A photovoltaic air conditioner and its DC component suppression method, electronic equipment, and dielectric.

Abstract

A photovoltaic air conditioner and its DC component suppression method, electronic equipment, and dielectric are disclosed. The suppression method includes: building a bus ripple detection circuit on the DC side of a single-phase inverter to obtain bus ripple sampling results; performing primary compensation of the DC component by generating a compensation current based on the DC bus voltage; subtracting the current from the collected actual grid-connected current to obtain a grid-connected current error value, which is then combined with a grid voltage feedforward signal and a capacitor current feedback signal to generate a duty cycle signal, which drives the inverter through SPWM modulation; performing secondary compensation of the DC component by using a SOGI-PLL with an FLL to perform phase tracking of the grid voltage and generate a phase-synchronized current modulation signal; adding this signal to the difference between the current and the current to obtain a compensation signal, which adjusts the inverter's duty cycle. This invention effectively reduces the grid-connected DC component of a photovoltaic household air conditioner.

Description

Technical Field

[0001] This invention belongs to the field of air conditioning technology, and more specifically, relates to a photovoltaic air conditioner and its DC component suppression method, electronic equipment, and dielectric. Background Technology

[0002] Combining a single-phase full-bridge topology with LCL filtering and a second-order generalized integral phase-locked loop (PLL) strategy is currently the mainstream method for achieving stable grid-connected photovoltaic (PV) inverters in residential split-type air conditioners. However, the single-phase full-bridge topology of PV split-type air conditioners suffers from DC component issues during grid connection. This topology lacks isolation for the DC circuitry, and the inverter generates a significant amount of DC component during grid-connected operation. When the grid voltage contains DC or harmonic components, the orthogonal signal output by the second-order generalized PLL will still exhibit significant DC offset, causing fluctuations in the obtained grid voltage frequency and phase information and affecting measurement accuracy.

[0003] Existing solutions include, but are not limited to, using a method for suppressing the DC component of the inverter's grid-connected output current and a photovoltaic system. However, this method can only be applied to the problem of DC component control failure of the output current caused by bus voltage imbalance. Existing technical documents also provide a control method and circuit for fast phase tracking compensation, but it cannot compensate for the DC component of the output current caused by bus voltage imbalance, and can only handle grid-connected functions when the DC bus voltage is in an ideal state. Existing technical solutions also include: using DC component detection methods, suppression methods, devices and power converters, but this method requires multi-stage sampling circuits, which increases costs and also increases electromagnetic interference to the system. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a photovoltaic air conditioner and its DC component suppression method, electronic equipment, and dielectric. By comprehensively considering the impact of DC bus ripple changes and frequency fluctuations on phase-locked loop accuracy, improvements are made to the hardware circuitry and software algorithm of the photovoltaic household air conditioner.

[0005] The present invention adopts the following technical solution.

[0006] A first aspect of the present invention provides a method for suppressing DC components, comprising the following steps:

[0007] A bus ripple detection circuit is built on the DC side of a single-phase inverter to obtain the bus ripple sampling results. ;

[0008] Perform a first-stage compensation for the DC component in the grid-connected voltage, including based on the bus ripple sampling results. With the collected DC bus voltage The current used for compensation is generated through error calculation and PI regulation. ; to the current Compared with the actual grid-connected current collected The difference is used to obtain the grid-connected current error value. The grid-connected current error value The duty cycle signal is generated by combining the PI regulation with the grid voltage feedforward signal and the capacitor current feedback signal, and then drives the inverter through SPWM modulation.

[0009] Secondary compensation of the DC component is performed, including adjusting the grid voltage using a second-order generalized integrator phase-locked loop with a frequency-adaptive phase-locked loop. Phase tracking is performed to obtain the sine value of the grid voltage phase; the sine value is multiplied by the AC current signal output from the inverter to the grid to generate a phase-synchronized current modulation signal; this signal is then multiplied by the current... With actual grid-connected current The difference is added together to obtain a compensation signal, and the duty cycle of the inverter is adjusted to achieve secondary compensation of the DC component.

[0010] Preferably, the step based on the bus ripple sampling result With the collected DC bus voltage The current used for compensation is generated through error calculation and PI regulation. include:

[0011] Based on the bus ripple sampling results Calculate DC component reference value and through DC bus voltage Calculate the grid-connected DC component The DC component reference value With the grid-connected DC component Subtracting the two values ​​yields the DC component tracking error, which is then passed through a PI controller. Processing to generate current for compensation. .

[0012] Preferably, the grid-connected current error value is... The duty cycle signal, generated by combining the PI regulation signal with the grid voltage feedforward signal and the capacitor current feedback signal, includes:

[0013] The grid-connected current error value via current PI controller The first control value output, the mains voltage via feedforward function The second control value output, and the capacitor current. The third control value, multiplied by the feedback coefficient, is added together to generate the duty cycle control signal.

[0014] Preferably, the voltage across the DC bus... Calculate the grid-connected DC component include:

[0015] The theoretical value of bus ripple voltage is expressed by the following formula:

[0016]

[0017] In the formula:

[0018] This is the theoretical value of the bus ripple voltage; Peak voltage of the power grid; This is the peak value of the grid-connected current; The angular frequency of the power grid; This refers to the grid-connected DC component. For bus capacitors; This represents the steady-state value of the DC bus voltage.

[0019] set up , ;

[0020] The theoretical value of bus ripple voltage The average DC bus voltage can be obtained by integrating the AC current period T of the power grid. :

[0021]

[0022] Based on the above formula, we obtain... and grid-connected DC component proportionality coefficient It can be expressed by the following formula:

[0023]

[0024] The average voltage of the DC bus and the proportionality coefficient The grid-connected DC component is obtained. .

[0025] Preferably, the second-order generalized integrator phase-locked loop with frequency adaptive phase-locked loop dynamically adjusts the center frequency by real-time detection of the orthogonal signal components output by the second-order generalized integrator.

[0026] A second aspect of the present invention provides a photovoltaic air conditioner, comprising: an inverter, a photovoltaic module, and performing a DC component suppression method as described in the first aspect of the present invention;

[0027] The inverter includes a full-bridge circuit, an LCL filter circuit, a bus ripple detection circuit, and a second-order generalized integral phase-locked loop circuit. The DC side of the full-bridge circuit is connected to the bus ripple detection circuit, and the AC side is connected to the LCL filter circuit. The inverter converts the DC power generated by the photovoltaic module into AC power.

[0028] Preferably, the bus ripple detection circuit includes: a high-frequency transformer, a high-pass filter, and an operational amplifier;

[0029] The high-frequency transformer is used for electrical isolation and to divide the bus voltage;

[0030] The high-pass filter is connected to the output terminal of the high-frequency transformer and is used to pass a ripple signal of a set frequency.

[0031] The operational amplifier is connected to the output of the high-pass filter and is used to amplify the ripple signal of the set frequency and output the bus ripple sampling result.

[0032] Preferably, the second-order generalized integrator phase-locked loop circuit includes: a second-order generalized integrator and a frequency-locked controller;

[0033] The output of the frequency lock controller is connected to the center frequency adjustment terminal of the second-order generalized integrator, and is used to adjust the center frequency of the second-order generalized integrator so that the frequency adaptively tracks.

[0034] A third aspect of the present invention provides an electronic device including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the computer program, when loaded onto the processor, implements a DC component suppression method according to the first aspect.

[0035] A fourth aspect of the present invention provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements a DC component suppression method according to a second aspect.

[0036] Compared with existing technologies, this invention utilizes bus ripple detection to achieve preliminary judgment of the DC component, performs primary compensation for this component in the control system of the original circuit topology, and employs an improved phase-locked loop (PLL) structure with frequency adaptation for secondary compensation of the DC component. The beneficial effects of this invention include at least: addressing the DC component problem caused by bus voltage instability by collecting data on DC bus ripple changes; using frequency-adaptive PLL technology to achieve rapid grid phase locking and switch to grid-connected operation control; reducing the grid-connected DC component of photovoltaic household split-type air conditioners; and enhancing the system's harmonic suppression capability. Attached Figure Description

[0037] Figure 1This is a diagram of a single-phase photovoltaic DC component suppression structure for bus ripple detection provided in accordance with an embodiment of the present invention;

[0038] Figure 2 This is a full-bridge topology diagram of a single-phase LCL filter provided according to an embodiment of the present invention;

[0039] Figure 3 This is a diagram of a conventional single-phase phase-locked loop structure provided according to an embodiment of the present invention;

[0040] Figure 4 This is a block diagram of an improved single-phase phase-locked loop structure provided according to an embodiment of the present invention. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of this invention. The described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the spirit of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this invention.

[0042] Embodiment 1 of the present invention provides a DC component suppression method, including primary compensation of the DC component in the grid-connected voltage and secondary compensation of the DC component.

[0043] The primary compensation of the DC component includes, for example: Figure 1 As shown, a bus ripple detection circuit is built on the DC side of a single-phase inverter to obtain the bus ripple sampling results. ;

[0044] like Figure 2 As shown, the bus ripple sampling results Calculate DC component reference value Through DC bus voltage Calculate the grid-connected DC component The DC component reference value With the grid-connected DC component The DC component tracking error is obtained by subtraction, and the DC component tracking error is then passed to a PI controller. Obtain the current used for compensation The reference current With actual grid-connected current The difference is used to obtain the grid-connected current error value. The grid-connected current error value via current PI controller The obtained output value and grid voltage via feedforward function The obtained output value and capacitor current The values ​​multiplied by the feedback coefficient are added together to obtain the duty cycle of the control signal. The inverter control is then performed through SPWM to achieve primary compensation of the DC component.

[0045] Preferably, but not limitingly, in a full-bridge topology with single-phase LCL filtering, the peak grid current is... and peak grid voltage The sampling process yields the grid-connected inverter output current expressed by the following formula:

[0046]

[0047] In the formula: For the output current of the grid-connected inverter, The DC component of the grid-connected current. This refers to the AC component of the grid-connected current.

[0048] The fundamental component of the grid-connected current can be expressed as: The grid voltage can be expressed as Combining the above formulas, the instantaneous power of the grid-connected inverter is expressed by the following formula:

[0049]

[0050] Under steady-state conditions, and All are fixed values, and The frequency remains constant within one power frequency cycle, using Instead, the grid-connected inverter outputs pulsating power. Expressed as follows:

[0051]

[0052] If the pulsating power is entirely supplied by the bus capacitor Absorption, steady-state value of DC bus voltage The theoretical value of bus ripple voltage is The pulsating power can be expressed by the bus voltage ripple using the following formula:

[0053]

[0054] Integrating, the bus voltage ripple is obtained as follows:

[0055]

[0056] In the formula:

[0057] ; ;

[0058] Therefore, it can be seen that, under ideal conditions, the DC component of the grid-connected current is only related to... Regarding this, integration processing can eliminate the second-harmonic ripple component in the DC bus and extract the first-harmonic ripple component, further refining the theoretical value of the bus ripple voltage. Integrating the AC current of the power grid over the period T yields the average DC bus voltage. :

[0059]

[0060] The above Substituting into the above formula, the proportionality coefficient can be calculated. Expressed as follows:

[0061]

[0062] pass and Calculate the grid-connected DC component The value. Those skilled in the art will know that, using the same algorithm, the measured value obtained from the bus ripple voltage measurement circuit can be used. Obtain the reference value of the grid-connected DC component. , combined Figure 1 The system block diagram described above can achieve the purpose of eliminating a portion of the DC component at once.

[0063] The secondary compensation of the DC component includes adjusting the grid voltage using a second-order generalized integrator phase-locked loop with a frequency-adaptive phase-locked loop. Phase tracking is performed to obtain the sine value of the grid voltage phase; the sine value is multiplied by the AC current signal output from the inverter to the grid to generate a phase-synchronized current modulation signal; this signal is then multiplied by the current... With actual grid-connected current The difference is added together to obtain a compensation signal, and the duty cycle of the inverter is adjusted to achieve secondary compensation of the DC component.

[0064] like Figure 2 As shown, the grid voltage The sinusoidal value of the grid voltage phase is obtained through a SOGI-PLL with a frequency adaptive phase-locked loop (FLL), and multiplied by the AC current and the reference current mentioned in the primary compensation. With actual grid-connected current The difference is added together to obtain the grid-connected current error value. This enables secondary compensation of the DC component.

[0065] Embodiment 2 of the present invention provides a photovoltaic air conditioner that operates a DC component suppression method as described in Embodiment 1, comprising: an inverter and a photovoltaic module.

[0066] like Figure 1 As shown, the inverter converts the DC power generated by the photovoltaic modules into AC power required by the air conditioner, and includes: a full-bridge circuit, an LCL filter circuit, a bus ripple detection circuit, and a second-order generalized integral phase-locked loop circuit; the DC side of the full-bridge circuit is connected to the bus ripple detection circuit, and the AC side is connected to the LCL filter circuit. Preferably, but not limitingly, the upper bridge arm power switches S1 and S3 and the lower bridge arm power switches S2 and S4 of the full-bridge circuit are alternately turned on, and the bus voltage... The full-bridge circuit generates alternating positive and negative voltages on the output side. The voltage output by the full-bridge circuit When the light passes through the LCL filter circuit, according to Kirchhoff's current law, the output current of the full-bridge circuit... The filter capacitor branch containing the filter capacitor C that is shunted to the LCL filter circuit is obtained. The grid-side inductor branch containing grid-side inductor L2 is obtained The high-frequency harmonic components preferentially pass through the filter capacitor branch due to the low impedance characteristics of the capacitor, thereby achieving effective filtering of high-frequency harmonics.

[0067] As one of the prominent substantive features of this invention, the bus ripple detection circuit is connected to the full-bridge circuit. The bus ripple detection circuit includes a high-frequency transformer, a high-pass filter, and an operational amplifier. Specifically, the high-frequency transformer can both provide isolation and perform voltage division. The high-pass filter passes the high-frequency ripple signal and suppresses low-frequency signal interference. The high-frequency ripple signal is output as the bus ripple sampling result by the operational amplifier.

[0068] The second-order generalized integrator phase-locked loop circuit includes a second-order generalized integrator (SOGI), a frequency-locked controller (FLL), and a phase-locked controller (PLL). The output of the frequency-locked controller is connected to the center frequency adjustment terminal of the second-order generalized integrator, and is used to adjust the center frequency of the second-order generalized integrator to enable frequency adaptive tracking.

[0069] like Figure 3 The diagram shown illustrates a traditional single-phase phase-locked loop (PLL). In a grid-connected inverter system, the inverter output current and grid voltage must maintain the same phase at all times. The PLL needs to quickly and accurately detect the phase and frequency information of the grid voltage and generate a reference signal that is synchronized with it. A traditional single-phase PLL includes a phase detector (PD), a loop filter (LF), and a voltage-controlled oscillator (VCO). The phase detector is used to compare the phase difference between the input signal (grid voltage) and the output signal (PLL feedback signal) in real time and output a signal containing phase error information. , It typically contains high-frequency AC components. The loop filter employs a low-pass filter or a proportional-integral (PI) controller to effectively filter out the output signal by setting a cutoff frequency or control parameters. The high-frequency AC signal in the circuit. The voltage-controlled oscillator adjusts the output frequency according to the filtered error signal, and finally generates an AC signal that is phase-synchronized with the grid voltage, so as to achieve precise tracking of the inverter output current and the grid voltage.

[0070] like Figure 4 As shown, a filtering process is added to the phase detector of the traditional phase-locked loop to eliminate DC components and enhance harmonic components. As one of the outstanding substantive features of this invention, in order to tune the center frequency of the second-order generalized integrator and avoid the influence of frequency deviation on the output frequency and phase of the phase-locked controller, the frequency-locked controller is added in the later stage to realize the frequency adaptive function.

[0071] Preferably, but not limitingly, the input signal is in the conventional second-order generalized integrator. To two output signals , The transfer function is:

[0072]

[0073] In the formula: s is the Laplace operator;

[0074] , , The set system gain;

[0075] This is the angular frequency of the power grid.

[0076] When the power grid frequency fluctuates, to avoid the impact of frequency deviation on the output frequency and phase of the phase-locked loop (PLL), a frequency-locked controller is added to achieve the frequency adaptive function of the PLL and adjust the input signal accordingly. To error signal List the transfer functions:

[0077]

[0078] Define error signal With output signal The ratio is ,make ,but Therefore, when hour, The error signal is in phase with the output signal, and vice versa. Therefore, by introducing a negative gain coefficient... After a limited time, the error signal can be adjusted to zero.

[0079] Embodiment 3 of the present invention provides an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the computer program is loaded onto the processor, it implements a DC component suppression method according to Embodiment 1.

[0080] Embodiment 4 of the present invention provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements a DC component suppression method according to Embodiment 1.

[0081] It is worth noting that in the embodiments of the present invention, "steps + numbers" is only a way of expressing a photovoltaic air conditioner and its DC component suppression method, electronic equipment, and dielectric specific implementation method, rather than an absolute restriction on the order of the steps. Under the guidance of the core concept of the present invention, changing the order of these steps to obtain the same or similar technical effects all fall within the scope of the present invention.

[0082] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the claims of the present invention.

Claims

1. A method for suppressing DC component, characterized in that, Includes the following steps: A bus ripple detection circuit is built on the DC side of the single-phase inverter to obtain the bus ripple sampling results. ; Perform a first-stage compensation for the DC component in the grid-connected voltage, including based on the bus ripple sampling results. With the collected DC bus voltage The current used for compensation is generated through error calculation and PI regulation. ; to the current Compared with the actual grid-connected current collected The difference is used to obtain the grid-connected current error value. The grid-connected current error value The duty cycle signal is generated by combining the PI regulation with the grid voltage feedforward signal and the capacitor current feedback signal, and then drives the inverter through SPWM modulation. The secondary compensation of the DC component includes adjusting the grid voltage using a second-order generalized integrator phase-locked loop with a frequency-adaptive phase-locked loop. Phase tracking is performed to obtain the sinusoidal value of the grid voltage phase; the sinusoidal value is multiplied by the AC current signal output by the inverter to the grid to generate a phase-synchronized current modulation signal; Combine it with the current With actual grid-connected current The difference is added together to obtain a compensation signal, and the duty cycle of the inverter is adjusted to achieve secondary compensation of the DC component.

2. The DC component suppression method according to claim 1, Its characteristics are: The bus ripple sampling results With the collected DC bus voltage The current used for compensation is generated through error calculation and PI regulation. include: Based on the bus ripple sampling results Calculate DC component reference value and through DC bus voltage Calculate the grid-connected DC component ; The DC component reference value With the grid-connected DC component Subtracting the two values ​​yields the DC component tracking error, which is then passed through a PI controller. Processing to generate current for compensation. .

3. The DC component suppression method according to claim 1, Its characteristics are: The grid-connected current error value The duty cycle signal, generated by combining the PI regulation signal with the grid voltage feedforward signal and the capacitor current feedback signal, includes: The grid-connected current error value via current PI controller The first control value output, the mains voltage via feedforward function The second control value output, and the capacitor current. The third control value, multiplied by the feedback coefficient, is added together to generate the duty cycle control signal.

4. A DC component suppression method according to claim 2, Its characteristics are: The DC bus voltage Calculate the grid-connected DC component include: The theoretical value of bus ripple voltage is expressed by the following formula: In the formula: This is the theoretical value of the bus ripple voltage; Peak voltage of the power grid; This is the peak value of the grid-connected current; The angular frequency of the power grid; This refers to the grid-connected DC component. For bus capacitors; This represents the steady-state value of the DC bus voltage. set up , ; The theoretical value of bus ripple voltage Integrating the AC current of the power grid over the period T yields the average DC bus voltage. : Based on the above formula, we obtain... and grid-connected DC component proportionality coefficient It can be expressed by the following formula: The average voltage of the DC bus and the proportionality coefficient The grid-connected DC component is obtained. .

5. The DC component suppression method according to claim 1, characterized in that... ； The second-order generalized integrator phase-locked loop with frequency adaptive phase-locked loop dynamically adjusts the center frequency by detecting the orthogonal signal components output by the second-order generalized integrator in real time.

6. A photovoltaic air conditioner, characterized in that, include: Inverters and photovoltaic modules shall implement a DC component suppression method as described in any one of claims 1 to 5; The inverter includes a full-bridge circuit, an LCL filter circuit, a bus ripple detection circuit, and a second-order generalized integral phase-locked loop circuit. The DC side of the full-bridge circuit is connected to the bus ripple detection circuit, and the AC side is connected to the LCL filter circuit. The inverter converts the DC power generated by the photovoltaic module into AC power.

7. A photovoltaic air conditioner according to claim 6, characterized in that... ； The bus ripple detection circuit includes: a high-frequency transformer, a high-pass filter, and an operational amplifier; The high-frequency transformer is used for electrical isolation and to divide the bus voltage; The high-pass filter is connected to the output terminal of the high-frequency transformer and is used to pass a ripple signal of a set frequency. The operational amplifier is connected to the output of the high-pass filter and is used to amplify the ripple signal of the set frequency and output the bus ripple sampling result.

8. A photovoltaic air conditioner according to claim 6, characterized in that; The second-order generalized integrator phase-locked loop circuit includes: a second-order generalized integrator and a frequency lock controller; The output of the frequency lock controller is connected to the center frequency adjustment terminal of the second-order generalized integrator, and is used to adjust the center frequency of the second-order generalized integrator so that the frequency adaptively tracks.

9. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the computer program is loaded into the processor, it implements the DC component suppression method according to any one of claims 1 to 5.

10. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by the processor, it implements the DC component suppression method according to any one of claims 1 to 5.

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