Circuit arrangement for monitoring an intermediate circuit voltage

Abstract

A circuit arrangement is proposed for measuring an intermediate circuit voltage of an intermediate circuit of an inverter for controlling an electric drive of a vehicle, the circuit arrangement comprising: a single-ended analog-digital converter with an input for supplying an input voltage of the intermediate circuit to be measured, a voltage divider connected to the input of the single-ended analog-digital converter and to ground for generating a partial voltage from the input voltage in order to supply this to the input of the single-ended analog-digital converter, and a pull-up resistor which is electrically contacted with one terminal to the input of the single-ended analog-digital converter and with another terminal to a reference voltage of the single-ended analog-digital converter and which is selected such that it generates a positive voltage offset at the input of the single-ended analog-digital converter.

Description

[0001] The present invention relates to the field of electromobility, in particular the monitoring of intermediate circuit voltages.

[0002] Electric or hybrid vehicles are designed with an electric drive system with an operating voltage of several hundred volts, currently between 400 and 900 volts, for example. This voltage is usually provided by batteries, which represent a direct current (DC) source. However, the electric machines require alternating current (AC) to operate. Therefore, so-called inverters (DC / AC converters) are installed between the DC source and the electric machine. Inverters convert the direct current provided by the DC source into an alternating current usable by the electric machine in a known manner using power semiconductor switches. Typically, a (voltage) intermediate circuit, also known as a DC link, is part of an inverter and is usually formed as a (DC link) capacitor.The intermediate circuit serves, among other things, to smooth the voltage and provides the inverter, or more precisely its power semiconductors, with a stable intermediate circuit voltage (DC voltage).

[0003] In order to control the power semiconductor switches appropriately, the intermediate circuit voltage must be known. Therefore, it must be measured. Conventional measurement methods for measuring an intermediate circuit voltage often use an operational amplifier to appropriately condition the voltage for the analog-to-digital converter. Alternatively, an analog-to-digital converter capable of differential measurement can be used. These solutions are expensive and require many additional components. These solutions must also ensure conformal galvanic isolation between high and low voltage potentials. In applications of the invention, a single-ended analog-to-digital converter is used.

[0004] It may happen that not only positive but also negative voltages must be measured at the intermediate circuit. Since this is not possible with the currently used circuit arrangement using a single-ended analog-to-digital converter, the invention is based on the object of adapting the circuit arrangement with the single-ended analog-to-digital converter in such a way that negative voltages can also be measured at the intermediate circuit.

[0005] This object is achieved by the features of the independent claims. Advantageous embodiments are the subject of the dependent claims.

[0006] A circuit arrangement is proposed for measuring an intermediate circuit voltage of an intermediate circuit of an inverter for controlling an electric drive of a vehicle, the circuit arrangement comprising: a single-ended analog-digital converter with an input for supplying an input voltage of the intermediate circuit to be measured, a voltage divider connected to the input of the single-ended analog-digital converter and to ground for generating a partial voltage from the input voltage in order to supply this to the input of the single-ended analog-digital converter, and a pull-up resistor which is electrically contacted with one terminal to the input of the single-ended analog-digital converter and with another terminal to a reference voltage of the single-ended analog-digital converter and which is selected such that it generates a positive voltage offset at the input of the single-ended analog-digital converter.

[0007] In one version, an RC element is connected between the voltage divider and the input of the single-ended analog-to-digital converter.

[0008] Furthermore, a power electronics device, in particular an inverter, is provided, comprising an intermediate circuit for providing an intermediate circuit voltage, as well as the circuit arrangement.

[0009] Furthermore, an electric drive, in particular an electric axle drive, of a vehicle with at least one electric machine, a transmission device and the power electronics device is provided.

[0010] In one embodiment, the power electronics device is formed as an inverter.

[0011] Furthermore, a vehicle is provided having the electric drive.

[0012] Further features and advantages of the invention will become apparent from the following description of exemplary embodiments of the invention, with reference to the figures of the drawing, which illustrate details of the invention, and from the claims. The individual features can be implemented individually or in combination in a variant of the invention.

[0013] Preferred embodiments of the invention are explained in more detail below with reference to the accompanying drawings. Fig. 1 shows a basic structure of a circuit arrangement with a single-ended analog-to-digital converter according to the prior art. Fig. 2 shows a basic structure of a circuit arrangement with a single-ended analog-to-digital converter according to an embodiment of the present invention.

[0014] In the following descriptions of the figures, the same elements or functions are provided with the same reference symbols.

[0015] As already mentioned at the beginning, several measuring methods for measuring the intermediate circuit voltage are known, whereby the use of operational amplifiers or differential analog-to-digital converters requires a large number of components, which is not optimal given the usually very limited installation space on the circuit board and the resulting higher costs.

[0016] Therefore, a so-called single-ended analog-to-digital converter is used in one application. In a single-ended analog-to-digital converter, the input signal is referenced directly to ground (or a predefined reference potential such as HV-, which is also 0V). The single-ended analog-to-digital converter is formed as part of a gate driver of the inverter's power semiconductors and is arranged on a circuit board as close as possible to the gate driver, with galvanic isolation between LV and HV potentials already in place. However, with the existing circuit arrangement, only positive voltages at the intermediate circuit (i.e., at HV+) can be measured.

[0017] In Fig. Figure 1 shows a circuit arrangement as used in the prior art. The circuit arrangement is arranged on a circuit board (printed circuit board) which carries both HV and LV potential. Shown is an input In_ADC of a single-ended analog-to-digital converter, hereinafter also referred to as A / D converter or ADC. The intermediate circuit voltage is applied to the In_ADC input via corresponding connections. The connection connected to the HV minus HV- (also referred to as DC) potential serves as the ground connection. The connection connected to the HV plus HV+ (also referred to as DC+) potential provides the intermediate circuit voltage to be measured as the input voltage to the single-ended analog-to-digital converter. The single-ended analog-to-digital converter has galvanic isolation.

[0018] A voltage divider R1; R3 connected to ground (here HV-) is also provided between the HV+ and HV- terminals of the intermediate circuit voltage and the In_ADC input. This divider divides the high intermediate circuit voltage of usually more than 400V (HV+) into a partial voltage so as not to exceed the maximum input voltage of the analog-to-digital converter. The voltage divider R1; R3 can consist of two or more resistors. In particular, R3 can be formed from a large number of resistors in order to divide the voltage at the HV+ potential accordingly to an input voltage suitable for the analog-to-digital converter. In addition to R1, one or more further resistors can also be provided for redundancy reasons, for example to meet requirements for maximum operating voltage, power dissipation or safety.In addition, an RC element R30, C30 is connected between the voltage divider R1; R3 and the input In_ADC, which acts as a low-pass filter for filtering high-frequency electrical signals. The voltage signal processed by the voltage divider R1; R3 and the RC element R30, C30 is fed to the single-ended analog-to-digital converter as the input signal HV_Out_ADC to be converted. As can be seen from . Fig. As can be seen in Figure 1, a current circuit R1; R3, R30, C30 for measuring the intermediate circuit voltage consists of a voltage divider from HV+ to HV-, whereby the voltage is measured via the lowest resistor R1.

[0019] The existing circuit can only measure positive voltages because the analog-to-digital converter is referenced to HV-. Since one of the objectives of the invention is to also be able to measure negative voltages (at HV+), the following circuit arrangement is proposed.

[0020] The proposed circuit arrangement is shown in Fig. 2. As can be seen, the Fig. The circuit shown in Figure 1 is expanded by a pull-up resistor R20 to the analog-to-digital converter's reference voltage V_Ref_ADC already available on the board. This resistor R20 is connected to the In_ADC input at one terminal and receives the analog-to-digital converter's reference voltage V_Ref_ADC (which is also referenced to HV and supplied via galvanic isolation) at its other terminal. The reference voltage V_Ref_ADC is already available on the board to enable other applications.

[0021] The additional pull-up resistor R20 and the existing voltage divider R1; R3 generate a positive voltage offset at the In_ADC input of the analog-to-digital converter. At a DC link voltage of 0V, a positive voltage is already present at the input of the analog-to-digital converter. This allows negative DC link voltages to be measured.

[0022] The size of the pull-up resistor R20 is selected by the specialist according to the application. Therefore, if a small negative voltage, e.g., down to -20V, is to be measured, the pull-up resistor R20 can be chosen significantly smaller than if a high negative voltage is to be measured.

[0023] By using the existing reference voltage V_Ref_ADC as a voltage source for the pull-up resistor R20, only very small additional tolerances are introduced into the circuit. Without the existing reference voltage V_Ref_ADC, an additional (expensive) reference voltage source would be required. A conventional (possibly additional) voltage source would require more space and introduce additional tolerances into the circuit, making meeting the tolerance requirements very difficult or even impossible. Using the existing analog-to-digital converter, including its reference voltage V_Ref_ADC, and the additional pull-up resistor R20 is a very cost-effective, practical, and reliable solution for meeting the tolerance requirements and the requirement to measure negative DC link voltages.

[0024] The proposed circuit arrangement expands the existing single-ended analog-to-digital converter by only a single component. This saves space and costs.

[0025] The circuit arrangement described is used, for example, in a power electronics device for driving an electric motor of a motor vehicle. Such a power electronics device is, for example, an inverter (AC / DC converter) that is fed by a voltage intermediate circuit that is electrically connected to the semiconductor switches of the inverter and usually has a so-called intermediate circuit capacitor. The two terminals of the voltage intermediate circuit are at different potentials HV+ and HV- (or DC+ / DC-), with the intermediate circuit voltage resulting from the potential difference. The intermediate circuit voltage must be sufficiently high to drive an electric motor of a motor vehicle. In current applications, it is between 400 and 900 volts. The intermediate circuit capacitor is charged during vehicle operation by a connected energy source, such as a rechargeable battery.

[0026] The motor vehicle may, in particular, have an axle driven electrically by the electric drive. The motor vehicle may, in principle, be designed as a purely internal combustion engine vehicle, a hybrid vehicle, or an electric vehicle. List of reference symbols In_ADC Input of the single-ended analog-to-digital converter R1;R3 voltage divider V_Ref_ADC Reference voltage of the single-ended analog-to-digital converter HV_Out_ADC processed measurement voltage supplied to the single-ended analog-to-digital converter R30, C30 RC element R20 pull-up resistor HV+ / HV- potential

Claims

[1] Circuit arrangement for measuring an intermediate circuit voltage of an intermediate circuit of an inverter for controlling an electric drive of a vehicle, the circuit arrangement comprising: - a single-ended analog-to-digital converter with one input (In_ADC) for supplying an input voltage (HV+) of the intermediate circuit to be measured, - a voltage divider (R1; R3) connected to the input (In_ADC) of the single-ended analog-to-digital converter and to ground (HV-) for generating a partial voltage from the input voltage (HV+) to supply it to the input (In_ADC) of the single-ended analog-to-digital converter, - a pull-up resistor (R20) electrically contacted with one terminal to the input (In_ADC) of the single-ended analog-to-digital converter and with another terminal to a reference voltage (V_Ref_ADC) of the single-ended analog-to-digital converter, which pull-up resistor is selected such that it generates a positive voltage offset at the input of the single-ended analog-to-digital converter. [2] Circuit arrangement according to claim 1, wherein an RC element (R30, C30) is interposed between the voltage divider (R1; R3) and the input (In_ADC) of the single-ended analog-digital converter. [3] Power electronics device, in particular inverter, comprising an intermediate circuit for providing an intermediate circuit voltage, and a circuit arrangement according to one of the preceding claims. [4] Electric drive, in particular electric axle drive, of a vehicle with at least one electric machine, a transmission device and a power electronics device according to claim 3. [5] Electric drive according to claim 4, wherein the power electronics device is formed as an inverter. [6] Vehicle comprising an electric drive according to claim 5.

Images