JPH11341832A - Partial resonance pwm inverter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a partial resonance PWM inverter capable of surely performing zero-voltage switching in a short zero-voltage period. SOLUTION: This inverter is provided with first and second main switching elements Q1 , Q2 , a first free wheeling diode G1 and a first capacitor for resonance C3 connected in parallel with the first main switching element Q1 , and a second free wheeling diode G2 and a second capacitor for resonance C4 connected in parallel with the second main switching element Q2 . First and second auxiliary switches Sa, Sb and a reactor for resonance L2 are connected between the intermediate junction of the first and second main switching elements Q1 , Q2 and a divided voltage outputting terminal where the half of a DC source voltage is outputted. Here, a drive circuit 40, 50 is provided for comparing both the terminal voltage of each of the first and second main switching element Q1 , Q2 with a preset reference voltage, to turn on that switching element Q1 , Q2 , when the both terminal voltage becomes the reference voltage or lower, and to make this on-state maintained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a partial resonance PWM inverter in which a plurality of main switch elements are turned on and off to obtain an AC voltage.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 8, a partial resonance PW provided with a partial resonance circuit for reducing switching loss.
An M inverter 1 is known.

In FIG. 8, three sets of partial resonance PWM inverters 1 are provided to obtain a three-phase AC voltage from a DC power supply E. The partial resonance PWM inverter 1 is operated by a control circuit 10. It is.

[0004] The control circuit 10 is a PWM for outputting a pulse.
It comprises a signal generator 11 and two signal delay circuits 12, 13 and the like.

[0005] The partial resonance PWM inverter 1 has two main switch elements S1 and S2 connected in series, and these main switch elements S1 and S2 are connected between both terminals of a DC power supply. The freewheel diodes D1 and D2 and the resonance capacitors C1 and C2 are connected in parallel to each of the main switch elements S1 and S2.

One terminal of a resonance reactor L1 is connected to an intermediate connection point between the main switch elements S1 and S2, and auxiliary switches SA and SB connected in parallel are connected to the other terminal of the resonance reactor L1. ing. CA and CB are capacitors for dividing the power supply voltage into two, and an intermediate connection point between the CA and CB is connected to the other terminal of the resonance reactor L1 via the auxiliary switches SA and SB.

The PWM signal generator 11 has a main switch element S
1 and S2 and a pulse signal for turning on and off the auxiliary switches SA and SB.
The pulse signal output from 1 is output after being delayed for a predetermined time. The signal delay circuit 13 delays the pulse signal output from the signal delay circuit 12 by a predetermined time and outputs the delayed pulse signal.

The operation shown in FIG. 9 shows a state in which a current IO flows through the freewheeling diode D2 and commutates to the main switch element S1.

Assuming that the current IO during the commutation period is constant, the current IL flowing through the resonance reactor L1 starts to increase linearly by turning on the resonance auxiliary switch SA at time t0. Here, t0 to t1 is the time until the current IL reaches the output current I0, and t1 to t2 is the period during which the current ΔIL that determines the resonance energy flows.

Now, when the main switch element S2 is turned off at the output timing t2 of the pulse signal output from the signal delay circuit 12, the resonance reactor L1 and the resonance capacitors C1 and C2 enter a resonance operation, and the output voltage VO is reduced. Going up. When the output voltage VO reaches the power supply voltage E (time t3), the free wheel diode D1 turns on. If the pulse signal is output from the signal delay circuit 13 to turn on the main switch element S1 at time tx within the period (time t3 to t4) in which the freewheeling diode D1 is on, zero voltage switching is performed. become.

When there is no loss in the circuit, the period (t1 to t1)
2) and the period (t3 to t4) are equal, but actually, due to the loss of the switching element S1 and the resonance reactor L1, etc.
t1 to t2> t3 to t4. The time points t6 to t9 indicate a state in which the current IO flows through the main switch element S1 to the commutation diode D2, and the operations of the time points t0 to t9 are repeated. During the period t3 to t7, that is, by changing the width of the output voltage Vo in FIG. 10, an AC voltage is output as shown by a broken line. A three-phase AC is obtained by combining three AC voltages.

Here, when the period t1 to t2 becomes shorter, the period t2 to t3 becomes longer and the period t3 to t4 becomes shorter. For this reason, it is difficult to turn on the main switch element S1 in the period t3 to t4 with the pulse signal output from the signal delay circuit 13. Main switch element S1 is in period t3
If the turn-on is made earlier or later than t4, the turn-on is performed with the charge remaining in the resonance capacitor C1, so that an excessive stress is applied to the main switch element S1, and the main switch element S1 may be damaged or cause noise. Will be.

Therefore, it is necessary to switch the main switching element S1 to zero voltage.

[0014]

In order to perform zero voltage switching, a period t0 to t1 corresponding to the output current, a period t1 to t2 for determining the resonance energy, and a commutation period t2 to t3.
, The turn-on timing tx of the main switch element S1 after commutation must come within a zero volt period t3 to t4 in which the voltage across the main switch element S1 is zero volt.

However, the output current I0 and the commutation period t2 to t3
In order to turn on the main switch element S1 with a pulse signal output from the signal delay circuit 13 in consideration of the variation of the switching elements S1, S2, SA, SB, the variation of the operation delay time, the control delay time, etc. Zero volt period t3 to t4
Need to be longer. In order to extend the zero volt period t3 to t4, the period t1 to t2 must be increased.

By extending this period t1 to t2,
The zero volt period t3 to t4 becomes longer, and the signal delay circuit 12
It is easy to turn on the main switch S1 by outputting a pulse signal from the signal delay circuit 13 at the time point tX based on the pulse signal output from the main switch S1.

However, when the period t1 to t2 is lengthened, the current IL (resonant current) of the resonance reactor L1 increases. Due to this increase, the main switch elements S1, S2 and the auxiliary switch S
A, SB conduction loss and freewheeling diodes D1, D2 conduction loss,
Circuit loss such as iron loss and copper loss of the resonance reactor L1 increases. In addition, the time required for a series of operations in the period from t0 to t5 becomes longer, and sufficient PWM control cannot be performed. Furthermore, since the resonance current IL increases, the switching elements S1, S2, SA, and SB for large current must be used, which results in an increase in cost due to an increase in the size of the switching elements and a decrease in efficiency due to an increase in loss of the resonance circuit. Many problems arise, such as becoming a factor.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a partial resonance PWM capable of reliably performing zero voltage switching within a short zero volt period.
An object of the present invention is to provide an inverter.

[0019]

In order to achieve the above object, an invention according to claim 1 includes a first and a second main switch element connected between both terminals of a DC power supply and connected in series, A first freewheeling diode and a first capacitor for resonance connected in parallel to the main switch element; and a second freewheeling diode and a second capacitor for resonance connected in parallel to the second main switch element. The first and second parallel-connected first and second voltage-divided output terminals, each of which outputs the voltage of the DC power supply divided into two, are connected between an intermediate connection point of the main switch element.
The second auxiliary switch is connected to a resonance reactor connected in series to the first and second auxiliary switches, and the first and second auxiliary switches are connected to each other.
In a partial resonance PWM inverter that alternately turns on and off a second main switch element to obtain an AC voltage from one terminal of the reactor, a voltage between both ends of the first main switch element is compared with a preset reference voltage. A first drive circuit for turning on the first main switch element when the voltage between both ends thereof is equal to or lower than the reference voltage and maintaining the first main switch element on;
A second drive for comparing the voltage between both ends of the second main switch element with a preset reference voltage, and turning on the second main switch element when the voltage between both ends falls below the reference to maintain this ON state. And a circuit.

According to a second aspect of the present invention, the driving circuit compares the voltage between both ends of the main switch element with a predetermined reference voltage to detect that the voltage between both ends is lower than a reference, When the comparator detects that the voltage between both ends is below the reference and outputs a detection signal, the detection signal is latched to turn on the main switch element and to keep the main switch element on. And a circuit.

According to a third aspect of the present invention, the first and second main switch elements connected between both terminals of the DC power supply and connected in series are connected between both terminals of the DC power supply and connected in series. Third and fourth main switch elements, and four return diodes and a resonance capacitor respectively connected in parallel to each main switch element, and a connection point between the first main switch element and the second main switch element. A first auxiliary switch, a resonance reactor, and a second auxiliary switch are connected in series between a connection point of the third main switch element and the fourth main switch element, and the four main switch elements are used to form a full-bridge inverter circuit. In the partial resonance PWM inverter configured as described above, at least one of the first and fourth main switch elements and at least one of the second and third main switch elements are provided. The voltage between both ends of these main switch elements is compared with a preset reference voltage to one of the main switches, and when the voltage between both ends becomes lower than the reference, the main switch elements are turned on to turn on the main switch elements. A driving circuit for maintaining the voltage is provided.

According to a fourth aspect of the present invention, the drive circuit compares the voltage between both ends of the main switch element with a preset reference voltage to detect that the voltage between both ends is equal to or less than a reference, A latch circuit for latching the detection signal when the comparator detects that the voltage between both ends thereof is lower than a reference and outputting a detection signal, turning on the main switch element, and maintaining this on state. It is characterized by having.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a partial resonance PWM inverter according to the present invention will be described below with reference to the drawings.

[First Embodiment] The partial resonance PW shown in FIG.
The M inverter 20 is operated by a control circuit 30. Three sets of the partial resonance PWM inverter 20 and the control circuit 30 are provided (not shown), and a three-phase AC voltage is obtained from the DC power supply E. It has become.

The control circuit 30 outputs a pulse signal P
It comprises a WM signal generator 31, a signal delay circuit 32 for outputting a delayed pulse signal with a predetermined time delay based on the pulse signal output from the PWM signal generator 31, and inverters 33, 34 and the like. .

The partial resonance PWM inverter 20 turns on and off the two main switching elements Q1 (first main switching element) and Q2 (second main switching element) connected in series, and the main switching elements Q1 and Q2. There are provided drive circuits 40 (first drive circuit), 50 (second drive circuit) and the like. The main switch elements Q1 and Q2 are connected between both terminals of the DC power supply E. Each main switch element Q1 and Q2 has a resonance capacitor C3.
(A first capacitor for resonance) and C4 (a second capacitor for resonance) are connected in parallel. In addition, each main switch element Q
The anode and cathode of the freewheeling diode G1 (first freewheeling diode) and G2 (second freewheeling diode) are connected to the emitter and collector of Q2, respectively.

One terminal of a resonance reactor L2 is connected to an intermediate connection point A between the main switch elements Q1 and Q2, and an auxiliary switch Q is connected to the other terminal of the resonance reactor L2.
A and QB are connected. The auxiliary switches QA and QB are connected in parallel with each other and connected to an intermediate connection point B between capacitors CA and CB that divide the voltage of the DC power supply E into two.

As shown in FIG. 2, the drive circuit 40 includes an anode of the freewheel diode G1, that is, a main switch element Q1.
A reference voltage generating circuit 42 for outputting a reference voltage of 0 to -1 V to the emitter of the reference voltage, and comparing the reference voltage with the cathode voltage of the return diode G1 (collector voltage of the main switch element Q1) to determine the cathode voltage The comparator 43 includes a comparator 43 that outputs a set signal when the voltage is equal to or lower than the reference voltage, and a latch circuit 44 that, when the set signal is output from the comparator 43, latches the set signal and turns on the main switch element Q1. The latch circuit 44 is reset when the output of the signal delay circuit 32 becomes L level, and the main switch element Q1 is turned off by this reset.

As shown in FIG. 3, the drive circuit 50 includes an anode of the freewheel diode G2, that is, a main switch element Q2.
And a reference voltage generating circuit 52 for outputting a reference voltage of 0 to -1 V to the emitter of the reference diode, and comparing the reference voltage with the cathode voltage of the return diode G2 (collector voltage of the main switch element Q2) to determine the cathode voltage. The comparator 53 includes a comparator 53 that outputs a set signal when the voltage is equal to or lower than the reference voltage, and a latch circuit 54 that latches the set signal when the comparator 53 outputs the set signal and turns on the main switch element Q2. The latch circuit 54 is reset when the output of the inverter 33 becomes L level, and the main switch element Q2 is turned off by this reset.

Next, the operation of the partial resonance PWM inverter 20 of the above embodiment will be described with reference to a time chart shown in FIG.

Now, a description will be given of a state in which the current IO is flowing back to the return diode G2 and commutates from this state to the main switch element Q1.

When an H-level pulse signal is output from the PWM signal generator 31 (time T0), the auxiliary switch QA is turned on and the current IL starts to flow through the reactor L2. Then, at time T2, which is delayed by a predetermined time from the time at which the pulse signal was output, an H-level delay signal is output from the signal delay circuit 32, and the output of the inverter 33 becomes L-level. The L level resets the latch circuit 54 of the drive circuit 50 and turns off the main switch element Q2.

When the main switch element Q2 is turned off, the resonance reactor L2 and the resonance capacitors C3 and C4 enter a resonance operation, and the output voltage VO increases. When the output voltage VO reaches the power supply voltage E (time T3), the return diode G1
Turns on.

When the return diode G1 is turned on, the cathode voltage of the return diode G1 becomes lower than the anode voltage, the cathode voltage becomes lower than the reference voltage, and the comparator 43 outputs a set signal (time Tx). This set signal is latched by the latch circuit 44, and the main switch element Q1 is turned on. The latch circuit 44 holds the ON state of the main switch element Q1 until reset. The comparator 43 outputs a set signal only during the zero volt period (time T3 to T4) when the return diode G1 is on.

As described above, when the return diode G1 is turned on, the comparator 43 and the latch circuit 44 turn on the main switch element Q1, so that fluctuations in the commutation periods T2 to T3 and the respective switch elements Q1, Q2, QA, Even if the zero volt period T3 to T4 is shortened due to the variation of the operation delay time of QB, or the timing of the zero volt period T3 to T4 is changed, the main switch element Q1 is switched to the zero volt period T3 to T4.
It can be reliably turned on within T4. That is, zero voltage switching can be reliably performed within the zero volt period T3 to T4.

[Second Embodiment] FIG. 5 shows a partial resonance PWM inverter 100 according to a second embodiment.
In the second embodiment, a single-phase AC voltage is obtained from a DC power supply E.

In this partial resonance PWM inverter 100, in addition to the main switch elements Q1, Q2,
Main switch elements Q3 (third main switch element), Q4
(Fourth main switch element) and the main switch elements Q3, Q
Drive circuit 60 (third drive circuit) for turning on / off 4, 7
0 (fourth drive circuit). Resonant capacitors C5 (third capacitor for resonance), C6 (fourth capacitor for resonance) and freewheel diodes G3 (third freewheel diode), G4 (fourth freewheel diode) are connected in parallel to each main switch element Q3, Q4. Have been. In addition, the main switching element Q
Auxiliary switches QA and QB are connected in series between an intermediate connection point A of the first and second switching elements Q2 and an intermediate connection point J of the main switching elements Q1 and Q2 with a resonance reactor L2 interposed therebetween.

The driving circuits 60 and 70 have exactly the same configuration as the driving circuit 40, and a description thereof will be omitted.

In the second embodiment, as shown in FIG. 6, the main switching elements Q2 and Q3 are turned off by the driving circuits 50 and 60 at the time T2, and the time Tx in the zero volt period T3 to T4.
The main switching elements Q1 and Q4 are turned on by the driving circuits 40 and 70 in the same manner as in the first embodiment.

In the second embodiment, the main switching elements Q1 to Q4 are turned on and off by the driving circuits 40 to 70. However, as shown in FIG. 7, only the main switching elements Q2 and Q3 are driven. Circuits 50 and 70 are provided, and the main switch elements (Q2, Q3),
(Q1, Q4) may be turned on / off.

[0041]

As described above, according to the present invention, even if the zero volt period is shortened or the timing of the zero volt period fluctuates, zero voltage switching can be reliably performed within the zero volt period. Thus, a highly efficient partial resonance PWM inverter with less waste can be provided.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a specific configuration of a partial resonance PWM inverter according to the present invention.

FIG. 2 is a block diagram illustrating a configuration of a driving circuit.

FIG. 3 is a block diagram illustrating a configuration of a driving circuit.

FIG. 4 is a time chart showing an operation of a main part of the partial resonance PWM inverter.

FIG. 5 is a circuit diagram showing a configuration of a second embodiment.

FIG. 6 is a time chart showing an operation of a main part of the second embodiment.

FIG. 7 is a circuit diagram showing a configuration of another example of the second embodiment.

FIG. 8 is a circuit diagram showing a configuration of a conventional partial resonance PWM inverter.

FIG. 9 is a time chart illustrating an operation of the partial resonance PWM inverter of FIG. 8;

FIG. 10 is an explanatory diagram showing an AC voltage.

[Explanation of symbols]

Q1 switch element (first switch element) Q2 switch element (second switch element) G1 freewheel diode (first freewheel diode) G2 freewheel diode (second freewheel diode) C3 resonance capacitor (first resonance capacitor) C4 resonance Capacitor (second capacitor for resonance) L2 Reactor for resonance 40 Drive circuit 50 Drive circuit

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[Procedure amendment]

[Submission date] May 28, 1998

[Procedure amendment 1]

[Document name to be amended] Drawing

[Correction target item name] Fig. 5

[Correction method] Change

[Correction contents]

FIG. 5

[Procedure amendment 2]

[Document name to be amended] Drawing

[Correction target item name] Fig. 8

[Correction method] Change

[Correction contents]

FIG. 8

Claims (4)

[Claims] 1. A first and a second main switch element connected between both terminals of a DC power supply and connected in series, a first freewheeling diode and a first resonance capacitor connected in parallel to the first main switch element. And a second freewheeling diode and a second capacitor for resonance connected in parallel to the second main switch element. The intermediate connection point between the first and second main switch elements and the voltage of the DC power supply are divided into two. First and second auxiliary switches connected in parallel and a resonance reactor connected in series to the first and second auxiliary switches are connected between the output voltage dividing terminal and the first and second auxiliary switches. In a partial resonance PWM inverter that alternately turns on and off a second main switch element to obtain an AC voltage from one terminal of the reactor, a voltage between both ends of the first main switch element is compared with a preset reference voltage. A first drive circuit for turning on the first main switch element when the voltage between both ends becomes equal to or lower than the reference voltage and maintaining the first main switch element to be on; a voltage between both ends of the second main switch element and a preset reference voltage; And a second drive circuit for turning on the second main switch element when the voltage between both ends thereof becomes equal to or lower than a reference and maintaining the second main switch element to be turned on. 2. The driving circuit according to claim 1, wherein the driving circuit compares a voltage between both ends of the main switch element with a preset reference voltage to detect that the voltage between both ends is lower than a reference. A latch circuit that latches the detection signal when the detection signal is output and detects that the voltage at both ends is below the reference, turns on the main switch element, and keeps the main switch element on. 2. The partial resonance PWM inverter according to claim 1, wherein: 3. The first and second main switch elements connected between both terminals of the DC power supply and connected in series, and the third and second main switch elements connected between both terminals of the DC power supply and connected in series. A fourth main switch element, four return diodes and a resonance capacitor respectively connected in parallel to each main switch element, a connection point between the first main switch element and the second main switch element, and a third main switch element A partial auxiliary resonance circuit in which a first auxiliary switch, a resonance vehicle, and a second auxiliary switch are connected in series between a connection point of the first main switch element and the fourth main switch element, and the four main switch elements constitute a full-bridge inverter circuit. In the PWM inverter, at least one of the first and fourth main switch elements
The two main switches and at least one of the second and third main switch elements are compared with the voltage between both ends of the main switch elements and a preset reference voltage. A partial resonance PW provided with a drive circuit for turning on the corresponding main switch element and maintaining the turn-on state when the following condition is satisfied:
M inverter. 4. A comparator for comparing a voltage between both ends of a main switch element with a preset reference voltage to detect that the voltage between both ends is equal to or lower than a reference. And a latch circuit for latching the detection signal when the detection signal is output and detecting that the voltage at both ends is below the reference, turning on the main switch element, and maintaining this on state. 4. The partial resonance PWM inverter according to claim 3, wherein: