JPH0648904B2 - Parallel resonant converter - Google Patents

Description

The present invention relates to a parallel resonance converter in which a load and a resonance capacitor are connected in parallel using self-turn-off switch elements such as transistors, FETs, GTOs, and IGBTs. .

[Problems to be Solved by Prior Art and Invention]

Conventionally, resonant converters using self-turning-off switch elements such as transistors, FETs, GTOs and IGBTs have no commutation failure like thyristors, and the current flowing through the switch elements is a half-sine wave with no switch loss. It is also used in various fields due to its advantages such as low noise.

However, in such a resonant converter, the operating mode is always controlled by detecting the current, voltage and phase of the circuit in order to always maintain the operating mode in the resonant mode even if the power supply or the load fluctuates. Is. Therefore, the control circuit becomes complicated and the operating frequency may reach the audible range when the output voltage is controlled to the lower limit. Therefore, a bridge circuit is composed of self-extinguishing switch elements with anti-parallel diodes, a series circuit of a resonance capacitor and a resonance inductance is connected between the AC terminals of the bridge circuit, and rectification is performed from both ends of the resonance capacitor. In a resonance type converter in which a DC output is taken out through a means, a method of controlling the output by pulse sub-control of a switching element has been proposed.

FIG. 1 is a connection diagram of a parallel type resonant converter circuit. In the figure, E is a DC power supply, S1 to S4 are switch elements bridge-connected across the power supply E, C1 is a resonance capacitor, L1 is a resonance inductance, and LS is an exciting inductance of an output transformer, which is not shown. It is connected in parallel with the resonance capacitor C1. B is a bridge rectifier circuit,
C2 is a filter capacitor and RL is a load.

In such a circuit, conventionally, the drive frequency fs of the switching elements S1 to S4 was usually set to fs ≈ fr to 0.6fr with respect to the resonance frequency fr of the resonance inductance and the capacitor. Then, as shown in FIGS. 2 (1) to (2), the switching elements S1 to S4 are alternately turned on at a pulse width T / 2 with a cycle of a substantially constant value T, shifted by 180 degrees, and the AC output point X, A square AC voltage Vxy as shown in Fig. 2 (3) is applied across Y. When the load condition is changed in this state, the operating mode of the inverter changes greatly, and the forward current and reverse current flowing through S1 to S4 change. By appropriately selecting the values of L1 and C1, S1 to S4
Fig. 2 (4) to (5) in the rated operating condition
As shown in, the forward current is almost mountainous with the peak value Ip in phase with the voltage Vxy (characteristic that the current rises from almost 0 when the switch elements S1 to S4 are closed and the current becomes almost 0 when the switch elements S1 to S4 open) , And the voltage Vc1 of C1, that is, the equivalent output voltage VO, can be raised to a value higher than E as shown in FIG. 2 (6). When the filter C2 is large enough, the bridges B, C2, and RL seen from both ends of C1 have voltage Vo
Can be regarded as a bipolar battery, and the voltage of C1 is clamped at Vo. By selecting L1 and C1 in this way, if Is1 and Is3 are taken as an example under heavy load condition, Fig. 2 (7)
As shown in (8), there is a lagging current with respect to Vxy.
It becomes a positive and negative triangular wave delayed by 90 degrees with Vxy. Fig. 2
In (7) and (8), the negative current indicates the reverse current of each switch element, that is, the current that returns to the power supply. The heavier the load, the more the feedback current increases. Isp becomes almost equal, and all the power supplied from the power supply to the resonant circuit of L1 and C1 is returned to the power supply.

[Problems to be Solved by the Invention]

However, in the conventional method that selects fs ≈ fr to 0.6 fr in this way, the other switching element turns on while one of the parallel diodes is on when the load is light, and the parallel diode recovers in the reverse direction. Recovery current flows to the switch element, excessive current flows to the switch element, and stress is applied. The broken line waveforms in Fig. 2 (9) and (10) show the current of the switch element at light load, and the whisker-shaped current in front of the waveform is the recovery current.

[Means for solving problems]

In order to solve the above problems, the present invention forms a bridge circuit by a self-extinguishing switch element having an anti-parallel diode, and a series circuit of a resonance capacitor and a resonance inductance between AC terminals of the bridge circuit. In a parallel resonance converter in which a DC output is taken out from both ends of the resonance capacitor via rectification means, the resonance frequency fr of the resonance capacitor and the inductance is set to the switching drive frequency of the self-extinguishing switch element. for fs
The present invention proposes a parallel type resonant converter characterized by being selected so that fr ≧ 2fs.

〔Example〕

FIG. 1 is a connection diagram of a parallel type resonant converter circuit. In the figure, E is a DC power supply, S1 to S4 are switch elements bridge-connected across the power supply E, C1 is a resonance capacitor, L1 is a resonance inductance, and LS is an exciting inductance of an output transformer, which is not shown. It is connected in parallel with the resonance capacitor C1. B is a bridge rectifier circuit,
C2 is a filter capacitor and RL is a load.

In the present invention, the operating frequency of the converter may be set to half or less of the natural frequency under no load, as shown by the solid lines in FIGS. 2 (9) and (10). for that purpose Select L1 and C1 that satisfy.

If the resonance inductance L1 at this time is, for example, L1 ≈ 0.11 E ² T / Po, the current waveform becomes almost sinusoidal as shown in Fig. 2 (4) and (5), and the equivalent output voltage is 1.4E. It will be ~ 1.5E. Then, C1 is determined by the above relational expression corresponding to this L1.
With the constant determined in this way, there is no recovery mode even under no load.

FIG. 3 shows an embodiment in which the resonant converter of the present invention is applied to a high voltage charger of a capacitor. E is DC power supply, Q1〜
Q4 is a FET, D1 bridged across the DC power supply E
~ D4 is each FET, Q1 ~ Q4 is a diode connected in anti-parallel, C1
Is a resonance capacitor, L1 is a resonance inductance, T1 is a step-up transformer, CW is a high-voltage rectifier circuit such as a Cockcroft-Walton circuit connected to the secondary side of T2, and Co is a capacitor to be charged.

The charging voltage of the capacitor Co is detected by the detection resistor R1 and the error amplifier A1 compares it with the reference voltage Vref to generate an error signal. Corresponding to this error signal, in the gate signal generation circuit A2, each FET Generates gate signals G1 to G4.

Here, when L1 and C1 are selected as described above, the transformer T1 is turned on when the currents of the FETs Q1 to Q4 have a mountain shape and the power source voltage is E.
The primary input voltage of becomes 1.5E.

In such a configuration, when the charge start command arrives, the error amplifier adds the gate signals G1 to G4 to turn on FETs, Q1 to Q4, and the maximum pulse width of about T / 2 until the charge voltage Vref is reached. Then, since the capacitor Co is initially equivalent to a load short circuit, this converter uses Is = ET as the primary converted output current.
/ 8L1 output current is supplied. If Io = Po / 1.5E, then Is = ET / 8L1 = ET / 8 × 0.11E ² ÷ Po = Po / 0.88E
Is / Io = 1.7 Therefore, the output current of about 1.7Io is supplied. This current decreases as the capacitor Co is charged as shown in FIG. 4, and when the charging voltage becomes Vo, the rated operation state of the rated current Io is reached. When the charging voltage reaches Vo, the error amplifier stops the gate signal,
Stop charging. This charging time tc can be made shorter than the charging time tc 'by the normal constant current Io. Actually the capacitor Co
Since the voltage of is reduced by the parasitic current of the circuit, this amount must be slightly supplemented.

After that, since the natural discharge of the capacitor Co is replenished, the converter operates at light load. At this time, according to the present invention, a recovery current does not occur, and since it is a sinusoidal resonance current as shown in FIGS. 2 (9) and (10), switching loss and noise do not occur.

Although the bridge circuit has been described in the embodiment, it can be implemented in a half bridge type by replacing the switch elements S1 and S4 and the capacitor in FIG. 1, for example. In practice, the resonant capacitor C1 is usually larger than the above calculated value due to the exciting inductance of the transformer. Further, the distributed capacitance of the transformer secondary winding can be used for part or all of C1.

〔The invention's effect〕

The present invention has the features as described above, and since there is no recovery mode at the time of no load, circuit parts for preventing an overcurrent of the switch element are unnecessary, and it is not necessary to use a capacitor charger or a traveling wave tube. It is safe and economical to use for equipment with many no-load operations.

[Brief description of drawings]

FIG. 1 shows a principle diagram of a resonant converter circuit according to the present invention, FIG. 2 shows waveform diagrams of respective parts for explaining the operation of the circuit shown in FIG. 1, and FIG. 3 shows a resonance diagram of the present invention. An example in which the type converter is applied to a high-voltage charger of a capacitor is shown, and FIG. 4 shows a waveform of a current flowing through the capacitor Co in the circuit shown in FIG. E ... DC power supply, B ... Bridge rectifier circuit S1 to S4 ... Switching element, C1 ... Resonance capacitor L1 ... Resonance inductance, RL ... Load C2 ... Filter capacitor, Q1-Q4 ... FET D1 ~ D4 ...... Diode, T1 ...... Step-up transformer CW ...... High voltage rectifier circuit, Co ...... Capacitor R1 ...... Detection resistor, Vref ...... Reference voltage A1 ...... Error amplifier, A2 ...... Gate signal generation circuit G1 to G4 ...... Gate signal

Claims (1)

[Claims] 1. A self-extinguishing switch element having an anti-parallel diode forms a bridge circuit, and a series circuit of a resonance capacitor and a resonance inductance is connected between AC terminals of the bridge circuit and the resonance capacitor is connected. In a parallel-type resonant converter that extracts DC output from both ends of a self-extinguishing switch element, the resonant frequency fr of the resonant capacitor and the inductance is compared with the switching drive frequency fs of the self-extinguishing switch element.
A parallel resonance converter characterized by being selected so that fr ≧ 2 fs.