An initial frequency discrimination method for a variable frequency wireless charging system

Abstract

This invention discloses an initial frequency identification method for a frequency conversion wireless charging system. The method comprises: S1, power-on initialization; S2, signal acquisition and processing; S3, timing value capture; S4, waveform type identification and phase angle calculation; S5, initial frequency identification and adjustment. Steps S2 to S5 are repeated until the switching frequency is adjusted to a preset range and meets the soft-switching conditions, thus completing the initial frequency identification. This invention relates to the fields of power electronics and wireless charging technology.

Description

Technical Field

[0001] This invention relates to the fields of power electronics and wireless charging technology, and more specifically, to an initial frequency identification method for frequency conversion wireless charging systems, particularly suitable for the initial frequency adjustment and system startup control of phase-shifted full-bridge topology wireless charging ground terminal converters. Background Technology

[0002] In wireless charging systems, frequency conversion phase-shift full-bridge modulation is the core technology for achieving precise power control. Its key technical objective is to simultaneously meet the soft-switching operating characteristics and impedance matching requirements by adjusting the phase matching relationship between the ground (transmitter) midpoint voltage and the resonant current, thereby ensuring the reliability of power devices and the overall stability of the system operation.

[0003] Existing technologies for phase control of ground-side converters have significant limitations. On the one hand, resonant cavity phase compensation technology can only achieve phase compensation within a small range with a fixed amplitude, and cannot be dynamically adjusted according to system operating conditions. On the other hand, while PLL (phase-locked loop) phase adjustment technology can be flexibly controlled, it imposes strict constraints on the size design of the vehicle-side (receiver) hardware, limiting its application in miniaturized scenarios. In comparison, ground-side frequency conversion modulation technology has greater application flexibility. However, when this technology is combined with phase-shifted full-bridge modulation, soft-switching failure and system detuning are prone to occur under low-to-medium power conditions, resulting in power devices experiencing significant switching losses and voltage stress.

[0004] More importantly, the proper determination of the system's initial operating state (especially the initial operating frequency) directly determines the performance of the wireless charging system during the startup phase. In existing technologies, the core of initial state determination is to detect the system's mutual inductance parameters and then match the corresponding initial startup frequency. A typical implementation involves first placing the vehicle-side rectifier circuit in a short-circuit state, then controlling the ground-side inverter to start and stop rapidly. By comparing the frequency differences under different start-stop states, the initial mutual inductance conditions of the system are deduced, ultimately determining the initial operating frequency. This method has significant drawbacks: 1. Complex operation process: It requires high coordination and control of the vehicle-side circuit and relies on short-circuit operation of the vehicle-side circuit, which reduces the flexibility of system startup.

[0005] 2. Safety risks: The instantaneous current under short-circuit conditions may cause potential damage to the vehicle-end devices.

[0006] 3. Inability to determine inductive / capacitive properties: Relying solely on mutual inductance to deduce the initial frequency, there is no independent and precise calibration mechanism, and it is impossible to determine the direction and degree of inductive / capacitive properties in the system based on the initial state. If the initial operating frequency is not selected properly, it will directly lead to a severe imbalance in the phase relationship between the midpoint voltage and the resonant current during the power-on phase, triggering soft-switching failure, or even damaging power devices due to excessive initial current surge.

[0007] Furthermore, traditional phase detection techniques (such as zero-crossing detection) suffer from significantly reduced detection accuracy under low-to-medium power conditions in phase-shifted full-bridge modulation due to the variable resonant current waveform (such as the appearance of wave packets and the uncertain number of zero-crossings). This makes it impossible to provide reliable phase feedback signals for the frequency conversion control algorithm, thus limiting the accuracy of phase control.

[0008] Therefore, there is an urgent need for a technical solution that can accurately determine the optimal initial operating frequency through autonomous detection at the ground terminal without relying on complex coordination of vehicle-end circuits, and can adapt to different resonant current waveform types. Summary of the Invention

[0009] The purpose of this invention is to provide an initial frequency identification method for a frequency conversion wireless charging system, so as to solve the problems in the prior art where the initial frequency determination relies on mutual inductance identification, the process is cumbersome, the adaptability is poor, and the inability to determine the inductance and capacitance leads to low startup reliability.

[0010] The technical solution adopted in this invention is an initial frequency identification method for a frequency conversion wireless charging system. This method is used in a grounding converter of a wireless charging system comprising a phase-shifted full-bridge converter, a resonant network, a transmitting coil, a current sampling module, a phase detection circuit, a pulse width calculation circuit, and a grounding controller. The method includes the following steps: S1. Power-on Initialization: After receiving the power-on command, the system controls the vehicle-side rectifier bridge to short-circuit, putting the secondary side into an unloaded resonant state; the ground-side controller outputs a preset small-angle phase shift. Drive the phase-shifted full-bridge converter to perform inverter oscillation at low power; S2. Signal Acquisition and Processing: The current sampling module acquires the resonant current ILrp of the resonant network, and generates a pulse signal ZCP with phase position information through phase detection; the phase detection circuit performs logical operations on the pulse signal ZCP and the bridge arm square wave signal PWMsyn replicated by the ground controller to generate a frequency-doubling pulse signal XOR with phase difference information. S3. Timing Value Acquisition: The pulse width calculation circuit receives the frequency-doubling pulse signal XOR and captures the count values ​​corresponding to the key edge moments within one switching cycle, including at least the first value representing the resonant current period. Num 1. The second numerical value representing the first phase difference Num 2. A third value representing information related to the second phase difference. Num 3 and the fourth value Num 4; S4. Waveform type identification and phase angle calculation: The ground controller will use the first value Num 1 converted to resonant current frequency f p and the preset switching frequency at the ground terminal fk Compare and define the frequency preset threshold as follows: △f ; If | f p - f k |> △f The resonant current waveform was determined to be a small phase-shift distorted waveform, and the phase angle was calculated using the first phase angle calculation algorithm. θ E ; If | f p - f k |< △f To determine whether the resonant current waveform is a symmetrical waveform with a large phase shift or a small phase shift waveform with strong capacitive characteristics, the phase angle is calculated using the second phase angle calculation algorithm. θ E ; S5. Initial Frequency Identification and Adjustment: The ground controller determines the initial frequency based on the calculated phase angle. θ E With the current phase angle Substitute the soft-switching criteria into the judgment: If the inductive condition is met, then increase the switching frequency; If the capacitive condition is met, then reduce the switching frequency; Repeat steps S2 to S5 until the switching frequency is adjusted to the preset range and meets the soft switching conditions, thus completing the initial frequency identification.

[0011] Furthermore, in step S4, the first phase angle calculation algorithm is applicable to waveforms with small phase shifts and distortions, where the resonant current experiences more than two zero-crossing points within a single switching cycle. The phase angle... θ E The calculation formula is: , At this point, the resonant current frequency is equal to the preset switching frequency at the ground terminal. f k ,use Num 3. Directly characterize the phase difference between the zero-crossing point on the right side of the wave packet and the bridge arm drive signal.

[0012] Furthermore, in step S4, the second phase angle calculation algorithm is applicable to symmetrical waveforms with large phase shifts or small phase shifts with strong capacitive characteristics. In this case, the resonant current experiences two zero-crossing points within one switching cycle. θ E The calculation formula is: , or , in, Num 1 represents the period count value of the resonant current.

[0013] Furthermore, in step S5, the soft-switching criterion is: compare 2... θ E + And the magnitude of π; When 2· θ E + When the value is greater than π, the resonant circuit is determined to be inductive, and the control ground controller increases the switching frequency by one unit step. When 2· θ E + When the value is less than π, the resonant circuit is determined to be capacitive, and the control ground controller reduces the switching frequency by one unit step.

[0014] Furthermore, in step S1, a preset small-angle phase shift angle is used. The range of values ​​for is [0, π].

[0015] Furthermore, step S5 is followed by step S6: Load connection and power closed loop: After the initial frequency identification is completed, the ground controller sends a command to control the vehicle end to cancel the rectifier bridge short circuit and connect the rectifier load; The ground controller dynamically adjusts the phase shift angle according to the target power. And monitor the output power in real time; If the output power does not reach the target value, return to steps S2 to S5 and continue to fine-tune the switching frequency and phase shift angle until the power reaches the target.

[0016] Furthermore, the phase detection circuit adopts an XOR gate logic circuit, with its input terminals connected to the pulse signal ZCP output by the phase detection module and the replicated bridge arm square wave signal PWMsyn output by the ground controller, and its output terminal connected to the pulse width calculation circuit.

[0017] Furthermore, the pulse width calculation circuit includes a buffer, a rising edge triggered 1-bit counter, a 1-bit address decoder, a group of flip-flops, and a rising counter; The trigger group includes a first rising edge trigger, a first falling edge trigger, a second rising edge trigger, and a second falling edge trigger; The rising counter counts under the drive of a clock signal and resets when the first rising edge of the flip-flop outputs a pulse. The count values ​​at the trigger times of the four flip-flops are recorded sequentially as... Num 1. Num 2. Num 3. Num 4.

[0018] Furthermore, in step S2, the phase detection employs a zero-crossing detection circuit or a peak phase detection circuit; when a zero-crossing detection circuit is used, a pulse signal is output after the resonant current crosses zero; when a peak phase detection circuit is used, a pulse signal is output between adjacent peak values ​​of the resonant current.

[0019] Furthermore, the frequency adjustment amount per unit step is 1Hz to 10Hz, and the adjustment period is 50ms to 200ms, until the deviation between the switching frequency and the preset value is ≤2%.

[0020] The beneficial effects of this invention are as follows: 1. Full phase shift adaptation to solve phase distortion: An adaptive phase calculation logic is proposed, which automatically identifies the resonant current waveform type by comparing timing thresholds. Appropriate calculation rules are adopted for large and small phase shift angles, which effectively avoids phase calculation distortion caused by waveform distortion under small phase shift angles, and provides a reliable basis for soft switching judgment.

[0021] 2. Soft switching priority to reduce startup risk: A startup frequency iteration mechanism with soft switching priority is designed. The initial frequency phase information is obtained through no-load resonance detection, and the frequency is dynamically adjusted in combination with soft switching criteria to ensure that the system operates in the capacitive soft switching range when it starts up, effectively reducing switching losses and avoiding current surges and device damage caused by hard switching.

[0022] 3. No-load detection eliminates interference and improves matching accuracy: By short-circuiting the rectifier bridge at the vehicle end, the system enters the no-load resonance mode, avoiding interference from the load on the frequency and phase detection, ensuring that the initial frequency is accurately matched with the inherent characteristics of the resonant cavity, and optimizing the power transmission efficiency.

[0023] 4. Full-link dynamic closed loop, smooth transition: A full-link dynamic control process of "frequency phase detection → frequency adjustment → load access → power closed loop" is constructed. By using small step frequency iteration to avoid sudden impact, the system's transition stability from no-load to load is improved. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of a ground converter with zero-crossing detection and phase calculation functions. Figure 2 This is a schematic diagram of the key waveform (symmetrical waveform) under a large phase shift angle condition. Figure 3 This is a schematic diagram of the pulse width calculation circuit; Figure 4 It is a waveform diagram of the calculated frequency and phase values ​​(taking zero-crossing detection as an example); Figure 5 This is a simulation diagram of the key waveforms under conditions of a large phase shift angle; Figure 6It is a key waveform simulation diagram under a relatively small phase shift angle condition (distorted waveform, multiple zero crossings); Figure 7 Key waveform simulation under relatively small phase shift angle conditions Figure 2 (Strong capacitance, double zero-crossing); Figure 8 It is a flowchart for determining the type of resonant current waveform, calculating the phase angle, and identifying the initial frequency; Figure 9 This is a waveform diagram of the capacitive case and when the wave packet is large in the embodiment; Figure 10 This is a waveform diagram of the capacitive case and when the wave packet is small in the embodiment; Figure 11 This is a waveform diagram of the inductive state when the soft-switching condition is met in the embodiment. Detailed Implementation

[0025] like Figure 1 As shown, this invention provides an initial frequency identification method for a frequency conversion wireless charging system. This method is used in a wireless charging system ground converter comprising a phase-shifted full-bridge converter, a resonant network, a transmitting coil, a current sampling module, a phase detection circuit, a pulse width calculation circuit, and a ground controller. The method includes the following steps: S1. Power-on Initialization: After receiving the power-on command, the system controls the vehicle-side rectifier bridge to short-circuit, putting the secondary side into an unloaded resonant state; the ground-side controller outputs a preset small-angle phase shift. Drive the phase-shifted full-bridge converter to perform inverter oscillation at low power; S2. Signal Acquisition and Processing: The current sampling module acquires the resonant current ILrp of the resonant network, and generates a pulse signal ZCP with phase position information through phase detection; the phase detection circuit performs logical operations on the pulse signal ZCP and the bridge arm square wave signal PWMsyn replicated by the ground controller to generate a frequency-doubling pulse signal XOR with phase difference information. S3. Timing Value Acquisition: The pulse width calculation circuit receives the frequency-doubling pulse signal XOR and captures the count values ​​corresponding to the key edge moments within one switching cycle, including at least the first value representing the resonant current period. Num 1. The second numerical value representing the first phase difference Num 2. A third value representing information related to the second phase difference. Num 3 and the fourth value Num 4; S4. Waveform type identification and phase angle calculation: The ground controller will use the first value Num 1 converted to resonant current frequency f p and the preset switching frequency at the ground terminal f k Compare and define the frequency preset threshold as follows:△f ; If | f p - f k |> △f The resonant current waveform was determined to be a small phase-shift distorted waveform, and the phase angle was calculated using the first phase angle calculation algorithm. θ E ; If | f p - f k |< △f To determine whether the resonant current waveform is a symmetrical waveform with a large phase shift or a small phase shift waveform with strong capacitive characteristics, the phase angle is calculated using the second phase angle calculation algorithm. θ E ; S5. Initial Frequency Identification and Adjustment: The ground controller determines the initial frequency based on the calculated phase angle. θ E With the current phase angle Substitute the soft-switching criteria into the judgment: If the inductive condition is met, then increase the switching frequency; If the capacitive condition is met, then reduce the switching frequency; Repeat steps S2 to S5 until the switching frequency is adjusted to the preset range and meets the soft switching conditions, thus completing the initial frequency identification.

[0026] Specifically, in step S4, the first phase angle calculation algorithm is applicable to waveforms with small phase shifts and distortions, where the resonant current experiences more than two zero-crossing points within a single switching cycle. θ E The calculation formula is: , At this point, the resonant current frequency is equal to the preset switching frequency at the ground terminal. f k ,use Num 3. Directly characterize the phase difference between the zero-crossing point on the right side of the wave packet and the bridge arm drive signal.

[0027] In step S4, the second phase angle calculation algorithm is applicable to symmetrical waveforms with large phase shifts or small phase shifts with strong capacitive properties. In this case, the resonant current experiences two zero-crossing points within one switching cycle. θ E The calculation formula is: , or , in, Num1 represents the period count value of the resonant current.

[0028] In step S5, the soft-switching criterion is: compare 2. θ E + And the magnitude of π; When 2· θ E + When the value is greater than π, the resonant circuit is determined to be inductive, and the control ground controller increases the switching frequency by one unit step. When 2· θ E + When the value is less than π, the resonant circuit is determined to be capacitive, and the control ground controller reduces the switching frequency by one unit step.

[0029] In step S1, a preset small-angle phase shift angle is used. The range of values ​​for is [0, π].

[0030] Step S5 is followed by step S6: Load connection and power closed loop: After the initial frequency identification is completed, the ground controller sends a command to control the vehicle end to cancel the rectifier bridge short circuit and connect the rectifier load; The ground controller dynamically adjusts the phase shift angle according to the target power. And monitor the output power in real time; If the output power does not reach the target value, return to steps S2 to S5 and continue to fine-tune the switching frequency and phase shift angle until the power reaches the target.

[0031] The phase detection circuit uses an XOR gate logic circuit. Its input terminals are respectively connected to the pulse signal ZCP output by the phase detection module and the replicated bridge arm square wave signal PWMsyn output by the ground controller, and its output terminal is connected to the pulse width calculation circuit.

[0032] The pulse width calculation circuit includes a buffer, a rising edge triggered 1-bit counter, a 1-bit address decoder, a group of flip-flops, and a rising counter. The trigger group includes a first rising edge trigger, a first falling edge trigger, a second rising edge trigger, and a second falling edge trigger; The rising counter counts under the drive of a clock signal and resets when the first rising edge of the flip-flop outputs a pulse. The count values ​​at the trigger times of the four flip-flops are recorded sequentially as... Num 1. Num 2. Num 3. Num 4.

[0033] In step S2, the phase detection uses a zero-crossing detection circuit or a peak phase detection circuit. When a zero-crossing detection circuit is used, a pulse signal is output after the resonant current crosses zero. When a peak phase detection circuit is used, a pulse signal is output between adjacent peak values ​​of the resonant current.

[0034] The frequency adjustment per unit step is 1Hz to 10Hz, and the adjustment period is 50ms to 200ms, until the deviation between the switching frequency and the preset value is ≤2%.

[0035] The present invention will now be described in further detail with reference to the accompanying drawings.

[0036] In this embodiment, due to the implementation of phase-shifted full-bridge modulation, its phase shift angle is... Since it is a control variable, the phase of the midpoint voltage can be considered known. The structure of a ground-terminal converter with zero-crossing detection and phase calculation functions is as follows: Figure 1 As shown.

[0037] The components in the diagram are as follows: Input voltage Vin: The input voltage of the inverter at the ground terminal. Generally, a PFC is connected in front to obtain the input voltage.

[0038] Midpoint voltage Upi: This is the output voltage of the phase-shifted full-bridge resonant cavity. It can be determined by the phase shift angle. and operating frequency f k This is used to adjust the waveform of the midpoint voltage, thereby controlling the output power and impedance of the wireless charging system.

[0039] Phase-shifted full-bridge converter: The input voltage Vin enters the phase-shifted full-bridge converter, which consists of four switching transistors Sp1 to Sp4. These transistors are controlled by the bridge arm drive signal and convert DC power into high-frequency AC power through phase-shift modulation technology, driving the resonant network and the transmitting coil to output electrical energy.

[0040] Resonant network and transmitting coil: Lrp is the ground resonant inductance. Cp is the ground parallel capacitor. Cps is the ground series capacitor. Lp is the inductance of the transmitting coil, which is used to represent the self-inductance of the transmitting coil. These components together form an LCC resonant circuit. Zero-crossing detection: The resonant current ILrp is acquired through a current sampling circuit and sent to the zero-crossing or peak phase detection module. This module outputs a pulse signal with phase position information, indicating the zero-crossing point of the resonant current.

[0041] Phase detection circuit: When a pulse signal enters the phase detection circuit, it is compared with a replicated square wave signal of a certain bridge arm to generate a frequency-doubled pulse with phase difference information.

[0042] Pulse width calculation circuit: A circuit that calculates frequency and phase values ​​from a frequency-doubled pulse signal with phase difference information.

[0043] Data storage and communication: The calculated frequency and phase values ​​are stored in EEPROM or other small memory and sent to the ground controller through a communication interface (usually IIC communication, but other communication methods can also be selected) for closed-loop frequency tracking control.

[0044] Phase-shifted full-bridge drive circuit: The ground controller adjusts the bridge arm modulation signal according to the received phase information, and then controls the phase-shifted full-bridge drive circuit to achieve precise driving of the switching transistors and ensure that the system works in the optimal state.

[0045] Ground controller: Typically a DSP or other type of controller, this component is a key part of the entire wireless charging system, responsible for receiving data such as frequency and phase values. The ground controller uses this data for closed-loop frequency tracking control. In this invention, frequency and phase values ​​stored in a small memory such as EEPROM are acquired via communication methods such as I2C. A modulation signal and a square wave signal replicating a specific bridge arm are then output to the phase detection circuit.

[0046] The structure and operation of each circuit will be described in detail below.

[0047] First, regarding Figure 1 The "current sampling" and "zero-crossing detection" mentioned here refer to the sampling of the resonant current ILrp. The specific method used can be a current transformer or a Hall sensor; the actual choice depends on the engineering requirements. This invention does not impose any specific restrictions on this, as it is independent of the implementation method. Both the sampling circuit and the zero-crossing detection are common and general-purpose circuits in power electronics technology, therefore, this invention will not elaborate further.

[0048] The phase detector can be an XOR gate. Since XOR gates are also common general-purpose circuits, this invention will not elaborate further.

[0049] The key waveforms of the above circuits are as follows: Figure 2 As shown. This is at a larger phase shift angle. The key waveform patterns under the given conditions are as follows. It can be seen that the resonant current crosses zero twice within one switching cycle, therefore the zero-crossing detection output ZCP will also produce a corresponding pulse within one switching cycle. XORing the pulse of the zero-crossing detection output ZCP with the square wave signal PWMsyn of a certain bridge arm yields a frequency-doubled pulse signal XOR containing phase pulse width information.

[0050] The following describes a circuit for calculating the phase pulse width information within one cycle. Figure 3A pulse width calculation circuit is demonstrated, which can operate on a "frequency-doubled pulse with phase pulse width information" output by a phase detector circuit. The function of this circuit is to calculate the phase information of the resonant current relative to a certain bridge arm drive voltage, including the frequency value and the phase value.

[0051] Figure 3 The symbols for each circuit in the diagram are based on national standards (GB / T). These symbols are typically used to represent specific digital circuits. The diagram contains commonly used standard symbols for digital circuits, which accurately represent the functions and connections of each logic unit.

[0052] Figure 3 The pulse width calculation circuit shown consists of the following circuit components: A buffer is a digital unit that enhances a signal and isolates a circuit without changing its logic value. In this invention, it is used to improve signal integrity, reduce signal delay, and avoid "race hazards."

[0053] Rising-edge triggered counter: A one-bit counter, the CLK in the component symbol has a triangle, indicating that it is a digital circuit with edge-triggered characteristics. The counter used in this invention is rising-edge triggered; its output toggles between 0 and 1 each time a rising edge of the input signal is detected. Its function is to generate the address signal for the address decoder and the enable signal for the flip-flop group.

[0054] A 1-bit address decoder: Its symbol A represents the address input, Y represents the signal input, and 0 and 1 represent the two outputs respectively. Its function is to route the input signal Y to one of the two outputs based on the state of the address input signal A.

[0055] The trigger group consists of four digital circuit elements: a "first rising edge trigger," a "first falling edge trigger," a "second rising edge trigger," and a "second falling edge trigger." The triangle in the element symbol indicates that it is a digital circuit with edge-triggered characteristics, and the circled area represents "negative correlation characteristics," i.e., "falling edge triggering." E is the enable port of the trigger, also circled, indicating "negative correlation characteristics," i.e., "active low." These triggers generate a pulse signal upon detecting the corresponding edge.

[0056] An up-counter, also called a rising counter, is a common digital circuit whose function is to automatically increment its output value by 1 with each valid clock pulse (usually the rising edge). Common up-counters include 12-bit, 16-bit, and 256-bit types, selected according to system requirements. It is necessary to ensure that overflow does not occur when calculating the pulse width (or that the time to complete one full counting cycle is greater than the drive cycle of the ground converter). The frequency of the matching clock signal is selected according to the system. The up-counter used in this invention can be triggered four times, and the pulse of the "first rising edge trigger" is specified to reset the counter value, and the counter value at the moment of each pulse signal of the trigger group is recorded sequentially. These values ​​will contain frequency and phase information. The key waveforms of this part are as follows: Figure 4 As shown.

[0057] The circuit triggers four times, and when the pulse of the "first rising edge trigger" arrives, the counter value is cleared and the counting starts again. Then, the counter value at the arrival time of each pulse signal of the trigger group is recorded separately.

[0058] The counter value at the arrival time of the pulse signal of the "first rising edge trigger" represents the period of the resonant current. Figure 4 The Num1 shown.

[0059] The counter value at the arrival time of the pulse signal of the "first falling edge trigger" represents the positive (or negative, with almost equal values) phase difference between the replicated bridge arm and the zero-crossing point of the resonant current. Figure 4 The Num2 shown.

[0060] The difference between the counter values ​​at the arrival times of the pulse signals of the "second rising edge trigger" and the "second falling edge trigger" is the phase difference of the other phase from the zero-crossing point of the resonant current in the replicated bridge arm. Figure 4 The difference between Num3 and Num4 is shown.

[0061] These four values ​​are automatically stored in EEPROM or other small memory and read by the ground controller via the communication bus (IIC communication is commonly used).

[0062] The frequency and phase angle of the resonant current can be directly calculated using these four values. The calculation method is as follows: Let the period of the clock signal of the rising counter be denoted as: T f , Therefore, the frequency of the resonant current can be calculated as follows: , The replicated phase angle of the bridge arm to the zero-crossing point of the resonant current, showing positive (or negative) phase: , or .

[0063] Under reasonable resonant parameter design, the two should be almost equal. This is because the phase relationship between the ground resonant current and the midpoint voltage of a wireless charging system should be symmetrical in both positive and negative phases.

[0064] In a wireless charging system employing phase-shifted full-bridge modulation, when the phase shift angle... At smaller values, the system output can be adjusted accordingly. However, at smaller phase shift angles... The waveform of the resonant current will change under certain conditions. Furthermore, determining the initial operating frequency requires a small phase shift angle before formal power-on. Enable the phase-shifting full bridge and correctly obtain the phase information at this time.

[0065] like Figure 5 The figure shows a simulation of a large phase shift angle. The key waveform situation is as follows. It can be seen that under a large phase shift angle, the simulated waveform and... Figure 2 The expected waveform is consistent. Within one switching cycle, the resonant current will exhibit two zero-crossing points, and the frequency of the frequency-doubled XOR pulse is exactly twice the switching frequency. At this point, Figure 4 The value of Num1 shown is consistent with the period of the resonant current. In reality, the period of the resonant current Ilrp and the period of the midpoint voltage Vpi may have slight differences, but they are basically the same.

[0066] However, a smaller phase shift angle The waveform of the resonant current changes under certain conditions. The wave packet of the resonant current Ilrp becomes larger, and more zero-crossings occur within a single cycle. This disrupts the circuit calculations described above, preventing the XOR function from accurately representing the frequency and phase information of the resonant current.

[0067] like Figure 6 The figure shows the phase shift angle at a smaller angle. Simulation diagrams of key waveforms under the given conditions. It can be seen that, due to the increased number of zero-crossing points (typically five or four) of the resonant current within a single switching cycle, the frequency of the frequency-doubled XOR pulse becomes higher. This leads to... Figure 4 The value of Num1 shown is inconsistent with the period of the resonant current. In this case, the method for calculating the phase information should be changed.

[0068] At this point, the rules for phase calculation will change accordingly. The phase angle of the resonant current can still be calculated using these four values, while the frequency of the resonant current... f p The frequency will be estimated as the midpoint voltage. f k equal.

[0069] Let the period of the clock signal of the rising counter be denoted as: T f , Therefore, the frequency of the resonant current can be calculated as: .

[0070] At this point, the resonant current packet will form an additional falling edge on the zero-crossing detection output. In the soft-switching judgment of a wireless charging system, it is necessary to ensure that the current at this point has already dropped to zero when the device on the bridge arm is turned on. Therefore, the relationship between the zero-crossing point on the right side of the resonant current packet and the phase shift angle should be used as the element for judging the soft-switching condition at this time.

[0071] The phase relationship between the ground resonant current and the midpoint voltage of the wireless charging system should be symmetrical in both positive and negative phases. Since the XOR frequency is four times the frequency of the midpoint voltage, the zero-crossing point on the right side of the resonant current packet, whether positive or negative, triggers the "second rising edge trigger," thus reading the value of Num3.

[0072] The phase angle of the replicated bridge arm to the zero-crossing point on the right side of the resonant current packet should be: , However, this waveform does not always occur when the phase shift angle of the phase-shifted full-bridge is small. Due to differences in the initial mutual inductance and the initial conditions of the resonant cavity, other waveforms may appear.

[0073] like Figure 7 As shown. This is also at a smaller phase shift angle. Simulation diagrams of key waveforms under the given conditions. Because the system's resonant cavity has strong capacitance, the resonant current packet will be above zero. Therefore, within one switching cycle, the resonant current still has two zero-crossing points. The frequency of the frequency-doubled XOR pulse is also exactly twice the switching frequency. In this case, both the frequency and phase angle of the resonant current are... Figure 5 The larger phase shift angle shown The calculation methods are consistent under the same conditions.

[0074] To maintain the soft-switching state of the grounding converter in the wireless charging system, the current in any arm of the phase-shifted full-bridge circuit must not exceed zero when it is turned on. Since the modulation signal of the phase-shifted full-bridge is generated by the grounding controller, the initial phase of the midpoint voltage vpi can be synchronously obtained by replicating the corresponding arm square wave signal. After the pulse width calculation circuit described above, four values ​​containing phase information, Num1, Num2, Num3, and Num4, can be obtained.

[0075] Phase shift value of a phase-shifted full-bridge It is a known value with a range of [0, π], reflecting the proportion of high-level voltage in the midpoint voltage. The actual phase shift value will be slightly smaller than the calculated value due to factors such as drive delay and Miller effect of the switching device. In engineering, they can be considered almost identical, differing only by a certain compensation amount.

[0076] When the ground converter of the wireless charging system enters the soft-switching condition, the phase angle of the system... θ E and phase shift value The following relationships will exist: 2. θ E + ≥π Simply put, it's the phase angle. θ E twice and phase shift value When the angles are exactly a supplementary angle, the soft-switching condition is just maintained. In engineering practice, the sum of their angles is usually made to be greater than π, typically around ten degrees. This formula applies to phase angle relationships calculated under the above conditions.

[0077] Therefore, in this wireless charging system employing frequency conversion phase-shift full-bridge modulation, it is first necessary to identify the waveform type of the resonant current, and then select different phase calculation methods. The identification method is based on the counter value Num1 at the arrival time of the pulse signal of the "first rising edge trigger" and the period 1 / of the midpoint voltage. f k Compare the phases. If the difference is too large, it indicates that the system has entered a condition with a small phase shift angle, and the rules for calculating the phase angle need to be changed accordingly.

[0078] This judgment and calculation process is as follows: Figure 8 As shown, the complete action flow is as follows (in the order of the flowchart). 1. Startup After the system triggers the power-on command, it first performs a short circuit at the vehicle end (short-circuiting the secondary rectifier bridge, allowing the system to enter a light-load resonant state). The ground controller outputs a small phase shift angle. It drives the phase-shifted full-bridge to perform an inverter oscillation process at low power.

[0079] 2. Frequency and phase detection and calculation After the circuit stabilizes, calculate the current resonant frequency and the phase difference between the resonant current and the midpoint voltage.

[0080] The calculated frequency is compared with the preset switching frequency at the ground terminal, and the phase angle is calculated in three cases: If the calculated frequencies are almost equal, use or Calculate the phase angle.

[0081] If the calculation frequency is higher, use Calculate the phase angle.

[0082] Entry into soft-switching condition judgment: Compare 2. θ E + The magnitude of π.

[0083] 3. Resonance polarity determination and frequency adjustment If 2· θ E + If the voltage is greater than π, the resonant circuit will be inductive (current lags voltage), and the switching frequency needs to be increased by one unit step.

[0084] If 2· θ E + If the current is less than π, the resonant circuit is capacitive (current leads voltage), and the switching frequency needs to be reduced by one unit step.

[0085] Repeat the "detect → calculate → judge → adjust" cycle until the frequency is close to the preset value and meets the soft switching conditions, and dynamically adjust the switching frequency during the power-on process.

[0086] 4. Load connection and power closed loop The ground terminal sends a command to the vehicle terminal to cancel the short circuit and connect to the rectifier bridge (switching from no-load mode to loaded mode).

[0087] The power loop calculates the phase shift angle based on the target power. The output power is dynamically adjusted, and it is checked whether the power has reached the target value for startup. If the condition is met, the boot process ends and the system enters normal operation.

[0088] If the desired result is not achieved, continue adjusting the phase shift angle. Repeat steps 2-3 above until the power reaches the target.

[0089] This invention uses this method to dynamically adjust the initial frequency during the power-on process, thereby adjusting the resonance state and impedance matching of the resonant cavity.

[0090] The present invention will now be described in more detail with reference to specific embodiments.

[0091] This embodiment provides a wireless charging grounding converter with a phase-shifted full-bridge topology, suitable for grounding power transmission and control scenarios in electric vehicle wireless charging systems. Its hardware structure is as follows: Figure 1 As shown, the initial frequency adjustment process upon startup is as follows: Figure 8 As shown in the accompanying drawings, its structure, working principle, and operation process will be described in detail below with reference to the accompanying drawings. This embodiment of the invention is demonstrated using a 10kW, 100V 100A testing machine.

[0092] I. Hardware Structure Implementation Examples (Comparison) Figure 1 ) 1. Core hardware components and connections Input voltage unit: The front end is connected to the PFC circuit, and the output DC input voltage Vin=870V provides a stable DC power supply for the phase-shifted full-bridge circuit. The PFC in this embodiment of the invention adopts a three-phase Vienna voltage, inputs a three-phase mains voltage of 220V, and has a boost voltage range of 670V to 870V.

[0093] Phase-shifted full-bridge converter: The full-bridge topology is composed of Sp1 to Sp4 of 4 N-channel MOSFETs. The gates of the switching transistors are connected to the phase-shifted full-bridge drive circuit. The drive signal is controlled by the phase-shifted PWM signal output by the ground controller.

[0094] Resonant network and transmitting coil: The LCC resonant topology is adopted, which includes a resonant inductor Lrp=38μH, a parallel capacitor Cp=86nF, a series capacitor Cps=64nF, and a transmitting coil inductance Lp=88μH, which together form a high-frequency resonant circuit to achieve efficient power transmission and impedance matching.

[0095] Current sampling and zero-crossing detection: A Hall current sensor (model: ACS724) is used to collect the resonant current ILrp. The output analog signal is amplified by an instrumentation operational amplifier (INA180) and then sent to a high-speed hysteresis comparator (LMV393) to realize zero-crossing detection, and outputs a pulse signal ZCP with phase information.

[0096] Phase detection and pulse width calculation circuit: An XOR gate (74HC86) is used as the phase detection circuit. The input is the ZCP pulse and the replicated bridge arm square wave signal PWMsyn, and the output is the frequency multiplier pulse signal XOR. The pulse width calculation circuit consists of a buffer, a 1-bit rising edge counter, a 1-bit address decoder, a group of flip-flops (including 2 rising edge flip-flops and 2 falling edge flip-flops) and a 16-bit incrementing counter, which is used to capture timing and calculate the frequency phase value.

[0097] Data storage and communication: Frequency phase data is stored in an EEPROM (model: AT24C02) with an I2C interface, and the ground controller reads the stored data through the I2C bus.

[0098] Ground controller: It uses a DSP (model Haawking DSC28035) as the core control unit, which is responsible for outputting phase-shifted PWM signals, replicating bridge arm square wave signals, receiving frequency phase data and performing closed-loop frequency adjustment.

[0099] 2. Hardware Working Principle The phase-shifting full-bridge controller adjusts the phase shift angle. With switching frequency f k The DC input voltage is converted into a high-frequency AC voltage to drive the LCC resonant network and the transmitting coil. The current sampling and zero-crossing detection module captures the zero-crossing moment of the resonant current. The phase detection circuit compares the phase difference between the current and the midpoint voltage. The pulse width calculation circuit converts the phase difference into a timing value and stores it. Based on the stored frequency and phase data, the ground controller dynamically adjusts the switching frequency and phase shift angle to ensure that the system operates in a soft-switching state.

[0100] II. Method Flow Examples (for comparison) Figure 8 ) 1. Power-on initialization and no-load resonance start-up After the system triggers the power-on command, the ground controller sends a communication command to the vehicle end, controlling the vehicle end rectifier bridge to short-circuit, so that the secondary side is in a near-purely resistive light-load state, and the ground resonant network enters the no-load resonant mode.

[0101] The ground controller outputs a small-angle phase shift angle. =15° ∈(0,π / 4]), driving the phase-shifted full bridge to perform inverter oscillation at low power (approximately 5% of rated power) to ensure resonance stability and eliminate overcurrent risk.

[0102] 2. Frequency and phase detection and adaptive calculation After the circuit resonance stabilizes (approximately 500ms or more, generally after the ground coil punctures, and after the vehicle end is connected to the internal power supply and stabilizes), the Hall sensor collects the resonant current ILrp, the zero-crossing detection module outputs the ZCP pulse; the XOR gate phase detector circuit outputs the frequency doubling pulse XOR, and the pulse width calculation circuit captures the timing and obtains four count values ​​Num1 to Num4.

[0103] The calculated resonant frequency f p With preset switching frequency f k =85kHz comparison: like f p andf k Deviation ≤ 5% (approximately equal), use the symmetrical phase angle formula Calculate the phase angle; like f p > f k The single-sided phase angle formula is used. Calculate the phase angle.

[0104] Soft switching condition judgment: Compare 2. θ E + The relationship between the magnitude of π and π.

[0105] 3. Resonance polarity determination and dynamic frequency adjustment If 2· θ E + >π: If the resonant circuit is determined to be inductive (current lags voltage), the controller will increase the switching frequency by one unit step (the unit step can be set to 5Hz, triggered once for each timer interrupt, and the timer interrupt time is set to 100ms) to move the frequency away from the resonant point and reduce the risk of hard switching.

[0106] If 2· θ E + <π: If the resonant circuit is determined to be capacitive (current leads voltage), the controller will reduce the switching frequency by one unit step to bring the frequency closer to the resonant point and optimize impedance matching.

[0107] Repeat the "detection → calculation → judgment → adjustment" cycle until the deviation of the switching frequency from the preset value is ≤2% and the soft switching condition is met, thus completing the initial frequency adaptation.

[0108] 4. Load connection and power closed-loop verification The ground controller sends a command to the vehicle to control the vehicle to cancel the short circuit of the rectifier bridge and connect the rectifier load, so that the system switches from no-load mode to load mode.

[0109] The power loop dynamically adjusts the phase shift angle based on the target power at startup (e.g., 10kW). Real-time detection of output power: If the power reaches the target value, the startup process ends and the system enters the normal power transmission state. If the power does not meet the standard, repeat the "frequency phase detection → frequency adjustment" process until the power meets the requirements.

[0110] III. Experimental diagrams of the embodiments An embodiment of the present invention is a 10kW, 100V100A testing machine, which is used to verify the function and implementation of the present invention.

[0111] Figures 9-11 The waveforms under several frequency conditions are demonstrated. These figures show waveforms for four channels: midpoint voltage, resonant current, zero-crossing signal, and harmonic signal. It can be seen that after reducing the frequency using the method of this invention, the pattern of the resonant current is correspondingly changed, resulting in an initial frequency suitable for system startup and enabling the system to enter a soft-switching state under resonant conditions.

[0112] Figure 9 It is similar to Figure 6 In this situation, the system has strong capacitance, and four or six zero-crossings occur within one cycle. There are four zero-crossings at the critical point and six in the capacitive state. Under these conditions, the frequency-doubled signal reaches the operating frequency. f k Four times that of the time, with a higher calculation frequency, using Calculate the phase angle. Therefore, by... Figure 8 The method determines that the system is capacitive (current leads voltage), and the switching frequency of the system is gradually reduced through this process.

[0113] After gradually reducing the frequency, the system reached... Figure 10 This is the capacitive case, where the wave packet is relatively small, which is closer to the key waveform condition for soft switching. Figure 10 It is similar to a simulation graphic. Figure 7 In this situation, the capacitive capacitance of the system's resonant cavity is still relatively strong, so the resonant current packet will be above zero. Within one switching cycle, the resonant current still has two zero-crossing points ( Figure 10 (One of the two waveforms shown on the oscilloscope). The frequency of the XOR pulse is also exactly twice the switching frequency. In this case, the frequency and phase angle of the resonant current are both... Figure 5 The larger phase shift angle shown The calculation methods are consistent under the same conditions.

[0114] Finally, after the system reached a suitable startup frequency, the system became... Figure 11 This situation is similar to the one simulated earlier. Figure 5 As expected, the system has now reached a relatively ideal start-up frequency.

[0115] Finally, it should be emphasized that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An initial frequency identification method for a frequency conversion wireless charging system, the method being used in a ground terminal converter of a wireless charging system comprising a phase-shifted full-bridge converter, a resonant network, a transmitting coil, a current sampling module, a phase detection circuit, a pulse width calculation circuit, and a ground terminal controller, characterized in that, The method includes the following steps: S1. Power-on Initialization: After receiving the power-on command, the system controls the vehicle-side rectifier bridge to short-circuit, putting the secondary side into an unloaded resonant state; the ground-side controller outputs a preset small-angle phase shift. Drive the phase-shifted full-bridge converter to perform inverter oscillation at low power; S2. Signal Acquisition and Processing: The current sampling module acquires the resonant current ILrp of the resonant network, and generates a pulse signal ZCP with phase position information through phase detection; the phase detection circuit performs logical operations on the pulse signal ZCP and the bridge arm square wave signal PWMsyn replicated by the ground controller to generate a frequency-doubling pulse signal XOR with phase difference information. S3, Timing Value Acquisition: The pulse width calculation circuit receives the frequency multiplication pulse signal XOR and captures the count value corresponding to the key edge moment within one switching cycle, including at least the first value Num1 representing the resonant current period, the second value Num2 representing the first phase difference, the third value Num3 representing the information related to the second phase difference, and the fourth value Num4. S4. Waveform type identification and phase angle calculation: The ground controller converts the first value Num1 into the resonant current frequency f. p and the ground-preset switching frequency f k The comparison is performed, and a preset frequency threshold of Δf is defined. If |f p -f k |>△f, determining that the resonant current waveform is a small phase-shifted distorted waveform, the phase angle θ is calculated using the first phase angle calculation algorithm. E ; If |f p -f k If | < Δf, determine whether the resonant current waveform is a symmetrical waveform with a large phase shift or a small phase shift waveform with strong capacitive characteristics. Calculate the phase angle θ using the second phase angle calculation algorithm. E ; S5. Initial Frequency Identification and Adjustment: The ground controller determines the initial frequency based on the calculated phase angle θ. E With the current phase angle Substitute the soft-switching criteria into the judgment: If the inductive condition is met, then increase the switching frequency; If the capacitive condition is met, then reduce the switching frequency; Repeat steps S2 to S5 until the switching frequency is adjusted to the preset range and meets the soft switching conditions, thus completing the initial frequency identification.

2. The initial frequency discrimination method according to claim 1, characterized in that, In step S4, the first phase angle calculation algorithm is applicable to waveforms with small phase shifts and distortions, where the resonant current experiences more than two zero-crossing points within a single switching cycle. The phase angle θ... E The calculation formula is: ， At this point, the resonant current frequency is equal to the preset switching frequency f at the ground terminal. k The phase difference between the zero-crossing point on the right side of the wave packet and the bridge arm drive signal is directly characterized using Num3.

3. The initial frequency discrimination method according to claim 1, characterized in that, In step S4, the second phase angle calculation algorithm is applicable to symmetrical waveforms with large phase shifts or small phase shifts with strong capacitive properties. In this case, the resonant current experiences two zero-crossing points within one switching cycle, and the phase angle θ... E The calculation formula is: ， or , Num1 represents the period count value of the resonant current.

4. The initial frequency discrimination method according to claim 1, characterized in that, In step S5, the soft-switching criterion is: compare 2·θ E + And the magnitude of π; When 2·θ E + When the value is greater than π, the resonant circuit is determined to be inductive, and the control ground controller increases the switching frequency by one unit step. When 2·θ E + < π, it is determined that the resonant circuit is capacitive, and the ground terminal controller is controlled to decrease the switching frequency by one unit step.

5. The initial frequency discrimination method according to claim 1, characterized in that, In step S1, a preset small-angle phase shift angle is used. The range of values ​​for is [0, π].

6. The initial frequency discrimination method according to claim 1, characterized in that, Step S5 is followed by step S6: Load connection and power closed loop: After the initial frequency identification is completed, the ground controller sends a command to control the vehicle end to cancel the rectifier bridge short circuit and connect the rectifier load; The ground controller dynamically adjusts the phase shift angle according to the target power. And monitor the output power in real time; If the output power does not reach the target value, return to steps S2 to S5 and continue to fine-tune the switching frequency and phase shift angle until the power reaches the target.

7. The initial frequency discrimination method according to claim 1, characterized in that, The phase detection circuit uses an XOR gate logic circuit. Its input terminals are respectively connected to the pulse signal ZCP output by the phase detection module and the replicated bridge arm square wave signal PWMsyn output by the ground controller, and its output terminal is connected to the pulse width calculation circuit.

8. The initial frequency discrimination method according to claim 1, characterized in that, The pulse width calculation circuit includes a buffer, a rising edge triggered 1-bit counter, a 1-bit address decoder, a group of flip-flops, and a rising counter. The trigger group includes a first rising edge trigger, a first falling edge trigger, a second rising edge trigger, and a second falling edge trigger; The rising counter counts under the drive of the clock signal and is reset when the first rising edge trigger outputs a pulse. The count values ​​at the trigger times of the four triggers are recorded sequentially as Num1, Num2, Num3, and Num4.

9. The initial frequency discrimination method according to claim 1, characterized in that, In step S2, the phase detection uses a zero-crossing detection circuit or a peak phase detection circuit; when a zero-crossing detection circuit is used, a pulse signal is output after the resonant current crosses zero. When a peak phase detection circuit is used, a pulse signal is output between adjacent peak values ​​of the resonant current.

10. The initial frequency discrimination method according to claim 4, characterized in that, The frequency adjustment per unit step is 1Hz to 10Hz, and the adjustment period is 50ms to 200ms, until the deviation between the switching frequency and the preset value is ≤2%.

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