Electrical system testing processes

1. A testing process for an electrical system, the electrical system comprising:

a power converter including:

two or more direct current (DC) converter terminals, and

at least one converter leg connected to the DC converter terminals, each converter leg including a plurality of semiconductor switches and an alternating current AC terminal that defines an AC phase of the electrical system and is connectable to a respective AC terminal of an electrical load,

wherein the plurality of semiconductor switches are controllable to put the converter leg in an off-state, or in one of a plurality of on-states that defines a respective voltage level of the converter leg;

a DC bus including:

two or more DC bus terminals, each DC bus terminal being connected to a respective DC converter terminal, and

at least one DC bus capacitor; and

a pre-charge circuit with a contactor;

the testing process being a fully automated testing process, comprising,

conducting a sequence of different diagnostic tests on the electrical system, each diagnostic test testing one of the power converter and the DC bus to determine if it is responding as expected or operating within normal parameters; and

conducting one or more first diagnostic tests where each converter leg is in the off-state, or in the same one of the plurality of on-states, each first diagnostic test comprising:

closing the pre-charge contactor for a period of time to supply the DC voltage to the DC bus,

checking the response time of the pre-charge contactor by measuring the time between a close signal being initiated and a feedback signal confirming the pre-charge contactor has closed being received,

generating a fault signal if the measured time is greater than an expected response time; and

measuring a DC bus voltage while a DC voltage is supplied to the DC bus for a period of time, and generating a fault signal if the measured DC bus voltage does not exceed a first expected DC bus voltage.

2. The testing process of claim 1 , wherein a plurality of first diagnostic tests are carried out sequentially with the converter legs in a different state for each first diagnostic test.

3. The testing process of claim 1 , further comprising:

a second diagnostic test comprising the steps of:

measuring a DC bus voltage while a DC voltage is supplied to the DC bus,

ending the supply of the DC voltage when the measured DC bus voltage exceeds a first DC bus voltage, and allowing the DC bus voltage to decrease gradually towards the first DC bus voltage,

when the measured DC bus voltage is substantially equal to the first DC bus voltage, controlling the power converter to provide an expected AC current in at least one AC phase of the electrical system,

measuring the AC current in the at least one AC phase of the electrical system, and

generating a fault signal if the measured AC current is not within a range defined by the corresponding expected AC current plus or minus a tolerance value.

4. The testing process of claim 3 , wherein the second diagnostic test further comprises:

controlling the power converter to provide an expected AC voltage in at least one of the AC phases or between two of the AC phases,

measuring the AC voltage in a least one of the AC phases or between two of the AC phases, and

generating a fault signal if the measured AC voltage is not within a range defined by the corresponding expected AC voltage plus or minus a tolerance value.

5. The testing process of claim 3 , wherein the second diagnostic test further comprises generating a fault signal if a measured DC bus voltage falls below an expected DC bus voltage while the power converter is being controlled.

6. The testing process of claim 3 , wherein the second diagnostic test further comprises controlling the power converter using a control scheme with a selected modulation index.

7. The testing process of claim 3 , further comprising:

a third diagnostic test comprising the steps of:

measuring a DC bus voltage while a DC voltage is supplied to the DC bus,

ending the supply of the DC voltage when the measured DC bus voltage exceeds a second DC bus voltage, and allowing the DC bus voltage to decrease gradually towards the second DC bus voltage, wherein the second DC bus voltage is greater than the first DC bus voltage,

when the measured DC bus voltage is substantially equal to the second DC bus voltage, controlling the power converter to provide an expected AC current in at least one AC phase of the electrical system,

measuring the AC current in the at least one AC phase of the electrical system, and

generating a fault signal if the measured AC current is not within a range defined by the corresponding expected AC current plus or minus a tolerance value.

8. The testing process of claim 1 , wherein the electrical system further comprises a chopper circuit connected to the DC bus, and wherein the testing process further comprises:

a fourth diagnostic test comprising the steps of:

operating the chopper circuit for a period of time to provide an expected DC bus voltage,

after the period of time, measuring the DC bus voltage, and

generating a fault signal if the measured DC bus voltage is not within a range defined by the expected DC bus voltage plus or minus a tolerance value, or if the DC bus voltage has not decreased by a certain percentage, relative to an initial DC bus voltage.

9. The testing process of claim 8 , wherein the fourth diagnostic test comprises operating the chopper circuit using a control scheme with a selected modulation index.

10. The testing process of claim 8 , further comprising a fifth diagnostic test comprising the steps of:

operating the chopper circuit to discharge the DC bus capacitor(s) until the DC bus voltage is below a third DC bus voltage, and

generating a fault signal if a measured DC bus voltage has not fallen below an expected DC bus voltage during a period of time.

11. The testing process of claim 1 , wherein the electrical system further includes a switching device, and each AC phase of the electrical system is connectable to the respective AC terminal of the electrical load by means of the switching device, and wherein the testing process further comprises:

a zeroth diagnostic test carried out before any of the other diagnostic tests, the zeroth diagnostic test comprising the steps of:

closing the switching device to connect the power converter to the electrical load,

checking the response time of the switching device by measuring the time between a close signal being initiated and a feedback signal confirming the switching device has closed being received, and

generating a fault signal if the measured time is greater than an expected response time.

12. The testing process of claim 11 , wherein the electrical system further comprises a cooling system including a contactor, and the zeroth diagnostic test further comprises the steps of:

closing the cooling system contactor,

checking the response time of the cooling system contactor by measuring the time between a close signal being initiated and a feedback signal confirming the cooling system contactor has closed being received, and

generating a fault signal if the measured time is greater than an expected response time.

13. An electrical system comprising:

a power converter including:

two or more DC converter terminals, and

at least one converter leg connected to the DC converter terminals, each converter leg including a plurality of semiconductor switches and an AC terminal that defines an AC phase of the electrical system and is connectable to a respective AC terminal of an electrical load;

a DC bus including:

two or more DC bus terminals, each DC bus terminal being connected to a respective DC converter terminal, and

at least one DC bus capacitor;

a DC voltage supply for supplying a DC voltage to the DC bus;

a control unit adapted to control the DC voltage supply and the plurality of semiconductor switches to put the converter leg in an off-state, or in one of a plurality of on-states that defines a respective voltage level of the converter leg;

at least one voltage sensor connected to the control unit for measuring a DC bus voltage;

a pre-charge circuit with a contactor; and

at least one current sensor connected to the control unit for measuring an AC current in least one AC phase of the electrical system;

wherein the control unit is further adapted to carry out a testing process being a fully automated testing process where a sequence of different diagnostic tests are carried out on the electrical system, each diagnostic test testing one of the power converter and the DC bus to determine if it is responding as expected or operating within normal parameters.

14. The electrical system of claim 13 , further comprising a chopper circuit connected to the DC bus.

15. The electrical system of claim 13 , further comprising a switching device, and each AC phase of the electrical system is connectable to the respective AC terminal of the electrical load by means of the switching device.

16. The electrical system of claim 13 , further comprising a cooling system including a contactor.