circuit

Abstract

Provided is a circuit that can improve power conversion efficiency and enhance the reliability and safety of a charger or an electric vehicle without causing an increase in cost. 【Solution means】An input terminal to which a first DC voltage is applied, a step-down circuit that steps down the first DC voltage applied to the input terminal to a second DC voltage at an arbitrary step-down ratio, an electrolytic capacitor that is charged by the second DC voltage via the step-down circuit, a boost circuit that has an input terminal connected to the output terminal of the step-down circuit via the electrolytic capacitor in parallel and boosts the second DC voltage to a third DC voltage at an arbitrary boost ratio, and an output terminal that outputs the third DC voltage from the boost circuit, and performs power conversion with the upper limit of the step-down ratio boost ratio multiplier obtained by multiplying the step-down ratio and the boost ratio set to 1.

Description

Technical Field

[0001] The present invention relates to a circuit, and more particularly to a charger or a circuit mounted on an electric vehicle itself for charging a secondary battery power source mounted on an electric vehicle.

Background Art

[0002] In recent years, as part of efforts to reduce carbon dioxide emissions, a gradual shift has been made from vehicles driven by internal combustion engines, i.e., engines, to electric vehicles centered on electric vehicles driven by a power source and a motor.

[0003] Patent Document 1 discloses that in a power supply device mounted on an electric vehicle that runs using a battery, when the remaining capacities of both a high-voltage battery and a low-voltage battery are more than the allowable minimum amount, the operation of a DC / DC converter is stopped to reduce the occurrence of conversion loss of the DC / DC converter.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] By the way, this type of electric vehicle runs when the secondary battery power source mounted on the electric vehicle is charged by a charger. However, in some cases, the charger also has a secondary battery power source. In this case, power is transferred between the secondary battery power source of the charger and the secondary battery power source of the electric vehicle.

[0006] When power is transferred between the secondary battery power supply of a charger and the secondary battery power supply of an electric vehicle, from the perspective of improving the efficiency of voltage conversion and the like, it is assumed that the necessity of mounting a DC / DC converter circuit on the charger or the electric vehicle increases.

[0007] When power is transferred between the secondary battery power supply of a charger and the secondary battery power supply of an electric vehicle, from the perspective of improving power conversion efficiency, it is desirable to suppress the temperature rise of the entire circuit board of the DC / DC converter circuit.

[0008] On the other hand, along with the electromagnetic noise emitted by the inverter or the like of the electric vehicle, a high-voltage surge is inadvertently applied to the switch element of the DC / DC converter circuit of the charger or the DC / DC converter circuit of the electric vehicle, and it is assumed that a situation occurs in which the switch element fails.

[0009] When the switch element of the DC / DC converter circuit fails, there is concern that the reliability and safety of the charger or the electric vehicle will decrease. On the other hand, if protective elements or the like are provided so as not to cause a decrease in reliability and safety, there is also concern that the cost will increase due to an increase in the number of parts.

[0010] The present invention has been made in view of the above circumstances, and an object thereof is to provide a circuit that can improve power conversion efficiency and improve the reliability and safety of a charger or an electric vehicle without causing an increase in cost.

Means for Solving the Problem

[0011] The circuit according to the present invention for achieving the above object includes an input terminal to which a first DC voltage is applied, a step-down circuit that steps down the first DC voltage applied to the input terminal to a second DC voltage at an arbitrary step-down ratio, an electrolytic capacitor that stores electricity by the second DC voltage via the step-down circuit, and an input end connected to the output end of the step-down circuit via the electrolytic capacitor in parallel, and a boost circuit that boosts the second DC voltage to a third DC voltage at an arbitrary boost ratio, and an output terminal that outputs the third DC voltage from the boost circuit, and performs power conversion with the upper limit of the step-down ratio boost ratio multiplier obtained by multiplying the step-down ratio and the boost ratio set to 1.

[0012] Furthermore, this circuit selectively changes either the step-down ratio or the boost ratio based on the detection result of any one of the first DC voltage, the third DC voltage, the temperature of the step-down circuit, or the temperature of the boost circuit, and performs power conversion.

[0013] According to this, even if the first DC voltage input to the input terminal fluctuates, the third DC voltage output from the output terminal can be stabilized, and the temperature rise of the step-down circuit or the boost circuit with a relatively high temperature can be suppressed, so it is expected to contribute to the improvement of the reliability of the circuit and the improvement of the power conversion efficiency.

[0014] On the other hand, the input terminal of this circuit is connected to any one of the output terminals of a secondary battery, a solar cell, or an arbitrary power conversion circuit, and the output terminal is connected to the input terminal of a secondary battery or an arbitrary power conversion circuit.

Effects of the Invention

[0015] According to this invention, it is possible to improve the power conversion efficiency and improve the reliability and safety for a charger or an electric vehicle without causing an increase in cost.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0017] Next, based on FIGS. 1 and 2, the circuit according to the embodiment of the present invention will be described.

[0018] FIG. 1 is a diagram for explaining the outline of the configuration of the circuit according to the present embodiment. As shown in the figure, the circuit 10 mainly includes an input terminal 20, a step-down circuit 30, an electrolytic capacitor 40, a boost circuit 50, and an output terminal 60.

[0019] In the present embodiment, two secondary battery cell groups 1 in which a plurality of lithium-ion secondary battery cells are connected in series are connected to the input terminal 20, and a first DC voltage V1 is applied from the secondary battery cell group 1 to the input terminal 20.

[0020] Note that instead of the secondary battery cell group 1, for example, a solar cell panel that outputs a DC voltage similar to the secondary battery cell group 1, or an output terminal of an arbitrary power conversion circuit that converts the power from a commercial power supply and outputs a DC voltage similar to the secondary battery cell group 1 may be connected to the input terminal 20.

[0021] In the present embodiment, the step-down circuit 30 includes a step-down side FET 31 to which the first DC voltage V1 is applied and a step-down side controller 32 that controls the step-down side FET 31, and steps down the applied first DC voltage V1 to a second DC voltage V2 at an arbitrary step-down ratio. Here, the step-down ratio is 25% in the present embodiment.

[0022] In this embodiment, a communication line 33 capable of communicating with a booster controller 44 described later is connected to the step-down controller 32. A control algorithm for switching the on / off of the step-down FET 31 is stored based on the detection results of the first DC voltage V1 communicated through the communication line 33 and the third DC voltage V3 described later.

[0023] By the control of this control algorithm, the on / off of the step-down FET 31 is switched, and the first DC voltage V1 is stepped down to the second DC voltage V2. The second DC voltage V2 obtained by stepping down the first DC voltage V1 is stored in the electrolytic capacitor 40 through the step-down circuit 30.

[0024] In this embodiment, the boost circuit 50 includes an input terminal 40A connected to the output terminal 30A of the step-down circuit 30 through the electrolytic capacitor 40 in parallel, a reactor 41, a diode 42, a boost-side FET 43, and a boost controller 44 that controls the boost-side FET 43, and boosts the second DC voltage V2 of the electrolytic capacitor 40 to the third DC voltage V3 at an arbitrary boost ratio. Here, the boost ratio is 200% in this embodiment.

[0025] In this embodiment, a voltage detection line 45 for detecting the first DC voltage V1 and a voltage detection line 46 for detecting the third DC voltage V3 are connected to the boost controller 44, and a control algorithm for switching the on / off of the boost-side FET 43 is stored based on the detection results of the first DC voltage V1 and the third DC voltage V3.

[0026] By the control of this control algorithm, the on / off of the boost-side FET 43 is switched, and the second DC voltage V2 is boosted to the third DC voltage V3. The third DC voltage V3 obtained by boosting the second DC voltage V2 is output to the output terminal 60 through the boost circuit 50.

[0027] In this embodiment, a single secondary battery cell group 2 having a rated voltage that is half of the rated voltage of the secondary battery cell group 1 connected to the input terminal 20 is connected to the output terminal 60, and the third DC voltage V3 is output from the output terminal 60 to the secondary battery cell group 2 to charge the secondary battery cell group 2.

[0028] Here, the step-down / step-up ratio multiplier obtained by multiplying the step-down ratio and the step-up ratio is 0.5, which is the step-down ratio (25%) × the step-up ratio (200%) in this embodiment.

[0029] Note that an input terminal of an arbitrary DC power conversion circuit may be connected to the output terminal 60 instead of the secondary battery cell group 2.

[0030] In the circuit 10 configured as described above, assuming that the secondary battery cell group 1 is a secondary battery built into the charger and the secondary battery cell group 2 is a secondary battery mounted on the electric vehicle, it can be considered that the first DC voltage V1 input to the input terminal 20 is output from the output terminal 60 as the third DC voltage V3 stepped down with a step-down ratio of 50% to the secondary battery cell group 2, corresponding to charging the secondary battery cell group 2 mounted on the electric vehicle.

[0031] Next, the outline of the control algorithm of the circuit 10 of this embodiment will be described.

[0032] FIG. 2 is a diagram for explaining the outline of the control algorithm. As shown in the figure, as an initial setting, for example, the step-down ratio of the second DC voltage V2 with respect to the first DC voltage V1 is set to 25%, and the step-up ratio of the third DC voltage V3 with respect to the second DC voltage V2 is set to 200%. At this time, the step-down / step-up ratio multiplier is 0.5.

[0033] In this case, in the first state which is the initial state, the voltage of each part of the circuit 10 is such that the first DC voltage V1 is 360V, the second DC voltage V2 is 90V, and the third DC voltage V3 is 180V.

[0034] Subsequently, assuming that the remaining capacity of the secondary battery cell group 1 has decreased, in the second state where the first DC voltage V1 has decreased from 360V to 180V, based on the initial setting, the second DC voltage V2 fluctuates to 45V and the third DC voltage V3 fluctuates to 90V.

[0035] On the other hand, in the first control of the control algorithm, when detecting a decrease in the third DC voltage V3 accompanying a decrease in the first DC voltage V1, if the temperature of the boost-side FET 43 is lower than the temperature of the buck-side FET 31, in order to increase the current flowing through the boost-side FET 43, selectively increase the boost ratio relatively (400%), set the buck ratio boost ratio multiplier to 1, and set the buck ratio corresponding to this boost ratio (25%).

[0036] Based on this, the buck-side controller 32 and the boost-side controller 44 execute control to switch the on / off of the buck-side FET 31 and the boost-side FET 43 so as to satisfy the changed buck ratio and boost ratio. As a result, the third DC voltage V3 fluctuates to 180V and becomes the same value as the first DC voltage V1 (the third state).

[0037] In the second control of the control algorithm, when the temperature of the buck-side FET 31 is lower than the temperature of the boost-side FET 43, in order to increase the current flowing through the buck-side FET 31, selectively increase the buck ratio relatively (50%), set the buck ratio boost ratio multiplier to 1, and set the boost ratio corresponding to this buck ratio (200%).

[0038] Based on this, the buck-side controller 32 and the boost-side controller 44 execute control to switch the on / off of the buck-side FET 31 and the boost-side FET 43 so as to satisfy the changed buck ratio and boost ratio. As a result, while the second DC voltage V2 fluctuates to 90V, the first DC voltage V1 and the third DC voltage V3 remain the same value (the fourth state).

[0039] In this way, even if the first DC voltage V1 input to the input terminal 20 fluctuates, the third DC voltage V3 output from the output terminal 60 can be stabilized, and the temperature rise of the relatively high-temperature buck-side FET 31 or boost-side FET 43 can be suppressed, which is expected to contribute to the improvement of the reliability of the circuit 10 and the improvement of the power conversion efficiency.

[0040] By the way, if the drain terminal and the source terminal of the step-down side FET31 are short-circuited and malfunction due to some factor, the current flowing from the secondary battery cell group 1 to the secondary battery cell group 2 via the step-down side FET31 flows into the electrolytic capacitor 40, and when the electrolytic capacitor 40 is fully charged, the current stops.

[0041] Therefore, since the current will not continue to flow uncontrollably from the secondary battery cell group 1 to the secondary battery cell group 2, the risk of ignition or the like of the secondary battery cell group 2 due to overcharging can be avoided in advance, and there is no need to provide a protection element or the like for suppressing overcharging, so that an increase in the number of components is not caused, and the complication of the structure and the increase in cost can be prevented.

[0042] On the other hand, if the drain terminal and the source terminal of the boost side FET43 are short-circuited and malfunction due to some factor, the boost side FET43 cannot be switched on / off, so the secondary battery cell group 2 cannot be charged. That is, the secondary battery cell group 2 does not reach an overcharged state.

[0043] Furthermore, if the drain terminal and the source terminal of the boost side FET43 are short-circuited and malfunction due to some factor, if the step-down side FET31 is turned off, the short-circuit current from the secondary battery cell group 1 via the boost side FET43 can be stopped, so that a decrease in safety is not caused.

[0044] (Comparative Example 1) Next, a comparative example 1 of the circuit 10 of the present embodiment will be described with reference to FIG. 3.

[0045] In FIG. 3, the same components as those of the circuit 10 are given the same reference numerals, and the description thereof will be omitted.

[0046] As shown in the figure, the circuit 100 mainly includes an input terminal 20 to which a voltage is input from the secondary battery cell group 1, an FET 101 to which the voltage from the input terminal 20 is applied, a controller 102 that controls the FET 101, and an output terminal 60 that outputs the voltage from the FET 101 to the secondary battery cell group 2.

[0047] In this circuit 100, based on the detection result of the voltage of the secondary battery cell group 2 detected by the voltage detection line 103, the controller 102 switches the on / off of the FET 101 to generate a voltage with a desired step-down ratio of 50%, and charges the secondary battery cell group 2 with this voltage.

[0048] In the circuit 100 with such a configuration, assuming that the secondary battery cell group 1 is a secondary battery built into a charger and the secondary battery cell group 2 is a secondary battery mounted on an electric vehicle, it can be considered that the voltage input to the input terminal 20 is output from the output terminal 60 to the secondary battery cell group 2 after being stepped down with a step-down ratio of 50% to charge the secondary battery cell group 2 mounted on the electric vehicle.

[0049] By the way, if the drain terminal and the source terminal of the FET 101 are short-circuited and malfunction due to some factor, an uncontrolled charging current will flow from the secondary battery cell group 1 to the secondary battery cell group 2 due to the voltage difference between the secondary battery cell group 1 and the secondary battery cell group 2. As a result, there is a risk of ignition of the secondary battery cell group 2, etc., and there are concerns about an increase in the number of components due to the provision of a protection element or the like for suppressing overcharging, and the accompanying complication of the structure and increase in cost.

[0050] On the other hand, the circuit 10 of the present embodiment can avoid in advance the risk of ignition or the like of the secondary battery cell group 2 caused by overcharging, and there is no need to provide a protection element or the like for suppressing overcharging. Therefore, it does not cause an increase in the number of components, and can prevent the complication of the structure and the increase in cost.

[0051] (Comparative Example 2) Next, with reference to FIG. 4, Comparative Example 2 of the circuit 10 of the present embodiment will be described.

[0052] In FIG. 4, components having the same configuration as those of the circuit 10 are denoted by the same reference numerals, and the description thereof will be omitted.

[0053] As shown in the figure, the circuit 200 mainly includes an input terminal 20 to which a voltage is input from the secondary battery cell group 1, a reactor 41 to which the voltage from the input terminal 20 is applied, a diode 42, an FET 201, a controller 202 that controls the FET 201, and an output terminal 60 that outputs the voltage from the FET 201 to the secondary battery cell group 2 having a rated voltage twice that of the secondary battery cell group 1.

[0054] In this circuit 200, based on the detection result of the voltage of the secondary battery cell group 2 detected by the voltage detection line 203, the controller 202 switches the on / off state of the FET 201, thereby generating a voltage with a desired boost ratio of 200% via the reactor 41 and the diode 42, and charging the secondary battery cell group 2 with this voltage.

[0055] In the circuit 200 having such a configuration, assuming that the secondary battery cell group 1 is a secondary battery built in a charger and the secondary battery cell group 2 is a secondary battery mounted on an electric vehicle, it can be considered that the voltage input to the input terminal 20 is boosted with a boost ratio of 200% and output from the output terminal 60 to the secondary battery cell group 2 to charge the secondary battery cell group 2 mounted on the electric vehicle.

[0056] By the way, if the drain terminal and the source terminal of the FET 201 are short-circuited and fail due to some factor, there is a risk that the secondary battery cell group 1 will experience an over-discharge failure associated with a short circuit with the reactor 41 as a load. In addition, there are concerns about an increase in the number of components due to the provision of a protection element or the like to suppress over-discharge, and an accompanying increase in the complexity of the structure and cost.

[0057] On the other hand, the circuit 10 of the present embodiment can avoid in advance the risk of failure of the secondary battery cell group 1 due to over-discharge, etc., and there is no need to provide a protection element or the like for suppressing over-discharge. Therefore, it does not cause an increase in the number of components, and can prevent the complication of the structure and the increase in cost.

[0058] Note that the present invention is not limited to the above embodiment, and various modifications are possible without departing from the spirit of the invention.

[0059] In the above embodiment, the circuit 10 has been described assuming that it is mounted on a charger incorporating the secondary battery cell group 1. However, it may be mounted on a charger that receives power from an existing commercial power grid, or may be mounted on a charger equipped with a solar cell panel, or may be mounted on an electric vehicle as part of a brake regeneration charging circuit of the electric vehicle.

[0060] In the above embodiment, the case where the input terminal of the secondary battery cell group 2 or an arbitrary power conversion circuit is connected to the output terminal 60 has been described. However, it may be one to which the DC input terminal of a power conditioner is connected.

Explanation of Reference Numerals

[0061] 10 Circuit 20 Input Terminal 30 Step-down Circuit 40 Electrolytic Capacitor 50 Boost Circuit 60 Output Terminal

Claims

1. an input terminal to which a first DC voltage is applied; a step-down circuit that steps down the first DC voltage applied to the input terminal to a second DC voltage at an arbitrary step-down ratio; an electrolytic capacitor that is charged by the second DC voltage via the step-down circuit; a boost circuit having an input terminal connected to an output terminal of the step-down circuit via the electrolytic capacitor in parallel, the step-up circuit boosting the second DC voltage to a third DC voltage at an arbitrary step-up ratio; an output terminal for outputting the third DC voltage from the boost circuit, The input terminal is connected to either a secondary battery, a solar cell, or an output terminal of any power conversion circuit; The output terminal is connected to an input terminal of a secondary battery or any power conversion circuit, and performing power conversion with an upper limit of a step-down ratio step-up ratio multiplier obtained by multiplying the step-down ratio and the step-up ratio set to 1. circuit.

2. performing the power conversion by selectively changing either the step-down ratio or the step-up ratio based on a detection result of either the first DC voltage, the third DC voltage, the temperature of the step-down circuit, or the temperature of the step-up circuit; The circuit of claim 1 .

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