BD-WPT system insensitive to external phase shift angle

Abstract

The invention provides a BD-WPT system insensitive to an external phase shift angle, which is used for solving the problems that the existing voltage-type output bidirectional wireless electric energy transmission system is very sensitive to the external phase shift angle of a primary side and a secondary side, and the requirement on the phase synchronization precision of the system is high. Comprising a primary side module and a secondary side module, each of the primary side module and the secondary side module comprises a direct-current power supply, a bus capacitor and a high-frequency inverter, and a diode control circuit is connected in series between the bus capacitor and the high-frequency inverter; the diode control circuit comprises a diode and a control switch tube which are arranged in parallel, the anode of the diode is connected with one input end of the high-frequency inverter, the cathode of the diode is connected with one end of the bus capacitor, and the other input end of the high-frequency inverter is connected with one end of the bus capacitor. According to the invention, the diode control circuit is connected in series between the bus capacitor and the full-bridge inverter, so that the external phase shift angle sensitivity of the BD-WPT system can be effectively reduced, and the control precision required by the system is greatly reduced.

Description

Technical Field

[0001] The invention relates to the field of wireless power transmission, and in particular to a BD-WPT system which is insensitive to an external phase shift angle. Background Art

[0002] In recent years, wireless power transmission technology has played an increasingly important role in the field of electric vehicle charging. Its safety, reliability, convenience, flexibility and strong environmental adaptability make electric vehicle charging very convenient.

[0003] At present, most wireless charging systems for electric vehicles use one-way charging, which cannot meet the growing demand for energy interconnection. Relevant scholars have proposed the technology of energy flow from electric vehicles to the grid (V2G). Using V2G technology, electric vehicles can be used as distributed energy resources to provide flexible energy support, play the role of "peak shaving and valley filling", and make the energy system more efficient and sustainable.

[0004] At present, most electric vehicle bidirectional wireless charging systems adopt bilateral symmetrical structures and have constant current output characteristics. The system is insensitive to the external phase shift angle and can easily achieve phase synchronization between the primary and secondary power converters. However, the voltage-type output bidirectional wireless power transmission system is very sensitive to the external phase shift angle between the primary and secondary sides, and requires high system phase synchronization accuracy. At present, no relevant research can solve this problem well. Summary of the invention

[0005] The purpose of the present invention is to provide a BD-WPT system that is insensitive to external phase shift angles, and is used to solve the technical problem that the existing voltage-type output bidirectional wireless power transmission system is very sensitive to the external phase shift angles of the primary and secondary sides, and has high requirements for system phase synchronization accuracy.

[0006] A BD-WPT system that is insensitive to an external phase shift angle, comprising a primary module and a secondary module, wherein the primary module comprises a primary DC power supply, a primary bus capacitor and a primary high-frequency inverter, and the secondary module comprises a secondary high-frequency inverter, a secondary bus capacitor and a secondary DC power supply, and a diode control circuit is serially connected between the primary bus capacitor and the primary high-frequency inverter and between the secondary bus capacitor and the secondary DC power supply;

[0007] The diode control circuit includes a diode and a control switch tube arranged in parallel, the anode of the diode is connected to an input end of the primary or secondary high-frequency inverter, the cathode of the diode is connected to one end of the primary or secondary bus capacitor, and the other input end of the primary or secondary high-frequency inverter is connected to one end of the primary or secondary bus capacitor.

[0008] Optionally, both the primary high-frequency inverter and the secondary high-frequency inverter are full-bridge inverters.

[0009] Optionally, two ends of the primary bus capacitor are respectively connected to two ends of the primary DC power supply, and two ends of the secondary bus capacitor are respectively connected to two ends of the secondary DC power supply.

[0010] Optionally, the primary module further includes a primary compensation circuit and a primary coil, and the secondary module further includes a secondary compensation circuit and a secondary coil;

[0011] The input end of the primary compensation circuit is connected to the output end of the primary high-frequency inverter, the output end of the primary compensation circuit is connected to the two ends of the primary coil, the input end of the secondary compensation circuit is connected to the two ends of the secondary coil, and the output end of the secondary compensation circuit is connected to the input end of the secondary high-frequency inverter.

[0012] Optionally, the primary side compensation circuit and the secondary side compensation circuit are LCC-S topology structures.

[0013] Optionally, when the system power is transmitted in the forward direction, the primary side control switch tube is closed and the secondary side control switch tube is opened;

[0014] When the system power is transmitted in reverse, the primary side control switch tube is opened and the secondary side control switch tube is closed.

[0015] Optionally, when the system power is transmitted in the forward direction, the bridge port voltage phase of the secondary full-bridge inverter is always the same as that of the primary full-bridge inverter;

[0016] When the system power is transmitted in reverse, the phase of the bridge port voltage of the primary full-bridge inverter is always the same as that of the secondary full-bridge inverter.

[0017] Due to the adoption of the above technical solution, the present invention has the following advantages:

[0018] The present application can effectively reduce the external phase angle sensitivity of the voltage-type output dual active bridge bidirectional wireless power transmission system by connecting a diode control circuit in series between the bus capacitor and the full-bridge high-frequency inverter, thereby greatly reducing the control accuracy required by the system.

[0019] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The accompanying drawings of the present invention are as follows.

[0021] Figure 1 It is a schematic diagram of the structure of the BD-WPT system of the present invention which is insensitive to the external phase shift angle.

[0022] Figure 2 It is a structural diagram of the existing BD-WPT system based on LCC-S compensation topology.

[0023] Figure 3 For the present invention Figure 2 Fundamental wave approximate model diagram of BD-WPT system.

[0024] Figure 4 For the present invention Figure 2 Equivalent model diagram of the secondary side module of the BD-WPT system.

[0025] Figure 5 For the present invention Figure 2 Partial voltage and current phase diagram of the BD-WPT system.

[0026] Figure 6 This is a driving signal diagram of the primary and secondary high-frequency inverters of the present invention.

[0027] Figure 7 This is a working mode diagram of the BD-WPT system of the present invention which is insensitive to the external phase shift angle.

[0028] Figure 8 This is a waveform diagram of the bridge port voltage and fundamental current of the high-frequency inverter of the primary and secondary side modules of the present invention.

[0029] Fig. 9 The voltage and current waveforms of the high-frequency inverter bridge ports on the primary and secondary sides of the system.

[0030] Fig.10 The voltage and current waveforms of the primary and secondary busbars and the bridge port.

[0031] Fig.11 It is the waveform diagram of the primary and secondary bridge ports at the commutation moment. DETAILED DESCRIPTION

[0032] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0033] Example:

[0034] The sensitivity characteristics of the external phase angle of the existing BD-WPT system are analyzed and the following Figure 2 The BD-WPT system based on the LCC-S compensation topology shown in the figure includes a primary module and a secondary module, wherein the primary module includes a primary DC power supply V dp , primary bus capacitance C in , primary high frequency inverter, primary compensation circuit and primary coil L p The secondary module includes a secondary coil L connected in sequence s, secondary side compensation circuit, secondary side high frequency inverter, secondary side bus capacitor C out and the secondary DC power supply V ds .

[0035] The primary high-frequency inverter and the secondary high-frequency inverter are both full-bridge inverters. The primary high-frequency inverter includes four MOSFET switches S1-S4, and the secondary high-frequency inverter includes four MOSFET switches T1-T4. The primary compensation circuit and the secondary compensation circuit are LCC-S topology structures. The primary compensation circuit includes a primary compensation inductor L fp , primary compensation capacitor C fp And the primary compensation capacitor C p The secondary side compensation circuit includes a secondary side compensation capacitor C s .

[0036] In this embodiment, the fundamental wave approximation (FHA) model of the above-mentioned existing BD-WPT system is as follows: Figure 3 As shown, R fp , R p and R s are the sum of the parasitic resistances of each branch. p,1 and U s,1 are the fundamental voltages output by the primary and secondary high-frequency inverters, U p,1 and U s,1 are the fundamental voltage amplitudes respectively. p,1 The phase of is taken as the reference, denoted as U p,1 ∠0°,U s,1 Hysteresis U p,1 Angle δ, denoted as U s,1 ∠-δ, U p,1 and U s,1 The expression of is shown in formula (1):

[0037]

[0038] In the formula, β p and β s is the internal phase shift angle of the primary and secondary high-frequency inverters, and δ is the external phase shift angle of the primary and secondary high-frequency inverters.

[0039] Since the resonant network has a filtering effect on high-frequency components, for the convenience of analysis, the high-frequency components in the resonant network are ignored, and the above model is defined as shown in formula (2), where ω is the angular frequency of the system operation.

[0040]

[0041] When the system is in resonance, the following relationship holds:

[0042]

[0043] According to Kirchhoff's law, the KVL equation of the system under the fundamental wave of each circuit is written as shown in equation (4).

[0044]

[0045] By solving equations (3) and (4), the primary and secondary currents I can be obtained: Lfp ,I Lp ,I Ls The expression of is shown in formula (5):

[0046]

[0047] Analysis of power bidirectional transmission conditions: The active power and reactive power expressions of the primary and secondary high-frequency inverter outputs can be obtained by calculation as shown in formula (6):

[0048]

[0049] Where P p , Q p , P s and Q s They represent the active power and reactive power transmitted from the primary side to the secondary side, and the active power and reactive power transmitted from the secondary side to the primary side respectively.

[0050] It can be seen from formula (6) that the reactive power of the BD-WPT system based on the LCC-S topology is related to the fundamental voltage amplitude U of the primary and secondary high-frequency inverter bridge ports of the system. p,1 and U s,1 It is also related to the system's external phase shift angle δ. By adjusting the system's external phase shift angle δ=π or δ=0, the system's reactive power can be achieved to zero.

[0051] At the same time, it can be seen that the active power transmitted by the system is not only affected by the external phase shift angle δ, but also related to the bridge port voltage of the primary and secondary high-frequency inverters, the size of the compensation inductance and the parasitic resistance of the system. In addition, changing the effective value of the bridge port voltage of the primary and secondary modules of the full-bridge inverter can not only change the size of the transmitted active power, but also change the direction of power transmission.

[0052] In order to further explore the bidirectional transmission conditions of the BD-WPT system based on the LCC-S topology, the higher-order terms of the line parasitic resistance are ignored, and the active power transmitted by the primary and secondary modules of the system can be obtained as shown in formula (7).

[0053]

[0054] When π / 2<δ<π and -π<δ<-π / 2, the active power transmitted between the primary and secondary sides of the system is:

[0055]

[0056] At this time, the active power transmitted to the outside by the primary and secondary modules is greater than 0, and the primary and secondary power of the system flows to the resonant network and coupling mechanism, which will cause the power capacity in the system to be very large and cause system damage. Therefore, it is necessary to avoid the system working in this state.

[0057] When -π / 2<δ<π / 2, the active power transmitted from the primary and secondary sides of the system is:

[0058]

[0059] Furthermore, it can be obtained that when δ = 0, the active power transmitted between the primary and secondary sides of the system is:

[0060]

[0061] Therefore, it can be obtained that when δ = 0, the bidirectional transmission condition of the BD-WPT system based on the LCC-S topology is:

[0062] (1)When U p,1 / U s,1 >L fp / M, the active power transmitted outward by the primary side is greater than 0, and the active power transmitted outward by the secondary side module is less than 0. At this time, the primary side outputs energy outward, and the secondary side absorbs energy inward. The direction of energy transmission is from the primary side to the secondary side.

[0063] (2)When U p,1 / U s,1 <L fp / M, the active power transmitted from the primary side is less than 0, and the active power transmitted from the secondary side module is greater than 0. At this time, the primary side absorbs energy inwards, and the secondary side outputs energy outwards. The direction of energy transmission is from the secondary side to the primary side.

[0064] (3)When U p,1 / U s,1 =L fp / M, the active power transmitted from the primary side and the active power transmitted from the secondary side are both 0. At this time, the energy transmitted by the system is 0.

[0065] External phase angle sensitivity analysis: The equivalent model of the secondary side module of the system can be expressed as Figure 4 As shown, where U Ls is the open-circuit voltage of the secondary coil. For ease of analysis, the internal resistance of each branch of the primary module is ignored, so U Ls It can be expressed as:

[0066]

[0067] So, U Ls Always with U p,1 In phase, U s,1 Hysteresis U p,1 Angle δ. Therefore, the secondary resonant cavity current I Ls It can be simplified as:

[0068]

[0069] When δ = 0, the phase relationship between the voltage and current of the system is as follows: Figure 5 As shown in (a), U Ls , U p,1 and U s,1 The phase is the same, the current I Ls Phase and U s,1 In reverse phase or in phase, the system power factor is 1 or -1.

[0070] When δ≠0, the phase relationship between the voltage and current of the system is as follows: Figure 5 (b) As shown in the figure, it can be seen from the phase relationship that when δ is not equal to 0, I Ls with U s,1 The phase angle will become 90°-δ / 2, which will bring a lot of reactive power to the system and reduce the power factor of the system. At the same time, it can be seen that the system is very sensitive to the external phase shift angle δ, and the system needs very precise control.

[0071] In view of the above problems, this application provides Figure 1 A BD-WPT system insensitive to an external phase shift angle is shown, comprising the above-mentioned BD-WPT system based on the LCC-S compensation topology, and a diode control circuit is connected in series between the primary bus capacitor and the primary high-frequency inverter and between the secondary bus capacitor and the secondary DC power supply;

[0072] The diode control circuit includes a diode and a control switch tube arranged in parallel, the anode of the diode is connected to an input end of the primary or secondary high-frequency inverter, the cathode of the diode is connected to one end of the primary or secondary bus capacitor, and the other input end of the primary or secondary high-frequency inverter is connected to one end of the primary or secondary bus capacitor.

[0073] In this embodiment, if Figure 1 As shown, the diode control circuit of the primary side module includes a diode D1 and a control switch tube Q1 arranged in parallel, and the diode control circuit of the secondary side module includes a diode D2 and a control switch tube Q2 arranged in parallel. In this embodiment, the control switch tube Q1 and the control switch tube Q2 are switching devices such as MOSFET switch tubes.

[0074] In this embodiment, when the BD-WPT system which is insensitive to the external phase shift angle transmits power forward, the primary and secondary high-frequency inverter driving signals of the system are as follows: Figure 6 As shown, the system working mode can be divided into six working modes, M1 to M6. In each working mode, the current flow direction of the secondary module is as follows: Figure 7 (a)~ Figure 7 (f) as shown.

[0075] Depend on Figure 7 It can be seen that the system works in six modes, M1 to M6, among which M2 and M5 will charge the capacitor. At this time, the secondary high-frequency inverter bridge port voltage is +V ds and -V ds In other modes, due to the clamping effect of the diode, the secondary resonant cavity works in a short-circuit state and the bridge voltage is 0. At this time, the bridge voltage and fundamental current waveforms of the high-frequency inverter of the primary and secondary modules are as follows: Figure 8 As shown, the system external phase shift angle of δ has the effect of an internal phase shift of 180°-2δ.

[0076] The diode connected in series between the bus capacitor and the full-bridge inverter switch tube makes the voltage phase of the secondary high-frequency inverter bridge port independent of the opening time of the secondary switch tube during forward power transmission, that is, independent of the system external phase shift angle δ, and the voltage phase of the secondary high-frequency inverter bridge port is always the same as that of the primary high-frequency inverter. Similarly, during reverse transmission, the voltage phase of the primary high-frequency inverter bridge port is always the same as that of the secondary high-frequency inverter. Therefore, the system's sensitivity to the external phase shift angle δ is greatly reduced, and the working range of δ is [-π / 4,π / 4].

[0077] Simulation and verification:

[0078] In MATLAB / SIMULINK simulation software, respectively establish Figure 1 The simulation model of the diode connected in series between the high-frequency inverter switch tube and the bus capacitor shown in FIG. Figure 2 The simulation model of the high-frequency inverter switch tube and the bus capacitor without a diode in series, the parameters of the two systems are shown in Table 1.

[0079] Table 1 Parameters of BD-WPT system based on LCC-S topology

[0080]

[0081] Comparison of external phase shift sensitivity suppression characteristics: When the external phase shift angle is -6°, the voltage and current waveforms of the primary and secondary high-frequency inverter bridge ports of the model without series diodes are as follows: Fig. 9 As shown in (a), the voltage and current waveforms of the primary and secondary high-frequency inverter bridge ports of the series diode model are as follows Fig. 9(b) As shown in the figure. In the model without series diode, the phase difference between the voltage and current at the secondary high-frequency inverter bridge port is close to 90°, and the peak currents at the primary and secondary bridge ports are extremely large, and the system has a large reactive power; in the model with series diode, the voltage at the secondary high-frequency inverter bridge port is in phase with the voltage at the primary high-frequency inverter bridge port, and the voltage and current at the secondary high-frequency inverter bridge port only differ by 12°, the reactive power of the system is small, and it is conducive to the soft switching of the secondary switch tube.

[0082] Improved topology power bidirectional transmission simulation with external phase angle insensitivity: The waveforms of the forward and reverse transmission bus voltage and current of the system are obtained by using the topology simulation of series diodes. Fig.10 As shown in (a), the voltage and current waveforms of the primary and secondary high-frequency inverter bridge ports are as follows: Fig.10 As shown in (b), the system switches from reverse transmission to forward transmission, the maximum transmission power of the system is 17kW, and the transmission efficiency reaches 95%.

[0083] When the system switches from reverse operation to forward operation, the changes in the voltage and current waveforms at the primary and secondary high-frequency inverter bridge ports are as follows: Fig.11 As shown in the figure, when the secondary full-bridge phase shift angle gradually decreases, the primary and secondary current amplitudes also gradually decrease; when the secondary full-bridge phase shift angle decreases to the point where the effective value of the secondary bridge port voltage is equal to the effective value of the primary bridge port voltage, the system current amplitude is zero, and the system completes the switching of the running direction; when the secondary full-bridge phase shift angle continues to decrease, the primary and secondary current amplitudes gradually increase.

[0084] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A BD-WPT system insensitive to external phase shift angle, comprising a primary module and a secondary module, wherein the primary module comprises a primary DC power supply, a primary bus capacitor and a primary high-frequency inverter, and the secondary module comprises a secondary high-frequency inverter, a secondary bus capacitor and a secondary DC power supply, characterized in that: A diode control circuit is connected in series between the primary bus capacitor and the primary high-frequency inverter and between the secondary bus capacitor and the secondary DC power supply; The diode control circuit includes a diode and a control switch tube arranged in parallel, the anode of the diode is connected to an input end of the primary or secondary high-frequency inverter, the cathode of the diode is connected to one end of the primary or secondary bus capacitor, and the other input end of the primary or secondary high-frequency inverter is connected to one end of the primary or secondary bus capacitor.

2. A BD-WPT system insensitive to external phase shift angle according to claim 1, characterized in that: The primary high-frequency inverter and the secondary high-frequency inverter are both full-bridge inverters.

3. The BD-WPT system insensitive to external phase shift angle according to claim 1, characterized in that: Two ends of the primary bus capacitor are connected to two ends of the primary DC power supply respectively, and two ends of the secondary bus capacitor are connected to two ends of the secondary DC power supply respectively.

4. The BD-WPT system insensitive to external phase shift angle according to claim 1, characterized in that: The primary module further includes a primary compensation circuit and a primary coil, and the secondary module further includes a secondary compensation circuit and a secondary coil; The input end of the primary compensation circuit is connected to the output end of the primary high-frequency inverter, the output end of the primary compensation circuit is connected to the two ends of the primary coil, the input end of the secondary compensation circuit is connected to the two ends of the secondary coil, and the output end of the secondary compensation circuit is connected to the input end of the secondary high-frequency inverter.

5. A BD-WPT system insensitive to external phase shift angle according to claim 4, characterized in that: The primary side compensation circuit and the secondary side compensation circuit are of LCC-S topology structure.

6. The BD-WPT system insensitive to external phase shift angle according to claim 1, characterized in that: When the system power is transmitted in the forward direction, the primary control switch tube is closed and the secondary control switch tube is opened; When the system power is transmitted in reverse, the primary side control switch tube is opened and the secondary side control switch tube is closed.

7. A BD-WPT system insensitive to external phase shift angle according to claim 6, characterized in that: When the system power is transmitted in the forward direction, the phase of the bridge port voltage of the secondary full-bridge inverter is always the same as that of the primary full-bridge inverter; When the system power is transmitted in reverse, the phase of the bridge port voltage of the primary full-bridge inverter is always the same as that of the secondary full-bridge inverter.

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