CN116960925A - Energy storage converter control method and system - Google Patents

Abstract

The application discloses a control method and a control system of an energy storage converter, which take a bidirectional Buck-Boost energy storage converter with a function of stabilizing a DC bus voltage as a research basis, adopt voltage compensation control on a voltage outer ring of the converter, and adopt second-order linear active disturbance rejection control on an inner loop and an outer loop of the converter. The method can remarkably improve the damping of the direct current micro-grid system while realizing inertial support, effectively inhibit disturbance fluctuation and oscillation fluctuation of the direct current bus voltage, enhance the stability of the system and comprehensively improve the power supply quality.

Description

Energy storage converter control method and system

Technical field

The invention relates to the field of stabilization control of light-storage island DC microgrid, in particular to an energy storage converter control method and system.

Background technique

The specific application scenarios and structure of the photovoltaic storage island DC microgrid include photovoltaic power generation, energy storage and constant power load. The photovoltaic power generation consists of the photovoltaic array and its interface converter Boost circuit with pre-capacitor, which constantly outputs the maximum power to the DC bus; the energy storage consists of the energy storage battery and its interface converter bidirectional Buck-Boost circuit, which can operate in two modes. The bus emits or absorbs power, and at the same time maintains a constant bus voltage; the constant power load consists of the equivalent resistance of the transmission line, the equivalent inductance and the Buck converter with equivalent input capacitance. Through feedback control, it can operate at a constant power absorption level. mode; the DC bus is the common connection line for the above three parts. The control method is usually: the generation of voltage instructions and the tracking control of the output voltage with respect to the instruction value.

The document "Virtual inertia control strategy for DC microgrid multi-port converter" proposes a virtual synchronous machine-like virtual inertia control strategy for DC microgrid multi-port converter. A small-signal model of the converter was established, and the stability of the converter after adding a VSG-like virtual inertia control strategy was analyzed. From the perspective of simulating the characteristics of synchronous generators in the power grid, the inertia of the system is improved, thereby improving the system's ability to suppress disturbances. However, the control of this method is more complex, there are many control variables, and the actual debugging is difficult.

Photovoltaic power generation uses MPPT maximum power control to inject a certain amount of power into the DC bus. Among them, C _PV1 is the pre-capacitor at the input end of the Boost converter, L _PV is the energy storage inductor for Boost boost, and C _PV2 is the Boost output voltage stabilizing capacitor; As the core part, energy storage is responsible for maintaining a relatively stable DC bus voltage. Its no-load output voltage is 750V. In order to improve the system power supply capacity and the ability to stabilize the DC bus voltage, multiple energy storage devices are used as voltage sources in parallel to output to the DC bus. On the bus, energy storage uniformly adopts droop control of voltage and current double loops. During droop control, the DC bus voltage v _Bus /v _Po /v _Bo has a wide voltage operating range, where L _B is the Buck-Boost energy storage inductor, C _B is the Buck-Boost output voltage stabilizing capacitor; as the only load type that absorbs power in the microgrid, constant power load adopts the voltage and current double-loop control mode and has constant power characteristics. Among them, L _L is the output filter inductor, and C _L is Output filter capacitor, R _L is the load resistance at the output of the Buck converter.

Contents of the invention

The technical problem to be solved by the present invention is to provide an energy storage converter control method and system to effectively suppress the disturbance fluctuations and oscillation fluctuations of the DC bus voltage and enhance the stability of the system in view of the shortcomings of the existing technology.

In order to solve the above technical problems, the technical solution adopted by the present invention is: an energy storage converter control method, which includes the following steps:

The actual bus voltage v _Bo of the energy storage converter is passed through the first-order inertia link, and the result obtained is subtracted from the actual bus voltage to obtain Δv _Bo0 ,;

Pass Δv _Bo0 through the correction link G _h = k _hp to obtain the output Δv _Bo ;

Add the output Δv _Bo to the actual bus voltage to obtain the output v ^* _Bo ;

Using v ^* _Bo as the input of the voltage and current double-loop control link, the duty cycle signal of the energy storage converter switching tube is obtained.

The expression of Δv _Bo is:

Among them, T is the time constant of an inertial link, and s is a complex variable representing the frequency in the Laplace transform domain.

The specific implementation process of obtaining the duty cycle signal by the voltage and current double-loop control link includes:

Add and subtract the first result with v _Bore f and v ^* _Bo to obtain v _dB , where v _Boref is the reference value of the DC bus voltage;

Pass v _dB through the voltage outer loop PI controller G _Bvc =P _Bvc +I _Bvc /s, and add the obtained result to the inductor current i _LB. The added result passes through the current inner loop PI controller G _Bic =P _Bic +I _Bic /s, get the second result;

Perform PWM modulation on the second result to obtain the duty cycle signal; where, P _Bvc and P _Bic are the proportional coefficients of the voltage outer loop PI controller and the current inner loop PI controller respectively, and I _Bvc and I _Bic are the voltage outer loop respectively. The integral coefficient of the PI controller and the current inner loop PI controller.

The expression of the inductor current i _LB is:

Among them, _dB is the duty cycle of the upper tube IGBT of the energy storage converter, that is, S _B2 , k _dB is the droop coefficient of the energy storage converter, and C _B is the output capacitance of the energy storage converter.

As an inventive concept, the present invention also provides an energy storage converter control system, which includes:

one or more processors;

The memory has one or more programs stored thereon, and when the one or more programs are executed by the one or more processors, the one or more processors implement the steps of the above method of the present invention.

Compared with the existing technology, the beneficial effects of the present invention are: the present invention provides a voltage-based method for the microgrid system that exhibits low inertia, weak damping and other characteristics to deal with disturbance fluctuations and oscillation fluctuations faced in the stable operation of the system. The energy storage converter stability control method of compensation and double-loop second-order linear active disturbance rejection control not only achieves inertial support, but also significantly improves the damping of the DC microgrid system, effectively suppresses the disturbance fluctuations and oscillation fluctuations of the DC bus voltage, and enhances the stability of the system. characteristics, comprehensively improving the quality of power supply.

Description of the drawings

Figure 1 is the structure diagram of the photovoltaic and storage island DC microgrid system;

Figure 2 is a structural diagram of a disturbance suppression method based on voltage compensation control according to an embodiment of the present invention;

Figure 3 is a structural diagram of an oscillation suppression method based on dual-loop second-order LADRC according to an embodiment of the present invention;

Figure 4 is an equivalent control block diagram of the second-order LADRC according to the embodiment of the present invention;

Figure 5 is a block diagram of the equivalent model control model of the energy storage converter under dual-loop second-order LADRC according to the embodiment of the present invention;

Figure 6 is a Bode change diagram of the impedance ratio T _vc as the load power P _L changes when the method of the embodiment of the present invention is not used;

Figure 7 is a control structure diagram of an energy storage converter based on voltage compensation and dual-loop second-order LADRC according to an embodiment of the present invention;

Figure 8 shows the waveform diagram of bus voltage changing with load power when the proposed method is not used for energy storage;

Figure 9 is a waveform comparison diagram of bus voltage changes with load power before and after energy storage adopts voltage compensation control according to the embodiment of the present invention;

Figure 10 is a waveform diagram of bus voltage changing with load power after energy storage adopts voltage compensation control according to the embodiment of the present invention;

Figure 11 shows the waveforms of voltage and current changing with constant power load power when the proposed method is not used;

Figure 12 shows the waveforms of bus voltage and current changing with load power after dual-loop second-order LADRC is used for energy storage;

Figure 13 is a waveform comparison chart of bus voltage and current changes with load power before and after the method of the embodiment of the present invention is adopted for energy storage;

Figure 14 shows the waveforms of the bus voltage and current changing with the load power after the energy storage method according to the embodiment of the present invention is adopted.

Detailed ways

In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments These are some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

The method of the embodiment of the present invention includes the following steps:

The disturbance suppression method based on voltage compensation control proposed by the embodiment of the present invention is shown in 2. In the voltage outer loop of the energy storage converter, first, the actual bus voltage v _Bo is processed through the first-order inertia link G _d = 1/(1+Ts), and is added and subtracted from the actual bus voltage v _Bo to obtain Δv _Bo0 . Then the correction link G _h is used to control the output Δv _Bo . Finally, the output value is added to the actual bus voltage to output v ^* _Bo . This value is used as the bus voltage of the droop control link of the energy storage converter, and is subject to subsequent voltage and current double-loop control. Output PWM duty cycle. In Figure 2, under the joint action of voltage compensation control and droop control, the effect of suppressing disturbances in the DC microgrid can be achieved and the inertia and stability of the system can be enhanced.

After the voltage compensation control link, there are:

Then the double-loop control loop of the energy storage converter is:

By mathematical transformation of equation (2), we can get

Analyzing the circuit and control of the energy storage converter, the following expression can be obtained:

Through the above formula, we can get:

Substituting equation (4) into equation (3) we can get

From equation (5), the inductor current i _LB can be obtained as:

For the energy flowing through the inductor, we have:

By combining equation (6) and equation (7), we can get:

Further simplifying equation (8) we can get:

In formula (9):

Then equation (9) is transformed into:

It can be seen from equation (10) that when the voltage compensation control link is not used, the energy flowing through the inductor is:

E _LB0 =AF ² (11)

Therefore, after using the voltage compensation control link, the change in energy flowing through the inductor is:

It can be seen from the system energy balance that when the input power of the constant power load suddenly increases and is greater than the total output power of photovoltaic power generation and energy storage, the bus voltage v _Bo will drop quickly, that is:

When k _hp is a positive number, there is:

so:

Analyzing formula (12), formula (13), formula (14) and formula (15) we can get:

ΔE _LB >0 (16)

Therefore, under the action of the voltage compensation control link, the energy flowing through the inductor is additionally increased.

It can be seen from the above analysis that when the input power of the constant power load suddenly increases and is greater than the total output power of photovoltaic power generation and energy storage, the bus voltage v _Bo will drop quickly. When the voltage compensation control link proposed in the embodiment of the present invention is adopted, The energy storage reacts quickly to output power, transfers more energy to the inductor, and controls the output to the system through the converter for constant power load consumption. Energy storage plays the role of balancing the output power of the source converter and the input power of the constant power load. Therefore, it can avoid excessive discharge of the DC bus output power and alleviate the problem of rapid and large drops in the DC bus voltage.

The double-loop second-order LADRC control method is used for the energy storage converter in the research scenario of the embodiment of the present invention. Compared with PI control, the positive damping characteristics of the energy storage converter can be significantly improved, thereby improving the damping of the DC microgrid system and avoiding Medium and high frequency oscillations occur in the system.

The structure diagram of the energy storage converter oscillation suppression method of double-loop second-order LADRC is shown in Figure 3. For the output of the controller, if the system parameters are set reasonably and the control effect is ideal, z ₁ tends to y infinitely, and z ₂ tends to y infinitely. z ₃ tends to f infinitely, and z ₁ is the observed value of the inductor current i _LB or the sum of the voltage outer loop bus voltage and the droop partial voltage. Since these current and voltage quantities can be actually measured by an ammeter or voltmeter , so the current or voltage in LSEF no longer uses the observed value of LESO, but directly uses the value measured by the ammeter or voltmeter. With the control method shown in Figure 3, the damping of the DC microgrid system can be improved, the oscillation of the DC bus voltage can be effectively suppressed, and the stability of the system can be enhanced.

Obtaining the transfer function by equivalently equating the control structure of the second-order LADRC will facilitate the analysis and research of the entire control system from the frequency domain perspective.

According to the LESO in Figure 3, first establish its state expression as follows:

Among them, β ₁ = 3w _o , β ₂ = 3w _o ² , β ₃ = _wo ³ , and w _o is the bandwidth of the observer.

From Figure 3, we can get the LSEF expression of the system as:

Among them, k _p =w _c ² and k _d =2w _c are the proportional and integral coefficients respectively, where w _c is the controller bandwidth.

Through the simultaneous equation (17) and equation (18), we can get

Perform Laplace transformation on both sides of (19) at the same time, we can get

in,

Furthermore, the following transfer function can be obtained:

Perform Laplace transformation on both sides of equation (21) at the same time, we can get

By combining equation (21) and equation (22), we can get:

Let the disturbance of Y(s) in equation (23) be zero, we can get:

Let the disturbance of R(s) in equation (24) be zero, we can get:

By analyzing equations (23), (24) and (25), the second-order LADRC controller can be equivalent to the control block diagram shown in Figure 4.

Among them: inner loop controller B ₂ (s) is:

The forward channel from R(s) to U(s) is:

Then from formula (26) and formula (27), we can get:

Through the above equivalent control structure of the second-order LADRC, the equivalent control model block diagram of the energy storage converter under dual-loop second-order LADRC in Figure 5 can be obtained, and further the following equations can be obtained:

Then by solving the above equations, the output impedance of the energy storage converter of the double-loop second-order LADRC can be obtained as:

Through the above theoretical analysis and derivation calculations, the expressions of B ₁ and B ₂ in the second-order LADRC equivalent model are obtained, and further the equivalent model block diagram and output impedance of the energy storage converter under double-loop second-order LADRC are obtained. Therefore, each transfer function in the DC microgrid can be derived, which provides theoretical support for the following dual-loop second-order LADRC control parameter design.

Figure 6 shows the changes in the system impedance Bode diagram under dual-loop second-order LADRC oscillation suppression for energy storage. It can be seen that near the impedance amplitude-frequency transfer frequency range of BVCC and BCCC, that is, the frequency range from 600Hz to 700Hz, the phase-frequency curve of BVCC impedance is always in the positive damping area, which will be beneficial to the stability of the system, and with constant As the power load power increases, the positive damping characteristics are further strengthened; for the BCCC impedance, there is almost no change; from the interactive influence of BVCC and BCCC, the phase-frequency characteristics of T _vc also increase with the strengthening of the positive damping characteristics of BVCC Continuously moving away from -180°, that is, as P _L increases, the phase margin of the impedance ratio T _vc continues to increase, and the stability of the system continues to improve.

The above respectively adopt the disturbance suppression method based on voltage compensation control and the oscillation suppression method of double-loop second-order LADRC, which can enhance the anti-interference ability of the DC microgrid and improve the system's ability to suppress oscillation. By using these two control methods at the same time in the DC microgrid and combining them reasonably and effectively, the control structure diagram of the energy storage converter based on voltage compensation control and dual-loop second-order LADRC can be obtained as shown in Figure 7. After using this method, The DC microgrid not only has the ability to enhance the anti-interference ability of the DC microgrid, but also has the ability to suppress the DC bus voltage oscillation, and at the same time achieves the purpose of transient stability control and steady-state stability control of the DC microgrid.

As shown in Figure 8, when the energy storage converter does not adopt the method proposed in the embodiment of the present invention, the waveforms of the DC bus voltage and current change with the constant power load power. It can be seen from the figure that when the load power suddenly increases or decreases, the bus voltage will cause a large drop, and the steady-state adjustment time will also be longer. Therefore, when the proposed method is not used, the system transient stability The performance is weak and the inertia is low, so the system's disturbance suppression ability is weak.

Figure 9 and Figure 10 are waveform comparison diagrams of DC bus voltage and current changes with constant power load power before and after the energy storage converter adopts the voltage compensation control method. The red color is the waveform when the energy storage converter does not adopt the voltage compensation control method. Green is the waveform when the energy storage converter adopts the voltage compensation control method. It can be seen from the figure that under the same scene working conditions, compared with not using the voltage compensation control method proposed by the embodiment of the present invention, the transient process performs better, not only the maximum drop amount is small, but also the steady state Adjustment time is also very short.

Figure 11 shows the waveforms of the DC bus voltage and current changing with the constant power load power when the method proposed by the embodiment of the present invention is not adopted. At 0.8s, P _L suddenly increased from 50kW to 70kW and lasted until 1.2s. The bus voltage _vBus first dropped and then rose and gradually diverged until it oscillated in the 61V voltage range. The maximum drop was 52V. At the same time, the bus current The i _Bus also oscillates synchronously with the bus voltage v _Bus .

Figure 12 shows the waveforms of the DC bus voltage and current changing with the constant power load power after the energy storage converter adopts a double-loop second-order LADRC. It can be found that after the energy storage converter adopts a second-order LADRC, the effect of suppressing the oscillation of the original system is achieved, and the improvement It improves the stable performance of the system and has the effect of improving the inertia to a certain extent.

Figures 13 and 14 are comparison diagrams of the waveforms of the DC bus voltage and current changing with the constant power load power before and after the energy storage converter adopts the voltage compensation and double-loop second-order LADRC method proposed by the embodiment of the present invention. The red and blue waveforms are The voltage and current waveforms are without using the method proposed in the embodiment of the present invention. The purple and pink waveforms are the voltage and current waveforms using the method proposed in the embodiment of the present invention. Through comparison, it can be found that after adopting the method proposed in the embodiment of the present invention, for the DC bus voltage v _Bus , not only a better oscillation suppression effect is obtained, the steady-state stability is improved, but also a better disturbance suppression effect is improved, and the The transient stability of the system; the bus current _iBus is also well suppressed in both steady state and transient processes.

The transient stability of the system is analyzed from the perspective of the maximum drop and rise of the bus voltage. After adopting the voltage compensation control and the double-loop second-order LADRC method proposed in the embodiment of the present invention, the bus voltage drop can be reduced to a great extent. amount or rise amount, and in the transient process of P _L changes at each stage, after the bus voltage v _Bus drops or rises to the maximum value, the overshoot and adjustment time of the bus voltage are significantly reduced.

Although the preferred embodiments of the present application have been described, those skilled in the art will be able to make additional changes and modifications to these embodiments once the basic inventive concepts are apparent. Therefore, it is intended that the appended claims be construed to include the preferred embodiments and all changes and modifications that fall within the scope of this application.

Obviously, those skilled in the art can make various changes and modifications to the present application without departing from the spirit and scope of the present application. In this way, if these modifications and variations of the present application fall within the scope of the claims of the present application and equivalent technologies, the present application is also intended to include these modifications and variations.

Claims (5)

1. The energy storage converter control method is characterized by comprising the following steps of:

actual bus voltage v of energy storage converter _Bo The obtained result is subtracted from the actual bus voltage through a first-order inertia link to obtain Deltav _Bo0 ；

Will Deltav _Bo0 Through correction link G _h ＝k _hp Obtain the output Deltav _Bo ；

Will output Deltav _Bo Adding the actual bus voltage to obtain an output v ^* _Bo ；

Will v ^* _Bo And the duty ratio signal of the switching tube of the energy storage converter is obtained as the input of a voltage-current double-loop control link.

2. The energy storage converter control method according to claim 1, wherein Δv _Bo The expression of (2) is:

where T is the time constant of a section of inertia, and s represents the frequency in the laplace transform domain.

3. The method for controlling an energy storage converter according to claim 1, wherein the specific implementation process of obtaining the duty cycle signal in the voltage-current dual-loop control link includes:

bus current i of energy storage converter _Bo A first result is obtained through a proportion link;

combining the first result with v _Boref 、v ^* _Bo Adding and subtracting to obtain v _dB Wherein v is _Boref Is a reference value of the DC bus voltage;

will v _dB Through the voltage outer loop PI controller G _Bvc ＝P _Bvc +I _Bvc S, the result obtained and the inductor current i _LB The added result passes through the current inner loop PI controller G _Bic ＝P _Bic +I _Bic S, obtaining a second result;

PWM modulation is carried out on the second result, and a duty ratio signal is obtained; wherein P is _Bvc And P _Bic Proportional coefficients of the voltage outer loop PI controller and the current inner loop PI controller respectively, I _Bvc And I _Bic The integral coefficients of the voltage outer loop PI controller and the current inner loop PI controller are respectively.

4. A method of controlling an energy storage converter according to claim 3, characterized in that the inductor current i _LB The expression of (2) is:

wherein d _B Duty ratio, k, of upper tube IGBT for energy storage converter _dB C is the sag coefficient of the energy storage converter _B An output capacitance of the energy storage converter.

5. An energy storage converter control system, comprising:

one or more processors;

a memory having one or more programs stored thereon, which when executed by the one or more processors, cause the one or more processors to implement the steps of the method of any of claims 1-4.