Power systems for hybrid electric vehicle (HEV)
A hybrid electric vehicle (HEV) power system is provided that includes a vehicle electrical system (VES), an inverter-controller unit (ICU) and an AC electric motor/generator unit (MGU). The VES includes a first DC voltage source and a second DC voltage source coupled in series with the first DC voltage source. The VES also includes a first electrical load coupled across the first DC voltage source, and a second electrical load coupled across the second DC voltage source. The ICU is coupled across the first DC voltage source and the second DC voltage source and is designed to convert DC power from the first DC voltage source and the second DC voltage source to generate AC power for the AC electric MGU. Together the DC voltage sources can replace a conventional high-voltage DC voltage source. In some implementations, techniques are provided for “charge balancing” the first DC voltage source and the second DC voltage source without expensive devices.
1. A hybrid electric vehicle (HEV) power system, comprising:
a vehicle electrical system (VES) comprising: a first DC voltage source; a first group of electrical loads comprising a first electrical load coupled across the first DC voltage source; a second DC voltage source coupled in series with the first DC voltage source at a common node that is at approximately ground potential; and a second group of electrical loads comprising a second electrical load coupled across the second DC voltage source;
an inverter-controller unit (ICU), coupled across the first DC voltage source and the second DC voltage source, the ICU designed to generate AC power based on the first DC voltage source and the second DC voltage source; and
an AC electric motor/generator unit (MGU) coupled to the ICU and designed to receive the AC power generated by the ICU, and wherein the AC electric motor/generator unit (MGU) further comprises: a first motor winding; a second motor winding; and a neutral point where the first motor winding is coupled to the second motor winding; and
a coupling entity that electrically couples the neutral point to the common node,
wherein coupling the first DC voltage source and the second DC voltage source to the neutral point of the Motor/Generator Unit (MGU) via coupling entity allows the Motor/Generator Unit (MGU) to perform a charge balancing function to maintain charge stored at the first DC voltage source and the second DC voltage source at substantially the same levels so that respective voltages (V bat ) at each of the first DC voltage source and the second DC voltage source are maintained at substantially the same levels regardless of usage of the first DC voltage source and the second DC voltage source.
2. A system according to claim 1 , wherein the coupling entity comprises at least one electrical connection that directly connects the neutral point to the common node.
3. A system according to claim 1 , wherein the inverter-controller unit (ICU) further comprises:
an inverter module coupled to the Motor/Generator Unit (MGU) and coupled to the Vehicle Electrical System (VES) across the first DC voltage source and the second DC voltage source such that the inverter module receives a compound voltage (V IN ) that comprises a sum of the first DC voltage source and the second DC voltage source, and converts the compound voltage (V IN ) to AC voltages to be applied to motor windings of the Motor/Generator Unit (MGU).
4. A system according to claim 3 , wherein the average voltage across the coupling entity is at one-half of the compound voltage (V IN ) across the inverter module.
5. A system according to claim 3 , wherein the Motor/Generator Unit (MGU) comprises a two-phase AC motor, and wherein the inverter module consists of:
a first inverter sub-module coupled to the first motor winding; and
a second inverter sub-module coupled to the second motor winding, wherein each of the first and second inverter sub-modules comprises a pair of switches.
6. A system according to claim 5 , wherein the ICU further comprises:
a control unit coupled to the inverter sub-modules, wherein the control unit controls a sequence at which the switches of inverter modules are turned on to maintain charge stored at the first DC voltage source and at the second DC voltage source at substantially the same levels so that the respective voltages at each of the first DC voltage source and the second DC voltage source are maintained at substantially the same levels regardless of usage of the first DC voltage source and the second DC voltage source, respectively.
7. A system according to claim 3 , wherein the Motor/Generator Unit (MGU) comprises a three-phase AC motor, and wherein the inverter module comprises:
a first inverter sub-module coupled to the first motor winding;
a second inverter sub-module coupled to the second motor winding; and
a third inverter sub-module coupled to the third motor winding, wherein each of the first, second and third inverter sub-modules comprises a pair of switches.
8. A system according to claim 7 , wherein each of the inverter sub-modules comprise at least one switch, wherein the ICU further comprises:
a control unit coupled to the inverter sub-modules, wherein the control unit controls a sequence at which the switches in inverter modules are turned on such that the correct amounts of energy are provided to maintain charge stored at the first DC voltage source and at the second DC voltage source at substantially the same levels so that the respective voltages at each of the first DC voltage source and the second DC voltage source are maintained at substantially the same levels regardless of usage of the first DC voltage source and at the second DC voltage source, respectively.
9. A system according to claim 1 , further comprising:
a first non-buffered load, and a first buffer filter that performs a buffering function between the first electrical load and the first non-buffered load to ensure that short-term voltage drops at the first DC voltage source do not impact voltage at the first electrical load;
a second non-buffered load, and a second buffer filter that performs a buffering function between the second electrical load and the second non-buffered load to ensure that short-term voltage drops at the second DC voltage source do not impact voltage at the second electrical load.
10. A system according to claim 1 , wherein the common node is coupled to a chassis of the hybrid electric vehicle (HEV),
wherein the first DC voltage source comprises:
a first auxiliary low-voltage battery comprising a negative terminal coupled to the chassis of the HEV at the common node; and
wherein the second DC voltage source comprises:
a second auxiliary low-voltage battery coupled in series to the first auxiliary low-voltage battery and to the chassis of the HEV at the common node,
wherein the first auxiliary low-voltage battery and the second auxiliary low-voltage battery generate a compound voltage equal to a sum of a first voltage (V bat ) of the first auxiliary low-voltage battery for powering the first group of electrical loads and a second voltage (V bat ) of the second auxiliary low-voltage battery for powering the second group of electrical loads, wherein the compound voltage is provided to the inverter module.
11. A system according to claim 1 , wherein each of the electrical loads comprise a vehicle accessory.
12. A system according to claim 1 , wherein the AC electric motor/generator unit (MGU) further comprises:
a first motor winding, a second motor winding and a third motor winding; and
wherein the inverter-controller unit (ICU) comprises an inverter module comprising: a first inverter sub-module and a second inverter sub-module, wherein the second DC voltage source is coupled between the first inverter sub-module and the second inverter sub-module.
13. A system according to claim 12 , wherein the inverter module comprises a delta inverter module that further comprises a third inverter sub-module.
14. A system according to claim 13 , wherein the first group of electrical loads is coupled to the first DC voltage source such that the first DC voltage source supplies power to the first group of electrical loads, and
wherein the second group of electrical loads is coupled to the second DC voltage source such that the second DC voltage source supplies power to the second group of electrical loads, and wherein the system further comprises:
a third DC voltage source coupled between the second inverter sub-module and the third inverter sub-module, wherein the third DC voltage source is coupled to the second inverter sub-module at a common node that is at ground potential; and
a third group of electrical loads comprising a third electrical load coupled to the third DC voltage source such that the third DC voltage source supplies power to the third group of electrical loads.
15. A system according to claim 14 , wherein the first group of electrical loads, the second group of electrical loads and the third group of electrical loads are substantially equal to one another such that the first DC voltage source, the second DC voltage source and the third DC voltage source each power one-third of the total electrical loads supported by the system.
16. A system according to claim 14 , wherein the first motor winding is coupled between the first inverter sub-module and the second DC voltage source, wherein the second motor winding is coupled between the second inverter sub-module and the third DC voltage source, and wherein the third motor winding is coupled between the third inverter sub-module and the first DC voltage source.
17. A system according to claim 14 , further comprising:
a first non-buffered load, and a first buffer filter that performs a buffering function between the first electrical load and the first non-buffered load to ensure that short-term voltage drops at the first DC voltage source do not impact voltage at the first electrical load;
a second non-buffered load, and a second buffer filter that performs a buffering function between the second electrical load and the second non-buffered load to ensure that short-term voltage drops at the second DC voltage source do not impact voltage at the second electrical load; and
a third non-buffered load, and a third buffer filter that performs a buffering function between the third electrical load and the third non-buffered load to ensure that short-term voltage drops at the third DC voltage source do not impact voltage at the third electrical load.
18. A hybrid electric vehicle (HEV) power system, comprising:
a vehicle electrical system (VES) comprising: a first DC voltage source; a first group of electrical loads comprising a first electrical load coupled across the first DC voltage source; a second DC voltage source coupled in series with the first DC voltage source at a common node that is at approximately ground potential; and a second group of electrical loads comprising a second electrical load coupled across the second DC voltage source;
an inverter-controller unit (ICU), coupled across the first DC voltage source and the second DC voltage source, the ICU designed to generate AC power based on the first DC voltage source and the second DC voltage source; and
an AC electric motor/generator unit (MGU) coupled to the ICU and designed to receive the AC power generated by the ICU, and wherein the AC electric motor/generator unit (MGU) further comprises: a first motor winding; a second motor winding; and a neutral point where the first motor winding is coupled to the second motor winding; and
a coupling entity that electrically couples the neutral point to the common node, wherein the coupling entity comprises at least one electrical connection that directly connects the neutral point to the common node.