CN117546388A

CN117546388A - Control entity and method for controlling a converter circuit to simulate an electrical output characteristic of a synchronous motor

Info

Publication number: CN117546388A
Application number: CN202280042431.7A
Authority: CN
Inventors: 弗朗西斯科·丹尼尔·弗赖耶多·费尔南德斯
Original assignee: Huawei Digital Power Technologies Co Ltd
Current assignee: Huawei Digital Power Technologies Co Ltd
Priority date: 2022-07-20
Filing date: 2022-07-20
Publication date: 2024-02-09
Also published as: WO2024017472A1

Abstract

The present invention relates to a control entity for controlling a converter circuit to simulate an electrical output characteristic of a synchronous motor. The converter circuit comprises a three-phase dc-ac converter and a filter comprising an inductance and a capacitance for each phase, the inductance and the capacitance being electrically connected in parallel to the output of the three-phase dc-ac converter. The converter circuit is configured to provide an output voltage at an output of the converter circuit using the voltage on the capacitor. The control entity is configured to: measuring a current flowing through the inductor and the voltage across the capacitor, controlling the voltage across the capacitor by controlling the current flowing through the inductor, and controlling the current flowing through the inductor by: the measured current and the measured voltage are used to control the output voltage of the three-phase dc-ac converter.

Description

Control entity and method for controlling a converter circuit to simulate an electrical output characteristic of a synchronous motor

Technical Field

The present invention relates to a control entity and a method for controlling a converter circuit to simulate an electrical output characteristic of a synchronous motor. Furthermore, the invention relates to a system comprising such a control entity and a converter circuit. In addition, the present invention relates to a computer program and a storage medium.

Background

The invention relates to a converter circuit comprising a three-phase dc-ac converter for providing a three-phase ac voltage. For example, the converter circuit may provide a three-phase alternating voltage to an alternating current grid, such as a mains supply. The term "power network" may be used as a synonym for the term "grid". The term "power converter" may be used as a synonym for the term "converter".

Disclosure of Invention

Today, the power network (ac grid) is faced with a situation where renewable energy sources are highly permeable and the power production of conventional power stations is reduced. Thus, the number of synchronous machines supplying power to (i.e., providing voltage to) an electrical power network is decreasing. That is, the amount of electricity generated using the synchronous motor is reduced. In this case of power generation, the rotational mass kinetic energy is available, which can be used for frequency control. Today, power electronics technology is being applied in integration to generate electricity. This generation can be said to be static, i.e. without rotation as in synchronous motors, and therefore there is no inertia based on power electronics technology.

From a power system level perspective, removing the synchronous motor may result in the aggregate inertia provided by the multiple rotating synchronous motors (i.e., the damper of rotational kinetic energy distributed in the power system) being removed. Lack of inertia can negatively impact power system frequency control because the balance between power generation and power consumption cannot be maintained.

In view of the above, the present invention aims to provide a method that enables power electronics (e.g. a converter circuit) to achieve similar performance as synchronous motors from a power system level perspective. It is an object of the invention to provide a method that enables a power electronic device, such as a converter circuit, to achieve a performance similar to a synchronous motor in terms of frequency and voltage control.

These and other objects are achieved by the solution of the invention described in the independent claims. Advantageous implementations are further defined in the dependent claims.

A first aspect of the invention provides a control entity for controlling a converter circuit to simulate an electrical output characteristic of a synchronous motor. The converter circuit comprises a three-phase dc-ac converter and a filter comprising an inductance and a capacitance for each phase, the inductance and the capacitance being electrically connected in parallel to the output of the three-phase dc-ac converter. The converter circuit is configured to provide an output voltage at an output of the converter circuit using the voltage on the capacitor. The control entity is configured to: measuring a current flowing through the inductor and the voltage across the capacitor, controlling the voltage across the capacitor by controlling the current flowing through the inductor, and controlling the current flowing through the inductor by: the measured current and the measured voltage are used to control the output voltage of the three-phase dc-ac converter.

The three-phase dc-ac converter may be referred to as a "three-phase inverter" or a "three-phase string inverter". A three-phase dc-ac converter may be used to convert direct current (dc voltage and/or dc current) to three-phase alternating current (ac voltage and/or ac current). The three-phase dc-ac converter may comprise three output terminals (which may be provided by the dc-ac converter) for three different phases of the three-phase ac power. The output of the dc-ac converter may comprise three output terminals of three phases. These three phases may be referred to as "three electrical phases". The respective inductances and capacitances of the filters may be electrically connected to each of the three output terminals of the three phases. The dc bus may provide dc power to a three-phase dc-ac converter. The dc bus may receive dc power from a renewable energy source (e.g., a Photovoltaic (PV) power station and/or a wind power station) and/or a battery energy storage system (e.g., one or more batteries, optionally one or more rechargeable batteries).

The three-phase dc-ac converter may be or may comprise an active switching dc-ac converter comprising at least one switch. The at least one switch may be at least one transistor, such as at least one bipolar transistor (bipolar junction transistor, BJT); at least one field effect transistor (field effect transistor, FET), such as at least one metal oxide semiconductor FET (metal oxide semiconductor FET, MOSFET); and/or at least one insulated gate bipolar transistor (insulated gate bipolar transistor, IGBT). The control entity may be for controlling the three-phase dc-ac converter of the converter circuit by controlling the switching of the at least one switch. The three-phase dc-ac converter may include one or more passive components, such as one or more inductors and/or capacitors, for power conversion and/or filtering.

The description of the measurement and control of the electrical variable/parameter is valid for each of the three phases accordingly. The terms "variable" and "parameter" may be used as synonyms. In other words, for each of the three phases, the converter circuit may be configured to provide an output voltage for that phase at an output of the converter circuit (e.g., at a respective output terminal of the converter circuit for that phase) using the phase voltage on the respective capacitor. The control entity may be arranged to measure the phase current flowing through the respective inductor and the phase voltage over the respective capacitor. The control entity may be arranged to control the phase voltage on the respective capacitor by controlling the phase current through the respective inductor. The control entity may be arranged to control the phase currents flowing through the respective inductances by: the measured phase current and the measured phase voltage are used to control the output voltage of the phase in a three-phase dc-ac converter.

The control of the converter circuit by the control entity enables the converter circuit to simulate the electrical output characteristics of the synchronous machine. The control entity provided by the first aspect of the invention thus enables the converter circuit to achieve similar performance as a synchronous motor from a power system level perspective. For example, the control entity enables the converter circuit to achieve similar performance in terms of frequency and voltage control as a synchronous motor. In other words, the first aspect provides a control entity for controlling the converter circuit to simulate the performance (e.g. electrical performance) of the synchronous motor. Synchronous motors are one example of motors. The synchronous motor may act as a synchronous generator.

It will be appreciated that the inductor and the capacitor are electrically connected together in parallel to the output of the three-phase dc-ac converter such that the output voltage of the three-phase dc-ac converter is equal to the sum of the voltage across the inductor and the voltage across the capacitor. In other words, the inductance and the capacitance are said to be electrically connected in series, wherein the series connection is electrically connected in parallel to the output of the three-phase dc-ac converter. The capacitance of the filter (for each phase) can play a critical role as an energy buffer for the analog synchronous motor. This capacitance may be referred to as an "output filter capacitance". The terms "simulate", "imitate" and "imitate" may be used as synonyms.

The control entity may be adapted to control the three-phase dc-ac converter such that the three-phase dc-ac converter effects ac voltage control of the capacitor for each phase of the filter.

Alternatively, the converter circuit may comprise a dc converter. The dc converter may be used to convert a first direct current (dc voltage and/or dc current) into a second direct current (dc voltage and/or dc current). The dc converter may be or may comprise an active switching dc converter comprising at least one switch. The at least one switch may be at least one transistor, such as at least one bipolar transistor (bipolar junction transistor, BJT); at least one field effect transistor (field effect transistor, FET), such as at least one metal oxide semiconductor FET (metal oxide semiconductor FET, MOSFET); and/or at least one insulated gate bipolar transistor (insulated gate bipolar transistor, IGBT). The control entity may be adapted to control the dc converter of the converter circuit by controlling the switching of the at least one switch. The dc converter may comprise one or more passive elements, such as one or more inductors and/or capacitors, for power conversion and/or filtering.

The output terminals of the three-phase dc-to-ac converter, the capacitors, and the dc side (i.e., the input terminal) of the three-phase dc-to-ac converter may be electrically connected in parallel with each other. The control entity may be used to control the dc converter such that the dc converter controls, optionally regulates, the flow of electric power from one or more electric energy sources, such as renewable energy sources, e.g. Photovoltaic (PV) power stations and/or wind power stations, and/or battery energy storage systems, e.g. one or more batteries, optionally one or more rechargeable batteries, and optionally the voltage over the aforementioned capacitor (dc link voltage).

The control entity may be implemented in software and/or hardware. Alternatively, the control entity may be a device that may include a processor or processing circuitry for performing, implementing, or initiating various operations of the control entity described herein. The processing circuitry may comprise hardware and/or the processing circuitry may be controlled by software. The hardware may include analog circuits or digital circuits, or both analog and digital circuits. The digital circuitry may include components such as application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA), digital signal processors (digital signal processor, DSP), or multi-purpose processors. The device may also include a storage circuit that stores one or more instructions executable by the processor or processing circuit (specifically, under control of software). For example, the storage circuitry may include a non-transitory storage medium storing executable software code that, when executed by a processor or processing circuitry, causes various operations of the device (i.e., the control entity) to be performed. In one embodiment, the processing circuitry includes one or more processors and a non-transitory memory coupled to the one or more processors. The non-transitory memory may carry executable program code that, when executed by one or more processors, causes an apparatus (i.e., a control entity) to perform, implement, or initiate the operations or methods described herein.

In one implementation form of the first aspect, the output of the converter circuit is electrically connected with a primary winding of a step-up transformer; the secondary winding of the step-up transformer is electrically connected to an ac power grid.

The leakage inductance of a step-up transformer is a physical parameter that closely mimics the inductance of a synchronous motor of the same power. The primary winding of the step-up transformer may be referred to as the "primary side" or the "low voltage primary side".

In one implementation form of the first aspect, the output of each of the plurality of converter circuits is electrically connected to a primary winding of a step-up transformer, a secondary winding of the step-up transformer being electrically connected to an ac power grid. The control entity may be adapted to control each of the plurality of converter circuits in accordance with a control of the converter circuit.

In other words, a plurality of converter circuits may be connected to the primary winding of the step-up transformer, wherein the output of each converter circuit is electrically connected to the primary winding of the step-up transformer. The control entity may be adapted to control each of the plurality of converter circuits to simulate an electrical output characteristic of the synchronous motor in accordance with a control of the converter circuit. This allows to simulate a multiphase synchronous machine. In other words, an equivalent synchronous motor may be considered a multiphase synchronous motor for which each of the plurality of converter circuits may power one three-phase portion of the overall machine (i.e., the number of terminals may be a multiple of three).

The term "multiphase" in the term "multiphase synchronous motor" may refer to a series of motors having a number of input terminals greater than three. For example, if ten converter circuits are connected to the primary winding of the step-up transformer, and each converter circuit has three input terminals for three phases, there are thirty input terminals in total. In this case, a synchronous motor can be simulated 30.

In other words, the above-described implementation of the first aspect is capable of simulating a multiphase synchronous motor for which each of the plurality of converter circuits is for powering one part of the virtual machine. The control entity enables the plurality of converter circuits (i.e. a set of converter circuits) to simulate a single multiphase motor, i.e. a single multiphase synchronous motor, instead of a set of uncorrelated three-phase motors. That is, the multi-phase motor has a greater number of phases than three phases of each three-phase motor. To this end, a control entity may be used to perform a distributed control (e.g. a distributed voltage control) of the plurality of converter circuits. That is, the control entity may be adapted to control each of the plurality of converter circuits in accordance with a control of the converter circuit. The distributed control of the plurality of converter circuits may mean that a set of local controllers may be implemented for each converter circuit (e.g. for a three-phase dc-ac converter of each converter circuit). That is, there is no sample-by-sample communication between the converter circuits. Therefore, the first converter circuit of the plurality of converter circuits does not use the input current or the like of the second converter circuit or the nth converter circuit (assuming that n is an integer equal to or greater than 2, n Σ2), but can achieve the control target of the entire system (i.e., the plurality of converter circuits). Thus, the control entity allows to control the plurality of converter circuits (i.e. the plurality of converter circuits) to operate in a coordinated manner providing at least one of: frequency control service, voltage control at the connection point (of the plurality of converter circuits with the primary winding of the step transformer), and short-circuit ratio similar to synchronous motors.

Distributed control (e.g., distributed voltage control) of the plurality of converter circuits supports implementations that handle balancing of power and voltages, and frequency generation, respectively. Since the capacitive voltages (e.g. power and/or voltage control) of the filter phases of the converter circuits can be controlled (the capacitive energy is proportional to the square of their voltage), the internal frequency of each converter circuit can be generated as it reflects the kinetic energy of the rotating electrical machine.

Thus, the generation of the internal frequency of the converter circuit (or of each of the plurality of converter circuits) supports an analogue/analogue synchronous motor. Since the three-phase dc-ac converter of the converter circuit (or of each of the plurality of converter circuits) is static (without rotating mass), its energy function can be obtained as a model equivalent. The energy stored in the filter capacitor for each phase can be used as energy that acts as rotational energy. Thus, if the energy decreases (i.e., the magnitude of the capacitor voltage of the corresponding phase decreases), the frequency will decrease. By implementing this in the converter circuit (or each of the plurality of converter circuits) by the control entity, the behaviour of the converter circuit (or the plurality of converter circuits) may be matched to the stability characteristics of the power system based on one or more synchronous machines.

When the arrangement including the plurality of converter circuits and the step-up transformer reaches a steady state, the output voltages of the plurality of converter circuits match, and they can simulate ("build up") an inverse electromotive force (counter potential or back electromotive force) behind the step-up transformer (i.e., on the secondary side/on the secondary winding side). That is, the ac power grid (distribution network) can see the synchronous motor at the secondary winding of the step-up transformer (i.e., at the secondary side of the step-up transformer).

Having a large equivalent synchronous motor (i.e., equivalent multiphase synchronous motor) formed by the cooperation of a step-up transformer and a plurality of converter circuits, when controlled by a control entity, can provide the following benefits at the system level: for example, if the plurality of converter circuits are used in a power generation system (e.g., a large Photovoltaic (PV) power plant), the converter circuits may be controlled by a control entity to simulate fewer but larger synchronous motors for each power generation system. This may make it easy to maintain at the power generation system level (i.e., power plant level). Furthermore, the control of the converter circuit by the control entity allows better utilization of the short-circuit ratio of the step-up transformer. The energy stored in the capacitor for each phase of the filters of the plurality of converter circuits may be regarded as a large buffer for providing energy of inertia and large short-circuit currents during a fault. The system has a large equivalent synchronous motor and can intelligently use a physical system. That is, leakage inductance of the step-up transformer can well simulate inductance of the motor. The leakage inductance of a step-up transformer is a physical parameter that closely mimics the inductance of a synchronous motor of the same power.

In one implementation of the first aspect, a node between the inductance and the capacitance is electrically connected to the output of the converter circuit. The control entity may be configured to: measuring or estimating an output current flowing from the node to the output of the converter circuit, and controlling the output voltage of the three-phase dc-ac converter using the measured or estimated output current in addition to the measured current and the measured voltage.

In an implementation manner of the first aspect, the node between the inductance and the capacitance is electrically connected to the output terminal of the converter circuit through a second inductance; the output current is a current flowing through the second inductor.

In other words, the control entity may be configured to: measuring or estimating a current flowing through the second inductance (from the node to the output of the converter circuit), and controlling the output voltage of the three-phase dc-ac converter using the measured or estimated current flowing through the second inductance in addition to the measured current and the measured voltage.

In an implementation form of the first aspect, the control entity is configured to calculate the reference value of the current flowing through the inductance using a reference value of the magnitude of the voltage on the capacitance and a magnitude of the measured voltage on the capacitance. The control entity may be configured to calculate a reference value for the output voltage of the three-phase dc-ac converter using the calculated reference value for the current flowing through the inductance.

In an implementation form of the first aspect, the control entity is configured to calculate the reference value of the output voltage of the three-phase dc-ac converter using the voltage phase angle reference value on the capacitor.

In an implementation form of the first aspect, the control entity is configured to calculate the reference value of the output voltage of the three-phase dc-ac converter by: converting the measured current flowing through the inductance into a dq coordinate system using the phase angle reference value; inputting the dq coordinate system of the reference value of the current flowing through the inductor and the converted measured current flowing through the inductor into a controller transfer function, wherein the dq coordinate system takes the calculated reference value of the current flowing through the inductor as q-axis or d-axis; and converting a value based on an output of the controller transfer function into an abc coordinate system using the phase angle reference value.

For the dq coordinate system of the reference value of the current flowing through the inductor, the other of the q-axis and the d-axis (the calculated reference value of the current not flowing through the inductor) may be zero amperes. In other words, the dq coordinate system of the reference value of the current flowing through the inductor may include zero ampere as the other of the q-axis and the d-axis (the calculated reference value of the current not flowing through the inductor). The magnitude of the voltage on the capacitor may be controlled in one control loop and the phase angle/frequency of the voltage on the capacitor may be controlled in another control loop. The conversion using the dq coordinate system enables the two control loops described above to be combined in one control loop. Thus, all relevant information can be in one control loop. This can simplify the control by the control entity and thus simplify the control entity.

The controller transfer function may be or may include a transfer matrix with non-zero decoupling terms. The transfer matrix may be a 2 by 2 matrix (2 x 2 matrix).

The control entity calculating the reference value of the output voltage of the three-phase dc-ac converter may be referred to as a current control loop (e.g., the innermost current control loop). That is, the current flowing through the inductor can be controlled by controlling the output voltage of the three-phase dc-ac converter. That is, the current control loop supports controlling, optionally regulating, the current delivered from the three-phase dc-ac converter to the inductance of the filter.

The abc coordinate system generated from the values based on the output of the controller transfer function is the output voltage reference value of the three-phase dc-ac converter. The abc coordinate system may include or be a pulse-width modulation (PWM) reference for setting PWM pulses or signals that may be used to control the three-phase dc-ac converter in the case where PWM pulses or signals are used to control the three-phase dc-ac converter. The control entity may be used to control the three-phase dc-ac converter using PWM pulses or signals.

In an implementation form of the first aspect, the control entity is configured to calculate the reference value of the output voltage of the three-phase dc-ac converter by: converting the voltage on the capacitor to a dq coordinate system using the phase angle reference, inputting the output of the controller transfer function and the converted voltage on the capacitor into a state feedback active damping unit, and converting the output of the state feedback active damping unit to the abc coordinate system using the phase angle reference.

The abc coordinate system generated from the output of the state feedback active damping unit is the output voltage reference value of the three-phase dc-ac converter. The abc coordinate system may include or be a pulse-width modulation (PWM) reference for setting PWM pulses or signals that may be used to control the three-phase dc-ac converter in the case where PWM pulses or signals are used to control the three-phase dc-ac converter. The control entity may be used to control the three-phase dc-ac converter using PWM pulses or signals. The state feedback active damping unit may be used for stability purposes, i.e. it may improve stability.

In an implementation form of the first aspect, the control entity is configured to calculate the reference value of the current flowing through the inductor by: calculating a difference between the magnitude of the measured voltage on the capacitor and the magnitude reference value of the voltage on the capacitor and inputting the calculated difference into a controller transfer function, wherein the controller transfer function is configured to calculate the reference value of the current flowing through the inductor using the input difference.

The reference value by which the control entity calculates the current through the inductor may be referred to as a back emf control loop (back emf control loop or back emf control loop, e.g., a distributed back emf/back emf control loop). This supports controlling the magnitude of the voltage across the capacitor. In particular, this enables the control entity to regulate the amplitude of the voltage on the capacitor itself (i.e. to perform voltage control) and to regulate the buffer of energy that can exert a similar effect as the kinetic energy in the rotation of the synchronous motor (i.e. the inertia of the frequency control action).

The controller transfer function may include a proportional controller (e.g., proportional gain). In other words, the control entity may be adapted to input the calculated difference value into a proportional controller adapted to calculate a reference value of the current through the inductor using the input difference value.

In an implementation form of the first aspect, the control entity is configured to calculate the amplitude reference value of the voltage on the capacitor by means of an equalization, wherein the equalization uses the measured or estimated output current to correct a main reference value of the voltage on the capacitor.

If the converter circuit (optionally a plurality of converter circuits) is used in a power generation system, such as a Photovoltaic (PV) power plant or a wind power plant, the main reference value may be set at a power generation system control level (i.e. a power plant control level). The control entity may receive a primary reference value of the voltage across the capacitor (e.g., from a user or operator, such as a user or operator of the power generation system). The main reference value of the voltage over the capacitor may be constant or a slowly varying parameter that varies slowly compared to the control of the converter circuit by the control entity. The primary reference value may be referred to as a "center reference value".

In an implementation form of the first aspect, the control entity is configured to correct the main reference value of the voltage on the capacitor by: the magnitude of the measured or estimated output current is input into a low pass filter transfer function for an analog equalization resistor and the output of the low pass filter transfer function is subtracted from the main reference value.

The term balancing resistor may be referred to as a "virtual balancing resistor". In other words, the control entity may be adapted to correct the main reference value by means of an equalization action, wherein the equalization uses the measured or estimated magnitude of the output current and passes it through a low-pass filter transfer function for simulating an equalization resistor. The transfer function supports taking into account bandwidth limitations (e.g., below 5 Hz) to avoid interaction with one or more other control loops. That is, the back electromotive force control loop (back electromotive force control loop or back electromotive force control loop) that can be performed by the control entity may be back electromotive force control with active equalization for power sharing between converter circuits (for example, in the case where a plurality of converter circuits are connected to the primary winding of the step-up transformer, i.e., to the same step-up transformer primary winding). In case the control entity controls a plurality of control circuits, each of which may be connected to one step-up transformer, the measured or estimated magnitude of the output current in combination with the low-pass filter transfer function enables an active sharing of power between the plurality of converter circuits. The magnitude of the measured or estimated output current may be a magnitude proportional to the torque and power delivered in a synchronous motor (e.g., synchronous generator) whose electrical output characteristics or performance may be modeled by a control entity controlling the converter circuit.

In an implementation form of the first aspect, the control entity is configured to estimate the magnitude of the estimated output current at the present point in time by: calculating a difference between the magnitude of the measured current flowing through the inductor at the present point in time and the estimated magnitude of the output current at a point in time prior to the present point in time; inputting the calculated difference value into an estimator model simulating capacitor charging and discharging; calculating a difference between a reference value of the voltage on the capacitor at the current point in time and an output of the estimator model; the calculated difference is input into a controller transfer function, wherein the controller transfer function is configured to calculate the magnitude of the estimated output current at the present point in time using the input difference.

The controller transfer function may include a proportional controller (e.g., proportional gain). In other words, the control entity may be adapted to input the calculated difference value into a proportional controller, wherein the proportional controller is adapted to use the input difference value to calculate the magnitude of the estimated output current at the present point in time. The capacitance that simulates charging and discharging by the estimator model may be the capacitance of the filter. The estimator model may be referred to as an "estimator". Alternatively, the estimator model is based on modeling the capacitance by a simplified direct current equivalent (which may be set in the dq coordinate system), which may take into account the input and output currents associated with the capacitance and how these currents charge and discharge the capacitance.

In an implementation form of the first aspect, the control entity is configured to calculate the phase angle reference value by inputting a frequency reference value of an ac power grid into an integrated unit, wherein an output of the integrated unit is the phase angle reference value.

The control entity calculating the phase angle reference value may be referred to as a frequency control loop (e.g., a distributed frequency control loop).

In an implementation form of the first aspect, the control entity is configured to calculate the frequency reference value of the ac power grid by means of an equalization, wherein the equalization uses the measured or estimated output current to correct a frequency main reference value of the ac power grid.

The control entity may receive a frequency primary reference value of the ac power grid (e.g., from a user or operator, such as a user or operator of the power generation system). The frequency main reference (center reference) of the ac grid may be constant (e.g., a constant parameter proportional to the rated frequency, typically 50 Hertz (Hertz, hz) in european ac grids, typically 60Hz in the united states). Alternatively, the frequency main reference value of the ac power grid may be a slowly varying parameter. For example, if the converter circuit (optionally a plurality of converter circuits) is used in a power generation system, such as a Photovoltaic (PV) power station or a wind power station, the frequency primary reference value of the ac power grid may be a slowly varying parameter set by the power generation system control (i.e. power station control), such as some value close to the nominal frequency setting (set at 50Hz or 60 Hz). The frequency primary reference value of the ac power grid may be a constant or slowly varying parameter (which varies slowly compared to the control of the converter circuit by the control entity) as an acting parameter of a slower frequency control scheme (compared to the control of the converter circuit by the control entity) at the power generation system level (i.e. at the power plant level), for example primary, secondary or tertiary frequency control performed from the power generation system level.

In an implementation form of the first aspect, the control entity is configured to correct the frequency master reference value of the ac power grid by: the magnitude of the measured or estimated output current is input into a low pass filter transfer function for an analog equalization resistor and the output of the low pass filter transfer function is subtracted from the main reference value.

For example, if the output of each of the plurality of converter circuits is electrically connected to the primary winding of the step-up transformer and equal active current sharing is achieved, then in steady state the magnitude of the measured or estimated output current may be used or applied for frequency droop control/function. One of the main objectives of droop control is to have a plurality of converter circuits operating during formation of the grid reach the same frequency in steady state, which is also a useful information of the kinetic energy stored in each of the plurality of converter circuits. By using the measured or estimated amplitude of the output current and the low pass filter transfer function, an ac grid frequency reference value consistent with all of the plurality of converter circuits may be calculated. This allows a good simulation of the operation of an electric power system based on a plurality of synchronous generators.

To implement the control entity provided in the first aspect of the present invention, some or all of the implementation manners and optional features of the first aspect may be combined with each other as described above.

A second aspect of the invention provides a system. The system comprises a control entity provided in the first aspect of the invention for controlling the converter circuit to simulate the electrical output characteristics of the synchronous motor, as described above. The system comprises the converter circuit comprising a three-phase dc-ac converter and a filter comprising one inductance and one capacitance for each phase, the inductance and the capacitance being electrically connected in parallel to the output of the three-phase dc-ac converter. The converter circuit is configured to provide an output voltage at an output of the converter circuit using the voltage on the capacitor.

Alternatively, the converter circuit may comprise a three-phase dc converter. The output of the dc-to-ac converter, the capacitor and the dc side (e.g. the input) of the three-phase dc-to-ac converter may be electrically connected in parallel to each other. The input of the dc converter may be adapted to be electrically connected to one or more sources of electrical energy (e.g. a renewable energy source such as a Photovoltaic (PV) power station and/or a wind power station, and/or one or more batteries, optionally one or more rechargeable batteries). The primary function of the circuit (which may be referred to as an internal circuit) comprising one or more batteries and/or any other energy storage system (i.e. any other source(s) of electrical energy) may be to ensure that the dc-ac converter is able to provide the active power and active current required by the controller (e.g. the control entity).

In one implementation of the second aspect, the system includes a step-up transformer and a plurality of the converter circuits. The output of each converter circuit of the system is electrically connected with a primary winding of the step-up transformer; the secondary winding of the step-up transformer is electrically connected to an alternating current power grid; the control entity is for controlling each converter circuit of the system.

The above description of the control entity provided in the first aspect is correspondingly valid for the system provided in the second aspect. For example, the description of the converter circuit in describing the control entity of the first aspect may also be valid for the converter circuit of the system.

The system of the second aspect and its implementation forms and optional features achieve the same advantages as the control entity of the first aspect and its corresponding implementation forms and corresponding optional features.

To implement the system provided by the second aspect of the present invention, some or all of the implementation manners and optional features of the second aspect may be combined with each other as described above.

A third aspect of the invention provides a method for controlling a converter circuit to simulate an electrical output characteristic of a synchronous motor. The converter circuit comprises a three-phase dc-ac converter and a filter comprising an inductance and a capacitance for each phase, the inductance and the capacitance being electrically connected in parallel to the output of the three-phase dc-ac converter. The converter circuit is configured to provide an output voltage at an output of the converter circuit using the voltage on the capacitor. The method comprises the following steps: measuring a current flowing through the inductor and the voltage across the capacitor, controlling the voltage across the capacitor by controlling the current flowing through the inductor, and controlling the current flowing through the inductor by: the measured current and the measured voltage are used to control the output voltage of the three-phase dc-ac converter.

In an implementation manner of the third aspect, the output terminal of the converter circuit is electrically connected with a primary winding of a step-up transformer; the secondary winding of the step-up transformer is electrically connected to an ac power grid.

In one implementation of the third aspect, the output of each of the plurality of converter circuits is electrically connected to a primary winding of a step-up transformer, a secondary winding of which is electrically connected to an ac power grid. The method may comprise controlling each of the converter circuits according to a control of the converter circuits.

In one implementation of the third aspect, a node between the inductance and the capacitance is electrically connected to the output of the converter circuit. The method may include: measuring or estimating an output current flowing from the node to the output of the converter circuit, and controlling the output voltage of the three-phase dc-ac converter using the measured or estimated output current in addition to the measured current and the measured voltage.

In an implementation manner of the third aspect, the node between the inductance and the capacitance is electrically connected to the output terminal of the converter circuit through a second inductance; the output current is a current flowing through the second inductor.

In one implementation of the third aspect, the method includes calculating a reference value of the current flowing through the inductor using a reference value of the magnitude of the voltage on the capacitor and a magnitude of the measured voltage on the capacitor. The method may include calculating a reference value of the output voltage of the three-phase dc-ac converter using the calculated reference value of the current flowing through the inductor.

In one implementation of the third aspect, the method includes calculating the reference value of the output voltage of the three-phase dc-ac converter using a phase angle reference value of the voltage on the capacitor.

In one implementation form of the third aspect, the method comprises calculating the reference value of the output voltage of the three-phase dc-ac converter by: converting the measured current flowing through the inductance into a dq coordinate system using the phase angle reference value; inputting the dq coordinate system of the reference value of the current flowing through the inductor and the converted measured current flowing through the inductor into a controller transfer function, wherein the dq coordinate system takes the calculated reference value of the current flowing through the inductor as q-axis or d-axis; and converting a value based on an output of the controller transfer function into an abc coordinate system using the phase angle reference value.

In one implementation form of the third aspect, the method comprises calculating the reference value of the output voltage of the three-phase dc-ac converter by: converting the voltage on the capacitor to a dq coordinate system using the phase angle reference, inputting the output of the controller transfer function and the converted voltage on the capacitor into a state feedback active damping unit, and converting the output of the state feedback active damping unit to the abc coordinate system using the phase angle reference.

In one implementation manner of the third aspect, the method includes calculating the reference value of the current flowing through the inductor by: calculating a difference between the magnitude of the measured voltage on the capacitor and the magnitude reference value of the voltage on the capacitor and inputting the calculated difference into a controller transfer function, wherein the controller transfer function is configured to calculate the reference value of the current flowing through the inductor using the input difference.

In one implementation of the third aspect, the method comprises calculating the amplitude reference value of the voltage on the capacitance by equalization, wherein the equalization uses the measured or estimated output current to correct a main reference value of the voltage on the capacitance.

In one implementation of the third aspect, the method includes correcting the main reference value of the voltage on the capacitor by: the magnitude of the measured or estimated output current is input into a low pass filter transfer function for an analog equalization resistor and the output of the low pass filter transfer function is subtracted from the main reference value.

In one implementation of the third aspect, the method comprises estimating the magnitude of the estimated output current at the present point in time by: calculating a difference between the magnitude of the measured current flowing through the inductor at the present point in time and the estimated magnitude of the output current at a point in time prior to the present point in time; inputting the calculated difference value into an estimator model simulating capacitor charging and discharging; calculating a difference between a reference value of the voltage on the capacitor at the current point in time and an output of the estimator model; the calculated difference is input into a controller transfer function, wherein the controller transfer function is configured to calculate the magnitude of the estimated output current at the present point in time using the input difference.

In one implementation of the third aspect, the method comprises calculating the phase angle reference value by inputting a frequency reference value of an ac power grid into an integrated unit, wherein an output of the integrated unit is the phase angle reference value.

In one implementation of the third aspect, the method comprises calculating the frequency reference value of the ac power grid by means of an equalization, wherein the equalization uses the measured or estimated output current to correct a frequency main reference value of the ac power grid.

In one implementation of the third aspect, the method includes correcting the frequency primary reference value of the ac power grid by: the magnitude of the measured or estimated output current is input into a low pass filter transfer function for an analog equalization resistor and the output of the low pass filter transfer function is subtracted from the main reference value.

The above description of the control entity provided in the first aspect is correspondingly valid for the method provided in the third aspect.

The method and implementation manner and optional features provided by the third aspect achieve the same advantages as the control entity of the first aspect and its corresponding implementation manner and corresponding optional features.

To implement the method provided by the third aspect of the present invention, some or all of the implementation manners and optional features of the third aspect may be combined with each other as described above.

A fourth aspect of the invention provides a computer program comprising instructions which, when executed by a computer, cause the computer to perform the method provided by the third aspect as described above.

A fifth aspect of the invention provides a storage medium storing executable program code which, when executed by a processor, causes the method provided by the third aspect as described above to be performed.

A sixth aspect of the invention provides a computer comprising a memory and a processor for storing and executing program code to perform the method provided in the third aspect as described above.

A seventh aspect of the invention provides a non-transitory storage medium storing executable program code which, when executed by a processor, causes the method provided by the third aspect as described above to be performed.

The computer program provided by the fourth aspect, the storage medium provided by the fifth aspect, the computer provided by the sixth aspect and the non-transitory storage medium provided by the seventh aspect, respectively, achieve the same advantages as the control entity of the first aspect and its respective implementations and respective optional features.

All steps performed by the various entities described in this application, as well as functions to be performed by the various entities described are intended to mean that the respective entities are adapted to perform the respective steps and functions. Although in the following description of specific embodiments, specific functions or steps performed by external entities are not reflected in the description of specific detailed elements of the entity performing the specific steps or functions, it should be clear to a skilled person that these methods and functions may be implemented by corresponding hardware or software elements or any combination thereof.

Drawings

The various aspects described above and the manner of attaining them will be elucidated with reference to the accompanying drawings, wherein:

FIG. 1 shows an example of a control entity provided by an embodiment of the present invention and an example of a system provided by an embodiment of the present invention;

FIG. 2 shows an example of a method provided by an embodiment of the present invention;

FIG. 3 shows an example of a control entity provided by an embodiment of the present invention and an example of a system provided by an embodiment of the present invention;

FIG. 4 shows an example of a control entity provided by an embodiment of the present invention and an example of a system provided by an embodiment of the present invention;

fig. 5 to 8 respectively show examples of one function of a control entity provided by an embodiment of the present invention;

FIG. 9 illustrates an example of a converter circuit controllable by a control entity provided by an embodiment of the present invention;

fig. 10 shows an example of a synchronous motor provided by an embodiment of the present invention, whose electrical output characteristics can be simulated by control performed by a control entity.

In the figures, corresponding elements are denoted by the same reference numerals.

Detailed Description

Fig. 1 shows an example of a control entity provided by an embodiment of the present invention and an example of a system provided by an embodiment of the present invention. The control entity 1 of fig. 1 is an example of a control entity provided in the first aspect of the invention. The description of the control entity provided for the first aspect is thus valid accordingly for the control entity 1 of fig. 1. System 5 is an example of a system provided by the second aspect of the present invention. Thus, the description of the system provided for by the second aspect is correspondingly valid for the system 5 of fig. 1.

The control entity 1 of fig. 1 is a control entity for controlling the converter circuit 2 to simulate the electrical output characteristics of a synchronous motor. The converter circuit 1 comprises a three-phase dc-ac converter 3 and a filter 4 comprising an inductance L for each phase _In And a capacitor C _n The inductance and the capacitance are electrically connected in parallel to the output of the three-phase dc-ac converter 3. It may be assumed that an energy buffer (e.g. an ideal voltage source, such as an ideal dc voltage source) is available on the dc side of the three-phase dc-ac converter 3 for absorbing or injecting power into the ac system (i.e. to the ac side of the converter circuit 2, where the ac side of the three-phase dc-ac converter 3 is present in the converter circuit 2), as required by the control entity 1. An example of such an energy buffer is shown in fig. 4, where one or more batteries may provide direct current p _st And/or receiving direct current p _st And/or one or more renewable energy sources (e.g. Photovoltaic (PV) power stations and/or wind power stations) may provide direct current (p) _gen . In fig. 1, the inductance L of only one of the three phases is shown _In And capacitor C _n . Nevertheless, it flows through the inductance L _In Is vector of the current 104 of (2)In the form of (a), the vector comprises for each phase a respective inductance L flowing through each of the three phases _In Is set, is provided) and is current 104. As well as in the other figures. Thus, in the figures, the other electrical parameters are represented in the form of vectors comprising the value of each of the three phases (e.g. vector +.>Capacitor C _n Vector of voltage 102 on->Vector of output voltage 103 at output of converter circuit 2 +.>From inductance L _In And capacitor C _n A vector of the output currents 105 flowing from the node N1 in between to the output of the converter circuit 2 +.>Etc.). That is, in each figure, a vector (vector signal) is used to represent three-phase electrical parameters/variables. The description of the measurement and control of the electrical parameters/variables is valid accordingly for each of the three phases. The converter circuit 2 is for using a capacitor C _n The upper voltage 102 provides an output voltage 103 at the output of the converter circuit 2. The control entity 1 is arranged to: measuring the inductance L of the flow _In Current 104 and capacitance C of (2) _n Voltage 102 across the inductor L is controlled by _In To control the capacitance C by the current 104 of (2) _n Voltage 102 across, and through inductance L is controlled in the following manner _In Is set to current 104: the measured current and the measured voltage are used to control the output voltage 101 of the three-phase dc-ac converter 3.

As shown in fig. 1, inductance L _In And capacitor C _n The node N1 in between is electrically connected to the output of the converter circuit 2. The control entity 1 may be arranged to: measuring or estimating flow transitions from node N1The output current 105 at the output of the converter circuit 2 and the measured or estimated output current 105 are used in addition to the measured current and the measured voltage to control the output voltage 101 of the three-phase dc-ac converter 3.

The control entity 1 may be implemented by hardware and/or software. Alternatively, the control entity 1 may be a device comprising a processor or processing circuitry (not shown) for performing, enforcing, or initiating various operations of the control entity described herein. The processing circuitry may comprise hardware and/or the processing circuitry may be controlled by software. The hardware may include analog circuits or digital circuits, or both analog and digital circuits. The digital circuitry may include components such as application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA), digital signal processors (digital signal processor, DSP), or multi-purpose processors. The device (control entity 1) may also comprise a storage circuit storing one or more instructions executable by a processor or processing circuit, in particular under control of software. For example, the storage circuitry may include a non-transitory storage medium storing executable software code that, when executed by a processor or processing circuitry, causes various operations of the device to be performed. In one embodiment, the processing circuitry includes one or more processors and a non-transitory memory coupled to the one or more processors. The non-transitory memory may carry executable program code that, when executed by one or more processors, causes the apparatus (control entity 1) to perform, implement or initiate the operations or methods described herein.

The control entity 1 may be used for controlling a three-phase dc-ac converter 3 (as indicated by the arrow in fig. 1). For example, the control entity 1 may be used to control the three-phase dc-ac converter 3 such that the three-phase dc-ac converter 3 implements a pair of capacitances C for each phase of the filter 4 _n Ac voltage control of (a) is provided.

The control entity 1 and the converter circuit 2 may constitute a system 5, as shown in fig. 1.

Examples of controls executable by the control entity 1 for controlling the converter circuit 2 (or the plurality of converter circuits 2, not shown in fig. 1) are described in connection with fig. 5 to 8.

Fig. 2 shows an example of a method provided by an embodiment of the present invention. The method of fig. 2 is an example of the method provided by the third aspect of the invention. Thus, the description of the method provided for the third aspect is correspondingly valid for the method of fig. 2. The control entity 1 of fig. 1 may be used to perform the method of fig. 2.

The method of fig. 2 is a method for controlling a converter circuit (e.g., the converter circuit of any of fig. 1, 3, and 4) to simulate an electrical output characteristic of a synchronous motor. The converter circuit comprises a three-phase dc-ac converter and a filter comprising an inductance and a capacitance for each phase, the inductance and the capacitance being electrically connected in parallel to the output of the three-phase dc-ac converter. The converter circuit is configured to provide an output voltage at an output of the converter circuit using the voltage on the capacitor. As shown in fig. 2, as a first step S1, the method comprises measuring a current flowing through an inductor and a voltage across a capacitor. In a second step S2, following the first step S1, the method comprises controlling the voltage across the capacitor by controlling the current through the inductor. In a third step S3, following the second step S2, the method comprises controlling the current through the inductor by: the measured current and the measured voltage are used to control the output voltage of the three-phase dc-ac converter.

Fig. 3 shows an example of a control entity provided by an embodiment of the present invention and an example of a system provided by an embodiment of the present invention. The control entity 1 and the system 5 of fig. 3 (e.g. the converter circuit 2) are examples of the control entity 1 and the system 5 of fig. 1 (e.g. the converter circuit 2), respectively. The description of fig. 1 is thus correspondingly valid for the control entity 1 and the system 5 of fig. 3 (e.g. the converter circuit 2), and additional features of the system 5 of fig. 3 (e.g. the converter circuit 2) are mainly described below.

As shown in fig. 3, inductance L _In And capacitor C _n The node N1 between the two is connected with the second inductor L _On Electrically connected to the converterThe output end of the path 2; the output current 105 flows through the second inductor L _On Is set in the above-described range). That is, the filter 4 includes an inductance L for each phase _In Capacitance C _n And a second inductance L _On 。

Fig. 4 shows an example of a control entity provided by an embodiment of the present invention and an example of a system provided by an embodiment of the present invention. The control entity 1 and the system 5 of fig. 4 (e.g. the converter circuit 2) are examples of the control entity 1 and the system 5 of fig. 3 (e.g. the converter circuit 2), respectively. The description of fig. 1 and 3 is thus correspondingly valid for the control entity 1 and the system 5 of fig. 4 (e.g. the converter circuit 2), and additional features of the system 5 of fig. 4 (e.g. the control entity 1 and the converter circuit 2) are mainly described below.

Optionally, a second inductance L for each phase of the filter 4 _On May be omitted. That is, in comparison to fig. 3, additional features of the system 5 of fig. 4 may be implemented in the system 5 of fig. 1.

As shown in fig. 4, the converter circuit 2 may include a dc converter 6 and a capacitor C _2n . Output end of three-phase DC converter 6, capacitor C _2n And the dc side (e.g., input) of the three-phase dc-ac converter 3 may be electrically connected in parallel with each other. The input of the dc converter may be adapted to be electrically connected to one or more sources of electrical energy, for example a renewable energy source such as a Photovoltaic (PV) power station and/or a wind power station, and/or one or more batteries, optionally one or more rechargeable batteries. The renewable energy source may provide a direct current p to the direct current converter 6 _gen . One or more batteries may provide direct current p to the dc converter 6 _st And/or receiving direct current p from the direct current converter 6 _st . The dc converter 6 can supply dc power p _in The DC-AC converter can receive DC power p _out 。

The control entity 1 may be used for controlling a three-phase dc converter 6 (not shown in fig. 4). For example, the control entity 1 may be used to control the three-phase direct current converter 6 such that the three-phase direct current converter 6 controls, optionally regulates, the power flow from one or more electrical energy sources (e.g. renewable energy sources such as Photovoltaic (PV) power stations and/or Wind power plant) and optionally a capacitance C _2n Voltage V on _dc (dc link voltage).

The control entity 1, the converter circuit 2 and optionally one or more sources of electrical energy, e.g. renewable energy sources such as Photovoltaic (PV) power stations and/or wind power stations, and/or one or more batteries, optionally one or more rechargeable batteries, may optionally constitute a system 5, as shown in fig. 4.

Fig. 5 to 8 respectively show examples of one function of the control entity provided by the embodiment of the present invention. The functions of any of fig. 5 to 8 may be performed by the control entity 1 of any of fig. 1, 3 and 4.

In the following, fig. 5 to 8 are described in connection with the control entity 1 and the system 5 of fig. 4. Furthermore, it is assumed that the input of the converter circuit 2 is electrically connected to a Photovoltaic (PV) power station. This is by way of example only, and the following description is therefore correspondingly valid for different implementations of the converter circuit 2 and/or for different sources of electrical energy. Alternatively, the control entity 1 may control a plurality of converter circuits 1, wherein the output of each of the plurality of converter circuits 1 is electrically connected to a primary winding of a step-up transformer, the secondary winding of which is electrically connected to an ac power grid (as exemplarily shown in fig. 9). That is, there may be a plurality of converter circuits, each of which is implemented as the converter circuit 1. The control entity 1 may control each of the plurality of converter circuits, and an output of each of the plurality of converter circuits is electrically connected with a primary winding of the step-up transformer. The control entity 1 may be adapted to perform (at the converter circuit level) a distributed control of one converter circuit 1 (as shown in any of fig. 1, 3 and 4) or of each of a plurality of converter circuits 1 (i.e. several converter circuits, as exemplarily shown in fig. 9).

Distributed control may be understood as high bandwidth control using local currents and voltages at the converter circuit point, i.e. actions performed at a sampling frequency equal to or higher than the switching frequency of a power electronic converter, such as a three-phase dc-ac converter 3. System level command mayTo transmit at a slower rate by communication means: for example, power plant control (i.e., control of a photovoltaic power plant) may control the capacitance C _n The amplitude reference value of the voltage 102 thereon is modified to a plurality of converter circuits (in case each of the plurality of converter circuits is connected to the primary winding of the step-up transformer) to achieve a given objective of the power plant level (the low bandwidth communication does not impair the distributed control features that depend on the converter circuit control, such as real-time control of the converter circuit). Further, it is assumed that the control entity 1 performs control of the converter circuit using conversion to the dq coordinate system. The following description works accordingly without using a conversion to the dq coordinate system. The magnetic flux can be assumed to be aligned with the d-axis according to a common standard for synchronous motor control. Thus, it is assumed that the back emf (counter potential) is aligned with the q-axis and that the torque/power flow can be controlled, optionally regulated, by acting on the q-axis current. Meanwhile, when working in the dq coordinate system domain, several basic dq axis definitions may be followed in view of similar performance. In other words, the present invention is not limited to the dq axis definition described herein. The descriptions of the various figures (e.g., fig. 5-8) are valid accordingly in the case of different definitions of the dq axes.

Fig. 5 shows a control, optionally regulation, of the flow of the three-phase dc-ac converter 3 through the inductance L _In Is shown, is an example of current 104. The control loop exemplarily shown in fig. 5 may be referred to as an innermost current control loop.

The control entity 1 may be arranged to: using capacitance C _n Amplitude reference value of voltage 102 and capacitance C _n The magnitude of the measured voltage 102 across it is used to calculate the flow-through inductance L _In A reference value 106 of the current 104 of (c). Fig. 6 shows an example of the control loop calculated as described above. As shown in fig. 5, the control entity 1 may be configured to: using a flowing-through inductance L _In The calculated reference value 106 of the current 104 of the three-phase dc-ac converter 3 to calculate a reference value 108 of the output voltage 101 of the three-phase dc-ac converter. In fig. 5, a vector of reference values 108 of the output voltage 101 of the three-phase dc-ac converter 3 is shownThe vector isFor each of the three phases, a respective reference value +.>As shown in fig. 5, the control entity 1 may be configured to: using capacitance C _n The phase angle reference 107 of the upper voltage 102 is used to calculate the reference 108 of the output voltage 101 of the three-phase dc-ac converter 3. In fig. 5, capacitance C _n The phase angle reference 107 of the voltage 102 is marked as "θ" _M ”。

As shown in fig. 5, the control entity 1 may be configured to calculate a reference value 108 of the output voltage 101 of the three-phase dc-ac converter 3 by: will flow through inductance L using phase angle reference 107 _In Is converted into a dq coordinate system; will flow through the inductance L _In Dq coordinate system of reference value of current 104 of (2) and flowing through inductance L _In Is input to the controller transfer function 8 (e.g., K _cc (z)) in which the dq coordinate system will flow through inductance L _In Is used as q-axis (e.g.) Or d-axis->And converting the value based on the output of the controller transfer function 8 into an abc coordinate system using the phase angle reference value 107. In fig. 5, the flow through inductance L is shown _In Vector of measured current 104 of (2)>The vector comprising, for each of the three phases, a current flowing through the respective inductance L _In Is the current i of (2) _Ian 、i _Ibn Or i _Icn . The conversion to the dq coordinate system is indicated in fig. 5 by a conversion box 6 of the abc coordinate system to the dq coordinate system. Through inductance L _In The dq coordinate system of the measured current 104 of (provided by the transformation box 6) is shown as a value "i" including the d-axis _IDn "and q-axis value" i _IQn "vector. TerminologyThe "d-axis value" and the "q-axis value" may be referred to as "d-value" and "q-value", respectively. The conversion to the abc coordinate system is indicated in fig. 5 by the conversion box 7 of the dq coordinate system to the abc coordinate system.

Alternatively, as shown in fig. 5, the control entity 1 may be adapted to calculate the reference value 108 of the output voltage 101 of the three-phase dc-ac converter 3 by: capacitor C using phase angle reference 107 _n The voltage 102 on is converted into dq coordinate system, the output of the transfer function 8 of the controller and the capacitance C _n The up-converted voltage is input into the state feedback active damping unit 9 and the output of the state feedback active damping unit 9 is converted into an abc coordinate system using the phase angle reference value 107. In FIG. 5, capacitance C is shown _n Vector of voltage 102 onThe vector comprises a respective capacitance C for each of the three phases _n Voltage e on _an 、e _bn Or e _cn . The controller transfer function 8 may be or may include a transfer matrix K with non-zero decoupling terms _cc (z). Transmission matrix K _cc (z) may be a 2 by 2 matrix (2 x 2 matrix).

FIG. 6 shows control, optionally adjustment of capacitance C _n An example of the magnitude of the upper voltage 102. The control loop exemplarily shown in fig. 6 may be referred to as a back emf (counter potential) control loop.

As shown in fig. 6, the control entity is configured to calculate the flow-through inductance L by _In Reference value 106 of current 104 of (2): calculating capacitance C _n Amplitude 110 of measured voltage 102 and capacitance C _n The difference between the amplitude reference 112 of the voltage 102 and the calculated difference is input to the controller transfer function 13 (e.g., K _bemf (z)) wherein the controller transfer function 13 is used to calculate the flow-through inductance L using the difference of the inputs _In A reference value 106 of the current 104 of (c). According to FIG. 6, by inductance L _In Reference value 106 of current 104 of (2) is exemplarily shown as q-value of dq coordinate systemAlternatively, as shown in FIG. 5, flows through inductance L _In The reference value 106 of the current 104 of (c) may be the d value of the dq coordinate system (not shown in fig. 6). In FIG. 6, capacitance C is shown _n Vector of voltage 102 on->The vector comprises a respective capacitance C for each of the three phases _n And a voltage on the same. The magnitude 110 of the measured voltage 102 may be the q-value E of the dq coordinate system _Qn (or alternatively the d value of the dq coordinate system) which can be determined by the vector +.>Size (norm) of (i.e., +.>) To calculate. Capacitor C _n The amplitude reference 112 of the voltage 102 on may be the q-value of the dq coordinate system +.>(or alternatively, the d value of the dq coordinate system). In fig. 6, the calculation of the above-described difference is indicated by a subtraction block 12.

As shown in fig. 6, the control entity 1 may be used to calculate the capacitance C by means of equalization _n Amplitude reference 112 of voltage 102 on, wherein equalization uses measured or estimated output current 105 to correct capacitance C _n A main reference 111 for the voltage 102. The control entity 1 may be used to correct the capacitance C by _n Primary reference value 111 of voltage 102 on: the measured or estimated magnitude of the output current 105 is input to a low pass filter transfer function 10 (e.g., H _eq (z)) and subtracting the output of the low pass filter transfer function 10 from the main reference value 111. In fig. 6, the calculation of the above-described difference is indicated by a subtraction block 11. Capacitor C _n The primary reference value 111 of the voltage 102 on is labeled "|e in fig. 6 _θ | ^* ". In FIG. 6, the direction of the measured or estimated output current 105 is shownMeasuring amountThe vector includes a measured or estimated output current for each of the three phases. The magnitude of the measured or estimated output current 105 may be the q-value of the dq coordinate system +.>(or alternatively the d value of the dq coordinate system) which can be determined by the vector +.>Size (norm) of (i.e., +.>) To calculate.

The control loop of fig. 6 is capable of controlling, optionally adjusting, the capacitance C _n The magnitude of the voltage 102 on itself (i.e., voltage control is performed) and is able to regulate the buffer of energy that can play a similar role as the kinetic energy in the rotation of the synchronous motor (i.e., inertia of the frequency control action). Capacitor C _n The primary reference value 111 of the upper voltage 102 may be set at a power plant control level (e.g., a photovoltaic power plant control level). The main reference value 111 may be a constant or a slowly varying parameter. The primary reference value 111 may be corrected using an equalization action: equalization may use a measured or estimated value of the output current 105 and pass it through a low pass filter transfer function 10 (e.g., H _eq (z)) (e.g., H _eq Direct current gain of (z). The low pass filter transfer function 10 may be defined as a transfer function in order to take into account bandwidth limitations (typically below 5Hz to avoid further interaction with other control loops). Once the capacitance C is set or calculated _n A magnitude reference 112 for the voltage 102 at the controller transfer function 13 (e.g., K _bemf (z)) can calculate the flow inductance L _In A reference value 106 of the current 104 of (c). Through inductance L _In The calculated reference value 106 of the current 104 of (c) may be fed as an input or provided to the control loop of fig. 5. Controller transfer functionNumber 13 may include a proportional controller (e.g., proportional gain).

Fig. 7 shows an example of estimating the magnitude of the estimated output current 105.

As shown in fig. 7, the control entity 1 may be used to estimate the estimated output current 105 at the present point in time byIs the magnitude of (1): calculating the inductance L flowing through at the current time point _In A difference between the magnitude of the measured current 104 and the magnitude of the estimated output current 105 at a point in time prior to the present point in time (e.g., indicated by subtraction block 16); the calculated difference is input to an analog capacitor (e.g. capacitor C _n ) An estimator model 17 of charge and discharge (e.gIn (a) and (b); calculating the capacitance C at the current time point _n The reference value 110 of the voltage 102 on and the output 113 of the estimator model 17 (e.g. +.>) The difference between (indicated, for example, by subtraction block 14); the calculated difference is input to the controller transfer function 15 (e.g., K _est (z)) wherein the controller transfer function 15 is used to calculate the magnitude of the estimated output current 105 at the present point in time using the input difference.

Fig. 8 shows a calculation example of the phase angle reference value 107. The control loop exemplarily shown in fig. 8 may be referred to as a frequency control loop (e.g., a distributed frequency control loop).

As shown in fig. 8, the control entity 1 may be arranged to control the ac grid by comparing a frequency reference 115 (e.g. ω _M ) Into the integrated unit 20 (e.g.)) To calculate the phase angle reference 107, wherein the output of the integrated unit is the phase angle reference 107. The phase angle reference 107 may be a discrete time integral of frequency. Such asAs shown in fig. 8, the control entity 1 may be used to calculate a frequency reference value 107 of the ac power network by means of an equalization, wherein the equalization uses the measured or estimated output current 105 to correct a frequency main reference value 114 of the ac power network (e.g.)>). The control entity 1 may be used to correct the frequency main reference 114 of the ac power grid by: the measured or estimated magnitude of the output current 105 is input to a low pass filter transfer function 18 (e.g., H _dr (z)) and subtracting (indicated by subtracting block 19 in fig. 8) the output of the low pass filter transfer function 18 from the main reference value 114. In FIG. 8, a vector of measured or estimated output currents 105 is shownThe vector includes a measured or estimated output current for each of the three phases. The magnitude of the measured or estimated output current 105 may be the q-value of the dq coordinate system +.>(or alternatively, the d value of the dq coordinate system), which can be represented by a vectorSize (norm) of (i.e., +.>) To calculate.

For example, if the output of each of the plurality of converter circuits 1 is electrically connected to the primary winding of the step-up transformer (as exemplarily shown in fig. 9) and equal active current sharing is achieved, then in steady state the measured or estimated magnitude of the output current 105 may be used or applied for frequency droop control/function. One of the main objectives of droop control is to have a plurality of converter circuits operating during formation of the grid reach the same frequency in steady state, which is also a useful information of the kinetic energy stored in each of the plurality of converter circuits. By using the measured or estimated amplitude of the output current and the low pass filter transfer function, an ac grid frequency reference value consistent with all of the plurality of converter circuits may be calculated. This simulates the inertia of the rotating synchronous machine.

As the power system load increases in real time, the internal frequency of each converter circuit controlled by the control entity (i.e., the proposed virtual synchronous motor embodiment) may also simultaneously decrease its internal frequency so that they may provide or deliver the requested increase in power demand: this behavior is much like the fast frequency control action (e.g., inertial response) of a rotating synchronous machine; in the case of reduced load consumption, the effect on the (virtual or real) rotating electrical machine is then the opposite.

Fig. 9 shows an example of a converter circuit controllable by a control entity provided by an embodiment of the invention. The control entity may be the control entity 1 in any of figures 1, 3 and 4.

As shown in fig. 9, an output terminal of each of the plurality of converter circuits 2 of fig. 3 or 4 may be electrically connected with the primary winding 21a of the step-up transformer 21. The secondary winding 21b of the step-up transformer 21 is electrically connected to an ac power grid (not shown in fig. 9). In other words, an output of each of the plurality of converter circuits, which may be the converter circuit 2 of fig. 3 or fig. 4, may be connected to the primary winding 21a of the transformer 21. According to fig. 9, three converter circuits are connected to the primary winding 21a of the transformer 21. This number of converter circuits is only by way of example and the number may be different. In fig. 9, only the second inductance L of the filter 4 of the respective converter circuit is shown _O1 、L _O2 Or L _On Capacitance C of a corresponding converter circuit _n The voltage (in the form of vector). The leakage inductance L of the step-up transformer 21 is shown in FIG. 9 _σ Which is a physical parameter that closely mimics the inductance of a synchronous motor of the same power. Step-up transformer 21 turns the primary windingThe voltage at 21a (represented by vector +.in FIG. 9>Representing that this vector comprises a respective value for each of the three phases) is converted into a larger voltage at the secondary winding 21 (in fig. 9 represented by the vector multiplied by the coefficient "k>Representation (i.e.)>)). Like the capacitance C of the converter circuit 2 _n Vector of corresponding voltages on->As indicated, the ac side of each converter circuit 2 is a three-phase system. That is, each part of the filter 4 of the respective converter circuit 2, e.g. the inductance L _In Capacitance C _n And optionally a second inductance L _On Is made up of or implemented by three components. In other words, the filter 4 of the respective converter circuit comprises an inductance L for each of the three phases _In Capacitance C _n And optionally a second inductance L _On 。

According to the example of fig. 10, a set of converter circuits, which may be implemented, for example, according to the converter circuit 2 of any of fig. 1, 3 and 4, may be connected to a voltage ofWhich represents the three phase voltages, i.e. the voltages of each of the three phases. The number of converter circuits of fig. 10 is by way of example only and the number may be different. Voltage->A primary (low voltage) terminal of a step-up transformer (e.g., the step-up transformer shown in fig. 9) is shown. In other words, the output terminal of each of the group of converter circuits is electrically connected to the primary winding (primary side) of the step-up transformer. In fig. 10, each converter circuit is represented by an ac voltage source 3, the ac voltage source 3 providing a three-phase voltage for each of the three phases of the filter of the converter circuit (represented by the respective vector +.>Representation) and inductance L _In 、L _I2 Or L _I1 Wherein the inductance is connected to an ac voltage source 3. The respective ac voltage source 3 corresponds to a three-phase dc-ac converter of the converter circuit 2 of any of fig. 1, 3 and 4. The respective inductance L of each of the three phases _In 、L _I2 Or L _I1 The inductance L of each of the three phases of the filter 4 of the converter circuit 2 corresponding to any of fig. 1, 3 and 4 _In . Through a respective inductance L of each of the three phases _In 、L _I2 Or L _I1 Is vector->These vectors include, for each phase, the respective inductance L flowing through each of the three phases _In 、L _I2 Or L _I1 Is set in the above-described range). Further, in fig. 10, for each converter circuit, the voltages on the capacitances of each of the three phases of the filter of the converter circuit are in vector +.>These vectors include, for each phase, the voltage on the corresponding capacitor for each of the three phases. The respective capacitance of each of the three phases corresponds to the capacitance C of each of the three phases of the filter 4 of the converter circuit 2 of any of figures 1, 3 and 4 _n . The leakage inductance L of the step-up transformer is shown in FIG. 10 _σ (existing on the primary side/Primary side of step-up Transformer)On the stage windings), which is a physical parameter, well mimics the inductance of a synchronous motor of the same power. Accordingly, the example of fig. 10 may correspond to the example of fig. 9, and the description of fig. 9 may be valid for fig. 10 accordingly. The secondary side of the step-up transformer may be connected to an ac power grid, such as a medium voltage power grid. The distributed control of the set of converter circuits by the control entity of any of fig. 1, 3 and 4 may shape the back emf signal, i.e. the voltage representing the primary (low voltage) terminal of the step-up transformer +. >Leakage inductance L of step-up transformer _σ The motor inductance can be exerted. The capacitive energy buffered by the set of converter circuits may play a role in the frequency regulation of the power system. As shown in fig. 10, each converter circuit can control, optionally regulate, the voltage (amplitude and phase angle) at the terminals of an equivalent multiphase motor as motor 22. The electric torque can be converted into a virtual mechanical torque T _OM And transmitted from the motor to the generator through the ideal shaft 23 to the equivalent generator 24, the equivalent generator 24 creating a virtual synchronous machine as seen in the electrical system. The torque T received by the generator 24 is thus taken into account by the ideal shaft 23 _IG Torque T to motor 22 _OM Matching (i.e. T _OM ＝T _IG ). Subsequently, the torque T received by the generator 24 _IG Can be completely converted into electric torque and electric power.

The invention has been described in connection with various embodiments as an example and implementations. However, other variations to the claimed subject matter can be understood and effected by those skilled in the art in practicing the claimed subject matter, from a study of the drawings, the invention, and the independent claims. In the claims and in the description, the word "comprising" does not exclude other elements or steps, and the "a" or "an" does not exclude a plurality. A single element or other unit may fulfill the functions of several entities or items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

1. A control entity (1) for controlling a converter circuit (2) to simulate an electrical output characteristic of a synchronous motor, characterized in that,

the converter circuit (1) comprises:

three-phase DC-AC converter (3)

A filter (4) comprising an inductance (L) _In ) And a capacitor (C _n ) The inductor and the capacitor are electrically connected in parallel to the output end of the three-phase direct current-alternating current converter (3); and

the converter circuit (2) is adapted to use the capacitance (C _n ) The upper voltage (102) provides an output voltage (103) at the output of the converter circuit (2); wherein the method comprises the steps of

The control entity (1) is configured to:

measuring the flow through the inductance (L _In ) And the capacitance (C) _n ) The voltage (102) at which,

by controlling the flow through said inductance (L _In ) Controls the capacitance (C) by the current (104) _n ) Said voltage (102) on

By controlling the flow through the inductance (L _In ) Is set to (104): -controlling an output voltage (101) of the three-phase dc-ac converter (3) using the measured current (104) and the measured voltage (102).

2. The control entity (1) according to claim 1, characterized in that,

the output of the converter circuit (2) is electrically connected to a primary winding (21 a) of a step-up transformer (21); and

The secondary winding (21 b) of the step-up transformer (21) is electrically connected to an ac power grid.

3. The control entity (1) according to claim 1, characterized in that,

-said output of each of a plurality of said converter circuits (2) is electrically connected to a primary winding (21 a) of a step-up transformer (21);

-the secondary winding (21 b) of the step-up transformer (21) is electrically connected to an ac power grid; and

the control entity is configured to control each of the plurality of converter circuits according to a control of the converter circuit.

4. The control entity (1) according to any of the preceding claims, characterized in that,

said inductance (L _In ) And the capacitance (C) _n ) -a node (N1) in between electrically connected to the output of the converter circuit (2); and

the control entity (1) is configured to:

measuring or estimating an output current (105) flowing from the node (N1) to the output of the converter circuit (2), and

the measured or estimated output current (105) is used in addition to the measured current (104) and the measured voltage (102) to control the output voltage (101) of the three-phase dc-ac converter (3).

5. The control entity (1) according to claim 4, characterized in that,

Said inductance (L _In ) And the capacitance (C) _n ) The node (N1) therebetween is connected to the first inductor (L _On ) Electrically connected to the output of the converter circuit (2); and

the output current (105) flows through the second inductance (L _On ) Is set in the above-described range).

6. The control entity (1) according to any of the preceding claims, characterized in that,

the control entity (1) is configured to:

using the capacitance (C _n ) An amplitude reference value (112) of the voltage (102) and the capacitance (C) _n ) -calculating the magnitude (110) of the measured voltage (102) across the inductance (L) _In ) A reference value (106) of the current (104), and

using a flow through the inductance (L _In ) -calculating a reference value (108) of the output voltage (101) of the three-phase dc-ac converter (3) from the calculated reference value (106) of the current (104).

7. The control entity (1) according to claim 6, characterized in that,

the control entity (1) is arranged to use the capacitance (C _n ) -calculating said reference value (108) of said output voltage (101) of said three-phase dc-ac converter (3) from a phase angle reference value (107) of said voltage (102).

8. The control entity (1) according to claim 7, characterized in that,

-the control entity (1) is configured to calculate the reference value (108) of the output voltage (101) of the three-phase dc-ac converter (3) by:

will flow through the inductance (L) using the phase angle reference value (107) _In ) Converts (6) the measured current (104) into a dq coordinate system (109),

will flow through the inductance (L _In ) Is a dq coordinate system of the reference value (106) of the current (104) and flows through the inductance (L _In ) Is input into a controller transfer function (8), wherein the dq coordinate system is to be passed through the inductance (L _In ) As q-axis or d-axis, and

-converting (7) a value based on the output of the controller transfer function (8) into an abc coordinate system (108) using the phase angle reference value (107).

9. The control entity (1) according to claim 8, characterized in that,

-using the phase angle reference value (107) to charge the capacitor (C _n ) Said voltage (102) being converted (6) into a dq coordinate system,

-comparing said output of said controller transfer function (8) with said capacitance (C _n ) The converted voltage is input into a state feedback active damping unit (9), and

-converting (7) the output of the state feedback active damping unit (9) into the abc coordinate system (108) using the phase angle reference value (107).

10. The control entity (1) according to any one of claims 6 to 9, characterized in that,

the control entity (1) is arranged to calculate the flow through the inductance (L _In ) Is defined, the reference value (106) of the current (104) of (a):

calculating (12) the capacitance (C _n ) Said magnitude (110) of said measured voltage (102) and said capacitance (C) _n ) A difference between the amplitude reference values (112) of the voltages (102) and

inputting the calculated difference value into a controller transfer function (13), wherein the controller transfer function (13) is used for calculating the difference value flowing through the inductor (L _In ) Is provided, the reference value (106) of the current (204).

11. The control entity (1) according to claim 10 when dependent on claim 4, characterized in that,

the control entity (1) is arranged to calculate the capacitance (C _n ) -said amplitude reference value (112) of said voltage (102) thereon, wherein said equalization uses said measured or estimated output current (105) to correct said capacitance (C) _n ) A main reference value (111) for said voltage (102).

12. The control entity (1) according to claim 11, characterized in that,

the control entity (1) is arranged to correct the capacitance (C _n ) -said main reference value (111) of said voltage (102) above:

inputting the measured or estimated magnitude of the output current (105) into a low pass filter transfer function (10) for an analog equalization resistor, and

-subtracting (11) the output of the low-pass filter transfer function (10) from the main reference value (111).

13. The control entity according to claim 4 or any one of claims 5 to 12 when dependent on claim 4, characterized in that,

the control entity (1) is configured to estimate the magnitude of the estimated output current (105) at the present point in time by:

calculating (16) the current time point flowing through the inductance (L _In ) Is a difference between the magnitude of the measured current (104) and the magnitude of the estimated output current (105) at a point in time before the present point in time,

inputting the calculated difference value into an estimator model (17) simulating the charge and discharge of the capacitor,

calculating (14) a difference between a reference value (110) of the voltage (102) on the capacitance at the current point in time and an output (113) of the estimator model (17), and

-inputting said calculated difference value into a controller transfer function (15), wherein said controller transfer function (15) is adapted to calculate said magnitude of said estimated output current (105) at said present point in time using said inputted difference value.

14. The control entity (1) according to claim 7 or any one of claims 8 to 13 when dependent on claim 7, characterized in that,

the control entity (1) is configured to calculate the phase angle reference value (107) by inputting a frequency reference value (115) of an alternating current network into an integrated unit (20), wherein an output of the integrated unit (20) is the phase angle reference value (107).

15. The control entity (1) according to claim 14, characterized in that,

the control entity (1) is configured to calculate the frequency reference value (115) of the ac power grid by means of an equalization, wherein the equalization uses the measured or estimated output current (105) to correct a frequency main reference value (114) of the ac power grid.

16. The control entity (1) according to claim 15, characterized in that,

the control entity (1) is configured to correct the frequency master reference value (114) of the ac power grid by:

Inputting the magnitude of the measured or estimated output current (105) into a low pass filter transfer function (18) for an analog equalization resistor, and

-subtracting (19) the output of the low-pass filter transfer function (18) from the main reference value (114).

17. A system (5), characterized by comprising:

the control entity (1) of any one of the preceding claims, for controlling a converter circuit (2) to simulate an electrical output characteristic of a synchronous motor, and

the converter circuit (2) comprises a three-phase DC-AC converter (3) and a filter (4), the filter (4) comprising one inductance (L) for each phase _In ) And a capacitor (C _n ) The inductance and the capacitance are electrically connected in parallel to the output of the three-phase dc-ac converter (3); wherein the method comprises the steps of

The converter circuit (2) is adapted to use the capacitance (C _n ) The upper voltage (102) provides an output voltage (103) at the output of the converter circuit (2).

18. The system (5) according to claim 17, wherein the system (5) comprises:

step-up transformer (21) and a plurality of said converter circuits (2), wherein

-said output of each converter circuit (2) of said system (5) is electrically connected to a primary winding (21 a) of said step-up transformer (21);

the control entity (1) is arranged to control each converter circuit (2) of the system (5).

19. A method for controlling a converter circuit to simulate an electrical output characteristic of a synchronous motor, characterized in that,

the converter circuit includes:

three-phase DC-AC converter

A filter comprising an inductance and a capacitance for each phase, said inductance and said capacitance being electrically connected in parallel to the output of said three-phase dc-ac converter; and

the converter circuit is used for providing an output voltage at an output end of the converter circuit by using the voltage on the capacitor; wherein the method comprises the steps of

The method comprises the following steps:

measuring (S1) the current flowing through said inductance and said voltage over said capacitance,

controlling (S2) the voltage across the capacitor by controlling the current through the inductor, an

-controlling (S3) the current flowing through the inductance by: the measured current and the measured voltage are used to control the output voltage of the three-phase dc-ac converter.

20. A computer program comprising instructions which, when executed by a computer, cause the computer to perform the method provided in claim 19.

21. A storage medium storing executable program code which, when executed by a processor, causes the method provided in claim 19 to be performed.