Multiple resonance type LLC resonant tank added with Anti-resonance and dc-dc converter using the same

Abstract

To provide a multiple resonance type LLC resonant tank which is applicable to an application of a wide control range of a voltage regulation and a large step-up / step-down ratio with less component elements and capable of sufficiently narrowing down output in the case of a lightweight load and with which sufficient output can be expected by a parameter of a high frequency transformer in the case of a heavy load.SOLUTION: A capacitor for anti-resonance is connected in parallel with a resonance inductor constituting an LLC resonant tank in which excitation inductance, a resonant inductor and a resonant capacitor are connected in series. Regarding anti-resonance, impedance becomes theoretically infinitely large in a resonant frequency, so that a voltage in an output end is zero. Therefore, a voltage conversion ratio of the LLC resonant tank becomes zero. Frequency control is performed between a normal resonant frequency (first resonant frequency) of the LLC resonant tank and a resonant frequency of newly configured anti-resonance (second resonant frequency), so that voltage regulation control can be performed over a wide range.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an LLC resonant tank with anti-resonance and an LLC resonant DC-DC converter using the same. [Background technology]

[0002] LLC resonant DC-DC converters, a type of complex resonant power converter, have excellent advantages, such as high insulation performance and the ability to transmit large power, as well as the ability to miniaturize equipment by enabling low-loss switching operation (soft switching) of power semiconductor devices under high-frequency conditions.For this reason, in recent years, LLC resonant DC-DC converters have been widely used in the power electronics field, such as power conditioners for new energy systems, electric vehicles, and microgrids. Generally, as the frequency increases, the efficiency decreases due to the increased switching loss, but in the case of LLC resonant DC-DC converters, by utilizing electrical resonant operation and the excitation current of a high-frequency transformer, it is possible to use soft switching technology under a wide range of load conditions. This has the advantage of significantly suppressing switching loss and realizing miniaturization without reducing efficiency. In addition, since the effect of noise suppression by the switching of power semiconductor devices is obtained, another advantage is low noise.

[0003] While it has these advantages, the LLC resonant DC-DC converter has a relatively narrow and limited voltage adjustment range. Therefore, in systems that require wide input / output voltage adjustment, it is common to use a two-stage configuration in which it is combined with a separate DC-DC converter (e.g., a chopper DC-DC, etc.). However, this increases the number of circuit elements, which causes problems such as an increase in the volume that can be mounted for the elements and costs, as well as a decrease in the overall power conversion efficiency.

[0004] To solve the above problems, efforts have been made to widen the range of LLC resonant DC-DC converters.Normally, LLC resonant DC-DC converters adjust the voltage by pulse frequency modulation (PFM) of power semiconductor elements, but to widen the range, in addition to normal PFM, the operating range has been expanded by combining various operating modes such as switching the circuit configuration with a switch and adding control by phase shift. However, such a method has problems such as complicated circuit control and difficulty in seamlessly transitioning between operation modes. Furthermore, LLC resonant DC-DC converters have the problem of excessive inrush current (rush current) occurring when the resonant tank and output capacitor are charged at start-up. To address this issue, it is necessary to add an inrush prevention circuit or soft-start control, or both.

[0005] To solve these problems, one of the inventors has already proposed a multiplex resonant LLC DC-DC converter (hereinafter also referred to as LLCLC converter) that applies an anti-resonant tank to the primary transformer side of a conventional LLC resonant DC-DC converter (Non-Patent Document 1). The LLCLC converter applies an LC parallel anti-resonant tank to the primary high-frequency transformer side of an LLC resonant DC-DC converter, and can set the anti-resonant frequency in a frequency range higher than the resonant frequency that is near the normal operating point, and can shift the switching frequency of the circuit to the anti-resonant frequency when the load is short-circuited or when starting up, thereby ensuring theoretically infinite impedance and effectively suppressing overcurrent and the resulting overvoltage generation in the LC series resonant tank.

[0006] In addition, a high impedance state that suppresses overcurrent due to small frequency fluctuations from the operating frequency band during normal operation can be generated, improving the responsiveness of DC-DC converter control. Furthermore, similarly, the effect of the anti-resonant tank makes it possible to realize large step-down operation that was difficult to achieve with conventional LLC resonant DC-DC converters, so it can also be used as a front-end DC-DC converter with a DC voltage step-up / step-down function that integrates pulse amplitude modulation (PAM) and HF link DC-DC conversion. In other words, it becomes possible to control power over a wide range even in the step-down range that was difficult to achieve with conventional LLC resonant DC-DC converters.

[0007] On the other hand, there are known documents that consider a series resonant LLC converter using an anti-resonant tank (Non-Patent Documents 2 and 3). Non-Patent Document 2 deals with an LC single resonant DC-DC converter that does not take into account (infinite) the excitation inductance of the high-frequency transformer, and the contents are discussed mainly as a theoretical consideration of a resonant DC-DC converter that has an operating point in a capacitive frequency domain that uses an anti-resonant tank as a variable capacitor. Non-Patent Document 3 also discusses a method for improving efficiency by generating a triple harmonic component of the switching frequency from the anti-resonant tank and injecting it into the primary-side resonant current of the high-frequency transformer to utilize the triple frequency component of the primary-side inverter square wave voltage. Therefore, it differs from the LLCLC converter that uses the above-mentioned LC parallel resonant tank (anti-resonant tank) having an operating point in the inductive load region from the viewpoint of realizing overvoltage / overcurrent suppression and step-down operation. [Prior art documents] [Patent documents]

[0008] [Non-Patent Document 1] Tomokazu Mishima et al., “Five-element Multiplex Resonant DC-DC Converter with Variable Inductive Reactance Function”, Transactions on Electrical Engineering of Japan, Vol. 135, No. 1, pp. 27-38 (2015). [Non-Patent Document 2] Kazuhiko Sakakibara, "A Constant-Voltage Output Series Resonant Converter with Improved Load Dependence of Operating Frequency", Transactions of the Institute of Electrical and Electronics Engineers, Vol. J71-B, No. 12, pp. 1682-1691 (1988). [Non-Patent Document 3] D. Fu et al., “Novel multi-element resonant converter for front-end dc / dc converters”, 2008 IEEE Power Electronics Specialists Conference, pp.250-256 (2008). Summary of the Invention [Problem to be solved by the invention]

[0009] The inventors have investigated the configuration of an LLC resonant tank that can achieve the wide voltage adjustment range of an LLC resonant tank with anti-resonance adopted in already proposed LLCLC converters with even fewer component elements, while reducing cost and size and providing an effect equal to or greater than that of an LLCLC converter. In other words, the present invention aims to provide a multiple resonant LLC resonant tank that uses fewer components, has a wide control range for voltage adjustment, is applicable to applications with a large step-up / step-down ratio, can sufficiently reduce output when the load is light, and can expect sufficient output depending on the transformer parameters when the load is heavy. [Means for solving the problem]

[0010] In order to solve the above problems, the multiple-resonance type LLC resonant tank of the present invention is characterized in that an anti-resonance capacitor is connected in parallel to a resonant inductor that constitutes an LLC resonant tank in which an excitation inductance of a high-frequency transformer, a resonant inductor, and a resonant capacitor are connected in series. An LC parallel anti-resonant circuit is formed by adding an anti-resonant capacitor in parallel to the resonant inductor that constitutes the LLC resonant tank. The impedance of the anti-resonant circuit is theoretically infinite at its resonant frequency, so the voltage at the output terminal is zero, and therefore the voltage conversion ratio of the LLC resonant tank is zero. In other words, by controlling the frequency between the normal resonant frequency (first resonant frequency) of the LLC resonant tank and the resonant frequency (second resonant frequency) of the newly constructed anti-resonant circuit, it becomes possible to control the voltage adjustment over a wide range from zero to the voltage conversion ratio (including the boost adjustment ability) that the LLC resonant tank originally possesses, and both boost and buck can be achieved by voltage adjustment only using pulse frequency modulation (PFM). In other words, the voltage conversion ratio can be expanded by changing the driving frequency of the power converter between the resonant frequency of the LLC resonant tank and the anti-resonant frequency of the anti-resonant tank (a resonant inductor and an anti-resonant capacitor connected in parallel), that is, by changing the driving frequency of the excitation power supply (high-frequency inverter) of the LLC resonant tank.

[0011] In this way, widening the voltage adjustment range of the LLC resonant tank alone eliminates the need for a DC-DC converter for voltage adjustment, realizing a smaller and cheaper system, and also facilitating control since voltage adjustment is possible with frequency modulation alone. That is, with conventional LLC resonant DC-DC converters, the voltage adjustment range is narrow, so it is necessary to combine it with a DC-DC converter for voltage adjustment to form a two-stage configuration, which required an auxiliary circuit to achieve soft switching in the DC-DC converter for voltage adjustment, but this auxiliary circuit is no longer necessary, and soft switching operation can be maintained over a wide range, just like with conventional LLC resonant DC-DC converters.

[0012] Here, it is preferable to select a capacitance of the anti-resonant capacitor added in parallel to the resonant inductor that is smaller than the capacitance of the series-connected resonant capacitors that make up the LLC resonant tank, and to set the anti-resonant frequency to a higher frequency than the resonant frequency of the LLC resonant tank. In the conventional LLC resonant converter, as described later, it is possible to perform a "step-up" operation by setting a frequency lower than the resonant frequency, and to perform a certain degree of "step-down" operation by setting a frequency higher than the resonant frequency. However, the conventional LLC resonant converter has a narrow voltage adjustment range and only a small step-down capability, so it is necessary to set the frequency very high in order to perform a sufficient step-down operation. In other words, the frequency sensitivity is weak on the high-frequency side of the resonant frequency of the LLC resonant converter, and there is no voltage adjustment function (step-down function) for frequency modulation. To compensate for this, the multiple resonant type LLC resonant tank of the present invention is loaded with an anti-resonant tank, and the anti-resonant frequency is set on the high-frequency side. In this way, the multiple-resonance type LLC resonant tank of the present invention has an anti-resonant tank added to it, expanding the step-down adjustment capability, and the anti-resonant frequency is configured to be higher than the resonant frequency, which is the step-down region of the conventional LLC resonant tank. This resonant frequency is set by adding a series-connected resonant inductor L r and the resonant capacitor C r Therefore, 1 / [2π√(L r C r )], while the anti-resonant frequency is determined by the parallel-connected resonant inductor L r and anti-resonance capacitor C a Therefore, 1 / [2π√(L r C a In the multiple resonant type LLC resonant tank of the present invention, the resonant inductor L r However, the inductor that constitutes the resonant frequency and the inductor that constitutes the anti-resonant frequency are both used, i.e., the same component is used. In other words, to set the anti-resonant frequency to a higher frequency than the resonant frequency, the anti-resonant capacitor C a necessarily has a resonant capacitor C r Therefore, the smaller the capacitance, the better.

[0013] Also, at the start of startup, it is possible to prevent inrush current (rush current) by gradually changing the operating frequency of the circuit from the resonant frequency of the newly configured anti-resonant circuit to the series resonant frequency of the LLC resonant DC-DC converter. By eliminating the need for a circuit to prevent inrush current, it is possible to achieve a smaller size and lower cost. Inrush current can also be prevented by simply frequency modulation, which gradually changes the frequency, making soft start control easier and shortening the startup time.

[0014] A DC-DC converter can be constructed by using the multiple resonant LLC resonant tank of the present invention, an inverter circuit having a full-bridge configuration or a half-bridge configuration, and a rectifier circuit connected via a high-frequency transformer. Here, the rectifier circuit includes a voltage doubler rectifier circuit, a voltage tripler rectifier circuit, a voltage quadruple rectifier circuit, and a center tap rectifier circuit. The resonant capacitor constituting the multiple resonant LLC resonant tank may be provided between the input power supply and the ground in the inverter circuit. The multiple resonance type LLC resonant tank of the present invention can be used as a bidirectional DC-DC converter by providing a similar multiple resonance type LLC resonant tank not only on the primary side but also on the secondary side via a transformer, and replacing the rectifier circuit on the secondary side with an inverter circuit composed of the same active switches as on the primary side. In this case, the component constants and resonant frequency constituting the multiple resonance type LLC resonant tank on the secondary side may be the same as those on the primary side, or may be different constants. Effect of the Invention

[0015] The multiple resonant LLC resonant tank of the present invention has the advantage that it is possible to expand the voltage adjustment range without adding a voltage adjustment circuit, and it can be applied to applications with a large step-up / step-down ratio with fewer component elements. [Brief description of the drawings]

[0016] [Figure 1] Circuit diagram of DC-DC converter using multiplex resonant type LLC resonant tank [Diagram 2]Equivalent circuit of multiplex-resonant LLC resonant tank [Diagram 3] Voltage transformation ratio graph of multiplexed LLC resonant tank [Figure 4] Explaining start-up switch control of a DC-DC converter using an LLC resonant tank [Diagram 5] An explanatory diagram of start-up switch control of a DC-DC converter using a multiplex resonant type LLC resonant tank [Figure 6] DC-DC converter circuit using a half-bridge multiplex resonant LLC resonant tank (Example 2) [Figure 7] A DC-DC converter circuit using a half-bridge multiplex resonant type LLC resonant tank with a resonant capacitor between the input power supply and GND (Example 2) [Figure 8] A DC-DC converter circuit using a multiplexed resonant LLC resonant tank and equipped with a voltage doubler rectifier circuit (Example 3) [Figure 9] Bidirectional DC-DC converter using multiplexed resonant type LLC resonant tank (Example 4) [Figure 10] Circuit configuration diagram of a conventional LLC resonant DC-DC converter [Figure 11] LLC Resonant Tank Equivalent Circuit [Figure 12] Graph of the Voltage Transformation Ratio of LLC Resonant Tank [Figure 13] A circuit combining a chopper DC-DC converter [Figure 14] Circuit equipped with inrush protection circuit [Figure 15] Circuit diagram of LLCLC converter [Figure 16] Equivalent circuit of LLCLC resonant tank (5-element configuration) [Figure 17] Voltage transformation ratio graph of LLCLC resonant tank (5-element configuration) BEST MODE FOR CARRYING OUT THEINVENTION

[0017] First, the load power and voltage control characteristics (voltage adjustment range) of a conventional LLC resonant DC-DC converter are explained, and their features and problems are clarified. Next, the circuit configuration, load power and voltage control characteristics (voltage adjustment range) of an LLCLC converter using an LC direct resonant tank and an LC parallel resonant tank (anti-resonant tank) are explained. Then, the DC-DC converter using a multiple resonant type LLC resonant tank of the present invention (hereinafter, also referred to as a "four-element configuration" because the circuit configuration of the resonant tank is composed of an LC direct resonant tank and an anti-resonant LC parallel resonant tank) is explained. In addition, for each converter circuit, the full-bridge type will be described, which is more useful when large-capacity applications such as medium-capacity and large-capacity applications are assumed.

[0018] Figure 10 shows the circuit configuration of a conventional LLC resonant DC-DC converter using the full-bridge method. The LLC resonant DC-DC converter consists of four blocks: a power switch, an LLC resonant tank, a transformer, and a diode rectifier. The power switch is made up of an inverter circuit configured in a full-bridge configuration, and the primary circuit consisting of the inverter circuit and the LLC resonant tank is connected to the secondary diode rectifier and the load via a high-frequency transformer (also called an HF transformer). The LLC resonant tank is made up of a series inductor L including the leakage inductance, which is a parasitic component of the HF transformer. r and the excitation inductance L m A resonant capacitor C is connected in series with r is connected. The primary inverter current i p and the secondary rectifier circuit current i through the transformer s is formed as a resonant current. The active switches (Q1 to Q4) perform ZVS (Zero Volt Switching) operation using the output capacitance of the power MOSFET or an external lossless snubber capacitor, while the secondary side rectifier diodes (D1 to D4) are s This performs ZCS (Zero Current Switching) operation.

[0019] Here, in order to facilitate the analysis of the input / output voltage ratio and output power characteristics with respect to the operating frequency of the LLC resonant DC-DC converter, the ZVS commutation section where the transient phenomenon of the power MOSFET appears is ignored, and the fundamental-harmonics approximation is applied. That is, as shown in Figure 11, for the equivalent circuit of the LLC resonant tank, the square-wave bridge voltage v of the primary inverter is p The fundamental component of v pl Considering only the secondary rectifier circuit including the HF transformer, the output filter C0, and the load resistance R0, we will collectively define the AC equivalent resistance R e It is expressed as: Voltage transformation ratio M of LLC resonant tank LLC (=V s / V p ) can be calculated from the equivalent circuit of the LLC resonant tank shown in Figure 11 as follows:

[0020]

number

[0021] Therefore, the voltage transformation ratio M of the LLC resonant tank LLC is expressed as follows:

[0022]

number

[0023] The series inductor L, which is an element of the LLC resonant tank r , excitation inductance L m , resonant capacitor C r The setting values ​​of L r = 12μH, L m = 65μH, C r When the voltage conversion ratio is calculated when the input capacitance is set to 48 nF, the graph in Figure 12 is obtained. From Figure 12, when the output resistance R0 is a light load such as 40 to 80 Ω (resistance R0 is high), the boost (M LLC>1), voltage regulation capability can be secured to a certain extent, LLC <1), almost no voltage regulation capability is obtained. On the other hand, in the case of a heavy load (resistance value R0 is low) such as an output resistance value R0 of 5 to 20 Ω, LLC <1), voltage regulation capability can be secured to a certain extent, but the boost (M LLC It can be seen that the voltage regulation capability of 1) has not been achieved at all. However, the voltage conversion ratio M LLC By adjusting the switching frequency at the operating point of =1, PFM control with small frequency fluctuations over a wide range of load fluctuations is possible. On the other hand, LLC In the high frequency region (inductive load region) beyond the operating point of V = 1, the rate of change of output voltage and power with respect to the operating frequency decreases. As a result, the input voltage V in is applied directly, and L r and C r This will cause excessive voltage stress on the Therefore, the controllable voltage conversion ratio is only 1 under all load conditions, and it is found that the conventional LLC resonant DC-DC converter has almost no voltage adjustment capability.

[0024] Therefore, in a system that requires a wide voltage adjustment range in a conventional LLC resonant DC-DC converter, it is necessary to configure a voltage adjustment DC-DC converter (such as a chopper DC-DC converter) in combination with the front stage (Fig. 13(1)) or rear stage (Fig. 13(2)) of the LLC resonant DC-DC converter. However, the addition of the voltage adjustment DC-DC converter increases both the size and cost of the system.

[0025] In addition, in a conventional LLC resonant DC-DC converter, when starting up under almost no load conditions, a large inrush current occurs due to charging the LLC resonant tank and output capacitor.LLC <1) Since there is almost no voltage regulation capability (voltage regulation function), no matter how high the frequency is set, a large rush current is generated in the empty output capacitor until the output voltage approaches the input voltage. One method to solve this problem is to provide an inrush current prevention circuit as shown in Figure 14, but the circuit size increases by the amount of the added inrush current prevention circuit.

[0026] As mentioned above, conventional LLC resonant DC-DC converters have almost no voltage regulation capability. Focusing on this problem, the above-mentioned LLCLC converter, which has an operating point in the inductive load region, was studied. Next, the circuit configuration, load power, and voltage control characteristics (voltage regulation range) of the LLCLC converter are explained. FIG. 15 shows the circuit configuration of an LLCLC converter. The LLCLC converter 21 is an LLCLC converter that is connected in parallel to an inverter circuit on the primary side of an HF transformer of a conventional LLC resonant DC-DC converter. a C a ) anti-resonant tank, which utilizes the principle that the impedance of the anti-resonant tank theoretically becomes infinite when the operating frequency reaches the anti-resonant frequency, to suppress overcurrent caused by load short circuit phenomena and voltage stress in the LC series resonant tank.

[0027] In the analysis of the input / output voltage ratio and output power characteristics for the operating frequency of the LLCLC converter, similar to the LLC resonant DC-DC converter, the ZVS commutation section is ignored and the fundamental wave approximation method is applied. For the equivalent circuit of the LLCLC resonant tank shown in Figure 16 (hereinafter, it is also called a "five-element configuration" because the circuit elements of the resonant tank are composed of LLC and anti-resonant LC), the square-wave primary inverter bridge voltage v p The fundamental component of v pl Considering only the secondary rectifier circuit, output filter C0, and load resistance R0, the AC equivalent resistance R e The voltage conversion ratio M of the LLCLC resonant tank (5-element configuration) is expressed as LLCLC (=V s / V p ) can be calculated from the equivalent circuit as follows:

[0028]

number

[0029] Therefore, the voltage transformation ratio M of the LLCLC resonant tank (five-element configuration) LLCLC is expressed as follows:

[0030]

number

[0031] The resonant inductor L, which is an element that configures the LLCLC resonant tank (five-element configuration), r , excitation inductance L m , resonant capacitor C r , the anti-resonant tank inductor L a , capacitor C a The setting values ​​of L r = 12μH, L m = 65μH, C r = 48nF, L a = 8μH, C a When the voltage conversion ratio is calculated when the input capacitance is set to 36 nF, the graph in Figure 17 is obtained. As shown in Figure 17, the voltage is increased (M LLCLC >1), the voltage regulation capability is lost, but the voltage conversion ratio always becomes zero at anti-resonance, so the step-down (M LLCLC <1), the voltage regulation capability is always ensured. In other words, when the output resistance R0 is a light load such as 40 to 80 Ω (resistance R0 is high), the voltage LLCLC >1) voltage regulation capability can be secured to the same extent as an LLC resonant tank, and unlike an LLC resonant tank, the step-down (M LLCLC <1), the voltage regulation capability is sufficiently secured. On the other hand, in the case of a heavy load (resistance value R0 is low) such as 5 to 20 Ω, the boost (M LLCLC >1), voltage regulation capability is not achieved at all, but LLCLC<1) Voltage regulation capacity is adequately secured.

[0032] Here, the above voltage conversion ratio M LLCLC In the load R e Regardless of M LLCLC becomes constant when M LLCLC The second denominator of the formula (R e Since the quadratic expression of the angular frequency ω becomes zero, there are two solutions for ω, and the ω 0- and ω 0+ From the two angular frequencies, f 0- (=ω 0- / 2π) and f 0+ (=ω 0+ / 2π) exists. Note that the inductor L r and inductor L a If (L r =L a ), voltage conversion ratio M LLCLC will be 1. In the case of a normal LLC resonant tank, as shown in Figure 12, when it is operated at a resonant angular frequency ω0, the output voltage is equal to the input voltage (when the HF transformer turns ratio is 1:1, but when the transformer turns ratio is not 1:1, the output voltage is n times the input voltage according to the turns ratio 1:n). Here, since this voltage relationship does not depend on the load, all the voltage conversion ratio characteristics with different load conditions overlap at this portion, and the load R e Regardless of M LLC Conversely, at frequencies other than the resonant angular frequency ω0, the output voltage fluctuates depending on the load. On the other hand, as shown in Figure 17, in the case of an LLCLC resonant tank (five-element configuration), there are two angular frequencies (ω 0- and ω 0+ ) exists, which has frequency f 0- and f 0+ It is. However, for an LLCLC resonant tank (five-element configuration), even with a 1:1 transformer turns ratio, f 0- and f 0+In this case, the output voltage does not necessarily equal the input voltage. The output voltage is equal to the input voltage when the inductor L r and inductor L a If (L r =L a ). Here, ω r is 1 / √(L r C r ) and ω a is 1 / √(L a C a In an LLCLC resonant tank (5-element configuration), the angular frequency at which the voltage conversion ratio is constant regardless of the load is ω 0- , ω 0+ There are two places, ω 0- ω r It is formed on the lower frequency side, and ω 0+ ω a It is formed on the higher frequency side.

[0033] In the following embodiment, an example of an embodiment of a multiple resonance type LLC resonant tank (four element configuration) of the present invention, which realizes a wide voltage adjustment range of an LLC resonant tank with anti-resonance adopted in an LLCLC converter with fewer component elements and reduces costs and size, will be described in detail with reference to the drawings. Note that the scope of the present invention is not limited to the following embodiment and illustrated examples, and many changes and modifications are possible. Example 1

[0034] FIG. 1 shows an example of a DC-DC converter circuit configuration diagram using the multiple resonant type LLC resonant tank (four-element configuration) of the present invention. A DC-DC converter using a multiple resonant type LLC resonant tank (four-element configuration) is composed of four blocks: a power switch, a multiple resonant type LLC resonant tank, an HF transformer, and a diode rectifier. The power switch is composed of an inverter circuit in a full-bridge configuration, but may be composed of an inverter circuit in a half-bridge configuration as described later. In addition, a primary side circuit composed of the inverter circuit and the multiple resonant type LLC resonant tank (four-element configuration) is connected to a secondary side diode rectifier and a load via an HF transformer. The multiple resonant type LLC resonant tank (four-element configuration) is composed of a resonant inductor L r and the excitation inductor L m and the resonant capacitor C r are connected in series, and the resonant inductor L r An anti-resonant capacitor is connected in parallel to the resonant tank. Other than this resonant tank, the converter is the same as the LCC resonant DC-DC converter and the LLCLC resonant DC-DC converter described above, and the primary inverter current i p and the secondary rectifier circuit current i through the transformer s is formed as a resonant current, and the active switches (Q1 to Q4) perform ZVS operation using the output capacitance of the power MOSFET or an external lossless snubber capacitor, while the secondary side rectifier diodes (D1 to D4) are s This performs ZCS operation.

[0035] A multiple-resonant LLC resonant tank (four-element configuration) is one in which a capacitor is added in parallel to the resonant inductor that constitutes the LLC resonant tank, to add anti-resonance. An anti-resonant tank is formed by adding a capacitor in parallel to the resonant inductor, and like the LLCLC resonant tank (five-element configuration), it utilizes the principle that when the operating frequency reaches the anti-resonant frequency, the impedance is theoretically infinite at the resonant frequency of the anti-resonant tank. In other words, since the voltage at the secondary output terminal is zero at the resonant frequency of the anti-resonant tank, the voltage conversion ratio of the multiple-resonant LLC resonant tank (four-element configuration) drops to near zero, allowing the voltage adjustment range to be expanded.

[0036] The LLCLC resonant tank (five-element configuration) can also expand the voltage adjustment range, but the anti-resonant tank (inductor L a and capacitor C a On the other hand, in the case of a multiple-resonance type LLC resonant tank (four-element configuration) with anti-resonance added, a resonant inductor L r In parallel with the capacitor C a The anti-resonance effect can be achieved simply by adding a capacitor, which is generally a smaller component than an inductor, so the effect of reducing cost and size is significant.

[0037] When configuring a conventional LLC resonant tank, the resonant inductor L r However, the leakage inductance of the HF transformer may be used instead of providing a separate resonant inductor L r When using it as a multi-resonance type LLC resonant tank (four-element configuration), the leakage inductance of the HF transformer is reduced by the resonant inductor L. r When using it as an anti-resonant inductor, L a and capacitor C aAlthough it is necessary to add a parallel circuit, this eliminates the need for a high-cost HF transformer with large losses such as a split winding, and makes it possible to use a highly efficient, low-cost HF transformer with high coupling.

[0038] In the analysis of the input / output voltage ratio and output power characteristics for the operating frequency of the DC-DC converter using the multiplex resonant type LLC resonant tank (four-element configuration) of the present invention, similarly to the LLC resonant DC-DC converter, the ZVS commutation section is ignored and the fundamental wave approximation method is applied. For the equivalent circuit of the multiplex resonant type LLC resonant tank (four-element configuration) shown in Figure 2, the square-wave bridge voltage v of the primary inverter is calculated. p The fundamental component of v pl Considering only the secondary rectifier circuit, output filter C0, and load resistance R0, the AC equivalent resistance R e The voltage conversion ratio M(=V s / V p ) can be calculated from the equivalent circuit as follows:

[0039]

number

[0040] Therefore, the voltage transformation ratio M of the multiplex resonant type LLC resonant tank (four-element configuration) is expressed as follows:

[0041]

number

[0042] Resonant inductor L, which is an element that configures the multiplex-resonant LLC resonant tank (four-element configuration) r , excitation inductance L m , resonant capacitor C r , anti-resonant capacitor C a The set values ​​of L r = 12μH, L m = 65μH, C r = 48nF, C aWhen the voltage conversion ratio is calculated when the input capacitance is set to 24nF, the graph in Figure 3 is obtained.

[0043] As shown in Figure 3, as in the case of the LLCLC resonant tank (5-element configuration), the voltage regulation capability for step-up (M>1) is lost depending on the heavy load (resistance value R0 is low resistance), but since the voltage conversion ratio always becomes zero in anti-resonance, the voltage regulation capability for step-down (M<1) is always ensured. That is, in the case of a light load (resistance value R0 is high resistance) such as an output resistance value R0 of 40 to 80 Ω, the voltage regulation capability for step-up (M>1) can be ensured to the same extent as the LLC resonant tank, and the voltage regulation capability for step-down (M<1) is sufficiently ensured, unlike the LLC resonant tank. On the other hand, in the case of a heavy load (resistance value R0 is low resistance) such as an output resistance value R0 of 5 to 20 Ω, the voltage regulation capability for step-up (M>1) is not obtained at all, but the voltage regulation capability for step-down (M<1) is sufficiently ensured, as in the case of the LLC resonant tank.

[0044] Here, if the voltage conversion ratio required for boosting is set by the winding ratio of the HF transformer, the resonant angular frequency ω0 and the resonant angular frequency ω a By controlling the frequency between these ranges, it is possible to control the entire voltage range. That is, the resonant angular frequency ω0 (first resonant angular frequency) of the multiple resonant type LLC resonant tank (four-element configuration) shown in FIG. 3 and the resonant angular frequency ω a By controlling the frequency between this frequency and the first resonant angular frequency (second resonant angular frequency), it becomes possible to control the voltage adjustment over a wide range, from zero to the voltage conversion ratio (including boost adjustment capability) that the multiple resonant LLC resonant tank (four-element configuration) originally possessed. Both step-up and step-down can be achieved simply by adjusting the voltage using pulse frequency modulation (PFM), which makes it possible to suppress overcurrent caused by load short circuits and voltage stress in the LC series resonant tank.

[0045] In the voltage transformation M of a multiplex resonant type LLC resonant tank (four-element configuration), the load R e The reason why M is constant regardless of the second denominator of the formula for calculating M above (R eThe quadratic expression of the angular frequency ω becomes zero, but ω2=1 / (L r ·(C r +C a )) and there is only one solution. In other words, one resonant angular frequency of ω0 shown in Figure 3 is obtained, and at the resonant frequency f0 (=ω0 / 2π), regardless of the load Re, (R e (regardless of Q related to the above), the voltage conversion ratio M is 1.

[0046] Next, we will explain the behavior at startup of a DC-DC converter using a multiple resonant type LLC resonant tank (four-element configuration). Figures 4 and 5 show circuit diagrams of a DC-DC converter using an LLC resonant tank and a DC-DC converter using a multiple resonant type LLC resonant tank (four-element configuration), respectively, graphs of the voltage conversion ratio, and explanatory diagrams of switch frequency control at startup. As mentioned above, in a DC-DC converter using an LLC resonant tank as shown in Figure 4(1), when starting up in an almost no-load state, a large rush current occurs due to charging the resonant tank and output capacitor. The voltage conversion ratio of the LLC resonant tank has extremely low step-down adjustment capability in the frequency range higher than the resonant frequency, so even if it is set to a fairly high frequency, a large voltage conversion ratio is maintained. Therefore, in order to achieve a soft start in an LLC resonant tank, it is first necessary to gradually increase the duty ratio from 0% to 50% at a frequency sufficiently higher than the resonant frequency (300kHz in the voltage conversion ratio graph in Figure 4(2)), and then gradually change the operating frequency to a stable point frequency while maintaining the duty ratio at 50% (see Figure 4(3)). However, this method has problems in that the control of the soft start becomes complicated and startup takes a long time. On the other hand, in a multiple-resonance type LLC resonant tank (four-element configuration) with anti-resonance added as shown in Figure 5 (1), there exists a frequency where the voltage adjustment ratio due to anti-resonance is zero (see the voltage conversion ratio graph in Figure 5 (2)), so soft-start control can be completed simply by gradually changing the frequency from the anti-resonant frequency to the stable point frequency (see Figure 5 (3)). There is no need to add an inrush prevention circuit or perform complex soft-start control, and startup can be completed in a short time. Example 2

[0047] A DC-DC converter using a multiplex resonant type LLC resonant tank (four-element configuration) can apply a full-bridge inverter circuit, but it can also apply a half-bridge inverter circuit as shown in Figures 6 (1) and (2). Here, FIG. 6(1) shows a symmetrical (DC voltage divided into two) half-bridge inverter, and FIG. 6(2) shows an asymmetrical half-bridge inverter.

[0048] As shown in Fig. 7, a half-bridge inverter circuit is applied, and a resonant capacitor C r A resonant capacitor C r´ It may be set as such. In Figure 7, two resonant capacitors C r´ By providing a resonant capacitor C r Regarding the point that can be considered the same as above, the resonant capacitor C r´ is connected in series with the HF transformer primary winding and the anti-resonant tank, and operates exactly the same as in Figure 6 (1). Note that the two resonant capacitors C r´ will be charging / discharging, but the DC voltage is sufficiently smoothed by the smoothing capacitor on the left, so the bus line (bus voltage) can maintain a constant voltage. Example 3

[0049] A DC-DC converter using a multiplexed resonant type LLC resonant tank (four-element configuration) may be configured to output a doubled voltage by applying a full-bridge inverter circuit as shown in Fig. 8 and replacing the rectifier circuit (diode rectifier) ​​on the secondary side of the HF transformer with a voltage doubler rectifier circuit 9. Note that the capacitor C s (=V0 / 2) is the bias capacitor. Example 4

[0050] A DC-DC converter using a multiple-resonance type LLC resonant tank (four-element configuration) can be configured as a bidirectional DC-DC converter by providing a multiple-resonance type LLC resonant tank 1 on both the primary and secondary sides as shown in Fig. 9 (1). In this case, the component constants and resonant frequency constituting the multiple-resonance type LLC resonant tank (four-element configuration) on the secondary side may be the same as those on the primary side, or different constants may be set. In addition, in the configuration of the bidirectional DC-DC converter shown in Fig. 9(1), either the primary side or the secondary side may be an LLCLC resonant tank (5-element configuration). Fig. 9(2) shows a circuit in which the primary side is a multiple-resonant LLC resonant tank (4-element configuration) 1, and the secondary side is an LLCLC resonant tank (5-element configuration) 21. In this case as well, the component constants and resonant frequency may be the same as those on the primary side, or different constants may be set. [Industrial Applicability]

[0051] Because the present invention expands the voltage adjustment range and enables system size and weight reduction, it is useful for chargers for EVs (Electric Vehicles) and power conditioners for V2H (Vehicle-to-Home), and is expected to contribute to the spread of electric mobility. [Explanation of symbols]

[0052] 1 Multiple resonance type LLC resonance tank (4 element configuration) 2,12 Inverter circuit 3,13 Diode rectifier 4,14 HF transformer 6,7 Half-bridge inverter circuit 8 Resonant Capacitor 9 Voltage multiplier rectifier circuit 11 LLC Resonant Tank 21 LLCLC resonant tank (5 element configuration)

Claims

1. A multiple resonance type LLC resonant tank, comprising an LLC resonant tank in which an exciting inductance of a high frequency transformer, a resonant inductor, and a resonant capacitor are connected in series, and an anti-resonant capacitor is connected in parallel to the resonant inductor.

2. 3. The multiple resonant LLC resonant tank of claim 2, wherein the voltage conversion ratio is expanded by changing the drive frequency of the power converter between the resonant frequency of the LLC resonant tank and the antiresonant frequency of the antiresonant tank in which the resonant inductor and the antiresonant capacitor are connected in parallel.

3. 2. The multiple-resonance type LLC resonant tank according to claim 1, wherein the capacitance of the anti-resonance capacitor is selected to be smaller than the capacitance of the resonant capacitor, and the anti-resonant frequency is set to be higher than the resonant frequency of the LLC resonant tank.

4. A multiple-resonant LLC resonant DC-DC converter comprising: a multiple-resonant LLC resonant tank according to any one of claims 1 to 3; an inverter circuit having a full-bridge configuration or a half-bridge configuration; and a rectifier circuit connected via a high-frequency transformer.

5. A power supply comprising: a multiple resonant type LLC resonant tank according to any one of claims 1 to 3; an inverter circuit having a half-bridge configuration; and a rectifier circuit connected via a high-frequency transformer; A multiple-resonance type LLC resonant DC-DC converter, characterized in that the resonant capacitor constituting the multiple-resonance type LLC resonant tank is provided between an input power supply and ground in the inverter circuit.

6. A multiple-resonant LLC resonant DC-DC converter comprising a multiple-resonant LLC resonant tank according to any one of claims 1 to 3 provided on the primary side and the secondary side via a high-frequency transformer, a first inverter circuit in a full-bridge configuration on the primary side and the multiple-resonant LLC resonant tank, and a second inverter circuit in a full-bridge configuration on the secondary side connected via a high-frequency transformer and the multiple-resonant LLC resonant tank.

7. The multiple resonant type LLC resonant DC-DC converter as described in claim 6, characterized in that the multiple resonant type LLC resonant tank on either the primary side or the secondary side is replaced with a resonant tank in which an excitation inductance of a high-frequency transformer, a resonant inductor, a resonant capacitor, and an LC parallel anti-resonant tank are connected in series.

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