Control method based on single-phase cascaded H-bridge energy storage converter

Abstract

The invention discloses a control method based on a single-phase cascaded H-bridge energy storage converter, and relates to the technical field of power electronic converters. The method comprises the steps of calculating a capacitor voltage average value and output reactive power; calculating an output alternating current reference amplitude based on the capacitor voltage average value; calculating an output current phase reference value based on the reactive power; combining the output alternating current reference amplitude and the output current phase reference value to generate an output alternating current reference value; calculating a difference value between the output alternating current reference value and the grid-connected point alternating current; and calculating a voltage modulation signal of the full-bridge DC / AC converter based on the difference value, and controlling the single-phase cascaded H-bridge energy storage converter. The method is simple in structure and easy to implement, specified power output can be achieved by controlling the full-bridge DC / AC converter, calculation complexity is effectively reduced on the basis of achieving power control, calculation efficiency can be improved, and the method has high application value in engineering design.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronic converters, and in particular to a control method based on a single-phase cascade H-bridge energy storage converter. Background Art

[0002] At present, renewable energy generation has a huge impact on the stability of the power grid and the quality of power: the output power is intermittent, random and volatile, which seriously affects the stable operation of the power system and further limits the application of renewable energy. In order to improve the reliability and utilization rate of renewable energy generation, battery energy storage technology has emerged. Compared with traditional energy storage technology, new battery energy storage technology has the characteristics of high efficiency, reliability, flexibility and environmental friendliness, and has gradually become the standard configuration of new energy power stations.

[0003] Cascaded H-bridge converters are widely used in high-voltage and large-capacity energy storage systems because of their high modularity, easy expansion, flexible configuration, high redundancy, and ability to connect directly to high-voltage grids without transformers to achieve high-voltage direct connection. In energy storage systems using cascaded H-bridge converters as energy storage converters, there are two configuration methods for energy storage batteries: (1) The energy storage battery is directly connected in parallel with the submodule capacitor; (2) The energy storage battery is connected in parallel with the submodule capacitor through a DC / DC converter.

[0004] If the energy storage battery is directly connected in parallel to the two ends of the submodule capacitor, the double frequency voltage ripple on the capacitor voltage will greatly reduce the service life of the energy storage battery and reduce the efficiency of the energy storage battery. SoC Estimation accuracy reduces system operation efficiency.

[0005] The basic control goal of the energy storage converter is to complete the system charging and discharging power control, issue the required power according to the active and reactive power dispatch instructions of the power grid, and realize balanced control in combination with the energy storage battery charge state obtained by the battery management system. At present, coordinate transformation is mostly used for power control of single-phase cascade H-bridge energy storage converters. The single-phase AC signal is transformed into a dq coordinate system to obtain a DC signal, and the voltage or power control is realized by controlling the corresponding components in the dq coordinate system. The above control methods are difficult to achieve the output of the specified power, and in the process of SoC The balancing speed is slow during balancing control, and there is overvoltage in the capacitor voltage during the power switching process. Summary of the invention

[0006] In order to solve the above technical problems existing in the prior art, the present invention adopts a control method based on a single-phase cascade H-bridge energy storage converter, which can realize the specified power output control of the energy storage converter, and the energy storage battery SoCThe control method has a simple structure and is easy to implement, and has great application value in engineering design.

[0007] Specifically, a control method based on a single-phase cascade H-bridge energy storage converter has the following technical solution: The single-phase cascade H-bridge energy storage converter includes N sub-modules connected in series; in the sub-modules, the energy storage battery is connected to the full-bridge DC / AC converter via a half-bridge DC / DC converter; wherein, N ≥2; The control method comprises the following steps: Step S1: Measure the capacitor voltage of each submodule u ci , calculate the average capacitor voltage u c_ave ;Measure the reactive power output of a single-phase cascaded H-bridge energy storage converter Q ac ;in, i =1,2,..., N ; Step S2: Based on the average value of capacitor voltage u c_ave Calculation of the output AC current reference amplitude of a single-phase cascaded H-bridge energy storage converter I Ampl ; Based on reactive power Q ac Calculate the output current phase reference value ; Step S3: Combined output AC current reference amplitude I Ampl and output current phase reference value Generate output AC current reference ; Calculate the output AC current reference value AC current at the grid connection point I PCC The difference d3; Step S4: Calculate the voltage modulation signal of the full-bridge DC / AC converter based on the difference d3 U m , to control the single-phase cascade H-bridge energy storage converter.

[0008] Preferably, based on the average value of the capacitor voltage u c_ave Calculation of the output AC current reference amplitude of a single-phase cascaded H-bridge energy storage converter I Ampl , including: Calculate the average capacitor voltage uc_ave With capacitor voltage reference value u c_ref The difference d1 is processed by the double notch filter and the PI controller in turn to obtain the output AC current reference amplitude I Ampl , the formula is as follows: ; In the formula, s is the Lagrangian operator, and are the notch coefficients of the double frequency notch filter, is the notch frequency, K P1 is the proportional coefficient of the voltage outer loop PI control, K I1 is the integral coefficient of the voltage outer loop PI control.

[0009] Preferably, based on the reactive power Q ac Calculate the output current phase reference value , including: Calculate output reactive power Q ac Reactive power reference value Q ref The difference d2 is processed by the PI controller to obtain the output current phase correction value of the single-phase cascade H-bridge energy storage converter. ; The AC voltage at the grid point U PCC Perform digital phase-locked loop processing to obtain voltage phase signal ; The output current phase correction value and voltage phase signal Phase superposition to obtain the output current phase reference value .

[0010] Preferably, step S4 specifically includes: The difference d3 is quasi-PR controlled and then compared with the AC voltage at the grid point. U PCC Phase superposition to obtain the voltage modulation signal of the full-bridge DC / AC converter U m , to control the single-phase cascade H-bridge energy storage converter, the formula is as follows: ; In the formula, K P is the proportional gain coefficient of the quasi-PR control, K R is the complex coefficient of the resonant gain of the quasi-PR control, is the cut-off frequency, is the resonant frequency.

[0011] further, N Each energy storage battery adopts dual-loop control charging and discharging, including: For i submodules to calculate the output power of the energy storage battery P Bati ; Calculate the output power reference value P refi Subtract output power P Bati The difference d4 is used to obtain the current inner loop current reference value through PI control. I refi , the formula is as follows: ; In the formula, K P3 is the proportional coefficient of the power outer loop PI control, K I3 is the integral coefficient of the power outer loop PI control; Calculate the current reference value of the current inner loop I refi Subtract the energy storage battery output current I Bati The difference d5 is processed by the PI controller to generate a duty cycle signal D i , to control the half-bridge DC / DC converter.

[0012] Furthermore, it also includes the proportional coefficient of the power outer loop PI control K P3 and the integral coefficient K I3 The calculation method is as follows: Calculate the average capacitor voltage u c_ave With capacitor voltage reference value u c_ref The difference d1 is processed by double notch filtering and then the absolute value is taken. x 1; Based on absolute value x 1 Calculate the proportional coefficient of the power outer loop PI control K P3 and the integral coefficient K I3 , the formula is as follows: ; ; In the formula, a 1. b 1. c 1 and l 1 are all power outer loop proportional conversion coefficients, a 2. b 2. c 2 and l 2 are the power outer loop integral transformation coefficients.

[0013] Furthermore, it also includes i Output power reference value of each submodule P refi The calculation method is as follows: Calculate the energy storage battery SoC value SoC i and N Energy storage battery SoC average value SoC ave The difference d6 is processed by gain and the charge and discharge state is judged and then added to 1 / N Phase superposition, and then with the active power reference value of the single-phase cascade H-bridge energy storage converter P ref Multiply to get the output power reference value P refi , the formula is as follows: ; In the formula, N is the number of submodules, is a symbolic function, when P ref >0, the value is 1, when P ref <0, the value is -1; K SoC is the gain equalization coefficient.

[0014] Furthermore, the gain equalization coefficient K SoC The calculation method is as follows: Sort descending N Energy storage battery SoC value, all adjacent SoC Difference of values, select the maximum difference d max , calculate the gain equalization coefficient K SoC , the formula is as follows: ; In the formula, a 3. b 3. c 3 andl 3 are gain equalization conversion coefficients, k is the output saturation value.

[0015] Obviously, the technical solution provided by the present invention has a simple structure and is easy to implement. It can achieve the specified power output by controlling the full-bridge DC / AC converter, and effectively reduce the calculation complexity on the basis of realizing power control, which helps to improve the calculation efficiency and has great application value in engineering design. Furthermore, the use of dual-loop control for energy storage batteries can achieve fast SoC balancing and effectively improve the operating stability of the energy storage converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of the topology structure of a single-phase cascaded H-bridge energy storage converter.

[0017] Figure 2 This is a block diagram of the power control strategy for a single-phase cascaded H-bridge energy storage converter.

[0018] Figure 3 Schematic diagram of the output active power and reactive power curve of the single-phase cascade H-bridge energy storage converter.

[0019] Figure 4 Energy storage battery for single-phase cascade H-bridge energy storage converter SoC Block diagram of the balancing control strategy.

[0020] Figure 5 Energy storage battery for single-phase cascade H-bridge energy storage converter SoC Equalization coefficient generation block diagram.

[0021] Figure 6 This is a block diagram of the dual-loop control strategy for charging and discharging the energy storage battery of a single-phase cascade H-bridge energy storage converter.

[0022] Figure 7 Single-phase cascade H-bridge energy storage converter is put into use SoC Balanced control energy storage battery SoC Schematic diagram of the change curve.

[0023] Figure 8 A block diagram is provided for generating the outer loop coefficient of the energy storage battery charging and discharging power considering the capacitor voltage fluctuation for the single-phase cascade H-bridge energy storage converter.

[0024] Fig. 9 Single-phase cascade H-bridge energy storage converter SoC Schematic diagram of capacitor voltage value variation curve when balancing control does not consider capacitor voltage fluctuation suppression control strategy.

[0025] Fig.10 Single-phase cascade H-bridge energy storage converter SoC Schematic diagram of capacitor voltage value variation curve considering capacitor voltage fluctuation suppression control strategy for balancing control. DETAILED DESCRIPTION

[0026] Hereinafter, the technical solution provided by the present invention will be further elaborated in combination with embodiments and drawings.

[0027] Embodiment 1: The topology structure of the single-phase cascade H-bridge energy storage converter in this embodiment is as follows: Figure 1 The specific system parameters are shown in Table 1.

[0028] Table 1 Single-phase cascade H-bridge energy storage converter system parameters .

[0029] Figure 1 In the figure, FB stands for Full Bridge.

[0030] This implementation method first models and analyzes the single-phase cascade H-bridge energy storage converter, and then designs a power control strategy based on the functional requirements of the single-phase cascade H-bridge energy storage converter for specified power output. The control strategy block diagram is shown in Figure 2 shown.

[0031] The specific process is: The capacitor voltage of each submodule of the single-phase cascade H-bridge energy storage converter u ci ( i =1,2,..., N ) and calculate the average value to get the average capacitor voltage u c_ave , the formula is as follows: ; In the formula, N is the number of submodules; The average value of the capacitor voltage u c_ave and capacitor voltage reference value u c_ref The difference is processed by the double frequency notch filter and then processed by the PI controller to obtain the output AC current reference amplitude of the single-phase cascade H-bridge energy storage converter. I Ampl , the formula is as follows: ; In the formula, s is the Lagrangian operator, and are the notch coefficients of the double frequency notch filter, is the notch frequency, K P1 is the proportional coefficient of the voltage outer loop PI control, K I1is the integral coefficient of the voltage outer loop PI control.

[0032] Calculate the output reactive power of the single-phase cascade H-bridge energy storage converter Q ac , and the reactive power reference value Q ref The output current phase correction value of the cascaded H-bridge energy storage converter is obtained by making a difference and processing it with the PI controller. , phase correction value The AC voltage at the grid point is processed by a digital phase-locked loop (PLL). U PCC The voltage phase signal obtained After superposition, the output current phase reference value is obtained , the formula is as follows: ; In the formula, K P1 is the proportional coefficient of the reactive power outer loop PI control, K I1 It is the integral coefficient of reactive power outer loop PI control.

[0033] Output AC current reference amplitude I Ampl The output current phase reference value Combined to generate output AC current reference value (i.e. the amplitude is I Ampl , the phase is Current value) and the output AC current of the cascaded H-bridge energy storage converter I PCC After the difference is made, the AC voltage is superimposed after being processed by the quasi-PR controller U PCC Get the voltage modulation signal of the full-bridge DC / AC converter in the cascaded H-bridge energy storage converter U m , the formula is as follows: ; In the formula, K P is the proportional gain coefficient of the quasi-PR control, K R is the complex coefficient of the resonant gain of the quasi-PR control, is the cut-off frequency, is the resonant frequency.

[0034] The schematic diagram of the output active power and reactive power curve of the single-phase cascade H-bridge energy storage converter is as follows: Figure 3 shown.

[0035] Furthermore, to realize the cascade H-bridge energy storage converter energy storage battery SoC Balanced control also requires the addition of a dual-loop control strategy for charging and discharging energy storage batteries SoC Balance control strategy, specifically:

[0036] Calculate the entire single-phase cascade H-bridge energy storage converter SoC average value SoC ave , the formula is as follows: ; like Figure 4 As shown, for each energy storage battery in each submodule, SoC value SoC i With the average SoC ave Do the difference processing, after the gain link processing and judging the charge and discharge status, superimpose 1 / N , N is the number of submodules and the active power reference value of the cascaded H-bridge energy storage converter P ref Multiply to get the reference value of the energy storage battery output power of each submodule P refi , the formula is as follows: ; In the formula, K SoC is the gain equalization coefficient; is a symbolic function, when P ref >0, the value is 1, when P ref <0, the value is -1.

[0037] Gain equalization coefficient of the gain link K SoC Generate a block diagram such as Figure 5 Specifically, its value is calculated by the following steps: SoC Arrange in descending order from large to small, make the difference between two adjacent values, and select the maximum difference d max , the corresponding gain equalization coefficient is obtained through mathematical calculation K SoC , to achieve SoC Fast equalization.

[0038] Specifically, the gain equalization coefficient K SoC The calculation formula is as follows: ; In the formula,a 3. b 3. c 3 and l 3 are gain equalization conversion coefficients, k is the output saturation value.

[0039] Furthermore, the dual-loop control strategy for charging and discharging the energy storage battery consists of an outer power loop and an inner current loop. The control strategy block diagram is shown in Figure 6 The power outer loop first calculates the output power of each submodule battery according to the power relationship P Bati , the formula is as follows: ; In the formula, U Bati and I Bati are the output voltage and output current of each submodule battery respectively.

[0040] Output power reference value P refi The difference is subtracted and the current reference value of the inner current loop is output through the power outer loop PI controller I refi , the formula is as follows: ; In the formula, K P3 and K I3 They are the proportional coefficient and integral coefficient of the power outer loop PI control respectively.

[0041] Current reference value I refi Subtract the submodule battery output current I Bati The difference between the two is used to generate the duty cycle signal of the half-bridge DC / DC converter in the cascaded H-bridge energy storage converter through the PI controller. D i , the formula is as follows: ; In the formula, K P4 and K I4 They are the proportional coefficient and integral coefficient of the current inner loop PI control respectively.

[0042] Through the duty cycle signal D i To realize the single-phase cascade H-bridge energy storage converter submodule battery SoC Average for the whole system SoC Zero-static tracking to achieve energy storage battery SoCBalance control.

[0043] SoC Balanced control energy storage battery SoC The schematic diagram of the change curve is as follows Figure 7 shown.

[0044] When investing in energy storage batteries SoC After the balanced control strategy is adopted, the submodule capacitor voltage is prone to large fluctuations, resulting in overvoltage. Therefore, the present invention introduces a dual-loop control strategy for energy storage battery charging and discharging that takes capacitor voltage fluctuations into consideration to suppress capacitor voltage overvoltage. K P3 With the integral coefficient K I3 Generate a block diagram such as Figure 8 As shown, it is calculated by the following steps: Average capacitor voltage u c_ave , and the capacitor voltage reference value u c_ref The difference is processed by the double frequency notch filter and the absolute value is taken. The obtained value is transformed by mathematics to obtain the proportional coefficient and K P3 Integration coefficient K I3 Specifically, the calculation formula is as follows: ; ; In the formula, a 1. b 1. c 1 and l 1 are all power outer loop proportional conversion coefficients, a 2. b 2. c 2 and l 2 are the power outer loop integral transformation coefficients.

[0045] Among them, the single-phase cascade H-bridge energy storage converter SoC The capacitor voltage value change curve of the balanced control strategy without considering the capacitor voltage fluctuation suppression control strategy is as follows Fig. 9 As shown in the figure, the capacitor voltage value change curve considering the capacitor voltage fluctuation suppression control strategy is as follows Fig.10 shown.

[0046] In summary, the technical solution provided by the present invention has a simple structure and is easy to implement. It can achieve the specified power output by controlling the full-bridge DC / AC converter, and effectively reduce the calculation complexity on the basis of realizing power control, which helps to improve the calculation efficiency and has great application value in engineering design. Furthermore, the dual-loop control of the energy storage battery can achieve SoC Rapid balancing effectively improves the operating stability of the energy storage converter; PI control considering capacitor voltage fluctuations can avoid capacitor voltage overvoltage problems during power switching; SoC The gain equalization coefficient calculated by the value K SoC , based on the gain equalization coefficient K SoC Obtain the output power reference value P refi ,yes SoC Further guarantee of rapid balance.

Claims

1. A control method based on a single-phase cascaded H-bridge energy storage converter, characterized in that: The single-phase cascade H-bridge energy storage converter comprises N sub-modules connected in series; in the sub-modules, the energy storage battery is connected to the full-bridge DC / AC converter via a half-bridge DC / DC converter; wherein, N ≥2; The following steps are involved: Step S1: Measure the capacitor voltage of each submodule u ci , calculate the average capacitor voltage u c_ave ;Measure the reactive power output of a single-phase cascaded H-bridge energy storage converter Q ac ;in, i =1,2,..., N ; Step S2: Based on the average value of capacitor voltage u c_ave Calculation of the output AC current reference amplitude of a single-phase cascaded H-bridge energy storage converter I Ampl ; Based on reactive power Q ac Calculate the output current phase reference value ; Step S3: Combined output AC current reference amplitude I Ampl and output current phase reference value Generate output AC current reference ; Calculate the output AC current reference value AC current at the grid connection point I PCC The difference d3; Step S4: Calculate the voltage modulation signal of the full-bridge DC / AC converter based on the difference d3 U m , to control the single-phase cascade H-bridge energy storage converter.

2. A control method based on a single-phase cascaded H-bridge energy storage converter as claimed in claim 1, characterized in that: The average value of the capacitor voltage u c_ave Calculation of the output AC current reference amplitude of a single-phase cascaded H-bridge energy storage converter I Ampl , specifically including: Calculate the average capacitor voltage u c_ave With capacitor voltage reference value u c_ref The difference d1 is processed by the double notch filter and the PI controller in turn to obtain the output AC current reference amplitude I Ampl , the formula is as follows: ； In the formula, s is the Lagrangian operator, and They are the notch coefficients of the double frequency notch filter. is the notch frequency, K P1 is the proportional coefficient of the voltage outer loop PI control, K I1 is the integral coefficient of the voltage outer loop PI control.

3. A control method based on a single-phase cascaded H-bridge energy storage converter as claimed in claim 1, characterized in that: The reactive power based Q ac Calculate the output current phase reference value , including: Calculate output reactive power Q ac and reactive power reference Q ref The difference d2 is processed by the PI controller to obtain the output current phase correction value of the single-phase cascade H-bridge energy storage converter. ; The AC voltage at the grid point U PCC Perform digital phase-locked loop processing to obtain voltage phase signal ; The output current phase correction value and voltage phase signal Phase superposition to obtain the output current phase reference value .

4. A control method based on a single-phase cascaded H-bridge energy storage converter as claimed in claim 1, characterized in that: Step S4 specifically includes: The difference d3 is controlled by quasi-PR and then compared with the AC voltage at the grid connection point. U PCC Phase superposition to obtain the voltage modulation signal of the full-bridge DC / AC converter U m , to control the single-phase cascade H-bridge energy storage converter, the formula is as follows: ； In the formula, K P is the proportional gain coefficient of the quasi-PR control, K R is the complex coefficient of the resonant gain of the quasi-PR control, is the cut-off frequency, is the resonant frequency.

5. A control method based on a single-phase cascaded H-bridge energy storage converter as claimed in claim 1, characterized in that: N Each energy storage battery adopts dual-loop control charging and discharging, including: For i submodules to calculate the output power of the energy storage battery P Bati ; Calculate the output power reference value P refi Subtract output power P Bati The difference d4 is used to obtain the current inner loop current reference value through PI control. I refi , the formula is as follows: ； In the formula, K P3 is the proportional coefficient of the power outer loop PI control, K I3 is the integral coefficient of the power outer loop PI control; Calculate the current reference value of the current inner loop I refi Subtract the output current of the energy storage battery I Bati The difference d5 is processed by the PI controller to generate a duty cycle signal D i , to control the half-bridge DC / DC converter.

6. A control method based on a single-phase cascaded H-bridge energy storage converter as claimed in claim 5, characterized in that: It also includes the proportional coefficient of the power outer loop PI control K P3 and the integral coefficient K I3 The calculation method is as follows: Calculate the average capacitor voltage u c_ave With capacitor voltage reference value u c_ref The difference d1 is processed by double notch filtering and then the absolute value is taken. x 1; Based on absolute value x 1 Calculate the proportional coefficient of the power outer loop PI control K P3 and the integral coefficient K I3 , the formula is as follows: ； ； In the formula, a 1. b 1. c 1 and l 1 are all power outer loop proportional conversion coefficients, a 2. b 2. c 2 and l 2 are the power outer loop integral transformation coefficients.

7. A control method based on a single-phase cascaded H-bridge energy storage converter as claimed in claim 5, characterized in that: Also includes i Output power reference value of each submodule P refi The calculation method is as follows: Calculate the energy storage battery SoC value SoC i and N Energy storage battery SoC average value SoC ave The difference d6 is processed by gain and the charge and discharge state is judged and then added to 1 / N Phase superposition, and then with the active power reference value of the single-phase cascade H-bridge energy storage converter P ref Multiply to get the output power reference value P refi , the formula is as follows: ； In the formula, N is the number of submodules; is a symbolic function, when P ref >0, the value is 1, when P ref <0, the value is -1; K SoC is the gain equalization coefficient.

8. A control method based on a single-phase cascaded H-bridge energy storage converter as claimed in claim 7, characterized in that: Also includes gain equalization coefficients K SoC The calculation method is as follows: Sort descending N Energy storage battery SoC value, all adjacent SoC Difference of values, select the maximum difference d max , calculate the gain equalization coefficient K SoC , the formula is as follows: ； In the formula, a 3. b 3. c 3 and l 3 are gain equalization conversion coefficients, k is the output saturation value.

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