Parallel power control method for bidirectional interface converter of alternating-current and direct-current hybrid micro-grid

Abstract

The invention provides a parallel power control method for a bidirectional interface converter of an AC / DC hybrid micro-grid, and the method comprises the steps: adding an inertia control link and a capacity distribution link into an active control loop of the parallel bidirectional interface converter; according to the alternating current side frequency deviation and the direct current side voltage deviation of the parallel bidirectional interface converter, an active power transmission reference value of each bidirectional interface converter is calculated through inertia control and capacity allocation links; and the active power transmission reference value of each bidirectional interface converter is sent to a power current control ring to obtain a signal for driving a switch in the three-phase bridge type conversion circuit. Power distribution is realized through inertia control and capacity distribution links, the control convenience and reliability of the parallel bidirectional interface converter are improved, the circulating power of the parallel bidirectional interface converter is solved, the complex calculation of control parameters of the parallel bidirectional interface converter is reduced, the power balance state of the parallel bidirectional interface converter is formed, and the reliability of the parallel bidirectional interface converter is improved. And meanwhile, the dynamic response of alternating-current frequency and direct-current voltage and current is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of bidirectional interface converter control, and in particular to a parallel power control method for bidirectional interface converters of an AC / DC hybrid microgrid. Background Art

[0002] The core device of AC / DC hybrid microgrid is bidirectional interface converter (BIC), and its effective control directly affects the stable operation of the system. As the connecting component between AC sub-microgrid and DC sub-microgrid, the main task of BIC is to transfer power and maintain the stability of voltage and frequency on both sides. With the continuous increase in the penetration rate of new energy and the demand for microgrid power level, the "double high" development trend of "high proportion of renewable energy" and "high proportion of power electronic equipment" in AC / DC hybrid microgrid is becoming more and more obvious, and the control demand for BIC in the multi-energy structure system has increased significantly. Multiple BICs in parallel can improve the power transmission capacity between AC / DC microgrids, but at the same time increase the difficulty of controlling power distribution. When using traditional droop control, when multiple BICs are connected in parallel, the droop control coefficient of each interface converter needs to be adjusted according to different rated capacities, and lacks inertial support. Therefore, a parallel power control method for bidirectional interface converters in AC / DC hybrid microgrids is proposed to solve the problems of poor dynamic characteristics and low power distribution accuracy of parallel bidirectional interface converters in AC / DC hybrid microgrids. Summary of the invention

[0003] In order to solve the deficiencies of the prior art in the above-mentioned background technology, the present invention provides a parallel power control method for bidirectional interface converters of an AC / DC hybrid microgrid, which can enable multiple bidirectional interface converters to be connected in parallel with better power distribution accuracy and provide inertial support optimization system dynamic response.

[0004] The present invention adopts the following technical solutions:

[0005] A method for controlling parallel power of bidirectional interface converters in an AC / DC hybrid microgrid, the control method is used to control a bidirectional interface converter, the bidirectional interconnected converter includes a three-phase bridge conversion circuit, and the control method has the following steps:

[0006] Step S1, calculating the AC side frequency deviation and the DC side voltage deviation of the bidirectional interface converter;

[0007] Step S2, adding inertia control and capacity allocation links to the active control loop of the bidirectional interface converter;

[0008] Step S3, the AC side frequency deviation and the DC side voltage deviation of the bidirectional interface converter are calculated through inertia control and capacity allocation to obtain an active power transmission reference value of the bidirectional interface converter;

[0009] Step S4, optimizing the power dynamic response of the parallel bidirectional interface converter according to the inertia coefficient J, adjusting the transmission capacity of the parallel bidirectional interface converter according to the capacity allocation coefficient D, and realizing the power transmission and allocation of multiple interface converters in parallel in the AC / DC hybrid microgrid system.

[0010] Furthermore, the active control loop in step S2 includes inertial control and capacity allocation links. Inertial control is used to reduce the transmission of disturbances between subgrids and optimize power transmission response. The capacity allocation link is used to clarify the transmission power of each bidirectional interface converter, limit frequency and voltage deviations, and enhance the stability of the AC / DC hybrid microgrid system.

[0011] Furthermore, the expression of the active power transmission reference value of the bidirectional interface converter in step S3 is as follows:

[0012]

[0013] P ref is the active reference power of the bidirectional interface converter, P0 is the initial active power of the bidirectional interface converter, ΔU dc is the voltage deviation on the DC side, Δf is the frequency deviation on the AC side, K is the output coefficient, J is the inertia coefficient, and D is the capacity distribution coefficient;

[0014] The output coefficient K is expressed as:

[0015]

[0016] |ΔU dc | max is the maximum allowable change in DC voltage, |Δf| max It is the maximum allowable change in AC frequency.

[0017] Furthermore, the capacity allocation coefficient D in step S4 is calculated as follows:

[0018]

[0019] Among them, S N It is the rated capacity of the bidirectional interface converter.

[0020] Furthermore, the active power transmission reference value of the bidirectional interface converter is calculated through power current loop control to obtain a driving signal, and the driving signal is subjected to space vector pulse width modulation to control the on and off of the switch in the three-phase bridge conversion circuit.

[0021] Compared with the prior art, the present invention adopts the above technical solution and has the following beneficial effects:

[0022] (1) The present invention provides a method for controlling the power of bidirectional interface converters in parallel in an AC / DC hybrid microgrid. The method adjusts the capacity allocation coefficient through a capacity allocation link to achieve flexible power allocation when multiple bidirectional interface converters are connected in parallel.

[0023] (2) The present invention proposes a method for parallel power control of bidirectional interface converters in an AC / DC hybrid microgrid, which optimizes the dynamic response of active power through the inertia link, suppresses the rapid propagation of disturbances between subgrids, enables the system to have better anti-interference performance, and improves the transient stability of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the structural diagram of the bidirectional interface converter in the AC / DC hybrid microgrid.

[0025] Figure 2 The present invention is a control block diagram of a parallel power control method for bidirectional interface converters of an AC / DC hybrid microgrid.

[0026] Figure 3 This is a block diagram of the power and current dual closed-loop control adopted by the present invention.

[0027] Figure 4 This is a parallel equivalent model diagram of the bidirectional interface converter proposed by the present invention.

[0028] Figure 5 This is a simulation waveform diagram of power distribution of a bidirectional interface converter when the AC side load fluctuates in an embodiment of the present invention.

[0029] Figure 6 This is a simulation waveform diagram of power distribution of a bidirectional interface converter when a DC side load fluctuates in an embodiment of the present invention.

[0030] Figure 7 It is a simulation waveform diagram of the AC side frequency of the bidirectional interface converter when the AC side load fluctuates in the embodiment of the present invention.

[0031] Figure 8 This is a simulated waveform diagram of the DC side voltage of the bidirectional interface converter when the AC side load fluctuates in an embodiment of the present invention.

[0032] Fig. 9 This is a simulation waveform diagram of the DC side current of the bidirectional interface converter when the AC side load fluctuates in an embodiment of the present invention.

[0033] Fig.10 This is a waveform diagram of the AC side frequency simulation of the bidirectional interface converter when the DC side load fluctuates in an embodiment of the present invention.

[0034] Fig.11 This is a simulation waveform diagram of the DC side voltage of the bidirectional interface converter when the DC side load fluctuates in an embodiment of the present invention.

[0035] Fig.12 This is a simulation waveform diagram of the DC side current of the bidirectional interface converter when the DC side load fluctuates in an embodiment of the present invention. DETAILED DESCRIPTION

[0036] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0037] like Figure 1 As shown in FIG. 1 , the AC / DC hybrid microgrid includes an AC subgrid, a DC subgrid, and a bidirectional interface converter component connecting the AC / DC subgrids. The bidirectional interface converter includes a three-phase full-bridge topology structure and a load, where C is the converter filter capacitor, L is the filter inductor, R is the equivalent impedance of the filter inductor, and C dc is the DC voltage stabilizing capacitor; U dc and I dc are the DC side voltage and current, u abc and i abc In the embodiment of the present invention, an ideal DC voltage source is connected in series with a resistor in the DC subnet to realize PU droop control in the DC subnet; an inverter is used as an equivalent distributed power supply in the AC subnet to realize Pf droop control in the AC subnet.

[0038] The control block diagram of the AC / DC hybrid microgrid bidirectional interface converter parallel power control method of the present invention is as follows: Figure 2 As shown, it includes an active control loop and a power current control loop. The bidirectional interface converter calculates the frequency deviation on the AC side and the voltage deviation on the DC side. The active power transmission reference value is obtained through the active control loop and sent to the power current control loop. The drive signal output by the power current control loop is subjected to sinusoidal pulse width modulation (SPWM) to control the on and off of the switch.

[0039] The DC subnet PU droop control and AC subnet Pf droop control can be expressed as:

[0040] ΔP u =K u ΔU dc

[0041] ΔP f =K f Δf

[0042] In the formula, ΔU dc is the voltage deviation on the DC side of the bidirectional interface converter, K u is the droop coefficient of the DC subnet PU, Δf is the frequency deviation of the AC side of the bidirectional interface converter, K f is the Pf droop coefficient of the AC subnetwork.

[0043] When there is a voltage deviation on the DC side and a frequency deviation on the AC side, the frequency deviation on the AC side is sent to the inertia control and capacity allocation link together with the voltage deviation on the DC side after passing through the output coefficient in the active control loop of the bidirectional interface converter. The output coefficient is:

[0044]

[0045] Among them, |ΔU dc | max is the maximum allowable change in DC voltage, |Δf| max It is the maximum allowable change in AC frequency.

[0046] The frequency deviation on the AC side and the voltage deviation on the DC side of the bidirectional interface converter are calculated through the inertial control and capacity allocation links added to the active control loop to obtain the active power transmission reference value of the bidirectional interface converter, which is expressed as:

[0047]

[0048] Among them, P ref is the active reference power of the bidirectional interface converter, P0 is the initial active power of the bidirectional interface converter, J is the inertia coefficient, and D is the capacity allocation coefficient.

[0049] The initial active power P0 of the bidirectional interface converter is set to 0, and the active reference power P of the bidirectional interface converter in steady state is ref It is expressed as:

[0050]

[0051] Furthermore, the rated capacity S of the bidirectional interface converter N It is expressed as:

[0052]

[0053] The capacity distribution coefficient D is expressed as:

[0054]

[0055] The rated capacity S of the bidirectional interface converter N It only relates to the capacity distribution coefficient D.

[0056] Furthermore, the DC subnet PU droop coefficient K u The droop coefficient K of the sum flow subnet Pf f It is expressed as:

[0057]

[0058] In the formula, it can be seen that the AC / DC hybrid microgrid bidirectional interface converter parallel power control has the same droop characteristic as the droop control in steady state.

[0059] When the AC / DC hybrid microgrid bidirectional interface converter parallel power control is in steady state, the rated capacity S of the bidirectional interface converter is used. N The relationship between the inertia coefficient J and the capacity allocation coefficient D is only calculated. By adjusting the capacity allocation coefficient D, the capacity and output of each bidirectional interface converter can be flexibly allocated, which effectively reduces the complexity of model building and calculation of multiple bidirectional interface converters in parallel. It has the same droop characteristics as droop control and can achieve power balance of the whole system. In the inertial control link, the inertia coefficient J acts on the moment when the voltage frequency and power of the microgrid system change too fast due to load fluctuations, so that the voltage frequency changes slowly, effectively reducing the impact of load disturbances and optimizing the dynamic response of the bidirectional interface converter to transmit power.

[0060] In this embodiment, the rated voltage of the DC side is set to U N =750V, the maximum allowable change of DC voltage ΔU dc | max =10%U N , AC side rated frequency f N =50Hz, the maximum allowable change in AC frequency is |Δf| max =1%f N In order to verify whether the active power transmission of the control method proposed in the present invention can be distributed according to the capacity of the bidirectional interface converter, three bidirectional interface converters are operated in parallel as an example, and the capacity ratio of the three bidirectional interface converters is set to 1:2:3. When the load is applied to the AC side and the DC side respectively, the output waveform of each BIC is as follows: Figure 5 , Figure 6 The BIC is a bidirectional interface converter. When the AC side load fluctuates, Figure 5 It can be seen that the active power of each BIC can be output stably, and the active power distribution error of BIC1 and BIC2 fluctuates when the load changes, and is almost 0 when the load is stable. When the DC side load fluctuates, the output waveform of each BIC is as follows: Figure 6 As shown. Similar to the AC side, the active power of each BIC can be output stably, and the active power distribution error of BIC1 and BIC2 fluctuates with the load change, and is almost 0 when the load is stable. The load fluctuation simulation waveform of the 0.1MW AC side of the bidirectional interface converter in the embodiment is as follows Figure 7-Figure 9As shown in FIG. 1 , since the present invention adds an inertial control link in the active power control of the bidirectional interface converter, the AC side frequency is supported, while the initial fluctuation of the DC voltage is improved or even eliminated, and the dynamic current response of the bidirectional interface converter is also reduced, maintaining good anti-interference performance. The simulated waveform of the 0.1MW DC side load fluctuation of the bidirectional interface converter in the embodiment is as follows: Figure 10-12 As shown, due to the addition of inertia link in the system, the oscillation of DC voltage and AC frequency is reduced, the anti-interference ability of the bidirectional interface converter is enhanced, the frequency on the AC side gradually becomes flat, and the voltage and current waveforms on the DC side are improved.

[0061] It can be seen from this embodiment that the value of the capacity allocation coefficient can be adjusted to flexibly control the capacity of each BIC and accurately allocate active power. The AC / DC hybrid microgrid bidirectional interface converter parallel power control method can realize the adjustment of the dynamic response of the bidirectional interface converter by connecting multiple interface converters in parallel on the basis of power sharing. When the power of the AC subnet or the DC subnet changes, the overall response speed of the microgrid can be controlled by adjusting the inertia coefficient to reduce the impact of power fluctuations between the AC subnet and the DC subnet.

[0062] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned specific embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned specific embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for controlling parallel power of bidirectional interface converters in an AC / DC hybrid microgrid, characterized in that: The control method is used to control a bidirectional interface converter, wherein the bidirectional interface converter includes a three-phase bridge conversion circuit, and the control method has the following steps: Step S1, calculating the AC side frequency deviation and the DC side voltage deviation of the bidirectional interface converter; Step S2, adding inertia control and capacity allocation links to the active control loop of the bidirectional interface converter; Step S3, the AC side frequency deviation and the DC side voltage deviation of the bidirectional interface converter are calculated through inertia control and capacity allocation to obtain an active power transmission reference value of the bidirectional interface converter; Step S4, optimizing the power dynamic response of the parallel bidirectional interface converter according to the inertia coefficient J, adjusting the transmission capacity of the parallel bidirectional interface converter according to the capacity allocation coefficient D, and realizing the power transmission and allocation of multiple interface converters in parallel in the AC / DC hybrid microgrid system.

2. The method for controlling parallel power of bidirectional interface converters in an AC / DC hybrid microgrid according to claim 1, characterized in that: The active control loop in step S2 includes inertial control and capacity allocation links. Inertial control is used to reduce the transmission of disturbances between subgrids and optimize power transmission response. The capacity allocation link is used to clarify the transmission power of each bidirectional interface converter, limit frequency and voltage deviations, and enhance the stability of the AC / DC hybrid microgrid system.

3. The method for controlling parallel power of bidirectional interface converters in an AC / DC hybrid microgrid according to claim 1, characterized in that: The expression of the active power transmission reference value of the bidirectional interface converter in step S3 is as follows: P ref is the active reference power of the bidirectional interface converter, P0 is the initial active power of the bidirectional interface converter, ΔU dc is the voltage deviation on the DC side, Δf is the frequency deviation on the AC side, K is the output coefficient, J is the inertia coefficient, and D is the capacity distribution coefficient; The output coefficient K is expressed as: |ΔU dc | max is the maximum allowable change in DC voltage, |Δf| max It is the maximum allowable change of AC frequency.

4. The method for controlling parallel power of bidirectional interface converters in an AC / DC hybrid microgrid according to claim 1, characterized in that: The calculation formula of the capacity distribution coefficient D in step S4 is as follows: Among them, S N It is the rated capacity of the bidirectional interface converter.

5. The method for controlling parallel power of bidirectional interface converters in an AC / DC hybrid microgrid according to claim 1, characterized in that: The active power transmission reference value of the bidirectional interface converter is calculated through power current loop control to obtain a driving signal, and the driving signal is modulated by space vector pulse width to control the on and off of the switch in the three-phase bridge conversion circuit.

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