A light load control method and device for a symmetric LCC type bidirectional wireless power transmission system oriented to battery energy storage

Abstract

This invention discloses a light-load control method and apparatus for a symmetrical LCC-type bidirectional wireless power transfer system for battery energy storage, relating to the field of wireless power transfer technology. By using the DC-side parameters of the symmetrical LCC-type bidirectional wireless power transfer system, the proportion of reactive power in apparent power and the light-load degree of the system's current operating condition relative to rated power are determined, thereby determining the light-load reactive power factor. The light-load operating condition is identified based on the upper and lower thresholds of the light-load reactive power factor. The minimum external phase shift angle and the constraint relationship between the reconfiguration and the internal phase shift angle of the primary and secondary full-bridge components are calculated to satisfy the zero-voltage switching requirement of the symmetrical LCC-type bidirectional wireless power transfer system under light-load conditions. This achieves adaptive power control under light-load conditions, suppressing reactive circulating current while realizing zero-voltage switching and improving the operating efficiency of the charging system.

Description

Technical Field

[0001] This invention relates to the field of wireless power transfer technology, and in particular to a light-load control method and apparatus for a symmetrical LCC-type bidirectional wireless power transfer system for battery energy storage. Background Technology

[0002] Compared to traditional wired charging, wireless power transfer systems achieve energy transfer through magnetic coupling or electromagnetic induction, effectively improving system safety and reliability. In wireless power transfer technology, symmetrical LCC wireless power transfer systems have become an important research direction in the fields of electric vehicles and energy storage due to their excellent resonant characteristics and bidirectional energy transfer capabilities. Currently, symmetrical LCC wireless power transfer systems generally adopt three-phase or multi-phase shift control methods, adjusting the phase shift angle of the primary and secondary full-bridge to regulate the transmitted power. However, existing symmetrical LCC bidirectional wireless power transfer systems rely solely on empirical classification based on output power or load resistance range for determining light-load conditions, lacking quantitative criteria for system power characteristics. Parameter allocation under light load lacks clear constraints. Under light load or weak coupling conditions, due to the system gain deviating from the design point, severe reactive circulating currents often occur, leading to a surge in resonant circuit losses, a decrease in battery system charging efficiency, and difficulty in maintaining zero-voltage switching (ZVS) conditions for the switching transistors across the entire range, severely limiting the system's engineering practicality. Summary of the Invention

[0003] This invention provides a light-load control method and apparatus for a symmetrical LCC-type bidirectional wireless power transfer system for battery energy storage, which solves the technical problem that existing symmetrical LCC-type bidirectional wireless power transfer systems lack quantitative criteria for determining the system power characteristics in light-load state determination, making it difficult to simultaneously achieve efficiency improvement and zero-voltage switching.

[0004] In view of this, the first aspect of the present invention provides a light-load control method for a symmetrical LCC-type bidirectional wireless power transfer system for battery energy storage, comprising:

[0005] Acquire DC parameters of a symmetrical LCC type bidirectional wireless power transfer system;

[0006] The proportion of reactive power in apparent power and the degree of light load of the current operating condition of the symmetrical LCC type bidirectional wireless power transmission system relative to the rated power are determined based on the DC parameters.

[0007] Based on the stated proportion and the light load degree, a light load reactive power factor is constructed, and an upper and lower threshold value for the light load reactive power factor is determined.

[0008] Based on the DC parameters, the minimum external phase shift angle and the constraint relationship on the internal phase shift angle of the primary and secondary full-bridge are determined and reconstructed to satisfy the zero-voltage switching of the symmetrical LCC type bidirectional wireless power transfer system.

[0009] Under light load conditions at the end of charging of the symmetrical LCC bidirectional wireless power transfer system, the power adaptive adjustment of the symmetrical LCC bidirectional wireless power transfer system is performed according to the constraints of the DC parameters, the minimum outward phase shift angle, and the inward phase shift angle of the primary and secondary full-bridge.

[0010] Optionally, the DC parameters include the DC bus voltage on the primary side, the DC bus current on the primary side, the DC bus voltage on the secondary side, the inner phase shift angle of the full bridge on the primary side, the inner phase shift angle of the full bridge on the secondary side, and the output current of the primary side bridge arm.

[0011] Optionally, the proportion of reactive power in apparent power is:

[0012] ;

[0013] ;

[0014] in, Q represents the proportion of reactive power in apparent power. For apparent power, C and D are both intermediate variables. The phase angle is the external shift of the original secondary side. This is the inward phase angle of the entire bridge on the original side. The inner phase shift angle of the entire bridge on the secondary side. This is the DC bus voltage on the primary side. This is the DC bus voltage on the secondary side. For primary-side compensation inductance, For secondary-side compensation inductance, The mutual inductance is between the primary and secondary sides.

[0015] Optionally, the current operating condition of the symmetrical LCC type bidirectional wireless power transfer system is light-load relative to its rated power as follows:

[0016] ;

[0017] in, P represents the light load condition of the symmetrical LCC type bidirectional wireless power transfer system relative to its rated power. This is the rated power.

[0018] Optionally, the light-load reactive power factor is:

[0019] ;

[0020] Where K is the light-load reactive factor.

[0021] Optionally, the minimum outward phase shift angle required for the symmetrical LCC type bidirectional wireless power transfer system to achieve zero-voltage switching is:

[0022] ;

[0023] in, To meet the minimum outward phase shift angle required for zero-voltage switching in the symmetrical LCC type bidirectional wireless power transfer system, This is the primary-side full-bridge output voltage. This is the output voltage of the secondary-side full-bridge. This refers to the minimum bridge arm commutation current amplitude required for the switching transistor to complete junction capacitance charging and discharging and achieve zero-voltage turn-on under given device parameters and dead time conditions. For primary-side compensation inductance, For secondary-side compensation inductance, For the mutual inductance of the primary and secondary sides, This is the system angular frequency.

[0024] Optionally, the constraint relationship of the reconstructed primary and secondary side full bridge internal phase shift angle is as follows:

[0025] ;

[0026] in, This is the inward phase angle of the entire bridge on the original side. The inner phase shift angle of the entire bridge on the secondary side. For constraint functions, This is the DC bus voltage on the primary side. This is the DC bus voltage on the secondary side. For primary-side compensation inductance, For secondary-side compensation inductance, The rated transmission current of the system, For the primary side bridge arm output current, For the primary coil, For the secondary coil, The mutual inductance is between the primary and secondary sides.

[0027] Optionally, under light load conditions at the end of charging in the symmetrical LCC bidirectional wireless power transfer system, power adaptive adjustment is performed on the symmetrical LCC bidirectional wireless power transfer system based on the constraints of the DC parameters, the minimum outward phase shift angle, and the inward phase shift angle of the primary and secondary full-bridge circuits, including:

[0028] Under light load conditions at the end of charging of the symmetrical LCC bidirectional wireless power transmission system, the actual active power of the system at the previous moment is calculated based on the real-time DC parameters. Based on the actual active power of the system at the current moment and the specific light load demand under the rated 1kW standard set by the system, the power deviation of the current control cycle is calculated.

[0029] The incremental PI control algorithm is invoked to process the power deviation of the current control cycle, and the inner phase shift angle of the original side full bridge in the current control cycle is updated.

[0030] Update the inner phase angle of the secondary side full bridge based on the updated inner phase angle of the primary side full bridge in the current control cycle;

[0031] Based on the minimum outward phase shift angle, the inward phase shift angle of the primary side full bridge in the current control cycle, and the inward phase shift angle of the secondary side full bridge, the phase register and the comparator register corresponding to the outward phase shift angle of the primary and secondary sides, the inward phase shift angle of the primary side full bridge in the current control cycle, and the inward phase shift angle of the secondary side full bridge are updated to generate multiple PWM signals with dead time to drive the switching transistors of the primary side full bridge and the secondary side full bridge respectively, thereby performing power adaptive adjustment of the symmetrical LCC type bidirectional wireless power transfer system.

[0032] Optionally, the update formula for the inner phase shift angle of the original side full bridge in the current control cycle is:

[0033] ;

[0034] ;

[0035] in, This represents the inward phase shift angle of the original side of the full bridge during the current control cycle. This represents the inward phase shift angle of the original side of the full bridge in the previous control cycle. This represents the deviation of the inner phase shift angle of the original side full bridge during the current control cycle. The power deviation for the current control cycle. This represents the power deviation from the previous control cycle. This is the proportionality coefficient. is the integral coefficient.

[0036] Optionally, the update formula for the inner phase angle of the secondary side full bridge is:

[0037] ;

[0038] ;

[0039] ;

[0040] in, This represents the inner phase shift angle of the secondary side of the full bridge during the current control cycle. For constraint functions, This is the DC bus voltage on the primary side. This is the DC bus voltage on the secondary side. For primary-side compensation inductance, For secondary-side compensation inductance, The rated transmission current of the system, For the primary side bridge arm output current, For the primary coil, For the secondary coil, The mutual inductance is between the primary and secondary sides.

[0041] A second aspect of the present invention provides a light-load control device for a symmetrical LCC-type bidirectional wireless power transfer system for battery energy storage, comprising:

[0042] The acquisition module is used to acquire DC parameters of a symmetrical LCC type bidirectional wireless power transfer system;

[0043] The calculation module is used to determine the proportion of reactive power in apparent power and the degree of light load of the current operating condition of the symmetrical LCC type bidirectional wireless power transmission system relative to the rated power based on the DC parameters.

[0044] The light-load reactive power factor construction module is used to construct the light-load reactive power factor according to the proportion and the light-load degree, and to determine the upper limit threshold and lower limit threshold of the light-load reactive power factor.

[0045] The constraint module is used to reconstruct the constraint relationship between the minimum external phase shift angle that satisfies the zero-voltage switching of the symmetrical LCC type bidirectional wireless power transfer system and the internal phase shift angle of the primary and secondary full-bridge based on the DC parameters.

[0046] An adaptive control module is used to adaptively adjust the power of the symmetrical LCC bidirectional wireless power transfer system under light load conditions at the end of charging, based on the constraints of the DC parameters, the minimum outward phase shift angle, and the inward phase shift angle of the primary and secondary full-bridge.

[0047] As can be seen from the above technical solutions, the light-load control method for a symmetrical LCC-type bidirectional wireless power transfer system for battery energy storage provided by the present invention has the following advantages:

[0048] The present invention provides a light-load control method for a symmetrical LCC-type bidirectional wireless power transfer system for battery energy storage. By using the DC-side parameters of the symmetrical LCC-type bidirectional wireless power transfer system, the method determines the proportion of reactive power in apparent power and the degree of light load relative to the rated power of the current system operation. This determines the light-load reactive power factor, and the method identifies the light-load operating condition based on the upper and lower thresholds of the light-load reactive power factor, achieving quantitative identification of the light-load operating condition. The method calculates the minimum outward phase shift angle and the constraint relationship between the reconfiguration and the inward phase shift angle of the primary and secondary full-bridge components under light-load conditions to achieve zero-voltage switching in the symmetrical LCC-type bidirectional wireless power transfer system. This enables adaptive power control under light-load conditions, suppressing reactive circulating current while achieving zero-voltage switching and improving the operating efficiency of the charging system. This method solves the technical problem of existing symmetrical LCC-type bidirectional wireless power transfer systems lacking quantitative criteria for determining the system's power characteristics during light-load state assessment, making it difficult to simultaneously achieve efficiency improvement and zero-voltage switching.

[0049] Meanwhile, the light-load control method for a symmetrical LCC-type bidirectional wireless power transfer system for battery energy storage provided by this invention determines the minimum external phase shift angle that satisfies zero-voltage switching based on soft-switching boundary constraints under light-load conditions, thus avoiding the technical problems of excessive parameter freedom and difficulty in suppressing light-load circulating current in traditional phase-shift control methods. Attached Figure Description

[0050] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0051] Figure 1 This is a flowchart illustrating a light-load control method for a symmetrical LCC-type bidirectional wireless power transfer system for battery energy storage provided in an embodiment of the present invention.

[0052] Figure 2 This is a circuit topology diagram of the symmetrical LCC type bidirectional wireless power transfer system provided in the embodiments of the present invention;

[0053] Figure 3 This is a schematic diagram showing the relationship between the inner and outer phase shift angles of the symmetrical LCC type bidirectional wireless power transfer system provided in this embodiment of the invention;

[0054] Figure 4 for Figure 2 The equivalent circuit schematic diagram;

[0055] Figure 5 This is a partition diagram of the resonant current corresponding to the light load reactive factor provided in the embodiments of the present invention;

[0056] Figure 6 This is a comparison of the efficiency of the light-load control method of the symmetrical LCC bidirectional wireless power transfer system for battery energy storage provided in this embodiment of the invention with that of the traditional method.

[0057] Figure 7 This is a schematic diagram of a light-load control device for a symmetrical LCC-type bidirectional wireless power transfer system for battery energy storage, provided in an embodiment of the present invention. Detailed Implementation

[0058] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and 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.

[0059] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the embodiments set forth herein; rather, they are provided so that this application will be thorough and complete, and will fully convey the concept of the exemplary embodiments to those skilled in the art. The same reference numerals in the drawings denote the same or similar parts, and therefore repeated descriptions of them will be omitted.

[0060] The described features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. Numerous specific details are provided in the following description to give a full understanding of embodiments of this disclosure. However, those skilled in the art will recognize that the technical solutions of this disclosure can be practiced without one or more of these specific details, or other methods, components, materials, devices, etc. In these cases, well-known structures, methods, devices, implementations, materials, or operations will not be shown or described in detail.

[0061] Furthermore, the terms “comprising” and “having”, and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the steps or units listed, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to such process, method, product, or apparatus.

[0062] The technical solutions of this application will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0063] For easier understanding, please refer to Figure 1 This invention provides an embodiment of a light-load control method for a symmetrical LCC-type bidirectional wireless power transfer system for battery energy storage, comprising:

[0064] Step 101: Collect DC parameters of the symmetrical LCC type bidirectional wireless power transfer system.

[0065] It should be noted that the circuit topology of the symmetrical LCC type bidirectional wireless power transfer system is as follows: Figure 2 As shown, the system includes a primary-side full-bridge inverter circuit, a secondary-side full-bridge rectifier circuit, a primary-side LCC resonant compensation network, a secondary-side LCC resonant compensation network, a load and filter circuit, and a wireless coupling coil for energy coupling. The primary-side full-bridge inverter circuit consists of four MOSFET switches. , , and Composition, the first bridge arm consists of a switching transistor and switching transistor Composed of, the second bridge arm consists of a switching transistor and switching transistor Composition. Switching transistor and switching transistor For the forearm, switching transistor and switching transistor A lag arm is formed; by introducing a phase shift angle to control the MOSFET turn-on time of the leading and lagging arms, phase shift control of the four switching transistors is achieved. The primary-side compensation network adopts an LCC-type resonant compensation topology, including the primary-side coil. Primary-side compensating inductor Primary-side compensation capacitor and Primary coil The upper end passes through the primary-side compensating inductor Primary-side series compensation capacitor After the series branch is connected to the positive end of the midpoint of the bridge arm, the primary coil... The lower end is connected to the negative terminal of the midpoint of the bridge arm; wherein, a compensation capacitor is connected in parallel on the primary side. Primary-side series compensation capacitor and primary-side compensation inductor They are connected in parallel to form a T-shaped structure.

[0066] The secondary-side full-bridge rectifier circuit adopts a symmetrical structure with the primary side, consisting of four MOSFET switching transistors. , , and Composition. The first bridge arm consists of a switching transistor. and switching transistor Composed of, the second bridge arm consists of a switching transistor and switching transistor Composition. Among them, the switching transistor... and switching transistor For the forearm, switching transistor and switching transistor A lag arm is formed; similarly, by introducing a phase shift angle to control the sequential turn-on time of the MOSFETs in the leading and lagging arms, phase shift control of the four switching transistors is achieved. The secondary-side compensation network includes a secondary-side coil. Secondary side compensating inductor Secondary side compensation capacitor and Secondary coil The upper end passes through the secondary compensation inductor Secondary-side series compensation capacitor After the series branch, it is connected to the positive terminal of the bridge arm midpoint, and the secondary coil. The lower end is connected to the negative terminal of the bridge arm midpoint; wherein, a compensation capacitor is connected in parallel on the secondary side. Secondary-side series compensation capacitor and secondary side compensation inductor The parallel connection forms a T-shaped structure; the symmetrical LCC topology enables the system to achieve bidirectional energy transfer under different phase-shift control methods.

[0067] The relationship between the inner and outer phase shift angles of a symmetrical LCC type bidirectional wireless power transfer system is as follows: Figure 3 As shown, Figure 3 In this context, the voltage at the midpoint of the leading arm on the primary side is used as the time reference. The delay angle of the voltage at the midpoint of the lagging arm on the primary side relative to this reference is defined as the inward phase shift angle of the primary side. The difference between the midpoint voltages of the two bridge arms is used to obtain the primary-side full-bridge output voltage. Similarly, for the secondary side, taking the midpoint voltage of the leading arm of the secondary side as a reference, the delay angle of the midpoint voltage of the lagging arm of the secondary side relative to it is defined as the internal phase shift angle of the secondary side. The difference between the two is the secondary-side full-bridge output voltage. Then, using the primary-side full-bridge output voltage... For reference, the secondary-side full-bridge output voltage relatively The phase shift is defined as the phase shift angle of the primary and secondary sides. .

[0068] The system operates at its resonant frequency f, and its corresponding angular frequency is . Given the high frequency selectivity of the LCC resonant network, the energy characteristics observed on the DC side are mainly determined by the fundamental frequency. The circuit is analyzed using the fundamental frequency analysis method, and the error is within the engineering allowable range. Furthermore, the residual error can be further eliminated through subsequent closed-loop adjustment. During the operation of the symmetrical LCC bidirectional wireless power transfer system, voltage and current sensors are installed on both the primary and secondary sides to sample the DC bus voltage on the primary side. and DC bus current and secondary side sampling DC bus voltage .

[0069] based on Figure 4 Based on the equivalent circuit principle, the frequency domain equations of the primary and secondary resonant networks can be established, and the relationship between the fundamental voltage, branch current, and mutual inductance reflection can be further derived. In a symmetrical LCC bidirectional wireless power transfer system, the output voltages of both the primary and secondary full-bridge circuits are phase-shifted square waves. Under the fundamental approximation, their fundamental voltages are expressed as:

[0070] ;

[0071] ;

[0072] in, This is the primary-side full-bridge output voltage. This is the output voltage of the secondary-side full-bridge. This is the DC bus voltage on the primary side. This is the DC bus voltage on the secondary side. This is the inward phase angle of the entire bridge on the original side. This is the inward phase angle of the entire bridge on the secondary side.

[0073] Taking the primary-side fundamental voltage as the reference phasor, the secondary-side fundamental voltage has an outward phase shift relative to the primary side. Let the primary-side full-bridge output voltage be... As the reference phasor, the secondary-side full-bridge output voltage Introducing an outward phase angle relative to the primary side :

[0074] .

[0075] Using the fundamental frequency analysis method at the resonant frequency, neglecting the switching transistor losses and parasitic resistances, and combining the KCL and KVL relationships to establish the frequency domain matrix equations of the primary and secondary circuits, we can simplify them into the following set of linear equations:

[0076] ;

[0077] Where A is a vector representing the network parameters and coupling relationship, x is a state vector, and b is the external excitation vector in the system frequency domain equation.

[0078] The state vector x is defined as:

[0079] ;

[0080] in, The fundamental current of the primary side bridge arm. The voltage at the node of the primary parallel branch. This is the primary-side series resonant branch current. For the fundamental current of the secondary arm, For the secondary parallel branch node voltage, This refers to the current in the secondary-side series resonant branch.

[0081] Vector A is defined as:

[0082] ;

[0083] in, For the coefficient submatrix of the primary-side resonant network, For the coefficient submatrix of the secondary resonant network, and This is the submatrix of the mutual inductance coupling term.

[0084] in:

[0085] ;

[0086] The external excitation vector b in the system frequency domain equations is defined as:

[0087] .

[0088] This allows us to obtain the analytical relationship between the fundamental current of the primary and secondary side arms, the node voltage, and the current of the series resonant branch.

[0089] The symmetrical LCC topology satisfies the compensation network resonance condition at the resonance point:

[0090] ;

[0091] .

[0092] Substituting the formula for the resonance condition of the compensation network into the above... From the formula, we obtain the mutual inductance and reflection relationship:

[0093] , .

[0094] Therefore, the expression for the current in the series resonant branch of the primary and secondary sides can be obtained as follows:

[0095] , .

[0096] Therefore, the primary arm output current under the fundamental frequency analysis model can be obtained as follows:

[0097] ;

[0098] The first term is the self-generated reactive power component determined by the primary side network, and the second term is the mutual inductance component reflected back from the secondary side to the primary side.

[0099] According to Euler's formula, we have:

[0100] ;

[0101] Complex power is defined as:

[0102] ;

[0103] Where P is active power and Q is reactive power.

[0104] Substituting the primary-side bridge arm output current formula and the secondary-side full-bridge output voltage formula under the fundamental analysis model into the complex power formula, we can obtain:

[0105] ;

[0106] By separating the real and imaginary parts, we can obtain the active power and reactive power:

[0107] ;

[0108] ;

[0109] Among them, active power is mainly composed of mutual inductance. DC bus voltage on the primary side DC bus voltage on the secondary side The inward phase angle of the entire bridge on the original side The inner phase angle of the entire bridge on the secondary side Phase angle shifted outward from the original secondary side The reactive power is jointly determined. In addition to being affected by the mutual inductance component, the reactive power also includes the inherent reactive power term generated by the primary voltage excitation.

[0110] Apparent power characterization of the system for:

[0111] .

[0112] To avoid excessively long expansions of the expression during subsequent criterion construction, intermediate variables C and D are introduced:

[0113] ;

[0114] We can obtain:

[0115] .

[0116] Step 102: Determine the proportion of reactive power in apparent power and the light load degree of the current operating condition of the symmetrical LCC bidirectional wireless power transmission system relative to the rated power based on the DC parameters of the current control cycle.

[0117] It should be noted that the proportion of reactive power in apparent power is:

[0118] ;

[0119] ;

[0120] in, This represents the proportion of reactive power in apparent power.

[0121] The current operating condition of the symmetrical LCC type bidirectional wireless power transfer system, relative to its rated power, is as follows:

[0122] ;

[0123] in, The current operating condition of the symmetrical LCC type bidirectional wireless power transfer system is a light load relative to its rated power. This is the rated power.

[0124] Step 103: Construct a light-load reactive power factor based on the current control cycle percentage and the light-load degree of the current control cycle, and determine the upper and lower threshold values ​​of the light-load reactive power factor.

[0125] It should be noted that in symmetrical LCC bidirectional wireless power transfer systems operating at high frequencies, AC side parameters are difficult to obtain stably. Traditional impedance identification methods fail under light loads due to the shunting effect of resonant elements, making direct and accurate measurement of AC side parameters difficult and costly. This invention constructs a light-load reactive power factor based on the current control cycle percentage and the light-load level of the current control cycle:

[0126] ;

[0127] Where K is the light-load reactive factor.

[0128] The light-load reactive power factor K increases with the increase of reactive power ratio and the decrease of transmission power, and is used to trigger the light-load optimization mode.

[0129] To verify the effectiveness of the light-load reactive power factor K in characterizing the degree of reactive circulating current in the system, the instantaneous current of the primary-side series resonant branch was collected. Its effective value is defined as By establishing the light-load reactive power factor K and The corresponding relationship shows that the light-load reactive power factor K can effectively reflect the changing trend of the system's reactive power ratio. When the system is lightly loaded, the effective energy transfer is weakened, but the primary resonant branch still maintains a large AC current, the circulating current component will be more prominent. The effective value of the resonant branch current often increases accordingly. The higher the value, the greater the proportion of reactive power and the lower the efficiency of the system. (See also...) Figure 5 , Figure 5 This is a partitioned map of the light-load reactive power factor K corresponding to the resonant current, achieved by setting an upper threshold for the light-load reactive power factor. With lower threshold Implement dual-threshold hysteresis comparison to switch between light-load optimization modes:

[0130] when At this time, the system enters light-load optimization mode;

[0131] when At this time, the system exits the light load optimization mode;

[0132] when At this time, the system maintains the current operating mode.

[0133] In this embodiment of the invention, based on the experimental results of the 1kW prototype and Figure 5 The resonant current corresponds to the partition diagram of the light-load reactive factor K, and the preferred value is... , To balance the sensitivity of light-load recognition and the stability of mode switching.

[0134] Step 104: Based on the DC parameters of the current control cycle, determine and reconstruct the minimum external phase shift angle and the constraint relationship of the internal phase shift angle of the primary and secondary full-bridge to achieve zero-voltage switching in the symmetrical LCC bidirectional wireless power transfer system that meets the requirements of the current control cycle.

[0135] It should be noted that in the light-load optimization mode, the definition is... This refers to the minimum bridge arm commutation current amplitude required for the switching transistor to complete junction capacitance charging and discharging and achieve zero-voltage turn-on under given device parameters and dead time conditions. When the fundamental current amplitude of the primary-side bridge arm meets... At this point, the system is considered to satisfy the zero-voltage switching condition. Definition To meet the minimum external phase shift angle required for the system to achieve zero-voltage switching, the system first determines the minimum external phase shift angle based on the soft-switching boundary constraints. Then, the constraint relationship of the phase shift angle of the original secondary side full bridge is reconstructed.

[0136] According to the formula and The fundamental current amplitude of the primary side bridge arm satisfies:

[0137] ;

[0138] From the above formula, it can be seen that when the system parameters are given, With the outward shift of the phase angle It increases with the increase of, therefore when When the system reaches the zero-voltage switching boundary, the outward phase shift angle obtained by inverse solving of this boundary condition is defined as the minimum outward phase shift angle that satisfies the zero-voltage switching condition. .when When the system satisfies the soft-switching boundary requirements, the inverse solution yields... :

[0139] .

[0140] Introducing constraint functions By product-coupling the leakage inductance level and the proportion of soft-switching current, accurate compensation for weakly coupled light-load conditions is achieved, ensuring that the constraint relationship of the phase shift angle between the primary and secondary sides is satisfied:

[0141] ;

[0142] in, This is the system's rated transmission current.

[0143] Step 105: Under the light load condition of the symmetrical LCC bidirectional wireless power transfer system in the current control cycle, based on the constraints of the DC parameters of the current control cycle, the minimum outward phase shift angle of the current control cycle, and the inward phase shift angle of the primary and secondary full-bridge in the current control cycle, perform adaptive power adjustment on the symmetrical LCC bidirectional wireless power transfer system in the current control cycle.

[0144] It should be noted that in the light-load optimization mode, the system determines the outer phase shift angle. Then, the DSP controller will execute power point tracking closed-loop control in each PWM control cycle. Specifically, this includes the following steps:

[0145] S1. Under light load conditions of a symmetrical LCC type bidirectional wireless power transmission system, calculate the actual active power of the system at the previous moment based on the real-time DC parameters, and calculate the power deviation of the current control cycle based on the actual active power of the system at the current moment and the specific light load requirements under the rated 1kW standard of the system.

[0146] It should be noted that the DSP controller acquires the DC bus voltage on the primary side in real time via an analog-to-digital converter. DC bus voltage on the secondary side DC bus current on the primary side Calculate the actual active power of the system in the current period (i.e., at the current time k), that is... The specific light-load requirement under the system's rated 1kW standard is denoted as... It can calculate the power deviation of the current control cycle. : .

[0147] S2. Call the incremental PI control algorithm to process the power deviation of the current control cycle and update the inner phase shift angle of the original side full bridge in the current control cycle.

[0148] It should be noted that, in order to eliminate steady-state error and improve the dynamic response of the system, the DSP internally calls an incremental PI control algorithm to handle power deviation. The system will adjust the power deviation. The input to the PI controller is directly mapped to the primary side's internal phase shift angle. The adjustment amount. The discretized control equation is:

[0149] ;

[0150] in, This represents the deviation of the inner phase shift angle of the original side full bridge during the current control cycle. This is the proportionality coefficient. The integral coefficient is... This represents the power deviation from the previous control cycle.

[0151] Then, update the original side inward phase angle for the current cycle: ,in, This represents the inward phase shift angle of the original side of the full bridge during the current control cycle. This is the inward phase angle of the original side of the full bridge in the previous control cycle.

[0152] S3. Based on the updated phase shift angle of the primary side full bridge in the current control cycle, update the phase shift angle of the secondary side full bridge.

[0153] It should be noted that, after obtaining the updated primary side inward phase angle... Subsequently, to ensure the balance of energy flow and the fulfillment of the soft-switching condition, the DSP controller automatically calculates the corresponding secondary side inward phase shift angle based on the dimension reduction constraint function. :

[0154] ;

[0155] ;

[0156] ;

[0157] in, This is the inner phase shift angle of the secondary side of the full bridge during the current control cycle.

[0158] S4. Based on the minimum outward phase shift angle of the current control cycle, the inward phase shift angle of the primary side full bridge of the current control cycle, and the inward phase shift angle of the secondary side full bridge of the current control cycle, update the phase register and comparison register corresponding to the outward phase shift angle of the primary and secondary sides of the current control cycle, the inward phase shift angle of the primary side full bridge of the current control cycle, and the inward phase shift angle of the secondary side full bridge of the current control cycle. Generate multiple PWM signals with dead time to drive the switching transistors of the primary side full bridge and the secondary side full bridge respectively, and perform power adaptive adjustment of the symmetrical LCC bidirectional wireless power transfer system in the current control cycle.

[0159] The present invention provides a light-load control method for a symmetrical LCC-type bidirectional wireless power transfer system for battery energy storage. By using the DC-side parameters of the symmetrical LCC-type bidirectional wireless power transfer system, the method determines the proportion of reactive power in apparent power and the degree of light load relative to the rated power of the current system operation. This determines the light-load reactive power factor, and the method identifies the light-load operating condition based on the upper and lower thresholds of the light-load reactive power factor, achieving quantitative identification of the light-load operating condition. The method calculates the minimum outward phase shift angle and the constraint relationship between the reconfiguration and the inward phase shift angle of the primary and secondary full-bridge components under light-load conditions to achieve zero-voltage switching in the symmetrical LCC-type bidirectional wireless power transfer system. This enables adaptive power control under light-load conditions, suppressing reactive circulating current while achieving zero-voltage switching and improving the operating efficiency of the charging system. This method solves the technical problem of existing symmetrical LCC-type bidirectional wireless power transfer systems lacking quantitative criteria for determining the system's power characteristics during light-load state assessment, making it difficult to simultaneously achieve efficiency improvement and zero-voltage switching.

[0160] Meanwhile, the light-load control method for a symmetrical LCC-type bidirectional wireless power transfer system for battery energy storage provided by this invention determines the minimum external phase shift angle that satisfies zero-voltage switching based on soft-switching boundary constraints under light-load conditions, thus avoiding the technical problems of excessive parameter freedom and difficulty in suppressing light-load circulating current in traditional phase-shift control methods.

[0161] To verify the effectiveness of the light-load control method for a symmetrical LCC-type bidirectional wireless power transfer system for battery storage provided by this invention, a specific application example is provided in this embodiment: the system primary DC bus voltage. 200V, secondary DC bus voltage The voltage is 200V, and the rated transmission power is 1kW. Primary coil. and secondary coil All are set to 160μH. Regarding the compensation network parameter settings, the primary-side compensation inductance... and secondary side compensation inductor All capacitors are 35μH; primary-side series compensation capacitors series compensation capacitor with secondary side All capacitors are 22nF; primary side parallel compensation capacitors Parallel compensation capacitor with secondary side All parameters are set to 100nF. A simulation model of a symmetrical LCC wireless power transfer system is established under the above parameter conditions, and the phase-shift control process of the system under different light load conditions is analyzed. Please refer to [link / reference]. Figure 6 , Figure 6 The efficiency comparison results between the proposed method and the symmetrical three-phase-shift modulation strategy within the power range of 0-1000W are presented. Figure 6 It can be seen that the method proposed in this invention improves efficiency in the light load power range compared to the symmetrical three-phase shift modulation strategy.

[0162] For easier understanding, please refer to Figure 7 This invention provides an embodiment of a light-load control device for a symmetrical LCC-type bidirectional wireless power transfer system for battery energy storage, comprising:

[0163] The acquisition module is used to acquire DC parameters of a symmetrical LCC type bidirectional wireless power transfer system;

[0164] The calculation module is used to determine the proportion of reactive power in apparent power and the degree of light load of the current operating condition of the symmetrical LCC type bidirectional wireless power transmission system relative to the rated power based on the DC parameters.

[0165] The light-load reactive power factor construction module is used to construct the light-load reactive power factor according to the proportion and the light-load degree, and to determine the upper limit threshold and lower limit threshold of the light-load reactive power factor.

[0166] The constraint module is used to reconstruct the constraint relationship between the minimum external phase shift angle that satisfies the zero-voltage switching of the symmetrical LCC type bidirectional wireless power transfer system and the internal phase shift angle of the primary and secondary full-bridge based on the DC parameters.

[0167] An adaptive control module is used to adaptively adjust the power of the symmetrical LCC bidirectional wireless power transfer system under light load conditions at the end of charging, based on the constraints of the DC parameters, the minimum outward phase shift angle, and the inward phase shift angle of the primary and secondary full-bridge.

[0168] A light-load control device for a symmetrical LCC-type bidirectional wireless power transfer system for battery energy storage, characterized in that the device includes a processor and a memory:

[0169] The memory is used to store program code and transmit the program code to the processor;

[0170] The processor is used to execute any one of the light-load control methods for a symmetrical LCC type bidirectional wireless power transfer system for battery energy storage as described in the foregoing embodiments, according to the instructions in the program code.

[0171] This application also provides a computer-readable storage medium for storing program code that executes any one of the light-load control methods for a symmetrical LCC-type bidirectional wireless power transfer system for battery energy storage described in the foregoing embodiments.

[0172] This application also provides a computer program product including instructions that, when run on a computer, cause the computer to execute any one of the light-load control methods for a symmetrical LCC type bidirectional wireless power transfer system for battery energy storage described in the foregoing embodiments.

[0173] The light-load control device, equipment, computer-readable storage medium, and computer program product of the symmetrical LCC type bidirectional wireless power transfer system for battery energy storage provided in this invention are all used to execute the light-load control method of the symmetrical LCC type bidirectional wireless power transfer system for battery energy storage provided in this invention. Their principles and the technical effects achieved are the same as those of the light-load control method of the symmetrical LCC type bidirectional wireless power transfer system for battery energy storage provided in this invention, and will not be repeated here.

[0174] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A light-load control method for a symmetrical LCC-type bidirectional wireless power transfer system for battery energy storage, characterized in that, include: Acquire DC parameters of a symmetrical LCC type bidirectional wireless power transfer system; The proportion of reactive power in apparent power and the degree of light load of the current operating condition of the symmetrical LCC type bidirectional wireless power transmission system relative to the rated power are determined based on the DC parameters. Based on the stated proportion and the light load degree, a light load reactive power factor is constructed, and an upper and lower threshold value for the light load reactive power factor is determined. Based on the DC parameters, the minimum external phase shift angle and the constraint relationship on the internal phase shift angle of the primary and secondary full-bridge are determined and reconstructed to satisfy the zero-voltage switching of the symmetrical LCC type bidirectional wireless power transfer system. Under light load conditions at the end of charging of the symmetrical LCC bidirectional wireless power transfer system, the power adaptive adjustment of the symmetrical LCC bidirectional wireless power transfer system is performed according to the constraint relationship between the DC parameters, the minimum external phase shift angle and the internal phase shift angle of the primary and secondary full-bridge. The proportion of reactive power in apparent power is: ； ； in, This represents the proportion of reactive power in apparent power. Q Reactive power Apparent power, C and D All are intermediate variables. The phase angle is the external shift of the original secondary side. This is the inward phase angle of the entire bridge on the original side. The inner phase shift angle of the entire bridge on the secondary side. This is the DC bus voltage on the primary side. This is the DC bus voltage on the secondary side. For primary-side compensation inductance, For secondary-side compensation inductance, For the mutual inductance of the primary and secondary sides, The system angular frequency; The current operating condition of the symmetrical LCC type bidirectional wireless power transfer system, relative to its rated power, is as follows: ； in, The current operating condition of the symmetrical LCC type bidirectional wireless power transfer system is a light load relative to its rated power. P Active power Rated power; Under light-load conditions at the end of charging in the symmetrical LCC bidirectional wireless power transfer system, based on the constraints of the DC parameters, the minimum outward phase shift angle, and the inward phase shift angle of the primary and secondary full-bridge circuits, the symmetrical LCC bidirectional wireless power transfer system undergoes adaptive power adjustment, including: Under light load conditions at the end of charging of the symmetrical LCC bidirectional wireless power transmission system, the actual active power of the system at the current moment is calculated based on the real-time DC parameters. Based on the actual active power of the system at the current moment and the specific light load demand under the rated 1kW standard set by the system, the power deviation of the current control cycle is calculated. The incremental PI control algorithm is invoked to process the power deviation of the current control cycle, and the inner phase shift angle of the original side full bridge in the current control cycle is updated. Update the inner phase angle of the secondary side full bridge based on the updated inner phase angle of the primary side full bridge in the current control cycle; Based on the minimum outward phase shift angle, the inward phase shift angle of the primary side full bridge in the current control cycle, and the inward phase shift angle of the secondary side full bridge, the phase register and the comparator register corresponding to the outward phase shift angle of the primary and secondary sides, the inward phase shift angle of the primary side full bridge in the current control cycle, and the inward phase shift angle of the secondary side full bridge are updated to generate multiple PWM signals with dead time to drive the switching transistors of the primary side full bridge and the secondary side full bridge respectively, thereby performing power adaptive adjustment of the symmetrical LCC type bidirectional wireless power transfer system.

2. The light-load control method for a symmetrical LCC-type bidirectional wireless power transfer system for battery energy storage according to claim 1, characterized in that, The DC parameters include the DC bus voltage on the primary side, the DC bus current on the primary side, the DC bus voltage on the secondary side, the inner phase shift angle of the full bridge on the primary side, the inner phase shift angle of the full bridge on the secondary side, and the output current of the primary side bridge arm.

3. The light-load control method for a symmetrical LCC-type bidirectional wireless power transfer system for battery energy storage according to claim 1, characterized in that, The light-load reactive power factor is: ； in, K This is the reactive factor under light load.

4. The light-load control method for a symmetrical LCC-type bidirectional wireless power transfer system for battery energy storage according to claim 1, characterized in that, The minimum outward phase shift angle required for the symmetrical LCC type bidirectional wireless power transfer system to achieve zero-voltage switching is: ； in, To meet the minimum outward phase shift angle required for zero-voltage switching in the symmetrical LCC type bidirectional wireless power transfer system, This is the primary-side full-bridge output voltage. This is the output voltage of the secondary-side full-bridge. This refers to the minimum bridge arm commutation current amplitude required for the switching transistor to complete junction capacitance charging and discharging and achieve zero-voltage turn-on under given device parameters and dead time conditions. For primary-side compensation inductance, For secondary-side compensation inductance, For the mutual inductance of the primary and secondary sides, Let be the system angular frequency.

5. The light-load control method for a symmetrical LCC-type bidirectional wireless power transfer system for battery energy storage according to claim 1, characterized in that, The constraint relationship of the reconstructed primary and secondary side full-bridge internal phase shift angle is as follows: ； in, This is the inward phase angle of the entire bridge on the original side. The inner phase shift angle of the entire bridge on the secondary side. For constraint functions, This is the DC bus voltage on the primary side. This is the DC bus voltage on the secondary side. For primary-side compensation inductance, For secondary-side compensation inductance, The rated transmission current of the system, For the primary side bridge arm output current, For the primary coil inductance, For the secondary coil inductance, The mutual inductance is between the primary and secondary sides.

6. The light-load control method for a symmetrical LCC-type bidirectional wireless power transfer system for battery energy storage according to claim 1, characterized in that, The update formula for the inner phase shift angle of the original side full bridge in the current control cycle is: ； ； in, This represents the inward phase shift angle of the original side of the full bridge during the current control cycle. This represents the inward phase shift angle of the original side of the full bridge in the previous control cycle. This represents the deviation of the inner phase shift angle of the original side full bridge during the current control cycle. The power deviation for the current control cycle. This represents the power deviation from the previous control cycle. This is the proportionality coefficient. is the integral coefficient.

7. The light-load control method for a symmetrical LCC-type bidirectional wireless power transfer system for battery energy storage according to claim 6, characterized in that, The update formula for the inner phase angle of the secondary side full bridge is: ； ； ； in, This represents the inner phase shift angle of the secondary side of the full bridge during the current control cycle. For constraint functions, This is the DC bus voltage on the primary side. This is the DC bus voltage on the secondary side. For primary-side compensation inductance, For secondary-side compensation inductance, The rated transmission current of the system, For the primary side bridge arm output current, For the primary coil inductance, For the secondary coil inductance, The mutual inductance is between the primary and secondary sides.

8. A light-load control device for a symmetrical LCC-type bidirectional wireless power transfer system for battery energy storage, characterized in that, include: The acquisition module is used to acquire DC parameters of a symmetrical LCC type bidirectional wireless power transfer system; The calculation module is used to determine the proportion of reactive power in apparent power and the degree of light load of the current operating condition of the symmetrical LCC type bidirectional wireless power transmission system relative to the rated power based on the DC parameters. The light-load reactive power factor construction module is used to construct the light-load reactive power factor according to the proportion and the light-load degree, and to determine the upper limit threshold and lower limit threshold of the light-load reactive power factor. The constraint module is used to reconstruct the constraint relationship between the minimum external phase shift angle that satisfies the zero-voltage switching of the symmetrical LCC type bidirectional wireless power transfer system and the internal phase shift angle of the primary and secondary full-bridge based on the DC parameters. An adaptive control module is used to adaptively adjust the power of the symmetrical LCC bidirectional wireless power transfer system under light load conditions at the end of charging, based on the constraints of the DC parameters, the minimum external phase shift angle, and the internal phase shift angle of the primary and secondary full-bridge. The proportion of reactive power in apparent power is: ； ； in, This represents the proportion of reactive power in apparent power. Q Reactive power Apparent power, C and D All are intermediate variables. The phase angle is the external shift of the original secondary side. This is the inward phase angle of the entire bridge on the original side. The inner phase shift angle of the entire bridge on the secondary side. This is the DC bus voltage on the primary side. This is the DC bus voltage on the secondary side. For primary-side compensation inductance, For secondary-side compensation inductance, For the mutual inductance of the primary and secondary sides, The system angular frequency; The current operating condition of the symmetrical LCC type bidirectional wireless power transfer system, relative to its rated power, is as follows: ； in, The current operating condition of the symmetrical LCC type bidirectional wireless power transfer system is a light load relative to its rated power. P Active power Rated power; Under light-load conditions at the end of charging in the symmetrical LCC bidirectional wireless power transfer system, based on the constraints of the DC parameters, the minimum outward phase shift angle, and the inward phase shift angle of the primary and secondary full-bridge circuits, the symmetrical LCC bidirectional wireless power transfer system undergoes adaptive power adjustment, including: Under light load conditions at the end of charging of the symmetrical LCC bidirectional wireless power transmission system, the actual active power of the system at the current moment is calculated based on the real-time DC parameters. Based on the actual active power of the system at the current moment and the specific light load demand under the rated 1kW standard set by the system, the power deviation of the current control cycle is calculated. The incremental PI control algorithm is invoked to process the power deviation of the current control cycle, and the inner phase shift angle of the original side full bridge in the current control cycle is updated. Update the inner phase angle of the secondary side full bridge based on the updated inner phase angle of the primary side full bridge in the current control cycle; Based on the minimum outward phase shift angle, the inward phase shift angle of the primary side full bridge in the current control cycle, and the inward phase shift angle of the secondary side full bridge, the phase register and the comparator register corresponding to the outward phase shift angle of the primary and secondary sides, the inward phase shift angle of the primary side full bridge in the current control cycle, and the inward phase shift angle of the secondary side full bridge are updated to generate multiple PWM signals with dead time to drive the switching transistors of the primary side full bridge and the secondary side full bridge respectively, thereby performing power adaptive adjustment of the symmetrical LCC type bidirectional wireless power transfer system.

Images