Charging apparatus capable of reducing low frequency leakage current

1. A charging apparatus capable of reducing a low-frequency leakage current, the charging apparatus comprising:

a filter that comprises two input-terminal Y-capacitors which are connected in series to input terminals, to which alternating-current (AC) power provided from an external charging facility is input, and a connection node of which is grounded;

a power factor correction converter that comprises a switching element, corrects a power factor of the AC power, provided from the external charging facility through the filter, through on/off control of the switching element to convert the AC power into direct-current (DC) power, and outputs the DC power;

a DC link capacitor that is connected to both ends of the power factor correction converter and forms a DC voltage;

a non-insulating DC-DC converter that converts a level of the DC voltage formed by the DC link capacitor into a voltage level required by an energy storage device to be charged;

two output-terminal Y-capacitors which are connected to an output terminal of the DC-DC converter and are connected to each other in series and a connection node of which is grounded; and

a duty controller that determines a duty of the switching element in the power factor correction converter based on a level of a common-mode component of an AC voltage of the AC power provided from the external charging facility, a level of the DC voltage formed by the DC link capacitor, and a leakage current flowing from the connection node of the two input-terminal Y-capacitors and the connection node of the two output-terminal Y-capacitors to a ground.

2. The charging apparatus of claim 1 , wherein the duty controller calculates the common-mode component of the AC voltage of the AC power using an equation below:

v g_CM =0.5[ v Y-Cap_in +{−( v g −v Y-Cap_in )}]= v Y-Cap_in −0.5 v g ,

where v g_CM denotes the common-mode component of the AC voltage of the AC power, v Y-Cap_in denotes a voltage value applied to one of the input-terminal Y-capacitors, and v g denotes the denotes the AC voltage of the AC power.

3. The charging apparatus of claim 1 , wherein the duty controller comprises:

a default duty generator that determines a first duty value for controlling the switching element such that the power factor correction converter outputs a preset level of voltage;

a minimum leakage current adaptation controller that calculates a gain for compensating for a level of the AC voltage of the AC power and outputs the gain at preset time intervals, the minimum leakage current adaptation controller receiving an average value of the leakage current flowing from the connection node of the two input-terminal Y-capacitors and the connection node of the two output-terminal Y-capacitors to the ground at the preset time intervals, and determining and outputting a currently output gain according to a change in the average value of the leakage current, input in advance, and a change in the gain;

a multiplier that outputs the level of the common-mode component of the AC voltage of the AC power multiplied by the gain output by the minimum leakage current adaptation controller; and

a divider that generates a common-mode compensation duty value by dividing an output value from the multiplier by the level of the DC voltage formed by the DC link capacitor and provides a value equal to the common-mode compensation duty value plus each of the first duty value and a value complementary to the first duty value as a duty value for on/off control of the switching element.

4. The charging apparatus of claim 3 , wherein the minimum leakage current adaptation controller:

compares a currently input average leakage current value with a most recently input average leakage current value and compares a most recently calculated gain with a gain calculated immediately before the most recently calculated gain at the preset time intervals;

outputs a value equal to the most recently calculated gain minus a preset gain variation Δ as a current gain when the currently input average leakage current value is greater than the most recently input average leakage current value and the most recently calculated gain is greater than the gain calculated immediately before the most recently calculated gain;

outputs a value equal to the most recently calculated gain plus the preset gain variation Δ as a current gain when the currently input average leakage current value is greater than the most recently input average leakage current value and the most recently calculated gain is less than the gain calculated immediately before the most recently calculated gain;

outputs a value equal to the most recently calculated gain plus a preset gain variation Δ as a current gain when the currently input average leakage current value is less than the most recently input average leakage current value and the most recently calculated gain is greater than the gain calculated immediately before the most recently calculated gain; and

outputs a value equal to the most recently calculated gain minus the preset gain variation Δ as a current gain when the currently input average leakage current value is less than the most recently input average leakage current value and the most recently calculated gain is less than the gain calculated immediately before the most recently calculated gain.

5. The charging apparatus of claim 4 , wherein the power factor correction converter comprises:

a first leg comprising a first switching element and a second switching element which are directly connected to each other; and

a second leg comprising a third switching element and a fourth switching element which are directly connected to each other,

the first leg and the second leg are connected in parallel to two input ports of input terminals of the DC-DC converter,

a connection node of the first switching element and the second switching element is connected to one terminal of the input terminals to which the AC power is provided, and

a connection node of the third switching element and the fourth switching element is connected to another terminal of the input terminals to which the AC power is provided.

6. The charging apparatus of claim 5 , wherein the duty controller provides a value equal to the first duty value plus the common-mode compensation duty value as a duty value for on/off control of the first switching element, provides a value complementary to the value equal to the first duty value plus the common-mode compensation duty value as a duty value for on/off control of the second switching element, provides a value equal to a value complementary to the first duty value plus the common-mode compensation duty value as a duty value for on/off control of the third switching element, and provides a value complementary to the value equal to the value complementary to the first duty value plus the common-mode compensation duty value as a duty value for on/off control of the fourth switching element.