Power supply system applied to electrically powered vehicle
A boost converter is configured of a boost chopper having a diode of an upper arm and a switching element of a lower arm. Output power from a battery to a load is limited such that a current flowing through boost converter does not exceed a current upper limit value for thermal protection of boost converter. The current upper limit value is set based not only on a cooling water temperature of boost converter but also on an output voltage VH of boost converter, in consideration of characteristics that, as output voltage VH rises, an amount of heat generated in diode decreases, diode being regarded as a main target of thermal protection since it receives a power running current to load. Thereby, the boost converter can be protected from overheating without excessively deteriorating vehicle traveling performance.
1. A power supply system of an electrically powered vehicle equipped with an electric motor for generating vehicle driving force, said power supply system comprising:
a first power line on a high voltage side and a second power line on a low voltage side that are connected to a load including said electric motor;
a power storage device storing electric power supplied to said electric motor;
a boost converter connected between said power storage device and said load,
said boost converter including
a diode connected between said first power line and a first node so as to form a current path extending from said first node to said first power line,
a switching element connected between said first node and said second power line, and
a reactor connected in series to said power storage device between said first node and said second power line, said power supply system further comprising:
a cooling device having a coolant circulation mechanism for cooling said diode and said switching element; and
a control device controlling an operation of each of said boost converter and said load,
said control device including
a voltage control unit controlling said switching element to be turned ON or OFF in order to control a direct-current (DC) voltage between said first and second power lines,
an upper limit current setting unit changing a current upper limit value of said boost converter in accordance with a change in each of a coolant temperature of said coolant circulation mechanism and said DC voltage, and
a power limitation unit for limiting electric power of said load such that a current flowing through said boost converter does not exceed said current upper limit value, wherein
said control device further includes
a lower limit voltage setting unit setting a lower limit voltage of said DC voltage to rise as said coolant temperature rises, using said coolant temperature and the current of said boost converter as variables, and
a voltage command value setting unit for setting a voltage command value of said DC voltage to fall within a voltage range higher than the lower limit voltage set by said lower limit voltage setting unit, and
said voltage control unit controls said switching element to be turned ON or OFF for controlling said DC voltage in accordance with said voltage command value.
2. The power supply system according to claim 1 , wherein
in a region where said coolant temperature is lower than a prescribed determination temperature, said upper limit current setting unit cancels a setting of said current upper limit value when said DC voltage is higher than a prescribed lower limit voltage, and sets said current upper limit value to be lower as said DC voltage is lower when said DC voltage is lower than said prescribed lower limit voltage.
3. The power supply system according to claim 1 , wherein
in a region where said coolant temperature is higher than said determination temperature, said upper limit current setting unit sets said current upper limit value using said DC voltage and said coolant temperature as variables such that said current upper limit value is lower as said DC voltage is lower.
4. The power supply system according to claim 1 , wherein
said power limitation unit sets a discharge power upper limit value from said power storage device based on a sum of a base value set in accordance with a state of said power storage device and a correction amount set at a negative value when the current of said boost converter is higher than said current upper limit value, and
an operation command of said load is generated while limiting an output voltage from said power storage device so as to fall within a range not exceeding said discharge power upper limit value.
5. The power supply system according to claim 4 , wherein said power limitation unit limits said base value so as not to exceed a minimum value of a power upper limit value that is set in accordance with a product of said current upper limit value and a voltage of said power storage device.
6. The power supply system according to claim 4 , wherein
said control device is configured to temporarily relax said discharge power upper limit value in accordance with an operation state of said electrically powered vehicle, and
said power limitation unit sets an adding amount of said discharge power upper limit value at a time of temporary relaxation so as to fall within a range in which said discharge power upper limit value after relaxation does not exceed the power upper limit value that is set in accordance with the product of said current upper limit value and the voltage of said power storage device.
7. A power supply system of an electrically powered vehicle equipped with an electric motor for generating vehicle driving force, said power supply system comprising:
a first power line on a high voltage side and a second power line on a low voltage side that are connected to a load including said electric motor;
a power storage device storing electric power supplied to said electric motor;
a boost converter connected between said power storage device and said load,
said boost converter including
a diode connected between said first power line and a first node so as to form a current path extending from said first node to said first power line,
a switching element connected between said first node and said second power line, and
a reactor connected in series to said power storage device between said first node and said second power line, said power supply system further comprising:
a cooling device having a coolant circulation mechanism for cooling said diode and said switching element; and
a control device controlling an operation of each of said boost converter and said load,
said control device including
a voltage control unit controlling said switching element to be turned ON or OFF in order to control a direct-current (DC) voltage between said first and second power lines,
an upper limit current setting unit changing a current upper limit value of said boost converter in accordance with a change in each of a coolant temperature of said coolant circulation mechanism and said DC voltage, and
a power limitation unit for limiting electric power of said load such that a current flowing through said boost converter does not exceed said current upper limit value, wherein
said power limitation unit sets a discharge power upper limit value from said power storage device based on a sum of a base value set in accordance with a state of said power storage device and a correction amount set at a negative value when the current of said boost converter is higher than said current upper limit value, and
an operation command of said load is generated while limiting an output voltage from said power storage device so as to fall within a range not exceeding said discharge power upper limit value.
8. The power supply system according to claim 7 , wherein
in a region where said coolant temperature is lower than a prescribed determination temperature, said upper limit current setting unit cancels a setting of said current upper limit value when said DC voltage is higher than a prescribed lower limit voltage, and sets said current upper limit value to be lower as said DC voltage is lower when said DC voltage is lower than said prescribed lower limit voltage.
9. The power supply system according to claim 7 , wherein
in a region where said coolant temperature is higher than said determination temperature, said upper limit current setting unit sets said current upper limit value using said DC voltage and said coolant temperature as variables such that said current upper limit value is lower as said DC voltage is lower.
10. The power supply system according to claim 7 , wherein said power limitation unit limits said base value so as not to exceed a minimum value of a power upper limit value that is set in accordance with a product of said current upper limit value and a voltage of said power storage device.
11. The power supply system according to claim 7 , wherein
said control device is configured to temporarily relax said discharge power upper limit value in accordance with an operation state of said electrically powered vehicle, and
said power limitation unit sets an adding amount of said discharge power upper limit value at a time of temporary relaxation so as to fall within a range in which said discharge power upper limit value after relaxation does not exceed the power upper limit value that is set in accordance with the product of said current upper limit value and the voltage of said power storage device.