Resonant inverter

Abstract

A resonant inverter (1) is a three-level converter and operates under zero voltage turn-on control at a time of discharge. An auxiliary resonance circuit (2) includes a negative-side resonance path (rn) that has a current polarity limited to a direction from a resonance inductor (Lr) to a neutral point (A), and that is opened and closed by a switch element (Tr6). The auxiliary resonance circuit (2) includes a positive-side regeneration path (D5 + Dsp) that has a current polarity limited to a direction from the resonance inductor (Lr) to a positive-side DC line (P). The auxiliary resonance circuit (2) includes a negative-side regeneration path (D6 + Dsn) that has a current polarity limited to a direction from a negative-side DC line (N) to the resonance inductor (Lr).

Description

Resonant Inverter

[0001] The present invention relates to a resonant inverter having an auxiliary resonant circuit.

[0002] An energy storage system such as an uninterruptible power supply includes an energy storage device and a PCS (power conditioner unit) with a built-in inverter that converts AC and DC between the energy storage device and an external power system. The energy storage device is configured with, for example, a plurality of energy storage modules each having a plurality of energy storage elements. In recent years, energy storage devices have become higher in voltage and capacity.

[0003] As the voltage and capacity of power storage devices increase, the switching loss and electromagnetic interference (EMI) noise in inverters become major problems. Resonant inverters are used as a method for reducing the switching loss and EMI noise (see, for example, Patent Documents 1, 2, and 3).

[0004] Patent No. 5195161 Patent No. 5569204

[0005] In the resonant inverter of Patent Document 1, when all switches are off, a path for the energy stored in the resonant inductor is secured by the snubber circuit, but efficiency decreases due to snubber loss.

[0006] In the resonant inverter of Patent Document 2, when all switches are off, the energy stored in the resonant inductor is regenerated to the DC link without loss by the auxiliary resonant circuit. The auxiliary resonant circuit serves as a path for the energy stored in the resonant inductor, and no snubber loss occurs. However, the auxiliary circuit requires the same high-voltage withstand elements as the main circuit. High-voltage withstand elements are not only limited in variety, but also have slow switching speeds, raising concerns about a decline in efficiency.

[0007] One aspect of the present invention provides a resonant inverter in which a lossless auxiliary resonant circuit, which serves as a path for energy stored in a resonant inductor, can be configured using elements with a lower withstand voltage than the main circuit.

[0008] One aspect of the present invention is a resonant inverter including a neutral point clamp circuit having a positive side capacitor and a negative side capacitor connected in series between a positive side DC line and a negative side DC line, with the junction of the positive side capacitor and the negative side capacitor serving as a neutral point. The resonant inverter includes a main leg having an upper arm switch and a lower arm switch connected in series between the positive side DC line and the negative side DC line, with the junction of the upper arm switch and the lower arm switch serving as an input / output point of the inverter current. The resonant inverter includes a first resonant capacitor and a second resonant capacitor connected in parallel with the upper arm switch and the lower arm switch. The resonant inverter includes a first anti-parallel diode and a second anti-parallel diode connected in anti-parallel to the upper arm switch and the lower arm switch. The resonant inverter includes a neutral phase leg having a positive side neutral phase switch and a negative side neutral phase switch that respectively open and close a positive side polarity path in which current polarity is limited from the neutral point to the input / output point and a negative side polarity path in which current polarity is limited from the input / output point to the neutral point. The resonant inverter comprises an auxiliary resonant circuit including a resonant inductor having one end connected to the input / output node. The auxiliary resonant circuit comprises a positive-side resonant path whose current polarity is limited to a direction from the neutral point to the resonant inductor and which is opened and closed by a positive-side resonant switch. The auxiliary resonant circuit comprises a negative-side resonant path whose current polarity is limited to a direction from the resonant inductor to the neutral point and which is opened and closed by a negative-side resonant switch. The auxiliary resonant circuit comprises a positive-side regenerative path whose current polarity is limited to a direction from the resonant inductor to the positive-side DC line. The auxiliary resonant circuit comprises a negative-side regenerative path whose current polarity is limited to a direction from the negative-side DC line to the resonant inductor.

[0009] According to one aspect of the present invention, the lossless auxiliary resonant circuit, which serves as a path for the energy stored in the resonant inductor, is clamped to the neutral point voltage by the positive side resonant path and the negative side resonant path, so that the elements that make up the auxiliary resonant circuit can be constructed using elements with a lower withstand voltage than the elements of the main leg, which is the main circuit.

[0010] 1 is a diagram showing a circuit configuration for one phase of an embodiment of a resonant inverter. FIG. 1 is a timing chart showing the discharge operation of the resonant inverter shown in FIG. 1. FIG. 2 is a diagram showing the operation of each mode shown in FIG. 2. FIG. 3 is a timing chart showing the operation of a clamp snubber in a positive direction. FIG. 4 is a diagram showing the operation of mode 5A shown in FIG. 4. FIG. 5 is a timing chart showing the discharge operation of the resonant inverter shown in FIG. 1. FIG. 6 is a diagram showing the operation of each mode shown in FIG. 6. FIG. 7 is a timing chart showing the operation of a clamp snubber in a negative direction. FIG. 8 is a diagram showing the operation of mode 15A shown in FIG. 8. FIG. 9 is a timing chart showing the charge operation of the resonant inverter shown in FIG. 1. FIG. 10 is a diagram showing the operation of each mode shown in FIG. 10. FIG. 11 is a timing chart showing the discharge operation of the resonant inverter shown in FIG. 12. FIG. 13 is a diagram showing a first application example of the auxiliary resonant circuit shown in FIG. 1. FIG. 14 is a diagram showing a second application example of the resonant inverter shown in FIG. 1. FIG. 15 is a diagram showing a third application example of the resonant inverter shown in FIG. 16.

[0011] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the following, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following embodiments, components having similar functions will be given the same reference numerals and descriptions thereof will be omitted as appropriate.

[0012] Referring to FIG. 1, the resonant inverter 1 of this embodiment is a three-level inverter having an auxiliary resonant circuit 2 of an NPC (neutral point clamped) type ARCP (auxiliary resonant commutated pole) topology.

[0013] The resonant inverter 1 includes a neutral point clamp circuit 3 in which a positive-side capacitor Cp and a negative-side capacitor Cn are connected in series. The neutral point clamp circuit 3 is connected between a positive-side DC line P and a negative-side DC line N. The capacitors Cp and Cn have the same capacitance. The connection point between the capacitors Cp and Cn is a neutral point A where a voltage Vdc / 2, which is half the voltage of the input DC voltage Vdc input between the positive-side DC line P and the negative-side DC line N, is generated.

[0014] The resonant inverter 1 includes a main leg 4, which is a series circuit including a switch element Tm1, which is an upper arm switch, arranged in an upper arm, and a switch element Tm2, ​​which is a lower arm switch, arranged in a lower arm. The switch elements Tm1 and Tm2 are configured, for example, by insulated gate bipolar transistors (IGBTs). The switch elements Tm1 and Tm2 may also be configured by MOSFETs. The main leg 4 is connected between a positive side DC line P and a negative side DC line N. The switch element Tm1 has a collector connected to the positive side DC line P and an emitter connected to the collector of the switch element Tm2. The switch element Tm2 has an emitter connected to the negative side DC line N. The connection point between the emitter of the switch element Tm1 and the collector of the switch element Tm2 serves as an input / output point B of the inverter current Iinv, and is connected to an AC input / output terminal via an inductor L1.

[0015] The switch element Tm1 includes an anti-parallel diode D1 connected in anti-parallel, i.e., having its cathode and anode connected to the collector and emitter of the switch element Tm1, respectively. The anti-parallel diode D1 is formed, for example, by the body diode of the switch element Tm1. The switch element Tm1 includes a resonant capacitor C1 connected in parallel. The resonant capacitor C1 is formed by the stray capacitance of the switch element Tm1 or an external capacitor.

[0016] The switch element Tm2 includes an anti-parallel diode D2 connected in anti-parallel, i.e., having its cathode and anode connected to the collector and emitter of the switch element Tm2, ​​respectively. The anti-parallel diode D2 is formed, for example, by the body diode of the switch element Tm2. The switch element Tm2 includes a resonant capacitor C2 connected in parallel. The resonant capacitor C2 is formed by the stray capacitance of the switch element Tm2 or an external capacitor.

[0017] The resonant inverter 1 includes a neutral phase leg 5. The neutral phase leg 5 includes a positive polarity path np and a negative polarity path nn. The positive polarity path np and the negative polarity path nn are connected in parallel between the neutral point A of the neutral point clamp circuit 3 and the input / output point B of the main leg 4.

[0018] The positive polarity path np is a series circuit consisting of a diode Dnp and a switch element Tn3, which limits the current polarity to one direction (from neutral point A to input / output point B) and is opened and closed by the switch element Tn3. The switch element Tn3 is composed of an IGBT or MOSFET. The anode of the diode Dnp is connected to the neutral point A, and the cathode is connected to the collector of the switch element Tn3. The emitter of the switch element Tn3 is connected to input / output point B.

[0019] The negative polarity path nn is a series circuit consisting of a diode Dnn and a switch element Tn4, which limits the current polarity to one direction (from input / output point B to neutral point A) and is opened and closed by the switch element Tn4. The switch element Tn4 is composed of an IGBT or MOSFET. The collector of the switch element Tn4 is connected to input / output point B, and the emitter is connected to the anode of the diode Dnn. The cathode of the diode Dnn is connected to neutral point A.

[0020] The auxiliary resonant circuit 2 includes a resonant inductor Lr, a positive-side resonant path rp, and a negative-side resonant path rn connected in parallel between an input / output point B of the main leg 4 and a neutral point A of the neutral point clamp circuit 3.

[0021] The positive-side resonant path rp includes a switch element Tr5 serving as a positive-side resonant switch and a diode Drp, which are connected in series from the other end of a resonant inductor Lr, one end of which is connected to the input / output point B. The switch element Tr5 is, for example, an insulated gate bipolar transistor (IGBT). The switch element Tr5 may also be a MOSFET.

[0022] One end of the resonant inductor Lr is connected to the input / output point B, and the other end is connected to the emitter of the switch element Tr5. The collector of the switch element Tr5 is connected to the cathode of the diode Drp, and the anode of the diode Drp is connected to the neutral point A.

[0023] The diode Drp limits the polarity of the current in the positive-side resonant path rp to one direction (from the neutral point A to the input / output point B). The switch element Tr5 opens and closes the positive-side resonant path rp.

[0024] The switch element Tr5 includes an anti-parallel diode D5 having a cathode and an anode connected to the collector and the emitter of the switch element Tr5, respectively. The anti-parallel diode D5 is formed, for example, by the body diode of the switch element Tr5.

[0025] The auxiliary resonant circuit 2 includes a lossless regenerative clamp snubber diode Dsp that connects the connection point between the collector of the switch element Tr5 and the cathode of the diode Drp to the positive DC line P. The lossless regenerative clamp snubber diode Dsp has an anode connected to the connection point between the collector of the switch element Tr5 and the cathode of the diode Drp, and a cathode connected to the positive DC line P.

[0026] The anti-parallel diode D5 of the switch element Tr5 and the lossless regenerative clamp snubber diode Dsp form a positive-side regenerative path in which the current polarity is limited to one direction (from the resonance inductor Lr to the positive-side DC line P).

[0027] The negative-side resonant path rn is configured as a series circuit including, from the other end of a resonant inductor Lr, one end of which is connected to the input / output point B, a switch element Tr6 serving as a negative-side resonant switch, and a diode Drn. The resonant inductor Lr is also used as the positive-side resonant path rp. The switch element Tr6 is configured, for example, by an insulated gate bipolar transistor (IGBT). The switch element Tr6 may also be configured by a MOSFET.

[0028] One end of the resonant inductor Lr is connected to the input / output point B, and the other end is connected to the collector of the switch element Tr6. The emitter of the switch element Tr6 is connected to the anode of the diode Drn, and the cathode of the diode Drn is connected to the neutral point A.

[0029] The diode Drn limits the polarity of the current in the negative-side resonant path rn to one direction (from the input / output point B to the neutral point A). The switch element Tr6 opens and closes the negative-side resonant path rn.

[0030] The switch element Tr6 includes an anti-parallel diode D6 having a cathode and an anode connected to the collector and the emitter of the switch element Tr6, respectively. The anti-parallel diode D6 is formed, for example, by the body diode of the switch element Tr6.

[0031] The auxiliary resonant circuit 2 includes a lossless regenerative clamp snubber diode Dsn that connects the connection point between the emitter of the switch element Tr6 and the anode of the diode Drn to the negative DC line N. The lossless regenerative clamp snubber diode Dsn has a cathode connected to the connection point between the emitter of the switch element Tr6 and the anode of the diode Drn, and an anode connected to the negative DC line N.

[0032] The anti-parallel diode D6 of the switch element Tr6 and the lossless regenerative clamp snubber diode Dsn form a negative side regenerative path in which the current polarity is limited to one direction (from the negative side DC line N to the resonant inductor Lr).

[0033] The resonant inverter 1 includes a control circuit 6 that controls the on / off of each of the switch elements Tm1, Tm2, ​​Tn3, Tn4, Tr5, and Tr6. The control circuit 6 turns on the switch element Tm1 at zero voltage during PWM control of the switch element Tm1 of the main leg 4 and the switch element Tn4 of the neutral phase leg 5. The control circuit 6 turns on the switch element Tm2 at zero voltage during PWM control of the switch element Tm2 of the main leg 4 and the switch element Tn3 of the neutral phase leg 5.

[0034] The discharge operation of the resonant inverter 1 when the output voltage Vo and the inverter current Iinv are positive will be described with reference to Figures 2 and 3. Figure 2 is a timing chart showing the operation of the resonant inverter 1. Figure 3 shows the operation in each mode shown in Figure 2 using an equivalent circuit of the resonant inverter 1.

[0035] Since the output voltage Vo is positive, the switching elements Tm1 and Tn4 alternately perform PWM operation. When the inverter current Iinv is positive, the target of zero voltage (ZV) turn-on control by resonance is the on timing of the switching element Tm1.

[0036] The control circuit 6 turns off the switch element Tn3 before resonant operation, thereby causing the resonant inverter 1 to operate as a two-level inverter and creating a mode in which the anti-parallel diode D2 of the switch element Tm2 is conductive. When the inverter current Iinv is positive, the control circuit 6 controls the switch element Tr5 of the positive-side resonant path rp before and after turning on the switch element Tm1 to cause resonant operation on the positive side.

[0037] Mode 0 shown in FIG. 3( a ) is a state in which the inverter current Iinv flows back through the positive polarity path np of the neutral phase leg 5 .

[0038] In mode 0, the collector-emitter voltages Vce of the switch elements Tm1 and Tm2 are both Vdc / 2. The inter-terminal voltages (Vce, reverse voltage VR) of the elements Tr5, Tr6, Dsp, Dsn, Drp, and Drn of the auxiliary resonant circuit 2 are Vdc / 4. The inter-terminal voltages of the elements of the neutral phase leg 5 are all 0 V.

[0039] In mode 1, at time t1, the switch elements Tn3 and Tn4 are simultaneously turned off, commutating the inverter current Iinv to the anti-parallel diode D2 of the lower-arm switch element Tm2. All other switch elements Tm1, Tm2, ​​Tr5, and Tr6 are in the off state. In mode 1, as shown in FIG. 3(b), the resonant capacitor C1 of the switch element Tm1 is charged, and the resonant capacitor C2 of the switch element Tm2 is discharged. Therefore, the switch element Tn3 is subjected to zero-voltage turn-off control by the lossless snubber.

[0040] In mode 1, Vce of switch element Tm1 changes from Vdc / 2 to Vdc, and Vce of switch element Tm2 changes from Vdc / 2 to 0 V. Regarding the terminal voltages of each element of auxiliary resonant circuit 2, Tr5, Dsp, and Drn change from Vdc / 4 to Vdc / 2, and Tr6, Dsn, and Drp change from Vdc / 4 to 0 V. Regarding the terminal voltages of each element of neutral phase leg 5, Tn3 and Dnn change from 0 V to Vdc / 2.

[0041] In mode 2, at time t2, Vce of switch element Tm1 changes to Vdc, Vce of switch element Tm2 changes to 0 V, and the inverter current Iinv circulates through the anti-parallel diode D2 of the lower-arm switch element Tm2, ​​as shown in FIG. 3(c).

[0042] In mode 2, the voltages across the terminals of each element of the auxiliary resonant circuit 2 are Vdc / 2 for Tr5, Drn, and Dsp, and 0 V for the other elements. The voltages across the terminals of each element of the neutral phase leg 5 are Vdc / 2 for Tn3 and Dnn, and 0 V for the other elements.

[0043] In mode 3, at time t3 during the dead time DT, the switch element Tr5 in the positive-side resonant path rp is subjected to zero current (ZC) turn-on control, and the inverter current Iinv is commutated to the resonant inductor Lr (positive-side resonant path rp) as shown in Fig. 3(d). Mode 3 continues until the anti-parallel diode D2 of the switch element Tm2 is turned off.

[0044] In mode 3, the voltages across the terminals of each element of the auxiliary resonant circuit 2 are Vdc / 2 for Dsp, Vdc / 4 for Tr6, Drn, and Dsn, and 0 V for the other elements. The voltages across the terminals of each element of the neutral phase leg 5 are the same as in mode 2.

[0045] In mode 4, commutation to resonant inductor Lr is completed at time t4, and Vce of switch element Tm1 and switch element Tm2 changes sinusoidally due to resonance with resonant capacitors C1 and C2, as shown by the dotted lines in Fig. 3E. In mode 4, Vce of switch element Tm1 changes from Vdc to 0 V, and Vce of switch element Tm2 changes from 0 V to Vdc.

[0046] In mode 4, the voltage across each element of the auxiliary resonant circuit 2 is the same as in mode 3. As for the voltage across each element of the neutral phase leg 5, Tn4 and Dnp change from 0 V to Vdc / 2, and Tn3 and Dnn change from Vdc / 2 to 0 V.

[0047] The period of mode 3+4 is the sum of the first commutation time Tcom1 [Lr÷Vdcn×Iinv] and the resonance time Tres [π×√(Lr×2Cr)]. Lr is the inductance of the resonance inductor Lr, and Cr is the capacitance of the resonance capacitors C1 and C2. Vdcn is the voltage across the capacitor Cn in the neutral point clamp circuit 3. The first commutation time Tcom1 is the time until the commutation of the inverter current Iinv to the resonance inductor Lr is completed. The resonance time Tres is ½ the period of the resonance at which the resonance frequency is (½π√(Lr×2Cr)).

[0048] In other words, the switch element Tr5 on the positive-side resonant path rp is controlled to be turned on (first commutation time Tcom1+resonant time Tres) before the turn-on timings of the switch elements Tm1 and Tn3.

[0049] In mode 5, at time t5 when Vce of the switch element Tm1 becomes 0 V, the switch elements Tm1 and Tn3 are subjected to zero-voltage turn-on control, as shown in FIG. 3( f), and the resonant inductor current ILr is commutated to the switch element Tm1.

[0050] In mode 5, the voltage across each terminal of the auxiliary resonant circuit 2 is the same as in mode 3. The voltage across each terminal of each element of the neutral phase leg 5, Tn3 and Dnn, is 0 V, and the voltage across the other elements is Vdc / 2.

[0051] The period of mode 5 is a second commutation time Tcom2 [Lr÷Vdcp×Iinv], where Vdcp is the voltage across the capacitor Cp in the neutral point clamp circuit 3. The second commutation time Tcom2 is the time required for the commutation of the inverter current Iinv to the switch element Tm1 to be completed.

[0052] In other words, the switch element Tr5 on the positive-side resonant path rp is controlled to be turned off after (the second commutation time Tcom2) the switch elements Tm1 and Tn3 are turned on.

[0053] In mode 6, upon completion of commutation of the resonant inductor current ILr to the switch element Tm1, the switch element Tr5 is controlled to be turned off at time t6, and power is discharged from the DC bus (positive side DC line P) to the load (AC system) as shown in FIG. 3( g).

[0054] In mode 6, the voltages across the terminals of each element of the auxiliary resonant circuit 2 are Vdc / 2 for Drp, Tr6, and Dsn, and 0 V for the other elements. The voltages across the terminals of each element of the neutral phase leg 5 are the same as in mode 5.

[0055] Mode 7 is a period from time t7 when the upper-arm switch element Tm1 is turned off to commutate the inverter current Iinv to the positive polarity path np of the neutral phase leg 5 until the dead time DT has elapsed after the turn-off control of the switch element Tm1. In mode 7, as shown in FIG. 3(h), the resonant capacitor C1 of the switch element Tm1 is charged, and the resonant capacitor C2 of the switch element Tm2 is discharged. Therefore, the switch element Tm1 is subjected to zero-voltage turn-off control by the lossless snubber.

[0056] At time t8 when the dead time DT has elapsed after the turn-off control of the switch element Tm1, the switch element Tn4 is subjected to zero-voltage turn-on control, and mode 0 is restored.

[0057] In mode 7, Vce of switch element Tm1 changes from 0 V to Vdc / 2, and Vce of switch element Tm2 changes from Vdc to Vdc / 2. Regarding the inter-terminal voltages of each element of the auxiliary resonant circuit 2, Drp, Tr6, and Dsn change from Vdc / 2 to Vdc / 4, and Drn, Tr5, and Dsp change from 0 V to Vdc / 4. Regarding the inter-terminal voltages of each element of the neutral phase leg 5, Tn4 and Dnp change from Vdc / 2 to 0 V.

[0058] The above modes 0 to 7 are repeated, and the switch elements Tm1 and Tn3 are subjected to zero-voltage turn-on control. The auxiliary resonant circuit 2 serves as a path for the energy stored in the resonant inductor Lr. The voltage across the terminals of the auxiliary resonant circuit 2 and each element of the neutral phase leg 5 never exceeds Vdc / 2 in any mode.

[0059] 4 and 5 show the operation of the resonant inverter 1 in mode 5A when the switch element Tr5 is turned off during the above-mentioned mode 5. Fig. 4 is a timing chart showing the operation of the resonant inverter 1. Fig. 5 shows the operation in mode 5A shown in Fig. 4 using an equivalent circuit of the resonant inverter 1.

[0060] Mode 5A is a state in which switching element Tr5 is turned off due to element variations, calculation variations, malfunction, or the like at time t5A while resonant inductor current ILr is commutating to switching element Tm1. Energy excited in the positive direction across resonant inductor Lr is regenerated to the DC bus without loss, as shown by the dotted line in Fig. 5 , by the conduction of lossless regenerative clamp snubber diode Dsn and the anti-parallel diode D6 of switching element Tr6. During this regeneration, auxiliary resonant circuit 2 is clamped to neutral point A of the DC bus, and therefore each element of auxiliary resonant circuit 2, including switching element Tr5 (diode Drn, lossless regenerative clamp snubber diode Dsp), is clamped at Vdc / 2.

[0061] The discharge operation of the resonant inverter 1 when the output voltage Vo and the inverter current Iinv are negative will be described with reference to Figures 6 and 7. Figure 6 is a timing chart showing the operation of the resonant inverter 1. Figure 7 shows the operation in each mode shown in Figure 6 using an equivalent circuit of the resonant inverter 1.

[0062] Since the output voltage Vo is negative, the switching elements Tm2 and Tn3 alternately perform PWM operation. When the inverter current Iinv is negative, the target of zero-voltage turn-on control by resonance is the on-timing of the switching element Tm2.

[0063] The control circuit 6 turns off the switch element Tn4 before resonant operation, thereby causing the resonant inverter 1 to operate as a two-level inverter and creating a mode in which the anti-parallel diode D1 of the switch element Tm1 is conductive. When the inverter current Iinv is negative, the control circuit 6 controls the switch element Tr6 of the negative-side resonant path rn before and after turning on the switch element Tm2 to cause resonant operation on the negative side.

[0064] Mode 10 shown in FIG. 7( a ) is a state in which the inverter current Iinv flows back through the negative polarity path nn of the neutral phase leg 5 .

[0065] In mode 10, the collector-emitter voltages Vce of the switch elements Tm1 and Tm2 are both Vdc / 2. The inter-terminal voltages (Vce, reverse voltages VR) of the elements Tr5, Tr6, Dsp, Dsn, Drp, and Drn of the auxiliary resonant circuit 2 are Vdc / 4. The inter-terminal voltages of the elements of the neutral phase leg 5 are all 0 V.

[0066] In mode 11, at time t11, the switch elements Tn3 and Tn4 are simultaneously turned off, commutating the inverter current Iinv to the anti-parallel diode D1 of the switch element Tm1 in the upper arm. All other switch elements Tm1, Tm2, ​​Tr5, and Tr6 are in the off state. In mode 11, as shown in FIG. 7(b), the resonant capacitor C2 of the switch element Tm2 is charged, and the resonant capacitor C1 of the switch element Tm1 is discharged. Therefore, the switch element Tn4 is subjected to zero-voltage turn-off control by the lossless snubber.

[0067] In mode 11, Vce of switch element Tm2 changes from Vdc / 2 to Vdc, and Vce of switch element Tm1 changes from Vdc / 2 to 0 V. Regarding the inter-terminal voltages of each element of auxiliary resonant circuit 2, Tr6, Dsn, and Drp change from Vdc / 4 to Vdc / 2, and Tr5, Dsp, and Drn change from Vdc / 4 to 0 V. Regarding the inter-terminal voltages of each element of neutral phase leg 5, Tn4 and Dnp change from 0 V to Vdc / 2.

[0068] In mode 12, at time t12, Vce of the switch element Tm2 changes to Vdc and Vce of the switch element Tm1 changes to 0 V, and the inverter current Iinv circulates through the anti-parallel diode D1 of the upper arm switch element Tm1, as shown in FIG. 7(c).

[0069] In mode 12, the voltages across the terminals of each element of the auxiliary resonant circuit 2 are Vdc / 2 for Tr6, Drp, and Dsn, and 0 V for the other elements. The voltages across the terminals of each element of the neutral phase leg 5 are Vdc / 2 for Tn4 and Dnp, and 0 V for the other elements.

[0070] In mode 13, at time t13 during the dead time DT, the switch element Tr6 in the negative-side resonant path rn is subjected to zero-current turn-on control, and the inverter current Iinv is commutated to the resonant inductor Lr (negative-side resonant path rn) as shown in Fig. 7(d) . Mode 13 continues until the anti-parallel diode D1 of the switch element Tm1 is turned off.

[0071] In mode 13, the voltages across the terminals of each element of the auxiliary resonant circuit 2 are Vdc / 2 for Dsn, Vdc / 4 for Tr5, Drp, and Dsp, and 0 V for the other elements. The voltages across the terminals of each element of the neutral phase leg 5 are the same as in mode 12.

[0072] In mode 14, commutation to resonant inductor Lr is completed at time t14, and Vce of switch element Tm1 and switch element Tm2 changes sinusoidally due to resonance with resonant capacitors C1 and C2, as shown by the dotted lines in Fig. 7E. In mode 14, Vce of switch element Tm2 changes from Vdc to 0 V, and Vce of switch element Tm1 changes from 0 V to Vdc.

[0073] In mode 14, the voltage across each element of the auxiliary resonant circuit 2 is the same as in mode 13. As for the voltage across each element of the neutral phase leg 5, Tn3 and Dnn change from 0 V to Vdc / 2, and Tn4 and Dnp change from Vdc / 2 to 0 V.

[0074] The period of mode 13+14 is the sum of the first commutation time Tcom1 [Lr÷Vdcp×Iinv] and the resonance time Tres [π×√(Lr×2Cr)]. The first commutation time Tcom1 is the time until the commutation of the inverter current Iinv to the resonance inductor Lr is completed. The resonance time Tres is ½ of the period of the resonance at which the resonance frequency is (½π√(Lr×2Cr)).

[0075] In other words, the switch element Tr6 of the negative-side resonant path rn is controlled to be turned on (first commutation time Tcom1+resonant time Tres) before the turn-on timing of the switch elements Tm2 and Tn4.

[0076] In mode 15, at time t15 when Vce of the switch element Tm2 becomes 0 V, the switch elements Tm2 and Tn4 are subjected to zero-voltage turn-on control, as shown in FIG. 7( f), and the resonant inductor current ILr is commutated to the switch element Tm2.

[0077] In mode 15, the voltage across each terminal of the auxiliary resonant circuit 2 is the same as in mode 13. The voltage across each terminal of each element of the neutral phase leg 5 is 0 V for Tn4 and Dnp, and Vdc / 2 for the other elements.

[0078] The period of mode 15 is a second commutation time Tcom2 [Lr / Vdcn×Iinv]. The second commutation time Tcom2 is the time until the commutation of the inverter current Iinv to the switching element Tm2 is completed.

[0079] In other words, the switch element Tr6 of the negative-side resonance path rn is controlled to be turned off after (the second commutation time Tcom2) the turn-on timing of the switch elements Tm2 and Tn4.

[0080] In mode 16, the switching element Tr6 is turned off at time t16 in response to the completion of commutation of the resonant inductor current ILr to the switching element Tm2. In mode 16, as shown in FIG. 7(g), power is discharged from the DC bus (negative DC line N) to the load (AC system).

[0081] In mode 16, the voltages across the terminals of each element of the auxiliary resonant circuit 2 are Vdc / 2 for Drn, Tr5, and Dsp, and 0 V for the other elements. The voltages across the terminals of each element of the neutral phase leg 5 are the same as in mode 15.

[0082] Mode 17 is a period from time t17 when the lower-arm switch element Tm2 is turned off to commutate the inverter current Iinv to the negative polarity path nn of the neutral phase leg 5, until the dead time DT has elapsed after the switch element Tm1 is turned off. In mode 17, as shown in FIG. 7( h), the resonant capacitor C2 of the switch element Tm2 is charged, and the resonant capacitor C1 of the switch element Tm1 is discharged. Therefore, the switch element Tm2 is subjected to zero-voltage turn-off control by the lossless snubber.

[0083] At time t18 when the dead time DT has elapsed after the turn-off control of the switch element Tm2, ​​the switch element Tn3 is subjected to zero-voltage turn-on control, and the mode returns to mode 10.

[0084] In mode 17, Vce of switch element Tm2 changes from 0 V to Vdc / 2, and Vce of switch element Tm1 changes from Vdc to Vdc / 2. Regarding the inter-terminal voltages of each element of auxiliary resonant circuit 2, Drn, Tr5, and Dsp change from Vdc / 2 to Vdc / 4, and Drp, Tr4, and Dsn change from 0 V to Vdc / 4. Regarding the inter-terminal voltages of each element of neutral phase leg 5, Tn4 and Dnp change from Vdc / 2 to 0 V.

[0085] The above modes 10 to 17 are repeated, and the switch elements Tm2 and Tn3 are subjected to zero-voltage turn-on control. The auxiliary resonant circuit 2 serves as a path for the energy stored in the resonant inductor Lr. The voltage across the terminals of the auxiliary resonant circuit 2 and each element of the neutral phase leg 5 does not exceed Vdc / 2 in any mode.

[0086] 8 and 9 show the operation of the resonant inverter 1 in mode 15A when the switch element Tr6 is turned off during the above-mentioned mode 15. Fig. 8 is a timing chart showing the operation of the resonant inverter 1. Fig. 9 shows the operation in mode 15A shown in Fig. 8 using an equivalent circuit of the resonant inverter 1.

[0087] Mode 15A is a state in which, at time t15A while the resonant inductor current ILr is commutating to the switch element Tm2, ​​the switch element Tr6 is turned off due to variations in elements, calculation variations, malfunctions, etc. The energy excited in the negative direction in the resonant inductor Lr is regenerated to the DC bus without loss, as shown by the dotted line in Fig. 9 , by the conduction of the lossless regenerative clamp snubber diode Dsp and the anti-parallel diode D5 of the switch element Tr5. During this regeneration, the auxiliary resonant circuit 2 is clamped to the neutral point A of the DC bus, and therefore each element of the auxiliary resonant circuit 2, including the switch element Tr6 (diode Drp, lossless regenerative clamp snubber diode Dsn), is clamped at Vdc / 2.

[0088] The charging operation of the resonant inverter 1 when the output voltage Vo is positive and the inverter current Iinv is negative will be described with reference to Figures 10 and 11. Figure 10 is a timing chart showing the operation of the resonant inverter 1. Figure 11 shows the operation in each mode shown in Figure 10 using an equivalent circuit of the resonant inverter 1.

[0089] Since the output voltage Vo is positive, the switching elements Tm1 and Tn4 alternately perform PWM operation. When the inverter current Iinv is negative, the target of zero-voltage turn-on control by resonance is the on-timing of the switching element Tn4.

[0090] 11A, the inverter current Iinv flows back through the anti-parallel diode D1 of the switch element Tm1. As shown in FIG. 11A, power is charged from the load (AC system) to the DC bus (positive DC line P).

[0091] In mode 20, Vce of the switch element Tm2 is Vdc. The voltages across the terminals of the elements of the auxiliary resonant circuit 2 are Vdc / 2 for Tr6, Drp, and Dsn, and 0 V for the other elements. The voltages across the terminals of the elements of the neutral phase leg 5 are 0 V for Tn3 and Dnn, and Vdc / 2 for the other elements.

[0092] 11B, the switching elements Tm1 and Tn3 are simultaneously turned off at time t21. In the mode 21, no change in state occurs from the mode 20.

[0093] In mode 22, at time t22 during the dead time DT, the switch element Tr6 in the negative-side resonant path rn is subjected to zero-current turn-on control, and the inverter current Iinv is commutated to the resonant inductor Lr (negative-side resonant path rn) as shown in Fig. 11(c) . Mode 22 continues until the anti-parallel diode D1 of the switch element Tm1 is turned off.

[0094] In mode 22, the voltages across the terminals of each element of the auxiliary resonant circuit 2 are Vdc / 2 for Dsn, Vdc / 4 for Tr5, Drp, and Dsp, and 0 V for the other elements. The voltages across the terminals of each element of the neutral phase leg 5 are the same as in mode 21.

[0095] In mode 23, commutation to resonant inductor Lr is completed at time t23, and Vce of switch element Tm1 and switch element Tm2 changes sinusoidally due to resonance with resonant capacitors C1 and C2 shown by dotted lines in Fig. 11(d). In mode 23, Vce of switch element Tm2 changes from Vdc to 0 V, and Vce of switch element Tm1 changes from 0 V to Vdc.

[0096] In mode 23, the voltage across each element of the auxiliary resonant circuit 2 is the same as in mode 22. As for the voltage across each element of the neutral phase leg 5, Tn3 and Dnn change from 0 V to Vdc / 2, and Tn4 and Dnp change from Vdc / 2 to 0 V.

[0097] The period of mode 22+23 is the sum of the first commutation time Tcom1 [Lr÷Vdcp×Iinv] and the resonance time Tres [π×√(Lr×2Cr)]. The first commutation time Tcom1 is the time until the commutation of the inverter current Iinv to the resonance inductor Lr is completed. The resonance time Tres is ½ of the period of the resonance at which the resonance frequency is (½π√(Lr×2Cr)).

[0098] In other words, the switch element Tr6 of the negative-side resonant path rn is controlled to be turned on (first commutation time Tcom1+resonant time Tres) before the turn-on timing of the switch elements Tm2 and Tn4.

[0099] 11( e), the switching elements Tm2 and Tn4 are subjected to zero-voltage turn-on control at time t24 when Vce of the switching element Tm2 becomes 0 V. In mode 24, the resonant inductor current ILr is commutated to the switching element Tm2 without being commutated to the neutral phase leg 5.

[0100] In mode 24, the voltage across each terminal of the auxiliary resonant circuit 2 is the same as in mode 23. The voltage across each terminal of each element of the neutral phase leg 5 is 0 V for Tn4 and Dnp, and Vdc / 2 for the other elements.

[0101] The period of mode 24 is a second commutation time Tcom2 [Lr / Vdcn×Iinv]. The second commutation time Tcom2 is the time until the commutation of the inverter current Iinv to the switching element Tm2 is completed.

[0102] In other words, the switch element Tr6 of the negative-side resonance path rn is controlled to be turned off after (the second commutation time Tcom2) the turn-on timing of the switch elements Tm2 and Tn4.

[0103] In mode 25, the switching element Tr6 is turned off at time t25 upon completion of commutation of the resonant inductor current ILr to the switching element Tm2.

[0104] In mode 25, the voltages across the terminals of each element of the auxiliary resonant circuit 2 are Vdc / 2 for Drn, Tr5, and Dsp, and 0 V for the other elements. The voltages across the terminals of each element of the neutral phase leg 5 are the same as in mode 24.

[0105] In mode 26, the lower-arm switch element Tm2 is turned off at time t26, thereby commutating the inverter current Iinv to the negative polarity path nn of the neutral phase leg 5. In mode 26, as shown in FIG. 11(g), the resonant capacitor C2 of the switch element Tm2 is charged, and the resonant capacitor C1 of the switch element Tm1 is discharged. Therefore, the switch element Tm2 is subjected to zero-voltage turn-off control by the lossless snubber.

[0106] In mode 26, Vce of switch element Tm2 changes from 0 V to Vdc / 2, and Vce of switch element Tm1 changes from Vdc to Vdc / 2. Regarding the voltages across the terminals of each element of the auxiliary resonant circuit 2, Drn, Tr5, and Dsp change from Vdc / 2 to Vdc / 4, and Drp, Tr4, and Dsn change from 0 V to Vdc / 4. Regarding the voltages across the terminals of each element of the neutral phase leg 5, Tn3 and Dnn change from Vdc / 2 to 0 V.

[0107] Mode 27 is a state in which commutation is completed and the inverter current Iinv is circulating through the negative polarity path nn of the neutral phase leg 5. In mode 27 after the completion of commutation to the negative polarity path nn of the neutral phase leg 5, the switch element Tn3 is subjected to zero-current turn-on control, thereby completing a series of zero-voltage turn-on operations.

[0108] In mode 27, the collector-emitter voltages Vce of the switch elements Tm1 and Tm2 are both Vdc / 2. The inter-terminal voltages (Vce, reverse voltages VR) of the elements Tr5, Tr6, Dsp, Dsn, Drp, and Drn of the auxiliary resonant circuit 2 are Vdc / 4. The inter-terminal voltages of the elements of the neutral phase leg 5 are all 0 V.

[0109] In mode 28, at time t28, the switch element Tn4 is turned off, and the inverter current Iinv is commutated to the switch element Tm1. In mode 28, as shown in FIG. 11(i), the resonant capacitor C2 of the switch element Tm2 is charged, and the resonant capacitor C1 of the switch element Tm1 is discharged. Therefore, the switch element Tn4 is subjected to zero-voltage turn-off control by the lossless snubber.

[0110] In mode 28, Vce of switch element Tm2 changes from Vdc / 2 to Vdc, and Vce of switch element Tm1 changes from Vdc / 2 to 0 V. Regarding the terminal voltages of each element of auxiliary resonant circuit 2, Tr6, Dsn, and Drp change from Vdc / 4 to Vdc / 2, and Tr5, Dsp, and Drn change from Vdc / 4 to 0 V. Regarding the terminal voltages of each element of neutral phase leg 5, Tn4 and Dnp change from 0 V to Vdc / 2.

[0111] At time t29 when the dead time DT has elapsed after the turn-off control of the switch element Tn4, the switch element Tm1 is subjected to zero-voltage turn-on control, and the mode returns to mode 20.

[0112] The above modes 20 to 28 are repeated, and the switch elements Tm1 and Tn4 are subjected to zero-voltage turn-on control. The auxiliary resonant circuit 2 serves as a path for the energy stored in the resonant inductor Lr. The voltage across the terminals of the auxiliary resonant circuit 2 and each element of the neutral phase leg 5 does not exceed Vdc / 2 in any mode.

[0113] If the switch element Tr6 is turned off during the above-described mode 24, the energy that has been negatively excited in the resonant inductor Lr is regenerated to the DC bus without loss, as in mode 15A shown in Fig. 9. The lossless regenerative clamp snubber diode Dsp and the anti-parallel diode D5 of the switch element Tr5 are conductive. During this regeneration, the auxiliary resonant circuit 2 is clamped to the neutral point A of the DC bus, and therefore each element of the auxiliary resonant circuit 2, including the switch element Tr6 (diode Drp and lossless regenerative clamp snubber diode Dsn), is clamped at Vdc / 2.

[0114] The charging operation of the resonant inverter 1 when the output voltage Vo is negative and the inverter current Iinv is positive will be described with reference to Figures 12 and 13. Figure 12 is a timing chart showing the operation of the resonant inverter 1. Figure 13 shows the operation in each mode shown in Figure 12 using an equivalent circuit of the resonant inverter 1.

[0115] Since the output voltage Vo is negative, the switching elements Tm2 and Tn3 alternately perform PWM operation. When the inverter current Iinv is positive, the target of zero-voltage turn-on control by resonance is the on-timing of the switching element Tn3.

[0116] 13A, the inverter current Iinv flows back through the anti-parallel diode D2 of the switch element Tm2. As shown in FIG. 13A, the DC bus (negative DC line N) is charged with power from the load (AC system).

[0117] In mode 30, Vce of the switch element Tm1 is Vdc. The voltages across the terminals of the elements of the auxiliary resonant circuit 2 are Vdc / 2 for Tr5, Drn, and Dsp, and 0 V for the other elements. The voltages across the terminals of the elements of the neutral phase leg 5 are 0 V for Tn4 and Dnp, and Vdc / 2 for the other elements.

[0118] 13B, the switching elements Tm2 and Tn4 are simultaneously turned off at time t31 in the mode 31. In the mode 31, no change in state occurs from the mode 30.

[0119] In mode 32, at time t32 during dead time DT, the switch element Tr5 in the positive-side resonant path rp is subjected to zero-current turn-on control, and the inverter current Iinv is commutated to the resonant inductor Lr (positive-side resonant path rp) as shown in Fig. 13(c) . Mode 32 continues until the anti-parallel diode D2 of the switch element Tm2 is turned off.

[0120] In mode 32, the voltages across the terminals of each element of the auxiliary resonant circuit 2 are Vdc / 2 for Dsp, Vdc / 4 for Tr6, Drn, and Dsn, and 0 V for the other elements. The voltages across the terminals of each element of the neutral phase leg 5 are the same as in mode 31.

[0121] In mode 33, commutation to resonant inductor Lr is completed at time t33, and Vce of switch element Tm1 and switch element Tm2 changes sinusoidally due to resonance with resonant capacitors C1 and C2 shown by dotted lines in Fig. 13(d). In mode 33, Vce of switch element Tm1 changes from Vdc to 0 V, and Vce of switch element Tm2 changes from 0 V to Vdc.

[0122] In mode 33, the voltage across each element of the auxiliary resonant circuit 2 is the same as in mode 32. As for the voltage across each element of the neutral phase leg 5, Tn4 and Dnp change from 0 V to Vdc / 2, and Tn3 and Dnn change from Vdc / 2 to 0 V.

[0123] The period of mode 32+33 is the sum of the first commutation time Tcom1 [Lr÷Vdcn×Iinv] and the resonance time Tres [π×√(Lr×2Cr)]. The first commutation time Tcom1 is the time until the commutation of the inverter current Iinv to the resonance inductor Lr is completed. The resonance time Tres is ½ of the period of the resonance at which the resonance frequency is (½π√(Lr×2Cr)).

[0124] In other words, the switch element Tr5 on the positive-side resonant path rp is controlled to be turned on (first commutation time Tcom1+resonant time Tres) before the turn-on timings of the switch elements Tm1 and Tn3.

[0125] 13( e), the switching elements Tm1 and Tn3 are subjected to zero-voltage turn-on control at time t34 when Vce of the switching element Tm1 becomes 0 V. In mode 34, the resonant inductor current ILr is commutated to the switching element Tm1 without being commutated to the neutral phase leg 5.

[0126] In mode 34, the voltage across each terminal of the auxiliary resonant circuit 2 is the same as in mode 33. The voltage across each terminal of each element of the neutral phase leg 5 is 0 V for Tn3 and Dnn, and Vdc / 2 for the other elements.

[0127] The period of mode 34 is a second commutation time Tcom2 [Lr / Vdcp×Iinv]. The second commutation time Tcom2 is the time until the commutation of the inverter current Iinv to the switch element Tm1 is completed.

[0128] In other words, the switch element Tr5 on the positive-side resonant path rp is controlled to be turned off after (the second commutation time Tcom2) the switch elements Tm1 and Tn3 are turned on.

[0129] In mode 35, the switching element Tr5 is turned off at time t35 upon completion of commutation of the resonant inductor current ILr to the switching element Tm1.

[0130] In mode 35, the voltages across the terminals of each element of the auxiliary resonant circuit 2 are Vdc / 2 for Drp, Tr6, and Dsn, and 0 V for the other elements. The voltages across the terminals of each element of the neutral phase leg 5 are the same as in mode 34.

[0131] In mode 36, the upper arm switch element Tm1 is turned off at time t36, thereby commutating the inverter current Iinv to the positive polarity path np of the neutral phase leg 5. In mode 36, as shown in FIG. 13(g), the resonant capacitor C1 of the switch element Tm1 is charged, and the resonant capacitor C2 of the switch element Tm2 is discharged. Therefore, the switch element Tm1 is subjected to zero-voltage turn-off control by the lossless snubber.

[0132] In mode 36, Vce of switch element Tm1 changes from 0 V to Vdc / 2, and Vce of switch element Tm2 changes from Vdc to Vdc / 2. Regarding the inter-terminal voltages of each element of auxiliary resonant circuit 2, Drp, Tr6, and Dsn change from Vdc / 2 to Vdc / 4, and Drn, Tr5, and Dsp change from 0 V to Vdc / 4. Regarding the inter-terminal voltages of each element of neutral phase leg 5, Tn4 and Dnp change from Vdc / 2 to 0 V.

[0133] Mode 37 is a state in which commutation is completed and inverter current Iinv is circulating through the positive polarity path np of neutral phase leg 5. In mode 37 after commutation to the positive polarity path np of neutral phase leg 5 is completed, zero-current turn-on control of switch element Tn4 is performed, thereby completing a series of zero-voltage turn-on operations.

[0134] In mode 37, the collector-emitter voltages Vce of the switch elements Tm1 and Tm2 are both Vdc / 2. The inter-terminal voltages (Vce, reverse voltages VR) of the elements Tr5, Tr6, Dsp, Dsn, Drp, and Drn of the auxiliary resonant circuit 2 are Vdc / 4. The inter-terminal voltages of the elements of the neutral phase leg 5 are all 0 V.

[0135] In mode 38, at time t38, the switch element Tn3 is turned off, and the inverter current Iinv is commutated to the switch element Tm2. In mode 38, as shown in FIG. 13(i), the resonant capacitor C1 of the switch element Tm1 is charged, and the resonant capacitor C2 of the switch element Tm2 is discharged. Therefore, the switch element Tn3 is subjected to zero-voltage turn-off control by the lossless snubber.

[0136] In mode 38, Vce of switch element Tm1 changes from Vdc / 2 to Vdc, and Vce of switch element Tm2 changes from Vdc / 2 to 0 V. Regarding the terminal voltages of each element of the auxiliary resonant circuit 2, Tr5, Dsp, and Drn change from Vdc / 4 to Vdc / 2, and Tr6, Dsn, and Drp change from Vdc / 4 to 0 V. Regarding the terminal voltages of each element of the neutral phase leg 5, Tn3 and Dnn change from 0 V to Vdc / 2.

[0137] At time t39 when the dead time DT has elapsed after the turn-off control of the switch element Tn3, the switch element Tm2 is subjected to zero-voltage turn-on control, and the mode returns to mode 30.

[0138] The above modes 30 to 38 are repeated, and the switch elements Tm2 and Tn3 are subjected to zero-voltage turn-on control. The auxiliary resonant circuit 2 serves as a path for the energy stored in the resonant inductor Lr. The voltage across the terminals of the auxiliary resonant circuit 2 and each element of the neutral phase leg 5 does not exceed Vdc / 2 in any mode.

[0139] If the switch element Tr5 is turned off during the above-described mode 34, the energy excited in the positive direction in the resonant inductor Lr is regenerated to the DC bus without loss, as in mode 5A shown in Fig. 5. The lossless regenerative clamp snubber diode Dsn and the anti-parallel diode D6 of the switch element Tr6 are conductive. During this regeneration, the auxiliary resonant circuit 2 is clamped to the neutral point A of the DC bus, and therefore each element of the auxiliary resonant circuit 2, including the switch element Tr5 (diode Drn and lossless regenerative clamp snubber diode Dsp), is clamped at Vdc / 2.

[0140] 14 shows a T-NPC inverter circuit 10 to which the auxiliary resonant circuit 2 is applied. In the T-NPC inverter circuit 10, the switch elements Tn3 and Tn4 are connected in series in such a manner that they can be controlled to withstand voltages in opposite directions, forming a neutral phase leg 5a connected between a neutral point A and an input / output point B. The collector of the switch element Tn3 is connected to the neutral point A and the emitter is connected to the emitter of the switch element Tn4, and the collector of the switch element Tn4 is connected to the input / output point B.

[0141] In the neutral phase leg 5a, the switch element Tn3 and the anti-parallel diode D4 of the switch element Tn4 function as a positive polarity path np opened and closed by the switch element Tn3. The switch element Tn4 and the anti-parallel diode D3 of the switch element Tn3 function as a negative polarity path nn opened and closed by the switch element Tn4.

[0142] 15 shows a full-bridge inverter circuit 11 to which the resonant inverter 1 is applied. The full-bridge inverter circuit 11 is a full-bridge configuration of the resonant inverter 1. The full-bridge inverter circuit 11 includes a U-phase main leg 4u, a U-phase neutral phase leg 5au of the U-phase main leg 4u, and a U-phase auxiliary resonant circuit 2u. The full-bridge inverter circuit 11 includes a W-phase main leg 4w, a W-phase neutral phase leg 5aw of the W-phase main leg 4w, and a W-phase auxiliary resonant circuit 2w.

[0143] The U-phase control circuit 6u and the W-phase control circuit 6w control the U-phase auxiliary resonant circuit 2u and the W-phase auxiliary resonant circuit 2w separately at different timings. The control of the U-phase auxiliary resonant circuit 2u varies depending on the switching state of the W-phase. The control of the W-phase auxiliary resonant circuit 2w varies depending on the switching state of the U-phase.

[0144] 16 shows a three-phase inverter circuit 12 to which the resonant inverter 1 is applied. The three-phase inverter circuit 12 is a three-phase version of the resonant inverter 1. The three-phase inverter circuit 12 includes a U-phase main leg 4u, a U-phase neutral phase leg 5au of the U-phase main leg 4u, and a U-phase auxiliary resonant circuit 2u. The three-phase inverter circuit 12 includes a V-phase main leg 4v, a V-phase neutral phase leg 5av of the V-phase main leg 4v, and a V-phase auxiliary resonant circuit 2v. The three-phase inverter circuit 12 includes a W-phase main leg 4w, a W-phase neutral phase leg 5aw of the W-phase main leg 4w, and a W-phase auxiliary resonant circuit 2w.

[0145] The U-phase control circuit 6u, V-phase control circuit 6v, and W-phase control circuit 6w control the U-phase auxiliary resonant circuit 2u, V-phase auxiliary resonant circuit 2v, and W-phase auxiliary resonant circuit 2w at individual timings. The control of the U-phase auxiliary resonant circuit 2u operates differently depending on the switching states of the V and W phases. The control of the V-phase auxiliary resonant circuit 2v operates differently depending on the switching states of the U and W phases, and the control of the W-phase auxiliary resonant circuit 2w operates differently depending on the switching states of the U and V phases.

[0146] 17, a case where the switch element Tm1 of the U-phase main leg 4u is turned on at zero voltage while the switch element Tm1 of the V-phase main leg 4v and the W-phase main leg 4w are both on will be described. The U-phase current is positive, and the V-phase current and the W-phase current are all negative.

[0147] Mode 40 shown in FIG. 17( a) is a state in which inverter current Iinv circulates through the anti-parallel diode D2 of switch element Tm2 of U-phase main leg 4u and the anti-parallel diode D1 of switch element Tm1 of V-phase main leg 4v and W-phase main leg 4w.

[0148] In mode 41, the switch element Tr5 in the U-phase auxiliary resonant circuit 2u of the U-phase main leg 4u is turned on, thereby commutating the inverter current Iinv to the positive-side resonant path rp (resonant inductor Lr) of the U-phase auxiliary resonant circuit 2u, as shown in Figure 17 (b).

[0149] In mode 42, commutation to resonant inductor Lr of U-phase auxiliary resonant circuit 2u is completed. In mode 42, Vce of switch elements Tm1 and Tm2 of U-phase main leg 4u changes sinusoidally due to resonance with resonant capacitors C1 and C2 of U-phase main leg 4u, as shown by the dotted line in FIG. 17(c). In mode 42, Vce of switch element Tm1 of U-phase main leg 4u changes from Vdc to 0 V, and Vce of switch element Tm2 of U-phase main leg 4u changes from 0 V to Vdc.

[0150] In mode 43, the switching element Tm1 of the U-phase main leg 4u is subjected to zero-voltage turn-on control as shown in Fig. 17(d) when the voltage Vce of the switching element Tm1 of the U-phase main leg 4u becomes 0 V. In mode 43, the resonant inductor current ILr is commutated to the switching element Tm1 of the U-phase main leg 4u.

[0151] In mode 44, upon completion of commutation of the resonant inductor current ILr to the switch element Tm1, the switch element Tr5 is controlled to be turned off, and as shown in FIG. 17(e), the current circulates between the input and output points of the inverter.

[0152] The above is the operation of the U-phase by the U-phase control circuit 6u. The V-phase control circuit 6v and the W-phase control circuit 6w control the V-phase and W-phase at individual timings, similar to the U-phase.

[0153] (Summary) The resonant inverter according to each embodiment of the present invention can also be described as follows. (1) A resonant inverter 1 according to one embodiment of the present invention includes a neutral point clamp circuit 3 including a capacitor Cp (positive-side capacitor) and a capacitor Cn (negative-side capacitor) connected in series between a positive-side DC line P and a negative-side DC line N. In the neutral point clamp circuit 3, the connection point between the capacitors Cp and Cn forms a neutral point A. The resonant inverter 1 includes a main leg 4 connected in series between the positive-side DC line P and the negative-side DC line N. The main leg 4 includes a switch element Tm1 (upper arm switch) and a switch element Tm2 (lower arm switch), and the connection point between the switch elements Tm1 and Tm2 forms an input / output point B of the inverter current. The resonant inverter 1 includes a resonant capacitor C1 (first resonant capacitor) and a resonant capacitor C2 (second resonant capacitor) connected in parallel with the switch elements Tm1 and Tm2. The resonant inverter 1 includes an anti-parallel diode D1 (first anti-parallel diode) and an anti-parallel diode D2 (second anti-parallel diode) connected in anti-parallel to the switch elements Tm1 and Tm2. The resonant inverter 1 includes a neutral phase leg 5 having a positive polarity path np, whose current polarity is limited to the direction from the neutral point A to the input / output point B, and a negative polarity path nn, whose current polarity is limited to the direction from the input / output point B to the neutral point A. The neutral phase leg 5 includes a switch element Tn3 (positive-side neutral phase switch) and a switch element Tn4 (negative-side neutral phase switch) that open and close the positive polarity path np and the negative polarity path nn, respectively. The resonant inverter 1 includes an auxiliary resonant circuit 2 including a resonant inductor Lr, one end of which is connected to the input / output point B. The auxiliary resonant circuit 2 includes a positive-side resonant path rp, whose current polarity is limited to the direction from the neutral point A to the resonant inductor Lr, and which is opened and closed by a switch element Tr5 (positive-side resonant switch). The auxiliary resonant circuit 2 includes a negative-side resonant path rn whose current polarity is limited to the direction from the resonant inductor Lr to the neutral point A and which is opened and closed by a switch element Tr6 (negative-side resonant switch).The auxiliary resonant circuit 2 includes a positive-side regenerative path (anti-parallel diode D3 of switch element Tr3+lossless regenerative clamp snubber diode Dsp) in which the current polarity is limited to the direction from resonant inductor Lr to positive-side DC line P. The auxiliary resonant circuit 2 includes a negative-side regenerative path (anti-parallel diode D4 of switch element Tr4+lossless regenerative clamp snubber diode Dsn) in which the current polarity is limited to the direction from negative-side DC line N to resonant inductor Lr.

[0154] According to the resonant inverter 1 described in (1) above, the auxiliary resonant circuit 2 provides a lossless regeneration path for the energy stored in the resonant inductor Lr. The auxiliary resonant circuit 2 is clamped to the voltage at the neutral point A by the positive-side resonant path rp and the negative-side resonant path rn. The elements constituting the auxiliary resonant circuit 2 can be configured with elements with a lower withstand voltage than the elements of the main leg 4, which is the main circuit. This broadens the range of elements that can be selected for the auxiliary resonant circuit 2, allowing it to be configured at low cost. The lossless regenerative clamp snubber diodes Dsp and Dsn provide a regeneration path for the energy of the resonant inductor Lr, enabling highly efficient overvoltage protection. By applying the auxiliary resonant circuit 2 to the resonant inverter 1, which is a three-level inverter, the efficiency of the resonant inverter 1 can be further improved. The resonant inverter 1 is capable of soft switching even at power factors other than unity, making it ideal for charging and discharging applications. The auxiliary resonant circuit 2 provides a heat dissipation effect, making the heat dissipation mechanism inexpensive.

[0155] (2) In the resonant inverter 1 described in (1) above, during a discharge operation in which the switch elements Tm1 and Tn4 are alternately controlled with a dead time DT in between, the switch element Tn3 may be controlled to be turned off simultaneously with the switch element Tn4 and may be controlled to be turned on simultaneously with the switch element Tm1.

[0156] According to the resonant inverter 1 described in (2) above, during the discharge operation in which the switch elements Tm1 and Tn4 are alternately controlled with the dead time DT in between, the resonant inverter 1 can be treated as a two-level converter, and the resonant operation can be easily controlled.

[0157] (3) In the resonant inverter 1 described in (2) above, the switch element Tr5 may be turned on during the dead time DT before the switch element Tm1 is turned on, and the switch element Tr5 may be turned off after the switch element Tm1 is turned on.

[0158] According to the resonant inverter 1 described in (3) above, during the discharge operation in which the switch elements Tm1 and Tn4 are alternately controlled with the dead time DT in between, the inverter current Iinv can be commutated to the auxiliary resonant circuit 2, thereby causing a resonant operation.

[0159] (4) In the resonant inverter 1 described in (2) or (3) above, the switch element Tr5 may be turned on at a timing before the timing of the turn-on control of the switch element Tm1, the timing being the sum of a first commutation time Tcom1 (first positive-side commutation time) and a resonance time Tres. The first commutation time Tcom1 (first positive-side commutation time) is the time until the commutation of the inverter current Iinv to the resonant inductor Lr is completed by the turn-on control of the switch element Tr5. The resonance time Tres is a half period of the resonance formed by the resonant inductor Lr and the resonant capacitors C1 and C2.

[0160] According to the resonant inverter 1 described in (4) above, zero-voltage turn-on control of the switch element Tm1 can be realized during the discharge operation in which the switch elements Tm1 and Tn4 are alternately controlled with the dead time DT therebetween.

[0161] (5) In the resonant inverter 1 described in any one of (2) to (3) above, the switch element Tr5 may be turned off at a timing that is a second commutation time Tcom2 (second positive side commutation time) after the timing of the turn-on control of the switch element Tm1. The second commutation time Tcom2 (second positive side commutation time) is the time until the commutation of the resonant inductor current ILr from the resonant inductor Lr to the switch element Tm1 is completed by the turn-on control of the switch element Tm1.

[0162] According to the resonant inverter 1 described in (5) above, during the discharge operation in which the switch elements Tm1 and Tn4 are alternately controlled with the dead time DT in between, the resonant operation can be quickly terminated after the zero voltage turn-on control of the switch elements Tm1 and Tn3.

[0163] (6) In the resonant inverter 1 described in (1) above, during a discharge operation in which the switch elements Tm2 and Tn3 are alternately controlled with a dead time DT therebetween, the switch element Tn4 may be controlled to be turned off simultaneously with the switch element Tn3 and turned on simultaneously with the switch element Tm2.

[0164] According to the resonant inverter 1 described in (6) above, during the discharge operation in which the switch elements Tm2 and Tn3 are alternately controlled with the dead time DT in between, the resonant inverter 1 can be treated as a two-level converter, and the resonant operation can be easily controlled.

[0165] (7) In the resonant inverter 1 described in (6) above, the switch element Tr6 may be turned on during the dead time DT before the switch element Tm2 is turned on, and the switch element Tr6 may be turned off after the switch element Tm2 is turned on.

[0166] According to the resonant inverter 1 described in (7) above, during the discharge operation in which the switch elements Tm2 and Tn3 are alternately controlled with the dead time DT in between, the inverter current Iinv can be commutated to the auxiliary resonant circuit 2, thereby causing a resonant operation.

[0167] (8) In the resonant inverter 1 described in (6) or (7) above, the switch element Tr6 may be turned on at a timing before the timing of the turn-on control of the switch element Tm2, ​​the timing being the sum of a first commutation time Tcom1 (first negative commutation time) and the resonant time Tres. The first commutation time Tcom1 (first negative commutation time) is the time until the commutation of the inverter current Iinv to the resonant inductor Lr is completed by the turn-on control of the switch element Tr6.

[0168] According to the resonant inverter 1 described in (8) above, zero-voltage turn-on control of the switch element Tm2 can be realized during the discharge operation in which the switch elements Tm2 and Tn3 are alternately controlled with the dead time DT therebetween.

[0169] (9) In the resonant inverter 1 described in any one of (6) to (7) above, the switch element Tr6 may be turned off at a timing that is a second commutation time Tcom2 (second negative commutation time) after the timing of the turn-on control of the switch element Tm2. The second commutation time Tcom2 (second negative commutation time) is the time until the commutation of the resonant inductor current ILr from the resonant inductor Lr to the switch element Tm2 is completed by the turn-on control of the switch element Tm2.

[0170] According to the resonant inverter 1 described in (9) above, during the discharge operation in which the switch elements Tm2 and Tn3 are alternately controlled with the dead time DT in between, the resonant operation can be quickly terminated after the zero voltage turn-on control of the switch elements Tm2 and Tn4.

[0171] Although the present invention has been described above with reference to specific embodiments, it goes without saying that the above embodiments are merely examples and can be modified and implemented without departing from the spirit of the present invention.

[0172] REFERENCE SIGNS LIST 1 Resonant inverter 2, 2u, 2v, 2w Auxiliary resonant circuit 3 Neutral point clamp circuit 4 Main leg 4u U-phase main leg 4v V-phase main leg 4w W-phase main leg 5 Neutral phase leg 5a Neutral phase leg 5au U-phase neutral phase leg 5av V-phase neutral phase leg 5aw W-phase neutral phase leg 5u U-phase neutral phase leg 5w W-phase neutral phase leg 6 Control circuit 6u U-phase control circuit 6v V-phase control circuit 6w W-phase control circuit 10 T-NPC type inverter circuit 11 Full bridge inverter circuit 12 Three-phase inverter circuit C1, C2 Resonant capacitor Cn, Cp Capacitor D1, D2, D3, D4, D5, D6 Anti-parallel diode Dnn, Dnp, Drn, Drp Diode Dsn, Dsp Lossless regenerative clamp snubber diodes L1 Inductor Lr Resonant inductor N Negative side DC line P Positive side DC line Tm1, Tm2, ​​Tn3, Tn4, Tr5, Tr6 Switching elements nn Negative side polarity path np Positive side polarity path rn Negative side resonant path rp Positive side resonant path

Claims

1. A neutral point clamp circuit comprising a positive side capacitor and a negative side capacitor connected in series between a positive side DC line and a negative side DC line, the junction between the positive side capacitor and the negative side capacitor being a neutral point; a main leg comprising an upper arm switch and a lower arm switch connected in series between the positive side DC line and the negative side DC line, the junction between the upper arm switch and the lower arm switch being an input / output point of an inverter current; a first resonant capacitor and a second resonant capacitor connected in parallel to the upper arm switch and the lower arm switch; a first anti-parallel diode and a second anti-parallel diode connected in anti-parallel to the upper arm switch and the lower arm switch; a neutral phase leg having a positive side neutral phase switch and a negative side neutral phase switch which respectively open and close a positive side polarity path in which the current polarity is limited to a direction from the neutral point to the input / output point and a negative side polarity path in which the current polarity is limited to a direction from the input / output point to the neutral point; and an auxiliary resonant circuit including a resonant inductor one end of which is connected to the input / output point, a positive side resonant path, the current polarity of which is limited to a direction from the neutral point to the resonant inductor, and which is opened and closed by a positive side resonant switch; a negative side resonant path, the current polarity of which is limited to a direction from the resonant inductor to the neutral point, and which is opened and closed by a negative side resonant switch; a positive side regenerative path, the current polarity of which is limited to a direction from the resonant inductor to the positive side DC line; and a negative side regenerative path, the current polarity of which is limited to a direction from the negative side DC line to the resonant inductor.

2. A resonant inverter as described in claim 1, wherein during discharge operation in which the upper arm switch and the negative side neutral phase switch are alternately controlled with a dead time in between, the positive side neutral phase switch is turned off simultaneously with the negative side neutral phase switch.

3. A resonant inverter as described in claim 2, wherein the positive side resonant switch is controlled to be turned on during the dead time before the upper arm switch is controlled to be turned on, and the positive side resonant switch is controlled to be turned off after the upper arm switch is controlled to be turned on.

4. The resonant inverter according to claim 2, wherein the positive side resonant switch is turned on at a timing before the timing of the turn-on control of the upper arm switch, which is the sum of a positive side first commutation time until the commutation of the inverter current to the resonant inductor is completed by the turn-on control of the positive side resonant switch and a resonance time which is 1 / 2 the period of resonance caused by the resonant inductor, the first resonant capacitor and the second resonant capacitor.

5. The resonant inverter according to claim 2, wherein the positive side resonant switch is controlled to be turned off at a timing that is a second positive side commutation time after the turn-on control of the upper arm switch, the time until the commutation of the resonant inductor current from the resonant inductor to the upper arm switch is completed by the turn-on control of the upper arm switch.

6. A resonant inverter as described in claim 1, wherein during discharge operation in which the lower arm switch and the positive side neutral phase switch are alternately controlled with a dead time in between, the negative side neutral phase switch is turned off simultaneously with the positive side neutral phase switch.

7. A resonant inverter as described in claim 6, wherein the negative side resonant switch is controlled to be turned on during the dead time before the lower arm switch is controlled to be turned on, and the negative side resonant switch is controlled to be turned off after the lower arm switch is controlled to be turned on.

8. The resonant inverter according to claim 6, wherein the negative side resonant switch is turned on at a timing before the timing of the turn-on control of the lower arm switch, which is the sum of a negative side first commutation time until the commutation of the inverter current to the resonant inductor is completed by the turn-on control of the negative side resonant switch and a resonance time which is 1 / 2 the period of resonance caused by the resonant inductor, the first resonant capacitor and the second resonant capacitor.

9. The resonant inverter according to claim 6, wherein the negative side resonant switch is controlled to be turned off at a timing that is a second negative side commutation time after the turn-on control of the lower arm switch, the time until the commutation of the resonant inductor current from the resonant inductor to the lower arm switch is completed by the turn-on control of the lower arm switch.

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