New energy converter system and method with electric energy management function

Abstract

The application provides a new energy converter system and method with electric energy management function, which comprises an inverter DC side capacitor used as an energy storage element, an inductive element used for transmission to a power grid, a voltage source inverter used as a power converter, a control unit, and sensors, fuses, radiators and the like. For the electric energy quality problem, the application proposes a harmonic controller structure containing an error-free harmonic estimator, which eliminates the mutual coupling with the fundamental current controller. In the structure, the output of the estimator is decoupled from the fundamental current, and there is no mutual coupling between the individual harmonics. In addition, the new harmonic suppression allows parallel operation with the current controller, and the two do not affect the accuracy and dynamic response of each other.

Description

Technical Field

[0001] This invention relates to the field of power quality control technology for new energy converter systems, and more specifically, to a new energy converter system and method with power management functions. Background Technology

[0002] The transition to sustainable energy has spurred the rapid proliferation of new microgrids, such as solar and photovoltaic (PV) systems, providing localized renewable energy generation for communities, industries, and remote areas. However, integrating solar and other renewable energy sources into microgrids presents significant challenges in maintaining power quality due to the volatility of solar power generation and the presence of nonlinear loads (such as inverters, DC-DC converters, uninterruptible power supplies, frequency converters, rectifiers, and other electronic loads). These nonlinear loads generate harmonics and other distortions, thereby degrading the power quality of microgrid systems. Power quality refers to the deviation of voltage, frequency, and current amplitude from their nominal values, which can potentially damage power infrastructure or equipment.

[0003] One of the main power quality disturbances in emerging microgrids such as solar and photovoltaic systems is harmonic distortion, which stems from voltage and current waveform distortion caused by the operation of these nonlinear devices. Based on their order, harmonics can be classified into three types: even harmonics, odd harmonics, and third harmonics. Addressing power quality issues in emerging microgrids such as solar and photovoltaic systems is crucial for ensuring the efficiency and reliability of these systems, especially as they become increasingly integrated into critical power infrastructure.

[0004] Harmonic currents can interfere with the operation of AC power grids with electronically controlled distributed power sources and loads. Harmonic suppression methods in grid-connected inverters suffer from limitations such as limited attenuation of low-order harmonics, poor suppression of high-order harmonics, and dynamic coupling between current and harmonic controllers, all of which degrade overall performance. In AC power grids containing inverters, even small current harmonics can lead to harmonic resonance, stability issues, frequent tripping, and power outages. These factors underscore the necessity of harmonic control solutions.

[0005] In view of this, the present invention proposes a harmonic controller that can suppress residual harmonics to at least 60 dB below the rated current. This structure includes a novel error-free harmonic estimator and an original controller that eliminates mutual coupling with the fundamental current controller. In this structure, the output of the estimator is decoupled from the fundamental current, and there is no mutual coupling between the individual harmonics. Furthermore, the novel harmonic suppression allows for parallel operation with the current controller without affecting each other's accuracy and dynamic response.

[0006] Patent application CN113067338A discloses a composite control type power quality controller, including a transformer, a passive filter, a control system, and an inverter. It generates a control signal input to the inverter by detecting the harmonic current signal of the transformer's primary winding and the voltage deviation signal of the nonlinear load, enabling the equivalent impedance of the transformer's primary winding to exhibit a four-quadrant continuously adjustable characteristic, thus achieving harmonic isolation and voltage compensation. However, this patent cannot completely solve the existing technical problems, nor can it meet the needs of this invention. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the purpose of this invention is to provide a new energy converter system and method with power management functions.

[0008] The new energy converter system with power management function provided by the present invention includes: inverter DC side capacitor, inductor, voltage source inverter, control unit and sensor; The inverter DC-side capacitor serves as an energy storage element; the inductor serves as a transmission element to the grid and connects the inverter phase to the grid; the voltage source inverter serves as a power converter; the control unit includes a synchronization algorithm module, a DC bus capacitor voltage regulation algorithm module, a harmonic extraction module, and a current control module. The DC side of the voltage source inverter is connected to the DC side capacitor of the inverter, and the AC side of the voltage source inverter is connected to the power grid through the inductor. The sensors are respectively installed on the DC side and AC side of the voltage source inverter to collect the DC side capacitor voltage signal, the grid side current signal and the load current signal, and transmit the collected signals to the control unit. The synchronization algorithm module receives the grid voltage signal collected by the sensor, generates a synchronization phase angle signal, and outputs it to the harmonic extraction module and the current control module respectively. The DC bus capacitor voltage regulation algorithm module receives the DC side capacitor voltage signal collected by the sensor, generates a DC current estimation signal, and outputs it to the current control module. The harmonic extraction module receives the load current signal collected by the sensor and the synchronization phase angle signal output by the synchronization algorithm module, performs Parker transformation on the three-phase load current, converts the three-phase load current in the three-phase stationary coordinate system into the three-phase load current in the rotating coordinate system, separates the fundamental component and harmonic components through a low-pass filter, performs inverse Parker transformation on the harmonic components to generate a reference current signal, and outputs the reference current signal to the current control module. The current control module receives the reference current signal, the estimated DC current signal, and the synchronization phase angle signal, generates a switching drive signal for controlling the voltage source inverter, and outputs it to the voltage source inverter, so that the voltage source inverter injects compensation current into the grid.

[0009] Preferably, the harmonic extraction module detects and extracts harmonic components based on a synchronous reference coordinate system method, specifically as follows: The Parker transform matrix is ​​applied to convert the three-phase load current in the three-phase stationary coordinate system into the three-phase load current in the rotating coordinate system. The reference phase angle is provided by the phase-locked loop synchronizer for sine and cosine calculation. In the rotating coordinate system, the fundamental component is a fixed waveform and the harmonic components are oscillating waveforms. A second-order low-pass filter is used to separate the fundamental and harmonic components. The required reference current is generated using the harmonic components extracted by the inverse Parker transform.

[0010] Preferably, the DC bus capacitor voltage regulation algorithm module uses a proportional-integral controller to compare the collected DC side capacitor voltage with the desired reference value and estimate the magnitude of the DC current used for DC side regulation. The estimated value is the value required to maintain the DC side capacitor voltage at the desired reference value to compensate for switching losses.

[0011] Preferably, the synchronization algorithm module employs a three-phase phase-locked loop (PLL). The PLL simulates a closed-loop control system, utilizing an internal frequency oscillator to track the frequency and phase of a sinusoidal three-phase signal. The input variables include: the normalized three-phase grid voltage signal expressed in per-unit values, the measured frequency in Hertz, and an angle varying between 0 and 2π and synchronized with the positive-sequence zero-crossing point of the A-phase fundamental wave, where π is pi. The angular velocity of the internal oscillator is used to convert the three-phase input signal into a rotating coordinate system via Parker transformation. The q-axis component of the signal is proportional to the phase difference between the three-phase signal and the rotating coordinate system of the internal oscillator. This q-axis component is filtered by an averaging module. A proportional-integral-derivative (PID) controller with automatic gain control acts on the controlled oscillator to keep the phase difference zero. The output of the PID controller corresponds to the angular velocity, which is converted into a frequency in Hertz after filtering.

[0012] Preferably, the current control module includes a harmonic controller, which contains an error-free harmonic estimator. The output of the harmonic estimator is decoupled from the fundamental current, and there is no mutual coupling between the harmonics. The harmonic controller operates in parallel with the fundamental current controller, and the sampling period of the harmonic controller is... Sampling period of the current control loop Integer multiples of, i.e. ,in It is an integer greater than or equal to 1; The harmonic controller includes decouplers for each harmonic, and the parameters of the decouplers are... Determine as follows:

[0013] in, Let be the real part parameters of the nth harmonic decoupler. The imaginary unit, Let be the imaginary part parameter of the nth harmonic decoupler. Let be the rotational angular velocity of the nth harmonic reference coordinate system. Let be the pulse transfer function of the current controller closed-loop system in the grid synchronous coordinate system for voltage disturbances. Let be the rotational angular velocity of the power grid synchronous coordinate system. The sampling interval is... Let e ​​be the transfer function of the LCL output filter in the stationary coordinate system, where e represents a parameter in the reference coordinate system. The voltage command output by the harmonic controller is divided by Obtain the voltage correction for each harmonic under consideration, and ensure that the current change generated by the voltage correction has the same phase and direction as the voltage command.

[0014] Preferably, the harmonic controller further includes a slope limiter module, which receives each harmonic control cycle. The updated reference value at the end, the voltage correction amount during the current control loop sampling period During the sampling period of the harmonic controller, the value linearly increases from the current value to the new reference point. The slope remains constant for the remaining half-cycle, and the slope of the slope limiter module is determined as follows:

[0015]

[0016] in, This represents the increment of the voltage disturbance. The slope of the voltage change. The sampling interval is... Let Z be a complex variable. This represents the steady-state final value of the current error under voltage ramp disturbance. For the gain of the current controller, Let be the rotational angular velocity of the power grid synchronous coordinate system. This is the equivalent load inductance.

[0017] Preferably, the tracking error in the harmonic controller It is fed into the input of the integrator REG, where The next harmonic control period for the nth harmonic in the dq coordinate system. The average value within the range, the output of the integrator REG, is processed by the decoupler to obtain the voltage correction value, and the voltage command of the harmonic controller. Represented as:

[0018] in, For feedback current Z-transform, The integral gain coefficient of the harmonic controller. Let Z be a complex variable. C is the imaginary unit, C is the real part of the decoupler parameter, and D is the imaginary part of the decoupler parameter. Characteristic polynomial of the closed loop of the harmonic controller for:

[0019] The stability limit of the characteristic polynomial appears to occur when... .

[0020] Preferably, when N grid-connected inverter units operate in parallel and share the same connection point PCC, the relationship between the total grid current and the harmonic current reference command of each grid-connected inverter unit is as follows: The total grid current is the sum of the output currents of each grid-connected inverter unit; Open-loop gain function for:

[0021] Closed-loop transfer function for:

[0022] The characteristic polynomial of the system for:

[0023] in, This refers to the total number of grid-connected inverter units operating in parallel. The ratio is the equivalent series impedance of the power grid. For real numbers, This is the equivalent output impedance of a single grid-connected inverter unit.

[0024] Preferably, the grid-side current in the current control module includes the response of residual harmonics and fundamental current to the reference current. The reference value of the current control loop is subtracted from the feedback value of the inverter-side current in the dq coordinate system after passing through the estimator to maintain the step response and decouple the harmonic controller. The expression for the grid-side current is:

[0025] in, This is an estimated value of the grid-side current in the synchronously rotating dq coordinate system; This is the pulse transfer function for the current control loop; The current loop fundamental reference current command; This refers to the residual harmonic current component. This is the fundamental current component; The estimated residual harmonic current components are obtained by subtracting the estimated fundamental current components from the grid-side current estimates:

[0026] in, The estimated residual harmonic current components; The estimated fundamental current component; This is an estimation model for the closed-loop pulse transfer function of the current control loop; This is the fundamental current reference command.

[0027] The new energy converter control method with power management function provided by the present invention includes the following steps: Step 1: Collect DC-side capacitor voltage, grid voltage, load current, and grid-side current; Step 2: Generate the synchronization phase angle using a synchronization algorithm; Step 3: Using the DC bus capacitor voltage adjustment algorithm, compare the collected DC side capacitor voltage with the expected reference value to generate an estimated DC current value; Step 4: Using the harmonic extraction algorithm, the three-phase load current is transformed by Parker transformation to convert the three-phase load current in the three-phase stationary coordinate system into the three-phase load current in the rotating coordinate system. The fundamental component and harmonic components are separated by a low-pass filter, and the harmonic components are transformed by inverse Parker transformation to generate the reference current. Step 5: Using a current control algorithm, generate the switching drive signal for the voltage source inverter based on the reference current, the estimated DC current value, and the synchronous phase angle; Step 6: Run the harmonic controller and the fundamental current controller in parallel. The harmonic controller includes an error-free harmonic estimator, and the output of the harmonic estimator is decoupled from the fundamental current. Step 7: Estimate the fundamental current response based on the reference current, subtract the estimated fundamental current response from the grid-side current to obtain the residual harmonic current, and input the residual harmonic current into the harmonic controller for harmonic suppression.

[0028] Compared with the prior art, the present invention has the following beneficial effects: (1) The harmonic controller proposed in this invention can suppress residual harmonics to at least 60 dB below the rated current, effectively solving the problems of limited attenuation of low-order harmonics and poor suppression of high-order harmonics in the prior art, and greatly improving the power quality management capability of grid-connected inverters for new energy. (2) Through the coordinated operation of the error-free harmonic estimator and the decoupler, the output of the estimator is completely decoupled from the fundamental current, and there is no mutual coupling between the harmonics. The harmonic controller and the current controller can run in parallel without affecting each other's accuracy and dynamic response, thus fundamentally eliminating the dynamic coupling problem between the current controller and the harmonic controller in the prior art. (3) The present invention obtains the residual harmonic signal by subtracting the estimated fundamental current response from the grid-side current, so that the harmonic estimate is not affected by the transient of the grid-connected inverter control loop, which greatly improves the accuracy of harmonic detection and the stability of harmonic control. (4) Through rigorous stability analysis and vector margin evaluation, this invention can operate stably in the presence of other grid-connected inverters, grid asymmetry and grid impedance changes. It can meet the stability conditions under both strong and weak grid conditions, and is particularly suitable for practical application scenarios where multiple grid-connected inverters are connected in parallel at close range. (5) The present invention has good robustness when parameters change, and integral control can achieve a stable and robust response without proportional action, which reduces the complexity of controller parameter tuning and improves the engineering applicability of the system. Attached Figure Description

[0029] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a schematic diagram of the new energy converter system proposed in this invention; Figure 2 The diagram shows the structure of the decoupled, error-free harmonic estimator (left) and harmonic controller (middle) proposed in this invention. Figure 3 For the present invention and Schematic diagram of signal acquisition and transformation; Figure 4 The present invention proposes and Figure 2 Delay time related to the middle harmonic controller; Figure 5 The circuit topology proposed in this invention consists of N grid-connected inverter GCI units. Detailed Implementation

[0030] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0031] like Figure 1 This invention presents a new energy converter system with power management capabilities, comprising a three-phase parallel active power filter (SAPF) connected to the main power supply, nonlinear load, and control algorithm. The SAPF is connected between the power supply / grid and the load / nonlinear load that generates harmonics. Overall, the system mainly consists of the following five parts: The DC-side capacitor of the inverter is used as an energy storage element. Inductors are used as components to transmit power to the grid and connect the inverter phases to the grid; Voltage source inverter (VSI) is used as a power converter; Control unit; Other components include sensors, fuses, and heat sinks.

[0032] The control unit includes a synchronization algorithm module, a DC bus capacitor voltage regulation algorithm module, a current control module, and a harmonic extraction module.

[0033] Nonlinear loads absorb fundamental and harmonic currents during operation. Furthermore, the power grid needs to supply both fundamental and harmonic currents to the nonlinear load. Therefore, the SAPF must generate a harmonic current of equal magnitude but opposite polarity to the harmonic current supplied by the power grid. The appropriate compensation current injected by the SAPF... It can compensate for and cancel harmonic components in the grid current, since the current at this time only contains the fundamental component, and the grid current... The waveform will be restored to a sine wave. Therefore, the total harmonic distortion (THD) of the grid-side current can be reduced as much as possible. Furthermore, the proposed SAPF structure has reactive power compensation capabilities; if reactive power compensation is required, the filter can provide it. This feature avoids sending or receiving additional reactive power to or from the grid, thereby improving the quality of transmitted power. If the SAPF needs to provide reactive power, it only needs to add a portion of the converted reactive power to the q component, thus compensating for a portion of the reactive power required by the load, thereby reducing the pressure on the grid.

[0034] In this invention, based on the current-based application scenario, either the Synchronous Reference Coordinate System (SRF) or the dq coordinate system method was selected to detect and extract harmonic components. A classic PI controller was used to adjust the DC-side capacitor voltage, and a synchronization algorithm based on a phase-locked loop (PLL) was employed. These methods were considered the best choice to easily meet the needs of this research.

[0035] Harmonic current extraction or detection is a prerequisite for the SAPF control unit. This algorithm, the first stage of SAPF control, is also known as the reference signal generation module. Its main task is to detect and separate harmonic components and generate a suitable reference signal accordingly. This part, operating quickly and accurately, generates a suitable reference current, thereby controlling the SAPF so that the compensator can regenerate the required injection current to reduce harmonics based on this correct reference current signal. These algorithms use a signal processing function called a distortion identifier, which receives the distorted nonlinear load current signal and generates a corresponding reference current signal by separating the distorted components from the original components. Harmonic extraction based on the Synchronous Reference Coordinate System (SRF, also known as dq theory or dq coordinate system) is accomplished by mathematically calculating the three-phase load current in the dq0 coordinate system. The Park transformation matrix is ​​applied to transform the three-phase load current in the abc coordinate system. Convert to three-phase load current in dq0 coordinate system Only the dq coordinate system participates in the extraction process, and the phase angle is referenced. Provided by a phase-locked loop (PLL) synchronizer, used for sine and cosine sin_cos calculations. In the dq coordinate system, the fundamental component... It manifests as a fixed waveform, while harmonic components... This manifests as an oscillating waveform. Typically, a second-order low-pass filter (LPF) is used to separate the fundamental and harmonic components. Finally, the harmonic components extracted via the inverse Parker transform are used to generate the desired reference current. .

[0036] A DC-side capacitor voltage regulator is a control algorithm that obtains the DC-side capacitor voltage. And compare it with the expected reference value. By comparing these values, the appropriate DC current for DC-side regulation can be estimated. (Estimated value) It is to maintain The desired reference value is the value required to adjust (compensate) switching losses. The DC-side capacitor is an energy storage element used to provide the active power difference between the power required by the load and the power provided by the power source during transients. It also provides a voltage with low ripple. In steady state, the active power provided by the power source must equal the active power required by the load plus the power caused by SAPF losses, which keeps the DC-side voltage constant at the reference value. Whenever load conditions change, the active power balance between the power source and the load is disrupted, and the power difference must be compensated by the DC-side capacitor. This causes the DC-side capacitor voltage to change and deviate from the reference value. For the capacitor to function properly, a certain amount of active current must be exchanged with the power source. This active current causes the capacitor to charge or discharge, and if the DC-side capacitor voltage remains constant at the reference value, the actual power consumed will equal the power supplied by the power source. Therefore, the magnitude of this active current received from the power source is controlled by a control circuit that keeps the DC-side capacitor voltage constant. A capacitor voltage lower than the reference value means that the power source is providing less active power to meet the load demand, and therefore more active current must be received from the power source. Similarly, if the capacitor voltage exceeds the reference value, the control module will attempt to reduce the active current received from the power supply. With a fixed DC voltage, the DC-side capacitor is only responsible for providing the DC voltage; therefore, the reactive power that should be compensated for by the load must be handled by this capacitor. The method chosen in this section is to use a classic proportional-integral (PI) controller.

[0037] A synchronization algorithm is required to ensure that SAPF remains in phase synchronization with the operating power system. Furthermore, a synchronization phase angle must be provided for coordinate transformations and related calculations. The three-phase phase-locked loop (PLL) module simulates a closed-loop control system that uses an internal frequency oscillator to track the frequency and phase of a sinusoidal three-phase signal. In this method, the input variables include: a normalized three-phase grid voltage signal expressed in per-unit values. Measurement frequency in Hertz The input signal is represented by an angle (in radians) Wt, varying between 0 and 2π and synchronized with the zero-crossing point of the fundamental (positive sequence) wave of phase A, where π is pi. The three-phase input signal is converted to a rotating coordinate system (Parker transform) dq0 using the angular velocity of the internal oscillator. The quadrature-axis (q-axis) component of the signal is proportional to the phase difference between the abc signal and the rotating coordinate system of the internal oscillator; this component is filtered by an averaging (frequency conversion) module. A proportional-integral-derivative (PID) controller with optional automatic gain control (AGC) operates on the controlled oscillator to maintain the phase difference at zero. The PID output corresponds to the angular velocity, which is then filtered and converted to a frequency in Hertz for use by the averaging module.

[0038] As the most important part, current control will focus on designing a control method to achieve fast and accurate tracking of the reference signal and maintain stable and robust operating conditions.

[0039] Controller structure and parameter design: Under conditions of decoupled and error-free harmonic estimation, a harmonic controller employing integral action and realizable control output possesses the prerequisites for suppressing dominant harmonics. The design of the harmonic controller should ensure that: (1) Stable operation in the presence of other grid-connected inverters (GCI), grid asymmetry and grid impedance changes; (2) Suppress residual current harmonics to at least 60 dB below the rated current; (3) The operation of the harmonic controller does not affect the dynamic characteristics of the current control loop; (4) The harmonic controller is not sensitive to transient phenomena in the current control loop; (5) It is robust when parameters change.

[0040] To suppress residual harmonics, the harmonic controller must provide a voltage correction amount. (See Figure 2 This is then superimposed on the voltage command of the current controller; n is a natural number greater than or equal to 1. The integral module REG is a necessary prerequisite to ensure that the steady-state error is zero. The subsequent design is based on the following fundamental assumption: the rate of change of grid harmonics is much slower than... and several The adjustment time of the cycle meets the requirements, among which, The sampling period of the current control loop. The sampling period of the harmonic controller; Figure 2 A decoupled and error-free harmonic estimator (left) and harmonic controller (middle). Input signal. It will be converted into the form in the reference coordinate system corresponding to each harmonic. The value in is The average value was obtained by taking the average over the time interval, and This is precisely q times the sampling period of the harmonic controller; q represents an integer. The voltage correction values ​​from each harmonic controller will be converted back to... In the coordinate system, the values ​​are then added together to obtain the final voltage correction value. .

[0041] The controller is designed as follows: The output of each harmonic estimator is used Figure 2 Left side This indicates that the harmonic controller can employ a quasi-integrator, a PI controller, or a simple integrator with a finite DC gain definition. Although Figure 2 The integral action of the integral module REG in the model is necessary to eliminate steady-state error. Based on stability analysis, it is shown that a stable and robust response can be achieved without proportional action.

[0042] Figure 2 Output of the intermediate integration module REG The instantaneous decoupling voltage correction vector used to calculate the nth harmonic. The system responds to voltage commands. The response is determined by the admittance The description states that this admittance introduces a significant phase delay. Since the frequency of the primary harmonics is relatively high, the corresponding delay could jeopardize the operation of the harmonic controller. This can be addressed by... Figure 2 A dedicated decoupler is placed before the integrator to suppress phase delay. Inaccurate calculation of the decoupler parameters will affect the integrator input and lead to steady-state error. Therefore, Figure 2 Decoupling in The output of the integrator After that, among them, Let be the real part parameters of the nth harmonic decoupler. The imaginary unit, Let be the imaginary part parameter of the nth harmonic decoupler.

[0043] The principle for setting the decoupler parameters is as follows: In most grid-connected inverter GCI units, the resonant frequency of the LCL output filter is... and the closed-loop bandwidth of the current controller All are much higher than It is reasonable to assume that any transient processes within the current loop and LCL output filter will... End of section, in which, This is the time increment. Because... The slowly varying execution voltage correction vector for the nth harmonic after slope limiting is 40ms. With slow The rate of change is slow, and the amplitude of the background harmonic voltage (BHV) changes slowly, so it is reasonable to assume that the system is sensitive to changes in the background harmonic voltage (BHV). The changing response can be obtained from the steady-state model of the LCL output filter and current controller. For design... Figure 2 The harmonic controller needs to obtain: (1) in, It is the nth harmonic. Voltage correction in a rotating coordinate system It is the first angular velocity of the subharmonic reference coordinate system It is the nth harmonic. The system response current in a rotating coordinate system; the subscript e indicates that this parameter is a quantity in the reference coordinate system; Let be the corresponding admittance matrix. Under steady state, the relevant voltage and current are both complex constants. They are in the three-phase stationary coordinate system and the first... Subharmonic The values ​​in the reference coordinate system are related through the following transformation: (2) in, The conduction angle; For the stationary coordinate system ( The voltage correction amount for the nth harmonic under the axis; Let be the rotational phase angle of the nth harmonic reference coordinate system; For the stationary coordinate system ( The system response current corresponding to the nth harmonic under the axis; n is the harmonic order.

[0044] Admittance This depends on the closed-loop dynamic characteristics of the internal current controller of the grid-connected inverter's GCI and the parameters of the LCL output filter. This is achieved through composite feedback. By introducing a current loop, the feedback change caused by the inverter voltage change can be determined by a single equivalent inductance. These are the inductors of the left and right capacitors connected in parallel to the LCL output filter, respectively. The capacitor current of the LCL output filter; This refers to the output of the current control loop used in the LCL output filter. In the grid synchronization coordinate system, the closed-loop current controller responds to disturbances. Feedback response The value is given by the step function, where It is the angular frequency of voltage disturbance in the power grid synchronous coordinate system, and It depends on the current controller and system parameters. Therefore, the transfer function can be changed from a rotational speed of... The power grid synchronous coordinate system is transformed to a rotational speed of (and ahead of the grid synchronization coordinate system) ) The subharmonic reference coordinate system, where... The angular frequency difference between the nth harmonic reference coordinate system and the power grid synchronization coordinate system is given by [reference coordinate system]. Let be the rotational angular velocity of the reference coordinate system for the nth harmonic.

[0045] (3) Where s represents the complex frequency; Indicates the sampling interval; z indicates that the transformation is a z-transform function; Let be the pulse transfer function of the current controller closed-loop system for voltage disturbances in the grid synchronization coordinate system; This represents the expression of the change in the composite feedback current in the Z-domain. This represents the increment of the voltage disturbance. The minimum value of the reference input quantity. The imaginary unit, It is the angular frequency of voltage disturbance in the power grid synchronous coordinate system; make Substitute: (4) in, It is the equivalent admittance transfer function of the current controller closed-loop system in the synchronous rotating coordinate system (dq axis) of the power grid; To be the admittance in the nth harmonic coordinate system, To convert the admittance of the power grid coordinate system through frequency shift The expression after transformation to the nth harmonic coordinate system; income Defined the first Composite feedback in the subharmonic reference coordinate system Steady-state relationship with voltage disturbances. In a stationary coordinate system, the grid-side current... With composite feedback The relationship is: (5) Where c represents the parallel capacitance value of the LCL output filter; This refers to the grid-side (power grid-side) current in a stationary coordinate system. The composite feedback current is in the stationary coordinate system. Let be the transfer function of the LCL output filter in the stationary coordinate system; Convert it to the first When using the subharmonic reference coordinate system, simply use Replace with Thus we get: (6) Calculate the coefficient corresponding to each harmonic according to the above formula. And used by the corresponding decoupler. Figure 2 In the middle, the output of the harmonic controller Divide by Obtain the voltage correction amount for each harmonic considered. Thus, the voltage correction amount The generated Changes and voltage commands They have the same phase and direction. In each At the end of the sampling interval, voltage command A step change occurs and a new correction value is taken. Figure 2 The structure is designed to drive the selected harmonics to zero. Tracking error. Sent to Figure 2 The input terminal of the integrator REG, where, For the nth harmonic in the dq coordinate system, one harmonic control period The average value within the range. Accurately setting the decoupler parameters. and And ignore Figure 2 When the slope limiter SLP module is used, the closed-loop gain of the system is The closed-loop transfer function is It has real poles And for any All can operate stably, among which, The integral gain coefficient of the harmonic controller. Let be a complex variable of the Z-transform.

[0046] Decoupled operation analysis of harmonic controller: In order to effectively suppress current harmonics, it is necessary to prevent the influence of the GCI current transient process of the grid-connected inverter on the residual harmonic detection.

[0047] Figure 3 Grid-side current Residual harmonics The response of the fundamental current to the reference current It consists of two parts: (7) in, This is the estimated value of the grid-side current in the synchronous rotating dq coordinate system (expressed in the Z domain). The pulse transfer function (closed-loop equivalent model) of the current control loop characterizes the dynamic relationship between the reference current and the actual fundamental current response. This is the fundamental reference current command for the current loop (Z domain), with the subscript F representing the fundamental frequency and the superscript F representing the fundamental frequency. These are reference values ​​after sampling or being given. The residual harmonic current component (in the dq coordinate system) is the target signal to be suppressed; This represents the fundamental current component (actual fundamental response). Figure 3 For the present invention and Schematic diagram of signal acquisition and transformation. Current loop reference value. After estimator Then, the feedback value of the inverter-side current in the dq coordinate system. Subtraction is performed to preserve the step response and decouple (center) the harmonic controller HC. The harmonic estimator is compared with the controller input. (Bottom right) is through from Subtract from The obtained capacitor current The resulting HC voltage correction value. Superimposed on the running reference value Top (right side).

[0048] The grid-side current also includes PWM ripple, which is eliminated by averaging over one PWM cycle based on equally spaced samples, and therefore does not affect... Figure 3 The input signal. If the signal in the above equation is used for harmonic estimation, the result may be affected. The effects of current transients are significant because these transients may contain spectral components of harmonic frequencies. A precise understanding of the pulse transfer function is crucial. Under the premise that the reference current can be used to calculate The transient component. Subtract After that, the remaining signal It no longer contains current loop transient components, but only residual harmonics: (8) in, The estimated residual harmonic current components (represented in the Z-domain in the synchronously rotating dq coordinate system); The estimated fundamental current component (represented in the Z-domain in the dq coordinate system); This is an estimation model for the closed-loop pulse transfer function of the current control loop; The fundamental current reference command (represented in the Z-domain of the dq coordinate system).

[0049] Due to the input to the harmonic estimator Not included Disturbances, therefore the harmonic estimates are protected from the transients of the grid-connected inverter's GCI control loop.

[0050] In addition to the measures mentioned above, the harmonic controller must also include measures to suppress the influence of its own control action on the transient response of the current control. Figure 2 Control quantity in This is a voltage correction value, which corresponds to an external disturbance for the current controller. Because the sampling time of the harmonic controller is... The corresponding dynamic phenomena are decoupled by at least two orders of magnitude. However, without Figure 2 The slope limiter SLP module, in each Update time at the end of the sampling interval, voltage correction amount Sudden changes can disrupt the operation of the current loop and introduce current errors. To avoid this unwanted coupling, the proposed harmonic controller includes a slope limiter (SLP) module to limit... The rate of change.

[0051] When the slope When sufficiently reduced, the resulting current error is negligible, where t is the unit of time. However, an excessively low slope can impair the performance of the harmonic controller. Therefore, it is necessary to establish a slope for a typical current controller. Approximate relationship between the error and the associated current. In synchronization... In the coordinate system, voltage disturbance Caused current error Depends on admittance : (9) in, This is the increment of the current error. This represents the increment of the voltage disturbance. This represents the reference current command of the current control loop in the synchronously rotating dq coordinate system. For the equivalent load inductance, This is the equivalent load resistance; set up It is the gain of the current controller. and These are equivalent load parameters. It is the sampling time of the current control loop, polynomial for: (10) in, This is the closed-loop characteristic polynomial of the current controller, used to analyze the stability and dynamic characteristics of the inner current loop. The slope is The voltage ramp can be expressed as: (11) If this voltage ramp persists, the current error will stabilize to: (12) in, The steady-state final value of the current error under voltage ramp disturbance; Under reasonable assumptions, and satisfying the following:

[0052] The maximum value does not exceed: (13) Figure 4 Showing with Figure 2 Delay time associated with the middle harmonic controller. Figure 4 The table shows the changes in voltage command and tracking error for a selected harmonic. Feedback ③ is obtained by averaging the harmonic estimates between times ① and ②. arrive The voltage command gradually changed to ④, This value is determined by ③ Real-time feedback Calculated.

[0053] The slope can be estimated as follows: assuming that any single step change in the background harmonic voltage (BHV) does not exceed a certain percentage of the rated voltage. And the harmonic controller in Internal compensation for such changes. In this case, each Within the period The change does not exceed The corresponding voltage slope is approximately No such amplitude change was detected during the experiment, except for the instant the harmonic controller was activated. , , At that time, the maximum current error was This error The impact of the harmonic controller on the operation of the current controller can be ignored. The calculated... The value was used in the design of the SPL slope limiter.

[0054] Figure 2 The slope limiter SLP module is designed as follows: In each At the end of the cycle, the module receives an updated reference value. The module outputs a signal. In the following (Equal to half a sampling period) During this period, the value rises linearly from the current value to a new reference point; During the remaining half of the cycle, Maintain a constant slope. The slope limiter SLP module works as follows: Figure 4 As shown.

[0055] Stability analysis, closed-loop poles and robustness analysis: Next, we will analyze the harmonic controller for one of the selected harmonics. Figure 4 subscript Indicates the observation sampling time . Figure 4 Voltage command in Due to tracking error The calculation yielded, where equal . The average value of the nth harmonic within one harmonic control period in the dq coordinate system is located in the interval [missing information]. Internal harmonic estimation value Obtained by averaging. For time-sampled variables. , and conduct Transformation yields its complex image function. , and Voltage command Represented as: (14) in, For feedback current Z-transform, Let be the real part of the decoupler parameter. This represents the imaginary part of the decoupler parameters; From the formula Voltage command The generated harmonic current is Considering the time intervals between sampling points From the piecewise linear transformation, we can obtain: (15) in, The average value of the harmonic current in the dq coordinate system (represented in the Z domain) within one harmonic control cycle. The instantaneous value of the harmonic current within the same harmonic period (represented in the Z-domain). From this, the loop gain of the developed harmonic controller can be derived. : (16) Characteristic polynomial of the closed loop of the harmonic controller for: (17) when When the closed-loop poles are real numbers, in The corresponding pole frequency in the domain is As the gain increases, the closed-loop poles become conjugate complex numbers, and their damping ratio... It gradually decreases. The stability limit appears at... .

[0056] In most cases, multiple GCI units operate in parallel close to each other, sharing the same connection point PCC. If all units are equipped with the proposed harmonic controller, it is necessary to verify whether stability conditions can be met under both strong and weak power grid conditions. The circuit topology is as follows: Figure 5 Represents a group A GCI unit is used, and its phasor voltage and current are considered for a selected harmonic, where... This represents the equivalent output impedance of a single GCI unit. The no-load voltage of the AC mains is... The equivalent series impedance is Harmonic voltages generated by each unit The harmonic current is determined by the output of the corresponding harmonic controller. That is Compared with background voltage The result of combined action.

[0057] Figure 5 A circuit consisting of N grid-connected inverter GCI units is connected to a power grid with finite impedance. Here, the steady-state voltage and current under the selected harmonics are considered.

[0058] Assume all grid-connected inverter GCI units have the same output impedance, the same harmonic controller, and the same parameters. Under the above assumptions, the voltage at PCC is GCI unit harmonic current It can be represented as: (18) in, This is the serial number of the grid-connected inverter (GCI) unit. This refers to the total number of grid-connected inverter (GCI) units operating in parallel. For voltage commands, the expression is: (19) in, This is the reference command value for harmonic current; This stability test is based on closed-loop pole calculations for a system containing multiple GCIs. Due to external disturbances... The perturbation can be reasonably assumed (without loss of generality) without affecting the system's characteristic polynomial and poles. Set to zero to simplify calculations.

[0059] At the frequency under consideration, the total grid current This is the sum of the output currents of each GCI unit. From the above two equations, the grid current can be obtained as: (20) From the above equation, the open-loop gain and closed-loop transfer function They are as follows: (21a) (21b) in, Z-transform of the total grid current; Z is the sum of the output currents of all GCI units. Z-transform of harmonic current reference command for a single GCI unit; At harmonic frequencies, and Both are primarily sensory, and the ratios Let be a real number, where, This is the equivalent output impedance of a single grid-connected inverter (GCI) unit. When hour, and The voltage drop across them is equal. Figure 5 The characteristic polynomial of the system for: (twenty two) The proposed Figure 2 Harmonic controller gain The curve relating to vector margin. The curve corresponds to... Different values ​​from 0 (strong grid) to 1.5 (weak grid). When the grid is an infinitely large strong grid, The characteristic polynomial of the above formula This is simplified to the characteristic polynomial of the harmonic controller closed loop. To explore... Applicable gain under changing conditions Range, depending on the transfer function Calculate the vector margin. The vector margin is defined as the ratio of the Nyquist curve to the point... The shortest distance, which characterizes the stability margin and reflects the system's ability to maintain stable operation when parameters change. Vector margin combines the commonly used gain margin and phase margin into a single index for evaluating the overall stability of the system.

[0060] The corresponding results clearly show that the proposed harmonic controller approaches its stability limit more easily under strong grid conditions than under weak grid conditions. At this time, the stability margin VM is maximized. If VM is required to be maximized... Then the gain needs to be limited to Larger The value can increase the bandwidth of the harmonic controller and its ability to suppress major harmonics. However, the gain... It will also amplify the harmonic feedback AC error caused by minute fluctuations in the power grid frequency. This error is approximately 61 dB below the fundamental frequency. Larger gains tend to increase residual harmonic chattering around zero. Due to the inherent averaging effect, applying FFT over several consecutive power grid cycles... The chattering might not be detectable at times, but it can be fully detected using a rigorous harmonic quantization method. Since a high gain is not required, and to reduce residual harmonic chattering, the experiment selected... .

[0061] Those skilled in the art will understand that, in addition to implementing the system, apparatus, and their modules provided by this invention in purely computer-readable program code, the same program can be implemented in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers by logically programming the method steps. Therefore, the system, apparatus, and their modules provided by this invention can be considered a hardware component, and the modules included therein for implementing various programs can also be considered structures within the hardware component; alternatively, modules for implementing various functions can be considered both software programs implementing the method and structures within the hardware component.

[0062] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A new energy converter system with power management function, characterized in that, include: Inverter DC-side capacitors, inductors, voltage source inverters, control units, and sensors; The inverter's DC-side capacitor is used as an energy storage element; The inductor serves as a component for transmitting power to the grid and connects the inverter phase to the grid; the voltage source inverter serves as a power converter; the control unit includes a synchronization algorithm module, a DC bus capacitor voltage regulation algorithm module, a harmonic extraction module, and a current control module. The DC side of the voltage source inverter is connected to the DC side capacitor of the inverter, and the AC side of the voltage source inverter is connected to the power grid through the inductor. The sensors are respectively installed on the DC side and AC side of the voltage source inverter to collect the DC side capacitor voltage signal, the grid side current signal and the load current signal, and transmit the collected signals to the control unit. The synchronization algorithm module receives the grid voltage signal collected by the sensor, generates a synchronization phase angle signal, and outputs it to the harmonic extraction module and the current control module respectively. The DC bus capacitor voltage regulation algorithm module receives the DC side capacitor voltage signal collected by the sensor, generates a DC current estimation signal, and outputs it to the current control module. The harmonic extraction module receives the load current signal collected by the sensor and the synchronization phase angle signal output by the synchronization algorithm module, performs Parker transformation on the three-phase load current, converts the three-phase load current in the three-phase stationary coordinate system into the three-phase load current in the rotating coordinate system, separates the fundamental component and harmonic components through a low-pass filter, performs inverse Parker transformation on the harmonic components to generate a reference current signal, and outputs the reference current signal to the current control module. The current control module receives the reference current signal, the estimated DC current signal, and the synchronization phase angle signal, generates a switching drive signal for controlling the voltage source inverter, and outputs it to the voltage source inverter, so that the voltage source inverter injects compensation current into the grid.

2. The new energy converter system with power management function according to claim 1, characterized in that, The harmonic extraction module detects and extracts harmonic components based on the synchronous reference coordinate system method, specifically as follows: The Parker transform matrix is ​​applied to convert the three-phase load current in the three-phase stationary coordinate system into the three-phase load current in the rotating coordinate system. The reference phase angle is provided by the phase-locked loop synchronizer for sine and cosine calculation. In the rotating coordinate system, the fundamental component is a fixed waveform and the harmonic components are oscillating waveforms. A second-order low-pass filter is used to separate the fundamental and harmonic components. The required reference current is generated using the harmonic components extracted by the inverse Parker transform.

3. The new energy converter system with power management function according to claim 1, characterized in that, The DC bus capacitor voltage regulation algorithm module uses a proportional-integral controller to compare the collected DC side capacitor voltage with the desired reference value and estimate the magnitude of the DC current used for DC side regulation. The estimated value is the value required to maintain the DC side capacitor voltage at the desired reference value to compensate for switching losses.

4. The new energy converter system with power management function according to claim 1, characterized in that, The synchronization algorithm module employs a three-phase phase-locked loop (PLL), which simulates a closed-loop control system. An internal frequency oscillator tracks the frequency and phase of a sinusoidal three-phase signal. Input variables include: a normalized three-phase grid voltage signal expressed in per-unit values, a measured frequency in Hertz, and an angle varying between 0 and 2π, synchronized with the positive-sequence zero-crossing point of the A-phase fundamental wave, where π is pi. The angular velocity of the internal oscillator is used to convert the three-phase input signal to a rotating coordinate system via Parker transformation. The q-axis component of the signal is proportional to the phase difference between the three-phase signal and the rotating coordinate system of the internal oscillator. This q-axis component is filtered by an averaging module. A proportional-integral-derivative (PID) controller with automatic gain control acts on the controlled oscillator to maintain the phase difference at zero. The output of the PID controller corresponds to the angular velocity, which is then converted to a frequency in Hertz after filtering.

5. The new energy converter system with power management function according to claim 1, characterized in that, The current control module includes a harmonic controller, which contains an error-free harmonic estimator. The output of the harmonic estimator is decoupled from the fundamental current, and there is no mutual coupling between the harmonics. The harmonic controller operates in parallel with the fundamental current controller. The sampling period of the harmonic controller is... Sampling period of the current control loop Integer multiples of, i.e. ,in It is an integer greater than or equal to 1; The harmonic controller includes decouplers for each harmonic, and the parameters of the decouplers are... Determine as follows: in, Let be the real part parameters of the nth harmonic decoupler. The imaginary unit, Let be the imaginary part parameter of the nth harmonic decoupler. Let be the rotational angular velocity of the nth harmonic reference coordinate system. Let be the pulse transfer function of the current controller closed-loop system in the grid synchronous coordinate system for voltage disturbances. Let be the rotational angular velocity of the power grid synchronous coordinate system. The sampling interval is... Let e ​​be the transfer function of the LCL output filter in the stationary coordinate system, where e represents a parameter in the reference coordinate system. The voltage command output by the harmonic controller is divided by Obtain the voltage correction for each harmonic under consideration, and ensure that the current change generated by the voltage correction has the same phase and direction as the voltage command.

6. The new energy converter system with power management function according to claim 5, characterized in that, The harmonic controller also includes a slope limiter module, which receives each harmonic control cycle. The updated reference value at the end, the voltage correction amount during the current control loop sampling period During this period, the value linearly increases from the current value to the new reference point, within the sampling period of the harmonic controller. The slope remains constant for the remaining half-cycle, and the slope of the slope limiter module is determined as follows: in, This represents the increment of the voltage disturbance. The slope of the voltage change. The sampling interval is... Let Z be a complex variable. This represents the steady-state final value of the current error under voltage ramp disturbance. For the gain of the current controller, Let be the rotational angular velocity of the power grid synchronous coordinate system. This is the equivalent load inductance.

7. The new energy converter system with power management function according to claim 6, characterized in that, Tracking error in the harmonic controller It is fed into the input of the integrator REG, where The next harmonic control period for the nth harmonic in the dq coordinate system. The average value within the range, the output of the integrator REG, is processed by the decoupler to obtain the voltage correction value, and the voltage command of the harmonic controller. Represented as: in, For feedback current Z-transform, The integral gain coefficient of the harmonic controller. Let Z be a complex variable. C is the imaginary unit, C is the real part of the decoupler parameter, and D is the imaginary part of the decoupler parameter. Characteristic polynomial of the closed loop of the harmonic controller for: The stability limit of the characteristic polynomial appears to occur when... .

8. The new energy converter system with power management function according to claim 7, characterized in that, When N grid-connected inverter units operate in parallel and share the same connection point PCC, the relationship between the total grid current and the harmonic current reference command of each grid-connected inverter unit is as follows: The total grid current is the sum of the output currents of each grid-connected inverter unit; Open-loop gain function for: Closed-loop transfer function for: The characteristic polynomial of the system for: in, This refers to the total number of grid-connected inverter units operating in parallel. The ratio is the equivalent series impedance of the power grid. For real numbers, This is the equivalent output impedance of a single grid-connected inverter unit.

9. The new energy converter system with power management function according to claim 8, characterized in that, The grid-side current in the current control module includes the response of residual harmonics and fundamental current to the reference current. The reference value of the current control loop is subtracted from the feedback value of the inverter-side current in the dq coordinate system after passing through the estimator to maintain the step response and decouple the harmonic controller. The expression for the grid-side current is: in, This is an estimated value of the grid-side current in the synchronously rotating dq coordinate system; This is the pulse transfer function for the current control loop; The current loop fundamental reference current command; This refers to the residual harmonic current component. This is the fundamental current component; The estimated residual harmonic current components are obtained by subtracting the estimated fundamental current components from the grid-side current estimates: in, The estimated residual harmonic current components; The estimated fundamental current component; This is an estimation model for the closed-loop pulse transfer function of the current control loop; This is the fundamental current reference command.

10. A control method for a new energy converter with power management function, characterized in that, The application of a new energy converter system with power management function as described in any one of claims 1 to 9 includes the following steps: Step 1: Collect DC-side capacitor voltage, grid voltage, load current, and grid-side current; Step 2: Generate the synchronization phase angle using a synchronization algorithm; Step 3: Using the DC bus capacitor voltage adjustment algorithm, compare the collected DC side capacitor voltage with the expected reference value to generate an estimated DC current value; Step 4: Using the harmonic extraction algorithm, the three-phase load current is transformed by Parker transformation to convert the three-phase load current in the three-phase stationary coordinate system into the three-phase load current in the rotating coordinate system. The fundamental component and harmonic components are separated by a low-pass filter, and the harmonic components are transformed by inverse Parker transformation to generate the reference current. Step 5: Using a current control algorithm, generate the switching drive signal for the voltage source inverter based on the reference current, the estimated DC current value, and the synchronous phase angle; Step 6: Run the harmonic controller and the fundamental current controller in parallel. The harmonic controller includes an error-free harmonic estimator, and the output of the harmonic estimator is decoupled from the fundamental current. Step 7: Estimate the fundamental current response based on the reference current, subtract the estimated fundamental current response from the grid-side current to obtain the residual harmonic current, and input the residual harmonic current into the harmonic controller for harmonic suppression.

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