Flexible power control method and system for multi-port DC-AC converter

Abstract

The invention relates to the technical field of power electronic converter control, in particular to a flexible power control method and system for a multi-port direct-current and alternating-current converter. The method comprises the following steps: acquiring voltage and current data of a three-phase power grid; alpha-beta conversion is carried out according to the acquired three-phase power grid voltage and current data, and a power grid voltage orthogonal component and power relation is generated; generating double modulation waves according to the power grid voltage; calculating a battery current reference according to a power grid voltage orthogonal component and a power relation; the zero-sequence injection amount is inversely calculated according to the double modulation waves and the battery current reference; carrying out carrier modulation by using the zero-sequence injection quantity; and performing inverter driving based on the carrier modulation signal. According to the invention, continuous control of the power of the battery port can be realized without depending on duty ratio adjustment of a traditional small vector pair, and a control dead zone under a high modulation degree / low power factor is avoided.

Description

Technical Field

[0001] This invention relates to the field of power electronic converter control technology, and in particular to a flexible power control method and system for a multi-port DC-AC converter. Background Technology

[0002] With the large-scale integration of renewable energy sources, photovoltaic (PV) power generation has been widely adopted due to its advantages such as being green and environmentally friendly, and having low operation and maintenance costs. However, PV output is significantly affected by sunlight and temperature, exhibiting randomness and intermittency, which can easily cause fluctuations in grid-connected power. To smooth power output and achieve peak shaving and valley filling, battery energy storage systems are typically coupled with PV systems to form a PV-battery hybrid system.

[0003] Multi-port DC-AC converters (MPDACs) can directly couple photovoltaic (PV) and battery ports to the AC side, avoiding intermediate DC-DC stages and offering advantages such as single-stage conversion, high power density, and low cost. However, MPDACs exhibit significant asymmetry and time-varying characteristics on the DC side: the PV port voltage varies with irradiance and the MPPT operating point, while the battery port voltage varies with the state of charge. These characteristics no longer satisfy the traditional assumption of a "constant and balanced DC bus" in multi-level inverters. This asymmetry makes it difficult to directly apply traditional modulation methods: both high-quality sinusoidal current output on the AC side and power distribution between the PV and battery must be achieved.

[0004] Existing power control methods generally employ two approaches: one is space vector pulse width modulation (SVPWM) with small vector duty cycle regulation, which achieves power distribution by selecting a proportion of redundant small vectors in an asymmetric space vector diagram; the other is carrier comparison pulse width modulation (CBPWM) and its variants. These methods generally perform well under balanced grid conditions and power factors close to 1. However, when low power factor operation or grid voltage imbalance occurs, the traditional regulation capability based on small vector pairs significantly decreases, easily leading to power regulation dead zones and noticeable power fluctuations. Especially when grid imbalance introduces second-harmonic power pulsations on the AC side, simply providing a battery current reference based on the average power balance is insufficient to suppress second-harmonic power fluctuations, causing the photovoltaic port to deviate from its maximum power point.

[0005] Therefore, there is an urgent need for a modulation and power control method that can maintain continuous and accurate battery port power regulation and high-quality grid-connected current output even under conditions of DC-side voltage asymmetry, full power factor range, and grid voltage imbalance. By injecting a zero-sequence component that satisfies volt-second balance and duty cycle constraints into the dual-modulation wave generated by CB-VSVPWM, the dwell time of the switching states related to the battery port in each phase is directly adjusted. This allows the average battery port current to be used as an explicit control quantity, achieving continuous and adjustable battery port charging and discharging power. Summary of the Invention

[0006] To address the aforementioned problems, this invention provides a flexible power control method and system for a multi-port DC-AC converter.

[0007] In a first aspect, the present invention provides a flexible power control method for a multi-port DC-AC converter, which adopts the following technical solution: A flexible power control method for a multi-port DC-AC converter includes: Collect three-phase power grid voltage and current data; Based on the collected three-phase power grid voltage and current data, αβ Transform and generate orthogonal components of grid voltage and power relationships; Generate a dual-modulation wave based on the grid voltage; Calculate the battery current reference based on the orthogonal components of the grid voltage and the power relationship; The zero-sequence injection amount is calculated by inverse calculation based on the dual-modulation wave and battery current reference. Carrier modulation is performed using zero-sequence injection. Inverter driving is based on carrier modulation signals.

[0008] Furthermore, the step of performing the analysis based on the collected three-phase power grid voltage and current data... αβ The transformation and generation of the grid voltage orthogonal components and power relationships involve first performing Clarke transforms on the three-phase voltages and currents to obtain... αβ Grid voltage components in coordinate system e α , e β and grid current components i α , i β , is represented as: , Then based on αβ Instantaneous power in the coordinate system, utilizing grid voltage components e α , e β With grid current components i α , i β From the inner product relationship, we obtain the power relationship on the AC side, which is expressed as: Simultaneously considering power fluctuations during grid imbalances, the orthogonal components of the grid voltage are obtained through SOGI. e 1α , e 1β , is represented as: , in, q This is the gain coefficient of SOGI. ω 0 represents the fundamental angular frequency of the grid voltage. s For the Laplace operator.

[0009] Furthermore, the generation of dual-modulation waves based on the grid voltage includes using carrier virtual space vector pulse width modulation (CB-VSVPWM) to convert virtual space vector modulation into a carrier comparison type, generating two modulation waves per phase, denoted as... m ′ x and m " x Each voltage vector is compared with a single carrier wave to synthesize the required voltage vector within one switching cycle. The volt-second balance relationship is expressed as follows: within one switching cycle... T S Within, each phase satisfies the volt-second balance between the DC and AC sides, among which... t hx , t lx , t 0x They are respectively states h , l 0 stay time ux Given the grid phase voltage for this phase, sort the three-phase voltages as follows: u max ≥ u mid ≥ u min The dwell time is mapped to the maximum / intermediate / minimum phases for easy unified derivation. The dwell time constraint is expressed as follows: to ensure the realizability of modulation physics, the dwell time of each phase satisfies the non-negativity constraint and the sum constraint, thus obtaining the fundamental dwell time. The dual-modulation wave is expressed as: the dwell time is demapped into a dual-modulation wave. m ′ x and m " x The amplitude of the modulation wave determines the duty cycle allocation of each state of the phase during the switching cycle; the corresponding PWM sequence is obtained by comparing the dual modulation wave with the carrier wave, as follows: .

[0010] Furthermore, the calculation of the battery current reference based on the orthogonal components of the grid voltage and the power relationship includes the grid balance and the expected power on the AC side. P ac_ref Given the average power balance relationship, calculate the average power demand at the battery port based on the photovoltaic port power command. P bat_ref , and by P bat_ref and V batObtain the average current reference at the battery port. i bat_ref , is represented as: When the low power factor originates from grid voltage imbalance, the three-phase instantaneous power contains a significant second harmonic component, which is relevant for average power balance calculations. i bat_ref In cases of insufficient power, a second-harmonic power pulsation is introduced, positioning the battery port as a power buffer unit. The battery port not only compensates for the difference between the average power on the AC side and the average power on the photovoltaic port, but also absorbs the second-harmonic power pulsation introduced by grid imbalance. P 2ω Therefore, the battery current reference considers both the average power and the second harmonic power, expressed as: Among them, the second harmonic power pulsation P 2ω Depend on αβ Grid voltage components in coordinate system e 0α , e 0β and its orthogonal components e 1α , e 1β The calculations show that the orthogonal components are obtained through an orthogonal signal generator, and are expressed as follows: .

[0011] Furthermore, the calculation of zero-sequence injection based on dual-modulation waveforms and battery current reference includes calculating zero-sequence injection based on battery current reference. To cover different modulation intensities, power factors, and DC-side imbalance conditions, three injection strategies are set and refined into five injection scenarios: Scenario 1 and Scenario 2 are common-mode (CM) injection, Scenario 3 is differential-mode (DM) injection, and Scenario 4 and Scenario 5 are combined-mode injection. Scenario 1 employs a common-mode injection strategy, with the injection location directed towards the largest phase. m ′ max And intermediate phase, minimum phase m " mid , m " min Injecting zero-sequence components, the maximum phase injection amount is denoted as... m cm1 The injection amounts of the intermediate phase and the minimum phase are determined by the imbalance coefficient. k Scaling is represented as: , Equivalent residence time increment is obtained by varying the injection amount and phase states. l The linear relationship between residence time increments is obtained, and the battery current expression is derived from the battery current definition and the relationship between residence time increments, as follows: Scenario 2 employs a common-mode injection strategy, where the injection locations include the maximum phase and intermediate phases. m ′ max , m ′ mid and the smallest phase m " min Injecting zero-sequence components, and then relating the injection amount to the state of each phase. l The residence time increment relationship is obtained from the residence time increment formula.

[0012] Furthermore, the step of calculating the zero-sequence injection amount based on the dual-modulation wave and battery current reference also includes employing a differential-mode injection strategy in case 3. In this strategy, the injection positions include not injecting zero-sequence components into the maximum and minimum phase modulation waves, but only injecting opposite-sign zero-sequence components into the two modulation waves of the intermediate phase, thus causing symmetrical biasing of the dual-modulation waves in the intermediate phase. m " mid Injection volume is m dm Then to m ′ mid Injection volume is the same as k The relevant proportionality coefficient multiplied by m dm , represented as: , The residence time increment relationship includes, according to case 3, the intermediate phase l When the state dwell time changes, but the maximum phase / minimum phase ratio remains unchanged, it is represented as: .

[0013] Furthermore, the step of calculating the zero-sequence injection amount based on the dual-modulation wave and battery current reference also includes adopting a combined mode injection strategy for scenario 4, with the first injection being the CM component. m cm1 The second injection is a DM component. m dm The superimposed double-modulated wave is represented as: ; Scenario 5 employs a combined mode injection strategy, where the injection location is based on common-mode injection superimposed with differential-mode injection, and the first injection is the CM component. m cm2 The second injection was a DM component. m dm .

[0014] Furthermore, the step of calculating the zero-sequence injection amount based on the dual-modulation wave and battery current reference also includes obtaining... i bat_refThen, the zero-sequence injection amount is calculated back using the battery current expression for the injection scenario; the injection amounts for scenarios 1, 2, and 3 are obtained from explicit formulas, expressed as: ; Cases 4 and 5 introduce a distribution coefficient λ to allocate the current contribution between CM and DM and obtain the injection amount, expressed as: .

[0015] Furthermore, the carrier modulation using zero-sequence injection includes, based on CB-VSVPWM, injecting zero-sequence components into the dual-modulation wave to change its state. l The residence time is adjusted to regulate the average current at the battery port. i bat In this process, by adding zero-sequence injection amounts to specific modulation waves of the maximum / intermediate / minimum phases respectively, the dwell time increment Δ is equivalently achieved. t hmax Δ t hmid Δ t 0mid Δ t 0min And this equation holds true in the volt-second equilibrium equation, expressed as: , To ensure that the volt-second balance and switching period constraints are still met after modulation, the zero-sequence injection quantity must satisfy a set of consistency conditions and ensure that all dwell times remain within [0, ... T S ].

[0016] Secondly, a flexible power control system for a multi-port DC-AC converter includes: The data acquisition module is configured to collect three-phase power grid voltage and current data; The conversion module is configured to perform conversion based on the collected three-phase power grid voltage and current data. αβ Transform and generate orthogonal components of grid voltage and power relationships; The dual-modulation wave module is configured to generate a dual-modulation wave based on the grid voltage. The reference module is configured to calculate the battery current reference based on the quadrature components of the grid voltage and the power relationship; The inverse calculation module is configured to inversely calculate the zero-sequence injection amount based on the dual-modulation wave and the battery current reference. The modulation module is configured to perform carrier modulation using zero-sequence injection.

[0017] The drive module is configured to drive the inverter based on a carrier modulation signal.

[0018] Thirdly, the present invention provides a computer-readable storage medium storing a plurality of instructions adapted to be loaded and executed by a processor of a terminal device as described in the flexible power control method for a multi-port DC-AC converter.

[0019] Fourthly, the present invention provides a terminal device, including a processor and a computer-readable storage medium, wherein the processor is used to implement various instructions; the computer-readable storage medium is used to store multiple instructions, the instructions being adapted to be loaded and executed by the processor to provide a flexible power control method for a multi-port DC-AC converter.

[0020] In summary, the present invention has the following beneficial technical effects: (1) Continuous control of battery port power can be achieved without relying on the duty cycle adjustment of traditional small vector pairs, avoiding the control dead zone under high modulation / low power factor; (2) Controllable power regulation within the full power factor and wide tuning range is achieved through CM / DM / combined injection and its allowable range derivation; (3) Buffer the second harmonic power pulsation under grid imbalance conditions, suppress power fluctuations and maintain the photovoltaic port at the maximum power point; (4) The calculation process is modular and simple to implement, and is suitable for digital controllers and engineering implementation. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of a typical topology of the multi-port DC-AC converter provided in Embodiment 1 of the present invention in a photovoltaic-cell hybrid system; Figure 2 This is a schematic diagram of three typical switching states and corresponding power flow paths of a single-phase bridge arm of a multi-port DC-AC converter provided in Embodiment 1 of the present invention. Figure 3 This is a schematic diagram of the PWM sequence obtained by comparing the CB-VSVPWM single-phase dual-modulation wave with the carrier wave provided in Embodiment 1 of the present invention; Figure 4 This is a schematic diagram of the modulation process in scenario 1 of embodiment 1 of the present invention; Figure 5 This is a schematic diagram of the modulation process in scenario 2 of embodiment 1 of the present invention; Figure 6 This is a schematic diagram of the modulation process in scenario 3 of embodiment 1 of the present invention; Figure 7 This is a schematic diagram of the modulation process in scenario 4 of embodiment 1 of the present invention; Figure 8 This is a schematic diagram of the modulation process in scenario 5 of embodiment 1 of the present invention; Figure 9This is a schematic diagram of the overall flow and module connections of the proposed method provided in Embodiment 1 of the present invention; Figure 10 This is a schematic diagram of the normalized battery current distribution under different power factors and modulation inclinations under the traditional small vector pair power control scheme provided in Embodiment 1 of the present invention. Figure 11 This is a schematic diagram of the normalized battery current distribution under different power factors and modulation intensities under the CB-VSVPWM power control scheme provided in Embodiment 1 of the present invention. Figure 12 The following is a simulation waveform diagram of the power grid balance and unbalance conditions provided in Embodiment 1 of the present invention, which is used to verify the power control and second harmonic power buffering capabilities of the present invention. Detailed Implementation

[0022] The present invention will be further described in detail below with reference to the accompanying drawings.

[0023] Example 1 Reference Figure 1 This embodiment of a flexible power control method for a multi-port DC-AC converter includes: Collect three-phase power grid voltage and current data; Based on the collected three-phase power grid voltage and current data, αβ Transform and generate orthogonal components of grid voltage and power relationships; Generate a dual-modulation wave based on the grid voltage; Calculate the battery current reference based on the orthogonal components of the grid voltage and the power relationship; The zero-sequence injection amount is calculated by inverse calculation based on the dual-modulation wave and battery current reference. Carrier modulation is performed using zero-sequence injection.

[0024] Inverter driving based on carrier modulation signal Specifically, it includes the following steps: S1. Collect three-phase power grid voltage and current data, including system topology, switch status, and power balance relationships, including the following: 1) Switch state definition: with any phase bridge arm x ( x ∈{ a , b , c For example,}) Figure 1 As shown, each phase arm of the multi-port DC-AC converter contains four active switches. S x1 , S x2 , S x3 , Sx4 (Specific device types may include IGBTs / MOSFETs, etc.). Within one switching cycle, the bridge arm can operate in three typical states, such as... Figure 2 As shown: High level state h Low level state l Zero-level state 0. Different states determine the output voltage at the phase terminals. v xN And from which DC port does energy flow to the AC side.

[0025] 2) State Table: Table 1 shows the gate signal combinations, phase voltage outputs, and power port attributes corresponding to the three states. For ease of patent description, the logic gate combinations in this specification can be understood according to Table 1. In specific implementation, complementary driving can be used and dead time can be considered.

[0026] Table 1 Typical switching states of a single-phase bridge arm in a multi-port DC-AC converter Switch status Gate signal <![CDATA[Phase voltage v xN > DC port participation (1,1,0,0) <![CDATA[ V pv (Photovoltaic voltage) Photovoltaic ports supply energy to the AC side (1,0,0,1) <![CDATA[ V bat (Battery voltage) Battery ports supply / absorb energy to the AC side 0 (0,0,1,1) 0 Do not connect to DC port (free-flow) 3) Power balance: Ignoring converter losses, the converter meets the power requirements of the photovoltaic port. P pv Battery port power P bat With AC side power P ac The instantaneous or average power balance relationship between them (Equation (1)).

[0027] (1) in P bat Available battery port voltage V bat Average current at the battery port during one switching cycle i bat Characterization (Equation (2)) (2) and i bat This can be further represented as the state of each phase in the battery's participation state. l Duration of stay t lx With phase current i x The weighted sum (Equation (3)).

[0028] (3) Therefore, regulation t lx The power at the battery port can be adjusted directly.

[0029] 4) Imbalance coefficient and normalized cell current: To characterize the asymmetry caused by the unequal DC-side photovoltaic voltage and cell voltage, an imbalance coefficient is introduced. k (Equation (4)) (4) And define the normalized battery current. B (Equation (5)) to facilitate cross-condition comparison and power control capability assessment.

[0030] (5) S2. Based on the collected three-phase power grid voltage and current data, perform... αβ Transform and generate orthogonal components of grid voltage and power relationships; Perform Clarke transforms on the three-phase voltages and currents respectively: (6) Further, the power relationship on the AC side was obtained: (7) Meanwhile, considering power fluctuations during grid imbalances, the orthogonal components of the grid voltage can be obtained through SOGI: (8) S3. Generate a dual-modulation wave based on the grid voltage, including dual-modulation wave generation based on the CB-VSVPWM working principle, specifically including: To avoid the inherent defects of traditional small vector pair schemes, this invention employs carrier virtual space vector pulse width modulation (CB-VSVPWM). CB-VSVPWM equates virtual space vector modulation to carrier comparison-type implementation: two modulation waves are generated for each phase (denoted as...). m ′ x and m " x Each of these is compared with the carrier wave to synthesize the desired voltage vector within one switching cycle.

[0031] 1) Volt-second balance relationship: in one switching cycle T S Within, each phase satisfies the volt-second balance between the DC side and the AC side (Equation (9)), where t hx , t lx , t 0x They are respectively states h , l 0 stay time ux This is the grid phase voltage (or reference voltage) for that phase. The three-phase voltages are ordered as follows: u max ≥u mid ≥ u min It is then mapped to the maximum / intermediate / minimum phases for easy unified derivation.

[0032] (9) 2) Dwell time constraint: To ensure the realization of modulation physics, the dwell time of each phase must satisfy the non-negativity constraint and the sum constraint (Equations (10)-(11)). Under this constraint, the basic dwell time expression can be obtained (Equation (12)).

[0033] (10) (11) (12) 3) Dual-modulation wave representation: Demapping the residence time into a dual-modulation wave m ′ x and m " x (Equation (13)). Its meaning is: the amplitude of the modulation wave determines the duty cycle of each state of the phase during the switching cycle; the corresponding PWM sequence is obtained after comparing the dual modulation wave with the carrier wave.

[0034] (13) 4) PWM sequence generation: such as Figure 3 As shown, taking any phase as an example, the output state when both modulated waves are higher than the carrier wave. h Output state when one signal is higher than the carrier and the other is lower than the carrier. l When both values ​​are below the carrier, the output state is 0. A complete three-phase gate drive sequence can be obtained by simultaneously performing this comparison process on all three phases.

[0035] To cover different modulation intensities, power factors, and DC-side imbalance conditions, this invention proposes three injection strategies and further refines them into five typical cases: Cases 1-2 are common-mode (CM) injection, Case 3 is differential-mode (DM) injection, and Cases 4-5 are combined-mode injection (CM first, then DM). The injection location, proportional relationship, constraint derivation logic, and battery current expression are given for each case below.

[0036] (a) Case 1: Common Mode Injection - Type 1 1) Injection location: such as Figure 4 As shown, towards the maximum phase m ′ max And intermediate phase, minimum phase m " mid , m " minInject the zero-sequence component. Let the maximum phase injection amount be... m cm1 The injection amounts of the intermediate phase and the minimum phase are determined by the imbalance coefficient. k Perform scaling (Equation (14)).

[0037] (14) 2) Equivalent residence time increment: injection volume and phase state l The increments in residence time satisfy a linear relationship (Equation (15)). This relationship shows that Case 1 forms a "same direction" in the three phases. l State dwell time adjustment is a type of common-mode adjustment.

[0038] (15) 3) Derivation of the allowable range: Based on (i) the dwell time of each state is non-negative, and (ii) not exceeding T S (iii)-1< k The physical range <1, for m cm1 The upper and lower bounds are derived (Equation (16)). These upper and lower bounds determine the maximum charge / discharge capacity of the battery in Case 1.

[0039] (16) 4) Battery current expression: From the definition of battery current and the relationship between residence time increment, we obtain... i bat and m cm1 The mapping (Equation (17)).

[0040] (17) (ii) Scenario 2: Common Mode Injection - Type 2 1) Injection location: such as Figure 5 As shown, towards the maximum phase and the intermediate phase m ′ max , m ′ mid and the smallest phase m " min Inject the zero-sequence component. Let the minimum phase injection amount be... m cm2 The injection amounts of the maximum phase and the intermediate phase are calculated according to... k Perform scaling (Equation (18)).

[0041] (18) 2) Residence time increment relationship: Injection volume and phase state lThe residence time increments satisfy equation (17). Similar to case 1, case 2 also forms common mode regulation, but its injection reference phase is different, resulting in different allowable ranges and control capabilities.

[0042] (19) 3) Permissible range: Also based on the stay time constraint and -1 < k <1 Derivation m cm2 The allowable range (Equation (20)).

[0043] (20) 4) Battery current expression: obtained from equation (3) and equation (17) i bat and m cm2 The mapping (Equation (21)).

[0044] (twenty one) (iii) Scenario 3: Differential injection 1) Injection location: such as Figure 6 As shown, the maximum and minimum phase modulated waves are not injected with zero-sequence components; only the two modulated waves of the intermediate phase are injected with zero-sequence components of opposite signs, causing symmetrical biasing of the intermediate phase dual modulated waves. Let the direction be... m " mid Injection volume is m dm Then to m ′ mid Injection volume is the same as k The relevant proportionality coefficient multiplied by m dm (Equation (22)).

[0045] (twenty two) 2) Residence time increment relationship: Case 3 makes the intermediate phase l The state dwell time changes, while the maximum phase / minimum phase remains unchanged, and its increment is given by equation (23). Since two modulation waves are injected with components of opposite sign, case 3 is essentially differential mode regulation.

[0046] (twenty three) 3) Permissible range: For m dm The upper and lower bounds of the injection are derived (Equation (24)) to ensure that the residence time of each state in the intermediate phase still satisfies [0, TS ].

[0047] (twenty four) 4) Battery current expression: obtained from equation (3) and equation (21) i bat and m dm The mapping (Equation (25)).

[0048] (25) (iv) Scenario 4: Combinatorial pattern injection 1) Injection strategy: To expand the adjustment margin and cover more operating conditions, such as... Figure 7 As shown, a common mode injection with limited amplitude is first applied (Case 1) to reserve modulation space for subsequent differential mode injection, and then differential mode injection is superimposed (Case 3).

[0049] 2) Dual-modulation wave representation: The first injection is the CM component. m cm1 The second injection is a DM component. m dm The superimposed dual-modulation wave is described by equation (26).

[0050] (26) 3) Permissible range: Because the second DM injection is limited by the modulation margin occupied by the first CM injection, m cm1 and m dm The feasible range becomes a coupling constraint (Equation (27)-Equation (28)), where the coefficients appear γ =(1+ k ) / (1- k ).

[0051] 27) (28) 4) Battery current expression: In case 4, the battery current is determined by both CM and DM, and can be written as: ibat = f ( m cm1 , m dm (Equation (29)).

[0052] (29) (v) Scenario 5: Combinatorial pattern injection 1) Injection strategy: such as Figure 8 As shown, scenario 3 differential mode injection is superimposed on scenario 2 common mode injection. The first injection is the CM component. m cm2 The second injection is a DM component.m dm .

[0053] 2) Expression of double modulation wave: The superimposed double modulation wave is described by equation (28).

[0054] (30) 3) Allowable range: Similarly, the second DM injection is constrained by the first CM injection, forming a coupled feasible region.

[0055] (31) (32) 4) Battery current expression: In scenario 5, the battery current is ibat = f ( m cm2 , m dm ).

[0056] (33) In summary, this invention establishes five zero-sequence injection scenarios and derives the allowable injection range and battery current expression for each scenario, providing a unified mathematical basis for subsequent "reverse calculation of zero-sequence injection amount" based on battery power commands.

[0057] (a) Battery current reference under balanced grid / high power factor scenarios: In scenarios where the grid is balanced and the desired power on the AC side is... P ac_ref When the average power balance relationship is known, the average power demand at the battery port can be calculated based on the photovoltaic port power command or MPPT output power. P bat_ref , and by P bat_ref and V bat Obtain the average current reference at the battery port. i bat_ref (Corresponding formula (34)).

[0058] (34) (ii) Power factor fluctuations introduced by grid voltage imbalance: When the low power factor originates from grid voltage imbalance, the three-phase instantaneous power contains a significant second-harmonic component. In this case, calculations based solely on average power balance are necessary. i bat_ref It is insufficient to maintain the maximum power point operation of the photovoltaic port because the second harmonic power pulsation on the AC side will force the photovoltaic port to bear part of the pulsating power and deviate from the MPPT.

[0059] Therefore, this invention positions the battery port as a power buffer unit: the battery port not only compensates for the difference between the average power on the AC side and the average power on the photovoltaic port, but also absorbs (or releases) the second-harmonic power pulsation introduced by grid imbalance. P 2ω Therefore, the battery current reference should take into account both the average power and the second harmonic power (corresponding to equation (35)).

[0060] (35) Among them, the second harmonic power pulsation P 2ω can be αβ Grid voltage components in coordinate system e α , e β and its orthogonal components e 1α , e 1β The calculation yields (corresponding to equation (36)). Orthogonal components can be obtained using an orthogonal signal generator (such as SOGI / DSOGI).

[0061] (36) S6. Zero-order injection reverse calculation Calculate the zero-sequence injection amount based on the battery current reference: [Result] i bat_ref Then, select any injection case (case 1-5) and use the battery current expression of the case to calculate the zero-sequence injection amount; the injection amount of case 1-3 can be directly obtained by explicit formula (corresponding to formula (37)), while case 4-5 introduces the distribution coefficient λ to distribute the current contribution between CM and DM and obtain the injection amount (corresponding to formula (38)).

[0062] (37) (38) (iv) Situation selection strategy: In practical applications, in order to obtain a wider power regulation range, the normalized battery current can be selected to meet the injection feasible region. B The injection scenario with the largest reach. This strategy is equivalent to selecting the scenario with the strongest adjustment capability among the five scenarios.

[0063] Based on the above, this invention, within the CB-VSVPWM framework, takes battery port power as the control objective: First, it solves for the basic dwell time of each switching state of the three phases based on the volt-second balance relationship and the non-negative / sum constraint of dwell time, and generates a three-phase dual-modulation wave; wherein the battery port current can be expressed as the battery participation state. lThe dwell time is a weighted sum of the phase currents, therefore, by injecting a zero-sequence component that meets the conditions into the dual-modulation wave, the state can be equivalently changed while maintaining the volt-second balance. l The dwell time is adjusted to achieve power regulation at the battery port.

[0064] Furthermore, based on the expected average power on the AC side and the photovoltaic port power command / MPPT output, an average power balance is established, and the reference average current at the battery port is calculated. ； When grid voltage imbalance causes double-frequency power pulsation on the AC side, the double-frequency power pulsation is taken into account, so that the battery port can buffer both the average power deviation and the double-frequency power pulsation to maintain the photovoltaic terminal's maximum power point operation and suppress power fluctuations.

[0065] Subsequently, among the five injection scenarios consisting of common-mode injection, differential-mode injection, and combined injection, the injection method that satisfies the feasible region constraint is selected. The zero-sequence injection amount is calculated by using the derived "battery current-zero-sequence injection amount" function relationship for each scenario and the amplitude limit is checked. Finally, the zero-sequence component is superimposed on the dual-modulation wave and compared with the carrier wave to output the gate drive signal, thereby realizing the continuous adjustment of the charging and discharging power of the battery port.

[0066] The key to this invention lies in: injecting a zero-sequence component into the dual-modulation wave to change the state, based on CB-VSVPWM. l The residence time is adjusted to regulate the average current at the battery port. i bat Specifically: by adding zero-sequence injection amounts to certain modulation waves of the maximum phase / intermediate phase / minimum phase respectively, the equivalent state is achieved. l Increment in dwell time Δ t hmax Δ t hmid Δ t 0mid Δ t 0min Equation (11) holds true in the volt-second balance equation.

[0067] (39) It is important to emphasize that, in order to ensure that the volt-second balance and switching period constraints are still met after modulation, the zero-sequence injection quantity must satisfy a set of consistency conditions (e.g., the sum of the injection quantities is zero or the equivalent volt-second remains unchanged), and ensure that all dwell times remain within [0, ... T S This is also the fundamental reason why the present invention derives the "allowable injection range" in various injection scenarios.

[0068] like Figure 9As shown, the control flow of this invention includes: collecting the voltage and current of the photovoltaic terminal and the battery terminal, as well as the three-phase voltage and current on the grid-connected side, and calculating them respectively. P pv , P bat and P ac Furthermore, when the power grid is unbalanced, the second harmonic power pulsation component is extracted from the power relationship. P 2ω A battery port current reference is generated based on power balance and power command. i bat , ref The basic modulation requirements are determined together with the grid-connected side current closed loop (Park transformation + PI regulation). After generating a dual-modulation wave in the PWM generator, the injection feasibility region is judged according to cases 1–5, and the zero-sequence injection amount is calculated in reverse. This is then superimposed on the dual-modulation wave and a carrier comparison is performed to obtain the gate drive signal. By changing the dwell time of the switching state coupled to the battery port through the zero-sequence injection, the continuous controllability of the battery port charging and discharging power is achieved, and it is used to suppress power fluctuations.

[0069] like Figure 10 As shown, this is a traditional small vector power control scheme with an imbalance coefficient of ( k The normalized battery current distribution under different power factors and modulation indices is shown in the figure (-0.2). It can be seen that in the low power factor and high modulation index region, the normalized battery current B value for both charging and discharging is relatively small, indicating that the battery port power regulation capability of the traditional scheme is greatly limited in this region.

[0070] like Figure 11 As shown, this illustrates the CB-VSVPWM power control scheme proposed in this paper with an imbalance coefficient of ( k Normalized battery current distribution under different power factors and modulation indices (=-0.2) conditions. Compared to... Figure 10 The proposed scheme significantly reduces the area with weak power control capability and further improves the power regulation capability of the battery port under high modulation index conditions.

[0071] Experimental verification To verify the feasibility of the method of this invention, this embodiment provides a set of typical simulation / experimental settings and phenomenon descriptions. Optional parameters: photovoltaic port voltage. V pv =120V; Battery port voltage V bat =72V; the effective value of the AC mains voltage is... u x_rms =60V; AC side reference current component i d=5A; Switching frequency fs =10kHz; Filter inductor L =3.5mH.

[0072] like Figure 12 As shown, under grid balance conditions, this invention can realize multiple daytime power regulation modes: the energy storage unit can selectively supply power (65W), absorb power (i.e., charge, -120W), or be in an idle state (neither charging nor discharging); correspondingly, the output power of the photovoltaic unit can be flexibly adjusted to 570W, 755W, or 635W, covering the core needs of peak shaving and valley filling.

[0073] Under unbalanced grid conditions (e.g., a voltage drop of approximately 50% in phase A), in order to maintain a constant load power on the AC side, it is necessary to adjust the AC side reference current component. i d =4.71A i q =-1.67A). At this time, a significant second harmonic power pulsation appears on the AC side. This invention addresses this by... P 2ω Merging i bat_ref This allows the battery port to absorb double-frequency power fluctuations from the AC side, thereby keeping the photovoltaic port operating stably at the maximum power point and suppressing power fluctuations.

[0074] Thus, Example 1 presents the complete steps from system topology, CB-VSVPWM modulation, zero-sequence injection strategy, allowable range derivation, reference battery current design to grid imbalance double frequency buffering, which can be regarded as a detailed writing of all the technical contributions of the paper in a "patented, step-by-step, and engineering-oriented" manner.

[0075] Example 2 This embodiment provides a flexible power control system for a multi-port DC-AC converter, presented in a modular form to facilitate engineering implementation, software encapsulation, and patent claim drafting. The system includes, but is not limited to, the following functional modules: (1) Sampling and signal preprocessing module: Acquires three-phase grid voltage, grid current, and DC side signal. V pv and V bat The sampled signal is then filtered, normalized, and synchronized.

[0076] (2) Coordinate transformation and orthogonal signal generation module: Completed abc → αβ The transformation generates orthogonal components of the grid voltage (e.g., using SOGI / DSOGI), providing input for zero-sequence component analysis and second harmonic power calculation.

[0077] (3) Unbalance detection and parameter calculation module: calculates the DC side unbalance coefficient. k It detects the degree of voltage imbalance in the power grid and provides a second-harmonic buffer enable signal.

[0078] (4) Power command management module: receives target power from the AC side. P ac_ref Configure the photovoltaic port MPPT power or power command, and set the battery port charge / discharge constraints and SOC limit strategies.

[0079] (5) Second harmonic power pulsation calculation module: Calculates under power grid imbalance conditions. P 2ω It outputs the pulsating power component that needs to be buffered by the battery port.

[0080] (6) Battery Current Reference Calculation Module: Calculates the average current reference at the battery port, taking into account both average power balance and second harmonic buffer requirements. i bat_ref .

[0081] (7) CB-VSVPWM basic modulation module: Based on the volt-second balance and dwell time constraints, a three-phase dual modulation wave is generated. m ′ x , m " x And the basic PWM sequence.

[0082] (8) Injection scenario selection module: based on modulation scheme m Power factor k Depending on the control requirements, select one of scenarios 1-5, or adaptively select according to the "maximum controllable range B" strategy.

[0083] (9) Zero-order injection inverse calculation module: based on the selected situation and i bat_ref Calculate the zero-sequence injection amount (CM / DM or combination) and calculate the allocation coefficient λ (if enabled).

[0084] (10) Limiting and consistency verification module: Limits the zero-sequence injection amount, verifies the non-negativity of the dwell time and the sum constraint, and avoids the modulation wave from going out of bounds; if necessary, backs up the situation or adjusts λ.

[0085] (11) Carrier Comparison and Drive Output Module: Compares the injected dual-modulated wave with the upper and lower triangular carriers and outputs the gate drive signals of each phase; complementary drive and dead time can be configured.

[0086] (12) Protection and fault tolerance module: including overvoltage, overcurrent, DC side undervoltage, overtemperature and other protections. In case of abnormality, it can operate at reduced rate or switch to safety modulation.

[0087] The working process of each module of the system is the same as that described in Example 1, and will not be repeated here.

[0088] A computer-readable storage medium storing a plurality of instructions adapted for loading and execution by a processor of an end device of the aforementioned flexible power control method for a multi-port DC-AC converter.

[0089] A terminal device includes a processor and a computer-readable storage medium, the processor being configured to implement various instructions; the computer-readable storage medium being configured to store multiple instructions adapted to be loaded and executed by the processor as described in the flexible power control method for a multi-port DC-AC converter.

[0090] The above are all preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, all equivalent changes made in accordance with the structure, shape and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A flexible power control method for a multi-port DC-AC converter, characterized in that, include: Collect three-phase power grid voltage and current data; Based on the collected three-phase power grid voltage and current data, αβ Transform and generate orthogonal components of grid voltage and power relationships; Generate a dual-modulation wave based on the grid voltage; Calculate the battery current reference based on the orthogonal components of the grid voltage and the power relationship; The zero-sequence injection amount is calculated by inverse calculation based on the dual-modulation wave and battery current reference. Carrier modulation is performed using zero-sequence injection. Inverter driving is based on carrier modulation signals.

2. The flexible power control method for a multi-port DC-AC converter according to claim 1, characterized in that, The process is based on the collected three-phase power grid voltage and current data. αβ The transformation and generation of the grid voltage orthogonal components and power relationships involve first performing Clarke transforms on the three-phase voltages and currents to obtain... αβ Grid voltage components in coordinate system e α , e β and grid current components i α , i β , is represented as: ， Then based on αβ Instantaneous power in the coordinate system, utilizing grid voltage components e α , e β With grid current components i α , i β From the inner product relationship, we obtain the power relationship on the AC side, which is expressed as: Simultaneously considering power fluctuations during grid imbalances, the orthogonal components of the grid voltage are obtained through SOGI. e 1α , e 1β , is represented as: ， in, q This is the gain coefficient of SOGI. ω 0 represents the fundamental angular frequency of the grid voltage. s For the Laplace operator.

3. The flexible power control method for a multi-port DC-AC converter according to claim 2, characterized in that, The process of generating dual-modulation waves based on the grid voltage includes using carrier virtual space vector pulse width modulation (CB-VSVPWM) to convert virtual space vector modulation into a carrier comparison type, generating two modulation waves per phase, denoted as... m ′ x and m " x Each voltage vector is compared with a single carrier wave to synthesize the required voltage vector within one switching cycle. The volt-second balance relationship is expressed as follows: within one switching cycle... T S Within, each phase satisfies the volt-second balance between the DC and AC sides, among which... t hx , t lx , t 0x They are respectively states h , l 0 stay time ux Given the grid phase voltage for this phase, sort the three-phase voltages as follows: u max ≥ u mid ≥ u min The dwell time is mapped to the maximum / intermediate / minimum phases for easy unified derivation. The dwell time constraint is expressed as follows: to ensure the realizability of modulation physics, the dwell time of each phase satisfies the non-negativity constraint and the sum constraint, thus obtaining the fundamental dwell time. The dual-modulation wave is expressed as: the dwell time is demapped into a dual-modulation wave. m ′ x and m " x The amplitude of the modulation wave determines the duty cycle allocation of each state of the phase during the switching cycle; the corresponding PWM sequence is obtained by comparing the dual modulation wave with the carrier wave, as follows: 。 4. The flexible power control method for a multi-port DC-AC converter according to claim 3, characterized in that, The battery current reference is calculated based on the orthogonal components of the grid voltage and the power relationship, including the grid balance and the expected power on the AC side. P ac_ref Given the average power balance relationship, calculate the average power demand at the battery port based on the photovoltaic port power command. P bat_ref , and by P bat_ref and V bat Obtain the average current reference at the battery port. i bat_ref , is represented as: When the low power factor originates from grid voltage imbalance, the three-phase instantaneous power contains a significant second harmonic component, which is relevant for average power balance calculations. i bat_ref In cases of insufficient power, a second-harmonic power pulsation is introduced, positioning the battery port as a power buffer unit. The battery port not only compensates for the difference between the average power on the AC side and the average power on the photovoltaic port, but also absorbs the second-harmonic power pulsation introduced by grid imbalance. P 2ω Therefore, the battery current reference considers both the average power and the second harmonic power, expressed as: ， Among them, the second harmonic power pulsation P 2ω Depend on αβ Grid voltage components in coordinate system e 0α , e 0β and its orthogonal components e 1α , e 1β The calculations show that the orthogonal components are obtained through an orthogonal signal generator, and are expressed as follows: 。 5. The flexible power control method for a multi-port DC-AC converter according to claim 4, characterized in that, The method of calculating the zero-sequence injection amount based on the dual-modulation wave and battery current reference includes calculating the zero-sequence injection amount based on the battery current reference. To cover different modulation intensities, power factors, and DC-side imbalance conditions, three injection strategies are set and further refined into five injection scenarios: Scenario 1 and Scenario 2 are common-mode (CM) injection, Scenario 3 is differential-mode (DM) injection, and Scenario 4 and Scenario 5 are combined-mode injection. Scenario 1 employs a common-mode injection strategy, with the injection location directed towards the largest phase. m ′ max And intermediate phase, minimum phase m " mid , m " min Injecting zero-sequence components, the maximum phase injection amount is denoted as... m cm1 The injection amounts of the intermediate phase and the minimum phase are determined by the imbalance coefficient. k Scaling is represented as: ， Equivalent residence time increment is obtained by varying the injection amount and phase states. l The linear relationship between residence time increments is obtained, and the battery current expression is derived from the battery current definition and the relationship between residence time increments, as follows: ； Scenario 2 employs a common-mode injection strategy, where the injection locations include the maximum phase and the intermediate phase. m ′ max , m ′ mid and the smallest phase m " min Injecting zero-sequence components, and then relating the injection amount to the state of each phase. l The residence time increment relationship is obtained from the residence time increment formula.

6. The flexible power control method for a multi-port DC-AC converter according to claim 5, characterized in that, The method of calculating the zero-sequence injection amount based on the dual-modulation wave and battery current reference also includes employing a differential-mode injection strategy in case 3. In this strategy, the injection locations include the maximum and minimum phase modulation waves where zero-sequence components are not injected; only the two modulation waves of the intermediate phase are injected with opposite-sign zero-sequence components, resulting in symmetrical biasing of the dual-modulation waves in the intermediate phase. m " mid Injection volume is m dm Then to m ′ mid Injection volume is the same as k The relevant proportionality coefficient multiplied by m dm , represented as: ， The residence time increment relationship includes, according to case 3, the intermediate phase l When the state dwell time changes, but the maximum phase / minimum phase ratio remains unchanged, it is represented as: 。 7. A flexible power control method for a multi-port DC-AC converter according to claim 6, characterized in that, The method of calculating the zero-sequence injection amount based on the dual-modulation wave and battery current reference also includes adopting a combined mode injection strategy for scenario 4, with the first injection being the CM component. m cm1 The second injection is a DM component. m dm The superimposed double-modulated wave is represented as: ; Scenario 5 employs a combined mode injection strategy, where the injection location is based on common-mode injection superimposed with differential-mode injection, and the first injection is the CM component. m cm2 The second injection is a DM component. m dm .

8. A flexible power control method for a multi-port DC-AC converter according to claim 7, characterized in that, The method of calculating the zero-sequence injection amount based on the dual-modulation wave and battery current reference also includes obtaining... i bat_ref Then, the zero-sequence injection amount is calculated by using the battery current expression for the injection situation; The injection amounts for scenarios 1, 2, and 3 are obtained using explicit formulas, expressed as follows: ； Cases 4 and 5 introduce a distribution coefficient λ to allocate the current contribution between CM and DM and obtain the injection amount, expressed as: 。 9. A flexible power control method for a multi-port DC-AC converter according to claim 8, characterized in that, The carrier modulation using zero-sequence injection includes, based on CB-VSVPWM, injecting zero-sequence components into the dual-modulation wave to change its state. l The residence time is adjusted to regulate the average current at the battery port. i bat In this process, by adding zero-sequence injection amounts to specific modulation waves of the maximum / intermediate / minimum phases respectively, the dwell time increment Δ is equivalently achieved. t hmax Δ t hmid Δ t 0mid Δ t 0min And this equation holds true in the volt-second equilibrium equation, expressed as: ， To ensure that the volt-second balance and switching period constraints are still met after modulation, the zero-sequence injection quantity must satisfy a set of consistency conditions and ensure that all dwell times remain within [0, ... T S ].

10. A flexible power control system for a multi-port DC-AC converter, characterized in that, include: The data acquisition module is configured to collect three-phase power grid voltage and current data; The conversion module is configured to perform conversion based on the collected three-phase power grid voltage and current data. αβ Transform and generate orthogonal components of grid voltage and power relationships; The dual-modulation wave module is configured to generate dual-modulation waves based on the quadrature components of the grid voltage. The reference module is configured to calculate the battery current reference based on the quadrature components of the grid voltage and the power relationship; The inverse calculation module is configured to inversely calculate the zero-sequence injection amount based on the dual-modulation wave and the battery current reference. The modulation module is configured to perform carrier modulation using zero-sequence injection. The drive module is configured to drive the inverter based on a carrier modulation signal.

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