Control method for improving efficiency of inverter

Abstract

A control method for improving the efficiency of an inverter, relating to the technical field of inverters, and aiming to solve the problems of difficulty in design of Boost and INV inductors, large switching loss of switch transistors, and low efficiency. The present invention comprises the following implementation steps: S1, the voltage and current of Boost and INV lines are sampled; S2, when an absolute value of a mains voltage is greater than a threshold, the Boost circuit modulates an output voltage into a steamed bun waveform equal to the mains electricity; S3: when the absolute value of the mains voltage is less than the threshold, the Boost / Buck outputs a BUS voltage equal to the threshold, while the INV works at a high frequency, and modulates the BUS voltage into a zero-crossing portion of the mains voltage, and in this case, the Boost / Buck works in a constant voltage source mode or a pass-through mode, and the INV works at a high frequency but with low working voltage and small working current. Thus, it is ensured that the output work factor can be adjusted within a certain range, the loss of the Boost and INV lines can also be reduced, and compared with traditional control modes, the overall boost ratio of the Boost line and the utilization rate of the BUS voltage of the INV portion are reduced.

Description

A control method for improving inverter efficiency Technical Field

[0001] The present invention relates to the technical field of inverters, and in particular to a control method for improving inverter efficiency. Background Art

[0002] A solar inverter is a key device for converting DC power into AC power. It is used to convert the DC power generated by solar photovoltaic panels into AC power suitable for home, commercial, and industrial power systems. Its primary function is to use electronic components and circuits to convert DC power into AC power of a specified frequency and voltage for use in homes or power grids. Based on the output voltage and current characteristics of the connected solar panels, it controls power regulation and inverter control to achieve maximum power point tracking and grid lock. Boost or INV circuits are typically used in solar inverters to achieve DC-to-AC voltage conversion.

[0003] In solar inverters, Boost or INV always operates at high frequency. In this case, the design of Boost and INV inductors is difficult, and the switching loss of the switch tube is large, resulting in low efficiency.

[0004] Therefore, a control method for improving inverter efficiency is proposed. Summary of the Invention

[0005] The purpose of the present invention is to provide a control method for improving the efficiency of an inverter, aiming to solve the problems in the above background technology that the design of Boost and INV inductors is difficult, the switching loss of the switch tube is large, and the efficiency is low.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a control method for improving inverter efficiency, comprising the following implementation steps:

[0007] S1: The CNTL unit samples the voltage and current of the Boost and INV lines and controls their switches. At the same time, a voltage is set as the threshold voltage Vth. The specific value is calculated based on the required output reactive power.

[0008] S2: When the absolute value of the mains voltage is higher than the threshold voltage Vth, the Boost circuit modulates the output voltage (i.e., BUS voltage) into a steamed wave equal to the mains voltage. At this time, INV switches at the mains frequency.

[0009] S3: When the absolute value of the mains voltage is less than the threshold voltage Vth, BOOST / Buck outputs a BUS voltage equal to the threshold value, and INV operates at a high frequency to modulate the BUS voltage into the zero-crossing voltage of the mains. At this time, Boost / Buck operates in constant voltage source mode or pass-through mode, and INV operates at a high frequency, but the operating voltage is very low and the operating current is very small.

[0010] Furthermore, in step S1, the specific calculation method of the reference voltage Vref is as follows:

[0011] S101: According to PF=cosθ, the current-voltage phase angle θ is inverted. From this phase angle, the mains voltage when the current passes through zero can be deduced as Vo=Vpeak*sin(ωt-θ), and the absolute value of this voltage is used as the reference voltage Vref (Vpeak is the mains peak voltage).

[0012] Furthermore, the inverter operates differently in two scenarios: when the power factor PF is 1 and when the power factor is not equal to 1. The specific execution process is as follows:

[0013] S21: The user sets the inverter PF value;

[0014] S22: The inverter obtains the PF setting value;

[0015] S23: Determine whether the PF setting value is equal to 1;

[0016] S24: When the PF setting value is equal to 1, the threshold voltage Vth is set to be equal to or higher than the Vdc voltage. When the PF setting value is not equal to 1, the reference voltage Vref is calculated according to a preset formula, the threshold voltage is also set, and |Vo| and Vth are determined.

[0017] Furthermore, in step S24, |Vo| and Vth are determined as follows:

[0018] S241: When |Vo| < Vth, the BOOST converter operates in constant voltage source mode, INV switches at high frequency, and VBUS equals Vth.

[0019] S242: When |Vo|≥Vth, the BOOST converter operates in current source mode, outputs a steamed bun waveform current with the AC voltage as a reference, and INV switches at the AC power frequency.

[0020] Furthermore, in step S24, when the PF setting value is equal to 1 and the threshold voltage Vth is set, if it is a non-isolated boost converter, Vth is set to Vdc or a value between Vdc-Vopeak; if it is an isolated converter, Vth is set to a value between 0V-Vopeak; when the PF setting value is not equal to 1 and the threshold voltage Vth is set, if it is a non-isolated boost converter, Vth is set to the larger of Vdc and Vref or a value between the larger of Vdc and Vref and Vopeak; if it is an isolated converter, Vth is set to a value between Vref-Vopeak.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The present invention proposes a control method for improving inverter efficiency. Through this working mode, it can not only ensure that the output power factor can be adjusted within a certain range, but also reduce the losses of the Boost and INV circuits. Compared with traditional control methods, the overall step-up ratio of the Boost circuit and the utilization rate of the BUS voltage of the INV part are reduced, the inductor design can be reduced, and the efficiency is improved as a whole and the cost, volume and weight are reduced. When the absolute value of the mains voltage is higher than the threshold value, the Boost circuit modulates the output voltage (i.e., the BUS voltage) into a steamed bun wave equal to the mains voltage. At this time, the INV switches at the mains frequency, greatly reducing the switching loss of the INV part switch tube. When the absolute value of the mains voltage is less than the threshold value, the BOOST / Buck outputs a BUS voltage equal to the threshold value, and the INV operates at a high frequency, modulating the BUS voltage into the zero-crossing voltage of the mains. At this time, the Boost / Buck operates in a low-duty situation or a direct-through situation, and the INV operates at a high frequency, but the operating voltage is very low and the operating current is very small, which greatly reduces the loss. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] FIG1 is a non-isolated BOOST / Buck circuit diagram of the present invention;

[0024] FIG2 is a BUS voltage and Boost drive / INV drive logic diagram of the present invention;

[0025] FIG3 is a flowchart illustrating execution of the inverter of the present invention in two scenarios where the power factor PF=1 and the power factor PF is not equal to 1. FIG. DETAILED DESCRIPTION

[0026] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0027] To address the difficulties in designing the Boost and INV inductors, as well as the high switching losses and low efficiency of the switch tubes, the following preferred technical solutions are provided, referring to Figures 1-3:

[0028] A control method for improving inverter efficiency includes the following implementation steps:

[0029] S1: The CNTL unit samples the voltage and current of the Boost and INV lines and controls their switches. At the same time, a voltage is set as the threshold voltage Vth. The specific value is calculated based on the required output reactive power.

[0030] S2: When the absolute value of the mains voltage is higher than the threshold voltage Vth, the Boost circuit modulates the output voltage (i.e., BUS voltage) into a steamed wave equal to the mains voltage. At this time, INV switches at the mains frequency.

[0031] S3: When the absolute value of the mains voltage is less than the threshold voltage Vth, BOOST / Buck outputs a BUS voltage equal to the threshold value, and INV operates at a high frequency to modulate the BUS voltage into the zero-crossing voltage of the mains. At this time, Boost / Buck operates in constant voltage source mode or pass-through mode, and INV operates at a high frequency, but the operating voltage is very low and the operating current is very small.

[0032] In step S1, the specific calculation method of the reference voltage Vref is as follows:

[0033] S101: According to PF=cosθ, the current-voltage phase angle θ is inverted. From this phase angle, the mains voltage when the current passes through zero can be deduced as Vo=Vpeak*sin(ωt-θ), and the absolute value of this voltage is used as the reference voltage Vref (Vpeak is the mains peak voltage).

[0034] The inverter operates differently in two scenarios: when the power factor is PF=1 and when the power factor is not equal to 1. The specific execution process is as follows:

[0035] S21: The user sets the inverter PF value;

[0036] S22: The inverter obtains the PF setting value;

[0037] S23: Determine whether the PF setting value is equal to 1;

[0038] S24: When the PF setting value is equal to 1, the threshold voltage Vth is set to be equal to or higher than the Vdc voltage. When the PF setting value is not equal to 1, the reference voltage Vref is calculated according to a preset formula, the threshold voltage is also set, and |Vo| and Vth are determined.

[0039] In step S24, |Vo| and Vth are determined as follows:

[0040] S241: When |Vo| < Vth, the BOOST converter operates in constant voltage source mode, INV switches at high frequency, and VBUS equals Vth.

[0041] S242: When |Vo|≥Vth, the BOOST converter operates in current source mode, outputs a steamed bun waveform current with the AC voltage as a reference, and INV switches at the AC power frequency.

[0042] For step S24, when the PF setting value is equal to 1 and the threshold voltage Vth is set, if it is a non-isolated boost converter, Vth is set to Vdc or a value between Vdc-Vopeak; if it is an isolated converter, Vth is set to a value between 0V-Vopeak; when the PF setting value is not equal to 1 and the threshold voltage Vth is set, if it is a non-isolated boost converter, Vth is set to the larger of Vdc and Vref or a value between the larger of Vdc and Vref and Vopeak; if it is an isolated converter, Vth is set to a value between Vref-Vopeak.

[0043] Specifically, this operating mode ensures that the output power factor can be adjusted within a certain range while reducing losses in the Boost and INV circuits. Compared to traditional control methods, it reduces the overall boost ratio of the Boost circuit and the utilization rate of the BUS voltage in the INV circuit, allowing for smaller inductor designs, thereby improving efficiency and reducing costs, volume, and weight. When the absolute value of the mains voltage is above a threshold, the Boost circuit modulates the output voltage (i.e., the BUS voltage) into a wave pattern equal to the mains voltage. At this time, the INV circuit switches at the mains frequency, significantly reducing switching losses in the INV circuit's switches. When the absolute value of the mains voltage is below the threshold, the Boost / Buck circuit outputs a BUS voltage equal to the threshold, while the INV circuit operates at a high frequency, modulating the BUS voltage to a voltage corresponding to the zero-crossing portion of the mains voltage. At this point, the Boost / Buck circuit operates in a low-duty or shoot-through state, while the INV circuit operates at a high frequency, but with a very low operating voltage and current, significantly reducing losses. The control algorithm enables the Boost and INV circuits to operate in stages, improving voltage utilization and ultimately increasing overall efficiency.

[0044] It should be noted that the Boost circuit is a bidirectional DC / DC circuit, including but not limited to non-isolated BUCK / BOOST, isolated bidirectional flyback, LLC, etc.

[0045] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus.

[0046] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A control method for improving inverter efficiency, characterized in that: The implementation steps include: S1: The CNTL unit samples the voltage and current of the Boost and INV lines and controls their switches. At the same time, a voltage is set as the threshold voltage Vth. The specific value is calculated based on the required output reactive power. S2: When the absolute value of the mains voltage is higher than the threshold voltage Vth, the Boost circuit modulates the output voltage (i.e., BUS voltage) into a steamed wave equal to the mains voltage. At this time, INV switches at the mains frequency. S3: When the absolute value of the mains voltage is less than the threshold voltage Vth, BOOST / Buck outputs a BUS voltage equal to the threshold value, and INV operates at a high frequency to modulate the BUS voltage into the zero-crossing voltage of the mains. At this time, Boost / Buck operates in constant voltage source mode or pass-through mode, and INV operates at a high frequency, but the operating voltage is very low and the operating current is very small.

2. The control method for improving inverter efficiency according to claim 1, wherein: In step S1, the specific calculation method of the reference voltage Vref is as follows: S101: According to PF=cosθ, the current-voltage phase angle θ is inverted. From this phase angle, the mains voltage when the current passes through zero can be deduced as Vo=Vpeak*sin(ωt-θ), and the absolute value of this voltage is used as the reference voltage Vref (Vpeak is the mains peak voltage).

3. The control method for improving inverter efficiency according to claim 2, wherein: The inverter operates differently in two scenarios: when the power factor is PF=1 and when the power factor is not equal to 1. The specific execution process is as follows: S21: The user sets the inverter PF value; S22: The inverter obtains the PF setting value; S23: Determine whether the PF setting value is equal to 1; S24: When the PF setting value is equal to 1, the threshold voltage Vth is set to be equal to or higher than the Vdc voltage. When the PF setting value is not equal to 1, the reference voltage Vref is calculated according to a preset formula, the threshold voltage is also set, and |Vo| and Vth are determined.

4. The control method for improving inverter efficiency according to claim 3, wherein: In step S24, |Vo| and Vth are determined as follows: S241: When |Vo| < Vth, the BOOST converter operates in constant voltage source mode, INV switches at high frequency, and VBUS equals Vth. S242: When |Vo|≥Vth, the BOOST converter operates in current source mode, outputs a steamed bun waveform current with the AC voltage as a reference, and INV switches at the AC power frequency.

5. The control method for improving inverter efficiency according to claim 4, characterized in that: For step S24, when the PF setting value is equal to 1 and the threshold voltage Vth is set, if it is a non-isolated boost converter, Vth is set to Vdc or a value between Vdc-Vopeak; if it is an isolated converter, Vth is set to a value between 0V-Vopeak; when the PF setting value is not equal to 1 and the threshold voltage Vth is set, if it is a non-isolated boost converter, Vth is set to the larger of Vdc and Vref or a value between the larger of Vdc and Vref and Vopeak; if it is an isolated converter, Vth is set to a value between Vref-Vopeak.

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