Energy storage converter control method based on virtual synchronous motor

Abstract

The invention discloses an energy storage converter control method based on a virtual synchronous motor. A phase-locked loop is used for extracting power grid frequency and phase information from a power grid voltage signal; actual active power and reactive power are calculated; setting reference values of active power and reactive power; controlling the current output by the inverter through a current controller according to the result of the power regulation so as to enable the output current to meet the set power requirement; performing coordinate transformation on the three-phase current, and converting the three-phase current into a current component under a dq coordinate system; and according to the current component of the dq coordinate system, the turn-on and turn-off time of an inverter switching device is controlled, so that the control of alternating current output is realized. By simulating the inertia characteristic of the synchronous generator, necessary inertia support is provided for the power grid, the fluctuation of new energy power generation is effectively inhibited, the instability of the frequency and voltage of the power grid is reduced, and the stability and reliability of the power grid are remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the field of power electronics and power system control, and in particular relates to a control method for an energy storage converter based on a virtual synchronous motor. Background Art

[0002] As an important way to achieve my country's dual carbon goals, the time-varying characteristics of renewable energy power generation have brought challenges to the stable operation of the power grid. To overcome this problem, the application of energy storage technology has emerged. It can make up for the defects of intermittent and volatile renewable energy power generation to a certain extent, realize the smooth access of renewable energy power generation to the power grid, and provide an effective solution to solve the unreasonable spatiotemporal structure of my country's energy. From the perspective of the power system, energy storage technology can achieve the separation of power generation and power consumption in time and space, thereby improving the imbalance between supply and demand between the power generation side and the power consumption side in my country.

[0003] As the core interface equipment for the access of new energy to the power system, the Power Conversion System (PCS) is responsible for completing the energy interaction between the new energy storage medium and the power grid or load, and undertakes other auxiliary functions. The energy storage converter plays an indispensable role in actively supporting microgrids, smoothing fluctuations in new energy generation, and managing voltage sags. Therefore, the preparation of high-power energy storage converters is a key issue in building large-scale energy storage systems.

[0004] As renewable energy generation is connected to the grid on a large scale through grid-connected devices composed of power electronic devices, the grid-connected devices under the traditional grid-connected control strategy cannot provide inertia and damping similar to generators, resulting in the renewable energy grid-connected system being more prone to instability when the power system faces frequency fluctuations and various fault problems. To solve this problem, Virtual Synchronous Generator (VSG) technology was proposed and applied to grid-connected converter control. The energy storage converter under the control of virtual synchronous motor technology can simulate the inertia and damping characteristics of real motors, which is of great significance to improving the stability of renewable energy access to the grid. Summary of the invention

[0005] The purpose of the present invention is to overcome the above problems existing in the prior art and to provide a control method for an energy storage converter based on a virtual synchronous motor.

[0006] In order to achieve the above technical objectives and the above technical effects, the present invention is implemented through the following technical solutions:

[0007] A control method for an energy storage converter based on a virtual synchronous motor includes a grid-connected implementation method, and the grid-connected implementation method includes the following steps:

[0008] The grid frequency and phase information are extracted from the grid voltage signal using a phase-locked loop;

[0009] Calculate the actual active power and reactive power;

[0010] According to system requirements and preset goals, set the reference value P of active power and reactive power ref and Q ref ;

[0011] Through the current controller, according to the result of power regulation, the current output by the inverter is controlled so that the output current meets the set power requirement;

[0012] The three-phase current is transformed into the current component i in the dq coordinate system. d and i q ;

[0013] According to the current component of the dq coordinate system, the on and off time of the inverter switch device is controlled, thereby realizing the control of the AC power output.

[0014] Furthermore, based on the DC current i output by the photovoltaic array Labc , and the grid voltage e gabc , calculate the actual active power and reactive power.

[0015] Furthermore, space vector pulse width modulation technology is used to generate a PWM pulse signal to control the on and off time of the inverter switch device.

[0016] Furthermore, a DC / AC control method is also included, including:

[0017] Obtain DC and AC parameters and grid voltage parameters;

[0018] Adjust the output voltage of the VSG to synchronize it with the grid voltage;

[0019] Set the voltage outer loop controller to control the amplitude of the AC side voltage; set the reference voltage value U ref , and compare it with the actual voltage value U0 to calculate the voltage error;

[0020] According to the model of virtual synchronous generator, set the DC / AC partial active loop to simulate the moment of inertia, damping effect and primary frequency modulation characteristics of the synchronous generator;

[0021] Add an excitation controller to adjust the excitation current of the synchronous motor in real time to adjust the amplitude of its potential and maintain the constant output voltage of the synchronous motor;

[0022] The closed-loop control equation of the excitation controller after considering the primary voltage regulation is obtained, and the reactive power Q of the synchronous motor is indirectly controlled by controlling the extreme voltage change. e Output, set the DC / AC part reactive loop to simulate the primary voltage regulation characteristics of the synchronous motor;

[0023] Introducing virtual impedance L v , γ v To obtain the reference of the DC / AC part current inner loop command in the three-phase static coordinate system;

[0024] The obtained current inner loop command reference is compared with the obtained three-phase inductor current feedback signal i Labc Perform coordinate transformation;

[0025] A current inner loop controller is constructed in a two-phase rotating coordinate system to achieve closed-loop control of the inverter output inductor current.

[0026] Furthermore, the DC and AC parameters include: DC side voltage U dc , AC side voltage amplitude and frequency, inductance L, capacitance C, moment of inertia J, damping coefficient K d .

[0027] Furthermore, the grid voltage parameters include: the phase of the grid voltage, the rated angular frequency ω n and amplitude.

[0028] The beneficial effects of the present invention are:

[0029] The PCS-VSG technology provides the necessary inertial support for the power grid by simulating the inertial characteristics of synchronous generators, effectively suppresses the volatility of renewable energy generation, reduces the instability of grid frequency and voltage, and significantly improves the stability and reliability of the grid. This technology has the frequency and voltage regulation capabilities of synchronous generators, and can be adjusted immediately when the grid faces frequency and voltage anomalies to ensure the stable operation of the grid. PCS-VSG can dynamically adjust its charging and discharging strategy according to the real-time needs of the grid, realize efficient distribution and utilization of energy, and improve the economy of system operation. At the same time, the application of PCS-VSG technology promotes the widespread access and efficient consumption of intermittent renewable energy such as wind power and photovoltaics, and helps to build a new power system architecture with renewable energy as the core. Compared with traditional physical synchronous generators, PCS-VSG has obvious advantages in cost-effectiveness and maintenance convenience, greatly reducing the construction and operation and maintenance costs of grid infrastructure, and providing strong support for the sustainable development and technological innovation of the power system. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of this application. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0031] Figure 1 It is a brief flow chart of the method of the present invention;

[0032] Figure 2 This is a typical control block diagram for the PV-VSG grid connection implementation of the present invention. DETAILED DESCRIPTION

[0033] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] like Figure 1 A control method for an energy storage converter based on a virtual synchronous motor is shown, including a grid-connected implementation method, and the grid-connected implementation method includes the following steps:

[0035] The grid frequency and phase information are extracted from the grid voltage signal using a phase-locked loop;

[0036] Based on the DC current i output by the photovoltaic array Labc , and the grid voltage e gabc , calculate the actual active power and reactive power;

[0037] According to system requirements and preset goals, set the reference value P of active power and reactive power ref and Q ref ;

[0038] Through the current controller, according to the result of power regulation, the current output by the inverter is controlled so that the output current meets the set power requirement;

[0039] The three-phase current is transformed into the current component i in the dq coordinate system. d and i q ;

[0040] According to the current component of the dq coordinate system, the space vector pulse width modulation technology is used to generate a PWM pulse signal to control the on and off time of the inverter switch device, thereby realizing the control of the AC power output.

[0041] It also includes DC / AC control methods, including:

[0042] Get the DC side voltage U dc , AC side voltage amplitude and frequency, inductance L, capacitance C, moment of inertia J, damping coefficient K d ;

[0043] The grid voltage parameters to be detected include: grid voltage phase, rated angular frequency ω n and amplitude; adjust the output voltage of the VSG to synchronize it with the grid voltage;

[0044] Set the voltage outer loop controller to control the amplitude of the AC side voltage; set the reference voltage value U ref , and compare it with the actual voltage value U0 to calculate the voltage error;

[0045] According to the model of virtual synchronous generator, set the DC / AC partial active loop to simulate the moment of inertia, damping effect and primary frequency modulation characteristics of the synchronous generator;

[0046] Add an excitation controller to adjust the excitation current of the synchronous motor in real time to adjust the amplitude of its potential and maintain the constant output voltage of the synchronous motor;

[0047] The closed-loop control equation of the excitation controller after considering the primary voltage regulation is obtained, and the reactive power Q of the synchronous motor is indirectly controlled by controlling the extreme voltage change. e Output, set the DC / AC part reactive loop to simulate the primary voltage regulation characteristics of the synchronous motor;

[0048] Introducing virtual impedance L v , γ v To obtain the reference of the DC / AC part current inner loop command in the three-phase static coordinate system;

[0049] The obtained current inner loop command reference is compared with the obtained three-phase inductor current feedback signal i Labc Perform coordinate transformation;

[0050] A current inner loop controller is constructed in a two-phase rotating coordinate system to achieve closed-loop control of the inverter output inductor current.

[0051] The specific calculation is as follows:

[0052] The traditional implementation method of virtual synchronous generator grid connection requires the equipment to be operated off-grid first, and pre-synchronization is achieved by detecting the inverter's own output voltage and the grid voltage. However, for PV-VSG connected to the large power grid, since it basically works in the grid-connected mode, there is no need to frequently operate off-grid. Therefore, if the traditional method is directly adopted, additional hardware costs (such as voltage sensors) and control complexity (such as off-grid / grid synchronization control) will be added. The PCS-VSG is connected to the grid first through DC / AC conversion, which can simplify the grid connection process and make it more suitable for the working environment of the large power grid. In this way, the PCS-VSG can first establish an electrical connection with the grid, and then synchronize the output voltage with the grid voltage through the control algorithm to ensure the stability and reliability of the grid connection process, thereby avoiding unnecessary hardware investment and control complexity, and improving the operation efficiency of the system.

[0053] In order to realize the primary frequency regulation function of the generator set (frequency-active power droop function), the prime movers in the generator set are equipped with speed regulators. The function of the speed regulator is that when the grid frequency is different from the rated frequency, the speed regulator will automatically change the opening of the prime mover valve, thereby changing the mechanical power output of the prime mover. The relationship between the prime mover output mechanical power and the grid voltage angular frequency is:

[0054] P m =P ref +D p (ω n -ω g ) (1-1)

[0055] Where P ref Indicates the given value of the prime mover's mechanical power (corresponding to the rated angular frequency w of the power grid) n ), which is usually given by the upper layer scheduling;

[0056] D p Indicates the frequency-active power droop coefficient.

[0057] Since the photovoltaic cell is the main input power source of the PV-VSG at this time, Pre in equation (1-1) can be equivalent to the output power of the photovoltaic cell.

[0058] P ref =(U dc -U deref )G dc (s) (1-2)

[0059] Where U dcref Represents the PV DC bus voltage reference instruction, which is usually obtained by the PV MPPT algorithm;

[0060] G dc (s) represents the DC bus voltage regulator function.

[0061] Considering the influence of the damping winding, the mechanical motion equation of the synchronous generator rotor is expressed as

[0062]

[0063] In the formula

[0064] P e represents the electromagnetic power of the synchronous generator;

[0065] J represents the moment of inertia of the synchronous generator;

[0066] w n Indicates the rated angular frequency;

[0067] K d Represents the mechanical damping coefficient.

[0068] By combining equations (1-1) to (1-3), we can get the active loop equation of the PV-VSG DC / AC part after considering the action of the speed regulator, that is,

[0069]

[0070] It can be seen from equation (1-4) that the active loop of the PV-VSG DC / AC part simulates the inertia, damping and primary frequency modulation characteristics of the synchronous generator very well.

[0071] Since the output voltage of the synchronous generator will decrease as the output current increases, an excitation controller is needed to adjust the excitation current of the synchronous generator in real time to adjust the amplitude of its internal potential and maintain the constant output voltage of the synchronous generator. The closed-loop control equation of the excitation controller is:

[0072] i f =G e (s)(U ref -U o ) (1-5)

[0073] Where U ref Indicates the reference voltage amplitude;

[0074] U o Indicates the output voltage amplitude of the synchronous generator;

[0075] G e (s) represents the regulator transfer function of the excitation controller. In order to ensure that the output voltage can track the reference voltage without static error, G e (s) must contain an integral component, which can be an integral regulator or a PI regulator, etc.

[0076] In order to realize the primary voltage regulation function (voltage-reactive power droop function) of PV-VSG, the amplitude of its reference voltage will change with the reactive power output, and its changing rule is:

[0077]

[0078] Where U n Indicates the rated voltage amplitude;

[0079] Q ref Indicates reactive power given (corresponding to rated voltage U n ), which is usually given by the upper layer scheduling;

[0080] Q e Indicates the actual output reactive power of PV-VSG;

[0081] D q Indicates the voltage-reactive power droop coefficient.

[0082] By combining equations (1-5) and (1-6), we can get the closed-loop control equation of the excitation controller after considering the primary voltage regulation effect, that is,

[0083]

[0084] When taking G e When (s) is an integral regulator, let G e (s) / D q =1 / Ks, then

[0085]

[0086] Formula (1-8) is the closed-loop control equation of the PV-VSG DC / AC partial excitation controller. Since the excitation regulator indirectly controls the reactive power output of the synchronous generator by controlling the change in the terminal voltage, and for the inverter controlled by high-frequency power electronic switches, the modulation wave in the low-frequency band and the bridge arm output voltage (equivalent synchronous generator terminal voltage) can be approximately regarded as a proportional relationship. Therefore, the output of the excitation regulator of Formula (1-8) can be made the PV-VSG modulation wave voltage, then Formula (1-8) can be rewritten as

[0087]

[0088] It can be seen from formula (1-9) that the reactive loop of the PV-VSG DC / AC part simulates the primary voltage regulation characteristics of the synchronous generator.

[0089] The PV-VSG active loop and reactive loop simulate the inertia damping and automatic frequency and voltage regulation characteristics of the synchronous generator respectively. The output of the active loop is used as the frequency and phase of the inverter bridge arm voltage instruction, and the output of the reactive loop is used as the amplitude of the inverter bridge arm voltage. The three-phase modulation wave e ma 、e mb and e mc The expression is

[0090]

[0091] At this point, the virtual impedance is introduced to obtain the reference of the PV-VSG DC / AC part current inner loop command in the three-phase stationary coordinate system, that is,

[0092]

[0093] Where L v 、r v Represents the constructed virtual impedance inductor and its parasitic resistance;

[0094] e gabc Indicates the three-phase grid voltage.

[0095] The obtained current inner loop command reference and the sampled three-phase inductor current feedback signal i Labc The coordinate transformation is performed, and the current inner loop controller is constructed in the two-phase rotating coordinate system to realize the closed-loop control of the inverter output inductor current. The current inner loop control equation is:

[0096]

[0097] Where i dref 、i qref represents the inductor current reference signal;

[0098] i Ld 、i Lq Represents the three-phase inductor current feedback signal;

[0099] E gd 、E gq It represents the grid voltage in the two-term rotating coordinate system d q The weight below the axis;

[0100] K p , K I Represents the proportional coefficient and integral coefficient of the current inner loop regulator. The current inner loop output signal M in the dq axis coordinate system vdq After the inverse Park transformation, the modulation signal M in the two-phase stationary coordinate system is further obtained. vαβ , and finally generate a duty cycle signal to control the DC / AC part of the PV-VSG through SVM.

[0101] The typical control block diagram of PV-VSG grid connection is as follows: Figure 2 As shown. In the initial stage of the PV-VSG DC / AC part, the traditional grid-connected inverter power closed-loop control strategy (phase locked loop-power control, PLL-PC) is used. That is, the grid-connected switch S is closed first. w , according to the sampling, the three-phase grid voltage e is obtained gabc The phase is locked to obtain the amplitude Egd and phase θ of the grid voltage in the two-phase rotating coordinate system. g . The grid-connected inverter power dispatch instruction P ref , Q ref Converted into the corresponding active and reactive current reference signal i dqref And the closed loop control is performed through the current loop. The current loop controller outputs the signal M dq After inverse park transformation, the corresponding modulation wave M is generated αβ . Control logic switch S selects M αβ , enter the space vector modulation to generate the duty cycle signal that controls the switching tube.

[0102] At the same time, the controller runs the PV-VSG control algorithm offline. In the PV-VSG system control, the control logic switches S to select the virtual calculated reactive power Q ve , virtual calculation of active power P ve , virtual calculation of inductor current i vLabc , enter the PV-VSG control loop offline closed-loop operation. At this time, the PV-VSG DC / AC system control equation is:

[0103]

[0104] The current inner loop output signal M in the PV-VSG system control vabc After the inverse Clark transform, the three-phase modulation wave M is obtained. vabe Since the inverter three-phase modulation wave is equivalent to the inverter bridge arm voltage fundamental component, in the offline operation environment, a virtual equivalent main circuit can be further constructed in the control strategy to obtain the corresponding three-phase virtual inductor current i vLabc ,Right now

[0105]

[0106] Where L f 、r f Indicates the filter inductance value and parasitic resistance value in the real main circuit of the PV-VSG inverter.

[0107] According to the obtained three-phase virtual inductor current ivLabc And the actual grid voltage e obtained by sampling gabc Calculate and generate virtual active power P ve . and virtual reactive power Q ve , and sent to the PV-VSG system control under offline operation.

[0108] The traditional grid-connected inverter PLL-PC control strategy running online and the PV-VSG control strategy running offline are run in the controller at the same time. When the power dispatch instructions in the two control strategies are exactly the same, the modulation wave M in the online PLL-PC control strategy is αβ The modulation wave M of the PV-VSG control strategy during offline operation vαβ The inverter system will inevitably remain approximately the same, thus meeting the conditions for switching the overall control strategy of the inverter system from the PLL-PC control strategy to the PV-VSG control strategy. At this time, it is only necessary to switch the logic selection switch S from the initial state of Q ve , P ve 、i vLabc 、M αβ Switch to Q e , P e 、i tabc 、M vαβ , the PV-VSG control algorithm of the grid-connected inverter can be converted from offline operation to online operation, and the overall switching of the grid-connected inverter control loop from the PLL-PC control strategy to the PV-VSG control algorithm can be achieved.

[0109] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0110] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of the present invention to be protected.

Claims

1. A control method for an energy storage converter based on a virtual synchronous motor, including a grid-connected implementation method, characterized in that: The grid connection implementation method includes the following steps: The grid frequency and phase information are extracted from the grid voltage signal using a phase-locked loop; Calculate the actual active power and reactive power; According to system requirements and preset goals, set the reference value P of active power and reactive power ref and Q ref ; Through the current controller, according to the result of power regulation, the current output by the inverter is controlled so that the output current meets the set power requirement; The three-phase current is transformed into the current component i in the dq coordinate system. d and i q ; According to the current component of the dq coordinate system, the on and off time of the inverter switch device is controlled, thereby realizing the control of the AC power output.

2. The energy storage converter control method based on a virtual synchronous motor according to claim 1, characterized in that: Based on the DC current i output by the photovoltaic array Labc , and the grid voltage e gabc , calculate the actual active power and reactive power.

3. The energy storage converter control method based on a virtual synchronous motor according to claim 1, characterized in that: Space vector pulse width modulation technology is used to generate PWM pulse signals to control the on and off time of the inverter switching devices.

4. A method for controlling an energy storage converter based on a virtual synchronous motor according to any one of claims 1 to 3, characterized in that: It also includes DC / AC control methods, including: Obtain DC and AC parameters and grid voltage parameters; Adjust the output voltage of the VSG to synchronize it with the grid voltage; Set the voltage outer loop controller to control the amplitude of the AC side voltage; set the reference voltage value U ref , and compare it with the actual voltage value U0 to calculate the voltage error; According to the model of virtual synchronous generator, set the DC / AC partial active loop to simulate the moment of inertia, damping effect and primary frequency modulation characteristics of the synchronous generator; Add an excitation controller to adjust the excitation current of the synchronous motor in real time to adjust the amplitude of its potential and maintain the constant output voltage of the synchronous motor; The closed-loop control equation of the excitation controller after considering the primary voltage regulation is obtained, and the reactive power Q of the synchronous motor is indirectly controlled by controlling the extreme voltage change. e Output, set the DC / AC part reactive loop to simulate the primary voltage regulation characteristics of the synchronous motor; Introducing virtual impedance L v , γ v To obtain the reference of the DC / AC part current inner loop command in the three-phase static coordinate system; The obtained current inner loop command reference is compared with the obtained three-phase inductor current feedback signal i Labc Perform coordinate transformation; A current inner loop controller is constructed in a two-phase rotating coordinate system to achieve closed-loop control of the inverter output inductor current.

5. The energy storage converter control method based on virtual synchronous motor according to claim 4 is characterized in that: DC and AC parameters include: DC side voltage U dc , AC side voltage amplitude and frequency, inductance L, capacitance C, moment of inertia J, damping coefficient K d .

6. The energy storage converter control method based on virtual synchronous motor according to claim 4 is characterized in that: The grid voltage parameters include: grid voltage phase, rated angular frequency ω n and amplitude.

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