Control method, device and system of distributed DC power supply

Abstract

The present application provides a control method, device, and system for a distributed direct current power supply, relating to the field of distributed direct current power supplies, and capable of achieving current sharing control of each distributed direct current power supply. The control method includes: periodically obtaining sampled current values ​​and sampled voltage values ​​on the transmission and distribution line on the grid-connected side of the direct current power supply; when a droop control mode flag is in a non-set state, and / or the absolute value of the difference between the sampled current value in the current sampling period and the sampled current value in the previous sampling period is greater than or equal to a first threshold, resetting the droop control mode flag, and entering an alternating cyclic control process of a virtual impedance adjustment mode for M sampling periods and a droop control mode for N sampling periods. In the virtual impedance adjustment mode for M consecutive sampling periods, when the absolute value of the difference between the sampled current value in m consecutive sampling periods and the sampled current value in the latest droop control mode is less than a second threshold, setting the droop control mode flag.

Description

Technical Field

[0001] The present application relates to the field of distributed DC power supplies, and in particular to a control method, device, and system for a distributed DC power supply. Background Art

[0002] A distributed power system refers to a power system that uses a network of multiple small power generation devices to jointly supply power to the load. Since small power generation devices can be flexibly arranged and do not need to be centrally arranged, it can also be called a distributed power source. Among them, the DC power supply system has the advantages of low system loss and low cost compared to the AC power supply system.

[0003] In actual systems, the distribution of distributed DC power sources has a certain degree of flexibility due to factors such as available resources and environmental conditions. The lengths of the transmission and distribution lines may vary greatly, resulting in large differences in the impedance of the transmission and distribution lines. This can easily cause uneven power distribution among the distributed DC power sources (that is, uneven current distribution among the distributed DC power sources), which in turn makes the distributed DC power supply system unstable.

[0004] In the related art, current sharing control of each distributed DC power supply is achieved based on a communication system. However, this method is extremely dependent on the reliability of the communication system, especially the communication delay has a great impact on the stability of the system, which limits the application scope of the distributed power generation system. For example, when the distributed power generation system is used to solve the electricity consumption in remote areas and complex terrain environments, due to the complex and harsh environment, it is difficult to meet the requirements of the distributed power generation system for the communication system. Summary of the Invention

[0005] The present application provides a control method, device, and system for a distributed DC power supply, which can achieve current sharing control of each distributed DC power supply without relying on a communication system.

[0006] The present application provides a control method for a distributed DC power supply, comprising:

[0007] Periodically obtain the sampled current value and sampled voltage value on the transmission and distribution line on the grid-connected side of the DC power supply.

[0008] In a single sampling cycle, when the flag of the droop control mode is in a non-set state, and / or the absolute value of the change between the sampled current value of the current sampling cycle and the sampled current value of the previous sampling cycle is greater than or equal to the first threshold, the flag of the droop control mode is reset, and the virtual impedance adjustment mode is entered. The virtual impedance value and the first voltage reference value are obtained based on the sampled current value, the sampled voltage value, the preset threshold value, and the latest sampled current value and sampled voltage value in the droop control mode of the current sampling cycle.

[0009] In the virtual impedance adjustment mode for M consecutive sampling cycles, when the absolute value of the change between the sampled current value in the consecutive m sampling cycles and the sampled current value in the latest droop control mode is less than the second threshold, the droop control mode flag is set; otherwise, after the virtual impedance adjustment mode for M consecutive sampling cycles is executed, the droop control mode is entered, and the second voltage reference value is obtained according to the sampled current value, the sampled voltage value, the preset threshold value and the virtual impedance value obtained in the latest virtual impedance adjustment mode in the current sampling cycle; after the droop control mode for N consecutive sampling cycles is executed, the virtual impedance adjustment mode for M sampling cycles is entered again; wherein M, N, and m are all positive integers greater than 1, and m is less than M; and the first threshold is greater than the second threshold.

[0010] The control method of the distributed DC power supply provided by the embodiment of the present application, by judging the flag of the droop control mode and the change in the sampled current value, can, when the output power of each distributed DC power supply changes, obtain a first reference voltage through the virtual impedance adjustment mode according to the difference between the current output power and the output power under the latest droop control mode to redistribute the output power of the DC power supply; and based on the virtual impedance value obtained in the virtual impedance adjustment mode, compensate the droop curve of each DC power supply through the droop control mode, obtain a second reference voltage to redistribute the output power of the DC power supply; by cyclically adjusting the output power of the DC power supply through the virtual impedance adjustment mode and the droop control mode, the output power difference of each distributed DC power supply is continuously narrowed and eventually tends to be average. In other words, the control method of the present application can, without relying on the communication system, adaptively eliminate the impedance difference on the transmission and distribution lines of each DC power supply by generating a virtual impedance after the system operating point changes, thereby achieving power balancing of each DC power supply and achieving the purpose of current sharing control.

[0011] In some possible implementations, the control method of a distributed DC power supply further includes: in a single sampling cycle, when a flag of a droop control mode is in a set state and the absolute value of the difference between the sampled current value of the current sampling cycle and the sampled current value of the previous sampling cycle is less than a first threshold, entering the droop control mode, and obtaining a second voltage reference value based on the sampled current value of the current sampling cycle, the sampled voltage value, a preset threshold, and the virtual impedance value obtained in the latest virtual impedance adjustment mode. In this case, when the operating point of the DC power supply does not change, by directly entering a constant downward vertical control mode, system jitter or power quality problems caused by the system being in a cyclic switching process between the virtual impedance adjustment mode and the droop control mode for a long time are avoided, thereby ensuring the stability of the current sharing control.

[0012] In some possible implementations, obtaining the virtual impedance value and the first voltage reference value according to the sampled current value, the sampled voltage value, the preset threshold value, and the latest sampled current value and sampled voltage value in the droop control mode in the current sampling period includes: V ref1 =V nom -r V I; where r V is the virtual impedance value; K r is the integration time constant; s is the integration operation in the frequency domain; P1 is the output power of the current sampling period; K u is the proportional constant; P0 is the output power in the latest droop control mode; V ref1 is the first voltage reference value; V nom is the preset parameter for voltage control; I is the sampled current value of the previous sampling cycle.

[0013] In some possible implementations, obtaining the second voltage reference value according to the sampled current value, the sampled voltage value, the preset threshold value, and the virtual impedance value obtained in the latest virtual impedance adjustment mode in the current sampling period includes: V ref2 =V nom -K p P1-r V I; where V ref2 is the second voltage reference value; V nom Preset parameters for voltage control; K p is the droop control constant; P1 is the output power of the current sampling period; r V is the virtual impedance value obtained in the latest virtual impedance adjustment mode; I is the sampled current value of the previous sampling cycle.

[0014] In some possible implementations, when the flag of the droop control mode is in a non-set state, and / or the absolute value of the change between the sampled current value of the current sampling period and the sampled current value of the previous sampling period is greater than or equal to a first threshold, the flag of the droop control mode is reset and the virtual impedance adjustment mode is entered, including: when the flag of the droop control mode is in a non-set state, or when the flag of the droop control mode is in a set state and the absolute value of the change between the sampled current value of the current sampling period and the sampled current value of the previous sampling period is greater than or equal to the first threshold, the flag of the droop control mode is reset and the virtual impedance adjustment mode is entered.

[0015] Compared with the determination of the change in the sampled current value, the state of the flag of the droop control mode is easier to determine. Therefore, the entire control process can be simplified by first determining the state of the flag of the droop control mode.

[0016] The embodiment of the present application also provides a control device for a distributed DC power supply, comprising: an acquisition circuit, a mode selection circuit, a virtual impedance adjustment circuit, and a droop control circuit; the acquisition circuit is connected to the grid-connected transmission and distribution line of the DC power supply; the mode selection circuit, the virtual impedance adjustment circuit, and the droop control circuit are all connected to the acquisition circuit; the mode selection circuit is connected to the virtual impedance adjustment circuit and the droop control circuit; the virtual impedance adjustment circuit is connected to the droop control circuit; the acquisition circuit is configured to periodically obtain sampled current values ​​and sampled voltage values ​​on the transmission and distribution line of the DC power supply; the droop control circuit is configured to perform a droop control mode, and obtain a second voltage reference value based on the sampled current value, sampled voltage value, preset threshold value, and the latest virtual impedance value obtained in the virtual impedance adjustment mode in the current sampling period; the virtual impedance adjustment circuit is configured to perform a virtual impedance adjustment mode, and obtain a virtual impedance value and a first voltage reference value based on the sampled current value, sampled voltage value, preset threshold value, and the latest sampled current value and sampled voltage value in the droop control mode in the current sampling period; the mode selection circuit is configured In a single sampling cycle, when the flag of the droop control mode is in a non-set state and / or the absolute value of the difference between the sampled current value in the current sampling cycle and the sampled current value in the previous sampling cycle is greater than or equal to a first threshold, the flag of the droop control mode is reset, and the virtual impedance adjustment circuit is controlled to enter the virtual impedance adjustment mode; the mode selection circuit is further configured to, when the virtual impedance adjustment circuit continuously executes the virtual impedance adjustment mode for M sampling cycles, set the flag of the droop control mode when the absolute value of the difference between the sampled current values ​​in m consecutive sampling cycles and the sampled current value in the latest droop control mode is less than a second threshold; otherwise, after the virtual impedance adjustment circuit continuously executes the virtual impedance adjustment mode for M sampling cycles, control the droop control circuit to enter the droop control mode; and after the droop control circuit continuously executes the droop control mode for N sampling cycles, control the virtual impedance adjustment circuit to enter the virtual impedance adjustment mode for M sampling cycles again; wherein M, N, and m are all positive integers greater than 1, and m is less than M; and the first threshold is greater than the second threshold.

[0017] The control device of the distributed DC power supply provided in the embodiment of the present application is used to judge the flag of the droop control mode and the change in the sampled current value through the mode selection circuit. When the output power of each distributed DC power supply changes, the virtual impedance adjustment circuit obtains a first reference voltage through the virtual impedance adjustment mode according to the difference between the current output power of the DC power supply and the output power under the latest droop control mode to redistribute the output power of the DC power supply; and according to the virtual impedance value obtained in the virtual impedance adjustment mode, the droop control circuit compensates the droop curve of each DC power supply through the droop control mode to obtain a second reference voltage to redistribute the output power of the DC power supply; through the cyclic adjustment of the output power of the DC power supply by the virtual impedance adjustment mode and the droop control mode, the output power gap of each distributed DC power supply is controlled to continuously narrow and eventually tend to be average; that is, the control device of the present application can eliminate the impedance difference on the transmission and distribution lines of each DC power supply by generating virtual impedance without relying on the communication system, thereby achieving power balancing of each DC power supply.

[0018] In some possible implementations, the virtual impedance adjustment circuit is configured to perform a virtual impedance adjustment mode, and obtaining the virtual impedance value and the first voltage reference value according to the sampled current value, the sampled voltage value, the preset threshold value, and the latest sampled current value and sampled voltage value in the droop control mode in the current sampling period includes:

[0019] according to V ref1 =V nom -r V I, obtain the virtual impedance value and the first voltage reference value; wherein, r V is the virtual impedance value; K r is the integration time constant; s is the integration operation in the frequency domain; P1 is the output power of the current sampling period; K u is the proportional constant; P0 is the output power in the latest droop control mode; V ref1 is the first voltage reference value; V nom is the preset parameter for voltage control; I is the sampled current value of the previous sampling cycle.

[0020] In some possible implementations, the droop control circuit is configured to perform a droop control mode, and obtaining the second voltage reference value according to the sampled current value, the sampled voltage value, the preset threshold value, and the latest virtual impedance value obtained in the virtual impedance adjustment mode in the current sampling period includes:

[0021] According to V ref2 =V nom -K p P1-r V I, obtain the second voltage reference value; where Vref2 is the second voltage reference value; V nom Preset parameters for voltage control; K p is the droop control constant; P1 is the output power of the current sampling period; r V is the virtual impedance value obtained in the latest virtual impedance adjustment mode; I is the sampled current value of the previous sampling cycle.

[0022] In some possible implementations, the mode selection circuit is further configured to control the droop control circuit to enter the droop control mode when a flag indicating the droop control mode is set in a single sampling cycle and the absolute value of the difference between the sampled current value in the current sampling cycle and the sampled current value in the previous sampling cycle is less than a first threshold. In this case, when the operating point of the DC power supply does not change, the system directly enters the constant droop control mode, thereby avoiding system jitter or power quality issues caused by the system being in the virtual impedance adjustment mode and the droop control mode for a long time, thereby ensuring the stability of the current sharing control.

[0023] In some possible implementations, the control device of the distributed DC power supply also includes: a voltage regulation circuit, a current regulation circuit, and a modulation unit; the voltage regulation circuit is connected to the virtual impedance regulation circuit, the droop control circuit, and the current regulation circuit; the current regulation circuit is connected to the converter connected to the DC power supply through the modulation unit; the voltage regulation circuit and the current regulation circuit are both connected to the acquisition circuit.

[0024] An embodiment of the present application further provides a distributed DC power supply system, comprising a plurality of distributed DC power supplies and a distributed DC power supply control device provided in any of the aforementioned possible implementation methods and connected to each distributed DC power supply. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A schematic diagram of a distributed DC power supply system provided in an embodiment of the present application;

[0026] Figure 2 A flow chart of a control method for a distributed DC power supply provided in an embodiment of the present application;

[0027] Figure 3 A simplified flow chart of a control method for a distributed DC power supply provided in an embodiment of the present application;

[0028] Figure 4 A diagram showing simulation results of a distributed DC power supply provided in an embodiment of the present application;

[0029] Figure 5 A schematic diagram of the structure of a control device for a distributed DC power supply provided in an embodiment of the present application. DETAILED DESCRIPTION

[0030] To make the objectives, technical solutions, and advantages of this application more clear, the technical solutions of this application will be clearly described below in conjunction with the accompanying drawings. Obviously, the embodiments described are only part of the embodiments of this application, not all of them. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of this application.

[0031] The terms "first," "second," and the like in the specification, examples, claims, and drawings of this application are used solely for descriptive purposes and should not be construed as indicating or implying relative importance or order. "At least one (item)" refers to one or more, and "plurality" refers to two or more. "And / or" is used to describe an association between associated objects, indicating that three possible relationships exist. For example, "A and / or B" can mean: only A exists, only B exists, and both A and B exist, where A and B can be singular or plural. The character " / " generally indicates that the associated objects are in an "or" relationship. "Connected," "connected," and the like should be broadly construed, meaning, for example, direct connection, indirect connection through an intermediary, or internal communication between two elements. Furthermore, the terms "including," "having," and any variations thereof, are intended to cover non-exclusive inclusions, such as inclusion of a series of steps or elements. A method, system, product, or device need not be limited to the steps or elements explicitly listed and may include other steps or elements not explicitly listed or inherent to such process, method, product, or device.

[0032] The present application provides a distributed DC power supply system. Figure 1 As shown, the distributed DC power supply system includes multiple distributed DC power supplies (such as 1, 2, and 3). Each DC power supply is connected to the DC bus (+, -) through a different converter 10 (such as a DC / DC converter, also known as a DC / DC converter) to supply power to the system load. Since in an actual system, the distribution of each distributed power supply is affected by factors such as available resources and environmental conditions and has a certain degree of flexibility, the length of the transmission and distribution lines (L1, L2) from each distributed DC power supply to the system load may vary, which in turn leads to the impedance of each transmission and distribution line (such as Figure 1 There are large differences among R1, R2, and R3.

[0033] An embodiment of the present application provides a control method for a distributed DC power supply in the aforementioned distributed DC power supply system. This control method can eliminate impedance differences on various transmission and distribution lines by generating virtual impedance without relying on a communication system, thereby ensuring that the power of each distributed DC power supply is substantially the same, achieving current sharing control of each distributed DC power supply, and effectively improving the performance of the distributed DC power supply system.

[0034] The following takes a DC power supply as an example to illustrate the control method of the distributed DC power supply. Figure 2 As shown, the control method includes:

[0035] Step 01: Periodically obtain the sampled current value I and the sampled voltage value V on the transmission and distribution line on the grid-connected side of the DC power supply.

[0036] Indicative, reference Figure 3 As shown, taking the sampling period as T as an example, the sampled current value I and the sampled voltage value V on the transmission and distribution line of the DC power supply can be obtained at every interval T. Step 02, in a single sampling period, when the flag of the droop control mode is in a non-set state, and / or the absolute value of the difference between the sampled current value I of the current sampling period and the sampled current value I0 of the previous sampling period is greater than or equal to the first threshold value I th1 When (i.e. |I-I0|≥I th1 ), reset the flag of the droop control mode, and enter the virtual impedance adjustment mode, according to the sampled current value I, sampled voltage value V, preset threshold value and the latest sampled current value I' and sampled voltage value V' in the droop control mode, obtain the virtual impedance value r V And the first voltage reference value V ref1 .

[0037] For step 02, refer to Figure 3 As shown, that is, step 02 is used to determine whether it is necessary to enter the cyclic adjustment mode (that is, the cyclic adjustment mode of the virtual impedance adjustment mode and the droop control mode). There are two judgment conditions for determining whether to enter the cyclic adjustment mode: Condition 1, the droop control mode flag is in a non-set state (for example, it can generally be "0"); Condition 2, the absolute value of the change between the sampled current value I of the current sampling period and the sampled current value I0 of the previous sampling period is greater than or equal to the first threshold value I th1 (i.e. |I-I0|≥I th1 ).

[0038] If one of the two conditions is met, it indicates that the operating point (or output power) of the DC power supply has changed, and the cyclic regulation mode is entered, through which the power of the DC power supply is redistributed.

[0039] If both conditions are not met, that is, the flag of the droop control mode is in the set state (for example, it can generally be "1"), and the absolute value of the difference between the sampling current value I of the current sampling period and the sampling current value I0 of the previous sampling period is less than the first threshold value I th1 (i.e. |I-I0|<I th1 ); it indicates that the operating point (or output power) of the DC power supply has basically not changed, so there is no need to redistribute the power; in this case, in order to avoid system jitter or power quality problems caused by switching between the virtual impedance adjustment mode and the droop control mode when in the cyclic adjustment mode for a long time, in some possible implementation methods, it is possible to directly enter the constant downward vertical control mode to ensure stable current sharing control.

[0040] In addition, for the judgment of condition one and condition two, considering that condition one is easier to judge than condition two, in some possible implementation methods, it is possible to first judge whether condition one is satisfied. If condition one is satisfied (for example, the flag of the droop control mode is in the non-set state "0"), the flag of the droop control mode is directly reset and the cyclic adjustment mode is entered; if condition one is not satisfied (for example, the flag of the droop control mode is in the set state "1"), it is further judged whether condition two is satisfied. If condition two is satisfied (that is, |I-I0|≥I th1 ), the flag of the droop control mode is reset and the cyclic adjustment mode is entered. If the second condition is not met (that is, the flag of the droop control mode is set and |I-I0|<I th1 ), then directly enter the constant downward vertical control mode.

[0041] In addition, refer to the above steps 02 and Figure 3 When at least one of the first and second conditions is met, the system enters the cyclic adjustment mode. Based on the time base, the system first enters the virtual impedance adjustment mode of M sampling cycles. By performing the virtual impedance adjustment mode in each of the M sampling cycles, the system obtains the virtual impedance value r according to the sampled current value I, the sampled voltage value V, the preset threshold value, and the latest sampled current value I' and sampled voltage value V' in the droop control mode. V And the first voltage reference value V ref1 In this way, the first voltage reference value V ref1 The converter 10 connected to the DC power supply is controlled to adjust the output power of the DC power supply.

[0042] Step 03: Reference Figure 3In the virtual impedance adjustment mode of executing M sampling cycles continuously, when the absolute value of the change between the sampled current value I in the continuous m sampling cycles and the sampled current value I0' in the latest droop control mode is less than the second threshold value (i.e. |I-I'0|<I th2 ), set the flag of the droop control mode (for example, the flag of the droop control mode can be set to "1"); otherwise, after executing the virtual impedance adjustment mode for M sampling cycles continuously, enter the droop control mode, and adjust the virtual impedance value r according to the sampled current value I, sampled voltage value V, preset threshold value and the latest virtual impedance adjustment mode in the current sampling cycle. V Get the second voltage reference value V ref2 After executing the droop control mode for N consecutive sampling cycles, the virtual impedance adjustment mode is entered again for M sampling cycles; wherein M, N, and m are all positive integers greater than 1, and m is less than M; the second threshold I th2 Less than the first threshold I th1 .

[0043] That is, reference Figure 3 , if step 02 is satisfied, the system enters a cyclic adjustment mode, in which a virtual impedance adjustment mode of M sampling cycles and a droop control mode of N sampling cycles are continuously executed; and in the virtual impedance adjustment mode of M sampling cycles, if the absolute value of the change between the sampled current value I in the continuous m sampling cycles and the sampled current value I'0 in the latest droop control mode is less than the second threshold value (|I-I'0|<I th2 ), it indicates that the operating point (or output power) of the DC power supply basically does not change, then the cycle regulation mode is exited and the droop control mode flag is set (such as "1").

[0044] In the loop regulation mode, the reference voltage (V ref1 、V ref2 ) to redistribute the output power of the DC power supply, and according to the difference between the current output power and the output power in the latest droop control mode, the virtual impedance value is updated through the virtual impedance adjustment mode, and the droop curve in the droop control mode is compensated based on the latest virtual impedance value to redistribute the output power of the DC power supply; through the cyclic adjustment of the virtual impedance adjustment mode and the droop control mode, the output power of each DC power supply is eventually made to be averaged.

[0045] It can be understood here that in the cyclic regulation mode, the present application compensates the droop curve in the droop control mode based on the latest virtual impedance value, which can ensure that the slope of the droop curve does not change, so the impact on the system dynamics is small and the system stability is high.

[0046] In addition, in the control method of the present application, based on the setting of step 02, a constant droop control mode can be performed after the system operating point stabilizes, and a stable current sharing control process can be entered; and after the system operating point changes, it can adaptively choose to enter the cyclic adjustment mode of the virtual impedance adjustment mode and the droop control mode again, thereby avoiding the occurrence of new power inequality due to changes in the system operating point.

[0047] In summary, the control method of the distributed DC power supply provided by the embodiment of the present application, by judging the flag of the droop control mode and the change in the sampled current value, can, when the output power of each distributed DC power supply changes, obtain a first reference voltage through the virtual impedance adjustment mode according to the difference between the current output power and the output power under the latest droop control mode to redistribute the output power of the DC power supply; and based on the virtual impedance value obtained in the virtual impedance adjustment mode, compensate the droop curve of each DC power supply through the droop control mode, obtain a second reference voltage to redistribute the output power of the DC power supply; through the cyclic adjustment of the output power of the DC power supply by the virtual impedance adjustment mode and the droop control mode, the output power of each distributed DC power supply is continuously narrowed and eventually tends to be average. In other words, the control method of the present application can, without relying on the communication system, adaptively eliminate the impedance difference on the transmission and distribution lines of each DC power supply by generating a virtual impedance after the system operating point changes, thereby achieving power balancing of each DC power supply and achieving the purpose of current sharing control.

[0048] In some possible implementations, the aforementioned virtual impedance adjustment mode obtains the virtual impedance value r according to the sampled current value I, the sampled voltage value V, the preset threshold value, and the latest sampled current value I' and sampled voltage value V' in the droop control mode of the current sampling period. V And the first voltage reference value V ref1 , which may include: virtual impedance adjustment mode according to formula (1) and formula (2), to obtain virtual impedance value r V , the first voltage reference value V ref1 .

[0049]

[0050] V ref1 =V nom -r V I (2)

[0051] In the above formulas (1) and (2), K r is the integration time constant; s is the integration operation in the frequency domain; P1 is the output power of the current sampling period; K u is the proportional constant (preset value); P0 is the output power in the latest droop control mode; V nom is the voltage control preset parameter; I is the sampled current value of the current sampling period. The output power P1 of the current sampling period can be obtained by multiplying the sampled current value I and the sampled voltage value V of the current sampling period, i.e., P1 = I·V. Similarly, the output power P0 in the latest droop control mode can be obtained by multiplying the sampled current value I' and the sampled voltage value V' collected in the latest droop control mode, i.e., P0 = I'·V'.

[0052] In some possible implementations, the droop control mode is based on the sampled current value I, the sampled voltage value V, the preset threshold value, and the virtual impedance value r obtained in the latest virtual impedance adjustment mode in the current sampling period. V Get the second voltage reference value V ref2 , which may include: the droop control mode obtains the second voltage reference value V according to formula (3): ref2 .

[0053] V ref2 =V nom -K p P1-r V I (3)

[0054] In the above formula (3), V nom Preset parameters for voltage control; K p is the droop control constant; P1 is the output power of the current sampling period; r V is the virtual impedance value obtained in the latest virtual impedance adjustment mode; I is the sampled current value of the current sampling period. The output power P1 of the current sampling period can be obtained by multiplying the sampled current value I and the sampled voltage value V of the current sampling period, that is, P1 = I·V.

[0055] In addition, the present application further simulates the control method of the present application through simulation, referring to Figure 4 As shown, the three DC power supplies (first DC power supply DG1, second DC power supply DG2, third DC power supply DG3) used in the control method have a line impedance ratio of 1:3:4 and the output powers of the three DC power supplies (DG1, DG2, DG3) are P out1 、P out2 、P out3 .

[0056] refer to Figure 4 As shown, it can be seen that due to the deviation of the line impedance, the initial power deviation of the first DC power supply DG1 and the second DC power supply DG2 reaches more than 20% of the average power, and the load power switching occurs at 2s, 8s, and 16s. At the 13th second, the converter of the DC power supply DG3 is put into operation, the system power fluctuates, and each DC power supply has a large power sharing deviation. The current sharing control method of the present application is adopted. After the system power fluctuates (2s, 8s, 13s, 16s), by continuously switching between the virtual impedance mode and the droop mode and adjusting the virtual impedance value, the output power gap of each distributed power generation unit is continuously narrowed, and finally a consensus is reached, power sharing is achieved, and the purpose of current sharing control is achieved.

[0057] An embodiment of the present application also provides a control device for a distributed DC power supply (hereinafter referred to as the control device). The control device can eliminate the impedance differences on each transmission and distribution line by generating virtual impedance without relying on a communication system, thereby ensuring that the power of each distributed DC power supply is basically the same, realizing current sharing control of each distributed DC power supply, and effectively improving the performance of the distributed DC power supply system.

[0058] In practice, different control devices can be configured for different DC power supplies, so that each control device can adjust the output power of the DC power supply to achieve the purpose of current sharing. The following uses a DC power supply as an example to illustrate the specific configuration of the control device.

[0059] like Figure 5 As shown, the control device includes an acquisition circuit 100 and a control circuit 200 connected to the acquisition circuit 100. The control circuit 200 includes a mode selection circuit 201, a virtual impedance adjustment circuit 202, and a droop control circuit 203. The acquisition circuit 100 is connected to the transmission and distribution lines (L1, L2) of the DC power supply; the mode selection circuit 201, the virtual impedance adjustment circuit 202, and the droop control circuit 203 are all connected to the acquisition circuit 100; the mode selection circuit 201 is connected to the virtual impedance adjustment circuit 202 and the droop control circuit 203; and the virtual impedance adjustment circuit 202 is connected to the droop control circuit 203.

[0060] The acquisition circuit 100 is configured to periodically obtain the sampled current value I and the sampled voltage value V on the transmission and distribution lines (L1, L2) on the grid-connected side of the DC power supply; that is, the acquisition circuit 100 periodically converts the current and voltage on the transmission and distribution lines (L1, L2) of the DC power supply into corresponding control signals in the system.

[0061] In some possible implementations, the acquisition circuit 100 can be connected to the transmission and distribution line between the DC power supply and the DC bus; in some possible implementations, the acquisition circuit 100 can be connected to the grid-connected port of the DC power supply, and also to the port connecting the DC power supply to the DC bus.

[0062] In some possible implementations, the acquisition circuit 100 may use a Hall current sensor or a current sensor to periodically acquire the sampled current value I on the DC power supply transmission and distribution lines (L1, L2); a differential amplifier circuit or a Hall voltage sensor may be used to periodically acquire the sampled voltage value V on the DC power supply transmission and distribution lines (L1, L2). The virtual impedance adjustment circuit 202 is configured to: perform a virtual impedance adjustment mode, and acquire a virtual impedance value r based on the sampled current value I, sampled voltage value V, a preset threshold, and the latest sampled current value I' and sampled voltage value V' acquired by the acquisition circuit 100 in the current sampling period in the droop control mode. V And the first voltage reference value V ref1 .

[0063] The control circuit 200 obtains the first voltage reference value V according to the virtual impedance adjustment circuit 202. ref1 The converter 10 is controlled to achieve redistribution of the output power of the DC power supply.

[0064] In some possible implementations, reference is made to Figure 5 As shown, the virtual impedance adjustment circuit 202 can be configured according to the formula V ref1 =V nom -r V I, to obtain the virtual impedance value r V , the first voltage reference value V ref1 The meanings of the relevant parameters in the formula can be referred to the corresponding explanation parts in formula (1) and formula (2) in the aforementioned control method embodiment, and will not be repeated here.

[0065] The droop control circuit 203 is configured to: perform the droop control mode, according to the sampling current value I, the sampling voltage value V, the preset threshold value and the virtual impedance value r obtained in the latest virtual impedance adjustment mode obtained by the acquisition circuit 100 in the current sampling period V , obtain the second voltage reference value V ref2 .

[0066] The control circuit 200 obtains the second voltage reference value V according to the droop control circuit 203. ref2 The converter 10 is controlled to achieve redistribution of the output power of the DC power supply.

[0067] In some possible implementations, reference is made to Figure 5 As shown, the droop control circuit 203 can be configured according to the formula V ref2 =V nom -K p P1-r V I, to obtain the second voltage reference value V ref2 The meanings of the relevant parameters in the formula can be referred to the corresponding description of formula (3) in the aforementioned control method embodiment, and will not be repeated here.

[0068] The mode selection circuit 201 is configured to: in a single sampling cycle, when the flag of the droop control mode is in a non-set state, and / or the absolute value of the difference between the sampled current value I of the current sampling cycle and the sampled current value I0 of the previous sampling cycle is greater than or equal to the first threshold value I th1 When (i.e. |I-I0|≥I th1 ), reset the flag of the droop control mode, and control the virtual impedance adjustment circuit 202 to enter the virtual impedance adjustment mode.

[0069] It can be understood that, for the mode selection circuit 201, condition 1: the flag of the droop control mode is in a non-set state (e.g., "0"); condition 2: the absolute value of the difference between the sampled current value I of the current sampling period and the sampled current value I0 of the previous sampling period is greater than or equal to the first threshold value I th1 (i.e. |I-I0|≥I th1 ); when only one of the two conditions is met (i.e., only condition one is met, or condition two is met, or both condition one and condition two are met), the mode selection circuit 201 resets the flag of the droop control mode (for example, the flag of the droop control mode can be set to "0") and controls the virtual impedance adjustment circuit 202 to enter the virtual impedance adjustment mode.

[0070] Considering that condition one is easier to judge than condition two, in some possible implementations, the mode selection circuit 201 may first judge whether condition one is satisfied. If condition one is satisfied, the flag of the droop control mode is directly reset, and the virtual impedance adjustment circuit 202 is controlled to enter the virtual impedance adjustment mode. If condition one is not satisfied, the mode selection circuit 201 further judges whether condition two is satisfied. If condition two is satisfied, the flag of the droop control mode is reset, and the virtual impedance adjustment circuit 202 is controlled to enter the virtual impedance adjustment mode. If condition two is not satisfied, that is, the flag of the droop control mode is in a set state (that is, the flag of the droop control mode is "1"), and |I-I0|<I th1; This indicates that the operating point (or output frequency) of the DC power supply has basically not changed. In this case, the mode selection circuit 201 can directly control the droop control circuit 203 to enter a constant lower vertical control mode to ensure stable current sharing control.

[0071] In addition, reference Figure 5 As shown, the mode selection circuit 201 is further configured to: in the virtual impedance adjustment mode in which the virtual impedance adjustment circuit 202 continuously performs M sampling cycles, when the absolute value of the change between the sampled current value I in the continuous m sampling cycles and the sampled current value I0' in the latest droop control mode is less than the second threshold value I th2 When (i.e. |I-I0'|<I th2 ), sets the flag of the droop control mode; otherwise, after the virtual impedance adjustment circuit 202 continuously executes the virtual impedance adjustment mode for M sampling cycles, the droop control circuit 203 is controlled to enter the droop control mode; and after the droop control circuit 203 continuously executes the droop control mode for N sampling cycles, the virtual impedance adjustment circuit 202 is controlled to enter the virtual impedance adjustment mode for M sampling cycles again; wherein M, N, and m are all positive integers greater than 1, and m is less than M; the second threshold I th2 Less than the first threshold I th1 .

[0072] That is, reference Figure 5 When at least one of the above-mentioned conditions 1 and 2 is satisfied, that is, when the operating point of the DC power supply changes, the mode selection circuit 201 controls the virtual impedance adjustment circuit 202 to enter the virtual impedance adjustment mode of M sampling cycles and the droop control circuit 203 to perform alternating cyclic control of the droop control mode of N sampling cycles based on the time reference St, thereby gradually reducing the change in the output power of the DC power supply (that is, the change in the sampled current value I gradually decreases); at the same time, when the virtual impedance adjustment circuit 202 performs the virtual impedance adjustment mode of M sampling cycles, when the absolute value of the change in the sampled current value I in the continuous m sampling cycles and the sampled current value I0' in the latest droop control mode are both less than the second threshold value I th2 When (i.e. |I-I0'|<I th2 ), which indicates that the sampling current value I tends to be stable and the operating point of the DC power supply basically does not change. In this case, the mode selection circuit 201 controls the virtual impedance adjustment circuit 202 and the droop control circuit 203 to stop the alternating cycle control process and sets the droop control mode flag (such as "1").

[0073] It should be noted here that, in the process of controlling the virtual impedance adjustment circuit 202 to perform the virtual impedance adjustment mode for M sampling periods and the droop control circuit 203 to perform the alternating cyclic control for N sampling periods, the mode selection circuit 201 selects and controls the virtual impedance adjustment mode for M sampling periods and the droop control mode for N sampling periods based on the time reference St set by the system; the time reference St can be set according to the reference of the sampling period. For example, when it is first determined that one of the conditions one and two is not met, the reference of the sampling period at this time is used as the time reference of the mode selection circuit 201 for subsequent cyclic control.

[0074] In addition, the first voltage reference value V obtained by the control circuit 200 in the virtual impedance adjustment mode ref1 , and the second voltage reference value V obtained in the droop control mode ref2 , to redistribute the power of the DC power supply, in some possible implementations, refer to Figure 5 As shown, the control circuit 200 may be provided with a voltage regulating circuit 204, a current regulating circuit 205, and a modulation circuit 206. The voltage regulating circuit 204 and the current regulating circuit 205 are both connected to the acquisition circuit 100, and the voltage regulating circuit 204 is connected to the virtual impedance regulating circuit 202, the droop control circuit 203, and the current regulating circuit 205; the current regulating circuit 205 is connected to the converter 10 connected to the DC power supply via the modulation circuit 206.

[0075] Illustratively, the voltage regulating circuit 204 may be a voltage regulator, the current regulating circuit 205 may be a current regulator, and the modulation circuit 206 may be a pulse width modulation (PWM) unit.

[0076] Specifically, the voltage regulating circuit 204 can obtain the first voltage reference value V from the virtual impedance regulating circuit 202. ref1 The current reference value I is obtained by obtaining the sampled voltage value V of the current sampling period from the acquisition circuit 100. ref and set the current reference value I ref Output to the current regulating circuit 205; the current regulating circuit 205 obtains the current reference value I from the current regulating circuit 205. ref The sampling current value I of the current sampling period obtained from the acquisition circuit 100 outputs a control signal to the modulation circuit 206, and outputs a driving signal to the converter 10 through the modulation circuit 206 to adjust the power of the driving DC power supply.

[0077] Similarly, the voltage regulating circuit 204 obtains the second voltage reference value V from the droop control circuit 203.ref2 The sampling voltage value V of the current sampling period obtained by the acquisition circuit 100 is used to obtain the current reference value I ref The current regulating circuit 205 obtains the current reference value I from the voltage regulating circuit 204. ref The sampling circuit 100 obtains the sampling current value I of the current sampling period, outputs a control signal to the modulation circuit 206, and outputs a driving signal to the converter 10 through the modulation circuit 206 to adjust the power of the driving DC power supply.

[0078] Of course, it is understandable that the converter 10 undertakes the main power transmission function, such as the common boost (BOOST) or buck (BUCK) chopper circuit; the converter 10 is generally provided with capacitors, inductors and semiconductor switching devices, etc. The converter 10 receives the drive signal output by the modulation circuit 206 and adjusts the power of the DC power supply by controlling the opening and closing of the semiconductor switching device.

[0079] The control device of the distributed DC power supply provided in the embodiment of the present application is used to judge the flag of the droop control mode and the change in the sampled current value through the mode selection circuit. When the output power of each distributed DC power supply changes, the virtual impedance adjustment circuit obtains a first reference voltage through the virtual impedance adjustment mode according to the difference between the current output power of the DC power supply and the output power under the latest droop control mode to redistribute the output power of the DC power supply; and according to the virtual impedance value obtained in the virtual impedance adjustment mode, the droop control circuit compensates the droop curve of each DC power supply through the droop control mode to obtain a second reference voltage to redistribute the output power of the DC power supply; through the cyclic adjustment of the output power of the DC power supply by the virtual impedance adjustment mode and the droop control mode, the output power gap of each distributed DC power supply is controlled to continuously narrow and eventually tend to be average; that is, the control device of the present application can eliminate the impedance difference on the transmission and distribution lines of each DC power supply by generating virtual impedance without relying on the communication system, thereby achieving power balancing of each DC power supply.

[0080] In addition, compared with the current sharing control device that uses a communication system, the control device of the present application does not rely on the communication system, and realizes the current sharing control of each DC power supply through an adaptive adjustment method, which has higher reliability and lower system cost; and the control device of the present application can be suitable for plug-and-play scenarios, and is particularly suitable for application scenarios of distributed power generation systems.

[0081] For relevant contents in the control device embodiment of the present application, reference may be made to the description of the corresponding parts in the aforementioned control method embodiment. For relevant contents in the control method embodiment, reference may also be made to the description of the corresponding parts in the control device embodiment, which will not be repeated here.

[0082] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of this application. Therefore, the scope of protection of this application should be based on the scope of protection of the claims.

Claims

1. A control method for a distributed DC power supply, characterized in that: include: Periodically obtain sampled current values ​​and sampled voltage values ​​on the transmission and distribution lines on the grid-connected side of the DC power supply; In a single sampling cycle, when the flag of the droop control mode is in a non-set state and / or the absolute value of the difference between the sampled current value of the current sampling cycle and the sampled current value of the previous sampling cycle is greater than or equal to the first threshold, the flag of the droop control mode is reset, and the virtual impedance adjustment mode is entered, and the virtual impedance value and the first voltage reference value are obtained according to the sampled current value, the sampled voltage value, the preset threshold value, and the latest sampled current value and sampled voltage value in the droop control mode in the current sampling cycle; In the virtual impedance adjustment mode for M consecutive sampling cycles, when the absolute value of the change between the sampled current value in the m consecutive sampling cycles and the sampled current value in the latest droop control mode is less than a second threshold, the droop control mode flag is set; otherwise, after the virtual impedance adjustment mode for M consecutive sampling cycles is executed, the droop control mode is entered, and the second voltage reference value is obtained based on the sampled current value, the sampled voltage value, the preset threshold value, and the virtual impedance value obtained in the latest virtual impedance adjustment mode in the current sampling cycle; After continuously executing the droop control mode for N sampling periods, entering the virtual impedance adjustment mode for M sampling periods again; wherein M, N, and m are all positive integers greater than 1, and m is less than M; The first threshold is greater than the second threshold.

2. The control method of a distributed DC power supply according to claim 1, characterized in that: The control method of the distributed DC power supply further includes: In a single sampling cycle, when the flag of the droop control mode is in a set state and the absolute value of the change between the sampled current value of the current sampling cycle and the sampled current value of the previous sampling cycle is less than the first threshold, the droop control mode is entered, and the second voltage reference value is obtained according to the sampled current value, the sampled voltage value, the preset threshold value and the latest virtual impedance value obtained in the virtual impedance adjustment mode of the current sampling cycle.

3. The control method of a distributed DC power supply according to claim 1 or 2, characterized in that: The acquiring of the virtual impedance value and the first voltage reference value according to the sampled current value, the sampled voltage value, the preset threshold value, and the latest sampled current value and sampled voltage value in the droop control mode in the current sampling period includes: Among them, r V is the virtual impedance value; K r is the integration time constant; s is the integration operation in the frequency domain; P1 is the output power of the current sampling period; K u is the proportional constant; P0 is the output power in the latest droop control mode; V ref1 is the first voltage reference value; V nom is the preset parameter for voltage control; I is the sampled current value of the previous sampling cycle.

4. The control method of a distributed DC power supply according to claim 1 or 2, characterized in that: The second voltage reference value is obtained according to the sampled current value, the sampled voltage value, the preset threshold value and the virtual impedance value obtained in the latest virtual impedance adjustment mode of the current sampling period, including: V ref2 =V nom -K p P1-r V I; Among them, V ref2 is the second voltage reference value; V nom Preset parameters for voltage control; K p is the droop control constant; P1 is the output power of the current sampling period; r V is the virtual impedance value obtained in the latest virtual impedance adjustment mode; I is the sampled current value of the previous sampling cycle.

5. The control method of a distributed DC power supply according to claim 1 or 2, characterized in that: When the flag of the droop control mode is in a non-set state and / or the absolute value of the change between the sampled current value of the current sampling period and the sampled current value of the previous sampling period is greater than or equal to the first threshold, the flag of the droop control mode is reset and the virtual impedance adjustment mode is entered, including: When the flag of the droop control mode is in a non-set state, or when the flag of the droop control mode is in a set state and the absolute value of the change between the sampled current value of the current sampling period and the sampled current value of the previous sampling period is greater than or equal to the first threshold, the flag of the droop control mode is reset and the virtual impedance adjustment mode is entered.

6. A control device for a distributed DC power supply, characterized in that: include: Acquisition circuit, mode selection circuit, virtual impedance adjustment circuit, droop control circuit; The acquisition circuit is connected to the transmission and distribution line on the grid-connected side of the DC power supply; the mode selection circuit, the virtual impedance adjustment circuit, and the droop control circuit are all connected to the acquisition circuit; the mode selection circuit is connected to the virtual impedance adjustment circuit and the droop control circuit; the virtual impedance adjustment circuit is connected to the droop control circuit; The acquisition circuit is configured to periodically acquire sampled current values ​​and sampled voltage values ​​on the transmission and distribution lines of the DC power supply; The droop control circuit is configured to perform a droop control mode and obtain a second voltage reference value based on a sampled current value, a sampled voltage value, a preset threshold value, and a virtual impedance value obtained in the latest virtual impedance adjustment mode in a current sampling period; The virtual impedance adjustment circuit is configured to perform a virtual impedance adjustment mode, and obtain a virtual impedance value and a first voltage reference value according to a sampled current value, a sampled voltage value, a preset threshold value, and a latest sampled current value and sampled voltage value in a droop control mode in a current sampling period; The mode selection circuit is configured to reset the droop control mode flag and control the virtual impedance adjustment circuit to enter the virtual impedance adjustment mode when the droop control mode flag is in a non-set state and / or when the absolute value of the difference between the sampled current value in the current sampling period and the sampled current value in the previous sampling period is greater than or equal to a first threshold value in a single sampling period; The mode selection circuit is further configured to, in the virtual impedance adjustment mode in which the virtual impedance adjustment circuit continuously executes M sampling cycles, set a droop control mode flag when the absolute value of the change between the sampled current value in the consecutive m sampling cycles and the sampled current value in the latest droop control mode is less than a second threshold; otherwise, after the virtual impedance adjustment circuit continuously executes the virtual impedance adjustment mode for M sampling cycles, control the droop control circuit to enter the droop control mode; and after the droop control circuit continuously executes the droop control mode for N sampling cycles, control the virtual impedance adjustment circuit to enter the virtual impedance adjustment mode for the M sampling cycles again; wherein M, N, and m are all positive integers greater than 1, and m is less than M; and the first threshold is greater than the second threshold.

7. The control device for a distributed DC power supply according to claim 6, wherein: The virtual impedance adjustment circuit is configured to perform a virtual impedance adjustment mode, and obtaining a virtual impedance value and a first voltage reference value according to a sampled current value, a sampled voltage value, a preset threshold value, and a latest sampled current value and sampled voltage value in a droop control mode in a current sampling period includes: according to V ref1 =V nom -r V 1. Obtain a virtual impedance value and a first voltage reference value; Among them, r V is the virtual impedance value; K r is the integration time constant; s is the integration operation in the frequency domain; P1 is the output power of the current sampling period; K u is the proportional constant; P0 is the output power in the latest droop control mode; V ref1 is the first voltage reference value; V nom is the preset parameter for voltage control; I is the sampled current value of the previous sampling cycle.

8. The control device for a distributed DC power supply according to claim 6, wherein: The droop control circuit is configured to perform a droop control mode, and obtaining a second voltage reference value according to a sampled current value, a sampled voltage value, a preset threshold value, and a virtual impedance value obtained in the latest virtual impedance adjustment mode in a current sampling period includes: According to V ref2 =V nom -K p P1-r V 1. Obtain a second voltage reference value; Among them, V ref2 is the second voltage reference value; V nom Preset parameters for voltage control; K p is the droop control constant; P1 is the output power of the current sampling period; r V is the virtual impedance value obtained in the latest virtual impedance adjustment mode; I is the sampled current value of the previous sampling cycle.

9. The control device for a distributed DC power supply according to claim 6, wherein: The mode selection circuit is further configured to, in a single sampling cycle, when a flag of the droop control mode is in a set state and an absolute value of a change between a sampled current value in a current sampling cycle and a sampled current value in a previous sampling cycle is less than a first threshold, control the droop control circuit to enter the droop control mode.

10. The control device for a distributed DC power supply according to any one of claims 6 to 9, characterized in that: The mode selection circuit is configured to reset the droop control mode flag and control the virtual impedance adjustment circuit to enter the virtual impedance adjustment mode when the droop control mode flag is in a non-set state and / or the absolute value of the difference between the sampled current value in the current sampling period and the sampled current value in the previous sampling period is greater than or equal to a first threshold value in a single sampling period, including: The mode selection circuit is configured to reset the flag of the droop control mode and enter the virtual impedance adjustment mode in a single sampling cycle when the flag of the droop control mode is in a non-set state, or when the flag of the droop control mode is in a set state and the absolute value of the change between the sampled current value of the current sampling cycle and the sampled current value of the previous sampling cycle is greater than or equal to a first threshold.

11. The control device for a distributed DC power supply according to any one of claims 6 to 9, characterized in that: Also includes: Voltage regulation circuit, current regulation circuit, modulation unit; The voltage regulation circuit is connected to the virtual impedance regulation circuit, the droop control circuit, and the current regulation circuit; the current regulation circuit is connected to a converter connected to a DC power supply through the modulation unit; the voltage regulation circuit and the current regulation circuit are both connected to the acquisition circuit.

12. A distributed DC power supply system, characterized in that: The invention comprises a plurality of distributed DC power supplies and a distributed DC power supply control device according to any one of claims 6 to 11 connected to each of the distributed DC power supplies.

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