JPH0270267A - Parallel resonance converter - Google Patents

Abstract

PURPOSE:To make an overcurrent-preventing circuit unnecessary by connecting a reactor and a capacitor resonating at a frequency fr between AC terminals of a bridge circuit formed by switching elements and by setting said frequency fr as fr>=2fs (fs is the switching drive frequency of said switching elements). CONSTITUTION:A bridge is formed by self-extinction of arc-type switching elements S1-S4 antiparallel-connecting diodes, and a capacitor C1 and a reactor L1 resonating at a frequency fr are connected between AC terminals X, Y. The exciting inductor LS and bridge rectifier circuit B of an output transformer are connected with the terminal of said capacitor C1, and a load RL and a filter capacitor C2 is connected between output terminals thereof. A resonance frequency fr is set as fr>=2fs relative to a frequency fs, at which switching elements S1-S4 are switching-driven. In this manner, no recovery mode exists even at the time of no load and overcurrent preventing parts of said switching elements are omitted. Therefore, the subject apparatus is suitable for apparatus undergoing a frequent no-load running such as travelling-wave tube and capacitor charger.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable to transistors, FETs, GTOs, and IGBs.
The present invention relates to a parallel resonant converter in which a load and a resonant capacitor are connected in parallel using a self-extinguishing switching element such as a T-type switch.

[Problems to be solved by the prior art and the invention] Conventionally, resonant converters using self-extinguishing switching elements such as transristors, FETs, GTOs, and IGBTs have been designed to avoid commutation failures like thyristors, and to avoid switching elements. The current flowing through the switch is a half-sine wave, there is no switch loss, and the noise is low, so it is used in a variety of fields.

However, with such a resonant converter.

In order to always maintain the operating mode in the resonance mode even if there are power supply fluctuations or load fluctuations, the current, voltage, phase, etc. of one circuit are usually detected and the operating frequency is controlled. Therefore,
When the IllS circuit becomes complex and the output voltage is controlled to the lower limit, the operating frequency may reach the audible range. Therefore, a bridge circuit is constructed using self-extinguishing switching elements having anti-parallel diodes, and a series circuit of a resonance capacitor and a resonance inductance is connected between the AC terminals of the bridge circuit, and rectification is carried out from both ends of the resonance capacitor. In a resonant converter in which the direct current is extracted through means, a method has been proposed in which the output is controlled by controlling the pulse width of a switching element.

FIG. 1 is a connection diagram of a parallel resonant converter circuit. In the figure, E is a DC power supply, and Sl to s4 are switch elements bridge-connected across the power supply E.

CI is a resonant capacitor, Ll is a resonant inductance, and LS is an excitation inductance of the output transformer (not shown), which is connected in parallel to the resonant capacitor c1. B is a bridge rectifier circuit, C2 is a filter capacitor, and RL is a load.

In such a circuit, conventionally the switch elements 31 to S
4 drive frequency ``S is the resonant frequency fr of the resonant inductance and capacitor.

It was common to set it at fs#fr to 0.6fr.

Then, switch elements 31 to S4 are shown in FIG. 2 (1) to (2).
As shown in , the pulse width is T/2 with the period being approximately constant T.
A square AC voltage Vxy as shown in Fig. 2 (3) is applied between the AC output points X and Y of BRI and J.
Add. In such a state, if the load state is changed, the operation mode of the inverter changes significantly, and the forward current and reverse current flowing through 5l-34 change. By appropriately selecting the values of Ll and CI.

When the current flowing through 5l-54 is in the rated operating state, it is in phase with the voltage Vxy and has a peak value of 1p, as shown in FIG. Switch element Sl~ rises from almost 0
The forward current has a characteristic that when S4 is open, the current is almost 0), and the voltage νcL of CI, that is, the isometric output voltage vO, can be increased to a value higher than E as shown in FIG. 2 (6). can. In addition, if filter C2 is large enough, C
Bridges B, C2, and RL seen from both ends of I can be regarded as a bipolar battery with voltage Vo, and the voltage of CI is clamped at Vo. By selecting Ll and CI in this way, in a single load state, Isl and rs3 are given as an example.
As shown in FIG. 2 (7), the current lags behind Vxy, and when the output is short-circuited, it becomes a positive and negative triangular wave that lags Vxy by 90 degrees as shown in (8). In Figure 2 (7) and (8), the negative direction 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, and in a short-circuit state, the forward current The current peaks [sp become approximately equal, and all the power supplied from the power supply to the resonant circuits of Ll and CI is fed back to the power supply.

[Problem to be solved by the invention]

However, 5 thus fs'; fr ~ 0.6fr
In the conventional method selected for @load, while one parallel diode is on, the other switch element turns on, and a recovery current flows until the parallel diode recovers in the reverse direction, causing an excessive load on the switch element. Current flows and stress is added. Figure 2 +91. The broken line waveform of Ql indicates the current of the switching element at light load, and the whisker-shaped current in front of the waveform is the recovery current.

[Means for solving problems]

In the present invention, in order to solve one or more of the above problems, a bridge circuit is constructed using a self-extinguishing switch element having an anti-parallel diode, and a series circuit of a resonance capacitor and a resonance inductance is connected between the AC terminals of the bridge circuit. In a parallel type resonant converter, the DC output is taken out from both ends of the resonant capacitor via rectifying means.

The present invention proposes a parallel type resonant converter characterized in that the resonant frequency fr of the resonant capacitor and the inductance is selected so that fr≧2rs with respect to the switching drive frequency @fs of the self-extinguishing switching element. .

〔Example〕

FIG. 1 is a connection diagram of a parallel resonant converter circuit. In FIG. 0, E is a DC power supply, and 51 to S4 are switch elements bridge-connected across the electric ME.

C1 is a resonant capacitor, Ll is a resonant inductance, and LS is an excitation inductance of the output transformer (not shown), which is connected in parallel to the resonant 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 less than half of the natural frequency under no load, as shown by the solid line at +41.0 m in FIG. For that purpose]/2 tt,
Select Ll and CI that satisfy rLIC1=fr≧2fs.

As the resonant inductance L1 at this time, for example, LL#0
．． 11 If E2T/Po.

The current waveform is shown in Figure 2 +41. (As shown in 51, the waveform is almost sinusoidal, and the equivalent output voltage is 1.4E −1,5
It becomes E.

Then, C1 is determined by the above relational expression corresponding to this Ll. With the constants determined in this way, there is no recovery mode even when there is no load.

Figure 3 shows an embodiment in which the resonant converter of the present invention is applied to a high voltage charger for a capacitor, where E is a DC power supply and Q is
1 to 14 are PETs connected across the DC power supply E, I) 1 to D4 are each FET, and a diode 1C1 connected in antiparallel to Ql to port 4 is a resonance capacitor.

Ll is the resonance inductance, and TI is the step-up transformer.

C- is the Kotscroft connected to the secondary side of this T2.
A high voltage rectifier circuit such as a Walton circuit, 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 ^1 compares it with the reference voltage Vref to generate an error signal. FET gate signal G
Generate 1-G4.

Here, if Ll and CI are selected as described above, this FETQ
When the currents from 1 to Q4 form a mountain shape and the power supply voltage is E,
The primary input voltage of transformer T1 becomes 1.5E.

In such a configuration, when a charging start command is received, the error amplifier operates as FET and Q until the charging voltage Vref is reached.
Gate signals 61 to G4 are applied so that l to q4 turn on the maximum pulse width, approximately T/2. Then, since the capacitor Co is initially equivalent to a load short circuit, this converter supplies an output current of l5=ET/8L1 as a primary conversion output current. Here, if Io= Po/1.5E, then Is=
ET/8L1= ET/8X O, 11E"÷Po=
With Po10.88E, Is/io = 1.7, thus providing an output current of approximately 1.71o. This current decreases as the capacitor Co is charged, as shown in Figure 4.
When the charging voltage reaches Vo, the battery enters a rated operating state with a rated current of 1o. When the charging voltage reaches Vo, the error amplifier stops the gate signal and stops charging. This charging time Lc can be made shorter than the charging time tC by using a normal constant current 1o. In reality, the voltage of the capacitor Go decreases due to the parasitic current in the circuit, so it is necessary to supplementally charge the capacitor Go to some extent.

Thereafter, the converter operates under light load to replenish the natural discharge of the capacitor Co. At this time, according to the present invention, no recovery current is generated, and since the current is a sine wave resonance current as shown in FIG. 2 (+9) (II), switching loss and noise are not generated.

In the above embodiments, the bridge circuit has been described. For example, by replacing the switch elements s1 and S4 in FIG. 1 with capacitors, the circuit can be implemented in a half-bridge type. In reality, the resonant capacitor c1 is usually set larger than the above calculated value depending on the excitation inductance of the transformer. Further, the distributed capacitance of the transformer secondary winding can be used for part or all of the CI.

〔Effect of the invention〕

The present invention has the features described above.

Since there is no recovery mode during no-load, there is no need for circuit components to prevent overcurrent in the switch element, making it safe and economical to use in devices that frequently operate without load, such as capacitor chargers or traveling wave tubes. .

[Brief explanation of the drawing]

FIG. 1 shows a principle diagram of a resonant converter circuit according to the present invention, FIG. 2 shows a waveform diagram of each part to explain the operation of the circuit shown in FIG. 1, and FIG. FIG. 4 shows the waveform of the current flowing through the capacitor Co of the circuit shown in FIG. 3. E...DC power supply B...Bridge rectifier circuit S1-S4...Switch element CI...Resonance capacitor Ll...Resonance inductance RL...Load C2...Filter capacitor Ql-Q4.・・F
ETDI-04...Diode T1...Step-up transformer C++...High voltage rectifier circuit Co...Capacitor R1...Detection resistor Vref...Reference voltage At
...Error amplifier ^2...Gate signal generation circuit 61
~G4...Gate signal patent applicant Origin Electric Co., Ltd.

Claims (1)

[Claims] A bridge circuit is constructed of self-extinguishing switching elements having anti-parallel diodes, and a series circuit of a resonance capacitor and a resonance inductance is connected between the AC terminals of the bridge circuit, and the resonance In a parallel resonant converter in which a DC output is taken out from both ends of a capacitor via a rectifier, the resonant frequency fr of the resonant capacitor and inductance is set so that fr≧2fs with respect to the switching drive frequency fs of the self-extinguishing switching element. A parallel type resonant converter characterized by being selected so that.