Converter, power conditioner, and power storage system

Abstract

The present invention comprises: a plurality of divided primary windings (Lp1, Lp2); and switching elements (Q1, Q2), the number of which corresponds to the number of the divided primary windings (Lp1, Lp2). In a converter (10), the switching elements (Q1, Q2) are respectively connected in series to the divided primary windings (Lp1, Lp2). The converter (10) performs on / off control of the switching elements (Q1, Q2) to intermittently apply an input voltage (Vi) to the primary winding (Lp) of a transformer (T), and rectifies, smooths, and outputs an induced voltage that is generated in a secondary winding (Ls) of the transformer T.

Description

Converters, power conditioners and energy storage systems

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

[0002] Demand for energy storage systems (ESS) is increasing due to the expansion of renewable energy use and the promotion of energy management. An energy storage system includes a storage battery that stores power and a power conditioner (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 transforms DC power and a converter that converts DC power and AC power.

[0003] When the transformer of the power conditioner is configured as an isolated type, a flyback converter 20 as shown in FIG. 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. By turning on and off the switching element Q, the input voltage Vi is intermittently applied to the primary winding Lp of the transformer T. 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, it outputs the stored energy 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, thereby performing so-called PWM control.

[0004] JP 2023-18328 A

[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 is approximately equal to the input voltage Vi at most. In other words, switching element Q needs to have a withstand voltage at least twice the input voltage Vi.

[0006] When a MOS-FET is used 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. When the input voltage Vi is a high voltage exceeding 500V, an expensive product must be selected for the switching element Q. In recent years, in the field of energy storage systems, high voltages exceeding 1000V are generated, which has the drawback of making the converters 20 used in such systems expensive. Since there are not an unlimited number of high-voltage products available for the switching element Q, there is an upper limit to the input voltage Vi that the converter 20 can handle.

[0007] 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. Additionally, 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 on 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.

[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.

[0011] According to one aspect of the present invention, the voltages applied to the respective switching elements are divided by the divided primary windings, so that 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.

[0012] 7 is a diagram showing a configuration example of a power storage system; FIG. 8 is a diagram showing a configuration of a first embodiment of a power storage system; FIG. 9 is a diagram showing a configuration of a second embodiment of a power storage system; FIG. 10 is a waveform diagram of each part of the drive circuit shown in FIG. 3; FIG. 11 is a diagram showing a configuration of a third embodiment of a power storage system; FIG. 12 is a diagram showing a configuration of a fourth embodiment of a power storage system; FIG. 13 is a diagram showing a configuration example of a conventional converter; and FIG. 14 is a diagram showing a configuration example in which the converters shown in FIG. 7 are connected in parallel.

[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 a 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 a power storage device that can charge and discharge power. For example, the power storage element 3 may be 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). Various other secondary batteries may also be 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] The transformer 4 includes a converter that boosts the DC power converted by the converter 6 and the DC power input from the input unit 5 to a high voltage suitable for charging the storage element 3 and controls charging. The transformer 4 includes a converter (hereinafter referred to as converter 10) that reduces the high voltage DC power discharged from the storage element 3 to a voltage suitable for conversion by the converter 6.

[0017] Converter 6 is an inverter that converts DC power into AC power and AC power into DC power. Converter 6 converts the DC power transformed by transformer 4 and the 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 the switching elements Q1 and Q2 at the same timing. The control circuit 11 adjusts the on-time of the switching elements Q1 and Q2 using control signals Vg1 and Vg2 generated based on the detected value of the output voltage Vo, thereby controlling the amount of energy output and regulating the output voltage Vo. The control circuit 11 performs so-called PWM control, for example, by adjusting the on-time of the switching element Q while keeping the 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] 3, a converter 10a according to a 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 of 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 split 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 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 terminal of the switching element Q1. A resistor R2 (approximately 10 kΩ) is connected between the control terminal and low-potential terminal of the switching element Q1 for surge voltage reduction. 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 reference signal Vg generated by the control circuit 21 has its DC component removed by the capacitor Cc and 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 the control signal Vg1 via resistors R1 and R2, and the voltage signal VLd2 is output as the control signal Vg2 via resistors R3 and R4. The control signals Vg1 and Vg2 have the same rising and falling timings and are suitable for driving the switching elements Q1 and Q2, respectively.

[0028] Third Embodiment Referring to FIG. 5, a converter 10b according to a 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] The 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 the capacitors C1 and C2 is connected to the connection point between the switching element Q1 and the primary winding Lp2.

[0030] The capacitors C1 and C2 correct variations in the switching currents of the switching elements Q1 and Q2. If the switching currents of the switching elements Q1 and Q2 vary for some reason, the capacitor voltages of the capacitors C1 and C2 will drop where more switching current flows, naturally correcting the variations in the switching currents. Because the capacitors C1 and C2 are connected in close proximity to the respective switching elements Q1 and Q2, 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 capacitance between capacitors C1 and C2.

[0032] 6, a converter 10c according to a 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 including 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, all of which 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 the switching elements Q1, Q2, and Q3 at the same timing. The control circuit 11c adjusts the on-time of the switching elements Q1, Q2, and Q3 using control signals Vg1, Vg2, and Vg3 generated based on the detected value of the output voltage Vo, thereby controlling the amount of energy output and regulating the output voltage Vo. The control circuit 11c performs, for example, so-called PWM control, which adjusts the on-time of the switching element Q while keeping the 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 voltage (input voltage Vi + flyback voltage Vr) applied to each of switching elements Q1, Q2, and Q3 is also divided by one-third. Therefore, switching elements Q1, Q2, and Q3 can be made of products with a withstand voltage of 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 junction between capacitors C1 and C2 is connected to the junction between switching element Q1 and primary winding Lp2, and the junction between capacitors C2 and C3 is connected to the junction between switching element Q2 and primary winding Lp3. Capacitors C1, C2, and C3 correct variations in the switching currents of 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 capacitance among 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 as the switching element Q.

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

[0039] According to the converter 10 of one embodiment of the present invention, the input voltage Vi is divided in half by the primary windings Lp1 and Lp2, and the voltages (input voltage Vi + flyback voltage Vr) applied to the switching elements Q1 and Q2 are also divided in half. Therefore, the switching elements Q1 and Q2 can be made of products with a withstand voltage equivalent to the input voltage Vi. By using the switching elements Q1 and Q2 with a low withstand voltage, a high input voltage can 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 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 an inexpensive and simple circuit configuration is possible.

[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 having different potentials.

[0044] (4) The converters 10 and 10a described in (1) to (3) above may each include capacitors C1 and C2 connected in parallel to the series circuits of the primary windings Lp1 and Lp2 and the switching elements Q1 and 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. Since the capacitors C1 and C2 are connected in close proximity to the respective switching elements Q1 and Q2, surge absorption by leakage inductance, etc., 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) The 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 the 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 1000 V using low-voltage switching elements.

[0050] (7) The energy 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 energy storage element 3.

[0051] According to the energy storage system 1 described in (7) above, it is possible to use low-voltage switching elements to accommodate the energy storage elements 3 that generate high voltages 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.

[0053] REFERENCE SIGNS LIST 1 Energy storage system 2 Power conditioner 3 Energy storage element 4 Transformer 10, 10a, 10b, 10c Converter 11, 11c Control circuit 12 Drive circuit C1, C2, C3 Capacitor DT Drive transformer Lp1, Lp2, Lp3 Primary winding Q1, Q2, Q3 Switching element R5 to R7 Resistor T1, T1c Transformer

Claims

1. A converter that applies an input voltage intermittently to a primary winding of a transformer by turning a switching element on and off, and rectifies and smooths the induced voltage generated in the secondary winding of the transformer before outputting the rectified voltage, the converter comprising: the primary winding divided into a plurality of sections; and the number of switching elements corresponding to the number of divisions of the primary winding, with the switching elements connected in series to each of the divided primary windings.

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. The converter according to claim 2, further comprising a drive circuit, 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 a reference signal generated by the control circuit.

4. A converter according to claim 1 or 2, further comprising a capacitor connected in parallel to each of the series circuits of the primary winding and the switching element.

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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