JP2011147205A - Converter and exhaust heat utilization system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a magnetic force from being lost in a reactor to properly convert a voltage by a converter by suppressing an iron loss increase of the reactor even in increasing a switching loss of the converter. <P>SOLUTION: The converter 20 includes a plurality of switching elements 21, 22 for stepping up a DC power of a battery 40. In the converter 20, a capacitor is connected in parallel between connection edges of the emitters and collectors of the switching elements 21, 22 and both ends of the battery 40, and a reactor 24 is connected in series. In this case, the switching elements 21, 22 are subjected to intermittent switching control so that they are repeatedly turned on and off in a short period during an on interval by a control unit 11. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention is used in a power converter or the like for controlling an electric motor mounted on a vehicle such as a hybrid vehicle, an electric vehicle, and a fuel cell vehicle, and a converter for increasing or decreasing a power supply voltage, and power conversion using the converter The present invention relates to an exhaust heat utilization system for a power converter using a converter that applies exhaust heat of a cooling refrigerant heated by a heater to a heating device via a heat exchanger.

  Conventionally, in a power converter that controls an electric motor mounted on a hybrid vehicle or the like, normally, as described in Patent Document 1, the switching frequency of the switching element of the converter of the power converter is set at a low load such as when the engine is started. The power loss is reduced to reduce the power loss, thereby increasing the power conversion efficiency of the converter.

  That is, the frequency f (= 1 / T) of the gate control signal G1 for performing on / off control of the switching element shown in FIG. The gate control signal G1 forms one cycle T from an “H” level section (on section) Ton1 in which the switching element is turned on and an “L” level section (off section) Toff1 in which the switching element is turned off. Is the switching frequency f.

  At the switching timing between the on section Ton1 and the off section Toff1, the rising and falling levels of the current I1 flowing through the switching element and the voltage V1 are switched as shown in FIG. This switching portion becomes a switching loss L1, which is a power loss during operation of the switching element, as shown in (c). This switching loss L1 is reduced to increase the power conversion efficiency of the converter.

  In the converter having such a configuration, when the switching frequency f is increased, the switching loss L1 increases. However, a cooling system that increases the switching loss L1 and warms the cooling refrigerant of the power converter, for example, LLC (Long Life Coolant: non-freezing organic solution), and uses the exhaust heat to quickly raise the battery temperature. Is described in Patent Document 2. According to this cooling system, a decrease in battery capacity due to a low temperature can be quickly recovered by rapidly heating the battery with exhaust heat of the cooling refrigerant.

JP 2008-302763 A JP 2008-189249 A

  By the way, in the converter described with reference to FIG. 1 above, when the switching frequency is increased and the switching loss L1 is increased to warm the refrigerant, the converter core iron loss also increases at the same time in order to increase the switching frequency. Since this iron loss induces heat generation, the temperature of the reactor rises due to an increase in iron loss, and when the reactor temperature exceeds the Curie temperature, which is the boundary temperature at which the material loses magnetic force, the magnetic force of the reactor is lost, There is a problem that the converter cannot properly perform voltage conversion.

  This invention is made in view of such a situation, and even if it increases the switching loss of a converter, it can suppress the increase in the iron loss of a reactor, and this prevents that the magnetic force of a reactor is lost. It is an object of the present invention to provide a converter and an exhaust heat utilization system that allow a converter to properly perform voltage conversion.

  In order to achieve the above object, the invention according to claim 1 has a plurality of switching elements for boosting the DC power of the battery, and between the connection ends of the emitter and collector of the switching elements and the ends of the battery. In the converter in which the capacitor is connected in parallel and the reactor is connected in series, and the switching element is controlled to be switched on and off by the control means at a constant cycle, the control means includes the switching element Intermittent switching control in which the switching element is turned off a plurality of times in an ON section of a certain period of time, and the intermittent switching control is performed so that the total time of turning off the plurality of times is shorter than half the time of the ON section. It is performed.

  According to this configuration, since the switching element is turned off a plurality of times during the ON period of the switching element, the rising and falling levels of the current and voltage flowing through the switching element at the time of turning off are switched, and this switching portion is switched. Loss. Therefore, in the case of normal switching control, the switching element generates a switching loss by switching between on and off. However, in the present invention, a switching loss is generated a plurality of times in the on section, so the switching loss is increased accordingly. It can be made. At this time, in the case of normal switching control, the switching loss does not increase unless the switching frequency with ON and OFF as one cycle is increased. However, in the present invention, when the switching element is turned off a plurality of times in a fixed period of the ON section, the total time of the plurality of OFF times is set to be smaller than half the time of the ON section. The substantial switching frequency is not increased when the total time is more than half of the ON period.

  When the switching loss is increased as in the present invention, in the process of increasing the magnetic flux density when the reactor is turned on in the BH curve (magnetic hysteresis curve) of the reactor, the curve rises while looping the number of intermittent off times. That is, when the switching element is intermittently turned off N times, both the hysteresis loss and the eddy current loss are reduced, and as a result, the reactor iron loss, which is the sum of the hysteresis loss and the eddy current loss, is also reduced. Therefore, even if the switching element is turned off a plurality of times in the ON section to increase the switching loss, it is possible to suppress an increase in the iron loss of the reactor. This allows the converter to properly perform voltage conversion.

  According to a second aspect of the present invention, when the control means performs the intermittent switching control, the time during which the switching element is on in the on section including the plurality of off times does not turn off the plurality of times. Control is performed so as to be the same as the ON time in the case.

  According to this configuration, when the switching element is controlled to be turned off a plurality of times in an on section having a fixed period, the current supply rate that is substantially turned on and off is turned on and off when not turned off a plurality of times. It can be the same as during normal switching control.

  According to a third aspect of the present invention, the control means controls the timing to turn off the switching element a plurality of times during the intermittent switching control so that the magnetic flux density in the magnetic hysteresis curve of the reactor is low. It is characterized by.

  According to this configuration, when the switching element is turned on and turned off a plurality of times at a position where the magnetic flux density is low, both the hysteresis loss and the eddy current loss are reduced, and the iron loss is also reduced. Thereby, the iron loss of the reactor can be further suppressed.

  According to a fourth aspect of the present invention, when the switching means turns off the switching element a plurality of times during the intermittent switching control, the off time is shortened, and the current flowing through the switching element drops to zero. It is characterized in that the control is turned on again without turning off.

  According to this configuration, a turn-off loss and a turn-on loss are generated while the intermittent switch control is turned off. If the OFF interval of intermittent switch control is shortened, these losses will overlap, but switching loss can still be increased.

  According to a fifth aspect of the present invention, the control means closes the timing at which the switching element is turned off a plurality of times during the intermittent switching control to a time when the switching element is turned on within a fixed period of the ON period. Control is performed at timing.

  According to this configuration, switching loss can be stably increased.

  The invention according to claim 6 is characterized in that the control means performs control so as to perform a cycle of turning off the switching element a plurality of times at the audible frequency or higher during the intermittent switching control.

  According to this configuration, since the cycle of turning off a plurality of times in the ON section of the fixed cycle is performed at an audible region frequency or higher, the off and on operations of the plurality of times cannot be heard. Therefore, it is possible to reduce the noise of the on / off operation when the switching loss increases.

  The invention according to claim 7 includes the converter according to any one of claims 1 to 6, wherein the operating heat of the switching element is cooled by the refrigerant, and the refrigerant is generated by the power converter. A heat exchanger that exchanges heat with the heated refrigerant that has been heated, a heater that uses the heated refrigerant that has been heat-exchanged with the heat exchanger, and a temperature of the refrigerant that is heated with a heat source that is supplied to the heater A temperature sensor for detecting the switching element, and the control means of the converter, when the temperature detected by the temperature sensor is equal to or lower than a predetermined threshold value, turns the switching element a plurality of times during an ON interval of the switching element. Control to turn off is performed.

  According to this configuration, for example, when the amount of heat generated from the heat source decreases or the heating load increases, the temperature of the cooling refrigerant of the heat source decreases, and the temperature sensor signal from the temperature sensor falls below a predetermined threshold The control means performs intermittent switching control of the converter of the power converter. This increases the switching loss of the converter and warms the refrigerant. Since this warmed refrigerant flows from the heat exchanger to the heater for heating, the heater for heating can perform immediate heating with the warmed refrigerant. Further, in the converter, even if the switching loss increases, the increase in the iron loss of the reactor is suppressed. Therefore, the converter can appropriately perform voltage conversion.

(A) It is a figure which shows the level of the gate control signal of the switching element in the conventional converter, (b) The level of the electric current and voltage which flow into a switching element, (c) The switching loss at the time of switching element operation | movement. It is a block diagram which shows the structure of the exhaust-heat utilization system of the power converter using the converter which concerns on embodiment of this invention. It is a block diagram which shows the structure of a power converter. It is a figure which shows the operation | movement at the time of normal switching control of the converter of the power converter of this embodiment. It is a figure which shows the operation | movement at the time of the intermittent switching control of the converter of the power converter of this embodiment. (A) It is a figure which shows the BH curve at the time of the normal switching control of the reactor of a converter, (b) The BH curve at the time of the intermittent switching control of a reactor. It is a related figure of load electric power and switching loss in a reactor of a converter. It is a related figure of the load electric power in the reactor of a converter, and the iron loss of a reactor.

  Embodiments of the present invention will be described below with reference to the drawings. However, parts corresponding to each other in all the drawings in this specification are denoted by the same reference numerals, and description of the overlapping parts will be omitted as appropriate.

  FIG. 2 is a block diagram showing the configuration of the exhaust heat utilization system of the power converter using the converter according to the embodiment of the present invention.

  A waste heat utilization system 10 shown in FIG. 2 is mounted on a vehicle such as a hybrid vehicle, an electric vehicle, and a fuel cell vehicle, and a vehicle motor generator according to a control signal 11 a from a control unit (control means) 11. Power converter 12 that performs drive control of the battery or regeneration control of power to the battery, heat exchanger 13, radiator 16, heating heater 17, temperature sensor 18, unillustrated engine, waste heat discharge portion, and the like The heat source 19 is configured.

  The power converter 12 and the heat exchanger 13 are connected by a flow path through which a cooling refrigerant for cooling the heat generated from the power converter 12 flows. Further, the heat exchanger 13 and the radiator 16, and the radiator 16 and the power converter 12 are also included. They are connected by a flow path in which the cooling refrigerant flows in the direction of the arrow.

  The heat exchanger 13 and the heating heater 17 are connected by a flow path that circulates and is connected to each other, and the heating heater 17 has a flow path through which the cooling refrigerant heated by the heat source 19 flows. Further, a temperature sensor 18 is disposed in the flow path of the cooling refrigerant from the heat source 19, detects the temperature of the heated cooling refrigerant, and outputs a temperature sensor signal 18a indicating the detected temperature to the control unit 11. It is like that.

  In such a flow path configuration, the high-temperature cooling refrigerant that flows from the heat exchanger 13 to the radiator 16 is cooled by the radiator 16, and the cooled cooling refrigerant flows to the power converter 12 to cool the power converter 12. . The cooling refrigerant having a high temperature due to this cooling flows to the heat exchanger 13. However, the heater 17 performs heating using the waste heat from the heat source 19, and the heat of the cooling refrigerant is taken away by the exhaust heat at the time of heating.

  On the other hand, when the temperature of the cooling refrigerant of the heat source 19 decreases when the heat generation from the heat source 19 decreases or the heating load increases, the temperature of the water from the heat source 19 used by the heater 17 decreases. At this time, heat is exchanged by the heat exchanger 13. Moreover, the heat exchanger 13 and the heater 17 are always exchanging heat.

  Next, as shown in FIG. 3, the power converter 12 includes an inverter 30 that drives and controls the converter 20 and the motor generator MG, and is configured to be controlled by the control unit 11. However, the control unit 11 controls both the converter 20 and the inverter 30, but a control signal 11 a to be described later for controlling the converter 20 is shown in the figure.

  A battery 40 is connected to the converter 20. The battery 40 supplies DC power to the converter 20 and stores DC power regenerated from the converter 20. Converter 20 boosts DC power supplied from battery 40 and outputs the boosted DC power to inverter 30, and steps down DC power output from inverter 30 and outputs it to battery 40. Further, the converter 20 includes a capacitor 23, a reactor 24, an upper arm switching element (power conversion switching element) 21 which is a high voltage side semiconductor element, and a lower arm which is a high voltage GND (ground) side semiconductor element. Switching element (power conversion switching element) 22 and diodes D1 and D2.

  In these components, one end of the capacitor 23 and the reactor 24 is connected to the positive electrode side of the battery 40, and the other end of the capacitor 23 and the emitter terminal of the switching element 22 are connected to the negative electrode side. The switching element 21 and the switching element 22 are connected in series, and the other end of the reactor 24 is connected between them, that is, the emitter terminal of the switching element 21 and the collector terminal of the switching element 22.

  The collector terminal of the switching element 21 for the upper arm is connected to one end side of an inverter 30 described later. The emitter terminal of the switching element 22 for the lower arm is connected to the other end side of the inverter 30. Between the collector and emitter of the switching element 21, a diode D <b> 1 that allows current to flow from the emitter side to the collector side is connected. Similarly, a diode D <b> 2 is also connected between the collector and emitter of the switching element 22.

  Motor generator MG is connected to inverter 30 and is driven by electric power supplied from battery 40. When working as a generator, AC power is output to the inverter 30.

  The inverter 30 includes a U phase, a V phase, and a W phase, and the U phase, the V phase, and the W phase are connected in parallel to the converter 20, and converts the DC power boosted by the converter 20 into a three-phase AC, Output to motor generator MG. When motor generator MG functions as a generator, AC power output from motor generator MG is converted to DC and output to converter 20. Furthermore, the inverter 30 includes a capacitor 31 for absorbing a surge voltage that also serves as a power storage, on the connection side with the converter 20.

  The U phase of the inverter 30 is formed by connecting a switching element 34 for the upper arm of the semiconductor element on the high voltage side and a switching element 35 for the lower arm of the semiconductor element on the high voltage GND side in series. Similarly, the switching element 36 for the upper arm and the switching element 37 for the lower arm are connected in the V phase, and the switching element 38 for the upper arm and the switching element 39 for the lower arm are connected in series in the W phase.

  Between the collectors and emitters of the respective switching elements 34 to 39, diodes D3 to D8 for passing a current from the emitter side to the collector side are respectively connected. An intermediate point of each UVW phase is connected to each phase end of each phase coil (not shown) of motor generator MG. Here, it is assumed that a power device such as an IGBT (Insulated Gate Bipolar Transistor) is used as the switching element included in each of the converter 20 and the inverter 30.

  Further, each of the switching elements 21 and 22 of the converter 20 and each of the switching elements 34 to 39 of the inverter 30 is such that when the upper arm switching element is on, the lower arm switching element is off and the upper arm switching element is off. When the switch is off, the control unit 11 performs switching control (on / off control) so that the lower arm switching element is turned on.

  According to the power converter 12 having such a configuration, the DC power of the battery 40 is converted by the converter 20 by switching control of the switching elements 21 and 22 of the converter 20 and the switching elements 34 to 39 of the inverter 30 by the control unit 11. The voltage is boosted and converted into a three-phase alternating current by the inverter 30, and the motor generator MG is driven by the three-phase alternating current. On the other hand, when motor generator MG functions as a generator, AC power output from motor generator MG is converted into DC power by inverter 30, further stepped down by converter 20, and regenerated by battery 40.

  Next, the converter 20 and the control unit 11 that are characteristic elements of the present embodiment will be described. In addition to the switching control of the converter 20 and the inverter 30 described above, the controller 11 controls the switching elements 21 and 22 of the converter 20 according to the control signal 11a corresponding to the temperature sensor signal 18a. To do.

  This intermittent switching control will be described. First, since the temperature sensor signal 18a indicates the temperature (detection temperature) of the cooling refrigerant of the heat source 19 detected by the temperature sensor 18, the controller 11 detects the detected temperature at which the temperature sensor signal 18a exceeds a predetermined threshold, That is, when the cooling refrigerant of the heat source 19 is at a high temperature suitable for heating, normal switching control is performed on the converter 20.

  This normal switching control will be described with reference to FIG. 4A shows the waveform of the gate control signal G22 supplied to the switching element 22 for the lower arm of the converter 20, and FIG. 4B shows the waveform of the gate control signal G21 supplied to the switching element 21 for the upper arm. Indicates. As shown in (a) and (b), on / off of the switching elements 22 and 21 of the converter 20 by the gate control signals G22 and G21 in which the on period Ton2 and the off period Toff2 are alternately switched in one cycle T2. Are controlled reciprocally. However, DT is a dead time.

  At this time, as shown in (c), a reactor current IL2 that gradually rises in the on section Ton2 and gradually falls in the off section Toff2 flows through the reactor 24. Further, at the switching timing of the on period Ton2 and the off period Toff2 of the gate control signal G22, the rising and falling levels of the current I22 flowing through each switching element 22 and the voltage V22 are switched as shown in (d). This switching portion is a switching loss L22 which is a power loss when the lower arm switching element 22 is operated as shown in FIG.

  Similarly, the rising and falling levels of the current I21 flowing through each switching element 21 and the voltage V21 are switched as shown in (f) at the switching timing between the ON period and the OFF period of the gate control signal G21. This switching portion is a switching loss L21, which is a power loss during the operation of the upper arm switching element 21 shown in (g).

  Next, when the temperature sensor signal 18a is a detected temperature that is equal to or lower than the threshold, that is, when the cooling refrigerant of the heat source 19 is at a low temperature that is not suitable for heating, the control unit 11 intermittently controls the switching elements 21 and 22 with the control signal 11a. Perform switching control. As shown in FIG. 5A, this intermittent switching control is performed N times (a plurality of times) at a predetermined interval for a time Ts sufficiently shorter than the ON section Ton3 in the ON section Ton3 of the gate control signal G22a. Times) Control to turn off. Similarly, as shown in FIG. 5B, in the on period Ton4 of the gate control signal G21a, each switching element 21 is turned off N times (multiple times) at a predetermined interval for a time Ts sufficiently shorter than the on period Ton4. Control is performed.

  However, the time Ts is hereinafter also referred to as a short off time Ts. Taking the gate control signal G22a as an example, the short off time Ts generated N times in the on period Ton3 of the gate control signal G22a has a relationship of Ton3 × 1/2> N × Ts. That is, the total time of N times of the short off time Ts is set to be smaller than half the time of the on section Ton3. This will be explained on the side of the gate control signal G22a. When the time of N × Ts is set to Ton3 × 1/2 or more, the length of the off section Toff3 in one cycle T3 is equal to or longer than the length of the on section Ton3. For this reason, it is substantially equivalent to raising the switching frequency, and the iron loss of the reactor is increased.

  Further, as shown in FIG. 5A, it is desirable that the plurality of short off times Ts in the gate control signal G22a be performed at the timing of the first half of the on period Ton3. This is because the iron loss of the reactor can be suppressed by performing the intermittent switching control at a timing when the magnetic flux density B and the magnetic field H in the magnetic hysteresis curve of the reactor are low at the timing of intermittent switching.

  Further, the ON period Ton3 at the time of intermittent switching control execution is such that even if it is OFF for N × Ts, the energy stored in the reactor in the normal switching control matches, that is, the peak value current of the IL2 reactor current matches. It is determined from the relationship Ton3−N × Ts = Ton2. That is, Ton3> Ton2. Further, T3 is determined from the relationship of Ton3 / T3 = Ton2 / T2 so that the energization rate does not change from the normal switching control even if intermittent switching control is performed. That is, the switching cycle T3 when the intermittent switching control is executed is longer than the normal switching cycle T2.

  However, the timing of the plurality of short off times Ts in the gate control signal G21a shown in FIG. 5B may be any of the on sections Ton4.

  When the switching elements 22 and 21 of the converter 20 are intermittently controlled by such gate control signals G22a and G21a, the reactor current ILa shown in FIG. This reactor current ILa rises with a predetermined time constant slope between the times t1 and t2 of the leading on time Ton3 in the on section Ton3 of FIG. 5A, and between the times t2 and t3 of the next short off time Ts. Fall at a predetermined time constant slope, rise at a predetermined time constant slope between the times t3 and t4 of the next on-time Ton, and tilt at a predetermined time constant between times t4 and t5 of the next short off-time Ts And rises with a predetermined time constant slope between times t5 and t6 of the next on-time Ton, and falls with a predetermined time constant slope between times t6 and t7 of the next off section Toff3. Thereafter, the rise and fall are repeated in the same manner.

  At the switching timing between the on-time Ton and the short off-time Ts and the switching timing between the on-section Ton3 and the off-section Toff3, as shown in FIG. 5D, the current I22a flowing through each switching element 22 and the voltage The rising and falling levels with V22a are switched. This switching portion is a switching loss L22a shown in FIG. This switching loss L22a can be increased N times in the 1-on section Ton3. Therefore, unlike the conventional case, it is not necessary to increase the switching frequency in which the on period Ton1 (or Ton2) and the off period Toff1 (Toff2) are one period T1. Similarly, in the switching element 21, as shown in FIG. 5 (f), the rising and falling levels of the current I21a flowing through each switching element 21 and the voltage V21a are switched, and this switching portion is shown in FIG. The switching loss L21a shown in FIG.

  Thus, when the switching losses L22a and L21a of the converter 20 are increased, an increase in the iron loss of the reactor 24 can be suppressed. The reason for this will be described on the lower arm switching element 22 side. The BH curve (magnetic hysteresis curve) 53 shown in FIG. 6A rises from time t6 in the direction of arrow Y1 to time t6 at time t1 shown in FIG. 5A and from time t6 to time t7 in the direction of arrow Y2. It becomes a falling curve.

  On the other hand, in the intermittent switching control, as shown by a solid line in FIG. 6B, the BH curve 55 becomes a curve that rises while looping the number of intermittent OFFs as shown by an arrow Y1. That is, at time t1, the signal rises in the direction of arrow Y1 until time t2, loops at time t2 to t3 and rises to time t4, loops at time t4 to t5 and rises to time t6, and further starts at time t6 in the direction of arrow Y2. The curve falls until t7.

Here, iron loss of reactor 24 = hysteresis loss + eddy current loss. Further, when the magnetic flux density B when each switching element 22 is OFF is Bm and the switching frequency is f, the hysteresis loss is proportional to f × Bm ² and the eddy current loss is proportional to f ² × Bm ² . Therefore, as shown in FIG. 6B, when the magnetic flux density of the BH curve 55 in the 1-on section Ton3 is B1, N short off-times Ts are obtained at the times t2 and t4 in the 1-on section Ton3. It is performed at the position, that is, the position of B1a and B1b where the magnetic flux density is low.

  In this way, when the magnetic flux densities B1a and B1b are low, when the switching element 22 is turned off in the short off time Ts, Bm becomes small, so that both hysteresis loss and eddy current loss are reduced, and iron loss is also reduced. That is, even if the switching loss L22a is increased in N short off times Ts, an increase in the iron loss of the reactor 24 is suppressed.

  Furthermore, when the switching element 22 is turned off in a short off time Ts so that the magnetic flux densities B1a and B1b become lower, that is, the switching element 22 is turned off in N short off times Ts immediately after the switching element 22 is turned on. When turned off N times, Bm becomes smaller. For this reason, hysteresis loss and eddy current loss are both reduced, and iron loss is also reduced. That is, even if the switching loss L22a is increased in N short off times Ts, the increase in the iron loss of the reactor 24 is further suppressed.

  The suppression of the increase in the iron loss of the reactor 24 will be described with reference to FIGS. FIG. 7 is a graph in which the horizontal axis represents the load power, the vertical axis represents the switching loss, and FIG. 8 is a graph in which the horizontal axis represents the load power and the vertical axis represents the reactor iron loss. For example, in FIG. 7, the switching loss at the time of normal switching control is indicated by a solid line L22, the switching loss at the time of intermittent switching control is indicated by a solid line L22a, and further, in normal switching control, it is equivalent to the switching loss L22a. The switching loss when the switching frequency is increased is indicated by a broken line L22b.

  When the switching loss L22 is obtained during normal switching control, the iron loss of the reactor 24 is a solid line L22-1 as shown in FIG. Further, when the switching loss L22b is obtained when the switching frequency is increased so as to be equivalent to the switching loss L22a during the normal switching control, the iron loss of the reactor 24 is larger than the solid line L22a-1 by the solid line L22b. -1. However, when the switching loss L22a is obtained during intermittent switching control, the iron loss of the reactor 24 is slightly higher than the iron loss L22-1 of the reactor 24 during normal switching control, as indicated by the solid line L22a-1. Become. That is, an increase in the iron loss of the reactor 24 is suppressed.

  The converter 20 according to this embodiment includes a plurality of switching elements 21 and 22 that boost the DC power of the battery 40, and the connection between the emitter and collector of the switching elements 21 and 22 and the both ends of the battery 40. In addition, a capacitor is connected in parallel and a reactor is connected in series, and the switching elements 21 and 22 are controlled to be switched by the control unit 11 so as to repeat ON and OFF at a constant cycle.

  In this configuration, as a feature of the present embodiment, the control unit 11 performs intermittent switching control in which the switching elements 21 and 22 are turned off a plurality of times in the ON period of the constant period of the switching elements 21 and 22. This intermittent switching control is performed in the switching element 22 such that the total time of turning off a plurality of times is shorter than half the time of the on section.

  Thereby, since the switching elements 21 and 22 are turned off a plurality of times in the ON section of the switching elements 21 and 22, the rising and falling levels of the current and voltage flowing through the switching elements 21 and 22 at the time of these switching are switched, This switching portion becomes a switching loss. Accordingly, in the case of normal switching control, the switching elements 21 and 22 cause switching loss by switching between on and off, but in this embodiment, multiple switching losses occur in the on section, and accordingly, Switching loss can be increased. At this time, in the case of normal switching control, the switching loss does not increase unless the switching frequency with ON and OFF as one cycle is increased. However, in the present invention, when the switching element 22 is turned off a plurality of times in a fixed period of the ON section, the total time of the plurality of OFF times is set to be smaller than half the time of the ON section. In this case, the substantial switching frequency is not increased when the total time is equal to or more than half of the ON period.

  When the switching loss is increased as in this embodiment, in the process of increasing the magnetic flux density at the time of ON in the reactor BH curve (magnetic hysteresis curve), the curve rises while looping the number of intermittent OFF times. That is, when the switching element is intermittently turned off N times, both the hysteresis loss and the eddy current loss are reduced, and as a result, the reactor iron loss, which is the sum of the hysteresis loss and the eddy current loss, is also reduced. Therefore, even if the switching elements 21 and 22 are turned off a plurality of times in the ON section to increase the switching loss, it is possible to suppress an increase in the iron loss of the reactor. Thereby, the converter 20 can appropriately perform voltage conversion.

  In addition, when the control unit 11 performs intermittent switching control, the time during which the switching element 22 is on in the on section including the plurality of times off is the same as the on time when the plurality of times are not turned off. To be controlled.

  As a result, when the switching elements 21 and 22 are controlled to be turned off a plurality of times in the ON period of a fixed period, the current supply rate that is substantially turned on and off is turned on and off when not turned off a plurality of times. It can be the same as during normal switching control.

  Moreover, the control part 11 was made to control so that the timing which turns off the switching elements 21 and 22 several times at the time of intermittent switching control may be performed in the position where the magnetic flux density in a magnetic hysteresis curve of a reactor is low.

  Accordingly, when the magnetic flux density is turned off a plurality of times after the switching elements 21 and 22 are turned on, both the hysteresis loss and the eddy current loss are reduced, and the iron loss is also reduced. Thereby, the iron loss of the reactor can be further suppressed.

  In addition, when the switching unit 21 and 22 are turned off a plurality of times during the intermittent switching control, the control unit 11 shortens the off time so that the current flowing through the switching elements 21 and 22 does not fall to zero. Control to turn on again was performed. In this control, if the turn-off loss is shortened and the turn-on loss is turned on again before the current does not fall to zero, the turn-on loss and the turn-off loss partially overlap. Even if they overlap in this way, an increase in the iron loss of the reactor can be suppressed.

  Moreover, the control part 11 was made to control so that the period which turns off the switching elements 21 and 22 several times at the time of intermittent switching control was performed more than an audible area | region frequency.

  As a result, the cycle of turning off a plurality of times in the ON section of the constant cycle of the switching elements 21 and 22 is performed at the audible region frequency or higher, so that the off and on operations of the plurality of times cannot be heard. Therefore, it is possible to reduce the noise of the on / off operation when the switching loss increases.

  Furthermore, it has an inverter 30 having a plurality of switching elements 34 to 39 that convert the converter 20 and the boosted voltage in the converter 20 into an AC voltage, and the operating heat of the switching elements 21, 22, and 34 to 39 is a refrigerant. The power converter 12 cooled by the power converter 12, the heat exchanger 13 for exchanging heat of the high-temperature refrigerant warmed by the power converter 12, and the heater for heating using the high-temperature refrigerant heat-exchanged by the heat exchanger 13 17 and a temperature sensor 18 for detecting the temperature of the refrigerant heated by the heat source 19 supplied to the heater 17, and the controller 11 of the converter 20 has a temperature detected by the temperature sensor equal to or lower than a predetermined threshold value. In this case, the switching elements 21 and 22 are controlled to be turned off a plurality of times during the ON period of the constant period of the switching elements 21 and 22.

  As a result, for example, when the amount of heat generated from the heat source 19 decreases or the heating load increases, the temperature of the cooling refrigerant of the heat source 19 decreases, and the temperature sensor signal 18a from the temperature sensor 18 falls below a predetermined threshold. In this case, the control unit 11 performs intermittent switching control of the converter 20 of the power converter 12 using the control signal 11a. By this control, the switching loss of the converter 20 increases, so that the refrigerant is warmed. Since this warmed refrigerant flows from the heat exchanger 13 to the heater 17 for heating, the heater 17 can perform immediate heating with the warmed refrigerant. At this time, in converter 20, an increase in iron loss of reactor 24 is suppressed even if a switching loss increases. Therefore, the converter 20 can appropriately perform voltage conversion.

DESCRIPTION OF SYMBOLS 10 Waste heat utilization system of power converter using converter 11 Control unit 11a Control signal 12 Power converter 13 Heat exchanger 16 Radiator 17 Heater 18 Heating sensor 18 Temperature sensor 19 Heat source 20 Converter 21, 22 Switching element 23 Capacitor 24 Reactor 30 Inverter 34-39 Switching element D1-D8 Diode MG Motor generator

Claims (7)

It has a plurality of switching elements that boost the direct current power of the battery, a capacitor is connected in parallel between the connection ends of the emitter and collector of these switching elements and both ends of the battery, and a reactor is connected in series, In the converter in which the switching element is controlled to be switched on and off at a constant cycle by the control means,
The control means performs intermittent switching control in which the switching element is turned off a plurality of times in an on section having a fixed period of the switching element, and the total time for which the intermittent switching control is turned off the plurality of times is half of the on section. A converter characterized in that it is performed so as to be shorter than the time.   When the control means performs the intermittent switching control, the time during which the switching element is on in the on section including the plurality of off times is the same as the on time when the plurality of times are not turned off. 2. The converter according to claim 1, wherein the converter is controlled as follows.   The control means controls the timing to turn off the switching element a plurality of times during the intermittent switching control so that the magnetic flux density in the magnetic hysteresis curve of the reactor is low. Converter described in.   When the switching element is turned off a plurality of times during the intermittent switching control, the control means shortens the off time, and controls to turn on again before the current flowing through the switching element does not fall to zero. The converter according to claim 1, wherein the converter is performed.   The control means performs control so that the timing at which the switching element is turned off a plurality of times during the intermittent switching control is performed at a timing close to the time during which the switching element is turned on within a fixed period of the on period. The converter according to any one of claims 1 to 4, wherein the converter is characterized.   The said control means controls so that the period which turns off the said switching element in multiple times at the time of the said intermittent switching control may be performed more than an audible area | region frequency. converter. A power converter comprising the converter according to any one of claims 1 to 6, wherein operating heat of a switching element of the converter is cooled by a refrigerant,
A heat exchanger for exchanging heat with the high-temperature refrigerant in which the refrigerant is warmed by the power converter;
A heater for heating using the high-temperature refrigerant heat-exchanged in the heat exchanger;
A temperature sensor for detecting a temperature of a refrigerant heated by a heat source supplied to the heater for heating,
When the temperature detected by the temperature sensor is equal to or lower than a predetermined threshold, the converter control means performs control to turn off the switching element a plurality of times during an on period of the constant period of the switching element. Waste heat utilization system.

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