An adaptive control method based on active compensation device of constant power load

Abstract

The present invention provides an adaptive control method based on a constant power load active compensation device, which is applicable to the technical field of isolated DC microgrid compensation devices, and comprises the following steps: a control system collects a constant power load input voltage u cpl and input current i cpl ; Determine whether the control system is in a steady state. If the control system is stable, proceed to the subsequent steps to adjust the control parameter R e Make corrections; determine whether the SOC of the battery at the input side of the compensation device is within the allowable range. If it is within the allowable range, then adjust the equivalent load resistance value R e Otherwise, the equivalent load resistance value R e The present invention can effectively improve the stability margin of the system, and at the same time adjust the compensation current by adjusting the slope of the equivalent resistance characteristic curve, thereby avoiding the high loss and low reliability problems under the traditional control strategy.

Description

Technical Field

[0001] The present invention is applicable to the technical field of isolated DC microgrid compensation devices, and specifically is an adaptive control method based on a constant power load active compensation device. Background Art

[0002] Reducing the constant power load and increasing the resistive load are relatively flexible measures to improve the stability margin of the isolated DC microgrid system. However, directly reducing the constant power load or increasing the resistive load will sacrifice user needs and increase unnecessary losses, so it is not practical. Constant power load and resistive load have completely different effects on system stability due to differences in input characteristics. By introducing an external compensation device, the input characteristics of the constant power load can be compensated to change it into the input characteristics corresponding to the resistive load, thereby improving the stability margin of the isolated DC microgrid.

[0003] Regarding the control strategy of the compensation device, the traditional control strategy is easy to implement, but there are the following problems: when the DC bus voltage drops, the constant power load input voltage u under the new steady-state operating point cpl Lower than the rated constant power load input voltage u ucpl_N When the compensation current i comp It will not automatically return to 0, but a negative value, causing the compensation side battery to continue to discharge. When the battery SOC is discharged to the lower limit, the compensation device will exit operation. When the new steady-state operating point u cpl Higher than u cpl_N The battery on the compensation side will be continuously charged, and when it is continuously charged until the SOC reaches the upper limit, the compensation device will exit operation. Therefore, if the compensation current cannot be automatically restored to 0 after the system reaches a new steady-state operating point, so that the battery on the input side of the compensation device exits charging / discharging, the system's working efficiency and operational reliability will be greatly reduced.

[0004] At present, domestic and foreign scholars have done a lot of research on the stability of DC microgrids with constant power loads and proposed many measures. According to the different modes of action, they can be divided into two categories: 1) improving the control strategy of the converter to achieve system additional damping to improve system stability; 2) adding primary equipment to the DC microgrid, such as filters, energy storage devices, compensators, etc., to improve the system stability margin. The first type of measures has a low cost, but is not universal. With the high integration and packaging of equipment, the control strategy in the original equipment cannot be changed at will. If modified, it may have an adverse effect on the equipment or even damage it. Some control strategies require high-performance control chips, which will increase costs. The second type of measures requires external equipment, which will increase system cost and volume. Compared with the first type, there is no need to adjust the control strategy, which will not affect the performance of the original controller. At the same time, the control strategy and working mode of the external equipment are independent of the converter, and can be modularly designed and packaged, which can achieve plug-and-play. Summary of the invention

[0005] In view of the above-mentioned deficiencies in the prior art, the technical problem to be solved by the embodiments of the present invention is to provide an adaptive control method based on a constant power load active compensation device.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0007] An adaptive control method based on a constant power load active compensation device comprises the following steps:

[0008] Step 1: The control system collects the constant power load input voltage u cpl and input current i cpl ;

[0009] Step 2: Determine whether the control system is in a steady state. If the control system is stable, proceed to the subsequent steps to adjust the control parameter R. e make corrections;

[0010] Step 3: Determine whether the SOC of the battery at the input side of the compensation device is within the allowable range. If so, proceed to step 4; otherwise, proceed to step 5.

[0011] Step 4: Equivalent load resistance value R e make corrections;

[0012] Step 5: If the SOC of the battery at the input side of the compensation device is outside the allowable range, the equivalent load resistance value R e make corrections;

[0013] Step 6: Use PI regulator to make the compensation current follow the given value.

[0014] As a further improvement of the present invention: in step 4, the equivalent load resistance value R e The correction steps are:

[0015] 4.1 Equivalent load resistance value R e The current constant power load input voltage steady-state value u cpl0 And the steady-state value of current i cpl0 , calculated according to formula (1),

[0016]

[0017] 4.2 Use variable step length ramp function to make R e Gradually transition from the old value to the new value R e ', when the constant power load is 0, R e Take the upper limit value R e_max , when the constant power load reaches the maximum value, R eTake the lower limit R e_min , R e_min It can be calculated by formula (2):

[0018]

[0019] Where P cpl_max is the maximum value of constant power load, U L is the lower limit of the DC bus voltage allowable range, and the critical value when the step size is switched is R e_c , in R e Value greater than R e_c Use a larger step size to ensure R e The correction speed, in R e Value is less than R e_c Select a smaller step size to avoid system instability caused by too fast compensation current changes. At the same time, set multiple R e_c To achieve a smooth transition of the compensation current from the old value to zero;

[0020] 4.3 Return to step 4.1 and continue to execute steps 4.1 to 4.2. After 3 to 4 iterations, when i comp =0, go to step 4.

[0021] As a further improvement of the present invention: in step 5, the equivalent load resistance value R e The correction steps are:

[0022] 5.1 If the SOC of the battery at the input side of the compensation device is lower than the set lower limit, reduce R e To R e1 , so that the compensation current i comp It becomes as shown in formula (3), actively charging the SOC of the battery on the input side of the compensation device to increase the SOC to within the allowable range; if the SOC of the battery on the input side of the compensation device is higher than the set upper limit, increase R e To R e2 , so that the compensation current i comp It becomes as shown in formula (4), actively discharging the SOC of the battery on the input side of the compensation device to reduce the SOC to within the allowable range;

[0023]

[0024]

[0025] In formula (3) and formula (4), i cpl1 This is the constant power load input current at the initial moment.

[0026] 5.2 Use variable step length ramp function to make R e Transition from old value to new value.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1. The control strategy and working state of the compensation device are independent of each source converter. There is no need to change the control strategy of the source converter. It can be modularly designed to achieve true plug-and-play.

[0029] 2. The compensation current can automatically return to zero after the system stabilizes, eliminating unnecessary losses and improving system operation reliability;

[0030] 3. After compensation, the DC bus capacitor only needs a smaller capacitance to ensure stable operation of the system, reducing the system operating cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a block diagram of the complete active compensation device control method;

[0032] Figure 2 It is a schematic diagram of a variable step length ramp function of a compensation device;

[0033] Figure 3 When the input voltage drops for constant power load, the moving trajectory of the system operating point under the improved adaptive control method is adopted;

[0034] Figure 4 The moving trajectory of the system operating point under the improved adaptive control method when the constant power load increases;

[0035] Figure 5 When the SOC of the battery on the compensation side is close to the threshold, R e Actively adjust and charge / discharge the compensation side battery;

[0036] Figure 6 A block diagram of the adaptive control method for the compensation device;

[0037] Figure 7 This is the structural diagram of the PI regulator of the compensation device;

[0038] Figure 8 This is the system simulation waveform when the DC bus voltage drops under the improved adaptive control strategy;

[0039] Fig. 9 This is the system simulation waveform when the constant power load increases under the improved adaptive control strategy;

[0040] Fig.10 The characteristic value change of the system after compensation under the improved adaptive control strategy when the bus capacitance is increased;

[0041] Fig.11 The characteristic value change of the system after compensation under the improved adaptive control strategy when the constant power load is increased;

[0042] In the figure:

[0043] i comp - compensating device current;

[0044] u ic —Battery voltage on the compensation side;

[0045] L Lc - Compensation device converter output line inductance;

[0046] R Lc - Compensation device converter output line resistance;

[0047] C bus - DC bus capacitor;

[0048] u bus —DC bus voltage;

[0049] u cpl0 —Steady-state value of input voltage for constant power load;

[0050] i cpl0 —Steady-state value of input current for constant power load. DETAILED DESCRIPTION

[0051] The technical solution of this patent is further described in detail below in conjunction with specific implementation methods.

[0052] An adaptive control method based on a constant power load active compensation device comprises the following steps:

[0053] Step 1: Figure 1 This is a complete block diagram of the active compensation device control method. The control system collects the constant power load input voltage u cpl and input current i cpl ;

[0054] Step 2: Determine whether the system is in a steady state. If the system is stable, proceed to the next step to adjust the control parameter R. e make corrections;

[0055] Step 3: Determine whether the SOC of the battery at the input side of the compensation device is within the allowable range. If so, proceed to step 4; otherwise, proceed to step 5.

[0056] Step 4: Equivalent load resistance value R e Make corrections, specifically,

[0057] 4.1 Equivalent load resistance value R e The current constant power load input voltage and current steady-state value u cpl0 、i cpl0, calculated according to formula (1).

[0058]

[0059] 4.2 Use a variable step length ramp function, such as Figure 2 As shown, R e Gradually transition from the old value to the new value R e '. When the constant power load is 0, R e Take the upper limit value R e_max , R e_max Theoretically, it is positive infinity, but too large an upper limit will cause the constant power load to increase from 0. e The value correction is too slow, so R can be set according to the system rated power and DC bus voltage level. e_max The value is 500Ω~1000Ω. When the constant power load reaches the maximum value, R e Take the lower limit R e_min , R e_min It can be calculated by formula (2), where P cpl_max is the maximum value of constant power load, U L is the lower limit of the DC bus voltage allowable range. The critical value when switching the step size is R e_c , in R e Value greater than R e_c Use a larger step size to ensure R e The correction speed, in R e Value is less than R e_c Select a smaller step size when compensating current to avoid system instability caused by too fast changes in compensation current. e_c In order to achieve a smooth transition of the compensation current from the old value to zero,

[0060]

[0061] 4.3 Return to step 4.1 and continue to execute steps 4.1 to 4.2. After 3 to 4 iterations, when i comp = 0, it reaches a new steady-state operating point. Figure 3 , 4 Click point ③ in the figure and go to step 4.

[0062] Step 5: If the SOC of the battery at the input side of the compensation device is outside the allowable range, the equivalent load resistance value R e Make corrections, specifically,

[0063] 5.1 If the SOC of the battery at the input side of the compensation device is lower than the set lower limit, reduce R e To R e1 , so that the compensation current i comp It becomes as shown in formula (3), where i cpl1The constant power load input current at the initial moment is used to actively charge the SOC of the battery on the input side of the compensation device, so that the SOC increases to within the allowable range, such as Figure 5 (a) If the SOC of the battery at the input side of the compensation device is higher than the set upper limit, increase R e To R e2 , so that the compensation current i comp It becomes as shown in formula (4), actively discharging the SOC of the battery on the input side of the compensation device to reduce the SOC to within the allowable range, such as Figure 5 (b)

[0064]

[0065]

[0066] 5.2 Use variable step length ramp function to make R e Transition from old value to new value.

[0067] Step 6: Enter the PI regulator to make the compensation current follow the given value. The overall control strategy block diagram of the system is as follows: Figure 6 As shown, the PI regulator structure is as follows Figure 7 shown.

[0068] The method described in the embodiment of the present invention is simulated and verified in Matlab / Simulink. Figure 8 This is the simulation waveform of the improved adaptive control method when the DC bus voltage drops. It can be seen that the DC bus voltage drops at 0.5s. When the system reaches a new steady-state operating point, R e It decreases from 16.9Ω to 16.25Ω, and after a transition time of about 1.5s, the compensation current returns from -1A to 0A. Fig. 9 This is the simulation waveform when the constant power load increases under the improved adaptive control method. At 0.5s, the constant power load increases from 10kW to 20kW. After reaching the new steady-state operating point, after 0.2s, R e It decreases from 16.9Ω to 8.3Ω, and after a transition time of 0.15s, the compensation current returns from -24.8A to 0A. Figure 8 , 9 It can be seen that under the improved adaptive control method, the compensation current automatically returns to 0 after the system reaches a new steady-state operating point and continues to remain stable. Fig.10 It is the change of characteristic value when the bus capacitance of the compensated system increases from 10uF to 100uF under the adaptive control method. Fig.11 This is the change of characteristic value when the constant power load of the compensated system increases from 1kW to 25kW under the adaptive control method. Fig.10 , 11It can be seen that under the improved adaptive control method, the stability margin of the system is significantly improved after compensation, and only a smaller bus capacitor value is required to ensure stable operation of the system.

[0069] The present invention introduces a constant power load input voltage u cpl With input current i cpl The steady-state value of the equivalent load resistance R e Correction is made so that the compensation current i comp After the system reaches a new steady-state operating point, it automatically returns to zero, so that the compensation side battery automatically exits the charge / discharge state. The present invention can solve the problem of high loss and low operating reliability of the compensation device caused by the compensation side battery being in a continuous charge / discharge state.

[0070] The above describes in detail the preferred implementation of this patent, but this patent is not limited to the above implementation. Various changes can be made within the knowledge scope of ordinary technicians in this field without departing from the purpose of this patent.

Claims

1. An adaptive control method based on a constant power load active compensation device, characterized in that: The steps include: Step 1: The control system collects the constant power load input voltage u cpl and input current i cpl ; Step 2: Determine whether the control system is in a steady state. If the control system is stable, proceed to the subsequent steps to adjust the control parameter R. e make corrections; Step 3: Determine whether the SOC of the battery at the input side of the compensation device is within the allowable range. If so, proceed to step 4; otherwise, proceed to step 5. Step 4: Equivalent load resistance value R e make corrections; In step 4, the equivalent load resistance value R e The correction steps are: 4.1 Equivalent load resistance value R e The current constant power load input voltage steady-state value u cpl0 And the steady-state value of current i cpl0 , calculated according to formula (1), 4.2 Use variable step length ramp function to make R e Gradually transition from the old value to the new value R e ', when the constant power load is 0, R e Take the upper limit value R e_max , when the constant power load reaches the maximum value, R e Take the lower limit R e_min , R e_min It can be calculated by formula (2): Where P cpl_max is the maximum value of constant power load, U L is the lower limit of the DC bus voltage allowable range, and the critical value when the step size is switched is R e_c , in R e Value greater than R e_c Use a larger step size to ensure R e The correction speed, in R e Value is less than R e_c Select a smaller step size to avoid system instability caused by too fast compensation current changes. At the same time, set multiple R e_c To achieve a smooth transition of the compensation current from the old value to zero; 4.3 Return to step 4.1 and continue to execute steps 4.1 to 4.

2. After 3 to 4 iterations, when i comp =0, it reaches the new steady-state operating point; Step 5: If the SOC of the battery at the input side of the compensation device is outside the allowable range, the equivalent load resistance value R e make corrections; In step 5, the equivalent load resistance value R e The correction steps are: 5.1 If the SOC of the battery at the input side of the compensation device is lower than the set lower limit, reduce R e To R e1 , so that the compensation current i comp It becomes as shown in formula (3), actively charging the SOC of the battery on the input side of the compensation device to increase the SOC to within the allowable range; if the SOC of the battery on the input side of the compensation device is higher than the set upper limit, increase R e To R e2 , so that the compensation current i comp It becomes as shown in formula (4), actively discharging the SOC of the battery on the input side of the compensation device to reduce the SOC to within the allowable range; In formula (3) and formula (4), i cpl1 is the constant power load input current at the initial moment; 5.2 Use variable step length ramp function to make R e Transition from old value to new value; Step 6: Use PI regulator to make the compensation current follow the given value.

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