Electronic power converter, electric motor control device and method for operating an electronic power converter

Abstract

The present invention relates to an electronic power converter, such as an inverter or converter, for an electrical application, such as a motor control device, an electrolysis device, or a charging device. The electronic power converter comprises a DC link and an active front end (AFE) which is connected to a power supply via a filter and a mains board with a first inrush current relay and a resistor device. The resistor device can be a resistor, in particular an NTC resistor or a PTC thermistor.The power supply board further comprises a second inrush current relay, wherein at least one of the inrush current relays is controlled to couple or disconnect during a commissioning phase of the electronic power converter and during anomalous mains voltage conditions, such that the DC link is charged via the resistor device or bypassing the resistor device, and such that the AFE is made available to raise the DC link voltage to a safe level and under controlled conditions. The invention also relates to an electric motor control device and a method for operating an electronic power converter.

Description

[0001] The present invention relates to an electronic power converter, such as an inverter or converter, for an electrical application, such as a motor control device, an electrolysis device, or a charging device. The electronic power converter comprises a DC link and an active front end (AFE) connected to a power supply via a filter and a first inrush current switch with a resistor. The inrush current switch could be any electronically controlled switch that is normally off, such as a semiconductor (e.g., MOSFET, IGBT, IGCT, etc.) or an electromechanical switch, such as a relay. Since relays are the most widely used devices, the term "relay" will be used hereafter, although a more general inrush current switch in the form of a semiconductor switch may be used.The resistance device can be a resistor, in particular an NTC resistor or a PTC thermistor. The power supply board further comprises a second inrush current relay, wherein at least one of the inrush current relays is controlled to couple or disconnect during a commissioning phase of the electronic power converter and during anomalous mains voltage conditions, such that the DC link is charged via the resistance device or bypassing the resistance device, and such that the AFE is made available to raise the DC link voltage to a safe level and under controlled conditions. The invention also relates to an electric motor control device according to claim 6 and a method for operating an electronic power converter according to claim 7.

[0002] The present invention relates to the field of inverters and converters used to supply electrical power for electronic applications, such as electric motors, from a mains power source. The present invention can relate to low harmonic distortion (LHD) or zero-distortion (ZD) control devices and applications for renewable energies, such as solar panels, wind turbines, fuel cells, power-to-X applications, and related fields such as electric (fast) charging devices and electrical energy storage systems. Active front ends (AFE) and power factor correction (PFC) can typically be used at all power levels in this context.

[0003] AFEs are typically equipped with a filter, such as an LCL filter. The LCL filter results in a continuous (reactive) current draw, which charges the inrush current circuitry while the inrush current relays are open. Under power grid fault conditions, such as low mains voltage, the electrical application, such as a motor control device, might fail to start up because the required DC link voltage is not reached. Conventional start-up strategies cannot reduce this level, as doing so would cause a power grid transient to generate a surge current, potentially destroying the AFE circuitry.Instead, the motor control device remains in an uncontrolled state, with the resistive device, such as an inrush current resistor / thermistor, being charged by the LCL filter and overheating, as it is typically designed to conduct current only for a very short time. Such events can reduce the reliability of the system, as mains faults can lead to aging of the AFE or, in some specific cases, even damage the electrical application. To prevent this, the same commissioning and fault strategies currently used for passive rectifiers can be employed.

[0004] The object of the invention is to overcome this problem. This object is achieved by an electronic power converter according to claim 1, an electric motor control device according to claim 6, and a method for operating an electronic power converter according to claim 7. Advantageous embodiments of the invention are the subject of the dependent claims.

[0005] According to claim 1, an electronic power converter, such as an inverter or converter, is provided for an electrical application, such as a motor control device, an electrolysis device, or a charging device. The electronic power converter comprises a DC link and an active front end (AFE) which is connected to the power grid via a filter and a first inrush current relay with a resistive device, such as a resistor, an NTC resistor, or a PTC thermistor, and a second inrush current semiconductor or a second inrush current relay.According to the invention, at least one of the inrush current relays is controlled to couple or disconnect during a commissioning phase of the electronic power converter and during an anomalous mains voltage condition, such that the DC link is charged via the resistor device or bypassing the resistor device, and such that the AFE is made available to raise the DC link voltage to a safe level and under controlled conditions. In particular, both inrush current relays can remain open in a first phase. After an adjustable time interval, the first inrush current relay can be closed, and after a further time interval, the second inrush current relay can be closed to control the total power input to the AFE.The inrush current relays can be provided on a network board, integrated into another board, a coil box, or can be freely movable as elements connected by individual cables.

[0006] The basic idea of ​​the invention is therefore that the AFE is used as early as possible to raise the DC intermediate circuit voltage in a controlled manner. In this way, the relays of the inrush current circuits can be closed within seconds and the inrush current resistor device or the inrush current resistors are never overloaded.

[0007] During voltage drops in normal operation, the electrical application can remain connected as long as at least one phase has a minimum voltage, e.g., 10% of the nominal voltage. The advantage of the invention lies in the significant reduction of the commissioning process by several minutes and in the avoidance of loss of control of the application.

[0008] In general, the present invention enables an increase in the resistance to mains faults and therefore the reliability of the electrical application. The passive sequence of the commissioning phase, in which the electrical application relies on normal mains conditions and correct installation, can be reduced to a level that is safe for the electrical application under any conditions. Furthermore, the cost and size of the electronic power converter can be reduced, since no additional fuses or a third relay are required.

[0009] With the proposed invention, the relays can close at much lower voltages, while simultaneously increasing their resistance to voltage surges. The proposed invention can also be applied to voltage drops during normal operation. In this case, the electrical application can remain in standby mode for extended voltage drops or even shutdowns, thus enabling it to restart safely and immediately once the power grid returns to normal voltage levels.

[0010] The present invention can be fully implemented at the software level of the electronic power converter. The present invention makes the electrical application more compact, cost-effective, and reliable. The invention also increases the operating time of the electrical application, even during power outages.

[0011] The present invention utilizes the additional capabilities of an AFE (Automatic Functional Electronic) such that additional effort is required for protective circuits and inrush current circuits. With the present invention, the electrical application becomes more robust against all problems related to voltage drops and is also protected against user error, such as connecting the control device to a power supply with an excessively low voltage.

[0012] In a preferred embodiment of the invention, the filter is an LCL or an LC filter. The filter may comprise components that are assigned to a specially provided coil box and / or a power board of the AFE.

[0013] In a further preferred embodiment of the invention, the first inrush current relay is provided on a first phase of the mains connection, and the second inrush current relay is provided on a second phase of the mains connection. A third phase of the mains connection can include a third inrush current relay or no inrush current relays at all and can provide a direct connection between the mains power supply and the filter.

[0014] In a further preferred embodiment of the invention, the inrush current relays are provided to be controlled separately from each other via a control board.

[0015] In a further preferred embodiment of the invention, the inrush current relays are controlled via a relay board which is supplied with energy via a DC power connection to the AFE, in particular to the control board of the AFE.

[0016] The invention is also directed to an electric motor control device comprising an electronic power converter.

[0017] The invention further relates to a method for operating an electronic power converter, wherein the method comprises the following steps: - Monitoring the mains voltage for normal mains voltage conditions and mains voltage drops; - Raising the DC link voltage when a mains voltage drop is detected while the motor-side inverter reduces its output power, such that the DC link voltage is maintained or increased; and - Setting the motor-side inverter to a setpoint when the regular mains voltage is detected.

[0018] In a preferred embodiment of the invention, the method comprises the following step: - To control the inrush current relay by means of a control unit, to couple or disconnect it during the commissioning phase of the electronic power converter and during anomalous mains voltage conditions, such that the DC intermediate circuit is charged via the resistor device or bypassing the resistor device without overloading the resistor device, and that the DC intermediate circuit voltage is increased.

[0019] In a preferred embodiment of the invention, the commissioning phase comprises a regular commissioning phase with a sequence of the following steps, preferably all and preferably in this given order: - the inrush current relays are open by default while the application is powered, the AFE and the motor-side inverter are off; - Applying mains voltage to the LCM terminals; - Providing the supply voltage for the control unit via a switched-mode power supply (SMPS); - preferably suspending the commissioning phase for a defined period to stabilize the DC intermediate circuit voltage; - Closing the inrush current relays; - then, when the mains voltage is below a normal value, the AFE begins to raise the DC link voltage while the motor-side inverter is switched off; and - then, when the mains voltage is within the limit values, the motor-side inverter is switched on and the power application is supplied with energy without power limitation.

[0020] In a further preferred embodiment of the invention, the commissioning phase comprises an anomalous commissioning phase with a sequence of the following steps, preferably all and preferably in this given order: - the inrush current relays are open by default before the application is powered on, the AFE and the motor-side inverter are off; - Applying mains voltage to the LCM terminals; - Providing the supply voltage for the control unit via a switched-mode power supply (SMPS); - preferably suspending the commissioning phase for a defined period to stabilize the DC intermediate circuit voltage; - Detecting an anomalous mains voltage; - Closing of the inrush current relays (1, 2); - immediate commencement of the DC link voltage increase by the AFE while the motor-side inverter is switched off; - depending on the mains voltage conditions, switching on the motor-side inverter and supplying the power application with energy with the power limitation; and - Detecting regular mains voltage conditions, switching on the motor-side inverter and supplying energy to the power application without power limitation.

[0021] In a further preferred embodiment of the invention, the protected commissioning sequence, when anomalous mains voltage conditions occur during regular operation, comprises the following steps, preferably all and preferably in this given order: a - the performance application is running or is in standby mode according to its current setpoint; b - Detecting anomalous mains voltage conditions such as a mains voltage drop; c - the AFE immediately begins to increase power, limited by the maximum rated current, while the motor-side inverter reduces power to ensure that the DC intermediate circuit voltage is constant or increased; d - when the mains voltage becomes regular (i.e. returns to a regular value), it usually exhibits an overvoltage; due to the high DC intermediate circuit voltage, the resulting inrush current is limited to a safe level; e - the motor-side inverter can immediately return to its setpoint.

[0022] Further details and advantages of the invention will be discussed with reference to Fig. 1 described, which shows a circuit diagram of the electronic power converter of the present invention.

[0023] The circuit diagram from Fig.Figure 1 shows a schematic representation of the electronic power converter of the present invention, with the mains supply at Lcm on the left and the DC link on the right, indicated by the bus rail. The AFE, or alternatively the power board of the AFE, is connected to the mains supply via a filter, indicated by the coil box, and via a power supply board. The power supply board comprises a first inrush current relay 1 with a parallel resistive device 3, such as a resistor, an NTC resistor, or a PTC thermistor, and a second inrush current relay 2. The resistive device 3 may be arranged in series with a fuse.At least one of the inrush current relays 1, 2 is controlled to couple or disconnect during a commissioning phase of the electronic power converter and during anomalous mains voltage conditions, such that the DC link is charged via the resistor device 3 or bypassing the resistor device 3. The AFE can therefore be provided to raise the DC link voltage to a safe level under controlled conditions.

[0024] In a conventional commissioning sequence, all relays are typically opened first, and the DC link is charged by the inrush current resistances. The relays remain open until the DC link voltage reaches its minimum value of, for example, 530 V through passive rectification, which corresponds to a mains voltage of 380 V. The SMPS and the control unit then begin operation, and the relays close. For anomalous mains conditions, such as a low mains voltage of, for example, 300 V, which provides a DC link voltage of only 424 V, the relays remain open to protect the electrical application from any transient events. This is not problematic for passive front ends such as rectifiers, as there are no LCL filter capacitors in the system, and the inrush current resistances do not charge significantly. In theory, the electrical application can remain in this state indefinitely.

[0025] With an AFE (Automatic Front End), the filter capacitors are typically selected to reduce system costs, size, and weight. Since these capacitors are connected to the mains power supply after the inrush current circuit, they are continuously charged and discharged due to the mains' AC voltage. The resulting current through the inrush current resistor is significantly higher, for example, 8 to 30 times greater, compared to a passive front end. Because losses in the inrush current resistor increase quadratically with current, they would need to be sized 50 to 1000 times larger than those for passive rectifiers to keep the electrical application running continuously at this stage. This is not a practical option due to losses, size, and cost considerations.Alternatively, the capacitors could be isolated by relays, or a third relay could be implemented to completely isolate the electrical application under such conditions. However, this approach also negatively impacts cost and size.

[0026] The present invention utilizes the fact that the AFE can boost the mains voltage to any desired DC link voltage. Furthermore, SMPS start operating at, for example, only 300 Vdc, which corresponds to a mains voltage of 212 Vac. According to the invention, the DC link voltage is boosted to 530 V or even 700 V when the mains voltage is, for example, between 212 V and 380 V. Only then can relays 1 and 2 be closed. Even if the mains voltage suddenly returns, this will not lead to an inrush current through the AFE, since the DC link voltage is at least as high as under normal conditions and prevents the mains voltage from inducing any inrush current flow. The additional boost, for example,Operating at 700 V can be advantageous because, under such conditions, the voltage often returns at an excessive level, preventing or at least significantly reducing a resulting surge current event and thus extending the operating time of the electrical application. LHD drive devices operating below a mains voltage of, for example, 212 Vac, need not be in a critical condition, as the currents through the capacitors and the inrush current circuit 3 are low enough to prevent resistor overheating. While the AFE is in boost mode, the motor-side inverter should be switched off to prevent overloading the AFE switches.

[0027] Voltage drops in the power grid during normal operation can occur in various ways. Short, deep drops down to zero volts can occur during drops at, for example, 80% of the nominal grid voltage and everything in between. In the case of voltage drops during normal operation, any driving device will idle because there is no power to drive the electrical application. Depending on the voltage drop, the electrical application will resume operation immediately after the voltage returns. However, if the DC link voltage drops below, for example, 530 V, the electrical application will shut down completely, and a full restart will be required. With an AFE (Automatic Voltage Release) and at least a very low minimum grid voltage on one of the phases, the electrical application can be kept running, and a restart can be avoided.Furthermore, all connections remain active and underload operation of the electrical application is possible with a certain amount of mains voltage.

[0028] The following sequences illustrate, by way of example, the operation of the electronic power converter of the present invention.

[0029] A typical commissioning sequence for the electronic power converter may include the following steps: b - The inrush current relay is open. c - The mains power voltage is applied to the LCM terminals. d - The SMPS (switching power supply) provides a supply voltage to the control unit(s). e - The motor-side inverter is kept switched off. f - Optionally: wait a few seconds to allow the DC intermediate circuit voltage to stabilize. g - The inrush current relay is closed. h - Increase the DC intermediate circuit voltage slightly (e.g. by 2%) via the AFE; the motor-side inverter is off. i - The motor-side inverter is active and the motor can be controlled without power limitation.

[0030] A protected commissioning sequence for the electronic power converter may include the following steps: a - The inrush current relay is open. b - The mains power voltage is applied to the LCM terminals. c - The SMPS (switching power supply) provides a supply voltage to the control unit(s). d - The motor-side inverter is kept switched off. e - A voltage drop occurs on the power grid. f - The inrush current relay is closed. g - Increase the DC link voltage through the AFE (e.g. to 2% above the nominal value of the rectified mains voltage), the motor-side inverter is off. h - The motor-side inverter is active and the motor can be controlled without power limitation.

[0031] Under an anomalous mains voltage condition, such as a voltage drop, the electronic power converter can be operated with a sequence that includes the following steps: a - The inrush current relays are closed and the electronic power converter is running at its setpoint. b - The mains voltage drops. c - The AFE immediately begins the boost, limited by the maximum rated current, while at the same time the motor-side inverter reduces the power to ensure that the DC intermediate circuit voltage is at least constant or, even more advanced, increased. d - When the mains voltage returns, it usually exhibits an overvoltage; due to the high DC intermediate circuit voltage, the resulting inrush current is limited to a safe level. e - The motor-side inverter can immediately return to a setpoint (no need to restart the control unit).

Claims

[1] An electronic power converter, such as an inverter or converter for an electrical application, such as a motor control device, an electrolysis device, or a charging device, comprising a DC link and an active front end (AFE) connected to a power grid via a filter and a first inrush current switch (1), such as a semiconductor or a relay, with a resistive device (3), such as a resistor, an NTC resistor, or a PTC thermistor, and a second inrush current semiconductor or a second inrush current relay (2), wherein at least one of the inrush current relays (1, 2) is controlled to couple or disconnect during a commissioning phase of the electronic power converter and during an anomalous grid voltage condition, such that the DC link is charged via the resistive device (3) or bypassing the resistive device (3), such thatthat the AFE is provided to raise the DC intermediate circuit voltage to a safe level and under controlled conditions. [2] Electronic power converter according to claim 1, characterized by that the filter is an LCL or an LC filter. [3] Electronic power converter according to any of the preceding claims, characterized by , that the first inrush current relay (1) is provided on a first phase of the network connection and the second inrush current relay (2) is provided on a second phase of the network connection. [4] Electronic power converter according to any of the preceding claims, characterized by , that the inrush current relays (1, 2) are designed to be controlled separately from each other via a control board. [5] Electronic power converter according to any of the preceding claims, characterized by, that the inrush current relays (1, 2) are controlled via a relay board which is supplied with energy via a DC power connection to the AFE, in particular the control board according to the preceding claim. [6] Electric motor control device comprising the electronic power converter according to any of the preceding claims. [7] Method for operating the electronic power converter according to any one of claims 1 to 5, characterized by the following steps: - Monitoring the mains voltage for normal mains voltage conditions and mains voltage drops; - Raising the DC link voltage when a mains voltage drop is detected while the motor-side inverter reduces its output power, such that the DC link voltage is maintained or increased; and - Setting the motor-side inverter to a setpoint when the regular mains voltage is detected. [8] Method according to claim 7, characterized by that the procedure includes the following step: - To control the inrush current relays (1, 2) by means of a control unit, to couple or disconnect during the commissioning phase of the electronic power converter and during anomalous mains voltage conditions, such that the DC intermediate circuit is charged via the resistor device or bypassing the resistor device without overloading the resistor device, and that the DC intermediate circuit voltage is increased. [9] Method according to claim 7 or 8, characterized by , that the commissioning phase comprises a regular commissioning phase with a sequence of the following steps, preferably all and preferably in this given order: - the inrush current relays are open by default before the application is powered on, the AFE and the motor-side inverter are off; - Applying mains voltage to the LCM terminals; - Providing the supply voltage for the control unit via a switched-mode power supply (SMPS); - preferably suspending the commissioning phase for a defined period to stabilize the DC intermediate circuit voltage; - Closing of the inrush current relays (1, 2); - then, when the mains voltage is below a normal value, the AFE begins to raise the DC link voltage while the motor-side inverter is switched off; and - then, when the mains voltage is within the limit values, the motor-side inverter is switched on and the power application is supplied with energy without power limitation. [10] Method according to claim 7 or 8, characterized by, that the commissioning phase comprises an anomalous commissioning phase with a sequence of the following steps, preferably all and preferably in this given order: - the inrush current relays are open by default before the application is powered on, the AFE and the motor-side inverter are off; - Applying mains voltage to the LCM terminals; - Providing the supply voltage for the control unit via a switched-mode power supply (SMPS); - preferably suspending the commissioning phase for a defined period to stabilize the DC intermediate circuit voltage; - Detecting an anomalous mains voltage; - Closing of the inrush current relays (1, 2); - immediate commencement of the DC link voltage increase by the AFE while the motor-side inverter is switched off; - depending on the mains voltage conditions, switching on the motor-side inverter and supplying the power application with energy with the power limitation; and - Detecting regular mains voltage conditions, switching on the motor-side inverter and supplying energy to the power application without power limitation. [11] Method according to any one of claims 7 to 10, characterized by , that if anomalous mains voltage conditions occur during regular operation, the protected commissioning sequence comprises the following steps, preferably all and preferably in this given order: a - the performance application is running or is in standby mode according to its current setpoint; b - Detecting anomalous mains voltage conditions such as a mains voltage drop; c - the AFE immediately begins to increase power, limited by the maximum rated current, while the motor-side inverter reduces power to ensure that the DC intermediate circuit voltage is constant or increased; d - when the mains voltage becomes regular, it usually exhibits an overvoltage due to the high DC intermediate circuit voltage; due to the high DC intermediate circuit voltage, the resulting inrush current is limited to a safe level; e - the motor-side inverter can immediately return to its setpoint.

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