Control device for power converter

Abstract

This enables stable control of the output current of power converters connected to the power system and DC power supply when an instantaneous voltage drop occurs in the power system. [Solution] The control device for the power converter of the present disclosure, when it detects an instantaneous voltage drop in the power system, holds the frequency of the system voltage immediately before the detection of the instantaneous voltage drop and the phase addition amount based on that frequency. While an instantaneous voltage drop is being detected, when the previously calculated value of the phase of the system voltage is less than a predetermined reference value at the zero-crossing timing of the system voltage, and when the previously calculated value is less than 2π at times other than the zero-crossing timing, it calculates the phase of the system voltage by adding the held phase addition amount to the previously calculated value at predetermined time intervals. When the previously calculated value of the phase is greater than or equal to the reference value at the zero-crossing timing, and when the previously calculated value is greater than or equal to 2π at times other than the zero-crossing timing, it resets the phase.

Description

Technical Field

[0001] The present disclosure relates to a control device for a power conversion device connected to a power system and a DC power supply.

Background Art

[0002] Conventionally, an inverter device that supplies power generated by a power generation facility of a hybrid vehicle to a power system is known (see, for example, Patent Document 1). This inverter device includes a zero-cross detection unit, a phase estimation unit, a phase addition amount calculation unit, a phase calculation unit, and a voltage command value calculation unit. The zero-cross detection unit detects the zero-cross timing at which the system voltage of the power system indicates zero volts. The phase estimation unit estimates the phase of the system voltage based on the system voltage after the first detection of the zero-cross timing and the effective value of the system voltage. The phase addition amount calculation unit calculates a phase addition amount for adjusting the amount of change in phase over time based on the frequency of the system voltage after the detection of the zero-cross timing for the second and subsequent times. The phase calculation unit corrects the offset deviation of the phase of the system voltage using the phase addition amount. The voltage command value calculation unit calculates a voltage command value for the power system based on the system voltage whose offset deviation of the phase has been corrected. Thereby, it is possible to prevent the voltage command from becoming discontinuous and suppress the occurrence of current surges when power is output to the power system.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, if an instantaneous voltage drop occurs in the power system to which the above-mentioned conventional inverter device is connected, the frequency of the system voltage will fluctuate significantly, making it difficult to accurately acquire the phase, and potentially making it impossible to stably control the output current from the inverter device.

[0005] Therefore, the primary objective of this disclosure is to enable stable control of the output current of a power converter connected to a power system and a DC power supply when an instantaneous voltage drop occurs in the power system. [Means for solving the problem]

[0006] The power converter control device of the present disclosure is a power converter control device that is connected to a power grid and a DC power supply and is capable of converting DC power from the DC power supply into AC power and outputting it to the power grid, and when an instantaneous voltage drop of the power grid is detected, the control device holds the frequency of the grid voltage immediately before the detection of the instantaneous voltage drop and a phase addition amount based on the frequency, and while the instantaneous voltage drop is detected, when the previously calculated value of the phase of the grid voltage is less than a predetermined reference value at the zero-crossing timing of the grid voltage, and when the previously calculated value is less than 2π at times other than the zero-crossing timing, the control device calculates the phase of the grid voltage by adding the held phase addition amount to the previously calculated value at predetermined time intervals, and when the previously calculated value of the phase is greater than or equal to the reference value at the zero-crossing timing, and when the previously calculated value is greater than or equal to 2π at times other than the zero-crossing timing, the control device resets the phase.

[0007] The control device for the power converter of this disclosure, upon detecting an instantaneous voltage drop in the power system, retains the frequency of the system voltage immediately before the detection of the instantaneous voltage drop and a phase addition amount based on that frequency. Furthermore, while an instantaneous voltage drop is detected, the control device calculates the phase of the system voltage by adding the retained phase addition amount to the previously calculated value at predetermined time intervals when the previously calculated value of the phase of the system voltage is less than a predetermined reference value at the zero-crossing timing of the system voltage, and when the previously calculated value of the phase is less than 2π at times other than the zero-crossing timing. The control device then resets the phase when the previously calculated value of the phase of the system voltage is greater than or equal to the reference value at the zero-crossing timing of the system voltage, and when the previously calculated value is greater than or equal to 2π at times other than the zero-crossing timing. As a result, even if the frequency of the system voltage fluctuates significantly due to an instantaneous voltage drop, the control device can appropriately estimate the phase of the system voltage assuming that the instantaneous voltage drop did not occur, based on the phase addition amount immediately before the detection of the instantaneous voltage drop, and stably control the output current of the power converter based on the obtained phase. [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic diagram showing an energy storage system including a control device for a power converter in this disclosure. [Figure 2] This flowchart shows the routines executed by the control unit of the power converter in this disclosure. [Figure 3] This diagram illustrates the procedure for calculating the phase of the grid voltage by the control device of the power converter of this disclosure when an instantaneous voltage drop occurs in the power grid. [Modes for carrying out the invention]

[0009] Next, with reference to the drawings, embodiments for carrying out the invention of this disclosure will be described.

[0010] Figure 1 is a schematic diagram showing a power storage system 1 including a control device 10 for a voltage converter according to the present disclosure. The power storage system 1 shown in the figure is a stationary power storage system connected to a power grid PS via a transformer Tr, and is capable of supplying power to the power grid PS and general households. As shown in Figure 1, in addition to the control device 10, the power storage system 1 includes a power conditioner (hereinafter referred to as "PCS") 2 as a voltage converter, a battery 3 as a DC power source, and a DC / DC converter 4.

[0011] The power grid PS supplies alternating current power and may include a power generation system that generates electricity from renewable energy sources such as wind power or solar power. The PCS2 is a power conversion device including an inverter (not shown) connected to the power grid PS and the DC / DC converter 4, which can convert alternating current power from the power grid PS into direct current power and also convert direct current power from the battery 3 into alternating current power. The battery 3 is, for example, a nickel-metal hydride secondary battery or a lithium-ion secondary battery, and is connected to the DC / DC converter 4 via a relay and a capacitor 5 (not shown).

[0012] The DC / DC converter 4 includes two transistors (e.g., insulated-gate bipolar transistors), two diodes connected in parallel in opposite directions to each transistor, and a reactor (all not shown), and is connected to the PCS2 via a capacitor 6. Capacitor 5 smooths the voltage fluctuations between the battery 3 and the DC / DC converter 4. Capacitor 6 smooths the voltage fluctuations between the DC / DC converter 4 and the PCS2. Note that the energy storage system 1 may include multiple sets of batteries 3 and DC / DC converters 4 connected in parallel to the PCS2, and the DC / DC converter 4 between the PCS2 and the battery 3 may be omitted from the energy storage system 1.

[0013] The control device 10 includes a computer (not shown) and acquires charge / discharge commands transmitted from an energy management device (EMS) (not shown), the grid voltage Vps supplied from the power grid PS to the PCS2 and detected by the grid voltage sensor 7, the charge / discharge current of the battery 3, the charge / discharge voltage, the battery temperature, etc., detected by sensors (not shown). Based on the acquired information, the control device 10 controls the PCS2 and the DC / DC converter 4.

[0014] In other words, when the power from the battery 3 converted by the PCS2 is output to the power grid PS side and supplied to the power grid PS or general households, the control device 10 obtains the frequency f of the system voltage Vps detected by the system voltage sensor 7 and calculates the phase ω of the system voltage Vps based on the obtained frequency f. The control device 10 also calculates the target AC current to be output from the PCS2 based on the system voltage Vps and phase ω. Furthermore, the control device 10 sets a target AC voltage based on the target AC current and controls the PCS2 and DC / DC converter 4 based on the target AC voltage, etc. Also, when the battery 3 is charged with power from the power grid PS converted by the PCS2, the control device 10 sets a target charging voltage according to the charging command from the EMS, etc. and controls the PCS2 and DC / DC converter 4 based on the system voltage Vps, target charging voltage, etc.

[0015] Next, with reference to Figure 2, the procedure for calculating the phase ω of the power system voltage Vps of the power system PS by the control device 10 will be explained.

[0016] Figure 2 is a flowchart of a routine that is repeatedly executed by the control device 10 at predetermined intervals (e.g., 100 μsec) to calculate the phase ω of the grid voltage Vps while the energy storage system 1 is in operation. When it is time to execute the routine in Figure 2, the control device 10 acquires the grid voltage Vps from the grid voltage sensor 7 (step S100), and determines whether or not an instantaneous voltage drop has occurred in the power system PS based on the acquired grid voltage Vps or the effective value calculated based on the grid voltage Vps (step S110). If the grid voltage Vps or the effective value is above a predetermined threshold and no instantaneous voltage drop in the power system PS is detected (step S110: NO), the control device 10 calculates the phase ω of the grid voltage Vps according to the normal setting procedure (step S200), and terminates the routine in Figure 2.

[0017] In step S200, when the system voltage Vps is at a zero-crossing timing indicating zero volts, the control device 10 resets (sets to zero) the phase ω of the system voltage Vps, updates the frequency f of the system voltage Vps, and calculates the phase addition amount Δω based on the updated frequency f and the execution period T of the routine in Figure 2 (e.g., 100 μsec), as Δω = 360 [deg] / (1 / f / T). The phase addition amount Δω represents the amount of discrepancy between the actual phase of the system voltage Vps and the phase ω calculated by the control device 10, which occurs because the zero-crossing timing cannot be accurately obtained in relation to the execution period T. Also, in step S200, when the current time is not a zero-crossing timing, the control device 10 calculates the phase ω by adding (integrating) the previously calculated value of phase ω with the phase addition amount Δω calculated at the most recent zero-crossing timing. In this case, the frequency f and the phase addition amount Δω are retained as they are. The phase sum Δω after the first zero-cross timing is obtained from the following relationship: Δω = arcsin(system voltage Vps obtained after the first zero-cross timing / (√2 × RMS value of system voltage Vps)).

[0018] On the other hand, if the system voltage Vps or RMS value is below a predetermined threshold and an instantaneous voltage drop in the power system PS is detected (step S110: YES), the control device 10 holds the frequency f and phase sum Δω (both values ​​from one cycle prior) immediately before the detection of the instantaneous voltage drop (step S120), and determines whether the current time is a zero-crossing timing based on the system voltage Vps (step S130). If the current time is a zero-crossing timing (step S130: YES), the control device 10 further determines whether the previously calculated value of phase ω (previous ω) is less than a predetermined reference value ωref (step S140). In this embodiment, the reference value ωref used as a threshold in step S140 is defined as, for example, ωref = 2π - Δω × α immediately before the detection of the instantaneous voltage drop (where "α" is an integer of about 1 to 3).

[0019] If the previously calculated value of phase ω is less than the reference value ωref (step S140: YES), the control device 10 calculates the phase angle ω by adding the phase addition amount Δω held in step S120 to the previously calculated value (step S150), and terminates the routine in Figure 2. Conversely, if the previously calculated value of phase ω is greater than or equal to the reference value ωref (step S140: NO), the control device 10 resets the phase ω (step S160), and terminates the routine in Figure 2.

[0020] Furthermore, if the current time is not the zero-cross timing (step S130: NO), the control device 10 determines whether the previously calculated value of phase ω is less than 2π (180deg) (step S170). If the previously calculated value of phase ω is less than 2π (step S170: YES), the control device 10 calculates the phase angle ω by adding the phase addition amount Δω held in step S120 to the previously calculated value (step S180), and terminates the routine in Figure 2. On the other hand, if the previously calculated value of phase ω is 2π or greater (step S170: NO), the control device 10 resets the phase ω (step S160), and terminates the routine in Figure 2.

[0021] As described above, when the control device 10 that controls the PCS 2 as a power conversion device detects an instantaneous voltage drop in the power system PS (step S110: YES), it holds the frequency f of the system voltage Vps immediately before the detection of the instantaneous voltage drop and the phase addition amount Δω based on the frequency f (step S120). Further, while the instantaneous voltage drop is being detected (step S110: YES), when the previous calculated value of the phase ω of the system voltage Vsp is less than a predetermined reference value ωref at the zero-crossing timing of the system voltage Vps (step S140: YES), and when the previous calculated value is less than 2π other than the zero-crossing timing (step S170: YES), the control device 10 calculates the phase ω of the system voltage Vps by adding the phase addition amount Δω held in step S120 to the previous calculated value every execution period T (predetermined time) (steps S150, S180). Then, when the previous calculated value of the phase ω of the system voltage Vsp is greater than or equal to the reference value ωref at the zero-crossing timing of the system voltage Vps (step S140: NO), and when the previous calculated value is greater than or equal to 2π other than the zero-crossing timing (step S170: NO), the control device 10 resets the phase ω (step S160).

[0022] As a result, even if the frequency f of the system voltage Vps fluctuates greatly due to an instantaneous voltage drop, on the control device 10 side, as shown by the solid line in FIG. 3, it is possible to appropriately estimate the phase of the system voltage Vps assuming that the instantaneous voltage drop did not occur, based on the phase addition amount Δω immediately before the detection of the instantaneous voltage drop. Further, when the previous calculated value of the phase ω is greater than or equal to the reference value ωref at the zero-crossing timing (step S140: NO), by resetting the phase ω (step S160), compared to the case where the phase ω is uniformly reset at the zero-crossing timing (see the broken line in FIG. 3), the phase difference between the system voltage Vps assuming that the instantaneous voltage drop did not occur and the phase ω calculated by the control device 10 can be made smaller. As a result, in the power storage system 1, it becomes possible to stably control the output current of the PCS 2 based on the phase ω calculated by the control device 10.

[0023] The invention of the present disclosure is not limited to the above embodiments, and it is needless to say that various changes can be made within the scope of the extension of the present disclosure. Furthermore, the above embodiments are merely specific forms of the invention described in the summary of the invention section, and do not limit the elements of the invention described in the summary of the invention section.

Industrial Applicability

[0024] The invention of the present disclosure can be used in the manufacturing industry of power conversion devices, energy storage systems, etc.

Explanation of Signs

[0025] 1 Energy storage system, 2 Power conditioner (power conversion device), 3 Storage battery, 4 DC / DC converter, 5,6 Capacitors, 7 System voltage sensor, 10 Control device, PS Power system.

Claims

[Claim 1] A control device for a power converter that is connected to a power grid and a DC power source and is capable of converting DC power from the DC power source into AC power and outputting it to the power grid, A control device for a power converter that, when it detects an instantaneous voltage drop in the power system, retains the frequency of the system voltage immediately before the detection of the instantaneous voltage drop and a phase addition amount based on the frequency, and while the instantaneous voltage drop is being detected, calculates the phase of the system voltage by adding the retained phase addition amount to the previously calculated value at predetermined time intervals when the previously calculated value of the phase of the system voltage is less than a predetermined reference value at the zero-crossing timing of the system voltage, and when the previously calculated value of the phase is greater than or equal to the reference value at the zero-crossing timing, and when the previously calculated value is greater than or equal to 2π at times other than the zero-crossing timing, resets the phase.

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