Method for controlling power conversion device, and power conversion device
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2023-09-01
- Publication Date
- 2026-03-12
Smart Images
Figure IB2023000519_12032026_PF_FP_ABST
Abstract
Description
Control method for power conversion device and power conversion device
[0001] The present invention relates to a control method for a power conversion device and a power conversion device.
[0002] Patent Document 1 describes a power conversion circuit that converts AC input power into high-frequency AC current using a class E inverter having an LC resonant circuit, rectifies the AC current using a rectifier circuit, and outputs the rectified current to a load. In the power conversion circuit of Patent Document 1, the switching frequency of the switch elements of the class E inverter is changed based on the input voltage of the power conversion circuit, thereby achieving low-loss zero voltage switching (ZVS).
[0003] JP 2021-145433 A
[0004] As in Patent Document 1, a power conversion circuit in which switching elements perform high-frequency switching operations in a high-voltage environment can be realized in a compact configuration. When increasing output, by connecting and operating multiple power conversion circuits in parallel, the heat source can be dispersed, thereby suppressing an increase in heat density. In a power conversion circuit, switching elements that perform high-frequency switching operations at high voltages generate high-frequency, high-voltage switching noise. When multiple power conversion circuits are connected and operated, it becomes necessary to increase the noise removal capability of the noise removal filter to accommodate the switching noise generated in each power conversion circuit. Increasing the noise removal capability may result in an increase in filter size.
[0005] The present invention aims to suppress an increase in noise superimposed on the power supplied from a power conversion device when increasing the output of the power conversion device using a power conversion circuit in which the switch elements of the inverter circuit perform high-voltage, high-frequency switching operations.
[0006] A power conversion device and a control method for a power conversion device according to one aspect of the present invention, which solves the above-mentioned problems, can be applied to a power conversion device including a pair of input terminals to which AC power is input, a power conversion circuit connected to the pair of input terminals, and a pair of output terminals to which a load is connected. At least two power conversion circuits are connected in parallel to the pair of input terminals. The power conversion circuit includes an inverter circuit and a rectifying element. The inverter circuit includes an LC resonant circuit and generates a high-frequency AC current from the AC power input to the pair of input terminals. The rectifying element rectifies the high-frequency AC current generated by the inverter circuit and outputs the rectified power to the pair of output terminals. The inverter circuit includes a bidirectional switch that switches the direction and on / off of the current flowing between the pair of input terminals, and a shunt capacitor connected in parallel with the bidirectional switch between the pair of input terminals. The at least two power conversion circuits include a first power conversion circuit and a second power conversion circuit connected to the pair of input terminals with the rectifying elements rectified in opposite directions. The switching operations of the bidirectional switches of the first and second power conversion circuits are controlled. Through this control, the power rectified by the rectifying element of the first power conversion circuit and the power rectified by the rectifying element of the second power conversion circuit are output alternately to a pair of output terminals at a period in which the polarity of the high-frequency AC current switches.
[0007] According to the present invention, when increasing the output of a power conversion device using a power conversion circuit in which the switch elements of the inverter circuit perform high-voltage, high-frequency switching operations, it is possible to suppress an increase in noise superimposed on the power supplied from the power conversion device.
[0008] Fig. 1 is a diagram showing the configuration of a power conversion device according to a first embodiment of the present invention. Fig. 2 is a diagram showing the relationship between the input voltage of the power conversion device of Fig. 1 and the control signals for the switch elements of each power conversion circuit. Fig. 3 is a diagram showing the relationship between the control signals of the switch elements connected to the common input terminal of Fig. 1. Fig. 4 is a diagram showing the relationship between the output voltages of the power conversion circuits of Fig. 1. Fig. 5 is a diagram showing the configuration of a power conversion device according to a second embodiment of the present invention.
[0009] Hereinafter, an embodiment of the present invention and its modifications will be described with reference to the drawings. In the description of the drawings, the same parts are given the same reference numerals and the description thereof will be omitted.
[0010] (First Embodiment) (Configuration of a Power Conversion Device According to a First Embodiment) FIG. 1 is a diagram showing the configuration of a power conversion device according to a first embodiment to which the present invention is applied. The power conversion device 1 according to the first embodiment includes a pair of input terminals IN1 and IN2 to which AC power AC is input, two power conversion circuits 10 and 20 connected to the input terminals IN1 and IN2, a pair of output terminals OUT1 and OUT2, and a control unit 40. A DC load RLoad is connected to the pair of output terminals OUT1 and OUT2. By connecting the two power conversion circuits 10 and 20 in parallel between the pair of input terminals IN1 and IN2 and the pair of output terminals OUT1 and OUT2, it is possible to increase the output of the power conversion device 1. The polarity of the input voltage of the power conversion device 1 is switched between positive and negative depending on the AC power of an AC power source AC input between the pair of input terminals IN1 and IN2. Hereinafter, the two power conversion circuits 10, 20 may be referred to as a first power conversion circuit 10 and a second power conversion circuit 20. The pair of input terminals IN1, IN2 and the pair of output terminals OUT1, OUT2 may also be referred to as a first input terminal IN1, a second input terminal IN2, a first output terminal OUT1, and a second output terminal OUT2, as necessary. The two power conversion circuits 10, 20 are connected in parallel to the pair of input terminals IN1, IN2.
[0011] The first power conversion circuit 10 has an inverter circuit 110 and a rectifier circuit 120. The second power conversion circuit 20 has an inverter circuit 210 and a rectifier circuit 220. The first power conversion circuit 10 and the second power conversion circuit 20 are connected to a pair of input terminals IN1 and IN2 such that the rectification directions of the rectifier elements of the rectifier circuits 120 and 220 are opposite to each other. The first power conversion circuit 10 and the second power conversion circuit 20 are connected to a pair of output terminals OUT1 and OUT2 such that the rectification directions of the rectifier elements of the rectifier circuits 120 and 220 are the same.
[0012] The inverter circuit 110 of the first power conversion circuit 10 generates a high-frequency alternating current from alternating current power AC input to the first input terminal IN1 and the second input terminal IN2. The inverter circuit 110 includes a choke inductor L11, a switch element 111, a shunt capacitor C11, and an LC resonant circuit 112.
[0013] The switch element 111 is connected between the first input terminal IN1 and the second input terminal IN2. A choke inductor L11 is connected in series to the connection point between the first input terminal IN1 and the switch element 111. A shunt capacitor C11 is connected in parallel to the switch element 111. In consideration of the symmetry of the inverter circuit 110, in addition to the choke inductor L11 between the first input terminal IN1 and the switch element 111, a choke inductor L11 may be further provided between the second input terminal IN2 and the switch element 111. In the following description, it is assumed that the choke inductor L11 is provided only between the first input terminal IN1 and the switch element 111, as shown in FIG. 1 .
[0014] The LC resonant circuit 112 is a series circuit of a resonant inductor Lr1 and a resonant capacitor Cr1. The resonant inductor Lr1 is connected to the connection point between the choke inductor L11 and the switch element 111. The inverter circuit 110 generates a high-frequency resonant current in the LC resonant circuit 112 by switching the switch element 111, and generates a high-frequency alternating current from the alternating current power AC input to a pair of input terminals IN1 and IN2.
[0015] The switch element 111 includes a series circuit of two switch elements. The switch elements are semiconductor switches known as power transistors. The semiconductor switches may be, for example, unipolar transistors such as MOSFETs (Metal Oxide Semiconductor Field Effect Transistors). In this embodiment, a series circuit of two MOSFETs Q11 and Q12 with source terminals connected to each other is used as the series circuit of the first and second switch elements constituting the switch element 111. In addition to MOSFETs, the semiconductor switches may be, for example, bipolar transistors such as IGBTs (Insulated Gate Bipolar Transistors). The switch element 111 using IGBTs may be, for example, a bidirectional IGBT in which two IGBTs are connected in anti-parallel. The switch element 111 using an IGBT may be configured by a reverse conducting IGBT (RC-IGBT) in which one IGBT and one FWD (Free Wheeling Diode) are connected in anti-parallel.
[0016] The rectifier circuit 120 includes a diode D11 as a rectifying element, a rectifier-side capacitor C12, an inductor L12, and an output-side capacitor C13. The cathode of the diode D11 is connected to the resonance capacitor Cr1 and is electrically connected to the first input terminal IN1 and the first output terminal OUT1. The anode of the diode D11 is connected to the shunt capacitor C11 and is electrically connected to the second input terminal IN2 and the second output terminal OUT2. The rectifier-side capacitor C12 is connected in parallel with the diode D11. The inductor L12 is connected to the cathode of the diode D11, the rectifier-side capacitor C12, and the first output terminal OUT1. The output-side capacitor C13 is connected between the first output terminal OUT1 and the second output terminal OUT2. The rectifier circuit 120 rectifies the resonant current of the LC resonant circuit 112 using a diode D11, and outputs the resulting DC voltage to the first output terminal OUT1 and the second output terminal OUT2.
[0017] The inverter circuit 210 of the second power conversion circuit 20 generates a high-frequency alternating current from alternating current power AC input to a pair of input terminals IN1 and IN2. The inverter circuit 210 has a choke inductor L21, a switch element 211, a shunt capacitor C21, and an LC resonant circuit 212. The choke inductor L21 and the shunt capacitor C21 of the inverter circuit 210 are configured similarly to the choke inductor L11 and the shunt capacitor C11 of the inverter circuit 110.
[0018] The LC resonant circuit 212 is a series circuit of a resonant inductor Lr2 and a resonant capacitor Cr2. The resonant inductor Lr2 is connected to the connection point between the choke inductor L21 and the switch element 211. The inverter circuit 210 generates a high-frequency resonant current in the LC resonant circuit 212 by switching the switch element 211, and generates a high-frequency alternating current from the alternating current power AC input to the pair of input terminals IN1 and IN2.
[0019] The switch element 211 includes a series circuit of two switch elements. The switch elements are, for example, semiconductor switches using MOSFETs or IGBTs. In this embodiment, the series circuit of two semiconductor switches of the switch element 211 is a series circuit of two MOSFETs Q21 and Q22 whose source terminals are connected to each other, similar to the switch element 111 of the inverter circuit 110.
[0020] The rectifier circuit 220 includes a diode D21 as a rectifying element, a rectifier-side capacitor C22, an inductor L22, and an output-side capacitor C23. The diode D21, rectifier-side capacitor C22, inductor L22, and output-side capacitor C23 are configured similarly to the diode D11, rectifier-side capacitor C12, inductor L12, and output-side capacitor C13 of the rectifier circuit 120. The rectification direction of the diode D21 with respect to the input terminals IN1 and IN2 is opposite to that of the diode D11. The cathode of the diode D21 is conductive with the second input terminal IN2 and the first output terminal OUT1, and the anode of the diode D11 is conductive with the first input terminal IN1 and the second output terminal OUT2. The rectifier circuit 220 rectifies the resonant current of the LC resonant circuit 212 using the diode D21 and outputs the resulting DC voltage to the first output terminal OUT1 and the second output terminal OUT2.
[0021] The first power conversion circuit 10 and the second power conversion circuit 20 are connected to a pair of input terminals IN1 and IN2, respectively, with the rectification directions of diodes D11 and D21 facing in opposite directions. In the first power conversion circuit 10, the cathode of diode D11 of the rectifier circuit 120 is connected to input terminal IN1, and the anode of diode D11 is connected to input terminal IN2. In the first power conversion circuit 10, the MOSFET Q11 of the inverter circuit 110 is connected to input terminal IN1, and the MOSFET Q12 is connected to input terminal IN2. In the second power conversion circuit 20, the anode of diode D21 of the rectifier circuit 220 is connected to input terminal IN1, and the cathode of diode D21 is connected to input terminal IN2. In the second power conversion circuit 20, the MOSFET Q21 of the inverter circuit 210 is connected to input terminal IN1, and the MOSFET Q22 is connected to input terminal IN2.
[0022] In the inverter circuit 110 of the first power conversion circuit 10, when MOSFETs Q11 and Q12 are used as the switch element 111, the parasitic capacitance of the MOSFETs Q11 and Q12 may be used as the shunt capacitor C11. The shunt capacitor C11 may be configured with a component that is also used for other purposes, like the parasitic capacitance of the MOSFETs Q11 and Q12. Of course, the shunt capacitor C11 may also be configured with a component dedicated to shunting. In the inverter circuit 210 of the second power conversion circuit 20, when MOSFETs Q21 and Q22 are used as the switch element 211, the shunt capacitor C21 may be configured in the same manner as the shunt capacitor C11 of the inverter circuit 110.
[0023] In the switch element 111 of the inverter circuit 110, one of the MOSFETs Q11 and Q12 is turned on with a 100% duty while the other is repeatedly turned on and off with a duty of less than 100%. By interchanging the element of the switch element 111 that is turned on with a 100% duty with the element that is turned on and off with a duty of less than 100%, the switch element 111 can function as a bidirectional switch. In the switch element 211 of the inverter circuit 210, by turning on and off the MOSFETs Q21 and Q22 in the same way as the MOSFETs Q11 and Q12, the switch element 211 can also function as a bidirectional switch.
[0024] The switch elements 111 and 211 functioning as bidirectional switches can switch the direction of current flowing through the switch elements 111 and 211 between the direction from MOSFETs Q11 and Q21 to MOSFETs Q12 and Q22 and the opposite direction. When the switch elements 111 and 211 are configured as bidirectional switches as in this embodiment, the switch elements 111 and 211 correspond to the positive and negative input voltages of the power conversion circuits 10 and 20. When the switch elements 111 and 211 are configured as bidirectional switches, the number of elements through which the input current passes in the power conversion circuits 10 and 20 is reduced compared to when the switch elements 111 and 211 are not configured as bidirectional switches. Reducing the number of elements through which the input current passes in the power conversion circuits 10 and 20 allows the power conversion circuits 10 and 20 to achieve highly efficient power conversion.
[0025] When the switch elements 111 and 211 perform zero voltage switching (ZVS), switching occurs while the voltage across the switch elements 111 and 211 is zero. When switching occurs while the voltage across the switch elements 111 and 211 is zero, loss when the switch elements 111 and 211 are turned on becomes zero. When the switch elements 111 and 211 perform switching that satisfies the ZVS condition, switching loss is reduced, and high-frequency switching of the switch elements 111 and 211 becomes possible. Switching the switch elements 111 and 211 at high frequency allows the inductors and capacitors of the inverter circuits 110 and 210 to be made smaller. By reducing the inductors and capacitors of the inverter circuits 110 and 210, the input current of the power conversion device 1 can be converted to high-frequency AC current by the inverter circuits 110 and 210 with high efficiency.
[0026] When the switch elements 111 and 211 are turned on and off at the resonant frequency of the resonant circuit of the inverter circuits 110 and 210, they can perform switching that satisfies the ZVS condition. The control unit 40 controls the switch elements 111 and 211 so that they perform switching that satisfies at least the ZVS condition. In general, an inverter in which the switch elements perform switching operations that satisfy the ZVS condition is called a quasi-class E inverter. In general, an inverter in which the switch elements perform switching operations that satisfy both the ZVS and zero derivative switching (ZDS) conditions is called a class E inverter. By controlling the switch elements 111 and 211 by the control unit 40, the inverter circuits 110 and 210 can operate as a quasi-class E inverter or a class E inverter.
[0027] The control unit 40 controls the switching operations of the switch elements 111 and 211 of the inverter circuits 110 and 210. In this embodiment, a case will be described in which the control unit 40 controls the switching operations of the switch elements 111 and 211 so as to operate the inverter circuits 110 and 210 as quasi-class E inverters. The control unit 40 can implement the control method for the power conversion device 1 according to this embodiment by performing the control described below.
[0028] (Control Signals of MOSFETs Q11, Q12, Q21, Q22) The control section 40 turns on and off the MOSFETs Q11, Q12, Q21, Q22 of the switch elements 111, 211 using the control signals shown in FIG.
[0029] MOSFET Q11 of switch element 111 and MOSFET Q22 of switch element 211 connected to first input terminal IN1 are controlled by a first control signal and a second control signal, respectively. As shown in Fig. 2, the first control signal and the second control signal repeatedly switch on and off at high frequency with a duty of less than 100% when the voltage of AC power input to input terminals IN1 and IN2 is positive (+). The first control signal and the second control signal are fixed to on with a duty of 100% when the voltage of AC power input to input terminals IN1 and IN2 is negative (-).
[0030] The control signals for MOSFET Q12 of switch element 111 and MOSFET Q21 of switch element 211 connected to second input terminal IN1 are controlled by a third control signal and a fourth control signal, respectively. As shown in Fig. 2, the third control signal and the fourth control signal repeat high-frequency on / off switching with a duty of less than 100% when the voltage of AC power input to input terminals IN1 and IN2 is negative (-). The third control signal and the fourth control signal are fixed to on with a duty of 100% when the voltage of AC power input to input terminals IN1 and IN2 is positive (+).
[0031] The first control signal and the second control signal may be, for example, signals that turn on the MOSFETs Q11 and Q22 in synchronization. In this embodiment, the first control signal and the second control signal rise from off to on in synchronization, as shown in FIG. 3 . The MOSFETs Q11 and Q22 are turned on in synchronization by the first control signal and the second control signal. The first control signal and the second control signal may be, for example, signals that turn on and off the MOSFETs Q11 and Q22 in the same cycle during the period in which the high-frequency signal is repeatedly turned on and off. In this embodiment, the first control signal and the second control signal are turned on and off at the same frequency, as shown in FIG. 3 . The frequency during the period in which the first control signal and the second control signal repeatedly turn on and off the high-frequency signal may be, for example, the resonant frequency of the LC resonant circuits 112 and 212 of the switch elements 111 and 211.
[0032] An error within an allowable range may occur in the rising edges of the first control signal and the second control signal. The allowable range of the error regarding the rising edges of the first control signal and the second control signal may be a range in which the effects described later by the power conversion device 1 of this embodiment are substantially obtained, and can be determined, for example, by experiment. A frequency difference within a predetermined range including zero may occur in the on / off of the first control signal and the second control signal. The allowable range of the frequency difference between the first control signal and the second control signal may be a range in which the effects described later by the power conversion device 1 of this embodiment are substantially obtained, and can be determined, for example, by experiment.
[0033] The third control signal and the fourth control signal may be signals that turn on the MOSFETs Q12 and Q21 in synchronization, for example. In this embodiment, the third control signal and the fourth control signal also rise from off to on in synchronization, as shown in FIG. 3 . The MOSFETs Q12 and Q21 are turned on in synchronization by the third control signal and the fourth control signal. The third control signal and the fourth control signal may be signals that turn on and off the MOSFETs Q12 and Q21 in the same cycle, for example, during the period in which the high-frequency signal is repeatedly turned on and off. In this embodiment, the third control signal and the fourth control signal are also turned on and off at the same frequency, as shown in FIG. 3 . The frequency during the period in which the third control signal and the fourth control signal repeatedly turn on and off the high-frequency signal may be, for example, the resonant frequency of the LC resonant circuits 112 and 212 of the switch elements 111 and 211. The rising and on / off of the third control signal and the fourth control signal may have errors and frequency differences similar to those of the first control signal and the second control signal. The tolerance ranges for the error and frequency difference of the third control signal and the fourth control signal may be, for example, similar to those of the first control signal and the second control signal.
[0034] (Operation and effect of power conversion device 1 of first embodiment) Under the control of control unit 40, in inverter circuit 110 of first power conversion circuit 10, high-frequency AC current caused by the on / off of MOSFET Q11 flows from the first input terminal IN1 to the second input terminal IN2 when the voltage of the AC power is positive (+). In a section where the voltage of the AC power is negative (-), high-frequency AC current caused by the on / off of MOSFET Q12 flows from the second input terminal IN2 to the first input terminal IN1. Under the control of control unit 40, in inverter circuit 210 of second power conversion circuit 20, high-frequency AC current caused by the on / off of MOSFET Q22 flows from the first input terminal IN1 to the second input terminal IN2 when the voltage of the AC power is positive (+). In a section where the voltage of the AC power is negative (-), high-frequency AC current caused by the on / off of MOSFET Q21 flows from the second input terminal IN2 to the first input terminal IN1.
[0035] Under the control of the control unit 40, high-frequency AC currents that have passed through the switch elements 111 and 211 flow into the diodes D11 and D21 of the rectifier circuits 120 and 220 in opposite directions during a section where the voltage of the AC power is positive (+). High-frequency AC currents that have passed through the switch elements 111 and 211 in a direction opposite to that of the section where the voltage of the AC power is positive (+) flow into the diodes D11 and D21 of the rectifier circuits 120 and 220 in opposite directions during a section where the voltage of the AC power is negative (-). The AC currents flowing into the diodes D11 and D21 have opposite polarities. There is a 180° phase shift between the AC currents flowing into the diodes D11 and D21. The AC currents flowing into the diodes D11 and D21 alternately pass through the diodes D11 and D21 in a cycle where the polarity of the flowing AC current switches. The rectified currents passing through the diodes D11 and D21 respectively have positive (+) rectified waveforms that are out of phase with each other by 180°, as shown in Fig. 4. The DC power of this rectified waveform is smoothed by the output-side capacitors C13 and C23 of the rectifier circuits 120 and 220 and is then output to a pair of output terminals OUT1 and OUT2.
[0036] The first power conversion circuit 10 and the second power conversion circuit 20 are connected to a pair of output terminals OUT1 and OUT2 such that the rectification directions of the rectifying elements of the rectifier circuits 120 and 220 are the same. DC power rectified by the diode D11 and DC power rectified by the diode D21 are alternately output to the pair of output terminals OUT1 and OUT2 after being smoothed. Noise present in the DC power rectified by the diodes D11 and D21 is not simultaneously output to the output terminals OUT1 and OUT2. Therefore, large noise, the sum of the noise present in the DC power rectified by the diodes D11 and D21, does not appear at the output terminals OUT1 and OUT2 to which the DC power converted by each power conversion circuit 10 and 20 is output.
[0037] If the diodes D11 and D21 have a cooler (not shown), such as a heat sink, parasitic capacitance may occur between the diodes D11 and D21 and the cooler. If parasitic capacitance occurs in the diodes D11 and D21, the parasitic capacitance of the diodes D11 and D21 will allow current from cathode to anode that does not pass through the diodes D11 and D21 to pass. The current passed by the parasitic capacitance of the diode D11 will be a common mode current of the same phase but opposite polarity to the current that passed from the anode to the cathode of the diode D21 during the same period. The current passed by the parasitic capacitance of the diode D21 will be a common mode current of the same phase but opposite polarity to the current that passed from the anode to the cathode of the diode D11 during the same period. The switch elements 111 and 211 have MOSFET Q11 and MOSFET Q22, and MOSFET Q12 and MOSFET Q21 that are turned on and off in synchronization, so that the switching operations of the switch elements 111 and 211 are performed with synchronized timing.
[0038] Noise generated by the switching operation of the switch elements 111 and 211 is superimposed, at the same time, on both the current passing through the diodes D11 and D21 and the current passed by the parasitic capacitance of the diodes D11 and D21. The noise component of the current passed by the parasitic capacitance of the diode D11 is canceled out by the noise component of the current passed by the diode D21 during the same period. The noise component of the current passed by the parasitic capacitance of the diode D21 is canceled out by the noise component of the current passed by the diode D11 during the same period. Even if the parasitic capacitance of the diodes D11 and D21 passes a current that does not pass through the diodes D11 and D21 during the period in which a current passes through the diodes D11 and D21, the noise superimposed on each current is not added together at the output terminals OUT1 and OUT2.
[0039] In this embodiment, when two power conversion circuits 10, 20 are connected in parallel to increase the output power of the power conversion device 1, noise generated in each of the power conversion circuits 10, 20 is prevented from being simultaneously output to the output terminals OUT1, OUT2 and added together to form a large noise. Because the noise generated in the power conversion circuits 10, 20 does not appear at a high volume at the output terminals OUT1, OUT2, an increase in noise superimposed on the power supplied to the load RLoad connected to the output terminals OUT1, OUT2 can be prevented. When removing noise generated in the power conversion circuits 10, 20 using a filter, it is sufficient to provide each power conversion circuit 10, 20 with a filter that corresponds to the magnitude of the noise generated in the power conversion circuits 10, 20. When removing noise generated in the power conversion circuits 10, 20 using a filter, a filter with a removal capacity that can remove a large noise resulting from the sum of the generated noises is not required. This prevents the noise filter from becoming larger as the output power of the power conversion device 1 increases.
[0040] The operation of the power conversion device 1, in which the two power conversion circuits 10, 20 alternately output converted DC power to the output terminals OUT1, OUT2, can be achieved by the control unit 40 controlling the switching operations of the switch elements 111, 211 of the power conversion circuits 10, 20. This control may be, for example, control to cause the switch elements 111, 211 to perform switching operations so that the direction of current flowing between the pair of input terminals IN1, IN2 is opposite between the first power conversion circuit 10 and the second power conversion circuit 20. This control makes it possible to suppress an increase in noise in the power supplied to the load RLoad connected to the output terminals OUT1, OUT2, even when the two power conversion circuits 10, 20 are connected in parallel to increase the output of the power conversion device 1.
[0041] The control unit 40 switches the MOSFET Q11 of the switch element 111 and the MOSFET Q22 of the switch element 211 connected to the first input terminal IN1 with first and second control signals whose rising edges are synchronized. The control unit 40 switches the MOSFET Q12 of the switch element 111 and the MOSFET Q21 of the switch element 211 connected to the second input terminal IN2 with third and fourth control signals whose rising edges are synchronized. When the rising edges of the first and second control signals are synchronized and the rising edges of the third and fourth control signals are synchronized, the turn-on of the MOSFETs Q11 and Q22 is synchronized with the turn-off of the MOSFETs Q12 and Q21. Furthermore, the turn-off of the MOSFETs Q11 and Q22 is synchronized with the turn-on of the MOSFETs Q12 and Q21. This synchronization increases the accuracy with which the DC power passing through the diodes D11 and D21 of the two power conversion circuits 10 and 20 is alternately output to the output terminals OUT1 and OUT2. This increased accuracy allows the noise components of the current passed by the parasitic capacitance of the diodes D11 and D21 to be canceled out with precision by the noise components of the current that passed through the diodes D11 and D21 during the same period. This makes it possible to more reliably output the DC power of the power conversion circuits 10 and 20 alternately to the output terminals OUT1 and OUT2, and to precisely suppress the noise level of the power supplied from the output terminals OUT1 and OUT2 to the load RLoad.
[0042] The control unit 40 switches the MOSFET Q11 of the switch element 111 and the MOSFET Q22 of the switch element 211 connected to the first input terminal IN1 with first and second control signals that turn them on and off with a frequency difference within a predetermined range including zero. The control unit 40 switches the MOSFET Q12 of the switch element 111 and the MOSFET Q21 of the switch element 211 connected to the second input terminal IN2 with third and fourth control signals that turn them on and off with a frequency difference within a predetermined range including zero. If the frequency difference between the first and second control signals is within a predetermined range including zero, the turn-on and turn-off timings of the MOSFETs Q11 and Q22 tend to be continuously synchronized. If the frequency difference between the third and fourth control signals is within a predetermined range including zero, the turn-on and turn-off timings of the MOSFETs Q12 and Q21 tend to be continuously synchronized. By continuously aligning this timing, the noise components of the current passed by the parasitic capacitance of the diodes D11 and D21 are continuously canceled out by the noise components of the current passed through the diodes D11 and D21 during the same period. By continuously aligning the turn-on and turn-off timings of the MOSFETs Q12 and Q21, it is possible to continuously align the timing at which the DC power output to the output terminals OUT1 and OUT2 is switched between the power conversion circuits 10 and 20. By continuously aligning this timing, it is possible to continuously suppress the noise level of the power supplied from the output terminals OUT1 and OUT2 to the load RLoad.
[0043] (Variation of the First Embodiment) The control unit 40 may measure the voltage of the DC power output to the output terminals OUT1 and OUT2 using, for example, the output voltage meter 50 shown in FIG. 1 and determine a balance state between the DC power of the first power conversion circuit 10 and the DC power of the second power conversion circuit 20 based on the measured voltage. When the control unit 40 determines that the DC power of the first power conversion circuit 10 and the DC power of the second power conversion circuit 20 are not balanced, the control unit 40 may adjust the content of at least one of the controls of the switch elements 111 and 211 based on the voltage measured by the output voltage meter 50. For example, when the control unit 40 determines that the DC power of the first power conversion circuit 10 exceeds the DC power of the second power conversion circuit 20, the control unit 40 may reduce the duty ratios of the first and second control signals. Instead of reducing the duty ratios of the first and second control signals, the control unit 40 may increase the duty ratios of the third and fourth control signals. The control unit 40 may decrease the duty ratios of the first and second control signals and increase the duty ratios of the third and fourth control signals. By performing such control by the control unit 40, the DC power of the first power conversion circuit 10 and the DC power of the second power conversion circuit 20 can be equalized throughout the entire power conversion device 1. This equalization allows noise components of the currents passed by the parasitic capacitance of the diodes D11 and D21 to be accurately canceled by noise components of the currents that passed through the diodes D11 and D21 during the same period. By adjusting the control content of the switch elements 111 and 211 of each power conversion circuit 10 and 20 by the control unit 40 based on the voltage of the DC power output to the output terminals OUT1 and OUT2, an increase in noise in the DC power can be efficiently suppressed.
[0044] (Second embodiment) (Configuration of power conversion device according to second embodiment) Fig. 5 is a diagram showing the configuration of a power conversion device according to a second embodiment to which the present invention is applied. In the power conversion device 1 of the second embodiment, the number of power conversion circuits connected in parallel between a pair of input terminals IN1, IN2 and a pair of output terminals OUT1, OUT2 is increased to three. Fig. 5 shows a case where the three power conversion circuits are two first power conversion circuits 10, 30 and one second power conversion circuit 20.
[0045] The inverter circuit 310 of the third power conversion circuit 30 generates a high-frequency alternating current from alternating current power AC input to a pair of input terminals IN1 and IN2. The inverter circuit 310 includes a choke inductor L31, a switch element 311, a shunt capacitor C31, and an LC resonant circuit 312. The choke inductor L31 and the shunt capacitor C31 of the inverter circuit 310 are configured similarly to the choke inductor L11 and the shunt capacitor C11 of the inverter circuit 110. The LC resonant circuit 312 is a series circuit of a resonant inductor Lr3 and a resonant capacitor Cr3. It is configured similarly to the LC resonant circuit 112 of the inverter circuit 110. The switch element 311 is a series circuit of two semiconductor switches, a first switch element and a second switch element, and similar to the switch element 111 of the inverter circuit 110, uses a series circuit of two MOSFETs Q31 and Q32 with their source terminals connected to each other.
[0046] The rectifier circuit 320 includes a diode D31 as a rectifying element, a rectifier-side capacitor C32, an inductor L32, and an output-side capacitor C33. The diode D31, rectifier-side capacitor C32, inductor L32, and output-side capacitor C33 are configured similarly to the diode D11, rectifier-side capacitor C12, inductor L12, and output-side capacitor C13 of the rectifier circuit 120. The rectification direction of the diode D31 with respect to the input terminals IN1 and IN2 is the same as that of the diode D11. The cathode of the diode D31 is conductive with the first input terminal IN1 and the first output terminal OUT1, and the anode of the diode D31 is conductive with the second input terminal IN2 and the second output terminal OUT2. The rectifier circuit 320 rectifies the resonant current of the LC resonant circuit 312 using the diode D31 and outputs the resulting DC voltage to the first output terminal OUT1 and the second output terminal OUT2.
[0047] The third power conversion circuit 10 is connected to a pair of input terminals IN1 and IN2 with the rectification direction of the diode D11 opposite to the rectification direction of the diode D21 of the second power conversion circuit 20. In the third power conversion circuit 30, the cathode of the diode D31 of the rectifier circuit 320 is connected to the input terminal IN1, and the anode of the diode D31 is connected to the input terminal IN2. In the third power conversion circuit 30, the MOSFET Q31 of the inverter circuit 310 is connected to the input terminal IN1, and the MOSFET Q32 is connected to the input terminal IN2. In the inverter circuit 310 of the third power conversion circuit 30, when MOSFETs Q31 and Q32 are used as the switch element 311, the shunt capacitor C31 can be configured similarly to the shunt capacitor C11 of the inverter circuit 110.
[0048] In the switch element 311 of the inverter circuit 310, one of the MOSFETs Q31 and Q32 is turned on with a 100% duty cycle while the other is repeatedly turned on and off with a duty cycle of less than 100%. By interchanging the element of the switch element 311 that is turned on with a 100% duty cycle with the element that is turned on and off with a duty cycle of less than 100%, the switch element 311 can function as a bidirectional switch.
[0049] In the second embodiment, the control unit 40 performs the control described below to implement the control method for the power conversion device 1 according to the present embodiment. The control unit 40 can, for example, control the switching operation of the switch element 311 of the inverter circuit 310 in the same manner as the switching operation of the switch element 111 of the inverter circuit 110. The control unit 40 can, for example, turn on and off the MOSFETs Q31 and Q32 of the third power conversion circuit 30 using control signals similar to the first and second control signals for the MOSFETs Q11 and Q12 of the first power conversion circuit 10. Turning on and off the MOSFETs Q31 and Q32 using these control signals can perform zero-voltage switching of the switch element 311. The control unit 40 can set the control content so that the sum of the DC powers output from the first and third power conversion circuits 10 and 30 to the output terminals OUT1 and OUT2 is balanced with the DC powers output from the second power conversion circuit 20 to the output terminals OUT1 and OUT2. For example, in the section where the control signals are turned on and off with a duty of less than 100%, the control section 40 may set the duty ratio of the control signals for MOSFETs Q11, Q12, Q31, and Q32 to half that of the control signals for MOSFETs Q21 and Q22. In the section where MOSFETs Q11, Q12, Q31, and Q32 are turned on and off with a duty of less than 100%, the duty ratio of the control signals for MOSFETs Q11 and Q12 may be different from that of the control signals for MOSFETs Q31 and Q32.
[0050] (Operation and Effect of the Power Conversion Device 1 of the Second Embodiment) In the second embodiment, a situation that occurs in the first power conversion circuit 10 of the first embodiment occurs in a distributed manner in the first power conversion circuit 10 and the third power conversion circuit 30. In the second embodiment, DC power rectified by the diodes D11 and D31 and DC power rectified by the diode D21 are smoothed and then alternately output to a pair of output terminals OUT1 and OUT2. Noise present in the DC power rectified by the diodes D11 and D31 and noise present in the DC power rectified by the diode D21 are not output to the output terminals OUT1 and OUT2 simultaneously. Therefore, large noise resulting from the sum of the noises present in the DC power rectified by the diodes D11, D21, and D31 does not appear at the output terminals OUT1 and OUT2 to which the DC power converted by each power conversion circuit 10, 20, and 30 is output.
[0051] If the diode D31 of the third power conversion circuit 30 includes a cooler (not shown) like the diodes D11 and D21, a parasitic capacitance also occurs between the diode D31 and the cooler. When a parasitic capacitance occurs in the diode D31, the parasitic capacitance of the diode D31 passes a current from cathode to anode that would not pass through the diode D31. The current passed by the parasitic capacitance of the diode D31, together with the current passed by the parasitic capacitance of the diode D11, becomes a common-mode current of the same phase but opposite polarity to the current that passed from the anode to the cathode of the diode D21 during the same period. The switch elements 111, 211, and 311 include MOSFETs Q11, Q22, and Q31, and MOSFETs Q12, Q21, and Q32, which are turned on and off synchronously. The switching operations of the switch elements 111, 211, and 311 are synchronized.
[0052] Noise generated by the switching operations of the switch elements 111, 211, and 311 is superimposed at the same time on the current passing through the diodes D11, D21, and D31 and on the current passed by the parasitic capacitance of the diodes D11, D21, and D31. The noise component of the current passed by the parasitic capacitance of the diodes D11 and D31 is canceled out by the noise component of the current passed by the diode D21 during the same period. The noise component of the current passed by the parasitic capacitance of the diode D21 is canceled out by the noise component of the current passed by the diodes D11 and D31 during the same period. The noise of the current passed by the diodes D11, D21, and D31 and the noise of the current passed by the parasitic capacitance of the diodes D11, D21, and D31 during the same period have opposite polarities, and therefore are not added together at the output terminals OUT1 and OUT2.
[0053] In this embodiment, when three power conversion circuits 10, 20, and 30 are connected in parallel to increase the output power of the power conversion device 1, noise generated in each of the power conversion circuits 10, 20, and 30 is not simultaneously output to the output terminals OUT1 and OUT2. This embodiment also prevents noise generated in the power conversion circuits 10, 20, and 30 from being added together at the output terminals OUT1 and OUT2 to produce large noise. Because the noise generated in the power conversion circuits 10, 20, and 30 does not appear at a large volume at the output terminals OUT1 and OUT2, it is possible to prevent an increase in noise superimposed on the power supplied to the load RLoad connected to the output terminals OUT1 and OUT2. When removing noise generated in the power conversion circuits 10, 20, and 30 using a filter, a filter corresponding to the magnitude of the noise generated in the power conversion circuits 10, 20, and 30 may be provided in each of the power conversion circuits 10, 20, and 30. When removing noise generated in the power conversion circuits 10, 20, and 30 using a filter, there is no need for a filter with the removal capacity to handle the large noise that is the sum of all the generated noises, so the noise filter can be prevented from becoming larger as the output of the power conversion device 1 increases.
[0054] (Variation of Second Embodiment) In the second embodiment, at least one of the control of the switch elements 111 and 311 of the first power conversion circuits 10 and 30 and the control of the switch element 211 of the second power conversion circuit 20 by the control unit 40 may be adjusted. The adjustment of the control by the control unit 40 may be performed based on the voltage of the DC power at the output terminals OUT1 and OUT2. The voltage of the DC power at the output terminals OUT1 and OUT2 may be measured by, for example, the output voltage meter 50 of FIG. 5. When the control unit 40 determines that the total DC power of the first power conversion circuits 10 and 30 is not balanced with the DC power of the second power conversion circuit 20, the control unit 40 may adjust at least one of the control of the switch elements 111 and 311 and the control of the switch element 211.
[0055] (Modifications of the First and Second Embodiments) In the first and second embodiments, two or three power conversion circuits are connected in parallel between the input terminals IN1, IN2 and the output terminals OUT1, OUT2. However, four or more power conversion circuits may be connected in parallel as long as there are at least two. In this case, the at least two or more power conversion circuits may include one or more first power conversion circuits and one or more second power conversion circuits. The number of first power conversion circuits and the number of second power conversion circuits may be the same or different.
[0056] The rectifying elements of the rectifier circuits 120, 220, 320 may be elements other than the diodes D11, D21, D31. For example, the body diodes, also called parasitic diodes, of the MOSFETs Q11, Q12, Q21, Q22, Q31, Q32 may be oriented with their cathodes and anodes aligned, and used as rectifying elements instead of the diodes D11, D21, D31. The rectifying elements may be, for example, switching elements that cut off one polarity section of the high-frequency AC power output by the inverter circuits 110, 210, 310.
[0057] The above-described embodiment is merely an example of the present invention, and therefore the present invention is not limited to the above-described embodiment, and various modifications can be made to the design and other aspects of the present invention without departing from the technical concept of the present invention.
[0058] REFERENCE SIGNS LIST 1 Power conversion device 10, 30 First power conversion circuit 20 Second power conversion circuit 40 Control unit 110, 210, 310 Inverter circuit 111, 211, 311 Switch element (bidirectional switch) 112, 212, 312 LC resonant circuit 120, 220, 320 Rectifier circuit C11, C21, C31 Shunt capacitor D11, D21, D31 Diode (rectifier element) IN1 First input terminal IN2 Second input terminal L11, L21, L31 Choke inductor Q11, Q21, Q31 MOSFET (first switch element) Q12, Q22, Q32 MOSFET (second switch element) RLoad DC load (load)
Claims
A control method for a power conversion device including a pair of input terminals to which AC power is input, at least two or more power conversion circuits connected in parallel to the pair of input terminals, and a pair of output terminals to which a load is connected, comprising: The power conversion circuit includes: an inverter circuit having an LC resonant circuit and configured to generate a high-frequency AC current from the AC power input to the pair of input terminals; a rectifying element that rectifies the high-frequency AC current generated by the inverter circuit and outputs the rectified power to the pair of output terminals; It has The inverter circuit includes: a bidirectional switch that switches the direction and on / off of a current flowing between the pair of input terminals; a shunt capacitor connected in parallel with the bidirectional switch between the pair of input terminals, the at least two or more power conversion circuits include a first power conversion circuit and a second power conversion circuit respectively connected to the pair of input terminals with the rectification directions of the rectification elements being opposite to each other; controlling switching operations of the bidirectional switches of the first power conversion circuit and the second power conversion circuit so that power rectified by the rectifying element of the first power conversion circuit and power rectified by the rectifying element of the second power conversion circuit are alternately output to the pair of output terminals in a period in which the polarity of the high frequency AC current is switched; A method for controlling a power conversion device.
2. The control method for a power conversion device according to claim 1, further comprising controlling switching operations of the bidirectional switches of the first power conversion circuit and the second power conversion circuit so that directions of currents flowing between the pair of input terminals in the first power conversion circuit and the second power conversion circuit are opposite to each other.
3. The method for controlling a power conversion device according to claim 1 or 2, wherein the bidirectional switch has a series circuit of a first switch element and a second switch element, and the first switch element of the bidirectional switch of the first power conversion circuit and the second switch element of the bidirectional switch of the second power conversion circuit, which are connected to a first input terminal of the pair of input terminals, are turned on in a synchronous manner, and the second switch element of the bidirectional switch of the first power conversion circuit and the first switch element of the bidirectional switch of the second power conversion circuit, which are connected to a second input terminal of the pair of input terminals, are turned on in a synchronous manner. The bidirectional switch has a series circuit of a first switch element and a second switch element, and the first switch element of the bidirectional switch of the first power conversion circuit and the second switch element of the bidirectional switch of the second power conversion circuit, which are connected to a first input terminal of the pair of input terminals, are turned on and off by a first control signal and a second control signal having a frequency difference within a predetermined range including zero, and the second switch element of the bidirectional switch of the first power conversion circuit and the first switch element of the bidirectional switch of the second power conversion circuit, which are connected to a second input terminal of the pair of input terminals, are turned on and off by a third control signal and a fourth control signal having a frequency difference within the predetermined range including zero, respectively.
5. The control method for a power conversion device according to claim 1, further comprising adjusting a control content of at least one of a switching operation of the bidirectional switch of the first power conversion circuit and a switching operation of the bidirectional switch of the second power conversion circuit so that a power rectified by the rectifying element of the first power conversion circuit and a power rectified by the rectifying element of the second power conversion circuit are equalized throughout the power conversion device, based on the power output from the pair of output terminals to the load. The method for controlling a power conversion device according to any one of claims 1 to 5, wherein the rectifying element is a diode. The inverter circuit is a class E inverter or a quasi-class E inverter having a choke inductor connected between at least one of the pair of input terminals and the bidirectional switch. The control method for the power conversion device according to any one of claims 1 to 5. A power conversion device including a pair of input terminals to which AC power is input, at least two or more power conversion circuits connected in parallel to the pair of input terminals, a pair of output terminals to which a load is connected, and a control unit, The power conversion circuit includes: an inverter circuit having an LC resonant circuit and configured to generate a high-frequency AC current from the AC power input to the pair of input terminals; a rectifying element that rectifies the high-frequency AC current generated by the inverter circuit and outputs the rectified power to the pair of output terminals; It has The inverter circuit includes: a bidirectional switch that switches the direction and on / off of a current flowing between the pair of input terminals; a shunt capacitor connected in parallel with the bidirectional switch between the pair of input terminals, the at least two or more power conversion circuits include a first power conversion circuit and a second power conversion circuit respectively connected to the pair of input terminals with the rectification directions of the rectification elements being opposite to each other; the control unit controls switching operations of the bidirectional switches of the first power conversion circuit and the second power conversion circuit so that power rectified by the rectifying element of the first power conversion circuit and power rectified by the rectifying element of the second power conversion circuit are alternately output to the pair of output terminals in a period in which the polarity of the high-frequency AC current is switched. Power conversion equipment.