A single-stage isolated inverter control method based on variable frequency and extended phase-shift modulation

Abstract

The application discloses a single-stage isolated inverter control method based on variable frequency and extended phase-shift modulation. The method comprises the following steps: sampling and acquiring input and output voltage and current of the converter and preset parameters; calculating real-time power and comparing the real-time power with a preset threshold to determine a heavy-load constant-frequency or light-load variable-frequency working mode; calculating a switching frequency, a theoretical inner phase-shift angle and an outer phase-shift angle based on the mode, and maintaining an effective phase-shift angle through variable frequency to ensure a zero-voltage turn-on range when the light load; predicting a switching tube turn-off current by using an analytical model; judging a switching state according to the predicted current, calculating a dead-time compensation correction quantity adaptive to the switching frequency variation, correcting the theoretical phase-shift angle, and obtaining a final control quantity. The application realizes high efficiency and soft-switching operation in a full power range by combining light-load variable frequency control with extended phase-shift modulation, and significantly improves the output current waveform quality and reduces total harmonic distortion through frequency-adaptive accurate dead-time compensation.

Description

Technical Field

[0001] This invention relates to the field of power electronic converter control technology, and in particular to a control method for a single-stage isolated inverter based on frequency conversion and extended phase-shift modulation. Background Technology

[0002] Single-stage isolated high-frequency DC / AC converters (typically based on DAB topology and its derivatives) are widely used in distributed generation, energy storage systems, and electric vehicle charging due to their advantages such as electrical isolation, bidirectional power transmission capability, high power density, and ease of soft switching. These converters typically employ a phase-shift control strategy, adjusting the phase shift angle between the primary and secondary full-bridge circuits to control the magnitude and direction of power transmission.

[0003] In practical applications, to prevent shoot-through short circuits in the bridge arms, a dead time must be set between the drive signals of the upper and lower transistors in the same bridge arm. In high-frequency switching conditions, the presence of dead time significantly alters the actual output voltage waveform of the converter, leading to output current distortion (such as clipping and zero-crossing oscillation) and power transmission errors. Especially in grid-connected inverter applications, this distortion severely affects the total harmonic distortion (THD) of the grid-connected current, reducing power quality.

[0004] In related technologies, patent application CN118801718A proposes a dead-zone compensation strategy based on single-phase-shift (SPS) modulation. Although SPS control is simple, the converter has a large return current power and is prone to losing ZVS under light load, resulting in reduced system efficiency and making it difficult to balance waveform quality and conversion efficiency.

[0005] In the literature “Yang Qiqing, Li Rui, Xu Jun. Optimization Modulation Strategy for Dual Active Bridge Microinverters Based on Mode Switching [J]. Proceedings of the CSEE, 2023, 43(23):9273-9284,” performance is optimized by switching multiple modulation modes in different power ranges. However, this method uses fixed-frequency control, and when the load becomes lighter, the phase shift angle approaches zero in order to maintain power balance. This causes the extended phase shift modulation to actually degenerate into a single phase shift mode, and the inner phase shift angle cannot maintain an effective zero-voltage turn-on (ZVS) range, resulting in soft switching failure. At this time, the dead-time effect and hard-switching interference are superimposed, resulting in severe distortion and spikes in the grid-connected current waveform under light load.

[0006] In summary, achieving high-efficiency energy conversion, wide-range soft-switching (ZVS) operation, and high-quality output waveforms (low THD) across the entire power range is a critical challenge that urgently needs to be addressed in single-stage isolated converter control technology. A control method that can break through fixed-frequency limitations and organically combine efficient modulation strategies with precise dead-time compensation is required. Summary of the Invention

[0007] In view of the above, this invention proposes a control method for a single-stage isolated inverter based on frequency conversion and extended phase-shift modulation. This invention achieves soft-switching operation, high-efficiency transmission, and high-quality waveform output of the converter across the entire power range by introducing frequency conversion control to extend the ZVS range under light load conditions, combining this with extended phase-shift modulation to optimize efficiency, and supplementing this with active dead-time compensation based on current prediction.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A control method for a single-stage isolated inverter based on frequency conversion and extended phase-shift modulation, characterized by comprising the following steps:

[0010] S1. Obtain the converter operating parameters, including the sampled input voltage u. dc Output voltage u ac Output current i ac Output current reference value i ref Transformer turns ratio n and transformer leakage inductance L k ;

[0011] S2. Calculate the real-time transmission power requirement P of the converter based on the converter operating parameters. cal and compare it with the preset power threshold P set The operating modes of the converter are determined by comparison; the operating modes include heavy-load constant frequency mode and light-load variable frequency mode.

[0012] S3. Based on the determined operating mode, calculate the current switching frequency f. s Theoretical internal phase shift angle D 1_cal And the theoretical outward phase angle D 2_cal ;

[0013] If in heavy-load constant frequency mode, the switching frequency f s Set to the rated frequency, and calculate D based on the extended phase-shift modulation strategy. 1_cal and D 2_cal ;

[0014] If in light-load inverter mode, adjust the switching frequency f according to the soft-switching zero-voltage turn-on boundary condition. s And based on the adjusted switching frequency, D is recalculated to meet the power requirements. 1_cal and D 2_cal ;

[0015] S4. Based on f determined in step S3 s D 1_cal and D 2_cal The instantaneous values ​​of the turn-off current of the primary-side switch and the secondary-side switch are predicted using an analytical model.

[0016] S5. Determine the current switching state based on the polarity of the instantaneous turn-off current value, calculate the dead-zone compensation correction, and correct the theoretical phase shift angle to obtain the compensated phase shift angle D. 1_comp and D 2_comp Finally, based on the phase shift angle D 1_comp and D 2_comp Generate driving signals.

[0017] The aforementioned single-stage isolated inverter control method based on frequency conversion and extended phase-shift modulation, wherein the preset power threshold P set It is set as: the minimum critical power at which the converter can maintain zero-voltage turn-on in heavy-load constant-frequency mode, or the inflection point power at which the converter efficiency curve decays as the power decreases.

[0018] The aforementioned single-stage isolated inverter control method based on frequency conversion and extended phase-shift modulation, wherein the theoretical internal phase-shift angle D in the heavy-load constant-frequency mode... 1_cal And the theoretical outward phase angle D 2_cal The expression is:

[0019] ;

[0020] ;

[0021] In the formula, m = |u ac | / (nu dc ) represents voltage gain, and M represents power transfer ratio. P N As the reference transmission power, P ac For AC side transmission power, .

[0022] The aforementioned single-stage isolation inverter control method based on frequency conversion and extended phase-shift modulation, when in light-load frequency conversion mode, adjusts the switching frequency f. s_opt The expression is:

[0023] ;

[0024] In the formula, m = |u ac | / (nu dc () represents the voltage gain.

[0025] The aforementioned control method for a single-stage isolated inverter based on frequency conversion and extended phase-shift modulation provides the following expressions for the instantaneous values ​​of the turn-off current for the primary and secondary switching transistors:

[0026] ;

[0027] The aforementioned single-stage isolated inverter control method based on frequency conversion and extended phase-shift modulation introduces a linear compensation coefficient K when calculating the dead-time compensation correction. COMP Its expression is:

[0028] ;

[0029] In the formula, I ZVS It is the current required to achieve zero-voltage turn-on, I off This is the turn-off current of the primary and secondary switching transistors.

[0030] The aforementioned single-stage isolation inverter control method based on frequency conversion and extended phase-shift modulation includes the following steps for calculating the dead-time compensation correction:

[0031] S1. Obtain the dead time T of the primary and secondary switching transistors. dead And according to the current switching frequency f s Calculate the dead time duty cycle D dead =T dead ×f s ;

[0032] S2. For the primary-side switching transistor, the minimum current required to achieve zero-voltage turn-on is I. zvs_pri If I off_pri > -I zvs_pri If so, it is determined to be a hard switch, and the expression for the compensated inner and outer phase shift angles is:

[0033] ;

[0034] S3. For the secondary-side switching transistor, the minimum current required to achieve zero-voltage turn-on is I. zvs_sec If I off_sec zvs_sec If so, it is determined to be a hard switch, and the final expression for the inner and outer phase shift angles is:

[0035] .

[0036] The single-stage isolated inverter control method based on frequency conversion and extended phase shift modulation according to claim 1 is characterized in that the method further includes a closed-loop feedback adjustment step: the output current is collected and compared with a reference value, a closed-loop fine-tuning amount ΔD is generated through a proportional-integral or proportional-resonant controller, and the closed-loop fine-tuning amount is superimposed on the final external phase shift angle after dead-zone compensation correction.

[0037] .

[0038] ​The aforementioned control method for a single-stage isolated inverter based on frequency conversion and extended phase-shift modulation, wherein the topology of the single-stage isolated inverter includes at least one full-bridge structure, specifically configured as a full-bridge-full-bridge structure, a full-bridge-half-bridge structure, or a half-bridge-full-bridge structure; wherein, when a full-bridge-half-bridge structure or a half-bridge-full-bridge structure is adopted, the extended phase-shift modulation strategy is only applied to the full-bridge side of the converter.

[0039] Compared with the prior art, the present invention has the following significant advantages:

[0040] 1. The core technology proposed in this invention lies in introducing frequency conversion control in the light load region to actively adjust the switching frequency to maintain an effective phase shift angle, enabling the converter to operate in the extended phase-shift modulation high-efficiency zero-voltage turn-on range even at extremely low power. This physically eliminates current spikes and oscillations caused by hard switching, fundamentally solving the problems of reduced efficiency and current distortion under light load, thereby significantly reducing the total harmonic distortion of the grid-connected current.

[0041] 2. The dead-time compensation method based on current prediction proposed in this invention creatively incorporates the real-time switching frequency as a key variable into the compensation model, enabling the dead-time duty cycle to adapt to the frequency conversion process and ensuring consistent compensation accuracy across all operating conditions. This method can effectively handle complex situations such as "partial soft switching," thereby significantly improving the quality of the output current waveform.

[0042] 3. This invention employs a unified extended phase-shift modulation framework, achieving a smooth transition between heavy-load and light-load modes with simplified control logic. This not only avoids the logical complexity and transient impact problems that may arise from traditional multi-mode switching control, but also improves the overall stability and reliability of the system.

[0043] 4. This invention adopts a composite control architecture that combines "feedforward optimization (frequency conversion and model prediction compensation) with feedback correction (closed-loop fine-tuning)". This architecture utilizes the model for rapid and forward-looking optimization while effectively suppressing model parameter errors and external disturbances through closed-loop feedback, thereby ensuring the control accuracy and robustness of the system under various operating conditions. Attached Figure Description

[0044] Figure 1 This is a flowchart of the control method proposed in the embodiments of the present invention.

[0045] Figure 2 This is a schematic diagram of the topology of a single-stage isolated inverter in an embodiment of the present invention.

[0046] Figure 3 This is a schematic diagram of the extended phase-shifted (EPS) modulation waveform in an embodiment of the present invention.

[0047] Figure 4The switching frequency f in the light-load inverter mode of this embodiment of the invention is s A graph showing how transmission power changes.

[0048] Figure 5 A comparison chart of the ZVS range of the method of this invention and the traditional fixed-frequency control method.

[0049] Figure 6 These are AC voltage and current waveforms obtained using the method of this invention and without using the method of this invention in one embodiment of the present invention. (a) is the AC voltage and current waveform obtained without using the method of this invention, and (b) is the AC voltage and current waveform obtained using the method of this invention. Detailed Implementation

[0050] To describe the present invention in more detail, the technical solution of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0051] Example: A control method for a single-stage isolated inverter based on frequency conversion and extended phase-shift modulation, such as... Figure 1 As shown, it includes the following steps:

[0052] S1. Obtain the converter operating parameters, including the sampled input voltage u. dc Output voltage u ac Output current i ac and control and calculation parameters; the control and calculation parameters include the output current reference value i ref Transformer turns ratio n and transformer leakage inductance L k ;

[0053] S2. Calculate the inverter's power transmission requirement P based on the converter's operating parameters. cal and with the preset power threshold P set The operating modes of the converter are determined by comparison. These operating modes include heavy-load constant-frequency mode and light-load variable-frequency mode.

[0054] S3. When in heavy-load constant frequency mode, the switching frequency f s Set to the rated value, based on the extended phase-shift (EPS) modulation strategy, with the goal of maximizing the ZVS range, the theoretical inner phase-shift angle D is calculated. 1_cal and outward phase angle D 2_cal .

[0055] When in light-load inverter mode, the switching frequency f is adjusted according to the soft-switching zero-voltage turn-on (ZVS) boundary condition. s And based on the adjusted frequency, recalculate D to meet the power requirements. 1_cal and D 2_cal .

[0056] S4. f determined based on the above steps s D 1_cal and D 1_cal The instantaneous turn-off current values ​​of the primary and secondary side switches are predicted using an analytical model.

[0057] S5. Determine the current switching state based on the polarity of the instantaneous turn-off current value, calculate the dead-zone compensation correction, and adjust the theoretical internal phase shift angle D. 1_cal and outward phase angle D 1_cal After correction, the final inner phase shift angle D is obtained. 1_final Outward phase angle D 2_final .

[0058] In this embodiment, the single-stage isolated high-frequency DC / AC converter adopts the following... Figure 2 The diagram shows a full-bridge / half-bridge dual active bridge (DAB) topology.

[0059] Specifically, the primary side of the transformer is a full-bridge circuit composed of switching transistors Q1 to Q4; the secondary side is a half-bridge circuit composed of switching transistors Q5 to Q8 and voltage-dividing capacitors C1 / C2. The switching transistors Q5 / Q6 and Q7 / Q8 on the secondary side are connected in reverse series to form two sets of bidirectional switching units, enabling bidirectional blocking and conduction control of the AC side voltage.

[0060] like Figure 3 The figure shows a typical driving timing waveform in this embodiment using extended phase-shifted (EPS) modulation. In the primary-side full-bridge configuration, the upper and lower switches (e.g., Q1 and Q3, Q2 and Q4) of the same bridge arm are turned on complementaryly with a 50% duty cycle; the secondary-side driving logic switches according to the polarity of the AC voltage. When u ac When u > 0, Q5 and Q7 conduct complementary high-frequency signals, while Q6 and Q8 remain normally on; conversely, when u ac When the frequency is less than 0, Q6 and Q8 conduct complementary high-frequency signals, while Q5 and Q7 remain normally on.

[0061] In the modulation strategy of this embodiment, each phase shift variable is defined as follows:

[0062] D1 is defined as the proportion of the time during which the drive signal of Q1 leads the drive signal of Q4 within the switching cycle, and D2 is defined as the proportion of the time during which the fundamental voltage of the primary side of the transformer leads the fundamental voltage of the secondary side within the switching cycle. Furthermore, to prevent bridge arm shoot-through, a dead time is set between the drive signals of all complementary conducting switches.

[0063] It should be understood that although this embodiment uses a "primary-side full-bridge - secondary-side half-bridge" structure as an example, the control method proposed in this invention is also applicable to primary-side full-bridge - secondary-side full-bridge or primary-side half-bridge - secondary-side full-bridge structures. As long as the side of the converter to which extended phase-shift modulation (EPS) is applied has full-bridge topology capability, it is covered within the protection scope of this invention.

[0064] In this embodiment, maximizing the ZVS range is the optimization objective. Specifically, based on the power transfer model of the dual active bridge converter and setting the transformer current expression when the switching transistor is turned on to zero, the analytical expression for the theoretically optimal phase shift angle combination is obtained as follows:

[0065] ;

[0066] ;

[0067] In the formula, m==|u ac | / (nu dc ) represents voltage gain, and M represents power transfer ratio. P N As the reference transmission power, P ac For AC side transmission power, .

[0068] Furthermore, when in light-load inverter mode, the switching frequency f is actively adjusted. s To force the outward phase shift angle D2 to remain above the ZVS threshold, and in conjunction with the EPS power transfer equation, the adjusted switching frequency f s_opt The expression is:

[0069] .

[0070] like Figure 4 The figure shown is a curve of the switching frequency changing with the transmission power under light load frequency conversion mode in an embodiment of the present invention.

[0071] It should be noted that, when using the light-load frequency conversion method proposed in this embodiment and when not using the light-load frequency conversion method proposed in this embodiment, respectively, under a light-load condition of 100W, the ZVS range is as follows: Figure 5 As shown, it can be seen that the external phase shift angle proposed in the embodiments of the present invention is greater than 0 within one AC cycle, and all operate under extended phase shift modulation, ensuring that the converter still has a large ZVS range and efficiency under light load.

[0072] Furthermore, in order to accurately compensate for the voltage distortion caused by the dead zone, it is necessary to accurately know the inductor current values ​​of the primary and secondary switches at the instant of turn-off (i.e., the commutation moment). The leakage inductance current has the symmetry of an odd harmonic function, and is determined by both the leakage inductance voltage and the initial state current. Therefore, the expressions for the instantaneous turn-off currents of the primary and secondary switches can be obtained as follows:

[0073] ;

[0074] Furthermore, merely satisfying the current polarity is insufficient to achieve ZVS; if the current is not large enough, partial soft switching may occur. Therefore, it is necessary to linearize the compensation value. In the linear compensation method, a linear coefficient K is added. COMP The expression is:

[0075] ;

[0076] In the formula, I ZVS It is the current required to achieve full ZVS, I off This is the turn-off current of the primary and secondary switching transistors.

[0077] Furthermore, since the junction capacitance Coss of the primary and secondary switching transistors are different, therefore I ZVS It's also different, in order to be in the dead time T dead The currents required for ZVS on the primary and secondary sides to completely remove the charge from the junction capacitance of the switching transistor are as follows:

[0078] ;

[0079] ;

[0080] In the formula, C oss_pri and C oss_sec T represents the junction capacitance of the primary and secondary switching transistors, respectively, taken from the typical values ​​in the switching transistor datasheet. dead_pri and T dead_pri These are the dead times of the primary and secondary switching transistors, respectively.

[0081] Furthermore, the calculation of the dead zone compensation correction includes the following steps:

[0082] S1. Obtain the dead time T of the primary and secondary switching transistors. dead And according to the current switching frequency f s Calculate the dead time duty cycle D dead =T dead ×f s

[0083] S2. For the primary-side switching transistor, the minimum current required to achieve ZVS is I. zvs_pri If Ioff_pri > -I zvs_pri If so, it is determined to be a hard switch, and the final expression for the inner and outer phase shift angles is:

[0084] ;

[0085] S3. For the secondary-side switch, the minimum current required to achieve ZVS is I. zvs_sec I off_sec zvs_sec If so, it is determined to be a hard switch, and the final expression for the inner and outer phase shift angles is:

[0086] ;

[0087] Furthermore, the method also includes a closed-loop feedback adjustment step: acquiring the real-time value of the output current or voltage and comparing it with a reference value, generating a closed-loop fine-tuning amount ΔD through a proportional-integral (PI) or proportional-resonant (PR) controller, and superimposing the closed-loop fine-tuning amount onto the outward phase angle after dead-zone compensation correction:

[0088] .

[0089] It should be noted that phase-shift control was performed at high frequencies (switching frequency 100kHz, dead time 200ns) using the dead-time compensation method proposed in this embodiment and without the proposed dead-time compensation method. The results are as follows: Figure 6 As shown in the figure, it can be seen that the power quality is significantly improved after the dead zone compensation method proposed in the embodiments of the present invention is used for control.

[0090] The above description of the embodiments is provided to enable those skilled in the art to understand and apply the present invention. Those skilled in the art can readily make various modifications to the above embodiments and apply the general principles described herein to other embodiments without creative effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made to the present invention by those skilled in the art based on the disclosure thereof should be within the scope of protection of the present invention.​

Claims

1. A control method for a single-stage isolated inverter based on frequency conversion and extended phase-shift modulation, characterized in that, Includes the following steps: S1. Obtain the converter operating parameters, including the sampled input voltage u. dc Output voltage u ac Output current i ac Output current reference value i ref Transformer turns ratio n and transformer leakage inductance L k ; S2. Calculate the real-time transmission power requirement P of the converter based on the converter operating parameters. cal and compare it with the preset power threshold P set The operating modes of the converter are determined by comparison; the operating modes include heavy-load constant frequency mode and light-load variable frequency mode. S3. Based on the determined operating mode, calculate the current switching frequency f. s Theoretical internal phase shift angle D 1_cal And the theoretical outward phase angle D 2_cal ; If in heavy-load constant frequency mode, the switching frequency f s Set to the rated frequency, and calculate D based on the extended phase-shift modulation strategy. 1_cal and D 2_cal ; If in light-load inverter mode, adjust the switching frequency f according to the soft-switching zero-voltage turn-on boundary condition. s And based on the adjusted switching frequency, D is recalculated to meet the power requirements. 1_cal and D 2_cal ; S4. Based on f determined in step S3 s D 1_cal and D 2_cal The instantaneous values ​​of the turn-off current of the primary-side switch and the secondary-side switch are predicted using an analytical model. S5. Determine the current switching state based on the polarity of the instantaneous turn-off current value, calculate the dead-zone compensation correction, and correct the theoretical phase shift angle to obtain the compensated phase shift angle D. 1_comp and D 2_comp Finally, based on the phase shift angle D 1_comp and D 2_comp Generate driving signals.

2. The single-stage isolation inverter control method based on frequency conversion and extended phase-shift modulation according to claim 1, characterized in that, The preset power threshold P set It is set as: the minimum critical power at which the converter can maintain zero-voltage turn-on in heavy-load constant-frequency mode, or the inflection point power at which the converter efficiency curve decays as the power decreases.

3. The single-stage isolation inverter control method based on frequency conversion and extended phase-shift modulation according to claim 1, characterized in that, The theoretical inner phase shift angle D under the heavy-load constant frequency mode 1_cal And the theoretical outward phase angle D 2_cal The expression is: ； ； In the formula, m = |u ac | / (nu dc ) represents voltage gain, and M represents power transfer ratio. P N As the reference transmission power, P ac For AC side transmission power, .

4. The single-stage isolation inverter control method based on frequency conversion and extended phase-shift modulation according to claim 1, characterized in that, When in light-load inverter mode, the adjusted switching frequency f s_opt The expression is: ； In the formula, m = |u ac | / (nu dc () represents the voltage gain.

5. The single-stage isolation inverter control method based on frequency conversion and extended phase-shift modulation according to claim 1, characterized in that, The expressions for the instantaneous values ​​of the turn-off current of the primary-side switch and the secondary-side switch are: 。 6. The single-stage isolation inverter control method based on frequency conversion and extended phase-shift modulation according to claim 1, characterized in that, When calculating the dead zone compensation correction, a linear compensation coefficient K is introduced. COMP Its expression is: ； In the formula, I ZVS It is the current required to achieve zero-voltage turn-on, I off This is the turn-off current of the primary and secondary switching transistors.

7. The single-stage isolation inverter control method based on frequency conversion and extended phase-shift modulation according to claim 1, characterized in that, The calculation of the dead zone compensation correction includes the following steps: S1. Obtain the dead time T of the primary and secondary switching transistors. dead And according to the current switching frequency f s Calculate the dead time duty cycle D dead =T dead ×f s ; S2. For the primary-side switching transistor, the minimum current required to achieve zero-voltage turn-on is I. zvs_pri If I off_pri > -I zvs_pri If so, it is determined to be a hard switch, and the expression for the compensated inner and outer phase shift angles is: ； S3. For the secondary-side switching transistor, the minimum current required to achieve zero-voltage turn-on is I. zvs_sec If I off_sec zvs_sec If so, it is determined to be a hard switch, and the final expression for the inner and outer phase shift angles is:​ 。 8. The single-stage isolation inverter control method based on frequency conversion and extended phase-shift modulation according to claim 1, characterized in that, The method further includes a closed-loop feedback adjustment step: the output current is collected and compared with a reference value, and a closed-loop fine-tuning amount ΔD is generated through a proportional-integral or proportional-resonant controller. The closed-loop fine-tuning amount is then superimposed on the final outward phase shift angle after dead-zone compensation correction. 。 9. The single-stage isolation inverter control method based on frequency conversion and extended phase-shift modulation as described in claim 1, characterized in that, The topology of the single-stage isolated inverter includes at least one full-bridge structure, specifically configured as a full-bridge-full-bridge structure, a full-bridge-half-bridge structure, or a half-bridge-full-bridge structure; wherein, when a full-bridge-half-bridge structure or a half-bridge-full-bridge structure is adopted, the extended phase-shift modulation strategy is applied only to the full-bridge side of the converter.

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