Converter, power conditioner and power storage system

Abstract

To provide a converter which can deal with high input voltage without increasing circuit scale by using a switching element with lower breakdown voltage.SOLUTION: A converter comprises: primary windings Lp1, Lp2 divided into a plurality of pieces; and switching elements Q1, Q2 of the number corresponding to the primary windings Lp1, Lp2 divided. In a converter 10, the switching elements Q1, Q2 are connected in series with the divided primary windings Lp1, Lp2, respectively. The converter 10 intermittently applies input voltage Vi to a primary winding Lp of a transformer T by performing on / off control of the switching elements Q1, Q2, rectifies and smooths induction voltage generated in a secondary winding Ls of the transformer T to be output.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] One embodiment of the present invention relates to a converter, a power conditioner, and a power storage system. [Background technology]

[0002] The need for energy storage systems (ESS) is increasing due to the expansion of renewable energy use and the promotion of energy management. Energy storage systems consist of a storage battery that stores electricity and a The power conditioner is a power conversion device that includes a transformer that converts DC power and a converter that converts DC power to AC power (see, for example, Patent Document 1). The storage battery is a rechargeable secondary battery. The power conditioner is a power conversion device that includes a transformer that converts DC power and AC power.

[0003] When the transformer of a power conditioner is configured as an isolated type, a flyback converter 20 as shown in Figure 7 is used. In the converter 20, a primary winding Lp of a transformer T and a switching element Q are connected in series with an input voltage Vi. The switching element Q is turned on and off by a control signal Vg generated by a control circuit 21. The input voltage Vi is intermittently applied to the primary winding Lp of the transformer T by turning the switching element Q on and off. The transformer T stores energy E = 1 / 2 Lp i2 each time the switching element Q is turned on, and when the switching element Q is turned off, the stored energy is output to the secondary winding Ls as a flyback voltage Vr. The flyback voltage Vr generated in the secondary winding Ls of the transformer T is rectified and smoothed by a diode D and a capacitor Co to generate an output voltage Vo. The control circuit 21 adjusts the on-time of the switching element Q using the control signal Vg generated based on the detected value of the output voltage Vo, thereby controlling the amount of output energy and regulating the output voltage Vo. The control circuit 21 adjusts the ON time of the switching element Q, for example, while keeping the frequency f constant, and performs so-called PWM control. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2023-18328 Summary of the Invention [Problem to be solved by the invention]

[0005] In converter 20, a flyback voltage Vr is applied to switching element Q in addition to input voltage Vi. The flyback voltage Vr varies slightly depending on the turns ratio of transformer T and the on-duty setting of switching element Q, but at most it is approximately equal to the input voltage Vi. In other words, switching element Q needs to be able to withstand a voltage at least twice as high as the input voltage Vi.

[0006] When using a MOS-FET as the switching element Q, there are products with various withstand voltages, but relatively inexpensive products are those with a withstand voltage up to 900V, and products with a withstand voltage of 900V or more are extremely expensive. If the input voltage Vi is a high voltage of over 500V, an expensive product must be selected for the switching element Q. In recent years, in the field of energy storage systems, high voltages of over 1000V are generated, which has the disadvantage that the converters 20 used in these systems end up being expensive. Since there are not an unlimited number of high-voltage switching elements Q available, there is an upper limit to the input voltage Vi that the converter 20 can handle.

[0007] As shown in Figure 8, by connecting converters 20 in series (connecting capacitors Ci1 and Ci2 in parallel), the voltage applied to each switching element Q can be reduced. The input voltage Vi is divided in half by the series circuit of capacitors Ci1 and Ci2, and converters 20 are connected in parallel to each other. Each switching element Q of the converters 20 connected in parallel can be a product with a withstand voltage similar to that of the input voltage Vi.

[0008] However, due to variations in the capacitance of capacitors Ci1 and Ci2, the divided voltages differ slightly. Furthermore, the control circuits 21 of the parallel-connected converters 20 perform PWM control based on the detected value of the output voltage Vo, but the reference voltages used to compare the detected value of the output voltage Vo also vary. Due to variations in the reference voltages, the output voltages Vo of the parallel-connected converters 20 differ slightly, resulting in unbalanced output currents. Therefore, a parallel-connected converter 20 must include a balancing circuit (not shown) to balance the currents. The balancing circuit configuration is complex because the potential difference between the converters 20 connected in parallel at their secondary sides is large. Therefore, a parallel-connected converter 20 requires a complex balancing circuit in addition to multiple converters 20, resulting in a large and expensive circuit.

[0009] One embodiment of the present invention provides a converter that can handle a high input voltage without increasing the circuit size by using a low-voltage switching element. [Means for solving the problem]

[0010] One aspect of the present invention is a converter that applies an input voltage intermittently to a primary winding of a transformer by controlling the on / off of a switching element, and rectifies and smooths an induced voltage generated in a secondary winding of the transformer, and outputs the rectified voltage. One aspect of the present invention includes the primary winding divided into multiple sections, and the number of switching elements equal to the number of divisions of the primary winding. In one aspect of the present invention, a switching element is connected in series to each of the divided primary windings. [Effects of the Invention]

[0011] According to one aspect of the present invention, the voltages applied to the respective switching elements are divided by the divided primary windings, and therefore, the switching elements can be made to have a withstand voltage of approximately the input voltage Vi, thereby providing a converter that can handle high input voltages using low-voltage switching elements without increasing the circuit size. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram illustrating a configuration example of a power storage system. [Figure 2] FIG. 1 is a diagram illustrating a configuration of a first embodiment of a power storage system. [Figure 3] FIG. 10 is a diagram illustrating a configuration of a power storage system according to a second embodiment. [Figure 4] 4 is a waveform diagram of each part of the drive circuit shown in FIG. 3. [Figure 5] FIG. 10 is a diagram illustrating a configuration of a power storage system according to a third embodiment. [Figure 6] FIG. 10 is a diagram illustrating a configuration of a power storage system according to a fourth embodiment. [Figure 7] FIG. 1 is a diagram illustrating an example of the configuration of a conventional converter. [Figure 8] 8 is a diagram illustrating an example of a configuration in which the converters illustrated in FIG. 7 are connected in parallel. DETAILED DESCRIPTION OF THE INVENTION

[0013] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the following, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following embodiments, components having similar functions will be given the same reference numerals and descriptions thereof will be omitted as appropriate.

[0014] (First embodiment) A converter 10 according to the first embodiment is provided in a power conditioner 2 or the like of a power storage system 1 shown in FIG. 1 as a transformer 4 that transforms DC power. The power storage system 1 includes a power storage element 3. The power storage element 3 is an energy storage device that can charge and discharge power. For example, a secondary battery such as a lithium ion battery or a lead storage battery, or a capacitor such as an electric double layer capacitor (EDLC) or a lithium ion capacitor (LIC) is used as the power storage element 3. Various other secondary batteries are also used.

[0015] The power conditioner 2 includes an input unit 5, and DC power generated by a power generation device 7 such as a solar cell (PV) or a fuel cell (FC) is input to the input unit 5. The power conditioner 2 includes a transformer 4 and a converter 6.

[0016] Transformer 4 includes a converter that controls charging by boosting the DC power converted by converter 6 or the DC power input from input unit 5 to a high voltage suitable for charging storage element 3. Transformer 4 includes a converter (hereinafter referred to as converter 10) that reduces the high voltage DC power discharged from storage element 3 to a voltage suitable for conversion by converter 6.

[0017] Converter 6 is an inverter that converts DC power into AC power and AC power into DC power. Converter 6 converts DC power transformed by transformer 4 and DC power input from input unit 5 into AC power and outputs it to power grid 8 and load 9. Converter 6 converts AC power input from power grid 8 into DC power.

[0018] 2, the converter 10 is a flyback-type transformer including a transformer T1. The transformer T1 includes divided primary windings Lp1 and Lp2 and a secondary winding Ls magnetically coupled to the primary windings Lp1 and Lp2. In other words, the transformer T1 includes multiple primary windings Lp1 and Lp2 connected in series with the input voltage Vi, and each primary winding Lp1 and Lp2 is magnetically coupled to the secondary winding Ls.

[0019] The converter 10 includes a switching element Q1 connected in series to a primary winding Lp1 and a switching element Q2 connected in series to a primary winding Lp2. The converter 10 has, as its primary side circuit, a series circuit made up of the primary winding Lp1 and the switching element Q1 and a series circuit made up of the primary winding Lp2 and the switching element Q2, which are connected in series with respect to the input voltage Vi.

[0020] The switching elements Q1 and Q2 are configured, for example, by metal oxide semiconductor field effect transistors (MOSFETs), but may also be configured by other power elements such as insulated gate bipolar transistors (IGBTs).

[0021] The converter 10 includes a diode D and a capacitor Co as a rectifying and smoothing circuit on the secondary side. A flyback voltage Vr, which is an induced voltage generated in a secondary winding Ls of a transformer T, is rectified and smoothed by the diode D and the capacitor Co to generate an output voltage Vo. The flyback voltage Vr may be rectified using synchronous rectification.

[0022] The converter 10 includes a control circuit 11 that controls the on-off of switching elements Q1 and Q2 at the same timing. The control circuit 11 adjusts the on-time of switching elements Q1 and Q2 using control signals Vg1 and Vg2 generated based on the detected value of output voltage Vo, thereby controlling the amount of energy output and regulating output voltage Vo. For example, the control circuit 11 performs so-called PWM control, which adjusts the on-time of switching element Q while keeping frequency f constant.

[0023] In converter 10, the input voltage Vi is divided in half by primary windings Lp1 and Lp2, and the voltages applied to switching elements Q1 and Q2 (input voltage Vi + flyback voltage Vr) are also divided in half. This allows switching elements Q1 and Q2 to use products with a withstand voltage of approximately the input voltage Vi. Converter 10 can handle an input voltage of approximately 900 V by using relatively inexpensive MOS-FETs with a withstand voltage of 900 V for switching elements Q1 and Q2.

[0024] In converter 10, control signals Vg1 and Vg2 generated by control circuit 11 are signals with identical rise and fall timings. Switching elements Q1 and Q2 are controlled to turn on and off at the same timing by control signals Vg1 and Vg2, so there is no significant variation in the power handled by the two switching elements Q1 and Q2. Converter 10 does not require the addition of a special balancing circuit or the like, enabling an inexpensive, simple circuit configuration.

[0025] (Second embodiment) 3, a converter 10a according to the second embodiment includes a control circuit 21 that generates a reference control signal Vg (hereinafter referred to as a reference signal Vg) instead of the control circuit 11 according to the first embodiment. The converter 10a also includes a drive circuit 12 that generates control signals Vg1 and Vg2 based on the reference signal Vg.

[0026] The drive circuit 12 includes a capacitor Cc, a drive transformer DT, and resistors R1 to R4. The capacitor Cc is a coupling capacitor that removes DC components from the reference signal Vg generated by the control circuit 21. The drive transformer DT includes a primary winding Lpa and divided secondary windings Ld1 and Ld2 in addition to the components of the converter 10 of the first embodiment. The primary winding Lpa and the secondary windings Ld1 and Ld2 are set to have the same number of turns. One end of the secondary winding Ld1 is connected to the control terminal of the switching element Q1 via a resistor R1 (approximately 10 Ω) for reducing surge current, and the other end is connected to the low-potential side terminal of the switching element Q1. A resistor R2 (approximately 10 kΩ) is connected between the control terminal and low-potential side terminal of the switching element Q1 to reduce surge voltage. One end of the secondary winding Ld2 is connected to the control terminal of the switching element Q2 via a resistor R3 (approximately 10 Ω) for reducing surge current, and the other end is connected to the low-potential terminal of the switching element Q2. A resistor R4 (approximately 10 kΩ) is connected between the control terminal and the low-potential terminal of the switching element Q2 for reducing surge voltage.

[0027] 3 and 4, the DC component of the reference signal Vg generated by the control circuit 21 is removed by a capacitor Cc, and the reference signal Vg is applied as a voltage signal VLpa to the primary winding Lpa of the drive transformer DT. FIG. 4 shows waveform diagrams of various components of the drive circuit 12. Because the primary winding Lpa and the secondary windings Ld1 and Ld2 have the same turn ratio, the voltage signals VLd1 and VLd2 generated in the secondary windings Ld1 and Ld2, respectively, have the same waveform as the voltage signal VLpa. The voltage signal VLd1 is output as a control signal Vg1 via resistors R1 and R2, and the voltage signal VLd2 is output as a control signal Vg2 via resistors R3 and R4. The control signals Vg1 and Vg2 have the same rising and falling timings, making them suitable for driving the switching elements Q1 and Q2, respectively.

[0028] (Third embodiment) Referring to FIG. 5, a converter 10b according to the third embodiment includes capacitors C1 and C2 and resistors R5 and R6 in addition to the components of the converter 10 according to the first embodiment.

[0029] Capacitors C1 and C2 are connected in parallel to the input voltage Vi as a series circuit that divides the input voltage Vi. The connection point between capacitors C1 and C2 is connected to the connection point between switching element Q1 and primary winding Lp2.

[0030] Capacitors C1 and C2 correct variations in the switching currents of switching elements Q1 and Q2. If the switching currents of switching elements Q1 and Q2 vary for some reason, the capacitor voltage of capacitors C1 and C2 will drop where more switching current flows, naturally correcting the variations in switching current. Capacitors C1 and C2 are connected in close proximity to their respective switching elements Q1 and Q2, so surge absorption by leakage inductance, etc. can also be expected.

[0031] Resistor R5 is connected in parallel with capacitor C1, and resistor R6 is connected in parallel with capacitor C2. Resistors R5 and R6 are high-resistance voltage balancers that correct voltage differences due to variations in the capacitance of capacitors C1 and C2.

[0032] (Fourth embodiment) 6, a converter 10c according to the fourth embodiment includes a primary winding Lp3, a switching element Q3, a capacitor C3, and a resistor R7 in addition to the components of the converter 10b according to the third embodiment. A transformer T1c of the converter 10c includes divided primary windings Lp1, Lp2, and Lp3. The converter 10c has a primary side circuit in which a series circuit including the primary winding Lp1 and the switching element Q1, a series circuit including the primary winding Lp2 and the switching element Q2, and a series circuit including the primary winding Lp3 and the switching element Q3 are connected in series with respect to the input voltage Vi.

[0033] The converter 10c includes a control circuit 11c that controls the on-off of switching elements Q1, Q2, and Q3 at the same time. The control circuit 11c adjusts the on-time of switching elements Q1, Q2, and Q3 using control signals Vg1, Vg2, and Vg3 generated based on the detected value of output voltage Vo, thereby controlling the amount of output energy and regulating output voltage Vo. For example, the control circuit 11c performs so-called PWM control, which adjusts the on-time of switching element Q while keeping frequency f constant.

[0034] In converter 10c, the input voltage Vi is divided by one-third by primary windings Lp1, Lp2, and Lp3, and the voltages applied to switching elements Q1, Q2, and Q3 (input voltage Vi + flyback voltage Vr) are also divided by one-third. Therefore, switching elements Q1, Q2, and Q3 can be made with products that have a withstand voltage approximately two-thirds of the input voltage Vi. Converter 10c can handle an input voltage of approximately 1,350 V by using relatively inexpensive 900 V MOS-FETs for switching elements Q1, Q2, and Q3.

[0035] Capacitors C1, C2, and C3 are connected in parallel to the input voltage Vi as a series circuit that divides the input voltage Vi. The connection point between capacitors C1 and C2 is connected to the connection point between switching element Q1 and primary winding Lp2, and the connection point between capacitors C2 and C3 is connected to the connection point between switching element Q2 and primary winding Lp3. Capacitors C1, C2, and C3 correct variations in switching currents in switching elements Q1, Q2, and Q3.

[0036] Resistor R5 is connected in parallel with capacitor C1, resistor R6 is connected in parallel with capacitor C2, and resistor R7 is connected in parallel with capacitor C3. Resistors R5, R6, and R7 are high-resistance voltage balancers that correct voltage value differences due to variations in the capacitance of capacitors C1, C2, and C3.

[0037] The number of divisions of the primary winding Lp and the number of switching elements Q may be four or more. The larger the number of divisions of the primary winding Lp, the larger the compatible input voltage Vi. If the number of divisions of the primary winding Lp and the number of switching elements Q are five, the compatible input voltage Vi will be about 2250 V when a relatively inexpensive 900 V MOS-FET is used for the switching elements Q.

[0038] (summary) The converter 10 according to each embodiment of the present invention can also be described as follows. (1) A converter 10 according to one embodiment of the present invention includes a primary winding Lp1, Lp2 divided into multiple sections (two sections), and switching elements Q1, Q2 whose number corresponds to the number (two sections) of the primary windings Lp1, Lp2. In the converter 10, switching elements Q1, Q2 are connected in series to the divided primary windings Lp1, Lp2, respectively. By controlling the on / off of the switching elements Q1, Q2, the converter 10 intermittently applies an input voltage Vi to a primary winding Lp of a transformer T, rectifies and smooths an induced voltage (flyback voltage Vr) generated in a secondary winding Ls of the transformer T, and outputs the induced voltage.

[0039] In converter 10 according to one embodiment of the present invention, the input voltage Vi is divided in half by primary windings Lp1 and Lp2, and the voltages applied to switching elements Q1 and Q2 (input voltage Vi + flyback voltage Vr) are also divided in half. Therefore, switching elements Q1 and Q2 can be made of products with a withstand voltage equivalent to the input voltage Vi. Using low-withstand-voltage switching elements Q1 and Q2 allows for a high input voltage to be accommodated without increasing the circuit size.

[0040] (2) The converter 10 described in (1) above includes a control circuit 11 that controls the on / off of the two switching elements Q1 and Q2 of the divided primary windings Lp1 and Lp2 at the same timing.

[0041] According to the converter 10 described in (2) above, there is no large variation in the power handled by the multiple (two) switching elements Q1 and Q2. The converter 10 does not require the addition of a special balancing circuit or the like, and can have an inexpensive and simple circuit configuration.

[0042] (3) The converter 10 described in (1) and (2) above includes a drive circuit 12. The drive circuit 12 uses a drive transformer DT to generate control signals Vg1 and Vg2 from a reference signal Vg generated by a control circuit 21, which drive the switching elements Q1 and Q2 of the divided number (two) of primary windings Lp1 and Lp2, respectively.

[0043] According to the converter 10a described in (3) above, it is possible to generate the control signals Vg1 and Vg2 suitable for driving the switching elements Q1 and Q2, which are different in potential, respectively.

[0044] (4) The converters 10, 10a described in (1) to (3) above may each include capacitors C1, C2 connected in parallel to the series circuits of the primary windings Lp1, Lp2 and the switching elements Q1, Q2, respectively.

[0045] According to the converter 10b described in (4) above, the capacitor voltages of the capacitors C1 and C2 drop as the switching current increases, naturally correcting variations in the switching current. Because the capacitors C1 and C2 are connected in close proximity to the respective switching elements Q1 and Q2, surge absorption by leakage inductance and the like can also be expected.

[0046] (5) The converter 10b described in (4) above may include resistors R5 and R6 connected in parallel to the capacitors C1 and C2, respectively.

[0047] According to the converter 10b described in (5) above, the resistors R5 and R6 are voltage balancers with high resistance, and can correct differences in voltage values ​​due to variations in the capacitance of the capacitors C1 and C2, etc.

[0048] (6) A power conditioner 2 according to one embodiment of the present invention includes the converters 10, 10a, 10b, and 10c described in (1) to (5) as a transformer 4 that transforms DC power.

[0049] According to the power conditioner 2 described in (6) above, it is possible to handle input and output of high voltages exceeding 1000V using low-voltage switching elements.

[0050] (7) The power storage system 1 according to one embodiment of the present invention includes the converters 10, 10a, 10b, and 10c described in (1) to (5) as the transformer 4 that transforms the discharge power of the power storage element 3.

[0051] According to the power storage system 1 described in (7) above, it is possible to use a low-voltage switching element to accommodate the power storage element 3 that generates a high voltage of over 1000V.

[0052] Although the present invention has been described above with reference to specific embodiments, it goes without saying that the above embodiments are merely examples and can be modified and implemented without departing from the spirit of the present invention. [Explanation of symbols]

[0053] 1. Energy storage system 2 Power conditioner 3. Energy storage element 4. Transformers 10, 10a, 10b, 10c converter 11, 11c Control circuit 12 Drive circuit C1, C2, C3 capacitors DT Drive Transformer Lp1, Lp2, Lp3 primary windings Q1, Q2, Q3 switching elements R5~R7 resistance T1, T1c transformers

Claims

1. A converter that applies an input voltage to a primary winding of a transformer by turning on and off a switching element, and rectifies and smooths an induced voltage generated in a secondary winding of the transformer, and outputs the induced voltage, the primary winding divided into a plurality of parts; the number of the switching elements corresponds to the number of divisions of the primary winding, A converter in which the switching elements are connected in series to the respective divided primary windings.

2. 2. The converter according to claim 1, further comprising a control circuit for controlling the on / off of the switching elements of the number of divisions of the primary winding at the same timing.

3. Equipped with a drive circuit, 3. The converter according to claim 2, wherein the drive circuit uses a drive transformer to generate control signals for driving each of the switching elements corresponding to a division number of the primary winding from the reference signal generated by the control circuit.

4. 3. The converter according to claim 1, further comprising a capacitor connected in parallel to each of the series circuits of the primary winding and the switching element.

5. 5. A converter as claimed in claim 4, further comprising a resistor connected in parallel with each of said capacitors.

6. A power conditioner comprising the converter according to claim 1 or 2.

7. A power storage system comprising: a power storage element; and the converter according to claim 1 or 2.

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