Active damping control structure and method for a dc transformer, dc power distribution network

Abstract

This invention discloses an active damping control structure and method for a DC transformer and a DC distribution network, belonging to the field of DC transformer control technology. In the control structure: a summation module sums the input voltages of M sub-modules to obtain voltage v. bus The filter module filters out voltage v bus The AC component in the equation yields the DC voltage v. DC The averaging module calculates the voltage v respectively. bus and DC voltage v DC Divide by M to obtain the reference value v avg and reference value v DCref The input voltage equalization controller realizes the input voltage v of each submodule j. in_j Compared with reference value v avg Zero steady-state error regulation, output power p ivs_j The input voltage regulator controller implements the input voltage v of each submodule j. in_j Compared with reference value v DCref Zero steady-state error regulation, output power p ivr_j The output voltage regulator achieves the output voltage V. o Compared with reference value V oref Zero steady-state error regulation, output power regulation p ove The actual power calculator calculates the actual power of each submodule j using the instruction p. pu_j The control structure and method of this invention ensure stable operation of the transformer.

Description

Technical Field

[0001] This invention belongs to the field of DC transformer control technology, and more specifically, relates to an active damping control structure and method for DC transformers and DC distribution networks. Background Technology

[0002] DC transformers are key equipment in DC distribution networks, responsible for converting medium-voltage DC to low-voltage DC power. Among them, the ISOP-DAB type DC transformer uses a dual active bridge (DAB) as its sub-modules, with each sub-module connected in an input-series-output-parallel (ISOP) configuration. Due to its advantages of electrical isolation, wide-range regulation, and high-voltage input with high-current output, it is widely used in DC distribution networks.

[0003] However, in actual operation, there is a non-negligible equivalent impedance on the medium-voltage DC bus. When it does not match the input impedance of the DC transformer, the voltage of the medium-voltage bus of the DC transformer will become unstable due to insufficient phase margin at the intersection of system impedances, resulting in low-frequency oscillations, affecting the power quality of the DC transformer, and in severe cases, affecting the safe operation of the DC transformer and even the DC distribution network. Summary of the Invention

[0004] In view of the above-mentioned defects or improvement needs of the prior art, the present invention provides an active damping control structure and method for DC transformers and DC distribution networks, the purpose of which is to achieve stable optimization of DC transformers.

[0005] To achieve the above objectives, according to one aspect of the present invention, an active damping control structure for an ISOP-DAB type DC transformer is provided, wherein the DC transformer has M sub-modules and the input terminals of sub-modules 1 to M are connected in series from the positive terminal of the bus voltage to the negative terminal of the bus voltage, and the active damping control structure includes;

[0006] The summation module sums the input voltages of the M sub-modules to obtain the total bus voltage v on the series side. bus ;

[0007] The filtering module is used to filter out the total bus voltage v. bus The AC component in the figure yields the DC bus voltage v on the series side. DC ;

[0008] The averaging module is used to calculate the total bus voltage v. bus Divide by M to obtain the input equalization voltage reference value v. avg And the DC voltage v of the bus DCDivide by M to obtain the input DC voltage reference value v. DCref ;

[0009] The input voltage equalization controller is used to realize the input voltage v of each submodule j in the first M-1 submodules. in_j Compared with the input equalization voltage reference value v avg Zero steady-state error regulation, the corresponding equalizing voltage regulation power p output ivs_j ;

[0010] The input voltage regulator controller is used to implement the input voltage v of each submodule j in the M submodules. in_j With DC voltage reference value v DCref Zero steady-state error regulation, the corresponding regulated power output p ivr_j ;

[0011] Output voltage regulator, used to achieve transformer output voltage V o With the set output voltage reference value V oref Zero steady-state error regulation, output dominant power regulation p ove ;

[0012] The actual power calculator is used to calculate the actual power instruction p of each submodule j in M ​​submodules. pu_j :

[0013]

[0014] In one embodiment, it further includes:

[0015] The sampling module is used to sample the input voltage v of each submodule j of the converter. in_j and the converter's output voltage v o .

[0016] In one embodiment, the input voltage equalization controller includes a first difference structure and a first PI regulation structure, wherein the first difference structure adjusts the input voltage v of submodule j. in_j Compared with the input equalization voltage reference value v avg After calculating the first deviation, the obtained first deviation is sent to the first PI control structure to regulate the power p through voltage equalization. ivs_j The first deviation is made to approach 0.

[0017] In one embodiment, the input voltage equalization controller includes M-1 first difference calculation structures and M-1 first PI adjustment structures, with the first difference calculation structures and the first PI adjustment structures connected in a one-to-one correspondence.

[0018] In one embodiment, the input voltage regulator controller includes a second difference structure and a second PI regulation structure, the second difference structure affecting the input voltage v of submodule j.in_j With DC voltage reference value v DCref After calculating the second deviation, the obtained second deviation is fed into the second PI regulation structure to regulate the power p through voltage regulation. ivr_j The second deviation is brought close to 0.

[0019] In one embodiment, the input voltage regulator includes M second difference structures and M second PI adjustment structures, with each second difference structure and the second PI adjustment structure connected in a one-to-one correspondence.

[0020] In one embodiment, the output voltage regulator includes a third difference structure and a third PI regulation structure, the third difference structure adjusting the transformer output voltage v o With the set output voltage reference value V oref After calculating the third deviation, the obtained third deviation is fed into the third PI control structure to control the dominant power adjustment amount p. ove The third deviation is made to approach 0.

[0021] In one embodiment, the actual power calculator includes M calculation structures, each used to calculate the actual power command of a different submodule.

[0022] According to another aspect of the present invention, an active damping control method for an ISOP-DAB type DC transformer is provided, comprising:

[0023] The input voltage v of each submodule j of the sampling converter in_j and the converter's output voltage v o ;

[0024] The total bus voltage v on the series side is obtained by summing the input voltages of the M sub-modules. bus Filter out the total bus voltage v bus The AC component in the figure yields the DC bus voltage v on the series side. DC ;

[0025] The total bus voltage v bus Divide by M to obtain the input equalization voltage reference value v. avg And the DC voltage v of the bus DC Divide by M to obtain the input DC voltage reference value v. DCref ;

[0026] The input voltage v of each submodule j in the first M-1 submodules in_j Compared with the input equalization voltage reference value v avg Perform zero steady-state error regulation and output the corresponding equalization regulation power p. ivs_j ;

[0027] The input voltage v of each submodule j in the M submodules in_j With DC voltage reference value v DCref Perform zero steady-state error regulation and output the corresponding regulated power p. ivr_j ;

[0028] For the transformer output voltage v o Compared with the set output voltage reference value v oref Perform zero steady-state error regulation, output dominant power regulation quantity p ove ;

[0029] Calculate the actual power command p for each submodule j in the M submodules. pu_j :

[0030]

[0031] Based on the actual power command p of each submodule j pu_j Adjust the power of each submodule j.

[0032] According to another aspect of the present invention, a DC distribution network is provided, including an ISOP-DAB type DC transformer and its control structure. The control structure is the above-mentioned active damping control structure for the ISOP-DAB type DC transformer. Under the control of the active damping control structure, the DC transformer realizes stable power conversion between medium-voltage DC and low-voltage DC.

[0033] In summary, compared with the prior art, the above-described technical solutions conceived by this invention can achieve the following beneficial effects:

[0034] This invention combines an input voltage equalization controller, an input voltage regulator, an output voltage regulator, and an actual power calculator to form a feedback network for controlling the DAB submodule. This network controls the input voltage v of each submodule. in_j Compared with the input equalization voltage reference value v avg Perform zero steady-state error regulation to keep the input voltage of all submodules equal. This is achieved by adjusting the input voltage v of each submodule. in_j With DC voltage reference value v DCref Perform steady-state error-free regulation to stabilize the input voltage of all submodules at the DC voltage reference value V. DCref The surrounding area ensures the stability of the input voltage. This is achieved by adjusting the transformer output voltage v. o With the set output voltage reference value V oref Zero steady-state error regulation ensures stable output voltage. Furthermore, the input voltage is balanced by an input voltage equalization controller. in_j Compared with the input equalization voltage reference value v avg With no steady-state error, the input voltage V is regulated by an input voltage regulator. in_jWith DC voltage reference value v DCref No steady-state error, indirectly regulating the total bus voltage v bus Make it approach the DC voltage of the bus. DC This removes the AC component, thereby maintaining the stability of the ISOP-DAB type DC transformer. Furthermore, the control structure of this invention can reshape the input impedance of the ISOP-DAB DC transformer, ensuring that its equivalent impedance with the medium-voltage DC bus satisfies the Nyquist criterion, thus guaranteeing the stability of the cascaded system. Attached Figure Description

[0035] Figure 1 This is a topology of a DC transformer in one embodiment;

[0036] Figure 2 This is a structural framework diagram of the active damping control structure of a DC transformer in one embodiment;

[0037] Figure 3 This is an impedance Bode plot of a DC transformer in one embodiment;

[0038] Figure 4 This is an experimental waveform in one embodiment when the active damping control method proposed in this invention is not used;

[0039] Figure 5 This is an experimental waveform obtained by utilizing the active damping control method proposed in this invention in one embodiment. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0041] like Figure 1 The diagram shows the topology of an ISOP-DAB type DC transformer, which includes a medium-voltage DC bus and a low-voltage DC bus, and has an equivalent reactance L. BUS and equivalent resistance R BUS The medium-voltage side input bus, ISOP-type connection structure, and M (M≥2) DAB converter submodules (SM) connected to the ISOP structure. Among them, the medium-voltage side DC regulated source V... DC The total voltage on the medium-voltage series side of DAB remains constant, and is v. bus The low-voltage parallel side voltage of DAB is v o For the j-th SM, the input voltage is v. in_j .

[0042] Example 1

[0043] like Figure 2 The diagram shows the structural block diagram of the active damping control structure for a DC transformer proposed in this invention. This control structure includes a summation module, a filtering module, an averaging module, an input voltage equalization controller, an input voltage regulator, an output voltage regulator, and an actual power calculator.

[0044] The summation module sums the input voltages of the M sub-modules to obtain the total bus voltage v on the series side. bus .

[0045] In one embodiment, a sampling module is further included for sampling the input voltage v of each submodule j of the converter. in_j and the converter's output voltage v o The input voltages (V) of the M sub-modules in_1 v in_2 , ..., v in_M The voltage is fed into the summation module for summation to obtain the total bus voltage v. bus :

[0046] v bus =v in_1 +v in_2 +v in_3 +……+v in_M

[0047] The filtering module is used to filter out the total bus voltage v. bus The AC component in the figure yields the DC bus voltage v on the series side. DC Due to the equivalent reactance L of the medium-voltage side input bus. BUS and equivalent resistance R BUS The existence of v bus The voltage may be a mixture of DC and low-frequency AC components, requiring the AC component to be filtered out. In one embodiment, the filtering module can be a low-pass filter to filter out the AC component.

[0048] The averaging module is used to calculate the total bus voltage v. bus Divide by M to obtain the input equalization voltage reference value v. avg And the DC voltage v of the bus DC Divide by M to obtain the input DC voltage reference value v. DCref ,Right now:

[0049]

[0050]

[0051] Among them, the input voltage equalization controller is used to realize the input voltage v of each submodule j in the first M-1 submodules. in_j Compared with the input equalization voltage reference value v avg Zero steady-state error regulation, the corresponding equalizing voltage regulation power p output ivs_j That is, the input equalization controller achieves zero steady-state error regulation between the first M-1 sub-modules and the input equalization voltage reference value.

[0052] In one embodiment, the input voltage equalization controller includes a first difference calculation structure and a first PI regulation structure G. ivs The first difference structure affects the input voltage v of submodule j. in_j Compared with the input equalization voltage reference value v avg After calculating the first deviation, the obtained first deviation is sent to the first PI control structure to regulate the power p through voltage equalization. ivs_j The goal is to make the first deviation approach 0. Specifically, this can include M-1 first difference-calculating structures and M-1 first PI adjustment structures, with each first difference-calculating structure and the first PI adjustment structure connected in a one-to-one correspondence. For the first M-1 sub-modules in ISOP-DAB, i.e., SM... j(j＝1,…M-1) , for v avg and v in_j(j＝1,…M-1) The difference is calculated, and the deviation is sent to the first PI controller G. ivs In this context, the regulator is used to achieve v in_j With v avg The zero steady-state error regulation between the inputs enables the ISOP-DAB to achieve input voltage equalization. The output of this regulator is defined as the corresponding input voltage equalization regulation power p. ivs_j(j＝1,…M-1) .

[0053] Among them, the input voltage regulator is used to realize the input voltage v of each submodule j in the M submodules. in_j With DC voltage reference value v DCref Zero steady-state error regulation, the corresponding regulated power output p ivr_j That is, the input voltage regulator controller is used to achieve the connection between the M sub-modules and the DC voltage reference value v. DCref Zero steady-state error adjustment.

[0054] In one embodiment, the input voltage regulator controller includes a second difference structure and a second PI regulation structure G. ivr The second difference structure affects the input voltage v of submodule j. in_j With DC voltage reference value v DCref After calculating the second deviation, the obtained second deviation is fed into the second PI regulation structure to regulate the power p through voltage regulation. ivr_jThe goal is to make the second deviation approach zero. Specifically, the input voltage regulator controller includes M second difference structures and M second PI adjustment structures, with each second difference structure and the second PI adjustment structure connected in a one-to-one correspondence. This applies to all submodules in ISOP-DAB, namely SM... j(j＝1,…M) , for v DCref and v in_j(j＝1,…M) The difference is calculated, and the deviation is fed into the PI controller G. ivr In this context, the regulator is used to achieve v in_j With v DCref The zero steady-state error regulation between the input and output voltages enables the ISOP-DAB to achieve stable input voltage. The output of this regulator is defined as the corresponding input voltage regulation power p. ivr_j(j＝1,…M) .

[0055] The output voltage regulator is used to achieve the transformer output voltage V. o With the set output voltage reference value V oref Zero steady-state error regulation, output dominant power regulation p ove .

[0056] In one embodiment, the output voltage regulator includes a third difference structure and a third PI regulation structure G. ovc The third difference structure affects the transformer output voltage v. o With the set output voltage reference value V oref After calculating the third deviation, the obtained third deviation is fed into the third PI control structure to control the dominant power adjustment amount p. ove To achieve the third deviation approaching 0. Specifically, for the output voltage reference value V... oref and output voltage v o The difference is calculated, and the deviation is sent to the third PI controller G. ovc In this context, the regulator is used to achieve v o With V oref The zero steady-state error regulation between the parameters achieves the function of stabilizing the output voltage. The output of this regulator is defined as the dominant power regulation quantity p. ovc .

[0057] The actual power calculator is used to calculate the actual power command p of each submodule j in M ​​submodules. pu_j :

[0058]

[0059] In one embodiment, the actual power calculator includes M calculation structures, each used to calculate the actual power command for a different submodule. Specifically, this is achieved through the dominant power adjustment amount p. ovc Subtract its corresponding voltage regulation power p ivr_j(j＝1,…M-1)Then subtract its corresponding equalization regulation power p ivs_j(j＝1,…M-1) This yields the actual power command p for the first M-1 SMs in ISOP-DAB. pu_j(j＝1,…M-1) ; through the dominant power regulation amount p ovc Subtract the voltage regulation power p ivr_M In addition, all the equalizing and regulating power Σp ivs_j The actual power command p of the Mth SM in ISOP-DAB is obtained. pu_M .Right now:

[0060]

[0061] The above text involves multiple instances of zero steady-state error regulation. Because the input voltage equalization controller, input voltage regulator, output voltage regulator, and actual power calculator form a feedback regulation network for the ISOP-DAB, adjusting the power of each submodule regulates the corresponding input voltage V. in_j Total bus voltage V bus DC voltage of the busbar v DC Input equalization voltage reference value v avg Input DC voltage reference value v DCref and output voltage v o All these parameters will change in tandem, and through zero steady-state error adjustment, three points will ultimately achieve zero steady-state error, thus stabilizing the input and output. The zero steady-state error adjustment structure can refer to conventional designs.

[0062] Furthermore, based on the aforementioned control structure, while maintaining stable input and output, the input impedance of the ISOP-DAB DC transformer can be reshaped so that its equivalent impedance with the medium-voltage DC bus satisfies the Nyquist criterion, ensuring the stability of the cascaded system. Understandably, after obtaining the actual power commands of each SM, the actual power commands p of each SM are used... pu_j(j＝1,…M) Direct power control is applied to ISOP-DAB.

[0063] Example 2

[0064] This invention also relates to an active damping control method for ISOP-DAB type DC transformers, comprising:

[0065] Step S1: Input voltage v of each submodule j of the sampling converter in_j and the converter's output voltage v o .

[0066] Step S2: Sum the input voltages of the M sub-modules to obtain the total bus voltage v on the series side. bus Filter out the total bus voltage v bus The AC component in the figure yields the DC bus voltage v on the series side. DC; the total bus voltage v bus Divide by M to obtain the input equalization voltage reference value v. avg And the DC voltage v of the bus DC Divide by M to obtain the input DC voltage reference value v. DCref .

[0067] Step S3: Input voltage v of each submodule j in the first M-1 submodules in_j Compared with the input equalization voltage reference value v avg Perform zero steady-state error regulation and output the corresponding equalization regulation power p. ivs_j The input voltage v of each submodule j in the M submodules in_j With DC voltage reference value v DCref Perform zero steady-state error regulation and output the corresponding regulated power p. ivr_j ; Regarding the transformer output voltage v o With the set output voltage reference value V oref Perform zero steady-state error regulation, output dominant power regulation quantity p ove .

[0068] Step S4: Calculate the actual power command p of each submodule j in the M submodules. pu_j :

[0069]

[0070] Step S5: Based on the actual power command p of each submodule j pu_j Adjust the power of each submodule j.

[0071] The specific implementation methods for each step can be found in the above description, and will not be repeated here.

[0072] Example 3

[0073] This invention also relates to a DC distribution network, including an ISOP-DAB type DC transformer and its control structure. The control structure is the active damping control structure for the ISOP-DAB type DC transformer described above. Under the control of the active damping control structure, the DC transformer achieves stable power conversion between medium-voltage DC and low-voltage DC.

[0074] Example 4

[0075] The impedance of the DC transformer with parameters shown in Table 1 was verified using MATLAB software.

[0076]

[0077] like Figure 3 The figure shows the impedance Bode plot obtained from the simulation, where the output impedance of the medium-voltage DC bus is Z.bus Before utilizing the active damping control method for DC transformers proposed in this invention, the input impedance of ISOP-DAB was Z. in_ISOP After utilizing the active damping control method proposed in this invention, the input impedance of ISOP-DAB is reshaped to Z. in_rs .from Figure 3 As can be seen from this, before utilizing the active damping method proposed in this invention, Z bus and Z in_ISOP The phase difference at the intersection of its amplitude-frequency curves is 183.2°, which is greater than 180°, failing to satisfy the Nyquist criterion, indicating system instability. After utilizing the active damping method proposed in this invention, Z... bus and Z in_rs The phase difference at the intersection of its amplitude-frequency curves is 101.4°, which is less than 180°, satisfying the Nyquist criterion, indicating system stability. It can be seen that the active damping method proposed in this invention effectively reshapes the input impedance of the ISOP-DAB.

[0078] like Figure 4 The figure shows the experimental waveforms without utilizing the active damping method proposed in this invention, where i L_1 i L_2 These represent the inductor currents in the first and second DAB modules, respectively, and the input voltages of each module before utilizing the active damping method proposed in this invention. vin_1 ,v in_2 The system is in an oscillating state and unstable; after using the active damping method proposed in this invention, the experimental waveform is as follows: Figure 5 As shown, the oscillation was eliminated 6ms after the active damping method was applied, and the system returned to stability, demonstrating the effectiveness of the active damping method proposed in this invention.

[0079] In summary, by utilizing the control structure and method of this invention, not only can the stability of the transformer's input and output be guaranteed, but the input impedance of the ISOP-DAB is also reshaped, so that the input impedance of the ISOP-DAB DC transformer and the output impedance of the medium-voltage DC bus satisfy the Nyquist criterion, further ensuring the stability of the system.

[0080] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An active damping control system for an ISOP-DAB type DC transformer, wherein the DC transformer has Submodules and submodules To submodule The input terminals are connected in series from the positive terminal of the bus voltage to the negative terminal of the bus voltage, characterized in that... The active damping control system includes: The summation module is used to calculate... The input voltages of each submodule are summed to obtain the total bus voltage on the series side. ; The filtering module is used to filter out the total voltage of the bus. The AC component in the figure is used to obtain the DC bus voltage on the series side. ; The averaging module is used to calculate the total bus voltage. Divide by The input equalization voltage reference value is obtained. and the DC voltage of the bus Divide by The input DC voltage reference value is obtained. ; Input equalization controller, used to achieve pre- Each submodule Input voltage Input equalization voltage reference value Zero steady-state error regulation, output corresponding equalizing power regulation. The input voltage equalization controller includes a first difference calculation structure and a first PI regulation structure. The first difference calculation structure is applied to the submodule. Input voltage Input equalization voltage reference value After calculating the first deviation, the obtained first deviation is sent to the first PI regulation structure to regulate the power through voltage equalization. To achieve the goal of making the first deviation approach 0; the input voltage equalization controller includes M-1 first difference calculation structures and M-1 first PI adjustment structures, with the first difference calculation structures and the first PI adjustment structures connected in a one-to-one correspondence. Input voltage regulator controller, used to implement Each submodule Input voltage DC voltage reference value Zero steady-state error regulation, corresponding regulated power output. The input voltage regulator controller includes a second difference structure and a second PI regulation structure. The second difference structure is paired with the submodule. Input voltage DC voltage reference value After calculating the second deviation, the obtained second deviation is fed into the second PI regulation structure to regulate the power through voltage regulation. Achieve the second deviation approaching 0; Output voltage regulator, used to adjust the transformer output voltage. Compared with the set output voltage reference value Zero steady-state error regulation, output dominant power regulation ; Actual power calculator, used to calculate Each submodule Actual power command : 。 2. The active damping control system for ISOP-DAB type DC transformer as described in claim 1, characterized in that, Also includes: The sampling module is used for various sub-modules of the sampling converter. Input voltage and the converter's output voltage .

3. The active damping control system for ISOP-DAB type DC transformer as described in claim 1, characterized in that, The input voltage regulator controller includes M second difference structures and M second PI adjustment structures, with each second difference structure and the second PI adjustment structure connected in a one-to-one correspondence.

4. The active damping control system for ISOP-DAB type DC transformer as described in claim 1, characterized in that, The output voltage regulator includes a third difference structure and a third PI regulation structure. The third difference structure regulates the transformer output voltage. Compared with the set output voltage reference value After calculating the third deviation, the obtained third deviation is fed into the third PI control structure to regulate the dominant power. The third deviation is made to approach 0.

5. The active damping control system for ISOP-DAB type DC transformer as described in claim 1, characterized in that, The actual power calculator includes M calculation structures, each used to calculate the actual power command of a different submodule.

6. An active damping control method for ISOP-DAB type DC transformers, characterized in that, The control method is implemented based on the control system as described in any one of claims 1 to 5, and the control method includes: Submodules of the sampling converter Input voltage and the converter's output voltage ; right The input voltages of each submodule are summed to obtain the total bus voltage on the series side. Filter out the total voltage of the bus. The AC component in the figure is used to obtain the DC bus voltage on the series side. ; Total bus voltage Divide by The input equalization voltage reference value is obtained. and the DC voltage of the bus Divide by The input DC voltage reference value is obtained. ; Forward Each submodule Input voltage Input equalization voltage reference value Perform zero steady-state error regulation and output the corresponding equalization regulation power. ; right Each submodule Input voltage DC voltage reference value Perform zero steady-state error regulation and output the corresponding regulated power. ; For transformer output voltage Compared with the set output voltage reference value Perform zero steady-state error regulation and output dominant power regulation. ; calculate Each submodule Actual power command : ； Based on each submodule Actual power command Adjust each submodule The power.

7. A DC distribution network, comprising an ISOP-DAB type DC transformer and its control system, characterized in that, The control system is the active damping control system for ISOP-DAB type DC transformer as described in any one of claims 1 to 5. Under the control of the active damping control system, the DC transformer realizes stable power conversion between medium-voltage DC and low-voltage DC.

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