WO2015117260A1

WO2015117260A1 - Circuit structure for inhibiting dynamic magnetic bias of high frequency isolated full-bridge circuit, and control method

Info

Publication number: WO2015117260A1
Application number: PCT/CN2014/001174
Authority: WO
Inventors: 毕大强; 柴建云; 孙旭东; 赵杨阳
Original assignee: 清华大学
Priority date: 2014-02-07
Filing date: 2014-12-25
Publication date: 2015-08-13
Also published as: CN103762693A; WO2015117261A1; CN103762693B

Abstract

A circuit for inhibiting the dynamic magnetic bias of a high frequency isolated full-bridge circuit, and control method; the circuit consists of a staggered parallel Buckboost circuit and a high frequency isolated two-way full-bridge DC/DC converter circuit. The control method comprises: when the change rate of a current instruction of a converter circuit is lower than the dynamic magnetic bias threshold of a high frequency transformer, the high frequency isolated two-way full-bridge DC/DC converter circuit operates in a current closed loop state, while the staggered parallel Buckboost circuit operates in an open loop running state having a 50% duty ratio; and when the change rate of the current instruction of the converter circuit is higher than or equal to the dynamic magnetic bias threshold of the high frequency transformer, the high frequency isolated two-way full-bridge DC/DC converter circuit maintains operation in an open loop state having a present duty ratio, while the staggered parallel Buckboost circuit operates in a current rapid closed loop state.

Description

Circuit structure and control method for suppressing dynamic bias of high-frequency isolated full-bridge circuit

Technical field

The invention belongs to the technical field of high-frequency isolated full-bridge circuit control, and particularly relates to a circuit structure and a control method for suppressing dynamic biasing of a high-frequency isolated full-bridge circuit.

Background technique

The high-frequency transformer is a power transformer with a working frequency exceeding 10 kHz, and is mainly used as a high-frequency switching power supply transformer in a high-frequency switching power supply. The high-frequency transformer can efficiently realize the functions of power transmission, step-up and step-down and electrical isolation, and is an important energy conversion device in power electronic converters. The energy transmission of the high-frequency transformer has two ways. One is that the transformer transmission mode is also called the forward mode, that is, the current applied to the primary winding causes the magnetic flux in the magnetic core to change, so that the secondary winding induces a voltage. Therefore, the electric energy is transmitted from the primary side to the secondary side; the other is that the inductor transmission mode is also called a flyback mode, that is, a voltage is applied to the primary winding, an exciting current is generated to magnetize the magnetic core, and the electrical energy is converted into magnetic energy to be stored. Then, by demagnetizing, the secondary winding induces a voltage, and the magnetic energy is converted into electrical energy to be released to the load.

The bidirectional full-bridge DC/DC circuit is a basic forward-excited circuit topology and is commonly used in isolated power electronic converters. With the improvement of the performance of semiconductor devices and the emergence of high-frequency soft magnetic materials, high-frequency isolated full-bridge circuits have attracted wide attention due to their high power density, small volume and weight, and high power transmission efficiency. However, due to the nonlinearity of the core magnetization curve, the saturation and bias phenomenon of the high-frequency transformer occur, and the saturation bias will cause the magnetizing inductance to decrease rapidly, and the single-phase magnetizing current will increase sharply, thereby damaging the power switch of the full-bridge circuit. This also becomes a major problem limiting the performance of high frequency isolated full bridge circuits.

At present, the research on the biasing of the transformer in the high-frequency isolated bidirectional full-bridge circuit is focused on the steady-state biasing caused by the time-integration effect due to the small volt-second product imbalance in the forward and reverse directions of the switching period. However, the problem of dynamic bias caused by excessive change of the duty cycle of two consecutive positive and negative cycles of the switch tube has not been deeply analyzed and experimentally studied.

Figure 1 shows the dynamic bias state diagram of the high frequency transformer. Under normal working conditions, the high-frequency transformer works in the first type of working state, that is, the solid line part of the figure. If a constant amplitude, constant duty cycle but opposite direction pulse square wave voltage is respectively loaded into the primary winding of the transformer, one duty cycle During the positive and negative half cycles, the square wave voltage causes the excitation current in the primary winding of the transformer to be the same size and opposite direction in the two half cycles. It can be seen from Fig. 1 that the magnetic flux generated in the transformer core is a 180-degree symmetrical curve centered on the zero point, that is, a hysteresis loop. In one cycle, the magnetic flux density changes from a positive maximum value to a negative maximum value, and the DC magnetization component in the magnetic core is largely cancelled. However, when the switching tube continuously changes the duty cycle of the two groups of positive and negative periods too much, that is, in the previous positive and negative alternating period, the core state stays at the critical saturation point A, if the forward duty ratio of the next period Very small, the transformer current will not return to zero, and because the transformer works in the high-frequency switching state, the resistance decay time of the transformer is close to the switching frequency, and the bias current cannot be completely attenuated, when it is the same as its pulse width. Re-acting the pulse on both ends of the transformer will cause the transformer to shift at a large equilibrium point in only two switching cycles, resulting in a dynamic bias phenomenon, and the working state of the high-frequency transformer becomes the dotted line in the figure. Once the bias occurs, the magnetizing inductance of the transformer is rapidly reduced, and the exciting current is sharply increased. The effect is equivalent to short-circuiting the tube through the short-circuit.

Therefore, by analyzing the mechanism of dynamic biasing of high-frequency transformers, a circuit structure and corresponding control method for effectively suppressing the dynamic bias of high-frequency transformers in bidirectional full-bridge converters are proposed. By limiting the conversion rate of the bidirectional full-bridge circuit duty cycle, the dynamic biasing is suppressed, and the staggered parallel BuckBoost circuit is added to compensate for the shortage of the bidirectional full-bridge dynamic adjustment speed, and the transformation is implemented with a small DC filter device under steady-state conditions. The minimum current ripple output characteristic of the device.

Summary of the invention

Aiming at the problem of dynamic bias caused by the excessive change of the duty cycle of the two sets of positive and negative cycles of the switch tube, a circuit structure and control method for suppressing the dynamic bias of the high-frequency isolated full-bridge circuit are proposed.

A circuit structure for suppressing dynamic biasing of a high-frequency isolated full-bridge circuit is composed of an interleaved parallel BuckBoost circuit and a high-frequency isolated bidirectional full-bridge DC/DC converter circuit; wherein the interleaved parallel BuckBoost circuit includes capacitors C1 and C2, and an inductor L1 and L2, switching transistors S1 to S4, diodes D1 to D4; high The frequency-isolated bidirectional full-bridge DC/DC converter circuit is a switch tube Sa1 to Sa4 with a self-contained anti-parallel diode connected to a bridge structure at the primary end of the high-frequency transformer T1, and the secondary end is connected to form a bridge structure. Switching tubes Sb1 to Sb4 with reversed diodes; high voltage DC bus capacitors C3 are connected in parallel between the upper and lower arms of the bridge structure connected to the secondary side.

One end of the capacitor C1 in the interleaved BuckBoost circuit is connected to one end of the inductors L1 and L2, and the other end of the inductor L1 is connected to the source of the switch S2 and the drain of the switch S4, and the source of the S4 and the capacitor C2 One end of the inductor L2 is connected to the source of the switch S1 and the drain of the switch S3. The source of the switch S3 is connected to one end of the capacitor C2, and the other end of the capacitor C1 is connected to the drain of the switch S1. The drain of the switch S2 is connected to the other end of the capacitor C2, and the capacitor C2 is connected in parallel with the upper and lower arms of the bridge structure connected to the primary end of the high-frequency transformer T1.

A control method for suppressing dynamic biasing of a high-frequency isolated full-bridge circuit, comprising:

Step 1. When starting the high-frequency isolated bidirectional full-bridge DC/DC converter circuit, the magnetic resonance of the high-frequency transformer T1 is performed by using a fixed 2% small duty-cycle open-loop method, so that the residual magnetism tends to zero;

Step 2: continuously sampling the current signal of the high-frequency transformer T1 and performing time integration on the same, thereby avoiding the steady-state biasing caused by the time integral effect caused by the small volt-second product imbalance in the forward and reverse directions in the switching period;

Step 3. When the rate of change of the current command of the converter circuit is less than the dynamic bias threshold of the high frequency transformer, the high frequency isolated bidirectional full-bridge DC/DC converter circuit operates in a current closed-loop state, and the interleaved parallel BuckBoost circuit operates 50% duty cycle open loop operation, and can achieve minimum current ripple output;

Step 4: When the rate of change of the current command of the converter circuit is greater than or equal to the dynamic bias threshold of the high frequency transformer, the high frequency isolated bidirectional full-bridge DC/DC converter circuit maintains open loop operation under the current duty cycle, and is interleaved The parallel BuckBoost circuit operates in a fast closed-loop state of the current, thereby rapidly changing the output power of the converter circuit.

The invention has the beneficial effects that the current change rate in the dynamic biasing threshold of the high-frequency transformer can ensure that the high-frequency transformer does not instantaneously operate near the saturation point due to the excessive difference between the duty cycles of the two front and the opening tubes. At the same time, the control system will still sample the transformer current signal and time-integrate it from It avoids the steady-state bias caused by the time integral effect due to the small volt-second product imbalance in the forward and reverse directions of the switching cycle. And when the converter is started, the high-frequency transformer is magnetically exercised by a fixed 2% small duty-cycle open-loop method, so that the residual magnetism tends to zero, and then enters the closed-loop operation.

DRAWINGS

Figure 1 is a dynamic bias state diagram of a high frequency transformer;

2 is a circuit structure for suppressing dynamic biasing of a high-frequency isolated full-bridge circuit;

Figure 3 is an experimental waveform diagram obtained by a conventional control method;

4 is an experimental waveform diagram obtained by the control method of the present invention.

detailed description

The preferred embodiments are described in detail below with reference to the accompanying drawings.

A circuit structure for suppressing dynamic bias of a high-frequency isolated full-bridge circuit, as shown in FIG. 2, comprising an interleaved parallel BuckBoost circuit and a high-frequency isolated bidirectional full-bridge DC/DC converter circuit; wherein the interleaved parallel BuckBoost circuit includes Capacitors C1 and C2, inductors L1 and L2, switching transistors S1 to S4, diodes D1 to D4; high-frequency isolated bidirectional full-bridge DC/DC converter circuits are connected to the bridge structure at the primary end of the high-frequency transformer T1 Switching tubes Sa1 to Sa4 with reversed diodes, the secondary ends are connected to the switching tubes Sb1 to Sb4 of the bridge structure with inverted diodes; and the upper and lower bridge arms of the bridge structure connected in parallel are connected with high voltage direct current Bus capacitor C3.

In order to further illustrate the beneficial effects of the present invention, a comparative test was carried out. The high-frequency transformer core material used in the experiment was nanocrystal, rated working frequency was 20 kHz, transformer ratio was 1:6, weight: 425 g, size: core width 29.mm, the outer diameter is 92.1mm, and the ring is 34.5mm wide.

As shown in Figure 3, when the isolated DC/DC converter performs fast closed-loop modulation, the transformer primary voltage is suddenly reduced from 45% to 5%, and the transformer current is suddenly biased to one side so that the core is biased. The magnetic working state, for the high-frequency transformer, working near the saturation point of the magnetic core will make the magnetic collecting inductance of the transformer rapidly become small, which will easily lead to the indirect straight-through of the bridge arm of the primary side and burn the switch tube.

As shown in FIG. 4, with the control method of the present invention, the duty ratio in a control cycle is only allowed to vary by 10%, and the duty ratio in the figure is changed from 45% to 35% at 0.016s, and it can be found that the transformer current can be compared. Quickly return to equilibrium without dynamic bias problems.

The above is only a preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily think of changes or within the technical scope disclosed by the present invention. Alternatives are intended to be covered by the scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

A circuit structure for suppressing dynamic biasing of a high-frequency isolated full-bridge circuit, characterized in that it is composed of an interleaved parallel BuckBoost circuit and a high-frequency isolated bidirectional full-bridge DC/DC converter circuit; wherein the interleaved parallel BuckBoost circuit includes a capacitor C1 And C2, inductors L1 and L2, switch tubes S1 to S4, diodes D1 to D4; the high-frequency isolated bidirectional full-bridge DC/DC converter circuit is connected to the primary end of the high-frequency transformer T1 to form a self-contained structure of the bridge structure The diodes are connected to the switch tubes Sa1 to Sa4, the secondary ends are connected to the bridge-type switch tubes Sb1 to Sb4 with the inverted diodes, and the high-voltage DC bus capacitors are connected in parallel between the upper and lower arms of the bridge structure connected to the secondary ends. C3.
The circuit structure according to claim 1, wherein one end of the capacitor C1 in the interleaved BuckBoost circuit is connected to one end of the inductors L1 and L2, and the other end of the inductor L1 is connected to the source of the switch S2 and the switch. The drain of S4 is connected, the source of S4 is connected to one end of capacitor C2, the other end of inductor L2 is connected to the source of switch S1 and the drain of switch S3, and the source of switch S3 is connected to one end of capacitor C2. The other end of the capacitor C1 is connected to the drain of the switch S1, the drain of the switch S2, and the other end of the capacitor C2. The capacitor C2 is connected in parallel with the upper and lower arms of the bridge structure connected to the primary end of the high-frequency transformer T1.
A control method for suppressing dynamic biasing of a high-frequency isolated full-bridge circuit, characterized in that it comprises:

Step 1. When starting the high-frequency isolated bidirectional full-bridge DC/DC converter circuit, the magnetic resonance of the high-frequency transformer T1 is performed by using a fixed 2% small duty-cycle open-loop method, so that the residual magnetism tends to zero;

Step 2: continuously sampling the current signal of the high-frequency transformer T1 and performing time integration on the same, thereby avoiding the steady-state biasing caused by the time integral effect caused by the small volt-second product imbalance in the forward and reverse directions in the switching period;

Step 3. When the rate of change of the current command of the converter circuit is less than the dynamic bias threshold of the high frequency transformer, the high frequency isolated bidirectional full-bridge DC/DC converter circuit operates in a current closed loop state, and the staggered parallel The BuckBoost circuit operates in a 50% duty cycle open-loop operating state and achieves a minimum current ripple output;

Step 4: When the rate of change of the current command of the converter circuit is greater than or equal to the dynamic bias threshold of the high frequency transformer, the high frequency isolated bidirectional full-bridge DC/DC converter circuit maintains open loop operation under the current duty cycle, and is interleaved The parallel BuckBoost circuit operates in a fast closed-loop state of the current, thereby rapidly changing the output power of the converter circuit.