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KR-20260067029-A - APPARATUS AND METHOD FOR CONTROLLING AC/DC SOLID-STATE TRANSFORMER

KR20260067029AKR 20260067029 AKR20260067029 AKR 20260067029AKR-20260067029-A

Abstract

The present invention relates to an AC/DC semiconductor transformer control device and method, wherein the AC/DC semiconductor transformer control device comprises a voltage acquisition unit for acquiring a DC side voltage from a semiconductor transformer including a DC/DC converter, and a DC/DC converter control unit for generating an average power command for controlling the average value of the DC side voltage based on the DC side voltage, generating a pulsating power command for controlling the pulsating value of the DC side voltage, and generating a control signal for the DC/DC converter based on the average power command and the pulsating power command, wherein in a situation where the AC voltage applied to the semiconductor transformer exceeds a reference value, the average value of the DC side voltage increases and the pulsating value of the DC side voltage decreases, and the average power command and the pulsating power command are generated in such a way that the average value of the DC side voltage increases and the pulsating value of the DC side voltage decreases.

Inventors

  • 김성민
  • 김동욱

Assignees

  • 한양대학교 에리카산학협력단

Dates

Publication Date
20260512
Application Date
20241105

Claims (8)

  1. A voltage acquisition unit for acquiring a DC side voltage from a semiconductor transformer including a DC/DC converter; and A DC/DC converter control unit that generates an average power command to adjust the average value of the DC link voltage based on the DC link voltage, generates a pulsating power command to adjust the pulsating value of the DC link voltage, and generates a control signal for the DC/DC converter based on the average power command and the pulsating power command; An AC/DC semiconductor transformer control device that generates the average power command and the pulsating power command such that, in a situation where the AC voltage applied to the semiconductor transformer exceeds a reference value, the average value of the DC link voltage increases and the pulsating value of the DC link voltage decreases.
  2. In paragraph 1, The above DC/DC converter control unit is, AC/DC semiconductor transformer control device that controls the average value of the DC link voltage to increase when the system voltage increases above the rated voltage, and generates an average power command such that the average value of the DC link voltage increases linearly with a slope greater than the slope of the increase of the average value of the DC link voltage when the AC voltage applied to the semiconductor transformer exceeds a reference value.
  3. In paragraph 2, The above DC/DC converter control unit is, AC/DC semiconductor transformer control device that obtains a system voltage at least at one point in time from the above voltage acquisition unit, and obtains a DC link voltage average value command signal corresponding to the system voltage based on the above system voltage, wherein the average voltage corresponding to the system voltage is detected using a predetermined function or graph defined differently for each of the normal situation, the above voltage rise situation, and the above reference exceedance situation, thereby obtaining the DC link voltage average value command signal.
  4. In paragraph 3, The above DC/DC converter control unit is, AC/DC semiconductor transformer control device that passes the DC link voltage through a notch filter to extract a DC component from the DC link voltage and obtain an average voltage value, subtracts the DC link voltage average value command signal from the average voltage value to obtain a combination result, and inputs the combination result into a function for PI control to generate an average power command.
  5. In paragraph 1, The above DC/DC converter control unit is, AC/DC semiconductor transformer control device for generating a pulsating power command to control the pulsating value of the DC link voltage using a linear function between the absolute value and the pulsating value of the system voltage.
  6. In paragraph 1, The above DC/DC converter control unit is, Obtain the pulsation value of the DC link voltage corresponding to the above DC link voltage, and Calculate the proportionality constant, wherein the proportionality constant is given as the ratio of the DC link pulsation voltage to the output link pulsation voltage, and The output terminal voltage is obtained from the above voltage acquisition unit, and a pulsation value for the above output terminal voltage is obtained, AC/DC semiconductor transformer control device that subtracts the pulsation value of the DC terminal voltage from the result of multiplying the proportionality constant and the pulsation value for the output terminal voltage.
  7. In paragraph 6, The above DC/DC converter control unit is, AC/DC semiconductor transformer control device that obtains the pulsating power command using a predetermined transfer function based on the result of subtracting the pulsating value of the DC terminal voltage from the result of multiplying the proportionality constant and the pulsating value for the output terminal voltage.
  8. A step of obtaining a DC side voltage from a semiconductor transformer including a DC/DC converter; A step of generating an average power command for adjusting the average value of the DC link voltage and a pulsating power command for adjusting the pulsating value of the DC link voltage based on the above DC link voltage; and The method includes the step of generating a control signal for the DC/DC converter based on the above average power command and the above pulsating power command; The step of generating an average power command for adjusting the average value of the DC link voltage and a pulsating power command for adjusting the pulsating value of the DC link voltage from the above DC link voltage is: A method for controlling an AC/DC semiconductor transformer, comprising the step of generating the average power command and the pulsating power command such that, in a situation where the AC voltage applied to the semiconductor transformer exceeds a reference value, the average value of the DC link voltage increases and the pulsating value of the DC link voltage decreases.

Description

Apparatus and Method for Controlling AC/DC Solid-State Transformer This invention relates to an AC/DC semiconductor transformer control device and a control method for an AC/DC semiconductor transformer. A semiconductor transformer is a device designed to perform power conversion using semiconductor elements. It utilizes high-speed switching power semiconductor devices (e.g., Insulated Gate Bipolar Transistors (IGBTs) or Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs)) to convert alternating current (AC) to direct current (DC) or vice versa. Since semiconductor transformers perform power conversion using semiconductor elements, they offer advantages such as miniaturization and weight reduction, low heat loss, and the ability to be easily applied to various voltages and frequencies through precise control. In particular, the adoption of semiconductor transformers has been steadily increasing recently due to the growing use of renewable energy, the development of smart grids, and the introduction of electric vehicle charging systems. Semiconductor transformers connected to a single-phase AC system may include an AC/DC converter and a DC/DC converter electrically connected to the AC/DC converter; it is common for the AC/DC converter to switch using a carrier-based pulse-width modulation method. Carrier-based pulse-width modulation is a technique that generates a switching signal by comparing an AC command voltage synthesized by a controller with a triangular wave carrier. FIG. 10 is a graph illustrating an example of a waveform for voltage in a carrier-based pulse width modulation (Carrier-based PWM) method. Referring to FIG. 10, in carrier-based pulse width modulation, the carrier voltage (V_c) has the form of a triangular wave, and the command voltage (V_r) has the form of a sine wave. If the command voltage (V_r) is greater than the carrier voltage (V_c), the inverter outputs a voltage (DC link voltage) of a predetermined magnitude (V_dc), and if not, outputs zero voltage. Here, for normal modulation to be possible, the magnitude of the command voltage (V_r) must be smaller than the magnitude of the carrier voltage (V_c). To properly express this, a modulation index (MI) defined as shown in Equation 1 below can be defined. [Mathematical Formula 1] Here, the operation in which an inverter performs modulation with a modulation index (MI) less than 1 is called linear modulation. However, depending on the situation, the magnitude of the command voltage (V_r) may become larger than the magnitude of the carrier voltage (V_c). In this case, the possible output voltage of the inverter exceeds the DC link voltage (V_dc), and the modulation index (MI) also becomes equal to or greater than 1, making it impossible to perform linear modulation normally. This is commonly referred to as over-modulation. Inverters are generally connected to the grid voltage, and the magnitude of this grid voltage often rises instantaneously within the normal range, causing the modulation index (MI) to increase and potentially exceed 1. In other words, overmodulation may occur. Conventionally, to solve this problem, the average value of the DC link voltage (V_dc) was increased in accordance with the rise in the grid voltage. However, if only the average value of the DC link voltage (V_dc) is increased, the 2nd harmonic ripple voltage remains unchanged, causing the maximum value of the DC link voltage (V_dc) to increase. An increase in the maximum value of the DC link voltage (V_dc) necessitates designing circuit components within the inverter's DC link, such as DC-link capacitors, snubber capacitors, and semiconductor switch elements, with higher voltage ratings than before, leading to problems such as increased component volume, increased overall device size, and additional costs. Meanwhile, there is also a method of limiting the output voltage of the inverter to relatively reduce the increase in the maximum value of the DC link voltage (V_dc). According to this, while it has the advantage of not requiring an increase in the size of components within the inverter's DC section, it has the disadvantage that the inverter's output power is significantly limited. FIG. 1 is a block diagram of an embodiment of an AC/DC semiconductor transformer system including an AC/DC semiconductor transformer and an AC/DC semiconductor transformer control device. FIG. 2 is a graph showing the change over time of the average DC voltage and the second harmonic pulsating voltage controlled by an AC/DC semiconductor transformer control device according to one embodiment. Figure 3 is a graph diagram illustrating an example of the operation of DC link voltage control when the AC input voltage magnitude increases. FIG. 4 is a graph diagram illustrating the control of the average value of the DC side voltage according to one embodiment. FIG. 5 is a graph diagram illustrating second harmonic pulsating voltage control according to one embodiment. FIG. 6 is