A power decoupling circuit and control method for an isolated multi-port DC converter

Abstract

The present invention relates to the technical field of multi-port DC converters, and in particular to a power decoupling circuit and control method for an isolated multi-port DC converter. The method includes adding a power relay port circuit to a traditional isolated multi-port DC converter, removing the port inductance of the relay port module and directly connecting it in parallel to a medium-high frequency AC bus, or connecting it in parallel to a winding with a small leakage inductance of a multi-winding medium-high frequency transformer, and controlling the power transmitted by other ports to relay, thereby reducing the mutual disturbance of power transmission between different ports, achieving power decoupling between ports, and improving the performance of the converter. At the same time, the isolated multi-port DC converter is decoupled into multiple independent isolated two-port DC converters in design, reducing the difficulty of analysis, design and control of the isolated multi-port DC converter.

Description

Technical Field

[0001] The present invention relates to the technical field of multi-port DC converters, and in particular to a power decoupling circuit and a control method of an isolated multi-port DC converter. Background Art

[0002] With the access of a large number of renewable energy sources, energy storage systems, electric vehicles and other new loads in the power system, the power system presents a trend of AC-DC hybrid connection. As a potential solution, the isolated multi-port DC converter has isolated ports from each other, can connect various voltage levels and different types of loads, has bidirectional energy transmission capability between ports, and can effectively reduce the intermediate power conversion link, which has attracted widespread attention from scholars. However, the ports of the isolated multi-port DC converter are coupled through medium-high frequency transformers or medium-high frequency AC busbars, which is a multiple-input multiple-output (MIMO) system. This leads to inherent cross-coupling of the transmission power between the converter ports, which is difficult to control. The power flow between the ports is controlled by changing the port phase shift angle, which causes the outputs of different ports to affect each other, affecting the control speed and accuracy of the system and reducing the system dynamic performance of the converter. It is very necessary to study a power decoupling method for an isolated multi-port DC converter.

[0003] To solve the problem of power coupling between ports, an article entitled "A Novel Three-phase Three-Port UPS Employing a Single High-Frequency Isolation Transformer" (2004 IEEE 35th Annual Power Electronics Specialists Conference, 2004) and a Chinese patent with publication number CN108365758 B proposed a decoupling method based on a feedforward compensator, which stores the pre-calculated offline gain matrix in the form of a lookup table in the controller to dynamically decouple the control loop. Although this method achieves good dynamic decoupling performance, it requires the controller to have strong computing power or digital storage capabilities. In addition, as the number of ports increases, the complexity of the decoupling controller increases further, and the decoupling gain matrix needs to be recalculated, which reduces the scalability of the method. The article entitled “A DC–DC Multiport-Converter-Based Solid-State Transformer Integrating Distributed Generation and Storage” (IEEE Transactions on Power Electronics, 2013, 28; 28(5; 5): 2192-2203) proposed a method to achieve power decoupling by selecting the control bandwidth of different ports. Ports with higher bandwidth respond faster in transient operation, but will transmit power disturbances to ports with lower control loop bandwidth. Therefore, the bandwidth of ports that need to be stable is set higher, while the bandwidth of ports that are insensitive to power fluctuations is set lower. This method has stronger scalability. However, since the interference caused by power fluctuations at ports with higher control bandwidth may affect ports with lower control bandwidth, the decoupling control performance is not optimal. In addition, since the selection of control bandwidths for different ports is limited, the controllability of the system is not high enough. The article entitled "Power Flow Control in Multi-Active-Bridge Converters: Theories and Applications" (2019 IEEE Applied Power Electronics Conference and Exposition, 2019) proposes a time-sharing control method that achieves power decoupling by controlling the multi-active bridge (MAB) converter as a dual-active bridge (DAB) converter. That is, at one control moment, only two ports are phase-shifted and the other ports act as diode rectifiers. This method is simpler to control.However, the disadvantage is that the dynamic response of this method is poor and the device stress is too high.

[0004] The above technologies all achieve power decoupling of isolated multi-port DC converters by improving control algorithms, which places high demands on the controller. To this end, the present invention proposes a hardware circuit for achieving power decoupling of isolated multi-port DC converters, which can achieve power decoupling between ports of multi-port DC converters without introducing complex control algorithms. Summary of the invention

[0005] In view of the defects existing in the prior art solutions, the present invention provides a power decoupling circuit and control method for an isolated multi-port DC converter, the purpose of which is to decompose the isolated multi-port DC converter into multiple two-port converters by adding a power relay port circuit, realize power decoupling between ports through simple control, and improve the dynamic performance of the system.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0007] In a first aspect, the present invention provides a power decoupling circuit of an isolated multi-port DC converter, which adds a power relay port circuit to the multi-port DC converter to decompose the isolated multi-port DC converter into multiple two-port converters;

[0008] The power relay port circuit is a power decoupling circuit of a medium-high frequency AC bus-coupled converter;

[0009] The power decoupling circuit of the medium-high frequency AC bus-coupled converter is specifically:

[0010] The multi-port DC converter has a total of n power transmission ports and 1 power relay port, specifically including n single-phase H-bridge modules, 1 power relay port single-phase H-bridge module, n+1 voltage stabilizing capacitors, n dual-winding medium and high frequency transformers and n medium and high frequency inductors;

[0011] The ports of the multi-port DC converter are power transmission ports. A voltage stabilizing capacitor is connected in parallel to the DC side of the single-phase H-bridge module. The DC side is connected to a DC load or an active device. The AC side of the single-phase H-bridge module is connected to the primary side of a dual-winding medium- and high-frequency transformer through a medium- and high-frequency inductor.

[0012] The secondary sides of the dual-winding medium and high frequency transformers are connected in parallel to form a medium and high frequency AC bus;

[0013] In the circuit of the power relay port, a voltage-stabilizing capacitor is connected in parallel on the DC side of the single-phase H-bridge module, and no device is connected on the DC side. The AC side of the single-phase H-bridge module is directly connected in parallel to the medium- and high-frequency AC bus. The switch control signal of the single-phase H-bridge module in the power relay port circuit is used as the reference phase of the phase shift control of the single-phase H-bridge module of the power transmission port, and the external phase shift angle of the power transmission port is changed. To change the transmission power between the power transmission port and the power relay port, to maintain the DC voltage stability of the relay port and to control the power transmission between the power transmission ports.

[0014] Based on the above scheme, by changing the external phase angle of the power transmission port The specific process to maintain the DC voltage stability of the relay port includes:

[0015] A power transmission port connected to a DC source on the DC side is selected as the source port, and the actual DC voltage of the power relay port is detected and compared with a given expected voltage value;

[0016] After voltage closed-loop control, the external phase shift angle of the power transmission port connected to the DC source is calculated ;

[0017] Control the amount of power transmitted to the power relay port so that the DC side voltage of the power relay port can stably track the given voltage value, thereby maintaining the DC voltage stability of the relay port.

[0018] Based on the above scheme, by changing the external phase angle of the power transmission port The specific process of controlling power transfer between power transmission ports includes:

[0019] The power transfer between the power transfer ports is decoupled by the power decoupling circuit of the isolated multi-port DC converter into power transfer between each power transfer port and the power relay port;

[0020] According to the control target of the power transmission port, detecting an actual value of the power transmission port and comparing it with a given expected value;

[0021] After closed-loop control, the external phase angle of the power transmission port is calculated , controlling the amount of power transferred between the power transmission port and the power relay port;

[0022] The DC side value of the power transmission port is made to stably track the given value, thereby controlling the power transfer between the power transmission ports.

[0023] Based on the above scheme, the control target is to stabilize the DC voltage or current.

[0024] On the basis of the above solution, the inner phase shift angle of the power transmission port is increased , used to optimize the current stress on the AC side of the port.

[0025] On the other hand, the present invention provides a power decoupling circuit for an isolated multi-port DC converter, which adds a power relay port circuit to the multi-port DC converter to decompose the isolated multi-port DC converter into multiple two-port converters;

[0026] The power relay port circuit is a power decoupling circuit of a multi-winding medium- and high-frequency transformer-coupled converter;

[0027] The power decoupling circuit of the multi-winding medium and high frequency transformer coupled converter is specifically:

[0028] The multi-port DC converter has a total of n power transmission ports and 1 power relay port, specifically including n single-phase H-bridge modules, 1 power relay port single-phase H-bridge module, n+1 voltage stabilizing capacitors, an n+1 winding medium-high frequency transformer and n medium-high frequency inductors;

[0029] The ports of the multi-port DC converter are power transmission ports. A voltage stabilizing capacitor is connected in parallel to the DC side of the single-phase H-bridge module. The DC side is connected to a DC load or an active device. The AC side of the module is connected to the winding of the n+1 winding medium and high frequency transformer through a medium and high frequency inductor.

[0030] The power of the power transmission port is coupled through the n+1 winding medium and high frequency transformer; in the circuit of the power relay port, a voltage stabilizing capacitor is connected in parallel on the DC side of the single-phase H-bridge module, no device is connected on the DC side, and the AC side of the single-phase H-bridge module is directly connected in parallel to the winding of the medium and high frequency transformer;

[0031] The switch control signal of the single-phase H-bridge module in the power relay port circuit is used as the reference phase of the phase shift control of the single-phase H-bridge module of the power transmission port, and the external phase shift angle of the power transmission port is changed. To change the transmission power between the power transmission port and the power relay port, to maintain the DC voltage stability of the relay port and to control the power transmission between the power transmission ports.

[0032] Based on the above scheme, by changing the external phase angle of the power transmission port The specific process to maintain the DC voltage stability of the relay port includes:

[0033] A power transmission port connected to a DC source on the DC side is selected as the source port, and the actual DC voltage of the power relay port is detected and compared with a given expected voltage value;

[0034] After voltage closed-loop control, the external phase shift angle of the power transmission port connected to the DC source is calculated ;

[0035] Control the amount of power transmitted to the power relay port so that the DC side voltage of the power relay port can stably track the given voltage value, thereby maintaining the DC voltage stability of the relay port.

[0036] Based on the above scheme, by changing the external phase angle of the power transmission port The specific process of controlling power transfer between power transmission ports includes:

[0037] The power transfer between the power transfer ports is decoupled by the power decoupling circuit of the isolated multi-port DC converter into power transfer between each power transfer port and the power relay port;

[0038] According to the control target of the power transmission port, detecting an actual value of the power transmission port and comparing it with a given expected value;

[0039] After closed-loop control, the external phase angle of the power transmission port is calculated , controlling the amount of power transferred between the power transmission port and the power relay port;

[0040] The DC side value of the power transmission port is made to stably track the given value, thereby controlling the power transfer between the power transmission ports.

[0041] Based on the above scheme, the control target is to stabilize the DC voltage or current.

[0042] Based on the above solution, it is characterized in that the inner phase shift angle of the power transmission port is increased , used to optimize the current stress on the AC side of the port.

[0043] Beneficial effects of the present invention:

[0044] 1) By adding a power decoupling circuit, power decoupling between power transmission ports is achieved, and the interaction between different power transmission port loops is eliminated. This can achieve high bandwidth and fast dynamic response of each port control loop, enhance the ability of the isolated multi-port DC converter to resist load disturbances and input voltage mutations, and improve the dynamic performance of the converter system.

[0045] 2) By adding a power decoupling circuit, the power flow analysis of the isolated multi-port DC converter can be simplified, and the isolated multi-port DC converter can be decomposed into multiple independent two-port converters, that is, the power transfer between the power transmission ports is decomposed into the power transfer between multiple power transmission ports and the power relay port. The control of each port is more independent and flexible, which facilitates the power flow regulation and management between the ports.

[0046] 3) By adding a power decoupling circuit, the circuit analysis and design of the isolated multi-port DC converter can be simplified, making it easier to design the parameters of circuit components such as medium- and high-frequency inductors and medium- and high-frequency transformers for each power transmission port. The number of ports of the converter can also be expanded, making the circuit more scalable.

[0047] 4) The isolated multi-port DC converter with the added power decoupling circuit does not require a complex decoupling control algorithm, is simpler to control, has low requirements on the controller, and is suitable for multi-port DC converters with any number of power transmission ports, and has stronger applicability.

[0048] 5) By increasing the phase shift angle within the power transmission port , does not affect the power transmission of other power transmission ports, and can optimize the current stress on the AC side of the port, reduce the return power, and increase the soft switching range of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] The present invention has the following accompanying drawings:

[0050] Figure 1 It is a circuit topology diagram of an existing medium-high frequency AC bus-coupled isolated n-port DC converter;

[0051] Figure 2 It is a circuit topology diagram of an existing multi-winding medium- and high-frequency transformer-coupled isolated n-port DC converter;

[0052] Figure 3 1 is a schematic diagram of the power decoupling circuit structure of a medium-high frequency AC bus-coupled isolated four-port DC converter in an embodiment of the present invention;

[0053] Figure 4 1 is a schematic diagram of the power decoupling circuit structure of a multi-winding medium- and high-frequency transformer-coupled isolated four-port DC converter in an embodiment of the present invention;

[0054] Figure 5 is a control block diagram of an isolated four-port DC converter decoupling circuit in an embodiment of the present invention;

[0055] Figure 6 It is an output voltage waveform diagram of the AC side of each port H-bridge module of the medium-high frequency AC bus-coupled isolated four-port DC converter in the embodiment of the present invention;

[0056] Figure 7 It is an output current waveform diagram of the AC side of each port H-bridge module of the medium-high frequency AC bus-coupled isolated four-port DC converter in the embodiment of the present invention;

[0057] Figure 8It is a DC side voltage and current waveform diagram when the load of port 3 of an existing medium-high frequency AC bus-coupled isolated four-port DC converter is switched when a power decoupling circuit is not added;

[0058] Fig. 9 It is a DC side voltage and current waveform diagram when the load of port 3 of the medium-high frequency AC bus-coupled isolated four-port DC converter with a power decoupling circuit added in the embodiment of the present invention is switched;

[0059] Fig.10 The voltage and current waveforms at the AC side of the H-bridge module at the power transmission port 1 and the power relay port r when single phase shift control is adopted in the example of the present invention;

[0060] Fig.11 It is a voltage and current waveform diagram of the AC side of the H-bridge module of the power transmission port 1 and the power relay port r after adding the internal phase shift angle in the example of the present invention. DETAILED DESCRIPTION

[0061] To make the objects, advantages and features of the present invention more apparent, the following Figure 1-11 The present invention is further described in detail with reference to the following specific embodiments.

[0062] The present invention proposes a power decoupling circuit and control method for an isolated multi-port DC converter. A power relay port circuit is added to the existing isolated multi-port DC converter to decompose the isolated multi-port DC converter into multiple two-port converters. Power decoupling between ports is achieved through simple control, thereby improving the dynamic performance of the system. The combination is as follows:

[0063] Decoupling circuit based on medium and high frequency AC bus coupled converter: Figure 1 The invention is an existing medium-high frequency AC bus coupled isolated n-port DC converter: the converter comprises n single-phase H-bridge modules, n voltage-stabilizing capacitors, n dual-winding medium-high frequency transformers and n medium-high frequency inductors (or leakage inductors of the medium-high frequency transformers). A voltage-stabilizing capacitor is connected in parallel to the DC side of each existing power transmission port of the single-phase H-bridge module and connected to a DC power supply or a DC load. The AC side of the module is connected to the primary side of the dual-winding medium-high frequency transformer through the medium-high frequency inductor. The secondary sides of the dual-winding medium-high frequency transformers of all modules are connected in parallel to form a medium-high frequency AC bus. After adding a power decoupling circuit, the AC side of the H-bridge module is directly connected in parallel to the medium-high frequency AC bus without adding a port medium-high frequency inductor to form a power relay port.

[0064] Decoupling circuit based on multi-winding medium and high frequency transformer coupled converter: Figure 2The invention relates to an existing multi-winding medium-high frequency transformer coupled isolated n-port DC converter: the converter comprises n single-phase H-bridge modules, n voltage-stabilizing capacitors, an n-winding medium-high frequency transformer and n medium-high frequency inductors (or leakage inductors of the medium-high frequency transformer). A voltage-stabilizing capacitor is connected in parallel to a DC power supply or a DC load on the DC side of each existing single-phase H-bridge module of a power transmission port, and the AC side of the module is connected to a corresponding winding of the n-winding medium-high frequency transformer through a medium-high frequency inductor. After adding a power decoupling circuit, the n-winding medium-high frequency transformer is changed to an n+1 winding, the leakage inductance of the newly added winding is designed to be as small as possible, and the medium-high frequency inductor of the non-added port on the AC side of the H-bridge module is directly connected in parallel to the newly added winding to form a power relay port.

[0065] The power relay port circuit is no longer connected to an active device or load on the DC side. After the capacitor voltage on its DC side reaches stability, the DC side no longer absorbs or emits power to the outside, and only transmits power bidirectionally on the AC side, serving as a relay for energy transmission of other power transmission ports; for the power transmission port circuit, the DC side is connected to an active device or load, and power can be transmitted bidirectionally on both the DC side and the AC side; the single-phase H-bridge module is used to realize the inversion or rectification function; the medium and high frequency inductors and medium and high frequency transformers are used to realize electrical isolation, voltage conversion and energy transmission functions.

[0066] The present invention further provides a control method for a power decoupling circuit of an isolated multi-port DC converter, which is applicable to any of the above-mentioned power decoupling circuits of an isolated multi-port DC converter:

[0067] 1) The switch control signal of the single-phase H-bridge module Hr in the power relay port circuit is used as the reference phase of the phase shift control of the single-phase H-bridge modules of other power transmission ports, and the external phase shift angle of other power transmission ports is changed. To change the transmission power between the power transmission port and the power relay port, and finally to maintain the DC voltage stability of the relay port and control the power transfer between the power transmission ports.

[0068] 2) The power transmission port increases the internal phase shift angle , so that the single-phase H-bridge module on the power transmission port outputs a three-level voltage on the AC side, which can optimize the current stress on the AC side of the port, reduce the return power, increase the soft switching range of the device, suppress transient DC bias and suppress high-frequency oscillation on the AC side.

[0069] In one possible embodiment, Figure 3This is a schematic diagram of the power decoupling circuit structure of the medium-high frequency AC bus-coupled isolated four-port DC converter in the embodiment of the present invention. The original four-port DC converter has a total of 4 power transmission ports, and now a power relay port circuit is added to realize power decoupling. The converter includes 4 single-phase H-bridge modules, 5 voltage-stabilizing capacitors, 4 dual-winding medium-high frequency transformers and 4 medium-high frequency inductors; Port 1 of the multi-port DC converter is a power transmission port, and a voltage-stabilizing capacitor C1 is connected in parallel on the DC side of the single-phase H-bridge module H1, and is connected to a DC source V1 with a rated voltage of 350V. The AC side of the module H1 is connected to the primary side of the dual-winding medium-high frequency transformer T1 through a medium-high frequency inductor Lσ1; Port 2 of the multi-port DC converter is also a power transmission port, and a voltage-stabilizing capacitor C2 is connected in parallel on the DC side of the single-phase H-bridge module H2, and is connected to a DC source V2 with a rated voltage of 350V. The AC side of the module H2 is connected to the primary side of the dual-winding medium-high frequency transformer T1 through a medium-high frequency inductor Lσ2. The primary side of the high-frequency transformer T2 is connected; Port 3 of the multi-port DC converter is also a power transmission port, a voltage-stabilizing capacitor C3 is connected in parallel on the DC side of the single-phase H-bridge module H3, and is connected to the load V3, with a rated voltage of 350V, and the AC side of the module H3 is connected to the primary side of the dual-winding medium-high frequency transformer T3 through a medium-high frequency inductor Lσ3; Port 4 of the multi-port DC converter is also a power transmission port, a voltage-stabilizing capacitor C4 is connected in parallel on the DC side of the single-phase H-bridge module H4, and is connected to the DC source V4, with a rated voltage of 350V, and the AC side of the module H4 is connected to the primary side of the dual-winding medium-high frequency transformer T4 through a medium-high frequency inductor Lσ4; All the above dual-winding medium-high frequency transformers T1 The secondary sides of T2, T3, and T4 are connected in parallel to form a medium- and high-frequency AC bus; the port r power relay port circuit, the DC side of the single-phase H-bridge module Hr is only connected in parallel with a voltage-stabilizing capacitor Cr, and the DC side is not connected to other DC sources or loads. The rated voltage is 250V, and the AC side of the single-phase H-bridge module Hr is directly connected in parallel to the medium- and high-frequency AC bus without adding medium- and high-frequency inductors.

[0070] Figure 5 It is a control block diagram of a medium-high frequency AC bus-coupled isolated four-port DC converter decoupling circuit, and the control method of the power decoupling circuit of the medium-high frequency AC bus-coupled isolated four-port DC converter is:

[0071] Port 1 is selected as the source port to maintain the stability of the DC voltage of the relay port r; Port 4 is selected as the source port, and the control target is to maintain the stability of the DC side input current; Port 3 is selected as the load port, and the control target is to maintain the stability of the DC side voltage; Port 2 is selected as the load port, and the control target is to maintain the stability of the DC port output current. After the relay port is decoupled, the control targets of these four ports can be simplified to the power transfer between the power transmission port and the power relay port r respectively. The switch control signal of the single-phase H-bridge module Hr in the power relay port r is used as the reference phase for the phase shift control of the single-phase H-bridge modules of other power transmission ports, and the external phase shift angle of other power transmission ports is changed. To change the transmission power between the power transmission port and the power relay port, and finally to maintain the DC voltage stability of the relay port and control the power transfer between the power transmission ports.

[0072] First, port 1 needs to maintain the DC voltage Vr of the power relay port r stable, and detect the difference between the actual DC voltage Vr of the power relay port and the given expected voltage value Vr_ref to obtain the error signal , after voltage closed-loop control, the external phase angle of the power transmission port 1 connected to the DC source is calculated , controls the power transmitted to the power relay port r, so that the DC side voltage Vr of the power relay port can stably track the given voltage value Vr_ref, thereby maintaining the DC voltage Vr of the relay port stable.

[0073] Next, the power transmission between each power transmission port is controlled. The control target of port 4 is to maintain the DC input current i4 stable, and the error signal is obtained by subtracting the actual DC input current i4 of power transmission port 4 from the given expected current value i4_ref. i4, after current closed-loop control, calculates the external phase angle of power transmission port 4 4, controls the power transmitted to the power relay port r, so that the actual DC input current i4 of the power transmission port 4 stably tracks the given current value i4_ref, and maintains the input current stability of the DC side of port 4; the control target of port 2 is to maintain the output current i2 of the DC side stable, and detects the difference between the actual DC output current i2 of the power transmission port 2 and the given expected current value i2_ref to obtain the error signal , after current closed-loop control, the external phase angle of power transmission port 2 is calculated 2. Control the power transmitted from the power relay port r, so that the actual DC output current i2 of the power transmission port 2 can stably track the given current value i2_ref, so as to maintain the output current stability of the DC side of port 2; the control target of port 3 is to maintain the output voltage V3 of the DC side stable, and the error signal is obtained by detecting the difference between the actual DC output voltage V3 of the power transmission port 3 and the given expected voltage value V3_ref. , after voltage closed-loop control, the external phase angle of power transmission port 3 is calculated 3. Control the power transmitted from the power relay port r, so that the actual DC output voltage V3 of the power transmission port 3 stably tracks the given voltage value V3_ref, thereby maintaining the output voltage stability on the DC side of port 3.

[0074] The power decoupling circuit control is based on the above single phase shift control, and the internal phase shift angles v1, v2, v3, and v4 are added to the AC side voltages of power transmission ports 1, 2, 3, and 4. , so that the AC side of the single-phase H-bridge module at the power transmission port outputs a three-level voltage. Figure 6 The output voltage waveform of the H-bridge module at each port of the converter on the AC side is shown in Figure 2. 1 is the external phase angle between port 1 and port r, 1 is the internal phase shift angle of the voltage square wave v1 at the AC side of port 1, 2 is the external phase angle between port 2 and port r, 2 is the internal phase shift angle of the AC side voltage square wave v2 at port 2, 3 is the external phase angle between port 3 and port r, 3 is the internal phase shift angle of the voltage square wave v3 at the AC side of port 3, 4 is the external phase angle between port 4 and port r, 4 is the inner phase shift angle of the voltage square wave v4 on the AC side of port 4. By calculating the inner phase shift angle of the port through a certain optimization algorithm, the current stress on the AC side of the port can be optimized and the soft switching range of the device can be increased. Figure 7 This is the output current waveform of the AC side of the H-bridge module at each port of the medium and high frequency AC bus-coupled isolated four-port DC converter.

[0075] In order to verify the feasibility and effectiveness of the present invention, this embodiment takes a 10kW 20kHz medium-high frequency AC bus-coupled isolated four-port DC converter as an example for simulation verification:

[0076] The DC side voltage and current waveforms of the medium-high frequency AC bus-coupled isolated four-port DC converter when the load of port 3 is switched are as follows: Figure 8As shown. At t=0.4s, the load on port 3 suddenly increases, causing the voltage V3 of port 3 to drop, and the currents i2 and i4 of port 2 and port 4 increase due to the influence of power coupling. At t=0.7s, the load on port 3 suddenly decreases, causing the voltage V3 of port 3 to rise, and the currents i2 and i4 of port 2 and port 4 drop due to the influence of power coupling. After adding the power decoupling circuit, the DC side voltage and current waveforms when the load of port 3 of the medium-high frequency AC bus coupled isolated four-port DC converter is switched are as follows Fig. 9 As shown. At t=0.4s, the load on port 3 suddenly increases, causing the voltage V3 of port 3 to drop. The currents i2 and i4 of port 2 and port 4 are greatly reduced by power coupling and have almost no fluctuation. At t=0.7s, the load on port 3 suddenly decreases, causing the voltage V3 of port 3 to rise. The currents i2 and i4 of port 2 and port 4 have almost no fluctuation. Figure 8 , Fig. 9 It can be seen that after adding a power decoupling circuit to the medium- and high-frequency AC bus-coupled isolated four-port DC converter, the power coupling between ports can be effectively suppressed, reducing the impact of port load fluctuations on the steady-state operation of other ports.

[0077] When the traditional single-phase shift control method is used, the voltage and current waveforms of the H-bridge module AC side at power transmission port 1 and power relay port r are as follows: Fig.10 As shown, the AC side voltages of the H-bridge modules at power transmission port 1 and power relay port r are both two-level waveforms, and there is only one external phase shift angle between the two AC voltages. , the AC current stress of port 1 is 34.6A; after adding the internal phase shift angle, the AC side voltage and current waveforms of the H-bridge module of power transmission port 1 and power relay port r are as follows Fig.11 As shown, the AC side voltage of the H-bridge module at power transmission port 1 is a three-level waveform, and the AC side voltage of the H-bridge module at power relay port r is a two-level waveform. There is an external phase shift angle between the two AC voltages. In addition, the AC voltage v1 at port 1 has an internal phase shift angle 1, at this time, the AC current stress of port 1 is 32.7A. Fig.10 , Fig.11 It can be seen that after adding the internal phase shift angle to the power transmission port, the port output current stress can be effectively reduced.

[0078] In another possible embodiment, Figure 4This is a schematic diagram of the power decoupling circuit structure of the multi-winding medium- and high-frequency transformer-coupled isolated four-port DC converter in the embodiment of the present invention. The original four-port DC converter has a total of 4 power transmission ports, and now a power relay port circuit is added to achieve power decoupling. The converter includes 4 single-phase H-bridge modules, 5 voltage-stabilizing capacitors, 1 n+1 winding medium- and high-frequency transformer, and 4 medium- and high-frequency inductors; port 1 of the multi-port DC converter is a power transmission port, and a voltage-stabilizing capacitor C1 is connected in parallel on the DC side of the single-phase H-bridge module H1, and is connected to a DC source V1 with a rated voltage of 350V. The AC side of the module H1 is connected via a medium- and high-frequency inductor. It is connected to the corresponding winding 1 of the n+1 winding medium and high frequency transformer T; port 2 of the multi-port DC converter is also a power transmission port. A voltage stabilizing capacitor C2 is connected in parallel to the DC side of the single-phase H-bridge module H2, and is connected to a DC source V2 with a rated voltage of 350V. The AC side of the module H2 is connected through a medium and high frequency inductor It is connected to the corresponding winding 2 of the n+1 winding medium and high frequency transformer T; port 3 of the multi-port DC converter is also a power transmission port. A voltage stabilizing capacitor C3 is connected in parallel on the DC side of the single-phase H-bridge module H3, and is connected to the load V3 with a rated voltage of 350V. The AC side of the module H3 is connected through a medium and high frequency inductor It is connected to the corresponding winding 3 of the n+1 winding medium and high frequency transformer T; port 4 of the multi-port DC converter is also a power transmission port. A voltage stabilizing capacitor C4 is connected in parallel on the DC side of the single-phase H-bridge module H4, and is connected to a DC source V4 with a rated voltage of 350V. The AC side of the module H4 is connected through a medium and high frequency inductor It is connected to the corresponding winding 4 of the medium and high frequency transformer T of the n+1 winding; port r is the added power relay port circuit, the DC side of the single-phase H-bridge module Hr is only connected in parallel with a voltage stabilizing capacitor Cr, and the DC side is not connected to other DC sources or loads, the rated voltage is 250V, and the AC side of the single-phase H-bridge module Hr is directly connected in parallel to the winding r of the medium and high frequency transformer T without adding medium and high frequency inductance, and the leakage inductance of winding r It should be close to 0 or much smaller than the winding leakage inductance of other power transmission ports.

[0079] The control method of this embodiment is exactly the same as that of the first embodiment, and will not be described again here.

[0080] The above implementation modes are only used to illustrate the present invention, but not to limit the present invention. Ordinary technicians in the relevant technical field can make various changes and modifications without departing from the essence and scope of the present invention. Therefore, all equivalent technical solutions also belong to the scope of the present invention. The scope of patent protection of the present invention should be limited by the claims.

[0081] The contents not described in detail in this specification belong to the prior art known to professional and technical personnel in this field.

Claims

1. A power decoupling circuit for an isolated multi-port DC converter, characterized in that: A power relay port circuit is added to the multi-port DC converter to decompose the isolated multi-port DC converter into multiple two-port converters; The power relay port circuit is a power decoupling circuit of a medium-high frequency AC bus-coupled converter; The power decoupling circuit of the medium-high frequency AC bus-coupled converter is specifically: The multi-port DC converter has a total of n power transmission ports and 1 power relay port, specifically including n single-phase H-bridge modules, 1 power relay port single-phase H-bridge module, n+1 voltage stabilizing capacitors, n dual-winding medium and high frequency transformers and n medium and high frequency inductors; The ports of the multi-port DC converter are power transmission ports, each of which includes a single-phase H-bridge module. A voltage stabilizing capacitor is connected in parallel to the DC side of each single-phase H-bridge module. The DC side is connected to a DC load device or an active device. The AC side of the single-phase H-bridge module is connected to the primary side of a dual-winding medium- and high-frequency transformer through a medium- and high-frequency inductor. The secondary sides of the dual-winding medium and high frequency transformers are connected in parallel to form a medium and high frequency AC bus; In the power relay port circuit, a voltage-stabilizing capacitor is connected in parallel on the DC side of the single-phase H-bridge module of the power relay port, no device is connected on the DC side, and the AC side of the single-phase H-bridge module of the power relay port is directly connected in parallel to the medium- and high-frequency AC busbar; a switch control signal of the single-phase H-bridge module of the power relay port is used as a reference phase for phase shift control of the single-phase H-bridge module in the power transmission port, and the DC voltage stability of the power relay port is maintained by changing the external phase shift angle of a power transmission port selected as a source port and connected to an active device on the DC side, and the power transfer between the power transmission ports is controlled by changing the external phase shift angles of the remaining power transmission ports.

2. The control method of a power decoupling circuit of an isolated multi-port DC converter according to claim 1, characterized in that: The specific process of maintaining the DC voltage stability of the power relay port by changing the external phase shift angle of a power transmission port connected to the active device on the DC side selected as the source port includes: A power transmission port connected to an active device on the DC side is selected as a source port, and the actual DC voltage of the power relay port is detected and compared with a given expected voltage value; Through voltage closed-loop control, the external phase shift angle of the power transmission port connected to the active device is calculated ; The power transmitted to the power relay port is controlled so that the DC voltage of the power relay port can stably track the expected voltage value, thereby maintaining the DC voltage stability of the power relay port.

3. The control method of a power decoupling circuit of an isolated multi-port DC converter according to claim 1, characterized in that: The specific process of controlling the power transfer between the power transmission ports by changing the outer phase shift angle of the remaining power transmission ports includes: The power transfer between the power transfer ports is decoupled by the power decoupling circuit into the power transfer between each power transfer port and the power relay port; According to the control target of the power transmission port, detecting the actual DC side value of the power transmission port and comparing it with a given expected value; After closed-loop control, the external phase angle of the power transmission port is calculated , controlling the amount of power transferred between the power transmission port and the power relay port; The DC side value of the power transmission port is made to stably track the expected value, thereby controlling the power transfer between the power transmission ports.

4. The control method of a power decoupling circuit of an isolated multi-port DC converter according to claim 3, characterized in that: The control target is to stabilize the DC voltage or current.

5. The control method of a power decoupling circuit of an isolated multi-port DC converter according to claim 2, characterized in that: Increase the internal phase shift angle of the power transmission port , used to optimize the current stress on the AC side of the port.

6. A power decoupling circuit for an isolated multi-port DC converter, characterized in that: A power relay port circuit is added to the multi-port DC converter to decompose the isolated multi-port DC converter into multiple two-port converters; The power relay port circuit is a power decoupling circuit of a multi-winding medium- and high-frequency transformer-coupled converter; The power decoupling circuit of the multi-winding medium- and high-frequency transformer-coupled converter is specifically: The multi-port DC converter has a total of n power transmission ports and 1 power relay port, specifically including n single-phase H-bridge modules, 1 power relay port single-phase H-bridge module, n+1 voltage stabilizing capacitors, an n+1 winding medium-high frequency transformer and n medium-high frequency inductors; The ports of the multi-port DC converter are power transmission ports, each of which includes a single-phase H-bridge module. A voltage stabilizing capacitor is connected in parallel to the DC side of each single-phase H-bridge module. The DC side is connected to a DC load device or an active device. The AC side of the single-phase H-bridge module is connected to the 1st to nth windings of the n+1 winding medium and high frequency transformer through medium and high frequency inductors. The power of the power transmission port is coupled through the n+1 winding medium and high frequency transformer; in the power relay port circuit, a voltage stabilizing capacitor is connected in parallel to the DC side of the single-phase H-bridge module of the power relay port, and no device is connected to the DC side, and the AC side of the single-phase H-bridge module of the power relay port is directly connected in parallel to the n+1th winding of the medium and high frequency transformer; The switch control signal of the single-phase H-bridge module of the power relay port is used as the reference phase for the phase shift control of the single-phase H-bridge module in the power transmission port, and the DC voltage stability of the power relay port is maintained by changing the external phase shift angle of a power transmission port selected as a source port and connected to an active device on the DC side, and the power transfer between the power transmission ports is controlled by changing the external phase shift angles of the remaining power transmission ports.

7. The control method of a power decoupling circuit of an isolated multi-port DC converter according to claim 6, characterized in that: The specific process of maintaining the DC voltage stability of the power relay port by changing the external phase shift angle of a power transmission port connected to the active device on the DC side selected as the source port includes: A power transmission port connected to an active device on the DC side is selected as a source port, and the actual DC voltage of the power relay port is detected and compared with a given expected voltage value; Through voltage closed-loop control, the external phase shift angle of the power transmission port connected to the active device is calculated ; The power transmitted to the power relay port is controlled so that the DC voltage of the power relay port can stably track the expected voltage value, thereby maintaining the DC voltage stability of the power relay port.

8. The control method of a power decoupling circuit of an isolated multi-port DC converter according to claim 6, characterized in that: The specific process of controlling the power transfer between the power transmission ports by changing the outer phase shift angle of the remaining power transmission ports includes: The power transfer between the power transfer ports is decoupled by the power decoupling circuit into the power transfer between each power transfer port and the power relay port; According to the control target of the power transmission port, detecting the actual value of the DC side of the power transmission port and comparing it with a given expected value; After closed-loop control, the external phase angle of the power transmission port is calculated , controlling the amount of power transferred between the power transmission port and the power relay port; The DC side value of the power transmission port is made to stably track the expected value, thereby controlling the power transfer between the power transmission ports.

9. The control method of a power decoupling circuit of an isolated multi-port DC converter according to claim 8, characterized in that: The control target is to stabilize the DC voltage or current.

10. The control method of a power decoupling circuit of an isolated multi-port DC converter according to claim 6, characterized in that: Increase the internal phase shift angle of the power transmission port , used to optimize the current stress on the AC side of the port.

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