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Figure 13. (a) Frequency change in the isolated power system—synchronous condenser disconnection. (b) Active power response of the HVDC BtB converter when db = 10 mHz. The initial conditions for the digital simulation were as follows: 1. The operating SC (synchronous condenser) disconnects with (—10 MW) load; 2. SC frequency control gain is 1250 MW/Hz and corresponds to 0.8% droop; 3. SC frequency control gain is 250 MW/Hz and corresponds to 4% droop; 4. the ramp speed of active power is 100 MW/s; 5. the dead-band of the system’s frequency change is 10 mHz, at a gain of K = 1250 MW/Hz; 6. SC reactive power is not transferred to the isolated EPS, and Q = 0 MVar. The simulation results are shown in Figures 13-16. FC here denotes Frequency Control.

Figure 13 (a) Frequency change in the isolated power system—synchronous condenser disconnection. (b) Active power response of the HVDC BtB converter when db = 10 mHz. The initial conditions for the digital simulation were as follows: 1. The operating SC (synchronous condenser) disconnects with (—10 MW) load; 2. SC frequency control gain is 1250 MW/Hz and corresponds to 0.8% droop; 3. SC frequency control gain is 250 MW/Hz and corresponds to 4% droop; 4. the ramp speed of active power is 100 MW/s; 5. the dead-band of the system’s frequency change is 10 mHz, at a gain of K = 1250 MW/Hz; 6. SC reactive power is not transferred to the isolated EPS, and Q = 0 MVar. The simulation results are shown in Figures 13-16. FC here denotes Frequency Control.

Related Figures (33)

Figure 1. Isolated power system scheme.
Figure 1. Isolated power system scheme.
Figure 2. Structure of the model design of the frequency and damping controller.
Figure 2. Structure of the model design of the frequency and damping controller.
G1, SC, P model: VGDS-1025/245/40UHL represents generator GI, which operates in Hydro-generator mode, Synchronous condenser mode, Motor pump mode, and does support the FFR function, but only when the hydro-generator has temporary droop settings and time constants. These settings are manually set. A mathematical model of generator G1’s structure is shown in Figure 4. Figure 4. Structure of the electromagnetic model of a bright pole generator.
G1, SC, P model: VGDS-1025/245/40UHL represents generator GI, which operates in Hydro-generator mode, Synchronous condenser mode, Motor pump mode, and does support the FFR function, but only when the hydro-generator has temporary droop settings and time constants. These settings are manually set. A mathematical model of generator G1’s structure is shown in Figure 4. Figure 4. Structure of the electromagnetic model of a bright pole generator.
Table 1. Hydro-generator G1’s main parameters. The G2 model uses a combined cycle gas turbine and turbogenerator and does support the FFR function, but it works on limited value. The G3 model is a TVV-220-2 turbogenera- tor and does support the FFR function. The G4 model is a TVF-150-2UZ turbogenerator and does not support the FFR function. The G5 model is a TVF-120-2 turbogenerator that does support the FFR function. A mathematical model of the structure of generators G2-G5 is shown in Figure 5.
Table 1. Hydro-generator G1’s main parameters. The G2 model uses a combined cycle gas turbine and turbogenerator and does support the FFR function, but it works on limited value. The G3 model is a TVV-220-2 turbogenera- tor and does support the FFR function. The G4 model is a TVF-150-2UZ turbogenerator and does not support the FFR function. The G5 model is a TVF-120-2 turbogenerator that does support the FFR function. A mathematical model of the structure of generators G2-G5 is shown in Figure 5.
Table 2. Main parameters of turbogenerators G2-G5.
Table 2. Main parameters of turbogenerators G2-G5.
Figure 5. Structure of the electromagnetic model of a blurred generator.
Figure 5. Structure of the electromagnetic model of a blurred generator.
Table 3. Frequency change in the isolated power system.
Table 3. Frequency change in the isolated power system.
Figure 6. (a) Frequency change in the isolated power system caused by a load increase (case A). (b) Voltage fluctuations on the 330 kV side caused by a load increase (case A).
Figure 6. (a) Frequency change in the isolated power system caused by a load increase (case A). (b) Voltage fluctuations on the 330 kV side caused by a load increase (case A).
Figure 7. Frequency change in the isolated power system caused by a load increase (case B).
Figure 7. Frequency change in the isolated power system caused by a load increase (case B).
Table 4. Frequency change in the isolated power system. After estimating the maximum possible disturbance (30 MW) with a calculated inertia of 7777 MWs, the reaction of the isolated EPS when two (case B) SC (synchronous condenser) units are operating in the system was analyzed. The inertia of the isolated EPS is 5793 + (SC1) 992 + (SC2) 992 MWs [15,21,22,25,26]. The simulation results are shown in Figure 9.
Table 4. Frequency change in the isolated power system. After estimating the maximum possible disturbance (30 MW) with a calculated inertia of 7777 MWs, the reaction of the isolated EPS when two (case B) SC (synchronous condenser) units are operating in the system was analyzed. The inertia of the isolated EPS is 5793 + (SC1) 992 + (SC2) 992 MWs [15,21,22,25,26]. The simulation results are shown in Figure 9.
A frequency increase in the isolated EPS is simulated by a soaring change of the active power flow through an HVDC BtB converter or with the operating generators of the system from 10 to 50 MW, in 10 MW increments. In the digital simulation, it was assumed that one unit (case A) was operating in SC (synchronous condenser mode). The simulation results are shown in Figure 8a,b. Figure 8. (a) Frequency change in the isolated power system caused by a load decrease (case A). (b) Voltage fluctuations on the 330 kV side caused by a load decrease (case A).
A frequency increase in the isolated EPS is simulated by a soaring change of the active power flow through an HVDC BtB converter or with the operating generators of the system from 10 to 50 MW, in 10 MW increments. In the digital simulation, it was assumed that one unit (case A) was operating in SC (synchronous condenser mode). The simulation results are shown in Figure 8a,b. Figure 8. (a) Frequency change in the isolated power system caused by a load decrease (case A). (b) Voltage fluctuations on the 330 kV side caused by a load decrease (case A).
Figure 9. Frequency change in the isolated power system caused by a load decrease (case B).
Figure 9. Frequency change in the isolated power system caused by a load decrease (case B).
Figure 10. Influence of filters on the active power transfer of the HVDC BtB converter. The impact on active power transmission is examined by increasing the load of the HVDC BtB converter by 30 MW. The filters are of capacitive type, so their rated reactive power is 92 MVar. The simulation results are shown in Figure 10.
Figure 10. Influence of filters on the active power transfer of the HVDC BtB converter. The impact on active power transmission is examined by increasing the load of the HVDC BtB converter by 30 MW. The filters are of capacitive type, so their rated reactive power is 92 MVar. The simulation results are shown in Figure 10.
Figure 11. (a) Frequency dependence of the isolated power system on the frequency control parame- ters of the HVDC BtB converter. (b) The response of an active power to a load change when the gain is K = 100 MW/Hz. Simulations were performed with different values of gain factor K of the HVDC BtB converter, when: K = 100 MW/Hz, K = 1250 MW/Hz, K = 2500 MW/Hz, and the ramp speed of active power: 100 MW/s, 200 MW/s, 600 MW/s, 1000 MW//s. Tho cimirtlahnann rocilte aro chawurn in Biowroac 11 anda 19
Figure 11. (a) Frequency dependence of the isolated power system on the frequency control parame- ters of the HVDC BtB converter. (b) The response of an active power to a load change when the gain is K = 100 MW/Hz. Simulations were performed with different values of gain factor K of the HVDC BtB converter, when: K = 100 MW/Hz, K = 1250 MW/Hz, K = 2500 MW/Hz, and the ramp speed of active power: 100 MW/s, 200 MW/s, 600 MW/s, 1000 MW//s. Tho cimirtlahnann rocilte aro chawurn in Biowroac 11 anda 19
Figure 12. (a) The response of an active power to a load change when the gain is K = 1250 MW/Hz. (b) The response of an active power to a load change when the gain is K = 2500 MW/Hz.
Figure 12. (a) The response of an active power to a load change when the gain is K = 1250 MW/Hz. (b) The response of an active power to a load change when the gain is K = 2500 MW/Hz.
Figure 14. (a) Active power response of the HVDC BtB converter. (b) Reaction of the HVDC BtB converter when FC is off.
Figure 14. (a) Active power response of the HVDC BtB converter. (b) Reaction of the HVDC BtB converter when FC is off.
Figure 15. (a) Active power compensation of the thermal power plant at different FC parameters. (b) Active power compensation of the thermal power plant at different FC parameters.
Figure 15. (a) Active power compensation of the thermal power plant at different FC parameters. (b) Active power compensation of the thermal power plant at different FC parameters.
Figure 16. Voltage fluctuations on the 330 kV side. The results in Figures 13-16 show that both with the gain factor K = 1250 MW/Hz and with K = 250 MW/Hz, damped active power oscillations in the HVDC BtB converter reaction were observed. It is recommended to use a gain of K = 250 MW/Hz during the operation of an isolated EPS.
Figure 16. Voltage fluctuations on the 330 kV side. The results in Figures 13-16 show that both with the gain factor K = 1250 MW/Hz and with K = 250 MW/Hz, damped active power oscillations in the HVDC BtB converter reaction were observed. It is recommended to use a gain of K = 250 MW/Hz during the operation of an isolated EPS.
Figure 17. (a) Frequency change in the isolated power system in response to SC disconnection. (b) Response of the HVDC BtB converter to SC disconnection.
Figure 17. (a) Frequency change in the isolated power system in response to SC disconnection. (b) Response of the HVDC BtB converter to SC disconnection.
Figure 18. Response of generator (G1) to SC disconnection.
Figure 18. Response of generator (G1) to SC disconnection.
Figure 19. Response of the HVDC BtB converter to SC disconnection.
Figure 19. Response of the HVDC BtB converter to SC disconnection.
Figure 20. (a) Load of SC at start-up. (b) Frequency change in the isolated power system. The simulation results are shown in Figures 20 and 21.
Figure 20. (a) Load of SC at start-up. (b) Frequency change in the isolated power system. The simulation results are shown in Figures 20 and 21.
Figure 21. Response of the HVDC BtB converter to SC activation (start-up).
Figure 21. Response of the HVDC BtB converter to SC activation (start-up).
Figure 22. (a) Frequency change when the HVDC BtB converter has a different frequency insensitivity range. (b) Response of the active power of the HVDC BtB converter to insufficient frequency. Frequency drops using different dead-bands are shown in Table 5. The results obtained show that the frequency control of the HVDC BtB converter reduces the frequency drop. The frequency drop directly depends on the set dead-band. In order to evaluate the frequency control capabilities of the HVDC BtB converter, the use of a 0 mHz dead-band is not recommended during the operation of an isolated EPS [15,21,22,32].
Figure 22. (a) Frequency change when the HVDC BtB converter has a different frequency insensitivity range. (b) Response of the active power of the HVDC BtB converter to insufficient frequency. Frequency drops using different dead-bands are shown in Table 5. The results obtained show that the frequency control of the HVDC BtB converter reduces the frequency drop. The frequency drop directly depends on the set dead-band. In order to evaluate the frequency control capabilities of the HVDC BtB converter, the use of a 0 mHz dead-band is not recommended during the operation of an isolated EPS [15,21,22,32].
Table 5. Frequency change in the isolated power system. The smallest frequency drop occurs when using the HVDC BtB converter dead-bands of 0-50 mHz. If possible, use a0 mHz HVDC BtB converter dead-band.
Table 5. Frequency change in the isolated power system. The smallest frequency drop occurs when using the HVDC BtB converter dead-bands of 0-50 mHz. If possible, use a0 mHz HVDC BtB converter dead-band.
Figure 23. Voltage fluctuations on the 330 kV side.
Figure 23. Voltage fluctuations on the 330 kV side.
Figure 24. (a) Frequency change when the HVDC BtB converter has a different frequency insensitivity range. (b) Response of the active power of the HVDC BtB converter to excess frequency. In the numerical simulation, it is assumed that the load change soars over 30 MW. The frequency control gain K of the HVDC BtB converter is 1250 MW/Hz. The active power ramp speed is 100 MW/s. The digital simulation is performed by setting different HVDC BtB converter frequency dead-bands: 0 mHz, 50 mHz, 100 mHz, 150 mHz, and 200 mHz. The simulation results are shown in Figures 24 and 25.
Figure 24. (a) Frequency change when the HVDC BtB converter has a different frequency insensitivity range. (b) Response of the active power of the HVDC BtB converter to excess frequency. In the numerical simulation, it is assumed that the load change soars over 30 MW. The frequency control gain K of the HVDC BtB converter is 1250 MW/Hz. The active power ramp speed is 100 MW/s. The digital simulation is performed by setting different HVDC BtB converter frequency dead-bands: 0 mHz, 50 mHz, 100 mHz, 150 mHz, and 200 mHz. The simulation results are shown in Figures 24 and 25.
Table 6. Frequency increase in the isolated power system.
Table 6. Frequency increase in the isolated power system.
Figure 25. Voltage fluctuations on the 330 kV side.
Figure 25. Voltage fluctuations on the 330 kV side.
Figure 26. (a) Frequency change in the isolated power system caused by disconnection of the unit operating in pump mode. (b) Response of the HVDC BtB converter to a disconnection of the unit operating in pump mode.
Figure 26. (a) Frequency change in the isolated power system caused by disconnection of the unit operating in pump mode. (b) Response of the HVDC BtB converter to a disconnection of the unit operating in pump mode.
Figure 27. Frequency change in the isolated power system caused by disconnection of the HVDC BtB converter. During the numerical simulation, a disconnection of the HVDC BtB converter is analyzed. The maximum power ramp speed of the HVDC BtB converter is 15 MW/s. The transmitted power of the HVDC BtB converter was reduced to 50 MW (minimum power that can be transmitted), and only then was the converter disconnected. The simulation results are shown in Figure 27.
Figure 27. Frequency change in the isolated power system caused by disconnection of the HVDC BtB converter. During the numerical simulation, a disconnection of the HVDC BtB converter is analyzed. The maximum power ramp speed of the HVDC BtB converter is 15 MW/s. The transmitted power of the HVDC BtB converter was reduced to 50 MW (minimum power that can be transmitted), and only then was the converter disconnected. The simulation results are shown in Figure 27.
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