Single-phase off-grid inverter bus normalization double-loop control method and system

Abstract

The application discloses a single-phase off-grid inverter bus normalization double-loop control method and system. The method obtains a DC bus voltage, an output voltage effective value given and a target output fundamental angular frequency, generates an output voltage instantaneous reference value; collects an inverter output voltage to construct a voltage error, and obtains an inductor current reference value through virtual impedance operation; collects an output filter inductor current to construct a current error, and obtains a control voltage quantity through a proportional resonant current regulator; then, a reference modulation quantity is obtained through DC bus voltage normalization, and a final modulation quantity is obtained by deducting an inductor current feedforward term, and then a unipolar frequency multiplication sine pulse width modulation is performed to generate a driving pulse. The application can reduce the influence of bus voltage fluctuation on modulation gain, and improve dynamic response and output voltage stabilization performance under load disturbance.

Description

Technical Field

[0001] This invention relates to the field of power electronic conversion and digital control technology, and in particular to a bus normalization dual-loop control method and system for a single-phase off-grid inverter. Background Technology

[0002] Single-phase off-grid inverters are widely used in portable energy storage, battery-powered devices, off-grid photovoltaic systems, and laboratory AC power supplies. These devices typically employ a full-bridge inverter main circuit and an LC output filter network to obtain a sinusoidal AC output that meets operational requirements at relatively high switching frequencies. In existing single-phase off-grid inverter control methods, a common approach is to achieve voltage regulation control through an outer output voltage loop and an inner current loop, supplemented by a proportional resonant (PR) or quasi-proportional resonant controller to improve AC tracking performance. On the other hand, to suppress the resonant peak of the LC filter network, active damping, virtual impedance, or current feedback branches are often used in engineering to improve the system's damping characteristics.

[0003] However, one type of existing solution relies on output voltage RMS compensation to form an outer third closed loop, which has problems such as long control links, strong parameter coupling, and the RMS calculation window affecting dynamic response. Another type of solution, although it adopts dual closed-loop control, does not take into account the modulation gain change caused by DC bus voltage fluctuation and the inductor current feedforward injection position in a unified manner. Therefore, under bus fluctuation, load change or nonlinear load conditions, there may still be problems such as modulation mismatch, slow output recovery and unstable vibration suppression effect.

[0004] Therefore, it is necessary to propose a control method that does not rely on the output voltage RMS value to compensate the third closed loop, but instead uses the output voltage RMS value given and sinusoidal reference generation, virtual impedance control of the output inductor current reference, inductor current PR inner loop, bus normalization, and the coordinated operation of the pre-modulation inductor current feedforward branch, so as to improve the voltage regulation capability and dynamic response performance of low-power single-phase off-grid inverters under complex load conditions. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of output oscillation, slow dynamic recovery, and unstable modulation gain that are prone to occur in existing single-phase off-grid inverters under conditions of LC filter network, load disturbance, and DC bus fluctuation. This invention provides a bus normalization dual-loop control method and system for single-phase off-grid inverters.

[0006] To achieve the above objectives, the present invention provides a bus normalization dual-loop control method for a single-phase off-grid inverter, comprising: Obtain the DC bus voltage, the RMS value of the output voltage, and the target output fundamental angular frequency; A momentary reference value for the output voltage is generated based on the given effective value of the output voltage and the target fundamental angular frequency of the output. The inverter output voltage is collected and a voltage error is constructed by comparing it with the instantaneous reference value of the output voltage. A virtual impedance calculation is performed on the voltage error to obtain a reference value for the inductor current; The output filter inductor current of the single-phase off-grid inverter is collected, and a current error is constructed by comparing it with the inductor current reference value. The current error is input into the proportional resonant current regulator to obtain the control voltage. The control voltage is normalized using the DC bus voltage to obtain a reference modulation amount; The inductor current feedforward term is constructed based on the output filter inductor current, and the inductor current feedforward term is subtracted from the reference modulation amount to obtain the final modulation amount. Based on the final modulation amount, unipolar frequency doubling sinusoidal pulse width modulation is performed to generate drive pulses for the four power switching devices of the full-bridge inverter main circuit in the single-phase off-grid inverter.

[0007] As a further improvement to the above technical solution, the step of generating the instantaneous reference value of the output voltage includes: determining the fundamental sine signal based on the target output fundamental angular frequency and the current time, and multiplying the given effective value of the output voltage by the fundamental sine signal to obtain the instantaneous reference value of the output voltage; the step of constructing the voltage error includes: subtracting the inverter output voltage from the instantaneous reference value of the output voltage to obtain the voltage error.

[0008] As a further improvement to the above technical solution, a virtual impedance calculation is performed on the voltage error to obtain an inductor current reference value, including: obtaining the inductor current reference value for the current control cycle according to a discrete update relationship based on preset virtual inductor parameters, virtual resistance parameters, and digital control cycle. ;in, , This is the reference value for the inductor current in the current control cycle. This is the reference value for the inductor current from the previous control cycle. The voltage error for the current control cycle. This is the voltage error from the previous control cycle. For virtual inductance parameters, For virtual resistance parameters, The digital control cycle is represented by k, where k is the control cycle number.

[0009] As a further improvement to the above technical solution, the current error is input to a proportional resonant current regulator to obtain a control voltage, including: proportionally resonantly regulating the current error according to a continuous domain transfer function to obtain the control voltage. ;in, Let be the continuous domain transfer function of the proportional resonant current regulator. This is the proportionality coefficient. The resonance coefficient, For the resonant bandwidth, The target output fundamental angular frequency is s, where s is a complex frequency domain variable.

[0010] As a further improvement to the above technical solution, the control voltage is normalized using the DC bus voltage to obtain a reference modulation quantity, including: dividing the control voltage by the DC bus voltage to obtain the reference modulation quantity, wherein the reference modulation quantity satisfies: ,in, As the reference modulation amount, To control the voltage level, This is the DC bus voltage.

[0011] As a further improvement to the above technical solution, constructing an inductor current feedforward term based on the output filter inductor current and subtracting the inductor current feedforward term from the reference modulation amount to obtain the final modulation amount includes: using the output filter inductor current as the inductor current feedback value and constructing an inductor current feedforward term based on the inductor current feedback value; subtracting the inductor current feedforward term from the reference modulation amount to obtain the final modulation amount, wherein the final modulation amount satisfies: Where m is the final modulation amount, As the reference modulation amount, This is for the output filter inductor current.

[0012] As a further improvement to the above technical solution, unipolar frequency-doubling sinusoidal pulse width modulation is performed according to the final modulation amount, including: generating a modulation reference signal according to the final modulation amount, and using modulation logic of inverted carriers of the two bridge arms of the full bridge and comparison of the modulation reference signal at the same frequency to generate complementary drive pulses corresponding to the two bridge arms of the full bridge respectively; the phases of the two bridge arm carriers are opposite, so that the equivalent switching frequency of the output terminal of the single-phase off-grid inverter is twice the carrier frequency.

[0013] The present invention also provides a single-phase off-grid inverter system, comprising: DC input unit, used to provide DC bus voltage; The full-bridge inverter main circuit is used to invert DC power into AC voltage; The output filtering unit is connected to the output terminal of the full-bridge inverter main circuit; Output voltage sampling unit, used to acquire inverter output voltage; Inductor current sampling unit, used to collect the output filter inductor current; The digital control unit is used to generate an instantaneous reference value for the output voltage based on the given effective value of the output voltage and the target fundamental angular frequency of the output voltage; construct a voltage error based on the inverter output voltage and the instantaneous reference value of the output voltage; perform virtual impedance calculation on the voltage error to obtain an inductor current reference value; construct a current error based on the output filter inductor current and the inductor current reference value; obtain a control voltage quantity through a proportional resonant current regulator; normalize the control voltage quantity using the DC bus voltage to obtain a reference modulation quantity; construct an inductor current feedforward term based on the output filter inductor current; and subtract the inductor current feedforward term from the reference modulation quantity to obtain the final modulation quantity. The drive and protection unit is used to drive the four power switching devices of the full-bridge inverter main circuit according to the unipolar frequency-doubled sinusoidal pulse width modulation drive pulse generated according to the final modulation amount.

[0014] The beneficial effects of the single-phase off-grid inverter bus normalized dual-loop control method and system provided by this invention are as follows: This invention employs a dual-closed-loop control system: the output voltage error is controlled by virtual impedance to generate an inductor current reference, which is then used to generate a modulation reference via the inner loop of the inductor current PR. This eliminates the need for a third closed loop formed by output voltage RMS compensation, thereby shortening the control chain and reducing the coupling complexity of external parameters. A DC bus voltage normalization stage is introduced after the PR current regulator to reduce modulation gain variations caused by DC bus fluctuations and improve voltage regulation consistency. Injecting a feedforward term based on inductor current feedback into the normalization modulation command terminal provides rapid correction to the PR output, improving load surge recovery performance and enhancing the dynamic quality of the output voltage. The use of unipolar frequency-doubled SPWM modulation increases the equivalent switching frequency at the output, reduces filtering pressure, and improves output waveform quality. The control chain and digital implementation sequence of this invention are clearly defined, facilitating engineering deployment on microcontroller, DSP, or FPGA platforms. Attached Figure Description

[0015] Figure 1 This is a flowchart of the bus normalization dual-loop control method for a single-phase off-grid inverter in an embodiment of the present invention; Figure 2 This is a structural diagram of the bus normalization dual-loop control system for a single-phase off-grid inverter in an embodiment of the present invention; Figure 3 This is a schematic diagram of the full-bridge inverter main circuit and LC output filter connection in an embodiment of the present invention; Figure 4 This is a control block diagram of dual-loop control, bus normalization, and inductor current feedforward term deduction in an embodiment of the present invention. Figure 5 This is a schematic diagram of the unipolar frequency doubling sinusoidal pulse width modulation logic in an embodiment of the present invention. Detailed Implementation

[0016] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0017] like Figure 1 As shown, this invention provides a bus normalization dual-loop control method for a single-phase off-grid inverter, which is applied to a single-phase off-grid inverter system. The method includes: S1 acquiring the DC bus voltage, the effective value of the output voltage, and the target output fundamental angular frequency; S2 generating an instantaneous reference value for the output voltage based on the effective value of the output voltage and the target output fundamental angular frequency; S3 acquiring the inverter output voltage and constructing a voltage error with the instantaneous reference value of the output voltage; S4 performing virtual impedance calculation on the voltage error to obtain an inductor current reference value; S5 acquiring the output filter inductor current of the single-phase off-grid inverter and constructing a current error with the inductor current reference value; S6 inputting the current error into a proportional resonant current regulator to obtain a control voltage quantity; S7 normalizing the control voltage quantity using the DC bus voltage to obtain a reference modulation quantity; S8 constructing an inductor current feedforward term based on the output filter inductor current and subtracting the inductor current feedforward term from the reference modulation quantity to obtain a final modulation quantity; S9 performing unipolar frequency doubling sinusoidal pulse width modulation based on the final modulation quantity to generate drive pulses for the four power switching devices of the full-bridge inverter main circuit in the single-phase off-grid inverter.

[0018] The aforementioned control method uses an outer loop for output voltage and an inner loop for inductor current to form the main control link. The outer loop converts the output voltage deviation into an inductor current reference value through virtual impedance calculation, while the inner loop generates the control voltage through a proportional resonant current regulator. Before the control voltage enters modulation, it is normalized using the DC bus voltage, and then a feedforward term for the inductor current constructed based on the output filter inductor current is subtracted after normalization, thus obtaining the final modulation amount for unipolar frequency-doubled sinusoidal pulse width modulation. This method does not rely on output voltage RMS compensation to form an outer third closed loop. The output voltage RMS value, total harmonic distortion, or power factor detection results can be used for operation monitoring, performance evaluation, or protection criterion generation.

[0019] Example 1 like Figure 2As shown, this embodiment provides a single-phase off-grid inverter system. The system includes a DC input unit, a full-bridge inverter main circuit, an output filter unit, an output voltage sampling unit, an inductor current sampling unit, a digital control unit, and a drive and protection unit. The DC input unit provides the DC bus voltage; the full-bridge inverter main circuit converts DC power into AC voltage; the output filter unit is connected to the output terminal of the full-bridge inverter main circuit; the output voltage sampling unit acquires the inverter output voltage; the inductor current sampling unit acquires the output filter inductor current; the digital control unit executes the single-phase off-grid inverter bus normalized dual-loop control method; and the drive and protection unit drives the power switching devices and performs protection control according to the drive signal output by the digital control unit.

[0020] like Figure 3 As shown, in one specific embodiment, the full-bridge inverter main circuit consists of four power switching devices. The output filtering unit is an LC output filtering unit connected to the output terminal of the full-bridge inverter main circuit, used to filter out high-frequency switching harmonics and output single-phase AC voltage. An output voltage sampling circuit is used to acquire the output voltage at the load terminal, and an inductor current sampling circuit is used to acquire the inductor current in the LC filter. The drive and protection circuit is used to perform power device drive, dead-time control, and overvoltage, overcurrent, and overheat protection.

[0021] In a preferred embodiment, the digital control unit can be implemented using a microcontroller with an analog-to-digital conversion module and a sinusoidal pulse width modulation (PWM) timer module, or it can be implemented using a digital signal processor (DSP) or a field-programmable gate array (FPGA). The digital control unit may include a sinusoidal reference generation module, a virtual impedance control module, a proportional resonant current adjustment module, a bus normalization module, an inductor current feedforward module, and a unipolar frequency-doubled sinusoidal pulse width modulation (QPWM) module; wherein the output of the inductor current feedforward module is connected between the output of the bus normalization module and the input of the unipolar frequency-doubled sinusoidal pulse width modulation (QPWM) module.

[0022] Example 2 like Figure 1 and Figure 4 As shown, in this embodiment, the digital control unit first sets Uset and the target output fundamental angular frequency based on the effective value of the output voltage. Generate a fundamental sinusoidal signal, and convert the effective value of the output voltage given Uset into the instantaneous reference amplitude of the output voltage. ,in, Furthermore, an instantaneous reference value for the output voltage is generated based on the instantaneous reference amplitude Um of the output voltage and the fundamental sine wave signal: In this context, t represents the current time.

[0023] Subsequently, the output voltage sampling unit acquires the inverter output voltage u_o. The digital control unit subtracts the inverter output voltage u_o from the instantaneous reference value u_ref of the output voltage to obtain the voltage error: e_u = u_ref - u_o. This voltage error is used for subsequent virtual impedance calculations to map the instantaneous deviation of the output voltage to an inductor current reference value.

[0024] Example 3 like Figure 4 As shown, in this embodiment, the digital control unit performs virtual impedance calculation on the voltage error e_u to obtain the inductor current reference value i_ref. The virtual impedance calculation can be executed by a discrete controller implemented by a program module. The discrete controller is used to update the inductor current reference value for the current control cycle based on the voltage error of the current control cycle, the voltage error of the previous control cycle, and the inductor current reference value of the previous control cycle.

[0025] In a preferred embodiment, the virtual impedance control element is implemented using a discrete RL element, and its discrete update relationship is as follows: ,in, .

[0026] in, This is the reference value for the inductor current in the current control cycle. This is the reference value for the inductor current from the previous control cycle. The voltage error for the current control cycle. This is the voltage error from the previous control cycle. For virtual inductance parameters, For virtual resistance parameters, The digital control cycle is represented by k, where k is the control cycle number.

[0027] Further, the inductor current sampling unit acquires the output filter inductor current i_L of the single-phase off-grid inverter. The digital control unit calculates the difference between the output filter inductor current i_L and the inductor current reference value i_ref to form a current error e_i, and inputs the current error e_i into the proportional resonant current regulator. The continuous domain expression of the proportional resonant current regulator can be expressed as: .

[0028] in, This is the proportionality coefficient. The resonance coefficient, For the resonant bandwidth, The target output fundamental angular frequency is determined. The proportional resonant current regulator outputs a control voltage. , is used to characterize the target modulation voltage that the inverter bridge should output within the current control cycle, and s is a complex frequency domain variable.

[0029] In a preferred embodiment, the proportional resonant current regulator is discretized using a bilinear transform, converting the continuous-domain transfer function into a z-domain difference form: in, This refers to the discrete control cycle number; For the first Control voltage amount per control cycle and The first The first control cycle and the first Control voltage amount per control cycle; For the first Current error per control cycle and The first The first control cycle and the first Current error per control cycle; and To output the recursive coefficients, , and Input coefficient for current error; , and These are the current term coefficient, first-order delay term coefficient, and second-order delay term coefficient of the denominator of the discretized transfer function of the proportional resonant current regulator, respectively. , and These are the coefficients of the current term, the first-order delay term, and the second-order delay term in the numerator of the discretized transfer function, respectively. For digital control cycle, For the resonant bandwidth, To output the fundamental angular frequency of the target wave, This is the proportionality coefficient. is the resonance coefficient.

[0030] The above coefficients can be determined during the initialization of the digital control unit based on the digital control cycle. Target output fundamental angular frequency Resonant bandwidth and proportionality coefficient resonance coefficient Calculate and store in advance. Kr is used to adjust the dynamic response speed and to improve the fundamental steady-state tracking accuracy. It is designed to balance resonant selectivity and frequency offset adaptability; the parameter tuning can be set in combination with output filter parameters, switching frequency and target harmonic index.

[0031] To prevent the modulation command from exceeding the linear modulation range of the inverter bridge, the control voltage amount... A limiting step is set; in one embodiment, a limiting step is implemented. The limiting range is set to [-Udc, Udc] or its equivalent normalized range. When the limiting threshold is reached, clamping or inverse feedback processing is performed on the discrete resonant state variables to suppress saturation accumulation and improve dynamic recovery stability.

[0032] Example 4 like Figure 4 As shown, in this embodiment, to reduce the impact of DC bus voltage fluctuations on the modulation gain, the control voltage output by the proportional resonant current regulator is... The reference modulation amount is obtained by normalizing the DC bus voltage Udc. .

[0033] Furthermore, based on the output filter inductor current... Construct an inductor current feedforward term. Specifically, the output filter inductor current... The current sampling ratio is converted to the inductor current reference value. Current feedback value with the same dimensions; when the digital control unit is implemented using per-unit scaling, it can be further divided by the reference current. Obtain the equivalent per-unit value and construct the inductor current feedforward term under the same dimensions. Where 0.1 is the scaling factor of the inductor current feedforward term.

[0034] In a preferred embodiment, the inductor current feedforward term is... From the reference modulation amount Subtracting from the middle, we obtain the final modulation amount: .

[0035] Combining the aforementioned bus normalization relationship, the final modulation amount can be obtained as: The aforementioned Located after the bus normalization stage and before the unipolar frequency-doubling sinusoidal pulse width modulation unit, this branch forms the inductor current feedforward correction branch. This branch enables rapid correction of the modulation command under sudden load changes and nonlinear load conditions, thereby improving the dynamic response of the inductor current and output voltage.

[0036] In a preferred embodiment, the proportional coefficient 0.1 can be determined through simulation and experimental tuning based on the rated bus voltage, filter inductor parameters, rated output current, and allowable output voltage overshoot under load mutation. Typically, this proportional coefficient can be selected in the range of 0.05 to 0.20, with 0.1 being a preferred value that balances dynamic compensation effect, modulation smoothness, and system stability margin.

[0037] Example 5 like Figure 5 As shown, in this embodiment, the digital control unit performs unipolar frequency-doubled sinusoidal pulse width modulation according to the final modulation amount m. The modulation method employs a method of inverting the carriers of the two bridge arms of the full-bridge inverter and comparing the modulation reference signal at the same frequency. A modulation reference signal is generated based on the final modulation amount m, and complementary drive pulses are generated for each of the two bridge arms. Because the carriers of the two bridge arms are inverted, the equivalent switching frequency at the inverter output is increased to twice the carrier frequency, thereby shifting the switching harmonics to a higher frequency band and reducing the processing pressure of the LC filter on low-order harmonics. The complementary drive pulses are output to the four power switching devices of the full-bridge inverter main circuit via the drive and protection unit.

[0038] In one specific embodiment, the four power switching devices are respectively the upper transistor S1 of the first bridge arm, the lower transistor S2 of the first bridge arm, the upper transistor S3 of the second bridge arm, and the lower transistor S4 of the second bridge arm; the complementary drive pulses of the first bridge arm correspond to S1 and S2 respectively, and the complementary drive pulses of the second bridge arm correspond to S3 and S4 respectively. The drive signals of the upper and lower transistors of the same bridge arm are complementary and a dead time is set. The dead time can be set to hundreds of nanoseconds to several microseconds according to the turn-on and turn-off characteristics of the power devices; when the drive and protection unit detects overcurrent, bus overvoltage, device overheating, or undervoltage abnormalities, it prioritizes blocking the drive output of the corresponding bridge arm or the entire bridge, and restores the pulse output according to a preset timing sequence after the fault is cleared, so as to realize the coordination between dead time control and protection output.

[0039] Within each digital control cycle, to ensure the consistency and real-time performance of digital control, the digital control unit executes control tasks in the following order: output voltage sampling; output filter inductor current sampling; virtual impedance control calculation and updating the inductor current reference value; proportional resonant current adjustment and generation of control voltage; DC bus voltage normalization calculation; inductor current feedforward term deduction; unipolar frequency doubling sinusoidal pulse width modulation duty cycle refresh; protection judgment and status monitoring.

[0040] By arranging the timing as described above, the additional control deviations caused by sampling and sinusoidal pulse width modulation refresh misalignment can be reduced, improving the stability of the method's implementation on the digital control platform. The output voltage RMS value, total harmonic distortion, or power factor detection modules can be set up as operation monitoring modules, but they do not participate in forming the outer third closed-loop control.

[0041] The embodiments of this application have been described above with reference to the accompanying drawings. However, this application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit and scope of the claims, and all of these forms are within the protection scope of this application.

Claims

1. A method for normalized dual-loop control of the busbar of a single-phase off-grid inverter, characterized in that, include: Obtain the DC bus voltage, the RMS value of the output voltage, and the target output fundamental angular frequency; A momentary reference value for the output voltage is generated based on the given effective value of the output voltage and the target fundamental angular frequency of the output. The inverter output voltage is collected and a voltage error is constructed by comparing it with the instantaneous reference value of the output voltage. A virtual impedance calculation is performed on the voltage error to obtain a reference value for the inductor current; The output filter inductor current of the single-phase off-grid inverter is collected, and a current error is constructed by comparing it with the inductor current reference value. The current error is input into the proportional resonant current regulator to obtain the control voltage. The control voltage is normalized using the DC bus voltage to obtain a reference modulation amount; The inductor current feedforward term is constructed based on the output filter inductor current, and the inductor current feedforward term is subtracted from the reference modulation amount to obtain the final modulation amount. Based on the final modulation amount, unipolar frequency doubling sinusoidal pulse width modulation is performed to generate drive pulses for the four power switching devices of the full-bridge inverter main circuit in the single-phase off-grid inverter.

2. The single-phase off-grid inverter bus normalization dual-loop control method according to claim 1, characterized in that, The step of generating the instantaneous reference value of the output voltage includes: determining the fundamental sine signal based on the target output fundamental angular frequency and the current time, and multiplying the given effective value of the output voltage by the fundamental sine signal to obtain the instantaneous reference value of the output voltage; the step of constructing the voltage error includes: subtracting the inverter output voltage from the instantaneous reference value of the output voltage to obtain the voltage error.

3. The single-phase off-grid inverter bus normalization dual-loop control method according to claim 1, characterized in that, The voltage error is subjected to virtual impedance calculation to obtain the inductor current reference value, including: obtaining the inductor current reference value for the current control cycle according to the preset virtual inductor parameters, virtual resistance parameters, and digital control cycle, based on a discrete update relationship. ;in, , This is the reference value for the inductor current in the current control cycle. This is the reference value for the inductor current from the previous control cycle. Voltage error in the current control cycle, This is the voltage error from the previous control cycle. For virtual inductance parameters, For virtual resistance parameters, The digital control cycle is represented by k, where k is the control cycle number.

4. The single-phase off-grid inverter bus normalization dual-loop control method according to claim 1, characterized in that, The current error is input into a proportional resonant current regulator to obtain a control voltage, including: proportionally resonantly regulating the current error according to a continuous domain transfer function to obtain the control voltage. ;in, Let be the continuous domain transfer function of the proportional resonant current regulator. This is the proportionality coefficient. The resonance coefficient, For the resonant bandwidth, The target output fundamental angular frequency is s, where s is a complex frequency domain variable.

5. The single-phase off-grid inverter bus normalization dual-loop control method according to claim 1, characterized in that, Normalizing the control voltage using the DC bus voltage to obtain a reference modulation quantity includes: dividing the control voltage by the DC bus voltage to obtain the reference modulation quantity, wherein the reference modulation quantity satisfies: ,in, As the reference modulation amount, To control the voltage level, This is the DC bus voltage.

6. The single-phase off-grid inverter bus normalization dual-loop control method according to claim 5, characterized in that, Constructing an inductor current feedforward term based on the output filter inductor current, and subtracting the inductor current feedforward term from the reference modulation amount to obtain the final modulation amount, includes: using the output filter inductor current as the inductor current feedback value, and constructing an inductor current feedforward term based on the inductor current feedback value; subtracting the inductor current feedforward term from the reference modulation amount to obtain the final modulation amount, wherein the final modulation amount satisfies: Where m is the final modulation amount, As the reference modulation amount, This is for the output filter inductor current.

7. The single-phase off-grid inverter bus normalization dual-loop control method according to claim 1, characterized in that, Performing unipolar frequency-doubling sinusoidal pulse width modulation according to the final modulation amount includes: generating a modulation reference signal according to the final modulation amount, and using modulation logic that compares the carriers of the two bridge arms of the full bridge with opposite phases and the modulation reference signal with the same frequency to generate complementary drive pulses corresponding to the two bridge arms of the full bridge respectively; the phases of the two bridge arm carriers are opposite, so that the equivalent switching frequency of the output terminal of the single-phase off-grid inverter is twice the carrier frequency.

8. A single-phase off-grid inverter system, characterized in that, include: DC input unit, used to provide DC bus voltage; The full-bridge inverter main circuit is used to invert DC power into AC voltage; The output filtering unit is connected to the output terminal of the full-bridge inverter main circuit; Output voltage sampling unit, used to acquire inverter output voltage; Inductor current sampling unit, used to collect the output filter inductor current; The digital control unit is used to generate an instantaneous reference value for the output voltage based on the given effective value of the output voltage and the target fundamental angular frequency of the output voltage; construct a voltage error based on the inverter output voltage and the instantaneous reference value of the output voltage; perform virtual impedance calculation on the voltage error to obtain an inductor current reference value; construct a current error based on the output filter inductor current and the inductor current reference value; obtain a control voltage quantity through a proportional resonant current regulator; normalize the control voltage quantity using the DC bus voltage to obtain a reference modulation quantity; construct an inductor current feedforward term based on the output filter inductor current; and subtract the inductor current feedforward term from the reference modulation quantity to obtain the final modulation quantity. The drive and protection unit is used to drive the four power switching devices of the full-bridge inverter main circuit according to the unipolar frequency-doubled sinusoidal pulse width modulation drive pulse generated according to the final modulation amount.

Images