3 are complementary conduction angles π, and an overlapping conduction time is inserted to ensure the freewheeling path of the charging and discharging current of the energy storage system, the seventh switch tube T7 and the eighth switch tube T8 of the fourth half-bridge H4 are complementary conduction angles π, and an overlapping conduction time is inserted to ensure the freewheeling path of the charging and discharging current of the energy storage system; the first full-bridge converter F1 adopts a phase shift control method in the isolation converter The primary side of the transformer generates a bipolar AC square wave voltage Ut, 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 phase shift angle between the first switch tube T1 and the third switch tube T3 is θ=Y*π, where θ is the phase shift angle, Y is the phase shift ratio, and the phase shift ratio is a value between -1 and 1; the reference 0 point of the drive signal is set, the falling edge of the first switch tube T1 leads the reference 0 point of the drive signal by θ / 2, the falling edge of the third switch tube T3 lags behind the reference 0 point of the drive signal by θ / 2, the falling edges of the fifth switch tube T5 and the eighth switch tube T8 lead the reference 0 point of the drive signal by π / 2, and the falling edges of the sixth switch tube T6 and the seventh switch tube T7 lag behind the reference 0 point of the drive signal by π / 2.

5. The partial power control energy storage system adopts the output voltage bipolar isolation DC / DC converter according to claim 2, claim 3 or claim 4 and the overall structure is as described in claim 1, characterized in that: The total DC bus voltage of the DC / AC converter is adjusted dynamically according to the voltage of the battery clusters in each energy storage branch. The lower limit of the given value of the total DC bus voltage of the DC / AC converter is the maximum value of the battery cluster voltage in each energy storage branch minus the amplitude of the voltage between the first output point O1 and the second output point O2 of the isolated DC / DC converter, which can be expressed as: Among them U dc,min is the lower limit 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 ith battery cluster, is the maximum value of the battery cluster voltage in each energy storage branch, U o，m is the amplitude of the voltage between the first output point O1 and the second output point O2 of the isolated DC / DC converter; the upper limit of the given value of the total DC bus voltage of the DC / AC converter is the minimum value of the battery cluster voltage in each energy storage branch plus the amplitude of the voltage between the first output point O1 and the second output point O2 of the isolated DC / DC converter, which can be expressed as: in is the lowest value of the battery cluster voltage in each energy storage branch; the total DC bus voltage set value of the DC / AC converter is between the lower limit and upper limit of the total DC bus voltage set value of the DC / AC converter. In order to ensure the reliable operation of the system, the total DC bus voltage set value of the DC / AC converter is selected by taking the average value of the lower limit and upper limit of the total DC bus voltage set value of the DC / AC converter, that is: Among them U dc,ref is the given value of the total DC bus voltage of the DC / AC converter.

6. A bus current ripple suppression modulation method for the partial power control type energy storage system according to claim 1 and the isolated DC / DC converter according to claim 1 and claim 4, wherein the technical feature is that the overall phase shift of the isolated DC / DC converter driving signal on the energy storage branch will cause the filter inductor current ripple to have the same phase shift angle as the filter inductor current ripple, and the driving signals of the first switch T1, the second switch T2, the third switch T3, the fourth switch T4, the fifth switch T5, the sixth switch T6, the seventh switch T7, and the eighth switch T8 of the isolated DC / DC converter are overall phase shifted to change the time when the filter inductor current peak and trough appear in the switching cycle Ts period, and the overall phase shift angle of the isolated DC / DC converter driving signal on each energy storage branch is adjusted so that the time intervals of the appearance of the current peak or valley of the filter inductor of each energy storage branch are distributed in the switching cycle Ts period; when the number of energy storage branches connected in parallel to the common DC bus is When n, the angle of each switching cycle of the isolated DC / DC converter is 2*π, then the reference 0 point of the isolated DC / DC converter drive signal in energy storage branch 2 is phase-shifted by 1 / n*π relative to the reference 0 point of the isolated DC / DC converter drive signal in energy storage branch 1, the reference 0 point of the isolated DC / DC converter drive signal in energy storage branch 3 is phase-shifted by 2 / n*π relative to the reference 0 point of the isolated DC / DC converter drive signal in energy storage branch 1, the reference 0 point of the isolated DC / DC converter drive signal in energy storage branch 4 is phase-shifted by 3 / n*π relative to the reference 0 point of the isolated DC / DC converter drive signal in energy storage branch 1, and so on, the reference 0 point of the isolated DC / DC converter drive signal in energy storage branch n is phase-shifted by (n-1) / n*π relative to the reference 0 point of the isolated DC / DC converter drive signal in energy storage branch 1. The modulation method can achieve the cancellation of current peaks and troughs between energy storage branches, and suppress the current ripple of the common DC bus.

7. A bus current ripple suppression modulation method for the partial power control type energy storage system according to claim 1 and the isolated DC / DC converter according to claim 2 and claim 3, wherein the technical feature is that the overall phase shift of the isolated DC / DC converter driving signal on the energy storage branch will cause the filter inductor current ripple to have the same phase shift angle as the filter inductor current ripple, and the overall phase shift of the driving signal of the first switch T1, the second switch T2, the third switch T3, the fourth switch T4, the fifth switch T5, the sixth switch T6, the seventh switch T7, the eighth switch T8, the ninth switch T9, the tenth switch T10, the eleventh switch T11, and the twelfth switch T12 of the isolated DC / DC converter is performed to change the time when the filter inductor current peak and trough appear in the switching cycle Ts period, and the overall phase shift angle of the isolated DC / DC converter driving signal on each energy storage branch is adjusted so that the time intervals of the appearance of the current peak or valley of the filter inductor of each energy storage branch are distributed in the switching cycle Ts period. ; When the number of energy storage branches connected in parallel to the common DC bus is n, and the angle of each switching cycle of the isolated DC / DC converter is 2*π, the reference 0 point of the isolated DC / DC converter drive signal in energy storage branch 2 is phase-shifted by 1 / n*π relative to the reference 0 point of the isolated DC / DC converter drive signal in energy storage branch 1, and the reference 0 point of the isolated DC / DC converter drive signal in energy storage branch 3 is phase-shifted by 2 / n*π relative to the reference 0 point of the isolated DC / DC converter drive signal in energy storage branch 1. The reference 0 point of the isolated DC / DC converter drive signal in energy storage branch 4 is phase-shifted by 3 / n*π relative to the reference 0 point of the isolated DC / DC converter drive signal in energy storage branch 1. Similarly, the reference 0 point of the isolated DC / DC converter drive signal in energy storage branch n is phase-shifted by (n-1) / n*π relative to the reference 0 point of the isolated DC / DC converter drive signal in energy storage branch 1. This modulation method can achieve the cancellation of current peaks and troughs between energy storage branches, thereby suppressing the current ripple of the common DC bus.

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