Isolated inverter system optimized for dynamic load conditions

Abstract

The present invention relates to an isolated inverter system optimized for dynamic load conditions. In order to prevent an abnormal phenomenon from occurring in the inverter system depending on load characteristics of an electric motor or the like, in a converter comprising a PWM IC chip, a switching element, a high-frequency transformer, and a photocoupler, the high-frequency transformer outputs a direct current voltage (Vout) through a secondary rectification stage and a smoothing operation of a capacitor, a feedback path is set such that a signal extracted from the direct current voltage (Vout) is applied to the PWM IC chip through the photocoupler, and a smoothing circuit for refining the extracted signal is added to the feedback path. According to the present invention, an inverter system having a structure in which an inverter is connected to an isolated DC-DC converter can be safely operated even under dynamic load conditions, and the risk of electric shock can be greatly reduced even if there is body contact with an output system of the inverter system.

Description

Isolated inverter system optimized for dynamic load conditions

[0001] The present invention relates to an isolated inverter system optimized for dynamic load conditions, and more specifically, to an isolated inverter system optimized for dynamic load conditions that can eliminate abnormal phenomena such as vibration or noise even in environments where load conditions change rapidly by improving the transmission path of a feedback signal for pulse width modulation (PWM) control provided in an isolated DC-DC converter to prevent abnormal phenomena from occurring depending on the load characteristics, such as a motor driven through the inverter system, and can reduce damage or malfunction of switching elements while eliminating the risk of electric shock in the power system applied to the load.

[0002] Inverter systems, representative of power conversion, are used to support smooth acceleration and deceleration when starting or stopping loads such as electric motors by regulating voltage and frequency. For this reason, inverter systems are widely applied in motor-based factory facilities, home appliances, and electric vehicles, and recently, their scope of application is expanding as an essential technology for realizing smart grids for new and renewable energy.

[0003] Among them, it is known that more than 60% of total power consumption is used to drive electric motors for industrial, office, and residential electrical devices, and most of these motors utilize inverter systems for smooth acceleration and deceleration control.

[0004] FIG. 1 shows a power system diagram for driving a general electric motor. In FIG. 1, an inverter system (100) is placed between an input power source and a load (200) to increase power efficiency and to easily control the rotation of the load motor. The inverter system (100) is configured to include a converter (110) that converts alternating current (AC) into direct current (DC) and an inverter (120) that converts direct current (DC) back into alternating current (AC). The converter (110) is designed to have voltage conversion as its main function, and the inverter (120) is designed to have frequency conversion as its main function.

[0005] Accordingly, the inverter system (100) evaluates designing the input converter (110) and the output inverter (120) to be connected in an optimal state as an important technical element. This is because, due to the rapid switching operation of the inverter system (100), the current flow inevitably flows in a spike-like manner, which can impair the stable operation of the converter (110) and cause damage (open or short circuit) to the semiconductor switching device, thereby providing a cause for operational errors and frequent failures of the inverter system.

[0006] For this reason, in fields such as electric vehicles, home appliances, factory automation, and wind power generation, the requirements for high quality, high performance, and high reliability of the output of the inverter system (100) are becoming increasingly stringent. In order to meet these requirements, research is currently being actively conducted to overcome problems such as malfunction of the inverter system (100) or damage to the switching element by eliminating or suppressing abnormal voltages included in the DC output of the converter (110).

[0007] Representative examples include Patent No. 10-1070540 (Prior Patent 1), which proposes a special type of pulse width modulation (PWM) method to reduce current stress on a switching element in order to prevent problems such as switching noise, overheating, mechanical vibration, and electromagnetic interference caused by harmonics included in the pulse pattern for driving the switching element; Patent No. 10-0999244 (Prior Patent 2), which discloses a technology designed to control the pulse width of a PWM module through a control signal generated based on an error calculated between the converter input current value and the user's command current value to eliminate the influence of low-frequency ripple components that inevitably occur due to the structural characteristics of the inverter circuit; and Patent No. 10-1235183 (Prior Patent 3), which discloses a technology to prevent the accumulation of fatigue in the element by preventing abnormal operation of the inverter system caused by harmonics or ripple components resulting from a failure of the switching element equipped in the converter.

[0008] However, although the above-mentioned conventional technologies have the effect of reducing the influence of harmonics or ripple to some extent, they were difficult to effectively deal with abnormal phenomena in the inverter system caused by sudden fluctuations in load, and they had a practical problem in that such abnormal output phenomena were carried in the feedback signal and had an adverse effect on the normal operation of the PWM module equipped in the converter (110).

[0009] [Prior Art Literature]

[0010] [Patent Literature]

[0011] Korean Registered Patent No. 10-1070540

[0012] Korean Registered Patent No. 10-0999244

[0013] Korean Registered Patent No. 10-1235183

[0014] The present invention is proposed to overcome the problems of the prior art described above. The objective of the present invention is to provide an inverter system that can operate efficiently and stably even when the converter output fluctuates rapidly under dynamic load conditions by utilizing an isolated DC-DC converter to reduce the risk of electric shock and by adding a smoothing circuit to the feedback signal system applied to the pulse width modulation circuit (PWM IC) of the converter.

[0015] An inverter system optimized for dynamic load conditions according to a preferred embodiment of the present invention is based on a structure in which an inverter for DC-AC conversion is combined with an isolated DC-DC converter, wherein the converter is designed based on a PWM IC chip, a switching element, a high-frequency transformer, and a photocoupler, wherein the output of the high-frequency transformer is configured to output a DC voltage (Vout) through a rectification stage and a smoothing action of a capacitor, and a feedback path is established so that a feedback signal extracted from the DC voltage (Vout) is applied to the PWM IC chip through the photocoupler, and a smoothing circuit for refining the DC voltage (Vout) is added to the driving circuit of the photocoupler included in the feedback path, and wherein the DC voltage (Vout) is configured to be applied to the inverter.

[0016] In addition, the smoothing circuit adopted in the present invention is provided with the function of purifying the DC component of the feedback signal extracted from the output voltage (Vout) of the converter, and the arrangement method of the smoothing circuit is characterized as being one of the methods of adding it to the light-emitting circuit or the light-receiving circuit of the photocoupler, or to both the light-emitting circuit and the light-receiving circuit.

[0017] In addition, the inverter system of the present invention is characterized by being designed to reduce the risk of electric shock caused by physical contact in the power system supplying power to the load through the inverter system by utilizing a high-frequency transformer and a photocoupler to separate the closed circuit of the input terminal and the closed circuit of the output terminal.

[0018] In addition, the smoothing circuit adopted in the present invention is characterized by being designed to support the generation of a feedback signal of a refined DC component by excluding the influence of spike currents caused by rapid changes in the load.

[0019] In addition, the inverter system of the present invention is characterized by having an EMI filter additionally added to the input side of the converter and the output side of the inverter as a countermeasure against various noise signals.

[0020] In addition, the smoothing circuit adopted in the present invention is configured using a diode, a resistor, and a capacitor, wherein the diode is provided with a buffering function to support the slow charging of the capacitor by the fluctuating output voltage, the resistor is provided with a voltage divider function for the output (Vout) to extract an appropriate feedback signal, and the capacitor is provided with a bypass function for high-frequency components included in the output voltage (Vout), thereby enabling the circuit to support the output voltage (Vout), controlled through the feedback signal, not to fall below a lower limit value specified in the design.

[0021] According to the configuration of the present invention, an inverter system having a structure in which an inverter is connected to an isolated DC-DC converter can be operated in a safe state, and even under dynamic load conditions where the acceleration and deceleration of the motor change rapidly, damage to the semiconductor device equipped in the converter can be prevented, and the occurrence of abnormal phenomena such as vibration or noise can be significantly reduced.

[0022] In addition, since the present invention adopts an isolated DC-DC converter, the risk of electric shock accidents can be expected to be significantly reduced even when physical contact occurs with the output system of the inverter system.

[0023] Figure 1 is a power system diagram for driving a general electric motor.

[0024] FIG. 2 is a block diagram illustrating an inverter system using a conventional isolated DC-DC converter circuit.

[0025] FIG. 3 is a block diagram illustrating the circuit configuration of an isolated DC-DC converter adopted in the present invention.

[0026] FIG. 4 is an illustrative diagram explaining the basic structure of a smoothing circuit added to the feedback path of the present invention.

[0027] Hereinafter, the isolated inverter system optimized for dynamic load conditions according to the present invention will be described in detail with reference to the attached drawings.

[0028] For reference, it should be noted that in describing the present invention, detailed descriptions of known configurations or functions are omitted if it is determined that such detailed descriptions may unnecessarily obscure the essence of the invention. It should also be noted that the technical terms used in the present invention are used merely to describe preferred embodiments, and are not intended to exclude the equivalent scope of the invention by limiting it to such terms.

[0029] FIG. 2 is a block diagram for explaining an inverter system (100) to which a conventional isolated PWM type DC-DC converter circuit is applied. The inverter system (100) of FIG. 2 shows a configuration including a converter (110) that converts AC input power into DC and an inverter (120) that generates AC commercial power based on the DC output of the converter (110).

[0030] Here, the converter (110) is configured based on a PWM IC chip (111), a switching unit (112), a high-frequency transformer (113), and a photocoupler (115), and the inverter (120) is structured to include a driver circuit, a switching unit, and a waveform shaping circuit. Additionally, an EMI filter (Electro Magnetic Interference Filter) is added to the input side of the converter (110) and the output side of the inverter (120) as a means to respond to various noise signals.

[0031] Meanwhile, the isolated DC-DC converter (110) of FIG. 2 has its input and output terminals separated through a high-frequency transformer (113) and a photocoupler (115) to form independent circuits. Because of this, the inverter system (100) of FIG. 2 operates with the closed circuit of the input terminal and the closed circuit of the output terminal separated, so the risk of electric shock due to physical contact in the commercial power output system of the inverter system (100) can be significantly reduced.

[0032] Looking at the operation process of the inverter system (100) shown in FIG. 2, the function of the converter (110) is to first rectify the AC input power to convert it into DC, and then apply it to the switching unit (112) after performing power factor correction (PFC) on the primary DC output. The pulse voltage generated in the switching unit (112) is output as a step-up voltage via a high-frequency transformer (113), and the step-up voltage is then output as a DC voltage after undergoing secondary rectification. At this time, the DC output voltage (Vout) is applied to the inverter (120) driver circuit in a state where it has been smoothed to some extent through the smoothing action of the capacitor (114).

[0033] And the converter (110) of FIG. 2 controls the DC output voltage (Vout) with a feedback signal so that the set target value is maintained constant. The feedback signal is transmitted to a PWM IC chip (111) to support a function that enables the variable duty cycle. At this time, the DC output voltage (Vout) of the converter (110) is designed to vary within the range of 310 to 600 V through the control of the duty cycle so that it can draw the rated output of 220 V of the inverter system (100).

[0034] What the inventors here focus on is whether a load (200), such as a motor, can be stably driven without any particular problems through an inverter system (100) in which an inverter (120) is connected to an isolated DC-DC converter (110).

[0035] Currently, most general inverter systems (100) are designed to directly connect an inverter (120) to a non-isolated converter. However, since the input and output terminals of the inverter system (100) are non-isolated, there is a disadvantage that there is always a risk of fatal electric shock if physical contact occurs with the output terminal. For this reason, research is actively being conducted to implement an inverter system (100) in which the inverter (120) is connected to an isolated DC-DC converter (110), thereby reducing the risk of electric shock while maintaining stable power conversion functions.

[0036] However, although the inverter system (100) with a structure in which an inverter (120) is connected to an isolated DC-DC converter (110) does not have any particular problems in a no-load state, when driving a load, the switching element of the isolated DC-DC converter (110) is destroyed or abnormal operation such as vibration and noise generation occurs due to the influence of spike-like current changes caused by the rapid change of the load, and this problem remains an unresolved issue. Furthermore, because the method of raising and lowering the output voltage (Vout) of the converter (110) using a conventional transformer consumes power even in a no-load state and fails to meet user requirements due to noise generation and excessive weight, the commercialization and creation of market demand for an inverter system (100) that operates safely by applying an isolated DC-DC converter (110) is still lagging.

[0037] Accordingly, the inventors recognized the above-mentioned practical problem and challenged themselves to develop an inverter system that could maintain its inherent performance while reducing the risk of electric shock. After experiencing countless trials and errors and failures and conducting repeated experiments, they discovered the cause of the problem in the feedback circuit of the isolated DC-DC converter (110), which was an unexpected area. They confirmed that it is possible to implement an inverter system that does not cause the destruction of the switching element of the isolated DC-DC converter (110) or generate vibration and noise, simply by improving the feedback circuit, thereby completing the present invention.

[0038] FIG. 3 shows the circuit configuration of an isolated DC-DC converter (110) adopted in the present invention. The present invention is based on the premise that the inverter (120) at the output end of a conventional inverter system (100) uses the conventional technology as is, and the structure of the isolated DC-DC converter (100) located at the input end is modified.

[0039] Under such a premise, FIG. 3 shows the structure of a converter (110) modified in the present invention. The converter (110) of the present invention is based on the conventional isolated DC-DC converter model exemplified in FIG. 2, but is characterized by being configured by selectively adding smoothing circuits (116, 117) to the feedback circuit (115) for PWM control. Here, the expression "selectively" implies that, based on the feedback circuit using a photocoupler, a smoothing circuit can be added to either the light-emitting circuit or the light-receiving circuit of the photocoupler (115), or to both.

[0040] The reason the inventors proposed the converter (110) structure illustrated in FIG. 3 is that they challenged the unresolved problem of the inverter system (100) manufactured by connecting an inverter (120) to an isolated DC-DC converter (110), namely, the problem of device damage or vibration and noise generation in the PWM IC chip (111) and switching unit (112) under dynamic load conditions, and discovered the cause in the feedback path, which is an unexpected area, and confirmed through repeated experiments that the problem can be solved with only a simple improvement of the feedback circuit.

[0041] FIG. 4 is an illustrative diagram for explaining a smoothing circuit added to a feedback path as a preferred embodiment of the present invention. The circuit of FIG. 4 shows a configuration in which a smoothing circuit (116) is added to a circuit (Block 1, Block 2) that supports driving the light-emitting part of a conventional photocoupler (115).

[0042] As shown in the circuit of FIG. 4, in the past, the feedback signal was extracted directly from the output (Vout) of the converter (110), but the present invention is configured to extract it via a smoothing circuit. At this time, the smoothing circuit (116) presented as a preferred embodiment of the present invention is designed so that the feedback signal, which has had spike voltages or high-frequency components removed from the output (Vout) of the converter (110), is applied to the photocoupler (115) through a circuit configuration that includes two diodes, two resistors, and two capacitors, as shown in FIG. 4.

[0043] At this time, a smoothing circuit is configured such that the diode is provided with a buffering function to support the fluctuating output voltage slowly charging the capacitor, the resistor is provided with a voltage divider function for the output (Vout) to extract an appropriate feedback signal, and the capacitor is provided with a bypass function for high-frequency components included in the output voltage (Vout) along with a unique charging function, so that the feedback signal refined into a flat DC component is applied to the PWM IC chip (111) to control the output voltage (Vout) so that it does not fall below the lower limit value specified in the design. For example, if the rated output of the inverter system (100) is designed to be 220V, the output voltage (Vout) needs to be maintained within a range from a lower limit value of 310V to an upper limit value of 600V, and the feedback signal extracted through the smoothing circuit (116 or 117) will control the output voltage (Vout) so that it does not fall below the lower limit value of 310V.

[0044] In this way, by adding a smoothing circuit (116, 117) to the feedback circuit of the converter (110), safe control of the PWM IC chip (111) is possible through a feedback signal of a refined DC component, so that damage to the switching element or operational errors can be reduced even in situations of sudden load fluctuations, and abnormal phenomena such as noise or vibration generation can be significantly reduced, as confirmed through repeated experiments.

[0045] Here, the smoothing circuit (116) of FIG. 4 is merely an example, and if it can satisfy the requirements of the user and extract a feedback signal of a refined DC component, the detailed structure of the smoothing circuit can be changed as much as possible.

[0046] On the other hand, even when the feedback signal is extracted directly from the output (Vout) of the converter (110), it is possible to apply a feedback signal of a refined DC component to the PWM IC chip (111) by adding a smoothing circuit (117) to the light-receiving circuit of the photocoupler (115). Even if the manufacturing cost is borne, if smoothing circuits (116, 117) are added to both the light-emitting and light-receiving parts of the photocoupler (115), it will be possible to provide a more stable and refined feedback signal of a DC component to the PWM IC chip (111). As such, changing the arrangement structure of the smoothing circuit (117) is a matter of simple choice, and the scope of the present invention should be considered to encompass all such changes in arrangement structure.

[0047] According to the configuration of the present invention described so far, an inverter system (100) having a structure in which an inverter (120) is connected to an isolated DC-DC converter (110) can be operated in a safe state even under dynamic load conditions, and damage to the semiconductor device provided in the converter (110) can be prevented even in situations where the acceleration and deceleration of the motor changes rapidly, and an effect of reducing abnormal phenomena such as vibration or noise generation can be expected.

[0048] In addition, since the present invention adopts an isolated DC-DC converter (110), it has the effect of significantly reducing the risk of electric shock accidents even when physical contact occurs with the output system of the inverter system (100).

[0049] Although preferred embodiments of the present invention have been described above, the present invention is not limited to the above description, and anyone skilled in the art can make various modifications within the scope of the invention without departing from its essence.

[0050] [Explanation of the symbol]

[0051] 100: Inverter system 110: Converter

[0052] 120 : Inverter 200 : Load

[0053] 111: PWM IC chip 112: Switching section

[0054] 113: High-frequency transformer 114: Capacitor

[0055] 115: Photocoupler 116, 117: Smoothing circuit

Claims

1. An isolated inverter system (100) optimized for dynamic load conditions, comprising a structure in which an isolated DC-DC converter (110) is combined with an DC-AC converter inverter (120), The above converter (110) is designed to include a PWM IC chip (111), a switching element (112), a high-frequency transformer (113), and a photocoupler (115), The output of the above high-frequency transformer (113) is configured to output a DC voltage (Vout) through a rectification step and a smoothing action of a capacitor (114), and A feedback path is established so that the feedback signal extracted from the above DC voltage (Vout) is applied to the PWM IC chip (111) through the above photocoupler (115), and An isolated inverter system optimized for dynamic load conditions, characterized in that a driving circuit of the photocoupler (115) included in the feedback path includes a smoothing circuit (116, 117) for refining the DC voltage (Vout), and the smoothing circuit (116, 117) is composed of a diode, a resistor, and a capacitor, wherein the diode is provided with a buffering function to support the fluctuating output voltage slowly charging the capacitor, the resistor is provided with a voltage divider function for the output voltage (Vout) to extract an appropriate feedback signal, and the capacitor is provided with a unique charging function along with a bypass function for high-frequency components included in the output voltage (Vout), thereby supporting the output voltage (Vout) controlled through the feedback signal not to fall below a lower limit value in the design, and the driver circuit of the inverter (120) is configured to apply the output voltage (Vout) of the converter (110).

2. In Paragraph 1, An isolated inverter system optimized for dynamic load conditions, characterized in that a smoothing circuit for refining the DC component of a feedback signal extracted from the above DC voltage (Vout) is added to the light receiving or light emitting part driving circuit of the above photocoupler (115).

3. In Paragraph 1, An isolated inverter system optimized for dynamic load conditions, characterized in that a smoothing circuit for refining the DC component of a feedback signal extracted from the above DC voltage (Vout) is added to both the light-emitting part and the light-receiving part driving circuit of the above photocoupler (115).

4. In Paragraph 1, The above inverter system (100) is an isolated inverter system optimized for dynamic load conditions, characterized by being designed to reduce the risk of electric shock in the output system of the inverter system (100) by separating the closed circuit of the input terminal and the closed circuit of the output terminal through the high-frequency transformer (113) and the photocoupler (115).

5. In Paragraph 1, The above smoothing circuit (116, 117) is characterized by supporting the feedback signal to have a refined DC component by excluding the influence of spike current caused by rapid change of load, in an isolated inverter system optimized for dynamic load conditions.

6. In Paragraph 1, An isolated inverter system optimized for dynamic load conditions, characterized in that an EMI filter is further added to the input terminal of the converter (110) and the output terminal of the inverter (120) as a countermeasure against various noise signals.

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