A Control Method Based on a Single-Phase Cascade H-Bridge Energy Storage Inverter

Abstract

The present invention discloses a control method based on a single-phase cascaded H-bridge energy storage converter, which relates to the technical field of power electronic converters. The method includes calculating the average value of the capacitor voltage and the output reactive power; calculating the reference amplitude of the output alternating current based on the average value of the capacitor voltage; calculating the reference value of the output current phase based on the reactive power; combining the reference amplitude of the output alternating current and the reference value of the output current phase to generate a reference value of the output alternating current; calculating the difference between the reference value of the output alternating current and the alternating current at the grid connection point; calculating the voltage modulation signal of the full-bridge DC / AC converter based on the difference, and controlling the single-phase cascaded H-bridge energy storage converter. The method has a simple structure and is easy to implement. It can achieve a specified power output by controlling the full-bridge DC / AC converter, and effectively reduces 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.

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:

[0004] (1) The energy storage battery is directly connected in parallel with the submodule capacitor;

[0005] (2) The energy storage battery is connected in parallel with the submodule capacitor through a DC / DC converter.

[0006] 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.

[0007] 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

[0008] 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 rapid equalization of (State Of Charge, SOC). This control method has a simple structure and is easy to implement, and has great application value in engineering design.

[0009] Specifically, a control method based on a single-phase cascaded H-bridge energy storage converter has the following technical solutions:

[0010] The single-phase cascaded 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 through a half-bridge DC / DC converter; among them, N ≥2;

[0011] The control method includes the following steps:

[0012] Step S1: Measure the capacitor voltage of each sub-module u ci , calculate the average value of the capacitor voltage u c_ave ; Measure the reactive power Q ac output by the single-phase cascaded H-bridge energy storage converter; among them, i =1,2,... N ;

[0013] Step S2: Based on the average value of the capacitor voltage u c_ave calculate the reference amplitude I Ampl of the output AC current of the single-phase cascaded H-bridge energy storage converter;

[0014] Based on the reactive power Q ac calculate the reference value of the output current phase;

[0015] Step S3: Combine the reference amplitude I Ampl of the output AC current and the reference value of the output current phase to generate the reference value of the output AC current; Calculate the difference d between the reference value I PCC of the output AC current and the grid-connected AC current 3 ;

[0016] Step S4: Based on the difference d 3 calculate the voltage modulation signal U m of the full-bridge DC / AC converter to control the single-phase cascaded H-bridge energy storage converter.

[0017] Preferably, based on the average value of the capacitor voltageu c_ave Calculate the reference amplitude of the output AC current of the single-phase cascaded H-bridge energy storage converter I Ampl , specifically including:

[0018] Calculate the average value of the capacitor voltage u c_ave The difference d from the reference value of the capacitor voltage u c_ref is obtained, and the difference d 1 is processed by a double-notch filter and a PI controller in sequence to obtain the reference amplitude of the output AC current 1 , and the formula is as follows: I Ampl , as follows:

[0019] ;

[0020] In the formula, s is the Laplace operator, and are both 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.

[0021] Preferably, based on the reactive power Q ac calculate the reference value of the output current phase , specifically including:

[0022] Calculate the output reactive power Q ac The difference d from the reference value of the reactive power Q ref is obtained, and the difference d 2 is processed by a PI controller to obtain the correction value of the output current phase of the single-phase cascaded H-bridge energy storage converter 2 ; ;

[0023] Perform digital phase-locked loop processing on the grid-connected AC voltage U PCC to obtain the voltage phase signal ;

[0024] Superimpose the correction value of the output current phase and the voltage phase signal to obtain the reference value of the output current phase .

[0025] Preferably, step S4 specifically includes:

[0026] After subjecting the difference d 3 to quasi-PR control and superimposing it on the AC grid-connected voltage U PCC the voltage modulation signal of the full-bridge DC / AC converter is obtained U m to control the single-phase cascaded H-bridge energy storage converter. The formula is as follows:

[0027] ;

[0028] In the formula, K P is the proportional gain coefficient of the quasi-PR control, K R is the complex resonance gain coefficient of the quasi-PR control, is the cut-off frequency, is the resonance frequency.

[0029] Furthermore, N the energy storage batteries are controlled for charging and discharging using a dual-loop control, which specifically includes:

[0030] For the i th sub-module, calculate the output power of the energy storage battery P Bati ;

[0031] Calculate the reference value of the output power P refi subtract the output power P Bati to obtain the difference d 4 and subject the difference d 4 to PI control to obtain the reference current of the inner current loop I refi . The formula is as follows:

[0032] ;

[0033] In the formula, K P3 is the proportional coefficient of the PI control of the outer power loop, K I3 is the integral coefficient of the PI control of the outer power loop;

[0034] Calculate the difference between the reference current of the inner current loop I refi and the output current of the energy storage battery I Bati to obtain the difference d 5 and subject the difference d 5 to processing by a PI controller to generate a duty cycle signal D i to control the half-bridge DC / DC converter.

[0035] Furthermore, it also includes the proportional coefficient of the outer power loop PI control K P3 and the integral coefficient K I3 The calculation method is as follows:

[0036] Calculate the average value of the capacitor voltage u c_ave and the difference d u c_ref from the capacitor voltage reference value 1 Then, take the absolute value after processing the difference d 1 through double notch filtering in sequence x 1 ;

[0037] Based on the absolute value x 1 calculate the proportional coefficient K P3 and the integral coefficient K I3 of the outer power loop PI control. The formulas are as follows:

[0038] ;

[0039] ;

[0040] In the formula, a 1 , b 1 , c 1 and l 1 are all proportional transformation coefficients of the outer power loop, a 2 , b 2 , c 2 and l 2 are all integral transformation coefficients of the outer power loop.

[0041] Furthermore, it also includes the calculation method of the output power reference value i of the P refi th sub-module. The specific method is as follows:

[0042] Calculate the SoC value SoC i of the energy storage battery N and the difference d SoC from the average value SoC ave of the6 ; After the difference d 6 is processed by gain and the charge-discharge state is judged, it is superimposed with 1 / N and then multiplied by the active power reference value of the single-phase cascaded H-bridge energy storage converter P ref to obtain the output power reference value P refi . The formula is as follows:

[0043] ;

[0044] In the formula, N is the number of sub-modules, is the sign function. When P ref > 0, the value is 1. When P ref < 0, the value is -1; K SoC is the gain equalization coefficient.

[0045] Furthermore, it also includes the calculation method of the gain equalization coefficient K SoC , specifically:

[0046] Arrange the N values of the energy storage batteries in descending order, take the difference between all adjacent SoC values, and select the maximum difference SoC max d SoC , and calculate the gain equalization coefficient K 3 . The formula is as follows:

[0047] ;

[0048] In the formula, a 3 , b 3 , c 3 and l 3 are all gain equalization transformation coefficients, k is the output saturation value.

[0049] Obviously, the technical solution provided by the present invention has a simple structure and is easy to implement. It can achieve 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 double-loop control of the energy storage battery can achieve fast SoC equalization and effectively improve the operation stability of the energy storage converter. Description of the Drawings

[0050] Figure 1 It is a schematic diagram of the topology of a single - phase cascaded H - bridge energy storage converter.

[0051] Figure 2 It is a block diagram of the power control strategy of a single - phase cascaded H - bridge energy storage converter.

[0052] Figure 3 It is a schematic diagram of the curves of the active power and reactive power output of a single - phase cascaded H - bridge energy storage converter.

[0053] Figure 4 It is for the energy storage battery of a single - phase cascaded H - bridge energy storage converter SoC Block diagram of the equalization control strategy.

[0054] Figure 5 It is for the energy storage battery of a single - phase cascaded H - bridge energy storage converter SoC Block diagram for generating the equalization coefficient.

[0055] Figure 6 It is a block diagram of the charge - discharge double - loop control strategy for the energy storage battery of a single - phase cascaded H - bridge energy storage converter.

[0056] Figure 7 It is for the single - phase cascaded H - bridge energy storage converter to be put into SoC Equalization control of the energy storage battery SoC Schematic diagram of the change curve.

[0057] Figure 8 It is a block diagram for generating the outer - loop coefficient of the charge - discharge power of the energy storage battery considering the capacitor voltage fluctuation of a single - phase cascaded H - bridge energy storage converter.

[0058] Figure 9 It is for a single - phase cascaded H - bridge energy storage converter SoC Schematic diagram of the change curve of the capacitor voltage value of the equalization control without considering the suppression control strategy of capacitor voltage fluctuation.

[0059] Figure 10 It is for a single - phase cascaded H - bridge energy storage converter SoC Schematic diagram of the change curve of the capacitor voltage value of the equalization control considering the suppression control strategy of capacitor voltage fluctuation. Specific implementation manners

[0060] Hereinafter, the technical solutions provided by the present invention will be further elaborated in detail in conjunction with embodiments and the accompanying drawings.

[0061] Embodiment 1:

[0062] In this embodiment, the topology of the single - phase cascaded H - bridge energy storage converter is as Figure 1 shown, and the specific system parameters are shown in Table 1.

[0063] Table 1 System parameter table of single - phase cascaded H - bridge energy storage converter

[0064] 。

[0065] Figure 1 In it, FB means Full Bridge, i.e., full bridge.

[0066] This implementation method first models and analyzes the single-phase cascaded H-bridge energy storage converter, and then designs a power control strategy according to the functional requirements of the specified power output of the single-phase cascaded H-bridge energy storage converter. The control strategy block diagram is as Figure 2 shown.

[0067] The specific process is as follows:

[0068] Sum the capacitor voltages of each sub-module of the single-phase cascaded H-bridge energy storage converter u ci ( i = 1, 2,..., N )and calculate the average value to obtain the average capacitor voltage u c_ave . The formula is as follows:

[0069] ;

[0070] In the formula, N is the number of sub-modules;

[0071] Subtract the average capacitor voltage u c_ave from the reference value u of the capacitor voltage c_ref , process it through a second-harmonic notch filter, and then process it through a PI controller to obtain the reference amplitude I Ampl of the AC current output by the single-phase cascaded H-bridge energy storage converter. The formula is as follows:

[0072] ;

[0073] In the formula, s is the Laplace operator, and are both notch coefficients of the second-harmonic 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.

[0074] Calculate the reactive power Q ac output by the single-phase cascaded H-bridge energy storage converter, and compare it with the reference value of the reactive power Q refTake the difference, and after being processed by a PI controller, obtain the phase correction value of the output current of the cascaded H-bridge energy storage converter. , the phase correction value is superimposed on the grid-connected AC voltage processed by a digital phase-locked loop (PLL) U PCC to obtain the voltage phase signal and then superimposed to obtain the reference value of the output current phase , and the formula is as follows:

[0075] ;

[0076] In the formula, K P1 is the proportional coefficient of the PI control of the reactive power outer loop, K I1 is the integral coefficient of the PI control of the reactive power outer loop.

[0077] The reference amplitude of the output AC current I Ampl and the reference value of the output current phase are combined to generate the reference value of the output AC current (that is, the current value with an amplitude of I Ampl and a phase of ) is subtracted from the output AC current of the cascaded H-bridge energy storage converter I PCC and then, after being processed by a quasi-PR controller, superimposed on the AC voltage U PCC to obtain the voltage modulation signal of the full-bridge DC / AC converter in the cascaded H-bridge energy storage converter U m , and the formula is as follows:

[0078] ;

[0079] In the formula, K P is the proportional gain coefficient of the quasi-PR control, K R is the resonant gain complex coefficient of the quasi-PR control, is the cut-off frequency, is the resonant frequency.

[0080] The schematic diagram of the active power and reactive power curves of the single-phase cascaded H-bridge energy storage converter is as Figure 3 shown.

[0081] Further, to achieve the balanced control of the energy storage battery of the cascaded H-bridge energy storage converter SoC an energy storage battery charge and discharge dual-loop control strategy needs to be addedSoC Balanced control strategy, specifically:

[0082] Calculate the average value of the entire single-phase cascaded H-bridge energy storage converter SoC Average value SoC ave , the formula is as follows:

[0083] ;

[0084] As Figure 4 shown, for the energy storage battery in each sub-module, subtract the SoC value SoC i of each energy storage battery from the average value SoC ave . After processing through the gain link and judging the charge and discharge state, superimpose 1 / N , N where P ref is the number of sub-modules, and multiply it by the active power reference value P refi of the cascaded H-bridge energy storage converter to obtain the output power reference value

[0085] ;

[0086] In the formula, K SoC is the gain balance coefficient; is the sign function. When P ref > 0, the value is 1. When P ref < 0, the value is -1.

[0087] The gain balance coefficient K SoC of the gain link is generated as shown in Figure 5 . Specifically, its value is calculated by the following steps: Arrange the SoC of each energy storage battery in descending order from large to small, subtract the adjacent two values, and select the largest difference d max obtained. Through mathematical calculation, the corresponding gain balance coefficient K SoC is obtained to achieve SoC fast balance.

[0088] Specifically, the calculation formula of the gain balance coefficient K SoC is as follows:

[0089] ;

[0090] In the formula, a 3 , b 3 , c 3 and l 3 are all gain equalization transformation coefficients, k is the output saturation value.

[0091] Furthermore, the charge-discharge double-loop control strategy of the energy storage battery consists of a power outer loop and a current inner loop, and its control strategy block diagram is as shown in Figure 6 . The power outer loop first calculates the output power P Bati of each sub-module battery according to the power relationship. The formula is as follows:

[0092] ;

[0093] In the formula, U Bati and I Bati are the output voltage and output current of each sub-module battery respectively.

[0094] The difference obtained by subtracting the output power reference value P refi from the output power reference value I refi is output as the current reference value

[0095] of the current inner loop through the PI controller of the power outer loop. The formula is as follows:

[0096] In the formula, K P3 and K I3 are the proportional coefficient and integral coefficient of the PI control of the power outer loop respectively.

[0097] The difference obtained by subtracting the output current I refi of the sub-module battery from the current reference value I Bati generates the duty cycle signal D i of the half-bridge DC / DC converter in the cascaded H-bridge energy storage converter through the PI controller. The formula is as follows:

[0098] ;

[0099] In the formula, K P4 and K I4They are the proportional coefficient and integral coefficient of the current inner-loop PI control respectively.

[0100] Through the duty cycle signal D i To achieve the battery of the sub-module of the single-phase cascaded H-bridge energy storage converter SoC Average the whole system SoC Of the static error-free tracking, so as to realize the SoC Balanced control.

[0101] SoC Balanced control of the energy storage battery SoC The schematic diagram of the change curve is as Figure 7 Shown.

[0102] When the balanced control strategy is applied to the energy storage battery SoC After that, the capacitor voltage of the sub-module is prone to large fluctuations and overvoltage phenomenon. Therefore, the present invention introduces a double-loop control strategy for charging and discharging of the energy storage battery considering the capacitor voltage fluctuation to suppress the overvoltage of the capacitor voltage. Among them, for the power outer loop part, the proportional coefficient K P3 And the integral coefficient K I3 The generation block diagram is as Figure 8 Shown, specifically calculated by the following steps:

[0103] The average value of the capacitor voltage u c_ave , and the reference value of the capacitor voltage u c_ref After subtraction and processing by a double-frequency notch filter and taking the absolute value, the obtained value is respectively obtained through mathematical transformation to obtain the proportional coefficient and K P3 Integral coefficient K I3 . Specifically, the calculation formula is as follows:

[0104] ;

[0105] ;

[0106] In the formula, a 1 , b 1 , c 1 And l 1 Are all proportional transformation coefficients of the power outer loop, a 2 , b 2 , c2 and l 2 are both integral transformation coefficients of the power outer loop.

[0107] Among them, for the single-phase cascaded H-bridge energy storage converter SoC The change curve of the capacitor voltage value of the equalization control without considering the capacitor voltage fluctuation suppression control strategy is as Figure 9 shown, and the change curve of the capacitor voltage value considering the capacitor voltage fluctuation suppression control strategy is as Figure 10 shown.

[0108] In summary, the technical solution provided by the present invention has a simple structure and is easy to implement. It can achieve a specified power output by controlling the full-bridge DC / AC converter, and effectively reduce the computational complexity on the basis of realizing power control, which helps to improve the computational efficiency and has great application value in engineering design; further, the double-loop control of the energy storage battery can achieve SoC fast equalization and effectively improve the operation stability of the energy storage converter; the PI control considering the capacitor voltage fluctuation can avoid the overvoltage problem of the capacitor voltage during the power switching process; the gain equalization coefficient SoC calculated based on the K SoC value of N energy storage batteries, and the output power reference value K SoC obtained based on the gain equalization coefficient P refi is SoC a further guarantee for fast equalization.

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; in, 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 inner loop current 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; Proportional coefficient of 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.

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 , specifically 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 .

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: 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.

6. A control method based on a single-phase cascaded H-bridge energy storage converter as claimed in claim 5, 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.

Images