Three-port semi-isolated DC converter and modulation method thereof, and hybrid energy storage system

Abstract

The present invention discloses a three-port semi-isolated DC converter and its modulation method and hybrid energy storage system. The three-port semi-isolated DC converter consists of three parts: a battery port, a supercapacitor port and a high-voltage port. The present invention can connect two energy storage media at the same time, and can realize the switching of power flow modes between multiple ports by controlling the solid-state isolating switch, the duty cycle of two full bridges and the phase shift between the bridge arms of the high-voltage port full bridge. The improved modulation method for the converter can realize the power distribution between the two energy storage medium ports by changing the duty cycle of the battery port full bridge and the phase shift between the high-voltage port full bridge arms, and reduce the peak value of the current passing through the transformer and the current stress of the switch tube by changing the duty cycle of the high-voltage port full bridge while ensuring the soft switching of all switch tubes. The present invention has the advantages of high safety, flexible structure, low cost, etc., and is suitable for systems containing multiple energy storage media.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronics, and in particular to a three-port semi-isolated DC converter and a modulation method thereof, and a hybrid energy storage system. Background Art

[0002] With the growth of global energy demand and the widespread adoption of renewable energy, energy storage technology has become an indispensable component of the power system. Hybrid energy storage systems combine the advantages of different energy storage media, which not only improves energy storage efficiency, but also enhances the flexibility and response speed of the system, thereby achieving higher comprehensive performance. However, to fully realize the potential of hybrid energy storage systems, advanced energy management strategies and highly flexible power electronic interfaces are required, which has prompted the development of multi-port converter technology. In this context, the three-port DC converter has become a key technology for achieving efficient energy conversion and management with its unique multi-port characteristics. The three-port energy storage converter can not only adapt to the needs of multi-energy input and output, but also achieve optimal energy distribution between different energy storage media through precise control. It has become the preferred solution for improving system efficiency and power density, and greatly improves the flexibility and stability of the energy storage system.

[0003] Among various hybrid energy storage DC converters, the semi-isolated three-port DC converter can selectively introduce a high-frequency transformer between specific ports to achieve electrical isolation according to application requirements. This is particularly beneficial when multiple energy storage media and loads of different voltage levels need to be connected at the same time. While improving the converter voltage gain capability, it also enhances the flexibility of the system. In addition, its modular design and device reuse also simplify the expansion and maintenance of the system to a certain extent, reducing costs.

[0004] Traditional non-isolated three-port converters show their advantages in low-power applications due to their simple structure and low cost. However, due to the limitation of voltage gain and the lack of electrical isolation, their use in specific occasions is limited. The fully isolated three-port DC-DC converter uses a high-frequency transformer to achieve electrical isolation between the ports, improving the safety and flexibility of the system. However, the introduction of the high-frequency transformer also brings about a loss of efficiency, and also leads to an increase in the volume, weight and cost of the overall system.

[0005] Semi-isolated three-port DC converters can selectively introduce high-frequency transformers between specific ports to achieve electrical isolation according to application requirements. This is particularly advantageous when multiple energy storage media and loads of different voltage levels need to be connected at the same time. While improving the voltage gain capability of the converter, it also enhances the flexibility of the system. In addition, the modular design and device reuse of the semi-isolated three-port converter simplify the expansion and maintenance of the system to a certain extent, reducing costs. Therefore, the semi-isolated three-port DC converter provides an effective technical approach for the integration of new energy and energy storage systems. However, many semi-isolated DC converters today can only perform unidirectional power transmission, and cannot achieve bidirectional power transmission at each port of the converter, making it difficult to meet the needs of hybrid energy storage systems.

[0006] Therefore, it is very important to study and innovate the topology and modulation method of semi-isolated three-port DC converter. Summary of the invention

[0007] The purpose of the present invention is to provide a three-port semi-isolated DC converter and a modulation method thereof, and a hybrid energy storage system, so as to solve the above technical problems.

[0008] To achieve the above object, the present invention is implemented according to the following technical solutions:

[0009] In a first aspect, the present invention provides a three-port semi-isolated DC converter, comprising a battery port, a supercapacitor port and a high-voltage port; the battery port is connected to the high-voltage port through the primary side of a high-frequency transformer T, and the supercapacitor port is connected to the high-voltage port through the secondary side of the high-frequency transformer T; the battery port and the supercapacitor port are used to connect energy storage media to achieve charging and discharging; the high-voltage port is used to connect a DC load or a DC bus.

[0010] In one embodiment, the battery port includes: a battery, a low-voltage side capacitor C Ba , Battery side inductance L in , the primary full-bridge circuit and the series inductor L including the transformer leakage inductance lk The primary full-bridge circuit includes a first bridge arm and a second bridge arm, wherein the first bridge arm includes a switch device S1 and a switch device S3 connected in series in sequence; the second bridge arm includes a switch device S2 and a switch device S4 connected in series in sequence, and D1-D4 and C1-C4 are anti-parallel diodes and parasitic capacitors corresponding to the switch devices S1-S4 respectively; the battery and the low-voltage side capacitor C Ba In parallel, the positive electrode of the battery and the input inductor L in The positive electrode is connected to the positive electrode, and the negative electrode is directly connected to the source of the switch device S2 and the source of the switch device S4 in the primary full-bridge circuit; the battery side inductor L inThe negative electrode is connected to the drain of the switch device S1 and the drain of the switch device S3 of the primary full-bridge circuit; the series inductor L lk The positive electrode is connected to the source of the switching device S1, and the negative electrode is connected to the same-name terminal of the primary side of the high-frequency transformer T; the opposite-name terminal of the primary side of the high-frequency transformer T is connected to the drain of the switching device S4;

[0011] The supercapacitor port includes: a supercapacitor, a reverse charging diode D SC , solid-state isolating switch T1 and two identical inductors L1 and L2 on the supercapacitor side; the solid-state isolating switch T1 and the reverse charging diode D SC In parallel, the positive electrode of the super capacitor and the reverse charging diode D SC The positive electrode of the reverse charging diode D SC The negative electrode of the inductor L1 is connected to the positive electrodes of the inductors L1 and L2, the negative electrode of the inductor L1 is connected to the same-name terminal of the secondary side of the high-frequency transformer T, and the negative electrode of the inductor L2 is connected to the opposite-name terminal of the secondary side of the high-frequency transformer T;

[0012] The high-voltage port includes: a secondary full-bridge circuit, a high-voltage side capacitor C o ; The secondary full-bridge circuit includes a third bridge arm and a fourth bridge arm, the third bridge arm includes a switch device S5 and a switch device S7 connected in series in sequence; the fourth bridge arm includes a switch device S6 and a switch device S8 connected in series in sequence; D5-D8 and C5-C8 are anti-parallel diodes and parasitic capacitors corresponding to the switch devices S5-S8 respectively; the midpoint of the third bridge arm and the fourth bridge arm of the secondary full-bridge circuit is connected to the secondary winding of the high-frequency transformer T; the high-voltage side capacitor C o The positive electrode is connected to the drain of the switching device S5 and the drain of the switching device S7, and the negative electrode is connected to the source of the switching device S6 and the source of the switching device S8.

[0013] In one embodiment, the three-port semi-isolated DC converter can switch between four operating modes, and the four operating modes include:

[0014] Working mode 1: the high-voltage port is connected to a load, and the solid-state relay T1 of the supercapacitor port is disconnected; the battery port and the supercapacitor port emit power, and the high-voltage port absorbs power;

[0015] Working mode 2: the high-voltage port is connected to a load, and the solid-state relay T1 of the supercapacitor port is closed; the battery port emits power, and the supercapacitor port and the high-voltage port absorb power;

[0016] Working mode 3: the high-voltage port is connected to the DC bus or power supply, and the solid-state relay T1 of the supercapacitor port is disconnected; the battery port absorbs power, and the supercapacitor port and the high-voltage port emit power;

[0017] Working mode 4: the high-voltage port is connected to a DC bus or a power supply, and the solid-state relay T1 of the supercapacitor port is closed; the battery port and the supercapacitor port absorb power, and the high-voltage port emits power.

[0018] In one embodiment, by performing modal analysis on the three-port semi-isolated DC converter in working mode 1, the working mode of working mode 1 in a switching cycle is divided into: a working mode in a heavy load state and a working mode in a light load state;

[0019] The heavy load state and light load state are defined by the following method:

[0020] According to the output voltage U of the semi-isolated three-port DC converter under specific working conditions o , battery voltage U Ba Define the proportion of the input inductor charging time of the low-voltage battery side in the entire switching cycle in half a switching cycle:

[0021] Rated output power P of the battery Ba Compare with critical power P0;

[0022] When P Ba >P0, the converter is defined as being in a heavy load state; if P Ba ≤P0, the converter is defined as a light load state at this time.

[0023] In a second aspect, the present invention provides a modulation method based on the above-mentioned three-port semi-isolated DC converter, wherein the method controls the opening and closing of the solid-state isolating switch T1, the duty cycle d1 of the switch devices S1-S4, the duty cycle d2 of the switch devices S5-S8 and the phase shift angle β between the high-voltage side bridge arms under different working conditions to realize the switching of the converter working mode, and the specific modulation method adopted in each working mode is:

[0024] The modulation method used in working mode 1 is:

[0025] Set all switch devices S1 to S8 to have the same switching frequency T s , the duty cycle of switch devices S1~S4 is d1, switch devices S1 and S3 are turned on or off at the same time, the turn-on signals of switch devices S2 and S4 lag behind half the switching cycle of S1 and S3, the duty cycle of switch devices S5~S8 is d2, the turn-off signals of S5 and S6 are triggered simultaneously with the turn-off signals of S1 and S2, respectively, and the turn-on and turn-off signals of S7 and S8 lag behind the turn-on and turn-off signals of S6 and S5 by βT respectively s ;

[0026] When the battery port and the supercapacitor port transmit power to the high-voltage port, the battery output power is controlled by adjusting d1 and d2, the supercapacitor output power is controlled by adjusting β, and d2 is adjusted to reduce the series inductance L. lk Peak value of current;

[0027] In working mode 2, the modulation method used is consistent with that of the traditional current-fed isolated DC converter;

[0028] In working mode 3, the modulation method used is consistent with the traditional voltage-type dual active bridge DC converter;

[0029] In working mode 4, the modulation method adopted is consistent with the traditional voltage-type dual active bridge DC converter.

[0030] In one embodiment, when the output voltage is constant, the output power is given, and all the switch devices are in the soft switching state, the operation mode 1 is set by connecting the series inductor L lk The value of duty cycle d2 when the current peak is minimum;

[0031] The setting is through the series inductance L lk The value of duty cycle d2 when the current peak is minimum includes:

[0032] According to the continuity and critical state of the high-voltage port output current, it is concluded that the series inductance L should be reduced under heavy load / light load conditions. lk Current i Llk The effective value range of d2 of the peak;

[0033] The relevant waveforms within a cycle are analyzed to obtain the duration of each mode of working mode 1, and the inductor volt-ampere characteristic equation is established by analyzing the volt-ampere characteristic of the inductor L1 at the supercapacitor port:

[0034] The current flowing through the series inductor L lk The current is regarded as a constant value, and the constant value is the effective value of the current I in_rate ;

[0035] By solving the inductor volt-ampere characteristic equation, the input inductor current effective value I is obtained in_rate , duty cycle d1 and P Ba The relationship between the duty cycle d2 and the series inductance L lk Current i Llk The peak value I Llk_peak ;

[0036] According to the series inductance L lk Current i Llk Will not exceed the effective value of the input inductor current I in_rate, and each switch device is in the soft switching state, it is concluded that the series inductor L lk The value of duty cycle d2 when the current peak is minimum.

[0037] In one embodiment, the series inductance L is reduced under the heavy load condition. lk Current i Llk The peak d2 has

[0038] The effective value range is:

[0039]

[0040] Under the light load condition, the series inductance L is reduced. lk Current i Llk The effective range of d2 of the peak is:

[0041]

[0042] In one embodiment, the series inductor L lk The value of duty cycle d2 when the current peak is minimum is:

[0043]

[0044] Under light load conditions, the series inductor L lk The value of duty cycle d2 when the current peak is minimum is:

[0045]

[0046] In one embodiment, under heavy load condition, the battery port output power P Ba The output power P of the supercapacitor port SC for:

[0047] P Ba =U Ba I in_rate

[0048]

[0049] Among them I SC1 with I SC2 They are:

[0050]

[0051] Under light load condition, the battery port output power P Ba The output power P of the supercapacitor port SC for:

[0052] P Ba =U Ba Iin_rate

[0053]

[0054] Among them I SC1 with I SC2 They are:

[0055]

[0056] In a third aspect, the present invention provides a hybrid energy storage system, the system comprising the above-mentioned three-port semi-isolated DC converter.

[0057] Beneficial effects of the present invention

[0058] In the converter circuit topology proposed by the present invention, the low-voltage battery side and the high-voltage side constitute a current-fed isolated DC converter, which has the advantages of small input current ripple, no power backflow, negligible diode overshoot oscillation, no duty cycle loss and easy current control, and has a higher rated power utilization rate than the traditional voltage-type isolated DC converter. The converter of the present invention can simultaneously connect two energy storage media and realize output power distribution, and can effectively reduce the peak value of the current passing through the transformer, reduce the current stress of the switching device, reduce heat generation, reduce costs, and improve the flexibility and stability of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] The accompanying drawings are part of the present invention and are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention, but do not constitute an improper limitation of the present invention. Obviously, the accompanying drawings described below are only some embodiments. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without creative work.

[0060] Figure 1 A circuit schematic diagram of a semi-isolated three-port DC converter provided by an embodiment of the present invention;

[0061] Figure 2 A schematic diagram of four power transmission modes of a semi-isolated three-port DC converter according to an embodiment of the present invention;

[0062] Figure 3 A main working waveform diagram of a semi-isolated three-port DC converter of the present invention in a heavy-load state within a switching cycle when the battery port and the supercapacitor port output power;

[0063] Figure 4 An equivalent circuit diagram of a semi-isolated three-port DC converter of the present invention in a heavy-load state within a switching cycle when the battery port and the supercapacitor port output power;

[0064] Figure 5 A main working waveform diagram of a semi-isolated three-port DC converter of the present invention in a light-load state within a switching cycle when the battery port and the supercapacitor port output power;

[0065] Figure 6 An equivalent circuit diagram of a semi-isolated three-port DC converter of the present invention in a light-load state within a switching cycle when power is output at a battery port and a supercapacitor port provided by an embodiment of the present invention;

[0066] Figure 7 It is the optimization of the duty cycle of the high-voltage side before and after L under heavy load. lk The current waveform is Figure 7 (a) is the current waveform before optimization, Figure 7 (b) is the current waveform after optimization.

[0067] Figure 8 It is the optimization of the duty cycle of the high-voltage side before and after L under light load condition. lk The current waveform is Figure 8 (a) is the current waveform before optimization, Figure 8 (b) is the current waveform after optimization.

[0068] It should be noted that these drawings and textual descriptions are not intended to limit the conceptual scope of the present invention in any way, but are intended to illustrate the concept of the present invention for those skilled in the art by referring to specific embodiments. DETAILED DESCRIPTION

[0069] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0070] The present invention proposes a three-port semi-isolated DC converter, the circuit schematic of which is shown in FIG. Figure 1 As shown, the converter includes a battery port, a supercapacitor port and a high-voltage port. The battery port is connected to the high-voltage port through the primary side of the high-frequency transformer T, and the supercapacitor port is connected to the high-voltage port through the secondary side of the high-frequency transformer T. The battery port and the supercapacitor port are used to connect the energy storage medium to realize charging and discharging; the high-voltage port is used to connect the DC load or the DC bus.

[0071] Furthermore, the battery port includes: a low voltage side capacitor C Ba , Battery side inductance L in, the primary full-bridge circuit and the series inductor L including the transformer leakage inductance lk The primary full-bridge circuit includes a first bridge arm and a second bridge arm, wherein the first bridge arm includes a switch device S1 and a switch device S3 connected in series in sequence; the second bridge arm includes a switch device S2 and a switch device S4 connected in series in sequence; D1-D4 and C1-C4 are anti-parallel diodes and parasitic capacitors corresponding to the switch devices S1-S4 respectively; the battery and the low-voltage side capacitor C Ba In parallel, the positive electrode of the battery and the input inductor L in The positive electrode of the battery is connected, and the negative electrode of the battery is directly connected to the source of the switch device S2 and the source of the switch device S4 in the primary full-bridge circuit; the input inductor L in The negative electrode is connected to the drain of the switch device S1 and the drain of the switch device S3 of the primary full-bridge circuit; the series inductor L lk The positive electrode is connected to the source of the switching device S1, and the inductor L is connected in series lk The negative pole of is connected to the same-name end of the primary side of the high-frequency transformer T, and the opposite-name end of the primary side of the high-frequency transformer T is connected to the drain of the switching device S4.

[0072] The supercapacitor port includes: supercapacitor, reverse charging diode D SC , solid-state isolation switch T1 and two identical inductors L1 and L2 on the supercapacitor side. The positive electrode of the supercapacitor and the reverse charging diode D SC The positive electrode of the super capacitor is connected to the source of the switch device S6 of the secondary full-bridge circuit; the reverse charging diode D SC The negative electrode of the inductor L1 and the positive electrode of L2 are connected, wherein the solid-state isolation switch T1 and the reverse charging diode D SC In parallel, the negative pole of inductor L1 is connected to the same-name terminal of the secondary side of high-frequency transformer T, and the negative pole of inductor L2 is connected to the opposite-name terminal of the secondary side of high-frequency transformer T. The high-voltage port includes: the secondary side full-bridge circuit, the high-voltage side capacitor C o The secondary full-bridge circuit includes a third bridge arm and a fourth bridge arm, wherein the third bridge arm includes a switch device S5 and a switch device S7 connected in series in sequence; the fourth bridge arm includes a switch device S6 and a switch device S8 connected in series in sequence; D5-D8 and C5-C8 are anti-parallel diodes and parasitic capacitors corresponding to the switch devices S5-S8, respectively. The secondary winding of the high-frequency transformer T is connected to the midpoint of the third bridge arm and the fourth bridge arm of the secondary full-bridge circuit; the high-voltage side capacitor C o The positive electrode is connected to the drain of the switch device S5 and the drain of the switch device S7, and the high-voltage side capacitor C o The cathode of is connected to the source of the switching device S6 and the source of the switching device S8.

[0073] Furthermore, the three-port semi-isolated DC converter can switch between four operating modes. The schematic diagram of the four power transmission modes is as follows: Figure 2 As shown, the four working modes include:

[0074] Working mode 1: The high-voltage port is connected to the load, and the solid-state relay T1 of the supercapacitor port is disconnected. The battery port sends power, the supercapacitor port sends power, and the high-voltage port absorbs power.

[0075] Working mode 2: The high-voltage port is connected to the load, and the solid-state relay T1 of the supercapacitor port is closed. The battery port emits power, the supercapacitor port absorbs power, and the high-voltage port absorbs power.

[0076] Working mode 3: The high-voltage port is connected to the DC bus or power supply, and the solid-state relay T1 of the supercapacitor port is disconnected. The battery port absorbs power, the supercapacitor port emits power, and the high-voltage port emits power.

[0077] Working mode 4: The high-voltage port is connected to the DC bus or power supply, and the solid-state relay T1 of the supercapacitor port is closed. The battery port absorbs power, the supercapacitor port absorbs power, and the high-voltage port emits power.

[0078] Furthermore, through the modal analysis of the three-port semi-isolated DC converter in working mode 1, the working mode of working mode 1 in a switching cycle is divided into: working mode under heavy load state and working mode under light load state; the heavy load state and the light load state are defined by the following method:

[0079] According to the output voltage U of the semi-isolated three-port DC converter under specific working conditions o , battery voltage U Ba Define the proportion of the input inductor charging time of the low-voltage battery side in the entire switching cycle in half a switching cycle:

[0080]

[0081] according to Figure 3 and Figure 5 It can be seen that when the rated output power and converter modulation parameters are different, the main waveform of the converter may be different. When d2 is large, the output current i o There will be no discontinuity in the process of changing from positive to negative, that is, there will be no Figure 3 The modes [t1~t3], [t 11 ~t 12 ]and Figure 5 The modes [t6~t7], [t 15 ~t 16 Therefore, according to the circuit theory analysis of the converter circuit in the two states, the definition of light load state and heavy load state can be obtained: when d1-d2+β>0.5, the converter is in Figure 3 and Figure 4 The heavy load state shown; when d1-d2+β≤0.5, the converter is in Figure 5 and Figure 6 The light load state shown in the figure and the power P0 output by the battery in the critical state are:

[0082]

[0083] The battery output power P Ba It is more intuitive to define the light load / heavy load state: when P Ba >P0, the converter is defined as being in a heavy load state; when P Ba ≤P0, the converter is defined as a light load state at this time.

[0084] Specifically, the main working waveforms and equivalent circuits of the semi-isolated three-port DC converter of the present invention in a heavy load state when the battery port and the supercapacitor port output power within one switching cycle are as follows: Figure 3 and Figure 4 shown.

[0085] Mode [t0~t1], such as Figure 4 As shown in (a), the switch devices S1, S2, and S3 in the battery port are turned on, and the anti-parallel diode of the switch device S4 is turned on for freewheeling; the inductor branches L1 and L2 in the supercapacitor port are turned on; and the anti-parallel diodes of the switch devices S6 and S7 at the high-voltage port are turned on for freewheeling.

[0086] Mode [t1~t2], such as Figure 4 As shown in (b), the switch devices S1 and S2 in the battery port are turned on, and the anti-parallel diodes of the switch devices S3 and S4 are turned on for freewheeling; the inductor branches L1 and L2 in the supercapacitor port are turned on; no current flows through the switch devices S5, S6, S7, and S8 at the high-voltage port.

[0087] Mode [t2~t3], such as Figure 4 As shown in (c), the switch devices S1, S2, and S3 in the battery port are turned on, and the anti-parallel diode of the switch device S4 is turned on for freewheeling; the reverse charging diode D SC The supercapacitor starts to discharge, and the inductor L1 and L2 branches are turned on; the high-voltage port switch device S6 is turned on.

[0088] Mode [t3~t4], such as Figure 4 As shown in (d), the switch devices S1, S2, and S3 in the battery port are turned on, and the anti-parallel diode of the switch device S4 is turned on for freewheeling; the reverse charging diode D SC The supercapacitor is turned on, the supercapacitor continues to discharge, the inductor L1 and L2 branches are turned on; the high-voltage port switch devices S6 and S7 are turned on.

[0089] Mode [t4~t7], such as Figure 4 As shown in (e), the switch devices S1, S2, and S4 in the battery port are turned on, and the anti-parallel diode of the switch device S3 is turned on for freewheeling; the inductor L1 and L2 branches in the supercapacitor port are turned on; and the switch devices S6 and S7 in the high-voltage port are turned on.

[0090] Mode [t7~t8], such as Figure 4 As shown in (f), the switch devices S1 and S4 in the battery port are turned on, and the anti-parallel diodes of the switch devices S2 and S3 are turned on for freewheeling; the inductor branches L1 and L2 in the supercapacitor port are turned on; the switch device S7 in the high-voltage port is turned on, and the anti-parallel diode of the switch device S5 is turned on for freewheeling.

[0091] Mode [t8~t9], such as Figure 4 As shown in (g), the switch devices S1 and S4 in the battery port are turned on, and the anti-parallel diodes of the switch devices S2 and S3 are turned on for freewheeling; the inductor branches L1 and L2 in the supercapacitor port are turned on; and the anti-parallel diodes of the switch devices S5 and S8 in the high-voltage port are turned on for freewheeling.

[0092] Mode [t9~t 10 ],like Figure 4 As shown in (h), the switch devices S1 and S4 in the battery port are turned on; the inductor branches L1 and L2 in the supercapacitor port are turned on; and the anti-parallel diodes of the switch devices S5 and S8 in the high-voltage port are turned on for freewheeling.

[0093] Mode [t 10 ~t 11 ],like Figure 4 As shown in (i), the switch devices S1 and S2 in the battery port are turned on, and the anti-parallel diodes of the switch devices S3 and S4 are turned on for freewheeling; the inductor branches L1 and L2 in the supercapacitor port are turned on; and the anti-parallel diodes of the switch devices S5 and S8 in the high-voltage port are turned on for freewheeling.

[0094] Mode [t 11 ~t 12 ],like Figure 4 As shown in (j), the switch devices S1 and S2 in the battery port are turned on, and the anti-parallel diodes of the switch devices S3 and S4 are turned on for freewheeling; the inductor branches L1 and L2 in the supercapacitor port are turned on; the switch device S5 in the high-voltage port is turned on, and the anti-parallel diode of the switch device S7 is turned on for freewheeling.

[0095] Mode [t 12 ~t 13 ],like Figure 4As shown in (k), the switch devices S1 and S2 in the battery port are turned on, and the anti-parallel diodes of the switch devices S3 and S4 are turned on for freewheeling; the inductor branches L1 and L2 in the supercapacitor port are turned on; and the switch devices S5 and S8 in the high-voltage port are turned on.

[0096] Mode [t 15 ~t 16 ],like Figure 4 As shown in (l), the switch devices S2 and S3 in the battery port are turned on, and the anti-parallel diodes of the switch devices S1 and S4 are turned on for freewheeling; the reverse charging diode D SC The supercapacitor starts to discharge, and the inductor L1 and L2 branches are turned on; the switch device S8 in the high-voltage port is turned on, and the anti-parallel diode of the switch device S6 is turned on for freewheeling.

[0097] Mode [t 16 ~t 17 ],like Figure 4 As shown in (m), the switch devices S2 and S3 in the battery port are turned on, and the anti-parallel diodes of the switch devices S1 and S4 are turned on for freewheeling; the reverse charging diode D SC The supercapacitor is turned on, the supercapacitor continues to discharge, and the inductor L1 and L2 branches are turned on; the anti-parallel diodes of the switch devices S6 and S7 in the high-voltage port are turned on for freewheeling.

[0098] Mode [t 17 ~t 18 ],like Figure 4 As shown in (n), the switch devices S2 and S3 in the battery port are turned on; the reverse charging diode D SC The supercapacitor is turned on, the supercapacitor continues to discharge, and the inductor L1 and L2 branches are turned on; the anti-parallel diodes of the switch devices S6 and S7 in the high-voltage port are turned on for freewheeling.

[0099] Specifically, the main working waveforms and equivalent circuits of the semi-isolated three-port DC converter of the present invention in a light-load state when the battery port and the supercapacitor port output power within one switching cycle are as follows: Figure 5 and Figure 6 shown.

[0100] Mode [t0~t3], such as Figure 6 (a) and Figure 6 As shown in (b), the switch devices S1 and S2 in the battery port are turned on, and the anti-parallel diodes of the switch devices S3 and S4 are turned on for freewheeling. lk The upper current decreases to 0 in the reverse direction, and then increases to the maximum value in the forward direction; the inductor L1 and L2 branches in the supercapacitor port are turned on; the high-voltage port switch devices S6 and S7 are turned on.

[0101] Mode [t3~t4], such as Figure 6 As shown in (c), the switch devices S1 and S4 in the battery port are turned on, and the anti-parallel diodes of the switch devices S2 and S3 are turned on for freewheeling; the inductor branches L1 and L2 in the supercapacitor port are turned on; the switch device S7 at the high-voltage port is turned on, and the anti-parallel diode of the switch device S5 is turned on for freewheeling.

[0102] Mode [t4~t5], such as Figure 6 As shown in (d), the switch devices S1 and S4 in the battery port are turned on, and the anti-parallel diodes of the switch devices S2 and S3 are turned on for freewheeling; the inductor branches L1 and L2 in the supercapacitor port are turned on; and the anti-parallel diodes of the switch devices S5 and S8 in the high-voltage port are turned on for freewheeling.

[0103] Mode [t5~t6], such as Figure 6 As shown in (e), the switch devices S1 and S4 in the battery port are turned on; the inductor branches L1 and L2 in the supercapacitor port are turned on; and the anti-parallel diodes of the switch devices S5 and S8 in the high-voltage port are turned on for freewheeling.

[0104] Mode [t6~t7], such as Figure 6 As shown in (f), the switch devices S1 and S4 in the battery port are turned on; the inductor branches L1 and L2 in the supercapacitor port are turned on; and no current flows through the switch devices S5, S6, S7, and S8 in the high-voltage port.

[0105] Mode [t7~t8], such as Figure 6 As shown in (g), the switch devices S1 and S4 in the battery port are turned on; the inductor branches L1 and L2 in the supercapacitor port are turned on; and the switch devices S5 and S8 in the high-voltage port are turned on.

[0106] Mode [t8~t 10 ],like Figure 6 (h) and Figure 6 As shown in (i), the switch devices S3 and S4 in the battery port are turned on, and the anti-parallel diodes of the switch devices S1 and S2 are turned on for freewheeling. lk The upper current decreases in the positive direction to 0, and then increases in the positive direction to the maximum value; the inductor L1 and L2 branches in the supercapacitor port are turned on; the switch devices S5 and S8 in the high-voltage port are turned on.

[0107] Mode [t 11 ~t 12 ],like Figure 6 As shown in (j), the switch devices S2 and S3 in the battery port are turned on, and the anti-parallel diodes of the switch devices S1 and S4 are turned on for freewheeling; the reverse charging diode D SC The supercapacitor starts to discharge, and the inductor L1 and L2 branches are turned on; the switch device S8 in the high-voltage port is turned on, and the anti-parallel diode of the switch device S6 is turned on for freewheeling.

[0108] Mode [t 12 ~t 13 ],like Figure 6 As shown in (k), the switch devices S2 and S3 in the battery port are turned on, and the anti-parallel diodes of the switch devices S1 and S4 are turned on for freewheeling; the reverse charging diode D SC The supercapacitor is turned on, the supercapacitor continues to discharge, and the inductor L1 and L2 branches are turned on; the anti-parallel diodes of the switch devices S6 and S7 in the high-voltage port are turned on for freewheeling.

[0109] Mode [t 13 ~t 14 ],like Figure 6 As shown in (l), the switch devices S2 and S3 in the battery port are turned on; the reverse charging diode D SC The supercapacitor is turned on, the supercapacitor continues to discharge, and the inductor L1 and L2 branches are turned on; the anti-parallel diodes of the switch devices S6 and S7 in the high-voltage port are turned on for freewheeling.

[0110] Mode [t 14 ~t 15 ],like Figure 6 As shown in (m), the switch devices S2 and S3 in the battery port are turned on; the inductor branches L1 and L2 in the supercapacitor port are turned on; and the anti-parallel diodes of the switch devices S6 and S7 in the high-voltage port are turned on for freewheeling.

[0111] Mode [t 15 ~t 16 ],like Figure 6 As shown in (n), the switch devices S2 and S3 in the battery port are turned on; the inductor branches L1 and L2 in the supercapacitor port are turned on; and no current flows through the switch devices S5, S6, S7, and S8 in the high-voltage port.

[0112] Mode [t 16 ~t 17 ],like Figure 6 As shown in (o), the switch devices S2 and S3 in the battery port are turned on; the reverse charging diode D SC The supercapacitor starts to discharge, and the inductor L1 and L2 branches are turned on; no current flows through the switch devices S5, S6, S7, and S8 in the high-voltage port.

[0113] Mode [t 17 ~t 18 ],like Figure 6 As shown in (p), the switch devices S2 and S3 in the battery port are turned on; the reverse charging diode D SC The supercapacitor is turned on, the supercapacitor continues to discharge, the inductor L1 and L2 branches are turned on; the switch devices S6 and S7 in the high-voltage port are turned on.

[0114] Mode [t 18 ~t 19 ],like Figure 6 As shown in (q), the switch devices S2 and S3 in the battery port are turned on; the inductor L1 and L2 branches in the supercapacitor port are turned on; and the switch devices S6 and S7 in the high-voltage port are turned on.

[0115] In one embodiment, a modulation method for a three-port semi-isolated DC converter is proposed. The method is based on the above three-port semi-isolated DC converter. The method controls the opening and closing of the solid-state isolating switch T1, the duty cycle d1 of the switch devices S1-S4, the duty cycle d2 of the switch devices S5-S8 and the phase shift angle β between the high-voltage side bridge arms under different working conditions to switch the working mode of the converter. The specific modulation method used in each working mode is:

[0116] The modulation method of the semi-isolated three-port DC converter proposed in the present invention in working mode 1 is as follows:

[0117] All switch devices S1 to S8 have the same switching frequency T s The duty cycle of switch devices S1 to S4 is d1. Switch devices S1 and S3 are turned on or off at the same time. The turn-on signals of switch devices S2 and S4 lag behind the turn-on signals of S1 and S3 by half a switching cycle. The duty cycle of switch devices S5 to S8 is d2. The turn-off signals of S5 and S6 are triggered simultaneously with the turn-off signals of S1 and S2, respectively. The turn-on and turn-off signals of S7 and S8 lag behind the turn-on and turn-off signals of S6 and S5 by βT, respectively. s .

[0118] When the battery port and the supercapacitor port transmit power to the high-voltage port, the output voltage of the high-voltage port is constant. The battery output power is controlled by adjusting d1 and d2, the supercapacitor output power is controlled by adjusting β, and d2 is adjusted to reduce the voltage through L lk Peak value of current.

[0119] In working mode 2, the modulation method used is consistent with that of the traditional current-fed isolated DC converter;

[0120] In working mode 3, the modulation method used is consistent with the traditional voltage-type dual active bridge DC converter;

[0121] In working mode 4, the modulation method adopted is consistent with the traditional voltage-type dual active bridge DC converter.

[0122] Furthermore, under the condition that the output voltage is constant, the output power is given and all the switching devices are in the soft switching state, the series inductor L is set. lk The value of duty cycle d2 when the current peak is minimum.

[0123] In the embodiment of the present application, the L lk The value of d2 when the current peak is minimum includes the following steps:

[0124] According to the continuity and critical state of the high-voltage port output current, it is concluded that the series inductance L should be reduced under heavy load / light load conditions. lk Current i Llk The effective value range of d2 of the peak;

[0125] The relevant waveforms within a cycle are analyzed to obtain the duration of each mode of working mode 1, and the inductor volt-ampere characteristic equation is established by analyzing the volt-ampere characteristic of the inductor L1 at the supercapacitor port:

[0126] The current flowing through the series inductor L lk The current is regarded as a constant value, and the constant value is the effective value of the current I in_rate ;

[0127] By solving the inductor volt-ampere characteristic equation, the input inductor current effective value I is obtained in_rate , duty cycle d1 and P Ba The relationship between the duty cycle d2 and the series inductance L lk Current i Llk The peak value I Llk_peak ;

[0128] According to the series inductance L lk Current i Llk Will not exceed the effective value of the input inductor current I in_rate , and each switch device is in the soft switching state, it is concluded that the series inductor L lk The value of duty cycle d2 when the current peak is minimum.

[0129] According to the series inductance L lk Current i Llk Will not exceed the effective value of the input inductor current I in_rate , and each switch device is in the soft switching state, it is concluded that the series inductor L lk The value of duty cycle d2 when the current peak is minimum.

[0130] It should be noted that due to the difference in waveforms under heavy load and light load, the formulas for calculating input current and output power are different, and the d2 to be optimized is also different.

[0131] Specifically, under heavy load conditions, in order to reduce the lk The current i Llk According to the continuous output current of the high voltage port and the above critical state, it can be concluded that the reduction of i under heavy load conditionLlk The effective value range of d2 of the peak is:

[0132]

[0133] right Figure 3 By analyzing the relevant waveforms within one cycle, the duration of each mode of working mode 1 can be obtained, and the inductor volt-ampere characteristic can be established by analyzing the volt-ampere characteristic of the inductor L1 at the supercapacitor port.

[0134] equation:

[0135]

[0136] Among them, combined with the results of modal analysis, we can get:

[0137]

[0138] Since the input inductance L in is relatively large, so the current flowing through it can be regarded as a constant value, specifically its effective current value I in_rate By solving the above equation, the effective value of the input inductor current I can be obtained. in_rate :

[0139] I in_rate =T s {n 4 L lk [2βU SC +U o (4d1+4d2-2x-3)]+n 2 L1L lk [4βU SC +U o (12d1+12d2-10x-7)]

[0140] +4L1 2 U o (2d1+2d2-2x-1)} / 4nL lk (2L1 2 +3n 2 L1L lk +n 4 L lk 2 )

[0141] d1 and P Ba The relationship with d2 is:

[0142]

[0143] At this time, Llk The peak value I Llk_peak for:

[0144]

[0145] To ensure i Llk Will not exceed the effective value of the input inductor current I in_rate , and each switch device is in the soft switching state, then the value of d2 should be:

[0146]

[0147] In this mode, the battery port output power P Ba The output power P of the supercapacitor port SC for:

[0148] P Ba =U Ba I in_rate

[0149]

[0150] Specifically, under light load conditions, in order to reduce the lk The current i Llk According to the continuous output current of the high voltage port and the above critical state, it can be concluded that the light load state can reduce i Llk The effective value range of d2 of the peak is:

[0151]

[0152] right Figure 5 By analyzing the relevant waveforms within one cycle, the duration of each mode can be obtained. And by analyzing the volt-ampere characteristics of the inductor L1 at the supercapacitor port, the equation can be established:

[0153]

[0154] Among them, combined with the results of modal analysis, we can get:

[0155]

[0156] t 11 -t7=(d2-β)T s

[0157]

[0158] Since the input inductance L in is relatively large, so the current flowing through it can be regarded as a constant value, specifically its effective current value I in_rate By solving the above equation, the effective value of the input inductor current I can be obtained. in_rate :

[0159]

[0160] d1 and P Ba The relationship with d2 is:

[0161]

[0162] At this time, Llk The peak value I Llk_peak for:

[0163]

[0164] In order to ensure Llk Will not exceed the effective value of the input inductor current I in_rate , and each switch device is in the soft switching state, then the value of d2 should be:

[0165]

[0166] In this mode, the battery port output power P Ba The output power P of the supercapacitor port SC for:

[0167] P Ba =U Ba I in_rate

[0168]

[0169] Among them I SC1 with I SC2 They are:

[0170]

[0171] pass Figure 7 Under heavy load condition, the duty cycle of high voltage side is optimized before and after L lk The current waveform and Figure 8 Under light load condition, the duty cycle of high voltage side is optimized before and after L lk From the current waveform diagram, it can be seen that the present invention can effectively reduce the peak value of the current passing through the transformer.

[0172] In one embodiment, a hybrid energy storage system is proposed, the system comprising: the above-mentioned three-port semi-isolated DC converter.

[0173] The description based on the three-port semi-isolated DC converter refers to the above embodiment and will not be repeated here.

[0174] In the description provided herein, a large number of specific details are described. However, it is understood that embodiments of the present invention can be practiced without these specific details. In some instances, well-known methods, structures and techniques are not shown in detail so as not to obscure the understanding of this description.

[0175] In addition, those skilled in the art will understand that, although some embodiments described herein include certain features included in other embodiments but not other features, the combination of features of different embodiments also means being within the scope of protection of the present invention and forming different embodiments. For example, in the above embodiments, those skilled in the art can use them in combination according to the known technical solutions and the technical problems to be solved by this application.

Claims

1. A modulation method for a three-port semi-isolated DC converter, characterized in that: It includes a battery port, a supercapacitor port and a high-voltage port; the battery port is connected to the high-voltage port through the primary side of a high-frequency transformer T, and the supercapacitor port is connected to the high-voltage port through the secondary side of the high-frequency transformer T; the battery port and the supercapacitor port are used to connect energy storage media to achieve charging and discharging; the high-voltage port is used to connect a DC load or a DC bus; The supercapacitor port includes: a solid-state isolating switch T1; The three-port semi-isolated DC converter can switch between four working modes, and the four working modes include: Working mode 1: the high-voltage port is connected to a load, and the solid-state isolating switch T1 of the supercapacitor port is disconnected; the battery port and the supercapacitor port emit power, and the high-voltage port absorbs power; Working mode 2: the high-voltage port is connected to a load, and the solid-state isolating switch T1 of the supercapacitor port is closed; the battery port emits power, and the supercapacitor port and the high-voltage port absorb power; Working mode 3: the high-voltage port is connected to the DC bus or power supply, and the solid-state isolation switch T1 of the supercapacitor port is disconnected; the battery port absorbs power, and the supercapacitor port and the high-voltage port emit power; Working mode 4: the high-voltage port is connected to the DC bus or power supply, and the solid-state isolation switch T1 of the supercapacitor port is closed; the battery port and the supercapacitor port absorb power, and the high-voltage port emits power; The battery port comprises: a primary full-bridge circuit, the primary full-bridge circuit comprises a first bridge arm and a second bridge arm, the first bridge arm comprises a switch device S1 and a switch device S2 connected in series in sequence; the second bridge arm comprises a switch device S3 and a switch device S4 connected in series in sequence; The high-voltage port comprises: a secondary full-bridge circuit, the secondary full-bridge circuit comprises a third bridge arm and a fourth bridge arm, the third bridge arm comprises a switch device S5 and a switch device S6 connected in series in sequence; the fourth bridge arm comprises a switch device S7 and a switch device S8 connected in series in sequence; A modulation method for a three-port semi-isolated DC converter, comprising: The switching of the converter working mode is achieved by controlling the opening and closing of the solid-state disconnector T1, the duty cycle d1 of the switch devices S1-S4, the duty cycle d2 of the switch devices S5-S8 and the phase shift angle β between the high-voltage side bridge arms under different working conditions; the specific modulation method used in each working mode is: The modulation method used in working mode 1 is: Set all switch devices S1 to S8 to have the same switching frequency T s , the duty cycle of switch devices S1~S4 is d1, switch devices S1 and S3 are turned on or off at the same time, the turn-on signals of switch devices S2 and S4 lag behind half the switching cycle of S1 and S3, the duty cycle of switch devices S5~S8 is d2, the turn-off signals of S5 and S6 are triggered simultaneously with the turn-off signals of S1 and S2, respectively, and the turn-on and turn-off signals of S7 and S8 lag behind the turn-on and turn-off signals of S6 and S5 by βT respectively s ; When the battery port and the supercapacitor port transmit power to the high-voltage port, the battery output power is controlled by adjusting d1 and d2, the supercapacitor output power is controlled by adjusting β, and d2 is adjusted to reduce the series inductance L. lk Peak value of current; In working mode 2, the modulation method used is consistent with that of the traditional current-fed isolated DC converter; In working mode 3, the modulation method used is consistent with the traditional voltage-type dual active bridge DC converter; In working mode 4, the modulation method adopted is consistent with the traditional voltage-type dual active bridge DC converter.

2. The modulation method of the three-port semi-isolated DC converter according to claim 1, characterized in that: The battery port includes: a battery, a low-voltage side capacitor C Ba , Battery side inductance L in , the primary full-bridge circuit and the series inductor L including the transformer leakage inductance lk The primary full-bridge circuit includes a first bridge arm and a second bridge arm, wherein the first bridge arm includes a switch device S1 and a switch device S2 connected in series in sequence; the second bridge arm includes a switch device S3 and a switch device S4 connected in series in sequence; D1-D4 and C1-C4 are anti-parallel diodes and parasitic capacitors corresponding to the switch devices S1-S4 respectively; the battery and the low-voltage side capacitor C Ba In parallel, the positive electrode of the battery and the input inductor L in The positive electrode is connected to the positive electrode, and the negative electrode is directly connected to the source of the switch device S2 and the source of the switch device S4 in the primary full-bridge circuit; the battery side inductor L in The negative electrode is connected to the drain of the switch device S1 and the drain of the switch device S3 of the primary full-bridge circuit; the series inductor L lk The positive electrode is connected to the source of the switching device S1, and the negative electrode is connected to the same-name terminal of the primary side of the high-frequency transformer T; the opposite-name terminal of the primary side of the high-frequency transformer T is connected to the drain of the switching device S4; The supercapacitor port includes: a supercapacitor, a reverse charging diode D SC , solid-state isolating switch T1 and two identical inductors L1 and L2 on the supercapacitor side; the solid-state isolating switch T1 and the reverse charging diode D SC In parallel, the positive electrode of the super capacitor and the reverse charging diode D SC The positive electrode of the reverse charging diode D SC The negative electrode of the inductor L1 is connected to the positive electrodes of the inductors L1 and L2, the negative electrode of the inductor L1 is connected to the same-name terminal of the secondary side of the high-frequency transformer T, and the negative electrode of the inductor L2 is connected to the opposite-name terminal of the secondary side of the high-frequency transformer T; The high-voltage port includes: a secondary full-bridge circuit, a high-voltage side capacitor C o ; The secondary full-bridge circuit includes a third bridge arm and a fourth bridge arm, the third bridge arm includes a switch device S5 and a switch device S6 connected in series in sequence; the fourth bridge arm includes a switch device S7 and a switch device S8 connected in series in sequence; D5-D8 and C5-C8 are anti-parallel diodes and parasitic capacitors corresponding to the switch devices S5-S8 respectively; the midpoint of the third bridge arm and the fourth bridge arm of the secondary full-bridge circuit is connected to the secondary winding of the high-frequency transformer T; the high-voltage side capacitor C o The positive electrode is connected to the drain of the switching device S5 and the drain of the switching device S7, and the negative electrode is connected to the source of the switching device S6 and the source of the switching device S8.

3. The modulation method of the three-port semi-isolated DC converter according to claim 2, characterized in that: Through the modal analysis of the three-port semi-isolated DC converter in working mode 1, the working modes of working mode 1 in a switching cycle are divided into: working mode under heavy load state and working mode under light load state; The heavy load state and light load state are defined by the following method: According to the output voltage U of the semi-isolated three-port DC converter under specific working conditions o , battery voltage U Ba Define the proportion of the input inductor charging time of the low-voltage battery side in the entire switching cycle in half a switching cycle: Rated output power P of the battery Ba Compare with critical power P0; When P Ba >P0, the converter is defined as being in a heavy load state; if P Ba ≤P0, the converter is defined as a light load state at this time.

4. The modulation method of the three-port semi-isolated DC converter according to claim 3, characterized in that: When the output voltage is constant, the output power is given and all switching devices are in the soft switching state, the working mode 1 is set by connecting the series inductor L lk The value of duty cycle d2 when the current peak is minimum; the setting is through the series inductor L lk The value of duty cycle d2 when the current peak is minimum includes: According to the continuity of the high-voltage port output current and the critical power that defines the heavy-load and light-load states, the reduction of the series inductance L under the heavy-load / light-load state is obtained. lk Current i Llk The effective value range of d2 of the peak; The relevant waveforms within a cycle are analyzed to obtain the duration of each mode of working mode 1, and the inductor volt-ampere characteristic equation is established by analyzing the volt-ampere characteristic of the inductor L1 at the supercapacitor port: The current flowing through the series inductor L lk The current is regarded as a constant value, and the constant value is the effective value of the current I in_rate ; By solving the inductor volt-ampere characteristic equation, the input inductor current effective value I is obtained in_rate , duty cycle d1 and P Ba The relationship between the duty cycle d2 and the series inductance L lk Current i Llk The peak value I Llk_peak ; According to the series inductance L lk Current i Llk Will not exceed the effective value of the input inductor current I in_rate , and each switch device is in the soft switching state, it is concluded that the series inductor L lk The value of duty cycle d2 when the current peak is minimum.

5. The modulation method of the three-port semi-isolated DC converter according to claim 4, characterized in that: Under the heavy load condition, reduce the series inductance L lk Current i Llk The effective range of d2 of the peak is: Under the light load condition, the series inductance L is reduced. lk Current i Llk The effective range of d2 of the peak is: Among them, T s is the switching frequency.

6. The modulation method of the three-port semi-isolated DC converter according to claim 5, characterized in that: Under heavy load conditions, the series inductor L lk The value of duty cycle d2 when the current peak is minimum is: Under light load conditions, the series inductor L lk The value of duty cycle d2 when the current peak is minimum is:

7. The modulation method of the three-port semi-isolated DC converter according to claim 6, characterized in that: Under heavy load condition, the battery port output power P Ba The output power P of the supercapacitor port SC for: P Ba =U Ba AND in_rate Among them I SC1 with I SC2 They are the two peak values ​​of the supercapacitor output current in one cycle, as follows: Under light load condition, the battery port output power P Ba The output power P of the supercapacitor port SC for: P Ba =U Ba AND in_rate Among them I SC1 with I SC2 They are: Wherein, L2 is the inductance of the supercapacitor port.

8. A hybrid energy storage system, characterized in that: The system includes the modulation method of the three-port semi-isolated DC converter according to any one of claims 1-3.

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