V-q dual-layer control method and system for single-stage ac / ac converter

Abstract

The application provides a V-Q double-layer control method and system of a primary AC / AC converter, and relates to the technical field of voltage management. The primary AC / AC converter is adopted to directly realize AC-to-AC conversion, improve energy conversion efficiency and simplify the system structure. By introducing the V-Q double-layer control mechanism, the reactive power regulation and the output voltage regulation are managed through independent control loops. When the grid reactive power fluctuates, the reactive power control loop can quickly respond and adjust the AC capacitor voltage, and the voltage control loop can ensure the stability of the output voltage on the load side. The decoupled control strategy makes the voltage regulation more direct and flexible, especially in the case of weak grid or frequent load changes, which can provide more stable and reliable voltage support. Through the double-layer control, the problems of complex control, resonance risk and difficulty in simultaneously realizing efficient and flexible voltage regulation that may exist in the traditional SVG can be effectively avoided.

Description

Technical Field

[0001] This invention relates to the field of voltage management technology, and more specifically, to a VQ two-layer control method and system for a single-stage AC / AC converter. Background Technology

[0002] In AC power systems, electrical power is divided into two categories: active power and reactive power. Reactive power flowing through the power grid increases line losses and reduces power supply efficiency; insufficient or excessive reactive power can also lead to voltage instability. Static Var Generators (SVG), with power electronic devices at their core, are primarily two-stage AC-DC-AC structures. Relying on PWM closed-loop continuous bidirectional reactive power regulation, they are currently the mainstream dynamic reactive power compensation devices. They are connected to the grid in parallel via a voltage source inverter and a reactor. Their basic principle is to adjust the amplitude and phase of the AC output voltage of the inverter, or directly control the AC current, so that the device absorbs or generates the required reactive power, achieving dynamic reactive power compensation.

[0003] Traditional SVG primarily influences voltage by regulating reactive power, but its voltage regulation effect is poor when the grid strength is weak. SVG also suffers from complex control, the potential to induce resonance, and difficulty in simultaneously achieving efficient and flexible voltage regulation. Summary of the Invention

[0004] The problem that this invention aims to solve is that traditional static var generators are complex to control, may cause resonance, and are difficult to achieve efficient and flexible voltage regulation at the same time.

[0005] To address the aforementioned problems, in a first aspect, the present invention provides a VQ two-layer control method for a single-stage AC / AC converter, comprising: Monitor the actual capacitor voltage on the AC capacitor and the actual output voltage on the load side in a single-stage AC / AC converter, wherein the single-stage AC / AC converter includes an AC capacitor, a first bridge arm, and a second bridge arm. The reactive power error is determined based on the actual capacitor voltage, capacitor bank capacitance, and preset reactive power. The reactive power error is input into the reactive power regulator to obtain the first control signal; The switching unit in the first bridge arm is turned on and off according to the first control signal to adjust the actual capacitor voltage; The voltage error is determined based on the actual output voltage and the preset output voltage. The voltage error is input into the voltage closed-loop regulator to obtain the second control signal; The switching unit in the second bridge arm is turned on and off according to the second control signal to adjust the actual output voltage.

[0006] Optionally, the single-stage AC / AC converter may also include: a grid-side inductor and a load-side inductor; The first bridge arm includes a first upper bridge arm and a first lower bridge arm, which are electrically connected; the second bridge arm includes a second upper bridge arm and a second lower bridge arm, which are electrically connected. The two ends of the first bridge arm are connected to the two ends of the second bridge arm, and also to the two ends of the AC capacitor; one end of the grid-side inductor is connected to the connection between the first upper bridge arm and the first lower bridge arm, and the other end of the grid-side inductor is used to connect to one end of the grid output side, and the other end of the grid output side is connected to one end of the AC capacitor; one end of the load-side inductor is connected to the connection between the second upper bridge arm and the second lower bridge arm, and the other end of the load-side inductor is connected to one end of the load, and the other end of the load is connected to one end of the AC capacitor.

[0007] Optionally, the first upper bridge arm, the first lower bridge arm, the second upper bridge arm, and the second lower bridge arm each include two switching units; Each switching unit includes a switching transistor and a diode. The current input terminal of the switching transistor is connected to the negative terminal of the diode, and the current output terminal of the switching transistor is connected to the positive terminal of the diode. Two switching units in the same bridge arm are connected top to top.

[0008] Optionally, controlling the switching unit in the first bridge arm to be on or off according to the first control signal includes: The first control signal is used to control the switching unit in the first upper bridge arm to turn on and off; The switching unit in the first lower bridge arm is controlled by a complementary signal to the first control signal.

[0009] Optionally, controlling the switching unit in the second bridge arm to be on or off according to the second control signal includes: The second control signal is used to control the switching unit in the second upper bridge arm to turn on and off; The switching unit in the second lower bridge arm is controlled by a complementary signal of the second control signal.

[0010] Optionally, after inputting the reactive power error into the reactive power regulator to obtain the first control signal, the method further includes: Based on the first control signal and the transmission model of the preceding controlled object, the adjusted actual capacitor voltage is obtained; The reactive power error is then updated based on the adjusted actual capacitor voltage and input to the reactive power regulator to achieve closed-loop control of reactive power.

[0011] Optionally, the preceding controlled object transfer model is: Where s represents the complex frequency domain, Indicates the grid-side inductance. This represents the effective value of the AC current in the grid-side inductance in steady state. This indicates the duty cycle of the first control signal. This represents the actual capacitor voltage. Indicates AC capacitance. This represents the equivalent AC resistance of the second bridge arm, the load-side inductance, and the load referred to both sides of the AC bus.

[0012] Optionally, after inputting the voltage error into the voltage closed-loop regulator to obtain the second control signal, the method further includes: Based on the second control signal and the subsequent controlled object transmission model, the adjusted actual output voltage is obtained; The voltage error is then updated based on the adjusted actual output voltage and input to the voltage closed-loop regulator to achieve closed-loop control of the output voltage.

[0013] Optionally, the subsequent controlled object transfer model is as follows: Where s represents the complex frequency domain, This represents the actual capacitor voltage. Indicates the load-side inductance. This indicates the resistance of the load.

[0014] Secondly, the present invention also provides a VQ two-layer control system for a single-stage AC / AC converter, comprising: The real-time monitoring module is used to monitor the actual capacitor voltage on the AC capacitor and the actual output voltage on the load side in the single-stage AC / AC converter, wherein the single-stage AC / AC converter includes an AC capacitor, a first bridge arm and a second bridge arm. The reactive power control loop is used to determine the reactive power error based on the actual capacitor voltage, capacitor bank capacitance and preset reactive power; input the reactive power error to the reactive power regulator to obtain the first control signal; and control the switching unit in the first bridge arm to turn on and off according to the first control signal to adjust the actual capacitor voltage. The voltage control loop is used to determine the voltage error based on the actual output voltage and the preset output voltage; the voltage error is input to the voltage closed-loop regulator to obtain the second control signal; the switching unit in the second bridge arm is controlled to turn on and off according to the second control signal to adjust the actual output voltage.

[0015] This invention provides a VQ two-layer control method and system for a single-stage AC / AC converter. Compared with the prior art, it has the following advantages: A single-stage AC / AC converter is employed to directly convert AC to AC, reducing intermediate steps and thus improving energy conversion efficiency and simplifying the system structure. By introducing a VQ dual-layer control mechanism, reactive power regulation and output voltage regulation are managed through independent control loops. When the grid reactive power fluctuates, the reactive power control loop can quickly respond and adjust the AC capacitor voltage, while the voltage control loop simultaneously ensures the stability of the load-side output voltage. This decoupled control strategy makes voltage regulation more direct and flexible, especially under conditions of weak grid strength or frequent load changes, providing more stable and reliable voltage support. Through this dual-layer control, this scheme effectively avoids the control complexity, resonance risk, and difficulty in simultaneously achieving efficient and flexible voltage regulation that may exist in traditional SVG systems, improving the overall system performance and robustness. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 A schematic diagram of the circuit structure of a single-stage AC / AC converter provided in an embodiment of the present invention; Figure 2 A flowchart illustrating a VQ two-layer control method for a single-stage AC / AC converter provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of the reactive power control loop provided in an embodiment of the present invention; Figure 4 This is a schematic diagram of the current path for operating mode 1 provided in an embodiment of the present invention; Figure 5 This is a schematic diagram of the current path for operating mode 2 provided in an embodiment of the present invention; Figure 6 This is a schematic diagram of the voltage control loop provided in an embodiment of the present invention; Figure 7 This is a schematic diagram of the current path for operating mode 3 provided in an embodiment of the present invention; Figure 8 This is a schematic diagram of the current path for operating mode 4 provided in an embodiment of the present invention; Figure 9 This is a schematic diagram of the VQ two-layer control system of a single-stage AC / AC converter provided in an embodiment of the present invention. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application are described clearly and completely. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0019] To better understand the above technical solutions, the following will provide a detailed explanation of the technical solutions in conjunction with the accompanying drawings and specific implementation methods.

[0020] like Figure 1 As shown, the single-stage AC / AC converter provided in this application embodiment includes an AC capacitor, a first bridge arm, a second bridge arm, a grid-side inductor, and a load-side inductor.

[0021] The first bridge arm includes a first upper bridge arm and a first lower bridge arm, which are electrically connected; the second bridge arm includes a second upper bridge arm and a second lower bridge arm, which are electrically connected.

[0022] The two ends of the first bridge arm are connected to the two ends of the second bridge arm, and also to the two ends of the AC capacitor; one end of the grid-side inductor is connected to the connection between the first upper bridge arm and the first lower bridge arm, and the other end of the grid-side inductor is used to connect to one end of the grid output side, and the other end of the grid output side is connected to one end of the AC capacitor; one end of the load-side inductor is connected to the connection between the second upper bridge arm and the second lower bridge arm, and the other end of the load-side inductor is connected to one end of the load, and the other end of the load is connected to one end of the AC capacitor.

[0023] Each of the first upper bridge arm, the first lower bridge arm, the second upper bridge arm, and the second lower bridge arm includes two switching units. Each switching unit includes a switching transistor and a diode. The current input terminal of the switching transistor is connected to the negative terminal of the diode, and the current output terminal of the switching transistor is connected to the positive terminal of the diode. The two switching units in the same bridge arm are connected top to bottom.

[0024] Specifically, the first upper bridge arm is composed of switch units T1 and T2 connected top to top, and the first lower bridge arm is composed of switch units T3 and T4 connected top to top. The first upper bridge arm is connected to the first lower bridge arm, that is, the end of switch unit T2 in the first upper bridge arm that is away from switch unit T1 is connected to the end of switch unit T3 in the first lower bridge arm that is away from switch unit T4. The second upper bridge arm is composed of switch units T5 and T6 connected top to top, and the second lower bridge arm is composed of switch units T7 and T8 connected top to top. The second upper bridge arm is connected to the second lower bridge arm, that is, the end of switch unit T6 in the second upper bridge arm that is away from switch unit T5 is connected to the end of switch unit T7 in the second lower bridge arm that is away from switch unit T8. The two ends of AC capacitor C0 are connected to the two ends of the first bridge arm and the second bridge arm, respectively. One end of AC capacitor C0 is connected to the end of switching unit T1 in the first upper bridge arm that is furthest from switching unit T2, and the end of switching unit T5 in the second upper bridge arm that is furthest from switching unit T6, respectively. The other end of AC capacitor C0 is connected to the end of switching unit T4 in the first lower bridge arm that is furthest from switching unit T3, and the end of switching unit T8 in the second lower bridge arm that is furthest from switching unit T7, respectively. One end of grid-side inductor L1 is connected at the junction of the first upper and first lower bridge arms, i.e., at the junction of switching units T2 and T3; the other end of grid-side inductor L1 is connected to one end of the grid output side, and the other end of the grid output side is connected to one end of AC capacitor C0. One end of load-side inductor L2 is connected at the junction of the second upper and second lower bridge arms, i.e., at the junction of switching units T6 and T7; the other end of load-side inductor L2 is connected to one end of the load, and the other end of the load is connected to one end of AC capacitor C0. Therefore, the other end of the grid output side is connected to the other end of the load.

[0025] The two switching units in each upper / lower arm can be alternately turned on through a specific control strategy to simulate the function of a bidirectional switch. The switching transistor is responsible for actively controlling the current on and off, while the diode typically acts as a freewheeling or reverse blocking device, protecting the switching transistor and providing a reverse current path. This connection method allows the switching unit to actively conduct in one direction and achieve freewheeling or reverse blocking in the other direction through the diode, thus supporting bidirectional current flow. Current can be transmitted through this arm regardless of whether the AC voltage is in the positive or negative half-cycle, and it can block voltage in both directions when turned off. The switching transistor can be an insulated gate bipolar transistor (IGBT) or a metal-oxide-semiconductor field-effect transistor (MOSFET), and the diode can be a fast recovery diode or a Schottky diode; alternatively, the switching transistor can also be a wide bandgap semiconductor device such as silicon carbide (SiC) or gallium nitride (GaN) to achieve higher switching frequencies and lower losses, and the diode can be a matched SiC Schottky diode.

[0026] like Figure 2 As shown in the embodiment of this application, a VQ two-layer control method for a single-stage AC / AC converter is provided, comprising: S1: Monitor the actual capacitor voltage on the AC capacitor and the actual output voltage on the load side in the single-stage AC / AC converter, wherein the single-stage AC / AC converter includes an AC capacitor, a first bridge arm, and a second bridge arm.

[0027] Specifically, a high-precision voltage sensor can be used to sample the voltage across the AC capacitor in real time, and then converted into a digital signal by an analog-to-digital converter (ADC) for processing by the controller. Similarly, a similar voltage sensor can be used to monitor the actual output voltage on the load side in real time.

[0028] S2: Determine the reactive power error based on the actual capacitor voltage, capacitor bank capacitance, and preset reactive power.

[0029] Specifically, by substituting the real-time measured actual capacitor voltage, the known capacitor bank capacitance value, and the preset reactive power required by the system into the preset reactive power calculation formula, the current reactive power is calculated and compared with the preset reactive power to obtain the reactive power error.

[0030] S3: Input the reactive power error into the reactive power regulator to obtain the first control signal.

[0031] Specifically, the reactive power regulator can employ a classic proportional-integral (PI) controller. This controller generates a continuous or discrete control quantity based on the magnitude and trend of the reactive power error. For example, when the reactive power error is positive, the PI controller outputs a control quantity that reduces reactive power; when the error is negative, it outputs a control quantity that increases reactive power. This control quantity is then converted into a first control signal, such as the duty cycle of a pulse width modulation (PWM) signal.

[0032] S4: Control the switching unit in the first bridge arm to turn on and off according to the first control signal, so as to adjust the actual capacitor voltage.

[0033] Specifically, the first control signal is sent to the PWM generator to generate gate signals that drive the power electronic switching unit in the first bridge arm. By adjusting the duty cycle and phase of these gate signals, the switching state of the first bridge arm can be precisely controlled, thereby changing the current flowing through the AC capacitor and thus adjusting the actual voltage across the AC capacitor. For example, when it is necessary to increase the AC capacitor voltage, the conduction time of the first bridge arm can be increased, allowing more energy to be injected into the AC capacitor.

[0034] S5: Determine the voltage error based on the actual output voltage and the preset output voltage.

[0035] Specifically, the controller compares the actual output voltage of the load side monitored in real time with the preset output voltage set by the system, and directly calculates the difference between the two, which is the voltage error.

[0036] S6: Input the voltage error into the voltage closed-loop regulator to obtain the second control signal.

[0037] Specifically, the voltage closed-loop regulator can employ a proportional-integral-derivative (PID) controller. The PID controller outputs a control quantity that can quickly and stably eliminate the voltage error based on its instantaneous value, cumulative value, and rate of change. This control quantity is then converted into a second control signal, such as a PWM signal for driving the second bridge arm.

[0038] S7: Control the switching unit in the second bridge arm to turn on and off according to the second control signal, so as to adjust the actual output voltage.

[0039] Specifically, the second control signal is fed into a PWM generator to generate gate signals that drive the power electronic switching units in the second bridge arm. By adjusting the duty cycle and phase of these gate signals, the switching state of the second bridge arm can be precisely controlled, thereby changing the voltage output to the load side. For example, when the load-side output voltage is lower than a preset value, the switching strategy of the second bridge arm can be adjusted to increase the output voltage and restore it to the target range.

[0040] Traditional static var generators (SVG) typically employ a two-stage AC-DC-AC structure, which involves numerous energy conversion stages, potentially leading to reduced efficiency and structural complexity. This solution utilizes a single-stage AC / AC converter to directly convert AC to AC, reducing intermediate stages, thereby improving energy conversion efficiency and simplifying the system structure.

[0041] Existing SVG technologies primarily influence voltage indirectly by regulating reactive power. However, their voltage regulation effectiveness may be poor under weak grid conditions, and their control is complex, potentially leading to resonance and hindering the simultaneous achievement of efficient and flexible voltage regulation. This solution introduces a VQ dual-layer control mechanism, managing reactive power regulation and output voltage regulation through independent control loops. When grid reactive power fluctuates, the reactive power control loop responds quickly and adjusts the AC capacitor voltage, while the voltage control loop simultaneously ensures the stability of the load-side output voltage. This decoupled control strategy makes voltage regulation more direct and flexible, especially under weak grid conditions or frequent load changes, providing more stable and reliable voltage support. Through this dual-layer control, this solution effectively avoids the control complexity, resonance risk, and difficulty in simultaneously achieving efficient and flexible voltage regulation inherent in traditional SVG technologies, improving the overall system performance and robustness.

[0042] In this optional embodiment, the reactive power control loop and the voltage control loop operate independently yet collaboratively. The reactive power control loop focuses on stabilizing the AC capacitor voltage to provide or absorb the required reactive power, thereby improving the power factor of the power grid. The voltage control loop focuses on stabilizing the output voltage on the load side to ensure the normal operation of sensitive equipment. Through this VQ dual-layer control method, even when the reactive power of the power grid fluctuates or the load changes, this single-stage AC / AC converter can respond quickly, while achieving precise management of reactive power and stability of output voltage, effectively solving the complex power supply requirements.

[0043] The following is a detailed description of each step.

[0044] S1: Monitors the actual capacitor voltage on the AC capacitor and the actual output voltage on the load side in a single-stage AC / AC converter.

[0045] S2: Determine the reactive power error based on the actual capacitor voltage, capacitor bank capacitance, and preset reactive power.

[0046] Specifically, such as Figure 3 As shown, the actual reactive power absorbed or generated by the AC capacitor. With the given preset reactive power By performing a difference comparison, the reactive power error is obtained. ,in, The system's operating angular frequency, This indicates the capacitance value of the AC capacitor. This represents the actual capacitor voltage. This indicates the preset capacitor voltage, i.e., the ideal capacitor voltage.

[0047] S3: Input the reactive power error into the reactive power regulator to obtain the first control signal.

[0048] Specifically, such as Figure 3 As shown, the reactive power error is fed into the reactive power regulator. Closed-loop control is implemented. The main function of the reactive power regulator is to dynamically compensate for reactive power errors and amplify them without steady-state error; its output is the control variable. (i.e., the first control signal), which reflects the energy scheduling action that the system needs to inject or extract into the front-stage converter (i.e., the first bridge arm) to eliminate the current reactive power error.

[0049] Following S3, the VQ two-layer control method for single-stage AC / AC converters also includes: S31: Based on the first control signal and the transmission model of the preceding controlled object, the adjusted actual capacitor voltage is obtained.

[0050] control variables Subsequently applied to the forward controlled object transfer model The preceding controlled object transfer model is as follows: Where s represents the complex frequency domain, Indicates the grid-side inductance. This represents the effective value of the AC current in the grid-side inductance in steady state. This indicates the duty cycle of the first control signal. This represents the actual capacitor voltage. Indicates AC capacitance. This represents the equivalent AC resistance of the second bridge arm, the load-side inductance, and the load referred to both sides of the AC bus.

[0051] This stage represents the process by which the front-end converter, driven by duty cycle or energy command, causes a dynamic response in the actual capacitor voltage, i.e., the duty cycle-voltage transfer relationship. Under the action of the first control signal, the actual capacitor voltage undergoes adaptive fluctuations.

[0052] S32: Then update the reactive power error based on the adjusted actual capacitor voltage and input it into the reactive power regulator to achieve closed-loop control of reactive power.

[0053] With the dynamic adjustment of the actual capacitor voltage, the actual reactive power in the feedback branch... This also changes the reactive power, causing the reactive power error to gradually approach zero. When the system reaches steady state, the actual reactive power completely follows the preset reactive power. At this point, the actual capacitor voltage or AC bus voltage automatically stabilizes at a new equilibrium point that can support the reactive power throughput, thus fully realizing the variable voltage adaptive operation characteristics.

[0054] S4: Control the switching unit in the first bridge arm to turn on and off according to the first control signal, so as to adjust the actual capacitor voltage. Controlling the switching unit in the first bridge arm to turn on and off according to the first control signal includes: The first control signal is used to control the switching unit in the first upper bridge arm to turn on and off.

[0055] The switching unit in the first lower bridge arm is controlled by a complementary signal to the first control signal.

[0056] Specifically, such as Figure 4 and Figure 5As shown, taking the positive half-cycle of AC voltage as an example, the first control signal controls the on / off state of switch unit T1 in the first upper bridge arm, with a duty cycle of D1; the complementary signal of the first control signal controls the on / off state of switch unit T3 in the first lower bridge arm, with a duty cycle of 1-D1. When the AC voltage switches to the negative half-cycle, the first control signal controls the on / off state of switch unit T2 in the first upper bridge arm; the complementary signal of the first control signal controls the on / off state of switch unit T4 in the first lower bridge arm.

[0057] S5: Determine the voltage error based on the actual output voltage and the preset output voltage.

[0058] like Figure 6 As shown, the actual output voltage With preset output voltage By performing a difference comparison, the voltage error is obtained. , This represents the actual output voltage in the S-domain. This represents the preset output voltage in the S-domain.

[0059] S6: Input the voltage error into the voltage closed-loop regulator to obtain the second control signal.

[0060] like Figure 6 As shown, the voltage error is fed into the voltage closed-loop regulator. For AC output systems, the main function of this voltage closed-loop regulator is to provide a fast response and zero steady-state error amplification of voltage errors, thereby generating control variables. (That is, the second control signal). This control variable This directly reflects the control variables required for the converter bridge arm to suppress the current voltage error.

[0061] Following S6, the VQ two-layer control method for single-stage AC / AC converters also includes: S61: Based on the second control signal and the subsequent controlled object transmission model, the adjusted actual output voltage is obtained.

[0062] Specifically, control variables Transmission model applied to subsequent controlled objects The subsequent controlled object transfer model is as follows: Where 's' in the above examples all represent the complex frequency domain. This represents the actual capacitor voltage. Indicates the load-side inductance. This represents the resistance of the load. Through this process, the control variable is converted into the actual physical voltage output.

[0063] S62: Then update the voltage error based on the adjusted actual output voltage and input it into the voltage closed-loop regulator to achieve closed-loop control of the output voltage.

[0064] Through this feedback loop, any harmonic distortion caused by sudden external load changes, such as the connection of a nonlinear load, or output voltage deviation caused by fluctuations in the upstream bus voltage, will be immediately reflected in the voltage error. In, and by regulator Quickly adjust control variables Suppression is achieved. Eventually, the system reaches dynamic equilibrium, enabling the actual output voltage to closely follow the preset output voltage with high precision and low distortion, thereby giving the system the external characteristics of an ideal rigid voltage source.

[0065] S7: Control the switching unit in the second bridge arm to turn on and off according to the second control signal, so as to adjust the actual output voltage.

[0066] The step of controlling the switching unit in the second bridge arm to be on or off according to the second control signal includes: The second control signal is used to control the switching unit in the second upper bridge arm to turn on and off.

[0067] The switching unit in the second lower bridge arm is controlled by a complementary signal of the second control signal.

[0068] Specifically, such as Figure 4 and Figure 7 As shown, taking the positive half-cycle of AC voltage as an example, the second control signal controls the on / off state of switch unit T6 in the second upper bridge arm, with a duty cycle of D2; the complementary signal of the second control signal controls the on / off state of switch unit T7 in the second lower bridge arm, with a duty cycle of 1-D2. When the AC voltage switches to the negative half-cycle, the second control signal controls the on / off state of switch unit T5 in the second upper bridge arm; the complementary signal of the second control signal controls the on / off state of switch unit T8 in the second lower bridge arm.

[0069] Due to the synchronous control of S4 and S7, and the alternating changes in control signals, multiple operating modes are formed. The following discussion will only focus on the positive half-cycle (e.g., Figure 4 As shown, the current flows out from the upper end of the power grid), and the specific states of the four operating modes are as follows.

[0070] Operating Mode 1: Controlling the first and second upper bridge arms to conduct; at this time, the current flows through the power grid, the power grid-side inductor L1, and the first upper bridge arm, then splits into two branches. One branch flows through the AC capacitor C0 back to the power grid, and the other branch flows through the second upper bridge arm, the load-side inductor L2, and the load back to the power grid. For example... Figure 4As shown, the switching transistors in switching unit T1 and switching unit T6 are turned on, while the other switching transistors are turned off. The current flow path is: grid → L1 → T2 → T1 → C0 → grid, grid → L1 → T2 → T1 → T5 → T6 → L2 → load → grid. At this time, the grid charges and stores energy for the grid-side inductor L1, the load-side inductor L2, and the AC capacitor C0, and simultaneously supplies power to the load. Similarly, to keep the first and second upper bridge arms on, during the negative half-cycle of AC (e.g., ... Figure 4 As shown, the current flows out from the lower end of the power grid. This can be changed to control the switching transistors in switch unit T2 and switch unit T5 to be turned on, while the other switching transistors are turned off, which can achieve the same effect as the above circuit flow path.

[0071] Operating Mode 2: Controlling the first lower bridge arm and the second upper bridge arm to conduct; at this time, the current flows through the power grid, the power grid-side inductor L1, and the first lower bridge arm back to the power grid; in addition, the energy stored in the AC capacitor C0 is released, and the current flows through the second upper bridge arm, the load-side inductor L2, and the load back to the AC capacitor C0. For example... Figure 5 As shown, the switching transistors in switching unit T4 and T5 are turned on, while the other switching transistors are turned off. The current flow path is: grid → L1 → T3 → T4 → grid, C0 → T5 → T6 → L2 → load → C0. At this time, the load-side inductor L2 and AC capacitor C0 release energy to supply power to the load, while the grid charges the grid-side inductor L1. Similarly, to keep the first lower bridge arm and the second upper bridge arm on, during the negative half-cycle of AC (e.g., ... Figure 5 As shown, the current flows out from the lower end of the power grid. This can be changed to control the switching transistors in switch unit T3 and switch unit T6 to be turned on, while other switching transistors are turned off, which can achieve the same effect as the above circuit flow path.

[0072] Operating Mode 3: Controlling the first upper bridge arm and the second lower bridge arm to conduct; at this time, the current flows through the power grid, the power grid-side inductor L1, the first upper bridge arm, the AC capacitor C0, and back to the power grid; in addition, the energy stored in the load-side inductor L2 is released to form current, which flows through the load and the second lower bridge arm, and then back to the load-side inductor L2. For example... Figure 7 As shown, the switching transistors in switching unit T1 and T7 are turned on, while the other switching transistors are turned off. The current flow path is: mains → L1 → T2 → T1 → C0 → mains. The load-side inductor L2 forms a freewheeling path to supply power to the load through switching units T7 and T8, while the mains charges the AC capacitor C0. Similarly, to keep the first upper bridge arm and the second lower bridge arm on, during the negative half-cycle of AC (e.g., ... Figure 7 As shown, the current flows out from the lower end of the power grid. This can be changed to control the switching transistors in switch unit T2 and switch unit T8 to be turned on, while other switching transistors are turned off, which can achieve the same effect as the above circuit flow path.

[0073] Operating Mode 4: Controlling the first and second lower bridge arms to conduct; at this time, the current flows through the grid, grid-side inductor L1, and the first lower bridge arm back to the grid; in addition, the energy stored in the load-side inductor L2 is released, and the current flows through the load and the second lower bridge arm back to the load-side inductor L2. For example... Figure 8 As shown, the switching transistors in switching unit T4 and T7 are turned on, while the other switching transistors are turned off. The current flow path is: grid → L1 → T3 → T4 → grid, load → L2 → T7 → T8 → load. At this time, the load-side inductor L2 releases energy to supply power to the load, and the grid charges the grid-side inductor L1. Similarly, to keep the first and second lower bridge arms on, during the negative half-cycle of AC (e.g., ... Figure 8 As shown, the current flows out from the lower end of the power grid. This can be changed to control the switching transistors in switch unit T3 and switch unit T8 to be turned on, while other switching transistors are turned off, which can achieve the same effect as the above circuit flow path.

[0074] By precisely controlling the switching on and off of the first upper arm, first lower arm, second upper arm, and second lower arm, the system can flexibly establish multiple controllable conduction paths during the positive and negative half-cycles of the AC voltage. This allows the topology to switch between different operating modes according to real-time changes in the grid voltage, thereby effectively compensating for and managing high and low voltage levels in the grid. This proactive control capability significantly improves the stability of the grid voltage and power quality, ensuring a stable voltage supply to the load side and avoiding adverse effects on the load caused by grid voltage fluctuations.

[0075] like Figure 9 As shown in the embodiment of this application, a VQ two-layer control system for a single-stage AC / AC converter includes: The real-time monitoring module is used to monitor the actual capacitor voltage on the AC capacitor and the actual output voltage on the load side in the single-stage AC / AC converter. The single-stage AC / AC converter includes an AC capacitor, a first bridge arm, and a second bridge arm.

[0076] The reactive power control loop is used to determine the reactive power error based on the actual capacitor voltage, capacitor bank capacitance and preset reactive power; input the reactive power error to the reactive power regulator to obtain the first control signal; and control the switching unit in the first bridge arm to turn on and off according to the first control signal to adjust the actual capacitor voltage.

[0077] The voltage control loop is used to determine the voltage error based on the actual output voltage and the preset output voltage; the voltage error is input to the voltage closed-loop regulator to obtain the second control signal; the switching unit in the second bridge arm is controlled to turn on and off according to the second control signal to adjust the actual output voltage.

[0078] In this optional embodiment, the VQ dual-layer control structure enables the reactive power control loop and the voltage control loop to operate independently yet collaboratively. The reactive power control loop focuses on stabilizing the AC capacitor voltage to provide or absorb the required reactive power and improve the power factor of the power grid; the voltage control loop focuses on stabilizing the output voltage on the load side to ensure the normal operation of sensitive equipment. This achieves decoupled control of reactive power regulation and voltage regulation, solving the technical problems of poor voltage regulation effect, complex control, and potential resonance in traditional static var generators when the grid strength is weak. It achieves the effect of simultaneously realizing efficient and flexible voltage regulation.

[0079] In summary, compared with existing technologies, it has the following beneficial effects: 1. Propose "variable voltage" adaptive control In traditional bus capacitors, the sole task of the intermediate capacitor is to maintain a constant DC voltage. This invention proposes a "variable voltage" control architecture that allows the intermediate bus voltage to adaptively fluctuate over a wide range in response to reactive power dispatch commands. The control system no longer establishes a rigid outer loop for the bus voltage; instead, it reconstructs the intermediate AC capacitor from a "passive voltage stabilization node" into an "energy buffer pool that actively participates in reactive power throughput."

[0080] Compared to existing technologies, this method breaks through the physical constraints of traditional constant voltage control on the system's dynamic reactive power compensation capability. By releasing the control degree of freedom of the bus voltage, it not only significantly reduces the system's dependence on large-capacity AC capacitors, but also significantly improves the converter's throughput boundary in dealing with grid reactive power transients or large-scale over-limit conditions, giving the system extremely strong flexible adaptive operation capability.

[0081] 2. VQ Dual Closed-Loop Architecture Traditional single-stage AC converters often employ a "single output voltage" control approach, severely limiting their system's degrees of freedom. The sole objective of the control algorithm is to maintain load-side voltage stability, causing the system to merely act as a "passive voltage regulator."

[0082] This invention breaks through the theoretical limitations of traditional single-variable control and constructs a VQ dual closed-loop decoupled control architecture based on "grid-side reactive power Q" and "load-side output voltage V".

[0083] Based on a single-stage topology, this invention utilizes the AC capacitor of the AC bus to provide reactive power, treating the "AC bus reactive power" as an independent control variable. It introduces a "VQ dual-closed-loop decoupling control" strategy to construct two independent and non-interfering control domains: The front-end reactive power control loop (Q loop) takes the actual reactive power absorbed / generated by the AC capacitor on the AC side bus as the directly controlled variable. Through fast closed-loop adjustment, it forces the converter to actively respond to the reactive power demand of the grid, realizing dynamic reactive power support on the grid side and flexible management of voltage sag / surge. The subsequent voltage control loop (V-loop) adopts a high-bandwidth zero steady-state error regulation algorithm. Under the "variable voltage" condition where the bus voltage fluctuates greatly, it drives the subsequent stage to perform load-side waveform reconstruction, and still ensures that the amplitude, frequency and waveform quality of the output voltage at the load end strictly meet the set requirements.

[0084] The aforementioned dual-ring architecture enables the converter to achieve complete decoupling of "grid-side flexible reactive power management" and "load-side rigid voltage protection" from both physical and control perspectives while completing bidirectional active power transmission.

[0085] An electronic device provided in this application includes a memory and a processor; the memory is used to store a computer program; the processor is used to implement the VQ two-layer control method of a single-stage AC / AC converter as described above when the computer program is executed.

[0086] This application provides a computer-readable storage medium storing a computer program. When the computer program is executed by a processor, it implements the VQ two-layer control method for a single-stage AC / AC converter as described above.

[0087] In this embodiment, the beneficial effects of the electronic device and the computer-readable storage medium are similar to those of the VQ two-layer control method of the single-stage AC / AC converter described above, and will not be repeated here.

[0088] The present invention describes electronic devices that can serve as servers or clients of this application, which are examples of hardware devices that can be applied to various aspects of this application. Electronic devices are intended to represent various forms of digital electronic computer devices, such as laptop computers, desktop computers, workstations, personal digital assistants, servers, blade servers, mainframe computers, and other suitable computers. Electronic devices can also represent various forms of mobile devices, such as personal digital assistant devices, cellular phones, smartphones, wearable devices, and other similar computing devices. The components shown herein, their connections and relationships, and their functions are merely examples and are not intended to limit the implementation of the application described and / or claimed herein.

[0089] Electronic devices include a computing unit that can perform various appropriate actions and processes based on a computer program stored in read-only memory (ROM) or loaded from a storage unit into random access memory (RAM). The RAM can also store various programs and data required for device operation. The computing unit, ROM, and RAM are interconnected via a bus. Input / output (I / O) interfaces are also connected to the bus.

[0090] Those skilled in the art will understand that all or part of the processes in the above embodiments can be implemented by a computer program instructing related hardware. The program can be stored in a computer-readable storage medium, and when executed, it can include the processes of the embodiments of the above methods. The storage medium can be a magnetic disk, optical disk, read-only memory (ROM), or random access memory (RAM), etc. In this application, the separately described modules may or may not be physically separate. Some or all of the modules can be selected to achieve the purpose of the embodiments of this application according to actual needs. Furthermore, the functional modules in the various embodiments of this application can be integrated into one processing unit, or each module can exist physically separately, or two or more modules can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0091] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0092] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A VQ two-layer control method for a single-stage AC / AC converter, characterized in that, include: Monitor the actual capacitor voltage on the AC capacitor and the actual output voltage on the load side in a single-stage AC / AC converter, wherein the single-stage AC / AC converter includes an AC capacitor, a first bridge arm, and a second bridge arm. The reactive power error is determined based on the actual capacitor voltage, capacitor bank capacitance, and preset reactive power. The reactive power error is input into the reactive power regulator to obtain the first control signal; The switching unit in the first bridge arm is turned on and off according to the first control signal to adjust the actual capacitor voltage; The voltage error is determined based on the actual output voltage and the preset output voltage. The voltage error is input into the voltage closed-loop regulator to obtain the second control signal; The switching unit in the second bridge arm is turned on and off according to the second control signal to adjust the actual output voltage.

2. The VQ two-layer control method for a single-stage AC / AC converter as described in claim 1, characterized in that, A single-stage AC / AC converter also includes: a grid-side inductor and a load-side inductor; The first bridge arm includes a first upper bridge arm and a first lower bridge arm, which are electrically connected; the second bridge arm includes a second upper bridge arm and a second lower bridge arm, which are electrically connected. The two ends of the first bridge arm are connected to the two ends of the second bridge arm, and also to the two ends of the AC capacitor; one end of the grid-side inductor is connected to the connection between the first upper bridge arm and the first lower bridge arm, and the other end of the grid-side inductor is used to connect to one end of the grid output side, and the other end of the grid output side is connected to one end of the AC capacitor; one end of the load-side inductor is connected to the connection between the second upper bridge arm and the second lower bridge arm, and the other end of the load-side inductor is connected to one end of the load, and the other end of the load is connected to one end of the AC capacitor.

3. The VQ two-layer control method for a single-stage AC / AC converter as described in claim 2, characterized in that, The first upper bridge arm, the first lower bridge arm, the second upper bridge arm, and the second lower bridge arm each include two switching units; Each switching unit includes a switching transistor and a diode. The current input terminal of the switching transistor is connected to the negative terminal of the diode, and the current output terminal of the switching transistor is connected to the positive terminal of the diode. Two switching units in the same bridge arm are connected top to top.

4. The VQ two-layer control method for a single-stage AC / AC converter as described in claim 2, characterized in that, The step of controlling the switching unit in the first bridge arm to be on or off according to the first control signal includes: The first control signal is used to control the switching unit in the first upper bridge arm to turn on and off; The switching unit in the first lower bridge arm is controlled by a complementary signal to the first control signal.

5. The VQ two-layer control method for a single-stage AC / AC converter as described in claim 2, characterized in that, The step of controlling the switching unit in the second bridge arm to be on or off according to the second control signal includes: The second control signal is used to control the switching unit in the second upper bridge arm to turn on and off; The switching unit in the second lower bridge arm is controlled by a complementary signal of the second control signal.

6. The VQ two-layer control method for a single-stage AC / AC converter as described in claim 1, characterized in that, After inputting the reactive power error into the reactive power regulator to obtain the first control signal, the process further includes: Based on the first control signal and the transmission model of the preceding controlled object, the adjusted actual capacitor voltage is obtained; The reactive power error is then updated based on the adjusted actual capacitor voltage and input to the reactive power regulator to achieve closed-loop control of reactive power.

7. The VQ two-layer control method for a single-stage AC / AC converter as described in claim 6, characterized in that, The preceding controlled object transfer model is as follows: Where s represents the complex frequency domain, Indicates the grid-side inductance. This represents the effective value of the AC current in the grid-side inductance in steady state. This indicates the duty cycle of the first control signal. This represents the actual capacitor voltage. Indicates AC capacitance. This represents the equivalent AC resistance of the second bridge arm, the load-side inductance, and the load referred to both sides of the AC bus.

8. The VQ two-layer control method for a single-stage AC / AC converter as described in claim 1, characterized in that, After inputting the voltage error into the voltage closed-loop regulator to obtain the second control signal, the method further includes: Based on the second control signal and the subsequent controlled object transmission model, the adjusted actual output voltage is obtained; The voltage error is then updated based on the adjusted actual output voltage and input to the voltage closed-loop regulator to achieve closed-loop control of the output voltage.

9. The VQ two-layer control method for a single-stage AC / AC converter as described in claim 8, characterized in that, The subsequent controlled object transfer model is as follows: Where s represents the complex frequency domain, This represents the actual capacitor voltage. Indicates the load-side inductance. This indicates the resistance of the load.

10. A VQ two-layer control system for a single-stage AC / AC converter, characterized in that, include: The real-time monitoring module is used to monitor the actual capacitor voltage on the AC capacitor and the actual output voltage on the load side in the single-stage AC / AC converter, wherein the single-stage AC / AC converter includes an AC capacitor, a first bridge arm and a second bridge arm. The reactive power control loop is used to determine the reactive power error based on the actual capacitor voltage, capacitor bank capacitance and preset reactive power; input the reactive power error to the reactive power regulator to obtain the first control signal; and control the switching unit in the first bridge arm to turn on and off according to the first control signal to adjust the actual capacitor voltage. The voltage control loop is used to determine the voltage error based on the actual output voltage and the preset output voltage; the voltage error is input to the voltage closed-loop regulator to obtain the second control signal; the switching unit in the second bridge arm is controlled to turn on and off according to the second control signal to adjust the actual output voltage.

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