Two-link converter with galvanic isolation

Abstract

This utility model pertains to electrical engineering, specifically to step-up converter devices incorporated into backup power supply devices for high-voltage loads obtained from a low-voltage battery. The converter is designed for highly efficient conversion of energy obtained from a low-voltage source, such as a battery, into a high, stabilized voltage for powering high-voltage loads, such as inverters or loads capable of being supplied with constant voltage. The technical result of this utility model is an increase in the efficiency of the output voltage while minimizing switching losses through soft switching and operation with low currents; increased reliability; and an expansion of the device's scope of application. This technical result is achieved through a combination of essential features.The essence of the utility model is that a two-link converter with galvanic isolation is connected to a primary source (1) and to an unregulated push-pull resonant step-up converter (2) connected to a control circuit (3) configured to form symmetrical current pulses alternately flowing from a common wire to a source through its half-winding of a transformer TR1 with a frequency set by the control circuit (3), wherein the unregulated push-pull resonant step-up converter (2) is connected to a step-up stabilized converter (4) connected to a control circuit (5) configured to convert a low, unstabilized input voltage at the terminals of the primary source (1) into a stabilized high voltage at the load (6).

Description

[0001] This utility model pertains to electrical engineering, specifically to step-up converter devices used in backup power supply systems for high-voltage loads, supplied by a low-voltage battery. The converter is designed for highly efficient conversion of energy from a low-voltage source, such as a battery, into a high, stabilized voltage for powering high-voltage loads, such as inverters or DC-powered loads.

[0002] When developing uninterruptible and backup power supply devices for various types of loads, the problem of converting low, unregulated DC voltage (with nominal values ​​of approximately 12-24 volts) (usually from a battery) into a stabilized high DC voltage (with nominal values ​​of approximately 200-400 volts) at a power of 100-300 watts often arises. This voltage is then used either to directly power the target load or to generate an alternating voltage of a specified waveform for powering various types of corresponding loads. One of the challenges encountered when implementing a device for such conversion is efficiency. During the process of converting low voltage to high voltage, relatively large currents circulate in the primary circuit, causing energy losses in the conductors, windings, and switching elements.In traditional circuits, conversion is performed in hard switching mode, resulting in switching losses on the switching elements, with these losses being the dominant factor. The efficiency of such devices, with an input voltage of 12 volts, is typically 75-82%. In addition to energy loss as heat, the challenge of dissipating this heat via massive heatsinks and forced cooling increases cost and reduces reliability. To address this low efficiency, an unregulated converter with soft switching was designed, supplemented by an output voltage stabilization circuit. This solution significantly increased the system's efficiency.

[0003] It's well known that when a step-up converter is operating, the current in the primary circuit is greater than the current in the secondary circuit, proportional to the conversion ratio. Moreover, the greater the current, the greater the losses at all system components—switches, conductors, fuses, and connectors. Of particular interest are the losses at the converter switches. While losses at all other components are caused by the ohmic resistance of the conductors and contacts, losses at the switches consist of two components:

[0004] Ptot = Pr + Pd,

[0005] where:

[0006] Ptot - total power loss on the key,

[0007] Pr - power loss on the open channel resistance of the key,

[0008] Pd - switching loss power.

[0009] Conventional converter circuits are typically based on high-frequency converters with hard switching of the switching keys. This type of converter can incur significant losses—approximately 10-15%—due to the Pd value. The circuit design of such converters has a single-link structure, provides output voltage boosting and stabilization with a single circuit element, and contains a relatively small number of components. However, the hard switching mode causes significant heat generation in the keys due to the useful energy stored in the low-voltage battery. Furthermore, this energy must be used to operate the fan cooling system, which, in addition to power consumption, is a consumable resource and requires periodic maintenance and replacement.

[0010] The technical result of the claimed utility model is to increase the efficiency of the output voltage while minimizing switching losses through soft switching and operation with low currents; increase reliability; and expand the device's scope of application. This technical result is achieved through a combination of essential features.

[0011] The essence of the utility model is that a two-link converter with galvanic isolation is connected to a primary source (1) and to an unregulated push-pull resonant step-up converter (2) connected to a control circuit (3) configured to form symmetrical current pulses alternately flowing from a common wire to a source through its half-winding of a transformer TR1 with a frequency set by the control circuit (3), wherein the unregulated push-pull resonant step-up converter (2) is connected to a step-up stabilized converter (4) connected to a control circuit (5) configured to convert a low unstabilized input voltage at the terminals of the primary source (1) into a stabilized high voltage at the load (6).

[0012] The utility model is explained graphically, where Fig. 1 schematically shows a generalized circuit diagram of the converter:

[0013] 1 - primary source;

[0014] 2 - Unregulated push-pull resonant step-up converter;

[0015] 3 - control circuit;

[0016] 4 - step-up stabilized converter;

[0017] 5 - control circuit;

[0018] 6 - ​​load.

[0019] The generalized circuit diagram of the claimed converter is shown in Fig. 1. The converter receives power from the primary source 1 from the input terminals U1, U2. From these terminals, voltage is supplied to the first element - an unregulated push-pull resonant step-up converter 2, implemented on the keys - transistors VT2 and VT3, transformer TR1, resonant capacitor C1 and rectifier VD1, VD2, VD3, VD4. The unregulated push-pull resonant step-up converter 2 operates under the control of the control circuit 3, which alternately opens the keys VT2 and VT3, forming symmetrical current pulses, alternately flowing from the common wire to the source through its half-winding of the transformer TR1 with a frequency f set by the control circuit 3. The pulse duty cycle is selected equal to d = 0.45. This duty cycle provides a pause between current pulses to eliminate the condition where both keys could be open, which is an emergency mode for this circuit.The flow of current pulses results in the appearance of an alternating voltage with a frequency f and an elevated voltage level on the secondary winding of the transformer. This voltage level is determined by the ratio of the turns of the half-winding to the secondary winding of the transformer. The circuit exploits the fact that transformer TR1 has leakage inductance—a parasitic parameter usually a design flaw. However, using capacitor C1, it is possible to create a series oscillatory circuit whose frequency is equal to the switching frequency f. This circuit enables ZVC (zero current commutation) mode for switches VT2, VT3, and the rectifier diodes. Switching near zero current dramatically reduces switching losses on the switches due to the power approaching zero at the moment of switching from the off-state to the on-state and vice versa.Thus, the losses in the switches are essentially determined by their on-state ohmic resistance, which is reduced to a few milliohms in modern switching transistors. The output voltage of the first element is thus generated on capacitor C2. This voltage is selected so that, at maximum input voltage, it does not exceed the target voltage at the load. The next element is step-up stabilized converter 4, implemented using transistor VT1, inductor L1, diode VD6, and capacitor C5. Step-up stabilized converter 4 operates under the control of control circuit 5. Control circuit 5 generates current pulses through inductor L1. After the switch closes, the inductor releases the energy stored in it to capacitor C5 via diode VD6.This voltage can be significantly higher than the input voltage taken from capacitor C2 and is determined by the pulse duty cycle 0 <d1<0,9, формируемого схемой управления 5 исходя из текущей нагрузки, текущего входного напряжения и целевого выходного напряжения. Схема управления 5 поддерживает целевой уровень напряжения на нагрузке и таким образом, в совокупности, из низкого нестабилизированного входного напряжения на клеммах U1, U2получается стабилизированное высокое на нагрузке 6. Таким образом, заявленное решение состоит из двух преобразователей 2 и 4, один из которых работает в режиме мягкого переключения на большом токе и обладает высоким коэффициентом преобразования, а другой работает в обычном режиме жесткого переключения, но работает с малым коэффициентом преобразования на малом токе при высоком напряжении (схема показана на фиг. 2).In this solution, converter 2 operates in soft-switching mode and provides an increased, unregulated output voltage, which is below the required level when battery 1 is fully charged. The second converter, 4, is a standard step-up converter and provides a stabilized output voltage at the required level. The proposed design topology increased the converter's efficiency from 85% to 93% with an input voltage of 12 VDC, an output voltage of 380 VDC, and a power output of 250 watts. Furthermore, the new converter did not require forced cooling. This proposed solution is promising for use in backup power supply systems that use a battery with a nominal voltage of 12 or 24 volts as the primary power source.

[0020] Based on the above, a converter layout was made with the following parameters:

[0021] Input voltage 10.5-13.5 VDC Output voltage 385 VDC The load power is constant 200 W Load power short-term 300 W* Efficiency not less than 94% at 200 watts

[0022] * tested for a few seconds in developer bench testing.

[0023] The resulting converter boasts an efficiency exceeding the typical 80-82% under these conditions. This reduces overall heat dissipation and conserves energy from the primary source, typically the battery. The prototype was tested and confirmed to be functional. During testing, weak points in the design were noted—the conductive paths and primary circuit fuse became very hot. When using the circuit in a real product, it is necessary to increase the power of these components to reduce their active resistance. One of the clear advantages is the lack of forced ventilation for this implementation. This circuit design can be used in devices requiring battery power at grid-level voltages, for example, when upgrading devices such as the Teplocom-300 or 250-350 VDC uninterruptible power supplies for POE switches.For loads of 50-250 watts, the circuit design of the prototype can be used directly. In the future, this circuit could be used to build higher-power converters with higher input voltage ratings (24; 36; 48 VDC). Furthermore, it becomes possible to design the input converter switches as SMD components. If necessary, the switches can be connected in parallel. A disadvantage of this converter design is the need to individually adjust the resonant conversion frequency.

[0024] The declared solution has several advantages: 1. High efficiency: increase from 85% to 93% at an input voltage of 12 VDC, an output voltage of 380 VDC and a power of 250 W; 2. No forced cooling: no fan cooling required; 3. Reduced heat dissipation: reduced requirements for heat dissipation; 4. Energy saving: saving the energy of the primary source (battery); 5. Increased reliability: due to reduced thermal load; 6. Possibility of using SMD components: the keys of the input converter can be made as SMD components; 7. Scalability: the ability to connect the keys in parallel if necessary.

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