Variable-frequency buck-boost AC-AC converter, system and control method

Abstract

The invention belongs to the technical field of power electronics, and discloses a variable-frequency buck-boost AC-AC converter, a variable-frequency buck-boost AC-AC system and a variable-frequency buck-boost AC-AC control method. The system comprises a variable-frequency bipolar buck-boost AC-AC converter, a polarity detector, a subtracter, a PI controller and a unipolar wave modulator PWM. The converter provided by the invention not only can realize buck-boost operation, but also can realize variable-frequency alternating current output. The control system has two input state quantities, an alternating current power supply input voltage, a load output voltage and five PWM switch signal outputs which are correspondingly connected with a power switch tube, so that the conversion control of alternating current is realized. According to the invention, the number of active and passive elements can be significantly reduced, continuous input and output current with low harmonic content can be provided, total harmonic distortion of input and output is reduced, and wider voltage gain coverage and higher efficiency are realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of power electronics, and in particular relates to a variable-frequency buck-boost AC-AC converter, a system and a control method. Background Art

[0002] As an important electronic device, AC-AC converters are widely used in industrial manufacturing, power, construction and other fields. However, in modern industrial applications, especially in the field of adjustable speed drive devices, the requirements for AC-AC conversion systems are becoming increasingly stringent. Among them, the flexible adjustment capability of the output voltage, especially the voltage amplitude and frequency adjustment capability, has become a key indicator for measuring system performance. Although the traditional direct AC-AC converter has a simple structure and shows certain advantages in the voltage adjustment range and relatively good output waveform, it is not suitable for many applications due to the lack of frequency conversion capability. In contrast, although the AC-DC-AC converter can achieve output voltage adjustment of arbitrary amplitude and frequency through multi-stage energy conversion, it requires the introduction of large DC bus capacitors and inductors in this process. This not only increases the cost and volume of the system, but also brings additional power loss, thus limiting its application in some occasions with strict requirements on cost, efficiency and space.

[0003] The Chinese patent publication number is CN117458856A, and the name is a patent application for a dual-mode bridgeless buck PFC converter. The PFC converter topology includes a switch tube , switch tube , Rectifier diode , Rectifier diode , output diode , output diode , Buck Inductor , Buck-boost inductor and output capacitor ; Switching tube , Buck Inductor , output diode Composed of buck conversion unit, which is connected with output capacitor , Rectifier diode Connection, used to achieve power conversion in the negative half cycle of AC input; switch tube , Buck-boost inductor , output diode The buck-boost conversion unit is composed of the output capacitor , Rectifier diode The converter of this patent has two working modes: buck and boost / step-up. In the positive half-cycle, the buck / step-down conversion can eliminate the current dead zone of the positive half-cycle, making the converter have higher PF and lower THDi. However, this patent cannot achieve boost / step-down and variable frequency AC output. Summary of the invention

[0004] In order to overcome the problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a variable-frequency buck-boost AC-AC converter, system and control method. The proposed converter can realize both boost and buck operations and variable-frequency AC power output. The proposed converter significantly reduces the number of active and passive components, and can provide continuous input and output currents with low harmonic content, reduce input and output total harmonic distortion, and achieve wider voltage gain coverage and higher efficiency.

[0005] To achieve the above object, the technical solution adopted by the present invention is: In a first aspect, the present invention provides a variable frequency bipolar buck-boost AC-AC converter, comprising: an AC power supply, a rectifier module, a high frequency AC link, a full-bridge inverter module, an output inductor , output capacitor 、Filter capacitor , the second capacitor 、IGBT switch tube and a load resistor R; the rectifier module includes a first diode , the second diode , the third diode and the fourth diode The full-bridge inverter module includes a first switch tube , the second switch tube , the third switch tube And the fourth switch The AC power supply The positive terminal of the first diode is connected Anode, AC power supply The cathode of the fourth diode is connected to The cathode of the first diode The anode of the second diode The cathode of the third diode is connected; The anode of the fourth diode The cathode of the first switch tube is connected; The source of the second switch The drain of the third switch tube The source of the fourth switch tube The drain of the IGBT switch is connected to The emitter of the second diode Anode, fourth diode The anode is connected to the first end of the primary side of the high-frequency AC link; the IGBT switch tube The collector of the first diode Cathode, third diode Cathode, filter capacitor The first end of the filter capacitor is connected to The second end of the output inductor is connected to the second end of the primary side of the high-frequency AC link; The first end of the first switch tube Source, second switch tube The drain is connected to the output capacitor. The first end of the output capacitor is connected to the first end of the load resistor R; The second end of the third switch tube Source, fourth switch tube The drain and the second end of the load resistor R are connected; the first end of the secondary side of the high-frequency AC link is connected to the second capacitor The first end of the first switch tube Drain and the third switch The second end of the secondary side of the high-frequency AC link is connected to the drain of the second capacitor The first end of the second switch tube And the fourth switch The source is connected.

[0006] Optionally, the high frequency AC link includes a high frequency transformer , magnetizing inductance and leakage inductance The leakage inductance With high frequency transformer The primary windings are connected in parallel; the magnetizing inductance With high frequency transformer The primary windings are connected in series.

[0007] Optionally, the IGBT switch tube It is a fully controlled IGBT switch.

[0008] Optionally, the first switch tube , the second switch tube , the third switch tube And the fourth switch All are fully controlled MOSFET switches.

[0009] In a second aspect, the present invention provides a variable frequency bipolar buck-boost system, comprising the variable frequency bipolar buck-boost AC-AC converter, and: The polarity detector is used to detect the input voltage The zero crossing point of the output control polarity signal ; Subtractor to calculate the reference output peak voltage and output voltage peak The difference between the two and outputs the error amplified signal ; PI controller, the PI controller is used to input the error amplification signal , and generates a control duty cycle signal ; The unipolar wave modulator PWM is used to generate a polarity signal and control duty cycle signal Feed to the IGBT switch , the first switch tube , the second switch tube , the third switch tube And the fourth switch .

[0010] In a third aspect, the present invention provides a control method for a variable frequency bipolar buck-boost system, comprising the following steps: Step 1: Detect input voltage The zero crossing point provides a control polarity signal ; Step 2: Detect output voltage The sampled output voltage instantaneous value Converted to peak voltage , and compare it with the reference peak voltage The difference is input into the PI controller to generate a control duty cycle signal. ; Step 3: Generate the polarity signal and control duty cycle signal It is fed to the unipolar wave modulator PWM to generate the corresponding PWM switch control signal.

[0011] Optionally, in step 1, the input voltage is detected , and add a DC bias voltage Make it positive and compare the resulting voltage with For comparison, if , a positive input voltage is detected, giving a control polarity signal =1; if , a negative input voltage is detected, giving a control polarity signal = 0.

[0012] Optionally, in step 2, the peak voltage The calculation formula is:

[0013] In the formula, is the instantaneous value of the output voltage, ω represents the angular frequency of the AC input signal; t represents time t.

[0014] Optionally, in step 2, the PI control system adopts a single neuron algorithm.

[0015] Optionally, the model equation of the single neuron algorithm is:

[0016] in represents the input signal of the i-th neuron, represents the weight of each input terminal connected to the i-th neuron, Indicates the output value.

[0017] Compared with the prior art, the present invention has the following beneficial effects: The present invention discloses a variable-frequency buck-boost AC-AC converter, system and control method. The AC-AC converter includes a rectifier module, a high-frequency DC link, an inverter module and a control loop. Compared with a traditional isolated AC-DC-AC converter, the proposed converter can realize both boost and buck operations and variable-frequency AC output.

[0018] The variable frequency bipolar buck-boost system of the present invention has two input state quantities, the AC power input voltage and the load output voltage, and has five PWM switch signal outputs, which are connected to the power switch tubes correspondingly, so as to realize the conversion control of AC power. In addition, the single neuron algorithm is introduced to be applied to the PI control system to realize parameter self-tuning. The proposed converter significantly reduces the number of active and passive components, and can provide continuous input and output currents with low harmonic content, reduce the input and output total harmonic distortion, and achieve a wider voltage gain coverage and higher efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The drawings described herein are for explanation purposes only and are not intended to limit the scope of the present invention in any way. In addition, the shapes and proportional dimensions of the components in the drawings are only for illustration purposes to help understand the present invention, and are not intended to specifically limit the shapes and proportional dimensions of the components of the present invention. In the drawings: Figure 1 A circuit topology diagram of an AC-AC converter provided in an embodiment of the present invention.

[0020] Figure 2 A control block diagram of an AC-AC converter provided in an embodiment of the present invention.

[0021] Figure 3 A structural diagram of a PI control system based on a single neuron in an AC-AC converter control method provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0022] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions 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 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 creative work should fall within the scope of protection of the present invention.

[0023] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. 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.

[0024] In the description of the embodiments of the present invention, it should be noted that if the terms "upper", "lower", "horizontal", "inner", etc. appear, the orientation or position relationship indicated is based on the orientation or position relationship shown in the accompanying drawings, or is the orientation or position relationship in which the product of the invention is usually placed when used. It is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0025] When an element is referred to as being "disposed on" another element, it may be directly on the other element or there may also be a central element. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may also be a central element. The terms "vertical", "horizontal", "left", "right" and similar expressions used herein are for illustrative purposes only and are not intended to be the only embodiments. If the term "horizontal" appears, it does not mean that the component is required to be absolutely horizontal, but it can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", which does not mean that the structure must be completely horizontal, but it can be slightly tilted.

[0026] It should be noted that similar reference numerals and letters represent similar items in the following figures, so once an item is defined in one figure, it does not need to be further defined and explained in the subsequent figures. In the description of the present invention, it is understood that the terms "include" and "comprise" indicate the presence of the described features, wholes, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or their collections.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art of the technical field of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. As used in the specification of the present invention and the appended claims, the singular forms of "a", "an" and "the" are intended to include plural forms unless the context clearly indicates otherwise.

[0028] The present invention is described in detail below with reference to the accompanying drawings.

[0029] like Figure 1 As shown, a variable frequency bipolar buck-boost AC-AC converter of the present invention is characterized by comprising: an AC power supply, a rectifier module, a high-frequency AC link, a full-bridge inverter module, an output inductor , output capacitor 、Filter capacitor , the second capacitor 、IGBT switch tube and a load resistor R; the rectifier module includes a first diode , the second diode , the third diode and the fourth diode The full-bridge inverter module includes a first switch tube , the second switch tube , the third switch tube And the fourth switch The AC power supply The positive terminal of the first diode is connected Anode, AC power supply The cathode of the fourth diode is connected to The cathode of the first diode The anode of the second diode The cathode of the third diode is connected; The anode of the fourth diode The cathode of the first switch tube is connected; The source of the second switch The drain of the third switch tube The source of the fourth switch tube The drain of the IGBT switch is connected to The emitter and the second diode Anode, fourth diode The anode is connected to the first end of the primary side of the high-frequency AC link; the IGBT switch tube Collector and first diode Cathode, third diode Cathode, filter capacitor The first end of the filter capacitor is connected to The second end of the output inductor is connected to the second end of the primary side of the high-frequency AC link; The first end of the first switch tube Source, second switch tube The drain is connected to the output capacitor. The first end and the first end of the load resistor R are connected; the output capacitor The second end and the third switch tube Source, fourth switch tube The drain and the second end of the load resistor R are connected; the first end of the secondary side of the high-frequency AC link is connected to the second capacitor The first end of the first switch tube Drain and the third switch The second end of the secondary side of the high-frequency AC link is connected to the drain of the second capacitor The first end of the second switch tube And the fourth switch The source is connected.

[0030] like Figure 2 As shown, a variable frequency bipolar buck-boost system of the present invention comprises the variable frequency bipolar buck-boost AC-AC converter, and: The polarity detector is used to detect the input voltage The zero crossing point of the output control polarity signal ; Subtractor to calculate the reference output peak voltage and output voltage peak The difference between the two and outputs the error amplified signal ; PI controller, the PI controller is used to input the error amplification signal , and generates a control duty cycle signal ; The unipolar wave modulator PWM is used to generate a polarity signal and control duty cycle signal Feed to the IGBT switch , the first switch tube , the second switch tube , the third switch tube And the fourth switch .

[0031] The control method of the variable frequency bipolar buck-boost system comprises the following steps: Step 1: Detect input voltage The zero crossing point provides a control polarity signal ; Step 2: Detect output voltage The sampled output voltage instantaneous value Converted to peak voltage , and compare it with the reference peak voltage The difference is input into the PI controller to generate a control duty cycle signal. ; Step 3: Generate the polarity signal and control duty cycle signal It is fed to the unipolar wave modulator PWM to generate the corresponding PWM switch control signal.

[0032] High-frequency bidirectional AC-AC converters stand out with their unique advantages. They can not only achieve efficient voltage and frequency regulation, but also reduce power loss while maintaining a small size and light weight. These characteristics make high-frequency bidirectional AC-AC converters an ideal choice for solving the AC-AC conversion problem in current industrial applications. Compared with traditional AC converters, they use fewer switching devices, have the advantages of high energy conversion efficiency, light weight, high power density, low total device power level, and safe commutation characteristics, and are suitable for applications that require variable voltage and variable frequency AC output.

[0033] Example 1 This embodiment provides a variable frequency bipolar buck-boost AC-AC converter, such as Figure 1 As shown, it includes AC power supply, rectifier module, high-frequency AC link, full-bridge inverter module, output inductor , output capacitor 、Filter capacitor , the second capacitor 、IGBT switch tube and load resistance R.

[0034] The rectifier module includes a first diode , the second diode , the third diode and the fourth diode The full-bridge inverter module includes a first switch tube , the second switch tube , the third switch tube And the fourth switch .

[0035] The AC power supply The positive terminal of the first diode is connected Anode, AC power supply The cathode of the fourth diode is connected to The cathode of the first diode The anode of the second diode The cathode of the third diode is connected; The anode of the fourth diode The cathode of the first switch tube is connected; The source of the second switch The drain of the third switch tube The source of the fourth switch tube The drain of the IGBT switch is connected to The emitter and the second diode Anode, fourth diode The anode is connected to the first end of the primary side of the high-frequency AC link; the IGBT switch tube Collector and first diode Cathode, third diode Cathode, filter capacitor The first end of the filter capacitor is connected to The second end of the output inductor is connected to the second end of the primary side of the high-frequency AC link; The first end of the first switch tube Source, second switch tube The drain is connected to the output capacitor. The first end and the first end of the load resistor R are connected; the output capacitor The second end and the third switch tube Source, fourth switch tube The drain and the second end of the load resistor R are connected; the first end of the secondary side of the high-frequency AC link is connected to the first end of the second capacitor C2 and the first switch tube Drain and the third switch The second end of the secondary side of the high-frequency AC link is connected to the drain of the second capacitor The first end of the second switch tube And the fourth switch The source is connected.

[0036] The variable frequency bipolar buck-boost AC-AC converter has three working modes: a common-phase buck-boost working mode, a reverse-phase buck-boost working mode, and a step-by-step frequency conversion working mode.

[0037] In a single switching cycle of the variable frequency bipolar buck-boost AC-AC converter, the ampere-second product flowing through the capacitor is kept balanced, and the volt-second product flowing through the inductor is kept balanced. According to the ampere-second balance principle and the volt-second balance principle of passive components in the circuit, it can be obtained that:

[0038] in, Represents filter capacitor The average voltage within a single cycle, Represents the input supply voltage.

[0039] in, Represents the second capacitor The average voltage in a single cycle, n represents the turns ratio of the high-frequency transformer, and D represents the duty cycle.

[0040]

[0041] in, Represents the average current of the output inductor in a single cycle, Represents the average current of the input inductor in a single cycle.

[0042] The input-output voltage gain M of the AC-AC converter is:

[0043] in, , Represent the input voltage and output voltage respectively, , Represent the input current and output current respectively.

[0044] The output voltage in inverting operation has a negative sign. This is because the output inductor current has a negative (reverse) polarity compared to the non-inverting mode.

[0045] Buck and boost operations are performed when n = 1. In addition, for deep voltage sag / swell compensation, the transformer turns ratio n can be increased; the buck operating area can also be increased by reducing the transformer turns ratio n.

[0046] By repeating the same-phase buck-boost operation and the opposite-phase buck-boost operation at specific time intervals, a step-frequency buck / boost output voltage can be generated.

[0047] Example 2 This embodiment provides a control method for a variable frequency buck-boost AC-AC converter as in Embodiment 1. Figure 3 : is a control block diagram of the AC-AC converter provided in this embodiment, and the control method provided specifically includes the following steps: Step 1: Detect input voltage The zero crossing point (polarity) of the , to generate the switching patterns required for the positive and negative half-cycles of the input voltage.

[0048] Specifically include: detecting input voltage , and add a DC bias voltage Make it positive and compare the resulting voltage with Make a comparison.

[0049] if , a positive input voltage is detected and a control polarity signal is given = 1; if , a negative input voltage is detected and a control polarity signal is given = 0.

[0050] Step 2: Detection output voltage The sampled output voltage instantaneous value Convert to peak .

[0051]

[0052] Wherein, ω represents the angular frequency of the AC input signal; t represents time t.

[0053] The reference output peak voltage of the bidirectional AC-AC converter With output voltage peak Compare, the difference Input to the PI controller to get the error amplification signal , Compare with the unipolar triangular carrier signal to generate a control duty cycle signal .

[0054] In this embodiment, the bipolar AC-AC converter as a whole adopts a PI control strategy based on voltage closed-loop control supplemented by a single neuron network algorithm.

[0055] The single neuron model equation is:

[0056] in represents the input signal of the i-th neuron, represents the weight of each input terminal connected to the i-th neuron, Indicates the output value.

[0057] Vectorize the above formula, and a single neuron is shown as follows:

[0058] Where Y represents the output vector of a single neuron; W represents the vector of weight coefficients; X represents the input vector of a single neuron.

[0059] A single neuron PI controller has an input and , corresponding to the proportional and integral links in PI control respectively, the input vector is as follows:

[0060]

[0061] in, Indicates the peak voltage output error of the AC-AC converter at the current moment; Indicates the output error at the previous moment.

[0062] The weight coefficient vector of a single neuron is expressed as:

[0063] in, and They represent the weight coefficients corresponding to the proportional link and the integral link respectively.

[0064] The control expression of a single neuron PI controller is:

[0065] According to the incremental PI control algorithm expression:

[0066] Then we get:

[0067] in, represents the integral coefficient of the PI controller, Represents the proportional coefficient of the PI controller. and They represent the weight coefficients corresponding to the proportional link and the integral link respectively.

[0068] The weight coefficient of a single neuron can be adaptively corrected according to the learning rule used to obtain the predicted value. Adjusting the weight coefficient through the learning algorithm is equivalent to real-time tuning of the control parameters of the controller, which effectively improves the self-learning ability and robustness of the controller. As shown in the following formula, the weight system is adjusted using the improved supervised Hebb learning rule.

[0069]

[0070]

[0071] Where e(k) represents the system error, u(k) represents the controller output, , Respectively represent the learning rates of the proportional and integral parameters of the output voltage closed-loop control, Reflects the first-order difference of the system error.

[0072] The sum of the neuron's input weights is 1, which is normalized:

[0073] Controller output for:

[0074] Among them, u(k) represents the output of the controller at the current moment, u(k-1) represents the output of the controller at the previous moment, and K represents the proportional coefficient of the single neuron algorithm. represents the amount of input required for single neuron learning, is the weighting coefficient corresponding to each input quantity.

[0075] Furthermore, when the K value is large, the system has good rapidity, but the overshoot is large, which may even make the system unstable; when the K value is too small, the system's rapidity will deteriorate, and even steady-state errors may occur. The selection of K value has a great influence on the performance of single neuron control.

[0076] The PSD (Proportional, Summation, Derivative) control law or fuzzy control concept is used to adjust the gain K value to form a single neuron PI controller with self-regulating gain.

[0077] Step 3: Generate the polarity signal and control duty signal Feed to the PWM logic block to generate 5 PWM switch control signals.

[0078] The present invention discloses a variable-frequency buck-boost AC-AC converter, system and control method. The AC-AC converter mainly includes a rectifier module, a high-frequency DC link, an inverter module and a control loop. Compared with a traditional isolated AC-DC-AC converter, the proposed converter can realize both boost and buck operations and variable-frequency AC output.

[0079] Control block diagram Figure 2 As shown in the figure, the control circuit has two input state quantities, the AC power input voltage and the load output voltage, and five PWM switch signal outputs, which are connected to the power switch tubes to realize the conversion control of AC power. In addition, the single neuron algorithm is introduced to apply to the PI control system to realize parameter self-tuning. The proposed converter significantly reduces the number of active and passive components, and can provide continuous input and output currents with low harmonic content, reduce input / output total harmonic distortion, and achieve a wider voltage gain coverage and higher efficiency.

[0080] Unless otherwise specified, the device elements involved in the above embodiments are all conventional device elements, and the structural settings, working modes or control modes involved are all conventional settings, working modes or control modes in the art unless otherwise specified.

[0081] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Other modifications or equivalent substitutions made to the technical solution of the present invention by ordinary technicians in the field should be included in the scope of the claims of the present invention as long as they do not depart from the spirit and scope of the technical solution of the present invention.

Claims

1. A variable frequency bipolar buck-boost AC-AC converter, characterized in that: include: AC power supply, rectifier module, high-frequency AC link, full-bridge inverter module, output inductor , output capacitor 、Filter capacitor , the second capacitor 、IGBT switch tube and a load resistor R; the rectifier module includes a first diode , the second diode , the third diode and the fourth diode The full-bridge inverter module includes a first switch tube , the second switch tube , the third switch tube And the fourth switch The AC power supply The positive terminal of the first diode is connected Anode, AC power supply The cathode of the fourth diode is connected to The cathode of the first diode The anode of the second diode The cathode of the third diode is connected; The anode of the fourth diode The cathode of the first switch tube is connected; The source of the second switch The drain of the third switch tube The source of the fourth switch tube The drain of the IGBT switch is connected to The emitter of the second diode Anode, fourth diode The anode is connected to the first end of the primary side of the high-frequency AC link; the IGBT switch tube The collector of the first diode Cathode, third diode Cathode, filter capacitor The first end of the filter capacitor is connected to The second end of the output inductor is connected to the second end of the primary side of the high-frequency AC link; The first end of the first switch tube Source, second switch tube The drain is connected to the output capacitor. The first end of the output capacitor is connected to the first end of the load resistor R; The second end of the third switch tube Source, fourth switch tube The drain and the second end of the load resistor R are connected; the first end of the secondary side of the high-frequency AC link is connected to the second capacitor The first end of the first switch tube Drain and the third switch The second end of the secondary side of the high-frequency AC link is connected to the drain of the second capacitor The first end of the second switch tube And the fourth switch The source is connected.

2. A variable frequency bipolar buck-boost AC-AC converter according to claim 1, characterized in that: The high frequency AC link includes a high frequency transformer , magnetizing inductance and leakage inductance The leakage inductance With high frequency transformer The primary windings are connected in parallel; the magnetizing inductance With high frequency transformer The primary windings are connected in series.

3. The variable frequency bipolar buck-boost AC-AC converter according to claim 1, characterized in that: The IGBT switch tube It is a fully controlled IGBT switch.

4. The variable frequency bipolar buck-boost AC-AC converter according to claim 1, characterized in that: The first switch tube , the second switch tube , the third switch tube And the fourth switch All are fully controlled MOSFET switches.

5. A variable frequency bipolar buck-boost system, characterized in that: A variable frequency bipolar buck-boost AC-AC converter comprising any one of claims 1 to 4, and: The polarity detector is used to detect the input voltage The zero crossing point of the output control polarity signal ; Subtractor to calculate the reference output peak voltage and output voltage peak The difference between the two and outputs the error amplified signal ; PI controller, the PI controller is used to input the error amplification signal , and generates a control duty cycle signal ; The unipolar wave modulator PWM is used to generate a polarity signal and control duty cycle signal Feed to the IGBT switch , the first switch tube , the second switch tube , the third switch tube And the fourth switch .

6. The control method of a variable frequency bipolar buck-boost system according to claim 5, characterized in that: The following steps are involved: Step 1: Detect input voltage The zero crossing point provides a control polarity signal ; Step 2: Detect output voltage The sampled output voltage instantaneous value Converted to peak voltage , and compare it with the reference peak voltage The difference is input into the PI controller to generate a control duty cycle signal. ; Step 3: Generate the polarity signal and control duty cycle signal It is fed to the unipolar wave modulator PWM to generate the corresponding PWM switch control signal.

7. The control method of a variable frequency bipolar buck-boost system according to claim 5, characterized in that: In step 1, detect the input voltage , and add a DC bias voltage Make it positive and compare the resulting voltage with For comparison, if , a positive input voltage is detected, giving a control polarity signal = 1; if , a negative input voltage is detected, giving a control polarity signal = 0.

8. The control method of a variable frequency bipolar buck-boost system according to claim 5, characterized in that: In step 2, the peak voltage The calculation formula is: In the formula, is the instantaneous value of the output voltage, ω represents the angular frequency of the AC input signal; t represents time t.

9. The control method of a variable frequency bipolar buck-boost system according to claim 5, characterized in that: In step 2, the PI control system adopts a single neuron algorithm.

10. The control method of a variable frequency bipolar buck-boost system according to claim 9, characterized in that: The model equation of the single neuron algorithm is: in represents the input signal of the ith neuron, represents the weight of each input terminal connected to the i-th neuron, Indicates the output value.

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