Control method of storage battery energy storage power management system

Abstract

The invention discloses a control method of a storage battery energy storage power management system in the technical field of storage battery power management, which comprises the following steps: S1, when the system is connected with a power supply, a power conversion circuit firstly operates in a Boost mode so as to identify the state of a battery; converting to a Buck mode or other adaptive modes according to the correlation between the battery pack and the bus voltage; s2, in the process of outputting the duty ratio by the DSP controller, introducing a 9-order pseudo-random binary sequence signal; by means of a system identification method, the impedance frequency domain characteristics of the battery port variables are expanded and analyzed, so that the actual state of the battery is judged; s3, PI control is carried out on the inductive current and the output voltage, the smaller value in the output duty ratio of the voltage loop and the current loop is selected to be superposed with the PRBS signal, and then the power conversion circuit is controlled, through the technical scheme, efficient management and control over the battery power can be achieved, and the stability and reliability of system operation are enhanced.

Description

Technical Field

[0001] The present invention relates to the technical field of battery power management, and particularly relates to a control method for a battery energy storage power management system. Background Art

[0002] In the battery energy storage power management system, accurate and efficient control measures play a decisive role in the performance of the system. The previous control mode of the power conversion circuit has significant drawbacks. Facing the dynamic changes of the battery state and the fluctuations of the input and output voltages, it is difficult to achieve flexible and accurate switching of the working mode, which undoubtedly greatly reduces the operating efficiency of the entire system. In addition, in the reasonable allocation of battery power, due to the lack of effective management planning, the potential energy of each battery pack cannot be fully exploited, resulting in a large amount of energy wasted.

[0003] In terms of the identification of the battery state, the current mainstream methods all expose different degrees of shortcomings. The experimental research methods centered on the battery cycle charge and discharge test not only consume a large amount of resources, have a long test cycle, but also cannot perform online real-time monitoring, and completely cannot meet the urgent need of the system to immediately grasp the battery state. The algorithm-based research methods relying on advanced algorithms, although seemingly advanced, actually require additional dedicated equipment, have a large amount of computation, and the final accuracy is also unsatisfactory, encountering many obstacles in the actual application scenarios. The above problems seriously restrict the popularization and performance improvement of the battery energy storage power management system. Summary of the Invention

[0004] Aiming at the deficiencies in the prior art, the present invention provides a control method for a battery energy storage power management system to solve the problems of inflexible control of the power conversion circuit, unreasonable battery power distribution, and inaccurate battery state identification in the prior art, realize the efficient and stable operation of the system, maximize the utilization of the battery pack energy, and accurately master the battery state.

[0005] The object of the present invention is achieved as follows: A control method for a battery energy storage power management system includes the following steps:

[0006] S1. System initialization and mode switching: After the system is powered on, control the power conversion unit to work in the Boost mode to identify the battery state; after the identification is completed, select the working mode according to the relationship between the minimum battery pack voltage and the bus voltage. If the minimum battery pack voltage is greater than the bus voltage, switch to the Buck mode, otherwise maintain or switch to other appropriate modes;

[0007] S2. Battery state identification: Introduce a 9th-order pseudo-random binary sequence (PRBS) signal to the output duty cycle of the DSP controller. Use the system identification method to analyze the impedance frequency-domain characteristics of the battery port variables, and judge the actual state of the battery according to the variation rules of the amplitude-frequency and phase-frequency characteristics.

[0008] S3. Control system regulation: Perform proportional-integral control on the inductor current and output voltage respectively. Compare the magnitudes of the duty cycles d1 and d2 output by the voltage loop and current loop, select the smaller value, add it to the PRBS signal, and then output it to the power conversion circuit. In the buck mode, according to the transfer function G id1 (s) of the inductor current with respect to the duty cycle and the transfer function G vd1 (s) of the voltage with respect to the duty cycle, perform current inner-loop compensator control; in the boost mode, based on the transfer functions G id2 (s) and G vd2 (s) of the voltage and current with respect to the duty cycle, perform current inner-loop compensator control, so as to realize the transformation of the inductor current of the power conversion circuit within a controllable range and limit the output voltage.

[0009] Furthermore, in S1, in the Boost mode, the switching transistors Q3 and Q4 are driven by a pair of complementary PWM signals, Q2 is turned off, and Q1 is always on; in the Buck mode, the switching transistors Q1 and Q2 are driven by a pair of complementary PWM signals, Q3 is turned off, and Q4 is always on.

[0010] Furthermore, in S2, the 9th-order PRBS signal is generated by a PRBS pattern generator composed of a linear feedback shift register (LFSR) and an exclusive-OR circuit. Its primitive polynomial is X 9 +X 5 +1, that is, the 9th and 5th bits of the register are XORed and then input to the 1st bit of the register, and the 9th bit of the register is used as the output.

[0011] Furthermore, the method of using system identification in S2 specifically includes: collecting the battery output voltage and output current data, sending them to the upper computer for system identification in MATLAB to obtain the impedance frequency-domain curve of the battery port, and comparing it with the historical waveform.

[0012] Furthermore, in S3, the current inner-loop compensator uses a type-II PI compensator with double poles and single zero. Its transfer function is C i1 (s) and C i2 (s) respectively according to the buck mode and boost mode; the voltage outer-loop compensator uses a PI compensator with single zero-pole and single zero, and compensates according to the principle of zero-pole cancellation. The transfer functions are C v1 (s) and C v2 (s) respectively.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0014] By introducing a PRBS signal into the duty cycle output from the DSP controller for battery state identification, the present invention can quickly and accurately judge the actual state of the battery without the need for complex battery cycle charge and discharge tests like traditional experimental methods, nor the need to rely on separate devices and perform a large number of complex calculations like algorithmic methods. In terms of battery power distribution, the master and slave controllers work together to flexibly adjust the output power ratio according to the actual state of the battery pack, avoiding energy waste. In the control and regulation, the control strategies and compensators invented for different working modes enable the system to operate stably under different working conditions, improving the system efficiency and dynamic performance.

[0015] Compared with conventional battery state recognition methods, the present invention is not interfered by the differences between battery samples, does not need to construct a unified battery model, and can more accurately understand the battery state by analyzing the impedance frequency domain curve; at the power distribution level, traditional means are difficult to flexibly change according to the real-time condition of the battery, while the present invention can achieve accurate power distribution and maximize the energy utilization degree of the battery pack; from the perspective of system control, the present invention comprehensively considers multiple factors such as voltage and current, and ensures the stable operation of the system by virtue of reasonable control strategies and the developed compensators, while traditional methods are often unable to cope when dealing with complex working conditions.

[0016] During the operation of the system, the control method of the present invention continuously adjusts the control parameters according to the battery state and system working conditions, making the system operation more stable and efficient. At the same time, by optimizing the control strategy, unnecessary energy consumption is reduced, and the energy utilization efficiency is improved. Moreover, the present invention solves the problem of non-uniform power supply voltage of the controller, simplifies the circuit design, and reduces the system cost investment. Preferably, when constructing the control method, the control parameters can be further optimized. For example, according to different battery characteristics and system operating environments, the proportional coefficient and integral coefficient of the PI controller are dynamically adjusted to achieve better control effects. At the same time, in terms of hardware selection, more suitable power switching tubes, sensors and other devices can be selected according to actual needs to improve the performance and reliability of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained according to the provided drawings without creative efforts.

[0018] Figure 1It is a schematic structural diagram of the battery energy storage power management system of the present invention.

[0019] Figure 2 It is a diagram showing two working states of the circuit in the Buck mode of the present invention.

[0020] Figure 3 It is a diagram showing two working states of the circuit in the Boost mode of the present invention.

[0021] Figure 4 It is a diagram of the 9th-order PRBS code pattern generator of the present invention.

[0022] Figure 5 It is an autocorrelation waveform diagram of the present invention.

[0023] Figure 6 It is a power spectral density diagram of the present invention

[0024] Figure 7 It is a control block diagram in the FSBB identification state of the present invention.

[0025] Figure 8 It is in the buck mode of the present invention G id1 (s) Waveform diagrams before and after compensation.

[0026] Figure 9 It is in the boost mode of the present invention G id1 (s) Waveform diagrams before and after compensation.

[0027] Figure 10 It is a waveform diagram of the voltage outer loop U1 before and after compensation of the present invention.

[0028] Figure 11 It is a waveform diagram of the voltage outer loop U2 before and after compensation of the present invention.

[0029] Figure 12 It is a system dynamic simulation voltage waveform diagram of the present invention.

[0030] Figure 13 It is a system dynamic simulation current waveform diagram of the present invention. Specific embodiments

[0031] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0032] A control method for a battery energy storage power management system includes the following steps:

[0033] S1. System Initialization and Mode Selection: After the system is powered on, the power conversion unit is controlled to operate in the Boost mode to ensure continuous inductor current and realize the identification of the battery state. After the identification is completed, the working mode is selected according to the relationship between the minimum battery pack voltage and the bus voltage. If the minimum battery pack voltage is greater than the bus voltage, the power conversion unit switches to the Buck mode; otherwise, it remains or switches to other appropriate modes (if any). In the Boost mode, the switching transistors Q3 and Q4 are driven by a pair of complementary PWM signals, Q2 is turned off, and Q1 is always on; in the Buck mode, the switching transistors Q1 and Q2 are driven by a pair of complementary PWM signals, Q3 is turned off, and Q4 is always on;

[0034] S2. Battery State Identification: A 9th-order pseudo-random binary sequence (PRBS) signal is introduced into the output duty cycle of the DSP controller. Using the system identification method, the impedance frequency-domain characteristics of the battery port variables are analyzed, and the actual state of the battery is judged according to the variation laws of the amplitude-frequency and phase-frequency; specifically, the battery output voltage and output current data are collected and sent to the host computer for system identification in MATLAB to obtain the impedance frequency-domain curve of the battery port and compare it with the historical waveform; among them, the 9th-order PRBS signal is generated by a PRBS waveform generator composed of a linear feedback shift register (LFSR) and an exclusive-OR circuit, and its primitive polynomial is X 9 +X 5 +1, that is, the 9th and 5th bits of the register are XORed and then input to the 1st bit of the register, and the 9th bit of the register is used as the output;

[0035] S3. Control System Regulation: In the control loop invention, proportional-integral (PI) control is performed on the inductor current and the output voltage respectively. Compare the magnitudes of the duty cycles d1 and d2 output by the voltage loop and the current loop, select the smaller value, add it to the PRBS signal and then output it to the power conversion circuit. In the buck mode, control is performed according to the transfer function of the duty cycle to the inductor current and the transfer function of the duty cycle to the voltage; in the boost mode, control is performed according to the transfer function of the duty cycle to the voltage and the transfer function of the duty cycle to the current, so as to realize the transformation of the inductor current of the power conversion circuit within a controllable range and limit the output voltage; at the same time, the control parameters are adjusted in real time according to the system operation state to ensure the stable operation of the system.

[0036] The present invention will be further described below with specific examples.

[0037] As Figure 1 shown in the battery energy storage power management system, the following control method is adopted, including the following steps:

[0038] S1. System Initialization and Mode Switching:

[0039] After the system is powered on, when the minimum battery pack voltage is greater than the bus voltage, that is, when voltage reduction is required, the FSBB needs to work in Buck mode.

[0040] In this mode, the switch tubes Q1 and Q2 are driven by a pair of complementary PWM signals to achieve synchronous rectification, reduce diode loss, and improve system efficiency. Q3 is cut off and Q4 is always on. The following is a small signal analysis of the equivalent circuit in Buck mode. To simplify the analysis, it is assumed that the power switch tubes Q1, Q2, Q3, and Q4 are ideal devices, and the inductor L and capacitors C1 and C2 are also ideal devices (the equivalent series resistance is 0):

[0041] In Buck mode, the circuit has two working states: switch Q1 is turned on and switch Q1 is turned off. The corresponding equivalent circuits are as follows: Figure 2 shown.

[0042] According to Kirchhoff's voltage and current laws, it is not difficult to get Figure 2 Formula (1) and formula (2) are derived.

[0043] (1)

[0044] (2)

[0045] When the duty cycle of the PWM signal driving the switch tubes Q1 and Q2 is d, the entire switch state is divided into dT and (1-d)T, which correspond to equations (1) and (2) respectively. The two equations can be combined to obtain equation (3):

[0046] (3)

[0047] It is generally believed that the input voltage is constant within the frequency band of the switching frequency. In order to analyze it in the field of classical control, a small signal disturbance is added near the steady-state value of the duty cycle D, and the instantaneous value variable can be written as:

[0048] (4)

[0049] This will bring about a small perturbation of the remaining state variables, namely:

[0050] (5)

[0051] Substituting equations (4) and (5) into equation (3), we obtain:

[0052] (6)

[0053] Expand it and separate the steady-state variables and small signals. Since the second-order AC small signal is much smaller than the first-order AC small signal, it can be ignored, and we get:

[0054] (7)

[0055] Performing Laplace transform on it, we get formula (8):

[0056] (8)

[0057] After finishing, we can get:

[0058] (9)

[0059] In the present invention, in order to achieve bidirectional power transfer, it is necessary to be able to control the flow direction of the inductor current. To this end, it is also necessary to write out the transfer function of the duty cycle to the inductor current, which can be easily obtained from formula (8):

[0060] (10)

[0061] After the system is powered on, in order to add disturbances to the inductor current when identifying the battery status, the inductor current needs to be continuous. Therefore, the FSBB needs to work in Boost mode.

[0062] In this mode, the switch tubes Q3 and Q4 are driven by a pair of complementary PWM signals to achieve synchronous rectification, reduce diode loss, and improve system efficiency. Q2 is cut off and Q1 is always on. The following is a small signal analysis of the equivalent circuit in Boost mode under ideal conditions. To simplify the analysis, it is assumed that the power switch tubes Q1, Q2, Q3, and Q4 are ideal devices, and the inductor L and capacitors C1 and C2 are also ideal devices (the equivalent series resistance is 0):

[0063] In Boost mode, the circuit is also divided into two working states: switch tube Q3 is turned on and switch tube Q3 is turned off. The corresponding equivalent circuits are as follows: Figure 3 shown.

[0064] From KVL and KCL, we can get:

[0065] (11)

[0066] (12)

[0067] When the duty cycle of the PWM signal driving the switch tubes Q3 and Q4 is d, the entire switch state is divided into dT and (1-d)T, which correspond to equations 3.11 and 3.12 respectively. The two equations can be combined to obtain equation (13):

[0068] (13)

[0069] Next, similarly ignoring the variation of the input voltage, a small-signal perturbation is added near the steady-state value of the duty cycle D, and the instantaneous value variables can be written as:

[0070]

[0071] (14)

[0072]

[0073] Substituting Equation (14) into Equation (13), we get:

[0074] (15)

[0075] Expanding it and separating the steady-state variables and the small-signal. Since the second-order AC small-signal is much smaller than the first-order AC small-signal, it can be ignored, and we get:

[0076] (16)

[0077] Performing a Laplace transform on it, we get:

[0078] (17)

[0079] Rearranging Equation (17) can obtain the transfer functions of the duty cycle with respect to voltage and the duty cycle with respect to current.

[0080] (18)

[0081] S2. Battery state identification:

[0082] Considering that the higher the order, the more complex the iteration in the digital signal processor, so the 9th-order PRBS signal that can sufficiently characterize the battery state is selected in the present invention. The primitive polynomial is X9 + X5 + 1. That is, after performing an exclusive OR operation on the 9th bit and the 5th bit of the register and inputting it to the 1st bit of the register, the 9th bit of the register is also the output of the PRBS9 generator, and the generated PRBS signal waveform is as Figure 4 shown. In order to prove that the number of its "0"s and "1"s conforms to the rules described above, it is necessary to perform an autocorrelation analysis on the number of its waveform points, and the result is as Figure 5 shown. It can be seen from the figure that the number of "0"s and "1"s is basically equal. Next, to prove that its waveform characteristics are similar to white noise and will not cause noise outside the control of the system, it is necessary to verify its power spectral density. Its power spectral density waveform is as Figure 6 shown. It can be found that its frequency spectral density waveform hovers around 0 dB, which is very close to the characteristics of white noise and meets the design requirements.

[0083] S3. Control system regulation:

[0084] In the design of the control loop of the present invention, it is necessary to select a small duty cycle from the output duty cycles of the voltage loop and the current loop. However, this duty cycle cannot be directly output because the battery needs to be identified. Therefore, it is necessary to introduce random fluctuations within a controllable range for its output current and output voltage. However, the added random fluctuations cannot introduce noise to the system. For this purpose, a PRBS signal needs to be introduced on the small duty cycle. The control block diagram of the system in the identification state is as follows Figure 7 shown. Where Gvd(s) is the transfer function of the duty cycle to the output voltage; Gid(s) is the transfer function of the duty cycle to the inductor current; Cv(s) is the voltage controller transfer function; Ci(s) is the current controller transfer function; Hv(s) is the voltage sensor transfer function; Hi(s) is the current sensor transfer function; vo is the output voltage; Vref is the given voltage reference signal, and Iref is the given current reference signal.

[0085] Considering the design of the control system when the FSBB is in different modes, when the FSBB is in the buck mode, the transfer function of the controlled object is as shown in Formulas (9) and (10); when the FSBB is in the boost mode, the transfer function of the controlled object is as shown in Formula 8. Among them, V s = 24V, the switching frequency is 40kHz, the inductor is 100uH, the output capacitor is 100uF, and the load resistance is 10Ω.

[0086] First, the compensator of the current inner loop is designed to compensate G id1 (s) in the buck mode and G id2 (s) in the boost mode. The II-type PI compensator with double poles and single zero is adopted in this design, and the structure of the controller is as shown in Equation (19).

[0087] (19)

[0088] The frequency characteristics of the cascaded system of G id1 (s) and H i1 (s) in the buck mode and the open-loop transfer function after adding the controller are obtained in MATLAB, as shown in Figure 8 shown. It can be found that the crossover frequency of the compensated system is 8.91kHz, and the phase margin is 79.3°, which can meet the dynamic and static performance requirements of the system. The frequency characteristics of the cascaded system of G id2 (s) and H i2 (s) in the boost mode and the open-loop transfer function after adding the controller are as shown in Figure 9 shown. The crossover frequency of the compensated system is 2.06kHz, and the phase margin is 64.5°, which can meet the dynamic and static performance requirements of the system.

[0089] To ensure the suppression of the low-frequency power flow in the bus, the cut-off frequency of the voltage outer loop is reduced, and the phase margin is increased to ensure no overshoot and ringing. The present invention uses a single zero-pole - single zero PI compensator to compensate the voltage outer loop. The structure of the controller is shown in Equation (20), and the compensation is carried out based on the principle of zero-pole cancellation.

[0090] (20)

[0091] Figure 10 and 11 are the waveforms of U1 and U2 before and after compensation respectively. It can be seen that after compensating U1, the crossover frequency is 195 Hz and the phase margin is 78.1°. After compensating U2, the crossover frequency is 95.8 Hz and the phase margin is 97.1°, which can meet the control requirements of the system.

[0092] In the simulation circuit, three groups of batteries with different voltages and their corresponding power conversion units (four-switch Buck-Boost circuits) are set, and independent local controllers for each power unit. The photovoltaic module is used to coordinate the power flow of the system. The method adopted is to suddenly remove the load at 0.25 s and observe the current flow direction. The voltage and current waveforms are as Figure 12 and 13 shown. The waveforms in the figure are the output voltages U1, U2, U3 of the sub-modules, the currents of inductors L1, L2, L3, and the bus voltage U o . By observing the waveforms, it can be found that the system removes the load at 0.25 s, and the output voltages of each sub-module and the bus voltage all show transient jumps. However, under the action of the controller, they quickly return to the set values. To maintain the power balance of the bus, the inductor current reverses, and the energy flows from the DC bus to the battery pack.

[0093] The description of the above embodiments is only used to help understand the method and its core idea of the present invention. It should be noted that for those of ordinary skill in the art of this technology, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A control method for a battery energy storage power management system, characterized in that It includes the following steps: S1. System initialization and mode switching: After the system is powered on, control the power conversion unit to work in the Boost mode to realize the identification of the battery state; After the identification is completed, select the working mode according to the relationship between the minimum battery pack voltage and the bus voltage. If the minimum battery pack voltage is greater than the bus voltage, switch to the Buck mode; otherwise, maintain or switch to other appropriate modes; S2. Battery state identification: Introduce a 9th-order pseudo-random binary sequence (PRBS) signal to the output duty cycle of the DSP controller, and use the system identification method to analyze the impedance frequency-domain characteristics of the battery port variables, and judge the actual state of the battery according to the change rules of the amplitude-frequency and phase-frequency; S3. Control System Regulation: Proportional-integral control is performed on the inductor current and the output voltage respectively. The duty ratios d1 and d2 output by the voltage loop and the current loop are compared, and the smaller value is selected. After adding it to the PRBS signal, it is output to the power conversion circuit; in the buck mode, current inner-loop compensator control is performed according to the transfer function G id1 (s) of the inductor current with respect to the duty ratio and the transfer function G vd1 (s) of the voltage with respect to the duty ratio; in the boost mode, current inner-loop compensator control is performed according to the transfer functions G id2 (s) and G vd2 (s) of the voltage and the current with respect to the duty ratio, so as to realize the transformation of the inductor current of the power conversion circuit within a controllable range and limit the output voltage.

2. The control method of a battery energy storage power management system according to claim 1, characterized in that, In S1, in the Boost mode, the switching transistors Q3 and Q4 are driven by a pair of complementary PWM signals, Q2 is turned off, and Q1 is always on; in the Buck mode, the switching transistors Q1 and Q2 are driven by a pair of complementary PWM signals, Q3 is turned off, and Q4 is always on.

3. The control method of a battery energy storage power management system according to claim 1 or 2, characterized in that, In S2, the 9th-order PRBS signal is generated by a PRBS pattern generator composed of a linear feedback shift register (LFSR) and an exclusive-OR circuit. Its primitive polynomial is X 9 +X 5 +1, that is, the exclusive-OR operation of the 9th and 5th bits of the register is input to the 1st bit of the register, and the 9th bit of the register is used as the output.

4. The control method of a battery energy storage power management system according to claim 1 or 2, characterized in that, The method of using system identification in S2 specifically includes: collecting the battery output voltage and output current data, sending them to the host computer for system identification in MATLAB to obtain the impedance frequency-domain curve of the battery port, and comparing it with the historical waveform.

5. The control method of a battery energy storage power management system according to claim 1 or 2, characterized in that, In S3, the current inner-loop compensator adopts a type-II PI compensator with double poles and single zero, and its transfer functions are C i1 (s) and C i2 (s) respectively according to the buck mode and the boost mode; the voltage outer-loop compensator adopts a PI compensator with single zero-pole and single zero, and compensates according to the principle of zero-pole cancellation, and the transfer functions are C v1 (s) and C v2 (s).

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