A control method and device of a converter and the converter

Abstract

This invention discloses a control method, apparatus, and converter for a converter, relating to the field of converters. The method includes determining an inner phase shift angle based on the input voltage and grid voltage; adjusting an outer phase shift angle based on the phase difference between the current in the resonant circuit and the voltage of the lagging bridge arm; and determining the switching frequencies of all switches in the primary and secondary circuits based on the secondary current reference, the inner phase shift angle, and the outer phase shift angle. By obtaining the phase difference between the current in the resonant circuit and the voltage of the lagging bridge arm, and dynamically adjusting the outer phase shift angle based on this phase difference, closed-loop precise control of the lagging bridge arm's turn-off current is achieved. By determining the inner phase shift angle using the input voltage and grid voltage, and combining the secondary current reference, the inner phase shift angle, and the outer phase shift angle to determine the switching frequency, precise regulation of the converter power is achieved. The switching frequency obtained in this application, based on actual measurements, is close to the actual operating conditions, resulting in more accurate converter control.

Description

Technical Field

[0001] This invention relates to the field of converters, and in particular to a control method, apparatus and converter for a converter. Background Technology

[0002] DC / AC (Direct Current / Alternating Current) converters are widely used in various power conversion scenarios. Their control typically involves adjusting the converter's phase shift angle and switching frequency to achieve power control. In existing dual active bridge converter control schemes, to ensure soft switching of power devices and reduce power return current, purely theoretical formulas are often used to approximate the zero-voltage turn-on condition of the lagging arm by controlling the phase difference between the primary and secondary sides. However, parasitic parameters, nonlinear characteristics, and non-ideal factors in actual circuits inherently deviate from theoretical formulas. Furthermore, within a single power frequency grid cycle, the current varies sinusoidally with the grid voltage, causing the turn-off current of the lagging arm to be dynamically changing. Therefore, relying solely on theoretical open-loop calculations in related technologies makes it difficult to accurately control the turn-off current of the lagging arm, resulting in incomplete soft switching, increased switching losses, and reduced system efficiency. Summary of the Invention

[0003] The purpose of this invention is to provide a control method, device, and converter for a converter. The switching frequency obtained based on actual measurement results is close to the actual operating conditions, resulting in more accurate control of the converter.

[0004] To solve the above technical problems, the present invention provides a control method for a converter. The converter includes a primary circuit, a transformer, a resonant circuit, and a secondary circuit. The input terminal of the primary circuit is connected to an input voltage, and the output terminal of the primary circuit is connected to the primary side of the transformer. The resonant circuit is connected to the secondary side of the transformer, the midpoint of the bridge arm of the secondary circuit, and the output terminal of the secondary circuit. The output terminal of the secondary circuit is connected to the power grid. Both the primary circuit and the secondary circuit include multiple switching transistors. The switching transistors in the primary circuit constitute a first bridge arm and a second bridge arm. The control method for the converter includes:

[0005] The inner phase shift angle is determined based on the input voltage and the grid voltage, wherein the inner phase shift angle is the phase difference between the drive signal of the first bridge arm and the drive signal of the second bridge arm;

[0006] Obtain the phase difference between the current of the resonant circuit and the voltage of the hysteresis bridge arm, wherein the hysteresis bridge arm is the bridge arm in which the driving signal phase lags behind that of the first bridge arm and the second bridge arm;

[0007] The outward phase shift angle is adjusted according to the phase difference, where the outward phase shift angle is the phase difference between the midpoint voltage of the bridge arm of the primary circuit and the midpoint voltage of the bridge arm of the secondary circuit.

[0008] The switching frequencies of all switching transistors in the primary circuit and the secondary circuit are determined based on the secondary current reference, the inner phase shift angle, and the outer phase shift angle.

[0009] On the other hand, determining the inner phase shift angle based on the input voltage and the grid voltage includes:

[0010] The voltage conversion ratio is determined based on the input voltage, the turns ratio of the transformer, and the grid voltage. The expression for the voltage conversion ratio is:

[0011] ;

[0012] in, The voltage conversion ratio is... The grid voltage is... The turns ratio of the transformer. The input voltage;

[0013] The inner phase shift angle is determined based on the voltage conversion ratio, and the expression for the inner phase shift angle is:

[0014] ;

[0015] in, The inner phase shift angle is denoted as .

[0016] On the other hand, obtaining the phase difference between the current in the resonant circuit and the voltage of the hysteresis bridge arm includes:

[0017] Obtain the current of the resonant circuit and convert the current of the resonant circuit into a first voltage signal;

[0018] The voltage at both ends of the hysteresis bridge arm is acquired, and the voltage at both ends of the hysteresis bridge arm is converted into a second voltage signal;

[0019] The first voltage signal and the second voltage signal are respectively input to the first input terminal and the second input terminal of the phase-locked loop;

[0020] The phase difference between the phase of the current output by the phase-locked loop and the phase of the voltage of the hysteresis bridge arm is obtained and used as the phase difference.

[0021] On the other hand, adjusting the outward phase shift angle according to the phase difference includes:

[0022] Obtain the preset target phase difference;

[0023] When the phase difference is less than the target phase difference, the outward phase angle is increased;

[0024] When the phase difference is greater than the target phase difference, the outward phase angle is reduced;

[0025] When the phase difference is equal to the target phase difference, it is determined that the current of the resonant circuit of the lagging arm at the turn-off moment is greater than or equal to the minimum current required for zero-voltage turn-on, and there is no need to adjust the outward phase angle.

[0026] On the other hand, obtaining the preset target phase difference includes:

[0027] When the target phase difference is a fixed value, the target phase difference is preset according to the rated operating parameters of the converter, and the target phase difference is stored in the controller of the converter;

[0028] When the target phase difference is a dynamically changing value, the target phase difference is adjusted according to the changes in the load current and secondary voltage of the converter, so that the current of the resonant circuit at the moment of the lag arm turn-off is greater than or equal to the minimum current required for zero voltage turn-on in the entire load range.

[0029] On the other hand, determining the switching frequencies of all switching transistors in the primary circuit and the secondary circuit based on the secondary current reference, the inner phase shift angle, and the outer phase shift angle includes:

[0030] The switching frequencies of all transistors in the primary and secondary circuits are determined based on the secondary current reference, the inner phase shift angle, and the outer phase shift angle. The expression for the switching frequency is:

[0031] , ;

[0032] in, The switching frequency, As an intermediate variable, The value of the resonant inductance is... The value of the resonant capacitance. The turns ratio of the transformer. The secondary voltage, The primary voltage, The inner phase shift angle, The outward phase angle is... This serves as the reference for the secondary current.

[0033] To address the aforementioned technical problems, the present invention also provides a control device for a converter, comprising:

[0034] Memory, used to store computer programs;

[0035] A processor is used to implement the steps of the control method for the converter described above when executing the computer program.

[0036] To address the aforementioned technical problems, the present invention also provides a converter, including the control device for the converter described above, and further comprising:

[0037] The primary circuit has an input terminal connected to the input primary voltage and an output terminal connected to the primary side of the transformer, used to convert the primary voltage into an AC square wave.

[0038] The transformer is used to perform voltage transformation on the high-frequency AC square wave output by the primary circuit.

[0039] The resonant circuit has a first end connected to the secondary side of the transformer, a second end connected to the midpoint of the bridge arm of the secondary circuit, and a third end connected to the output end of the secondary circuit, which is used to form a resonant circuit with the transformer.

[0040] The secondary circuit has its output terminal connected to the power grid, and is used to convert the voltage processed by the resonant circuit into AC power that matches the power grid.

[0041] On the other hand, it also includes:

[0042] A first voltage detection circuit has a first input terminal connected to the input terminal of the primary circuit, a second input terminal connected to the output terminal of the secondary circuit, and an output terminal connected to the control device, used to detect the primary voltage and the secondary voltage.

[0043] A current detection circuit, with its input terminal connected to the resonant circuit and its output terminal connected to the control device, is used to detect the current in the resonant circuit.

[0044] The second voltage detection circuit has its input terminal connected to both ends of the hysteresis bridge arm and its output terminal connected to the control device, and is used to detect the voltage of the hysteresis bridge arm.

[0045] The driving circuit has its input terminal connected to the control device and its output terminal connected to the control terminals of the switching transistors in the primary circuit and the secondary circuit, respectively. It is used to control the on and off of each switching transistor based on the driving signal output by the control device of the converter.

[0046] On the other hand, the primary-side circuit includes a first bridge arm and a second bridge arm. The first bridge arm includes a first switch and a second switch, and the second bridge arm includes a third switch and a fourth switch. The first terminals of the first switch and the third switch are both connected to the positive terminal of the input voltage, and the second terminals of the second switch and the fourth switch are both connected to the negative terminal of the input voltage. The common terminal connecting the second terminal of the first switch and the first terminal of the second switch is connected to the first terminal of the primary side of the transformer, and the common terminal connecting the second terminal of the third switch and the first terminal of the fourth switch is connected to the second terminal of the primary side of the transformer. The lagging bridge arm is the bridge arm in which the driving signal phase lags behind between the first bridge arm and the second bridge arm.

[0047] The secondary circuit includes a third bridge arm and a fourth bridge arm connected in series. The third bridge arm includes a fifth switch and a sixth switch connected in series. The fourth bridge arm includes a seventh switch and an eighth switch connected in series.

[0048] The resonant circuit includes a first resonant inductor, a first resonant capacitor, and a second resonant capacitor. The first end of the first resonant inductor is connected to the first end of the secondary side of the transformer. The second end of the first resonant inductor is connected to the common terminal of the sixth and seventh switching transistors. The first end of the first resonant capacitor and the first end of the fifth switching transistor are both connected to the positive terminal of the power grid. The second end of the first resonant capacitor and the first end of the second resonant capacitor are connected, and their common terminal is connected to the second end of the secondary side of the transformer. The second end of the second resonant capacitor and the second end of the eighth switching transistor are both connected to the negative terminal of the power grid.

[0049] This application provides a control method, apparatus, and converter for a converter, relating to the field of converters. The method includes determining an inner phase shift angle based on the input voltage and grid voltage; adjusting an outer phase shift angle based on the phase difference between the current in the resonant circuit and the voltage of the lagging bridge arm; and determining the switching frequencies of all switches in the primary and secondary circuits based on a secondary current reference, the inner phase shift angle, and the outer phase shift angle. By obtaining the phase difference between the current in the resonant circuit and the voltage of the lagging bridge arm, and dynamically adjusting the outer phase shift angle based on this phase difference, closed-loop precise control of the lagging bridge arm's turn-off current is achieved. The inner phase shift angle is determined by the input voltage and grid voltage, and the switching frequency is determined by combining the secondary current reference, the inner phase shift angle, and the outer phase shift angle, thus achieving precise regulation of the converter's power. The switching frequency obtained by this application based on actual measurements is close to the actual operating conditions, resulting in more accurate control of the converter. Attached Figure Description

[0050] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the prior art and embodiments 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.

[0051] Figure 1 A flowchart of a converter control method provided by the present invention;

[0052] Figure 2 A schematic diagram of the structure of a converter provided by the present invention;

[0053] Figure 3 This is a waveform diagram of the converter under normal operating conditions;

[0054] Figure 4 A flowchart of another converter control method provided by the present invention;

[0055] Figure 5 A waveform diagram of a converter provided by the present invention;

[0056] Figure 6 A current-voltage vector diagram of a resonant circuit provided by the present invention;

[0057] Figure 7 A schematic diagram of controlling the turn-off current of the hysteresis bridge arm provided by the present invention;

[0058] Figure 8 This is a schematic diagram of the control device for a converter provided by the present invention. Detailed Implementation

[0059] The core of this invention is to provide a control method, device, and converter for a converter. The switching frequency obtained based on actual measurement results is close to the actual operating conditions, resulting in more accurate control of the converter.

[0060] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0061] The converter includes a primary circuit, a transformer, a resonant circuit, and a secondary circuit. The input terminal of the primary circuit is connected to the input voltage, and the output terminal of the primary circuit is connected to the primary side of the transformer. The resonant circuit is connected to the secondary side of the transformer, the midpoint of the bridge arm of the secondary circuit, and the output terminal of the secondary circuit. The output terminal of the secondary circuit is connected to the power grid. Both the primary and secondary circuits include multiple switching transistors. The switching transistors in the primary circuit constitute the first and second bridge arms.

[0062] The converter provided in this application is a dual active bridge (DAB) DC / AC converter. The dual active bridge converter is an isolated bidirectional DC / DC / DC / AC conversion topology with advantages such as high power density, electrical isolation, and ease of soft switching. It is widely used in power conversion scenarios such as new energy power generation, energy storage systems, electric vehicle charging, and microgrids.

[0063] like Figure 2 As shown, the converter in this embodiment includes a primary-side circuit, a transformer, a resonant circuit, and a secondary-side circuit. The input terminal of the primary-side circuit is connected to the input voltage (DC bus voltage). The output of the primary circuit is connected to the primary side of the transformer to convert the DC input voltage into a high-frequency AC square wave. The transformer is used for voltage transformation and electrical isolation; its primary and secondary sides are magnetically coupled with a turns ratio of N. The resonant circuit is connected to the secondary side of the transformer, the midpoint of the bridge arm of the secondary circuit, and the output of the secondary circuit, forming a resonant circuit with the transformer. This provides necessary resonant energy for soft switching and shapes the current waveform to reduce current stress. The output of the secondary circuit is connected to the power grid to convert the AC power processed by the resonant circuit into AC power that matches the power grid.

[0064] Figure 3 The diagram shows the waveform of the converter under normal operating conditions. Both the primary and secondary circuits include multiple switching transistors. The switching transistors in the primary circuit constitute the first and second bridge arms. The first bridge arm is usually called the leading bridge arm, and the second bridge arm is called the lagging bridge arm. In a full-bridge topology, when there is a phase difference between the drive signals of the two bridge arms, the leakage inductance of the transformer or the energy stored in the resonant inductor can be used to achieve zero-voltage turn-on of the switching transistors, thereby significantly reducing switching losses. The lagging bridge arm refers to the bridge arm whose drive signal is delayed in phase relative to the first bridge arm; this delay angle is the inward phase shift angle. Simultaneously, to achieve zero-current turn-off and further reduce turn-off losses, it is necessary to precisely control the current value at the turn-off moment of the lagging bridge arm to be as small as possible. This application achieves near-zero-current turn-off by precisely controlling the phase difference between the resonant current and the voltage of the lagging bridge arm, ensuring that the turn-off current of the lagging bridge arm is exactly equal to the minimum current required for zero-voltage turn-on, provided that the junction capacitance charging and discharging commutation is completed.

[0065] like Figure 1 As shown, the control method of the converter includes:

[0066] S11: Determine the inner phase shift angle based on the input voltage and the grid voltage, where the inner phase shift angle is the phase difference between the drive signal of the first bridge arm and the drive signal of the second bridge arm;

[0067] Input voltage refers to the DC bus voltage at the input terminal of the primary circuit, while grid voltage refers to the effective or instantaneous value of the AC grid voltage connected to the output terminal of the secondary circuit. The inner phase shift angle is the phase difference between the drive signals of the first and second bridge arms. The existence of the inner phase shift angle ensures that when the lagging bridge arm is turned off, the current in the resonant circuit has a certain initial value. This current can charge and discharge the junction capacitance of the lagging bridge arm, thereby achieving zero-voltage turn-on. Furthermore, the inner phase shift angle can reduce power return current, i.e., reduce the reactive power returning from the grid side to the input terminal, thereby reducing the reactive power loss of the converter.

[0068] S12: Obtain the phase difference between the current of the resonant circuit and the voltage of the lagging bridge arm. The lagging bridge arm is the bridge arm in the first and second bridge arms where the driving signal phase lags behind.

[0069] The current in the resonant circuit is the current flowing through the resonant inductor and resonant capacitor, and the voltage of the lagging arm is the voltage across the lagging arm (i.e., the midpoint voltage between the two switching transistors of the second arm). Whether the lagging arm can achieve zero-voltage turn-on depends on the direction and amplitude of the resonant current at the turn-off moment, and the current state at this turn-off moment can be accurately characterized by the phase relationship between the resonant current and the lagging arm voltage. When the phase of the resonant current lags behind the lagging arm voltage by a certain angle, the current at the turn-off moment of the lagging arm is precisely in a direction and amplitude that can complete the charging and discharging commutation of the junction capacitance.

[0070] S13: Adjust the outward phase shift angle according to the phase difference. The outward phase shift angle is the phase difference between the midpoint voltage of the primary circuit arm and the midpoint voltage of the secondary circuit arm.

[0071] The outward phase shift angle φ is defined as the phase difference between the midpoint voltage of the primary circuit arm and the midpoint voltage of the secondary circuit arm. The outward phase shift angle determines the magnitude and direction of the converter's power transmission. By adjusting the outward phase shift angle, the phase relationship between the resonant current and the lagging arm voltage can be changed, thereby converging the phase difference to the target value. Using the phase difference as a feedback quantity and the outward phase shift angle as a control quantity, a negative feedback closed loop is constructed. This ensures that even when there are deviations between the actual circuit parameters and the theoretical model, the turn-off current of the lagging arm can still be accurately controlled within the range that meets the soft-switching requirements.

[0072] S14: Determine the switching frequencies of all switching transistors in the primary and secondary circuits based on the secondary current reference, the inner phase shift angle, and the outer phase shift angle.

[0073] The secondary current reference is a current command value calculated and issued in real time by the controller, and the switching frequency is the common operating frequency of all switching transistors. After determining the inner and outer phase shift angles, the switching frequency needs to be adjusted to ensure that the converter's output current accurately tracks the current reference. The inner phase shift angle, outer phase shift angle, and switching frequency together determine the converter's power transfer characteristics. Among them, the inner phase shift angle mainly affects the soft-switching conditions and return power, the outer phase shift angle mainly affects the magnitude of the transmitted power, and the switching frequency affects the resonant impedance and current waveform.

[0074] First, the inner phase shift angle is determined based on voltage matching conditions to ensure basic soft-switching conditions and reduce return power. Then, the actual phase difference between the resonant current and the lag arm voltage is obtained through a phase-locked loop or zero-crossing detection. Next, the outer phase shift angle is adjusted to converge this phase difference to the target value. Finally, the switching frequency is determined in conjunction with the current reference. Based on real-time detection of actual physical quantities, the system can automatically compensate for the effects of circuit parameter deviations and load changes, thereby achieving precise soft-switching control across the entire voltage and load range.

[0075] This application provides a control method for a converter, relating to the field of converters. The method includes determining an inner phase shift angle based on the input voltage and the grid voltage; adjusting an outer phase shift angle based on the phase difference between the current in the resonant circuit and the voltage of the lagging bridge arm; and determining the switching frequencies of all switches in the primary and secondary circuits based on the secondary current reference, the inner phase shift angle, and the outer phase shift angle. By obtaining the phase difference between the current in the resonant circuit and the voltage of the lagging bridge arm, and dynamically adjusting the outer phase shift angle based on this phase difference, closed-loop precise control of the lagging bridge arm's turn-off current is achieved. By determining the inner phase shift angle using the input voltage and the grid voltage, and combining the secondary current reference, the inner phase shift angle, and the outer phase shift angle to jointly determine the switching frequency, precise regulation of the converter power is achieved. The switching frequency obtained by this application based on actual measurements is close to the actual operating conditions, resulting in more accurate converter control.

[0076] Based on the above embodiments:

[0077] Figure 4 A flowchart of another converter control method provided by the present invention. Figure 5 This is a waveform diagram of a converter provided by the present invention. Figure 6 A current-voltage vector diagram of a resonant circuit provided by the present invention;

[0078] In some embodiments, determining the inner phase shift angle based on the input voltage and the grid voltage includes:

[0079] The voltage conversion ratio is determined based on the input voltage, the transformer turns ratio, and the grid voltage. The expression for the voltage conversion ratio is:

[0080] ;

[0081] in, Voltage conversion ratio, This is the grid voltage. The turns ratio of the transformer. Input voltage;

[0082] The inner phase shift angle is determined based on the voltage conversion ratio. The expression for the inner phase shift angle is:

[0083] ;

[0084] in, This is the inward phase shift angle.

[0085] Please refer to Figure 4 , Figure 5 and Figure 6 The zero-crossing time of the resonant circuit current is t4a, and the turn-off time of the lagging bridge arm is t4. β = t4a - t4 is the phase difference between the resonant current and the lagging bridge arm voltage. By changing the external phase shift angle φ to control the value of β, it can be ensured that the current ilag at the turn-off time meets the soft-switching requirements. Figure 5 in,i lag S1 represents the current at the moment the lagging bridge arm turns off, S8 represents the drive signals for the first to eighth switches, Nvp represents the voltage at the left end of the resonant cavity, vlag represents the voltage of the lagging bridge arm, is represents the resonant cavity current, vs represents the voltage at the right end of the resonant cavity, vlr represents the voltage across the resonant cavity (the vector difference between Nvp and vs), α represents the phase difference between vlag and vs, β represents the phase difference between is and vlag, and (π-θ) / 2 represents the phase difference between Nvp and vlag. Please refer to... Figure 7 The resonant current and the voltage signal of the lagging bridge arm are sent to the PLL phase-locked loop through hardware detection to obtain the value of the outer phase shift angle φ. By controlling the value of φ, the turn-off current of the lagging bridge arm can be precisely controlled to meet the soft switching requirements.

[0086] In a dual active bridge converter, determining the inner phase shift angle requires first calculating the voltage conversion ratio, which is the ratio of the grid voltage to the product of twice the transformer turns ratio N and the input voltage. The power transfer characteristics and soft-switching conditions of a dual active bridge converter are closely related to the degree of matching between the input and output voltages. When the voltage conversion ratio M equals 1, the converter is in optimal matching condition, with the highest power transfer efficiency and the widest soft-switching range. When M deviates from 1, the converter enters a voltage mismatch condition. If single-phase shift control is still used in this condition, a large backflow power will occur, and some switches may lose their zero-voltage turn-on condition. Therefore, before determining the inner phase shift angle, the voltage conversion ratio M must first be calculated to quantify the degree of voltage matching.

[0087] M reflects the normalized value of the converter voltage gain. NVp in the denominator is the amplitude of the transformer secondary-side port voltage (twice the primary-side voltage after transformer turns ratio adjustment), and Vg in the numerator is the actual grid voltage. When M < 1, it indicates that the grid voltage is lower than the adjusted secondary-side port voltage, and the converter operates in buck mode; when M > 1, it indicates that the grid voltage is higher than the adjusted secondary-side port voltage, and the converter operates in boost mode; when M = 1, the converter operates in matched mode.

[0088] First, the input voltage Vp and the grid voltage Vg are sampled by a voltage detection circuit. Second, the transformer turns ratio N is obtained; this parameter is an inherent design parameter of the converter and is pre-stored in the controller. Then, the voltage conversion ratio M is calculated. The calculated value of M is transmitted to the controller for subsequent determination of the inner phase shift angle.

[0089] The optimal control strategy for the dual active bridge converter differs under the two operating conditions: M<1 and M≥1. When M<1, the converter is in buck mode. In this case, introducing an inner phase shift angle can widen the soft-switching range of the lagging arm while reducing the return current power. Based on the optimal inner phase shift angle expression derived jointly from the soft-switching constraint and the minimum return current power constraint, when M≥1, the converter is in boost mode or matched mode. In this case, fixing the inner phase shift angle to π (i.e., the maximum inner phase shift angle) allows the lagging arm to obtain the widest soft-switching range.

[0090] The working principle of the inward phase shift angle is explained below in two cases:

[0091] When M < 1, the grid voltage is lower than the converted secondary port voltage. Under this condition, if single-phase shift control (i.e., =π), the soft-switching condition of the lagging arm becomes stringent, especially under light load conditions, where the lagging arm may completely lose its zero-voltage switching capability. Based on the equivalent circuit model of the resonant circuit, soft-switching constraints (lagging arm turn-off current ≥ minimum current required for zero-voltage switching) and minimum return power constraints (minimizing reactive power returning from the grid to the input) are established, and the optimal inner phase shift angle is obtained by solving them simultaneously. The physical meaning of this formula is that the inner phase shift angle increases with the increase of M, and when M approaches 0, When M approaches 0; when M approaches 1, It approaches π.

[0092] When M≥1, the grid voltage is higher than or equal to the converted secondary port voltage. Under this condition, the converter is in boost mode or matched mode. When M=1, the converter is in optimal matched state, and setting the inner phase shift angle to 0 ensures soft switching of all switches. When M>1, the soft switching conditions in boost mode are relatively relaxed, and fixing the inner phase shift angle to π can maximize the soft switching margin of the lagging arm. Setting the inner phase shift angle to π means that the drive signals of the two primary arms are completely out of phase. At this time, the primary output voltage is a standard 50% duty cycle square wave, and the converter actually operates in single-phase shift mode.

[0093] In some embodiments, obtaining the phase difference between the current in the resonant circuit and the voltage of the hysteresis bridge arm includes:

[0094] Obtain the current of the resonant circuit and convert the current of the resonant circuit into a first voltage signal;

[0095] Obtain the voltage across the lagging bridge arm and convert the voltage across the lagging bridge arm into a second voltage signal;

[0096] The first voltage signal and the second voltage signal are respectively input to the first input terminal and the second input terminal of the phase-locked loop;

[0097] The phase difference between the phase of the current in the resonant circuit output by the phase-locked loop and the phase of the voltage in the lagging bridge arm is obtained as the phase difference.

[0098] The current in the resonant circuit is sampled by a current detection circuit (such as a current transformer or a Hall effect current sensor). The current sensor is connected in series in the resonant circuit, and its output is a current signal or voltage signal proportional to the resonant current. If the sensor output is a current signal, it is converted into a voltage signal through a sampling resistor; if the sensor output itself is a voltage signal, it is directly processed. The reason for setting up a current-to-voltage conversion is that the subsequent phase-locked loop (PLL) processes voltage signals, therefore the current signal needs to be converted into a voltage signal to match the input requirements of the PLL.

[0099] The voltage across the lagging bridge arm is acquired and converted into a second voltage signal. The voltage across the lagging bridge arm is sampled by a voltage detection circuit. This voltage detection circuit typically uses a resistor divider network in conjunction with an isolation amplifier or differential amplifier to attenuate and isolate the high-voltage signal into a low-voltage signal, while preserving the phase and amplitude information of the voltage waveform.

[0100] The first and second voltage signals are input to the first and second input terminals of the phase-locked loop (PLL), respectively. A PLL is a closed-loop control system capable of automatically tracking the frequency and phase of an input signal. The first voltage signal, representing the phase information of the resonant current, and the second voltage signal, representing the phase information of the lag arm voltage, are connected to the two input terminals of the PLL. The phase detector, loop filter, and voltage-controlled oscillator within the PLL work together to calculate the phase difference between the two input signals in real time. The PLL has advantages such as strong anti-interference capability and high phase detection accuracy, and can stably output accurate phase difference information even under grid frequency fluctuations and harmonic interference.

[0101] The first input of the phase-locked loop (PLL) receives a first voltage signal representing the resonant current, and the second input receives a second voltage signal representing the lag arm voltage. An internal phase detector compares the phases of the two signals, generating an error signal proportional to the phase difference. A loop filter filters this error signal to remove high-frequency noise. The voltage-controlled oscillator (VCO) adjusts its output frequency based on the filtered error signal, locking the PLL to the frequency of the input signal. In the locked state, the phase difference output by the PLL is the actual phase difference between the resonant current and the lag arm voltage.

[0102] In some embodiments, adjusting the outward phase shift angle based on the phase difference includes:

[0103] Obtain the preset target phase difference;

[0104] When the phase difference is less than the target phase difference, increase the outward phase shift angle;

[0105] When the phase difference is greater than the target phase difference, decrease the outward phase shift angle;

[0106] When the phase difference equals the target phase difference, it is determined that the current of the resonant circuit at the turn-off moment of the lagging arm is greater than or equal to the minimum current required for zero-voltage turn-on, and there is no need to adjust the external phase angle.

[0107] Obtain the preset target phase difference βref. The target phase difference refers to the desired phase difference value to ensure that the lagging arm meets the zero-voltage turn-on condition at the turn-off moment. This target value can be a fixed value or a value that changes dynamically according to the operating conditions. The phase difference β is a continuously changing physical quantity, and a clear target value is needed as the adjustment benchmark for closed-loop control to be implemented.

[0108] When the phase difference is less than the target phase difference, the outer phase shift angle is increased. Specifically, the controller compares the real-time detected phase difference β with the target phase difference βref. If β < βref, it indicates that the phase of the resonant current is insufficiently lagging (or excessively leading) relative to the phase of the lagging arm voltage. In this case, the current amplitude at the turn-off moment of the lagging arm may be insufficient to complete the charging and discharging commutation of the junction capacitance. To increase the current amplitude at the turn-off moment, the outer phase shift angle φ needs to be increased. Increasing the outer phase shift angle will change the voltage vector relationship of the resonant circuit, causing changes in the amplitude and phase of the resonant current, thereby increasing β and converging towards βref.

[0109] When the phase difference is greater than the target phase difference, the outer phase shift angle is reduced. If β > βref, it indicates that the phase of the resonant current lags too much relative to the phase of the lagging arm voltage. Although the soft-switching condition may be met, the excessive phase difference will lead to an increase in the effective value of the resonant current, increasing line losses. To reduce the effective value of the current, the outer phase shift angle φ needs to be reduced. Reducing the outer phase shift angle causes β to decrease and converge towards βref.

[0110] When the phase difference equals the target phase difference, it is determined that the current in the resonant circuit at the turn-off moment of the lagging arm is greater than or equal to the minimum current required for zero-voltage turn-on, and no adjustment of the external phase shift angle is needed. When β=βref, it indicates that the phase relationship between the resonant current and the voltage of the lagging arm has reached the target state. At this time, the resonant current at the turn-off moment of the lagging arm just meets the amplitude and direction conditions required for zero-voltage turn-on, so the current external phase shift angle can be maintained unchanged.

[0111] The change in the outward phase angle φ alters the phase relationship between the midpoint voltage of the primary and secondary bridge arms, thus affecting the voltage vector across the resonant circuit. According to the equivalent circuit model of the resonant circuit, the amplitude and phase of the resonant current are determined by the voltage vector difference across the resonant circuit. Therefore, adjusting φ essentially adjusts the voltage vector across the resonant circuit, thereby changing the amplitude and phase of the resonant current. By using closed-loop regulation to make β converge to βref, the goal is to ensure that the instantaneous value of the resonant current at the moment the lagging bridge arm turns off is precisely equal to the target value required for zero-voltage turn-on, while simultaneously minimizing the current value at the moment of turn-off, achieving near-zero-current turn-off.

[0112] In some embodiments, obtaining a preset target phase difference includes:

[0113] When the target phase difference is a fixed value, the target phase difference is preset according to the rated operating parameters of the converter and stored in the converter's controller;

[0114] When the target phase difference is a dynamically changing value, the target phase difference is adjusted according to the changes in the load current and secondary voltage of the converter, so that the current of the resonant circuit at the moment of the lagging arm turn-off is greater than or equal to the minimum current required for zero voltage turn-on in the entire load range.

[0115] The target phase difference is a fixed value. When the target phase difference is a fixed value, the target phase difference is preset according to the rated operating parameters of the converter and stored in the converter's controller.

[0116] For a given converter topology and parameters (including transformer turns ratio N, resonant inductance L, resonant capacitance C, and switch junction capacitance), the minimum turn-off current required to achieve zero-voltage turn-on is determined. According to the equivalent model of the resonant circuit, the phase difference β corresponding to this minimum turn-off current is a fixed angle value. Therefore, this fixed value can be determined through theoretical calculations or simulation optimization during the converter design phase and pre-stored in the controller's non-volatile memory. During converter operation, the controller directly reads this fixed value as the target phase difference. The advantage of a fixed target phase difference lies in its simplicity and low computational cost, making it suitable for applications with minimal operating conditions and cost sensitivity.

[0117] The target phase difference is a dynamically changing value. When the target phase difference is dynamically changing, it is adjusted in real time according to the changes in the converter's load current and secondary voltage, ensuring that the current in the resonant circuit at the moment of the lagging arm's turn-off is greater than or equal to the minimum current required for zero-voltage turn-off across the entire load range. The minimum turn-off current required for zero-voltage turn-off is not fixed but varies with load current and voltage conditions. When the load current increases, the junction capacitance of the switching transistor requires a larger current to charge and discharge, thus increasing the required minimum turn-off current accordingly. When the secondary voltage changes, the operating point of the resonant circuit shifts, also affecting the required turn-off current. Therefore, to achieve accurate soft switching across the entire voltage and load range, the target phase difference needs to be adjusted in real time according to the operating conditions.

[0118] During converter operation, the load current (indirectly reflected by the secondary current reference iref) and secondary voltage Vg are monitored in real time. Based on the current values ​​of the load current and secondary voltage, the controller determines the optimal target phase difference βref_opt for the current operating condition through table lookup or online calculation. This optimal value ensures that the resonant current at the turn-off moment is just greater than or equal to the minimum current required for zero-voltage turn-on, while minimizing the effective value of the resonant current, thus achieving the best trade-off between soft switching and efficiency. Across the entire voltage and load range, this dynamic adjustment method ensures that the resonant current at the turn-off moment of the lagging arm meets the zero-voltage turn-on condition, overcoming the limitation of traditional schemes that only achieve soft switching under specific operating conditions. The advantage of the dynamic target phase difference lies in its strong adaptability, maintaining optimal soft-switching performance across the entire voltage and load range.

[0119] Two flexible target phase difference setting methods are provided, allowing users to choose the appropriate method based on specific application requirements. For cost-sensitive and stable applications, a fixed value method can be selected; for high-performance and wide-range applications, a dynamically changing value method can be selected. Both methods ensure that the hysteresis arm meets the zero-voltage turn-on condition across the entire voltage and load range.

[0120] In some embodiments, determining the switching frequencies of all switching transistors in the primary and secondary circuits based on the secondary current reference, the inner phase shift angle, and the outer phase shift angle includes:

[0121] The switching frequencies of all transistors in the primary and secondary circuits are determined based on the secondary current reference, the inner phase shift angle, and the outer phase shift angle. The expression for the switching frequency is:

[0122] , ;

[0123] in, For switching frequency, As an intermediate variable, This is the resonant inductance value. This is the resonant capacitance value. The turns ratio of the transformer. This is the secondary voltage. The primary voltage, This is the inward phase angle. For the outward phase angle, It serves as the reference for the secondary current.

[0124] In a dual active bridge converter, there is a defined mathematical relationship between the switching frequency fs, phase shift angles (θ and φ), and output current. Once the inner phase shift angle θ and outer phase shift angle φ are determined, the voltage transfer characteristics of the converter are established. At this point, adjusting the switching frequency fs allows the output current to precisely track the current reference iref. This formula is derived from the converter's equivalent circuit model and power balance equations, reflecting the quantitative relationship between fs, θ, φ, and iref. The controller obtains the secondary current reference iref (given by the upper-level controller), combines it with the determined inner and outer phase shift angles θ and φ, as well as the converter's inherent parameters (L, C, N) and the real-time detected voltage values ​​(Vg, Vp), and calculates the switching frequency fs according to the above formula. The calculated fs is used to generate the drive signals for all switches. Determining the switching frequency through a precise mathematical formula achieves accurate control of the output current. This formula comprehensively considers voltage conditions, phase shift angles, and the current reference, enabling the converter to adaptively adjust the switching frequency under different operating conditions, achieving precise power output while ensuring soft switching. At the same time, the formula requires little computation and is suitable for real-time implementation in embedded controllers.

[0125] Figure 8 This is a schematic diagram of a control device for a converter provided by the present invention. The control device for the converter includes:

[0126] Memory 21 is used to store computer programs;

[0127] The processor 22 is used to implement the steps of the control method for the converter described above when executing a computer program.

[0128] The description of the control device for the converter provided in this application is given in the above embodiments and will not be repeated here.

[0129] Figure 2 This invention provides a schematic diagram of a converter, which includes the aforementioned converter control device and further includes:

[0130] The primary circuit has its input terminal connected to the primary voltage and its output terminal connected to the primary side of the transformer. It is used to convert the primary voltage into an AC square wave.

[0131] A transformer is used to transform the voltage of a high-frequency AC square wave output from a primary circuit.

[0132] The resonant circuit has its first terminal connected to the secondary side of the transformer, its second terminal connected to the midpoint of the bridge arm of the secondary circuit, and its third terminal connected to the output terminal of the secondary circuit, in order to form a resonant circuit with the transformer.

[0133] The secondary circuit, with its output connected to the power grid, is used to convert the voltage processed by the resonant circuit into AC power that matches the power grid.

[0134] The input terminal of the primary circuit is connected to the input primary voltage, and the output terminal is connected to the primary side of the transformer. It is used to convert the input primary voltage (DC voltage) into a high-frequency AC square wave.

[0135] The primary-side circuit includes a first bridge arm and a second bridge arm. The first bridge arm includes a first switch Q1 and a second switch Q2 connected in series. The first terminal of the first switch Q1 (such as the drain of a MOSFET or the collector of an IGBT) is connected to the positive terminal of the input voltage, and the second terminal of the second switch Q2 (such as the source of a MOSFET or the emitter of an IGBT) is connected to the negative terminal of the input voltage. The common terminal connecting the second terminal of the first switch Q1 and the first terminal of the second switch Q2 serves as the midpoint of the first bridge arm and is connected to the first terminal of the primary side of the transformer.

[0136] The second bridge arm includes a third switch Q3 and a fourth switch Q4 connected in series. The first terminal of the third switch Q3 is connected to the positive terminal of the input voltage, and the second terminal of the fourth switch Q4 is connected to the negative terminal of the input voltage. The common terminal connecting the second terminal of the third switch Q3 and the first terminal of the fourth switch Q4 serves as the midpoint of the second bridge arm and is connected to the second terminal of the primary side of the transformer.

[0137] The lagging arm is the arm in the first and second arms whose drive signal phase lags behind. In specific implementations, the second arm (Q3, Q4) is usually set as the lagging arm, that is, the drive signals of Q3 and Q4 lag behind the drive signals of Q1 and Q2 by an angle θ.

[0138] The drive signal output by the control device controls the on and off of the four switching transistors according to a certain timing sequence. When Q1 and Q4 are on simultaneously, the input voltage is applied forward to the primary side of the transformer; when Q2 and Q3 are on simultaneously, the input voltage is applied backward to the primary side of the transformer. By introducing an inward phase shift angle θ between the two bridge arms, conditions are created for the soft switching of the lagging bridge arm.

[0139] Each switching transistor is preferably a MOSFET or IGBT, with a diode (body diode or external diode) connected in anti-parallel to achieve bidirectional conduction and freewheeling. A junction capacitance (or external capacitor) is also connected in parallel across each switching transistor to absorb voltage spikes when the transistor is turned off and to participate in resonant commutation when turned on at zero voltage. For example, C1 and D1 are the anti-parallel diode and junction capacitance connected to the first switching transistor Q1; C2 and D2 are the anti-parallel diode and junction capacitance connected to the second switching transistor Q2; C3 and D3 are the anti-parallel diode and junction capacitance connected to the third switching transistor Q3; and C4 and D4 are the anti-parallel diode and junction capacitance connected to the fourth switching transistor Q4.

[0140] The transformer Tr is used to transform the high-frequency AC square wave output from the primary circuit. Its primary side is connected to the output terminal of the primary circuit, and its secondary side is connected to the resonant circuit. The turns ratio of the transformer is N (primary turns: secondary turns = 1:N). In addition to voltage transformation and electrical isolation, the leakage inductance of the transformer can also participate in resonance as part of the resonant inductance, which helps to broaden the soft-switching range.

[0141] The first end of the resonant circuit is connected to the secondary side of the transformer, the second end is connected to the midpoint of the bridge arm of the secondary circuit, and the third end is connected to the output end of the secondary circuit, which is used to form a resonant circuit with the transformer.

[0142] The switching transistors in the secondary circuit are controlled by superimposing an external phase shift angle φ on the drive signals of the switching transistors in the primary circuit. The secondary circuit converts the high-frequency AC square wave output from the transformer secondary side into AC power with the same frequency and phase as the grid voltage, realizing the DC / AC inverter function.

[0143] In some embodiments, it also includes:

[0144] The first voltage detection circuit has a first input terminal connected to the input terminal of the primary circuit, a second input terminal connected to the output terminal of the secondary circuit, and an output terminal connected to the control device. It is used to detect the primary voltage and the secondary voltage.

[0145] The current detection circuit has its input terminal connected to the resonant circuit and its output terminal connected to the control device. It is used to detect the current in the resonant circuit.

[0146] The second voltage detection circuit has its input terminal connected to both ends of the hysteresis bridge arm and its output terminal connected to the control device. It is used to detect the voltage of the hysteresis bridge arm.

[0147] The drive circuit has its input terminal connected to the control device, and its output terminal connected to the control terminals of the switching transistors in the primary circuit and the secondary circuit, respectively. It is used to control the conduction and cutoff of each switching transistor based on the drive signal output by the converter's control device.

[0148] The converter also includes various detection circuits for real-time acquisition of the various physical quantities required for control.

[0149] The first voltage detection circuit has its first input terminal connected to the input terminal of the primary circuit, its second input terminal connected to the output terminal of the secondary circuit, and its output terminal connected to the control device. It is used to detect the primary voltage Vp and the secondary voltage Vg. The reason for setting up the first voltage detection circuit is that the primary and secondary voltages are necessary input parameters for determining the inner phase shift angle θ and calculating the switching frequency fs, and they need to be obtained in real time and accurately.

[0150] The current detection circuit, with its input connected to the resonant circuit and its output connected to the control device, is used to detect the current is of the resonant circuit. The reason for setting up the current detection circuit is that the resonant current is is the basis for obtaining the phase difference β, and it is also a key physical quantity for determining whether soft switching has been achieved.

[0151] The second voltage detection circuit, with its input connected to both ends of the lagging bridge arm and its output connected to the control device, is used to detect the voltage vlag of the lagging bridge arm. The reason for setting up the second voltage detection circuit is that the lagging bridge arm voltage vlag is another key physical quantity required to obtain the phase difference β; its phase information, combined with the phase information of the resonant current, jointly determines the phase difference β.

[0152] The input of the drive circuit is connected to the control device, and the output is connected to the control terminals of each switch in the primary circuit and the secondary circuit, respectively. It controls the switching on and off of each switch based on the drive signals output by the control device. The drive signals output by the control device are low-voltage logic signals (typically 3.3V or 5V), insufficient to directly drive the switches (especially high-voltage, high-power switches, which typically require 10V~20V and several amperes of drive current). The drive circuit converts the low-voltage logic signals into voltage and current signals suitable for driving the switches, while providing electrical isolation (through optocouplers or magnetic couplings) to protect the control device from interference from the high-voltage side.

[0153] The drive circuit also includes a dead-time control function, which inserts a short idle time (dead time) between the drive signals of the two switching transistors in the same bridge arm to prevent the upper and lower transistors from conducting simultaneously and causing a short circuit. The dead time setting needs to be coordinated with the soft-switching control to ensure that the junction capacitor can complete the charging and discharging commutation within the dead time.

[0154] In some embodiments, the primary-side circuit includes a first bridge arm and a second bridge arm. The first bridge arm includes a first switch Q1 and a second switch Q2. The second bridge arm includes a third switch Q3 and a fourth switch Q4. The first terminals of the first switch Q1 and the third switch Q3 are both connected to the positive terminal of the input voltage. The second terminals of the second switch Q2 and the fourth switch Q4 are both connected to the negative terminal of the input voltage. The common terminal connecting the second terminal of the first switch Q1 and the first terminal of the second switch Q2 is connected to the first terminal of the primary side of the transformer. The common terminal connecting the second terminal of the third switch Q3 and the first terminal of the fourth switch Q4 is connected to the second terminal of the primary side of the transformer. The lagging bridge arm is the bridge arm in the first and second bridge arms where the driving signal phase lags behind.

[0155] The secondary circuit includes a third bridge arm and a fourth bridge arm connected in series. The third bridge arm includes a fifth switch Q5 and a sixth switch Q6 connected in series. The fourth bridge arm includes a seventh switch Q7 and an eighth switch Q8 connected in series.

[0156] The resonant circuit includes a first resonant inductor, a first resonant capacitor, and a second resonant capacitor. The first end of the first resonant inductor is connected to the first end of the secondary side of the transformer. The second end of the first resonant inductor is connected to the common terminal of the sixth and seventh switching transistors. The first end of the first resonant capacitor and the first end of the fifth switching transistor Q5 are both connected to the positive terminal of the power grid. The second end of the first resonant capacitor and the first end of the second resonant capacitor are connected, and their common terminal is connected to the second end of the secondary side of the transformer. The second end of the second resonant capacitor and the second end of the eighth switching transistor are both connected to the negative terminal of the power grid.

[0157] The input terminal of the primary circuit is connected to the input voltage (DC bus voltage Vp), and the output terminal is connected to the primary side of the transformer. It is used to convert the input DC voltage into a high-frequency AC square wave. The purpose of setting up the primary circuit is to invert the DC input voltage into a high-frequency AC voltage, which is then transmitted to the secondary side through the transformer. At the same time, the alternating conduction of the switching transistors enables bidirectional power flow.

[0158] The primary-side circuit includes a first bridge arm and a second bridge arm. The first bridge arm includes a first switch Q1 and a second switch Q2 connected in series. The first terminal of the first switch Q1 (such as the drain of a MOSFET or the collector of an IGBT) is connected to the positive terminal of the input voltage, and the second terminal of the second switch Q2 (such as the source of a MOSFET or the emitter of an IGBT) is connected to the negative terminal of the input voltage. The common terminal connecting the second terminal of the first switch Q1 and the first terminal of the second switch Q2 serves as the midpoint of the first bridge arm and is connected to the first terminal of the primary side of the transformer. This connection method ensures that the voltage at the midpoint of the first bridge arm is the positive potential of the input voltage when Q1 is on and the negative potential of the input voltage when Q2 is on, thereby generating a high-frequency square wave voltage at the midpoint of the bridge arm.

[0159] The second bridge arm consists of a third switch Q3 and a fourth switch Q4 connected in series. The first terminal of the third switch Q3 is connected to the positive terminal of the input voltage, and the second terminal of the fourth switch Q4 is connected to the negative terminal of the input voltage. The common terminal connecting the second terminal of the third switch Q3 and the first terminal of the fourth switch Q4 serves as the midpoint of the second bridge arm, which is connected to the second terminal of the primary winding of the transformer. The operating principle of the second bridge arm is the same as that of the first bridge arm; its midpoint also generates a high-frequency square wave voltage. The voltage difference between the midpoints of the first and second bridge arms is the voltage applied to the primary winding of the transformer.

[0160] Each switching transistor is preferably a MOSFET or IGBT, with a diode (body diode or external diode) connected in anti-parallel to achieve bidirectional conduction and freewheeling. A junction capacitance (or external capacitor) is also connected in parallel across each switching transistor to absorb voltage spikes when the transistor is turned off and to participate in resonant commutation during zero-voltage turn-on. Zero-voltage turn-on essentially utilizes the resonant current to charge and discharge the junction capacitance across the switching transistor. When the voltage across the junction capacitance discharges to zero, the body diode of the switching transistor conducts, allowing the transistor to be turned on at this point, thus eliminating turn-on losses. The presence of the junction capacitance is a fundamental physical condition for soft switching.

[0161] The drive signals output by the control device control the on and off of the four switching transistors according to a specific timing sequence. When Q1 and Q4 are on simultaneously, the input voltage is applied forward to the primary side of the transformer (positive half-cycle); when Q2 and Q3 are on simultaneously, the input voltage is applied backward to the primary side of the transformer (negative half-cycle). By introducing an inward phase shift angle θ between the two bridge arms, a groove is generated in the primary-side output voltage waveform. This groove keeps the primary-side voltage of the transformer at zero during commutation, creating a time window for the soft switching of the lagging bridge arm. At any given moment, the drive signal of one bridge arm is delayed relative to the drive signal of the other bridge arm; the delayed bridge arm is the lagging bridge arm. Typically, the second bridge arm (Q3, Q4) is set as the lagging bridge arm, meaning that the drive signals of Q3 and Q4 lag behind the drive signals of Q1 and Q2 by an angle θ. When the lagging bridge arm is off, the primary-side voltage of the transformer is zero, at which point the resonant current is large, making zero-voltage turn-on the easiest to achieve.

[0162] The output of the secondary circuit is connected to the power grid, used to convert the voltage processed by the resonant circuit into AC power that matches the power grid. The switching transistors of the secondary circuit correspond to those of the primary circuit in terms of driving timing, and the magnitude and direction of power transmission are controlled by shifting the phase angle φ outward.

[0163] The secondary circuit includes a third and a fourth bridge arm connected in series. The third bridge arm includes a fifth switch Q5 and a sixth switch Q6 connected in series, with the connection point of the fifth switch Q5 and the sixth switch Q6 being the midpoint of the first bridge arm of the secondary circuit. The fourth bridge arm includes a seventh switch Q7 and an eighth switch Q8 connected in series, with the connection point of the seventh switch Q7 and the eighth switch Q8 being the midpoint of the second bridge arm of the secondary circuit.

[0164] The first terminal of the fifth switch Q5 is connected to the positive terminal of the power grid, and the second terminal of the sixth switch Q6 is connected to the negative terminal of the power grid. The first terminal of the seventh switch Q7 is connected to the positive terminal of the power grid, and the second terminal of the eighth switch Q8 is connected to the negative terminal of the power grid. The first terminal of the sixth switch Q6 and the second terminal of the seventh switch Q7 are connected, and their common terminal is connected to the second terminal of the first resonant inductor. The sixth switch Q6 and the seventh switch Q7 are connected at the midpoint, forming a common node, which serves as the midpoint of the secondary side bridge arm and is connected to the resonant inductor. The fifth switch Q5 and the sixth switch Q6 form the third bridge arm, and the seventh switch Q7 and the eighth switch Q8 form the fourth bridge arm.

[0165] The secondary circuit switches are controlled by adding an external phase shift angle φ to the drive signals of the primary circuit switches. Specifically, the fifth switch Q5 and the eighth switch Q8 are turned on simultaneously, and the sixth switch Q6 and the seventh switch Q7 are turned on simultaneously, with the two sets of switches conducting alternately to generate AC voltage on the secondary side. The secondary circuit converts the high-frequency AC square wave output from the transformer secondary side into AC power with the same frequency and phase as the grid voltage, realizing the DC / AC inverter function.

[0166] The resonant circuit includes a first resonant inductor Lk, a first resonant capacitor Cr1, and a second resonant capacitor Cr2. The first terminal of the first resonant inductor Lk is connected to the first terminal of the secondary winding of the transformer, and the second terminal of the first resonant inductor Lk is connected to the midpoint of the bridge arm of the secondary winding circuit. The first terminal of the first resonant capacitor Cr1 is connected to the positive terminal of the power grid, and the second terminal of the first resonant capacitor Cr1 is connected to the first terminal of the second resonant capacitor Cr2, with the common terminal of this connection connected to the second terminal of the secondary winding of the transformer. The second terminal of the second resonant capacitor Cr2 is connected to the negative terminal of the power grid. Ls is the output inductance.

[0167] The resonant inductor Lk and resonant capacitors Cr1 and Cr2 form a series or series-parallel resonant network. Near the switching frequency, the resonant network exhibits specific impedance characteristics, which can shape the current waveform and reduce current stress. More importantly, the energy in the resonant network participates in commutation during the switching process of the switching transistor, providing the necessary current for zero-voltage turn-on.

[0168] The output of the secondary circuit is connected to the power grid to convert the voltage processed by the resonant circuit into AC power that matches the power grid.

[0169] The converter provided in this application is described in the above embodiments and will not be repeated here.

[0170] It should also be noted that, in this specification, 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.

[0171] Those skilled in the art will further recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of both. To clearly illustrate the interchangeability of hardware and software, the components and steps of the various examples have been generally described in terms of functionality in the foregoing description. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0172] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A control method for a converter, characterized in that, The converter includes a primary-side circuit, a transformer, a resonant circuit, and a secondary-side circuit. The input terminal of the primary-side circuit is connected to the input voltage, and the output terminal of the primary-side circuit is connected to the primary side of the transformer. The resonant circuit is connected to the secondary side of the transformer, the midpoint of the bridge arm of the secondary-side circuit, and the output terminal of the secondary-side circuit. The output terminal of the secondary-side circuit is connected to the power grid. Both the primary-side circuit and the secondary-side circuit include multiple switching transistors. The switching transistors in the primary-side circuit constitute the first bridge arm and the second bridge arm. The control method of the converter includes: The inner phase shift angle is determined based on the input voltage and the grid voltage, wherein the inner phase shift angle is the phase difference between the drive signal of the first bridge arm and the drive signal of the second bridge arm; Obtain the phase difference between the current of the resonant circuit and the voltage of the hysteresis bridge arm, wherein the hysteresis bridge arm is the bridge arm in which the driving signal phase lags behind that of the first bridge arm and the second bridge arm; The outward phase shift angle is adjusted according to the phase difference, where the outward phase shift angle is the phase difference between the midpoint voltage of the bridge arm of the primary circuit and the midpoint voltage of the bridge arm of the secondary circuit. The switching frequencies of all switching transistors in the primary circuit and the secondary circuit are determined based on the secondary current reference, the inner phase shift angle, and the outer phase shift angle.

2. The control method for the converter as described in claim 1, characterized in that, Determining the inner phase shift angle based on the input voltage and the grid voltage includes: The voltage conversion ratio is determined based on the input voltage, the turns ratio of the transformer, and the grid voltage. The expression for the voltage conversion ratio is: ； in, The voltage conversion ratio is... The grid voltage is... The turns ratio of the transformer. The input voltage; The inner phase shift angle is determined based on the voltage conversion ratio, and the expression for the inner phase shift angle is: ； in, The inner phase shift angle is denoted as .

3. The control method for the converter as described in claim 1, characterized in that, Obtaining the phase difference between the current in the resonant circuit and the voltage of the hysteresis bridge arm includes: Obtain the current of the resonant circuit and convert the current of the resonant circuit into a first voltage signal; The voltage at both ends of the hysteresis bridge arm is acquired, and the voltage at both ends of the hysteresis bridge arm is converted into a second voltage signal; The first voltage signal and the second voltage signal are respectively input to the first input terminal and the second input terminal of the phase-locked loop; The phase difference between the phase of the current output by the phase-locked loop and the phase of the voltage of the hysteresis bridge arm is obtained and used as the phase difference.

4. The control method for the converter as described in claim 1, characterized in that, Adjusting the outward phase shift angle according to the phase difference includes: Obtain the preset target phase difference; When the phase difference is less than the target phase difference, the outward phase angle is increased; When the phase difference is greater than the target phase difference, the outward phase angle is reduced; When the phase difference is equal to the target phase difference, it is determined that the current of the resonant circuit of the lagging arm at the turn-off moment is greater than or equal to the minimum current required for zero-voltage turn-on, and there is no need to adjust the outward phase angle.

5. The control method for the converter as described in claim 4, characterized in that, Obtain the preset target phase difference, including: When the target phase difference is a fixed value, the target phase difference is preset according to the rated operating parameters of the converter, and the target phase difference is stored in the controller of the converter; When the target phase difference is a dynamically changing value, the target phase difference is adjusted according to the changes in the load current and secondary voltage of the converter, so that the current of the resonant circuit at the moment of the lag arm turn-off is greater than or equal to the minimum current required for zero voltage turn-on in the entire load range.

6. The control method for the converter as described in claim 1, characterized in that, The switching frequencies of all transistors in the primary and secondary circuits are determined based on the secondary current reference, the inner phase shift angle, and the outer phase shift angle, including: The switching frequencies of all transistors in the primary and secondary circuits are determined based on the secondary current reference, the inner phase shift angle, and the outer phase shift angle. The expression for the switching frequency is: ， ； in, The switching frequency, As an intermediate variable, The value of the resonant inductance is... The value of the resonant capacitance. The turns ratio of the transformer. The secondary voltage, The primary voltage, The inner phase shift angle, The outward phase angle is... This serves as the reference for the secondary current.

7. A control device for a converter, characterized in that, include: Memory, used to store computer programs; A processor, configured to implement the steps of the control method for the converter as described in any one of claims 1 to 6 when executing the computer program.

8. A converter, characterized in that, The control device for the converter as described in claim 7 further includes: The primary circuit has an input terminal connected to the input primary voltage and an output terminal connected to the primary side of the transformer, used to convert the primary voltage into an AC square wave. The transformer is used to perform voltage transformation on the high-frequency AC square wave output by the primary circuit. The resonant circuit has a first end connected to the secondary side of the transformer, a second end connected to the midpoint of the bridge arm of the secondary circuit, and a third end connected to the output end of the secondary circuit, which is used to form a resonant circuit with the transformer. The secondary circuit has its output terminal connected to the power grid, and is used to convert the voltage processed by the resonant circuit into AC power that matches the power grid.

9. The converter as claimed in claim 8, characterized in that, Also includes: A first voltage detection circuit has a first input terminal connected to the input terminal of the primary circuit, a second input terminal connected to the output terminal of the secondary circuit, and an output terminal connected to the control device, used to detect the primary voltage and the secondary voltage. A current detection circuit, with its input terminal connected to the resonant circuit and its output terminal connected to the control device, is used to detect the current in the resonant circuit. The second voltage detection circuit has its input terminal connected to both ends of the hysteresis bridge arm and its output terminal connected to the control device, and is used to detect the voltage of the hysteresis bridge arm. The driving circuit has its input terminal connected to the control device and its output terminal connected to the control terminals of the switching transistors in the primary circuit and the secondary circuit, respectively. It is used to control the on and off of each switching transistor based on the driving signal output by the control device of the converter.

10. The converter as claimed in claim 9, characterized in that, The primary-side circuit includes a first bridge arm and a second bridge arm. The first bridge arm includes a first switch and a second switch, and the second bridge arm includes a third switch and a fourth switch. The first terminals of the first switch and the third switch are both connected to the positive terminal of the input voltage, and the second terminals of the second switch and the fourth switch are both connected to the negative terminal of the input voltage. The common terminal connecting the second terminal of the first switch and the first terminal of the second switch is connected to the first terminal of the primary side of the transformer, and the common terminal connecting the second terminal of the third switch and the first terminal of the fourth switch is connected to the second terminal of the primary side of the transformer. The lagging bridge arm is the bridge arm in which the driving signal phase lags behind that of the first bridge arm and the second bridge arm. The secondary circuit includes a third bridge arm and a fourth bridge arm connected in series. The third bridge arm includes a fifth switch and a sixth switch connected in series. The fourth bridge arm includes a seventh switch and an eighth switch connected in series. The resonant circuit includes a first resonant inductor, a first resonant capacitor, and a second resonant capacitor. The first end of the first resonant inductor is connected to the first end of the secondary side of the transformer. The second end of the first resonant inductor is connected to the common terminal of the sixth and seventh switching transistors. The first end of the first resonant capacitor and the first end of the fifth switching transistor are both connected to the positive terminal of the power grid. The second end of the first resonant capacitor and the first end of the second resonant capacitor are connected, and their common terminal is connected to the second end of the secondary side of the transformer. The second end of the second resonant capacitor and the second end of the eighth switching transistor are both connected to the negative terminal of the power grid.

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