A method and system for frequency modulation of a resonant circuit

Abstract

The present invention belongs to the field of new energy technologies, and provides a method and a system for frequency modulation of a resonant circuit. When the system is operating stably and the charging current of the battery is large, that is, when the charging current > the first current threshold, the operating frequency of the resonant circuit can be made to work within a range slightly greater than the resonant frequency, that is, between the control lower limit frequency and the control upper limit frequency, thereby reducing the stress on the switching tubes of the resonant circuit. At the same time, when the charging current of the battery is small, by selecting appropriate initial values of the bus voltage and the first current threshold, when the charging current of the battery < the first current threshold, the turn-off current of the switching tubes of the resonant circuit is relatively small. Even if the operating frequency of the resonant circuit is not near the resonant frequency, the stress on the switching tubes of the resonant circuit is also within an acceptable range.

Description

Technical Field

[0001] The present invention relates to the technical field of new energy, and particularly relates to a frequency modulation method and system for a resonant circuit. Background Art

[0002] DC / DC technology and defects of existing energy storage products:

[0003] In order to reduce the stress on the MOS transistors of the resonant circuit, some products adopt the regulation of a front-stage buck (step-down) closed loop + a rear-stage resonant circuit open loop in the DC / DC link; although this technology reduces the stress on the MOS transistors and can also ensure the stability of charging, the addition of the switching transistors and sampling circuit of the buck circuit undoubtedly increases the cost of the product.

[0004] In order to reduce the product cost, some products remove the front-stage buck (step-down) circuit in the DC / DC and adopt open-loop regulation of the resonant circuit; although this technology removes the buck (step-down) circuit and reduces the product cost, the open-loop regulation of the resonant circuit cannot ensure the stability of charging, that is, the charging voltage / current is very easy to get out of control. Especially when charging with a small current or the battery is suddenly disconnected, the out-of-control battery voltage / current is very easy to cause battery protection.

[0005] In order to ensure the charging stability, the resonant circuit of some products adopts closed-loop regulation, but the bus (busbar) voltage remains constant or has a fixed proportional relationship with the battery voltage; although this technology ensures the charging stability, the bus voltage and the battery voltage have a fixed proportional relationship; under different charging current conditions, the operating frequency range of the MOS transistors in the resonant circuit changes relatively large, and it is difficult to ensure that it is near the resonant frequency; if the operating frequency of the MOS transistors in the resonant circuit is far from the resonant frequency, it will undoubtedly increase the stress on the MOS transistors; in order not to damage the MOS transistors, it is necessary to select MOS transistors with higher stress, resulting in an increase in product cost. Summary of the Invention

[0006] The purpose of the present invention is to provide a frequency modulation method for a resonant circuit to solve the problem that the prior art cannot balance cost and stability.

[0007] The present invention provides a frequency modulation method for a resonant circuit, and the method includes:

[0008] Step 1: Initialize the bus voltage Vbus to k0*Vbat;

[0009] Step 2: Determine whether the current charging current of the battery is greater than the first current threshold;

[0010] If so, proceed to Step 3; if not, keep the bus voltage unchanged at the initial value;

[0011] Step 3: Collect the operating frequency of the resonant circuit;

[0012] Step 4: Determine whether the operating frequency is greater than the control upper limit frequency;

[0013] If it is, go to Step 5; if not, determine whether the operating frequency is less than the control lower limit frequency. If it is, go to Step 6; if not, return to Step 4;

[0014] Step 5: Reduce the bus voltage, and the operating frequency will decrease accordingly until it is less than the control upper limit frequency;

[0015] Step 6: Increase the bus voltage, and the operating frequency will increase accordingly until it is greater than the control lower limit frequency;

[0016] Wherein, Vbat is the battery voltage, k0*Vbat is the initial value of the bus voltage, k0 is the proportionality coefficient, the first current threshold is 0.2 - 0.25 times the rated current of the resonant circuit, the control upper limit frequency is the resonant frequency * k1, the control lower limit frequency is the resonant frequency * k2, the range of k1 is [1.15, 1.3], and the range of k2 is (1, 1.15).

[0017] Further, when the AC power supply provides power for the resonant circuit, the operating frequency of the resonant circuit is the average frequency within the power frequency period; when only the DC power supply provides power for the resonant circuit, the operating frequency of the resonant circuit is the instantaneous frequency or the average frequency within the power frequency period.

[0018] Further, the method for obtaining the average frequency within the power frequency period includes:

[0019] Within each power frequency period T, the instantaneous frequency is collected once every T / N, and after accumulating the instantaneous frequency N times, the average value is calculated, and the average value is used as the operating frequency of the resonant circuit. Wherein, N is a positive integer, the range of the power frequency period T is [16.6ms, 20ms], and the range of N is [300, 400].

[0020] Further, Step 5 is specifically:

[0021] Gradually reduce the bus voltage, and then gradually reduce the operating frequency of the resonant circuit until it is less than the control upper limit frequency.

[0022] Further, Step 6 is specifically:

[0023] Gradually increase the bus voltage, and then gradually increase the operating frequency of the resonant circuit until it is greater than the control lower limit frequency.

[0024] Further, k1 is 1.2 and k2 is 1.1.

[0025] Further, the k 0 is k * 1.03 - k * 1.04, where k is the transformer turns ratio of the resonant circuit.

[0026] Further, the initial value of the bus voltage is V bus = k 0 * V bat , where k 0 is selected according to the transformer turns ratio k of the resonant circuit, and k 0 is k * 1.03 - k * 1.04, where V bat is the battery voltage.

[0027] The present invention also provides a resonant circuit frequency modulation system, and the foregoing frequency modulation method is applicable to the frequency modulation system. The frequency modulation system includes a control chip, a power supply module, a DC bus, a resonant circuit, and a battery. Among them,

[0028] The control chip is used to collect the bus voltage, the current charging current of the battery, and the operating frequency of the resonant circuit and make judgments, control the power supply module to step up, step down, or stabilize the voltage of the DC bus, and control the increase and decrease of the operating frequency of the resonant circuit;

[0029] The DC bus charges the battery through the resonant circuit;

[0030] The control chip includes a first judgment module, a second judgment module, and a third judgment module. The first judgment module is used to judge whether the current charging current of the battery is greater than a first current threshold; the second judgment module is used to judge whether the operating frequency is greater than the control upper limit frequency; the third judgment module is used to judge whether the operating frequency is less than the control lower limit frequency.

[0031] Further, the power supply module is a DC conversion module or / and a rectification module.

[0032] Further, the control chip is any one of a DSP module, an ARM module, or an MCU module.

[0033] The above-mentioned resonance circuit frequency modulation method and system. The present invention belongs to the field of new energy technologies and provides a resonance circuit frequency modulation method and system. When the system is operating stably and the charging current of the battery is relatively large, that is, when the charging current > the first current threshold, the operating frequency of the resonance circuit can be made to work within a range slightly greater than the resonance frequency, that is, between the control lower limit frequency and the control upper limit frequency, thereby reducing the stress on the switching tubes of the resonance circuit. At the same time, when the charging current of the battery is relatively small, by selecting appropriate initial values of the bus voltage and the first current threshold, when the charging current of the battery < the first current threshold, the turn-off current of the switching tubes of the resonance circuit is relatively small, that is, even if the operating frequency of the resonance circuit is not near the resonance frequency, the stress on the switching tubes of the resonance circuit is still within an acceptable range. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a topological diagram of a resonance circuit according to an embodiment of the present invention;

[0035] Figure 2 It is a flowchart of a resonance circuit frequency modulation method according to an embodiment of the present invention;

[0036] Figure 3 It is a system block diagram of a resonance circuit frequency modulation method according to an embodiment of the present invention;

[0037] Figure 4 It is a system block diagram of a resonance circuit frequency modulation method according to an embodiment of the present invention;

[0038] Figure 5 It is a system block diagram of a resonance circuit frequency modulation method according to an embodiment of the present invention;

[0039] Figure 6 For the present invention Figure 3 - Figure 5 Schematic diagram of the main control chip in the embodiment;

[0040] Figure 7 It is a system block diagram of a resonance circuit frequency modulation method according to an embodiment of the present invention;

[0041] Figure 8 It is a system block diagram of a resonance circuit frequency modulation method according to an embodiment of the present invention;

[0042] Figure 9 It is a system block diagram of a resonance circuit frequency modulation method according to an embodiment of the present invention;

[0043] Figure 10 For the present invention Figure 7 - Figure 9 Schematic diagram of the control chip in the embodiment;

[0044] Figure 11 It is a relationship diagram between the equivalent gain and the operating frequency of a resonance circuit according to an embodiment of the present invention;

[0045] The following specific embodiments will further illustrate the present invention in conjunction with the above-mentioned drawings. Specific Embodiments

[0046] For ease of understanding the present invention, the present invention will be described more comprehensively below with reference to the relevant drawings. Several embodiments of the present invention are shown in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, these embodiments are provided so that the disclosure of the present invention is thorough and comprehensive.

[0047] It should be noted that when an element is referred to as being "fixed to" another element, it can be directly on the other element or there can also be an intermediate element. When an element is considered to be "connected" to another element, it can be directly connected to the other element or there may be an intermediate element at the same time. The terms "vertical", "horizontal", "left", "right" and similar expressions used herein are for illustrative purposes only.

[0048] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0049] Please refer to Figure 1 , Figure 1 which is a topology diagram of a resonant circuit. Among them, the primary side (left side) of the transformer Tr is connected to a full-bridge and a series resonant topology for the DC bus, and the secondary side (right side) of the transformer Tr is connected to a battery with a full-bridge synchronous rectification topology; C1 and C2 are the primary side capacitor and the secondary side capacitor, which play a role in smoothing and filtering. In some embodiments, C1 and C2 can be removed. Among them, Vbus represents the DC bus voltage, Vbat represents the battery voltage, and the DC bus is simply referred to as the bus; the full-bridge on the primary side is formed by connecting the switching tubes Q1-Q4 in series in pairs and then in parallel, that is, the switching tubes Q1 and Q2 are in series, and the switching tubes Q3 and Q4 are in series and then in parallel with each other; the series resonant topology is composed of a resonant inductor Lr, a resonant capacitor Cr and the magnetizing inductor Lm of the transformer Tr in series, and the full-bridge rectification topology on the secondary side is formed by connecting the switching tubes Q5-Q8 in series in pairs and then in parallel, that is, the switching tubes Q5 and Q6 are in series, and the switching tubes Q7 and Q8 are in series and then in parallel with each other. In one embodiment, the switching tubes Q1-Q8 are all MOS tubes.

[0050] It should be noted that Figure 1Only an example of a resonant circuit is described. In other embodiments, the full bridge on the primary side of the resonant circuit can be replaced by a half bridge, and the series resonant topology on the primary side can be replaced by a parallel resonant topology or a series-parallel resonant topology; the full bridge synchronous rectification topology on the secondary side can be replaced by a half bridge synchronous rectification topology, or a full bridge uncontrolled rectification topology, or a half bridge uncontrolled rectification topology, and so on.

[0051] Please refer to Figure 2 , a method for frequency modulation of a resonant circuit provided by an embodiment of the present invention, the method includes:

[0052] Step 1: Initialize the bus voltage Vbus to k0*Vbat.

[0053] Among them, Vbat is the battery voltage, k0*Vbat is the initial value of the bus voltage, k0 is a proportionality coefficient, and k 0 is selected according to the turns ratio of the transformer of the resonant circuit (the ratio of the number of turns of the primary side to the number of turns of the secondary side) k; in one embodiment, k0 is k*1.03 - k*1.04; initializing the bus voltage Vbus means obtaining an initial value of the bus voltage, that is, k0*Vbat, by charging the bus before the resonant circuit starts; in other embodiments, k0 can be selected as other values according to actual needs.

[0054] Step 2: Determine whether the current charging current of the battery is greater than the first current threshold.

[0055] In one embodiment, the first current threshold is selected according to the stress of the switching tube (such as a MOS tube) of the resonant circuit, for example, it is 0.2 - 0.25 times the rated current of the resonant circuit; in other embodiments, according to actual needs, the first current threshold can be other multiples of the rated current, for example, the first current threshold is 0.15 - 0.25 times the rated current, and so on.

[0056] If yes, go to Step 3; if no, keep the bus voltage unchanged at the initial value.

[0057] Among them, the initial value is k0*Vbat.

[0058] Step 3: Collect the operating frequency of the resonant circuit.

[0059] In one embodiment, only a DC power supply provides electrical energy for the resonant circuit. At this time, the operating frequency fsw of the resonant circuit is the instantaneous frequency or the average frequency within the power frequency period. When using the instantaneous frequency as the operating frequency of the resonant circuit, the timeliness is stronger; when using the average frequency within the power frequency period as the operating frequency of the resonant circuit, it may be more accurate.

[0060] In one embodiment, electrical energy is supplied to the resonant circuit only by an AC power supply, or by both an AC power supply and a DC power supply simultaneously. At this time, the operating frequency fsw of the resonant circuit is the average frequency within the power frequency period. Supplying electrical energy to the resonant circuit only by an AC power supply, or by both an AC power supply and a DC power supply simultaneously, is collectively referred to as supplying electrical energy to the resonant circuit by an AC power supply.

[0061] In one embodiment, the method for obtaining the average frequency within the power frequency period is as follows: within each power frequency period T, the instantaneous frequency is collected once every T / N, and after accumulating the instantaneous frequency N times, the average value is calculated and taken as the operating frequency of the resonant circuit. Here, N is a positive integer, the range of the power frequency period T is [16.6 ms, 20 ms], and the range of N is [300, 400]. For example, when the power frequency is 50 Hz, within each power frequency period of 20 ms, the instantaneous frequency is collected once every 50 μs, and after accumulating the instantaneous frequency 400 times, the average value is calculated and taken as the operating frequency of the resonant circuit.

[0062] Step 4: Determine whether the operating frequency is greater than the control upper limit frequency.

[0063] If it is, proceed to Step 5. If not, then determine whether the operating frequency is less than the control lower limit frequency. If it is, proceed to Step 6. If not, return to Step 4.

[0064] Among them, the control upper limit frequency is the resonant frequency of the resonant circuit * k1, and the control lower limit frequency is the resonant frequency of the resonant circuit * k2. In one embodiment, the range of k1 is [1.15, 1.3], and the range of k2 is (1, 1.15); in one embodiment, k1 is 1.2 and k2 is 1.1; in other embodiments, k1 and k2 can be selected as other values according to actual needs, but it is necessary to satisfy k1 > k2 > 1.

[0065] Step 5: Reduce the bus voltage, and the operating frequency decreases accordingly until it is less than the control upper limit frequency.

[0066] In one embodiment, when the operating frequency fsw of the resonant circuit is greater than the control upper limit frequency fup, the bus voltage is gradually reduced, and then the operating frequency of the resonant circuit is gradually reduced until it is less than the control upper limit frequency. More specifically, when the operating frequency fsw of the resonant circuit is greater than the control upper limit frequency fup, the power supply module gradually reduces the bus voltage in real time according to the operating frequency fsw. After detecting the reduction of the bus voltage, according to the battery voltage and the set charging current, the operating frequency of the resonant circuit is gradually decreased until it is less than the control upper limit frequency fup.

[0067] Step 6: Increase the bus voltage, and the operating frequency increases accordingly until it is greater than the control lower limit frequency.

[0068] In one embodiment, when the operating frequency fsw is less than the control lower limit frequency fdown, the bus voltage is gradually increased, and then the operating frequency of the resonant circuit is gradually increased until it is greater than the control lower limit frequency fdown. More specifically, when the operating frequency fsw is less than the control lower limit frequency fdown, the power supply module gradually increases the bus voltage in real time according to the operating frequency fsw. After detecting the increase in the bus voltage, the operating frequency of the resonant circuit is gradually increased according to the battery voltage and the set charging current until it is greater than the control lower limit frequency fdown.

[0069] It can be understood that during the operation of the resonant circuit, the adjustment of the bus voltage in the above steps 5 and 6 has a certain limit. Its upper limit voltage is Vup = kup * Vbat, and its lower limit voltage is Vdown = kdown * Vbat, where kup > kdown > k. In one embodiment, the range of kup is [k * 1.05, k * 1.06], and the range of kdown is generally [k * 1.01, k * 1.02]; in other embodiments, other values of kup and kdown can also be selected as needed.

[0070] For easy understanding, the logical relationship between the bus voltage and the operating frequency is described as follows:

[0071] When charging the battery through the resonant circuit, the relationship between the DC bus voltage Vbus and the battery voltage Vbat is Vbat = (Kr / k) * Vbus. Correspondingly, Vbus = Vbat * (k / Kr). Where k is defined as above and is the transformer turns ratio, and Kr is the equivalent gain of the resonant circuit. Figure 11 Shows the relationship between the operating frequency fsw of the resonant circuit and the equivalent gain Kr of the resonant circuit. In particular, the equivalent gain Kr corresponding to the resonant frequency f0 is 1. From Figure 11 It can be seen that the equivalent gain Kr of the resonant circuit decreases as the operating frequency fsw increases, and vice versa, that is, the change trends of the two (the equivalent gain Kr of the resonant circuit and the operating frequency fsw) are inversely proportional. According to the formula between the DC bus voltage Vbus and the battery voltage Vbat mentioned above, the bus voltage Vbus and the equivalent gain Kr of the resonant circuit are inversely proportional, so the bus voltage Vbus and the operating frequency fsw are directly proportional in terms of change trend. Since the battery voltage Vbat and the transformer turns ratio k remain constant, when the DC bus voltage Vbus is decreased, according to the aforementioned formula, in order to keep the system stable, the equivalent gain Kr needs to increase correspondingly. By Figure 11From the relationship between fsw and Kr, it can be seen that the corresponding increase in the equivalent gain Kr can be achieved by correspondingly reducing the operating frequency fsw, thereby maintaining system stability; when the DC bus voltage Vbus is increased, according to the aforementioned formula, in order to maintain system stability, the equivalent gain Kr needs to be correspondingly reduced. From Figure 11 From the relationship between fsw and Kr, it can be seen that the corresponding reduction in the equivalent gain Kr can be achieved by correspondingly increasing the operating frequency fsw, thereby maintaining system stability. That is, when the bus voltage is reduced, the operating frequency of the resonant circuit is correspondingly reduced; when the bus voltage is increased, the operating frequency of the resonant circuit is correspondingly increased.

[0072] In the above method for frequency modulation of the resonant circuit, the DC bus passes through the resonant circuit to obtain a lower voltage for charging the battery. When the system is operating stably and the charging current of the battery is large, that is, the charging current > the first current threshold, the operating frequency of the resonant circuit can be made to work within a range slightly greater than the resonant frequency (i.e., between the control lower limit frequency and the control upper limit frequency), thereby reducing the stress on the switching tubes (such as MOS tubes) of the resonant circuit; at the same time, when the charging current of the battery is small, by selecting appropriate initial values of the bus voltage and the first current threshold, when the charging current of the battery < the first current threshold, the turn-off current of the switching tubes (such as MOS tubes) of the resonant circuit is relatively small, that is, even if the operating frequency of the resonant circuit is not near the resonant frequency, the stress on the switching tubes (such as MOS tubes) of the resonant circuit is also within the acceptable range. That is, for different charging currents, the stress on the switching tubes (such as MOS tubes) of the resonant circuit can be made within the tolerable range, thereby achieving stable control of the battery charging current on the premise of saving the front-stage boost / buck circuit.

[0073] Currently, the control chips of energy storage products generally have two architectures: (1) The main control chip controls the power supply module, and the slave control chip controls the resonant circuit; (2) The same control chip controls the power supply module and the resonant circuit at the same time. Below, different system block diagrams are proposed for these two control architectures respectively. The corresponding system block diagram and partial block diagram of the first type are as Figures 3 - 6 shown, and the corresponding system block diagram and partial block diagram of the second type are as Figures 7 - 10 shown.

[0074] Please refer to Figure 3 , A resonant circuit frequency modulation system provided by the present invention, the system includes a main control chip, a slave control chip, a rectification module, a DC conversion module, a DC bus, a resonant circuit, and a battery. Among them, the rectification module and the DC conversion module are collectively referred to as the power supply module. The rectification module is an AC-to-DC conversion module, and the DC conversion module is a DC-to-DC conversion module; in one embodiment, the input of the rectification module, that is, the AC power supply, is the power grid, and the input of the DC conversion module, that is, the DC power supply, is the solar panel; in other embodiments, the DC power supply can also be other types of DC power supplies.

[0075] Among them, the main control chip and the slave control chip are collectively referred to as the control chip; the slave control chip is used to collect the DC bus voltage (abbreviated as the bus voltage), the current charging current of the battery, and the operating frequency of the resonant circuit and transmit them to the main control chip, and to control the increase and decrease of the operating frequency of the resonant circuit; the main control chip judges the aforementioned signals received, so as to control the power supply module to boost, step down or stabilize the voltage of the DC bus (that is, keep the bus voltage unchanged); for the specific control logic, please refer to the aforementioned frequency modulation method.

[0076] It can be understood that the signal transmission between the main control chip and the slave control chip can be SCI transmission, SPI transmission or other wired transmission methods.

[0077] It can be understood that the operating frequency of the resonant circuit collected by the slave control chip can be the instantaneous frequency or the average frequency within the power frequency period: when only the AC power supply supplies power to the resonant circuit after passing through the rectification module and the DC bus, or when the AC power supply supplies power to the resonant circuit after passing through the rectification module and the DC bus, and at the same time the DC power supply supplies power to the resonant circuit after passing through the DC conversion module and the DC bus, at this time, the slave control chip collects the average frequency within the power frequency period of the resonant circuit as the operating frequency of the resonant circuit; when only the DC power supply supplies power to the resonant circuit after passing through the DC conversion module and the DC bus, at this time, the slave control chip collects the instantaneous frequency of the resonant circuit as the operating frequency of the resonant circuit, or the slave control chip collects the average frequency within the power frequency period of the resonant circuit as the operating frequency of the resonant circuit.

[0078] In an embodiment of the present invention, as Figure 6 shown, the main control chip includes a first judgment module, a second judgment module, and a third judgment module. The first judgment module is used to judge whether the current charging current of the battery is greater than the first current threshold, the second judgment module is used to judge whether the operating frequency of the resonant circuit is greater than the control upper limit frequency; the third judgment module is used to judge whether the operating frequency of the resonant circuit is less than the control lower limit frequency.

[0079] Among them, the power supply module boosts, steps down or stabilizes the voltage of the DC bus, including the following situations: First, only the AC power supply boosts, steps down or stabilizes the voltage of the DC bus through the rectification module; Second, only the DC power supply boosts, steps down or stabilizes the voltage of the DC bus through the DC conversion module; Third, both the AC power supply passes through the rectification module and the DC power supply passes through the DC conversion module to boost, step down or stabilize the voltage of the DC bus. After the electric energy of the power supply module is transmitted to the DC bus, the DC bus charges the battery through the resonant circuit.

[0080] In one embodiment of the present invention, the main control chip and the slave control chip are any one of a DSP module, an ARM module, or an MCU module to implement functions such as control.

[0081] Please refer to Figure 4 , the present invention also provides another resonant circuit frequency modulation system, which is different from the Figure 3 embodiment shown in that in the resonant circuit frequency modulation system of Figure 4 , the power supply module is only a rectification module. If it is necessary to boost, step down, or regulate the voltage of the DC bus, only the AC power supply boosts, steps down, or regulates the voltage of the DC bus through the rectification module.

[0082] Please refer to Figure 5 , the present invention also provides another resonant circuit frequency modulation system, which is different from the Figure 3 embodiment shown in that in the resonant circuit frequency modulation system of Figure 5 , the power supply module is only a DC conversion module. If it is necessary to boost, step down, or regulate the voltage of the DC bus, only the DC power supply boosts, steps down, or regulates the voltage of the DC bus through the DC conversion module.

[0083] Please refer to Figure 7 , the present invention also provides another resonant circuit frequency modulation system, which is different from the Figure 3 embodiment shown in that in the resonant circuit frequency modulation system of Figure 7 , there is only 1 control chip, and the control chip has the functions of acquisition, judgment, and control. Specifically, the control chip is used to collect the DC bus voltage (abbreviated as the bus voltage), the current charging current of the battery, and the operating frequency of the resonant circuit and transmit them to the main control chip, and judge the foregoing signals received, so as to control the power supply module to boost, step down, or regulate the voltage of the DC bus (that is, keep the bus voltage unchanged), and control the rise and fall of the operating frequency of the resonant circuit. For the specific control logic, please refer to the foregoing frequency modulation method.

[0084] It can be understood that the operating frequency of the resonant circuit collected by the control chip can be the instantaneous frequency or the average frequency within the power frequency period: when only the AC power supply supplies power to the resonant circuit through the rectification module and the DC bus, or when the AC power supply supplies power to the resonant circuit through the rectification module and the DC bus, and at the same time the DC power supply supplies power to the resonant circuit through the DC conversion module and the DC bus, at this time, the control chip collects the average frequency within the power frequency period of the resonant circuit as the operating frequency of the resonant circuit; when only the DC power supply supplies power to the resonant circuit through the DC conversion module and the DC bus, at this time, the control chip collects the instantaneous frequency of the resonant circuit as the operating frequency of the resonant circuit, or the control chip collects the average frequency within the power frequency period of the resonant circuit as the operating frequency of the resonant circuit.

[0085] In one embodiment of the present invention, the control chip is any one of a DSP module, an ARM module, or an MCU module to achieve the control function.

[0086] In one embodiment of the present invention, as Figure 10 shown, the control chip includes a first judgment module, a second judgment module, and a third judgment module. The first judgment module is used to judge whether the current charging current of the battery is greater than a first current threshold value. The second judgment module is used to judge whether the operating frequency of the resonant circuit is greater than the control upper limit frequency. The third judgment module is used to judge whether the operating frequency of the resonant circuit is less than the control lower limit frequency.

[0087] Please refer to Figure 8 , the present invention also provides another resonant circuit frequency modulation system, which is different from the Figure 7 embodiment shown in that, Figure 8 in the resonant circuit frequency modulation system of, the power supply module is only a rectification module. If it is necessary to boost, step down, or stabilize the DC bus, only the AC power supply passes through the rectification module to boost, step down, or stabilize the DC bus.

[0088] Please refer to Figure 9 , the present invention also provides another resonant circuit frequency modulation system, which is different from the Figure 7 embodiment shown in that, Figure 9 in the resonant circuit frequency modulation system of, the power supply module is only a DC conversion module. If it is necessary to boost, step down, or stabilize the DC bus, only the DC power supply passes through the DC conversion module to boost, step down, or stabilize the DC bus.

[0089] For the above-mentioned resonant circuit frequency modulation system, the AC power supply or / and the DC power supply pass through the power supply module to obtain a DC bus with a higher voltage, and then pass through the resonant circuit to obtain a lower voltage to charge the battery. Combining the foregoing frequency modulation method, when the system operates stably, for different charging currents of the battery (whether greater than the first current threshold or less than the first current threshold), the stress of the switching tube (such as a MOS tube) of the resonant circuit can be within an acceptable range. Thus, stable control of the charging current is achieved on the premise of saving the pre-stage boost / buck circuit.

[0090] The above embodiments only represent several implementation manners of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the patent of the present invention. For those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention should be subject to the appended claims.

Claims

1. A resonant circuit frequency modulation method, characterized in that: The method comprises: Step 1: The bus voltage is initialized to k0*Vbat, where k0 is k*1.03-k*1.04, where k is the transformer turns ratio of the resonant circuit; Step 2: Determine whether the current charging current of the battery is greater than the first current threshold; If yes, proceed to step 3; if no, keep the bus voltage unchanged at the initial value; Step 3: Collect the operating frequency of the resonant circuit; Step 4: Determine whether the operating frequency is greater than the upper control limit frequency; If yes, proceed to step 5; if no, determine whether the operating frequency is less than the control lower limit frequency; if yes, proceed to step 6; if no, return to step 4; Step 5: The bus voltage is reduced, and the operating frequency is reduced accordingly until it is less than the control upper limit frequency; Step 6: Increase the bus voltage, and the operating frequency increases accordingly until it is greater than the control lower limit frequency; Among them, Vbat is the battery voltage, k0*Vbat is the initial value of the bus voltage, k0 is the proportional coefficient, the first current threshold is 0.2-0.25 times the rated current of the resonant circuit, the upper control limit frequency is the resonant frequency*k1, the lower control limit frequency is the resonant frequency*k2, the range of k1 is 1.15≤k1≤1.3, and the range of k2 is 1<k2<1.

15.

2. The resonant circuit frequency modulation method according to claim 1, characterized in that: When the resonant circuit is provided with electric energy by an AC power supply, the operating frequency of the resonant circuit is the average frequency within the power frequency cycle; when the resonant circuit is provided with electric energy only by a DC power supply, the operating frequency of the resonant circuit is the instantaneous frequency or the average frequency within the power frequency cycle.

3. The resonant circuit frequency modulation method according to claim 2, characterized in that: The method for obtaining the average frequency within the power frequency period includes: In each power frequency cycle T, the instantaneous frequency is collected every T / N, and the instantaneous frequency is accumulated N times and then the average value is calculated. The average value is used as the operating frequency of the resonant circuit, wherein N is a positive integer, the range of the power frequency cycle T is 16.6ms≤T≤20ms, and the range of N is 300≤N≤400.

4. The resonant circuit frequency modulation method according to claim 1, characterized in that: The fifth step is specifically as follows: The bus voltage is gradually reduced, and then the operating frequency of the resonant circuit is gradually reduced until it is less than the control upper limit frequency.

5. The resonant circuit frequency modulation method according to claim 1, characterized in that: The sixth step is specifically as follows: The bus voltage is gradually increased, and then the operating frequency of the resonant circuit is gradually increased until it is greater than the control lower limit frequency.

6. The resonant circuit frequency modulation method according to claim 1, characterized in that: The k1 is 1.2, and the k2 is 1.

1.

7. A resonant circuit frequency modulation system, wherein the frequency modulation method according to any one of claims 1 to 6 is applicable to the frequency modulation system, characterized in that: The frequency modulation system includes a control chip, a power supply module, a DC bus, a resonant circuit, and a battery, wherein: The control chip is used to collect the bus voltage, the current charging current of the battery and the operating frequency of the resonant circuit and make judgments, control the power supply module to boost, reduce or stabilize the DC bus, and control the rise and fall of the operating frequency of the resonant circuit; The DC bus charges the battery through a resonant circuit; The control chip includes a first judgment module, a second judgment module, and a third judgment module. The first judgment module is used to judge whether the current charging current of the battery is greater than a first current threshold; the second judgment module is used to judge whether the operating frequency is greater than an upper control limit frequency; and the third judgment module is used to judge whether the operating frequency is less than a lower control limit frequency.

8. The resonant circuit frequency modulation system according to claim 7, characterized in that: The power supply module is a DC conversion module and / or a rectification module.

9. The resonant circuit frequency modulation system according to claim 8, characterized in that: The control chip is any one of a DSP module, an ARM module or an MCU module.

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