Inverter current control method
By adopting a single-stage dual active bridge inverter circuit in the inverter, and using the control methods of internal phase shift and external phase shift, the efficiency of inverter current control and grid adaptability are achieved, and the problems of high cost and poor adaptability in the prior art are solved.
Patent Information
- Application Number
- CN202411743804.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-30
- Publication Date
- 2025-02-25
AI Technical Summary
The existing inverter current control method requires high-precision isolated AC current sensors, which leads to high system costs and cannot perform real-time grid voltage feedforward, and poor grid adaptability.
A current control method based on a single-stage dual active bridge inverter circuit is adopted. Through the control of internal phase shift and external phase shift, complementary PWM control signals and normally closed control signals are used to convert the DC voltage into a high-frequency alternating voltage, reducing the dependence on high-precision isolated AC current sensor.
No high-precision isolated AC current sensor is required, which reduces system costs and realizes direct feedforward of grid voltage, improving grid suitability.
Smart Images
Figure CN119518940A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to an inverter current control method, belonging to the technical field of inverter control. Background Art
[0002] The inverter converts the low DC voltage of the photovoltaic panel into the high AC voltage of the power grid. In order to improve the conversion efficiency and power density of the inverter, a single-stage dual active bridge inverter circuit can be used.
[0003] The existing current control method requires a high-precision isolated AC current sensor, which has high system cost. In addition, the existing current control method cannot perform real-time grid voltage feedforward and has poor grid adaptability. Summary of the invention
[0004] The purpose of the present invention is to solve the deficiencies of the above-mentioned prior art and propose an inverter current control method in view of the problem that traditional current control requires the use of a high-precision isolated AC current sensor, which leads to high costs.
[0005] In order to achieve the above object, the technical solution adopted by the present invention is: An inverter current control method is based on a single-stage dual active bridge inverter circuit, the single-stage dual active bridge inverter circuit includes a DC power supply side, an AC power supply side, and an isolation transformer T1 located between the DC power supply side and the AC power supply side, the DC power supply side includes a DC power supply DC and a DC side switch component, the DC power supply DC has a DC filter capacitor C1, the DC side switch component includes a switch device Q1, a switch device Q2, a switch device Q3, and a switch device Q4, the AC power supply side includes an AC power supply AC and an AC side switch component, the AC power supply AC has a resonant path and a filter path, the resonant path is provided with a resonant capacitor C2 and a resonant capacitor C3, the filter path is provided with an AC filter capacitor C4, and the AC side switch group includes a switch device Q5, a switch device Q6, a switch device Q7, and a switch device Q8; The inverter current control method comprises: The switching device Q3 and the switching device Q4 are internally phase-shifted relative to the switching device Q1 and the switching device Q2. The switching device Q1 and the switching device Q2 are driven by complementary PWM control signals. The switching device Q3 and the switching device Q4 are driven by complementary PWM control signals. The DC voltage is converted into a high-frequency alternating voltage on one side of the isolation transformer T1 through the complementary PWM control signals. The internal phase shift angle is α, ,in , is the instantaneous value of the AC voltage, is the instantaneous value of DC voltage, N is the transformer ratio; When the AC voltage is positive, the switch device Q5 and the switch device Q7 are outwardly phase-shifted relative to the DC side switch component, the drive signals of the switch device Q5 and the switch device Q7 are complementary PWM control signals, and the drive signals of the switch device Q6 and the switch device Q8 are normally closed control signals; When the AC voltage is negative, the switch device Q6 and the switch device Q8 are outwardly phase-shifted relative to the DC side switch component, the drive signals of the switch device Q6 and the switch device Q8 are complementary PWM control signals, and the drive signals of the switch device Q5 and the switch device Q7 are normally closed control signals; The AC voltage is converted into a DC voltage through the alternating changes of the AC side switch components, and then the DC voltage is converted into a high-frequency alternating voltage on one side of the isolation transformer T1 through the complementary PWM control signal of the AC side switch components.
[0006] Preferably, the average voltage of the DC power supply DC is defined as The average current is ; The effective value of the voltage of the AC power supply is , the effective value of current is , the power factor is , from the average power is equal to: , Define the instantaneous current on the AC side of the AC power supply as , is the voltage phase angle of the AC power source, then: , Define the instantaneous current on the DC side of the DC power supply as ,but: , therefore: , The relationship between current and phase shift angle is obtained from the phase shift control principle: ,in is the resonant frequency, , , F is the frequency ratio, , is the switching frequency; The outward shift phase angle is β, .
[0007] Preferably, the external phase shift angle β is a fundamental phase shift angle, and when performing external phase shift control of the AC side switch component, phase shift angle compensations of the third external phase shift angle β3, the fifth external phase shift angle β5, and the seventh external phase shift angle β7 are added.
[0008] The beneficial effects of the present invention are mainly reflected in: 1. Current control does not require the use of high-precision isolated AC current sensors, reducing system costs.
[0009] 2. It meets the direct feedforward requirement of grid voltage and improves the applicability of grid. BRIEF DESCRIPTION OF THE DRAWINGS
[0010] Other features, objects and advantages of the present application will become more apparent by reading the detailed description of non-limiting embodiments made with reference to the following drawings: Figure 1 The present invention is a schematic diagram of the control process of the inner phase shift angle in the inverter current control method.
[0011] Figure 2 The present invention is a schematic diagram of a control flow of an external phase shift angle in an inverter current control method.
[0012] Figure 3 It is a circuit structure schematic diagram of a single-stage dual active bridge inverter circuit in the present invention. DETAILED DESCRIPTION
[0013] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are 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 creative work are within the scope of protection of the present invention.
[0014] The present application will be further described in detail below in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are only used to explain the relevant inventions, rather than to limit the inventions. It should also be noted that, for ease of description, only the parts related to the relevant inventions are shown in the accompanying drawings. It should be noted that, in the absence of conflict, the embodiments in the present application and the features in the embodiments can be combined with each other.
[0015] The invention provides an inverter current control method based on a single-stage dual active bridge inverter circuit.
[0016] like Figure 3As shown, the single-stage dual active bridge inverter circuit includes a DC power supply side, an AC power supply side, and an isolation transformer T1 located between the DC power supply side and the AC power supply side. The DC power supply side includes a DC power supply DC and a DC side switch component. The DC power supply DC has a DC filter capacitor C1. The DC side switch component includes a switch device Q1, a switch device Q2, a switch device Q3, and a switch device Q4. The AC power supply side includes an AC power supply AC and an AC side switch component. The AC power supply AC has a resonant path and a filter path. The resonant path is provided with a resonant capacitor C2 and a resonant capacitor C3. The filter path is provided with an AC filter capacitor C4. The AC side switch group includes a switch device Q5, a switch device Q6, a switch device Q7, and a switch device Q8.
[0017] The single-stage dual active bridge inverter circuit belongs to the prior art. Figure 3 As shown, the DC side switch assembly includes a first switch branch and a second switch branch connected in parallel to the DC power supply DC, switch devices Q1 and Q2 are arranged on the first switch branch, switch devices Q3 and Q4 are arranged on the second switch branch, and the connection path between switch devices Q1 and Q2 and the connection path between switch devices Q3 and Q4 are respectively connected to the two terminals on the DC side of the isolation transformer T1; the AC side switch assembly has two AC connection paths respectively connected to the AC power supply AC and the isolation transformer T1, switch devices Q5 and Q6 are arranged on one of the AC connection paths, and switch devices Q7 and Q8 are arranged on the other AC connection path. This circuit refers to Figure 3 As shown, the connection relationship will not be described in detail.
[0018] Inverter current control methods include: like Figure 1 and Figure 3 As shown, the DC side switch component is composed of a switch device Q1, a switch device Q2, a switch device Q3 and a switch device Q4. In order to reduce the switching current and increase the zero voltage turn-on range, the switch device Q3 and the switch device Q4 are internally phase-shifted relative to the switch device Q1 and the switch device Q2. The drive of the switch device Q1 and the switch device Q2 is a complementary PWM control signal, and the drive of the switch device Q3 and the switch device Q4 is a complementary PWM control signal. The DC voltage is converted into a high-frequency alternating voltage on one side of the isolation transformer through the complementary PWM control signal.
[0019] Specifically, the inner phase angle is ,in , is the instantaneous value of the AC voltage, is the instantaneous value of DC voltage, and N is the transformer ratio.
[0020] like Figure 2 and Figure 3As shown, the AC side switch assembly is composed of switch devices Q5, Q6, Q7 and Q8. To achieve power transmission, the AC side switch assembly performs an external phase shift relative to the DC side switch assembly. The external phase shift angle is .
[0021] Since the AC voltage is a voltage that alternates between positive and negative, when the AC voltage is positive, the switch devices Q5 and Q7 perform an outward phase shift relative to the DC side switch devices, the drive signals of the switch devices Q5 and Q7 are complementary PWM control signals, and the drive signals of the switch devices Q6 and Q8 are normally closed control signals. When the AC voltage is negative, the switch devices Q6 and Q8 perform an outward phase shift relative to the DC side switch devices, the drive signals of the switch devices Q6 and Q8 are complementary PWM control signals, and the drive signals of the switch devices Q5 and Q7 are normally closed control signals. The AC voltage is converted into a DC voltage through the alternating changes of the switch devices Q5, Q6, Q7, and Q8, and then the DC voltage is converted into a high-frequency AC voltage on one side of the transformer through the complementary PWM control signals.
[0022] The actual working state of the photovoltaic inverter is to integrate the maximum power of photovoltaic power generation into the grid. First, the maximum power point tracking is performed. The maximum power point tracking is achieved through PV voltage disturbance. The PV voltage is controlled by the PV current. Therefore, the final control object reflected is the PV current. In order not to affect the photovoltaic power generation, a larger DC side filter capacitor is usually used to filter out the grid cycle ripple current. Therefore, the PV current is an average DC current, and the grid current reflects the current effective value and power factor in a grid cycle. The average PV voltage is defined as , the average PV current is , the effective value of the grid voltage is , the effective value of the grid current is , the power factor of the power grid is , from the average power is equal to: ; The instantaneous current on the AC side is defined as , is the grid voltage phase angle, which can be obtained by the grid voltage phase-locked loop, then: ; The instantaneous current on the DC side is defined as ,but: ; therefore: ; The relationship between current and phase shift angle is obtained from the phase shift control principle of dual active bridge circuit: ,in is the resonant frequency, , , F is the frequency ratio, , is the switching frequency.
[0023] The outward phase angle is obtained as .
[0024] The above relationship between current and phase shift angle only considers the fundamental wave. In reality, there will be higher harmonics. Therefore, it is necessary to add the phase shift angle compensation of the third external phase shift angle β3, the fifth external phase shift angle β5, and the seventh external phase shift angle β7.
[0025] The grid voltage to the transformer voltage is converted from AC to DC through the AC side switch component. When there is reactive power output, the current and voltage have a certain phase angle. , so the direction of the current needs to be changed. When the grid voltage and current are in the same direction, the DC instantaneous current is positive, and when the grid voltage and current are in opposite directions, the DC instantaneous current is negative.
[0026] From the above description, it can be found that the current control does not need to use a high-precision isolated AC current sensor, which reduces the system cost. It satisfies the direct feedforward of the grid voltage and improves the applicability of the grid.
[0027] The term "comprise" or any other similar term is intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus / device that includes a list of elements includes not only those elements but also other elements not expressly listed, or also includes elements inherent to such process, method, article, or apparatus / device.
[0028] So far, the technical solutions of the present invention have been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it is easy for those skilled in the art to understand that the protection scope of the present invention is obviously not limited to these specific embodiments. Without departing from the principle of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will fall within the protection scope of the present invention.
Claims
1. An inverter current control method, based on a single-stage dual active bridge inverter circuit, the single-stage dual active bridge inverter circuit comprises a DC power supply side, an AC power supply side, and an isolation transformer T1 located between the DC power supply side and the AC power supply side, the DC power supply side comprises a DC power supply DC and a DC side switch assembly, the DC power supply DC has a DC filter capacitor C1, the DC side switch assembly comprises a switch device Q1, a switch device Q2, a switch device Q3, and a switch device Q4, the AC power supply side comprises an AC power supply AC and an AC side switch assembly, the AC power supply AC has a resonant path and a filter path, the resonant path is provided with a resonant capacitor C2 and a resonant capacitor C3, the filter path is provided with an AC filter capacitor C4, and the AC side switch group comprises a switch device Q5, a switch device Q6, a switch device Q7, and a switch device Q8; Features The inverter current control method comprises: The switching device Q3 and the switching device Q4 are internally phase-shifted relative to the switching device Q1 and the switching device Q2. The switching device Q1 and the switching device Q2 are driven by complementary PWM control signals. The switching device Q3 and the switching device Q4 are driven by complementary PWM control signals. The DC voltage is converted into a high-frequency alternating voltage on one side of the isolation transformer T1 through the complementary PWM control signals. When the AC voltage is positive, the switch device Q5 and the switch device Q7 are outwardly phase-shifted relative to the DC side switch component, the drive signals of the switch device Q5 and the switch device Q7 are complementary PWM control signals, and the drive signals of the switch device Q6 and the switch device Q8 are normally closed control signals; When the AC voltage is negative, the switch device Q6 and the switch device Q8 are outwardly phase-shifted relative to the DC side switch component, the drive signals of the switch device Q6 and the switch device Q8 are complementary PWM control signals, and the drive signals of the switch device Q5 and the switch device Q7 are normally closed control signals; The AC voltage is converted into a DC voltage through the alternating changes of the AC side switch components, and then the DC voltage is converted into a high-frequency alternating voltage on one side of the isolation transformer T1 through the complementary PWM control signal of the AC side switch components.
2. The inverter current control method according to claim 1, characterized in that: The internal phase shift angle is α, ,in , is the instantaneous value of the AC voltage, is the instantaneous value of DC voltage, and N is the transformer ratio.
3. The inverter current control method according to claim 1, characterized in that: The average voltage of the DC power supply is defined as The average current is ; The effective value of the voltage of the AC power supply is , the effective value of current is , the power factor is , from the average power is equal to: ， Define the instantaneous current on the AC side of the AC power supply as , is the voltage phase angle of the AC power source, then: ， Define the instantaneous current on the DC side of the DC power supply as ,but: ， therefore: ， The relationship between current and phase shift angle is obtained from the phase shift control principle: ,in is the resonant frequency, , , F is the frequency ratio, , is the switching frequency; The outward shift phase angle is β, .
4. The inverter current control method according to claim 3, characterized in that: The external phase shift angle β is the fundamental phase shift angle. When performing external phase shift control on the AC side switch component, phase shift angle compensations of the third external phase shift angle β3, the fifth external phase shift angle β5, and the seventh external phase shift angle β7 are added.