Voltage coordination control method of multi-structure network type energy storage parallel system

Abstract

The invention discloses a voltage coordination control method for a multi-construction-network type energy storage parallel system. The method comprises the following steps: step 1, constructing the multi-construction-network type energy storage parallel system comprising a plurality of energy storage converter parallel units; step 2, generating a mathematical model based on the multi-network energy storage parallel system; and step 3, adjusting the drift error generated by the oscillator based on the GPS wireless interconnection technology, and realizing synchronous adjustment of the voltage and frequency of the output power of the common AC bus by the plurality of energy storage converter parallel units. According to the voltage coordination control method provided by the invention, the coordination operation of a plurality of parallel energy storage converters is realized through a small amount of communication, and the voltage amplitude, phase and frequency of the common alternating current bus can be accurately managed.

Description

Technical Field

[0001] The present invention relates to the technical field of grid-type energy storage, and in particular to a voltage coordination control method for a multi-grid-type energy storage parallel system. Background Art

[0002] With the large-scale access of renewable energy, the operation of the power system faces greater volatility and uncertainty. These new energy sources are greatly affected by natural conditions and are intermittent and unstable, making the frequency and voltage control of the power system more complicated. The emergence of grid-type energy storage systems has enhanced the regulation ability and adaptability of the power grid. It can not only smooth the fluctuations of renewable energy power generation, but also provide power support at load peaks, reducing the pressure on traditional peak-shaving power sources. At the same time, grid-type energy storage can also improve the stability of the power grid through power dispatching and frequency response, especially when the power grid fails or in extreme situations, the energy storage system can respond quickly, provide reliable power support, and help the system restore stability.

[0003] For multi-grid energy storage parallel systems, each converter needs to adjust the voltage and frequency of the common AC bus to achieve synchronous operation. However, due to differences in distribution location, line impedance, and inconsistent inverter control parameters, voltage / frequency instability or even oscillation may occur. In addition, power distribution between converters needs to be based on their capacity or a predetermined ratio. However, due to the mismatch of line impedance or the dynamic changes in load distribution, the accuracy of power distribution is difficult to guarantee, which may cause overload of some converters or uneven power distribution of the system as a whole. Therefore, formulating an effective coordinated control strategy is the key to ensuring the stable operation of multi-grid energy storage parallel systems and achieving accurate power distribution.

[0004] At present, the coordinated control strategies of multi-networked converters mainly include master-slave control, peer control and hierarchical control. In master-slave control, the master converter is responsible for voltage and frequency control, and other slave converters follow, which can achieve accurate power distribution and voltage regulation. However, failure of the master converter will affect the stability and control performance of the entire system, and the communication network is required to support information interaction between the master and slave converters, which increases the complexity and dependence of the system. Peer control has the advantages of decentralization, high reliability, and suitability for large-scale distributed systems, but it has limitations in global coordination, power distribution accuracy and global optimization. The hierarchical control structure based on the traditional droop mechanism can use multiple parallel inverters for coordinated networking to jointly maintain the voltage and frequency stability of the system. However, the power distribution accuracy of droop control may be low, especially when the line impedance is mismatched or the load changes suddenly, the control performance is limited. Summary of the invention

[0005] The purpose of the present invention is to overcome the limitations of the coordinated control strategy of multi-grid converters in the prior art in terms of global coordination, power distribution accuracy and global optimization, and the defects that the multi-grid energy storage parallel system is relatively complex and has a strong dependence on information interaction, and to provide a voltage coordinated control method for a multi-grid energy storage parallel system.

[0006] The purpose of the present invention is achieved through the following technical solutions: A voltage coordination control method for a multi-grid energy storage parallel system comprises the following steps: Step 1, constructing a multi-grid energy storage parallel system including multiple energy storage converter parallel units; Step 2, generating a mathematical model based on a multi-grid energy storage parallel system; Step 3, based on GPS wireless interconnection technology, the drift error generated by the oscillator is adjusted to achieve synchronous adjustment of the voltage and frequency of the common AC bus output power by multiple energy storage inverter parallel units.

[0007] Preferably, the multi-grid energy storage parallel system comprises: A plurality of energy storage converter parallel units are connected to a common AC bus through an LC filter circuit and an AC line, and the AC side contains a three-phase load; the energy storage converter parallel unit comprises a three-phase full-bridge inverter circuit and a control system thereof; the three-phase full-bridge inverter circuit is connected to the LC filter circuit and then connected to the common AC bus; the control system comprises a synchronization signal generator module, a coordinate transformation module, a current reference value generation module, a voltage coordination control module and a sinusoidal pulse width modulation SPWM module.

[0008] Preferably, the synchronization signal generator module is used to calculate the phase angle of the synchronous rotating coordinate system; the coordinate transformation module uses the acquired phase angle to perform coordinate transformation on the three-phase AC signal to obtain the signal value in the dq coordinate system; the current reference value generation module uses the collected signal to obtain the ideal value of the current; the voltage coordination control module uses the current error signal to generate a control voltage signal, and uses the phase angle to perform coordinate transformation to form a modulated wave signal; the sinusoidal pulse width modulation SPWM module is used to obtain a switch control pulse signal, which is output to the energy storage inverter for control.

[0009] Preferably, the step 2 is specifically as follows: Step 2a, establish a mathematical model of a single energy storage converter. The mathematical model of the LC filter circuit is as follows: The subscripts d and q indicate that the variable is in the dq coordinate system. f is the current on the filter inductor, is the rate of change of current on the filter inductor, L fis the value of the filter inductor, u f is the voltage at the converter outlet, ω is the angular frequency, u c is the voltage on the filter capacitor; The mathematical model of the AC line is shown below: Among them, i o is the current on the AC line, is the rate of change of current in the AC line, L l is the value of the AC line inductance, R l is the value of the AC line resistance, u o is the voltage of the public AC bus; The two circuit models are related through the filter capacitor, and the mathematical model of the filter capacitor is as follows: in, is the voltage change rate on the filter capacitor, C f is the value of the filter capacitor; Step 2b, establish a mathematical model of multiple parallel energy storage converters, based on the equal voltage of the common AC bus, the mathematical model of the filter circuit and the AC line, and assume that there are n parallel energy storage converters in the system, the mathematical model can be obtained as follows: Where i is the serial number of the parallel energy storage converter, Indicates the acceleration of the current change in the AC line; Step 2c, considering the impact of three-phase load on the system model, the expression of load power is as follows: Among them, P L is the load active power, Q L is the load reactive power, i ld is the load current; The d and q components of the grid-connected current of the i-th energy storage converter are expressed as follows: Among them, a i is the proportion of the d-axis component of the grid-connected current of the negative i-th energy storage converter in the d-axis component of the load current, b i is the proportion of the q-axis component; Step 4: After the combination, the mathematical model of the constructed multi-grid energy storage parallel system is as follows:

[0010] Preferably, the step 3 is specifically as follows: Step 3a, using the sawtooth wave generated by the oscillating device inside the control system of each energy storage converter parallel unit to obtain the reference value of the phase angle for realizing the coordinate transformation, the solution expression is as follows: Among them, t is the current time, θ i is the phase angle reference value, ω0 is the rated angular velocity, and θ0 is the initial phase angle; Step 3b, using the pulse signal generated by GPS as the time reference, adjust the drift error generated by the oscillating device and initialize the synchronization signal. The recorded time deviation is as follows: t py =mod{t c ,1} Among them, t py is the time offset between the GPS pulse and the oscillating device, t c is the time when the GPS pulse rises; Then, the phase angle value for coordinate transformation can be obtained as follows: θ=mod{ω0(t l -t py )+θ0,2p} Among them, t l is the local time.

[0011] Preferably, the voltage coordination control method of the multi-grid energy storage parallel system further includes step 4, using the backstepping method to design the controller to achieve global stability and fast response voltage regulation, and the specific steps are as follows: Step 4a, assuming i ld And its derivatives of all orders are bounded, and the Lyapunov function is constructed as follows: Among them, u err,d ,u err,q are the tracking errors of the common AC bus voltage in the d and q axis components respectively; Step 4b, the expression for constructing the reference value of the dummy control variable is as follows: Among them, K d , K q , L d , L q is a constant greater than 0, variables with superscript * are reference values, and sign is a sign function; Step 4c, construct the Lyapunov function based on the current tracking error as follows: The derived expression is as follows: Step 4d, the voltage coordination control strategy design is as follows: Among them, k i,d and k i,q Custom constants for the controller; Step 4e, the modulation wave signals of the d and q axes can be converted into a three-phase stationary coordinate system through the coordinate transformation module, and then the switch pulse control signal is obtained through the sinusoidal pulse width modulation SPWM module and input into the three-phase inverter circuit of the i-th energy storage converter for control.

[0012] The beneficial effect of the present invention is that the voltage coordination control method proposed in the present invention realizes the coordinated operation of multiple parallel energy storage converters through a small amount of communication, and can accurately manage the voltage amplitude, phase and frequency of the public AC bus.

[0013] In the case of uncertain load power, the backstepping method is used to design the controller to ensure that the system has global stability and fast-response voltage regulation capabilities. In addition, this method can still achieve automatic and accurate distribution of load power according to the preset ratio when the unknown line impedance and inverter filter parameters are inconsistent. It can optimize and adjust the voltage of the grid connection point in a variety of application scenarios, and can also accurately control the distribution of load power, thereby improving the stability and reliability of the operation of the multi-grid energy storage parallel system. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Schematic diagram of an equivalent circuit of n parallel energy storage converters connected to a common bus in one embodiment of the present invention; Figure 2 A schematic diagram of voltage coordination control of parallel converters in a preferred embodiment of the present invention; Figure 3 A schematic diagram of a multi-grid energy storage parallel system in a preferred embodiment of the present invention; Figure 4 A schematic diagram of the real-time simulation system architecture in a preferred embodiment of the present invention; Figure 5 It is a schematic diagram for verifying the simulation effect of the control method proposed in a preferred embodiment of the present invention.

[0015] Among them: (a) is the active power waveform when the load increases, (b) is the reactive power waveform when the load increases, (c) is the frequency / voltage amplitude waveform at the common AC bus when the load increases, and (d) is the output current waveform of each converter when the load increases. DETAILED DESCRIPTION

[0016] Example embodiments will now be described more fully with reference to the accompanying drawings. However, example embodiments can be implemented in a variety of forms and should not be construed as limited to the examples set forth herein; rather, these embodiments are provided so that this application will be more comprehensive and complete and fully convey the concept of the example embodiments to those skilled in the art.

[0017] In addition, described feature, structure or characteristic can be combined in one or more embodiments in any suitable manner. In the following description, many specific details are provided to provide a full understanding of the embodiments of the present application. However, those skilled in the art will appreciate that the technical scheme of the present application can be put into practice without one or more of the specific details, or other methods, components, devices, steps, etc. can be adopted. In other cases, known methods, devices, realizations or operations are not shown or described in detail to avoid blurring the various aspects of the application.

[0018] The block diagrams shown in the accompanying drawings are merely functional entities and do not necessarily correspond to physically independent entities. That is, these functional entities may be implemented in software form, or in one or more hardware modules or integrated circuits, or in different networks and / or processor devices and / or microcontroller devices.

[0019] The flowcharts shown in the accompanying drawings are only exemplary and do not necessarily include all the contents and operations / steps, nor must they be executed in the order described. For example, some operations / steps can be decomposed, and some operations / steps can be combined or partially combined, so the actual execution order may change according to actual conditions.

[0020] Example: A voltage coordination control method for a multi-grid energy storage parallel system comprises the following steps: Step 1, constructing a multi-grid energy storage parallel system including multiple energy storage converter parallel units; Step 2, generating a mathematical model based on a multi-grid energy storage parallel system; Step 3, based on GPS wireless interconnection technology, the drift error generated by the oscillator is adjusted to achieve synchronous adjustment of the voltage and frequency of the common AC bus output power by multiple energy storage inverter parallel units.

[0021] Generate a mathematical model based on a multi-grid energy storage parallel system in order to accurately analyze, design and control the behavior and performance of the system. Through the mathematical model, we can deeply understand the interaction between the various parts of the system and their impact on the overall system performance. Based on the mathematical model, more accurate and effective control strategies can be designed and developed to achieve accurate management of system voltage, frequency and power distribution. At the same time, it also provides the necessary theoretical support for synchronous regulation of voltage and frequency. In this embodiment, in the present invention, the drift error generated by the oscillator is adjusted based on GPS wireless interconnection technology, combined with an accurate mathematical model, which can significantly improve the reliability of signal synchronization.

[0022] like Figure 1 As shown, the multi-grid energy storage parallel system includes: Multiple energy storage converter parallel units are connected to a common AC bus through an LC filter circuit and an AC line, and the AC side contains a three-phase load; the energy storage converter parallel unit includes a three-phase full-bridge inverter circuit and its control system. The control system block diagram is shown in Figure 2 As shown; the three-phase full-bridge inverter circuit is connected to the LC filter circuit and then connected to the public AC bus; the control system includes a synchronization signal generator module, a coordinate transformation module, a current reference value generation module, a voltage coordination control module and a sinusoidal pulse width modulation SPWM module.

[0023] The synchronous signal generator module is used to calculate the phase angle of the synchronous rotating coordinate system; the coordinate transformation module uses the acquired phase angle to perform coordinate transformation on the three-phase AC signal to obtain the signal value in the dq coordinate system; the current reference value generation module uses the collected signal to obtain the ideal value of the current; the voltage coordination control module uses the current error signal to generate a control voltage signal, and uses the phase angle to perform coordinate transformation to form a modulated wave signal; the sinusoidal pulse width modulation SPWM module is used to obtain a switch control pulse signal, which is output to the energy storage converter for control.

[0024] The step 2 is specifically as follows: Step 2a, establish a mathematical model of a single energy storage converter. The mathematical model of the LC filter circuit is as follows: The subscripts d and q indicate that the variable is in the dq coordinate system. f is the current on the filter inductor, is the rate of change of current on the filter inductor, L f is the value of the filter inductor, u f is the voltage at the converter outlet, ω is the angular frequency, u c is the voltage on the filter capacitor; The mathematical model of the AC line is shown below: Among them, i o is the current on the AC line, is the rate of change of current in the AC line, L l is the value of the AC line inductance, R l is the value of the AC line resistance, u o is the voltage of the public AC bus; The two circuit models are related through the filter capacitor, and the mathematical model of the filter capacitor is as follows: in, is the voltage change rate on the filter capacitor, C f is the value of the filter capacitor; Step 2b, establish a mathematical model of multiple parallel energy storage converters, based on the equal voltage of the common AC bus, the mathematical model of the filter circuit and the AC line, and assume that there are n parallel energy storage converters in the system, the mathematical model can be obtained as follows: Where i is the serial number of the parallel energy storage converter, Indicates the acceleration of the current change in the AC line; Step 2c, considering the impact of three-phase load on the system model, the expression of load power is as follows: Among them, P L is the load active power, Q L is the load reactive power, i ld is the load current; The d and q components of the grid-connected current of the i-th energy storage converter are expressed as follows: Among them, a i is the proportion of the d-axis component of the grid-connected current of the negative i-th energy storage converter in the d-axis component of the load current, b i is the proportion of the q-axis component; Step 4: After the combination, the mathematical model of the constructed multi-grid energy storage parallel system is as follows:

[0025] The step 3 is specifically as follows: Step 3a, using the sawtooth wave generated by the oscillating device inside the control system of each energy storage converter parallel unit to obtain the reference value of the phase angle for realizing the coordinate transformation, the solution expression is as follows: Among them, t is the current time, θi is the phase angle reference value, ω0 is the rated angular velocity, and θ0 is the initial phase angle; Step 3b, using the pulse signal generated by GPS as the time reference, adjust the drift error generated by the oscillating device and initialize the synchronization signal. The recorded time deviation is as follows: t py =mod{t c ,1} Among them, t py is the time offset between the GPS pulse and the oscillating device, t c is the time when the GPS pulse rises; Then, the phase angle value for coordinate transformation can be obtained as follows: θ=mod{ω0(t l -t py )+θ0,2p} Among them, t l is the local time.

[0026] The voltage coordination control method of the multi-grid energy storage parallel system also includes step 4, using the backstepping method to design the controller to achieve global stability and fast response voltage regulation. The specific steps are as follows: Step 4a, assuming i ld And its derivatives of all orders are bounded, and the Lyapunov function is constructed as follows: Among them, u err,d ,u err,q are the tracking errors of the common AC bus voltage in the d and q axis components respectively; Step 4b, the expression for constructing the reference value of the dummy control variable is as follows: Among them, K d , K q , L d , L q is a constant greater than 0, variables with superscript * are reference values, and sign is a sign function; Step 4c, construct the Lyapunov function based on the current tracking error as follows: The derived expression is as follows: Step 4d, the voltage coordination control strategy design is as follows: Among them, k i,d and k i,qCustom constants for the controller; Step 4e, the modulation wave signals of the d and q axes can be converted into a three-phase stationary coordinate system through the coordinate transformation module, and then the switch pulse control signal is obtained through the sinusoidal pulse width modulation SPWM module and input into the three-phase inverter circuit of the i-th energy storage converter for control.

[0027] by Figure 3 The parallel system of four energy storage converters with different capacities shown in FIG. Figure 4 The model was built in the real-time simulation system shown in the figure, and a real-time simulation test was performed to verify the response of the system when the load changes in the system. The initial active value of the load is 20kW, and the initial reactive value is 10kVar. The four converters distribute the load in a ratio of 4:3:2:1 according to the rated capacity. At 15s, the load capacity in the system doubles. The real-time simulation results of the system are shown in the figure below. Figure 5 As shown in the figure. The results show that even if the filter parameters and line impedance of each converter are different, the system can still distribute active and reactive loads in a relatively accurate proportion in steady state. When the load increases, the voltage frequency and amplitude at the common AC bus remain within the rated range, showing a good voltage regulation effect. In addition, the output current waveforms of the four converters are stable, without oscillation or overshoot, proving that the system has good dynamic response capabilities.

[0028] Those skilled in the art will readily appreciate other embodiments of the present application after considering the specification and practicing the embodiments disclosed herein. The present application is intended to cover any variations, uses or adaptations of the present application, which follow the general principles of the present application and include common knowledge or customary technical means in the art that are not disclosed in the present application.

[0029] It should be understood that the present application is not limited to the precise structures that have been described above and shown in the drawings, and that various modifications and changes may be made without departing from the scope thereof. The scope of the present application is limited only by the appended claims.

Claims

1. A voltage coordination control method for a multi-grid energy storage parallel system, characterized in that: The following steps are involved: Step 1, constructing a multi-grid energy storage parallel system including multiple energy storage converter parallel units; Step 2, generating a mathematical model based on a multi-grid energy storage parallel system; Step 3, based on GPS wireless interconnection technology, the drift error generated by the oscillator is adjusted to achieve synchronous adjustment of the voltage and frequency of the common AC bus output power by multiple energy storage inverter parallel units.

2. The voltage coordination control method of a multi-grid energy storage parallel system according to claim 1 is characterized in that: The multi-grid energy storage parallel system comprises: A plurality of energy storage converter parallel units are connected to a common AC bus through an LC filter circuit and an AC line, and the AC side contains a three-phase load; the energy storage converter parallel unit comprises a three-phase full-bridge inverter circuit and a control system thereof; the three-phase full-bridge inverter circuit is connected to the LC filter circuit and then connected to the common AC bus; the control system comprises a synchronization signal generator module, a coordinate transformation module, a current reference value generation module, a voltage coordination control module and a sinusoidal pulse width modulation SPWM module.

3. The voltage coordination control method of a multi-grid energy storage parallel system according to claim 2 is characterized in that: The synchronous signal generator module is used to calculate the phase angle of the synchronous rotating coordinate system; the coordinate transformation module uses the acquired phase angle to perform coordinate transformation on the three-phase AC signal to obtain the signal value in the dq coordinate system; the current reference value generation module uses the collected signal to obtain the ideal value of the current; the voltage coordination control module uses the current error signal to generate a control voltage signal, and uses the phase angle to perform coordinate transformation to form a modulated wave signal; the sinusoidal pulse width modulation SPWM module is used to obtain a switch control pulse signal, which is output to the energy storage converter for control.

4. The voltage coordination control method of a multi-grid energy storage parallel system according to claim 3 is characterized in that: The step 2 is specifically as follows: Step 2a, establish a mathematical model of a single energy storage converter. The mathematical model of the LC filter circuit is as follows: The subscripts d and q indicate that the variable is in the dq coordinate system. f is the current on the filter inductor, is the rate of change of current on the filter inductor, L f is the value of the filter inductor, u f is the voltage at the converter outlet, ω is the angular frequency, u c is the voltage on the filter capacitor; The mathematical model of the AC line is shown below: Among them, i o is the current on the AC line, is the rate of change of current in the AC line, L l is the value of the AC line inductance, R l is the value of the AC line resistance, u o is the voltage of the public AC bus; The two circuit models are related through the filter capacitor, and the mathematical model of the filter capacitor is as follows: in, is the voltage change rate on the filter capacitor, C f is the value of the filter capacitor; Step 2b, establish a mathematical model of multiple parallel energy storage converters, based on the equal voltage of the common AC bus, the mathematical model of the filter circuit and the AC line, and assume that there are n parallel energy storage converters in the system, the mathematical model can be obtained as follows: Where i is the serial number of the parallel energy storage converter, Indicates the acceleration of the current change in the AC line; Step 2c, considering the impact of three-phase load on the system model, the expression of load power is as follows: Among them, P L is the load active power, Q L is the load reactive power, i ld is the load current; The d and q components of the grid-connected current of the i-th energy storage converter are expressed as follows: Among them, a i is the proportion of the d-axis component of the grid-connected current of the negative i-th energy storage converter in the d-axis component of the load current, b i is the proportion of the q-axis component; Step 2d, after the combination, the mathematical model of the constructed multi-grid energy storage parallel system is as follows:

5. The voltage coordination control method of a multi-grid energy storage parallel system according to claim 4 is characterized in that: The step 3 is specifically as follows: Step 3a, using the sawtooth wave generated by the oscillating device inside the control system of each energy storage converter parallel unit to obtain the reference value of the phase angle for realizing the coordinate transformation, the solution expression is as follows: Among them, t is the current time, θ i is the phase angle reference value, ω0 is the rated angular velocity, and θ0 is the initial phase angle; Step 3b, using the pulse signal generated by GPS as the time reference, adjust the drift error generated by the oscillating device and initialize the synchronization signal. The recorded time deviation is as follows: t py =mod{t c ,1} Among them, t py is the time offset between the GPS pulse and the oscillating device, t c is the time when the GPS pulse rises; Then, the phase angle value for coordinate transformation can be obtained as follows: θ=mod{ω0(t l -t py )+θ0,2p} Among them, t l is the local time.

6. The voltage coordination control method of a multi-grid energy storage parallel system according to claim 4 is characterized in that: It also includes step 4, using the backstepping method to design a controller to achieve global stability and fast response voltage regulation. The specific steps are as follows: Step 4a, assuming i ld And its derivatives of all orders are bounded, and the Lyapunov function is constructed as follows: Among them, u err,d ,u err,q are the tracking errors of the common AC bus voltage in the d and q axis components respectively; Step 4b, the expression for constructing the reference value of the dummy control variable is as follows: Among them, K d , K q , L d , L q is a constant greater than 0, variables with superscript * are reference values, and sign is a sign function; Step 4c, construct the Lyapunov function based on the current tracking error as follows: The derived expression is as follows: Step 4d, the voltage coordination control strategy design is as follows: Among them, k i,d and k i,q Custom constants for the controller; Step 4e, the modulation wave signals of the d and q axes can be converted into a three-phase stationary coordinate system through the coordinate transformation module, and then the switch pulse control signal is obtained through the sinusoidal pulse width modulation SPWM module and input into the three-phase inverter circuit of the i-th energy storage converter for control.

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