Topology and modulation method of partial power control type energy storage system

Abstract

The application discloses a topology structure and a modulation method of a partial power control type energy storage system. The topology structure of a second full-bridge converter in an existing isolated DC / DC converter is improved, and the dead time of a switch tube in the second full-bridge converter is improved to be the overlapping conduction time of the switch tube. In the time, the upper and lower switches of the half-bridge are simultaneously conducted, so that the freewheeling path for the charging and discharging current of the energy storage system is ensured during the alternate conduction of the switch tubes of the second full-bridge converter. The characteristic that the overall phase shift of the driving signals of the isolated DC / DC converter on the energy storage branch will cause the same phase shift angle of the ripple current of the filter inductor is utilized. By adjusting the overall phase shift angle of the driving signals of the isolated DC / DC converter on each energy storage branch, the occurrence time intervals of the current peak value or the valley value of the filter inductor of each energy storage branch are distributed in the switching period Ts, the current wave peak and the wave valley among the energy storage branches are cancelled, and the DC bus current ripple is reduced.

Description

Technical Field

[0001] This invention relates to the field of energy storage system control technology, and in particular to the topology and modulation method of a partial power control type energy storage system. Background Technology

[0002] Under the "dual carbon" background, my country is accelerating the construction of a new power system based on renewable energy. With the increasing penetration rate of new energy sources, the randomness, volatility, and intermittency of wind and solar power output are having a growing impact on the safe, stable, and efficient operation of the power system. Energy storage is a key technology for solving these problems. Energy storage systems can not only effectively mitigate the volatility caused by large-scale renewable energy grid integration and promote the balance of power sources and loads in power system operation, 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 renewable energy.

[0003] Existing power-controlled energy storage systems consist of multiple energy storage branches and DC / AC converters, such as... Figure 1 As shown, each energy storage branch consists of a battery cluster, an isolated DC / DC converter, and a filter inductor. The filter inductor, the output 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 for the energy storage system. The common DC bus serves as the input to the isolated DC / DC converters within the multiple energy storage branches and achieves grid-connected operation of the energy storage system through a DC / AC converter. This energy storage system uses an isolated DC / DC converter as a partial power controller. This partial power controller has advantages such as simple modulation method and topology, high stability, and low system cost. However, existing partial power control type energy storage systems 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 such as high cost and high stress on components. At the same time, common DC bus energy storage systems often use multiple energy storage branches in parallel to increase the power level. The DC bus current suffers from the problem of peak-to-peak value doubling due to the overlapping of the peaks and troughs of the currents of multiple energy storage branches. The DC bus current has large ripple, resulting in large DC bus voltage ripple. Suppressing the DC bus voltage ripple requires increasing the value of the filter inductance of the energy storage branch or the DC bus capacitor value, which is costly. Summary of the Invention

[0004] The partial power control type energy storage system to which this invention applies consists 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 multiple energy storage branches are connected in parallel to the main DC bus of the DC / AC converter. Each energy storage branch consists of a filter inductor, an isolated DC / DC converter, and a battery pack. The filter inductor, the output terminal of the isolated DC / DC converter, and the battery pack are connected in series and then connected in parallel as a whole to the main DC bus of the DC / AC converter. The input terminals of each isolated DC / DC converter are connected in parallel to the main DC bus or one of the multiple DC buses of the DC / AC converter. When the input terminals of each isolated DC / DC converter are connected in parallel to one of the multiple DC buses, the input terminals of each isolated DC / DC converter are evenly connected in parallel to 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 for a partially power controlled energy storage system with unipolar output voltage, as follows: Figure 3As shown. This topology consists of two full-bridge converters interconnected by 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 form the first half-bridge H1, and the third switch T3 and the fourth switch T4 form 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 form the third half-bridge H3, and the seventh switch T7 and the eighth switch T8 form the fourth half-bridge H4. The source of the first switch T1 and the drain of the second switch T2 are interconnected, forming the first half-bridge H3 on the primary side of the isolation transformer. A first AC connection point P1 on 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, forming the second AC connection point P2 on the primary side of the isolation transformer. The second AC connection point P2 on 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, forming the third AC connection point S3 on the secondary side of the isolation transformer. The third AC connection point S3 on the secondary 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. A series capacitor is connected to one end of the secondary side of the isolation transformer; the source of the seventh switch T7 and the drain of the eighth switch T8 are connected to each other to form the fourth AC connection point S4 of the secondary side of the isolation transformer. The fourth AC connection point S4 of the secondary side of the isolation transformer is directly or connected to the other end of the secondary side of the isolation transformer via a series capacitor; the drain of the first switch T1 and the drain of the third switch T3 are connected to each other to form the 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 the second input point I2 of the isolated DC / DC converter; the fifth switch... The drains of switch T5 and the seventh switch T7 are interconnected to form the first output point O1 of the isolated DC / DC converter. The sources of switch T6 and the eighth switch T8 are interconnected to form the second output point O2 of the isolated DC / DC converter. Switches T1, T2, T3, T4, T5, T6, T7, and T8 are controllable switches with anti-parallel diodes, such as MOSFETs and IGBTs. The charge / discharge modulation method for this isolated DC / DC converter is as follows: Figure 4As shown, in the isolated DC / DC converter, the angle of each switch in one cycle is 2*π. The first switch T1 and the second switch T2 of the first half-bridge H1 are complementary in conduction angle π, and a dead zone is inserted to prevent shoot-through. The third switch T3 and the fourth switch T4 of the second half-bridge H2 are complementary in conduction angle π, and a dead zone is inserted to prevent shoot-through. The fifth switch T5 and the sixth switch T6 of the third half-bridge H3 are complementary in conduction angle π, and an overlapping conduction time is inserted to ensure the freewheeling path of the energy storage system's charging and discharging current. The seventh switch T7 and the eighth switch T8 of the fourth half-bridge H4 are complementary in conduction angle π, and an overlapping conduction time is inserted to ensure the freewheeling path of the energy storage system's charging and discharging current. The first full-bridge converter F1 uses phase-shift control to generate a bipolar AC square wave voltage Ut on the primary side of the isolation transformer. 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 T1 and the third switch 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. A reference 0 point for the drive signal is set. The falling edge of the first switch T1 leads the reference 0 point of the drive signal by θ / 2, the falling edge of the third switch T3 lags the reference 0 point of the drive signal by θ / 2, the falling edges of the fifth switch T5 and the eighth switch T8 lead the reference 0 point of the drive signal by π / 2, and the falling edges of the sixth switch T6 and the seventh switch T7 lag the reference 0 point of the drive signal by π / 2. Compared with existing isolated DC / DC topologies, this invention eliminates the need for a freewheeling capacitor C connected in parallel between the first output point O1 and the second output point O2 of the isolated DC / DC converter, saving system costs. Compared with existing modulation methods, this invention improves the dead time Td of the switching transistors in the second full-bridge converter modulation method to an overlapping conduction time To. During this time, the fifth switch T5 and the sixth switch T6 are simultaneously turned on, and the seventh switch T7 and the eighth switch T8 are simultaneously turned on, 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 switching transistors of the second full-bridge converter. Compared with the existing modulation methods of partially power-controlled energy storage systems, its significant difference lies in avoiding the use of the freewheeling capacitor C at the output end of the isolated DC / DC converter, further reducing system costs and component stress.

[0006] The first isolated DC / DC converter topology for partially power controlled energy storage systems with bipolar output voltage proposed in this invention is as follows: Figure 5As shown. This topology consists of two full-bridge converters interconnected by an isolation transformer. The first full-bridge converter F1, connected to the primary side of the isolation transformer, is composed of the first half-bridge H1 and the second half-bridge H2. The first switch T1 and the second switch T2 form the first half-bridge H1, and the third switch T3 and the fourth switch T4 form the second half-bridge H2. The second full-bridge converter F2, connected to the secondary side of the isolation transformer, is composed of the third half-bridge H3 and the fourth half-bridge H4. The fifth switch T5, the sixth switch T6, the seventh switch T7, and the eighth switch T8 form the third half-bridge H3, and the ninth switch T9, the tenth switch T10, the eleventh switch T11, and the tenth switch T2 form the third half-bridge H3. Two switches T12 form 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 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 connected in series with a capacitor to one end of the primary side of the isolation transformer; the source of the third switch T3 and the drain of the fourth switch T4 are connected to each other, forming the second AC connection point P2 on the primary side of the isolation transformer. The second AC connection point P2 on the primary side of the isolation transformer is directly or connected in series with a capacitor to the other end of the primary side of the isolation transformer; the drain of the fifth switch T5 is connected to the drain of the sixth switch T6, and the seventh switch T7... The source of switch T9 is connected to the source of switch T8. The source of switch T5 is connected to the drain of switch T7, forming the third AC connection point S3 on the secondary side of the isolation transformer. The third AC connection point S3 on the secondary side of the isolation transformer is directly or connected in series with a capacitor to one end of the secondary side of the isolation transformer. The drain of switch T9 is connected to the drain of switch T10. The source of switch T11 is connected to the source of switch T12. The source of switch T9 and the drain of switch T11 are connected to each other, forming the fourth AC connection point S4 on the secondary side of the isolation transformer. Point S4 is directly or in series with a capacitor and then connected to the other end of the secondary side of the isolation transformer; the drains of the first switch T1 and the third switch T3 are connected to each other to form the first input point I1 of the isolated DC / DC converter; the sources of the second switch T2 and the fourth switch T4 are connected to each other to form the second input point I2 of the isolated DC / DC converter; the sources of the sixth switch T6 and the tenth switch T10 are connected to each other to form the first output point O1 of the isolated DC / DC converter; the drains of the eighth switch T8 and the twelfth switch T12 are connected to each other to form the second output point O2 of the isolated DC / DC converter.The first switch T1, second switch T2, third switch T3, fourth switch T4, fifth switch T5, sixth switch T6, seventh switch T7, eighth switch T8, ninth switch T9, tenth switch T10, eleventh switch T11, and 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). Switches T5 and T6 are connected in series in reverse and can be interchanged; switches T7 and T8 are connected in reverse and can be interchanged; switches T9 and T10 are connected in reverse and can be interchanged; and switches T11 and T12 are connected in reverse and can be interchanged. This 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 type of isolated DC / DC converter topology for partially power controlled energy storage systems with bipolar output voltage proposed in this invention is as follows: Figure 6As shown. This topology consists of two full-bridge converters interconnected by an isolation transformer. The first full-bridge converter F1, connected to the primary side of the isolation transformer, is composed of the first half-bridge H1 and the second half-bridge H2. The first switch T1 and the second switch T2 form the first half-bridge H1, and the third switch T3 and the fourth switch T4 form the second half-bridge H2. The second full-bridge converter F2, connected to the secondary side of the isolation transformer, is composed of the third half-bridge H3 and the fourth half-bridge H4. The fifth switch T5, 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 form the third half-bridge H3. The ninth switch T9, the tenth switch T10, the fifth diode D5, the sixth diode D6, and the eleventh switch T10 form the third half-bridge H3. Switches T11, Twelfth switch T12, seventh diode D7, and eighth diode D8 form 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 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 connected in series with a capacitor to one end of the primary side of the isolation transformer. The source of the third switch T3 and the drain of the fourth switch T4 are connected to each other, forming the second AC connection point P2 on the primary side of the isolation transformer. The second AC connection point P2 on the primary side of the isolation transformer is directly or connected in series with a capacitor to the other end of the primary side of the isolation transformer. 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, and the source of the fifth switch T5 is connected to the drain of the seventh switch T7, forming the third AC connection point S3 on the secondary side of the isolation transformer. The third AC connection point S3 on the secondary side of the isolation transformer is connected directly or in series with a capacitor to one end of the secondary side of the isolation transformer. 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, and the anode of the sixth diode D6 is connected to the source of the tenth switch T10. The eleventh... The drain of 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, and the source of the ninth switch T9 is connected to the drain of the eleventh switch T11, forming the 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 directly or connected in series with a capacitor to the other end of the secondary side of the isolation transformer. The drains of the first switch T1 and the third switch T3 are connected to form the first input point I1 of the isolated DC / DC converter, and the sources of the second switch T2 and the fourth switch T4 are connected to form the 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, and the anode of the fifth diode D5 is connected to the cathode of the sixth diode D6. The anodes of the first diode D1 and the fifth diode D5 are interconnected to form the 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, and the cathode of the seventh diode D7 is connected to the anode of the eighth diode D8. The anodes of the third diode D3 and the seventh diode D7 are interconnected to form the second output point O2 of the isolated DC / DC converter. The switches T1, T2, T3, T4, T5, T6, T7, T8, T9, and T10 are connected to each other. Switches T10, T11 (eleventh), and T12 are controllable switches with anti-parallel diodes, such as MOSFETs and IGBTs. Specifically, switch T5 is in series with diode D1 and their positions are interchangeable; switch T6 is in series with diode D2 and their positions are interchangeable; switch T7 is in series with diode D3 and their positions are interchangeable; switch T8 is in series with diode D4 and their positions are interchangeable; switch T9 is in series with diode D5 and their positions are interchangeable; switch T10 is in series with diode D6 and their positions are interchangeable; switch T11 is in series with diode D7 and their positions are interchangeable; and switch T12 is in series with diode D8 and their positions are interchangeable. This 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 / discharge modulation method of the bipolar isolated DC / DC converter topology shown is as follows: Figure 7As shown, the improved modulation method is as follows: For this topology, the angle of each switch in the isolated DC / DC converter is 2π per cycle. The first switch T1 and the second switch T2 of the first half-bridge H1 have complementary conduction angles of π, and a dead zone is inserted to prevent shoot-through. The third switch T3 and the fourth switch T4 of the second half-bridge H2 have complementary conduction angles of π, and a dead zone is inserted to prevent shoot-through. The fifth switch T5 and the sixth switch T6 of the third half-bridge H3 switch simultaneously, and the seventh switch T7 and the eighth switch T8 switch simultaneously. The fifth switch T5, the sixth switch T6, the seventh switch T7, and the eighth switch T8 have complementary conduction angles of π, and overlapping conduction times are inserted to ensure the freewheeling path of the energy storage system's charging and discharging current. The fourth half-bridge H4... The ninth switch T9 and the tenth switch T10 are switched simultaneously, and the eleventh switch T11 and the twelfth switch T12 are switched simultaneously. The ninth switch T9, the tenth switch T10, the eleventh switch T11, and the twelfth switch T12 have complementary conduction angles 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 uses phase-shift control to generate a bipolar AC square wave voltage Ut on the primary side of the isolation transformer. 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 T1 and the third switch 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 T1 leads the reference 0 point of the drive signal by θ / 2. The falling edge of the third switch T3 lags the reference 0 point of the drive signal by θ / 2. The falling edges of the fifth switch T5, the sixth switch T6, the eleventh switch T11, and the twelfth switch T12 lead the reference 0 point of the drive signal by π / 2. The falling edges of the seventh switch T7, the eighth switch T8, the ninth switch T9, and the tenth switch T10 lag the reference 0 point of the drive signal by π / 2.

[0009] The third type of isolated DC / DC converter topology for partially power controlled energy storage systems with bipolar output voltage proposed in this invention is as follows: Figure 8As shown, this topology consists of two full-bridge converters interconnected by an isolation transformer. The first full-bridge converter F1, connected to the primary side of the isolation transformer, comprises a first half-bridge H1 and a second half-bridge H2. The first switch T1 and the second switch T2 form the first half-bridge H1, and the third switch T3 and the fourth switch T4 form the second half-bridge H2. The second full-bridge converter F2, connected to the secondary side of the isolation transformer, comprises a third half-bridge H3 and a fourth half-bridge H4. The fifth switch T5 and the sixth switch T6 form the third half-bridge H3, and the seventh switch T7 and the eighth switch T8 form the fourth half-bridge H4. The source of the first switch T1 and the drain of the second switch T2 are interconnected, forming the first AC connection point on the primary side of the isolation transformer. P1, the first AC connection point P1 on the primary side of the isolation transformer, is directly or connected in series with a capacitor to one end of the primary side of the isolation transformer; 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 on the primary side of the isolation transformer, which is directly or connected in series with a capacitor to the other end of the primary side of the isolation transformer; the source of the fifth switch T5 and the drain of the sixth switch T6 are connected to each other to form the third AC connection point S3 on the secondary side of the isolation transformer, which is directly or connected in series with a capacitor to the other end of the primary side of the isolation transformer. One end of the circuit is connected; the source of the seventh switch T7 and the drain of the eighth switch T8 are connected to each other to form the fourth AC connection point S4 of the secondary side of the isolation transformer. The fourth AC connection point S4 of the secondary side of the isolation transformer is directly or connected in series with a capacitor 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 the 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 the 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 sources of the sixth switch T6 and the eighth switch T8, which are interconnected to form the 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 MOSFETs and IGBTs. The fifth switch T5, the sixth switch T6, the seventh switch T7, and the eighth switch T8 are controllable switches without anti-parallel diodes that support bidirectional current flow. This bipolar isolated DC / DC converter structure has advantages such as simple modulation methods and topology, high stability, and low system cost.

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

[0011] In some power-controlled energy storage systems, the overlapping conduction of the upper and lower bridge switches of the second full-bridge converter is achieved by using a drive signal duty cycle D greater than 0.5. The overlapping conduction time of the second full-bridge converter switches is set by adjusting the portion of the duty cycle exceeding 0.5. Let To be the overlapping conduction time, D be the duty cycle of the second full-bridge converter drive signal, Ts be the switching period of the switching transistor, fs be the switching frequency of the switching transistor, and T... s =1 / f s Db is the reference duty cycle of the switching transistor, which is 0.5. Do is the portion of the switching transistor's duty cycle exceeding 0.5, corresponding to the overlapped conduction time To. D = D b +D o Adjusting the value of Do allows for adjustment of the overlap conduction time To. As described above, the formula for calculating the overlap conduction time To can be expressed as: T o =D o ×T sThis improved modulation method provides a continuous current 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 existing partially power controlled energy storage systems, it avoids the use of a freewheeling capacitor at the output of the partial power controller, further reducing system cost, reducing component stress, and improving system reliability.

[0012] In a partially power-controlled energy storage system employing bipolar isolated DC / DC converters with the first, second, and third output voltages, the total DC bus voltage of the DC / AC converter is dynamically adjusted based on the voltage of the battery clusters in each energy storage branch. The lower limit of the setpoint for the total DC bus voltage of the DC / AC converter is the highest 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: U dc,min U is the lower limit given for the total DC bus voltage of the DC / AC converter, where n is the total number of energy storage branches (i.e., battery clusters). be,i Let be the voltage of the i-th battery cluster. U represents the highest value of the battery cluster voltage in each energy storage branch. o，m 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 total DC bus voltage setpoint 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 This represents the minimum voltage value of the battery clusters in each energy storage branch. The setpoint for the total DC bus voltage of the DC / AC converter lies between its lower and upper limits. To ensure reliable system operation, one method for selecting the setpoint is to take the average of the lower and upper limits, which is: U dc，ref This is the given value for the total DC bus voltage of the DC / AC converter.

[0013] This invention proposes a method suitable for partial power control type energy storage systems and adopts... Figure 2 , Figure 3 and Figure 8 Bus current ripple suppression modulation methods for isolated DC / DC converters, such as Figure 9As shown. This modulation method utilizes the characteristic that a phase shift in the overall phase of the drive signal of the isolated DC / DC converter on the energy storage branch will cause the ripple current of the filter inductor to exhibit the same phase shift angle. By performing an overall phase shift on the drive signals of the first switch T1, second switch T2, third switch T3, fourth switch T4, fifth switch T5, sixth switch T6, seventh switch T7, and eighth switch T8 of the isolated DC / DC converter, the timing of the peak and trough of the filter inductor current within the switching period Ts is changed. By adjusting the overall phase shift angle of the drive signals of the isolated DC / DC converter on each energy storage branch, the peak or trough current of the filter inductor in each energy storage branch is distributed at equal time intervals within the switching period Ts. When the number of energy storage branches connected in parallel to the common DC bus is n, the angle of each switch of the isolated DC / DC converter in one cycle is 2*π. Therefore, the energy storage branch... The reference 0 point of the drive signal of the internally isolated DC / DC converter in energy storage branch 2 is phase-shifted by 1 / n*π relative to the reference 0 point of the drive signal of the internally isolated DC / DC converter in energy storage branch 1; the reference 0 point of the drive signal of the internally isolated DC / DC converter in energy storage branch 3 is phase-shifted by 2 / n*π relative to the reference 0 point of the drive signal of the internally isolated DC / DC converter in energy storage branch 1; the reference 0 point of the drive signal of the internally isolated DC / DC converter in energy storage branch 4 is phase-shifted by 3 / n*π relative to the reference 0 point of the drive signal of the internally isolated DC / DC converter in energy storage branch 1; and so on, the reference 0 point of the drive signal of the internally isolated DC / DC converter in energy storage branch n is phase-shifted by (n-1) / n*π relative to the reference 0 point of the drive signal of the internally isolated DC / DC converter in energy storage branch 1. This 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. It solves the problems of the DC bus current peak-to-peak value doubling and large ripple caused by the overlap of current peaks and troughs in multiple energy storage branches, and significantly reduces the volume of the filter inductor in the energy storage branch, thereby reducing the cost of the energy storage system.

[0014] This invention proposes a method suitable for partial power control type energy storage systems and adopts... Figure 5 and Figure 6 Bus current ripple suppression modulation methods for isolated DC / DC converters, such as Figure 10As shown, this modulation method utilizes the characteristic that a phase shift in the overall phase of the drive signal of the isolated DC / DC converter on the energy storage branch will cause the ripple current of the filter inductor to exhibit the same phase shift angle. By performing an overall phase shift on the drive signals of the first switch T1, second switch T2, third switch T3, fourth switch T4, fifth switch T5, sixth switch T6, seventh switch T7, eighth switch T8, ninth switch T9, tenth switch T10, eleventh switch T11, and twelfth switch T12 of the isolated DC / DC converter, the timing of the peak and trough of the filter inductor current within the switching period Ts is changed. By adjusting the overall phase shift angle of the drive signals of the isolated DC / DC converter on each energy storage branch, the peak or trough current of the filter inductor in each energy storage branch is distributed at equal time intervals within the switching period Ts. 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... If 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. This 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. It solves the problems of the DC bus current peak-to-peak value doubling and large ripple caused by the overlap of current peaks and troughs in multiple energy storage branches, and significantly reduces the volume of the filter inductor in the energy storage branch, thereby reducing the cost of the energy storage system.

[0015] The advantages of additional aspects of the invention will be set forth more clearly in the following description or will be learned by practice of the invention. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a partial power-controlled energy storage system topology according to an embodiment of the present invention;

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

[0019] Figure 3 This is an example of a unipolar isolated DC / DC converter topology with output voltage according to an embodiment of the present invention;

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

[0021] Figure 5 This is an example of a bipolar isolated DC / DC converter topology for output voltage according to an embodiment of the present invention;

[0022] Figure 6 This is an example of a bipolar isolated DC / DC converter topology for output voltage according to an embodiment of the present invention;

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

[0024] Figure 8 This is an example of a bipolar isolated DC / DC converter topology for output voltage according to an embodiment of the present invention;

[0025] Figure 9 This invention relates to an overall modulation method for a partially power-controlled energy storage system containing four battery clusters, as described in an embodiment of the present invention.

[0026] Figure 10 This invention relates to an overall modulation method for a partially power-controlled energy storage system containing four battery clusters, as described in an embodiment of the present invention.

[0027] Figure 11 The DC bus ripple current of a partial power control energy storage system containing four battery clusters after adopting the overall modulation method of this invention;

[0028] Figure 12 It refers to the DC bus ripple current of a partially power-controlled energy storage system containing four battery clusters after adopting existing modulation methods. Detailed Implementation

[0029] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

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

[0031] It should also be understood that terms such as those defined in general dictionaries should be understood to have meanings consistent with their meanings in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless defined as here.

[0032] Those skilled in the art will understand that, unless specifically stated otherwise, the singular forms “a,” “an,” “the,” and “the” used herein may also include the plural forms. It should be further understood that the term “comprising” as used in this specification means the presence of the stated 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, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of those different embodiments or examples.

[0034] To facilitate understanding of the present invention, the present invention will be further explained and described below with reference to the accompanying drawings and specific embodiments. However, 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 accompanying drawings are merely schematic diagrams of embodiments, and the components in the drawings are not necessarily essential for implementing the present invention.

[0036] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0037] Example 1: Some power-controlled energy storage systems according to embodiments of the present invention, such as... Figure 1As shown, the energy storage system consists of multiple energy storage branches and a DC / AC converter. Each energy storage branch comprises a battery cluster, an isolated DC / DC converter, and a filter inductor. The filter inductor, the output 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 for the energy storage system. This common DC bus is used to construct positive and negative DC buses through two split capacitors. The positive or negative DC buses are alternately used as the inputs to the isolated DC / DC converters within the multiple energy storage branches. The common DC bus enables grid-connected operation of the energy storage system through a DC / AC converter. A unipolar output voltage isolated DC / DC converter topology is shown in the figure. Figure 3As shown, this topology consists of two full-bridge converters interconnected by 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 form the first half-bridge H1, and the third switch T3 and the fourth switch T4 form 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 form the third half-bridge H3, and the seventh switch T7 and the eighth switch T8 form the fourth half-bridge H4. The source of the first switch T1 and the drain of the second switch T2 are interconnected, forming the first AC connection point P1 on the primary side of the isolation transformer. The first AC connection point P1 is directly or connected in series with a capacitor to one end of the primary side of the isolation transformer. The source of the third switch T3 and the drain of the fourth switch T4 are interconnected, forming the second AC connection point P2 on the primary side of the isolation transformer. The second AC connection point P2 is directly or connected in series with a capacitor to the other end of the primary side of the isolation transformer. The source of the fifth switch T5... The drains of the sixth switch T6 are interconnected to form the third AC connection point S3 on the secondary side of the isolation transformer. The third AC connection point S3 on the secondary side of the isolation transformer is directly or connected in series with a capacitor to one end of the secondary side of the isolation transformer. The source of the seventh switch T7 and the drain of the eighth switch T8 are interconnected to form the 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 directly or connected in series with a capacitor to the other end of the secondary side of the isolation transformer. The drains of the first switch T1 and the third switch T3 are interconnected to form the 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 interconnected to form the second input point I2 of the isolated DC / DC converter. The drains of the fifth switch T5 and the seventh switch T7 are interconnected to form the first output point O1 of the isolated DC / DC converter. The source of the sixth switch T6 and the source of the eighth switch T8 are interconnected to form the second output point O2 of the isolated DC / DC converter. Switches T1, T2, T3, T4, T5, T6, T7, and T8 are controllable switches with anti-parallel diodes, such as MOSFETs and IGBTs. This unipolar isolated DC / DC converter structure has the advantages of simple modulation methods and topology, high stability, and low system cost.

[0038] Example 2: A modulation method for a single isolated DC / DC converter with a unipolar output voltage applicable to the partially power-controlled energy storage system described in Example 1, as follows: Figure 4As shown, the improved modulation method is as follows: the angle of each switch in the isolated DC / DC converter is 2*π per cycle. The first switch T1 and the second switch T2 of the first half-bridge H1 are complementary in conduction angle π, and a dead zone is inserted to prevent shoot-through. The third switch T3 and the fourth switch T4 of the second half-bridge H2 are complementary in conduction angle π, and a dead zone is inserted to prevent shoot-through. The fifth switch T5 and the sixth switch T6 of the third half-bridge H3 are complementary in conduction angle π, and an overlapping conduction time is inserted to ensure the freewheeling path of the charging and discharging current. The seventh switch T7 and the eighth switch T8 of the fourth half-bridge H4 are complementary in conduction angle π, and an overlapping conduction time is inserted to ensure the freewheeling path of the charging and discharging current. The first full-bridge converter F1 uses phase-shift control to generate a bipolar AC square wave voltage Ut on the primary side of the isolation transformer. 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 T1 and the third switch T3 is θ = Y * π, where θ is the phase shift angle, Y is the phase shift ratio, and the phase shift ratio ranges from 0 to 1. A reference 0 point for the drive signal is set. The falling edge of the first switch T1 leads the reference 0 point of the drive signal by θ / 2, the falling edge of the third switch T3 lags the reference 0 point of the drive signal by θ / 2, the falling edges of the fifth switch T5 and the eighth switch T8 lead the reference 0 point of the drive signal by π / 2, and the falling edges of the sixth switch T6 and the seventh switch T7 lag the reference 0 point of the drive signal by π / 2. This invention improves the F2 modulation method of the second full-bridge converter in an isolated DC / DC converter. The dead time Td of the switching transistors in the existing F2 modulation method is changed to an overlapping conduction time To. During this time, the fifth switch T5 and the sixth switch T6 are simultaneously turned on, and the seventh switch T7 and the eighth switch T8 are simultaneously turned on. This ensures that a freewheeling path is always provided for the charging and discharging current of the energy storage system during the alternating conduction of the switching transistors in the second full-bridge converter. Compared with existing energy storage system charging and discharging modulation methods, its significant difference lies in avoiding the use of the freewheeling capacitor C at the output of part of the power controller, i.e., the isolated DC / DC converter, further reducing system cost and component stress.

[0039] Example 3: Based on the partially power controlled energy storage system described in Example 1, a two-level, bipolar output voltage topology of the isolated DC / DC converter within this energy storage system is as follows: Figure 5As shown, this topology consists of two full-bridge converters interconnected by 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 form the first half-bridge H1, and the third switch T3 and the fourth switch T4 form 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 form the third half-bridge H3, and the ninth switch T9, the tenth switch T10, and 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, forming the 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 connected in series with a capacitor to one end of the primary side of the isolation transformer; the source of the third switch T3 and the drain of the fourth switch T4 are connected to each other, forming the second AC connection point P2 on the primary side of the isolation transformer. The second AC connection point P2 on the primary side of the isolation transformer is directly or connected in series with a capacitor to the other end of the primary side of the isolation transformer; the drain of the fifth switch T5 is connected to the drain of the sixth switch T6; the seventh switch... The source of switch T7 is connected to the source of switch T8. The source of switch T5 is connected to the drain of switch T7, forming the third AC connection point S3 on the secondary side of the isolation transformer. The third AC connection point S3 on the secondary side of the isolation transformer is directly or connected in series with a capacitor to one end of the secondary side of the isolation transformer. The drain of switch T9 is connected to the drain of switch T10. The source of switch T11 is connected to the source of switch T12. The source of switch T9 and the drain of switch T11 are connected to each other, forming the fourth AC connection point S4 on the secondary side of the isolation transformer. Contact S4 is directly or connected in series with a capacitor to the other end of the secondary side of the isolation transformer; the drains of the first switch T1 and the third switch T3 are connected to form the first input point I1 of the isolated DC / DC converter; the sources of the second switch T2 and the fourth switch T4 are connected to form the second input point I2 of the isolated DC / DC converter; the sources of the sixth switch T6 and the tenth switch T10 are connected to form the first output point O1 of the isolated DC / DC converter; the drains of the eighth switch T8 and the twelfth switch T12 are connected to form the second output point O2 of the isolated DC / DC converter.The first switch T1, second switch T2, third switch T3, fourth switch T4, fifth switch T5, sixth switch T6, seventh switch T7, eighth switch T8, ninth switch T9, tenth switch T10, eleventh switch T11, and 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). Switches T5 and T6 are connected in series in reverse and can be interchanged; switches T7 and T8 are connected in reverse and can be interchanged; switches T9 and T10 are connected in reverse and can be interchanged; and switches T11 and T12 are connected in reverse and can be interchanged. This bipolar isolated DC / DC converter structure has the advantages of simple modulation method, high stability, bipolar output voltage, and wide adjustment range.

[0040] Example 4: Based on the partially power controlled energy storage system described in Example 1, a two-level, bipolar output voltage topology of the isolated DC / DC converter within this energy storage system is as follows: Figure 6As shown, this topology consists of two full-bridge converters interconnected by 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 form the first half-bridge H1, and the third switch T3 and the fourth switch T4 form 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 form the third half-bridge H3. The ninth switch T9, the tenth switch T10, the fifth diode D5, the sixth diode D6, the seventh switch T7, the eighth switch T8, the third diode D3, and the fourth diode D4 form the third half-bridge H3. Switches eleven (T11), twelfth (T12), seventh (D7), and eighth (D8) form 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 P1 on the primary side of the isolation transformer. This first AC connection point P1 is directly connected to one end of the primary side of the isolation transformer, either in series or via a capacitor. The source of the third switch (T3) and the drain of the fourth switch (T4) are connected to each other, forming the second AC connection point P2 on the primary side of the isolation transformer. This second AC connection point P2 is directly connected to the other end of the primary side of the isolation transformer, either in series or via 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; and the source of the fifth switch T5 is connected to the drain of the seventh switch T7, forming the third AC connection point S3 on the secondary side of the isolation transformer. This third AC connection point S3 is directly or in series with a capacitor and then connected to one end of the secondary side of the isolation transformer. 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; and the anode of the sixth diode D6 is connected to the source of the tenth switch T10. The drain of switch T11 is connected to the source of switch T12, the anode of diode D7 is connected to the source of switch T11, the cathode of diode D8 is connected to the drain of switch T12, and the source of switch T9 is connected to the drain of switch T11, forming the fourth AC connection point S4 of the secondary side of the isolation transformer. The fourth AC connection point S4 of the secondary side of the isolation transformer is connected directly or in series with a capacitor to the other end of the secondary side of the isolation transformer. The drains of switch T1 and T3 are connected to form the first input point I1 of the isolated DC / DC converter, and the sources of switch T2 and T4 are connected to form the 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, and the anode of the fifth diode D5 is connected to the cathode of the sixth diode D6. The anodes of the first diode D1 and the fifth diode D5 are interconnected to form the 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, and the cathode of the seventh diode D7 is connected to the anode of the eighth diode D8. The anodes of the third diode D3 and the seventh diode D7 are interconnected to form the second output point O2 of the isolated DC / DC converter. The switches T1, T2, T3, T4, T5, T6, T7, T8, T9, and T10 are connected to each other. Switches T10, T11 (eleventh), and T12 are controllable switches with anti-parallel diodes, such as MOSFETs and IGBTs. Specifically, switch T5 is in series with diode D1 and their positions are interchangeable; switch T6 is in series with diode D2 and their positions are interchangeable; switch T7 is in series with diode D3 and their positions are interchangeable; switch T8 is in series with diode D4 and their positions are interchangeable; switch T9 is in series with diode D5 and their positions are interchangeable; switch T10 is in series with diode D6 and their positions are interchangeable; switch T11 is in series with diode D7 and their positions are interchangeable; and switch T12 is in series with diode D8 and their positions are interchangeable. This bipolar isolated DC / DC converter structure has the advantages of simple modulation method, high stability, bipolar output voltage, and wide adjustment range.

[0041] Example 5: An improved modulation method for a single isolated DC / DC converter with bipolar output voltage applicable to the partially power-controlled energy storage systems described in Examples 3 and 4, as follows: Figure 7As shown, the improved modulation method is as follows: For this topology, the angle of each switch in the isolated DC / DC converter is 2π per cycle. The first switch T1 and the second switch T2 of the first half-bridge H1 have complementary conduction angles of π, and a dead zone is inserted to prevent shoot-through. The third switch T3 and the fourth switch T4 of the second half-bridge H2 have complementary conduction angles of π, and a dead zone is inserted to prevent shoot-through. The fifth switch T5 and the sixth switch T6 of the third half-bridge H3 switch simultaneously, and the seventh switch T7 and the eighth switch T8 switch simultaneously. The fifth switch T5, the sixth switch T6, the seventh switch T7, and the eighth switch T8 have complementary conduction angles of π, and overlapping conduction times are inserted to ensure the freewheeling path of the energy storage system's charging and discharging current. The fourth half-bridge H4... The ninth switch T9 and the tenth switch T10 are switched simultaneously, and the eleventh switch T11 and the twelfth switch T12 are switched simultaneously. The ninth switch T9, the tenth switch T10, the eleventh switch T11, and the twelfth switch T12 have complementary conduction angles 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 uses phase-shift control to generate a bipolar AC square wave voltage Ut on the primary side of the isolation transformer. 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 T1 and the third switch 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 T1 leads the reference 0 point of the drive signal by θ / 2. The falling edge of the third switch T3 lags the reference 0 point of the drive signal by θ / 2. The falling edges of the fifth switch T5, the sixth switch T6, the eleventh switch T11, and the twelfth switch T12 lead the reference 0 point of the drive signal by π / 2. The falling edges of the seventh switch T7, the eighth switch T8, the ninth switch T9, and the tenth switch T10 lag the reference 0 point of the drive signal by π / 2.

[0042] Example 6: Based on the partially power-controlled energy storage system described in Example 1, a two-level, bipolar output voltage topology of the isolated DC / DC converter within this energy storage system is as follows: Figure 8As shown, this topology consists of two full-bridge converters interconnected by an isolation transformer. The first full-bridge converter F1, connected to the primary side of the isolation transformer, comprises a first half-bridge H1 and a second half-bridge H2. The first switch T1 and the second switch T2 form the first half-bridge H1, and the third switch T3 and the fourth switch T4 form the second half-bridge H2. The second full-bridge converter F2, connected to the secondary side of the isolation transformer, comprises a third half-bridge H3 and a fourth half-bridge H4. The fifth switch T5 and the sixth switch T6 form the third half-bridge H3, and the seventh switch T7 and the eighth switch T8 form the fourth half-bridge H4. The source of the first switch T1 and the drain of the second switch T2 are interconnected, forming the first AC connection point on the primary side of the isolation transformer. P1, the first AC connection point P1 on the primary side of the isolation transformer, is directly or connected in series with a capacitor to one end of the primary side of the isolation transformer; 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 on the primary side of the isolation transformer, which is directly or connected in series with a capacitor to the other end of the primary side of the isolation transformer; the source of the fifth switch T5 and the drain of the sixth switch T6 are connected to each other to form the third AC connection point S3 on the secondary side of the isolation transformer, which is directly or connected in series with a capacitor to the other end of the primary side of the isolation transformer. One end of the circuit is connected; the source of the seventh switch T7 and the drain of the eighth switch T8 are connected to each other to form the fourth AC connection point S4 of the secondary side of the isolation transformer. The fourth AC connection point S4 of the secondary side of the isolation transformer is directly or connected in series with a capacitor 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 the 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 the 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 sources of the sixth switch T6 and the eighth switch T8, which are interconnected to form the 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 MOSFETs and IGBTs. The fifth switch T5, the sixth switch T6, the seventh switch T7, and the eighth switch T8 are controllable switches without anti-parallel diodes that support bidirectional current flow. This bipolar isolated DC / DC converter structure has advantages such as simple modulation methods and topology, high stability, and low system cost.

[0043] Example 7: An improved modulation method applicable to the single isolated DC / DC converter with bipolar output voltage described in Example 6, as follows: Figure 4As shown, the improved modulation method is as follows: the angle of each switch in the isolated DC / DC converter is 2*π per cycle. The first switch T1 and the second switch T2 of the first half-bridge H1 are complementary in conduction angle π, and a dead zone is inserted to prevent shoot-through. The third switch T3 and the fourth switch T4 of the second half-bridge H2 are complementary in conduction angle π, and a dead zone is inserted to prevent shoot-through. The fifth switch T5 and the sixth switch T6 of the third half-bridge H3 are complementary in conduction angle π, and an overlapping conduction time is inserted to ensure the freewheeling path of the charging and discharging current. The seventh switch T7 and the eighth switch T8 of the fourth half-bridge H4 are complementary in conduction angle π, and an overlapping conduction time is inserted to ensure the freewheeling path of the charging and discharging current. The first full-bridge converter F1 uses phase-shift control to generate a bipolar AC square wave voltage Ut on the primary side of the isolation transformer. 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 T1 and the third switch T3 is θ = Y * π, where θ is the phase shift angle, Y is the phase shift ratio, and the phase shift ratio ranges from -1 to 1. A reference 0 point for the drive signal is set. The falling edge of the first switch T1 leads the reference 0 point of the drive signal by θ / 2, the falling edge of the third switch T3 lags the reference 0 point of the drive signal by θ / 2, the falling edges of the fifth switch T5 and the eighth switch T8 lead the reference 0 point of the drive signal by π / 2, and the falling edges of the sixth switch T6 and the seventh switch T7 lag the reference 0 point of the drive signal by π / 2.

[0044] Example 8: In a partially power-controlled energy storage system, the overlapping conduction of the upper and lower bridge switches of the second full-bridge converter is achieved by using a drive signal duty cycle D greater than 0.5. The overlapping conduction time of the second full-bridge converter switches is set by adjusting the portion of the duty cycle exceeding 0.5. Let To be the overlapping conduction time, D be the duty cycle of the second full-bridge converter drive signal, Ts be the switching period of the switching transistor, fs be the switching frequency of the switching transistor, and T... s =1 / f s Db is the reference duty cycle of the switching transistor, which is 0.5. Do is the portion of the switching transistor's duty cycle exceeding 0.5, corresponding to the overlapped conduction time To. D = D b +D o Adjusting the value of Do allows for adjustment of the overlap conduction time To. As described above, the formula for calculating the overlap conduction time To can be expressed as: T o =D o ×T s This improved modulation method provides a continuous current 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 existing partially power controlled energy storage systems, it avoids the use of a freewheeling capacitor at the output of the partial power controller, further reducing system cost, reducing component stress, and improving system reliability.

[0045] Example 9: Using as follows Figure 5 , Figure 6 and Figure 8 The output voltage is shown as a bipolar isolated DC / DC converter, and the overall structure is as follows. Figure 1 The partial power-controlled energy storage system shown dynamically adjusts the total DC bus voltage of the DC / AC converter based on the voltage of the battery clusters in each energy storage branch. The lower limit of the setpoint for the total DC bus voltage of the DC / AC converter is the highest 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 / AC converter, which can be expressed as: U dc,min U is the lower limit given for the total DC bus voltage of the DC / AC converter, where n is the total number of energy storage branches (i.e., battery clusters). be,i Let be the voltage of the i-th battery cluster. U represents the highest value of the battery cluster voltage in each energy storage branch. o,m 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 total DC bus voltage setpoint 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 This represents the minimum voltage value of the battery clusters in each energy storage branch. The setpoint for the total DC bus voltage of the DC / AC converter lies between its lower and upper limits. To ensure reliable system operation, one method for selecting the setpoint is to take the average of the lower and upper limits, which is: U dc,ref This is the given value for the total DC bus voltage of the DC / AC converter.

[0046] Example 10: One embodiment of the present invention is applicable to a battery cluster containing four battery cells and employing... Figure 2 , Figure 3 and Figure 8 The overall modulation method of a partially power controlled energy storage system using an isolated DC / DC converter is as follows: Figure 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. Therefore, the reference 0 point of the drive signal of the isolated DC / DC converter in energy storage branch 2 is phase-shifted by 1 / 4*π relative to the reference 0 point of the drive signal of the isolated DC / DC converter in energy storage branch 1, the reference 0 point of the drive signal of the isolated DC / DC converter in energy storage branch 3 is phase-shifted by 1 / 2*π relative to the reference 0 point of the drive signal of the isolated DC / DC converter in energy storage branch 1, and the reference 0 point of the drive signal of the isolated DC / DC converter in energy storage branch 4 is phase-shifted by 3 / 4*π relative to the reference 0 point of the drive signal of the isolated DC / DC converter in energy storage branch 1. This 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. This method solves the problems of increased peak-to-peak value and large ripple in the DC bus current caused by overlapping peaks and troughs in multiple energy storage branches. It also significantly reduces the filter inductance of the energy storage branches and the filter capacitor of the DC bus, thereby lowering the cost of the energy storage system. In this embodiment, there are four energy storage branches. The phase shift angles of the reference 0 point of the isolated DC / DC converter drive signal in energy storage branches 2, 3, and 4 relative to the reference 0 point of the isolated DC / DC converter drive signal in energy storage branch 1 are 1 / 4π, 1 / 2π, and 3 / 4π, respectively. The DC bus current ripple after using this modulation method is as follows: Figure 11 As shown, the cancellation of current peaks and troughs among the four energy storage branches suppresses the ripple of the common DC bus current. In contrast, the DC bus ripple current using existing modulation methods is as follows: Figure 12 As shown, the peak-to-peak value of the DC bus current ripple caused by the overlap of current peaks and troughs in the four energy storage branches is four times that of a single energy storage branch. Therefore, the modulation method proposed in this invention achieves the cancellation of current peaks and troughs between energy storage branches, which can significantly reduce the filter inductance of the energy storage branches and the filter capacitance of the DC bus, thereby reducing the cost of the energy storage system.

[0047] Example 11: An embodiment of the present invention is applicable to a battery cluster containing four battery cells and employing... Figure 5 and Figure 6 The overall modulation method of a partially power controlled energy storage system using an isolated DC / DC converter is as follows: Figure 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. Therefore, the reference 0 point of the drive signal of the isolated DC / DC converter in energy storage branch 2 is phase-shifted by 1 / 4*π relative to the reference 0 point of the drive signal of the isolated DC / DC converter in energy storage branch 1, the reference 0 point of the drive signal of the isolated DC / DC converter in energy storage branch 3 is phase-shifted by 1 / 2*π relative to the reference 0 point of the drive signal of the isolated DC / DC converter in energy storage branch 1, and the reference 0 point of the drive signal of the isolated DC / DC converter in energy storage branch 4 is phase-shifted by 3 / 4*π relative to the reference 0 point of the drive signal of the isolated DC / DC converter in energy storage branch 1. Through this improved modulation method, the current peaks and troughs between energy storage branches can be canceled, and the current ripple of the common DC bus can be suppressed. This method solves the problems of increased peak-to-peak value and large ripple in the DC bus current caused by overlapping peaks and troughs in multiple energy storage branches. It also significantly reduces the filter inductance of the energy storage branches and the filter capacitor of the DC bus, thereby lowering the cost of the energy storage system. In this embodiment, there are four energy storage branches. The phase shift angles of the reference 0 point of the isolated DC / DC converter drive signal in energy storage branches 2, 3, and 4 relative to the reference 0 point of the isolated DC / DC converter drive signal in energy storage branch 1 are 1 / 4π, 1 / 2π, and 3 / 4π, respectively. The DC bus current ripple after using this modulation method is as follows: Figure 11 As shown, the cancellation of current peaks and troughs among the four energy storage branches suppresses the ripple of the common DC bus current. In contrast, the DC bus ripple current using existing modulation methods is as follows: Figure 12 As shown, the peak-to-peak value of the DC bus current ripple caused by the overlap of current peaks and troughs in the four energy storage branches is four times that of a single energy storage branch. Therefore, the modulation method proposed in this invention achieves the cancellation of current peaks and troughs between energy storage branches, which can significantly reduce the filter inductance of the energy storage branches and the filter capacitance of the DC bus, thereby reducing the cost of the energy storage system.

[0048] Although the illustrative specific embodiments of the present invention have been described above to enable those skilled in the art to understand the invention, it should be understood that the invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes will be obvious as long as they are within the spirit and scope of the invention as defined and determined by the appended claims, and all inventions utilizing the concept of the present invention are protected.

Claims

1. A modulation method for the topology of a partially power controlled energy storage system, wherein the topology of the partially power controlled energy storage system consists 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 multiple energy storage branches are connected in parallel to the main DC bus of the DC / AC converter. Each energy storage branch consists of a filter inductor, an isolated DC / DC converter, and a battery pack. The filter inductor, the output of the isolated DC / DC converter, and the battery pack are connected in series and then connected in parallel as a whole to the main DC bus of the DC / AC converter. The input of each isolated DC / DC converter is connected to the main DC bus or one of the multiple DC buses of the DC / AC converter. Parallel connection; when the input terminals of each isolated DC / DC converter are connected in parallel with one of the multiple DC buses, the input terminals of each isolated DC / DC converter are evenly connected in parallel with each DC bus to balance the input and output power of each DC bus; among them, a two-level, unipolar output voltage topology of the isolated DC / DC converter is as follows: the topology consists of two full-bridge converters connected to each other through an isolation transformer. The first full-bridge converter F1 connected to the primary side of the isolation transformer 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 the third half-bridge H3 and the fourth half-bridge H4. The fifth switch T5 and the sixth switch T6 form the third half-bridge H3, and the seventh switch T7 and the eighth switch T8 form the fourth half-bridge H4. The source of the first switch T1 and the drain of the second switch T2 are interconnected, forming the first AC connection point P1 on the primary side of the isolation transformer. This first AC connection point P1 is directly connected to one end of the primary side of the isolation transformer, either in series or via a capacitor. The source of the third switch T3 and the drain of the fourth switch T4 are interconnected, forming the second AC connection point P2 on the primary side of the isolation transformer. This second AC connection point P2 is directly connected to the other end of the primary side of the isolation transformer, either in series or via a capacitor. The source of the fifth switch T5 and the drain of the sixth switch T6 are interconnected, forming the third AC connection point S3 on the secondary side of the isolation transformer. The third AC connection point S3 of the isolation transformer is directly or connected in series with a capacitor to one end of the secondary side of the isolation transformer; the source of the seventh switch T7 and the drain of the eighth switch T8 are connected to each other to form the 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 connected in series with a capacitor 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 the 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 the 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 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. 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. The controllable switches include metal-oxide-semiconductor field-effect transistors and insulated-gate bipolar transistors. The improved modulation method applicable to this topology is as follows: In the isolated DC / DC converter, the angle of each switch in one cycle is 2π. In the first half-bridge H1, the first switch T1 and the second switch T2 have complementary conduction angles of π, and a dead zone is inserted to prevent shoot-through. In the second half-bridge H2, the third switch T3 and the fourth switch T4 have complementary conduction angles of π, and a dead zone is inserted to prevent shoot-through. In the third half-bridge H3, the fifth switch T5 and the sixth switch T6 have complementary conduction angles of π, and overlapping conduction time is inserted to ensure the freewheeling path of the energy storage system's charging and discharging current. In the fourth half-bridge H4, the seventh switch T7 and the eighth switch T8 have complementary conduction angles of π, and overlapping conduction time is inserted to ensure the freewheeling path of the energy storage system's charging and discharging current. The first full-bridge converter F1 uses phase-shift control to generate a bipolar AC square wave voltage Ut on the primary side of the isolation transformer. 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 first switch T1 and the third switch T2... The phase shift angle between the switching transistors 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 drive signal is set. The falling edge of the first switching transistor T1 leads the reference 0 point of the drive signal by θ / 2, the falling edge of the third switching transistor T3 lags the reference 0 point of the drive signal by θ / 2, the falling edges of the fifth switching transistor T5 and the eighth switching transistor T8 lead the reference 0 point of the drive signal by π / 2, and the falling edges of the sixth switching transistor T6 and the seventh switching transistor T7 lag the reference 0 point of the drive signal by π / 2. A two-level, bipolar output voltage topology of an isolated DC / DC converter is as follows: This topology consists of two full-bridge converters interconnected by 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, consists of the third half-bridge H3 and the fourth half-bridge H4. The fifth switch T5, the sixth switch T6, the seventh switch T7, and the eighth switch T8 form the third half-bridge H3, while the ninth switch T9, the tenth switch T10, the eleventh switch T11, and the twelfth switch T12 form the fourth half-bridge H4. The source of the first switch T1 and the drain of the second switch T2 are interconnected, forming the 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 connected directly or in series with a capacitor. The third switch T3 and the fourth switch T4 are connected to each other, forming the second AC connection point P2 on the primary side of the isolation transformer. This second AC connection point P2 is connected to the other end of the primary side of the isolation transformer, either directly or in series with a capacitor. The drain of the fifth switch T5 is connected to the drain of the sixth switch T6, and the source of the seventh switch T7 is connected to the source 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 the third AC connection on the secondary side of the isolation transformer. Contact S3, the third AC connection point S3 on the secondary side of the isolation transformer, is directly or connected in series with a capacitor to one end of the secondary side of the isolation transformer; 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 and the drain of the eleventh switch T11 are interconnected, forming the 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 directly or connected in series with a capacitor to the other end of the secondary side of the isolation transformer; The drains of switch T1 and the third switch T3 are connected to form the first input point I1 of the isolated DC / DC converter; the sources of switch T2 and the fourth switch T4 are connected to form the second input point I2 of the isolated DC / DC converter; the sources of switch T6 and the tenth switch T10 are connected to form the first output point O1 of the isolated DC / DC converter; and the drains of switch T8 and the twelfth switch T12 are connected to form the 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. These controllable switches include metal-oxide-semiconductor field-effect transistors (MOSFETs) and insulated-gate bipolar transistors (IGBTs). The fifth switch T5 and the sixth switch T6 are connected in series in opposite directions and can be interchanged; the seventh switch T7 and the eighth switch T8 are connected in series in opposite directions and can be interchanged; the ninth switch T9 and the tenth switch T10 are connected in series in opposite directions and can be interchanged; and the eleventh switch T11 and the twelfth switch T12 are connected in series in opposite directions and can be interchanged.

2. Reverse series connection with interchangeable positions; the improved modulation method applicable to this topology is as follows: the angle of each switch in the isolated DC / DC converter is 2*π per cycle. The first switch T1 and the second switch T2 of the first half-bridge H1 are complementary in conduction angle π, and a dead zone is inserted to prevent shoot-through. The third switch T3 and the fourth switch T4 of the second half-bridge H2 are complementary in conduction angle π, and a dead zone is inserted to prevent shoot-through. The fifth switch T5 and the sixth switch T6 of the third half-bridge H3 are switched simultaneously, and the seventh switch T7 and the eighth switch T8 are switched simultaneously. The fifth switch T5, the sixth switch T6, the seventh switch T7, and the eighth switch T8 are complementary in conduction angle π, and overlapping conduction is inserted. The timing ensures the freewheeling path of the energy storage system's charging and discharging current. In the fourth half-bridge H4, the ninth switch T9 and the tenth switch T10 switch simultaneously, and the eleventh switch T11 and the twelfth switch T12 switch simultaneously. The ninth switch T9, the tenth switch T10, the eleventh switch T11, and the twelfth switch T12 have complementary conduction angles π, and the overlapping conduction time ensures the freewheeling path of the energy storage system's charging and discharging current. The first full-bridge converter F1 uses phase-shift control to generate a bipolar AC square wave voltage Ut on the primary side of the isolation transformer. 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 first switch T... The phase shift angle between switch 1 and the third switch 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 T1 leads the reference 0 point of the drive signal by θ / 2, the falling edge of the third switch T3 lags the reference 0 point of the drive signal by θ / 2, the falling edges of the fifth switch T5, the sixth switch T6, the eleventh switch T11, and the twelfth switch T12 lead the reference 0 point of the drive signal by π / 2, and the falling edges of the seventh switch T7, the eighth switch T8, the ninth switch T9, and the tenth switch T10 lag the reference 0 point of the drive signal by π / 2.

2. The modulation method for the topology of the partially power controlled energy storage system according to claim 1, wherein a two-level, bipolar output voltage topology of the isolated DC / DC converter is as follows: the topology consists of two full-bridge converters interconnected by 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; 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, and the second diode D2 are connected to the secondary side of the isolation transformer. The seventh switch T7, the eighth switch T8, the third diode D3, and the fourth diode D4 form 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 twelfth switch T12, the seventh diode D7, and the eighth diode D8 form 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 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 connected in series with a capacitor to one end of the primary side of the isolation transformer; the source of the third switch T3 and the drain of the fourth switch T4 are connected to each other, forming the second AC connection point P2 on the primary side of the isolation transformer. The second AC connection point P2 on the primary side is directly or in series with a capacitor and connected to the other end of the isolation transformer's primary side; 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, and the source of the fifth switch T5 and the drain of the seventh switch T7 are interconnected, forming the third AC connection point S3 on the secondary side of the isolation transformer. The third AC connection point S3 on the secondary side of the isolation transformer is directly or in series with a capacitor and connected to the isolation transformer's primary side. One end of the secondary side of the transformer is connected; 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, and the source of the ninth switch T9 and the drain of the eleventh switch T11 are connected to each other, forming the fourth AC connection point S4 of the secondary side of the isolation transformer. The fourth AC connection point S4 of the secondary side of the isolation transformer is directly or connected in series with a capacitor to the other end of the secondary side of the isolation transformer.The drains of the first switch T1 and the third switch T3 are connected to form the first input point I1 of the isolated DC / DC converter. The sources of the second switch T2 and the fourth switch T4 are connected to form the 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, and the anode of the fifth diode D5 is connected to the cathode of the sixth diode D6. The anodes of the first diode D1 and the fifth diode D5 are connected to form the 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, and the cathode of the seventh diode D7 is connected to the anode of the eighth diode D8. The cathodes of diodes 3 and 7 are interconnected to form the second output point O2 of the isolated DC / DC converter. Switches T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, and T12 are controllable switches with anti-parallel diodes. These controllable switches include metal-oxide-semiconductor field-effect transistors (MOSFETs) and insulated-gate bipolar transistors (IGBTs). Switch T5 is connected in series with diode D1 and their positions are interchangeable; switch T6 is connected in series with diode D2 and their positions are interchangeable; and switch T7 is connected in series with diode D3. The positions of the switches are interchangeable: the eighth switch T8 and the fourth diode D4 are interchangeable in series; the ninth switch T9 and the fifth diode D5 are interchangeable in series; the tenth switch T10 and the sixth diode D6 are interchangeable in series; the eleventh switch T11 and the seventh diode D7 are interchangeable in series; and the twelfth switch T12 and the eighth diode D8 are interchangeable in series. An improved modulation method suitable for this topology is as follows: the angle of each switch in the isolated DC / DC converter is 2π per cycle. The first switch T1 and the second switch T2 of the first half-bridge H1 are complementary conduction angles of π, and a dead zone is inserted to prevent shoot-through. The third switch T3 and the fourth switch T4 of the second half-bridge H2 are complementary conduction angles of π, and a dead zone is inserted. To prevent direct current flow, the fifth switch T5 and the sixth switch T6 of the third half-bridge H3 are switched simultaneously, as are the seventh switch T7 and the eighth switch T8. The fifth switch T5, the sixth switch T6, the seventh switch T7, and the eighth switch T8 have complementary conduction angles of π, and the overlapping conduction time is inserted to ensure the freewheeling path of the energy storage system's charging and discharging current. The ninth switch T9 and the tenth switch T10 of the fourth half-bridge H4 are switched simultaneously, as are the eleventh switch T11 and the twelfth switch T12. The ninth switch T9, the tenth switch T10, the eleventh switch T11, and the twelfth switch T12 have complementary conduction angles of π, and the overlapping conduction time is inserted to ensure the freewheeling path of the energy storage system's charging and discharging current.The first full-bridge converter F1 uses phase-shift control to generate a bipolar AC square wave voltage Ut on the primary side of the isolation transformer. 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 T1 and the third switch 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. A reference 0 point for the drive signal is set. The falling edge of the first switch T1 leads the reference 0 point of the drive signal by θ / 2, the falling edge of the third switch T3 lags the reference 0 point of the drive signal by θ / 2, the falling edges of the fifth switch T5, the sixth switch T6, the eleventh switch T11, and the twelfth switch T12 lead the reference 0 point of the drive signal by π / 2, and the falling edges of the seventh switch T7, the eighth switch T8, the ninth switch T9, and the tenth switch T10 lag the reference 0 point of the drive signal by π / 2.

3. The modulation method for the topology of the partially power controlled energy storage system according to claim 1, wherein a two-level, bipolar output voltage topology of the isolated DC / DC converter is as follows: the topology is formed by two full-bridge converters interconnected by 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, consists of the third half-bridge H3 and the fourth half-bridge H4. The fifth switch T5 and the sixth switch T6 form the third half-bridge H3, and the seventh switch T7 and the eighth switch T8 form the fourth half-bridge H4. The source of the first switch T1 and the drain of the second switch T2 are interconnected, forming the first AC connection point P1 on the primary side of the isolation transformer. This first AC connection point P1 is directly connected to one end of the primary side of the isolation transformer, either in series or via a capacitor. The source of the third switch T3 and the drain of the fourth switch T4 are interconnected, forming the second AC connection point P2 on the primary side of the isolation transformer. This second AC connection point P2 is directly connected to the other end of the primary side of the isolation transformer, either in series or via a capacitor. The source of the fifth switch T5 and the drain of the sixth switch T6 are interconnected, forming the third AC connection point S3 on the secondary side of the isolation transformer. The third AC connection point S3 of the isolation transformer is directly or connected in series with a capacitor to one end of the secondary side of the isolation transformer; the source of the seventh switch T7 and the drain of the eighth switch T8 are connected to each other to form the 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 connected in series with a capacitor 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 the 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 the 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 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. The first switch T1, the second switch T2, the third switch T3 and the fourth switch T4 are controllable switches with anti-parallel diodes. The controllable switches include metal-oxide-semiconductor field-effect transistors and insulated-gate bipolar transistors. The fifth switch T5, the sixth switch T6, the seventh switch T7 and the eighth switch T8 are controllable switches without anti-parallel diodes that support bidirectional current flow. The improved modulation method applicable to this topology is as follows: In the isolated DC / DC converter, the angle of each switch in one cycle is 2π. In the first half-bridge H1, the first switch T1 and the second switch T2 have complementary conduction angles of π, and a dead zone is inserted to prevent shoot-through. In the second half-bridge H2, the third switch T3 and the fourth switch T4 have complementary conduction angles of π, and a dead zone is inserted to prevent shoot-through. In the third half-bridge H3, the fifth switch T5 and the sixth switch T6 have complementary conduction angles of π, and overlapping conduction times are inserted to ensure the freewheeling path of the energy storage system's charging and discharging current. In the fourth half-bridge H4, the seventh switch T7 and the eighth switch T8 have complementary conduction angles of π, and overlapping conduction times are inserted to ensure the freewheeling path of the energy storage system's charging and discharging current. The first full-bridge converter F1 uses phase-shift control in the isolated transformer... The primary side of the transformer generates a bipolar AC square wave voltage Ut. 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 T1 and the third switch 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 T1 leads the reference 0 point of the drive signal by θ / 2, the falling edge of the third switch T3 lags the reference 0 point of the drive signal by θ / 2, the falling edges of the fifth switch T5 and the eighth switch T8 lead the reference 0 point of the drive signal by π / 2, and the falling edges of the sixth switch T6 and the seventh switch T7 lag the reference 0 point of the drive signal by π / 2.

4. The modulation method for the topology of a partially power controlled energy storage system according to claim 1, characterized in that: The total DC bus voltage of the DC / AC converter is dynamically adjusted according to the voltage of the battery clusters in each energy storage branch. The lower limit of the setpoint value of the total DC bus voltage of the DC / AC converter is the highest 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 / AC converter, which can be expressed as: U dc,min U is the lower limit given for the total DC bus voltage of the DC / AC converter, where n is the total number of energy storage branches (i.e., battery clusters). be,i Let be the voltage of the i-th battery cluster. U represents the highest value of the battery cluster voltage in each energy storage branch. o,m 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 total DC bus voltage setpoint 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 This represents the lowest value of the battery cluster voltage in each energy storage branch; the setpoint of the total DC bus voltage of the DC / AC converter is between the lower and upper limits of the setpoint. To ensure reliable system operation, the setpoint of the total DC bus voltage of the DC / AC converter is selected by taking the average of the lower and upper limits, which is: U dc,ref This is the given value for the total DC bus voltage of the DC / AC converter.

5. The modulation method for the topology of a partially power-controlled energy storage system according to claim 1, characterized in that, utilizing the characteristic that the overall phase shift of the drive signal of the isolated DC / DC converter on the energy storage branch will cause the filter inductor current ripple to have the same phase shift angle, by performing an overall phase shift on the drive signals of the first switch T1, second switch T2, third switch T3, fourth switch T4, fifth switch T5, sixth switch T6, seventh switch T7, and eighth switch T8 of the isolated DC / DC converter, the timing of the peak and trough of the filter inductor current within the switching period Ts is changed. By adjusting the overall phase shift angle of the drive signals of the isolated DC / DC converter on each energy storage branch, the timing of the peak or trough of the filter inductor current in each energy storage branch is distributed at equal time intervals within the switching period Ts; when the number of energy storage branches connected in parallel to the common DC bus is n, the isolated DC / DC converter... If the angle of each switching 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. This 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.

6. The modulation method for the topology of a partially power-controlled energy storage system according to claim 1, characterized in that, utilizing the characteristic that overall phase shifting of the drive signals of the isolated DC / DC converters on the energy storage branches causes the filter inductor current ripple to exhibit the same phase shift angle, the drive signals of the first switch T1, second switch T2, third switch T3, fourth switch T4, fifth switch T5, sixth switch T6, seventh switch T7, eighth switch T8, ninth switch T9, tenth switch T10, eleventh switch T11, and twelfth switch T12 of the isolated DC / DC converters are phase-shifted to change the timing of the peak and trough of the filter inductor current within the switching period Ts. By adjusting the overall phase shift angle of the drive signals of the isolated DC / DC converters on each energy storage branch, the timing of the peak or trough of the filter inductor current in each energy storage branch is distributed at equal time intervals within the switching period Ts; when the number of energy storage branches connected in parallel to the common DC bus... When the value is n, the angle of each switching cycle of the isolated DC / DC converter is 2π. Therefore, the reference 0 point of the drive signal of the isolated DC / DC converter in energy storage branch 2 is phase-shifted by 1 / nπ relative to the reference 0 point of the drive signal of the isolated DC / DC converter in energy storage branch 1. The reference 0 point of the drive signal of the isolated DC / DC converter in energy storage branch 3 is phase-shifted by 2 / nπ relative to the reference 0 point of the drive signal of the isolated DC / DC converter in energy storage branch 1. The phase shift of the isolated DC / DC converter in energy storage branch 4 is... The reference 0 point of the drive signal of the type DC / DC converter is phase-shifted by 3 / n*π relative to the reference 0 point of the drive signal of the isolated type DC / DC converter in energy storage branch 1. Similarly, the reference 0 point of the drive signal of the isolated type DC / DC converter in energy storage branch n is phase-shifted by (n-1) / n*π relative to the reference 0 point of the drive signal of the isolated type DC / DC converter in energy storage branch 1. This 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.

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