Hydroelectric Frequency Regulation via Double-Fed Asynchronous Machine
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Solution Overview
Problem
Classic hydroelectric power plants are limited by the inertia of the water column and water pressure, allowing only slow regulation of electrical output, which is insufficient for short-term grid frequency control, such as the requirements specified in the UK's National Grid Code that demands rapid injection or absorption of electrical output within less than a second.
Innovation Solution
A hydroelectric power plant design featuring a double-fed asynchronous machine connected to a frequency converter with a resistor in the DC link, allowing for rapid power control by braking or accelerating the turbine and asynchronous machine to release or absorb energy quickly, and optionally using a pump to store energy as potential energy for later use.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a classic hydroelectric power plant operates with water flow through the turbine, then it generates electrical power, but the regulation of electrical output is slow (10-30 seconds) due to water column inertia
Solution Approach 1:
The patent segments the power regulation function into two independent parts: (1) a fast-responding asynchronous machine with frequency converter that can rapidly inject or absorb power within one second, and (2) a traditional turbine system that provides sustained power generation. This segmentation allows the asynchronous machine to handle rapid frequency regulation while the turbine maintains baseline generation, resolving the contradiction between fast response and sustained operation.
Solution Approach 2:
The asynchronous machine serves multiple functions: it can operate as a generator during normal power production, as a rapid-response frequency regulator by injecting or absorbing power within one second, and can be controlled via frequency converter to perform both power injection and absorption. This multi-functionality enables a single device to address both sustained power generation and rapid frequency control requirements.
2Speed
If the asynchronous machine and turbine are braked to minimum speed, then power can be delivered to the grid quickly (less than one second), but the turbine must be rapidly accelerated afterward to restore power generation capacity
Solution Approach 1:
The system performs preliminary acceleration of the turbine and asynchronous machine to above-synchronous speeds before a frequency regulation event occurs. The frequency converter pre-charges the DC link and the turbine is positioned ready to rapidly brake. This preliminary preparation enables the system to deliver power to the grid within one second by simply braking, without needing time-consuming acceleration afterward, as the kinetic energy is already stored in the rotating mass.
3Loss of energy
If the pump is used to accelerate the asynchronous machine and turbine, then less energy needs to be converted to heat in the resistor, but the pump itself consumes power from the network
Solution Approach 1:
The patent converts the harmful energy dissipation in the resistor into a beneficial process by using the pump to drive the turbine, which generates electrical power that offsets the pump's power consumption. Instead of simply wasting energy as heat in the resistor, the system uses the same energy to drive the pump-turbine assembly, which then generates power back into the grid. This transforms the energy loss into a productive cycle where the pump's power consumption is partially or fully compensated by the turbine's power generation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables rapid power control on a timescale of less than one second, meeting the requirements for short-term grid frequency regulation while maintaining flexibility for long-term capacity matching, with the ability to provide or absorb power quickly and efficiently.
Implementation Method 1
a double-fed asynchronous machine (5), which is mechanically coupled to the turbine (4)
Implementation Method 2
the rotor of which is coupled to the turbine (4) via a frequency converter (6)
Implementation Method 3
a resistor (8) in the DC intermediate circuit of the frequency converter (6), which can be switched in such a way that it connects the strands of the DC intermediate circuit to one another
Implementation Method 4
at least one pump (9), which is arranged in such a way that it can pump water from the lower water basin (2) into the upper water basin (1)
Data Source
Figure 1
Figure 2
AI summary
The invention relates to a hydroelectric power plant for regulating the frequency of a power supply network, comprising an upper water pool (1), a lower water pool (2), a waterway (3) which connects the upper water pool (1) to the lower water pool (2), a turbine (4) which is arranged in the waterway (3) and comprises an impeller, a guide unit and a device for exhausting the impeller chamber, the hydroelectric power plant further comprising an electrical double-fed asynchronous machine (5) which is mechanically connected to the turbine (4), a frequency converter (6) which is electrically connected to the asynchronous machine, a network transformer (7) which is electrically connected to the asynchronous machine (5), the frequency converter (6) and the power supply network, a resistor (8) which is arranged in the direct current intermediate circuit of the frequency converter (6) such that it can connect the strands of the direct current intermediate circuit to one another, and a device for cooling the resistor (8).