DE102008033428B4 - Method and arrangement for voltage measurement with galvanic isolation - Google Patents

Abstract

Method for measuring the voltage of a DC voltage source (UZK), characterized in that a) a circuit arrangement is used which comprises at least two circuits which are coupled to one another via at least two inductances (L1, L2) with numbers of turns (N1, N2), but are electrically isolated from one another are separated,b) wherein the first circuit comprises a diode (D1) with a forward voltage (UDL1) connected in series with the direct voltage source (UZK), which is arranged in the reverse direction with respect to the direct voltage source (UZK), and the inductor (L1),c) the second circuit comprises the opposite inductance (L2) connected in series with an auxiliary voltage source (UH) and a switching element (M2),d) a control device is provided which controls the switching element (M2) in such a way that a current (I1) flows through the Diode (D1) of the first circuit flows ande) a measuring device for indirectly measuring the voltage (U1) induced in the inductance (L1) of the first circuit is provided, wherein the measuring device comprises a third galvanically isolated circuit which comprises an inductance (L3) which is coupled in the same direction and (L2) in the opposite direction to the inductances (L1), the inductance (L3) of the third circuit being connected in series with a diode (D3) arranged in the same sense as the diode (D1) of the first circuit with respect to the inductances (L1) and (L3), and a resistor (R3), and a device connected in parallel with the resistor (R3 ) measures the current (IR3) flowing through the resistor (R3), or which measures the voltage UM = IR3*R3, the control device closing the switching element (M2) at a time (ton), at a later time ( toff) is opened and at a point in time between (toff) and (tm) the current (IR3) flowing through the resistor (R3) or the voltage UM is measured, from which the value of the voltage to be measured (UZK) is determined to UZK= (IR3*R3+UDL3 ) * N1/N3- UDL1.

Description

The invention relates to a method and an arrangement for voltage measurement with galvanic isolation, in particular in the high-voltage range for use in hybrid and/or electric vehicles according to the preamble of claim 1 or 6.

The state of the art for measuring potential-affected voltages and the transmission of the measured variable via potential barriers is the use of voltage dividers for measuring high electrical voltages with divider ratios of, for example, 1000:1.

The main disadvantage of this measurement method is that it requires active elements and a voltage source on the high-voltage side of the circuit.

The object of the present invention is therefore a method and an arrangement for voltage measurement that manages with a smaller number of components on the high-voltage side and reliably determines the voltage on the high-voltage side.

The object is achieved by a method and an arrangement for voltage measurement with the features of claims 1 and 6, respectively. Advantageous developments of the invention result from the dependent claims, with combinations and developments of individual features being conceivable.

The method according to the invention uses a circuit arrangement that includes at least two circuits that are coupled to one another via at least two inductances with a predetermined number of turns, but are electrically isolated from one another.

The DC voltage source to be measured is connected to the first circuit, which comprises a diode connected in series in the reverse direction to the DC voltage source to be measured and the inductance of this circuit. The DC voltage source to be measured can in particular provide a DC voltage in the high-voltage range (greater than 60 volts); in this case, the first circuit is the high-voltage circuit. In this case, the DC voltage source is referred to as a high-voltage source. The DC voltage source to be measured can also be, in particular, the voltage source of the intermediate circuit of a hybrid and/or electric vehicle.

The second circuit includes an auxiliary voltage source, a switching element and the inductance of this circuit, which is arranged in the opposite direction to the inductance of the circuit. The switching element is preferably a semiconductor switch, e.g. B. a metal oxide semiconductor field effect transistor (MOSFET). The auxiliary voltage source supplies the operating voltage for the switching element.

The circuit arrangement according to the invention comprises a control device which controls the switching element in such a way that a voltage is induced in the inductance of the first circuit via the inductance of the second circuit.

This induced voltage is so large that a current flows through the diode of the first circuit. The control device can preferably consist of a signal generator which provides the gate voltage for the transistor.

The circuit arrangement also includes a device for indirectly measuring the voltage induced in the inductance of the first circuit. Indirectly means that the voltage induced in the inductance is not measured directly in the first circuit, since the invention aims to avoid active elements and an additional voltage supply in this circuit, but in the second or optionally in a third circuit.

The main advantage of the method according to the invention is that it requires no active components and no additional power supply in the first circuit. The number of components to which the DC voltage to be measured is applied is very small. Another advantage is that the point in time at which the control device triggers a measurement can be freely determined. In the case of an intermediate circuit voltage measurement in particular, the accuracy can be increased by measuring at defined points in time that are coordinated with other switching processes.

According to a preferred embodiment, the indirect measurement of the voltage induced in the inductance of the first circuit can be carried out by measuring the voltage that drops across the switching element in the second circuit. To do this, proceed as follows:

At a first point in time, the switching element is closed by the control device. At a second point in time, the switching element is opened, and at an even later point in time, the voltage that drops across the switching element is measured using a voltage measuring device.

By closing the switching element at the first time, practically the entire voltage from the auxiliary voltage source falls across the Inductance of the second circuit. The current flowing through this inductor increases linearly. At this time, no current flows through the inductance of the first circuit, since the diode of the first circuit is blocked.

If the switching element is now opened at the second point in time, the voltage at the inductance of the second circuit reverses polarity due to the law of induction and increases sharply in terms of absolute value. A voltage is induced in the inductance of the first circuit by the inductive coupling with that of the second circuit.

The voltage induced in the inductance of the first circuit is the sum of the forward voltage of the diode of the first circuit and the voltage to be measured. Since the forward voltage is well below the voltage to be measured (typical values: 0.7 V and 200 V), the voltage at the inductance of the first circuit roughly corresponds to the voltage to be measured.

While the switching element of the second circuit is open, the voltage at the inductance of the first circuit is transformed back according to the turns ratio of the two inductances. This effect is also known as kickback voltage. The voltage across the inductance of the second circuit can be determined by measuring the voltage drop across the switching element, since the voltage of the auxiliary voltage source is known. The voltage is preferably measured a short time after the transistor opens, in the case of a MOS-FET directly at the drain pin. The time of the measurement should be selected so that a current is flowing through the diode of the first circuit at this time.

The elegant procedure for measuring a potential-bearing voltage requires comparatively little effort. The turns ratio can be used to influence the magnitude of the voltage that drops across the switching element of the second circuit and is actually measured. This voltage can be well below the voltage to be measured in the first circuit. A further advantage of this embodiment can be seen in the fact that no third circuit is required, which saves on components. The measurement signal is difficult to detect.

In practice, it is often expedient, according to a further preferred exemplary embodiment, to integrate a third, galvanically isolated electric circuit into the circuit arrangement for indirectly measuring the voltage induced in the inductance of the first electric circuit. The third circuit includes a third inductor which is co-coupled with that of the first circuit and inversely coupled with that of the second circuit. The third circuit comprises a diode, which is arranged in the same sense as the diode of the first circuit in relation to the inductances, a resistor and a device which either measures the current flowing through this resistor, connected in parallel with the resistor, or measures the voltage which applied to the cathode of the diode of the third circuit.

After opening the switching element, an induced voltage then occurs at the inductance of this third circuit, which is coupled to the two existing inductances, which voltage corresponds to the voltage at the inductance of the first circuit multiplied by the transformation ratio. The voltage generates a current in the third circuit, which is fed to a resistor via a diode. The current flowing through the resistor is measured using an appropriate device. In order to determine the voltage to be measured from the DC voltage source of the first circuit, the product of the measured current and the value of the resistance to the forward voltage of the diode of the third circuit are added, the result is multiplied by the number of turns of the first inductor divided by the number of turns of the third inductor and then subtracts the forward voltage of the diode of the first circuit.

The advantage of this embodiment is that measuring the current does not pose any significant difficulties. The method becomes particularly simple if the number of turns of the inductances and the forward voltages of the diodes of the first and third circuits are identical in each case. The voltage to be measured from the DC voltage source of the first circuit then corresponds to the product of the measured current and the value of the resistance in the third circuit or the measured voltage (at the cathode of the diode).

In a preferred embodiment, a field effect transistor is used as the switching element. The drain pin of the field effect transistor is connected to the inductance of the second circuit, the source pin to ground and the gate pin to a signal generator that controls the transistor using the generated gate voltage. In this embodiment, the indirect measurement of the voltage induced in the inductance of the first circuit can be done by determining the voltage present at the drain pin.

A resistance can advantageously be introduced into the second circuit, either between the auxiliary voltage source and the inductance or between source pin and ground. The resistor stabilizes the current rise and prevents the inductance of the second circuit from saturating.

In a preferred embodiment, the method or the arrangement is used to measure higher voltages (>60 V), such as occur in particular in hybrid and/or electric vehicles.

In principle, the method presented uses a side effect (the kickback voltage) to measure an unknown (high) DC voltage. However, the measurement voltage is not applied continuously, but rather only shortly after the switching element is blocked, as long as the diode of the first circuit is conductive. Such voltage curves are known from the use of flyback converters. In terms of function, the switching element and the coupled inductances form a flyback converter. Here, however, the flyback converter is not primarily used to generate fixed voltages, but is operated with low power.

• 1 zeigt eine Schaltungsanordnung mit zwei Stromkreisen.
• 2 zeigt den prinzipiellen Spannungs- und Stromverlauf.
• 3 zeigt eine Schaltungsanordnung mit drei Stromkreisen.
• 4a und 4b zeigen Schaltungsanordnungen mit einem zusätzlichen Widerstand im zweiten Stromkreis.

Two exemplary embodiments of the invention are explained in more detail below with reference to drawings.

• 1 shows a circuit arrangement with two circuits.
• 2 shows the basic voltage and current curve.
• 3 shows a circuit arrangement with three circuits.
• 4a and 4b show circuit arrangements with an additional resistance in the second circuit.

The circuit arrangement in 1 shows two circuits that are galvanically isolated from one another, but are coupled to one another via the inductances (L ₁ ) and (L ₂ ). The first circuit comprises a direct voltage source to be measured (U _ZK ) and a diode (D ₁ ) connected in series in the reverse direction. A current can only flow when a voltage is induced in the inductor (L ₁ ).

The second circuit is fed by an auxiliary DC voltage source (U _H ). The auxiliary voltage (U _H ) is typically well below the voltage to be measured (U _ZK ) of the first circuit. It can be 12 or 14 volts, for example. The auxiliary voltage source (U _H ) is connected in series with the opposite inductance (L ₂ ) and a switching element (M ₂ ). In the illustrated embodiment, the switching element (M ₂ ) is a MOS-FET. The drain pin (D) of the MOS-FET (M ₂ ) is connected to the inductor (L ₂ ), the source pin (S) to ground and the gate pin (G) is connected via a signal generator (V ₄ ). driven.

When the MOS-FET (M ₂ ) turns on at time (t _on ), a current builds up in the inductance (L ₂ ) and increases linearly. When the MOS-FET (M ₂ ) is switched off at a later point in time (t _off ), a high voltage (U ₁ ) of opposite polarity occurs in the inductance (L ₁ ) of the first circuit. Due to its polarity, this voltage causes the diode (D ₁ ) to become conductive and a current (I ₁ ) to flow as long as (t _off <t<t _m ) until the time (t _m ) the diode (D ₁ ) blocks again. Up to this point in time (t _m ), U ₁ =U _ZK +U _DL1 applies. The inverse transformation of this voltage (U ₁ ) on the inductor (L ₂ ) causes a kickback voltage (U ₂ ) there, which corresponds to U ₁ *N ₂ /N ₁ . By measuring the voltage U _DS =U ₂ +U _H at the drain pin (D) of the MOSFET (M ₂ ), conclusions can be drawn about the voltage to be measured (U _ZK ).

2 shows the basic time course of the voltages at the gate pin (G) and at the drain pin (D) as well as the currents (I ₁ , I ₂ ) in the inductances (L ₁ , L ₂ ) during a measurement process. The control device (V ₄ ), in this case the signal generator, supplies the 2a shown gate voltage (U _gate ). At the point in time (t _on ), the gate voltage (U _gate ) rises suddenly, as a result of which the switching element (M ₂ ), in this case the MOSFET (M ₂ ), becomes conductive.

This leads to a corresponding drop in the voltage (U _DS ) at the drain pin (D), so that the auxiliary voltage (U _H ) now drops almost exclusively across the inductance (L ₂ ) ( 2 B) .

At this point in time, a current (I ₂ ) begins to flow through the inductance (L ₂ ), which increases linearly ( 2c ).

At the time (t _off ), the signal generator turns off the gate voltage (U _Gate ), which blocks the MOS-FET (M ₂ ). Due to the law of induction, when the MOS-FET (M ₂ ) is turned off, the voltages at the coupled inductances (L ₁ ,L ₂ ) reverse polarity ( 2 B) . Current (I ₂ ) can no longer flow in the second circuit because the MOS-FET (M ₂ ) blocks ( 2c ).

Now the diode (D ₁ ) of the first circuit becomes conductive. The induced voltage (U ₁ ) at the inductor (L ₁ ) is equal to the sum of the voltage to be measured (U _ZK ) and the forward voltage (U _DL1 ) of the diode (D ₁ ). A current (I ₁ ) flows through the diode (D ₁ ) ( 2d ). As long as a current (I ₁ ) flows through the diode (D ₁ ), there is a suitable point in time for the measurement.

In this exemplary embodiment, the voltage (U _DS ) is measured at the drain pin (D) of the MOSFET (M ₂ ) in the second circuit. This voltage (U _DS ) corresponds to the sum of the auxiliary voltage (U _H ) and the voltage (U ₂ ) at the inductance (L ₂ ) of the second circuit.

The voltage (U ₂ ) at the inductance (L ₂ ) of the second circuit corresponds to the voltage (U ₁ at the inductance (L ₁ ) of the first circuit due to the inverse transformation multiplied by the turns ratio of the inductances (L ₁ ,L ₂ ).

The voltage to be measured (U _ZK ) finally results from the formula: $${\text{u}}_{\text{CC}}=\left({\text{u}}_{\text{DS}}-{\text{u}}_{\text{H}}\right)*\text{N}1/\text{N}2-{\text{u}}_{\text{DL}1}$$

3 10 additionally shows as an alternative exemplary embodiment 1 a third galvanically isolated circuit comprising a further inductance (L ₃ ) with a number of turns (N ₃ ) which is coupled to the two existing inductances (L ₁ ) and (L ₂ ). A diode (D ₃ ), the direction of which corresponds _to the diode (D ₁ ) of the first circuit, and a resistor (R ₃ ) are connected in series with this inductor (L 3 ). In addition, a device (U _H ) is provided which, connected in parallel with the resistor (R ₃ ), measures the current ( _IR3 ) flowing through the resistor (R ₃ ), or directly measures the voltage (U _H ). U _M = I _R3 *R ₃ applies. The voltage to be measured (U _ZK ) is transmitted according to the method already described and is determined from the measured current (I _R3 ) through the resistor (R ₃ ) as follows: $${\text{u}}_{\text{CC}}=\left({\text{I}}_{\text{R}3}*{\text{R}}_3+{\text{u}}_{\text{DL}3}\right)*{\text{N}}_1/{\text{N}}_3-{\text{u}}_{\text{DL}1}$$

If the number of turns (N ₁ ) and (N ₃ ) of the inductances (L ₁ ) and (L ₃ ) of the first and third circuits are identical, the calculation is simplified to: $${\text{u}}_{\text{CC}}={\text{I}}_{\text{R}3}*{\text{R}}_3+{\text{u}}_{\text{DL}3}{\text{u}}_{\text{DL}1}$$

da die Durchlassspannungen der Dioden (D₁) und (D₃) annähernd gleich sind.Which in general can be further simplified to: $${\text{u}}_{\text{CC}}={\text{I}}_{\text{R}3}*{\text{R}}_3={\text{u}}_{\text{M}}$$

since the forward voltages of the diodes (D ₁ ) and (D ₃ ) are approximately the same.

4a and 4b show as two further advantageous embodiments, each starting from 3 an additional resistance (R ₂ ) in the second circuit. In 4a the resistor (R ₂ ) is arranged between the auxiliary voltage source (U _H ) and the inductance (L ₂ ). In 4b the resistor (R ₂ ) is arranged between the source pin (S) of the MOS-FET (M ₂ ) and ground. The resistor (R ₂ ) stabilizes the current rise (I ₂ ) ( 2c ) and prevents the inductor (L ₂ ) from saturating.

Reference List

UCC

DC voltage source to be measured

D1

Diode of the first circuit

UDL1

Forward voltage of the diode of the first circuit

L1

Inductance of the first circuit

N1

Number of turns of the inductance L ₁

U1

voltage induced in the inductance L ₁

I1

Current through the inductance L ₁

uh

Auxiliary DC voltage source

L2

Inductance of the second circuit

N2

Number of turns of the inductance L ₂

U2

Voltage across the inductance L ₂

I1

Current through the inductance L ₁

M2

switching element

S

source pin

D

drain pin

G

gate pin

USD

Voltage at the drain pin

V4

signal generator

UGate

gate voltage

L3

Inductance of the third circuit

N3

Number of turns of the inductance L ₃

D3

Diode of the third circuit

UDL3

Forward voltage of the 3rd circuit diode

R3

Resistance

IR3

Current through the resistor R ₃

Claims (10)

Method for measuring the voltage of a DC voltage source (U _ZK) , characterized in that a) a circuit arrangement is used which comprises at least two circuits which have at least two inductances (L ₁ , L ₂ ) with numbers of turns (N ₁ , N ₂ ) coupled to each other but galvanically isolated from each other, b) wherein the first circuit comprises a diode (D ₁ ) with a forward voltage (U _DL1 ) connected in series with the direct voltage source (U _ZK ), which is arranged in the reverse direction with respect to the direct voltage source (U _ZK ), and the inductor (L ₁ ), c) the second circuit comprises the opposite inductance (L ₂ ) connected in series with an auxiliary voltage source (U _H ) and a switching element (M ₂ ), d) a control device is provided which controls the switching element (M ₂ ) in such a way that a Current (I ₁ ) flows through the diode (D ₁ ) of the first circuit and e) a measuring device for indirectly measuring the voltage (U ₁ ) induced in the inductance (L ₁ ) of the first circuit is provided, with the measuring device providing a third galvanically comprises a separate circuit comprising an inductance (L ₃ ) which is coupled to the inductances (L ₁ ) in the same sense and (L ₂ ) in opposite senses, the inductance (L ₃ ) of the third circuit being connected in series is arranged with a diode (D ₃ ), which is related to the inductances (L ₁ ) and (L ₃ ) in the same sense as the diode (D ₁ ) of the first circuit, and a resistor (R ₃ ), and a device which connected in parallel to the resistor (R ₃ ) measures the current ( _IR3 ) flowing through the resistor (R ₃ ), or which measures the voltage UM = I _R3 *R ₃ , the switching element (M ₂ ) being closed by the control device is closed at a point in time (t _on ), is opened at a later point in time (t _off ) and at a point in time between (t _off ) and (t _m ) the current (I _R3 ) flowing through the resistor (R ₃ ), or the voltage UM is measured, from which the value of the voltage to be measured (U _ZK ) is determined as U _ZK =(I _R3 *R ₃ +U _DL3 )*N ₁ /N ₃ -U _DL1 . procedure after claim 1 , characterized in that the switching element (M ₂ ) is closed by the control device at a point in time (t _on ), is opened at a later point in time (t _off ) and at a point in time between (t _off ) and (t _m ) with the aid a measuring device, the voltage (U _DS ) is measured, which drops across the switching element (M ₂ ). procedure after claim 2 , characterized in that the value of the voltage to be measured (U _ZK ) is determined from the measured voltage (U _DS ) from: $${\text{u}}_{\text{CC}}=\left({\text{u}}_{\text{DS}}-{\text{u}}_{\text{H}}\right)*\text{N}1/\text{N}2-{\text{u}}_{\text{DL}1}$$

or approximately from: $${\text{u}}_{\text{CC}}\approx \left({\text{u}}_{\text{DS}}-{\text{u}}_{\text{H}}\right)*\text{N}1/\text{N}2$$

procedure after claim 1 , characterized in that the number of turns of the inductances (L ₁ ) and (L ₃ ) are identical: N ₁ =N ₃ , whereby the voltage to be measured is determined according to: U _ZK ≈I _R3 *R ₃ . Procedure according to one of Claims 1 until 4 for measuring DC voltages greater than 60 volts in hybrid and/or electric vehicles. Arrangement for measuring the voltage of a DC voltage source (U _ZK ), characterized in that a) the circuit arrangement comprises at least two circuits which are coupled to one another via at least two inductances (L ₁ , L ₂ ) with numbers of turns (N ₁ , N ₂ ), but are electrically isolated from one another, b) the first circuit having a diode (D ₁ ) with a forward voltage (U _DL1 ) connected in series with the direct voltage source (U _ZK ), which is arranged in the reverse direction with respect to the direct voltage source (U _ZK ), and the inductance ( L ₁ ), c) the second circuit comprises the inductance (L ₂ ) connected in series with an auxiliary voltage source (U _H ) and a switching element (M ₂ ), d) a control device is provided which controls the switching element (M ₂ ) controls such that a current (I ₁ ) flows through the diode (D ₁ ) and e) a measuring device for indirectly measuring the inductance (L ₁ ) induced voltage (U ₁ ) is provided, the measuring device htung comprises a third galvanically isolated circuit with an inductance (L ₃ ) which is coupled in the same direction to the inductances (L ₁ ) and (L ₂ ) in the opposite sense, this inductance (L ₃ ) being connected in series with a diode (D ₃ ) which, with respect to the inductances (L ₁ ) and (L ₃ ), is arranged in the same sense as the diode (D ₁ ) of the first circuit, and a resistor (R ₃ ), and a device which is connected in parallel with the resistor (R ₃ ) measures the current flowing through the resistor (R ₃ ) or the voltage U _M = I _R3 *R ₃ . Arrangement for measuring the voltage of a DC voltage source claim 6 , characterized in that the measuring device for indirect measurement of the induced voltage (U ₁ ) measures the voltage (U _DS ) which drops across the switching element (M ₂ ). Arrangement for measuring the voltage of a DC voltage source claim 7 , characterized in that the switching element (M ₂ ) is a field effect transistor whose drain pin (D) to the inductance (L ₂ ), source pin (S) is connected to ground, whose gate pin (G) of a Signal generator (V ₄ ) is driven with the gate voltage (U _Gate ) and the measuring device measures the voltage (U _DS ) applied to the drain pin (D) of the switching element (M ₂ ). Arrangement for measuring the voltage of a DC voltage source claim 8 , characterized in that a resistor (R ₂ ) between the auxiliary voltage source (U _H ) and inductance (L ₂ ) or between the source pin (S) and ground is provided. Arrangement for measuring the voltage of a DC voltage source according to one of Claims 6 until 9 for measuring DC voltages greater than 60 volts in hybrid and/or electric vehicles.

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